In situ residual stress analysis in a phenolic resin and copper composite material during curing

Herein, in situ analysis of the residual stress in a phenolic resin and copper foil composite material during curing and thermal-cycle testing was performed via time-resolved X-ray diffraction measurements. The semicured resin–copper composite exhibited a large compressive stress in copper before the curing process. This indicates that the adhesive interface between resin and copper was first formed when the resin melted in the molding process and the magnitude of the thermal contraction of the resin was larger than that of copper in the subsequent cooling to room temperature after the molding. The difference in the magnitude was caused by the difference in the coefficients of thermal expansion between resin and copper. This compressive stress decreased as the temperature was increased to curing temperature of 180 °C. As the curing proceeded, the compressive stress in the copper again increased because of cure shrinkage of the resin. When the cured sample was reheated to the curing temperature, the compressive stress in the copper at 180 °C was relaxed. This thermal-annealing-induced stress relaxation suggests that cross-linking reactions during the curing process caused structural strains near the interface between resin and copper, where phenolic resins are two-dimensionally constrained by the copper foil, and that the cross-link strains were relaxed via macroscopic deformation induced by thermal contraction and expansion of the resin. In situ analysis of the residual stress in a phenolic resin and copper foil composite material during curing and thermal-cycle testing was performed via time-resolved X-ray diffraction measurements using the sin2Ψ method. [Display omitted] •Residual stress in a phenolic resin and copper composite material during curing and thermal-cycle testing was investigated.•In situ residual stress analysis was performed via time-resolved X-ray diffraction with sin2Ψ method.•The progress of curing was observed as an increase in the compressive stress in the copper due to cure shrinkage of resin.•When the cured sample was reheated to the curing temperature, relaxation of the compressive stress in copper was observed.