4.1 This test method is useful in that the joint configuration closely simulates the actual joint configuration of many bonded assemblies. Surface preparation of the adherends can affect the apparent shear strength of the adhesive and can be one of the variables under study.

4.2 This test method is also useful as an in-process quality control test for laminated assemblies. In practice the laminated assembly is either made over size and test specimens removed from it or a percentage of the assemblies are destructively tested.

4.3 The misuse of strength values obtained from this test method as design allowable stress values for structural joints could lead to product failure, property damage, and human injury. The apparent shear strength of an adhesive obtained from a given small single-lap specimen may differ from that obtained from a joint made with different adherends or by a different bonding process. The normal variation of temperature and moisture in the service environment causes the adherends and the adhesive to swell and shrink. The adherends and adhesive are likely to have different thermal and moisture coefficients of expansion.

4.4 The apparent shear strength measured with a single-lap specimen is not suitable for determining design allowable stresses for designing structural joints that differ in any manner from the joints tested without thorough analysis and understanding of the joint and adhesive behaviors.

4.5 Single-lap tests may be used for comparing and selecting adhesives or bonding processes for susceptibility to fatigue and environmental changes, but such comparisons must be made with great caution since different adhesives may respond differently in different joints. Review Guide D4896 for further discussion of concepts for interpretation of adhesive-bonded single-lap joint data.