Characterisation of damage mechanisms in oxide ceramics indented at dynamic and quasi-static strain rates

C.E.J Dancer,J.N.F Spawton,S Falco,N Petrinic,R.I Todd

doi:10.1016/j.jeurceramsoc.2019.06.054

C.E.J Dancer, J.N.F Spawton + Show 3 more

Open Access

https://doi.org/10.1016/j.jeurceramsoc.2019.06.054

Copy DOI

Abstract

Ceramic materials are known to display rate dependent behaviour under impact. Tests to establish the strain-rate dependent variations in damage mechanisms have been carried out on debased alumina, an alumina-zirconia composite, and 3Y-TZP. Materials were indented dynamically and quasi-statically using identical sharp hardened steel projectiles while recording the load profile. Characteristics typical of both sharp and blunt indentation types were observed using scanning electron microscopy and piezospectroscopic mapping. At dynamic strain rates both the depth of the indentation and the residual stress in the material were lower than for quasi-static tests. This was attributed to temperature-induced softening of the projectile. Unusual behaviour was observed in the 3Y-TZP samples due to the reversible transformation from tetragonal to monoclinic crystal structures during mechanical loading. These effects and the observed superior mechanical strength against impact suggest that zirconia or zirconia-composite materials may have advantages over debased alumina for application as ceramic armour materials.

Highlights

Ceramic materials are both strong under compressive loads and extremely hard [1], and have excellent resistance to indentation
This strain rate-dependent behaviour is one of the reasons why the performance of ceramic materials impacted at high strain rates is not related in a straightforward way to their mechanical properties as measured at quasi-static low strain rates [7,8]
We extend our previously-described dynamic test [11,12] developed for alumina to study impact and indentation of both a composite zirconia-alumina material and 3Y-tetragonal zirconia polycrystals (TZP), and compare their behaviour to that of debased polycrystalline alumina tested under identical conditions

Summary

Introduction

Ceramic materials are both strong under compressive loads and extremely hard [1], and have excellent resistance to indentation. 102-103 s−1 for both polycrystalline alumina and silicon carbide [5,6] This strain rate-dependent behaviour is one of the reasons why the performance of ceramic materials impacted at high strain rates (e.g. ballistic velocities) is not related in a straightforward way to their mechanical properties as measured at quasi-static low strain rates [7,8]. Ballistic testing involves high velocity (> 700-800 m/s) impact of a sphere, rod or sharpened bullet, sometimes encased in a metal sheath, on relatively large ceramic discs or tiles [14,15] Such testing, while effective at establishing a qualitative relative performance of material compositions against the specific threat tested [8], will typically result in a high degree of destruction of the ceramic material. The projectile is sharp, so the strain-rate at the point of impact is locally very high and so gives information relevant in more energetic impacts

Methods

Results

Discussion

Conclusion