Finite Element Computer Code Research Articles

Estimation of fracture conditions of ceramics by thermal shock with laser beams using the maximum compressive stress criterion.

Structural ceramics are attracting attention in the development of space ships, aircraft and nuclear fusion reactors because they have excellent wear-resistant and heat-resistant characteristics. However, in some applications it is anticipated that they will be exposed to very high temperatures of the order of thousands of degrees. Therefore, it is very important to investigate their thermal shock characteristics. In this report, the distributions of temperatures and thermal stresses of cylindrically shaped ceramics under laser beams are discussed using the finite element computer code (MARC) with arbitrary quadrilateral axisymmetric ring elements. The relationships between spot diameters of laser beams and maximum values of compressive thermal stresses are derived for various power densities. From these relationships, a critial fracture curve is obtained, and it is compared with the experimental result.

Design of composite straps

A finite element computer code was developed for calculating the stresses and strains in, and elongations of, racetrack shaped composite straps loaded by two pins in tension. A procedure was also established for estimating the failure loads of such straps, by utilizing the results provided by the finite element method and the Tsai-Wu failure criteria. Tests were performed to validate the stress analysis and the failure model. Forty-three steps were made of either T300/976, T1000/081, IM6/081 graphite-epoxy, K49/081 kevlar-epoxy, or S-2/081 glass-epoxy. The strains and failure loads of these straps were measured, and the data were compared to the calculated strains and failure loads. The calculated values agreed well with the data. Charts were also developed for estimating the failure loads of racetrack shaped straps. Lastly, the design of composite straps loaded by two or more pins is discussed.

放射性物質輸送容器の衝突解析用簡易計算コードの開発，（Ｉ） 緩衝体付き輸送容器衝突計算コードＣＲＵＳＨ

In impact analysis for radioactive materials transport casks, it has become possible to perform them in detail by using finite element and finite difference computer codes, such as HONDO-II, DYNA2D, DYNA3D and PISCES. However, the considerable cost and computer execution time are necessary to perform analyses by these computer codes. Therefore, simplified computer codes which are capable of reducing cost and computer execution time are needed. To meet the above requirements, CRUSH code has been developed. CRUSH is a static calculation computer code capable evaluating the maximum acceleration of the cask body and the maximum displacement of the shock absorber.Analytical results obtained by CRUSH code are compared with experimental results and the detailed computer code DYNA3D. Good agreements were obtained between simplified results and experimental and detailed analysis ones.

Experimentation and finite element simulation of adiabatic shear bands in controlled penetration impact

Distinct shear bands were generated in a controlled-penetration impact experiment. The experimental set-up included a projectile, an indentor, a stopper, and a backup ring. Impact tests with steel specimens of different flow stresses showed that the shear band length is directly proportional to the flow stress and the indentation depth, and inversely proportional to the back-up hole diameter. A finite element computer code simulation showed that shear bands could be formed without initial disturbances or defects. The calculated shear band length was in good agreement with the experimentally measured ones.

Determination of heat transfer coefficient using transient temperature response chart

An inverse finite element computer code is developed to predict surface heat flux and surface temperature in conjunction with the measured thermocouple temperature history. Determination of convective heat-transfer coefficient and combustion gas temperature is carried out employing transient temperature response chart. Examples are illustrated which are typical of those that arise in thermal design of rocket nozzle. The results demonstrate that the method is remarkable in its ability to estimate unknown boundary conditions.

Prediction of the ultimate capacity of wide flange link beams under cyclic loading

The objective of this investigation is to develop an analytical model to evaluate the seismic performance of the active links in eccentrically braced frames. The ADINA finite element computer code is used to gain insight into the behaviour of the links under cyclic loading. An available experimental set-up and testing program was modelled. It was found that it is possible to develop a simple yet effective finite element approach to model the very complex behaviour of the links. Comparison between analytical predictions and available experimental results showed good agreement.

Numerical Modeling of Structure‐Frozen Soil/Ice Interaction

A finite element computer code is developed to analyze the creep deformation of frozen media by using a time‐incrementing algorithm and the power‐law constitutive model to describe creep. The accuracy of the code is established by simulating a cavity expansion problem in a thick‐walled cylinder of viscoelastic material, and the deflection of a viscoelastic beam under a vertical load, and comparing the numerical results with the available analytical results. The code is then used to model static‐loaded and penetration‐rate—controlled penetrometer tests on frozen soils, using three indenter shapes. Load‐displacement‐time relationships thus developed could later be useful for interpretation of creep properties in the field. Modeling the interaction between embedded cylindrical foundations and frozen soils shows the strong influence of the creep parameters on the settlement behavior. The code is presented as a convenient tool to obtain a preliminary estimate of the time‐dependent performance of foundation ele...

An analytical and experimentall investigation of natural convection heat transfer in vertical channels with a single obstruction

An experimental and numerical investigation was made of laminar natural convection flow of air in a vertical channel with a single obstruction. In the experimental study, optical techniques were used to obtain measurement of both quantitative data (heat fluxes and temperatures) and qualitative data (flow visualization). Only uniform wall temperature (UWT) boundary conditions were investigated experimentally. In the numerical study, a general purpose, finite element computer code called NACHOS was used. Thermal boundary conditions, uniform wall temperature (UWT), and uniform heat flux (UHF) were investigated numerically. The experimental and numerical results were in close agreement. The results indicate that for UWT boundary conditions the presence of an obstruction reduces the average Nusselt number by 5% at a Rayleigh number of 10 4 to about 40% at a Rayleigh number of 10. It is also noted that the location of the obstruction along the wall affects the rate of heat transfer. Moving the obstruction away from the entrance towards the exit reduces the average heat transfer rate for the channel. For UHF boundary conditions, the maximum temperature (which occurs at the intersection of the top edge of the obstruction and the wall) is only 4% higher than the maximum temperature for an unobstructed channel (which occurs at the exit of the channel).

Hot Working — Constitutive Equations and Computational Procedures

A state variable constitutive model for large deformation, isotropic thermo-elasto-viscoplasticity, and an implicit time-integration procedure to integrate the evolution equations for the state variables have been developed. The constitutive equations and time integration procedure have been incorporated into the general purpose finite element computer code ABAQUS via its “user material” subroutine option. By using this program, representative problems have been numerically analyzed. The predictions from the analysis concerning the forging load as a function of ram travel, and the overall shape changes are found to be in excellent agreement with measurements made in similar laboratory experiments.

Thermal finite-element analysis of space shuttle main engine turbine blade

Finite-element, transient heat transfer analyses were performed for the first-stage blades of the space shuttle main engine high-pressure fuel turbopump. The analyses were based on test engine data provided by Rocketdyne. Heat transfer coefficients were predicted by performing a boundary-layer analysis at steady-state conditions with the Stan5 boundary-layer code. Two different peak-temperature overshoots were evaluated for the startup transient. Cutoff transient conditions were also analyzed. A reduced gas temperature profile based on actual thermocouple data was also considered. Transient heat transfer analyses were conducted with the Marc finite-element computer code.

Theoretical prediction of remote-field eddy current response for the nondestructive evaluation of metallic tubes : Journal of applied physics, vol. 61 no. 8, pp. 3202–3204 (15 Apr. 1987)

The remote‐field eddy current effect refers to low‐frequency eddy current nondestructive testing (NDT) phenomenon in tubular conductors in which the behavior of both amplitude and phase of induced magnetic field are in apparent contradiction to the well‐known ‘‘skin‐effect’’ theory. Near‐equal detection sensitivity across the wall thickness, the ability to measure wall thickness, and the absence of lift‐off problems are some of the attractive features of this technique. Despite its early recognition and useful application in down‐hole inspection of oil‐well casing, no development of adequate scientific basis that could explain this phenomenon has been reported in the open literature. Modeling of the remote‐field eddy current phenomenon using the axisymmetric finite element computer code is described in this paper. The results presented show that the finite element numerical technique originally developed for the computation of fields in electrical and magnetic devices can be used as well for the modeling ...

The use of stereo X-ray and deply techniques for evaluating instability of composite cylindrical panels with delaminations

The buckling loads of eight-ply AS4/3501-6 graphite/epoxy cylindrical panels with delaminations were determined experimentally. The delaminations fabricated into the laminate with Mylar and Teflon inserts, represent the effect of low-velocity projectile impact damage. The Mylar was found to cause partial delamination while the Teflon inserts caused total delamination. Two types of insert positions were considered; eccentric or off-midsurface, and midsurface. The eccentric delaminations were placed progressively through the thickness of the laminate. STAGSC-1 finite-element computer code results for undelaminated composite panels were compared to the experimental results to obtain a percent strength degradation. The experimental testing was accomplished by the Air Force Flight Dynamics Laboratory. The test device provided boundary conditions of clamped top and bottom edges and simply supported vertical sides. Two destructive techniques, stereo X-ray and deply, were used to determine the total delaminated areas and locations. Based in part on these results, one equivalent delamination was obtained corresponding to the total area of the multiple partial delaminations. The panels with multiple delaminations were found to be approximately five-percent weaker than a single delaminated area of the same total size.

Viscoplastic behaviour of stainless steels AISI 316L and 316H

The theory of viscoplasticity based on total strain and overstress is used in order to simulate the sensitivity to the rate of loading of two commonly used stainless steels, namely AISI 316L and 316H. The consitutive model has been implemented within a transient finite element computer code using a stress update algorithm based on the elastic predictor-return mapping concept. Both monotonic and cyclic loading conditions are considered in one or more space dimensions.

Use of dynamic stress-strain characteristic in the prediction of stainless and carbon steel pipe response

A theoretical study of uncracked pipes in bending under dynamic conditions is presented. The pipes evaluated are a 6 in. carbon steel and an 8 in. stainless steel. The effect of the dynamic loads is to increase the yield stress and the flow stress of the material. The analysis performed in the study has been done using a finite element computer code. The failure mode considered was by plastic collapse at the moment in which the outer fiber of the pipe reached the flow stress. The code has been validated against a test run on a stainless steel pipe. The Net Section Collapse Load (NSCL) criterion has also been considered for comparison with the code results. The results indicate that if the failure mode is by plastic deformation the pipes should respond to the dynamic action of the loads about 10% better than to the static ones.

Analysis of a High-Speed Flexible Four-Bar Linkage: Part I—Formulation and Solution

Derived from the principle of virtual displacement, a general finite element analysis computer code (FEMAP) of the flexible four-bar linkage is developed on the Apollo computer. In this part, virtual displacement method is presented as a basic theory for the general formulation of the equations of motion. Based on these results, a general finite element computer code of planar four-bar linkage is developed. All the links of the mechanism are considered to be flexible. The nonlinear terms such as coupling between the rigid body and elastic deformation terms and the effect of the axial forces are included. The Newmark direct integration method is used as solution scheme.

Simulation of Sheet Bending Processes by Elastic-Plastic Finite Element Method

An elastic-plastic incremental finite element computer code is developed to simulate sheet bending processes. The updated Lagrangian scheme is employed as the base of the code, and bending processes are simulated under the plane strain condition. Important feature of this code is a newly developed r-minimum algorithm which can deal with deformation-dependent sheet-tool contact conditions precisely in incremental manner. Simulation of bending processes such as UO-bending of steel sheets to form pipes and U-bending of the steel-plastic laminate sheets are carried out. The simulation clearly demonstrates efficiency of the code.

Three-dimensional eddy current calculation using finite element method with A-V in conductor and Omega in vacuum

Three-dimensional eddy current equations are formulated in terms of a magnetic vector potential A and an electric scalar potential V in the conductive regions and a reduced magnetic scalar potential Omega in the nonconductive region. A finite-element computer code, EDDY3DT, has been developed using this A-V formulation. Application to test problems and comparison with the analytical solutions or results by other methods show that the A-V formulation is effective for problems involving anisotropic and discontinuous conductivities, cracks, and holes. >

Energy conversion in a gas shock tube: Theory and experiments

The gas shock tube used in these experiments consists of a low pressure chamber and a high pressure chamber, divided by a metal-diaphragm-to-rupture. In contrast to the shock mode of operation, where incident and reflected shocks in the low pressure chamber are studied which occur within 3.5 ms, in this work the compression mode of operation was studied, whose maxima occur (in the low pressure chamber) about 9 ms after rupture. Theoretical analysis was done with the finite element computer code EURDYN-1M, where the computation was carried out to 30 ms. The compression mode was enforced by inserting on the low pressure side, just behind the diaphragm, a small piston. In the corresponding analysis the computation time was up to 112 ms. Results showed that the work done on the low pressure gas could be approached with adiabatic compression. It was extrapolated that at high pressure loads, the work done corresponded to 1.5% of the potential energy in the high pressure chamber when no piston was used, and to 4% when a piston was used.

Theoretical prediction of remote-field eddy current response for the nondestructive evaluation of metallic tubes

The remote-field eddy current effect refers to low-frequency eddy current nondestructive testing (NDT) phenomenon in tubular conductors in which the behavior of both amplitude and phase of induced magnetic field are in apparent contradiction to the well-known ‘‘skin-effect’’ theory. Near-equal detection sensitivity across the wall thickness, the ability to measure wall thickness, and the absence of lift-off problems are some of the attractive features of this technique. Despite its early recognition and useful application in down-hole inspection of oil-well casing, no development of adequate scientific basis that could explain this phenomenon has been reported in the open literature. Modeling of the remote-field eddy current phenomenon using the axisymmetric finite element computer code is described in this paper. The results presented show that the finite element numerical technique originally developed for the computation of fields in electrical and magnetic devices can be used as well for the modeling of remote-field eddy current NDT problems.

Structural analysis of the controlled impact demonstration of a jet transport airplane

An analytical method has been developed for assessing crash dynamics of large transport aircraft, such as in the NASA Controlled Impact Demonstration (CID) jet crash test on December 1, 1984. The DYCAST nonlinear finite-element computer code was used in a series of progressively more difficult tasks to model complete transport aircraft crashes. Single aircraft frames and fuselage section vertical drop tests were modeled and analyzed to obtain comparisons with experimental data and to develop hybrid element crash springs for use in the large CID model. Predictions of crash and acceleration levels from a symmetric CID model agreed well with data from the CID experiment.