Atomic disorder causes characteristic mechanical property in a crystallographic material. Since atoms near a junction of interfaces are instable, it is important to comprehend the properties in connection with atomic structure. In this study, the atomic structure and the formation energy of Σ5 tilt grain boundary, (100) surface and their junction in aluminum are analyzed by molecular dynamics simulation based on the Effective Medium Theory(EMT). The results obtained are summarized as follows. (1) The grain boundary energy and the surface energy obtained are 0.476J/m2 and 0.921J/m2, respectively. (2) The structure on the (100) surface near the junction is identified. The formation energy of their junction calculated is 7.76×10-10J/m.
Due to the strain-induced martensitic transformation during plastic deformation, a transformation-induced plasticity (TRIP) phenomenon is generated. With the TRIP phenomenon, the TRIP steel possesses favorable mechanical properties such as high strength, ductility and toughness, and is frequently employed as a structural material. In the past study, it was clarified that the deformation behavior of TRIP steel depends upon the austenitic grain size. In order to obtain the expected mechanical properties of TRIP steel, prediction and control of the material characteristics in the deformation processes is essential. Here, the strain-induced martensitic transformation kinetics and the constitutive equation of TRIP steels which the dependence of the austenitic grain size can be described are proposed. Then, the deformation behavior of a type 304 austenitic stainless steel cylinder is simulated under the different environmental temperature with the various austenitic grain sizes by the finite-element method. The possibility of the improvement of the ductility through control of the austenitic grain size is discussed.
Thin CO2 laser beam system is applied to the line-quenching process of a carbon steel block under traveling heat condition. Since it is very difficult to experimentally evaluate the temperature variation, characteristic property of laser irradiated zone and residual stresses during and after the operation, especially, in heat traveling condition, numerical simulation by finite element simulation code “HEARTS” is implemented based on metallo-thermo-mechanics developed by the authors. The results of the simulated stress distribution seem to represent the practical mode of tensile and compressive stresses after quenching, and characteristics of the martensite transformed region is compared with the observed micrograph in cross section of the block. Stress distribution and volume fraction of martensite of the edge of starting and finishing the beam reveal to differ from the data at the intermediate part. Some numerical simulation is carried out to evaluate the effect of operating condition.
It is known that bending strength (MOR) of a glued laminated beam (glulam) is decreasing when the depth of the glulam is increasing. The first study on this phenomenon in which the Weibull brittle fracture theory was applied to wood was reported by Bohannan (1966), He studied clear wood beams and found that for geometrically similar beams MOR was proportional to the depth of the beam to the power 1/9 (B-model). On the other hand, Komatsu (1997) proposed the equation for predicting MOR of glulams composed arbitrary laminae without using the so-called “size-effect factor” (K-model). We attempted to compare these two models to the experimental results of Japanese larch gulams as reported by us. The types of used glulams were horizontally laminated timbers (H-type) and vertically laminated timbers (V-type). First, we compared two models to the experimental data of H-type. In higher grade, the estimates by K-model had good agreements with the data, but not in lower grade. Then, the estimates by using size-effect factor obtained from strength distribution of finger-jointed and without-joint laminae agreed with the data in lower grade. This differences between higher and lower grades may be caused by the quantity of defects excluding finger-joint. For V-type, the estimates by the “average model” proposed by Hayashi (1992) agreed with the data in both grades.
The static shear strength and fatigue life were measured at room temperature in transversal compression. The geometory of testing specimen was the double lap joint type, laminated by rubber and steel plate having rounded or chambered edge. A significant difference in observed strength was found between the specimens having rounded and chambered edges. The static strength of the rounded (R) or chambered (C) edge specimen increased about 10% with that of the non-curved edge (FL) specimens. The non-dimensional shape parameter (Se) was introduced to evaluate the edge shape effect. This parameter is defined by the edge dimension divided by the thickness of the laminated rubber. Internal stress distribution was solved by the nonlinear FEM analysis. The stress concentration point around the edge coincided with the initiation point of the failure observed by microscope camera. The fatigue life of rounded or chambered edge specimens (R, C specimen) was nearly equal or longer than that of non-curved edge specimens. The fatigue life, however, little increases with an increase of the dimensions of R at the edge.
In order to investigate the fracture process of CFRP with high toughness, a plate specimen of a uni-directionally reinforced AS4/PEEK is subjected to transverse tension at room temperature. The results obtained are summarized as follows; (1) At 83% of fracture stress, small cracks are initiated along the interfaces of fiber and matrix in a group on or near the edge of specimen. (2) The cracks are semi-circular and they are arrested just after the initiation. (3) Although the number of the cracking regions increases as the applied stress increases, the area of each cracking region does not grow due to the crack arrest. (4) The boundary element analysis and the finite element analysis reveal that the arrest is caused by the cylindrical shape of the interface. (5) The cracks restart to grow and make coalescence when the stress field near the crack tip satisfies the condition of crack kinking. (6) The main crack formed brings about the specimen breaks down when the stress intensity factor reaches the macroscopic toughness, which is evaluated by DCB specimen.
In woven fabric composite materials, several kinds of failure mode such as matrix cracking, fiber breaking and transverse cracking in fiber bundle occur at frequent intervals under monotonic loading condition. The damage mechanism is very complicated and difficult to reveal by experiments. Hence, three-dimensional finite element analysis based on damage mechanics has been developed. Anisotropic damage equation for unidirectional lamina is applied to fiber bundle and microscopic damage development is simulated by incremental method. In addition to the procedure of damage development analysis, the technique to generate finite element mesh for heterogeneous body composed of weaving fiber bundle and matrix is presented. For the numerical example, the damage development of plain woven fabric composite material under on-axis tensile load has been analyzed and has been observed by CCD camera. As a results, it is recognized that the calculational and the experimental results have a good agreement and that the proposed procedure is very useful for the design of structures using woven fabric composite materials.
The fatigue strength reduction factor (Kf) of fatigue crack initiation life (Nc) basis was previously proposed by one of the authors as a function of the elastic stress concentration factor (Kt) and work hardening constants in the cyclic hysteresis loop. The validity of the fundamental relation was shown mainly through the experimental investigations using mild steel, high strength steel and weld metals. In the present study, an applicability of the relation to an austenitic stainless steel was investigated, by tension-compression axial loading fatigue tests of double side notched plate specimens of SUS316NG steel. The Kt was changed from 1.08 to 6. As a result of the fatigue tests, Kf of Nc basis showed a linear relationship against Kt, but the Kf was always lower than Kt, though the former was nearly equal to the latter in the previous investigation, The theoretical equation predicting Kf as a function of Kt was partially modified by applying a new concept on the hysteresis energy per cycle so as to show a good agreement between experimental and theoretical values of Kf.
An in situ fluorescence microprobe spectroscopy approach is applied to clarify the effect of grain morphology on fracture toughness of Al2O3 ceramics. Fluorescence spectroscopy enables to experimentally determine a map of the crack-wake bridging stress distribution with micrometer precision and, thus, to predict the R-curve and the crack opening displacement (COD) behavior of the material. Platelet-shape grain morphology was found to significantly enhance the bridging stresses in the neighborhood behind the crack tip, as compared to equiaxed Al2O3. A maximum bridging stress of about 350MPa was found to arise from elastic bridging sites, according to microscopy observation. The experimentally determined bridging stress distribution produces a rising R-curve behavior and a COD profile consistent with those experimentally measured.
Fracture mechanisms for two kinds of ABS mold plates of copolymerized ABS and mechanically blended ABS are investigated on various mold temperatures and positions of the mold plate by means of acoustic emission (AE) frequency analysis. It can be found that, when the values of peak frequency represent the damage modes, the AS cracking dominates the fracture mechanisms of the copolymerized ABS, and the AS cracking and the B rubber aggregate/AS debonding dominate the fracture mechanisms of the mechanically blended ABS at final fracture.
Characterization of anodically oxidized carbon black (CB) has been investigated from the discussion of its surface properties, such as wettability, electric conductivity, rate constant of H2O2 decomposition. This work also describes the relationship between the surface properties and the electrochemical behavior of the electrodes with anodically modified CB in an aqueous KOH solution. The results are as follows: the CB surface changes hydrophobic to hydrophilic; the conductance of CB decreases with the oxidation; and the oxidation enhances the H2O2 decomposition ability of CB. The polarization behavior of an oxygen electrode has been significantly improved by the oxidation. From experiment using a rotating disk electrode, the electrochemical reduction of oxygen on CB surface is mainly a two-electron pathway forming an intermediate, H2O2, and no change in the number of electrons per mole of oxygen has been observed between the untreated CB electrode and the oxidized one. The electrode reaction rate of the oxidized CB electrode has been higher than that of the untreated CB electrode. The diffusion rate of the active material in the oxidized CB electrode was higher than that of the untreated CB electrode.
As a part of study on the applicability of laser beam machining to woodceramics, the response of MDF to laser beam has been investigated under various irradiation conditions. The results are summarized as follows: (1) Removal depth increases with increasing materials density. (2) The difference in the extent of burning, between upper and lower layer of machined surface, increases with increase in the energy density of laser beam. (3) The kerf on the machined surface contains taper. The amount of taper depends on both energy density and defocus distance of laser beam. (4) The kerf width increases with increase in beam power as well as in defocus distance.
High-velocity flame spraying of WC-Co cermet was applied on a tool steel substrate (JIS: SKD5). After the specimens were heated in air or vacuum, edge-indentation tests of the specimens were carried out to examine the change of delamination energy. For the specimens heated at 773K in air or vacuum within 144ks, delamination load did not change. When the heating temperature was 873K and hold time was longer than 144ks, the delamination load decreased. Delamination area decreased when the hold time exceeded 3.6ks. Delamination energy Ed of the specimen heated at 773K increased with increasing hold time within 144ks without decreasing hardness of coating and substrate, and the Ed was larger for the specimen heated in air than in vacuum. The Ed of the specimen heated at 873K in air increased with increasing hold time, but the hardness of coating and substrate decreased. The increase in delamination energy by heating was due to the diffusion of Fe and Co elements across the interface between coating and substrate.
An aluminum projectile was impact-welded on a titanium target using a nitrogen gas gun at impact velocities of 200m/s or more. Effect of thickness of the target on the compound layer at the joint interface was examined regarding some points. The bonding area was estimated using scanning acoustic tomography. The microstructures and element distribution in the joint were analyzed by means of SEM and Energy dispersive X-ray spectroscopy. The bonded area did not depend on the thickness of the target, but increased with the impact velocity. The increase in the thickness of the target caused a decrease in the maximum thickness of the compound layer formed at the joint interface because of the increase in deformed volume. However, the concentration of the elements in the compound layer varied very little with the impact velocity, thickness of the target and position in the layer.