Analysis of indentation of brittle materials (original) (raw)
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The influence of the indenter tip-radius on indentation testing of brittle materials
1999
Indentation testing of a brittle material using a notionally 'sharp'indenter may reveal several important physical properties, including fracture toughness, surface finish information and the residual stress state. In the case of shallow cone indenters, the contact and fracture mechanics is well defined and closed-form solutions exist in elasticity theory. However, no real indenter is atomically sharp, and the scope of the present article is to quantify how a finite apex radius may modify the stress state induced by a conical indenter.
The influence of the indenter tip-radius on indentation testing of brittle materials.pdf
Indentation testing of a brittle material using a notionally`sharp' indenter may reveal several important physical properties, including fracture toughness, surface ®nish information and the residual stress state. In the case of shallow cone indenters, the contact and fracture mechanics is well de®ned and closed-form solutions exist in elasticity theory. However, no real indenter is atomically sharp, and the scope of the present article is to quantify how a ®nite apex radius may modify the stress state induced by a conical indenter. In particular, implications for the load-displacement relation, occurrence of yielding and maximum contact pressure induced are found. A brief discussion of the in¯uence of edge radius on the¯at-ended indenter, once used to induce Hertzian type ring cracks, is also included, as this may be treated by a similar procedure. #
Numerical analysis of indentation fracture in quasi-brittle materials
Engineering Fracture Mechanics, 2004
The process of indentation of brittle and quasi-brittle materials has been investigated both from the experimental and the theoretical point of view. As far as we know, only a few studies have tried to explain the mechanics of cutting due to an indenter which penetrates inside the material. In this paper, an attempt is made to find some general relations for the cutting process in brittle and quasi-brittle materials, under different hypotheses for the microscopic failure behaviour. Fracture patterns in homogeneous brittle solids are obtained by the finite element method in the framework of linear elastic fracture mechanics. Microstructural heterogeneities are taken into account by the lattice model simulation. Although the reality is often much more complex than the theoretical models applied, the study provides interesting indications for improving performance of cutting tools.
Mechanical behaviour of glass during cyclic instrumented indentation
MATERIALS SCIENCE-POLAND
Indentation techniques are largely used nowadays for characterizing the intrinsic mechanical properties of brittle materials. A cyclic indentation tests have been carried out on soda lime glass and borosilicate glass using an instrumented indentation apparatus. Repeated post-threshold Vickers indentations were made using various peak loads. The hardness, elastic modulus and fracture toughness of the two glasses were evaluated using the consecutive load-displacement curves. Their properties of were compared and discussed.
Determination of the hardness and elastic modulus from continuous vickers indentation testing
Journal of Materials Science, 1996
Continuous Vickers (Hv) indentation tests were performed on different materials (ion crystals, metals, ceramics, silica glass and plastic). Load-indentation depth curves were taken during the loading as weil as during the unloading period by a computer controlled hydraulic mechanical testing machine (MTS 810). The indentation work measured both the loading and the unloading periods, and these were used for the evaluation of parameters characterizing the materials. It was found empirically that there were linear connections between the maximum load to the power 312 and the indentation work. These connections were used to relate the conventional hardness number, Hv, and Young's modulus, E, with the work performed during loading and unloading. This work can be determined with great accuracy from the measurements.
ACTA IMEKO, 2019
In this paper, the experimental procedure and calculation model for the measurement of the indentation modulus by using the primary hardness standard machine at INRiM in the macro-scale range at room temperature is described. The indentation modulus is calculated based on the Doerner-Nix linear model and from accurate measurements of indentation load, displacement, contact stiffness, and hardness indentation imaging. Measurements are performed with both pyramidal (Vickers test) and spherical indenters (Brinell test). Test force is provided by a dead-weight machine, and the occurring displacement is measured by a laser-interferometric system. The geometrical dimensions of both the Vickers and Brinell indentations are measured by means of a micro-mechanical system and optical microscopy imaging techniques. Applied force and indentation depth are measured simultaneously, at a 16 Hz sampling rate, and the resultant loading-unloading indentation curve is obtained. Preliminary tests are performed on metal and alloy samples. Considerations and comments on the accuracy of the proposed method and analysis are discussed.
On indentation and initiation of fracture in glass
2008
The influence of indenter elasticity on Hertzian fracture initiation at frictional dissimilar elastic contact has been examined experimentally and numerically. In flat float glass specimens initiation of cone cracks has been observed and fracture loads measured with steel and tungsten carbide indenters at monotonically increasing loading and during a load cycle. The observed effect of indenter elasticity on fracture loads was found to be qualitatively different from the one predicted by the Hertz contact theory. This discrepancy may be explained by the presence of interfacial friction. The friction coefficient between the indenters and the specimen was measured and a contact cycle at finite Coulomb friction has been analyzed numerically. The influence of the indenter elasticity and the friction coefficient on the surface maximum tensile stress has been investigated and the results concerning the influence of these parameters on the fracture loads as given based on a critical stress fracture criterion. The obtained computational results were found to be in better agreement with experimental findings as compared to the predictions based on the frictionless contact theory. A remaining quantitative discrepancy was attributed to the well-known fact that a Hertzian macro-crack initiates from pre-existing defects on the specimen's surface. In order to account for the influence of the random distribution of these defects a Weibull statistics was introduced. The predicted critical loads corresponding to the 50% failure probability were found to be in close agreement with experimentally observed ones.
International Journal of Solids and Structures, 2006
Knowledge of the relationship between the penetration depth and the contact radius is required in order to determine the mechanical properties of a material starting from an instrumented indentation test. The aim of this work is to propose a new penetration depth-contact radius relationship valid for most metals which are deformed plastically by parabolic and spherical indenters. Numerical simulation results of the indentation of an elastic-plastic half-space by a frictionless rigid paraboloïd of revolution show that the contact radius-indentation depth relationship can be represented by a power law, which depends on the reduced YoungÕs modulus of the contact, on the strain hardening exponent and on the yield stress of the indented material. In order to use the proposed formulation for experimental spherical indentations, adaptation of the model is performed in the case of a rigid spherical indenter. Compared to the previous formulations, the model proposed in the present study for spherical indentation has the advantage of being accurate in the plastic regime for a large range of contact radii and for materials of well-developed yield stress. Lastly, a simple criterion, depending on the material mechanical properties, is proposed in order to know when piling-up appears for the spherical indentation.