Overlap shear test

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.

Shear strength is measured via a simple single overlap shear specimen of standard dimensions (Fig. 9). In contrast to its simple appearance, the forces in a thin-adherend shear specimen can be quite complex due to the inherent offset loading of the specimen and subsequent bending in the substrates. The single overlap shear test is anything but a pure shear test, but the configuration is easy to manufacture, simple to test and is firmly entrenched in the industry as a primary examination technique for materials qualifications, inspection and process control. 

Lap shear testing Shear can be applied in a number of ways cyclic, intermittent, static (or constant), or increasing. A simple overlap shear test is described in ASTM-D-1002. This can be illustrated again using two strong microscope slides. Here, the microscope slides are adhered in parallel to one another except offset. After the appropriate set-up time, the top and bottom of the slide combination are attached to the shear tensile-measuring device and the experiment is carried out. 

The influence of unbonded regions at the edges of completed welds on sample failure during overlap-shear testing is illustrated in Fig. 12.47. Failure initiated from unbonded regions located on either side of the spot weld, and as the fracture propagated, the transition from... 

Many types of tests for evaluating and/or predicting the durability of metal-to-metal adhesive bonds are known in the literature. In our laboratory we have made extensive use of the sustained load overlap shear test at high temperature and high humidity for this purpose. As a result of more than 10 years of evaluation we are able to make qualitative correlations of the durability of metal-to-metal adhesive bonds as a function of adhesive type, temperature of cure, type of adherend, type of surface preparation and the amount of load placed on the specimen. 

Work of some value for stress analysis was done in the early years. This was the so-called long overlap shear testing. It was recognized early on that increasing the overlap in lap shear specimens did not result in a proportionate increase in strength. A length of lap is quickly reached where no further load increase is possible. 

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 ... 

Recommended Practice for Metal to Metal Overlap Shear Strength Test for Automotive Type Adhesives... 

The lap-shear test was used to determine the room-temperature cohesive strength of the modified asphalts and to follow the thickening process in both air and water. Two aluminum strips 1 mm thick and 2.5 cm wide were overlapped 2.5 cm and firmly bonded together with a drop of molten asphalt. The test pieces were held in this position with alligator clips until ready for shear testing. In a few experiments pieces of traprock were polished and similarly bonded together as shown in... 

Figure 7 Shear testing (a) 178° shear (b) horizontal shear (c) overlap shear.

Shear Test (PSTC-7) - Dead load shear test 1/4 sq. in. (1/2 in. X 1/2 in.) overlap of Mylar backed adhesive is bonded to the panel under 4 1/2-lb. roller pressure. Sample... 

Overlap shear (OLS) made by bonding 20 mil etched aluminum to 63 mil etched aluminum using 160°C bond-line temperature, 2 secs dwell, 14 lbs gauge pressure. (2) Peel bonds made by bonding 4.5 mil aluminum foil to test substrates using 320°F (160°C) bondline temperature, 2 secs dwell, 14 lbs gauge pressure. (3) Adhesion tests done at 2 in./min for peel, 2 in./min for OLS. 

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. 

The strength of bonded PP joints can be measured in accordance with the well-known testing standards such as, for example, DIN 53281, 53282, 53383 or 53289. In some cases, the thickness of the adherends should be different from that used on normal metal parts because the strength of PP is lower. For example, in the case of shear tests with single overlapped joints, the thickness of the PP parts should be 4 mm or more. Also the aging conditions can be in accordance with standards such as DIN 53286 or ASDM B117 (salt spray test). T) ical test methods for bonded... 

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