July 28, 2015 | by Paul Du Bois | views 4750
FAA William J Huges Technical Center (NJ) conducts a research project to simulate failure in aeroengines and fuselages, main purpose is blade-out containment studies. This involved the implementation in LS-DYNA of a tabulated generalisation of the Johnson-Cook material law with regularisation to accommodate simulation of ductile materials.
...read full post
Mechanical
Metals
Rate Dependency
Yielding/Failure Analysis
Aerospace and Defense
Automotive
High Speed Testing
LS-DYNA
Presentations
Validation
July 27, 2015 | by Paul Du Bois | views 4841
The need for accurate material models to simulate the deformation, damage and failure of polymer matrix composites is becoming critical as these materials are gaining increased usage in the aerospace and automotive industries. While there are several composite material models currently available within LS-DYNA, there are several features that have been identified that could improve the predictive capability of a composite model. To address these needs, a combined plasticity and damage model suitable for use with both solid and shell elements is being developed and is being implemented into LS-DYNA as MAT_213. A key feature of the improved material model is the use of tabulated stress-strain data in a variety of coordinate directions to fully define the stress-strain response of the material. To date, the model development efforts have been focused on creating the plasticity portion of the model. The Tsai-Wu development efforts have focused on creating the plasticity portion of the model. The Tsai-Wu composite failure model has been generalized and extended to a strain-hardening based orthotropic material model with a non-associative flow rule. The coefficients of the yield function, and the stresses to be used in both the yield function and the flow rule are computed based on the input stress-strain curves using the effective plastic strain as the tracking variable. The coefficients in the flow rule are computed based on the obtained stress-strain data. The developed material model is suitable for implementation within LS-DYNA for use in analyzing the nonlinear response of polymer composites.
...read full post
Mechanical
Plasticity
Yielding/Failure Analysis
Aerospace and Defense
Automotive
High Speed Testing
LS-DYNA
Composites
Research Papers
Validation
July 27, 2015 | by Paul Du Bois | views 4451
"A general purpose orthotropic elasto-plastic computational constitutive material model has been
developed to accurately predict the response of composites subjected to high velocity impact.
The three-dimensional orthotropic elasto-plastic composite material model is being implemented
initially for solid elements in LS-DYNA® as MAT213. In order to accurately represent the
response of a composite, experimental stress-strain curves are utilized as input, allowing for a
more general material model that can be used on a variety of composite applications. The
theoretical details are discussed in a companion paper. This paper documents the
implementation, verification and validation of the material model using the T800-F3900
fiber/resin composite material."
...read full post
Mechanical
Plasticity
Yielding/Failure Analysis
Aerospace and Defense
Automotive
High Speed Testing
LS-DYNA
Composites
Research Papers
Validation
July 27, 2015 | by Paul Du Bois | views 4578
"Recently new materials were introduced to enhance different aspects of automotive safety while minimizing the
weight added to the vehicle. Such foams are no longer isotropic but typically show a preferred strong direction due
to their manufacturing process. Different stress/ strain curves are obtained from material testing in different
directions. A new material model was added to the LS-DYNA code in order to allow a correct numerical simulation
of such materials. Ease-of-use was a primary concern in the development of this user-subroutine: we required stress/
strain curves from material testing to be directly usable as input parameters for the numerical model without
conversion. The user-subroutine is implemented as
MAT_TRANSVERSELY_ANISOTROPIC_CRUSHABLE_FOAM, Mat law 142 in LS-DYNA Version 960-1106.
In this paper we summarize the background of the material law and illustrate some applications in the field of
interior head-impact. The obvious advantage of incorporating such detail in the simulation lies in the numerical
assessment of impacts that are slightly offset with respect to the foam’s primary strength direction."
...read full post
Mechanical
Foams
Rate Dependency
Automotive
High Speed Testing
LS-DYNA
Research Papers
July 27, 2015 | by Paul Du Bois | views 4322
Lightweight design is one of the major principles in automotive engineering and has made polymer materials to inherent parts of modern cars. In addition to their lightweight thermoplastics, elastomers, fabric and composites also incur important functions in passive safety. In the age of virtual prototyping, assuring these functions requires the accurate modeling of the mechanical behavior of each component. Due to their molecular structure, polymer materials often show viscoelastic characteristics such as creep, relaxation and recovery. However, considering the general state of the art in crash simulation, the viscoelastic characteristics are mainly neglected or replaced by viscoplastic or hyperelastic and strain rate dependent material models. This is either due to the available material models that are often restricted to linear viscoelasticity and thus cannot model the experimental data or due to the time consuming parameter identification. In this study, a nonlinear viscoelastic material model for foams is developed and implemented as a user material subroutine in LS-DYNA. The material response consists of an equilibrium and a non-equilibrium part. The first one is modeled with a hyperelastic formulation based on the work of Chang [8] and formerly implemented as *MAT_FU_CHANG_FOAM in LS-DYNA (*MAT_083). The second one includes the nonlinear viscoelastic behavior following the multiple integral theory by Green and Rivlin [9]. The polyurethane foam Confor CF-45 used as part of the legform impactor in pedestrian safety was chosen for its highly nonlinear viscoelastic properties to test the presented approach. The investigation shows the ability of the method to reliably simulate some important nonlinear viscoelastic phenomena such as saturation.
...read full post
Mechanical
Foams
Viscoelastic
Automotive
Nonlinear Material Models
LS-DYNA
Research Papers
July 27, 2015 | by Paul Du Bois | views 4310
"Heavy trucks have large masses and only small deformation zones. Because of this, they are loaded
relatively severe in case of a crash. Under those conditions structural response is characterised not
only by plastic deformation but also by failure in terms of cracks or fracture. Hence, failure prediction is
essential for designing such parts.
The following article describes the procedure of generating material models for failure prognosis of
solid parts in the Commercial Vehicles Division at Daimler.
Sheet metal parts are mostly discretised by shell elements. In this case the state of stress is
characterized by hydrostatic pressure over von-Mises effective stress, the so-called triaxiality. For
many real-life load cases which can be modeled by thin shells this ratio is between –2/3 and –2/3.
Within this range the Gurson material model with the Tvergaard Needlemann addition leads to
sufficiently accurate results. Furthermore, the Gurson material model allows considering the effect of
element size, which amongst others is important for ductile materials.
Most often however, in the case of solid parts the state of stress is more complex, which results in a
triaxiality smaller than –1 or larger than 2/3. Gurson material models are usually validated based on
shell meshes and tensile tests with flat bar specimen. If applied to solid parts, these models tend to
underpredict failure . Thus, for solid parts the GURSON_JC material model is used.
The Johnson Cook parameters are derived from an existing Gurson material model. Afterwards the
material model is adapted to test results by modifying the load curve giving failure strain against
triaxiality. This requires tensile tests"
...read full post
Mechanical
Metals
Rate Dependency
Yielding/Failure Analysis
Automotive
High Speed Testing
LS-DYNA
Research Papers
Validation
July 27, 2015 | by Paul Du Bois | views 4434
"To assess the problem of containment after a blade-off accident in an aero-engine by numerical
simulation the FAA has instigated a research effort concerning failure prediction in a number of
relevant materials. Aluminium kicked off the program which involved an intensive testing program
providing failure data under different states of stress, different strain rates and different temperatures.
In particular split Hopkinson bars were used to perform dynamic punch tests on plates of different
thicknesses allowing to investigate the transition between different failure modes such as petaling and
plugging. Ballistic impact tests were performed at NASA GRC for the purpose of validation.
This paper focuses on the numerical simulation effort and a comparison with experimental data is
done. The simulations were performed with LS-DYNA and a tabulated version of the Johnson-Cook
material law was developed in order to increase the generality, flexibility and user-friendliness of the
material model."
...read full post
Mechanical
Metals
Yielding/Failure Analysis
Aerospace and Defense
High Speed Testing
LS-DYNA
Research Papers
Validation
July 27, 2015 | by Paul Du Bois | views 3930
"Reliable prediction of the behavior of structures made from polymers is a topic under considerable investigation in
engineering practice. Especially, if the structure is subjected to dynamic loading, constitutive models considering
the mechanical behavior properly are still not available in commercial finite element codes yet. In our paper, we
present a new constitutive law for polymers which recovers important phenomena like necking, crazing, strain rate
dependency, unloading behavior and damage. In particular, different yield surfaces in compression and tension and
strain rate dependent failure, the latter with damage induced erosion, is taken into account. All relevant parameters
are given directly in the input as load curves, i.e. time consuming parameter identification is not necessary. Moreover,
the models by von Mises and Drucker-Prager are included in the description as special cases.
With the present formulation, standard verification test can be simulated successfully: tensile and compression test,
shear test and three point bending tests."
...read full post
Mechanical
Plastics
Plasticity
Rate Dependency
Yielding/Failure Analysis
Automotive
High Speed Testing
LS-DYNA
Research Papers
July 27, 2015 | by Paul Du Bois | views 6367
"Reliable prediction of damage and failure in structural parts is a major challenge posed
in engineering mechanics. Although solid material models predicting the deformation
behaviour of a structure are increasingly available, reliable prediction of failure remains
still open.
With SAMP (a Semi-Analytical Model for Polymers), a general and flexible plasticity
model is available in LS-DYNA since version 971. Although originally developed for
plastics, the plasticity formulation in SAMP is generally applicable to materials that
exhibit permanent deformation, such as thermoplastics, crushable foam, soil and metals.
In this paper, we present a generalized damage and failure procedure that has been implemented
in SAMP and will be available in LS-DYNA soon. In particular, important
effects such as triaxiality, strain rate dependency, regularization and non-proportional
loading are considered in SAMP. All required physical material parameters are provided
in a user-friendly tabulated way. It is shown that our formalism includes many different
damage and failure models as special cases, such as the well-known formulations by
Johnson-Cook, Chaboche, Lemaitre and Gurson among others. "
...read full post
Mechanical
Plastics
Plasticity
Rate Dependency
Yielding/Failure Analysis
Automotive
High Speed Testing
LS-DYNA
Research Papers
July 22, 2015 | by Paul Du Bois | views 4368
Generating a LS-DYNA material model from cupon-level quasi-static experimental data, developing appropriate failure characteristics, and scaling these characteristics to mesh sizes appropriate for a variety of simulation models requires a regularization procedure. During an Investigation of an anisotropic material model for extruded aluminum, numerical accuracy issues led to unrealistic mesh regularization curves and non-physical simulation behavior. Sensitivity problems due to constitutive material behavior, small mesh sizes, single precision simulations, and simulated test velocity all contributed to these accuracy issues. Detailed analysis into the sources of innaccuracy led to the conclusion that in certain cases, double precision simulations are necesscary for accurate material characterization and mesh regularization.
...read full post
Mechanical
Metals
Yielding/Failure Analysis
Aerospace and Defense
Automotive
Extrusion
Nonlinear Material Models
LS-DYNA
Research Papers
July 22, 2015 | by Paul Du Bois | views 4650
"Simulation of rubber-like materials is usually based on hyperelasticity. If strain-rate dependency has to be
considered viscous dampers are added to the rheological model. A disadvantage of such a description is timeconsuming
parameter identification associated with the damping constants. In this paper, a tabulated formulation is
presented which allows fast generation of input data based on uniaxial static and dynamic tensile tests at different
strain rates. Unloading, i.e. forming of a hysteresis, can also be modeled easily based on a damage formulation. We
show the theoretical background and algorithmic setup of our model which has been implemented in the explicit
solver LS-DYNA [1]-[3]. Apart from purely numerical examples, the validation of a soft and a hard rubber under
loading and subsequent unloading at different strain rates is shown."
...read full post
Mechanical
Rubbers
Hyperelastic
Rate Dependency
Yielding/Failure Analysis
Automotive
High Speed Testing
LS-DYNA
Research Papers
July 22, 2015 | by Paul Du Bois | views 4508
"Reliable prediction of the behaviour of structures made from polymers is a topic
under considerable investigation in engineering practice. Especially, if the
structure is subjected to dynamic loading, constitutive models considering the
mechanical behaviour properly are still not available in commercial finite element
codes.
First, we give an overview of material laws for thermoplastics and show how the
behaviour can be characterized and approximated by using visco-elasticity and
metal plasticity, respectively. Experimental work is presented to point out
important phenomena like necking, strain rate dependency, unloading behaviour
and damage. A constitutive model including the experimental findings is derived.
In particular, different yield surfaces in compression and tension and strain rate
dependent failure, the latter with damage induced erosion, need to be taken into
account. With the present formulation, standard verification tests can be
simulated successfully. Also, an elastic damage model is used to approximate
the unloading behaviour of thermoplastics adequately."
...read full post
Mechanical
Rate Dependency
Yielding/Failure Analysis
Automotive
High Speed Testing
LS-DYNA
Research Papers
July 22, 2015 | by Paul Du Bois | views 4120
"During the past years polymer materials have gained enormous importance in the automotive industry. Especially
their application for interior parts to help in passenger safety load cases and their use for bumper fascias in pedestrian
safety load cases have driven the demand for much more realistic finite element simulations. For such applications
the material model 187 (i.e. MAT_SAMP-1) in LS-DYNA® has been developed.
In the present paper the authors show how the parameters for the rather general model may be adjusted to allow for
the simulation of crazing effects during plastic loading. Crazing is usually understood as inelastic deformation that
exhibits permanent volumetric deformations. Hence a material model that is intended to be applied for polymer
components that show crazing effects during the experimental study, should be capable to produce the correct volumetric
strains during the respective finite element simulation. The paper discusses the real world effect of crazing,
the ideas to capture these effect in a numerical model and exemplifies the theoretical ideas with a real world structural
component finite element model."
...read full post
Mechanical
Plastics
Rate Dependency
Automotive
High Speed Testing
LS-DYNA
Research Papers
April 28, 2015 | by Paul Du Bois | views 4153
"The simulation of rubber materials is becoming increasingly
important in automotive crashworthiness simulations.
Although highly sophisticated material laws are available in
LS-DYNA to model rubber parts, the determination of material
properties can be non-trivial and time consuming. In many
applications, the rubber component is mainly loaded uniaxially
at rather high strain rates. In this paper a simplified material
model for rubber is presented allowing for a fast generation of
input data based on uniaxial static and dynamic test data."
...read full post
Mechanical
Rubbers
Hyperelastic
Rate Dependency
Automotive
High Speed Testing
LS-DYNA
Research Papers
October 14, 2005 | by Paul Du Bois | views 4071
The numerical simulation of structural parts made from plastics is becoming increasingly important nowadays. The fact that almost any structural requirement can be combined in a lightweight, durable and cost effective structure is the driving force behind its widespread application. More and more structural relevant parts are being constructed and manufactured from plastics. This on the other hand drives the demand for reliable and robust methods to design these parts and to predict their structural behaviour. the key ingredients that need to be available are verified, calibrated and validated constitutive models for any family of plastic material. This holds not only true for crashworthiness applications but for any other application field.
...read full post
Plastics
Plasticity
Rate Dependency
Yielding/Failure Analysis
Automotive
Nonlinear Material Models
LS-DYNA
"SImplified Rubber Material Model for Dynamic Loading Applications"
Credits to Dynamore for hosting this paper ...click to view
"The Influence of Permanent Volumetric Deformation on the Reduction of the Load Bearing Capability of Plastic Components"
"During the past years polymer materials have gained enormous importance in the automotive industry. Especially
their application for interior parts to help in passenger safety load cases and their use for bumper fascias in pedestrian
safety load cases have driven the demand for much more realistic finite element simulations. For such applications
the material model 187 (i.e. MAT_SAMP-1) in LS-DYNA® has been developed.
In the present paper the authors show how the parameters for the rather general model may be adjusted to allow for
the simulation of crazing effects during plastic loading. Crazing is usually understood as inelastic deformation that
exhibits permanent volumetric deformations. Hence a material model that is intended to be applied for polymer
components that show crazing effects during the experimental study, should be capable to produce the correct volumetric
strains during the respective finite element simulation. The paper discusses the real world effect of crazing,
the ideas to capture these effect in a numerical model and exemplifies the theoretical ideas with a real world structural
component finite element model."
...click to view
"A semi-analytical model for polymers subjected to high strain rates"
"Reliable prediction of the behaviour of structures made from polymers is a topic
under considerable investigation in engineering practice. Especially, if the
structure is subjected to dynamic loading, constitutive models considering the
mechanical behaviour properly are still not available in commercial finite element
codes.
First, we give an overview of material laws for thermoplastics and show how the
behaviour can be characterized and approximated by using visco-elasticity and
metal plasticity, respectively. Experimental work is presented to point out
important phenomena like necking, strain rate dependency, unloading behaviour
and damage. A constitutive model including the experimental findings is derived.
In particular, different yield surfaces in compression and tension and strain rate
dependent failure, the latter with damage induced erosion, need to be taken into
account. With the present formulation, standard verification tests can be
simulated successfully. Also, an elastic damage model is used to approximate
the unloading behaviour of thermoplastics adequately."
...click to view
"A Simplified Approach for Strain-Rate Dependent Hyperelastic Materials with Damage"
"Simulation of rubber-like materials is usually based on hyperelasticity. If strain-rate dependency has to be
considered viscous dampers are added to the rheological model. A disadvantage of such a description is timeconsuming
parameter identification associated with the damping constants. In this paper, a tabulated formulation is
presented which allows fast generation of input data based on uniaxial static and dynamic tensile tests at different
strain rates. Unloading, i.e. forming of a hysteresis, can also be modeled easily based on a damage formulation. We
show the theoretical background and algorithmic setup of our model which has been implemented in the explicit
solver LS-DYNA [1]-[3]. Apart from purely numerical examples, the validation of a soft and a hard rubber under
loading and subsequent unloading at different strain rates is shown."
...click to view
"Accuracy Issues in the Simulation of Quasi-Static Experiments for the Purpose of Mesh Regularization"
Generating a LS-DYNA material model from cupon-level quasi-static experimental data, developing appropriate failure characteristics, and scaling these characteristics to mesh sizes appropriate for a variety of simulation models requires a regularization procedure. During an Investigation of an anisotropic material model for extruded aluminum, numerical accuracy issues led to unrealistic mesh regularization curves and non-physical simulation behavior. Sensitivity problems due to constitutive material behavior, small mesh sizes, single precision simulations, and simulated test velocity all contributed to these accuracy issues. Detailed analysis into the sources of innaccuracy led to the conclusion that in certain cases, double precision simulations are necesscary for accurate material characterization and mesh regularization.
...click to view
"A Comparative Review of Damage and Failure Models and a Tabulated Generalization"
"Reliable prediction of damage and failure in structural parts is a major challenge posed
in engineering mechanics. Although solid material models predicting the deformation
behaviour of a structure are increasingly available, reliable prediction of failure remains
still open.
With SAMP (a Semi-Analytical Model for Polymers), a general and flexible plasticity
model is available in LS-DYNA since version 971. Although originally developed for
plastics, the plasticity formulation in SAMP is generally applicable to materials that
exhibit permanent deformation, such as thermoplastics, crushable foam, soil and metals.
In this paper, we present a generalized damage and failure procedure that has been implemented
in SAMP and will be available in LS-DYNA soon. In particular, important
effects such as triaxiality, strain rate dependency, regularization and non-proportional
loading are considered in SAMP. All required physical material parameters are provided
in a user-friendly tabulated way. It is shown that our formalism includes many different
damage and failure models as special cases, such as the well-known formulations by
Johnson-Cook, Chaboche, Lemaitre and Gurson among others. "
...click to view
"A Constitutive Formulation for Polymers Subjected to High Strain Rates"
"Reliable prediction of the behavior of structures made from polymers is a topic under considerable investigation in
engineering practice. Especially, if the structure is subjected to dynamic loading, constitutive models considering
the mechanical behavior properly are still not available in commercial finite element codes yet. In our paper, we
present a new constitutive law for polymers which recovers important phenomena like necking, crazing, strain rate
dependency, unloading behavior and damage. In particular, different yield surfaces in compression and tension and
strain rate dependent failure, the latter with damage induced erosion, is taken into account. All relevant parameters
are given directly in the input as load curves, i.e. time consuming parameter identification is not necessary. Moreover,
the models by von Mises and Drucker-Prager are included in the description as special cases.
With the present formulation, standard verification test can be simulated successfully: tensile and compression test,
shear test and three point bending tests."
...click to view
"Experimental and Numerical Investigation of Fracture in Aluminium"
"To assess the problem of containment after a blade-off accident in an aero-engine by numerical
simulation the FAA has instigated a research effort concerning failure prediction in a number of
relevant materials. Aluminium kicked off the program which involved an intensive testing program
providing failure data under different states of stress, different strain rates and different temperatures.
In particular split Hopkinson bars were used to perform dynamic punch tests on plates of different
thicknesses allowing to investigate the transition between different failure modes such as petaling and
plugging. Ballistic impact tests were performed at NASA GRC for the purpose of validation.
This paper focuses on the numerical simulation effort and a comparison with experimental data is
done. The simulations were performed with LS-DYNA and a tabulated version of the Johnson-Cook
material law was developed in order to increase the generality, flexibility and user-friendliness of the
material model."
...click to view
"Development of Material Input Data for Solid Elements under Crash Loads"
"Heavy trucks have large masses and only small deformation zones. Because of this, they are loaded
relatively severe in case of a crash. Under those conditions structural response is characterised not
only by plastic deformation but also by failure in terms of cracks or fracture. Hence, failure prediction is
essential for designing such parts.
The following article describes the procedure of generating material models for failure prognosis of
solid parts in the Commercial Vehicles Division at Daimler.
Sheet metal parts are mostly discretised by shell elements. In this case the state of stress is
characterized by hydrostatic pressure over von-Mises effective stress, the so-called triaxiality. For
many real-life load cases which can be modeled by thin shells this ratio is between –2/3 and –2/3.
Within this range the Gurson material model with the Tvergaard Needlemann addition leads to
sufficiently accurate results. Furthermore, the Gurson material model allows considering the effect of
element size, which amongst others is important for ductile materials.
Most often however, in the case of solid parts the state of stress is more complex, which results in a
triaxiality smaller than –1 or larger than 2/3. Gurson material models are usually validated based on
shell meshes and tensile tests with flat bar specimen. If applied to solid parts, these models tend to
underpredict failure . Thus, for solid parts the GURSON_JC material model is used.
The Johnson Cook parameters are derived from an existing Gurson material model. Afterwards the
material model is adapted to test results by modifying the load curve giving failure strain against
triaxiality. This requires tensile tests"
...click to view
"Nonlinear viscoelastic modeling for foams"
Lightweight design is one of the major principles in automotive engineering and has made polymer materials to inherent parts of modern cars. In addition to their lightweight thermoplastics, elastomers, fabric and composites also incur important functions in passive safety. In the age of virtual prototyping, assuring these functions requires the accurate modeling of the mechanical behavior of each component. Due to their molecular structure, polymer materials often show viscoelastic characteristics such as creep, relaxation and recovery. However, considering the general state of the art in crash simulation, the viscoelastic characteristics are mainly neglected or replaced by viscoplastic or hyperelastic and strain rate dependent material models. This is either due to the available material models that are often restricted to linear viscoelasticity and thus cannot model the experimental data or due to the time consuming parameter identification. In this study, a nonlinear viscoelastic material model for foams is developed and implemented as a user material subroutine in LS-DYNA. The material response consists of an equilibrium and a non-equilibrium part. The first one is modeled with a hyperelastic formulation based on the work of Chang [8] and formerly implemented as *MAT_FU_CHANG_FOAM in LS-DYNA (*MAT_083). The second one includes the nonlinear viscoelastic behavior following the multiple integral theory by Green and Rivlin [9]. The polyurethane foam Confor CF-45 used as part of the legform impactor in pedestrian safety was chosen for its highly nonlinear viscoelastic properties to test the presented approach. The investigation shows the ability of the method to reliably simulate some important nonlinear viscoelastic phenomena such as saturation.
...click to view
"A Material Model for Transversely Anisotropic Crushable Foams in LS-DYNA"
"Recently new materials were introduced to enhance different aspects of automotive safety while minimizing the
weight added to the vehicle. Such foams are no longer isotropic but typically show a preferred strong direction due
to their manufacturing process. Different stress/ strain curves are obtained from material testing in different
directions. A new material model was added to the LS-DYNA code in order to allow a correct numerical simulation
of such materials. Ease-of-use was a primary concern in the development of this user-subroutine: we required stress/
strain curves from material testing to be directly usable as input parameters for the numerical model without
conversion. The user-subroutine is implemented as
MAT_TRANSVERSELY_ANISOTROPIC_CRUSHABLE_FOAM, Mat law 142 in LS-DYNA Version 960-1106.
In this paper we summarize the background of the material law and illustrate some applications in the field of
interior head-impact. The obvious advantage of incorporating such detail in the simulation lies in the numerical
assessment of impacts that are slightly offset with respect to the foam’s primary strength direction."
...click to view
"Verification and Validation of a Three-Dimensional Generalized Composite Material Model"
"A general purpose orthotropic elasto-plastic computational constitutive material model has been
developed to accurately predict the response of composites subjected to high velocity impact.
The three-dimensional orthotropic elasto-plastic composite material model is being implemented
initially for solid elements in LS-DYNA® as MAT213. In order to accurately represent the
response of a composite, experimental stress-strain curves are utilized as input, allowing for a
more general material model that can be used on a variety of composite applications. The
theoretical details are discussed in a companion paper. This paper documents the
implementation, verification and validation of the material model using the T800-F3900
fiber/resin composite material."
...click to view
"Theoretical Development of an Orthotropic Elasto-Plastic Generalized Composite Material Model"
The need for accurate material models to simulate the deformation, damage and failure of polymer matrix composites is becoming critical as these materials are gaining increased usage in the aerospace and automotive industries. While there are several composite material models currently available within LS-DYNA, there are several features that have been identified that could improve the predictive capability of a composite model. To address these needs, a combined plasticity and damage model suitable for use with both solid and shell elements is being developed and is being implemented into LS-DYNA as MAT_213. A key feature of the improved material model is the use of tabulated stress-strain data in a variety of coordinate directions to fully define the stress-strain response of the material. To date, the model development efforts have been focused on creating the plasticity portion of the model. The Tsai-Wu development efforts have focused on creating the plasticity portion of the model. The Tsai-Wu composite failure model has been generalized and extended to a strain-hardening based orthotropic material model with a non-associative flow rule. The coefficients of the yield function, and the stresses to be used in both the yield function and the flow rule are computed based on the input stress-strain curves using the effective plastic strain as the tracking variable. The coefficients in the flow rule are computed based on the obtained stress-strain data. The developed material model is suitable for implementation within LS-DYNA for use in analyzing the nonlinear response of polymer composites.
...click to view
"Development, implementation and Validation of 3-D Failure Model for Aluminium 2024 for High Speed Impact Applications"
FAA William J Huges Technical Center (NJ) conducts a research project to simulate failure in aeroengines and fuselages, main purpose is blade-out containment studies. This involved the implementation in LS-DYNA of a tabulated generalisation of the Johnson-Cook material law with regularisation to accommodate simulation of ductile materials.
...click to view
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