Experimental crushing behavior and energy absorption of angular gradient honeycomb structures under quasi-static and dynamic compression

The high variability of shock in terrorist attacks poses a threat to people's lives and properties,necessitating the development of more effective protective structures.This study focuses on the angle gradient and proposes four different configurations of concave hexagonal honeycomb structures.The structures'macroscopic deformation behavior,stress-strain relationship,and energy dissipation characteristics are evaluated through quasi-static compression and Hopkinson pressure bar impact experiments.The study reveals that,under varying strain rates,the structures deform starting from the weak layer and exhibit significant interlayer separation.Additionally,interlayer shear slip becomes more pronounced with increasing strain rate.In terms of quasi-static compression,symmetric gradient structures demonstrate superior energy absorption,particularly the symmetric negative gradient structure(SNG-SMS)with a specific energy absorption of 13.77 J/cm~3.For dynamic impact,unidirectional gradient structures exhibit exceptional energy absorption,particularly the unidirectional positive gradient honeycomb structure(UPG-SML)with outstanding mechanical properties.The angle gradient design plays a crucial role in determining the structure's stability and deformation mode during impact.Fewer interlayer separations result in a more pronounced negative Poisson's ratio effect and enhance the structure's energy absorption capacity.These findings provide a foundation for the rational design and selection of seismic protection structures in different strain rate impact environments.

Compressive deformation behavior of AZ31 magnesium alloy under quasi-static and dynamic loading

Compressive properties of AZ31 alloy were investigated at temperatures from room temperature to 543 K and at strain rates from 10-3to 2×10 4s-1.The results show that the compressive behavior and deformation mechanism of AZ31 depend largely on the temperature and strain rate.The flow stress increases with the increase of strain rate at fixed temperature,while decreases with the increase of deformation temperature at fixed strain rate.At low temperature and quasi-static condition,the true stress-true strain curve of AZ31 alloy can be divided into three stages(strain hardening,softening and stabilization) after yielding.However,at high temperature and high strain rate,the AZ31 alloy shows ideal elastic-plastic properties.It is therefore suggested that the change in loading conditions(temperature and strain rate) plays an important role in deformation mechanisms of AZ31 alloy.

Dynamic Compressive Deformation and Fracture of a Hollow Bulk Metallic Glass

The dynamic mechanical behaviors of hollow Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 bulk metal glass (BMG) are investigated using a splitting Hopkinson pressure bar (SHPB) in this study. Upon dynamic compressive loading, the hollow specimen exhibit lower strength and poor ductility, caused by the higher stress concentration for the hollow one through FEM modeling. The different strain-rate responses for the hollow specimen are compared and explained. On the fracture surface of the hollow samples, there are highly dense vein patterns, many liquid drops and fishbone-like patterns.

High temperature deformation and recrystallization behavior of magnesium bicrystals with 90°<1010>and 90°<1120>tilt grain boundaries

The deformation mechanisms and dynamic recrystallization(DRX)behavior of specifically grown bicrystals with a symmetric 90°<1010>and 90°<1120>tilt grain boundary,respectively,were investigated under deformation in plane strain compression at 200℃and 400℃.The microstructures were analyzed by panoramic optical microscopy and large-area electron backscatter diffraction(EBSD)orientation mapping.The analysis employed a meticulous approach utilizing hundreds of individual,small EBSD maps with a small step size that were stitched together to provide comprehensive access to orientation and misorientation data on a macroscopic scale.Basal slip primarily governed the early stages of deformation at the two temperatures,and the resulting shear induced lattice rotation around the transverse direction(TD)of the sample.The existence of the grain boundary gave rise to dislocation pile-up in its vicinity,leading to much larger TD-lattice rotations within the boundary region compared to the bulk.With increasing temperature,the deformation was generally more uniform towards the bulk due to enhanced dislocation mobility and more uniform stress distribution.Dynamic recrystallization at 200℃was initiated in{1011}-compression twins at strains of 40%and higher.At 400℃,DRX consumed the entire grain boundary region and gradually replaced the deformed microstructure with progressing deformation.The recrystallized grains displayed characteristic orientations,such that their c-axes were perpendicular to the TD and additionally scattered between 0°and 60°from the loading axis.These recrystallized grains displayed mutual rotations of up to 30°around the c-axes of the initial grains,forming a discernible basal fiber texture component,prominently visible in the{1120}pole figure.It is noteworthy that the deformation and DRX behaviors of the two analyzed bicrystals exhibited marginal variations in response to strain and deformation temperature.

Microstructural evolution of zirconium alloy under dynamic compression at strain rate of 1000s^(-1)

Microstructural evolution of the zirconium alloy deformed at a strain rate of about 1000 s-1 was investigated. Four different strain levels of the zirconium alloy subjected to dynamic compression were designed by several-times impacting at almost the same strain rate. The results show that abundant low angle boundaries at different strain levels were observed in the deformed microstructures, and the quantity and density of low angle boundary increase dramatically with the strain increasing. Besides low angle boundaries and high angle boundaries observed in grain boundary maps, the twin boundaries including the tensile twins {10 2}, {11 1} and compressive twins {11 2} were distinguished at different strain levels, and most twin boundaries were indexed as {10 2} twins. With the stain increasing, the twin boundary density in the deformed microstructures increases indistinctively. Based on the characterization of the deformed microstructures at the different strain levels, the deformation and evolution processes of the zirconium alloy subjected to dynamic loading were proposed. Microhardness measurements show that the microhardness in the impacted specimens increases gradually with the strain increasing, which should be associated with the strain hardening caused by the tangled dislocation.

Temperature Effect on the Mechanical Behavior of Acrylic Polymers under Quasi-static and Dynamic Loading

In this paper, the mechanical behavior of acrylic polymers at elevated temperature was investigated. Four acrylic polymers were tested at high strain rate by using compression Hopkinson bar and at quasi-static strain rate by using an Instron servo hydraulic axial testing machine with the testing temperature from 218K to 393K. The results show that the mechanical property of acrylic polymers depends heavily on the testing temperature. The yield stress and Young's modulus were found to decrease with increasing temperature at low strain rate. At very low temperature, the materials display typical brittle fracture; however their plasticity improves remarkably at high temperatures. The predictions of the mechanical behavior including the effect of temperature and strain rate using a proposed theoretical model have a good agreement with experimental results.

Dynamic modeling of twin roll casting AZ41 magnesium alloy during hot compression processing

A dynamic material model of Mg-4.51Al-1.19Zn-0.5Mn-0.5Ca(AZ41,mass fraction,%)magnesium alloy was put forward.The results show that the dynamic material model can characterize the deformation behavior and microstructure evolution and describe the relations among flow stress,strain,strain rates and deformation temperatures.Statistical analysis shows the validity of the proposed model.The model predicts that lower deformation temperature and higher strain rate cause the sharp strain hardening. Meanwhile,the flow stress curve turns into a steady state at high temperature and lower strain rate.The moderate temperature of 350 ℃and strain rate of 0.01 s-1 are appropriate to this alloy.

Hot deformation behavior of KFC copper alloy during compression at elevated temperatures

The hot deformation behavior of a KFC copper alloy was studied by compression deformation tests on Gleeble 1500 machine at strain rates ranging between 0.01?10 s?1 and deformation temperature of 650?850 ℃, and associated structural changes were studied by observations of metallography and TEM. The results show that the true stress–true strain curves for a KFC copper alloy are characterized by multiple peaks or a single peak flow, and tend to a steady state at high strains. The peak stress can be represented by a Zener-Hollomon parameter in the hyperbolic-sine-type equation with the hot deformation activation energy Q of 289 kJ/mol. The dynamic recrystallization(DRX) occurs by bulging out of part serrated grain-boundary, and the dynamic recrystallization grain size is dependent sensitively on deformation temperature T and strain rate ε&, also a function of Z. The dynamic spherical Fe-rich precipitates and successive dynamic particles coarsening has been assumed to be responsible for flow softening at high strains, and this is more effective when samples deformed at low temperatures and higher strain rates.

Quasi-Static and Dynanmic Deformation Behaviors of Medium-Carbon Steels in a Wide Temperature Range

This paper presents a study of the quasistatic and dynamic deformation behaviors of conventional and microalloyed medium-carbon steels in a wide temperature range. As strain rate increased, the flow stress increased at room temperature, but occasionally did not at elevated temperatures. The flow stress of the microalloyed steel containing precipitates was less sensitive to strain rate at room temperature than that of the conventional steel due to a relatively larger activation length. Microstructural observation of the steels deformed after compression test indicated that inhomogeneous deformation became more serious with increasing strain rate and temperature without fracturing in the highly localized region.

Hot compressive deformation behavior and microstructure evolution of HIPed FGH96 superalloy

Hot deformation behavior and microstructure evolution of hot isostatically pressed FGH96 P/M superalloy were studied using isothermal compression tests. The tests were performed on a Gleeble-1500 simulator in a temperature range of 1000-1150 °C and strain rate of 0.001-1.0 s-1, respectively. By regression analysis of the stress—strain data, the constitutive equation for FGH96 superalloy was developed in the form of hyperbolic sine function with hot activation energy of 693.21 kJ/mol. By investigating the deformation microstructure, it is found that partial and full dynamical recrystallization occurs in specimens deformed below and above 1100 °C, respectively, and dynamical recrystallization （DRX） happens more readily with decreasing strain rate and increasing deformation temperature. Finally, equations representing the kinetics of DRX and grain size evolution were established.

Molecular dynamics simulation and micropillar compression of deformation behavior in iridium single crystals

The compression behaviors of iridium single crystals with different crystalline orientations were investigated by micropillar compression tests and molecular dynamics(MD) simulations.The results indicated that the deformation process of iridium single crystals with [100]and [110] orientations was presented as the stacking faults expansion and the formation of Lomer-Cottrell locks.And the occurrence of Lomer-Cottrell locks was considered as the interaction of stacking faults on {111} planes by MD simulations.The evolution of crystal structure in compression indicated that the Lomer-Cottrell locks might contribute to the large plastic deformation of iridium single crystals.Moreover,the deformation features in MD simulations showed that the elastic modulus(E) and yield stress(σ_(s)) of iridium single crystals were significantly influenced by the temperature.The elastic modulus and yield stress gradually decreased with an increased temperature for all orientations.Meanwhile,the single crystal with a closely spaced lattice structure exhibited superior mechanical properties at a same temperature.

Hot deformation behavior and processing map of Cu-Ni-Si-P alloy

The high-temperature deformation behavior of Cu-Ni-Si-P alloy was investigated by using the hot compression test in the temperature range of 600-800 ℃ and strain rate of 0.01-5 s-1. The hot deformation activation energy, Q, was calculated and the hot compression constitutive equation was established. The processing maps of the alloy were constructed based on the experiment data and the forging process parameters were then optimized based on the generated maps for forging process determination. The flow behavior and the microstructural mechanism of the alloy were studied. The flow stress of the Cu-Ni-Si-P alloy increases with increasing strain rate and decreasing deformation temperature, and the dynamic recrystallization temperature of alloy is around 700 ℃. The hot deformation activation energy for dynamic recrystallization is determined as 485.6 kJ/mol. The processing maps for the alloy obtained at strains of 0.3 and 0.5 were used to predict the instability regimes occurring at the strain rate more than 1 s-1 and low temperature （〈650 ℃）. The optimum range for the alloy hot deformation processing in the safe domain obtained from the processing map is 750-800 ℃ at the strain rate of 0.01-0.1 s i The characteristic microstructures predicted from the processing map agree well with the results of microstructural observations.

Hot deformation behavior of Al-9.0Mg-0.5Mn-0.1Ti alloy based on processing maps

Hot deformation behavior of extrusion preform of the spray-formed Al-9.0Mg-0.5Mn-0.1Ti alloy was studied using hot compression tests over deformation temperature range of 300-450 ℃ and strain rate range of 0.01-10 s-1. On the basis of experiments and dynamic material model, 2D processing maps and 3D power dissipation maps were developed for identification of exact instability regions and optimization of hot processing parameters. The experimental results indicated that the efficiency factor of energy dissipate （η） lowered to the minimum value when the deformation conditions located at the strain of 0.4, temperature of 300 ° C and strain rate of 1 s-1. The softening mechanism was dynamic recovery, the grain shape was mainly flat, and the portion of high angle grain boundary （〉15°） was 34%. While increasing the deformation temperature to 400 ° C and decreasing the strain rate to 0.1 s-1, a maximum value of η was obtained. It can be found that the main softening mechanism was dynamic recrystallization, the structures were completely recrystallized, and the portion of high angle grain boundary accounted for 86.5%. According to 2D processing maps and 3D power dissipation maps, the optimum processing conditions for the extrusion preform of the spray-formed Al？9.0Mg？0.5Mn？0.1Ti alloy were in the deformation temperature range of 340-450 ° C and the strain rate range of 0.01-0.1 s-1 with the power dissipation efficiency range of 38%？43%.

Deformation behavior and microstructure of an Al-Zn-Mg-Cu-Zr alloy during hot deformation

The hot deformation behavior and microstructures of Al-7055 commercial alloy were investigated by axisymmetric hot compres- sion at temperatures ranging from 300℃ to 450℃ and strain rates from 10^-2 to 10 s^-1, respectively. Microstructures of deformed 7055 alloy were investigated by transmission electron microscopy （TEM）. The dependence of peak stress on deformation temperature and strain rate can be expressed by the hyperbolic-sine type equation. The hot deformation activation energy of the alloy is 146 kJ/mol. Moreover, the flow stress curves predicted by the modified constitutive equations are reasonably consistent with the experimental results, which confirms that the proposed deformation constitutive equations can provide evidence for the selection of hot forming parameters. TEM results indicate that dy- namic recovery is the main softening mechanism during hot deformation.

Deformation Behavior and Microstructure Evolution of Wrought Magnesium Alloys

There are many researches on the deformation behavior of wrought magnesium alloys, such as AZ31, AZ80, AZ91, and ZK60 magnesium alloys at different temperatures and strain rates, but few of them focuses on the deformation behavior of AZ41M and ZK60M alloys, especially under the twin-roll casting (TRC) state. Meanwhile, the existing researches only focus on the grain refinement law of the magnesium alloys under deformation conditions, the deformation mechanism has not been revealed yet. The hot compression behavior of AZ41M and ZK60M magnesium alloys under the temperature and strain rate ranges of 250-400 ℃ and 0.001-1 s-1 are studied by thermal simulation methods using Gleeble 1500 machine and virtual simulation using finite element analysis software. Simulation results show that sine hyperbolic law is the most suitable flow stress model for wider deformation conditions. The most reasonable selected deformation conditions of ZK60M alloy is 350 oC/0.1 s-1 for TRC and 350 oC/1 s-1 for conventional casting (CC), while AZ41M alloy is 300 oC/0.01 s-1 for TRC and 350 oC/0.1 s-1 for CC. Deformation behavior and dynamic recrystallization (DRX) mechanism of them are analyzed at the same deformation conditions. The microstructures of AZ41M and ZK60M alloys are observed at different deformed conditions by optical microscopy (OM) and electron back scatter diffraction (EBSD) and it reveals the flow behavior and deformation mechanism of them. Working harden and work soften contribute to the activation of basal, non-basal slip systems which promote DRX. The proposed research reveals the deformation behavior and mechanism of the AZ41M and ZK 60M magnesium alloys and concludes their optimized deformation parameters and processes and provides a theory basis for their manufacturing and application.

挤压态Mg-Al-Mn-(0.2Sr)镁合金的准静态压缩变形行为

采用准静态压缩实验研究了挤压态Mg-Al-Mn-(0.2Sr)镁合金在0.0001~0.33 s^(-1)应变速率范围内的变形行为。结果表明:挤压态Mg-Al-Mn-(0.2Sr)镁合金的流变应力响应行为具有一定的应变速率相关性,具体表现为流变应力随加载应变速率的增加呈现先降低,后增加,再降低的演变趋势。在压缩变形过程中,两种镁合金试样均产生了较为明显的动态应变时效(DSA)。产生DSA所需的临界应变随加载应变速率的增加而增加,且应力-应变曲线的锯齿类型具有强的应变速率相关性。添加Sr元素降低了镁合金沿径向压缩的流变应力,但对DSA行为具有一定的促进作用。相同应变速率下,挤压态Mg-Al-Mn-0.2Sr镁合金产生DSA的临界应变明显较小,且锯齿幅值略大。此外,Sr元素对孪生也具有一定的抑制作用,导致挤压态Mg-Al-Mn-0.2Sr镁合金的孪晶界出现不同程度的扭曲。

应变速率对7065铝合金等温压缩软化机制的影响

采用等温压缩实验并结合电子背散射衍射手段,研究了应变速率对7065铝合金热变形行为的影响规律。结果表明,随着应变速率由0.001 s^(-1)增加到30 s^(-1),合金的动态再结晶面积分数先显著减少,在1 s^(-1)时达到较低水平,而后变化幅度小于10%,当应变速率大于1 s^(-1)时,合金的亚结构面积分数显著增加。低应变速率阶段(0.001~1 s^(-1))的软化机制为动态再结晶(DRX)机制和动态回复(DRV)机制,而高应变速率阶段(1~30 s^(-1))的软化机制为DRV机制。随着应变速率的增加,等温压缩变形后合金的形变储能逐渐增加。

铸态Cu-1.16Ni-0.36Cr合金热变形行为及热加工图

利用Gleeble-1500型热模拟试验机,研究了Cu-1.16Ni-0.36Cr合金在变形量为50%、变形温度为750~950℃、变形速率为0.01~10 s^(-1)下的热压缩变形行为,建立该合金热变形的本构方程和热加工图。结果表明:Cu-1.16Ni-0.36Cr合金在700~900℃的变形温度下以动态回复为主,在950℃下发生完全的动态再结晶。通过真应力应变曲线得到了该合金热变形的本构方程和热加工图。根据应变对流变应力的影响对本构方程进行修正,通过修正后的回归方程对流变应力进行模拟,模拟结果与实验结果吻合。热加工图表明,该合金适宜的热变形工艺参数为900~950℃和0.1~1 s^(-1),其中950℃和1 s^(-1)变形条件下组织状态最佳,为晶粒细小均匀的等轴晶。

Nb-10Zr合金的热变形行为、组织特征及热加工图

Nb-10Zr合金可作为特种薄膜功能材料应用于太阳能行业。深入理解Nb-10Zr合金的热变形行为是实现该应用的前提,然而国内目前围绕该合金热加工过程的材料加工性能相关研究十分匮乏。建立热材料加工图可实现描述指定条件下的材料可加工性,明确合金的变形窗口,指导材料加工工艺的制定和优化。选用均匀化处理后的电铸熔炼铸锭Nb-10Zr合金,采用热模拟试验机开展了热模拟压缩试验,并基于动态材料模型,通过对应变速率敏感系数m、功率耗散系数η和失稳系数ξ的数据分析,建立了材料不同温度和应变速率条件下的流变稳态区和非稳态区的热加工图。同时,通过微观组织观察,分析和验证了加工图的准确性。研究结果表明,Nb-10Zr合金铸锭在1300℃下经24 h均匀化处理后,未出现Zr元素偏聚所形成的缺陷,也未见裂纹、气孔、疏松和夹渣等其他类型的缺陷。铸态组织中存在粗大晶粒和细小晶粒,晶粒尺寸分别为500—800μm和20—30μm。在应变为0.4和0.6条件下,Nb-10Zr合金存在2个合理的热加工窗口,即变形温度1060—1100℃和应变速率0.01—0.04 s^(-1),以及变形温度1080—1100℃和应变速率0.3—1 s^(-1)。在不同变形条件下,变形后的Nb-10Zr合金均获得了细小的动态再结晶组织。在温度1100℃和应变速率0.01 s^(-1)下,合金晶粒尺寸为80—100μm;而在温度1100℃及应变速率1 s^(-1)下,合金晶粒尺寸为40—60μm。此外,通过不同工艺制备参数下合金组织形貌的观察,证明了所确定加工窗口的合理性。本研究为Nb-10Zr生产过程中的工艺选择和工艺参数的优化提供了理论指导。

强夯在冲积层坝基处理中的应用

阿庆争水库是一个典型的山区小型水库。勘察发现,其河床坝基冲积层承载力低、易发生压缩变形和地震液化。对比换填法和强夯法后,选择了经济环保的强夯法处理坝基。强夯后,冲积层的干密度、承载力、密实度和剪切波速显著提高,孔隙比和渗透系数大幅降低,且不影响下游坝基排水。观测结果显示,大坝施工及封顶至今未见异常沉降变形和排水问题,有效解决了工程地质问题。此强夯处理可为类似工程提供参考。