Radial Fracture During Indentation by Acute Probes: I, Description by an Indentation Wedging Model

Abstract

Extension of the indentation fracture toughness estimation method to very small length scales often requires the use of an indenting punch much more acute than the oft-used Vickers probe. Experimental results for very acute, sharp probes have motivated a new approach to the indentation fracture mechanics of radial crack development. An extension of the standard two-component (residual elastic-plastic + elastic contact) stress-field model of radial fracture is proposed, based on the concept that a sufficiently acute indenter can also act as a 'wedge,' prying open the surface-located radial cracks. In this, the first of a two-part series, a three-component wedging indentation model is constructed, and some general characteristics of the model are explored. In particular, the implications of the three-component stress field of the model for the description of radial crack development during load-unload indentation cycles of acute probes are considered. Explicit predictions of crack development are compared with the qualitative features of experimental observations, providing a basis for the quantitative comparisons in Part II.

Indentation fracture of low-dielectric constant films: Part I. Experiments and observations

“…In this and following figures, a data point represents the mean, and error bars one standard deviation in measured crack length; where not seen, the error bars are smaller than the symbol size. The conventional residual elastic-plastic field model of indentation fracture 3,19 shows that c will vary as P 2/3 for a homogeneous, ideally brittle, material. The P 2/3 slope is shown on Fig.…”

Loading rate effects on the fracture behaviour of solar control coatings during nanoindentation

“…However, when the indenter edges come into contact with the surface the stress concentration effect magnifies the local stresses and, at a critical load, cracking starts and propagates through the coating following the edge of the indenter which is in contact with it. The edge of the indenter causes a wedging effect opening the crack [11,12]. As the load increases the crack can extend, but is constrained within the impression by the substrate plastic deformation.…”

Fracture Behavior of Granular Polycrystalline Silicon Using Micro-scale and Macro-scale Indentation Techniques

“…[16] In our measurements we use toughness T rather than using mode I fracture toughness K IC because of the absence of pre-cracks and the indistinct use of indentation-induced fracture. Figure 2(b) shows the average crack vs applied load where Eq.…”

“…The toughness of the material was then determined by the relationship between the applied load and the crack size. [16] The hardness and elastic modulus were measured using a Hysitron Triboindenter 900, where a quasistatic test was performed with maximum applied loads between 1800 and 9000 lN. In order to avoid any influence on the properties of the materials, all measurements were done at areas much smaller than the pore spacing in the granular material.…”