A.P. Mouritz

Review of applications for advanced three-dimensional fibre textile composites

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 advanced composite structures for naval ships and submarines

The recent applications of fibre-reinforced polymer composites to naval ships and submarines are reviewed. Since the mid-1980s the use of composites has increased considerably as the military strive to reduce the acquisition and maintenance costs and improve the structural and operational performance of naval craft. A wide range of new applications of composites to naval vessels are described, including their current and potential use in the superstructures, decks, bulkheads, advanced mast systems, propellers, propulsion shafts, rudders, pipes, pumps, valves, machinery and other equipment on large warships such as frigates, destroyers and aircraft carriers. Potential applications of composites to submarines are also described, such as their possible use in propulsors, control surfaces, machinery and fittings. The growing use of composites in the complete construction of fast patrol boats, minehunting ships and corvettes is discussed. For each application the major benefits gained from using composites instead of conventional shipbuilding materials, such as steel and aluminium alloys, are identified. The paper also outlines the main drawbacks of using composites in naval vessels.

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

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 mechanistic approach to the properties of stitched laminates

Abstract New insights are presented into the mechanisms responsible for changes to the in-plane mechanical properties of polymer matrix laminates as a result of through-the-thickness stitching. A critical appraisal of a large amount of published mechanical property data reveals that stitching usually reduces the stiffness, strength and fatigue resistance of a laminate by not more than 10–20%, although in a few cases the properties remain unchanged or increase slightly. This range of changes is observed for loading in compression, tension, bending or shear. Softening and strengthening mechanisms are proposed to account for the changes in properties due to stitching. Areas of research that are needed to further the understanding of the relationships between mechanisms and properties are identified. These include more detailed reporting of the physical properties of the stitched and unstitched laminates (e.g. fiber content, fiber distortions), the stitching conditions (e.g. yarn tension) and more thorough examination of observed mechanisms.

Laminate Theory Analysis of Composites under Load in Fire

Laminate analysis is used to model a loaded composite plate under one-sided heat flux. The input to the laminate analysis comes from a thermal/ablative model, which predicts the temperature evolution through the thickness. It also gives the profile of residual resin content, which reflects the extent of thermal damage. Relationships are proposed to enable the computation of the elastic constants and other mechanical properties as functions of temperature and resin content. The model was applied to a 12 mm thick woven glass/polyester laminate exposed to a heat flux of 75 kW m 2. The laminate A, B, and D matrices were modeled, along with the variation of failure loads in compression and tension. The predictions agreed well with experimental values for compression of a constrained plate. Both the local buckling load, which is proportional to √D1 D2, and the compressive failure load fall rapidly on exposure to heat flux. The bending/tensile coupling matrix, B, which is zero initially, becomes finite due to the asymmetric thermal profile, then declines as the thermal front progresses. For tensile loading, the residual properties after fire were accurately modeled, but the fall in tensile failure load was somewhat over-predicted.

Flexural strength and interlaminar shear strength of stitched GRP laminates following repeated impacts

Abstract The flexural strength and interlaminar shear strength of stitched and non-stitched glass-reinforced plastic (GRP) laminates were studied under conditions of increasing impact energy and increasing number of repeated impacts. The GRP was stitched through the thickness with Kevlar thread in two orientations with a low or high stitch density. The Mode I interlaminar fracture toughness, GIc, increased with stitch density whereas the Mode II toughness, GIIc, was not changed by stitching. The three-point flexural strength and short-beam interlaminar shear strength of the GRP before impact loading were reduced by stitching as a result of stitching damage. Under short-beam loading, the stitches become sites of stress concentration and this contributed to the reduction in interlaminar shear strength. The strengths of the laminates were reduced slightly with increasing impact energy after one impact. The strengths were reduced considerably with increasing number of impacts. The laminates suffered severe microstructural damage under repeated impacts, including shear cracking of the resin, delaminations, and crushing and fracture of the glass fibres. The impact damage resistance, the post-impact flexural strength and the interlaminar shear strength of the GRP were not improved by stitching, and this finding differs from other impact studies on stitched composites.

Tensile properties and failure mechanisms of 3D woven GRP composites

Abstract Tensile tests were performed on glass reinforced polymer (GRP) composites with three-dimensional (3D) orthogonal, normal layered interlock, and offset layered interlock woven fibre architectures. The mechanical properties and failure mechanisms under tensile loading were similar for the three composites. Cracks formed at low strains within the resin-rich channels between the fibre tows and around the through-thickness binder yarns in the composites, although this damage did not alter the tensile properties. At higher applied tensile stresses the elastic modulus was reduced by 20–30% due to inelastic tow straightening and cracking around the most heavily crimped in-plane tows. Further softening occurred at higher strains by inelastic straightening of all the tows. Composite failure occurred within a localised region and the discrete tow rupture events that have caused tow lock-up and pullout mechanisms in other 3D woven composites were not observed.

The Integrity of Polymer Composites during and after Fire

This paper reports on changes to the mechanical properties of woven glass laminates with polyester, vinyl ester and phenolic resins during fire exposure. Two sets of experiments were carried out. First, unstressed laminates were exposed to a constant one-sided heat flux (50 kW m 2) for various times, and the residual post-fire strength at room temperature was reported. In a second series of experiments, laminates were tested under load. The times corresponding to a given loss of properties were 2-3 times shorter than in the previous case. It was found in both cases that modes of loading involving compressive stress were more adversely affected by fire exposure than those involving tension. A simple ‘two-layer’ model is proposed, in which the laminate is assumed to comprise (i) an unaffected layer with virgin properties and (ii) a heat-affected layer with zero properties. For residual properties after fire, the ‘effective’ thickness of undamaged laminate was calculated using this model and compared with measured values. A thermal model was employed to predict the temperature and the residual resin profile through the laminate versus time. Comparing the model predictions with the measured values of effective laminate thickness enabled simple criteria to be developed for determining the position of the ‘boundary’ between heat-affected and undamaged material. For post-fire integrity of unloaded laminates, this boundary corresponds to a Residual Resin Content (RRC) of 80%, a criterion that applies to all the resin types tested. For polyester laminate under load in fire, the boundary in compressive loading (buckling failure) appears to correspond to the point where the resin reaches 170 C. In tensile loading, significant strength is retained, because of the residual strength of the glass reinforcement. The model was used to produce predictions for ‘generic’ composite laminates in fire.

Mode I interlaminar fracture toughness properties of advanced textile fibreglass composites

Abstract The Mode I interlaminar fracture toughness properties of vinyl ester-based composites reinforced with fibreglass manufactured by the advanced textile technologies of braiding, knitting, stitching and through-the-thickness weaving are assessed in comparison to a variety of traditional composites made from fibreglass such as unidirectional or woven rovings. The interlaminar fracture toughness ( G Ic ) of braided and knitted composites are higher than traditional composites by factors of more than two and four, respectively. Toughening in these textile composites was caused by extensive crack branching as the interlaminar crack was forced to follow a tortuous path through the complex fibre architectures. The G Ic values of the composites reinforced in the through-thickness direction by weaving or stitching were higher than traditional composites by factors of nearly two and three, respectively, with the main toughening mechanism being crack bridging by the through-thickness binder yarns/stitches. A review of Mode I interlaminar fracture data collected from papers shows that advanced textile techniques are capable of manufacturing composites with substantially improved delamination resistance.

Effect of weaving damage on the tensile properties of three-dimensional woven composites

This research paper examines the damage mechanisms and reductions to the tensile properties of E-glass yarns during weaving of three-dimensional (3D) fabrics for polymer-based composites. The paper also assesses the influence of weaving damage to load-bearing glass yarns on the tensile properties of 3D orthogonal woven composites. It is found that damage occurs to yarns at most stages of the 3D weaving process due to abrasion and breakage caused when sliding against the loom machinery. The abrasion damage causes a large reduction (∼30%) to the tensile strength of the dry woven yarns, although the tensile stiffness remains unaffected. The damage and reduction to the tensile properties of the dry yarns at different weaving stages are described. Tensile studies performed on single yarn/resin composites and larger coupons of 3D orthogonal woven composites reveal that weaving damage is responsible for a significant reduction to the tensile strength.