CERAMICS INTERNATIONAL ELSEVIER Ceramics International 29(2003)777-784 www.elsevier.com/locate/ceramint Fracture toughness of ceramics and ceramic composites George A Gogotsi Institute for Problems of strength, 2 Timiryazevskaya Street, Kiev 01014, Ukrain Received 22 July 2002: received in revised form 9 September 2002: accepted 10 November 2002 Abstract The fracture toughness of zirconia, alumina, and silicon nitride ceramics, zirconia and alumina single crystals, silicon carbide as well as silicon nitride ceramic particulate composites, silicon nitride laminated composites, and other ceramics materials were studied by a single edge v-notched beam (SEVNB) method Manual and mechanical procedures for V-notch polishing-out and three-and four-point flexure tests were developed. Load-deflection diagrams for V-notched specimens contributed to better understanding of the deformation behavior of ceramics at room temperature and 1300-1400C sEnb (single edge notched beam) and sEPB (single edge precracked beam) as well as micro-Raman spectroscopy data were used to analyze the sevPb results. The ratio between SevNb and senb results is about 0.6 for elastic materials, over 0.9 for inelastic ones, and about 1.0 for laminated ceramic composite. The polishing-out of a V-notch does not lead to the tetragonal-monoclinic phase transformation in zirconia C 2003 Elsevier Ltd and Techna S r l. All rights reserved Keywords: B Composites; B Spectroscopy: C. Fracture; C. Toughness; Ceramics; SEVNB-method 1. ntroduction steps in this field. Leading specialists from different countries engaged in those investigations performed Ceramics and ceramic composites are promising statistical analyses to compare the test methods sum materials having rather high strength characteristics but marized in Table 1. They were helpful for creating the luite low crack resistance properties at the same time. basis of more reliable determination of the fracture This is one of the major factors hindering the wide-scale toughness characteristics of ceramics. For a long time, application of these materials in various fields of human no particular preference was given to any of the meth activities. The crack resistance is critical not only for ods considered because each of them had appreciable ceramic products operating under extreme mechanical shortcomings, which restricted their application [2, 3] and thermal loads but also for structural components Recently, much attention has been focused on the whose brittle fracture is intolerable even under arbitrary SEVNB method [4], which is a further development of a loads simple and widely used the single edge notched beam For many years, the performance of ceramics has (SENB) method suitable only for rough fracture tough been evaluated on the basis of full-scale tests. However, ness evaluations. The test data obtained by the SEVnB their fracture toughness characteristics have not always method were found to be comparable to those obtained been the object of scientific interest. Wide-scale fracture by the single edge precracked beam (SEPB) method toughness investigations were started only in the late usually considered as providing the real values of cri- 1980s International prestandard studies(Round Robin tical stress intensity factor(Klc) but this test is often on Fracture Toughness-RRFT [ID aimed at the assess- difficult to realize in practice [5]. To evaluate the poten ment of the accuracy and reliability of the data obtained tials of the SEvnb method as a standard one for testing by commonly accepted test methods were important ceramics, its analysis was performed [6]. We verified the efficiency of our procedures and demonstrated the applicability of the SEVNB method to different ceramic E-mail address: ggogotsi @ipp. adam. kiev. ua(GA. Gogotsi). materials 0272-8842/03/$30.00@ 2003 Elsevier Ltd and Techna S.r.l. All rights reserved. doi:10.l016/S0272-8842(02)00230-4Fracture toughness of ceramics and ceramic composites George A. Gogotsi Institute for Problems of Strength, 2 Timiryazevskaya Street, Kiev 01014, Ukraine Received 22 July 2002; received in revised form 9 September 2002; accepted 10 November 2002 Abstract The fracture toughness of zirconia, alumina, and silicon nitride ceramics, zirconia and alumina single crystals, silicon carbide as well as silicon nitride ceramic particulate composites, silicon nitride laminated composites, and other ceramics materials were studied by a single edge V-notched beam (SEVNB) method. Manual and mechanical procedures for V-notch polishing-out and three- and four-point flexure tests were developed. Load–deflection diagrams for V-notched specimens contributed to better understanding of the deformation behavior of ceramics at room temperature and 1300–1400
C. SENB (single edge notched beam) and SEPB (single edge precracked beam) as well as micro-Raman spectroscopy data were used to analyze the SEVPB results. The ratio between SEVNB and SENB results is about 0.6 for elastic materials, over 0.9 for inelastic ones, and about 1.0 for laminated ceramic composite. The polishing-out of a V-notch does not lead to the tetragonal-monoclinic phase transformation in zirconia ceramics. # 2003 Elsevier Ltd and Techna S.r.l. All rights reserved. Keywords: B. Composites; B. Spectroscopy; C. Fracture; C. Toughness; Ceramics; SEVNB-method 1. Introduction Ceramics and ceramic composites are promising materials having rather high strength characteristics but quite low crack resistance properties at the same time. This is one of the major factors hindering the wide-scale application of these materials in various fields of human activities. The crack resistance is critical not only for ceramic products operating under extreme mechanical and thermal loads but also for structural components whose brittle fracture is intolerable even under arbitrary loads. For many years, the performance of ceramics has been evaluated on the basis of full-scale tests. However, their fracture toughness characteristics have not always been the object of scientific interest. Wide-scale fracture toughness investigations were started only in the late 1980s. International prestandard studies (Round Robin on Fracture Toughness–RRFT [1]) aimed at the assess￾ment of the accuracy and reliability of the data obtained by commonly accepted test methods were important steps in this field. Leading specialists from different countries engaged in those investigations performed statistical analyses to compare the test methods sum￾marized in Table 1. They were helpful for creating the basis of more reliable determination of the fracture toughness characteristics of ceramics. For a long time, no particular preference was given to any of the meth￾ods considered because each of them had appreciable shortcomings, which restricted their application [2,3]. Recently, much attention has been focused on the SEVNB method [4], which is a further development of a simple and widely used the single edge notched beam (SENB) method suitable only for rough fracture tough￾ness evaluations. The test data obtained by the SEVNB method were found to be comparable to those obtained by the single edge precracked beam (SEPB) method usually considered as providing the real values of cri￾tical stress intensity factor (KIc) but this test is often difficult to realize in practice [5]. To evaluate the poten￾tials of the SEVNB method as a standard one for testing ceramics, its analysis was performed [6]. We verified the efficiency of our procedures and demonstrated the applicability of the SEVNB method to different ceramic materials. 0272-8842/03/$30.00 # 2003 Elsevier Ltd and Techna S.r.l. All rights reserved. doi:10.1016/S0272-8842(02)00230-4 Ceramics International 29 (2003) 777–784 www.elsevier.com/locate/ceramint E-mail address: ggogotsi@ipp.adam.kiev.ua (G.A. Gogotsi)