Strain Rate Effects on Vehicle Crash Performance

Transcription

1 Strain Rate Effects on Vehicle Crash Performance Paul Wood, Claus Schley Materials Characterisation and Simulation Project

2 Project Partners OEM SUPPLIERS IARC CONSULTING IARC SUPPLIERS 2

3 NCAP Crash Test Procedures A B C D 3

4 Example of NCAP Crash Test Results a. Example of Low NCAP Score (c.2003) b. Example of High NCAP Score (c.2003) Adult occupant rating Pedestrian rating Test Scores: Front 4 (25%) Side 14 (78%) Pedestrian 4 (11%) Adult occupant rating Pedestrian rating Test Scores: Front 15 (94%) Side 18 (100%) Pedestrian 10 (28%) 4

5 Virtual Crash Testing Structure Acceleration versus Time During Impact Acceleration (g) Time (sec) Protection: Good Adequate Marginal Weak Poor NCAP SCORE 5

6 Simulation Inputs for Virtual Crash Testing $ $ ==================== $ MAT (Material) cards $ ==================== $ *MAT_PIECEWISE_LINEAR_PLASTICITY $ Steel Type? Grade? Batch? Date? $ MID Density E Poisson'sR YielStr E $SR Param C P LC (Load curve or table ID) $ *DEFINE_CURVE $ $ Usage: $ Family of strain rate dependent flow curves Typical material card format in commercial simulation software (ARUP LS-Dyna) 6

7 Variability in Tensile Material Data at Low Speed Engineering Stress-strain for Steel tested in 0 direction Engineering Stress-Strain Data, Steel DP600 (standard specimen (EN : in 0 deg. 50 direction, mm gauge 50 mm length) gauge length) Stress [MPa] Specimen A1 Specimen A2 Specimen B1 Specimen B2 Specimen B3 Specimen B4 Specimen B5 Specimen C1 Specimen C2 Specimen C Strain [%] 7

8 Comparing Tensile Material Data Tested at a Strain Rate of 10 s -1 across Ten Labs 8

9 Process to Validate Strain Rate Dependent Material Data for Crash Design Level 1 Level 2 Level 3 Generate material data across strain rate range of interest 9

10 New High Speed Test Facility at IARC Fast Jaw Grip Knock-out wedge Specimen Fixed or static grip head 10

11 High Speed Tensile Testing Process Aim Comparing Machine and Specimen Mounted Force Load-Filtered Actuator Position, Steel DP600 (2mm), Dynamic (5 m/s) Sensor Outputs for Test Speed of 5 m/s (~ 60/s) Develop economical process that delivers the necessary quality strain rate data Load [kn] Machine Mounted Force Sensor Output Specimen Mounted Force Sensor Output Process Specimen design & control of test boundary conditions 0 0 LVDT Actuator Position [mm] Comparing Machine and Specimen Mounted Force Sensor Outputs for Test Speed of 15 m/s (~ 600/s) COMPARING RAW SENSOR OUTPUTS FOR TARGET VELOCITY 15.1 m/s (~ STRAIN RATE = 605 s-1, DAQ Frequency set to 2.5 MHz) System of measurement Data reduction to create material card Force (kn) LVDT Actuator Velocity 4 2 MACHINE MOUNTED FORCE SENSOR OUTPUT SPECIMEN MOUNTED FORCE SENSOR OUTPUT LVDT VELOCITY m/s (OPEN LOOP CONTROL) LVDT Actuator Position (mm) 11

12 IARC Specimen Designs for High Speed Testing Gauge length Target Strain Rate 80/s = 60 mm Target Strain Rate 600/s = 25 mm Moving grip end Fixed end To a first approximation Strain Rate = Applied Velocity Initial Gauge Length 12

13 Instrumentation of High Speed Tensile Specimen Moving grip end Specimen Calibrated under Quasi-static load 7 Strain Gauge on Gauge Length (quarter bridge) Voltage Output From Strain StrainGauge Signal, Circuits Gain 1000 [v] y = x R 2 = y = x R 2 = mm GL 25 mm GL Linear (60 mm GL) Linear (25 mm GL) Strain Gauges on Static Tab End Force (static load cell) [N] Static Force Applied to Specimen (full bridge) 13

14 Validating Material Data Aim Develop crash component tests to validate strain rate dependent material data Process Crush - Quasi-static and dynamic tests Double hat versus single hat 3-point bend - Quasi-static and dynamic tests 14

15 Crushing on Sled Rig Double Hat Top Hat 15

16 Crush Deformation Modes Double Hat Top Hat Sled impact tests results Zwick quasi-static tests results 16

17 Crush Strain Rate Sensitivity and Model Correlation Average Force Computed Over Successive Displacement Intervals Crush Force (normalised by peak load in double hat ) % 13% 20% 27% 33% 60% Percentage Crush Displacement (normalised by initial length of crush member ). Test impact speed 6500 mm/s. Test low speed 5 mm/s. Model impact speed Model low speed Double hat Top hat 17

18 3-Point Bend Strain Rate Sensitivity and Model Correlation 18