Tensile shear adhesion test

Table III. Tensile Shear Adhesive Strength of Ozonized Lignin/Epoxy Resins. (Normal Test)...

The two most important specifications worldwide are the European Norms EN and the American Standards ANSI 118.1-1999. The biggest difference between the two standards is the principal test setup. The European Standards require mostly tensile bond adhesion testing where else the American Standard uses shear bond testing. The other difference is clearly the storage conditions for the specimen before testing. A listing of both standards is shown in Tab. 13-2. 

The routine compositional and functional testing done on the adhesives includes gas chromatographic testing for purity, potentiometric titrations for acid stabilizer concentrations, accelerated thermal stabiUty tests for shelf life, fixture time cure speed tests, and assorted ASTM tests for tensile shear strengths, peel and impact strengths, and hot strengths. 

ISO 9653 1998 Adhesives - Test method for shear impact strength of adhesive bonds ISO 9664 1993 Adhesives - Test methods for fatigue properties of structural adhesives in tensile shear... 

Table II. Tensile Shear Bond Strength of Adhesives from Phenolysis Lignin in Normal Test and after Repeated Boil Treatment...

FIGURE 3.9 Plot of tensile shear strength of an aluminum joint bonded with an elevated-temperature curing epoxy adhesive as a function of test temperature. 

PMDA or trimellitic anhydride has also been shown to provide epoxy adhesive formulations with high-temperature properties. Table 12.13 shows the elevated-temperature tensile shear strength of an epoxy adhesive cured with 4 pph of PMDA. Another specialized formulation employing PMDA was found to provide high shear strength when tested at 260°C even after aging 1000 h at 260°C.15... 

Structural adhesives usually require curing by the application of heat, the addition of a catalyst, the addition of pressure, or a combination of the three. The strength developed in the adhesive joint at various times during the curing process may be determined by lap shear tensile specimens. This test is commonly used to determine when an adhesive or sealant is fully cured or when the system reaches a handling strength so that the assembled product can be moved with moderate care. 

A standard test report usually documents the resulting measurements, such as tensile shear strength and peel strength. It should also indicate all the pertinent conditions that are required to ensure reproducibility in subsequent testing. It is often very useful to describe the failure mode of the tested specimens. An analysis of the type (or mode) of failure is an extremely valuable tool to determine the cause of adhesive failure. The failed joint should be visually examined to determine where and to what extent failure occurred. The percent of the failure that is in the adhesion mode and that in the cohesion mode should be provided. A description of the failure mode itself (location, percent coverage, uniformity, etc.) is often quite useful. The purpose of this exercise is to establish the weak link in the joint to better understand the mechanism of failure. 

Tensile Shear Tests. The lap shear or tensile shear test measures the strength of the adhesive in shear. It is the most common adhesive test because the specimens are inexpensive,... 

ISO/DIS 9664 1993 Test methods for fatigue properties of structural adhesive in tensile shear. 

This test is carried out according to the standard DIN EN 1465 Adhesives - Determination of the tensile shear strength of high strength lap joints. The test piece has the dimensions according to Figure 10.2. 

Tensile shear strength (adhesive strength), in the sense of this standard, is defined as the maximum force Fmax at the break of the bonded joint in relation to adherend surface A. The adherend surface A results from the test piece width h (25 mm) and the overlap length lu (12.5 mm) ... 

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). 

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 4. Diagram of force F against the shear defoimation v (left) of a classical tensile-shear test which is used to characterize an adhesive layer connecting two beech members (right).

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

As an overview. Table 1 summarizes the properties of a selected number of the adhesive mixes which were formulated and tested in tensile shear. 

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