Common composite manufacturing defects include void of different shapes and sizes, different location of void (i.e. within the matrix or in between two adjacent plies). Other forms of manufacturing defects in composite laminates result from hand-Layup and automated fiber placement processes, which can cause intra-ply overlap resulting in fiber waviness and/or resin rich pocket gap defects. The presence of gaps containing resin rich pockets and/or wavy fibers affects the performance of laminate modulus and strength properties. It is important to account for manufacturing defects and their variability on material and structural response.
Modeling manufacturing defects by means of finite element analysis (FEA) is impractical. The modeling of voids and fiber waviness is very time consuming. Additionally, use of FEA will introduce other challenges as some voids, when modeled, can cause stress concentration issues. Micro-mechanics based approach is the most efficient approach to model and analyze effects from composite manufacturing defects.
Not accounting for the deterministic and probabilistic nature of composite manufacturing defects can increase the risk associated with the use of composite sin critical structures such as those used in aerospace. For example, manufacturing defects can reduce the stability of composite structures and reduce their impact resistance. To account for such defects, designers tend to reduce the strength allowables used in design, resulting in increased weight and cost.
AlphaSTAR devised a numerical approach combining multi-scale progressive failure analysis to predict the in-situ degraded ply properties containing voids of different sizes and shapes and gaps.
GENOA’s PFA module allows the insertion of manufacturing defects in composite laminates for use in progressive failure analysis.
AlphaSTAR assessed risks associated with composite manufacturing defects for aerospace and automotive industries.
J. Sawicki, P. J. Minguet, “The Effect of Interply Overlaps and Gaps upon the Compression Strength of Composite Laminates” 39th AIAA/SDM Conference Paper, AIAA-98-1786, Long Beach, CA, 1998