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A parallel computational environment for modeling the resin transfer molding manufacturing process has been developed at the U.S. Army Research Laboratory. This environment utilizes an implicit numerical method for modeling resin flow, a thermal model for analyzing convection and conduction, and a resin kinetics model to compute the heat generated and degree of resin cure during the curing process. The computing environment also includes a multiscale thermal residual stress model for computing the distortions and residual stresses in the composite component caused by the manufacturing process. All of these models have been tied together within a parallel object-oriented programming framework. This paper will discuss the computing environment in detail and its utility to real world applications. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The paper presents the modeling and simulation for the extrusion technology of a new type of spark plug body for Dacia Supernova car. This technology was simulated using the finite elements modeling and analysis SuperForm software, designed for the simulation of plastic deformation processes. There is also presented a comparison between the results of the simulation and the industrial results. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

It has long been found that, during deformation process, the crystal orientations would gradually rotate around some ideal orientations, and then would affect the later deformation properties of sheet metal. So it is very important to introduce texture model into metal forming processes. In this paper, a rate-independent polycrystalline plasticity model is developed and introduced into dynamic explicit element method. Metal flow is assumed to occur by crystallographic slip on given slip systems within each crystal. Every integration point represents a single crystal. Then cup drawing of sheet metal is studied using crystalline plasticity finite element analysis. For the rolled aluminum sheet, which contains strong {001}<110> texture, earing is formed at 45° direction after cup drawing. For the annealing aluminum sheet, due to the balance between two main textures, the flange earing tendency is not obvious. And for the soft steel sheet with a faintish orientation distribution, the flange earing tendency is not obvious, too. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The critical issue during finite element analysis of tailor welded blank is the handling of the weld region — either the weld may be treated just as a weld line (without imposing mechanical properties) or as a weld zone (by imposing separate mechanical properties to the weld zone). The formability of TWB will be affected not only by the weld characteristics but also by the relative mechanical properties of the weld zone and the base metal. The above effects will be discussed in this paper by considering the tensile and Limiting Dome Height (LDH) testing of the TWB. Tensile testing will be modeled using standard tensile specimen. In LDH simulations, samples deforming near plane strain and balanced biaxial stretching will be modeled. Load-progression behavior will be monitored. Throughout this study , simulations will be performed by finite element analysis. By analyzing the simulation results, the specific conditions where the weld zone assumption should be followed will be identified. It is found from the analysis that modeling weld region as weld line is not accurate for all the weld conditions. Also the domain of weld conditions wherein weld line assumption breaks down depends on the deformation mode or part shape. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Tailor welded blanks (TWBs) are made by welding same or different materials having same/different properties into a single blank. They can be tailored to any specific shape and size. The formability of these blanks depend on material and geometric parameters like strength ratio and thickness ratio. This paper studies the effect of thickness ratio on the formability of tailor welded blanks by FE simulation. The formability is assessed by considering the Tensile and Limit Dome Height (LDH) tests. The weld region has been assumed as a line in all the simulations. While modeling tensile test, the ultimate tensile strength and the uniform elongation were monitored. In all LDH simulations, near plane strain condition is considered Uniaxial tensile testing shows that TWB formed will have lower elongation as compared to the base metal and the load bearing capacity will be comparable to that of thinner blank in case of transverse welded TWB. Thickness and thickness strain distribution along the blank show that the effective deforming area in a transversely welded TWB is that of the thinner blank. Both tests indicate that as the thickness ratio increases, the formability of TWB reduces. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

One of the most important methods for improving the flexibility of sheet metal forming process is the deformation with discrete surfaces. The method developed by Hardt, consists in a spatial discretization of the continuous active elements surfaces with a number of pins. As the spatial positions of the pins are of a great importance, in the paper is developed, based on surface generation method, a mathematical model for pins coordinates determination. Then using the finite element code DYNAFORM, it was modeled the process of deformation for obtaining two types of parts geometries namely: a simple curved geometry and a double curved geometry. Finally, as a result of simulation it was point out the advantages and disadvantages of using this type of deformation. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Problems associated with finite element simulation of the forming processes are characterized by large elastoplastic deformations, evolutive contact with friction, geometrical non linearities inducing a severe distortion of the computational mesh of the domain. Frequent remeshing of the deformed domain during computation is necessary to obtain an accurate solution and complete the computation until the termination of the numerical simulation process. This paper presents a new adaptive remeshing method of thin sheets for numerical simulation of metal forming processes in three dimensions. The proposed remeshing technique includes adaptive refinement and coarsening procedures. It has been implemented with triangular and quadrilateral elements. The method is based on geometrical criteria and does not use the geometry of the forming tools. It is integrated in a computational environment using the ABAQUS solver. Numerical examples are given to show the efficiency of the proposed approach. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

A new non-finite element friction model for tube hydroforming corner fill analysis has been introduced. The proposed model, which is applicable to 90-degree die corners, is based upon geometric considerations and does not require an incremental solution scheme. Hoop strain distributions are evaluated using both FEA and the proposed theory. Overall correlation between the FEA and proposed solutions is quite respectable in light of the fact that the proposed friction model is based upon a non-finite element theory which does not account for the intermediate deformation. This paper helps lay the groundwork for improvements in numerical modeling of friction effects on the hoop strain distribution in tubular hydroforming corner fill analysis when closed form solutions are required. The long term-intent of this effort is to mold the proposed theory into a form that is accommodating to a more global contact model. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Although deformation features of ECAP have been widely studied and investigated through numerical approaches, experimental observations are very scarce in the literature. Therefore, in this paper, quasi-3D strains in multi-sectioned samples during one pass of ECAP are analyzed, for different friction conditions and material properties. From this study, it can be concluded that ECAP is a plane-strain process and friction and material properties affect the strain distribution, strain homogeneity and also the work-piece geometry. Furthermore, ECAP can be interpreted as a combination of shear and stretch. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Homogenization theory has been well accepted by the applied mechanics modeling community for its ability to integrate small-scale microstructure phenomena into bulk continuum equations using convergent features of asymptotics. This paper describes an extension of the method to handle asymptotically small atomic scale systems at zero temperature embedded within a deforming continuum. A so-called inner displacement naturally arises in the formulation that enables the consideration of distributed anharmonic crystalline effects that would otherwise be unapproachable with bulk continuum methods alone. The result is a simple computational mechanics method that, first, maps instantaneous continuum deformation gradients to deforming defected crystalline arrangements then, second, provides convergent effective material properties to be used for consistent continuum calculations. The intended applications are those involving patterned defects, either in bulk or on surfaces, which allude to possible manufacturing scenarios. Simple 2-D examples are shown for in-plane deformation of graphene possessing various types of point defects. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

With advances in computer capabilities, cost of sheet metal forming has being reducing mainly due to the reduction of trial and error approaches. At the moment, a complete process can be simulated on computer and appropriate forming conditions optimized before actual industrial forming process is carried out. While formability predictions have improved, the problem of springback exhibited by most metal, including aluminum alloy AA6111-T4, after forming persist and often leads to significant part fit-up problems during assembly. There are a number of factors that affect springback and perhaps the most significant one is constitutive equation. In this paper springback predicted by six advanced kinematic models are evaluated. In addition an improved constitutive kinematic model is presented. It is shown that by adding stress correction term (SCT) to Armstrong-Frederick model a relatively simple and yet accurate stress prediction could be obtained. The SCT was developed with the assumption that the yield surface remains convex, yield center depends on translation, size and shape variations of the yield surface. The model is implemented in a commercial finite element code (ABAQUS/Standard) via its user material interface (UMAT). Numerical simulations of U-bending were performed using automotive aluminum sheet material (AA6111-T4). It was noted that springback has inverse relationship with residual stress. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

In this paper, we propose a multi-time scale modeling technique for analyzing cyclic plastic deformation in crystalline solids subject to periodic loading. An asymptotic expansion of the variables in the time domain, together with homogenization forms the basis of multi-time scaling. In the macroscopic scale analysis, the oscillatory behavior of the load is averaged out and neglected, and the rate of averaged material behavior is quite slow in cyclic deformation. Implicitly, this means that the periodicity of some variables may be assumed for the oscillatory potion of the material behavior may be approximated. In this formulation, the governing equations are divided into two initial-boundary value problems with two different time scale: one is long time scale problem for describing the smooth averaged solution (global problem) and the other is for the remaining oscillatory potion (local problem). For the global problem, long time increments, which are longer than one cycle period, can be used and this multi-time scaling becomes an effective integrator. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

In this paper, we propose a multi-time scale modeling technique for analyzing cyclic plastic deformation in crystalline solids subject to periodic loading. An asymptotic expansion of the variables in the time domain, together with homogenization forms the basis of multi-time scaling. In the macroscopic scale analysis, the oscillatory behavior of the load is averaged out and neglected, and the rate of averaged material behavior is quite slow in cyclic deformation. Implicitly, this means that the periodicity of some variables may be assumed for the oscillatory potion of the material behavior may be approximated. In this formulation, the governing equations are divided into two initial-boundary value problems with two different time scale: one is long time scale problem for describing the smooth averaged solution (global problem) and the other is for the remaining oscillatory potion (local problem). For the global problem, long time increments, which are longer than one cycle period, can be used and this multi-time scaling becomes an effective integrator. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

New production technologies have been developed in these last few years as answers to new market needs such as high production flexibility, low volume batches, more complex shapes of the final pieces and new materials. In particular, for sheet forming the new developed technologies are flexible forming, sheet die-less forming and sheet fluid forming. In previous works the authors have already described the results obtained studying a new sheet forming process based on general purpose CNC machine (called sheet incremental forming on CNC machines) equipped with special tool. This kind of process can be used to produce prototypes of industrial components and also for low volume batches. The present paper reports the results of the analysis conducted on the produced pieces in terms of metallographic structure, hardness distribution and breaking conditions. These results are very interesting in order to understand the physical limits of the material when subjected to this peculiar deformation process. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

When performed in conjunction with neutron diffraction, in situ loading offers unique insights on microstructural deformation mechanisms. This is by virtue of the penetration and phase sensitivity of neutrons. At Los Alamos National Laboratory room and high temperature (up to 1500°C) polycrystalline constitutive response is modeled using finite element and self-consistent models. The models are compared to neutron diffraction measurements. In doing so the implications of slip and creep to microstructural response have been explored. Recently we have been considering low temperature phenomena. This includes changes in deformation mechanisms such as the increased predilection for twinning over slip. Since this is associated with measurable texture changes as well as microstructural strain effects, it is well suited for study using neutron diffraction. This paper outlines the design and rationale for a cryogenic loading capability that will be used on the Spectrometer for MAterials Research at Temperature and Stress (SMARTS) at the Los Alamos Neutron Science Center (LANSCE). © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The mode coupling theory (MCT) for the glass transition is in reasonable accord with observations on attractive colloids at high densities. This paper presents a brief review of the MCT. This is followed by a more detailed discussion of two recent extensions of it. These address (i) nonlinear rheology and jamming in colloids under shear and (ii) weak gelation of colloids at low densities. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

A number of strain rate dependent material strength models have been implemented in AWE hydrocodes. This paper serves to highlight the current capability to model material deformation, the advances made with the implementation of rate dependent models, and the basic differences between them in modelling a simple dynamic experiment. The comparison was carried out on tantalum — a material for which every rate-dependent model has published data. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

An Edge of Light™ (EOL) computer vision-based system is used for detection and measurement of pillowing deformation in aircraft fuselage lap joints. Two approaches are described for the interpretation of the EOL images. The first approach is based on reconstruction of the inspection surface using the slope angle associated with each corresponding pixel. The second method uses image pattern with the principle component analysis. A simple device simulation corrosion pillowing named “pillowing simulator” is described and used to study the two approaches in terms of their quantification capability. Also, an algorithm to identify rivets in the EOL images is developed and presented in this paper. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

This paper presents an overview on current activities and results concerning NDE of material degradation by embrittlement and fatigue. In general we differentiate between NDT methods for the characterization of embrittlement and fatigue which are either microstructure or crack sensitive. At the present time there is no reliable NDE technique known which can be used on technical components to detect the onset of failure during the early stages of embrittlement and fatigue. Therefore, microstructure sensitive methods are required which have potential for detecting degradation during the early stages and for infield capability. Such methods are micro-magnetic methods, eddy current methods and thermal methods. These techniques, however, have only been tested under laboratory conditions to date. The micro-magnetic method will be discussed concerning embrittlement. Results on eddy current testing by using GMR and thermal methods are documented concerning fatigue characterization. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

In work reported at last year’s QNDE meeting, a first step towards the development of a model for the Scanning Laser Source (SLS) technique was presented, which provides an analytical formulation for the transient response of an isotropic, homogeneous, linearly elastic half-space submitted to a pulsed laser line source operating in the thermoelastic regime. The formulation takes into account optical penetration into the material and thermal diffusion from the source, and is therefore a suitable representation not only for the far field, but also for the field near the laser source, where these effects become significant. In the present paper, we report the progress made in the numerical analysis by the Boundary Element Method of the interactions of the previously obtained laser generated field with surface-breaking cracks. Some preliminary simulations of SLS experimental observations are presented. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

This paper presents a study of crack detection methods for holes in structures with limited accessibility containing fasteners with variable interface conditions. For far crack detection, a method was first designed using models, and refined using a signal processing parameter optimization scheme and an iterative neural network training process. For near crack detection, a method incorporating the spatial variation of the principal components was developed. Using these methods, improvements in crack detection performance were achieved. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

This paper presents a study of ultrasonic NDE models for a cylindrical hole containing an elastic layer and a fluid-filled hole. For the elastic layer case, both dispersion relations and analytical solutions were solved to assess the sensitivity of leaky Rayleigh waves to annulus properties. A BEM model was formulated for the scattering of shear waves by a fluid-filled hole with a notch. Through simulated studies, a viable inspection technique was derived and validated experimentally. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

In this paper, the images provided by a flying-spot camera dedicated to open-crack detection are considered. In this type of active thermography, thermal effect and the optical effects contribute to the elaboration of photothermal images. In this contribution a signal processing method, based on multiple principal component analysis is proposed in order to separately identify both thermal and optical effects from the raw images. The detection performance enhancement is characterized thanks to Receiver Operating Characteristic curves. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

Using non-destructive methods for estimation of degradation of strength properties of a material of structures intended for a long-time operation at high temperatures, in aggressive environments or under radioactive radiation is very important for prediction of the residual safe life of such structures. This is especially important for the cases where the life of the structures is close to the design service limit. The search for such methods is a real challenge, as they are very helpful for solving the problems associated with prevention of accidents and extension of service life. The paper considers a number of approaches based on a combination of mathematical models of degradation of strength properties of structural steels under certain service conditions with practicable measurements of variations in the corresponding physical properties of a material, correlating with the degree of degradation of the strength properties. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

There are several existing methods for damage detection based on identifying changes in strain energy mode shapes. Most of these methods require knowing strain energy mode shapes for a structure without damage in order to establish a baseline for damage detection. Usually, the mode shapes from the structure under test should be compared to the baseline mode shapes to identify and locate damage. However, these methods of damage detection are not very suitable for application on structures where baseline mode shapes cannot be readily obtained, for example, structures with preexisting damage. Conventional methods, like building a finite element model of a structure to be used as a baseline might be an expensive and time-consuming task that can be impossible for complex structures. A new (non-baseline) method for the extraction of localized changes (damage peaks) from strain energy mode shapes based on Fourier analysis of the strain energy mode shapes has been developed and analytically proved for the cases of a pinned-pinned and a free-free beam. The new method looks for characteristic changes in the power spectrum of the strain energy mode shapes in order to locate and identify damage. The analytical results have been confirmed both by the finite element model and impact testing experiments on a free-free aluminum beam, including single and multiple damage scenarios. This paper presents results of testing the non-baseline method on a complex structure — Armored Vehicle Launched Bridge, which consists of loosely coupled hinged beams with variable cross-section. The results of testing confirm applicability of the non-baseline method to damage detection in complex structures and highlight certain particularities of its use. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

During fabrication, metallic thin films and lines typically develop high levels of stress that affect their performance and can lead to failure of devices based on them. A quantitative reliability assessment requires a thorough understanding of the mechanical behavior of these metallic structures that can only be attained if the dominant inelastic mechanisms are identified and characterized. In this paper, we discuss the inelastic behavior of Ag and Cu thin films, and damascene Cu lines. For the thin films, we identified the dominant inelastic mechanisms that generate plastic deformation during thermal cycling: diffusional creep at high temperatures (approximately above 0.3 of the melting temperature), and dislocation-mediated plasticity controlled by the thermally activated glide of dislocations through forest obstacles at low temperatures. As expected, the characteristic lengthscale for diffusional creep is determined by the microstructure (i.e. average grain size and film thickness). The characteristic lengthscale for dislocation plasticity is the length of the moving dislocation segments, which was found to depend on film thickness and to be on the order of 50–100 nm. Our experimental results indicate that the mechanical behavior of the lines is essentially identical to that of the films, and that it can also be understood in terms of diffusional creep and dislocation plasticity. Finally, a simple constitutive equation, based on the dislocation-mediated inelastic mechanism, is presented. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In many interesting physical settings, such as the vulcanization of rubber, the introduction of permanent random constraints between the constituents of a homogeneous fluid can cause a phase transition, known as the vulcanization transition, to a random solid state. In this random solid state, particles are permanently but randomly localized, and a rigidity to shear deformations emerges. Owing to the permanence of the random constraints, this phase transition is an equilibrium transition, which confers on it a simplicity (at least relative to the conventional glass transition) in the sense that it is amenable to established techniques of equilibrium statistical mechanics. The aims of this paper are two-fold: First, the briefest sketch will be given of aspects of the mean-field theory of the vulcanization transition and the emergent random solid state. (These aspects have been reviewed elsewhere rather recently.) Second, a more detailed account will be given of various new results on the vulcanization transition beyond mean-field theory. [ABSTRACT FROM AUTHOR]

A thermodynamically consistent strength and failure model for granite under dynamic loading has been developed and evaluated. The model agrees with static strength measurements and describes the effects of pressure hardening, bulking, porous compaction, porous dilation, tensile failure, and failure under compression due to distortional deformations. This paper briefly describes the model and the sensitivity of the simulated response to variations in the model parameters and in the inelastic deformation processes used in different simulations. 1D simulations of an underground explosion in granite are used in the sensitivity study. [ABSTRACT FROM AUTHOR]

The paper presents results of experimental studies of metal balls deformation by quasi-spherical shock waves. With use of sequential increase of explosive layer thickness characterizing level of shock wave loading for ball surface, we recorded various extents of ball from saving of material continuity to fragmentation. Results of explosive loading of metals with different strength and plastic properties are discussed. [ABSTRACT FROM AUTHOR]