Fracture behavior of brittle circular rings subjected to concentrated impulsive loading

The influence of impact velocity and ring geometry in the fracture patterns produced by in-plane concentrated impulsive loading on brittle circular rings has been studied both experimentally and theoretically. The experiments were performed by impacting circular rings made of plaster with a steel plate. The fracture behavior was photographed by a camera with a flash, and the crack-initiation time was measured using a memoriscope. The fracture behavior is explained using dynamic photoelasticity and the theory of flexural motion of a circular ring. With the addition of an impact-fracture criterion to this theory, the fracture patterns of brittle circular rings are predicted.     

Buckling of short viscoplastic cylindrical shells subjected to radial impulse

The dynamic buckling of thin viscoplastic cylindrical shells is considered in the formulation developed by Abrahamson and Goodier [1]. The constitutive equations employed describe the rate sensitive plastic material and a biaxial state of stress is considered. The influence of the viscosity parameter on the buckling process is discussed in detail and in the limiting case the solution for a perfectly plastic material is obtained. From the analysis of the final deflections as a function of the applied impulse the “stability effect” of the viscous properties of the material on the buckling process is determined.     

Optimal location of additional supports for plastic cylindrical shells subjected to impulsive loading

Necessary optimality conditions for location of the additional supports, restricting the dynamic response of a rigid perfectly plastic cylindrical shell subjected to an initial transverse velocity, are deduced. Incorporating the concept of the mode-form motions the problem is treated as a self-conjugate problem of the optimal control theory with distributed parameters. We use the control technique, developed previously for the case in which the state variables (the bending moment, the shear force, the deflection and its rate) together with these derivatives, being continuous in certain subdomains, may have discontinuities on the boundaries of these subregions. A particular case. associated with the uniform initial impulse is examined in detail.     

考虑材料损伤累积单层柱面网壳在强震下的失效研究

采用考虑钢材损伤累积的本构模型,对跨度15米单层柱面网壳在强震下的失效进行了系统的研究。在大量算例的基础上,考察了屋面质量、矢跨比、初始几何缺陷和长宽比等结构几何参数的变化对柱面网壳失效特征和失效极限荷载的影响,探讨了结构的强震失效模式及失效机理。对大量强度破坏算例在失效时刻的特征响应进行统计分析,建立了考虑材料损伤累积的单层柱面网壳动力损伤模型,可对结构在不同荷载强度下的损伤程度进行评估;提出了单层柱面网壳强震失效判别准则,用于判别单层柱面网壳在强震下的失效极限荷载。     

Expansion of cylindrical shells subjected to internal explosive detonations

Two explosively loaded cylindrical shell experiments were conducted to provide experimental data for benchmarking numerical codes. Each shell was subjected to internal high-explosive detonations, which caused it to expand outwardly at strain rates on the order of 10⁴ s^–1. At approximately 150 percent strain, multiple plastic instabilities appeared on the surface of these shells in a quasi-periodic pattem. These instabilities continued to develop into bands of localized shear and eventually formed cracks before causing the shell to fragment. Diagnostic equipment on these experiments included a Fabry-Perot interferometer and a fast-framing camera. The experiments and the data obtained from the diagnostic equipment are discussed and illustrated.     

夹芯圆柱壳在水下爆炸载荷作用下的抗冲击特性

采用声固耦合方法对夹芯圆柱壳和等质量的普通圆柱壳在爆炸载荷作用下的应变、速度和加速度进行有限元计算。结果表明:夹芯防护层对爆炸冲击波可起到较好的衰减作用,即通过芯层的塑性变形,耗散了冲击过程中产生的大部分能量,对里面的圆柱壳体起到较好的保护作用,由于夹芯防护层的存在,与等质量的普通圆柱壳相比,夹芯圆柱壳能够承受更强的爆炸冲击波,降低结构的整体变形。     

Dynamic stability of rotating cylindrical shells subjected to periodic axial loads

In this paper, the dynamic stability of rotating cylindrical shells under static and periodic axial forces is investigated using a combination of the Ritz method and Bolotin’s first approximation. The kernel particle estimate is employed in hybridized form with harmonic functions, to approximate the 2-D transverse displacement field. A system of Mathieu–Hill equations is obtained through the application of the Ritz energy minimization procedure. The principal instability regions are then obtained via Bolotin’s first approximation. In this formulation, both the hoop tension and Coriolis effects due to the rotation are accounted for. Various boundary conditions are considered, and the present results represent the first instance in which, the effects of boundary conditions for this class of problems, have been reported in open literature. Effects of rotational speeds on the instability regions for different modes are also examined in detail.     

Fracture mechanics of laminated glass subjected to blast loading

A failure criterion based on energy balance approach is introduced for the laminated glass panel subjected to blast loading. Based on this failure criterion, a damage factor is developed to assess the failure of the laminated glass panel. If the damage factor is less than one, the plate is safe otherwise unsafe. Trigonometric function is employed to express the transverse deflection and the Airy’s stress function in von Karman’s large deflection equations of a thin plate. The nonlinear ordinary differential equation of motion obtained using the Galerkin method is solved using Runge–Kutta method. The predicted results indicate that the breakages of the laminated glass may be caused by the negative phase of the blast load if the positive phase blast load is not violent enough to cause failure. Also, the size of glass shards the laminated glass plies breaks in to is predicted using the surface energy based failure model.     

撞击载荷下泡沫铝夹层板的动力响应

应用泡沫金属子弹撞击加载的方式研究了固支方形夹层板和等质量实体板的动力响应,分别应用激光测速装置和位移传感器测量了泡沫子弹的撞击速度和后面板中心点的位移历史,给出了夹层板的变形与失效模式,研究了子弹冲量、面板厚度、泡沫芯层厚度及芯层密度对夹层板抗撞击性能的影响。结果表明,后面板中心点挠度最大,周边最小,整体变形为穹形,且伴有花瓣形的变形。参数研究表明,通过增加面板厚度或芯层厚度均能有效控制后面板的挠度,改善夹层板的能量吸收能力,结构响应对子弹冲量和芯层密度比较敏感。实验结果对多孔金属夹层结构的优化设计具有一定的参考价值。 更多还原     

Stability of reinforced cylindrical shells under combined loading

A new approach to solving buckling problems for ribbed cylindrical shells subject to longitudinal force and pressure is proposed. Results for shells reinforced with stringers and rings are presented     

Plastic buckling of cylindrical shells under biaxial loading

The predictions for plastic buckling of shells are significantly affected by the plasticity model employed, in particular in the case of nonproportional loading. A series of experiments on plastic buckling of cylindrical aluminum alloy shells under biaxial loading (external pressure and axial tension), with well-defined loading and boundary conditions, was therefore carried out to provide experimental data for evaluation of the suitability of different, plasticity models. In the experiments, initial imperfections and their growth under load were measured and special attention was paid to buckling detection and load path control. The Southwell plot was applied with success to smooth the results. The results show that axial tension decreases resistance to buckling under external pressure in the plastic region due to softening of the material behavior. Comparison with numerical calculations usingJ ₂ deformation and incremental theories indicate that both theories do not predict correctly plastic buckling under nonproportional loading.Babcock (SEM Member), deceased, was Professor of Aeronautics and Applied Mechanics, California Institute of Technology, Pasadena, CA 91125.     

Fracture of cylindrical shells with cracks in tension

In practice, cracks may frequently be introduced in structural components during the course of the technological manufacturing and service. Studies concerning the strength prediction of structures with cracks are therefore of considerable importance. During the fracture process of thin-walled structure elements, material local to the crack may buckle. The fracture characteristics may be affected considerably. Both theoretical and experimental studies of this problem were made for plates [1]. In this work, experimental results are presented for the deformation and fracture of cylindrical shells with cracks.     

Dynamic behaviour of thin cylindrical shells subjected to high-speed travelling inner pressures

Summary The behaviour of dynamic stresses is investigated for the case of thin cylindrical shells subjected to high speed travelling inner pressures. The cylinder is clamped at one end and free at the other end or simply supported at both ends. The effects of travelling velocity and dimensions of the cylinder on hoop stresses and bending stresses in the longitudinal direction are studied. To simplify calculus, the effects of rotatory inertia, shear and solid viscosities are neglected.

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Übersicht Es werden die dynamischen Spannungen in dünnen zylindrischen Schalen untersucht, die schnellen Druckwellen ausgesetzt sind. Der Zylinder ist an einem Ende fest eingespannt, am anderen Ende frei oder auch an beiden Enden einfach gelagert. Der Einfluß der Wandergeschwindigkeit und der Zylinderdimensionen auf die Ringspannungen und die Biegespannungen wird untersucht. Zur Vereinfachung der Berechnungen werden Drehträgheit, Querkraft und innere Dämpfungen vernachlässigt.