The application of indentation techniques to the evaluation of fracture toughness is examined critically, in two parts. In this first part, attention is focused on an approach which involves direct measurement of Vickers-produced radial cracks as a function of indentation load. A theoretical basis for the method is first established, in terms of elastic/plastic indentation fracture mechanics. It is thereby asserted that the key to the radial crack response lies in the residual component of the contact field. This residual term has important implications concerning the crack evolution, including the possibility of post indentation slow growth under environment-sensitive conditions. Fractographic observations of cracks in selected “reference” materials are used to determine the magnitude of this effect and to investigate other potential complications associated with departures from ideal indentation fracture behavior. The data from these observations provide a convenient calibration of the Indentation toughness equations for general application to other well-behaved ceramics. The technique is uniquely simple in procedure and economic in its use of material.

A Critical evaluation of indentation techniques for measuring fracture toughness

Occurrence, behavior and effects of nanoparticles in the environment.

The basic principles and practical applications of indentation fracture are reviewed.

Indentation fracture: principles and applications

Results of a data evaluation exercise are presented for a particular specification of sintered alpha-alumina (mass fraction of Al2O3, ≥0995; relative density (rho/rhotheoretical), ≥098; and nominal grain size, 5 μm) A comprehensive set of material property data is established based on published physical, mechanical, and thermal properties of alumina specimens that conform to the constraints of the material specification The criteria imposed on the properties are that the values should be derived from independent experimental studies, that the values for physically related properties should be mutually self-consistent, and that the sets of values should be compatible with established material property relations The properties assessed in this manner include crystallography, thermal expansion, density, sound velocity, elastic modulus, shear modulus, Poisson's ratio, bulk modulus, compressive strength, flexural strength, Weibull characteristic strength, Weibull modulus, tensile strength, hardness, fracture toughness, creep rate, creep rate stress exponent, creep activation energy, friction coefficient, wear coefficient, melting point, specific heat, thermal conductivity, and thermal diffusivity

Evaluated Material Properties for a Sintered alpha-Alumina

https://personalpages.manchester.ac.uk/staff/j.gough/lectures/te/7_8_bone/BONE_ENG/ceramic/ceram1.pdf

Biphasic calcium phosphate nanocomposite porous scaffolds for load-bearing bone tissue engineering.

The uniaxial strength of engineering ceramics is often measured by the well-known flexure strength test method there is a risk that flexure data are not representative of the properties of fabricated components. Reliability estimates for components based upon statistical extrapolation techniques from flexure data may not be valid. This paper reviews the problem and judges the usefulness of flexure data for design purposes. It is shown that some of the limitations of flexure data apply; to other modes of testing, including direct tension testing

Design Data for Engineering Ceramics: A Review of the Flexure Test

Thermophysical properties for the solid and liquid phases of several Ni based superalloys (CMSX-4, CMSX-10, CM186LC, IN 738 and Rene 80) have been measured. The following properties were measured: heat capacity and enthalpy, thermal expansion coefficient and density, thermal diffusivity, viscosity and surface tension. Analysis of these measurements showed that that γ′ phase (Ni3Al) affected the values for the following properties; C p, enthalpy, electrical resistivity, thermal diffusivity and conductivity. Relationships have been identified between properties and the γ′ phase content (which can be represented by mass% Al in the alloy). These relations were then used to calculate property values of the alloys from chemical composition. Other relations were developed to estimate the viscosities and surface tensions of Ni based superalloys. The predicted property values were found to be in good agreement with the measured values.

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Measurement and estimation of thermophysical properties of nickel based superalloys

A series of glasses of stoichiometric composition with varying proportions of TiO2 and/or ZrO2 as nucleating agent have been studied to examine the effect of nucleation addition on the sequence of crystallization and transformation to the stable phase, cordierite. It is shown that TiO2 is the most effective nucleating agent and that if large amounts of ZrO2 are substituted for TiO2 cristobalite forms as an intermediate phase and is associated with rapid volume changes and consequently with weak porous products. Substitution of ZrO2 for TiO2 also causes other changes in phase development, especially in the relative proportions of β-quartz solid solution and magnesian petalite produced during the early stages of crystallization. The use of a combination of experimental techniques (dilatometry, DTA, X-ray diffraction and electron microscopy) has proved most effective in studying phase development and the relationship between processing characteristics and composition.

Cordierite glass-ceramics-effect of TiO2 and ZrO2 content on phase sequence during heat treatment

The driving forces for the recent development of nanoscale features in conventional ceramic materials for both mechanical and functional reasons are discussed, and the causes of some of the resulting property enhancements are identified. Examples from the technical literature are examined, and the potential for future applications is assessed in terms of the tradeoff between enhanced properties and the added costs and difficulties of processing ultrafine powders.

Nanostructured ceramics: a review of their potential

The concept of edge chipping as a pragmatic way of ranking materials for toughness is now well established for brittle materials, but has some limitations for tougher materials such as hardmetals and tool steels. This paper reviews our current understanding of the process of quasi-static edge chipping or flaking. Issues of flake shape, statistics of flaking load and linearity of flaking load vs. distance from edge relationships are discussed. Based on experimental work, the `universal' relationship between edge toughness, defined as flaking load divided by distance of indentation from the edge, and fracture energy GIC, as evaluated by McCormick and Almond, is re-evaluated with improved statistics and found to be correct.

Roger Morrell

Papers

Design Data for Engineering Ceramics: A Review of the Flexure Test

Measurement and estimation of thermophysical properties of nickel based superalloys

Cordierite glass-ceramics-effect of TiO2 and ZrO2 content on phase sequence during heat treatment

Nanostructured ceramics: a review of their potential

Edge chipping of hard materials