Center for Ocean EngineeringNaval Construction & Engineering ProgramDepartment of Mechanical Engineering

Fracture and Plasticity Characterization of DH-36 Navy Steel

Presented to: Naval Construction and Engineering Ship Design and Technology Symposium

Presented by: LT Chris MacLean, USN

3 May 2012

Center for Ocean EngineeringNaval Construction & Engineering ProgramDepartment of Mechanical EngineeringAgenda

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• Motivation• Background / Introduction• Experimental Testing• Specimens• FE Simulations• Calibration

Center for Ocean EngineeringNaval Construction & Engineering ProgramDepartment of Mechanical EngineeringMotivation

• Calibrate the fracture model for DH-36– Common Ship Construction Steel– Used for extensive testing at NSWC Dahlgren – Blast Protection– Need to fully understand the steel before analyzing the

sandwiched plates consisting of steel backing plates coated with a thick layer of polyurea

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Center for Ocean EngineeringNaval Construction & Engineering ProgramDepartment of Mechanical Engineering

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0 0.05 0.1 0.15 0.2 0.25 0.3

Stre

sses

σ [M

Pa]

Strains ε

Stress vs. strain

Plastic Region

Neck

Background –Yield vs. Fracture

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Elastic Region

Yield Point

Rupture

Onset of Fracture

Young’s Modulus, Density, and Yield Stress

Calibrated Fracture Model

Center for Ocean EngineeringNaval Construction & Engineering ProgramDepartment of Mechanical Engineering

Background – Fracture Models

• Polycrystalline Structure Model

• Mechanism based Model (nucleation, void growth and propagation)

• Phenomenological Physics Based Model

(examples shown)

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Center for Ocean EngineeringNaval Construction & Engineering ProgramDepartment of Mechanical Engineering

Modified Mohr Coulomb (MMC) Fracture Model

• Developed by Professor Wierzbicki and his team at the Impact and Crashworthiness Lab (ICL) at MIT

• Technology developed under the sponsorships of steel, automotive, and aerospace industries

• Proven to require less inputs parameters and result in superior accuracy

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• Fracture is dependent on the state of stress (triaxiality and lode angle) and equivalent strain

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Center for Ocean EngineeringNaval Construction & Engineering ProgramDepartment of Mechanical EngineeringExperimental Testing

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• Specifically designed loading frames and specimens to achieve varying 3D stress states

Center for Ocean EngineeringNaval Construction & Engineering ProgramDepartment of Mechanical EngineeringSpecimens

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• Dogbone– Establish Stress strain– Test Anisotropy

• Notched and Central Hole

• Punch

Center for Ocean EngineeringNaval Construction & Engineering ProgramDepartment of Mechanical EngineeringSpecimens, contd.

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• Butterfly (ICL) (shear)

• Industry Shear

Center for Ocean EngineeringNaval Construction & Engineering ProgramDepartment of Mechanical Engineering

2D and 2D Digital Image Correlation (DIC)

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– Accurate Strain Data– Match Experiment to Simulation

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Center for Ocean EngineeringNaval Construction & Engineering ProgramDepartment of Mechanical EngineeringSimulations

• FE Simulations conducted and validated (matching force - displacement) for all specimens

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0 0.5 1 1.5 2 2.5

Force [kN]

Displacement [mm]

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t_2

Simulation

Center for Ocean EngineeringNaval Construction & Engineering ProgramDepartment of Mechanical EngineeringCalibration

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• Find and record the exact point of the onset of fracture

Center for Ocean EngineeringNaval Construction & Engineering ProgramDepartment of Mechanical EngineeringCalibration

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• Parameters from the surface can be used in a Abaqus (FE software) sub-routine to give element deletion (fracture).

Center for Ocean EngineeringNaval Construction & Engineering ProgramDepartment of Mechanical EngineeringConclusions

• Calibration complete and successful• Industry shear specimen gives inaccurate results• Future Work

– Higher Strain Rates (Impact and Explosive Loading)– Polyurea (Bi-axial modeling)– Pulyurea and DH-36, optimized configuration for blast and impact

protection

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Center for Ocean EngineeringNaval Construction & Engineering ProgramDepartment of Mechanical Engineering

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Questions

• References– Bai, Y., and T. Wierzbicki. "A new model of metal plasticity and

fracture with pressure and lode." International Journal of Plasticity, 2008: 1071-1096

– Xue, Liang, Willis Mock, and Ted Belytschko . "Penetration of DH-36 Steel Plates With and Without Polyurea Coating." Mechanics of Materials, 2010: 981-1003

– Wierzbicki, T, and D Mohr. Research Proposal to establish the Industrial Fracture Consortium 2011-2013. Research Proposal, Cambridge: Impact and Crashworthiness Lab, 2010