高温环境下汽油机排气歧管振动特性及疲劳寿命研究

为研究热载荷与机械载荷的耦合作用对排气歧管疲劳寿命的影响,对一款汽油机排气歧管进行热机耦合下的振动疲劳寿命分析。通过双向流固耦合的方法得到排气歧管的温度场,进而根据热应力及温度分布建立排气歧管的热机耦合模型,进行热载荷下的频率响应分析。通过计算对比发现,应力刚化效果及温度升高引起的材料力学性能退化使得排气歧管的刚度发生变化,导致频率响应分析得到的应力传递函数发生相应的改变,响应应力幅值及峰值频率均发生了不同程度的变化。振动疲劳寿命预测结果表明,考虑热机耦合的疲劳寿命较不考虑热机耦合的振动疲劳寿命降低了32.7%,热机耦合作用对疲劳寿命影响显著,不可忽视。     

基于力电响应的压电悬臂梁疲劳寿命预测EI北大核心CSCD

针对压电振动能量收集器的疲劳问题,旨在研究基于力电响应的压电悬臂梁振动疲劳寿命预测方法。结合压电悬臂梁振动疲劳试验测得的试验结果,以剩余刚度理论和“两段式”疲劳寿命分析模型为基础提出一种基于谐振频率的压电悬臂梁疲劳寿命预测方法;进一步分析振动疲劳过程中谐振频率变化与负载功率变化的关系模型,提出一种基于负载功率的压电悬臂梁疲劳寿命预测方法。结果表明:基于谐振频率的压电悬臂梁疲劳寿命预测方法的平均误差在10%~20%之间,其误差范围控制在1.5倍误差线以内;而基于负载功率的压电悬臂梁疲劳寿命预测方法的平均误差集中于25%左右,误差范围均控制在2倍误差线以内且属于偏安全的预测效果。     

基于随机振动理论的焊接结构疲劳寿命概率预测方法研究

为了能够在设计阶段对承受随机载荷作用的焊接结构的焊缝进行疲劳寿命预测,该文以随机振动理论为基础,结合主S-N曲线法,通过推导证明了用于焊接结构疲劳寿命评估的等效结构应力与激励载荷之间存在线性传递关系,从而提出了一个频域的焊接结构随机振动疲劳寿命概率预测新方法。该方法能够解决多随机载荷作用下复杂焊接结构振动疲劳寿命预测问题。通过T型接头的算例对比分析,证明了该方法能够考虑激励载荷的频率对焊缝疲劳寿命的影响。直接以线路实测随机加速度谱做为激励载荷,对某轨道集装箱平车车体结构关键焊缝的振动疲劳寿命进行预测,结果表明:该方法的预测结果与实际情况吻合,便于工程应用。     

航空发动机外部管路振动疲劳寿命估算方法研究综述

航空发动机外部管路长期在振动环境下工作，易产生振动疲劳损伤与失效。根据振动疲劳寿命估算方法，分析了时域和频域下航空发动机外部管路的振动疲劳寿命估算方法。给出了时域法和频域法对航空发动机外部管路寿命估算的适用特点，为航空发动机外部管路的振动疲劳寿命估算提供了理论依据。     

基于EMD的灰色模型的疲劳剩余寿命预测方法研究

工程上的振动信号多为非线性非平稳信号,为了利用工程振动信号预测机械产品的疲劳剩余寿命,提出改进的经验模态分解方法对振动信号进行分解,分离故障特征频率到某本征模态函数中,计算全寿命周期各阶段故障特征频率所在本征模态函数的均方根值、峭度等时域特征指标,将其作为刻画机械产品健康状态的退化特征量,形成退化特征量序列,根据经验设定机械产品完全失效对应的退化特征量阈值.用退化特征量序列训练灰色模型,然后用训练好的灰色模型预测退化特征量的变化趋势,判断不同退化特征量用于刻画机械产品退化过程的可行性,估计可用退化特征量达到退化特征量阈值的时间并据此预测机械产品的剩余疲劳寿命.通过6205深沟球轴承全寿命周期振动信号对其进行验证,结果表明,可用的退化特征量结合该方法可以有效地预测小型球轴承的疲劳剩余寿命.     

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,疲劳寿命模型预测结果与实验结果吻合较好,该方法可应用于PBGA封装焊点在随机振动载荷下的疲劳寿命评估,为PBGA封装器件的设计与使用提供指导。     

金属材料和结构的疲劳寿命预测概率模型及应用研究进展

疲劳过程的不确定性以及影响疲劳寿命的不确定性因素较多,导致疲劳寿命的分散性难以预测,在疲劳寿命预测模型中采用统计学和概率论的概念和方法是描述疲劳过程不确定性和疲劳寿命分散性的一种重要手段。本文针对疲劳寿命预测概率模型进行综述,总结和介绍了疲劳寿命经验公式和参数的随机化模型、表征疲劳寿命离散性的统计模型、基于材料微结构和疲劳物理机制的疲劳寿命预测概率模型以及研究广布疲劳损伤的概率模型,并对金属材料与结构的疲劳寿命预测方法进行了展望。     

考虑结构裂纹扩展的振动疲劳寿命计算方法

工程实践中任何结构都存在不同程度的裂纹损伤,振动激励下动响应与疲劳裂纹扩展之间互相耦合,直接影响结构振动疲劳寿命.为了考虑结构振动疲劳耦合效应对疲劳寿命的影响,提出了一种考虑结构裂纹扩展的振动疲劳寿命计算方法.分析时,通过建立若干个含不同长度裂纹的结构有限元模型模拟结构裂纹扩展,采用Paris方程分段计算结构振动疲劳裂纹扩展寿命,通过试验确定的固有频率降变化规律反推结构裂纹萌生寿命,最后累计得到结构疲劳总寿命.结论表明,仿真计算结果与试验结果比较吻合.     

履带车辆行星传动装置疲劳寿命的仿真及预测

行星传动装置是履带车辆的重要传动机构,由于没有准确的载荷数据,因此采用静载荷设计行星传动装置。由于静载荷和实际载荷的差距相当大,因此行星传动装置在使用过程中故障率较高,导致整车可靠性低。为解决实际工况下行星传动装置动态载荷的难题,基于ADAMS.ATV建立履带车辆行星传动装置虚拟行驶试验平台,获得了行星传动装置各零部件的动态载荷。基于FE-Fatigue软件建立了行星传动装置的疲劳分析模型,获得了行星传动装置关键/重要部件的疲劳寿命。预测仿真实例证明了对行星传动装置构件进行疲劳寿命预测的可行性,解决了复杂工况载荷条件下履带车辆行星疲劳寿命的预测难题,研究成果还可推广应用于相关工程领域,具有非常重要的实用意义。     

等离子热障涂层构件高温热疲劳寿命预测研究

针对等离子热障涂层构件的变形特点,在总结热障涂层热疲劳寿命相关文献研究成果的基础上,合理设计了平板和圆管试样的高温氧化与热疲劳试验。根据菲克定律,结合高温氧化实验数据建立粘接层Al贫化的数学模型。把粘接层Al浓度作为耦合氧化损伤的控制参量引入寿命预测模型,建立氧化损伤和热疲劳损伤耦合作用的等离子热障涂层寿命预测模型。寿命预测结果表明该寿命预测模型合理、方法可行。     

循环荷载作用下钢桥面铺装疲劳损伤失效行为研究

针对钢桥面铺装工程中普遍采用的改性沥青(Stone Matrix Asphalt,SMA)、浇筑式沥青(Guss asphalt,GA)、环氧沥青(Epoxy asphalt,EP)混合料双层铺装结构,进行了循环车载作用下钢桥面与沥青混凝土铺装疲劳损伤特性理论分析与试验研究。基于疲劳损伤度,研究了钢桥面铺装疲劳损伤失效行为和疲劳开裂过程中损伤场、应力和应变场动态演变机制,推导出疲劳失效时的损伤场、应力和应变场计算表达式,并给出钢桥面铺装疲劳寿命理论公式。以三座钢箱梁桥桥面铺装(润扬长江大桥2005,南京长江三桥2005,苏通大桥2008)为例,对不同铺装结构组合方案下的复合梁进行疲劳试验分析和使用寿命理论预测。实例研究结果表明,钢桥面铺装疲劳损伤失效行为预估模型合理可行;相较于改性沥青、浇筑式沥青,环氧沥青混合料具有较强高的强度低变形能力,更适合于大跨径钢桥面铺装抗疲劳的设计要求;由环氧沥青混合料组合而成的“双层环氧沥青混凝土”和“浇注式沥青混凝土(下层)+环氧沥青混凝土(上层)”的抗疲劳性能优于其它沥青混合料铺装结构组合方案,同等厚度组合情况下疲劳使用寿命可延长1倍~2倍以上;“双层环氧沥青混凝土”已应用于润扬长江大桥、南京长江三桥和苏通长江大桥钢桥面工程,并已成功运行10年以上,其跟踪观测结果良好。     

Investigating the effects of loading,mechanical properties and layers geometry on fatigue life of asphalt pavements

In this paper, fatigue life, crack growth trajectory, and stress intensity factors of top‐down and bottom‐up cracks have been investigated in a multilayered asphalt pavement using numerical method. Finite element models, Paris law, and maximum tangential stress criteria were used to determine the effects of vehicle position, thickness, and stiffness of layers on fatigue life of pavements. The results show that the minimum fatigue life of pavements with top‐down crack occurs when the wheels are symmetrically located relative to the crack plane. On the other side, in pavements with bottom‐up crack, it occurs when the front tire located on top of the crack. Moreover, the result reveals that the top‐down crack grows slower than bottom‐up crack. Also, the surface layer's stiffness has the most effect on fatigue life of pavement.     

基于几何特征的不平整路面三维建模与分析研究

在对比利时路关键几何特征、特征的分布特点及其约束条件进行分析的基础上,提出了基于几何特征的参数化路面三维建模方法。通过比利时路三维理论模型与生成的三维随机路面融合,得到真实准确的比利时路三维模型;在建立标准化车辆振动模型的基础上,以IRI指数和车身振动加速度均方根值(RMS)作为评价指标,分析了比利时路的关键几何参数对车辆振动的影响。通过实测道路数据与所建立模型对比分析,验证模型的准确性;提出的道路三维建模方法可以扩展至卵石路、鱼鳞坑路、波纹路、搓板路等几乎所有不平整强化试验路面,为全面构建车辆虚拟试验场提供了一种参数可调、真实准确的道路三维建模途径。     

A comprehensive life cycle costs analysis of in-place recycling and conventional pavement construction and maintenance practices

Recent studies based on Life Cycle Assessment (LCA) have highlighted the potential of in-place recycling techniques to enhance the sustainability of agency pavement management decisions for asphalt pavements. However, a solution which an LCA finds environmentally advantageous might not be preferred over another which is technically equivalent, if it is not economically competitive. In this context, it is necessary to evaluate the economic costs of such alternatives taking into account the perspective of the main stakeholders who interact with a pavement system throughout its life cycle. This paper presents a comprehensive pavement life cycle costs (LCC) model that accounts for the different categories of costs incurred by highway agencies and road users in every phase of the pavement life cycle. The results of the application of the pavement LCC model to a specific highway rehabilitation project in the state of Virginia showed that in-place recycling practices are beneficial for both highway agencies and road users.     

A damage gradient model for fatigue life prediction of notched metallic structures under multiaxial random vibrations

In the present paper, a damage gradient model combing the damage concept with the theory of critical distance (TCD) is established to estimate the fatigue lives of notched metallic structures under multiaxial random vibrations. Firstly, a kind of notched metallic structure is designed, and the biaxial random vibration fatigue tests of the notched metallic structures are carried out under different correlation coefficients and phase differences between two vibration axes. Then, the fatigue lives of the notched metallic structures are evaluated utilizing the proposed model with the numerical simulations. Finally, the proposed model is validated by the experiment results of the biaxial random vibration fatigue tests. The comparison results demonstrate that the proposed model can provide fatigue life estimation with high accuracy.     

变速磁流变半主动悬架车辆与随机路面系统的模糊振动控制

建立半主动悬架车辆和随机路面系统模型,在采用磁流变减振器的基础上,应用模糊逻辑控制理论,进行车辆半主动悬架模糊控制器的设计,获得在模糊控制理论下可调阻尼力随时间变化的关系,应用simulink编制车路模型的仿真程序,研究在模糊控制算法下的匀变速行驶车辆路面系统平顺性问题。计算结果表明,与被动悬架的车辆相比,模糊控制的磁流变半主动悬架车辆可以改善行驶平顺性,同时还可减少车对路面的作用力,这对于车路系统是有利的,对于深入分析路面结构动力响应也具有重要的参考价值。     

Dynamic Stiffness Assessment of Construction Materials by the Resonant and Non-resonant Methods

Dynamic stiffness of pavement surfaces is a structural property related to surface vibration and traffic noise. It is one of the mechanisms involved in tire/road noise generation. An equipment for measuring dynamic stiffness was designed and built to perform in-situ nondestructive testing on road surfaces. Laboratory studies on samples are presented to compare different measurement procedures. Measurements of the dynamic stiffness were carried out by the Resonant and Non-resonant Method. Moreover, a Dynamic Stiffness Index is proposed in order to compare the stiffness of the studied samples. Construction materials with different characteristics were studied, from resilient materials for acoustic insulation to rigid materials for pavement construction. Results show that the Non-resonant Method is more suitable for dynamic stiffness measurements, since this method could be carried out on real pavements, and both, driving point and transfer functions could be measured simultaneously. Little dynamic stiffness differences were found among road construction materials, compared to those of the resilient materials. However, the presented testing procedures are able to establish differences among these materials.     

Assessment of the relationship between the international roughness index and dynamic loading of heavy vehicles

Due to imperfect surface profiles, heavy vehicles moving at high speed on flexible pavement structures oscillate in the vertical axis. This phenomenon induces dynamic loads, which oscillate at lower and higher values than the average load associated with static load considered with most pavement analysis and design applications. Higher loads applied to flexible pavements are likely to significantly reduce pavement service life. A new multibody dynamic truck model was used to study heavy vehicle wheel load for various pavement profiles of varying international roughness index (IRI). The modelled heavy vehicle wheel load response were used to calculate the dynamic load coefficient, and a relationship with IRI was proposed. On the basis of this relationship, the evolving pavement surface profile, and thus evolving IRI, was used to determine the evolution of dynamic loading with pavement life. A comparison of pavement service life for the classical static loading and for dynamic loading was made for three highway flexible pavement structures. When dynamic loads are considered, it was found that the pavement service life reduction may be reduced of about 29 and 20% for bottom-up fatigue cracking and structural rutting failure criteria.     

Development of degradation model for urban asphalt pavement

There is a lack of a profound understanding of urban pavement deterioration pattern. This is due to the complexity of traffic conditions and the variety of pavement structures in urban roads. The lack of a suitable deterioration model for the urban pavements limits the possibility of making any scientific and cost-effective repair and maintenance strategy. There is a need for a better understanding of the long-term behaviour of urban pavements by which predictive pavement condition models can be derived and consequently a suitable maintenance management system can be built. In response to this need, a comprehensive field study was performed in three Iranian cosmopolitan cities. Pervasive pavement damages were defined and an urban pavement condition index was established. A deterioration model was developed by monitoring and analysing the conditions of road pavements in a period of four years. This model varies as the structural and loading conditions of the pavement change. The efficiency and practicability of the model in predicting the conditions of the pavements were illustrated.     

履带车辆不平路面越野平均速度预测方法研究

为了研究路面不平度对履带车辆越野平均速度的影响规律,本文建立了履带车辆多体动力学模型,提出了振动响应指标并通过试验验证了模型的可信性;根据试验设计进行仿真计算,建立振动响应与车速、路面不平度间的近似模型;以振动响应指标的门限值为约束条件,采用目标寻优方法拟合了路面不平度与车速间的数学关系,提出了随机不平路面条件下的越野速度预测方法。应用该方法计算了车辆通过某试验场综合路面,结果表明：所建模型可以反映路面不平度对车速的影响,为车辆机动性预测提供了有效的量化手段。