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1.
根据损伤应变能释放率的定义表达式,将各向同性材料应力二三轴性因子拓展到正交异性材料,定义了含有3个弹性常数的镍基单晶应力三轴性因子。用它修正Mises应变范围作为疲劳损伤参量,可以显著消除晶体取向和多轴载荷对疲劳寿命的影响。用损伤应变能释放率作为热力学广义力描述正交异性材料的疲劳损伤过程,引入取向函数和损伤驱动力循环特征参数反映晶体各向异性对疲劳损伤的非线性影响以及循环载荷的交变特性,提出了单晶合金低周疲劳损伤模型。利用CMSX-2镍基单晶合金薄壁圆筒试样的拉一扭循环载荷低周疲劳试验数据和DD3镍基单晶合金缺口试样的低周疲劳试验数据,运用多元线性回归分析方法拟合模型的材料常数,试验所得数据分别落在2.5倍和2.0倍偏差分布带内。  相似文献   

2.
研究了特定试验条件下,镍基单晶DD10取向偏离[001]的程度对其低周疲劳行为的影响。结果表明:取向偏离度对DD10合金的低周疲劳行为影响明显。疲劳寿命随取向偏离度的增加而明显降低,在同等偏离度下,晶体取向靠近[001]-[011]的合金低周寿命优于取向靠近[001]-[111]的合金;分析发现:不同取向偏离度合金DD10低周疲劳寿命的差异源于其每循环周次的可累计塑性变形的差异。另一方面,取向偏离度对疲劳总应力幅和塑性应变幅的影响却截然相反,但对疲劳裂纹萌生和扩展方式影响不大。  相似文献   

3.
本文研究了特定试验条件下,镍基单晶DD10取向偏离[001]的程度对其低周疲劳行为的影响。结果表明:取向偏离度对DD10合金的低周疲劳行为影响明显。疲劳寿命随取向偏离度的增加而明显降低,在同等偏离度下,晶体取向靠近[001]-[011]的合金低周寿命优于取向靠近[001]-[11]的合金;分析发现:不同取向偏离度合金DD10低周疲劳寿命的差异源于其每循环周次的可累计塑性变形的差异。另一方面,取向偏离度对疲劳总应力幅和塑性应变幅的影响却截然相反,但对疲劳裂纹萌生和扩展方式影响不大。  相似文献   

4.
研究了2种高温条件下镍基单晶合金的低周疲劳行为。试验温度和总应变幅是影响合金低周疲劳寿命的2个主要因素,在相同温度下,低周疲劳寿命随应变幅的减小而增大;在同一应变幅下,870℃的疲劳寿命均小于760℃的疲劳寿命。二次细小y相有效阻碍了位错的滑移,提高了合金在760℃低周疲劳变形抗力,位错滑移带成为疲劳裂纹萌生及扩展的主要途径;870℃循环应力曲线前期出现短暂硬化和后期软化的现象,y'相逐渐粗化和高密度的位错缠结是循环软化的主要原因。局部应力集中与合金内微孔的交互作用是疲劳裂纹萌生的源头。  相似文献   

5.
研究了2种高温条件下镍基单晶合金的低周疲劳行为。试验温度和总应变幅是影响合金低周疲劳寿命的2个主要因素,在相同温度下,低周疲劳寿命随应变幅的减小而增大;在同一应变幅下,870℃的疲劳寿命均小于760℃的疲劳寿命。二次细小y相有效阻碍了位错的滑移,提高了合金在760℃低周疲劳变形抗力,位错滑移带成为疲劳裂纹萌生及扩展的主要途径;870℃循环应力曲线前期出现短暂硬化和后期软化的现象,y’相逐渐粗化和高密度的位错缠结是循环软化的主要原因。局部应力集中与合金内微孔的交互作用是疲劳裂纹萌生的源头。  相似文献   

6.
镍基铸造高温合金具有优异的高温性能,广泛应用于航空发动机涡轮叶片等热端部件之中。航空发动机涡轮叶片是发动机中工作环境最为恶劣、结构最为复杂的零件之一,在发动机运行过程中所产生的高温交变应力的作用下,合金承受着严重的应力、应变循环损伤,裂纹往往在合金中的薄弱区域形成并扩展,使合金以低周疲劳的模式失效,严重影响了合金的服役寿命,因此对合金低周疲劳性能的研究尤为重要。本文详细阐述了影响镍基铸造高温合金低周疲劳性能的表面缺陷、内部组织及缺陷、晶体取向和低周疲劳试验条件等四方面因素,从位错运动方式和形态变化特点出发,研究了不同温度下镍基铸造合金的变形机制,最后总结了合金低周疲劳寿命预测的应力应变准则、能量准则、损伤累积准则及临界面和临界距离准则。  相似文献   

7.
镍基高温合金在承受高温和机械应力时很容易产生低周疲劳损伤,疲劳寿命预测对于镍基高温合金的实际应用是非常重要的。为了研究总应变和晶粒尺寸对镍基高温合金低周疲劳行为的影响,本文作者对一种镍基高温合金进行高温低周疲劳试验。结果表明,合金的疲劳寿命随应变振幅和晶粒尺寸的增加而减小。建立一个考虑晶粒尺寸对疲劳寿命影响的低周疲劳寿命预测模型。误差分析表明,低周疲劳寿命模型的预测精度高于Manson-Coffin和Ostergren能量法模型的预测精度。  相似文献   

8.
建立了考虑背应力演化和损伤演化的晶体塑性模型,利用所建立的晶体塑性模型研究了应变速率对镍基单晶合金基体相、强化相的影响。结果表明,镍基单晶基体相和强化相均表现出明显的率相关性。单晶双相合金的细观非均质性导致非均匀的微观应力和微观塑性滑移。塑性滑移变形首先发源于基体相。微观应力和塑性滑移的非均匀性可能是材料微观损伤积累和孔洞形核的根源。  相似文献   

9.
Zr—4双轴低周疲劳寿命估算   总被引:2,自引:0,他引:2  
肖林  宋凯 《金属学报》1999,35(4):397-402
测定了拉-扭复合加载下,主应变比φ=-0.5,0.63,-0.7,-0.8,和等效应变幅△εeq=0.5%,0.7%,0.8%,1.0%,1.1%下,Zr-4低周疲劳寿命曲线,分别采用最大主应力、应变,COD应力,应变,最大剪应力,应变,Mises等效应力,应变,LE应变,BMK应变准则,估算了Zr-4单轴、双轴低周疲劳寿命。结果表明:应变准则能较好地描述了Zr-4双轴低周疲劳寿命,特别是Mies  相似文献   

10.
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。  相似文献   

11.
The strain-controlled low cycle fatigue (LCF) and creep-fatigue interaction (CFI) tests of a newly developed Ti-45Al-8Nb-0.2W-0.2B-0.02Y (at.%) alloy were carried out at 750 °C in air. The hysteresis loop, cyclic stress response and life modeling as well as failure mechanism of the alloy were investigated in detail. It was revealed that the tensile and compressive mean stresses would generate when the dwell condition was introduced at minimum and maximum strain, respectively. In addition, the dwell condition, especially for the compressive dwell condition, would significantly decrease the fatigue life. The typical continuum damage accumulation(CDA) and modified CDA life models proposed in the present study were employed to predict both LCF and CFI life of the alloy, which showed that the modified CDA life model had a higher accuracy than the typical CDA life one. Moreover, only single crack initiation source was observed at 92% (i.e. 11/12) of LCF fracture while multiple crack initiation sources at 84% (i.e. 31/37) of CFI fracture. Apparently different from LCF specimen showing more transgranular appearance, CFI specimen shows more intergranular appearance.  相似文献   

12.
The low cycle fatigue(LCF)properties of as-extruded AZ31 Mg alloy were investigated under total strain amplitudes in the range of 0.4%-1.2%with strain rate of 1×10- 2s -1.Due to the twinning effect in compression during loading and the detwinning effect during unloading,the alloy showed an asymmetric hysteresis loop.The cyclic stress response exhibited cyclic hardening at high total strain amplitudes.The cyclic deformation behaviors were discussed using the Coffin-Manson plot,which divided the plastic strain amplitudes into the tension side and the compression side.Through the LCF tests that were started from either tension or compression under a total strain amplitude of 1.0%,the interaction between the twinning effect and dislocation was analyzed.The twinning effect during the LCF test and the variation of the dislocation density were investigated using optical microscopy and transmission electron microscopy,respectively.  相似文献   

13.
镍基单晶高温合金[111]取向拉压不对称分析   总被引:1,自引:0,他引:1  
试验表明,[111]取向镍基单晶高温合金宏观滑移迹线符合六面体滑移特征,而微观位错滑移机制为八面体滑移。针对上述宏、微观现象,提出了一种"之"字形交滑移模型,使宏观六面体滑移迹线与微观位错的八面体滑移在该模型中得到了很好的统一。同时,在上述"之"字形交滑移变形机制的基础上,对[111]取向的拉压不对称特性进行了分析,提出一种位错分解方式,对[111]取向产生拉压不对称特性的微观机制进行了表征。最终,基于上述两种机理,建立了[111]取向镍基单晶高温合金的拉压不对称预测模型。该模型不仅能够对[111]取向镍基单晶高温合金屈服强度进行预测,而且可以表征屈服强度的拉压不对称特性,即压缩屈服强度大于拉伸屈服强度以及拉压不对称随温度升高愈加严重的现象。  相似文献   

14.
The influence of crystal orientations on the low-cycle fatigue(LCF) behavior of a 3Re-bearing Ni-based single-crystal superalloy at 980 °C has been investigated. It is found that the orientation dependence of the fatigue life not only depends on the elastic modulus, but also the number of active slip planes and the plasticity of materials determine the LCF life,especially for the [011] and [111] specimens. The [011] and [111] specimens with better plasticity withstand relatively concentrated inelastic deformation caused by fewer active slip planes, compared to the [001] specimens resisting widespread deformation caused by a higher number of active slip planes. Additionally, fatigue fracture is also influenced by cyclic plastic deformation mechanisms of the alloy with crystal orientations, and the [001] specimens are plastically deformed by wave slip mechanism and fracture along the non-crystallographic plane, while the [011] and [111] specimens are plastically deformed by planar slip mechanism and fracture along the crystallographic planes. Moreover, casting pores,eutectics, inclusions and surface oxide layers not only initiate the crack, but also reduce the stress concentration around crack tips. Our results throw light upon the effect of inelastic strain on the LCF life and analyze the cyclic plastic deformation for the alloy with different orientations.  相似文献   

15.
Nickel-based superalloys are easy to produce low cycle fatigue (LCF) damage when they are subjected to high temperature and mechanical stresses. Fatigue life prediction of nickel-based superalloys is of great importance for their reliable practical application. To investigate the effects of total strain and grain size on LCF behavior, the high temperature LCF tests were carried out for a nickel-based superalloy. The results show that the fatigue lives decreased with the increase of strain amplitude and grain size. A new LCF life prediction model was established considering the effect of grain size on fatigue life. Error analyses indicate that the prediction accuracy of the new LCF life model is higher than those of Manson-Coffin relationship and Ostergren energy method.  相似文献   

16.
张璠 《贵金属》2019,40(3):1-4, 10
基于分子动力学模拟方法计算了铱单晶纳米线在室温下的拉伸和压缩变形行为。计算结果表明,铱单晶纳米线在拉伸和压缩时的力学性能均存在尺寸效应。铱单晶纳米线的拉伸和压缩变形行为具有非对称性,在拉伸条件下其伸长率为14%,而在压缩条件下表现出较好的塑性,在压缩过程中有堆垛层错产生,压缩应变达到0.499后模型还未发生断裂。  相似文献   

17.
This paper presents experimental studies on low cycle fatigue (LCF) life of super-elastic shape memory alloy (SESMA) wires. The effect of frequency of the loading and amplitude of the strain on the fatigue life has been studied individually. Various loading frequencies have been considered to study the effect of frequency, by keeping the amplitude constant. From the experimental data, it was found that the LCF life of the SESMA reduces with increase in the frequency. The effect of amplitude on the LCF life of SESMA has also been studied, and it was found that the SESMA cycled at lower net strain has more fatigue life than the one cycled at higher net strain. Further, the plastic strain accumulation is also more in the samples tested at the higher net strain loadings. The modulus of austenite is found to be by and large independent of the frequency and amplitude of the loading. Further, martensitic unloading modulus is same for all the minimum strain amplitudes.  相似文献   

18.
在420~650℃的温度范围内,研究了PM FGH95高温合金在应变率0.0001~0.01 s-1范围内的拉伸性能及在不同应力比R=-1及R=0下的低周疲劳性能.拉伸试验结果表明:在此温度范围内,应变率对弹性模量、拉伸屈服强度及塑性模量的影响可以忽略不计;并且应变率自0.0001 s-1增大至0.01 s-1时,弹性模量、拉伸屈服强度及塑性模量受温度的影响也不明显.PM FGH95合金受材料微结构的影响很大,材料含有的微缺陷对其力学性能有非常不利的影响.LCF试验结果表明:PM FGH95合金是循环硬化材料.当应力比R=-1时,温度对LCF寿命的影响很小;但在应力比R=0时,LCF寿命受温度的影响很大,且随着温度的增加材料的低周疲劳寿命减小.SEM断口扫描发现,断裂表面有很多的解理面,但没有疲劳条带,且此断裂模式下没有明显的塑性变形,所以FGH95合金的低周疲劳寿命几乎是由裂纹萌生阶段决定的.  相似文献   

19.
Experimental investigations on the fatigue behavior of a near-alpha titanium alloy under typical cyclic loadings were carried out to simulate the service loading states applied on the engine blades.The axial stress-controlled tension–tension low-cycle fatigue(LCF) tests were carried out over a range of maximum stresses and stress ratios.The rotary bending tests were conducted using a step-loading procedure to reveal the high-cycle fatigue(HCF) limit stresses.The cyclic softening effect is observed in this material,and the strain ratcheting occurs obviously at the maximum LCF loading of 900 MPa.The LCF resistance is found to be dependent on both the maximum loading and the stress ratio.The HCF limit stresses for 1 9 107 and 1 9 106 cycles are determined as405.7 and 457.6 MPa,respectively.The macroscopic fatigue fracture mode and the failure features on fracture surfaces were analyzed by scanning electron microscope(SEM).  相似文献   

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