The toughness data obtained from Charpy impact tests are presented by a temperature-energy relationship. Data fitting for quantitative comparing of transition temperature with upper shelf energy, ductile-brittle transition, in other words, the representation with general mathematical model equation for energy variation according to the temperature is necessary. In this study, the Charpy impact tests to two kinds of the representative steel were carried out as a work for the material property standardization technique development. The fitting procedure of the scattering in data according to materials and temperature in the transition region was described. The data fitting procedure was established through the variances treatment in the transition region using the tangent hyperbolic function.
In order to investigate the behavior of fatigue crack growth of SiC-particulate- reinforced Al-Si alloy composites, fatigue tests using single edge notched tension(SENT) specimens were performed. Composite materials were manufactured by using both permanent die casting and extrusion processes with different volume fractions of 10% and 20%. SiCp-reinforced Al-Si composites showed the increased levels of threshold stress intensity factor range, ΔKth, for the increased volume fractions of SiC particles, which implies the increased fatigue crack growth resistance at the threshold or low ΔK levels, compared to the unreinforced Al-Si alloy. In the Paris region, however, the composites showed the increased rate of crack growth resulting in the unfavorable effects on the fatigue crack growth resistance. Critical stress intensity factor range at unstable crack growth leading to final fracture decreased as the volume fraction of SiC particle increased, because of the reduced fracture toughness of the composites. Extruded materials showed higher threshold and critical values than the cast materials.
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