In this paper, tensile strength and behavior of low-intensity UV light irradiated poly-p-phenylene benzobisoxazole (PBO) fiber were investigated in monofilament tests. The tensile tests of a monofilament were carried out at a gauge length of 12.5 mm and deformation rate of 0.5 mm/min. Irradiation time was set to 0h, 1h, 10h, 100h and 1,000h, while radiance was arranged to become 2, 4 and 8 W/m². It was found that the tensile strength distribution of UV irradiated PBO fibers can be approximated to a normal distribution. Regardless of the degree of radiance, the tensile strength tends to decrease gradually with an increase in irradiation time. As radiance intensifies, however, corresponding curved lines move to lower positions, an indication of the dependency of the tensile strength on radiance. The relationship between radiation dosage and tensile strength converges on this one curved line irrespective of the degree of radiance. Therefore radiation dosage should be a valid parameter to measure the degradation of the strength of the PBO fibers exposed to UV light irradiation. In addition, it is found by SEM observation that there are distinct differences between the fracture surface image of UV non-irradiated fiber and that of irradiated fiber. Regardless of UV-irradiation, PBO fibers have split in the direction in which it is set. But the split part in UV-irradiated fiber is shorter than in the UV-non-irradiated fiber because UV-irradiated fiber has split vertically in portions.

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An experimental study of the pressure dependence of the interfacial stiffnesses of contacting solid-solid surfaces and their nonlinear ultrasonic responses is presented. To this purpose, the contact-pressure dependence of the reflection coefficients of longitudinal and transverse waves were measured at normal incidence to three types of contacting interfaces of aluminum blocks with different surface conditions, namely, polished surfaces, roughened surfaces and fractured surfaces. The results show remarkable influence of the surface condition on the pressure-dependent variation of the normal and tangential stiffnesses as well as their ratio. Based on the obtained stiffness-pressure relations, the second harmonic generation behavior for normal-incidence longitudinal wave is examined theoretically according to the foregoing theoretical results by a nonlinear interface model, and it is shown that smoother surfaces exhibit harmonic generation more significantly than rougher ones. Relevant experimental results are demonstrated for polished surfaces and discussed in comparison to the theoretical predictions.

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The objective of this research is to investigate the crack behavior in five harness satin woven carbon fiber reinforced polymer (CFRP) composite laminates with temperature-dependent material properties under tension at cryogenic temperatures. A situation of generalized plane strain is considered, and cracks are assumed to have occurred in the transverse fiber bundles. Also, both cases where the tips of the cracks are located in the fiber bundles or at the interfaces between two fiber bundles are treated, and a finite element technique utilizing special singular elements is used to obtain the stress intensity factors at the tips of the transverse cracks in two-layer woven CFRP laminates. The numerical results are then discussed in detail.

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This paper presents a study on welding penetration control of fixed pipe in Tungsten Inert Gas (TIG) welding using fuzzy inference system. The welding penetration control is essential to the production quality welds with a specified geometry. For pipe welding using constant arc current and welding speed, the bead width becomes wider as the circumferential welding of small diameter pipes progresses. Having welded pipe in fixed position, obviously, the excessive arc current yields burn through of metals; in contrary, insufficient arc current produces imperfect welding. In order to avoid these errors and to obtain the uniform weld bead over the entire circumference of the pipe, the welding conditions should be controlled as the welding proceeds. This research studies the intelligent welding process of aluminum alloy pipe 6063S-T5 in fixed position using the AC welding machine. The monitoring system used a charge-coupled device (CCD) camera to monitor backside image of molten pool. The captured image was processed to recognize the edge of molten pool by image processing algorithm. Simulation of welding control using fuzzy inference system was constructed to simulate the welding control process. The simulation result shows that fuzzy controller was suitable for controlling the welding speed and appropriate to be implemented into the welding system. A series of experiments was conducted to evaluate the performance of the fuzzy controller. The experimental results show the effectiveness of the control system that is confirmed by sound welds.

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In this report, adhesive strength criteria are investigated experimentally and analytically. Both the cylindrical butt joint specimen subjected to various combined tensile and torsion loadings and the round bar butt joint specimen with various angles of interface edge are used for the experiments. Temperature dependency is also investigated. Principal stress, principal strain and von Mises stress distributions at the adhesive interface of these specimens under the critical load are obtained by the elastic-plastic finite element analysis using MARC. As a result, the mean value of von Mises stress distribution at the singularity area is found to be the most dominant factor of adhesive strength. This fact is confirmed also for the strength evaluation of the double lap joint subjected to tension through the additional examination and the corresponding three dimensional elastic-plastic FEM analysis. The critical von Mises stress can be obtained directly by a usual experimental method using a cylindrical butt joint specimen under torsion without any numerical analysis.

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In this study, the impact deformation of thin-walled circular tubes filled with aluminum foam in lateral compression was investigated using a special load cell for long time measurement and a high-speed video camera to check the displacement of specimens. It was found that the absorbed energy up to the deformation of 60% of the specimen diameter obtained from impact tests is greater than that obtained in static tests, because of strain rate dependency of aluminum foam. The loaddisplacement curve of circular tubes with aluminum foam just inserted was consistent with the sum of the curves individually obtained. In both dynamic and static tests, however, the load of the tube with the foam inserted and glued by adhesive resin became larger than the sum of the individual loads, because of the interaction between circular tubes and aluminum foam cores.

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In order to clarify the hydrogen effect on the fatigue strength at 10⁷ cycles in a plain specimen of type 316L austenitic stainless steel, rotating bending fatigue tests in laboratory air and plane bending fatigue tests in 1.0 MPa dry hydrogen gas and in air at 313 K were carried out. The main results obtained are as follows. The observed fatigue behavior showed that the fatigue strength at 10⁷ cycles in both environments is determined by the non-propagation of a fatigue crack of the order of the grain size. Also, the strength at 10⁷ cycles in hydrogen gas is slightly higher than that in air. In the region of high-cycle fatigue, the fatigue life in hydrogen gas is longer than that in air, which is mainly caused by the longer crack initiation life in hydrogen gas. The crack propagation life in hydrogen gas is shorter than that in air but has only a small ratio to the fatigue life in this region.

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