Process-induced strains measurements through a multi-axial characterization during the entire curing cycle of an interlayer toughened Carbon/Epoxy prepreg

High dimensional accuracy of thermoset composite parts is a challenging issue for manufacturers in the aeronautical industry. A deep understanding of the cure behavior is required in order to prevent internal stresses generation as being responsible of shape deformations. However, the specific challenge of experimental investigations is to cover all of the stages of the cure process including the pre-gelation region. In this paper, the characterization of the process-induced strains throughout the cure is based on using a laboratory scale bench named as PvT-HADDOC. Tests were performed on a unidirectional interlayer toughened aerospace prepreg. The device enables the measurements of the induced strains simultaneously along the out-of-plane and the in plane directions. The consolidation of the uncured material is captured. The measured coefficients of thermal expansion are proved to be higher through the thickness direction in the liquid and cured states. The chemical shrinkage is measured before and after gelation along both transverse directions. The orthotropic behavior of IMA/M21 system is attributed to the presence of interleaf layers of resin within the prepreg plies.

Automated summary

The high dimensional accuracy of thermoset composite parts poses a challenge for manufacturers in the aeronautical industry, requiring a deep understanding of cure behavior to prevent shape deformations caused by internal stresses. Experimental investigations using PvT-HADDOC reveal higher coefficients of thermal expansion along the thickness direction in liquid and cured states. The orthotropic behavior of the IMA/M21 system is attributed to the presence of interleaf layers of resin within the prepreg plies.