Local compression fatigue properties of peripherally clamped HSP have been studied in consideration of usage condition as a floor panel. In this study, the effect of cell wall thickness on local compression fatigue of HSP was clarified. For that purpose, a series of fatigue test of HSP was carried out by changing the cell wall thickness, the thickness of face sheet contacted the indenter and the maximum load value. When the cell wall thickness was thin, the fracture pattern of face sheet contacted the indenter changed from the tensile type to shearing type with the increase in the thickness of face sheet contacted the indenter. In the transitional region between these two fracture types, the only dent without crack was observed on the face sheet contacted the indenter. On the other hand, when the cell wall thickness was thick, the shearing fracture around dent was observed instead of the dent type in the transitional region.This was because of the increase of buckling strength of cell wall which constrained the formation of dent. This situation resulted in the increase in the shearing stress around the dent.

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Lithium-ion batteries (LIBs) are expected to be main power sources of automobiles. Nevertheless, LIBs easily lead to serious incidents because LIBs have high energy density. For application to automobiles, the reliability of LIBs should be guaranteed against various external loads. Especially, static loads and cyclic loads are constantly applied on LIBs because of vibration and thermal stress induced in automobiles, and fatigue damage occurs in electrodes of the LIBs. In this respect, it is important to evaluate mechanical strength and mechanical fatigue property of electrodes, such as tensile strength and S-N curves. This study has proposed a simple evaluation method of the mechanical strength and the fatigue property of electrodes for LIBs by using mechanical models of the electrodes. The actual alignment of particles of active material is random, and mechanical models based on the actual alignment are too complex to derive the main factor of mechanics of the electrodes. The proposed models approximate the alignment of the particles as the body-centered cubic (bcc) and the face-centered cubic (fcc) which are the well-known crystal lattices. In order to verify the proposed method, static tensile tests and bending fatigue tests of negative electrodes for LIBs have been conducted. From the test results, the tensile strength of the negative electrodes estimated by the proposed models agree with the experimental values, and the difference between the bcc model and the fcc model is smaller than the variation of the experimental values. The estimation value of the stress that initiates a crack on the negative electrodes by 1 cycle agrees with the tensile strength. The number of cycles linearly increases in the log scale with the decrease of the stress amplitude, and the stress amplitude at the 10 6-10 7 cycles agrees with the half of the tensile strength.

Lithium-ion battery is a rechargeable battery with high energy density, and it is fabricated by laminating of electrodes with separator. In fabrication process, it is important for evaluation of contact state of laminated electrodes to estimate current density between the electrodes. This paper describes a novel technique to estimate the current density by using magnetic sensor. This technique applies an inverse analysis on magnetic flux density induced around the lithium-ion battery impressed with inspection current. In the inverse analysis, boundary element method for thin plate is applied to derive the observation equation relating the current density to the magnetic flux density. Then truncated singular value decomposition is applied on the observation equation. In order to demonstrate the validity of the proposed technique, numerical simulations have been performed by using a model consisted with the electrodes and separator. In the numerical simulations, the correct distribution of the current density was given in advance, and the direct analysis was applied to obtain the simulation data of the magnetic flux density. Then the inverse analysis was applied on the simulation data. The results show that the correct distribution of the current density can be obtained by the proposed technique. In addition, though the estimation accuracy is lower when fewer number of decimals of the magnetic flux density data is utilized, the tendency of the correct distribution can be obtained due to the truncation of the rank of the singular value matrix.