Sufficient evaluation of the changes in mechanical properties, such as elastic, plastic, and failure properties, due to neutron irradiation in service is required to precisely predict fuel performance. This paper presents the results of the uniaxial tensile tests performed for recrystallized (850 K, 2.5 h) Zircaloy-2 claddings irradiated in commercial BWRs to fluences of 5 × 1023 to 4 × 1025 n/m2 (E > 1 MeV). The material constants of irradiated Zircaloy-2 were obtained precisely, using a high temperature elongation detector in a hot-cell and computer analyses of digital stress-strain data. The tensile tests were carried out at 298 to 673 K at strain rates of 0.05 to 5%/min, using tubular specimens cut to 135 mm lengths from the claddings. From these tests, Young's modulus, strain hardening exponent, strain rate sensitivity, and fracture behavior were obtained and evaluated. Young's modulus of specimens irradiated to 1024 n/m2 is nearly equal to that of unirradiated ones, but irradiation to 1025 n/m2 shows values 7% higher than for unirradiated ones. The irradiation-induced increments in yield stress are rapid below 1 × 1024 n/m2, then slow down above this fluence becoming proportional to (φt)0.1 for fluences of 1 × 1024 to 4 × 1025 n/m2, where φt is fluence. The strain hardening exponent before irradiation is 0.15 and a constant which is independent of strain levels, but after irradiation it decreases depending on strain increase. The strain rate sensitivity at the 0.2% plastic strain decreases from 0.037 to 0.021 by irradiation. There are two types of fracture morphologies after irradiation: necking and spiral types. In the latter, a shear band propagates along only one direction. Both are accompanied by localized deformation bands caused by dislocation channelling. The spiral type is predominant at about 573 K, in high irradiation and at high strain rate. The fracture surfaces of the unirradiated and irradiated materials are all ductile, while the number of small dimples, whose nuclei appear to be irradiation defects, increases with fluence. The ratio of the number for unirradiated, irradiation to 1 × 1024 n/m2, and irradiation to 1 × 1025 n/m2 is 1:2.7:2.9.

This research deals with the mechanical strengthening and crack closure effect of shape-memory alloy (SMA) fiber reinforced polycarbonate (PC) composite. Three kinds of TiNi alloy with different atomic ratio and heat treatment were used which have various phase transformation points. The shape memory effect is caused by electric resistance heating method in the range from the low temperature of -40°C to 80°C to generate the reverse phase transformation and recovery force in the composite. The influence factors concerning pre-strain, fibers number, stress concentration, heating conditions which are related to control mechanical properties and the crack closure effect, are investigated quantitatively. The partial thermal stresses generated by electric resistance heating and its effect on the crack closure are evaluated by the photo elasticity method. By measuring of the displacement change of the test piece, the shape recovery force is evaluated in SMA embedded fibers of the composite test piece.

Destructive tests are generally applied to evaluate the fixed strength of spot-welding nuggets of zinc-plated steel (which is a widely used primary structural material for automobiles). These destructive tests, however, are expensive and time-consuming. This paper proposes a nondestructive method for evaluating the fixed strength of the welded joints using surface electrical resistance. A direct current nugget-tester and probes have been developed by the authors for this purpose. The proposed nondestructive method uses the relative decrease in surface electrical resistance, a. The proposed method also considers the effect of the corona bond. The nugget diameter is estimated by two factors: R Quota , which is calculated from variation of resistance, and a constant that represents the area of the corona bond. Since the maximum tensile strength is correlated with the nugget diameter, it can be inferred from the estimated nugget diameter. When appropriate measuring conditions for the surface electrical resistance are chosen, the proposed method can effectively evaluate the fixed strength of the spot-welded joints even if the steel sheet is zinc-plated.

The shape-memory effect of shape-memory alloy (SMA) and the character of the super elasticity are common and effective in today's usage. This paper advances these characteristics by discussing the research of an intelligent composite which functions in a wide-ranging ambient conditions TiNi type SMA fiber was used in the experiment and the embedded test piece was used in a polymer matrix. The influence factor of the actuator function by the shape-memory effect was evaluated in real-time by measuring the length change of the test piece during electric resistance heating. Using composite materials with the electric heating method resulted in a quantitative understanding of the primary factor influencing the shape recovery force. It has been understood that the shape recovery force is greatly influenced by the ambient temperature to which the composite material is applied, and this paper describes detailed information for the best composite materials and their condition characteristic mechanical control by the electric heating.

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