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Several recent studies have revealed, that the structural resistance of stainless steel members under compressive loading determined in accordance with the current European standard does not satisfy sufficiently small level of failure probability. It has been observed, that currently utilized flexural buckling curves overestimate the ultimate structural resistance of stainless steel members of certain material grades and cross-sectional geometries. Not negligible differences have been achieved between the estimations based on standards and experimental data, mainly for specific range of member slenderness values. Compared to carbon steel, stainless steel has higher ductility, and in order to properly describe the stress-strain material behavior, higher numbers of material parameters are required. The subject of this article is to closely investigate the influence of these parameters (material, cross-sectional geometry and also parameters to describe global imperfection) on the ultimate resistance of the members exposed to flexural buckling. Previously validated numerical finite element models of the circular hollow cross-section (CHS) members are created in ANSYS Classic software utilizing parametric APDL macros. Statistical characteristics of all the input parameters along with their mutual correlations are obtained from recent comprehensive statistical research study. The sensitivity analysis is conducted for three different material grades of stainless steel: Austenitic, grade 1.4307, Ferritic 1.4003 and Duplex 1.4462, and for various values of the member slenderness. The purpose of the numerical models is to determine the ultimate limit state of the CHS members exposed to compressive loading utilizing geometrically and materially nonlinear analyses with initial geometrical imperfections. Influence of each input parameter on the model output (ultimate resistance) is investigated, and the results are well documented and discussed. The sensitivity analysis reveals, which of these parameters have the highest influence on the structural resistance, hence are the most significant for the monitored output, considering their statistical distribution and value range. Study also provides data for the subsequent optimization process of the flexural buckling curves, which can be feasibly conducted utilizing the first order reliability method. [ABSTRACT FROM AUTHOR]

The performance and potential ambiguity in casing thickness evaluation using pulsed eddy current (PEC) measurement interpretation based on response time to depth mapping is assessed for realistic downhole settings. Casing eccentering sensitivity analysis based on 3D finite-element method is performed for PEC sensors of variable lengths. The effect of defect size, approaching defects and casing collars for three casing configurations is also studied to highlight the increased interpretation uncertainty in realistic noncentered environments [ABSTRACT FROM AUTHOR]

The strength of mechanical joints is the weakness of laminates, therefore, mechanical joints require a special attention to be focused during both a designing and a manufacturing process. The aim of the paper is to present sensitivity analysis of a mechanical joint in a composite structure on selected parameters. Parameters of this analysis were classified into four groups: geometrical, stiffness, material failure and initial stress. Global stiffness and strength of laminate, two methods of the nut washer and the bolt head modelling, residual stiffness, initial delamination and other parameters were taken into account. A double-shear bolted joint with four fasteners is the object of analysis. The inner part of the specimen was made of a quasi-isotropic CFRP laminate. The outer elements were made of 2024T3 aluminum alloy sheet, typically used in aircraft structures. Nonlinear finite element analysis of a metal-composite joint was performed using Newton-Raphson method with MSC. Marc code. The numerical and the experimental results were compared. [ABSTRACT FROM AUTHOR]

In the paper, the polynomial approximation is presented by which the Sobol sensitivity analysis can be evaluated with all sensitivity indices. The nonlinear FEM model is approximated. The input area is mapped using simulations runs of Latin Hypercube Sampling method. The domain of the approximation polynomial is chosen so that it were possible to apply large number of simulation runs of Latin Hypercube Sampling method. The method presented also makes possible to evaluate higher-order sensitivity indices, which could not be identified in case of nonlinear FEM. [ABSTRACT FROM AUTHOR]

The paper analyses the seismic vulnerability of two different masonry buildings. It provides both an advanced 3D modelling with solid elements and an equivalent frame modelling. The global structural behaviour and the dynamic properties of the compound have been evaluated using the Finite Element Modelling (FEM) technique, where the nonlinear behaviour of masonry has been taken into account by proper constitutive assumptions. A sensitivity analysis is done to evaluate the effect of the choice of the structural models. [ABSTRACT FROM AUTHOR]

The paper deals with the problem of identification of microstructure evolution model on the basis of two-step compression test. This test is characterized by non-uniform fields of strains, stresses and temperatures in the deformation zone. Therefore, the inverse approach with finite element model for the experiment - direct problem, was applied to eliminate the influence of these inhomogeneities. Inverse solution for two-step compression test is time consuming. Thus, sensitivity analysis was performed and an influence of the parameters of the microstructure model on the goal function defined in the inverse solution was evaluated. Data generated for sensitivity analysis was reused in the inverse approach to reduce the computation costs of identification. [ABSTRACT FROM AUTHOR]

The paper deals with statical and sensitivity analyses of resistance of simply supported I-beams under bending. The resistance was solved by geometrically nonlinear finite element method in the programme Ansys. The beams are modelled with initial geometrical imperfections following the first eigenmode of buckling. Imperfections were, together with geometrical characteristics of cross section, and material characteristics of steel, considered as random quantities. The method Latin Hypercube Sampling was applied to evaluate statistical and sensitivity resistance analyses. [ABSTRACT FROM AUTHOR]

The reliability of NDE can be quantified by using the Probability of Detection (POD) approach. Former studies have shown the potential of the model-assisted POD (MAPOD) approach to replace expensive experimental determination of POD curves. In this paper, we make use of CIVA software to determine POD curves for a manual ultrasonic inspection of a heavy component, for which a whole experimental POD campaign was not available. The influential parameters were determined by expert analysis. The semi-analytical models used in CIVA for wave propagation and beam-defect interaction have been validated in the range of variation of the influential parameters by comparison with finite element modelling (Athena). The POD curves are computed for « hit/miss » and « â versus a » analysis. The verification of Berens hypothesis is evaluated by statistical tools. A sensitivity study is performed to measure the relative influence of parameters on the defect response amplitude variance, using the Sobol sensitivity index. A meta-model is also built to reduce computing cost and enhance the precision of estimated index. [ABSTRACT FROM AUTHOR]

Analytical wave models are inadequate to describe complex metallic microstructure interactions especially for near field anisotropic property effects and through geometric features smaller than the wavelength. In contrast, finite element ultrasound simulations inherently capture microstructure influences due to their reliance on material definitions rather than wave descriptions. To better understand and quantify heterogeneous crystal orientation effects to ultrasonic wave propagation, a finite element modeling case study has been performed with anisotropic titanium grain structures. A parameterized model has been developed utilizing anisotropic spheres within a bulk material. The resulting wave parameters are analyzed as functions of both wavelength and sphere to bulk crystal mismatch angle. [ABSTRACT FROM AUTHOR]

ATHENA2D is a finite element code dedicated to the wave propagation simulation. The good agreement between experimental and simulated data necessitates the use of accurate input data. Generally the input data are provided by experimental measurements and are consequently tainted with uncertainties. The aim of this study is to investigate the impact of these uncertainties on the numerical simulations using a probabilistic approach. This allows the determination of confidence intervals on ATHENA2D's output parameters. [ABSTRACT FROM AUTHOR]

Aerospace structures contain multi-layer components subjected to cyclic loading conditions; fatigue cracks and disbonds can develop, often at fastener holes. High-frequency guided waves have the potential for non-destructive damage detection at critical and difficult to access locations from a stand-off distance. Using commercially available ultrasonic transducers, high frequency guided waves were generated that penetrate through the complete thickness of a model structure, consisting of two adhesively bonded aluminum plates. The wave propagation along the specimen was measured and quantified using a laser interferometer. The wave propagation and scattering at internal defects was simulated using Finite Element (FE) models and good agreement with the measurement results found. The detection sensitivity using standard pulse-echo measurements was verified and the influence of the stand-off distance predicted from the FE simulation results. [ABSTRACT FROM AUTHOR]

GMR sensors are increasingly used for magnetic surface inspection due to their high sensitivity and high spatial resolution. In case of simple planar or cylindrical shaped components, the GMR-based inspection procedure can be automated easily. We present GMR measurements of real fatigue cracks. In addition, we present a probe design using a local magnetization unit and commercially available GMR sensors. The design was carried out by means of finite-element method (FEM) simulations. Using the local probe we measured bearings containing artificial reference cracks of different depths and orientations. Cracks with a depth of 40 μm could be resolved with a signal-to-noise ratio better than 6. A further reduction of the measuring time can be obtained using a sensor array. For this purpose we present a study of the optimized size of the sensing GMR-layers for a NDE-adapted sensor array. The geometric sensor parameters were investigated through simulations of the magnetic flux leakage of surface cracks using an analytic model. [ABSTRACT FROM AUTHOR]

The beam directivity from an ultrasonic transducer in isotropic materials is well documented. However, beam directivities in elastically anisotropic materials and their effect on ultrasonic NDE inspection has been investigated far less extensively. In this paper, analytical and numerical finite element models are developed to predict the beam directivity in a single crystal nickel-based superalloy. This material is highly anisotropic and is used widely in the gas-turbine industry. The developed models are used to investigate the effect of the crystallographic orientation on the beam directivity. In turn, the effect of beam directivity on defect detection sensitivity and characterization capability using an ultrasonic array is demonstrated. It is shown that the effect is particularly important for the accurate sizing of small defects. [ABSTRACT FROM AUTHOR]

This paper presents a veritable finite element approach for simulating the inelastic buckling response of steel braces. A number of techniques are considered to identify computationally efficient modeling approaches that yield consistent results with experimental data. Ultimately, brace members and gusset plates are represented with deformable and rigid shell elements, respectively; and the overall method is based on dynamic analyses with explicit time integration. There is inherent damping in the proposed model due to inelasticity; additional viscous damping and mass scaling factors are used to extract/simulate the system's quasi-static responses. Static sensitivity analyses are conducted to optimize mesh sizes and the most suitable imperfection shapes and amplitudes for the brace elements. Additional (dynamic) sensitivity analyses are employed to calibrate the imperfection, loading amplitude, time period, artificial viscous damping and mass scaling factors. Results indicate that the proposed techniques can accurately mimic experimentally observed quasi-static responses. [ABSTRACT FROM AUTHOR]

This paper presents a validated, high fidelity finite element modeling procedure for Diagonally Braced Moment-Resisting Frames (DBMRFs). The model can accurately capture the DBMRF response prior to and through the brace-buckling regime. The model was calibrated through parametric sensitivity studies, which were performed to ascertain the effects of mesh refinement, initial brace imperfection shapes and amplitudes, and the effects of beam-column connection types on the developed analytical model. The validated analytical model can be used for further investigations on the buckling characteristics of the gusset brace system, and for predicting the yield mechanisms, failure modes, and deformation capacities of multistory DBMRFs. The model can also be used for determining frame ductilities, as well as regions of concentration of plastic strains within the frame members and the gusset brace system. [ABSTRACT FROM AUTHOR]

The main focus of the paper is the analysis of the influence of residual stress on the ultimate limit state of a hot-rolled member in compression. The member was modelled using thin-walled elements of type SHELL 181 and meshed in the programme ANSYS. Geometrical and material non-linear analysis was used. The influence of residual stress was studied using variance-based sensitivity analysis. In order to obtain more general results, the non-dimensional slenderness was selected as a study parameter. Comparison of the influence of the residual stress with the influence of other dominant imperfections is illustrated in the conclusion of the paper. All input random variables were considered according to results of experimental research. [ABSTRACT FROM AUTHOR]

The failure prediction in sheet metal forming is typically realized by evaluating the so called forming limit curves (FLC). Up to now, the FLC determination was performed with failed specimens of Nakajima or Marciniak test setups. Standard methods determine the failure by considering the occurrence of cracking and do not consider the possibility of time continuous recording of the Nakajima test. Consequently forming limit curves which have been evaluated in such way are often 'laboratory dependent' and deviate for identical materials significantly. This contribution presents an algorithm for a fully automatic and time-dependent determination of the beginning plastic instability based on physical effects. The algorithm is based on the evaluation of the strain distribution based on the displacement field which is evaluated by optical measurement and treated as a mesh of a finite element calculation. The critical deformation states are then defined by 2D-consideration of the strain distribution and their time derivatives using a numerical evaluation procedure for detecting the beginning of the localization. The effectiveness of the proposed algorithm will be presented for different materials used for the Numisheet'08 Benchmark-1 with Nakajima test. Additionally the effect of strain rate sensitivity on the beginning instability of local necking is discussed. It can be shown that the strain rate sensitivity is from major importance and should not be neglected for the forming simulation of sheet metal materials. [ABSTRACT FROM AUTHOR]

An experimental observation on a large welded plate found that the weld can concentrate and guide the energy of a guided wave traveling along the direction of the weld. An attractive shear weld guided mode was discovered by the authors, which is non-attenuative and almost non-dispersive. It is interesting to explore the possibilities of applying this mode as a screening tool to quickly inspect for defects along a long distance of the weld. In this work, the interaction of the shear weld guided mode with different types of defects has been studied, including cracks perpendicular or parallel to the weld and circular holes, in the heat affected zone next to the weld. The results are obtained from both Finite Element simulations and experimental measurements, showing good agreement. The sensitivity of the weld-guided mode to different defects has been discussed and suitable choices of frequency to detect these defects have been suggested. [ABSTRACT FROM AUTHOR]

Maintenance processes used in heavy industries often include high speed milling operations. The reliability of the post-process material state has to be studied. Numerical simulation appears to be a very interesting way to supply an efficient residual stresses (RS) distribution prediction. Because the adiabatic shear band and the serrated chip shaping are features of the austenitic stainless steel high speed machining, a 2D high speed orthogonal cutting model is briefly presented. This finite element model, developed on Forge® software, is based on data taken from Outeiro & al.'s paper [1]. A new behaviour law fully coupling Johnson-Cook's constitutive law and Latham and Cockcroft's damage model is detailed in this paper. It ensures results that fit those found in literature. Then, the numerical tools used on the 2D model are integrated to a 3D high speed milling model. Residual stresses distribution is analysed, on the surface and into the depth of the material. Various revolutions and passes of the two teeth hemispheric mill on the workpiece are simulated. Thus the sensitivity of the residual stresses generation to the cutting conditions can be discussed. In order to validate the 3D model, a comparison of the cutting forces measured by EDF R&D to those given by numerical simulations is achieved. [ABSTRACT FROM AUTHOR]

This paper presents a two-dimensional finite element model of orthogonal cutting. The proposed model has been developed with Abaqus/explicit software. An Arbitrary Lagrangian-Eulerian (ALE) formulation is used to predict chip formation, temperature, chip-tool contact length, chip thickness, and cutting forces. This numerical model of orthogonal cutting will be validated by comparing these process variables to experimental and numerical results obtained by Filice et al. [1]. This model can be considered to be reliable enough to make qualitative analysis of entry parameters related to cutting process and frictional models. A sensitivity analysis is conducted on the main entry parameters (coefficients of the Johnson-Cook law, and contact parameters) with the finite element model. This analysis is performed with two levels for each factor. The sensitivity analysis realised with the numerical model on the entry parameters has allowed the identification of significant parameters and the margin identification of parameters. [ABSTRACT FROM AUTHOR]

Springback prediction and compensation is nowadays a widely recommended discipline in finite element modeling. Many researches have shown an improvement of the accuracy in prediction of springback using advanced modeling techniques, e.g. by including the Bauschinger effect. In this work different models were investigated in the commercial simulation program AutoForm for a large series production part, manufactured from the dual phase steel HC340XD. The work shows the differences between numerical drawbead models and geometrically modeled drawbeads. Furthermore, a sensitivity analysis was made for a reduced kinematic hardening model, implemented in the finite element program AutoForm. [ABSTRACT FROM AUTHOR]

Within the framework of sheet metal forming, the importance of hardening models for springback predictions has been often emphasized. While some specific applications require very accurate models, in many common situations simpler (isotropic hardening) models may be sufficient. In these conditions, investigation of the impact of hardening models requires well defined test configurations and accurate measurements to generate the reference data. Specific draw-bend tests have been especially conceived for this purpose. In this work, such a draw-bending experimental device has been designed, for use on a biaxial tension machine. Three different steel sheets have been tested (one mild steel sheet and two HSS sheets) with thicknesses between 0.8 and 2 mm. Up to three different back-force levels were used for the tests. Wall curvatures and springback angles were measured. Finite element simulations of the tests were performed. A parameter sensitivity analysis has been carried out in order to determine the numerical parameters ensuring accurate springback results. The tests were simulated using an isotropic hardening model and a combined isotropic-kinematic hardening model. The impact of the hardening model is explored for the various test configurations and conclusions are drawn concerning their relative importance. [ABSTRACT FROM AUTHOR]

We propose in this paper a methodology to model tube bending process and a coupling with a pressure test. A sensitivity analysis and an optimization study are also presented. We take into account the whole process that is bending, mandrel move back and tube springback. The first step is to model the tube bending process and validate it with experimental results. Angles after springback and tube section distortion are compared. Because of the difficulty to measure the true friction between the tube and the tools, a sensitivity analysis on friction coefficients is performed. The second step is to study the bending process influence on the tube behavior under a pressure test. At last, an optimization study of the residual stress after bending is performed. Instead of a direct method the optimization was done on an approximation of the model response. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

Roll forming is applied for several decades to manufacture thin gauged profiles. However, the knowledge about this technology is still based on empirical approaches. Due to the complexity of the forming process, the main effects on profile properties are difficult to identify. This is especially true for the interaction of technological parameters and material parameters. General considerations for building a finite-element model of the roll forming process are given in this paper. A sensitivity analysis is performed on base of a statistical design approach in order to identify the effects and interactions of different parameters on profile properties. The parameters included in the analysis are the roll diameter, the rolling speed, the sheet thickness, friction between the tools and the sheet and the strain hardening behavior of the sheet material. The analysis includes an isotropic hardening model and a nonlinear kinematic hardening model. All jobs are executed parallel to reduce the overall time as the sensitivity analysis requires much CPU-time. The results of the sensitivity analysis demonstrate the opportunities to improve the properties of roll formed profiles by adjusting technological and material parameters to their optimum interacting performance. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]