Determination of gun propellants erosivity: Experimental and theoretical studies

Requirements for higher and higher performances of contemporary guns intensify investigations concerning influence of various factors on barrel erosion. The most important parameter for the life of the gun is the type of the gun propellant. The device based on modification of 37 mm M39 gun for investigating influence of gun propellant on barrel erosion is used. The nozzle (main part of device) mass loss during firing was the measure of gun propellant erosivity. The theory of nozzle erosion includes basic thermal, chemical and metallurgical factors. The main thermal and chemical factors are maximum nozzle inside surface temperature and gun propellant composition. The maximum nozzle surface temperature was determined theoretically by developed interior ballistic model with heat transfer, and experimentally by micro thermocouples measurements and solution of inverse heat conduction problem. The coefficients of gun propellants erosivity are determined in experimental and theoretical way.     

Impact initiation of explosives and propellants via statistical crack mechanics

A statistical approach has been developed for modeling the dynamic response of brittle materials by superimposing the effects of a myriad of microcracks, including opening, shear, growth and coalescence, taking as a starting point the well-established theory of penny-shaped cracks. This paper discusses the general approach, but in particular an application to the sensitivity of explosives and propellants, which often contain brittle constituents. We examine the hypothesis that the intense heating by frictional sliding between the faces of a closed crack during unstable growth can form a hot spot, causing localized melting, ignition, and fast burn of the reactive material adjacent to the crack. Opening and growth of a closed crack due to the pressure of burned gases inside the crack and interactions of adjacent cracks can lead to violent reaction, with detonation as a possible consequence.This approach was used to model a multiple-shock experiment by Mulford et al. [1993. Initiation of preshocked high explosives PBX-9404, PBX-9502, PBX-9501, monitored with in-material magnetic gauging. In: Proceedings of the 10th International Detonation Symposium, pp. 459-467] involving initiation and subsequent quenching of chemical reactions in a slab of PBX 9501 impacted by a two-material flyer plate. We examine the effects of crack orientation and temperature dependence of viscosity of the melt on the response. Numerical results confirm our theoretical finding [Zuo, Q.H., Dienes, J.K., 2005. On the stability of penny-shaped cracks with friction: the five types of brittle behavior. Int. J. Solids Struct. 42, 1309-1326] that crack orientation has a significant effect on brittle behavior, especially under compressive loading where interfacial friction plays an important role. With a reasonable choice of crack orientation and a temperature-dependent viscosity obtained from molecular dynamics calculations, the calculated particle velocities compare well with those measured using embedded velocity gauges.     

Reliability-based multidisciplinary design optimization using incremental shifting vector strategy and its application in electronic product design

Use of multidisciplinary analysis in reliability-based design optimization (RBDO) results in the emergence of the important method of reliability-based multidisciplinary design optimization (RBMDO). To enhance the efficiency and convergence of the overall solution process, a decoupling algorithm for RBMDO is proposed herein. Firstly, to decouple the multidisciplinary analysis using the individual disciplinary feasible (IDF) approach, the RBMDO is converted into a conventional form of RBDO. Secondly, the incremental shifting vector (ISV) strategy is adopted to decouple the nested optimization of RBDO into a sequential iteration process composed of design optimization and reliability analysis, thereby improving the efficiency significantly. Finally, the proposed RBMDO method is applied to the design of two actual electronic products: an aerial camera and a car pad. For these two applications, two RBMDO models are created, each containing several finite element models (FEMs) and relatively strong coupling between the involved disciplines. The computational results demonstrate the effectiveness of the proposed method.     

Multiscale modeling of heterogeneous propellants from particle packing to grain failure using a surface-based cohesive approach

In the present work,a computational framework is established for multiscale modeling and analysis ofsolid propellants.A packing algorithm,considering the ammonium perchlorate(AP) and aluminum(Al) particles asspheres or discs is developed to match the size distributionand volume fraction of solid propellants.A homogenizationtheory is employed to compute the mean stress and strainof a representative volume element(RVE).Using the meanresults,a suitable size of RVE is decided.Without considering the interfaces between particles and matrix,several numerical simulations of the relaxation of propellants are performed.The relaxation effect and the nonlinear mechanicalbehavior of propellants which are dependent on the appliedloads are discussed.A new technology named surface-basedcohesive behavior is proposed to describe the phenomenonof particle dewetting consisting of two ingredients:a damageinitiation criterion and a damage evolution law.Several examples considering contact damage behavior are computedand also nonlinear behavior caused by damaged interfaces isdiscussed in this paper.Furthermore the effects of the critical contact stress,initial contact stiffness and contact failuredistance on the damaged interface model have been studied.     

Tensile and compression testing under high pressures,and fluid-to-fluid extrusion of metals

The late Percy W. Bridgman emphasized the large increases in ductility made possible by a high-pressure environment. He also showed that many brittle materials became ductile under high pressures and could be plastically deformed without cracking or fracture. This work has led to tensile and compression testing as relatively routine under fluid pressures up to about 450,000 psi. Information so generated is employed to determine pressure levels at which working under pressure can be done without fracture or cracking. There is presented in this paper information on tensile and compressive tests under pressure and on application to the fluid-to-fluid extrusion process.     

Evaluation of granule structure and strength properties of green packed beds in iron ore sintering using high-resolution X-ray tomography and uniaxial compression testing

The strength properties of green sinter beds,including the Young's modulus and maximum bed strain,were evaluated using uniaxial compression tests.The green-sint...     

一种新型结构火炮身管膛线的计算分析

针对传统的火炮身管内弹道结构形式,提出了一种新型结构形式的火炮身管膛线——渐变截面结构膛线。以大口径火炮身管膛线作为研究对象,计算分析传统等截面结构膛线和渐变截面结构膛线的弹丸弹带挤进阻力、导转侧向力、膛线截面面积和膛线摩擦力的变化情况。计算结果表明,新型渐变截面结构膛线有利于增强弹丸弹带的挤入能力,减少膛线根部应力集中,减少弹丸弹带对膛线的冲击和磨损,有效提升弹丸弹带的闭气性能,同时渐变结构膛线可有效减小弹丸在膛内运动时受到的扰动,使得弹丸在膛内运行平稳,减少炮口章动,在保证射击精度的同时,有利于提高身管的使用寿命。     

On the transverse compression response of Kevlar KM2 using fiber-level finite element model

Flexible textile composites like woven Kevlar fabrics are widely used in high velocity impact (HVI) applications. Upon HVI they are subjected to both longitudinal tensile and transverse compressive loads. To understand the role of transverse properties, the single fiber and tow transverse compression response (SFTCR and TTCR) of Kevlar KM2 fibers are numerically analyzed using plane strain finite element (FE) models. A finite strain formulation with a minimum number of 84 finite elements is determined to be required for the fiber cross section to capture the finite strain SFTCR through a mesh convergence study. Comparison of converged numerical solution to the experimental results indicates the dominant role of geometric stiffening at finite strains due to growth in contact width. The TTCR is studied using a fiber length scale FE model of a single tow comprised of 400 fibers transversely loaded between rigid platens. This study along with micrographs of yarn after mechanical compaction illustrates fiber spreading and fiber–fiber contact friction interactions are important deformation mechanisms at finite strains. The TTCR is also studied using homogenized yarn level models with properties from the literature. Comparison of TTCR between fiber length scale and homogenized yarn length scale models indicate the need for a nonlinear material model for homogenized approaches to accurately predict the transverse compression response of the fabrics.     

Control of a perturbed chaotic system by using a trajectory trapping strategy

This paper proposed a trajectory sliding control strategy for a nonlinear chaotic system subject to external disturbance. For a given chaotic system, a trapping region is designed based on the invariant ellipsoid control method. Existence of the control region is characterized by a feasibility issue of linear matrix inequalities. According to the path information of the chaotic system, we classify the trajectories by a couple of ellipsoid regions subject to volume minimization. Then a target trapping region that the center locates close to the designed sliding surface is determined. As a result, when the trajectories of the chaotic system enter the prescribed region, it will be trapped inside the invariant ellipsoid for all the subsequent time and finally be guided toward to the origin. Numerical simulations are given to demonstrate the effectiveness and the advantages of the proposed trajectory trapping control approach.     

Buckling test and optimum design of fiber reinforced composite plates under compression

In this paper, the conclusion that the experimental results coincide with theoretical analysis has been got through buckling test of 283 composite rectangular plates. It is confirmed that the critical loads of composite plates calculated by buckling theoretical formula of anisotropic plate are reliable. The selections of optimal content of matrix and optimal off-axis which make fiber reinforced composite plates reach biggest critical loads are also discussed in this paper. The result of analysis may be used in the design for the products.     

The oscillatory testing of pharmaceutical semi-solids using a transfer function analyser

Summary The rheological investigation of pharmaceutical materials such as pastes and creams has been limited to continuous shear experiments although it is known that complex rheological behaviour (visco-elasticity) is present and that analysis of hysteresis loops can only give a qualitative estimate of structure and rheological properties. Oscillatory testing has been avoided largely due to the lengthy measurements involved in calculation of amplitudes and phase angle and the difficulty in obtaining a clean wave form. Solartron Electronic Group Ltd. have recently introduced an apparatus that overcomes these objections: the transfer function analyser J. M. 1600 and mechanical reference synchroniser J. X. 1606. Electronic noise can be filtered out and the results are available almost instantaneously.This apparatus has been used in conjunction with aWeissenberg rheogoniometer to study the rheological properties of a variety of pharmaceutical materials, including emulsions, creams and ointment bases. The change in phase angle and amplitude has been studied over the frequency range 25 Hz to 7.9 × 10^–3 Hz for parallel plate and concentric cylinder geometries. The systems examined have demonstrated a large range of rheological behaviour ranging from essentially linear Newtonian liquid to very non linear plastic solid.It is concluded that the Solartron apparatus will provide a rapid and accurate method for the rheological analysis of complex pharmaceutical materials.

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Zusammenfassung Rheologische Untersuchung von pharmazeutischen Produkten wie Pasten und Cremen war bisher auf Experimente mit kontinuierlicher Scherbeanspruchung beschränkt. Man weiß jedoch, daß es komplexes rheologisches Verhalten gibt und daß die Untersuchung der Hysteresisschleife nur ein qualitatives Erfassen von Strukturen und Theologischen Eigenschaften ermöglicht. Untersuchungen unter oszillierenden Bedingungen wurden vermieden, hauptsächlich wegen der zeitverbrauchenden Messungen, die die Berechnung von Amplitude und Phasenwinkel mit sich bringen und wegen der Schwierigkeiten, eine saubere Wellenform zu erhalten. Die Solartron Electronic Group Ltd. hat vor kurzem ein Gerät entwickelt, das diese Schwierigkeiten überwindet: den transfer function analyser JM 1600 und den mechanical reference synchroniser JX 1606.Unschärfe wegen Interferenz kann durch Filtern vermieden werden und Ergebnisse können fast augenblicklich erhalten werden.Dieses Gerät wurde in Verbindung mit demWeissenberg-Rheogoniometer benützt, um das rheologische Verhalten von pharmazeutischen Produkten wie Emulsionen, Cremen und Salbengrundlagen zu testen. Die Änderung von Phasenwinkel und Amplitude wurde mit parallelen Platen und konzentrischen Zylindern im Bereich von 25 Hz bis 7,9 · 10^–3 Hz untersucht. Das rheologische Verhalten der untersuchten Systeme wurde über einen weiten Bereich variiert, von linearen newtonischen Flüssigkeiten zu nichtlinearen plastischen Festprodukten.Man kann daraus schließen, daß das Solartrongerät ein schnelles und genaues Verfahren bietet, um rheologische Bestimmungen von komplexen pharmazeutischen Produkten durchzuführen.

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Paper presented at the Conference on Experimental Rheology, University of Bradford, April 17–19, 1968.     

Bifurcation analysis of a nonlinear pendulum using recurrence and statistical methods: applications to fault diagnostics

The problem of maintenance of expensive and heavy systems has increased the need for powerful tools to analyze their performance. The methods of recurrence plots (RPs) and statistical measurement have been used as data-driven tools for diagnostics with no possibility of classifying the nature of defect and poor ability to localize it. In order to enhance the efficiency of the forecast, innovative approaches consist of using physics-based features to train a data-based assessment methods. This requires proper analysis of the physical system using appropriate methods. For this purpose, this paper focusses on the bifurcation dynamics of nonlinear systems using the recurrence and statistical methods. Considering the nonlinear pendulum as a model, the qualitative behavior of the system is discussed through the bifurcation diagram of some recurrence quantification analysis (RQA) parameters, namely the recurrence rate, determinism, and laminarity. These parameters are used to measure the level of complexity and transition from regular to chaotic motion and vice versa. Statistical parameters such as crest factor, skewness, and kurtosis are used to identify various bifurcation and amplitudes in the system, and to measure the orientation and the level of asymmetry. Plots of recurrence diagrams and histograms are presented to support our observations. Examples of detection of dynamic changes using these two methods are provided. The interesting results obtained in this paper show that statistical methods complement results obtained from RPs. In addition, the paper demonstrates how the RPs can be employed in conjunction with the physics-based model.     

高压气体驱动二级轻气炮发射过程的数值模拟方法及应用

二级轻气炮是一种常见的超高速发射装置,多年来其数值研究大多采用简化一维模型,鲜有三维有限元模型。以14 mm口径高压气体驱动二级轻气炮为研究对象,采用耦合欧拉-拉格朗日（coupled Eulerian-Lagrangian, CEL）算法,根据膜片破裂与否,将二级轻气炮模型解耦为2个分级三维数值模型。为确定实验难以测得的参数（材料摩擦因数和膜片破膜压力）,设计正交试验,拟合确定活塞与泵管间摩擦因数为0.82,弹丸与发射管摩擦因数为0.30和膜片破膜压力为11.73 MPa。正交结果表明,摩擦因数对计算结果影响较大,在高压气体驱动二级轻气炮的计算中不应忽略。通过上述方法建立数字化高压气体驱动二级轻气炮,完整复现气炮发射过程,计算的弹丸终速与实验结果吻合度高。选取验证工况详细分析了气炮发射过程内流场变化,并呈现关键时刻的压力云图。该气炮简化方法、分级思想和关键参数确认方法可推广应用于固体发射药驱动、爆轰驱动等其他驱动形式的二级/多级轻气炮。

     

Secondary buckling of a flat plate under uniaxial compression: Part 2. Analysis of clamped plate by F.E.M. and comparison with experiments

In Part 1, a theoretical analysis was used to study the secondary buckling of a simply supported plate. In Part 2, a clamped plate is analysed by the finite element method. The stability criterion for a non-linear post-buckling equilibrium state is evaluated by the sign of the determinant of the stiffness matrix. It should be noted that the secondary buckling loads of clamped plates are unexpectedly smaller than those of simply supported plates and are only one and a half times the primary buckling loads. In previous analyses, only a quarter segment of the plate was considered by assuming a stable equilibrium state with symmetrical mode. However, instability can also be predicted by considering the unsymmetrical mode over the whole plate. Results of experimental analysis of secondary instability of clamped square plates under uniaxial compression agreed with the numerical results.     

Development of a generalised active vibration suppression strategy for a cantilever beam using internal resonance

In this paper, the potential to utilise modal coupling effects in the formulation of a generalised vibration suppression algorithm is investigated. The plant, a flexible cantilever beam undergoing first mode oscillation, is modelled by a second order differential equation with a spring constant and damping coefficient that are representative of the first mode flexibility and material damping of the beam, respectively.In order to establish an internal resonance condition, a second equation, designated the supplementary equation or controller, is appended to the plant to render a two-degree-of-freedom system. The objective is to generate an internally resonant pair. Upon successful completion of this task, a suppression technique is implemented whereby energy is removed from the plant via the supplementary system.The introduction of the supplementary system results in a set of design parameters which are employed to realise a state of internal resonance and to establish the desired dynamic response. The choice of 2:1 internal resonance models results in a unidirectional control torque making this technique particularly attractive for systems using thrusters or tendons as actuators. A similar structural configuration regulated under a PD (Proportional-Derivative) control law is compared to the proposed control scheme via simulation.     

Identification of material parameters for inelastic constitutive models: statistical analysis and design of experiments

In this paper we introduce stochastic methods to describe the influence of scattering test data on the identification of material parameters. We employ the viscoplastic constitutive model of Chan, Bodner, and Lindholm in its uniaxial form. The available test data result from three types of experiments performed at 600 °C on AINSI SS316 stainless steel, namely creep tests, constant strain rate tension tests with intermediate relaxation, and cyclic tension–compression tests. Each test has been performed with 12 specimens at different strain rates and stress rates respectively. However, for a serious statistical evaluation a larger number of experiments is required. In order to increase the number of tests we introduce stochastic simulations based on time series analysis which generate artificial data with the same stochastic behaviour as the experimental data. The method of stochastic simulation presents a widely accepted technique in engineering which does not add complexity to the process of parameter identification, but allows an investigation of the confidence in the fits of the material parameters. To keep the computation time for the identification of the material parameters as low as possible, very efficient numerical methods have to be implemented. The methods applied here for integration and nonlinear optimization are briefly introduced. The optimization strategy contains stochastic elements. Furthermore, we apply the method of statistical design of experiments to derive which combination of tests yields the most important information for an effective identification of material parameters.     

Cryptanalysis and improvement of a chaotic map-based key agreement protocol using Chebyshev sequence membership testing

Recently, Gong et al. (Nonlinear Dyn, doi:10.1007/s11071-012-0628-3, 2012) proposed a chaotic map-based key agreement protocol without using smart cards. They claimed that the protocol is secure against password-guessing attacks. However, we show that Gong et al.’s protocol is vulnerable to partition attacks, whereby the adversary can guess the correct password off-line. We also demonstrate that the protocol suffers from a a stolen-verifier attack along with password change pitfalls. Thereafter, we proposed an chaotic map-based key agreement protocol without using smart cards to conquer the mentioned weaknesses. The security analysis of the proposed protocol shows that it is suitable for the applications with higher security requirement.