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Research Papers

Numerical Modeling of the Failure of Magnesium Tubes Under Compressive Loading

[+] Author and Article Information
Jonathan Rossiter

Department of Mechanical and Mechatronics Engineering,  University of Waterloo, Waterloo, ON, N2L 3G1, Canada

Kaan Inal

Department of Mechanical and Mechatronics Engineering,  University of Waterloo, Waterloo, ON, N2L 3G1, Canadakinal@uwaterloo.ca

Raja Mishra

General Motors Research and Development Center, 30500 Mound Road, Warren, MI 48090-9055raj.k.mishra@gm.com

J. Eng. Mater. Technol 134(2), 021008 (Mar 27, 2012) (9 pages) doi:10.1115/1.4005918 History: Received July 27, 2011; Revised December 23, 2011; Published March 26, 2012; Online March 27, 2012

A new finite element (FE) specific failure criterion utilizing hardening rates to quantify bending stress is implemented into the MAT_124 material model in the commercial software LS-DYNA to simulate fracture of extruded AZ31 and cast AM60 magnesium alloy tubes. The simulations are performed by requiring element erosion of hexahedral solid elements in a three-dimensional (3D) FE model when the failure criterion is satisfied at any point in the simulation. Experimental stress–strain curves from tensile and compression tests of the materials are used as inputs in the model. The simulations reproduce the measured load displacement data as well as general features of the experimental failure modes of round and rectangular tubes undergoing axial crush tests. The model is applied to investigate the effects of a variety of design features, such as varying tube wall thickness, preformed bulges, alternate bands of Al and Mg alloys, and cladding Al on magnesium, on the macroscopic strain to failure. The results show that adding multiple preformed bulges to the tubes can increase the strain to failure and reduce the force required to cause deformation. Adding a single bulge concentrates the strain causing reduced macroscopic strain to failure. Placing sections of reduced wall thickness or brazing in sections of aluminum causes stress concentrations which reduce the macroscopic strain to failure. Cladding aluminum onto the outside of the magnesium tube is shown to improve strain to failure.

Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Square tube used in initial validation of the failure criteria

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Figure 3

Square tube mesh

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Figure 4

Room temperature stress versus strain curves for AZ31

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Figure 5

Room temperature stress versus strain curves for AM60

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Figure 6

Room temperature stress versus strain curve for AL5182

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Figure 7

Aluminum (left) and magnesium (right) tubes after 12% deformation. Magnesium resists buckling.

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Figure 8

Tube outer surface longitudinal stress (kPa) due to buckle geometry for round tube axial crush just prior to failure

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Figure 9

Hardening rate versus true strain curves for AZ31

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Figure 10

Failure pattern for round tube simulation

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Figure 11

Failure of round tube experiment

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Figure 12

Failure of square tube simulation

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Figure 13

Failure of square tube experiment [5]

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Figure 14

Stress versus strain curves for two experimental round tube crush tests and the simulated crush test

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Figure 15

Failure of round tube when only strain based failure modes are considered

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Figure 16

Round tube with sections of wall thickness thinned to promote buckling

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Figure 17

Round tube with thinned wall thickness shown in Fig. 1 after deformation

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Figure 18

Round tube with initial preformed buckle

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Figure 19

Round tube with initial preformed buckle shown in Fig. 1 after deformation

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Figure 20

Round tube with multiple preformed bulges

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Figure 21

Round tube with multiple preformed bulges shown in Fig. 2 after deformation

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Figure 22

Stress versus strain curve for round tube with four 3.75 mm preformed bulges

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Figure 23

Round tube with alternating 30 mm layers of aluminum and magnesium

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Figure 24

Round tube with alternating 30 mm layers of aluminum shown in Fig. 2 after deformation

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Figure 25

Round tube of 1 mm magnesium with 1.5 mm aluminum clad to the outside of the tube at failure

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