On the mechanics of edge chipping from spherical indentation

• Published in: International journal of fracture Vol. 169; no. 1; pp. 85 - 95
• Main Author: Chai, Herzl
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01.05.2011; Springer; Springer Nature B.V
• Subjects: Automotive Engineering; Brittle materials; Brittleness; Characterization and Evaluation of Materials; Chemistry and Materials Science; Chipping; Chips; Civil Engineering; Classical Mechanics; Crack initiation; Diamond pyramid hardness; Exact sciences and technology; Exact solutions; Failure modes; Fracture mechanics; Fracture mechanics (crack, fatigue, damage...); Fracture toughness; Fundamental areas of phenomenology (including applications); Impact analysis; Impact damage; Indentation; Materials Science; Mechanical contact (friction...); Mechanical Engineering; Original Paper; Physics; Soda-lime glass; Solid mechanics; Static elasticity (thermoelasticity...); Structural and continuum mechanics; Structural integrity; Vibration, mechanical wave, dynamic stability (aeroelasticity, vibration control...); Ball; Median cracks; Vickers; Edge chipping; Toughness; Indentation; Vickers hardness; Hardness test; Cone; Low speed; Brittle fracture; Chip formation; Structure integrity; Brittle material; Mechanical contact; Modeling; Soda-lime glasses; Plate; Exact solution; Fracture toughness; Static analysis; Mechanical shock; Crack; Cutting force
• ISSN: 0376-9429; 1573-2673
• DOI: 10.1007/s10704-011-9589-7

Edge chipping is a basic failure mode in brittle materials which is dictated by a wealth of material and geometric variables. Here we examine the effect of indenter bluntness on chipping load and chip dimensions. Soda-lime glass and YTZP plates are subject to surface-normal loading near an edge by a W/C ball or a Vickers tool. The ball radius r is varied from 0.2 to 8.7 mm while the indent distance h is varied from several millimeters down to a few microns. Although cone cracks are a common feature under spherical indentation, the chipping event is dominated by median-radial cracks formed under the contact. The fracture behavior is characterized by a “large” indent distance regime where the median cracks progress stably up to chipping and a “small” one where they grow unstably to form a chip once initiated. Closed-form relations for chipping load P F under spherical indentation is developed with the aid of the test data and non-dimensional arguments. While in the “large” distance regime P F is proportional to h 3/2 irrespective of tool bluntness, in the “small” regime P F is proportional to r 1/2 h 3/4 . Interestingly, the chip dimensions are virtually independent of ball radius, varying linearly with h . Beyond relevance to structural integrity, the chipping test facilitates a simple means for determining fracture toughness K C as well as the load needed to initiate median cracks in opaque brittle materials. An attempt is made to extend the static analysis to low-velocity impact. The results show that the damage formed during the fracture process has a major influence on dynamic chipping.