合金元素Cu对α-Al2O3体结构拉伸强度和断裂性能影响的第一性原理研究

随着粉末冶金技术的发展,金属粉末被广泛用于金属-氧化铝基陶瓷复合材料的制备,具有提高烧结活性、增强增韧的作用。为了从原子尺度研究金属元素对氧化铝陶瓷结构的力学性能影响,采用基于密度泛函理论的第一性原理计算手段,建立合金元素Cu替代α-Al2O3中Al3+的掺杂晶胞模型与纯净α-Al2O3晶胞模型,通过第一性原理计算模拟拉伸试验方法（FPCTT）研究了二者的拉伸变形过程与断裂机制,该方法能够模拟晶胞沿单轴方向的理想拉伸变形过程。借助电荷密度分布图及差分图,Mulliken电荷布居分析等方法,从原子构型与电子结构方面研究了合金元素Cu对陶瓷材料α-Al2O3的影响作用与机理。研究发现：纯净α-Al2O3晶胞在应变为0.18时达到理论拉伸强度（55.51GPa）,并且伴随着Al原子向邻近的O原子层弛豫,具有明显的屈服效应。在合金元素掺杂模型中,由于Cu与O较弱的键合作用,变形过程伴随着Cu-O键的衰弱断裂,杂质体系在应变为0.12时发生断裂,拉伸强度为40.33GPa,其断裂方式为脆性断裂。结果表明：纯净的α-Al2O3结构单向拉伸变形过程伴随着较弱Al-O键的断裂且Al原子向O原子层弛豫,而合金元素Cu的进入基体结构后形成了键能更弱的Cu-O键,并在单向拉伸变形过程中率先断裂,导致体结构的断裂。说明合金元素Cu以原子替代方式进入α-Al2O3体结构中弱化了体结构的粘附性能,导致整体结构拉伸强度的降低。     

改性高水材料尺寸与形状效应研究

高水材料广泛应用于地下采空区充填支护,其形状和尺寸对力学性质影响显著。为了研究不同形状和尺寸改性高水材料的力学性质,借助四川大学ETM力学试验系统,通过对不同尺寸和形状下的改性高水材料的破坏过程、抗压强度和变形特性等性质的测试,系统研究了改性高水材料的尺寸和形状效应。结果表明：改性高水材料是一种弹塑性材料,其变形破坏过程可以分为弹性阶段、屈服阶段、塑形阶段和破坏阶段四个过程;改性高水材料的尺寸仅影响其应力—应变曲线峰值强度,而形状对应力—应变曲线的峰值强度和形状均有较大影响;在一定范围内,随着材料尺寸的增加,圆柱体和立方体试件的抗压强度、弹性模量和变形模量均在一定范围内逐渐减小;在相同条件下,圆柱体试件的抗压强度、弹性模量大于立方体试件,变形模量小于立方体试件。     

Rheological properties of surrounding rock in deep hard rock tunnels and its reasonable support form

Second lining stability, which is the last protection in tunnel engineering, is critically important. The rheological properties of the surrounding rock heavily affect second lining stability. In this work, we used laboratory triaxial compressive rheological limestone tests to study nonlinear creep damage characteristics of surrounding rock mass in construction projects. We established a nonlinear creep damage constitutive model for the rock mass, as well as a constitutive model numerical implementation made by programming. Second, we introduced a new foam concrete with higher compression performance and good ductility and studied its mechanical properties through uniaxial and triaxial tests. This concrete was used as the filling material for the reserved deformation layer between the primary support and second lining. Finally, we proposed a high efficiency and accuracy staged optimization method. The minimum reserved deformation layer thickness was established as the optimization goal, and the presence of plastic strain in the second lining after 100 years of surrounding rock creep was used as an evaluation index. Reserved deformation layer thickness optimization analysis reveals no plastic strain in the second lining when the reserved deformation minimum thickness layer is 28.50 cm. The results show that the new foam concrete used as a reserved deformation layer filling material can absorb creep deformation of surrounding rock mass, reduce second lining deformation that leads to plastic strain, and ensure long-term second lining stability.     

Characterization of plastic flow in two Zr-based bulk metallic glasses

1 Introduction Bulk metallic glasses (BMGs) have attracted a great attention due to their excellent properties, such as high strength, good wear resistance, excellent elasticity and easily forming in viscous state. However, structural applications are currently limited by the lack of macroscopic plasticity at room temperature, characterized by strain-softening which results in the formation of intense localized shear bands. Fracture typically occurs after very small plastic strain in compress…     

Principal shear bands in metal plastic deformation

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Structure realization method for collapse threshold of plastic deformation in train collision condition

To protect passengers, absorb enough kinetic energy and meet the special requirements for trains which are different from the other means of transportation, a method is presented to realize the plastic deformation threshold based on three main aspects of train connection structure, crashworthy vehicle structure, energy-absorbing component. In practical engineering, trains need enough strength and stiffness to transfer longitudinal force under the normal operation condition, and have to produce controllable large plastic deformation to absorb energy shortly under the collision condition. To realize the structural damage threshold of connecting structure in terminal end, two control methods are also proposed which can be divided as the parametric method based on ‘extrusion’ and ‘cutting’ theories; the method which can cut the connecting components between coupler-buffer devices and train bodies and separate them away when the damage thresholds of coupler-buffer devices are more than the pre-supposed damage thresholds. The damage thresholds can be realized based on changing the parameters of the number of shearing bolts, material parameters, etc. To realize the collision threshold of energy-absorbing components of trains, a control method is presented based on the ways of setting plastic deformation induced structure, local hole and pre-deformation structure. To realize the threshold of the controllable plastic structure of energy-absorbing vehicles, a control method is proposed for the multi-level longitudinal stiffness of train terminal structures.     

900 MPa级高强钢应变疲劳行为研究

通过应变控制疲劳试验,对1种900MPa级高强钢的循环软硬化行为、循环应变机制及塑性应变能与循环软化的关系进行研究.结果表明：试样的循环软硬化行为随应变幅增加而发生改变,应变幅低于0.3％时,试样主要发生弹性变形,循环行为表现为循环稳定,应变幅为0.4％时,试样的变形行为由弹性变形为主过渡到塑性变形为主,循环行为由循环稳定过渡为循环软化,应变幅高于0.6％时,试样主要发生塑性变形,循环行为表现为循环软化;试样的塑性应变能密度受应变幅的影响且具有循环相关性,应变幅高于0.6％时,试样的塑性应变能密度较高,但随周次变化较小,应变幅低于0.4％时,试样的塑性应变能密度较小,但随周次变化较大;试样的循环软化率随塑性应变能吸收量的增加而提高.     

Mechanical analysis of temperature impact on stability during superplastic tensile deformation

Based on state equation that stress is the function of strain, strain-rate and temperature, the paper establishes the differential constitutive equation used for analyzing load-stability and the variational constitutive equation used for analyzing geometry-stability during superplastic tensile deformation, which contain strain hardening index, strain-rate sensitivity index, temperature sensitivity index introducted for the first time and temperature undulation index introducted for the first time in the paper. And then, based on the universal condition of plastic elementary theory, the paper analyzes load-stability and geometry-stability under continuously rising temperature and under the non-uniform temperature along the axes of specimen respectively. The results prove the impact of continuously rising speed and non-uniform value of temperature on deformation stability is that the faster temperature rises and the more non-uniform temperature is, the smaller the corresponding uniform strain of load-stability and geometry-stability are; strain hardening index is the necessary condition of stability during superplastic tensile deformation, and geometry-instability will not happen when load-instability occurs, but happen when uniform deformation has lasted after load-instability; in the superplastic temperature field, constant temperature is not necessary condition of superplasticitiy, but during the deformation, the slower temperature rises and the more uniform temperature is, the more stable deformation is.     

分散控制系统的输出能控性

研究了分散控制系统的输出能控性问题，给出该系统输出能控的定义及判别条件。还讨论了输出能控性与固定模等基本概念之间的关系。     

结构弹塑性应力分析的弹性试验模型

材料的塑性表现是弹性表现的延续和发展,二者在物理与力学性质上既有密切的联系,又各有不同．以弹塑性力学的模型理论和塑性力学形变理论的相似方程为基础,根据塑性模型理论以及原型材料的广义应力σi与广义应变εi曲线的关系,提出了以弹性解为原始数据,将其转换为不同塑性变形程度的弹塑性应力分析的弹性试验模型,并讨论了弹性与塑性应力转换的计算方法．     

Plastic deformation behavior of ZK60 magnesium alloy with addition of neodymium

The hot deformation simulation of a ZK60 magnesiuln alloy at different temperatures from 373 to 673 K and different strain rates of 0.1, 0.01 and 0.002 s^-1 was studied by using the Gleebe-1500 simulator. The plastic deformation behavior was measured and the deformation activation energy was calculated. The microstructures of ZK60 magnesium alloy with an addition of neodymium during the deformation process were observed by using Polyvar-MET optical microscope and Tecnai G^2 20 TEM. The results show that the working hardening, the dynamic recovery and the dynamic recrystallization occur during the plastic deformation process at different temperatures and strain rates. The dynamic recrystallization starts when the temperature is over 473 K and the DRX grain size after hot deformation is only 5-10 μm. So the refined grains improve both the tensile strength and the elongation of alloys at room temperature. Neodymium is added into the alloy and a precipitate phase Mg12Nd that impedes the movement of dislocations is formed, which benefits to increasing mechanical properties of ZK60 magnesium alloy.     

地震作用下框架整体与局部损伤的相关性

根据框架结构耗散塑性变形能与存储弹性变形能能力的损失界定结构的整体损伤,根据塑性铰耗散塑性变形能能力的损失来界定局部损伤,并以拟力法为基础推导了局部损伤与整体损伤的解析表达式,进而讨论框架结构局部损伤与整体损伤的相关性。研究表明,控制框架结构整体损伤的手段有：减小局部损伤区域的强度衰减、提高局部损伤区域的极限转动能力和减小局部损伤区域的残余变形。其机理是通过提高局部损伤区域的耗能能力与约束能力来提高整个结构耗散与存储地震能量的能力;框架结构整体损伤与局部损伤的加权值较为接近,可以采用框架局部损伤的加权值来近似估计结构的整体损伤值。     

粘弹塑性土工格栅加筋尾矿流变模型研究

分析土工格栅工程力学特性对加筋尾矿结构变形和长期稳定的影响,基于四参数粘弹塑性模型表征土工格栅长期低应力作用下的力学特性,提出了土工格栅加筋尾矿的流变模型,把加筋复合体受力分析分为两个阶段,分别对应尾矿处于弹性状态和塑性状态,将尾矿产生塑性变形的时间（塑性到达时间）作为两个阶段分界点,并给出了两个阶段的加筋复合体本构关系表达式。研究表明：四参数粘弹塑性模型能够准确反映土工格栅的衰减型蠕变和应力松弛特征;第1阶段,筋材中的应力随时间减小,导致尾矿中的微观应力重新分布,直到尾矿达到屈服条件进入第2阶段,筋材的应力开始保持不变,加筋复合体整体应变由于筋材的蠕变而增加;加筋复合体受力快速由第1阶段过渡到第2阶段,第1阶段变形很小,复合体整体应变主要由第2阶段导致;塑性到达时间受到土工格栅模型参数中Kelvin系数和尾矿强度参数内摩擦角的影响显著。     

Fe对Zr55Al10Ni5Cu30非晶形成能力及力学性能的影响

为了进一步提高锆基大块非晶合金的玻璃形成能力及力学性能,采用铜模吹铸法制备了（Zr0.55Al10Ni0.05Cu0.30）100-xFex（X=1,5,10）系列合金,通过X射线衍射（XRD）、差示扫描量热法（DSC）以及压缩实验和SEM进行材料分析。研究表明：微量Fe有助于改善非晶合金在压缩变形时剪切带内的应力分布,提高材料的综合性能,当Fe添加量为1％时,塑性应变εp达到5．9％,强度达到1．89GPa,同时,随着Fe添加量的增加,过冷温度区间ΔTx减小,热稳定性减小,非晶形成能力降低。     

Adiabatic shear localization evolution for steel based on the Johnson-Cook model and gradient-dependent plasticity

Gradient-dependent plasticity is introduced into the phenomenological Johnson-Cook model to study the effects of strainhardening, strain rate sensitivity, thermal-softening, and microstructure. The microstructural effect （interactions and interplay among microstructures） due to heterogeneity of texture plays an important role in the process of development or evolution of an adiabatic shear band with a certain thickness depending on the grain diameter. The distributed plastic shear strain and deformation in the shear band are derived and depend on the critical plastic shear strain corresponding to the peak flow shear stress, the coordinate or position, the internal length parameter, and the average plastic shear strain or the flow shear stress. The critical plastic shear strain, the distributed plastic shear strain, and deformation in the shear band are numerically predicted for a kind of steel deformed at a constant shear strain rate. Beyond the peak shear stress, the local plastic shear strain in the shear band is highly nonuniform and the local plastic shear deformation in the band is highly nonlinear. Shear localization is more apparent with the increase of the average plastic shear strain. The calculated distributions of the local plastic shear strain and deformation agree with the previous numerical and experimental results.     

Constitutive analysis of AZ31 magnesium alloy plate

The plastic deformation simulation of AZ31 magnesium alloy at different elevated temperatures (from 473 to 723 K) was performed on Gleeble-1500 thermal mechanical simulator at the strain rates of 0.01, 0.1, 1, 5 and 10 s-1 and the maximum deformation degree of 80%. The relationship between the flow stress and deformation temperature as well as strain rate was analyzed. The materials parameters and the apparent activation energy were calculated. The constitutive relationship was established with a Zener-Holl...     

Size effect of deformation nanotwin bundles on their strengthening and toughening in heterogeneous nanostructured Cu

Herein, we fabricated a heterogeneous nanostructured Cu with deformation nanotwin bundles(NTBs) embedded in a matrix of nanograins by means of dynamic plastic deformation at liquid nitrogen temperature. We conducted fracture mechanical measurements to investigate the effect of longitudinal length of the NTBs on their strengthening and toughening. Results suggest that an increase in the NTB length had a marginal influence on the tensile strength; however, it remarkably promoted both fracture initiation toughness and crack growth toughness. Longer NTBs are more effective not only in intrinsically enhancing crack tip plasticity by suppressing the strain localization and void nucleation but also in serving as crack bridges behind the crack front to extrinsically resist the fracture by shielding the crack tip.     

线性切换系统一致能控性和能观性的充要条件

研究线性切换系统的一致能控、能观和能达性.首先给出轨道算子、一致能控状态集和一致能达状态集的概念，然后利用轨道算子、一致能控和一致能达状态集，分别给出了线性切换系统的一致能控、能达和能观性的充要条件.证明了线性切换系统一致完全能控、能达或能观的充要条件是，每一个子系统都是能控、能达或能观的.     

正交切削变形区的力学研究

对正交切削过程的力学边界条件进行合理假设。根据力学边界条件构造金属切削过程塑性变形区的滑移线场和速度场。     

平面塑性变形的剪切变形线

基于平面塑性变形的特点，提出了平面剪切变形线的概念，从而为塑性理论平面问题补充了一个新概念。剪切变形线作为平面塑性变形的一个基本物理特征，使得平面应变问题和平面应力问题的特征理论有了统一的物理解释。