E Vanswijgenhoven

Acoustic emission during tensile testing of SiC-fibre-reinforced BMAS glass-ceramic composites

One of the problems preventing the industrial application of ceramic-matrix composites is the lack of an efficient method to detect and discriminate among types of damage occurring during service. With this in mind, the mechanical response, damage development and acoustic emission activity during monotonic tensile testing of a BMAS glass-ceramic matrix reinforced with SiC fibres have been investigated. Damage initiation and propagation were easily detected and evaluated using the acoustic emission technique. Comparing the acoustic emission activity characteristics in simple lay-ups with those of more complex lay-ups allowed discrimination between matrix microcracking, matrix macrocracking accompanied by interface debonding, and delamination cracking. In this way, the paper contributes to the development of the acoustic emission technique for in situ monitoring of damage development in ceramic-matrix composites.

Transverse cracking and Poisson's ratio reduction in cross-ply carbon fibre-reinforced polymers

Gradual damage development in carbon fibre-reinforced polymers (CFRP) and its effect on the mechanical properties have been important subjects of investigation for many years. Most authors have studied transverse matrix cracking in cross-ply lay-ups and used the longitudinal Youngs modulus as an indicator of the extent of damage development. Reductions of typically only a few percent have been found at saturation crack spacing. Some authors have studied the effect of matrix cracking on Poissons ratio. The results show large reductions, but few data are available on the evolution of Poissons ratio throughout the process of gradual matrix cracking and on the influence of the 0°/90° ply thickness ratio. Moreover, none of the available models seems to accurately predict the quantitative evolution of Poissons ratio. In this work the degradation of the longitudinal and the transverse properties of a number of cross-ply CFRP laminates due to transverse matrix cracking under longitudinal tension was studied. The longitudinal Youngs modulus appeared to be less sensitive to damage development, in contrast to Poissons ratio which exhibited significant reductions in all lay-ups. A micromechanical model, based on the shear lag theory, was developed to predict the evolution of Poissons ratio and the effect of the 0°/90° ply thickness ratio. The correlation between experiment and theory was very satisfactory.

The relationship between longitudinal stress and transverse strain during tensile testing of unidirectional fibre toughened ceramic matrix composites

Abstract A comprehensive, micromechanical model, relating the longitudinal stress and transverse strain during tensile testing of unidirectional fibre toughened ceramic matrix composites, has been developed. The model uses different unit-cells to describe the composite and considers all relevant damage as it develops throughout a tensile test. Specifically, the proposed model takes into account the Poisson contraction of fibre and matrix, the redistribution of mechanical stress and the relief of thermal stress due to the development of damage, and the build-up of compressive radial stresses at the interface due to the radial mismatch between fibre and matrix after interface debonding and sliding. Consequently, the modelled transverse strain response depends on a wide variety of structural and mechanical parameters. The followed approach has been assessed by comparing the simulated and experimentally observed response of a unidirectional SiC CAS composite. Theory and experiment are in excellent agreement for an experimentally determined set of constituent properties, but a parametric study shows the important effect of some of these, such as the radial interfacial mismatch, which are difficult to determine experimentally.

Comparative study of the surface roughness of Nicalon and Tyranno silicon carbide fibres

The fibre roughness plays an important role in the mechanical response of fibre-reinforced ceramic matrix composites. With this in mind, the surface roughness of six different silicon carbide fibre grades was investigated using atomic force microscopy. Values for both the roughness amplitude and wavelength are presented and discussed.

The transverse strain response of cross-plied fibre-reinforced ceramic-matrix composites

Abstract A micromechanical model for the transverse strain response of cross-plied fibre-reinforced ceramic-matrix composites has been developed. The model uses different unit-cells to describe the composite material and takes into account all damage developing during tensile testing. The followed approach has been assessed by comparing the simulated and experimentally observed response of three different SiC f /CAS composites. Theory and experiment are in excellent agreement and a parametric study shows the limited impact of the simplifying assumptions made.

Fatigue Behaviour of SiC Fibre Toughened Barium Magnesium Aluminosilicate Glass-Ceramic Laminates

Ceramic fibre glass-ceramic matrix composites combine a potential as high temperature material with a relatively easy processing route [1, 2]. The carbon rich interface layer in as-produced SiC fibre aluminosilicate matrices ensures both controlled damage development and failure through interface debonding, fibre fracture and fibre pull-out [1, 2, 3].

A model for the transverse strain response of unidirectional ceramic matrix composites during tensile testing

A comprehensive micromechanical model relating the longitudinal stress and transverse strain of unidirectional fibre toughened ceramic matrix composites (CMCs) is presented. The model uses different cylindrical unit-cells to describe the composite throughout a tensile test and considers all relevant damage mechanisms. The proposed model takes into account the Poisson contraction of fibre and matrix, the relief of thermal residual stresses upon damage development, and the build-up of compressive radial stresses at the interface due to mismatch between fibre and matrix after debonding and sliding. Thus the modelled transverse strain response depends on a wide range of microstructural and micromechanical parameters. The approach is checked by comparing the experimentally observed and simulated response of a unidirectional SiC/CAS composite of which all constituent properties were determined experimentally. The agreement between experiment and theory is excellent.