功能梯度涂层滚压强化的有限元分析

在功能梯度涂层模型的基础上引入了刚性轧辊,建立了功能梯度涂层滚压强化的力学分析模型,并研究功能梯度涂层的非均匀材料参数、滚压速度对其涂层的等效应力和残余应力的影响,通过计算表明,非均匀材料参数对涂层前部和后部的等效应力有明显的影响,而对涂层中部基本没有影响;在整个涂层表面的残余应力是不相等的,最大等效残余应力为400MPa,最小等效残余应力为30MPa,两者相差近10倍,而滚压速度对于涂层的等效应力没有影响。这为滚压强化功能梯度涂层材料的设计提供了理论支持。     

功能梯度涂层滚压强化的有限元分析

在功能梯度涂层模型的基础上引入了刚性轧辊,建立了功能梯度涂层滚压强化的力学分析模型,并研究功能梯度涂层的非均匀材料参数、滚压速度对其涂层的等效应力和残余应力的影响,通过计算表明,非均匀材料参数对涂层前部和后部的等效应力有明显的影响,而对涂层中部基本没有影响;在整个涂层表面的残余应力是不相等的,最大等效残余应力为400MPa,最小等效残余应力为30MPa,两者相差近10倍,而滚压速度对于涂层的等效应力没有影响。这为滚压强化功能梯度涂层材料的设计提供了理论支持。     

梯度涂层结构设计制备及应用研究现状

梯度涂层以其优异的物理及力学性能表现出巨大的工程应用前景,在航空、航天及原子能等领域有着广泛的应用。对梯度涂层结构设计、制备方法、工艺及梯度涂层组元材料匹配的国内外研究现状进行综述,分析梯度涂层在机械零件表面应用过程中存在的问题。为将梯度涂层应用到机械零件表面改性处理上,提出需要建立和完善适合机械零件表面的梯度涂层结构设计模型,并开展梯度涂层组元材料匹配性能的研究。     

生物活性梯度涂层热应力场的模拟分析

使用有限元分析软件ANSYS建立涂层模型并模拟喷涂后涂层的残余应力场,可以有效设计出合理的涂层梯度分布,从而制备出残余应力较小的涂层.讨论了随着涂层梯度层数的变化,涂层中应力的变化情况.通过模拟得出以下结论:梯度涂层厚度增大,涂层应力明显增大;喷涂温度升高,涂层应力略有增加.     

生物活性梯度涂层热应力场的模拟分析

使用有限元分析软件ANSYS建立涂层模型并模拟喷涂后涂层的残余应力场,可以有效设计出合理的涂层梯度分布,从而制备出残余应力较小的涂层。讨论了随着涂层梯度层数的变化,涂层中应力的变化情况。通过模拟得出以下结论:梯度涂层厚度增大,涂层应力明显增大;喷涂温度升高,涂层应力略有增加。     

功能梯度涂层热残余应力

涂层中的残余应力严重影响着涂层零件的机械完整性与操作可靠性。对于功能梯度涂层,由于各界面位移协调条件的限制,很难得到涂层内部残余应力的闭合解。基于传统的悬臂梁理论,获得了功能梯度涂层热残余应力的闭合解;这一分析模型的优点是残余应力的闭合解与涂层层数无关。讨论了采用传统的近似解所带来的误差, 针对含不同层数的ZrO2/NiCoCrAlY功能梯度涂层内部的残余应力进行了计算。另外,对应力诱导的涂层失效模型也进行了分析。     

热障涂层成分结构工艺的改进

针对现代航空发动机用热障涂层的最新发展，进行了全面的综述分析。系统阐述了涂层成分中加入HfO2，CeO2，La2ZO2等比单纯YO2填充的ZrO2的性能有突出的改变，讨论了多层涂层及梯度涂层结构的内罚函数及黄金分割优化设计的特性。提出获得均匀致密，功能性强的各种喷涂设备的适应性，探索了涂层的微结构形成机理。并指出了热障涂层今后的发展方向。     

金属基/陶瓷复合双涂层的正接触应力分析

以球形压头为模型，采用I—deasCAD／CAE软件对Hertz弹性接触状态下金属基／陶瓷双涂层系统的应力分布情况进行了理论建模，并基于模型计算了在不同的涂层厚度／接触半宽度比和外涂层／过渡层／基体弹性模量比情况下的应力分布情况。双层系统具有相同的厚度和不同的弹性模量。论述了无涂层弹性半空间体的有限元分析结果与经典的Hertz接触力学解析解结果的一致性，计算结果有助于工程中陶瓷涂层的设计与应用。     

等离子喷涂Fe3Al-Al2O3陶瓷梯度涂层

用等离子喷涂方法制备了FeAl-Al2O3陶瓷梯度涂层，并对涂层的结合硬度、显微硬度及抗热震性进行了试验研究。结果表明，梯度涂层设计为成分的阶梯过滤，实现了成分和组织的连续梯度变化，没有明显的组织突变和宏观界面，梯度涂层的组织表现出宏观不均匀性和微观连续性的分布特征。其结合强度较高，涂层的显微硬度值在含75％Al2O3的区域达到最高值。基体与涂层的界面是基体-涂层体系中的薄弱环节。FeAl-Al2O3梯度涂层的800℃抗热震性优于Al2O3涂层。     

含MoSi2热障梯度涂层的抗热震性能研究

对添加MoSi2和未加MoSi2的ZrO2-A1／Ni梯度热障涂层的抗热震性能的比较，并结合微观组织和能谱对此进行了分析。结果表明，，MoSi2在热震过程中发生了反应，添加MoSi2可提高涂层的抗热震性能。     

Mean stress effects in fretting fatigue life estimation method using fatigue damage gradient correction factor

In our previous study, we developed a fretting fatigue life estimation method that considers stress gradient effect [Journal of Mechanical Science and Technology 28 (2014) 2153–2159]. In this method, fatigue damage value at the cracking location is corrected with the factor that is a function of fatigue damage gradient, and the corrected value is treated as the fatigue damage value in plain fatigue for life estimation. In the present study, we examined the effect of mean stress on fatigue damage gradient correction function, because the reliability of the developed method was only verified at a stress ratio (R) of ?1 in previous studies. Fretting fatigue experiments were conducted to obtain the fatigue life data of three different fretting pad shapes with R values ranging from ?1.0 to 0.3. Finite element analyses were then conducted to evaluate the fatigue damage parameter in the cracking region. The results revealed that fretting fatigue life decreases at increased stress ratio. Furthermore, the fatigue damage gradient correction function was unaffected by the stress ratio, although it is affected by plastic deformation at the cracking location. Thus, a correction function for the occurrence of plastic deformation and another for the absence of plastic deformation are necessary. The developed method was demonstrated to predict the fretting fatigue life at various levels of stress ratio with the use of plain fatigue data.     

对称型梯度功能陶瓷材料的非定常热应力

采用摄动法推导出对称型梯度功能材料平板的一维非定常温度场及非定常热应力场的解析表达式，对Ａｌ２Ｏ３／（Ｗ，Ｔｉ）Ｃ系对称型梯度功能陶瓷平板表面冷却及加热过程中的非定常温度场及非定常热应力场进行了计算。讨论了提高陶瓷刀具材料抗热震性的方法即采用梯度功能陶瓷刀具材料，并结合断续车削试验进行了验证。     

大型升船机船厢门有限元优化设计

构建了某大型升船机弧形船厢门Ansys有限元模型,定义了16个参数化设计变量。采用最优梯度法,分析了各参数化设计变量对结构质量、最大VonMises应力、最大综合位移及结构第1阶固有频率的灵敏度,筛选了设计变量,评估了状态变量的变化趋势。以船厢门质量为优化目标,以船厢门结构应力、位移及结构第1阶固有频率为状态变量,采用子问题近似法进行有限元优化计算,得到了1组圆整的结构设计参数,满足结构刚度和强度要求,总质量降低22.19%,第1阶固有频率提高4.4%。     

梯度功能陶瓷刀具切削淬硬钢的研究

在国内首先研制成功梯度功能陶瓷刀具材料FG-1，并研究了该刀具车削淬硬工具钢T10A的切削性能及耐磨性。结果表明，FG－1具备优异的物理力学性能：在低速切削条件下，FG－1与普通陶瓷刀具LT55及SG－4的耐磨性相差不大；而随着切削速度的提高，FG-1的性能明显优于LT55和SG－4刀具。其原因是刀具材料成分的梯度组成发挥了缓解热应力的作用。     

Assessment of two-parameter mixed models for large eddy simulations of transitional and turbulent flows

In the present study, improved two-parameter mixed models for large eddy simulations are proposed based on previous two-parameter mixed models of Salvetti and Banerjee [1] and Horiuti [2]. The subgrid-scale (SGS) stress in our models is decomposed into the modified Leonard stress, modified cross stress and modified SGS Reynolds stress terms. Although the modified Leonard stress term is explicitly calculated based on the scale-similarity, the modified cross stress term is built using an extension of the filtered Bardina model proposed by Horiuti [3] for better predictions of the interaction between resolved and unresolved scales (i.e., energy exchange). The modified SGS Reynolds stress is modeled by the dynamic Smagorinsky model or by a dynamic global model, leading to two unknown model coefficients for the modified cross stress and the modified SGS Reynolds stress terms. In order to demonstrate the reliability of the proposed SGS models, large eddy simulations of two types of flows (i.e., a fully developed turbulent channel flow and a transitional boundary layer flow) are performed. It is shown that the modified cross stress term makes an important contribution to the accurate predictions of such flows because the emergence of negative SGS dissipation (backward scatter) by the modified cross stress term decreases the excessive positive SGS dissipation (forward scatter). A direct comparison of the turbulent statistics with those from previous SGS models shows that the proposed SGS models result in better prediction performance both in transitional and turbulent flows.

     

Nondestructive testing and characterization of residual stress field using an ultrasonic method

To address the difficulty in testing and calibrating the stress gradient in the depth direction of mechanical components, a new technology of nondestructive testing and characterization of the residual stress gradient field by ultrasonic method is proposed based on acoustoelasticity theory. By carrying out theoretical analysis, the sensitivity coefficients of different types of ultrasonic are obtained by taking the low carbon steel(12%C) as a research object. By fixing the interval distance between sending and receiving transducers, the mathematical expressions of the change of stress and the variation of time are established. To design one sending-one receiving and oblique incidence ultrasonic detection probes, according to Snell law, the critically refracted longitudinal wave (LCR wave) is excited at a certain depth of the fixed distance of the tested components. Then, the relationship between the depth of LCR wave detection and the center frequency of the probe in Q235 steel is obtained through experimental study. To detect the stress gradient in the depth direction, a stress gradient LCR wave detection model is established, through which the stress gradient formula is derived by the relationship between center frequency and detecting depth. A C-shaped stress specimen of Q235 steel is designedto conduct stress loading tests, and the stress is measured with the five group probes at different center frequencies. The accuracy of ultrasonic testing is verified by X-ray stress analyzer. The stress value of each specific depth is calculated using the stress gradient formula. Accordingly, the ultrasonic characterization of residual stress field is realized. Characterization results show that the stress gradient distribution is consistent with the simulation in ANSYS. The new technology can be widely applied in the detection of the residual stress gradient field caused by mechanical processing, such as welding and shot peening.     

轴对称塑性变形区内一点流动方向的探索

为研究塑性变形体中金属流动方向与局部应力场之间的关系,首先给出塑性变形中局部应力场的平均应力梯度的近似求解算法,并计算圆柱体镦粗、圆环镦粗和正挤压塑性区等典型轴对称应力场中各点的平均应力梯度方向。将应力场中各点的平均应力梯度方向和速度方向同时可视化,并对比统计二者的相似程度,结果显示在轴对称应力场中质点的流动方向与平均应力梯度方向大致保持一致。将变形区中各点的运动分解为刚体运动和相对运动(流动)两个分量,认为刚体运动主要由工具运动决定;在不考虑刚体运动的情况下,轴对称塑性变形区中的质点流动方向与附近区域的局部应力场在该点的平均应力梯度方向大致保持一致。     

Creep damage evaluation of thick-walled spheres using a long-term creep constitutive model

This paper describes a numerical model developed for the computation of creep damages in a thick-walled sphere subjected to an internal pressure and a thermal gradient. The model predicts the creep damage histories during the life of the sphere, owing to variations in stresses with time and through-thickness variations. The creep damage fraction is based on the Robinson’s linear life fraction damage rule, which has been incorporated in a nonlinear time-dependent stress analysis. Following the stress histories, the effective stress histories are obtained and the creep damages are calculated and summed during the life of the sphere. The material long-term creep properties up to the rupture and creep rupture data are defined by the Θ projection concept [1]. The damage histories up to 38 years are calculated and the results show that the maximum damages are always located at the inner surface of the sphere, while the outer surface of the vessel sustains minimum damages.     

磁记忆二维检测的研究与工程应用

磁记忆检测作为早期诊断的新兴技术已受到国内外无损检测界广泛关注,但现有的磁记忆检测技术主要以单一方向上的漏磁场信号(法向分量)来进行判断,没有充分利用磁记忆检测信号的全部信息,容易出现漏检、误检等问题。针对该项检测技术的不足,介绍一种将磁记忆检测信号法向分量存在过零点和切向分量存在极大值的特征曲线联合应用的二维检测方法。该方法同时采集法向和切向的磁记忆信号,利用矢量合成法获取切向最大值,然后求取法向、切向分量一阶微分后合成的李萨如图,利用李萨如图的面积对应力状态进行分析,并将自主研制的磁记忆二维仪器应用到工程实践中。实践证明,该二维系统及检测方法能高效地对应力集中进行判定,可望成为实现磁记忆检测定量分析的新方法。     

纺杯轴承系统动力优化设计

对试件的测试表明,优化的纺杯轴承系统的功耗、轴承座振动和轴承所受动载荷等均得到有效降低。这对延长高速件工作寿命、提高工作转速和节能等均有明显的实际意义。