Al ion implantation was carried out to aim for suppressing an absorption of hydrogen from environment into Ti-Ni shape memory alloy. A layer of 100nm thick with high density Al was formed at the surface by ion implantation. Starting stress of martensite accommodation did not change by ion implantation and hydrogen absorption. On the contrary, the deformation stress corresponding to a strain of 4% in martensite phase and shape recovery stress changed by both the ion implantation and hydrogen absorption. The implanted specimen with a low dose revealed an effect of suppressing the hydrogen absorption. In this case, the surface ion implanted layer was supposed to prevent diffusion of hydrogen, which absorbed near the surface, toword the inside of the specimen. While, the implanted specimen with a high dose lost their shape memory properties due to the composition change indicated by the shift of transformation temperatures. In any cases, the ion implantation affected the shape memory properties with and without existence of hydrogen into massive of cross section, although the ion implanted layer was limited in the vicinity of the outmost surface.
The fatigue crack growth tests near the stage I region were carried out on three spheroidal graphite cast irons (SGI) with matrix of ferrite, bull's-eye and mainly pearlite, having tensile strength of 380, 500 and 700MPa, respectively. The crack growth rate da/dN of the ferrite matrix SGI decreased continuously with a decrease in stress intensity factor range ΔK. On the other hand, the bulls-eye and pearlite matrix SGI showed discontinuous ranges on the da/dN vs. ΔK diagrams. The results were compared with local ΔK calculated at the crack tip by fracture mechanics. The ΔK at the lower end of the discontinuous range agreed well with the value calculated on the assumption that a single graphite particle is included in the tension-compression region at the crack tip. The ΔK at the higher end agreed well with the calculated value for including no graphite particles in this region. In the ferrite matrix SGI, however, the calculated value was smaller than ΔKth; the cyclic stress region is presumed to include plural graphite particles. The fatigue fracture mechanism of SGI is believed to be significantly affected by the interaction of graphite particle spacing, the size of plastic region at the crack tip, and the stress concentration around the graphite particle.
Fatigue tests were performed using (α+γ) duplex stainless steel specimens which had been deformed superplastically in the various strain range. The effect of the changes in the variables such as microstructure and surface roughness of the specimens during superplastic deformation on the fatigue strength of the deformed specimens were investigated. The fatigue strength of the superplastically deformed duplex satainless was found to decrease with increasing in the superplastic straining. The reduction in the fatigue strength was caused by the coarsening of the grains and the increasing in surface roughness of the specimens during superplastic flow. The fatigue strength of the specimens was also proved to be not affected by the formation of cavities during superplastic flow. Moreover, it was shown that the increase in surface roughness of the specimens with the superplastic straining was large at the initial stage of straining and this behavior resulted in the remarkable reduction in the fatigue strength of the specimens. The post-deformed fatigue strength of the specimens with the surface polished treatment, however, could be improved by superplastic straining up to 200%.
The present paper describes the effect of humidity on the fracture mechanisms and associated morphology of the S-N curve in a high strength steel, JIS SNCM439. Fatigue tests were conducted on cantilever-type rotating bending fatigue testing machines operating at a frequency of 3150rpm in laboratory air and in dry air up to long life region around 109 cycles. The dew point of dry air was -60°C. In laboratory air, fatigue failure occurred at stress levels below the conventional fatigue limit, leading to a step-wise S-N curve. Also in dry air, similar step-wise S-N curve was obtained, but the horizontal part of the S-N curve shifted to a higher stress level than in laboratory air. Fatigue lives were the same in both environments at stress levels above the horizontal part in dry air and below the horizontal part in laboratory air, because the same fracture mode operated in those regions, surface-related initiation in the former and subsurface crack initiation with a fish-eye in the latter. At stress levels between the horizontal parts in both environments, surface-related initiation and subsurface crack initiation were seen in laboratory air and in dry air, respectively. Fatigue lives were significantly shorter in laboratory air due to humidity-assisted crack initiation and small crack growth. Based on the experimental results, the environment dependence of fracture mode and associated morphology of S-N curve is discussed.
Friction welding of 6061 aluminum alloy was carried out in order to examine the relationship between deformation heat input during upset stage, upset burn-off length and joint performance. The joint performance was evaluated by tensile test and fatigue test. Stabilized tensile strength was obtained, when deformation heat input during upset stage and upset burn-off length were over about 200J/s and over about 4mm, respectively. The welding condition at the weld interface and the width of softened area effected on fatigue strength more so than tensile strength. That is, in the joint of which the welding at the weld interface is good and the softened area is wide, fatigue strength become high because the stress is dispersed in the softened area. On the other hand, in the joint of which the welding at the weld interface is good and the softened area is narrow and in the joint of which the welding at the weld interface is poor in spite of having the wide softened area, fatigue strength become low because the stress concentrates at the weld interface. Judging from the fatigue limit obtained from the fatigue test, in over value in which there are deformation heat input during upset stage and upset burn-off length, the sound joint can be produced.
Hydrostatic pressure dependence in mechanical behavior of polymers is studied for the constitutive modeling with the yield surface described by the first invariant and the second invariant of stress and the nonassociated flow rule satisfying incompressible hypothesis. An internal variable theory of rate-independent plasticity is presented incorporating isotropic hardening as a function of accumulated plastic strain. After determination of material constants under uniaxial tension and compression, the model shows that the von Mises type effective stress-plastic strain curves under multiaxial load are quite different from those under uniaxial load. The model is compared with the experimental results in uniaxial tension and compression by Spitzig and Richmond and in torsion by Silano et. al under high pressure.
In the previous paper, it was found that a constitutive equation based on the kinematic hardening creep theory of Malinin-Khadjinsky and the nonlinear kinematic hardening rule of Armstrong-Frederick cannot describe strain recovery of polymer-matrix composites in the process of unloading; this was found to be attributable to rapid development of back stress just after the start of unloading. Thus, in order to describe the intrinsic strain recovery of the composites, the Armstrong-Frederick model of kinematic hardening is modified by taking into account a new concept of transient recovery surface proposed by the authors. In order to modify the model, a transient recovery term is introduced into the evolution equation of back stress, and the term is active under unloading to suppress strain hardening of back stress when viscous strain state is inside the transient recovery surface defined in viscous strain space. By using the modified model incorporated into the kinematic hardening creep theory of Malinin-Khadjinsky, hysteresis loops in stress-strain relation including the processes of loading, unloading and reloading are simulated, and the validity of the modification is discussed.
The strength evaluation method of welded joints for truck frames is studied by fatigue tests of actual-sized component models and small-sized component models. The following results were obtained from the tests. (1) The calculation method by FEM analysis for the stress intensity factor K of the welded joints is verified by the stress distribution and fatigue test results of component models. (2) Configurations of the fatigue fracture occurred at the root of the welds are clarified by actual-sized component models testing. Judging from these results, it was proven that the strength evaluation method mentioned in this report is valid in practical use for actual truck frames.
Sheet Moulding Compound (SMC) has been widely applied to industries such as automotive exterior parts and housing facilities for its excellent mechanical properties, relatively low cost and lightweight and good design possibilities. Typical SMC products have some ribs in order to reduce weight of the structures without loss of stiffness. However, in these products, various problems such as sink mark, weld lines, warpage and heat cracks often occur. These problems are caused by complexity of fibre distribution and fibre orientation. In these cases, while it is needed to change the design of the mould, moulding tools are expensive and moreover it costs greatly to change the design of them. So, CAE system is needed to improve the efficiency of mould design. But defects of SMC products formed by compression moulding are greatly influenced by moulding conditions, especially material flow. But the material flow of SMC is complex and unsteady. And in ribs, it is more difficult to predict the material flow of SMC and fibre distribution and orientation and so on. Therefore it is useful to apply the database that can express these factors simply. And we are trying to construct the CAE system to predict the stiffness of structure in SMC compression moulding. In this paper, we investigated mechanical properties in rib part of SMC products. From the results, we constructed a method for estimation of Young's modulus in rib part in consideration of heterogeneity as fibre orientation and its distribution and resin-rich. As the results, in predicting Young's modulus in rib part, we get good agreement with theoretical value and experimental value.
The purpose of this study is to investigate the vibration damping properties of adhesive structure plates with delamination by transient dynamic analysis. The adhesive structure plates used in this work consist of carbon fiber reinforced plastics (CFRP), and aluminum as two adherends and adhesion with high damping properties as an adhesive layer. The proposed numerical model is constructed independently modeled as adherend with shell element and adhesive with beam element respectively. The proposed method of numerical analysis was used to analyze the damping factors of the adhesive structure plates. The validity of the numerical model for the damping analysis of adhesive structure plates was checked through comparisons with experimental results. It was found that delaminated plate had the higher damping property than virgin plate. Using this model, the influences of area and position of delamination in adhesive layer upon the damping factors are discussed.
Damage mechanism and hydrogen storage ability variation of palladium (Pd) were investigated on hydrogen absorption-desorption multi-cycles. In order to study this problem, palladium plates and round bars with mechanical working or annealing have been used. Specimens were hydrogenated cyclically by the electrochemical method, and hydrogen absorption ratio (H/Pd) as well as deformation of specimens were measured at each hydrogenation cycle. As results, it was shown that damage mechanism of Pd specimens was occurred differently with their geometries and mechanical or heat treatment. In thin plate Pd specimens, the thickness increased in increasing hydrogenation cycles whereas length and width decreased, and grains were greatly deformed however damage of micro and macro structures were scarcely observed, and also hydrogen storage ability scarcely changed. On the other hand, in round Pd specimens, both length and diameter increased with increasing hydrogenation cycles, and significant damage of structures were widely observed which resulted in decrease of the ratio H/Pd to -4.2% at the final hydrogenation stage. The damage of structures and deformation were by far intensive in the specimens with mechanical working than with heat treatment however the hydrogen storage ability were not so different within the two type specimens.
The effect of curing temperature on hardening of α-alumina slurry including ρ-alumina was investigated by X-ray diffraction (XRD), thermal analysis (DTA) and scanning electron microscopy (SEM). From the experimental results, it was clarified that the penetration resistance rapidly increased as the curing temperature increased. It was thought that the hardening of the slurry was progressed with following two stages. At the first stage, alumina particles were mainly coagulated by the neutralization effect of polynuclear hydroxo-aluminum ion which was produced by the dissolution of ρ-alumina. At the second stage, alumina particles were bound to each other with the pseudoboehmite which was produced by the hydration reaction of ρ-alumina. The logarithmic time required to reach the same penetration resistance increased almost linearly with an increase of the reciprocal curing temperature, after the correction for the delay time which was caused by heating from the initial temperature (280K) to the curing temperatures (318-363K). The apparent activation energy for the hardening was approximately 79kJ/mol. This value was nearly equal to the apparent activation energy for the dissolution of aluminum anodic oxide film. This suggested that the dissolution of ρ-alumina was the rate-controlling step of the hardening.
A number of cases of deterioration of concrete structures caused by Alkali-silica reaction (ASR) have been reported. In previous study, loading carrying behavior of reinforced concrete members were not changed by damage of ASR. However, concrete structures severely deteriorated due to ASR have been reported. Strengthening have been applied for concrete pier damaged by ASR in order to improve ductility and to reduce expansion. In this study, the effect of transverse confinement on reducing alkali-silica expansion was investigated. The effect of ASR on the loading carrying behavior (strength and ductility) of concrete member and multiple damage due to ASR and steel corrosion was discussed. Transverse confinement with FRP sheet was useful for reducing expansion of concrete structures damaged by ASR. Ductility of concrete member damaged by ASR may be reduced. Furthermore, ductility of concrete member damaged multiply by ASR and steel corrosion was reduced largely.
Recently, a new type of artificial light-weight aggregate has been developed. This aggregate has lower water absorption ratio than ordinary light-weight aggregate because of its tight surface structure, and can be used for concrete mixing without pre-wetting procedure. Another advantage of this aggregate is its spherical shape that is expected to increase the fluidity of concrete. In this study, this new light-weight aggregate was applied to self-compacting concrete, and the self-campactability of this concrete was investigated and discussed. The results show that self-compacting concrete with this aggregate has higher self-compactability than that with crushed stone, while the deformation rate of concrete is very small. Segregation between the aggregate and mortar, however, tends to be large because of larger difference of specific gravity between them than in the case of ordinary self-compacting concrete with crushed stone. Increase of unit mass of the light-weight aggregate does not affect so much on self-compactability of concrete. Also, a drop of self-compactability of self-compacting concrete with the light-weight aggregate with the lapse of time after mixing is less than that with crushed stone.
Recently, the position sensitive proportional counter (PSPC) has been becoming popular as a detector for X-ray stress measurement. However, little information is available in the literature regarding the effects of specimen mis-setting on the stress measurement using the PSPC. In this paper, a modeling of the Ω assembly X-ray stress measurement using a PSPC as the detector is presented enabling us to simulate the stress measurement under the various conditions including specimen mis-setting. As the results of simulation, it was found that the use of collimator yields an apparent stress (intrinsic stress), and that the absolute value of the stress increases with the increase in the width of the collimator and decreases with the increase in its effective length. It was also found that the error in stress measurement due to specimen mis-setting is expressed as a linear relation of the ratio L/R0 (L: offset of mis-setting, R0: goniometer radius), and that the coefficient in the relation is given as a function of secondary order of the ratio 2bψ/Cl (2bψ: width of collimator, Cl: effective length of collimator).
Study aims to estimate the impact force history and correlate it with damage occurrence in a cross-ply CFRP plate impacted by flying steel ball (φ7mm) at 10 to 45m/s velocities. Both the plate deflection and Lamb AE waves were monitored for 2mm thick [0°4/90°4]sym. cross-ply CFRP plate. We estimated the impact force from the plate deflection and the force history by the simplex-assisted Lamb waveform simulation, and compared with that calculated from energy balance and spring-mass models. The time history estimated by the Lamb waveform simulation agreed well with that calculated by the spring-mass model, however the force amplitude estimated by Lamb wave is 3.5 times smaller than that by the spring-mass model, but about half that by energy balance model. The maximum force amplitude estimated from the plate deflection agreed with that by the energy balance model at ball velocities below 20m/s, but the former significantly deviated at ball velocities higher than 30m/s at which large delamination occurred. Data deviation indicates a possibility of determining the critical ball velocity to cause serious internal damage. We discuss the detail of agreement and disagreement between the experimental data and models.
The new inhibitor for stainles steel (mainly high purity ferritic stainless steel) in the high temperature concentrated aqueous solution of lithium bromide was investigated. According to the results of the electrochemical measurements, and the immersion tests using autoclaves, the mixture of three chemicals, LiOH+Na2SO3+SbCl3, is effective as an inhibitor for stainles steel to prevent hydrogen generation, pitting corrosion and macro-cell corrosion with copper. The reasons of this result are assumed that the sodium sulfite in this inhibitor remains the free-corrosion potential of stainless steel lower, and antimony in this inhibitor prevents hydrogen generation. This inhibitor also prevents stress corrosion cracking of austenitic stainless steel in the high temperature concentrated aqueous solution of lithium bromide.