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TECHNICAL PAPERS

Dynamic Compressive Response of Stainless-Steel Square Honeycombs

[+] Author and Article Information
D. D. Radford, G. J. McShane, V. S. Deshpande

Department of Engineering, University of Cambridge, Trumpington Street, Cambridge, CB2 1PZ, United Kingdom

N. A. Fleck1

Department of Engineering, University of Cambridge, Trumpington Street, Cambridge, CB2 1PZ, United Kingdomnaf1@eng.cam.ac.uk

1

Corresponding author.

J. Appl. Mech 74(4), 658-667 (May 09, 2006) (10 pages) doi:10.1115/1.2424717 History: Received January 20, 2006; Revised May 09, 2006

The dynamic out-of-plane compressive response of stainless-steel square honeycombs has been investigated for impact velocities ranging from quasi-static values to 300ms1. Square-honeycomb specimens of relative density 0.10 were manufactured using a slotting technique, and the stresses on the front and back faces of the dynamically compressed square honeycombs were measured using a direct impact Kolsky bar. Three-dimensional finite element simulations of the experiments were performed to model the response and to help interpret the experimental results. The study has identified three distinct factors governing the dynamic response of the square honeycombs: material rate sensitivity, inertial stabilization of the webs against buckling, and plastic wave propagation. Material rate sensitivity and inertial stabilization of the webs against buckling cause the front and back face stresses to increase by about a factor of two over their quasi-static value when the impact speed is increased from 0 to 50ms1. At higher impact velocities, plastic wave effects cause the front face stress to increase linearly with velocity whereas the back face stress is almost independent of velocity. The finite element predictions are in reasonable agreement with the measurements.

Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Sketch of the manufacturing technique for the square honeycomb

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Figure 2

(a) The measured quasi-static tensile stress versus strain response of the AISI 304 stainless steel and the estimated high strain rate response at three additional values of the applied strain rate using the data of Stout and Follansbee (10). (b) The dynamic strength enhancement ratio R as a function of plastic strain rate ε̇p for the AISI 304 stainless steel at a plastic strain εp=0.1(10).

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Figure 3

Quasi-static compressive stress versus strain response of the ρ¯=0.10 square honeycombs, of cell height H=6mm and H=30mm

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Figure 4

Sketches of the direct impact Kolsky bar setup for measuring the stress versus time histories in (a) front face and (b) back face configurations. All dimensions are in mm.

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Figure 5

Stress versus time history measured in the Kolsky bar during a calibration test. A 0.5m long steel striker is fired at the Kolsky bar at νo=9.0ms−1.

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Figure 6

(a) Measured front and back face stress versus normalised time histories in the H=30mm honeycomb specimens impacted at νo=20ms−1; and (b) the corresponding high speed photographic sequence of the deformation in the front face configuration at an interframe time of 100μs. The finite element predictions (constant velocity boundary condition) are included in (a).

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Figure 7

(a) Measured front and back face stress versus normalised time histories in the H=30mm honeycomb specimens impacted at νo=50ms−1; and (b) the corresponding high speed photographic sequence of the deformation in the front face configuration at an interframe time of 100μs. The finite element predictions (constant velocity boundary condition) are included in (a).

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Figure 8

(a) Measured front and back face stress versus normalised time histories in the H=30mm honeycomb specimens impacted at νo=240ms−1; and (b) the corresponding high speed photographic sequence of the deformation in the front face configuration at an inter-frame time of 40μs. The finite element predictions (constant velocity boundary condition) are included in (a).

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Figure 9

Measured peak front face stress σfp and back face stress σbp versus impact velocity νo in the H=30mm honeycomb specimens. The measured dynamic stresses are normalized by peak quasi-static stress σs from Fig. 3. The predictions of the dynamic stresses based on material strain-rate sensitivity and one-dimensional plastic wave propagation are included.

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Figure 12

The four modes of initial imperfections introduced into the FE model of the H=30mm square honeycomb: (a) Mode I; (b) Mode II; (c) Mode III; and (d) Mode IV. A section through the midplane of the honeycomb is shown in each case.

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Figure 13

FE predictions of the front and back face stress versus time histories for the H=30mm compressed at a velocity (a)νo=20ms−1 (front face); and (b)νo=240ms−1 (front and back face). In both cases, results are shown for the four modes of initial imperfections with an imperfection amplitude 0.05b.

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Figure 14

A comparison between the FE predictions for a constant applied velocity and for impact boundary conditions (H=30mm honeycomb specimen with νo=20ms−1)

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Figure 10

The measured front and back face stress versus normalised time histories of the (a)H=30mm; and (b)H=6mm square-honeycomb specimens for an impact velocity νo=100ms−1. The finite element predictions (constant velocity boundary condition) are included in the figures.

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Figure 11

Measured dynamic peak front (σfp) and back (σbp) face stresses in the H=6mm honeycomb specimens as a function of the impact velocity νo. The measured dynamic stresses are normalized by peak quasi-static stress σs from Fig. 3. The predictions of the dynamic stresses based on material strain-rate sensitivity and one-dimensional plastic wave propagation are included.

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Figure 15

Experimental estimates and FE predictions of the normalized striker velocity νb(t)∕νo as a function of the normalized time νot∕H for the back face configuration with initial striker velocities of νo=20ms−1 and 50ms−1

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Figure 16

The FE predictions of the deformation mode of the H=30mm honeycomb specimen, subjected to a constant applied velocity νo=50ms−1 at: (a)t=55μs; and (b)t=155μs. These times correspond to the times of the high speed photographs in Fig. 7. A section through the midplane of the honeycomb is shown.

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Figure 17

Comparisons between the rate independent and rate dependent FE predictions (constant applied velocity) of the front and back face stresses: (a)H=30mm; and (b)H=6mm square-honeycombs, for νo=100ms−1

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