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Research Papers

Plasticity and Fracture Modeling/Experimental Study of a Porous Metal Under Various Strain Rates, Temperatures, and Stress States

[+] Author and Article Information
P. G. Allison

US Army Engineer Research &
Development Center (ERDC),
Vicksburg, MS 39081;
Department of Mechanical Engineering,
Mississippi State University,
Mississippi State, MS 39762

H. Grewal, M. F. Horstemeyer

Department of Mechanical Engineering,
Mississippi State University,
Mississippi State, MS 39762

Y. Hammi

Center for Advanced Vehicular
Systems (CAVS),
Mississippi State University,
Mississippi State, MS 39762

Contributed by the Materials Division of ASME for publication in the JOURNAL OF ENGINEERING MATERIALS AND TECHNOLOGY. Manuscript received December 29, 2011; final manuscript received August 1, 2013; published online September 19, 2013. Editor: Hussein Zbib.

This material is declared a work of the US Government and is not subject to copyright protection in the United States. Approved for public release; distribution is unlimited.

J. Eng. Mater. Technol 135(4), 041008 (Sep 19, 2013) (13 pages) Paper No: MATS-11-1288; doi: 10.1115/1.4025292 History: Received December 29, 2011; Revised August 01, 2013

A microstructure-based internal state variable (ISV) plasticity-damage model was used to model the mechanical behavior of a porous FC-0205 steel alloy that was procured via a powder metal (PM) process. Because the porosity was very high and the nearest neighbor distance (NND) for the pores was close, a new pore coalescence ISV equation was introduced that allows for enhanced pore growth from the concentrated pores. This coalescence equation effectively includes the local stress interaction within the interpore ligament distance between pores and is physically motivated with these highly porous powder metals. Monotonic tension, compression, and torsion tests were performed at various porosity levels and temperatures to obtain the set of plasticity and damage constants required for model calibration. Once the model calibration was achieved, then tension tests on two different notch radii Bridgman specimens were undertaken to study the damage-triaxiality dependence for model validation. Fracture surface analysis was performed using scanning electron microscopy (SEM) to quantify the pore sizes of the different specimens. The validated model was then used to predict the component performance of an automotive PM bearing cap. Although the microstructure-sensitive ISV model has been employed for this particular FC-0205 steel, the model is general enough to be applied to other metal alloys as well.

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References

Figures

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Fig. 1

Coalescence enhancement as a function of strain portraying how an increasing pore diameter increased the coalescence for pore growth

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Fig. 2

Coalescence enhancement as a function of strain portraying how an increasing coalescence exponential, ζ, increased the coalescence for pore growth

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Fig. 3

Coalescence enhancement as a function of strain portraying how a decreasing pore nearest neighbor distance, NND, increased the coalescence for pore growth

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Fig. 4

Internal state variable plasticity-damage model calibration for mean monotonic stress–strain behavior under different stress states and temperatures with a relatively low initial porosity (9%); (a) shows long range transients of the stress–strain behavior up to 20% strain and (b) shows the short range transients up to 2% strain

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Fig. 5

Internal state variable plasticity-damage model calibration for mean monotonic stress–strain behavior under different stress states and temperatures with a high initial porosity (19%): (a) shows long range transients of the stress–strain behavior up to 20% strain and (b) shows the short range transients up to 2% strain

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Fig. 6

Internal state variable plasticity-damage model calibration for mean monotonic tension experimental data with an initial relatively low porosity (9%) and high porosity (19%)

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Fig. 7

Experimental and finite element model simulated stress–strain curves and the associated damage evolution for the uniaxial tension tests carried out at (a) 293 K and (b) 573 K

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Fig. 8

Initial porosity optical micrograph of notch tensile specimens at 293 K for the relatively low porosity (9%) specimen

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Fig. 9

SEM fracture surface images of Bridgman specimens with notch radii of (a) 0.38 cm and (b) 0.15 cm

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Fig. 10

Boundary conditions of the notch Bridgman specimens for finite element analysis with different states of stress triaxiality

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Fig. 11

Comparison of failure location for the (a) R38 and (b) R15 notch Bridgman tensile speciments with failure denoted by the damage parameter in the qaurter space finite element simulations

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Fig. 12

Load–displacement comparison between the experimental results and the FEA results for notch tensile tests (R15 and R38 specimens)

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Fig. 13

Test fixture and loading application of the powder metal steel MBC

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Fig. 14

Plot of load–displacement results for the main bearing caps

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Fig. 15

Finite element model for monotonically loaded test showing (a) the initial porosity solution (SDV28) of the main bearing cap transferred from the compaction model results and (b) the performance model configuration with applied boundary conditions.

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Fig. 16

Comparison of (a) finite element model with (b) experimental results indicating crack initiation at point C and (c) the regions of maximum Von Mises stress with the (d) tabulated results

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Fig. 17

Comparison of the experimental data with the finite element model at two different locations of the main bearing cap (where the strain gage was located)

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