Response of impulsively loaded cylindrical shells

Experiments were performed to identify the structural response modes of thin cylindrical shells, with and without internal pressure, subjected to external radial impulsive loads. For unpressurized shells the response modes consisted of dynamic pulse buckling followed by large inward deflections of the loaded surface. In shells with high internal pressure, these response modes were followed by an outward motion driven by the internal pressure. Energy balance equations were formulated which modelled the important features of the observed response mechanisms. These equations were then used to determine the shell load-damage relationships and to predict failure.     

Influence of autofrettage on metal matrix composite reinforced gun barrels

Advanced materials are considered as candidates for the replacement of traditional gun barrel steel with the hope that weapons as durable as steel but at a fraction of the weight will be developed. Through an analytical model that simulates the effects of autofrettage on a cylindrical gun barrel, the resultant compressive residual stresses are quantified, and different materials examined as to their possible resistance to fracture under repeated internal pressure loads. This study investigates a traditional low-alloy gun steel, a high temperature SiC/titanium-alloy metal matrix composite, as well as various hybrid combinations of these materials, for their ability to develop the necessary residual stress and inelastic strain states necessary for durability. It is discovered that a hybrid composite comprised of low-alloy gun steel on the inner region of the gun barrel and circumferentially wound SiC/Ti–24Al–11Nb on the outer region can still exhibit the same compressive residual stress (and corresponding inelastic strains) seen in homogeneous steel barrels, but with a weight savings of up to 37%, while maintaining the original barrel dimensions.     

Die Scheiteldruckprüfung korrosionsbeanspruchter Hoch- und Höchstdruckrohre zur Untersuchung des Bauteil-Rißwachstumsverhaltens unter Modus II-Schwingungsrißkorrosion

External Crown Fatigue Loading of High and Ultrahigh Pressure Tubes Subjected to Corrosion – a Highly Informative Test Predicting the Crack Growth Behaviour of Tubular Components under Mode II Corrosion Fatigue Conditions Stressing high and ultrahigh pressure tubes by external static or fatigue loads has been qualified as a convenient method to simulate the load case “internal pulsating pressure” by analysing the stress state of thick walled tubes when loaded by internal pressure and external crown loads, respectively. The results of different analytical calculations were compared with that of a Finite-Element-Computation demonstrating, for tubes with nominal pressures in the range of 325–3600 bar, an excellent correspondence. Tests with 86 tube cuttings of steel X 6 CrNiMoTi 17 12 2 (W.-No. 1.4571; ASTM UNS S 31635; BS 320531) showed the following results: In air, pulsating pressures of 325 bar (corresponding to the maximum allowable operating pressures) are sustained indefinitely. Under mode II-corrosion fatigue in 0,1 N H₂SO₄ (30°C) failure occures after 3,8 · 10⁷ mode cycles. A twentyfold H₂SO₄ concentration will lower the number of cycles to fracture to one tenth of this value without leaving mode II. Under mode II corrosion fatigue crack growth will propagate faster in radial direction than in air, so that leak-before-break under internal pressure will be likely. Crack growth rates in radial direction increased with increasing acid concentration so that the probability for leak-before-break will further increase. Highest priority for the surveillance strategy of components loaded in mode II CF has, however, the prove that crack initiation in this environment is commencing much earlier than in air, and definitely earlier than found for compact specimens tested in a mode II pulsating fatigue or rotating bending test.     

反对称正交铺层剪切圆柱壳在外压下的屈曲和后屈曲

给出了反对称正交铺层剪切圆柱壳广义大挠度Donnell 型方程, 并运用位移型摄动技术构造出该圆柱壳在均匀外压作用下的后屈曲渐近级数解。考虑到边界效应对中短圆柱壳的影响及边值问题摄动解的一致性, 详细研究了该圆柱壳端部边界层方程和奇异摄动解, 以便与中部正则摄动解相匹配。文中同时给出一些典型例子并讨论了横向剪切变形、Batdo rf 数、弹性模量比和初始几何缺陷对圆柱壳屈曲与后屈曲性态的影响。比较显示, 横向剪切变形对圆柱壳的屈曲与后屈曲有重要影响。      

外压作用下椭圆截面柱壳的弹性屈曲

基于能量法推导了外压作用下椭圆截面柱壳弹性屈曲临界荷载的理论解,推导中考虑了椭圆截面连续变化的曲率,引入带有衰减系数的位移函数以反映外压作用下椭圆柱壳的变形特点,并利用里兹法求解外压椭圆柱壳的能量方程。由椭圆柱壳理论解退化求得的圆柱壳外压屈曲荷载与已有文献的经典解吻合良好,与有限元分析结果的比较进一步验证了该文理论解的准确性。基于理论解的参数分析表明:在外压作用下,椭圆柱壳具备比圆柱壳更优越的力学性能;椭圆柱壳的外压屈曲荷载随椭圆截面比的增大而增大,随壳体名义径厚比的减小而增大;椭圆柱壳的外压屈曲荷载随壳体长度的增大而降低,但当名义长径比大于1左右后,屈曲荷载基本保持不变。     

Crushing of axially compressed steel tubes filled with aluminium foam

Summary This study, with the emphasis on experiments, investigates the applicability of aluminium foam as filler material in tubes made of mild steel having square or circular cross sections, which are crushed axially at low loading velocities. In addition to the experiments finite element studies are performed to simulate the crushing behaviour of the tested square tubes, were a crushable foam material model is shown to be suitable for describing the inelastic response of aluminium foam with respect to the considered problems. The experimental results for the square tubes reveal efficiency improvements with respect to energy absorption of up to 60%, resulting from changed buckling modes of the tubes and energy dissipation during the compression of the foam material itself. The principal features as well as the changes of the crushing process due to filling can also be studied by the numerical simulations. A global failure mechanism due to a high foam density can be observed for filled circular tubes. Aluminium foam is shown to be a suitable material for filling thin-walled tubular steel structures, holding the potential of enhancing the energy absorption capacity considerably, provided the plastic buckling remains characterized by local modes.Dedicated to Prof. Dr. Dr. h. c. Franz Ziegler on the occasion of his 60th birthday     

Strength and Failure Modes of Hoop Wound CFRP Tubes Under Compressive High Rates of Loading

A study was undertaken to investigate the response of hoop wound carbon fibre reinforced plastic (CFRP) tubes to dynamic compressive loading at strain rates in the range of 5–200/sec. An experimental rig was designed and built to test short tubular specimens under external radial pressure with minimum end constraints. The load was applied by detonating a small explosive charge inside a water filled, steel, cylindrical chamber enclosing the test specimen. For each test the external pressure and the strains, in both circumferential and longitudinal directions, were recorded on suitable digital processing equipment. Two distinct modes of failure were identified; material and structural (buckling). The mode of failure was dependent on the rate of loading and the tube diameter/thickness ratio. For 100 mm diameter tubes with diameter/thickness=40, buckling failure dominated at strain rates below 10/s. However, at higher strain rates, material failure and a considerable enhancement in burst strength was observed. For 100 mm diameter tubes, with diameter/thickness=80, a buckling mode of failure was in evidence in all the tests, irrespective of the rate of loading.R. Ahmad: Presently at School of Mechanical Engineering, University Sains Malaysia, Pulau Pinang, Malaysia.     

框架柱横向撑杆对钢板剪力墙结构作用效应研究

为研究设有横向撑杆的十字形加劲约束构件对钢板剪力墙结构墙板变形的抑制作用,框架梁柱连接衬板的加强效应,以及横向撑杆对框架柱"沙漏"现象的减缓效应,完成了两榀1:3比例单跨3层钢板剪力墙的拟静力试验,探究了两种结构的破坏顺序和破坏模式,对比分析了两者的滞回性能,墙板、框架柱及梁柱节点的变形和受力情况。研究结果表明:设有横向撑杆的十字加劲约束钢板墙较非加劲钢板剪力墙,具有更好的耗能能力,横向撑杆的设置显著改善了钢板和框架的受力性能,提高了墙体的承载力和刚度,有效减少了滞回曲线的"捏缩"现象,降低薄板墙的噪音及震颤。较非加劲钢板剪力墙,设有横向撑杆的十字加劲约束钢板墙结构框架柱的挠曲值变形量降低20%,梁柱节点的转动需求量略小,但节点应力要求大幅度降低。     

Nonaxisymmetric elastoacoustic analysis of a submerged eccentric hollow sphere: an exact solution

The classical Navier equations of linear elasticity and the Helmholtz equation for the internal/external acoustic domains in conjunction with the translational addition theorem for spherical vector wave functions are employed to present an exact solution for three-dimensional nonaxisymmetric steady-state sound radiation from an eccentric hollow elastic sphere, immersed in and filled with acoustic fluids, and subjected to arbitrary time-harmonic mechanical drives at its internal/external surface. The analytical results are illustrated with numerical examples in which air-filled, water-submerged, thick-walled concentric and eccentric steel spheres are driven by harmonic concentrated or distributed radial internal/external loads. The numerical results reveal the important effects of sphere eccentricity, loading configuration, and excitation frequency on the sound radiation characteristics of the submerged structure. Limiting cases are considered and the validity of results is established with the aid of a commercial finite element package as well as by comparison with the data in the existing literature.     

复杂载荷下钢带缠绕增强复合管力学特性

为研究海洋油气输送用钢带缠绕增强复合管在复杂载荷下的力学响应特性,考虑非线性接触,建立钢带缠绕增强复合管数值计算模型,研究由内外压、弯曲及拉伸载荷组合作用下钢带缠绕增强复合管的变形及承载性能.结果表明,压差(外压大于内压,≤2MPa)越大钢带缠绕增强复合管的柔性越高.与纯弯曲相比,拉伸载荷和压差的附加联合作用使钢带缠绕...     

A probabilistic fracture mechanics model including 3D ductile tearing of bi-axially loaded pipes with surface cracks

This paper presents a probabilistic fracture mechanics model established from three-dimensional FEM analyses of surface cracked pipes subjected to tension load in combination with internal pressure. The models are particularly interesting for offshore pipelines under operational conditions or during laying, where inelastic deformations may occur. In the numerical models, the plastic deformations, including ductile tearing effects, are accounted for by use of the Gurson-Tvergaard-Needleman model. This model is calibrated to represent a typical X65 pipeline steel behaviour under ductile crack growth and collapse. Several parameters are taken into account, such as crack depth, crack length and material hardening. Another important topic is the examination of the influence of bi-axial loading due to internal pressure on capacity. From the results of the deterministic analyses a probabilistic fracture mechanics model is established using the response surface methodology. Two failure criteria are examined to represent the structural capacity. Based on the established model, we illustrate the methodology by examples employing the two different failure criteria solved with first and second order reliability methods.     

Nonlinear behavior and buckling of cylindrical shells subjected to localized external pressure

Buckling loads and postbuckling behavior of cylindrical shells subjected to localized external pressure are considered. The modified extended Kantorovich method with path-tracing technique is applied to determine the buckling loads of the cylindrical shells. It is found that the load is dependent nonmonotonically on geometrical parameters of the area subjected to external pressure. Respective postbuckling shapes show correlation with the shapes corresponding to secondary bifurcation paths for the cases of a cylindrical shell under uniform external pressure and a cylindrical shell under uniform axial load.     

Preliminary design of composite riser stress joints

The objective of this paper is to investigate the technical feasibility of using hybrid carbon and glass-fibre reinforced epoxy composite tubes as production risers for a tension leg oil platform tethered in 1000 m of water. The axial forces and bending moment distributions applied to the riser were calculated by hydrodynamic finite element analysis, taking into consideration the extreme environmental conditions, large displacements, waves, currents and platform motions, which could occur in a 100 year recurrent storm. Loads induced by pre-tensioning the riser, the weight of the riser, external water pressure and the internal pressure that could arise in the event of a blow-out in the well were also considered.The riser was of 220 mm internal diameter and the walls were reinforced with layers of carbon-fibre wound at ±20° to the tubes axis, sandwiched between circumferentially wound glass-fibre reinforced epoxy layers on the inner and outer surfaces. The thickness of the carbon-fibre reinforced layers tapered along the 24 m lengths of the top and bottom sections of the riser, which are described as tapered joints. The strengths at various sections of the composite tubes were calculated using orthotropic, laminated, thick cylinder theory and progressive failure analysis. The wall thicknesses were chosen by comparing the predicted first failure load and 1/3rd final failure load envelopes with the various combinations of axial tensile and bending loads and internal and external pressures that the tubes could encounter. The possibility of delamination occurring at the ply drop-offs in the walls of the tapered joints was investigated using finite element methods and fracture mechanics.The composite riser was shown to satisfy all the design requirements and to weigh less than half the weight of an equivalent steel component.     

Elastic–plastic response of structural foams subjected to localized static loads

Structural foams are increasingly used in engineering applications where high strength and low weight are important. They are used also as energy absorbers. Sandwich structures are a typical area for application of structural foams (as core materials). In a sandwich structure, the core transfers the transverse forces as shear stresses and supports the face sheets against buckling and wrinkling. The structural foams are notoriously sensitive to failure by the application of localized surface loads. Thus, the proper design requires an understanding of the mechanical response of the foam materials to localized external loads.In this paper, the elastic–plastic behavior of closed-cell cellular foams subjected to point and line loads is investigated both experimentally and numerically. Two types of Divinicell foam (H60 and H100) are studied. A finite element modeling procedure is developed using the ABAQUS package. Both plane and axisymmetric formulations for local indentations by rigid bodies are considered. The plastic behavior is described using the *CRUSHABLE FOAM HARDENING material model. This model is calibrated using experimental curves from uniaxial compression tests. Geometrical non-linearity is also taken into account. Both indentation and unloading phases are modeled. Static indentation tests of foam panels and beams are performed using spherical and cylindrical indentors, respectively. A comparison of indentation response obtained from the numerical analysis and from the tests is carried out. A good agreement between the modeling and the experimental data is achieved. In perspective view, the present investigation can contribute towards the development of a damage tolerance methodology for rigid foams.     

闭合截面压弯钢拱的平面外稳定性能研究

该文针对压弯作用下闭合截面圆弧拱的平面外弹性屈曲性能及稳定设计方法进行研究。首先通过势能驻值原理分析均匀轴压力和弯矩同时作用下,钢拱的平面外弹性屈曲性能。在此基础上,在弹塑性范围内讨论弯矩对钢拱的平面外稳定削弱作用,推导得到考虑弯矩作用的压弯钢拱正则化长细比,进而将压弯钢拱的平面外稳定问题简化为纯压钢拱的稳定问题。该文提出的压弯钢拱平面外稳定设计方法与数值分析计算结果吻合较好,可用于钢拱的平面外稳定承载力设计。     

The effect of thermo-mechanical loading on fracture-related parameters of austenitic steel

Failure analysis shows that 80–85% of emergency boiler shutdowns at power plants result from heating surface damage. When in service, the tubes are exposed to alternating thermo-mechanical loads, which trigger phase change affecting the individual service life. The service life sometimes differs significantly from its estimated value. This research is based on the hypothesis about the role and influence of internal structural stresses on the actual strength and long-term performance of tube products made of steels and alloys. The purpose of this work is to determine the limit state region of internal stresses of the first kind, in which microdamage will not lead to fracture. For that, we did a set of experiment studies to model the accelerated aging processes by thermal cycling and cold cyclic deformation. We chose a tube made of austenitic steel 10Cr13Mn12Si2Ni2Cu2Nb (Di59) as the object of research. The methods used were XRD analysis, microhardness testing, X-ray spectroscopy, and microstructure analysis. Due to redistributing properties, steel has no stable states: all its states are short-term and dependent on external disturbances. In accordance with the suggested hypothesis, the research findings make it possible to forecast the trends and direction of changes in the material properties. This allows us to evaluate the achievement of the limit state by the object and to use relaxations of internal stresses as a sign determining the conditions of crack initiation and propagation. The results are confirmed by the data obtained from the microstructure analysis of fractured tubes of a superheater from a functioning boiler.     

新型带竖向缝隙的矩形钢管排柱剪力墙及其抗侧性能

针对传统薄钢板剪力墙以及带竖缝钢板剪力墙存在的问题,提出了一种新型带竖向缝隙的矩形钢管排柱剪力墙。基于机构控制法,设计了新型剪力墙的典型算例,并进行了弹性屈曲、弹塑性抗侧和滞回性能分析。结果表明:新型剪力墙的一阶弹性屈曲均为钢管壁的局部屈曲,且临界荷载远大于弹塑性极限承载力;新型剪力墙具有优异的弹塑性抗侧性能,延性系数可达20以上;弹塑性滞回性能曲线饱满,耗能能力佳。在此基础上,提出了新型剪力墙的弹性抗侧刚度、屈服荷载和极限抗侧承载力等关键性能参数的计算方法,同时对截面宽厚比、连接焊缝的高度等构造措施提出了要求。     

现场发泡夹心墙平面外抗震性能模型试验与数值试验研究

为研究现场发泡夹心墙平面外抗震性能,寻求改善墙体抗震性能的有效手段,制作了7 片现场发泡夹心墙和1 片实心墙,进行了平面外的抗震性能模型试验和数值试验研究。对比分析表明,现场发泡夹心墙的破坏形态、承载力、变形能力和协调变形能力等二者均较好吻合,相互验证了二者的有效性。研究结果表明梁挑耳对内外页墙体具有较大的协调变形能力,塑料钢筋拉接件可以起到对开裂墙体支撑或拉结的作用,有效防止墙面倒塌掉落。变形性能分析结果表明现场发泡夹心墙的耗能能力较大、延性系数较高,并且具有良好的协调变形能力。     

Curvature effects on pressure-induced buckling of empty or filled double-walled carbon nanotubes

Summary The curvature effects of interlayer van der Waals (vdW) forces on pressure-induced buckling of empty or filled double-walled carbon nanotubes (DWNTs) are studied for various radii, length-to-radius ratios, end conditions and internal-to-external pressure ratios. The analysis is based on a double-elastic shell model and assumes that the interlayer vdW pressure at a point between the inner and outer tubes depends not only on the change of the interlayer spacing, but also on the change of the curvatures of the inner and outer tubes at that point. Here the role of filling substances inside DWNTs is modeled by a uniformly distributed internal pressure. The present work aims to study the curvature effects on critical radial pressure. An explicit formula is obtained for the external buckling pressure of empty or filled DWNTs. The critical value of external pressure is estimated with various internal-to-external pressure ratios. It is shown that the curvature effects play a more significant role in buckling problems under radial pressure for small radii DWNTs than under pure axial stress. Our results show that loading transfer through vdW forces prior to buckling is important for the pressure-induced buckling of DWNTs rather than axially compressed buckling.     

Lateral collapse of short‐length sandwich tubes compressed by different indenters and exposed to external constraints

In this paper, sandwich tube components which consist of thin‐walled circular tubes with aluminium foam core are proposed as energy absorption systems. The sandwich tubes were laterally crushed under quasi‐static loading conditions. The sandwich tubes were crushed under two types of indenters and exposed to three different types of external constraints. The collapsing behaviour and the energy absorption responses of these systems were investigated by nonlinear finite element analysis through ANSYS‐LS‐DYNA. Various indicators which describe the effectiveness of energy absorbing systems were used as a marker to compare the various systems. It was found that the sandwich tube systems compressed by cylindrical indenters particularly the unconstrained system and the system with inclined constraints offered a very desirable force‐deflection in which the force is almost constant in the post collapse stage. The employing of external constraints was noticed as a feasible method of increasing the SEA particularly when cylindrical indenter is used.