The Hertzian fracture test

Wilshaw, T. R.

doi:10.1088/0022-3727/4/10/316

Cited by 159 publications

(78 citation statements)

References 17 publications

(16 reference statements)

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“…Hertzian indentation toughness Many attempts have been made to use Hertzian indentation -where a hard sphere is pressed into the flat surface of a brittle substrate -to determine fracture toughness of brittle materials [23][24][25]. In this study, early experimental limitations on the use of this technique are overcome by following the protocol proposed by Warren [10] which simply requires measurement of the fracture load.…”

Section: Gradementioning

confidence: 99%

Fracture toughness of cemented carbides: Testing method and microstructural effects

Sheikh

M’Saoubi²,

Flasar

et al. 2015

International Journal of Refractory Metals and Hard Materials

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Fracture toughness is one the most important parameters for design applications and performance assessment of WC-Co cemented carbides (hardmetals). Different from hardness, fracture toughness is commonly a property more difficult to evaluate, particularly in brittle materials. A large number of different testing methods have been introduced to evaluate toughness of hardmetals, but in general all of them have either theoretically debatable issues or important experimental difficulties. In this study, three different fracture toughness testing methodologies are investigated: three-point bending on Chevron notched specimen ("reference" baseline), Palmqvist indentation test, and Hertzian indentation method. The work is conducted in several cemented carbide grades with different microstructures, in terms of both WC grain size and Co binder content. It is found that Chevronnotched three-point bending test yields suitable fracture toughness values for a wide range of cemented carbide grades with varying hardness. Concerning indentation methods, the Hertzian one may be particularly recommended, as compared to Palmqvist method, as far as hardness (HV30) drops below 1300. On the other hand, if HV30 is higher than 1300 Palmqvist indentation procedure yields reliable fracture toughness measurements. Experimental findings are finally analyzed and discussed on the basis of two theoretical models proposed in the literature.

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Section: Gradementioning

confidence: 99%

Fracture toughness of cemented carbides: Testing method and microstructural effects

Sheikh

M’Saoubi²,

Flasar

et al. 2015

International Journal of Refractory Metals and Hard Materials

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“…This approach differs from previous work [24][25][26][27][28][29] where it was assumed that the crack path initially followed along the trajectory of the minimum principal stress, σ 3 . However, it is likely that small surface cracks (produced by polishing and grinding) lie perpendicular to the free surface, and only when they start to grow will they follow the minimum principal stress trajectory, σ 3 , (this path is normal to the maximum principal stress, σ 1 ).…”

Section: Stress Intensity Factor K Imentioning

confidence: 99%

“…Specimens were ground with 600-grit SiC slurry using a Logitech PM2A polishing machine 3 , and polished with 6 µm polycrystalline diamond powder 4 in distilled water. Specimens of two types of surface finish were prepared for testing:…”

Section: Surface Preparationmentioning

confidence: 99%

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Surface mechanical analyses by Hertzian indentation

Franco

Roberts

2004

Cerâmica

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of grain-boundary glassy phase [14][15][16][17]. The use of conventional fracture toughness evaluations to predict resistance to wear, erosion, and machining may lead to incorrect choices of materials for such applications.Fracture toughness may be determined from Hertzian tests by measuring the minimum load, P min , necessary to propagate cracks in a set of tests [18] on abraded samples (i.e., ones with a high surface flaw density). The test method uses flaws a few microns deep, and so gives results relevant to wear and erosion properties.Here we present surface flaw sizes of polished polycrystalline alumina specimens, with G=1.2, 3.8 and 14.1 µm, determined using the Hertzian indentation method [6][7][8]18], and fracture toughness values determined by the Hertzian method. These fracture toughness values are compared to those derived from Vickers indentation tests. The results are also compared to the rates of wet erosive wear for the same materials. AbstractHertzian indentation technique was used to measure surface flaw sizes on polished dense polycrystalline alumina specimens with grain sizes G = 1.2, 3.8 and 14.1 µm. Two surfaces finishes were studied: well-polished (Syton) and coarse-polished (45 µm diamond paste). Flaw sizes depended on the surface finish and increased with increasing grain size. Fracture toughness (K Ic ) for each material (relating to the propagation of flaws of a few µm depth) was determined from the minimum fracture load in a series of Hertzian tests. K Ic values were 3.58, 3.45 and 2.96 MPam 1/2 for G=1.2, 3.8 and 14.1 µm, respectively. Fracture toughness values were also determined by Vickers indentation over a range of loads; the K Ic values determined from the Hertzian tests were consistent with the trends in K Ic with crack size from the Vickers indentation tests. Keywords: surface, Hertzian indentation, flaw size, alumina. Resumo A técnica de indentação Hertziana foi usada para medir o tamanho das trincas nas superfícies de amostras densas de alumina Theoretical background -Hertzian indentationThe Hertzian indentation test is an alternative to the familiar Vickers indentation test for evaluation of the fracture properties of brittle materials. A great advantage of the Hertzian indentation test is that the deformation in the substrate produced by the indenter is wholly elastic until fracture occurs. This means that the complications associated with the residual stresses in Vickers indentation test do not exist. The stress field is independent of the plasticity properties of the substrate and varies continuously and smoothly near to the contact area. The contact stress field is not substantially affected by minor defects in the indenter geometry. The stress state induced can be found rigorously and exactly [19].On the other hand the Hertzian indentation test has some drawbacks. The stress fields have steep gradients in depth, thus it is difficult to accurately estimate the stress intensity factors for cracks driven by Herztian loads. The principal data needed are the loads at whic...

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“…A number of theoretical models have been developed to predict both the fracture load and the subsequent length of the cracks [9][10][11]. Frank and Lawn [9] investigated the development of the cone crack from the ring crack in the strongly inhomogeneous Hertzian stress field.…”

Section: Surface Crack Defectsmentioning

confidence: 99%

Rolling Contact Fatigue of Ceramics

Wereszczak¹,

Wang

et al. 2006

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The Hertzian fracture test

Cited by 159 publications

References 17 publications

Fracture toughness of cemented carbides: Testing method and microstructural effects

Fracture toughness of cemented carbides: Testing method and microstructural effects

Surface mechanical analyses by Hertzian indentation

Rolling Contact Fatigue of Ceramics

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