An experimental technique to measure projectile deceleration history during normal penetration into plain concrete

The present paper presents a new experimental method to measure the deceleration time history of projectiles penetrating into concrete in full-size test. The experiment can be carried out by using an onboard accelerometer to measure the projectile deceleration history and the data are transmitted to a ground recording system. With this experimental method, a series of tests on hemisphere-nose steel projectiles penetrating normally into plain concrete at the velocity region 150–400 m/s have been executed and the deceleration histories obtained. The high frequency portion in the deceleration data has been investigated and proved to be the structure response of projectile. The characteristics of deceleration history have also been analyzed and discussed.     

Temperature and rise-time effects on dynamic strain measurement

Strain pulses in a test specimen were measured over a temperature range of ?73 to +149°C with foil and semiconductor strain gages. These tests were performed to determine if the rise time and amplitude of the gage output change as a function of temperature. The existence of a constant that should be added to the theoretical rise times of resistance strain gages, as suggested by Koshiro Oi, was reexamined. ‘Long’ rise-time strain pulses were produced in the test specimen by an impacting steel ball. The rise times of these pulses were on the order of 7 μs and the amplitudes were approximately 65 μm/m. The results of these tests show that the rise time and amplitude of the gage do not change as a function of temperature. ‘Short’ rise-time strain pulses of approximately 500 μm/m with a rise time of 2 μs were produced in a test specimen by a short pendulum-type hammer apparatus. The results of these tests showed that the amplitude of the gage output was relatively independent of test temperatures but exhibited a slight hysteresis effect. The rise times for these tests remained constant up to a temperature of 93°C, then started to increase. The rise times at 149°C were approximately 100 percent longer than at room temperature. Under optimum conditions, a pulse with a measured rise time of 0.18 μs could be generated. The results of these tests indicated that the theoretical rise-time additive constant of resistance strain gages is 0.05 μs or less. This is one-half the value that Bickle arrived at by reevaluating Oi's data. However, since the real rise time of the pulse was unknown, this additive constant is not necessarily a property of the gage.     

非等比例缩比侵彻/贯穿相似规律研究

高速侵彻弹体的弹载部件/关键元器件的生存性与可靠性考核是引战系统研制领域的热点与难点问题，受原型试验的成本限制，利用缩比弹体搭载原型引信部件开展非等比例缩比试验研究是可行途径。针对传统等比例缩比方案无法满足弹体刚体过载相似性要求的情况，研究了非等比例缩比侵彻/贯穿相似规律，提出了非等比例缩比侵彻试验设计方法。数值计算结果表明:侵彻半无限厚混凝土靶条件下，非等比例缩比弹刚体过载的脉宽、幅值均可实现与原型弹刚体过载一致的加载条件；贯穿多层薄靶的条件下，通过调节靶板布置及弹体初速等试验工况，合理设计缩比弹体结构，可使非等比例缩比试验的弹体刚体过载峰值和脉宽覆盖原型试验。通过缩比模型试验得到的刚体过载特性可以为弹体及引信部件抗过载防护设计提供可靠的参考依据。     

较低应变率大应变条件下聚氨脂泡沫材料的态力学性能实验

利用加长型分离式霍普金森压杆(入射杆长6000mm、子弹长800mm)研究聚氨脂泡沫材料在较 低应变率大应变条件一维应力状态下的动态力学性能,获得了约550s的长加载脉冲,得到了该材料在应变 率520s-1、应变0.15条件下的应力应变曲线,对较低应变率条件下,应变率与动态应力平衡之间的关联进行 了讨论。     

T22铁基粉末冶金摩阻材料的研制与应用

重载机械的发展对摩阻材料提出了更高的技术要求。铁基粉末冶金摩阻材料是以铁为基体,含有适量摩擦组元和润滑组元的多相复合材料,成本较低,适用于制作重载机械制动瓦。作者介绍了自行研制的用于制作装甲履带车辆制动瓦的T22铁基粉末冶金摩阻材料的基本组成和性能,并将这种制动瓦与铸铁瓦进行了对比试验,表明前者不仅在热稳定性和耐磨性上都明显地比后者的好,而且它还具有车辆减速度高、制动距离短和使用寿命长等优点,可以满足转向灵活、使用可靠的要求,提高了装甲履带车辆的机动性。     

Friction Between Steel and a Confined Inert Material Representative of Explosives Under Severe Loadings

The ignition of a confined explosive submitted to an impact strongly depends on the friction conditions between the explosive and the confinement material (generally steel). A test has been developed to study the friction between steel and a material mechanically representative of an explosive. The scope of interest is that of high pressures and high relative velocities (respectively 20 MPa and 10 m/s). The friction device consists of making a cylinder, formed of the material, slide through a steel tube. Axial prestress enabling the steel-material contact stress to be generated is performed by means of a screw-nut system. This confinement state avoids any fracture of the material from occurring throughout the test. Two kinds of tests are carried out: low-velocity (around 1 mm/min) and high-velocity (around 10 m/s). The relative displacement is obtained using a testing machine during the low-velocity tests, and thanks to a Hopkinson bars system during the high-velocity tests. Examination of the measurements obtained during high-velocity tests shows that a workable steady state of equilibrium has been reached. As the interface stresses cannot be measured, the friction coefficient must be determined using indirect data: force measurements obtained from the machine or from the Hopkinson bars and strain measurements made on the exterior of the tube. The procedure to identify the steel-material friction coefficient from these measurements entails analytical modelling and finite element simulations of the mechanical behaviour of the tube-specimen assembly. The friction coefficient identified during the high-velocity tests is far higher than the coefficient identified during the low-velocity tests.     

高g值加速度发生器中的波形整形技术

以Hopkinson压杆实验装置作为火工品抗过载实验中的高g值加速度发生器,通过数值模拟分析了子弹（形状）、波形整形器（材料、直径、厚度）对加载脉冲的影响规律,并获得了所需的加速度脉冲,实现了有效控制和改善火工品冲击实验中的加载环境。研究结果可为检验火工品在冲击环境下或经冲击后性能可靠度的实验设计、测试等提供依据。     

小当量水中爆炸气泡的脉动现象

为研究水中爆炸气泡的脉动现象,设计了用于小当量(10 g TNT)水中爆炸研究的爆炸水箱,在爆炸水箱装置中进行了多次0.125、1.000、3.370、8.000 g TNT当量的PETN球形炸药水中爆炸试验。采用高速摄影系统获得了气泡脉动图片;给出试验范围内气泡脉动过程中气泡直径、速度及加速度随时间变化的拟合曲线。对气泡脉动直径和周期数据进行了分析,这些数据基本符合爆炸相似律。     

一种基于SHTB的Ⅱ型动态断裂实验技术

冲击剪切载荷作用下动态断裂韧性的测定是材料力学性能和断裂行为研究中重要组成部分.为了测定材料的Ⅱ型动态断裂韧性,许多学者采用不同的试样与实验方法进行了实验,但限于实验条件,裂纹断裂模式往往是I+Ⅱ复合型,而不是纯Ⅱ型,因而不能准确测得材料的Ⅱ型动态断裂韧性.鉴于此,本文基于分离式霍普金森拉杆(split Hopkinson tension bar,SHTB)实验技术,提出一种改进的紧凑拉伸剪切(modified compact tension shear,MCTS)试样,通过夹具对MCTS试样施加约束,从而保证试样按照纯Ⅱ型模式断裂.采用实验-数值方法对MCTS试样动态加载过程进行分析,将实验测得的波形输入有限元软件ANSYS-LSDYNA,得到了裂纹尖端应力强度因子-时间曲线,并与紧凑拉伸剪切(compact tension shear,CTS)试样进行了对比.同时采用数字图像相关法进行了实验,验证了有限元分析结果.结果表明,MCTS试样在整个加载过程中K_I K_Ⅱ,裂纹没有张开;而CTS试样在同样的加载过程中K_IK_Ⅱ,出现裂纹张开现象.这说明MCTS试样能够准确地测定材料的Ⅱ型动态断裂韧性,为材料动态力学测试提供了一种有效的实验技术.     

Longitudinal wave propagation in axisymmetric structures with material and/or aereal discontinuity

For the purpose of delineating the applicability of simple uniaxial wave-propagation theory to a class of axisymmetric structures, an experimental and a two-dimensional numerical investigation involving the transmission of longitudinal waves produced by impact of steel spheres was conducted. The axisymmetric samples were fabricated by cementing together two components of equal length; the constituents were either uniform circular bars or tubes of aluminum or steel of different diameters that produced a target either with an abrupt discontinuity or a continuous lateral surface at the center. The principal tests involved pulse durations of about 50 μs corresponding to a minimum pulse length-to-bar diameter ratio of 6.7 where the transmitted and reflected stress ratios obtained from surface strain-gage measurement were generally found to be predicted by elementary bar theory within experimental error no larger than ±3 percent. Much poorer correlation in these values was obtained for tests involving pulses of substantially shorter duration; here, the dispersive effects capable of being predicted only by higher-order theories were prominently manifested. A two-dimensional analysis for a few configurations was executed using a finite-element procedure and compared with the predictions from elementary theory and with test results; for the 30-μs pulse duration employed, this calculation provided no improvement relative to elementary theory for the predictions of strain histories at stations even only slightly removed from the discontinuity. Both measurement and the results of the two-dimensional calculations indicated that stress uniformity across the section was achieved at stations as close as two bar diameters from the discontinuity for pulse durations ranging from 25 to 50 μs.     

Evaluation of Viscoelastic Characteristics of Short-fiber Reinforced Composite by Indentation Method

Indentation tests are performed to evaluate the viscoelastic characteristics of a short-fiber reinforced composite. Finite element analysis is also carried out to estimate the macroscopic viscoelastic characteristics of the composite by using a unit cell models. The results of indentation tests show that a force-displacement curve obtained by the indentation test depends on the area of the fibers appeared in the impression. The creep compliance evaluated by these indentation tests is compared to that by the finite element analysis. As the results, it is suggested that the result of indentation test performed on the surface of the composite without fibers means the measurement result for isotropic composite or anisotropic composite in the direction of the smallest rigidity. On the other hand, indentation test performed on the fiber indicates the measurement result of anisotropic composite in the direction of the largest rigidity. These results present the method to measure the macroscopic characteristics of short-fiber reinforced composite by indentation tests.     

复合射孔压力加载下铜柱测压计测试实验和数值分析

进行基于铜柱测压和实测压力时间曲线的石油井射孔压裂实验,建立铜柱测压计的数学模型,并 采用交互式计算方法得出其作用过程的解析解。分析结果表明,井下射孔压裂过程中,压力上升沿很陡,活塞 在外部压力达到峰值时,速度很大,会继续压缩铜柱直到速度为零。活塞的运动可以分为加速和减速撞击2 个过程。活塞的最大速度决定了铜柱测压计最终测试值,且与速度成正比。射孔脉冲压力加载过程中铜柱测 压计的误差取决于压力上升时间、脉冲宽度、峰值压力等影响因素。火炮膛压加载下铜柱测压计误差较小。     

Simple Testing System for Pure Bending Tests with Large Deflections

The potential uses of new materials in structural elements are growing constantly. The focus is on the use of composites with high strengths and strains [1], among other properties. This means that their mechanical properties and failure modes need to be described. Bending tests are widely used for these purposes due to their advantages compared to other types of tests. In particular, pure bending tests are very useful when calculating mechanical parameters and failure modes. These tests do not superimpose different types of loading on the specimens and do not introduce shear stresses which often make the test difficult to carry out properly (for example, in sandwich beams that exhibit great changes in curvature and therefore have a small core thickness). Nonetheless, if long specimens with large allowable strains or curved specimens need to be tested, then traditional bending test methods may fail to apply; making the displacement of support points and load application necessary. This work proposes a pure bending test method that overcomes these disadvantages. It is based on a pulley system which, in addition to introducing the necessary rotations, allows the reduction of the distance between test specimen supports and guarantees pure bending. After the corresponding kinematic study that shows the foregoing, the tests carried out on a test specimen yield uniform characteristics known to confirm the validity of the design.     

Resonant frequencies in an elevated spherical container partially filled with water: FEM and measurement

In this paper, a numerical-experimental study of the overall dynamical response of elevated spherical tanks subjected to horizontal base motion is presented. The main objective is to gain insight in the physical response of this particular structural typology widely used in the petrochemical industry as liquefied petroleum gas (LPG) containers. In order to identify the natural frequencies of the modes that mainly contribute to the response, experimental free vibration tests on an elevated spherical tank model for different liquid levels were carried out. Next, a numerical model that takes into account the coupling between fluid and structure was developed and validated against the experimental results. A very good agreement between experimental and numerical results was obtained. The results obtained show the influence of liquid levels on natural frequencies and indicate that the sloshing has a significant effect on the dynamical characteristics of the analyzed system. In order to obtain a good representation of the overall dynamical behaviour of the system by means of a simplified lumped mass model, a minimum of three masses is suggested. Finally, appropriate names of these three masses are proposed in the present paper.     

Numerical analysis of progressive damage in nonwoven fibrous networks under tension

Understanding a mechanical behaviour of polymer-based nonwoven materials that include large-strain deformation and damage can help to evaluate a response of nonwoven fibrous networks to various loading conditions. Here, a nonwoven felt made by thermal bonding of polypropylene fibres was used as a model system. Its deformation and damage behaviour was analysed by means of experimental assessment of damage evolution based on single-fibre failure and finite-element simulations. Tensile tests of nonwoven fabrics were carried out to characterise their damage behaviour under in-plane mechanical loading. It was found that progressive failure of fibres led to localization of damage initiation and propagation, ultimately resulting in failure of the nonwoven felt. To obtain the criteria that control the onset and propagation of damage in these materials, tensile tests on single fibres, extracted from the felt with bond points attached to their ends, were performed. A finite-element model was developed to study damage initiation and propagation in nonwovens. In the model, structural randomness of a nonwoven fibrous network was implemented by means of direct introduction of fibres according to the orientation distribution function. The evolution of damage in the network was controlled by a single-fibre failure criterion obtained experimentally. The proposed numerical model not only captured the macroscopic response of the felt successfully but also reproduced the underlying mechanisms involved in deformation and damage of nonwovens.     

Analyses of the penetration process considering mass loss

Based on the dynamic cavity-expansion theory and momentum theorem, the key parameters of projectile penetrating into concrete target, i.e., the penetration time and time histories of DOP, deceleration, mass loss, instant mass loss rate and nose shape, are obtained by incremental calculation considering mass loss of projectile. The calculation results are consistent with the experimental results. Due to the mass loss and thus nose blunting effects, the pulse shape of deceleration may be quite different from that obtained in the analysis of a rigid projectile, and then the dissimilarity is analyzed. It is found that the pulse shape of deceleration is determined by the drag force and essentially determined by the performances of target and projectile, i.e., the shear strength of target, the Moh’s hardness of aggregate in concrete and the CRH value of projectile nose. Further analysis indicates that the pulse shape of deceleration is more sensitive to the performance of target than that of projectile.     

Performance and robustness analysis of a Hardware In the Loop full-scale roller-rig for railway braking and traction testing

Traditionally, braking and traction on-board subsystems, such as traction systems, braking plants and safety subsystems (e.g. WSP devices) can be tested and verified through fullscale roller-rigs, to avoid expensive on-track tests. In this work the authors investigate the test-rig built in the research center “Centro di Dinamica Sperimentale Osmannoro-Firenze (CDSO)” by Rete Ferroviaria Italiana (RFI), in which the braking and traction systems are tested using an innovative Hardware In the Loop (HIL) architecture able to perform the simulation of a known wheel-rail adhesion pattern (in particular degraded adhesion condition). The objective of this work is to study, starting from the knowledge of the system characteristics, the performances and the robustness of the HIL architecture during a simulation of braking and traction phases under degraded adhesion conditions. This work has been developed in collaboration with Italcertifer S.p.a. and Trenitalia S.p.a. that provided the technical data of the test rig and the considered railway vehicle (the E464 locomotive).     

Dynamic compressive responses of intact and damaged ceramics from a single split Hopkinson pressure bar experiment

A novel dynamic compressive experimental technique has been developed based on a split Hopkinson pressure bar. This new method dynamically loads the ceramic specimen by two consecutive stress pulses. The first pulse determines the dynamic response of the intact ceramic materiaal and then crushes the specimen, and the second pulse determines the dynamic compressive constitutive behavior of the ceramic rubble. Precise pulse shaping ensures that the specimen deforms at nearly constant strain rates under dynamic stress equilibrium during the loading by both stress pulses. Pulse shaping also controls the amplitudes of loading pulses, the values of strain rates, the maximum strains in the rubble specimens, and the proper separation time between the two loading pulses. The feasibility of the new technique is demonstrated by the experimental results obtained on an AD995 alumina.     

飞机模型高速撞击钢筋混凝土载荷特性实验研究

为得到大型商用飞机撞击的冲击载荷特性及其计算方法,基于火箭橇加载试验平台,搭建了飞机模型撞击钢筋混凝土运动靶体测试系统,开展了两种不同尺寸飞机模型的撞击试验,利用高速摄影技术获得了飞机模型撞靶前的姿态、着速及飞机模型撞靶的破坏过程。采用加速度测试系统和激光干涉测速系统,分别得到撞击过程中运动靶体的加速度和速度历史,据此得到靶体受到的冲击载荷-时间曲线,二者吻合,验证了测试系统的可靠性。通过飞机模型上安装的机载存储过载测试系统,获得了撞击过程中飞机模型的负加速度-时间曲线,由此确定了修正的Riera理论模型中的静载荷项,并进一步计算得到靶体受到的冲击载荷-时间曲线,与通过测试靶体的加速度或速度得到的结果一致,验证了使用修正的Riera理论模型计算飞机模型冲击载荷的合理性及计算方法的正确性,同时确定了适合于本试验中飞机模型的修正系数α。