The aim of the project is to provide a non destructive technique to characterize damage in aluminium matrix composites, which may negatively influence their fitness for use.
The aim of the project is to provide a nondestructive technique to detect and characterize damage in aluminium matrix particle reinforced composites, which may negatively influence their fitness for use.
Fatigue tests have been carried out and the most promising techniques were selected, being: determination of the acoustoelastic constants, the thermoelastic constants, phase velocity, backscattering techniques and high precision absolute velocity measurements. The selected nondestructive testing (NDT) techniques were improved for application to the specific materials and have been applied in various stages of the fatigue life. Modelling indicated the detectable damage levels.
None of the tests revealed conclusive results. This indicates that the assumed damage models of gradual increasing voids to cracks are inappropriate and that early warning damage detection is extremely difficult. This may be regarded as a serious drawback of this material, which may seriously hamper future applications.
Mechanical and thermo-mechanical behaviour depends strongly on the microstructural situation (e.g. volume fraction, defects introduced by fabrication, size distribution, etc.), the damage of the materials and the residual stress state. In addition to this, damage accumulation during service life restrict the lifetime. At present there is some empirical evidence of correlation between the results of ultrasonic tests, the microstructure and the progress of fatigue damage in metal matrix composites. Further progress requires understanding of the physical processes underlaying this correlation. This project aims at providing such an analysis, leading to a multiparameter approach for the ultrasonic characterization of metal matrix composites.