Single lap shear

Fig. I. Comparison of unprimed and eleetroprimed single lap-shear adhesive joint strengths for steel coupons bonded with imidazole-cured epoxy [43].

In essence, the durability of metal/adhesive joints is governed primarily by the combination of substrate, surface preparation, environmental exposure and choice of adhesive. As stated earlier, the choice of the two-part nitrile rubber modified epoxy system (Hughes Chem - PPG) was a fixed variable, meeting the requirement of initial joint strength and cure cycle and was not, at this time, examined as a reason for joint failure. Durability, as influenced by substrate, surface preparation, and environmental exposure were examined in this study using results obtained from accelerated exposure of single lap shear adhesive joints. 

Forced sinusoidal shear imposed by piezoelectric driver to single-lap shear specimen... 

Yoon TH, Arnold CA, McGrath JE (1989) Titanium 6/4 single lap shear adhesive performance of polyimide homopolymers and poly(siloxane imide) segmented copolymers. Mater Res Soc Symp Proc 153 (Interfaces Polym Met Ceram) 211... 

Figure 3. Test-prediction comparisons for 3mm adherend single lap shear specimens.

The shear adhesion strength of the PU formulations was tested by single lap shear joints, according to ASTM D 1002-94 (at a rate of 1.3mmmin ). Peel strength was evaluated by T-Peel (ASTM 1876-95) (at a rate of 254 mm min ). 

In some cases a silane (A-187 Union Carbide) was applied to the A1 adherends as a coupling agent for better chemical bonding. Single lap shear (SLS) joints were primed with all four PAMAMs, bonded with epoxy or PU adhesives, and tested in shear according to ASTM D-1002 at a loading speed of 2 mmmin . ... 

Table 15.4 Single lap shear strength [MPa] of epoxy-bonded Al ad- ...

The same effect as on aluminum adherend was also found with magnesium and PEI adherend. The optimum concentrations of each of the primers studied were applied to PEI (Ultem 1000) and magnesium alloy (AZ-91). Table 15.6 summarizes the single lap shear strengths of the resulting bonded joints. The results show that PAMAMs are effective in improving lap shear strength on... 

Table 15.7 presents the single lap shear strength of Al adherends primed with G3 and G4 dendrimers bonded with epoxy adhesive. On anodized Al, results show improvement of 33-53% in lap shear strength and in failure mode using dendrimers as a primer. 

In order to understand the aim of surface treatments for composite bonding, we wiU concentrate on a real composite bonding problem for aeronautical purposes. Since classical surface treatments like peel ply can be limited by a cohesive failure occurring in the material, we wiU focus on a new kind of surface treatment (excimer laser) which can completely change surface parameters. The different aspects are presented in two steps the first consists in the surface characterization of the composite material and the second is related to results of destructive single lap shear tests of composite assemblies. Finally, both steps are Hnked in order to derive general mles on phenomena governing adhesion properties of polymer composites. 

Previous work performed on our composite materials [16] provided clear evidence of the influence of surface pollution prior to the use of any surface treatment on adhesion behavior. Several surface treatments can be performed to remove this surface pollution and increase single lap shear performances. As described in Section 20.1.2, peel ply treatment acts very specifically on composite materials. As several authors have already described [3, 5, 17] removing the peel ply before the application of the adhesive provides a rough (Fig. 20.2) and clean surface, free of pollution from the manufacturing process. 

Fig. 20.6 Single lap shear results of glass/epoxy and carbon/ epoxy composites after several different laser treatments.

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. 

For the adhesive joints which were investigated here, only some aspects wiU be discussed. The general results can be summarized as follows. A one-year exposure of bonded single lap shear samples to European and Californian ch-mates did not show any influence on the static strength of the joints. Higher temperatures (70 °C) reduced the strength by a factor between 0.25 and 0.65. 

To apply an external or internal patch (single lap joint) the surface is cleaned and lightly abraded prior to laying up the repair. Single lap shear joints are not as... 

A total of 45 single lap shear specimens made of beech wood were produced by the adhesive manufacturer as described in Section 3.2. The samples were glued with the five adhesive types used in the delamination test 3 plastic adhesives no. 009, 013 and 014, and 2 elastic adhesives no. 062 and 071. The adhesive layers of the lap shear specimens had the following nominal thicknesses 0.5, 1.0 and 3.0 mm. For each adhesive type and thickness batch, 3 specimens per batch were tested. 

Bond strengths of PU adhesives were obtained from single lap-shear determinations. Substrate/adhesive/substrate joints were made with ABS and PVC coupons, 8 x 2.5 cm, as substrates the overlap area was 4.5 cm. The reference PU here was compounded with glass beads to provide adhesive layers with uniform thicknesses of 1.27 mm. Lap... 

Wake(37) and by Adams and Wake(5), and Kinloch(4) summarises the evolution of the approach of the many stress analysts. The most common shear test comprises the single lap shear joint embodied in BS 5350(10) and ASTM 01002-72(11) (Fig. 4.7(a)). With reference to Figs. 4.1(a) and 4.8 it can be seen that the resulting stress concentrations can be extremely large at the joint ends (points X and Y in Fig. 4.8(b)). The analysis of Volkersen(15) predicts that for identical adherends, the elastic shear stress concentration factor, for the adhesive due to adherend tensile strain is given by... 

Subjected to stress, moisture and temperature uses peel joint As above, but uses single-lap shear joint loaded in tension As above but uses a wedge test Exposure to moisture and temperature... 

The fracture experiments were conducted on single lap shear joints with an overlap length of 1.27 cm, bond area of... 

Radiation-cured versus heat-cured formulations of Epocryl 12 (Shell). Comparisons of single lap shear strength at elevated temperatures. 

EFFECT OF ELASTOMERS ON ADHESIVE PROPERTIES Single Lap Shear Bond Testing... 

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