Hannah Harel

The influence of thermal history on the mechanical properties of poly(ether ether ketone) matrix composite materials

Abstract The purpose of this study is to provide insight into the microstructural factors that affect the flexural fatigue performance of carbon-fibre-reinforced poly(ether ehter ketone) (PEEK) composites. Specifically, the effect of the degree of crystallinity on the mechanical properties is examined at two crystallinity levels of the as-received composites (35%) and of quenched composites (10%). Higher static flexural strength and modulus as well as longer fatigue life are observed for the higher crystallinity level. By varying the loading angle with respect to the fibre direction it is shown that the crystallinity effect is not matrix dependent alone. Rather, a strong effect is evident in the fibre direction, which is attributed to the influence of the transcrystalline layer formed on the fibre surface in the high-crystallinity material. As a result, the longitudinal fatigue life at 1·7GPa of the 35% crystallinity material is three orders of magnitude higher than that of the 10% crystallinity composite.

Fatigue behaviour of flat filament-wound polyethylene composites

Abstract Flat polyethylene/polyethylene composite strips were produced by pressing filament-wound preforms. The fibre continuity in the filament wound strips resulted in higher failure strains, better fracture toughness and longer fatigue lives compared with the equivalent angleply composites. As expected for angle-ply composites, the mechanical properties depended on the high shear deformation of the matrix which in turn depended on the winding angle.

Thermal treatment effects on the crystallinity and the mechanical behaviour of carbon fibre-poly(ether ether ketone) composites

Casali Institute of Applied Chemistry, Graduate School of Applied Science, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel Our recent study on the influence of thermal history on the mechanical properties of poly(ether ether ketone) matrix composites [1] presented the effect of the degree of crystallinity on the static and dynamic mechanical properties of carbon-fibre-reinforced PEEK composites. It showed that the flexural modulus and strength, as well as the fatigue life, were significantly higher for the maximum 35% crystallinity in isothermally crystallized samples, compared with the 10% minimum, obtained by a quenching procedure. This effect, being essentially a matrix property, was observed regardless of the loading angle with respect to the fibre direction, and was particularly strong in the fibre-dominated longi- tudinal direction. This posed an apparent paradox that could be reconciled by recognizing the presence and the role of the fibre/matrix transcrystalline layer, expected to relieve residual thermal stresses in the longitudinal direction. A fractographic investigation of the fracture sur- faces

The rate-dependence of flexural shear fatigue and uniaxial compression of carbon- and aramid-fibre composites and hybrids

Abstract The purpose of this work is to provide important insight into the factors that determine the unique flexural-fatigue performance of aramid-fibre/carbon-fibre (ACA) sandwich hybrid composites and its dependence on strain rate. The understanding of the response to strain rate of the single components under compression and shear conditions is the focus of this paper. Axial-compression strength, static-shear, and shear-fatigue results as a function of strain rate are analysed independently and compared in an attempt to explain the flexural behaviour of the ACA hybrid. The possibilities that the rate-dependence of the flexural-fatigue behaviour of the ACA hybrid result from contributions of those components are eliminated. The likely source of this behaviour may be related to the strain-rate gradient for the ACA beam under flexural loading, which follows the plastic yielding in compression of the aramid skin.

Stress Intensity Factor Measurements in Composite Sandwich Structures

In composite materials, the stress intensity factor is significantly affected by the reinforcement geometry. This geometry affects the degree of anisotropy of the material. It is maintained that in order to obtain valid stress intensity factor values, the compliance calibration procedure presented should be carried out for every new reinforcement geometry.