On a Paradoxical Situation Related to Bonded Joints: Could Stiffer Mid-Portions of a Compliant Attachment Result in Lower Thermal Stress?

Abstract

The objective of the analysis is to find out to what extent the thermal stress in a bonded assembly could be reduced as a result of employing a compliant bonding layer with an interfacial compliance varying along the assembly. It has been determined that by employing such a layer one can achieve in an assembly of any size a low stress level and the same type of the stress distribution that takes place in a small size assembly: the interfacial shearing stress changes linearly along the assembly and the normal stresses in the adherends follow a parabolic law. We have encountered a rather paradoxical situation taking place in an assembly with an optimized longitudinal distribution of the interfacial compliance (that increases in accordance with a parabolic law from a next-to-zero value in the mid-portion of the assembly to large values at its ends): the maximum stress in such an assembly is lower than the maximum stress in an assembly with a highly compliant bonding layer of constant compliance of the same magnitude as the (high) compliance at the ends of an assembly with an optimized compliance. We conclude that this situation occurs because the peripheral interfacial displacements in an assembly with the varying compliance are reduced owing to the stiffer (less compliant) mid-portion of the bonding layer.