共查询到19条相似文献,搜索用时 140 毫秒
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金属材料与结构的疲劳失效被视为工程领域的“癌症”,是微观结构逐渐劣化的结果,因此从微观角度准确预测材料与结构的疲劳裂纹萌生就显得极为必要与迫切。基于晶体塑性有限元的疲劳指示因子(Fatigue indicator parameters, FIP)能从微观角度较好地表征剪应变主导的疲劳裂纹驱动力,目前已经形成了累积塑性滑移类、应变能耗散类与多轴疲劳寿命预测准则改进的FIP等。累积塑性滑移类FIP是基于位错滑移与应力集中理论所建立,多个应用案例也表明能较好地描述疲劳驻留滑移带与三叉晶界应力集中等现象,具有形式简单、参数少等优点;应变能耗散类FIP是基于能量理论,不区分载荷模式与裂纹扩展优先方向,在高应变幅或复杂载荷状况下较累积塑性滑移类FIP更可靠;多轴疲劳寿命预测准则改进的FIP主要有基于Fatemi-Socie准则、Dang Van准则与Tanaka-Mura准则等修正的FIP,虽工程应用广泛,但是由于经验模型需要大量试验确定参数且临界平面与位错滑移平面的关系不明。为此,指出研究多轴疲劳损伤的临界平面与晶体塑性的滑移平面的物理一致性、以晶粒旋转数据直接构建晶体塑性FIP模型以及采用模糊... 相似文献
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为探究TWIP钢高温条件下的塑性变形机理,建立了耦合温度效应的晶体塑性本构模型,考虑温度对TWIP钢滑移和孪生的影响,提出了耦合温度效应的流动法则和硬化法则。结合在500 ℃和750 ℃条件下的原位SEM高温拉伸试验,建立了描述TWIP钢热变形过程的晶体塑性有限元模型。模拟获得不同温度条件下的应力应变曲线、应变硬化率和孪晶体积分数与试验结果相吻合,验证了该模型的正确性。进而,基于所建立的模型研究了温度对TWIP钢塑性变形过程滑移、孪生演化及应变硬化过程的影响规律,结果表明:滑移阻力、孪生阻力和应变硬化率随温度的升高呈不均匀降低的趋势,且断后伸长率呈现降低的趋势,由25 ℃时53.4%降低至750 ℃时16.5%。同时,随温度升高,孪生受到抑制,但滑移受温度的影响较小,表现为滑移主导的塑性变形机制。 相似文献
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《机电工程》2015,(9)
针对纳米晶材料拥有较高强度但是塑性较低的问题,对高塑性的纳米晶材料进行了归纳,对高强度高塑性的梯度纳米晶材料的微观结构和变形机制进行了研究。提出了一个基于晶粒尺寸和晶界取向角的新理论模型讨论晶粒大小为20 nm~300 nm的梯度纳米晶结构的变形机制。研究了晶界滑移过程中晶界上位错的堆积情况,描述了晶界滑移和晶界迁移的能量特征。根据晶粒大小和晶界取向角这两个参数,通过能量法计算并定量分析了晶界滑移与晶界迁移能量特征之间的关系。研究结果表明,在梯度纳米晶材料中存在两种主要变形机制,相互竞争的两种变形机制最终导致梯度纳米晶材料不仅强度高而且韧性好;晶粒尺寸小于170 nm时主导变形机制为晶界迁移,大于170 nm时主导变形机制变为晶界滑移。 相似文献
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通过分子动力学模拟、黏塑性本构模型和纳米压痕试验验证相结合的研究方法,系统研究了双峰结构(晶粒尺寸服从统计学中双峰分布)纳米晶铜的变形机理与力学性能。结果表明:在塑性变形过程中位错首先在纳米晶铜的细晶区形核和扩展,且方向互相平行;而粗晶区的位错滑移方向相互交叉,且粗晶尺寸越大,越容易发生位错缠绕和交滑移。双峰结构纳米晶铜的流变应力随着粗晶尺寸的增大而增大,硬度随着粗晶体积分数的增大而减小。由黏塑性本构方程计算得到的应力变化规律与由经验公式和分子动力学模拟得到的结果一致,且本构方程计算得到的流变应力和经验公式所得结果的相对误差小于5%。 相似文献
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《机械强度》2013,(6):760-765
通过对不同钢种(优质碳素结构钢S550、高韧性合金结构钢SCM3、高碳铬轴承钢SUJ2、碳素工具钢SK3)的试件材料进行淬火回火等热处理,制备一定硬度范围(HV340HV860)的高低不同硬度的试件,以此试件作为夏比冲击试验的研究对象。试验的整个过程是在确定冲击载荷测定试验方法的基础上,通过各种不同变形速度的试验,测得不同硬度试件的应力-应变关系曲线,从而测得不同材料的动强度,建立和确认动强度与硬度之间的关系。同时讨论了冲击载荷及其能量吸收的硬度依存性。结果表明,虽然随钢种不同有所差异,但在塑性应变率为100 s-1左右时的动强度大致高出静强度20%HV860)的高低不同硬度的试件,以此试件作为夏比冲击试验的研究对象。试验的整个过程是在确定冲击载荷测定试验方法的基础上,通过各种不同变形速度的试验,测得不同硬度试件的应力-应变关系曲线,从而测得不同材料的动强度,建立和确认动强度与硬度之间的关系。同时讨论了冲击载荷及其能量吸收的硬度依存性。结果表明,虽然随钢种不同有所差异,但在塑性应变率为100 s-1左右时的动强度大致高出静强度20%30%左右;虽然强度随着硬度的增加而增加,但硬度在HV700左右时取最大值;能量吸收的硬度依存性基本以最大弯曲载荷P max对应的硬度域为界,硬度越高能量吸收越少;尤其以SUJ2材料的能量吸收为最大。 相似文献
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通过单次压痕试验与有限元模拟相结合的方法,结合反向分析方法与模拟退火粒子群算法,从获得的载荷-深度曲线加载部分提取材料的塑性参数,基于Ludwig硬化模型预测了不同金属材料的强度,并与单轴拉伸试验结果进行对比。结果表明:模拟得到的载荷-深度曲线与试验得到的几乎重合,二者的相对误差小于0.5%,说明模拟退火粒子群算法可有效地从压痕载荷-深度曲线中提取出金属材料的塑性参数;基于Ludwig硬化模型,利用反向分析方法从压痕载荷-深度曲线中提取的真应力-真塑性应变曲线不是唯一的,但从真应力-真塑性应变曲线计算得到的强度具有明显的收敛趋势;采用压痕试验得到不同金属材料的强度均接近于由拉伸试验得到的,屈服强度与抗拉强度的最大相对误差分别为5.9%,4.3%,说明采用压痕试验法可以准确地评价金属材料的强度。 相似文献
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I.N. Mastorakos N. Abdolrahim H.M. Zbib 《International Journal of Mechanical Sciences》2010,52(2):295-1187
Using molecular dynamics simulations, the deformation behavior of two types of nanocomposite metallic materials (nano-layered thin films and composite nanowires) is investigated and compared with that of the bulk materials. The first structure is a hybrid nano-layered metallic composite formed by alternating layers of Cu, Ni, Cu, and Nb layers. The nanocomposite has a pre-existing dislocation structure inside it, generated by initially loading a perfect structure to a high strain to nucleate dislocations, then completely unloading it, and loading it again. Four different structures are considered all having the same Cu and Ni layers thickness and varying Nb thickness. Comparison of the deformation behavior between the different structures revealed that the addition of Nb layer makes the material stronger. However, this behavior has a critical limit below which the strength of the material decreases. This is attributed to the extended shearing of the interface that results from the accumulation of dislocations in the Cu/Nb interface. The second structure discussed is a composite nanowire made of a Ni layer sandwiched between two Cu layers. We show that the natural development of coherency stresses at the interfaces between the two layers increases the ability of the wire to deform by a twinning process under tensile loading. This process results in the reorientation of the composite nanowire that, under unloading, forces the nanowire to completely recover the straining, leading to a pronounced pseudoelastic behavior. 相似文献
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对新型汽轮机焊接转子材料25Cr2Ni2MoV焊接接头及其母材进行应变控制的低周疲劳试验,并进行了相应的断裂位置统计和循环变形特征分析。试验结果表明,焊接削弱了焊接接头的疲劳强度,受到结构非均匀性和各部分力学性能的相对不匹配等因素的影响,焊接接头的断裂位置体现出明显的应变水平依赖性;焊接接头和母材在循环变形过程中均表现出循环软化特性,且存在明显的拉压不对称性,拉压不对称程度随应变水平的增加而增加;与母材相比,焊接接头表现出更加明显的平均应力松弛现象,且平均应力绝对值随着循环周次不断减小最后趋于常值。 相似文献
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Ki Nam Kim Hye Won Kim Gyeong Su Shin Myung Chul Park Jun Ki Kim Seon Jin Kim 《Tribology Letters》2012,48(3):417-424
The effects of Ni and Mn concentrations and also the impact velocity on the solid particle erosion behavior of Fe?C12Cr?C0.4C?CxNi/Mn (x?=?5 and 10) alloys were investigated with respect to strain-induced martensitic transformation. The critical strain energy (CSE), which is defined as the energy required to initiate the martensitic transformation increased with increasing Ni and Mn concentrations. As the impact velocity decreased, the solid particle erosion resistance of the low CSE alloy improved compared to that of the high CSE alloy under the given ranges of impingement angles and impact velocities. This result was most likely due to an increase in the volume fraction of martensite that formed during the solid particle erosion test in the low CSE alloy when the impact velocity was decreased. 相似文献
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本文研究了超载对300M超高强度钢冲击疲劳裂纹起始寿命的影响。结果表明,在一定范围内,拉伸超载可以延长冲击疲劳裂纹起始寿命;超载造成的残余应力是引起该钢超载效应的主要机制而超载造成的材料性能变化对超载效应的贡献不大;超载后冲击疲劳裂纹起始寿命Ni与缺口根部残余应变εR之间的关系可表示为:NI=N0·exp(λεR)。 相似文献
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A. Abdul-Latif G.F. Dirras S. Ramtani A. Hocini 《International Journal of Mechanical Sciences》2009,51(11-12):797-806
A novel experimental methodology to produce ultrafine-grained metallic microstructures, which is applied on aluminum is proposed in this work. In fact, the ultrafine-grained aluminum polycrystal is made from commercial purity powder by a combination of hot isostatic pressing (HIP) and dynamic severe plastic deformation (DSPD). After the first step, the bulk consolidated material showed a random texture and homogeneous microstructure of equiaxed grains with an average size of 2 μm. The material is then subsequently impacted, using a falling weight at a maximum impact velocity of 9.2 m/sec. The resulting material shows a microstructure having an average grain size of about 500 nm with a strong gradient of fiber-like crystallographic texture perpendicular to the impact direction. The mechanical properties of the impacted material are then characterized under compression tests at room temperature under a strain rate of 10?4 s?1. The effect of the change of the deformation path on the mechanical response parallel and perpendicular to the impact direction is also investigated. These results are discussed in relation with microstructure. Further, a new extension of a micromechanical approach developed by Abdul-Latif et al., [2] is proposed to predict the grain size effect on the enhancement of the mechanical strength of polycrystals. Within the framework of small strain hypothesis, the elastic anisotropy of the grain and grain rotation are neglected for the sake of simplicity. The local inelastic deformation heterogeneity is determined through the slip theory. It is assumed that the yield strength increases linearly with decreasing grain size as in Hall–Petch relationship. It is obviously recognized that the model with its new extension describes fairly well the effect of the grain size on the strain–stress behavior of the sub-micrometer aluminum. 相似文献
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In the present study the sliding wear behavior of pulse electrodeposited nanocrystalline Ni coatings as a function of grain size including bulk annealed Ni has been systematically studied using pin-on-disc configuration against the WC-Co counter body. The sliding wear has been analyzed with respect to wear rate, coefficient of friction, subsurface deformation and composition of wear debris. The result indicates that the sliding wear rate and coefficient of friction of Ni decreases with decreasing grain size. The subsurface beneath the worn pin surface is composed of a near surface shear region and beneath it a region of bulk plastic deformation. The ratio of the depth of the shear region to the depth of bulk deformed region decreases with decreasing grain size indicating a greater localization of near surface deformation with decreasing grain size. 相似文献
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分别采用静态拉伸试验机和冲击拉伸试验机测定了AM60压铸镁合金在不同应变率下(0.000 1,0.01,300和1 400 S-1)的拉伸力学性能,重点分析了高应变率对合金力学性能的影响,并用扫描电镜(SEM)对拉伸断口进行了分析.结果表明:在应变率很低和很高时,合金的屈服强度、抗拉强度随着应变率的增加变化不大;从静态和动态(高应变率)结果综合比较来看,应变率对强度和断后伸长率有一定的影响,而弹性模量则对应变率不敏感;另外,动态和静态的断裂方式基本相同,都是以准解理断裂为主,局部区域呈沿晶断裂,局部区域存在典型的缩松断裂形貌. 相似文献
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在阻尼性能最佳的Fe-17Mn二元合金中加入质量分数5%铬元素以及1%的铝、钛或镍,采用真空感应熔炼法制备Fe-17Mn,Fe-17Mn-5Cr,Fe-17Mn-5Cr-1Al,Fe-17Mn-5Cr-1Ti和Fe-17Mn-5Cr-1Ni合金,经锻造和固溶处理后,研究了铬、铝、钛、镍元素对合金阻尼性能、力学性能和耐腐蚀性能的影响。结果表明:添加铬元素后,合金强度显著提高,耐腐蚀性能增强,在较低应变振幅(200×10-6~900×10-6)下的阻尼性能提高,在高应变振幅(大于900×10-6)下的阻尼性能降低;在Fe-17Mn-5Cr合金中添加质量分数1%的铝元素或钛元素后,合金的耐腐蚀性能变化不大,强度降低,其中添加钛后的阻尼性能变差,添加铝后的阻尼性能变化不大;在Fe-17Mn-5Cr合金中添加质量分数1%镍元素后,合金的强度和阻尼性能变化不大,耐腐蚀性能略有降低,但仍优于Fe-17Mn合金的;Fe-17Mn-5Cr-1Ni合金的综合性能最优异。 相似文献
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通过分离式霍普金森压杆(SHPB)动态压缩试验研究了体积分数为45%的铝基碳化硅颗粒增强复合材料(SiCp/2024Al)在大应变率和变形温度范围内的热变形行为,分析了热变形参数(变形温度和应变率)对流动应力的影响。研究发现:变形温度和应变率对复合材料的流变应力、抗压强度、弹性模量、应变率敏感性有显著影响;抗压强度、弹性模量随变形温度的增大而减小,而抗压强度、弹性模量、应变率敏感性随应变率的增大出现了拐点。根据试验结果,结合热力学和统计损伤力学理论,建立了描述SiCp/2024Al复合材料动态热变形行为的连续损伤本构模型,预测的流动应力与试验结果吻合较好,表明所建立的模型能够准确地描述SiCp/2024Al复合材料动态热变形行为。 相似文献