不同拉伸应变率下金纳米线拉伸力学行为的分子动力学模拟

采用分子动力学方法模拟了不同拉伸应变率下金纳米线的拉伸力学行为。模拟结果表明，相同截面尺寸、拉伸温度、拉伸方向的金纳米线在较高的拉伸应变率下，屈服强度较大，屈服发生的较早；更高应变率下的金纳米线在屈服时对应的应变更大，并且更容易发生二次屈服。金纳米线的弹性模量随着拉伸应变率的增大有所增加，但是幅度不是很明显。     

不同拉伸应变率下金纳米线拉伸力学行为的分子动力学模拟

采用分子动力学方法模拟了不同拉伸应变率下金纳米线的拉伸力学行为。模拟结果表明,相同截面尺寸、拉伸温度、拉伸方向的金纳米线在较高的拉伸应变率下,屈服强度较大,屈服发生的较早;更高应变率下的金纳米线在屈服时对应的应变更大,并且更容易发生二次屈服。金纳米线的弹性模量随着拉伸应变率的增大有所增加,但是幅度不是很明显。     

高应变率加载下复合泡沫塑料的吸能特性及失效机理研究

通过SHPB冲击实验装置对空心玻璃微球填充聚氨酯复合泡沫塑料进行了动态压缩实验,获得了不同密度复合泡沫塑料在高应变率加载条件下的应力-应变曲线,研究了材料的动态力学性能。基于所获得的应力-应变曲线,进一步分析和讨论了复合泡沫塑料的能量吸收特性,发现材料最佳吸能点的包络线是同一直线。此外,通过动态变形试件的扫描电镜分析,还研究了这类新材料的动态失效问题。     

聚碳酸酯中应变率压缩力学特性研究

利用高速液压伺服试验机开展聚碳酸酯中应变率压缩实验,同时开展低、高应变率压缩的对比实验,验证了中应变率实验的有效性.基于不同温度下各应变率的压缩真实应力-应变曲线,获得了聚碳酸酯在中应变率压缩下的力学特征.结果表明:聚碳酸酯在中应变率下的压缩经历了弹性形变、屈服、应变软化和应变硬化四个阶段,材料力学行为的应变率和温度相关性表现为:提高应变率或降低温度,压缩屈服强度和屈服应变均增大;反之,升高温度或降低应变率,材料的应变软化更为显著.基于实验结果,构建了可描述聚碳酸酯中应变率压缩过程力学特征的 ZWT 非线性黏弹本构模型,该模型可为透明件结构设计与鸟撞仿真提供有力支撑.     

纯钛高应变率拉伸力学行为的实验研究

利用MTS809材料试验机和旋转盘式间接杆杆型冲击拉伸实验装置,对多晶纯钛进行了室温环境下应变率为0.001,0.01s-1的准静态和300,1400s-1的动态拉伸实验,获得了纯钛等温和绝热拉伸应力-应变曲线;实施了应变率为300s-1的冲击拉伸复元实验,获得了纯钛在高应变率下的等温应力-应变曲线。结果表明:纯钛的拉伸力学行为具有明显的应变硬化效应、应变率强化效应和绝热温升软化效应。采用修正的KHL模型较好地表征了纯钛在准静态和动态实验应变率范围内的拉伸力学行为。     

冲击拉伸下Fe3Al力学性能的应变率相关性研究

利用自行研制的旋转盘式杆杆型冲击拉伸试验装置于Ｆｅ３Ａｌ实施了不同应变率的冲击拉伸试验，获得了不同应变率下的完整的应力应变曲线，结果表明在应变率从８０Ｓ＾－１至１２００Ｓ＾－１范围内，Ｆｅ３Ａｌ存在明显的动态韧性现象及应变率强化效应，其屈服应力，破坏应力以及破坏应变都随应变率的提高而增加，用最小二乘法拟合得到其屈服应力，破坏应力以及失稳应变与应变率的关系，并根据Ｂｏｎｄｎｅｒ－Ｐａｒｔｏｎ的理论建     

不同应变率下Kevlar49纤维束拉伸力学性能的实验研究

利用M TS810材料试验机及旋转盘式杆杆型冲击拉伸试验装置对Kevlar49纤维束进行了准静态拉伸及冲击拉伸实验研究, 首次在应变率为10-4/ s～ 103/s 范围内得到了Kevlar49纤维束完整的应力应变曲线。实验结果表明, Kevlar49纤维束的力学性能是与应变率相关的。在低应变率下Kevlar49纤维束对应变率不太敏感, 但比玻璃纤维束高; 在高应变率下Kevlar49纤维束对应变率敏感, 但不如玻璃纤维束强烈; 中应变率区是Kevlar49纤维束由应变率不太敏感到应变率敏感的过渡区。      

应变控制加载下砼本构关系的试验研究

本文采用应变控制加载方式对砼的应力应变全过程曲线进行试验研究，完成了砼试块在单轴拉伸、单轴压缩、双轴压缩及双轴拉压状态下的全过程曲线测试，克服了荷载控制方式下不能测取其下降段的缺陷。     

关于在应变空间中屈服面与其内部所构成的集合为凸集的证明

本文证明了满足ИЛЪЮШИН塑性公设的材料在应变空间中的屈服面与其内部所构成的集合为凸集，从数学上严格证明了应变空间中屈服面的外凸性及残余应力增量的方向问题，并通过引入凸集概念，为进一步深入研究以变空间中屈服面性状开辟了新途径。     

中低应变率下砂岩动力特性试验研究

为研究岩石在中低速冲击下的动力特性,利用MTS和落锤冲击试验系统进行了红砂岩准静态和动态单轴压缩试验,获得了10-2-101.7 s-1应变率范围砂岩全应力-应变曲线。结果表明,中低应变率加载条件下,砂岩经历典型压密、弹性变形、非稳定裂纹发展至脆性破裂后阶段。随着加载应变率的提高,砂岩峰值应力及其对应应变、残余应变均逐步增加,破坏模式则由X状共轭剪切破坏转变为劈裂破坏;动态强度增长遵循热活化和宏观黏性机制联合作用规律;中低应变率下岩石的吸收总能量和弹性应变能随变形演化规律基本一致,且弹性应变能和较耗散应变能的应变率效应更为显著。     

High strain rate mechanical behavior of epoxy under compressive loading: Experimental and modeling studies

Investigations on high strain rate behavior of epoxy LY 556 under compressive loading are presented. Compressive Split Hopkinson Pressure Bar (SHPB) apparatus was used for the experimental investigations. The studies are presented in the strain rate range of 683-1890 per second. It was generally observed that the compressive strength is enhanced at high strain rate loading compared with that at quasi-static loading. During SHPB testing of the specimens, it was observed that the peak force obtained from the strain gauge mounted on the transmitter bar is lower than the peak force obtained from the strain gauge mounted on the incident bar. Further, an analytical method is presented based on variable rate power law for the prediction of compressive strength at high strain rate loading for epoxy LY 556. Using the analytical method, high strain rate compressive stress-strain behavior is presented up to strain rate of 10,000 per second.     

Texture evolution and dynamic mechanical behavior of cast AZ magnesium alloys under high strain rate compressive loading

In this study, texture and compressive mechanical behavior of three cast magnesium alloys, including AZ31, AZ61 and AZ91, were examined over a range of strain rates between 1000 and 1400 s⁻¹ using Split Hopkinson Pressure Bar. Texture measurements showed that after shock loading, initial weak texture of the cast samples transformed to a relatively strong (00.2) basal texture that can be ascribed to deformation by twinning. Furthermore, increasing the aluminum content in the alloys resulted in increase in the volume fraction of β-Mg₁₇Al₁₂ and Al₄Mn phases, strength and strain hardening but ductility decreased at all strain rates. Besides, it was found for each alloy that the tensile strength and total ductility increased with strain rate. By increasing the strain rate, the maximum value of strain hardening rate occurred at higher strains. Also, it is suggested that a combination of twinning and second phase formation would affect the hardening behavior of the cast AZ magnesium alloys studied in this research.     

Dynamic expansion modeling of a thick-walled cylinder under internal high strain rate loading

This article presents analysis of the dynamic behavior of a thick-walled cylinder under the assumption of nonlinear strain rate hardening behavior under high strain rate loading before any fracture on the surface. The theoretical model applies both to direct and indirect use of dynamic strength of material and instant boundary conditions to establish a differential equation for radial expansion velocity. Further, detailed discussion will be given with emphasis on the main aspects of the cylinder behavior, i.e., radial displacement, internal pressure, strain rate, flow stress, radial and tangential stress, and the influence of the different material rate sensitive exponent.     

中低应变率加载下弱胶结软岩动力学特性

我国西部侏罗系煤层上覆巨厚白垩系富水软岩,为了解此类软岩在冲击荷载作用下的力学本构关系及损伤演化规律,利用Hopkinson压杆装置对干燥、饱和红砂软岩进行中低应变率下的冲击试验,结果表明:红砂软岩峰值应力、峰值应变均表现出明显的应变率效应,其中峰值应力与应变率呈指数关系;相同应变率下,干燥红砂软岩的强度大于饱和状态,对冲击荷载表现出更强的抵抗能力,但饱和红砂软岩的宏观破坏强度大于干燥状态;低应变率加载下,干燥红砂软岩出现负损伤;结合微观机理分析,低应变率下,水对红砂软岩的弱化作用占据主导地位,随着应变率的增大,在惯性效应和水的Stefan效应共同作用下,饱和红砂软岩的动态强度得到强化;基于Z-W-T模型和应变等效原理,建立了服从Weibull分布的损伤本构方程,经验证能很好的反映红砂软岩的动态本构关系,具有一定的工程实际意义。     

中等应变率下泡沫铝的吸能特性

进行了不同密度、高度和压缩方向下泡沫铝的准静态压缩试验和中等应变率下(＜100 s-1)的冲击试验,研究了具有不同密度的闭孔泡沫铝在准静态压缩和冲击工况下的吸能特性.结果表明,泡沫铝是一种近似的各向同性结构,具有较高的单位质量吸能特性,是一种较好的吸能材料.在准静态和中等应变率冲击条件下,泡沫铝对应变率不敏感,其应力应变关系与应变率关系不大.不同的泡沫铝,其平台应力与密度之间的关系不同,在研究其性能时,必须测量应力-应变关系.泡沫铝的致密区对其吸能特性有很大的影响.     

Influence of stress triaxiality and strain rate on the failure behavior of a dual-phase DP780 steel

To better understand the in-service mechanical behavior of advanced high-strength steels, the influence of stress triaxiality and strain rate on the failure behavior of a dual-phase (DP) 780 steel sheet was investigated. Three flat, notched mini-tensile geometries with varying notch severities and initial stress triaxialities of 0.36, 0.45, and 0.74 were considered in the experiments. Miniature specimens were adopted to facilitate high strain rate testing in addition to quasi-static experiments. Tensile tests were conducted at strain rates of 0.001, 0.01, 0.1, 1, 10, and 100 s⁻¹ for all three notched geometries and compared to mini-tensile uniaxial samples. Additional tests at a strain rate of 1500 s⁻¹ were performed using a tensile split Hopkinson bar apparatus. The results showed that the stress–strain response of the DP780 steel exhibited mainly positive strain rate sensitivity for all geometries, with mild negative strain rate sensitivity up to 0.1 s⁻¹ for the uniaxial specimens. The strain at failure was observed to decrease with strain rate at low strain rates of 0.001–0.1 s⁻¹; however, it increased by 26% for an increase in strain rate from 0.1 to 1500 s⁻¹ for the uniaxial condition. Initial triaxiality was found to have a significant negative impact on true failure strain with a decrease of 32% at the highest triaxiality compared to the uniaxial condition at a strain rate of 0.001 s⁻¹. High resolution scanning electron microscopy images of the failure surfaces revealed a dimpled surface while optical micrographs revealed shearing through the thickness indicating failure occurred via ductile-shear. Finite element simulations of the tests were used to predict the effective plastic strain versus triaxiality history within the deforming specimens. These predictions were combined with the measured conditions at the onset of failure in order to construct limit strain versus triaxiality failure criteria.     

动载下胶结充填体的力学特性试验研究

胶结充填体的稳定性对于矿山安全生产至关重要。为了研究动载作用下充填体的动力学特性,利用霍普金森压杆(SHPB)对充填体进行单轴冲击试验,研究充填体应力应变曲线、动态抗压强度、动态强度增长因子与平均应变率之间的关系。结果表明,当平均应变率低于60 s^(-1)时,应力应变曲线峰后阶段为"应变回弹"类型;超过80 s(-1)时,应力应变曲线峰后阶段为"应变回弹"类型;超过80 s^(-1)时,为"峰后塑性"类型;介于二者之间时,为"应力跌落"类型;随着平均应变率的增大,试样动态抗压强度先迅速增大,后趋于稳定,对应的平均应变率临界值为80 s(-1)时,为"峰后塑性"类型;介于二者之间时,为"应力跌落"类型;随着平均应变率的增大,试样动态抗压强度先迅速增大,后趋于稳定,对应的平均应变率临界值为80 s^(-1)。利用Gompertz模型能较好的描述充填体动态抗压强度与平均应变率之间的关系;动态强度增长因子与平均应变率正相关,当平均应变率处于40～130 s(-1)。利用Gompertz模型能较好的描述充填体动态抗压强度与平均应变率之间的关系;动态强度增长因子与平均应变率正相关,当平均应变率处于40～130 s^(-1),动态强度增长因子范围在1.5～3之间。     

中低应变率下闭孔泡沫铝动态力学性能研究

为探索闭孔泡沫铝的动态力学性能与吸能特性,基于万能材料试验机和高速液压伺服材料试验机在常温下分别对闭孔泡沫铝在准静态和中应变率下(0.001~100s^-1)的动态力学性能进行了测试,分析了不同应变率、不同相对密度和不同泡沫铝基体特性下闭孔泡沫铝的应力应变曲线特征和吸能特性变化。研究结果表明:中低应变率下的纯铝基体泡沫铝并不具备应变率效应,高脆性、相对密度较小的泡沫铝具备更好的吸能特性,塑性和脆性基体泡沫铝变形带分别呈现“V”形和“X”形,脆性基体泡沫铝同样不具备应变率效应。