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Many engineering applications using composite materials require an assembly of components which can be accomplished using adhesives, welding, or fasteners. The last requires the machining of holes, which are usually done via conventional drilling or abrasive water jet process. The choice of the machining process is important because it has a direct impact on the surface quality of the machined holes, and, consequently, on the performance of the composite structure. Although most studies on the effect of machining methods were focused on conventional composites, little is known about the effect of conventional drilling (CD) and Abrasive water jet (AWJ) machining methods on the mechanical behaviour of flax composites with holes. This study is the first to experimentally investigate the influence of the machining process in pure flax/epoxy composites with three different layups, namely, unidirectional (F[0]), cross-ply (F[0/90]) and angle-ply (F[±45]). A delamination factor was employed to evaluate the degree of delamination damage around the surface of the hole. The lowest delamination factor at the exit of the hole was observed for F[0]-AWJ with a value of 0.777 and the highest was observed for the F[±45]-AWJ with a value of 1.484. Damage analyses of the layups under a quasi-static loading condition showed that the average final stiffness damage for F[0]-CD was 13% greater than that of F[0]-AWJ, and for F[0/90]-AWJ and F[±45]-AWJ were respectively 25% and 27% greater than their counterpart samples machined by CD method. The damage results correlate well with the delamination factor.

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Most of the research on hybrid natural fiber composites has been focused on non-structural applications. The aim of this research is to improve the understanding of how to use hybrid natural fiber composites for structural applications, such as in the aerospace and automotive industries. The joining of subassemblies with rivets, bolts, or screws is a prominent feature in these industries, which implies that the presence of holes in the structural members is unavoidable. The study of the effect of holes on the mechanical behavior of these members is therefore imperative, especially given that holes are stress risers. An important factor in the design of open-hole hybrid flax composites is their fatigue behavior under cyclic loading because it accounts for most failures in composite structures. The investigation of this behavior is reported in this study where three types of 16-ply symmetric hybrid composites that were manufactured using woven carbon (C) and unidirectional flax (F), namely, unidirectional (CF[0]), cross-ply (CF[0/90]) and angle-ply (CF[[Formula: see text] 45]) are employed. A circular hole was made in the center of each specimen using either an abrasive water jet or conventional drilling methods. The observed machining-induced critical defect was delamination, which manifested in three forms: peel-up, push-out, and secondary. Stepwise fatigue tests were conducted to determine the damage evolution and high-cycle fatigue strength of each layup. The damage evolution of the material was assessed via stiffness damage, thermographic methods, and dissipated energy per cycle. It was observed that CF[0] layups are unaffected by the machining process and they have an identical high-cycle fatigue strength. For the CF[0/90] and CF[[Formula: see text] 45] layups, conventional drilling specimens have a higher high-cycle fatigue strength than their abrasive water jet counterparts.