Effect of strain rate on the dynamic compressive mechanical behaviors of rock material subjected to high temperatures

Strain rate is not only an important measure to characterize the deformation property, but also an important parameter to analyze the dynamic mechanical properties of rock materials. In this paper, by using the SHPB test system improved with high temperature device, the dynamic compressive tests of sandstone at seven temperatures in the range of room temperature to 1000 °C and five impact velocities in the range of 11.0–15.0 m/s were conducted. Investigations were carried out on the influences of strain rate on dynamic compressive mechanical behaviors of sandstone. The results of the study indicate that the enhancement effects of strain rates on dynamic compressive strength, peak strain, energy absorption ratio of sandstone under high temperatures still exist. However, the increase ratios of dynamic compressive strength, peak strain, and energy absorption ratio of rock under high temperature compared to room temperature have no obvious strain rate effects. The temperatures at which the strain rates affect dynamic compressive strength and peak strain most, are 800, and 1000 °C, respectively. The temperatures at which the strain rates affect dynamic compressive strength and peak strain weakest, are 1000 °C, and room temperature, respectively. At 200 and 800 °C, the strain rate effect on energy absorption ratio are most significant, while at 1000 °C, it is weakest. There are no obvious strain rate effects on elastic modulus and increase ratio of elastic modulus under high temperatures. According to test results, the relationship formula of strain rate with high temperature and impact load was derived by internalizing fitting parameters. Compared with the strain rate effect at room temperature condition, essential differences have occurred in the strain rate effect of rock material under the influence of high temperature.     

应变率对硫化橡胶压缩力学性能的影响

利用分离式霍普金森压杆(SHPB)和材料实验机MTS810对硫化橡胶进行动态和准静态单轴压缩实验,获得硫化橡胶的应力-应变响应曲线,研究了应变率对其压缩力学性能的影响。实验结果表明,硫化橡胶在低应变率时的应变率效应不明显,然而在较高应变率时,应变率对其动态应力-应变关系有明显的影响,弹性模量、屈服应力以及流动应力都随应变率的增大而增大。采用基于应变能函数理论的橡胶本构模型来描述硫化橡胶压缩荷载下的力学行为。数值模拟了硫化橡胶的应力-应变历程,并与实验数据进行比较,结果显示两者吻合良好。     

Effect of strain rate on tensile behavior of carbon fiber reinforced aluminum laminates

In this paper, the tensile behavior of carbon fiber reinforced aluminum laminates (CRALL) has been determined at a strain rate range from 0.001 s^− 1 to 1200 s^− 1. Experimental results show that CRALL composite is a strain rate sensitive material, and the tensile strength and failure strain both increased with increasing strain rate. A linear strain hardening model has been combined with Weibull distribution function to establish a constitutive equation for CRALL at different strain rates. The analysis of the model shows that the Weibull scale parameter, σ₀, increased with increasing strain rate, but Weibull shape parameter, β, can be regarded as a constant.     

E玻璃纤维增强环氧树脂基复合材料轴向拉伸力学性能的应变率效应

采用MTS-810材料试验机、Zwick-HTM5020高速拉伸试验机及分离式Hopkinson拉杆（SHTB）实验装置,并结合数字图像相关性（Digital image correlation,DIC）分析方法,对E玻璃纤维增强环氧树脂基复合材料棒材在10^-3~2 400 s^-1应变率范围内的轴向拉伸力学性能进行了较系统的实验研究,获得了不同应变率下材料的应力-应变曲线,揭示了应变率对材料的拉伸强度和断裂应变的影响规律。通过显微分析拉伸试样的断口形貌,揭示了试样的断裂机制及对应变率的依赖性。实验结果表明：E玻璃纤维增强环氧树脂基复合材料的力学性能具有强烈的应变率效应,归一化拉伸强度随着应变率对数线性增加,而归一化断裂应变则随着对数应变率线性减小;断口显微分析显示：E玻璃纤维增强环氧树脂基复合材料的轴向拉伸断裂模式依赖于应变率,低应变率加载下试样发生沿45°方向的剪切断裂,随着应变率增大,试样断裂模式逐渐过渡到沿轴向的拉伸断裂,特别是在高应变加载下,观察到大量的玻璃纤维丝被拉断,同时环氧树脂基体也发生严重的碎裂现象,这反映了基体材料与玻璃纤维之间相互约束作用在增强。     

Effect of fiber array on damping behaviors of fiber composites

This study aims to investigate the fiber array effect on modal damping behaviors of fiber composites. Three different fiber arrays, i.e., square edge packing (SEP), square diagonal packing (SDP), and hexagonal packing (HP), were considered to represent the microstructures of the unidirectional composites. Repeating unit cells (RUCs) suitable for describing the characteristics of the microstructure were adopted in the generalized method of cell (GMC) micromechanical analysis. The energy dissipation concept was then employed to calculate the specific damping capacities of composites in the material principal directions. The specific damping capacities obtained from micromechanical analysis were regarded as the equivalent damping properties homogenizing in the composites. In conjunction with the modal shapes of the composite structures determined from the finite element analysis, the specific damping capacity was extended to characterize the corresponding modal damping of the composite rods and plates. Both free–free and clamped-free boundary conditions were taken into account in the composite structures. Results indicated that the structures constructed from the composites with SDP fibers exhibit better damping behaviors than the other two cases.     

2D-SiC/SiC复合材料损伤耦合力学行为

基于轴向和45°偏轴加载实验,分别获得2D-SiC/SiC复合材料在单一轴向应力和复合应力状态下纤维束轴向方向上的拉伸、压缩和面内剪切应力-应变行为,计算分析材料在复合应力状态下的损伤耦合力学行为。结果表明,在45°偏轴拉伸和压缩复合应力状态下材料损伤耦合力学行为的起始应力分别约为40MPa和-100MPa。复合应力状态下材料纤维束轴向方向上的拉伸损伤和面内剪切损伤进程间具有相互促进作用,面内剪切损伤对压缩损伤进程具有促进作用,但是压缩应力分量对面内剪切损伤进程具有明显的抑制作用;上述损伤耦合作用随着应力水平的增加而越发显著。由试件断口电镜扫描结果可知,复合应力状态下材料纤维束轴向方向上3个应力分量对材料内部0°/90°和45°3种取向基体裂纹开裂损伤进程的影响作用,是2D-SiC/SiC复合材料产生损伤耦合力学行为的主要细观损伤机制。     

Atomistic simulation of the mechanical behaviors of co-continuous Cu/SiC nanocomposites

In this paper, molecular dynamics (MDs) simulation was employed to investigate the mechanical behaviors of co-continuous Cu/SiC nanocomposites. The calculated results show the Young’s modulus and yield stress of the nanocomposites increase nonlinearly with the volume fraction (VF) of SiC. The Young’s modulus predicted by MD simulation is in good agreement with the micromechanics methods. The interfacial properties are found to play an important role in the plastic deformation of the nanocomposites. With the temperature increase, the co-continuous Cu/SiC nanocomposites show a brittle-to-ductile transition at about 700 K and the ultimate yield stress decreases linearly with the increase of temperature. This research is intended to give an insight into the mechanical behaviors of co-continuous nanocompoistes at an atomistic level.     

应变速率对热冲压淬火-配分钢显微组织与力学性能的影响EI北大核心CSCD

采用分离式Hopkinson压杆对热冲压淬火-配分(HS-Q&P)钢在0~12000 s^(-1)应变速率范围内进行动态压缩实验,利用SEM,EBSD,XRD等分析表征手段探究动态压缩过程中试样的变形行为。结果表明:实验钢在不同速率下的变形行为基本相似且分为3个阶段,在平台处应力有小幅度增加,增幅更多体现在应变上。在压缩过程中出现的绝热升温会带来软化效应。残余奥氏体的存在会提高实验钢的强度和塑性变形能力。钢中残余奥氏体发生相变诱导塑性(transformation induced plasticity,TRIP)效应减少的体积分数与马氏体增加的体积分数基本一致,证明TRIP效应为钢中主要的强化机制。同时,通过SEM可观测到残余奥氏体发生TRIP效应转变成细小针状马氏体,随着应变速率增加,晶格畸变越来越严重,EBSD图像中可以观测到部分形变孪晶,在不同应变速率下,〈001〉取向的晶粒都会更容易产生形变孪晶。     

Effect of temperature and strain rate on tensile mechanical properties of ARALL-1 laminates

The combined effect of temperature and strain rate of the mechanical properties for unidirectional 3/2 ARALL^®-1 laminates was studied. In this paper, the effect of strain rates from 0.00083–0.833 min^–1 on tensile behaviour at temperatures up to 250°F (121 °C) has been conducted. It is demonstrated that tensile strength, tensile modulus, and fracture strain are found to depend on temperature and strain rate. However, the effect of strain rates at 75 °F (24 °C) and 180 °F (82 °C) was found to be insignificant except the lowest strain rate at 180 °F. It was also observed that the tensile yield strength decreased as the strain rate decreased. The tensile properties were moderately reduced at high temperatures and were higher at high strain rates than at low strain rates. The temperature effect is more significant than that due to the strain rate. Scanning electron photomicrographs of the fracture surfaces observed in the aramid/epoxy layer of ARALL-1 laminates at the lowest strain rate are shown to be significantly different only at 250 °F (121 °C). But this phenomenon is not obvious when the highest strain rate is employed.     

Effect of strain rate on interfacial fracture behaviors of Sn-58Bi/Cu solder joints

The interfacial reactions and mechanical properties of Sn-58Bi/Cu solder joints reflowed at different temperatures ranging from 180 to 220 °C for constant time of 10 min were investigated with various strain rates. Only a continuous Cu₆Sn₅ intermetallic compound (IMC) layer was formed at the interface between the Sn-58Bi solder and the Cu substrate during reflow. The equivalent thickness of the Cu₆Sn₅ layer increased with increasing reflow temperature, and the relationship between Cu₆Sn₅ layer equivalent thickness (X) and reflow temperature (T) is obtained by using method of linear regression and presented as $ X = 0.01 \times T + 0.187 $ . For the tensile property, the tensile strength of solder joint gradually decreased as the reflow temperature it increased, whereas it increased with increasing strain rate. Moreover, the fracture behavior of Sn-58Bi/Cu solder joint indicated the ductile fracture with low strain rate (5 × 10^?4 and 1 × 10^?3 s^?1), while toward brittle fracture with high strain rate (2 × 10^?3 and 1 × 10^?2 s^?1). The strain rate sensitivities of the solder joints fractured with various modes were also investigated, and it is found that the tensile strength of the solder is more sensitive to the strain rate than that of the IMC layer.     

Tensile mechanical behavior of T300 and M40J fiber bundles at different strain rate

Tensile mechanical behavior of T300 fiber bundles and M40J fiber bundles have been studied in the strain rate range from 0.001 1/s to 1300 1/s and complete stress strain curves were obtained. Results show that both ultimate strength and failure strain of two materials are strain rate insensitive, and T300 fiber and M40J fiber can be regarded as strain rate insensitive materials. On basis of the fiber bundles model and the statistic theory of fiber strength, single Weibull distribution model and bimodal Weibull distribution model have been developed to describe mechanical behavior of fiber bundles. And a method for determine the statistic parameters of fibers by tensile tests of fiber bundles is established, too. The simulated stress strain curves from the model are in good agreement with the test data. Simulated results show that the strength of T300 fiber can be described by single Weibull distribution function, and the strength of M40J fiber should be described by bimodal Weibull distribution function.     

Effect of drawing strain rate on microstructure and mechanical properties of cold-drawn pearlitic steel wires

Journal of Materials Science - Microstructural evolution of cold-drawn pearlitic steel wires (CPWs) with different drawing strain rates and their effects on mechanical properties of CPWs were...     

Effect of strain rate on the mechanical properties of composites with a weak fibre/matrix interface

Modelling studies have indicated a strong effect of the rate of deformation on the tensile strength of composites with a weak fibre/matrix interface. At high rates, the mode of deformation changes from a fibre pull-out to a fibre breaking mechanism typical of good adhesion composites. As a result, the mechanical properties become independent of those of the fibre/matrix interface. The model predictions are of great importance because they allow a straightforward identification of composites with poor fibre-matrix adhesion.