Experimental Characterization of the Properties of Double-Lap Needled and Hybrid Joints of Carbon/Epoxy Composites

Abstract

The effect of through-thickness reinforcement by thin 1 mm steel needles (z-pins) on the static tensile strength of double-lap joints of a carbon/epoxy composite was investigated. Two types of joints—z-pinned and hybrid (including glued ones)—were considered. The joints were reinforced in the overlap region with 9, 25, or 36 z-pins. Comparing mechanical properties of the double-lap joints with the corresponding characteristics of their unpinned counterparts, the z-pins were found to be highly effective: the strength and stiffness of the pinned joints increased up to 300% and 280%, respectively. These improvements were due to a transition in the failure mechanism from debonding of the joint in the absence of z-pins to pullout or shear rupture of z-pins or to the tensile failure of laminate adherends, depending on the volume content of the pins.

Experimental investigation on stiffness and strength of single-lap z-pinned joints in a laminated CFRP stress-ribbon strip

“…This study extends previous findings, concerning the double-lap joints (Arnautov et al 2015), for the case of analysis of applicability of the hybrid connection technology in producing the laminated stress-ribbon strips. Application of z-pins improved the mechanical properties of the joints.…”

“…For the hybrid joints, the pin effect is less evident though the 20% increase in strength and 230% in stiffness was achieved concerning the mechanically connected counterparts. The previous research (Arnautov et al 2015) indicated that the proposed hybrid joint was rather effective for the double-lap joints (securing symmetric distribution of the tensile forces in the joint)the 280% increase in both strength and stiffness (due to the additional adhesive connection) was observed experimentally. Thus, additional means are necessary to avoid eccentric load distribution of the forces in the joint (e.g., the confinement rollers schematically shown in Fig.…”

“…Such connection is efficient for controlling the fatigue resistance of thin-skinned structures (Pantelakis, Tserpes 2014) and strengthening purposes (Grbniak et al 2014(Grbniak et al , 2015. However, effectiveness of the adhesive bond is limited by a relatively low inter-laminar shear strength (Arnautov et al 2015). Furthermore, failure of the adhesive joints is often brittle.…”

Tensile and fatigue properties of single lap joints of aluminium alloy/glass fibre reinforced composites fabricated with different joining methods

“…For the past few decades, the joining techniques used were adhesive bonding, bolt fastening, and adhesive-bolt hybrid joining; this has led to various researches studies on the combination of dissimilar materials and the joining methods [5]: single-lap [6], double-lap [7][8][9], scarf [10,11], strapped [12,13], and tapered joints [6]. The mechanical fastening methods riveting, screw-type fasteners, washers and bolt and nut were used in the bolting condition and always required drill holes on the substrates.…”

Strengthening of Fibre Reinforced Concrete Elements: Synergy of the Fibres and External Sheet

“…In this study, thin steel pins are used to fasten the CFRP sheets. The authors of [30,31] developed this hybrid jointing technology. Basically, on top of the epoxy adhesive, the CFRP sheet is mechanically fixed to the concrete by small steel pins.…”