Rate of Strength Decrease of Fiber-Reinforced Ceramic-Matrix Composites during Fatigue

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65181/1/j.1151-2916.2000.tb01412.x.pd

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

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. (C) 1997 Acta Metallurgica Inc.status: publishe

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. (C) 1998 Elsevier Science S.A. All rights reserved.status: publishe

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

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 lakes 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 SiCf/CAS composites. Theory and experiment are in excellent agreement and a parametric study shows the limited impact of the simplifying assumptions made. (C) 1999 Elsevier Science Ltd. All rights reserved.status: publishe

The influence of loading frequency on the high-temperature fatigue behavior of a Nicalon-fabric-reinforced polymer-derived ceramic-matrix composite

The frequency dependence of fatigue life of a Nicalon-fabric-reinforced ceramic-matrix composite was investigated at 1200°C in air. It was shown that the number of cycles to failure increased as loading frequency was increased. However, the time to failure decreased as loading frequency was increased. Additional work in progress is directed at identifying the relative importance of high-temperature fatigue mechanisms such as creep, creep-strain-recovery, mechanical cycle-by-cycle damage, and embrittlement.status: publishe

Transverse Strain Response of Hi-Nicalon Fibre Reinforced Silicon Nitride Matrix Composites.

In this paper, the Etr response of a series of Hi-Nicalon (SiC) fibre reinforced silicon nitride matrix composites is studied. At first, the processing route of the material is briefly described. Axial and transverse tensile mechanical behaviour, along with matrix crack density measurements , are then shown. Characterisation of the interface properties and evaluation of thermal residual stresses, obtained by modelling of axial hysterisis loops are finally presented. This is followed by a short description of a micromechanical model for the Etr response UD- CMCs. To conclude, experimental and theoretical transverse strain evolution are compared and discussed.JRC.(IAM)-Institute For Advanced Material

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. (C) 1997 Elsevier Science Limited.status: publishe

Transverse strain response of Hi-Nicalon fibre reinforced silicon nitride matrix composites

status: publishe