Revisiting bimaterial curvature measurements for CTE of adhesives

摘要

Quantifying the coefficient of thermal expansion (CTE), stress-free temperature, and residual stress state is of critical importance for many applications involving bonded systems such as coatings, adhesives, and other laminated systems. This paper revisits Timoshenko's solution for curvature of a bimaterial strip (plane stress) by identifying optimal configurations which improve sensitivity and minimize effects of time dependent changes in moduli. A similar solution is developed from classical lamination theory for plate-like geometries. We find that when the material system is optimized, the curvature calculation is virtually insensitive to the modulus change. For thin layer systems, the bimaterial system is much more sensitive than the bulk material system in the curvature measurement. Such techniques can be easily implemented in modern thermal mechanical analysis equipment which is readily available in most polymer laboratories.