Through-thickness reinforcement

Through-thickness reinforcement, z-pinning, bridging law, mode 1 delamination, Double-Cantilever-Beam (DCB), pull-out. 

Currently available data indicate that 3D reinforcements typically result in high values of Gc compared with the unidirectional laminate made from the same fibre and matrix. Whether the high delamination resistance of 3D FRP laminates does represent material values or apparent values, for example depending on specific test and specimen parameters, is still debated (see e.g. Ref. [92]). More generally, the applicability of linear elastic fracture mechanics to through-thickness reinforced FRP composites is questionable [98]. 

Sridhar N, Massabo R, Cox BN, Beyerlein U. Delamination dynamics in through-thickness reinforced laminates with application to DCB specimens. Int J Fract 2002 118 119-44. http //dx.doi.Org/10.1023/A 1022884410968. 

Cox BN, Massabo R. Towards standardization for through-thickness reinforcement of laminates. In Loud S, Karbhari V, Adams DO, Strong AB, editors. Proceedings 45th international SAMPE symposium 2000. pp. 1526—37. 

The 21st century has already seen rapid advances in the field of textile-based composites. In addition to traditional two-dimensional woven fabrics, multiaxial non-crimp fabrics are now very widely used, with a rapidly growing number of applications for braided composites. Developments in three-dimensional weaving, combining through-thickness reinforcement with excellent in-plane properties, provide new design solutions for situations where delamination must be avoided. Textile reinforcement is thus providing major new areas of opportunity for composite materials worldwide. 

Aktas A, Potlnri P, Porat I. Development of through-thickness reinforcement in advanced composites incorporating rigid cellular foams. Appl Compos Mater 2013 20(4) 553-68. 

Mouritz, A.P., 2008. Tensile fatigue properties of 3D composites with through-thickness reinforcement. Compos. Sci. Technol. 68, 2503 2510. 

D braids are characterized by the existence of through-thickness reinforcements, that is, fibres that are oriented in through-thickness direction. 2D braids do not have through-thickness direction. Thus, the definition of 2D and 3D braids is independent of the actual geometry of the structure but depends on the braided stmcture itself. A 2D braid with a 3D geometry is depicted in Figure 7.2. As can be seen, the fibres are... 

Farley, G.L. (1992). A mechanisms responsible for reducing compressive strength of through-thc-thickness reinforced composite materials. J. Composite Mater. 26, 1784-1795. 

Farley. G.L., Smith. B.T. and Maiden. J. (1992). Compression response of thick layer composite laminates with through-the-thickness reinforcement. J. Reinforced Plast. Composites 11, 787-810. 

The presence of Z-pins as the through-the-thickness reinforcement has been shown to result in dramatic increases in the apparent resistance to crack propagation under Mode I and Mode II loading conditions, in laboratory tests on standard unidirectional (UD) beam samples [2]. The Z-pin pull-out has been identified as the dominant energy micro-mechanism responsible for the resistance to delamination under Mode I conditions. The behaviour of individual Z-pins in pull-out from a UD-laminate has been characterised and modelled and the single Z-pin pull-out curves used as input into a 2D Finite Element (FE) model of delamination under Mode I [3, 4]. 

The through-the-thickness reinforcement acts as a crack bridging, which requires new concepts and methods to be used for the fracture resistance calculation. 

Rugg KL, Cox BN, Massabo R. Mixed mode delamination of polymer composite laminates reinforced through thickness by z-fibers. Compos Part A Appl Sci Manuf 2002 33 177-90. http //dx.doi.org/10.1016/S1359-835X(01)00109-9. 

Gray PJ, McCarthy CT. An analytical model for the prediction of through-thickness stiffness in tension-loaded composite bolted joints. Compos Struct 2012 94(8) 2450—9. Lapczyk I, Hurtado JA. Progressive damage modeUing in fibre-reinforced materials. Compos Part A-Applied Sci Manuf 2007 28 2333-41. 

Almost identical properties in all directions. With fiber reinforeed composites, this can be achieved through at least three differently oriented layers of identieaUy thick reinforcing material... 

As there are no fibers aligned in the through-thickness direction of 2-D fiber-reinforced composites, a possible mode of failure is by shear between the fabric plies. Hence, interlaminar shear strength is an important property. Tests were conducted using the ASTM D2344-84 short beam method. The average interlaminar shear strength from five samples was measured to be 62 MPa at room temperature. 

The increases in through-the-thickness reinforcement achieved by NCFs have been demonstrated by a number of authors. For example. Backhouse et aV compared the ease of delaminating polyester stitched 0/ 45 carbon fibre NCF with equivalent carbon fibre/epoxy UD laminates. There were large increases, some 140%, in the measured... 

Three dimensional structures of multiaxial warp knitted fabrics have been recently developed for multidirectional reinforcement of composites. Multilayers of linear yams are assembled in warp (0°), weft (90°) and bias ( 0) directions to provide in-plane reinforcement in specific directions and they are stitched together by knitting yams to provide structural integrity and through the thickness reinforcement [1,2,3,4,5]. 

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