Static and dynamic flexural strength of 99.5% alumina: Relation to surface roughness

• Published in: Mechanics of materials Vol. 54; pp. 91 - 99
• Main Authors: Belenky, A., Rittel, D.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.11.2012
• Subjects: 1-Point impact; Alumina; Aluminum oxide; Defects; Dynamics; Flexural strength; Modulus of rupture in bending; Polished; Pores; Strength; Surface roughness; 1-Point impact; Surface roughness; Pores; Alumina; Flexural strength
• ISSN: 0167-6636; 1872-7743
• DOI: 10.1016/j.mechmat.2012.07.003

► Static and dynamic flexural strengths vs. surface roughness are studied. ► The present work includes detailed fractographic and surface roughness studies. ► The surface conditions alone do not control the strength. ► Microstructural aspects play a significant part, even for thoroughly polished specimens. The dynamic flexural strength of ceramics is an important property for all applications involving impact loading conditions. Therefore, this work reports a systematic comparison of static and dynamic flexural strength results for 99.5% commercial alumina, obtained using a recently reported adaptation of the 1-point impact experimental technique. Specimens of the same size and systematically varying surface roughness conditions were used in this study to assess the influence of the latter on the static and dynamic strength of this material. The investigated roughness levels ranged from 0.8μm (coarse) to 0.05μm (fine, polished). Under static loading, reducing the surface roughness causes a 10% increase in flexural strength for polished specimens. By contrast, the dynamic flexural strength is apparently not influenced by the surface roughness. A thorough microstructural and fractographic examination reveals the presence of bulk (surface) pore-like flaws that are not obliterated by the polishing process and therefore govern the failure process. It is suggested that strength improvements can be reached by suitable surface preparation, provided no bulk pores are native in the material, some of which are present on its surface. The identification of the role of surface flaws is expected to clarify the discrepancy found in the literature as to the influence of surface roughness on the mechanical properties of brittle materials.