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Mechanical Spectroscopy of Thermal Stress Relaxation in Aluminium Alloys Reinforced with Short Alumina Fibres
Summary
The mechanical behavior of aluminum composites reinforced with short alumina fibers was studied under thermal cycling using mechanical spectroscopy, revealing a loss peak during cooling that reflects thermal stress relaxation at matrix-fiber interfaces. The peak height increases with fiber volume fraction, providing a sensitive measure of interfacial stress state in metal matrix composites.
The mechanical behaviour under low temperature thermal cycling of aluminium-based composites reinforced with short Al2O3 SAFFIL fibres has been investigated by mechanical spectroscopy (mechanical loss and elastic shear modulus measurements). A mechanical loss maximum has been observed during cooling which originates in the relaxation of thermal stresses at the interfaces due to the differential thermal expansion between matrix and reinforcement. The maximum height increases with the volumetric fibre content. In addition, if the matrix strength is increased by the appropriated choice of alloy and thermal treatment, the maximum diminishes and shifts to lower temperatures. No damage accumulation at the interfaces has been detected during long period thermal cycling in the range 100 to 500 K. A description of the damping behaviour is made in terms of the development of microplastic zones which surround the fibres.