Current and future potential applications for three-dimensional (3D) fibre reinforced polymer composites made by the textile processes of weaving, braiding, stitching and knitting are reviewed. 3D textile composites have a vast range of properties that are superior to traditional 2D laminates, however to date these properties have not been exploited for many applications. The scientific, technical and economic issues impeding the more widespread use of 3D textile composites are identified. Structures that have been made to demonstrate the possible uses of 3D composites are described, and these include applications in aircraft, marine craft, automobiles, civil infrastructure and medical prosthesis.

Review of applications for advanced three-dimensional fibre textile composites

This paper reviews published research into polymer composite laminates reinforced in the through-thickness direction with z-pins. Research into the manufacture, microstructure, delamination resistance, damage tolerance, joint strength and mechanical properties of z-pinned composites is described. Benefits of reinforcing composites with z-pins are assessed, including improvements to the delamination toughness, impact damage resistance, post-impact damage tolerance and through-thickness properties. Improvements to the failure strength of bonded and bearing joints due to z-pinning are also examined. The paper also reviews research into the adverse effects of z-pins on the in-plane mechanical properties, which includes reduced elastic modulus, strength and fatigue performance. Mechanisms responsible for the reduction to the in-plane properties are discussed, and techniques to minimise the adverse effect of z-pins are described. The benefits and drawbacks of z-pinning on the interlaminar toughness, damage tolerance and in-plane mechanical properties are compared against other common types of through-thickness reinforcement for composites, such as 3D weaving and stitching. Gaps in our understanding and unresolved research problems with z-pinned composites are identified to provide a road map for future research into these materials.

Review of z-pinned composite laminates

This paper reviews over fifty studies into the effect of through-the-thickness stitching on the in-plane mechanical properties of fibre-reinforced polymer composites. Reviewed are the in-plane tensile, compressive, flexure, interlaminar shear, creep, fracture and fatigue properties, although little work has been undertaken on the last three properties. When comparing studies it is apparent that many contradictions exist: some studies reveal that stitching does not affect or may improve slightly the in-plane properties while others find that the properties are degraded. In reviewing these studies it is demonstrated that predicting the influence of stitching on the in-plane properties is difficult because it is governed by a variety of factors, including the type of composite (eg. type of fibre, resin, lay-up configuration), the stitching conditions (eg. type of thread, stitch pattern, stitch density, stitch tension, thread diameter), and the loading condition. The implications of these findings for the use of stitching in lightweight engineering structures are discussed.

A review of the effect of stitching on the in-plane mechanical properties of fibre-reinforced polymer composites

In this study, we examine the interlaminar shear strength (ILSS) of traditional glass fiber reinforced epoxy composites enhanced by strategically injecting multi-walled carbon nanotube (MWNT)–epoxy suspensions into stationary glass fiber mats. The suspensions were prepared by combining the techniques of high-speed mechanical stirring, ultrasonic agitation and acid oxidation. Two types of process designs were introduced to fabricate the hybrid MWNT/glass/epoxy composites and their relative merits were discussed. Short beam shear (SBS) and compression shear tests (CST) were conducted on the manufactured components to characterize the influence of the process and the weight percentage of nanotubes on the ILSS. The results show that the introduction of MWNT into the composite increased the ILSS by up to 33%. The preferential orientation of the MWNTs in the thickness direction was found to contribute to the increase in the interlaminar shear properties.

Interlaminar shear strength of glass fiber reinforced epoxy composites enhanced with multi-walled carbon nanotubes

Improved mechanical properties of carbon fiber/graphene oxide-epoxy hybrid composites

On the effect of stitching on mode i delamination toughness of laminated composites

Determination of mode II delamination toughness of stitched laminated composites

Two simple micromechanics based models are proposed to predict the effect of through-thickness reinforcement (stitching) on the improvement of delamination crack growth resistance in end-notched flexure (ENF) specimens. In the first model, it is assumed that stitches stretch elastically and then rupture when the load carried approaches the failure load. In the second model, it is assumed that stitches are discontinuous and that the stitch thread-matrix interface is completely frictional. Approximate closed form solutions for energy release rates are obtained, and the effects of stitch density, matrix-stitch thread interfacial shear stress, stitch thread diameter, volume fraction of stitches, critical energy release rate and Young's modulus are then examined. A simple design study for sizing the ENF specimen to minimise geometric nonlinear response is presented. The influences of interlaminar shear deformation and friction between the crack surfaces on the strain energy release rate are examined.

Lalit K. Jain

Papers

On the effect of stitching on mode i delamination toughness of laminated composites

Determination of mode II delamination toughness of stitched laminated composites

Analysis of stitched laminated ENF specimens for interlaminar mode II fracture toughness

Failure of transversely stitched RTM lap joints

Further validation of the Jain and Mai models for interlaminar fracture of stitched composites