Mechanism and Method of Testing Fracture Toughness and Impact Absorbed Energy of Ductile Metals by Spherical Indentation Tests

To address the problem of conventional approaches for mechanical property determination requiring destructive sampling, which may be unsuitable for in-service structures, the authors proposed a method for determining the quasi-static fracture toughness and impact absorbed energy of ductile metals from spherical indentation tests (SITs). The stress status and damage mechanism of SIT, mode I fracture, Charpy impact tests, and related tests were frst investigated through fnite element (FE) calculations and scanning electron microscopy (SEM) observations, respectively. It was found that the damage mechanism of SITs is diferent from that of mode I fractures, while mode I fractures and Charpy impact tests share the same damage mechanism. Considering the diference between SIT and mode I fractures, uniaxial tension and pure shear were introduced to correlate SIT with mode I fractures. Based on this, the widely used critical indentation energy (CIE) model for fracture toughness determination using SITs was modifed. The quasi-static fracture toughness determined from the modifed CIE model was used to evaluate the impact absorbed energy using the dynamic fracture toughness and energy for crack initiation. The efectiveness of the newly proposed method was verifed through experiments on four types of steels: Q345R, SA508-3, 18MnMoNbR, and S30408.

Experimental Research on the Dynamic Energy Absorbing Capacity of the Honeycomb Paperboard Filled with Polyurethane

A kind of composite buffering material was made by filling the voids of honeycomb paperboard with polyurethane. Drop tests were performed to evaluate the dynamic energy absorption capacity of the material. Based on the tests results,the mechanical behaviors of the material under low velocity dynamic impact conditions were analyzed. It was shown that the absorbed energy of the composite material varies inversely with the void diameter. The absorbed energy of the composite material is 1- 2 times than that of honeycomb paperboard and polyurethane. The energy absorption efficiency of the composite material is better than those of honeycomb paperboard and polyurethane.

3D printed modular Bouligand dissipative structures with adjustable mechanical properties for gradient energy absorbing

Three-dimensional(3D)printing allows for the creation of complex,layered structures with precise micro and macro architectures that are not achievable through traditional methods.By designing 3D structures with geometric precision,it is possible to achieve selective regulation of mechanical properties,enabling efficient dissipation of mechanical energy.In this study,a series of modular samples inspired by the Bouligand structure were designed and produced using a direct ink writing system,along with a classical printable polydimethylsiloxane ink.By altering the angles of filaments in adjacent layers(from 30◦to 90◦)and the filament spacing during printing(from 0.8 mm to 2.4 mm),the mechanical properties of these modular samples can be adjusted.Compression mechanical testing revealed that the 3D printed modular Bouligand structures exhibit stress-strain responses that enable multiple adjustments of the elastic modulus from 0.06 MPa to over 0.8 MPa.The mechanical properties were adjusted more than 10 times in printed samples prepared using uniform materials.The gradient control mechanism of mechanical properties during this process was analyzed using finite element analysis.Finally,3D printed customized modular Bouligand structures can be assembled to create an array with Bouligand structures displaying various orientations and interlayer details tailored to specific requirements.By decomposing the original Bouligand structure and then assembling the modular samples into a specialized array,this research aims to provide parameters for achieving gradient energy absorption structures through modular 3D printing.

Transferability of Charpy Absorbed Energy to Fracture Toughness Based on Weibull Stress Criterion

The relationship between Charpy absorbed energy and the fracture toughness by means of the (crack tip opening displacement (CTOD)) method was analyzed based on the Weibull stress criterion. The Charpy absorbed energy and the fracture toughness were measured for the SN490B steel under the ductile-brittle transition temperature region. For the instrumented Charpy impact test, the curves between the loading point displacement and the load against time were recorded. The critical Weibull stress was taken as a fracture controlled parameter, and it could not be affected by the specimen configuration and the loading pattern based on the local approach. The parameters controlled brittle fracture are obtained from the Charpy absorbed energy results, then the fracture toughness for the compact tension (CT) specimen is predicted. It is found that the results predicted are in good agreement with the experimental. The fracture toughness could be evaluated by the Charpy absorbed energy, because the local approach gives a good description for the brittle fracture even though the Charpy impact specimen or the CT specimen is used for the given material.

Microwave Absorbing Performance of RE-Fe Based Alloys

REI3Fes4Cr3（RE=Ce, Pr, Tb, Er） and Pr13_XFes4Cr3Ti（x=0, 2, 4, 6） alloy powders were prepared by are smelting method and high energy ball milling technique. The phase structure and the morphology of the alloy powders were investigated by X-ray diffraction （XRD） and scanning electron microscopy （SEM）, and their microwave absorbing properties were determined by a vector network analyzer. The results show that the alloys with light rare earths （Ce, Pr） have good low frequency absorbing property and those with heavy rare earths （Tb, Er） exhibit an improved high frequency absorbing property. The minimum refleetivity at the absorbing peak frequency of RE,FeuCr3（RE=Ce, Pr, Tb, Er） are -9.49 dB at 5.76 GHz, -22.38 dB at 7.92 GHz, -18.52 dB at 11.68 GHz and -17.59 dB at 10.24 GHz, respectively. The absorbing bandwidth under -10 dB of the Pr13FesaCr3 powder was widened from 1.91 GI-Iz to 3.89 GHz by adding 2% Ti, but the reflectivity of the alloy was increased from -22.38 dB to -14.91 riB.

Dynamics Analysis of Nonlinear Energy Sink for Metal-Rubber Vibration Absorber

Recent advances in the application of the nonlinear energy sink under a sinusoidal excitation make it possible to investigate metal-rubber vibration absorber. To provide such a vibration absorber for the integrated spacecraft platform,we analyze the targeted energy transfer of the simplified model with nonlinear energy sink using the complex-variables averaging method. Theoretical study shows two quasi-periodic responses that are essentially different in this nonlinear system. The steady-state response which is one of two quasi-periodic responses is caused by the linear instability of system,and another one appears as a result of the nonlinear normal modes between the linear and nonlinear oscillators,resulting from the energy transfer of different oscillators,and it can be used to vibration absorber. Secondly,this paper also discusses the performance of the proposed nonlinear absorber by using the phase portraits. All conclusion derived by the analytic model is verified numerically and the results are consistent with numerical simulations.

Vibration energy regeneration of electric vehicle shock absorber

The twin-tube shock absorber was studied and the relevant factors of thermal equilibrium were simulated. The dynamic model of the shock absorber was constructed and simulation curves of force-displacement and force-velocity were output. The experiment of the twin-tube shock absorber was carried out, and the results were compared with the modeling resultss. Further, the vibration energy regeneration model was established, and the bench simulation study was carried out. The re- sults showed that the energy regeneration model not only absorbed shock energy but also converted vibration energy into electricity energy.

Industrial Progress:New Energy-Efficient Absorbents for the CO_(2) Separation from Natural Gas,Syngas and Flue Gas

The CO2 separation from natural gas, syngas or flue gas represents an important industrial field of applications. An economic and energy-efficient CO2 separation from these gas streams is a prerequisite for sustainable industry contributions to the megatrends resource efficiency and globalization of technologies. One way of reducing operational expenditure for these separation processes is the development of better performing CO2 absorbents. Although a number of absorbents for the separation of CO2 from process gas streams exist, the need for the development of CO2 absorbents with an improved absorption performance, less corrosion and foaming, no nitrosamine formation, lower energy requirement and therefore less operational expenditure remains. Recent industrial activities have led to the development of novel high-performance CO2 scrubbing agents that can be employed in numerous industrial processes such as natural gas treatment, purification of syngas and the scrubbing of flue gas. The objective of this paper is to introduce these new high-performance scrubbing agents and to compare their performance with other state-of-the-art absorbents. It turned out, that the evaluated absorbents offer high cyclic capacities in the range of 2.4 to 2.6 mol CO2/kg absorbent and low absorption enthalpies (–30 kJ/mol) allowing for distinctive savings in the regeneration energy of the absorbent. Calculations with the modified Kremser model resulted in a reduction of the specific reboiler heat duty of 55%. Furthermore, the absorbents are less corrosive than standard amines as indicated by the measured corrosion rates of 0.21 mm/y versus 1.18 mm/y for a piperazine/methyldiethanolamine mixture. Based on new experimental results it is shown how substantial savings in operational and capital expenditure can be realized due to favorable absorbent properties. The novel high-performance CO2 system solutions meet recent industrial absorbent requirements and allow for more efficient or new CO2 separation processes.

An Energy Absorber with Force Modificator

Thin-walled tubes are extensively applied in engineering, especially in vehicle structures to resist axial or traversal impact loads, for their excellent energy absorbing capacity. However, in the axial deformation mode, the force history has an extremely high peak force which may bring not only fatal injury to occupants but also damage to structures, cargo and environment. Aiming to develop energy absorbers with impact-force modificator, square metal tube with force modificator is investigated which can monitor the force-deformation history of the tube. A small device is designed to serve as an impact-force modificator, which introduces desired imperfections to the square tube just before the impact happens between the impactor and the tube, so as to reduce the peak force. Prototypes with various governing parameters were manufactured and tested both quasi-statically and dynamically to study the effects of these parameters on the characteristics of energy absorption. The results show that the force modificator can achieve the desired reduction of the peak force well whilst remaining the specific energy absorption capacity of the original square tube. With future improvements, it could be applied to vehicles or roadside safety hardware to mitigate the consequences produced by traffic accidents.

Characteristics of New-type Energy Absorber for Vehicle Collision

A new type energy absorber was introduced,which is composed of thousands of thin ring plates with different diameters.Because it can switch the impact to thousands of shearing actions among thin ring plates inside the absorber,the impact energy is decentralized and dissipated gradually,the impact acting time is extended and the peak of acceleration is reduced obviously.Numerical simulations by finite element method (FEM) coupled with smoothed particle hydrodynamics (SPH) method were preformed to predict the energy absorption characteristics.Energy absorption ability with different impact velocities was studied and the effects of thickness and material of ring plates were discussed.The sled crash test was carried out to validate the result of simulations.The new type absorber is effective for collision that impact velocity is lower than 40 km/h.

Improvement of Impact Absorbed Energy of CFRPs on Adding the Nanoparticles into Epoxy Resins

The present study investigates the effect of the addition of nanoparticles into epoxy resins as the matrix on the impact absorbed energy of CFRP （carbon fiber reinforced polymer）. Impact absorbed energy is one of the main properties to evaluate the CFRP＇s performance for transportation and aerospace structures. Two types of nanoparticle, namely nanofibers and nano-silica beads, were added into the epoxy resin to improve the impact absorption capacity of the CFRP. Two modified additives and conventional epoxy resins were quantitatively compared. The impact test results showed that impact absorbed energy for nanofibers was higher than nano-silica beads, and nanofibers as the additive promoted about 11% of impact absorbed energy compared with neat epoxy resin.

Interaction of Counter Propagating Electromagnetic Waves with the Absorbing Plate in the Waveguide

The interaction of two coherent counter propagating TE （transverse-electric） and TM （transverse-magnetic） electromagnetic waves with different initial phases in the absorbing plate placed in the regular ideal waveguide is considered. The losses of energy of TE and TM waves in the absorbing plate are calculated. Some features of tunnel interference in the absorbing plate in the waveguide are revealed. It is shown that the losses of energy strongly depend on the various parameters describing the interaction of the counter propagating waves. Definitely choosing the parameters we can control the electromagnetic processes in this case.

多胞体汽车后防撞吸能器耗能机制研究与结构优化设计

为有效提升后防撞系统耐撞性能以满足碰撞冲击载荷作用下的车辆被动安全需求,研发了6种正多边形镶嵌的多胞体薄壁吸能器。基于简化超折叠单元理论分析了截面参数和肋板连接方式对薄壁吸能器的能量耗散途径与影响机制;采用ABAQUS数值仿真探究了各种吸能器吸能特性,同时揭示了正八边形截面、肋板对边连接的薄壁吸能器吸能特性优异;依托拉丁超立方试验方法和基于Kriging代理模型的NSGA-II遗传算法进行多目标优化,确定了吸能器内薄壁管截面尺寸、管壁和肋板厚度分别为18.073 mm、1.669 mm、1.924 mm。结果分析表明,参数优化后的正八边形多胞体吸能器压溃吸能过程平稳可靠,能够为后防撞系统吸能器的结构设计提供参考。

防冲击地压薄壁吸能构件的压溃吸能机理分析

当煤矿井下发生冲击地压时,矿用液压支架的冲击性失效,常常会引起巷道支护系统的破坏,进而引发巷道坍塌,造成矿难。当前通过添加吸能构件来提高支架的防冲击性能是防治巷道冲击地压的有效途径之一。而不同类型吸能构件的压溃变形模式不同,表现出的吸能特性和力学特性也不同。本文采用数值方法对不同类型、支座和壁厚的吸能构件进行了冲击压溃模拟,通过对各相关防冲吸能参数的对比分析可知:预折纹吸能构件支撑反力最大、具有良好的吸能能力,但变形过程稳定性较差;外翻式吸能构件的塑性变形能力强,有效让位行程最大,但支撑力较小,不适合单独使用;扩径式吸能构件变形过程稳定性最好,其塑性变形后的径向位移较小,节省工作空间,但支撑能力较差,适用于小型液压支架或用作其他特殊用途。

正弦波纹管填充乳化液式吸能构件吸能特性研究

预折纹式吸能构件是目前冲击地压矿井中唯一使用的吸能结构,具有优异的吸能特性,但在屈曲变形过程中存在载荷波动较大、由于摩擦的作用产生火花等问题。针对上述情况,设计了一种正弦波纹管(变径圆管)填充乳化液构成固液耦合体吸能构件(组合构件),研究了波纹管壁厚、母线振幅与出液口直径三个因素对吸能构件吸能特性的影响。建立平均载荷、载荷波动系数与比吸能的预测模型,利用Abaqus有限元软件的光滑粒子流体动力学(Smoothed Particle Hydrodynamics,SPH)粒子算法对模型进行流固耦合分析,通过响应面法对吸能构件的结构参数进行寻优并得到优化结果。研究结果表明,当波纹管壁厚3.959 mm,母线振幅3.721 mm,出液口直径22.161 mm时的吸能构件吸能特性最佳,平均载荷为438.684 kN,载荷波动系数为1.178,比吸能12.123 kJ/kg。通过对比验证,结果具有较高的可信度,为防冲支护装备的吸能环节提供了一种优越的吸能构件。

崩塌危岩体减震消能复合加固结构抗震性能试验研究

地震区工程建设中崩塌危岩体的加固方式目前主要是锚固和支挡两类结构形式。加固结构与危岩体的连结都采用刚性连结,结构与危岩体之间几乎无变形能力,因此抗震性能较差。在地震作用下,特别是强震作用下极易破坏失效,造成崩塌灾害,在我国西南地震区工程中大量存在此类破坏现象。为解决目前加固结构存在的问题,设计了一种允许地震作用下危岩体能够有限度的变位、可以缓冲危岩体的地震冲击力、具有减震消能功能的崩塌危岩体复合加固结构,结构由锚杆(索)、减震锚头(一级消能)、连梁、支撑桩以及设于连梁与支撑桩之间的作为二级减震消能装置所组成。为验证复合加固结构的功效,除理论分析外,利用振动台进行与同等条件普通锚杆加固结构的物理模型对比试验。试验选用具有地区代表性的不同波形、幅值与频率的地震波作为输入波形。理论分析与试验结果表明:复合加固结构相较于无防护措施的同样崩塌体理论分析,其位移增长速度显著降低,累积位移幅度显著减小;相较于传统锚杆加固结构,所承受的拉力和压力显著减小;峰值加速度放大系数明显降低。证明复合加固结构利用自身的弹塑性变形以及阻尼力,有效抵御由于地震作用在危岩体上产生的动应力,有效转移了危岩体的冲击动能,减震消能作用明显,避免加固结构损坏,从而阻止崩塌灾害的发生,证明复合加固结构能够分层次地削弥小震、中震、大震时产生的地震能峰值。减震消能复合结构为地震区崩塌危岩体的加固提供了一种新的加固方案,对于提升地震区工程中崩塌危岩体的加固技术具有较大的现实意义。

液压支架立柱防冲吸能构件优化仿真及压溃实验研究

液压支架作为煤炭开采主要支护设备,经常受到冲击地压影响,防冲吸能构件起到保护液压支架作用,为获得更大的初始支反力峰值与吸能量、更小的支反力分散度,对吸能构件参数细化并通过ABAQUS有限元软件进行吸能构件的建模与压溃冲击仿真,获取吸能构件的吸能性能及屈曲变形形态,验证最优尺寸的吸能性能;对比吸能构件平均支反力的预测数据与有限元仿真数据,误差在15%以内,最优尺寸构件的平均支反力模型预测误差为−3.40%,验证吸能构件预测模型所预测数据较为准确;搭建吸能构件压溃实验台,选择5种加载速度,以准静态压溃方式对定制加工的吸能构件进行轴向加载压溃实验,实验结果表明:不同加载速度轴向压溃实验,支反力波动基本一致,最大初始支反力峰值为2253.52 kN,最大支反力标准差为206.23 kN,最小初始支反力峰值为2096.26 kN,最小支反力标准差为189.83 kN,初始支反力峰值的平均值为2149.32 kN,支反力标准差平均值为196.77 kN;不同压溃速度下的轴向压溃实验数据与吸能构件有限元仿真数据对比,初始支反力峰值、支反力标准差的相对误差分别为5.6%、11.07%;对最优尺寸吸能构件通过预测模型法、有限元仿真法、压溃实验法三种方法进行吸能性能分析,预测模型法的平均支反力为1879.7 kN,有限元仿真法的平均支反力为1945.9 kN,压溃实验法平均支反力为1919.8 kN,预测模型误差3.41%,压溃实验误差−1.3%,通过3种方法的数据验证结果,证明了吸能构件分析方法的可靠性和可行性。

基于可见-近红外光谱技术的果蔬品质检测方法

可见-近红外光谱技术利用波长在380~2 500 nm的电磁波获取果蔬中有机分子含氢基团的特征信息,根据样品对不同波长光的吸收信息,实现果蔬的外部、内部缺陷及营养成分定性、定量分析,是目前主流的果蔬内外部品质快速无损检测技术。综述了目前基于吸光度谱和能量谱对果蔬营养物质含量定量分析及缺陷定性分析,所使用的检测模型和变量筛选模型及其检测准确性,为相关研究人员选择高效准确的检测模型提供技术支撑。

多孔轻质混凝土力学性能敏感性试验研究

选择市售复合发泡剂、P.O 42.5水泥、80目细砂、Ⅰ级粉煤灰及15 mm短丝聚乙烯醇纤维,得到基准配合比m水泥∶m粉煤灰∶m细砂=1∶0.250∶0.375,水胶比W=m水/(m水泥+m粉煤灰)=0.35,粉胶比F=m粉煤灰/(m水泥+m粉煤灰)×100%=20%,砂胶比S=m细砂/(m水泥+m粉煤灰)=0.3,聚乙烯醇纤维掺入百分比f=m纤维/(m水泥+m粉煤灰+m细砂)×100%=0.1%,泡沫掺入体积比N=V新鲜泡沫∶V水泥砂浆=2.0;采用控制单一变量法,通过调整W=0.40、0.45、0.50、0.55,F=15%、10%、5%、0%,N=1.5、1.0、0.5、0,分别制备了12组多孔轻质混凝土试样进行单轴压缩试验,分析了不同配合比多孔轻质混凝土应力-应变曲线阶段性特征与力学参数变化规律;通过多因素交互效应响应模型分析了W-N、N-F、W-F交互效应下多孔轻质混凝土峰值强度σpeak、弹性模量E的响应敏感性规律。结果表明:单轴压缩加载下,多孔轻质混凝土的残余强度σre约为σpeak的70%,表现出“让压吸能”特征,该特征的显著性随着N的增大而增大;多因素交互效应下,多孔轻质混凝土σpeak与E的响应曲面形态基本相同;多孔轻质混凝土内部中型孔隙占比最大,约18.37%;“蜂窝状”孔隙结构可有效传递并分散外部荷载;伴随“让压吸能”特征,多孔轻质混凝土细观孔隙结构的损伤过程包含分布损伤与局部破坏2个阶段。

抗冲击地压复合夹芯组合板的静、动态力学性能研究

基于吸能防冲的理念,设计了一种由玻璃纤维复合材料(glass fiber reinforced polymer, GFRP)顶底板和三角锥点阵夹芯层(芯杆为LY160低屈服点钢)组成的复合夹芯组合板,它可与金属支架结合形成两级吸能防冲支护体系。测试并获得了GFRP和LY160低屈服点钢在准静态以及动态试验条件下的抗拉强度等基本力学参数,拟合得到了LY160低屈服点钢的C-S(Couper-Symonds)动态本构模型参数。开展了复合夹芯组合板的准静态平压试验,进行了夹芯板抗冲击性能的有限元参数分析。结果表明,随着芯杆直径的增加,试件单位体积吸收的能量显著增加,芯杆直径为6 mm试件吸收能量是直径为4 mm试件的6.0倍,单位质量吸收的能量也有所提升,但芯杆直径超过6 mm后变化不明显。当冲击地压震级为3级时,芯杆直径与单胞宽度对夹芯板结构的能量吸收率和单位质量吸收能量值影响显著,当芯杆直径为6 mm时,能量吸收率可达90%以上,而当单胞宽度为140 mm时,夹芯板兼顾吸能效率和经济性。