Finite Element Computer Code Research Articles

In Situ Scanning Electron Microscope Observation and Finite Element Method Analysis of Delayed Hydride Cracking Propagation in Zircaloy-2 Fuel Cladding Tubes

Abstract The objective of the present research is to build a modeling method for delayed hydride cracking (DHC) of zirconium alloys. DHC tests were carried out on Zircaloy-2 cladding tubes in the chamber of a scanning electron microscope to directly observe the crack propagation and measure the crack velocity in the radial direction. These in situ observations showed that a sharply tipped crack propagated at a relatively high rate, while the velocity decreased when the crack tip was blunted, supporting the occurrence of intermittent crack propagation that could be expected from the DHC mechanism. V-KI curves or diagrams of crack velocity, V, versus stress intensity factor at a crack tip, KI, were obtained as a function of 0.2 % offset yield stress, hydride orientation, and pre-crack depth. The steady state crack velocity and the threshold stress intensity factor for the onset of the crack propagation tended to increase or decrease, respectively, with an increase in the 0.2 % offset yield stress. Analyses of stress distribution and hydrogen diffusion around a crack tip were made using a finite element computer code. The analyses showed that a strong hydrostatic pressure field was generated concentrically around the crack tip and hydrogen diffused towards the crack tip according to the hydrostatic pressure gradient. The crack velocity was estimated from the calculated hydrogen flux rate assuming the critical hydrogen quantity for the crack propagation. There was good agreement between the experiments and the calculations regarding the crack velocity and its dependency on KI. Calculations showed that the increase in the 0.2 % offset yield stress would accelerate the crack propagation by increasing the hydrostatic pressure at the crack tip.

Degenerated shell element analysis of circular rail drawing of sheet metal

The prediction of formability in sheet metal forming by numerical simulation allows the manufacturer to reduce the costs of designing tools and to shorten the time‐to‐market cycle. This research aims to create an elastoplastic incremental finite element computer code to simulate a circular rail drawing process of sheet metals. A methodology of formulating an elastoplastic three‐dimensional finite element model, based on the Prandtl–Reuss flow rule and von Mises yield criterion respectively and associated with an updated Lagrangian formulation, is developed to simulate the sheet metal forming process. The shape function derived from a four‐node quadrilateral degenerated shell element is associated into the stiffness matrix to constitute the finite element model. An extended rmin algorithm is proposed to formulate the boundary condition, such as nodal penetration and separation, strain and rotation increment, and altered elastoplastic state of material. The proposed solution for simulation includes algorithms implemented in the finite element code which make it possible to obtain accurate prediction results. Numerical simulation can produce information on the whole deformation history, such as the distribution of thickness, the distribution of stress, the distribution of strain, and the shape after the drawing process. The simulation result was then compared with experimental data to verify the feasibility and reliability in simulation process using this finite element analysis program. It shows good agreement between the simulated results and experimental outcomes. Therefore, the elastoplastic large deformation finite element program can reasonably simulate the circular rail drawing process.

Hydro-mechanical constitutive model for unsaturated compacted bentonite–sand mixture (BSM): Laboratory tests, parameter calibrations, modifications, and applications

A bentonite–sand mixture (BSM) is one of the clay-based sealing components proposed for use in a Canadian deep geological repository (DGR) for used nuclear fuel. Numerical modelling to assess the overall design of the proposed DGR requires characterisation of the hydraulic–mechanical (H–M) of each of the components of the sealing system, including the BSM. The BSM currently under consideration is a 50/50 mixture (by dry mass) of bentonite and well-graded silica sand, compacted to a dry density of at least 1.67 Mg/m 3. This paper presents the H–M constitutive model parameters, calibrated for BSM specimens under saturated and unsaturated conditions, based on various laboratory tests. A set of parameters for an elastoplastic model for unsaturated soil, Basic Barcelona Model (BBM), have been determined to simulate the mechanical behaviour of the BSM specimen. A set of parameters for van Genuchten’s Soil–Water Characteristic Curve (SWCC) and Kozeny’s hydraulic permeability model have been determined to simulate the hydraulic behaviour of the BSM specimen. Using a finite element computer code, CODE_BRIGHT, these sets of parameters have been used to simulate H–M processes in BSM specimens during water infiltration under constant volume (CV) and constant mean stress (CMS) boundary conditions. The key features of the selected constitutive models that are different from the laboratory tests of the BSM specimen have been summarised. The functions to improve the capability of the selected constitutive models to match the laboratory test results of the BSM specimen have been proposed.

Assuring life in composite systems

A computational simulation method is presented to assure life in composite systems by using dynamic buckling of smart composite shells as an example. The combined use of composite mechanics, finite element computer codes, and probabilistic analysis enable the effective assessment of the dynamic buckling load of smart composite shells. A universal plot is generated to estimate the dynamic buckling load of composite shells at various load rates and probabilities. The shell structure is also evaluated with smart fibers embedded in the plies right below the outer plies. The results show that, on the average, the use of smart fibers improved the shell buckling resistance by about 10% at different probabilities and delayed the buckling occurrence time. The probabilistic sensitivities results indicate that uncertainties in the fiber volume ratio and ply thickness have major effects on the buckling load. The uncertainties in the electric field strength and smart material volume fraction have moderate effects and thereby in the assured life of the shell.

Optimization of Fiber-Reinforced Composite Plate for Maximum Buckling Strength (Dept.M)

An advantage of composite materials over conventional ones is the possibility of tailoring their properties to the specific requirements of a given application. The tailoring is mostly achieved by maximizing the mechanical properties as a result of selecting the fiber angles of the layers optimally so A numerical study was carried out, First to determine the effects of symmetric and anti-symmetric laminate configuration and various boundary conditions on the buckling behavior of E/glass-epoxy composite plates using two different initial laminate configurations ([90/45/-45/0]as and [90/45/-45/0]) as initial fiber orientation, Second to optimize the fiber orientation (ply angles) for maximizing the critical buckling load of B/glass-epoxy composite plates, Finally the initial buckling values and initial fiber angles were compared with optimum buckling values and Optimum fiber angles for the same boundary condition. The four boundary conditions in this study are (clamped-clamped [CC], clamped-pinned (CP], pinned-pinned [PP] and Clamped-Free (CF]). The results mirrored that the buckling load have great effect by changing the boundary conditions. The maximum critical buckling load value is for clamped clamped boundary condition and the minimum value is for clamped free boundary condition. The buckling loads and fiber orientations of the laminated composite were calculated and optimized by ANSYS finite-element computer code.

Hydroelastic vibration of a cantilever cylindrical shell partially submerged in a liquid

The dynamic characteristics of a circular cylindrical shell in contact with a liquid are theoretically studied. The cantilevered cylindrical shell with open ends is partially submerged in a liquid which is unbounded in the radial direction, but bounded by a rigid and flat bottom. Since the liquid is assumed to be incompressible and inviscid, the liquid motion can be described as the velocity potentials written in terms of the appropriate Bessel functions for both the inner and the outer liquid regions. The compatibility of the dynamic displacement along the contacting surfaces between the shell and liquid leads the resulting equations, satisfying both the shell and liquid motions, which are solved by using the collocation method. Finally, the Rayleigh–Ritz method is applied to extract the wet natural frequencies and the mode shapes of the liquid-coupled system. The validity of the theoretical method is established with the aid of a commercial finite element computer code. In order to evaluate the dynamic characteristics of the liquid-coupled system, the effects of the submerged depth and the axial gap between the bottom end of the shell and the bottom surface of the liquid are demonstrated.

Much ado about shear correction factors in Timoshenko beam theory

Many shear correction factors have appeared since the inception of Timoshenko beam theory in 1921. While rational bases for them have been offered, there continues to be some reluctance to their full acceptance because the explanations are not totally convincing and their efficacies have not been comprehensively evaluated over a range of application. Herein, three-dimensional static and dynamic information and results for a beam of general (both symmetric and non-symmetric) cross-section are brought to bear on these issues. Only homogeneous, isotropic beams are considered. Semi-analytical finite element (SAFE) computer codes provide static and dynamic response data for our purposes. Greater clarification of issues relating to the bases for shear correction factors can be seen. Also, comparisons of numerical results with Timoshenko beam data will show the effectiveness of these factors beyond the range of application of elementary (Bernoulli–Euler) theory. An issue concerning principal shear axes arose in the definition of shear correction factors for non-symmetric cross-sections. In this method, expressions for the shear energies of two transverse forces applied on the cross-section by beam and three-dimensional elasticity theories are equated to determine the shear correction factors. This led to the necessity for principal shear axes. We will argue against this concept and show that when two forces are applied simultaneously to a cross-section, it leads to an inconsistency. Only one force should be used at a time, and two sets of calculations are needed to establish the shear correction factors for a non-symmetrical cross-section.

A new test method for determining the fracture toughness of concrete materials

The Spiral Notch Torsion Test (SNTT) determines the intrinsic fracture toughness (KIC) of structural materials by applying pure torsion to cylindrical specimens having a notch line that spirals around the specimen at a 45° pitch. KIC values are obtained with the aid of a three-dimensional finite-element computer code, TOR3D-KIC. The SNTT method is suitable for testing a wide variety of materials used extensively in pressure vessel and piping structural components and weldments, as well as ceramic and graphite materials. One important characteristic of SNTT is that neither a fatigue precrack nor a deep notch is required for evaluation of brittle materials, significantly reducing the sample size requirement. Results are reported for a Portland cement-based mortar demonstrating applicability of the SNTT method to cementitious materials. The estimated KIC of the tested mortar samples with compressive strength of 34.45 MPa was found to be 0.360 ± 0.017 MPa √m.

A control strategy to assure safety conditions in the thermal treatment of meat products using a numerical algorithms

A finite element computational code was programmed in Matlab language to establish time–temperature specifications, in order to assure thermal inactivation of Escherichia coli O157:H7 in black sausages, produced in small scale plants. Even though the heating system in these plants may have a temperature control operating on the gas burners, the immersion water temperature can decrease significantly if the load ratio (sausage/water mass) increases; the thermal inertia of the system makes it difficult to re-establish this temperature instantaneously. The effect of the ratio between the amount of thermally treated sausages and the heat capacity of the system, on the temperature drop in the water bath, was mathematically simulated and experimentally validated. Computer simulations were performed by coupling the numerical solution of the microscopic heat conduction equation in the product with the macroscopic heat balance, which considers the heat flux of the gas burners. The model satisfactorily predicted experimental time–temperature results (mean error less than 5%) and constitutes a useful tool for meat processors and plant operators since it allows to determine adequate time–temperature conditions as a function of load ratio and initial water temperature, combining the microbial lethality kinetics with the main program.

Application of a micromechanical model to cavity excavation analysis in argillite

This paper presents an application of a micromechanical model to the analysis of cavity excavation in heterogeneous rocks by taking into account influences of mineralogical compositions. The Callovo-Oxfordian argillite is considered here in the context of feasibility studies for geological storage of nuclear waste storage. Based on the microstructural analysis, a micromechanical model is first proposed using nonlinear homogenization techniques for heterogeneous materials. The argillite is seen as a three phase composite with elastoplastic clay matrix, elastic damaged calcite grains and elastic quartz grains. Using the proposed model, the variations of elastic and plastic properties of material with mineralogical compositions at different depths are systematically taken into account. Comparisons between experimental data and model's predictions are presented. The proposed model, implemented into a finite element computation code, is finally applied to the analysis of excavation of a vertical shaft.

Creep Behaviour and Stress Analysis of a Seventeen-Year Service-Exposed Primary Super Heater Tube in a Thermal Power Plant

The elastic, inelastic deformation and stress distribution pattern of a seventeen year service-exposed primary super heater tube in a 120 MW boiler of a thermal power plant have been evaluated by using both analytical and numerical techniques. The commercial finite element computer code ANSYS® was used for stress analysis. The methodology is a valuable design tool for development of new boiler tubes as well as for considering the effects of numerous operating variables on creep life. The health of the tube was also assessed based on microstructure, hardness and a few conventional creep tests carried out at 500 °C at various stress levels (40 to 177 MPa). Results revealed that there was not much variation in the microstructure and hardness of the service-exposed tubes compared to the virgin material. Creep deformation behaviour of the service-exposed and virgin tubes of the same material at 40 MPa revealed that deterioration of the creep properties fell within the 20% scatter band, which is well within the specified limits of ASTM standard. The service-exposed primary super heater tube is thus in a good state of health.

Flaring and nosing process for composite annoy tube in circular cone tool application

An elasto-plastic incremental finite element computer code based on an updated Lagrangian formulation was developed to simulate the flaring and nosing processes of a metal tube in the asisymmetric condition. The extended r min technique was used to treat the elastic–plastic stress state and to solve contact problems at the tool–metal interface. A modified Coulomb’s friction law was introduced to treat the alternation of the sliding–sticking state of friction at the contact interface. The forming performed analysis using the finite element method and experiment. To examine the influence of the thickness ratio and the optimum punch semi-angle and friction on the forming load of the two-ply metal tubes consisting of soft aluminum, hard aluminum, and copper. The calculated tube geometries and the relationship between punch load and stroke are in good agreement with the experimental data.

An innovative technique for evaluating fracture toughness of graphite materials

Spiral notch torsion fracture toughness test (SNTT) was developed recently to measure the intrinsic fracture toughness ( K IC) of structural materials. The SNTT system operates by applying pure torsion to uniform cylindrical specimens with a notch line that spirals around the specimen at a 45° pitch. The K IC values are obtained with the aid of a three-dimensional finite-element computer code, TOR3D-KIC. The SNTT method is uniquely suitable for testing a wide variety of materials used extensively in pressure vessel and piping structural components and weldments, including others such as ceramics, their composites, and concrete.

One‐dimensional finite element solution for non‐uniform tall building structures and loading

AbstractBy using a one‐dimensional finite element numerical version based on the continuous medium technique, plane panels of variable geometry and loading are considered, in order to emphasize the capacity of a corresponding very simple computer code. Twin shear walls linked by lintel beams, with walls of lower storeys having bigger cross‐section than the next upper floors, are considered under variable horizontal wind loading through the building height. Afterwards, in that same panel, stronger discrete lintel beam is subsequently placed at each floor position. Results may show where is the optimum level to place those reinforcements in order to get, for example, the smaller top horizontal deflection. The second example considers the case of shear wall curtailment, in the frame shear wall association by pinned bars. Due to the individual behaviour of a single shear wall and of a single frame, it is possible (and real construction may permit that) to construct the wall up to a certain level, smaller than the building height, without having any significant change in the panel top displacement. By using the particular continuous medium finite element computer code, developed by the first author, it is possible to analyse several modelled structures, each having the curtailed wall at subsequent levels, from base to top, and to build an ‘influence line’ to find out the optimum curtailment level. Comparisons with the matrix discrete method and with analytical solutions were considered. Reference to free vibration solutions for such structures was also made. Copyright © 2008 John Wiley & Sons, Ltd.

Poromechanical Modelling and Inverse Approach of Drying Tests on Weakly Permeable Porous Rocks

The present paper deals with the determination of permeability in partially saturated conditions for weakly permeable porous rocks such as argillites or deep clayey formations. The level of permeability can be obtained via the measurements of transient weight loss of a sample submitted to a decrease in relative humidity imposed by saline solution in a hermetic chamber. An identification method based on simplified uncoupled 1D-linear and 1D-non-linear modelling was presented in a previous paper (Giraud et al. Trans Porous Media 69(2):259–280, 2006). The present paper takes into account generalized mass transfer phenomena such as Darcean advective transport of liquid and gas mixtures and Fickean diffusive transport of the vapour specie inside a gas mixture. Poromechanical coupling as well as 3D effects due to the geometry and finite dimensions of the tested samples are also covered by this approach. The coupled THM finite element computer code Code_Aster is then used to model the forward problem. The parameter identification procedure is based upon the solution of an inverse problem. The Levenberg–Marquardt algorithm was used for the problem of minimization. Comparisons between previous simplified 1D modelling and 2D-axisymmetrical coupled modelling show that the former method efficiently provides the correct order of magnitude of the level of permeability or the equivalent storage coefficients. Due to the boundary condition, the real 2D-axisymmetrical geometry of the sample must not be neglected if we are to obtain accurate results.

Stress Analysis and Creep Behavior of Service Exposed Primary Superheater Tube in a Thermal Power Plant

The elastic, inelastic deformation and stress distribution pattern of a seventeen years service exposed primary superheater tube in a 120 MW boiler of a thermal power plant have been evaluated by using both analytical and numerical techniques. The commercial finite element computer code ANSYS was used for stress analysis. The methodology is a valuable design tool for development of new boiler tubes as well as for considering the effects of numerous operating variables on creep life. The health of the tube was also assessed based on microstructure, hardness and a few conventional creep tests carried out at 500 degrees C at various stress levels (40-177 MPa). Results revealed that there was not much variation in the microstructure and hardness of the service exposed tubes compared to the virgin material. Creep deformation behavior of the service exposed and virgin tubes of the same material at 40 MPa reveal that deterioration of the creep properties fall within the 20% scatter band, which is well within the specified limits of ASTM standard. The service exposed primary superheater tube is thus in a good state of health.

Hydromechanical modelling of shaft excavation in Meuse/Haute-Marne laboratory

This paper presents a numerical modeling of hydromechanical response of a vertical shaft subjected to excavation in hard clay called argillite. The excavation procedure of the shaft is first presented. Based on experimental data obtained in conventional laboratory tests, a unified plastic and viscoplastic model is used to describe poromechanical behavior of the argillite in saturated and unsaturated conditions. This model takes into account the main features of poromechanical behavior of the material such as non-linear yield surface, non-associated plastic flow, sensitivity to water saturation, instantaneous and time-dependent plastic deformations. The model’s parameters are determined from experimental data obtained in triaxial compression tests and triaxial creep tests. The proposed model is implemented in a fully coupled finite element computer code in order to perform numerical modeling of boundary values problems. The numerical simulation of the shaft is then presented in the second part. Evolutions of displacement and pore pressure are evaluated during the excavation and compared with in situ measurement. It is shown that the hydromechanical responses of rock are affected by drying process inside the shaft. However, the influence of creep deformation seems to be negligible due to the relatively short duration of excavation.

Buckling Characteristics of Symmetrically and Antisymmetrically Laminated Composite Plates with Central Cutout

A numerical and experimental study was carried out to determine the effects of anti-symmetric laminate configuration, cutout and length/thickness ratio on the buckling behavior of E/glass-epoxy composite plates. The buckling loads were presented for symmetrically and anti-symmetrically laminated plates subjected to axial compression load. The study included two different laminate configurations ([90/45/−45/0]as and [90/45/−45/0]s), two different cutout shapes (circular and semi-circular), two different length/thickness ratios (L/t = 75 and 37.5) and three boundary conditions (clamped–clamped [CC], clamped–pinned [CP] and pinned–pinned [PP]). Firstly, the buckling loads of eight-ply E/glass-epoxy rectangular plates were determined experimentally. Then, the buckling loads of the laminated composites were calculated by ANSYS finite-element computer code. The changing in buckling load of the composites due to the presence of cutout and changing of length/thickness ratio was calculated. Finally, the experimental test results were compared to the buckling loads of plates obtained from the finite element analysis.

Behavior of Ultrahigh-Strength Prestressed Concrete Panels Subjected to Blast Loading

This paper presents the results of an experimental investigation conducted in Woomera, South Australia in May 2004 on the blast-resistance of concrete panels made of ultrahigh-strength concrete (UHSC) material. A special concrete supporting frame was designed for testing concrete panel targets against blast loading. Four 2 m×1 m panels with various thicknesses and reinforcement details were tested under a 6 t TNT equivalent explosion at standoff distances of 30 and 40 m . Data collected from each specimen included blast pressures and deflections of panels. The test data were analyzed to assess the performance of UHSC and normal-strength concrete (NSC) panels. The test results and observations showed that the 100-mm-thick UHSC panels performed extremely well surviving the blast with minor cracks. The 75-mm-thick UHSC panel suffered moderate damage while the 100-mm-thick NSC panel was breached. Test results from this experimental program were used to validate a finite-element computer code that was develope...

Local crushing of HCP100 structural foam due to low-velocity impact

An experimental and numerical study of the local crushing of Divinycell HCP100 structural foam due to low-velocity impact is undertaken. The study deals with a two-dimensional configuration, where foam beams are subjected to normal impact by gravity driven steel cylindrical impactors. During the impact tests, the foam specimens are entirely rested on a stiff steel substrate to limit the overall bending deformation. The quantities, measured during the impact tests, are the contact force, the load-time response, and the deflection. A two-dimensional numerical model is developed to simulate the deformation induced in the impact process. For this purpose, the ABAQUS/Explicit finite element computer code is used. The HCP100 foam is modeled as an elastic–plastic material with hardening. Results from finite element analysis are compared to test data and the correlation is found to be very good. The present work is a step towards developing a damage tolerance design methodology of HCP100 structural foam.