Specialist in high strain rate testing and material characterisation for finite element simulation
AutoCAE Ford Supplier ID: ERBSA
Technical Report B
Material Characterisation for Txxxxx
Customer:
xxx
Report Date:
March 20xx
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Report Title: Material Characterisation for Material Txxxxx
Specialist in high strain rate testing and material characterisation for finite element simulation
AutoCAE Ford Supplier ID: ERBSA
Table of Contents Part 1: Tensile Tests Process & MAT24 Card Generation ……………………….. 3 1. 2. 3. 4. 5. 6. 7.
Part 1 – Summary …………………………………………………………………………….. 4 Part 1 – Introduction ………………………………………………………………………….. 4 Tensile tests specimens and test procedures ………………………………………………….. 4 Tensile test results …………………………………………………………………………….. 5 Tensile test data process ………………...……………………………………………….……. 8 MAT24 input card …………………………………………………………………………… 12 Part 1 – Conclusion ……………………………………………………………………………14
Part 2: DYNATUP Test Process & MAT24 Validation …….……………………. 15 1. 2. 3. 4. 5. 6.
Part 2 – Summary ……………………………………………………………………………..16 Part 2 – Introduction …………………………………………………………………………..16 Dynamic drop test - DYNATUP ……………..……………………………………………….17 CAE Model ………………………….…………………………………………………….… 22 MAT24 card validation through DYNATUP correlation ………………………………..……25 Part 2 – Conclusion ……………………………………………………………………………26
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Report Title: Material Characterisation for Material Txxxxx
Specialist in high strain rate testing and material characterisation for finite element simulation
AutoCAE Ford Supplier ID: ERBSA
Part 1
Material Characterisation for Material Txxxxx - Tensile Tests Process - MAT24 Card Generation
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Report Title: Material Characterisation for Material Txxxxx
Specialist in high strain rate testing and material characterisation for finite element simulation
AutoCAE Ford Supplier ID: ERBSA
1. Part 1 - Summary This report provides the data analysis and post process of tensile tests of material TXXXXX with different strain rates in support of the material property characterisation. The MAT24 card for LS-DYNA analysis is then created. The executive summary of the mechanical properties of material TXXXXX at different strain rates are listed in the table below. Strain Rate 0.01 0.1 1 10 100 500
E [MPa] 139320 147653 181350 203763 212641 268776
UTS [MPa] 823 872 890 900 910 962
Yeild [MPa] 500 510 540 590 610 620
UTS At [% ] 24.45% 26.64% 15.87% 14.76% 20.97% 14.21%
2. Part 2 - Introduction Tensile tests with different loading rates of material TXXXXX have been requested by XXX in supporting of the material property characterisation and corresponding MAT24 card. 3. Specimens and Test Procedures The specimens are manufactured from the metal sheets supplied by XXX as shown in Fig. 1. The tests were carried out on AutoCAE high strain rate test machine (Fig. 1) at quasi-static (0.01) and nominal strain rates of 0.1, 1.0, 10, 100 and 500 strain/sec at ambient condition. The displacement/strain control uses an 8mm extensometer. The width of the specimen is 3.18 and thickness 1.5mm.
Fig.1 Specimen geometry and AutoCAE High Strain Rate Test Machine ____________________________________________________________________________________________
Report Title: Material Characterisation for Material Txxxxx
Specialist in high strain rate testing and material characterisation for finite element simulation
AutoCAE Ford Supplier ID: ERBSA
4. Tensile Test Results Figs. 2 to 6 display the engineering stress-strain curves with 5 repeat tests at different strain rates.
Fig.2. Quasi-static tests
Fig.3. Strain rate 0.1 tests ____________________________________________________________________________________________
Report Title: Material Characterisation for Material Txxxxx
Specialist in high strain rate testing and material characterisation for finite element simulation
AutoCAE Ford Supplier ID: ERBSA
Fig.4. Strain rate 1 tests
Fig.5. Strain rate 10 tests
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Report Title: Material Characterisation for Material Txxxxx
Specialist in high strain rate testing and material characterisation for finite element simulation
AutoCAE Ford Supplier ID: ERBSA
Fig.6. Strain rate 100 tests
Fig.7. Strain rate 500 tests
The repeatability of the tests at lower strain rates is good. However, samples 3 and 2 in 0.1 and 10 strain rate test groups are clearly an outliner. Therefore, it is not considered in the data process. The test curves in higher strain rates (higher than 10) are slightly scattered. The average data is then used for the data process. ____________________________________________________________________________________________
Report Title: Material Characterisation for Material Txxxxx
Specialist in high strain rate testing and material characterisation for finite element simulation
AutoCAE Ford Supplier ID: ERBSA
5. Tensile Test Data Process Figure 8 shows a well-known stress-strain curve with definition of key terminologies.
Fig.8. Key terminologies in tensile test curve True stress-strain curves can be calculated based on the equation shown below, where Ɛ and σ are true strain and stress, Ɛ0 and σ0 are engineering strain and stress.
The hardening curve before the necking is reliable. As the section decreases locally and strain tends to increase in that region after necking, the true stress and equivalent plastic strain obtained in above equation is not accurate. The common way to describe the hardening curve after necking is to use theoretical curve fitting equation (up to necking), and then extrapolate the curve beyond the necking. In this report, theoretical Ramberg-Osgood equation is used for this purpose.
Ramberg-Osgood equation:
1
n E K
Where E is the Young's modulus, K and n are the material constants. Figures 9-14 show the engineering, true stress-strain curves and curve fitting K-n based on RambergOsgood equation. The true stress-strain curve is plotted up to UTS. Post-necking behaviour can be described by K-n curve.
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Report Title: Material Characterisation for Material Txxxxx
Specialist in high strain rate testing and material characterisation for finite element simulation
AutoCAE Ford Supplier ID: ERBSA
Figure 9 Quasi-static
Figure 10 Strain rate 0.1
Figure 11 Strain rate 1 ____________________________________________________________________________________________
Report Title: Material Characterisation for Material Txxxxx
Specialist in high strain rate testing and material characterisation for finite element simulation
AutoCAE Ford Supplier ID: ERBSA
Figure 12 Strain rate 10
Figure 13 Strain rate 100
Figure 14 Strain rate 500 ____________________________________________________________________________________________
Report Title: Material Characterisation for Material Txxxxx
Specialist in high strain rate testing and material characterisation for finite element simulation
AutoCAE Ford Supplier ID: ERBSA
Figure 15 shows the overlay-plot of true stress-strain curves with 6 strain rates.
Figure 15 Overlay-plot of true stress-strain curves
Table 1 shows the summary of the key mechanic properties of the material at different strain rates.
Strain Rate 0.01 0.1 1 10 100 500
E [MPa] 139320 147653 181350 203763 212641 268776
UTS [MPa] 823 872 890 900 910 962
Yeild [MPa] 500 510 540 590 610 620
UTS At [% ] 24.45% 26.64% 15.87% 14.76% 20.97% 14.21%
K [MPa] 1378 1432 1390 1343 1340 1410
n 0.208 0.207 0.175 0.1458 0.135 0.1408
A [mm2 ] 4.77 4.77 4.77 4.77 4.77 4.77
Fmax [KN] 3.925 4.159 4.339 4.293 4.274 4.591
____________________________________________________________________________________________
Report Title: Material Characterisation for Material Txxxxx
Specialist in high strain rate testing and material characterisation for finite element simulation
AutoCAE Ford Supplier ID: ERBSA
The strain-rate dependent stress-strain relationship can be described by using Cowper-Simpson equation shown below.
d y
1
] [
1 p
C
Where σy can be yield or ultimate stress, έ is strain rate. In the equation, parameters c and p are determined through numeric test curves fitting. Figure 16 shows the curve-fitting to determine parameters c and p. Therefore, the strain-rate dependent stress-strain relationship of material TXXXXX can be described using Cowper-Simpson equation stated above with c = 1.18E8, p = 8.314 and σy as yield stress.
Figure 16 Cowper-Simpson curve-fitting
6. MAT24 Input Card In LS-DYNA, MAT24 card uses the equivalent plastic strain and stress curves with different strain rates. To derive the material property for MAT card, the true strain is split into two parts, elastic strain and equivalent plastic strain.
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Report Title: Material Characterisation for Material Txxxxx
Specialist in high strain rate testing and material characterisation for finite element simulation
AutoCAE Ford Supplier ID: ERBSA
Then, the elastic strain is removed by “shift and shrink�. This results in the hardening curve that gives yield stress as a function of equivalent plastic strain, as shown below.
The true stress-strain curves of material TXXXXX have been processed in this way. The MAT24 input card for material TXXXXX has been generated in LS-DYNA format as attached file. Figure 17 shows the stress and equivalent plastic strains at different strain rates as MAT24 input.
Figure 17 Yield stress vs equivalent plastic strain as MAT24 input
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Report Title: Material Characterisation for Material Txxxxx
Specialist in high strain rate testing and material characterisation for finite element simulation
AutoCAE Ford Supplier ID: ERBSA
7. Part 1 - Conclusions High strain rate tests on material TXXXXX have been conducted in AutoCAE high strain rate testing machine. Test data has been analysed and processed. The mechanical property of the material has been characterised. MAT24 input card has been generated. MAT24 card has been checked in Oasys Perimer and no error message is found. Depend on the setup of Perimer, one may see one “Warning” message as “Strain X values for table curves are not regular”. This is not a concern and users should ignore this message. MAT24 card has also been used and run in an LY-DYNA model as another checking point. The model runs through with normal termination.
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Report Title: Material Characterisation for Material Txxxxx
Specialist in high strain rate testing and material characterisation for finite element simulation
AutoCAE Ford Supplier ID: ERBSA
Part 2
Material Characterisation for Material TXXXXX - Dynamic Drop Tests Process - MAT24 Card Validation
____________________________________________________________________________________________
Report Title: Material Characterisation for Material Txxxxx
Specialist in high strain rate testing and material characterisation for finite element simulation
AutoCAE Ford Supplier ID: ERBSA
1. Part 2 - Summary In Part 1 of this report, tensile test data of TXXXXX has been processed and MAT24 card has been generated. To validate MAT24 card, dynamic drop tests (knowing as DYNATUP tests) are conducted. Through the correlation to DYNATUP tests, MAT24 input card has been validated for TXXXXX material. 2. Part 2 - Introduction XXX require material property characterisations of sheet metal material TXXXXX to support CAE MAT24 input card in their vehicle crash CAE analysis. Tensile tests at different strain rates have been conducted and test data has been processed to generate original LS-DYNA material MAT24 input cards, which has been presented in Part 1 of this report. Tensile test is one-dimensional test and it provides basic mechanical properties of the material. However, in real life application such as vehicle crash, material undergoes the multi-dimensional loading. Due to such difference, it is always recommended that mechanical properties of material obtained from tensile tests (component tests) should be validated through correlation to sub-system tests, such as dynamic drop test (DYNATUP) or tube crush tests. The process is illustrated in Figure 1. The material property generated through such exercises will provide the high confident material property input in system vehicle crash model. Following this process, XXX has requested sub-system DYNATUP tests with two impact speeds. AutoCAE has conducted the dynamic drop tests for material TXXXXX. CAE model has been generated for the correlation. Through the correlation, original material properties have been validated through the correlation to the response of the dynamic drop tests.
Figure 1 Recommended process for material characterisation ____________________________________________________________________________________________
Report Title: Material Characterisation for Material Txxxxx
Specialist in high strain rate testing and material characterisation for finite element simulation
AutoCAE Ford Supplier ID: ERBSA
3. Dynamic Drop Tests - DYNATUP Dynamic drop test (DYNATUP) is a simple drop test with hammer head impacting to the sample material TXXXXX with defined impact velocity. The test configurations are listed below: (1) Hammer head: 8mm diameter, 23.76kg mass (2) TXXXXX Sample dimension: 105mm*110mm*1.5mm plate cut from the metal sheet supplied by client. The plate is clamped in the test machine. The test area has 76.2mm in diameter in the plate. (3) Nominal impact velocity: velocity 1 - 1m/s, velocity 2 - 8m/s During the tests, data of displacement vs time, acceleration vs time, force vs time are directly measured and force vs displacement and energy vs time are then derived. Figure 2 shows plots of displacement vs time, velocity vs time, force vs displacement and energy vs time for TXXXXX sample 1 test with impact velocity 1m/s (actual measured velocity is 1.03m/s). The details for other samples can be found in the detailed test report Excel sheet.
Figure 2 Key data measurements – example from Sample 1 test @ velocity 1m/s Figure 3 shows force vs time for sample 2-5 tests. Figure 4 shows the overlay plot of force vs time for five repeat sample tests. It is clear that the test curves are very similar. ____________________________________________________________________________________________
Report Title: Material Characterisation for Material Txxxxx
Specialist in high strain rate testing and material characterisation for finite element simulation
AutoCAE Ford Supplier ID: ERBSA
Figure 3 Force vs time for Sample 2-5 @ velocity 1m/s
Figure 4 Overlay plot for force vs time of five repeat tests @ velocity 1m/s ____________________________________________________________________________________________
Report Title: Material Characterisation for Material Txxxxx
Specialist in high strain rate testing and material characterisation for finite element simulation
AutoCAE Ford Supplier ID: ERBSA
At low impact velocity, the hammer head is not able to penetrate the metal sheet. Figure 5 show the tested sample.
Figure 5 Tested Sample 1 @ 1m/s impact velocity Figure 6 shows plots of displacement vs time, velocity vs time, force vs displacement and energy vs time for TXXXXX sample 1 test with impact velocity 8m/s (actual measured velocity is 7.86m/s). The details for other samples can be found in the detailed test report Excel sheet.
Figure 6 Key data measurements – example from Sample 1 test @ velocity 8m/s ____________________________________________________________________________________________
Report Title: Material Characterisation for Material Txxxxx
Specialist in high strain rate testing and material characterisation for finite element simulation
AutoCAE Ford Supplier ID: ERBSA
Figure 7 shows force vs time for sample 2-5 tests. Figure 8 shows the overlay plot of force vs time for five repeat sample tests. It is clear that the test curves are very similar.
Figure 7 Force vs time for Sample 2-5 @ velocity 8m/s
Figure 8 Overlay plot for force vs time of five repeat tests @ velocity 8m/s ____________________________________________________________________________________________
Report Title: Material Characterisation for Material Txxxxx
Specialist in high strain rate testing and material characterisation for finite element simulation
AutoCAE Ford Supplier ID: ERBSA
At high impact velocity, the hammer head is able to penetrate the metal sheet. Figure 9 show the tested sample.
Figure 9 Tested Sample 1 @ 8m/s impact velocity
Figure 10 shows the overlay plot of force vs displacement and force vs time between impact velocity 1m/s and 8m/s.
Force vs Displacement
Force vs Time
Figure 10 Overlay plot of force vs displacement and force vs time between 1m/s and 8m/s
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Report Title: Material Characterisation for Material Txxxxx
Specialist in high strain rate testing and material characterisation for finite element simulation
AutoCAE Ford Supplier ID: ERBSA
4. CAE Model AutoCAE standard CAE model replicating the dynamic drop test is shown in Figure 11 below.
Figure 11 AutoCAE standard CAE model of dynamic drop test The tested sample plate is meshed with nominal element mesh size of 0.5mm. Shell elements are used. The section card for the sample plate is shown in Figure 12.
Figure 12 Section card of the sample plate The sample plate is clamped in blue area outside the test area by using boundary condition SPC illustrated in Figure 13. Rotation of edge is not constrained.
Figure 13 Boundary condition card in the model ____________________________________________________________________________________________
Report Title: Material Characterisation for Material Txxxxx
Specialist in high strain rate testing and material characterisation for finite element simulation
AutoCAE Ford Supplier ID: ERBSA
For material MAT24 card, the TXXXXX material card generated from the tensile test data in Part 1 of this report has been used. Figure 14 shows the MAT24 card and strain rate dependent stress-strain curves used in the correlation.
Figure 14 TXXXXX MAT24 card in the correlation ____________________________________________________________________________________________
Report Title: Material Characterisation for Material Txxxxx
Specialist in high strain rate testing and material characterisation for finite element simulation
AutoCAE Ford Supplier ID: ERBSA
Hammer head is modelled as solid elements with elastic material. The mass of the head is set up as the same mass in the DYNATUP tests. The velocity is also set up as the physical test velocity in the correlation.
Figure 15 Hammer head model set up
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Report Title: Material Characterisation for Material Txxxxx
Specialist in high strain rate testing and material characterisation for finite element simulation
AutoCAE Ford Supplier ID: ERBSA
5. MAT24 Card Validation through DYNATUP Correlation Material TXXXXX MAT24 card has been validated through the correlation of two DYNATUP tests: low velocity and high velocity. The correlation to low velocity impact is able to validate the low strain rate data. The correlation to high velocity impact is able to validate the high strain rate data. Figure 16 show the key parameters for two validation models.
Valiadtion Models Velocity m/s Sample Thickness (mm) Sample Diameter (mm) Hammer Head Diameter (mm) Hammer Head Mass (kg)
Model 1
Model 2
1.04
7.86 1.5 76.2 8 23.76
Figure 16 Key parameters of validation models
Material MAT24 validation in low velocity impact test: at low velocity, the hammer is not able to penetrate through the plate, but local dent around hammer head can be seen clearly for both physical test and validation model, as shown in Figure 17. The local peak stress is higher than UTS in necking phase as shown in Figure 18. Figure 19 shows the force vs time between physical test data and validation model, where both curves are matched quite well.
Figure 17 Low velocity validation model – local dent
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Report Title: Material Characterisation for Material Txxxxx
Specialist in high strain rate testing and material characterisation for finite element simulation
AutoCAE Ford Supplier ID: ERBSA
Figure 18 Low velocity validation model – local stress concentration
Figure 19 Low velocity validation model – Force vs Time comparison
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Report Title: Material Characterisation for Material Txxxxx
Specialist in high strain rate testing and material characterisation for finite element simulation
AutoCAE Ford Supplier ID: ERBSA
Material MAT24 validation in high velocity impact test: at high velocity, the hammer punches through the plate in a very short time, as shown in Figure 20. The impact has created shock wave as this can be seen in stress plot in Figure 21 with circular pattern of the stress wave, which is not seen in low velocity case. As MAT24 is not able to model the complicated progressive failure mechanism of material damage, in the validation simple “Failure Strain” method is used to allow hammer penetrating through the metal. Figure 22 shows the force vs time comparison between validation model and physical test. It is noticed that the discrepancy starts between validation model and physical test when micro-cracks (damage) starts in the physical test marked with red circle. This is because that MAT24 is not capable to model progressive failure mechanism. Otherwise, validation result matches onset of the test curve well.
Figure 20 High velocity validation model – penetration through
Figure 21 High velocity validation model – shock wave
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Report Title: Material Characterisation for Material Txxxxx
Specialist in high strain rate testing and material characterisation for finite element simulation
AutoCAE Ford Supplier ID: ERBSA
Figure 22 High velocity validation model – Force vs Time comparison
Validations with low and high velocities of impact use the same model and MAT24 card. The only different parameter is impact velocity. Yet, the both validations match physical tests well. Therefore, TXXXXX MAT24 card generated from AutoCAE high strain rate tests has been validated.
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Report Title: Material Characterisation for Material Txxxxx
Specialist in high strain rate testing and material characterisation for finite element simulation
AutoCAE Ford Supplier ID: ERBSA
6. Part 2 - Conclusions DYNATUP dynamic impact tests with low and high impact velocities have been conducted at AutoCAE for TXXXXX materials. The correlation to low velocity impact is able to validate the low strain rate data. The correlation to high velocity impact is able to validate the high strain rate data. Using MAT24 card generated from AutoCAE high strain rate tests (Part 1), validation models demonstrate good match between physical tests and CAE models. Therefore, TXXXXX MAT24 card has been validated for system vehicle crash CAE application.
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Report Title: Material Characterisation for Material Txxxxx