CN111442993A

CN111442993A - Creep testing device, wood creep testing system and testing method

Info

Publication number: CN111442993A
Application number: CN202010239217.3A
Authority: CN
Inventors: 董春雷
Original assignee: Southwest Forestry University
Current assignee: Southwest Forestry University
Priority date: 2020-03-30
Filing date: 2020-03-30
Publication date: 2020-07-24

Abstract

The invention discloses a creep testing device and a testing system aiming at the improved creep testing device, the wood creep testing system provided by the invention can simultaneously test a certain number of test piece samples during the creep test of wood, the whole system can continuously and stably detect, record and display the general creep of the wood and the complex variable-humidity creep deflection, dry shrinkage and wet expansion amount and environmental temperature and humidity parameters for a long time, provide reliable testing basis and testing platform for the exploration of the MSC behavior rule and the creep mechanism of the wood, and also provide reference for the development of moisture absorption/desorption behavior testing equipment of moisture absorption materials except the wood.

Description

Creep testing device, wood creep testing system and testing method

Technical Field

The invention relates to a physical and mechanical property testing device of wood, in particular to a wood creep testing system.

Background

The wood has the ability to absorb gaseous moisture to high humidity ambient air (shortly: moisture absorption) and release gaseous moisture to low humidity ambient air (shortly: desorption). During the Moisture absorption/desorption process, the Moisture Content (MC) inside the wood is in a gradient distribution and dynamic change state, and the Moisture content is gradually increased/decreased from the surface to the inside along with the Average Moisture content when the dry/wet wood absorbs/desorbs, which is abbreviated as: AMC) until a uniform Moisture content (abbreviated as: EMC) state.

Researchers find that the change rule of the static bending and wetting creep deflection of the wood repeatedly increased/reduced by repeated moisture absorption/desorption and AMC has a large difference with the rule that EMC and static bending and constant wetting creep deflection have a positive correlation under the existing domestic and foreign standard laboratory conditions, and the total deflection of the wetting creep is far greater than the total deflection of the constant wetting creep under the same time length and high EMC. This has become common in the art.

The applicant has found that contrary to conventional wisdom, wooden beams in natural environments have less static deflection in rainy seasons than in dry seasons. The discovery arouses high attention of the engineering world at home and abroad and also arouses strong interest of scientific research on the mechanism of wood moisture-changing creep (the mechanism is unknown, and the mechanism is called mechanical adsorption creep (MSC for short) in general by predecessors), but the defects of the MSC testing technology and the defects of the recognition of the gradient distribution and the dynamic change of the moisture content in the wood in the moisture absorption/desorption process block the research process of people on the scientific mechanism and the engineering application of the MSC.

Therefore, in order to solve the problems of insufficient control mode and control precision of environmental parameters (temperature, humidity and wind speed), insufficient test sensitivity and precision of creep deformation, insufficient intelligent data acquisition and processing, insufficient system safety protection and the like commonly existing in the wood bending and creep testing, a set of wood bending and moisture changing creep precision testing system is urgently needed to obtain the accurate behavior rule of the bending MSC which is limited by the testing and cognition conditions but not obtained by the prior people, and provide a basis for finding the influence of the bearing wood MSC on the practical engineering application under the scientific mechanism and natural condition of the MSC.

Disclosure of Invention

The invention provides a creep testing device and a wood creep testing system using the same for solving the problems of the prior art, the system can continuously and stably detect, record and display the deflection, the dry shrinkage and wet expansion amount and the environmental temperature and humidity parameters of the general creep and the complex wetting creep of the wood for a long time, provide a reliable testing basis and a testing platform for the exploration of the MSC behavior rule and the creep mechanism of the wood, and simultaneously provide reference for the development of moisture absorption/desorption behavior testing equipment of moisture absorbing materials except the wood.

The invention is realized by the following technical contents:

the creep testing device comprises a test piece support, a creep load and a hanging rack thereof, and a linear displacement sensor, wherein the test piece support is used for placing a test piece for testing, the test piece support comprises a pair of identical rolling supporting rollers, the supporting rollers are arranged in parallel, and the supporting rollers are used for horizontally placing the test piece for creep testing; the creep load provides an acting force acting on the test piece during the creep test; the creep load is hung at the bottom of the hanging rack, and acting force is applied to a test piece for creep test through the top of the hanging rack; the linear displacement sensor collects displacement data during creep test of the test piece.

The linear displacement sensors are arranged oppositely along the vertical direction, and are respectively arranged on the upper surface and the lower surface of a test piece to be subjected to creep test and used for respectively collecting the vertical displacement of the upper surface and the lower surface of the test piece. The displacement of the vertical plane is the creep amount, and meanwhile, the dry shrinkage and wet expansion variation of the thickness of the wood test piece is obtained through calculating the difference value of the displacement and the creep amount.

As an improvement of the test piece support, the same placing plates are respectively arranged on the supporting rollers, the bottoms of the placing plates are fixed on the supporting rollers, and the placing plates rotate coaxially with the supporting rollers; the upper surface of placing the board is smooth plane, and the upper surface of placing the board is used for placing the test piece of creep test, and the test piece and the upper surface sliding fit who places the board can furthest reduce the surface indentation of test piece.

Under the general condition, the general test standard of the static bending performance of the wood in a dry environment requires a support roller with a certain radian and capable of rolling to be used as a stress support end of a simply supported beam, and the aim is to allow the wood to be freely bent and deformed and reduce indentation. But the wood is wetted and softened in a humid environment, and the existing supporting mode still causes larger indentation on the wood, so that the invention changes the arc-shaped support of the supporting roller into the flat plate support of the placing plate, and can solve the problem of indentation on the premise of meeting the testing principle.

The improved hanging rack for hanging the creep load is characterized in that two identical hanging racks are arranged on each creep testing device, and the hanging racks are arranged on two sides of a test piece for creep testing in parallel and oppositely. The same side of the top of each pair of hangers is respectively connected through a connecting piece, and the hangers are placed on a test piece for creep test through the connecting pieces.

The upper part of each hanger is a pair of vertical parts which are parallel to each other, the top ends of the vertical parts are in the same plane, and the plane where the top ends are located is vertical to the vertical parts; the top ends of the vertical parts at the same side of the two hanging racks are respectively connected through a connecting piece.

The below of the vertical portion of every stores pylon is equipped with the arch of the rectangle form of outwards bending the formation, and the stores pylon is outside protruding to make things convenient for test piece below linear displacement sensor's fixed, the operation of the creep test of also being convenient for simultaneously.

The top of the vertical part of each hanger is rigidly connected.

The four-point bending test is a test method for measuring the bending performance of a material, a strip-shaped sample is placed in a bending test fixture to form a simple beam form, the distance between two lower supporting points for supporting the sample is adjustable according to the length of the sample, and two symmetrical loading points are arranged above the sample. The loading mode of four-point bending needs two hanging points for hanging weight, but the problem of even distribution of the hanging weight of the two hanging points and the problem of shaking of the hanging rack along with the hanging weight are brought.

The invention aims at the improvement of the hanging rack, and provides a double-hanging-point hanging rack device consisting of double hanging racks, wherein the hanging racks are provided with two connecting pieces, and when a creep test is carried out, the hanging racks can be hung at trisection points of the span of a test piece through the connecting pieces, so that the test piece bears two-point vertical loading, and forms a four-point bending loading mode with supporting rollers supported at two ends of the test piece. The top rigid connection of the vertical part of each hanging rack can prevent the hanging racks from sliding inwards when the test piece is bent and deformed and continuously maintain the fixity of the stress point of the test piece, so that the load loading stability during creep test is further improved.

The invention aims at the further improved technical scheme of the connecting piece:

the connecting piece is in running fit with the vertical part. Furthermore, the connecting piece is a rotating roller, namely the connecting piece is preferably of a rolling shaft type structure, so that on one hand, the influence of the clamping of the hanging rack on the loaded direction of the test piece can be avoided, and on the other hand, the change of the loaded mode caused by the displacement of the loading point after the test piece is loaded, bent and deformed can be avoided.

An annular limiting groove is arranged in the middle of the connecting piece along the circumferential surface, and the width of the limiting groove is equal to that of the test piece. The connecting piece with the limiting groove and the hanging rack rigidly connected to the top have the synergistic effect, so that the hanging rack can be prevented from shaking front and back and left and right, and the loading stability during creep test is further improved.

And a pressure-proof gasket is arranged at the position, which is contacted with the connecting piece, on the test piece for creep test, and the length of the pressure-proof gasket is greater than the perimeter of the circumferential surface of the connecting piece. The function of the anti-pressing gasket is to prevent the connecting piece from leaving an impression on the upper surface of the test piece.

The invention aims at the technical scheme of further improving the load required by the creep test: creep load is hung under each pair of hanging racks through the load distributing parts, two ends of the load distributing parts are respectively connected with the bottoms of the hanging racks on two sides, and the gravity center of the creep load, the gravity center of the load distributing parts and the top diagonal of the hanging racks are on the same vertical straight line. The acting force of the creep load can effectively act in the same vertical gravity direction.

The bottom of each hanger is the same U-shaped bent part. The load distribution accessory is cylindrical and horizontally arranged in the U-shaped bent parts of the two hanging racks, the circumferential side surface of the load distribution accessory is provided with a hanging groove at least at the part contacted with the U-shaped bent parts, and the U-shaped bent parts are positioned in the hanging grooves.

The top of the creep load is provided with a hook, the bottom of the hook is fixedly connected with the creep load, the top of the hook is provided with an arc end, the load distribution part penetrates through the arc end of the hook, at least the part of the circumferential side surface in the center of the load distribution part, which is in contact with the hook, is provided with a hook groove, and the arc end of the hook is positioned in the hook groove.

The setting of grooving and grooving is that the stability that rocks the stores pylon for the load that prevents the creep load distributes unequally and the load causes the influence, corresponding to stores pylon and couple, the grooving is located the central authorities of the heavy accessory of load, and the grooving then equidistance lies in the both sides of grooving, not only makes the load evenly divide equally to two stores pylons and can prevent great rocking like this, relies on the point contact of grooving and grooving to make two stores pylons, couple and load distribution spare three synergism with the load automatic centering of creep load simultaneously.

The invention aims at the improvement of a wood creep test system, and the wood creep test system comprises a sealable box body, wherein the box body is provided with a constant temperature and humidity device, and at least one group of creep test devices improved by the invention is arranged in the box body.

The device frame is arranged in the box body and used for fixing the creep testing device, the device frame at least comprises a pair of cross beams which are horizontally fixed in the box body, and the cross beams are parallel to each other; the crossbeam is provided with at least one group of creep testing devices.

The creep testing device comprises two test piece supports of each group of creep testing devices, the test piece supports are oppositely arranged on two cross beams, each test piece support is provided with a supporting roll, and the supporting rolls are parallel to the cross beams.

And a barrier strip is arranged on the cross beam right below the test piece and positioned between the hanging racks on two sides of the test piece, and two ends of the barrier strip are fixedly connected with the cross beam.

In order to prevent the shock and the damage of the whole test system caused by the sudden fracture of the test piece under different properties and different experimental conditions, the technical scheme of the invention is that the barrier strip is arranged between the two hanging racks to prevent the hanging racks from continuously falling when the test piece is fractured.

The bottom below of every group creep testing arrangement is equipped with the elevating gear who is used for going up and down the creep load, and elevating gear's top is equipped with the horizontally and puts the thing platform, can test the same advance carry and the uninstallation of a set of or multiunit test piece.

The lifting device is a hydraulic jack.

The wood creep test system provided by the invention needs a certain number of test piece sample quantities during the wood creep test, has higher requirements on the creep quantity timing starting points of all test pieces, and needs a device for loading the loads of a plurality of test pieces simultaneously in order to obtain the simultaneity of moisture absorption/desorption and creep loading. The creep load with the hook is raised to a suitable height using a hydraulic jack so that the load distributing fittings can pass through the hook and fall onto the U-bend at the bottom of the pylon. When a creep test is started, the hydraulic jack is opened, the creep load slowly descends under the support of the object placing table due to the gravity of the creep load, until the hook falls into the hook groove of the load weight distribution accessory, and the U-shaped bent part of the hanger is hung in the hanging groove. At the moment, the creep load is separated from the object placing table, and the load is loaded at the same time. Meanwhile, only opposite operations are needed to be executed during unloading, and the operation process is very convenient.

The wind speed control device is arranged in the box body, the hot-wire anemometer and the temperature and humidity sensor are arranged in the box body, and the temperature and humidity alarm device, the computer and the power supply of the test system are arranged outside the box body. Thereby forming the capacity of stably generating, conveying, maintaining and exhausting the humid air with specific humidity and temperature in a quantitative, constant-speed and directional manner, and ensuring that the wood test piece can stably absorb or exhaust the gaseous moisture; the humidity, temperature and flow rate of the wet air and the variation range of the humidity, temperature and flow rate are regulated, the control precision of the relative humidity of the wet air is not more than +/-2%, and the control precision of the temperature is not more than +/-0.1 ℃.

The whole system can continuously and stably detect, record and display the general creep and the complex variable-humidity creep deflection, the dry shrinkage and wet swelling capacity and the environmental temperature and humidity parameters of the wood for a long time, provide a reliable test basis and a test platform for the exploration of the MSC behavior rule and the creep mechanism of the wood, and simultaneously provide reference for the development of test equipment for the moisture absorption/desorption behavior tests of moisture absorbing materials except the wood.

The test method utilizing the wood creep test system comprises the following steps,

step 1, horizontally penetrating a test piece between two hanging racks, placing two ends of the test piece on a placing plate of a supporting roller, and lightly placing a connecting piece of the two hanging racks on the upper surface of the test piece;

step 2, fixing the positions of the linear displacement sensors above and below the test piece, and respectively abutting the contact tips of the linear displacement sensors against the upper surface and the lower surface of the test piece span;

step 3, preparing creep load, placing the creep load on a placing table, placing a hook between the bottoms of the hangers, and sequentially penetrating load weight distribution accessories through the bottom of the hanger and the hook;

step 4, descending the placing table through a hydraulic jack until creep load is suspended on the hanging frame;

step 5, starting the constant temperature and humidity device to control the temperature and humidity in the box body, starting the air inlet device and adjusting the air speed of the position where the test piece is located through the air speed adjusting device; monitoring data in real time through a temperature and humidity sensor and an air speed sensor;

and 6, inputting the temperature, humidity and wind speed in the box body acquired in the step 5 and the displacement signal of the test piece into a computer, and storing, processing, analyzing and displaying data.

Drawings

FIG. 1 is a schematic structural diagram of a creep test apparatus according to the present invention.

FIG. 2 is a front view of a creep test apparatus according to the present invention.

FIG. 3 is a schematic view of a test piece holder according to the present invention.

FIG. 4 is a diagram showing the use state of the specimen holder according to the present invention.

FIG. 5 is another schematic view of the test piece holder according to the present invention.

Fig. 6 is a schematic view of the overall structure of the hanger of the present invention.

FIG. 7 is a schematic view of a hanger attachment of the present invention.

Fig. 8 is another schematic structural view of the hanger of the present invention.

Fig. 9 is a schematic diagram of the position structure of the linear displacement sensor according to the present invention.

FIG. 10 is a schematic view of the structure of the load-sharing assembly of the present invention.

FIG. 11 is a structural schematic diagram of creep loading in accordance with the present invention.

FIG. 12 is a schematic structural diagram of a wood creep test system according to the present invention.

FIG. 13 is a schematic structural diagram of a box of the wood creep testing system of the present invention.

FIG. 14 is a schematic view of the frame structure of the wood creep testing system of the present invention.

FIG. 15 is a first view of the assembly frame of the wood creep testing system according to the present invention.

FIG. 16 is a diagram of a second state of the device frame of the wood creep testing system of the present invention.

Fig. 17 is an enlarged view of a portion a in fig. 16.

FIG. 18 is a block diagram of the components of the creep test system of the present invention.

FIG. 19 shows the in-box humidity values and displacement values measured by 6 humidity sensors and linear displacement sensors in real time during the wood creep test according to the present invention.

FIG. 20 is a graph of wood wet creep for inventive wood creep test 112 d.

FIG. 21 is a graph showing the dynamic wet swelling and dry shrinkage of wood in the creep test of the wood of the present invention for 240 h.

Detailed Description

As shown in fig. 1, the creep test apparatus of the present invention includes a specimen holder 100 for holding a specimen 101 for a creep test during the creep test, a creep load 200 for providing an acting force required for the creep test to the specimen 101, a hanger 300 for mounting the creep load 200 on the specimen 101, and a linear displacement sensor 400 for acquiring displacement data of the specimen 101 during the creep test.

As shown in fig. 4, the specimen holder 100 is used for placing a specimen 101 for testing, and includes a pair of identical rollable support rollers 102, the support rollers 102 are arranged in parallel, and the specimen 101 for creep testing is horizontally placed on the support rollers 102.

In the present embodiment, as shown in fig. 1 and 3, the test piece holder 100 is provided with the support roller 102 in a U-shaped chassis 103, and the support roller 102 is actually implemented by directly penetrating the chassis 103 with a bolt, fixing the other end of the bolt with a nut, and rotatably engaging the bolt with two sides of the chassis 103 to form the support roller 102. The support roller 102 is composed of a bolt and a sleeve sleeved on the bolt, the bolt is fixed on two sides of the bottom frame 103, and the sleeve can rotate by taking the bolt as a shaft. The surfaces of the objects to be rotationally engaged, whether of the first or second type, need to be treated to reduce friction, such as by smoothing the surfaces, filling with a lubricating medium, etc. Or by using bearings, as is common in the art, selected according to the conditions.

Under the general condition, the general test standard of the static bending performance of the wood in a dry environment requires a support roller with a certain radian and capable of rolling to be used as a stress support end of a simply supported beam, and the aim is to allow the wood to be freely bent and deformed and reduce indentation. But the wood is softened by moisture in a humid environment, and the existing supporting mode still causes larger indentation on the wood. Therefore, in the present embodiment, as shown in fig. 3 and 4, the same placing plate 104 is provided on the supporting rollers 102, respectively, the bottom of the placing plate 104 is fixed on the supporting rollers 102, and the placing plate 104 rotates coaxially with the supporting rollers 102.

In order to reduce friction between the test piece 101 and the placing plate 104, the upper surface of the placing plate 104 is a smooth plane, the test piece 101 is placed on the upper surface of the placing plate 104, and the test piece 101 is in sliding fit with the upper surface of the placing plate 104. The present embodiment solves the indentation problem by providing the placing plate 104 on the premise of satisfying the testing principle.

The specimen holder 100 in this embodiment is composed of two independent bottom frames 103 provided with supporting rollers 102, and when in use, the specimen holders 100 are respectively fixed by other supporting mechanisms, and a space as shown in fig. 1 is formed between the specimen holders 100, so that the linear displacement sensor 400 can be conveniently placed. However, the test piece holder 100 may be configured as shown in fig. 5, in which the test piece holder 100 includes a long base frame 103 'having a U-shaped cross section, and support rollers 102 are provided on the base frame 103' at positions near both ends. In order not to obstruct the linear displacement sensor 400 from acting on the lower surface of the test piece 101, the middle of the bottom frame 103' must be hollow.

The creep test needs a force to act on the test piece, in this embodiment, the creep load 200 applies an acting force to the test piece 101 of the creep test through the hanger 300, the top of the hanger 300 is hung on the test piece 101 of the creep test, the creep load 200 is hung at the bottom of the hanger 300, and the acting force is applied to the test piece 101 through the top of the hanger 300.

As shown in fig. 1, in the present embodiment, two identical hangers 300 are provided for the creep test apparatus, and the hangers 300 are provided on two sides of the test piece 101 for creep test in parallel and oppositely. The same side of the top of each pair of hangers 300 is connected through a connecting piece 310, and the connecting piece 310 is placed on the test piece 101.

The hanging rack 300 is hung at the trisection point of the span of the test piece 101 through the connecting piece 310, so that the test piece 101 is subjected to two-point vertical loading, and as shown in fig. 1 and fig. 2, the connecting piece 310 and the supporting roller 102 form a four-point bending loading mode. A four-point bending loading mode is a test method for measuring the bending performance of a material, a strip-shaped test piece is placed in a fixture for a bending test to form a simple beam form, the distance between two lower supporting points of the supporting test piece is adjustable according to the length of the test piece, and two symmetrical stress points are arranged above the test piece.

As shown in fig. 6, in the present embodiment, the upper portion of each hanger 300 is a pair of vertical portions 320 parallel to each other, the top ends of the vertical portions 320 are in the same plane, the plane where the top ends are located is perpendicular to the vertical portions 320, and the top ends of the vertical portions 320 on the same side of the two hangers 300 are respectively connected by a connecting member 310.

The length of the vertical part 320 of the hanger 300 depends on the overall size of the creep testing device, the main body part of the hanger 300 can be completely vertical, but the hanger 300 is hung on the test piece 101 through the connecting piece 310, the volume of the test piece 101 is not required to be too large no matter the actual use environment or the testing requirement, the preferred size of the test piece 101 is 110 × 10 × 5mm (length × is × times higher), so the length of the connecting piece 310 does not need to be too much longer than the width of the test piece 101, about 3 times is enough, otherwise the hangers 300 on the two sides of the test piece 101 are easy to shake.

Therefore, the distance between the hangers 300 on both sides of the specimen 101 and the distance between the vertical portions 320 on the same hanger 300 are limited. Since one linear displacement sensor 400 is also required to be disposed under the test piece 101, in order not to obstruct the linear displacement sensor 400, a required space is made for accommodating the linear displacement sensor 400 and the sensor holder 401 thereof, as shown in fig. 2 and 6, a rectangular protrusion 321 bent outward is provided under the vertical portion 320 of each hanger 300.

In order to prevent the top of the rack 300 from sliding inwards when the test piece 101 in the creep test is bent and deformed so as to keep the stress point of the test piece 101 fixed, the top of each rack 300 is rigidly connected, as shown in fig. 6, in this embodiment, the top of the vertical part 320 on the same rack 300 is fixedly connected through the limiting piece 322. In practical application, the hanging rack 300 may also be formed by bending a whole, as shown in fig. 8, through holes 323 are reserved at two right-angled corners of the top for fixing the connecting members 310.

The creep testing device of the invention has the advantages that the double hanging points formed by the double hanging racks need to be provided with two hanging points for hanging weight, so that the problem of even distribution of the hanging weight of the two hanging points and the problem of shaking of the hanging racks along with the hanging weight can be caused, therefore, the top of the hanging rack 300 is rigidly connected, the hanging racks are prevented from sliding inwards when a test piece is bent and deformed, the stress point of the test piece is kept unchanged, and the load loading stability during the creep testing is improved.

As shown in fig. 4, the distance b between the contact point of the connecting member 310 on the top of the hanger 300 and the test piece 101 is one third of the distance a between the supporting rollers 102. The length of the test piece 101 is larger than the distance between the support rollers 102, and the center of the distance between the test piece 101 and the support rollers 102 is on the same vertical straight line.

In this embodiment, the connector 310 is rotationally engaged with the upright portion 320. The connecting member 310 is a roller, and the structure of the connecting member is the same as that of the supporting roller 102, and there are many technical means for realizing the roller function in the prior art, as shown in fig. 7. The connecting piece 310 is set to be a rotating roller, so that on one hand, the influence of the rack on the loaded direction of the test piece can be avoided, and on the other hand, the change of the loaded mode caused by the displacement of the loading point after the test piece is loaded, bent and deformed can be avoided.

An annular limiting groove 311 is formed in the middle of the connecting piece 310 along the circumferential surface, and the width of the limiting groove 311 is equal to that of the test piece 101. The connecting piece 310 with the limiting groove 311 and the top rigidly connected hanger 300 cooperate to prevent the hanger 300 from swinging back and forth and left and right, thereby further improving the stability of loading during creep test.

In order to prevent the connecting member 310 from leaving an impression on the upper surface of the test piece 101, a pressure-proof gasket 312 is provided on the test piece 101 at a position contacting the connecting member 310, and as shown in fig. 4 and 17, the length of the pressure-proof gasket 312 is greater than the circumference of the circumferential surface of the connecting member 310, so as to prevent the connecting member 310 from falling off the pressure-proof gasket 312.

In the creep test, in order to prevent the weight of the creep load, that is, uneven distribution of the load, and the influence of the shaking of the load on the stability of the racks, the creep load 200 of each set of devices in this embodiment is hung under each pair of racks 300 through the load distributing member 330, as shown in fig. 1, 2, and 11, two ends of the load distributing member 330 are respectively connected with the bottoms of the racks 300 on two sides, and the gravity center of the creep load 200, the gravity center of the load distributing member 330, and the top diagonal line of the racks 300 are on the same vertical straight line, so that the acting force of the creep load 200 can effectively act in the same vertical gravity direction, and can uniformly act on the stressed point of the test piece 101 through the racks 300.

Referring to fig. 6, the bottom of each hanger 300 is formed with the same U-shaped bent portion 340, referring to fig. 11, the load distributing member 330 is formed in a cylindrical shape and horizontally disposed in the U-shaped bent portions 340 of the two hangers 300, a hanging groove 331 is formed at least in a portion contacting the U-shaped bent portion 340 on the circumferential side surface of the load distributing member 330, and the U-shaped bent portion 340 is disposed in the hanging groove 331.

As shown in fig. 1 and 11, a hook 201 is provided on the top of a creep load 200, the bottom of the hook 201 is fixedly connected to the creep load 200, an arc end is provided on the top of the hook 201, a load distributing member 330 passes through the arc end of the hook 201, a hook groove 332 is provided on at least a portion of a circumferential side surface of the center of the load distributing member 330, which is in contact with the hook 201, and the arc end of the hook 201 is located in the hook groove 332.

Referring to fig. 10 and 11, the hanging groove 331 and the hooking groove 332 in this embodiment are disposed around the circumference of the load distributing member 330.

The hook groove 332 is located at the center of the load weight distribution member 330 corresponding to the hanger 300 and the hook 201, and the hook groove 331 is located at both sides of the hook groove 332 at equal distance, so that the load can be evenly distributed to the two hangers 300 and can be prevented from large shaking, and the two hangers 300, the hook 201 and the load weight distribution member 330 can be automatically centered by the cooperation of the three parts of the hook groove 331 and the hook groove 332.

Referring to fig. 1, 2 and 9, linear displacement sensors 400 are provided on the upper and lower surfaces of a test piece 101 to be subjected to a creep test, respectively, for acquiring vertical displacement amounts of the upper and lower surfaces of the test piece 101, respectively. The displacement of the vertical plane is the creep amount, and the dry shrinkage and wet expansion variation of the thickness of the wood test piece is obtained by calculating the difference value of the displacement and the creep amount. The test precision and the resolution of the deformation of the test piece are not lower than 0.01 mm.

Specifically, the linear displacement sensor 400 is fixed by a sensor fixing base 401, and the sensor fixing base 401 is fixed by a sensor fixing base 402 on other fixed structures of the environment where the creep test device is used, for example, the bottom of the sensor fixing base 402 may be vertically fixed on a table on which the creep test device is placed. Depending on the test environment, the existing technical means can be selected for fixing.

As shown in FIG. 12, in the wood creep testing system of the present invention, the creep testing device is disposed in a sealable box 500, the box 500 is disposed in a constant temperature and humidity device 501, and at least one set of creep testing devices is disposed in the box.

Specifically, a device frame 510 for fixing the creep testing device is arranged in the box body 500, the device frame 510 at least comprises a pair of cross beams 511 which are horizontally fixed in the box body, and the cross beams 511 are parallel to each other. The cross member 511 may be directly fixed at both ends to both side walls of the box body 500, or as shown in fig. 14, the assembly frame 510 in this embodiment is a rectangular frame structure, and the vertical leg structures at both sides may be vertically fixed to the bottom surface of the interior of the box body 500 as shown in fig. 12.

In order to solve the test error caused by the non-homogeneity of wood and many internal defects, a certain number of test pieces are required to be tested simultaneously in the same environment in the wood creep test, so at least one group of creep test devices is arranged on the cross beam 511, as shown in fig. 15 and 16, six groups of creep test devices are arranged in the embodiment.

Referring to fig. 1 and 4, the specimen holder 100 of each creep test device is composed of two independent bottom frames 103 provided with supporting rollers 102, as shown in fig. 17, the specimen holder 100 is oppositely arranged on two cross beams 511, and the supporting rollers 102 on each specimen holder 100 are parallel to the cross beams 511.

As shown in fig. 17, a barrier strip 512 is arranged on the cross beam 511 right below the test piece 101, the barrier strip 512 is positioned between the hangers 300 on both sides of the test piece 101, and both ends of the barrier strip 512 are fixedly connected with the cross beam 511. The barrier rib 512 is arranged between the two hangers 300 to prevent the test piece from suddenly breaking to cause vibration and damage of the whole test system under different properties and different experimental conditions, and when the test piece 101 breaks, the connecting piece 310 of the hanger 300 is stopped falling due to the barrier rib 512.

As shown in fig. 15, in this embodiment, a sensor fixing beam 403 is disposed on the cross beam 511, beside each group of creep test devices, and may be directly made of a section of cut angle steel, and two ends of the bottom of the sensor fixing beam 403 are respectively fixed on the two cross beams 511. The sensor mount 402 is fixed vertically downward on the sensor mount beam 403. The fixing mode can be bolt connection or welding, but the bolt connection is preferred for the convenience of disassembly and assembly.

The wood creep test system provided by the invention needs a certain number of test piece sample quantities during the wood creep test, has higher requirements on the creep quantity timing starting points of all test pieces, and needs a device for loading the loads of a plurality of test pieces simultaneously in order to obtain the simultaneity of moisture absorption/desorption and creep loading. With reference to fig. 1 and fig. 15, a lifting device 513 for lifting the creep load 200 is arranged below the bottom of each group of creep testing devices, and a horizontal object placing table 514 is arranged on the top of the lifting device 513, so that one or more groups of test pieces can be simultaneously loaded and unloaded. In this embodiment, the lifting device 513 is a hydraulic jack.

The use of hydraulic jacks to raise the creep load with the hook to a suitable height allows the load sharing fitting to pass through the hook and land on the U-bend at the bottom of the pylon as shown in figure 11. When the creep test is started, the hydraulic jack is opened, the creep load 200 is slowly descended under the support of the object placing table 514 due to the self gravity until the hook 201 falls into the hook groove 332 of the load weight distribution fitting 330, and the U-shaped bent part 340 of the hanger 300 is hung in the hanging groove 331. At this time, the creep load 200 is separated from the stage 514, and the load is applied at the same time. Meanwhile, only opposite operations are needed to be executed during unloading, and the operation process is very convenient.

With reference to fig. 12 and 18, the complete creep testing system of the present invention further includes an air intake device 502, an air speed adjusting device and a temperature and humidity sensor 517 disposed in the box 500, and a temperature and humidity alarm device 518, a computer 519 and a power supply 520 of the testing system disposed outside the box 500. The wind speed adjusting means comprises a hot wire anemometer 516 and a rotational speed regulator 515. The capability of stably generating, conveying, maintaining and exhausting wet air with specific humidity and temperature in a quantitative, constant-speed and directional manner is formed through the wind speed adjusting device and the temperature and humidity sensor, so that the wood test piece can stably absorb or exhaust gaseous moisture; the humidity, temperature and flow rate of the wet air and the variation range of the humidity, temperature and flow rate are regulated, the control precision of the relative humidity of the wet air is not more than +/-2%, and the control precision of the temperature is not more than +/-0.1 ℃.

In the embodiment, the invention adopts a Binder MKF720 type constant temperature and humidity box produced by the Germany Binder company as the box body 500 of the test system, the volume (width × and depth × and height) in the box is 937 × 576 × 1250mm, the humidity adjustable range RH is 10-98% (precision +/-2%) and the temperature adjustable range is-40-180 ℃ (precision +/-0.1 ℃), the box body 500 of the type is provided with the constant temperature and humidity device 501 at the lower part and the air inlet device 502 in the box body 500, although the basic conditions for supplying low temperature and humidity air to the box body are provided, the maximum adjustable air speed is only 1m/s, and the basic rule of the wood moisture change creep under high air speed air flow (for example, the air speed of the plateau or coastal outdoor environment is more than 2.2 m/s in a year) cannot be simulated and researched.

Therefore, aiming at the original layout of space limitation and air flow channels in the box body, the air inlet device 502 is firstly improved into a set of small speed-adjustable double-turbine fan, the highest air speed in the box body can be increased to 5.6m/s, meanwhile, the air speed adjusting device is additionally arranged and comprises a hot-wire anemometer 516 and a rotating speed adjuster 515, the hot-wire anemometer 516 is arranged on the device frame 510 and close to the test piece 101, and the rotating speed adjuster 515 is arranged outside the box body 500, so that the rotating speed of the fan of the air inlet device 502 can be adjusted manually. By means of the wind speed adjusting device and experimental and theoretical analysis, it is proved that the change of the wind speed can obviously influence the air flow rate on the surface of the wood test piece, and further influence the moisture absorption or desorption rate of the wood test piece.

In actual implementation, in order to prevent the influence of daily changes of the ambient humidity and temperature around the box body on the humidity and temperature in the box body, especially the influence of opening a door, and simultaneously to maintain the consistency of the temperature and the humidity of an experimental operation space outside the box and parameters in the box as much as possible, the experiment can be carried out in the environment with a humidifying/dehumidifying machine and an air conditioner, the adjustable range of the ambient temperature around the box body is 10-40 ℃, and the precision is +/-1 ℃; the relative humidity adjustable range is 40-80%, and the precision is +/-5%.

The space of the box 500 is limited, so the occupied volume of the creep load 200 is as small as possible and the creep load 200 is conveniently made into a standard shape, and meanwhile, in consideration of economic cost, a steel plate with a large density is preferably adopted as the creep load 200, as shown in fig. 11, in the embodiment, steel plates with the same length and width but different thicknesses are adopted, so that the creep tests with different load levels can be conveniently matched and used, as shown in table 1.

TABLE 1 creep load Specification

Simultaneously, all steel sheets are all blued to prevent that it from influencing load uniformity and stability because of the too high rust of incasement humidity in the creep test process.

The most important raw data collected in real time in the wood static bending-to-wet creep test are: the environmental temperature and the environmental humidity in the box body, the wind speed of the position of the test piece and the displacement of the test piece across the upper surface and the lower surface.

The testing system of the invention adopts the technical scheme that a linear displacement sensor is respectively arranged at the middle point of the middle upper surface and the middle lower surface of the span of the test piece, as shown in figure 1, the vertical displacement measured by the lower surface is used for representing the static bending deflection of the test piece, and the difference between the displacement of the upper surface and the displacement of the lower surface of the test piece measured simultaneously is used as the wet expansion or dry shrinkage of the test piece in the thickness direction, so that the real-time thickness wet expansion and dry shrinkage of the test piece and the section inertia moment of the test piece are obtained to facilitate later.

As shown in fig. 12 and 18, the present invention uses the transmitter 521 and the data wire 522 to input the collected temperature, humidity, and displacement signals into the computer 519, and then the real-time storage, real-time processing analysis, and display of data can be realized through the programming software based on the VB language. The collected real-time original data are stored in a text format in a database form and used for software real-time data processing and analysis, and meanwhile, the data can be exported at any time and copied as backup, so that the data can be conveniently processed and analyzed offline. Data are obtained by the temperature and humidity sensor 517, and a real-time coordinate graph with time as a horizontal mark and temperature and relative humidity in the box as a vertical mark can be obtained after recording and processing by matched software. And (3) processing the displacement original data in real time by using software to form a progressive coordinate graph with time as a horizontal standard and static bending deflection and wet expansion and dry shrinkage of the test piece as longitudinal standards, and using the progressive coordinate graph for real-time monitoring.

In this embodiment, in order to prevent indication deviation or errors caused by possible electronic component failure of the temperature and

humidity sensor

517, 6 temperature and humidity sensors 517 are provided in the box 500, such as an Ecolog series temperature and humidity recorder (RH ± 0.5%, T ± 0.1 ℃) manufactured by switzerland E L PRO group, where the temperature and humidity sensor 517 of this type can monitor and record temperature and humidity data in the box 500 in real time, as shown in fig. 12, in the 6 temperature and humidity sensors 517, one temperature and humidity sensor is respectively provided at four corners inside the box 500, and then one temperature and humidity sensor is provided at each of two sides of the middle upper portion of the device frame 510, so as to monitor and record temperature and humidity of different portions in the box and sample accessories, in fig. 13, one temperature and humidity sensor 517 may be provided near the middle portion of the left door frame of the box 500, which can detect temperature and humidity together with other 6 temperature and humidity sensors, and can detect temperature and humidity data at a door seam of the box 500, and when an abnormality is found, a door sealing condition of the box.

As shown in fig. 12 and 18, to prevent unexpected power failure during the test, the present embodiment configures a power generation device of appropriate power as a power supply source 520, supplies the power demand of the entire test system, and prevents interruption of the experiment due to power failure.

In this embodiment, in order to prevent the experiment failure caused by the fact that the environmental parameters in the test system exceed the set parameter range due to mechanical or electronic faults when the experimenter is not on the spot, the test system is further equipped with a temperature and humidity alarm 518. For example, HE2508GSM short message alarm module manufactured by hua-tuo corporation, the module is connected with a temperature and humidity recorder placed in the box 500, temperature and humidity values are set, and as long as the temperature and humidity values exceed the temperature and humidity values, the temperature and humidity alarm device 518 can be started, for example, the device sends out a buzzing sound, sends out information reminding to a mobile phone of an experimenter, and other alarm measures.

When the wood creep test system is used for testing, the following steps can be carried out:

step 5, starting the constant temperature and humidity device to control the temperature and humidity in the box body, starting the air inlet device and adjusting the air speed of the position where the test piece is located through the air speed adjusting device, and maintaining the environment in the box body under the conditions of constant temperature of 20 ℃, cyclic humidity change of 42-80% of relative humidity and constant humidity of 65% of relative humidity; monitoring data in real time through a temperature and humidity sensor and an air speed sensor;

and 6, inputting the temperature, humidity and wind speed in the box body acquired in the step 5 and the displacement signal of the test piece into a computer, and storing, processing, analyzing and displaying data. The time interval of data recording can be set, and the length of the time interval is set according to the material and the characteristics of the test piece.

The real-time detection results of humidity, static bending creep deflection and humidity, temperature and displacement in the box for the wet-expansion dry-shrinkage analysis, which are measured by 6 temperature and humidity sensors 517 in the box and 12 linear displacement sensors 400 at the upper part and the lower part in real time, are shown in fig. 19 to 21, and in the whole test process, the environmental temperature and humidity data in the box are very uniform and consistent. Meanwhile, as can be seen from fig. 19 to 21, the system can sensitively and stably capture the creep deflection, humidity, temperature and specimen wet expansion and dry shrinkage of the wood specimen when the humidity changes and is constant for a long time, and the sampling interval time (shown by an ellipse in fig. 19) can be arbitrarily and manually changed during the experiment.

Through test operation inspection and correction, the verification on the scientificity, accuracy, sustainability and reliability of the test system provided by the invention shows that the system can obtain real-time detection data of the static bending and moisture changing creep of the wood and data for later fine research and analysis.

The accurate test result of the system also finds that the creep test result is different from the creep test result of a test piece and the like treated by steam spraying by the predecessor, such as static bending deflection in the moisture absorption process is not increased reversely, and the like, as shown in fig. 20 and 21. Thereby providing strong evidence for the innovative disclosure of the mechanism of the wood static bending-to-wet creep.

Claims

1. Creep testing arrangement, its characterized in that: comprises a test piece support, a creep load, a hanging rack thereof and a linear displacement sensor, wherein

The test piece support is used for placing a test piece for creep test and comprises a pair of identical rollable supporting rollers which are arranged in parallel and used for horizontally placing the test piece for creep test;

the creep load provides an acting force acting on the test piece during the creep test;

the creep load is hung at the bottom of the hanging rack, and acting force is applied to a test piece for creep test through the top of the hanging rack;

the linear displacement sensor collects displacement data during creep test of the test piece.

2. The creep test apparatus of claim 1, wherein: the two linear displacement sensors are arranged oppositely along the vertical direction and respectively collect the vertical plane displacement of the upper surface and the lower surface of the test piece.

3. The creep test apparatus of claim 1, wherein: the same placing plates are respectively arranged on the supporting rollers, the bottoms of the placing plates are fixed on the supporting rollers, and the placing plates rotate coaxially with the supporting rollers; the upper surface of placing the board is smooth plane, and the upper surface of placing the board is used for placing the test piece of creep test, test piece and the upper surface sliding fit who places the board.

4. The creep test apparatus of claim 1, wherein: the hanging racks are arranged in two identical numbers, and are arranged on two sides of the test piece for creep test in parallel and oppositely; the same side of the top of each pair of hangers is respectively connected through a connecting piece, and the hangers are placed on a test piece for creep test through the connecting pieces.

5. The creep test apparatus of claim 4, wherein: the upper part of each hanger is a pair of vertical parts which are parallel to each other, the top ends of the vertical parts are in the same plane, and the plane where the top ends are located is vertical to the vertical parts; the top ends of the vertical parts at the same side of the two hanging racks are respectively connected through a connecting piece.

6. The creep test apparatus of claim 5, wherein: a rectangular bulge which is bent outwards is arranged below the vertical part of each hanging rack.

7. The creep test apparatus of claim 5, wherein: the top of the vertical part of each hanger is rigidly connected.

8. The creep test apparatus of claim 5, wherein: the connecting piece is in running fit with the vertical part.

9. The creep test apparatus of claim 8, wherein: the connecting piece is a rotating roller, an annular limiting groove is formed in the middle of the connecting piece along the circumferential surface, and the width of the limiting groove is equal to that of the test piece.

10. Creep testing device according to claim 8 or 9, characterized in that: and the position of the upper surface of the test piece, which is in contact with the connecting piece, is provided with a pressure-proof gasket, and the length of the pressure-proof gasket is greater than the circumference of the circumferential surface of the connecting piece.

11. Creep testing apparatus according to any of claims 4 to 9, characterized in that: creep load is hung under each pair of hanging racks through the load distributing parts, two ends of the load distributing parts are respectively connected with the bottoms of the hanging racks on two sides, and the gravity center of the creep load, the gravity center of the load distributing parts and the top diagonal of the hanging racks are on the same vertical straight line.

12. The creep test apparatus of claim 11, wherein: the bottom of each hanger is the same U-shaped bent part.

13. The creep test apparatus of claim 12, wherein: the load distribution accessory is cylindrical and horizontally arranged in the U-shaped bent parts of the two hanging racks, the circumferential side surface of the load distribution accessory is provided with a hanging groove at least at the part contacted with the U-shaped bent parts, and the U-shaped bent parts are positioned in the hanging grooves.

14. The creep test apparatus of claim 13, wherein: the top of the creep load is provided with a hook, the bottom of the hook is fixedly connected with the creep load, the top of the hook is provided with an arc end, the load distribution part penetrates through the arc end of the hook, at least the part of the circumferential side surface in the center of the load distribution part, which is in contact with the hook, is provided with a hook groove, and the arc end of the hook is positioned in the hook groove.

15. Timber creep test system, including the box that can seal, the box is equipped with constant temperature and humidity device, its characterized in that: at least one set of creep testing devices according to any one of claims 1 to 14 is provided in the housing.

16. The wood creep test system of claim 15, wherein: the device frame is arranged in the box body and used for fixing the creep testing device, the device frame at least comprises a pair of cross beams which are horizontally fixed in the box body, and the cross beams are parallel to each other; the crossbeam is provided with at least one group of creep testing devices.

17. The wood creep test system of claim 16, wherein: the creep testing device comprises two test piece supports of each group of creep testing devices, the test piece supports are oppositely arranged on two cross beams, each test piece support is provided with a supporting roll, and the supporting rolls are parallel to the cross beams.

18. The wood creep test system of claim 17, wherein: the hanging rack is positioned between the two cross beams.

19. The wood creep test system of claim 18, wherein: and a barrier strip is arranged on the cross beam right below the test piece and positioned between the hanging racks on two sides of the test piece, and two ends of the barrier strip are fixedly connected with the cross beam.

20. The wood creep test system according to any one of claims 16 to 19, wherein: the bottom below of every group creep testing arrangement is equipped with the elevating gear who is used for going up and down creep load, and elevating gear's top is equipped with the horizontally and puts the thing platform.

21. The wood creep test system of claim 20, wherein: the lifting device is a hydraulic jack.

22. The wood creep test system of claim 15, wherein: the wind speed regulating device is arranged in the box body, and the wind speed regulating device is arranged in the box body.

23. The wood creep test system of claim 22, wherein: the wind speed adjusting device includes a hot wire anemometer and a rotational speed regulator.

24. A test method using the wood creep test system according to any of claims 15 to 23, characterized by: comprises the following steps of (a) carrying out,