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Theoretical Development of an Orthotropic Elasto-Plastic Generalized Composite Material Model

by Paul Du Bois6,223 views

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.

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Aerospace and DefenseAutomotiveCompositesHigh Speed TestingLS-DYNAMechanicalPlasticityResearch PapersValidationYielding/Failure Analysis

Verification and Validation of a Three-Dimensional Generalized Composite Material Model

by Paul Du Bois5,840 views

"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."

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Aerospace and DefenseAutomotiveCompositesHigh Speed TestingLS-DYNAMechanicalPlasticityResearch PapersValidationYielding/Failure Analysis

Experimental and Numerical Investigation of Fracture in Aluminium

by Paul Du Bois5,801 views

"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."

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Aerospace and DefenseHigh Speed TestingLS-DYNAMechanicalMetalsResearch PapersValidationYielding/Failure Analysis

Accuracy Issues in the Simulation of Quasi-Static Experiments for the Purpose of Mesh Regularization

by Paul Du Bois5,676 views

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.

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Aerospace and DefenseAutomotiveExtrusionLS-DYNAMechanicalMetalsNonlinear Material ModelsResearch PapersYielding/Failure Analysis

The Use of Digital Image Correlation (DIC) and Strain Gauges to Validate Simulation 

by DatapointLabs5,829 views

As part of Cornell University's mechanical engineering curriculum and study of classical beam theory, an aluminium beam is deformed to a specific load. Theoretical strains are calculated at certain points along the beam using beam theory, and then verified by using strain gauges placed at these points on the beam. This experiment is then extended to simulation of the same test setup in simulation software, where strains are analyzed at the same points. Discrepancies between the simulation, theory, and strain gauge results have often plagued the test, especially when incorporating more complex beam design. Through use of digital image correlation (DIC) it is possible to pinpoint some of the problem areas in the beam analysis and provide a better understanding of the localized strains that occur at any point in the deformed beam. The use of DIC provides a full field validation of simulation data, rather than a single spot check that strain gauges can provide. This validation technique helps to eliminate error that is associated with strain gauge placement and the possibility of missing strain hot spots that can arise when analyzing complex deformations or geometries.

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ANSYSAerospace and DefenseAutomotiveBiomedicalBuilding MaterialsCAE Vendor/SupplierConsumer ProductsElectonics/ElectricalIndustrial GoodsMaterial SupplierMetalsMold Maker/DesignerPlasticsPresentationsStructural AnalysisToys/Sporting Goods

Validating Simulation Using Digital Image Correlation 

by DatapointLabs5,843 views

There is interest in quantifying the differences between simulation and real life experimentation. This kind of work establishes a baseline for more complex simulations bringing a notion of traceability to the practice of CAE. We present the use of digital image correlation as a way to capture strain fields from component testing and compare these to simulation. Factors that are important in ensuring fidelity between simulation and experiment will be discussed.

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AbaqusAerospace and DefenseAutomotiveBiomedicalCAE Vendor/SupplierCompositesElectonics/ElectricalMaterial SupplierNonlinear Material ModelsPlasticsPresentationsSIMULIAStructural Analysis

Use of Digital Image Correlation to Obtain Material Model Parameters for Composites 

by DatapointLabs5,637 views

The development of material parameters for FEA is heavily reliant on precision material data that captures the stress-strain relationship with fidelity. While conventional methods involving UTMs and extensometers are quite adequate for obtaining such data on a number of materials, there are important cases where they have been known to be inadequate. The testing of composites to obtain directional properties remains a complex task because of the difficulty related to measuring these properties in different orientations. Digital Image Correlation (DIC) methods are able to capture the stress-strain relationship all the way to failure. In this paper, we combine DIC and conventional methods to measure directional properties of composites. We exploit the unique capability of DIC to retroactively place virtual strain gauges in areas of critical interest in the test specimen. Utilising an Iosipescu fixture, we measure shear properties of structured composites in a variety of orientations to compute the parameters of an orthotropic linear elastic material model. Model consistency is checked by validation using Abaqus.

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AbaqusAerospace and DefenseCompositesNonlinear Material ModelsResearch PapersSIMULIAStructural Analysis

Understanding and Coping with Material Modeling Limitations in FEA 

by DatapointLabs5,791 views

The limitations of modeling materials for simulation are discussed, including lack of clarity in material model requirements, gaps between the material data and the model to which it will be fitted, issues in obtaining pertinent properties, difficulties in parameter conversion (fitting), and preparation of input files for the software being used. Means to address these limitations are presented, including understanding the model completely, measuring the correct data with precision on the right material, selecting the best model for the data and ensuring the best fit of the model to the data, validating the model against a simple experiment, and following best practices to create an error-free input file.

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Aerospace and DefenseAutomotiveBiomedicalConsumer ProductsElectonics/ElectricalFoamsHome AppliancesIndustrial GoodsMaterial SupplierPackagingPlasticsPresentationsRubbersToys/Sporting Goods

A Robust Methodology to Calibrate Crash Material Models for Polymers

by DatapointLabs6,875 views

High strain rate material modelling of polymers for use in crash and drop testing has been plagued by a number of problems. These include poor quality and noisy data, material models unsuited to polymer behaviour and unclear material model calibration guidelines. The modelling of polymers is thus a risky proposition with a highly variable success rate. In previous work, we tackled each of the above problems individually. In this paper, we summarize and then proceed to present a material modelling strategy that can be applied for a wide variety of polymers.

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ANSYSAbaqusAerospace and DefenseAltair RADIOSSAutomotiveConsumer ProductsHigh Speed TestingHome AppliancesIndustrial GoodsLS-DYNAMSC.DYTRANMaterial SupplierMechanicalNonlinear Material ModelsPAM-CRASHPackagingPlasticsResearch PapersStructural Analysis

Simulating Plastics in Drop and Crash Tests 

by DatapointLabs5,659 views

If you want a crash simulation involving plastics to yield useful results, it is important to model the material behavior appropriately. The high strain rates have a significant effect on the properties, and failure can be ductile or brittle in nature, depending on a number of factors.

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ANSYSAbaqusAerospace and DefenseAltair RADIOSSAutomotiveBiomedicalConsumer ProductsHigh Speed TestingIndustrial GoodsLS-DYNAMSC.DYTRANMaterial SupplierNonlinear Material ModelsPAM-CRASHPackagingPlasticsResearch PapersStructural AnalysisToys/Sporting Goods