The influence of dispersions of particles on the recrystallization behavior has been examined in industrially processed specimens of a Cu-Fe-P alloy (CDA194). The specimens are produced through the steps of hot rolling, cold rolling, aging and final cold rolling. The γ→α martensitic transformation of small coherent γ-Fe precipitate particles which form on decreasing temperature during hot rolling is induced by subsequent cold rolling. Aging following the cold rolling produces fine γ-Fe particles, which are transformed to α-Fe by final cold rolling. The nucleation of recrystallization occurs predominantly at coarse Fe3P particles, observed after the hot rolling, larger than about 1μm in diameter. A denser dispersion of smaller α-Fe particles shows a larger retarding effect on grain-boundary migration. A specimen with smaller α-Fe and smaller Fe3P particles has a higher heat resistance and a higher strength.
Three kinds of epoxy resins were decomposed by nitric acid in order to establish a recycling method of epoxy resin. Specimens were immersed in 80°C nitric acid (4M and 6M) and decomposed products were recovered. The molecular weight distributions and chemical structures of the products were analyzed by using Size Eliminated Chromatograph and FT-IR, respectively. For the case of bisphenol A type epoxy resin cured with amine, a derivative of monomer was formed due to the decomposition at C-N bonds. The derivative of monomer was dissolved in nitric acid and was extracted with ethyl acetate. 2, 4, 6-trinitrophenol, which was produced by the breakage of main chain and subsequent nitration, was also recovered. Nitric acid attacked the C-N bonds in bisphenol F type epoxy resin cured with amine more selectively because of the existence of methylene group in the main chain. The yield of recovered decomposed product which contained derivative of the monomer of bisphenol F type epoxy resin was more than the case of bisphenol A. With regard to tetraglycidyl diamino diphenyl methane (TGDDM) resin cured with diamino diphenyl methane (DDM), the chemical structure of cured resin is symmetric and repetitive. Hence, decomposed product of TGDDM/DDM was recovered as a nearly single compound of 2, 4, 6-trinitroaniline.
An analytical model for FRP crossply laminates subjected to a bending load is developed in the framework of continuum damage mechanics. Constitutive equations for a cracked ply are firstly formulated under an assumption of equivalence between a cracked ply and a work-softening material. After dividing a laminated beam into small beam elements, the derived constitutive equations for a cracked ply are introduced into the lamination theory to predict the damage evolution in the laminated beam with a cracked ply. Each beam element is analyzed independently to compute the stress state and curvature of the element, and they are reconnected with each other to predict the deflection of the overall laminate beam. Two kinds of crossply laminate beams having different cracked ply thickness were tested in bending, and corresponding theoretical predictions were made. The prediction for crack distribution as well as load-displacement relations were in good agreement with the experimental results for each laminate.
Static tensile test and in-situ observation of unidirectional Si-Ti-C-O/BMAS (barium magnesium aluminosilicate glass) composite materials were carried out at room temperature in order to clarify the fracture behavior in mesoscopic scale. In-situ observation showed the fracture behavior as follows: First breakage of matrix initiated at the place where fiber-spacing was wide at the stress level of about 200MPa. Then, the number of matrix cracking increased with increase in strain. As a result, the slope of the stress-strain curve decreased from the initial one. In spite of cracking of matrix, the interfacial debonding was suppressed by the compressive residual stress of the matrix. Breakage of fibers occurred when the stress of composite reached about 90% of its fracture strength. Once it occurred, large scale debonding was caused due to the tensile residual stress of fiber. Finally, overall fracture of the composite occurred, accompanied by a large number of fiber breakage. A simulation of the fracture process was performed using the modified shear lag analysis combined with the Mote Carlo method. The characteristics of the fracture process observed experimentally could be simulated fairly well by this method.
A series of strength tests on FW (filament winding) CFRP tubes was carried out to clarify the effects of fiber orientation (FW) angle and test temperature. The experimental results revealed that the static strength was lower than that theoretically predicted by the simple laminate theory based on the strength data for unidirectional coupon specimens. As the test temperature increased, non-linearity in the stress-strain relationship became remarkable. Although the modulus obtained by using thin specimens is the same as that obtained by using thick specimens, the strength of thick specimens was higher than that of thin specimens. Thicker specimens are preferable to utilize their mechanical properties under torsinal moment as much as possible although there exists an optimized dimension for a given angle and compositions of the specimen. Fatigue tests were also conducted at room temperature and 140°C using thicker specimens. In the case of low temperature, modulus decay with respect to loading cycles was divided into three regions: initial region where the modulus decreases steeply soon after the test started, middle region where the modulus is almost constant, final region where the modulus again decreases abruptly followed by the final failure of the specimen. On the other hand, in the case of high temperature, there exists no middle region and the modulus continuously decreases with respect to loading cycle until the final region comes.
SnO2 microcapsules containing Cu were synthesized by an interfacial reaction method using W/O type emulsion with dispersing phases including Cu spherical particles. The microcapsules with different SnO2/Cu ratios were prepared and used as electrical conductive components of semiconductive glass composites. The effect of the SnO2/Cu ratio on the electrical properties of the glass composite was investigated by comparing with glass composites fabricated with Cu and SnO2 powders. The SnO2 microcapsule with average particle size of 2.73μm was obtained. The wall of the microcapsule had about 0.65μm thickness and consisted of about 15 particle layers of fine SnO2 particles of 0.05μm. The electrical properties of the glass composites with the SnO2 microcapsules had small dependence on the SnO2/Cu ratio. The glass composite with relatively small temperature dependence of electrical resistance was obtained because a good compensating effect between SnO2 and Cu on the electrical properties of the glass composites would appear by the use of the microcapsules. On the other hand, the glass composites using SnO2 and Cu powders had large compositional dependence of the electrical properties, and showed metallic properties at about 25vol% Cu.
In order to clarify the shear instability condition of local field, which induces a dislocation nucleation, 10 times of molecular dynamics simulations in a tension of nickel nano-wire (cross section: 30a×30a) were carried out. The results obtained are summarized as follows. (1) The partial dislocation nucleated from the edge of wire at εzz=0.093-0.096 (2) Dislocation nucleation site was different in each simulation due to the statistical fluctuation. (3) The strain concentration was observed in a 1/4 sphere of 3.0nm radius from the nucleation site before the dislocation appeared. (4) Detail observation revealed that the dislocation nucleated when the strain distribution in the region exceeded a criterion (critical curve). (5) The local strain concentration disappeared by the fluctuation when the strain distribution was lower than the critical curve. (6) The strain distribution on the critical curve brought about the dislocation nucleation when the rate of number of unstable lattices was higher than 0.1s-1.
In the X-ray stress measurement of single crystal, crystal oscillation operation is required in order to obtain perfect diffraction profile. Accurate diffraction profiles can be measured by using the χψ-oscillation method proposed in this study. Using this oscillation method, the elasticity applied stress measurement of the silicon single crystal used as a material of semiconductor device was carried out. Lattice strain was obtained from peak shift of diffraction profile. Stress was calculated by using lattice strain of three different diffraction planes. As a result, the measured stress agree well with the applied stress evaluated from a strain gage. Therefore, the possibility of elastically applied stress measurement of the single crystal by the χψ-oscillation method was confirmed. Also, the relationship between setting error of the test piece and stress error was theoretically examined. It was confirmed that the effect of misalignment on X-ray stress measurement of single crystal materials is much larger than in the case of polycrystalline materials. In this study, a microscope was used to set the specimen.
As the welding of polymer materials has a process to phase transformation, the simulation of welding should be considered the thermomechanical coupling effect on stress and strain. In addition, the welding has the contact phenomenon between two bodies incorporated with thermal deformation. So it is also necessary to consider the contact between two bodies in any shape and the change of thermal boundary conditions. In this paper, a numerical procedure with phase transformation for welding of polymer is proposed and the computer program has been developed. As an example, the processes of heating and cooling for polyethylene joint with shape recovery have been simulated. In case of the coupler without shape recovery, it is also revealed that the end of coupler does not contact with the pipe, since the bending deformation is taken place by non-uniform distribution of temperature to thick direction. But the whole part of coupler can be joined by shape recovery effect. The change of stress with time on the contact surface is calculated in cooling process and the residual stress can be evaluated. As the result, it is recognized that the effect of shape recovery on fusion joint is evaluated by the developed computer program.
The lifetime prediction of ceramics has been discussed on the basis of the relationship between the crack velocity, V, and the stress intensity factor KI. In the present study, crack growth tests by double torsion (DT) method were carried out under static and cyclic loadings in order to examine the effect of both water environment and stress cycling on the KI-V characteristics for alumina and zirconia. In both materials in static and cyclic loading crack velocity in water was higher than that in air, and that tendency was more remarkable in zirconia. In addition, the decrease in crack propagation parameter n and the increase in crack velocity due to cyclic stress were clearly observed in both materials in air and water environment. The KI-V characteristics determined by double torsion method were used to predict time-to-failure under static and cyclic loading of alumina and zirconia ceramics. The predictions agreed qualitatively with the experimental results.
When metallic materials are plastically deformed, the physical effects which are listed as work hardening, the development of anisotropy and the Bauschinger effect occur. In order to measure these effects off-axis torsion test by the combined loading is developed. In this test the principal shear stress direction φ can be changed from 0° to 90° while the ratio of maximum and minimum principal stresses is kept-1. Experiments were carried out on tubular specimens of fully annealed and torsional-prestrained mild steels, and the yield loci and strain behavior were examined at three offset levels. The yield stress of the prestrained steel decreases with increasing angle φ. The difference between the directions of the principal shear stress and principal shear strain increment rises to a maximum value and then decreases. The occurrence of this maximum difference corresponds to the angle where the slope of the tangent to the yield locus is steepest. These behaviors strongly depend on the offset value used in defining the yield stress, and severe anisotropy appears when the small offset strain value is used. It is shown that the proposed off-axis torsion test is a very useful method for analyzing the anisotropic hardening behavior of materials.
Recently, damage to the adhesive layer has been investigated by in-situ observation under several load conditions. However, these observation have been limited to the surface of the adhesive layer. If an adhesively bonded butt joint with a very thin adhesive layer could be tested, damage to the interior of the adhesive layer could be observed under transmitted light, which would facilitate clarification of the fracture mechanism of adhesively bonded joints. In this study, to observe the damage interior to the adhesive layer, adhesively bonded butt joint specimens were made using 0.3mm-thick steel plates with plasticizer and rubber modified epoxy adhesives. Then, cyclic tensile fatigue tests were conducted using these joints, where damage to the adhesive layer was observed by a microscopic videocamera under transmitted light. The main results were as follows: In the case of a butt joint with plasticizer-modified adhesive, an initial crack appeared at the end of the adhesive/adherend interface. On the other hand, in the case of a butt joint with rubber-modified adhesive, the damage zone appeared in the middle of the adhesive layer. These observations were discussed from the viewpoint of stress and strain distributions of the adhesive layer.
The fatigue crack propagation behavior and the fracture surface appearance under several load conditions in polyvinyl chloride were investigated. The crack closure behavior was also examined. The fatigue crack propagation rate, da/dN, under constant amplitude loading increased with increasing stress ratio in the relationship of da/dN versus the stress intensity factor range, ΔK. This effect of stress ratio on da/dN was closely related to the crack closure behavior when the stress ratio was not so high. Discontinuous growth bands (D.G.B.) on the fracture surface seemed to be difficult to be formed when the stress ratio was very high. The width of D.G.B. was found to be dominated by the effective stress intensity factor range, ΔKeff. The crack extension during loading a single peak overload was very large and so it could be clearly identified on the fracture surface. This region of the crack extension on the fracture surface revealed granular markings containing many voids, which was similar to that found in D.G.B.. The amount of this crack extension was about equal to the size of the plastic zone at the crack tip formed by the overload under a plane strain condition.
In order to discuss the delamination energy obtained by the edge-indentation method on a viewpoint of fracture mechanics, the crack initiation and propagation behavior were examined by the microscopic observation along interface under the indenter as well as the three dimensional finite-element stress analysis of the zone. The results show that the interfacial crack starts at a little distant position from the indentation center, and the triangular-shaped delamination of coating extends stably for a certain distance with increasing indentation load. When an apex of the triangular-shaped coating with partially delaminated interfacial crack is pushed by the side of indenter, the critical value of interfacial strain-energy release rate or the interfacial fracture toughness, 2γ12, is expressed by the following equation: 2γ12=1/8π2k2B1Ee1cos2θ/tan2α(P0/x)2 where B1 is coating thickness, Ee1 is elastic constant of coating, θ is a half of delamination angle, α is apex angle of indenter, P0 is indentation load at delamination, x is indentation distance from edge, and k is a constant. The interfacial fracture toughness, 2γ12, corresponds to the delamination energy, Ed, which has been defined experimentally from indentation load vs. displacement curve in the previous paper.