Single-lap

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. 

Under the best of conditions, single lap joint samples do not fail in pure shear due to the tensile and peel forces present at the ends of the overlap. These non-shear forces are exacerbated when using thin gauge adherends. Because of this, the lap joint dimensions as well as the testing rate were modified from the ASTM D-1002 standard as a result of earlier work on thin gauge steel adherends. 

Sawyer, J.W. (1985). Effect of stitching on the strength of bonded composite single lap joints. AIAA J. 23, 1744-1748. 

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

Fig. 4. The nominal breaking stress (Amsier testing machine) of aluminium alloy/epoxy single lap joints as a function of the hydroxyl content of the epoxy raised to the two-thirds power51 (Reprinted from Ref. 51, p.307, by courtesy of Society of Chemical Industry)...

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... 

D 4896 Guide for the Use of Adhesive Bonded Single Lap-Joint Specimen Test... 

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

Fig. 2. Photograph of the co-cured lap joint specimens, (a) Co-cured single lap joint (b) co-cured double lap joint.

In the case of the dynamic tensile test, co-cured single lap joint specimens selected in this paper... 

The bond length of the specimens under cyclic tensile test was 20mm. Cyclic tensile tests were performed under the condition of stress ratio 7 = 0.1 and a loading frequency / = 5 Hz. Cyclic tensile loads applied to the co-cured single lap joint specimens were 30%, 40%, 50%, 60%, and 70% of the tensile load bearing capacity obtained from the static tensile load test. 

Figure 4 shows typical failure surfaces obtained from tensile tests of the co-cured single and double lap Joint specimens. In the case of the co-cured single lap Joint, as the surface preparation on the steel adherend is better, a greater amount of carbon fibers and epoxy resin is attached to the steel adherend. Failure mechanism is a partial cohesive failure mode at the C ply of the composite adherend. In contrast with the co-cured single lap joint, failure mechanism of the co-cured double lap joint is the partial cohesive failure or interlaminar delamination failure at the 1 ply of the composite adherend because interfocial out-of-plane peel stress... 

Fig. 10. Interfacial out-of-plane transverse stress distribution, a , of the co-cured single lap joint along the interface between steel and composite adherends. (a) [0]32t stacking sequence and (b) [ 45]4s s stacking sequence.

Fig. 11. Interfacial out-of-plane shear stress distribution, a , of the co-cured single lap joint...

Fig. 14. Comparison of tensile load bearing capacities of co-cured single lap joint (fabricated under 0.7 MPa manufacturing pressure) calculated from the two failure criteria with experimental results.

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