三维多粗糙峰涂层等效应力分析与表征

利用有限元方法建立了刚性平面与多粗糙峰涂层的弹性接触模型,研究了刚性平面分别与二维涂层粗糙峰、三维涂层粗糙峰的接触状态,揭示了涂层/基体弹性模量比、涂层厚度、粗糙峰问距、刚性平面压下深度对涂层粗糙峰表面、涂层/基体界面等效应力分布及涂层基体变形的影响规律.计算结果表明:压下深度对涂层粗糙峰表面最大等效米塞斯应力的影响最大,涂层厚度和涂层/基体弹性模量比的影响次之,粗糙峰间距的影响最小;增大涂层厚度,减小压下深度、粗糙峰间距和低弹性模量比,会使得最大等效应力值显著降低.     

流-固-热多工况耦合作用下梯度复合涂层应力分布仿真分析*

针对复合涂层的现有仿真方法多基于单一物理场的影响,不能反映多物理场耦合作用等实际工况下的力学性能。以航空发动机附件机匣的典型工况环境为背景,建立描述流-固-热耦合作用下梯度复合涂层各物理参数变化的数学模型,计算涂层不同分布方式下其内部的 von Mises 应力分布。结果表明,过渡层材料组分的渐变方式对涂层热应变和层内 von Mises 应力分布有较大影响,以航空发动机附件机匣中某型花键副为例,在施加实际工况下的载荷和温度条件后,温度场引起的热应力较载荷-润滑引起的应力更大,在润滑、热场和载荷的耦合作用下,三种分布方式的涂层最大应力均位于表层,随梯度的增大逐渐向基体扩散;梯度增大的过渡方式在涂层内可以获得最小的最大 von Mises 应力。在所关注的温度范围内,与梯度减小的过渡方式相比,使用梯度增大的过渡方式可使最大 von Mises 应力减小 14.5%。所建立的仿真方法可模拟近似实际工况, 研究结果可用于指导梯度复合涂层的设计和制备。     

考虑表面形貌的接触应力分析

目的 研究规则和实际表面形貌对二维平面线接触模型的影响.方法 基于线接触几何特性,考虑表面受载后的弹性变形特性,结合规则和实际粗糙表面的形貌特征,并考虑磨合对表面的影响,采用移动平均滤波方法对实际粗糙表面进行光滑处理,利用共轭梯度法,求解表面接触压力和摩擦力,计算二维平面内接触近场应力分布,同时采用修正的离散卷积快速傅里叶变换方法提高计算效率.对比验证二维接触模型的准确性,并对比规则和实际粗糙形貌表面受法向载荷和切向载荷时平面应力分布云图中的应力分布和大小.结果 圆面与圆形微凸体接触时,圆形凸体半径越小,最大Mises应力值越大,半径增大,最大Mises应力减小.多个圆形微凸体及正弦微凸体对应力分布影响类似.当考虑切向力时,会对应力分布云图中的应力分布形状和大小产生巨大影响.在相同平面表面形貌时,摩擦系数越大,Mises应力越大,并且应力沿摩擦力方向发生偏移.结论 数值模型能准确计算出粗糙平面的应力.当圆面与规则表面轮廓平面接触时,与光滑表面接触时相比,Mises应力分布呈现很大不同,微凸体越小,应力越集中;摩擦力会使接触压力和近场Mises应力产生偏移,摩擦系数越大,偏移越明显.当考虑实际粗糙表面时,在粗糙界面尖端接触区域产生应力集中.经过磨合表面采用平均滤波光滑处理后,粗糙界面尖端接触区域应力集中将大幅减小.     

喷砂预处理对HVOF喷涂TiAl-Nb/NiCrAl涂层结合强度的影响

采用不同的喷砂压力对基体表面进行喷砂预处理,研究了基体表面状态的变化对HVOF喷涂TiAl-Nb/NiCrAl涂层结合强度的影响。结果表明：随着喷砂压力的增大,基体粗糙度及表面凹坑的深度和宽度增大,NiCrAl层与基体结合界面处孔洞等缺陷增多,同时基体表面残余砂粒的面积分数增加;涂层结合强度随基体粗糙度的增大,先增大后减小,当基体粗糙度为8.33μm时,结合强度达到最大值44.5 MPa。     

双涂层界面接触应力分析

目的研究在接触应力作用下,双涂层的总厚度及厚度比对其界面应力的影响规律。方法采用有限元方法研究两个界面,即涂层与基底界面和涂层间界面的Mises应力突变量和界面最大剪应力。结果总厚度一定时,涂层厚度比变化对涂层/基底界面应力的影响较小,而对涂层间界面应力的影响明显。对于薄涂层,涂层间界面Mises应力突变量和最大剪应力随着中间层厚度比例的增大而减小;对于厚涂层,涂层间界面Mises应力突变量和最大剪应力随着中间层厚度比例的增大而减小。涂层厚度比一定时,随着涂层总厚度增加,涂层间界面Mises应力突变量和最大剪应力先增大,后减小。结论双涂层的总厚度及厚度比对其界面应力有显著影响。     

双涂层界面接触应力分析

目的研究在接触应力作用下,双涂层的总厚度及厚度比对其界面应力的影响规律。方法采用有限元方法研究两个界面,即涂层与基底界面和涂层间界面的Mises应力突变量和界面最大剪应力。结果总厚度一定时,涂层厚度比变化对涂层/基底界面应力的影响较小,而对涂层间界面应力的影响明显。对于薄涂层,涂层间界面Mises应力突变量和最大剪应力随着中间层厚度比例的增大而减小;对于厚涂层,涂层间界面Mises应力突变量和最大剪应力随着中间层厚度比例的增大而减小。涂层厚度比一定时,随着涂层总厚度增加,涂层间界面Mises应力突变量和最大剪应力先增大,后减小。结论双涂层的总厚度及厚度比对其界面应力有显著影响。     

SiC颗粒对轧辊表面镀层应力影响的有限元分析*

目前针对多颗粒复合镀层有限元模型的建立尚不准确。以轧辊的服役工况为背景,利用Python语言和ABAQUS软件建立试块底面带有SiC颗粒增强Ni基复合镀层的环-块滑动摩擦有限元模型,系统研究SiC颗粒含量和尺寸对涂层表面及涂层-基体界面峰值等效应力的影响规律。结果表明：当SiC颗粒含量为3 vol.%～9 vol.%时,涂层表面和涂层-基体界面峰值应力随颗粒含量的增大而增大,分别增大了78.01%和32.06%;当SiC颗粒含量为9 vol.%～15 vol.%时,随着颗粒含量的增大,涂层表面峰值应力呈下降趋势,降低了13.02%,而涂层-基体界面峰值应力基本保持不变;当SiC颗粒直径为0.8～1μm时,涂层表面及涂层-基体界面峰值应力随颗粒尺寸的减小而增大,分别增大了51.5%和32.6%;当SiC颗粒直径为0.3～0.8μm时,涂层表面及涂层-基体界面峰值应力基本保持不变。综合考虑轧辊表面镀层的性能需求以及实际复合电镀工艺,依据界面应力与镀层结合状态之间的关系,SiC颗粒含量以9 vol.%左右为宜,SiC颗粒直径以0.8μm左右为宜。所建立的多颗粒随机分布涂层基体的有限元模型更接...     

Q235钢基体表面微晶玻璃功能梯度涂层接触应力的数值模拟

接触应力状态是涂层材料表层破坏、整体分层剥落的重要影响因素。运用有限元软件ANSYS对Q235钢基体表面TiN/LZAS微晶玻璃梯度涂层在法向静载下的接触应力进行了分析,建立了该复合涂层的有限元分析模型,通过比较有限元数值解和Hertz理论解,验证了有限元模型的可靠性,探讨了不同层数和层厚对涂层体系接触应力分布的影响。结果表明:涂层的径向接触应力和Mises应力的最大值均位于接触区域中心处,最大剪切应力位于接触中心附近;涂层层数和厚度对涂层表面径向应力、界面剪切应力和整体Mises应力均有明显影响。模拟分析的结果可以为该复合材料的设计和制备提供一定的理论依据。     

扭转载荷作用下熔接涂层与基体结合界面处应力特性仿真研究

目的通过有限元仿真获得熔接涂层与基体结合界面处的应力分布特性,得到熔接涂层与基体的力学性能匹配性。方法应用ABAQUS有限元软件,将模型沿轴向和径向剖切,讨论不同扭矩载荷下镍基合金涂层和基体轴结合界面的应力分布规律,分析涂层厚度对结合界面处应力的影响。结果从模型剖切后采样结点的应力变化曲线看,基体和涂层的内部应力变化均匀,在基体和涂层结合处应力存在突变,涂层上的应力大于基体上的应力。涂层厚度从0.5 mm增大到1.0 mm时最大应力减小量约为18 MPa,从1.0 mm增大到2.5 mm时最大应力的减小量约为1 MPa,涂层厚度大于1.0 mm后最大应力减小量变化不明显。结合面两侧涂层和基体应力差值的最大值Δσ_(max)随着涂层厚度的增大有所减小,在涂层厚度小于1.0 mm时,变化较为明显。结合面底面处的应力突变随涂层厚度的增加而略有减小。结论在涂层和基体结合界面处存在应力突变,最大应力出现在涂层外表面的中心位置,增大涂层厚度可以减小应力突变,在涂层厚度较小时效果明显。     

加热温度对Al-Si涂层热成形钢组织及性能的影响

利用粗糙度仪、扫描电镜、硬度计、辉光放电原子发射光谱仪等检测方法,研究分析了热冲压成形工艺过程中的加热温度对Al-Si涂层22MnB5热成形钢组织及性能的影响。结果表明,随着加热温度的升高,Fe沿垂直于表面方向由热成形钢基体向Al-Si涂层表面的迁移量逐渐增大,O沿垂直于表面方向由Al-Si涂层表面向热成形钢基体的迁移量逐渐增大,且迁移的最大深度约为2.80 μm。Fe沿垂直于表面方向由热成形钢基体向Al-Si涂层表面的迁移量直接决定了Fe-Al-Si相的形态、生成位置及界面结合层厚度。随着加热温度的升高,Al-Si涂层表面粗糙度R_a、峰值计数R_pc值先增大后减小;当加热温度为930 ℃时,涂层表面粗糙度R_a达到最大值1.89 μm,峰值计数R_pc值达到最大值218。随着加热温度的升高,Al-Si涂层总厚度从27.78 μm增加至40.46 μm,界面结合层厚度从1.08 μm增加至15.11 μm。当加热温度为930 ℃时,热成形钢基体的硬度达到最大值505 HV0.2。     

钛基 / TiN 涂层接触应力有限元分析

目的研究在接触载荷作用下,钛基/TiN涂层的应力变化规律。方法利用ABAQUS软件建立可靠有限元模型,分析涂层厚度不同的钛基/TiN涂层系统在球压头作用下的接触应力。结果钛基/TiN涂层系统最大Mises应力出现在距表面约0.4a(a为接触半径)处的亚表层或者亚表层附近的界面处。在接触应力和弯曲应力作用下,涂层弯曲变形会影响涂层的径向应力和剪应力分布。结论在接触载荷作用下,涂层内存在接触应力和自身弯曲两种应力作用。分析结果有利于理解钛基Ti N涂层的失效机理。     

Critical Maximum Contact Pressure for Yielding in Hard Coating under Sliding Contact

In order to design the best combination of the coating and the substrate for preventing the yield,the semi-analytical method(SAM)was used to analyze the von Mises stress distributions in the contact system,and calculate the critical maximum contact pressure for yielding at the interface and surface in hard coating under both normal and tangential loads on three-dimensional elastic half space.From the results,it can be concluded that,to obtain a higher maximum critical contact pressure for the yield at the interface,increasing the substrate hardness and the ratio value of the coating thickness to the Hertzian contact radius(t/a0)is more effective when t/a0 is larger than 0.5 while increasing the substrate hardness or making the friction coefficient smaller is better when t/a0 is very small;to prevent yielding at the surface,choosing a relatively lower friction system or increasing the yield strength ratio of the coating to the substrate(Yf/Yb)will be effective.     

Fatigue damage initiation and growth from artificial defects in Zr-based metallic glass

An array of well-defined and micrometer-sized circular and line defects were produced on the surface of Zr-based bulk metallic glass bend specimens using a focused ion beam (FIB) in order to study the effect of the defect size, orientation and shape on fatigue damage initiation and growth. Damage evolution was recorded using a surface-replicating technique. Damage was observed to initiate and grow as shear bands or mixed-mode cracks before reaching a characteristic length when they abruptly changed growth direction and propagated orthogonal to the maximum stress axes. Additionally, specimens with circular defect pairs were fabricated so that defect interaction under fatigue loading could be observed. Analysis of the stress state around the defect pairs indicated that damage initiation occurred in regions of highest equivalent (von Mises) stress. Stress-life measurements for bending specimens with FIB surface defects were found to be similar to those for bending specimens without defects at the same applied stress amplitude.     

深海液压缸活塞杆密封仿真分析

为分析深海环境下液压缸活塞杆Y形圈的密封性能,利用ANSYS软件建立Y形圈的仿真模型,分析不同工作状态下活塞杆Y形圈的密封应力.结果表明:由海面下潜至深海5 km过程中,安装、活塞杆外伸和收回3个工作状态下,最大von Mises应力基本不变、最大接触应力最大增幅约37％;增大压缩率,最大接触应力均减小、最大von Mises应力变化不一致.按照现有标准设计的液压缸活塞杆Y形圈密封结构能够满足深海密封的要求.     

冷喷涂对2219铝合金搅拌摩擦焊接头残余应力与力学性能的影响

为了改善铝合金搅拌摩擦焊接头残余应力与力学性能,在4 mm厚2219铝合金搅拌摩擦焊接头上表面进行冷喷涂试验,研究分析了冷喷涂前后接头残余应力与力学性能的变化. 结果表明,焊态接头纵向残余应力呈不对称“M”形分布,残余应力峰值位于前进侧靠轴肩附近;冷喷涂后,接头残余应力大幅度降低,残余应力峰值由186 MPa降低至43 MPa.涂层沉积厚度约200 μm,涂层与基体界面产生了较大的塑性变形,基体界面附近组织晶粒得以细化.由于冷喷涂过程的喷丸效应,接头上表面显微硬度平均提高了25 HV,作用深度约1 mm.接头拉伸性能也获得明显改善,抗拉强度提升6.3%,断后伸长率提升78.6%,焊态与冷喷涂态的拉伸试样均在接头前进侧的热影响区附近发生断裂,符合在低硬度区或弱结合面产生裂纹并扩展的弱区断裂的特征.     

Edge-chipping reduction in rotary ultrasonic machining of ceramics: Finite element analysis and experimental verification

Rotary ultrasonic machining (RUM) is one of the machining processes for advanced ceramics. Edge chipping (or chamfer), commonly observed in RUM of ceramic materials, not only compromises geometric accuracy but also possibly causes an increase in machining cost. In this paper, a three-dimensional finite element analysis (FEA) model is developed to study the effects of three parameters (cutting depth, support length, and pretightening load) on the maximum normal stress and von Mises stress in the region where the edge chipping initiates. Two failure criteria (the maximum normal stress criterion and von Mises stress criterion) were used to predict the relation between the edge chipping thickness and the support length. Furthermore, a solution to reduce the edge chipping is proposed based upon the FEA simulations and verified by experiments.     

Cold Gas-Sprayed Deposition of Metallic Coatings onto Ceramic Substrates Using Laser Surface Texturing Pre-treatment

Cold spraying enables a variety of metals dense coatings onto metal surfaces. Supersonic gas jet accelerates particles which undergo with the substrate plastic deformation. Different bonding mechanisms can be created depending on the materials. The particle–substrate contact time, contact temperature and contact area upon impact are the parameters influencing physicochemical and mechanical bonds. The resultant bonding arose from plastic deformation of the particle and substrate and temperature increasing at the interface. The objective was to create specific topography to enable metallic particle adhesion onto ceramic substrates. Ceramic did not demonstrate deformation during the impact which minimized the intimate bonds. Laser surface texturing was hence used as prior surface treatment to create specific topography and to enable mechanical anchoring. Particle compressive states were necessary to build up coating. The coating deposition efficiency and adhesion strength were evaluated. Textured surface is required to obtain strong adhesion of metallic coatings onto ceramic substrates. Consequently, cold spray coating parameters depend on the target material and a methodology was established with particle parameters (diameters, velocities, temperatures) and particle/substrate properties to adapt the surface topography. Laser surface texturing is a promising tool to increase the cold spraying applications.     

Effect of atomic-level stresses on local dynamic and mechanical properties in CuxZr100−x metallic glasses: A molecular dynamics study

In this article, molecular dynamics simulations of Cu_xZr_100−x metallic glasses are performed to study the dynamic and mechanical behaviors of structural defects. Based on atomic-level stress theory, atomic strain energy and von Mises shear stress were correlated with the local dynamic/mechanical properties of MGs. Atoms with high atomic strain energy (n-type/p-type defects) are found to exhibit larger mean square displacements than solid-like atoms during structural relaxation process, indicating that these atoms have faster dynamics than solid-like entities. Additionally, simulated shear loading was conducted to investigate the relationship between von Mises shear stress and local shear properties in MGs. By monitoring the von Mises shear strain for each atom, γ-defects (atoms with excessive shear stress) are proven to be fertile regions for shear transformations.