中途高温回火对40Cr钢疲劳寿命的影响

采用控制应力疲劳实验方法，对中碳合金钢40Cr进行了拉一压疲劳实验。将调质处理后的40Cr钢疲劳试样在实时疲劳损伤监测的情况下循环到不同的损伤阶段，中止疲劳实验，进行中途高温回火处理，然后继续在相同条件下进行应力疲劳实验，讨论中途高温回火对40Cr钢疲劳寿命的影响。结果表明，中途回火大大增加了试样的疲劳寿命。循环到疲劳寿命的30％的试样中途回火后疲劳寿命增加了20％，循环到疲劳寿命的4JD％的试样中途回火后疲劳寿命增加了40％，循环到疲劳寿命的50％的试样中途回火后疲劳寿命增加了77％。微观分析表明，疲劳断口上韧窝的增大增深、疲劳源数量增加等是疲劳寿命增加的主要原因。     

铁电陶瓷材料在交变电场作用下疲劳研究进展

通过对铁电陶瓷疲劳失效研究现状的文献综述，概述了国内外存电疲劳和电致疲劳的机理、影响因素和实验手段等方面的研究进展。通过分别对各类电疲劳机理和各种电致疲劳模犁进行讨论，比较了各种理论和模型之间的不同之处，指出了为掌握铁电陶瓷疲劳失效机理尚需解决和澄清的问题。     

人工神经网络在球墨铸铁疲劳寿命预测中的应用

在研究了球墨铸铁疲劳过程中磁导率的变化和疲劳寿命间的关系基础上，建立了球墨铸铁疲劳寿命预测的神经网络模型，根据网络的计算结果可以预报球墨铸铁的疲劳损伤度，预测其寿命。     

氮离子注入对铝合金A1CuMgPb疲劳特性的影响

本文采用了旋转式弯曲疲劳试验机．在力应比R=-1的条件下，研究了氮离子注入对于铝合金AlCuMgPb的疲劳寿命的影响。疲劳寿命是由一个计数器来记录的，它显示b 由弯曲疲劳引起的断裂时试样的总转结果表明，对于注入剂量较低的试样，合金的疲劳寿命有所增加，但当注入剂量超过某一界限时，试样的疲劳寿命不但没有改善，反而有所下降。对于造成这一复杂现象的原因在本文作了初步的探讨。     

锆—4合金的时间相关低周疲劳

研究了锆－４合金在不同应变速率下的低周疲劳和带应变保持时间相关低周疲劳行为。结果表明：在不同加载方式下，锆－４合金均表现为循环硬化，应变保持和应变速率降低均进一步提高环孢和应力。应变保持降低材料的疲劳寿命，特别是在高应变幅区域。随着应变速率降低、材料疲劳寿命降低。疲劳变形亚结构观察表明：锆－４合金时间相关疲劳过程中以｛１０１↑－０｝柱面滑移和晶界滑移方式变形。     

高浓度渗碳及其性能研究

对比研究了高浓度渗碳与常规渗碳后试样的组织和性能。结果表明：高浓度渗碳试样的硬度，耐磨性，接触疲劳性能最高，弯曲疲劳性能与常规渗碳试样的大致相同，并对试验结果进行了较为系统的微观机理分析。     

初教六飞机疲劳点分析

通过对初教飞飞机疲劳破坏事例进行分析，确定其疲劳点为前叉活塞杆、汽油箱和转轴三项，针对造成疲劳的原因提出改进措施，使临界疲劳趋向极限，为监控、检测和寿命设计提供了基础。     

含20%Ni金属基陶瓷的热冲击疲劳

研究了含２０％Ｎｉ的Ｔｉ（Ｃ，Ｎ）基金属陶瓷的热冲击疲劳，试验结果表明：随循环温度的上升和冷却速率的加快，热冲击疲劳裂纹的形成孕育期缩短，裂纹扩展速率加快。缺口也使裂纹形成的孕育期缩短，观察还表明，热冲击疲劳断口中存在的疲劳条纹。     

不同介质中Si3N4陶瓷的静疲劳与循环疲劳

系统研究了Si3N4陶瓷在空气、水、煤油3种介质中的静疲劳及循环疲劳特性。结果发现，在不同介质条件下，循环疲劳的应力腐蚀指数(n)相差不大，且远远低于相同介质条件下静疲劳的应力腐蚀指数。经分析发现，循环载荷部分或全部消除了显微组织屏蔽作用，对材料造成附加损伤，导致其疲劳寿命远远低于静疲劳寿命。     

热处理对钢结硬质合金抗疲劳性能的影响

本文以钢质硬质合金ＧＪＨ－２为研究对象，通过对不同热处理状态试样的热疲劳破坏试验，得出了提高钢结硬质合金的抗热疲劳性能的最佳热处理工艺，并借助于扫描电镜，研究了热疲劳裂纹萌生的位置、扩展途径和断口特征，为钢结硬质合金在热作模具上的应用提供了依据。     

Aging and mechanical properties of NR/BR blends

The mechanical properties and post-thermal aging properties of natural rubber (NR) and polybutadiene rubber (BR) blends at different blending ratios are investigated herein. The experimental results show that both tensile and tear strengths of NR/BR blends increase with increasing NR content. BR has a higher compression stiffness than NR. The deformation of BR is less than that of NR under the same load conditions. With regard to aging properties, both tensile stress and strain of NR/BR blends decrease after prolonged aging. In addition, the stress loss of BR is lower than that of NR, meaning that the aging resistance property of BR is superior to that of NR. Furthermore, accumulated thermal history has shifted the glass transition temperature (T _g) of NR/BR blends toward lower temperatures while the loss tangent (tan δ) value increases with prolonged thermal aging.     

Fatigue behaviour and life estimation of Mg/Al ultrasonic spot weld bonding welds

Mg/Al dissimilar joints with favourable static and dynamic mechanical properties were obtained utilising ultrasonic spot welding and ultrasonic spot weld bonding technology. The fatigue behaviour, fatigue failure mode, and typical fatigue fracture surface morphology of Mg/Al ultrasonic spot welding and ultrasonic spot weld bonding joints were compared and observed to get a better understanding of the fatigue failure mechanism. In general, the Mg/Al ultrasonic spot weld bonding joint exhibited better fatigue performance than the ultrasonic spot welding joint. The two kinds of joints presented different fatigue failure modes with decreasing applied load level. A fatigue life prediction model was established, and the fatigue life prediction results were in good agreement with the experimental fatigue results.     

Thermal shock fatigue behavior of TiC/Al2O3 composite ceramics

The thermal shock fatigue behaviors of pure hot-pressed alumina and 30 wt. % TiC/Al2O3 composites were studied. The effect of TiC and Al2O3 starting particle size on the mechanical properties of the composites was discussed. Indentation-quench test was conducted to evaluate the effect of thermal fatigue temperature difference (ΔT) and number of thermal cycles (N) on fatigue crack growth (Δα). The mechanical properties and thermal fatigue resistance of TiC/Al2O3 composites are remarkably improved by the addition of TiC. The thermal shock fatigue of monolithic alumina and TiC/Al2O3 composites is due to a "true" cycling effect (thermal fatigue). Crack deflection and bridging are the predominant reasons for the improvement of thermal shock fatigue resistance of the composites.     

钛合金BT20焊接接头腐蚀疲劳性能的实验研究

BT20钛合金焊接接头的轴向疲劳性能在应力集中系数K_t=1时的各种应力比的条件下,盐雾环境和SO₂酸性盐雾环境下的疲劳寿命都有所降低,其中 SO₂酸性盐雾环境对疲劳寿命影响最显著;在疲劳寿命N=10⁵处,应力比 R由0.5变为0.06时,潮湿空气使疲劳强度下降18%,盐雾腐蚀使疲劳强度下降16%,SO₂酸性盐雾使疲劳强度下降7%。     

High cycle fatigue and fracture behavior of 2124-T851 aluminum alloy

The high cycle fatigue properties and fracture behavior of 2124-T851 aluminum alloy were investigated roundly, including the fatigue crack growth rate, fracture toughness and fatigue S--N curve. Furthermore, the fatigue crack growth rate was analyzed by fitting the curves. And the microstructure of the alloy was studied using by optical microscopy, transmission electron microscopy and X-ray diffractometry, scanning electron microscop1/2 The results show that the fatigue strength and the fracture toughness of 2124-T851 thick plate are 243 MPa and 29.6 MPa.m at room temperature and R=0. 1, respectively. At high cycle fatigue condition, the characteristics of fatigue facture were observed obviously. And the higher the stress amplitude, the wider the space between the fatigue striations, the faster the rate of fatigue crack developing and going into the intermittent fracture area and the greater the ratio between the intermittent fracture area and the whole fracture area.     

超声频分量双周疲劳载荷作用下焊接接头疲劳行为

使用带超声频载荷分量的双周疲劳试验装置对Q345钢焊接接头分别进行纯低周、纯高周以及双周循环加载条件下的疲劳试验.应力比R为O.5,高周载荷频率约19 kHz.结果表明,叠加于大幅低周循环载荷上的小幅高周循环载荷及叠加于大幅高周循环载荷上的小幅低周循环载荷都能够对焊接接头造成严重的疲劳损伤.通过按外包络线表征双周疲劳强度,如果疲劳寿命使用低周载荷循环周次表征,低估了高周载荷分量对焊接接头造成的损伤;如果疲劳寿命使用高周载荷循环周次表征,又高估了低周载荷分量对焊接接头造成的损伤.     

航空铝合金疲劳参数的理论估算方法分析

基于12种航空铝合金的力学性能及疲劳试验结果,通过绘制疲劳寿命图的方法,将预测寿命与试验寿命进行对比,得到5种常用疲劳参数估算方法预测疲劳寿命的精度.结果表明:5种方法中,四点关联法和修正的四点关联法在中、低周疲劳范围内寿命预测结果比较理想,而在高周疲劳范围内各方法的寿命预测结果均不理想;硬度法不适用于航空铝合金的疲劳...     

FATIGUE PROPERTIES OF AUSTEMPERED DUCTILE IRON （ADI） IN WATER ENVIRONMENT

The acicular ferrite in austempered ductile iron (ADI) matrix around graphite was corroded preferentially in wet condition, promoting crack origination and propagation and resulting in the disappearance of ADI fatigue limit. ADI fatigue strength was gradually reduced with increasing the time of test and was reduced by 50% in wet condition at 10^7 cycles compared with the fatigue limit in dry condition.The fatigue strength variation of ferritic ductile iron in wet condition was similar to that of ADI.The ferritic ductile iron, however, has better corrosion resistance so that the fatigue strength was lowered only by 10^7 in wet condition at 10^7 cycles compared with the fatigue limit in dry condition. On the other hand, the fatigue limits of ADI and ferritic ductile iron were dropped by 32% and 25% in tap water dipping 480h/dry condition respectively compared with those in dry condition.The reduction of fatigue limit was attributed to corrosion pits formation correlated with stress concentration, resulting in origination and propagation of fatigue crack.     

焊补对SMA490BW焊接接头疲劳性能的影响

利用MTS-810疲劳试验机测试了耐候钢SMA490BW对接接头原始焊件、一次焊补件、二次焊补件的疲劳性能. 分别拟合了三类接头的均值S-N曲线和存活率95%、置信度75%的P-C-S-N曲线. 分析了焊补对焊接接头疲劳性能的影响. 结果表明,三组疲劳数据点基本在允许的分散带内,焊补没有对焊接接头疲劳性能造成明显的影响. 将三组数据整合在一起作为一个样本,运用成组法和升降法数据处理思想获得疲劳曲线. 并通过八节点法绘制了疲劳极限图Goodman-Smith图,为转向架焊补后疲劳强度校核提供了依据.     

INFLUENCE OF TOP TEMPERATURE OF THERMAL CYCLE ON THERMAL STRESS/STRAIN AND THERMAL FATIGUE BEHAVIOR OF PURE IRON

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