共查询到18条相似文献，搜索用时 156 毫秒
1.
LZ50车轴钢疲劳裂纹扩展试验研究 总被引：1，自引：0，他引：1
完成了连铸和模铸LZ50车轴钢疲劳裂纹扩展试验,得到了两类LZ50车轴钢的疲劳裂纹扩展曲线。采用Paris公式和另一种全范围表达式研究了两种铸造工艺下LZ50车轴钢的疲劳裂纹扩展规律。研究结果表明:Paris公式仅能描述LZ50车轴钢疲劳裂纹稳定扩展阶段的规律;全范围表达式对LZ50车轴钢的全范围疲劳裂纹扩展规律描述较好,且得到的疲劳裂纹扩展门槛值与试验曲线得到的门槛值接近,相对误差小于3%;连铸LZ50车轴钢的疲劳裂纹扩展速率门槛值低于模铸LZ50车轴钢,其疲劳裂纹扩展性能不如模铸LZ50车轴钢。 相似文献
2.
Paris模型、Walker模型和Forman模型是常用的3种疲劳裂纹扩展速率模型,为比较3种模型在不同应力比下,拟合疲劳裂纹稳定扩展阶段速率的异同,采用标准紧凑拉伸试样进行疲劳裂纹扩展速率试验,由试验数据拟合得到3种模型公式的参数,并进行对比分析。结果表明,3种模型拟合精度均随应力比增大逐渐降低;对于单一应力比下的疲劳裂纹扩展,3种模型均具有较好的精度,但对于不同应力比下的疲劳裂纹扩展,Walker模型的拟合结果随应力比增大略有失真;而Forman模型的拟合结果随应力比增大有较大失真。 相似文献
3.
直升机结构设计的损伤容限分析,需要使用材料疲劳裂纹扩展速率曲线性能。在总结传统疲劳裂纹扩展曲线的基础上,本文讨论了四参数全范围da/dt曲线公式。根据断裂性能测试标准,分别实验测试了直升机桨叶根部材料断裂韧性K1C,3个应力比下的裂纹扩展门槛值ΔKth和裂纹扩展速率da/dt;然后,利用多元线性回归法对试验数据进行了曲线拟合,分别得到了断裂等寿命曲线和四参数全范围da/dt曲线公式的参数估计式;最后,将此公式运用于不同应力比下的裂纹扩展速率试验数据,拟合得到该材料四参数全范围da/dt曲线公式。 相似文献
4.
朱锡雄 《宁波大学学报(教育科学版)》1989,(1)
本文在内参量热力学的理论框架内详细讨论了线弹性裂纹体的裂纹扩展问题。对线弹性断裂力学中所涉及到的各种能量关系作了统一的整理,其中包括Irwin的弹性能释放率——裂纹扩展力,Griffith的脆性断裂准则,以及Irwin-Kies的柔度公式和Paris的位移公式。本文以中心裂纹体为例,详细计算了裂纹扩展的稳定性,并区分恒载荷和恒位移两种情况,对材料断裂韧性测试中所遇到的失稳扩展,稳定扩展以及进发现象提供了理论说明。 相似文献
5.
WENG Yong-gang 《实验室研究与探索》2007,(10)
应用软件FCG(MTS Fatigue Crack Growth TestW are)采用七点递增多项式局部拟合的方法,计算疲劳裂纹扩展速率da/dN,导致计算值分散度很大。经过详细分析,提出采用正交多项式的线性组合作为疲劳裂纹长度a与载荷循环数N之间关系的拟合目标函数,再用直接求导的方法计算da/dN。这样减小了da/dN的分散度,提高了Paris公式参数拟合和门槛值计算的精度。 相似文献
6.
以新一代超低碳贝氏体桥梁用钢为研究对象,从冲击韧性、J积分和CTOD三个方面进行试验研究与分析,讨论了试验温度对冲击裂纹起始功Wi、扩展功Wp及冲击总功Wt的影响,绘制出CTOD和J积分阻力曲线。结果表明:裂纹起始功Wi、扩展功Wp和冲击总功Wt都随温度的降低而减小,在-80℃时,冲击总功为310J,材料没有发生韧脆转变。利用阻力曲线计算出δ0.2BL为0.31mm,J0.2BL为273.75kN/m。 相似文献
7.
基于Paris 公式建立TBM 刀盘的裂纹扩展模型,利用Workbench 模拟裂纹的开裂过程,计算出其循环次数与应力强度因子。 并改变双裂纹的初始长度、距离、角度,分析多部位损伤时筋板的裂纹扩展寿命。 结果表明,裂纹的初始长度越长构件越容易失效,每增加2.5 mm 寿命将减少35%,而双裂纹距离对寿命的影响较小,在10%以内。 当裂纹方向和受力方向垂直时,构件容易失效,反之则对寿命的影响越小。 该研究可为刀盘设计过程中疲劳寿命领域提供参考。 相似文献
8.
高压富气输送管道要求发展管道钢的裂纹尖端张开角的测试方法。采用准静态的撕裂过程和长裂纹扩展长度试件,进行了X70管道钢的裂纹扩展试验,用摄像机跟踪拍摄裂纹扩展全过程,从获得的照片上直接测量出裂纹扩展全过程的CTOA值,分析了裂纹扩展中的断裂力学行为。试验结果表明,试件的韧带厚度越小,越容易获得稳定的扩展过程,且稳态裂纹扩展的CTOA值随试件韧带厚度的增加而增大,太厚的试件不易得到稳态扩展过程。韧带厚度为4 mm、8 mm试件的稳态的裂纹扩展阶段分别为7.6°、11.3°,裂纹扩展长度与韧带厚度比在4~25、4~10之间。 相似文献
9.
直流电位法自动检测高温疲劳裂纹长度的研究及应用 总被引：2，自引：0，他引：2
利用Johnson的分析型关系式,研究了一种适用于自动检测高温疲劳裂纹长度的直流电位法,成功地应用于三种铝合金和两种钛合金的高温疲劳裂纹扩展试验。用直流电位法和光学视频法所检测的裂纹长度相当吻合,其检测精度在±3%之内。对研究材料的疲劳门槛值、宽板的裂纹扩展速率和小裂纹试验有其推广应用价值。 相似文献
10.
CUI Hong-bin 《实验室研究与探索》2007,(10)
由于高强度钢在疲劳断裂过程中很难产生辉纹,给裂纹扩展的研究带来一定的困难。本文在对接焊平板的疲劳断裂试验中,采用降载勾线法制造出"海滩状花纹",借此对裂纹扩展过程中裂纹前缘形状和裂纹扩展速率进行分析,并与Newman-Raju公式的计算结果进行比较。 相似文献
11.
The mechanism and criterion of crack initiation and propagation of rocks were investigated by many researchers,And the creep behaviour of rocks was also theoretically and experimentally studied by some scientists and engineers.The characteristics of crack initation and propagation of rocks under creep condition.however,are very improtant for rock engineering and still not paid enough attention by researchers,In this paper,the criterion and mechanism of crack initiation and propagation under creep condition were investigated using specimens collected from sandstone rock formations outcropping in the Emei Mountain,the Sichuan Province of China.Cuboid specimens under three point bending were used in this investigation.All specimens were classified into four sorts and used for Mode-I fracutre of creep frcture tests.The experimental result shows that due to creep deformation.rock crack will inevitably initialt and propagate under a load of KI,which is less than fracture toughness KIC but not less than a constant(marked as KIC2),KIC2 indicates the ability of rock to resist crack initiation and propagation under creep conditions and is less than fracture tough ness KIC.defined as creep fracture toughness in this paper,KIC2 should be considered as an importnat parameter on design and computation of rock engineering.The microstructureal mechanism for crack initiation and propagation of rock materials under creep condition was introduced based on competitive model between softening effect and hardening effect,and the validity of test result was explained.The test result was also verified in rheological theory.When KI is more than KIC2 but less than KIC,rock crack will initiate and propagate after a time interval of sustained loading under creep condition.In order to find the relation between duration of sustained lading.which can lead to crack initiation and propagation,and the initial stress intensity factor KI,an unequal0interval time sequence forecasting and predicting model was introduced,and the relation was obtained for homogeneous and isotropic fine-grained red sandstone.Finally a modified fracture toughness formula was given,in which the influence of fracture process zone(FPZ) was fully considered. 相似文献
12.
Fatigue crack growth rate test using a frequency sweep method 总被引：1，自引：0，他引：1
Xun ZHOU Xiao-li YU 《浙江大学学报(A卷英文版)》2008,9(3):346-350
Fatigue crack propagation characteristics of a diesel engine crankshaft are studied by measuring the fatigue crack growth rate using a frequency sweep method on a resonant fatigue test rig. Based on the phenomenon that the system frequency will change when the crack becomes large, this method can be directly applied to a complex component or structure. Finite element analyses （FEAs） are performed to calibrate the relation between the frequency change and the crack size, and to obtain the natural frequency of the test rig and the stress intensity factor （SIF） of growing cracks. The crack growth rate i.e. da/dN-AK of each crack size is obtained by combining the testing-time monitored data and FEA results. The results show that the crack growth rate of engine crankshaft, which is a component with complex geometry and special surface treatment, is quite different from that of a pure material. There is an apparent turning point in the Paris＇s crack partition. The cause of the fatigue crack growth is also discussed. 相似文献
13.
Fatigue and fracture behavior of nickel-based superalloy Inconel 718 up to the very high cycle regime 总被引：2，自引：0，他引：2
Xian-feng Ma Zheng Duan Hui-ji Shi Ryosuke Murai Eiichi Yanagisawa 《浙江大学学报(A卷英文版)》2010,11(10):727-737
The fatigue and fracture behavior of nickel-based superalloy Inconel 718 was investigated up to the very high cycle regime under rotary bending tests at room temperature. It was found that this superalloy can still fracture after exceeding 107 cycles. Fractographic analysis revealed that there was a transition from fatigue crack initiation at multi-sites to single initiation with decreasing stress levels. The fracture surface can be divided into four areas according to the appearance, associated with fracture mechanics analysis of the corresponding stress intensity factors. The fracture mechanism dominant in each area was disclosed by scanning electron microscope examination and analyzed in comparison with those obtained from the crack growth tests. Subsequently, life prediction modeling was proposed by estimating the crack initiation and propagation stage respectively. It was found that Chan （2003）＇s model for initiation life and the Paris law for growth life can provide comparable predictions against the experimental life. 相似文献
14.
15.
利用2种不同的方法加筋沥青罩面:①在沥青混合料中加入短切玻璃纤维改善沥青混凝土的特性,②采用玻璃格珊加筋沥青混凝土.应用断裂力学方法分析沥青路面裂缝扩展机理.采用沥青混合料设计试验、三点弯曲试验和疲劳裂缝扩展试验,确定加筋沥青混凝土的临界应力强度因子KIC,测量每一种沥青罩面抗裂系统的裂缝扩展速率.本研究的主要特点是提出复合型抗裂罩面系统,分析了多层加筋沥青罩面裂缝扩展过程,推荐了若干沥青路面抗裂系统.结果证明,加筋材料可以提高沥青罩面的抗裂特性,复合型抗裂罩面系统能够有效地阻止反射裂缝的扩展. 相似文献
16.
用原位拉伸研究复合材料的机械性能 总被引：5，自引：0，他引：5
用扫描电镜原位拉伸的方法研究了碳化硅纤维增强镁铝复合材料的机械性能. 通过对材料中裂纹的起源、扩展、断裂过程的观察研究, 发现在拉伸状态下, 裂纹最初起源于碳化硅纤维; 在碳化硅纤维与基体结合较强时, 裂纹首先在碳化硅纤维中扩展, 同时裂纹附近的碳化硅纤维亦开始产生微观裂纹、镁铝金属基体发生塑性变形, 最终断裂; 而在碳化硅纤维与基体结合较弱的状态下, 材料的韧性较高. 相似文献
17.
全世海 《天津职业院校联合学报》2013,(6):109-111,120
预埋管灌浆是化学灌浆技术结合仿生自修复机理应用于混凝土裂缝修补的一种新的尝试,通过初始粘度和粘结拉伸强度测试选择适宜的环氧树脂浆液配方,采用通长配置2Ф4钢丝和壁厚1㎜中性白玻管的混凝土抗折试块作模拟灌浆试件,以抗折强度恢复率比较预埋管灌浆和传统钻孔灌浆两种不同灌浆方式的修补效果,试验结果表明:预埋管灌浆可达到甚至超过钻孔灌浆的修复效果,但要推广应用于工程实践,还有很多的技术关键有待深入研究和完善。 相似文献