Blast response of a lined cavity in a porous saturated soil

The paper proposes a comprehensive approach to simulate the blast response of a lined cavity in a porous soil. To calculate the soil–structure contact pressure, the coupled Godunov-variational-difference approach was developed. The lining is modeled by a Timoshenko elastic–plastic shell with kinematic linear hardening. To solve the problem in the lining domain, the variational-difference method is applied. The soil is modeled by the Lyakhov three-phase model that takes into account both bulk and shear elastic–plastic behavior, including the effect of soil pressure on the yield strength for the stress tensor deviator. The problem of blast wave propagation within the soil medium is solved by the Godunov method. The coupled approach to calculate the soil–lining contact pressure is based on the relationships on the shock and rarefaction waves with finite-difference equations of the shell motion using a simple iteration method. It allows the reduction of the contact problem to the self-similar symmetric Riemann problem. Solution of the problem of an explosion in a porous medium, and analysis of the soil–obstacle interaction under the blast action using the proposed method show good correspondence with available experimental results. Also, the plane problem of blast response of the circular cavity lined by a thin steel lining was solved. The effect of the gas volumetric content in the soil on the incident shock wave pressure as well as on the contact pressure and lining meridian strain was studied.     

Analytical calculation of blast-induced strains to buried pipelines

The aim of this paper is to introduce a robust methodology for the analytical calculation of strains in flexible buried pipelines due to surface point-source blasts. Following a brief bibliographic overview regarding the characteristics of ground waves produced by surface explosions, a method used to model wave propagation with radial attenuation and spherical front is presented. Strains due to P- and Rayleigh waves, which dominate the waveform generated by an explosion, are accordingly calculated by modeling the pipeline as a three-dimensional (3-D) cylindrical thin shell and ignoring soil–structure interaction. To simplify the design procedure, a set of easy-to-use relations for the calculation of maximum strains and their position along the pipeline axis is supplied. The derived expressions are evaluated through comparison against 3-D dynamic numerical analyses, field strain measurements in flexible pipelines due to a series of full scale blasts, and state-of-practice design methods. Comparisons show that the proposed methodology provides improved accuracy at no major expense of simplicity, as well as the advantage of properly accounting for the effect of local soil conditions.     

箱包炸弹内爆作用下单层球面网壳结构的动力响应分析

运用ANSYS/LS-DYNA建立跨度40 m凯威特K8单层球面网壳,采用流固耦合算法,考虑箱包炸弹在网壳内部爆炸的最不利类型,获取其动力响应规律。研究结果表明:在不同炸点水平位置下,网壳内部流场分布特征、冲击波传播路径以及冲击波与网壳作用过程存在差异,各特征响应随炸点水平位置的改变变化较大,网壳杆件塑性应变百分率大致在网壳半跨的3/4处达到极值;环杆塑性应变百分率较斜杆以及肋杆高,环杆轴向应力呈现的高频率、高幅值的"环杆效应"特征与环杆所处的位置有关,且主要位于网壳的倒数1~3环区域;由于冲击波的局部增强效应,内爆荷载作用下网壳结构的易损薄弱部位主要有柱脚、支座附近杆件以及网壳环杆3部分。     

Explosion‐induced dynamic soil–structure interaction analysis with the coupled Godunov–variational difference approach

The paper presents a coupled 2D Godunov–variational difference approach for soil–structure interaction due to a nearby explosion. Owing to the high‐intensity dynamic loads, complex processes take place, including transient separation of the buried structure from the surrounding soil, large deformations of the buried structure including loss of stability, and so on. The approach takes into account the irreversible bulk compaction of the soil medium and is based on the relationships of the shock and rarefaction waves with finite‐difference equations of the shell motion, using a simple iteration method. The model reduces the contact problem to the self‐similar symmetric Riemann problem. The proposed approach is demonstrated by the solution of a buried explosion in the proximity of a lined tunnel buried in soil. The peak contact pressure envelope along the lining was studied. It was found that for an explosion in the proximity of a relatively rigid shell, the maximum value of this envelope is located at some distance from the lining's axis of symmetry. Copyright © 2008 John Wiley & Sons, Ltd.     

Underground explosion of a cylindrical charge near a buried wall

The paper investigates the explosion characteristics of a cylindrical explosive that is buried in soil close to a rigid obstacle. The soil is modeled as a bulk compressible elastic plastic medium, including full bulk locking and dependence of the current deviatoric yield stress on the pressure. The Lagrange approach and the modified variational-difference method are used to simulate the process. The pressure distribution along the rigid obstacle has been studied for various stand of distances of the explosive from the obstacle. It was shown that when the explosion is relatively close to the obstacle, the envelope of the pressure distributions (connecting the maximum stress values of all distributions along the wall) shows a maximum value that is located at some distance away from the axis of symmetry and not along the axis as is the case for a distant explosion. It was found that this phenomenon appears when the interaction of the reflected wave with the explosive cavity yields significant deformation of the cavity frontal part that it is sharply deformed and becomes planar. When the explosive stand of distance from the obstacle is moderate or large, the explosion cavity remains cylindrical during all times and the peak pressure is developed along the axis of symmetry.     

Lebensdauerberechnung gekerbter Bauteile auf Basis der elastisch‐plastischen Schwingbruchmechanik

Fatigue life calculation of notched components based on the elastic‐plastic fatigue fracture mechanics The life of notched components is subdivided into the pre‐crack, or crack‐initiation, and crack propagation phases within and outside notch area. It is known that a major factor governing the service life of notched components under cyclic loading is fatigue crack growth in notches. Therefore a uniform elastic‐plastic crack growth model, based on the J‐Integral, was developed which especially considers the crack opening and closure behaviour and the effect of residual stresses for the determination of crack initiation and propagation lives for cracks in notches under constant and variable‐amplitude loading. The crack growth model will be introduced and verified by experiments.     

A study of the interaction between a guardrail post and soil during quasi-static and dynamic loading

A roadside guardrail system is anchored in gravel beside a roadway to eliminate the risk of fatal accidents during off-road crashes and collisions with hazardous roadside objects. The desired safety behaviour is ensured not only by the guardrail structure itself, but also by the interaction between the gravel and the guardrail post. The interaction of gravel with a Sigma-post of a standard Swedish guardrail was studied in experiments and numerical analysis. The aim was to measure the strength of the single post embedded in gravel and use the data to validate a computer model for the investigation of the soil–post interaction. A quasi-static and dynamic test series were designed and carried out. Two corridors were formed by the test data for the quasi-static and dynamic loading conditions, respectively. A parametric study was subsequently conducted to investigate the influence of the gravel stiffness on the soil–post interaction through computer simulations using LS-DYNA. The numerical results showed that the LS-DYNA soil and concrete model and the Cowper–Symonds steel model effectively captured the soil–post interaction since the calculated strength of the post agreed with the corridors of the test data. The input parameters for the soil and concrete material model were recommended for roadside gravel in crash analyses.     

爆炸荷载作用下深埋圆形隧洞饱和土-衬砌系统的动力响应

考虑隧洞衬砌内壁对爆炸波的反射作用及其负压效应,将衬砌视为弹性介质,研究了深埋圆形隧洞饱和土-弹性衬砌耦合系统在隧洞轴线发生爆炸时的轴对称瞬态动力响应。首先,基于Biot理论和弹性理论,考虑边界条件以及弹性衬砌和饱和土接触面处的连续性条件,利用Laplace变换得到饱和土和弹性衬砌位移、应力和孔隙水压力等在Laplace变换域中的解析表达式。在此基础上,利用Laplace数值逆变换得到其时间域的动力响应,数值分析重点考察了不同隧洞模型和不同爆炸载荷模型对饱和土动力响应的影响,并进行了参数研究。结果表明:爆炸波反射产生的负压效应对饱和土体的动力响应有显著影响。同时,饱和土-壳体衬砌系统、饱和土-弹性衬砌系统和无衬砌饱和土隧洞的响应性态基本一致,但响应周期和幅度依次增大。     

爆破地质体中动载应力的表达形式及某些问题的讨论

简要讨论了在爆破地质中由不同的动载形成弹性波、冲击波、爆轰波、弹塑性波、粘弹性波和粘弹塑性波传播的动应力表达形式及一些需要进一步研究的问题.     

黏弹性土中衬砌隧道振动响应的解析解

该文采用解析方法在频率域内对黏弹土层和衬砌结构简谐振动特性进行了研究。首先, 将土骨架视为具有分数阶导数本构关系的黏弹性体, 根据黏弹性理论, 推导得到了简谐荷载作用下分数导数型黏弹性土层的位移和应力等解析表达式。其次, 建立了两种类型的衬砌运动方程:第一, 将衬砌结构视为均匀弹性介质, 研究了分数导数黏弹性土中弹性衬砌结构的动力特性;第二, 将衬砌等效为薄壁壳体结构, 利用Flügge薄壳理论, 得到了衬砌结构的运动方程, 并对分数导数黏弹性土和壳体衬砌的动力相互作用进行了分析。根据连续性边界条件, 得到了相关待定系数的表达式。再次, 与以往的解析解进行了对比。最后, 通过算例分析了土体和衬砌各参数对系统动力特性的影响, 结果表明:薄壁壳体衬砌结构条件下系统的动力响应大于均匀弹性衬砌结构条件下系统的动力响应;随着土体和衬砌模量比的增加, 响应幅值逐渐减小。分数导数本构参数对系统的动力特性有较大影响。     

Lebensdauerberechnung festgewalzter Kerbproben unter Axialbelastung auf der Basis eines Rißfortschrittskonzepts

Axial fatigue life calculation of fillet rolled specimens by means of a crack growth model Fillet rolling is a method which significantly improves the fatigue strength of members. Residual compressive stresses induced in the surface layer during the fillet rolling process are able to retard or prevent crack propagation. An elastic‐plastic on the J‐integral based crack growth model considering the crack opening and closure phenomenon in nonhomogeneous plastic stress fields is described. Experimentally determined crack growth curves and fracture fatigue life curves at constant amplitude loading were used to verify the developed model.     

Kontaktwechselwirkung einer Rohrleitung mit der Reparaturbandage aus einem Kompositwerkstoff

In the present work the contact interaction of a long cylindrical shell with a coaxial cylindrical wrap made of a composite material is investigated. The composite material is modeled as a homogeneous orthotropic medium with known effective elastic properties. Based on the classical shell theory governing equations for the contact problems and general solutions to the deflections and internal forces are formulated. The unknown integration constants and the contact surface area are determined numerically using the software package Maple. Three characteristic lengths of the wrap, for which the transition from one contact mode to another takes place, have been determined. It was found that the change in the internal pressure does not affect the transition between the contact modes. The nature of the contact interaction is determined by the geometric parameters of the contact pair and elastic material properties of the shell and the repair wrap.     

Three-dimensional numerical simulations of dynamic fracture in silicon carbide reinforced aluminum

The three-point bending test by Kolsky-bar apparatus is a convenient technique to test the dynamic fracture properties of materials. This paper presents detailed three-dimensional finite element simulations of a silicon particle reinforced aluminum (SiC_p/Al) experiment (Li et al., [Proceedings of the US Army Symposium on Solid Mechanics]. In the simulations, the interaction between the input bar and the specimen is modeled by coupled boundary conditions. The material model includes large plastic deformations, strain-hardening and strain-rate hardening mechanisms. Furthermore, crack initiation and propagation processes are simulated by a cohesive element model. The simulation results quantitatively agree with the experimental measurements on three fronts: (1) the structural response of the specimen, (2) the time of unstable crack propagation, and (3) the local deformations at the crack-tip zone. The simulations reveal crack propagation characteristics, including crack-tip plastic deformation, crack front curving, and crack velocity profile. The effectiveness of Kolsky-bar type fracture tests is verified. It is shown that a rate-independent cohesive model can describe the complicated dynamic elastic–plastic fracture process in the SiC_p/Al material.     

Fatigue crack growth from small defects under out-of-phase combined loading

A modified linear elastic fracture mechanics analysis is presented for the evaluation of the crack growth and threshold behavior of small cracks initiated from small defects under combined loading fatigue. For the detailed evaluation of the behavior of small fatigue cracks, the Kitagawa effect, the elastic–plastic behavior of cracks in biaxial stress fields and crack closure effects are taken into account. In-phase and out-of-phase combined tension and torsion fatigue tests were conducted using annealed carbon steel specimens containing small holes. The direction of crack propagation, S–N curves and fatigue limits were found to be in good agreement with the theoretical predictions.     

水中爆炸的殉爆试验方法

为了研究弹药水中爆炸的安全性,依据水中爆炸的特点,建立了一种利用冲击波峰值压力和气泡周期判断水中殉爆的试验方法,可以确定炸药的殉爆距离、殉爆安全距离以及被发装药的殉爆反应程度,通过水中爆炸试验进行了验证。结果表明:主发装药为带壳1.5 mm铝壳的GUHL-1装药、被发装药为带壳1.0 mm铝壳的RS211装药时,殉爆距离L100约为60 mm,殉爆安全距离L0约为120 mm。根据水中爆炸的冲击波压力和气泡周期可以可靠地判断被发装药是否发生殉爆,并可以定量估算被发装药的反应程度。     

Mechanisms and modeling of low cycle fatigue crack propagation in a pressure vessel steel Q345

The fatigue process near crack is governed by highly concentrated strain and stress in the crack tip region. Based on the theory of elastic–plastic fracture mechanics, we explore the cyclic J-integral as breakthrough point, an analytical model is presented in this paper to determine the CTOD for cracked component subjected to cyclic axial in-plane loading. A simple fracture mechanism based model for fatigue crack growth assumes a linear correlation between the cyclic crack tip opening displacement (ΔCTOD) and the crack growth rate (da/dN). In order to validate the model and to calibrate the model parameters, the low cycle fatigue crack propagation experiment was carried out for CT specimen made of Q345 steel. The effects of stress ratio and crack closure on fatigue crack growth were investigated by elastic–plastic finite element stress–strain analysis of a cracked component. A good comparison has been found between predictions and experimental results, which shows that the crack opening displacement is able to characterize the crack tip state at large scale yielding constant amplitude fatigue crack growth.     

Smoothed particle hydrodynamics for numerical simulation of underwater explosion

 Underwater explosion arising from high explosive detonation consists of a complicated sequence of energetic processes. It is generally very difficult to simulate underwater explosion phenomena by using traditional grid-based numerical methods due to the inherent features such as large deformations, large inhomogeneities, moving interface and so on. In this paper, a meshless, Lagrangian particle method, smoothed particle hydrodynamics (SPH) is applied to simulate underwater explosion problems. As a free Lagrangian method, SPH can track the moving interface between the gas produced by the explosion and the surrounding water effectively. The meshless nature of SPH overcomes the difficulty resulted from large deformations. Some modifications are made in the SPH code to suit the needs of underwater explosion simulation in evolving the smoothing length, treating solid boundary and material interface. The work is mainly focused on the detonation of the high explosive, the interaction of the explosive gas with the surrounding water, and the propagation of the underwater shock. Comparisons of the numerical results for three examples with those from other sources are quite good. Major features of underwater explosion such as the magnitude and location of the underwater explosion shock can be well captured. Received: 2 April 2002 / Accepted: 20 September 2002     

偏心爆炸荷载下网壳结构的动力响应分析

利用ANSYS/LS-DYNA动力有限元软件平台建立了包含网壳杆件、檩托、檩条、铆钉、屋面板、墙体和地面在内的40m跨度精细化典型K8单层球面网壳结构有限元模型,采用流固耦合算法对结构在内部偏心爆炸荷载作用下的动力响应进行了有限元数值模拟研究,得到了网壳结构在偏心爆炸荷载作用下的四种响应模式：结构无损伤、构件塑性发展、网壳大变形、泄爆型破坏。获得了不同爆炸点位置、杆件截面、矢跨比、支承条件、屋面板厚度等参数条件下的结构动力响应结果,通过对比分析,总结了各参数对结构动力响应的影响程度与规律,为网壳抗爆防御设计提供了依据。     

Explosion and detonation characteristics of dimethyl ether

In this study, the explosion and detonation characteristics of dimethyl ether (DME) were experimentally investigated. A spherical pressure vessel with an internal volume of 180L was used as the explosion vessel. Therefore, tubes 10m in length with internal diameters of 25mm and 50mm were used as detonation tubes. In addition, we compared the characteristics of DME with those of propane since DME is considered as a substitute fuel for liquid petroleum gas (LPG). At room temperature and atmospheric pressure, the maximum explosive pressure increased tenfold. The explosion index (K(G) values), an indicator of the intensity of an explosion, was larger than that of propane, indicating that the explosion was intense. No experimental study has been conducted on the detonation behavior of DME so far, but this research confirmed a transition to detonation. The detonation characteristics were similar to the characteristics of the Chapman-Jouguet detonation, and the concentration range for detonation was from 5.5% to 9.0%.     

Preparation and magnetic behavior of carbon-encapsulated iron nanoparticles by detonation method

Carbon-encapsulated iron (Fe@C) nanoparticles with core/shell structure have been successfully synthesized by detonation method, using a homemade composite explosive precursor. The detonation reaction was ignited by a non-electric detonator in nitrogen gas in an explosion vessel. The as-prepared detonation products were characterized by X-ray Diffraction, Transmission electron Microscopy, Raman spectroscopy and X-ray fluorescence. The magnetic behavior of the Fe@C materials was measured by vibrating sample magnetometer. The results showed that the detonation products were made up of the body centered cubic iron core and the graphitic carbon shell, of which the core diameter was in the range of 15–50 nm. Raman spectroscopy indicated that both graphitic and amorphous carbon occured in the outside shell structures. The hysteresis loops showed the as-made Fe@C nanoparticles were of superparamagnetic at 300 K temperature. A detonation reaction mechanism was proposed to explain the growth process of Fe@C nanoparticles based on these results.