Joints shear testing

The principal type of shear test specimen used in the industry, the lap shear specimen, is 2.54 cm wide and has a 3.23-cm overlap bonded by the adhesive. Adherends are chosen according to the industry aluminum for aerospace, steel for automotive, and wood for constmction appHcations. Adhesive joints made in this fashion are tested to failure in a tensile testing machine. The temperature of test, as weU as the rate of extension, are specified. Results are presented in units of pressure, where the area of the adhesive bond is considered to be the area over which the force is appHed. Although the 3.23-cm ... 

Fig. 1, Schematic of commonly u.sed methods for testing the strength of adhesive joints, (a) Peel test. Note that the peel angle can be changed depending on the test requirements, (b) Double overlap shear test. In this test, the failure is predominantly mode II. (c) Single overlap shear test. In this test the failure mode is mixture of mode I and mode II. (d) Blister test.

The lap shear test involves measuring the adhesive shear strength between two surface fluorinated polyolefin sheet tokens that are adhesively secured with a reinforcement resin. The tokens are individually reinforced with steel backing plates to eliminate flexural distortion in the shear joint. Lap shear tests carried out with various reinforcing polyester-type resins, contrasting fluorination and oxyfluorination as surface treatment, are shown in Table 16.8. 

In applications where possible degrading elements exist, candidate adhesives must be tested under simulated service conditions. Standard lap shear tests, such as ASTM D1002, which use a single rate of loading and a standard laboratory environment, do not yield optimal information on the service life of the joint. Important information such as the maximum load that the adhesive joint will withstand for extended periods and the degrading effects of various chemical environments are addressed by several test methods. Table 15.2 lists common ASTM environmental tests that are often reported in the literature. 

The paper is presented in three parts. First, the tests employed to determine the mixed mode fracture envelope of a glass fibre reinforced epoxy composite adhesively bonded with either a brittle or a ductile adhesive are briefly described. These include mode I (DCB), and mixed mode (MMB) with various mixed mode (I/II) ratios. In the second part of the paper different structural joints will be discussed. These include single and double lap shear and L-specimens. In a recent European thematic network lap shear and double lap shear composite joints were tested, and predictions of failure load were made by different academic and industrial partners [9,10]. It was apparent that considerable differences existed between different analytical predictions and FE analyses, and correlation with tests proved complex. In particular, the progressive damage development in assemblies bonded with a ductile adhesive was not treated adequately. A more detailed study of damage mechanisms was therefore undertaken, using image analysis combined with microscopy to examine the crack tip strain fields and measure adherend displacements. This is described below and correlation is made between predicted displacements and failure loads, based on the mixed mode envelope determined previously, and measured values. 

Shear test A method of deforming a sealed or bonded joint by forcing the substrates to slide over each other. 

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. 

Freeney et al. (Ref 21) evaluated the effect of process parameters on FSSW of AA5052 using a plunge-type FSW machine. Sheets with two different thicknesses were used. The dwell time and revolutions per minute were process variables. Lap-shear tests were performed in two-sheet and three-sheet configurations to determine the influence of processing parameters on the mechanical properties of lap-joint friction stir spot welds. 

Generally, multiple experimental test data of adhesive material are necessary for an adequate representation of the joint behavior under loading. Uniaxial tension, compression and single lap shear tests were therefore performed. 

Lap shear tests were carried out using single lap joint specimens of the aluminum alloy (5052H34). Sample dimensions are shown in Fig. 34.6. Surface pretreatment and curing conditions of the joint specimens were similar to the other specimens used for the dismantlement test The lap shear strength of the... 

Single Lap-Joint Specimen Test Results, is intended to give insight into the interpretation of the results from all the lap shear tests. At other points in ASTM Vol. 15.06 and in this chapter, reference is made to other standard tests that use shear-type specimens to explore moisture, and other environmental, fatigue, and creep effects in adhesive joints. 

Liu Shungui, et al. 2008. Direct shear tests and PFC numerical simulation of intermittent joints. Chinese Journal of Rock Mechanics and Engineering, 27 1828-1836. (in Chinese). 

Table 7.3 Adhesive strength of ABS/PU joints (all data are lap-shear tests at 30 °C) ...

---