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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
1 May 2012 2
• 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
1 May 2012 3
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
1 May 2012 4
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)
1 May 2012 5
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
∙
Center for Ocean EngineeringNaval Construction & Engineering ProgramDepartment of Mechanical EngineeringExperimental Testing
1 May 2012 7
• Specifically designed loading frames and specimens to achieve varying 3D stress states
Center for Ocean EngineeringNaval Construction & Engineering ProgramDepartment of Mechanical EngineeringSpecimens
23 February 2012 8
• Dogbone– Establish Stress strain– Test Anisotropy
• Notched and Central Hole
• Punch
Center for Ocean EngineeringNaval Construction & Engineering ProgramDepartment of Mechanical EngineeringSpecimens, contd.
23 February 2012 9
• Butterfly (ICL) (shear)
• Industry Shear
Center for Ocean EngineeringNaval Construction & Engineering ProgramDepartment of Mechanical Engineering
2D and 2D Digital Image Correlation (DIC)
1 May 2012
– 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
1 May 2012 11‐2
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0 0.5 1 1.5 2 2.5
Force [kN]
Displacement [mm]
t_1
t_2
Simulation
Center for Ocean EngineeringNaval Construction & Engineering ProgramDepartment of Mechanical EngineeringCalibration
1 May 2012 12
• Find and record the exact point of the onset of fracture
Center for Ocean EngineeringNaval Construction & Engineering ProgramDepartment of Mechanical EngineeringCalibration
1 May 2012 13
• 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
1 May 2012 14
Center for Ocean EngineeringNaval Construction & Engineering ProgramDepartment of Mechanical Engineering
1 May 2012 15
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
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