α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εF ο υο υο υο υο υ n δ εδ εδ εδ εδ ε r ’ s δ α ψ δ α ψ δ α ψ δ α ψ δ α ψ S ρ ερ ερ ερ ερ ε c i ααααα l I s s u εεεεε

I S S U E N O . 3 0 9 • O C T O B E R 2 0 0 9 • 409

C H A R A C T E R I Z A T I O N O F A L U M I N A C E R A M I C S

U N D E R S H O C K L O A D I N G

ABSTRACT

This work reports the characterization of sintered Alumina ceramics, before and after shock

l o a d i n g , i n a G a s G u n f a c i l i t y i n d i g e n o u s l y d e v e l o p e d a t B A R C , M u m b a i . T h e

Nanoindentation technique was uti l ized, to ref lect the decrease in hardness and Young’s

modulus of Alumina ceramics due to shock loading. Detailed Scanning Electron Microscopy

(SEM) and Field Emission Scanning Electron Microscopy (FESEM) was utilized, to understand

the nature and degree of fai lure propagation and the interrelat ion between such damage

evolut ion and the degradat ion in local mechanical propert ies, in these br i t t le ceramics.

This study demonstrated for the f irst t ime, that shear stress dominated fai lure, could play

a major role in damage evolut ion, in shock loaded alumina ceramics.

Introduction

Alumina is the most well established, commercially

utilized ceramic, for armour applications. The preferred

experimental technique to determine properties of

materials under shock-loading conditions, is that of

plate impact. Here a flat and parallel plate of known

shock response is impacted onto an equally flat and

parallel plate of the material of interest. The mechanical

response can be determined by a number of methods,

including rear surface velocity measurements such

as VISAR (velocity interferometry system for any

reflector), or stress gauges, mounted in various

orientations to the loading axis. The mechanical

properties that can be extracted include the dynamic

yield strength—the Hugoniot Elastic Limit (HEL),

the dynamic tensile spall strength due to interactions

between release waves from the rear of the

flyer and target plates, and shear strength.

Several researchers have investigated the

T h i s p a p e r r e c e i v e d t h e P o s t e r A w a r d 2 0 0 8 a t t h e 5 3 r d D A E S o l i d S t a t e

P h y s i c s S y m p o s i u m h e l d a t B A R C a n d T I F R , M u m b a i d u r i n g

D e c e m b e r 1 6 - 2 0 , 2 0 0 8

A.K. Mukhopadhyay and S.Bhattacharyya

Mechanical Test Sect ion, Analyt ical Faci l i ty Div is ion

Central Glass and Ceramic Research Inst itute, Kolkata

and

K.D. Joshi, A. Rav and S.C. Gupta

Appl ied Phys ics Div is ion

and

S. Biswas

Non-Oxide Ceramic Sect ion

Central Glass and Ceramic Research Inst itute, Kolkata

410 • I S S U E N O . 3 0 9 • O C T O B E R 2 0 0 9

α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εD R . H O M I B H A B H A C E N T E N A R Y Y E A R

behaviour of alumina ceramics under plate and / or

rod impact conditions; however, there has not been a

significant effort so far, to compare the

nanomechanical properties of shocked and unshocked

alumina ceramics. This is precisely the aim of the

present report. One of the established experimental

techniques, for evaluation of mechanical properties

at the ultra-structural low dimension of the sample,

is nanoindentation. Here the mechanical disturbance

made by the external probe, can be made to span

length scales comparable to or even less than the

microstructural length scale of the sample.

In recent times, the nanoindentation technique has

proved to be a powerful means of characterizing near-

surface mechanical properties, such as Young’s

modulus (E), hardness (H) etc. of materials. This

technique relies on high-resolution instruments that

continuously monitor the loads, P, and displacements,

h, of an indenter, usually a Berkovich type, as it is

pushed into and withdrawn from a material. Important

information obtained from the resultant P–h curve,

are the peak load, Pmax

, the maximum penetration

depth, hmax

, final penetration depth, hf, and the

contact stiffness, S. The nanoindentation load–

displacement curve, is usually described by a power

law function of the formm

fhhP )( −= α where, αand m are empirically determined fitting parameters.

Based on the observation that predicted m values are

1 for plat punch, 1.5 for paraboloid of revolution and

2 for conical indenter [1] whereas the experimentally

determined m-values vary from 1.25 to 1.51 and have

an average value of 1.40 [2], it was decided to check

out first, how α and m would vary with the

nanoindentation load, for the un-shocked alumina

samples.

Materials and Methods

99.99% pure alumina powder (Morimura Bros. Inc.,

Tokyo, Japan) was pressureless-sintered at 13100C, to

a density of 97.5% of theoretical (4.02 gm/cc) and

an average grain size of 10.1 ± 0.23 μm. Both as

prepared and shocked samples were characterized by

conventional XRD, SEM and Image Analysis

techniques. Micromechanical characterization of

polished samples was done, using a nanoindentation

machine in a load range between 0.4 and 1000 μN,

with force and depth sensing resolutions of 0.2 μN

and 0.1μm. All the shock experiments were conducted

at the Gas Gun facility available at BARC, Mumbai.

Details of the standard experimental facilities are

reported elsewhere [3] and will be only briefly

described here. Two types of shock experiments were

conducted. In the first type of experiment, the alumina

sample was shock loaded to peak pressure for complete

destruction. This experiment though, provided a data

point on the Hugoniot but due to complete destruction

of the sample, no post shock analysis was possible.

For this experiment, alumina disk of diameter 25 mm

and thickness 2.5 mm was fitted in a matching hole,

made on a Perspex disc of diameter 60 mm and

thickness 5 mm. The sample was placed in the central

hole of this disc in such a way that one surface of the

sample was flushed with one surface of the Perspex

disc. This surface was used as the impact surface.

Two shock arrival sensors were used to measure the

shock arrival at the impact surface and the back surface

of the sample. For this purpose the two sensors were

placed in such a way, that the sensing end of one of

the sensors was flushed with the impact surface,

however, the same of the other sensor was resting on

the back surface of the sample. The second type of

experiments were recovery experiments in which, the

samples after unloading from peak shock pressures

were recovered for post shock analysis. In two separate

shock recovery experiments similar alumina

disks as mentioned above were shocked to impact

pressures, of 6.5 and 12 GPa, respectively and

subsequently collected through a dedicated catcher

arrangement [3].

In the first type of experiment, from the measured

shock arrival times at the two surfaces and the

measured thickness, the shock velocity (Us) in sample

could be determined. The impactor plate used in the

experiment was of SS304, whose shock Hugoniot was

already known. The velocity of the impacting plate

(Vp) just before the impact was measured, using (Up)

electrical pins connected to the input of a pulse

forming network. From the measured Us (in the

α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εF ο υο υο υο υο υ n δ εδ εδ εδ εδ ε r ’ s δ α ψ δ α ψ δ α ψ δ α ψ δ α ψ S ρ ερ ερ ερ ερ ε c i ααααα l I s s u εεεεε

I S S U E N O . 3 0 9 • O C T O B E R 2 0 0 9 • 411

sample),Vp and known Hugoniot of SS304, the particle

velocity and shock pressure in the sample could be

derived, by using the impedance match method. In

second type of experiments, the samples could reach

peak pressures through a number of revervations.

Results and Discussion

In the first type of experiment, the measured impact

velocity and shock velocity in the sample, were

0.48 km/s and 7.03 km/s, respectively. The Up

determined from these measurements and known

Hugoniot of SS304 was 0.28 km/s. The shock pressure

(P) in the sample evaluated by substituting the initial

density of 3.89 g/cc, measured Us and Up in second

jump condition was 7.6 GPa. The compression ratio

(V/V0) was evaluated as 0.96. These values of P, Us,

Up and V/V0 agree well with published Hugoniot

data .

The samples recovered from recovery experiments were

analyzed through nanoindentation, XRD and SEM

techniques. The XRD data of both unshocked and

shocked sintered alumina was taken and the main

intense peak was compared with standard data of α-

alumina (JCPDS-43-1484). It was found that the major

peaks of sintered alumina disc, matched with the

standard peaks of α -Alumina, but a little shift of peaks

of the shocked sample occurred, with respect to those

of the unshocked alumina, possibly suggesting the

presence of a strained lattice. The nanoindentation

data of the unshocked alumina, showed a small

indentation size effect at depths, less than 300 nm

(eg. the hardness decreased at the rate of 0.03 GPa/

nm) but at higher depths the hardness was nearly

constant at about 20 GPa. Attempt was made to

analyze this data in terms of the famous Nix and Gao

model [4].

Interestingly, both hf and h

max showed an empirical

power law dependence of the type h – β Pn on load

where β and n are empirical fitting parameters.

However, β, n were very different e.g. ~ (18 and

0.56) for hf and (1.58 and 0.80) for h

max. The reason

for variation of hardness with depth could be

rationalized in terms of the load dependencies of the

elastic (WE/W

T) and plastic (W

P/W

T) components of

the energy spent in the indentation process. While at

lower loads, most of the energy spent in indentation

involved elastic deformation energy, the scenario

changed at higher load of indentation, where most

of the energy spent in indentation process involved

the irreversible deformation or the plastic component.

Preliminary nanoindentation experiments on alumina,

deformed at shock levels of 6.5 and 12 GPa, showed

a trend of drastically decreased hardness, especially

at higher loads e.g. 1000 μN. We could not compare

our results with published data because no data was

available on nanoindentation hardness of shock loaded

alumina ceramics. Also, the evaluation results of αand m parameters showed interesting behaviour with

respect to variation in nanoindentation load. The

typical brittle failure pattern observed in the fracture

surface of the as-received alumina, was in sharp

contrast to the localized plastic deformation zones

observed in the fracture surface of the shocked

alumina, where a large number of microcracks along

with a macrocrack were present. Both intergranular

and transgranular fractures had occurred during the

shock-induced failure process. An attempt is made

here to develop a plausible picture of mechanisms

involved in the shock failure process.

Summary and Conclusion

In our work, SEM and FESEM evidence provides for

the first time, a plausible picture of shear dominated

failure that affects the damage evolution and

consequent failure, propagation process, in shock

loaded alumina ceramics, which shows drastic r

eduction in mechanical properties as evaluated by the

nanoindentation technique.

References

1. I. N. Sneddon, Int. J. Engg. Sci. 3 (1965) 47.

2. W.C. Oliver and G. M. Pharr, J. Matter. Res.

7 (1992) 1564.

3. K. D. Joshi et al, Proceedings of DAE Solid

State Physics Symposium (2007).

4. W. D. Nix and H. Gao, J. Mech. Phys. Solids

46 (1998) 411.

412 • I S S U E N O . 3 0 9 • O C T O B E R 2 0 0 9

α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξα β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξφ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εψ ζ α β χ δ ε φ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ ε φ γ η ι ϕ κ λ μ ν ο π θ ρ σ τ υ ϖ ω ξ ψ ζ α β χ δ εD R . H O M I B H A B H A C E N T E N A R Y Y E A R

A B O U T T H E A U T H O R S

Dr. Satish C. Gupta joined BARC in 1972 through the 15th batch of BARC training school.

He has published a large number of publications in reputed international journals. He is a

recipient of the prestigious DAE Special Contribution award. His research interests are in

the field of behaviour of high energy density matter and response of materials to dynamic

compression, at high strain rate using shock wave. Presently he is leading the activities of

the Applies Physics Division.

Mr. K.D. Joshi joined BARC after graduating from the 36th batch of BARC training school.

He was awarded the prestigious DAE Special Contribution award. He has contributed to

about 50 publications in various journals and conference proceedings. He is involved in

theoretical as well as experimental studies on response of materials to high pressures.

Mr. A. Rav completed his B.E. in electronics from Gujarat University and joined BARC

from the 44th batch of BARC training school. He is engaged in development of

instrumentation, required for diagnostics in shock wave experiments.