A stress analyzing instrument was developed based on the energy dispersive X-ray diffractometry. 4-point bending stress in steel specimens was tried to measure by using the side-inclination method. It was found that the energy-sin²ψ (En-sin²ψ) diagram, which corresponds to 2θ-sin²ψ in the side-inclination method, showed good linearity and accuracy as same as the conventional method. The relationship between the mechanically determined stress and X-ray determined stress was also linear. In conclusion, this method is useful to stress measurement.

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The present paper deals with the multi-indentation model in which the residual stress can be easily estimated not only experimentally but also analytically to clarify the fundamental characteristics of residual stress of ground ceramics, the stress distribution, the contribution of hardness of the materials to the stress, and the effect of X-ray penetration depth on the stress measurement. In the experiments, Vickers multi-indentation was performed on the surface of ceramics and metal, and then the residual stress was measured with several characteristic X-rays. In the analysis, the residual stress distribution in the multi-indented surface layer was estimated by applying the Hill's solution for spherical-cavity expansion and the residual stress, which is equivalent to the stress measured by X-ray, was evaluated by taking the weighted average of the distribution into account. The residual stress based on the analysis was confirmed to coincide with those obtained from the experiments. The characteristics of the residual stress was discussed in detail based on the results of the elastic/plastic analysis. The main results obtained are as follows.
(1) The compressive residual stress in the multi-indented surface has a peak at the depth right beneath the bottom of indentation. Its magnitude can be estimated as k(b/L)²Hv: b=size of plastic zone multi-indented, L=indentation interval, Hv=Vickers hardness, k=constant (-0.69 for Si₃N₄, -0.35 for S15C).
(2) The compressive residual stress decreased linearly with increasing depth. The compression stress attained zero when the depth was about 80% of b.
(3) The residual stress of ceramics measured by X-ray is considerably smaller than the peak stress even if the characteristic X-ray with shallower penetration depth is used. This result shows that the effective penetration depth of X-ray is not sufficiently shallow in comparison with the depth where the compressive stress exists in ceramic materials.

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Specimens of tetragonal zirconia containing 3mol% Y₂O₃ were ground wetly and dryly with a grinding wheel of grain size 200/230. The residual stress and the monoclinic content were measured by the X-ray diffraction method. The monoclinic content on the surface ground wetly with enough coolant was raised to about 7 percent. For wet ground Y-TZP, bending stress was applied in directions parallel and perpendicular to the grinding direction. The bending strength in both directions increased because of compressive residual stress. Fracture did not start from grinding cracks. For Y-TZP ground dryly without coolant, the bending stress was applied in the direction pallaled to the grinding direction. Many grinding cracks were introduced on the ground surface and no compressive residual stress was measured. Since the ground surface was heated to a high temperature, the transformation to the monoclinic phase did not occur. The bending strength of dry-ground Y-TZP was reduced remarkably. The breadth of X-ray line broadening measured on the dry-ground furface was larger than that of the wet-ground surface. The depth of the grinding-affected zone was 10μm for the dry-ground surface and 30μm for the wet-ground surface.

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The sin²ψ method of X-ray stress measurement was successfully applied to hipped hydroxy-apatite. The X-ray elastic constants of (072+352) diffraction by Mn-Kα radiation was determined experimentally. It is close to the value calculated from the elastic constants of single crystals on the basis of Kröner's model. The residual stress measured on the lapped and ground surfaces was tension, because micro-fracturing was predominant in the grinding process of hydroxyapatite. The bending fracture was started from the cluster of pores. The critical value of the stress intensity factor calculated from the bending strength and the size of the fracture origin was nearly equal to the fracture toughness determined by bending specimens with a single-edge V-shaped sharp notch.

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The stress due to the difference in coefficient of thermal expansion between matrix and fiber was measured by the X-ray diffraction method. The triaxial state of the matrix thermal residual stress in a 17μm diameter Al₂O₃ fiber/Al matrix composite was determined. In the matrix of the annealed composite a tensile residual stress state was observed. On the measurement after cooling the annealed composite to liquid nitrogen temperature, the matrix showed a compressive stress state in the composite. In both of the matrix stress states, the longitudinal residual stress parallel to the fibers was the maximum principal stress and the transverse residual stress normal to the fibers was about 40% of the longitudinal residual stress in magnitude. The stress normal to the surface was found to be about a half of the transverse stress. This can be due to the relaxation of the component of residual stress in the matrix near the surface layer. The X-ray in-situ measurements were made on the heating process of the annealed composite from 290K to 350K. The matrix tensile residual stress at 290K decreased linearly with increasing measurement temperature. The experimental results agreed well with the prediction based on a simple elastic concentric cylinder model.

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Crystal orientation and residual stress development in AlN films deposited on BLC glass (Borosilicate glass; the thermal expansion coefficient of which is nearly equal to that of AlN) substrate were investigated by an X-ray diffraction. Deposition was made by a conventional planar magnetron sputtering system under the nitrogen gas pressure of 0.65Pa at the substrate temperature between 423K and 523K. In order to investigate the effect of plasma contamination, the distance between the target and the substrate holder (target distance d_T) was chosen at 30mm and 60mm.
The intensity of 00·2 diffraction showed that the c-axis orientation of AlN films was improved by the deposition with a short target distance (d_T=30mm). However, in all the AlN films deposited with d_T=30mm, fine cracks were observed probably due to the effect of plasma contamination. In the films deposited with a long target distance (d_T=60mm), large tensile residual stress greater than 1GPa was found at every substrate temperature used in the present investigation. In the films deposited with d_T=30mm, tensile residual stress became larger with increasing substrate temperature. As compared with the AlN films deposited with d_T=60mm, the tensile residual stress in AlN films deposited with d_T=30mm considerably decreased because of the effect of ion bombardment.

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The stress measurement method with characteristic X-ray has been already estabilished as one of the most effective nondestructive evaluation methods of residual stress. However, the classical sin²ψ method with characteristic X-ray cannot evaluate accurately residual stress in the subsurface of metallic material which is treated with cold rolling or grinding, because the three-dimensional stress distribution or a steep stress gradient occurs in its subsurface. Therefore, various characteristic X-ray methods to evaluate the stress distribution have been proposed. This paper presents a new measurement method with polychromatic X-rays for residual stress along the depth direction in a subsurface layer. In this method, the surface stress and stress gradient in a subsurface layer is evaluated by using the theoretical equation describing the relationship between diffracted beam peaks of polychromatic X-rays and a strain distribution along the depth direction. Then, the stress distribution of a JIS SKS51 steel plate ground on its surface was measured as an example of applying this method. In consequence, it is confirmed that the residual stress distribution along the depth direction in a subsurface layer can be determined by using this method.

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X-ray stress measurement for TiAl intermetallic compound of interest as a new structural material was investigated. Arc-melted Ti-48mol% Al alloy employed in this study exhibited rather preferred orientation because of its lamellar structure. Two approaches were adopted to the measurement for TiAl(311) plane by using Cr-Kα characteristic radiation and a position sensitive proportional counter (PSPC): an oscillation method and a method utilizing only two {311} reflections that belong to one zone axis.
The results obtained are summarized as follows:
(1) The measurement with the oscillation method resulted in the X-ray stress constant, K=-383MPa/deg, and X-ray elastic constant, E_x/(1+ν_x)=129GPa or E_x=166GPa.
(2) The X-ray value of E_x in TiAl phase was intermediate between the mechanical values of Young's modulus of the present material and Ti-50mol% Al consisting of almost TiAl single phase reported by R.E. Schafrik.
(3) The X-ray stress constant determined by the latter method was -347MPa/deg and agreed nearly with that obtained by the former method.
(4) The non-linearity observed in sin²ψ diagram was caused by X-ray optics of the fixed ψ₀ method. The oscillation method by using PSPC was, however, considered to be able to provide the reliable approximate values of K and E_x by reason of above (1) and (2).

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It is well known that strength of rock decreases with moisture content. However, very limited data are available concerning the effect of moisture on time-dependent behaviour of rock. Therefore, a series of uniaxial compression creep tests were carried out under air-dried and water-saturated conditions. It was found that;
(1) Life time is proportional to exp {δ(σ_F-σ_c)}, where δ is a material constant and does not depend on moisture content.
(2) Primary creep follows the logarithmic creep law under both air-dried and water-saturated conditions.
(3) In the tertiary creep region, the strain rate under both conditions is inversely proportional to residual life.
In a recent paper, authors proposed a constitutive equation based on the uniaxial compression tests under various strain rates. In this study, creep tests were numerically simulated by the proposed constitutive equation. The results of computer simulation reveal that the constitutive equation can be applied not only to constant strain rate tests but also creep tests. For example, the calculated creep strain-rate vs. elapsed time curve coincides well with the experimental one.

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Identification of creep damage variable D of continuum damage theory from the metallographical A-parameter is discussed. By preforming a stochastic analysis, A-parameter defined as the observed fraction of cavitated grain boundaries on the observation plane was first related to the cavity area fraction on the gain boundary facet planes. Based on the results of this analysis, the cavitation damage states of some engineering alloys were estimated by use of data of the measured A-parameter. Finally, according to the usual interpretation of the damage variable D, specific D-A relations were derived. The validity and the utility of the proposed D-A relations were discussed based on the test results of an engineering alloy.

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This paper discusses the mechanism of matrix cracking evolution in crossply composite laminates. The evolution of matrix cracking cannot be understood by the notion of ‘strength’ of cracking ply, since matrix cracks are sequentially formed above the stress level of the strength of cracking ply. By assuming that the ply has inherently a distribution of defects which act as the nucleation sites of matrix cracks, the cracking mechanism is discussed. This mechanism can explain the behavior of the averaged maximum stress in the whole stage of evolution. A simple numerical simulation is performed in order to visualize the cracking behavior and the change in stress due to cracking.

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In order to evaluate the notch fatigue strength and notch sensitivity of aluminum-lithium alloys, 2090 and 8090, rotating bending fatigue tests have been carried out using circumferential notched specimens with different stress concentration factors. The results obtained were compared with those of conventional aluminum alloys, 2024-T4 and 7075-T6511. It was found that aluminum-lithium alloys showed superior notch fatigue strength to conventional aluminum alloys. The notch sensitivities for crack initiation limit of aluminum-lithium alloys were lower than those of 7075-T6511, while they were nearly equal to those of 2024-T4 for blunt notches, but tended to become lower with further increase of the sharpness of notch. The notch sensitivities for crack propagation limit were also lower in aluminum-lithium alloys, in particular 8090 alloy, than in conventional aluminum alloys. It was suggested that the decreased notch sensitivities of aluminum-lithium alloys were attributed to crack propagation mode and high propagation resistance related to their microstructures.

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The aim of this work was to investigate the effects of lamination of TiN and Ti₂N and prefatigue damage on the fatigue crack nucleation and fatigue life of the steel modified by a dynamic mixing method. The fatigue tests were performed on two types of specimens with or without coating a Titanium film between the laminating film and the steel substrate. The specimens were prefatigued up to 30% and 50% of the fatigue life of substrate. At high stress levels, the laminated films scarcely affected the fatigue life. As the stress level decreased to 250MPa, the fatigue life was improved by laminating the films. Particularly, a thin Ti film between the laminated film and the substrate shorten the fatigue life. The fatigue limit of the laminated specimens increased about 25% more than that of the substrate. The prefatigue damage resulted in a decrease in fatigue life for the laminated specimens. The fatigue crack initiation process depended on the stress range. At high stress levels, cracks nucleated from the film surface. As the stress level decreased, the crack initiation occurred from the interface between the film and the substrate. This change in crack initiation process strongly contributes to the improvement of fatigue life by laminating the films.

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Thermal shock tests of SUS304 stainless steel subjected to local, instantaneous and repeated laser heating shocks were carried out to investigate the thermal resistivity and damage of the material. A Nd: YAG pulse laser with the maximum power of 50 J/1 pps was employed as a heating source. The heating damages and microstructures of the heated surface and interior were analyzed with scanning electron micrographs. The experimental results showed the appearance of various damage patterns, depending upon the incident heating energy strength and repeated number. High strength heating shocks induced large-sized internal damages, while low strength and repeated heating shocks induced an interface region between the phase transformation area the base SUS304 stainless steel. This region consists of many microcracks or low strength slender microstructures. These results suggest that the internal damages deserve more attention from the view point of material strength.

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Fatigue small crack growth behavior was studied in three kinds of Ni-base superalloys at high temperature and was compared with the physically long crack behavior; a single crystal alloy, CMSX-2, a directionally-solidified alloy, CM247LC-DS and a polycrystalline alloy, CM247LC-CC. The crack opening-closing behavior was also measured by means of a new device originally developed and improved. The experimental results indicated that the small cracks exhibited a higher growth rate than the long cracks at the same stress intensity factor range in all of the materials. However, the rates of small crack growth in the CMSX-2 and CM247LC-DS agreed with those of the long crack, when they were correlated with the effective stress intensity factor. This shows that the crack opening-closing effect is mainly responsible for difference of small and long crack growth rates. In contrast to these two materias, the lack of similitude between small and long crack propagation rates was still found in CM247LC-CC, even if the crack closure effect was taken into account.

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Tensile tests were carried out on SUS304 Stainless steel single crystals, whose respective tensile axes were parallel to [001], [111] and 0.5 in Schmid factor, under cathodic charging in 0.5kmol/m³ H₂SO₄ solution with a small amount of NaAsO₂ at room temperature, and the characterristics of hydrogen embrittlement of this material in tension were evaluated from the nominal stress-strain curve.
The susceptibility to hydrogen embrittlement appeared prominently in the elongation and fracture morphology. The elongation decreased with increasing current density and the resulting fracture surface morphology changed from ductile to cleavage manner. The cracks produced by hydrogen initiated at the deformation bands and propagated perpendicular to the tensile axis, then connected each other and fractured.
The orientation dependence of hydrogen embrittlement was recognized on the fracture morphology when the current density was between 4 to 10A/m². The morphology of fracture surface under the present test condition was dependent on both amount of martensite induced by deformation and the concentration of hydrogen.

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The susceptibility to potential-free and potential-controlled stress corrosion cracking (SCC) of SUS304 steel has been investigated in various MgCl₂ solutions under two stress conditions.
The threshold concentration for SCC occurrence under the constant load condition was about 37%, above which the susceptibility to SCC had a maximum at 42%. Such a tendency, however, did not appear under the slow strain rate condition. The cracking susceptibility also decreased with decreasing temperature of MgCl₂ solution, regardless of stress conditions. The critical potentials of SCC under the constant load and slow strain rate conditions were about -320mV and -360mV, respectively. Following each of SCC ranges, the uneven general corrosion occurred as the potential was shifted to more noble values. The transgranular fracture was susceptible to the larger concentration, higher temperature and noble potential conditions, and changed gradually to intergranular fracture. The corroded regions (e.g., pitting, corrosion groove and others) were found by AES and EDX analysis to be almost depleted of iron and nickel, and highly enriched in chromium and magnesium of which both phases were most likely oxides, In the stressed specimens, therefore, it is supposed that chloride ions penetrate the oxide cracks at the early stage of SCC. In addition, it is important for the potential-free SCC tests under the slow strain rate condition to choose a solution in which the peak corrosion potential has a value about equal to that under the constant load condition, i.e., the use of lower MgCl₂ concentration.

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In order to clarify the influence of plasma-sprayed coating on the corrosion fatigue strength of 13Cr stainless steel, WC-Co, ZrO₂, Cr₃C₂ and Co-Cr-Ni-W were plasma-sprayed on round bar fatigue test specimens of 13Cr stainless steel. The surface, the cross section of these coatings and the interface between these coatings and base metal were examined by SEM and optical microscope. Rotating corrosion fatigue tests of these coated specimens were conducted in 3% NaCl aqueous solution at a testing speed of 3600rpm.
The WC-Co and ZrO₂ coatings with low porosity improved corrosion fatigue strength at 10⁷ cycles by about 70 percent. It might be concluded that the effective coating to improve corrosion fatigue strength should be of very low porosity and firmly adhesive to the base metal.
On the other hand, no improvement of corrosion fatigue strength was observed by the Cr₃C₂ and Co-Cr-Ni-W coatings with relatively high porosity. In these specimens, corrosion fatigue cracks initiated from corrosion pits at the surface of the base metal and propagated predominantly through the intergranular path.

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In order to clarify the effect of thermal-sprayed (WC-Cr-Ni) cermet coating on the corrosion fatigue strength of high strength SKD11 steel, rotating bending corrosion fatigue tests were conducted in a 2 mass% ZnSO₄ aqueous solution environment. It was found that the corrosion fatigue strength of the (WC-Cr-Ni) cermet thermal-sprayed specimen with 100μm thickness was 318.6MPa at 2×10⁷ cycles in 2 mass% ZnSO₄ aqueous solution and was about three times larger than that of the SKD11 base metal at the same number of cycles. The effective thickness of the (WC-Cr-Ni) cermet thermal-sprayed coating to improve the corrosion fatigue strength of SKD11 steel was about 100μm. The principal cause of improvement of the corrosion fatigue strength of steel by thermal-sprayed (WC-Cr-Ni) cermet coating is the insulation of SKD11 steel surface from the permeation of ZnSO₄ aqueous soultion. Impregnation of fluorine-contained resin into the thermal-sprayed (WC-Cr-Ni) cermet was ineffective to improve the corrosion fatigue life of SKD11 steel at a high stress region. However, the corrosion fatigue strength at 2×10⁷ cycles was improved by about 22%. In the high stress region of S-N curves, the insulation effect was not enough due to an exfoliation of fluorine-contained resin from the thermal-sprayed (WC-Cr-Ni) cermet coating.
Corrosion fatigue crack initiated at a corrosion pit in the SKD11 base metal surface and propagated through the transcrystalline path.

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Electrical conductivity and mechanical tanδ of poly (alkyl methacrylate) (PRMA) composites filled with carbon black (CB) were measured as functions of CB content and temperature. The dispersion of CB particles was investigated by means of the optical photograph. The critical volume fraction V_c, at which the electrical conductivity increases rapidly, and the rate of electrical conductivity increase at the parcolation threshold differed depending upon the kind of matrix polymer. It was found that CB particles easily aggregated and formed the fine electro-conductive network in the composites with matrix polymers having lower surface tention and lower miscibility for CB particles, resulting in the higher rate of electrical conductivity increase at the threshold as well as the higher value of V_c. For the composites with polymers having the high T_g, the plasticizing effect appeared strongly owing to the presence of CB particles, so that T_g shifted to a lower temperature side as much as 25°C.

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