The microscopic fracture behavior of carbon-fiber/epoxy composite laminates was investigated by in-situ tensile tests using a specimen-with artificial notches. The effects of strain rate on microscopic crack growth behavior were discussed with comparing the present test results with the previous test results obtained by mode I interlaminar fracture toughness test. The tendency was similar between the present test results and the previous test results; the microscopic crack pass was near the interlarface between carbon-fiber and matrix resin at lower rate of strain, whereas it was mainly in the matrix resin at higher rate of strain. The subcritical growth of microscopic crack and the growing process of damaged zone were observed in front of the main crack tip.

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The scatter of the strength of notched UD composites is discussed. Tensile tests have been carried out on four kinds of fiber angle and six kinds of notch shape, three specimens are prepared for each notch shape. The notches are observed with plastic replica and photographs to consider the effect of the machined damage. Moreover, each elastic field of specimens is analysed with Body Force Method to discuss the fracture process.

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Considering the space environment, it is important to study the effects of thermal cycling on the mechanical properties in CFRP laminates. In the present study, thermal cycling induced matrix cracking in CFRP laminates is investigated experimentally. Two kinds of carbon/epoxy systems, T800H/3631 and T300/2500, are used. Laminate configurations are (0/90)_s and (90/0)_s for both material systems. The specimens are thermally cycled between -196℃ and 100℃. Thermal cycling tests are performed up to 1000 cycles. In T800H/3631 (0/90)_s, (90/0)_s and T300/2500 (0/90)_s, (90/0)_s laminates, matrix cracking is observed in 90°ply by thermal cycling. Tensile tests after thermal cycling are also performed. The effect of thermal cycling on matrix cracking under tension is evaluated by the change in the critical energy release rate and the critical stress.

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It is expected to apply the smart structure to the aircraft by embedding optical fibers in the composite materials. The influence of the existence of optical fiber, which have usually larger diameter than reinforced fibers, on the strength properties has been studied for 3-D heat resistant composites under compression loading. In this study, we investigated the effect of the optical fiber direction and the reinforced fiber direction surrounding the optical fiber on the compression strength including the comparison with 2-D textile composites in which the out-of-plane yarn was eliminated.

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A short-term stress relaxation behavior of a unidirectional carbon fiber-rein forced composite (T800H/Epoxy) has been examined under off-axis loading condition at elevated temperature. Stress relaxation tests were performed at 100℃ on plain coupon specimens with various off-axis angles: θ=0, 10, 30, 45, and 90°. For each of these off-axis angles, the stress relaxation tests were carried out at three different strain levels. The stress relaxation phenomenon was clearly observed for all off-axis angles. Just after the total strain was kept constant, the stress rapidly relaxed with time in a short period. The stress relaxation rate tended to immediately vanish. Then, the off-axis stress relaxation behavior was simulated using a phenomenological viscoplastic constitutive model based on the overstress. This model favorably reproduced the off-axis relaxation behavior of this material system at 100℃.

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Oxidation tests under loading were carried out to clarify the effect of loading on the oxidation mechanism. And tensile tests were carried out under various conditions to understand the degradation of stiffness and strength. To predict the stiffness degradation, the analytical model based on both Shear-Lag Model and Diffusion Model was proposed. Analytical prediction was compared to experimental results to estimate the effectiveness of proposed model.

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When the deformation behavior of both fiber and matrix is ductile in composite materials, ductile fibers exhibit uniform elongation or multiple necking depending on their volume fraction in matrix. In the present study, deformation behavior of Nb-Ti filaments in Nb-Ti/Cu superconducting composite wire was investigated using finite element analysis. Large displacement elastic-plastic analysis was carried out for monofilament composites of volume fraction of filament (V_f) of 0.14 to 1.0. Slight reduction of diameter was given to the filament to initiate necking. Multiple necking was observed for composites whose V_f was less than 0.3. The interval of multiple necking was also investigated by placing several initiation points on the filament in the analysis. The results showed that the interval of the multiple necking was about three. These results agreed well with the experimental observation for Nb-Ti/Cu and W/Cu composites.

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The number of aged person is increasing having a disease for bone, tooth and innards. So the necessity of these substitute materials must be increasing. Alumina ceramics are used for substitute materials as bonehead of a thighbone joint, because of its high strength and bio-inert properties. For many biomaterials a fracture occurs due to both corrosion and fatigue. In this study, effects of similar body fluid (SBF) environment on mechanical properties and microstructure of Al_2O_3 were investigated. Microstructural changes of Al_2O_3 ceramics due to SBF corrosion degradation were also examined by scanning electron microscope after long time immersion into SBF at 37℃. Degradation of bending strength and fracture toughness (K_C) were evaluated.

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In this work, a recently proposed strain gradient and rate-dependent crystallographic formulation is used to investigate length scale effects on the macroscopic behaviour of two-phase FCC single crystal and polycrystalline alloys. The multi-scale constitutive approach incorporates strain gradient phenomena at both the microscopic (i.e. reinforcing phase) and mesoscopic (i.e. grain) scales and relies on strain gradient concepts to account for the additional strengthening mechanism caused by presence of interfacial and geometrically necessary dislocations (GNDs). The total slip resistance of the homogenised single crystal at the mesoscale is assumed to be due to a mixed population of mobile and sessile forest obstacles arising from both statistically stored (SSDs) and GNDs, and their evolutionary behaviour is formulated in terms of material parameters which depend explicitly on the characteristics of the reinforcing phase (e.g. precipitates) at the micrdscale. A parametric study is conducted on a three-dimensional specimen of a poly crystalline superalloy to quantify the effects of precipitate and grain sizes on its deformation behaviour.

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Formulation and some results for the analysis of particulate composite materials undergoing stress induced dilatational phase transformation are presented. Analyses are carried out by using a boundary element method (BEM), which is developed based on integral equations and analytical solutions for ellipsoidal inclusions such as Eshelby's tensor. The homogenization method is then adopted for meso-scale unit cell analyses. Present approach does not require any interior discretizations and is quite efficient even when there are a number of particles in the unit cell. Furthermore, by using present approach, the detailed meso-stress field in particulate composite material can be analyzed and visualized. Some numerical results are presented.

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The damaged interface affects the strain field in two ways. First, it makes the strain field inside inclusions no longer uniform as that of inclusions with perfectly bonded interface. Secondly, it contributes to the average strain in composite by an integration of relative displacement between matrix and inclusion over their interface. In present paper, the first effet is considered by using an averaged Eshelby's S-tensor. The second effect is expressed in terms of the corresponding eigenstrain, by introducing a damage-relevant tensor D. A rigorous constitutive model of self-consistency was schemed. Both the tangential and normal discontinuities at the interface are independently modeled. It is found that the imperfect interface conditions of debonding and/or sliding give detrimental effects on the overall properties of composites. Thus, the establishment of the most appropriate model describing properly the meso-local phenomena.

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In order to describe the dislocation cell structure formation process in the light of collective dislocation behavior, the reactions of dislocations such as multiplication, mobilization, immobilization and dynamic recovery are indispensable. In this study, we employ Reaction-Diffusion equation for time evolution equation of dislocation densities. This paper aims to reveal the cell formation process in terms of microscopic variable (dislocation density distribution) and macroscopic variable (effective stress). We also perform stability analysis on simultaneous Reaction-Diffusion equations and critical wave length which characterizes the dislocation cell structure is obtained as a function of effective stress.

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Two dimensional polycrystal models which include about 2400 crystal grains of regular or irregular shape are developed and their elastic deformation under uniaxial tensile load are analyzed by finite element method. The results show that elastic stress distribution form long range structures with stripe pattern. Fourier analysis of the distribution of the normal stress in the loading direction shows that the wave length in the direction parallel to the loading direction rages as large as the lateral dimension of the whole specimen, while the wave length in the direction perpendicular to the loading direction has its spectrum peak near the average grain diameter. Effect of the irregularity in the shape of crystal grains on the stress distribution is prominent in the spectrum power at wave length shorter than the average grain diameter.

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The present study has attempted to establish a new method of non-destructive inspection method for material degradation by using martensitic transformation. Martensitic phase transformation occurs in an austenitic stainless steel SUS304 and thus resultant magnetization is induced due to severe deformation or to high applied stress. Peaks of vertical magnetic flux density B_z were measured in the plates of SUS304 stainless steel with fatigue cracks by flux gate sensor. The distance 2l between the minimum and the maximum peaks of the B_z distribution shows a linear correlation with real fatigue crack length 2a. The values of minimum and maximum peaks also have a linear relationship with the applied stress intensity factor range ΔK, a kind of a fatigue damage parameter imposed. These results imply that the measurement of the vertical magnetic flux density above a fatigue crack can estimate real crack length 2a and the amount of damage the specimens has suffered.

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In a partially stabilized zirconia (PSZ) containing tetragonal Z_rO_2 particles, a crack may be closed due to dilatational transformation strain of the particles induced in both a process zone and its wake surrounding the crack by enhanced stress at the vicinity of the tip of crack. In this study, micromechanical analysis on the toughness of such a PSZ is performed by modeling a crack surrounded by a process zone and its wake as a mixed double inclusion of the first kind which is an ellipsoidal inhomogeneous inclusion surrounded by an annular inclusion. Stress Intensity Factor of the crack in the PSZ, K^I_T, is derived and then its decrease ΔK due to stress-induced transformation of particles is formulated as a function of the transformation strain, the thickness of zone wake, and the volume fraction of particles. Numerical results of ΔK is good agreement with the experimental ones obtained by Swain et.al.

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A theory of bars with thermal effects is studied using a concept of the Cosserat continuum. Since beam theory is regarded as a one-dimensional Cosserat theory, the present theory can be called a thermal beam theory. In this report, discussions are confined to the effects of heat conductivity on thermal beams. Constitutive equations for heat flux and its moment are obtained expressing thermal mesoscopic structures. It is shown that the value of a thermal sectional modulus corresponding to the second moment of inertia in the beam theory can be derived numerically by finite element analyses.

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Space apparatus subject heavy thermal loads in operating conditions in space. So, to design these space apparatus with sufficient reliability, the accurate thermal analysis of these apparatus in vacuum condition is indispensable. In this paper we have derived a new method for estimating thermal conductance at the contact interface between metal surfaces. The method takes into account surface roughness and thermal conductance of surface materials such as oxidized layers. And it uses Hertz's formula to estimate the real contact area. The estimated thermal contact conductance is confirmed to agree with the experimentally measured conductance by using bar-type specimens. It is shown that the new method can estimate the thermal conductance at the contact interface between different metals more accurately than traditional methods such as [1,2].

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