Co-authors​ :

 James R DAVIDSON (UNITED KINGDOM), Danijela STANKOVIC (UNITED KINGDOM), Colin ROBERT (UNITED KINGDOM), Murat ÇELIK (UNITED KINGDOM), Edward D MCCARTHY (UNITED KINGDOM), Conchúr M Ó BRÁDAIGH (UNITED KINGDOM) 

Pneumatic-splicing has the potential to achieve step-change improvements in composite sustainability by enabling waste off-cuts to be readily re-introduced into the manufacturing supply chain. In this process, consistent and robust mechanical bonds are formed by overlapping two distinct yarn ends, placing them within a specially designed (trapezoidal) chamber, and agitating the fibres with a blast of high-speed, turbulent air. Though excellent spliced connection strengths have been observed in test samples from earlier publications, the implications of embedding highly entangled spliced fibres within composite structures are not currently known. Correspondingly, the influence of carbon-carbon spliced tow connections within composite structural (‘c-section’) beams is the focus of this work. The performance of dry-fibre connections between individual tows was initially considered to provide insight into parameters which influence (pre-infusion) performance. Tensile tests were conducted using a bespoke test fixture, such that statistical trends for strength and linear stiffness were obtained. Notably, fibre count, sizing type, and blast pressure were all demonstrated to have significant influence on connection stiffness and strength. In view of these outcomes and typical industrial requirements, carbon fibre (twill) fabrics—where pneumatically-spliced connections were periodically distributed across the (in-plane) fabric area—were specified for the reinforcing materials. Structural beams were correspondingly manufactured via wet-laying onto a bespoke 2-part mould, followed by curing within a pneumatic press. Performance comparisons between sections containing and not containing spliced connections were assessed via quasi-static 3-point bending and compression testing. Furthermore, optical and scanning electronic microscopy (SEM) at specimen fracture locations were used to qualitatively characterise failure mechanisms. Results indicated that locally spliced regions had relatively minor implications on component performance, with marginal decreases in both strength and rigidity, depending on the specific reinforcement configuration. With further optimisation, it is anticipated that structural members containing spliced connections have the potential to exhibit indistinguishable mechanical performances from those containing pristine reinforcement. Additionally, outcomes from this work suggest that pneumatic splicing could also be utilised as an effective processing/remanufacturing technique for recycled fibres.