Laser peening has recently been developed as a surface modification technique. When a high-energy laser pulse irradiates a material surface submerged in water, high-pressure plasma is generated immediately on the surface. The plasma induces an impulse wave that penetrates into the surface layer. In the present study, a laser beam of diameter about 10mm is converged by the converging lens with focal length of 250mm, and irradiates the aluminum surface. The second harmonic generation of Yttrium-Aluminum-Garnet (YAG) laser was used at a pulse frequency of 10 Hz. The effect of laser power density and scanning speed on residual stress in the laser peened aluminum alloy surface was investigated by X-ray diffraction. The following results were obtained : (1) compressive residual stress was induced in the surface of all samples ; (2) many fused traces and many micro-cracks were formed in laser peened aluminum surface ; (3) for the series of experiments with the fixed scanning speed of 2.0mm/s, the maximum compressive residual stress was induced at the laser power density of 31MW/mm2 ; and (4) for the fixed laser power density of 61 MW/mm2, that was induced at scanning speed of 1.0mm/s.
The distribution of an out-of-plane stress, sigma σ3, in a thermal barrier coating (TBC) can be obtained from the combination of the data measured with laboratory X-rays and high-energy synchrotron X-rays. This method is called the hybrid method. To improve the hybrid method, the penetration depth is taken into account in the relation between a diffraction angle, 2θ, and sin2ψ. The distribution of the in-plane stress, σ1, was obtained by the stress measurement with laboratory X-rays after successive removal of the surface layer. Assuming the distribution of sigma σ3 as a cubic function, the parameters of the function were optimized by minimizing the error between the measured and calculated 2θ-sin2ψ relations. In the top coating oxidized for 500h at 1373K, the out-of-plane stress became large tension near the interface between the top and the bond coating due to the interface roughness and the thermally grown oxide (TGO). For the top coating oxidized for 1000h, the TGO more grew and the out-of-plane stress near the interface was released due to the initiation of spalling cracks. However, the in-plane stress was maintained and the compressive stress region was extended. As a result, the behavior of the degradation of the oxidized TBCs corresponded to the change in the distributions of the residual stress.
Welding technique is utilized for many structures as a technique jointing some components. The residual stress, however, induced by welding affects the mechanical properties or failure mechanism. Therefore, it is important to know the residual stress states near the weld zone accurately for improving the reliability of structures. In this study, the residual stress distributions of a double-V butt weld plate were measured using neutron diffraction technique, and the generating mechanism of residual stresses was also discussed. The double-V butt weld plate was fabricated by using Ni-Cr steel (SNC631) which is one of the high tensile strength steel, and its residual stress distributions were measured using diffractometer for residual stress analysis (RESA) located in JRR-3 at Japan Atomic Energy Research Institute. At first, some coupon samples were cut from weld plate in order to measure the lattice constant in stress-free condition. As a result of measuring the lattice constant using coupon samples, the lattice constant was increasing near the weld zone because of some phase transformations such as martensitic transformation due to weld process. Secondly, the residual stress distributions of weld plate were measured with αFe110, αFe200, and αFe211. The residual stress distributions evaluated by each diffraction were almost the same profile throughout the welded plate since no plastic strain was observed near the weld zone. The residual stress near the weld zone was tensile stress of almost half value of yield strength of Ni-Cr steel. It might be reasons why we obtained these results that the tensile residual stresses did not reach yield strength since the transformation expansion of high tensile strength steel is larger than that of mild steel and the tensile residual stress starts to generate at low temperature. It was, therefore, confirmed that the neutron stress measurement can determine the residual stress distribution of welded sample of high tensile strength steel without consideration of the plastic deformation.
The loading stresses in a monolithic aluminum alloy and an aluminum alloy reinforced with silicon carbide particles were measured by time-of-flight neutron diffraction method. Under uniaxial loading, the longitudinal and transverse strains were measured by high resolution powder diffractometer, Sirius, at KENS. The elastic constants measured by the neutron diffraction method were compared with the values predicted by analytical models. The intensity of Al200 diffraction was high enough to determine the lattice strain in both longitudinal and transverse directions. The elastic constants agreed well with the predicted values. For the composite, the loading stresses in each constituent phase of the aluminum alloy and the silicon carbide particles were measured. Diffractions from SiC102, SiC110 and Al200 were suitable for determination of lattice strains. The measured strains were compared with the values predicted by the inclusion models. When the diffraction intensity is sufficiently high, the measured elastic constants are close to the predicted values. The macro stress calculated by the rule of mixture agreed very well with applied stress.
Single edge notched specimens of a unidirectional SiC long fiber reinforced titanium alloy were fatigued under four point bending. Propagation behavior of fatigue cracks was observed on the basis of the effect of the fiber bridging. The branched fatigue cracks were initiated from the notch root. The crack propagation rate decreased with crack extension due to the crack bridging by reinforced fibers. The longitudinal stress in the reinforced fiber was measured by using high spatial resolution synchrotron radiation. The interfacial frictional stress between the matrix and the fiber could be directly determined by X-ray method. The bridging stress was also measured as a function of a distance from a crack-tip. The stress intensity factor range corrected on the basis of the shielding effect agreed well with that for the monolithic titanium alloy, when compared at the same crack propagation rate.
Titanium nitride (TiN) thin films with the thickness of 0.1, 0.2, 0.5, 1.0, 2.0 and 4.0μm were coated on a carbon steel substrate by the ion beam mixing method. The film had a strong fiber texture with ‹001› axis perpendicular to the film surface. The distribution of the residual stress in thin films was measured by the grazing incidence X-ray diffraction (GIXD) and the scattering vector (SV) methods. The in-plane stress measurement by GIXD was applicable to the thickness down to 0.2μm of TiN films. The stress was a compression of around 2 to 3GPa. The compressive stress was found to increase in the very-near surface region of 20 to 30nm in depth. Thinner films had a steeper increase of the compressive stress in the very-near surface region. The strain distribution measured by the SV method using Cr-Kα radiation was nearly constant over the region of the penetration depth between 0.3 and 0.6μm from the surface, and that by using synchrotron X-rays was also constant over the penetration depth from 0.4 to 1μm. The stress distributions measured by the in-plane measurement and the one-tilt method combined with the surface removal method showed a good agreement with each other. The compressive residual stress was uniform within thin films except very near the surface of about 20 to 30nm in depth.
Residual stress on the weld metal of nickel based alloy was evaluated through x-ray diffraction and metallurgical study of the microstructure. Weld metal specimens were prepared from Alloy182 (JIS DNiCrFe-3) and Alloy132 (JIS DNiCrFe-1J) deposited on a steel plate. X-ray diffraction results show a strong  preferred orientation nearly normal to the surface of the weld metal. Crystallographic consideration predicts that dominant 311 diffractions appear around 25.2 and 72.5 degrees of ψ angle. For each diffraction, the peak shift was measured at the ψ angle showing the maximum diffraction intensity, using the side-inclination method (ψ-goniometer method) with a Mn x-ray tube and a PSPC (position sensitive proportional counter). The residual stress was determined by the peak shifts according to the two tilt method. The x-ray stress constant, K, on Alloy 182 was determined experimentally. The depth profile of the residual stress was measured on the ground specimens with and without laser peening. Tensile residual stress due to the grinding work is observed in the surface layer of the unpeened specimen; however it changes to compressive after laser peening. The overall behavior of the depth profile of laser peened material agrees well with that of Alloy600 base metal measured in the previous studies, where the compressive residual stress with several hundred MPa at the surface gradually decreases and reaches to around 0MPa at the depth of about 1 mm.
The microstructure and mechanical properties of thermo-mechanically treated Cu-2.0mass%Ni-0.5mass%Si alloys with and without 0.1mass%Mg have been investigated. The Mg addition increases the formation rate of disk-shaped Ni2Si particles. The Mg addition produces higher strength and resistance to stress relaxation. The improvement of strength or stress relaxation resistance is caused by the decrease in interparticle spacing by the Mg addition or by the Mg-atom-drag effect on dislocation motion. The stress relaxation resistance for the Cu-Ni-Si alloy with a large grain size of 150μm is higher than that for the alloy with a small grain size of 10μm because the density of mobile dislocations in the former alloy is lower. The effect of equal channel angular pressing (ECAP) and subsequent heat treatment on the mechanical properties of the Cu-Ni-Si alloy has also been studied. The heat-treated ECAP alloy shows larger values of 0.2% proof stress and ultimate tensile stress and a slightly smaller value of elongation to failure compared with the thermo-mechanically treated Cu-Ni-Si alloy.
The strain-concentration factor was calculated using finite element method for plane-strain rectangular bars with a single-edge U-notch under pure bending. The strain-concentration factor employed is newly defined under the triaxial stress state at the net section. This new strain-concentration factor increases from its elastic value to the maximum as plastic deformation develops from the notch root. The maximum strain-concentration factor of a shallow notch is considerably greater than that of a deep notch, although the elastic strain-concentration factor is reversed. Plastic deformation around the notch root has a stronger effect on the strain-concentration factor of shallow notches. This is because plastic deformation develops mainly in the vicinity of the notch root for shallow notches. The strain-concentration factor employed here corresponds well to the distribution of the longitudinal strain at the net section. The variation of the strain-concentration factor with M/MY, the ratio of bending moment to that at yielding at the notch root, is dependent on the stress-strain curve for shallow notches, especially beyond the deformation level at which the maximum strain-concentration factor occurs. The integral of the longitudinal strain at the net section is negative in elastic deformation for single-edge notches. It varies from negative to positive value with plastic deformation around the notch root.
The bottle-neck shaped seal of bags for holding liquid is particularly convenient for pouring the liquid into another container. In recent years, bags have frequently broken at the bottle-neck shaped seal because the bags were subjected to the impact during loading and unloading. Taking this into consideration, we performed impact tensile tests using two types of bags with bottle-neck shaped seals, one with barrier characteristics, i.e., laminate films of NY/alumina-evaporation PET/XA-S and NY/AL/XA-S, and one without barrier characteristics, i.e., NY/XA-S for bottle neck shaped seal diameters of 7.5, 10, 12.5, 13, 14, 15 and 20mm and flat seal bags. When the seal diameter of NY/aluminaevaporation PET/XA-S, NY/AL/XA-S or NY/XA-S is 15mm or greater, the impact tensile load at break is almost the same as that of flat seal bags.
In this research, the effect of pre-fatigue on the impact tensile properties of the welded butt joint of high strength steel plates, HR590 and HR780, was investigated by means of the split Hopkinson bar method for tensile test. For comparison, quasi-static tensile tests were also performed to examine the effect of strain rate on the strength and the elongation. It was found that the effect of pre-fatigue on the tensile strength of welded butt joints is quite small if the applied stress in the pre-fatigue is less than the apparent yield stress of the welded butt joints. In the results of quasistatic and impact tensile tests for the welded butt joint of HR780 steel, however, the fracture strain of the specimens subjected to high cycle pre-fatigue was larger than that of the virgin specimens. This may be caused by the increase in hardness due to pre-fatigue observed in the weld zone of the joints.
An actual joint structure of ceramics-metal in the airtight seal parts for a neutron detector was studied on the residual stress generated in the joint process due to the difference of the thermal expansion coefficient between ceramics and metal. The influences of shape and dimension of the joint structure on the residual stress were clarified analytically by finite element method (FEM) and verified experimentally by checking cracks generated in prototype samples. Based on fracture mechanics, equivalent stress intensity factor KIeq was calculated in consideration of a latent flaw in the residual stress fields, and optimal geometries of the joint structure were proposed for reducing the residual stress. The residual joint strength was discussed by using the difference ΔKIeq between fracture toughness KIC and KIeq. The main results obtained are summarized as follows : the residual joint stress increases with the thickness of a Cu-Ti eutectic reaction layer; the residual joint stress decreases with the reduction in taper angle of the end of Cu interlayer; the residual joint stress is hardly influenced by wall thickness in the end of SUS304 pipe. On the basis of these results, the optimization in the structural factors can decrease the residual stress because of reducing stress concentration field near the interface of ceramic and metal, and so the residual joint strength increase with decreasing of the residual stress depending in the structural factors as the thickness of a Cu-Ti eutectic reaction layer, taper angle of the end of Cu interlayer and wall thickness in the end of SUS304 pipe.
A calcium phosphate compound (Hydroxyapatite) has similar composition and crystal structure to an organism bone. Except an absorbent calcium phosphate compound, the composition that resembled apatite and a deposit having configuration generate it on the surface of apatite ceramic in vivo. In other words apatite ceramics does an organism bone and direct bonding through an apatite deposit without causing negativism. Generally this function is named bioactivity. These functions can inhibit ionic elution, roosting, wear and fretting occurring in metal biomaterial, and be extremely important from a point of view to use in vivo. However, ceramics material is extremely inferior in mechanical properties in comparison with metal material. Therefore, an application to locus accompanied by high load is difficult. It is used as bone filling material such as shank or body of vertebra under the present conditions. In other words low load is applied to locus to be accompanied by. Therefore, static load than cyclic load is important when long-term use was considered. However, bioactivity ability of apatite ceramic material and relation of mechanical properties were not clarified. A fatigue characteristic in consideration of organism environment is particularly unclear. Furthermore, it is necessary to evaluate a fatigue characteristic and crack propagation behavior when microstructure changes by apatite and chemical reaction with body fluid. This study, a static fatigue characteristic of apatite ceramics in simulated body fluid environment was examined.
Fatigue crack growth tests were carried out using CT specimens of ultra-fine grained P/M (Powder Metallurgy) aluminum alloy of which grain size was from 200 to 500nm. Fatigue crack growth behavior was investigated under constant amplitude and repeated two-step variable amplitude load sequences. It was found that roughness induced crack closure played an important role in closure behavior of this material. Although the roughness of fracture surface was smaller than the other conventional aluminum alloys, the roughness induced crack closure was dominant because of the small crack tip opening displacement (CTOD) with respect to the roughness level. Under repeated two-step loading, crack opening load was lower than that under constant amplitude loading with the same K value as the high level load, and the crack growth retardation caused by load history was not prominent comparing with other aluminum alloys. It is considered that the crack opening load under variable amplitude loading was dominated by the roughness induced crack closure. The small contribution of the plasticity induced crack closure was due to the constraint of plastic strain by the grain boundaries of ultra-fine grains.
This paper studies crack growth behaviors in thermal fatigue tests for René80 conventional cast and YH61 single crystal nickel base superalloys. A cylindrical specimen with 19.5mm outer diameter and 2mm thickness was used in the thermal fatigue tests. A rapid temperature gradient in cylinder thickness was realized by induction heating of the outer surface and water cooling of the inner surface. Thermal fatigue tests were conducted by changing the outer surface temperature from 303 to 1173K and temperature holdings of 10 and 60minits were inserted at 1173K. Temperature gradient in thickness was 650K. Crack growth behaviors were inspected with interrupting tests. Crack initiation sites coincided with the ‹100› direction on the outer surface whereas ‹110› direction on the inner surface. It was confirmed that crack initiation sites coincide with stress distribution obtained from a structural analysis considering the anisotropy of the single crystal. Cracks were arrested at the depth of approximately 1.0mm due to stress gradients in the specimen.
Effect of firing atmosphere on the electrical properties of Gd-Fe-codoped BaTiO3 ceramics added with B2O3 was studied by measuring their electrical resistivity, diffuse reflectance spectra and electron spin resonance (ESR) spectroscopy. The bulk density of the samples fired above 1300°C, except Fe-doped samples fired in air, was as high as 94% of the theoretical value. Semiconducting BaTiO3 was obtained in the case of Fe-doped and un-doped samples fired in Ar at all range of firing temperature. The room temperature resistivity of the samples fired in Ar was lowered with increase in firing temperature. It was considered that the lowering of the resistivity was due to the grain growth with rise of temperature. The PTCR jump for Fe-doped samples fired in Ar was much larger in all range of firing temperature than that for Fe-undoped samples fired in Ar. This result indicated that Fe ions segregated in the grain boundary and acted as an acceptor.
In this paper, corroding process of reinforcement in concrete and mortar subjected to sulfuric acid attack was investigated by visual observation, by measuring profile of sulfate ion and pH with respective indicators, and by measuring corrosion area and weight loss of reinforcement. Application of the electro-chemical monitoring methods (half-cell potential, polarization resistance, and concrete resistivity), which are usually used for reinforcement subjected to chloride induced corrosion, to the sulfuric acid attack was also discussed Obtained results showed that sulfate ion affected the corrosion initiation of reinforcement before the cover concrete was dissolved, and that the corrosion initiation can be detected by the concrete resistivity.
Polymer-modified mortars which consist of a polymer emulsion and cement materials have been widely developed in the construction materials fields. Forming process of the polymer-modified cement membrane simultaneously involves evaporation of water within the polymer emulsion and hydration of cement. It is important for the polymer-modified cement paste that the hydrate crystal of cement is generating by the hydration during the setting process under existence of the polymer emulsion. In this study, hydration process for calcium-aluminate cement under existence of poly (ethylene-vinyl acetate) (EVA) emulsion (polymer-cement ratio = 100%) was investigated by X-ray diffraction method using synchrotron radiation (SPring-8). The diffraction peaks of calcium aluminate (CA) disappeared after the hardening, on the other hand, the peaks of hydrate crystals of calcium-aluminate cement (C2AH8 and C3AH6) could be observed. This polymer-modified cement paste hydrated using the water within the polymer emulsion. The hydration of C2AH8 from CA started at around 300min, and then C3AH6 hydrate crystal increased after 700min at ambient temperature. This implies that the conversion from C2AH8 to C3AH6 occurred to be more stable phase. The setting temperature affected the reaction rate. In case of hydration at 35°C, the start time of the hydration for calcium-aluminate cement was quicker than that in the ambient temperature four or more times.