4.1 This test method may be used as an accelerated screening test for assessing the strength properties of adhesives and adhesive joints at subzero temperatures. This test method may also be used to determine the effects of various surface preparations, substrates, or adhesive systems on the durability of the adhesive joints at subzero temperatures.

4.2 Tensile shear strengths of various adhesives, surface preparations, and substrates may be compared by using this test method for uniform sets of conditions. To assess the overall tensile shear strength of a given adhesive, surface preparation, and substrate should be tested under a range of stress and temperatures. For a specific end use, the needed strength properties using only one set of test conditions may be obtained.

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.

4.3.1 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 or shrink. The adherends and adhesive are likely to have different thermal and moisture coefficients of expansion. Even in small specimens, short-term environment changes can induce internal stresses of chemical changes in the adhesive that permanently affect the apparent strength and other properties of the adhesive.

4.3.2 The problem of predicting joint behavior in a changing environment is even more difficult if a different type of adherend is used in a larger structural joint than was used in the small specimen.

4.3.3 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.

4.3.4 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. See Guide D4896 for further discussion of the concepts relative to interpretation of adhesive-bonded single-lap-joints.