Influence of Different Surface Treatments of H13 Hot Work Die Steel on Its Thermal Fatigue Behaviors

Thermal fatigue checking is the general failure of hot work die steels, which is relative with the structures and properties of the steels and the stress alternated during the employment. The Uddeholm test method on thermal fatigue is used to compare the behaviors of different samples, which are treated with plasma nitriding、plasma sulfur carbon nitriding、boronizing or not treated. The results show that the nitriding improves the thermal fatigue property of the tool steel, while the plasma sulfur carbon nitriding and the boronizing impair the property. The mechanisms are induced as follows. By increasing the hardness and changing the stress distribution in the surface layer, surface treatment can decrease the plastic deformation and the tensile stress during the cycling. Therefore, the generation and growth of the cracks are restrained. On the other hand, as results of surface treating, in the surface layer the toughness declines and the expanding coefficient ascendes; the latter change caused the strengthening of the tensile and compressive stress during the cycling. Thus the resistance to thermal fatigue is weakened. Whether or not the surface treatment is favor to thermal fatigue of tool steels relies on which factor is dominant.

CYCLIC SOFTENING IN HOT-WORKING DIE STEELS DURING LOW-CYCLE FATIGUE

The characteristics and microstructural changes of cyclic softening in hot-working die steels 5CrNiMo and 5Cr2NiMoVSi were studied under strain controlled low-cycle fatigue.The re- sults show that the cyclic softening is featured in both steels hardened in different conditions under the strain controlled amplitude range of Δε_t/2=0.6-1.8×10^(-2).The softening effect mainly occurs in some initial cycles and the stress amplitude varies slightly in the sequential cycles,i.e.the softening effect is minified.No obvious stress saturation phenomenon was ob- served during the whole cyclic deformation.The TEM analysis shows that the cyclic softening is related to heterogenity of plastic deformation.The softening of the tested steels is caused by the formation of the dislocation cell structure with low density and low internal stress,and by the fragmentation and redissolution of fine carbides into matrix.

Study on Large Power Tractor Driver's Heart Rate and Fatigue in Sowing Work

In order to reduce the driving fatigue in sowing work, this paper based on heart rate （HR） as the main indicator to survey, tested and analyzed the fatigue condition of the drivers of three imported tractors and one domestic tractor in sowing work. The results showed that when driving the imported tractors in sowing work, the HR increasing rate was 10.4%-14.3%, labor intensity belonged to the light level; when driving domestic tractor in sowing work, the HR increasing rate was 23.4%-33.0%, it was remarkably bigger than that of driving imported tractors （P〈0.05）, labor intensity belonged to the middle level. The main effects on driving fatigue included the control methods, tractors＇ cab environment, processing time, operating content, and so on. Finally, we proposed the concrete measures and suggestions to reduce driving fatigue and improve drivers＇ work condition.

Evaluation of the Fatigue Characteristics of Laser-processed Hot Work Tool Steel Based on Reliability

It is reported that laser-processing is effective to repair the heat checks, which are fine shallow cracks on a surfaceof die-casting dies. In this study, the rotating bending fatigue tests have been carried out to evaluate the fatiguecharacteristics of laser-processed hot working tool steel. Because test results are scattered, S-N curves are decidedbased on the evaluation of fatigue strength distribution. As a result, the fatigue strength of the laser-processedspecimens decreases remarkably in comparison with that of base metal. However, it can be recovered to almostinitial value by heat treatment at secondary hardening temperature. This procedure is also effective to decrease thescatter of fatigue strength. The laser-processing can be carried out at low cost and this method is effective for theextension of the work life of dies.

The Effect of Stress, Fatigue, and Sleep Quality on Shift-Work Nurses in Japan

Purpose: To investigate the relationship between stress, fatigue and sleep quality among shift work nurses in Japan. Design: A descriptive correlation design using self-administered surveys. Methods: Questionnaires on stress, fatigue and sleep quality (the Pittsburgh Sleep Quality Index;PSQI-J) among shift work nurses were distributed to 653 nurses in Japan from January 2015 to February 2015. Results: Participants who reported higher levels of fatigue reported higher levels of stress (r = 0.774, p = 0.000), lower levels of sleep satisfaction (r = −0.411, p = 0.000) and overall lower levels of health (r = −0.323, p = 0.000).PSQI scores were also significantly correlated with reported levels of stress (r = 0.294, p = 0.000), fatigue (r = 0.291, p = 0.000) and levels of health (r = −0.370, p = 0.000). Nurses who have stress-relieving recourses were younger (t = −2.842, p = 0.005), reported higher levels of overall health (t = 2.727, p = 0.007), had higher levels of sleep quality measured by the PSQI (t = −2.560, p = 0.011), and required less time to fall asleep (t = −3.207, p = 0.001). Conclusions: This study showed an association between stress and sleep satisfaction among shift work nurses in Japan. In addition, nurses that engage in activities to manage stress might achieve higher levels of health and high sleep quality.

Methods of Random Fatigue Design for Vehicle Transmission System Components

Some representative working conditions were measured, and the amplitude distribution rule of each representative working condition after analysis of measured data was got. The building of 2 D distributing function between the range and the mean of random load was discussed. Experiment was carried out to get the fatigue strength data of the material of transmission component. Accessing the P S a S m N camber of combined load of bending and torsion on this material after analysis. And the process of calculating the 2 D fatigue life in multi working condition was discussed.

Fatigue in patients with inflammatory bowel disease in Eastern China

BACKGROUND Fatigue is a very common but relatively neglected problem in patients with inflammatory bowel disease(IBD).The prevalence rate of IBD in China is the highest in Asia,but there is little research on fatigue in patients with IBD.Neither the relationship between fatigue and quality of life(QoL)nor the relationship between fatigue and work productivity(WP)in Chinese IBD patients has been reported.AIM To investigate the prevalence of fatigue related to IBD in Eastern China,to identify the risk factors associated with fatigue,to assess the impact of fatigue on QoL,and to evaluate the relationship between fatigue and WP.METHODS A cross-sectional study was conducted in a Regional Tertiary IBD Diagnostic and Treatment Center in Eastern China.Clinical data of patients were collected,and disease activity was evaluated.Blood samples were analyzed to assess anemia,albumin,and inflammation.Fatigue was assessed using the multidimensional fatigue inventory.QoL and WP were measured using the short inflammatory bowel disease questionnaire and the work productivity and activity impairment general health questionnaire,respectively.The patients also completed assessments of depression(Patient Health Questionnaire-9)and anxiety(Generalized Anxiety Disorder 7-item Scale).RESULTS A total of 311 IBD patients,comprising 168 Crohn's disease patients and 143 ulcerative colitis patients,were enrolled.The prevalence of fatigue in patients with IBD was 60.77%.In a univariate logistic regression analysis,factors such as disease activity,depression,anxiety,anemia,and IBD-related surgery were individually related to a significantly increased risk of fatigue in IBD patients.Multivariate logistic regression analysis indicated that depression[odds ratio(OR)=8.078,95%confidence interval(CI):4.113-15.865],anxiety(OR=2.373,95%CI:1.100-5.119),anemia(OR=2.498,95%CI:1.290-4.834),and IBD-related surgery(OR=2.035,95%CI:1.084-3.819)were related to fatigue in IBD patients.There was a negative correlation between fatigue and QoL(r=-0.831;P<0.0001)but a positive correlation between fatigue and WP loss.CONCLUSION The prevalence of fatigue in IBD patients in Eastern China is remarkably high even in clinical remission.Factors such as depression,anxiety,anemia,and IBDrelated surgery are major risk factors for fatigue in IBD patients.In addition,fatigue has a negative impact on QoL and is positively correlated with WP loss.

Review: Energy Methods for Multiaxial Fatigue Life Prediction

Fatigue fracture of materials and structures is one of the most common failure modes in engineering applications.Under multiaxial non proportional loading condition,a large number of materials show non proportional hardening characteristics,which results in a significant reduction of fatigue life.In this paper,a review on energy methods for multiaxial fatigue life prediction has been carried out.The energy methods are divided into three categories:energy based models without considering the loading path effect,energy based models combined with the critical plane method,and energy based models considering the loading path effect.Among these categories,energy based models considering the loading path effect are introduced in detail since they involve the non proportional hardening effect in multiaxial fatigue.

Influence of Rare Earths on Contact Fatigue of Rail Steels

Rail/wheel contact fatigue of NbRE rail, Nb rail and U74 rail was investigated using contact fatigue tester. Microstructure and morphology as well as microhardness in the fatigue profiles were analyzed by scanning electron microscope and Vickers hardness respectively. The experimental results show that rare earths are able to delay the initiation and the propagation of fatigue cracks and postpone the surface shelling or spalling, even more, to reduce the crack propagation angle and the crack propagation depth in steady stab as well as the plastic deformation area, and to improve work-hardening of the rail steel.

Experiences of Fatigue at Sea—A Comparative Study in European and Chinese Shipping Industry

Fatigue has negative impacts on the general working population as well as on seafarers. In order to study seafarers’ fatigue, a questionnaire-base survey was conducted to gain information about potential risk factors for fatigue and construct indexes indicating fatigue. The study applies T-test to compare strata of seafarers to analyse work and sleep patterns in global seafaring. Qualitative analysis are also employed to explore the impacts of fatigue on seafarer’s occupational health and safety.

基于Solidworks的船舶结构强度评估分析方法研究

由于船舶在海上航行时受到海浪撞击、机械碰撞、振动等因素的干扰,船舶结构会发生疲劳破坏等失效形式,引发船舶停运等事故,造成巨大的经济损失。因此,船舶结构的强度校核对于提高船舶的抗干扰能力和使用寿命有重要的意义。本文结合三维建模软件Solidworks和快速有限元分析软件COSMOS,对船舶舱段结构的接触应力和应变进行系统分析,该分析对改善船舶舱段的结构强度,提高舱段的抗波浪冲击性能等具有一定的指导作用。

Effect of Rare Earth Composite Modification on Microstructure and Properties of a New Cast Hot-Work Die Steel

The effects of RE modification on structure and the properties of a new cast hot work die (CHD) steel were investigated. The grains of the CHD steel are refined by RE modification. With the increase of RE addition, both grain size and inclusion amount are reduced. Appropriate amount of RE results in decrease in inclusion amount and formation of spheroidal inclusions uniformly-distributed in steel, so that the morphology and distribution of inclusions are improved. RE composite modification favors the formation of bainite, austenite and fine lath martensite with dense dislocation. When the residual RE content reaches 0.02%, no obvious changes in strength and hardness are found, while fracture toughness and threshold of fatigue crack growth are increased. The impact toughness, elongation and reduction of cross sectional area are increased by a factor of two, and thermal fatigue resistance is also improved.

Repair Effect of Hot Work Tool Steel by Laser-Melting Process

Both wear and crack due to heat checking in hot work tool steel are major failure modes.It is desirable to find amethod to lengthen the tool life while reducing manufacturing cost.This paper suggests a method to improve toollife for hot work tool steel(SKD6)with crack by laser-melting process.The method has been evaluated using theimpact and fatigue test results.It is demonstrated that a repair of the crack by a laser-melting process is effectivefor life extension of the damaged tool.

基于Solid works的玉米收获机割台框架的疲劳分析

以Solid works软件为工具建立玉米收获机割台框架的三维模型,以由于路面不平而引起的不规则振动为激励,利用Solid works Simulation对玉米收获机割台框架进行静力分析,获取到关键部位的应力、应变强度等相关信息;同时以静力分析为基础,根据Q235钢材料的疲劳曲线对割台框架进行疲劳分析,得到损坏图解等相关数据。其结果在理论上对于以后进行同类产品的设计、检验、改进及安全评估具有一定的参考价值。

Study on Microstructures and Properties of Several Kinds of Hot Working Die Steel

This paper deals with the microstructures and properties of AISI H13(4Cr5MoSiV1), UHB QRO 90M and 4Cr3Mo2V steels, and then discusses the means of improving the service life of hot working die. The results show that increase of quenching temperature improves the resistance to thermal fatigue and tempering stability. Fine heat treatment process can produce fine dispersed carbides. Shot peening and cryogenic treatments can raise the compressive stresses at surface as well as the resistance of tempering greatly. Under the condition that a compound layer is not engendered, ionnitriding process can restrain the initiation and propagation of fatigue crack and enhance the resistance to thermal fatigue. Vapor surface treatment provides the ways to protect and lubricate the die by the porous films of Fe 3O 4, which are formed on the die surface. Electrical spark surface strengthening process forms compounds with high melting point and high stability on the die surface and thus enhances the properties of die's resistance to oxidation efficaciously. Besides, QRO 90M and 4Cr3Mo2V steels, because of the superiority in designing of composition, have better tempering stability and softening resistance than 4Cr5MoSiV1 steel.

APPLICATION OF RARE EARTH IN SURFACE HEAT TREATMENT OF HOT-WORKING DIE STEELS

This paper studies a compound treatment. i. e. liquid S , N,C co-diffusing with rare earth (RE) and then oxidization , for hot-working die steels , and the effect of RE on thermal fatigue behavior of the diffused layer. XRD and SEM energy spectrum prove that trace RE element actually penetrates into the surface layer of steels. The result shows that RE can reduce the gradient of change of hardness in diffused layer, improve the morphology and distribution of compounds , and reduce the degree of surface alligator crack for thermal fatigue. The behavior of thermal fatigue of hot-working die steels is raised by 70% or so after the application of RE. The effect of RE is analysed according to the theory.

江苏省高年资护士共情疲劳的潜在类别分析

目的了解江苏省高年资护士共情疲劳的现状及潜在类别,分析其影响因素,为高年资护士的人本化管理提供参考。方法采用便利抽样法,选取江苏省苏中、苏南、苏北地区护理工作年限≥10年的高年资护士3509人作为研究对象,采用一般资料调查表、中文版共情疲劳量表及中文版护士工作环境感知量表进行调查。结果高年资护士职业倦怠得分为(24.58±6.50)分,继发性创伤应激得分为(26.80±6.07)分,同情满足得分为(36.57±7.38)分。中度及以上共情疲劳者为2386人(68.0%)。潜在剖面分析显示,共情疲劳分为共情疲劳优势组(32.00%)、中度共情疲劳组(63.12%)和共情疲劳应激组(4.87%)3个潜在类别。logistic回归分析显示,职务、月收入、班次、对工作环境感知是共情疲劳不同潜在类别的影响因素(均P<0.05)。结论高年资护士共情疲劳存在3个潜在类别,呈现群体异质性。护理管理者需采用多元化、人本化管理策略,激发高年资护士工作热情,降低共情疲劳水平。

手过头静态作业的上肢肌肉疲劳特性研究

为探究手过头不同高度下静态作业的上肢肌肉疲劳特性,通过实验设计采集了被试的表面肌电信号(surface electromyography,sEMG)及基于Borg CR-10量表的主观疲劳状态,研究了sEMG的时域与频域特征处理方法,并利用多分类支持向量机(support vector machine,SVM)识别肌肉疲劳状态。通过对肌肉贡献率、主客观肌肉疲劳特征的相关性、不同高度下的肌肉疲劳累积排序及肌肉疲劳分类识别进行分析,结果表明:肌肉平均贡献率超过10%的肌肉为肱二头肌、三角肌与斜方肌,且其累积贡献率超过70%;对疲劳累积程度在3个高度下排序,肱二头肌和斜方肌为H_(3)>H_(2)>H_(1),三角肌为H_(2)>H_(3)>H_(1);随着手过头静态作业时间增加,上肢肌肉疲劳逐渐积累,时域特征值增加、频域特征值减小且其变化具有一致性;多分类SVM对手过头静态作业中的上肢肌肉疲劳识别准确率大于90%。

手过头作业上肢肌肉疲劳状态识别研究

为对手过头作业中的上肢肌肉疲劳状态进行有效识别,结合复杂装备的维修任务设计了手过头作业试验。通过采集被试的表面肌电信号(Surface Electromyography,SEMG)和主观疲劳状态及研究SEMG信号的时域、频域、非线性及参数模型特征计算方法,基于支持向量机(Support Vector Machine,SVM)采用核主成分分析(Kernel Principal Component Analysis,KPCA)进行特征降维并对手过头作业的肌肉疲劳状态进行识别。研究结果表明:手过头作业中斜方肌的SEMG贡献率最高;KPCA-SVM对训练集和测试集的疲劳识别率分别为0.99827和0.83218,与其他疲劳识别算法相比具有优越性。

管制员不良工作状态与疲劳状态分析

为分析管制员不良的工作状态与疲劳状态之间的关系,监测管制员工作状态,采用主观评价方法收集185名管制员的主观看法,通过灰色关联分析不良工作状态和疲劳状态的影响因素,对其重要性进行排序,并通过疲劳自评量表研究了管制员处于不良工作状态时对应的疲劳程度。结果表明,管制员不良工作状态与疲劳状态影响因素之间存在差异性和统一性,且当管制员处于中度疲劳后,其工作状态将受到影响,因此,对管制员疲劳状态的研究应当更多关注于中度及重度疲劳的识别。