Monitoring the residual strain formation in CFRP/PMI foam core sandwich structures

Using CFRP/PMI foam core sandwich structures for primary structures in commercial aviation a lot of advantages could provide. With the cost effective manufacturing process of vacuum infusion several integral structures with high light weight potential can be built. A disadvantage is the residual strain that is mainly caused by the different coefficients of thermal expansion and stiffness's of the sandwich components. It already occurs at the manufacturing process during cool down from curing to room temperature. In this study the formation of these residual strains was observed experimentally during the manufacturing process. Outgoing from these results concepts of reduced residual strains of the cured sandwich structure were derived and tested. To determine the foam core strains left after manufacturing a curvature measurement of the halved sandwich specimen was done to validate the measured in-situ strain data.