DE10344544B3 - Apparatus for mechanical testing of fiber-reinforced materials to determine pressure characteristic values, has clamping pads at clamping blocks operated by hydraulic cylinders on both workpiece ends - Google Patents

Abstract

The apparatus for the mechanical testing of materials and especially fiber-reinforced plastics, to determine the pressure characteristic value on pressure along a single axis, has a lower clamping block (5) and a parallel upper clamping block (6) with an axial sliding movement along at least one guide column (9). Each clamping block has a set of clamping pads (2,3). Each with a fixed pad (2.1,2.2) and a moving pad (3.1,3.2) operated by a hydraulic cylinder (4.1,4.2). The sample workpiece (1) is clamped with an equal force at both ends, with a test shear force applied to it through the sets of clamping pads.

Description

The The invention relates to a device for mechanical material testing for Determination of the pressure characteristics of materials with uniaxial compressive stress. In particular, the invention relates to a device for compressive stress of fiber reinforced Plastics according to the currently applicable Standards.

typical Pressure characteristics, such. As the compressive strength, the modulus of elasticity and the Elongation at break, are defined mechanical material parameters, the serve to determine the mechanical material behavior. From great Interest is the pressure characteristics with regard to the dimensioning of Components at critical pressure loads.

devices for determining material characteristics under compressive stress known from the technical standard and regulations.

The usual applied devices differ in terms of load or test force introduction into the sample body, namely with frontal force application and force transmission via shear forces. at the devices with thrust introduction solutions are with a clamping force generation according to the wedge principle or by clamping screws known. The straight line guide the specimen takes place in the previously known solutions either by direct support the specimen using bulges, through a guide the clamping jaw sets in a sleeve or by separate guide column.

The pressure test with frontal test force introduction using a bulge support has for the exam of high strength specimens not proven, because on the one hand in the field of force introduction often sample breaks occur and on the other hand, the measurement results by friction effects on the Beulstütze falsified become. In the test practice finds to a so-called Celanese device application. In evaluation The test results showed that there was an undesirable bend in the sample bodies can not be avoided. The led to that for a big Number of samples the measurement results had to be discarded.

The validity the pressure test is in enforcement of the applicable standard only then guaranteed when the specimen within or at the end of the clamping length breaks and the strains on two opposite ones sample areas within a given tolerance. Furthermore Standardization only provides a defined number and special training of failure modes of the specimen firmly.

In front the background, that it is often expensive to try Sample materials is involved in complex instrumentation is This condition is not only unbearable for economic reasons.

From the US 4,840,070 A a pressure testing device for determining pressure characteristics of materials is known, which has clamping blocks and clamping jaws and guide columns. In this case, a stabilizer is used, which is to stabilize the specimen during the test.

A clamping head for a traction machine for lateral force-free Probeneinspannung is in the DE 199 26 408 A1 discloses, in which the clamping jaws are coupled to each other free-floating transverse to the traction axis.

The US 3 498 121 discloses sample centering means for testing machines in which diametrically opposed hydraulically piston operated gripping elements are provided to center the sample.

Other From the prior art previously known devices are due quite complicated in terms of their closed design, which leads to long sample change times and the test at deviating test conditions from standard climate (23 ° C, 50% rel. Humidity) extremely difficult.

Also offer these devices only a very limited accessibility for instrumentation the specimen, z. B. with strain gauges or for the application of optical measurement.

devices with a pressure force generation according to the wedge principle have the disadvantage on that the device construction tolerances add up, what to a very poor one Straight line of the specimen and thus too inadmissible Bending stresses leads.

The Tensioning screws is the disadvantage of its own, that no uniform application of pressure into the sample body can be done.

Basically you can determine that the devices known from the prior art for the determination of material characteristics under compressive stress with respect to the parallel guidance and Bulging of the specimens and the emergence of shear forces in the tester are problematic.

task The invention is a pressure testing device for mechanical Materials testing to develop with a sample body safely and evenly adjusted and can be strained, with the series of measurements, even with different ones Specimen geometries fast and easy be carried out conveniently can and with the number of valid pressure tests elevated can be. Another object of the invention is overlaying To reliably exclude the compressive stresses with bending stresses.

These Tasks are inventively characterized solved, by a lower clamping block and a parallel to this axially displaceable arranged upper terminal block are provided along at least a leadership column sliding are stored. Each clamping block has a clamping jaw set, consisting of a fixed first jaw and a complementary flying mounted second jaw and one in operative connection with consists of the second jaw standing hydraulic cylinder. The two clamping jaw sets Be there by the associated two hydraulic cylinders of the clamping blocks with a same clamping force so that a specimen at both ends with the same clamping force is clamped and the test load by the thrust on the Jaw sets be initiated.

The two terminal blocks are on a rack between a pressure plate and a pressure body on top of each other arranged. The axial guide the two terminal blocks is realized by the guide column, the releasably on the pressure plate this is attached. The terminal blocks point to ensure an axial movement executions, penetrated by the guiding column become. In the field of bushings are ball cages arranged, which is a low-friction sliding of the terminal blocks along ensure the guide column.

In a preferred embodiment are two guide columns provided which are arranged diagonally to each other vertically on the pressure plate. Under pressure load therefore extends the sample clamping axis diagonally from a guide column to the another guide pillar. The Arrangement of the guide columns to each other is not limited only to the diagonal arrangement, but rather can also considering a uniform force distribution arbitrarily.

Of the Way of the inventive concept will not leave even if the upper terminal block and the lower terminal block open to the edge region groove-like Have moldings in which the guide columns at least partially intervention.

The Pressure plate is ring-shaped, polygonal or plate-shaped formed and consists of a metallic material or a Plastic-metal composite and lets Almost any shape, structure and surface design.

The Said hydraulic cylinders have the task of non-positively and / or positively locking the sample body respectively between the fixed jaws and the complementary flying clamp mounted jaws. The clamping takes place on both sides above and below a failure area of the specimen. At a preferred embodiment of the invention, the hydraulic cylinder by means of a connection particularly advantageous to the hydraulic system a material testing machine be connected or alternatively with a separate hydraulic unit operated as a self-sufficient unit. In the preferred embodiment clamping forces up to 100 kN can be applied by the hydraulic cylinders.

In order to is ensured during that the test procedure the same holding forces at the ends of the specimen act and thus a relative movement between the sample body and the jaws is reduced.

According to one advantageous embodiment of the invention is due to the immediate Contact the sample ends on the pressure plate and / or on the pressure body and / or indirect contact by means of inserts in addition to the introduction of thrust by means of the clamping jaw sets a test force entry via the test force introduction in the front sides of the specimen realizable. This is the combination in a particularly advantageous manner of thrust introduction over the clamping jaws and the frontal Prüfkrafteinleitung allows.

The two parallel spaced hydraulic cylinders are respectively arranged on a first short inner edge of the C-shaped clamping blocks. An upper and a lower jaw set is each of the associated Hydraulic cylinder simultaneously subjected to the same pressure force.

At a second short inner edge of each terminal block, in each case the first clamping jaw is arranged, which is preferably permanently connected to the terminal block. The hydraulic cylinders and the first jaws are disposed in confronting relation within the C-shaped clamping blocks according to the present invention. This first tension Bake can each be formed on the second short inner edge of the terminal blocks or attached as a separate component to the terminal blocks. Each fixed clamping jaw is associated with a complementary, cantilevered second clamping jaw, which is held with one of its narrow sides on the terminal block. Each of the two clamping blocks may have a guide or else a holding device for receiving the two second clamping jaws. Regardless of the type of attachment, however, it is ensured that when Druckkraftbeaufschlagung by the hydraulic cylinder, the second jaws can be moved in the direction of the first, fixedly arranged complementary clamping jaws. In a particularly advantageous embodiment of the invention, each of the two second clamping jaws is magnetically formed and adheres to one of its front side and / or one of its side surfaces on the inner edge of the terminal block. These second clamping jaws are each arranged between their associated hydraulic cylinders and the complementary first clamping jaws. For an inspection or cleaning of the clamping surfaces by the operator of the pressure tester, these second jaws can thus easily remove from the terminal block. Each fixedly arranged clamping jaw and its complementary cantilevered clamping jaw thus form a clamping jaw set, namely in each case one for the upper and the lower clamping block.

The C-shaped Training the two terminal blocks allows easy handling of the pressure testing device, especially when removing the second jaw and when changing of the specimen and offers excellent performance due to the all-round accessibility of the specimen Options, various strain gage systems, such. B. a strain gauge, a video extensometer or a grayscale analyzer. The terminal blocks are preferably made of a hard and wear-resistant material, such. Steel, manufactured.

The terminal blocks also each have two trained as holes bushings on, in the assembled state of the pressure tester penetrated by the guide columns become. It goes without saying that the holes of both terminal blocks a same longitudinal axis exhibit. In the field of these bushings low-friction ball cages are arranged. These ball cages contribute to distorting the measurement results frictional forces between the guide columns and the two terminal blocks be avoided as far as possible.

The frontal Prüfkraftbeaufschlagung of the specimen is by means of a pressure hull realized, which sits on the upper terminal block. The pressure body is preferably cylindrical or plate-shaped and in turn has a connected material testing machine or over designed as a self-sufficient unit hydraulic unit with pressure applied. The while The pressure or test force applied to the pressure test is measured by means of a load cell recorded.

The terminal blocks can be removed from the frame of Druckprüfvorrichtung individually and if necessary replace with other terminal blocks.

the The idea of the invention is inherent in such a construction also samples with tested different geometry can be. For larger or smaller samples can the pressure tester be scaled. An easier way, the pressure tester to beulend threatened specimen with long measuring lengths However, to adapt, is that the jaws with receptacles equipped, intervene in the so-called Beulstützen force and / or positive fit.

• • Sicherung einer zuverlässigen und reproduzierbaren Probenkörpereinspannung durch eine messbare und gleichmäßige hydraulische Druckkraftbeaufschlagung,
• • Verbesserung der Geradführung der Probenkörper und damit Erhöhung der gültigen Druckversuche durch Linearführung der Klemmbacken mittels Führungssäule,
• • Möglichkeit des Einsatzes optischer Aufzeichnungsverfahren während des Druckversuchs durch verbesserte Zugänglichkeit des Probenkörpers durch offene C-förmig ausgebildete Klemmbacken,
• • Verringerung der Probenkörperwechselzeiten durch einfache Bauweise und
• • Reinigung und Inspektion der Spannbackensätze durch die entnehmbaren, fliegend gelagerten zweiten Spannbacken problemlos möglich.

The significant advantages and features of the invention over the prior art are essentially:

• • Ensuring a reliable and reproducible sample body clamping by a measurable and uniform hydraulic pressure application,
• • Improvement of the straight guidance of the specimens and thus increase of the valid compression tests by linear guidance of the jaws by means of guide column,
• Possibility of using optical recording methods during the printing test due to improved accessibility of the sample body through open C-shaped clamping jaws,
• • Reduction of sample body change times through simple construction and
• • Cleaning and inspection of the jaw sets by means of the removable, cantilevered second clamping jaws easily possible.

Various solutions and advantages of the invention will be apparent to those skilled in the art from the following detailed description of a preferred embodiment with reference to the attached drawings; in these show:

1 : A perspective view of Druckprüfvorrichtung invention and

2 : a front view of the erfindungsge proper pressure test device.

The 1 and 2 illustrate a perspective view and a front view of Druckprüfvorrichtung invention 13 for mechanical material testing, in particular for determining the pressure characteristics parallel to the laminate level of fiber-reinforced plastics. The frame consists of a pressure plate 7 , one parallel to the printing plate 7 spaced pressure hull 8th and two guide columns 9 ,

Between the printing plate 7 and the pressure body 8th are two identically constructed C-shaped terminal blocks 5 . 6 arranged one above the other, axially in the direction of the longitudinal extension of the two guide columns 9 are displaceable. As in 1 can be seen, the terminal blocks 5 . 6 trained as holes bushings 13 on, by the guide pillar 9 be penetrated. The upper terminal block 6 and the lower terminal block 5 are formed open on the operating side so that the placement of the pressure tester 12 with a specimen 1 can be done easily.

At the viewer's left inner edge of the C-shaped terminal blocks 5 . 6 are each a hydraulic cylinder 4.1 respectively. 4.2 arranged. The hydraulic cylinders 4.1 . 4.2 are always spaced parallel to each other in the static state and also during the testing process.

Opposite the hydraulic cylinder 4.1 . 4.2 are at the viewer's right inner edge of the C-shaped terminal blocks fixed jaws 2.1 . 2.2 arranged, which form flat clamping surfaces on their broad sides. Each of the first, fixed jaws 2.1 . 2.2 is a complementary, cantilevered second jaw 3.1 . 3.2 assigned between the fixed jaw 2.1 . 2.2 and the associated hydraulic cylinder 4.2 . 4.2 is held. The holder of the overhung jaws 3.1 . 3.2 takes place in this case the front side by means of a magnet which, starting from the wide inner edge of the upper terminal block 5 up to the wide inner flank of the lower terminal block 6 extends.

The two hydraulic cylinders 5 . 6 each act on the cantilever mounted second jaws 3.1 . 3.2 , The clamping force of the hydraulic cylinders 5 . 6 Therefore, it acts orthogonally to the compressive force of a material testing machine, not shown, the front side of the sample body 1 pressurized.

The handling of the pressure tester 12 is very simple. Usually, the pressure testing device according to the invention 12 used in conjunction with a Werkstoffprüfmaschine not shown, which produces a linear movement with a crosshead speed of typically 0.5 mm to 1.5 mm / min. The linear movement takes place in the direction of the longitudinal axis of the sample body 1 ,

At the beginning of the pressure test are both hydraulic cylinders 4.1 . 4.2 retracted, all jaws 2.1 . 2.2 . 3.1 . 3.2 are thus relieved of pressure. With the removal of the overhung second clamping jaws 3.1 respectively. 3.2 from the upper terminal block 6 or lower terminal block 5 a sufficiently large space is released to the specimen 1 in the pressure testing device 12 introduce. After inserting the overhung jaws 3.1 . 3.2 becomes the specimen 1 adjusted and fixed on both sides above and below. With the subsequent extension of the hydraulic cylinder 4.1 . 4.2 become the cantilevered jaws 3.1 . 3.2 subjected to a compressive force to the sample body 1 firmly clamp. In this case, a uniform Druckkraftbeaufschlagung on the two cantilevered jaws 3.1 . 3.2 , The specimen 1 is thus up to an expected failure area by a direct area contact between the jaws 2.1 . 3.1 such as 3.1 . 3.2 evenly clamped. The hydraulic compressive stress of the specimen 1 Now takes over the on the upper terminal block 6 seated pressure hull 8th , The continuous linear movement of the Werkstoffprüfmaschine thereby generates a compressive force, the front side of the pressure hull 8th acts. This causes the upper and lower terminal block 6 . 5 to move towards each other.

During the Pressure test become the linear expansion and the power recorded. These values become after the end of the experiment typically the modulus of elasticity, strength and elongation at break calculated.

At the end of the pressure test, the two hydraulic cylinders 4.1 . 4.2 and the pressure body 8th depressurized, the two cantilever jaws 3.1 . 3.2 taken and the broken specimen 1 the pressure test device 12 taken.

With the pressure tester according to the invention 12 The basic problems that regularly arise in the determination of realistic pressure characteristics according to the applicable test standards, such as: As the superposition of compressive stresses with bending stresses, are largely avoided. Through an improved parallel guidance of the clamping blocks 5 . 6 In addition, a very stiff guidance of the sample body 1 be achieved.

A not to be underestimated advantage of the invention is that not only fiber reinforced Plastics, but rather also metallic materials, ceramics and composites can be subjected to a pressure test. The robustness of the pressure tester 12 and the ability to reliably high test loads over (the hydraulic cylinder 4.1 . 4.2 and) the pressure body 8th initiate ensures a high number of valid test results.

1

specimen

2

first, fixed clamping jaws

2.1

first Clamping jaw, below

2.2

first Clamping jaw, top

3

second, flying jaws

3.1

second Clamping jaw, below

3.2

second Clamping jaw, top

4

hydraulic cylinders

4.1

lower hydraulic cylinders

4.2

upper hydraulic cylinders

5

first terminal block

6

second terminal block

7

printing plate

8th

pressure vessels

9

guide column

10

connection of the hydraulic cylinder

11

effective direction the pressure force

12

Pressure tester

13

execution

Claims (8)

Pressure testing device for mechanical material testing, in particular for determining the pressure characteristics of materials, with clamping blocks and guide column, characterized in that a lower terminal block ( 5 ) and a parallel to this axially displaceably arranged upper terminal block ( 6 ) are provided along at least one guide column ( 9 ) are slidably mounted, wherein the lower terminal block ( 5 ) and the upper terminal block ( 6 ) each a clamping jaw set, consisting of a fixed first jaw ( 2.1 respectively. 2.2 ) and a complementary overhung second clamping jaw ( 3.1 respectively. 3.2 ), as well as in operative connection with the second clamping jaw ( 3.1 respectively. 3.2 ) standing hydraulic cylinder ( 4.1 respectively. 4.2 ), wherein the hydraulic cylinders ( 4.1 . 4.2 ) act on the associated clamping jaw set with a similar clamping force, so that a sample body ( 1 ) is clamped at both ends with the same clamping force and the test force is introduced as a thrust force on the jaw sets. Pressure testing device according to claim 1, characterized in that the clamping blocks ( 5 . 6 ) one above the other on a rack between a pressure plate ( 7 ) and a pressure body ( 8th ) are arranged, and the terminal blocks ( 5 . 6 ) Bushings ( 13 ), through which the guide column (s) ( 9 ) to ensure an axial displacement of the terminal blocks ( 5 . 6 ) is / are. Pressure testing device according to claim 1 or 2, characterized in that the clamping blocks ( 5 . 6 ) Are C-shaped, and on an inner edge of each terminal block ( 5 respectively. 6 ) of the hydraulic cylinders ( 4.1 respectively. 4.2 ) and in opposition to each of the first jaw ( 2.1 respectively. 2.2 ) is arranged and the complementary cantilever second clamping jaw ( 3.1 respectively. 3.2 ) between the hydraulic cylinder ( 4.1 respectively. 4.2 ) and the first jaw ( 2.1 respectively. 2.2 ) is held by a magnet and over the open C-side of the terminal block ( 5 respectively. 6 ) is removable. Pressure testing device according to one of claims 1 to 3, characterized in that the pressure body ( 8th ) and the pressure plate ( 7 ) in such a way that the test force in the sample body ( 1 ) in addition to the thrust input via the clamping jaw sets ( 2.1 . 2.2 and 3.1 and 3.2 ) over the end faces of the specimen ( 1 ) can be introduced. Pressure testing device according to one of claims 1 to 4, characterized in that the clamping jaws ( 2 . 3 ) Have receptacles in which forceps and / or form-fit intermesh with buckling supports in order to prevent damage to specimens ( 1 ) can be clamped and tested with a large test length. Pressure testing device according to one of claims 1 to 5, characterized in that the hydraulic cylinders ( 4 ) can be connected to the hydraulic system of a Werkstoffprüfmaschine or can be operated with a separate hydraulic unit as a self-sufficient unit. Pressure testing device according to one of claims 1 to 6, characterized in that the clamping blocks ( 5 . 6 ) in the area of their bushings ( 13 ) have low-friction ball cages. Pressure testing device according to one of claims 1 to 7, characterized in that the pressure testing device is designed such that the sample body ( 1 ) is accessible on all sides during the pressure test, whereby various strain gage systems, such. As strain gauges, video extensometers or grayscale analyzers can be used.