Single bolt in plane tension joint tests on E-glass/epoxy composite plate

Abstract

The evaluation and prediction of failure probability and safe levels of composite materials is of extreme importance in terms of manufacturing and structural design. The experimental investigations described in the present paper were conducted to study the strength and failure behaviour of composite plate under pin loaded conditions. Pin bearing tests were carried out on E-glass/epoxy composite plate fabricated by hand lay-up. The experiments investigated the effect of important parameters, including specimen geometry and stacking sequence, on the failure characteristics. Tests were performed with two different stacking sequences: [0/90/+30/−30]s and [0/90/+60/−60]s. Geometrical configurations of specimens such as ratio of edge distance to pin diameter (E/D) and ratio of specimen width to pin diameter (W/D) were suitably varied to observe all possible failure modes. A total of 150 different pin loaded composite plate specimens, two laminate configurations, five edge: pin/diameter ratios, five width: pin/diameter ratios and three samples for each condition were tested under static loading conditions. Failure strength and failure modes were observed in specimens. The specimen tested exhibited different failure modes, consisting of bearing, net tension and shear out, depending on the geometry adopted. Based on the experiments, effects of stacking sequence and geometric parameters on bearing strength, shearing and net tension stress at failure were systematically investigated. Net tension and shear out failure modes were catastrophic, therefore they were undesirable. These modes were also not as safe as bearing failure mode. Bearing failure was desirable for pin loaded composites, due to non-catastrophic damage progression with increasing load. From the experiments, it was shown that the failure mode was a strong function of W/D. The experimental measurements indicated that the load carrying capacity of a pin loaded hole could be changed by altering the specimen geometry and stacking sequence. Therefore, the geometry of the pin connected joints was designed to undertake bearing failure only. In addition, it was found that glass/epoxy with [0/90/±30]s yielded the highest bearing strengths. High bearing strengths were reached when E/D and W/D ratios were ≥4 for both [0/90/+30/−30]s and [0/90/+60/−60]s stacking sequences.