Influence of rest periods on the fatigue strength of structural steel

The effect of rest periods on fatigue life was investigated. Small size specimen and constant load amplitudes were used with a new developed fatigue testing machine in alternating bending. Rest periods of 1.5 min were introduced after each half cycle. The cycling rate was 0.25 cpm. Comparative tests on specimen tested without rest periods showed a substantial increase in fatigue life due to rest periods.     

体脑疲劳交互影响下煤矿工人作业改善研究

采用主观疲劳评价法,对陕西某矿业公司采煤工人的体疲劳和脑疲劳进行调查与研究,了解工人的工作内容与休息时间。用SPSS软件进行数据分析,得出煤矿工人的疲劳值,分析疲劳产生的原因,并结合实际情况提出相应的建议和解决方案。结果显示,煤矿工人的体疲劳主要发生在腰部、肩膀、前臂和后臂等部位,噪声疲劳和视疲劳是影响工人脑疲劳的主要因素,因而建议对矿工的作业动作进行优化,极大化地改善工人工作环境,优化生产流程和管理制度。目的在于减轻煤矿工人的体脑疲劳,预防人因失误,提升生产过程安全性。     

LABORATORY STUDIES OF REPETITIVE WORK. II : PROGRESS REPORT ON RESULTS FROM TWO SUBJECTS

This experiment is the first or a series undertaken to test proposals put forward earlier by the first author that in repetitive work (i) output would be higher and variability less if breaks were given at the end of an actite period (period of optimum performance) rather than at the point when output decreased; (ii) the end of an actile period would be indicated by the onset of irregularity in performance which could be determined by the incidence longcycle times in unpaced work and an increase in the number of missed cycles in paced work; and (iii) the length of an actile period will depend on the demand made by the job and upon the capacity of the worker to meet the demand (her actility)

Results from two subjects tested for a period of 3 1/ 2 months suggest that proposal (i) is correct. A condition in which two breaks were given at limes indicated by an increase in long times in unpaced performance gave a significantly better output and lower variance than a condition in which one break was given at a time indicated by a fall in output. Both subjects had relatively fewer misses in the paced condition when three breaks were given than when working continuously

The technique for obtaining long times in unpaced work which formed part of (ii) was found to be practical and a simpler method was devised. The results obtained seem to confirm that the method has validity. No definite conclusions can be drawn on paced work

There is some tentative confirmation of (iii); in the paced condition the actile period seems to have been 1 hour compared with 1 1/4hours in the unpaced condition. Further, the better worker gave her best unpaced performance when rest was given after 1 1/4 hours whereas the less good worker did best when rest was given after 1 hour.     

新型粘滞-弹性阻尼器的力学性能试验与理论研究

研制开发了一种新型粘滞-弹性阻尼器,对DS1~DS8八种不同型号的粘滞-弹性阻尼器进行了低周循环加载试验和抗低周疲劳性能试验研究,研究了新型粘滞-弹性阻尼器的耗能性能、参数相关性能和抗低周疲劳性能,基于Kelvin模型建立了粘滞-弹性阻尼器的恢复力模型,并对该模型进行了验证分析。研究结果表明:粘滞-弹性阻尼器具有良好的耗能性能和抗低周疲劳性能,工作性能稳定、密封性好;基于Kelvin模型建立的粘滞-弹性阻尼器的恢复力模型能够很好地反映阻尼器的实际受力情况,理论与试验滞回曲线吻合性良好;阻尼器能够同时附加刚度和阻尼,并可兼作限位保护装置,在动力或静力荷载作用下均能发挥作用。     

液体黏性软启动装置输出轴的有限元分析

针对液体黏性软启动装置的工作特点,要求输出轴传动力矩和输出转速变化范围较大,轴变形应该保持在较小范围内,输出轴的性能对液体黏性软启动装置正常工作有重要影响,需要对输出轴的结构作进一步分析.通过建立液体黏性软启动装置输出轴的Pro/E三维模型,采用有限元软件ANSYS Workbench对启动装置的输出轴进行有限元分析,确定输出轴的变形和应力状况,计算输出轴的模态和疲劳损伤.仿真结果表明：输出轴损伤最大部位位于较粗轴端键槽一侧.提出了一些改进措施,为液体黏性软启动装置输出轴的结构设计和疲劳寿命估算提供参考依据.     

Fracture mechanics based fretting fatigue life predictions in Ti-6Al-4V

A fracture mechanics based crack propagation analysis is developed to work directly with the output of a contact mechanics stress analysis for fretting fatigue. A series of remote load fatigue tests were conducted on specimens that had previously been subjected to fretting fatigue loading conditions. The growth of these prior fretting induced cracks were monitored and compared to results from the crack propagation analysis. A combined fatigue crack formation and propagation analysis was then applied to other fretting fatigue experiments with good success. The creation of fretting fatigue stress-life curves is also demonstrated.     

Durability of automotive jounce bumper

This study was carried out to predict the durability of automotive car jounce bumper using Finite Element Analysis (FEA). Fatigue life correlations were taken from literatures and it was incorporated into FEA codes. The simulated results were validated with experimental work. The FEA results showed good agreement with the experiment conducted on the jounce bumper in term of load–displacement response. In term of the durability of the component, the fatigue life predicted shows agreement at lower fatigue strains. However, the error becomes larger as the fatigue strains become higher. The differences between the predicted fatigue life and the experimental fatigue life were discussed. Finally, the predicted crack initiation side was also validated in the experiment.     

外企知识型员工心理疲劳的影响因素研究——以博世无锡柴油系统公司为例

目的针对知识型员工这一特殊群体的心理疲劳问题,分析现阶段外企知识型员工心理疲劳问题现状,并对影响心理疲劳的因素进行探讨。方法选择博世无锡柴油系统公司的知识型员工为样本,编制外企知识型员工心理疲劳调查问卷进行调研和统计分析。结果（1）工作性质、社会环境二个维度对心理疲劳的影响程度最大;（2）男性的综合疲劳度高于女性;（3）已婚者的综合疲劳度大于未婚者;（4）心理疲劳程度有随着年龄增加的趋势;（5）心理疲劳程度随着工作年限的增加先增再减,最后达到最高点;（6）管理人员和技术人员的心理疲劳程度最高;（7）心理疲劳程度随着学历水平的增加而逐渐降低。结论不同类型外企知识型员工的心理疲劳程度存在差异,前因变量各维度对该群体心理疲劳的影响程度存在差异。     

The influence of scientific research output of academics on economic growth in South Africa: an autoregressive distributed lag (ARDL) application

An increasing number of researchers have recently shown interest in the relationship between economic growth of a country and its research output, measured in scientometric indicators. The answer is not only of theoretical interest but it can also influence the specific policies aimed at the improvement of a country’s research performance. Our paper focuses on this relationship. We argue that research output is a manifestation of the improvement of human capital in the economy. We examine this relationship specifically in South Africa for the period 1980–2008. Using the autoregressive distributed lag method, we investigate the relationship between GDP and the comparative research performance of the country in relation to the rest of the world (the share of South African papers compared to the rest of the world). The relationship is confirmed for individual fields of science (biology and biochemistry, chemistry, material sciences, physics, psychiatry and psychology). The results of this study indicate that in South Africa for the period 1980–2008 the comparative performance of the research output can be considered as a factor affecting the economic growth of the country. Similarly, the results confirm the results of Vinkler (2008) and Lee et al. (2011). In contrast, economic growth did not influence the research output of the country for the same period. Policy implications are also discussed.     

含低速冲击损伤复合材料层合板剩余压缩强度及疲劳性能试验研究

对T300/QY8911复合材料层板进行了低速冲击、 冲击后压缩以及冲击后疲劳试验研究。通过对冲击后的层板进行目视检测和超声C扫描获得了层板受低速冲击后的若干损伤特征; 在压-压疲劳试验中, 测量了损伤的扩展情况。讨论了冲击能量与损伤面积以及冲击后剩余压缩强度的关系, 分析了含冲击损伤层合板在压缩载荷及压-压疲劳载荷下的主要破坏机制。结果表明, 低速冲击损伤对该类层板的强度和疲劳性能影响很大, 在3.75 J/mm的冲击能量下, 层板剩余压缩强度下降了65%; 在压-压疲劳载荷作用下, 其损伤扩展大致可分为两个阶段, 占整个疲劳寿命约60%的前一阶段损伤扩展较为缓慢; 而疲劳寿命的后半阶段损伤则开始加速扩展, 并导致材料破坏。     

复合材料单钉接头疲劳累积损伤破坏分析

基于时间增量原理 , 推导了层合板接头疲劳加载累积损伤应力2应变分析的虚功方程。同时 , 引入Hashin三维疲劳失效准则进行材料的损伤判定 , 并结合建立的疲劳加载材料退化模型、 4种基本损伤机制相互关联作用的材料性能退化方法及复合材料接头最终失效判据 , 建立了层合板接头疲劳载荷作用下三维累积损伤分析的寿命预测方法。最后 , 对层合板接头拉2拉疲劳载荷作用下的损伤累积扩展与失效规律进行了仿真分析 , 并与试验结果进行了对比 , 结果表明 : 本文中建立的寿命预测方法能够很好地预测层合板接头的寿命以及损伤发生、扩展及最终失效。      

残余应力和粗糙度对叶片振动疲劳性能的影响

为了研究叶片表面完整性对其振动疲劳性能的影响,本文模拟分析了某型高温合金叶片在振动疲劳实验过程中的动力学应力响应,获得叶片共振时应力幅值随时间的变化规律,分析了残余应力和粗糙度对叶片振动疲劳寿命和疲劳极限的影响规律.结果表明:叶片共振过程中的应力响应幅值先增大后减小呈周期性变化,属于"拍"现象,满足关系σ=1 046sin(242.83t)sin(5 828t);叶片的振动疲劳极限和疲劳寿命均随残余应力和粗糙度的增大而减小,振动疲劳极限和残余应力之间的关系满足σfat=510.9-0.31-70.93σrest;而疲劳极限和粗糙度之间的关系则满足σfat=9.67R2roughness-70.93Rroughness+713.23.     

Modeling and assessment of self-healing and thixotropy properties for modified binders

The fatigue endurance limit of binders is the results of more phenomena (e.g. viscoelasticity, damage, healing, thixotropy, steric hardening) that interact simultaneously making the mechanisms behind the fatigue behavior not properly understood.Currently, there is no consolidated analytical approach inclusive of such phenomena to characterize fatigue performance.This research proposes a criterion to determine the fatigue resistance of binders subjected to monotonous cyclic loading with multiple rest periods. The main rheological properties are measured during each stage using a Dynamic Shear Rheometer and the modeling of their evolution is proposed. The experimental program includes different binders in order to investigate the effects of SBS modification levels and aged binder contents on self-healing potential and fatigue behavior.The proposed criterion enables to identify fundamental contributions leading to a comprehensive fatigue endurance limit. This approach allows different binders to be distinguished taking into account their self-healing capacity and can help to establish a better correlation with in-service performance of mixtures.Moreover, a comparison with a previous analytical approach based on the same kind of test (time sweep) with only one rest period is proposed in order to evaluate the effectiveness and reliability of the proposed criterion. Results show that multiple rest periods are needed in order to fully understand the self-healing and fatigue behavior of bituminous binders and to quantify the contributions given by thixotropy.     

心理负荷多维主观评定的实验研究

本研究在总结前人成果的基础上将心理负荷主观反应归纳为“任务难度”等８个方面，并结合追踪作业负荷实际加以实验检验。通过敏感性分析和因素分析，作者最终提出“任务复杂性”、“任务压力”、“心理努力与疲劳”和“紧张水平”是主观心理负荷最重要的维度，建议设计多维主观评定量表时考虑这４个方面。     

Improving fatigue performance of Ti-6Al-4V alloy via ultrasonic surface rolling process

The effect of a gradient nanostructured (GNS) surface layer obtained by ultrasonic surface rolling process (USRP) on the fatigue behavior of Ti-6Al-4 V alloy has been studied in this paper. Microstructure, surface topography, surface roughness and residual stress measurements were performed to characterize the surface under different conditions. Rotating bending fatigue tests were carried out to evaluate the fatigue behavior of different treatments. The results present a remarkable fatigue performance enhancement for the Ti-6Al-4 V alloy with a GNS surface layer obtained by application of USRP with respect to the untreated condition, notwithstanding its considerable surface roughness due to severe ultrasonic impacts and extrusions. Mechanical surface polishing treatment further enhances the beneficial effects of USRP on the fatigue performance. The significantly improved fatigue performance can mainly be ascribed to the compressive residual stress. Simultaneously, the GNS surface layer and surface work hardening have a synergistic effect that accompanies the effect of compressive residual stress.     

Joint performance of the glass fiber reinforced polypropylene leaf spring

Commercial utilization of the composite leaf springs in the suspension application is significantly decided by its eye end joint performance. Present work attempts to design and evaluate the performance of double bolted end joint for thermoplastic composite leaf spring. Injection molded 20% glass fiber reinforced polypropylene leaf springs were considered for the joint strength evaluation. Servo hydraulic test facility is utilized to evaluate the static and fatigue performance of the bolted joint. Various bolt sizes were utilized for the joint and its performances were evaluated under static loading condition to understand the effect of fit between bolt and its hole of the joints. Ultimate bearing strength of the joint is found to decrease with the increase in the clearance between bolt and part hole. Joints were subjected to various amplitudes of completely reversed fatigue loads to evaluate the endurance strength. Load–deflection hysteresis plot of the joint under fatigue conditions is continuously measured and used as the bearing damage index of the joint. Inspection of the bearing surface tested under static and fatigue loading condition revealed severe matrix deformation and fibrillation. In spite of unidirectional load being acted at the joint, curved nature of the bearing surface induces bi-axial stresses, which results in severe matrix fibrillation at the bearing surface. Failure morphology under static conditions shows net-tension beside the bearing damage. Failure morphology under fatigue condition revealed net-tension, and shear-out failures besides the bearing damages.     

Synchrotron diffraction investigation of the distribution and influence of residual stresses in fatigue

This paper presents some results obtained from synchrotron diffraction investigations into two somewhat related areas of interest to the fatigue community. Firstly, the influence of fatigue cycling on the distribution and magnitude of residual strains and stresses and, secondly, the residual strains and stresses engendered around a growing fatigue crack. Its main premise is that modern tools such as automated synchrotron strain scanning offer the potential for more complete insight into the distribution of residual strains and stresses and their influence on fatigue performance. The first part of the work was accomplished using friction‐stir welded (FSW) and metal‐inert gas (MIG) welded specimens. The particular interest in these specimens was obtaining detailed knowledge regarding as‐welded variation in residual stresses between specimens, the location of peak values relative to local microstructure and stress concentrations, and of their modification during fatigue cycling. Such information may indicate a route forward to the selection of welding process parameters for optimised fatigue performance. The second part of the work considered an established fatigue crack in a compact tension (CT) specimen and examined the ability of synchrotron diffraction to characterize the stresses associated with the plastic enclave around a fatigue crack. This work is of interest in the context of better knowledge of crack‐tip shielding by plasticity‐induced closure and its incorporation into life prediction methodologies.     

考虑工人疲劳的工作排程研究

为提高企业整体生产力,降低工人累积性疲劳对生产过程的影响,在综合考虑工人疲劳与作业负荷的基础上,以单人多任务排程为研究对象,工人的最大可接受工作时间为休息与否的判定依据,构建了单人工作-休息排程的数学模型。从不同的工作休息组合中选出最佳的排程组合,以优化最小化任务的最大完工时间和因工人工作时间超过最大可接受工作时间而产生的额外能量消耗双目标函数。应用线性加权和法将多目标化为单目标用遗传算法求解,通过算例分析得出模型的满意解,从而得到任务的排序以及工人的休息时间和休息次数的排程组合方案。模型存在多个满意解,为管理者提供多种备选方案,管理者根据实际情况选择实施最优化的组合方案。     

Driver state examination—Treading new paths

A large proportion of crashes in road driving can be attributed to driver fatigue. Several types of fatigue are discussed, comprising sleep-related fatigue, active task-related fatigue (as a consequence of workload in demanding driving situations) as well as passive task-related fatigue (as related to monotonous driving situations). The present study investigated actual states of fatigue in a monotonous driving situation, using EEG measures and a long-lasting driving simulation experiment, in which drivers had to keep the vehicle on track by compensating crosswind of different strength. Performance data and electrophysiological correlates of mental fatigue (EEG Alpha and Theta power, Inter Trial Coherence (ITC), and auditory event-related potentials to short sound stimuli) were analyzed. Driving errors and driving lane variability increased with time on task and with increasing crosswind. The posterior Alpha and Theta power also increased with time on task, but decreased with stronger crosswind. The P3a to sound stimuli decreased with time on task when the crosswind was weak, but remained stable when the crosswind was strong. The analysis of ITC revealed less frontal Alpha and Theta band synchronization with time on task, but no effect of crosswind. The results suggest that Alpha power in monotonous driving situations reflects boredom or attentional withdrawal due to monotony rather than the decline of processing abilities as a consequence of high mental effort. A more valid indicator of declining mental resources with increasing time on task seems to be provided by brain oscillatory synchronization measures and event-related activity.     

碳纤维束疲劳损伤失效试验

为了解碳纤维束的疲劳特性及疲劳加载后剩余强度的变化, 为建立碳纤维复合材料疲劳性能的细观力学分析模型提供必要的基础数据, 研究设计了碳纤维束静载力学性能及疲劳特性试验方案, 并进行了试验。采用最小二乘法拟合得到了单束碳纤维的应力-寿命(S-N)曲线。对经过预疲劳的碳纤维束试验件进行了剩余强度试验, 采用最小二乘法拟合得到了碳纤维束疲劳加载剩余强度模型。试验结果表明: 试验所用碳纤维束的条件疲劳极限为静拉伸强度的80.47%; 碳纤维束经历一定循环次数的拉-拉疲劳可以提高其强度, 其剩余强度随着疲劳加载循环次数的增加先增加后减小。