Process monitoring with FBG sensors during vacuum infusion of thick composite laminates

During manufacturing of thick (>20 mm) laminates, thermal gradients through the thickness may arise due to, for example, exothermal reactive heat release. These thermal variations may result in residual strain gradients through the thickness as well as variations in polymer matrix properties, such as degree of cure. For prediction and simulation of the residual strains, it is essential that the manufacturing process is monitored, in order to identify the parameters responsible for the residual strain build-up. The research described in this paper, proposes the use of Fibre Bragg Grating sensors as an experimental tool to determine variations in (thermal) residual strain levels through the thickness in a thick glass fibre reinforced thermoset laminate. In addition, other manufacturing issues, such as the flow behaviour that could be identified with these sensors were addressed. Moreover, the results of a first attempt to identify polymer property variations through the thickness by means of the microhardness test are reported

Characterization of resistance-welded thermoplastic composite double-lap joints under static and fatigue loading

An experimental investigation of resistance welding of thermoplastic composite double lap shear (DLS) joints is presented. DLS specimens consisting of unidirectional carbon fibre/polyetheretherketone (CF/PEEK), carbon fibre/polyetherketoneketone (CF/PEKK), carbon fibre/polyetherimide (CF/PEI) and 8-harness satin weave fabric glass fibre/polyetherimide (GF/PEI) composites were resistance welded using a stainless steel mesh heating element. The welded specimens were tested under static and fatigue loadings, and the quality of the welds was examined using optical and scanning electron microscopy. Weld strengths of 53, 49, 45 and 34 MPa were obtained for CF/PEEK, CF/PEKK, CF/PEI and GF/PEI DLS joints, respectively. Indefinite fatigue lives were obtained between 20 and 30% of the ultimate static failure loads of the joints. Performances of the resistance-welded DLS and single lap shear (SLS) joints were compared. It was shown that the effect of joint geometry, that is, DLS versus SLS, on the mechanical performance of the resistance-welded joints is minimal, indicating a good resistance of welded joints to peel stresses.Peer reviewed: YesNRC publication: Ye

Continuous resistance welding of thermoplastic composites: Modelling of heat generation and heat transfer

A process model composed of electrical and heat transfer models was developed to simulate continuous resistance welding of thermoplastic composites. Glass fabric reinforced polyphenylenesulfide welded in a lap-shear configuration with a stainless steel mesh as the heating element was considered for modelling and experimental validation of the numerical results. The welding temperatures predicted by the model showed good agreement with the experimental results. Welding input power and welding speed were found to be the two most important parameters influencing the welding temperature. The contact quality between the electrical connectors and the heating element was found to influence the distribution of the welding temperature transverse to the welding direction. Moreover, the size of the electrical connectors was found to influence the achievable welding speed and required power input for a certain welding temperature.Peer reviewed: YesNRC publication: Ye