共查询到19条相似文献，搜索用时 359 毫秒
1.
基于临界面模型的方法提出一个新的(修正的)多轴低周疲劳损伤准则.该准则与目前的临界面法所不同的是,在预测多轴低周疲劳寿命的模型中,同时考虑临界面上最大剪应变和正应变在不同加载路径下对多轴低周疲劳损伤的贡献。试验结果表明,本文提出的多轴低周疲劳寿命预测模型,对于GH4169合金高温多轴疲劳寿命估算具有较高的准确性。 相似文献
2.
推导了应力控制和应变控制模式下沥青混合料的热力学疲劳损伤模型.选取回弹模量作为损伤硬化参数,提取出一个与动态模量相关的损伤变量作为评估指标.所获得的2种控制模式下的损伤演化规律中保留了一个与加载水平有关的非负材料参数m,具有与Chaboche疲劳模型相似的形式.在每种控制模式下,采用4组加载水平所获得的疲劳损伤试验数据校核模型并确定参数.由此发现参数m与荷载水平呈指数关系.利用所获得的演化方程可阐述2种控制模式下的损伤演化差异,即在应变控制模式下,疲劳损伤演化由快变慢,在应力控制模式下情况则相反.通过利用损伤等效原理计算等效荷载循坏次数,该模型还解释了在多级加载条件下,2种控制模式的疲劳演化差异:在应变控制的疲劳模式下,所加荷载等级按照从低荷载到高荷载的顺序会加速损伤演化,而在应力控制的疲劳模式下,相反的荷载施加顺序可延长疲劳寿命. 相似文献
3.
利用薄壁管试样,在MTS809疲劳试验机上对GH4169镍基高温合金进行了650oC下的高温多轴拉扭低周疲劳试验,通过对应力应变迟滞迴线分析发现,拉扭分量应力应变迟滞迴线形状与试件的加载波形和加载路径相关,塑性应变不断增大。利用FEI-Quanta 200扫描电镜和EDAX Genesis 2000 X-射线能谱仪对试样疲劳断口微观分析,结果表明,GH4169镍基高温合金材料在高温循环加载下有氧化现象。综合不同等效应变下材料的断口形貌差异,推断在高温循环加载下有蠕变氧化作用。 相似文献
4.
对高温合金材料GH4169加工成的拉扭薄壁管试样在650℃下进行了多轴变幅疲劳试验,利用有限元分析软件计算各种加载情况下薄壁管的应力应变场,并通过对加载特殊位置处应力、应变的计算结果进行分析和比较,确定出主导材料疲劳损伤的危险点,为以后薄壁管试件的寿命预测奠定基础。 相似文献
5.
6.
单点与双点拉剪点焊试样的疲劳特性比较 总被引：1，自引：0，他引：1
对单点与两点焊拉剪点焊疲劳试样分别进行了疲劳试验,观测了疲劳裂纹的形状和萌生位置,分析了两种试样的疲劳性能。通过有限元模型分析了同等载荷作用下两种试样的变形,对比两种试样的载荷幅寿命关系,认为两点试样的承载能力约为单点试样的两倍。基于此,使用单点试样的载荷幅寿命曲线,预测了两点试样的疲劳寿命,寿命预测结果与实验寿命结果一致。 相似文献
7.
为了研究沥青混凝土的疲劳特性,提出了基于双线性内聚力模型（CZM）的数值模拟方法．建立了疲劳损伤演化模型并将其与内聚力模型耦合,以反映沥青混凝土在循环荷栽作用下的软化行为．通过编制用户材料子程序。实现了疲劳损伤模型在有限元软件ABAQUS中的应用,并对劈裂疲劳试验进行了模拟．研究结果表明：模拟得到的疲劳寿命与实验室结果基本一致;疲劳损伤随加载次数的累积是非线性的,且损伤累积阶段是疲劳破坏的主要阶段;应力比增大时,损伤稳态发展阶段的寿命明显减小．可以发现提出的疲劳损伤数值模型是一种预估沥青混凝土疲劳损伤的有效方法． 相似文献
8.
对GH4169镍基高温合金制成的薄壁圆管试样的多轴循环相关特性进行了研究。试验在MTS809-250 kN/2000 Nm电液伺服拉-扭低周疲劳试验机上进行,采用恒幅总应变控制,对称加载,轴向应变与扭转应变的加载采用三种不同相位(0°、45°和90°),其加载频率分别为0.1 Hz和0.2 Hz,试验温度为650℃.通过对薄壁圆管高温多轴比例和非比例循环加载试验,研究了该材料在多轴循环载荷下的应力-应变响应和循环相关特性。试验结果表明,GH4169合金在试验温度下不通加载路径下均呈现为循环软化现象,其循环软化程度与等效应变和轴向与剪切方向之间的相位差密切相关。 相似文献
9.
一种腐蚀疲劳损伤的非线性累加演化模型 总被引：1，自引：0，他引：1
研究目的：提出一种新的腐蚀疲劳损伤演化模型,建立基于损伤演化的腐蚀疲劳寿命预测模型。创新要点：将应力腐蚀损伤与疲劳损伤非线性耦合,建立腐蚀疲劳损伤演化律,依托实验确定腐蚀疲劳损伤演化参数,形成基于损伤演化律的腐蚀疲劳寿命预测模型。研究方法：采用理论研究与实验验证相结合的研究方法。选取特定材料设计应力腐蚀实验,回归应力腐蚀门槛值应力和损伤参数（图2）;查阅疲劳实验数据建：立变幅疲劳损伤模型,将应力腐蚀损伤与变幅疲劳损伤非线性累加形成腐蚀疲劳损伤非线性演化模型。根据腐蚀疲劳实验结果,验证腐蚀疲劳损伤演化模型并确定非线性损伤累加参数（图5和6）,形成基于损伤演化律的腐蚀疲劳寿命预测模型。重要结论：从损伤力学角度,将材料的腐蚀疲劳损伤处理成应力腐蚀损伤与疲劳损伤的非线性累加,形成腐蚀疲劳损伤演化模型。结合LY12CZ铝合金的试验结果,验证了损伤演化模型的可行性。该方法可以为材料腐蚀疲劳的寿命评价研究提供新的思路。 相似文献
10.
研究目的:提出一种新的腐蚀疲劳损伤演化模型,建立基于损伤演化的腐蚀疲劳寿命预测模型。创新要点:将应力腐蚀损伤与疲劳损伤非线性耦合,建立腐蚀疲劳损伤演化律,依托实验确定腐蚀疲劳损伤演化参数,形成基于损伤演化律的腐蚀疲劳寿命预测模型。研究方法:采用理论研究与实验验证相结合的研究方法。选取特定材料设计应力腐蚀实验,回归应力腐蚀门槛值应力和损伤参数(图2);查阅疲劳实验数据建立变幅疲劳损伤模型,将应力腐蚀损伤与变幅疲劳损伤非线性累加形成腐蚀疲劳损伤非线性演化模型。根据腐蚀疲劳实验结果,验证腐蚀疲劳损伤演化模型并确定非线性损伤累加参数(图5和6),形成基于损伤演化律的腐蚀疲劳寿命预测模型。重要结论:从损伤力学角度,将材料的腐蚀疲劳损伤处理成应力腐蚀损伤与疲劳损伤的非线性累加,形成腐蚀疲劳损伤演化模型。结合LY12CZ铝合金的试验结果,验证了损伤演化模型的可行性。该方法可以为材料腐蚀疲劳的寿命评价研究提供新的思路。 相似文献
11.
Based on the nonlinear continuum damage model(CDM) developed by Chaboche,a modified model for high cycle fatigue of TC4 alloy was proposed.Unsymmetrical cycle fatigue tests were conducted on rod specimens at room temperature.Then the material parameters needed in the CDM were obtained by the fatigue tests,and the stress distribution of the specimen was calculated by FE method.Compared with the linear damage model(LDM),the damage results and the life prediction of the CDM show a better agreement with the test and they are more precise than the LDM.By applying the CDM developed in this study to the life prediction of aeroengine blades,it is concluded that the root is the most dangerous region of the whole blade and the shortest life is 58 211 cycles.Finally,the Cox proportional hazard model of survival analysis was applied to the analysis of the fatigue reliability.The Cox model takes the covariates into consideration,which include diameter,weight,mean stress and tensile strength.The result shows that the mean stress is the only factor that accelerates the fracture process. 相似文献
12.
采用周期浸润加速腐蚀试验的方法,对某型飞机42框横梁模拟件分组进行了不同时间的加速预腐蚀试验,并通过随机载荷谱下的疲劳试验获得了预腐蚀后模拟件的疲劳寿命。结果表明,在加速腐蚀时间不大于300小时的情况下,预腐蚀对42框横梁结构模拟件疲劳寿命的影响不明显。 相似文献
13.
Thermal fatigue (TF) is one of the most important factors that influence turbine’s life. This paper establishes a 3D solid-fluid
coupling model for a steady temperature analysis of a high-pressure turbine nozzle at different turbine inlet gas total temperatures
(TIGTTs). The temperature analysis supplies the temperature load for subsequent 3D finite element analysis to obtain the strain
values. Following this, the prediction of the TF life is made on the basis of equivalent strain range. The results show that
the strain increases with TIGTT, and the predicted TF life decreases correspondingly. This life prediction was confirmed by
one TF test. 相似文献
14.
Fatigue tests were conducted on tapered plain concrete prism specimens under triaxial constant-amplitude tension-compression cyclic loading. The low stress of the cyclic loading was taken as 0.2fc and the upper stress ranged from 0.20ft to 0.65ft. Three constant lateral pressures were 0.1fc, 0.2fc and 0.3fc respectively. Based on the results, the three-stage evolution nile of the fatigue stiffness, maximttm(minimum) longitudinal strain and damage were analyzed, and a unified S-N curve to calculate fatigue strength factors was worked out. The results show that the fatigue strength and fatigue life under triaxial constant-amplitude tension-compression cyclic loading are smaller than those under uniaxial fatigue condition. Moreover, the secondary strain creep rate is related to the fatigue life, a formula for describing their relation was derived. The investigation of this paper can provide information for the fatigue design of concrete structures. 相似文献
15.
16.
Due to traffic and wave actions, cast steel joints are subjected to variable-amplitude fatigue loading, which may cause fatigue problems. The ratio of the minimum strain to the maximum strain(strain ratio)can be employed to analyze the influence of variable-amplitude fatigue both in the elastic and plastic ranges. To evaluate the effect of the strain ratio on G20Mn5QT cast steel, the fatigue tests of smooth specimens were carried out at the strain ratio of 0.1. The cyclic deformation and the relationships between the strain amplitude, the stress amplitude, the Smith, Watson and Topper(SWT)parameter and fatigue life were studied and compared with those at the strain ratio of -1. Compared with other methods, Basquin formula and Solonberg formula provide reliable and appropriate ranges of S-N curve and fatigue limit at different strain ratios respectively. The SWT parameter can be used to predict the fatigue life at other strain ratios accurately. 相似文献
17.
采用国产NiTi形状记忆合金,在Af温度以上对其进行比例、非比例循环疲劳,结果表明:随着加载路径的非比例度的增加,稳定的平台应力和疲劳寿命降低而循环过程中的残余应变和马氏体的起始转变应力增加. 相似文献
18.
Numerical Derivation of Strain Rate Effects on Material Properties of Masonry with Solid Clay Bricks
In this paper, numerical method is used to study the strain rate effect on masonry materials. A typical unit of masonry is selected to serve as a representative volume element (RVE). Numerical model of RVE is established with detailed distinctive modeling of brick and mortar with their respective dynamic material properties obtained from laboratory tests. The behavior of brick and mortar are characterized by a dynamic damage model that accounts for rate-sensitive and pressuredependent properties of masonry materials. Dynamic loads of different loading rates are applied to RVE. The equivalent homogenized uniaxial compressive strength, threshold strain and elastic modulus in three directions of the masonry are derived from the simulated responses of the RVE. The strain rate effect on the masonry material with clay brick and mortar, such as the dynamic increase factor (DIF) of the ultimate strength and elastic modulus as a function of strain rate are derived from the numerical results. 相似文献
19.
ZHAN Liang-tong CHEN Ping NG C.W.W. 《浙江大学学报(A卷英文版)》2007,8(5):699-706
A laboratory study was carried out on both natural and compacted specimens to investigate the complex soil-water interaction in an unsaturated expansive clay. The laboratory study includes the measurement of soil-water characteristic curves, 1D free swelling tests, measurement of swelling pressure and shrinkage tests. The test results revealed that the air-entry value of the natural specimen was quite low due to cracks and fissures present. The hydraulic hysteresis of the natural specimen was relatively insignificant as compared with the compacted specimen. Within a suction range 0 to 500 kPa, a bilinear relationship between free swelling strain (or swelling pressure) and initial soil suction was observed for both the natural and compacted specimens. As a result of over-consolidation and secondary structures such as cementation and cracks, the natural specimens exhibited significant lower swelling (or swelling pressure) than the compacted specimen. The change of matric suction exerts a more significant effect on the water phase than on the soil skeleton for this expansive clay. 相似文献