凸轮轴三点弯曲断裂载荷与挠度的关系研究

使用WE-500型液压式万能拉伸试验机测定了1AE6半激冷合金铸铁凸轮轴的三点弯曲断裂载荷,研究了其三点弯曲断裂载荷和挠度之间的关系。研究表明:(1)不同炉次的凸轮轴的三点弯曲断裂载荷存在一定的分散性;(2)凸轮轴的三点弯曲断裂载荷与挠度之间存在正相关关系,凸轮轴中含有适量碳化物对其强度和挠度都是有益的。     

基于三点弯曲的马氏体超高强钢弯曲性能试验

基于三点弯曲试验,研究了马氏体超高强钢的弯曲性能。利用二分法原理安排了"基于凸模尺寸"的试验。得到了不同弯曲角度下、以最小相对弯曲半径为表征的弯曲成形性能,并分析了其影响因素。对于1180 MPa级别及以下马氏体钢,在120°弯曲角及以下,均有Rmin/t1。对于1300MS和1400MS,Rmin/t≥2.5;且大于90°弯曲角后,弯曲性能对弯曲角度不敏感。各向异性对马氏体超高强钢最小相对弯曲半径的影响显著,沿轧制方向(L)的弯曲性能优于垂直于轧制方向(T);各向异性指数不能准确地表述马氏体超高强钢不同方向的弯曲变形行为和弯曲性能差异。随着强度的升高,断后伸长率接近线性下降,弯曲变形时相对弯曲半径值增大,弯曲性能下降,但并无很好的线性关系。     

负压铸渗法制备铸铁表面Ni／WC复合渗层三点弯曲性能测试

采用负压铸渗法制备了铸铁表面不同WC含量的Ni基复合渗层, 观察了渗层与基体结合形貌并对试样进行三点弯曲测试.结果表明:渗层与基体熔合良好;随着渗层中WC含量的增加,渗层的韧性变差,变形的能力变差;弯曲破坏形貌和断口分析表明,不同WC含量的渗层破坏形貌基本相同,断裂机理也相同,基体沿石墨断裂,渗层沿WC断裂.     

通用中空凸轮轴三点弯曲断裂载荷的统计分析

采用Weibull统计分析方法分析了通用中空冷激铸铁凸轮轴三点弯曲断裂载荷的分布规律。Weibull统计分析表明,通用中空冷激合金灰铸铁凸轮轴三点弯曲断裂载荷符合Weibull统计规律,其Weibull模量为15.9。断口分析表明,渗碳体体积分数高的凸轮轴,其三点弯曲断裂载荷也高,反之亦然。凸轮轴中渗碳体体积分数的差异是导致其三点弯曲断裂载荷分散的原因。     

镁合金型材三点弯曲数值模拟及试验验证

建立了常温拉应力和压应力状态下AZ31B镁合金型材的材料本构模型。根据所建立的材料本构模型,模拟了型材的三点弯曲变形过程。研究表明:对于成形力、外壁塌陷和回弹量而言,数值模拟的结果与试验结果吻合较好;但内壁凹陷二者差别比较大,这是在建立材料模型时忽略了各向异性所致。通过模拟镁合金型材三点弯曲变形过程,验证了材料本构模型的准确性,对镁合金型材弯曲数值模拟研究具有一定指导意义。     

冷激铸铁凸轮轴三点弯曲断裂载荷的统计分析

采用直方图分析和Weibull统计分析相结合的方法,分析了TU5GP4型冷激铸铁凸轮轴三点弯曲断裂载荷的分布规律。结果表明:(1)TU5GP4型冷激铸铁凸轮轴三点弯曲断裂载荷的分布直方图属偏态型,标准偏差S=0.223,说明数据分布集中程度高,离散程度小。(2)Weibull模量为33.4,表明其三点弯曲断裂载荷集中程度高,凸轮轴生产工艺可靠性高。     

Invar 36合金厚板三点弯曲回弹规律研究

采用Ls-Dyna软件,利用Swift硬化模型、Mises屈服准则,建立三点弯曲有限元模型,模拟研究了不同厚度、不同温度下Invar 36合金厚板的回弹规律。依据模拟结果,设计制作三点弯曲模具,在万能液压机上进行三点弯曲回弹试验。结果表明,板料厚度越大,成形温度越高,回弹程度越小。室温下材料厚度从12.7增加至19.05 mm时,回弹量由19.73%降至10.76%,减小了45.5%;19.05 mm厚度的板料成形温度为室温时回弹量为10.76%,而当成形温度升高至800℃时回弹量则降至1.4%,减小了87.0%。有限元模拟结果和试验结果吻合度高,表明该有限元模型、材料模型可有效预测Invar 36合金不同厚度、不同温度下的回弹情况。     

基于三点弯曲的1000MPa级超高强马氏体钢最大弯曲角度

基于三点弯曲模具结构,设计可在线观察折弯件变形区域的简易装置,实现了对弯曲外表面微裂纹的实时观察;配合数显角度尺,实现了实时测量弯曲角度的功能。针对1 000MPa级别超高强度马氏体钢板进行三点弯曲实验,得到了以不同弯曲半径下最大弯曲角度为表征的弯曲成形性能,并分析了其影响因素。结果表明,超高强度钢随相对弯曲半径的增大,弯曲角度也变大,但随着材料强度升高,弯曲半径的敏感程度降低;最大弯曲角受轧向的影响较大,各向异性r值不能准确反映材料在弯曲平面应变状态下的各向异性特性;最大弯曲角随材料强度的升高而减小,但减小的幅度有所降低;最大弯曲角与延伸率无关联。     

钢面板泡沫铝夹心板的三点弯曲行为

采用胶粘法制备大尺寸钢质泡沫铝夹心板,测试夹心板的三点弯曲强度,分析面板厚度、芯层厚度对夹心板弯曲性能的影响规律,研究弯曲载荷作用下的夹心板失效机理。结果表明：钢质泡沫铝夹心板可承受很高的弯曲载荷,夹心板抗弯强度随着芯层泡沫铝厚度的提高而提高。增加钢面板的厚度,夹心板抗弯强度整体呈增强趋势。当面板厚度为8 mm、芯层厚度为50 mm时,夹心板的极限抗弯强度可达66.06 kN。芯层泡沫铝内泡壁表面的大尺寸裂纹是夹心板在弯曲载荷作用下失效的主要原因;采用熔体发泡法制备的泡沫铝板材,因冷却强度过大而导致的附加应力使泡壁的强度下降,也是影响夹心板力学性能的主要因素。     

热喷涂涂层界面断裂韧性的反向三点弯曲法试验

以热喷涂NiCrBSi涂层/钢基体为材料模型,利用将涂层置于受压侧的反向三点弯曲法试验,对热喷涂涂层界面断裂现象进行分析并建立相应的界面断裂韧性计算模型。结果表明,界面裂纹起始于三点弯曲试样中部,对应于加载压头与涂层接触区域正下方的界面上,并向两侧扩展,伴随涂层屈曲,形成分层屈曲的破坏形貌。根据分层屈曲形貌建立计算模型,通过分层屈曲几何参数与屈曲临界应力、涂层内真实应力以及界面断裂韧性的关系,获得界面断裂韧性值。     

拉伸法测量金属丝弹性模量的试验探讨

试验采用光杠杆的放大原理,利用一种新型的弹性模量测量装置,测出了在载力作用下金属丝发生的微小变形,结合弹性模量公式,计算出了金属丝的弹性模量。试验结果表明：弹性模量的测量值能较好地吻合理论值。     

Determination of Young's modulus and Poisson's ratio for coatings

Designing thin-film coatings to meet engineering needs requires the knowledge of accurate mechanical properties of the coatings. Young's modulus and Poisson's ratio are two basic mechanical properties of materials, which should be conveniently measured. This paper reports a direct and non-destructive method for the measurement of the Young's modulus and Poisson's ratio of a thin-film coating and its substrate based on the extended Hertz theory for the contact of coated bodies. The theory is used to analyze load-displacement data from a spherical indentation in the elastic range, in which the substrate effect is intrinsically modeled. The Young's modulus and Poisson's ratio are determined at the same time through minimizing the difference between the measured and specially defined modified Young's moduli. Two sets of validation experiments are also reported. This new method does not require any assumptions on pressure distribution and Poisson's ratio and can be easily incorporated into current indentation analysis systems.     

Determination of reduced Young＇s modulus of thin films using indentation test

The flat cylindrical indentation tests with different sizes of punch radius were investigated using finite element method (FEM) aimed to reveal the effect of punch size on the indentation behavior of the film/substrate system. Based on the FEM results analysis, two methods was proposed to separate film's reduced Young's modulus from a film/substrate system. The first method was based on a new weight function that quantifies film's and substrate's contributions to the overall mechanical properties of the film/substrate system in the flat cylindrical indentation test. The second method, a numerical approach, including fitting and extrapolation procedures was put forward. Both of the results from the two methods showed a reasonable agreement with the one input FE model. At last, the effect of maximum indentation depth and the surface micro-roughness of the thin film on the reduced Young's modulus of the film/substrate system were discussed. The methods proposed in the present study provide some new conceptions on evaluating other properties of thin films, e.g. creep, for which a flat-ended punch is also employed.     

A constitutive model for spring-back prediction in which the change of Young's modulus with plastic deformation is considered

In order to improve the prediction capability of spring-back in the computational analysis of sheet metal forming processes, a stress–strain constitutive formulation of non-linear combined hardening rule has been proposed in this paper according to non-linear kinematic hardening theory of Lemaitre and Chaboche and Hill's 1948 anisotropic yielding function. Traditionally, Young's modulus is considered as a constant in engineering application and numerical simulation. In fact, it decreases with plastic deformation. So the effect of the change of Young's modulus with plastic strain on spring-back is considered in the constitutive model. The algorithm of stress update is elastic prediction, plastic correcting and radial returning. Numerical results and experimental results show that the proposed constitutive model significantly improves the prediction accuracy of spring-back.     

板料弯曲的变薄系数

给出了板料弯曲的应力应变中性层和纯弯曲应变中性层的计算公式,并推出板料弯曲时的变薄系数计算公式.通过与文献中的变薄系数以及弯曲试件实测厚度进行比较和分析,说明变薄系数的计算公式可用于板料弯曲的变薄计算,分析讨论了计算值与实测值偏差较大的情况,并对计算公式进行了修正,修正后的计算公式提高了变薄系数计算的精度.     

针状铁素体钢的高温屈服应力及弹性模量

用热模拟试验机研究了C-Mn-Mo-Nb针状铁素体钢的相变特性,采用拉伸和压缩方法检测了试验钢在奥氏体化加热后冷却至不同温度时的屈服应力和弹性模量,采用高温拉伸试验机对比检测了加热至奥氏体化以下,试验温度时钢的屈服应力和弹性模量。结果表明：在奥氏体化后冷却过程中,钢的屈服应力在650～500℃相变温度范围内从约75 MPa提高至约450 MPa,但弹性模量在针状铁素体相变温度区间（600℃左右）出现谷值。在550℃以上,从室温加热至试验温度拉伸方法获得钢的屈服应力和弹性模量较奥氏体化加热法的高。相变过程中,晶体结构转变及位错密度增加是弹性模量波谷产生的主要原因;晶体结构转变、位错密度增加和析出使屈服应力急剧增加。而相同组织状态下,钢的屈服强度和弹性模量主要受温度影响。不同测试方法所得数据的差异,主要是由不同的组织结构转变而非测试方法造成。     

Determination of Young's modulus and yield stress of porous low-k materials by nanoindentation

In the present study, the concept of the ‘effectively shaped indenter’ was used to analyse nanoindentation data of rather soft films on hard substrates. This approach was introduced for monolithic materials by Pharr and co-workers some years ago [G.M. Pharr, A. Bolshakov: J. Mater. Res. 17 (2002) 2660, A. Bolshakov, W.C. Oliver, G.M. Pharr, MRS Symp. Proc 356 (1995) 675]. Substrate to layer moduli ratios range from nearly 60 to 160. With such soft and brittle materials (Young's modulus nearly 3 GPa or smaller, yield strength around 100 MPa), no completely elastic measurements can be performed even at low loads. Hence, an established method for the determination of yield stresses by means of nanoindentation, namely that of loading-partial-unloading [N. Schwarzer: ASME J. Tribology 122 (2000) 672, T. Chudoba, N. Schwarzer, F. Richter: Thin Solid Films 355-356 (1999) 284, T. Chudoba, N. Schwarzer, F. Richter: Surf. Coat. Technol. 127 (2000) 9] was not applicable. However, the ‘effectively shaped indenter concept’ allows one to separate the elastic stresses due to the penetration from the residual stresses caused by the inelastic deformation, assuming that their influence on the elastic stress field is small. Thus, by using this approach critical yield stresses of soft porous materials have been obtained. Additionally, the Young's modulus of these materials has also been determined by means of laser-generated surface acoustic wave (LSAW) measurements and the Oliver and Pharr method. In the latter case, a special extrapolation method for the indentation modulus had to be applied to correct for the substrate influence. The results by the different methods are compared and their deviations are discussed. As there is no complete solution available for the correction of the substrate influence on Young's modulus of the film when plastic deformation occurs during indentation, the authors are searching for an approach to approximate the elastic properties of a soft film on a hard substrate. It seems that the determination of the Young's modulus of very soft films cannot be separated from the determination of the yield stress. As an example for a low-k material actually of interest, porous silica xerogel films on silicon with porosities of 38 up to 51 vol.% were investigated.     

薄板激光弯曲机理的研究

试件在激光与材料非熔凝作用下动态变形过程实时测量的结果表明：薄板在激光照射下所引起最终变形的方向取决于材料的性质，可能是朝向激光束或背向激光束。研究结果进一步完善了薄板激光弯曲的变形机理，并为研究薄板激光弯曲过程奠定了基础。     

Tensile testing as a method for determining the Young''s modulus of thin hard coatings

The present paper describes and evaluates a tensile testing method for determination of the Young's modulus of thin hard coatings. When applied to PVD TiN and NbN coatings on stainless steel foils, the elastic modulus obtained through force—strain plots ranged between 380 and 425 GPa for TiN coatings, and was 350 GPa for the single NbN coating tested. It is concluded that the method is easy to perform and allows reliable determination of the Young's modulus of thin hard coatings, and that it can be applied to almost any kind of coating on a wide range of substrate materials.     

板金弯曲成形回弹问题的理论研究

分析了板金弯曲成形过程的回弹过程 ,利用成形过程中弯曲区域的平面应变和恒定厚度假设 ,根据VonMises屈服准则 ,建立了弹塑性材料线性硬化条件下板金弯曲成形的回弹计算模型 ,导出了纯弯曲条件下板金件的最小弯曲半径计算公式 ,并讨论了弯曲成形一般不等角平面弯曲问题的数值解法