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Strain Rate Dependent FEM of Laser Shock Induced Residual Stress

  • Colin C. Engebretsen
  • Anthony Palazotto
  • Kristina Langer
Conference paper
Part of the Conference Proceedings of the Society for Experimental Mechanics Series book series (CPSEMS)

Abstract

Laser Shock Peening (LSP) is a process by which the energy of a laser burst produces a plasma shock, transmitting mechanical forces into a substrate material. On metallic structures, LSP produces residual stresses in the substrate which can extend fatigue life and improve surface hardness (Eisensmith, Fatigue effects of laser shock peening minimally detectable partial-through thickness surface cracks. MS thesis, Air Force Institute of Technology, 2017). These resulting stresses are difficult to predict, however, as the LSP process is difficult to model. This difficulty stems from the relatively unknown temporospatial profile of the pressure impulse in relation to settings in the LSP process. A better correlation is desired between FEM predictions, and empirical residual stresses. Residual stress profiles on LSP treated workpieces have been determined by Neutron diffraction in prior work (Eisensmith, Fatigue effects of laser shock peening minimally detectable partial-through thickness surface cracks. MS thesis, Air Force Institute of Technology, 2017). Simulations using Johnson-Cook equations and Mie-Grüneisen equation of state (EOS) were run in Abaqus using an assumed pressure impulse. Initial results show qualitative agreement with empirical LSP results, but still have room for model optimization.

Keywords

Laser shock peen Residual stress Finite element Johnson-Cook Mie-Grüneisen 

Nomenclature

A, B, C, m, n

Johnson-Cook Constants (Material Properties)

c0

Bulk Sound Speed (Material Property)

Em

Energy per Unit Mass

P

Pressure

s

Hugoniot Slope Coefficient (Material Property)

T

Temperature

Tm

Melting Temperature

T0

Reference Temperature

Up

Particle Velocity

Us

Shock Velocity

Γ0

Mie-Grüneisen Constant (Material Property)

η

Nominal Volumetric Compressive Strain

ε

Strain

ε

Strain Rate

ε0

Reference Strain Rate

ρ

Density

ρ0

Reference Density

σy

Flow Stress

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Copyright information

© The Society for Experimental Mechanics, Inc. 2019

Authors and Affiliations

  • Colin C. Engebretsen
    • 1
  • Anthony Palazotto
    • 1
  • Kristina Langer
    • 2
  1. 1.Air Force Institute of TechnologyWright-Patterson AFBUSA
  2. 2.Air Force Research LaboratoryWright-Patterson AFBUSA

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