激光冲击强化后航空发动机疲劳寿命精准度量研究

激光冲击强化可以提升航空发动机表面强度、增强材料韧性。然而,航空发动机处于复杂的工作环境,疲劳寿命受到多个因素的影响。尤其是在激光冲击强化后,材料性能参数变化较大,导致航空发动机疲劳寿命度量难度增加,因此,提出激光冲击强化后航空发动机疲劳寿命精准度量方法。首先,分析航空发动机激光冲击强化工作原理,根据疲劳损伤理论与Von-Mises屈服准则建立航空发动机疲劳损伤函数。然后,结合疲劳损伤函数与灰色关联度分析法对影响发动机疲劳寿命的多因素展开权值分析得到航空发动机疲劳指标,从而实现航空发动机疲劳寿命的精准度量。实验结果表明,所提方法能够实现对航空发动机疲劳寿命退化轨迹的精准监测,可以精准分析发动机表面疲劳寿命的分布情况,说明该方法的航空发动机疲劳寿命度量结果更为精准。

抗车辙剂改性沥青混合料疲劳性能试验研究

为研究抗车辙剂改性沥青混合料的疲劳特性,基于三点弯曲疲劳试验通过改变施加应力和加载频率,模拟分析了抗车辙剂掺量、车载水平、车辆速度率等因素对抗车辙剂改性沥青混合料疲劳寿命的影响规律,并与普通沥青混合料抗疲劳性能进行了比较。结果表明,当抗车辙剂掺量超过0.3%时,混合料疲劳寿命降低幅度明显;抗车辙剂改性沥青混合料疲劳寿命随施加应力增加而快速降低,且两者满足幂函数疲劳方程;提高加载频率,混合料的疲劳寿命随之增加,且在低应力水平下,加载频率变化引起的疲劳寿命差异更大。

机动车驾驶员疲劳状态的仿真分析研究

通过对驾驶员的驾驶操纵过程进行分析,应用传递函数这一经典控制理论工具,构建了驾驶员的行为操纵模型,并在MATLAB/Simulink仿真环境下实现,通过对机动车驾驶员的正常状态和疲劳状态进行仿真比较分析,表明驾驶员在疲劳状态时比正常状态时需要更长的操纵时间才能跟随着道路环境的变化,其果断性和灵敏性、实时性均下降很多,为进一步研究机动车驾驶员的疲劳状态奠定了理论基础。

嵌入项目疲劳和多样偏好的聚合推荐算法

为了解决推荐列表偏向于热门项目,多样性差的问题,提出了ARIFDP算法(aggregation recommendation algorithm for embedding item fatigue and diversity preference)。首先通过对用户历史反馈数据分析用户的多样性偏好,得出用户的多样倾向度,进而构造了与评价次数负相关的项目疲劳函数,最终将矩阵分解与项目疲劳函数相聚合,并加入多样倾向度调节项目疲劳函数所占权重,增加了冷门项目被推荐的概率。实验结果表明,ARIFDP算法能在保证准确率的前提下有效提高推荐结果的多样性。

样本容量和分布类型对疲劳寿命分布的推断影响分析

应用蒙特卡罗数值仿真方法,就样本容量及分布类型的选取对产品疲劳寿命概率分布函数推断的影响进行了研究,给出不同样本容量及分布函数类型下,各分布函数通过拟合优度检验被接受作为产品疲劳寿命概率分布函数的概率。还探讨了选取非真实分布函数作为产品疲劳寿命概率分布函数对累积失效概率的影响,并将对应给定百分位点下,由非真实分布函数求得的累积失效概率与真实累积失效概率进行了对比分析。所得结论对产品的设计和安全性评估均有参考价值。

抗车辙剂改性沥青混合料疲劳性能试验研究

为研究抗车辙剂改性沥青混合料的疲劳特性,基于三点弯曲试验模拟分析了抗车辙剂掺量、车载水平、车辆速度率等因素对抗车辙剂改性沥青混合料疲劳寿命的影响规律,并与普通沥青混合料疲劳性能进行了比较。结果表明:当抗车辙剂掺量超过0.3%时,混合料疲劳寿命降低幅度明显;抗车辙剂改性沥青混合料疲劳寿命随施加应力增加而快速降低,且两者满足幂函数疲劳方程;提高加载频率,混合料的疲劳寿命随之增加,且在低应力水平下,加载频率变化引起的疲劳寿命差异更大。

受长尾约束分布的多样性信息推荐技术

现有的推荐系统大多侧重于热点项目的推荐,难以全面覆盖所有用户的需求,为此,提出了一种受长尾约束分布的偏好多样性的推荐算法。在用户查询历史的基础上对其多样性偏好进行倾向度分析,构造与评价次数呈反比例关系的项目疲劳函数,并将其与矩阵分解相整合,通过多样倾向度对函数比重进行调节,提高冷门项目出现在推荐列表中的概率。实验结果表明,该算法能够在不影响准确率的前提下实现高度多样化的项目推荐。

Fatigue reliability quantitative analysis of cement concrete for highway pavement under high stress ratio

In order to obtain the change law of the fatigue reliability of cement concrete for highway pavement under high stress ratios, first, the probability densities of monotonic random variables including concrete fatigue life are deduced. And then, the fatigue damage probability densities of the Miner and Chaboche-Zhao models are deduced. By virtue of laboratory fatigue test results, the fatigue damage probability density functions of the two models can be obtained, considering different stress ratios. Finally, substituting load cycles into them, the change law of cement concrete fatigue reliability about load cycles can be acquired. The results show that under the same stress ratio, with the increase in the load cycle, the fatigue reliability declines from almost 100% to 0% gradually. No matter under what stress ratio, during the initial stage of the load action, there is always a relatively stable phase for fatigue reliability. With the increase in the stress ratio, the stable phase gradually shortens and the load cycle corresponding to the reliability of 0% also decreases. In the descent phase of reliability, the higher the stress ratio is, the lower the concrete reliability is for the same load cycle. Besides, compared with the Chaboche-Zhao fatigue damage model, the Miner fatigue damage model is safer.

MINER RULE CONSIDERING FUZZINESS OF STRESS DAMAGE UNDER DIFFERENT LOAD SEQUENCES

Since the traditional Miner rule ignores the influence of the load sequence on the fatigue life, the fuzzy rules are used to analyze the fuzziness of the fatigue damage caused by the stress nearby the fatigue limit under different load sequences. The improved fuzzy Miner rule can reflect the influence of the load sequence on the fatigue life. Results of the example show that the prediction error can be reduced from 61.6% to 21.7%.

疲劳荷载权函数下混凝土疲劳累积损伤值的研究

在一定应力水平的疲劳荷载作用下,混凝土强度会衰减,混凝土结构发生疲劳破坏.为了能反映出混凝土疲劳荷载作用的先后性(或时间性),论文提出了混凝土疲劳荷载权函数的概念,以剩余强度定义了累积损伤的变量,建立了累积损伤变量与疲劳荷载作用次数的曲线方程.继而分别推导了以混凝土剩余强度所定义的单级和多级荷载疲劳荷载权函数的数学表达式;通过建立的疲劳荷载权函数,推得单级和多级荷载作用下混凝土疲劳累积损伤的计算式,并分别推导和论证了混凝土疲劳破坏时的累积损伤值大于1,不同应力水平的疲劳荷载和不同的荷载作用次序所得到的混凝土疲劳累积损伤值不等同,相同荷载、不同作用顺序对结构疲劳累积损伤贡献不等等重要结论.

Parameters Estimation and Evaluation for the Probability Density Function of Structural Fatigue Stress of a Container Vessel

Fatigue stress measurement has been playing a significant role in the ship structural health monitoring and ship structural safety assessment. The PDF （probability density function） of the measured stress is one of the essentials for the further studyin this domain. This paper, based on the strain-stress data collected from a container ship, focuses on the spectrum feature of the ship structural fatigue stress. A general analysis procedure for ship hull health estimation was firstly demonstrated. With the guidance of this procedure, the estimation and test of the parameters for the PDF of the stress were conducted, which showed that the stress spectrums fit well with the Weibull distribution. To review the fatigue state, the PDF and distribution function of fatigue damage increment were further developed and examined. The structural healthy assessment of this vessel shown the daily relative fatigue damage increment obeys log-normal or Weibull distribution and the increment of the fatigue damage on steel box girders of the ship hull was very low. Finally, the analyzing results yielded that the girder structure of the ship hull had a very low failure probability, matching well with the actual relative low working load of the ship.

Influence of surface treatments on fatigue life of a two-stroke free piston linear engine component using random loading

This paper describes the finite element (FE) analysis technique to predict fatigue life using the narrow band frequency response approach. The life prediction results are useful for improving the component design methodology at the very early development stage. The approach is found to be suitable for a periodic loading but requires very large time records to accurately describe random loading processes. This paper is aimed at investigating the effects of surface treatments on the fatigue life of the free piston linear engine’s components. Finite element modelling and frequency response analysis were conducted using computer aided design and finite element analysis commercial codes, respectively. In addition, the fatigue life prediction was carried out using finite element based fatigue analysis commercial code. Narrow band approach was specially applied to predict the fatigue life of the free piston linear engine cylinder block. Significant variation was observed between the surface treatments and untreated cylinder block of free piston engine. The obtained results indicated that nitrided treatment yielded the longest life. This approach can determine premature products failure phenomena, and therefore can reduce time to market, improve product reliability and customer confidence.

Fatigue Crack Initiation Sizing Using Acoustic Emission

One of the major concerns in structures is early detection of a growing crack to prevent fracture, predict remaining useful life, schedule maintenance and reduce costly downtimes. AE （acoustic emission） is a non-destructive testing method with potential applications for locating and monitoring fatigue cracks. This paper focuses on in-situ monitoring of structural health, specifically detection of small crack growth and crack initiation in structures using AE technology. A probabilistic AE-based model for small fatigue cracks was developed and the uncertainties of the model were estimated. The paper discusses the methodology used, experimental approach, results obtained and predictive models developed.The developed model can be used to evaluate the integrity of structures and assess structural health by estimating the probability density function of the length of detected cracks. The outcome of this research has significant potential to be used for in-situ monitoring and evaluation of structural integrity.

Fatigue reliability for LNG carrier

The procedure of reliability-based fatigue analysis of liquefied natural gas(LNG) carrier of membrane type under wave loads is presented. The stress responses of the hotspots in regular waves with different wave heading angles and wave lengths are evaluated by global ship finite element method(FEM) . Based on the probabilistic distribution function of hotspots' short-term stress-range using spectral-based analysis,Weibull distribution is adopted and discussed for fitting the long-term probabilistic distribution of stress-range. Based on linear cumulative damage theory,fatigue damage is characterized by an S-N relationship,and limit state function is established. Structural fatigue damage behavior of several typical hotspots of LNG middle ship section is clarified and reliability analysis is performed. It is believed that the presented results and conclusions can be of use in calibration for practical design and initial fatigue safety evaluation for membrane type LNG carrier.