Indentation

About: Indentation is a research topic. Over the lifetime, 13002 publications have been published within this topic receiving 340476 citations.

Anisotropy of Fracture Toughness of Piezoelectric Ceramics

Abstract: The anisotropy of fracture toughness of PZT- and barium titanate-based piezoelectric ceramics was studied using doubletorsion and indentation methods. The influence of elastic anisotropy and the piezoelectric effect in calculating the Kc value are discussed. The fracture toughness in the polarization plane is greater than that in the perpendicular plane. A model is suggested to explain the observed anisotropy; it is based on assumption of a stress-induced domain reorientation zone near the crack tip.

Effects of Pores on Mechanical Properties of Plasma‐Sprayed Ceramic Coatings

Abstract: The effects of pore sizes, shapes, and orientations on the mechanical properties of thermally sprayed ceramic coatings are investigated. The analysis is conducted using detailed finite-element models with geometries similar to those of actual ceramic coatings containing many embedded pores. These microstructural models include many randomly placed pores of different sizes and shapes and are loaded in tension to determine their effective elastic moduli along the spray and transverse directions. We modeled coatings with statistical distributions of pore sizes and shapes that followed those of actual Al2O3–TiO2 coatings. Because the pores in such a model are of different sizes and shapes, the model must be large enough to contain sufficient pores before the average modulus obtained from uniaxial loading can be identified as an effective property. Using differently sized models, we determined the variability of the average moduli. Such information is valuable when homogenized or continuum material models are used in the stress analyses of coatings. Our computed results show that a model must be large enough to contain 50–100 pores before the averaging of properties is accurate. Using the Al2O3–TiO2 models, we also simulated microindentation tests. Unlike the results determined from uniaxial loading, the elastic moduli estimated from indentation possessed large variations. Apparently, the morphology of the pores immediately beneath the indentation or within the zone of influence has a significant effect on the response of the indenter and the measured modulus. The implications of these results and the computational capability to predict the mechanical properties of porous, plasma-sprayed ceramic coatings are discussed here.

Surface Effects on Nanoindentation

Abstract: In this paper, we report on a study of the surface effect on nanoindentation and introduce the apparent surface stress that represents the energy dissipated per unit area of a solid surface in a nanoindentation test. The work done by an applied indentation load contains both bulk and surface work. Surface work, which is related to the apparent surface stress and the size and geometry of an indenter tip, is necessary in the deformation of a solid surface. Good agreement is found between theoretical first-order approximations and empirical data on depth-dependent hardness, indicating that the apparent surface stress plays an important role in depth-dependent hardness. In addition, we introduce a critical indentation depth. The surface deformation predominates if the indentation depth is shallower than the critical depth, while the bulk deformation predominates when the indentation depth is deeper than the critical depth.