Paper number 328


W. Schäff, F. Heinrich, C. Körner and R. F. Singer

Department of Materials Science (LS WTM), University of Erlangen-Nürnberg
Martensstr. 5, D-91058 Erlangen, Germany

Summary Magnesium with local reinforcement of carbon long fibers is extremely attractive for weight saving in structural applications. However, due to the dissimilar material properties between the reinforced and the unreinforced region, temperature changes induce high internal stresses during fabrication and service. Locally reinforced ring specimens with graded and ungraded composition were produced and subsequently thermally cycled. Besides the measurement of the crack density a shear test was used to document the damage accumulation as a function of the number of temperature cycles. The experiments were supplemented by FE calculations of the thermal stresses. It is shown that with partially reinforced ungraded rings thermal cycling results very early in severe macroscopic damage near the interface between reinforced and unreinforced areas. The cracks are initiated by radial stresses during heating. A graded composition offers the capability to improve the thermal fatigue behaviour significantly as the material strength in the critical regions near the interface is improved and the stresses are somewhat lowered.
Keywords graded structure, local reinforcement, carbon magnesium composite, thermal cycling, shear testing, interfacial cracks, interfacial strength, thermal stresses.

Theme : Metal Matrix Composites ; Thermo-mechanical behaviour

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