Finite width effect of thin-films buckling on compliant substrate: Experimental and theoretical studies

Buckling of stiff thin films on compliant substrates has many important applications ranging from stretchable electronics to precision metrology and sensors. Mechanics plays an indispensable role in the fundamental understanding of such systems. Some existing mechanics models assume plane-strain deformation, which do not agree with experimental observations for narrow thin films. Systematic experimental and analytical studies are presented in this paper for finite-width stiff thin films buckling on compliant substrates. Both experiments and analytical solution show that the buckling amplitude and wavelength increase with the film width. The analytical solution agrees very well with experiments and therefore provides valuable guide to the precise design and control of the buckling profile in many applications. The effect of film spacing is studied via the analytical solutions for two thin films and for periodic thin films.     

Unixial compression testing of M30 and JA2 gun propellants using a statistical design strategy

A statistical factorial design strategy is used to determine the uniaxial compressive mechanical response of two energetic polymers, M30 and JA2 gun propellants, as a function of strain rate,, temperature,T, specimen aspect ratio,l/d, and specimen-end lubrication,L. A model of the mechanical response,y=y(,T,l/d,L) is formed using least-squares minimization of observed behavior with a secondorder polynomial model in the independent variables. It is found that aspect ratio and end-lubrication variables can influence the overall mechanical behavior of these materials, so that their effects must be quantitatively evaluated and screened prior to the development of constitutive models. Model predictions and global root-mean-square, RMS, errors in yield stress and strain, strain-energy density at yield, compressive and failure moduli for these materials compare favorably with historical values obtained from a replicate test design strategy.     

Two-phase flows in gun barrel: Theoretical and experimental studies

In the paper theoretical and numerical model of two-phase flow of solid granular propellant and its products of combustion in the gun barrel during interior ballistic cycle is given. Two cases are considered: base ignition of propellant charge and ignition by igniter. The theoretical model includes the balance equations of mass, momentum and energy for both phases, as well as necessary constitutive laws. The igniter efflux in the propellant chamber is obtained by incorporation in the model the two-phase flow model of igniter function. The convergent, unconditionally stable, numerical procedure is formed to solve the system of equations of the theoretical model. An original procedure of numerical grid adaptation to the flow field increase, caused by the projectile motion down the gun bore, is developed. The TWOPIB code for the computation of whole interior ballistic cycle of ammunition is developed. Four kinds of experimental investigations were carried out:igniter function in open air, flamespreading through propellant charge in the fibreglass tube during base ignition or during ignition by igniter, and firing of 100 mm APFSDS projectile. Verification of the theoretical–numerical approach by the comparison with experimental data is carried out. The great number of computational results is presented for the parameters that can not be measured, but which are necessary for more complete understanding of examined processes. The presented theoretical–numerical access enables, not only the complete optimisation of propellant charges, but more successful solutions of many interior ballistic problems.     

Experimental and theoretical studies of convective heat transfer in a cylindrical porous medium

Convective heat transfer at constant heat flux through unconsolidated porous media has been studied both experimentally and theoretically. Heat transfer measurements have been performed for convective heat transfer over a wide range of operational parameters at constant heat fluxes. In addition to heat transfer coefficients, pressure drop and temperature profiles both in radial and axial direction have been recorded. The equations of motion and energy which account for the non-Darcian effect are used to describe the flow and convective heat transfer through the porous medium. Mathematical models for the prediction of heat transfer coefficients and temperature profiles are presented which predict the experimental data with good accuracy.     

Experimental and theoretical studies of explosive-induced large dynamic and permanent deformations of simple structures

Explosive-loading and structural-response measurement techniques are described for obtaining definitive large dynamic and permanent-deformation data on simple structures which undergo (a) two-dimensional deformations, or (b) general three-dimensional deformations. In the former category, explosively loaded structures discussed include freely suspended single-layer circular rings, freely suspended unbonded concentric rings, and flat circular plates with clamped edges. Representing category (b) is an explosively loaded cylindrical panel with clamped edges. To define the impulse which was imparted explosively to these structures, appropriate impulse-calibration tests were performed on high-explosive-loaded single-layer and unbonded double-layer specimens; these testing techniques and the results obtained are discussed. General numerical methods for predicting large elasticplastic dynamic and permanent deformations of structures which undergo either two-dimensional or general three-dimensional deformations are described briefly. Dynamic responses and permanent deformations predicted with these methods are compared with data from the present experiments. Certain problems, both experimental and theoretical, requiring further investigation are indicated.     

Experimental and theoretical studies on buckling of thin-walled MHS compressed between two rigid plates

This paper presents the theoretical and experiment results of buckling behavior of thin-walled metallic hollow sphere (MHS) compressed between two rigid plates. The first critical buckling load of MHS has been derived. It is shown that the critical load is related to the radius, thickness of the sphere shell, the elastic modulus, and Poisson’s Ratio of the material. Two hemispheres are welded to make the MHS with three different angles of welding-line. The quasi-static compressive experiment of the MHS has been carried out, and the load-deformation curves are obtained. To match theoretical and experimental results, a modified equation is presented. Then a good agreement between the theoretical and the experimental results is obtained.     

新型发射药爆炸TNT当量系数的实验研究

TNT当量系数是危险品工程抗爆设计和安全距离确定的重要依据。为确定H1和H2两种新型高能发射药的TNT当量系数,分别开展了10 kg TNT和新型发射药的空气自由场静爆实验。基于修正的当量系数计算方法和测量得到的不同爆心距离处冲击波超压时程曲线,确定了不同比例距离处两种高能发射药的超压和比冲量TNT当量系数。研究结果表明,发射药爆炸产生的冲击波传播规律与TNT炸药爆炸产生的冲击波传播规律相同,符合爆炸相似律,相同质量发射药爆炸产生的冲击波超压和比冲量都显著高于TNT的。随着比例距离的增大,H1的超压当量系数先增大后减小,最大值为1.34;H2的超压当量系数逐渐减小,最大值为1.26。两种新型发射药的比冲量TNT当量系数均随比例距离的增大先减小后增大,H2的比冲量TNT当量系数大于H1的,最大值为1.38。本文中修正的计算方法能更准确计算被试样品的TNT当量系数,实验结果可为提高抗爆结构安全性设计提供参考。     

Experimental and theoretical investigations of falling film evaporation

In this study, a mathematical model was developed for falling film evaporation in vacuum using heat transfer relations. An experimental device was designed. experimental set-up which was used was equipped with a triangular weir distribution device and it had the ability to record data up to 3?m. Experiments were performed in a single-effect process with sucrose–water solution varying from 3 to 20% concentration rate of sucrose and we used a vertical tube evaporator with the dimensions of laboratory scale. The model that was developed considers convection, shear stress, viscosity and conjugate heat transfer while most of the previous works ignored these factors. The main factors influencing the heat transfer mechanism performance of the unit were investigated and analyzed. We concluded that the experimental studies are verified by the developed model. Furthermore, it was also concluded that, the heat transfer is affected by the mass flow rate, sucrose concentration rate in solution, film thickness and pressure.     

Experimental and theoretical determination of frequencies of elastic toroids

Experiments are described which determine natural frequencies of five toroidal models whose major diameters are of 10 in. and whose minor diameters vary from 0.25 to 2 in. The experimentally determined frequencies are compared with the theoretical frequencies derived using the elementary theories for the in-plane and out-of-plane vibrations of circular rings of R. Hoppe and J. H. Michell, as well as the method of internal constraints. The comparative results for the frequencies are presented in tabular form.     

Experimental and theoretical aspects of the two-roll mill problem

Experiments are described in which two cylinders of the same radii-rotate with identical speeds in a bath of Newtonian or non-Newtonian liquid. The torque on one of the cylinders is measured as a function of rotational speed for various values of the cylinder separation and the flow patterns are observed by a dye-injection technique.The observed experimental results for a Newtonian liquid correlate well with the theoretical predictions but a similar correlation in the case of elastic liquids is made difficult by the strongly three-dimensional nature of the flow in this case and the difficulty in estimating the amount of liquid passing through the rollers. The possibility of flow reversal effects due to the high Trouton ratios in the case of the elastic liquids is investigated both experimentally and theoretically.     

电炮驱动薄膜飞片的运动速度

用双灵敏度激光干涉测速技术测量了充电电压为18 kV的电炮加载下薄膜飞片自由面的速度历史。介绍了相关的实验装置及测量方法,给出了实验结果,并讨论了影响测速的一些关键技术。整个测速过程约为1.6 s,最终速度为6.7 km/s。     

炮钢材料等离子淬火后动态力学性能研究

为提高炮钢材料在较高冲击作用下的动态力学性能,采用等离子淬火技术对炮钢材料进行表面处理,并使用分离式霍普金森压杆(SHPB)系统对原始炮钢材料与等离子淬火后的炮钢材料进行对比分析,方法为对两种试样在试验前后的长度压缩量以及二者在不同应变率下的动态应力-应变曲线进行比较。结果表明,随着应变率的增加两种试样的应力-应变关系、屈服强度都有不同程度的强化效应,都表现出一定的应变率敏感性;在相同气压下两种试样在长度方向上都产生了一定的塑性变形,但淬火试样的压缩量明显小于原始试样。并且气压相同时试样经过等离子淬火后其抗冲击性能有显著提升,具体表现为应变与应变率降低,屈服强度与极限强度升高。     

Experimental and theoretical investigation of galloping of transversely inclined slender prisms

Galloping is characterized by large and periodical oscillations which may lead to collapse of slender structures. This study is the first attempt of a comprehensive experimental and theoretical investigation of galloping of transversely inclined prisms. A modified quasi-steady model is proposed with a constant term to estimate the galloping of a transversely inclined prism, which is later experimentally investigated by conducting a static Synchronous Multi-Pressure Sensing System (SMPSS) test and an aeroelastic test in a boundary layer wind tunnel. The galloping responses of the prisms were measured in the aeroelastic test, while the aerodynamic force coefficients were determined from the SMPSS test. These experimental results were subsequently utilized to validate the quasi-steady model. Based on the proposed model, the galloping responses of the prisms were predicted and compared with the experimental results. The experimentally measured and theoretically predicted galloping responses are discussed with respect to aerodynamic damping ratios, onset galloping wind speeds, distributed pressure coefficients, point pressure spectra and vortex shedding frequencies. Interesting findings are summarized.     

Experimental and theoretical study of short fiber orientation in diverging flows

Two types of experiments have been carried out to study the fiber orientation in flow through a divergent channel. First, a reinforced polyamid mold sprue containing two types of orientation was investigated: near the center, the fibers are mostly oriented perpendicular to the flow lines, whereas on the periphery, they are oriented parallel to them. Second, direct observation of copper fibers moving in a corn syrup was performed in a transparent diverging device: the fibers rapidly become oriented transverse to the flow lines. The solution of Stokes equations for the undisturbed fluid motion gives the shear rate and elongation rate, which are then substituted in Jeffery's orientation equations. The resolution shows two types of behavior: in a large area in the center, the fiber tends to a stable equilibrium position which depends strongly on the flow line on which it moves. On the periphery, the fiber follows a shear-like behavior. The strong influence of the elongational component relative to the shear component is demonstrated and the time necessary for orientation is calculated. The theoretical results are found to be in agreement with the observations.     

Experimental and theoretical investigation of Kolmogorov flow on a cylindrical surface

A laboratory model of Kolmogorov flow in a channel on a cylindrical surface, which eliminates the channel end effect observed in plane channels, has been investigated theoretically and experimentally. The number of half-periods of the external force could be varied from two to 22. It is shown that the type of secondary flow depends on the number of half-periods of the basic flow: traveling wave for an odd number of half-periods, quasisteady vortex structure for an even number of half-periods, and a self-oscillating regime when the channel width is equal to four half-periods. The theoretical analysis is based on the use of the Galerkin approximation of the equations of hydrodynamics. The system of equations obtained is solved numerically in conjunction with an analysis of the naturally arising eigenvalue problems.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 25–31, September–October, 1989.The authors are grateful to A. M. Obukhov for his interest in the work, G. G. Dement'ev for help with the experimental apparatus, and V. A. Dovzhenko and F. V. Dolzhanskii for useful discussions.     

Experimental and theoretical/numerical investigations of thin films bonding strength

A laser spallation facility has been developed to measure the strength of planar interfaces between a substrate and a thin coating. This quantity is a central requirement in contemporary thin film and protective coatings technology and its successful measurement should improve the scientific/technological potential for the design of advanced composites, protective coatings of composites that operate in hostile environments, and in joining of dissimilar materials. The technique involves impinging a laser pulse of ultra short duration on the rear surface of the substrate, which is coated by a thin layer of energy absorbing metal such as Sn and Pb. The explosive evaporation of the metallic layer, confined between a fused quartz crystal and the substrate, induces a compressive shock wave, which propagates through the substrate toward the material interface. Upon reflection from the free surface of the coating, the pressure pulse is converted into a tensile wave which, under certain conditions, can lead to spallation at the interface. It is shown by mathematical simulation that atomic bond rupture is the mechanism of separation in this experiment. Since the interaction of laser energy with matter is a complicated, highly non-linear process, our investigations, at first, were based on measurement of the pressure pulse generated by the threshold flux level that leads to spallation, by using a micro-electronics device with a piezo-electric crystal, and on computation of the tensile stress experienced at the material interface, by numerical simulation of the induced stress wave propagation. Several substrate/coating (ceramic/ceramic and ceramic/metal) systems have been investigated such as, 1–15 μm SiC by CVD, 1–4 μm TiC and TiN by PVD coatings on sapphire substrates, as well as 1–2 μm Au, Sn and Ag coatings by sputtering on sapphire, fused quartz and glass substrates. For identically prepared specimens, the measured threshold energy levels are reproducible, thus leading to reproducible bond strength values, while the spall size, as expected, is dependent on the laser pulse energy level. Finally, the bond strength values obtained are in very good agreement with similar data derived by direct experimental techniques based on Laser-Doppler-Interferometry.     

Experimental and theoretical study of penetration of spherical solids into wet sand

Results of a series of inverted laboratory experiments on the normal impact of spherical bodies onto targets made of wet sand (with humidity of 10%) and water-saturated sand (with humidity of 18–20%) placed into cylindrical metallic containers are reported. Experimental data are compared with results calculated by a modified Godunov difference method. Changes in the forces of resistance to penetration at different stages of the impact interaction process are analyzed, and the influence of humidity and granulometric composition of sand on the maximum values of forces at different impact velocities is studied. The maximum force of resistance for sand with 20% humidity is found to be smaller by a factor of 1.5–2 than that for dry sand.     

Experimental and theoretical observations of elastic instabilities in eccentric cylinder flows: local versus global instability

A theoretical and experimental investigation of the stability of the viscoelastic flow of a Boger fluid between eccentric cylinders is presented. In our theoretical study, a local linear stability analysis for the flow of an Oldroyd-B fluid suggests that the flow is elastically unstable for all eccentricities. A global solution to the stability problem is obtained by a perturbation eigenvalue analysis, incorporating the azimuthal variation of the base state flow at the same order as the streamwise variation of the stability function. A comparison between the local and global stability predictions is made. Flow visualization experiments with a solution of high molecular weight polyisobutylene dissolved in a viscous solvent clearly show the transition from a purely azimuthal flow to a secondary toroidal flow. Comparison of these experimental results with the local linear stability theory shows good agreement between the measured and predicted critical conditions for the onset of the non-inertial cellular instability at small δ, where δ is the eccentricity made dimensionless with the average gap thickness. At higher eccentricities, experiment and local linear stability theory cease to agree. Evidence will be given that this disagreement is due to a global affect, i.e. the convection of stress not included the local theory. Specifically, it is suggested that convection of polymeric stresses in the base flow as well as in the disturbance flow can stabilize the instabilities found in this geometry. Finally, the discovery of a new localized purely elastic instability associated with the recirculation flow in the co-rotating eccentric cylinder geometry is presented.