Model for Cyclic Fatigue of Quasi‐Plastic Ceramics in Contact with Spheres

Abstract

A model of contact damage accumulation from cyclic loading with spheres and ensuing strength degradation in relatively tough, heterogeneous ceramics is developed. The damage takes the form of a quasi-plastic zone beneath the contact, consisting of an array of closed frictional shear faults with attendant "wing" microcracks at their ends. Contact fatigue takes place by attrition of the frictional resistance at the sliding fault interfaces, in accordance with an empirical degradation law, allowing the microcracks to extend. At large numbers of cycles or loads the microcracks coalesce, ultimately into radial cracks. Fracture mechanics relations for the strength degradation as a function of number of cycles and contact load are derived. Indentation-strength data from two well-studied coarse-grain quasi-plastic ceramics, a micaceous glass-ceramic and a silicon nitride, are used to evaluate the model. Comparative tests in static and cyclic contact loading confirm a dominant mechanical component in the fatigue. At the same time, the presence of water is shown to enhance the fatigue. The model accounts for the broader trends in the strength degradation data, and paves the way for consideration of key variables in microstructural design for optimum fatigue resistance.

Silicon Nitride Bearings for Total Joint Arthroplasty

“…Indeed, scuffing, microcracks, and microfracture were observed on the high-wear Si 3 N 4 bearings. This wear pattern is consistent with the findings of other investigators who reported that heterogeneous acicular ceramic microstructures exhibit this type of wear behavior [129][130][131]. Thermally activated dissolution of the bearing surface (or wear debris) and reformation of the tribochemical film ensued which lowered friction, until the bearing once again came to its next stop in the cycle, resulting in a repetition of stick-slip behavior.…”

Effect of Yb2SiO5 addition on the physical and mechanical properties of sintered mullite ceramic as an environmental barrier coating material

“…Quasi-plastic mechanical behavior is commonly reported in the local and repetitive spherical indentation of tough ceramics. However, quasi-plastic damage causes the development of radical cracking under repetitive cyclic contact fatigue and, finally, collapse [30]; therefore, it is thought that deeper displacement of the 6Yb-mullite sample will most likely be relatively harmful. This type of quasi-plastic damage behavior may be beneficial regarding the impact of foreign object debris on ceramic coatings for gas turbine application [31].…”

Theoretical and experimental analysis of material deformation by microcontact

“…Spherical indentation techniques are used to evaluate the contact damage behavior and damage tolerance properties of materials. [6][7][8][9][10][11][12][13] A constant loading force is applied to the flat surface of the materials using a hard tungsten carbide (WC) ball with a uniform radius. Since cone-shaped fractures are produced during contact between glass lenses, indentation mechanics are extensively used in the analysis and characterization of the mechanical properties of materials.…”