Analysis and compression testing of laminates optimised for damage tolerance

Barely Visible Impact Damage (BVID) can occur when laminated composite material is subject to out-of-plane impact loads and can result in a significant reduction in compressive strength. This paper reports on three compression tests of laminates optimised to maximise damage tolerance. Results from these tests were analysed using a semi-analytical, fracture mechanics based method that predicts the strain below which laminated coupons containing BVID subject to axial compression will not fail. A further experiment was conducted on an artificially delaminated coupon in order to validate the modelling methodology. Results from one of the two optimised stacking sequences considered show an increase of over 40% in Compression After Impact (CAI) strength compared with a baseline configuration. Analysis of results has indicated that CAI strength is dependent to a great extent on damage morphology and stability of damage growth, both of which are functions of laminate stacking sequence.