Lap-shear tests

Fig. 8. The dependence on contact angle of the magnitude and location of maximum stress concentration in a lap shear test. As the contact angle decreases, the stress concentration decreases, and its locus moves toward the center-plane of the adhesive phase. Redrawn from ref. [51].

Lap Shear Test Based on an Adaptation ofASTM D1002-72... 

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. 

Table 16.12. Adapted ASTM D1002-72 Lap Shear Tests on Sheet Materials"...

Table IV Lap Shear Tests Titanium-Titanium Adherend BTDA-m,m -DABP...

The 6th material Is a condensation-cure product which has been previously used for medical Implant protection (I). As verified by lap shear tests, (described below), the first 3 elastomers provide minimal adhesion In the absence of a surface primer. The last 3 are self-prlmlng materials. To permit visual examination, we tried to select clear materials. All of the elastomers are clear except for types 5 and 6. 

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 degree of bonding analysis has been verified for both compression molding and online consolidation of thermoplastic composites. In these studies, composite test specimens were consolidated under controlled processing conditions. The most common types of tests performed to measure the interply bond strength were the interlaminar (short beam) shear test [21,25] or the lap shear test [12,21,26]. 

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. 

FIGURE 20.5 Standard lap shear test specimen design (a) form and dimension of lap shear specimen (b) standard test panel of five lap shear specimens. (From ASTM D 1002.)... 

In light of these qualifications, it can only be said that the maximum measured value of 10 kg/mni seems reasonable. It also compares favorably with shear strength measurements derived from epoxy-bonded, lap-shear tests (9). 

The initial research objectives included developing a simple experimental procedure to study how the graft polymers, polystyrene, and a commercial phenol formaldehyde resin interact when combined with wood under heat and pressure. Two-ply lap shear test specimens were used for a comparative test. 

General Procedure for Lap Shear Testing Using Pig Skin... 

TABLE 1. Instron lap shear testing results for selected a-cyanoacrylate monomeric derivatives. 

The results of tensile lap-shear tests of coatings produced on FRP substrates for different process schemes with and without plasma pretreatment are shown in Table 21.1. Examination of failed surfaces showed that separation occurred at the interface between the substrate and the bottom of the plasma film. No failure occurred between the plasma film and electrocopper layer. 

Tabie 21.3 Chemical Composition of the Initial Plasma-Coated Layer and the Failure Surface after Tensile Lap-Shear Testing (Copper Electrode)... 

Surface. After Tensile Lap-Shear Testing (Silver Electrode) ... 

Following ASTM D1002-72 (1983), the lap shear tests were undertaken. Aluminum alloy sheets that had a thickness of 1.626 mm were bonded and press-laminated as described above for the peel tests. The panels were then cut into 25.4-mm panels and tested at a rate of 5 mm/min. 

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 1. Lap-shear tests performed with thin strips of aluminum. In a few experiments traprock was used as the adherend. In the latter case, adhesion to the traprock approached zero when the assembly was placed in water for a few days.

Electron Spectroscopy for Chemical Analysis. Lap shear test (see Fig. 7.2). Supplied by WL Gore Corporation. Treatment with a 1 mole soulution of sodium naphthalenide in tetrahydrofuran at room temperature. 

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