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金子 智徳, 宇治橋 貞幸
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発行日: 2006/09/15
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Impact tests of CFRP laminae are carried out, and impact load is measured. These load histories are transformed using discrete wavelet transform, and these results are compared to actual damage observed in tested specimens. The relationship between both is considered. Comparing damaged and non-damaged results together, case of the damaged laminae. This characteristic waveform may be observed beginning at the failure time. So it is suggested that impact damage of CFRP laminae can be evaluated using load history data transformed by discrete wavelet transform.
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片岡 保人
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A Material, which has zero or very small thermal expansion coefficient, is expected in parts for precision machines and optical instruments. An analytical model for a short fiber composite is developed to evaluate thermal expansion coefficients by applying the Eshelby's equivalent inclusion method to two kinds of inhomogeneities, i.e. fiber and filler. The effects of distributions of fiber-orientation, fiber-aspect ratios and volume fractions on thermal expansion coefficients are investigated. A carbon fiber/epoxy resin composite is estimated, and zero and very small thermal expansion coefficients are shown in case that fiber-aspect ratios are relatively large.
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松井 和己, 西谷 明之, 山田 貴博
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The nonlinear global-local analysis methods for the poling process of piezo-electoelastic materials, based on the mathematical homogenization method, are developed in this paper. The most of piezoelectoric ceramics are known to be polycrystalline structures in their micro-structure, in which each perovskite crystal or each domain has different direction of polarization. The macroscopic charging or loading switch the spontaneous polarizations in each crystalline structure, and this microscopic domain switch observed as hysteresis behavior or poling process from the macro-scale. In this study, the polycrystalline structures and switching phenomena are modeled as the microscopic structures in context of the multi-scale modeling, and the macroscopic nonlinear piezo-electoric properties affected by the microstructures are evaluated by using the homogenization method.
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上辻 靖智, 戸田 雄介, 小川 良太, 仲町 英治
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発行日: 2006/09/15
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In order to investigate on material testing of piezoelectric thin film fabricated on a substrate, the deformation behaviors under electric field have been analyzed by finite element method. The effect of thickness and length of the substrate was evaluated, and then displacement response was investigetd by changing the thickness of piezoelectric thin film and the radius of top electrode. The computational results indicated that the single-point displacement mesearing is effective for only thick substrate without deflection, and that there is no dependence of the specimen size if the radius of top electrode is over 100μm. On the other hand, the double-point displacement mesearing is available for not only thick but olso thin substrates. 100μm is the best radius of top electrode for evaluation of psedo-piezoelectric strain constant.
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上辻 靖智, 黄 輝心, 福田 経, 仲町 英治
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発行日: 2006/09/15
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A piezoelectric actuator for blood extraction pump in health monitoring system was developed. We devised the geometry of piezoelectric actuator with some slits, that allows the stretching and contracting deformation in in-plane direction to create large deflection in out-of-plane direction. The static behaviors under uniform electric field have been analyzed by finite element method. The computational results indicated that a bimorph actuator with cross slit under outside fixed condition is the most suitable for blood extraction pump. Abimorph actuator with cross slit l=4.0, w=0.5mm has been manufactured as an experiment. As a result, the developed actuator was proved to increase the deflection to 2.1 times at resonance frequency f=6460Hz.
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小田切 望, 水野 衛, 岡安 光博
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In the present paper, lead zirconate titanate (PZT) and lead zirconate piezoelectric ceramics were subjected to both high electric field (which is higher than the coercive electric field) with low frequency and low electric field with high frequency (which is the resonance frequency). After applying certain electric field systematically, resonance and anti-resonance frequencies and an electrostatic capacity were measured by means of an impedance analyzer, and an electromechanical coupling coefficient, a dielectric constant, a Young's modulus and a piezoelectric constant were evaluated from them. Then variation of the material properties in process of time was investigated experimentally, and the dependence of the variation of the properties on applied electric field was elucidated.
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進藤 裕英, 成田 史生, 堀口 勝三
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The theory of ferromagnetic elastic materials of multidomain structure is applied to develop a crack growth rate equation of a finite crack in a soft ferromagnetic material under Mode I tensile loading and uniform magnetic field. The plane strain and plane stress problems are considered. Dugdale's assumption regarding the plastic zone in metals is applied to estimate the effect of yield around the crack tip. The accumulated plastic displacement criterion is used for developing a solution for the crack growth rate. Numerical values of crack growth rate are obtained for a soft ferromagnetic strip with a single-edge crack and the results are displayed graphically. Crack growth rate tests are also conducted on nickel-iron soft magnetic materials with a single-edge cracked plate specimen geometry in the bore of a superconducting magnet, and a comparison is made between numerical results and experimental data.
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荒居 善雄, 土田 栄一郎, 尾笹 一成, 大橋 正音, Yuan-Hua Liang
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The location identification method of quantum dots (QDs) is described from view points of experiments which is nanoprobe elastic-indentation on photoluminescence (PL) of In_<0.5>Ga_<0.5>As/GaAs QDs and simulations. The large blue shifts in horizontal scan experiments, which were performed in a high vacuum, low temperature (10K) under an equal load, were non-linear for scan distance. The simulations are carried out based on finite element of axis symmetry and six-band strain Hamiltonian. We found the possibility that position of QDs could be decided by making the difference between scan experiment results and simulation results minimum. Consequently, most of QDs were observed the emission when these passed through near the edge of indenter, and it is found out that the luminescence was not observable under central part of indenter by comparison with a distribution of the valence band due to indentation.
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植松 美彦, 戸崎 康成, 戸梶 恵郎
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The effect of tool geometry on microstructure and static strength in friction stir spot welds of 6061 aluminium alloy sheets was studied. Tools with three different probe lengths were evaluated. The weld microstructures varied depending on probe length, tool rotational speed and tool holding time. Two particular aspects in the microstructures were identified: the thickness of the upper sheet under the shoulder indentation and the actual nugget size. The tensile shear strength increased with increasing probe length, while the cross tension strength was not affected significantly by probe length. Two fracture modes were observed in both tensile shear and cross tension tests. The dependence of static strength on probe length and the fracture mechanisms were discussed based on observation of the microstructures.
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矢島 大地, 中上 泰二郎, 猪股 渉, 小堀 孝史
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Bellows are accordion-shaped expansion joints that absorb the displacement of pipes. Bellows receive cyclic stress from the thermal expansion and contraction of pipes. The allowable number of cycles is indicated by Kellogg's expression and the S-N curve for design of JIS. However, it is not clear whether long-term used bellows are applicable to various S-N curves. Therefore, in this research, fatigue tests were performed on used bellows and new bellows, and a comparison with various S-N curves for design was made. As a result, it was confirmed that the durability of used bellows exceeds Kellogg's expression and closely approximates the S-N curve for design of JIS.
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加藤 活浩, 岡部 顕史, 冨岡 昇
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In this study, the method for calculating nominal structure stress of the spot-welded structures which authors developed was expanded, and the method to calculate nominal structure stress of the arc-welded structures was proposed. The finite element model of arc welding was made in order to obtain general loads and node displacements as a necessity for the nominal structure stress calculation. General loads and node displacements were well obtained in this model, and the excellent nominal structure stress was obtained as the result. Then, it was shown that the fatigue life prediction in the arc-welded structure was possible using this nominal structure stress.
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久保 文武, 岡部 顕史, 冨岡 昇
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発行日: 2006/09/15
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To improve the fatigue life prediction technology by CAE, authors proposed the new method to calculate an accurate nominal structural stress value of the spot welding. This method can calculate the nominal structural stress value by using the plate theory when displacements around the spot-welding are given as the boundary condition. However, about the structure spot-welded at corner of plate, the problem that some displacements around the spot-welding cannot be obtained is caused in this method. In this study, in order to solve this problem, the accuracy of the stress solution obtained by this method was studied using the structure to extend the plate.
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中村 昌弘, 冨岡 昇, 岡部 顕史, 早川 博高
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In this study, the theoretical analysis method of shearing force through the spot welding, stresses and deformations around the spot welding on irregular pitch spot welded box section beam which receives the torsion was proposed. In addition, bending-torsion finite element for the spot welded member was proposed using local warping got from the proposed method. Stress analysis and torsional rigidity analysis of adjacency spot welded member were carried out using these techniques. Stresses and torsional rigidity of adjacency spot welded member were clarified, while the effectiveness of this technique was shown by comparing with the results of experiment and finite element method.
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大宮 慎一, 藤井 秀樹, 真鍋 康夫, 藤川 隆男, 直井 利勝
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緒形 俊夫
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A simple testing method for mechanical properties evaluation under highly pressurized hydrogen gas was developed without using high-pressured gas chamber. Tensile properties of austenitic stainless steels, SUS 304, 304L, and 316L under 10MPa level hydrogen gas at low temperatures were obtained with this testing method and the hydrogen environmentl embrittlement for this steels was examined. Influences of highly pressurized hydrogen gas on the reduction of area at low temperatures were maximum around 200K and disappeared at 77K, which almost agreed to the reports so far and proves the effectiveness of this testing procedure.
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羽木 秀樹
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発行日: 2006/09/15
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We have investigated the entry of hydrogen into SUS304 stainless steel by cathodic polarization. The specimens of stainless steel sheets of 0.1mm thick were annealed at 800℃ in vacuum, and cathodically polarized at 100A/m^2 in 0.5kmol/m^3 H_2SO_4 solution containing of 5g/m^3 As_2O_3 at 25℃. Immediately after interruption of cathodic current, hydrogen analysis was done by the thermal desorption spectroscopy method. In the thermal spectrum of hydrogen evolution, two hydrogen evolution peaks (peak(1) and peak(2)) were observed near 40℃ and 250℃, irrespective of cathodic polarization time. These peaks became large with increase in cathodic polarization time, while change of a shape was not observed. Cathodic polarization time dependence of peak temperature and peak height of the hydrogen evolution peaks was investigated. The peak temperatures of peak(1) and peak(2) were almost constant, irrespective of cathodic polarization time, while the peak heights of them became large with increase in cathodic polarization time. These experimental results indicate that hydrogen is introduced into SUS304 stainless steel by cathodic polarization, and that there are two kinds of the potential energy of dissolved hydrogen.
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笛田 宗広, 久保田 祐信, 栄 中, 近藤 良之
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発行日: 2006/09/15
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Absorption of hydrogen into the material might be occurred during long-term operation when the hydrogen utilization machines are used in the high-pressurized hydrogen gas. Therefore, investigation of fatigue strength properties of hydrogen charged materials is important. And the effect of hydrogen on fatigue strength might be different depending on the material hardness. In this study, highly work-hardened stainless steel SUS304 was used for fatigue test. Micro fatigue crack, which depth was 25μm was introduced to the fatigue specimen as initial defect. And smooth specimen was also used. Hydrogen charge was done by cathodic charge method before fatigue test. Fatigue strength of pre-cracked specimen was significantly reduced by hydrogen pre-charge. Crack propagation rate was increased and ΔK_<th> shows a trend to reduce. There was little effect of hydrogen pre-charge on fatigue strength of the smooth specimen.
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箕島 弘二, 菅田 淳, 中谷 正憲, 崎原 雅之
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Slow strain rate tests (SSRT) and fatigue tests were conducted to investigate the influence of internal hydrogen state on the quasi static SSRT strength and fatigue strength for cold drawn eutectoid steel specimens which were cathodically hydrogen charged. Internal hydrogen states were changed as follows: (a) non-charged sample, (b) the sample that contained both diffusive and non-diffusive hydrogen, and (c) the one that contained only non-diffusive hydrogen. The results of SSRT indicated that only the diffusive hydrogen caused hydrogen embrittlement under the quasi-static loading condition. S-N curves had a large scatter and the influence of non-diffusive hydrogen on the fatigue strength was unclear, because the fatigue crack was initiated at internal inclusion. Therefore, the fatigue strength was discussed based on the stress intensity factor, ΔK_<inc>, calculated from stress and inclusion size. ΔK_<inc>, giving the same N_f decreased in the order of the non-charged specimen, only non-diffusive hydrogen charged specimen and the specimen having both diffusive and non-diffusive hydrogen, indicating that non-diffusive hydrogen caused a decrease in fatigue strength.
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津曲 隆行, 宇山 英幸, 峯 洋二, 村上 敬宜
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発行日: 2006/09/15
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The effects of hydrogen on the near threshold fatigue crack growth behavior was studied on a high-strength steel SCM435. The crack growth rate of hydrogen-charged specimens was faster than that of uncharged specimens. Hydrogen decreased threshold stress intensity factor range ΔK_<th> in specimens with low residual stress. However, there was no clear difference in ΔK_<th> between the hydrogen-charged specimen and uncharged the specimen with high residual stress. The fracture surface near ΔK_<th> of hydrogen-charged specimen with low residual stress was flatter than that of uncharged specimen with that. The crack in the hydrogen-charged specimen was thinner than that in the uncharged specimen. The crack in the hydrogen-charged specimen was less zigzag. Transgranular fracture caused by fatigue was dominant and intergranular fracture was little in specimens with low residual stress. It is presumed that the effects of hydrogen is related to crack closure and plastic deformation of the crack tip.
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田中 裕之, 本間 紳浩, 松岡 三郎, 村上 敬宜
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Low cycle fatigue tests on SCM435 steel tempered at 580℃ were carried out under the frequencies of 0.2, 2 and 20Hz with specimens containing a small artificial hole. The fatigue life of the hydrogen charged specimens decreased in comparison with the uncharged specimens. The acceleration of fatigue crack growth rate was observed at ΔK<40MPa√<minf=20Hz>, ΔK<60MPa√<minf=2Hz> and ΔK<100MPa√<minf=0.2Hz>. Facets were formed on the fracture surface of hydrogen charged specimens in the ΔK region where the crack growth rate was accelerated. Many slip bands were observed at the crack tip of the uncharged specimens. On the other hand, slip bands were not clear the hydrogen-charged specimens.
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西口 廣志, 本田 淳, 福島 良博, 松岡 三郎, 村上 敬宜, 松本 和博
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The effects of hydrogen on Charpy impact properties of JIS-SGP carbon steel pipe for hydrogen pipelines were investigated. The brittle-ductile transition temperature was not changed by hydrogen charge. The Charpy impact values above the brittle-ductile transition temperature were decreased 20〜40J/cm^2 by the effect of hydrogen. The brittle fracture area of hydrogen-charged specimens was smaller than that of uncharged specimens. The elongated dimple area near the notch of hydrogen-charged specimens was larger than that of uncharged specimens. It is presumed that, the basic mechanism of so-called hydrogen embrittlement was produced by the enhancement of localized plasticity rather than lattice decohesion.
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村上 憲一, 楢崎 千尋, 峯 洋二, 松岡 三郎, 村上 敬宜
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Hydrogen penetration properties of austenitic stainless steels, SUS304, SUS316L and SUS310S pre-strained and exposed to high pressure hydrogen was investigated. In SUS304, hydrogen penetrated more deeply with the increase of strain-induced martensite phase. In SUS316L and SUS310S where the amount of martensite didn't increase with pre-strain in this study, it raised hydrogen content but hardly influenced the diffusion of hydrogen. In the hydrogen-charged specimens of SUS304, the fatigue crack growth rate was accelerated. The acceleration was larger in the pre-strained SUS304 than in the SUS304 which was free from pre-strain. The crack in the hydrogen-charged specimens were less zigzag than in the uncharged specimens. The fracture surfaces in the hydrogen-charged specimens had flat areas. These are considered to be caused by slip localization.
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尾田 安司, 浦松 剛, 野口 博司
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In order to investigate the effect of hydrogen environment on fatigue crack growth characteristics of a low carbon steel JIS S1OC, fatigue crack growth tests were conducted in a low pressure hydrogen gas environment Fatigue crack growth rate in hydrogen gas is higher than that in nitrogen gas. It seems that a crack in the range of low growth rate prefers to propagate along the grain boundaries under hydrogen environment, while in the range of high growth rate across the grains accompanied by brittle striation patterns or river patterns. It seems important to clarify how hydrogen affects the crack growth behavior of different stages of crack growth.
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河本 恭平, 尾田 安司, 野口 博司, 東田 賢二
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In order to investigate whether hydrogen enhance the fatigue crack growth (FCG) rate of stable austenitic stainless steels or not, FCG tests of a type 310 steel were performed in a hydrogen gas environment and in a nitrogen gas environment. The FCG rate tested at 5.0Hz in hydrogen is higher than that in nitrogen. It seems that the acceleration of FCG rate in hydrogen does not necessarily need the formation of strain-induced α' martensite, though it increases the degree of the acceleration. The cause of the acceleration of type 310 seems to be hydrogen enhanced concentration of slip at a crack tip. The degree of the acceleration became smaller in a frequency of 0.1Hz. It seems that the generation of heat at the crack tip concern. Further investigation is necessary.
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萩原 聡佳, 尾田 安司, 野口 博司
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In order to investigate the effects of hydrogen on the fatigue crack growth characteristics of friction stir welded (FSW) joints of A6061-T6 aluminum alloy, bending fatigue tests were conducted on the specimen with a small blind hole in a low pressure hydrogen gas environment. A crack was in-situ monitored using a scanning laser microscope. The fatigue crack growth life of an FSW joint in hydrogen gas is about one half of that in nitrogen gas. And the fatigue crack growth rate of an FSW joint specimen is enhanced by hydrogen in earlier stage of crack growth than that of the parent material specimen.
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松野 浩之, 青木 雄太, 萩原 聡佳, 尾田 安司, 野口 博司
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In order to investigate the effect of hydrogen on the fatigue strength and the crack propagation behavior of an austenitic stainless steel JIS SUS304, bending fatigue tests were carried out on specimens with small twin holes in a low pressure hydrogen gas. Fatigue process was in-situ observed using a scanning laser microscope. Non-propagation phenomena of a crack from holes are observed not only in air also in hydrogen. Fatigue limit in hydrogen gas is rather higher than that in air and fatigue crack growth rate near fatigue limit in hydrogen gas is lower than that in argon gas and in air in spite that hydrogen gas enhance the crack growth rate in high stress intensity range. These phenomena are discussed through crack closure.
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田中 康博, 久保田 祐信, 栄 中, 近藤 良之
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The effect of hydrogen gas environment on fretting fatigue strength was investigated. The materials were low alloy steel SCM435H and precipitation hardened stainless steel SUH660, which will be used for hydrogen utilization machines. And the effectiveness of nitriding in hydrogen gas environment was also examined. Hydrogen gas pressure was 0.12MPa in absolute pressure. Fretting fatigue strength of both materials in hydrogen gas was slightly increased than in air. However, in SUH660, fretting fatigue strength in hydrogen gas was decreased than that in air in long-life region. Failure of specimen was caused at approximately 20% lower stress amplitude compared with fretting fatigue limit in air defined as at 3×10^7 cycles. Improvement of fretting fatigue strength by nitriding in hydrogen gas environment was at the same level as that obtained in air.
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武富 紳也, 横堀 壽光
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Transgranular facet like brittle fracture for ductile materials under corrosive conditions is caused by the typical pile-up of dislocations. It was found that the mechanical interaction between dislocations and hydrogen induces the typical pile-up of dislocations. Therefore, the analysis of interaction between dislocations and hydrogen under cyclic loading condition was conducted to investigate the distribution behavior of dislocations under corrosion fatigue conditions. In this analysis, the effect of applied stress wave forms on distribution and pile-up behavior of dislocations was investigated. Furthermore, concerning the concentration of dislocations at the site of hydrogen atom, dislocation pile-up intensity factor A was defined. The effect of stress wave form on ΔA was found to concern the feasibility of the occurrence of facet like fracture. Based on the concept of ΔA, the facet like fracture is found to be promoted under Fast-Slow stress wave form condition.
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池田 淳, 大崎 修平, 木下 勝之, 一谷 幸司, 竹島 義雄, 佐々木 侑慥
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In order to evaluate the susceptibility to hydrogen embrittlement(HE) of aluminum alloys 6061-T6 and 7075-T6 as candidate materials for high pressure-hydrogen container liner, SSRT (slow strain-rate technique) tests under wet air with 90% relative humidity have been carried out in a range of strain rate 3.47×10^<-7>〜1.39×10^<-5>/s by using smooth-and notched-plate specimens. 7075-T6 showed a significant susceptibility to HE, resulting in intergranular fracture, while in contrast, 6061-T6 exhibited a superior resistance, accompanying rather a trend to enhanced plasticity. Difference in form of crack extension between smooth-and notched-specimens of 7075-T6 was found. The observation supports the HE process includes both effects of plastic deformation and hydrostatic stress gradient on hydrogen transport.
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永田 晃市, 福島 良博, 松岡 三郎, 村上 敬宜
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The effect of hydrogen on fracture toughness of PZT for the ultrasonic hydrogen flow sensor was investigated by micro-indentation method. PZT specimens were charged with hydrogen gas at 1.0MPa and 303K for 70 hours. No hydrogen was detected in both hydrogen-charged specimens and uncharged specimens. In consequence, there were no definite differences in indentation crack lengths and fracture toughness Kic even after hydrogen-charge. During the loading process, indentation cracks were initiated and propagated only in a plane perpendicular to sensor's vibration axe. These cracks increased in length during the unloading process as well. The residual tensile stress, which probably affected the indentation crack formation, was generated during the unloading process. K_<IC> of PZT in the maximum tensile stress direction was evaluated as 0.55MPa・m^<1/2> by using Niihara's evaluation formula. Three-dimensional shape of cracks and plastic zone beneath the indentation were observed by serial sectioning method.
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宇都宮 登雄, 新井 象午, 八幡 真純, 渡辺 勝彦
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発行日: 2006/09/15
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Storage tanks and pipelines for transporting gaseous fuel are considered to be use in low temperature environment. In the materials used for those infrastructures, cryogenic brittlement and hydrogen brittlement are possible to occur one upon another. In this study, fracture experiments for hydrogen charged materials of COR-TEN O steel and its welded material were carried out over the temperature range from -196℃ to room temperature. Through the experimental results, brittle-ductile transition behavior was observed with the increase of temperature in addition to the fracture mode change from mode I (opening) type to mode II (in-plane shearing) type. It was shown that, for the hydrogen charged materials, a dramatic increase of fracture resistance occurs by brittle-ductile transition.
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本間 紳浩, 田中 裕之, 福島 良博, 松岡 三郎, 村上 敬宜
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発行日: 2006/09/15
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We investigated the effect of hydrogen on tensile properties of SCM435 steel used for hydrogen storage cylinders. The two types of tensile specimens in the longitudinal and transverse directions were machined out from the SCM435 steel cylinder. The specimens were immersed in an aqueous solution of NH_4SCN and then charged with hydrogen. The hydrogen content in hydrogen-charged specimens was 0.14ppm and 0.93ppm. The tensile strength of hydrogen-charged and uncharged specimens was 930MPa. Increase in hydrogen content reduced the reduction of area from 72% to 44% for longitudinal specimens and from 63% to 44% for transverse specimens. The observation of fracture surfaces suggested that the mechanism of the hydrogen embrittlement was based on the hydrogen enhanced localized plasticity rather than the lattice decohesion.
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遠藤 春男, 大瀧 直樹, 樋渡 洋一郎, 星宮 務
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発行日: 2006/09/15
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Nondestructive testing (NDT) of tilted surface defect with wedge shape using Photoacoustic microscope (PAM) has been demonstrated. The specimens used in the experiments were pure aluminum plates. The tilted surface defect considered was a slit-type simulated defect with a wedge shape, whose length and maximum depth were fixed to be approximately 3.0mm and 0.3mm, respectively. The tilting surface defect with a width of 0.3mm was introduced into the specimen by mechanical processing. The angles (θ) of the surface defect were 60, 70, 80, and 90 degrees. The obtained signal distributions depend strongly upon the tilt angle and wedge shape of the defects. Furthermore, it was shown that the estimation of the complicated surface defect shape was plausible with this method.
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福田 勝己, 澤田 崇, 伊藤 拓嗣, 小林 光男, 鈴木 健司, 堤 博貴
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発行日: 2006/09/15
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It is important that make clear to materials property. In this study, with three Indentation Fracture method suggested in JIS, we evaluate brittleness materials. We suggest a new equation by Nnanoindentation method. And I inspect of the evaluation method that I suggested by comparing it with a conventional evaluation method. In this study, we use Sillicon (Miller index 100) for specimen, used Vickers Indentation and Berkovich Indentation.
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阪上 隆英, 西村 隆, 山口 直希, 久保 司郎, 高田 佳彦
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発行日: 2006/09/15
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In the conventional lock-in infrared thermography for thermoelastic stress measurement, thermoelastic temperature change is correlated with external reference loading signal. The present authors developed a self-reference lock-in thermography which enabled us to conduct thermoelastic temperature measurement without external reference signal. In the self-reference lock-in thermography, reference signal is constructed from a part of the same sequential thermal image data. Temperature change in a region of interest was correlated with that in a remote area for reference signal construction. Proposed self-reference lock-in thermography was applied for crack identification based on the detection of significant thermoelastic temperature change due to the stress singularity in.the vicinity of crack tips. In this study, the feasibility of the proposed technique was demonstrated for the fatigue crack detection and measurement in actual steel bridges.
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佐藤 大輔, 込山 貴仁, 阪上 隆英, 久保 司郎
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発行日: 2006/09/15
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We had applied infrared thermography to inspection of concrete structures, for preventing them from the falling accident of concrete fragment. However, the thermographic NDT has a shortcoming that the measurement results are affected by atmospheric radiation due to the sunlight, sky or surrounding materials. To reduce the influence of these disturbance noises, the infrared thermography with detectable wavelength from 5 to 8μm, which coincides with absorption range of moisture, is utilized. In this research, a new infrared thermography with 5 to 8μm wavelength range by applying a band pass filter and an uncooled microbolometer infrared array detector.
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豊貞 雅宏, 後藤 浩二
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発行日: 2006/09/15
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Two important concepts, which are "Equivalent Distributed Stress" and "Representative Surface Crack", for applying FLARP to the fatigue crack initiation and growth simulation are introduced in this paper. Equivalent distributed stress corresponds to the distributed stress in an infinite plane with a straight crack for which the relationship between the crack length and the stress intensity factor is the same as in the considered cracked body. The stress is proposed in order to prevent the numerical simulation of crack opening/closing for a surface crack. Representative surface crack corresponds to the single surface crack replacing plural surface cracks generated at the sound stress concentration site. This concept is introduced in order to prevent direct crack growth simulation for plural cracks.
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豊貞 雅宏, 小沼 恵太郎, 田 鵬程, 後藤 浩二
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発行日: 2006/09/15
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In order to define the plastic constraint factor(λ) for fatigue crack which initiate from notch root, crack opening/closing model based on the extended Dugdale's cohesive force model is shown. With this model, fictitious COD is calculated for half circler notch and half ellipse notch. From comparison of these fictitious COD and integrated value of plastic strain which are calculated by non-linear FEM analysis, when λ=1.11, these values present high consistency and fictitious COD can be characterized as integrated value of plastic strain (inherent displacement).
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堤 成一郎, 豊貞 雅宏
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発行日: 2006/09/15
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The deformation behaviour of structures under cyclic loading condition is simulated by using FE analysis in which a cyclic plasticity model, so-called a subloading surface model, is incorporated. The adopted cyclic plasticity model is categorized in the framework of unconventional plasticity models premising that the interior of the yield surface is not a purely elastic domain. In this study, several examples of FEM analysis on the cyclic deformation behaviour are presented to show the potential of the developed FEM program and the incorporated cyclic plasticity model.
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杉谷 大輔, 村上 幸治, 後藤 浩二, 豊貞 雅宏
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発行日: 2006/09/15
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Validity of the fatigue crack growth model in the first grain boundary adjacent notch root, which corresponds to the fatigue crack nucleation region, proposed by some of authors are investigated by comparing in-situ observed results by applying servo hydraulic fatigue test machine with scanning electric microscope (SEM). Besides, fatigue crack growth curves in the first grain boundary are measured and compared with the estimation results by the numerical simulation code FLARP into which the model is implemented. It is confirmed the validity of the proposed model and FLARP enables to estimate the fatigue crack growth curve in the first grain boundary.
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後藤 浩二, 永田 幸伸, 豊貞 雅宏
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発行日: 2006/09/15
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In welded structures, fatigue cracks usually initiate from the welded toe and propagate to the plate thickness direction in the cross section. Stress distributions along the crack path are required in order to estimate the precise fatigue life prediction by using fracture mechanics. But stress distributions along the path are not obtained in practical structural design because the shell elements are used in finite element analyses at the design stage. A simple estimation method of the stress distribution normal to cross section at weld toe, which corresponds to the fatigue crack path in case that cracks grow from a weld toe, is proposed in this paper. Input data for this estimation are calculation results of FEM with shell element and geometrical conditions (radius, flank angle of toe and plate thickness). The validity of this method is confirmed by comparing estimation results with ones by finite element analyses with fine solid elements.
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島貫 広志, 野瀬 哲郎
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発行日: 2006/09/15
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This paper shows the analysis result of the effect of the stress ratio on the fatigue crack growth behavior using RPG load based on the comparison between the FE-analysis results and estimation results by FLARP system. Crack opening stress during fatigue crack is growing, independent of stress ratio, but the increase in plastic strain at the re-plastic zone depends on the stress ratio. The re-plastic zone size is almost same as the size of re-compressive plastic zone.
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誉田 登, 川畑 友弥, 久保 諭, 鈴木 秀一, 勝田 順一
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発行日: 2006/09/15
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河角 省治, 楠葉 貞治
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発行日: 2006/09/15
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Fatigue life estimation system for the fatigue crack growth numerical simulation code FLARP is under development. In order to offer the easy to use system for engineer, it is important to link with general-purpose FEM code. In the fatigue life estimation by FLARP, an equivalent distributed stress must be calculated and input to FLARP. In this paper, concept of the system and overview of the functions are introduced.
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角 洋一
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セッションID: 3532
発行日: 2006/09/15
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In welded plate structures, fatigue cracks may initiate at the intersection between the flange of a longitudinal stiffeners and the web stiffener attached to a transverse girders. In the present paper, a simulation program has been developed for multiple cracks propagating in a 3-dimensional plate structure. It can predict fatigue crack remaining lives and paths taking into account the interaction of multiple cracks, load shedding during crack propagation and welding residual stress. It is found that the crack propagation behavior may significantly change depending on the loading conditions, structural details and residual stress distributions.
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毛利 雅志, 角 洋一, 浅野 隆
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発行日: 2006/09/15
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Fatigue Cracks may initiate and propagate due to repeated load in welded structures. To maintain the fitness for the structure, we had developed system in prediction fatigue crack path, named CP-SYSTEM, which can make use of the FEM model for structural design. Further we have combined FLARP with CP-SYSTEM to improve accuracy of fatigue crack propagation life estimation. FLARP is able to simulate behavior of crack opening and closing and obtain parameter ΔK_<RP> correspond to repeated plastic deformation at the crack tip. To investigate applicability of the modified system, the predicted crack propagation lives are compared with experimental result of fatigue test of welded structure.
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大川 鉄平, 角 洋一
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発行日: 2006/09/15
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A new crack opening/closing simulation method is developed utilizing the crack tip stress field parameters evaluated by FEM. By combining this method and the CP-System, the growth behavior of fatigue cracks can be computed for large-scale structures under variable amplitude loading. In order to demonstrate the usefulness of the developed program, fatigue crack propagation in a ship structure is computed under realistic wave load sequence.
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楠葉 貞治, 勝田 順一
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セッションID: 3535
発行日: 2006/09/15
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In many cases, the fatigue crack initiates at the weld toe and propagate to plate thickness direction. To secure the structural integrity, it is important to estimate the crack initiation life and crack propagation rate. Fatigue tests on bead-on-plate welded specimen were carried out to investigate the crack initiation and propagation behavior. For predicting fatigue crack initiation and propagation, numerical simulation code "FLARP" based on ΔK_<RPG> was developed by Toyosada et al. In this paper, numerical simulations on fatigue tests are performed to verify the validity of numerical methodology of FLARP. It is confirmed that crack initiation life and propagation rate estimated by FLARP agree well with experimental results.
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西村 基, 丸山 和士
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発行日: 2006/09/15
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It is important to predict the entire fatigue life of a structure from its initiation until fracture. Toyosada et al. have developed a simulation program called FLARP which enables analysis of the complete fatigue life utilizing a newly defined stress intensity factor ΔK_<RPG>. In this report, the effectiveness of FLARP is studied. Fatigue tests of a steel plate with a center hole were conducted to examine its reliability. The results show that the experimental results and calculated simulation results agree appreciably with each other.
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福岡 哲二, 武村 理弘
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発行日: 2006/09/15
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Fatigue crack initiation and propagation analysis by "FLARP" developed by Toyosada has been applied to the fatigue test results of cruciform-welded joint with K-butt welds of 355 N/mm^2 class steel. As input data for FLARP analysis, the relation of stress intensity factors to crack depths was calculated by using influence coefficients for a semi-elliptical surface crack in flat plate by Shiratori and stress distribution calculated by FE analysis in the section including weld toe from which a crack occurred.
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