A Critical Evaluation of Indentation Techniques for Measuring Fracture Toughness: I, Direct Crack Measurements

Abstract

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.

Design maps for failure of all-ceramic layer structures in concentrated cyclic loading

“…d = d c = 0.5 mm and d v = 0 [8]. Toughness values were determined from crack measurements at Vickers indentations [36]. Crack velocity exponents were obtained from existing cyclic fatigue data on these or similar ceramics [37].…”

Carbon materials with tailored porosity by self-assembly method: Influence of the synthesis conditions

“…Raman spectra were obtained by Raman spectrometer XY modular (Dilor) with a CCD4 detector. The excitation source used was an argon laser, model Specra-Physics 265, which used the green line of H v is the relationship between applied load P and the surface area of the diagonals of indentation [22]. Wear tests were carried out under dry sliding conditions using a tribometer ball-on-disk according to ASTM wear testing standard G99-03.…”

Indentation properties of ZrO2–SiO2 coatings on glass substrates

“…Different loads were tested ranging from 10 to 1000 g. For loads lower than 500 g no mechanical parameter could be calculated, since no imprint from the indenter was obtained. Mechanical parameters from indentation tests were determined from the experiments performed with 500 and 1000 g loads, by using the expressions given in [19], following the procedure explained by Rincón and Capel [20]. Experimental errors for Vickers microhardness (H V ), Young modulus (E) and critical stress intensity factor (K IC ) measurements was ±0.5 GPa, ±5 GPa and ±0.1 MPa m 1/2 , respectively.…”