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根据有限元精细网格计算结果,分析材料硬化及裂尖塑性变形对直通型CT试样(front force compacttension,FFCT)及三点弯曲试样(single edged notched bending,SEB)COD转换的影响。结果表明,材料硬化及裂尖塑性变形对上述两种试样的COD转换均存在影响,但影响较小,均可忽略。通过其试样变形几何关系,提出用于FFCT试样断裂韧性测试中计算J积分塑性功的裂纹嘴张开位移与加载线张开位移的弹塑性转换公式;对于SEB试样,通过对不同本构参数有限元精细网格计算结果进行耦合的方法获得COD转换公式。该文公式形式均较为简单,且与有限元结果相对误差较小,具有较高的置信度。 相似文献
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根据柔度法测量金属材料裂纹长度的原理,讨论了测量三点弯曲SE(B)试样弹性模量的影响因素,并分析了主要因素的影响。在此基础上,用柔度法测量了裂纹尖端张开位移(CTOD)试验用大尺寸SE(B)试样预制疲劳裂纹的长度。经断口测量发现,用柔度法测量的两组母材与焊缝试样的原始裂纹长度具有很好的同一性,为进一步进行CTOD试验提供了保证。 相似文献
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大口径316L不锈钢管数控弯曲回弹规律研究 总被引:1,自引:1,他引:0
针对Φ123 mm×3.97 mm×350 mm规格的大口径316L厚壁不锈钢管,基于显/隐式弹塑性有限元仿真结合实验研究,对其数控弯曲卸载后的回弹现象进行了研究.采用单向拉伸试验和三维数字散斑动态应变测量方法获得了大口径316L不锈钢管大应变范围(真应变为49.02%)的力学性能参数,通过摩擦磨损实验获得管材316L不锈钢与45钢模具材料在不同压力和转速条件下的摩擦系数.基于ABAQUS平台,建立了大口径316L不锈钢管弯曲、抽芯、卸载回弹全过程数控弯曲有限元模型,并实验验证了所建模型的可靠性.研究表明,大口径316L不锈钢管回弹现象显著,在350 mm弯曲半径(相对弯曲半径D/t为2.846)条件下达到7.2°左右.芯棒伸出量e、芯球个数n和弯曲角度θ对卸载回弹有显著影响. 相似文献
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为了研究316L不锈钢在含Cl-环境中的腐蚀行为,采用浸泡和电化学相结合的方法,研究了其在不同Cl-浓度溶液中不同浸泡时间的腐蚀行为,采用扫描电镜(SEM)观察了腐蚀形貌.结果表明:316L不锈钢在含Cl-环境中的点蚀程度与Cl-浓度密切相关,随着Cl-浓度的增加,点蚀程度先增大后减弱,当Cl-浓度为3%时,点蚀最严重,当Cl-浓度超过3%时,点蚀减缓;316L不锈钢在NaCl溶液中钝化膜的形成是缓慢的,膜结构具有不完整性,为点蚀的孕育、萌生提供了结构条件,而点蚀一旦形成,在自催化作用下继续发展;316L不锈钢在含Cl-体系中的腐蚀行为是Cl-浓度与溶解氧含量两因素共同作用的结果,溶液中Cl-含量的增加一方面为加速腐蚀提供了物质条件,促进腐蚀;另一方面减少了介质中溶解氧的含量,抑制了腐蚀,两者的综合作用使腐蚀得以控制. 相似文献
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采用电化学测量、交流阻抗技术、扫描电镜观察和能谱分析等实验方法,研究了316L不锈钢在铁氧化菌(IOB)溶液中的腐蚀电化学行为,分析了炼油厂冷却水系统微生物腐蚀的特征及机制,结果表明,在含有IOB溶液中的自腐蚀电位(Ecorr)、点蚀电位(Epit)和极化电阻(Rp)均随浸泡时间的增加呈现出降-升-降的变化趋势;在含有IOB溶液中的腐蚀速率均大于在无菌溶液中;IOB的生长代谢活动及其生物膜的完整性和致密性影响了316L不锈钢表面的腐蚀过程,使不锈钢表面的钝化膜层腐蚀破坏程度增加,加速了316L不锈钢的点蚀. 相似文献
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Qi-Zhi Wang 《International Journal of Fracture》1997,85(3):231-240
A sandwich three-point bend specimen has recently been proposed to test mode-I interlaminar fracture toughness for fiber-reinforced
composite materials. The test composite consist of a thin layer bonded by two lateral reusable steel bars (Sohn et al. 1995).
Some time earlier this specimen configuration was used to test fracture toughness of adhesives (Zdaniewsk et al. 1987). However,
formulae for analysing its fracture mechanics parameters such as stress intensity factor and energy release rate can not be
found in the literature. The lack of adequate formulae may explain why suitable quantitative analysis using this specimen
configuration has not been achieved. In this paper, a simple and effective homogenisation method is used to change the bi-material
system, which represents the specimen, into single uniform test material. This physical homogenisation is carried out by geometric
change of the cross section of lateral steel parts based on equal deflection rigidity. For the transformed specimen configuration
of single uniform material, the corresponding stress intensity factor solution from handbooks is available. Two formulae of
stress intensity factor for the sandwich three-point bend specimen are given as upper limit and lower limit respectively,
they are plotted with varying elastic tensile modulus mismatch. Then the relation between stress intensity factor and energy
release rate, with special consideration of orthotropy of the tested composite material, is used to derive its energy release
rate. The specimen and its formulae can also be applied to test other materials such as wood, welded joints (Burstow and Ainsworth,
1995), as well as to test dynamic fracture toughness.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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《Materials Characterization》2007,58(4):363-370
This paper describes the use of a material testing system (MTS) and a compressive split-Hopkinson bar to investigate the impact behaviour of sintered 316L stainless steel at strain rates ranging from 10− 3 s− 1 to 7.5 × 103 s− 1. It is found that the flow stress–strain response of the sintered 316L stainless steel depends strongly on the applied strain rate. The rate of work hardening and the strain rate sensitivity change significantly as the strain rate increases. The flow behaviour of the sintered 316L stainless steel can be accurately predicted using a constitutive law based on Gurson's yield criterion and the flow rule of Khan, Huang and Liang (KHL). Microstructural observations reveal that the degree of localized grain deformation increases at higher strain rates. However, the pore density and the grain size vary as a reversible function of the strain rate. Impacts at strain rates higher than 5.6 × 103 s− 1 are found to induce adiabatic shear bands in the specimens. These specimens subsequently fail as a result of crack propagation along the dominant band. The fracture surfaces of the failed specimens are characterized by dimple-like structures, which are indicative of ductile failure. The depth and the density of these dimples are found to decrease with increasing strain rate. This observation indicates a reduction in the fracture resistance and is consistent with the observed macroscopic flow stress–strain response. 相似文献
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S. HOSSAIN C. E. TRUMAN D. J. SMITH 《Fatigue & Fracture of Engineering Materials & Structures》2011,34(9):654-666
Residual stresses are created in type 316H stainless steel fracture mechanics specimens using the process of local out‐of‐plane compression (LOPC). Three sets of LOPC tools are used to create different distributions of residual stress near to the crack tip. Also the tools create different levels of prior plastic strain. Residual stresses are measured using the neutron diffraction method and compared with the stress predictions obtained from finite element (FE) simulations of LOPC. The specimens are then subjected to thermal exposure at 550 °C for several thousand hours. A creep deformation and damage model is introduced into the FE analysis to predict the relaxation of stresses and creation of damage in the specimens. Neutron diffraction experiments are undertaken to measure the relaxed residual stresses and fractographic analysis of thermally exposed samples measured the extent of creep damage. A comparison between measured and simulated results demonstrates that the prior plastic strain has a significant effect on damage accumulation but this is not accounted for in the current creep damage models. 相似文献
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The fracture toughness of alloy HT-9,2 a martensitic stainless steel under consideration for fast reactor and fusion reactor applications, was determined from circular compact tension specimens using the multi-specimen R-curve method. Specimens with thicknesses of 11.94, 7.62 and 2.54mm and widths of 23.88 and 11.94 mm were tested to investigate the effects of specimen size on fracture toughness. The test results obtained from all specimens are in good agreement and thickness requirements for a valid J1c test are satisfied. The experiment indicates that small specimens of HT-9 may be used for post-irradiation fracture toughness testing.Fractographic examination of the fracture surfaces reveals that fracture in HT-9 is significantly influenced by delta ferrite stringers present in the material. The fracture surface examination and crack opening displacement measurements for specimens tested at various temperatures are consistent with the temperature dependence of the J1c results. 相似文献
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More on compliance of the three-point bend specimen 总被引:1,自引:0,他引:1
John H. Underwood Joseph A. Kapp Francis I. Baratta 《International Journal of Fracture》1985,28(2):R41-R45
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A detailed investigation of low cycle fatigue (LCF) and thermo-mechanical fatigue (TMF) of a 316FR type stainless steel is presented in this paper in order to identify the failure mechanism based on the experimental results and the subsequent metallography of the samples. The LCF–TMF servohydraulic testing with a temperature uniformity of less than ±5 °C within the gauge section of the specimens was employed to conduct the experimental tests. Fully-reversed, strain-controlled isothermal tests were conducted at 650 °C for the strain ranges of Δɛ = ±0.4%, ±0.8%, ±1.0% and ±1.2%. Strain-controlled in-phase (IP) thermo-mechanical fatigue tests were conducted on the same material and the temperature was cycled between 500 °C and 650 °C. Additionally, the creep–fatigue interactions were investigated with the introduction of symmetrical hold time under both LCF–TMF tests. The cyclic behaviour was further studied by performing microstructural investigations using the scanning electron microscope (SEM). 相似文献
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Shang-Xian Wu 《Engineering Fracture Mechanics》1984,19(2):221-232
Stress intensity factor formulas and dimensionless compliance formula of chevron-notch three point bend specimen obtained by use of straight-through-crack assumption (STCA) and Bluhm's slice model have been presented. Two stress intensity factor coefficient formulas have been compared with the experimental data of GCr 15 bearing steel. The comparison has shown that the formula obtained using slice model is in better agreement with experimental data. The plane-strain fracture toughness measurements by chevron-notch specimen and by ASTM E399 standard method have been compared and are in agreement. The effect of slot width of chevron notch on the measurements has been studied. 相似文献