In recent years, reducing the size and weight of consumer products requires the joining of thin sheets of magnesium alloys with both thickness and joining area of less than 1mm, especially for packaging purposes. Conventional welding processes are difficult to joint a thin sheet magnesium alloy because of high heat input, which in turns leads to various problems such as burn through and cracks. In this study, lap fillet welding of thin sheet magnesium alloy AZ31B with a thickness of 0.3 mm has been carried out using a pulsed Nd:YAG laser beam. The influences of gap, laser beam center location and scan speed on joint appearances have been investigated. It was found that defects were significantly reduced when the gap width was less than 35 µm when the laser beam center was located just on the edge of the upper specimen (x=0), and scan speed was varied from 400 to 450 m/min. Wider bond width at average value of 300 µm was achieved when the beam center was at x=0 with a wide range of scan speeds from 250 to 450 mm/min compared with the cases at x=-0.1 and -0.2 mm from edge. Increases in bond width and minimal defects at x=0 improve fracture load by 68% compared with those at x=-0.1 mm.

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Ti-Ni-Cu shape memory alloy was fabricated by mixed elemental powders using a pulse-current pressure sintering equipment. The effect of Cu addition on the phase transformation behavior of the sintered alloys was investigated. An increase in Cu content changed the crystal structure of the alloy. The 5at%Cu and 10at%Cu alloys consists of B2 and B19' phases, but the 15 at%Cu and 20 at%Cu alloys consists of B2, B19' and B19 phases. Especially, the 20 at%Cu alloy clearly showed the two-step transformation. The transformation hysteresis of the 20at%Cu alloy was approximately 10 K. It is similar to that of the wrought alloy. Thus, it was found that the P/M alloy obtained shows sufficient shape recovery property.

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In order to evaluate the interfacial shear strength between fiber bundle and matrix of jute/poly(lactic acid) (PLA), a fiber bundle pull-out test method is proposed. Shear stress distribution was calculated based on the parabolic shear-lag analysis. Fiber bundle pull-out tests were conducted to evaluate the effects of molding condition on the interfacial shear strength. The interfacial shear strength increased with increasing molding temperature up to 185°C. Then gradual decrease in the interfacial shear strength with molding temperature was observed. Similar tendency was also observed in the effect of molding time, whereas the interfacial shear strength decreased with increasing molding pressure. Comparing the result of the tensile tests in the previous study, interfacial shear strength has corelations with tensile strength.

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Glass/epoxy interfacial tensile strength is investigated by the cruciform specimen method. The conventional transverse tensile test for single fiber composite is one of methods for evaluating the interfacial tensile strength, but stress singularity at the specimen edge is a very complicated problem to be solved. A cruciform specimen which has large width only around fiber embedded in transverse direction can potentially prevent the stress singularity problem. The cruciform specimen geometry is first discussed by means of finite element analysis considering experimental conditions. Transverse tensile test is conducted and an interfacial debonding which initiates at the middle of specimen not at edge is observed using the cruciform specimens. The interfacial tensile strength can be obtained by the value of stress concentration factor at interface multiplied by specimen stress. The location which the debonding initiates from is discussed and the validity of the evaluation method in this study is verified when interfacial tensile strength is as high as or lower than interfacial shear strength.

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The effect of the lattice parameter of orthotropic composite materials on the stress fields near crack tips was investigated by means of non-local theory. By use of the Fourier transform, the problem can be solved with the help of a pair of dual integral equations, in which the unknown variable is the displacement along the crack surfaces. To solve the dual integral equations, the displacement along the crack surfaces was directly expanded as a series of Jacobi polynomials. The solution can be obtained by means of the Schmidt method. Different from the classical solutions, that the present soluction exhibits no stress singularity at the crack tips, i.e. the stress field near the crack tips is finite. The effect of the lattice parameter on the stress field near the crack tips was displayed graphically.

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