基于数值仿真的防波板焊接结构圆弧过渡分析

为提升路面洗扫机械的水箱在服役过程中的可靠性,针对水箱中防波板焊接结构在水流冲击载荷下出现疲劳裂纹失效问题,在立板根部采用圆弧过渡的结构优化方案,以降低焊接结构的应力集中程度,从而提升防波板的使用寿命。采用有限元仿真系统地分析了过渡圆弧位置和半径对应力分布的影响规律。仿真结果表明,焊接结构应力集中导致防波板抗疲劳性能弱化,而圆弧过渡结构对应力集中效应具有明显的缓解作用,其缓解程度与圆弧位置和半径有显著的关联。随着圆弧与焊道距离的减小或者圆弧半径的增加,防波板应力集中降低,载荷由低周疲劳向高周疲劳的转变越明显。     

基于ABAQUS/FE-SAFE的TC4钛合金板材疲劳寿命仿真与实验

目的建立钛合金材料的疲劳寿命预测模型,并通过实验研究验证此模型在预测滚磨光整加工后钛合金材料疲劳寿命的可行性。方法采用有限元软件ABAQUS和疲劳分析软件FE-SAFE,通过有限元仿真和多元正交回归实验的方法,研究了粗糙度以及残余应力对TC4钛合金疲劳寿命的影响规律。结果拟合出疲劳寿命与粗糙度以及残余应力的关系方程式,进而通过实验验证了仿真结果以及公式的正确性。结论滚磨光整加工后,表面粗糙度R_z值由加工前的3.16变为1.69,残余应力由拉应力50 MPa变为压应力-228 MPa,疲劳寿命从加工前的28 083次提高到39 510次,提高了40.6%,实验结果与仿真结果相比,误差在5%左右,证明仿真结果的可行性,为滚磨光整加工钛合金提供了疲劳寿命预测模型。     

Development of nonlinear spectral correlation between ultrasonic modulation components

When a damaged structure is exposed to ultrasonic waves at two distinct frequencies, nonlinear wave modulation resulted from a damage such as a fatigue crack can be observed in the corresponding response, offering an opportunity for early damage detection. This study attempted to improve nonlinear wave modulation-based damage detection by applying statistically weak-linked inputs over two distinct frequencies to the target structure and then conducting a cyclostationarity analysis of the corresponding structural response. The cyclostationary nature of the structural response produces a statistical variation over time, allowing the structural response to be processed using a spectral correlation function. The spectral correlation can thus be used to transform the structural response into two dimensions characterized by their cyclic and spectral frequencies. Then, the damage-induced nonlinear modulation can be detected by studying the spectral correlation values for the specific cyclic and spectral frequencies defined by the modulation frequencies. This premise forms the basis for nonlinear spectral correlation, which is a new damage feature that is superior in terms of its sensitivity for nonlinear damage and improved robustness against noise compared to a conventional spectral density function. The performance of the proposed technique was validated by conducting an experiment with aluminum plates containing real fatigue cracks. The results of this experiment showed that the proposed technique could detect damage even under severely noisy conditions.     

装载机销轴断裂分析

某厂家生产的销轴在使用过程中多次在同一部位发生断裂。采用断口分析、化学成分分析、金相组织分析、硬度检验及CAE模拟受力分析等试验方法对两个销轴的断裂原因进行了分析。结果表明：销轴径向油孔位置具有随机性,当油孔位于最大弯曲应力一侧时,由于油孔的应力集中作用,导致油孔口位置的应力过大,在油孔口位置萌生疲劳裂纹,故油孔位置不合适是销轴断裂的主要原因。另外,销轴表面硬化层深度偏低,降低了失效件的疲劳强度,也是销轴早期疲劳断裂的重要原因。因此,通过在销轴生产时避免将油孔置于弯曲应力最大的一侧,同时增加表面硬化层的深度,可有效地避免类似故障的发生。     

TC4与TA15钛合金氩弧焊疲劳特性对比分析

选用TC4和TA15的氩弧焊焊接件作为研究对象,分别进行4个应力水平下的恒幅疲劳试验。依据文建立的三参数疲劳寿命模型对试验结果进行对比分析,TA15的氩弧焊的疲劳性在10⁴~10⁶范围内略优于TC4氩弧焊,并讨论了可能的影响因素。     

Laser generation of stress waves in metal

Today surface treatments are very important in the mechanical industry to increase the fatigue life of metal components. In addition to classical treatments such as shot peening, a new process is being developed. The laser shock surface treatment permits the creation of plastic strains and induction of compressive residual stresses in metals. It consists in irradiating a metallic sample with a short but intense laser pulse. As a consequence a high temperature high pressure plasma is created at the sample surface. An elastic-plastic wave propagates in the sample, creating plastic strains. The present study deals with the effects of laser-induced stress waves on residual stresses, microhardness and surface quality of a standard steel (0.55% C). The residual stresses generated are compressive for a depth of up to 1 mm. With optimum conditions, we can produce homogeneous cover strips without surface deterioration.     

基于动力学的导弹发动机故障分析

本文对某发动机简体爆破故障原因进行了分析。裂纹形态观察理论分析、动力学仿真和验证试验结果表明，导弹在发射筒内与螺旋导轨多次撞击而产生的冲击载荷作用于导弹发动机筒体，形成的扭转应力波的叠加导致局部应力过大是导弹发动机简体破裂的主要原因。根据故障分析结论，提出了预防和解决该故障的相应可行措施：改发射方案为发射筒内变距螺线起旋，以便从源头降低冲击载荷；在结构主应力反射点上人为制造局部自由端，避免筒壁上的主应力叠加点形成应力峰值叠加；在传力路线上加入内衬材料，从而达到降低应力波强度的目的；采用变截面旋压技术加工发动机壳体，以提高壳体局部强度。     

高温超声冲击处理Q345钢焊接接头的疲劳性能

利用自行研制的超声冲击处理装置,对Q345钢对接接头焊趾区分别进行了室温(20℃),250,350及450℃下的高温超声冲击处理,并对处理后接头的疲劳性能进行了研究.结果表明,在应力比R=0.1的条件下,室温及高温超声冲击处理均能有效改善Q345钢对接接头的疲劳性能,且250℃超声冲击处理接头的疲劳性能与原始焊态相比,改善程度最大,高达99.41%.此外,在残余应力和应力集中因素的影响下,焊接接头疲劳强度的改善程度随超声冲击温度的升高呈先上升后下降的趋势.     

Evaluation of vibration stress of TA11 titanium alloy blade by quantitative fractography

Vibration fatigue is the main failure mode of compressor blade. Evaluating the vibration stress of blade that leads to cracking is very useful for analysis of vibration fatigue. In this paper, fatigue stress estimation methods by quantitative fractography were studied through experimental blade and in-service first-stage compressor blade in order to evaluate the initiation vibration stress of in-service blade. The analysis process of initiation vibration stress was established. The evaluating result of vibration stress of in-service blade subjected to centrifugal force and bending vibration stress agrees with aero engine test result. It is shown that the evaluation method can not only evaluate the equivalent fatigue stresses of different crack depths but also yield the initiation equivalent fatigue stress.     

A Three-Parameter Model for Predicting Fatigue Life of Ductile Metals Under Constant Amplitude Multiaxial Loading

In this article, a fatigue damage parameter is proposed to assess the multiaxial fatigue lives of ductile metals based on the critical plane concept: Fatigue crack initiation is controlled by the maximum shear strain, and the other important effect in the fatigue damage process is the normal strain and stress. This fatigue damage parameter introduces a stress-correlated factor, which describes the degree of the non-proportional cyclic hardening. Besides, a three-parameter multiaxial fatigue criterion is used to correlate the fatigue lifetime of metallic materials with the proposed damage parameter. Under the uniaxial loading, this three-parameter model reduces to the recently developed Zhang’s model for predicting the uniaxial fatigue crack initiation life. The accuracy and reliability of this three-parameter model are checked against the experimental data found in literature through testing six different ductile metals under various strain paths with zero/non-zero mean stress.     

基于Corten-Dolan法则的低压训练舱疲劳寿命预测

训练舱舱体作为低压模拟设备的结构支撑，其主要破坏形式是由于舱体壁承受的压差载荷，加剧了应力集中部位的疲劳损伤，从而导致结构部分失效。针对负压大型舱体结构的疲劳损伤问题，以企业某型低压舱为原型，创建包括内加强筋、过渡舱在内的几何模型，进行了静力学和动力学分析，确保结构设计的合理性；同时，采用三点雨流法统计并获取对应的循环载荷谱；选择Goodman方程进行平均应力的修正，提高预测的准确性；最后，利用舱体材料的 S-N 曲线和Corten-Dolan法则，对其结构进行疲劳寿命预测分析，获取了危险单元部位在对应循环载荷作用下的循环次数、疲劳损伤和雨流矩形图。仿真结果表明：疲劳损伤严重部位的损伤值为1.018×10-5，局部可循环次数为9.822×104次，预计可使用寿命达15年左右；由雨流矩形图可知，平均应力主要集中在202.1~281.7 MPa之间，最大应力幅为211.8 MPa，平均应力以拉应力为主。     

TP304不锈钢三通失效分析

电厂脱硝设施中所使用的TP304不锈钢三通出现裂纹缺陷,通过成分分析、断口宏观和微观分析、微观组织观察、硬度检测,并结合生产工艺对三通裂纹的产生原因进行分析。研究结果表明：材料中Ni含量偏低使材料的奥氏体稳定化程度降低;基体内含有的2.5~3.0级球状非金属夹杂物对基体造成撕裂作用,促进疲劳裂纹的萌生;同时,三通在加工完成后也缺少固溶处理步骤,使得材料内应力过大。这些原因综合导致材料奥氏体含量降低,硬度过高,同时造成材料塑性变形部位内应力过高,在支管颈部产生较大的应力集中现象。三通内表面同时存在大量加工损伤,强化了应力集中现象,在疲劳载荷的作用下,促进了三通裂纹的萌生。     

预腐蚀疲劳寿命影响系数模型研究

针对腐蚀环境下飞机结构疲劳寿命评定问题,研究了恒幅应力水平下的地面停放预腐蚀影响系数C模型，根据统计分析推导出C曲线的关系式;疲劳试验数据分析结果建立了预腐蚀影响系数C模型.结果表明，随着腐蚀时间的增加,疲劳寿命影响系数C不断下降;同一时间下,应力水平S高,影响系数C大;应力水平S低,影响系数C小；在一定的腐蚀疲劳条件(时间、应力水平)下,可求出任一给定可靠度p时的Cp值和疲劳寿命预测值.     

非承载角焊缝十字接头疲劳性能

文中基于结构应力方法对非承载角焊缝接头的疲劳性能进行了数值分析与试验研究。首先根据不同焊脚尺寸的十字接头焊趾截面结构应力,发现焊脚尺寸越大,接头疲劳性能反而越低,疲劳试验也证明了这一现象。同时,试验数据与BS 7608标准中F级S-N曲线的对比说明了疲劳评估时进行应力修正的必要性。然后,分别利用含装配间隙和熔深的有限元模型计算接头结构应力,证明两者对接头的疲劳性能影响很小。文中还通过与承载角焊缝接头的对比,证明细节特征对接头疲劳性能的影响程度与接头受力状态直接相关。在定义焊缝缺欠质量等级时,应考虑接头在结构中的受力状态,制定合理的控制参数,从而降低结构的制造成本。     

用超声波法测试20钢低周疲劳过程中弹性常数的变化

研究了20钢在300MPa静拉应力作用下的低周疲劳过程。对20钢在试验过程中纵波声速和横波声速的变化进行了分析。进而给出了弹性常数及应变随着疲劳周次的变化情况，表明可以用材料弹性常数的变化来反应材料的疲劳状况。     

Fatigue crack monitoring in engine-grade titanium alloy by dynamic subtraction of surface acoustic wavemodulation

The initiation and evolution of fatigue cracks in forged titanium alloy samples are monitored ultrasonically during fatigue testing. An in-situ surface wave acoustic method is applied during fatigue with an overlaid small low-frequency periodic loading, resulting in a nonlinear modulation of reflected ultrasonic pulses. The acoustic wave time traces in the sample are collected for a range of applied fatigue and modulation load levels and for a range of spatial propagation positions within each fatigue cycle. These samples are characterised by strong microstructure-induced ultrasonic scattering. To improve the signal-to-noise ratio a post-processing subtraction technique is introduced with the aim of enhancing initiated crack detectability.     

Stress-induced martensitic transformation in metastable austenitic stainless steels: Effect on fatigue crack growth rate

This paper addresses the influence of cyclic stress-induced martensitic transformation on fatigue crack growth rates in metastable austenitic stainless steels. At low applied stress and mean stress values in AISI type 301 stainless steel, fatigue crack growth rate is substantially retarded due to a cyclic stress-induced γ-α′ and γ-ε martensitic transformation occurring at the crack-tip plastic zone. It is suggested that the transformation products produce a compressive residual stress at the tip of the fatigue crack, which essentially lowers the effective stress intensity and hence retards the fatigue crack growth rate. At high applied stress or mean stress values, fatigue crack growth rates in AISI type 301 steels become almost equal to those of stable AISI type 302 alloy. As the amount of transformed products increases (with an increase in applied or mean stress), the strain-hardening effect brought about by the transformed martensite phase appears to accelerate fatigue crack growth, offsetting the contribution from the compressive residual stress produced by the positive volume change of γ → α′ or ε transformation.     

柴油发动机活塞连杆机构失效原因分析

某柴油发动机活塞连杆机构在使用过程中发生故障,拆解后发现缸套、活塞和连杆均发生不同程度的断裂失效。通过断口宏观检验和微观分析、化学成分分析和显微组织检验等手段,结合零件生产工艺流程进行综合分析。结果表明,连杆是引发此次连锁故障的肇事件,缸套与活塞为受牵连件。连杆表面存在由喷丸工艺不当造成的折叠缺陷,因应力集中而诱发了材料最初的疲劳损伤;同时显微组织不良在一定程度上弱化了连杆的整体强度。在复杂的循环应力及较大的惯性力作用下,连杆发生高周疲劳断裂,并引发缸套、活塞的相继损坏。     

板厚对不锈钢车体激光叠焊接头抗剪强度和疲劳强度的影响

为了研究板厚对不锈钢激光叠焊接头抗剪强度和疲劳强度的影响,该文针对0.8 mm +2 mm和2 mm +2 mm2种不同板厚搭配的不锈钢激光叠焊接头分别进行了拉伸试验和疲劳试验。结果表明,2 mm +2 mm接头的抗剪强度和疲劳强度均高于0.8 mm +2 mm接头。失效分析发现,2种接头的拉伸破坏由焊肉部位剪断引起的;2种接头的疲劳裂纹均萌生于2 mm未焊透板,裂纹起始位置在2个焊板之间靠近焊核附近未焊透板的热影响区,裂纹沿着焊核边缘向未焊透板外表面方向扩展,直至穿透未焊透板。对焊接接头部位的有限元受力分析可知,2种接头的应力集中程度的不同是造成它们抗剪强度和疲劳强度差异的主要原因。     

AZ31镁合金在高周疲劳过程中微观组织和孪晶演变特征

利用扫描电子显微镜（SEM）和电子背散射衍射（EBSD）技术研究了室温条件下AZ31镁合金在不同加载频率（3和30 Hz）和不同应力幅值（90,95,100,105,110 MPa）疲劳变形后的组织演变规律及断口形貌特征。结果表明：随着加载应力增加,基体内残余孪晶数量增加,残余孪晶主要以拉伸孪晶形式存在。随着应力幅值的增加晶粒逐渐细化,这是由于在循环过程中,拉伸孪晶演变诱导晶粒细化。随着应力幅值的增加,织构强度显著减弱,这与试样疲劳后的再结晶机制有关。通过对试样疲劳断口的分析,发现孪晶片层处容易引起裂纹萌生,随着应力的增加,试样中裂纹扩展区面积逐渐减小,在疲劳裂纹扩展区观察到明显的疲劳辉纹。最终断裂区表面粗糙,主要存在韧窝、撕裂脊以及二次裂纹等形貌。在最终断裂区可观察到韧窝,韧窝尺寸随着循环应力的增加,在较高加载频率下,韧窝的尺寸与数量均减小。