基于应力概率密度和功率谱密度法的随机声疲劳寿命预估方法研究

针对航空发动机燃烧室火焰筒结构的声疲劳问题,研究了一种用于随机载荷下结构疲劳寿命预估的有效方法。首先,对薄壁结构在随机载荷作用下的Von Mises应力过程的概率分布作了研究,给出了应力峰值概率密度函数的表达式。基于Miner线性理论,提出了基于应力概率密度和功率谱密度法的随机声疲劳寿命预估方法,并建立了疲劳寿命预估模型。以某型航空发动机燃烧室火焰筒结构为例,在采用耦合的有限元和边界元方法计算出随机声疲劳应力基础上,应用所建立的模型进行了疲劳寿命估算,并对计算结果进行了宽带修正。结果表明,该方法对航空薄壁结构随机疲劳寿命分析具有实用性。     

汽车悬架控制臂拉压溃分析及疲劳寿命预测

以某汽车的后悬架上控制臂为研究对象,建立悬架控制臂有限元仿真模型。对悬架控制臂在拉、压工况下,进行拉溃力和压溃力分析,并进行试验验证。试验结果表明,该控制臂拉、压溃试验结果与有限元分析结果基本一致。通过对该控制臂进行有限元分析,提取危险部位的应力应变信息建立疲劳损伤参量,引入临界平面法建立疲劳寿命预测模型。运用该模型进行疲劳寿命分析与预测,并进行试验验证。疲劳试验结果表明,控制臂疲劳寿命的平均试验值与预测值比较贴近,说明所采用的疲劳损伤模型,可以应用于汽车金属零部件的疲劳寿命预测上。     

桥壳多轴向多激励虚拟试验系统研究EI北大核心CSCD

为提出一种多轴向多激励的桥壳试验方法,并为桥壳虚拟疲劳试验研究提供有效的输入手段。建立桥壳有限元模型并进行模态分析与模态试验,分析模态和试验模态不仅振型一致,而且各阶固有频率误差均<5%;在此基础上,采用模态综合法提取出桥壳柔性体文件;通过有限元柔性体文件替换法,建立了桥壳多轴向多激励的刚柔耦合虚拟试验系统,并基于简谐信号和随机信号进行系统仿真验证。基于道路模拟激励谱进行桥壳虚拟道路模拟仿真试验,并采用多轴向多激励道路模拟试验系统进行了试验验证,结果表明仿真与试验信号在幅值和趋势上具有较高的一致性,所建立的桥壳多轴向多激励虚拟试验系统具有较高的准确性,从而为桥壳设计验证和评价提供了一种高效准确的手段和方法。     

桥壳多轴向多激励虚拟试验系统研究

为提出一种多轴向多激励的桥壳试验方法,并为桥壳虚拟疲劳试验研究提供有效的输入手段。建立桥壳有限元模型并进行模态分析与模态试验,分析模态和试验模态不仅振型一致,而且各阶固有频率误差均5%;在此基础上,采用模态综合法提取出桥壳柔性体文件;通过有限元柔性体文件替换法,建立了桥壳多轴向多激励的刚柔耦合虚拟试验系统,并基于简谐信号和随机信号进行系统仿真验证。基于道路模拟激励谱进行桥壳虚拟道路模拟仿真试验,并采用多轴向多激励道路模拟试验系统进行了试验验证,结果表明仿真与试验信号在幅值和趋势上具有较高的一致性,所建立的桥壳多轴向多激励虚拟试验系统具有较高的准确性,从而为桥壳设计验证和评价提供了一种高效准确的手段和方法。     

U形波纹管疲劳寿命有限元分析

运用ANSYS有限元软件对波纹管进行应力分析,得出波纹管应力集中位置,借助Fatigue tool模块,采用E—N方法进行疲劳寿命分析,得到波纹管的疲劳寿命分布。有限元分析结果与经验公式及试验结果的比较,得出有限元模拟结果比经验公式更加接近试验结果。最后指出了在进行波纹管疲劳寿命有限元分析过程中需要注意的问题。     

2024铝合金喷丸试件疲劳寿命试验及仿真研究

现有的喷丸材料疲劳性能研究扩展有限元模型没有考虑残余应力对裂纹扩展的影响。对2024铝合金的喷丸与未喷丸试样进行三弯疲劳试验,以明确喷丸工艺对试件疲劳寿命的强化作用。通过ABAQUS建立试件的二维平面应力模型,导入残余应力并利用扩展有限元法模拟循环载荷下裂纹的萌生与扩展,对比试验结果来验证该扩展有限元数值模型的正确性。最后基于该数值模型,改变载荷工况,研究不同载荷工况下残余应力对疲劳寿命的影响,得到喷丸残余应力强化作用与载荷工况的关系。结果表明:喷丸引入的残余应力可以有效地增强试件的疲劳寿命;过大的循环载荷可能造成喷丸残余应力发生松弛;在最大载荷不变的前提下,应力比越小,试件疲劳寿命越短;应力比越大,残余应力对疲劳寿命强化效果越明显。     

路面激励作用下的桥壳动载荷研究

针对在汽车行驶过程中桥壳容易发生疲劳破坏的情况,使用了一种操作方便、成本低、数据可靠的方法来获取桥壳处的动载荷信号.采集了汽车行驶在搓板路、鱼鳞坑路和扭曲路这3种典型路面上时桥壳处受到的加速度信号,通过对轮胎悬架系统进行求解计算得到桥壳处受到的力信号,以该力信号作为输入载荷对该桥壳进行了疲劳寿命预测,预测结果符合常理,该方法具有可参考性.     

钢丝绳拉伸疲劳寿命仿真分析与试验研究

为研究钢丝绳在拉伸载荷下的疲劳寿命预测问题,以6×36 WS结构钢丝绳为研究对象,建立了钢丝绳的有限元模型,仿真分析了其在轴向拉伸载荷下的应力分布。对仿真结果中应力最大的钢丝进行拉伸疲劳试验,得到钢丝试件的载荷寿命曲线。在此基础上进行了钢丝绳疲劳寿命的仿真分析,并通过钢丝绳的疲劳试验进行了验证。钢丝绳疲劳仿真结果表明,在轴向拉伸载荷作用下,最大应力位于相邻两个绳股接触区域,对应的此处区域疲劳寿命最短。钢丝绳疲劳寿命仿真与试验结果具有较好的吻合度,由仿真数据拟合的载荷寿命曲线为钢丝绳疲劳寿命的预测提供了依据。     

随机振动载荷下塑封球栅阵列含铅焊点疲劳寿命模型

对塑封球栅阵列(PBGA)封装器件Sn37Pb焊点进行了正弦振动、随机振动实验,得到各个载荷下焊点的疲劳寿命结果.建立了三维有限元模型,进行与实验条件一致的有限元分析,计算焊点的应力;将实验结果与有限元计算相结合,并基于Steinberg寿命预测模型,发展了随机振动载荷下焊点疲劳寿命预测方法.结果表明,疲劳寿命模型预测...     

2E12铝合金中心孔板材疲劳寿命分析

以2E12铝合金光滑疲劳实验为基础,结合有限元软件ABAQUS和疲劳分析软件MSC.Fatigue,详细地介绍了疲劳寿命预测的流程和实现过程.进行疲劳寿命分析,分析结果表明孔径与板长之比D/L对板材疲劳寿命有显著的影响,D/L与对数寿命呈幂函数关系.数值模拟结果与理论计算结果基本相吻合,进行疲劳寿命分析,分析结果表明孔径与板长之比D/L对板材疲劳寿命有显著的影响,D/L与对数寿命呈幂函数关系.     

Probabilistic fatigue crack growth analysis of spot‐welded joints

This paper presents a probabilistic fatigue crack growth life prediction methodology for spot‐welded joints under variable amplitude loading history. The loading is multi‐axial and is obtained from transient response analysis of a vehicle model using finite‐element analysis. A three‐dimensional (3D) finite element model of a simplified joint with four spot welds is developed, and the static stress analysis of this joint is performed. Then the fatigue crack inside the base material sheet is modelled as a surface crack. Probabilistic crack growth model is combined with the stress analysis result to develop a probabilistic fatigue crack growth life prediction methodology for spot welds. This new method is implemented with MSC/NASTRAN and MSC/FATIGUE and is useful for the reliability assessment of spot‐welded joints against fatigue crack growth.     

Damage tolerance reliability analysis of automotive spot-welded joints

This paper develops a damage tolerance reliability analysis methodology for automotive spot-welded joints under multi-axial and variable amplitude loading history. The total fatigue life of a spot weld is divided into two parts, crack initiation and crack propagation. The multi-axial loading history is obtained from transient response finite element analysis of a vehicle model. A three-dimensional finite element model of a simplified joint with four spot welds is developed for static stress/strain analysis. A probabilistic Miner's rule is combined with a randomized strain-life curve family and the stress/strain analysis result to develop a strain-based probabilistic fatigue crack initiation life prediction for spot welds. Afterwards, the fatigue crack inside the base material sheet is modeled as a surface crack. Then a probabilistic crack growth model is combined with the stress analysis result to develop a probabilistic fatigue crack growth life prediction for spot welds. Both methods are implemented with MSC/NASTRAN and MSC/FATIGUE software, and are useful for reliability assessment of automotive spot-welded joints against fatigue and fracture.     

Numerical modelling of deep rolling influence over crankshaft bending and correlation with fatigue behaviour

The requirements for mechanical reliability of automotive crankshafts are continuously increasing, thus pushing the demand for an optimized processing. Nonetheless, the manufacturing‐induced residual stresses at critical sites for fatigue enhancement are not clarified in the state‐of‐the‐art on the topic. In particular, there is a lack of information on the effect of final manufacturing stages to improve the component life endurance, such as deep rolling, in the overall stress state while the component is under operational loads. This study deepens the validation of a finite element deep rolling model under development with the aid of an in‐house developed crankshaft resonance fatigue test rig. The stress state obtained from the deep rolling simulation was input as a predefined stress field for the simulation of operational conditions experimented at the test rig. Test results produced cracks at the fillet radii of the cast iron crankshafts as anticipated. Overlapping the fractography with the simulation's final stress field yielded interesting correlation with the crack morphology. This contributed with a strong indication of the model correctness. Moreover, it can be further implemented to indicate whether the process parameters such as roller force and angle are fully optimized for each particular crankshaft application.     

Measurement and analysis of wheel loads for design and fatigue evaluation of vehicle chassis components

Using a multiaxial‐randomly loaded air‐suspension rear‐axle for commercial vehicles as an example, this paper gives an insight in the mechanics and interactions of wheel forces and moments, forces acting in the suspension components and the stress response of the axle casing. Taking load‐time and stress‐time data measured on a prototype vehicle on a test track as a basis, fatigue, frequency and correlation analyses for all relevant manoeuvres and straight‐ahead driving situations are performed. Special focus is given to the study and determination of appropriate correlations between the mentioned properties for manoeuvres and straight ahead driving on rough roads. The results point out all decisive load situations which may affect the fatigue behaviour of the axle under operational conditions and were taken into account for the derivation of optimized design solutions, as well as for the experimental verification of the final solution in the test rig.     

复杂面内应力状态下平面编织高铝纤维增强氧化铝基复合材料强度及疲劳寿命预测方法

针对平面编织氧化铝基复合材料提出了一种复杂面内应力状态下的强度准则和疲劳寿命预测方法。通过拉伸、压缩及纯剪切试验,分别获得了材料的静强度指标。考虑材料拉、压性能的差异和面内拉-剪联合作用对材料强度的影响机制,提出了修正的Hoffman强度理论。采用该强度理论预测得到的偏轴拉伸强度与试验结果基本一致,偏差不超过10%。开展了偏轴角θ=0°、15°、30°、45°,应力比R=0.1,频率f=10 Hz的拉伸疲劳试验,试验结果表明随着偏轴角的增加,相同轴向拉伸载荷下的疲劳寿命逐渐降低。由于面内剪切应力分量的作用,疲劳失效由纤维主导逐渐过渡到纤维和基体共同主导的模式。基于单轴疲劳寿命曲线,采用Broutman-Sahu剩余强度模型表征剩余强度随疲劳循环次数的变化规律,结合剩余强度演化模型和修正的Hoffman强度理论,提出了一种面内复杂载荷条件下的疲劳寿命预测模型,并引入疲劳剪切损伤影响因子表征拉-剪应力联合作用对材料疲劳行为的影响。采用本文提出的疲劳寿命预测模型,预测不同偏轴角拉伸疲劳寿命,预测结果与试验结果基本一致,偏差在1倍寿命范围内。比较结果表明在给定应力比、温度和疲劳载荷频率条件下,该疲劳寿命预测模型可以用来预测平面编织氧化铝基复合材料拉-剪复杂面内载荷条件下疲劳寿命。      

Fatigue life prediction of a rubber mount based on test of material properties and finite element analysis

Failure analysis and fatigue life prediction are very important in the design procedure to assure the safety and reliability of rubber components. The fatigue life of a rubber mount was predicted by combining test of material properties and finite element analysis (FEA). The natural rubber material material’s fatigue life equation was acquired based on uniaxial tensile test and fatigue life tests of the natural rubber. The strain distribution contours and the maximum total principal strains of the rubber mount at different loads in the x and y directions were obtained using finite element analysis method. The critical region cracks prone to arise were obtained and analyzed. Then the maximum total principal strain was used as the fatigue parameter, which was substituted into the natural rubber’s fatigue life equation, to predict the fatigue life of the rubber mount. Finally, fatigue lives of the rubber mount at different loads were measured on a fatigue test rig to validate the accuracy of the fatigue life prediction method. The test results imply that the fatigue lives predicted agree well with the test results.     

Research on fatigue reliability prediction model and structural improvement of welded drive axle housing based on master S-N Curve method

Fatigue reliability prediction of welded structures is mainly based on nominal stress or hot spot stress method, but there are some problems such as grid sensitivity and joint geometry dependence. The Master S-N curve method can solve these problems well, but the corresponding reliability model needs to be studied. In this paper, the fatigue reliability model of welded structures based on the Master S-N curve method is studied. Considering the randomness of life and the correlation of failure, a reliability model is proposed, which reduces the computational burden by establishing a median damage-random threshold rule. Taking the welded drive axle housing as an object, the system reliability is analyzed under the bench test condition, and verified by the experimental data. After the verification, this method is used to predict the reliability of the axle housing under variable amplitude loading collected in the test field, and the results are verified by Monte Carlo (MC) method. When the P-S-N curves are parallel, the model is accurate, which is the characteristic of the Master S-N curve method. This method only needs to input the median damage value of the weak part, which is easy to be applied. This method can speed up the reliability prediction cycle of welded structures, which is beneficial to product innovation and optimal design. Finally, an improved design scheme is proposed for the weak parts of welding, and the effects of welding leg width, welding depth, and closed weld on fatigue life are revealed.     

Failure analysis of fretting fatigue initiation and growth on railway axle press-fits

Fretting fatigue failure of press fitted railway axle-wheel assembly was presented. Size, distribution and propagation profiles of the circumferential fretting cracks on the full-scale axles were determined by magnetic particle and metallographic slicing methods. The distribution of multiaxial stress cycle along the press-fit seat was obtained by finite element analysis (FEA). The obtained stress path was used for interpretation of fractographic evidence collected at crack initiation sites and the crack propagation plane. Metallurgical and mechanical characterization of the axle material (34CrMo4) was made on the specimens sampled from the broken axles. The threshold conditions for propagation of small fretting cracks were determined by Kitagawa analysis and El-Haddad correction method. The results of the experimental study were compared with EA1N grade steel which is given as the reference axle material in the EN standards. The metallurgical factors affecting the fretting fatigue crack initiation and propagation were investigated. The causes of the examined axle failures were associated with the deteriorated mechanical properties of the axle material.     

Multiaxial fretting fatigue testing and prediction for splined couplings

This paper presents a combined experimental and computational methodology for fretting fatigue life prediction of aeroengine splined couplings under combined loading cycles involving cyclic torque and axial load, as well as rotating bending and fluctuating torque. The experimental method is based on the concept of a simplified representative test, which mimics the multiaxial fretting conditions between spline teeth via biaxial loading of specially-designed bridge pads and a fatigue specimen. The numerical method is based on a three-dimensional finite element model of the test rig assembly, including frictional contact effects, along with a multiaxial, critical-plane fatigue parameter for crack nucleation followed by crack growth prediction in the Paris regime using El Haddad small crack correction. The prediction methodology is shown to successfully capture the effect of the key fretting fatigue stress, which mimics the spline rotating bending moment, on total fatigue life.     

Fatigue Crack Growth in a Solid Circular Shaft Under Fully Reversed Rotating Bending

The axle of a load train failed after 5.37?×?10⁶ cycles from its service. Macro-fractography showed clearly the fatigue fracture. The stress distribution in the shaft revealed that the maximum alternating stress was considerably less than the material modified fatigue limit obtained at 10⁷ cycles from the S?CN diagram. Micro-fractography reported from the metallurgical laboratory proved the existence of a surface flaw. Ultimately, fatigue crack growth simulation was performed based on the simple Paris?CErdogan model for estimating the fatigue life of the defective axle. The results showed that the actual life of the axle could be satisfactorily predicted by means of the Paris?CErdogan model.