镀镍深冲钢带层间切应力的分析与测量方法研究

镀镍深冲钢带是生产一次或二次碱性电池钢壳的重要材料，普通深冲钢带镀镍后在深冲时极易引起镀层脱落。在对镍和深冲钢带的“应力应变”曲线进行分析比较的基础上，进一步研究了深冲时引起镀层脱落的原因。因为深冲变形时镀层和钢带结合面的两侧所承受的应力大小不同，在结合面上产生了较大的层间切应力，并引起较大的切应变，从而导致深冲变形过程中镀层的脱落。而镀镍深冲钢带所能承受的最大层间切应力是该材料的一项重要的力学性能参数，也是评定该材料在深冲变形过程中能否有效防止镀层失效的一个重要的参数指标。经研究并设计出正确的实验装置，通过拉伸试验机对该材料所能承受的最大层间切应力进行测量，具有重要的理论意义和实际意义。     

基于动力显式算法的镍镀层钢带成形模拟

利用LS-DYNA软件采用实体单元及动力显式算法模拟了镍镀层钢带深冲成形过程。板料与模具之间采用主从面对算法,摩擦力服从库仑摩擦定律,界面结合采用固连断开接触模型。结果表明:镀层与基体在深冲成形过程中不会出现界面失效,基体与镀层应力-应变分布以及材料流动规律大致相同,但镀层的应力-应变分布情况更复杂,表现为个别地方分布的不均匀;同时通过改变板料与模具间的摩擦因数,可减小摩擦有利于材料成形性能的改善。     

镀镍钢带的冲压成型性能

在RG2000型微机控制电子万能试验机上对镀镍钢带进行冲压成型试验,研究了镀镍钢带在不同压边力作用下的成型性能,对比了镀镍钢带与未镀镍钢带在冲压成型中所需的冲头载荷,对不同冲压深度杯形件侧壁内表面形貌变化做了比较研究。结果表明:在不同的压边力作用下镀镍钢带具有不同的成型特性;与未镀镍钢带相比,镀镍钢带的冲压成型需要更大的冲头载荷;杯形件侧壁内表面的裂纹在冲压深度为12 mm时形成,其数量随着冲压深度的增加而增加;镍镀层比低碳钢基体更容易出现裂纹。     

Ni－P－Si_3N_4复合镀层中P含量对残余应力和磨损性能的影响

采用Ｘ射线法测量了Ｎｉ－Ｐ－Ｓｉ３Ｎ４复合镀层经热处理后在镀层中产生的残余应力，并与Ｎｉ－Ｐ镀层进行了对比研究。同时，着重分析了镀层残余应力和磨损性能的关系。结果表明，Ｎｉ－Ｐ－Ｓｉ３Ｎ４复合镀层中Ｐ含量较低时为压应力，镀层磨损量较低；Ｐ含量较高时为拉应力，镀层脆性脱落严重，磨损量增大。对于ＮｉＰ镀层，随着镀层中Ｐ含量的增大，拉应力逐渐增大，磨损加剧；而Ｐ含量较低时，表现为粘着磨损。     

Ni－P－Si_3N_4复合镀层中P含量对残余应力和磨损性能的影响

采用Ｘ射线法测量了Ｎｉ－Ｐ－Ｓｉ３Ｎ４复合镀层经热处理后在镀层中产生的残余应力，并与Ｎｉ－Ｐ镀层进行了对比研究。同时，着重分析了镀层残余应力和磨损性能的关系。结果表明，Ｎｉ－Ｐ－Ｓｉ３Ｎ４复合镀层中Ｐ含量较低时为压应力，镀层磨损量较低；Ｐ含量较高时为拉应力，镀层脆性脱落严重，磨损量增大。对于ＮｉＰ镀层，随着镀层中Ｐ含量的增大，拉应力逐渐增大，磨损加剧；而Ｐ含量较低时，表现为粘着磨损。     

拉应力对低碳钢带硬度和弹性模量的影响

在自制的微型拉伸仪上对低碳钢带施加拉应力,对其受拉状态时的硬度和弹性模量进行了测试,并分析了拉应力与它们之间的关系;用有限元模拟了两种材料钢带在不同拉应力下的硬度。结果表明:钢带的硬度随着拉应力的增大呈现先减小后增大的趋势,以屈服强度为转折点;小于屈服强度的拉应力对钢带的硬度影响很小,而超过屈服强度后对硬度的影响显著,模拟结果与试验结果基本相符;当拉应力较大、材料硬化率较大时,拉应力对其硬度的影响反而较小;拉应力对钢带弹性模量没有明显影响。     

电沉积镍涂层冲压过程的界面特性

采用有限元方法对电沉积镍涂层钢带的冲压成形过程进行了数值模拟,得到了电沉积镍涂层在界面上的应力场、应变场等冲压成形特性。计算结果表明：在冲压过程中,涂层与基体界面上的应力大小、拉压性质都是变化的,且正应力一般在-50～50MPa之间,剪应力一般在-40～30MPa之间;界面上涂层中的应变比基体中的应变大得多,但两者在变形过程中是比较匹配的。     

二维编织SiC/SiC复合材料的剪切性能

通过单向以及循环加卸载面内剪切试验,结合试件失效分析,研究了二维编织SiC/SiC复合材料的面内剪切特性。将试件剪切响应分为弹性部分和非弹性部分,分别由卸载模量和残余应变表征,由此得到剪切应力-应变关系表达式。试验结果表明,卸载模量随应力以指数形式衰减,残余应变随应力以指数形式增大。预测剪切应力-应变曲线与试验曲线吻合很好。     

合金化镀锌板的镀层脱落分析

跟踪拍摄合金化镀锌板双球冲成形时的镀层脱落过程,发现双球冲行程变化影响镀层脱落时间、部位与程度。结合自行开发的镀层自动评价系统分析镀层脱落程度,表明双球冲行程会影响镀层应变,镀层脱落程度与镀层应变有关。脱落主要发生在压应变区域,压应变越大,脱落程度越大。对各变形阶段应变进行有限元仿真,对比镀层的实际脱落过程,进一步发现压应变对镀层脱落的影响关系：只有压应变增大到某极限值,镀层才开始脱落;压应变继续增大,脱落继续且程度加大;压应变到达最大值之后再减小,脱落过程随即中止。     

拉磁效应及其在内应力无损检测中的应用

报道了用双探头磁应力仪及单探头磁应力仪对航天器件用材料电铸镍的力－磁特性进行了部分基础性研究工作。研究结果发现：电铸镍具有与低碳钢固有的压磁效应绝然不同的明显的拉磁效应。揭示出电铸镍内在的这一基本力－磁特性，为航天工程用电铸镍器件残余应力磁性法无损检测中拉压应力信号的正确判定提供了重要的理论和实验依据。     

镍涂层复合板拉延过程的数值模拟

采用有限元动力显式算法模拟了电沉积镍涂层复合板的拉延成形过程,得到了涂层与基体的应力应变场,计算结果和其他方法及试验进行了一定的比较。涂层与基体采用Belytschko-W ong-Ch iang四节点壳单元,模具与压边圈采用刚体壳单元。基体采用随动强化模型,涂层与基体结合界面采用固连断开接触。对该材料的拉延模拟计算表明,该涂层与基体在拉延成形过程中不会出现界面失效,但涂层在拉延过程中的应力变化比基体复杂,且涂层的等效塑性应变与基体相差较大,说明涂层的拉延过程比基体复杂。计算出的冲压力曲线可供拉延工艺参考。     

Sliding wear resistance of metallic coated surfaces

The role of metallic coatings in sliding wear is examined experimentally. The results indicate that the tribological behavior of soft coatings is consistent with the delamination theory of wear, especially the critical nature of the plating thickness. It is shown that a reduction in wear rate of three orders of magnitude is possible when the coating material is softer than the substrate and thinner than a critical thickness. The optimum plate thickness is found to be of the order of 0.1 μm for cadmium, silver, gold or nickel plated on various types of steel. Cadmium, silver and nickel reduce wear only in non-oxidizing environments, whereas gold reduces wear both in air and in inert atmospheres.The roughness of the substrate surface prior to plating and the nature of the coating/substrate bond have significant effects on the life of these coatings. The life of the coatings is increased by polishing the substrate to 0.1 μm (c.l.a.) prior to plating, and also by diffusion of the plated material into the substrate, which increases the coating/substrate bond strength.     

Sensitivity analysis of plating conditions on mechanical properties of thin film for MEMS applications

In this paper, we report the detailed investigation into the effects of plating temperature and applied current density upon the mechanical properties of plated nickel film such as Young’s modulus and residual stresses. This method uses the resonance method of atomic force microscope, which does not require specially microfabricated cantilevers and additional experimental set-up. Thin layers of nickel are electroplated onto the tip surface of AFM cantilevers and plating thicknesses were measured at the end of each plating step. The self-deformation of the released AFM cantilever is also measured as a function of the plated nickel thickness, which is converted into the quantitative residual stress by appropriate mechanics. The measured Young’s modulus is as high as that of bulk nickel at low plating temperature and at low applied current density, but drastically drops at high temperature or current density. The dependence of Young’s modulus on the plating thickness is negligible in thin film less than few microns. The residual stress is also a strong function of the process conditions, and decreased with the elevation of the current density and plating temperature. And the intrinsic and extrinsic stresses of plated nickel are separated from the measured residual stress, and correlated with plating conditions. Dependence of the plated thickness on Young’s modulus and residual stress is also considered.     

Application of a neural network to predict thickness strains and finite element simulation of hydro-mechanical deep drawing

In this paper an artificial neural network (ANN) is used to predict the thickness along a cup wall in hydro-mechanical deep drawing. This model uses a feed-forward back-prorogation neural network. After using the experimental results to train and test the network, the model was applied to new data for the prediction of thickness strains in hydro-mechanical deep drawing. The results are promising. In the present work, we also attempt to perform a finite element simulation of the process for the two dimensional axi-symmetric case using explicit finite element code LS-DYNA 2D. Counter pressure on the blank is applied by specifying the pressure boundary conditions. A comparison was made between simulated, experimental and ANN results of hydro-mechanical deep drawing using low carbon extra deep drawing grade steel sheets of 0.96 mm thickness. It was also found that by hydro-mechanical deep drawing, a higher drawability and a more uniform thickness distribution were obtained when compared to conventional deep drawing.     

热浸镀55%Al-Zn后钢的拉伸性能和耐蚀性能研究

研究了热浸镀55%Al-Zn合金镀层钢的室温拉伸性能和耐蚀性能。结果表明：Q235钢板经热浸镀55%Al-Zn合金后的室温屈服强度和抗拉强度均高于Q235钢，而伸长率没有降低。经SEM观察，55%Al-Zn合金镀层钢的拉伸断口由钢基体的韧窝断口和Fe-Al-Zn-Si合金层的穿晶解理断口组成。腐蚀试验结果显示：热浸镀55%Al-Zn合金后钢的耐蚀性在盐雾中是镀锌钢的6倍，在盐水中是镀锌钢的3倍，并同样具有镀锌层对钢基体的电化学保护能力。     

真空度对Ni80Cr20薄膜中性度的影响

理论计算了Ni、Cr和Ni80Cr20三种材料的光学特性,确定了镍铬成份变化对Ni80Cr20的影响。在高低两个真空度条件下采用电子枪蒸发工艺进行了Ni80Cr20的镀膜实验,结果表明,低真空度时"薄"膜的中性度较好,而高真空度时"厚"膜中性度较好。采用X射线能谱分析发现"薄"膜铬含量高于膜料,而"厚"膜更高,高真空度薄膜略有氧化,而低真空度氧化更严重。从残余气体和蒸发方式方面分析了镍铬成份差异的原因,再结合氧化对薄膜特性的影响,确定了不同真空度薄膜中性度差异的原因。     

Surface failure of soft and surface-hardened steel rollers in rolling contact

To study the mechanism of rolling contact fatigue failure, annealed thermally refined 0.43% carbon steel and case-hardened nickel chromium steel rollers were tested under conditions of pure rolling and sliding/rolling. The failure mechanism was examined by fractographic observation and by calculation of the amplitudes of the ratio of stress to strength.It was found that pitting cracks initiated on the roller surface and were induced by the normal stress in the circumferential direction of the roller or by the maximum principal stress. Spalling cracks initiated beneath the surface and were induced by the orthogonal shear stress.     

Behavior of medium carbon steel under combined fatigue and wear

The combined fatigue-wear life of medium carbon steel (AISI 1045) was investigated under various combinations of loads and sliding wear conditions using a rotating beam test. The direction of the maximum tensile stress due to bending was perpendicular to that due to wear [1]. Tests were also performed with specimens plated with a thin layer of cadmium or nickel-gold. All of the tests were conducted in the high cycle regime. The results show that the fatigue life of all the specimens at a stress level higher than the endurance limit of the specimen was within the experimental scatter of a typical fatigue test. The effect of sliding wear on fatigue life is manifested primarily by the stress field imposed by the slider on the specimen. In the case of plated specimens, the fatigue life was not significantly affected, although the wear rate was decreased by an order of magnitude.     

电沉积纳米镍薄板的超塑微拉深性能

采用脉冲电沉积工艺制备了厚度为0．1mm的纳米镍薄板，在不同的温度和应变速率下对该薄板进行单向拉伸试验，确定了其超塑性变形的最佳工艺条件，在此基础上进行了纳米镍薄板的微拉深性能实验。实验结果表明：纳米镍薄板的微拉深性能随成形温度的升高而提高；在温度为723K、半球形拉深凸模直径为1mm、拉深速度为1～5mm／min的条件下，均可成功拉深出半球件。采用透射电镜和扫描电镜对拉深变形前的沉积态组织和拉深变形后的微观组织进行了观察比较，结果表明，微拉深后大部分镍晶粒长大到微米量级。根据实验结果，初步探讨了超塑微拉深的主要变形机制。