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.

Processing the rig test data of an air filling twin-tube shock absorber

A separation method is proposed to design and improve shock absorber according to the characteristics of each force. The method is validated by rig test. The force data measured during rig test is the resultant force of damping force, rebound force produced by pressed air, and friction force. Different characters of damping force, air rebound force and friction force can be applied to seperate each force from others. A massive produced air filling shock absorber is adopted for the validation. The statistic test is used to get the displacement-force curves. The data are used as the input of separation calculation. Then the tests are carried out again to obtain the force data without air rebound force. The force without air rebound is compared to the data derived from the former tests with the separation method. The result shows that this method can separate the damping force and the air elastic force.

Experimental Study on Vibration Control of Offshore Wind Turbines Using a Ball Vibration Absorber

To minimize the excessive vibration and prolong the fatigue life of the offshore wind turbine systems, it is of value to control the vibration that is induced within the structure by implementing certain kinds of dampers. In this paper, a ball vibration absorber (BVA) is experimentally investigated through a series of shake table tests on a 1/13 scaled wind turbine model. The reductions in top displacement, top acceleration, bottom stress and platform stress of the wind turbine tower system subjected to earthquakes and equivalent wind-wave loads, respectively, with a ball absorber are examined. Cases of the tower with rotating blades are also investigated to validate the efficacy of this damper in mitigating the vibration of an operating wind turbine. The experimental results indicate that the dynamic performance of the tested wind turbine model with a ball absorber is significantly improved compared with that of the uncontrolled structure in terms of the peak response reduction.

Theoretical analysis and experimental investigation of a high-performance viscoelastic material shock absorber

To improve the performance of traditional mechanical shock absorber, a new type of high molecular polymer is formulated and applied to overloaded vehicle shock absorber. According to the operating principle of high-performance viscoelastic material shock absorber, the geometrical structure of shock absorber is designed and machined. Then its theoretical model is derived by using analytical method, and the impact test is carried out on high-performance viscoelastic material shock absorber. The results show that experimental and theoretical damping force curves have good agreement, which validates the credibility of theoretical model. The investigation provides a potential way to enhance damping performance and increase vehicle load.

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.

A review on the performance of conventional and energy-absorbing rockbolts

This is a review paper on the performances of both conventional and energy-absorbing rockbolts manifested in laboratory tests. Characteristic parameters such as ultimate load, displacement and energy absorption are reported, in addition to load-displacement graphs for every type of rockbolt. Conventional rockbolts refer to mechanical rockbolts, fully-grouted rebars and frictional rockbolts. According to the test results, under static pull loading a mechanical rockbolt usually fails at the plate; a fully-grouted rebar bolt fails in the bolt shank at an ultimate load equal to the strength of the steel after a small amount of displacement; and a frictional rockbolt is subjected to large displacement at a low yield load. Under shear loading, all types of bolts fail in the shank. Energy-absorbing rockbolts are developed aiming to combat instability problems in burst-prone and squeezing rock conditions. They absorb deformation energy either through ploughing/slippage at predefined load levels or through stretching of the steel bolt. An energy-absorbing rockbolt can carry a high load and also accommodate significant rock displacement, and thus its energy-absorbing capacity is high. The test results show that the energy absorption of the energy-absorbing bolts is much larger than that of all conventional bolts. The dynamic load capacity is smaller than the static load capacity for the energy-absorbing bolts displacing based on ploughing/slippage while they are approximately the same for the D-Bolt that displaces based on steel stretching.

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.

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。

空间管路结构振动控制技术研究

飞行器在服役过程中,管路结构会产生大量级振动响应,严重时会发生断裂失效。振动控制是延缓管路结构失效,提升可靠性的主要途径。本文通过边界简化及焊接部位建模,建立了复杂空间三维管路结构动力学模型,模态仿真结果与试验模态结果对比最大误差小于3%。在此基础上,使用金属减振器进行振动控制。通过计算,获得随机振动载荷下使用金属减振器前后空间管路结构的减振效率为8.46%;通过试验获得金属减振器实际的减振效率达到14.26%。本文计算和试验结果表明使用金属减振器能够显著降低复杂空间管路结构的振动响应。

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。

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。

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。

动力吸振器在直升机减振上的应用及效果验证

基于无阻尼动力吸振器设计原理和直升机实际指标需求设计了一种可变刚度和可调质量的动力吸振器,并利用有限元模型对吸振器进行了动特性分析和减振效率分析,最终通过飞行试验验证动力吸振器的实际装机效果。测试数据结果表明动力吸振器有较好的减振效果,为后续其它型号的动力吸振器研制积累了工程经验,提供了参考。

塔式太阳能吸热器曲面涂层吸收率测试方法研究

吸热器涂层吸收率的准确测量对吸热器性能评估、优化具有重要意义。目前吸热器涂层吸收率的实验研究大多局限于平面金属基材。以塔式太阳能熔盐吸热器圆柱形吸热管为研究对象,提出蓝丁胶法和漫反射盒法2种广泛适用的测量曲面涂层吸收率测试方法。蓝丁胶法器材准备简单,操作复杂;漫反射盒法器材准备复杂,操作简单。2种方法在测量过程中隔绝环境光线干扰,得到各种涂层附着于平板和圆管表面的测量吸收率,通过不同涂层在平板和圆管上的吸收率对应关系建立拟合曲线,从而修正测量数据得到吸热管涂层吸收率,拟合曲线精确性R^(2)≥0.995;不遮光条件下直接测量2.5cm直径吸热管吸收率,最大相对误差为13.39%,使用蓝丁胶法和漫反射盒法后相对误差分别降为0.27%和0.45%,2种方法各点结果相对误差之差小于0.30%,测量过程中涂层吸收率越大,各因素对测量结果影响越小;在蓝丁胶测试方法中,吸热管直径越大,测得的吸收率越小。

成型方式对应力吸收层沥青混合料性能的影响

开展了旋转压实与马歇尔击实成型对应力吸收层沥青混合料体积和力学性能的影响分析。试验结果表明,应力吸收层配合比设计中可用马歇尔击实50次代替旋转压实50次成型试件,旋转压实试件与马歇尔试件的劈裂抗拉强度、贯入应力均具有良好相关性,换算系数分别为1.347和0.910。提出了基于马歇尔击实方法的应力吸收层设计要求,可更好地进行配合比设计和工地现场质量控制。

弱动力扰动作用下岩石微裂隙演化特征及灾害防控

【目的】高应力叠加弱动力扰动是诱发冲击地压的关键因素,但不同扰动幅值、频率、卸载范围下的岩石微裂纹扩展特征和能量耗散规律尚不明确,无法为冲击地压防治提供技术支撑。【方法】基于真三轴卸载动力扰动试验,分析了不同扰动幅值(5、10 MPa)、频率(4、10 Hz)、三向应力卸载(0、12MPa)下深部围岩失稳破坏规律,并结合SEM扫描分析了岩石微裂隙特征。通过锚杆拉拔试验,优化了锚杆肋间距和肋高,提高了其吸能支护作用,提出了“吸能锚杆-低阻抗混凝土注浆-喷浆-挂网”组合支护技术。利用传感器对巷道进行长期监测,得到治理前后压力与振动数据。【结果和结论】研究表明:(1)随着扰动幅值和频率的增加,裂纹增加显著且不规则,岩石断口的方向分形维数降低。当扰动为10MPa、10Hz时,分形维数降至最低值0.62,孔隙方向角80°~120°孔隙定向频率达到最大值的52%,约为原始岩石的1.68倍。说明岩石受扰动后颗粒的应力不均匀,导致应力集中,断裂方向明显。(2)随着扰动幅值和频率的增加,SEM图像的微孔隙面积先快速增加,后缓慢增加且增加趋势越来越小。扰动频率每增加2 Hz,岩石微裂隙面积增加约24.13%。(3)现场测试表明随着锚杆肋间距和肋高增加,拉拔曲线形态由“弹塑性阶段-破坏失效阶段-残余阶段”逐渐过渡为“弹塑性阶段-微量屈服阶段-大量强化阶段-破坏失效阶段-残余阶段”,肋间距48mm、肋高2mm的螺纹钢锚杆吸能效果最好。经现场监测可将巷道压力稳定在36 N左右,峰值加速度控制在8000mm/s^(2)以内。研究揭示了卸载动力扰动作用下围岩破坏及能量释放规律,提出的“吸能锚杆-低阻抗混凝土注浆-喷浆-挂网”支护技术,可为类似深部工程提供理论指导。

缩管式恒阻大变形锚杆抗冲击特性及其治理岩爆潜力研究

深部岩体非线性大变形特性引发的岩爆灾害一直是岩土工程的世界性难题,严重制约了工程建设的施工进度和工程安全,加强对岩爆防治措施的深入研究刻不容缓。基于钢管挤压变形原理,提出了一种新型的缩管式恒阻大变形锚杆,该种锚杆可在容许较大的变形量的同时提供较高的恒阻力。在前期研究的基础上,通过落锤冲击试验探索了缩管式恒阻大变形锚杆的抗冲击性能。试验结果表明:在整个冲击过程中,缩管式恒阻大变形锚杆的工作阻力稳定在150~180 kN范围内,恒阻特性显著;缩管式恒阻大变形锚杆吸收能量大、效率高,单次可吸收冲击能量为53kJ;在冲击过程中,试件压缩率仅减小了0.54%~1.43%,变形情况较为稳定。缩管式恒阻大变形锚杆具有良好的抗冲击特能,可为地下工程建设过程中岩爆灾害的治理提供有力的技术支撑。

用于中子吸收的铪酸铕陶瓷性能研究

近年来,一些具有高熔点、无α粒子辐射优点的新型中子吸收材料被法国和日本等国提出。本研究以摩尔比为1:1的氧化铕和氧化铪混合物为原料,通过陶瓷烧结工艺研制了一种具有萤石稳定相的铪酸铕(Eu_(2)HfO_(5))中子吸收材料。对样品开展了包括熔点、热物性、力学性能等在内的一系列堆外测试。另外还进行了中子剂量达到1×10^(20)cm^(-2)的辐照考验,通过对比辐照前后的抗压强度等性能变化研究该材料的辐照性能。结果表明,所烧结的Eu_(2)HfO_(5)陶瓷中子吸收材料致密度高,物相为单一的萤石结构,熔点超过2 400℃,与理论值符合较好。同时该材料具有较好的亚临界水腐蚀性能。经过中子辐照后材料的密度和外观未发生明显改变,但中子吸收能力略有减小,抗弯强度和抗压强度略有增大。本研究得到了较为全面的堆外性能测试数据,并开展了辐照实验的考验,验证了所研制的Eu_(2)HfO_(5)陶瓷材料具备了预期的优点,为该材料的后续应用积累了基础数据。

水泥基材料自修复颗粒的制备及修复效果事前快速评价方法

针对多数水泥基材料自修复技术在渗漏水条件下修复物质被冲走、裂缝自修复效果难以达到预期且可修复裂缝宽度较窄的问题,本工作结合物理膨胀修复和化学反应修复的优点,以螯合处理的高吸水性树脂(Chelation super absorbent polymer,C-SAP)为物理修复剂,以反应修复剂(Reactive healing agents,RHA)和高性能混凝土膨胀剂(High performance calcium sulpho aluminate,HCSA)为化学修复剂,设计并制备了一种能在渗漏水条件下快速、高效修复裂缝的自修复颗粒,并改进了自制裂缝水渗透实验装置,开展了自修复颗粒修复效果的事前快速评价,最后采用X射线衍射分析方法分析了修复产物的物相组成。结果表明:自制裂缝水渗透实验装置能在将自修复颗粒应用于水泥基材料前有效且快速地评价颗粒的自修复效果,从而实现自修复颗粒组成的快速优选。当自修复颗粒中m(C-SAP)∶m(RHA)∶m(HCSA)=7.5∶32.5∶60,颗粒掺量为20%和30%时,其能够在672 h时完全封堵0.5 mm的裂缝;颗粒中的m(C-SAP)∶m(RHA)∶m(HCSA)=10∶30∶60且颗粒掺量为30%时,其能够在1008 h时完全封堵0.6 mm的裂缝。在裂缝修复早期,C-SAP解螯合并吸水膨胀,快速封堵裂缝,降低水流量;随后,化学修复物质通过化学反应生成白云石、钙矾石和方解石等结晶产物,从而将裂缝修复。