Papers by Tadaharu Adachi
This paper describes an alternative estimating method for the current drop weight impact test use... more This paper describes an alternative estimating method for the current drop weight impact test used to determine the mechanical properties of Fibre-Reinforced Plastics (FRP). The method proposed here measures the strain variations in time of the drop weight and uses the one-dimensional wave equation to convert the measurements into load and displacement variations in time. Then, a dynamic load and displacement relationship is obtained by eliminating time from the load and displacement variations in time, thus determining the mechanical properties of GFRP and CFRP plates subjected to drop weight impact with considerable accuracy.
Transactions of the Japan Society of Mechanical Engineers Series A, 1999
Transactions of the Japan Society of Mechanical Engineers Series A, 1999
Transactions of the Japan Society of Mechanical Engineers Series A, 1995
Transactions of the Japan Society of Mechanical Engineers Series A, 1989
International Journal of Modern Physics B, 2008
The in-plane impact behaviors of honeycomb structures with some cells randomly filled with stiff ... more The in-plane impact behaviors of honeycomb structures with some cells randomly filled with stiff inclusions were analyzed by using the finite element method (FEM). The effect of the random arrangement of inclusions on the deformation processes of the honeycomb structures was considered. During these deformation processes, the growth of shear bands was disturbed by the inclusions and the cell region surrounded by inclusions did not deform. The average stress increased and densification strain decreased with increasing volume fraction of inclusions. A honeycomb with volume fraction of inclusions of 0.5 could not be deformed. Below 0.5, the average stress steeply increased and densification strain approached zero. Some models for less than a volume fraction of inclusions of 0.25 had higher absorbed energy than the model with no inclusions and others had lower energy. Above 0.25, the absorbed energy decreased and linearly reached zero at a volume fraction of inclusions of 0.5.
Applied Mechanics and Materials, 2014
The dynamic behavior of circular straight and stepped tubes made of aluminum alloy under high-vel... more The dynamic behavior of circular straight and stepped tubes made of aluminum alloy under high-velocity impacts was investigated by performing finite element analyses (FEA) and an experiment. The FEA and experiment on the straight tubes suggested that while an increase in the impact velocity enhanced the absorbed energy through compressive deformation just after impact, the peak load at the fixed end was not affected by the velocity. A stepped tube that was thicker near the impacted end was designed on the basis of the results for the straight tubes, and its dynamic behavior was investigated through FEA. The stepped tube absorbed a large amount of impact energy through compressive deformation at the thicker portion during the higher-velocity impact, without increasing the maximum fixed-end load from that of the straight tube.
Journal of the Society of Materials Science, Japan, 2004
Transactions of the Japan Society of Mechanical Engineers Series A, 1990
Key Engineering Materials, 2006
The development characteristics of impact-induced damage in carbon-fiber-reinforcedplastics (CFRP... more The development characteristics of impact-induced damage in carbon-fiber-reinforcedplastics (CFRP) laminates were experimentally studied using a drop-weight impact tester. Five types of CFRP laminates were used to investigate the effect of stacking sequences and thicknesses. The efficiency of absorbed energy to impact energy was different for CFRP laminates with different stacking sequences or thicknesses. The DA/AE ratio of delamination area (DA) to absorbed energy (AE) was almost the same for CFRP laminates with the same stacking sequence regardless of the thickness. We found that the DA/AE ratio could be used as a parameter to characterize the impact damage resistance in CFRP laminates with different stacking sequences.
Key Engineering Materials, 2007
The effect of adding a high molecular weight epoxy monomer (epikote 1001) to a low molecular weig... more The effect of adding a high molecular weight epoxy monomer (epikote 1001) to a low molecular weight one (epikote 828) on fracture toughness properties was investigated according to the crosslinking degree and density heterogeneity. To characterize the crosslinking degree and density heterogeneity, the glass transition temperature, Tg, and fragility, m, were deduced from thermo-viscoelastic properties. The characterization of Tg and m revealed that blends can be divided into two groups: one group with (φ < 10 wt%) and another one with (φ > 10 wt%), where φ is the weight ratio of epikote 1001 to epikote 828. The first group had the same average crosslinking degree (the same Tg) but different density heterogeneities (m decreased). The other group had a lower crosslinking degree (Tg decreased) and even more density heterogeneity (m decreased). The fracture toughness results showed that KIC of blends of the first group was approximately constant because the increase in density hete...
JSME International Journal Series A, 1999
Journal of the European Ceramic Society, 2009
ABSTRACT In the present study, the effect of mechanical tensile stress on oxygen mobility in 8 mo... more ABSTRACT In the present study, the effect of mechanical tensile stress on oxygen mobility in 8 mol% yttria-stabilized zirconia (8YSZ) was investigated. The experimental results show that the ionic conductivity increases with stress and saturates. The maximum improvement in the conductivity was about 18% observed at 973 K. The simulation results show that the diffusion coefficient increases with stress and decreases with excessive stress. The maximum improvement was about 40% observed at 973 K. The improvement was larger at lower temperatures in both the experiment and the simulation. The strain caused by the stress is considered to have caused the gradient in the potential energies of the neighbouring oxygen sites, especially around the yttrium ions, which probably facilitated the migration of the oxygen ions.
Journal of Applied Polymer Science, 2005
ABSTRACT
Journal of Applied Polymer Science, 2002
The relationship between the postcuring conditions and fracture toughness on three silica particu... more The relationship between the postcuring conditions and fracture toughness on three silica particulate‐filled epoxy composites was investigated. The glass transition temperature, Tg, and the fragility parameter, m, derived from the thermo‐viscoelasticity, were used to characterize the composites, which were postcured under various conditions. The glass transition temperature and fragility both depended on both of the curing conditions and the volume fraction of silica particles. The glass transition temperature increased with the postcuring time and temperature, while the fragility generally decreased as the volume fraction increased. There was no direct correlation between the glass transition temperature and fragility. The fracture toughness depended on both the glass transition temperature and fragility. The composites with a high glass transition temperature and low fragility had high fracture toughness. These results indicate that the glass transition temperature and fragility a...
Journal of Applied Polymer Science, 2002
The relationship between the postcuring conditions and the fracture toughness of a bisphenol A‐ty... more The relationship between the postcuring conditions and the fracture toughness of a bisphenol A‐type epoxy resin cured with acid anhydride was investigated. The glass transition temperature and fragility parameter, derived from the thermo‐viscoelasticity, were used to characterize the epoxy resin postcured under various conditions. Relationship between these two parameters and the fracture toughness was then investigated, based on the fractography results of a microscopic roughness examination of a fractured surface. The values of the glass transition temperature and fragility greatly depended on the postcuring conditions. The glass transition temperature was approximately 400 K when the crosslinking reaction was saturated. The fragility was independent of the saturation of the reaction and varied between 50 and 180. The results of the fracture test and fractography examination showed that there was no direct correlation between the glass transition temperature, the fracture toughnes...
Journal of Applied Polymer Science, 2008
The viscoelasticity of epoxy resin/silica hybrid materials manufactured by the sol-gel process wi... more The viscoelasticity of epoxy resin/silica hybrid materials manufactured by the sol-gel process with an acid anhydride curing agent was investigated in terms of morphology. Transmission microscopy observations demonstrated that all the prepared hybrid samples had a two-phased structure consisting of an epoxy phase and a silica phase. The formed silica had either nanosized particles or coarse domains, depending on the catalyst for the sol-gel process. Raman spectroscopy analysis showed that the formed silica had features typical of sol-gel derived silica glass and that the ring-opening reactions of the epoxy groups developed in the hybrid samples and in the neat epoxy samples. In dynamic mechanical thermal analysis, there were two transition temperatures due to epoxy chain mobility and epoxy network relaxation, through which the moduli changed by nearly 3 orders of magnitude. The hybridization disturbed epoxy network formation but also reinforced the epoxy network with the formed silica, which was characterized by the activation energy of the network relaxation; therefore, the modulus of the rubbery state was correlated to the activation energy.
Japanese Journal of Applied Physics, 1995
ABSTRACT
International Journal of Impact Engineering, 2005
International Journal of Impact Engineering, 2005
ABSTRACT The effect of transverse impact on the buckling behavior of a column under axial impact ... more ABSTRACT The effect of transverse impact on the buckling behavior of a column under axial impact loading was numerically investigated using finite element analysis. A column under axial impact was subjected to transverse impact to instantaneously reduce its structural stiffness. Absorption of the axial impact energy increased due to post-buckling deformation being enlarged by transverse impact, though the axial impact load decreased. The numerical results of the finite element analysis qualitatively proved the results of a previous experiment. A transverse impact applied almost simultaneously with an axial impact produced the highest energy absorption. The impulse of transverse impact seems to be the governing parameter when a transverse impact is applied just after an axial one. It is confirmed that a transverse impact could increase the axial energy absorption of a column without losing any structural stiffness or static strength.
Uploads
Papers by Tadaharu Adachi