Nonlinear creep damage constitutive model for soft rocks
NASA Astrophysics Data System (ADS)
Liu, H. Z.; Xie, H. Q.; He, J. D.; Xiao, M. L.; Zhuo, L.
2016-06-01
In some existing nonlinear creep damage models, it may be less rigorous to directly introduce a damage variable into the creep equation when the damage variable of the viscous component is a function of time or strain. In this paper, we adopt the Kachanov creep damage rate and introduce a damage variable into a rheological differential constitutive equation to derive an analytical integral solution for the creep damage equation of the Bingham model. We also propose a new nonlinear viscous component which reflects nonlinear properties related to the axial stress of soft rock in the steady-state creep stage. Furthermore, we build an improved Nishihara model by using this new component in series with the correctional Nishihara damage model that describes the accelerating creep, and deduce the rheological constitutive relation of the improved model. Based on superposition principle, we obtain the damage creep equation for conditions of both uniaxial and triaxial compression stress, and study the method for determining the model parameters. Finally, this paper presents the laboratory test results performed on mica-quartz schist in parallel with, or vertical to the schistosity direction, and applies the improved Nishihara model to the parameter identification of mica-quartz schist. Using a comparative analysis with test data, results show that the improved model has a superior ability to reflect the creep properties of soft rock in the decelerating creep stage, the steady-state creep stage, and particularly within the accelerating creep stage, in comparison with the traditional Nishihara model.
Constitutive modeling of solid propellant materials with evolving microstructural damage
NASA Astrophysics Data System (ADS)
Xu, F.; Aravas, N.; Sofronis, P.
Solid propellants are composite materials with complex microstructure. In a generic form, the material consists of polymeric binder, crystal oxidizer (e.g., ammonium perchlorate), and fuel particles (e.g., aluminum). Severe stressing and extreme temperatures induce damage which is manifested in particle cracking, dewetting along particle/polymer interfaces, void nucleation and growth. Damage complicates the overall constitutive response of a solid propellant over and above the complexities associated with the differing constitutive properties of the particle and binder phases. Using rigorous homogenization theory for composite materials, we propose a general 3-D nonlinear macroscopic constitutive law that models microstructural damage evolution upon straining through continuous void formation and growth. The law addresses the viscous deformation rate within the framework of additive decomposition of the deformation rate and the concept of back stress is used to improve the model performance in stress relaxation. No restriction is placed on the magnitude of the strains. Experimental data from the standard relaxation and uniaxial tension tests are used to calibrate the model parameters in the case of a high elongation solid propellant. It is emphasized that the model parameters are descriptors of individual phase constitutive response and criticality conditions for particle decohesion which can systematically be determined through experiment. The model is used to predict the response of the material under more complex loading paths and to investigate the effect of crack tip damage on the mechanical behavior of a compact tension fracture specimen.
Stender, Michael E; Regueiro, Richard A; Klisch, Stephen M; Ferguson, Virginia L
2015-08-01
Traumatic injuries and gradual wear-and-tear of articular cartilage (AC) that can lead to osteoarthritis (OA) have been hypothesized to result from tissue damage to AC. In this study, a previous equilibrium constitutive model of AC was extended to a constitutive damage articular cartilage (CDAC) model. In particular, anisotropic collagen (COL) fibril damage and isotropic glycosaminoglycan (GAG) damage were considered in a 3D formulation. In the CDAC model, time-dependent effects, such as viscoelasticity and poroelasticity, were neglected, and thus all results represent the equilibrium response after all time-dependent effects have dissipated. The resulting CDAC model was implemented in two different finite-element models. The first simulated uniaxial tensile loading to failure, while the second simulated spherical indentation with a rigid indenter displaced into a bilayer AC sample. Uniaxial tension to failure simulations were performed for three COL fibril Lagrangian failure strain (i.e., the maximum elastic COL fibril strain) values of 15%, 30%, and 45%, while spherical indentation simulations were performed with a COL fibril Lagrangian failure strain of 15%. GAG damage parameters were held constant for all simulations. Our results indicated that the equilibrium postyield tensile response of AC and the macroscopic tissue failure strain are highly dependent on COL fibril Lagrangian failure strain. The uniaxial tensile response consisted of an initial nonlinear ramp region due to the recruitment of intact fibrils followed by a rapid decrease in tissue stress at initial COL fibril failure, as a result of COL fibril damage which continued until ultimate tissue failure. In the spherical indentation simulation, damage to both the COL fibril and GAG constituents was located only in the superficial zone (SZ) and near the articular surface with tissue thickening following unloading. Spherical indentation simulation results are in agreement with published experimental
A procedure for utilization of a damage-dependent constitutive model for laminated composites
NASA Technical Reports Server (NTRS)
Lo, David C.; Allen, David H.; Harris, Charles E.
1992-01-01
Described here is the procedure for utilizing a damage constitutive model to predict progressive damage growth in laminated composites. In this model, the effects of the internal damage are represented by strain-like second order tensorial damage variables and enter the analysis through damage dependent ply level and laminate level constitutive equations. The growth of matrix cracks due to fatigue loading is predicted by an experimentally based damage evolutionary relationship. This model is incorporated into a computer code called FLAMSTR. This code is capable of predicting the constitutive response and matrix crack damage accumulation in fatigue loaded laminated composites. The structure and usage of FLAMSTR are presented along with sample input and output files to assist the code user. As an example problem, an analysis of crossply laminates subjected to two stage fatigue loading was conducted and the resulting damage accumulation and stress redistribution were examined to determine the effect of variations in fatigue load amplitude applied during the first stage of the load history. It was found that the model predicts a significant loading history effect on damage evolution.
Constitutive and damage material modeling in a high pressure hydrogen environment
NASA Astrophysics Data System (ADS)
Russell, D. A.; Fritzemeier, L. G.
1991-05-01
Numerous components in reusable space propulsion systems such as the SSME are exposed to high pressure gaseous hydrogen environments. Flow areas and passages in the fuel turbopump, fuel and oxidizer preburners, main combustion chamber, and injector assembly contain high pressure hydrogen either high in purity or as hydrogen rich steam. Accurate constitutive and damage material models applicable to high pressure hydrogen environments are therefore needed for engine design and analysis. Existing constitutive and cyclic crack initiation models were evaluated only for conditions of oxidizing environments. The main objective is to evaluate these models for applicability to high pressure hydrogen environments.
Constitutive and damage material modeling in a high pressure hydrogen environment
NASA Technical Reports Server (NTRS)
Russell, D. A.; Fritzemeier, L. G.
1991-01-01
Numerous components in reusable space propulsion systems such as the SSME are exposed to high pressure gaseous hydrogen environments. Flow areas and passages in the fuel turbopump, fuel and oxidizer preburners, main combustion chamber, and injector assembly contain high pressure hydrogen either high in purity or as hydrogen rich steam. Accurate constitutive and damage material models applicable to high pressure hydrogen environments are therefore needed for engine design and analysis. Existing constitutive and cyclic crack initiation models were evaluated only for conditions of oxidizing environments. The main objective is to evaluate these models for applicability to high pressure hydrogen environments.
A damage-softening statistical constitutive model considering rock residual strength
NASA Astrophysics Data System (ADS)
Wang, Zhi-liang; Li, Yong-chi; Wang, J. G.
2007-01-01
Under stress, the microcracks in rock evolve (initiation, growth and coalescence) from damage to fracture with a continuous process. In order to describe this continuous process, a damage-softening statistical constitutive model for rock was proposed based on the Weibull distribution of mesoscopic element strength. This model usually adopts the Drucker-Prager criterion as its distribution parameter of mesoscopic element strength, which may produce larger damage zone in numerical simulations. This paper mainly studies the effects of strength criteria and residual strength on the performance of this damage-softening statistical constitutive model of rock. Main works include following three aspects: Firstly, the mechanical behaviors of rock are comparatively studied when the Drucker-Prager and the Mohr-Coulomb criteria are employed, respectively, as the distribution parameter. Then, a coefficient is introduced to make this constitutive model be capable of describing the residual strength of rock. Finally, a user-defined subroutine is concisely developed for this model and checked through typical strain paths. The current work lays a good foundation for further application of this model in geotechnics and geosciences.
Ma, Songyun; Scheider, Ingo; Bargmann, Swantje
2016-09-01
An anisotropic constitutive model is proposed in the framework of finite deformation to capture several damage mechanisms occurring in the microstructure of dental enamel, a hierarchical bio-composite. It provides the basis for a homogenization approach for an efficient multiscale (in this case: multiple hierarchy levels) investigation of the deformation and damage behavior. The influence of tension-compression asymmetry and fiber-matrix interaction on the nonlinear deformation behavior of dental enamel is studied by 3D micromechanical simulations under different loading conditions and fiber lengths. The complex deformation behavior and the characteristics and interaction of three damage mechanisms in the damage process of enamel are well captured. The proposed constitutive model incorporating anisotropic damage is applied to the first hierarchical level of dental enamel and validated by experimental results. The effect of the fiber orientation on the damage behavior and compressive strength is studied by comparing micro-pillar experiments of dental enamel at the first hierarchical level in multiple directions of fiber orientation. A very good agreement between computational and experimental results is found for the damage evolution process of dental enamel. PMID:27294283
NASA Astrophysics Data System (ADS)
Augustins, L.; Billardon, R.; Hild, F.
2016-01-01
The present paper details an elasto-viscoplastic constitutive model for automotive brake discs made of flake graphite cast iron. In a companion paper (Augustins et al. in Contin Mech Thermodyn, 2015), the authors proposed a one-dimensional setting appropriate for representing the complex behavior of the material (i.e., asymmetry between tensile and compressive loadings) under anisothermal conditions. The generalization of this 1D model to 3D cases on a volume element and the associated challenges are addressed. A direct transposition is not possible, and an alternative solution without unilateral conditions is first proposed. Induced anisotropic damage and associated constitutive laws are then introduced. The transition from the volume element to the real structure and the numerical implementation require a specific basis change. Brake disc simulations with this constitutive model show that unilateral conditions are needed for the friction bands. A damage deactivation procedure is therefore defined.
NASA Astrophysics Data System (ADS)
Revil-Baudard, Benoit; Cazacu, Oana; Flater, Philip; Chandola, Nitin; Alves, J. L.
2016-03-01
In this paper, we present an experimental study on plastic deformation and damage of polycrystalline pure HCP Ti, as well as modeling of the observed behavior. Mechanical characterization data were conducted, which indicate that the material is orthotropic and displays tension-compression asymmetry. The ex-situ and in-situ X-ray tomography measurements conducted reveal that damage distribution and evolution in this HCP Ti material is markedly different than in a typical FCC material such as copper. Stewart and Cazacu (2011) anisotropic elastic/plastic damage model is used to describe the behavior. All the parameters involved in this model have a clear physical significance, being related to plastic properties, and are determined from very few simple mechanical tests. It is shown that this model predicts correctly the anisotropy in plastic deformation, and its strong influence on damage distribution and damage accumulation. Specifically, for a smooth axisymmetric specimen subject to uniaxial tension, damage initiates at the center of the specimen, and is diffuse; the level of damage close to failure being very low. On the other hand, for a notched specimen subject to the same loading the model predicts that damage initiates at the outer surface of the specimen, and further grows from the outer surface to the center of the specimen, which corroborates with the in-situ tomography data.
NASA Astrophysics Data System (ADS)
Chaabane, Makram; Chaabane, Makram; Dalverny, Olivier; Deramecourt, Arnaud; Mistou, Sébastien
The super-pressure balloons developed by CNES are a great challenge in scientific ballooning. Whatever the balloon type considered (spherical, pumpkin...), it is necessary to have good knowledge of the mechanical behavior of the envelope regarding to the flight level and the lifespan of the balloon. It appears during the working stages of the super pressure balloons that these last can exploded prematurely in the course of the first hours of flight. For this reason CNES and LGP are carrying out research programs about experimentations and modelling in order to predict a good stability of the balloons flight and guarantee a life time in adequacy with the technical requirement. This study deals with multilayered polymeric film damage which induce balloons failure. These experimental and numerical study aims, are a better understanding and predicting of the damage mechanisms bringing the premature explosion of balloons. The following damages phenomena have different origins. The firsts are simple and triple wrinkles owed during the process and the stocking stages of the balloons. The second damage phenomenon is associated to the creep of the polymeric film during the flight of the balloon. The first experimental results we present in this paper, concern the mechanical characterization of three different damage phenomena. The severe damage induced by the wrinkles of the film involves a significant loss of mechanical properties. In a second part the theoretical study, concerns the choice and the development of a non linear viscoelastic coupled damage behavior model in a finite element code.
Interpretation of the Superpave IDT strength test using a viscoelastic-damage constitutive model
NASA Astrophysics Data System (ADS)
Onifade, Ibrahim; Balieu, Romain; Birgisson, Bjorn
2016-03-01
This paper presents a new interpretation for the Superpave IDT strength test based on a viscoelastic-damage framework. The framework is based on continuum damage mechanics and the thermodynamics of irreversible processes with an anisotropic damage representation. The new approach introduces considerations for the viscoelastic effects and the damage accumulation that accompanies the fracture process in the interpretation of the Superpave IDT strength test for the identification of the Dissipated Creep Strain Energy (DCSE) limit from the test result. The viscoelastic model is implemented in a Finite Element Method (FEM) program for the simulation of the Superpave IDT strength test. The DCSE values obtained using the new approach is compared with the values obtained using the conventional approach to evaluate the validity of the assumptions made in the conventional interpretation of the test results. The result shows that the conventional approach over-estimates the DCSE value with increasing estimation error at higher deformation rates.
Interpretation of the Superpave IDT strength test using a viscoelastic-damage constitutive model
NASA Astrophysics Data System (ADS)
Onifade, Ibrahim; Balieu, Romain; Birgisson, Bjorn
2016-08-01
This paper presents a new interpretation for the Superpave IDT strength test based on a viscoelastic-damage framework. The framework is based on continuum damage mechanics and the thermodynamics of irreversible processes with an anisotropic damage representation. The new approach introduces considerations for the viscoelastic effects and the damage accumulation that accompanies the fracture process in the interpretation of the Superpave IDT strength test for the identification of the Dissipated Creep Strain Energy (DCSE) limit from the test result. The viscoelastic model is implemented in a Finite Element Method (FEM) program for the simulation of the Superpave IDT strength test. The DCSE values obtained using the new approach is compared with the values obtained using the conventional approach to evaluate the validity of the assumptions made in the conventional interpretation of the test results. The result shows that the conventional approach over-estimates the DCSE value with increasing estimation error at higher deformation rates.
Probabilistic constitutive law for damage in ligaments.
Guo, Zheying; De Vita, Raffaella
2009-11-01
A new constitutive equation is presented to describe the damage evolution process in parallel-fibered collagenous tissues such as ligaments. The model is formulated by accounting for the fibrous structure of the tissues. The tissue's stress is defined as the average of the collagen fiber's stresses. The fibers are assumed to be undulated and straightened out at different stretches that are randomly defined according to a Weibull distribution. After becoming straight, each collagen fiber is assumed to be linear elastic. Damage is defined as a reduction in collagen fiber's stiffness and occurs at different stretches that are also randomly defined by a Weibull distribution. Due to the lack of experimental data, the predictions of the constitutive equation are analyzed by varying the values of its structural parameters. Moreover, the results are compared with the available stress-strain data in the biomechanics literature that evaluate damage produced by subfailure stretches in rat medial collateral ligaments. PMID:19665914
Crushed Salt Constitutive Model
Callahan, G.D.
1999-02-01
The constitutive model used to describe the deformation of crushed salt is presented in this report. Two mechanisms -- dislocation creep and grain boundary diffusional pressure solution -- are combined to form the basis for the constitutive model governing the deformation of crushed salt. The constitutive model is generalized to represent three-dimensional states of stress. Upon complete consolidation, the crushed-salt model reproduces the Multimechanism Deformation (M-D) model typically used for the Waste Isolation Pilot Plant (WIPP) host geological formation salt. New shear consolidation tests are combined with an existing database that includes hydrostatic consolidation and shear consolidation tests conducted on WIPP and southeastern New Mexico salt. Nonlinear least-squares model fitting to the database produced two sets of material parameter values for the model -- one for the shear consolidation tests and one for a combination of the shear and hydrostatic consolidation tests. Using the parameter values determined from the fitted database, the constitutive model is validated against constant strain-rate tests. Shaft seal problems are analyzed to demonstrate model-predicted consolidation of the shaft seal crushed-salt component. Based on the fitting statistics, the ability of the model to predict the test data, and the ability of the model to predict load paths and test data outside of the fitted database, the model appears to capture the creep consolidation behavior of crushed salt reasonably well.
The constitutive representation of high-temperature creep damage
NASA Technical Reports Server (NTRS)
Chan, K. S.
1988-01-01
The elastic-viscoplastic constitutive equations of Bodner-Partom were applied to modeling creep damage in a high temperature Ni-alloy, B1900 + Hf. Both tertiary creep in bulk materials and creep crack growth in flawed materials were considered. In the latter case, the energy rate line integral was used for characterizing the crack driving force, and the rate of crack extension was computed using a local damage formulation that assumed fracture was controlled by cavitation occurring within the crack-tip process zone. The results of this investigation were used to assess the evolution equation for isotropic damage utilized in the Bodner-Partom constitutive equations.
Constitutive representation of damage development and healing in WIPP salt
Chan, K.S.; Bodner, S.R.; Fossum, A.F
1994-12-31
There has been considerable interest in characterizing and modeling the constitutive behavior of rock salt with particular reference to long-term creep and creep failure. The interest is motivated by the projected use of excavated rooms in salt rock formations as repositories for nuclear waste. It is presumed that closure of those rooms by creep ultimately would encapsulate the waste material, resulting in its effective isolation. A continuum mechanics approach for treating damage healing is formulated as part of a constitutive model for describing coupled creep, fracture, and healing in rock salt. Formulation of the healing term is, described and the constitutive model is evaluated against experimental data of rock salt from the Waste Isolation Pilot Plant (WIPP) site. The results indicate that healing anistropy in WIPP salt can be modeled with an appropriate power-conjugate equivalent stress, kinetic equation, and evolution equation for damage healing.
Hammerand, Daniel Carl; Scherzinger, William Mark
2007-09-01
The Library of Advanced Materials for Engineering (LAME) provides a common repository for constitutive models that can be used in computational solid mechanics codes. A number of models including both hypoelastic (rate) and hyperelastic (total strain) constitutive forms have been implemented in LAME. The structure and testing of LAME is described in Scherzinger and Hammerand ([3] and [4]). The purpose of the present report is to describe the material models which have already been implemented into LAME. The descriptions are designed to give useful information to both analysts and code developers. Thus far, 33 non-ITAR/non-CRADA protected material models have been incorporated. These include everything from the simple isotropic linear elastic models to a number of elastic-plastic models for metals to models for honeycomb, foams, potting epoxies and rubber. A complete description of each model is outside the scope of the current report. Rather, the aim here is to delineate the properties, state variables, functions, and methods for each model. However, a brief description of some of the constitutive details is provided for a number of the material models. Where appropriate, the SAND reports available for each model have been cited. Many models have state variable aliases for some or all of their state variables. These alias names can be used for outputting desired quantities. The state variable aliases available for results output have been listed in this report. However, not all models use these aliases. For those models, no state variable names are listed. Nevertheless, the number of state variables employed by each model is always given. Currently, there are four possible functions for a material model. This report lists which of these four methods are employed in each material model. As far as analysts are concerned, this information is included only for the awareness purposes. The analyst can take confidence in the fact that model has been properly implemented
Constitutive modeling for isotropic materials
NASA Technical Reports Server (NTRS)
Lindholm, U. S.
1984-01-01
A state-of-the-art review of applicable constitutive models with selection of two for detailed comparison with a wide range of experimental tests was conducted. The experimental matrix contained uniaxial and biaxial tensile, creep, stress relaxation, and cyclic fatigue tests at temperatures to 1093 C and strain rates from .0000001 to .001/sec. Some nonisothermal cycles will also be run. The constitutive models will be incorporated into the MARC finite element structural analysis program with a demonstration computation made for advanced turbine blade configuration. In the code development work, particular emphasis is being placed on developing efficient integration algorithms for the highly nonlinear and stiff constitutive equations. Another area of emphasis is the appropriate and efficient methodology for determing constitutive constants from a minimum extent of experimental data.
Constitutive modeling for isotropic materials
NASA Technical Reports Server (NTRS)
Lindholm, Ulric S.
1985-01-01
The objective is to develop a unified constitutive model for finite element structural analysis of turbine engine hot-section components. This effort constitutes a different approach for non-linear finite-element computer codes which have heretofore been based on classical inelastic methods. The unified constitutive theory to be developed will avoid the simplifying assumptions of classical theory and should more accurately represent the behavior of superalloy materials under cyclic loading conditions and high temperature environments. During the first two years of the program, extensive experimental correlations were made with two representative unified models. The experiments were both uniaxial and biaxial at temperatures up to 1093 C (2000 F). In addition, the unified models were adopted to the MARC finite element code and used for stress analysis of notched bar and turbine blade geometries.
Constitutive modeling for isotropic materials
NASA Technical Reports Server (NTRS)
Chan, K. S.; Lindholm, U. S.; Bodner, S. R.
1988-01-01
The third and fourth years of a 4-year research program, part of the NASA HOST Program, are described. The program goals were: (1) to develop and validate unified constitutive models for isotropic materials, and (2) to demonstrate their usefulness for structural analysis of hot section components of gas turbine engines. The unified models selected for development and evaluation were those of Bodner-Partom and of Walker. The unified approach for elastic-viscoplastic constitutive equations is a viable method for representing and predicting material response characteristics in the range where strain rate and temperature dependent inelastic deformations are experienced. This conclusion is reached by extensive comparison of model calculations against the experimental results of a test program of two high temperature Ni-base alloys, B1900+Hf and Mar-M247, over a wide temperature range for a variety of deformation and thermal histories including uniaxial, multiaxial, and thermomechanical loading paths. The applicability of the Bodner-Partom and the Walker models for structural applications has been demonstrated by implementing these models into the MARC finite element code and by performing a number of analyses including thermomechanical histories on components of hot sections of gas turbine engines and benchmark notch tensile specimens. The results of the 4-year program have been published in four annual reports. The results of the base program are summarized in this report. The tasks covered include: (1) development of material test procedures, (2) thermal history effects, and (3) verification of the constitutive model for an alternative material.
Constitutive modeling for isotropic materials
NASA Technical Reports Server (NTRS)
Lindholm, Ulric S.; Chan, Kwai S.
1986-01-01
The objective of the program is to evaluate and develop existing constitutive models for use in finite-element structural analysis of turbine engine hot section components. The class of constitutive equation studied is considered unified in that all inelastic deformation including plasticity, creep, and stress relaxation are treated in a single term rather than a classical separation of plasticity (time independent) and creep (time dependent) behavior. The unified theories employed also do not utilize the classical yield surface or plastic potential concept. The models are constructed from an appropriate flow law, a scalar kinetic relation between strain rate, temperature and stress, and evolutionary equations for internal variables describing strain or work hardening, both isotropic and directional (kinematic). This and other studies have shown that the unified approach is particularly suited for determining the cyclic behavior of superalloy type blade and vane materials and is entirely compatible with three-dimensional inelastic finite-element formulations. The behavior was examined of a second nickel-base alloy, MAR-M247, and compared it with the Bodner-Partom model, further examined procedures for determining the material-specific constants in the models, and exercised the MARC code for a turbine blade under simulated flight spectrum loading. Results are summarized.
Testing of constitutive models in LAME.
Hammerand, Daniel Carl; Scherzinger, William Mark
2007-09-01
Constitutive models for computational solid mechanics codes are in LAME--the Library of Advanced Materials for Engineering. These models describe complex material behavior and are used in our finite deformation solid mechanics codes. To ensure the correct implementation of these models, regression tests have been created for constitutive models in LAME. A selection of these tests is documented here. Constitutive models are an important part of any solid mechanics code. If an analysis code is meant to provide accurate results, the constitutive models that describe the material behavior need to be implemented correctly. Ensuring the correct implementation of constitutive models is the goal of a testing procedure that is used with the Library of Advanced Materials for Engineering (LAME) (see [1] and [2]). A test suite for constitutive models can serve three purposes. First, the test problems provide the constitutive model developer a means to test the model implementation. This is an activity that is always done by any responsible constitutive model developer. Retaining the test problem in a repository where the problem can be run periodically is an excellent means of ensuring that the model continues to behave correctly. A second purpose of a test suite for constitutive models is that it gives application code developers confidence that the constitutive models work correctly. This is extremely important since any analyst that uses an application code for an engineering analysis will associate a constitutive model in LAME with the application code, not LAME. Therefore, ensuring the correct implementation of constitutive models is essential for application code teams. A third purpose of a constitutive model test suite is that it provides analysts with example problems that they can look at to understand the behavior of a specific model. Since the choice of a constitutive model, and the properties that are used in that model, have an enormous effect on the results of an
CONSTITUTIVE RELATIONSHIP OF TISSUE BEHAVIOR WITH DAMAGE ACCUMULATION OF HUMAN CORTICAL BONE
Luo, Qing; Leng, Huijie; Acuna, Rae; Dong, Xuanliang; Rong, Qiguo; Wang, Xiaodu
2010-01-01
Microdamage accumulation has been identified as a major conduit for bone tissues to absorb fracture energy. Due to the poor understanding of its underlying mechanism, however, an adequate constitutive relationship between damage accumulation and the mechanical behavior of bone has not yet been established. In this study, the constitutive relationship between the damage accumulation induced by overload and the evolution of mechanical properties of bone with incremental deformation was established based on the experimental results obtained from a novel progressive loading protocol developed in our laboratory. First, a decayed exponential model was proposed to capture the damage accumulation (modulus loss) with increasing applied strain. Next, a power law function was proposed to represent the progression of plastic deformation with damage accumulation. Finally, a linear combination of the Kohlrausch-Williams-Watts (KWW) function and Debye function was used to depict the viscoelastic behavior of bone associated with damage accumulation. The results of this study may help develop a constitutive model for predicting the mechanical behavior of cortical bone tissues. PMID:20472239
Constitutive modeling for isotropic materials
NASA Technical Reports Server (NTRS)
Ramaswamy, V. G.; Vanstone, R. H.; Dame, L. T.; Laflen, J. H.
1985-01-01
The first year of progress on a NASA-Lewis contract with the General Electric Co is documented. The purpose of this contract (NAS3-23927) is to develop and evaluate unified constitutive equations for applications to hot-path components of aircraft gas turbine engines such as high pressure turbine blades and vanes. To accomplish this goal, uniaxial, notched, and multiaxial specimens made of conventionally cast Rene 80 are being tested under conditions that simulate engine operating conditions. To reduce the raw data, automated data reduction techniques are being developed that produce computer files containing the information needed to analyze proposed constitutive theories. Described are the analytical methods being developed to determine the parameters for these nonlinear unified theories by using the reduced data files. In another activity, a dedicated finite-element computer code is being developed to use unified theories in the structural analysis of hot-section components. This code was extensively verified for one such theory by successfully predicting the strain histories measured experimentally at the notch root of complex specimens taken from complex laboratory specimens.
Constitutive modeling of inelastic anisotropic material response
NASA Technical Reports Server (NTRS)
Stouffer, D. C.
1984-01-01
A constitutive equation was developed to predict the inelastic thermomechanical response of single crystal turbine blades. These equations are essential for developing accurate finite element models of hot section components and contribute significantly to the understanding and prediction of crack initiation and propagation. The method used was limited to unified state variable constitutive equations. Two approaches to developing an anisotropic constitutive equation were reviewed. One approach was to apply the Stouffer-Bodner representation for deformation induced anisotropy to materials with an initial anisotropy such as single crystals. The second approach was to determine the global inelastic strain rate from the contribution of the slip in each of the possible crystallographic slip systems. A three dimensional finite element is being developed with a variable constitutive equation link that can be used for constitutive equation development and to predict the response of an experiment using the actual specimen geometry and loading conditions.
Crushed-salt constitutive model update
Callahan, G.D.; Loken, M.C.; Mellegard, K.D.
1998-01-01
Modifications to the constitutive model used to describe the deformation of crushed salt are presented in this report. Two mechanisms--dislocation creep and grain boundary diffusional pressure solutioning--defined previously but used separately are combined to form the basis for the constitutive model governing the deformation of crushed salt. The constitutive model is generalized to represent three-dimensional states of stress. New creep consolidation tests are combined with an existing database that includes hydrostatic consolidation and shear consolidation tests conducted on Waste Isolation Pilot Plant and southeastern New Mexico salt to determine material parameters for the constitutive model. Nonlinear least-squares model fitting to data from the shear consolidation tests and a combination of the shear and hydrostatic consolidation tests produced two sets of material parameter values for the model. The change in material parameter values from test group to test group indicates the empirical nature of the model but demonstrates improvement over earlier work with the previous models. Key improvements are the ability to capture lateral strain reversal and better resolve parameter values. To demonstrate the predictive capability of the model, each parameter value set was used to predict each of the tests in the database. Based on the fitting statistics and the ability of the model to predict the test data, the model appears to capture the creep consolidation behavior of crushed salt quite well.
New Damage Remedies for Violations of Constitutional Rights.
ERIC Educational Resources Information Center
Russell, Billy W.
1979-01-01
Examines the concept of sovereign (governmental) immunity from prosecution for violating citizens' civil liberties. Attention is given to immunity under 42 U.S.C.A. Section 1983 and under the Constitution. Available from Baylor University Law School, Waco, Texas 76703; sc $4.00. (IRT)
A constitutive mechanical model for energetic materials
Hobbs, M.L.; Baer, M.R.; Gross, R.J.
1994-06-01
Cookoff modeling of energetic materials has traditionally addressed reactive heat flow with the goal of defining the onset of runaway combustion behavior. Current modeling efforts are now aimed toward predicting the violence of the event. Combined thermal, chemical, and mechanical response must be modeled, since confinement results in pressure buildup which can breach confinement or enhance gas-phase combustion rates leading to runaway combustion behavior. Thermally induced stresses can also cause gaps which inhibit heat flow. These mechanical effects must also be included in cookoff modeling. A new reactive elastic-plastic constitutive model for micromechanical response has been developed which represents a stress-strain relation for reacting materials such as explosives, propellants, pyrotechnics, or burning foams. This micromechanical model is based on bubble mechanics. A local force balance, with mass continuity constraints, forms the basis of the constitutive model requiring input of temperature and reacted fraction. This constitutive material model has been incorporated into a quasistatic mechanics code, SANTOS. To provide temperature and reacted gas fraction, the thermal-chemical solver, XCHEM, has been coupled to SANTOS. This paper summarizes the development of the micromechanical model with material property estimates for conventional energetic materials. This study shows that large pressures can arise from small reacted fractions which implies that cookoff modeling must consider the strong interaction between thermochemistry and mechanics.
Relationships among certain joint constitutive models.
Segalman, Daniel Joseph; Starr, Michael James
2004-09-01
In a recent paper, Starr and Segalman demonstrated that any Masing model can be represented as a parallel-series Iwan model. A preponderance of the constitutive models that have been suggested for simulating mechanical joints are Masing models, and the purpose of this discussion is to demonstrate how the Iwan representation of those models can yield insight into their character. In particular, this approach can facilitate a critical comparison among numerous plausible constitutive models. It is explicitly shown that three-parameter models such as Smallwood's (Ramberg-Osgood) calculate parameters in such a manner that macro-slip is not an independent parameter, yet the model admits macro-slip. The introduction of a fourth parameter is therefore required. It is shown that when a macro-slip force is specified for the Smallwood model the result is a special case of the Segalman four-parameter model. Both of these models admit a slope discontinuity at the inception of macro-slip. A five-parameter model that has the beneficial features of Segalman's four-parameter model is proposed. This model manifests a force-displacement curve having a continuous first derivative.
Cumulative fatigue damage models
NASA Technical Reports Server (NTRS)
Mcgaw, Michael A.
1988-01-01
The problem of calculating expected component life under fatigue loading conditions is complicated by the fact that component loading histories contain, in many cases, cyclic loads of widely varying amplitudes. In such a case a cumulative damage model is required, in addition to a fatigue damage criterion, or life relationship, in order to compute the expected fatigue life. The traditional cumulative damage model used in design is the linear damage rule. This model, while being simple to use, can yield grossly unconservative results under certain loading conditions. Research at the NASA Lewis Research Center has led to the development of a nonlinear cumulative damage model, named the double damage curve approach (DDCA), that has greatly improved predictive capability. This model, which considers the life (or loading) level dependence of damage evolution, was applied successfully to two polycrystalline materials, 316 stainless steel and Haynes 188. The cumulative fatigue behavior of the PWA 1480 single-crystal material is currently being measured to determine the applicability of the DDCA for this material.
Evaluation of constitutive models for crushed salt
Callahan, G.D.; Loken, M.C. [RE Hurtado, L.D.; Hansen, F.D.
1996-05-01
Three constitutive models are recommended as candidates for describing the deformation of crushed salt. These models are generalized to three-dimensional states of stress to include the effects of mean and deviatoric stress and modified to include effects of temperature, grain size, and moisture content. A database including hydrostatic consolidation and shear consolidation tests conducted on Waste Isolation Pilot Plant (WIPP) and southeastern New Mexico salt is used to determine material parameters for the models. To evaluate the capability of the models, parameter values obtained from fitting the complete database are used to predict the individual tests. Finite element calculations of a WIPP shaft with emplaced crushed salt demonstrate the model predictions.
Constitutive Modeling of Crosslinked Nanotube Materials
NASA Technical Reports Server (NTRS)
Odegard, G. M.; Frankland, S. J. V.; Herzog, M. N.; Gates, T. S.; Fay, C. C.
2004-01-01
A non-linear, continuum-based constitutive model is developed for carbon nanotube materials in which bundles of aligned carbon nanotubes have varying amounts of crosslinks between the nanotubes. The model accounts for the non-linear elastic constitutive behavior of the material in terms of strain, and is developed using a thermodynamic energy approach. The model is used to examine the effect of the crosslinking on the overall mechanical properties of variations of the crosslinked carbon nanotube material with varying degrees of crosslinking. It is shown that the presence of the crosslinks has significant effects on the mechanical properties of the carbon nanotube materials. An increase in the transverse shear properties is observed when the nanotubes are crosslinked. However, this increase is accompanied by a decrease in axial mechanical properties of the nanotube material upon crosslinking.
Elastic-Plastic Constitutive Equation of WC-Co Cemented Carbides with Anisotropic Damage
Hayakawa, Kunio; Nakamura, Tamotsu; Tanaka, Shigekazu
2007-05-17
Elastic-plastic constitutive equation of WC-Co cemented carbides with anisotropic damage is proposed to predict a precise service life of cold forging tools. A 2nd rank symmetric tensor damage tensor is introduced in order to express the stress unilaterality; a salient difference in uniaxial behavior between tension and compression. The conventional framework of irreversible thermodynamics is used to derive the constitutive equation. The Gibbs potential is formulated as a function of stress, damage tensor, isotropic hardening variable and kinematic hardening variable. The elastic-damage constitutive equation, conjugate forces of damage, isotropic hardening and kinematic hardening variable is derived from the potential. For the kinematic hardening variable, the superposition of three kinematic hardening laws is employed in order to improve the cyclic behavior of the material. For the evolution equation of the damage tensor, the damage is assumed to progress by fracture of the Co matrix - WC particle interface and by the mechanism of fatigue, i.e. the accumulation of microscopic plastic strain in matrix and particles. By using the constitutive equations, calculation of uniaxial tensile and compressive test is performed and the results are compared with the experimental ones in the literature. Furthermore, finite element analysis on cold forward extrusion was carried out, in which the proposed constitutive equation was employed as die insert material.
Elastic-Plastic Constitutive Equation of WC-Co Cemented Carbides with Anisotropic Damage
NASA Astrophysics Data System (ADS)
Hayakawa, Kunio; Nakamura, Tamotsu; Tanaka, Shigekazu
2007-05-01
Elastic-plastic constitutive equation of WC-Co cemented carbides with anisotropic damage is proposed to predict a precise service life of cold forging tools. A 2nd rank symmetric tensor damage tensor is introduced in order to express the stress unilaterality; a salient difference in uniaxial behavior between tension and compression. The conventional framework of irreversible thermodynamics is used to derive the constitutive equation. The Gibbs potential is formulated as a function of stress, damage tensor, isotropic hardening variable and kinematic hardening variable. The elastic-damage constitutive equation, conjugate forces of damage, isotropic hardening and kinematic hardening variable is derived from the potential. For the kinematic hardening variable, the superposition of three kinematic hardening laws is employed in order to improve the cyclic behavior of the material. For the evolution equation of the damage tensor, the damage is assumed to progress by fracture of the Co matrix — WC particle interface and by the mechanism of fatigue, i.e. the accumulation of microscopic plastic strain in matrix and particles. By using the constitutive equations, calculation of uniaxial tensile and compressive test is performed and the results are compared with the experimental ones in the literature. Furthermore, finite element analysis on cold forward extrusion was carried out, in which the proposed constitutive equation was employed as die insert material.
Constitutive modeling for isotropic materials (HOST)
NASA Technical Reports Server (NTRS)
Lindholm, Ulric S.; Chan, Kwai S.; Bodner, S. R.; Weber, R. M.; Walker, K. P.; Cassenti, B. N.
1984-01-01
The results of the first year of work on a program to validate unified constitutive models for isotropic materials utilized in high temperature regions of gas turbine engines and to demonstrate their usefulness in computing stress-strain-time-temperature histories in complex three-dimensional structural components. The unified theories combine all inelastic strain-rate components in a single term avoiding, for example, treating plasticity and creep as separate response phenomena. An extensive review of existing unified theories is given and numerical methods for integrating these stiff time-temperature-dependent constitutive equations are discussed. Two particular models, those developed by Bodner and Partom and by Walker, were selected for more detailed development and evaluation against experimental tensile, creep and cyclic strain tests on specimens of a cast nickel base alloy, B19000+Hf. Initial results comparing computed and test results for tensile and cyclic straining for temperature from ambient to 982 C and strain rates from 10(exp-7) 10(exp-3) s(exp-1) are given. Some preliminary date correlations are presented also for highly non-proportional biaxial loading which demonstrate an increase in biaxial cyclic hardening rate over uniaxial or proportional loading conditions. Initial work has begun on the implementation of both constitutive models in the MARC finite element computer code.
Constitutive modeling for isotropic materials (HOST)
NASA Technical Reports Server (NTRS)
Chan, Kwai S.; Lindholm, Ulric S.; Bodner, S. R.; Hill, Jeff T.; Weber, R. M.; Meyer, T. G.
1986-01-01
The results of the third year of work on a program which is part of the NASA Hot Section Technology program (HOST) are presented. The goals of this program are: (1) the development of unified constitutive models for rate dependent isotropic materials; and (2) the demonstration of the use of unified models in structural analyses of hot section components of gas turbine engines. The unified models selected for development and evaluation are those of Bodner-Partom and of Walker. A test procedure was developed for assisting the generation of a data base for the Bodner-Partom model using a relatively small number of specimens. This test procedure involved performing a tensile test at a temperature of interest that involves a succession of strain-rate changes. The results for B1900+Hf indicate that material constants related to hardening and thermal recovery can be obtained on the basis of such a procedure. Strain aging, thermal recovery, and unexpected material variations, however, preluded an accurate determination of the strain-rate sensitivity parameter is this exercise. The effects of casting grain size on the constitutive behavior of B1900+Hf were studied and no particular grain size effect was observed. A systematic procedure was also developed for determining the material constants in the Bodner-Partom model. Both the new test procedure and the method for determining material constants were applied to the alternate material, Mar-M247 . Test data including tensile, creep, cyclic and nonproportional biaxial (tension/torsion) loading were collected. Good correlations were obtained between the Bodner-Partom model and experiments. A literature survey was conducted to assess the effects of thermal history on the constitutive behavior of metals. Thermal history effects are expected to be present at temperature regimes where strain aging and change of microstructure are important. Possible modifications to the Bodner-Partom model to account for these effects are outlined
Constitutive modeling for isotropic materials (HOST)
NASA Technical Reports Server (NTRS)
Lindholm, U. S.; Chan, K. S.; Bodner, S. R.; Weber, R. M.; Walker, K. P.; Cassenti, B. N.
1985-01-01
This report presents the results of the second year of work on a problem which is part of the NASA HOST Program. Its goals are: (1) to develop and validate unified constitutive models for isotropic materials, and (2) to demonstrate their usefulness for structural analyses of hot section components of gas turbine engines. The unified models selected for development and evaluation are that of Bodner-Partom and Walker. For model evaluation purposes, a large constitutive data base is generated for a B1900 + Hf alloy by performing uniaxial tensile, creep, cyclic, stress relation, and thermomechanical fatigue (TMF) tests as well as biaxial (tension/torsion) tests under proportional and nonproportional loading over a wide range of strain rates and temperatures. Systematic approaches for evaluating material constants from a small subset of the data base are developed. Correlations of the uniaxial and biaxial tests data with the theories of Bodner-Partom and Walker are performed to establish the accuracy, range of applicability, and integability of the models. Both models are implemented in the MARC finite element computer code and used for TMF analyses. Benchmark notch round experiments are conducted and the results compared with finite-element analyses using the MARC code and the Walker model.
NASA Astrophysics Data System (ADS)
Labergere, C.; Saanouni, K.; Benafia, S.; Galmiche, J.; Sulaiman, H.
2013-05-01
This paper presents the modelling and adaptive numerical simulation of the fine blanking process. Thermodynamically-consistent constitutive equations, strongly coupled with ductile damage, together with specific boundary conditions (particular command of forces on blank holder and counterpunch) are presented. This model is implemented into ABAQUS/EXPLICIT using the Vumat user subroutine and connected with an adaptive 2D remeshing procedure. The different material parameters are identified for the steel S600MC using experimental tensile tests conducted until the final fracture. A parametric study aiming to examine the sensitivity of the process parameters (die radius, clearance die/punch) to the punch force and fracture surfaces topology (convex zone, sheared zone, fracture zone and the burr).
Constitutive modelling of composite biopolymer networks.
Fallqvist, B; Kroon, M
2016-04-21
The mechanical behaviour of biopolymer networks is to a large extent determined at a microstructural level where the characteristics of individual filaments and the interactions between them determine the response at a macroscopic level. Phenomena such as viscoelasticity and strain-hardening followed by strain-softening are observed experimentally in these networks, often due to microstructural changes (such as filament sliding, rupture and cross-link debonding). Further, composite structures can also be formed with vastly different mechanical properties as compared to the individual networks. In this present paper, we present a constitutive model presented in a continuum framework aimed at capturing these effects. Special care is taken to formulate thermodynamically consistent evolution laws for dissipative effects. This model, incorporating possible anisotropic network properties, is based on a strain energy function, split into an isochoric and a volumetric part. Generalisation to three dimensions is performed by numerical integration over the unit sphere. Model predictions indicate that the constitutive model is well able to predict the elastic and viscoelastic response of biological networks, and to an extent also composite structures. PMID:26851172
Multiscale Constitutive Modeling of Asphalt Concrete
NASA Astrophysics Data System (ADS)
Underwood, Benjamin Shane
Multiscale modeling of asphalt concrete has become a popular technique for gaining improved insight into the physical mechanisms that affect the material's behavior and ultimately its performance. This type of modeling considers asphalt concrete, not as a homogeneous mass, but rather as an assemblage of materials at different characteristic length scales. For proper modeling these characteristic scales should be functionally definable and should have known properties. Thus far, research in this area has not focused significant attention on functionally defining what the characteristic scales within asphalt concrete should be. Instead, many have made assumptions on the characteristic scales and even the characteristic behaviors of these scales with little to no support. This research addresses these shortcomings by directly evaluating the microstructure of the material and uses these results to create materials of different characteristic length scales as they exist within the asphalt concrete mixture. The objectives of this work are to; 1) develop mechanistic models for the linear viscoelastic (LVE) and damage behaviors in asphalt concrete at different length scales and 2) develop a mechanistic, mechanistic/empirical, or phenomenological formulation to link the different length scales into a model capable of predicting the effects of microstructural changes on the linear viscoelastic behaviors of asphalt concrete mixture, e.g., a microstructure association model for asphalt concrete mixture. Through the microstructural study it is found that asphalt concrete mixture can be considered as a build-up of three different phases; asphalt mastic, fine aggregate matrix (FAM), and finally the coarse aggregate particles. The asphalt mastic is found to exist as a homogenous material throughout the mixture and FAM, and the filler content within this material is consistent with the volumetric averaged concentration, which can be calculated from the job mix formula. It is also
Improvements to constitutive material model for fabrics
NASA Astrophysics Data System (ADS)
Morea, Mihai I.
2011-12-01
The high strength to weight ratio of woven fabric offers a cost effective solution to be used in a containment system for aircraft propulsion engines. Currently, Kevlar is the only Federal Aviation Administration (FAA) approved fabric for usage in systems intended to mitigate fan blade-out events. This research builds on an earlier constitutive model of Kevlar 49 fabric developed at Arizona State University (ASU) with the addition of new and improved modeling details. Latest stress strain experiments provided new and valuable data used to modify the material model post peak behavior. These changes reveal an overall improvement of the Finite Element (FE) model's ability to predict experimental results. First, the steel projectile is modeled using Johnson-Cook material model and provides a more realistic behavior in the FE ballistic models. This is particularly noticeable when comparing FE models with laboratory tests where large deformations in projectiles are observed. Second, follow-up analysis of the results obtained through the new picture frame tests conducted at ASU provides new values for the shear moduli and corresponding strains. The new approach for analysis of data from picture frame tests combines digital image analysis and a two-level factorial optimization formulation. Finally, an additional improvement in the material model for Kevlar involves checking the convergence at variation of mesh density of fabrics. The study performed and described herein shows the converging trend, therefore validating the FE model.
A constitutive model for predicting rock fragmentation by blasting
NASA Astrophysics Data System (ADS)
Liu, Liqing; Katsabanis, P. D.
1996-05-01
This paper describes the development of a constitutive model for predicting rock damage and fragment size distribution due to explosive loading. The model is based on continuum mechanics and statistical fracture mechanics, assuming the rock medium is an isotropic, continuous and homogeneous material with pre-existing microcracks. In the model, damage to the rock medium is defined as the probability of fracture at a given crack density which is obtained by integrating a crack density function over time. The material constants used in the crack density function are determined according to their physical meaning. The minimum damage value at which the fragments may be formed is set by assuming that there is at least one crack per unit volume. Fragment size distribution is achieved considering the equilibrium between kinetic energy and surface energy. The simulation results are in good accordance with the theory of explosive energy partitioning in a rock medium. As a result, the damage zone induced by the shock wave and stress waves, once established, remains stable. The model has been calibrated by field crater blasting and small scale bench blasting tests.
Constitutive Models for Shape Memory Alloy Polycrystals
NASA Technical Reports Server (NTRS)
Comstock, R. J., Jr.; Somerday, M.; Wert, J. A.
1996-01-01
Shape memory alloys (SMA) exhibiting the superelastic or one-way effects can produce large recoverable strains upon application of a stress. In single crystals this stress and resulting strain are very orientation dependent. We show experimental stress/strain curves for a Ni-Al single crystal for various loading orientations. Also shown are model predictions; the open and closed circles indicate recoverable strains obtained at various stages in the transformation process. Because of the strong orientation dependence of shape memory properties, crystallographic texture can be expected to play an important role in the mechanical behavior of polycrystalline SMA. It is desirable to formulate a constitutive model to better understand and exploit the unique properties of SMA.
Lee, H.K.; Simunovic, S.
1999-09-01
A micromechanical damage constitutive model is presented to predict the overall elastoplastic behavior and damage evolution in random carbon fiber polymer matrix composites (RFPCs).To estimate the overall elastoplastic damage responses,an effective yield criterion is derived based on the ensemble-volume averaging process and first-order effects of eigenstrains due to the existence of spheroidal (prolate) fibers.The proposed effective yield criterion,to ether with the assumed overall associative plastic flow rule and hardening law, constitutes the analytical foundation for the estimation of effective elastoplastic behavior of ductile matrix composites.First,an effective elastoplastic constitutive dama e model for aligned fiber-reinforced composites is proposed.A micromechanical damage constitutive model for RFPCs is then developed.The average process over all orientations upon overning constitutive field equations and overall yield function for aligned fiber-reinforced composites i s performed to obtain the constitutive relations and effective yield function of RFPCs.The discrete numerical integration algorithms and the continuum tan ent operator are also presented to implement the proposed dama e constitutive model.The dama e constitutive model forms the basis for the pro ressive crushing in composite structures under impact loading.
Mesoscale constitutive modeling of magnetic dispersions.
Bhandar, Anand S; Wiest, John M
2003-01-15
A constitutive model for dispersions of acicular magnetic particles has been developed by modeling the particles as rigid dumbbells dispersed in a solvent. The effects of Brownian motion, anisotropic hydrodynamic drag, a steric force in the form of the Maier-Saupe potential, and, most importantly, a mean-field magnetic potential are included in the model. The development is similar to previous models for liquid-crystalline polymers. The model predicts multiple orientational states for the dispersion, and this phase behavior is described in terms of an orientational order parameter S and an average alignment parameter J; the latter is introduced because the magnetic particles have distinguishable direction due to polarity. A transition from isotropic to nematic phases at equilibrium is predicted. Multiple nematic phases-both prolate and oblate-are predicted in the presence of steady shear flow and external magnetic field parallel to the flow. The effect of increasing magnetic interparticle interactions and particle concentration is also presented. Comparisons with experimental data for the steady shear viscosity show very good agreement. PMID:16256493
Constitutive modeling for single crystal superalloys
NASA Technical Reports Server (NTRS)
Stouffer, D. C.; Jayaraman, N.; Sheh, M.; Alden, D.
1986-01-01
The inelastic response of single crystal gamma/gamma prime superalloys is quite different from the behavior of polycrystalline nickel base superalloys. Upto a critical temperature the yield stress of single crystal alloys is a function of the material orientation relative to the direction of the applied stress and the material exhibits significant tension/compression asymmetry. This behavior is primarily due to slip on the octahedral slip system. Above the critical temperature there is a sharp drop in the yield stress, cube slip becomes more predominant and the tension/compression asymmetry is reduced. Similar orientation and tension/compression asymmetry is observed in creep and secondary creep above the critical temperature is inferred to occur by octahedral slip. There are two exceptions to this behavior. First, loading near the (111) orientation exhibits cube slip at all temperatures, and; second, loading near the (001) orientation produces only octahedral slip at all temperatures. The constitutive model is based on separating the total global strain into elastic and inelastic components. This model is developed and briefly discussed.
Failure Behavior and Constitutive Model of Weakly Consolidated Soft Rock
Wang, Wei-ming; Zhao, Zeng-hui; Wang, Yong-ji; Gao, Xin
2013-01-01
Mining areas in western China are mainly located in soft rock strata with poor bearing capacity. In order to make the deformation failure mechanism and strength behavior of weakly consolidated soft mudstone and coal rock hosted in Ili No. 4 mine of Xinjiang area clear, some uniaxial and triaxial compression tests were carried out according to the samples of rocks gathered in the studied area, respectively. Meanwhile, a damage constitutive model which considered the initial damage was established by introducing a damage variable and a correction coefficient. A linearization process method was introduced according to the characteristics of the fitting curve and experimental data. The results showed that samples under different moisture contents and confining pressures presented completely different failure mechanism. The given model could accurately describe the elastic and plastic yield characteristics as well as the strain softening behavior of collected samples at postpeak stage. Moreover, the model could precisely reflect the relationship between the elastic modulus and confining pressure at prepeak stage. PMID:24489511
Constitutive model development for lightly cemented scrap rubber tire chips
NASA Astrophysics Data System (ADS)
Tsoi, Wa Yeung
2005-11-01
Rubber-soil (lightly cemented scrap rubber tire chips) is a promising solution for the global scrap tire problem. It is also a promising material for various geotechnical engineering applications because of its advantageous properties such as lightweight, high permeability, high ductility and ease to cast. Intensive laboratory studies, mostly under triaxial testing, are conducted and a constitutive model is proposed. Firstly, the effective stress principle is proven applicable for Rubber-soil under normal engineering stress level although the inter-particle contact area is large. Secondly, because of the gravel-sized surface voids on the testing samples, membrane penetration is serious so an integrated remedy method is proposed, where the surface voids are patched up first and then a lubricated reinforced membrane is dressed on. It is found that the volumetric deformation of Rubber-soil is very recoverable even after 20% volume contraction but the over consolidation results illustrate a decreasing stiffness, which is believed due to volumetric damage. Shearing on the sample gives typical results as sands where clear phase transformation is observed, but the strains involved are higher and more recoverable. Besides, shear stiffness is observed decreasing with deformation, which is believed due to shear damage. There are other observations such as the difference in the curvatures of unloading and reloading curves in CD tests, which might be a frictional phenomenon. Based on the laboratory observations and on the analogy of a continuum spring-block system, a constitutive model termed as Analogical Model is proposed. Fifteen model parameters are involved but most of them are typical soil parameters. The remaining ones have clear physical meanings and can be easily calibrated. It is found that the model can satisfactorily capture many features observed from the experiments, such as hardening, softening, apparent permanent deformations, stiffness decay due to damage
Constitutive modeling of shock response of polytetrafluoroethylene
NASA Astrophysics Data System (ADS)
Resnyansky, A. D.; Bourne, N. K.; Millett, J. C. F.; Brown, E. N.
2011-08-01
Polytetrafluoroethylene (PTFE) is a polymer with a simple atomic structure that shows complex behavior under pressure and demonstrates a highly variable metastable phase structure in shock waves with amorphous and crystalline components. In turn, the crystalline component has four known phases with the high-pressure transition of the crystalline domain from crystalline phase IV at ambient through phase II to III. At the same time, as has been recently studied using spectrometry, the crystalline region nucleates from the amorphous one with load. Stress and velocity shock-wave profiles acquired recently with embedded gauges demonstrate features that may be related to the impedance mismatch between the phase domains subjected to such transitions resulting in variations of mechanical and thermophysical characteristics. We consider the inter-phase non-equilibrium and the amorphous-to-crystalline and inter-crystalline transitions that are associated with the high pressure and temperature transformations under shock wave loading as possible candidates for the analysis. The present work utilizes a multi-phase constitutive model that considers strength effects to describe the observed response under shock loading of the PTFE material. Experimental plate impact shock-wave histories are compared with calculated profiles using kinetics describing the transitions. The study demonstrates that the inter-phase pressure non-equilibrium of the state parameters plays the key role in the delay of the shock wave attenuation. At the same time, the forward transition associated with the crystallization might be responsible for the velocity spike in the experimental velocity profiles at high impact velocity and the modulus variation at low impact velocity. On the other hand, an accelerated attenuation of the velocity in the rarefaction wave is associated with another transition resulting in the residual crystallinity change during unloading.
Life prediction and constitutive models for anisotropic materials
NASA Technical Reports Server (NTRS)
Bill, R. C.
1982-01-01
The intent of this program is to develop a basic understanding of cyclic creep-fatigue deformation mechanisms and damage accumulation, a capability for reliable life prediction, and the ability to model the constitutive behavior of anisotropic single crystal (SC) and directionally solidified or recrystallized (DSR) comprise the program, and the work breakdown for each option reflects a distinct concern for two classes of anisotropic materials, SC and DSR materials, at temperatures encountered in the primary gas path (airfoil temperatures), and at temperatures typical of the blade root attachment and shank area. Work directed toward the higher temperature area of concern in the primary gas path includes effects of coatings on the behavior and properties of the materials of interest. The blade root attachment work areas will address the effects of stress concentrations associated with attachment features.
Material modeling and structural analysis with the microplane constitutive model
NASA Astrophysics Data System (ADS)
Brocca, Michele
The microplane model is a versatile and powerful approach to constitutive modeling in which the stress-strain relations are defined in terms of vectors rather than tensors on planes of all possible orientations. Such planes are called the microplanes and are representative of the microstructure of the material. The microplane model with kinematic constraint has been successfully employed in the past in the modeling of concrete, soils, ice, rocks, fiber composites and other quasibrittle materials. The microplane model provides a powerful and efficient numerical and theoretical framework for the development and implementation of constitutive models for any kind of material. The dissertation presents a review of the background from which the microplane model stems, highlighting differences and similarities with other approaches. The basic structure of the microplane model is then presented, together with its extension to finite strain deformation. To show the effectiveness of the microplane model approach, some examples are given demonstrating applications of microplane models in structural analysis with the finite element method. Some new constitutive models are also introduced for materials characterized by very different properties and microstructures, showing that the approach is indeed very versatile and provides a robust basis for the study of a broad range of problems. New models are introduced for metal plasticity, shape memory alloys and cellular materials. The new models are compared quantitatively with the existing models and experimental data. In particular, the newly introduced microplane models for metal plasticity are compared with the classical J2-flow theory for incremental plasticity. An existing microplane model for concrete is employed in finite element analysis of the 'tube-squash' test, in which concrete undergoes very large deviatoric deformation, and of the size effect in compressive failure of concrete columns. The microplane model for shape
Towards a Simple Constitutive Model for Bread Dough
NASA Astrophysics Data System (ADS)
Tanner, Roger I.
2008-07-01
Wheat flour dough is an example of a soft solid material consisting of a gluten (rubbery) network with starch particles as a filler. The volume fraction of the starch filler is high-typically 60%. A computer-friendly constitutive model has been lacking for this type of material and here we report on progress towards finding such a model. The model must describe the response to small strains, simple shearing starting from rest, simple elongation, biaxial straining, recoil and various other transient flows. A viscoelastic Lodge-type model involving a damage function. which depends on strain from an initial reference state fits the given data well, and it is also able to predict the thickness at exit from dough sheeting, which has been a long-standing unsolved puzzle. The model also shows an apparent rate-dependent yield stress, although no explicit yield stress is built into the model. This behaviour agrees with the early (1934) observations of Schofield and Scott Blair on dough recoil after unloading.
Constitutive Modeling and Numerical Simulation of Frp Confined Concrete Specimens
NASA Astrophysics Data System (ADS)
Smitha, Gopinath; Ramachandramurthy, Avadhanam; Nagesh, Ranganatha Iyer; Shahulhameed, Eduvammal Kunhimoideen
2014-09-01
Fiber-reinforced polymer (FRP) composites are generally used for the seismic retrofit of concrete members to enhance their strength and ductility. In the present work, the confining effect of Carbon Fiber-Reinforced Polymer (CFRP) composite layers has been investigated by numerical simulation. The numerical simulation has been carried out using nonlinear finite element analysis (FEA) to predict the response behaviour of CFRP-wrapped concrete cylinders. The nonlinear behaviour of concrete in compression and the linear elastic behaviour of CFRP has been modeled using an appropriate constitutive relationship. A cohesive model has been developed for modeling the interface between the concrete and CFRP. The interaction and damage failure criteria between the concrete to the cohesive element and the cohesive element to the CFRP has also been accounted for in the modeling. The response behaviour of the wrapped concrete specimen has been compared with the proposed interface model and with a perfectly bonded condition. The results obtained from the present study showed good agreement with the experimental load-displacement response and the failure pattern in the literature. Further, a sensitivity analysis has been carried out to study the effect of the number of layers of CFRP on the concrete specimens. It has been observed that wrapping with two layers was found to be the optimum, beyond which the response becomes flexible but with a higher load-carrying capacity
Salajegheh, Nima; Abedrabbo, Nader; Pourboghrat, Farhang
2005-08-05
An efficient integration algorithm for continuum damage based elastoplastic constitutive equations is implemented in LS-DYNA. The isotropic damage parameter is defined as the ratio of the damaged surface area over the total cross section area of the representative volume element. This parameter is incorporated into the integration algorithm as an internal variable. The developed damage model is then implemented in the FEM code LS-DYNA as user material subroutine (UMAT). Pure stretch experiments of a hemispherical punch are carried out for copper sheets and the results are compared against the predictions of the implemented damage model. Evaluation of damage parameters is carried out and the optimized values that correctly predicted the failure in the sheet are reported. Prediction of failure in the numerical analysis is performed through element deletion using the critical damage value. The set of failure parameters which accurately predict the failure behavior in copper sheets compared to experimental data is reported as well.
NASA Astrophysics Data System (ADS)
Salajegheh, Nima; Abedrabbo, Nader; Pourboghrat, Farhang
2005-08-01
An efficient integration algorithm for continuum damage based elastoplastic constitutive equations is implemented in LS-DYNA. The isotropic damage parameter is defined as the ratio of the damaged surface area over the total cross section area of the representative volume element. This parameter is incorporated into the integration algorithm as an internal variable. The developed damage model is then implemented in the FEM code LS-DYNA as user material subroutine (UMAT). Pure stretch experiments of a hemispherical punch are carried out for copper sheets and the results are compared against the predictions of the implemented damage model. Evaluation of damage parameters is carried out and the optimized values that correctly predicted the failure in the sheet are reported. Prediction of failure in the numerical analysis is performed through element deletion using the critical damage value. The set of failure parameters which accurately predict the failure behavior in copper sheets compared to experimental data is reported as well.
NASA Astrophysics Data System (ADS)
Gray, G. T., III; Livescu, V.; Rigg, P. A.; Trujillo, C. P.; Cady, C. M.; Chen, S. R.; Carpenter, J. S.; Lienert, T. J.; Fensin, S.
2015-09-01
For additive manufacturing (AM), the certification and qualification paradigm needs to evolve as there exists no "ASTM-type" additive manufacturing certified process or AM-material produced specifications. Accordingly, utilization of AM materials to meet engineering applications requires quantification of the constitutive properties of these evolving materials in comparison to conventionally-manufactured metals and alloys. Cylinders of 316L SS were produced using a LENS MR-7 laser additive manufacturing system from Optomec (Albuquerque, NM) equipped with a 1kW Yb-fiber laser. The microstructure of the AM-316L SS is detailed in both the as-built condition and following heat-treatments designed to obtain full recrystallization. The constitutive behavior as a function of strain rate and temperature is presented and compared to that of nominal annealed wrought 316L SS plate. The dynamic damage evolution and failure response of all three materials was probed using flyer-plate impact driven spallation experiments at a peak stress of 4.5 GPa to examine incipient spallation response. The spall strength of AM-produced 316L SS was found to be very similar for the peak shock stress studied to that of annealed wrought or AM-316L SS following recrystallization. The damage evolution as a function of microstructure was characterized using optical metallography.
Multivariate pluvial flood damage models
Van Ootegem, Luc; Verhofstadt, Elsy; Van Herck, Kristine; Creten, Tom
2015-09-15
Depth–damage-functions, relating the monetary flood damage to the depth of the inundation, are commonly used in the case of fluvial floods (floods caused by a river overflowing). We construct four multivariate damage models for pluvial floods (caused by extreme rainfall) by differentiating on the one hand between ground floor floods and basement floods and on the other hand between damage to residential buildings and damage to housing contents. We do not only take into account the effect of flood-depth on damage, but also incorporate the effects of non-hazard indicators (building characteristics, behavioural indicators and socio-economic variables). By using a Tobit-estimation technique on identified victims of pluvial floods in Flanders (Belgium), we take into account the effect of cases of reported zero damage. Our results show that the flood depth is an important predictor of damage, but with a diverging impact between ground floor floods and basement floods. Also non-hazard indicators are important. For example being aware of the risk just before the water enters the building reduces content damage considerably, underlining the importance of warning systems and policy in this case of pluvial floods. - Highlights: • Prediction of damage of pluvial floods using also non-hazard information • We include ‘no damage cases’ using a Tobit model. • The damage of flood depth is stronger for ground floor than for basement floods. • Non-hazard indicators are especially important for content damage. • Potential gain of policies that increase awareness of flood risks.
Modeling of glass fracture damage using continuum damage mechanics - Static spherical indentation
Sun, Xin; Khaleel, Mohammad A.
2004-07-01
Continuum damage mechanics based constitutive model is used to study the stone-impact resistance of automotive windshields. An axisymmetric finite element model is created to simulate the transient dynamic response and impact induced damge tensors for laminated glass layers subject to stone-impact loading. The windshield glass consists of two glass outer layers laminated by a thin poly-vinyl butyral (PVB) layer. The constitutive behavior of the glass layers is simulated suing continuum damage mechanics model with linear damage evolution. The PVB layer is modeled with linear viscoelastic solid. The model is used to predict and examine damage patterns on different glass surfaces for different windshield designs including variations in ply thickness and curvatures.
Constitutive modeling of fiber-reinforced cement composites
NASA Astrophysics Data System (ADS)
Boulfiza, Mohamed
a diffused damage is more appropriate in the pre-peak regime whereas, NLFM is more suitable in the post-peak stage where the opening and propagation of a major crack will control the response of the material and not a deformation in a continuum sense as opposed to the pre-cracking zone. Tensile and compressive tests have been carried out for the sole purpose of calibrating the constitutive models proposed and/or developed in this thesis for FRC materials. The suitability of the models in predicting the response of different structural members has been performed by comparing the models' forecasts with experimental results carried out by the author, as well as experimental results from the literature. The different models proposed in this thesis have the possibility to account for the presence of fibers in the matrix, and give fairly good results for both high fiber volume fractions (vsb{f}≥2%) and low fiber volume fractions (vsb{f}<2%). Use of interface elements in a finite element code has been shown to be a powerful tool in analyzing the behavior of concrete substrate-FRC repair materials by the introduction of a zero thickness layer of interface elements to account for the interface properties which usually control the effectiveness of the repair material. ftnsp1NLFM: Non Linear Fracture Mechanics.
A Thermodynamically Consistent Damage Model for Advanced Composites
NASA Technical Reports Server (NTRS)
Maimi, Pere; Camanho, Pedro P.; Mayugo, Joan-Andreu; Davila, Carlos G.
2006-01-01
A continuum damage model for the prediction of damage onset and structural collapse of structures manufactured in fiber-reinforced plastic laminates is proposed. The principal damage mechanisms occurring in the longitudinal and transverse directions of a ply are represented by a damage tensor that is fixed in space. Crack closure under load reversal effects are taken into account using damage variables established as a function of the sign of the components of the stress tensor. Damage activation functions based on the LaRC04 failure criteria are used to predict the different damage mechanisms occurring at the ply level. The constitutive damage model is implemented in a finite element code. The objectivity of the numerical model is assured by regularizing the dissipated energy at a material point using Bazant's Crack Band Model. To verify the accuracy of the approach, analyses of coupon specimens were performed, and the numerical predictions were compared with experimental data.
A New Uncoupled Viscoplastic Constitutive Model
NASA Technical Reports Server (NTRS)
Bradley, W. L.; Yuen, S.
1983-01-01
A new uncoupled viscoplastic model has been proposed along with experiments and analysis to define the various material constraints. Distinguishing between rate sensitive and rate insensitive strain allows the rate sensitive strain to be modelled over a wide range of temperatures with very little variation in the stress component 'n'. Furthermore, it allows the rounded corners on stress-strain hysteresis loops to be achieved very naturally.
A phenomenological constitutive model for low density polyurethane foams
Neilsen, M.K.; Morgan, H.S.; Krieg, R.D.
1987-04-01
Results from a series of hydrostatic and triaxial compression tests which were performed on polyurethane foams are presented in this report. These tests indicate that the volumetric and deviatoric parts of the foam behavior are strongly coupled. This coupling behavior could not be captured with any of several commonly used plasticity models. Thus, a new constitutive model was developed. This new model was based on a decomposition of the foam response into two parts: (1) response of the polymer skeleton, and (2) response of the air inside the cells. The air contribution was completely volumetric. The new constitutive model was implemented in two finite element codes, SANCHO and PRONTO. Results from a series of analyses completed with these codes indicated that the new constitutive model captured all of the foam behaviors that had been observed in the experiments. Finally, a typical dynamic problem was analyzed using the new constitutive model and other constitutive models to demonstrate differences between the models. Results from this series of analyses indicated that the new constitutive model generated displacement and acceleration predictions that were between predictions obtained using the other models. This result was expected. 9 refs., 45 figs., 4 tabs.
Study on the Constitutive Model for Jointed Rock Mass
Xu, Qiang; Chen, Jianyun; Li, Jing; Zhao, Chunfeng; Yuan, Chenyang
2015-01-01
A new elasto-plastic constitutive model for jointed rock mass, which can consider the persistence ratio in different visual angle and anisotropic increase of plastic strain, is proposed. The proposed the yield strength criterion, which is anisotropic, is not only related to friction angle and cohesion of jointed rock masses at the visual angle but also related to the intersection angle between the visual angle and the directions of the principal stresses. Some numerical examples are given to analyze and verify the proposed constitutive model. The results show the proposed constitutive model has high precision to calculate displacement, stress and plastic strain and can be applied in engineering analysis. PMID:25885695
Constitutive Modeling of Piezoelectric Polymer Composites
NASA Technical Reports Server (NTRS)
Odegard, Gregory M.; Gates, Tom (Technical Monitor)
2003-01-01
A new modeling approach is proposed for predicting the bulk electromechanical properties of piezoelectric composites. The proposed model offers the same level of convenience as the well-known Mori-Tanaka method. In addition, it is shown to yield predicted properties that are, in most cases, more accurate or equally as accurate as the Mori-Tanaka scheme. In particular, the proposed method is used to determine the electromechanical properties of four piezoelectric polymer composite materials as a function of inclusion volume fraction. The predicted properties are compared to those calculated using the Mori-Tanaka and finite element methods.
Evaluation of potential crushed-salt constitutive models
Callahan, G.D.; Loken, M.C.; Sambeek, L.L. Van; Chen, R.; Pfeifle, T.W.; Nieland, J.D.
1995-12-01
Constitutive models describing the deformation of crushed salt are presented in this report. Ten constitutive models with potential to describe the phenomenological and micromechanical processes for crushed salt were selected from a literature search. Three of these ten constitutive models, termed Sjaardema-Krieg, Zeuch, and Spiers models, were adopted as candidate constitutive models. The candidate constitutive models were generalized in a consistent manner to three-dimensional states of stress and modified to include the effects of temperature, grain size, and moisture content. A database including hydrostatic consolidation and shear consolidation tests conducted on Waste Isolation Pilot Plant and southeastern New Mexico salt was used to determine material parameters for the candidate constitutive models. Nonlinear least-squares model fitting to data from the hydrostatic consolidation tests, the shear consolidation tests, and a combination of the shear and hydrostatic tests produces three sets of material parameter values for the candidate models. The change in material parameter values from test group to test group indicates the empirical nature of the models. To evaluate the predictive capability of the candidate models, each parameter value set was used to predict each of the tests in the database. Based on the fitting statistics and the ability of the models to predict the test data, the Spiers model appeared to perform slightly better than the other two candidate models. The work reported here is a first-of-its kind evaluation of constitutive models for reconsolidation of crushed salt. Questions remain to be answered. Deficiencies in models and databases are identified and recommendations for future work are made. 85 refs.
Remarks on ConstitutiveModeling of Nanofluids
Massoudi, Mehrdad; Tran X. Phuoc
2012-01-01
Nanofluids are made by adding nanoscale particles in low volumetric fractions to a fluid in order to enhance or improve their rheological, mechanical, optical, and thermal properties. The base fluid can be any liquid such as oil, water, ethylene glycol, or conventional fluid mixtures. Limited available studies on nanofluid viscosity have been reported [1-19]. In most of these studies, the behavior of the viscosity and the shear stress of nanofluids have been interpreted using the widely used empirical model developed by Casson [20].
The courthouse doors do not close: constitutional challenges to non-economic damage caps.
Bashshur, Ramona
2011-01-01
Following efforts at addressing health care reform that spanned decades, the US Congress passed massive health reform legislation in 2010, with key provisions to be implemented over the next few years. This legislation has been heralded as the ultimate legislative response to the spiraling cost of care and inequity of access to care. Yet, these reforms have left many unanswered questions about the perennial issue of tort reform, in particular, caps on non-economic damages. This article begins with a broad perspective on tort reform and the debate surrounding the issue, and ends with a search for common ground where the threat of litigation may be reduced while the constitutional rights of citizens remain safeguarded. PMID:21812354
Acute MUS81 depletion leads to replication fork slowing and a constitutive DNA damage response
Xing, Meichun; Wang, Xiaohui; Palmai-Pallag, Timea; Shen, Huahao; Helleday, Thomas; Hickson, Ian D.; Ying, Songmin
2015-01-01
The MUS81 protein belongs to a conserved family of DNA structure-specific nucleases that play important roles in DNA replication and repair. Inactivation of the Mus81 gene in mice has no major deleterious consequences for embryonic development, although cancer susceptibility has been reported. We have investigated the role of MUS81 in human cells by acutely depleting the protein using shRNAs. We found that MUS81 depletion from human fibroblasts leads to accumulation of ssDNA and a constitutive DNA damage response that ultimately activates cellular senescence. Moreover, we show that MUS81 is required for efficient replication fork progression during an unperturbed S-phase, and for recovery of productive replication following replication stalling. These results demonstrate essential roles for the MUS81 nuclease in maintenance of replication fork integrity. PMID:26415217
Constitutive modeling of shock response of PTFE
Brown, Eric N; Reanyansky, Anatoly D; Bourne, Neil K; Millett, Jeremy C F
2009-01-01
The PTFE (polytetrafluoroethylene) material is complex and attracts attention of the shock physics researchers because it has amorphous and crystalline components. In turn, the crystalline component has four known phases with the high pressure transition to phase III. At the same time, as has been recently studied using spectrometry, the crystalline region is growing with load. Stress and velocity shock-wave profiles acquired recently with embedded gauges demonstrate feature that may be related to impedance mismatches between the regions subjected to some transitions resulting in density and modulus variations. We consider the above mentioned amorphous-to-crystalline transition and the high pressure Phase II-to-III transitions as possible candidates for the analysis. The present work utilizes a multi-phase rate sensitive model to describe shock response of the PTFE material. One-dimensional experimental shock wave profiles are compared with calculated profiles with the kinetics describing the transitions. The objective of this study is to understand the role of the various transitions in the shock response of PTFE.
Analysis of a microcrack model and constitutive equations for time-dependent dilatancy of rocks
NASA Astrophysics Data System (ADS)
Chen, Zuan
2003-11-01
Based on experimental observations and theoretical analyses, the author introduces an ideal microcrack model in which an array of cracks with the same shape and initial size is distributed evenly in rocks. The mechanism of creep dilatancy for rocks is analysed theoretically. Initiation, propagation and linkage of pre-existing microcracks during creep are well described. Also, the relationship between the velocity of microcrack growth and the duration of the creep process is derived numerically. The relationship agrees well with the character of typical experimental creep curves, and includes three stages of creep. Then the damage constitutive equations and damage evolution equations, which describe the dilatant behaviour of rocks, are presented. Because the dilatant estimated value is taken as the damage variable, the relationship between the microscopic model and the macroscopic constitutive equations is established. In this way the mechanical behaviour of rocks can be predicted.
Asymmetric Damage Segregation Constitutes an Emergent Population-Level Stress Response.
Vedel, Søren; Nunns, Harry; Košmrlj, Andrej; Semsey, Szabolcs; Trusina, Ala
2016-08-01
Asymmetric damage segregation (ADS) is a mechanism for increasing population fitness through non-random, asymmetric partitioning of damaged macromolecules at cell division. ADS has been reported across multiple organisms, though the measured effects on fitness of individuals are often small. Here, we introduce a cell-lineage-based framework that quantifies the population-wide effects of ADS and then verify our results experimentally in E. coli under heat and antibiotic stress. Using an experimentally validated mathematical model, we find that the beneficial effect of ADS increases with stress. In effect, low-damage subpopulations divide faster and amplify within the population acting like a positive feedback loop whose strength scales with stress. Analysis of protein aggregates shows that the degree of asymmetric inheritance is damage dependent in single cells. Together our results indicate that, despite small effects in single cell, ADS exerts a strong beneficial effect on the population level and arises from the redistribution of damage within a population, through both single-cell and population-level feedback. PMID:27426983
Constitutive models for rubber networks undergoing simultaneous crosslinking and scission.
Thompson, Aidan Patrick; Curro, John G.; Rottach, Dana R.; Grest, Gary Stephen; Budzien, Joanne L.; Lo, David Chi S.
2006-01-01
Constitutive models for chemically reacting networks are formulated based on a generalization of the independent network hypothesis. These models account for the coupling between chemical reaction and strain histories, and have been tested by comparison with microscopic molecular dynamics simulations. An essential feature of these models is the introduction of stress transfer functions that describe the interdependence between crosslinks formed and broken at various strains. Efforts are underway to implement these constitutive models into the finite element code Adagio. Preliminary results are shown that illustrate the effects of changing crosslinking and scission rates and history.
Xu, Yidong; Qian, Chunxiang
2013-01-01
Based on meso-damage mechanics and finite element analysis, the aim of this paper is to describe the feasibility of the Gurson–Tvergaard–Needleman (GTN) constitutive model in describing the tensile behavior of corroded reinforcing bars. The orthogonal test results showed that different fracture pattern and the related damage evolution process can be simulated by choosing different material parameters of GTN constitutive model. Compared with failure parameters, the two constitutive parameters are significant factors affecting the tensile strength. Both the nominal yield and ultimate tensile strength decrease markedly with the increase of constitutive parameters. Combining with the latest data and trial-and-error method, the suitable material parameters of GTN constitutive model were adopted to simulate the tensile behavior of corroded reinforcing bars in concrete under carbonation environment attack. The numerical predictions can not only agree very well with experimental measurements, but also simplify the finite element modeling process. PMID:23342140
Damage modeling for Taylor impact simulations
NASA Astrophysics Data System (ADS)
Anderson, C. E., Jr.; Chocron, I. S.; Nicholls, A. E.
2006-08-01
G. I. Taylor showed that dynamic material properties could be deduced from the impact of a projectile against a rigid boundary. The Taylor anvil test became very useful with the advent of numerical simulations and has been used to infer and/or to validate material constitutive constants. A new experimental facility has been developed to conduct Taylor anvil impacts to support validation of constitutive constants used in simulations. Typically, numerical simulations are conducted assuming 2-D cylindrical symmetry, but such computations cannot hope to capture the damage observed in higher velocity experiments. A computational study was initiated to examine the ability to simulate damage and subsequent deformation of the Taylor specimens. Three-dimensional simulations, using the Johnson-Cook damage model, were conducted with the nonlinear Eulerian wavecode CTH. The results of the simulations are compared to experimental deformations of 6061-T6 aluminum specimens as a function of impact velocity, and conclusions regarding the ability to simulate fracture and reproduce the observed deformations are summarized.
Requirements for energy based constitutive modeling in tire mechanics
NASA Astrophysics Data System (ADS)
Luchini, John R.; Peters, Jim M.; Mars, Will V.
1995-08-01
The history, requirements, and theoretical basis of a new energy based constitutive model for (rubber) material elasticity, hysteresis, and failure are presented. Energy based elasticity is handled by many constitutive models, both in one dimension and in three dimensions. Conversion of mechanical energy to heat can be modeled with viscoelasticity or as structural hysteresis. We are seeking unification of elasticity, hysteresis, and failure mechanisms such as fatigue and wear. An energy state characterization for failure criteria of (rubber) materials may provide this unification and also help explain the interaction of temperature effects with failure mechanisms which are described as creation of growth of internal crack surface. Improved structural modeling of tires with FEM should result from such a unified constitutive theory. The theory will also guide experimental work and should enable better interpretation of the results of computational stress analyses.
Requirements for energy based constitutive modeling in tire mechanics
NASA Technical Reports Server (NTRS)
Luchini, John R.; Peters, Jim M.; Mars, Will V.
1995-01-01
The history, requirements, and theoretical basis of a new energy based constitutive model for (rubber) material elasticity, hysteresis, and failure are presented. Energy based elasticity is handled by many constitutive models, both in one dimension and in three dimensions. Conversion of mechanical energy to heat can be modeled with viscoelasticity or as structural hysteresis. We are seeking unification of elasticity, hysteresis, and failure mechanisms such as fatigue and wear. An energy state characterization for failure criteria of (rubber) materials may provide this unification and also help explain the interaction of temperature effects with failure mechanisms which are described as creation of growth of internal crack surface. Improved structural modeling of tires with FEM should result from such a unified constitutive theory. The theory will also guide experimental work and should enable better interpretation of the results of computational stress analyses.
Deformation modeling and constitutive modeling for anisotropic superalloys
NASA Technical Reports Server (NTRS)
Milligan, Walter W.; Antolovich, Stephen D.
1989-01-01
A study of deformation mechanisms in the single crystal superalloy PWA 1480 was conducted. Monotonic and cyclic tests were conducted from 20 to 1093 C. Both (001) and near-(123) crystals were tested, at strain rates of 0.5 and 50 percent/minute. The deformation behavior could be grouped into two temperature regimes: low temperatures, below 760 C; and high temperatures, above 820 to 950 C depending on the strain rate. At low temperatures, the mechanical behavior was very anisotropic. An orientation dependent CRSS, a tension-compression asymmetry, and anisotropic strain hardening were all observed. The material was deformed by planar octahedral slip. The anisotropic properties were correlated with the ease of cube cross-slip, as well as the number of active slip systems. At high temperatures, the material was isotropic, and deformed by homogeneous gamma by-pass. It was found that the temperature dependence of the formation of superlattice-intrinsic stacking faults was responsible for the local minimum in the CRSS of this alloy at 400 C. It was proposed that the cube cross-slip process must be reversible. This was used to explain the reversible tension-compression asymmetry, and was used to study models of cross-slip. As a result, the cross-slip model proposed by Paidar, Pope and Vitek was found to be consistent with the proposed slip reversibility. The results were related to anisotropic viscoplastic constitutive models. The model proposed by Walter and Jordan was found to be capable of modeling all aspects of the material anisotropy. Temperature and strain rate boundaries for the model were proposed, and guidelines for numerical experiments were proposed.
The anisotropic material constitutive models for the human cornea.
Li, Long-yuan; Tighe, Brian
2006-03-01
This paper presents an anisotropic analysis model for the human cornea. The model is based on the assumption that the fibrils in the cornea are organised into lamellae, which may have preferential orientation along the superior-inferior and nasal-temporal directions, while the alignment of lamellae with different orientations is assumed to be random. Hence, the cornea can be regarded as a laminated composite shell. The constitutive equation describing the relationships between membrane forces, bending moments, and membrane strains, bending curvatures are derived. The influences of lamella orientations and the random alignment of lamellae on the stiffness coefficients of the constitutive equation are discussed. PMID:16426861
Unified constitutive model for single crystal deformation behavior with applications
NASA Technical Reports Server (NTRS)
Walker, K. P.; Meyer, T. G.; Jordan, E. H.
1988-01-01
Single crystal materials are being used in gas turbine airfoils and are candidates for other hot section components because of their increased temperature capabilities and resistance to thermal fatigue. Development of a constitutive model which assesses the inelastic behavior of these materials has been studied in 2 NASA programs: Life Prediction and Constitutive Models for Engine Hot Section Anisotropic Materials and Biaxial Constitutive Equation Development for Single Crystals. The model has been fit to a large body of constitutive data for single crystal PWA 1480 material. The model uses a unified approach for computing total inelastic strains (creep plus plasticity) on crystallographic slip systems reproducing observed directional and strain rate effects as a natural consequence of the summed slip system quantities. The model includes several of the effects that have been reported to influence deformation in single crystal materials, such as shear stress, latent hardening, and cross slip. The model is operational in a commercial Finite Element code and is being installed in a Boundary Element Method code.
Constitutive modeling of human liver based on in vivo measurements.
Mazza, Edoardo; Grau, Patrick; Hollenstein, Marc; Bajka, Michael
2008-01-01
In vivo aspiration experiments on human livers are analyzed and material parameters for a non-linear-viscoelastic constitutive model are determined. A novel procedure is applied for the inverse analysis that accounts for the initial tissue deformation in the experiment and for the non-homogeneity of liver tissue. A numerical model is used consisting of a surface layer (capsule) and an underlying non-linear-viscoelastic solid (parenchyma). The capsule is modeled as hyperelastic membrane using data from measurements on bovine and human tissue. In a two step optimization procedure the set of constitutive model parameters for the "average" response of liver parenchyma is obtained. The proposed model is in line with literature values of high strain rate elastic modulus obtained from dynamic elastography. The model can be used to predict the nonlinear, time dependent behavior of human liver in computer simulations related to surgery training and planning. PMID:18982669
Probabilistic constitutive relationships for cyclic material strength models
NASA Technical Reports Server (NTRS)
Boyce, L.; Chamis, C. C.
1988-01-01
A methodology is developed that provides a probabilistic treatment for the lifetime of structural components of aerospace propulsion systems subjected to fatigue. Material strength degradation models, based on primitive variables, include both a fatigue strength reduction model and a fatigue crack growth model. Probabilistic analysis is based on simulation, and both maximum entropy and maximum penalized likelihood methods are used for the generation of probability density functions. The resulting constitutive relationships are included in several computer programs.
The Constitutive Modeling of Thin Films with Randon Material Wrinkles
NASA Technical Reports Server (NTRS)
Murphey, Thomas W.; Mikulas, Martin M.
2001-01-01
Material wrinkles drastically alter the structural constitutive properties of thin films. Normally linear elastic materials, when wrinkled, become highly nonlinear and initially inelastic. Stiffness' reduced by 99% and negative Poisson's ratios are typically observed. This paper presents an effective continuum constitutive model for the elastic effects of material wrinkles in thin films. The model considers general two-dimensional stress and strain states (simultaneous bi-axial and shear stress/strain) and neglects out of plane bending. The constitutive model is derived from a traditional mechanics analysis of an idealized physical model of random material wrinkles. Model parameters are the directly measurable wrinkle characteristics of amplitude and wavelength. For these reasons, the equations are mechanistic and deterministic. The model is compared with bi-axial tensile test data for wrinkled Kaptong(Registered Trademark) HN and is shown to deterministically predict strain as a function of stress with an average RMS error of 22%. On average, fitting the model to test data yields an RMS error of 1.2%
Numerical considerations in the development and implementation of constitutive models
NASA Technical Reports Server (NTRS)
Haisler, W. E.; Imbrie, P. K.
1985-01-01
Several unified constitutive models were tested in uniaxial form by specifying input strain histories and comparing output stress histories. The purpose of the tests was to evaluate several time integration methods with regard to accuracy, stability, and computational economy. The sensitivity of the models to slight changes in input constants was also investigated. Results are presented for In100 at 1350 F and Hastelloy-X at 1800 F.
Rate dependent constitutive models for fiber reinforced polymer composites
NASA Technical Reports Server (NTRS)
Gates, Thomas S.
1990-01-01
A literature survey was conducted to assess the state-of-the-art in rate dependent constitutive models for continuous fiber reinforced polymer matrix composite (PMC) materials. Several recent models which include formulations for describing plasticity, viscoelasticity, viscoplasticity, and rate-dependent phenomenon such as creep and stress relaxation are outlined and compared. When appropriate, these comparisons include brief descriptions of the mathematical formulations, the test procedures required for generating material constants, and details of available data comparing test results to analytical predictions.
Unified constitutive modeling for proportional and nonproportional cyclic plasticity responses
NASA Astrophysics Data System (ADS)
Krishna, Shree
Several features of cyclic plasticity, e.g. cyclic hardening/softening, ratcheting, relaxation, and their dependence on strain range, nonproportionality of loading, time, and temperature determine the stress-strain responses of materials under cyclic loading. Numerous efforts have been made in the past decades to characterize and model these responses. Many of these responses can be simulated reasonably by the existing constitutive models, but the same models would fail in simulating the structural responses, local stress-strain or global deformation. One of the reasons for this deficiency is that the constitutive models are not robust enough to simulate the cyclic plasticity responses when they interact with each other. This deficiency can be understood better or resolved by developing and validating constitutive models against a broad set of experimental responses and two or more of the responses interacting with each other. This dissertation develops a unified constitutive model by studying the cyclic plasticity features in an integrated manner and validating the model by simulating a broad set of proportional and nonproportional cyclic plasticity responses. The study demonstrates the drawbacks of the existing nonlinear kinematic hardening model originally developed by Chaboche and then develop and incorporate novel ideas into the model for improving its cyclic response simulations. The Chaboche model is modified by incorporating strain-range dependent cyclic hardening/softening through the kinematic hardening rule parameters, in addition to the conventional method of using only the isotropic hardening parameters. The nonproportional loading memory parameters of Tanaka and of Benallal and Marquis are incorporated to study the influence of nonproportionality. The model is assessed by simulating hysteresis loop shape, cyclic hardening-softening, cross-effect, cyclic relaxation, subsequent cyclic softening, and finally a series of ratcheting responses under
Hyperelastic anisotropic microplane constitutive model for annulus fibrosus.
Caner, Ferhun C; Guo, Zaoyang; Moran, Brian; Bazant, Zdenek P; Carol, Ignacio
2007-10-01
In a recent paper, Peng et al. (2006, "An Anisotropic Hyperelastic Constitutive Model With Fiber-Matrix Interaction for the Human Annulus Fibrosis," ASME J. Appl. Mech., 73(5), pp. 815-824) developed an anisotropic hyperelastic constitutive model for the human annulus fibrosus in which fiber-matrix interaction plays a crucial role in simulating experimental observations reported in the literature. Later, Guo et al. (2006, "A Composites-Based Hyperelastic Constitutive Model for Soft Tissue With Application to the Human Fibrosis," J. Mech. Phys. Solids, 54(9), pp. 1952-1971) used fiber reinforced continuum mechanics theory to formulate a model in which the fiber-matrix interaction was simulated using only composite effect. It was shown in these studies that the classical anisotropic hyperelastic constitutive models for soft tissue, which do not account for this shear interaction, cannot accurately simulate the test data on human annulus fibrosus. In this study, we show that the microplane model for soft tissue developed by Caner and Carol (2006, "Microplane Constitutive Model and Computational Framework for Blood Vessel Tissue," ASME J. Biomech. Eng., 128(3), pp. 419-427) can be adjusted for human annulus fibrosus and the resulting model can accurately simulate the experimental observations without explicit fiber-matrix interaction because, in microplane model, the shear interaction between the individual fibers distributed in the tissue provides the required additional rigidity to explain these experimental facts. The intensity of the shear interaction between the fibers can be adjusted by adjusting the spread in the distribution while keeping the total amount of the fiber constant. A comparison of results obtained from (i) a fiber-matrix parallel coupling model, which does not account for the fiber-matrix interaction, (ii) the same model but enriched with fiber-matrix interaction, and (iii) microplane model for soft tissue adapted to annulus fibrosus with two
Modeling Fatigue Damage in Long-Fiber Thermoplastics
Nguyen, Ba Nghiep; Kunc, Vlastimil; Bapanapalli, Satish K.
2009-10-30
This paper applies a fatigue damage model recently developed for injection-molded long-fiber thermoplastics (LFTs) to predict the modulus reduction and fatigue lifetime of glass/polyamide 6,6 (PA6,6) specimens. The fatigue model uses a multiscale mechanistic approach to describe fatigue damage accumulation in these materials subjected to cyclic loading. Micromechanical modeling using a modified Eshelby-Mori-Tanaka approach combined with averaging techniques for fiber length and orientation distributions is performed to establish the stiffness reduction relation for the composite as a function of the microcrack volume fraction. Next, continuum damage mechanics and a thermodynamic formulation are used to derive the constitutive relations and the damage evolution law. The fatigue damage model has been implemented in the ABAQUS finite element code and has been applied to analyze fatigue of the studied glass/PA6,6 specimens. The predictions agree well with the experimental results.
Development of a viscoelastic continuum damage model for cyclic loading
NASA Astrophysics Data System (ADS)
Sullivan, R. W.
2008-12-01
A previously developed spectrum model for linear viscoelastic behavior of solids is used to describe the rate-dependent damage growth of a time dependent material under cyclic loading. Through the use of the iterative solution of a special Volterra integral equation, the cyclic strain history is described. The spectrum-based model is generalized for any strain rate and any uniaxial load history to formulate the damage function. Damage evolution in the body is described through the use of a rate-type evolution law which uses a pseudo strain to express the viscoelastic constitutive equation with damage. The resulting damage function is used to formulate a residual strength model. The methodology presented is demonstrated by comparing the peak values of the computed cyclic strain history as well as the residual strength model predictions to the experimental data of a polymer matrix composite.
Temperature Dependent Constitutive Modeling for Magnesium Alloy Sheet
Lee, Jong K.; Lee, June K.; Kim, Hyung S.; Kim, Heon Y.
2010-06-15
Magnesium alloys have been increasingly used in automotive and electronic industries because of their excellent strength to weight ratio and EMI shielding properties. However, magnesium alloys have low formability at room temperature due to their unique mechanical behavior (twinning and untwining), prompting for forming at an elevated temperature. In this study, a temperature dependent constitutive model for magnesium alloy (AZ31B) sheet is developed. A hardening law based on non linear kinematic hardening model is used to consider Bauschinger effect properly. Material parameters are determined from a series of uni-axial cyclic experiments (T-C-T or C-T-C) with the temperature ranging 150-250 deg. C. The influence of temperature on the constitutive equation is introduced by the material parameters assumed to be functions of temperature. Fitting process of the assumed model to measured data is presented and the results are compared.
Unified constitutive models for high-temperature structural applications
NASA Technical Reports Server (NTRS)
Lindholm, U. S.; Chan, K. S.; Bodner, S. R.; Weber, R. M.; Walker, K. P.
1988-01-01
Unified constitutive models are characterized by the use of a single inelastic strain rate term for treating all aspects of inelastic deformation, including plasticity, creep, and stress relaxation under monotonic or cyclic loading. The structure of this class of constitutive theory pertinent for high temperature structural applications is first outlined and discussed. The effectiveness of the unified approach for representing high temperature deformation of Ni-base alloys is then evaluated by extensive comparison of experimental data and predictions of the Bodner-Partom and the Walker models. The use of the unified approach for hot section structural component analyses is demonstrated by applying the Walker model in finite element analyses of a benchmark notch problem and a turbine blade problem.
Temperature Dependent Constitutive Modeling for Magnesium Alloy Sheet
NASA Astrophysics Data System (ADS)
Lee, Jong K.; Lee, June K.; Kim, Hyung S.; Kim, Heon Y.
2010-06-01
Magnesium alloys have been increasingly used in automotive and electronic industries because of their excellent strength to weight ratio and EMI shielding properties. However, magnesium alloys have low formability at room temperature due to their unique mechanical behavior (twinning and untwining), prompting for forming at an elevated temperature. In this study, a temperature dependent constitutive model for magnesium alloy (AZ31B) sheet is developed. A hardening law based on non linear kinematic hardening model is used to consider Bauschinger effect properly. Material parameters are determined from a series of uni-axial cyclic experiments (T-C-T or C-T-C) with the temperature ranging 150-250° C. The influence of temperature on the constitutive equation is introduced by the material parameters assumed to be functions of temperature. Fitting process of the assumed model to measured data is presented and the results are compared.
Comparison of two laryngeal tissue fiber constitutive models
NASA Astrophysics Data System (ADS)
Hunter, Eric J.; Palaparthi, Anil Kumar Reddy; Siegmund, Thomas; Chan, Roger W.
2014-02-01
Biological tissues are complex time-dependent materials, and the best choice of the appropriate time-dependent constitutive description is not evident. This report reviews two constitutive models (a modified Kelvin model and a two-network Ogden-Boyce model) in the characterization of the passive stress-strain properties of laryngeal tissue under tensile deformation. The two models are compared, as are the automated methods for parameterization of tissue stress-strain data (a brute force vs. a common optimization method). Sensitivity (error curves) of parameters from both models and the optimized parameter set are calculated and contrast by optimizing to the same tissue stress-strain data. Both models adequately characterized empirical stress-strain datasets and could be used to recreate a good likeness of the data. Nevertheless, parameters in both models were sensitive to measurement errors or uncertainties in stress-strain, which would greatly hinder the confidence in those parameters. The modified Kelvin model emerges as a potential better choice for phonation models which use a tissue model as one component, or for general comparisons of the mechanical properties of one type of tissue to another (e.g., axial stress nonlinearity). In contrast, the Ogden-Boyce model would be more appropriate to provide a basic understanding of the tissue's mechanical response with better insights into the tissue's physical characteristics in terms of standard engineering metrics such as shear modulus and viscosity.
A review of nonlinear constitutive models for metals
NASA Technical Reports Server (NTRS)
Allen, David H.; Harris, Charles E.
1990-01-01
Over the past two decades a number of thermomechanical constitutive theories have been proposed for viscoplastic metals. These models are in most cases similar in that they utilize a set of internal state variables which provide locally averaged representations of microphysical phenomena such as dislocation rearrangement and grain boundary sliding. The state of development of several of these models is now at the point where accurate theoretical solutions can be obtained for a wide variety of structural problems at elevated temperatures. The fundamentals of viscoplasticity are briefly reviewed and a general framework is outlined. Several of the more prominent models are reviewed, and predictions from models are compared to experimental results.
Fault models and constitutive laws across the lithosphere
NASA Astrophysics Data System (ADS)
Shimamoto, T.
2011-12-01
Establishment of fault model is important not only for modeling earthquake cycles (stress accumulation, earthquake generation and afterslip), but also for analyzing tectonics of lithosphere. Since Sibson (1977, J. Geol. Soc. London) proposed a famous fault model, several fault models have been proposed (Scholz, 1988, Geol. Rundschau; Shimamoto, 1989, J. Struct. Geol.; Kawamoto and Shimamoto, 1998, Tectonophy). There has not been much progress in fault models since then, and even those fault models had limited applications in the modeling earthquakes and tectonics because no constitutive laws describing brittle to high-temperature ductile deformation across the lithosphere have been proposed. Moreover there was no additional experimental data reported to cover the brittle-ductile transition under large shearing deformation. However, the situation has been changing since Shimamoto (2004, JpGU) and Shimamoto and Noda, 2010, AGU) proposed an empirical friction to flow law which describes the transition from friction to fully plastic flow under shear for halite. Only frictional constitutive parameters and parameters in flow law are used and properties in the transitional regime can be predicted once those parameters are known. Thus this law provides a working model for reanalyzing diverse fault properties such as clay-bearing faults, for planning experimental researches to produce friction to flow behavior for realistic rocks, and for modeling fault and plate-boundary behaviors including generation of large earthquakes. I will summarize the current status on fault models and friction to flow constitutive laws across the lithosphere focusing the following aspects. (1) Friction to flow transition for important rocks. Existing friction and flows laws will be combined to propose constitutive property across the lithosphere (e.g., rate and state friction law combined with flow law for diabase). I will show how such a law can be used in the modeling using 2D modeling of
Mesoscale constitutive modeling of non-crystallizing filled elastomers
NASA Astrophysics Data System (ADS)
Harish, Ajay B.; Wriggers, Peter; Jungk, Juliane; Hojdis, Nils; Recker, Carla
2016-04-01
Elastomers are exceptional materials owing to their ability to undergo large deformations before failure. However, due to their very low stiffness, they are not always suitable for industrial applications. Addition of filler particles provides reinforcing effects and thus enhances the material properties that render them more versatile for applications like tyres etc. However, deformation behavior of filled polymers is accompanied by several nonlinear effects like Mullins and Payne effect. To this day, the physical and chemical changes resulting in such nonlinear effect remain an active area of research. In this work, we develop a heterogeneous (or multiphase) constitutive model at the mesoscale explicitly considering filler particle aggregates, elastomeric matrix and their mechanical interaction through an approximate interface layer. The developed constitutive model is used to demonstrate cluster breakage, also, as one of the possible sources for Mullins effect observed in non-crystallizing filled elastomers.
A variational constitutive model for porous metal plasticity
NASA Astrophysics Data System (ADS)
Weinberg, K.; Mota, A.; Ortiz, M.
2006-01-01
This paper presents a variational formulation of viscoplastic constitutive updates for porous elastoplastic materials. The material model combines von Mises plasticity with volumetric plastic expansion as induced, e.g., by the growth of voids and defects in metals. The finite deformation theory is based on the multiplicative decomposition of the deformation gradient and an internal variable formulation of continuum thermodynamics. By the use of logarithmic and exponential mappings the stress update algorithms are extended from small strains to finite deformations. Thus the time-discretized version of the porous-viscoplastic constitutive updates is described in a fully variational manner. The range of behavior predicted by the model and the performance of the variational update are demonstrated by its application to the forced expansion and fragmentation of U-6%Nb rings.
Dynamic mechanical behavior and the constitutive model of concrete subjected to impact loadings
NASA Astrophysics Data System (ADS)
Ning, Jianguo; Liu, Haifeng; Shang, Lin
2008-11-01
Based on the theory of consecutive damage mechanics, micro-mechanics, statistics and the visco-plastic constitutive equation of Perzyna, a coupled model of damage and plasticity is developed to describe the complex behavior of concrete subjected to impact loadings. In this model, some suppositions about deformation of the material and evolution of the damage are made. First, concrete is macroscopically assumed to be homogeneous and consecutive, while it is microscopically filled with large amounts of micro-crack and micro-void defects. Second, the damage evolution of the micro-cracks is caused by the nucleation, growth and coalescence of the micro-cracks due to the interior tensile stress in concrete, which leads to a degradation in the strength and stiffness of concrete. Third, compaction of concrete is physically a collapse of the material micro-void. It produces irreversible plastic strains in the material and, at the same time, an increase in the bulk modulus. Fourth, there is no interaction between the micro-crack and the micro-void. Last, when the damage reaches a critical value, the concrete may fail totally. The model parameters for concrete are determined by plate impact experiments. The model predictions fit the experimental results well. So the model can be used to simulate the dynamic mechanical behavior of concrete under impact loadings.
A constitutive model of nanocomposite hydrogels with nanoparticle crosslinkers
NASA Astrophysics Data System (ADS)
Wang, Qiming; Gao, Zheming
2016-09-01
Nanocomposite hydrogels with only nanoparticle crosslinkers exhibit extraordinarily higher stretchability and toughness than the conventional organically crosslinked hydrogels, thus showing great potential in the applications of artificial muscles and cartilages. Despite their potential, the microscopic mechanics details underlying their mechanical performance have remained largely elusive. Here, we develop a constitutive model of the nanoparticle hydrogels to elucidate the microscopic mechanics behaviors, including the microarchitecture and evolution of the nanoparticle crosslinked polymer chains during the mechanical deformation. The constitutive model enables us to understand the Mullins effect of the nanocomposite hydrogels, and the effects of nanoparticle concentrations and sizes on their cyclic stress-strain behaviors. The theory is quantitatively validated by the tensile tests on a nanocomposite hydrogel with nanosilica crosslinkers. The theory can also be extended to explain the mechanical behaviors of existing hydrogels with nanoclay crosslinkers, and the necking instability of the composite hydrogels with both nanoparticle crosslinkers and organic crosslinkers. We expect that this constitutive model can be further exploited to reveal mechanics behaviors of novel particle-polymer chain interactions, and to design unprecedented hydrogels with both high stretchability and toughness.
Slag Behavior in Gasifiers. Part II: Constitutive Modeling of Slag
Massoudi, Mehrdad; Wang, Ping
2013-02-07
The viscosity of slag and the thermal conductivity of ash deposits are among two of the most important constitutive parameters that need to be studied. The accurate formulation or representations of the (transport) properties of coal present a special challenge of modeling efforts in computational fluid dynamics applications. Studies have indicated that slag viscosity must be within a certain range of temperatures for tapping and the membrane wall to be accessible, for example, between 1,300 °C and 1,500 °C, the viscosity is approximately 25 Pa·s. As the operating temperature decreases, the slag cools and solid crystals begin to form. Since slag behaves as a non-linear fluid, we discuss the constitutive modeling of slag and the important parameters that must be studied. We propose a new constitutive model, where the stress tensor not only has a yield stress part, but it also has a viscous part with a shear rate dependency of the viscosity, along with temperature and concentration dependency, while allowing for the possibility of the normal stress effects. In Part I, we reviewed, identify and discuss the key coal ash properties and the operating conditions impacting slag behavior.
Bayesian calibration of hyperelastic constitutive models of soft tissue.
Madireddy, Sandeep; Sista, Bhargava; Vemaganti, Kumar
2016-06-01
There is inherent variability in the experimental response used to characterize the hyperelastic mechanical response of soft tissues. This has to be accounted for while estimating the parameters in the constitutive models to obtain reliable estimates of the quantities of interest. The traditional least squares method of parameter estimation does not give due importance to this variability. We use a Bayesian calibration framework based on nested Monte Carlo sampling to account for the variability in the experimental data and its effect on the estimated parameters through a systematic probability-based treatment. We consider three different constitutive models to represent the hyperelastic nature of soft tissue: Mooney-Rivlin model, exponential model, and Ogden model. Three stress-strain data sets corresponding to the deformation of agarose gel, bovine liver tissue, and porcine brain tissue are considered. Bayesian fits and parameter estimates are compared with the corresponding least squares values. Finally, we propagate the uncertainty in the parameters to a quantity of interest (QoI), namely the force-indentation response, to study the effect of model form on the values of the QoI. Our results show that the quality of the fit alone is insufficient to determine the adequacy of the model, and due importance has to be given to the maximum likelihood value, the landscape of the likelihood distribution, and model complexity. PMID:26751706
Constitutive modeling of crimped collagen fibrils in soft tissues.
Grytz, Rafael; Meschke, Günther
2009-10-01
A microstructurally oriented constitutive formulation for the hyperelastic response of crimped collagen fibrils existing in soft connective tissues is proposed. The model is based on observations that collagen fibrils embedded in a soft matrix crimp into a smooth three-dimensional pattern when unloaded. Following ideas presented by Beskos and Jenkins [Beskos, D., Jenkins, J., 1975. A mechanical model for mammalian tendon. ASME Journal of Applied Mechanics 42, 755-758] and Freed and Doehring [Freed, A., Doehring, T., 2005. Elastic model for crimped collagen fibrils. Journal of Biomechanical Engineering 127, 587-593] the collagen fibril crimp is approximated by a cylindrical helix to represent the constitutive behavior of the hierarchical organized substructure of biological tissues at the fibrillar level. The model is derived from the nonlinear axial force-stretch relationship of an extensible helical spring, including the full extension of the spring as a limit case. The geometrically nonlinear solution of the extensible helical spring is carried out by an iterative procedure. The model only requires one material parameter and two geometrical parameters to be determined from experiments. The ability of the proposed model to reproduce the biomechanical response of fibrous tissues is demonstrated for fascicles from rat tail tendons, for porcine cornea strips, and for bovine Achilles tendons. PMID:19627859
A constitutive model for magnetostriction based on thermodynamic framework
NASA Astrophysics Data System (ADS)
Ho, Kwangsoo
2016-08-01
This work presents a general framework for the continuum-based formulation of dissipative materials with magneto-mechanical coupling in the viewpoint of irreversible thermodynamics. The thermodynamically consistent model developed for the magnetic hysteresis is extended to include the magnetostrictive effect. The dissipative and hysteretic response of magnetostrictive materials is captured through the introduction of internal state variables. The evolution rate of magnetostrictive strain as well as magnetization is derived from thermodynamic and dissipative potentials in accordance with the general principles of thermodynamics. It is then demonstrated that the constitutive model is competent to describe the magneto-mechanical behavior by comparing simulation results with the experimental data reported in the literature.
Life prediction and constitutive models for engine hot section
NASA Technical Reports Server (NTRS)
Swanson, G. A.; Meyer, T. G.; Nissley, D. M.
1986-01-01
The purpose of this program is to develop life prediction models for coated anisotropic materials used in gas turbine airfoils. In the program, two single crystal alloys and two coatings are being tested. These include PWA 1480, Alloy 185, overlay coating (PWA 286), and aluminide coating (PWA 273). Constitutive models are also being developed for these materials to predict the time independent (plastic) and time dependent (creep) strain histories of the materials in the lab tests and for actual design conditions. This nonlinear material behavior is particularly important for high temperature gas turbine applications and is basic to any life prediction system. Some of the accomplishments of the program are highlighted.
Image guided constitutive modeling of the silicone brain phantom
NASA Astrophysics Data System (ADS)
Puzrin, Alexander; Skrinjar, Oskar; Ozan, Cem; Kim, Sihyun; Mukundan, Srinivasan
2005-04-01
The goal of this work is to develop reliable constitutive models of the mechanical behavior of the in-vivo human brain tissue for applications in neurosurgery. We propose to define the mechanical properties of the brain tissue in-vivo, by taking the global MR or CT images of a brain response to ventriculostomy - the relief of the elevated intracranial pressure. 3D image analysis translates these images into displacement fields, which by using inverse analysis allow for the constitutive models of the brain tissue to be developed. We term this approach Image Guided Constitutive Modeling (IGCM). The presented paper demonstrates performance of the IGCM in the controlled environment: on the silicone brain phantoms closely simulating the in-vivo brain geometry, mechanical properties and boundary conditions. The phantom of the left hemisphere of human brain was cast using silicon gel. An inflatable rubber membrane was placed inside the phantom to model the lateral ventricle. The experiments were carried out in a specially designed setup in a CT scanner with submillimeter isotropic voxels. The non-communicative hydrocephalus and ventriculostomy were simulated by consequently inflating and deflating the internal rubber membrane. The obtained images were analyzed to derive displacement fields, meshed, and incorporated into ABAQUS. The subsequent Inverse Finite Element Analysis (based on Levenberg-Marquardt algorithm) allowed for optimization of the parameters of the Mooney-Rivlin non-linear elastic model for the phantom material. The calculated mechanical properties were consistent with those obtained from the element tests, providing justification for the future application of the IGCM to in-vivo brain tissue.
A new constitutive model for nitrogen austenitic stainless steel
NASA Astrophysics Data System (ADS)
Fréchard, S.; Lichtenberger, A.; Rondot, F.; Faderl, N.; Redjaïmia, A.; Adoum, M.
2003-09-01
Quasi-static, quasi-dynamic and dynamic compression tests have been performed on a nitrogen alloyed austenitic stainless steel. For all strain rates, a high strain hardening rate and a good ductility have been achieved. In addition, this steel owns a great strain rate sensitivity. The temperature sensitivity bas been determined between 20°C and 400°C. Microstructural analysis has been performed after different loading conditions in relation to the behaviour of the material. Johnson-Cook and Zerilli-Armstrong models have been selected to fit the experimental data into constitutive equations. These models do not reproduce properly the behaviour of this type of steel over the complete range. A new constitutive model that fits very well all the experimental data at different strain, strain rate and temperature has been determined. The model is based on empirical considerations on the separated influence of the main parameters. Single Taylor tests have been realized to validate the models. Live observations of the specimen during impact have been achieved using a special CCD camera set-up. The overall profile at different times are compared to numerical predictions using LS-DYNA code.
Micromechanics and constitutive modeling of connective soft tissues.
Fallah, A; Ahmadian, M T; Firozbakhsh, K; Aghdam, M M
2016-07-01
In this paper, a micromechanical model for connective soft tissues based on the available histological evidences is developed. The proposed model constituents i.e. collagen fibers and ground matrix are considered as hyperelastic materials. The matrix material is assumed to be isotropic Neo-Hookean while the collagen fibers are considered to be transversely isotropic hyperelastic. In order to take into account the effects of tissue structure in lower scales on the macroscopic behavior of tissue, a strain energy density function (SEDF) is developed for collagen fibers based on tissue hierarchical structure. Macroscopic response and properties of tissue are obtained using the numerical homogenization method with the help of ABAQUS software. The periodic boundary conditions and the proposed constitutive models are implemented into ABAQUS using the DISP and the UMAT subroutines, respectively. The existence of the solution and stable material behavior of proposed constitutive model for collagen fibers are investigated based on the poly-convexity condition. Results of the presented micromechanics model for connective tissues are compared and validated with available experimental data. Effects of geometrical and material parameters variation at microscale on macroscopic mechanical behavior of tissues are investigated. The results show that decrease in collagen content of the connective tissues like the tendon due to diseases leads 20% more stretch than healthy tissue under the same load which can results in connective tissue malfunction and hypermobility in joints. PMID:26807767
A homeostatic-driven turnover remodelling constitutive model for healing in soft tissues.
Comellas, Ester; Gasser, T Christian; Bellomo, Facundo J; Oller, Sergio
2016-03-01
Remodelling of soft biological tissue is characterized by interacting biochemical and biomechanical events, which change the tissue's microstructure, and, consequently, its macroscopic mechanical properties. Remodelling is a well-defined stage of the healing process, and aims at recovering or repairing the injured extracellular matrix. Like other physiological processes, remodelling is thought to be driven by homeostasis, i.e. it tends to re-establish the properties of the uninjured tissue. However, homeostasis may never be reached, such that remodelling may also appear as a continuous pathological transformation of diseased tissues during aneurysm expansion, for example. A simple constitutive model for soft biological tissues that regards remodelling as homeostatic-driven turnover is developed. Specifically, the recoverable effective tissue damage, whose rate is the sum of a mechanical damage rate and a healing rate, serves as a scalar internal thermodynamic variable. In order to integrate the biochemical and biomechanical aspects of remodelling, the healing rate is, on the one hand, driven by mechanical stimuli, but, on the other hand, subjected to simple metabolic constraints. The proposed model is formulated in accordance with continuum damage mechanics within an open-system thermodynamics framework. The numerical implementation in an in-house finite-element code is described, particularized for Ogden hyperelasticity. Numerical examples illustrate the basic constitutive characteristics of the model and demonstrate its potential in representing aspects of remodelling of soft tissues. Simulation results are verified for their plausibility, but also validated against reported experimental data. PMID:27009177
Damage modeling and damage detection for structures using a perturbation method
NASA Astrophysics Data System (ADS)
Dixit, Akash
This thesis is about using structural-dynamics based methods to address the existing challenges in the field of Structural Health Monitoring (SHM). Particularly, new structural-dynamics based methods are presented, to model areas of damage, to do damage diagnosis and to estimate and predict the sensitivity of structural vibration properties like natural frequencies to the presence of damage. Towards these objectives, a general analytical procedure, which yields nth-order expressions governing mode shapes and natural frequencies and for damaged elastic structures such as rods, beams, plates and shells of any shape is presented. Features of the procedure include the following: 1. Rather than modeling the damage as a fictitious elastic element or localized or global change in constitutive properties, it is modeled in a mathematically rigorous manner as a geometric discontinuity. 2. The inertia effect (kinetic energy), which, unlike the stiffness effect (strain energy), of the damage has been neglected by researchers, is included in it. 3. The framework is generic and is applicable to wide variety of engineering structures of different shapes with arbitrary boundary conditions which constitute self adjoint systems and also to a wide variety of damage profiles and even multiple areas of damage. To illustrate the ability of the procedure to effectively model the damage, it is applied to beams using Euler-Bernoulli and Timoshenko theories and to plates using Kirchhoff's theory, supported on different types of boundary conditions. Analytical results are compared with experiments using piezoelectric actuators and non-contact Laser-Doppler Vibrometer sensors. To illustrate the ability of the procedure to effectively model the damage, it is applied to beams using Euler-Bernoulli and Timoshenko theories and to plates using Kirchhoff's theory, supported on different types of boundary conditions. Analytical results are compared with experiments using piezoelectric actuators and
Constitutive Modeling of Nanotube-Reinforced Polymer Composites
NASA Technical Reports Server (NTRS)
Odegard, G. M.; Gates, T. S.; Wise, K. E.
2002-01-01
In this study, a technique is presented for developing constitutive models for polymer composite systems reinforced with single-walled carbon nanotubes (SWNT). Because the polymer molecules are on the same size scale as the nanotubes, the interaction at the polymer/nanotube interface is highly dependent on the local molecular structure and bonding. At these small length scales, the lattice structures of the nanotube and polymer chains cannot be considered continuous, and the bulk mechanical properties can no longer be determined through traditional micromechanical approaches that are formulated by using continuum mechanics. It is proposed herein that the nanotube, the local polymer near the nanotube, and the nanotube/polymer interface can be modeled as an effective continuum fiber using an equivalent-continuum modeling method. The effective fiber serves as a means for incorporating micromechanical analyses for the prediction of bulk mechanical properties of SWNT/polymer composites with various nanotube shapes, sizes, concentrations, and orientations. As an example, the proposed approach is used for the constitutive modeling of two SWNT/LaRC-SI (with a PmPV interface) composite systems, one with aligned SWNTs and the other with three-dimensionally randomly oriented SWNTs. The Young's modulus and shear modulus have been calculated for the two systems for various nanotube lengths and volume fractions.
Constitutive Modeling of Nanotube-Reinforced Polymer Composite Systems
NASA Technical Reports Server (NTRS)
Odegard, Gregory M.; Harik, Vasyl M.; Wise, Kristopher E.; Gates, Thomas S.
2001-01-01
In this study, a technique has been proposed for developing constitutive models for polymer composite systems reinforced with single-walled carbon nanotubes (SWNT). Since the polymer molecules are on the same size scale as the nanotubes, the interaction at the polymer/nanotube interface is highly dependent on the local molecular structure and bonding. At these small length scales, the lattice structures of the nanotube and polymer chains cannot be considered continuous, and the bulk mechanical properties of the SWNT/polymer composites can no longer be determined through traditional micromechanical approaches that are formulated using continuum mechanics. It is proposed herein that the nanotube, the local polymer near the nanotube, and the nanotube/polymer interface can be modeled as an effective continuum fiber using an equivalent-continuum modeling method. The effective fiber retains the local molecular structure and bonding information and serves as a means for incorporating micromechanical analyses for the prediction of bulk mechanical properties of SWNT/polymer composites with various nanotube sizes and orientations. As an example, the proposed approach is used for the constitutive modeling of two SWNT/polyethylene composite systems, one with continuous and aligned SWNT and the other with discontinuous and randomly aligned nanotubes.
Constitutive Modeling of Nanotube-Reinforced Polymer Composites
NASA Technical Reports Server (NTRS)
Odegard, G. M.; Gates, T. S.; Wise, K. E.; Park, C.; Siochi, E. J.; Bushnell, Dennis M. (Technical Monitor)
2002-01-01
In this study, a technique is presented for developing constitutive models for polymer composite systems reinforced with single-walled carbon nanotubes (SWNT). Because the polymer molecules are on the same size scale as the nanotubes, the interaction at the polymer/nanotube interface is highly dependent on the local molecular structure and bonding. At these small length scales, the lattice structures of the nanotube and polymer chains cannot be considered continuous, and the bulk mechanical properties can no longer be determined through traditional micromechanical approaches that are formulated by using continuum mechanics. It is proposed herein that the nanotube, the local polymer near the nanotube, and the nanotube/polymer interface can be modeled as an effective continuum fiber using an equivalent-continuum modeling method. The effective fiber serves as a means for incorporating micromechanical analyses for the prediction of bulk mechanical properties of SWNT/polymer composites with various nanotube lengths, concentrations, and orientations. As an example, the proposed approach is used for the constitutive modeling of two SWNT/polyimide composite systems.
Constitutive Modeling of Nanotube-Reinforced Polymer Composite Systems
NASA Technical Reports Server (NTRS)
Odegard, Gregory M.; Harik, Vasyl M.; Wise, Kristopher E.; Gates, Thomas S.
2004-01-01
In this study, a technique has been proposed for developing constitutive models for polymer composite systems reinforced with single-walled carbon nanotubes (SWNT). Since the polymer molecules are on the same size scale as the nanotubes, the interaction at the polymer/nanotube interface is highly dependent on the local molecular structure and bonding. At these small length scales, the lattice structures of the nanotube and polymer chains cannot be considered continuous, and the bulk mechanical properties of the SWNT/polymer composites can no longer be determined through traditional micromechanical approaches that are formulated using continuum mechanics. It is proposed herein that the nanotube, the local polymer near the nanotube, and the nanotube/polymer interface can be modeled as an effective continuum fiber using an equivalent-continuum modeling method. The effective fiber retains the local molecular structure and bonding information and serves as a means for incorporating micromechanical analyses for the prediction of bulk mechanical properties of SWNT/polymer composites with various nanotube sizes and orientations. As an example, the proposed approach is used for the constitutive modeling of two SWNT/polyethylene composite systems, one with continuous and aligned SWNT and the other with discontinuous and randomly aligned nanotubes.
Anisotropic effects on constitutive model parameters of aluminum alloys
NASA Astrophysics Data System (ADS)
Brar, Nachhatter S.; Joshi, Vasant S.
2012-03-01
Simulation of low velocity impact on structures or high velocity penetration in armor materials heavily rely on constitutive material models. Model constants are determined from tension, compression or torsion stress-strain at low and high strain rates at different temperatures. These model constants are required input to computer codes (LS-DYNA, DYNA3D or SPH) to accurately simulate fragment impact on structural components made of high strength 7075-T651 aluminum alloy. Johnson- Cook model constants determined for Al7075-T651 alloy bar material failed to simulate correctly the penetration into 1' thick Al-7075-T651plates. When simulation go well beyond minor parameter tweaking and experimental results show drastically different behavior it becomes important to determine constitutive parameters from the actual material used in impact/penetration experiments. To investigate anisotropic effects on the yield/flow stress of this alloy quasi-static and high strain rate tensile tests were performed on specimens fabricated in the longitudinal "L", transverse "T", and thickness "TH" directions of 1' thick Al7075 Plate. While flow stress at a strain rate of ~1/s as well as ~1100/s in the thickness and transverse directions are lower than the longitudinal direction. The flow stress in the bar was comparable to flow stress in the longitudinal direction of the plate. Fracture strain data from notched tensile specimens fabricated in the L, T, and Thickness directions of 1' thick plate are used to derive fracture constants.
Brittle damage models in DYNA2D
Faux, D.R.
1997-09-01
DYNA2D is an explicit Lagrangian finite element code used to model dynamic events where stress wave interactions influence the overall response of the system. DYNA2D is often used to model penetration problems involving ductile-to-ductile impacts; however, with the advent of the use of ceramics in the armor-anti-armor community and the need to model damage to laser optics components, good brittle damage models are now needed in DYNA2D. This report will detail the implementation of four brittle damage models in DYNA2D, three scalar damage models and one tensor damage model. These new brittle damage models are then used to predict experimental results from three distinctly different glass damage problems.
NASA Technical Reports Server (NTRS)
Saleeb, A. F.; Chang, T. Y. P.; Wilt, T.; Iskovitz, I.
1989-01-01
The research work performed during the past year on finite element implementation and computational techniques pertaining to high temperature composites is outlined. In the present research, two main issues are addressed: efficient geometric modeling of composite structures and expedient numerical integration techniques dealing with constitutive rate equations. In the first issue, mixed finite elements for modeling laminated plates and shells were examined in terms of numerical accuracy, locking property and computational efficiency. Element applications include (currently available) linearly elastic analysis and future extension to material nonlinearity for damage predictions and large deformations. On the material level, various integration methods to integrate nonlinear constitutive rate equations for finite element implementation were studied. These include explicit, implicit and automatic subincrementing schemes. In all cases, examples are included to illustrate the numerical characteristics of various methods that were considered.
Constitutive modelling of evolving flow anisotropy including distortional hardening
Pietryga, Michael P.; Vladimirov, Ivaylo N.; Reese, Stefanie
2011-05-04
The paper presents a new constitutive model for anisotropic metal plasticity that takes into account the expansion or contraction (isotropic hardening), translation (kinematic hardening) and change of shape (distortional hardening) of the yield surface. The experimentally observed region of high curvature ('nose') on the yield surface in the loading direction and flattened shape in the reverse loading direction are modelled here by means of the concept of directional distortional hardening. The modelling of directional distortional hardening is accomplished by means of an evolving fourth-order tensor. The applicability of the model is illustrated by fitting experimental subsequent yield surfaces at finite plastic deformation. Comparisons with test data for aluminium low and high work hardening alloys display a good agreement between the simulation results and the experimental data.
Constitutive modeling and computational implementation for finite strain plasticity
NASA Technical Reports Server (NTRS)
Reed, K. W.; Atluri, S. N.
1985-01-01
This paper describes a simple alternate approach to the difficult problem of modeling material behavior. Starting from a general representation for a rate-tpe constitutive equation, it is shown by example how sets of test data may be used to derive restrictions on the scalar functions appearing in the representation. It is not possible to determine these functions from experimental data, but the aforementioned restrictions serve as a guide in their eventual definition. The implications are examined for hypo-elastic, isotropically hardening plastic, and kinematically hardening plastic materials. A simple model for the evolution of the 'back-stress,' in a kinematic-hardening plasticity theory, that is entirely analogous to a hypoelastic stress-strain relation is postulated and examined in detail in modeling finitely plastic tension-torsion test. The implementation of rate-type material models in finite element algorithms is also discussed.
A constitutive model for ballistic gelatin at surgical strain rates.
Ravikumar, Nishant; Noble, Christopher; Cramphorn, Edward; Taylor, Zeike A
2015-07-01
This paper describes a constitutive model for ballistic gelatin at the low strain rates experienced, for example, by soft tissues during surgery. While this material is most commonly associated with high speed projectile penetration and impact investigations, it has also been used extensively as a soft tissue simulant in validation studies for surgical technologies (e.g. surgical simulation and guidance systems), for which loading speeds and the corresponding mechanical response of the material are quite different. We conducted mechanical compression experiments on gelatin specimens at strain rates spanning two orders of magnitude (~0.001-0.1s(-1)) and observed a nonlinear load-displacement history and strong strain rate-dependence. A compact and efficient visco-hyperelastic constitutive model was then formulated and found to fit the experimental data well. An Ogden type strain energy density function was employed for the elastic component. A single Prony exponential term was found to be adequate to capture the observed rate-dependence of the response over multiple strain rates. The model lends itself to immediate use within many commercial finite element packages. PMID:25863009
Anisotropic Effects on Constitutive Model Parameters of Aluminum Alloys
NASA Astrophysics Data System (ADS)
Brar, Nachhatter; Joshi, Vasant
2011-06-01
Simulation of low velocity impact on structures or high velocity penetration in armor materials heavily rely on constitutive material models. The model constants are required input to computer codes (LS-DYNA, DYNA3D or SPH) to accurately simulate fragment impact on structural components made of high strength 7075-T651 aluminum alloys. Johnson-Cook model constants determined for Al7075-T651 alloy bar material failed to simulate correctly the penetration into 1' thick Al-7075-T651plates. When simulations go well beyond minor parameter tweaking and experimental results are drastically different it is important to determine constitutive parameters from the actual material used in impact/penetration experiments. To investigate anisotropic effects on the yield/flow stress of this alloy we performed quasi-static and high strain rate tensile tests on specimens fabricated in the longitudinal, transverse, and thickness directions of 1' thick Al7075-T651 plate. Flow stresses at a strain rate of ~1100/s in the longitudinal and transverse direction are similar around 670MPa and decreases to 620 MPa in the thickness direction. These data are lower than the flow stress of 760 MPa measured in Al7075-T651 bar stock.
An Experimental Study and Constitutive Modeling of Saturated Porous Rocks
NASA Astrophysics Data System (ADS)
Xie, S. Y.; Shao, J. F.
2015-01-01
This paper is devoted to the experimental characterization and constitutive modeling of saturated porous rocks. A typical porous chalk is investigated. Drained hydrostatic and triaxial compression tests are first performed to characterize the basic mechanical behavior of chalk. Drained triaxial tests with constant interstitial pressure are then carried out to study the effects of interstitial pressure on the plastic deformation and failure criterion. Finally, undrained triaxial compression tests are performed to investigate poromechanical coupling in saturated conditions. Based on the experimental data and some relevant micromechanical considerations, a micromechanics-based plastic model is proposed and extended to poroplastic coupling using the effective stress concept. The proposed model is verified through comparisons between the numerical results and experimental data for both drained and undrained tests.
Materials constitutive models for nonlinear analysis of thermally cycled structures
NASA Technical Reports Server (NTRS)
Kaufman, A.; Hunt, L. E.
1982-01-01
Effects of inelastic materials models on computed stress-strain solutions for thermally loaded structures were studied by performing nonlinear (elastoplastic creep) and elastic structural analyses on a prismatic, double edge wedge specimen of IN 100 alloy that was subjected to thermal cycling in fluidized beds. Four incremental plasticity creep models (isotropic, kinematic, combined isotropic kinematic, and combined plus transient creep) were exercised for the problem by using the MARC nonlinear, finite element computer program. Maximum total strain ranges computed from the elastic and nonlinear analyses agreed within 5 percent. Mean cyclic stresses, inelastic strain ranges, and inelastic work were significantly affected by the choice of inelastic constitutive model. The computing time per cycle for the nonlinear analyses was more than five times that required for the elastic analysis.
Ductile damage model with void coalescence
Tonks, D.L.
1995-03-01
A general model for ductile damage in metals is presented. It includes damage induced by shear stress as well as damage caused by volumetric tension. Spallation is included as a special case. Strain induced damage is also treated. Void nucleation and growth are included and give rise to strain rate effects. Strain rate effects also arise in the model through elastic release wave propagation between damage centers. Underlying physics of the model is the nucleation, growth, and coalescence of voids in a plastically flowing solid. Implementation of the model in hydrocodes is discussed.
A 3D Orthotropic Strain-Rate Dependent Elastic Damage Material Model.
English, Shawn Allen
2014-09-01
A three dimensional orthotropic elastic constitutive model with continuum damage and cohesive based fracture is implemented for a general polymer matrix composite lamina. The formulation assumes the possibility of distributed (continuum) damage followed b y localized damage. The current damage activation functions are simply partially interactive quadratic strain criteria . However, the code structure allows for changes in the functions without extraordinary effort. The material model formulation, implementation, characterization and use cases are presented.
NASA Technical Reports Server (NTRS)
Allen, David H.; Groves, Scott E.; Harris, Charles E.
1988-01-01
The present cumulative damage model for the prediction of stiffness loss in graphite/epoxy laminates applies a thermomechanical constitutive theory for elastic composites with distributed damage. The model proceeds from a continuum mechanics and thermodynamics approach in which the distributed damage is characterized by a set of second-order tensor-valued internal state variables. A set of damage-dependent laminated plate equations is obtained; this is developed by modifying classical Kirchhoff plate theory.
A Micromechanics Based Constitutive Model For Brittle Failure at High Strain Rates
NASA Astrophysics Data System (ADS)
Bhat, H. S.; Rosakis, A.; Sammis, C. G.
2011-12-01
The micromechanical damage mechanics formulated by Ashby and Sammis [1] and generalized by Desh- pande and Evans [2] has been extended to allow for a more generalized stress state and to incorporate an ex- perimentally motivated new crack growth (damage evo- lution) law that is valid over a wide range of loading rates. This law is sensitive to both the crack tip stress field and its time derivative. Incorporating this feature produces strain-rate sensitivity in the constitutive re- sponse. The model is also experimentally verified by predicting the failure strength of Dionysus-Pentelicon marble over strain rates ranging from ˜ 10-6 to 103 s-1. Model parameters determined from from quasi-static experiments were used to predict the failure strength at higher loading rates. Agreement with experimental results was excellent.
High rate constitutive modeling of aluminium alloy tube
NASA Astrophysics Data System (ADS)
Salisbury, C. P.; Worswick, M. J.; Mayer, R.
2006-08-01
As the need for fuel efficient automobiles increases, car designers are investigating light-weight materials for automotive bodies that will reduce the overall automobile weight. Aluminium alloy tube is a desirable material to use in automotive bodies due to its light weight. However, aluminium suffers from lower formability than steel and its energy absorption ability in a crash event after a forming operation is largely unknown. As part of a larger study on the relationship between crashworthiness and forming processes, constitutive models for 3mm AA5754 aluminium tube were developed. A nominal strain rate of 100/s is often used to characterize overall automobile crash events, whereas strain rates on the order of 1000/s can occur locally. Therefore, tests were performed at quasi-static rates using an Instron test fixture and at strain rates of 500/s to 1500/s using a tensile split Hopkinson bar. High rate testing was then conducted at rates of 500/s, 1000/s and 1500/s at 21circC, 150circC and 300circC. The generated data was then used to determine the constitutive parameters for the Johnson-Cook and Zerilli-Armstrong material models.
Constitutive modeling of ascending thoracic aortic aneurysms using microstructural parameters.
Pasta, Salvatore; Phillippi, Julie A; Tsamis, Alkiviadis; D'Amore, Antonio; Raffa, Giuseppe M; Pilato, Michele; Scardulla, Cesare; Watkins, Simon C; Wagner, William R; Gleason, Thomas G; Vorp, David A
2016-02-01
Ascending thoracic aortic aneurysm (ATAA) has been associated with diminished biomechanical strength and disruption in the collagen fiber microarchitecture. Additionally, the congenital bicuspid aortic valve (BAV) leads to a distinct extracellular matrix structure that may be related to ATAA development at an earlier age than degenerative aneurysms arising in patients with the morphological normal tricuspid aortic valve (TAV). The purpose of this study was to model the fiber-reinforced mechanical response of ATAA specimens from patients with either BAV or TAV. This was achieved by combining image-analysis derived parameters of collagen fiber dispersion and alignment with tensile testing data. Then, numerical simulations were performed to assess the role of anisotropic constitutive formulation on the wall stress distribution of aneurysmal aorta. Results indicate that both BAV ATAA and TAV ATAA have altered collagen fiber architecture in the medial plane of experimentally-dissected aortic tissues when compared to normal ascending aortic specimens. The study findings highlight that differences in the collagen fiber distribution mostly influences the resulting wall stress distribution rather than the peak stress. We conclude that fiber-reinforced constitutive modeling that takes into account the collagen fiber defect inherent to the aneurysmal ascending aorta is paramount for accurate finite element predictions and ultimately for biomechanical-based indicators to reliably distinguish the more from the less 'malignant' ATAAs. PMID:26669606
Mechanistic Constitutive Models for Rubber Elasticity and Viscoelasticity
Puso, M
2003-01-21
Physically based models which describe the finite strain behavior of vulcanized rubber are developed. Constitutive laws for elasticity and viscoelasticity are derived by integrating over orientation space the forces due to each individual polymer chain. A novel scheme is presented which effectively approximates these integrals in terms of strain and strain invariants. In addition, the details involving the implementation of such models into a quasi-static large strain finite element formulation are provided. In order to account for the finite extensibility of a molecular chain, Langevin statistics is used to model the chain response. The classical statistical model of rubber assumes that polymer chains interact only at the chemical crosslinks. It is shown that such model when fitted for uniaxial tension data cannot fit compression or equibiaxial data. A model which incorporates the entanglement interactions of surrounding chains, in addition to the finite extensibility of the chains, is shown to give better predictions than the classical model. The technique used for approximating the orientation space integral was applied to both the classical and entanglement models. A viscoelasticity model based on the force equilibration process as described by Doi and Edwards is developed. An assumed form for the transient force in the chain is postulated. The resulting stress tensor is composed of an elastic and a viscoelastic portion with the elastic stress given by the proposed entanglement model. In order to improve the simulation of experimental data, it was found necessary to include the effect of unattached or dangling polymer chains in the viscoelasticity model. The viscoelastic effect of such chains is the manifestation of a disengagement process. This disengagement model for unattached polymer chains motivated an empirical model which was very successful in simulating the experimental results considered.
Derenzini, Enrico; Agostinelli, Claudio; Imbrogno, Enrica; Iacobucci, Ilaria; Casadei, Beatrice; Brighenti, Elisa; Righi, Simona; Fuligni, Fabio; Di Rorà, Andrea Ghelli Luserna; Ferrari, Anna; Martinelli, Giovanni; Pileri, Stefano; Zinzani, Pier Luigi
2015-01-01
The recent finding that MYC-driven cancers are sensitive to inhibition of the DNA damage response (DDR) pathway, prompted us to investigate the role of DDR pathway as therapeutic target in diffuse large B-cell lymphoma (DLBCL), which frequently overexpresses the MYC oncogene. In a preliminary immunohistochemical study conducted on 99 consecutive DLBCL patients, we found that about half of DLBCLs showed constitutive expression of the phosphorylated forms of checkpoint kinases (CHK) and CDC25c, markers of DDR activation, and of phosphorylated histone H2AX (γH2AX), marker of DNA damage and genomic instability. Constitutive γH2AX expression correlated with c-MYC levels and DDR activation, and defined a subset of tumors characterised by poor outcome. Next, we used the CHK inhibitor PF-0477736 as a tool to investigate whether the inhibition of the DDR pathway might represent a novel therapeutic approach in DLBCL. Submicromolar concentrations of PF-0477736 hindered proliferation in DLBCL cell lines with activated DDR pathway. These results were fully recapitulated with a different CHK inhibitor (AZD-7762). Inhibition of checkpoint kinases induced rapid DNA damage accumulation and apoptosis in DLBCL cell lines and primary cells. These data suggest that pharmacologic inhibition of DDR through targeting of CHK kinases may represent a novel therapeutic strategy in DLBCL. PMID:25544753
Derenzini, Enrico; Agostinelli, Claudio; Imbrogno, Enrica; Iacobucci, Ilaria; Casadei, Beatrice; Brighenti, Elisa; Righi, Simona; Fuligni, Fabio; Ghelli Luserna Di Rorà, Andrea; Ferrari, Anna; Martinelli, Giovanni; Pileri, Stefano; Zinzani, Pier Luigi
2015-03-30
The recent finding that MYC-driven cancers are sensitive to inhibition of the DNA damage response (DDR) pathway, prompted us to investigate the role of DDR pathway as therapeutic target in diffuse large B-cell lymphoma (DLBCL), which frequently overexpresses the MYC oncogene. In a preliminary immunohistochemical study conducted on 99 consecutive DLBCL patients, we found that about half of DLBCLs showed constitutive expression of the phosphorylated forms of checkpoint kinases (CHK) and CDC25c, markers of DDR activation, and of phosphorylated histone H2AX (γH2AX), marker of DNA damage and genomic instability. Constitutive γH2AX expression correlated with c-MYC levels and DDR activation, and defined a subset of tumors characterised by poor outcome. Next, we used the CHK inhibitor PF-0477736 as a tool to investigate whether the inhibition of the DDR pathway might represent a novel therapeutic approach in DLBCL. Submicromolar concentrations of PF-0477736 hindered proliferation in DLBCL cell lines with activated DDR pathway. These results were fully recapitulated with a different CHK inhibitor (AZD-7762). Inhibition of checkpoint kinases induced rapid DNA damage accumulation and apoptosis in DLBCL cell lines and primary cells. These data suggest that pharmacologic inhibition of DDR through targeting of CHK kinases may represent a novel therapeutic strategy in DLBCL. PMID:25544753
NASA Astrophysics Data System (ADS)
Nagel, T.; Böttcher, N.; Görke, U. J.; Kolditz, O.
2014-12-01
The design process of geotechnical installations includes the application of numerical simulation tools for safety assessment, dimensioning and long term effectiveness estimations. Underground salt caverns can be used for the storage of natural gas, hydrogen, oil, waste or compressed air. For their design one has to take into account fluctuating internal pressures due to different levels of filling, the stresses imposed by the surrounding rock mass, irregular geometries and possibly heterogeneous material properties [3] in order to estimate long term cavern convergence as well as locally critical wall stresses. Constitutive models applied to rock salt are usually viscoplastic in nature and most often based on a Burgers-type rheological model extended by non-linear viscosity functions and/or plastic friction elements. Besides plastic dilatation, healing and damage are sometimes accounted for as well [2]. The scales of the geotechnical system to be simulated and the laboratory tests from which material parameters are determined are vastly different. The most common material testing modalities to determine material parameters in geoengineering are the uniaxial and the triaxial compression tests. Some constitutive formulations in widespread use are formulated based on equivalent rather than tensorial quantities valid under these specific test conditions and are subsequently applied to heterogeneous underground systems and complex 3D load cases. We show here that this procedure is inappropriate and can lead to erroneous results. We further propose alternative formulations of the constitutive models in question that restore their validity under arbitrary loading conditions. For an efficient numerical simulation, the discussed constitutive models are integrated locally with a Newton-Raphson algorithm that directly provides the algorithmically consistent tangent matrix for the global Newton iteration of the displacement based finite element formulation. Finally, the finite
Constitutive modeling of calcium carbonate supersaturated seawater mixtures
NASA Astrophysics Data System (ADS)
Reis, Martina; Sousa, Maria De Fátima; Bertran, Celso; Bassi, Adalberto
2014-11-01
Calcium carbonate supersaturated seawater mixtures have attracted attention of many researchers since the deposition of CaCO3(s) from such solutions can lead to scaling problems in oil fields. However, despite their evident practical importance in petroleum engineering, the hydro and thermodynamic behaviors of these mixtures have not been well-understood yet. In this work, a constitutive model based on the foundations of the constitutive theory of continuum mechanics, and the Müller-Liu entropy principle is proposed. The calcium carbonate supersaturated seawater mixture is regarded as a reactive viscous fluid with heat and electrical conductions. The obtained results indicate that the thermodynamic behavior of CaCO3 supersaturated seawater mixtures is closely related to the individual dynamics of each constituent of the mixture, particularly to the linear momentum, and mass exchanges. Furthermore, the results show that, unlike classical continuum mixtures, the extra entropy flux is not null, and higher-order gradients of deformation contribute to the residual entropy production of the class of mixtures under study. The results of this work may be relevant for the prevention of the mineral scale formation in oil fields. The first author acknowledges the São Paulo Research Foundation (Grant 2013/ 20872-2) for its funding.
Constitutive models for static and dynamic response of geotechnical materials
NASA Astrophysics Data System (ADS)
Nemat-Nasser, S.
1983-11-01
The objective of this research program has been to develop realistic macroscopic constitutive relations which describe static and dynamic properties of geotechnical materials (soils and rocks). To this end a coordinated theoretical and experimental activity has been followed. The theoretical work includes a balanced combination of statistical microscopic (at the grain size level) modeling and a nonclassical elasto-plastic macroscopic formulation. The latter includes the effects of internal friction, plastic compressibility, and pressure sensitivity, as well as anisotropy which is commonly observed in geotechnical materials. The following specific goals have been sought: (1) to develop three-dimensional constitutive relations under ordinary or high pressures (such as those induced by blasting or tectonic forces which may cause a large amount of densification by relative motion and possible crushing of grains); and (2) to examine and characterize the behavior of saturated granular materials under dynamic loading. The latter item includes characterization of possible liquefaction and subsidence which may be induced in granular materials under confining pressure by ground vibration or passage of waves. The theoretical work has been carefully coordinated with key experiments in order to: (1) understand the basic physics of the process, both at macroscopic and microscopic levels; (2) to verify the corresponding theoretical predictions; and (3) to establish relevant material parameters.
Constitutive modelling of dual phase steel sheet and tube
NASA Astrophysics Data System (ADS)
Thompson, A. C.; Salisbury, C. P.; Worswick, M. J.; Mayer, R.
2006-08-01
Automobile manufacturers are currently striving to improve vehicle fuel efficiency through reduction of vehicle weight. Dual phase steels are good candidates for automotive bodies due to their high strength-to-weight ratio, and good formablity and weldability. As part of a project on the interaction between forming and crashworthiness, constitutive parameters of a dual phase steel were determined for both sheet and tube stock in order to support analysis of the tube response throughout forming processes and in crash simulations. Stress - strain data was collected at a quasi-static rate as well as rates from 0.1 to 1500 s - 1. The intermediate strain rate response was captured using an instrumented falling weight tensile tester (35 100 s - 1), while a tensile split Hopkinson bar (500 1500 s - 1) was used to capture the high-rate response. This range of strain rates is typical of the rates seen in a crash simulation. Tests were also performed at higher temperatures (150°C and 300°C) at rates of 500 and 1500 s - 1 to capture the thermal softening response. The dual phase steel sheet and tube show an appreciable amount of strain rate sensitivity throughout the complete range of strain rates. It also exhibited a large amount of thermal softening. The thermal sensitivity is identical for the sheet and tube. Fits to the Johnson-Cook constitutive model were obtained from the experimental results.
Modeling the Constitutive Behaviour of PET for Stretch Blow Moulding
NASA Astrophysics Data System (ADS)
Yan, S. Y.; Menary, G.
2011-05-01
There are a substantial amount of constitutive models that have been developed to capture the finite deformation behavior of polymers for forming simulations. Most of these models have been used to capture the behavior in uniaxial and simultaneous biaxial modes of deformation. However, very few have attempted to model the sequential biaxial deformation behavior which is more appropriate for the stretch blow moulding process. The aim of this work is to develop a model for PET to successfully capture the sequential stress-strain behavior as a function of temperature and strain rate, thus making it suitable for use in simulations of stretch blow moulding. Biaxial test data has been generated at temperatures and strain rates appropriate for stretch blow moulding and a model developed by Buckley et al. has been implemented within the commercial finite element package Abaqus/Explicit. In parallel, an efficient automatic curve fitting procedure has been developed to enable the material parameters to be easily found from biaxial test data. The results show that the Buckley model can predict the stress response of equibiaxial deformation well, but cannot predict the sequential biaxial deformation.
An uncoupled viscoplastic constitutive model for metals at elevated temperature
NASA Technical Reports Server (NTRS)
Haisler, W. E.; Cronenworth, J.
1983-01-01
An uncoupled constitutive model for predicting the transient response of thermal and rate dependent, inelastic material behavior is presented. The uncoupled model assumes that there is a temperature below which the total strain consists essentially of elastic and rate insensitive inelastic strains only. Above this temperature, the rate dependent inelastic strain (creep) dominates. The rate insensitive inelastic strain component is modeled in an incremental form with a yield function, flow rule and hardening law. Revisions to the hardening rule permit the model to predict temperature-dependent kinematic-isotropic hardening behavior, cyclic saturation, asymmetric stress-strain response upon stress reversal, and variable Bauschinger effect. The rate dependent inelastic strain component is modeled using a rate equation in terms of back stress, drag stress and exponent n as functions of temperature and strain. A sequence of hysteresis loops and relaxation tests are utilized to define the rate dependent inelastic strain rate. Evaluation of the model is performed by comparison with experiments involving various thermal and mechanical load histories on 5086 aluminum alloy, 304 stainless steel and Hastelloy-X.
NASA Astrophysics Data System (ADS)
Vidal-Sallé, Emmanuelle; Chassagne, Pierre
2007-06-01
This paper presents a nonlinear viscoelastic orthotropic constitutive equation applied to wood material. The proposed model takes into account mechanical and mechanosorptive creep via a 3D stress ratio and moisture change rate for a cylindrical orthotropic material. Orthotropic frame is based on the grain direction (L), radial (R) and hoop (T) directions, which are natural wood directions. Particular attention is taken to ensure the model to fulfill the necessary dissipation conditions. It is based on a rheological generalized Maxwell model with two elements in parallel in addition with a single linear spring taking into account the long term response. The proposed model is implemented in the finite element code ABAQUS/Standard® via a user subroutine UMAT and simple example is shown to demonstrate the capability of the proposed model. Future works would deal with damage and fracture prediction for wooden structures submitted to climate variations and mechanical loading.
Some advances in experimentation supporting development of viscoplastic constitutive models
NASA Technical Reports Server (NTRS)
Ellis, J. R.; Robinson, D. N.
1985-01-01
The development of a biaxial extensometer capable of measuring axial, torsion, and diametral strains to near-microstrain resolution at elevated temperatures is discussed. An instrument with this capability was needed to provide experimental support to the development of viscoplastic constitutive models. The advantages gained when torsional loading is used to investigate inelastic material response at elevated temperatures are highlighted. The development of the biaxial extensometer was conducted in two stages. The first involved a series of bench calibration experiments performed at room temperature. The second stage involved a series of in-place calibration experiments conducted at room and elevated temperature. A review of the calibration data indicated that all performance requirements regarding resolution, range, stability, and crosstalk had been met by the subject instrument over the temperature range of interest, 21 C to 651 C. The scope of the in-place calibration experiments was expanded to investigate the feasibility of generating stress relaxation data under torsional loading.
Some advances in experimentation supporting development of viscoplastic constitutive models
NASA Technical Reports Server (NTRS)
Ellis, J. R.; Robinson, D. N.
1985-01-01
The development of a biaxial extensometer capable of measuring axial, torsion, and diametral strains to near-microstrain resolution at elevated temperatures is discussed. An instrument with this capability was needed to provide experimental support to the development of viscoplastic constitutive models. The advantages gained when torsional loading is used to investigate inelastic material response at elevated temperatures are highlighted. The development of the biaxial extensometer was conducted in two stages. The first involved a series of bench calibration experiments performed at room temperature. The second stage involved a series of in-place calibration experiments performed at room temperature. A review of the calibration data indicated that all performance requirements regarding resolution, range, stability, and crosstalk had been met by the subject instrument over the temperature range of interest, 21 C to 651 C. The scope of the in-placed calibration experiments was expanded to investigate the feasibility of generating stress relaxation data under torsional loading.
A microstructurally inspired damage model for early venous thrombus.
Rausch, Manuel K; Humphrey, Jay D
2015-03-01
Accumulative damage may be an important contributor to many cases of thrombotic disease progression. Thus, a complete understanding of the pathological role of thrombus requires an understanding of its mechanics and in particular mechanical consequences of damage. In the current study, we introduce a novel microstructurally inspired constitutive model for thrombus that considers a non-uniform distribution of microstructural fibers at various crimp levels and employs one of the distribution parameters to incorporate stretch-driven damage on the microscopic level. To demonstrate its ability to represent the mechanical behavior of thrombus, including a recently reported Mullins type damage phenomenon, we fit our model to uniaxial tensile test data of early venous thrombus. Our model shows an agreement with these data comparable to previous models for damage in elastomers with the added advantages of a microstructural basis and fewer model parameters. We submit that our novel approach marks another important step toward modeling the evolving mechanics of intraluminal thrombus, specifically its damage, and hope it will aid in the study of physiological and pathological thrombotic events. PMID:26523784
A Micromechanics Finite-Strain Constitutive Model of Fibrous Tissue
Chen, Huan; Liu, Yi; Zhao, Xuefeng; Lanir, Yoram; Kassab, Ghassan S.
2011-01-01
Biological tissues have unique mechanical properties due to the wavy fibrous collagen and elastin microstructure. In inflation, a vessel easily distends under low pressure but becomes stiffer when the fibers are straightened to take up the load. The current microstructural models of blood vessels assume affine deformation; i.e., the deformation of each fiber is assumed to be identical to the macroscopic deformation of the tissue. This uniform-field (UF) assumption leads to the macroscopic (or effective) strain energy of the tissue that is the volumetric sum of the contributions of the tissue components. Here, a micromechanics-based constitutive model of fibrous tissue is developed to remove the affine assumption and to take into consideration the heterogeneous interactions between the fibers and the ground substance. The development is based on the framework of a recently developed second-order homogenization theory, and takes into account the waviness, orientations, and spatial distribution of the fibers, as well as the material nonlinearity at finite-strain deformation. In an illustrative simulation, the predictions of the macroscopic stress-strain relation, and the statistical deformation of the fibers are compared to the UF model, as well as finite-element (FE) simulation. Our predictions agree well with the FE results, while the UF predictions significantly overestimate. The effects of fiber distribution and waviness on the macroscopic stress-strain relation are also investigated. The present mathematical model may serves as a foundation for native as well as for engineered tissues and biomaterials. PMID:21927506
A micromechanics finite-strain constitutive model of fibrous tissue
NASA Astrophysics Data System (ADS)
Chen, Huan; Liu, Yi; Zhao, Xuefeng; Lanir, Yoram; Kassab, Ghassan S.
2011-09-01
Biological tissues have unique mechanical properties due to the wavy fibrous collagen and elastin microstructure. In inflation, a vessel easily distends under low pressure but becomes stiffer when the fibers are straightened to take up the load. The current microstructural models of blood vessels assume affine deformation, i.e., the deformation of each fiber is assumed to be identical to the macroscopic deformation of the tissue. This uniform-field (UF) assumption leads to the macroscopic (or effective) strain energy of the tissue that is the volumetric sum of the contributions of the tissue components. Here, a micromechanics-based constitutive model of fibrous tissue is developed to remove the affine assumption and to take into consideration the heterogeneous interactions between the fibers and the ground substance. The development is based on the framework of a recently developed second-order homogenization theory, and takes into account the waviness, orientations and spatial distribution of the fibers, as well as the material nonlinearity at finite-strain deformation. In an illustrative simulation, the predictions of the macroscopic stress-strain relation and the statistical deformation of the fibers are compared to the UF model, as well as finite-element (FE) simulation. Our predictions agree well with the FE results, while the UF predictions significantly overestimate. The effects of fiber distribution and waviness on the macroscopic stress-strain relation are also investigated. The present mathematical model may serves as a foundation for native as well as for engineered tissues and biomaterials.
Imanishi, Satoshi; Umezu, Tomohiro; Ohtsuki, Kazushige; Kobayashi, Chiaki; Ohyashiki, Kazuma; Ohyashiki, Junko H
2014-06-01
5-Azacytidine (AZA) exerts its anti-tumor effects by exerting cytotoxicity via its incorporation into RNA and DNA, which causes the reactivation of aberrantly silenced growth-regulatory genes by promoter demethylation, as well as DNA damage. AZA is used for patients with myelodysplastic syndrome and acute myeloid leukemia. However, some patients demonstrate resistance to AZA, the mechanisms of which are not fully elucidated. We therefore sought to better characterize the molecular mechanism of AZA resistance using an in vitro model of AZA resistance. We established AZA-resistant cell lines by exposing the human leukemia cell lines U937 and HL-60 to clinical concentrations of AZA, and characterized these cells. AZA-resistant cells showed a down-regulation of the DNMT3A protein, in correlation with their marked genome-wide DNA hypomethylation. Furthermore, genes involved in pyrimidine metabolism were down-regulated in both AZA-resistant cell lines; AZA sensitivity was restored by inhibition of CTP synthase. Of note is that the DNA damage response pathway is constitutively activated in the AZA-resistant cell lines, but not in the parental cell lines. Inhibition of the DNA damage response pathway canceled the AZA resistance, in association with an increase in apoptotic cells. We found that the molecular mechanism underlying AZA resistance involves pyrimidine metabolism and the DNA damage response through ATM kinase. This study therefore sheds light on the mechanisms underlying AZA resistance, and will enable better understanding of AZA resistance in patients undergoing AZA treatment. PMID:24680865
Nonlinear ultrasound modelling and validation of fatigue damage
NASA Astrophysics Data System (ADS)
Fierro, G. P. Malfense; Ciampa, F.; Ginzburg, D.; Onder, E.; Meo, M.
2015-05-01
Nonlinear ultrasound techniques have shown greater sensitivity to microcracks and they can be used to detect structural damages at their early stages. However, there is still a lack of numerical models available in commercial finite element analysis (FEA) tools that are able to simulate the interaction of elastic waves with the materials nonlinear behaviour. In this study, a nonlinear constitutive material model was developed to predict the structural response under continuous harmonic excitation of a fatigued isotropic sample that showed anharmonic effects. Particularly, by means of Landau's theory and Kelvin tensorial representation, this model provided an understanding of the elastic nonlinear phenomena such as the second harmonic generation in three-dimensional solid media. The numerical scheme was implemented and evaluated using a commercially available FEA software LS-DYNA, and it showed a good numerical characterisation of the second harmonic amplitude generated by the damaged region known as the nonlinear response area (NRA). Since this process requires only the experimental second-order nonlinear parameter and rough damage size estimation as an input, it does not need any baseline testing with the undamaged structure or any dynamic modelling of the fatigue crack growth. To validate this numerical model, the second-order nonlinear parameter was experimentally evaluated at various points over the fatigue life of an aluminium (AA6082-T6) coupon and the crack propagation was measured using an optical microscope. A good correlation was achieved between the experimental set-up and the nonlinear constitutive model.
Constitutive Modeling of Superalloy Single Crystals and Directionally Solidified Materials
NASA Technical Reports Server (NTRS)
Walker, K. P.; Jordan, E. H.
1985-01-01
A unified viscoplastic constitutive relation based on crystallographic slip theory was developed for the deformation analysis of nickel base face centered cubic superalloy single crystals at elevated temperature. The single crystal theory is embedded in a self consistent method to derive a constitutive relation for a directionally solidified material comprised of a polycrystalline aggregate of columnar cylindrical grains. One of the crystallographic axes of the cylindrical crystals points in the columnar direction while the remaining crystallographic axes are oriented at random in the basal plane perpendicular to the columnar direction. These constitutive formulations are coded in FORTRAN for use in nonlinear finite element and boundary element programs.
A constitutive model for Sn-Pb solder.
Neilsen, Michael K.; Vianco, Paul Thomas; Boyce, Brad Lee
2010-10-01
A unified creep plasticity damage (UCPD) model for Sn-Pb solder is developed in this paper. Stephens and Frear (1999) studied the creep behavior of near-eutectic 60Sn-40Pb solder subjected to low strain rates and found that the inelastic (creep and plastic) strain rate could be accurately described using a hyperbolic Sine function of the applied effective stress. A recently developed high-rate servo-hydraulic method was employed to characterize the temperature and strain-rate dependent stress-strain behavior of eutectic Sn-Pb solder over a wide range of strain rates (10{sup -4} to 10{sup 2} per second). The steady state inelastic strain rate data from these latest experiments were also accurately captured by the hyperbolic Sine equation developed by Stephens and Frear. Thus, this equation was used as the basis for the UCPD model for Sn-Pb solder developed in this paper. Stephens, J.J., and Frear, D.R., Metallurgical and Materials Transactions A, Volume 30A, pp. 1301-1313, May 1999.
Intelligent-based Structural Damage Detection Model
Lee, Eric Wai Ming; Yu, K.F.
2010-05-21
This paper presents the application of a novel Artificial Neural Network (ANN) model for the diagnosis of structural damage. The ANN model, denoted as the GRNNFA, is a hybrid model combining the General Regression Neural Network Model (GRNN) and the Fuzzy ART (FA) model. It not only retains the important features of the GRNN and FA models (i.e. fast and stable network training and incremental growth of network structure) but also facilitates the removal of the noise embedded in the training samples. Structural damage alters the stiffness distribution of the structure and so as to change the natural frequencies and mode shapes of the system. The measured modal parameter changes due to a particular damage are treated as patterns for that damage. The proposed GRNNFA model was trained to learn those patterns in order to detect the possible damage location of the structure. Simulated data is employed to verify and illustrate the procedures of the proposed ANN-based damage diagnosis methodology. The results of this study have demonstrated the feasibility of applying the GRNNFA model to structural damage diagnosis even when the training samples were noise contaminated.
Downs, J. Crawford; Burgoyne, Claude F.; Suh, J-K. Francis
2009-01-01
Background The sclera is the white outer shell and principal load-bearing tissue of the eye as it sustains the intraocular pressure. We have hypothesized that the mechanical properties of the posterior sclera play a significant role in, and are altered by the development of glaucoma – an ocular disease manifested by structural damage to the optic nerve head. Method of Approach An anisotropic hyperelastic constitutive model is presented to simulate the mechanical behavior of the posterior sclera under acute elevations of intraocular pressure. The constitutive model is derived from fiber-reinforced composite theory, and incorporates stretch-induced stiffening of the reinforcing collagen fibers. Collagen fiber alignment was assumed to be multi-directional at local material points, confined within the plane tangent to the scleral surface, and described by the semi-circular von-Mises distribution. The introduction of a model parameter, namely the fiber concentration factor, was used to control collagen fiber alignment along a preferred fiber orientation. To investigate the effects of scleral collagen fiber alignment on the overall behaviors of the posterior sclera and optic nerve head, finite element simulations of an idealized eye were performed. The four output quantities analyzed were the scleral canal expansion, the scleral canal twist, the posterior scleral canal deformation and the posterior laminar deformation. Results A circumferential fiber organization in the sclera restrained scleral canal expansion but created posterior laminar deformation, whereas the opposite was observed with a meridional fiber organization. Additionally, the fiber concentration factor acted as an amplifying parameter on the considered outputs. Conclusions The present model simulation suggests that the posterior sclera has a large impact on the overall behavior of the optic nerve head. It is therefore primordial to provide accurate mechanical properties for this tissue. In a companion
How useful are complex flood damage models?
NASA Astrophysics Data System (ADS)
Schröter, Kai; Kreibich, Heidi; Vogel, Kristin; Riggelsen, Carsten; Scherbaum, Frank; Merz, Bruno
2014-04-01
We investigate the usefulness of complex flood damage models for predicting relative damage to residential buildings in a spatial and temporal transfer context. We apply eight different flood damage models to predict relative building damage for five historic flood events in two different regions of Germany. Model complexity is measured in terms of the number of explanatory variables which varies from 1 variable up to 10 variables which are singled out from 28 candidate variables. Model validation is based on empirical damage data, whereas observation uncertainty is taken into consideration. The comparison of model predictive performance shows that additional explanatory variables besides the water depth improve the predictive capability in a spatial and temporal transfer context, i.e., when the models are transferred to different regions and different flood events. Concerning the trade-off between predictive capability and reliability the model structure seem more important than the number of explanatory variables. Among the models considered, the reliability of Bayesian network-based predictions in space-time transfer is larger than for the remaining models, and the uncertainties associated with damage predictions are reflected more completely.
NASA Astrophysics Data System (ADS)
Andrews, Benjamin J.
The phenomena of creep and fatigue have each been thoroughly studied. More recently, attempts have been made to predict the damage evolution in engineering materials due to combined creep and fatigue loading, but these formulations have been strictly empirical and have not been used successfully outside of a narrow set of conditions. This work proposes a new creep-fatigue crack growth model based on constitutive creep equations (adjusted to experimental data) and Paris law fatigue crack growth. Predictions from this model are compared to experimental data in two steels: modified 9Cr-1Mo steel and AISI 316L stainless steel. Modified 9Cr-1Mo steel is a high-strength steel used in the construction of pressure vessels and piping for nuclear and conventional power plants, especially for high temperature applications. Creep-fatigue and pure creep experimental data from the literature are compared to model predictions, and they show good agreement. Material constants for the constitutive creep model are obtained for AISI 316L stainless steel, an alloy steel widely used for temperature and corrosion resistance for such components as exhaust manifolds, furnace parts, heat exchangers and jet engine parts. Model predictions are compared to pure creep experimental data, with satisfactory results. Assumptions and constraints inherent in the implementation of the present model are examined. They include: spatial discretization, similitude, plane stress constraint and linear elasticity. It is shown that the implementation of the present model had a non-trivial impact on the model solutions in 316L stainless steel, especially the spatial discretization. Based on these studies, the following conclusions are drawn: 1. The constitutive creep model consistently performs better than the Nikbin, Smith and Webster (NSW) model for predicting creep and creep-fatigue crack extension. 2. Given a database of uniaxial creep test data, a constitutive material model such as the one developed for
Probabilistic constitutive relationships for material strength degradation models
NASA Technical Reports Server (NTRS)
Boyce, L.; Chamis, C. C.
1989-01-01
In the present probabilistic methodology for the strength of aerospace propulsion system structural components subjected to such environmentally-induced primitive variables as loading stresses, high temperature, chemical corrosion, and radiation, time is encompassed as an interacting element, allowing the projection of creep and fatigue effects. A probabilistic constitutive equation is postulated to account for the degradation of strength due to these primitive variables which may be calibrated by an appropriately curve-fitted least-squares multiple regression of experimental data. The resulting probabilistic constitutive equation is embodied in the PROMISS code for aerospace propulsion component random strength determination.
NASA Technical Reports Server (NTRS)
Allen Phillip A.; Wilson, Christopher D.
2003-01-01
The development of a pressure-dependent constitutive model with combined multilinear kinematic and isotropic hardening is presented. The constitutive model is developed using the ABAQUS user material subroutine (UMAT). First the pressure-dependent plasticity model is derived. Following this, the combined bilinear and combined multilinear hardening equations are developed for von Mises plasticity theory. The hardening rule equations are then modified to include pressure dependency. The method for implementing the new constitutive model into ABAQUS is given.
Application of damage models in metal forming
Zhu, Y.Y.; Zacharia, T.
1995-06-01
The development of damage models in the analysis of metal forming processes, to characterize the formability limits, is an important area of ongoing research. In this paper, two energy-based damage models for the simulation of crack initiation in metal forming processes are presented. The first one is an isotropic damage model with two damage variables. The second one is an anisotropic model with a damage characteristic tensor. The damage models are developed within the general framework of continuum thermodynamics for irreversible processes by identifying a proper set of internal variables together with their associated generalized forces. An approach is proposed to account for microcrack opening and closing. A viscoplastic regularization algorithm is used to take into account the strain rate effect and to improve numerical stability. Both models have been incorporated into the finite element code, LAGAMINE. The models were applied to simulations of upsetting of collar cylinders and nonisothermal hemispherical punch stretching. The results of the analyses were validated by comparing the finite element simulations with experimentally obtained data.
Modeling laser damage to the retina
NASA Astrophysics Data System (ADS)
Clark, Clifton D.
This dissertation presents recent progress in several areas related to modeling laser damage to the retina. In Chapter 3, we consider the consequences of using the Arrhenius damage model to predict the damage thresholds of multiple pulse, or repetitive pulse, exposures. We have identified a few fundamental trends associated with the multiple pulse damage predictions made by the Arrhenius model. These trends differ from what would be expected by non-thermal mechanisms, and could prove useful in differentiating thermal and non-thermal damage. Chapter 4 presents a new rate equation damage model hypothesized to describe photochemical damage. The model adds a temperature dependent term to the simple rate equation implied by the principle of reciprocity that is characteristic of photochemical damage thresholds. A recent damage threshold study, conducted in-vitro, has revealed a very sharp transition between thermal and photochemical damage threshold trends. For the wavelength used in the experiment (413 nm), thermal damage thresholds were observed at exposure levels that were twice the expected photochemical damage threshold, based on the traditional understanding of photochemical damage. Our model accounts for this observed trend by introducing a temperature dependent quenching, or repair, rate to the photochemical damage rate. For long exposures that give a very small temperature rise, the model reduces to the principle of reciprocity. Near the transition region between thermal and photochemical damage, the model allows the damage threshold to be set by thermal mechanisms, even at exposure above the reciprocity exposure. In Chapter 5, we describe a retina damage model that includes thermal lensing in the eye by coupling beam propagation and heat transfer models together. Thermal lensing has recently been suggested as a contributing factor to the large increase in measured retinal damage thresholds in the near infrared. The transmission of the vitreous decreases
Improving Flood Damage Assessment Models in Italy
NASA Astrophysics Data System (ADS)
Amadio, M.; Mysiak, J.; Carrera, L.; Koks, E.
2015-12-01
The use of Stage-Damage Curve (SDC) models is prevalent in ex-ante assessments of flood risk. To assess the potential damage of a flood event, SDCs describe a relation between water depth and the associated potential economic damage over land use. This relation is normally developed and calibrated through site-specific analysis based on ex-post damage observations. In some cases (e.g. Italy) SDCs are transferred from other countries, undermining the accuracy and reliability of simulation results. Against this background, we developed a refined SDC model for Northern Italy, underpinned by damage compensation records from a recent flood event. Our analysis considers both damage to physical assets and production losses from business interruptions. While the first is calculated based on land use information, production losses are measured through the spatial distribution of Gross Value Added (GVA). An additional component of the model assesses crop-specific agricultural losses as a function of flood seasonality. Our results show an overestimation of asset damage from non-calibrated SDC values up to a factor of 4.5 for tested land use categories. Furthermore, we estimate that production losses amount to around 6 per cent of the annual GVA. Also, maximum yield losses are less than a half of the amount predicted by the standard SDC methods.
NASA Technical Reports Server (NTRS)
Koharchik, Michael; Murphy, Lindsay; Parker, Paul
2012-01-01
An impact model was developed to predict how three specific foam types would damage the Space Shuttle Orbiter insulating tiles. The inputs needed for the model are the foam type, the foam mass, the foam impact velocity, the foam impact incident angle, the type being impacted, and whether the tile is new or aged (has flown at least one mission). The model will determine if the foam impact will cause damage to the tile. If it can cause damage, the model will output the damage cavity dimensions (length, depth, entry angle, exit angle, and sidewall angles). It makes the calculations as soon as the inputs are entered (less than 1 second). The model allows for the rapid calculation of numerous scenarios in a short time. The model was developed from engineering principles coupled with significant impact testing (over 800 foam impact tests). This model is applicable to masses ranging from 0.0002 up to 0.4 pound (0.09 up to 181 g). A prior tool performed a similar function, but was limited to the assessment of a small range of masses and did not have the large test database for verification. In addition, the prior model did not provide outputs of the cavity damage length, entry angle, exit angle, or sidewall angles.
Dislocation Density-Based Constitutive Model for the Mechanical Behavior of Irradiated Cu
Arsenlis, A; Wirth, B D; Rhee, M
2003-04-10
Performance degradation of structural steels in nuclear environments results from the development of a high number density of nanometer scale defects. The defects observed in copper-based alloys are composed of vacancy clusters in the form of stacking fault tetrahedra and/or prismatic dislocation loops, which impede dislocation glide and are evidenced in macroscopic uniaxial stress-strain curves as increased yield strengths, decreased total strain to failure, decreased work hardening and the appearance of a distinct upper yield point above a critical defect concentration (neutron dose). In this paper, we describe the development of an internal state variable model for the mechanical behavior of materials subject to these environments. This model has been developed within an information-passing multiscale materials modeling framework, in which molecular dynamics simulations of dislocation--radiation defect interactions, inform the final coarse-grained continuum model. The plasticity model includes mechanisms for dislocation density growth and multiplication and for radiation defect density evolution with dislocation interaction. The general behavior of the constitutive (single material point) model shows that as the defect density increases, the initial yield point increases and the initial strain hardening decreases. The final coarse-grained model is implemented into a finite element framework and used to simulate the behavior of tensile specimens with varying levels of irradiation induced material damage. The simulation results compare favorably with the experimentally observed mechanical properties of irradiated materials in terms of their increased strength, decreased hardening, and decreased ductility with increasing irradiation dose.
An Irreversible Constitutive Law for Modeling the Delamination Process using Interface Elements
NASA Technical Reports Server (NTRS)
Goyal, Vinay K.; Johnson, Eric R.; Davila, Carlos G.; Jaunky, Navin; Ambur, Damodar (Technical Monitor)
2002-01-01
An irreversible constitutive law is postulated for the formulation of interface elements to predict initiation and progression of delamination in composite structures. An exponential function is used for the constitutive law such that it satisfies a multi-axial stress criterion for the onset of delamination, and satisfies a mixed mode fracture criterion for the progression of delamination. A damage parameter is included to prevent the restoration of the previous cohesive state between the interfacial surfaces. To demonstrate the irreversibility capability of the constitutive law, steady-state crack growth is simulated for quasi-static loading-unloading cycle of various fracture test specimens.
An Irreversible Constitutive Law for Modeling the Delamination Process Using Interface Elements
NASA Technical Reports Server (NTRS)
Goyal, Vinay K.; Johnson, Eric R.; Davila, Carlos G.; Jaunky, Navin; Bushnell, Dennis M. (Technical Monitor)
2002-01-01
An irreversible constitutive law is postulated for the formulation of interface elements to predict initiation and progression of delamination in composite structures. An exponential function is used for the constitutive law such that it satisfies a multi-axial stress criterion for the onset of delamination, and satisfies a mixed mode fracture criterion for the progression of delamination. A damage parameter is included to prevent the restoration of the previous cohesive state between the interfacial surfaces. To demonstrate the irreversibility capability of the constitutive law, steady-state crack growth is simulated for quasi-static loading-unloading cycle of various fracture test specimens.
Nucleation in models of damage mechanics
NASA Astrophysics Data System (ADS)
Gran, J. D.; Rundle, J. B.; Klein, W.; Turcotte, D. L.
2010-12-01
A variety of studies have modeled the physics of material deformation and damage as examples of generalized phase transitions, involving either critical phenomena or spinodal nucleation. Here we study two cellular automaton models of damage mechanics which. The first model is a modified slider-block model with failure threshold weakening. A block is considered partially damaged after its first slip, and any subsequent failure of that block will occur at reduced failure threshold. Damage here is defined as the fraction of blocks that have a reduced failure threshold. The threshold weakening parameter is viewed as a scaling field similar to the occupation probability in site percolation. The second model is time-dependent fiber-bundle model, where the time to failure for each element is specified from a Poissonian distribution and the hazard rate is assumed to have a power-law dependence on stress. Damage here is defined to be the fraction of blocks or fibers that have failed. Because there is no healing, catastrophic failure occurs. The transient behavior prior to rupture propagation is studied and scaling laws are obtained. We compare both models to mean-field percolation which has been shown to be representative of spinodal nucleation and to laboratory experiments that display power-law behavior.
Prediction Of Formability In Sheet Metal Forming Processes Using A Local Damage Model
Teixeira, P.; Santos, Abel; Cesar Sa, J.; Andrade Pires, F.; Barata da Rocha, A.
2007-05-17
The formability in sheet metal forming processes is mainly conditioned by ductile fracture resulting from geometric instabilities due to necking and strain localization. The macroscopic collapse associated with ductile failure is a result of internal degradation described throughout metallographic observations by the nucleation, growth and coalescence of voids and micro-cracks. Damage influences and is influenced by plastic deformation and therefore these two dissipative phenomena should be coupled at the constitutive level. In this contribution, Lemaitre's ductile damage model is coupled with Hill's orthotropic plasticity criterion. The coupling between damaging and material behavior is accounted for within the framework of Continuum Damage Mechanics (CDM). The resulting constitutive equations are implemented in the Abaqus/Explicit code, for the prediction of fracture onset in sheet metal forming processes. The damage evolution law takes into account the important effect of micro-crack closure, which dramatically decreases the rate of damage growth under compressive paths.
Modeling of rock friction 1. Experimental results and constitutive equations
Dieterich, J.H.
1979-01-01
Direct shear experiments on ground surfaces of a granodiorite from Raymond, California, at normal stresses of ??6 MPa demonstrate that competing time, displacement, and velocity effects control rock friction. It is proposed that the strength of the population of points of contacts between sliding surfaces determines frictional strength and that the population of contacts changes continuously with displacements. Previous experiments demonstrate that the strength of the contacts increases with the age of the contacts. The present experiments establish that a characteristic displacement, proportional to surface roughness, is required to change the population of contacts. Hence during slip the average age of the points of contact and therefore frictional strength decrease as slip velocity increases. Displacement weakening and consequently the potential for unstable slip occur whenever displacement reduces the average age of the contacts. In addition to this velocity dependency, which arises from displacement dependency and time dependency, the experiments also show a competing but transient increase in friction whenever slip velocity increases. Creep of the sliding surface at stresses below that for steady state slip is also observed. Constitutive relationships are developed that permit quantitative simulation of the friction versus displacement data as a function of surface roughness and for different time and velocity histories. Unstable slip in experiments is controlled by these constitutive effects and by the stiffness of the experimental system. It is argued that analogous properties control earthquake instability. Copyright ?? 1979 by the American Geophysical Union.
Continuum damage model for ferroelectric materials and its application to multilayer actuators
NASA Astrophysics Data System (ADS)
Gellmann, Roman; Ricoeur, Andreas
2016-05-01
In this paper a micromechanical continuum damage model for ferroelectric materials is presented. As a constitutive law it is implemented into a finite element (FE) code. The model is based on micromechanical considerations of domain switching and its interaction with microcrack growth and coalescence. A FE analysis of a multilayer actuator is performed, showing the initiation of damage zones at the electrode tips during the poling process. Further, the influence of mechanical pre-stressing on damage evolution and actuating properties is investigated. The results provided in this work give useful information on the damage of advanced piezoelectric devices and their optimization.
Integrated research in constitutive modelling at elevated temperatures, part 2
NASA Technical Reports Server (NTRS)
Haisler, W. E.; Allen, D. H.
1986-01-01
Four current viscoplastic models are compared experimentally with Inconel 718 at 1100 F. A series of tests were performed to create a sufficient data base from which to evaluate material constants. The models used include Bodner's anisotropic model; Krieg, Swearengen, and Rhode's model; Schmidt and Miller's model; and Walker's exponential model.
NASA Astrophysics Data System (ADS)
Iseri, Y.; Iwasaki, A.; Miyazaki, C.; Kanae, S.
2014-12-01
Tropical cyclones (TCs) sometimes cause serious damages to human society and thus possible changes of TC properties in the future have been concerned. In fact, the Fifth Assessment Report (AR5) by IPCC (Intergovernmental Panel on Climate Change) mentions likely increasing in intensity and rain rate of TCs. In addition, future change of socioeconomic condition (e.g. population growth) might worsen TC impacts in the future. Thereby, in this study, we developed regression models to estimate economic damages by TCs (hereafter TC damage model), and employed those models to project TC economic damages under several future climate and socioeconomic scenarios. We developed the TC damage models for each of 4 regions; western North Pacific, North American, North Indian, and Southern Hemisphere. The inputs for TC damage model are tropical cyclone central pressure, populations in the area exposed by tropical cyclone wind, and GDP (Gross Domestic Product) per capita. The TC damage models we firstly developed tended to overestimate very low damages and also underestimate very high damages. Thereby we modified structure of TC damage models to improve model performance, and then executed extensive validation of the model. The modified model presented better performance in estimating very low and high TC damages. After the modification and validation of the model, we determined the structure of TC damage models and projected TC economic damages. The result indicated increase in TC economic damage in global scale, while TC economic damage against world GDP would decrease in the future, which result is consistent with previous study.
Modeling of nonlinear constitutive relations of woven ceramic composites
Kuo, Wen-Shyong; Chou, Tsu-Wei
1991-08-01
The linear and nonlinear tensile behavior of SiC/SiC composites is examined. This analysis is based on the observed stress-strain behavior and damage evolution from a series of loading and unloading tensile tests. Stress distribution of the composite with transverse cracks in the transverse yarns is examined, and the nonlinearity of the composite stress-strain relation due to the presence of transverse cracks is predicted by application of a maximum failure strain criterion for the transverse yarn. 7 refs.
A Constitutive Model for Long Time Duration Mechanical Behavior in Insensitive High Explosives
Darnell, I M; Oh, S; Hrousis, C A; Cunningham, B J; Gagliardi, F J
2010-03-09
An anisotropic constitutive model for the long term dimensional stability of insensitive high explosives is proposed. Elastic, creep, thermal, and ratchet growth strains are developed. Pressure and temperature effects are considered. The constitutive model is implemented in an implicit finite element code and compared to a variety of experimental data.
Girard, Michaël J A; Downs, J Crawford; Burgoyne, Claude F; Suh, J-K Francis
2009-05-01
The sclera is the white outer shell and principal load-bearing tissue of the eye as it sustains the intraocular pressure. We have hypothesized that the mechanical properties of the posterior sclera play a significant role in and are altered by the development of glaucoma-an ocular disease manifested by structural damage to the optic nerve head. An anisotropic hyperelastic constitutive model is presented to simulate the mechanical behavior of the posterior sclera under acute elevations of intraocular pressure. The constitutive model is derived from fiber-reinforced composite theory, and incorporates stretch-induced stiffening of the reinforcing collagen fibers. Collagen fiber alignment was assumed to be multidirectional at local material points, confined within the plane tangent to the scleral surface, and described by the semicircular von Mises distribution. The introduction of a model parameter, namely, the fiber concentration factor, was used to control collagen fiber alignment along a preferred fiber orientation. To investigate the effects of scleral collagen fiber alignment on the overall behaviors of the posterior sclera and optic nerve head, finite element simulations of an idealized eye were performed. The four output quantities analyzed were the scleral canal expansion, the scleral canal twist, the posterior scleral canal deformation, and the posterior laminar deformation. A circumferential fiber organization in the sclera restrained scleral canal expansion but created posterior laminar deformation, whereas the opposite was observed with a meridional fiber organization. Additionally, the fiber concentration factor acted as an amplifying parameter on the considered outputs. The present model simulation suggests that the posterior sclera has a large impact on the overall behavior of the optic nerve head. It is therefore primordial to provide accurate mechanical properties for this tissue. In a companion paper (Girard, Downs, Bottlang, Burgoyne, and Suh, 2009
Mathematical modeling of damage in unidirectional composites
NASA Technical Reports Server (NTRS)
Goree, J. G.; Dharani, L. R.; Jones, W. F.
1981-01-01
A review of some approximate analytical models for damaged, fiber reinforced composite materials is presented. Using the classical shear lag stress displacement assumption, solutions are presented for a unidirectional laminate containing a notch, a rectangular cut-out, and a circular hole. The models account for longitudinal matrix yielding and splitting as well as transverse matrix yielding and fiber breakage. The constraining influence of a cover sheet on the unidirectional laminate is also modeled.
Constitutive modeling for blast-induced wave propagation
NASA Astrophysics Data System (ADS)
Drumm, E. C.
1985-03-01
The description of stress-time history acting on a buried structure is a major source of error in the analysis of underground structures to weapons loadings. The stress wave propagating spherically from the weapon is attenuated as it travels from the source. This attenuation is a function of the inelastic response of the soil, and results in an increase in the loading rise time or decrease in the loading rate. Since the inelastic soil response is a function of the loading rate, a wave propagation analysis should be conducted to determine the stresses on the structure. At the interface between the soil and structure, the stress is modified further by soil-structure interaction effects. Thus, the stress on the structure is a function of both the structural and soil properties as well as the distance traveled by the stress wave. These related phenomena can be included in a numerical analysis, but the accuracy depends on the constitutive representation of the materials. One-dimensional wave propagation experiments and impact tests with various soils are reviewed, and the attenuation as a function of the soil stress-strain response is discussed.
Integrated research in constitutive modelling at elevated temperatures, part 1
NASA Technical Reports Server (NTRS)
Haisler, W. E.; Allen, D. H.
1986-01-01
Topics covered include: numerical integration techniques; thermodynamics and internal state variables; experimental lab development; comparison of models at room temperature; comparison of models at elevated temperature; and integrated software development.
A micro to macro approach to polymer matrix composites damage modeling : final LDRD report.
English, Shawn Allen; Brown, Arthur A.; Briggs, Timothy M.
2013-12-01
Capabilities are developed, verified and validated to generate constitutive responses using material and geometric measurements with representative volume elements (RVE). The geometrically accurate RVEs are used for determining elastic properties and damage initiation and propagation analysis. Finite element modeling of the meso-structure over the distribution of characterizing measurements is automated and various boundary conditions are applied. Plain and harness weave composites are investigated. Continuum yarn damage, softening behavior and an elastic-plastic matrix are combined with known materials and geometries in order to estimate the macroscopic response as characterized by a set of orthotropic material parameters. Damage mechanics and coupling effects are investigated and macroscopic material models are demonstrated and discussed. Prediction of the elastic, damage, and failure behavior of woven composites will aid in macroscopic constitutive characterization for modeling and optimizing advanced composite systems.
Survey of four damage models for concrete.
Leelavanichkul, Seubpong; Brannon, Rebecca Moss
2009-08-01
Four conventional damage plasticity models for concrete, the Karagozian and Case model (K&C), the Riedel-Hiermaier-Thoma model (RHT), the Brannon-Fossum model (BF1), and the Continuous Surface Cap Model (CSCM) are compared. The K&C and RHT models have been used in commercial finite element programs many years, whereas the BF1 and CSCM models are relatively new. All four models are essentially isotropic plasticity models for which 'plasticity' is regarded as any form of inelasticity. All of the models support nonlinear elasticity, but with different formulations. All four models employ three shear strength surfaces. The 'yield surface' bounds an evolving set of elastically obtainable stress states. The 'limit surface' bounds stress states that can be reached by any means (elastic or plastic). To model softening, it is recognized that some stress states might be reached once, but, because of irreversible damage, might not be achievable again. In other words, softening is the process of collapse of the limit surface, ultimately down to a final 'residual surface' for fully failed material. The four models being compared differ in their softening evolution equations, as well as in their equations used to degrade the elastic stiffness. For all four models, the strength surfaces are cast in stress space. For all four models, it is recognized that scale effects are important for softening, but the models differ significantly in their approaches. The K&C documentation, for example, mentions that a particular material parameter affecting the damage evolution rate must be set by the user according to the mesh size to preserve energy to failure. Similarly, the BF1 model presumes that all material parameters are set to values appropriate to the scale of the element, and automated assignment of scale-appropriate values is available only through an enhanced implementation of BF1 (called BFS) that regards scale effects to be coupled to statistical variability of material
Constitutive Modeling of the Mechanical Properties of Optical Fibers
NASA Technical Reports Server (NTRS)
Moeti, L.; Moghazy, S.; Veazie, D.; Cuddihy, E.
1998-01-01
Micromechanical modeling of the composite mechanical properties of optical fibers was conducted. Good agreement was obtained between the values of Young's modulus obtained by micromechanics modeling and those determined experimentally for a single mode optical fiber where the wave guide and the jacket are physically coupled. The modeling was also attempted on a polarization-maintaining optical fiber (PANDA) where the wave guide and the jacket are physically decoupled, and found not to applicable since the modeling required perfect bonding at the interface. The modeling utilized constituent physical properties such as the Young's modulus, Poisson's ratio, and shear modulus to establish bounds on the macroscopic behavior of the fiber.
A constitutive model of polyether-ether-ketone (PEEK).
Chen, Fei; Ou, Hengan; Lu, Bin; Long, Hui
2016-01-01
A modified Johnson-Cook (JC) model was proposed to describe the flow behaviour of polyether-ether-ketone (PEEK) with the consideration of coupled effects of strain, strain rate and temperature. As compared to traditional JC model, the modified one has better ability to predict the flow behaviour at elevated temperature conditions. In particular, the yield stress was found to be inversely proportional to temperature from the predictions of the proposed model. PMID:26409233
Constitutive models used to simulate penetration and perforation of concrete targets
Akers, S.A.; Adley, M.D.
1996-12-31
Only a limited number of nonlinear constitutive models are available in wave propagation codes to simulate geologic materials, and these models often do not capture the fundamental and often complex mechanical behavior of these materials. Researchers at the WES have recently implemented two models, which were specifically designed for geologic materials, into the large-strain Lagrangian wave-propagation code EPIC. These models are currently being used in finite-element simulations of penetration and ground-shock problems. In this paper, the formulation of the constitutive models is examined and the implementation of the models into EPIC is briefly described. Results from a series of calculations are presented to illustrate the effect of the constitutive models on penetration and perforation problems. Three models are compared, one of the new WES models, the EPIC crushable-solids model, which is often employed to model geologic materials, and EPIC`s Holmquist-Johnson-Cook model for concrete.
Modeling and Algorithmic Approaches to Constitutively-Complex, Microstructured Fluids
Miller, Gregory H.; Forest, Gregory
2011-12-22
We present a new multiscale model for complex uids based on three scales: microscopic, kinetic, and continuum. We choose the microscopic level as Kramers' bead-rod model for polymers, which we describe as a system of stochastic di erential equations with an implicit constraint formulation. The associated Fokker-Planck equation is then derived, and adiabatic elimination removes the fast momentum coordinates. Approached in this way, the kinetic level reduces to a dispersive drift equation. The continuum level is modeled with a nite volume Godunov-projection algorithm. We demonstrate computation of viscoelastic stress divergence using this multiscale approach.
Evaluation of Inelastic Constitutive Models for Nonlinear Structural Analysis
NASA Technical Reports Server (NTRS)
Kaufman, A.
1983-01-01
The influence of inelastic material models on computed stress-strain states, and therefore predicted lives, was studied for thermomechanically loaded structures. Nonlinear structural analyses were performed on a fatigue specimen which was subjected to thermal cycling in fluidized beds and on a mechanically load cycled benchmark notch specimen. Four incremental plasticity creep models (isotropic, kinematic, combined isotropic-kinematic, combined plus transient creep) were exercised. Of the plasticity models, kinematic hardening gave results most consistent with experimental observations. Life predictions using the computed strain histories at the critical location with a Strainrange Partitioning approach considerably overpredicted the crack initiation life of the thermal fatigue specimen.
Experience in calibrating the double-hardening constitutive model Monot
NASA Astrophysics Data System (ADS)
Hicks, M. A.
2003-11-01
The Monot double-hardening soil model has previously been implemented within a general purpose finite element algorithm, and used in the analysis of numerous practical problems. This paper reviews experience gained in calibrating Monot to laboratory data and demonstrates how the calibration process may be simplified without detriment to the range of behaviours modelled. It describes Monot's principal features, important governing equations and various calibration methods, including strategies for overconsolidated, cemented and cohesive soils. Based on a critical review of over 30 previous Monot calibrations, for sands and other geomaterials, trends in parameter values have been identified, enabling parameters to be categorized according to their relative importance. It is shown that, for most practical purposes, a maximum of only 5 parameters is needed; for the remaining parameters, standard default values are suggested. Hence, the advanced stress-strain modelling offered by Monot is attainable with a similar number of parameters as would be needed for some simpler, less versatile, models. Copyright
Vianco, P.T.; Burchett, S.N.; Neilsen, M.K.; Rejent, J.A.; Frear, D.R.
1999-04-12
Thermal mechanical fatigue (TMF) is an important damage mechanism for solder joints exposed to cyclic temperature environments. Predicting the service reliability of solder joints exposed to such conditions requires two knowledge bases: first, the extent of fatigue damage incurred by the solder microstructure leading up to fatigue crack initiation, must be quantified in both time and space domains. Secondly, fatigue crack initiation and growth must be predicted since this metric determines, explicitly, the loss of solder joint functionality as it pertains to its mechanical fastening as well as electrical continuity roles. This paper will describe recent progress in a research effort to establish a microstructurally-based, constitutive model that predicts TMF deformation to 63Sn-37Pb solder in electronic solder joints up to the crack initiation step. The model is implemented using a finite element setting; therefore, the effects of both global and local thermal expansion mismatch conditions in the joint that would arise from temperature cycling.
What Constitutes a Relevant Animal Model of the Ketogenic Diet?
Holmes, Gregory L.
2009-01-01
Summary Animal models of human disease have been enormously important in improving our understanding of the pathophysiological basis and the development of novel therapies. In epilepsy, modeling using both in vivo and in vitro preparations has provided insight into fundamental neuronal mechanisms. Indeed, much of our understanding of seizure mechanisms comes from animal studies. The conceptual advances in understanding basic mechanisms of epilepsies have been largely validated in humans, attesting to the validity of the rationale and providing a basis for bridging the gaps between experimental and human data. While the ketogenic diet is clearly efficacious in a wide variety of seizure types and syndromes, the mechanism of action of the diet has not been established. Animal models will continue to be enormously important in furthering our understanding of how dietary therapy can help individuals with epilepsy. PMID:19049589
A kinematically driven anisotropic viscoelastic constitutive model applied to tires
NASA Astrophysics Data System (ADS)
Johnson, Arthur R.; Tanner, John A.; Mason, Angela J.
1995-08-01
Aircraft tires are composite structures manufactured with viscoelastic materials such as carbon black filled rubber and nylon cords. When loaded they experience large deflections and moderately large strains. Detailed structural models of tires require the use of either nonlinear shell or nonlinear three dimensional solid finite elements. Computational predictions of the dynamic response of tires must consider the composite viscoelastic material behavior in a realistic fashion. We describe a modification to a nonlinear anisotropic shell finite element so it can be used to model viscoelastic stresses during general deformations. The model is developed by introducing internal variables of the type used to model elastic strain energy. The internal variables are strains, curvatures, and transverse shear angles which are in a one-to-one correspondence with the generalized coordinates used to model the elastic strain energy for nonlinear response. A difference-relaxation equation is used to relate changes in the observable strain field to changes in the internal strain field. The internal stress state is introduced into the equilibrium equations by converting it to nodal loads associated with the element's displacement degrees of freedom. In this form the tangent matrix in the Newton-Raphson solution algorithm is not modified from its form for the nonlinear statics problem. Only the gradient vector is modified and the modification is not computationally costly. The existing finite element model for the Space Shuttle nose gear tire is used to provide examples of the algorithm. In the first example, the tire's rim is displaced at a constant rate up to a fixed value. In the second example, the tire's rim is enforced to follow a saw tooth load and unload curve to generate hysteresis loops.
A kinematically driven anisotropic viscoelastic constitutive model applied to tires
NASA Technical Reports Server (NTRS)
Johnson, Arthur R.; Tanner, John A.; Mason, Angela J.
1995-01-01
Aircraft tires are composite structures manufactured with viscoelastic materials such as carbon black filled rubber and nylon cords. When loaded they experience large deflections and moderately large strains. Detailed structural models of tires require the use of either nonlinear shell or nonlinear three dimensional solid finite elements. Computational predictions of the dynamic response of tires must consider the composite viscoelastic material behavior in a realistic fashion. We describe a modification to a nonlinear anisotropic shell finite element so it can be used to model viscoelastic stresses during general deformations. The model is developed by introducing internal variables of the type used to model elastic strain energy. The internal variables are strains, curvatures, and transverse shear angles which are in a one-to-one correspondence with the generalized coordinates used to model the elastic strain energy for nonlinear response. A difference-relaxation equation is used to relate changes in the observable strain field to changes in the internal strain field. The internal stress state is introduced into the equilibrium equations by converting it to nodal loads associated with the element's displacement degrees of freedom. In this form the tangent matrix in the Newton-Raphson solution algorithm is not modified from its form for the nonlinear statics problem. Only the gradient vector is modified and the modification is not computationally costly. The existing finite element model for the Space Shuttle nose gear tire is used to provide examples of the algorithm. In the first example, the tire's rim is displaced at a constant rate up to a fixed value. In the second example, the tire's rim is enforced to follow a saw tooth load and unload curve to generate hysteresis loops.
Density Functional Theory Models for Radiation Damage
NASA Astrophysics Data System (ADS)
Dudarev, S. L.
2013-07-01
Density functional theory models developed over the past decade provide unique information about the structure of nanoscale defects produced by irradiation and about the nature of short-range interaction between radiation defects, clustering of defects, and their migration pathways. These ab initio models, involving no experimental input parameters, appear to be as quantitatively accurate and informative as the most advanced experimental techniques developed for the observation of radiation damage phenomena. Density functional theory models have effectively created a new paradigm for the scientific investigation and assessment of radiation damage effects, offering new insight into the origin of temperature- and dose-dependent response of materials to irradiation, a problem of pivotal significance for applications.
Formation of algae growth constitutive relations for improved algae modeling.
Gharagozloo, Patricia E.; Drewry, Jessica L.
2013-01-01
This SAND report summarizes research conducted as a part of a two year Laboratory Directed Research and Development (LDRD) project to improve our abilities to model algal cultivation. Algae-based biofuels have generated much excitement due to their potentially large oil yield from relatively small land use and without interfering with the food or water supply. Algae mitigate atmospheric CO2 through metabolism. Efficient production of algal biofuels could reduce dependence on foreign oil by providing a domestic renewable energy source. Important factors controlling algal productivity include temperature, nutrient concentrations, salinity, pH, and the light-to-biomass conversion rate. Computational models allow for inexpensive predictions of algae growth kinetics in these non-ideal conditions for various bioreactor sizes and geometries without the need for multiple expensive measurement setups. However, these models need to be calibrated for each algal strain. In this work, we conduct a parametric study of key marine algae strains and apply the findings to a computational model.
A Robust Damage Assessment Model for Corrupted Database Systems
NASA Astrophysics Data System (ADS)
Fu, Ge; Zhu, Hong; Li, Yingjiu
An intrusion tolerant database uses damage assessment techniques to detect damage propagation scales in a corrupted database system. Traditional damage assessment approaches in a intrusion tolerant database system can only locate damages which are caused by reading corrupted data. In fact, there are many other damage spreading patterns that have not been considered in traditional damage assessment model. In this paper, we systematically analyze inter-transaction dependency relationships that have been neglected in the previous research and propose four different dependency relationships between transactions which may cause damage propagation. We extend existing damage assessment model based on the four novel dependency relationships. The essential properties of our model is also discussed.
Constitutive Models for Debris-bearing Ice Layers
NASA Astrophysics Data System (ADS)
Moore, P. L.
2013-12-01
Rock debris is incorporated within many glaciers and ice sheets, particularly in basal ice layers and englacial debris bands. Field observations and laboratory experiments have shown that debris inclusions can both strengthen and weaken ice by as much as two orders of magnitude compared to debris-free ice under the same conditions. Nevertheless, models of glacier flow usually neglect any effect of debris-bearing layers. Where debris-bearing ice is present, proper treatment of its deformation could profoundly impact model results. A three-phase mechanical model is presented that reproduces many of the key observations of debris-bearing ice rheology. First order variables in the model are limited to debris concentration, particle size, solute concentration and temperature. At low debris concentrations (less than about 40% by volume), the mixture is treated under the framework of a dispersion-strengthened metal alloy but with a fluidity that is enhanced by premelted water at ice-debris interfaces. While debris strengthens the ice by interfering with the motion of dislocations, thermally-activated detachment can reduce the effect at temperatures close to melting. At these warm temperatures, recovery aided by unfrozen interfacial water acts to weaken the mixture, an effect that is further ehnanced by the presence of solutes at particle surfaces. Whether the debris-bearing ice is stronger or weaker than debris-free ice in the model depends strongly on the specific surface area of the debris and on a parameter that describes the thermal detachment of dislocations. As debris concentrations exceed about 40%, dispersion-strengthened ice flow still governs bulk deformation but the effective viscosity is further increased by enhanced strain rates in the ice "matrix" as the average inter-particle distance declines. At still higher concentrations (greater than about 52% by volume for sand), deformation is primarily frictional. The mixture is thus treated as a dilatant Coulomb
A continuous damage model based on stepwise-stress creep rupture tests
NASA Technical Reports Server (NTRS)
Robinson, D. N.
1985-01-01
A creep damage accumulation model is presented that makes use of the Kachanov damage rate concept with a provision accounting for damage that results from a variable stress history. This is accomplished through the introduction of an additional term in the Kachanov rate equation that is linear in the stress rate. Specification of the material functions and parameters in the model requires two types of constituting a data base: (1) standard constant-stress creep rupture tests, and (2) a sequence of two-step creep rupture tests.
Constitutive Relationships and Models in Continuum Theories of Multiphase Flows. [conferences
NASA Technical Reports Server (NTRS)
Decker, Rand (Editor)
1989-01-01
In April, 1989, a workshop on constitutive relationships and models in continuum theories of multiphase flows was held at NASA's Marshall Space Flight Center. Topics of constitutive relationships for the partial or per phase stresses, including the concept of solid phase pressure are discussed. Models used for the exchange of mass, momentum, and energy between the phases in a multiphase flow are also discussed. The program, abstracts, and texts of the presentations from the workshop are included.
Non-linear approach in visco-hyperelastic constitutive modelling of polyurethane nanocomposite
NASA Astrophysics Data System (ADS)
Pawlikowski, Marek
2014-02-01
The constitutive modelling of the polyurethane nanocomposite presented in the paper is done in the context of its possible application as one of the components of the intervertebral disc prosthesis. The constitutive study is a part of the researches aiming at creation of the new prosthetic device. The material is considered as incompressible, isotropic and visco-hyperelastic one. The focus of the work lies on the formulation of a constitutive equation for its further implementation in finite element analyses. The equation is formulated on the basis of uniaxial monotonic compression tests and relaxation tests performed at room temperature. The constants of the constitutive model are determined from the experimental data by means of the curve-fitting approach employing least-squares optimisation method. The constitutive modelling consisted of two steps. In the first one pure hyperelastic model was determined. The Mooney-Rivlin model proved to be the best one to describe hyperelastic behaviour of the material. In the second step non-linear visco-hyperelastic model was derived. Relaxation times, characteristic amplitudes and Mooney-Rivlin hyperelastic constants were calibrated on the basis of strain-stress curves (hysteresis loops) obtained experimentally at three strain rates, i.e. and . The constitutive law is validated on the basis of relaxation test. The paper concludes with summary and plans for further investigations in the area.
A continuum damage model of fatigue-induced damage in laminated composites
NASA Technical Reports Server (NTRS)
Harris, Charles E.; Allen, David H.
1988-01-01
A model is presented which predicts the stress-strain behavior of continuous fiber reinforced laminated composites in the presence of microstructural damage. The model is based on the concept of continuum damage mechanics and uses internal state variables to characterize the various damage modes. The associated internal state variable growth laws are mathematical models of the loading history induced development of microstructural damage. The model is demonstrated by using it to predict the response of damaged AS-4/3502 graphite/epoxy laminate panels.
NASA Astrophysics Data System (ADS)
Grelot, Frédéric; Agenais, Anne-Laurence; Brémond, Pauline
2014-05-01
In France, since 2011, it is mandatory for local communities to conduct cost-benefit analysis (CBA) of their flood management projects, to make them eligible for financial support from the State. Meanwhile, as a support, the French Ministry in charge of Environment proposed a methodology to fulfill CBA. Like for many other countries, this methodology is based on the estimation of flood damage. Howerver, existing models to estimate flood damage were judged not convenient for a national-wide use. As a consequence, the French Ministry in charge of Environment launched studies to develop damage models for different sectors, such as: residential sector, public infrastructures, agricultural sector, and commercial and industrial sector. In this presentation, we aim at presenting and discussing methodological choices of those damage models. They all share the same principle: no sufficient data from past events were available to build damage models on a statistical analysis, so modeling was based on expert knowledge. We will focus on the model built for agricultural activities and more precisely for agricultural lands. This model was based on feedback from 30 agricultural experts who experienced floods in their geographical areas. They were selected to have a representative experience of crops and flood conditions in France. The model is composed of: (i) damaging functions, which reveal physiological vulnerability of crops, (ii) action functions, which correspond to farmers' decision rules for carrying on crops after a flood, and (iii) economic agricultural data, which correspond to featured characteristics of crops in the geographical area where the flood management project studied takes place. The two first components are generic and the third one is specific to the area studied. It is, thus, possible to produce flood damage functions adapted to different agronomic and geographical contexts. In the end, the model was applied to obtain a pool of damage functions giving
NASA Astrophysics Data System (ADS)
Grelot, Frédéric; Agenais, Anne-Laurence; Brémond, Pauline
2015-04-01
In France, since 2011, it is mandatory for local communities to conduct cost-benefit analysis (CBA) of their flood management projects, to make them eligible for financial support from the State. Meanwhile, as a support, the French Ministry in charge of Environment proposed a methodology to fulfill CBA. Like for many other countries, this methodology is based on the estimation of flood damage. However, existing models to estimate flood damage were judged not convenient for a national-wide use. As a consequence, the French Ministry in charge of Environment launched studies to develop damage models for different sectors, such as: residential sector, public infrastructures, agricultural sector, and commercial and industrial sector. In this presentation, we aim at presenting and discussing methodological choices of those damage models. They all share the same principle: no sufficient data from past events were available to build damage models on a statistical analysis, so modeling was based on expert knowledge. We will focus on the model built for agricultural activities and more precisely for agricultural lands. This model was based on feedback from 30 agricultural experts who experienced floods in their geographical areas. They were selected to have a representative experience of crops and flood conditions in France. The model is composed of: (i) damaging functions, which reveal physiological vulnerability of crops, (ii) action functions, which correspond to farmers' decision rules for carrying on crops after a flood, and (iii) economic agricultural data, which correspond to featured characteristics of crops in the geographical area where the flood management project studied takes place. The two first components are generic and the third one is specific to the area studied. It is, thus, possible to produce flood damage functions adapted to different agronomic and geographical contexts. In the end, the model was applied to obtain a pool of damage functions giving
Modeling Coal Seam Damage in Cast Blasting
Chung, S.H.; Preece, D.S.
1998-11-23
A discrete element computer program named DMC_BLAST (Distinct Motion Code) has been under development since 1987 for modeling rock blasting (Preece & Taylor, 1989). This program employs explicit time integration and uses spherical or cylindrical elements that are represented as circles in two dimensions. DMC_BLAST calculations compare favorably with data from actual bench blasts (Preece et al, 1993). Coal seam chilling refers to the shattering of a significant portion of the coal leaving unusable fines. It is also refereed to as coal damage. Chilling is caused during a blast by a combination of explosive shock energy and movement of the adjacent rock. Chilling can be minimized by leaving a buffer zone between the bottom of the blastholes and the coal seam or by changing the blast design to decrease the powder factor or by a combination of both. Blast design in coal mine cast blasting is usually a compromise between coal damage and rock fragmentation and movement (heave). In this paper the damage to coal seams from rock movement is examined using the discrete element computer code DMC_BLAST. A rock material strength option has been incorporated into DMC_BLAST by placing bonds/links between the spherical particles used to model the rock. These bonds tie the particles together but can be broken when the tensile, compressive or shear stress in the bond exceeds the defined strength. This capability has been applied to predict coal seam damage, particularly at the toe of a cast blast where drag forces exerted by movement of the overlying rock can adversely effect the top of the coal at the bench face. A simulation of coal mine cast blasting has been performed with special attention being paid to the strength of the coal and its behavior at t he bench face during movement of the overlying material.
Life prediction and constitutive models for engine hot section anisotropic materials
NASA Technical Reports Server (NTRS)
Swanson, G. A.; Linask, I.; Nissley, D. M.; Norris, P. P.; Meyer, T. G.; Walker, K. P.
1987-01-01
The results are presented of a program designed to develop life prediction and constitutive models for two coated single crystal alloys used in gas turbine airfoils. The two alloys are PWA 1480 and Alloy 185. The two oxidation resistant coatings are PWA 273, an aluminide coating, and PWA 286, an overlay NiCoCrAlY coating. To obtain constitutive and fatigue data, tests were conducted on uncoated and coated specimens loaded in the CH76 100 CH110 , CH76 110 CH110 , CH76 111 CH110 and CH76 123 CH110 crystallographic directions. Two constitutive models are being developed and evaluated for the single crystal materials: a micromechanic model based on crystallographic slip systems, and a macroscopic model which employs anisotropic tensors to model inelastic deformation anisotropy. Based on tests conducted on the overlay coating material, constitutive models for coatings also appear feasible and two initial models were selected. A life prediction approach was proposed for coated single crystal materials, including crack initiation either in the coating or in the substrate. The coating initiated failures dominated in the tests at load levels typical of gas turbine operation. Coating life was related to coating stress/strain history which was determined from specimen data using the constitutive models.
NASA Astrophysics Data System (ADS)
Haberman, Keith
2001-07-01
A micromechanically based constitutive model for the dynamic inelastic behavior of brittle materials, specifically "Dionysus-Pentelicon marble" with distributed microcracking is presented. Dionysus-Pentelicon marble was used in the construction of the Parthenon, in Athens, Greece. The constitutive model is a key component in the ability to simulate this historic explosion and the preceding bombardment form cannon fire that occurred at the Parthenon in 1678. Experiments were performed by Rosakis (1999) that characterized the static and dynamic response of this unique material. A micromechanical constitutive model that was previously successfully used to model the dynamic response of granular brittle materials is presented. The constitutive model was fitted to the experimental data for marble and reproduced the experimentally observed basic uniaxial dynamic behavior quite well. This micromechanical constitutive model was then implemented into the three dimensional nonlinear lagrangain finite element code Dyna3d(1998). Implementing this methodology into the three dimensional nonlinear dynamic finite element code allowed the model to be exercised on several preliminary impact experiments. During future simulations, the model is to be used in conjunction with other numerical techniques to simulate projectile impact and blast loading on the Dionysus-Pentelicon marble and on the structure of the Parthenon.
An investigation of the material and model parameters for a constitutive model for MSMAs
NASA Astrophysics Data System (ADS)
Dikes, Jason; Feigenbaum, Heidi; Ciocanel, Constantin
2015-04-01
A two dimensional constitutive model capable of predicting the magneto-mechanical response of a magnetic shape memory alloy (MSMA) has been developed and calibrated using a zero field-variable stress test1. This calibration approach is easy to perform and facilitates a faster evaluation of the three calibration constants required by the model (vs. five calibration constants required by previous models2,3). The calibration constants generated with this approach facilitate good model predictions of constant field-variable stress tests, for a wide range of loading conditions1. However, the same calibration constants yield less accurate model predictions for constant stress-variable field tests. Deployment of a separate calibration method for this type of loading, using a varying field-zero stress calibration test, also didn't lead to improved model predictions of this loading case. As a result, a sensitivity analysis was performed on most model and material parameters to identify which of them may influence model predictions the most, in both types of loading conditions. The sensitivity analysis revealed that changing most of these parameters did not improve model predictions for all loading types. Only the anisotropy coefficient was found to improve significantly field controlled model predictions and slightly worsen model predictions for stress controlled cases. This suggests that either the value of the anisotropy coefficient (which is provided by the manufacturer) is not accurate, or that the model is missing features associated with the magnetic energy of the material.
Modeling neural activity with cumulative damage distributions.
Leiva, Víctor; Tejo, Mauricio; Guiraud, Pierre; Schmachtenberg, Oliver; Orio, Patricio; Marmolejo-Ramos, Fernando
2015-10-01
Neurons transmit information as action potentials or spikes. Due to the inherent randomness of the inter-spike intervals (ISIs), probabilistic models are often used for their description. Cumulative damage (CD) distributions are a family of probabilistic models that has been widely considered for describing time-related cumulative processes. This family allows us to consider certain deterministic principles for modeling ISIs from a probabilistic viewpoint and to link its parameters to values with biological interpretation. The CD family includes the Birnbaum-Saunders and inverse Gaussian distributions, which possess distinctive properties and theoretical arguments useful for ISI description. We expand the use of CD distributions to the modeling of neural spiking behavior, mainly by testing the suitability of the Birnbaum-Saunders distribution, which has not been studied in the setting of neural activity. We validate this expansion with original experimental and simulated electrophysiological data. PMID:25998210
Interacting damage models mapped onto ising and percolation models
Toussaint, Renaud; Pride, Steven R.
2004-03-23
The authors introduce a class of damage models on regular lattices with isotropic interactions between the broken cells of the lattice. Quasistatic fiber bundles are an example. The interactions are assumed to be weak, in the sense that the stress perturbation from a broken cell is much smaller than the mean stress in the system. The system starts intact with a surface-energy threshold required to break any cell sampled from an uncorrelated quenched-disorder distribution. The evolution of this heterogeneous system is ruled by Griffith's principle which states that a cell breaks when the release in potential (elastic) energy in the system exceeds the surface-energy barrier necessary to break the cell. By direct integration over all possible realizations of the quenched disorder, they obtain the probability distribution of each damage configuration at any level of the imposed external deformation. They demonstrate an isomorphism between the distributions so obtained and standard generalized Ising models, in which the coupling constants and effective temperature in the Ising model are functions of the nature of the quenched-disorder distribution and the extent of accumulated damage. In particular, they show that damage models with global load sharing are isomorphic to standard percolation theory, that damage models with local load sharing rule are isomorphic to the standard ising model, and draw consequences thereof for the universality class and behavior of the autocorrelation length of the breakdown transitions corresponding to these models. they also treat damage models having more general power-law interactions, and classify the breakdown process as a function of the power-law interaction exponent. Last, they also show that the probability distribution over configurations is a maximum of Shannon's entropy under some specific constraints related to the energetic balance of the fracture process, which firmly relates this type of quenched-disorder based damage model
Interacting damage models mapped onto Ising and percolation models.
Toussaint, Renaud; Pride, Steven R
2005-04-01
We introduce a class of damage models on regular lattices with isotropic interactions between the broken cells of the lattice. Quasi-static fiber bundles are an example. The interactions are assumed to be weak, in the sense that the stress perturbation from a broken cell is much smaller than the mean stress in the system. The system starts intact with a surface-energy threshold required to break any cell sampled from an uncorrelated quenched-disorder distribution. The evolution of this heterogeneous system is ruled by Griffith's principle which states that a cell breaks when the release in potential (elastic) energy in the system exceeds the surface-energy barrier necessary to break the cell. By direct integration over all possible realizations of the quenched disorder, we obtain the probability distribution of each damage configuration at any level of the imposed external deformation. We demonstrate an isomorphism between the distributions so obtained and standard generalized Ising models, in which the coupling constants and effective temperature in the Ising model are functions of the nature of the quenched-disorder distribution and the extent of accumulated damage. In particular, we show that damage models with global load sharing are isomorphic to standard percolation theory and that damage models with a local load sharing rule are isomorphic to the standard Ising model, and draw consequences thereof for the universality class and behavior of the autocorrelation length of the breakdown transitions corresponding to these models. We also treat damage models having more general power-law interactions, and classify the breakdown process as a function of the power-law interaction exponent. Last, we also show that the probability distribution over configurations is a maximum of Shannon's entropy under some specific constraints related to the energetic balance of the fracture process, which firmly relates this type of quenched-disorder based damage model to standard
Development of a unified constitutive model for an isotropic nickel base superalloy Rene 80
NASA Technical Reports Server (NTRS)
Ramaswamy, V. G.; Vanstone, R. H.; Laflen, J. H.; Stouffer, D. C.
1988-01-01
Accurate analysis of stress-strain behavior is of critical importance in the evaluation of life capabilities of hot section turbine engine components such as turbine blades and vanes. The constitutive equations used in the finite element analysis of such components must be capable of modeling a variety of complex behavior exhibited at high temperatures by cast superalloys. The classical separation of plasticity and creep employed in most of the finite element codes in use today is known to be deficient in modeling elevated temperature time dependent phenomena. Rate dependent, unified constitutive theories can overcome many of these difficulties. A new unified constitutive theory was developed to model the high temperature, time dependent behavior of Rene' 80 which is a cast turbine blade and vane nickel base superalloy. Considerations in model development included the cyclic softening behavior of Rene' 80, rate independence at lower temperatures and the development of a new model for static recovery.
Damage Propagation Modeling for Aircraft Engine Prognostics
NASA Technical Reports Server (NTRS)
Saxena, Abhinav; Goebel, Kai; Simon, Don; Eklund, Neil
2008-01-01
This paper describes how damage propagation can be modeled within the modules of aircraft gas turbine engines. To that end, response surfaces of all sensors are generated via a thermo-dynamical simulation model for the engine as a function of variations of flow and efficiency of the modules of interest. An exponential rate of change for flow and efficiency loss was imposed for each data set, starting at a randomly chosen initial deterioration set point. The rate of change of the flow and efficiency denotes an otherwise unspecified fault with increasingly worsening effect. The rates of change of the faults were constrained to an upper threshold but were otherwise chosen randomly. Damage propagation was allowed to continue until a failure criterion was reached. A health index was defined as the minimum of several superimposed operational margins at any given time instant and the failure criterion is reached when health index reaches zero. Output of the model was the time series (cycles) of sensed measurements typically available from aircraft gas turbine engines. The data generated were used as challenge data for the Prognostics and Health Management (PHM) data competition at PHM 08.
NASA Technical Reports Server (NTRS)
Walker, K. P.
1981-01-01
Results of a 20-month research and development program for nonlinear structural modeling with advanced time-temperature constitutive relationships are reported. The program included: (1) the evaluation of a number of viscoplastic constitutive models in the published literature; (2) incorporation of three of the most appropriate constitutive models into the MARC nonlinear finite element program; (3) calibration of the three constitutive models against experimental data using Hastelloy-X material; and (4) application of the most appropriate constitutive model to a three dimensional finite element analysis of a cylindrical combustor liner louver test specimen to establish the capability of the viscoplastic model to predict component structural response.
NASA Astrophysics Data System (ADS)
Gu, Sendong; Zhang, Liwen; Zhang, Chi; Shen, Wenfei
2016-03-01
The hot deformation characteristics of nickel-based alloy Nimonic 80A were investigated by isothermal compression tests conducted in the temperature range of 1,000-1,200°C and the strain rate range of 0.01—5 s-1 on a Gleeble-1500 thermomechanical simulator. In order to establish the constitutive models for dynamic recrystallization (DRX) behavior and flow stress of Nimonic 80A, the material constants α, n and DRX activation energy Q in the constitutive models were calculated by the regression analysis of the experimental data. The dependences of initial stress, saturation stress, steady-state stress, dynamic recovery (DRV) parameter, peak strain, critical strain and DRX grain size on deformation parameters were obtained. Then, the Avrami equation including the critical strain for DRX and the peak strain as a function of strain was established to describe the DRX volume fraction. Finally, the constitutive model for flow stress of Nimonic 80A was developed in DRV region and DRX region, respectively. The flow stress values predicted by the constitutive model are in good agreement with the experimental ones, which indicates that the constitutive model can give an accurate estimate for the flow stress of Nimonic 80A under the deformation conditions.
Life prediction and constitutive models for engine hot section anisotropic materials program
NASA Technical Reports Server (NTRS)
Swanson, G. A.; Linask, I.; Nissley, D. M.; Norris, P. P.; Meyer, T. G.; Walker, K. P.
1986-01-01
This report presents the results of the first year of a program designed to develop life prediction and constitutive models for two coated single crystal alloys used in gas turbine airfoils. The two alloys are PWA 1480 and Alloy 185. The two oxidation resistant coatings are PWA 273, an aluminide coating, and PWA 286, an overlay NiCoCrAlY coating. To obtain constitutive and/or fatigue data, tests were conducted on coated and uncoated PWA 1480 specimens tensilely loaded in the 100 , 110 , 111 , and 123 directions. A literature survey of constitutive models was completed for both single crystal alloys and metallic coating materials; candidate models were selected. One constitutive model under consideration for single crystal alloys applies Walker's micromechanical viscoplastic formulation to all slip systems participating in the single crystal deformation. The constitutive models for the overlay coating correlate the viscoplastic data well. For the aluminide coating, a unique test method is under development. LCF and TMF tests are underway. The two coatings caused a significant drop in fatigue life, and each produced a much different failure mechanism.
NASA Astrophysics Data System (ADS)
Misra, Anil; Singh, Viraj
2015-09-01
Thermomechanics and granular micromechanics approaches are combined to derive constitutive equations for modeling rate-dependent granular materials with damage and plasticity. The derivation is motivated by the recognition that the effect of micro-scale mechanisms upon the macro-scale behavior is known to be significant for granular materials. A general thermomechanical framework applicable to rate-dependent granular materials with damage and plasticity is developed. Based upon this framework, an expression for macro-scale Cauchy stress tensor is obtained in terms of the micro-scale grain interaction forces and the relationship between micro- and macro-scale kinematics. In addition, a Clausius-Duhem type inequality applicable to inter-granular interaction is derived, which is used to establish micro-scale constitutive relations for particular type of inter-granular interactions. The expression for Cauchy stress tensor and the micro-scale constitutive relations is then combined under a mean field kinematic assumption to obtain evolution-type macro-scale constitutive equations. The advantage of the granular micromechanics approach is that the damage and plasticity are defined using simple 1d functions at micro-scale, and complicated plastic potentials, damage functions and rules for their evolution are not required. The resultant model is applied to investigate primary, secondary and tertiary creep, creep-recovery as well as rate-dependent response under uniaxial compressive loading. Model applicability is also demonstrated for asymmetric tensile-compressive response under creep-recovery loading. The model is used to evaluate the evolution of elastic energy, and viscous, plastic and damage dissipation at the macro- and micro-scale with respect to creep time and loading level. The results show the development of loading-induced anisotropy due to damage and plasticity in these materials.
Christian Gasser, T
2011-06-01
Understanding the failure and damage mechanisms of soft biological tissue is critical to a sensitive and specific characterization of tissue injury tolerance and its relation to biological responses. Despite increasing experimental and analytical efforts, failure-related irreversible effects of soft biological tissue are still poorly understood. There is still no clear definition of what "damage" of a soft biological material is, and conventional macroscopic indicators, as known from damage of engineering materials for example, may not identify the tissue's tolerance to injury appropriately. To account for the complex three-dimensional arrangement of collagen, a microfiber model approach is applied, where constitutive relations for collagen fibers are integrated over the unit sphere, which in turn defines the tissue's macroscopic properties. A collagen fiber is represented by a bundle of proteoglycan cross-linked collagen fibrils that undergoes irreversible deformations when exceeding its elastic tensile limit. The proposed constitutive model is able to predict strain stiffening at physiological strain levels and does not exhibit a clear macroscopic elastic limit, two typical features known from soft biological tissue testing. An elastic-predictor/plastic-corrector implementation of the model is followed and constitutive parameters are estimated from in vitro test data from a particular abdominal aortic aneurysm (AAA). Damage-based structural instabilities of the AAA under different inflation conditions are investigated, where the collagen orientation density has been estimated from its in vivo stress state. PMID:21338718
NASA Astrophysics Data System (ADS)
Yin, Yajun; Xue, Mingde; Yu, Shouwen
A lower bound rigid plastic constitutive model for porous materials has been published recently, but its reliability and accuracy is still kept unknown. Therefore, this paper is confined to examine this model by comparing it with other ones such as the upper bound one and experimental-based one. Under three loading states (i.e. uniaxial stress condition, biaxial equal stress condition and uniaxial strain condition), the sintered copper’s ductility, compressibility, strength property, deformation characteristics, stress˜strain curves and damage evolution process predicted by these models are systematically compared. The advantage of the lower bound model in describing the yield property and its limitations in evaluating the ductility, compressibility, strength variation and damage evolution process of porous materials are clarified. Systematical analysis reveals that these limitations may be attributed to the short of void interaction mechanism in the lower bound model. This discovery lays the foundation for further improvement and modification of the lower bound model in the future research.
Modeling the viscoplastic and damage behavior in deep argillaceous rocks
NASA Astrophysics Data System (ADS)
Souley, Mountaka; Armand, Gilles; Su, Kun; Ghoreychi, Mehdi
In order to demonstrate the feasibility of a radioactive waste repository in the Callovo-Oxfordian claystone formation, the French national radioactive waste management agency (ANDRA) started in 2000 to build an underground research laboratory at Bure (East of France). One of the key issues is to understand long term behavior of the drifts. More than 400 m horizontal galleries at the main level of -490 m have been instrumented since April 2005. The continuous measurements of convergence of the galleries are available, allowing a better understanding of the time-dependent response of the claystone at natural scale. Results indicate that the viscoplastic strain rates observed in the undamaged area far from the gallery walls are of the same order of magnitude as those obtained on rock samples, whereas those recorded in the damaged or fractured zone near the gallery walls are one to two orders of magnitude higher, indicating the significant influence of damage or/and macro-fractures on the viscoplastic strains. Based on these observations, a macroscopic viscoplastic model which aims to improve the viscoplastic strain prediction in the EDZ is proposed and implemented in FLAC3 D©. Both the instantaneous and the time-dependent behavior are considered in the model. The short term response is assumed to be elactoplastic with strain hardening/softening whereas the time-dependent behavior is based on the concepts of viscoplasticity (Lemaıˆtre’s model). Finally, the damage-induced viscoplastic strains changes is examined through the plastic deformation (assumed to approach the damage rate). In order to verify both constitutive equations and their implementations, several simulations are performed: (a) triaxial tests at different confining pressures; (b) single- and multi-stage creep tests; (c) relaxation tests with different total axial strain levels, etc. Finally, an example of a blind prediction of the excavation of a drift parallel to the horizontal minor stress,
Modeling of viscoelasticity and damage in composite laminates by continuum thermodynamics
NASA Astrophysics Data System (ADS)
Ahci, Elif
Time dependent analysis of fiber reinforced polymer matrix composites is essential if these materials are used in applications involving the effect of severe environmental conditions such as high temperature and humidity in addition to mechanical loading. The present research is focused on understanding and modeling the overall nonlinear viscoelastic response of polymer matrix composites incorporating the effects of distributed damage. A constitutive framework incorporating the effect of high temperature and distributed damage is developed for polymer matrix composite laminates. The use of this framework for woven fabric composites is illustrated. The viscoelastic material response and the material properties under severe environmental conditions are studied both theoretically and experimentally. The approach uses continuum thermodynamics based formulation in which stress and temperature are allowed as independent variables along with the so-called hidden variables associated with viscous flow and internal variables representing damage. The damage variables incorporate time-dependent crack separation response as well crack surface orientation. The material coefficients in the polynomial expansion of the free energy are evaluated by a computational model. A user defined material subroutine is developed to include the nonlinear viscoelastic constitutive relations into ABAQUS finite element analysis package in computational study. A combined analytical and numerical procedure to determine the unknown constants in the theoretical model is also presented. The effect of damage on the residual viscoelastic response of the material is studied by experiments to get a satisfactory and complete model. The effect of high temperature on the damage initiation and evolution is studied by microscopic observations of the undamaged and damaged specimen edges, which are exposed to high temperature. A systematic experimental procedure is followed to determine the critical temperature
Ductile damage modeling based on void coalescence and percolation theories
Tonks, D.L.; Zurek, A.K.; Thissell, W.R.
1995-09-01
A general model for ductile damage in metals is presented. It includes damage induced by shear stress as well as damage caused by volumetric tension. Spallation is included as a special case. Strain induced damage is also treated. Void nucleation and growth are included, and give rise to strain rate effects. Strain rate effects also arise in the model through elastic release wave propagation between damage centers. The underlying physics of the model is the nucleation, growth, and coalescence of voids in a plastically flowing solid. The model is intended for hydrocode based computer simulation. An experimental program is underway to validate the model.
Constitutive modeling of aluminum foam and finite element implementation for crash simulations
NASA Astrophysics Data System (ADS)
Bi, Jing
In the past decades metallic foams have been increasingly used as filler materials in crashworthiness applications due to their relatively low cost and high capacity of energy absorption. Due to the destructive nature of crashes, studies on the performance of metallic foams using physical testing have been limited to examining the crushing force histories and/or folding patterns that are insufficient for crashworthiness designs. For this reason, numerical simulations, particularly nonlinear finite element (FE) analyses, play an important role in designing crashworthy foam-filled structures. An effective and numerically stable model is needed for modeling metallic foams that are porous and encounter large nonlinear deformations in crashes. In this study a new constitutive model for metallic foams is developed to overcome the deficiency of existing models in commercial FE codes such as LS-DYNA. The new constitutive model accounts for volume changes under hydrostatic compression and combines the hydrostatic pressure and von Mises stress into one yield function. The change of the compressibility of the metallic foam is handled in the constitutive model by allowing for shape changes of the yield surface in the hydrostatic pressure-von Mises stress space. The backward Euler method is adopted to integrate the constitutive equations to achieve numerical accuracy and stability. The new foam model is verified and validated by existing experimental data before used in FE simulations of crushing of foam-filled columns that have square and hexagonal cross-sections.
Constitutive model of creep in polycrystalline halite based on workhardening and recovery
Munson, D.E.
1993-07-01
A multimechanism constitutive model of creep has been developed which incorporates the workhardening and recovery transient creep behavior. This model has been applied to the creep of polycrystalline halite. The specific application of the model is in the calculation of the closure of underground rooms in layered salt deposits. Through the use of finite element calculations, this model, with appropriate laboratory material parameters and a Tresca flow potential, has predicted the measured closure of a number of large in situ experimental rooms.
A micromechanics constitutive model of transformation plasticity with shear and dilatation effect
NASA Astrophysics Data System (ADS)
Sun, Q. P.; Hwang, K. C.; Yu, S. W.
B ASED on micromechanics, thermodynamics and microscale t → m transformation mechanism considerations a micromechanics constitutive model which takes into account both the dilatation and shear effects of the transformation is proposed to describe the plastic, pseudoelastic and shape memory behaviors of structural ceramics during transformation under different temperatures. In the derivation, a constitutive element (representative material sample) was used which contains many of the transformed m-ZrO 2 grains or precipitates as the second phase inclusions embedded in an elastic matrix. Under some basic assumptions, analytic expressions for the Helmholtz and complementary free energy of the constitutive element are derived in a self-consistent manner by using the Mori-Tanaka method which takes into account the interaction between the transformed inclusions. The derived free energy is a function of externally applied macroscopic stress (or strain), temperature, volume fraction of transformed phase and the averaged stressfree transformation strain (eigenstrain) of all the transformed inclusions in the constitutive element, the latter two quantities being considered to be the internal variables describing the micro-structural rearrangement in the constitutive element. In the framework of the Hill-Rice internal variable constitutive theory, the transformation yield function and incremental stress strain relations, in analogy to the theory of metal plasticity, for proportional and non-proportional loading histories are derived, respectively. The theoretical predictions are compared with the available experimental data of Mg-PSZ and Ce-TZP polycrystalline toughening ceramics.
NASA Technical Reports Server (NTRS)
Koenig, Herbert A.; Chan, Kwai S.; Cassenti, Brice N.; Weber, Richard
1988-01-01
A unified numerical method for the integration of stiff time dependent constitutive equations is presented. The solution process is directly applied to a constitutive model proposed by Bodner. The theory confronts time dependent inelastic behavior coupled with both isotropic hardening and directional hardening behaviors. Predicted stress-strain responses from this model are compared to experimental data from cyclic tests on uniaxial specimens. An algorithm is developed for the efficient integration of the Bodner flow equation. A comparison is made with the Euler integration method. An analysis of computational time is presented for the three algorithms.
Constitutive model for the dynamic response of a NiTi shape memory alloy
NASA Astrophysics Data System (ADS)
Shi, Xiaohong; Zeng, Xiangguo; Chen, Huayan
2016-07-01
In this paper, based on irreversible thermodynamic theory, the Helmholtz free energy function, was selected to deduce both the master equations and evolution equations of the constitutive model of a NiTi alloy under high strain. The Helmholtz free energy function contains the parameters of the reflecting phase transition and plastic property. The constitutive model for a NiTi alloy was implemented using a semi-implicit stress integration algorithm. Four successive stages can be differentiated and simulated: parent phase elasticity, martensitic phase transition, martensitic elasticity, and dislocation yield. The simulation results are in good agreement with the experimental results.
Turbulence constitutive modeling of the square root of the Reynolds stress
NASA Astrophysics Data System (ADS)
Ariki, Taketo
2015-11-01
A methodology for turbulence constitutive modeling is discussed on the basis of the square-root tensor of the Reynolds stress. The present methodology can satisfy the realizability condition for the Reynolds stress proposed by Schumann [Phys. Fluids 20, 721 (1977)], 10.1063/1.861942 in a more general manner than the conventional methodologies. The definition and uniqueness of the square-root tensor have been discussed, and its boundary condition has been properly obtained consistently with that of the Reynolds stress. Examples of possible constitutive models of both tensor-expansion and transport-equation types have been proposed.
Turbulence constitutive modeling of the square root of the Reynolds stress.
Ariki, Taketo
2015-11-01
A methodology for turbulence constitutive modeling is discussed on the basis of the square-root tensor of the Reynolds stress. The present methodology can satisfy the realizability condition for the Reynolds stress proposed by Schumann [Phys. Fluids 20, 721 (1977)] in a more general manner than the conventional methodologies. The definition and uniqueness of the square-root tensor have been discussed, and its boundary condition has been properly obtained consistently with that of the Reynolds stress. Examples of possible constitutive models of both tensor-expansion and transport-equation types have been proposed. PMID:26651782
A Dynamic Damage Mechanics Source Model for Explosions in Crystalline Rock
NASA Astrophysics Data System (ADS)
Mihaly, J. M.; Bhat, H. S.; Sammis, C. G.; Rosakis, A.
2011-12-01
The micromechanical damage mechanics formulated by Ashby and Sammis [PAGEOPH, 1990] and generalized by Deshpande and Evans [J. Mech. Phys. Solids, 2008] has been extended to allow for a more generalized stress state and to incorporate an experimentally motivated crack growth (damage evolution) law that is valid over a wide range of loading rates. This law is sensitive to both the crack tip stress field and its time derivative, and thus produces strain-rate sensitivity in the constitutive response. The model is experimentally verified by predicting the failure strength of Dionysus-Pentelicon marble over strain rates ranging from to . This rate-dependent damage mechanics has been implemented in the ABAQUS dynamic finite element code and used to explore the effects of burn rate (loading rate) and lithostatic stress on the spatial extent of fracture damage and S waves generated by explosions in crystalline rock. Slower rise times and longer pressure pulses produce more damage and stronger S waves.
Biomechanical behavior of bovine periodontal ligament: Experimental tests and constitutive model.
Oskui, Iman Z; Hashemi, Ata; Jafarzadeh, Hamid
2016-09-01
A viscohyperelastic constitutive model with the use of the internal variables approach was formulated to evaluate the nonlinear elastic and time dependent anisotropic mechanical behavior of the periodontal ligament (PDL). Since the relaxation response was found to depend on the applied stretch, the adoption of the nonlinear viscous behavior in the present model was necessary. In this paper, Helmholtz free energy function was assigned to the material as the sum of hyperelastic and viscous terms which is based on the physical concept of internal variables. The constitutive model parameters were evaluated from the comparison of the proposed model and experimental data. For this purpose, tensile response of the bovine PDL samples under different stretch rates was obtained. The good correspondence between the proposed model and the experimental results confirmed the capability of the model to interpret the stretch rate behavior of the PDL. Moreover, the validity of structural model parameters was checked according to the results of the stress relaxation tests. PMID:27315371
Constitutive Modeling of Porcine Liver in Indentation Using 3D Ultrasound Imaging
Jordan, P.; Socrate, S.; Zickler, T.E.; Howe, R.D.
2009-01-01
In this work we present an inverse finite-element modeling framework for constitutive modeling and parameter estimation of soft tissues using full-field volumetric deformation data obtained from 3D ultrasound. The finite-element model is coupled to full-field visual measurements by regularization springs attached at nodal locations. The free ends of the springs are displaced according to the locally estimated tissue motion and the normalized potential energy stored in all springs serves as a measure of model-experiment agreement for material parameter optimization. We demonstrate good accuracy of estimated parameters and consistent convergence properties on synthetically generated data. We present constitutive model selection and parameter estimation for perfused porcine liver in indentation and demonstrate that a quasilinear viscoelastic model with shear modulus relaxation offers good model-experiment agreement in terms of indenter displacement (0.19 mm RMS error) and tissue displacement field (0.97 mm RMS error). PMID:19627823
NASA Technical Reports Server (NTRS)
Dame, L. T.; Stouffer, D. C.
1986-01-01
A tool for the mechanical analysis of nickel base single crystal superalloys, specifically Rene N4, used in gas turbine engine components is developed. This is achieved by a rate dependent anisotropic constitutive model implemented in a nonlinear three dimensional finite element code. The constitutive model is developed from metallurigical concepts utilizing a crystallographic approach. A non Schmid's law formulation is used to model the tension/compression asymmetry and orientation dependence in octahedral slip. Schmid's law is a good approximation to the inelastic response of the material in cube slip. The constitutive equations model the tensile behavior, creep response, and strain rate sensitivity of these alloys. Methods for deriving the material constants from standard tests are presented. The finite element implementation utilizes an initial strain method and twenty noded isoparametric solid elements. The ability to model piecewise linear load histories is included in the finite element code. The constitutive equations are accurately and economically integrated using a second order Adams-Moulton predictor-corrector method with a dynamic time incrementing procedure. Computed results from the finite element code are compared with experimental data for tensile, creep and cyclic tests at 760 deg C. The strain rate sensitivity and stress relaxation capabilities of the model are evaluated.
Life prediction and constitutive models for engine hot section anisotropic materials program
NASA Technical Reports Server (NTRS)
Nissley, D. M.; Meyer, T. G.; Walker, K. P.
1992-01-01
This report presents a summary of results from a 7 year program designed to develop generic constitutive and life prediction approaches and models for nickel-based single crystal gas turbine airfoils. The program was composed of a base program and an optional program. The base program addressed the high temperature coated single crystal regime above the airfoil root platform. The optional program investigated the low temperature uncoated single crystal regime below the airfoil root platform including the notched conditions of the airfoil attachment. Both base and option programs involved experimental and analytical efforts. Results from uniaxial constitutive and fatigue life experiments of coated and uncoated PWA 1480 single crystal material formed the basis for the analytical modeling effort. Four single crystal primary orientations were used in the experiments: group of zone axes (001), group of zone axes (011), group of zone axes (111), and group of zone axes (213). Specific secondary orientations were also selected for the notched experiments in the optional program. Constitutive models for an overlay coating and PWA 1480 single crystal materials were developed based on isothermal hysteresis loop data and verified using thermomechanical (TMF) hysteresis loop data. A fatigue life approach and life models were developed for TMF crack initiation of coated PWA 1480. A life model was developed for smooth and notched fatigue in the option program. Finally, computer software incorporating the overlay coating and PWA 1480 constitutive and life models was developed.
Life prediction and constitutive models for engine hot section anisotropic materials program
NASA Technical Reports Server (NTRS)
Nissley, D. M.; Meyer, T. G.
1992-01-01
This report presents the results from a 35 month period of a program designed to develop generic constitutive and life prediction approaches and models for nickel-based single crystal gas turbine airfoils. The program is composed of a base program and an optional program. The base program addresses the high temperature coated single crystal regime above the airfoil root platform. The optional program investigates the low temperature uncoated single crystal regime below the airfoil root platform including the notched conditions of the airfoil attachment. Both base and option programs involve experimental and analytical efforts. Results from uniaxial constitutive and fatigue life experiments of coated and uncoated PWA 1480 single crystal material form the basis for the analytical modeling effort. Four single crystal primary orientations were used in the experiments: (001), (011), (111), and (213). Specific secondary orientations were also selected for the notched experiments in the optional program. Constitutive models for an overlay coating and PWA 1480 single crystal material were developed based on isothermal hysteresis loop data and verified using thermomechanical (TMF) hysteresis loop data. A fatigue life approach and life models were selected for TMF crack initiation of coated PWA 1480. An initial life model used to correlate smooth and notched fatigue data obtained in the option program shows promise. Computer software incorporating the overlay coating and PWA 1480 constitutive models was developed.
Constitutive modelling of creep in a long fiber random glass mat thermoplastic composite
NASA Astrophysics Data System (ADS)
Dasappa, Prasad
The primary objective of this proposed research is to characterize and model the creep behaviour of Glass Mat Thermoplastic (GMT) composites under thermo-mechanical loads. In addition, tensile testing has been performed to study the variability in mechanical properties. The thermo-physical properties of the polypropylene matrix including crystallinity level, transitions and the variation of the stiffness with temperature have also been determined. In this work, the creep of a long fibre GMT composite has been investigated for a relatively wide range of stresses from 5 to 80 MPa and temperatures from 25 to 90°C. The higher limit for stress is approximately 90% of the nominal tensile strength of the material. A Design of Experiments (ANOVA) statistical method was applied to determine the effects of stress and temperature in the random mat material which is known for wild experimental scatter. Two sets of creep tests were conducted. First, preliminary short-term creep tests consisting of 30 minutes creep followed by recovery were carried out over a wide range of stresses and temperatures. These tests were carried out to determine the linear viscoelastic region of the material. From these tests, the material was found to be linear viscoelastic up-to 20 MPa at room temperature and considerable non-linearities were observed with both stress and temperature. Using Time-Temperature superposition (TTS) a long term master curve for creep compliance for up-to 185 years at room temperature has been obtained. Further, viscoplastic strains were developed in these tests indicating the need for a non-linear viscoelastic viscoplastic constitutive model. The second set of creep tests was performed to develop a general non-linear viscoelastic viscoplastic constitutive model. Long term creep-recovery tests consisting of 1 day creep followed by recovery has been conducted over the stress range between 20 and 70 MPa at four temperatures: 25°C, 40°C, 60°C and 80°C. Findley's model
Iig, Patrick
2011-01-01
Complex fluids, such as polymers, colloids, liquid-crystals etc., show intriguing viscoelastic properties, due to the complicated interplay between flow-induced structure formation and dynamical behavior. Starting from microscopic models of complex fluids, a systematic coarse-graining method is presented that allows us to derive closed-form and thermodynamically consistent constitutive equations for such fluids. Essential ingredients of the proposed approach are thermodynamically guided simulations within a consistent coarse-graining scheme. In addition to this new type of multiscale simulations, we reconstruct the building blocks that constitute the thermodynamically consistent coarse-grained model. We illustrate the method for low-molecular polymer melts, which are subject to different imposed flow fields like planar shear and different elongational flows. The constitutive equation for general flow conditions we obtain shows rheological behavior including shear thinning, normal stress differences, and elongational viscosities in good agreement with reference results. PMID:21678766
Experimental study of cancellous bone under large strains and a constitutive probabilistic model.
Kefalas, V; Eftaxiopoulos, D A
2012-02-01
Experimental study of bovine cancellous bone up to compaction under uniaxial compression and up to fracture under tension, has been pursued in this article. Compression experiments have revealed the known three stages of the constitutive response, namely the initial increasing and softening branches at moderate strains, the plateau region at large strains and the hardening part at very large strains under compaction. Tension tests have quantified the increasing and softening branches of the stress-strain curve up to fracture. Subsequently, a constitutive mechanical model, for the simulation of the experimental findings up to very large strains (75% engineering strain under compression), is proposed. The model is based on the statistical description of (a) the failure process of the trabecular structure at small and moderate strains and (b) the compaction process of the trabecular mass at very large strains under compression. Several fitting cases indicated that the presented constitutive law can capture the evolution of the experimental results. PMID:22301172
Constitutive model for shape memory alloys and its use in design and finite element analysis
NASA Astrophysics Data System (ADS)
Bose, Sudip; Santhanam, Sridhar
2002-07-01
A constitutive model for predicting the thermomechanical behavior of Shape Memory Alloys (SMAs) has been developed and validated. The model uses an approach similar to Brinson, Liang and Rogers, and Tanaka. It links key thermomechanical variables: stress, strain, temperature, and martensite fraction. A basic differential form for the SMA constitutive behavior, developed by Tanaka, forms the foundation of the model. The model is completed with a definition of the rules governing the behavior of martensite fraction. Like Brinson, the model distinguishes between de-twinned and twinned martensite. The phase transition temperatures are assumed to be a linear function of applied stress. The forward and reverse phase transformations are described by piecewise exponential functions. There are a number of parameters in the model that need to be determined using experimental data. The critical transformation temperatures are determined by resistivity measurements. All other parameters are determined by mechanical tension testing followed by nonlinear least-squares estimations. Mechanical testing consisted of displacement controlled, tension tests on Nitinol wires at several temperatures. The effectiveness of this model is demonstrated by its use in the design of an SMA actuated robotic arm. The constitutive model is used in conjunction with a lumped heat transfer model, a kinematic model, and a dynamic model to predict the behavior of the arm. Comparison between predictions and experimentally observed behavior is very good indicating a sound constitutive model. The model is also built into a finite element code that simulates pseudoelastic SMA behavior. The code considers geometric and material nonlinearities. The behavior of a simple pseudoelastic device is shown to be well predicted by the finite element code.
Damage and fatigue described by a fractional derivative model
NASA Astrophysics Data System (ADS)
Caputo, Michele; Fabrizio, Mauro
2015-07-01
As in [1], damage is associated with fatigue that a material undergoes. In this paper, because we work with viscoelastic solids represented by a fractional model, damage is described by the order of the fractional derivative, which represents the phase field satisfying Ginzburg-Landau equation, which describes the evolution of damage. Finally, in our model, damage is caused, not only by fatigue, but also directly by a source related to environmental factors and described by a positive time function.
Multi-step loading/unloading experiments that challenge constitutive models of glassy polymers
NASA Astrophysics Data System (ADS)
Caruthers, James; Medvedev, Grigori
2014-03-01
The mechanical response of glassy polymers depends on the thermal and deformational history, where the resulting relaxation phenomenon remains a significant challenge for constitutive modeling. For strain controlled experiments the stress response is measured during loading/unloading ramps and a constant strain. By judiciously combining the basic steps, a set of multi-step experiments have been designed to challenge existing constitutive models for glassy polymers. A particular example is the ``stress memory'' experiment, i.e. loading through yield, unloading to zero stress, and holding at final strain, where the subsequent evolution of the stress exhibits an overshoot. The observed dependence of the overshoot on the loading strain rate cannot be explained by the models where the relaxation time is a function of stress or strain. Another discriminating multi-step history experiment involves strain accumulation to test the common assumption that the phenomenon of strain hardening is caused by a purely elastic contribution to stress. Experimental results will be presented for a low Tg epoxy system, and the data will be used to critically analyze the predictions of both traditional viscoelastic/viscoplastic constitutive models and a recently developed Stochastic Constitutive Model.
Modeling and characterization of recompressed damaged materials
Becker, R; Cazamias, J U; Kalantar, D H; LeBlanc, M M; Springer, H K
2004-02-11
Experiments have been performed to explore conditions under which spall damage is recompressed with the ultimate goal of developing a predictive model. Spall is introduced through traditional gas gun techniques or with laser ablation. Recompression techniques producing a uniaxial stress state, such as a Hopkinson bar, do not create sufficient confinement to close the porosity. Higher stress triaxialities achieved through a gas gun or laser recompression can close the spall. Characterization of the recompressed samples by optical metallography and electron microscopy reveal a narrow, highly deformed process zone. At the higher pressures achieved in the gas gun, little evidence of spall remains other than differentially etched features in the optical micrographs. With the very high strain rates achieved with laser techniques there is jetting from voids and other signs of turbulent metal flow. Simulations of spall and recompression on micromechanical models containing a single void suggest that it might be possible to represent the recompression using models similar to those employed for void growth. Calculations using multiple, randomly distributed voids are needed to determine if such models will yield the proper behavior for more realistic microstructures.
Continuum-Based FEM Modeling of Ceramic Powder Compaction Using a Cap-Plasticity Constitutive Model
ARGUELLO JR.,JOSE G.; FOSSUM,ARLO F.; ZEUCH,DAVID H.; EWSUK,KEVIN G.
2000-05-01
Software has been developed and extended to allow finite element (FE) modeling of ceramic powder compaction using a cap-plasticity constitutive model. The underlying, general-purpose FE software can be used to model even the most complex three-dimensional (3D) geometries envisioned. Additionally, specialized software has been developed within this framework to address a general subclass of axisymmetric compacts that are common in industry. The expertise required to build the input deck, run the FE code, and post-process the results for this subclass of compacts is embedded within the specialized software. The user simply responds to a series of prompts, evaluates the quality of the FE mesh that is generated, and analyzes the graphical results that are produced. The specialized software allows users with little or no FE expertise to benefit from the tremendous power and insight that FE analysis can bring to the design cycle. The more general underlying software provides complete flexibility to model more complicated geometries and processes of interest to ceramic component manufacturers but requires significantly more user interaction and expertise.
Modeling, simulation and experimental verification of constitutive models for energetic materials
Haberman, K.S.; Bennett, J.G.; Assay, B.W.
1997-09-01
Simulation of the complete response of components and systems composed of energetic materials, such as PBX-9501 is important in the determination of the safety of various explosive systems. For example, predicting the correct state of stress, rate of deformation and temperature during penetration is essential in the prediction of ignition. Such simulation requires accurate constitutive models. These models must also be computationally efficient to enable analysis of large scale three dimensional problems using explicit lagrangian finite element codes such as DYNA3D. However, to be of maximum utility, these predictions must be validated against robust dynamic experiments. In this paper, the authors report comparisons between experimental and predicted displacement fields in PBX-9501 during dynamic deformation, and describe the modeling approach. The predictions used Visco-SCRAM and the Generalized Method of Cells which have been implemented into DYNA3D. The experimental data were obtained using laser-induced fluorescence speckle photography. Results from this study have lead to more accurate models and have also guided further experimental work.
Coupled Hydro-Mechanical Constitutive Model for Vegetated Soils: Validation and Applications
NASA Astrophysics Data System (ADS)
Switala, Barbara Maria; Veenhof, Rick; Wu, Wei; Askarinejad, Amin
2016-04-01
It is well known, that presence of vegetation influences stability of the slope. However, the quantitative assessment of this contribution remains challenging. It is essential to develop a numerical model, which combines mechanical root reinforcement and root water uptake, and allows modelling rainfall induced landslides of vegetated slopes. Therefore a novel constitutive formulation is proposed, which is based on the modified Cam-clay model for unsaturated soils. Mechanical root reinforcement is modelled introducing a new constitutive parameter, which governs the evolution of the Cam-clay failure surface with the degree of root reinforcement. Evapotranspiration is modelled in terms of the root water uptake, defined as a sink term in the water flow continuity equation. The original concept is extended for different shapes of the root architecture in three dimensions, and combined with the mechanical model. The model is implemented in the research finite element code Comes-Geo, and in the commercial software Abaqus. The formulation is tested, performing a series of numerical examples, which allow validation of the concept. The direct shear test and the triaxial test are modelled in order to test the performance of the mechanical part of the model. In order to validate the hydrological part of the constitutive formulation, evapotranspiration from the vegetated box is simulated and compared with the experimental results. Obtained numerical results exhibit a good agreement with the experimental data. The implemented model is capable of reproducing results of basic geotechnical laboratory tests. Moreover, the constitutive formulation can be used to model rainfall induced landslides of vegetated slopes, taking into account the most important factors influencing the slope stability (root reinforcement and evapotranspiration).
Creep crack growth predictions in INCO 718 using a continuum damage model
NASA Technical Reports Server (NTRS)
Walker, K. P.; Wilson, D. A.
1985-01-01
Creep crack growth tests have been carried out in compact type specimens of INCO 718 at 1200 F (649 C). Theoretical creep crack growth predictions have been carried out by incorporating a unified viscoplastic constitutive model and a continuum damage model into the ARAQUS nonlinear finite element program. Material constants for both the viscoplastic model and the creep continuum damage model were determined from tests carried out on uniaxial bar specimens of INCO 718 at 1200 F (649 C). A comparison of the theoretical creep crack growth rates obtained from the finite element predictions with the experimentally observed creep crack growth rates indicates that the viscoplastic/continuum damage model can be used to successfully predict creep crack growth in compact type specimens using material constants obtained from uniaxial bar specimens of INCO 718 at 1200 F (649 C).
A Constitutive Model of 6111-T4 Aluminum Alloy Sheet Based on the Warm Tensile Test
NASA Astrophysics Data System (ADS)
Hua, Lin; Meng, Fanzhi; Song, Yanli; Liu, Jianing; Qin, Xunpeng; Suo, Lianbing
2014-03-01
As main light-weight material, aluminum alloy sheets have been widely applied to produce auto body panels. In order to predict the formability and springback of aluminum alloy sheets, a precise constitutive model is a necessity. In this article, a series of warm tensile tests were conducted on Gleeble-1500D thermal mechanical simulator for 6111-T4 aluminum alloy sheets. The corresponding strain rate ranged from 0.015 to 1.5 s-1, and the temperature ranged from 25 to 350 °C. The relationship between the temperature, the strain rate, and the flow stress were discussed. A constitutive model based on the updated Fields-Backofen equation was established to describe the flow behavior of 6111-T4 aluminum alloy during the warm tensile tests. Subsequently, the average absolute relative error (AARE) was introduced to verify the predictability of the constitutive model. The value of AARE at the uniform plastic deformation stage was calculated to be 1.677%, which demonstrates that the predicted flow stress values were in accordance with the experimental ones. The constitutive model was validated by the fact that the simulated results of the warm tensile tests coincided with the experimental ones.
Skacel, Pavel; Bursa, Jiri
2015-01-01
Several constitutive models have been proposed for the description of mechanical behaviour of soft tissues containing collagen fibres. Some of the commonly used approaches accounting for the dispersion of fibre orientations are based on the summation of (mechanical) contributions of differently oriented fibre families. This leads to the need of numerical integration on the sphere surface, and the related numerical consumption is the main disadvantage of this category of constitutive models. The paper is focused on the comparison of various numerical integration methods applied to a specific constitutive model applicable for arterial walls. Robustness and efficiency of several integration rules were tested with respect to application in finite element (FE) codes. Among all the analysed numerical integration rules, the best results were reached by Lebedev quadrature; the related parameters for the specific constitutive model are presented in the paper. The results were implemented into the commercial FE code ANSYS via user subroutines, and their applicability was demonstrated by an example of FE simulation with non-homogenous stress field. PMID:24168517
Modeling continuous-fiber reinforced polymer composites for exploration of damage tolerant concepts
NASA Astrophysics Data System (ADS)
Matthews, Peter J.
This work aims to improve the predictive capability for fiber-reinforced polymer matrix composite laminates using the finite element method. A new tool for modeling composite damage was developed which considers important modes of failure. Well-known micromechanical models were implemented to predict material values for material systems of interest to aerospace applications. These generated material values served as input to intralaminar and interlaminar damage models. A three-dimensional in-plane damage material model was implemented and behavior verified. Deficiencies in current state-of-the-art interlaminar capabilities were explored using the virtual crack closure technique and the cohesive zone model. A user-defined cohesive element was implemented to discover the importance of traction-separation material constitutive behavior. A novel method for correlation of traction-separation parameters was created. This new damage modeling tool was used for evaluation of novel material systems to improve damage tolerance. Classical laminate plate theory was used in a full-factorial study of layerwise-hybrid laminates. Filament-wound laminated composite cylindrical shells were subjected to quasi-static loading to validate the finite element computational composite damage model. The new tool for modeling provides sufficient accuracy and generality for use on a wide-range of problems.
A solidification constitutive model for NIKE2D and NIKE3D
Raboin, P.J.
1994-03-17
This memo updates the current status of a solidification material model development which has been underway for more than a year. Significant modeling goals such as predicting cut-off stresses, thermo-elasto-plasticity, strain rate dependent plasticity and dynamic recovery have been completed. The model is called SOLMAT for solidification material model, and while developed for NIKE2D, it has already been implemented in NIKE3D and NIT03D by B. Maker. This memo details the future development strategy of SOLMAT including liquid and solid constitutive improvements, coupling of deviatoric and dilatational deformation and a plan to switch between constitutive theories. It explains some of the difficulties associated solidification modeling and proposes two experiments to measure properties for using SOLMAT. Due to the sensitive nature of these plans in relation to programmatic and CRADA concerns, this memo should be treated as confidential document.
An experimental assessment of internal variables constitutive models for viscoelastic materials
NASA Astrophysics Data System (ADS)
Borges, F. C. L.; Castello, D. A.; Magluta, C.; Rochinha, F. A.; Roitman, N.
2015-01-01
The present work is aimed at presenting an experimental assessment of a constitutive model used to describe viscoelastic behavior. This strategy is built on the basic principles of the Verification and Validation (V&V) philosophy. The mechanical model used to describe the viscoelastic behavior is a constitutive one based on the concept of internal variables. The parameter estimation of the model is performed using frequency domain data through the Particle Swarm Optimization algorithm. A set of different experimental set-ups were built in order to span the structural operational domain from which data can be measured. The model validation is performed based on the use of validation metrics which take into account uncertainties both in the model predictions and observed data.
An internal variable constitutive model for the large deformation of metals at high temperatures
NASA Technical Reports Server (NTRS)
Brown, Stuart; Anand, Lallit
1988-01-01
The advent of large deformation finite element methodologies is beginning to permit the numerical simulation of hot working processes whose design until recently has been based on prior industrial experience. Proper application of such finite element techniques requires realistic constitutive equations which more accurately model material behavior during hot working. A simple constitutive model for hot working is the single scalar internal variable model for isotropic thermal elastoplasticity proposed by Anand. The model is recalled and the specific scalar functions, for the equivalent plastic strain rate and the evolution equation for the internal variable, presented are slight modifications of those proposed by Anand. The modified functions are better able to represent high temperature material behavior. The monotonic constant true strain rate and strain rate jump compression experiments on a 2 percent silicon iron is briefly described. The model is implemented in the general purpose finite element program ABAQUS.
A nonlinear magneto-thermo-elastic coupled hysteretic constitutive model for magnetostrictive alloys
NASA Astrophysics Data System (ADS)
Jin, Ke; Kou, Yong; Zheng, Xiaojing
2012-06-01
This paper presents a general hysteretic constitutive law of nonlinear magneto-thermo-elastic coupling for magnetostrictive alloys. The model considered here is thermodynamically motivated and based on the Gibbs free energy function. A nonlinear part of the elastic strain arising from magnetic domain rotation induced by the pre-stress is taken into account. Furthermore, the movement of the domain walls is incorporated to describe hysteresis based on Jiles-Atherton's model. Then a set of closed and analytical expressions of the constitutive law for the magnetostrictive rods and films are obtained, and the parameters appearing in the model can be determined by those measurable experiments in mechanics and physics. Comparing this model with other existing models in this field, the quantitative results show that the relationships obtained here are more effective to describe the effects of the pre-stress or in-plane residual stress and ambient temperature on the magnetization or the magnetostriction hysteresis loops.
An automated procedure for material parameter evaluation for viscoplastic constitutive models
NASA Technical Reports Server (NTRS)
Imbrie, P. K.; James, G. H.; Hill, P. S.; Allen, D. H.; Haisler, W. E.
1988-01-01
An automated procedure is presented for evaluating the material parameters in Walker's exponential viscoplastic constitutive model for metals at elevated temperature. Both physical and numerical approximations are utilized to compute the constants for Inconel 718 at 1100 F. When intermediate results are carefully scrutinized and engineering judgement applied, parameters may be computed which yield stress output histories that are in agreement with experimental results. A qualitative assessment of the theta-plot method for predicting the limiting value of stress is also presented. The procedure may also be used as a basis to develop evaluation schemes for other viscoplastic constitutive theories of this type.
NASA Astrophysics Data System (ADS)
Dass, W.; Merkle, D. H.; Bratton, J. L.
1983-04-01
Constitutive modeling of cohesionless soil for both standard static test conditions and insitu impulsive dynamic load conditions is discussed in this annual report. Predicted laboratory response for several different types of models is evaluated using data from a coordinated testing program. The modeling of insitu soil response to explosive events (CIST and DISC Test) is considered, and the laboratory-derived models are tested for their convenience and accuracy in predicting ground motions. Several important laboratory and insitu phenomena which were not reflected by the model exercises are discussed. Based on the conclusions from this study, testing and modeling requirements for dynamic loading situations are proposed.
NASA Technical Reports Server (NTRS)
Goldberg, Robert K.; Stouffer, Donald C.
1998-01-01
Recently applications have exposed polymer matrix composite materials to very high strain rate loading conditions, requiring an ability to understand and predict the material behavior under these extreme conditions. In this first paper of a two part report, background information is presented, along with the constitutive equations which will be used to model the rate dependent nonlinear deformation response of the polymer matrix. Strain rate dependent inelastic constitutive models which were originally developed to model the viscoplastic deformation of metals have been adapted to model the nonlinear viscoelastic deformation of polymers. The modified equations were correlated by analyzing the tensile/ compressive response of both 977-2 toughened epoxy matrix and PEEK thermoplastic matrix over a variety of strain rates. For the cases examined, the modified constitutive equations appear to do an adequate job of modeling the polymer deformation response. A second follow-up paper will describe the implementation of the polymer deformation model into a composite micromechanical model, to allow for the modeling of the nonlinear, rate dependent deformation response of polymer matrix composites.
Micromechanics and constitutive models for soft active materials with phase evolution
NASA Astrophysics Data System (ADS)
Wang, Binglian
Soft active materials, such as shape memory polymers, liquid crystal elastomers, soft tissues, gels etc., are materials that can deform largely in response to external stimuli. Micromechanics analysis of heterogeneous materials based on finite element method is a typically numerical way to study the thermal-mechanical behaviors of soft active materials with phase evolution. While the constitutive models that can precisely describe the stress and strain fields of materials in the process of phase evolution can not be found in the databases of some commercial finite element analysis (FEA) tools such as ANSYS or Abaqus, even the specific constitutive behavior for each individual phase either the new formed one or the original one has already been well-known. So developing a computationally efficient and general three dimensional (3D) thermal-mechanical constitutive model for soft active materials with phase evolution which can be implemented into FEA is eagerly demanded. This paper first solved this problem theoretically by recording the deformation history of each individual phase in the phase evolution process, and adopted the idea of effectiveness by regarding all the new formed phase as an effective phase with an effective deformation to make this theory computationally efficient. A user material subroutine (UMAT) code based on this theoretical constitutive model has been finished in this work which can be added into the material database in Abaqus or ANSYS and can be easily used for most soft active materials with phase evolution. Model validation also has been done through comparison between micromechanical FEA and experiments on a particular composite material, shape memory elastomeric composite (SMEC) which consisted of an elastomeric matrix and the crystallizable fibre. Results show that the micromechanics and the constitutive models developed in this paper for soft active materials with phase evolution are completely relied on.
The relationship between observed fatigue damage and life estimation models
NASA Technical Reports Server (NTRS)
Kurath, Peter; Socie, Darrell F.
1988-01-01
Observations of the surface of laboratory specimens subjected to axial and torsional fatigue loadings has resulted in the identification of three damage fatigue phenomena: crack nucleation, shear crack growth, and tensile crack growth. Material, microstructure, state of stress/strain, and loading amplitude all influence which of the three types of fatigue damage occurs during a dominant fatigue life fraction. Fatigue damage maps are employed to summarize the experimental observations. Appropriate bulk stress/strain damage parameters are suggested to model fatigue damage for the dominant fatigue life fraction. Extension of the damage map concept to more complex loadings is presented.
NASA Astrophysics Data System (ADS)
Huang, Zhipeng; Gao, Lihong; Wang, Yangwei; Wang, Fuchi
2016-06-01
The Johnson-Cook (J-C) constitutive model is widely used in the finite element simulation, as this model shows the relationship between stress and strain in a simple way. In this paper, a cluster global optimization algorithm is proposed to determine the J-C constitutive model parameters of materials. A set of assumed parameters is used for the accuracy verification of the procedure. The parameters of two materials (401 steel and 823 steel) are determined. Results show that the procedure is reliable and effective. The relative error between the optimized and assumed parameters is no more than 4.02%, and the relative error between the optimized and assumed stress is 0.2% × 10-5. The J-C constitutive parameters can be determined more precisely and quickly than the traditional manual procedure. Furthermore, all the parameters can be simultaneously determined using several curves under different experimental conditions. A strategy is also proposed to accurately determine the constitutive parameters.
Li, Hua; Yuan, Z; Ng, T Y; Lee, H P; Lam, K Y; Wang, Q X; Wu, Shunnian; Fu, Jie; Hanes, Justin
2003-01-01
The deployment of electroactive ionic polymer hydrogel-metal composites in artificial muscle and BioMEMS applications has recently been intensively investigated. In order to analyse their electromechanical responses to externally applied electrical fields, it is critical to develop a constitutive model linking the macro-mechanical moduli with the micro-mechanical characteristics, and to determine the geometric size and shape of the micro-structural cluster and investigate the effect of cluster morphology on the effective electro-elastic moduli of the polymer hydrogels. As a typical ionic polymer-based hydrogel, the Nafion membrane is studied in this work. Based on the Biot poroelasticity theory, a multi-scale constitutive model which includes both macro and micro characteristics is developed using an asymptotic homogenisation method. The effect of water-volume fraction on the effective elastic moduli of the hydrogel membrane is examined for different equivalent weights. Numerical investigations show that the simulated effective constitutive moduli agree well with experimental data. The presently developed constitutive model is thus validated. In order to determine the micro-structural shape of the polymer skeleton subject to fluid pressure, a representative volume element (RVE) is designed by topology optimisation of the periodic microstructures of the Nafion hydrogels, through the minimisation of the electro-elastic interaction energy between the polymer-based fluorocarbon matrix and the surrounding fluid. This optimal RVE correctly predicts the geometric shapes of the clusters. PMID:14768907
Constitutive Modeling of Nanotube/Polymer Composites with Various Nanotube Orientations
NASA Technical Reports Server (NTRS)
Odegard, Gregory M.; Gates, Thomas S.
2002-01-01
In this study, a technique has been proposed for developing constitutive models for polymer composite systems reinforced with single-walled carbon nanotubes (SWNT) with various orientations with respect to the bulk material coordinates. A nanotube, the local polymer adjacent to the nanotube, and the nanotube/polymer interface have been modeled as an equivalent-continuum fiber by using an equivalent-continuum modeling method. The equivalent-continuum fiber accounts for the local molecular structure and bonding information and serves as a means for incorporating micromechanical analyses for the prediction of bulk mechanical properties of SWNT/polymer composite. As an example, the proposed approach is used for the constitutive modeling of a SWNT/LaRC-SI (with a PmPV interface) composite system, with aligned nanotubes, three-dimensionally randomly oriented nanotubes, and nanotubes oriented with varying degrees of axisymmetry. It is shown that the Young s modulus is highly dependent on the SWNT orientation distribution.
Implementation of two geologic constitutive models in the HONDO finite-element code
Swenson, D.V.
1983-05-01
Two constitutive models for use with geologic materials have been incorporated into the HONDO finite-element program. Both models have the same behavior in tension, using a stress criterion to form cracks normal to the maximum principal stress. In compression, the two models give upper and lower bound solutions to the unconfined postfailure strength. The first model uses a Coulomb criterion to form explicit shear cracks, while the second model uses an elastic-plastic formulation developed by Krieg. Two sample applications, an indentor test and fracture of a borehole, are presented.
Multi-step deformations - a stringent test for constitutive models for polymer glasses
NASA Astrophysics Data System (ADS)
Medvedev, Grigori; Caruthers, James
A number of constitutive models have been proposed to describe mechanical behavior of polymer glasses, where the focus has been on the stress-strain curve observed in a constant strain rate deformation. The stress-strain curve possesses several prominent features, including yield, post-yield softening, flow, and hardening, which have proven challenging to predict. As a result, both viscoplastic and nonlinear viscoelastic constitutive models have become quite intricate, where a new mechanism is invoked for each bend of the stress-strain curve. We demonstrate on several examples that when the models are used to describe the multi-step deformations vs. the more common single strain rate deformation, they produce responses that are qualitatively incorrect, revealing the existing models to be parameterizations of a single-step curve. A recently developed stochastic constitutive model has fewer problems than the traditional viscoelastic/viscoplastic models, but it also has difficulties. The implications for the mechanics and physics of glassy polymers will be discussed.
Application of symbolic computations to the constitutive modeling of structural materials
NASA Technical Reports Server (NTRS)
Arnold, Steven M.; Tan, H. Q.; Dong, X.
1990-01-01
In applications involving elevated temperatures, the derivation of mathematical expressions (constitutive equations) describing the material behavior can be quite time consuming, involved and error-prone. Therefore intelligent application of symbolic systems to faciliate this tedious process can be of significant benefit. Presented here is a problem oriented, self contained symbolic expert system, named SDICE, which is capable of efficiently deriving potential based constitutive models in analytical form. This package, running under DOE MACSYMA, has the following features: (1) potential differentiation (chain rule), (2) tensor computations (utilizing index notation) including both algebraic and calculus; (3) efficient solution of sparse systems of equations; (4) automatic expression substitution and simplification; (5) back substitution of invariant and tensorial relations; (6) the ability to form the Jacobian and Hessian matrix; and (7) a relational data base. Limited aspects of invariant theory were also incorporated into SDICE due to the utilization of potentials as a starting point and the desire for these potentials to be frame invariant (objective). The uniqueness of SDICE resides in its ability to manipulate expressions in a general yet pre-defined order and simplify expressions so as to limit expression growth. Results are displayed, when applicable, utilizing index notation. SDICE was designed to aid and complement the human constitutive model developer. A number of examples are utilized to illustrate the various features contained within SDICE. It is expected that this symbolic package can and will provide a significant incentive to the development of new constitutive theories.
Modeling flow stress constitutive behavior of SA508-3 steel for nuclear reactor pressure vessels
NASA Astrophysics Data System (ADS)
Sun, Mingyue; Hao, Luhan; Li, Shijian; Li, Dianzhong; Li, Yiyi
2011-11-01
Based on the measured stress-strain curves under different temperatures and strain rates, a series of flow stress constitutive equations for SA508-3 steel were firstly established through the classical theories on work hardening and softening. The comparison between the experimental and modeling results has confirmed that the established constitutive equations can correctly describe the mechanical responses and microstructural evolutions of the steel under various hot deformation conditions. We further represented a successful industrial application of this model to simulate a forging process for a large conical shell used in a nuclear steam generator, which evidences its practical and promising perspective of our model with an aim of widely promoting the hot plasticity processing for heavy nuclear components of fission reactors.
A simplified constitutive model for predicting shape memory polymers deformation behavior
NASA Astrophysics Data System (ADS)
Li, Yunxin; Guo, Siu-Siu; He, Yuhao; Liu, Zishun
2015-12-01
Shape memory polymers (SMPs) can keep a temporary shape after pre-deformation at a higher temperature and subsequent cooling. When they are reheated, their original shapes can be recovered. Such special characteristics of SMPs make them widely used in aerospace structures, biomedical devices, functional textiles and other devices. Increasing usefulness of SMPs motivates us to further understand their thermomechanical properties and deformation behavior, of which the development of appropriate constitutive models for SMPs is imperative. There is much work in literatures that address constitutive models of the thermo-mechanical coupling in SMPs. However, due to their complex forms, it is difficult to apply these constitutive models in the real world. In this paper, a three-element model with simple form is proposed to investigate the thermo-mechanical small strain (within 10%) behavior of polyurethane under uniaxial tension. Two different cases of heated recovery are considered: (1) unconstrained free strain recovery and (2) stress recovery under full constraint at a strain level fixed during low temperature unloading. To validate the model, simulated and predicted results are compared with Tobushi's experimental results and good agreement can be observed.
NASA Astrophysics Data System (ADS)
Merkle, D. H.; Dass, W. C.
1985-04-01
This study sought to develop a general soil stress-strain model which can be used to solve a wide range of soil dynamics problems. The approach used was to review existing soil constitutive models used to predict the response of soil masses to complex dynamic loads, and then formulate a new model for that purpose. Eight existing soil dynamic stress-strain models were studied. The Lade model was selected as the best point of departure for developing a new soil stress-strain model for complex dynamic loading, because of its accuracy and flexibility in representing soil stress-strain behavior, ease of parameter determination, and ease of developing intuition for parameter physical significance and accuracy. The new conic model is so called because its principal mathematical surfaces are conic sections. The computer code used to exercise all nine soil constitutive models under eleven stress and strain paths is called the Soil Element Model (SEM). It can be incorporated in large finite difference or finite element codes for analyzing the response of soil masses to complex dynamic loads. The conic model performs well over a wide range of loading conditions. The parameters are determined in a straightforward manner, and the model reflects the influence of the intermediate principal stress on shear strength through a shear failure surface involving three independent stress invariants: the first total stress invariant and the second and third deviator stress invariants.
Bergström, J S; Rimnac, C M; Kurtz, S M
2003-04-01
The development of theoretical failure, fatigue, and wear models for ultra-high molecular weight polyethylene (UHMWPE) used in joint replacements has been hindered by the lack of a validated constitutive model that can accurately predict large deformation mechanical behavior under clinically relevant, multiaxial loading conditions. Recently, a new Hybrid constitutive model for unirradiated UHMWPE was developed Bergström et al., (Biomaterials 23 (2002) 2329) based on a physics-motivated framework which incorporates the governing micro-mechanisms of polymers into an effective and accurate continuum representation. The goal of the present study was to compare the predictive capability of the new Hybrid model with the J(2)-plasticity model for four conventional and highly crosslinked UHMWPE materials during multiaxial loading. After calibration under uniaxial loading, the predictive capabilities of the J(2)-plasticity and Hybrid model were tested by comparing the load-displacement curves from experimental multiaxial (small punch) tests with simulated load-displacement curves calculated using a finite element model of the experimental apparatus. The quality of the model predictions was quantified using the coefficient of determination (r(2)). The results of the study demonstrate that the Hybrid model outperforms the J(2)-plasticity model both for combined uniaxial tension and compression predictions and for simulating multiaxial large deformation mechanical behavior produced by the small punch test. The results further suggest that the parameters of the HM may be generalizable for a wide range of conventional, highly crosslinked, and thermally treated UHMWPE materials, based on the characterization of four material properties related to the elastic modulus, yield stress, rate of strain hardening, and locking stretch of the polymer chains. Most importantly, from a practical perspective, these four key material properties for the Hybrid constitutive model can be measured
NASA Astrophysics Data System (ADS)
Horstemeyer, M. F.; McDowell, D. L.; McGinty, R. D.
1999-03-01
To bridge length scales in plastic flow of polycrystalline fcc metals, the salient features of 3D polycrystalline elastoviscoplasticity at the crystal level (mesoscale) were studied to determine the relative influences on macroscale behaviour. This 3D study builds upon the 2D planar double-slip analysis performed by Horstemeyer and McDowell in which the relative influence of the constitutive-law features on macroscale properties in polycrystal plasticity were quantified for oxygen-free, high-conductivity copper. The mesoscale constitutive-law features considered include single-crystal elastic properties, slip-system-level hardening law, latent hardening, slip-system-level kinematic hardening, and intergranular constraint relation. Volume-averaged macroscale responses included the effective flow stress, plastic spin, elastic moduli, hardening behaviour, and axial extension (for the free-end torsion case). Each response was evaluated at 10% and 50% effective strain levels under rectilinear shear straining. In the existing literature, only one type of behaviour (e.g. texture or stress-strain response) is typically considered when assessing these various elements of the constitutive framework. In this paper, we develop a more comprehensive understanding of the relative importance of constitutive-law features as deformation proceeds. This study suggests that the design of experiments methodology is a valuable tool to assist in selecting relevant features for polycrystalline simulations and for development of macroscale unified-creep-plasticity models. In general, the results indicated that the intergranular constraint and kinematic hardening were more influential overall than the type of constitutive model used, whether isotropic or anisotropic elasticity was used, and whether or not latent hardening was used. Finally, 3D results were similar to the previous 2D planar double-slip study of Horstemeyer and McDowell, except that latent hardening had a stronger influence on
Continuum Fatigue Damage Modeling for Use in Life Extending Control
NASA Technical Reports Server (NTRS)
Lorenzo, Carl F.
1994-01-01
This paper develops a simplified continuum (continuous wrp to time, stress, etc.) fatigue damage model for use in Life Extending Controls (LEC) studies. The work is based on zero mean stress local strain cyclic damage modeling. New nonlinear explicit equation forms of cyclic damage in terms of stress amplitude are derived to facilitate the continuum modeling. Stress based continuum models are derived. Extension to plastic strain-strain rate models are also presented. Application of these models to LEC applications is considered. Progress toward a nonzero mean stress based continuum model is presented. Also, new nonlinear explicit equation forms in terms of stress amplitude are also derived for this case.
Zhang, Lei; Feng, Xiao; Wang, Xin; Liu, Changyong
2014-01-01
The nitrogen-containing austenitic stainless steel 316LN has been chosen as the material for nuclear main-pipe, which is one of the key parts in 3rd generation nuclear power plants. In this research, a constitutive model of nitrogen-containing austenitic stainless steel is developed. The true stress-true strain curves obtained from isothermal hot compression tests over a wide range of temperatures (900–1250°C) and strain rates (10−3–10 s−1), were employed to study the dynamic deformational behavior of and recrystallization in 316LN steels. The constitutive model is developed through multiple linear regressions performed on the experimental data and based on an Arrhenius-type equation and Zener-Hollomon theory. The influence of strain was incorporated in the developed constitutive equation by considering the effect of strain on the various material constants. The reliability and accuracy of the model is verified through the comparison of predicted flow stress curves and experimental curves. Possible reasons for deviation are also discussed based on the characteristics of modeling process. PMID:25375345
Constitutive modeling of time-dependent response of human plantar aponeurosis.
Pavan, P G; Pachera, P; Stecco, C; Natali, A N
2014-01-01
The attention is focused on the viscoelastic behavior of human plantar aponeurosis tissue. At this purpose, stress relaxation tests were developed on samples taken from the plantar aponeurosis of frozen adult donors with age ranging from 67 to 78 years, imposing three levels of strain in the physiological range (4%, 6%, and 8%) and observing stress decay for 240 s. A viscohyperelastic fiber-reinforced constitutive model with transverse isotropy was assumed to describe the time-dependent behavior of the aponeurotic tissue. This model is consistent with the structural conformation of the tissue where collagen fibers are mainly aligned with the proximal-distal direction. Constitutive model fitting to experimental data was made by implementing a stochastic-deterministic procedure. The stress relaxation was found close to 40%, independently of the level of strain applied. The agreement between experimental data and numerical results confirms the suitability of the constitutive model to describe the viscoelastic behaviour of the plantar aponeurosis. PMID:24701249
Cady, C.M.; Chen, S.R.; Gray, G.T. III
1996-08-23
The objective of this study was to characterize the dynamic mechanical properties of four different structural sheet steels used in automobile manufacture. The analysis of a drawing quality, special killed (DQSK) mild steel; high strength, low alloy (HSLA) steel; interstitial free (IF); and a high strength steel (M-190) have been completed. In addition to the true stress-true strain data, coefficients for the Johnson-Cook, Zerilli-Armstrong, and Mechanical Threshold Stress constitutive models have been determined from the mechanical test results at various strain rates and temperatures and are summarized. Compression, tensile, and biaxial bulge tests and low (below 0.1/s) strain rate tests were completed for all four steels. From these test results it was determined to proceed with the material modeling optimization using the through thickness compression results. Compression tests at higher strain rates and temperatures were also conducted and analyzed for all the steels. Constitutive model fits were generated from the experimental data. This report provides a compilation of information generated from mechanical tests, the fitting parameters for each of the constitutive models, and an index and description of data files.
NASA Technical Reports Server (NTRS)
Arnold, S. M.
2006-01-01
Materials property information such as composition and thermophysical/mechanical properties abound in the literature. Oftentimes, however, the corresponding response curves from which these data are determined are missing or at the very least difficult to retrieve. Further, the paradigm for collecting materials property information has historically centered on (1) properties for materials comparison/selection purposes and (2) input requirements for conventional design/analysis methods. However, just as not all materials are alike or equal, neither are all constitutive models (and thus design/ analysis methods) equal; each model typically has its own specific and often unique required materials parameters, some directly measurable and others indirectly measurable. Therefore, the type and extent of materials information routinely collected is not always sufficient to meet the current, much less future, needs of the materials modeling community. Informatics has been defined as the science concerned with gathering, manipulating, storing, retrieving, and classifying recorded information. A key aspect of informatics is its focus on understanding problems and applying information technology as needed to address those problems. The primary objective of this article is to highlight the need for a paradigm shift in materials data collection, analysis, and dissemination so as to maximize the impact on both practitioners and researchers. Our hope is to identify and articulate what constitutes "sufficient" data content (i.e., quality and quantity) for developing, characterizing, and validating sophisticated nonlinear time- and history-dependent (hereditary) constitutive models. Likewise, the informatics infrastructure required for handling the potentially massive amounts of materials data will be discussed.
Galactinol and Raffinose Constitute a Novel Function to Protect Plants from Oxidative Damage1[W][OA
Nishizawa, Ayako; Yabuta, Yukinori; Shigeoka, Shigeru
2008-01-01
Galactinol synthase (GolS) is a key enzyme in the synthesis of raffinose family oligosaccharides that function as osmoprotectants in plant cells. In leaves of Arabidopsis (Arabidopsis thaliana) plants overexpressing heat shock transcription factor A2 (HsfA2), the transcription of GolS1, -2, and -4 and raffinose synthase 2 (RS2) was highly induced; thus, levels of galactinol and raffinose increased compared with those in wild-type plants under control growth conditions. In leaves of the wild-type plants, treatment with 50 μm methylviologen (MV) increased the transcript levels of not only HsfA2, but also GolS1, -2, -3, -4, and -8 and RS2, -4, -5, and -6, the total activities of GolS isoenzymes, and the levels of galactinol and raffinose. GolS1- or GolS2-overexpressing Arabidopsis plants (Ox-GolS1-11, Ox-GolS2-8, and Ox-GolS2-29) had increased levels of galactinol and raffinose in the leaves compared with wild-type plants under control growth conditions. High intracellular levels of galactinol and raffinose in the transgenic plants were correlated with increased tolerance to MV treatment and salinity or chilling stress. Galactinol and raffinose effectively protected salicylate from attack by hydroxyl radicals in vitro. These findings suggest the possibility that galactinol and raffinose scavenge hydroxyl radicals as a novel function to protect plant cells from oxidative damage caused by MV treatment, salinity, or chilling. PMID:18502973
Micromechanical Modeling of Impact Damage Mechanisms in Unidirectional Composite Laminates
NASA Astrophysics Data System (ADS)
Meng, Qinghua; Wang, Zhenqing
2016-05-01
Composite laminates are susceptible to the transverse impact loads resulting in significant damage such as matrix cracking, fiber breakage and delamination. In this paper, a micromechanical model is developed to predict the impact damage of composite laminates based on microstructure and various failure models of laminates. The fiber and matrix are represented by the isotropic and elastic-plastic solid, and their impact failure behaviors are modeled based on shear damage model. The delaminaton failure is modeling by the interface element controlled by cohesive damage model. Impact damage mechanisms of laminate are analyzed by using the micromechanical model proposed. In addition, the effects of impact energy and laminated type on impact damage behavior of laminates are investigated. Due to the damage of the surrounding matrix near the impact point caused by the fiber deformation, the surface damage area of laminate is larger than the area of impact projectile. The shape of the damage area is roughly rectangle or elliptical with the major axis extending parallel to the fiber direction in the surface layer of laminate. The alternating laminated type with two fiber directions is more propitious to improve the impact resistance of laminates.
A surrogate-model-based identification of fractional viscoelastic constitutive parameters
NASA Astrophysics Data System (ADS)
Zhang, Guoqing; Yang, Haitian; Xu, Yongsheng
2015-02-01
In order to reduce the computational expense, a Kriging surrogate model is developed as an approximation of a numerical model based on FEM (finite element method) and FDM (finite difference method) to solve direct fractional viscoelastic problems and then is combined with a gridding-partition-based continuous ant colony algorithm to identify constitutive parameters of fractional viscoelastic materials. Three kinds of modeling strategies are presented to generate the Kriging surrogate model, that is, global modeling, piecewise modeling, and reduced modeling. Two numerical examples are given to illustrate the proposed approach in terms of computing accuracy and expense. The utilization of Kriging surrogate model not only can provide a sufficient computing accuracy, but also can significantly reduce the computational cost in solving inverse fractional viscoelastic problems. In addition, regional inhomogeneity and impact of noisy data are taken into account.
A constitutive model for the forces of a magnetic bearing including eddy currents
NASA Technical Reports Server (NTRS)
Taylor, D. L.; Hebbale, K. V.
1993-01-01
A multiple magnet bearing can be developed from N individual electromagnets. The constitutive relationships for a single magnet in such a bearing is presented. Analytical expressions are developed for a magnet with poles arranged circumferencially. Maxwell's field equations are used so the model easily includes the effects of induced eddy currents due to the rotation of the journal. Eddy currents must be included in any dynamic model because they are the only speed dependent parameter and may lead to a critical speed for the bearing. The model is applicable to bearings using attraction or repulsion.
Analyses for Debonding of Stitched Composite Sandwich Structures Using Improved Constitutive Models
NASA Technical Reports Server (NTRS)
Glaessgen, E. H.; Sleight, D. W.; Krishnamurthy, T.; Raju, I. S.
2001-01-01
A fracture mechanics analysis based on strain energy release rates is used to study the effect of stitching in bonded sandwich beam configurations. Finite elements are used to model the configurations. The stitches were modeled as discrete nonlinear spring elements with a compliance determined by experiment. The constitutive models were developed using the results of flatwise tension tests from sandwich material rather than monolithic material. The analyses show that increasing stitch stiffness, stitch density and debond length decrease strain energy release rates for a fixed applied load.
Ding, J.L.; Liu, K.C.; Brinkman, C.R.
1992-12-31
A constitutive model capable of describing deformation and predicting rupture life was developed for high temperature ceramic materials under general thermal-mechanical loading conditions. The model was developed based on the deformation and fracture behavior observed from a systematic experimental study on an advanced silicon nitride (Si{sub 3}N{sub 4}) ceramic material. Validity of the model was evaluated with reference to creep and creep rupture data obtained under constant and stepwise-varied loading conditions, including the effects of annealing on creep and creep rupture behavior.
Mitochondrial DNA damage and efficiency of ATP biosynthesis: mathematical model.
Beregovskaya, N; Maiboroda, R
1995-01-21
The role of mitochondrial DNA (mtDNA) damage in ageing processes and in malignant transformation of a cell is discussed. A mathematical model of the mtDNA population in a cell and in tissue is constructed. The model describes the effects of mtDNA damages accumulated during ageing and some features of malignant transformation and regeneration. PMID:7891454
Constitutive model for predicting dynamic interactions between soil ejecta and structural panels
NASA Astrophysics Data System (ADS)
Deshpande, V. S.; McMeeking, R. M.; Wadley, H. N. G.; Evans, A. G.
2009-08-01
A constitutive model is developed for the high-rate deformation of an aggregate comprising of mono-sized spherical particles with a view to developing an understanding of dynamic soil-structure interactions in landmine explosions. The constitutive model accounts for two regimes of behaviour. When the particle assembly is widely dispersed ( regime I), the contacts between particles are treated as collisions, analogous to those between molecules in a gas or liquid. At high packing densities ( regime II) the contacts are semi-permanent and consolidation is dominated by particle deformation and inter-particle friction. Regime I is modelled by extending an approach proposed by Bagnold (1954. Experiments on a gravity-free dispersion of large solid particles in a Newtonian fluid under shear. Proceedings of the Royal Society of London A 225, 49-63) to a general strain history comprising volumetric and deviatoric deformation. For regime II, classical soil mechanics models (such as Drucker-Prager) are employed. The overall model is employed to investigate the one-dimensional impact of sand against a rigid stationary target. The calculations illustrate that, unlike single-particle impact, the momentum transmitted to a rigid target is insensitive to the particle co-efficient of restitution, but strongly dependent on initial density. The constitutive model is also used to examine the spherical expansion of a shell of sand (both dry and water saturated). In line with initial experimental observations, the wet sand is predicted to form clumps while the dry sand fully disperses. The model shows that this clumping of explosively loaded wet sand exerts higher pressures on nearby targets compared to equivalent dry sand explosions.
A 3-D constitutive model for pressure-dependent phase transformation of porous shape memory alloys.
Ashrafi, M J; Arghavani, J; Naghdabadi, R; Sohrabpour, S
2015-02-01
Porous shape memory alloys (SMAs) exhibit the interesting characteristics of porous metals together with shape memory effect and pseudo-elasticity of SMAs that make them appropriate for biomedical applications. In this paper, a 3-D phenomenological constitutive model for the pseudo-elastic behavior and shape memory effect of porous SMAs is developed within the framework of irreversible thermodynamics. Comparing to micromechanical and computational models, the proposed model is computationally cost effective and predicts the behavior of porous SMAs under proportional and non-proportional multiaxial loadings. Considering the pressure dependency of phase transformation in porous SMAs, proper internal variables, free energy and limit functions are introduced. With the aim of numerical implementation, time discretization and solution algorithm for the proposed model are also presented. Due to lack of enough experimental data on multiaxial loadings of porous SMAs, we employ a computational simulation method (CSM) together with available experimental data to validate the proposed constitutive model. The method is based on a 3-D finite element model of a representative volume element (RVE) with random pores pattern. Good agreement between the numerical predictions of the model and CSM results is observed for elastic and phase transformation behaviors in various thermomechanical loadings. PMID:25528691
Numerical simulation of soil creep with a visco-hypoplastic constitutive model
NASA Astrophysics Data System (ADS)
Wang, Shun; Wu, Wei
2016-04-01
Slow-moving landslides make up a great part of geohazards in the Three Gorges reservoir (TGR) in China. Most of them move at speed of several centimeters per year (or even less) and show evidence of creep behaviour. It has been suggested that motion of creep landslides is mainly governed by the viscous properties of sheared materials forming the rupture zone, as these zones are where most of the slope deformation localizes. Understanding of creep behaviour of slipping material calls for laboratory tests as well as advanced constitutive models. For this purpose, a high order visco-hypoplastic constitutive model has been introduced. Unlike some of the visco-hypoplasric models, which consider the total strain rate as a combination of reversible strain rate and viscous strain rate respectively, such as dot{bm{e}}=dot{bm{e}}^e+dot{bm{e}}vis (where dot{bm{e}}, dot{bm{e}}e and dot{bm{e}}vis are the total strain rate ,reversible strain rate and viscous strain rate respectively), the proposed visco-hypolastic constitutive model decompose the Cauchy stress into a statical part and a dynamical part, bm{s}=hat{bm{s}}+\\check{bm{s}} (where bm{s},hat{bm{s}} and \\check{bm{s}} are total stress ,statical stress and dynamical stress respectively), whereas the strain rate has been considered as a whole. Within in this framework, stress change induced by strain acceleration can be taken into account. Moreover, compared with some special creep models, which may only valid for one or two stages of the three-state creep, i.e. primary creep, secondary creep and tertiary creep, this novel scheme is able to describe creep test with the whole three stages. This model has been also implemented into FEM code to evaluate some boundary-value problems. An explicit adaptive Rung-Kutta-Fehlberg algorithm is applied for stress-point integration. For verification of this model, numerical triaxial tests compared with laboratory tests have been conducted. Then a homogenous slope has been taken as an
NASA Technical Reports Server (NTRS)
Arnold, S. M.; Tan, H. Q.; Dong, X.
1989-01-01
Development of new material models for describing the high temperature constitutive behavior of real materials represents an important area of research in engineering disciplines. Derivation of mathematical expressions (constitutive equations) which describe this high temperature material behavior can be quite time consuming, involved and error prone; thus intelligent application of symbolic systems to facilitate this tedious process can be of significant benefit. A computerized procedure (SDICE) capable of efficiently deriving potential based constitutive models, in analytical form is presented. This package, running under MACSYMA, has the following features: partial differentiation, tensor computations, automatic grouping and labeling of common factors, expression substitution and simplification, back substitution of invariant and tensorial relations and a relational data base. Also limited aspects of invariant theory were incorporated into SDICE due to the utilization of potentials as a starting point and the desire for these potentials to be frame invariant (objective). Finally not only calculation of flow and/or evolutionary laws were accomplished but also the determination of history independent nonphysical coefficients in terms of physically measurable parameters, e.g., Young's modulus, was achieved. The uniqueness of SDICE resides in its ability to manipulate expressions in a general yet predefined order and simplify expressions so as to limit expression growth. Results are displayed when applicable utilizing index notation.
Zhang, Da-Guang; Li, Meng-Han; Zhou, Hao-Miao
2015-10-15
For magnetostrictive rods under combined axial pre-stress and magnetic field, a general one-dimension nonlinear magneto-elastic coupled constitutive model was built in this paper. First, the elastic Gibbs free energy was expanded into polynomial, and the relationship between stress and strain and the relationship between magnetization and magnetic field with the polynomial form were obtained with the help of thermodynamic relations. Then according to microscopic magneto-elastic coupling mechanism and some physical facts of magnetostrictive materials, a nonlinear magneto-elastic constitutive with concise form was obtained when the relations of nonlinear strain and magnetization in the polynomial constitutive were instead with transcendental functions. The comparisons between the prediction and the experimental data of different magnetostrictive materials, such as Terfenol-D, Metglas and Ni showed that the predicted magnetostrictive strain and magnetization curves were consistent with experimental results under different pre-stresses whether in the region of low and moderate field or high field. Moreover, the model can fully reflect the nonlinear magneto-mechanical coupling characteristics between magnetic, magnetostriction and elasticity, and it can effectively predict the changes of material parameters with pre-stress and bias field, which is useful in practical applications.
A size-dependent constitutive modelling framework for localised failure analysis
NASA Astrophysics Data System (ADS)
Nguyen, Giang D.; Nguyen, Chi T.; Nguyen, Vinh P.; Bui, Ha H.; Shen, Luming
2016-08-01
Localised deformation of materials usually takes place in thin bands during the nonlinear phase of the deformation process. The orientation and size of these localisation bands are important properties characterising the post-localisation behaviour of the materials, and hence should be taken into account in constitutive modelling. In this research, a new approach is proposed for the integration of both size and orientation of a localisation band in the constitutive description beyond the onset of localisation. Since a length scale related to the size of the localisation band appears in the model description, its post-localisation response then scales with both the band size and the size of the volume element containing it. Therefore, size effects are intrinsically included and post-localisation behaviour is correctly captured, which helps ensure convergence of numerical solutions upon discretisation refinement in numerical analysis of boundary value problems. The concept together with implementation features of the framework and its performances at constitutive level and in the analysis of boundary value problems are presented in this paper.
A size-dependent constitutive modelling framework for localised failure analysis
NASA Astrophysics Data System (ADS)
Nguyen, Giang D.; Nguyen, Chi T.; Nguyen, Vinh P.; Bui, Ha H.; Shen, Luming
2016-04-01
Localised deformation of materials usually takes place in thin bands during the nonlinear phase of the deformation process. The orientation and size of these localisation bands are important properties characterising the post-localisation behaviour of the materials, and hence should be taken into account in constitutive modelling. In this research, a new approach is proposed for the integration of both size and orientation of a localisation band in the constitutive description beyond the onset of localisation. Since a length scale related to the size of the localisation band appears in the model description, its post-localisation response then scales with both the band size and the size of the volume element containing it. Therefore, size effects are intrinsically included and post-localisation behaviour is correctly captured, which helps ensure convergence of numerical solutions upon discretisation refinement in numerical analysis of boundary value problems. The concept together with implementation features of the framework and its performances at constitutive level and in the analysis of boundary value problems are presented in this paper.
A meso-scale layer-specific structural constitutive model of the mitral heart valve leaflets.
Zhang, Will; Ayoub, Salma; Liao, Jun; Sacks, Michael S
2016-03-01
Fundamental to developing a deeper understanding of pathophysiological remodeling in mitral valve (MV) disease is the development of an accurate tissue-level constitutive model. In the present work, we developed a novel meso-scale (i.e. at the level of the fiber, 10-100μm in length scale) structural constitutive model (MSSCM) for MV leaflet tissues. Due to its four-layer structure, we focused on the contributions from the distinct collagen and elastin fiber networks within each tissue layer. Requisite collagen and elastin fibrous structural information for each layer were quantified using second harmonic generation microscopy and conventional histology. A comprehensive mechanical dataset was also used to guide model formulation and parameter estimation. Furthermore, novel to tissue-level structural constitutive modeling approaches, we allowed the collagen fiber recruitment function to vary with orientation. Results indicated that the MSSCM predicted a surprisingly consistent mean effective collagen fiber modulus of 162.72MPa, and demonstrated excellent predictive capability for extra-physiological loading regimes. There were also anterior-posterior leaflet-specific differences, such as tighter collagen and elastin fiber orientation distributions (ODF) in the anterior leaflet, and a thicker and stiffer atrialis in the posterior leaflet. While a degree of angular variance was observed, the tight valvular tissue ODF also left little room for any physically meaningful angular variance in fiber mechanical responses. Finally, a novel fibril-level (0.1-1μm) validation approach was used to compare the predicted collagen fiber/fibril mechanical behavior with extant MV small angle X-ray scattering data. Results demonstrated excellent agreement, indicating that the MSSCM fully captures the tissue-level function. Future utilization of the MSSCM in computational models of the MV will aid in producing highly accurate simulations in non-physiological loading states that can
Chen, Z.; Schreyer, H.L.
1995-09-01
The response of underground structures and transportation facilities under various external loadings and environments is critical for human safety as well as environmental protection. Since quasi-brittle materials such as concrete and rock are commonly used for underground construction, the constitutive modeling of these engineering materials, including post-limit behaviors, is one of the most important aspects in safety assessment. From experimental, theoretical, and computational points of view, this report considers the constitutive modeling of quasi-brittle materials in general and concentrates on concrete in particular. Based on the internal variable theory of thermodynamics, the general formulations of plasticity and damage models are given to simulate two distinct modes of microstructural changes, inelastic flow and degradation of material strength and stiffness, that identify the phenomenological nonlinear behaviors of quasi-brittle materials. The computational aspects of plasticity and damage models are explored with respect to their effects on structural analyses. Specific constitutive models are then developed in a systematic manner according to the degree of completeness. A comprehensive literature survey is made to provide the up-to-date information on prediction of structural failures, which can serve as a reference for future research.
NASA Astrophysics Data System (ADS)
Roy, Koushik; Bhattacharya, Bishakh; Ray-Chaudhuri, Samit
2015-08-01
The study proposes a set of four ARX model (autoregressive model with exogenous input) based damage sensitive features (DSFs) for structural damage detection and localization using the dynamic responses of structures, where the information regarding the input excitation may not be available. In the proposed framework, one of the output responses of a multi-degree-of-freedom system is assumed as the input and the rest are considered as the output. The features are based on ARX model coefficients, Kolmogorov-Smirnov (KS) test statistical distance, and the model residual error. At first, a mathematical formulation is provided to establish the relation between the change in ARX model coefficients and the normalized stiffness of a structure. KS test parameters are then described to show the sensitivity of statistical distance of ARX model residual error with the damage location. The efficiency of the proposed set of DSFs is evaluated by conducting numerical studies involving a shear building and a steel moment-resisting frame. To simulate the damage scenarios in these structures, stiffness degradation of different elements is considered. It is observed from this study that the proposed set of DSFs is good indicator for damage location even in the presence of damping, multiple damages, noise, and parametric uncertainties. The performance of these DSFs is compared with mode shape curvature-based approach for damage localization. An experimental study has also been conducted on a three-dimensional six-storey steel moment frame to understand the performance of these DSFs under real measurement conditions. It has been observed that the proposed set of DSFs can satisfactorily localize damage in the structure.
NASA Technical Reports Server (NTRS)
Wilt, T. E.
1995-01-01
The Generalized Method of Cells (GMC), a micromechanics based constitutive model, is implemented into the finite element code MARC using the user subroutine HYPELA. Comparisons in terms of transverse deformation response, micro stress and strain distributions, and required CPU time are presented for GMC and finite element models of fiber/matrix unit cell. GMC is shown to provide comparable predictions of the composite behavior and requires significantly less CPU time as compared to a finite element analysis of the unit cell. Details as to the organization of the HYPELA code are provided with the actual HYPELA code included in the appendix.
Life prediction and constitutive models for engine hot section anisotropic materials program
NASA Technical Reports Server (NTRS)
Swanson, G. A.
1985-01-01
The purpose is to develop life prediction models for coated anisotropic materials used in gas temperature airfoils. Two single crystal alloys and two coatings are now being tested. These include PWA 1480; Alloy 185; overlay coating, PWA 286; and aluminide coating, PWA 273. Constitutive models are also being developed for these materials to predict the plastic and creep strain histories of the materials in the lab tests and for actual design conditions. This nonlinear material behavior is particularily important for high temperature gas turbine applications and is basic to any life prediction system.
Influence of twinning on the constitutive response of Zr: Experiments and modeling
Chen, Shuh Rong; Gray, G.T. III
1997-05-01
The stress-strain response of Zr due to twinning is distinctly different from that due to slip as a function of temperature and strain rate. When the applied stress is lower than the transition stress, dislocation slip is the dominant deformation mechanism. The traditional MTS model is shown to adequately represent the constitutive behavior of Zr. Above the transition stress twinning becomes the dominant deformation mechanism where the flow stress increases linearly with strain. In this regime the rate-dependent strain hardening can be described by equations based on thermal activation theory that are very similar to the formula used in the MTS model.
NASA Astrophysics Data System (ADS)
Sarbandi, B.; Besson, J.; Boussuge, M.; Ryckelynck, D.
2010-06-01
Slip cast ceramic components undergo both sintering shrinkage and creep deformation caused by gravity during the firing cycle. In addition sintering may be anisotropic due to the development of preferential directions during slip casting. Both phenomena induce complex deformations of parts which make the design of casting molds difficult. To help solving this problem, anisotropic constitutive equations are proposed to represent the behavior of the ceramic compacts during sintering. The model parameters are identified using tests allowing to characterize both sintering and creep. The model was implemented in a finite element software and used to simulate the deformation of a traditional ceramic object during sintering.
Sarbandi, B.; Besson, J.; Boussuge, M.; Ryckelynck, D.
2010-06-15
Slip cast ceramic components undergo both sintering shrinkage and creep deformation caused by gravity during the firing cycle. In addition sintering may be anisotropic due to the development of preferential directions during slip casting. Both phenomena induce complex deformations of parts which make the design of casting molds difficult. To help solving this problem, anisotropic constitutive equations are proposed to represent the behavior of the ceramic compacts during sintering. The model parameters are identified using tests allowing to characterize both sintering and creep. The model was implemented in a finite element software and used to simulate the deformation of a traditional ceramic object during sintering.
Identification of Two Constitutive Models for a Low Alloy Structural Steel S355K2G3
NASA Astrophysics Data System (ADS)
Mespoulet, Jerome; Lachaud, Aurelien; Hereil, Pierre
2009-06-01
An experimental characterization of the dynamic response of a low strength structural steel (S355K2G3) has been investigated using various experimental techniques performed at THIOT INGENIERIE impact shock physics test facility: Taylor impacts, hat shaped shear tests, dynamic tensile tests and plate impact experiments. This paper presents simulations of these experiments performed in a wide range of strain-rate conditions. The objective is to simulate impact, blast and explosion on a whole structure. Impacts generate huge gradients of stress and strain because of shock waves propagation and interaction on free surfaces. Blast and explosion have a tendency to induce large strains. Based on the overall experiments, it is proposed to identify two classical constitutive models (Johnson-Cook and Zerilli-Amstrong) integrated in two non-linear explicit finite element hydrocodes ANSYS-AUTODYN and LS-DYNA. Both hydrocodes take into account various modes of fracture from single conventional fracture thresholds such as critical strain value or hydro tensile failure model to more complex modes such as Johnson Holmquist damage failure model. Choice between models is discussed with respect to material nature and to solicitations the material is subjected to.
Modeling of delamination damage evolution in laminated composites subjected to low velocity impact
NASA Technical Reports Server (NTRS)
Lo, David C.; Allen, David H.
1994-01-01
This study examines the delamination evolution, under quasi-static conditions, of laminated polymeric composites with mechanically nonlinear resin rich interfaces. The constitutive behavior of the interface is represented by two models developed by Needleman and Tvegaard. These models assumed that the interfacial tractions, a function of only the interfacial displacement, will behave similarly to the interatomic forces generated during the interatomic seperation. The interface material's parameters control the load at which the delamination growth initiates and the final delamination size. A wide range of damage accumulation responses have been obtained by varying the model parameters. These results show that Tvergaard's model has been found to be better suited of the two models in predicting damage evolution for the configurations examined.
Aerodynamic Effects and Modeling of Damage to Transport Aircraft
NASA Technical Reports Server (NTRS)
Shah, Gautam H.
2008-01-01
A wind tunnel investigation was conducted to measure the aerodynamic effects of damage to lifting and stability/control surfaces of a commercial transport aircraft configuration. The modeling of such effects is necessary for the development of flight control systems to recover aircraft from adverse, damage-related loss-of-control events, as well as for the estimation of aerodynamic characteristics from flight data under such conditions. Damage in the form of partial or total loss of area was applied to the wing, horizontal tail, and vertical tail. Aerodynamic stability and control implications of damage to each surface are presented, to aid in the identification of potential boundaries in recoverable stability or control degradation. The aerodynamic modeling issues raised by the wind tunnel results are discussed, particularly the additional modeling requirements necessitated by asymmetries due to damage, and the potential benefits of such expanded modeling.
Problems of orthotropic plastic constitutive models: Non-associated flow and evolution of anisotropy
NASA Astrophysics Data System (ADS)
Pan, Haizhen
Two main topics are addressed in this thesis for anisotropic plastic behavior, e.g. textured polycrystals: (i) non-associated plastic flow and (ii) deformation-induced evolution of microstructure. We consider a class of elastic-plastic materials that possess local orthotropic symmetry which is represented in terms of second-order orientation tensors. In developing constitutive equations, significant use is made of representation theory for functions of tensors (Wang, 1969, 1970; Smith, 1969, 1970). Recent developments in multiscale modeling have unequivocally demonstrated that plastic flow in a wide range of crystalline materials is non-associative (i.e., distinct yield and flow functions) due to the effects of non-glide stresses on the motion of dislocations and slip. As a consequence, experimental observations of tension and compression asymmetries are widely approached. To describe orthotropic, non-associated behavior for polycrystals, yield and flow functions are developed based upon representation theory. Anisotropic plastic flow is commonplace for all materials possessing non-random microstructures. The second part of work focuses on the development of anisotropic elastic-plastic constitutive models to account microstructural evolution. Examples of material systems include polycrystals, whisker-reinforced composites, polymers, as well as complex viscoplastic fluids. For persistent orthotropic behavior, microstructural evolution is represented by the rotation of orthonormal vectors, which is governed by the constitutive relations for plastic spin. Representations for scalar- and tensor-valued functions of tensors are also utilized to develop phenomenological constitutive relations for plastic spin. Good agreement is demonstrated with experimental data for microstructural evolution in textured polycrystals. The effects of both non-associated flow and evolution of microstructure on strain localization are investigated. From the analyses of stress and load maxima
Bass, B.R.; Pugh, C.E.; Swindeman, R.W.
1986-01-01
Various viscoplastic constitutive models and several nonlinear fracture criteria are being installed in the ADINA general purpose finite element computer program, and the combined predictive capabilities are being evaluated through applications to the HSST wide-plate experiments. The first two constitutive models selected for installation in ADINA were a variation of the Perzyna elastic-viscoplastic model with linear strain hardening and the Bodner-Partom viscoplastic model with strain hardening. Other models being examined include those due to Robinson-Pugh and Hart. The fracture criteria being examined for use with nonlinear analyses include several path-independent integrals that were formulated to remove limitations on the original J-integral of Rice. Some of these integrals represent slight modifications of the J-integral, while others have a different theoretical basis. This paper describes applications of these nonlinear techniques to the first series of six HSST wide-plate crack-arrest tests that have been performed. These experiments include crack initiations at low temperatures and relatively long (20 cm) cleavage propagation phases which are terminated by arrest in high-temperature regions. Crack arrests are then followed by ductile tearing events. Consequently, the crack-front regions in these tests are exposed to wide ranges of strain rates and temperatures.
NASA Astrophysics Data System (ADS)
Tricerri, Paolo; Dedè, Luca; Deparis, Simone; Quarteroni, Alfio; Robertson, Anne M.; Sequeira, Adélia
2015-03-01
This paper considers numerical simulations of fluid-structure interaction (FSI) problems in hemodynamics for idealized geometries of healthy cerebral arteries modeled by both nonlinear isotropic and anisotropic material constitutive laws. In particular, it focuses on an anisotropic model initially proposed for cerebral arteries to characterize the activation of collagen fibers at finite strains. In the current work, this constitutive model is implemented for the first time in the context of an FSI formulation. In this framework, we investigate the influence of the material model on the numerical results and, in the case of the anisotropic laws, the importance of the collagen fibers on the overall mechanical behavior of the tissue. With this aim, we compare our numerical results by analyzing fluid dynamic indicators, vessel wall displacement, Von Mises stress, and deformations of the collagen fibers. Specifically, for an anisotropic model with collagen fiber recruitment at finite strains, we highlight the progressive activation and deactivation processes of the fibrous component of the tissue throughout the wall thickness during the cardiac cycle. The inclusion of collagen recruitment is found to have a substantial impact on the intramural stress, which will in turn impact the biological response of the intramural cells. Hence, the methodology presented here will be particularly useful for studies of mechanobiological processes in the healthy and diseased vascular wall.
NASA Astrophysics Data System (ADS)
Sherburn, J. A.; Horstemeyer, M. F.; Bammann, D. J.; Baumgardner, J. R.
2011-03-01
We describe how the Bammann internal state variable (ISV) constitutive approach, which has proven highly successful in modelling deformation processes in metals, can be applied with great benefit to silicate rocks and other geological materials in modelling their deformation dynamics. In its essence, ISV theory provides a constitutive framework to account for changing history states that arise from inelastic dissipative microstructural evolution of a polycrystalline solid. In this paper, we restrict our attention to a Bammann ISV elastic-viscoplastic model with temperature and strain rate dependence and use isotropic hardening and anisotropic hardening as our two ISVs. We show the Bammann model captures the inelastic behaviour of olivine aggregates (with and without water), lherzolite (with and without water), Carrara marble and rock salt using some experimental data found in the literature. These examples illustrate that when more experimental stress-strain data are gathered on other rock materials, much more realistic numerical simulation of rock behaviour becomes feasible. Though not available in the literature, we outline a set of experiments to obtain unique Bammann ISV model constants.
A size-dependent constitutive model of bulk metallic glasses in the supercooled liquid region
NASA Astrophysics Data System (ADS)
Yao, Di; Deng, Lei; Zhang, Mao; Wang, Xinyun; Tang, Na; Li, Jianjun
2015-01-01
Size effect is of great importance in micro forming processes. In this paper, micro cylinder compression was conducted to investigate the deformation behavior of bulk metallic glasses (BMGs) in supercooled liquid region with different deformation variables including sample size, temperature and strain rate. It was found that the elastic and plastic behaviors of BMGs have a strong dependence on the sample size. The free volume and defect concentration were introduced to explain the size effect. In order to demonstrate the influence of deformation variables on steady stress, elastic modulus and overshoot phenomenon, four size-dependent factors were proposed to construct a size-dependent constitutive model based on the Maxwell-pulse type model previously presented by the authors according to viscosity theory and free volume model. The proposed constitutive model was then adopted in finite element method simulations, and validated by comparing the micro cylinder compression and micro double cup extrusion experimental data with the numerical results. Furthermore, the model provides a new approach to understanding the size-dependent plastic deformation behavior of BMGs.
A size-dependent constitutive model of bulk metallic glasses in the supercooled liquid region.
Yao, Di; Deng, Lei; Zhang, Mao; Wang, Xinyun; Tang, Na; Li, Jianjun
2015-01-01
Size effect is of great importance in micro forming processes. In this paper, micro cylinder compression was conducted to investigate the deformation behavior of bulk metallic glasses (BMGs) in supercooled liquid region with different deformation variables including sample size, temperature and strain rate. It was found that the elastic and plastic behaviors of BMGs have a strong dependence on the sample size. The free volume and defect concentration were introduced to explain the size effect. In order to demonstrate the influence of deformation variables on steady stress, elastic modulus and overshoot phenomenon, four size-dependent factors were proposed to construct a size-dependent constitutive model based on the Maxwell-pulse type model previously presented by the authors according to viscosity theory and free volume model. The proposed constitutive model was then adopted in finite element method simulations, and validated by comparing the micro cylinder compression and micro double cup extrusion experimental data with the numerical results. Furthermore, the model provides a new approach to understanding the size-dependent plastic deformation behavior of BMGs. PMID:25626690
Majumder, Rupamanjari; Jangsangthong, Wanchana; Feola, Iolanda; Ypey, Dirk L.; Pijnappels, Daniël A.; Panfilov, Alexander V.
2016-01-01
Atrial fibrillation (AF) is the most frequent form of arrhythmia occurring in the industrialized world. Because of its complex nature, each identified form of AF requires specialized treatment. Thus, an in-depth understanding of the bases of these arrhythmias is essential for therapeutic development. A variety of experimental studies aimed at understanding the mechanisms of AF are performed using primary cultures of neonatal rat atrial cardiomyocytes (NRAMs). Previously, we have shown that the distinct advantage of NRAM cultures is that they allow standardized, systematic, robust re-entry induction in the presence of a constitutively-active acetylcholine-mediated K+ current (IKACh-c). Experimental studies dedicated to mechanistic explorations of AF, using these cultures, often use computer models for detailed electrophysiological investigations. However, currently, no mathematical model for NRAMs is available. Therefore, in the present study we propose the first model for the action potential (AP) of a NRAM with constitutively-active acetylcholine-mediated K+ current (IKACh-c). The descriptions of the ionic currents were based on patch-clamp data obtained from neonatal rats. Our monolayer model closely mimics the action potential duration (APD) restitution and conduction velocity (CV) restitution curves presented in our previous in vitro studies. In addition, the model reproduces the experimentally observed dynamics of spiral wave rotation, in the absence and in the presence of drug interventions, and in the presence of localized myofibroblast heterogeneities. PMID:27332890
A size-dependent constitutive model of bulk metallic glasses in the supercooled liquid region
Yao, Di; Deng, Lei; Zhang, Mao; Wang, Xinyun; Tang, Na; Li, Jianjun
2015-01-01
Size effect is of great importance in micro forming processes. In this paper, micro cylinder compression was conducted to investigate the deformation behavior of bulk metallic glasses (BMGs) in supercooled liquid region with different deformation variables including sample size, temperature and strain rate. It was found that the elastic and plastic behaviors of BMGs have a strong dependence on the sample size. The free volume and defect concentration were introduced to explain the size effect. In order to demonstrate the influence of deformation variables on steady stress, elastic modulus and overshoot phenomenon, four size-dependent factors were proposed to construct a size-dependent constitutive model based on the Maxwell-pulse type model previously presented by the authors according to viscosity theory and free volume model. The proposed constitutive model was then adopted in finite element method simulations, and validated by comparing the micro cylinder compression and micro double cup extrusion experimental data with the numerical results. Furthermore, the model provides a new approach to understanding the size-dependent plastic deformation behavior of BMGs. PMID:25626690
Bammann, Douglas J.; Johnson, G. C. (University of California, Berkeley, CA); Marin, Esteban B.; Regueiro, Richard A.
2006-01-01
In this report we present the formulation of the physically-based Evolving Microstructural Model of Inelasticity (EMMI) . The specific version of the model treated here describes the plasticity and isotropic damage of metals as being currently applied to model the ductile failure process in structural components of the W80 program . The formulation of the EMMI constitutive equations is framed in the context of the large deformation kinematics of solids and the thermodynamics of internal state variables . This formulation is focused first on developing the plasticity equations in both the relaxed (unloaded) and current configurations. The equations in the current configuration, expressed in non-dimensional form, are used to devise the identification procedure for the plasticity parameters. The model is then extended to include a porosity-based isotropic damage state variable to describe the progressive deterioration of the strength and mechanical properties of metals induced by deformation . The numerical treatment of these coupled plasticity-damage constitutive equations is explained in detail. A number of examples are solved to validate the numerical implementation of the model.
Probabilistic flood damage modelling at the meso-scale
NASA Astrophysics Data System (ADS)
Kreibich, Heidi; Botto, Anna; Schröter, Kai; Merz, Bruno
2014-05-01
Decisions on flood risk management and adaptation are usually based on risk analyses. Such analyses are associated with significant uncertainty, even more if changes in risk due to global change are expected. Although uncertainty analysis and probabilistic approaches have received increased attention during the last years, they are still not standard practice for flood risk assessments. Most damage models have in common that complex damaging processes are described by simple, deterministic approaches like stage-damage functions. Novel probabilistic, multi-variate flood damage models have been developed and validated on the micro-scale using a data-mining approach, namely bagging decision trees (Merz et al. 2013). In this presentation we show how the model BT-FLEMO (Bagging decision Tree based Flood Loss Estimation MOdel) can be applied on the meso-scale, namely on the basis of ATKIS land-use units. The model is applied in 19 municipalities which were affected during the 2002 flood by the River Mulde in Saxony, Germany. The application of BT-FLEMO provides a probability distribution of estimated damage to residential buildings per municipality. Validation is undertaken on the one hand via a comparison with eight other damage models including stage-damage functions as well as multi-variate models. On the other hand the results are compared with official damage data provided by the Saxon Relief Bank (SAB). The results show, that uncertainties of damage estimation remain high. Thus, the significant advantage of this probabilistic flood loss estimation model BT-FLEMO is that it inherently provides quantitative information about the uncertainty of the prediction. Reference: Merz, B.; Kreibich, H.; Lall, U. (2013): Multi-variate flood damage assessment: a tree-based data-mining approach. NHESS, 13(1), 53-64.
Cornejo, Melanie G.; Kharas, Michael G.; Werneck, Miriam B.; Bras, Séverine Le; Moore, Sandra A.; Ball, Brian; Beylot-Barry, Marie; Rodig, Scott J.; Aster, Jon C.; Lee, Benjamin H.; Cantor, Harvey; Merlio, Jean-Philippe
2009-01-01
The tyrosine kinase JAK3 plays a well-established role during normal lymphocyte development and is constitutively phosphorylated in several lymphoid malignancies. However, its contribution to lymphomagenesis remains elusive. In this study, we used the newly identified activating JAK3A572V mutation to elucidate the effect of constitutive JAK3 signaling on murine lymphopoiesis. In a bone marrow transplantation model, JAK3A572V induces an aggressive, fatal, and transplantable lymphoproliferative disorder characterized by the expansion of CD8+TCRαβ+CD44+CD122+Ly-6C+ T cellsthat closely resemble an effector/memory T-cell subtype. Compared with wild-type counterparts, these cells show increased proliferative capacities in response to polyclonal stimulation, enhanced survival rates with elevated expression of Bcl-2, and increased production of interferon-γ (IFNγ) and tumor necrosis factor-α (TNFα), correlating with enhanced cytotoxic abilities against allogeneic target cells. Of interest, the JAK3A572V disease is epidermotropic and produces intraepidermal microabscesses. Taken together, these clinical features are reminiscent of those observed in an uncommon but aggressive subset of CD8+ human cutaneous T-cell lymphomas (CTCLs). However, we also observed a CD4+ CTCL-like phenotype when cells are transplanted in an MHC-I–deficient background. These data demonstrate that constitutive JAK3 activation disrupts T-cell homeostasis and induces lymphoproliferative diseases in mice. PMID:19139084
NASA Astrophysics Data System (ADS)
Wu, Zhang; Jinchun, Tang
2002-04-01
This paper establishes a piezoelectric constitutive computational approach based on generalized eigenvalue and multivariable finite element solutions with potential applications to accurate and effective analysis of layered piezoelectric microstructures of arbitrary geometries and different anisotropic materials, to ease the limitation of current computer capacity in analyzing large-scale high-frequency disturbed surface acoustic waves (DSAW) by mounted electrodes in piezoelectric devices such as microchip SAW resonators. A new incompatible generalized hybrid/mixed element GQM5 is also proposed for improving predictions of the piezoelectric surface mount thermal stresses that are shear-dominated. The (generalized) plane strain constitutive model is numerically verified for piezoelectric finite element computation. With the help of computational piezoelectricity (electro-mechanics) for general layered structures with metal electrodes and anisotropic piezoelectric substrates, some new interesting, reliable and fundamental constitutive finite element results are obtained for high-frequency piezoelectric and mechanical SAW propagations and can be used for further applications. The ST-cut FEA results agree quite well with available exact and lab solutions for free surface case.
Damage and fracture of brittle viscoelastic solids with application to ice load models
NASA Astrophysics Data System (ADS)
Xiao, Jing
1997-12-01
In this work a multiaxial constitutive theory for brittle, viscoelastic materials is presented based on viscoelasticity, continuum damage theory and fracture mechanics. The microstructural nature of the material and micromechanical processes have been modelled by damage mechanics using averaging procedures with a finite collection of state variables. The change in the state variable is directly related to the individual deformation process. The constitutive model includes the effects of damage including microcracking, dynamic recrystallization and pressure melting on the reduction in elastic modulus and the enhancement in creep deformation. Damage evolution is based on Schapery's approach using the generalized J integral theory. The influence of confining pressure on damage progress is included. Volumetric deformation under compression is also investigated which is mostly dilatation due to microstructural changes (damage). A triaxial test program has been carried out in the laboratory at Memorial University. A description of the test program, specimen preparation, test equipment and procedure used has been presented. The experimental observations and results have been discussed and are summarized. Triaxial tests were designed to investigate the deformation of ice and the influence of damage on the mechanical properties of ice. These tests have also served to verify the constitutive modelling. The theoretical model provides good agreement with test results. The role of fracture and spalling in ice-structure interaction has been investigated. Fracture analysis, using the J-integral, has been carried out in the numerical scheme, which is based on finite elements and the computer program ABAQUS. This analysis is consistent with the damage mechanics and has been carried out on the basis of plane strain assumptions and the direction of crack propagation was calculated by maximizing the strain energy release rate. The direction of maximum tensile stress was also
A three-dimensional constitutive model for the stress relaxation of articular ligaments.
Davis, Frances M; De Vita, Raffaella
2014-06-01
A new nonlinear constitutive model for the three-dimensional stress relaxation of articular ligaments is proposed. The model accounts for finite strains, anisotropy, and strain-dependent stress relaxation behavior exhibited by these ligaments. The model parameters are identified using published uniaxial stress-stretch and stress relaxation data on human medial collateral ligaments (MCLs) subjected to tensile tests in the fiber and transverse to the fiber directions (Quapp and Weiss in J Biomech Eng Trans ASME 120:757-763, 1998; Bonifasi-Lista et al. in J Orthop Res 23(1):67-76, 2005). The constitutive equation is then used to predict the nonlinear elastic and stress relaxation response of ligaments subjected to shear deformations in the fiber direction and transverse to the fiber direction, and an equibiaxial extension. A direct comparison with stress relaxation data collected by subjecting human MCLs to shear deformation in the fiber direction is presented in order to demonstrate the predictive capabilities of the model. PMID:23990018
NASA Astrophysics Data System (ADS)
Zhang, Ling; Min, Junying; Wang, Bin; Lin, Jianping; Li, Fangfang; Liu, Jing
2016-03-01
In practical engineering, finite element(FE) modeling for weld seam is commonly simplified by neglecting its inhomogeneous mechanical properties. This will cause a significant loss in accuracy of FE forming analysis, in particular, for friction stir welded(FSW) blanks due to the large width and good formability of its weld seam. The inhomogeneous mechanical properties across weld seam need to be well characterized for an accurate FE analysis. Based on a similar AA5182 FSW blank, the metallographic observation and micro-Vickers hardness analysis upon the weld cross-section are performed to identify the interfaces of different sub-zones, i.e., heat affected zone(HAZ), thermal-mechanically affected zone(TMAZ) and weld nugget(WN). Based on the rule of mixture and hardness distribution, a constitutive model is established for each sub-zone to characterize the inhomogeneous mechanical properties across the weld seam. Uniaxial tensile tests of the AA5182 FSW blank are performed with the aid of digital image correlation(DIC) techniques. Experimental local stress-strain curves are obtained for different weld sub-zones. The experimental results show good agreement with those derived from the constitutive models, which demonstrates the feasibility and accuracy of these models. The proposed research gives an accurate characterization of inhomogeneous mechanical properties across the weld seam produced by FSW, which provides solutions for improving the FE simulation accuracy of FSW sheet forming.
A microplane constitutive model for shape memory alloys considering tension-compression asymmetry
NASA Astrophysics Data System (ADS)
Karamooz Ravari, M. R.; Kadkhodaei, M.; Ghaei, A.
2015-07-01
Shape memory alloys are a group of advanced materials that have found several industrial applications due to their interesting mechanical properties including a shape memory effect and superelasticity. In order to optimize the use of such materials in manufacturing different devices, appropriate advanced constitutive models are required. Recent experiments show that shape memory alloys exhibit an asymmetric response during tension and compression loading. In this paper, a new three-dimensional constitutive law is proposed based on microplane theory with the purpose of describing the tension-compression asymmetry. The model utilizes an equivalent stress on the foundation of second and third invariants of the deviatoric stress tensor in combination with two internal variables to distinguish between martensite volume fraction as well as martensite elastic modulus during tension and compression. The proposed model is then used to simulate uniaxial tension-compression loading in superelasticity as well as ferroelasticity regimes. The simulation results are compared with the corresponding results obtained by experiment and previous models reported in the literature, and a good agreement is observed. In addition, a four-point bending test is simulated for NiTi tubes in several cases. The predicted moment-curvature response and variations in the position of the neutral axis correlate fairly well with the experimental findings reported in the literature.
MRAC Control with Prior Model Knowledge for Asymmetric Damaged Aircraft
Xu, Xieyu; Yang, Lingyu; Zhang, Jing
2015-01-01
This paper develops a novel state-tracking multivariable model reference adaptive control (MRAC) technique utilizing prior knowledge of plant models to recover control performance of an asymmetric structural damaged aircraft. A modification of linear model representation is given. With prior knowledge on structural damage, a polytope linear parameter varying (LPV) model is derived to cover all concerned damage conditions. An MRAC method is developed for the polytope model, of which the stability and asymptotic error convergence are theoretically proved. The proposed technique reduces the number of parameters to be adapted and thus decreases computational cost and requires less input information. The method is validated by simulations on NASA generic transport model (GTM) with damage. PMID:26180839
NASA Astrophysics Data System (ADS)
Salari, S.; Naderi, M.; Bleck, W.
2015-02-01
Simulation of hot stamping process needs reliable material data, especially at high temperatures where plastic deformation takes place in austenitic microstructure. In the current study, high-temperature non-isothermal compression tests (NICT) at different ranges of temperature, strain and strain rate as well as constitutive modeling of the flow curves were carried out. The Johnson-Cook and the Nemat-Nasser phenomenological models for isothermal deformation conditions were revised and applied to fit the flow curves during high-temperature NICT. It was shown that the models can satisfactorily predict the material flow stress at the mentioned conditions. Furthermore, the models were employed in order to describe the work-hardening behavior of the material. The results indicated that the fitted work-hardening rate can successfully follow the experimental data during deformation till no strain-induced phase transformation is initiated.
NASA Astrophysics Data System (ADS)
Vanini, Seyed Ali Sadough; Abolghasemzadeh, Mohammad; Assadi, Abbas
2013-07-01
Functionally graded steels with graded ferritic and austenitic regions including bainite and martensite intermediate layers produced by electroslag remelting have attracted much attention in recent years. In this article, an empirical model based on the Zener-Hollomon (Z-H) constitutive equation with generalized material constants is presented to investigate the effects of temperature and strain rate on the hot working behavior of functionally graded steels. Next, a theoretical model, generalized by strain compensation, is developed for the flow stress estimation of functionally graded steels under hot compression based on the phase mixture rule and boundary layer characteristics. The model is used for different strains and grading configurations. Specifically, the results for αβγMγ steels from empirical and theoretical models showed excellent agreement with those of experiments of other references within acceptable error.
Application of an Uncoupled Elastic-plastic-creep Constitutive Model to Metals at High Temperature
NASA Technical Reports Server (NTRS)
Haisler, W. E.
1983-01-01
A uniaxial, uncoupled constitutive model to predict the response of thermal and rate dependent elastic-plastic material behavior is presented. The model is based on an incremental classicial plasticity theory extended to account for thermal, creep, and transient temperature conditions. Revisions to he combined hardening rule of the theory allow for better representation of cyclic phenomenon including the high rate of strain hardening upon cyclic reyield and cyclic saturation. An alternative approach is taken to model the rate dependent inelastic deformation which utilizes hysteresis loops and stress relaxation test data at various temperatures. The model is evaluated and compared to experiments which involve various thermal and mechanical load histories on 5086 aluminum alloy, 304 stainless steel and Hastelloy-X.
A Damage Model for the Simulation of Delamination in Advanced Composites under Variable-Mode Loading
NASA Technical Reports Server (NTRS)
Turon, A.; Camanho, P. P.; Costa, J.; Davila, C. G.
2006-01-01
A thermodynamically consistent damage model is proposed for the simulation of progressive delamination in composite materials under variable-mode ratio. The model is formulated in the context of Damage Mechanics. A novel constitutive equation is developed to model the initiation and propagation of delamination. A delamination initiation criterion is proposed to assure that the formulation can account for changes in the loading mode in a thermodynamically consistent way. The formulation accounts for crack closure effects to avoid interfacial penetration of two adjacent layers after complete decohesion. The model is implemented in a finite element formulation, and the numerical predictions are compared with experimental results obtained in both composite test specimens and structural components.
Damage mechanics in engineering materials
Voyiadjis, G.Z.; Woody Ju, J.W.; Chaboche, J.L.
1998-12-31
This book contains thirty peer-reviewed papers that are based on the presentations made at the symposium on Damage Mechanics in Engineering Materials on the occasion of the Joint ASME/ASCE/SES Mechanics Conference (McNU97), held in Evanston, Illinois, June 28--July 2, 1997. The key area of discussion was on the constitutive modeling of damage mechanics in engineering materials encompassing the following topics: macromechanics/micromechanical constitutive modeling, experimental procedures, numerical modeling, inelastic behavior, interfaces, damage, fracture, failure, computational methods. The book is divided into six parts: study of damage mechanics; localization and damage; damage in brittle materials; damage in metals and metal matrix composites; computational aspects of damage models; damage in polymers and elastomers.
NASA Astrophysics Data System (ADS)
François, Bertrand; Labiouse, Vincent; Dizier, Arnaud; Marinelli, Ferdinando; Charlier, Robert; Collin, Frédéric
2014-01-01
Boom Clay is extensively studied as a potential candidate to host underground nuclear waste disposal in Belgium. To guarantee the safety of such a disposal, the mechanical behaviour of the clay during gallery excavation must be properly predicted. In that purpose, a hollow cylinder experiment on Boom Clay has been designed to reproduce, in a small-scale test, the Excavation Damaged Zone (EDZ) as experienced during the excavation of a disposal gallery in the underground. In this article, the focus is made on the hydro-mechanical constitutive interpretation of the displacement (experimentally obtained by medium resolution X-ray tomography scanning). The coupled hydro-mechanical response of Boom Clay in this experiment is addressed through finite element computations with a constitutive model including strain hardening/softening, elastic and plastic cross-anisotropy and a regularization method for the modelling of strain localization processes. The obtained results evidence the directional dependency of the mechanical response of the clay. The softening behaviour induces transient strain localization processes, addressed through a hydro-mechanical second grade model. The shape of the obtained damaged zone is clearly affected by the anisotropy of the materials, evidencing an eye-shaped EDZ. The modelling results agree with experiments not only qualitatively (in terms of the shape of the induced damaged zone), but also quantitatively (for the obtained displacement in three particular radial directions).
Numerical Simulation of Damage using an Elastic-Viscoplastic Model with Directional Tensile Failure
Lomov, I
2003-03-17
A new continuum model for directional tensile failure has been developed that can simulate weakening and void formation due to directional tensile failure. The model is developed within the context of a properly invariant nonlinear thermomechanical theory. A second order damage tensor is introduced which allows simulation of weakening to tension applied in one direction, without weakening to subsequent tension applied in perpendicular directions. This damage tensor can be advected using standard methods in computer codes. Porosity is used as an isotropic measure of volumetric void strain and its evolution is influenced by tensile failure. The rate of dissipation due to directional tensile failure takes a particularly simple form, which can be analyzed easily. Specifically, the model can be combined with general constitutive equations for porous compaction and dilation, as well as viscoplasticity. A robust non-iterative numerical scheme for integrating these evolution equations is proposed. This constitutive model has been implemented into an Eulerian shock wave code with adaptive mesh refinement. A number of simulations of complicated shock loading of different materials have been performed including problems of fracture of rock. These simulations show that directionality of damage can play a significant role in material failure.
O’Connell, Grace D.; Sen, Sounok; Elliott, Dawn M.
2012-01-01
The annulus fibrosus (AF) of the intervertebral disc undergoes large and multidirectional stresses and strains. Uniaxial tensile tests are limited for measuring AF material properties, because freely contracting edges can prevent fiber stretch and are not representative of in situ boundary conditions. The objectives of this study were to measure human AF biaxial tensile mechanics and to apply and validate a constitutive model to determine material properties. Biaxial tensile tests were performed on samples oriented along the circumferential-axial and the radial-axial directions. Data were fit to a structurally-motivated anisotropic hyperelastic model composed of isotropic extrafibrillar matrix, nonlinear fibers, and fiber-matrix interactions (FMI) normal to the fibers. The validated model was used to simulate shear and uniaxial tensile behavior, to investigate AF structure-function, and to quantify the effect of degeneration. The biaxial stress-strain response was described well by the model (R2>0.9). The model showed that the parameters for fiber nonlinearity and the normal FMI correlated with degeneration, resulting in an elongated toe region and lower stiffness with degeneration. The model simulations in shear and uniaxial tension successfully matched previously published circumferential direction Young’s modulus, provided an explanation for the low values in previously published axial direction Young’s modulus, and was able to simulate shear mechanics. The normal FMI were important contributors to stress and changed with degeneration, therefore, their microstructural and compositional source should be investigated. Finally, the biaxial mechanical data and constitutive model can be incorporated into a disc finite element model to provide improved quantification of disc mechanics. PMID:21748426
Modeling the effect of orientation on the shock response of a damageable composite material
NASA Astrophysics Data System (ADS)
Lukyanov, Alexander A.
2012-10-01
A carbon fiber-epoxy composite (CFEC) shock response in the through thickness orientation and in one of the fiber directions is significantly different. The hydrostatic pressure inside anisotropic materials depends on deviatoric strain components as well as volumetric strain. Non-linear effects, such as shock effects, can be incorporated through the volumetric straining in the material. Thus, a new basis is required to couple the anisotropic material stiffness and strength with anisotropic shock effects, associated energy dependence, and damage softening process. This article presents these constitutive equations for shock wave modeling of a damageable carbon fiber-epoxy composite. Modeling the effect of fiber orientation on the shock response of a CFEC has been performed using a generalized decomposition of the stress tensor [A. A. Lukyanov, Int. J. Plast. 24, 140 (2008)] and Mie-Grüneisen's extrapolation of high-pressure shock Hugoniot states to other thermodynamics states for shocked CFEC materials. The three-wave structure (non-linear anisotropic, fracture, and isotropic elastic waves) that accompanies damage softening process is also proposed in this work for describing CFEC behavior under shock loading which allows to remove any discontinuities observed in the linear case for relation between shock velocities and particle velocities [A. A. Lukyanov, Eur. Phys. J. B 74, 35 (2010)]. Different Hugoniot stress levels are obtained when the material is impacted in different directions; their good agreement with the experiment demonstrates that the anisotropic equation of state, strength, and damage model are adequate for the simulation of shock wave propagation within damageable CFEC material. Remarkably, in the through thickness orientation, the material behaves similar to a simple polymer whereas in the fiber direction, the proposed in this paper model explains an initial ramp, before at sufficiently high stresses, and a much faster rising shock above it. The
Molecular simulation guided constitutive modeling on finite strain viscoelasticity of elastomers
NASA Astrophysics Data System (ADS)
Li, Ying; Tang, Shan; Kröger, Martin; Liu, Wing Kam
2016-03-01
Viscoelasticity characterizes the most important mechanical behavior of elastomers. Understanding the viscoelasticity, especially finite strain viscoelasticity, of elastomers is the key for continuation of their dedicated use in industrial applications. In this work, we present a mechanistic and physics-based constitutive model to describe and design the finite strain viscoelastic behavior of elastomers. Mathematically, the viscoelasticity of elastomers has been decomposed into hyperelastic and viscous parts, which are attributed to the nonlinear deformation of the cross-linked polymer network and the diffusion of free chains, respectively. The hyperelastic deformation of a cross-linked polymer network is governed by the cross-linking density, the molecular weight of the polymer strands between cross-linkages, and the amount of entanglements between different chains, which we observe through large scale molecular dynamics (MD) simulations. Moreover, a recently developed non-affine network model (Davidson and Goulbourne, 2013) is confirmed in the current work to be able to capture these key physical mechanisms using MD simulation. The energy dissipation during a loading and unloading process of elastomers is governed by the diffusion of free chains, which can be understood through their reptation dynamics. The viscous stress can be formulated using the classical tube model (Doi and Edwards, 1986); however, it cannot be used to capture the energy dissipation during finite deformation. By considering the tube deformation during this process, as observed from the MD simulations, we propose a modified tube model to account for the finite deformation behavior of free chains. Combing the non-affine network model for hyperelasticity and modified tube model for viscosity, both understood by molecular simulations, we develop a mechanism-based constitutive model for finite strain viscoelasticity of elastomers. All the parameters in the proposed constitutive model have
Development and Application of a Strength and Damage Model for Rock under Dynamic Loading
Antoun, T H; Lomov, I N; Glenn, L A
2001-03-12
Simulating the behavior of geologic materials under impact loading conditions requires the use of a constitutive model that includes the effects of bulking, yielding, damage, porous compaction and loading rate on the material response. This paper describes the development, implementation and calibration of a thermodynamically consistent constitutive model that incorporates these features. The paper also describes a computational study in which the model was used to perform numerical simulations of PILE DRIVER, a deeply-buried underground nuclear explosion detonated in granite at the Nevada Test Site. Particle velocity histories, peak velocity and peak displacement as a function of slant range obtained from the code simulations compare favorably with PILE DRIVER data. The simulated attenuation of peak velocity and peak displacement also agrees with the results from several other spherical wave experiments in granite.
Track structure model of cell damage in space flight
NASA Technical Reports Server (NTRS)
Katz, Robert; Cucinotta, Francis A.; Wilson, John W.; Shinn, Judy L.; Ngo, Duc M.
1992-01-01
The phenomenological track-structure model of cell damage is discussed. A description of the application of the track-structure model with the NASA Langley transport code for laboratory and space radiation is given. Comparisons to experimental results for cell survival during exposure to monoenergetic, heavy-ion beams are made. The model is also applied to predict cell damage rates and relative biological effectiveness for deep-space exposures.
Experimental analysis and constitutive modelling of steel of A-IIIN strength class
NASA Astrophysics Data System (ADS)
Kruszka, Leopold; Janiszewski, Jacek
2015-09-01
Fundamentally important is the better understanding of behaviour of new building steels under impact loadings, including plastic deformations. Results of the experimental analysis in wide range of strain rates in compression at room temperature, as well as constitutive modelling for and B500SP structural steels of new A-IIIN Polish strength class, examined dynamically by split Hopkinson pressure bar technique at high strain rates, are presented in table and graphic forms. Dynamic mechanical characteristics of compressive strength for tested building structural steel are determined as well as dynamic mechanical properties of this material are compared with 18G2-b steel of A-II strength class, including effects of the shape of tested specimens, i.e. their slenderness. The paper focuses the attention on those experimental tests, their interpretation, and constitutive semi-empirical modelling of the behaviour of tested steels based on Johnson-Cook's model. Obtained results of analyses presented here are used for designing and numerical simulations of reinforced concrete protective structures.
Zhurov, Alexei I; Limbert, Georges; Aeschlimann, Daniel P; Middleton, John
2007-06-01
This study is devoted to the development of a non-linear anisotropic model for the human periodontal ligament (PDL). A thorough knowledge of the behaviour of the PDL is vital in understanding the mechanics of orthodontic tooth mobility, soft tissue response and proposed treatment plans. There is considerable evidence that the deformation of the PDL is the key factor determining the orthodontic tooth movement. The paper focuses on the biomechanical aspect of the behaviour of the PDL. In terms of continuous mechanics, the PDL may be treated as an anisotropic poro-visco-hyperelastic fibre-reinforced compressible material which is subject to large deformations and has an essentially non-linear behaviour. Furthermore, there are issues related to the non-linear tooth and PDL geometry. A new constitutive model for the PDL is proposed. The macroscopic continuum approach is used. The model is based on the non-linear large deformation theory, involving the Lagrangian description. The material is assumed to be compressible, visco-hyperelastic and transversely isotropic. A free-energy function is suggested that incorporates the properties. It also takes into account that the PDL behaves differently in tension and compression. The free-energy function and the associated constitutive equations involve several material parameters, which are to be evaluated from experimental strain-stress data available from the literature and the tooth movement experiments conducted by our team using novel optical motion analysis techniques. PMID:17558650
A New Creep Constitutive Model for 7075 Aluminum Alloy Under Elevated Temperatures
NASA Astrophysics Data System (ADS)
Lin, Y. C.; Jiang, Yu-Qiang; Zhou, Hua-Min; Liu, Guan
2014-12-01
Exposure of aluminum alloy to an elastic loading, during "creep-aging forming" or other manufacturing processes at relatively high temperature, may lead to the lasting creep deformation. The creep behaviors of 7075 aluminum alloy are investigated by uniaxial tensile creep experiments over wide ranges of temperature and external stress. The results show that the creep behaviors of the studied aluminum alloy strongly depend on the creep temperature, external stress, and creep time. With the increase of creep temperature and external stress, the creep strain increases quickly. In order to overcome the shortcomings of the Bailey-Norton law and θ projection method, a new constitutive model is proposed to describe the variations of creep strain with time for the studied aluminum alloy. In the proposed model, the dependences of creep strain on the creep temperature, external stress, and creep time are well taken into account. A good agreement between the predicted and measured creep strains shows that the established creep constitutive model can give an accurate description of the creep behaviors of 7075 aluminum alloy. Meanwhile, the obtained stress exponent indicates that the creep process is controlled by the dislocation glide, which is verified by the microstructural observations.
An elasto-viscoplastic interface model for investigating the constitutive behavior of nacre
NASA Astrophysics Data System (ADS)
Tang, H.; Barthelat, F.; Espinosa, H. D.
2007-07-01
In order to better understand the strengthening mechanism observed in nacre, we have developed an interface computational model to simulate the behavior of the organic present at the interface between aragonite tablets. In the model, the single polymer-chain behavior is characterized by the worm-like-chain (WLC) model, which is in turn incorporated into the eight-chain cell model developed by Arruda and Boyce [Arruda, E.M., Boyce, M.C., 1993a. A three-dimensional constitutive model for the large stretches, with application to polymeric glasses. Int. J. Solids Struct. 40, 389-412] to achieve a continuum interface constitutive description. The interface model is formulated within a finite-deformation framework. A fully implicit time-integration algorithm is used for solving the discretized governing equations. Finite element simulations were performed on a representative volume element (RVE) to investigate the tensile response of nacre. The staggered arrangement of tablets and interface waviness obtained experimentally by Barthelat et al. [Barthelat, F., Tang, H., Zavattieri, P.D., Li, C.-M., Espinosa, H.D., 2007. On the mechanics of mother-of-pearl: a key feature in the material hierarchical structure. J. Mech. Phys. Solids 55 (2), 306-337] was included in the RVE simulations. The simulations showed that both the rate-dependence of the tensile response and hysteresis loops during loading, unloading and reloading cycles were captured by the model. Through a parametric study, the effect of the polymer constitutive response during tablet-climbing and its relation to interface hardening was investigated. It is shown that stiffening of the organic material is not required to achieve the experimentally observed strain hardening of nacre during tension. In fact, when ratios of contour length/persistent length experimentally identified are employed in the simulations, the predicted stress-strain behavior exhibits a deformation hardening consistent with the one measured
Micro-mechanical modeling of perforating shock damage
Swift, R.P.; Krogh, K.E.; Behrmann, L.A.; Halleck, P.M.
1997-11-17
Shaped charge jet induced formation damage from perforation treatments hinders productivity. Manifestation of this damage is in the form of grain fragmentation resulting in fines that plug up pore throats along with the breakdown of inter-grain cementation. The authors use the Smooth Particle Hydrodynamic (SPH) computational method as a way to explicitly model, on a grain pore scale, the dynamic interactions of grains and grain/pores to calculate the damage resulting from perforation type stress wave loading. The SPH method is a continuum Lagrangian, meshless approach that features particles. Clusters of particles are used for each grain to provide representation of a grain pore structure that is similar to x-ray synchrotron microtomography images. Numerous damage models are available to portray fracture and fragmentation. In this paper the authors present the results of well defined impact loading on a grain pore structure that illustrate how the heterogeneity affects stress wave behavior and damage evolution. The SPH approach easily accommodates the coupling of multi-materials. Calculations for multi-material conditions with the pore space treated as a void, fluid filled, and/or clay filled show diverse effects on the stress wave propagation behavior and damage. SPH comparisons made with observed damage from recovered impacted sandstone samples in gas gun experiments show qualitatively the influence of stress intensity. The modeling approach presented here offers a unique way in concert with experiments to define a better understanding of formation damage resulting from perforation completion treatments.
On the two-potential constitutive modeling of rubber viscoelastic materials
NASA Astrophysics Data System (ADS)
Kumar, Aditya; Lopez-Pamies, Oscar
2016-02-01
This Note lays out the specialization of the two-potential constitutive framework - also known as the "generalized standard materials" framework - to rubber viscoelasticity. Inter alia, it is shown that a number of popular rubber viscoelasticity formulations, introduced over the years following different approaches, are special cases of this framework. As a first application of practical relevance, the framework is utilized to put forth a new objective and thermodynamically consistent rubber viscoelastic model for incompressible isotropic elastomers. The model accounts for the non-Gaussian elasticity of elastomers, as well as for the deformation-enhanced shear thinning of their viscous dissipation governed by reptation dynamics. The descriptive and predictive capabilities of the model are illustrated via comparisons with experimental data available from the literature for two commercially significant elastomers.
Application of constitutive model considering nonlinear unloading behavior for Gen.3 AHSS
NASA Astrophysics Data System (ADS)
Sun, Li; Wagoner, R. H.
2013-05-01
Nonlinear unloading behavior has been reported as an important factor for accurate springback prediction. In this study, a newly proposed special component of strain: "Quasi-Plastic-Elastic" ("QPE") strain was utilized to study the springback behavior of Advanced High Strength Steels (AHSS). Several types of steels, including IF steel, DP780, TRIP780, DP980, TWIP980 and QP980 were considered in this research. The results showed that all the tested steels have following behavior: 1) QPE strain is recoverable, like elastic deformation. 2) It dissipates work, like plastic deformation. A 3-D constitutive model considering QPE behavior was implemented in Abaqus/Standard with shell element and applied to draw-bend springback test for Gen. 3 AHSS, QP980. Predictions for springback using the QPE model were more accurate compared with standard elastic-plastic models.
A model for the human cornea: constitutive formulation and numerical analysis.
Pandolfi, A; Manganiello, F
2006-11-01
Abstract The human cornea (the external lens of the eye) has the macroscopic structure of a thin shell, originated by the organization of collagen lamellae parallel to the middle surface of the shell. The lamellae, composed of bundles of collagen fibrils, are responsible for the experimentally observed anisotropy of the cornea. Anomalies in the fibril structure may explain the changes in the mechanical behavior of the tissue observed in pathologies such as keratoconus. We employ a fiber-matrix constitutive model and propose a numerical model for the human cornea that is able to account for its mechanical behavior in healthy conditions or in the presence of keratoconus under increasing values of the intraocular pressure. The ability of our model to reproduce the behavior of the human cornea opens a promising perspective for the numerical simulation of refractive surgery. PMID:16444515
Constitutive model used in computer simulation of time-resolved, shock-wave data
NASA Astrophysics Data System (ADS)
Steinberg, D. J.
1986-10-01
A constitutive model was designed for use with high-speed, hydrodynamic computer codes. The model, valid at high-deformation rates, accounts for pressure and temperature dependence of the yield strength and shear modulus, work hardening, pressure-dependent melting, Bauschinger and strain-rate effects, and spall. There are a minimum number of parameters needed to implement the model, and most can be determined without recourse to shock-wave data. At Lawrence Livermore National Laboratory, we assembled a library of these material properties for 44 metals, alloys, mixtures, and compounds. Shock and release data from plate-impact experiments for Be, U, Ta, Cu, 1100-0, and 6061-T6 al, with peak stresses from 6.4 to 230 GPa, are successfully compared against calculations.
Theory and identification of a constitutive model of induced anisotropy by the Mullins effect
NASA Astrophysics Data System (ADS)
Machado, G.; Chagnon, G.; Favier, D.
2014-02-01
Rubber-like materials present a stress softening phenomenon after a first loading known as the Mullins effect. Some recent experimental data on filled silicone rubber are presented in the literature, using uniaxial and biaxial tests to precondition samples thus induce some primary stress softening. A generic modeling based on the polymer network decomposition into an isotropic hyperelastic one, and a stress-softening evolutive one, is proposed taking into account the contribution of many spatial directions. A new stress softening criterion is built by means of a tensor that measures the repartition of energy in space. A general form of the stress softening function associated to a spatial direction is written by the way of two variables: one, the maximal eigenvalue of the energy tensor; the other, the energy in the considered direction. Finally, a particular form of constitutive equation is proposed. The model is fitted and compared to experimental data. The capacities of such modeling are finally discussed.
NASA Astrophysics Data System (ADS)
Michel, Jean-Claude; Suquet, Pierre
2016-05-01
In 2003 the authors proposed a model-reduction technique, called the Nonuniform Transformation Field Analysis (NTFA), based on a decomposition of the local fields of internal variables on a reduced basis of modes, to analyze the effective response of composite materials. The present study extends and improves on this approach in different directions. It is first shown that when the constitutive relations of the constituents derive from two potentials, this structure is passed to the NTFA model. Another structure-preserving model, the hybrid NTFA model of Fritzen and Leuschner, is analyzed and found to differ (slightly) from the primal NTFA model (it does not exhibit the same variational upper bound character). To avoid the "on-line" computation of local fields required by the hybrid model, new reduced evolution equations for the reduced variables are proposed, based on an expansion to second order (TSO) of the potential of the hybrid model. The coarse dynamics can then be entirely expressed in terms of quantities which can be pre-computed once for all. Roughly speaking, these pre-computed quantities depend only on the average and fluctuations per phase of the modes and of the associated stress fields. The accuracy of the new NTFA-TSO model is assessed by comparison with full-field simulations. The acceleration provided by the new coarse dynamics over the full-field computations (and over the hybrid model) is then spectacular, larger by three orders of magnitude than the acceleration due to the sole reduction of unknowns.
Constitutive Modeling of Hot Deformation Behavior of High-Strength Armor Steel
NASA Astrophysics Data System (ADS)
Bobbili, Ravindranadh; Madhu, Vemuri
2016-05-01
The hot isothermal compression tests of high-strength armor steel under a wide range of deformation temperatures (1100-1250 °C) and strain rates of (0.001-1/s) were performed. Based on the experimental data, constitutive models were established using the original Johnson-Cook (JC) model, modified JC model, and strain-compensated Arrhenius model, respectively. The modified JC model considers the coupled effects of strain hardening, strain rate hardening, and thermal softening. Moreover, the prediction accuracy of these developed models was determined by estimating the correlation coefficient ( R) and average absolute relative error (AARE). The results demonstrate that the flow behavior of high-strength armor steel is considerably influenced by the strain rate and temperature. The original JC model is inadequate to provide good description on the flow stress at evaluated temperatures. The modified JC model and strain-compensated Arrhenius model significantly enhance the predictability. It is also observed from the microstructure study that at low strain rates (0.001-0.01/s) and high temperatures (1200-1250 °C), a typical dynamic recrystallization (DRX) occurs.
Constitutive Modeling of the Dynamic-Tensile-Extrusion Test of PTFE
NASA Astrophysics Data System (ADS)
Resnyansky, Anatoly; Brown, Eric; Trujillo, Carl; Gray, George
2015-06-01
Use of polymers in the defence, aerospace and industrial application at extreme conditions makes prediction of behaviour of these materials very important. Crucial to this is knowledge of the physical damage response in association with the phase transformations during the loading and the ability to predict this via multi-phase simulation taking the thermodynamical non-equilibrium and strain rate sensitivity into account. The current work analyses Dynamic-Tensile-Extrusion (DTE) experiments on polytetrafluoroethylene (PTFE). In particular, the phase transition during the loading with subsequent tension are analysed using a two-phase rate sensitive material model implemented in the CTH hydrocode and the calculations are compared with experimental high-speed photography. The damage patterns and their link with the change of loading modes are analysed numerically and are correlated to the test observations.
Su, Xiang; Wang, Gang; Li, Jianfeng; Rong, Yiming
2016-01-01
The effects of strain rate and temperature on the dynamic behavior of Fe-based high temperature alloy was studied. The strain rates were 0.001-12,000 s(-1), at temperatures ranging from room temperature to 800 °C. A phenomenological constitutive model (Power-Law constitutive model) was proposed considering adiabatic temperature rise and accurate material thermal physical properties. During which, the effects of the specific heat capacity on the adiabatic temperature rise was studied. The constitutive model was verified to be accurate by comparison between predicted and experimental results. PMID:27186468
NASA Astrophysics Data System (ADS)
Varela-Jiménez, M. I.; Vargas Luna, J. L.; Cortés-Ramírez, J. A.; Song, G.
2015-04-01
Magnetorheological fluid (MRF) is a smart material whose rheological properties can be varied by a magnetic field; it has been applied in the development of semiactive dampers for a variety of applications. The material essentially consists of a suspension of magnetic particles in a nonmagnetic carrier fluid. It is important to understand the magnetic response of MRF and its dependence on several parameters for improving and designing MRF devices. The purpose of this work is to develop a constitutive model that describes the behavior of the shear yield stress of the material as function of the magnetic field and composition. Taking into account that the material changes its rheology and apparent viscosity according to magnetic field, a magnetically induced state transition is proposed; by the use of a state transition equation, a constitutive model for shear yield stress is defined, consisting of an expression that relates composition of the material and the stimulus applied, it also associates the volume fraction of particles, magnetic field and the material that composes the particles.
NASA Astrophysics Data System (ADS)
Abed, Farid H.
2010-11-01
A constitutive relation is presented in this paper to describe the plastic behavior of ferritic steel over a broad range of temperatures and strain rates. The thermo-mechanical behavior of high strength low alloy (HSLA-65) and DH-63 naval structural steels is considered in this study at strains over 40%. The temperatures and strain rates are considered in the range where dynamic strain aging is not effective. The concept of thermal activation analysis as well as the dislocation interaction mechanism is used in developing the flow model for both the isothermal and adiabatic viscoplastic deformation. The flow stresses of the two steels are very sensitive to temperature and strain rate, the yield stresses increase with decreasing temperatures and increasing strain rates. That is, the thermal flow stress is mainly captured by the yield stresses while the hardening stresses are totally pertained to the athermal component of the flow stress. The proposed constitutive model predicts results that compare very well with the measured ones at initial temperature range of 77 K to 1000 K and strain rates between 0.001 s-1 and 8500 s-1 for both steels.
NASA Astrophysics Data System (ADS)
Li, Guoqiang; Xu, Wei
2011-06-01
Programming is a key process for thermally activated stress or strain recovery of shape memory polymers (SMPs). Typically, programming requires an initial heating above the glass transition temperature ( Tg), subsequent cooling below Tg and removal of the applied load, in order to fix a temporary shape. This work adopted a new approach to program thermoset SMPs directly at temperatures well below Tg, which effectively simplified the shape fixing process. 1-D compression programming below Tg and free shape recovery of a thermoset SMP were experimentally investigated. Functional stability of the shape fixity under various environmental attacks was also experimentally evaluated. A mechanism-based thermoviscoelastic-thermoviscoplastic constitutive model incorporating structural and stress relaxation was then developed to predict the nonlinear shape memory behavior of the SMP trained below Tg. Comparison between the prediction and the experiment showed good agreement. The structure dependence of the thermomechanical behavior of the SMP was further discussed through a parametric study per the validated constitutive model. This study validates that programming by cold-compression is a viable alternative for thermally responsive thermoset SMPs.
NASA Astrophysics Data System (ADS)
Sanders, B. F.; Gallegos, H. A.; Schubert, J. E.
2011-12-01
The Baldwin Hills dam-break flood and associated structural damage is investigated in this study. The flood caused high velocity flows exceeding 5 m/s which destroyed 41 wood-framed residential structures, 16 of which were completed washed out. Damage is predicted by coupling a calibrated hydrodynamic flood model based on the shallow-water equations to structural damage models. The hydrodynamic and damage models are two-way coupled so building failure is predicted upon exceedance of a hydraulic intensity parameter, which in turn triggers a localized reduction in flow resistance which affects flood intensity predictions. Several established damage models and damage correlations reported in the literature are tested to evaluate the predictive skill for two damage states defined by destruction (Level 2) and washout (Level 3). Results show that high-velocity structural damage can be predicted with a remarkable level of skill using established damage models, but only with two-way coupling of the hydrodynamic and damage models. In contrast, when structural failure predictions have no influence on flow predictions, there is a significant reduction in predictive skill. Force-based damage models compare well with a subset of the damage models which were devised for similar types of structures. Implications for emergency planning and preparedness as well as monetary damage estimation are discussed.
Constitutive modelling of lubricants in concentrated contacts at high slide to roll ratios
NASA Technical Reports Server (NTRS)
Tevaarwerk, J. L.
1985-01-01
A constitutive lubricant friction model for rolling/sliding concentrated contacts such as gears and cams was developed, based upon the Johnson and Tevaarwerk fluid rheology model developed earlier. The friction model reported herein differs from the earlier rheological models in that very large slide to roll ratios can now be accommodated by modifying the thermal response of the model. Also the elastic response of the fluid has been omitted from the model, thereby making it much simpler for use in the high slide to roll contacts. The effects of this simplification are very minimal on the outcome of the predicted friction losses (less than 1%). In essence then the lubricant friction model developed for the high slide to roll ratios treats the fluid in the concentrated contact as consisting of a nonlinear viscous element that is pressure, temperature, and strain rate dependent in its shear response. The fluid rheological constants required for the prediction of the friction losses at different contact conditions are obtained by traction measurements on several of the currently used gear lubricants. An example calculation, using this model and the fluid parameters obtained from the experiments, shows that it correctly predicts trends and magnitude of gear mesh losses measured elsewhere for the same fluids tested here.
NASA Astrophysics Data System (ADS)
Pietruszczak, Stanisław; Haghighat, Ehsan
2015-02-01
In this paper, the problem of modeling of mixed mode cracking in concrete structures is addressed within the context of a constitutive law with embedded discontinuity (CLED). This approach, which was originally developed for describing the propagation of localized deformation in a "smeared" sense, is enhanced here to model a discrete nature of crack propagation. The latter is achieved by coupling the CLED approach with the level-set method, which is commonly used within the framework of Extended Finite Element (XFEM). Numerical simulations of experimental tests conducted at Delft University, which involve four-point bending of a notched concrete beam under the action of two independent actuators, are presented. The results based on enhanced CLED approach are directly compared with XFEM simulations. The predictions from both these methodologies are quite consistent with the experimental data, thereby giving advantage to CLED scheme in view of its simplicity in the numerical implementation.
Constitutive modeling of cyclic plasticity and creep, using an internal time concept
NASA Technical Reports Server (NTRS)
Watanabe, O.; Atluri, S. N.
1986-01-01
Using the concept of an internal time as related to plastic strains, a differential stress-strain relation for elastoplasticity is rederived, such that (1) the concept of a yield-surface is retained; (2) the definitions of elastic and plastic processes are analogous to those in classical plasticity theory; and (3) its computational implementation, via a 'tangent-stiffness' finite element method and a 'generalized-midpoint-radial-return' stress-integration algorithm, is simple and efficient. Also, using the concept of an internal time, as related to both the inelastic strains as well as the Newtonian time, a constitutive model for creep-plasticity interaction, is discussed. The problem of modeling experimental data for plasticity and creep, by the present analytical relations, as accurately as desired, is discussed. Numerical examples which illustrate the validity of the present relations are presented for the cases of cyclic plasticity and creep.
Constitutive and life modeling of single crystal blade alloys for root attachment analysis
NASA Technical Reports Server (NTRS)
Meyer, T. G.; Mccarthy, G. J.; Favrow, L. H.; Anton, D. L.; Bak, Joe
1988-01-01
Work to develop fatigue life prediction and constitutive models for uncoated attachment regions of single crystal gas turbine blades is described. At temperatures relevant to attachment regions, deformation is dominated by slip on crystallographic planes. However, fatigue crack initiation and early crack growth are not always observed to be crystallographic. The influence of natural occurring microporosity will be investigated by testing both hot isostatically pressed and conventionally cast PWA 1480 single crystal specimens. Several differnt specimen configurations and orientations relative to the natural crystal axes are being tested to investigate the influence of notch acuity and the material's anisotropy. Global and slip system stresses in the notched regions were determined from three dimensional stress analyses and will be used to develop fatigue life prediction models consistent with the observed lives and crack characteristics.
A constitutive model for stress-induced permeability and porosity evolution of Berea sandstone
NASA Astrophysics Data System (ADS)
Morris, J. P.; Lomov, I. N.; Glenn, L. A.
2003-10-01
Many applications in geophysics require good estimates of permeability evolution in response to deformation, pore collapse, dilatancy, and microfracturing. Simulations of the upper crust, oil well completion, and nuclear waste repositories depend upon reliable predictions of changes in rock permeability. For some applications, permeability can affect the strength of rock by influencing the pore pressure and effective stress. For example, the pore pressure during production from an oil bearing formation is controlled by the evolving permeability field. The rock strength, however, depends upon the effective stress which is influenced by the pore pressure. Accurate prediction of possible failure in such formations requires reliable estimates of permeability change. Ideally, such estimates could be obtained by directly simulating the changes in pore space connectivity at the microscale. In practice the system being studied is sufficiently large that constitutive models must be developed which address permeability evolution macroscopically. We develop a model for predicting porosity and permeability changes in Berea sandstone. The model has been kept as simple as possible in order to facilitate incorporation of the model into existing mechanics codes. For this reason we assume the existence of a separate material model capable of predicting the stress-strain response of the rock. In addition, the model assumes that the original pores and pores created by microfracturing can be treated separately with respect to permeability and porosity evolution. Despite these simplifying assumptions, the model is able to reproduce most of the key features observed in previously reported triaxial experiments performed on Berea sandstone.
A Volume-Fraction Based Two-Phase Constitutive Model for Blood
Zhao, Rui; Massoudi, Mehrdad; Hund, S.J.; •Antaki, J.F.
2008-06-01
Mechanically-induced blood trauma such as hemolysis and thrombosis often occurs at microscopic channels, steps and crevices within cardiovascular devices. A predictive mathematical model based on a broad understanding of hemodynamics at micro scale is needed to mitigate these effects, and is the motivation of this research project. Platelet transport and surface deposition is important in thrombosis. Microfluidic experiments have previously revealed a significant impact of red blood cell (RBC)-plasma phase separation on platelet transport [5], whereby platelet localized concentration can be enhanced due to a non-uniform distribution of RBCs of blood flow in a capillary tube and sudden expansion. However, current platelet deposition models either totally ignored RBCs in the fluid by assuming a zero sample hematocrit or treated them as being evenly distributed. As a result, those models often underestimated platelet advection and deposition to certain areas [2]. The current study aims to develop a two-phase blood constitutive model that can predict phase separation in a RBC-plasma mixture at the micro scale. The model is based on a sophisticated theory known as theory of interacting continua, i.e., mixture theory. The volume fraction is treated as a field variable in this model, which allows the prediction of concentration as well as velocity profiles of both RBC and plasma phases. The results will be used as the input of successive platelet deposition models.
Two-phase Damage Models of Magma Fracturing
NASA Astrophysics Data System (ADS)
Cai, Z.; Bercovici, D.
2011-12-01
pulse-like shock waves may prove effective at promoting fluid migration through hydro- and magma-fracturing. Our model of damage-enhanced solitary waves includes the onset of fast moving porosity pulses associated with the generation of micro-fractures, which may explain the transition from porous flow to fracturing and diking during magma migration.
Modeling of Stone-impact Resistance of Monolithic Glass Ply Using Continuum Damage Mechanics
Sun, Xin; Khaleel, Mohammad A.; Davies, Richard W.
2005-04-01
We study the stone-impact resistance of a monolithic glass ply using a combined experimental and computational approach. Instrumented stone impact tests were first carried out in controlled environment. Explicit finite element analyses were then used to simulate the interactions of the indentor and the glass layer during the impact event, and a continuum damage mechanics (CDM) model was used to describe the constitutive behavior of glass. The experimentally measured strain histories for low velocity impact served as validation of the modeling procedures. Next, stair-stepping impact experiments were performed with two indentor sizes on two glass ply thickness, and the test results were used to calibrate the critical stress parameters used in the CDM constitutive model. The purpose of this study is to establish the modeling procedures and the CDM critical stress parameters under impact loading conditions. The modeling procedures and the CDM model will be used in our future studies to predict through-thickness damage evolution patterns for different laminated windshield designs in automotive applications.
Distributed Damage Estimation for Prognostics based on Structural Model Decomposition
NASA Technical Reports Server (NTRS)
Daigle, Matthew; Bregon, Anibal; Roychoudhury, Indranil
2011-01-01
Model-based prognostics approaches capture system knowledge in the form of physics-based models of components, and how they fail. These methods consist of a damage estimation phase, in which the health state of a component is estimated, and a prediction phase, in which the health state is projected forward in time to determine end of life. However, the damage estimation problem is often multi-dimensional and computationally intensive. We propose a model decomposition approach adapted from the diagnosis community, called possible conflicts, in order to both improve the computational efficiency of damage estimation, and formulate a damage estimation approach that is inherently distributed. Local state estimates are combined into a global state estimate from which prediction is performed. Using a centrifugal pump as a case study, we perform a number of simulation-based experiments to demonstrate the approach.
Dynamic brittle material response based on a continuum damage model
Chen, E.P.
1994-12-31
The response of brittle materials to dynamic loads was studied in this investigation based on a continuum damage model. Damage mechanism was selected to be interaction and growth of subscale cracks. Briefly, the cracks are activated by bulk tension and the density of activated cracks are described by a Weibull statistical distribution. The moduli of a cracked solid derived by Budiansky and O`Connell are then used to represent the global material degradation due to subscale cracking. This continuum damage model was originally developed to study rock fragmentation and was modified in the present study to improve on the post-limit structural response. The model was implemented into a transient dynamic explicit finite element code PRONTO 2D and then used for a numerical study involving the sudden stretching of a plate with a centrally located hole. Numerical results characterizing the dynamic responses of the material were presented. The effect of damage on dynamic material behavior was discussed.
NASA Astrophysics Data System (ADS)
Farabi, E.; Zarei-Hanzaki, A.; Abedi, H. R.
2015-01-01
Characterizing the high temperature flow behavior of a lead bearing duplex brass in a wide range of forming temperatures (673-1073 K) and strain rates (0.001-0.1 s-1) has been conducted in the present work. In order to establish the constitutive equations, two major modeling procedures, phenomenological (the Original Johnson-Cook and the Arrhenius-type) and physically based (the modified Zerilli-Armstrong) models, have been employed. The capability and accuracy of each model has been assessed via standard statistical parameters such as average absolute relative error and correlation coefficient. The comparative and comprehensive study of the flow behavior indicated that the accuracy of the phenomenological models was strongly dependent on the range of the testing temperatures and the corresponding mechanism which operate under the specified deformation conditions. It has been indicated that by limiting the temperature range a more precise Q-value is reached, which positively influences the accuracy of the Arrhenius-type model. In contrast, the modified Zerilli-Armstrong model was capable to overcome these limitations and properly considers the physical characteristics including dislocation dynamics and thermal activation to develop the materials constants.
The contribution of mouse models to the understanding of constitutional thrombocytopenia
Léon, Catherine; Dupuis, Arnaud; Gachet, Christian; Lanza, François
2016-01-01
Constitutional thrombocytopenias result from platelet production abnormalities of hereditary origin. Long misdiagnosed and poorly studied, knowledge about these rare diseases has increased considerably over the last twenty years due to improved technology for the identification of mutations, as well as an improvement in obtaining megakaryocyte culture from patient hematopoietic stem cells. Simultaneously, the manipulation of mouse genes (transgenesis, total or conditional inactivation, introduction of point mutations, random chemical mutagenesis) have helped to generate disease models that have contributed greatly to deciphering patient clinical and laboratory features. Most of the thrombocytopenias for which the mutated genes have been identified now have a murine model counterpart. This review focuses on the contribution that these mouse models have brought to the understanding of hereditary thrombocytopenias with respect to what was known in humans. Animal models have either i) provided novel information on the molecular and cellular pathways that were missing from the patient studies; ii) improved our understanding of the mechanisms of thrombocytopoiesis; iii) been instrumental in structure-function studies of the mutated gene products; and iv) been an invaluable tool as preclinical models to test new drugs or develop gene therapies. At present, the genetic determinants of thrombocytopenia remain unknown in almost half of all cases. Currently available high-speed sequencing techniques will identify new candidate genes, which will in turn allow the generation of murine models to confirm and further study the abnormal phenotype. In a complementary manner, programs of random mutagenesis in mice should also identify new candidate genes involved in thrombocytopenia. PMID:27478199
The contribution of mouse models to the understanding of constitutional thrombocytopenia.
Léon, Catherine; Dupuis, Arnaud; Gachet, Christian; Lanza, François
2016-08-01
Constitutional thrombocytopenias result from platelet production abnormalities of hereditary origin. Long misdiagnosed and poorly studied, knowledge about these rare diseases has increased considerably over the last twenty years due to improved technology for the identification of mutations, as well as an improvement in obtaining megakaryocyte culture from patient hematopoietic stem cells. Simultaneously, the manipulation of mouse genes (transgenesis, total or conditional inactivation, introduction of point mutations, random chemical mutagenesis) have helped to generate disease models that have contributed greatly to deciphering patient clinical and laboratory features. Most of the thrombocytopenias for which the mutated genes have been identified now have a murine model counterpart. This review focuses on the contribution that these mouse models have brought to the understanding of hereditary thrombocytopenias with respect to what was known in humans. Animal models have either i) provided novel information on the molecular and cellular pathways that were missing from the patient studies; ii) improved our understanding of the mechanisms of thrombocytopoiesis; iii) been instrumental in structure-function studies of the mutated gene products; and iv) been an invaluable tool as preclinical models to test new drugs or develop gene therapies. At present, the genetic determinants of thrombocytopenia remain unknown in almost half of all cases. Currently available high-speed sequencing techniques will identify new candidate genes, which will in turn allow the generation of murine models to confirm and further study the abnormal phenotype. In a complementary manner, programs of random mutagenesis in mice should also identify new candidate genes involved in thrombocytopenia. PMID:27478199
NASA Technical Reports Server (NTRS)
Haisler, W. E.
1983-01-01
An uncoupled constitutive model for predicting the transient response of thermal and rate dependent, inelastic material behavior was developed. The uncoupled model assumes that there is a temperature below which the total strain consists essentially of elastic and rate insensitive inelastic strains only. Above this temperature, the rate dependent inelastic strain (creep) dominates. The rate insensitive inelastic strain component is modelled in an incremental form with a yield function, blow rule and hardening law. Revisions to the hardening rule permit the model to predict temperature-dependent kinematic-isotropic hardening behavior, cyclic saturation, asymmetric stress-strain response upon stress reversal, and variable Bauschinger effect. The rate dependent inelastic strain component is modelled using a rate equation in terms of back stress, drag stress and exponent n as functions of temperature and strain. A sequence of hysteresis loops and relaxation tests are utilized to define the rate dependent inelastic strain rate. Evaluation of the model has been performed by comparison with experiments involving various thermal and mechanical load histories on 5086 aluminum alloy, 304 stainless steel and Hastelloy X.
Constitutive Model Constants for Al7075-T651 and Al7075-T6
NASA Astrophysics Data System (ADS)
Brar, N. S.; Joshi, V. S.; Harris, B. W.
2009-12-01
Aluminum 7075-T651 and 7075-T6 are characterized at quasi-static and high strain rates to determine Johnson-Cook (J-C) strength and fracture model constants. Constitutive model constants are required as input to computer codes to simulate projectile (fragment) impact or similar impact events on structural components made of these materials. Although the two tempers show similar elongation at breakage, the ultimate tensile strength of T651 temper is generally lower than the T6 temper. Johnson-Cook strength model constants (A, B, n, C, and m) for the two alloys are determined from high strain rate tension stress-strain data at room and high temperature to 250°C. The Johnson-Cook fracture model constants are determined from quasi-static and medium strain rate as well as high temperature tests on notched and smooth tension specimens. Although the J-C strength model constants are similar, the fracture model constants show wide variations. Details of the experimental method used and the results for the two alloys are presented.
Constitutive Model Constants for Al7075-T651 and Al7075-T6
NASA Astrophysics Data System (ADS)
Brar, Nachhatter; Joshi, Vasant; Harris, Bryan
2009-06-01
Aluminum 7075-T651 and 7075-T6 are characterized at quasi-static and high strain rates to determine Johnson-Cook (J-C) strength and fracture model constants. Constitutive model constants are required as input to computer codes to simulate projectile (fragment) impact or similar impact events on structural components made of these material. J-C strength model constants (A, B, n, C, and m) for the two alloys are determined from tension stress-strain data at room and high temperature to 250^oC. J-C strength model constants for Al7075-T651 are: A=527 MPa, B=676 MPa, n=0.71, C=0.017, and m=1.61 and for Al7075-T6: A = 546 MPa, B = 674 MPa, n = 0.72, C = 0.059, and m =1.56. J-C fracture model constants are determined form quasi-static and high strain rate/high temperature tests on notched and smooth tension specimens. J-C fracture model constants for the two alloys are: Al7075-T651; D1 = 0.110, D2 = 0.573, D3= -3.4446, D4 = 0.016, and D 5= 1.099 and Al7075-T6; D1= 0.451 D2= -0.952 D3= -.068, D4 =0.036, and D5 = 0.697.
NASA Astrophysics Data System (ADS)
Agboola, Babatunde Omogbolahan
Continuum thermodynamic constitutive phase field models are developed to simulate the rate dependent, thermomechanical response and precipitate formation in shape memory alloys (SMAs). The two models are based on the application of the balance of configurational forces, a scalar order parameter (a phase field) and atomic concentration to extend standard continuum thermodynamics approach. Constitutive field equations that capture the kinetics of solid-solid martensitic phase transition in SMA and the diffusion mediated precipitate formation in an elastic solid are developed. The coupled set of thermodynamically consistent field equations results from balance of configuration forces, balance of linear momentum, balance of energy and balance of atomic species mass. The field equations capture the kinetics of phase transition, deformation and elastic wave, heat transfer and atomic diffusion respectively. The first model is thermomechanical and is used to simulate the macroscopic response of SMA such as pseudoelasticity; transformation induced pseudo-creep, stress relaxation as well as the effect of cooling rate on mechanical and thermally induced phase transformation of SMA. The second model couples diffusion with elasticity to simulate growth and coarsening of precipitate and experimentally observed concentration depletion near the precipitates Results of the simulations of the macroscopic SMA response are in very good agreement with experimental observation. Simulations suggest that rate dependent and complex thermomechanical response of SMA are due to the interaction of an inherent time scale ( as well as length scale) of phase transformation, introduced through the balance of configurational forces, with other time scales. This work contributes to improved SMA modeling, scientific understanding and design. In particular, for aerospace application under stringent requirement and severe environmental conditions. Contribution of fundamental use of balance of
Constitutive Model Constants for Low Carbon Steels from Tension and Torsion Data
NASA Astrophysics Data System (ADS)
Brar, Nachhatter; Joshi, Vasant; Harris, Bryan
2007-06-01
Low carbon C1010 steel is characterized under tension and torsion to determine Johnson-Cook (J-C) strength model constants. Constitutive model constants are required as input to computer codes to simulate projectile (fragment) impact on structural components made of this material. J-C model constants (A, B, n, C, and m) for the alloy are determined from tension and torsion stress-strain data. Tension tests are performed at a strain rate of ˜1/s at room temperature. Tests at high strain rates are performed at high temperatures to 750^oC. J-C strength model constants determined from these data are: A=367 MPa, B=700 MPa, n=0.935, C=0.045, and m=0.643. Similar values for other low carbon steels (1006, 1008, and 1020) are compared. Torsion tests at quasi-static and high strain rates are performed at room and high temperatures. J-C model constants are evaluated from equivalent tensile stress-strain data obtained from torsion data using von Mises flow rule. These constants are compared to those determined from directly measured tensile data.
NASA Astrophysics Data System (ADS)
Trinh, B. T.; Hackl, K.
2014-07-01
A model for high temperature creep of single crystal superalloys is developed, which includes constitutive laws for nonlocal damage and viscoplasticity. It is based on a variational formulation, employing potentials for free energy, and dissipation originating from plasticity and damage. Evolution equations for plastic strain and damage variables are derived from the well-established minimum principle for the dissipation potential. The model is capable of describing the different stages of creep in a unified way. Plastic deformation in superalloys incorporates the evolution of dislocation densities of the different phases present. It results in a time dependence of the creep rate in primary and secondary creep. Tertiary creep is taken into account by introducing local and nonlocal damage. Herein, the nonlocal one is included in order to model strain localization as well as to remove mesh dependence of finite element calculations. Numerical results and comparisons with experimental data of the single crystal superalloy LEK94 are shown.
NASA Technical Reports Server (NTRS)
Veazie, David R.
1998-01-01
Advanced polymer matrix composites (PMC's) are desirable for structural materials in diverse applications such as aircraft, civil infrastructure and biomedical implants because of their improved strength-to-weight and stiffness-to-weight ratios. For example, the next generation military and commercial aircraft requires applications for high strength, low weight structural components subjected to elevated temperatures. A possible disadvantage of polymer-based composites is that the physical and mechanical properties of the matrix often change significantly over time due to the exposure of elevated temperatures and environmental factors. For design, long term exposure (i.e. aging) of PMC's must be accounted for through constitutive models in order to accurately assess the effects of aging on performance, crack initiation and remaining life. One particular aspect of this aging process, physical aging, is considered in this research.
Downscaling parameters from groundwater model scale to properties of the constituting litho classes
NASA Astrophysics Data System (ADS)
Lourens, Aris; van Geer, Frans
2015-04-01
Like other numerical models, groundwater models are created using the best knowledge available. Still, these models usually suffer from data uncertainty and model misconceptions. Calibration of such a model may yield parameter values with which the model produces output more closely to the observed values of the dependent variables than the uncalibrated model does. In groundwater models, the model parameters are often an aggregation of two or more observed properties. For example, the transmissivity is defined as the product of the layer thickness and the conductivity of the deposits, and the vertical resistance as the quotient of the layer thickness and the conductivity. Moreover, the parameters used in groundwater models are often constructed by vertical upscaling and horizontally interpolation of small geological units (litho-layers). When calibrating the groundwater model parameters, a better fit to the groundwater head data is achieved, but it is not clear to what extent the thickness or the conductivity of the individual litho-layers should be modified. This may yield parameter values at the litho-layer scale which are not very likely from geological point of view. The question is how can we downscale the calibrated model parameters to arrive at the most likely set of conductivities and thicknesses of the individual litho-layers, respecting the prior uncertainty from geological point of view. Here, we present a method to find the most likely values of parameters of constituting litho-layers of an aquitard, based on the parameter values of a calibrated groundwater model. The objective of this method is twofold. On one hand, finding the most likely parameter values for the thicknesses and the hydraulic conductivities of each individual litho layer. On the other hand, the most likely parameter values of the litho-layers may be very unlikely from geological perspective and, herewith, indicate connectional model errors. The properties of each litho-class at the
Fan, Rong; Sacks, Michael S.
2014-01-01
Computational implementation of physical and physiologically realistic constitutive models is critical for numerical simulation of soft biological tissues in a variety of biomedical applications. It is well established that the highly nonlinear and anisotropic mechanical behaviors of soft tissues are an emergent behavior of the underlying tissue microstructure. In the present study, we have implemented a structural constitutive model into a finite element framework specialized for membrane tissues. We noted that starting with a single element subjected to uniaxial tension, the non-fibrous tissue matrix must be present to prevent unrealistic tissue deformations. Flexural simulations were used to set the non-fibrous matrix modulus because fibers have little effects on tissue deformation under three-point bending. Multiple deformation modes were simulated, including strip biaxial, planar biaxial with two attachment methods, and membrane inflation. Detailed comparisons with experimental data were undertaken to insure faithful simulations of both the macro-level stress-strain insights into adaptations of the fiber architecture under stress, such as fiber reorientation and fiber recruitment. Results indicated a high degree of fidelity and demonstrated interesting microstructural adaptions to stress and the important role of the underlying tissue matrix. Moreover, we apparently resolve a discrepancy in our 1997 study (J Biomech. 1997 Jul;30(7):753–6) where we observed that under strip biaxial stretch the simulated fiber splay responses were not in good agreement with the experimental results, suggesting non-affine deformations may have occurred. However, by correctly accounting for the isotropic phase of the measured fiber splay, good agreement was obtained. While not the final word, these simulations suggest that affine kinematics for planar collagenous tissues is a reasonable assumption at the macro level. Simulation tools such as these are imperative in the design
ASPH modeling of Material Damage and Failure
Owen, J M
2010-04-30
We describe our new methodology for Adaptive Smoothed Particle Hydrodynamics (ASPH) and its application to problems in modeling material failure. We find that ASPH is often crucial for properly modeling such experiments, since in most cases the strain placed on materials is non-isotropic (such as a stretching rod), and without the directional adaptability of ASPH numerical failure due to SPH nodes losing contact in the straining direction can compete with or exceed the physical process of failure.
Observation and Modeling of Fault Damage Zones at Reservoir Depths
NASA Astrophysics Data System (ADS)
Johri, M.; Zoback, M. D.; Dunham, E. M.; Hennings, P.
2011-12-01
We report a study of sub-surface fault damage zones adjacent to the San Andreas Fault in central California and series of first- and second-order faults in a gas field in Southeast Asia. We compare the observations with theoretically-predicted damage zones from dynamic rupture propagation modeling. The importance of characterizing damage zones arises from the important role that damage zones and natural fractures play in governing fluid flow in low permeability rocks. While there are many published studies of exposed damage zones, there is an absence of studies utilizing subsurface data that characterizes damage zones at depth. Damage zones associated with second-order faults adjacent to the San Andreas Fault are studied in well-cemented arkosic sandstones immediately southwest of the fault at the SAFOD site using electrical image logs and physical property measurements. The peak fracture intensity is between three and six fractures per meter in thee damage zones which persist about 50-80 meters from the second-order faults. Fracture intensity in these damage zones in both the regions of study decreases according to a power law where the rate of decrease is approximately -0.8 . The gas reservoir in Southeast Asia is associated with a large, basement master fault and twenty-seven seismically resolvable second-order faults. Four to seven fractures per meter are observed in electrical image logs from five wells in the 50-80m wide damage zones of the second-order faults. The second part of this work involves predicting damage zone widths utilizing two-dimensional plane-strain dynamic rupture models with strong rate-weakening fault friction and off-fault Drucker-Prager plasticity. The number of induced third-order faults and fractures are calculated by assuming that the dilatational plastic strain is manifested in the form of discrete fault planes. The theoretical results suggest that the damage zones are approximately 60-100 meters wide and the fracture intensity
Modelling blast induced damage from a fully coupled explosive charge
Onederra, Italo A.; Furtney, Jason K.; Sellers, Ewan; Iverson, Stephen
2015-01-01
This paper presents one of the latest developments in the blasting engineering modelling field—the Hybrid Stress Blasting Model (HSBM). HSBM includes a rock breakage engine to model detonation, wave propagation, rock fragmentation, and muck pile formation. Results from two controlled blasting experiments were used to evaluate the code’s ability to predict the extent of damage. Results indicate that the code is capable of adequately predicting both the extent and shape of the damage zone associated with the influence of point-of-initiation and free-face boundary conditions. Radial fractures extending towards a free face are apparent in the modelling output and matched those mapped after the experiment. In the stage 2 validation experiment, the maximum extent of visible damage was of the order of 1.45 m for the fully coupled 38-mm emulsion charge. Peak radial velocities were predicted within a relative difference of only 1.59% at the nearest history point at 0.3 m from the explosive charge. Discrepancies were larger further away from the charge, with relative differences of −22.4% and −42.9% at distances of 0.46 m and 0.61 m, respectively, meaning that the model overestimated particle velocities at these distances. This attenuation deficiency in the modelling produced an overestimation of the damage zone at the corner of the block due to excessive stress reflections. The extent of visible damage in the immediate vicinity of the blasthole adequately matched the measurements. PMID:26412978
Constitutive Model Constants for Low Carbon Steels from Tension and Torsion Data
NASA Astrophysics Data System (ADS)
Brar, N. S.; Joshi, V. S.; Harris, B. W.
2007-12-01
Low carbon C1010 steel is characterized under tension and torsion to determine Johnson-Cook (J-C) strength model constants. Constitutive model constants are required as input to computer codes to simulate projectile (fragment) impact on structural components made of this material. J-C model constants (A, B, n, C, and m) for the alloy are determined from tension and torsion stress-strain data. Reference tension tests are performed at a strain rate of ˜1/s at room temperature. Tests at high strain rates are performed at temperatures to 750 °C. Torsion tests at quasi-static and high strain rates are performed at both room and high temperatures. Equivalent plastic tensile stress-strain data are obtained from torsion data using von Mises flow rule and compared directly to measured tensile data. J-C strength model constants are determined from these data. Similar low carbon steels (1006, 1008, and 1020) have their J-C constants compared.
Identification of an advanced constitutive model of Magnesium alloy AZ31B
Liu, Z. G.; Massoni, E.
2011-05-04
The main aim of this paper is to study the flow behavior of the AZ31B magnesium alloy by means of tensile tests performed in extended ranges of temperature and strain rates. The flow stress-strain curves analyzed by power law type constitutive equation can only fit well with experimental curves at the work-hardening stage. A new mathematical model is studied to describe the softening behavior of material based on tensile experiments. The relative parameters are obtained by fitting the equation with the experimental data. The genetic algorithm has been used to obtain the global optimal fitting parameters. The comparison between the fitted and experimental data proves the effectiveness of the model. The results indicate that this model leads to a better simulation of the flow stress during the softening stage than that of the power law equation. Based on this model, the deep drawing process has been simulated with the commercial finite element code FORGE registered. The punch load and thickness distribution of AZ31 sheet have been studied. The study of the results is helpful to the application of the stamping technology for the magnesium alloy sheet.
Mathematical, Constitutive and Numerical Modelling of Catastrophic Landslides and Related Phenomena
NASA Astrophysics Data System (ADS)
Pastor, M.; Fernández Merodo, J. A.; Herreros, M. I.; Mira, P.; González, E.; Haddad, B.; Quecedo, M.; Tonni, L.; Drempetic, V.
2008-02-01
Mathematical and numerical models are a fundamental tool for predicting the behaviour of geostructures and their interaction with the environment. The term “mathematical model” refers to a mathematical description of the more relevant physical phenomena which take place in the problem being analyzed. It is indeed a wide area including models ranging from the very simple ones for which analytical solutions can be obtained to those more complicated requiring the use of numerical approximations such as the finite element method. During the last decades, mathematical, constitutive and numerical models have been very much improved and today their use is widespread both in industry and in research. One special case is that of fast catastrophic landslides, for which simplified methods are not able to provide accurate solutions in many occasions. Moreover, many finite element codes cannot be applied for propagation of the mobilized mass. The purpose of this work is to present an overview of the different alternative mathematical and numerical models which can be applied to both the initiation and propagation mechanisms of fast catastrophic landslides and other related problems such as waves caused by landslides.
NASA Technical Reports Server (NTRS)
Yamakov, V.; Saether, E.; Glaessgen, E. H.
2008-01-01
Intergranular fracture is a dominant mode of failure in ultrafine grained materials. In the present study, the atomistic mechanisms of grain-boundary debonding during intergranular fracture in aluminum are modeled using a coupled molecular dynamics finite element simulation. Using a statistical mechanics approach, a cohesive-zone law in the form of a traction-displacement constitutive relationship, characterizing the load transfer across the plane of a growing edge crack, is extracted from atomistic simulations and then recast in a form suitable for inclusion within a continuum finite element model. The cohesive-zone law derived by the presented technique is free of finite size effects and is statistically representative for describing the interfacial debonding of a grain boundary (GB) interface examined at atomic length scales. By incorporating the cohesive-zone law in cohesive-zone finite elements, the debonding of a GB interface can be simulated in a coupled continuum-atomistic model, in which a crack starts in the continuum environment, smoothly penetrates the continuum-atomistic interface, and continues its propagation in the atomistic environment. This study is a step towards relating atomistically derived decohesion laws to macroscopic predictions of fracture and constructing multiscale models for nanocrystalline and ultrafine grained materials.
Adaptive Finite Element Methods for Continuum Damage Modeling
NASA Technical Reports Server (NTRS)
Min, J. B.; Tworzydlo, W. W.; Xiques, K. E.
1995-01-01
The paper presents an application of adaptive finite element methods to the modeling of low-cycle continuum damage and life prediction of high-temperature components. The major objective is to provide automated and accurate modeling of damaged zones through adaptive mesh refinement and adaptive time-stepping methods. The damage modeling methodology is implemented in an usual way by embedding damage evolution in the transient nonlinear solution of elasto-viscoplastic deformation problems. This nonlinear boundary-value problem is discretized by adaptive finite element methods. The automated h-adaptive mesh refinements are driven by error indicators, based on selected principal variables in the problem (stresses, non-elastic strains, damage, etc.). In the time domain, adaptive time-stepping is used, combined with a predictor-corrector time marching algorithm. The time selection is controlled by required time accuracy. In order to take into account strong temperature dependency of material parameters, the nonlinear structural solution a coupled with thermal analyses (one-way coupling). Several test examples illustrate the importance and benefits of adaptive mesh refinements in accurate prediction of damage levels and failure time.
Development of in vivo constitutive models for liver: application to surgical simulation.
Lister, Kevin; Gao, Zhan; Desai, Jaydev P
2011-03-01
Advancements in real-time surgical simulation techniques have provided the ability to utilize more complex nonlinear constitutive models for biological tissues which result in increased haptic and graphic accuracy. When developing such a model, verification is necessary to determine the accuracy of the force response as well as the magnitude of tissue deformation for tool-tissue interactions. In this study, we present an experimental device which provides the ability to obtain force-displacement information as well as surface deformation of porcine liver for in vivo probing tasks. In addition, the system is capable of accurately determining the geometry of the liver specimen. These combined attributes provide the context required to simulate the experiment with accurate boundary conditions, whereby the only variable in the analysis is the material properties of the liver specimen. During the simulation, effects of settling due to gravity have been taken into account by a technique which incorporates the proper internal stress conditions in the model without altering the geometry. Initially, an Ogden model developed from ex vivo tension and compression experimentation is run through the simulation to determine the efficacy of utilizing an ex vivo model for simulation of in vivo probing tasks on porcine liver. Subsequently, a method for improving upon the ex vivo model was developed using different hyperelastic models such that increased accuracy could be achieved for the force characteristics compared to the displacement characteristics, since changes in the force variation would be more perceptible to a user in the simulation environment, while maintaining a high correlation with the surface displacement data. Furthermore, this study also presents the probing simulation which includes the capsule surrounding the liver. PMID:21161684
Electromagnetomechanical elastodynamic model for Lamb wave damage quantification in composites
NASA Astrophysics Data System (ADS)
Borkowski, Luke; Chattopadhyay, Aditi
2014-03-01
Physics-based wave propagation computational models play a key role in structural health monitoring (SHM) and the development of improved damage quantification methodologies. Guided waves (GWs), such as Lamb waves, provide the capability to monitor large plate-like aerospace structures with limited actuators and sensors and are sensitive to small scale damage; however due to the complex nature of GWs, accurate and efficient computation tools are necessary to investigate the mechanisms responsible for dispersion, coupling, and interaction with damage. In this paper, the local interaction simulation approach (LISA) coupled with the sharp interface model (SIM) solution methodology is used to solve the fully coupled electro-magneto-mechanical elastodynamic equations for the piezoelectric and piezomagnetic actuation and sensing of GWs in fiber reinforced composite material systems. The final framework provides the full three-dimensional displacement as well as electrical and magnetic potential fields for arbitrary plate and transducer geometries and excitation waveform and frequency. The model is validated experimentally and proven computationally efficient for a laminated composite plate. Studies are performed with surface bonded piezoelectric and embedded piezomagnetic sensors to gain insight into the physics of experimental techniques used for SHM. The symmetric collocation of piezoelectric actuators is modeled to demonstrate mode suppression in laminated composites for the purpose of damage detection. The effect of delamination and damage (i.e., matrix cracking) on the GW propagation is demonstrated and quantified. The developed model provides a valuable tool for the improvement of SHM techniques due to its proven accuracy and computational efficiency.
Model-based damage evaluation of layered CFRP structures
NASA Astrophysics Data System (ADS)
Munoz, Rafael; Bochud, Nicolas; Rus, Guillermo; Peralta, Laura; Melchor, Juan; Chiachío, Juan; Chiachío, Manuel; Bond, Leonard J.
2015-03-01
An ultrasonic evaluation technique for damage identification of layered CFRP structures is presented. This approach relies on a model-based estimation procedure that combines experimental data and simulation of ultrasonic damage-propagation interactions. The CFPR structure, a [0/90]4s lay-up, has been tested in an immersion through transmission experiment, where a scan has been performed on a damaged specimen. Most ultrasonic techniques in industrial practice consider only a few features of the received signals, namely, time of flight, amplitude, attenuation, frequency contents, and so forth. In this case, once signals are captured, an algorithm is used to reconstruct the complete signal waveform and extract the unknown damage parameters by means of modeling procedures. A linear version of the data processing has been performed, where only Young modulus has been monitored and, in a second nonlinear version, the first order nonlinear coefficient β was incorporated to test the possibility of detection of early damage. The aforementioned physical simulation models are solved by the Transfer Matrix formalism, which has been extended from linear to nonlinear harmonic generation technique. The damage parameter search strategy is based on minimizing the mismatch between the captured and simulated signals in the time domain in an automated way using Genetic Algorithms. Processing all scanned locations, a C-scan of the parameter of each layer can be reconstructed, obtaining the information describing the state of each layer and each interface. Damage can be located and quantified in terms of changes in the selected parameter with a measurable extension. In the case of the nonlinear coefficient of first order, evidence of higher sensitivity to damage than imaging the linearly estimated Young Modulus is provided.
Constitutive modeling of coronary arterial media--comparison of three model classes.
Hollander, Yaniv; Durban, David; Lu, Xiao; Kassab, Ghassan S; Lanir, Yoram
2011-06-01
Accurate modeling of arterial elasticity is imperative for predicting pulsatile blood flow and transport to the periphery, and for evaluating the mechanical microenvironment of the vessel wall. The goal of the present study is to compare a recently developed structural model of porcine left anterior descending artery media to two commonly used typical representatives of phenomenological and structure-motivated invariant-based models, in terms of the number of model parameters, model descriptive and predictive powers, and requisite different test protocols for reliable parameter estimation. The three models were compared against 3D data of radial inflation, axial extension, and twist tests. Also checked are the models predictive capabilities to response data not used for estimation, including both tests outside the range of estimation database, as well as protocols of a different nature. The results show that the descriptive estimation error (model fit to estimation database), measured by the sum of squared residuals (SSE) between full 3D data and model predictions, was about twice as low for the structural (4.58%) model compared to the other two (9.71 and 8.99% for the phenomenological and structure-motivated models, respectively). Similar SSE ratios were obtained for the predictive capabilities. Prediction SSE at high stretch based on estimation of two low stretches yielded an SSE value of 2.81% for the structural model, and 10.54% and 7.87% for the phenomenological and structure-motivated models, respectively. For the prediction of twist from inflation-extension data, SSE values for the torsional stiffness was 1.76% for the structural model and 39.62 and 2.77% for the phenomenological and structure-motivated models. The required number of model parameters for the structural model is four, whereas the phenomenological model requires six to nine and the structure-motivated has four parameters. These results suggest that modeling based on the tissue structural
Logarithmic rate based elasto-viscoplastic cyclic constitutive model for soft biological tissues.
Zhu, Yilin; Kang, Guozheng; Yu, Chao; Poh, Leong Hien
2016-08-01
Based on the logarithmic rate and piecewise linearization theory, a thermodynamically consistent elasto-viscoplastic constitutive model is developed in the framework of finite deformations to describe the nonlinear time-dependent biomechanical performances of soft biological tissues, such as nonlinear anisotropic monotonic stress-strain responses, stress relaxation, creep and ratchetting. In the proposed model, the soft biological tissue is assumed as a typical composites consisting of an isotropic matrix and anisotropic fiber aggregation. Accordingly, the free energy function and stress tensor are divided into two parts related to the matrix and fiber aggregation, respectively. The nonlinear biomechanical responses of the tissues are described by the piecewise linearization theory with hypo-elastic relations of fiber aggregation. The evolution equations of viscoplasticity are formulated from the dissipation inequalities by the co-directionality hypotheses. The anisotropy is considered in the hypo-elastic relations and viscoplastic flow rules by introducing some material parameters dependent on the loading direction. Then the capability of the proposed model to describe the nonlinear time-dependent deformation of soft biological tissues is verified by comparing the predictions with the corresponding experimental results of three tissues. It is seen that the predicted monotonic stress-strain responses, stress relaxation, creep and ratchetting of soft biological tissues are in good agreement with the corresponding experimental ones. PMID:27108349
Kao, Philip H; Lammers, Steven R; Hunter, Kendall; Stenmark, Kurt R; Shandas, Robin; Qi, H Jerry
2010-04-01
Many biological materials are composites composed of a soft matrix reinforced with stiffer fibers. These stiffer fibers may have a tortuous shape and wind through the soft matrix. At small material deformation, these fibers deform in a bending mode and contribute little to the material stiffness; at large material deformation, these fibers deform in a stretching mode and induce a stiffening effect in the material behavior. The transition from bending mode deformation to stretching mode deformation yields a characteristic J-shape stress-strain curve. In addition, the spatial distribution of these fibers may render the composite an anisotropic behavior. In this paper, we present an anisotropic finite-deformation hyperelastic constitutive model for such materials. Here, the matrix is modeled as an isotropic neo-Hookean material. "The behaviors of single tortuous fiber are represented by a crimped fiber model". The anisotropic behavior is introduced by a structure tensor representing the effective orientation distribution of crimped fibers. Parametric studies show the effect of fiber tortuosity and fiber orientation distribution on the overall stress-strain behaviors of the materials. PMID:21822502
A constitutive model for layered wire mesh and aramid cloth fabric
Neilsen, M.K.; Pierce, J.D.; Krieg, R.D.
1993-09-01
A new package for the air transport of hazardous materials is currently being developed in the Transportation Systems Department at Sandia National Laboratories. The baseline design has a unique impact limiter which uses layers of aluminum screen wire and aramid cloth fabric. A primary motivation for selecting this unusual combination of materials is the need for the impact limiter to not only limit the amount of load transmitted to the primary container but also remain in place during impact events so that it provides a thermal barrier during a subsequent fire. A series of uniaxial and confined compression tests indicated that the layered material does not behave like other well characterized materials. No existing constitutive models were able to satisfactorily capture the behavior of the layered material; thus, a new plasticity model was developed. The new material model was then used to characterize the response of air transport packages with layered impact limiters to hypothetical accidental impact events. Responses predicted by these analyses compared favorably with experiments at Sandia`s rocket sled test facility in which a one-fourth scale package was subjected to side and end impacts at velocities of 428 and 650 fps, respectively.
Mechanical effects of ionic replacements in articular cartilage. Part I: The constitutive model.
Loret, Benjamin; Simões, Fernando M F
2005-11-01
A three-phase multi-species electro-chemo-mechanical model of articular cartilage is developed that accounts for the effect of two water compartments, namely intra-fibrillar water stored in between collagen fibrils and extra-fibrillar water covering proteoglycans. The collagen fibers constitute the solid phase while intra-fibrillar water and dissolved NaCl and CaCl(2) on one hand and extra-fibrillar water, ions Na(+), Ca(2+) and Cl(-) and proteoglycans on the other hand, form the two fluid phases. The complete picture that includes time-dependent mass transfers between the two fluid phases, diffusion of water and ions and electrical flow emerges from the Clausius-Duhem inequality but it is deferred to further study. The analysis is restricted to equilibrium states. The present work complements the mechanical model developed in Loret and Simões (Mech Material 36(5-6): 515-541, 2004a) where the presence of the sole NaCl was considered. In its current version, the model can handle mechanical and chemical loadings and unloadings involving the two salts, NaCl and CaCl(2). In order to reproduce experimental data, the shielding effects are made cation-dependent. Strong orientation of collagen fibers parallel to the joint surface implies anisotropic mechanical properties. Electro-chemo-mechanical couplings result in a chemistry-dependent apparent tensile Poisson's ratio, that increases to large values as the solution gets fresher. The model captures these aspects as well. The features of the model are first exposed in an infinitesimal strain context. Subsequently, large strains that typically occur in uniaxial traction under deionized water are accounted for, and a nonlinear anisotropic hyper-elastic behavior is developed. Parametric identification and simulations of actual loading processes are described in a companion paper, Loret and Simões (Biomech Model Mechanobiol, in press, DOI 10.1007/s10237-004-0063-6). PMID:16001249
Kramer, Sharlotte Lorraine Bolyard; Scherzinger, William M.
2014-09-01
The Virtual Fields Method (VFM) is an inverse method for constitutive model parameter identication that relies on full-eld experimental measurements of displacements. VFM is an alternative to standard approaches that require several experiments of simple geometries to calibrate a constitutive model. VFM is one of several techniques that use full-eld exper- imental data, including Finite Element Method Updating (FEMU) techniques, but VFM is computationally fast, not requiring iterative FEM analyses. This report describes the im- plementation and evaluation of VFM primarily for nite-deformation plasticity constitutive models. VFM was successfully implemented in MATLAB and evaluated using simulated FEM data that included representative experimental noise found in the Digital Image Cor- relation (DIC) optical technique that provides full-eld displacement measurements. VFM was able to identify constitutive model parameters for the BCJ plasticity model even in the presence of simulated DIC noise, demonstrating VFM as a viable alternative inverse method. Further research is required before VFM can be adopted as a standard method for constitu- tive model parameter identication, but this study is a foundation for ongoing research at Sandia for improving constitutive model calibration.
NASA Technical Reports Server (NTRS)
Turon, Albert; Camanho, Pedro P.; Costa, Josep; Davila, Carlos G.
2004-01-01
A thermodynamically consistent damage model for the simulation of progressive delamination under variable mode ratio is presented. The model is formulated in the context of the Damage Mechanics (DM). The constitutive equations that result from the variation of the free energy with damage are used to model the initiation and propagation of delamination. A new delamination initiation criterion is developed to assure that the formulation can account for changes in the loading mode in a thermodynamically consistent way. Interfacial penetration of two adjacent layers after complete decohesion is prevented by the formulation of the free energy. The model is implemented into the commercial finite element code ABAQUS by means of a user-written decohesion element. Finally, the numerical predictions given by the model are compared with experimental results.
Irreversible entropy model for damage diagnosis in resistors
Cuadras, Angel Crisóstomo, Javier; Ovejas, Victoria J.; Quilez, Marcos
2015-10-28
We propose a method to characterize electrical resistor damage based on entropy measurements. Irreversible entropy and the rate at which it is generated are more convenient parameters than resistance for describing damage because they are essentially positive in virtue of the second law of thermodynamics, whereas resistance may increase or decrease depending on the degradation mechanism. Commercial resistors were tested in order to characterize the damage induced by power surges. Resistors were biased with constant and pulsed voltage signals, leading to power dissipation in the range of 4–8 W, which is well above the 0.25 W nominal power to initiate failure. Entropy was inferred from the added power and temperature evolution. A model is proposed to understand the relationship among resistance, entropy, and damage. The power surge dissipates into heat (Joule effect) and damages the resistor. The results show a correlation between entropy generation rate and resistor failure. We conclude that damage can be conveniently assessed from irreversible entropy generation. Our results for resistors can be easily extrapolated to other systems or machines that can be modeled based on their resistance.
Continuum damage modeling and simulation of hierarchical dental enamel
NASA Astrophysics Data System (ADS)
Ma, Songyun; Scheider, Ingo; Bargmann, Swantje
2016-05-01
Dental enamel exhibits high fracture toughness and stiffness due to a complex hierarchical and graded microstructure, optimally organized from nano- to macro-scale. In this study, a 3D representative volume element (RVE) model is adopted to study the deformation and damage behavior of the fibrous microstructure. A continuum damage mechanics model coupled to hyperelasticity is developed for modeling the initiation and evolution of damage in the mineral fibers as well as protein matrix. Moreover, debonding of the interface between mineral fiber and protein is captured by employing a cohesive zone model. The dependence of the failure mechanism on the aspect ratio of the mineral fibers is investigated. In addition, the effect of the interface strength on the damage behavior is studied with respect to geometric features of enamel. Further, the effect of an initial flaw on the overall mechanical properties is analyzed to understand the superior damage tolerance of dental enamel. The simulation results are validated by comparison to experimental data from micro-cantilever beam testing at two hierarchical levels. The transition of the failure mechanism at different hierarchical levels is also well reproduced in the simulations.
Kim, Jaeuk U.; Ku, Boncho; Kim, Young-Min; Do, Jun-Hyeong; Jang, Eunsu; Jeon, Young Ju; Kim, Keun Ho; Kim, Jong Yeol
2013-01-01
Sasang constitutional medicine (SCM) shares its philosophy with that of personalized medicine: it provides constitution-specific treatment and healthcare individualized for each patient. In this work, we propose the concept of the Sasang Health Index (SHI) as an attempt to assess the individualized health status in the framework of SCM. From the target population of females in their fifties and older, we recruited 298 subjects and collected their physiological data, including complexion, radial pulse, and voice, and their questionnaire responses. The health status of each subject was evaluated by two Korean medical doctors independently, and the SHI model was obtained by combining all the integrative features of the phenotype data using a regression technique. As a result, most subjects belonged to either the healthy, subhealthy, or slightly diseased group, and the intraclass correlation coefficient between the two doctors' health scoring reached 0.95. We obtained an SHI model for each constitution type with adjusted R-squares of 0.50, 0.56, and 0.30, for the TE, SE, and SY constitution types, respectively. In the proposed SHI model, the significant characteristics used in the health assessment consisted of constitution-specific features in accordance with the classic literature and features common to all the constitution types. PMID:23843888
Prostaglandin ethanolamides attenuate damage in a human explant colitis model.
Nicotra, Lauren L; Vu, Megan; Harvey, Benjamin S; Smid, Scott D
2013-01-01
Endocannabinoids are protective in animal colitis models. As endocannabinoids also form novel prostaglandin ethanolamides (prostamides) via COX-2, we investigated the effects of prostamides and other COX-2 mediators on tissue damage in an ex vivo human mucosal explant colitis model. Healthy human colonic mucosae were incubated with pro-inflammatory cytokines TNF-α and IL-1β to elicit colitis-like tissue damage. The PGF-ethanolamide analogue, bimatoprost decreased colitis scores which were reversed by a prostamide-specific antagonist AGN 211334, but not the FP receptor antagonist AL-8810. PGF-ethanolamide and PGE-ethanolamide also reduced cytokine-evoked epithelial damage. Anandamide was protective in the explant colitis model; however COX-2 inhibition did not alter its effects, associated with a lack of COX-2 induction in explant mucosal tissue. These findings support an anti-inflammatory role for prostamides and endocannabinoids in the human colon. PMID:23380599
Flight Dynamics Modeling and Simulation of a Damaged Transport Aircraft
NASA Technical Reports Server (NTRS)
Shah, Gautam H.; Hill, Melissa A.
2012-01-01
A study was undertaken at NASA Langley Research Center to establish, demonstrate, and apply methodology for modeling and implementing the aerodynamic effects of MANPADS damage to a transport aircraft into real-time flight simulation, and to demonstrate a preliminary capability of using such a simulation to conduct an assessment of aircraft survivability. Key findings from this study include: superpositioning of incremental aerodynamic characteristics to the baseline simulation aerodynamic model proved to be a simple and effective way of modeling damage effects; the primary effect of wing damage rolling moment asymmetry may limit minimum airspeed for adequate controllability, but this can be mitigated by the use of sideslip; combined effects of aerodynamics, control degradation, and thrust loss can result in significantly degraded controllability for a safe landing; and high landing speeds may be required to maintain adequate control if large excursions from the nominal approach path are allowed, but high-gain pilot control during landing can mitigate this risk.
A constitutive-relationship model for film flow on rough fracture surfaces
NASA Astrophysics Data System (ADS)
Liu, H. H.
Film flow on fracture surfaces may be an important mechanism for fast flow in unsaturated fractured rocks. Incorporating this mechanism into a numerical model requires knowledge of constitutive relationships for film flow. Based on fractal concepts and a conceptual argument of Tokunaga et al. that water films could be treated as analogues to water in unsaturated porous media, a simple constitutive-relationship model has been developed. The validity of the model is supported by excellent agreements between calculation results and experimental observations for two different fracture surfaces. L'écoulement en film sur les surfaces de fracture peut être un mécanisme important pour l'écoulement rapide dans les roches fracturées non saturées. L'incorporation de ce mécanisme dans un modèle numérique nécessite la connaissance des relations fondamentales pour l'écoulement en film. Basé sur des concepts fractals et sur un argument conceptuel de Tokunaga et al. selon lequel des films d'eau peuvent être considérés comme des analogues de l'eau en milieu poreux non saturé, un modèle simple des relations fondamentales a été développé. La validité de ce modèle est confirmée grâce à une excellente concordance entre les résultats du calcul et les observations expérimentales pour deux surfaces différentes de fractures. El flujo pelicular en la superficie de las fracturas puede ser un mecanismo importante para el flujo rápido en rocas fracturadas no saturadas. Incorporarlo en un modelo numérico requiere conocer las relaciones constitutivas del flujo pelicular. Se ha desarrollado un modelo de una relación constitutiva sencilla partiendo de conceptos fractales y de un argumento conceptual de Tokunaga et al., según el cual las películas de agua pueden ser tratadas como análogos del agua en medios porosos no saturados. La validez del modelo es corroborada por los excelentes ajustes entre los resultados numéricos y las observaciones experimentales en dos
Characterization, testing and constitutive modelling of an impact-modified polypropylene
NASA Astrophysics Data System (ADS)
Wang, Yan
2002-01-01
Impact modified polypropylenes (or TPOs) are polymer blends of isotactic polypropylene (iPP), ethylene-propylene-diene monomer elastomer (EPDM), and high density polyethylene (HDPE). Currently, TPOs are extensively used in impact applications, such as car bumpers. However, the design process of TPO parts for impact applications is still an expensive, trial-and-error procedure. In this project, we aim to develop a material model with specific physical bases to represent a TPO material, so that TPO part design can be effective and efficient. In order to achieve our objective, morphology characterization and mechanical testing have been conducted to examine the intrinsic mechanisms of TPO. Tests were conducted over a broad range of strain rates using both a servohydraulic apparatus and an Aluminum split Hopkinson pressure bar. The TPO system we examined is multi-phasic in which an EPDM and HDPE blend forms the minor domain, distributed in the iPP matrix. The large deformation TPO response includes strain rate dependent initial stiffness; temperature, deformation state and strain rate dependent yield; temperature and deformation state dependent strain hardening. Its response is not unlike that of glassy polymers in many ways, owing to the flexibility of the iPP matrix, however the TPO shows a moderate strain hardening rate and little strain recovery upon unloading. A three-dimensional, four-element constitutive model has been developed for this TPO. The model includes rate dependent stiffness, rate and temperature dependent yield, temperature dependent strain hardening, and crystallographic slip. The model has been examined to be robust over a wide range of strain rates from quasi-static to impact, and predictive of different deformation states, such as uniaxial compression and plane strain compression. The model has been shown to capture the post-yield thermal softening and apparent lack of post-yield strain hardening at impact test conditions.
Damage evaluation of reinforced concrete frame based on a combined fiber beam model
NASA Astrophysics Data System (ADS)
Shang, Bing; Liu, ZhanLi; Zhuang, Zhuo
2014-04-01
In order to analyze and simulate the impact collapse or seismic response of the reinforced concrete (RC) structures, a combined fiber beam model is proposed by dividing the cross section of RC beam into concrete fiber and steel fiber. The stress-strain relationship of concrete fiber is based on a model proposed by concrete codes for concrete structures. The stress-strain behavior of steel fiber is based on a model suggested by others. These constitutive models are implemented into a general finite element program ABAQUS through the user defined subroutines to provide effective computational tools for the inelastic analysis of RC frame structures. The fiber model proposed in this paper is validated by comparing with experiment data of the RC column under cyclical lateral loading. The damage evolution of a three-dimension frame subjected to impact loading is also investigated.
Models for predicting damage evolution in metal matrix composites subjected to cyclic loading
Allen, D.H.; Hurtado, L.D.; Helms, K.L.E.
1995-03-01
A thermomechanical analysis of a continuous fiber metal matrix composite (MMC) subjected to cyclic loading is performed herein. The analysis includes the effects of processing induced residual thermal stresses, matrix inelasticity, and interface cracking. Due to these complexities, the analysis is performed computationally using the finite element method. Matrix inelasticity is modelled with a rate dependent viscoplasticity model. Interface fracture is modelled by the use of a nonlinear interface constitutive model. The problem formulation is summarized, and results are given for a four-ply unidirectional SCS-6/{beta}21S titanium composite under high temperature isothermal mechanical fatigue. Results indicate rate dependent viscoplasticity can be a significant mechanism for dissipating the energy available for damage propagation, thus contributing to improved ductility of the composite. Results also indicate that the model may be useful for inclusion in life prediction methodologies for MMC`s.
Dynamic rupture in a damage-breakage rheology model
NASA Astrophysics Data System (ADS)
Lyakhovsky, Vladimir; Ben-Zion, Yehuda; Ilchev, Assen; Mendecki, Aleksander
2016-05-01
We present a thermodynamically-based formulation for modeling dynamic rupture processes in the brittle crust using a continuum damage-breakage rheology. The model combines aspects of a continuum viscoelastic damage framework for brittle solids with a continuum breakage mechanics for granular flow within dynamically generated slip zones. The formulation accounts for the density of distributed cracking and other internal flaws in damaged rocks with a scalar damage parameter, and addresses the grain size distribution of a granular phase in the slip zone with a breakage parameter. A dynamic brittle instability is associated with a critical level of damage in the solid, leading to loss of convexity of the solid strain energy, localization, and transition to a granular phase associated with lower energy level. The continuum damage-breakage rheology model treats the localization to a slip zone at the onset of dynamic rupture and post-failure recovery process as phase transitions between solid and granular states. The model generates sub- and super-shear rupture velocities and pulse-type ruptures seen also in frictional models, and additional important features such as strong dynamic changes of volumetric strain near the rupture front and diversity of nucleation mechanisms. The propagation of rupture front and slip accumulation at a point are correlated with sharp dynamic dilation followed by a gradual decay to a level associated with the final volumetric change associated with the granular phase transition in the slipping zone. The local brittle failure process associated with the solid-granular transition is expected to produce isotropic radiation in addition to the deviatoric terms. The framework significantly extends the ability to model brittle processes in complex geometrical structures and allows analyzing the roles of gouge thickness and other parameters on nucleation, rupture and radiation characteristics.
Dynamic rupture in a damage-breakage rheology model
NASA Astrophysics Data System (ADS)
Lyakhovsky, Vladimir; Ben-Zion, Yehuda; Ilchev, Assen; Mendecki, Aleksander
2016-08-01
We present a thermodynamically based formulation for modelling dynamic rupture processes in the brittle crust using a continuum damage-breakage rheology. The model combines aspects of a continuum viscoelastic damage framework for brittle solids with a continuum breakage mechanics for granular flow within dynamically generated slip zones. The formulation accounts for the density of distributed cracking and other internal flaws in damaged rocks with a scalar damage parameter, and addresses the grain size distribution of a granular phase in the slip zone with a breakage parameter. A dynamic brittle instability is associated with a critical level of damage in the solid, leading to loss of convexity of the solid strain energy, localization and transition to a granular phase associated with lower energy level. The continuum damage-breakage rheology model treats the localization to a slip zone at the onset of dynamic rupture and post-failure recovery process as phase transitions between solid and granular states. The model generates sub- and supershear rupture velocities and pulse-type ruptures seen also in frictional models, and additional important features such as strong dynamic changes of volumetric strain near the rupture front and diversity of nucleation mechanisms. The propagation of rupture front and slip accumulation at a point are correlated with sharp dynamic dilation followed by a gradual decay to a level associated with the final volumetric change associated with the granular phase transition in the slipping zone. The local brittle failure process associated with the solid-granular transition is expected to produce isotropic radiation in addition to the deviatoric terms. The framework significantly extends the ability to model brittle processes in complex geometrical structures and allows analysing the roles of gouge thickness and other parameters on nucleation, rupture and radiation characteristics.
NASA Astrophysics Data System (ADS)
Cao, Y.; Di, H. S.; Misra, R. D. K.; Zhang, Jiecen
2014-12-01
The hot deformation behavior of a Fe-Ni-Cr austenitic Alloy 800H was explored in the intermediate temperature range of 825-975 °C and strain rate range of 0.01-10 s-1. The study indicates that dynamic recrystallization (DRX) occurred at 875-975 °C for strain rates of 0.01-0.1 s-1 and adiabatic heating generated at high strain rates accelerated the DRX process. Based on the experimental data, the Johnson-Cook, modified Johnson-Cook, and Arrhenius-type constitutive models were established to predict the flow stress during hot deformation. A comparative study was made on the accuracy and effectiveness of the above three developed models. The microstructure analysis indicated that all the deformation structures exhibited elongated grains and evidence of some degree of DRX. The multiple DRX at 975 °C and 0.01 s-1 led to an increase in the intensity of {001} <100> "cube" texture component and a significant reduction in the intensity of {011} <211> "brass" component. Additionally, the average values of grain average misorientation and grain orientation spread for deformed microstructure were inversely proportional to the fraction of DRX.
NASA Astrophysics Data System (ADS)
Nie, Longfei; Zhang, Liwen; Zhu, Zhi; Xu, Wei
2013-12-01
The hot deformation behavior of solution and aging FGH96 superalloy were investigated in the deformation temperature range of 1000-1175 °C and strain rate range of 0.001-5.0/s on a Gleeble-1500 thermo-mechanical simulator. The results show that the true stress-strain curves are typical of the occurrence of dynamic recrystallization (DRX). The value of the activation energy and materials constants of A and n was obtained through the hyperbolic sine function between the peak stress and Zener-Hollomon parameter. Optical microscopy observations of the grains showed that Zener-Hollomon parameter affected the DRX grain size obviously. In addition, the constitutive equations and DRX kinetics model were also built. The processing maps with the strain of 0.3 and 0.6 were obtained on the basis of dynamic materials model. The results predicted that there existed instability regions at around 1050 °C when the strain rate exceeds 0.01/s.
Conjugated kinetic and kinematic measures for constitutive modeling of the thermoelastic continua
NASA Astrophysics Data System (ADS)
Darijani, H.
2015-11-01
In this paper, the energy-type terms such as the stress power, the rate of the heat transferred to the system and the rate of the specific internal energy are presented in the Lagrangian, Eulerian and two-point descriptions for thermoelastic continua. In order to solve a problem based on the energy viewpoint, the mechanical, thermal and thermo-mechanical tensors conjugate to the Seth-Hill strains, and a general class of Lagrangian, Eulerian and two-point strain tensors are determined. Also, the energy pairs for thermoelastic continua are simplified for special cases of isentropic and isothermal deformation processes as well as the so-called entropic elastic materials (rubber-like materials and elastomers). At the end, a strain energy density function of the Saint Venant-Kirchhoff type in terms of different strain measures and temperature is considered for modeling the thermo-mechanical behavior of the rubber-like materials and elastomers. It is shown that this constitutive modeling can give results which are in good agreement with the experimental data.
B.D. WIrth; Ian M. Robertson
2007-11-29
Radiation damage to structural and cladding materials, including austenitic stainless steels, ferritic steels, and zirconium alloys, in nuclear reactor environments results in significant mechanical property degradation, including yield strength increases, severe ductility losses and flow localization, which impacts reliability and performance. Generation IV and advanced fuel cycle concepts under consideration will require the development of advanced structural materials, which will operate in increasingly hostile environments. The development of predictive models is required to assess the performance and response of materials in extreme Gen IV reactor operating conditions (temperature, stress, and pressure), to decrease the time to rapidly assess the properties of new materials and insert them into technological applications (Gen IV and Advanced Fuel Cycle Operations).
Nickel based superalloy containment case design: constitutive modeling and computational analysis
NASA Astrophysics Data System (ADS)
Ruggiero, Andrew; Bonora, Nicola; Torrice, Giovanni; di Sciuva, Marco; Degiovanni, Marco; Mattone, Massimiliano; Gherlone, Marco; Frola, Carlo
2007-06-01
Quasi-static and dynamic characterization of nickel based superalloy Waspaloy has been performed at the University of Cassino. Quasy-static tensile tests have been carried out on both round bar specimens, to obtain the flow stress curve at low strain rates, and hourglass specimens, to investigate damage evolution with plastic strain. The mechanical behavior at high strain rates has been obtained by means of a direct tension split Hopkinson Bar, which allows the characterization of the material up to failure. Experimental results show that when strain rates increases, the failure strain increases while the yield strength decreases, in some intervals of the range considered. This singular behavior has been modeled and implement in a Finite Element Method commercial code in order to perform numerical simulations of experimental ballistic tests carried out at the Polytechnics of Turin, using an airgun facility. Good agreement has been found between FEM simulations and experimental results..
Nickel Based Superalloy Containment Case Design: Constitutive Modeling and Computational Analysis
NASA Astrophysics Data System (ADS)
Ruggiero, A.; Bonora, N.; Torrice, G.; Di Sciuva, M.; Degiovanni, M.; Mattone, M.; Gherlone, M.; Frola, C.
2007-12-01
Quasi-static and dynamic characterization of nickel based superalloy Waspaloy® has been performed at the University of Cassino. Quasi-static tensile tests have been carried out on both round bar specimens, to obtain the flow stress curve at low strain rates, and hourglass specimens, to investigate damage evolution with plastic strain. The mechanical behavior at high strain rates has been obtained by means of a direct tension split Hopkinson Bar, which allows the characterization of the material up to failure. Experimental results show that when strain rates increases, the failure strain increases while the yield strength decreases, in some intervals of the range considered. This singular behavior has been modeled and implement in a Finite Element Method commercial code in order to perform numerical simulations of experimental ballistic tests carried out at the Politecnico di Torino, using an airgun facility. Good agreement has been found between FEM simulations and experimental results.
NASA Astrophysics Data System (ADS)
Bielefeldt, Brent R.; Benzerga, A. Amine; Hartl, Darren J.
2016-04-01
The ability to monitor and predict the structural health of an aircraft is of growing importance to the aerospace industry. Currently, structural inspections and maintenance are based upon experiences with similar aircraft operating in similar conditions. While effective, these methods are time-intensive and unnecessary if the aircraft is not in danger of structural failure. It is imagined that future aircraft will utilize non-destructive evaluation methods, allowing for the near real-time monitoring of structural health. A particularly interesting method involves utilizing the unique transformation response of shape memory alloy (SMA) particles embedded in an aircraft structure. By detecting changes in the mechanical and/or electromagnetic responses of embedded particles, operators could detect the formation or propagation of fatigue cracks in the vicinity of these particles. This work focuses on a finite element model of SMA particles embedded in an aircraft wing using a substructure modeling approach in which degrees of freedom are retained only at specified points of connection to other parts or the application of boundary conditions, greatly reducing computational cost. Previous work evaluated isolated particle response to a static crack to numerically demonstrate and validate this damage detection method. This paper presents the implementation of a damage model to account for crack propagation and examine for the first time the effect of particle configuration and/or relative placement with respect to the ability to detect damage.
Progressive Damage Modeling of Durable Bonded Joint Technology
NASA Technical Reports Server (NTRS)
Leone, Frank A.; Davila, Carlos G.; Lin, Shih-Yung; Smeltzer, Stan; Girolamo, Donato; Ghose, Sayata; Guzman, Juan C.; McCarville, Duglas A.
2013-01-01
The development of durable bonded joint technology for assembling composite structures for launch vehicles is being pursued for the U.S. Space Launch System. The present work is related to the development and application of progressive damage modeling techniques to bonded joint technology applicable to a wide range of sandwich structures for a Heavy Lift Launch Vehicle. The joint designs studied in this work include a conventional composite splice joint and a NASA-patented Durable Redundant Joint. Both designs involve a honeycomb sandwich with carbon/epoxy facesheets joined with adhesively bonded doublers. Progressive damage modeling allows for the prediction of the initiation and evolution of damage. For structures that include multiple materials, the number of potential failure mechanisms that must be considered increases the complexity of the analyses. Potential failure mechanisms include fiber fracture, matrix cracking, delamination, core crushing, adhesive failure, and their interactions. The joints were modeled using Abaqus parametric finite element models, in which damage was modeled with user-written subroutines. Each ply was meshed discretely, and layers of cohesive elements were used to account for delaminations and to model the adhesive layers. Good correlation with experimental results was achieved both in terms of load-displacement history and predicted failure mechanisms.
Li, Kui; Zhao, Hui; Liu, Wenjun; Yin, Zhiyong
2015-01-01
Background The mechanical characterization of infant porcine cerebellum tissue in tension at high strain rate is crucial for modeling traumatic cerebellum injury, which is in turn helpful for understanding the biomechanics of such injuries suffered in traffic accidents. Material and Method In this study, the infant porcine cerebellum tissue was given three loading velocities, ie, 2s-1, 20s-1 and 100s-1 with up to 30% strain to investigate the tensile properties. At least six tensile tests for each strain rate were validly performed. Fung, Gent, Ogden and exponential models were applied to fit the constitutive equations, so as to obtain material parameters from the experimental data. Results The Lagrange stress of infant porcine cerebellum tissue in tension appeared to be no more than 3000Pa at each loading velocity. More specifically, the Lagrange stress at 30% strain was (393.7±84.4)Pa, (928.3±56.3)Pa and (2582.4±282.2)Pa at strain rates of 2s-1, 20s-1 and 100s-1, respectively. Fung (0.833≤R2≤0.924), Gent (0.797≤R2≤0.875), Ogden (0.859≤R2≤0.944) and exponential (0.930≤R2≤0.972) models provided excellent fitting to experimental data up to 30% strain. Conclusions The infant cerebellum tissue shows a stiffer response with increase of the loading speed, indicating a strong strain-rate sensitivity. This study will enrich the knowledge on the material properties of infant brain tissue, which may augment the biofidelity of finite element model of human pediatric cerebellum. PMID:25830545
NASA Astrophysics Data System (ADS)
Nagel, T.; Shao, H.; Linder, M.; Wörner, A.; Kolditz, O.
2013-12-01
Heat processes in industry and for power generation can be made more cost-efficient and climate friendly by the integration of thermal energy storage devices. Due to high storage densities and superior long term storage characteristics, systems relying on thermochemical reactions are of great interest and often based on porous or granular media. As such, they share characteristic features in terms of mass and heat transport that are strongly coupled by physical and chemical phenomena. We have employed the theory of porous media to establish a model featuring reactive multicomponent compressible fluid mass transport through solid particle bed coupled to local thermal nonequilibrium heat transport. The model development has been based on an extensive evaluation of the Clausius-Duhem inequality to derive thermodynamically consistent constitutive relations for secondary variables as well as direct and indirect coupling terms. The model has then been implemented into the open source scientific simulation code OpenGeoSys using the finite element method. Lab and pilot scale thermochemical heat storage reactors with different reaction systems (oxidation reactions, hydration reactions) have been simulated successfully using axisymmetric geometries. The simulations show the strong coupling of pressure, concentration and temperature fields as well as the gas-solid reactions occurring inside the reactors. The effect of certain process parameters, such as mass flow and particle size, on the occurrence of local thermal nonequilibrium is illustrated. It is shown that the reactors can be used in a number of operating modes such as the extraction or release of heat accompanied by significant temperature drops or raises; the buffering or smoothing of temperature fluctuations at the inlet; the up- or downgrading of heat. The developed model therefore represents a useful tool to understand reactor behavior, optimize operating parameters, estimate thermal and parasitic losses, and
An in vitro model for retinal laser damage
NASA Astrophysics Data System (ADS)
Denton, Michael L.; Foltz, Michael S.; Schuster, Kurt J.; Estlack, Larry E.; Hodnett, Harvey M.; Noojin, Gary D.; Thomas, Robert J.
2007-02-01
Ocular laser exposures resulting in damage at the retina typically involve cellular alterations in the retinal pigment epithelial (RPE) layer. To provide guidelines for eye-safe exposure to lasers, the laser safety community has relied on damage assessment in nonhuman primate studies. Simple and reliable model systems for laser bioeffects that use cultured RPE cells, rather than animals, are thus desirable. We have characterized our artificially pigmented hTERT-RPE1 model by identifying ED 50 thresholds over a wide range of laser parameters and cell culture conditions. When summarized as action spectra and temporal action profiles (log threshold fluence versus log exposure duration), trends (pigment-dependent) in our cell model data are strikingly similar to the threshold trends reported for animal models (literature). In addition, the rapidity and flexibility (laser delivery) with which studies are performed in our culture model has benefited computational modeling efforts.
Stephens, Elizabeth V.; Vetrano, John S.; Koeppel, Brian J.; Chou, Y. S.; Sun, Xin; Khaleel, Mohammad A.
2009-09-05
This paper discusses experimental determination of solid oxide fuel cell (SOFC) glass-ceramic seal material properties and seal/interconnect interfacial properties to support development and optimization of SOFC designs through modeling. Material property experiments such as dynamic resonance, dilatometry, flexure, creep, tensile, and shear tests were performed on PNNL’s glass-ceramic sealant material, designated as G18, to obtain property data essential to constitutive and numerical model development. Characterization methods for the physical, mechanical, and interfacial properties of the sealing material, results, and their application to the constitutive implementation in SOFC stack modeling are described.
NASA Astrophysics Data System (ADS)
Xu, Qiang; Barrans, Simon
Within the framework of a phenomenological approach a set of multi-axial creep damage constitutive equations for 0.5Cr0.5Mo0.25V ferritic steel at 590°C is developed in which a new formulation is employed. The deficiency of the previous formulation and the need for improvement became apparent after a critical review of the development of creep damage constitutive equations for 316 stainless steel(1). The need for improvement was further underpinned by a call for modification of the constitutive equations(36). Recently, a specific formulation was proposed and validated(2)-(4). This paper reports the latest developments of the multi-axial creep constitutive equations for 0.5Cr0.5Mo0.25V ferritic steel at 590°C including: 1) the fundamental requirement; 2) formulation; 3) validation; and 4) conclusion. It systematically shows the suitability of this new set of constitutive equations and the incapability of the previous ones. Furthermore, it contributes knowledge to the methodology.
Neurocomputational models of the remote effects of focal brain damage.
Reggia, James A
2004-11-01
Sudden localized brain damage, such as occurs in stroke, produces neurological deficits directly attributable to the damaged site. In addition, other clinical deficits occur due to secondary "remote" effects that functionally impair the remaining intact brain regions (e.g., due to their sudden disconnection from the damaged area), a phenomenon known as diaschisis. The underlying mechanisms of these remote effects, particularly those involving interactions between the left and right cerebral hemispheres, have proven somewhat difficult to understand in the context of current theories of hemispheric specialization. This article describes some recent neurocomputational models done in the author's research group that try to explain diaschisis qualitatively. These studies show that both specialization and diaschisis can be accounted for with a single model of hemispheric interactions. Further, the results suggest that left-right subcortical influences may be much more important in influencing hemispheric specialization than is generally recognized. PMID:15564108
Thermomechanics of damageable materials under diffusion: modelling and analysis
NASA Astrophysics Data System (ADS)
Roubíček, Tomáš; Tomassetti, Giuseppe
2015-12-01
We propose a thermodynamically consistent general-purpose model describing diffusion of a solute or a fluid in a solid undergoing possible phase transformations and damage, beside possible visco-inelastic processes. Also heat generation/consumption/transfer is considered. Damage is modelled as rate-independent. The applications include metal-hydrogen systems with metal/hydride phase transformation, poroelastic rocks, structural and ferro/para-magnetic phase transformation, water and heat transport in concrete, and if diffusion is neglected, plasticity with damage and viscoelasticity, etc. For the ensuing system of partial differential equations and inclusions, we prove existence of solutions by a carefully devised semi-implicit approximation scheme of the fractional-step type.
A statistical damage model with implications for precursory seismicity
NASA Astrophysics Data System (ADS)
Lee, Ya-Ting; Turcotte, Donald; Rundle, John; Chen, Chien-Chih
2012-06-01
Acoustic emissions prior to rupture indicate precursory damage. Laboratory studies of frictional sliding on model faults feature accelerating rates of acoustic emissions prior to rupture. Precursory seismic emissions are not generally observed prior to earthquakes. To address the problem of precursory damage, we consider failure in a fiber-bundle model. We observe a clearly defined nucleation phase followed by a catastrophic rupture. The fibers are hypothesized to represent asperities on a fault. Two limiting behaviors are the equal load sharing p = 0 (stress from a failed fiber is transferred equally to all surviving fibers) and the local load sharing p = 1 (stress from a failed fiber is transferred to adjacent fibers). We show that precursory damage in the nucleation phase is greatly reduced in the local-load sharing limit. The local transfer of stress from an asperity concentrates nucleation, restricting precursory acoustic emissions (seismic activity).
NASA Astrophysics Data System (ADS)
Placidi, Luca
2016-03-01
A one-dimensional displacement second-gradient damage continuum theory has been already presented within the framework of a variational approach. Damage is associated with strain concentration. Therefore, not only non-local effects of displacement second-gradient modelling should be considered in a comprehensive model, but also any plastic effects. The aim of this paper is therefore to extend such a model to plasticity. The action is intended to depend not only with respect to first and second gradient of displacement field and to a scalar damage field, but also to further two internal variables, i.e. the accumulated plastic tension and the accumulated plastic compression. A constitutive prescription on the stiffness is given in terms of the scalar damage parameter in a usual way, i.e. as in many other works, it is prescribed to decrease as far as the damage increases. On the other hand, the microstructural material length (i.e. the square of the constitutive function in front of the squared displacement second-gradient term in the action functional) is prescribed to increase as far as the damage increases, being this last assumption connected to the interpretation that a damage state induces a microstructure in the continuum and that such a microstructure is more important as far as the damage increases. Initial damage threshold and yield stresses are naturally introduced in the action in front of linear terms, respectively, of damage and plastic internal variables. The hardening matrix is also introduced in a natural way as the coefficient matrix in front of the quadratic terms of the two plastic internal variables. At a given value of damage and plastic parameters, the behaviour is referred to second-gradient linear elastic material. However, the damage and plastic evolutions make the model not only nonlinear, but also inelastic. The second principle of thermodynamics is considered by assuming that the scalar damage and plastic parameters do not decrease their
Fatigue damage modeling for coated single crystal superalloys
NASA Technical Reports Server (NTRS)
Nissley, David M.
1988-01-01
A high temperature, low-cycle fatigue life prediction method for coated single crystal nickel-base superalloys is being developed. The method is being developed for use in predicting crack initiation life of coated single crystal turbine airfoils. Although the models are being developed using coated single crystal PWA 1480, they should be readily adaptable to other coated nickel-base single crystal materials. The coatings choosen for this effort were of two generic types: a low pressure plasma sprayed NiCoCrAlY overlay, designated PWA 286, and an aluminide diffusion, designated PWA 273. In order to predict the useful crack initiation life of airfoils, the constitutive and failure behavior of the coating/substrate combination must be taken into account. Coatings alter the airfoil surface microstructure and are a primary source from which cracks originate. The adopted life prediction approach addresses this complexity by separating the coating and single crystal crack initiation regimes. This provides a flexible means for using different life model formulations for the coating and single crystal materials. At the completion of this program, all constitutive and life model formulations will be available in equation form and as software. The software will use the MARC general purpose finite element code to drive the constitutive models and calculate life parameters.
SIMULATION OF GEOMATERIALS USING CONTINUUM DAMAGE MODELS ON AN EULERIAN GRID
Lomov, I; Antoun, T H
2004-09-17
A new continuum model for directional tensile failure has been developed that can simulate weakening and void formation due to directional tensile failure. The model is developed within the context of a properly invariant nonlinear thermomechanical theory. A second order damage tensor is introduced which allows simulation of weakening to tension applied in one direction, without weakening to subsequent tension applied in perpendicular directions. This damage tensor can be advected using standard methods in computer codes. Porosity is used as an isotropic measure of volumetric void strain and its evolution is influenced by tensile failure. The rate of dissipation due to directional tensile failure takes a particularly simple form, which can be analyzed easily. Specifically, the model can be combined with general constitutive equations for porous compaction and dilation, as well as viscoplasticity. A robust non-iterative numerical scheme for integrating these evolution equations is proposed. This constitutive model has been implemented into an Eulerian shock wave code with adaptive mesh refinement. A comparison of experimental results and computational simulations of spherical wave propagation in Danby marble was made. The experiment consisted of a 2-cm-diameter explosive charge detonated in the center of a cylindrical rock sample. Radial particle velocity histories were recorded at several concentric locations in the sample. An extensively damaged region near the charge cavity and two networks of cracks were evident in the specimen after the test. The first network consists of radial cracks emanating form the cavity and extending about halfway through the specimen. The second network consists of circumferential cracks occurring in a relatively narrow band that extends from the outer boundary of the radially cracked region toward the free surface. The calculations indicated load-induced anisotropy such as was observed in the experiment.
Magnetic measurement of creep damage: modeling and measurement
NASA Astrophysics Data System (ADS)
Sablik, Martin J.; Jiles, David C.
1996-11-01
Results of inspection of creep damage by magnetic hysteresis measurements on Cr-Mo steel are presented. It is shown that structure-sensitive parameters such as coercivity, remanence and hysteresis loss are sensitive to creep damage. Previous metallurgical studies have shown that creep changes the microstructure of he material by introducing voids, dislocations, and grain boundary cavities. As cavities develop, dislocations and voids move out to grain boundaries; therefore, the total pinning sources for domain wall motion are reduced.This, together with the introduction of a demagnetizing field due to the cavities, results in the decrease of both coercivity, remanence and hence, concomitantly, hysteresis loss. Incorporating these structural effects into a magnetomechanical hysteresis model developed previously by us produces numerical variations of coercivity, remanence and hysteresis loss consistent with what is measured. The magnetic model has therefore been used to obtain appropriately modified magnetization curves for each element of creep-damaged material in a finite element (FE) calculation. The FE calculation has been used to simulate magnetic detection of non-uniform creep damage around a seam weld in a 2.25 Cr 1Mo steam pipe. In particular, in the simulation, a magnetic C-core with primary and secondary coils was placed with its pole pieces flush against the specimen in the vicinity of the weld. The secondary emf was shown to be reduced when creep damage was present inside the pipe wall at the cusp of the weld and in the vicinity of the cusp. The calculation showed that the C- core detected creep damage best if it spanned the weld seam width and if the current in the primary was such that the C- core was not magnetically saturated. Experimental measurements also exhibited the dip predicted in emf, but the measurements are not yet conclusive because the effects of magnetic property changes of weld materials, heat- affected material, and base material have
Incorporating Micro-Mechanics Based Damage Models into Earthquake Rupture Simulations
NASA Astrophysics Data System (ADS)
Bhat, H.; Rosakis, A.; Sammis, C. G.
2012-12-01
The micromechanical damage mechanics formulated by Ashby and Sammis, 1990 and generalized by Deshpande and Evans 2008 has been extended to allow for a more generalized stress state and to incorporate an experimentally motivated new crack growth (damage evolution) law that is valid over a wide range of loading rates. This law is sensitive to both the crack tip stress field and its time derivative. Incorporating this feature produces additional strain-rate sensitivity in the constitutive response. The model is also experimentally verified by predicting the failure strength of Dionysus-Pentelicon marble over a wide range of strain rates. Model parameters determined from quasi-static experiments were used to predict the failure strength at higher loading rates. Agreement with experimental results was excellent. After this verification step the constitutive law was incorporated into a Finite Element Code focused on simulating dynamic earthquake ruptures with specific focus on the ends of the fault (fault tip process zone) and the resulting strong ground motion radiation was studied.
Role of interactions and damage in a cohesive fracture model
NASA Astrophysics Data System (ADS)
Gran, Josesph; Rundle, John; Turcotte, Donald; Klein, William
2012-02-01
We study the influences of local and long range interactions in a numerical model of tensile fracture. Our model simulates fracture events on a 2D square lattice plane with a Metropolis algorithm. We chose a Hamiltonian that is written as a function of the crack separation (offset field) and includes contributions from an external field, interactions, as well as a cohesive energy across the crack surfaces. Included in our study is both a ferromagnetic-type (attractive) and antiferromagnetic-type (repulsive) interactions. We test both of these interactions individually as well as a hybrid interaction in which over a short range the interaction is antiferromagnetic and in the long range the interaction becomes ferromagnetic. This dual interaction approximates a Lennard-Jones potential. We also propose a characterization of damage and investigate the increase of damage in time for fractures occurring by a static-load as well as a time-dependent load. Damaged sites do not interact with neighboring sites and cannot hold any load. We compare our damage model to previous studies of fiber-bundle models.
Constitutive modeling of the Mullins effect and cyclic stress softening in filled elastomers
NASA Astrophysics Data System (ADS)
Dargazany, Roozbeh; Itskov, Mikhail
2013-07-01
The large strain behavior of filled rubbers is characterized by the strong Mullins effect, permanent set, and induced anisotropy. Strain controlled cyclic tests also exhibit a pronounced hysteresis as a strain rate independent phenomenon. Prediction of these inelastic features in elastomers is an important challenge with immense industrial and technological relevance. In the present paper, a micromechanical model is proposed to describe the inelastic features in the behavior of filled elastomers. To this end, the previously developed network decomposition concept [Dargazany and Itskov, Int. J. Solids Struct.IJSOAD0020-768310.1016/j.ijsolstr.2009.03.022 46, 2967 (2009)] is extended and an additional network (CP network) is added to the classical elastic rubber (CC) and polymer-filler (PP) networks. The new network is considered to account for the damage of filler aggregates in the cyclic deformation as the source of hysteresis energy loss. The accuracy of the resulting model is evaluated in comparison to a new set of experimental data.
Amelioration of inflammation and tissue damage in sickle cell model mice by Nrf2 activation.
Keleku-Lukwete, Nadine; Suzuki, Mikiko; Otsuki, Akihito; Tsuchida, Kouhei; Katayama, Saori; Hayashi, Makiko; Naganuma, Eriko; Moriguchi, Takashi; Tanabe, Osamu; Engel, James Douglas; Imaizumi, Masue; Yamamoto, Masayuki
2015-09-29
Sickle cell disease (SCD) is an inherited disorder caused by a point mutation in the β-globin gene, leading to the production of abnormally shaped red blood cells. Sickle cells are prone to hemolysis and thereby release free heme into plasma, causing oxidative stress and inflammation that in turn result in damage to multiple organs. The transcription factor Nrf2 (nuclear factor erythroid 2-related factor 2) is a master regulator of the antioxidant cell-defense system. Here we show that constitutive Nrf2 activation by ablation of its negative regulator Keap1 (kelch-like ECH-associated protein 1) significantly improves symptoms in SCD model mice. SCD mice exhibit severe liver damage and lung inflammation associated with high expression levels of proinflammatory cytokines and adhesion molecules compared with normal mice. Importantly, these symptoms subsided after Nrf2 activation. Although hemolysis and stress erythropoiesis did not change substantially in the Nrf2-activated SCD mice, Nrf2 promoted the elimination of plasma heme released by sickle cells' hemolysis and thereby reduced oxidative stress and inflammation, demonstrating that Nrf2 activation reduces organ damage and segregates inflammation from prevention of hemolysis in SCD mice. Furthermore, administration of the Nrf2 inducer CDDO-Im (2-cyano-3, 12 dioxooleana-1, 9 diene-28-imidazolide) also relieved inflammation and organ failure in SCD mice. These results support the contention that Nrf2 induction may be an important means to protect organs from the pathophysiology of sickle cell-induced damage. PMID:26371321
A prediction model for ocular damage - Experimental validation.
Heussner, Nico; Vagos, Márcia; Spitzer, Martin S; Stork, Wilhelm
2015-08-01
With the increasing number of laser applications in medicine and technology, accidental as well as intentional exposure of the human eye to laser sources has become a major concern. Therefore, a prediction model for ocular damage (PMOD) is presented within this work and validated for long-term exposure. This model is a combination of a raytracing model with a thermodynamical model of the human and an application which determines the thermal damage by the implementation of the Arrhenius integral. The model is based on our earlier work and is here validated against temperature measurements taken with porcine eye samples. For this validation, three different powers were used: 50mW, 100mW and 200mW with a spot size of 1.9mm. Also, the measurements were taken with two different sensing systems, an infrared camera and a fibre optic probe placed within the tissue. The temperatures were measured up to 60s and then compared against simulations. The measured temperatures were found to be in good agreement with the values predicted by the PMOD-model. To our best knowledge, this is the first model which is validated for both short-term and long-term irradiations in terms of temperature and thus demonstrates that temperatures can be accurately predicted within the thermal damage regime. PMID:26267496
Continuum-based FEM modeling of ceramic powder compaction using a cap-plasticity constitutive model
ARGUELLO JR.,JOSE G.; FOSSUM,ARLO F.; ZEUCH,DAVID H.; EWSUK,KEVIN G.
2000-01-25
Common ceramic component manufacturing typically involves the processing of the raw materials in powder form. Granulated powder is formed into a green body of the desired size and shape by consolidation, often by simply pressing nominally dry powder. Ceramic powders are commonly pressed in steel dies or rubber bags with the aim of producing a near-net-shape green body for subsequent sintering. Density gradients in these compacts, introduced during the pressing operation, are often severe enough to cause distortions in the shape of the part during sintering due to nonuniform shrinkage. In such cases, green machining or diamond grinding operations may be needed to obtain the desired final shape and size part. In severe cases, nonuniform shrinkage may even cause fracture in the parts during sintering. Likewise, density gradients can result in green bodies that break during ejection from the die or that are too fragile to be handled during subsequent processing. Empirical relationships currently exist to describe powder compaction but provide little understanding of how to control die design or compaction parameters to minimize density gradients thereby forcing the designer to use expensive and time consuming trial and error procedures. For this reason, interest has grown in developing computational tools to address this problem (Aydin et al., 1996 and Coube, 1998). The goal of the present work was to develop a general continuum-based finite element model for ceramic powder compaction that can be used to aid and guide the design and pressing of ceramic powders. Such a model can be used to improve both part and die/bag pressing design, resulting in more efficient and cost effective ways to make better parts.
De Focatiis, Davide S. A.; Buckley, C. Paul; Embery, John
2008-07-07
This paper investigates the behaviour of a well-characterised monodisperse grade of entangled atactic polystyrene across a very wide temperature and strain rate range through linear and non-linear melt rheology and solid-state deformation. In an effort to construct a constitutive model for large deformations able to describe rheological response right across this wide timescale, two well-established rheological models are combined: the well known RoliePoly (RP) conformational melt model and the Oxford glass-rubber constitutive model for glassy polymers. Comparisons between experimental data and simulations from a numerical implementation of the model illustrate that the model can cope well with the range of deformations in which orientation is limited to length-scales longer than an entanglement length. One approach in which the model can be expanded to incorporate the effects of orientation on shorter length scales using anisotropic viscoplastic flow is briefly discussed.
Theoretical model of impact damage in structural ceramics
NASA Technical Reports Server (NTRS)
Liaw, B. M.; Kobayashi, A. S.; Emery, A. G.
1984-01-01
This paper presents a mechanistically consistent model of impact damage based on elastic failures due to tensile and shear overloading. An elastic axisymmetric finite element model is used to determine the dynamic stresses generated by a single particle impact. Local failures in a finite element are assumed to occur when the primary/secondary principal stresses or the maximum shear stress reach critical tensile or shear stresses, respectively. The succession of failed elements thus models macrocrack growth. Sliding motions of cracks, which closed during unloading, are resisted by friction and the unrecovered deformation represents the 'plastic deformation' reported in the literature. The predicted ring cracks on the contact surface, as well as the cone cracks, median cracks, radial cracks, lateral cracks, and damage-induced porous zones in the interior of hot-pressed silicon nitride plates, matched those observed experimentally. The finite element model also predicted the uplifting of the free surface surrounding the impact site.
NASA Technical Reports Server (NTRS)
Goldberg, Robert K.; Carney, Kelly S.; DuBois, Paul; Hoffarth, Canio; Rajan, Subramaniam; Blankenhorn, Gunther
2016-01-01
The need for accurate material models to simulate the deformation, damage and failure of polymer matrix composites under impact conditions is becoming critical as these materials are gaining increased usage in the aerospace and automotive communities. In order to address a series of issues identified by the aerospace community as being desirable to include in a next generation composite impact model, an orthotropic, macroscopic constitutive model incorporating both plasticity and damage suitable for implementation within the commercial LS-DYNA computer code is being developed. The plasticity model is based on extending the Tsai-Wu composite failure model into a strain hardening-based orthotropic plasticity model with a non-associative flow rule. The evolution of the yield surface is determined based on tabulated stress-strain curves in the various normal and shear directions and is tracked using the effective plastic strain. To compute the evolution of damage, a strain equivalent semi-coupled formulation is used in which a load in one direction results in a stiffness reduction in multiple material coordinate directions. A detailed analysis is carried out to ensure that the strain equivalence assumption is appropriate for the derived plasticity and damage formulations that are employed in the current model. Procedures to develop the appropriate input curves for the damage model are presented and the process required to develop an appropriate characterization test matrix is discussed
NASA Technical Reports Server (NTRS)
Goldberg, Robert K.; Carney, Kelly S.; DuBois, Paul; Hoffarth, Canio; Rajan, Subramaniam; Blankenhorn, Gunther
2016-01-01
The need for accurate material models to simulate the deformation, damage and failure of polymer matrix composites under impact conditions is becoming critical as these materials are gaining increased usage in the aerospace and automotive communities. In order to address a series of issues identified by the aerospace community as being desirable to include in a next generation composite impact model, an orthotropic, macroscopic constitutive model incorporating both plasticity and damage suitable for implementation within the commercial LS-DYNA computer code is being developed. The plasticity model is based on extending the Tsai-Wu composite failure model into a strain hardening-based orthotropic plasticity model with a non-associative flow rule. The evolution of the yield surface is determined based on tabulated stress-strain curves in the various normal and shear directions and is tracked using the effective plastic strain. To compute the evolution of damage, a strain equivalent semi-coupled formulation is used in which a load in one direction results in a stiffness reduction in multiple material coordinate directions. A detailed analysis is carried out to ensure that the strain equivalence assumption is appropriate for the derived plasticity and damage formulations that are employed in the current model. Procedures to develop the appropriate input curves for the damage model are presented and the process required to develop an appropriate characterization test matrix is discussed.
Failure Predictions for VHTR Core Components using a Probabilistic Contiuum Damage Mechanics Model
Fok, Alex
2013-10-30
The proposed work addresses the key research need for the development of constitutive models and overall failure models for graphite and high temperature structural materials, with the long-term goal being to maximize the design life of the Next Generation Nuclear Plant (NGNP). To this end, the capability of a Continuum Damage Mechanics (CDM) model, which has been used successfully for modeling fracture of virgin graphite, will be extended as a predictive and design tool for the core components of the very high- temperature reactor (VHTR). Specifically, irradiation and environmental effects pertinent to the VHTR will be incorporated into the model to allow fracture of graphite and ceramic components under in-reactor conditions to be modeled explicitly using the finite element method. The model uses a combined stress-based and fracture mechanics-based failure criterion, so it can simulate both the initiation and propagation of cracks. Modern imaging techniques, such as x-ray computed tomography and digital image correlation, will be used during material testing to help define the baseline material damage parameters. Monte Carlo analysis will be performed to address inherent variations in material properties, the aim being to reduce the arbitrariness and uncertainties associated with the current statistical approach. The results can potentially contribute to the current development of American Society of Mechanical Engineers (ASME) codes for the design and construction of VHTR core components.
Creating a model of diseased artery damage and failure from healthy porcine aorta.
Noble, Christopher; Smulders, Nicole; Green, Nicola H; Lewis, Roger; Carré, Matt J; Franklin, Steve E; MacNeil, Sheila; Taylor, Zeike A
2016-07-01
Large quantities of diseased tissue are required in the research and development of new generations of medical devices, for example for use in physical testing. However, these are difficult to obtain. In contrast, porcine arteries are readily available as they are regarded as waste. Therefore, reliable means of creating from porcine tissue physical models of diseased human tissue that emulate well the associated mechanical changes would be valuable. To this end, we studied the effect on mechanical response of treating porcine thoracic aorta with collagenase, elastase and glutaraldehyde. The alterations in mechanical and failure properties were assessed via uniaxial tension testing. A constitutive model composed of the Gasser-Ogden-Holzapfel model, for elastic response, and a continuum damage model, for the failure, was also employed to provide a further basis for comparison (Calvo and Peña, 2006; Gasser et al., 2006). For the concentrations used here it was found that: collagenase treated samples showed decreased fracture stress in the axial direction only; elastase treated samples showed increased fracture stress in the circumferential direction only; and glutaraldehyde samples showed no change in either direction. With respect to the proposed constitutive model, both collagenase and elastase had a strong effect on the fibre-related terms. The model more closely captured the tissue response in the circumferential direction, due to the smoother and sharper transition from damage initiation to complete failure in this direction. Finally, comparison of the results with those of tensile tests on diseased tissues suggests that these treatments indeed provide a basis for creation of physical models of diseased arteries. PMID:26945437
Janečka, Adam Průša, Vít
2015-04-28
We discuss the benefits of using the so-called implicit type constitutive relations introduced by K. R. Rajagopal, J. Fluid Mech. 550, 243-249 (2006) and K. R. Rajagopal, Appl. Math. 48, 279-319 (2003) in the description of the behaviour of non-Newtonian fluids. In particular, we focus on the benefits of using the implicit type constitutive relations in the mathematical modelling of fluids in which the shear stress/shear rate dependence is given by an S-shaped curve, and in modelling of fluids that exhibit nonzero normal stress differences. We also discuss a thermodynamical framework that allows one to cope with the implicit type constitutive relations.
NASA Astrophysics Data System (ADS)
Augustins, L.; Billardon, R.; Hild, F.
2016-07-01
One of the critical points of the thermomechanical fatigue design process is the correct description of the cyclic behavior of the material. This work focuses on the material of automotive brake discs, namely flake graphite cast iron. The specificity of this material is its asymmetric behavior under tensile and compressive loadings, which is due to the shape of graphite that acts as small cracks. Multiscale models inspired from the literature are first presented. They lead to a good description of the material behavior under cyclic loadings. An elastoviscoplastic constitutive model is then proposed in a one-dimensional setting in order to accurately describe cyclic tests from room temperature up to {600^{circ}{C}}.
ERIC Educational Resources Information Center
Zachlod, Michelle, Ed.
California State Standard 5.7 is delineated in the following manner: "Students describe the people and events associated with the development of the U.S. Constitution and analyze the Constitution's significance as the foundation of the American republic." Students answer six questions about the Constitution and present suggestions for addressing…
A continuum thermo-inelastic model for damage and healing in self-healing glass materials
Xu, Wei; Sun, Xin; Koeppel, Brian J.; Zbib, Hussein M.
2014-07-08
Self-healing glass, a recent advancement in the class of smart sealing materials, has attracted great attention from both research and industrial communities because of its unique capability of repairing itself at elevated temperatures. However, further development and optimization of this material rely on a more fundamental and thorough understanding of its essential thermo-mechanical response characteristics, which is also pivotal in predicting the coupling and interactions between the nonlinear stress and temperature dependent damage and healing behaviors. In the current study, a continuum three-dimensional thermo-inelastic damage-healing constitutive framework has been developed for the compliant self-healing glass material. The important feature of the present model is that various phenomena governing the mechanical degradation and recovery process, i.e. the nucleation, growth, and healing of the cracks and pores, are described with distinct mechanism-driven kinetics, where the healing constitutive relations are propagated from lower-length scale simulations. The proposed formulations are implemented into finite element analyses and the effects of various loading conditions and material properties on the material’s mechanical resistance are investigated.
Bread dough rheology: Computing with a damage function model
NASA Astrophysics Data System (ADS)
Tanner, Roger I.; Qi, Fuzhong; Dai, Shaocong
2015-01-01
We describe an improved damage function model for bread dough rheology. The model has relatively few parameters, all of which can easily be found from simple experiments. Small deformations in the linear region are described by a gel-like power-law memory function. A set of large non-reversing deformations - stress relaxation after a step of shear, steady shearing and elongation beginning from rest, and biaxial stretching, is used to test the model. With the introduction of a revised strain measure which includes a Mooney-Rivlin term, all of these motions can be well described by the damage function described in previous papers. For reversing step strains, larger amplitude oscillatory shearing and recoil reasonable predictions have been found. The numerical methods used are discussed and we give some examples.
A stochastic model of radiation-induced bone marrow damage
Cotlet, G.; Blue, T.E.
2000-03-01
A stochastic model, based on consensus principles from radiation biology, is used to estimate bone-marrow stem cell pool survival (CFU-S and stroma cells) after irradiation. The dose response model consists of three coupled first order linear differential equations which quantitatively describe time dependent cellular damage, repair, and killing of red bone marrow cells. This system of differential equations is solved analytically through the use of a matrix approach for continuous and fractionated irradiations. The analytic solutions are confirmed through the dynamical solution of the model equations using SIMULINK. Rate coefficients describing the cellular processes of radiation damage and repair, extrapolated to humans from animal data sets and adjusted for neutron-gamma mixed fields, are employed in a SIMULINK analysis of criticality accidents. The results show that, for the time structures which may occur in criticality accidents, cell survival is established mainly by the average dose and dose rate.
Sandia/Stanford Unified Creep Plasticity Damage Model for ANSYS
2006-09-03
A unified creep plasticity (UCP) model was developed, based upon the time-dependent and time-independent deformation properties of the 95.5Sn-3.9Ag-0.6Cu (wt.%) soldier that were measured at Sandia. Then, a damage parameter, D, was added to the equation to develop the unified creep plasticity damage (UCPD) model. The parameter, D, was parameterized, using data obtained at Sandia from isothermal fatigue experiments on a double-lap shear test. The softwae was validated against a BGA solder joint exposed tomore » thermal cycling. The UCPD model was put into the ANSYS finite element as a subroutine. So, the softwae is the subroutine for ANSYS 8.1.« less
Multiple Damage Progression Paths in Model-Based Prognostics
NASA Technical Reports Server (NTRS)
Daigle, Matthew; Goebel, Kai Frank
2011-01-01
Model-based prognostics approaches employ domain knowledge about a system, its components, and how they fail through the use of physics-based models. Component wear is driven by several different degradation phenomena, each resulting in their own damage progression path, overlapping to contribute to the overall degradation of the component. We develop a model-based prognostics methodology using particle filters, in which the problem of characterizing multiple damage progression paths is cast as a joint state-parameter estimation problem. The estimate is represented as a probability distribution, allowing the prediction of end of life and remaining useful life within a probabilistic framework that supports uncertainty management. We also develop a novel variance control mechanism that maintains an uncertainty bound around the hidden parameters to limit the amount of estimation uncertainty and, consequently, reduce prediction uncertainty. We construct a detailed physics-based model of a centrifugal pump, to which we apply our model-based prognostics algorithms. We illustrate the operation of the prognostic solution with a number of simulation-based experiments and demonstrate the performance of the chosen approach when multiple damage mechanisms are active
An empirical modified fatigue damage model for impacted GFRP laminates
NASA Astrophysics Data System (ADS)
Naderi, S.; Hassan, M. A.; Bushroa, A. R.
2014-10-01
The aim of the present paper is to evaluate the residual strength of GFRP laminates following a low-velocity impact event under cyclic loading. The residual strength is calculated using a linear fatigue damage model. According to an investigation into the effect of low-velocity impact on the fatigue behavior of laminates, it seems laminate fatigue life decreases after impact. By normalizing the fatigue stress against undamaged static strength, the Fatigue Damage parameter “FD” is presented with a linear relationship as its slope which is a linear function of the initial impact energy; meanwhile, the constants were attained from experimental data. FD is implemented into a plane-stress continuum damage mechanics based model for GFRP composite laminates, in order to predict damage threshold in composite structures. An S-N curve is implemented to indicate the fatigue behavior for 2 mm thickness encompassing both undamaged and impacted samples. A decline in lifespan is evident when the impact energy level increases. Finally, the FD is intended to capture the unique GFRP composite characteristics.
Modeling and Characterization of Damage Processes in Metallic Materials
NASA Technical Reports Server (NTRS)
Glaessgen, E. H.; Saether, E.; Smith, S. W.; Hochhalter, J. D.; Yamakov, V. I.; Gupta, V.
2011-01-01
This paper describes a broad effort that is aimed at understanding the fundamental mechanisms of crack growth and using that understanding as a basis for designing materials and enabling predictions of fracture in materials and structures that have small characteristic dimensions. This area of research, herein referred to as Damage Science, emphasizes the length scale regimes of the nanoscale and the microscale for which analysis and characterization tools are being developed to predict the formation, propagation, and interaction of fundamental damage mechanisms. Examination of nanoscale processes requires atomistic and discrete dislocation plasticity simulations, while microscale processes can be examined using strain gradient plasticity, crystal plasticity and microstructure modeling methods. Concurrent and sequential multiscale modeling methods are being developed to analytically bridge between these length scales. Experimental methods for characterization and quantification of near-crack tip damage are also being developed. This paper focuses on several new methodologies in these areas and their application to understanding damage processes in polycrystalline metals. On-going and potential applications are also discussed.
Modeling the Study of DNA Damage Responses in Mice
Specks, Julia; Nieto-Soler, Maria; Lopez-Contreras, Andres J; Fernandez-Capetillo, Oscar
2016-01-01
Summary Damaged DNA has a profound impact on mammalian health and overall survival. In addition to being the source of mutations that initiate cancer, the accumulation of toxic amounts of DNA damage can cause severe developmental diseases and accelerate ageing. Therefore, understanding how cells respond to DNA damage has become one of the most intense areas of biomedical research in the recent years. However, whereas most mechanistic studies derive from in vitro or in cellulo work, the impact of a given mutation on a living organism is largely unpredictable. For instance, why BRCA1 mutations preferentially lead to breast cancer whereas mutations compromising mismatch repair drive colon cancer is still not understood. In this context, evaluating the specific physiological impact of mutations that compromise genome integrity has become crucial for a better dimensioning of our knowledge. We here describe the various technologies that can be used for modeling mutations in mice, and provide a review of the genes and pathways that have been modeled so far in the context of DNA damage responses. PMID:25636482
Arrieta-Cruz, Isabel; Pfaff, Donald W; Shelley, Deborah N
2007-06-01
Diffuse brain damage following anoxia due to cardiac failure, drowning, carbon monoxide exposure or other accidents constitutes a major medical problem. We have created a novel mouse model using the breathing of pure nitrogen, followed by a recently developed assay that reflects an operational definition of generalized arousal. The operational definition is precise, complete, and leads to quantitative, physical measures in a genetically tractable animal. Exposure to pure nitrogen for controlled periods had a surprising bifurcate effect: about half the mice survived with neurological measures that were virtually normal while the other half died. The new assay detected behavioral deficits unrevealed by neurological screening. Two important features of the results were that (i) deficits were not equal across the circadian cycle, and (ii) deficits were not equal across all the measures within the operational definition of arousal. Specific voluntary motor measurements were decreased in a manner that depended on the phase of the circadian cycle. Sensory responses were also decreased, with an emphasis on vertical movement responses; but, interestingly, fear learning was not damaged. This study establishes the first useful approach to diffuse brain damage in a genetically tractable animal. The model and its outcome measurements will be useful during future attempts at amelioration of acquired neurological disabilities following hypoxic-ischemic injuries. PMID:17448465
Constitutive Modeling of High-Temperature Flow Behavior of Al-0.62Mg-0.73Si Aluminum Alloy
NASA Astrophysics Data System (ADS)
Sun, Y.; Ye, W. H.; Hu, L. X.
2016-04-01
The high-temperature flow behavior of an aerospace structural material Al-0.62 Mg-0.73Si aluminum alloy was researched in this work. The isothermal compression tests were carried out in the temperature range of 683-783 K and strain rate range of 0.001-1 s-1. Based on the obtained true stress-true strain curves, the constitutive relationship of the alloy was revealed by establishing the Arrhenius-type constitutive model and a modified Johnson-Cook model. It was found that the flow characteristics were closely related to deformation temperature and strain rate. The activation energy of the studied material was calculated to be approximately 174 kJ mol-1. A comparative study has been conducted on the accuracy and reliability of the proposed models using statistics analysis method. It was proved by error analysis that the Arrhenius-type model had a better performance than the modified Johnson-Cook model.
NASA Astrophysics Data System (ADS)
Marchand, Basile; Chamoin, Ludovic; Rey, Christian
2015-11-01
In this work we propose a new identification strategy based on the coupling between a probabilistic data assimilation method and a deterministic inverse problem approach using the modified Constitutive Relation Error energy functional. The idea is thus to offer efficient identification despite of highly corrupted data for time-dependent systems. In order to perform real-time identification, the modified Constitutive Relation Error is here associated to a model reduction method based on Proper Generalized Decomposition. The proposed strategy is applied to two thermal problems with identification of time-dependent boundary conditions, or material parameters.
Predictability of formation damage: An assessment study and generalized models
Civan, F.
1991-01-01
The project objective is to develop improved generalized predictive models to be used for investigation of reservoir formation damage and control for various fluid and rock conditions and to account for these effects in reservoir simulation. To accomplish its objective the proposed study will first critically study and evaluate the previous modeling efforts and the experimental studies reported in the literature. Then, generalized predictive models will be formulated by combining the previous attempts and by improving and generalizing the modeling approaches to accommodate for a wide variety of conditions encountered in actual field applications. A critical review of the previous work addressing their theoretical basis, assumptions and limitations, and the generalized and improved model developed in this study will be presented in a systematic manner in terms of a standardized definition and nomenclature for direct comparison. Case studies with the generalized model will be presented to demonstrate its capacity and validity. User friendly computer programs implementing the improved modeling approaches will also be supplied. This study will form an assessment of the presently available models and methods for evaluating and predicting formation damage and present improved models. Therefore, it will be an important reference for the petroleum industry. 1 tab.
Search-based model identification of smart-structure damage
NASA Technical Reports Server (NTRS)
Glass, B. J.; Macalou, A.
1991-01-01
This paper describes the use of a combined model and parameter identification approach, based on modal analysis and artificial intelligence (AI) techniques, for identifying damage or flaws in a rotating truss structure incorporating embedded piezoceramic sensors. This smart structure example is representative of a class of structures commonly found in aerospace systems and next generation space structures. Artificial intelligence techniques of classification, heuristic search, and an object-oriented knowledge base are used in an AI-based model identification approach. A finite model space is classified into a search tree, over which a variant of best-first search is used to identify the model whose stored response most closely matches that of the input. Newly-encountered models can be incorporated into the model space. This adaptativeness demonstrates the potential for learning control. Following this output-error model identification, numerical parameter identification is used to further refine the identified model. Given the rotating truss example in this paper, noisy data corresponding to various damage configurations are input to both this approach and a conventional parameter identification method. The combination of the AI-based model identification with parameter identification is shown to lead to smaller parameter corrections than required by the use of parameter identification alone.
Constitutive Modeling of High-Temperature Flow Behavior of an Nb Micro-alloyed Hot Stamping Steel
NASA Astrophysics Data System (ADS)
Zhang, Shiqi; Feng, Ding; Huang, Yunhua; Wei, Shizhong; Mohrbacher, Hardy; Zhang, Yue
2016-03-01
The thermal deformation behavior and constitutive models of an Nb micro-alloyed 22MnB5 steel were investigated by conducting isothermal uniaxial tensile tests at the temperature range of 873-1223 K with strain rates of 0.1-10 s-1. The results indicated that the investigated steel showed typical work hardening and dynamic recovery behavior during hot deformation, and the flow stress decreased with a decrease in strain rate and/or an increase in temperature. On the basis of the experimental data, the modified Johnson-Cook (modified JC), modified Norton-Hoff (modified NH), and Arrhenius-type (AT) constitutive models were established for the subject steel. However, the flow stress values predicted by these three models revealed some remarkable deviations from the experimental values for certain experimental conditions. Therefore, a new combined modified Norton-Hoff and Arrhenius-type constitutive model (combined modified NH-AT model), which accurately reflected both the work hardening and dynamic recovery behavior of the subject steel, was developed by introducing the modified parameter k ɛ. Furthermore, the accuracy of these constitutive models was assessed by the correlation coefficient, the average absolute relative error, and the root mean square error, which indicated that the flow stress values computed by the combined modified NH-AT model were highly consistent with the experimental values (R = 0.998, AARE = 1.63%, RMSE = 3.85 MPa). The result confirmed that the combined modified NH-AT model was suitable for the studied Nb micro-alloyed hot stamping steel. Additionally, the practicability of the new model was also verified using finite element simulations in ANSYS/LS-DYNA, and the results confirmed that the new model was practical and highly accurate.
Towards Industrial Application of Damage Models for Sheet Metal Forming
NASA Astrophysics Data System (ADS)
Doig, M.; Roll, K.
2011-05-01
Due to global warming and financial situation the demand to reduce the CO2-emission and the production costs leads to the permanent development of new materials. In the automotive industry the occupant safety is an additional condition. Bringing these arguments together the preferable approach for lightweight design of car components, especially for body-in-white, is the use of modern steels. Such steel grades, also called advanced high strength steels (AHSS), exhibit a high strength as well as a high formability. Not only their material behavior but also the damage behavior of AHSS is different compared to the performances of standard steels. Conventional methods for the damage prediction in the industry like the forming limit curve (FLC) are not reliable for AHSS. Physically based damage models are often used in crash and bulk forming simulations. The still open question is the industrial application of these models for sheet metal forming. This paper evaluates the Gurson-Tvergaard-Needleman (GTN) model and the model of Lemaitre within commercial codes with a goal of industrial application.
A damage model based on failure threshold weakening
NASA Astrophysics Data System (ADS)
Gran, Joseph D.; Rundle, John B.; Turcotte, Donald L.; Holliday, James R.; Klein, William
2011-04-01
A variety of studies have modeled the physics of material deformation and damage as examples of generalized phase transitions, involving either critical phenomena or spinodal nucleation. Here we study a model for frictional sliding with long-range interactions and recurrent damage that is parameterized by a process of damage and partial healing during sliding. We introduce a failure threshold weakening parameter into the cellular automaton slider-block model which allows blocks to fail at a reduced failure threshold for all subsequent failures during an event. We show that a critical point is reached beyond which the probability of a system-wide event scales with this weakening parameter. We provide a mapping to the percolation transition, and show that the values of the scaling exponents approach the values for mean-field percolation (spinodal nucleation) as lattice size L is increased for fixed R. We also examine the effect of the weakening parameter on the frequency-magnitude scaling relationship and the ergodic behavior of the model.
NASA Astrophysics Data System (ADS)
Burkett, Michael W.; Clancy, Sean P.; Maudlin, Paul J.; Holian, Kathleen S.
2004-07-01
Previously developed constitutive models and solution algorithms for continuum-level anisotropic elastoplastic material strength and an isotropic damage model TEPLA have been implemented in the three-dimensional Eulerian hydrodynamics code known as CONEJO. The anisotropic constitutive modeling is posed in an unrotated material frame of reference using the theorem of polar decomposition to compute rigid-body rotation. TEPLA is based upon the Gurson flow surface (a potential function used in conjunction with the associated flow law). The original TEPLA equation set has been extended to include anisotropic elastoplasticity and has been recast into a new implicit solution algorithm based upon an eigenvalue scheme to accommodate the anisotropy. This algorithm solves a two-by-two system of nonlinear equations using a Newton-Raphson iteration scheme. Simulations of a shaped-charge jet formation, a Taylor cylinder impact, and an explosively loaded hemishell were selected to demonstrate the utility of this modeling capability. The predicted deformation topology, plastic strain, and porosity distributions are shown for the three simulations.
Rastgou Talemi, Soheil; Kollarovic, Gabriel; Lapytsko, Anastasiya; Schaber, Jörg
2015-01-01
Mathematical modelling has been instrumental to understand kinetics of radiation-induced DNA damage repair and associated secondary cancer risk. The widely accepted two-lesion kinetic (TLK) model assumes two kinds of double strand breaks, simple and complex ones, with different repair rates. Recently, persistent DNA damage associated with telomeres was reported as a new kind of DNA damage. We therefore extended existing versions of the TLK model by new categories of DNA damage and re-evaluated those models using extensive data. We subjected different versions of the TLK model to a rigorous model discrimination approach. This enabled us to robustly select a best approximating parsimonious model that can both recapitulate and predict transient and persistent DNA damage after ionizing radiation. Models and data argue for i) nonlinear dose-damage relationships, and ii) negligible saturation of repair kinetics even for high doses. Additionally, we show that simulated radiation-induced persistent telomere-associated DNA damage foci (TAF) can be used to predict excess relative risk (ERR) of developing secondary leukemia after fractionated radiotherapy. We suggest that TAF may serve as an additional measure to predict cancer risk after radiotherapy using high dose rates. This may improve predicting risk-dose dependency of ionizing radiation especially for long-term therapies. PMID:26359627
Rastgou Talemi, Soheil; Kollarovic, Gabriel; Lapytsko, Anastasiya; Schaber, Jörg
2015-01-01
Mathematical modelling has been instrumental to understand kinetics of radiation-induced DNA damage repair and associated secondary cancer risk. The widely accepted two-lesion kinetic (TLK) model assumes two kinds of double strand breaks, simple and complex ones, with different repair rates. Recently, persistent DNA damage associated with telomeres was reported as a new kind of DNA damage. We therefore extended existing versions of the TLK model by new categories of DNA damage and re-evaluated those models using extensive data. We subjected different versions of the TLK model to a rigorous model discrimination approach. This enabled us to robustly select a best approximating parsimonious model that can both recapitulate and predict transient and persistent DNA damage after ionizing radiation. Models and data argue for i) nonlinear dose-damage relationships, and ii) negligible saturation of repair kinetics even for high doses. Additionally, we show that simulated radiation-induced persistent telomere-associated DNA damage foci (TAF) can be used to predict excess relative risk (ERR) of developing secondary leukemia after fractionated radiotherapy. We suggest that TAF may serve as an additional measure to predict cancer risk after radiotherapy using high dose rates. This may improve predicting risk-dose dependency of ionizing radiation especially for long-term therapies. PMID:26359627
Modeling polyethylene wear acceleration due to femoral head dislocation damage.
Kruger, Karen M; Tikekar, Nishant M; Heiner, Anneliese D; Lannutti, John J; Callaghan, John J; Brown, Thomas D
2014-08-01
Scratching, scraping, and metal transfer to femoral heads commonly accompany acetabular shell contact during dislocation and closed reduction maneuvers. While head damage conceptually leads to accelerated wear, reports on this subject are mainly anecdotal, and differ widely on the potency of such effect. Towards better understanding this relationship, a physically validated finite element (FE) model was used to compute polyethylene wear acceleration propensity of specific head damage patterns on thirteen retrievals. These FE models estimated wear increases averaging half an order of magnitude when compared to simulations for undamaged heads. There was no correlation between the number of dislocations sustained and wear acceleration. These results underscore the importance of implant-gentle closed reduction, and heightened wear monitoring of successfully reduced dislocation patients. PMID:24851789
A Mathematical Model for Estimating Biological Damage Caused by Radiation
NASA Astrophysics Data System (ADS)
Manabe, Yuichiro; Ichikawa, Kento; Bando, Masako
2012-10-01
We propose a mathematical model for estimating biological damage caused by low-dose irradiation. We understand that the linear non threshold (LNT) hypothesis is realized only in the case of no recovery effects. In order to treat the realistic living objects, our model takes into account various types of recovery as well as proliferation mechanism, which may change the resultant damage, especially for the case of lower dose rate irradiation. It turns out that the lower the radiation dose rate, the safer the irradiated system of living object (which is called symbolically ``tissue'' hereafter) can have chances to survive, which can reproduce the so-called dose and dose-rate effectiveness factor (DDREF).
Analytical modeling for gamma radiation damage on silicon photodiodes
NASA Astrophysics Data System (ADS)
Jafari, H.; Feghhi, S. A. H.
2016-04-01
Radiation-induced damage in PIN silicon photodiode induces degradation of the photodiode parameters. In this work, by presenting an analytical model, the effect of gamma dose on the dark current in a PIN photodiode array was investigated. Geant4 was used to obtain the damage constant as a result of primary incident particle fluence and NIEL distribution calculations. Experimental measurements as well as numerical simulation of the semiconductor with ATLAS were carried out to verify and parameterize the analytical model calculations. A reasonable agreement has been found between analytical results and experimental data for BPX65 silicon photodiodes irradiated by a Co-60 gamma source at total doses up to 500 krad under different reverse voltages. Moreover, the results showed that the dark current of each photodiode array pixel has considerably increased by gamma dose irradiation.
NASA Astrophysics Data System (ADS)
Meng, Lie; Wang, Menghan; Liu, Xiao; Wang, Fenglin
2016-04-01
In order to reveal the flow characteristics of Cu-6 %Ag alloy on the condition of hot deformation, the isothermal compression experiments are carried out at the temperatures of 973-1123 K under strain rates of 0.01-10 s-1. The effects of deformation condition on the hot compression deformation behavior are investigated. The low instability strain (ɛ i) behavior at high strain rate (10 s-1) is discussed in this paper. According to the experiment results and analyses, the deformation twinning and inhomogeneous grains are thought to be the possible reasons for low strain cracking. Then, a modified physically based constitutive model is established. The strain for maximum softening rate (\\varepsilon_{ *} ) is quoted in the constitutive equation which is proved that there is a nearly linear relationship between { ln }\\varepsilon_{ *} and { ln }Z . What's more, the correlation coefficient (R) and the average absolute relative error (AARE) are used to evaluate the accuracy of the established constitutive model. The values of R and AARE are 0.99612 and 3.47 %, respectively, which show that the modified constitutive model can exactly reveal the flow stress of Cu-6 %Ag alloy.
NASA Astrophysics Data System (ADS)
Safari, Keivan H.; Zamani, Jamal; Guedes, Rui M.; Ferreira, Fernando J.
2016-02-01
An adiabatic constitutive model is proposed for large strain deformation of polycarbonate (PC) at high strain rates. When the strain rate is sufficiently high such that the heat generated does not have time to transfer to the surroundings, temperature of material rises. The high strain rate deformation behavior of polymers is significantly affected by temperature-dependent constants and thermal softening. Based on the isothermal model which first was introduced by Mulliken and Boyce et al. (Int. J. Solids Struct. 43:1331-1356, 2006), an adiabatic model is proposed to predict the yield and post-yield behavior of glassy polymers at high strain rates. When calculating the heat generated and the temperature changes during the step by step simulation of the deformation, temperature-dependent elastic constants are incorporated to the constitutive equations. Moreover, better prediction of softening phenomena is achieved by the new definition for softening parameters of the proposed model. The constitutive model has been implemented numerically into a commercial finite element code through a user material subroutine (VUMAT). The experimental results, obtained using a split Hopkinson pressure bar, are supported by dynamic mechanical thermal analysis (DMTA) and Decompose/Shift/Reconstruct (DSR) method. Comparison of adiabatic model predictions with experimental data demonstrates the ability of the model to capture the characteristic features of stress-strain curve of the material at very high strain rates.
NASA Astrophysics Data System (ADS)
Zhou, Hao-Miao; Li, Meng-Han; Li, Xiao-Hong; Zhang, Da-Guang
2016-08-01
For a giant magnetostrictive rod under the action of multiple physical loads, such as an external magnetic field, temperature and axial pre-stress, this paper proposes a general one-dimensional nonlinear magneto-thermo-mechanical coupled constitutive model. This model is based on the Taylor expansion of the elastic Gibbs free energy of giant magnetostrictive material and thermodynamic relations from the perspective of macro continuum mechanics. Predictions made using this model are in good agreement with experimental data for magnetization and the magnetostrictive strain curve under the collective effect of pre-stress and temperature. Additionally, the model overcomes the drawback of the existing magneto-thermo-mechanical constitutive model that cannot accurately predict the magnetization and magnetostrictive strain curve for different temperatures and pre-stresses. Furthermore, the constitutive model does not contain an implicit function and is compact, and can thus be applied in both situations of tensile and compressive stress and to both positive and negative magnetostrictive materials, and it is thus appropriate for engineering applications. Comprehensive analysis shows that the model fully describes the nonlinear coupling properties of a magnetic field, magnetostrictive strain and elasticity of a magnetostrictive material subjected to stress, a magnetic field and heat.
Discrete Element Modeling of Impact Damage on Thermal Barrier Coatings
NASA Astrophysics Data System (ADS)
Minor, Peter Michel
Natural gas turbines have become an increasingly important part of the energy landscape in the United States, currently accounting for 19% of all electricity production. Efforts to increase thermal efficiency in gas turbines has led to the adoption of highly porous ceramic thermal barrier coatings (TBCs), which are susceptible to erosion and foreign object impact damage. Despite significant investment to improve the design of TBCs, few numerical tools exist which are capable of both accurately capturing the specific failure mechanisms inherent to TBCs and iterating design parameters without the requirement for coupled experimental data. To overcome these limitations, a discrete element model (DEM) was created to simulate the microstructure of a TBC using a large-scale assembly of bonded particles. Acting as Lagrangian nodes, the particles can be combined to create accurate representations of TBC geometry and porosity. The inclusion of collision-driven particle dynamics and bonds derived from displacement-dependent force functions endow the microstructure model with the ability to deform and reproduce damage in a highly physical manner. Typical TBC damage mechanisms such as compaction, fracture and spallation occur automatically, without having to tune the model based on experimental observation. Therefore, the first order performance of novel TBC designs and materials can be determined numerically, greatly decreasing the cost of development. To verify the utility and effectiveness of the proposed damage model framework, a nanoindentation materials test simulation was developed to serve as a test case. By varying model parameters, such as the porosity of the TBC and maximum applied indenter force, nanoindentation data from more than one hundred distinct permutations was gathered and analyzed. This data was used to calculate the elastic modulus (E) and hardness (H) of the simulated microstructure, which could then be compared to known experimental material property
NASA Technical Reports Server (NTRS)
Kaufman, A.; Laflen, J. H.; Lindholm, U. S.
1985-01-01
Unified constitutive material models were developed for structural analyses of aircraft gas turbine engine components with particular application to isotropic materials used for high-pressure stage turbine blades and vanes. Forms or combinations of models independently proposed by Bodner and Walker were considered. These theories combine time-dependent and time-independent aspects of inelasticity into a continuous spectrum of behavior. This is in sharp contrast to previous classical approaches that partition inelastic strain into uncoupled plastic and creep components. Predicted stress-strain responses from these models were evaluated against monotonic and cyclic test results for uniaxial specimens of two cast nickel-base alloys, B1900+Hf and Rene 80. Previously obtained tension-torsion test results for Hastelloy X alloy were used to evaluate multiaxial stress-strain cycle predictions. The unified models, as well as appropriate algorithms for integrating the constitutive equations, were implemented in finite-element computer codes.
NASA Technical Reports Server (NTRS)
Kaufman, A.; Laflen, J. H.; Lindholm, U. S.
1985-01-01
Unified constitutive material models were developed for structural analyses of aircraft gas turbine engine components with particular application to isotropic materials used for high-pressure stage turbine blades and vanes. Forms or combinations of models independently proposed by Bodner and Walker were considered. These theories combine time-dependent and time-independent aspects of inelasticity into a continuous spectrum of behavior. This is in sharp contrast to previous classical approaches that partition inelastic strain into uncoupled plastic and creep components. Predicted stress-strain responses from these models were evaluated against monotonic and cyclic test results for uniaxial specimens of two cast nickel-base alloys, B1900+Hf and Rene' 80. Previously obtained tension-torsion test results for Hastelloy X alloy were used to evaluate multiaxial stress-strain cycle predictions. The unified models, as well as appropriate algorithms for integrating the constitutive equations, were implemented in finite-element computer codes.
Residual stresses and damage in unidirectional model composites
Chatterjee, A.; Moschler, J.W.; Mall, S.; Kerans, R.J.; Pagano, N.J.
1989-10-01
Unidirectional model composites were fabricated with SiC fibers and different borosilicate glasses to study the effect of residual stress states on the damage progression in these composites. A specially designed straining stage was employed to study the failure modes in these materials under stepwise loading. Although both fiber and matrix cracks were observed in all specimens, the mechanisms of failure were found to be different and strongly dependent on the residual stress state in these materials. 15 refs.
Kinetic Modeling of Damage Repair, Genome Instability, and Neoplastic Transformation
Stewart, Robert D
2007-03-17
Inducible repair and pathway interactions may fundamentally alter the shape of dose-response curves because different mechanisms may be important under low- and high-dose exposure conditions. However, the significance of these phenomena for risk assessment purposes is an open question. This project developed new modeling tools to study the putative effects of DNA damage induction and repair on higher-level biological endpoints, including cell killing, neoplastic transformation and cancer. The project scope included (1) the development of new approaches to simulate the induction and base excision repair (BER) of DNA damage using Monte Carlo methods and (2) the integration of data from the Monte Carlo simulations with kinetic models for higher-level biological endpoints. Methods of calibrating and testing such multiscale biological simulations were developed. We also developed models to aid in the analysis and interpretation of data from experimental assays, such as the pulsed-field gel electrophoresis (PFGE) assay used to quantity the amount of DNA damage caused by ionizing radiation.
ERIC Educational Resources Information Center
Berkowitz, Peter
2009-01-01
After their dismal performance in election 2008, conservatives are taking stock. As they examine the causes that have driven them into the political wilderness and as they explore paths out, they should also take heart. After all, election 2008 shows that America's constitutional order is working as designed. Indeed, while sorting out their errors…
Sparks, Jessica L; Dupaix, Rebecca B
2008-11-01
An understanding of the mechanical deformation behavior of the liver under high strain rate loading conditions could aid in the development of vehicle safety measures to reduce the occurrence of blunt liver injury. The purpose of this study was to develop a constitutive model of the stress-strain behavior of the human liver in blunt impact loading. Experimental stress and strain data was obtained from impact tests of 12 unembalmed human livers using a drop tower technique. A constitutive model previously developed for finite strain behavior of amorphous polymers was adapted to model the observed liver behavior. The elements of the model include a nonlinear spring in parallel with a linear spring and nonlinear dashpot. The model captures three features of liver stress-strain behavior in impact loading: (1) relatively stiff initial modulus, (2) rate-dependent yield or rollover to viscous "flow" behavior, and (3) strain hardening at large strains. Six material properties were used to define the constitutive model. This study represents a novel application of polymer mechanics concepts to understand the rate-dependent large strain behavior of human liver tissue under high strain rate loading. Applications of this research include finite element simulations of injury-producing liver or abdominal impact events. PMID:18751900
Hong, Ming; Su, Zhongqing; Wang, Qiang; Cheng, Li; Qing, Xinlin
2014-03-01
A dedicated modeling technique for comprehending nonlinear characteristics of ultrasonic waves traversing in a fatigued medium was developed, based on a retrofitted constitutive relation of the medium by considering the nonlinearities originated from material, fatigue damage, as well as the "breathing" motion of fatigue cracks. Piezoelectric wafers, for exciting and acquiring ultrasonic waves, were integrated in the model. The extracted nonlinearities were calibrated by virtue of an acoustic nonlinearity parameter. The modeling technique was validated experimentally, and the results showed satisfactory consistency in between, both revealing: the developed modeling approach is able to faithfully simulate fatigue crack-incurred nonlinearities manifested in ultrasonic waves; a cumulative growth of the acoustic nonlinearity parameter with increasing wave propagation distance exists; such a parameter acquired via a sensing path is nonlinearly related to the offset distance from the fatigue crack to that sensing path; and neither the incidence angle of the probing wave nor the length of the sensing path impacts on the parameter significantly. This study has yielded a quantitative characterization strategy for fatigue cracks using embeddable piezoelectric sensor networks, facilitating deployment of structural health monitoring which is capable of identifying small-scale damage at an embryo stage and surveilling its growth continuously. PMID:24156928
Molecular dynamics modelling of radiation damage in zircon
NASA Astrophysics Data System (ADS)
Grechanovsky, A. E.
2009-04-01
Zircon (ZrSiO4) is among actinide-bearing phases which has been proposed as a crystalline confinement matrix for nuclear waste management, especially for weapon-grade plutonium and UO2 spent fuel in the USA. Zircon is also widely used in geochronology. But, with accumulating α-decay damage, zircon undergoes a radiation induced transition to an amorphous (or metamict) state. So, in the present work molecular dynamics simulations (MD simulations) of zircon structure have been performed to study radiation damage in zircon. In this technique, one simulates the propagation of an energetic particle in a system of atoms interacting via model potentials, by integrating the Newton equations of motion. Author has used version 3.09 of the DL_POLY molecular simulation package. Zircon structure containing 181944 atoms (19x19x21 unit cells) was equilibrated at 300 K for 10 ps, and one Zr atom (usually called the primary knock-on atom, PKA) was given a velocity corresponding to an implantation energy of about 20 keV. MD simulations were performed in the microcanonical ensemble that is under conditions of constant particle number, volume and energy. Results of the MD simulations show that the number of interstitials is equal to 840 atoms. This is very close (4000-5000 atoms for 70 keV recoil atom 234Th) to what is measured in the diffuse x-ray scattering and NMR experiments on amorphous metamict samples (damaged by natural irradiation) of geological age. It has been shown that the damaged structure contains several depleted regions with characteristic sized up to 2,5 nm after single event and up to 4,5 nm after three overlapping events. Furthermore, these events produce channels of depleted matter between the overlapping damaged regions. These channels provide a high-diffusivity path for radiogenic Pb (percolation effect). Loss of radiogenic Pb may result in to incorrect dating of rocks.
NASA Astrophysics Data System (ADS)
Zhang, Wen-Feng; Sha, Wei; Yan, Wei; Wang, Wei; Shan, Yi-Yin; Yang, Ke
2014-08-01
A constitutive equation was established to describe the deformation behavior of a nitride-strengthened (NS) steel through isothermal compression simulation test. All the parameters in the constitutive equation including the constant and the activation energy were precisely calculated for the NS steel. The result also showed that from the stress-strain curves, there existed two different linear relationships between critical stress and critical strain in the NS steel due to the augmentation of auxiliary softening effect of the dynamic strain-induced transformation. In the calculation of processing maps, with the change of Zener-Hollomon value, three domains of different levels of workability were found, namely excellent workability region with equiaxed-grain microstructure, good workability region with "stripe" microstructure, and the poor workability region with martensitic-ferritic blend microstructure. With the increase of strain, the poor workability region first expanded, then shrank to barely existing, but appeared again at the strain of 0.6.
Multiscale modeling of damage in multidirectional composite laminates
NASA Astrophysics Data System (ADS)
Singh, Chandra Veer
90°-plies. The predictions agree well with published experimental data as well as independent FE computations. Limited parametric studies are performed to show usability of SDM for more general laminates. To predict the initiation and growth of intralaminar cracks, an energy based model is proposed in which these cracks initiate and multiply when the work required to form new set of cracks exceeds a laminate dependent critical energy release rate. The approach requires determination of average crack opening and sliding displacements at varying crack spacing. This task is performed through a suitable 3-D FE analysis. In case of off-axis ply cracking, a mixed mode fracture criterion is utilized, where the critical energy release rates in normal and shear modes are determined by fitting the damage model with the experimental data for a reference laminate. The predictions from the model for [0/+/-theta4/01/2]s and [0/90/∓45]s laminates show remarkable agreement with the experimental results. The methodology and the results covered in this dissertation will be of interest to mechanics of materials researchers as well as to engineers in industry where composite materials for structural applications are of interest.
Life prediction modeling based on cyclic damage accumulation
NASA Technical Reports Server (NTRS)
Nelson, Richard S.
1988-01-01
A high temperature, low cycle fatigue life prediction method was developed. This method, Cyclic Damage Accumulation (CDA), was developed for use in predicting the crack initiation lifetime of gas turbine engine materials, where initiation was defined as a 0.030 inch surface length crack. A principal engineering feature of the CDA method is the minimum data base required for implementation. Model constants can be evaluated through a few simple specimen tests such as monotonic loading and rapic cycle fatigue. The method was expanded to account for the effects on creep-fatigue life of complex loadings such as thermomechanical fatigue, hold periods, waveshapes, mean stresses, multiaxiality, cumulative damage, coatings, and environmental attack. A significant data base was generated on the behavior of the cast nickel-base superalloy B1900+Hf, including hundreds of specimen tests under such loading conditions. This information is being used to refine and extend the CDA life prediction model, which is now nearing completion. The model is also being verified using additional specimen tests on wrought INCO 718, and the final version of the model is expected to be adaptable to most any high-temperature alloy. The model is currently available in the form of equations and related constants. A proposed contract addition will make the model available in the near future in the form of a computer code to potential users.
Constitutive modelling of magnetic shape memory alloys with discrete and continuous symmetries
Haldar, K.; Lagoudas, D. C.
2014-01-01
A free energy-based constitutive formulation is considered for magnetic shape memory alloys. Internal state variables are introduced whose evolution describes the transition from reference state to the deformed and transformed one. We impose material symmetry restrictions on the Gibbs free energy and on the evolution equations of the internal state variables. Discrete symmetry is considered for single crystals, whereas continuous symmetry is considered for polycrystalline materials. PMID:25197247
Constitutive modelling of magnetic shape memory alloys with discrete and continuous symmetries.
Haldar, K; Lagoudas, D C
2014-09-01
A free energy-based constitutive formulation is considered for magnetic shape memory alloys. Internal state variables are introduced whose evolution describes the transition from reference state to the deformed and transformed one. We impose material symmetry restrictions on the Gibbs free energy and on the evolution equations of the internal state variables. Discrete symmetry is considered for single crystals, whereas continuous symmetry is considered for polycrystalline materials. PMID:25197247
A constitutive model for the warp-weft coupled non-linear behavior of knitted biomedical textiles.
Yeoman, Mark S; Reddy, Daya; Bowles, Hellmut C; Bezuidenhout, Deon; Zilla, Peter; Franz, Thomas
2010-11-01
Knitted textiles have been used in medical applications due to their high flexibility and low tendency to fray. Their mechanics have, however, received limited attention. A constitutive model for soft tissue using a strain energy function was extended, by including shear and increasing the number and order of coefficients, to represent the non-linear warp-weft coupled mechanics of coarse textile knits under uniaxial tension. The constitutive relationship was implemented in a commercial finite element package. The model and its implementation were verified and validated for uniaxial tension and simple shear using patch tests and physical test data of uniaxial tensile tests of four very different knitted fabric structures. A genetic algorithm with step-wise increase in resolution and linear reduction in range of the search space was developed for the optimization of the fabric model coefficients. The numerically predicted stress-strain curves exhibited non-linear stiffening characteristic for fabrics. For three fabrics, the predicted mechanics correlated well with physical data, at least in one principal direction (warp or weft), and moderately in the other direction. The model exhibited limitations in approximating the linear elastic behavior of the fourth fabric. With proposals to address this limitation and to incorporate time-dependent changes in the fabric mechanics associated with tissue ingrowth, the constitutive model offers a tool for the design of tissue regenerative knit textile implants. PMID:20688383
A damage model for the absence of significant precursory seismicity
NASA Astrophysics Data System (ADS)
Lee, Y.; Turcotte, D. L.; Rundle, J.; Chen, C.
2010-12-01
Acoustic emissions prior to rupture indicate precursory damage. Laboratory studies of frictional sliding on model faults feature accelerating rates of acoustic emissions prior to rupture. Precursory seismic emissions are not generally observed prior to earthquakes. To address the problem of precursory damage we consider failure in a fiber-bundle model. We observe a clearly defined nucleation phase followed by a catastrophic rupture. The fibers are hypothesized to represent asperities on a fault. Two limiting behaviors are equal load sharing (stress from a failed fiber is transferred equally to all surviving fibers) and local load sharing (stress from a failed fiber is transferred to adjacent fibers). We show that precursory damage in the nucleation phase is greatly reduced in the local-load sharing limit. We argue that laboratory experiments on fracture involve near-uniform load sharing whereas actual faults involve local load sharing. When one asperity fails on a fault the force carried by the asperity is transferred to adjacent asperities. We argue that this explains the absence of a well defined nucleation phase prior to an earthquake.
A thermodynamically consistent, damage-dependent, interface debonding model for composites
Johnson, J.N.; Clements, B.E.; Addessio, F.L.; Williams, T.O.
1998-12-31
This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The ability to design composite materials and analyze processing procedures relies on the availability of constitutive models that describe their dynamic response accurately. The strength, damage evolution, and failure of interfaces within composites often dominate their macroscopic performance but are not well characterized. The design of such composites for particular applications requires adequate knowledge of interfacial characteristics. Given the large number of potential loading scenarios that an engineering composite can be subjected to, it is obviously beneficial to have reliable and accurate theoretical methods for their quantitative treatment in numerical calculation. This project addresses the fundamental aspects of interfacial debonding in composites, and examines the basic behavior in practical situations.
Unified Creep Plasticity Damage (UCPD) Model for Rigid Polyurethane Foams.
Neilsen, Michael K.; Lu, Wei-Yang; Scherzinger, William M.; Hinnerichs, Terry D.; Lo, Chi S.
2015-06-01
Numerous experiments were performed to characterize the mechanical response of several different rigid polyurethane foams (FR3712, PMDI10, PMDI20, and TufFoam35) to large deformation. In these experiments, the effects of load path, loading rate, and temperature were investigated. Results from these experiments indicated that rigid polyurethane foams exhibit significant volumetric and deviatoric plasticity when they are compressed. Rigid polyurethane foams were also found to be very strain-rate and temperature dependent. These foams are also rather brittle and crack when loaded to small strains in tension or to larger strains in compression. Thus, a new Unified Creep Plasticity Damage (UCPD) model was developed and implemented into SIERRA with the name Foam Damage to describe the mechanical response of these foams to large deformation at a variety of temperatures and strain rates. This report includes a description of recent experiments and experimental findings. Next, development of a UCPD model for rigid, polyurethane foams is described. Selection of material parameters for a variety of rigid polyurethane foams is then discussed and finite element simulations with the new UCPD model are compared with experimental results to show behavior that can be captured with this model.
Life prediction and constitutive models for engine hot section anisotropic materials
NASA Technical Reports Server (NTRS)
Swanson, G. A.
1984-01-01
The development of directionally solidified and single crystal alloys is perhaps the most important recent advancement in hot section materials technology. The objective is to develop knowledge that enables the designer to improve anisotropic gas turbine parts to their full potential. Two single crystal alloys selected were PWA 1480 and Alloy 185. The coatings selected were an overlay coating, PWA 286, and an aluminide diffusion coating, PWA 273. The constitutive specimens were solid and cylindrical; the fatigue specimens were hollow and cylindrical. Two thicknesses of substrate are utilized. Specimens of both thickness (0.4 and 1.5 mm) will be coated and then tested for tensile, creep, and fatigue properties.
NASA Astrophysics Data System (ADS)
Lin, Y. C.; Zhao, Chun-Yang; Chen, Ming-Song; Chen, Dong-Dong
2016-08-01
The flow behaviors of Ti-6Al-4V alloy are studied by isothermal compressive experiments at the deformation temperature from 850 to 950 °C and strain rate from 0.001 to 1 s-1. To analyze the uncertainties induced by material itself and testing procedure, repetitive compressive tests are conducted under each experimental condition. It is found that the uncertainties of flow behaviors are too great to be ignored. The innovation of the study is that the probability theory is introduced to model flow behaviors. 312 (=531,441) sets of flow curves are created by the resampling method, in which 10,000 sets are used to determine the material parameters of constitutive equations. Therefore, the probability densities of material parameters can be easily obtained. It is found that the probability density functions of the most material parameters are similar to the normal distribution. The values of material parameters with the maximum probability density are selected for the established constitutive model. The advantage of the established constitutive model is that it can describe the most probable flow characteristics of Ti-6Al-4V alloy.
Experimental models of perinatal hypoxic-ischemic brain damage.
Vannucci, R C
1993-01-01
Animal research has provided important information on the pathogenesis of and neuropathologic responses to perinatal cerebral hypoxia-ischemia. In experimental animals, structural brain damage from hypoxia-ischemia has been produced in immature rats, rabbits, guinea pigs, sheep and monkeys (18, 20, 24, 25, 38). Of the several available animal models, the fetal and newborn rhesus monkey and immature rat have been studied most extensively because of their similarities to humans in respect to the physiology of reproduction and their neuroanatomy at or shortly following birth. Given the frequency of occurrence of human perinatal hypoxic-ischemic brain damage and the multiple, often severe neurologic handicaps which ensue in infants and children, it is not surprising that the above described animal models have been developed. These models have provided the basis for investigations to clarify not only physiologic and biochemical mechanisms of tissue injury but also the efficacy of specific management strategies. Hopefully, such animal research will continue to provide important information regarding how best to prevent or minimize the devastating consequences of perinatal cerebral hypoxia-ischemia. PMID:8311995
Elastic-plastic models for multi-site damage
NASA Technical Reports Server (NTRS)
Actis, Ricardo L.; Szabo, Barna A.
1994-01-01
This paper presents recent developments in advanced analysis methods for the computation of stress site damage. The method of solution is based on the p-version of the finite element method. Its implementation was designed to permit extraction of linear stress intensity factors using a superconvergent extraction method (known as the contour integral method) and evaluation of the J-integral following an elastic-plastic analysis. Coarse meshes are adequate for obtaining accurate results supported by p-convergence data. The elastic-plastic analysis is based on the deformation theory of plasticity and the von Mises yield criterion. The model problem consists of an aluminum plate with six equally spaced holes and a crack emanating from each hole. The cracks are of different sizes. The panel is subjected to a remote tensile load. Experimental results are available for the panel. The plasticity analysis provided the same limit load as the experimentally determined load. The results of elastic-plastic analysis were compared with the results of linear elastic analysis in an effort to evaluate how plastic zone sizes influence the crack growth rates. The onset of net-section yielding was determined also. The results show that crack growth rate is accelerated by the presence of adjacent damage, and the critical crack size is shorter when the effects of plasticity are taken into consideration. This work also addresses the effects of alternative stress-strain laws: The elastic-ideally-plastic material model is compared against the Ramberg-Osgood model.
A radiation damage repair model for normal tissues
NASA Astrophysics Data System (ADS)
Partridge, Mike
2008-07-01
A cellular Monte Carlo model describing radiation damage and repair in normal epithelial tissues is presented. The deliberately simplified model includes cell cycling, cell motility and radiation damage response (cell cycle arrest and cell death) only. Results demonstrate that the model produces a stable equilibrium system for mean cell cycle times in the range 24-96 h. Simulated irradiation of these stable equilibrium systems produced a range of responses that are shown to be consistent with experimental and clinical observation, including (i) re-epithelialization of radiation-induced lesions by a mixture of cell migration into the wound and repopulation at the periphery; (ii) observed radiosensitivity that is quantitatively consistent with both rate of induction of irreparable DNA lesions and, independently, with the observed acute oral and pharyngeal mucosal reactions to radiotherapy; (iii) an observed time between irradiation and maximum toxicity that is consistent with experimental data for skin; (iv) quantitatively accurate predictions of low-dose hyper-radiosensitivity; (v) Gomperzian repopulation for very small lesions (~2000 cells) and (vi) a linear rate of re-epithelialization of 5-10 µm h-1 for large lesions (>15 000 cells).
Constitutive modeling for Ti-6Al-4V alloy machining based on the SHPB tests and simulation
NASA Astrophysics Data System (ADS)
Chen, Guang; Ke, Zhihong; Ren, Chengzu; Li, Jun
2016-06-01
A constitutive model is critical for the prediction accuracy of a metal cutting simulation. The highest strain rate involved in the cutting process can be in the range of 104-106 s-1. Flow stresses at high strain rates are close to that of cutting are difficult to test via experiments. Split Hopkinson compression bar (SHPB) technology is used to study the deformation behavior of Ti-6Al-4V alloy at strain rates of 10-4-104s-1. The Johnson Cook (JC) model was applied to characterize the flow stresses of the SHPB tests at various conditions. The parameters of the JC model are optimized by using a genetic algorithm technology. The JC plastic model and the energy density-based ductile failure criteria are adopted in the proposed SHPB finite element simulation model. The simulated flow stresses and the failure characteristics, such as the cracks along the adiabatic shear bands agree well with the experimental results. Afterwards, the SHPB simulation is used to simulate higher strain rate(approximately 3×104 s-1) conditions by minimizing the size of the specimen. The JC model parameters covering higher strain rate conditions which are close to the deformation condition in cutting were calculated based on the flow stresses obtained by using the SHPB tests (10-4-104 s-1) and simulation (up to 3×104 s-1). The cutting simulation using the constitutive parameters is validated by the measured forces and chip morphology. The constitutive model and parameters for high strain rate conditions that are identical to those of cutting were obtained based on the SHPB tests and simulation.
Modeling and simulation for collateral damage estimation in combat
NASA Astrophysics Data System (ADS)
Gordon, Steven C.; Martin, Douglas D.
2005-05-01
Modeling and simulation (M&S) is increasingly used for decision support during combat operations: M&S is going to war! One of the key operational uses of M&S in combat is collateral damage estimation (CDE). Reducing undesired collateral damage (CD) in war and in operations other than war is important to the United States of America. Injuries to noncombatants and damage to protected sites are uniformly avoided by our forces whenever possible in planning and executing combat operations. This desire to limit unwanted CD presents unique challenges to command and control (C2), especially for time-sensitive targeting (TST). The challenges begin the moment a target is identified because CD estimates must meet specified criteria before target approval is granted. Therefore, CDE tools must be accurate, responsive, and human-factored, with graphics that aid C2 decisions. This paper will describe how CDE tools are used to build three-dimensional models of potential target areas and select appropriate munitions, fusing, and delivery in order to minimize predicted CD. The paper will cover the evolution of CDE from using only range rings around the target to improvements through Operation Allied Force, Operation Enduring Freedom, and Operation Iraqi Freedom. Positive CDE feedback from various sources, including the Secretary of Defense, lessons learned, and warfighters will be presented. Current CDE tools in the field and CDE tools used in reachback are being improved, and short-term and long-term improvements in those tools and in the CDE methodology will be described in this paper.
Modelling the shock response of a damageable anisotropic composite material
NASA Astrophysics Data System (ADS)
Lukyanov, Alexander A.
2012-09-01
The purpose of this paper is the investigation of the effect of fibre orientation on the shock response of a damageable carbon fibre-epoxy composite (CFEC). A carbon fibre-epoxy composite (CFEC) shock response in the through-thickness orientation and in one of the fibre directions is significantly different. Modelling the effect of fibre orientation on the shock response of a CFEC has been performed using a generalised decomposition of the stress tensor [A.A. Lukyanov, Int. J. Plasticity 24, 140 (2008)] and an accurate extrapolation of high-pressure shock Hugoniot states to other thermodynamics states for shocked CFEC materials. The analysis of the experimental data subject to the linear relation between shock velocities and particle velocities has shown that damage softening process produces discontinuities both in value and slope in the generalized bulk shock velocity and particle velocity relation [A.A. Lukyanov, Eur Phys J B 74, 35 (2010)]. Therefore, in order to remove these discontinuities, the three-wave structure (non-linear anisotropic, fracture and isotropic elastic waves) that accompanies damage softening process is proposed in this work for describing CFEC behavior under shock loading. A numerical calculation shows that Hugoniot Stress Levels (HELs) agree with the experimental data for selected CFEC material in different directions at low and at high intensities. In the through-thickness orientation, the material behaves similar to a simple polymer. In the fibre direction, the proposed model explains a pronounced ramp, before at sufficiently high stresses, and a much faster rising shock above it. The results are presented and discussed, and future studies are outlined.
Labus, Kevin M; Puttlitz, Christian M
2016-09-01
Computational models of the brain require accurate and robust constitutive models to characterize the mechanical behavior of brain tissue. The anisotropy of white matter has been previously demonstrated; however, there is a lack of data describing the effects of multi-axial loading, even though brain tissue experiences multi-axial stress states. Therefore, a biaxial tensile experiment was designed to more fully characterize the anisotropic behavior of white matter in a quasi-static loading state, and the mechanical data were modeled with an anisotropic hyperelastic continuum model. A probabilistic analysis was used to quantify the uncertainty in model predictions because the mechanical data of brain tissue can show a high degree of variability, and computational studies can benefit from reporting the probability distribution of model responses. The axonal structure in white matter can be heterogeneous and regionally dependent, which can affect computational model predictions. Therefore, corona radiata and corpus callosum regions were tested, and histology and transmission electron microscopy were performed on tested specimens to relate the distribution of axon orientations and the axon volume fraction to the mechanical behavior. These measured properties were implemented into a structural constitutive model. Results demonstrated a significant, but relatively low anisotropic behavior, yet there were no conclusive mechanical differences between the two regions tested. The inclusion of both biaxial and uniaxial tests in model fits improved the accuracy of model predictions. The mechanical anisotropy of individual specimens positively correlated with the measured axon volume fraction, and, accordingly, the structural model exhibited slightly decreased uncertainty in model predictions compared to the model without structural properties. PMID:27214689
Ning, Jinfeng; Xu, Shaowen; Wang, Ying; Lessner, Susan M; Sutton, Michael A; Anderson, Kevin; Bischoff, Jeffrey E
2010-12-01
A series of pressurization and tensile loading experiments on mouse carotid arteries is performed with deformation measurements acquired during each experiment using three-dimensional digital image correlation. Using a combination of finite element analysis and a microstructure-based constitutive model to describe the response of biological tissue, the measured surface strains during pressurization, and the average axial strains during tensile loading, an inverse procedure is used to identify the optimal constitutive parameters for the mouse carotid artery. The results demonstrate that surface strain measurements can be combined with computational methods to identify material properties in a vascular tissue. Additional computational studies using the optimal material parameters for the mouse carotid artery are discussed with emphasis on the significance of the qualitative trends observed. PMID:21142324
Bergström, J S; Kurtz, S M; Rimnac, C M; Edidin, A A
2002-06-01
When subjected to a monotonically increasing deformation state, the mechanical behavior of UHMWPE is characterized by a linear elastic response followed by distributed yielding and strain hardening at large deformations. During the unloading phases of an applied cyclic deformation process, the response is characterized by nonlinear recovery driven by the release of stored internal energy. A number of different constitutive theories can be used to model these experimentally observed events. We compare the ability of the J2-plasticity theory, the "Arruda-Boyce" model, the "Hasan-Boyce" model, and the "Bergström-Boyce" model to reproduce the observed mechanical behavior of ultra-high molecular weight polyethylene (UHMWPE). In addition a new hybrid model is proposed, which incorporates many features of the previous theories. This hybrid model is shown to most effectively predict the experimentally observed mechanical behavior of UHMWPE. PMID:12013180
NASA Astrophysics Data System (ADS)
Sun, Yu; Hu, Lianxi; Ren, Junshuai
2015-03-01
In the present work, the isothermal compression tests of PM alloy Ti-47Al-2Nb-2Cr were carried out in the temperature range of 950-1200 °C. A Gleeble 1500D thermosimulation machine was used, and samples were tested at strain rates ranging from 10-3 to 10-1 s-1. Based on the obtained flow stress curves, the hot deformation behavior was presented. The constitutive relationship of powder metallurgy (PM) Ti-47Al-2Nb-2Cr alloy was developed using an Arrhenius-type constitutive model that involves strain compensation in addition to an artificial neural network model. The accuracy and reliability of the developed models were quantified in terms of statistical parameters such as correlation coefficient and absolute value of relative error. It was found that deformation temperature and strain rate have obvious effects on the flow characteristics, and the flow stress increases with the increasing strain rate and the decreasing temperature. Moreover, the proposed models possess excellent prediction capability of flow stresses for the present alloy during hot deformation. Compared with the traditional Arrhenius-type model, the backpropagation neural network model is more accurate when presenting the isothermal compressing deformation behavior at elevated temperatures for PM Ti-47Al-2Nb-2Cr alloy.
Evaluation for rheological constitutive relations, using the indentation technique
NASA Astrophysics Data System (ADS)
Fang, Lei
1992-01-01
A simple experimental method of determining the rheological constitutive relations is proposed. The method relies upon an analysis of the frictionless contact of a rigid spherical indenter and the rheological materials. The proposal addresses problems in two fields: rheological constitutive models and contact mechanics. It attempts to evaluate the rheological constitutive relations using an indentation technique. A systematic, optimization-based material parameter/function indentation model is proposed. The identification algorithm is based on a modified Marquardt-Levenberg method. A new integral constitutive equation for viscoelastic materials is derived. The derivation is carried out so that a damage function is included in the model in a relatively convenient form. Inclusion of damage effects makes this constitutive equation considerably more general than the widely accepted K-BKZ integral model. The single-step and double-step stress relaxation indentation experiments on asphalt materials were performed. The K-BKZ, Wagner, and nonlinear Volterra models were evaluated. It is demonstrated that the new integral constitutive model shows a very good agreement with the experimental data. The idea of damage function is introduced not only to have a better fit of data, but the damage (or irreversibility) is observed experimentally. Also, the creep indentation tests on composites were presented. A multiaxial theory of creep deformation for particle-strengthened metal matrix composites (Zhu-Weng Theory) was evaluated. The goal of the proposed research is to develop the indentation technique for use in basic mechanical studies. From the indentation test, material response is measured. The data are used in conjunction with the material parameter identification model to optimally back calculate the constitutive relations.
A damage mechanics model for power-law creep and earthquake aftershock and foreshock sequences
NASA Astrophysics Data System (ADS)
Main, Ian G.
2000-07-01
It is common practice to refer to three independent stages of creep under static loading conditions in the laboratory: namely transient, steady-state, and accelerating. Here we suggest a simple damage mechanics model for the apparently trimodal behaviour of the strain and event rate dependence, by invoking two local mechanisms of positive and negative feedback applied to constitutive rules for time-dependent subcritical crack growth. In both phases, the individual constitutive rule for measured strain ɛ takes the form ɛ(t)=ɛ0[1+t/mτ]m, where τ is the ratio of initial crack length to rupture velocity. For a local hardening mechanism (negative feedback), we find that transient creep dominates, with 0
NASA Astrophysics Data System (ADS)
Kuznetsov, E. B.; Leonov, S. S.
2016-03-01
The strain-strength characteristics of aerostructures made of hardening materials under uniaxial tension in creep conditions are determined. The problem is reduced to a system of ordinary differential equations of the kinetic theory of creep with one scalar damage parameter. The approximate solutions of the problem are obtained with the help of the implicit Euler method and of the arc length method in combination with the explicit methods of the Runge-Kutta family for cylindrical St.45 steel samples and 3V titanium alloy plates.
NASA Astrophysics Data System (ADS)
Saptono Duryat, Rahmat; Kim, Choong-Un
2014-06-01
This paper presents further development of the constitutive equations based on model-inspired phenomenological approach. In our previous approach, three figures of merit functions were examined to study the temperature-dependence of yield stress and found two model equations that may work especially well for the small volume materials in the moderate temperature ranges (2
Implementation of integral viscoelastic constitutive models in OpenFOAMxAE computational library
NASA Astrophysics Data System (ADS)
de Araújo, Manuel Silvino Batalha; Fernandes, Célio; Ferrás, Luís Lima; Tukovic, Željko; Jasak, Hrvoje; Nóbrega, João Miguel
2015-04-01
This work reports the implementation and verification of a new solver in OpenFOAM® open source computational library, able to cope with integral viscoelastic models based on the integral upper-convected Maxwell model. The code is verified through the comparison of its predictions with analytical solutions and numerical results obtained with the differential upper-convected Maxwell model.
NASA Astrophysics Data System (ADS)
Williams, Kevin Vaughan
Rapid growth in use of composite materials in structural applications drives the need for a more detailed understanding of damage tolerant and damage resistant design. Current analytical techniques provide sufficient understanding and predictive capabilities for application in preliminary design, but current numerical models applicable to composites are few and far between and their development into well tested, rigorous material models is currently one of the most challenging fields in composite materials. The present work focuses on the development, implementation, and verification of a plane-stress continuum damage mechanics based model for composite materials. A physical treatment of damage growth based on the extensive body of experimental literature on the subject is combined with the mathematical rigour of a continuum damage mechanics description to form the foundation of the model. The model has been implemented in the LS-DYNA3D commercial finite element hydrocode and the results of the application of the model are shown to be physically meaningful and accurate. Furthermore it is demonstrated that the material characterization parameters can be extracted from the results of standard test methodologies for which a large body of published data already exists for many materials. Two case studies are undertaken to verify the model by comparison with measured experimental data. The first series of analyses demonstrate the ability of the model to predict the extent and growth of damage in T800/3900-2 carbon fibre reinforced polymer (CFRP) plates subjected to normal impacts over a range of impact energy levels. The predicted force-time and force-displacement response of the panels compare well with experimental measurements. The damage growth and stiffness reduction properties of the T800/3900-2 CFRP are derived using published data from a variety of sources without the need for parametric studies. To further demonstrate the physical nature of the model, a IM6
A model for damage of microheterogeneous kidney stones
NASA Astrophysics Data System (ADS)
Szeri, Andrew J.; Zohdi, Tarek I.; Blake, John R.
2005-04-01
In this paper, a theoretical framework is developed for the mechanics of kidney stones with an isotropic, random microstructure-such as those comprised of cystine or struvite. The approach is based on a micromechanical description of kidney stones comprised of crystals in a binding matrix. Stress concentration functions are developed to determine load sharing of the particle phase and the binding matrix phase. As an illustration of the theory, the fatigue of kidney stones subject to shock wave lithotripsy is considered. Stress concentration functions are used to construct fatigue life estimates for each phase, as a function of the volume fraction and of the mechanical properties of the constituents, as well as the loading from SWL. The failure of the binding matrix is determined explicitly in a model for the accumulation of distributed damage. Also considered is the amount of material damaged in a representative non-spherical collapse of a cavitation bubble near the stone surface. The theory can be used to assess the importance of microscale heterogeneity on the comminution of renal calculi and to estimate the number of cycles to failure in terms of measurable material properties.
Liu, Kaifeng; Ovaert, Timothy C
2011-04-01
Hydrogels are cross-linked polymer networks swollen with water and are being considered as potential replacements for deceased load bearing tissues such as cartilage. Hydrogels show nonlinear time dependent behavior, and are a challenge to model. A three-element poro-viscoelastic constitutive model was developed based on the structure and nature of the hydrogel. To identify the material parameters, an inverse finite element (FE) technique was used that combines experimental results with FE modeling and an optimization method. Unconfined compression creep tests were conducted on poly(vinyl alcohol) (PVA) and poly(ethylene-co-vinyl alcohol)-poly(vinyl pyrrolidone) (EVAL-PVP) hydrogels manufactured by injection molding. Results from the creep experiments showed that for PVA hydrogels, an increase in polymer concentration correlates with a decrease in the equilibrium water content (EWC) and the creep strain. In EVAL-PVP hydrogels, an increase in the hydrophobic segments (EVAL) correlates with a decrease in the EWC as well as the creep strain. An inverse FE method was used to identify the viscoelastic material parameters of the hydrogels in combination with creep testing using the poro-viscoelastic three-element constitutive model. The elastic modulus estimated from the inverse FE technique showed good agreement with the modulus estimated directly from the test data. PMID:21316632
NASA Astrophysics Data System (ADS)
Wang, L.; Liu, F.; Cheng, J. J.; Zuo, Q.; Chen, C. F.
2016-04-01
Hot deformation behavior of Nickel-based corrosion-resistant alloy (N08028) was studied in compression tests conducted in the temperature range of 1050-1200 °C and the strain rate range of 0.001-1 s-1. The flow stress behavior and microstructural evolution were observed during the hot deformation process. The results show that the flow stress increases with deformation temperature decreasing and strain rate increasing, and that the deformation activation energy ( Q) is not a constant but increases with strain rate increasing at a given strain, which is closely related with dislocation movement. On this basis, a revised strain-dependent hyperbolic sine constitutive model was established, which considered that the "material constants" in the original model vary as functions of the strain and strain rate. The flow curves of N08028 alloy predicted by the proposed model are in good agreement with the experimental results, which indicates that the revised constitutive model can estimate precisely the flow curves of N08028 alloy.
NASA Astrophysics Data System (ADS)
Chan, Roger W.
2003-10-01
Previous studies have shown that vocal fold tissues exhibit nonlinear viscoelastic behavior under different loading conditions. Hysteresis and strain rate dependence of stress-strain curves have been observed for vocal fold ligament and muscle tissues when subjected to sinusoidal tensile loading. Nonlinear viscoelastic response and tissue failure have also been described for vocal fold mucosa subjected to constant strain-rate tests under large-strain shear. These findings cannot be adequately described by the traditional constitutive formulations of linear and quasilinear viscoelasticity. This study attempts to characterize some nonlinear behavior of vocal fold tissues under tensile loading based on a modified version of the Arruda-Boyce (Bergström-Boyce) hyperelastic model for polymers, which has been shown to adequately predict the rate-dependent behavior of some elastomers and biological tissues. Results indicated that the model was only capable of describing the relatively linear portion of the nonlinear stress-strain curves of the vocal fold muscle (at strain smaller than 20%), while failing to predict the exponential increase of stress at higher strain. However, the model was capable of predicting the dependence of stress on strain rate reasonably well. This finding was consistent with the model's assumptions on the constitutive behavior of the two constituent polymer networks.
Constitutive Modeling of Skeletal Muscle Tissue with an Explicit Strain-Energy Function
Odegard, G.M.; Donahue, T.L. Haut; Morrow, D.A.; Kaufman, K.R.
2010-01-01
While much work has previously been done in the modeling of skeletal muscle, no model has, to date, been developed that describes the mechanical behavior with an explicit strain-energy function associated with the active response of skeletal muscle tissue. A model is presented herein that has been developed to accommodate this design consideration using a robust dynamical approach. The model shows excellent agreement with a previously published model of both the active and passive length-tension properties of skeletal muscle. PMID:19045546
I. M. Robertson; A. Beaudoin; J. Lambros
2004-01-05
OAK-135 Development and validation of constitutive models for polycrystalline materials subjected to high strain rate loading over a range of temperatures are needed to predict the response of engineering materials to in-service type conditions (foreign object damage, high-strain rate forging, high-speed sheet forming, deformation behavior during forming, response to extreme conditions, etc.). To account accurately for the complex effects that can occur during extreme and variable loading conditions, requires significant and detailed computational and modeling efforts. These efforts must be closely coupled with precise and targeted experimental measurements that not only verify the predictions of the models, but also provide input about the fundamental processes responsible for the macroscopic response. Achieving this coupling between modeling and experimentation is the guiding principle of this program. Specifically, this program seeks to bridge the length scale between discrete dislocation interactions with grain boundaries and continuum models for polycrystalline plasticity. Achieving this goal requires incorporating these complex dislocation-interface interactions into the well-defined behavior of single crystals. Despite the widespread study of metal plasticity, this aspect is not well understood for simple loading conditions, let alone extreme ones. Our experimental approach includes determining the high-strain rate response as a function of strain and temperature with post-mortem characterization of the microstructure, quasi-static testing of pre-deformed material, and direct observation of the dislocation behavior during reloading by using the in situ transmission electron microscope deformation technique. These experiments will provide the basis for development and validation of physically-based constitutive models, which will include dislocation-grain boundary interactions for polycrystalline systems. One aspect of the program will involve the dire ct
Pal, Saikat; Lindsey, Derek P.; Besier, Thor F.; Beaupre, Gary S.
2013-01-01
Cartilage material properties provide important insights into joint health, and cartilage material models are used in whole-joint finite element models. Although the biphasic model representing experimental creep indentation tests is commonly used to characterize cartilage, cartilage short-term response to loading is generally not characterized using the biphasic model. The purpose of this study was to determine the short-term and equilibrium material properties of human patella cartilage using a viscoelastic model representation of creep indentation tests. We performed 24 experimental creep indentation tests from 14 human patellar specimens ranging in age from 20 to 90 years (median age 61 years). We used a finite element model to reproduce the experimental tests and determined cartilage material properties from viscoelastic and biphasic representations of cartilage. The viscoelastic model consistently provided excellent representation of the short-term and equilibrium creep displacements. We determined initial elastic modulus, equilibrium elastic modulus, and equilibrium Poisson’s ratio using the viscoelastic model. The viscoelastic model can represent the short-term and equilibrium response of cartilage and may easily be implemented in whole-joint finite element models. PMID:23027200
Two-phase damage models of magma-fracturing
NASA Astrophysics Data System (ADS)
Cai, Zhengyu; Bercovici, David
2013-04-01
Damage and fracturing in two-phase and porous flows are relevant for geological process such as magma-fracturing during melt migration, which is associated with the propagation of a pore-generating damage front ahead of high-pressure fluid injection. We therefore examine the propagation of porous flow in a damageable matrix by applying the two-phase theory for compaction and damage proposed by Bercovici et al. (2001a) and Bercovici and Ricard (2003). The movement of the fluid and the solid is governed by the two-phase flow laws, while damage (void generation and microcracking) is treated by considering the generation of interfacial surface energy by deformational work. Calculations of one-dimensional (1-D) flow of fluid migrating buoyantly through compacting and damageable matrix show that damage is mitigated in steady-state largely because of the loss of the velocity gradient at the fluid front. However, in time-dependent flows, linear stability analysis shows that the propagation velocity of porosity waves is strongly dependent on damage. In the damage-free case porosity waves are dispersive in that wave-speed decreases with wavenumber (inverse wavelength); however with damage the dispersion flattens and beyond a critical damage reverses (the wave speed increases with wavenumber). Since normal dispersive behavior balances breaking in the nonlinear wave case, such reversed dispersion implies that damage has a profound effect in the nonlinear limit by facilitating wave front steepening and higher wave velocities. Nonlinear solitary wave solutions are obtained numerically and show that the transmission of porosity waves induces high stress and damage that can push the damage front forward. With damage the porosity waves sharpen and calculations suggest that they can transform from shape-conserving solitary waves into faster high amplitude waves, which is also predicted by the linear theory. Such pulse-like sharper waves may prove effective at promoting fluid
A General Reversible Hereditary Constitutive Model. Part 2; Application to a Titanium Alloy
NASA Technical Reports Server (NTRS)
Arnold, S. M.; Saleeb, A. F.; Castelli, M. G.
1997-01-01
Given the mathematical framework and specific viscoelastic model in Part 1 our primary goal in this second part is focused on model characterization and assessment for the specific titanium alloy, TIMETAL 21S. The model is motivated by experimental evidence suggesting the presence of significant rate/time effects in the so-called quasilinear, reversible, material response range. An explanation of the various experiments performed and their corresponding results are also included. Finally, model correlations and predictions are presented for a wide temperature range.
NASA Technical Reports Server (NTRS)
Arnold, S. M.; Saleeb, A. F.; Tan, H. Q.; Zhang, Y.
1993-01-01
The issue of developing effective and robust schemes to implement a class of the Ogden-type hyperelastic constitutive models is addressed. To this end, special purpose functions (running under MACSYMA) are developed for the symbolic derivation, evaluation, and automatic FORTRAN code generation of explicit expressions for the corresponding stress function and material tangent stiffness tensors. These explicit forms are valid over the entire deformation range, since the singularities resulting from repeated principal-stretch values have been theoretically removed. The required computational algorithms are outlined, and the resulting FORTRAN computer code is presented.
A robust operational model for predicting where tropical cyclone waves damage coral reefs.
Puotinen, Marji; Maynard, Jeffrey A; Beeden, Roger; Radford, Ben; Williams, Gareth J
2016-01-01
Tropical cyclone (TC) waves can severely damage coral reefs. Models that predict where to find such damage (the 'damage zone') enable reef managers to: 1) target management responses after major TCs in near-real time to promote recovery at severely damaged sites; and 2) identify spatial patterns in historic TC exposure to explain habitat condition trajectories. For damage models to meet these needs, they must be valid for TCs of varying intensity, circulation size and duration. Here, we map damage zones for 46 TCs that crossed Australia's Great Barrier Reef from 1985-2015 using three models - including one we develop which extends the capability of the others. We ground truth model performance with field data of wave damage from seven TCs of varying characteristics. The model we develop (4MW) out-performed the other models at capturing all incidences of known damage. The next best performing model (AHF) both under-predicted and over-predicted damage for TCs of various types. 4MW and AHF produce strikingly different spatial and temporal patterns of damage potential when used to reconstruct past TCs from 1985-2015. The 4MW