On the determination of the Young’s modulus of thin films using indentation tests

The main difficulty with the characterization of thin coatings using depth-sensing indentation tests is related to the determination of the contributions of the substrate and the film to the measured properties. In this study, three-dimensional numerical simulations of the Vickers hardness test are used in order to examine the influence of the elastic and plastic properties of the substrate and the film on the composite’s Young’s modulus results. The hardness of the film is equal to or higher than the substrate hardness. A study of the stress distributions and the indentation geometry of composites, film/substrate, was performed, taking into account the relative mechanical properties of the film and substrate. In addition, stress evolution during indentation was studied, in order to quantify the critical indentation depth under which the substrate is not elastically deformed. The accurate evaluation of the Young’s modulus of the films using weight functions is also examined: some of these have previously been proposed and one was introduced for this study. Two different fitting procedures were used to compare the results obtained from eight fictive film/substrate combinations using six weight functions. The first procedure, commonly used, considers the substrate’s modulus as a known parameter in the fitting process. In the second, the film and the substrate’s modulus are considered as unknown variables that are calculated simultaneously during the fitting process. The validity of the conclusions obtained using the fictive materials was checked by applying the weight functions to four real composites.     

搅拌摩擦焊接残余应力及残余变形数值分析

建立了搅拌摩擦焊接顺序热力耦合有限元模型,用移动热源模拟搅拌头的作用,对搅拌摩擦焊接进行数值模拟.瞬态温度场及残余应力场与试验结果吻合良好,从而验证了该模型的正确性.本文研究了焊接过程中应力变化过程,指出应力场的不均匀分布引起板的弯曲变形.建立了不同尺寸有限元模型,研究板的尺寸对残余变形的影响.板的宽度对纵向残余变形曲率影响较大,长度对变形曲率影响较小.当焊接长度足够长,模型宽度相同时,不同模型远离端部区域纵向弯曲曲率相同.板的横向残余变形主要由焊缝区域变形引起,远离焊缝区域几乎没有弯曲变形发生,且板的尺寸对变形曲率影响很小.     

爆速对爆炸焊接铝/不锈钢复合管界面及结合性能的影响

通过在粉状乳化炸药中添加不同比例的密度调节剂,配制了爆速范围为1 450~2 550 m/s的低爆速炸药;采用该爆速炸药进行了铝/不锈钢复合管爆炸焊接实验,结合最小碰撞速度理论,对实验结果及其界面微观结构和结合强度进行了测试和分析,确定该复合管爆炸焊接的合适爆速约为1 950~2 150 m/s,其结合质量能够满足后续加工要求;同时发现界面由介于直线与波形之间的波状形态组成,且呈现不太规则的扁平波状结合,经分析,炸药爆速、复合管的爆炸焊接环境和爆炸产物飞散条件对界面结合波形及熔化层厚度有很大影响。     

Numerical simulation of welding induced damage and residual stress of martensitic steel 15-5PH

This paper is about the modeling of damage and residual stresses induced by a complex history of thermo-elasto-plastic multiphase in welding heat affected zone (HAZ). A two-scale model for elasto-plastic damaged multiphase is developed. The constitutive equations of the model are coupling ductile damage, elasto-plastic strains, phase transformation and transformation plasticity. In this study, an equation of damage evolution is proposed based on the continuum damage mechanics. In order to validate the proposed damage evolution, a set of flat notched bars with various notches are to simulated and then compared to experimental results. An example of laser heated disk is simulated to elaborate the two-scale model and the simulated results of the two-scale model in CAST3M^® is compared the results calculated by a homogenized macroscopic model in SYSWELD^®. The study shows the two-scale model provides valuable freedom to choose the material or mechanical law for each phase. The proposed damage equation extends the application of existing ductile damage models. In the calculation of residual stresses, damage decreases the residual stresses in HAZ by a small amount.     

爆炸焊接复合界面波与温度场物质点法分析

爆炸焊接是一门双金属复合工程技术,在炸药爆轰载荷驱动下,飞板高速冲击基板时,两金属板复合界面处在高温高压作用下材料发生塑性流动并形成周期性波状界面,波状界面的形成与复合界面处的材料熔化和变形直接相关。本文应用物质点法对爆炸焊接界面波的形成和界面温度场进行数值模拟,同时开展双金属爆炸焊接实验,并结合物质点法的三维数值模拟对爆炸焊接界面波的形态和界面材料高温软化进行分析。     

Al2O3陶瓷引弧微爆炸加工温度场模拟

建立了Al2O3陶瓷引弧微爆炸加工(micro-detonationofstrikingarcmachining,MDSAM)过程的传热模型,基于有限元理论,利用ANSYS软件对加工过程中的温度场分布进行了模拟。结合材料性质,对模拟和实验得到的蚀坑尺寸进行了比较,并分析了加工参数对温度场的影响。模拟结果表明,Al2O3陶瓷引弧微爆炸加工时在给定的加工参数下的最高温度可达13435℃,且高温影响区范围很小,加工实验与模拟结果符合较好。随着脉冲宽度和工作电流的增加,加工区域的温度以及蚀坑的半径和深度增大;随着喷嘴半径的增大,加工区域的温度降低而蚀坑的径深比增大。模拟结果可为Al2O3 陶瓷引弧微爆炸加工过程中表面形貌的预测、材料去除机理的揭示以及加工参数的选择等提供参考。     

Dissimilar ultrasonic spot welding of Mg-Al and Mg-high strength low alloy steel

Sound dissimilar lap joints were achieved via ultrasonic spot welding (USW), which is a solid-state joining technique. The addition of Sn interlayer during USW effectively blocked the formation of brittle al₁₂Mg₁₇ intermetallic compound in the Mg-Al dissimilar joints without interlayer, and led to the presence of a distinctive composite-like Sn and Mg₂Sn eutectic structure in both Mg-Al and Mg-high strength low alloy (HSLA) steel joints. The lap shear strength of both types of dissimilar joints with a Sn interlayer was significantly higher than that of the corresponding dissimilar joints without interlayer. Failure during the tensile lap shear tests occurred mainly in the mode of cohesive failure in the Mg-Al dissimilar joints and in the mode of partial cohesive failure and partial nugget pull-out in the Mg-HSLA steel dissimilar joints.     

有序态Fe3Al合金在水环境中的磨粒磨损行为

研究了不同载荷下含Ｃｒ的Ｂ２和ＤＯ３有序态Ｆｅ３Ａｌ合金在水中的磨粒磨损行为。采用扫描电镜分析了合金的磨损表面形貌和磨屑形貌。二次离子质谱分析结果表明：在水环境磨损条件下，随着载荷的增加，进入Ｆｅ３Ａｌ合金表层的氢浓度升高，合金表层的氢损伤加剧。在高载荷下由机械磨损所引起的材料流失仍占主导地位，相同载荷下Ｂ２有序态Ｆｅ３Ａｌ合金的磨损质量损失比ＤＯ３有序态Ｆｅ３Ａｌ合金低。     

Finite Element Analysis of Shape Memory Alloy Adaptive Trusses with Geometrical Nonlinearities

This contribution deals with the nonlinear analysis of shape memory alloy (SMA) adaptive trusses employing the finite element method. Geometrical nonlinearities are incorporated into the formulation together with a constitutive model that describes different thermomechanical behaviors of SMA. It has four macroscopic phases (three variants of martensite and an austenitic phase), and considers different material properties for austenitic and martensitic phases together with thermal expansion. An iterative numerical procedure based on the operator split technique is proposed in order to deal with the nonlinearities in the constitutive formulation. This procedure is introduced into ABAQUS as a user material routine. Numerical simulations are carried out illustrating the ability of the developed model to capture the general behavior of shape memory bars. After that, it is analyzed the behavior of some adaptive trusses built with SMA actuators subjected to different thermomechanical loadings.     

输电塔线体系断线动力响应及杆塔破坏模拟研究

利用ABAQUS软件建立500kV典型输电线路段塔线耦合体系的精细有限元模型,数值模拟覆冰塔线耦合体系断线后的动态响应和杆塔破坏过程。对杆塔引入等效塑性应变破坏准则,当单元的最大等效塑性应变达到许用值时,删除单元以模拟杆塔的破坏。数值模拟结果与按我国电力设计规程以及IEC设计规程的计算结果比较表明:地线断线时用塔线模型和规程计算得到的杆塔应力的差别较导线断线时大,地线和导线断线时杆塔的最大应力均大于两种规程的计算值;杆塔上与地线连接的角担是断线时的薄弱区域。现行电力设计规程中采用静力分析方法对断线产生的冲击动力作用的估计不足。     

不同坡口形状铍环激光钎焊温度场和应力场分析

本文对不同坡口形状镀环焊接过程进行了数值模拟,分析了坡口形状和焊接速度对铍环钎焊温度场和应力场的影响,结果表明:开坡口后铍环焊接的熔深和熔宽增大,而热影响区的焊接残余应力相对降低,特别是对于降低铍和AlSi12熔合面处的应力集中具有明显的效果;同时,坡口角度的增加主要对铍环热影响区的应力分布也有一定的影响.因此,铍环接头处开坡口不仅能够降低焊缝区的残余应力,还能减少铍材熔化引起的开裂.     

Transient temperature fields and residual stress fields of metallic materials under welding

Based on the situation of welding thermal conduction and thermo-elasto-plasticityresearch,Ms paper explores some problems in this field.First,the boundary elementmethod for nonlinear problems is improved by linearization of nonlinear problems and usedin welding thermal conduction analysis.Second,the thermo-elasto-plastic finite elementmethod is used for the welding stress calculation,in which the phase transformation isconsidered by the"equivalent linear expansion coefficient method".The comparison of the calculated results with experimental data shows that themethods provided in this paper are available.     

Ward identities and the retrieval of Green’s functions in the correlations of a diffuse field

That diffuse field correlations are essentially identical to Green’s functions is becoming widely accepted. Here, a new derivation is provided for that identity, a derivation that generalizes to a larger variety of wave systems and furthermore permits derivation of other, related but distinct, identities that may be useful.     

Pressure and temperature history in diamond silicon mixtures during dynamic compaction

Diamond powders with silicon additives were shock compressed by using a flyer impact technique. Pressure and temperature histories in the powder mixtures were numerically simulated in order to determine the optimum experimental condition which resulted in the highest Vicker's hardness. This was found to be: an initial diamond particle size of 2–4m at 7.2 % silicon by volume. The results of the simulations were consistent with the distribution of the microstructure and the microhardness in the compact.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1990.     

Numerical simulation and control of welding distortion for double floor structure of high speed train

The welding heat source models and the plastic tension zone sizes of a typical weld joint involved in the double floor structure of high speed train under different welding parameters were calculated by a thermal-elastic-plastic FEM analysis based on SYSWELD code.Then,the welding distortion of floor structure was predicted using a linear elastic FEM and shrinkage method based on Weld Planner software.The effects of welding sequence,clamping configuration and reverse deformation on welding distortion of floor structure were examined numerically.The results indicate that the established elastic FEM model for floor structure is reliable for predicting the distribution of welding distortion in view of the good agreement between the calculated results and the measured distortion for real double floor structure.Compared with the welding sequence,the clamping configuration and the reverse deformation have a significant influence on the welding distortion of floor structure.In the case of30 mm reverse deformation,the maximum deformation can be reduced about 70%in comparison to an actual welding process.     

Analysis of transient temperature field in coke drums

One of the primary reasons leading to bulging and cracking in a coke drum is the severe temperature gradient due to cyclic temperature variation. Based on the twodimensional heat conduction theory, an analytical solution of the transient temperature field in the coke drum is obtained, which is different from the known FEM results. The length of the coke drum is considered finite. The dynamic boundary conditions caused by fluid uninterrupted rising in oiling and watering stages are simulated with the iteration method. Numerical results show that the present theoretical model can accurately describe basic features of the transient temperature field in the coke drum. Effects of the geometry of the coke drum and the rising velocity of quench water on the axial temperature gradient are also discussed.     

在氮气介质中WC-Co/Ti6Al4V摩擦副的摩擦磨损性能研究

在THT07-135型高温摩擦磨损试验机上采用销-盘式接触形式,研究了WC-Co硬质合金/Ti6Al4V钛合金摩擦副在氮气介质中的摩擦磨损性能,并与空气介质中的摩擦磨损性能进行对比.结果表明:与空气介质相比,在氮气介质中WC-Co/Ti6Al4V摩擦副的摩擦系数稍低;WC-Co硬质合金比Ti6Al4V钛合金的磨损量低得多,氮气介质具有一定的减磨作用;钛合金材料的主要磨损机理为摩擦副之间产生较强的犁沟与挤压撕裂,而硬质合金的主要磨损机理为磨粒磨损与粘结剥落.