Papers by Author: Kikuo Kishimoto

Abstract: This present study has been re-established to investigate failure mode and resistance characteristics of the PC/ABS blends and their ABS constituents under impact for a range of rubber contents. This present study has still been experimentally performed under an instrumented-drop weight impact test (DWIT) at a room temperature. It has been finally revealed that with a particular size of rubber particle, content of rubber significantly influenced impact failure modes and impact resistances of the PC/ABS blends and their ABS constituents as well. The test results showed that impact strength of the blends was improved about 23.22% and 155.33% due to increase in content of rubber up to 15 wt% and 20 wt%, respectively. There was also found that an increase in impact toughness of the blends for 57.48% and 239.23% was due to increase in content of rubber up to 15 wt% and 20 wt%, respectively. Whilst, impact strength of the ABS was improved about 392.98% and 190.12% due to increase in content of rubber up to 15 wt% and 20 wt%, respectively. An increase in impact toughness of the ABS for 308.20% and 172.56% was due to increase in content of rubber up to 15 wt% and 20 wt%, respectively.

Abstract: This study presents an experimental study on failure modes and resistances of polycarbonate (PC)/Acrylonitrile Butadiene Styrene (ABS) blends and their ABS constituents under a drop weight impact test (DWIT). Failure modes and impact resistances such as impact strength and impact toughness of such blends are generally influenced by molecular weight of the PC, rubber content and size of rubber particle in ABS system. A preliminary study on ABS materials using a DWIT showed that size of rubber particle not only determined their failure modes but also influencing their resistance characteristics. However, in a previous study performed using the similar DWIT on PC/ABS blends with a 10 wt% rubber content, it was revealed that size of rubber particle did not significantly influence their resistances. Their failure modes were even macroscopically very difficult to be distinguished. This study, hence, is aimed to further explore role of the size of rubber particle on failure mode and impact resistance characteristics of the PC/ABS blends and their ABS constituents with a higher rubber content. The impact test results have revealed that with a 20 wt% rubber content, size of rubber particle only influenced the resistances of the PC/ABS blends. It did not significantly contribute to affect failure mode of the PC/ABS blends. Whilst, it significantly influenced failure modes and resistances of the ABS. The DWIT results also re-confirmed that blending a brittle ABS into PC led to produce a tougher PC/ABS blend.

Abstract: In this paper, the flexural wave propagation and localization in randomly disordered binary periodic beams with the axial load are studied. Based on the continuity conditions, the transfer matrix between the constitutive unit cells is derived. The expression of the localization length in the disordered periodic system is presented. Numerical calculations are performed to illustrate the localization characteristics of the flexural wave. The effects of the axial load on the band gap structures and the localization properties are discussed. From the results, we can observe that the properties of the pass band and stop band for the perfect system can be tuned by the axial load. Moreover, the localization properties of the flexural wave will be strengthened by the higher disordered degree.

Abstract: It was investigated that the influences of the peeling behavior of adhesive tapes in peeling tests on IC chip pick-up performance. Needles peel off an IC chip with an adhesive film from the base material in the pick-up process, by sticking out the backside of the base material. In the case that the peeling forces of the adhesive tape decrease as the peeling speeds increase in peeling tests, only two kinds of behaviors were observed in pick-up test; the peeling propagated little and the IC chip was not peeled off under critical needle displacement while the pick-up was completed instantaneously over critical needle displacement. In the case that the peeling forces of the adhesive tape increase as the peeling speeds increase, the pick-up time decreased as the needle displacement increased. As a result, it can be concluded that the needle displacement where the peeling propagates instantaneously is critical for succeeded pick-up if the peeling forces of the adhesive tape decrease as the peeling speeds increase. If the peeling forces of the adhesive tape increase as the peeling speeds increase, the information of peeling speeds at each needle displacement are needed to estimate how long it takes to pick-up a chip.

Abstract: The propagation behavior of Love waves in a functionally graded material layered half-space with initial stress is taken into account. The Wentzel-Kramers-Brillouin (WKB) asymptotic technique is adopted for the theoretical derivations. The analytical solutions are obtained for the dispersion relations and the distributions of mechanical displacement and stress along thickness direction in the layered structure. Firstly, these solutions are used to study effects of the initial stress on the dispersion relations and phase velocities, then influences of the initial stress on the distributions of mechanical displacement and shear stresses along thickness direction are discussed in detail. Numerical results obtained indicate that the phase velocity of Love wave increases with the increase of the magnitude of the initial tensile stress, while decreases with the increase of the magnitude of the initial compression stress. The effects on the dispersion relations of the Love wave propagation are negligible as the magnitudes of the initial stress are less than 100MPa. Some other results are shown for distributions of field quantities along thickness direction. The results obtained are not only meaningful for the design of functionally graded structures with high performance but also effective for the evaluation of residual stress distribution in the layered structures.

Abstract: In this paper, the prediction and comparison of the behavior of thin-walled prismatic structures (square tube, top-hat and double-hat sections) in absorbing energy using theoretical and numerical analysis are presented. Equations to predict crushing length and dynamic mean crushing force of top-hat and double-hat sections were applied for material mild steel St37 and the effect of spot weld positions are also figured out. For comparison, an explicit non-linear commercial finite element code LS-DYNA was used to predict the response of the structures subjected to axial crushing. It was found that results of numerical methods and theoretical prediction have good agreement. Assuming that the failure of spot-weld is neglected, mean dynamic crushing force of double-hat section is 90% higher compared to that of square tube.

Abstract: Experimental works using a drop weight impact test method have been performed on a circular sheet specimen to evaluate and to characterize the impact resistance of the sheet-type plastic components designed for automotive wheel covers. Evaluation has been conducted for a set of engineering plastics: polycarbonate (PC), acrylonitrile-butadiene-styrene (ABS) and their blend (PC/ABS). The testing results showed that the PC/ABS blend specimens failed in brittle manner under higher impact speeds with very few of whitening zones. Secondary cracks captured perpendicular to fracture surface were also found in the mid-plane of the scattered PC/ABS blend specimens. Investigation is then focused on this blend and the testing results describe that impact resistance of the specimen made of this alternative material is determined by ABS not by PC. Combination of structures between PC and ABS through the thickness in the core due to their immiscibility was observed by scanning electron microscope (SEM) on the etched PC/ABS specimen. This latter result well correlates the results obtained from the testing. It therefore reveals that immiscibility between PC and ABS in the blend plays an important role in determining the impact resistance of the components. This paper also presents simulative results of the test obtained from a FEA work by introducing a 3D- layered finite element (FE) model of the PC/ABS specimen to take into account effect of a layer in the core on the behavior of the blend.

Abstract: Adhesives are widely used in our life and industrial world. However, it is difficult to characterize their mechanical properties because those strongly depend on environmental and mechanical conditions such as temperature, humidity or strain rate. In this paper, we focus on the strain rate dependence of the interfacial strength and investigate the interfacial strength by peel tests under several peel rates. The results show that, in lower rate region (under 1.0 mm/s), the interfacial strength is constant and, in transition region (1.0 to 10 mm/s) the interface strength increased with the peel rate. In middle rate region (10 to 103 mm/s), the interfacial strength is constant again. Over 103 mm/s region, the interfacial strength drops and became lower than those in middle rate cases. From the observation of peeling front by a high speed video camera, the deformation behavior of adhesives changes with the peel rate.􀀁Finite element analysis by using cohesive zone model is also conducted, and influence of the rate dependency of adhesive and base material is discussed.

Abstract: A method to predict impact load caused by drop impact of thin cone-shaped structures is investigated. The Hertzian contact theory and the spherical shell theory are applied for modeling the contact stiffness of the impact tip of the cone. Experiments and finite element simulations are performed for several cones to evaluate the accuracy of impact load prediction. It is shown that appropriate choice of contact stiffness model depending on the curvature and thickness of impact tip of the cone is necessary in order to predict the impact load accurately.

Abstract: The diffraction of Lamb waves by a finite delamination situated on a random plane parallel to the symmetric plane of a laminated plate is taken into account. Two imaginary planes are introduced to solve the problem by adopting the method of mode matching. By taking an appropriate finite number of terms of the infinite expansion series and some selected points on the two imaginary planes through convergence and precision tests, a matrix equation is obtained to evaluate the expansion coefficients numerically. Reflection coefficients versus the normalized length a/h and the relative location h1/h of the delamination are calculated in the low-frequency domain, the relative errors are found to be less than 1%. Results obtained indicate that the theory developed in this paper is meaningful for the detection of both the size and the location of a delamination in a laminated plate by cooperating with experimental techniques for the non-destructive evaluation (NDE) technology.