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© 2018 Elsevier Ltd The strain-rate sensitivity and stress relaxation of self-reinforced polypropylene (SRPP) and hybrid carbon fibre/SRPP composites were analysed under bending loads. For this purpose, three point bending static tests were performed at room temperature and displacement rates of 200, 20, 2, 0.2 and 0.02 mm/min. Tests of stress relaxation were also carried out, where a fixed strain was applied and the stress was recorded during the loading time. The study concluded that, for all materials, the bending stress and strain at the maximum bending stress were sensitive to the strain rate. The bending modulus, however, was found to be insensitive to the strain rate for hybrid composites, and sensitive (with a linear increase) for SRPP composites. From the stress relaxation tests and for both materials, the stress decreased with time and this decrease was more significant for higher strains. The results were fitted following the Kohlrausch-Williams-Watts model, evidencing good accuracy of the model for the stress relaxation time. ispartof: COMPOSITE STRUCTURES vol:209 pages:802-810 status: published

The paper investigates the split-disk test methodology for measuring mechanical properties of a filament wound composite. Hoop strain is measured by three-dimensional (3D) Digital Image Correlation (DIC) on the outer surface of ring specimens . A finite element model (FEM) is employed to investigate the strain distribution along the circumference and the thickness of the ring and the effect of friction between the ring and the disk. The FE simulation shows that the effect of friction between the ring and the disk is significant, but precise quantification is difficult because of irregularities of the ring/disk contact. Both DIC strain map and FE simulation show a low strain area at the level of the split, caused by local bending of the ring. In conclusion of this work, the authors recommend: (1) to measure the strain, which is used in the stiffness calculation in the area with a 10° offset from the disk split, where the influence of the local bending becomes insignificant, (2) to use 3D DIC for precise hoop strain measurement, (2) to use concurrent FEM to estimate errors related to the difference between the surface strains and the average strains over the entire ring thickness.

In this paper, the bending fatigue behaviour and damage development during fatigue of polyurethane (PUR)-epoxy 3D woven sandwich composites is investigated. 3D sandwich fabrics are produced by a velvet weaving technique. It allows relatively easy production of delamination-resistant sandwich panels, compared to more traditional sandwich structures with honeycomb or foam cores. In this paper, the 3D sandwich fabrics made of glass fibre are impregnated with epoxy resin while the empty core can be foamed up with PUR to improve shear resistance of the panels. Core properties and static bending strength of the panels were evaluated. Three-point bending (3PB) fatigue tests were performed on four different materials (two unfoamed epoxy panels and two PUR foamed epoxy panels) with varying static properties. After fatigue testing, the Wohler curves for each panel were determined. The relation between the observed damage development, the property degradation during bending fatigue and the static properties of the panels was investigated.