U形件通过凹模圆角时不产生表面塑性压痕的方法研究

分析了U形件变形时板料通过凹模圆角的变形机理,通过设计一套实验设备来获得压痕,最后按照实验分析结果来进行弯曲凸模和凹模镶块的设计与制造,给出了详细的设计和制造工艺流程。

局部载荷下材料性能影响压痕弹塑性行为的研究

利用有限元法分析了不同材料在载荷作用下接触区域的弹塑性行为,探讨了弹塑性行为与载荷、屈服强度、弹性模量和泊松比之间的关系,并构建1套压痕实验装置予以实验验证。研究结果表明:载荷、材料屈服强度对压痕弹塑性行为影响大,而弹性模量、泊松比对其压痕弹塑性行为影响较小。研究结果描述了载荷增加时其压痕弹塑性行为的发展,压痕参数与屈服强度之间的关系,为压痕法根据压痕参数确定屈服强度提供参考。

基于离散相模型的电潜泵叶轮磨损数值计算

基于离散相模型结合弹塑性压痕破裂理论对电潜泵叶轮磨损进行数值计算研究,对不同工况下的叶轮磨损进行分析,得到电潜泵叶轮的磨损规律,运用三坐标测量机对实际工作的电潜泵叶轮中存在的磨损情况进行测量,以实现对数值模拟结果的验证。结果表明：叶轮磨损加剧的颗粒粒径临界点是0.06-0.08 mm;磨损最严重的区域位于叶片凹面;转速、颗粒粒径增大均会加剧冲蚀磨损,导致磨损严重的区域由凹面中部的几个零散点向整个面扩展;数值模拟结果与验证结果吻合较好。

Effect of indentation size and grain/sub-grain size on microhardness of high purity tungsten

Hardness of materials depends significantly on the indentation size and grain/sub-grain size via microindentation and nanoindentation tests of high-purity tungsten with different structures.The grain boundary effect and indentation size effect were explored.The indentation hardness was fitted using the Nix-Gao model by considering the scaling factor.The results show that the scaling factor is barely correlated with the grain/sub-grain size.The interaction between the plastically deformed zone（PDZ） boundary and the grain/sub-grain boundary is believed to be the reason that leads to an increase of the measured hardness at the specific depths.Results also indicate that the area of the PDZ is barely correlated with the grain/sub-grain size,and the indentation hardness starts to stabilize once the PDZ expands to the dimension of an individual grain/sub-grain.

Elastic-plastic properties of thin film on elastic-plastic substrates characterized by nanoindentation test

To characterize the elastic-plastic properties of thin film materials on elastic-plastic substrates,a simple theory model was proposed,which included three steps:dimensionless analysis,finite element modeling and data fitting.The dimensionless analysis was applied to deriving two preliminary nondimensional relationships of the material properties,and finite element modeling and data fitting were carried out to establish their explicit forms.Numerical indentation tests were carried out to examine the effectiveness of the proposed model and the good agreement shows that the proposed theory model can be applied in practice.

Experimental and finite element analysis for fracture of coating layer of galvannealed steel sheet

Mechanical properties of galvannealed (GA) steel sheet used for automotive exposed panel and predicted failure phenomenon of its coating layer were evaluated using finite element method. V-bending test was performed to understand better the fracture of coating layer of GA steel sheet during plastic deformation. Yield strength of the coating layer was calculated by using a relative difference between hardness of coating layer measured from the nano-indentation test and that of substrate. To measure shearing strength at the interface between substrate and coating layer, shearing test with two specimens attached by an adhesive was carried out. Using the mechanical properties measured, a series of finite element analyses coupled with a failure model was performed. Results reveal that the fracture of coating layer occurs in an irregular manner at the region where compressive deformation is dominant. Meanwhile, a series of vertical cracks perpendicular to material surface are observed at the tensile stressed-region. It is found that 0.26-0.28 of local equivalent plastic strain exists at the coating and substrate at the beginning of failure. The fracture of coating layer depends on ductility of the coating layer considerably as well.

减定径机变速箱档位齿轮内轴承改造

马钢高速线材轧机的减定径机变速箱是2003年从德国西马克引进的,由于设计缺陷,其档位齿轮内轴承使用1个月后,滚动体和滚道就产生塑性压痕,寿命仅为半年。通过改造,大幅提高了轴承的承载能力,改善了轴承的定位方式,取得了良好的效果。

Cross-scale indentation scaling relationships of strain gradient plastic solids:Influence of inclusions near the indenter tip

The indentation test is a localized testing technique;therefore,the role of the material size-effect and local non-uniformity is of much importance.The influence of the heterogeneity in size-independent materials has been studied previously.The present work detailedly investigated the influence of the material size-effect and heterogeneity(inclusions near the indenter tip)on the indentation hardness using a size-dependent strain gradient plastic theory.And it was found that when considering the material size-ffect,shallow hard inclusions in the heterogeneous materials more significantly enhance the material indentation hardness compared with the size-independent materials which are based on the conventional plastic theory.This hardening effect is be-lieved to be related to the elevation of the load and local constraints of large deformation.The effect of material inhomogeneity mainly comes from the non-uniformity of the structure rather than the inclusion modulus itself especially when the size-effect is involved,and the transition range of the inclusion modulus'influence is pretty narrow.The effect of non-uniformity becomes negligible after the initial inclusion depth is larger than its diameter.The horizontal offset of the indenter from the inclusion is also of much sensitivity to the influence of the heterogeneous indentation.This paper focuses on the scaling relationships in micro-and nanoindentation,the influence of non-uniformity in microscopic materials is studied and supplemented as well.

A new method to determine the elastoplastic properties of ductile materials by conical indentation

Based on load-displacement curves,indentation is widely used to extract the elastoplastic properties of materials.It is generally believed that such a measure is non-unique and a full stress-strain curve cannot be obtained using plural sharp and deep spherical indenters.In this paper we show that by introducing an additional dimensionless function of A/A (the ratio of residual area to the area of an indenter profile) in the reverse analysis,the elastoplastic properties of several unknown materials that exhibit visually indistinguishable load-displacement curves can be uniquely determined with a sharp indentation.

Ultrasonic-assisted plastic flow in a Zr-based metallic glass

Ultrasonic vibration can be used for the micro-molding of metallic glasses(MGs)due to stress-softening and fast surface-diffusion effects.However,the structural rearrangement under ultrasonic vibration and its impact on the mechanical response of metallic glasses remain a puzzle.In this work,the plastic flow of the Zr35Ti30Cu8.25Be26.75 metallic glass with the applied ultrasonic-vibration energy of 140 J was investigated by nanoindentation.Both Kelvin and Maxwell-Voigt models have been adopted to analyze the structural evolution during the creep deformation.The increase of the characteristic relaxation time and the peak intensity of relaxation spectra can be found in the sample after ultrasonic vibration.It effectively improves the activation energy of atomic diffusion during the glass transition(Eg)and the growth of the crystal nucleus(Ep).A more homogenous plastic deformation with a weak loading-rate sensitivity of stress exponent is observed in the ultrasonic-vibrated sample,which coincides with the low pile-up and penetration depth as shown in the cross profile of indents.The structural rearrangement under resonance actuation demonstrated in this work might help us better understand the defect-activation mechanism for the plastic flow of amorphous systems.