Plastic Deformation of Steel Plates under High Impact Loading

This work was done by National Security Technologies, LLC, under Contract No. DE-AC52-06NA25946 with the U.S. Department of Energy and supported by the

Site-Directed Research and Development Program. Center for Materials & Structures

Plastic Deformation of Steel Plates under High Impact Loading

University of Nevada Las Vegas (UNLV) National Security Technologies LLC (NSTec)

Symposium, March 28 2014

Presented by: Brendan O’Toole, UNLV Professor of Mechanical Engineering

UNLV Collaborators:

Mohamed Trabia, Richard Jennings, Shawoon Roy, Muna Slewa Deepak Somasundarum, Jagadeep Thota, Melissa Matthes

NSTec Collaborators:

Steven Becker, Edward Daykin, Eric Machorro, Timothy Meehan, Robert Hixson, Michael Pena, Carlos Perez, Nathan Snipe, Aaron Luttman, Kristen Crawford, Steven Gardner

DOE/NV/25946--1924



UNLV Two-stage Light Gas Gun

A two-stage light gas gun is used to launch a cylindrical projectile into a target plate at a velocity range of 4.5-6 km/s.

The gun uses either Hydrogen or Helium

• Projectile: Lexan (5.6 mm diameter)

• Target: A36 steel plate (152.4 × 152.4 × 12.7 mm)

The target is bolted on a mounting plate during the experiment.

Laser intervalometer system is used to measure projectile velocity.

UNLV Two-stage Light Gas Gun

Lexan Projectile

Target Mounting Plate Target Chamber Assembly



Experimental Measurements

Single/multi channel Photonic Doppler Velocimetry (PDV/MPDV) system is used to measure velocity from the back surface of the target plate.

PDV is an interferometric technique which measures velocity using Doppler shift of reflected light from moving surface.

For the MPDV system, 9-probe and 25-probe arrangements are used so far.

Flowchart of a single probe PDV system

Typical 25-probe MPDV arrangement

MPDV system assembly Laser unit assembly



Physical Results of Impact on Target Plates

A small crater with a bulge on the back side of the target plate is created as a result of impact.

Spall failure

– Spalling happens on the rear side of the target.

– Shock wave reaches a free boundary surface and the surface is subjected to tensile force.

– The material fails when the tensile pressure is above the material strength.

Physical measurements of crater and bulge are taken typically after every experiment.

Spalling of target plate (sectioned)

Front Side

Back Side

Typical target plate after experiment

Impact crater diameter

measurement

Depth of penetration

measurement

Bulge measurement



Research Objectives • Validate the accuracy and repeatability of the PDV and MPDV

systems for measurement of target plate back face velocity. – Explore probe layout and orientation options. – Use high speed video when available for additional experimental

measurements.

• Compare computational simulation methods for predicting the response of target materials to severe impact loading. – Determine the most appropriate material models for use in the

simulations. – Is there a phase change in A36 steel under these impact conditions. – Compare simulation predictions to experimental data. – Compare deformation geometry of target when subject to different

impact velocities.

• Determine gas gun projectile velocity as a function of operating parameters (type of gas, gas pressure, gun powder mass, …)

• Develop a collaborative working relationship between UNLV and NSTec



Computational Analysis Methods • LS-Dyna

– Smooth Particle Hydrodynamics (SPH)

– Physical domain discretized with particles

– Lagrangian collocative method (explicit)

– Good for large deformation and hypervelocity impact

– 2D Axisymmetry

• CTH – Family of codes developed at Sandia

National Laboratories

– Multi-material, large deformation, strong shocks

– Mass, momentum, and energy conservation equations solved with a two-step 2nd order Eulerian algorithm

• Analysis Variables

– Zone size/particle spacing

– Impact velocity (5.1 – 6.6 km/sec)

– Run Time (5 – 40 msec)

– Material Models

– Material Properties



Material Models used in Computational Analysis

Johnson-Cook Material Model with Failure

Constitutive law: 𝜎𝑦 = 𝐴 + 𝐵𝜀 𝑝𝑛

1 + 𝐶𝑙𝑛 𝜀 ∗ 1 − 𝑇∗𝑚

5 Material constants: A, B, C, n, m

Failure strain: 𝜀𝑓 = 𝐷1 + 𝐷2𝑒𝐷3𝜎

∗1 + 𝐷4𝑙𝑛 𝜀 ∗ 1 + 𝐷5𝑇

∗

5 Damage constants: D1, D2, D3, D4, D5

Tensile Failure (spall): Pmin

Gruneisen Equation of State

C, S1, S2, S3 , g0 , a

𝒑 =𝝆𝟎𝑪

𝟐𝝁 𝟏 + 𝟏 −𝜸𝟎𝟐

𝝁 −𝒂𝟐𝝁𝟐

𝟏 − 𝑺𝟏 − 𝟏 𝝁 − 𝑺𝟐𝝁𝟐

𝝁 + 𝟏− 𝑺𝟑

𝝁𝟑

𝝁 + 𝟏 𝟐

𝟐 + 𝜸𝟎 + 𝒂𝝁 𝑬 Compression Pressure:

Expansion Pressure:

5 Constants:

𝒑 = 𝝆𝟎𝑪𝟐𝝁 + 𝜸𝟎 + 𝒂𝝁 𝑬

Data Sources for Lexan and A36 Ref #1: Littlewood, D. J., ‘Simulation of Dynamic Fracture using Peridynamics, Finite Element Modeling, and Contact’, Proceedings of the ASME 2010 International Mechanical Engineering Congress and Exposition. Vancouver, Canada, 2010. Ref #2: Seidt, J.D., Gilat, A., Klein, J.A., Leach, J.R., “High Strain Rate, High Temperature Constitutive and Failure Models for EOD Impact Scenarios”, Proceedings of the 2007 SEM Annual Conference and Exposition on Experimental and Applied Mechanics, Springfield, MA, June, 2007.

Ref # 3: Steinberg, D. J. ‘Equation of State and Strength Properties of Selected Materials’; UCMRL−MA−106439; Lawrence Livermore National Laboratory: Livermore, CA, 1996. Ref # 4: Elshenawy, T., Li, Q. M., ‘Influences of Target Strength and Confinement on the Penetration Depth of An Oil Well Perforator’, International Journal of Impact Engineering, V. 54, pp 130-137, April 2013.



Simulation Comparison: Crater and Deformation Both LS-DYNA and CTH simulations have been able to capture the deformation progression due to impact.

Comparison of crater and bulge dimensions with LS-DYNA simulations are listed below

Typical LS-DYNA simulation Typical CTH simulation Damaged Plate



Simulation Comparison: Free Surface Velocity

Both LS-DYNA and CTH simulations have been able to reasonably able to simulate the free surface velocity profiles.

Further refinement of simulations are still in progress!

Typical single probe PDV data compared with CTH and LS-DYNA simulation



High Speed Video of Experiments

Target

Back surface camera - 680,000 frame/s - 32 x 128 resolution - 1.09 μs exposure

Front surface camera - 906,666 frame/s - 128 x 16 resolution - 0.749 μs exposure

• Two cameras [1 for front surface & 1 for back surface]

• Both of the camera captures video respectively to describe the experiment.



Microscopy of Failure Surface: Is Phase Change an Issue?

Acknowledgement: Dr. Thomas Hartmann helped with initial microscopy work.

Typical microstructure shows a combination of phases: - Ferrite (white) - Pearlite (black)

Change of microstructure along the thickness (material flow).

Thic

knes

s

Impact zone A zone of compressed grains with a mixture of ferrite, pearlite and bainite, is found along the thickness of the plate behind the impact zone.



Electron Back Scatter Diffraction (EBSD) of Failure Surfaces

• The region of interest was approximately 90x90 square microns and located in a compressed region just below the impact crater near a cracked/separation region.

• Different orientations and crystalline phases are visible in the maps.

• The predominant phase is body-centered cubic (Bcc), accounting for 96.7% of the area indexed.

• Face-centered cubic (Fcc) and hexagonal-close-packed (Hcp) phases are also indexed, at 2.9% and 0.4% respectively.



On-going Plans and Future Work

• Multi-Channel PDV to measure velocity at up to 32 discrete points on the back surface of the target. – Potential multi-axis velocity measurement of single point.

• High speed video to capture impact and deformation of target. It could provide independent velocity data for projectile and spalled particles.

• Refined computational simulations to include spall simulation.

• Larger projectiles and symmetric impact (A36 steel projectile hitting A36 steel target).

• Additional target materials (HY100 and 304/304L)

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Plastic Deformation of Steel Plates under High Impact Loading

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