A Model of the Fatigue Life Distribution of Composite Laminates Based on Their Static Strength Distribution

The reasons of the static strength dispersion and the fatigue life dispersion of composite laminates are analyzed in this article. It is concluded that the inner original defects, which derived from the manufacturing process of composite laminates, are the common and major reason of causing the random distributions of the static strength and the fatigue life. And there is a correlative relation between the two distributions. With the study of statistical relationship between the fatigue loading and the fatigue life in the uniform confidence level and the same survival rate S-N curves of material, the relationship between the static strength distribution and the fatigue life distribution through a material S-N curve model has been obtained. And then the model which is used to describe the distributions of fatigue life of composites, based on their distributions of static strength, is set up. This model reasonably reflects the effects of the inner original defects on the static strength dispersion and on the fatigue life dispersion of composite laminates. The experimental data of three kinds of composite laminates are employed to verify this model, and the results show that this model can predict the random distributions of fatigue life for composites under any fatigue loads fairly well.

Study on Strength and Life of Anisotropic Single Crystal Blade - Part I: Crystallographic Constitutive Models and Applications

The single crystal blade is one of the key technologies for improving the performance, durability and reliability of aero-engines and ground gas-turbine engines. However, the anisotropic mechanical properties of the single crystal material makes a great deal of difficulties on the development and the application of the single crystal blade, which is a challenge for the engineering application of the single crystal superalloy and the theoretic bases of the application. Some researches on the strength analysis and the life prediction of the anisotropic single crystal blade were carried out by the authors' research team. They are as follows. The crystallographic constitutive models for the plastic and the creep behaviors and the method of the rupture life prediction were established and verified. The tensile or the creep experiments for DD3 single crystal alloy with different orientations under different temperatures and different tensile rates or under different temperatures and different stress levels were carried out. The experimental data and the anisotropic properties at intermediate and high temperatures revealed by the experiments are significant for the application of the single crystal alloy. In addition, the experimental research for a kind of single crystal blade was also made. As the application of the researches the strength analysis and the life prediction were carried out for the single crystal blade of a certain aero-engine. In this part, the constitutive models and their applications are described, and the experimental research work will be described in part II.

A two-parameter model to predict fatigue life of high-strength steels in a very high cycle fatigue regime

In this paper, ultrasonic （20 kHz） fatigue tests were performed on specimens of a high-strength steel in very high cycle fatigue （VHCF） regime. Experimental results showed that for most tested specimens failed in a VHCF regime, a fatigue crack originated from the interior of specimen with a fish-eye pattern, which contained a fine granular area （FGA） centered by an inclusion as the crack origin. Then, a two-parameter model is proposed to predict the fatigue life of high-strength steels with fish-eye mode failure in a VHCF regime, which takes into account the inclusion size and the FGA size. The model was verified by the data of present experiments and those in the literature. Furthermore, an analytic formula was obtained for estimating the equivalent crack growth rate within the FGA. The results also indicated that the stress intensity factor range at the front of the FGA varies within a small range, which is irrespective of stress amplitude and fatigue life.

RESIDUAL STRENGTH AND FATIGUE LIFE OF 2-D AND 3-D CARBON FABRIC COMPOSITES

The fatigue behavior and damage mechanisms of 2 D and 3 D carbon/epoxy composites with approximately the same 51% fiber volume fraction were investigated. A test program was conducted on fatigue residual strength and fatigue life under constant amplitude tensile fatigue loading. Equations of predicting the fatigue life for both 2 D and 3 D composites were provided. Comparison of the 2 D and 3 D composites indicated that due to the through thickness reinforcement, the 3 D composite has considerably better fatigue performance. Comparison of experimental data with calculation results shows good agreement, thus confirming the usefulness of the predictions.

Schroth疗法联合核心力量训练改善轻度青少年特发性脊柱侧凸患者的侧凸角度

背景:青少年特发性脊柱侧凸明确的发病原因尚未可知,寻找解决青少年特发性脊柱侧凸的临床方法迫在眉睫。目的:探讨Schroth疗法联合核心力量训练对轻度青少年特发性脊柱侧凸的效果,为轻度青少年特发性脊柱侧凸的临床治疗提供更多依据。方法:选择2022年7月至2024年1月在南通大学附属医院康复医学科与脊柱外科就诊的轻度青少年特发性脊柱侧凸患者110例作为研究对象,根据患者及家长意愿,分为试验组和对照组,每组55例。对照组观察随访,试验组进行Schroth疗法联合核心力量训练,每天45 min,坚持24周。比较两组患者治疗前后影像学参数、体表指标、三维超声成像角度和生活质量的差异。结果与结论:①治疗24周后,试验组主弯Cobb角、顶椎偏距、颈椎前凸角均较治疗前有显著改善(P<0.05),而对照组无显著差异(P>0.05);试验组主弯Cobb角、顶椎偏距明显优于对照组(P<0.05);②治疗24周后,试验组躯干旋转角度明显低于治疗前(P<0.05),而对照组无显著差异(P>0.05);试验组躯干旋转角度明显低于对照组(P<0.05);③治疗24周后,试验组三维超声成像椎板中心法角度明显减小(P<0.05),而对照组无显著差异(P>0.05);试验组三维超声成像椎板中心法角度明显低于对照组(P<0.05);④治疗24周后,在生活质量上,试验组的疼痛维度评分显著增高(P<0.05),试验组和对照组的自我形象维度评分均较治疗前显著增高(P<0.05),两组的心理健康维度评分较治疗前显著降低(P<0.05);疼痛、自我形象、心理健康和满意度维度评分,试验组均明显高于对照组(P<0.05);⑤提示Schroth疗法联合核心力量训练能改善轻度青少年特发性脊柱侧凸患者的主弯Cobb角、顶椎偏距、颈椎前凸角,降低躯干旋转角度,减少三维超声成像角度,提高生活质量,对轻度青少年特发性脊柱侧凸治疗有效。

CONSTANT AMPLITUDE FATIGUE STRENGTH AND P-S_a-S_m-N CAMBER FAMILY

Functions of the P-Sa-Sm-N camber family in constant amplitude cyclic loading are established by combining the P-S-N curve family and constant life diagrams, which is feasible in engineering application. Meanwhile, the preconditions of mechanics and probability-statistics are clearly presented. According to Weibull's assumptions i.e., monotone decreasing and nonintersecting about individual S-N curves, the relation of isostructural measure preserving transformation (IMPT) between the probability spaces of constant amplitude fatigue life and constant amplitude fatigue strength is proved based on the measure theory. Therefore, an individual specimen possesses the same percentile value in different probability spaces of fatigue life and fatigue strength under constant amplitude loading. The P-Sa -Sm-N cambers of individual, population and sample are also distinguished.

Strength degradation of sandstone and granodiorite under uniaxial cyclic loading

Change in mechanical properties of rocks under static loading has been widely studied and documented.However, the response of rocks to cyclic loads is still a much-debated topic. Fatigue is the phenomenon when rocks under cyclic loading fail at much lower strength as compared to those subjected to the monotonic loading conditions. A few selected cored granodiorite and sandstone specimens have been subjected to uniaxial cyclic compression tests to obtain the unconfined fatigue strength and life. This study seeks to examine the effects of cyclic loading conditions, loading amplitude and applied stress level on the fatigue life of sandstone, as a soft rock, and granodiorite, as a hard rock, under uniaxial compression test. One aim of this study is to determine which of the loading conditions has a stronger effect on rock fatigue response. The fatigue response of hard rocks and soft rocks is also compared. It is shown that the loading amplitude is the most important factor affecting the cyclic response of the tested rocks. The more the loading amplitude, the shorter the fatigue life, and the greater the strength degradation. The granodiorite specimens showed more strength degradation compared to the sandstone specimens when subjected to cyclic loading. It is shown that failure modes of specimens under cyclic loadings are different from those under static loadings. More local cracks were observed under cyclic loadings especially for granodiorite rock specimens.

Residual strength model for composite laminates

To research the approach of predicting composites fatigue life,the cumulative fatigue damage of fiber-reinforced plastic laminates(FRP) was investigated,and based on the complex exponential function,the residual strength model was obtained. This model can accurately describe the propagation of cumulative fatigue damage of FRP in three stages,especially in the initial stage and the ceasing stage. Applying this model in the experiment with two loading cycles,it can be found that the prediction result has good coincidence with experimental data. So a reliable residual strength model can be provided for studying the cumulative fatigue damage of FRP.

Malnutrition Reduces Quality of Life and Performance in Hospitalized Elderly

Objectives: Severe protein energy malnutrition results in muscle wasting and loss of subcutaneous tissue and has serious implications for health, recovery from illness or surgery, and hospital costs;however this condition is often underestimated and considered as one of the aspects of aging. We measure the incidence of malnutrition and its consequences on general health, physical and mental performance in a cohort of elderly patients. Study Design: This is a cross-sectional study conducted in a geriatric inpatient unit. Three hundred patients admitted to the clinic who fulfilled the inclusion criteria were enrolled. Main Outcome Measures: Nutritional status was evaluated by Mini Nutritional Assessment (MNA) questionnaire, macro and micronutrients intake, anthropometric measures and biochemical parameters. Physical and mental performances were recorded by questionnaires. Muscular strength was measured by a hand dynamometer and clinical outcomes were recorded. Results: Patients with poor nutritional status have lower physical and mental performance as respect to well nourished patients. Undernourished patients have longer hospitalization and worst outcomes. We observe a high prevalence of severe hypovitaminosis D and the intake of various micronutrients was severely unbalanced. The incidence of malnutrition was 25% (75 patients);39% (119 patients) were at risk of malnutrition. MNA was inversely related with the length of hospital stay (R = -0.25, p = 0.012) and with Geriatric Depression Scale (GDS) (R = -0.56, p = 0.000), whereas directly related with cognitive performance measured through Mini Mental State Examination (MMSE) (R = 0.5, p = 0.000) and hand grip strength (R = 0.35, p = 0.000). Conclusions: Malnutrition significantly reduced quality of life, physical and mental performance and worsened patients’ prognosis.

Improvement of Toughness of Ultrahigh Strength Steel Aermet 100

The influence of double aging on the microstructure and mechanical properties of ultrahigh strength steel Aermet 100 was analyzed. Under the double aging, there is no apparent decrease in the strength of steel. However, the impact fatigue life can be prolonged by 35.5% and dynamic fracture toughness be raised by 22.6% respectively, as compared with the normal aging. Based on the observation of microscopic structure, the physical mechanism of the prolongation of impact fatigue life and the enhancement of stability of the reverted austenite, AR, is analyzed further. The results show that this new technique is a breakthrough of combination optimization between strength and toughness for Aermet 100 steel. In the light of the current understanding on this subject, the volume fracture of soften and tough AR formed in process of heat preservation at higher temperature of double aging increases drastically. Moreover, during the treatment of lower temperature of double aging, the carbon separating from the martensitic ferrite will diffuse into AR, resulting that the martensitic brittleness decreases and the stability of AR increases.

Life History Research in Education

Life history research,as one of the most powerful research methods in sociology,brings some re-freshened air into interpretive research.In this paper,the development of life history research,from modernism to postmodernism,from life story to life history,is firstly illustrated.Then the process of conducting life history research is analyzed specifically,which is followed by its unique strengths.Finally,its issues,its general issues and its special issues in Chinese context,are critically examined.

Development of a Nickel-base Cast Superalloy with High Strength and Superior Creep Properties

Derived from Russian alloy CHS88U, six experimental Ni-base alloys named as A to F in the Ni-Cr-Co-W-Ti-Al-Hf system are designed, evaluated and processed. One of these alloys, F, shows excellent high temperature tensile strength and ductility with superior creep rupture properties. As predicted by using modeling tools such as PHACOM and NEW PHACOMP, there is hardly the tendency for formation of topologically close-packed phase (TCP) phase in alloy F. Furthermore, through microstructural observation, it is also found that no TCP phase is formed in alloy F after long-time exposure at high temperature. So alloy F has well balance of phase stability and mechanical properties in view of application for gas turbines. It is proved that d-electron approach can be applied for design and development of nickel-base superalloys for gas turbine application.

Analysis of the effect of geometrical parameters on fatigue performance of spot-weld joint for ultra-high strength steel

This paper studied the spot welding structure of ultra-high strength steel 22MnB5.ANSYS software was adopted to simulate its static strength;BS5400 algorithm was used to calculate the fatigue life;and the grouping method was used to test the fatigue performance of tensile shear spot weld specimens.The simulation results were in good agreement with the experimental values.Based on the validation of the simulation method,influences of different structural parameters on static strength and fatigue life were explored by adopting single factor.The results showed that within the selected structure parameter range,increase of the sheet thickness,nugget diameter,sheet width and overlapping length can lead to longer fatigue life.Besides,the fatigue life of spot weld took on a linear relationship with the overlapping length,a DoseResp relationship with the sheet thickness,and a single exponential decay relationship with the sheet width and the nugget diameter.Moreover,in order to estimate the impact from various parameters on the fatigue life of the specimens,the Taguchi orthogonal design method was applied in the simulation design.The simulating result indicated that influence of the sheet thickness on fatigue life was the most significant.In addition,the effects of nugget diameter,sheet width and overlapping length on fatigue life were reduced in turn.

社区高龄老人握力和生活质量的关系研究

目的 本研究基于社会隔离和抑郁2个中介变量,构建多重中介模型,探讨高龄老人的握力对其生活质量的影响机制。方法 于2020年10月-2021年4月,利用方便整群抽样法对上海市400名≥80岁社区高龄老人,采用Lubben社会网络量表(LSNS-6)、老年抑郁量表简表(GDS-5)、世界卫生组织生活质量评定量表老年模块(WHOQOL-OLD)和握力计对高龄老人的社会隔离、抑郁、生活质量及握力进行测量。采用SPSS PROCESS程序检验链式中介效应。结果 相关性分析结果显示:握力、社会隔离、抑郁和生活质量间显著相关(P<0.01)。中介效应,分析结果显示:握力可直接影响高龄老人的生活质量[效应值=0.394;95%CI=(0.219,0.532)],还可以通过3条中介效应链对生活质量造成影响:社会隔离[效应值=0.219;95%CI=(0.125,0.328)],抑郁[效应值=0.054;95%CI=(0.029,0.087)],及社会隔离、抑郁的链式作用[效应值=0.054;95%CI=(0.029,0.087)];总中介效应占总效应的51.2%。结论 握力降低是高龄老人生活质量下降的重要风险因素,且社会隔离和抑郁是这一影响的重要解释机制。社区卫生工作者应重视握力对高龄老人生活质量的影响,并基于社会隔离和抑郁的作用路径制定干预策略,以改善高龄老人的生活质量、促进健康老龄化。

An Improved Iterated Greedy Algorithm for Solving Rescue Robot Path Planning Problem with Limited Survival Time

Effective path planning is crucial for mobile robots to quickly reach rescue destination and complete rescue tasks in a post-disaster scenario.In this study,we investigated the post-disaster rescue path planning problem and modeled this problem as a variant of the travel salesman problem(TSP)with life-strength constraints.To address this problem,we proposed an improved iterated greedy(IIG)algorithm.First,a push-forward insertion heuristic(PFIH)strategy was employed to generate a high-quality initial solution.Second,a greedy-based insertion strategy was designed and used in the destruction-construction stage to increase the algorithm’s exploration ability.Furthermore,three problem-specific swap operators were developed to improve the algorithm’s exploitation ability.Additionally,an improved simulated annealing(SA)strategy was used as an acceptance criterion to effectively prevent the algorithm from falling into local optima.To verify the effectiveness of the proposed algorithm,the Solomon dataset was extended to generate 27 instances for simulation.Finally,the proposed IIG was compared with five state-of-the-art algorithms.The parameter analysiswas conducted using the design of experiments(DOE)Taguchi method,and the effectiveness analysis of each component has been verified one by one.Simulation results indicate that IIGoutperforms the compared algorithms in terms of the number of rescue survivors and convergence speed,proving the effectiveness of the proposed algorithm.

基于静强度分布参数的复合材料剩余强度及寿命预测

为探讨剩余强度及疲劳寿命与初始静强度分布参数之间的关系,构建基于初始静强度分布参数的剩余强度和疲劳寿命计算模型。在模型构建过程中未涉及复合材料结构的层数、铺层厚度和铺层方向,适应性强。模型参数可通过静力试验和剩余强度试验获得,试验成本相对疲劳试验较低。剩余强度和疲劳寿命与初始静强度变异系数及其分布参数有关,当初始静强度服从威布尔分布时,疲劳寿命亦服从威布尔分布,可为开展疲劳可靠性提供借鉴和参考。算例表明,基于建立的模型,剩余强度计算结果最大误差为-1.58%,疲劳寿命与试验数据吻合较好。

运动疗法在膝关节骨性关节炎中的应用效果

目的 观察膝骨性关节炎治疗中运动疗法的临床疗效。方法 选取2022年2月至2023年10月本院门诊30例膝关节骨性关节炎患者,分为运动疗法组和对照组,各15例。运动疗法组在常规保守治疗基础上加入肌力训练及关节活动度训练等运动疗法,对照组行常规保守治疗。每周治疗1~2次。连续6周为一个疗程。治疗前后统计分析两组膝关节功能、功能障碍程度、疼痛程度、生活质量、血清NO水平、肌力、临床疗效。结果 运动疗法组患者的疼痛、屈膝畸形、活动度、稳定性、肌力、功能评分均高于对照组(P <0.05),疼痛、僵硬程度、日常生活难度评分均低于对照组(P <0.05),VAS评分低于对照组(P <0.05),SF-36评分高于对照组(P <0.05),血清NO水平低于对照组(P <0.05)。运动疗法组患者的肌力Ⅰ级、Ⅱ级、Ⅲ级比例均低于对照组,Ⅳ级、Ⅴ级比例均高于对照组(P <0.05)。运动疗法组总有效率93.33%(14/15)高于对照组66.67%(10/15)(P <0.05)。结论 膝骨性关节炎治疗中运动疗法能改善关节周围肌肉力量,提高关节稳定性及运动表现,缓解关节疼痛,提高生活质量。

30CrMnSiNi2A合金钢含损伤结构剩余疲劳寿命分散性及其影响因素试验研究

为挖掘含损伤结构满足高可靠度要求下的剩余疲劳寿命潜力,开展合金钢材料30CrMnSiNi2A含损伤结构剩余疲劳寿命测试试验,对剩余疲劳寿命分散性及其影响因素进行分析。通过含预裂损伤与预置线切割损伤试验件在等幅谱载荷作用下的疲劳对比预试验分析结果,简化正式试验流程。开展不同热处理工艺、不同载荷水平下含损伤结构剩余疲劳寿命定性分析试验。分析试验数据得出:通过热处理工艺提高合金钢材料强度极限,降低载荷水平,可有效提升含损伤结构剩余疲劳寿命;不同处理工艺及不同载荷水平条件下,随损伤尺寸的增加,剩余疲劳寿命分散系数差异增大;在较大损伤尺寸下,热处理后的含损伤结构试验件在低载荷水平下的剩余疲劳寿命分散性较低。降低热处理强化后的30CrMnSiNi2A合金钢含损伤结构载荷水平可有效提高满足可靠度要求的剩余疲劳安全寿命。

倾覆力耦合的大兆瓦风机主轴-齿轮箱法兰结构疲劳寿命研究

大兆瓦风机主轴-齿轮箱法兰连接受倾覆力及其他交变载荷的作用,极易产生疲劳破坏。文中建立了考虑倾覆力耦合作用的法兰连接有限元数值模型,分析了特定工况下法兰连接各部件应力场分布规律;通过GH-Bladed获得主轴实际转矩变化数据,根据雨流计数法计算得到了主轴和螺栓多种工况下载荷-时间历程曲线,基于Brown-Miller准则并结合材料的S-N曲线,使用FE-SAFE给出了不同预紧力条件下主轴和螺栓的疲劳寿命,疲劳分析结果表明:随着预紧力的减小,主轴的疲劳寿命大于螺栓的,螺栓在风机运行过程中更容易发生疲劳破坏。基于VDI2230规范,结合法兰界面涂层增摩工艺,得到了法兰界面摩擦因数、螺栓预紧力与法兰结构疲劳寿命的理论模型。该研究对于大兆瓦风机主轴-齿轮箱法兰连接结构设计和疲劳寿命提升具有一定的指导意义。