Compaction, flow and mechanical properties in lap joints for large multilayer VARTM preforms

Reinforcement preforms for the vacuum assisted resin transfer moulding (VARTM) manufacturing of large composite parts are made from different layers where presence of double curvature and varying fibre orientation imposes the use of superimposed lap joints. A series of tests were conducted to investigate the compaction of jointed preforms, flow through jointed preforms and the structural behaviour of composite parts featuring superimposed lap joints.;The compaction of reinforcements was evaluated using a novel thickness measurement system for preforms. The thickness measurement system utilizes Hall effect sensors. The local fibre volume fraction, vf, was derived from the readings of Hall effect sensors positioned at selected locations above the jointed preforms. Different vf values were observed around joints; consequently, simulations of the manufacturing and performance of jointed composite parts must feature variable vf at the joints.;The effective permeability to resin of jointed preforms parallel to the joints was investigated. The flow of resin in the preform was different from that in un-cut preforms. Specimens cut from cured panels were tested in four-point bending tests based on ASTM standard D790-03. The structural stiffness, maximum flexural stress and failure mode of specimens, were investigated. The structural stiffness and failure mode followed clear trends, while the maximum flexural stress was affected by local stress concentration at the joints.;It is concluded that the presence of lap joints in VARTM preforms changes the behaviour during manufacturing and in service. This should be considered in design of parts and simulation of VARTM manufacturing.;A variety of lap joint configurations was investigated, characterized by specific values of overlap length, OL, horizontal distance between joints, HD, and number of immediately superimposed joints, NS, for a random matt and a woven reinforcement.