Crush Performance of Thin Walled Spot-Welded and Weld-Bonded Sections

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Derrick Miller
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1 Crush Performance of Thin Walled Spot-Welded and Weld-Bonded Sections Paul Davidson*, M.S Engineering Prof. Donald Malen University of Michigan, Ann Arbor, MI

2 Acknowledgement This project was sponsored by the Weld Bond Project Team of the Auto Steel Partnership

3 Objective Determine influence of weld pitch and adhesive on axial load deflection characteristics of a hexagonal thin walled section.

4 Expected results Adhesive improves stability and average crush force for thin metals. Adhesive has little effect on thicker, more stable sections. Adhesive is more effective for greater spot weld spacing.

5 Model Geometry - Hex Section column was considered for this drop test simulation. - A 400mm tall column axial impact-loaded with rigid mass of 139kg and 11.15m/s velocity. - Adhesive with uniform thickness of 0.66mm was considered. - Simulation was conducted using LSDYNA Explicit code. Rigid Mass Impacting velocity

Gurson solid model Adhesive Modeling Two modeling methods and 5 Adhesive models benchmarked

6 Physical section Metal Mid Plane Adhesive Mid Plane Metal Mid Plane Continuum model 1. Gurson shell model 2. Gurson solid model Adhesive Modeling Two modeling methods and 5 Adhesive models benchmarked with physical test. Gurson shell model was selected for this study. Cohesive model 1. Arup solid model 2. Johnson-Cook solid model Shell Model Solid Model Tie Break Contact

7 Between spot weld buckling Work Breakdown Without adhesive With adhesive Planar flange Imperfect flange Planar flange Imperfect flange HSLA 350 Thickness (mm) Pitch (mm) DP 590 Thickness (mm) Pitch (mm) HSLA 350 Thickness (mm) Pitch (mm) DP 590 Thickness (mm) Pitch (mm) IHS140 DP 980 Thickness (mm) Pitch (mm ) Thickness (mm) Pitch (mm ) IHS140 DP 980 Thickness (mm) Pitch (mm ) Thickness (mm) Pitch (mm )

8 Response reported are: Fmax Maximum load. Fatotal - Average force taken over the entire displacement. Energy absorbed is given by Responses F max Cripple event Crush event Force Fa total D max Displacement (mm)

9 Low strength Low thickness Data Analysis High strength Low thickness High strength High thickness Pitch [mm] Low strength High thickness Comparison of behavior at the extreme parameters of design. DP890 and IF140 were characterized with strain rate sensitivity.

10 IF140 No Adhesive p = 20mm 60mm 100mm 0.7mm Fmax Fatotal Dmax Fmax Fatotal Dmax Fmax Fatotal Dmax mm m Fmax Fatotal Dmax Fmax Fatotal Dmax Fmax Fatotal Dmax t = 2.2mm Fmax Fatotal Dmax Fmax Fatotal Dmax Fmax Fatotal Dmax All forces in x10 4 N

11 IF140 With Adhesive 20mm 60mm 100mm 0.7mm Fmax Favg Dmax Fmax Favg Dmax Fmax Favg Dmax mm m Fmax Favg Dmax Fmax Favg Dmax Fmax Favg Dmax mm Fmax Favg Dmax Fmax Favg Dmax Fmax Favg Dmax All forces in x10 4 N

12 Qualitative Observations IF140 p=100mm, t=2.2mm Pitch [mm]

13 Cripple Event IF140 p=100mm, t=2.2mm time=0.002sec No Adhesive Adhesive Puckering No Puckering Expected difference in flange buckling mode

14 No adhesive Adhesive Crush Event IF140 p=100mm, t=2.2mm No adhesive case: interweld buckling initiates crush mode with low average force level Force (N) 450, , , , , , , ,000 50,000 no adhesive time=0.010s with adhesive Deformation (m)

15 Qualitative Observations IF140 p=100mm, t=0.7mm Pitch [mm m]

16 Cripple Event No Adhesive IF140 p=100mm, t=0.7mm time=0.001sec Cripple Event Adhesive Puckering No Puckering Expected difference in flange buckling modes Note: natural buckling wave length does not depend on spot weld spacing for no-adhesive case

17 No adhesive Adhesive Crush Event IFS140. t=0.7mm, p=100mm No adhesive case: Expected flange buckling mode -Flange folding. -Euler buckling of corner Force (N) 140, , ,000 80,000 no adhesive 60,000 40,000 time=0.016s with adhesive 20, Deformation (m)

18 Flange Folding v v v v Ivv v v

19 Unstable Crush No adhesive Adhesive IFS140. t=0.7mm, p=100mm Adhesive case: Euler buckling of corner initiates an unstable crushing mode Force (N) 140, , ,000 80,000 60,000 40,000 20,000 0 time=0.034s no adhesive with adhesive Deformation (m)

20 Qualitative Observations DP980 p=100mm, t=2.2mm Pitch [mm m]

average force level no adhesive with adhesive 1,000,000 time=0.

21 Crush Event No adhesive Adhesive DP980 p=100mm, t=2.2mm For this impact energy level, corner crippling dominates average force level no adhesive with adhesive 1,000,000 time=0.004s Force (N) 800, , , , Deformation (m)

22 Qualitative Observations DP980 p=100mm, t=0.7mm Pitch [mm m]

23 DP980, t=0.70mm, p=100mm No adhesive Crush Event Adhesive Adhesive case: corner initiates an unstable 350,000 crushing mode Force (N) 300, , , , ,000 time=0.015s 50, Deformation (m) no adhesive with adhesive

24 EXPECTED Expected v.s Observed OBSERVED Adhesive improves stability and average crush force for thin metals. Adhesive has little effect on thicker, more stable sections. Adhesive is more effective for greater spot weld spacing. Adhesive lowers stability and average crush force for thin metals. Adhesive increases average crush force for thicker sections. Adhesive is not always more effective for greater spot weld spacing.

25 Adhesive v/s No adhesive: Favg 100 Favg: IF Favg: DP980 Pe ercentage Improvement [%] mm 1.5mm 2.2mm SW 20mm 60mm 100mm Per rcentage Improvement [%] mm 1.5mm 2.2mm SW 20mm 60mm 100mm -20 t -20 t Relation of Fatotal improvement is inconsistent with spot weld pitch. Also there is no clear relationship between thickness and Fatotal

26 Adhesive v/s No adhesive: Fmax Percentage Improvement [%] Fmax: IF t SW 0.7mm 20mm 1.5mm 60mm 2.2mm 100mm centage Improvement [%] Per Fmax: DP980 DP590 DP t SW 20mm 60mm 100mm IF140 shows expected increase in F max at low thicknesses.

27 Work done 100 Percentage Improvement [%] mm 1.5mm 2.2mm SW 20mm 60mm 100mm MODELING SIMULATIONS RESULTS -20 t CORRELATION CALCULATION ANALYSIS 5.00E E+05 σ cr-p >σ y DP mm σ cr-p <σ y F Favg[N] 4.00E E E E E E+05 HSLA350 IF140 DP mm :With adhesive : No adhesive Axial deformation Axial force 0m m peak ~25mm >100mm? 1.00E E mm Thick walled section 0.00E p Thin walled section

28 Conclusion For the fixed energy level used in this DOE (mv 2 /2), the mean crush force for the thicker and higher strength conditions was dominated by corner crippling behavior Spot weld pitch does not have a strong, consistent influence on mean crush force improvement with adhesive Plate slenderness is an important indicator for mean crush force. The benefit of adhesive bonding is greater for less slender plates (β small) An adhesive bonded flange can precipitate an unstable crush mode particularly for sections with slender plates Before extending the DOE, it is necessary to understand progressive buckling behavior of the structure (see suggestions for Future Work)

29 Future work Theoretical study of: Buckling Modes Progression during crush Sensitivity study (Robustness) Pillowing Imperfection: flange angle, section shape, etc Strain rate Crush initiator presence and type

30 Thank You!

Crush Performance of Thin Walled Spot- Welded and Weld-Bonded Sections

Crush Performance of Thin Walled Spot- Welded and Weld-Bonded Sections Paul Davidson AUTO503 Capstone Project Submitted to Donald E. Malen, project advisor Sponsored by: Weld-bond group Auto-steel Partnership