Experimental and numerical study of the effect of design and processing parameters on spring-in in composite parts

Abstract

Residual stresses appearing during cure of thermoset composite laminates lead to distortions such as spring-in. The dimensional changes in the produced parts cause the parts not to mate closely with the other parts in the assembly. To solve the problems regarding dimensional changes in the part, a trial and error approach is preferred in applications but this method is very expensive and time consuming in the production of large components. Therefore distortions should be predicted closely before manufacturing parts. In this study, the effect of design and processing parameters such as stacking sequence, part thickness, and corner radius on spring-in were examined experimentally and numerically. A U-shaped steel mold was manufactured to fabricate L-shaped composite laminates. The composite material used was AS4/8552 prepreg system. The mold (tool) was heated by plate heaters, not by hot air, which is different from autoclave systems. To predict spring-in value for L-shaped composite laminates due to the cure process, a 2-D finite element model was used. The finite element model consists of three steps: viscous state, rubbery state, and glassy state. For the deformation of the parts, generalized plane strain elements were preferred in the first and second step and in the third step generalized plane stress condition was used.