Destructive and Ultrasonic Investigations of Damage Development in Metallic Materials
Damage development due to creep under uniaxial tension at elevated temperatures is assessed using destructive and non-destructive methods in steels, commonly used in power plants or chemical industry, and in aluminium alloy used in aircrafts for responsible elements. The results obtained using two different destructive methods for assessments of damage development are critically discussed. In the first method the specimens of steel after different amounts of creep prestraining were stretched up to failure and variations of the selected tension parameters were taken into account for damage identification. In the second one, a damage degree was evaluated by studying variations of an initial yield locus position in the stress space and by determination of the yield loci dimensions. The ultrasonic investigations were selected as the non-destructive method for damage development evaluation.
Effect of cyclic loading on the yield surface evolution of 18G2A low-alloy steel
Experimental analysis is presented of the plastic properties of 18G2A steel (notation according to Polish Standards) in the as-received state, and of the same material subjected to cyclic predeformation in different directions of the two-dimensional stress space (σxx, τxy). The analysis was made by studying the position in stress space and by determination of typical dimensions of the yield surfaces. The initial yield surface has been determined using a number of specimens which were loaded up to the plastic range along different stress directions, and this surface was used as the starting point for comparative studies of yield surfaces of the cyclic prestrained material. Cyclic predeformations were induced by loading at ambient temperature. After predeformation, yield surfaces were determined by the technique of sequential probes of the single specimen. The anisotropic yield condition due to Szczepinski was shown to model the experimental results well. Prior cyclic loading induced the softening effect observed during subsequent monotonic loading of the steel in the plastic strain range considered.
ROOM- AND HIGH-TEMPERATURE MAGNETIC PROPERTIES OF Sm(CobalFexCu0.088Zr0.025)7.5 (x=0.30) SINTERED MAGNETS
The effect of Fe content on room- and high-temperature magnetic properties of Sm(CobalFexCu0.088Zr0.025)7.5 (x=0-0.30) sintered magnets, prepared by the conventional powder metallurgy method, has been systematically studied. With increasing Fe content, the remanences BT and maximum energy products (BH)max at room temperature gradually increase and reach optimal values of 1.055 T with x=0.27 for BT, and 205 kJ/m3 with x=0.21 for (BH)max, respectively, and then drop sharply with further Fe increase. An excessive addition of Fe (x≥0.24) results in rapid deterioration of permanent magnetic properties due to the formation of a considerable amount of FeCo soft magnetic phase. It was found that the effect of Fe content on high temperature stability is huge. The lower the Fe content, the smaller the temperature coefficient of coercivity. When x=0.07, a temperature coefficient of coercivity of -0.14%/K (293-723 K) can be achieved, as compared with -0.23%/K for x=0.21. BT of 0.725 T, bHc of 517 kA/m, iHc of 764 kA/m, and (BH)max of 95 kJ/m3 at 723 K were obtained, and the B-H demagnetization curve remains a straight line.