Cycle counting for fatigue crack growth analysis

Fatigue crack propagation tests were carried out on an Al-Cu alloy under specially designed complex load sequences. Electron fractography of the fatigue fracture surfaces suggests that rainflow cycle counting is applicable to the analysis of fatigue crack growth under complex load sequences.     

Decision analysis for deteriorating structures

Measures that improve durability of a structure usually increase its initial cost. Thus, in order to make a decision about a cost-effective solution the life-cycle cost of a structure including cost of structural failure needs to be considered. Due to uncertainties associated with structural properties, loads and environmental conditions the cost of structural failure is a random variable. The paper derives probability distributions of the cost of failure of a single structure and a group of identical structures when single or multiple failures are possible during the service life of a structure. The probability distributions are based on cumulative probabilities of failure of a single structure over its service life. It is assumed that failures occur at discrete points in time, the cost of failure set at the time of decision making remains constant for a particular design solution and the discount rate is a deterministic parameter not changing with time. The probability distributions can be employed to evaluate the expected life-cycle cost or the expected utility, which is then used in decision making. An example, which considers the selection of durability specifications for a reinforced concrete structure built on the coast, illustrates the use of the derived probability distributions.     

Matrix-MP method for the analysis of inelastic arch structures

A general matrix formulation and mathematical programming techniques are used for the analysis of arch bridge structures in the inelastic range. Discretization of the structural model and of the constitutive laws of the material enables the solution of a number of engineering problems by a unified computer program. The capability of the method includes and limit load and deformation analysis, historical load–deformation analysis and shakedown load analysis. All these problmes but the last one are covered in the paper and are illustrated in the example of an actual reinforced concrete arch bridge with a stiffening girder.     

Limit analysis for structures with flaws

An analysis is described which aims at computing the limit load for an imperfect structure containing internal defects or flaws. A criterion is proposed for evaluation of the ultimate stress at a certain admissible crack size. This approach incorporates some plastic properties of the material and it requires an experimental determination of the critical stress intensity factor the given range of the crack length. A safety factor defined with regard to catastrophic crack propagation is introduced in addition to standard safety factors used in the design. Finally, some numerical examples are given to illustrate the procedures for evaluation of an admissible crack size and for estimating the corresponding safety factors.     

Ageing management of safety-related concrete structures to provide improved bases for continuing the service of nuclear power plants

Resume On décrit les structures en béton se rapportant à la sécurité des installations nucléaires, et on détermine les facteurs de dégradation susceptibles de compromettre la conformité de ces structures aux critères de fonctionnement et de performance qui leur sont assignés. On donne ici, de fa?on résumée, les exigences d’inspection en service. On examine l’évaluation des performances des éléments en béton dans les installations nucléaires. Enfin, on trace les grandes lignes d’un programme pour gérer le vieillissement des structures en béton en rapport avec la sécurité des installations nucléaires, et améliorer leur capacité de service. On résume également les différents aspects du programme.      

冠状动脉支架纵向柔顺性能有限元分析

纵向柔顺性是支架很重要的一个力学性能,它决定了支架能否被顺利地输送到病变部位并与血管相适应.主要目的就是利用有限元法来研究支架的设计参数对柔顺性能的影响.利用多点约束单元,在支架的简化模型上均匀地加栽弯矩使支架发生弯曲变形.结果显示,S型支架的柔顺性最好,L型支架的柔顺性最差;支架支撑体宽度和波形环曲率半径对柔顺性的影响甚微;增加支架连接杆的长度能够提高支架的柔顺性,但是,增加支架连接杆的宽度或者厚度会降低支架的柔顺性.因此,有限元法对支架力学行为分析具有很大的帮助,为支架的临床选择及优化设计提供了重要指导作用.     

A simulation analysis of factors influencing the flexibility of cellular manufacturing

The performance of cellular manufacturing (CM) systems in a variable demand and flexible workforce environment has been examined using simulation modelling. Discrepancies between academicians and practitioners’ findings with respect to flexibility and uneven machine utilization in CM systems are discussed. The views of two parties were incorporated in simulation models to rectify the existing discrepancies. While the results of this study confirm the previous findings of academicians regarding the deterioration of the performance of CM in a variable product mix situation, it appears that those results may be significantly influenced by considering a flexible workforce. The simulation results show that the practice of using flexible crossed-trained operators can improve the flexibility of CM in dealing with an unstable demand and can reduce load imbalance inherent in machine dedication in manufacturing cells.     

Hermitian-method for the nonlinear analysis of arbitrary thin shell structures

The present paper couples the geometrically nonlinear shear deformation theory of thin shell structures [finite rotations; small strains; Baar (1987)] with the Hermitian-method (Collatz 1966; Almannai 1976).It presents a brief review of a nonlinear theory considering shear deformations by means of an operator formulation and the transformation of partial differential equations into algebraic equations by means of appropriate two-dimensional finite-difference operators. The nonlinearity can be treated by an incremental-iterative procedure. Finally the efficiency of the developed numerical method will be demonstrated by selected examples. Special attention is focussed on the convergence behaviour and the reliability of geometrically interpretable forces with respect to engineering applications.     

Refined shell elements for the analysis of functionally graded structures

The present paper considers the static analysis of plates and shells made of Functionally Graded Material (FGM), subjected to mechanical loads. Refined models based on the Carrera’s Unified Formulation (CUF) are employed to account for grading material variation in the thickness direction. The governing equations are derived from the Principle of Virtual Displacement (PVD) in order to apply the Finite Element Method (FEM). A nine-nodes shell element with exact cylindrical geometry is considered. The shell can degenerate in the plate element by imposing an infinite radius of curvature. The Mixed Interpolation of Tensorial Components (MITC) technique is extended to the CUF in order to contrast the membrane and shear locking phenomenon. Different thickness ratios and orders of expansion for the displacement field are analyzed. The FEM results are compared with both benchmark solutions from literature and the results obtained using the Navier method that provides the analytical solution for simply-supported structures subjected to sinusoidal pressure loads. The shell element based on refined theories of the CUF turns out to be very efficient and its use is mandatory with respect to the classical models in the study of FGM structures.     

A finite element for the analysis of reinforced concrete structures

Formulation of a four-node isoparametric element suitable for modelling cracks in reinforced concrete structures is presented. The standard isoparametric element is known to give spurious shear stresses. The conventional remedy of selective integration breaks down in a ‘cracked’ element. It is shown that the proposed formulation gives superior results as compared to both the standard isoparametric element and the conventional selectively integrated element.     

Material model for the analysis of reinforced concrete surface structures

A material model for the analysis of reinforced concrete surface structures is developed. The constitutive model employs the smeared crack concept, i.e. only average stresses are considered at an integration point. While uncracked concrete is modelled with a plasticity approach, the paper focuses on the numerical treatment of cracked reinforced concrete in a state of plane stress. Special attention is given to the modelling of the tension stiffening effect, the re-orientation of the principal tensile strain direction and the compressive strength of cracked concrete. The material model has been implemented in the finite element program SEGNID and tested extensively. Here the comparisons of calculated and experimentally measured results on reinforced concrete surface structures-several panels, a plate subjected to torsion and a free-formed shell-are presented.List of symbols d bar diameter - D stiffness matrix - D _c stiffness matrix of concrete - D _s stiffness matrix of reinforcement - D rotational stiffness matrix - f stress - f _c stresses in concrete - f _c1 tensile stress in concrete - f _c2 compressive stress in concrete - f _c2,min concrete compressive strength - f _c cylinder crushing strength - f _s stresses in reinforcement - f _t concrete tensile strength - f _y yield strength of reinforcement - f ₁ applied principal tensile stress - f ₂ applied principal compressive stress - F tension force - F _y yield force - l length - M moment - Q dowel resistance - r _xy vector of unbalanced stresses - s applied load - s applied stress vector - T ₁, T ₂ transformation matrices - w crack width - x, y reference coordinate system - 1, 2 crack oriented coordinate system - curvature - _xy incremental strain in the reference coordinate system Extended version of the contribution Two-dimensional FE-analysis of reinforced concrete membrane elements to the International Conference on Computational Engineering Science, Atlanta, April 10–14, 1988, presented by the second named author     

Determining the order parameter for the morphological analysis of two-dimensional structures

Problems encountered in determining the order parameter for two-dimensional structures are considered. The task is solved using two approaches, which are based on the spectral transformations (Fourier and Walsh) and the information entropy concept. The results of calculations for particular structures are used for a comparative analysis, showing both advantages and drawbacks of these methods.     

Bounding-surface plasticity for non-linear analysis of space structures

This paper presents a method for the non-linear analysis of space structures subjected to static and cyclic loading. A bounding-surface kinematic hardening plasticity model is used to simulate the hardening and hysteritic material behaviour. The model is used in conjunction with the lumped plasticity assumption coupled with the concept of a yield surface in force space. A hardening coefficient matrix which is a function of the plastic strain and the elastic stiffness matrix is introduced while the vectorial nature of the material memory parameters is maintained. This provides a smooth transition from the elastic to the plastic regime which simulates the hysteresis loops quite accurately. An updated Lagrangian formulation is used together with a predictor/corrector solution method. Several examples are presented to demonstrate the accuracy and efficiency of the method.     

Flow-graph approach for optical analysis of planar structures

The flow-graph approach (FGA) is applied to optical analysis of isotropic stratified planar structures (ISPS's) at inclined light incidence. Conditions for the presence of coherent and noncoherent light interaction within ISPS's are determined. Examples of the use of FGA for calculation of the transmission and the reflection of two-layer ISPS's for different types of light interaction are given. The advantages of the use of FGA for optical analysis of ISPS's are discussed.     

BEM analysis of thin structures for thermoelastic problems

A new boundary element method is developed for solving thin-body thermoelastic problems in this paper. Firstly, the novel regularized boundary integral equations (BIEs) containing indirect unknowns are proposed to cancel the singularity of fundamental solutions. Secondly, a general nonlinear transformation available for high-order geometry elements is introduced in order to remove or damp out the near singularity of fundamental solutions, which is crucial for accurate solutions of thin-body problems. Finally, the domain integrals arising in both displacement and its derivative integral equations, caused by the thermal loads, are regularized using a semi-analytical technique. Six benchmark examples are examined. Results indicate that the proposed method is accurate, convergent and computationally efficient. The proposed method is a competitive alternative to existing methods for solving thin-walled thermoelastic problems.     

Use of screw translational symmetry for the vibration analysis of structures

A method for the exploitation of screw translation symmetry for the vibration analysis of structures is presented. The method is capable of providing significant computational economies over the use of the lower axial translational symmetry of such structures.     

Preconditioned conjugate gradient technique for the analysis of symmetric anisotropic structures

An officient preconditioned conjugate gradient (PCG) technique and a computational procedure are presented for the analysis of symmetric anisotropic structures. The technique is based on selecting the preconditioning matrix as the orthotropic part of the global stiffness matrix of the structure, with all the nonorthotropic terms set equal to zero. This particular choice of the preconditioning matrix results in reducing the size of the analysis model of the anisotropic structure to that of the corresponding orthotropic structure. The similarities between the proposed PCG technique and a reduction technique previously presented by the authors are identified and exploited to generate from the PCG technique direct measures for the sensitivity of the different response quantities to the non-orthotropic (anisotropic) material coefficients of the structure. The effectiveness of the PCG technique is demonstrated by means of a numerical example of an anisotropic cylindrical panel.     

An expert system for the design and analysis of composite structures

A prototype expert system is described for concurrent design and analysis of composite structures. This system integrates symbolic, numerical and knowledge-based tools in an object-oriented programming environment for design synthesis, evaluation and modification. The system determines structural behavior utilizing a combination of analytical and numerical tools. Design modifications and structural optimization are performed using heuristic and experientially derived knowledge bases. The different domain-specific programs and commercial packages utilized by the system are integrated using a generic interfacing mechanism. The utility of the system is demonstrated by means of a design case study for a typical aircraft or rotorcraft structural component.