LapShear

Lapshear refers to the shear stress that develops in a lap joint, typically in adhesive bonding, where two overlapping members are bonded together. The term can also denote the testing method used to quantify an adhesive bond’s resistance to shear, commonly called a lap shear test.

In a single-lap joint, the load applied in tension induces shear in the adhesive across the overlap area and peel stresses at the ends of the overlap. This combination often governs failure. The lap-shear strength is defined as the maximum load the joint can sustain divided by the nominal bonded area, and is usually reported in units of stress such as megapascals.

Specimens for lap shear testing are prepared with specified overlap length and width, adhesive type, and cure conditions. The test involves applying a monotonic load until failure, recording the maximum load and sometimes displacement. Mixed-mode stresses and fixture misalignment can complicate interpretation, so standardized fixtures and procedures are used to ensure repeatability.

Design considerations aim to minimize peel and eccentric loading. Approaches include using double-lap joints to balance bending, optimizing overlap geometry, and selecting adhesives compatible with service conditions. Lap shear testing is widely used across industries such as automotive, aerospace, electronics, and wood products to compare adhesive performance and validate bonding processes.

Standards and organizations provide specific test method procedures, with ASTM D1002 among commonly cited references. Results are used to characterize material compatibility, assess quality control, and guide structural design.