Effective use of metallic Z-pins for composites' through-thickness reinforcement

Abstract

Z-pins offer effective through-thickness reinforcement for laminated composites. Various studies have however shown that metal Z-pins are less effective at bridging Mode I delaminations than carbon-fibre composite Z-pins, due to poor interfacial bonding with the laminate. This is exacerbated by high thermal mismatch between the metallic Z-pins and the laminate. This study investigates inserting metallic Z-pins at angles offset from the laminate normal, to improve the Mode I bridging in composites. The effects on the apparent fracture toughness under pure and mixed Mode I/II loads using single pin specimens is investigated. Results show that, unlike orthogonally inserted metal Z-pins, inclined Z-pins exhibit high energy absorption throughout the mixed mode range. Double Cantilever Beam (DCB) tests show that the inclined metal Z-pins increase the Mode I apparent fracture toughness by a factor of 2 compared to traditional carbon fibre Z-pins. In End Loaded Split (ELS) tests, the Mode II apparent fracture toughness of inclined stainless steel Z-pins, although less than their uninclined

Mode-II fracture behaviour of aerospace-grade carbon fibre/epoxy composites interleaved with thermoplastic veils

“…and nano-clay [3]; (2) changing the architecture of the fibre mats using various techniques, i.e. 3D textile weaving [4], Z-pinning [5] and stitching [6]; and (3) interlaying the FRPs using various materials, including carbon fibres [7], carbon nanomaterials [8], stainless steel fibres [9], thermoplastic films [10] and thermoplastic veils [11]. Various levels of success have been achieved based on different strategies.…”

Phase field fracture predictions of microscopic bridging behaviour of composite materials

“…Fracture process zone To date, most research efforts have used experimental techniques to investigate crack bridging effects on fracture toughness. Several crack bridging paradigms have been explored, including the use of toughened thermoplastic particles [8], carbon nanotubes [9], Z-pin [10,11] and 3D woven composite architectures [12]. However, these trial-and-error approaches are expensive and time-consuming, often leading to sub-optimal designs.…”

An energy-equivalent bridging map formulation for modelling delamination in through-thickness reinforced composite laminates

“…As mentioned above, a Matlab® script has been written to solve the system of nonlinear ordinary differential equations. The output of the micro-scale model is a single text file containing tabulated records of the dissipated energy calculated according to Equation (7) and the total displacement at which complete pull-out or z-pin rupture occurs. These are defined according with Equation ( 8), where and represent the pull-out and sliding displacements, respectively.…”