Strain-rate sensitivity and stress relaxation of hybrid self-reinforced polypropylene composites under bending loads

© 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.status: publishe

Fatigue behaviour of Kevlar composites with nanoclay-filled epoxy resin

The fatigue behaviour of Kevlar fibre-reinforced composites is a subject not often studied and requires a better understanding. The objective of this study is to characterize the fatigue strength of a Kevlar/epoxy laminate composite as well as the benefits obtained using a nanoclay-filled epoxy matrix. The filler used was an organoclay Cloisite 30B after applying an appropriate silane treatment and other proprietary chemicals to improve the dispersion and interface adhesion. Twelve ply laminates, all in the same direction, of woven bidirectional Kevlar 292, were prepared by hand lay-up, using an SR 1500 epoxy resin. The composite sheets were produced by a vacuum moulding process. The addition of nanoclays reduced static strength and increased the stiffness in both tension and bend loading. Filled composites exhibited tensile fatigue strengths 12% higher than unfilled matrices, but in three-point bending the fatigue strength of filled composites was lower. </jats:p

Experimental study of temperature effect on the mechanical properties of GFRP and FML interface

Interface between laminates has always been the weakest part of bonded materials which is prone to delamination. This is even more prevalent in bonding of two different materials. The research aims to evaluate delamination of dissimilar materials under a range of temperature. This is a part of the experimental study to investigate the potential of fiber metal laminates (FML) to be used in high temperature environment. The mechanical response of interface of hybrid laminate was characterized at temperatures ranging from 30 to 110 °C. Double cantilevered beam (DCB) and end notched flexure (ENF) tests were conducted on glass fiber laminated aluminum specimens to obtain Mode-I and Mode-II delamination properties with use of data reduction. Mode-I fracture toughness (GIC) is significantly degraded by 59.45% at 70 °C and up to 83.65% at 110 °C. Mode-II fracture toughness (GIIC) only slightly degrades by 10.91% at 70 °C but drops rapidly by 82.84% at 110 °C

Impact Behaviour and Damage Analysis of Laminated Composites Made of Glass Fibres/Nano-Reinforced Thermoplastic Matrix

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