Measurement of residual stress effects by means of single-particle composite tests

The effects of thermal residual stresses on adhesion have been quantitatively examined by means of a single-particle composite technique. Residual stresses were varied systematically by controlling the molding time-temperature profile for single, surface-modified glass spheres embedded in a thermoplastic polymeric matrix. Interfacial failure was induced by tensile straining of single particle composites until debonding at the geometric poles was observed between the matrix and spherical particle. The interfacial strength was calculated and is reported as a function of residual hoop stresses, the magnitude of the latter determined by the processing conditions, i.e. different residual stress states within the matrix. A preliminary study was conducted using two interfaces: an octylsilane/poly(vinyl butyral) interface and a di-aminosilane/poly(vinyl butyral) interface. The former is a weak bond with only Lifshitz-van der Waals forces operating across the interface, and the latter a strong bond featuring a molecular penetration mechanism. Both interfaces were deleteriously affected by increases in residual stresses, with the former having the highest level of residual stress with complete interfacial strength loss. Experimental requirements for a more quantitative study are described.