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Indentation

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


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Journal ArticleDOI
Xiaofeng Li1, H.B. Li1, Yuhai Liu1, Qiuju Zhou1, Xusheng Xia1 
TL;DR: In this paper, a novel clustered assembly approach with irregular boundaries for grain-based brittle rock is incorporated into the particle flow code (PFC) to calibrate the macro-responses such as the low tensile to compressive strength ratio observed in laboratory tests.

90 citations

Journal ArticleDOI
TL;DR: In this article, the authors compared various methods to measure fracture toughness using indentation precracks using soda-lime glass as a test material and found that stress intensity factors based on classical half-penny crack shapes overestimate toughness values and produce an apparent R-curve effect.
Abstract: Various methods to measure fracture toughness using indentation precracks were compared using soda-lime glass as a test material. In situ measurements of crack size as a function of applied stress allow both the toughness K[sub c] and the residual-stress factor [chi] to be independently determined. Analysis of the data showed that stress intensity factors based on classical half-penny crack shapes overestimate toughness values and produce an apparent R-curve effect. This is due to a constraint on crack shape imposed by primary lateral cracks in soda-lime glass. Models based on elliptical cracks were developed to account for the crack-shape effects.

90 citations

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the influence of the lateral confining stress on the development of the plastic zone under the indenter and on the initiation of tensile fractures in the indentation.
Abstract: The paper reports results of a numerical analysis of the wedge indentation problem. The main objective of this research is to investigate the influence of the lateral confining stress on the development of the plastic zone under the indenter and on the initiation of tensile fractures. Numerical analysis indicates that the location of maximum tensile stress (interpreted as the point of crack initiation) moves away from the indentation axis as the lateral confinement increases. It is found that a small increase in the confining stress from zero induces a large increase in the inclination of this point on the indentation axis. However, the confinement does not reduce significantly the maximum tensile stress and it hardly influences the indentation pressure. These numerical results shed some light on the mechanism of formation of lateral or sub-horizontal tensile cracks observed in the indentation experiments.

90 citations

Journal ArticleDOI
TL;DR: The zirconia based ceramic has mechanical properties that may allow it to withstand the loading found in posterior areas, and transformation toughening was found when high loads impacted on the surface of zIRconia.
Abstract: Objectives: Yttria partially-stabilized zirconia polycrystalline (Y-TZP) has been the subject of extensive research because of its high strength and toughness. The aim of this study was to evaluate the biaxial flexural strength, fatigue life, and to investigate in more detail on single cycle specimens, the pressure-induced phase transformation of a Y-TZP dental ceramic using Raman microspectroscopy. Materials and Methods: Thirty standardized discs (15 x 1.2 mm(2)) were used to examine the biaxial flexural strength (ISO 6872 standard) using a Dartec HC10 Servohydraulic testing machine (Zwick Ltd., UK). The specimens were also submitted to Vickers hardness (on polished and as-received surfaces within the same specimen) and dynamic fatigue test. The initial bulk phases were examined via X-ray diffraction and the local phase transformations that occurred in the zirconia induced by the various Vickers indentation loads (20-50 kg) were examined via Raman microspectroscopy on single cycle specimens. The fracture surface after biaxial flexural testing was also examined via Raman spectroscopy. Results: The Cercon specimens tested had flexural strength and Weibull modulus (m) of similar to 823.3 (+/- 114.7) MPa and 8.3, respectively. As-received surfaces (1378.7 +/- 51.8 Hv) had slightly higher hardness value compared with polished surfaces (1354.33 +/- 50.9 Hv); however, two-way analysis of variance showed no significant difference in hardness values between polished and as-received surfaces (P > 0.05). Additionally, the specimens survived to 5 x 10(5) cycles when using a load of 70% of the mean biaxial flexural strength or lower. Raman microspectroscopy showed transformation of tetragonal to cubic and monoclinic phases within the indentation area. The fraction of monoclinic phase showed only limited variation with load or distance from the center to indentation edge. The level of cubic phase, however, was greatest at the indentation center. Transformation to cubic phase was observed on the lower surfaces (tension side) of fractured specimens. It was also observed near the specimen center exposed upon fracture. In the latter region an increase in monoclinic phase was additionally observed. Further work will be carried out using Raman microspectroscopy to assess the effect of fatigue on phase transformations. Conclusion: The zirconia based ceramic has mechanical properties that may allow it to withstand the loading found in posterior areas. Transformation toughening was found when high loads impacted on the surface of zirconia. However it should be born in mind that this work was not carried out on veneered specimens, which exhibit different failure modes. (c) 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 88B: 366-377, 2009

90 citations

Journal ArticleDOI
TL;DR: In this paper, the authors used the nonlinear elastic response upon unloading to verify if the hardness values measured on the super- and ultrahard coatings are self-consistent, and the analytical solutions were also used to estimate the tensile strength of the coatings.
Abstract: Hertzian analysis of the nonlinear elastic response upon unloading provides analytical solutions that were used to verify if the hardness values measured on the super- and ultrahard coatings are self-consistent. The analytical solutions were also used to estimate the tensile strength of the coatings. The highest tensile stress occurs at the periphery of the contact between the coating and the indenter and, in the case of ultrahard coatings, it can reach values in the range of tens of Gpa, thus giving an estimate of their tensile strength. The results show that the tensile strength of the superhard nanocomposites reaches an appreciable fraction of the ideal cohesive strength that is predicted on the basis of the universal binding energy relation. The data are compared with finite element computer modeling in order to obtain a deeper insight into the complex problems. Reliable values of the hardness can be obtained if coatings of a thickness greater than 8 μm are used and the load-independent values are measured at sufficiently large indentation depths of greater than 0.3 μm.

90 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023517
20221,124
2021457
2020510
2019566
2018526