Indentation strength of a piezoelectric ceramic: Experiments and simulations
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D.V. Kubair Department of Aerospace Engineering, Indian Institute of Science, Bangalore 560012, India
U. Ramamurtya) Department of Materials Engineering, Indian Institute of Science, Bangalore 560012, India (Received 15 August 2008; accepted 27 October 2008)
The spherical indentation strength of a lead zirconate titanate (PZT) piezoelectric ceramic was investigated under poled and unpoled conditions and with different electrical boundary conditions (arising through the use of insulating or conducting indenters). Experimental results show that the indentation strength of the poled PZT is higher than that of the unpoled PZT. The strength of a poled PZT under a conducting indenter is higher than that under an insulating indenter. Poling direction (with respect to the direction of indentation loading) did not significantly affect the strength of material. Complementary finite element analysis (FEA) of spherical indentation of an elastic, linearly coupled piezoelectric half-space is conducted for rationalizing the experimental observations. Simulations show marked dependency of the contact stress on the boundary conditions. In particular, contact stress redistribution in the coupled problem leads to a change in the fracture initiation, from Hertzian cracking in the unpoled material to subsurface damage initiation in poled PZT. These observations help explain the experimental ranking of strength the PZT in different material conditions or under different boundary conditions.
I. INTRODUCTION
Piezoelectric materials, wherein a first-order coupling between mechanical and electrical fields exists, are extensively used in many branches of modern technology, including aerospace, automotive, medical, and electronic industries, as actuators as well as sensors. However, a major drawback of the piezoelectric ceramics such as the widely used lead zirconate titanate (PZT) is their brittleness. Significant advances have been made in the processing and manufacturing of these materials in the recent past. However, mechanical failure as well as electrical degradation caused by the presence and growth of various defects such as cracks, holes, and inclusions are still of major concern from the reliability viewpoint. Consequently, role of defects on the strength of these materials has been extensively investigated.1–11 Generally piezoelectric actuators, sensors, and other components are in the form of thin films, beams, and plates. With increasing miniaturization (and the advent of technologies such as MEMS), the dimensions of these components are getting smaller. Naturally, property a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0115
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J. Mater. Res., Vol. 24, No. 3, Mar 2009
assessment of such small-volume materials is a challenge and using the indentation technique for such measurements is a viable and attractive option.12–14 Further, indentation provides a method for assessing a given piezoelectric material’s response to the contact loading, which also plays an importa
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