Papers by Author: Katsuhiko Sasaki

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Authors: Yusuke Tomizawa, Takehito Suzuki, Katsuhiko Sasaki, Ken-Ichi Ohguchi, Daisuke Echizenya
Abstract: Recently, Halt (Highly accelerated limit test) is widely employed for evaluation of reliability of electronic products. Halt condition is quite severe. The tested products are subjected to mechanical impacts, thermal shock, and vibration at same time. However, there has not been a reasonable and accurate evaluation method for Halt yet. To construct an accurate evaluation method of Halt, basic deformation mechanism of parts of the electronic products should be clarified from both experimental and theoretical points of view. In this paper, focusing on solder joints of circuit boards of electronic products, ratchetting deformation, especially, biaxial ratchetting deformation of solder joints is revealed from both experimentally and theoretically. The authors have already conducted biaxial ratchetting test combining axial and torsional cyclic loading using a tubular specimen of Type 304 stainless steel. However, as for solders, it is difficult to make tubular specimen. Since size of the solder joints is micron, a small size joint specimen of copper tube and solder is employed in this paper. First, to confirm the quality of the joint specimen such as boundary between copper and solder, both the tensile and cyclic loading tests are conducted at several temperatures using Sn-3Ag-0.5Cu. The basic characteristic of tensile and fatigue failure is obtained from these tests. After the confirmation of the accuracy of the joint specimen, biaxial ratchetting tests are conducted superposing the tensile load on cyclic torsion. The biaxial ratchetting tests are conducted using a biaxial loading testing machine developed for the joint specimens of solder and copper.
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Authors: Ken-Ichi Ohguchi, Katsuhiko Sasaki
Abstract: The fatigue tests under both loading conditions of the Fast-Slow and the Slow-Fast were conducted to discuss validity of an inelastic strain analysis method which was proposed previously. The development behaviors of plastic and creep strains during the tests were analyzed by employing the stepped ramp wave (SW) loading. Using the analysis results, the difference of the development behaviors of plastic and creep strains between the Fast-Slow condition and the Slow-Fast condition was clarified. Then, the fatigue failure surfaces obtained from the tests were observed by using SEM to clarify the difference of the fracture surface between the Fast-Slow condition and the Slow-Fast condition. By correlating the aspect of fracture surface with the development behavior of plastic and creep strain, the validity of the proposed inelastic strain analysis method was discussed.
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Authors: Atsuko Takita, Katsuhiko Sasaki, Ken-Ichi Ohguchi, Hiroyuki Fujiki
Abstract: In design of the electronic device, FEM analyses considering the creep deformation of solder joints in-situ should be conducted to evaluate the strength reliability. The indentation test is one of effective method to evaluate the creep deformation in microscopic region. However, the result obtained by the indentation test does not coincide with that obtained by the tensile creep test. To solve the problem, the method to determine the suitable area for the indentation test had also been proposed by using the numerical test. To apply the proposed method for the actual indentation test, the homogeneity of specimen should be considered. In this paper, the analyses of the proposed indentation tests were conducted by using the homogeneous and inhomogeneous specimen models of Sn-3.0Ag-0.5Cu. Three types of the deformation behavior were given for the initial phase and the indenter was pushed into in the specimen at the three locations. As a result, it was found that there was not difference in the distribution of the principal stress caused by variation in the indent location. However, the proposed method can successfully determine the reference area except for the case when the deformation behaviors of the constituent phases have a large difference.
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Authors: Atsuko Takita, Katsuhiko Sasaki, Ken-Ichi Ohguchi, H. Fujiki
Abstract: For accurate evaluation of the reliability of electronic package, FEM analyses considering the creep deformation of solder joint in-situ should be conducted. It is well known that the indentation creep test has an advantage to evaluate the creep deformation in microscopic region although there are the problems. Authors already modified the indentation creep test and proposed the method to estimate the steady state creep deformation by the modified test. For lead free solders generally used for the solder joint, the transient creep deformation should be measured by the indentation test in addition to the steady state creep deformation. The transient creep strain occurs in the indentation process. Therefore, it needs to separate the strain into the elastic-plastic strain and the creep strain. In this paper, the method to obtain the stress-strain relation using the indentation test is proposed. New indentation test used the stepped load was proposed to obtained the stress variation during the indenter was pushed and conducted by the numerical test. The suitable measurement point to obtain the relationship between the stress and the strain was identified. The stress variation estimated by proposed area well coincides with the equivalent stress variation of the nodal solution. Therefore, if the method to obtain the strain variation during the indentation process by the indentation in future is developped, it may be possible to estimate the stress-strain curve expressed the uniaxial deformation in the microscopic region.
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Authors: Takuji Kobayashi, Katsuhiko Sasaki, Ken-Ichi Ohguchi, Yoshihiro Narita
Abstract: This paper discusses ratchetting deformation of lead-free solder Sn/3Ag/0.5Cu and lead-containing solder alloy Sn/37Pb with several stress amplitudes and stress ratios of the maximum stress to the minimum stress. First the uniaxial ratchetting testsare conducted with three maximum stresses and five stress ratios. The all tests are conducted using cylindrical bulk specimens of the solder alloys at 313 K. The test results show that there is the difference in the viscoplastic deformation behavior between two solder alloys. The relationship between ratchetting strain and time is estimated by Biley-Norton law to explain that the uniaxial ratchetting deformation is strongly dominated by the viscous deformation. Finally, the ratchetting deformation is simulated by the dislocation based constitutive model proposed by Estrin [1]. The simulations show that there is a possibility to simulate the uniaxial ratchetting by clarifying the dislocation mechanism of the solder alloys.
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Authors: Shinya Honda, Yoshihiro Narita, Katsuhiko Sasaki
Abstract: Structural plate elements in composite structures are typically fabricated by stacking orthotropic layers, each of which is composed of reinforcing fibers and matrix materials. In this work, three optimum design approaches are compared to clarify the advantages and disadvantages for optimizing the buckling performance of laminated composite plates. The first approach is developed recently by the authors, where the buckling load is maximized with respect to the lamination parameters by a gradient method and then the optimum lay-up design is determined by minimizing the errors between the optimum parameters and parameters for all possible discrete lay-ups. The second approach is the layerwise optimization (LO) approach where the fiber orientation angle in each layer is optimized step-by-step by repeating one dimensional search. The third one is a direct application of a simple genetic algorithm (SGA). In numerical examples, three sets of results are compared to discuss on the methodology for buckling optimization.
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Authors: Takuma Kawakami, Yoshihiro Narita, Katsuhiko Sasaki
Abstract: Composite materials are frequently used in automobile and other moving vehicle structures. External and internal sounds sometimes cause unpleasant effects on the users and environment, and reduction of such sound is one of the key engineering problems. This study presents an acoustic radiation analysis from forced vibration of laminated rectangular plates and proposes a design approach to reduce the sound pressure from the plates. In the analysis the sound pressure at an arbitrary point over the plate is derived and is used as an object function in the optimization. A set of the fiber orientation angles is used as the design variable, and is optimized to minimize the sound pressure at the designated point. It is shown in numerical examples that the optimum design for sound pressure reduction is possible by the present approach.
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Authors: Tsuyoshi Mayama, Katsuhiko Sasaki, Yoshihiro Narita
Abstract: In the present study, a new approach is conducted to evaluate dislocation structure induced by cyclic plasticity. First, cyclic plastic loading tests are carried out up to 100 cycles with three different small strain amplitudes on SUS316L stainless steel at room temperature. The test result presents the dependence of the strain amplitude on cyclic hardening and softening behaviors. Specifically, it is found that the cyclic loading test with strain amplitude of 0.25% shows both cyclic hardening and cyclic softening, while the cyclic loading tests with strain amplitudes of 0.75% and 1.0% show no cyclic softening. Secondly, the dislocation structures of the specimens after cyclic loading are observed by using a transmission electron microscope (TEM), and this observation reveals that the dislocation structure after cyclic loading test depends on the strain amplitude. Finally, a quantitative evaluation method of the dislocation structure is also proposed. The TEM images are converted into binary images and the resolution dependence of the generated binary image is used to visualize the characteristics of the dislocation structure. The relationship between strain amplitudes of cyclic plasticity and dislocation structure organization is clarified by the evaluation method. Finally, the heterogeneity of the dislocation structure is discussed.
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