Nanoindentation of Fused Quartz at Loads Near the Cracking Threshold
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© 2019, Society for Experimental Mechanics. Nanoindentation with triangular pyramidal indenters with centerline-to-face angles of 35.3°, 45°, 55°, 65.3° and 75° at loads in the range 1–500 mN was conducted on fused quartz to explore how cracks first form and develop in brittle materials during sharp indentation contact. The cracking behavior was documented using high resolution scanning electron microscopy and serial cross sectioning by focused ion beam milling. Results show that cracking is enhanced by sharper indenters and that there is a distinct threshold load below which no cracking is observed. The threshold increases rapidly with indenter angle. A series of indentations made at increasing load with the 45° indenter shows that the first cracks to form are relatively straight radials that emanate outward from the corners of the indentation. However, underneath the indent they do not connect to the hardness impression but rather terminate at what appears to be the elastic-plastic boundary. With increasing load, the radial cracks extend outward and downward, but at an intermediate load they branch to the sides beneath the hardness impression to form lateral cracks. Cracking does not appear to initiate from pre-existing flaws, but is generated from processes associated with plastic deformation beneath the indenter. Results are discussed in terms of prevailing ideas on the origin of the cracking threshold.
author list (cited authors)
Mound, B. A., & Pharr, G. M.