Compressive shear specimen

Compression shear tests are also commonly used. ASTM D 2182 describes a simple compression specimen geometry and the compression shear test apparatus. The compression shear design also reduces bending and, therefore, peeling at the edges of the laps. Higher and more realistic strength values are obtained with the compression shear specimen over the standard lap shear specimen. 

Flexural strength is determined using beam-shaped specimens that are supported longways between two rollers. The load is then applied by either one or two rollers. These variants are called the three-point bend test and the four-point bend test, respectively. The stresses set up in the beam are complex and include compressive, shear and tensile forces. However, at the convex surface of the beam, where maximum tension exists, the material is in a state of pure tension (Berenbaum Brodie, 1959). The disadvantage of the method appears to be one of sensitivity to the condition of the surface, which is not surprising since the maximum tensile forces occur in the convex surface layer. 

Stress/strain relationships are commonly studied in tension, compression, shear or indentation. Because in theory all stress/strain relationships except those at breaking point are a function of elastic modulus, it can be questioned as to why so many modes of test are required. The answer is partly because some tests have persisted by tradition, partly because certain tests are very convenient for particular geometry of specimens and partly because at high strains the physics of rubber elasticity is even now not fully understood so that exact relationships between the various moduli are not known. A practical extension of the third reason is that it is logical to test using the mode of deformation to be found in practice. 

In both polymers, creep of compression-molded specimens is caused mainly by crazing, with shear processes accounting for less than 20% of the total time-dependent deformation. Crazing is associated with an increasing creep rate and a substantial drop in modulus. The effects of stress upon creep rates are described by the Eyring equation, which also offers an explanation for the effects of rubber content upon creep kinetics. Hot-drawing reduces creep rates parallel to the draw direction and increases the relative importance of shear mechanisms. 

In unidirectional cloth specimens the fracture mode was essentially compressive there was compressive shear at lower temperatures and buckling after the peak, but tensile fracture apparently became dominant at moderate temperatures. For bidirectional cloth specimens the fracture is almost controlled by tension but it shifts to compressive shear and then to buckling at higher temperatures. 

In general, the notched Charpy (ISO 179) [26] and Izod (ISO 180) [27] tests are not meaningful for composites, and ISO 179 recommends that only unnotched specimens should be tested. The difficulty with these tests is that in the notched condition the majority of specimens tested perpendicular to the plane of the test panel delaminate at the root of the notch. This reduces the specimen to a thinner version of the unnotched specimen, which as described above for the interlaminar shear test (see Section 5.4) is susceptible to compression-initiated failures under complex local loads. Specimens cut in the plane of the laminate or sheet will be less susceptible to delamination at the notch tip, and crack growth will be possible from the notch tip. However, other compression shear failure modes are still possible in some composites, and they will not be loaded in this direction in most applications. 

Specially developed methods were used for investigation of the strength of adhesive specimens imder normal compression and shear. Specimens fixed with Sprut-5M and VAK in air, under water, and in oil remained in these media until tests began. The specimens were exposed to compression in the stresses range iTc = 0—28.0MPa and failed under the action of shear stresses t. 

In order to gain some knowledge about the degradation of the adhesive layer during the delamination test, the specimens which successfully passed the test were further tested in compression shear (Fig. 24). For these tests, blocks with a cross section of 50 by 50 mm were cut out of the tested specimens. As a control, specimens of a similar size were cut from the part of the original sample which had not been subjected to the delamination tests. The compression shear tests conhrmed that the five adhesive layers which passed the delamination tests did not suffer any degradation during the harsh treatment. Their shear resistance was hardly reduced after the harsh delamination tests. 

EN 15416-2 2008, Adhesives for load bearing timber structures — Test methods — Part 2 Static load test of multiple bondfine specimens in compression shear. 

Compression shear tests are also commonly used. ASTM D2182 (withdrawn 1983) describes sample geometry similar to the lap-shear specimen... 

Another compressive shear test used for wood joints is ASTM D905-49. Test joints are prepared by bonding two blocks of wood, free from defects, with the grain of each block parallel to the length direction. Test specimens are cut from this bonded joint and tested in a special shearing apparatus (Figure 13). Loads are applied using a crosshead movement of 0.015 inch/min. The shear stress is calculated with the failure load and bonded shear area. 

Part 2 Static load test of multiple bond line specimens in compression shear. 

D-4501. Test Method for Shear Strength of Adhesive Bonds Between Rigid Substrates by the Block-Shear Method. Fig. 9 shows the two specimen configurations and the test head for this new, general-purpose, compression shear test which should be suitable for testing adhesives for plastics, metals, glass, wood, and other substrates. 

Fig. 20. Compression shear creep specimen and spring loading device for metal bonding adhesives (D-2293).

Fig. 22. New compression shear creep specimen and spring actuated loading device for wood bonding adhesives (D-4680).

The standard ASTM D4680 Standard Test Method for Creep and Time to Failure of Adhesives in Static Shear by Compression Loading (Wood-to-Wood) also applies a compressive force to shear specimens to monitor the creep properties of wood adhesives in lap shear geometry. 

Stresses that are computed from the tensile, compressive, shear, and torsional force states represented in Figure 6.1 act either parallel or perpendicular to planar faces of the bodies represented in these illustrations. Note that the stress state is a function of the orientations of the planes upon which the stresses are taken to act. For example, consider the cylindrical tensile specimen of Figure 6.4 that is subjected to a tensile stress cr applied parallel to its axis. Furthermore, consider also the plane p-p that is oriented at some arbitrary angle 0 relative to the plane of the specimen end-face. Upon this plane p-p, the applied stress is no longer a pure tensile one. Rather, a more complex stress state is present that consists of a tensile (or normal) stress a that acts normal to the p-p plane and, in addition, a shear stress t that acts parallel to this plane both of these stresses are represented in the figure. Using... 

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