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Model for predicting the strain rate dependence - Impact performance of plastic components

High fidelity material models with finite element method-based engineering design tools are useful for predicting the structural performance of plastic components. When compared to metallic materials, plastic distinguishes itself as being highly temperature and loading rate sensitive. Moreover, plastic exhibits special post yield behavior with strain softening and hardening. Therefore, through the use of constitutive models, conceptual designs can be assessed and optimized, thereby shortening the costly prototyping and testing cycles.

This project, sponsored by the American Chemistry Council, is aimed at producing a material database for thermoplastics and developing constitutive models to predict the mechanical responses and failures of polymers. Compression, tension, and impact tests are performed on selected polymeric materials to capture their time, temperature, and stress state dependence, as well as failure mechanisms and large-strain mechanical responses. An Internal State Variable Model (ISV)-based model (MSU model) was developed to account for the time and temperature dependence of these thermoplastics. The MSU material model was implemented into commercial finite element code (ABAQUS), and the model’s predictions were validated through various tests available at different strain rates and temperatures.

The selected thermoplastic materials for this project are:

PC - Lexan 101 (SABIC) (compression)

PC - Lexan LS2 (SABIC) (tensile)

PC - Lexan 141 (DOW) (impact)

PP - PP1105E1 (ExxonMobil)

Co-PP – AX03BE3 (ExxonMobil)


ACC Project Phases

Phase I

During Phase I, experimental tests at room temperature were performed under compression, tension, and impact loading. A material database was established to characterize the time-dependence and the strain to failure for the thermoplastic polycarbonate (PC). An ISV Material Model (MSU model) was evaluated. A fitting routine was established and the model prediction was validated through various tests available in compression, tension, and impact. The MSU model showed its ability to predict the mechanical behavior in compression and tension at 25˚C under various strain rates. Regarding the impact tests, the failure strain obtained from numerical analysis using the MSU model was in good agreement with the impact test results and the data available from prior publications for PC.

GOALS:


1) Perform compressive, tensile, and impact tests at three loading rates at room temperature for polycarbonate (PC).

2) Perform model correlation on the available tension and compression data with loading rate dependencies.

3) Predict and validate the material models on an impact disk for PC.

FINAL REPORT (download link)

Phase II

For Phase II, experimental tests were performed under compression, tension, impact, and three-point bend loading at different strain rates and temperatures for two different thermoplastics: an amorphous polycarbonate (PC) and a semicrystalline polypropylene (PP). A material database was established to capture the time, temperature, and stress state dependencies, as well as failure mechanisms and large-strain mechanical responses of PC and PP. The ISV-based MSU model was improved from Phase I, and the model’s predictions were validated for PC and PP through various tests available at different strain rates and temperatures. The MSU model showed its ability to predict the mechanical behavior of PC and PP in compression, tension, impact and three-point bending tests. Failure criteria, based on the maximum principal stress and equivalent plastic strain, were investigated with mixed results to predict the brittle and ductile failure of PC.

GOALS:

1) Enhance the material database from Phase I by including compression, tension, impact, and three point bending test data performed at different strain rates and temperatures for two different thermoplastics: an amorphous polycarbonate (PC) and a semicrystalline polypropylene (PP).

2) Improve the MSU material model for thermoplastics (developed in Phase I) by accounting for the temperature dependence of thermoplastics.

3) Perform model correlation on the available tension and compression data with loading rate and temperature dependencies for PC and PP.

4) Predict and validate the material model on impact disk and three point bending tests and compare with the failure criteria available in the TED Calculator [Woods and Trantina, 1998] for brittle and ductile failure.

FINAL REPORT (download link)

Phase III

In continuation of the work began in Phase I and II, Phase III continues the development of a structure-property relationship database for selected polymeric materials along with a constitutive framework which captures the material response and failure of the polymers. This phase focused on studying a copolymer polypropylene (co-PP). Compression, tension, impact, and three point bend tests were performed on the co-PP to capture the time, temperature, and stress state dependence of co-PP. The ISV-based MSU model developed during Phase I and II was applied, and fitting routines were used to calibrate the material parameters. The model’s predictions for co-PP were validated through various tests available at different strain rates and temperatures. Failure criteria, obtained from numerical analysis, were applied to predict the brittle or ductile failure of co-PP in the three-point bending tests.

GOALS:

1) Enhance the material database developed in the previous contract by including compression, tension, impact, and three point bending test data performed at different strain rates and temperatures for a copolymer polypropylene (co-PP). (link to test matrix)

2) Improve the MSU material model (developed in previous contract) for PP material.

3) Perform model correlation on the available tension and compression data with loading rate and temperature dependencies for co-PP.

4) Predict and validate the material model on impact disk and three-point bending tests and for co-PP.


FINAL REPORT (download link)

Thermoplastic Materials
Polycarbonate (PC) Polypropylene (PP) Copolymer Polypropylene (co-PP)
Test Matrix (link) Test Matrix (link) Test Matrix (link)
Test Results (link to repository) Test Results (link to repository) Test Results (link to repository)
Model Results (link) Model Results (link) Model Results (link)


Test matrix designed for the mechanical characterization of PC

Series Purpose Specimen Tests Parameters
INSTRON-Compression tests Time and temperature dependence and large deformation Cylindrical (D=12.7 mm,T= 6.35 mm) Temperatures: {-20˚C, 25˚C, 100˚C },Strain rates: {0.0005/s, 0.001/s, 0.007/s}
INSTRON-Tensile tests Time and temperature dependence, large deformation, failure From ASTM D638-03 (Type I) Temperatures: {-20˚C, 25˚C, 100˚C },Strain rates: {0.0005/s, 0.001/s, 0.007/s}
IMPACT Tests with velocity control Time and temperature dependence, failure stress, failure energy Disk(D=100.5 mm,T=3.1 mm) Temperatures: {-20˚C, 25˚C, 100˚C }, Strain rates: {3 mm/s, 30 mm/s, 300 mm/s}
Three-point bending tests on notched specimens Failure (brittle/ductile) Notched Specimens (102 mm x 12.56 mm)Thin Spec.: T=3 mm Thick Spec.: T=6 mm Notch 1: D1=1.6 mm Notch 2: D2=0.38 mm At 25˚C and 0.166 mm/s

Test matrix designed for the mechanical characterization of PP

Series Purpose Specimen Tests Parameters
XRD Crystallinity - -
DMA Viscoelasticity and transition temperatures Rectangular (35.7 mm x 12.7 mm x 3 mm) TTemperatures: [-50˚C; 100˚C],

Strain rates: {1 Hz, 10 Hz]

INSTRON-Compression tests Time and temperature dependence and large deformation Cylindrical (D=5 mm and T=2.5 mm) emperatures: {-20˚C, 25˚C, 70˚C },

Strain rates: {0.0005/s, 0.001/s, 0.01/s, 0.1/s}

INSTRON-Tensile tests Time and temperature dependence, large deformation, failure From ASTM D638-03 (Type I) Temperatures: {-50˚C, 100˚C },

Strain rates: {0.0005/s, 0.007/s, 0.1/s}

IMPACT Tests with velocity control Time and temperature dependence, failure stress, failure energy Plaque (100 mm x 95 mm,T=3 mm) Temperatures: {-20˚C, 25˚C, 70˚C }, Strain rates: {0.3 mm/s, 3 mm/s, 30 mm/s}
Three-point bending tests on notched specimens Failure (brittle/ductile) Notched Specimens (102 mm x 12.56 mm)Thin Spec.: T=3 mm Thick Spec.: T=6 mm Notch 1: D1=1.6 mm Notch 2: D2=0.38 mm At 0.166 mm/s, for temperatures of 25˚C and 70˚C

Test matrix designed for the mechanical characterization of co-PP

Series Purpose Specimen Tests Parameters
INSTRON-Compression tests Time and temperature dependence and large deformation Cylindrical (D=5 mm and T=2.5 mm) Temperatures: {-20˚C, 25˚C, 70˚C },

Strain rates: {0.0005/s, 0.001/s, 0.01/s, 0.1/s}

INSTRON-Tensile tests Time and temperature dependence, large deformation, failure From ASTM D638-03 (Type I) Temperatures: {-20˚C, 25˚C, 70˚C },

Strain rates: {0.0005/s, 0.001/s, 0.01/s}

IMPACT Tests with velocity control Time and temperature dependence, failure stress, failure energy Plaque(100 mm x 95 mm,T=3 mm) TTemperatures: {-20˚C, 25˚C, 70˚C }, Strain rates: {0.3 mm/s, 3 mm/s, 30 mm/s}
Three-point bending tests on notched specimens Failure (brittle/ductile) Notched Specimens (63.25 mm x 12.52 mm) Thin Spec.: T=3.17 mm Thick Spec.: T=5.69 mm Notch 1: D1=1.58 mm Notch 2: D2=0.38 mm At 0.166 mm/s, for temperatures of 25˚C and 70˚C

Model results: See the web page https://icme.hpc.msstate.edu/mediawiki/index.php/Model_Thermoplastic

Test Setups

Test Results


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