共查询到20条相似文献,搜索用时 0 毫秒
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在6级轴向逐级增加的系列恒应变幅(0.3%~1.0%)控制下,室温空气中,采用光滑圆形横截面试样,研究了10CrNiMo结构钢在低周疲劳作用下的应力-总应变及应力-塑性应变的滞后回线特性。结果表明:在小应变幅(0.3%~0.4%)控制下,虽然弹性应变占绝对优势,但塑性应变并不为零,且逐级增长;而在大应变幅(0.6%~1.0%)控制下,塑性应变增长较快,并逐渐占主导地位。无论应变幅大小,只须几个循环,材料便进入稳定状态,而初始循环与失稳循环却表现出不稳定的特征。 相似文献
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以汽车曲轴常用材料40Cr钢为研究对象,用透射电镜对经过不同疲劳周次的试样进行显微组织观察,研究其显微组织与机械疲劳的对应关系。研究表明:在同一应力水平下,随着疲劳循环次数的增加,位错从晶界出发向晶内扩展,位错的形态由无规律的分布到形成位错条带,最后形成亚晶粒组织。机械疲劳循环次数与位错密度的函数关系为p=2.88X10^8N+5.2712X10^8。 相似文献
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PMN—PNN—PZ—PT四元系铁电陶瓷的电疲劳特性 总被引:2,自引:1,他引:1
本文研究了PMN-PNN-PZ-PT四元系铁电陶瓷的电疲劳特性。在反复的交变电场作用下,经过约10^7 ̄10^8次循环后,材料的极化强度减小,而矫顽场强也减小。但经过一段时间的放置的,材料疲劳的性能逐渐恢复。这种现象与通常我电陶瓷疲劳特性不同,可能的疲劳机制是电荷的钉轧。 相似文献
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Saeed Kahrobaee Hossein Norouzi Sahraei Iman Ahadi Akhlaghi 《Research in Nondestructive Evaluation》2013,24(5):303-315
ABSTRACTThe aim in this article is to evaluate microstructural changes, hardness variations, and wear behavior of H13 hot work tool steel as a function of austenitizing and tempering temperature using nondestructive magnetic hysteresis loop method. To obtain different microstructural characteristics in the H13 specimens, austenitizing and tempering temperatures were varied in the range of 1,050–1,100°C and 200–650°C, respectively. The microstructural features, hardness, and wear loss were characterized using X-ray diffraction/metallographic examinations, hardness measurements, and a pin-on-disk wear tester, respectively. The relations between features obtained from the conventional methods and parameters extracted from the magnetic hysteresis loops were established. Results demonstrate that the proposed nondestructive method is able to assess the wear behavior of the heat treated H13 tool steels. Besides, a standard Generalized Regression Neural Network (GRNN) was trained with a training dataset and then used to estimate the hardness of a given sample with its measured values of magnetic parameters. Experimental results indicate that, if the training dataset has sufficient samples, the proposed method will have a very high accuracy to estimate hardness of the sample, nondestructively. 相似文献
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V. Kliman 《International Journal of Fatigue》1985,7(1):39-44
A procedure for estimating the useful life of a component for a given (admissable) probability of fatigue fracture origination under random loading is presented. The method uses material constants obtained from the S/N and cyclic stress/strain curves, standard deviation and probability density distribution of the loading process and a macroblock of harmonic cycles obtained by applying the rainflow cycle counting method to the random loading process. Theoretical and experimental lives are found to exhibit good agreement. 相似文献
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飞机典型机械紧固连接件腐蚀疲劳性能的试验研究EI 总被引:1,自引:1,他引:0
本文研究了飞机机械紧固连接件在腐蚀环境下的疲劳性能。试验结果表明,腐蚀环境在大多数情况下降低紧固件的疲劳寿命,其中盐雾环境对双剪密封铆接件的疲劳寿命的影响最为严重。给出了机械紧固件在不同状态下的细节疲劳额定值(DFR)和可靠性寿命(N_(95/95))。 相似文献
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杨永生 《理化检验(物理分册)》2010,(7):472-474
采用宏观和微观检验等手段对曲轴疲劳试样不同部位磁痕产生的原因进行了分析。结果表明:磁痕是由于带状组织、疲劳裂纹和磨削裂纹等原因造成的。磨削裂纹主要是由于磨削时摩擦应力过大造成的。原材料中存在较严重的带状组织,导致淬火组织和残余应力不均匀,对磨削裂纹的产生起到了促进作用。 相似文献
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P. A. SOLIMINE C. J. LISSENDEN 《Fatigue & Fracture of Engineering Materials & Structures》2004,27(10):943-955
Fatigue life of fibrous metal matrix composites is limited by the distribution of fibre strengths, the fibre‐matrix interfacial strength, and the fatigue resistance of the matrix. The aim of this work is to provide fatigue results for a beta titanium alloy over a range of temperatures and stresses that can be used as input for predicting fatigue life of a titanium matrix composite. Stress controlled tests having fatigue ratios between ?1 and ?0.2 were conducted on a limited number of samples machined from unreinforced laminated Ti‐15Mo‐3Al‐2.7Nb‐0.2Si (TIMETAL®21S) sheets to represent as closely as possible the in situ matrix material. Stress control was used to enable quantification of strain ratcheting for tensile mean stresses and a fast loading rate was used to minimize time‐dependent (creep) deformation. Stress amplitude‐life data at 20, 482 and 648 °C for fully reversed loading are well fit by a power law. Normalizing the stress amplitude with respect to the power law coefficient appears to account for the temperature dependence of the S–N curves. As the tests had large strains and lives were in the low‐cycle fatigue range, strain range at the half‐life was also correlated to life. For tensile mean stress cycling at 482 and 648 °C, the rate of strain ratcheting per cycle increased to failure; shakedown was not observed. 相似文献
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Abstract: The article focuses on the application of a recently developed damage operator‐based lifetime calculation to a thermomechanically loaded exhaust downpipe. The damage operator approach enabling online continuous damage calculations for isothermal and non‐isothermal loading with mean stress corrections is reviewed. The article also highlights an extension of the strain‐life approach to take into account viscoplastic effects and creep. The transient results from thermal and structural analyses using finite element analyses have been applied to the exhaust downpipe in LMS Virtual.Lab and the damage predicted. Tested exhaust downpipes were then subjected to the same loading conditions as in the calculation, and load cycles were repeated up to the point of failure. Simulated and test results are comparable. 相似文献
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V. T. Troshchenko 《Strength of Materials》2000,32(5):427-433
General regularities in the variation of threshold stress intensity factors of metals are considered taking into account the influence of various factors. Justification is offered of the possibility of predicting fatigue limits for smooth specimens and specimens under conditions of fretting from the known characteristics of threshold stress intensity factors. 相似文献
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M. G. A. BAHIA B. M. GONZALEZ V. T. L. BUONO 《Fatigue & Fracture of Engineering Materials & Structures》2006,29(7):518-523
Endodontic files made of nickel–titanium (NiTi) superelastic wires can be employed in rotary techniques for cleaning and shaping curved root canals, suffering tensile–compressive strain cycles with maximum amplitudes between 3 and 5%. The aim of this work was to study the fatigue behaviour of this material under such high deformation conditions, using NiTi instruments and superelastic wires taken from their production line. One hundred load–unload tensile cycles in the superelastic regime (4% elongation) were applied to NiTi wires. New endodontic instruments were fatigue‐tested simulating the geometrical conditions found in their clinical use. It was found that only small changes took place in the parameters describing the mechanical behaviour of the cycled wires. The measured average number of cycles to failure varies inversely with the maximum tensile strain amplitude in the fatigue tests (r= 0.993). 相似文献
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压印连接是近年来新兴的连接方式,因其具有简单高效、低耗环保等优点,在连接应用方面越来越受到重视,而疲劳破坏是机械零件失效的主要形式。对钛合金压印接头的疲劳性能进行了实验研究,与母材的力学性能进行了对比分析,并对疲劳失效断口进行了断口分析和能谱分析。实验结果显示钛合金压印接头的平均拉伸-剪切强度约为同等尺寸材料拉伸-剪切强度的36.7%;钛合金压印接头的疲劳极限约为材料疲劳极限的46%,平均载荷约为接头最大静强度的42%。微观特征显示断口呈脆性疲劳断裂特征,由于微动磨损和氧化作用产生了成分为氧化钛的微动磨屑,且其硬度较高,因此在微动过程中起到磨粒的作用,从而加速了磨损和裂纹扩展,最终导致疲劳失效。 相似文献
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采用自主设计研制的首台国产连续管弯曲疲劳试验机,对某国产CT80钢级连续油管进行疲劳试验,并对影响连续油管低周疲劳寿命的各种因素进行了研究。结果表明:增加连续油管的壁厚、减小连续油管的外径、提高连续油管的屈服强度、减小管内压力、减少管体表面损伤以及提高连续油管焊接质量均能显著提高连续油管的弯曲疲劳寿命; 相似文献