Photothermoelastic analysis of bonded propellant grains

A two-dimensional model of the transversal cross section of a bonded rocket propellant grain was subjected to uniform and steady thermal loading and, alternatively, to mechanically applied uniform radial displacements on the outer boundary. The optimization of perforation contours (attained in previous research programs by applying uniform pressure on the outer boundary of the grain model) was confirmed for both types of thermal loading. The concentration factor at the fillets of the inner contour was determined. An attempt was made to predict the maximum strain in the actual propellant subjected to the same thermal conditions. The material used for the model was a urethane rubber. The thermoelastic properties of the model material were determined.     

Shear layer instability and acoustic interaction in solid propellant rocket motors

Segmentation of solid propellant rocket motors has been demonstrated to be a source of unpredicted and undesirable pressure and thrust oscillations. Surface discontinuities are the primary cause of these vortex-shedding-driven oscillations, which result from a strong coupling between the shear layer instability and the acoustic motion in the chamber. The analysis of an axisymmetric geometry corresponding to a {1\over 15} subscale P230 motor of the Ariane 5 rocket is numerically computed. With a suitable mesh for the viscosity value studied, the aeroacoustics in the chamber is fully described. A coupling between the hydrodynamic instability and the organ-pipe acoustic mode is clearly demonstrated. The mechanism for frequency selection is discussed. © 1997 John Wiley & Sons, Ltd.     

Effect of propellant morphology on acoustics in a planar rocket motor

This paper reports the results of numerical simulations of the acoustics in a two-dimensional (plane) motor using a high-order accurate, low-dissipation numerical solver. For verification we compare solutions to Culick’s (AIAA J 4(8):1462–1464, 1966) asymptotic solution for constant injection, and to recent results of Hegab and Kassoy (AIAA J 44(4):812–826, 2006) for a space- and time-dependent mass injection. We present results when the injection boundary condition is described by propellant morphology and by white noise. Morphology strongly affects the amplitude of the longitudinal acoustic modes, and in this connection white noise is not a suitable surrogate.      

两模块装药点传火过程及药粒散布特性

模块装药点传火过程中药粒堆积形态对膛内起始压力波特性有重要影响,而模块装药点传火过程中药盒破裂后药粒飞散过程决定了药粒最终堆积形态。为此设计了模块装药可视化点传火模拟试验装置,通过高速摄像系统,观测不同初始装填位置的两模块装药点传火、药盒破裂及药粒散布过程。试验结果表明,两模块初始装填位置远离底火端且两药盒装填间距增大时,药室内传火时间变长,两个模块药盒燃烧更充分,模块盒的破裂面增大。点传火试验结束后,药室内模拟药粒散布在以底火侧端面中心为起点的轴向195～500 mm区域。其中,药粒主要分布于药室右侧陡坡状堆积区域。基于试验建立了模块装药点传火过程中药盒破裂后药粒散布的三维非稳态气固两相流模型,并进行了模拟计算。计算得到的最终药粒散布与试验测得结果基本吻合,验证了模型的合理性。     

固体火箭推进剂起爆技术

针对便携式防空导弹的聚醚复合推进剂进行了余药起爆试验。试验表明,在聚能装药起爆器作用下成功地起爆了推进剂药柱。该技术对战斗部 发动机一体化设计有重要应用价值。     

含人工脱粘层固体装药结构应力应变场分析

针对某翼柱型固体装药结构,选取1/16子结构进行了有限元分析。通过将其分割成若干具有单一拓扑型式的组合体,获得了精度较高的结构化网格。在三维线性粘弹性理论和边界非线性理论基础上,基于接触算法模拟了人工脱粘层的边界条件;研究了固化降温过程含人工脱粘层固体装药结构的变形特征和应变场,并与无人工脱粘层的计算结果进行了对比,结果表明:人工脱粘层可以显著地改善固体装药结构端部的应变水平,最大的等效VonMises应变从无人工脱粘的30.1%下降为23.0%。此外,探讨了人工脱粘层前缘的应力水平以及工程上界面脱粘的快速近似计算方法。     

Local stresses and strains in axially cracked cylindrical shells

A perturbation solution is obtained for the local stress-strain fields in an axially cracked cylindrical shell. The tenth-order differential equations are used that take into account the transverse shear deformation. The perturbation of a curvature parameter, λ, is employed, where . The stress intensity factors for finite size cylindrical shells subjected to bending and internal pressure are evaluated. Sufficient accuracy can be obtained without using fine mesh sizes in regions near the crack tip. Also analyzed are the influence of cylinder diameter and shearing stiffness on bulging.     

Experimental separation of load and thermal stresses

Three possible methods for determining, separately, thermal and load stresses in a structure from the results of strain measurements are considered. It is shown theoretically that only one of these is feasible. An experimental verification of the proposed method, for temperatures up to 350° F, was obtained by means of thermal and load tests of a flat plate, and through analysis of data obtained by other investigators in experiments on a box beam.     

Experimental determination of residual stresses in paperboard

A method for the experimental determination of the through-thickness residual stress distribution in paperboard is presented. The successive removal of thin layers from strips of board through surface grinding changes the stress-state and the bending stiffness resulting in a changed curvature, which is measurable. From tests of strips in both in-plane directions, stress distributions can then be evaluated using the Treuting-Read method. Geometrically nonlinear effects at the large deformations taking place are avoided through a proper choice of strip dimensions. Typical results are presented and factors influencing the accuracy of the determination are thoroughly discussed.     

Analytical elasto-creep model of interfacial thermal stresses and strains in trilayer assemblies

A two-dimensional model has been developed for thermal stresses, elastic strains, creep strains, and creep energy density at the interfaces of short and long trilayer assemblies under both plane stress and plane strain conditions. Both linear (viscous) and non-linear creep constitutive behavior under static and cyclic thermal loading can be modeled for all layers. Interfacial stresses and strains are approximated using a combination of exact elasticity solutions and elementary strength of materials theories. Partial differential equations are linearized through a simple finite difference discretization procedure. The approach is mathematically straightforward and can be extended to include plastic behavior and problems involving external loads and a variety of geometries. The model can provide input data for thermal fatigue life prediction in solder or adhesive joints. For a typical solder joint, it is demonstrated that the predicted cyclic stress–strain hysteresis shows shakedown and a rapid stabilization of the creep energy dissipation per cycle in agreement with the predictions of finite element analysis.     

Bounds on stresses caused in structures by bounded anelastic strains

Summary Bounds are obtained on the stresses that can develop at an arbitrary section of a structure (such as a continuous beam, or a rigid frame) by anelastic strains of unknown distribution but bounded magnitudes. Examples of a continuous beam with two equal spans, and a portal frame are worked out in detail to illustrate the procedure.

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Übersicht Es werden Grenzen für die Spannungen ausgerechnet, die in beliebigen Querschnitten eines Tragwerkes (z. B. in einem durchlaufenden Balken oder in einem Fachwerk) entstehen können, wenn nichtelastische Dehnungen begrenzter Größe aber unbekannter Verteilung auftreten. Als Beispiele werden ein durchlaufender Balken mit zwei Feldern sowie ein Fundamentrahmen durchgerechnet, um die Einzelheiten des Berechnungsganges zu zeigen.

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This research was supported by the Advanced Research Projects Agency (Project DEFENDER) and was monitored by the U.S.Army Research Office-Durham under Contract DA.31-124-ARO-D.257.     

Determination of elastic-plastic stresses and strains from measured surface strain data

A rigorous approach founded in the fundamental principles of plasticity is used to develop an accurate numerical algorithm for the determination of stresses and elastic and plastic strains from total strain data measured on a structure surface. The approach used to develop the algorithm and its relationship to both the flow theory of plasticity and recent advances in tangent stiffness-based numerical solution procedures for elastic-plastic boundary value problems are presented. Verification of the method for plane stress problems is demonstrated. A discussion of how the method can be used with measured surface displacement data is proved.