CN214668249U - Test device for measuring axial compression performance of composite pipe for structural engineering - Google Patents
Test device for measuring axial compression performance of composite pipe for structural engineering Download PDFInfo
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Abstract
The utility model relates to a measure test device of combined material tubular axial compressibility for structural engineering, its characterized in that: the device comprises an upper end plate, a lower end plate, a semicircular steel bar, an axial strain gauge and a circumferential strain gauge; the upper end plate and the lower end plate have the same structure and respectively comprise a circular end plate and a cylindrical bulge positioned in the center of the end plate, the two semicircular steel bars are fixed on the end plate through glue, an annular groove is formed between the two semicircular steel bars and the cylindrical bulge and used for accommodating the end part of a tubular pressurized sample, and high-strength gypsum is filled in the groove to fix the end part of the sample and the end plate; the axial strain gauges and the annular strain gauges are uniformly distributed on the outer surface of the sample around the circumference of the sample and are positioned in the middle of the sample. The utility model discloses simple structure, test method flexible operation, convenient, extensive applicability, it is high to detect the precision, belongs to structural material performance detection technical field among the civil engineering.
Description
Technical Field
The utility model relates to a structural material performance detection technique among the civil engineering, concretely relates to measure combined material tubular axial compressibility's test device for structural engineering.
Background
Fiber Reinforced Polymer (FRP) has excellent properties such as high strength and good corrosion resistance as a novel material, and has been widely used in the field of civil engineering in recent years, with the most typical application being a Fiber Reinforced composite pipe (hereinafter referred to as "composite pipe") Reinforced concrete. The composite pipe can be manually manufactured by adopting a fiber cloth wet laying method, and can also be directly manufactured by pultrusion or fiber winding. Under the effect of axial pressure, the lateral expansion of concrete can be effectively restrained by the fibers which are close to the annular arrangement, thereby greatly improving the strength and the ductility of the combined member. In addition, the outer composite pipe in the combined member can be used as a template for pouring concrete, and a certain construction load needs to be borne when the concrete is poured, so that the composite pipe for structural engineering often needs to have certain axial rigidity. However, because their fibers are predominantly arranged in a nearly circumferential direction, the composite pipe exhibits significant non-linearity under axial compression. Therefore, for the application research and practice of the composite pipe in civil engineering, the accurate determination of the axial compression performance of the composite pipe, including axial compression linear parameters (axial compression strength, axial compression elastic modulus and poisson ratio) and the consideration of non-linear parameters, has important significance. In addition to the conventional straight strip sheet compression test, various test methods have been proposed by students in various countries all over the world, but the existing methods have certain limitations in practical engineering application.
The compression test method of straight strip sheets for measuring the compression performance of fiber reinforced composites is explicitly described in test specifications of many countries and regions, such as "Standard test method for unsupported Cross-section compression Performance of Polymer matrix composites under shear load" (ASTM D3410/D3410M-16(2014) "," Standard test method for compression Performance of Polymer matrix composites Using Combined load compression test apparatus "(ASTM D6641/D6641-16 (2016)"), and "test method for in-plane compression Performance of fiber reinforced plastics" (GB/T5258 (2008)), etc. However, the straight strip sheet compression test method is mainly applicable to continuous unidirectional fiber reinforced composite panels. For the composite pipe for structural engineering, in order to ensure that the composite pipe has certain axial rigidity, the winding or laying direction of fibers often has a certain included angle with the horizontal direction, and for discontinuous off-axis materials, especially under the condition of large off-axis, the straight strip-shaped sheet material compression test method cuts off the fiber materials at the edge of a sample to form an edge effect, so that the performance error of the material measured by the test is large; on the other hand, for the composite material pultrusion or winding pipe, a sample cut along the axial direction of the composite material pultrusion or winding pipe has a certain radian, so that the method cannot be applied to a straight strip-shaped sheet material compression test method; for the composite pipe manufactured by the manual wet laying method, although a straight strip-shaped sheet material sample with the same material and the same laying layer as the pipe can be manufactured and subjected to a compression test, due to the difference of the curvatures of the two and the difference of the manufacturing methods, the actual performance of the composite pipe is difficult to accurately calibrate by the result of the straight strip-shaped sheet material compression test method.
In order to eliminate adverse effects such as boundary effect, sample arc and the like, the best solution is to directly use an integral pipe section as a sample when measuring the axial compression performance of the composite pipe, such as the method adopted in the standard test method for the transverse compression performance of a circular pipe made of hoop winding polymer matrix composite material [ ASTM D5449/D5449M-16(2016) ] and the test method for the axial compression performance of a fiber reinforced thermosetting plastic pipe [ GB/T5350-. In the former, the end part of a circular tube is embedded in a groove of an end plate, and then the axis of a sample is pressurized through the end plate, but the groove of the end plate is very narrow, so that the device is difficult to adapt to the fluctuation of the pipe diameter and the change of the wall thickness of a fiber winding pipe in industrial production, and a test device is difficult to reuse; in the latter, the end of a tubular sample is reinforced and then the sample is directly pressurized, but the method is only suitable for a composite pipe with a nominal diameter of 50-100 mm and a ratio of the diameter to the reinforcing thickness of not more than 50.
In addition, aiming at the obvious nonlinearity of the composite pipe for structural engineering, which is expressed in the axial direction under the bidirectional stress state, no measuring method and expression mode which can be directly used exist at home and abroad.
Therefore, in order to solve the limitation of the existing axial compression test method for the composite pipe, according to the existing technical conditions, a test device and a test method which are simple, feasible, reliable in structure and wide in applicability and aim at measuring the axial compression performance (including axial compression linear parameters and non-linear parameters) of the composite pipe are provided.
SUMMERY OF THE UTILITY MODEL
To the technical problem who exists among the prior art, the utility model aims at: the test device is specially used for measuring the axial compression performance of the composite pipe for the structural engineering and used for the high-precision measurement of the tubular composite pipe.
In order to achieve the above purpose, the utility model adopts the following technical scheme:
measure test device of combined material tubular axial compressibility for structural engineering, its characterized in that: the device comprises an upper end plate, a lower end plate, a semicircular steel bar, an axial strain gauge and a circumferential strain gauge; the upper end plate and the lower end plate have the same structure and respectively comprise a circular end plate and a cylindrical bulge positioned in the center of the end plate, the two semicircular steel bars are fixed on the end plate through glue, an annular groove is formed between the two semicircular steel bars and the cylindrical bulge and used for accommodating the end part of a tubular pressurized sample, and high-strength gypsum is filled in the groove to fix the end part of the sample and the end plate; the axial strain gauges and the annular strain gauges are uniformly distributed on the outer surface of the sample around the circumference of the sample and are positioned in the middle of the sample.
Preferably, the test device for measuring the axial compression performance of the composite pipe for structural engineering further comprises a plurality of steel sheets, and the steel sheets are padded between the end part of the sample and the end plate so as to ensure that the pipe wall of the sample is perpendicular to the end plate. After the arrangement is adopted, the axial center pressure of the sample at the later stage is ensured.
Preferably, the outer diameter of the cylindrical protrusion is 10mm smaller than the nominal diameter of the test specimen.
Preferably, the semicircular steel bars have an inner diameter 40mm greater than the nominal diameter of the test specimen. After the arrangement is adopted, the position of the semicircular steel bar is positioned according to the pipe diameter and the wall thickness of the tubular sample so as to adapt to the fluctuation of the pipe diameter and the change of the wall thickness of the sample.
Preferably, an axial strain gauge arranged along the axial direction and a circumferential strain gauge arranged along the circumferential direction form a set of strain gauges; the number of the strain gauges is multiple groups, and the strain gauges are uniformly adhered to the outer wall of the sample along the circumference at the position of half of the height of the sample.
Preferably, the test device for measuring the axial compression performance of the composite pipe for structural engineering further comprises a pressurizing device for pressurizing the sample in the axial direction.
The test method for measuring the axial compression performance of the composite tube for the structural engineering adopts a test device for measuring the axial compression performance of the composite tube for the structural engineering, and comprises the following steps:
a. sample preparation: a sample is taken from the composite tube.
b. And (3) sample installation: sleeving the upper end of the sample into a cylindrical bulge at the center of an upper end plate, and preliminarily centering; adjusting the end face of the sample through an angle square along two vertical radial directions of the sample, and ensuring that the wall of the sample pipe is vertical to an end plate through a method of adding a steel sheet on the end face of the sample; fixing two semicircular steel bars on the end plate through viscose, and temporarily sealing the gap between the two semicircular steel bars by using adhesive tapes; preparing high-strength gypsum colloid and filling the high-strength gypsum colloid into the grooves; and after the high-strength gypsum in the groove is hardened, inverting the sample, and mounting the lower end plate by the same method as that of the upper end plate.
c. Loading: the pressurizing equipment for the test adopts a microcomputer control electro-hydraulic servo testing machine, and the tonnage is selected so that the applied load of the sample falls within the range of 10% -90% of the full load (falls on one side of the full load as much as possible) and is not less than 4% of the maximum tonnage of the testing machine; the sample is uniformly pressurized, the pressurizing speed is 0.06 percent of the axial strain per minute of the sample, and the upper end plate and the lower end plate are ensured to be parallel in the loading process.
d. Selecting and calculating data: and selecting test data of the specified axial strain range in the test process, and calculating to obtain axial compression linear parameters and non-linear parameters of the composite pipe.
Preferably, in the step a, the samples are taken from the composite pipes in the same batch used for the test or the engineering practice, and the total number of the samples is not less than 5; and (5) polishing the end part of the sample, and flattening the burrs or protrusions on the pipe wall.
Preferably, in step d, the axial compression linear parameters include axial compression strength, axial compression elastic modulus and poisson's ratio, and the non-linear parameters include axial compression secant modulus and axial compression secant poisson's ratio.
As a preferred, calculation procedure is,
the axial compressive strength of the sample was calculated according to equation (1):
in the formula:
Pc-axial compressive strength (MPa) of the sample;
Fc,max-the maximum axial compressive load (N) of the specimen;
d-average internal diameter (mm) of the specimen;
t-average thickness of the sample (mm);
the axial stress of the sample is calculated according to equation (2):
in the formula:
σx-axial stress (MPa) of the specimen;
Fc-the axial compression load (N) of the specimen;
the modulus of elasticity in axial compression is calculated according to equation (3):
in the formula:
Ex-axial compression modulus of elasticity (MPa) of the sample;
Δεx-the average increase in axial strain over the elastic range of the sample should be at least 0.2%, preferably in the range of 0.1% to 0.3% average axial strain;
Δσxwith the mean axial strain increment Δ εxA corresponding mean axial stress increment (MPa);
the poisson's ratio of the sample is calculated according to equation (4):
in the formula:
νxθ-the axial compression poisson's ratio of the sample;
Δεθwith the mean axial strain increment Δ εxA corresponding average hoop strain increment;
the strain energy density of the axial compression of the sample is calculated according to equation (5):
in the formula:
εx,ithe ith average axial strain of the sample is taken from the point of being more than or equal to 0.01 percent to the point of maximum axial load;
σx,i-and εx,iThe corresponding ith axial stress (MPa);
Ui-and εx,iA corresponding ith axial compressive strain energy density (MPa);
the axial compression secant modulus of the sample was calculated according to equation (6):
in the formula:
Ex,sec,i-and εx,iThe corresponding ith axial compression secant modulus;
calculating the Poisson's ratio of the axial compression secant of the sample according to the formula (7):
in the formula:
νxθ,sec,i-and εx,iThe corresponding i-th axial compression secant poisson ratio;
εθ,i-and εx,iThe corresponding ith average hoop strain;
respectively drawing the axial compression strain energy density-axial secant modulus U according to the calculation resultsi～Ex,sec,iAnd axial compression strain energy density-axial secant Poisson ratio Ui～νxθ,sec,iA data point;
and (3) fitting the obtained data points by a least square method to obtain the axial secant modulus expressed by the strain energy density of the composite material pipe under the composite stress state, namely under the two-way stress state or the three-way stress state, expressed by the formula (8):
in the formula:
Ex，secthe axial secant modulus (MPa) of the composite pipe in a bidirectional stress state;
a, B and C are axial secant modulus nonlinear coefficients obtained by fitting test axial compression strain energy density-secant modulus data;
U*-axial compressive strain energy density (MPa) at maximum load of the axial compression test specimen;
d, F-is U > U*Rear axial secant modulus non-linear parameter, respectively using formula (9)And (10) calculating:
under the composite stress state of the composite material pipe, the axial Poisson ratio expressed by the strain energy density is expressed by the formula (11):
in the formula:
νxθ,sec-the axial poisson's ratio of the composite pipe in a bidirectional stressed state;
a, b and c are axial secant Poisson ratio nonlinear coefficients obtained by fitting test axial compression strain energy density-secant Poisson ratio data;
d, f-is U > U*The rear axial secant Poisson ratio nonlinear parameter is calculated by the following formulas (12) and (13):
for the composite material pipe for structural engineering, usually, the shear deformation of the composite material pipe is ignored, the composite material pipe is in the axial compression and hoop tension states, and the composite material pipe is considered to be in the bidirectional stress state, so the strain energy density of the composite material pipe in the bidirectional stress state is calculated by the formula (14):
in the formula:
σx，εx-axial stress (MPa) and strain, respectively, under bi-directional stress of the composite pipe;
σθ，εθ-the hoop stress (MPa) and strain are respectively under bidirectional stress of the composite pipe;
therefore, the strain energy density of the bidirectional stressed composite pipe at any moment is obtained through the formula (14), namely the nonlinear axial secant modulus E of the composite pipe under the current stress state is obtained through the formulas (8) to (13)x,secAnd axial secant Poisson's ratio vxθ,sec。
The utility model has the advantages of as follows:
1. the utility model discloses a simple and easy test device, axial compression performance that can the accurate measurement compound material pipe, including axial compression linear parameter (axial compressive strength, axial elastic modulus, axial poisson's ratio) and nonlinear parameter (axial compression secant modulus, axis compression secant poisson's ratio).
2. The utility model discloses an axial pressure device, with the tip embedding end plate's of tubulose sample recess and fill the tip that the sample was consolidated to the high strength gypsum, the recess of end plate has a bit degree of regulation, the fluctuation of adaptable compound pipe diameter and wall thickness.
3. The utility model discloses extensive applicability's characteristics mainly embody in following three aspect: (1) in addition to typical composite pultruded and wound tubes, composite tubes made by hand using a wet-laid process may be suitable for use in this process; (2) the method has high acceptance on the discrete level of the measured geometric dimension (diameter and thickness) of the composite pipe; (3) the composite pipe is suitable for composite pipes with any fiber winding or laying angle.
4. The axial center pressurization of the composite pipe can be realized.
5. The testing device is convenient to operate, simple in structure and reusable.
Drawings
Fig. 1 is a side view of a test specimen.
FIG. 2 is a schematic view of the placement of strain gages on a test piece.
Figure 3a is a side view of the upper endplate and the lower endplate.
Figure 3b is a top view of the upper endplate and the lower endplate.
Figure 3c is a perspective view of the upper endplate and the lower endplate.
Figure 4a is a side view of two semicircular bars.
Figure 4b is a top view of two semicircular bars.
Figure 4c is a perspective view of two semicircular bars.
Fig. 5 is a perspective view of the semicircular steel bar after being installed.
Fig. 6a-6d are schematic illustrations of the installation of the test device.
Fig. 7 is a perspective view of the test apparatus.
FIG. 8 is a plot of axial stress versus strain for the experiments;
FIG. 9 is a plot of the strain energy density versus axial modulus and Poisson's ratio for the tests.
Wherein, 1 is the upper end plate, 2 is the lower plate, 3 are cylindrical protruding, 4 are semi-circular billet, 5 are the sample, 6 are axial strain gauge, 7 are hoop strain gauge.
Detailed Description
The present invention will be described in further detail with reference to specific embodiments.
The test device for measuring the axial compression performance of the composite tube for structural engineering comprises an upper end plate, a lower end plate, a semicircular steel bar, an axial strain gauge and a circumferential strain gauge. The upper end plate and the lower end plate have the same structure and respectively comprise a circular end plate and a cylindrical bulge positioned in the center of the end plate, two semicircular steel bars are fixed on the end plate through glue and form an annular groove with the cylindrical bulge in the center of the end plate, and the positions of the semicircular steel bars are positioned according to the pipe diameter and the wall thickness of a tubular sample so as to adapt to the fluctuation of the pipe diameter of the sample and the change of the wall thickness; the pressure sample is tubular, the polished end parts of the pressure sample are respectively arranged in the grooves of the upper end plate and the lower end plate, and the sample is fixed on the upper end plate and the lower end plate by filling a high-strength gypsum colloid material in the grooves; the finally fixed upper end plate and the lower end plate are required to be vertical to the axis of the sample so as to ensure that the axis of the sample is pressed at the later stage; the multi-group strain gauges are evenly attached to the middle of the outer wall of the sample, and each group of strain gauges comprises an axial strain gauge and a hoop strain gauge which are arranged in the axial direction and the hoop strain gauge so as to measure the axial strain and the hoop strain of the sample in the compression process.
The following is a detailed description:
1 sample (1)
1.1 sample type
The samples are taken from the composite pipes used in the test or the same batch used in the engineering practice, and the total number of the samples is not less than 5. The end of the sample is polished to smooth the nodules or protrusions on the tube wall, and the sample pattern is shown in fig. 1. D is the outer diameter of the sample; d is the inner diameter of the sample; h is the height of the sample; t is the specimen thickness.
1.2 sample size
Sample height H2 x stiff end height L + sample effective height L, wherein sample effective height L equals 100mm, the stiff end height L of sample: when the diameter d is less than or equal to 200mm, l is more than or equal to 20 mm; when the diameter d is more than 200mm and less than or equal to 400, l is more than or equal to 30 mm; when the diameter d is more than 400mm and less than or equal to 600, l is more than or equal to 40 mm; when the diameter d is larger than 600mm, l is larger than or equal to 50 mm.
1.3 end face requirement of the sample
The end face of the sample is smooth and has no delamination, tearing and the like, and the rest surfaces are not damaged. The two end faces of the sample are required to be parallel to the greatest extent and perpendicular to the axis of the sample, and the parallelism is not more than 0.1 mm.
1.4 sticking of the sample Strain gage
As shown in fig. 2, 4-8 sets of strain gauges are uniformly stuck to the cross section at half the height of the sample along the outer surface thereof, and if the diameter of the sample is large, the number of sets of strain gauges can be increased appropriately. Each group of strain gauges comprises two unidirectional strain gauges, one strain gauge is arranged along the axial direction of the sample, the other strain gauge is arranged along the circumferential direction, and the strain gauges with the gauge length of 5mm to 20mm are suitable to be adopted.
1.5 sample number
Each group of the mechanical property samples is not less than 5, 5 effective samples are guaranteed to exist in the same batch, and the physical property samples are regulated according to corresponding standards.
2 conditions of the test
2.1 test environmental conditions
2.2.1 Standard environmental conditions in the laboratory
Temperature: (23 + -2) deg.C; relative temperature: (50. + -. 10)%.
2.2.2 laboratory non-Standard environmental conditions
If the standard environmental condition of the laboratory is not available, the environmental condition of the laboratory close to the standard environmental condition of the laboratory is selected.
2.2 test Condition adjustment
The test was carried out under the conditions of at least 4 hours at a temperature (23. + -. 2). degree.C. The test was performed at ambient laboratory temperature without the conditions.
3 device and apparatus
3.1 test device
The test device of the composite pipe axial compression test method consists of an upper steel end plate, a lower steel end plate and four semicircular steel bars, as shown in figures 3a-3c, 4a-4c and 5.
3.1.1 Upper and lower end plates
3.1.1.1 the end plate of the test unit is circular and has a cylindrical protrusion in the center, as shown in FIGS. 3a-3 c. The surface of the end plate should be flat and smooth.
3.1.1.2 end plate diameter D1Is (the outer diameter D +20) mm, and the diameter D of the cylindrical bulge at the center of the end plate2Is (the inner diameter of the composite pipe is d-5) mm; height h of end plate1(excluding the thickness of the cylindrical projection) is 10 to 20mm, and the height h of the cylindrical projection is2Equal to the fixed end length l of the sample.
3.1.2 semicircular steel bars
3.1.2.1 every two semicircular steel bars form a set, which can form a circle with two gaps, as shown in fig. 4a-4 c.
3.1.2.2 circular diameter D formed by two semicircular steel bars3Is (the outer diameter D +5) mm, and the width b of the gap is 2-5 mAnd m is selected. Thickness t of steel strip1Is 10mm, height h3The same as the fixed end height l of the sample.
3.1.3 the end plate is assembled with two semicircle billet back, and the cylindrical arch in end plate central authorities is (the compound material pipe thickness t +5) mm with the recess width B that the semicircle billet formed, can let the sample tip card go into in the recess, as shown in fig. 5. And filling a high-strength gypsum material in the groove to serve as an anchoring end when the axle center of the sample is loaded.
3.2 mounting of the test device
3.2.1 the upper end of the sample is fitted into a cylindrical boss in the center of the upper end plate and initially centered as shown in FIG. 6 a. The end faces of the samples were adjusted by an angle square along two perpendicular radial directions of the samples, and the method of adding small steel sheets on the end faces of the samples ensures that the walls of the samples and the end plates are kept perpendicular, as shown in fig. 6b and 6 c.
3.2.2 the two semicircular bars are fixed to the end plate by means of glue, as shown in fig. 6d, the gap between the two bars can be temporarily closed with a tape.
3.2.3 preparing high-strength gypsum colloid and filling the high-strength gypsum colloid into the grooves.
3.2.4 after the gypsum in the groove of the upper end plate is hardened, inverting the sample, and installing the lower end plate by the same method as the installation of the upper end plate by 3.2.1-3.2.3. The final test set-up was complete as shown in figure 7.
3.3 test device
The pressurizing equipment for the test is an electro-hydraulic servo testing machine controlled by a microcomputer, and the tonnage is selected so that the applied load of the test sample falls within the range of 10% -90% of the full load (falls on one side of the full load as much as possible) and is not less than 4% of the maximum tonnage of the testing machine.
3.4 Loading speed
The axial loading rate was 0.06% increase in axial strain of the specimen per minute.
3.5 centering of the samples
In order to ensure the axial pressurization of the sample, the sample needs to be centered and debugged before the formal loading is started. The sample is initially loaded until the axial strain reaches about 0.02 percent, and the error value in the symmetrically arranged axial strain is judged to be not more than 10 percent of the average value of the axial strain and the axial strain, namely the requirement of sample centering is met. Otherwise, the position of the sample needs to be adjusted until the centering requirement is met.
4 test procedure
4.1 sample preparation the specifications of 1.1, 1.2, 1.3 and 1.4 were followed.
4.2 the samples were visually inspected and if defective and not of the required dimensions and preparation, the samples were discarded.
4.3 the acceptable samples are numbered and the sample size is measured. The inner diameter and the outer diameter of the sample and the thickness of the sample are respectively measured, and the measurement is accurate to 0.01 mm. On the two end faces of the sample, the outer diameters in two directions perpendicular to each other were measured, respectively, and the average value thereof was taken as the average outer diameter. And measuring the wall thickness at eight equal intervals of any end face of the sample, discarding the maximum value and the minimum value, taking the average value of the rest points as the average wall thickness, and taking the wall thickness of the sample as the average value of the average wall thicknesses of the two end faces.
4.4 sample Condition as specified in 2.2.
4.5 sample installation as specified by 3.2.
4.6 the sample was uniformly and continuously pressurized at a loading rate of 3.4 until the sample broke.
The 4.7 sample pair is required to be specified as 3.5.
4.8 during the test, the data to be collected and stored include: load, strain of the sample and pressing time.
5 calculation of composite pipe linear axial performance parameters
5.1 FIG. 8 shows the axial stress-strain curve of a typical composite pipe for structural engineering during the whole axial compression performance test, with the end point of the curve being the maximum axial load. The specified pressure is positive and the pull is negative.
5.2 calculating the axial compressive strength of the sample according to the formula (1):
in the formula:
Pc-axial compressive strength (MPa) of the sample;
Fc,max-the maximum axial compressive load (N) of the specimen;
d-average internal diameter (mm) of the specimen;
t-average thickness (mm) of the sample.
5.3 axial stress of the sample is calculated according to equation (2):
in the formula:
σx-axial stress (MPa) of the specimen;
Fc-the axial compression load (N) of the specimen;
5.4 axial compression modulus of elasticity was calculated according to equation (3):
in the formula:
Ex-axial compression modulus of elasticity (MPa) of the sample;
Δεxthe average axial strain increase in the elastic range of the sample, as shown in fig. 8, should be at least 0.2%, suggesting a range of 0.1% to 0.3% average axial strain;
Δσxwith the mean axial strain increment Δ εxCorresponding mean axial stress increase (MPa).
5.5 calculate the Poisson's ratio of the sample according to equation (4):
in the formula:
νxθ-the axial compression poisson's ratio of the sample;
Δεθwith the mean axial strain increment Δ εxCorresponding average hoop strain increments.
6 nonlinear axial performance of composite pipe under bidirectional stress
The nonlinear axial performance parameters of the composite pipe are expressed using strain energy density based on the Jones and Nelson's models.
6.1 calculate the strain energy density of the axial compression of the sample according to equation (5):
in the formula:
εx,ithe ith average axial strain of the sample is taken from more than or equal to 0.01 percent to the maximum load point;
σx,i-and εx,iThe corresponding ith axial stress (MPa);
Ui-and εx,iThe corresponding ith axial compressive strain energy density (MPa).
6.2 axial compression secant modulus of the sample was calculated according to equation (6):
in the formula:
Ex,sec,i-and εx,iThe corresponding ith axial compression secant modulus.
6.3 calculating the Poisson's ratio of the axial compression secant of the sample according to the formula (7):
in the formula:
νxθ,sec,i-and εx,iThe corresponding i-th axial compression secant poisson ratio;
εθ,i-and εx,iCorresponding ith average hoop strain.
6.4 plotting axial compression from the results of the calculations of 6.1, 6.2 and 6.3, respectivelyStrain energy density-axial secant modulus (U)i～Ex,sec,i) And axial compressive strain energy density-axial secant Poisson's ratio (U)i～νxθ,sec,i) Data points, as shown in fig. 9.
6.5 as shown in fig. 9, the data points obtained by the least square method fitting 6.4 are obtained, and the axial secant modulus expressed by the strain energy density of the composite pipe in the composite stress (bidirectional stress or three-directional stress) state is expressed by the formula (8):
in the formula:
Ex,secthe axial secant modulus (MPa) of the composite pipe under the bidirectional stress state;
a, B and C are axial secant modulus nonlinear coefficients obtained by fitting test axial compression strain energy density-secant modulus data;
U*-axial compressive strain energy density (MPa) at maximum load of the axial compression test specimen;
d, F-is U > U*The rear axial secant modulus nonlinear parameter is calculated by the following equations (9) and (10), respectively:
under the composite stress state of the composite pipe, the axial Poisson ratio expressed by the strain energy density is expressed by the formula (11):
in the formula:
νxθ,sec-axial poisson's ratio of the composite pipe for structural engineering under bidirectional stress state;
a, b and c are axial secant Poisson ratio nonlinear coefficients obtained by fitting test axial compression strain energy density-secant Poisson ratio data;
d, f-is U > U*The Poisson's ratio nonlinear coefficient of the rear axial secant is calculated by the following equations (12) and (13):
for the composite pipe for structural engineering, the shear deformation of the composite pipe is usually ignored, the composite pipe is in an axial compression state and a hoop stretching state, and the composite pipe can be considered to be in a bidirectional stress state, so the strain energy density of the composite pipe in the bidirectional stress state is calculated by the formula (14):
in the formula:
σx，εx-axial stress (MPa) and strain, respectively, of the composite pipe under bidirectional stress;
σθ，εθthe hoop stress (MPa) and the strain of the composite pipe in a bidirectional stress state are respectively adopted.
Thereby having a bidirectional stressed composite materialThe strain energy density of the pipe at any time, formula (14), can obtain the nonlinear axial secant modulus E of the composite pipe under the current stress state by the formulas (8) to (13)x,secAnd axial secant Poisson's ratio vxθ,sec。
7 results of the test
The arithmetic mean, standard deviation, dispersion coefficient, etc. of the test results such as the axial initial elastic modulus, the axial initial poisson's ratio, etc. should be obtained. For larger dispersion coefficients, specific reasons should be analyzed. If the quality of the sample is a problem, a batch of samples should be prepared again for testing.
7.1 Property values for each sample: x1，X2，X3…, Xn. If necessary, the failure of each sample should be described.
7.2 calculate the arithmetic mean according to equation (15) to three significant figures:
in the formula:
Xi-a property value for each sample;
n is the number of samples.
7.3 calculate the standard deviation S according to equation (16) to a two-digit significant figure:
in the formula:
s-standard deviation.
7.4 calculating the coefficient of dispersion C according to equation (17)vCalculate to two significant digits:
in the formula:
Cv-discrete coefficients.
7.5 confidence intervals for the mean.
Calculated according to ISO 2602: 1980.
The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be equivalent replacement modes, and all are included in the scope of the present invention.
Claims (6)
1. Measure test device of combined material tubular axial compressibility for structural engineering, its characterized in that: the device comprises an upper end plate, a lower end plate, a semicircular steel bar, an axial strain gauge and a circumferential strain gauge; the upper end plate and the lower end plate have the same structure and respectively comprise a circular end plate and a cylindrical bulge positioned in the center of the end plate, the two semicircular steel bars are fixed on the end plate through glue, an annular groove is formed between the two semicircular steel bars and the cylindrical bulge and used for accommodating the end part of a tubular pressurized sample, and high-strength gypsum is filled in the groove to fix the end part of the sample and the end plate; the axial strain gauges and the annular strain gauges are uniformly distributed on the outer surface of the sample around the circumference of the sample and are positioned in the middle of the sample.
2. The test device for measuring the axial compression performance of a composite pipe for structural engineering according to claim 1, characterized in that: the test tube also comprises a plurality of steel sheets, and the steel sheets are padded between the end part of the test sample and the end plate so as to ensure that the tube wall of the test sample is perpendicular to the end plate.
3. The test device for measuring the axial compression performance of a composite pipe for structural engineering according to claim 1, characterized in that: the outer diameter of the cylindrical protrusion is 10mm smaller than the nominal diameter of the test specimen.
4. The test device for measuring the axial compression performance of a composite pipe for structural engineering according to claim 1, characterized in that: the semicircular bars had an inner diameter 40mm greater than the nominal diameter of the specimen.
5. The test device for measuring the axial compression performance of a composite pipe for structural engineering according to claim 1, characterized in that: the axial strain gauge is arranged along the axial direction, and the annular strain gauge is arranged along the annular direction to form a group of strain gauges; the number of the strain gauges is multiple groups, and the strain gauges are uniformly adhered to the outer wall of the sample along the circumference at the position of half of the height of the sample.
6. The test device for measuring the axial compression performance of a composite pipe for structural engineering according to claim 1, characterized in that: the device also comprises a pressurizing device for pressurizing the sample in the axial direction.
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