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Research Papers

An Experimental and Numerical Study of Ballistic Impacts on a Turbine Casing Material at Varying Temperatures

[+] Author and Article Information
B. Erice1

Department of Materials Science,Universidad Politécnica de Madrid (UPM), Calle del Profesor Aranguren s/n,28040, Madrid, Spain;  Research Centre on Safety and Durability of Structures and Materials (CISDEM), UPM-CSIC, Calle del Profesor Aranguren s/n,28040, Madrid, Spainborjaerice@mater.upm.es

F. Gálvez, D. A. Cendón, V. Sánchez-Gálvez

Department of Materials Science,Universidad Politécnica de Madrid (UPM), Calle del Profesor Aranguren s/n,28040, Madrid, Spain;  Research Centre on Safety and Durability of Structures and Materials (CISDEM), UPM-CSIC, Calle del Profesor Aranguren s/n,28040, Madrid, Spain

T. Børvik

Structural Impact Laboratory (SIMLab) and Department of Structural Engineering,  Norwegian University of Science and Technology, NO-7491 Trondheim, Norway; Norwegian Defence Estates Agency, Research and Development Department, NO-0103 Oslo, Norway

1

Corresponding author.

J. Appl. Mech 78(5), 051019 (Aug 05, 2011) (11 pages) doi:10.1115/1.4004296 History: Received November 26, 2010; Revised March 29, 2011; Published August 05, 2011; Online August 05, 2011

An experimental and numerical study of ballistic impacts on steel plates at various temperatures (700 °C, 400 °C and room temperature) has been carried out. The motivation for this work is the blade-off event that may occur inside a jet engine turbine. However, as a first attempt to understand this complex loading process, a somewhat simpler approach is carried out in the present work. The material used in this study is the FV535 martensitic stainless steel, which is one of the most commonly used materials for turbine casings. Based on material test data, a Modified Johnson-Cook (MJC) model was calibrated for numerical simulations using the LS-DYNA explicit finite element code. To check the mesh size sensitivity, 2D axisymmetric finite element models with three different mesh sizes and configurations were used for the various temperatures. Two fixed meshes with 64 and 128 elements over the 2 mm thick plate and one mesh with 32 elements over the thickness with adaptive remeshing were used in the simulations. Both the formation of adiabatic shear bands in the perforation process and the modeling of the thermal softening effects at high temperatures have been found crucial in order to achieve good results.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 2

Perforated plate after impact at an initial velocity of v0=506.7m/s and room temperature; (a) Plug formed during perforation and (b) perforated plate specimen

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Figure 3

SEM picture showing adiabatic shear band in the plate after impact

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Figure 4

Yield stress versus temperature for two different strain rates for the FV535 stainless steel. Closed symbols correspond to experimental data for ¯·ɛp=10-4s−1 and open symbols correspond to experimental data for ¯·ɛp=103s−1 .

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Figure 5

Finite element model with 128 elements over the target thickness in the impact zone. The mesh is reduced towards the boundary with two 5:3 transition zones.

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Figure 6

Initial versus residual velocity curves for (a) 32 elements over the target thickness, adaptive remeshing and two different values of m and (b) 128 elements over the target thickness, a fixed mesh and three different values of m

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Figure 7

Initial versus residual velocity curves for 64 elements over the target thickness a fixed mesh and three different values of m: (a) without temperature cut-off and (b) with temperature cut-off at Tc=0.96Tm

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Figure 8

Plots showing the effect of the thermal softening exponent m on the localization and plugging process at the same time (t=6.2μs) and impact velocity (v0=600 m/s) in three simulations. The simulations were run with 64 elements over the target thickness applying the temperature cut-off criterion.

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Figure 9

Plots showing the effect of the thermal softening exponent m on the localization and plugging process at the same time (t=6.2μs) and impact velocity (v0=625 m/s) in three simulations. The simulations were run with 128 elements over the target thickness applying the temperature cut-off criterion.

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Figure 10

Predicted initial versus residual velocity curves of ballistic impacts at high temperatures: (a) simulations with Tr=400 °C and Tr=400 °C. (b) Recalibration of D5 in the MJC fracture criterion assuming 400 °C as a limit temperature

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Figure 11

Plots showing the difference in predicted results using the original and the recalibrated value for D5 in the MJC fracture criterion. The simulations were run using 128 elements over the target thickness, m=4.5 and an initial velocity v0=420 m/s.

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Figure 12

Simulations with the finer fixed mesh for three different temperatures with 128 elements over the impact zone thickness. (top) Room temperature with thermal softening of m = 2.0 and (bottom) 400 °C. Temperature contours are shown in  °C.

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Figure 13

Initial versus residual velocity curves from ballistic impact simulations at high temperature and varying Tm; (a) simulations with T0=400 °C, Tr=400 °C and Tm from 1500 °C to 870 °C and (b) simulations with T0=700 °C, Tr=700 °C and Tm from 1500 °C to 1000 °C

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Figure 1

Initial versus residual velocity curves from ballistic impact tests at various ambient temperatures

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