Experimental investigations on residual stresses during the fabrication of intrinsic CFRP-steel laminates

Abstract

This paper focuses on process-related thermal residual stress in fibre metal laminates, consisting of thin steel foils and CFRP prepreg layers. Different process modifications during fabrication were investigated, modifying temperature, pressure and the vacuum bagging arrangement. The impact of these parameters is measured on the deflection of asymmetrical specimens, enabling the evaluation of the potential of specific configurations. For detailed investigations, a cure monitoring system with fibre bragg grating (FBG) sensors was used to measure the in-plane strains during processing. The investigations show a relationship between cure reaction and processing strains. This allows the characterisation of the co-cure bonding process and the resulting residual stress state in nearly any FML configuration. A new method is presented for quantitative predictions of residual stresses in CFRP-steel laminates. It is characterized by the subsequent removal of the steel layers and in-situ measurements of the resulting strain changes with the help of embedded FBG-sensors.