Influence of testing velocity on mechanical strength and failure modes of single-lap joints made with hot-melt adhesive and polyolefin substrates

The mechanical behaviour of adhesive joints under dynamic loadings is an active area of research due to their significant industrial applications. Furthermore, the absence of a unique adopted standard for the study of bonded joints under impact loading increases the scientific and practical interests in this topic. In this work, the static and the dynamic responses of adhesive joints, bonded with a polyolefin hot-melt adhesive (HMA), were experimentally investigated by means of Single Lap Joint (SLJ) specimens, tested using a tensile machine and an instrumented pendulum. The substrates used in this activity were made of a polypropylene copolymer with 10% in weight of talc. In the last decades, HMAs have been used in automotive application for bonding internal and external plastic components. Indeed, HMAs are capable to bond several kinds of materials, including plastics that are difficult to bond with other adhesives. The results of the mechanical tests show that there is a clear influence of the loading rate on the force-displacement diagram and on the maximum force for the tested adhesive. Failure modes were finally analysed and compared. A change in the failure mode was noticed: in quasi-static tests the SLJs failed cohesively within the adhesive, whereas in dynamic tests the SLJs failed adhesively, with low energy absorption.