A Study on the Effects of Clearance and Interference Fits in a Pin-Loaded Cross-Ply FGRP Laminate

Abstract

The elastic behavior of a cross-ply fiber glass-reinforced epoxy laminate loaded in tension through a pin fitted with clearance and interference is examined. A nonlinear contact analysis using the Finite Element Method and an experimental study by Speckle Interferometry are performed, showing fairly good correlation. An interesting comparison is performed between FEM results and Hertzian contact theory. Major conclusions are: (I) clearance causes high compressive stress in the bearing area, and does not influence the peak tensile stress; (2) interference has beneficial effects on the joint, as (a) it lowers the peak circumferential stress, and (b) it decreases the change of stress due to the application of the load. This last conclusion suggests that interference can improve the fatigue life of the joint.

An experimental and numerical study on the interference-fit pin installation process for cross-ply glass fiber reinforced plastics (GFRP)

“…This may be also due to fiber reinforcement at 0°and 90°direction. According to the results of the previous studies [5,13], the stress magnitude was consistent regardless of the directions. This study presented stresses in both radial and tangential directions can vary depending on the angles around the hole.…”

“…Fatigue enhancement by interference-fit may be due to local pre-compression stresses induced by interference-fit, which improves the joint stiffness. It was also found that interference-fit decreases the degradation rate of joint stiffness per unit bearing area over the fatigue cycles, resulting in delaying damage progression [5,6].…”

“…In order to predict failure of the joints, it is necessary to understand the stress distribution in the vicinity of the composite hole. There are a number of factors affecting the stress distribution of the hole on the composite joints and they are material properties, laminate lay-up, ply orientation, and fit between the fastener and the hole [5][6][7].…”

“…This interference-fit technique has been adapted to the composites and some studies showed the positive results despite of the concerns of potential composite hole damage [6,[11][12][13][14][15][16][17]. The effect of interference-fit of 0.02% and 0.04% to the stress distribution in orthotropic pin-loaded composite laminates has been studied by Di Scalea et al [5] using a two-dimensional (2-D) finite element analysis (FEA) and Digital Speckle Pattern Interferometry (DSPI) on a glass fiber reinforced composite (GFRP) crossply laminate. They reported that the interference-fit exhibited a peak stress 20% less than the neat fit case.…”

“…Also, many researchers conducted frictionless contact analyses for composite joint based on assumption that the friction was insignificant. Di Scalea et al [5] performed a nonlinear contact analysis using a 2-D FEA study to examine the elastic behavior of a cross-ply fiber glass-reinforced epoxy laminate loaded in tension through a pin fitted with clearance and interference. They found that clearance causes high compressive stress in the bearing area and interference has beneficial effects to the joint.…”