单丸粒撞击金属靶材的有限元分析

本文应用商用有限元软件ABAQUS对单个丸粒撞击金属靶材进行了三维有限元分析,建立模拟弹丸撞击靶材的有限元模型。首先将单个丸粒撞击靶材产生残余应力的模拟结果与Meguid等人用ANSYS软件所模拟的结果进行对比,从而来验证本文模拟结果的可靠性。然后本文系统地研究了不同弹丸参数对于残余应力场分布规律的影响。模拟结果表明,弹丸参数对于喷丸残余应力场分布规律的影响各不相同。但是,无论这些参数如何变化,靶材次表层的最大残余压应力值所处的位置基本保持不变,始终位于靶材表面以下25%dshot处。根据有限元模拟的结果,可对喷丸强化工艺参数进行优化控制,提高喷丸强化的加工工艺水平,以实现更好的喷丸效果。     

喷丸过程中的能量转化及残余应力分布研究

本文建立了喷丸表面强化过程的三维有限元模型,研究了靶材的力学性能及弹丸喷射速度对能量转化率和残余应力分布的影响规律。通过对有限元计算结果的分析发现,杨氏模量与屈服强度之比E/&;#61555;y较大,应变硬化率较低的靶材喷丸效率较高。屈服强度的提高使得最大残余压应力变大,残余压应力场深度变小。应变硬化率和喷丸速度的提高均会使最大残余压应力及其深度变大,同时会使表面残余压应力减小并向拉应力转变。本文的研究结果从能量转化的角度为喷丸强化件材料的选择提供了理论基础     

湿法喷丸工艺有限元分析

目的 分析TC4钛合金的湿喷丸强化过程。方法 利用ABAQUS有限元软件中的CEL方法以及随机分布函数建立弹丸随机分布的湿喷丸冲击强化模型,研究喷丸覆盖率对残余应力场和表面粗糙度的影响规律,进行TC4钛合金板材的湿喷丸强化实验,对比验证模拟结果。结果 表面粗糙度随着喷丸覆盖率的增加而变大;对于残余应力场,随着覆盖率从50%增加到100%,最大残余压应力值和其所处位置的深度均增加。当覆盖率增加至200%,最大残余压应力值不再增加。不同喷丸覆盖率下表面残余应力值基本相同。经对比验证,构建的有限元模型的仿真结果与湿喷丸实验规律相一致。结论 湿喷丸模型能够较好地模拟湿喷丸强化后板材表层残余压应力场和表面粗糙度的变化规律。     

300M钢多弹丸喷丸强化的有限元模拟

过去,结合喷丸气压和弹丸动能进行数值模拟研究喷丸强化效果的报道不多。采用ABAQUS/Explicit有限元软件对300M钢喷丸强化过程进行数值模拟,在喷丸气压和动能相等的条件下,通过改变弹丸直径确定不同工艺参数对金属靶材进行喷丸处理,对比分析了金属靶材表面残余应力场变化曲线、表面法向位移变化曲线以及表面等效塑性应变。结果表明:不同的喷丸工艺下均可使金属靶材表面获得一定深度的残余压应力场,靶材表面的能残余压应力场强度随弹丸直径增加而增加;对靶材金属施加相同弹丸动能输入时,不同喷丸工艺喷丸效果差距不明显,这为相同喷丸强化要求条件下选取不同喷丸工艺参数提供了理论依据。     

喷丸强度对不同粗糙度表面超高强度钢疲劳性能的影响

不同方式加工的高强度钢零件具有不同的表面状态,对其采用相同的喷丸工艺是否合理尚不明确。对不同表面粗糙度23Co14Ni12Cr3Mo E超高强度钢作不同强度的喷丸强化。采用扫描电镜及白光干涉仪观察了喷丸试样的表面形貌,采用金相显微镜观察喷丸试样的表面组织,采用旋弯疲劳试验机测试了喷丸试样的疲劳性能,采用X射线衍射残余应力测试仪测试喷丸试样的残余应力。研究了喷丸强度对不同表面粗糙度超高强度钢的表面组织、形貌、残余应力场及疲劳性能的影响。结果表明:喷丸过程可以细化表面组织,引入残余压应力场,改变表面形貌特征,从而引起表面应力集中状况的改变,其改善效果与原始表面状态有关;对于初始表面粗糙度Ra≤0.4μm的表面,喷丸强化过程能有效提高材料的疲劳寿命,促使疲劳裂纹源内移;随表面粗糙度的提高,当应力集中状况过于严重时,表面组织细化和残余压应力对疲劳性能的提升作用会被抑制,喷丸工艺对疲劳寿命的提升效果大幅下降,疲劳裂纹源均位于表面。     

喷丸强化对OCr13Ni8Mo2Al钢疲劳性能的影响

研究了表面喷丸强化后表面残余应力、表面粗糙度和表面层残余压应力场对0Cr13Ni8Mo2Al钢疲劳性能的影响.结果表明:0Cr13Ni8Mo2Al钢经喷丸强化后,在表面层残余压应力场的作用下疲劳裂纹源由表面被"驱赶"到表面强化层下,疲劳寿命得到显著提高.     

喷丸强化对0Cr13Ni8Mo2Al钢疲劳性能的影响

研究了表面喷丸强化后表面残余应力,表面粗糙度和表面层残余应力场对0Cr13Ni8Mo2Al钢疲劳性能的影响,结果表明：0Cr13Ni8Mo2Al钢经喷丸强化后,在表面层残余应力场的作用下疲劳裂纹源由表面被“驱赶”到表面强化层下,疲劳寿命得到显著提高。     

42CrMo曲轴钢喷丸强化有限元模拟

喷丸强化能够有效提高42CrMo曲轴钢的抗疲劳性能,且喷丸数值模拟是制定喷丸工艺方案、评估喷丸后工件表面疲劳抗力的主要理论工具。为了体现喷丸过程中的随机性,利用MATLAB软件提供的Rand随机函数产生弹丸的位置,建立随机喷丸模型,并在此模型基础上研究弹丸直径、弹丸材料、冲击速度以及覆盖率与残余应力间的分布规律,进一步讨论喷丸工艺对42CrMo曲轴钢表面粗糙度的影响。研究发现:随着弹丸直径以及速度的增大,残余应力增大,抗疲劳性能提高,但粗糙度也相应增大;随着覆盖率的增大,残余应力增大,表面残余应力分布更加均匀,稳定性提高;同时弹丸强度越高,残余应力越大。通过喷丸试验对随机多弹丸模型进行验证,为喷丸工艺的精确控制提供了科学依据和理论基础。     

喷丸强化对20CrMoH渗碳齿轮表层组织和性能的影响

利用主减速齿轮20CrMoH渗碳淬火材料进行强力喷丸试验,结合蔡司光学显微镜、显微硬度计、TimeSurf粗糙度仪和X射线应力分析仪对喷丸后齿轮材料的性能进行了分析,系统地研究了喷丸强化对齿轮显微组织、硬度、表面粗糙度和齿轮表面及不同层深残余应力的影响规律,对比了复合喷丸与单一喷丸的强化效果。结果表明:喷丸强化能够显著细化表面和微区的晶粒组织,提高材料的表面硬度和表面及微区的残余压应力,降低齿轮表面粗糙度;复合喷丸的强化作用要显著大于单一强化喷丸。     

复合喷丸对铝-铜-镁合金表面形貌和硬度的影响

对铝-铜-镁合金试样进行复合喷丸处理,通过观察喷丸处理后试样的表面形貌和测量试样的表面粗糙度、残余应力、衍射峰半峰宽及显微硬度等参数,分析了复合喷丸处理对铝-铜-镁合金表面形貌和力学性能的影响。结果表明:铝-铜-镁合金试样经复合喷丸处理后表面粗糙度变化不大,由0.70μm增加到2.97μm,试样表面整体细密、均匀,完整性较高,表面质量较好;引入较深的残余压应力场,最大残余压应力为306 MPa,且压应力场整体分布均匀,能够起到很好的强化效果;表面衍射半峰宽增大,为0.275°;表面显微硬度增大,为180.8 HV,比基体的硬度120 HV增加了50%。     

Comparison of the Consequences of Shot Peening Treatment Methods on the Surface Layer Characteristics of Ti6246

Shot peening, as a technique to enhance the surface characteristics of rotating parts in aircraft engines is well known as a way to prevent the initiation and propagation of cracks. However, shot peening generally increases the surface roughness and therefore, reduces aerodynamic efficiency on aerofoil. This paper aims to compare different shot peening procedures as regards roughness, hardness, residual stress magnitude and depth in Ti6246, in order to identify a method, which leads to the required mechanical properties, but keeps the increase of surface roughness to a minimum. Therefore, Ti6246 specimens, processed similarly to integral bladed compressor disks, are treated with defined target intensity and coverage. The changes in surface roughness, residual stress, and hardness are measured and discussed.     

Mechanism modelling of shot peening effect on fatigue life prediction

A new mechanism modelling is proposed in this paper to explain the shot peening effect on fatigue life predictions of mechanical components. The proposed methodology is based on the crack growth analysis of shot peened specimens, which are affected by the interaction of surface roughness and residual stress produced during the shot peening process. An asymptotic stress intensity factor solution is used to include the surface roughness effect and a time‐varying residual stress function is used to change the crack tip stress ratio during the crack propagation. Parametric studies are performed to investigate the effects of surface roughness and the residual stress relaxation rate. Following this, a simplified effective residual stress model is proposed based on the developed mechanism modelling. A wide range of experimental data is used to validate the proposed mechanism modelling. Very good agreement is observed between experimental data and model predictions.     

High- and very high-cycle plain fatigue resistance of shot peened high-strength aluminum alloys: The role of surface morphology

The present paper is aimed at investigating the effect of shot peening on the high and very-high cycle plain fatigue resistance of the Al-7075-T651 alloy. Pulsating bending fatigue tests (R = 0.05) were carried out on smooth samples exploring fatigue lives comprised between 10⁵ and 10⁸ cycles. Three peening treatments were considered to explore different initial residual stress profiles and surface microstructural conditions. An extensive analysis of the residual stress field was carried out by measuring with the X-ray diffraction (XRD) technique the residual stress profile before and at the end of the fatigue tests. Fatigue crack initiation sites were investigated through scanning electron microscopy (SEM) fractography. The surface morphology modifications induced by shot peening were evaluated using an optical profilometer. The influence of surface finishing on the fatigue resistance was quantified by eliminating the surface roughness in some peened specimens through a tribofinishing treatment. The capability of shot peening to hinder the initiation and to retard the subsequent propagation of surface cracks is discussed on the basis of a model combining a multiaxial fatigue criterion and a fracture mechanics approach.     

Influence of surface integrity on fatigue strength of 40CrNi2Si2MoVA steel

Influence of surface integrity (including surface roughness, residual stresses, and microstructure in surface) on fatigue limit of 40CrNi2Si2MoVA steel specimens is investigated comprehensively in this work according to a systematic consideration. The surface integrity of specimens is changed due to several widely used manufacturing procedures: heat-treatment, grinding, electro-polishing, hard chromium plating and shot peening. In comparison with specimen electro-polished after grinding, the specimen without polishing has 10% lower fatigue limit due to higher surface roughness; while shot peening improves the fatigue limit for about 36% due to inducing of compressive residual stress field in the surface and transferring the fatigue crack source from surface to interior. The fatigue limit of specimen with decarburized layer after grinding is lower about 13%, but the shot peening can eliminate its detrimental effect. Hard chromium plating decreases the fatigue limit dramatically. The shot peening carried before plating can improve the fatigue limit of specimen and cause it to get to a level even higher than that of specimen without plating.     

Effects of shot peening on fatigue properties of 0Cr13Ni8Mo2Al steel

Abstract

The influence of shot peening on the fatigue properties of 0Cr13Ni8Mo2Al steel has been studied. Changes in surface roughness, surface topography and residual compressive stress field were determined by experiments. The experimental results show that shot peening improves the fatigue property and the fatigue crack sources are pushed to the region beneath the hardened layer. Low Almen intensities should be used when 0Cr13Ni8Mo2Al steel is shot peened because of its sensitiveness to the surface roughness.     

Experimental results in fretting fatigue with shot and laser peened Al 7075-T651 specimens

This work focuses on determining the effect of shot and laser peening on fretting fatigue in the Al 7075-T651 alloy. These surface treatments generate a residual compressive stress field near the treated surface where contact under fretting fatigue produces high stress levels. The fretting fatigue resistance of shot and laser peened specimens was assessed in a series of tests involving measurements of the residual stress field, residual stress relaxation under the action of cyclic loads, the friction coefficient, surface roughness and material hardness. The obtained results are compared with those for untreated specimens. The tests show the beneficial effect of the compressive residual stresses and the improvement that surface roughness causes in fretting fatigue life, especially in shot peened specimens. Another important effect observed, is the partial residual stress relaxation produced during the fretting fatigue tests.     

Improvement of spring fatigue strength by new warm stress double shot peening process

Abstract

Shot peening technology plays a very important role in improving the fatigue strength of springs. In the present paper a new warm stress double shot peening (WSDSP) process developed by the authors is described. The authors have previously proposed a warm stress shot peening (WSSP) process, which is a combination of warm shot peening (WSP) and stress shot peening (SSP). Double shot peening (DSP) has been the method employed most widely for improved fatigue strength to date. The fatigue strengths resulting from these shot peening processes are compared in the present work. The new WSDSP process leads to significant improvement of spring fatigue strength because it includes an additional shot peening stage with small shot size (0.2 mm dia.), elevated temperature (300°C), and stressed condition (735 MPa), all not found in WSSP. After 300 000 cycles, the standard required life span, WSDSP results in a fatigue strength as high as 735 ± 590 MPa. In comparison, DSP gives a fatigue strength of 735 ± 300 MPa and WSSP of 735 ± 500 MPa. The WSDSP treated material gives the highest performance because the use of small shot size for the additional warm stress shot peening increases the compressive residual stress and hardness near the surface, and decreases the surface roughness.