Thick-adherend lap shear

For thick adherend lap shear test specimens a surface treatment was performed. The aluminium adherends were 10 mm thick and 25 mm wide. After the specimens were cured and postcured, the adherends were cut to form a test area with an 8 mm lap length. 

Thick adherend lap shear tests (TALST) were not based on any standard. However, standard practice used in the tests was followed. The displacement rate used was 0.3 mm/min. The adhesive layer displacement was measured using two in-house built KGR-1 type extensometers. 

Several testing techniques are possible which use different specimen configurations, different loading modes, and various loading frequencies. Marceau et al. have described results for thick adherend lap shear and double cantilever beam (DCB) specimens exposed to 140 F/100%... 

Figure 2 is a schematic drawing of the KGR-1 with the thick adherend lap shear specimen currently in use. Two instruments are used they are mirror images of each other and are mounted on opposite sides of the specimen. The signal of either individual instrument can be read, or their average signal can be obtained by combination. 

FIGURE 3. KGR-1 extensometer mounted on a thick adherend lap shear specimen. 

Adhesives by the Thick Adherend Tensile Lap Specimen D 4027 Test Method for Measuring Shear Properties of Structural Adhesive by the... 

ASTMD3933-98 Standard practice for measuring strength and shear modulus of non-rigid adhesives by the thick adherend tensile lap specimen. 

FIGURE 27.1. Diagram of an ASTM D1002 lap shear specimen. The adherends are usually 2.54 cm wide and 10.16 cm long. The thickness of the adherend depends upon the adherend material. If the adherend is aluminum, that thickness is usually 0.16 cm thick. 

Measuring Strength and Shear Modulus of Nonrigid Adhesives by the Thick Adherend Ihnsile Lap Specimen, Practice for (D 3983)... 

As with tensile tests, it is sometimes necessary to test dissimilar materials in shear or materials which cannot be easily fabricated into adherends. For these cases, ASTM D3164-73 describes the testing of a lap shear sandwich joint. The test specimens consist of two metal adherends, typically 0.064 inch thick aluminum, the structural adhesive, and a 0.010-inch thin film of plastic. The sandwich joint is shown in Figure 8. 

ASTM (2007), D5656-04E01, Standard test method for Thick-adherend metal lap-shear joints for determination of the stress-strain behaviour of adhesives in shear by tension loading , in Annual Book of ASTM Standards, 2007 edn. West Conshohocken, PA ASTM International. 

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The thick adherend shear test also provides data on the modulus of the adhesive. If we use this data along with a knowledge of the modulus and thermal expansion of the two materials being bonded together, it is possible to compute the stress levels experienced by a simple lap joint. 

It has been shown that a very simple approach can be used for predicting the lap shear strength of adhesively bonded Joints for ductile adherends and ductile adhesives. However, it cannot take into account such more complex situations as thermal stresses or changes in adherend thickness (stepped or tapered joints). 

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