Improvement of low-velocity impact and compression-after-impact performance by z-fibre pinning

Abstract

Z-fibre pinning is a new method of through-thickness reinforcement of laminated composites. This paper presents an experimental test and theoretical analysis on how and why these pins can improve the resistance to impact loading and post-impact compression. Specimens were made of carbon/epoxy T300/914C with nominal thicknesses of 2, 4, and 6 mm. For the specimens tested in this study, z-pinning reduced impact damage area by 19-64% depending on the specimen thickness and impact energy. Experimental results obtained also indicate that z-pins can significantly increase the compression-afterimpact (CAI) strength by about 45%. In this paper all of these observations are discussed in the context of theoretical and numerical models that have been developed previously to predict the critical impact force and z-pinning performance in terms of the laminate in-plane stiffness and mode I delamination fracture toughness with the z-fibre bridging effect.

Impact damage and CAI strength of a woven CFRP material with fire retardant properties

“…Many authors have addressed the issue of assessing and even enhancing the fracture toughness response to impact loading and the subsequent resistance to CAI. For example by using different matrix thermosetting or thermoplastic materials [23] or by applying veils which are other layered materials within the laminates [24,25] or even by applying metallic materials in the form of titanium pins in the transverse direction [26].…”

The effect of needleless electrospun nanofibrous interleaves on mechanical properties of carbon fabrics/epoxy laminates

“…In such cases, improving the interlaminar properties can lead to a decrease of in-plane properties. Stitching [15], z-fiber pinning and other methods [16] can be applied to clench the layers, but these procedures can cause fiber breaks in the primary reinforcement that can also lead to a decrease in in-plane properties and generate additional production costs. Using nanofibrous layers can be a feasible way to enhance interlaminar properties without compromising other mechanical properties.…”

Experimental analysis of CFRP laminates subjected to compression after impact: The role of impact-induced cracks in failure

“…Sometimes, it is even possible to observe the propagation of delamination due to this buckling [13,18,26,27]. The majority of researchers agree that, indeed, the buckling (especially local buckling) plays a key role in the final rupture [13,15,18,[25][26][27][28][29][30][31]. However, this phenomenon is not sufficient to explain the final failure of the structure, since in most cases the delamination does not propagate over the entire width of the plate, and the final rupture is due to the sudden propagation of a crack from the impact zone to the edges of the structure.…”

“…Indeed, among the experimental studies, some focus on the influence of material properties on the evolution of the residual strength: fibre [8,11], resin [11][12][13], interface [14], stacking [15], transverse reinforcement like stitching [16,17] or Z-pinning [18], fabric instead of unidirectional tape [12,19], curing temperature [19]. There are also some experimental studies concerning the influence of test conditions such as: temperature during impact [20], hygrothermal conditions [12,[21][22][23], fatigue loading [24], or use of protective layer [25].…”