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A Comparative Review of Damage and Failure Models and a Tabulated Generalization

by Paul Du Bois7,793 views

"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. "

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AutomotiveHigh Speed TestingLS-DYNAMechanicalPlasticityPlasticsRate DependencyResearch PapersYielding/Failure Analysis

A Simplified Approach for Strain-Rate Dependent Hyperelastic Materials with Damage

by Paul Du Bois5,972 views

"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."

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AutomotiveHigh Speed TestingHyperelasticLS-DYNAMechanicalRate DependencyResearch PapersRubbersYielding/Failure Analysis

A semi-analytical model for polymers subjected to high strain rates

by Paul Du Bois5,770 views

"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."

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AutomotiveHigh Speed TestingLS-DYNAMechanicalRate DependencyResearch PapersYielding/Failure Analysis

The Influence of Permanent Volumetric Deformation on the Reduction of the Load Bearing Capability of Plastic Components

by Paul Du Bois5,463 views

"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."

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AutomotiveHigh Speed TestingLS-DYNAMechanicalPlasticsRate DependencyResearch Papers

Comparison of Crash Models for Ductile Plastics

by DatapointLabs6,503 views

There is interest in quantifying the accuracy of different material models being used in LS-DYNA today for the modeling of plastics. In our study, we characterize two ductile, yet different materials, ABS and polypropylene for rate dependent tensile properties and use the data to develop material parameters for the material models commonly used for plastics: MAT_024 and its variants, MAT_089 and MAT_187. We then perform a falling dart impact test which produces a complex multi-axial stress state and simulate this experiment using LS-DYNA. For each material model we are able to compare simulation to actual experiment thereby obtaining a measure of fidelity of the simulation to reality. In this way, we can assess the benefits of using a particular material model for plastics simulation.

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LS-DYNAMechanicalPlasticsRate DependencyResearch PapersValidation

A Simplified Approach to the Simulation of Rubber-like Materials under Dynamic Loading

by Paul Du Bois5,554 views

"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."

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AutomotiveHigh Speed TestingHyperelasticLS-DYNAMechanicalRate DependencyResearch PapersRubbers

Pre-processor Software for Calibration of LS-DYNA® Material Models

by Matereality5,198 views

LS-DYNA contains a wealth of material models that allow for the simulation of transient phenomena. These models are often quite complex and difficult to calibrate. We present CAE Modeler, a generalized pre-processor software used to convert material property data into material parameters for different material models used in CAE. In this paper, CAE Modeler is used to streamline the conversion of rate dependent stress-strain data into material parameters for the MAT_024 material model. The interactive software is capable of handling all three rate dependency options of MAT_024 and outputs a data file that can be read directly into LS-DYNA. Support for other material models is envisaged.

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LS-DYNANonlinear Material ModelsPapersRate DependencyStructural Analysis

SAMP-1: A Semi-Analytical Model for the Simulation of Polymers

by Paul Du Bois5,337 views

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.

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AutomotiveLS-DYNANonlinear Material ModelsPlasticityPlasticsRate DependencyYielding/Failure Analysis

A Novel Technique to Measure Tensile Properties of Plastics at High Strain Rates

by DatapointLabs6,760 views

High strain-rate properties have many applications in the simulation of automotive crash and product drop testing. These properties are difficult to measure. These difficulties result from inaccuracies in extensometry at high strain rates due to extensometer slippage and background noise due to the sudden increase in stress at the start of the test. To eliminate these inaccuracies we use an inferential technique that correlates strain to extension at low strain rates and show that this can be extended to measure strain at higher strain rates

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ANSYSAbaqusAerospace and DefenseAutomotiveConsumer ProductsHigh Speed TestingHome AppliancesLS-DYNAMSC.DYTRANMaterial SupplierMechanicalNonlinear Material ModelsPAM-CRASHPackagingPlasticsRate DependencyResearch PapersStructural AnalysisToys/Sporting Goods