Spring-back behavior on L-shaped composite structures: A statistical analysis of angular recovery as a function of time and residual cure

This work investigates the spring-in behavior as a function of time on L-shaped composites. Spring-in represents the angular deformation measured immediately after fabrication of a composite. Over time after fabrication of up to three years, there is an easing back of the spring-in deformation. The main aim of this paper is to reclassify this deformation as spring-back effect, as angular deformation recovered over time. The spring-back effect is measured as a function of time for 27 design of experiments (DOE). We used three different autoclave cooling rates, CR1, CR2, CR3, for an average of 81 samples, and we found that the spring-back effect is approximately 30.0 percent in a period of 30 months. Results also indicate a close connection between the spring-back effect and the cooling rate. Statistical results proved that the degree of cure associated with the cooling rate and with extensional rigidity has a significant effect on spring-back.