Fracture toughness testing for advanced technical ceramics: internationally agreed good practice

Abstract

The development of robust methods for determining fracture toughness and for interlaboratory assessment of results is discussed with respect to procedural standardisation. Acceptable methods are based on meeting several criteria, including ease and cost-effectiveness of testpiece manufacture, the method of introducing a sharp precrack and the acceptability of appropriate fracture toughness analysis. The four simplest methods meeting these criteria are reviewed in detail, together with information on their reproducibility gathered during international round robin exercises. Not all these methods are effective on all materials, and users need to be aware of their limitations. Details of calibration equations and some experimental nuances are given.

On the Mechanics of Fatigue and Fracture in Teeth

“…In addition, unlike the standard methods it does not require a precrack. Yet, there are significant concerns regarding the use of the indentation approach for estimating fracture toughness [72][73][74], especially in evaluations involving biomaterials or hard tissues [75]. One consideration is that there are over 30 different models for estimating the fracture toughness from indentation cracks [74,76], and many of these have been developed from curve fits to data rather than from physical models for Fig.…”

Influence of the notch root radius on the fracture toughness of brittle metals: Nanostructure tungsten alloy, a case study

“…The main problem encountered is that the fatigue stress necessary to nucleate the crack is very close to the fracture threshold stress and accurate control is very dependent on the specimen preparation. As a result, the probability of introducing reproducible sharp notches close to a crack without a high loss of material is reduced [3,4] and a more functional and reproducible alternative is required.…”

Simplified method for determining fracture toughness of two dental ceramics

“…Criteria for standardized tests were recommended in order that they can provide good estimations of fracture toughness 8) . The tests that meet criteria for a standard test, for example, the chevron notch beam (CNB), the single edge precracked beam (SEPB), the surface crack in flexure (SCF), the short chevron-notched, the double cantilever beam and the single edge V-notch beam (SEVNB).…”

“…The advantage of the technique is that it requires a small sample for rapid evaluation of mechanical properties and it may also be useful for material development or quality control 10,12) . However, the Vickers indentation technique has been criticized as an unreliable method for calculating the fracture toughness or any other fracture resistance parameter, and even for a comparative reason 8,13) . It can only be used for a first rough estimation for fracture toughness 4) because most calibration constants are empirically determined and adjusted until a reasonable value is achieved according to the materials under investigation 13) .…”