Mechanical fracture characterization of adhesive interfaces: Introducing a new concept for evaluating adhesive quality

Abstract

Abstract For the evaluation of adhesive quality, the prevailing situation shows that standardized mechanical tests do not generate significant quality parameters as they indicate merely the maximum bonding strength of the specimen under investigation. Furthermore, most product data sheets provided by adhesive manufacturers supply only a few technical parameters (i. e. maximum tensile strength), which, from a technical point of view, limits the selection criteria for adhesives. Considering this fact, adhesive selection can be very dangerous when relying on bonding strength alone. This is crucial for industries where human safety has top priority, such as aeronautical, automotive or medicine. Consequently, the present study introduces a new approach, using both fracture mechanics and a special test arrangement for adhesively bonded composites to overcome the above mentioned handicaps. The key benefit of this novel evaluation concept is its ability to monitor the post-cracking behavior of bonded interfaces in a stable and steady manner even for brittle adhesives. This is a major advantage over commonly practiced techniques, both from a mechanical and a fracture mechanical point of view, as they basically tend to measure instability if brittle interfaces come about. To demonstrate this new technique, experiments were conducted on six different adhesives kindly provided by SIKA and MUREXIN. The results found opposite interactions between adhesive bonding strength and fracture resistance, meaning that high tensile strength values do not automatically lead to the best results. Such findings show that the selection of adhesives with the help of fracture analysis seems quite desirable for the future.