Structurally stitched NCF CFRP laminates. Part 1: Experimental characterization of in-plane and out-of-plane properties

Structurally stitched NCF CFRP laminates. Part 2: Finite element unit cell based prediction of in-plane strength

“…Therefore, unstitched laminates composed from 90°UD NCFs ( Fig. 1 and Table 1 in [1]) and RTM 6 aerospace grade epoxy resin (Hexcel Composites GmbH) using a vacuum assisted resin infusion process were subjected to uni-axial tension, compression and shear in servohydraulic testing machines until ultimate failure as given in Table 1. Upon loading the force and the elongation parallel to the loading direction were recorded from which the strength and modulus were evaluated according to the given standards.…”

“…Experimental investigations on structurally stitched NCF carbon fiber reinforced plastic laminates (CFRP) subjected to in-plane loading (Figs. 14, 16 and 17 in [1]) showed that depending on the stitching parameters applied, at best similar, but in the majority of cases reduced tension, compression and shear strengths up to 36%, 31% and 22% compared to the unstitched laminate must be expected [1,20,21]. A comprehensive analysis of published data of 3-D reinforced composites including stitching was published in a review article by Mouritz and Cox [22] which includes quantifications and a thorough discussion of candidate mechanisms on fiber architecture, in-plane stiffness, in-plane and out-of-plane strength as well as on fatigue strength.…”

“…Fig. 15 in [1]), which may affect the in-plane stiffness and strength properties of the laminate. In [3,10,[15][16][17][18][19] it was reported that in comparison to the unstitched reference, structural stitching reduces the stiffness and strength under tension, compression and bending loading by 10-20%, while, in some cases, no change or even a slight increase was reported.…”

“…The experimental results presented in [1] are used to validate the strength prediction of structurally stitched NCF laminates under in-plane tension, compression and shear loading. As shown in [44][45][46][47][48][49] acoustic emissions (AE) analyses are suitable to detect damage initiation in textile laminates.…”

“…3-D reinforcement by stitching provides a possibility to enhance the out-of-plane properties of fiber reinforced plastic laminates (FRP) [6][7][8][9][10][11][12][13][14]. In comparison to the unstitched laminate stitching enables to increase the compression strength after impact by up to +50% [1,6,7] and the mode I energy release rate by up to a factor of +8 [12][13][14]. On the other hand, non-structural binding yarns and structural stitching in non-crimp fabric (NCF) dry fiber preforms dislocate the in-plane fibers, leading to resin-filled pockets after resin infusion (cf.…”