共查询到20条相似文献,搜索用时 31 毫秒
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Tomas Månsson 《International Journal of Cast Metals Research》2013,26(6):373-378
An engineering method based on fracture mechanics is suggested for life predictions of components of nodular cast iron. The method should be applicable to any structure containing defects which can cause crack initiation. Component testing was performed and the observed results were compared with model predictions. Fatigue crack growth data were obtained by testing on CT specimens even for load ratios R < 0. By accounting for crack closure the R-effect on the growth rates can also be effectively eliminated for this type of material. 相似文献
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V. M. A. Leitao M. H. Aliabadi D. P. Rooke R. Cook 《Journal of Materials Engineering and Performance》1998,7(3):352-360
Two boundary element methods of simulating crack growth in the presence of residual stress fields are presented, and the results
are compared to experimental measurements. The first method utilizes linear elastic fracture mechanics (LEFM) and superimposes
the solutions due to the applied load and the residual stress field. In this method, the residual stress fields are obtained
from an elastoplastic BEM analysis, and numerical weight functions are used to obtain the stress intensity factors due to
the fatigue loading. The second method presented is an elastoplastic fracture mechanics (EPFM) approach for crack growth simulation.
A nonlinear J-integral is used in the fatigue life calculations. The methods are shown to agree well with experimental measurements
of crack growth in prestressed open hole specimens. Results are also presented for the case where the prestress is applied
to specimens that have been precracked. 相似文献
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通过试验和3D有限元模拟相结合的方法分析了焊接热模拟X80管线钢在不同温度(-90,-60,-30和0℃)下的断裂韧度.文中选取标准三点弯曲试样在不同温度下进行断裂韧度测试,同时对测试件进行三维有限元实体建模与分析计算.结果表明,X80管线钢的断裂韧性随温度减低显著减小,并使其倾向于脆性断裂.材料在不同温度下的真实应力-应变曲线行为从光滑拉伸到断裂力学试样具有良好的可传递性,温度对材料的硬化行为没有明显影响,有限元计算的结果表明,应用该方法可以准确地计算X80钢焊接热影响区不同温度下的CTOD值. 相似文献
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以AZ31镁合金的强力旋压成形工艺为例,通过6道次旋压成形获得镁合金筒形件,对其各道次组织演变规律及筒坯的微纳力学性能进行了分析。原始筒坯壁厚为10mm经6道次强力旋压成形,获得了壁厚为1mm的成形良好、无鼓包等缺陷的镁合金筒形件;采用金相显微镜对各道次的筒坯试样的显微组织进行分析,结果表明:组织由原始粗大的、不均匀组织逐步转变为以孪晶为主、细小的均匀的组织;采用G200微纳力学测试系统对各道次的镁筒坯试样进行纳米压痕测试分析,结果表明:镁合金筒坯硬度随着旋压道次的增加而提高,原始镁合金筒坯硬度为0.377GPa,6道次旋压后镁合金筒坯的硬度为1.053GPa,提高约2.8倍,而旋压前后模量值保持基本不变;采用万能试验机对旋压成形的筒形件进行拉伸试验并对其断口进行SEM分析,结果表明:旋压前后的镁合金筒坯断口均呈现塑性断裂,但是原始镁合金断口中韧窝大而深,经多道次旋压后的断口中韧窝小而浅。 相似文献
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Mohammad Mobin 《Journal of Materials Engineering and Performance》2010,19(2):257-263
This study deals with the investigations concerning with the suitability of coated steel piping system as an economically
viable alternative to costly stainless steel piping for high pressure seawater reverse osmosis (SWRO) application. The piping
system selected for investigation is a carbon steel piping coated internally and externally with thermoplastic coating (coating
powder Plascoat PPA 571). The performance of thermoplastic coating was investigated by conducting SWRO pilot plant test, salt
spray test, mechanical tests and testing of the coating under crevices (both in pilot plant and laboratory), and for leachable
organics and inorganics (both in laboratory and pilot plant test). The testing of coating in the pilot plant resulted in the
formation of some blisters on the internal surface of the pipes. The blisters were broken causing the corrosion of underneath
steel. The coating showed a poor resistance to salt fog test. In general, the coating performed satisfactorily under the crevices
but showed blistering on either side of the test panels. The adhesive strength of the coating was found to be poor; however,
it showed good flexibility. The results of chemical analysis did not show the leaching of organic or inorganic pollutants
from the coating. 相似文献
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The characterization and interpretation of ductile fracture mechanisms in AL2024-T351 using X-ray and focused ion beam tomography 总被引:1,自引:0,他引:1
K.L. TaylorA.H. Sherry 《Acta Materialia》2012,60(3):1300-1310
This paper describes an experimental investigation into the mechanism of ductile fracture in the aluminum alloy AL2024-T351 using a combination of synchrotron X-ray and focused ion beam tomography. Microstructural features that influence fracture at the micro- and nanoscale were characterized in virgin material in three-dimensions. The nature and volume fraction of ductile damage was then quantified as a function of distance below the fracture surfaces of tested notched and fatigue pre-cracked laboratory specimens. In both specimens the ductile fracture process initiates with the brittle fracture of large irregular intermetallic particles at low levels of plastic strain. With increasing plasticity, the resulting voids grow and combine with pre-existing porosity to increase the overall void volume fraction. Once a critical void volume fraction is attained, final failure occurs by the fracture or decohesion of dispersoids from the matrix, initiating a second population of nanoscale voids, which interlinks the larger voids. The critical void volume fraction for coalescence and the distribution of ductile damage below the fracture surface is markedly different between blunt-notched and pre-cracked specimens, with notched specimens exhibiting a significantly lower critical void volume fraction and a more extensive distribution of ductile damage below the fracture surface than is observed in pre-cracked specimens. This observation, related to the gradients in stress triaxiality and plastic strain in each specimen type, has important implications for the calibration of ductile damage mechanics models against notched-specimen data and their use to predict crack behavior in engineering structures. 相似文献
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X. B. Cao J. Zhao J. H. Fan M. H. Zhang G. J. Shao 《International Journal of Cast Metals Research》2014,27(6):362-368
AbstractThe fatigue behaviour of A356 cast aluminium alloy under 104 cycles was investigated by a servo-hydraulic machine at the temperature of 150°C. The specimens for the fully reversible tension compression tests were cut from cylinder head castings of automobile engines. The testing data were treated by S–N curve and the staircase method and the mean values of fatigue property coincided with each other by these two methods, though the data scattered with different casting defects. The fracture surfaces of fatigue specimens were examined by OM, SEM and EDS. It was found that in most of the specimens two or more fatigue crack initiations appeared at a fracture surface. Compared with casting defects such as oxide film, inclusion and blowhole, shrinkage porosity is more detrimental to the fatigue behaviour of aluminium alloy castings. 相似文献
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ZL205A铝合金铸件偏析缺陷分析和等级研究 总被引:1,自引:0,他引:1
以生产过程中ZL205A铸件的偏析缺陷为研究对象,采用SEM、EDS、DSC分析手段,研究了偏析对铸件力学性能、断口形貌、组织成分和熔化温度的影响.结果表明,随着偏析缺陷级别的提高,试样抗拉强度呈下降趋势,但其值高于I级指标;试样屈服强度变化较小;试样伸长率呈快速下降,多数低于4%;试样硬度(HV)均高于100.无缺陷试样断裂主要表现为韧性断裂,偏析试样断裂为沿晶脆性断裂.偏析试样基体以α(Al)固溶体为主,晶界上分布有未完全溶解残留物Al2Cu等低熔点共晶相,共晶相熔化温度为544 ℃,α(Al)固溶体熔化温度为625~640 ℃.根据试验分析结果制订出偏析等级底片. 相似文献
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Li YizheGong BaomingLiu XiuguoWang DongpoDeng Caiyan 《金属学报》2018,(12):1785-1791
The crack-tip stress and strain fields of single edge notch tension (SENT) specimen are similar to those of the full-scale pipe containing surface cracks under longitudinal tension and/or internal pressure. It is well known that material's fracture toughness is not constant, and the specimen size has a significant influence on fracture toughness. It is thus essential to consider the transferability from fracture specimens in laboratory testing to practical structures, i.e., size effects or constraint effects. However, the specimen dimensions for SENT specimens recommended by current design procedures have not validated the out-of-plane constraint effect on the fracture toughness. In this work, the effect of specimen thickness on the crack tip opening displacement (CTOD) of SENT specimen was investigated using an API X90 grade steel. Full-field deformation measurement by digital image correlation (DIC) technique and stretching zone width (SZW) examination were performed to analyze the size effects on fracture toughness. The results show that the critical crack initiation toughness is highly sensitive to specimen thickness, and decreases significantly as specimen thickness increases until the thickness-to-width ratio (B/W) equals to 4, beyond which the effect of specimen thickness becomes relatively weak. As the specimen thickness increases, the maximum longitudinal strain and stretching zone width decrease sharply, and the location of high-strain zones changes significantly; when B/W >= 3, strain is initiated from the area oppo-site the cracked side rather than from the crack tip, indicating a strong loss of plasticity for thicker specimens. A dimension size is recommended for the fracture toughness testing to take the out-of-plane constraint into account for SENT specimen. 相似文献
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本文介绍了一个分析铆焊桥梁安全性的简化方法根据新的有限元计算法,推导出一个含裂缝的桥梁的断裂负荷公式,从1890年至1930年间建造的铆焊桥梁材料中取样测定了400多个强度与断裂力学数据,做为断裂力学分析的原始输入数据.从长期服役的桥梁上以及未服役现代结构钢材(屈服强度350-890MPa)上取样,进行了大尺度样品测试,以评估该方法的正确性. 相似文献
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本文介绍了一个分析铆焊桥梁安全性的简化方法。根据新的有限元计算法,推导出一个含裂缝的桥梁的断裂负荷公式,从1890年至1930年间建造的铆焊桥梁材料中取样测定了400多个强度与断裂力学数据,做为断裂力学分析的原始输入数据。从长期服役的桥梁上以及未服役现代结构钢材(屈服强度350-890MPa)上取样,进行了大尺度样品测试,以评估该方法的正确性。 相似文献
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Chemically bonded sand cores and molds are more commonly referred to as precision sand systems in the high production automotive powertrain sector. Their behavior in contact with molten metal can lead to casting defects. Consequently, the interaction is of great interest and an important part of metal casting technology. The American Foundry Society(AFS) sand testing is based on physical, mechanical, thermal and chemical properties of the sand system. Foundry engineers have long known that certain AFS sand tests provide limited information regarding control of molding and casting quality. The inadequacy is due to the fact that sand casting processes are inherently thermo-mechanical, thermo-chemical and thermo-physical. Non-standard foundry sand testing has proven useful for laboratory measurement of these characteristics in foundry sand using a disc-shaped specimen. Similarly, the equivalent disc-shaped specimens are used for casting trials. In order to accomplish near-net-shape casting with minimal defects, it is necessary to understand both the properties of the sand system, as well as the interface of molten metal when different binders, additives and/or refractory coatings are used. The methodology for the following non-standard chemically bonded sand tests is described:(1) disc transverse;(2) impact;(3) modified permeability;(4) abrasion;(5) thermal distortion;(6) quick loss on ignition. The data related to the non-standard sand tests were analyzed and interpreted. The test results indicate that there is relatively lower test-to-test variability with the disc-shaped specimens. The non-standard tests were able to discriminate between the chemically bonded polyurethane cold box sand specimens. Further studies should be conducted on various other sand and binder systems as well as on different specimen thicknesses. 相似文献
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《Science & Technology of Welding & Joining》2013,18(4):187-196
AbstractThe present study considers the effect of strength mismatch on the fracture behaviour of diffusion bonded joints between commercially pure (CP) Ti and Ti-6Al-4V (Ti64), including dissimilar joints and sandwich structures with strength undermatching and overmatching. The aim of the investigation is to determine the influence of the interlayer thickness (for both higher and lower strength interlayers) and the bond quality on the deformation behaviour and fracture toughness of the joints. The influence of mechanical heterogeneity (strength mismatch) on the fracture behaviour of the interface in dissimilar joints was also investigated. Round bars of CP Ti and Ti64 having a diameter of 40 mm were diffusion bonded as dissimilar butt joints and sandwich structures containing lower strength (undermatching) and higher strength (overmatching) interlayers of different thicknesses. Round transverse tensile specimens and standard four point bend (single edge notch bend) specimens were extracted from the joints via spark erosion cutting. The four point bend specimens were fatigue precracked to introduce a sharp crack after introducing machine notches at the centre of the interlayers in the sandwich structures and at the interface in the dissimilar joints, and tested at room temperature. Some specimens were also prepared with the crack positioned away from the interface to determine the effect of notch position on fracture behaviour. The effect of strength mismatch on the crack tip opening displacement fracture toughness parameter of the joints has been evaluated. Crack initiation, crack growth, and crack deviation processes have been examined and fracture resistance curves (R curves) constructed for the joints. These results were used to explain the influence of mechanical heterogeneity of the joints and interlayer thickness on fracture behaviour. 相似文献