平潭跨海大桥防船撞拦阻系统阻拦效能实验研究

本文介绍了一种新型的桥梁防船撞拦阻系统,以及该系统应用于平潭跨海大桥时所进行的实船拦阻实验。该防船撞拦阻系统由浮体、限载式拦索及锚链等组成,可以在船舶驶入时自动翻转并通过拖曳损耗船体动能最终保护桥梁安全。针对实船实验较为恶劣的环境,利用单目视觉测量技术,通过高速影像记录、数字图像处理及力学模型分析得到了实验船在受阻拦条件下的运动及受力,进而评估船舶进入阻拦区后阻拦系统的工作过程及工作效能。实验结果表明该技术能有效地对桥梁进行撞击防护。     

惯性平台系统火箭橇试验数据处理方法

火箭橇试验具有产生大过载、高速度、强振动和冲击等综合条件的能力,可以在综合环境条件下对惯性测量装置的功能和精度进行验证.针对惯性平台系统开展了3 km火箭橇轨道的功能验证试验,对振动传感器的数据进行了过载分析和振动量级的谱分析.研究了惯性平台系统火箭橇试验后的数据处理方法,包括振动传感器对橇体运行的过载和振动量的分离方法,遮光板光电组件的位置和速度微分方法,以及惯性平台系统的导航算法等,并通过数据比较,对惯性平台系统的性能和功能进行评价.由于遮光板外测系统的采样时间和观测量与捷联惯性测量装置不同,还探讨了试验后观测信息之间的转换、同一时刻不同信息数据的比较等数据处理方法,通过数据比较验证了惯性平台系统在火箭橇试验时的功能正常.该研究对惯性平台系统进一步开展精度验证和误差系数的分离奠定了基础.     

一种新型轻质泡沫混凝土挤入行为的试验研究

轻质泡沫混凝土是一种很重要的拦阻飞机/车辆等运动的新型阻滞材料。为了研究其挤入特性,利用CSS4410电子万能试验机和Dynatup9250落锤试验机,针对不同相对密度的轻质泡沫混凝土,在挤入速度从2×10-5 m/s到7.8m/s范围内的力学特征、破坏形式、减速度特性和抗压强度模型进行了系统研究。结果表明:此材料抗挤入阻力随挤入速度和材料相对密度增加而显著增加;挤入过程为材料脆性压溃/压实界面在弹性区的运动过程;挤入前端材料压溃/压实体积随挤入深度增加而增大且头部更尖锐;抗挤入过载加速度值与材料相对密度呈二次幂关系。故为保障人员及飞机等安全,应尽可能采用低相对密度材料。     

轻质结构材料力学性能虚拟教学实验平台的开发与应用

结合“新工科”力学类人才培养体系的要求,开发了轻质结构材料力学性能虚拟仿真实验平台。该平台采用基于Unity3D的WebGL技术,能够开展轻质点阵夹层结构设计与力学性能的三维仿真实验;利用该平台学生可以进行轻质结构材料的设计流程训练、点阵夹层结构设计方法训练、点阵夹层结构力学性能实验表征方法训练,从而掌握轻质结构材料力学设计流程、设计方法以及设计原理,增进对轻质结构材料承载需求的了解。实验核心内容包括轻质结构材料典型单胞设计及力学性能实验表征,实验结果为满足承载要求的轻质结构材料尺寸及力学性能实验数据。实践证明,该虚拟仿真实验有效解决了新材料设计实验教学难度大、成本高、耗时长,以及实验资源匮乏、无法满足新时期本科教学的问题。     

气相爆轰驱动二级轻气炮内弹道数值模拟

二级轻气炮是超高速弹丸驱动技术中使用最广泛的技术之一, 它在超高速气动物理现象及材料高速碰撞下力学性能的实验研究和验证方面起着不可或缺的作用. 中国科学院力学研究所基于爆轰驱动方法研制了一座大型二级轻气炮, 可弥补高压气体驱动能力有限和火药使用受限的不足. 本文基于经过实验验证的准一维数值模拟方法, 详细研究了该设备的内弹道动力学参数及发射性能, 并探讨了不同发射方法及装填参数对设备性能的影响规律和机理. 研究结果表明, 氢氧爆轰驱动相比于高压气体驱动具有明显优势; 不同爆轰驱动方式对弹丸发射性能影响较小, 但其影响到整个设备的强度设计; 对装填运行参数的研究表明增大爆轰段充气压力可以有效加强轻气炮发射性能, 而活塞质量变化对发射速度的影响较为复杂, 轻气炮实际运行中受设备设计指标及模型材料性能的限制, 优化过程中需要同时调整3种参数以达到轻气炮最佳性能.      

综述：微纳米尺度材料与结构的原位疲劳实验及性能研究进展

随着集成电路芯片、传感器、柔性电路系统、微/纳机电系统等微机械装置向集成化和小型化不断发展,如何预测其内部微纳米尺度结构和材料的机械性能及其可靠性成为了制约上述微机械装置进一步发展和应用的关键问题之一。在这些装置的长期使役过程中,微纳米尺度材料的疲劳性能又成为了近年来人们关注的热点问题。针对上述问题,首先,调研了与微纳米尺度材料原位疲劳实验方法和疲劳性能研究有关的文献。然后,总结了微纳米尺度原位疲劳实验方法和疲劳性能的研究现状,包括含有孪晶组织金属、梯度组织或粗细晶金属以及在单轴、多轴应力状态下的金属疲劳性能研究,并归纳了微纳米尺度界面疲劳损伤行为的研究现状。最后,对微纳米尺度材料的疲劳性能研究进行了展望,提出了对未来发展方向的思考。     

基于Hopkinson压杆的动态压剪复合加载实验研究

提出了一种可用于研究压剪复合加载下, 材料动态力学性能的实验装置, 该装置基于Hopkinson压杆, 通过添加一个带倾斜端面的垫块, 实现压剪复合加载.分析了该实验装置的基本数据处理方法, 并利用有限元分析验证了此分析方法的可行性;然后利用该装置对常规金属材料进行了相同冲击速度, 不同倾斜角度(0$^\circ$,30$^\circ$, 45$^\circ$)下的一系列实验. 实验结果表明, 该装置能实现压剪复合加载, 并且能得到材料的动态屈服面, 为研究材料在复杂应力状态下的动态力学性能提供了新的实验方法.      

基于LabVIEW的捷联惯性导航算法研究平台

为了研究利用LabVIEW仿真技术评估各种捷联惯导姿态更新算法的可行性,建立了基于LabVIEW的捷联惯性导航算法研究平台.该平台采用LabVIEW图形化编程软件编成,遵循了平台功能设计模块化和结构化的要求;通过设定轨迹参数生成模拟的惯性敏感器数据,对两种不同的导航姿态更新算法进行了比较.实验结果表明,该平台能够有效地评估不同捷联惯性导航算法的性能,克服了传统平台编程复杂、扩展性差的缺点,为进一步使用LabVIEW进行组合导航系统仿真奠定了基础.     

个人导航用压力传感器的三维打印制备数字模型

基于微喷三维打印机制造压力传感器,用于可穿戴的个人导航系统中。在基底表面不规则或者使用中经常被折弯的情况下,微喷打印工艺制备的MEMS器件精度更高,性能更好。研究了器件的可打印模型和工艺,给出压力传感器可打印的分层物理结构;研究了平面结构投影到三维基底上的投影空间,基于Terzopoulos弹性模型使用材料弹性度和结构弹性度模型给出投影空间;使用射线投影NURBS曲线来拟合边界轮廓,给出分层切片模型。为验证打印PZT膜的压电性能以及设计的压力传感器件的功能,使用不同的机械负荷测试其刚度,使用不同的直流偏置来测试耗损因数、品质因数等。通过比较实验对象的测量值和理论预测值之间的关系可以看出,打印的压力传感器薄膜具有很好的机械和电气性能。     

金属切屑塑性流动的稳定性

对金属正交切削过程中切屑形成机制和材料塑性流动行为进行实验研究和理论分析. 通过对4 种常用金属材料正交切削过程的实验研究和切屑形貌的微观观察,确定了连续切屑转变成锯齿切屑的临界速度. 结果表明该临界速度与材料性能相关. 在实验观察基础上,提出描述材料正交切削过程的二维分析模型. 该模型假设切屑形成区为包括主剪切区和次剪切区的一个平行四边形. 载荷有主剪切区中的剪应力和次剪切区中的正压力;通过量纲分析得到描述材料正交切削过程的无量纲主控参数和无量纲形式的基本控制方程;应用线性稳定性分析方法建立平面应变状态下评价材料塑性流动稳定性的普遍准则;求得切屑形成区内材料塑性变形的速度和应力近似解. 讨论切屑形成、形貌转变以及相关的塑性失稳机制. 分析结果表明, 表征材料惯性与阻尼之比的无量纲参数— 雷诺数可以作为主控参数描述金属切削过程以及切屑材料塑性流动的稳定性.      

不同材料参数和内压的轮胎对单腹板轮毂变形的影响

将轮胎材料简化为各向同性超弹性材料特性，考虑轮胎与轮毂和地面之间的三维接触以及轮胎中钢丝圈的影响，建立飞机单腹板机轮整体结构有限元模型。主要分析不同轮胎材料参数和内压下，单腹板轮毂轮缘处的径向变形，结果表明；轮毂剖面上测点的应变值与实验结果基本一致。轮胎下沉量与轮毂测点的径向变形和轮毂所受的载荷基本呈线性关系；凸出一侧的轮缘变形最大；轮胎下沉量较大时。轮胎材料参数对轮毂的径向变形影响明显；轮毂测点径向变形在1-2.5mm时，相同的径向变形，轮毂受到的总载荷受轮胎材料参数变化而变化，而在变形较大或较小时，影响不明显。对于同一种轮胎材料，不同的内压，轮毂的变形减轻比较大，气压越高，对于相同的轮胎下沉量，轮毂受到总体荷载也越高。     

Experimental analysis of vertical soil reaction and soil stress distribution under off-road tires

In this study, the vertical soil reaction acting on a driven wheel was measured by strain gages bonded to the left rear axle of a 2WD tractor driven under steady-state condition on different soil surfaces, tractor operations, and combinations of static wheel load and tire inflation pressure. In addition, the measurements of radial and tangential stresses on the soil–tire interface were made simultaneously at lug’s face and leading side near the centerline of the left rear tire using spot pressure sensors. The experimental results indicate that the proposed method of vertical soil reaction measurement is capable of monitoring the real-time vertical wheel load of a moving vehicle and provides a tool for further studies on vehicle dynamics and dynamic wheel–soil interaction. Furthermore, the measured distributions of soil stresses under tractor tire could provide more real insight into the soil–wheel interactions.     

Steering forces on undriven tractor wheel

The steering forces on an undriven, angled wheel mounting a 6-16 8PR tire were measured on a wheel test carriage at zero camber angle and at 1.5 km/h forward speed in a soil bin with sandy clay loam soil. The lateral force developed was found to be a function of slip angle, normal load, and inflation pressure for a particular soil condition. An exponential relationship could estimate the coefficient of lateral force of the 6-16 tire. The coefficients of this equation were found to be linearly related to inflation pressure. Rolling resistance of the wheel tested was found to be a function of slip angle, normal load, and inflation pressure for the soil condition tested. A linear relationship existed between the rolling resistance and slip angle, where the coefficients were found to be a function of inflation pressure and normal load. The generalized equations developed in the present study for estimating coefficients of lateral force and rolling resistance by taking both the tire and operating parameters into account, were found to be reasonably good by looking at the high coefficient of determination between experimental and estimated values.     

A new field single wheel tester

A new field single wheel testing device, as part of a field testing unit, was developed to perform traction tests on agricultural or cross country tires in the field. The tire testing device is mounted at the rear of a heavy wheeled tractor that also carries a unique soil property testing device at the front. The vertical, horizontal and side forces are measured inside a frame that holds the test wheel, while the torque is measured by a separate linkage system. The tire testing device is capable of testing tires up to 2 m in diameter; it can apply vertical force up to 50 kN, and torque up to 31 kNm.     

An indoor traction measurement system for agricultural tires

To reliably study soil–wheel interactions, an indoor traction measurement system that allows creation of controlled soil conditions was developed. This system consisted of: (i) single wheel tester (SWT); (ii) mixing-and-compaction device (MCD) for soil preparation; (iii) soil bin; (iv) traction load device (TLD). The tire driving torque, drawbar pull, tire sinkage, position of tire lug, travel distance of the SWT and tire revolution angle were measured. It was observed that these measurements were highly reproducible under all experimental conditions. Also relationships of slip vs. sinkage and drawbar pull vs. slip showed high correlation. The tire driving torque was found to be directly influenced by the tire lug spacing. The effect of tire lug was also discussed in terms of tire slip.     

高速切削实验平台在力学实验教学中的应用

传统的力学实验已无法满足研究生创新性实验教学的需要。为了使研究生在科学研究中掌握实验分析的基本方法和技能,本文基于Hopkinson压杆加载技术建立了一套高速切削实验系统。该实验系统作为一个科研平台,能够实现切削过程的瞬态冻结并完成变形场和切削力的实时测量,可为高速切削机理研究提供基础实验数据。同时,该实验系统也是一个综合性的实验平台。基于该平台,可以完成金相分析、光栅光纤测力、变形场测量以及塑性本构分析等力学实验教学。高速切削实验平台将力学实验与科学研究相结合,有利于培养研究生独立分析与研究的能力,为研究生未来的科研工作打下基础。     

Tire slip-angle force measurements on winter surfaces

Tire lateral force data on winter surfaces cannot be obtained with the traditional laboratory test technique of an instrumented tire on a moving belt surface. Furthermore, changing snow and ice conditions can drastically change the tire/surface interaction. In this study the Cold Regions Research and Engineering Laboratory’s (CRREL’s) Instrumented Vehicle (CIV) was used in a unique configuration to measure tire lateral force versus slip-angle data on ice and snow at various temperatures, moisture contents, depths, and densities. The vehicle is instrumented to record longitudinal, lateral, and vertical force at the tire contact patch of each wheel as well as vehicle speed, tire speed, and front tire slip angle. The tests were conducted at the Keweenaw Research Center (KRC) in northern Michigan in February 2005 and March 2006. Tests were conducted on ice, packed snow from 0.50 to 0.58 g/cc, remixed snow depths of 2.5–20.3 cm at 0.43 to 0.48 g/cc and freshly fallen snow with depths of 0.5–17 cm at 0.07 to 0.23 g/cc. Surface air temperatures during testing ranged from −14 to 1.6 °C. The data collected show that peak lateral force and the shape of the lateral force versus slip-angle curve are related to snow properties and depths.     

Effects of tire inflation pressure and tractor velocity on dynamic wheel load and rear axle vibrations

The objective of this study was to evaluate the effects of agricultural tire characteristics on variations of wheel load and vibrations transmitted from the ground to the tractor rear axle. The experiments were conducted on an asphalt road and a sandy loam field using a two-wheel-drive self-propelled farm tractor at different combinations of tractor forward speeds of approximately 0.6, 1.6 and 2.6 m/s, and tire inflation pressures of 330 and 80 kPa. During experiments, the vertical wheel load of the left and right rear wheels, and the roll, bounce and pitch accelerations of the rear axle center were measured using strain-gage-based transducers and a triaxial accelerometer. The wavelet and Fourier analyses were applied to measured data in order to investigate the effects of self-excitations due to non-uniformity and lugs of tires on the wheel-load fluctuation and rear axle vibrations. Values for the root-mean-square (RMS) wheel loads and accelerations were not strictly proportional and inversely proportional to the forward speed and tire pressure respectively. The time histories and frequency compositions of synthesized data have shown that tire non-uniformity and tire lugs significantly excited the wheel load and accelerations at their natural frequencies and harmonics. These effects were strongly affected by the forward speed, tire pressure and ground deformation.     

Laboratory experimental study of tire tractive performance on soft soil: Towing mode,traction mode,and multi-pass effect

Tire tractive performance, soil behavior under the traffic, and multi-pass effect are among the key topics in the research of vehicle off-road dynamics. As an extension of the study (He et al., 2019a), this paper documents the testing of a tire moving on soft soil in the traction mode or towing mode, with a single pass or multiple passes, and presents the testing results mainly from the aspects of tire tractive performance parameters, soil behavior parameters, and multi-pass effect on these parameters. The influence of tire inflation pressure, initial soil compaction, tire normal load, or the number of passes on the test data has been analyzed; for some of the tests, the analysis was completed statistically. A multi-pass effect phenomenon, different from any phenomenon recorded in the available existing literature, was discovered and related to the ripple formation and soil failure. The research results of this paper can be considered groundwork for tire off-road dynamics and the development of traction controllers for vehicles on soft soil.     

Prediction of soil compaction under pneumatic tires a using fuzzy logic approach

Artificial intelligence systems are widely accepted as a technology offering an alternative way to tackle complex and ill-defined problems. They can learn from examples, are fault tolerant in the sense that they are able to handle noisy and incomplete data, are able to deal with non-linear problems, and once trained can perform prediction and generalization at high speed. Compared with traditional approaches, fuzzy logic is more efficient in linking the multiple inputs to a single output in a non-linear domain. The purpose of this study was to investigate the relationship between tire working parameters and soil compaction characteristics, and to illustrate how Fuzzy expert system might play an important role in prediction of soil. All experimental values were collected from soil bin. The trials were conducted in different tire types, vertical loads, inflation pressures and forvard velocities. In this paper, a sophisticated intelligent model, based on Mamdani approach fuzzy modeling principles, was developed to predict the changes in penetration resistance, final pressure and bulk density of soil due to wheel traffic. The verification of the proposed model is achieved via various numerical error criteria. For all parameters, the relative error of predicted values was found to be less than the acceptable limits (10%).