Tensile shear loading testing

ASTM D 1780-72—Conducting creep tests of metal-to-metal adhesives (tensile shear loading)... 

Tensile shear-loaded joints (Fig. la) have the highest strength (see Shear tests). Stress is distributed over the bond area. Joints that have load applied as a shear loading are most resistant to bond failure. 

When loading this test piece with force F it is noticed that, unlike in the tensile shear test, the force is not applied to an area A (= b x fu), but to a line X... X. The other area of the adhesive layer remains unstressed. Thus, in this case strength cannot be defined as force per area , but the force referring to a line is called peel resistance. If the test piece shown in Figure 10.5 is tom apart by means of force F, and the force over the peeled distance is recorded, the following peel diagram results (Figure 10.6). 

All mechanical tests were done at ambient temperatures (20° C). Tensile, shear, and compression tests were done using a stress rate of 25 MPa/s. Load and extension data were recorded by computer data collection. ... 

The optimized results depicted in Figs 2 and 3 will only be possible if the adhesive connection exhibits a certain stiffness. The load-bearing behaviour of adhesive layers is normally tested in tensile shear with small beech specimens (Fig. 4). The adhesive layer is typically b = 20 mm wide and 10 mm long according to Eurocode 5 [7]. The force (F) is measured in newtons and the shear deformation v in millimetres. 

Figure 5. The requisite load-bearing behaviour of the adhesive layers (left), as tested with small tensile-shear beech specimens (right).

BS EN 302-1 2004 Adhesives for load bearing timber structures. Test methods. Determination of bond strength in longitudinal tensile shear strength. 

In 1985 cracking was noticed in the floor slabs of a multi-storey office building in Leeds. The cracks were adjacent to the external columns and the central lift well and design checks indicated a deficiency in both shear capacity and top flexural reinforcement. A combination of soffit supporting brackets and steel plates bonded to the top surface adjacent to supports was adopted to restore capacity and control cracking (Fig. 6.11). Subsequent load tests revealed that the steel plates were attracting tensile stresses up to 40 N/mm at 1.35 times design load. 

It is very desirable to fabricate a standard test specimen in the dame cycle as the part being bonded. This specimen should be designed for a test method that is indicative of the prime structural loading requirement. For example, if the critical item is normally loaded in tensile shear, the specimen should be of the lap-shear type. 

Shear stresses cause sliding in an element of material as shown in Fig. 1(a). All shear tests are variants of either an overlap or a torsional joint and these are illustrated schematically in Figs. 1(b) and (c). The shear in the first is induced by transfer of the tensile/compressive load from one substrate to the other, while in the second it is caused by transfer of torsional loads from one substrate to the other. The tests have been grouped according to the manner in which the shearing has been induced. 

Ultimate strength n. The maximum nominal stress a material can withstand when subjected to an applied tensile, compressive, or shear load. If the mode of loading is not specified, it is assumed to be tensile. In materials that exhibit a definite yield strength, ultimate strength will usually mean the nominal stress at break, which can be less than the maximum. Shah V (1998) Handbook of plastics testing technology. John Wiley and Sons, New York. 

The capabilities of structural adhesives allow improved performance relative to other joining techniques in many applications. To insure the performance of structural adhesives, proper testing, analysis, and design are required. Testing provides insight into mechanical properties of the structural adhesives. These properties are dependent on the mode of load application such as tensile, shear, peel, impact, or any combination of these. 

Typically, bonded structures are designed so that the structural adhesive will be under shear loads most of the time. Adhesives are stronger in shear than they are in tensile or peel loading. Shear testing is very common because samples are easily fabricated and simple to test. 

The standard test for measuring the shear behavior of fabrics is the shear-frame test, also known as trellis-frame test, or the picture-frame test, as shown in Fig. 6.12. In this test, a fabric specimen is clamped with the yams typically directed perpendicular and parallel to the four clamping bars. Shear deformation is developed by fixing one corner and applying a tensile load on the opposing corner. The deformation of the fabric in the shear-frame test is shown in Fig. 6.13. 

Other less well-known types of nonlinearities include interaction and intermode . In the former, stress-strain response for a fundamental load component (e.g. shear) in a multi-axial stress state is not equivalent to the stress-strain response in simple one component load test (e.g. simple shear). For example. Fig. 10.3 shows that the stress-strain curve under pure shear loading of a composite specimen varies considerably from the shear stress-strain curve obtained from an off-axis specimen. In this type of test, a unidirectional laminate is tested in uniaxial tension where the fiber axis runs 15° to the tensile loading axis. A 90° strain gage rosette is applied to the specimen oriented to the fiber direction and normal to the fiber direction and thus obtain the strain components in the fiber coordinate system. Using simple coordinate transformations, the shear response of the unidirectional composite can be found (Daniel, 1993, Hyer, 1998). At small strains in the linear range, the shear response from the two tests coincide. 

In-plane shear properties In simple shear loading, two parallel faces move in opposite parallel directions. In pure shear, the plane is subjected to tensile forces on one axis and compressive forces of equal magnitude on the orthogonal axis. Many different techniques have been proposed for the determination of the in-plane and through-plane shear properties with variations appropriate to composite plates, rods and tubes [1]. Inter-laminar shear strength The inter-laminar shear strength (ILSS) test is a three-point bend test at very... 

This is one of the most important tests because adhesive bonds show a good resistance to tensile shear stresses and it is always recommended to load the bonded parts in tensile shear mode in order to get the highest resistance (refer to the chapters Design and calculation of bonded joints in Volume 2 and Bonding metals in Volume 5). 

The test will be performed as for the tensile shear resistance but with the required configuration of the joints. The bonded parts should be aligned very carefully as is explained in the above standards, because if they are not there will be some cleavage effect and as the adhesives do not resist to cleavage the puU value will be low, and this is the reason why the bonded joints should never be loaded in pure tensile mode. For the same bonded area, the tensile value will be lower than the tensile shear value. 

Adhesives determination of tensile lap-shear strength of rigid-to-rigid bonded assemblies Adhesives diuabUity of stmctural adhesive joints exposure to humidity and temperature under load Adhesives test methods for fatigue properties of stmctural adhesives in tensile shear... 

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