钨合金细观参数对其宏观屈服强度的影响

通过细观分析,给出钨颗粒相的形状、组分和两相力学参数对钨合金宏观屈服强度的影响.其中,钨颗粒看作基体上的夹杂,在小变形条件下假设钨颗粒仅发生弹性变形,而钨合金的宏观屈服强度决定于基体相的屈服强度.在该假设基础上,利用Eshelby方法及Mori-Tanake平均应力概念计算分析了不同钨合金材料,特别是不同变形量工艺处理的钨合金材料的宏观屈服强度,计算结果与实验结果基本一致.     

高比重钨合金力学性能影响因素分析

首先考虑液相烧结工艺条件及组分对高比重钨合金微结构和各相性质的影响，再从细观力学的角度考虑高体积百分比钨合金微结构及各相性质对复合材料有效力学性质的影响，从而架起工艺条件及组分与钨合金力学性能之间关系的桥梁，为分析高比重钨合金性能从理论上建立一套方法，从材料设计和制备的角度实现对这种材料性能优化提供一种方案。并应用上述模型和方法对用粉末冶金法制备的两种不同钨含量的钨合金材料微结构和力学性能进行分析。     

电镀钨合金镀层组织及其耐腐蚀性能研究

主要分析了电镀钨合金镀层质量及其耐H2S-CO2腐蚀性能。通过SEM、EDX和XRD分析发现镀层与基体结合强度较高,但镀层淬火处理时出现龟裂现象,裂纹均匀排布于镀层表面。腐蚀评价表明腐蚀作用只发生在镀层淬火所形成的裂缝部位,造成裂缝内部充满大量腐蚀产物,非裂纹表面未见腐蚀。指出镀钨合金若用于酸性环境,尚需优化配方、降低硬度、增加韧性,此外还应检测基材屈服强度85%拉应力下的镀层应力腐蚀开裂行为。     

电沉积铁镍钨合金性能研究

钨合金沉积机理至今未得到合理的解释.采用循环伏安法研究了柠檬酸铵盐体系中电沉积铁镍钨合金的规律,分析了主盐浓度、pH值、电流密度、温度对铁镍钨合金镀层组分及阴极电流效率的影响.结果表明,在pH值恒定为8的条件下,镀层中钨和铁的含量受各因素影响的趋势是一致的,随溶液中铁盐、钨盐、柠檬酸盐的含量、电流密度及温度的增加而增加;镀层组分受pH值的影响较大,镀层中钨含量值在pH值为6时最大.根据X射线衍射结果可知,铁镍钨镀层随着钨含量的增加,由纳米结构转变为非晶态结构.     

钨合金易断裂面的研究

介绍了易断裂面的几种形成方式,主要研究在冷等静压成型过程中用模具预制缺口法形成的易断裂面对钨合金力学性能的影响,并用有限元ANSYS程序模拟缺口试样拉伸实验,实验结果与模拟结果一致.     

钨合金动态力学性能的三维数值模拟研究

采用数值模拟的方法对钨合金在冲击载荷作用下的动态力学响应进行了研究。运用有限元动力分析程序建立了具有典型微观结构钨合金三维有限元单胞模型,对钨合金在拉伸载荷作用下的动态力学性能进行了数值模拟研究,分析了应变率对其力学性能的影响,给出了不同应变率条件下单胞模型的应力和应变分布云图,在与实验结果对比的基础上验证了该有限元模型的可靠性。     

钎焊参数对钨合金/钢钎焊接头性能的影响

目的研究钎焊温度和保温时间对接头性能的影响。方法在氩气氛围中用AgCu30钎料对钨合金(91WNiFe)与超高强合金钢(DT1900类ASME100)进行钎焊,并对接头进行组织观察和力学性能测试。结果通过改变钎焊温度(780~840℃),发现随着钎焊温度增加,钎焊接头钎缝中的气孔所占体积减少,钎焊接头的剪切强度先增加后减少;通过改变保温时间(0~30 min),发现随着保温时间的增加,钎焊接头钎缝中的气孔所占体积减少,钎焊接头的剪切强度先增大后趋于平缓。结论当钎焊温度为820℃和保温时间为30 min时,钎焊接头的剪切强度达到最大,为107.73 MPa。     

钨、铀合金破片侵彻性能对比数值研究

为研究不同形状钨破片和铀破片的侵彻性能的优劣,在有关试验的基础上通过AUTODYN软件开展了3组Ф7mm钨球侵彻Q235钢板的验证性仿真模拟,模拟结果与实验结果均吻合,由此验证了仿真方法和相关参数的正确性;分别开展了3种不同形状钨、铀合金破片在不同着靶姿态下侵彻10mm厚Q235钢靶的数值仿真.结果表明:在形状和初速均相同的条件下无论以何种姿态着靶,铀破片的侵彻能力都要强于钨破片;无论钨破片还是铀破片,棱角着靶姿态和棱边着靶姿态的立方体破片侵彻能力最佳,圆柱形水平姿态和面着靶姿态的立方形破片侵彻能力最差.     

均质钽2.5钨合金加工工艺研究

采用"锻造+多向轧制"工艺,研究了均质钽2.5钨合金材料在不同方向、不同部位和不同热处理工艺条件下的拉伸性能和显微组织,最终确定了均质钽2.5钨合金的加工工艺。     

液力挤压法制备新型钨合金穿甲弹芯材料技术

采用液力挤压法制备新型钨合金穿甲弹芯材料,较常规钨合金材料变形加工技术相比,其最大优势是仅通过一次变形可使钨合金材料的性能得到大幅度提高.可对现役、在研各口径、各长细比钨合金穿甲弹进行技术改造和移植.为钨合金穿甲弹芯材料的变形加工提供新的有效技术途径.     

Computational method of inverse elastostatics for anisotropic hyperelastic solids

The paper presents a computational method for predicting the initial geometry of a finitely deforming anisotropic elastic body from a given deformed state. The method is imperative for a class of problem in stress analysis, particularly in biomechanical applications. While the basic idea has been established elsewhere Comput. Methods Appl. Mech. Eng. 1996; 136 :47–57; Int. J. Numer. Meth. Engng 1998; 43 : 821–838), the implementation in general anisotropic solids is not a trivial exercise, but comes after a systematic development of Eulerian representations of constitutive equations. In this paper, we discuss the general representation in the context of fibrous hyperelastic solids, and provide explicit stress functions for some commonly used soft tissue models including the Fung model and the Holzapfel model. A three‐field mixed formulation is introduced to enforce quasi‐incompressibility constraints. The practical utility of this method is demonstrated using an example of aneurysm stress analysis. Copyright © 2006 John Wiley & Sons, Ltd.     

Basis mapping methods for forward and inverse problems

This paper describes a novel method for mapping between basis representation of a field variable over a domain in the context of numerical modelling and inverse problems. In the numerical solution of inverse problems, a continuous scalar or vector field over a domain may be represented in different finite‐dimensional basis approximations, such as an unstructured mesh basis for the numerical solution of the forward problem, and a regular grid basis for the representation of the solution of the inverse problem. Mapping between the basis representations is generally lossy, and the objective of the mapping procedure is to minimise the errors incurred. We present in this paper a novel mapping mechanism that is based on a minimisation of the L² or H¹ norm of the difference between the two basis representations. We provide examples of mapping in 2D and 3D problems, between an unstructured mesh basis representative of an FEM approximation, and different types of structured basis including piecewise constant and linear pixel basis, and blob basis as a representation of the inverse basis. A comparison with results from a simple sampling‐based mapping algorithm shows the superior performance of the method proposed here. © 2016 The Authors. International Journal for Numerical Methods in Engineering Published by John Wiley & Sons Ltd.     

A non‐iterative finite element method for inverse heat conduction problems

A non‐iterative, finite element‐based inverse method for estimating surface heat flux histories on thermally conducting bodies is developed. The technique, which accommodates both linear and non‐linear problems, and which sequentially minimizes the least squares error norm between corresponding sets of measured and computed temperatures, takes advantage of the linearity between computed temperatures and the instantaneous surface heat flux distribution. Explicit minimization of the instantaneous error norm thus leads to a linear system, i.e. a matrix normal equation, in the current set of nodal surface fluxes. The technique is first validated against a simple analytical quenching model. Simulated low‐noise measurements, generated using the analytical model, lead to heat transfer coefficient estimates that are within 1% of actual values. Simulated high‐noise measurements lead to h estimates that oscillate about the low‐noise solution. Extensions of the present method, designed to smooth oscillatory solutions, and based on future time steps or regularization, are briefly described. The method's ability to resolve highly transient, early‐time heat transfer is also examined; it is found that time resolution decreases linearly with distance to the nearest subsurface measurement site. Once validated, the technique is used to investigate surface heat transfer during experimental quenching of cylinders. Comparison with an earlier inverse analysis of a similar experiment shows that the present method provides solutions that are fully consistent with the earlier results. Although the technique is illustrated using a simple one‐dimensional example, the method can be readily extended to multidimensional problems. Copyright © 2003 John Wiley & Sons, Ltd.     

注射成形高密度钨合金脱脂工艺的研究

采用石蜡基多组元粘结剂体系,研究了注射成形高密度钨合金喂料的热脱脂工艺参数,包括样品厚度,温度,低温预脱脂和升温速率的。实验表明,当温度小于２５０℃时,脱脂量的对数与厚度的倒数呈比例,在长时间情况下,ＰＷ可以在２５０℃以衣全部脱除。温度,脱脂量和升温速率的撑峭当将导致脱脂缺陷的产生。     

Conjugate gradient method for the Robin inverse problem associated with the Laplace equation

This paper studies a non-linear inverse problem associated with the Laplace equation of identifying the Robin coefficient from boundary measurements. A variational formulation of the problem is suggested, thereby transforming it into an optimization problem. Mathematical properties relevant to its numerical computation are established. The optimization problem is solved using the conjugate gradient method in conjunction with the discrepancy principle, and the algorithm is implemented using the boundary element method. Numerical results are presented for several benchmark problems with both exact and noisy data, and the convergence of the algorithm with respect to mesh refinement and decreasing the amount of noise in the data is investigated. Copyright © 2006 John Wiley & Sons, Ltd.     

Determination of the state parameters of explosive detonation products by computational inverse method

A computational inverse method is presented to determine the state parameters of Jones-Wilkins-Lee (JWL) equation of explosive detonation products based on cylinder test. In this method, the inverse problem of identifying the JWL parameters is formulated through minimizing the errors of the measured radial displacements on the cylinder surface and those computed by the forward solver. An available numerical model simulated by finite element method is built for the sake of obtaining results using the given JWL parameters. Because of the difference of coordinate systems between experiment and numerical model, it is necessary to conduct the transformation between the two coordinate systems. The sensitivity analysis method is adopted to evaluate the influence of the JWL parameters on the responses and find out the parameters those are suitable to be identified. In order to improve the computational efficiency, radial basis function approximate model is constructed to replace the time-consuming numerical model. In the process of constructing approximate model, the truncated singular value decomposition method is used to deal with the ill-condition of the model. At last, the intergeneration projection genetic algorithm is adopted to identify the parameters. The numerical results demonstrate that the proposed inverse method is potentially available to effectively identify the JWL parameters.     

NiTi合金主动脉支架弯曲变形行为的研究

利用Pro/E和Ansys软件建立了胸主动脉支架轴向柔顺性分析模型,对27种NiTi合金支架的柔顺性进行了模拟分析与实验验证。在此基础上,又进一步系统地分析了弯曲变形时支架结构尺寸变化对中央部位横截面变形行为的影响。结果显示,减少圆周方向上的连接体的数量,增加支撑体的长度或数量,都能够提高支架的柔顺性,但是减少连接体的数量比增加支撑体的长度或数量对支架柔顺性的影响程度要大。支架弯曲变形时连接体的数量对支架中央部位横截面的变形具有显著的影响。     

A new stochastic inverse identification of the mechanical properties of human skin

The study of the mechanical properties of human skin is a key point to better understand surgery, skin ageing and pathologies. As the skin is a living tissue, it must be studied in vivo, hence analytical solutions are really difficult to obtain. In this study, a new stochastic inverse method for the identification of its mechanical properties is proposed. The developed optimization method is first presented. It is based on an iterative stochastic approach which ensures the identification of a global extremum. The suction actual case study is then analysed through comparisons between experimental data and finite element models of this test. Only the elastic components of the skin are considered here. The solutions for the recursive least squares and Gauss-Newton's problems are finally compared with the proposed approach to conclude this study and to briefly present our future works.     

Autonomous decentralized finite element method and its applications

In this paper, a new solution procedure using the finite element technique in order to solve problems of structure analysis is proposed. This procedure is called the autonomous decentralized finite element method because it is based on the characteristic autonomy and decentralization in life or biological systems (life‐like approach). The fundamental approach is developed according to an idea of cellular automata manipulation by the new neighbourhood model. The finite element method with an algorithm of the relaxation method is adopted as the solution procedure in this approach. The proposed procedure demonstrates that it is a powerful means of numerical analysis for many kinds of structural problems that are structural morphogenesis, structural optimization and structural inverse problems. Our procedure is applied to numerical analysis of three simple plane models: (1) The structural shape analysis problem for the prescribed displacement mode of a truss structure, (2) An adaptive structure remodelling problem on an elastic continuum, (3) An identification problem of thermal conductivity on a continuum. The effectiveness and validity of our idea are shown from their numerical results. Copyright © 2003 John Wiley & Sons, Ltd.