基于荷载时程分析法的商用飞机撞击钢板混凝土结构安全壳的有限元分析

由于钢板混凝土墙背部钢板能够有效地约束混凝土在撞击方向上的运动以及限制混凝土碎片的飞溅,为了抵御商用飞机撞击,新型核电机组的核岛厂房外墙通常设计为钢板混凝土结构(SC)。本文基于荷载时程分析法,运用经典的显式非线性动力分析软件ANSYS/LS-DYNA,进行了波音707-320型号商用飞机撞击某钢板混凝土结构安全壳的响应分析。计算结果表明,即使在安全壳筒身最不利撞击部位冲击作用下,像波音707-320型号的商用飞机对该安全壳的影响是较小的,且增大钢板的厚度能够有效的减小冲击作用下结构的响应。     

Numerical modelling of crack growth profiles in integral skin-stringer panels

Integral (monolithic) structures can play a significant role in high efficiency structural design. According to the current technological manufacture methods, integral structures have an impact on fabrication cost and on weight reduction. However, until now, some critical aspects have limited the use of these structures. Conventional structures with mechanical or chemical (by adhesion) joints are advantageous because of their damage tolerant and fail safe behaviour. The presence of two separate parts, skins and stringers, guarantee the structural integrity of the component when propagating defects and cracks are present and are thus the key factor in aircraft structures. Focusing our attention on aircraft related structures, the aim of this paper is to show the application of numerical methodologies to evaluate the behaviour of integrally machined skin-stringer panels in the presence of propagating cracks. The described activity resulted from the “Analytical Round Robin on Crack Growth and Residual Strength Prediction in Integral Structures” proposed by ASTM Task Group E08.04.05 while different FE approaches for a single type integral panel with a propagating crack have been introduced in this paper. The crack growth evaluation based on the numerical models agrees well with the experimental results.     

Failure analysis of UHPFRC panels subjected to aircraft engine model impact

Using the finite element approach, this paper evaluates the punching resistance of ultra-high performance fiber reinforced concrete (UHPFRC) panels subjected to the impact of an aircraft engine. The models are analyzed using LS-DYNA, a commercially available software program. The structural components of the UHPFRC panels, aircraft engine model, and their contacts are fully modeled. Included in the analysis is material nonlinearity, which considers damage and failure. The analysis results are then verified with the test results. A parametric study with varying fiber contents is carried out to investigate the punching behavior of the UHPFRC panels under aircraft engine impact. The penetration depth, residual velocity of the aircraft engine, scabbing area, and failure mode of various UHPFRC panels are examined. Punching resistance capacities of reinforced concrete (RC) and steel plated concrete (SC) panels are also investigated in this study.     

大型商用飞机撞击核电站屏蔽厂房荷载研究

采用有限元方法建立飞机与核电站屏蔽厂房非线性模型,利用发动机以不同速度撞击钢筋混凝土板试验验证撞击分析中飞机与核电站屏蔽厂房有限元模型非线性材料本构及参数,并分析飞机网格尺寸效应。对大型商用飞机以200m/s速度撞击核电站屏蔽厂房非线性撞击过程模拟计算及假设核电站分别为线弹性、刚性本构模型撞击过程计算。获得大型商用飞机撞击核电站屏蔽厂房的荷载时程曲线,分析飞机撞击力及核电站屏蔽厂房结构变形特点及核电站结构刚度对撞击力影响规律,并讨论在核电站初步设计中常用飞机撞击力计算方法-Riera方法的适用性。     

Numerical simulation of bird strike damage prediction in airplane flap structure

Numerical analyses of bird impact damage in complex aircraft structures have been performed using ABAQUS/Explicit. A Lagrangian formulation was used for the bird model in combination with various material models. Several failure and damage modes have been considered for different material models used in the inboard flap of a typical large transport aircraft. A submodeling approach has been used to reduce computational time. Parametric analyses have been performed using different bird sizes, impact locations and velocity vectors.     

The design of advanced aircraft structures to resist acoustic fatigue; work in progress

Details of the current research activities in the Department of Aeronautics and Astronautics, on the response of advanced aircraft structures to acoustic loading, are presented. Both box type and sandwich structures, employing aluminium alloy, carbon fibre reinforced plastic, and GLARE composite materials, are being investigated. In order to develop design guidelines for these complex structures, it is necessary to combine theoretical predictions, using the finite element method, with experimental measurements of the structural response to random acoustic loading. Both types of structure will be tested in the Progressive Wave Tube facility at Southampton. In addition, it is hoped that a more comprehensive damping guide will be produced for the type of structure used in advanced aircraft design.     

A Standard Analysis Methodology for the Stress Analysis of Repaired Aircraft Structures with the Method of Composite Patch Repair

The method of composite patch repair is a very modern method of repairing damaged aircraft structures, which presents many advantages over the traditional methods of repair. Many analytical as well as numerical methods have been suggested, from time to time, for the stress analysis of such bonded repairs. The engineer (especially one with not very much experience or theoretical background) who will be asked to design a repair may find it difficult to choose the most appropriate method for the specific problem that he has to deal with, among the large number of available analysis methods. The scope of this paper is to suggest a very specific, standardized, step by step analysis methodology for damaged/repaired aircraft structural components.     

钢筋混凝土建筑结构施工短暂状况设计分析

现浇钢筋混凝土结构施工期间,新浇楼板的混凝土自重荷载和施工活荷载,由模板支撑体系与早龄期钢筋混凝土结构组成的临时承载体系,即时变结构体系承担。对其受力性能的认识不足,设计分析理论的欠缺,导致施工期工程质量事故和倒塌事故频繁发生。基于施工时变结构体系中的早龄期钢筋混凝土结构是建筑结构设计产品的早期形态,不可能因施工而更改永久构件的观点,提出了早龄期钢筋混凝土结构验算与模板支撑系统设计相结合的钢筋混凝土结构施工短暂状况设计分析原则。基于理论分析和现场实测以及对模板支撑施工误差和时变结构体系承担施工荷载的随机性的认识,建立了钢筋混凝土结构施工期设计分析方法,并用钢筋混凝土结构施工期设计分析的实例加以说明。     

复合材料管状结构的能量吸收性能

复合材料结构作为防撞结构的能量吸收元件,已经逐步得到工程领域的广泛认同。复合材料结构的能量吸收能力是一种特殊要求的力学性能,它的研究目标和研究手段有其独特之处。综述了近年来复合材料管状结构能量吸收性能研究的最新进展,以及有待进一步研究的问题。     

Numerical analysis of oblique impact on reinforced concrete

This study proposes a simple but efficient methodology based on the equivalent inclusion method and finite element analysis. Oblique impacting is considered to investigate the residual velocity and ricochet limit of an ogive-nose steel projectile with various impact velocities against a reinforced concrete slab. The computational results are compatible with Tate’s formula for the ricochet limit as a function of the impact velocity. The proposed methodology is useful for designing defense structures, and the ricochet limit is one of the important parameters that govern the performance of a weapon system. The methodology can be further developing for designing the protection of military structures and nuclear power plants against high velocity projectiles.     

Numerical prediction of damage in composite structures from soft body impacts

The paper summarises recent progress on materials modelling and numerical simulation of soft body impact damage in fibre reinforced composite aircraft structures. The work is based on the application of finite element (FE) analysis codes to simulate damage in composite shell structures under impact loads. Composites ply damage models and interply delamination models have been developed and implemented in commercial explicit FE codes. Models are discussed for predicting impact loads on aircraft structures arising from deformable soft bodies such as gelatine (synthetic bird) and ice (hailstone). The composites failure models and code developments are briefly summarised and applied in the paper to numerical simulation of synthetic bird impact on idealised composite aircraft structures.     

Microplane finite element analysis of tube‐squash test of concrete with shear angles up to 70°

Finite element analysis of the response of concrete structures to impact events such as missile penetration, explosive driving of anchors, blast, ground shock or seismic loading, requires knowledge of the stress–strain relations for concrete for finite strain at high pressures. A novel type of material test achieving very large shear angles of concrete at very large pressures, called the tube‐squash test, can be used to calibrate a concrete model taking into account plastic deformation at extreme pressures. A finite element analysis of such a test is performed by using a finite strain generalization of microplane models for concrete and steel. The results obtained are in good agreement with those previously obtained with a simplified method of analysis. Thus, they provide a validation of the microplane model, which is shown to be capable of reproducing the response of concrete not only for small strains at small pressures, which is predominantly brittle, but also for high pressures and large finite strains, which is predominantly frictional plastic. Copyright © 2001 John Wiley & Sons, Ltd.     

Numerical simulations of low-velocity impact on an aircraft sandwich panel

The potential hazards resulting from a low-velocity impact (bird-strike, tool drop, runway debris, etc.) on aircraft structures, such as engine nacelle or a leading edge, has been a long-term concern to the aircraft industry. Certification authorities require that exposed aircraft components must be tested to prove their capability to withstand low-velocity impact without suffering critical damage.

This paper describes the results from experimental and numerical simulation studies on the impact and penetration damage of a sandwich panel by a solid, round-shaped impactor. The main aim was to prove that a correct mathematical model can yield significant information for the designer to understand the mechanism involved in the low-velocity impact event, prior to conducting tests, and therefore to design an impact-resistant aircraft structure.

Part of this work presented is focused on the recent progress on the materials modelling and numerical simulation of low-velocity impact response onto a composite aircraft sandwich panel. It is based on the application of explicit finite element (FE) analysis codes to study aircraft sandwich structures behaviour under low-velocity impact conditions. Good agreement was obtained between numerical and experimental results, in particular, the numerical simulation was able to predict impact damage and impact energy absorbed by the structure.     

Minimum expected cost-oriented optimal maintenance planning for deteriorating structures: application to concrete bridge decks

Civil engineering structures are designed to serve the public and often must perform safely for decades. No matter how well they are designed, all civil engineering structures will deteriorate over time and lifetime maintenance expenses represent a substantial portion of the total lifetime cost of most structures. It is difficult to make a reliable prediction of this cost when the future is unknown and structural deterioration and behavior are assumed from a mathematical model or previous experience. An optimal maintenance program is the key to making appropriate decisions at the right time to minimize cost and maintain an appropriate level of safety. This study proposes a probabilistic framework for optimizing the timing and the type of maintenance over the expected useful life of a deteriorating structure. A decision tree analysis is used to develop an optimum lifetime maintenance plan which is updated as inspections occur and more data is available. An estimate which predicts cost and behavior over many years must be refined and reoptimized as new information becomes available. This methodology is illustrated using a half-cell potential test to evaluate a deteriorating concrete bridge deck. The study includes the expected life of the structure, the expected damage level of the structure, costs of inspection and specific repairs, interest rates, the capability of the test equipment to detect a flaw, and the management approach of the owner towards making repairs.     

Structural collapse analysis of framed structures under impact loads using ASI-Gauss finite element method

The main objective of this study is to devise a technique, which, when implemented into finite-element codes, is efficiently applicable to impact collapse analyses of framed structures. In this study, the formerly developed adaptively shifted integration (ASI) technique for the linear Timoshenko beam element is modified into the ASI-Gauss technique by placing the numerical integration points of the two consecutive elements forming an elastically deformed member in such a way that stresses and strains are evaluated at the Gaussian integration points of the two-element member. On comparison with the ASI technique, the ASI-Gauss technique proves its higher accuracy and efficiency in elastic range. Moreover, instead of applying impact loads in the form of nodal forces, we consider the impact phenomenon by means of contacts between the elements involved and the elemental contact algorithm is verified from the point of conservation of energy. Impact analyses considering member fracture with different sets of parameters are performed using a high-rise framed structure and a small aircraft. From the results obtained, we can observe propagation phenomena of impact loads and shock waves. Also, a proper difference in impact damage is obtained by different sets of parameters. The results also indicate that the mass of the aircraft has a stronger influence on impact damage than its velocity. Moreover, soon after impact, tensile stresses are observed in the columns that were compressed by dead loads before impact.     

Flexural analysis of reinforced concrete beams strengthened with a cement based high strength composite material

The structural behaviour of reinforced concrete beams strengthened with a system made by fibre nets embedded into an inorganic stabilized cementitious matrix named Fibre Reinforced Cementitious Mortars (FRCM), was investigated in this paper. The main issues focussed in the paper are: (i) the strengthening effect of the FRCM system on the flexural behaviour of reinforced concrete beams in terms of both ultimate capacity, deflections and ductility and (ii) the influence of the fibre reinforcement ratio on the occurrence of premature failure modes.The analysis refers to a FRCM system made by ultra-high strength fibre meshes such as the Polypara-phenylene-benzo-bisthiazole (PBO) fibres; PBO fibres have, in fact, great impact tolerance, energy absorption capacity superior than the other kind of fibres and chemical compatibility with the cementitious mortar.A total of 12 reinforced concrete beams strengthened in flexure with the PBO-FRCM system have been tested. The influence of some mechanical and geometrical parameters on the structural behaviour of strengthened beams, is analysed both at serviceability and the ultimate conditions. Results of a comparison between experimental results and theoretical predictions, obtained by models usually adopted for the analysis of FRP strengthened concrete structures, are, also, presented and discussed.     

具有隔震构造的安全壳飞机撞击耦合动力响应模拟分析

建筑物隔震构造主要用于削弱地基中地震荷载对上部结构的影响,而来自上部的飞机撞击对于安全壳隔震体系的影响如何是保证核电安全值得探讨的重要问题。为评价核电站安全壳隔震体系与飞机撞击的耦合动力效应,该文提供了一种细致的模拟耦合动力分析的手段,建立了安全壳细致的动力数值模型,针对不同刚度的隔震支座及无隔震条件,进行多种类型飞机撞击作用下安全壳的动力响应分析。结果显示,飞机撞击作用期间,不同刚度的隔震支座与无隔震条件相比,撞击位置中心节点位移与冲击力的大小具有相关性,因而存在差异,而对于安全壳混凝土结构损伤区域分布则差异不大;但在撞击荷载作用后,不同刚度的隔震支座则会对安全壳振动衰减过程有较大影响。研究表明在隔震体系设计阶段,不能片面的考虑隔震体系在削弱地震响应方面的需求,需要与飞机撞击振动衰减过程耦合分析,从而确定适宜的隔震支座水平刚度等参数。     

In-service inspections of thick-walled concrete structures

Ageing management and renewal of the operating license of existing NPP’s are at present the main problems of nuclear power industry. For the ageing management of concrete structures the OECD-Nuclear Energy Agency, Committee on the Safety on Nuclear Installations defined as the first priority ISI techniques for reinforced concrete structures having thick sections and areas not directly accessible for inspections. We discuss the NRI Rez research and development program in this field, as well as results, which will be used for qualification of the ISI techniques. __________ Translated from Problemy Prochnosti, No. 4, pp. 64–78, July–August, 2006.     

A survey of numerical models for hail impact analysis using explicit finite element codes

Hailstone impact is an actual threat for the integrity of aircraft structures such as leading edges, and forward sections. Though the analysis of weather conditions reduces the occurrence of intersections between flight routes and hailstorm regions, sometimes the passage through a hailstorm becomes inevitable and, in such a case, it is mandatory that the aircraft structures show an appropriate level of tolerance to damages caused by a hail impact. Therefore, as experimental tests are both expensive and troublesome, it is important to develop numerical models, which eventually support the design of high-efficient and hail-proof structures. Accordingly, in the present research, using LSTC LS-Dyna, three numerical models of hailstone have been developed: finite element, arbitrary Lagrangian Eulerian, and smoothed particle hydrodynamics model. Initially, these three models had been validated referring to a documented experimental test and, subsequently, used to reproduce the impact of a hailstone with the nose-lip of a nacelle intake. Advantages and disadvantages of the three hail models have been evaluated and it has been concluded that the smoothed particle hydrodynamics model is the most efficient and effective for the analysis of the event.     

Experiment-Based Explicit Dynamics Analysis for Bird Strike Damage Prediction in Composite Structures

Bird strike analysis is a common type of analysis performed during the design and analysis of rotorcraft. These simulations are carried out in order to predict whether various designs will pass the necessary certification tests. In the past, the only way to determine whether forward-facing aeronautical composite structures could withstand bird strikes was with time-consuming physical tests. In the research of bird striking, the bird impact test is the most effective method. But the existing data of test results are highly disperse, so that they do less help for the design of aeronautical composite structures and also cost more. Tests usually needed to be repeated several times because components often failed and were required for each new design. There is a large variability in numerical bird models, composite modeling approaches and complexity of simulation processes to design the sandwich structures of an aircraft. This paper investigates the composite structures modeling for bird strike phenomenon by using state-of-the-art modeling tools capable of predicting the experiment-based composite structural damage, damage location, failure size and failure mode due to impact and addresses a critical review on analysis techniques. This paper also demonstrates the state-of-the-art bird strike simulation methodology developed, and the accuracy of modeling approaches available in explicit codes is discussed.