火箭橇靴轨接触特性数值分析

为研究火箭橇靴轨接触特性,采用Eluer-Bernouli梁单元对火箭橇橇体进行离散,建立了考虑轨道不平顺度的靴轨非线性接触力模型,通过Newmark-β结合Newton-Raphson局部迭代求解包含靴轨非线性接触力的橇轨动力学方程,并通过试验验证了数值解的正确性,数值计算结果表明:在700 m/s速度下,靴轨接触力...     

热敏电阻在液体火箭发动机试验中的应用

阐述了目前应用于低温推进剂液体火箭发动机试验的热敏电阻温度传感器的特点，介绍了热敏电阻温度传感器在液体火箭发动机试验中的应用方案，包括信号变换器设计、传感器校准数据处理方法、传感器自热效应分析以及测量系统组成，分析了影响测量不确定度的因素，给出了应用热敏电阻温度传感器的测量不确定度小于0．3K。     

航天运载火箭部件低温试验系统改进

为了获得运载火箭某部件(阀门)准确、可靠的低温试验数据,建立了阀门低温试验系统,提供阀门低温试验所需要的低温温度、气体压力等试验条件,并具有在低温温区进行相关试验参数测量的数据检测系统.利用该低温试验系统,进行了不同类型阀门、不同试验要求的多次试验.试验数据表明,该试验系统的低温性能技术指标稳定,能够很好地模拟火箭飞行状态中阀门的温度、压力、振动等参数,具备对火箭部件性能进行低温鉴定的功能.     

小推力液体火箭发动机动态推力测试台架设计

推力测试台架是准确测量火箭发动机推力的关键技术之一，但现有的测试台架能够很好兼顾长、短脉冲测试的较少。针对此况，采用传感器陶瓷厚膜技术，设计了100N范围内小推力液体火箭发动机动态推力测试台架，通过热试车试验考核，该台架可兼顾长、短脉冲的测量，在满足稳态精度的同时，具有良好的动态特性，为小推力液体火箭发动机测试台架的设计提供了一种新思路。     

Responses of side impact dummies in sled tests

Sled tests were conducted at a velocity of 6.7 m/s using side impact dummies (SID, BioSID, ES-2, and WorldSIDp) and the resulting biomechanical responses were compared with responses from post mortem human subjects (PMHS). Initial impact conditions were with and without pelvic offset in combination with and without padding on the impacting wall. Impact forces, thoracic trauma index, chest compression, and viscous criteria were evaluated. The probability of injury was estimated and rates of deformation were computed for each body region. Dummy responses were not always similar in terms of trend and injury criteria when compared with PMHS tests under the same initial conditions. Response variations will be of value in improving the biofidelity characteristics of dummies for crashworthiness evaluations.     

Measurement of fracture initiation toughness and crack resistance in instrumented Charpy impact testing

A new method has been developed involving direct measurement of the load-line displacement during instrumented Charpy testing. The method uses a laser interferometer to measure displacement in addition to the load-line displacement derived from the load signal. Tests were conducted using fatigue precracked and V-notched test pieces in the temperature range +23°C to −80°C on a conventional ship grade steel, a pressure vessel steel and two welded joints. Good correlation was found between the J_0.2 initiation fracture toughness determined by the multi-specimen method and the J_i fracture toughness determined from single specimens using the new method to detect ductile fracture initiation.     

Fracture parameters determination at yield point and fracture initiation in instrumented impact testing

A method of fracture parameters determination at yield point and fracture initiation is derived from theoretical analysis of bending load-time response of materials during CHARPY impact testing. It allows to overcome the difficulties due to inertial effect and specimen vibrations. Furthermore, the method enables to determine the time at which fracture initiates, that is when the specimen crack begins to extend. The procedure has been applied to various model materials such as steel, aluminum alloy, PMMA and soda-lime glass in order to specify the fracture parameters which can be carried out by the method. Depending on the type of materials K_id and J_Id can be determined.     

Retardation of high-velocity streams in various media

Strong waves were generated in Plexiglas and in aluminum under a pressure of 2.9 and 7.1 mbars respectively. The retardation of high-velocity streams in air and in inert gases is analyzed.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 24, No. 2, pp. 354–356, February, 1973.     

Shock-spall asymmetry in high-velocity impact of solids

A new, previously unreported physical phenomenon has been observed in experiments with high-velocity impact of various strikers on metal targets of finite thickness. According to this, sufficiently strong and tough structural materials (armor steel, titanium alloys, etc.) exhibit fractionation of the spall plate formed upon dynamic contact with the striker or its deformed part. This always results in an odd number of fragments (three, five, seven, etc.) of similar configuration. Systematic experiments on retained samples revealed progressive fractionation of the spall plates, with the number of fragments increasing up to eleven. Further evolution was difficult to follow because trapping of the fragments was hindered by their high velocities, which led to unavoidable additional fragmentation of the spall plates in the course of their interaction with a gradient package of trapping material (ranging from felting to sand).     

Vortex structures in a ceramic under high-velocity impact

A finite-element method in a two-dimensional axisymmetric formulation is used to analyze the characteristics of shock-wave processes in a ceramic plate under the impact of a high-speed cylinder. It is established that a vortex structure is formed and the evolution of the vortices is investigated. Pis’ma Zh. Tekh. Fiz. 23, 86–90 (December 26, 1997)     

Fatigue crack initiation in AA2024: A coupled micromechanical testing and crystal plasticity study

A new combined experimental and modelling approach has been developed in order to understand the physical mechanisms that lead to crack nucleation in a polycrystalline aluminium alloy AA2024 undergoing cyclic loading. Four‐point bending low‐cycle fatigue tests were performed inside the chamber of a scanning electron microscope on specimens with a through‐thickness central hole, introduced to localize stresses and strains in a small region on the top surface of the sample. Fatigue crack initiation and small crack growth mechanisms were analyzed through high‐resolution scanning electron microscope images, local orientation measurements using electron‐back‐scattered‐diffraction, and local strain measurements using digital image correlation. A crystal plasticity finite element model was developed to simulate the cyclic deformation behaviour of AA2024. Two‐dimensional Voronoi‐based microstructures were generated, and the material parameters for the constitutive equations (including both isotropic and kinematic hardening) were identified using monotonic and fully reversed cyclic tests. A commonly used fatigue crack initiation criterion found in the literature, the maximum accumulated plastic slip, was evaluated in the crystal plasticity finite element model but could not predict the formation of cracks away from the edge of the hole in the deformed specimens. A new criterion combining 2 parameters: The maximum accumulated slip over each individual (critical) slip system and the maximum accumulated slip over all slip systems were formulated to reproduce the experimental locations of crack nucleation in the microstructure.     

Some fracture mechanics properties in high-velocity impact-damaged aluminium plates

The paper describes the results of an experimental programme aimed at the evaluation of the fracture mechanics properties of high velocity, about 6  km  s⁻¹ , impact-damaged aluminium plates, 2219-T851. The energy of the impacts was the ballistic limit, i.e. large bumps were produced but the plates were not perforated. Test were carried out to evaluate the residual stress field in the impact-damaged area, the static resistance of the plates in the presence of a through crack and the crack propagation rate of a through crack located at the centre of the impact-damaged area. The results of the tests clearly show that the mechanical properties of the material remain practically unchanged after the high-velocity impact. Furthermore, by taking into account the geometry of the bumps, the mean crack propagation rate of a defect can be predicted quite accurately.     

An oblique impact anomaly in high-velocity liquid impact on glass

The residual strength of glass discs after impact by high-velocity water jets has been found as a function of impact angle. An unexpected result is that under certain conditions the damage suffered is a maximum for non-normal impact. This effect is shown to be caused by radial cracks forming during the oblique impact. These cracks are not observed for normal impact and their formation is dependent upon specimen geometry. The result is of practical significance to the rain erosion situation where aircraft and missile components may suffer damage by encounters with rain drops.     

Model-based inverse characterization of high-velocity tension impact failure in composites

This study presents the material characterization of high-velocity tension impact failure in composites using the split Hopkinson bar (SHB) test and the inverse analysis. A simulation code for the SHB test was developed using finite element analysis. In the code, the Hashin failure criterion is used to characterize the impact failure phenomena in composites. Material characterization is achieved to identify the material parameters for the Hashin criterion through inverse analysis from the measured strain histories during the SHB test. The advantage of this characterization is to obtain the true dynamic failure properties of composites without strict assumptions of elastic wave propagation on a specimen during the SHB test. Numerical examples are used to demonstrate the effectiveness of the present characterization.     

A study of fatigue failure initiation in high cycle high-pressure automotive applications and conventional rotating bending fatigue testing

The search for greater power and efficiency from automotive engines places components under ever increasing stress. This study compares results obtained from testing of engine components under extreme operating conditions with those obtained from laboratory-based tests. Conventional rotating bending fatigue testing has been applied to high strength alloy steel samples processed and heat treated under the same conditions as engine test components. The results are compared with those obtained from engine components tested under high-pressure cyclic loading using specially designed engine test rigs. Failure initiation sites in the high strength alloy steel samples have been identified and categorised using scanning electron microscopy with X-ray mapping. The influence of inclusion content, heat treatment process and surface finish have been determined and used to inform design considerations, heat treatment processing conditions and material selection.     

Heat transfer in a nuclear rocket engine

Special features of heat transfer in the reactor of a nuclear rocket engine (NRE) are dealt with. It is shown that the design of the cooling system of the NRE reactor is governed by its stability to small deviations of the parameters from the corresponding calculated values and the possibility of compensating for effects due to nonuniformities and disturbances of various types and scales.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 67, Nos. 1–2, pp. 27–31, July–August, 1994.     

The role of numerical simulation in the study of high-velocity impact

The issue of the role of numerical simulation in solving the high-velocity impact problems is discussed. The applicability of some most often used models to describe the shock wave processes is analyzed. The model of deformation and fracture of materials under the action of dynamic loading, which combines the macro- and microstructural representations of the deformation and fracture mechanisms, is described. The solutions of some problems which demonstrate the posibilities of the model in studying physical regularities of the high-velocity impact process are presented.     

Thermal layers near a friction surface of bodies in high-velocity slip

Thermal layers generated when one body slips over the surface of another are considered. Exactness of the solutions obtained by the methods of the boundary layer theory is analyzed.Institute of New Physical and Applied Problems of the Ukrainian Academy of Sciences, Kiev. Translated from Inzhenerno-fizicheskii Zhurnal, Vol. 63, No. 6, pp. 760–766, December, 1992.     

In situ synchrotron ultrasonic fatigue testing device for 3D characterisation of internal crack initiation and growth

This work presents a new ultrasonic fatigue testing device for studying the initiation and propagation mechanisms of internal microstructurally short fatigue cracks using in situ synchrotron tomography. Its principle is described as well as the method used for automatically detecting crack initiation and its subsequent growth. To promote internal crack initiation, specimens containing internal casting defects were tested between the high cycle and very high cycle fatigue regimes (10⁷‐10⁹ cycles). Preliminary results show the ability of this new device to initiate an internal microstructurally short crack in a reasonable testing time and monitor its growth.