Investigation of the influence of design parameters onto the cracked lap shear specimen

Abstract

The Cracked Lap Shear (CLS) specimen allows a mixed-mode loading condition to be generated without a special test fixture using a simple tensile test. The mixed-mode ratio generated is nearly constant over a wide range of crack growth and is representative of the loading conditions in many structural applications of bonded joints. However, this specimen is not standardised, leading to very dissimilar specimen designs in the literature. In this study, the primary design parameter is the sample width in terms of its application for adhesive characterisation, with a typical layup having a 0° layer in contact with the bond line. The results of quasi-static and fatigue tests using varying specimen widths between 5 mm and 40 mm emphasise the specimen width's influence. Moreover, CLS specimens with the same layup but without an adhesive layer between the adherends are investigated to study the effects of width scaling without a toughened adhesive bond. While the static tests show a linear relationship between specimen width and joint strength, it is different in fatigue tests, where the crack growth rate increases with decreasing specimen width, both for specimens with and without adhesive bond between the joining partners.