Deformation of metal surfaces by the oblique impact of square plates

The impact of rigid square plates onto ductile steel targets has been studied theoretically and experimentally, in order to investigate a type of impact which occurs in cases of erosion by solid particles. Impacts may be classified according to the sense of rotation of the plate after impact; for the more common sense, of forward ratation, experimental measurements of energy loss, crater volume and rotational energy after impact were made and showed good agreement with the theoretical predictions.     

An experimental study on the behaviour under impact loading of metallic cellular materials

This paper presents an experimental study on the impact response of metallic cellular materials, i.e. aluminium honeycombs of various cell sizes and wall thicknesses, aluminium foams made from two different manufacturing processes (IFAM and Cymat), as well as hollow sphere agglomerates (nickel and iron). A 60 mm diameter nylon Hopkinson pressure bar is used to improve the signal/noise ratio and to host larger samples containing a sufficient number of cells. Quasi-static and classical Split Hopkinson Pressure Bar (SHPB) tests as well as direct impact Hopkinson bar tests (higher speeds up to 50 m/s) are performed. Significant rate sensitivities are observed for most of the cellular materials studied. Analyses of the potential causes of this macroscopic rate sensitivity show that the microinertia effect in the successive folding process could be an important factor.     

An analytical and experimental study of stretch flanging

A stretch flanging operation on a flat circular sheet with a hole in the center has been analyzed by means of a total strain membrane theory of rigid-plasticity which incorporates strain hardening and anisotropy in the direction normal to the sheet. Numerical procedures are used to calculate the stress and strain distributions in the sheet. Numerical results so obtained indicate that the state of stress in the flange is dominantly uniaxial. By making use of this observation, an approximate theory for the stretch flanging has been developed, and a closed-form expression for the maximum strain in the flange has been obtained in terms of the geometrical variables of the flange. Experimental data, using aluminum-killed steel sheets, have been obtained and compared with the corresponding theoretical results. It was found that, for strains less than 100 per cent (which is the region of practical interest), the calculated results are in good agreement with the experimental data.     

An apparatus for the study of wear under dynamic loading conditions

A multipurpose wear testing apparatus has been designed, constructed and calibrated. The apparatus is primarily an impact wear testing device, but it may also be used for vibratory and oscillatory wear experimentation. The system utilizes a versatile displacement- and force-controlled device, which allows accurate control and measurement of the load cycles and their frequencies and the relative normal and transverse velocities between the wear surfaces as well as their time of contact. Features of this design permit testing at elevated frequencies and investigation of the effect of individual parameters on the wear process. These features include a facility to manipulate the system stiffness, the ability to control the impact and rotational velocities independently, feedback to maintain a constant nominal stress parameter, the ability to use spherical or cylindrical wear specimens and a method of applying the load and relative transverse motion in a constant, random or prescribed manner. The design facilitates modifications to include lubrication and environmental control, measurement of friction forces and fretting wear capabilities. Some initial results are included.     

冲击作用下的载荷波形对动态应力集中系数的影响

本文从理论上证明了在一定条件下阶越波入射产生的最大应力集中系数是冲击作用下种瞬态波形入射时的极限值。有限元法计算结果不仅证实了这一结论，而且展示了在一般无理论解的情况下获得极值应力集中系数的可行性。     

7075铝合金板淬火残余应力模拟及实验研究

铝合金板在淬火过程中产生较大的残余应力,导致构件出现变形、翘曲。采用准耦合法对7075铝合金板在淬火过程中的温度场和应力场进行数值模拟,利用盲孔法对淬火后的残余应力分布进行实验测量。结果表明,7075铝合金板淬火后残余应力呈现出外压内拉的分布状态,淬火过程中形成的较大温度梯度造成的不均匀塑性变形是应力产生的主要因素,铝板表层和心部冷却速度的变化导致了应力分布状态的转变。实验结果验证了准耦合模拟方法的可行性,研究结论为残余应力控制提供重要依据。     

An experimental and analytical investigation of the dynamic characteristics of a flexible sandwich plate filled with electrorheological fluid

This paper investigates the dynamic characteristics of a sandwich plate embedded with an electrorheological (ER) fluid. A laser holographic interference experiment and modal testing were conducted to identify natural frequencies, modal damping and shapes of the composite structure, under different electric fields applied to the fluid domain. Moreover, the influence of the ER effect on the structural dynamic responses were recorded. It was found that both of the damping and natural frequencies of the sandwich plate increase monotonously with an increasing electric field; while, at the same time, the resonant peaks of the frequency response and the amplitudes of dynamic responses decrease. Furthermore, based on the special properties of the ER fluid, a discrete dynamic model of the sandwich plate containing ER fluids was developed and validated. The numerical simulation verifies the effect of the ER material on the structure, and the calculated dynamic parameters show the coincident changes with the experimental results.     

Numerical study of 2024 T3 aluminum plates subjected to impact and perforation

The paper describes a work focused on the process of perforation of aluminum sheet. A numerical investigation has been carried out to analyze in details the perforation process subjected to normal impact by different nose shapes of projectiles. The perforation process has been simulated by the application of 3D analysis using IMPACT dynamic FE program suite. The comparison on failure modes depending on the projectile nose shape have been studied and evaluated. An appropriate constitutive relation was applied to describe the material behavior of the aluminum sheet. The study covered different failure modes including petalling, plug ejection and circumference necking of perforated aluminum sheet according to different level of impact velocity ranging from 100 m/s to 600 m/s. In this investigation, a special attention will be given on the deformation and failure.     

An analytical solution for free vibration analysis of circular plates in axisymmetric modes based on the two variables refined plate theory

This paper presents, for the first time, an analytical solution for free vibrations of an isotropic circular plate in axisymmetric modes based on the two variables refined plate theory. This theory accounts for a quadratic variation of the transverse shear strains across the thickness, and satisfies the zero traction boundary conditions on the surfaces of the plate without using shear correction factors. Governing equations are derived using Hamilton’s principle and an analytical method on the basis of using Bessel functions is introduced to solve them. By this procedure, final form of the governing equations is obtained in matrix form. These equations are solved for classical boundary conditions and comparison studies are performed to verify the validity of the present results. It is found that the results obtained using RPT and TSDT are close to each other. As a benchmark, numerical results are presented in a dimensionless form for various values of thickness to radius ratio.     

An experimental study of the ratchetting and creep of thick flanged tubes subjected to steady axial mechanical loading and transient thermal loading

The aims of the investigation were to obtain experimental data against which finite element predictions can be assessed and to see whether the lead alloy used was suitable as a “ratchetting” model material. Thermal ratchetting tests were performed on lead alloy flanged tube components. In some of the tests, dwell periods were allowed between successive thermal shocks. Electrical resistance strain gauges were used to measure the ratchet and creep strains in plain tube and stress concentration regions.It was found that both the plain tube and peak fillet ratchet strains increased with increasing mechanical and thermal load for short dwell periods. However, the ratio of the peak fillet to plain tube ratchet strains reduced with increasing mechanical and thermal load. Also, the ratio of the peak fillet to plain tube ratchet strains increased with increasing dwell period.The data obtained from the lead alloy model component tests were found to correlate with data from a number of different components made from various materials, indicating that the material may be useful as a “ratchetting” model material.     

The study of 3-dimensional structure at the node of ranvier and specimen contrast enhancement techniques

In determining what to write about for this volume to honor Keith Porter, we thought about our projects and considered which ones Keith had either stimulated or otherwise influenced with his technological wizardry or intuition about cell structure and function. Perhaps, not surprisingly, we found something of Keith in everything we are working on. We therefore chose a topic that we presently are very interested in, and that we hope he will enjoy reading about and following in the years to come.     

基于单片机的细胞动态张应力试验系统设计

针对目前国内外还没有一种可以给细胞样本试验提供动态张应力的试验系统的现状,作者研制了膜式变应力波细胞动态张应力试验系统,该系统采用了基于M68HC908J12单片机的DDC控制系统.本文论述了该试验系统的结构和工作原理,重点阐明了控制系统的工作原理,硬件结构,并给出了相应的软件流程图.经试验验证:该系统具有优良的控制精度和稳定性,经济可行.     

An experimental study of the dynamic characteristics of the catenary-pantograph interface in high speed trains

The dynamic characteristics of the catenary-pantograph interface in high-speed trains are evaluated. During a test run signals from accelerometers, load cells, and strain gauges attached to various parts of the pantograph assembly are collected and processed. The signals are analyzed in both the time and frequency domains to determine the dynamic characteristics of the catenary-pantograph interface constituting the critical part of the current collection system of the high-speed train. It is found that there are major frequency components of the pantograph motion at the interface that shift in direct proportion to the train speed as well as components that are stationary in the frequency domain such as the 8.5 Hz component representing the fundamental resonant mode of the panhead assembly. The contact force at the interface shows that while the mean contact force stays almost invariant, the fluctuating component is significantly dependent on the filtering frequency applied to the accelerometer signal during estimation of the inertia force of the panhead. An important implication of the finding is that analytical or numerical investigations based on lumped element models of the pantograph may provide accurate predictions on mean values of the contact force at the catenary-pantograph interface, but are inherently limited in estimating high-frequency fluctuations in the contact force. Since the ratio of the fluctuating portion to the steady-state portion (i.e., the mean value) increases with increased train speed, the predictive capacity of the investigations based on numerical simulations diminishes with increasing train speed.     

Experimental and analytical studies of dynamic friction at the head/disk interface

Friction is an important parameter that critically impacts the tribological performance of a head/disk interface. The head/disk interface with laser zone texture affords a model system for the study of dynamic friction by virtue of its precisely-controlled contact geometry. By using two types of head sliders, i.e. the conventional slider and the padded slider, and a matrix of hard disks with a wide range of laser zone texture parameters, head/disk contacts involving a small number as well as a large number of bumps are realized. A rich variety of dynamic friction behaviors are observed with respect to bump height and bump density variations. To shed new light on the nature of HDI dynamic friction, an analytical model that treats both the deformational and the adhesive friction components on equal footings is formulated. It is shown that, based on the model analysis, the friction is deformation-dominated for HDIs involving a small number of contacting bumps and adhesion-dominated for HDIs involving a large number of contacting bumps. In the former case the friction decreases with bump density, whereas in the latter the friction increases with bump density.     

Theoretical and experimental dynamic analysis aimed at the improvement of an acoustic method for fresco detachment diagnosis

An acoustic non-invasive method for the diagnosis of detachment in frescos was previously proposed by the authors. This method is based on the indirect evaluation of the vibrations due to detachments, by means of a surface inspection. In this paper the relations between the dynamics of the structure to be inspected and the operational principles of the acoustic method of diagnosis are presented. The dynamic analysis is carried out using experimental investigations and analytical and numerical models. It shows that the quality of the diagnosis depends on the capability of the acoustic device to excite the structural resonances related to the detachments. These results are useful for future improvements, in particular to enhance the sensitivity of the proposed method.     

An analytical study of the wear pattern of an abraded rubber surface: the interaction model

ABSTRACT

The relationship between the volume loss rate and the wear pattern along an abraded rubber surface has been confirmed. Experimentally, long and short pattern spacings are formed along the abraded direction that, respectively, represent the initial and final pattern spacings. By modelling the abrasion, or the sliding contact, as a vibration system, an analytical study to identify the pattern spacing is carried out. There are two proposed interaction models of the contact between the rubber surface and the abrader, i.e. separation and unification, thus, the interaction along the sliding contact is a combination of both. It is confirmed that the separation model is correlated to the initial pattern spacing. The results are obtained that the final pattern spacing not only depends on the static load of the abrader but also depends on the dynamic load due to the inertia effect of the moving parts of abrasion apparatus.     

Numerical and experimental study on the three-dimensional extrusion of square section from square billet through a polynomial shaped curved die

The geometry of die profile plays a major role in reducing the extrusion pressure and ensuring the smooth flow of material. In general, the extrusion process is mostly affected by billet geometry, die geometry, and interface frictional force at the die billet geometry. In the present investigation, an analysis using three-dimensional upper bound method using fifth-order die profile function has been carried out for extrusion of square sections from square billet. The extrusion pressure and optimum die length have been computed by multivariable optimization technique. The present die shape profile is found to be superior to many other profiles. The results obtained will help in design of optimum die profile and investigation of its performance.     

An experimental study on the flow and heat transfer characteristics of an impinging jet

The flow and heat transfer characteristics of an impinging jet is investigated in two major stages. The first stage is about the investigation of the three dimensional mean flow and the turbulent flow quantities in free jet, stagnation and wall jet region. After a complete documentation of the flow field, the convective heat transfer coefficient distributions on the impingement plate are presented, during the second stage of the study. Heat transfer experiments using the new hue-capturing technique result in high resolution wall heating rate distributions. The technique is fully automated using a true color image processing system. The present heat transfer results are discussed in detail in terms of the flow characteristics. The measurements from the new method are compared with conventional heat flux sensors located on the same model. These heat transfer distributions are also compared with other studies available from the literature. The new non-intrusive heat transfer method is highly effective in obtaining high resolution heat transfer maps with good accuracy.     

An experimental study on the effect of square grooves on decay characteristics of a supersonic jet from a circular nozzle

In this experimental work, the effect of square grooves on the structure of a supersonic jet emanating from a circular nozzle has been investigated at three different nozzle inlet total pressures i.e 360 kPa, 550 kPa and 720 kPa. The nominal exit Mach number is 1.8. A new empirical relation for predicting the supersonic core length for grooved nozzle has been suggested. Further, a new parameter “groove effectiveness” has also been suggested to quantify the effect of the groove by using the total pressure data in the supersonic core length. Experimental results suggest that at higher nozzle inlet total pressure, the groove effectiveness plays a minor role. From the jet centreline total pressure data, supersonic core length, the locations at which 50 % and 90 % decay occurs have been obtained. It has been observed that higher groove effectiveness is associated with smaller values of supersonic core length, L_50% and L_90%. Schlieren images of the jet structure shows unsymmetrical shock pattern of jets emanating from a single grooved nozzle.     

基于感测控制的钢轨承载变形实验研究

本文有针对性的对承载的钢轨从理论和实验两方面进行应力应变分析,得出相关的数值及其分布规律,并作出了枕上钢轨轨腰处作为感测对象最为显著的结论,同时提出了利用应力集中提高感测灵敏度的新理念。为基于火车自动控制的传感器研发提供了依据。