共查询到19条相似文献,搜索用时 140 毫秒
1.
本工作研究了2090和8090合金名义门槛值、本征门槛值和闭合效应对裂纹尾迹的响应关系。Al-Li合金具有优良的疲劳长裂纹门槛值和强的短裂纹效应,其物理本质是高的裂纹闭合效应和裂纹闭合效应的尾迹依赖性.2090合金微小裂纹的扩展抗力劣于7075合金,系因△Ki低;8090合金的△Ki与2024合金相当,其短裂纹扩展抗力相当或优于2024合金,微量稀土元素Ce可显著改善2090合金的本征门槛值,有益于裂纹闭合效应,较大幅度提高其疲劳长、短裂纹扩展抗力。Ce降低8090合金的本征门槛值,有损于其疲劳长、短裂纹扩展抗力。 相似文献
2.
Ce对Al—Li合金物理短裂纹扩展特性的影响 总被引:2,自引:0,他引:2
本工作研究了2090和8090合金名义门槛值、本征门槛值和闭合效应对裂纹尾迹的响应关系。Al-Li合金具有优良的疲劳长裂纹门槛值和强的短裂纹效应,其物理本质是高的裂纹闭合效应和裂纹闭合效应的尾迹依赖性。2090合金微小裂纹的扩展抗力劣于7075合金,系因ΔKi低;8090合金的ΔKi与2024合金相当,其短裂纹扩展抗力相当或优于2024合金。微量稀土元素Ce可显著改善2090合金的本征门槛值,有益 相似文献
3.
采用原位观察疲劳试验方法研究了变形TiAl合金在650℃下的三维小裂纹扩展行为,利用传统疲劳裂纹扩展试验方法研究了该合金在650~800℃温度范围内的长裂纹扩展行为。结果显示,650℃下,变形TiAl合金的三维小裂纹在低于长裂纹扩展门槛值的区域依然能够扩展,并且扩展速率高于长裂纹;位于试样棱边的横向机械加工刻痕是合金三维小裂纹萌生的主要位置之一,小裂纹在扩展过程中发生偏折并在偏折处合并,合金的疲劳寿命对试样表面的不规则条状加工缺陷不敏感;在650~800℃温度范围内,合金的疲劳长裂纹稳态扩展速率对温度变化不敏感,裂纹扩展过程均显示为解理断裂,裂纹扩展门槛值受韧/脆转变温度影响,韧/脆转变温度以下温度的门槛值较低。 相似文献
4.
5.
6.
7.
8.
应用弹塑性断裂力学和△J参数,研究了16Mng钢短裂纹的纯机械疲劳和氢蚀疲劳特性。并用da/dN=C(△J)^n计算了裂纹的扩展速度和门槛值。用金相法考察了裂纹扩展途径。结果表明,氢的渗入降低了裂纹扩展的门槛值,加速了裂纹的扩展速度。 相似文献
9.
10.
本文研究了LD10铝合金和Ti-6Al-4V合金近门槛值疲劳裂纹扩展的断口形貌。SEM观察表明:两种合金的近门槛值区域(1×10~(-7)-1×10~(-5)mm/cycle)的微观断口形貌均为循环解理刻面;在LD10铝合金中循环解理刻面多数呈锯齿型或梯田状,而在Ti-6Al-4V合金中主要为孤岛状循环解理刻面。 本文在实验观察的基础上,进一步阐明了近门槛值疲劳裂纹扩展机理。 相似文献
11.
CHEN Zheng Northwestern Polytechnical University Xi′an China Lab.No. Northwestern Polytechnical University Xi′an 《金属学报(英文版)》1991,4(2):135-138
Threshold of fatigue for short through cracks for Al-Li alloy 8090 was evaluated to be lowerthan that of long cracks,and to decrease with the shortening of the crack length.The correla-tion among the threshold,crack wake,and crack tip shielding of the short fatigue cracks wasdiscussed.The super demarcation length and lowest theoretical threshold of short through fa-tigue cracks were presented. 相似文献
12.
通过考察碳素工具钢的表面滑移、疲劳破坏及表面裂纹的扩展条件,以统一的局部应力讨论了光滑试样和裂纹试样的疲劳特征。分析和实验结果表明,在裂纹试样的名义应力小于光滑试样表面滑移门槛应力的范围内,线弹性断裂力学是有效的,对应裂纹扩展门槛值的裂尖性区为一常数。 相似文献
13.
目的 研究腐蚀环境中EA4T车轴钢疲劳性能,为车轴的腐蚀检测和使用寿命评估提供依据.方法 采用旋转弯曲疲劳试验机,在人造雨水模拟的腐蚀环境和空气环境中,对EA4T车轴钢试样进行疲劳试验,以获得不同环境下试样的疲劳S-N曲线、表面损伤以及裂纹扩展规律.然后对扩展裂纹进行概率统计,通过扫描电镜对疲劳失效的断口进行观察,并分析对比不同环境中裂纹扩展门槛值的变化.结果 空气环境中,试样的疲劳极限为355 MPa,而在腐蚀环境中,试样不存在疲劳极限,107循环周次对应的疲劳强度降低到245 MPa,相比空气环境中降低了31%.Gumbel分布统计与Weibull双参数分布统计相比,更适合描述EA4T车轴钢试样表面腐蚀裂纹长度随加载次数的变化.腐蚀环境中,疲劳裂纹萌生于表面腐蚀坑,并存在多个裂纹源.腐蚀环境显著降低了试样裂纹扩展门槛值,空气环境下,该值为6.29 MPa·m1/2,腐蚀环境下降低到4.1 MPa·m1/2.结论 腐蚀环境降低EA4T钢疲劳寿命的主要原因是,腐蚀环境降低了裂纹扩展门槛值,加快了裂纹萌生以及短裂纹扩展.而当裂纹达到一定长度时,腐蚀环境对裂纹扩展几乎没有影响. 相似文献
14.
PEI Hongxun YANG Jingjun KE Wei Institute of Corrosion Protection of Metals Academia Sinica Shenyang China PEI Hongxun Institute of Corrosion Protection of Metals Academia Sinica Shenyang China 《金属学报(英文版)》1989,2(9):167-171
The effects of environmental media,both in atmosphere and in 3.5% NaCl aqueous solution,on the growth of short cracks in comparison with the long ones have been investigated underfatigue loading on the specimens of single-edge crack about 0.05—0.15 mm for A537CLIsteel.The growth rate of short cracks is faster than those of long ones around the threshohtstress intensity.The threshold stress intensity for short crack growth decreases with de-creasing crack length.The acceleration effect of the salt water,as compared with atmosphereenvironment,on the growth of short cracks under fatigue is much greater than that on thegrowth of long cracks. 相似文献
15.
16.
工业结构钢疲劳极限的断裂力学研究 总被引:1,自引:0,他引:1
文章提出一种预测材料疲劳极限的简便方法。该方法仅需获得一个材料参数(如材料硬度)便可确定材料的裂纹扩展抵抗阻力曲线。由于有效应力强度因子范围门槛值ΔKeffth∞是一个与裂纹长度及应力比无关的材料常数,只需将裂纹张开应力强度因子门槛值Kopth表示为裂纹长度的函数,作出材料的疲劳断裂曲线,就可以预测任意应力比下光滑试样的疲劳极限。利用这种方法作出的预测值与试验结果一致。 相似文献
17.
18.
《Science & Technology of Welding & Joining》2013,18(5):430-438
AbstractCurrent fracture mechanics methods for fatigue assessment, including those that consider thresholds for crack propagation, are based on long crack behaviour. The present work is concerned with an attempt to predict the fatigue strength of welded joints using a fracture mechanics approach that takes into account the fatigue behaviour of short cracks. The methodology estimates the fatigue crack propagation rate as a function of the difference between the applied driving force and the material threshold for crack propagation, which is a function of crack length. The fatigue strength of butt welded specimens stressed transversely was analysed. Experimental results from the literature were used for comparison. Estimations are obtained by using only the fatigue limit and the fatigue propagation threshold for long cracks, and the applied stress distribution along the crack path obtained from simple finite element models. The influence of plate thickness, initial crack length, and reinforcement angle on fatigue strength of butt welded joints was analysed. Results show good agreement with experimental trends. 相似文献
19.
The short fatigUe cracks for aluminum-lithitim alloys are mainly in the field of mechanicalcharacteristic research [l--31. It is found thataluminum-lithium alloys eallibit the strongershort crack effect, which is difficult to overcome. In this icicle, the thresholds of short fatigUe cracks for alUminUm-lithium alloys 2090and 2090 Ce have been quantitatively stUdiedand evaluated. By adding Ce into alloy 2090, thebeneficial influence over the microstrUcture andproperties can be achieved [4, 5… 相似文献