Experimental and boundary element analysis of Hertzian cone cracking
Abstract
Quasi-static indentation of brittle materials with a spherical indenter induces Hertzian cone cracks. In brittle materials, cone cracking is a potential failure mode in concentrated contacts. Cone cracking also forms the basis for a potential fracture toughness test and is a possible material removal mechanism during fine polishing. The variation of cone crack length and angle with indenter load is measured by indenting soda-lime glass blocks with 3.17 mm and 6.34 mm diameter steel balls and photographing the cracks through the side of the blocks. An axisymmetric boundary element code is developed and used to accurately calculate stress intensity factors along the edge of the cone crack by adapting the modified crack closure integral. The boundary element results are verified through comparison to finite element calculations. Calculations show that the Mode II stress intensity factor is less than 10% of the Mode I stress intensity factor at the cone crack tip and that the Mode I stress intensity factor is a positive monotonically decreasing function of cone crack length provided that the contact diameter is not greater than the cone crack diameter at the surface. A potential mechanism which inhibits the contact diameter from being larger than the cone crack diameter at the surface is discussed. Assuming that cone crack growth arrests when the Mode I stress intensity equals the fracture toughness leads to good agreement between measured and predicted cone crack lengths.
Degree
Ph.D.
Advisors
Farris, Purdue University.
Subject Area
Aerospace materials|Mechanical engineering|Mechanics
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