Indentation Plastometry of Very Hard Metals (original) (raw)
Related papers
Acta Materialia, 2003
Indentation testing is a common method to assess the mechanical properties of materials near their surface. The elasto-plastic properties may be determined from the force penetration curves measured in indentation using inverse methods. In this spirit, Dao et al. [1] (Acta Materialia, 49, 2001) have established a forward and a reverse analysis for engineering metals using the equivalent conical indenter of the Berkovich and the Vickers pyramids, which has an included angle q of 70.3°. Extending Dao's approach, we studied, based on a finite element analysis on elasto-plastic materials, the influence of the included angle of conical indenters (q = 70.3, 60, 50 and 42.3°) and the friction coefficient on the force penetration curves. Based on this analysis, we suggest a more general method for determining the plastic properties of metals. The mechanical behaviour is modeled with the Young's modulus, E, the yield strength, s y , and the strain hardening exponent, n. We have shown that friction has a significant effect on the normal force measured on tips having included angles lower or equal to 50°. We have constructed, for each indenter geometry, a dimensionless function relating the characteristic parameters of the loading curve in indentation to the elasto-plastic parameters of metals. These functions have been generalized for any included angle. We show that the use of a second indenter with an included angle lower than q = 70.3°allows us to determine the strain hardening exponent with greater accuracy. Moreover, the sharper the indenter, the better the accuracy.
Elastic-plastic property evaluation using a nearly flat instrumented indenter
International Journal of Solids and Structures, 2017
A 100-µm diameter, nearly flat, instrumented, indenter is used to indent aluminum AA-6463 and X80 pipeline steel. In contrast to sharp and spherical indenters, a rising load-displacement response is followed by a concave-downwards response during indentation. The substrate materials are characterized using tension and compression tests. Yield strengths measured under compression are within +/-10% of the tensile values thereby providing partial support for assuming symmetric tension-compression response. Based on imaging of the actual indenter using a Scanning Electron Microscope, a model of the indenter that accounts for the curved contact profile was created, assumed to be rigid and used in the finite element simulations. In the simulations, tensile yield strength and flow properties, obtained by tensile testing are used to describe the behavior of the substrate and good agreement with measured indentation force-displacement curves was obtained when the exact shape of the indenter was used. The agreement is poor when the contact profile of the indenter was idealized as flat. In the context of the inverse approach, using the Efficient Global Optimization technique, fits to the stress-strain curves of both of the alloys were obtained, and again the curvature of the indenter contact profile is found to be crucial. This work sets the stage for a large-scale deployment of the inverse approach to map the stress-strain response of heterogeneous microstructures such as welds.
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. #
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.
2019
A new technique that can determine the elastic-plastic properties of metallic materials using an instrumented indentation testing and iterative finite element (FE) simulations is proposed. This non-destructive technique can be applied to isotropic, additively manufactured, and/or surface treated metallic components of various scale. Currently, the measurement of material properties using the instrumented microor nanoindentation test is limited to the elastic modulus and surface hardness. A number of experimental and numerical approaches have been suggested for prediction of monotonic properties of metallic materials including yield strength, strain hardening parameters, ultimate strength, and fracture toughness. However, the past efforts to measure the stress-strain behavior using a single instrumented indentation test were not successful because there is no straightforward correlation between forcedisplacement relation and the elastic-plastic relation. In this study, both experimen...
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2009
Experimental applications of the methodology developed for spherical indentation are proposed in this paper. Two quasi-spherical indenters with different shapes were used in order to evaluate the stress-strain curve of five steels. Although the shape of the indenter was not perfectly spherical, it was shown that models developed for spherical indentation can be used with an adequate correction. The results are in good agreement with those obtained by tensile tests. Moreover, the case of the austenitic alloy (AISI 316L) revealed the importance of sample preparation for the experimental results.
In-Situ Measurements of Mechanical Properties Using Novel Automated Ball Indentation System
1993
ABSTRACT: Determination of the integrity of any metallic structure is required either to ensure that failure will not occur during the service life of the components (particularly following any weld repair) or to evaluate the lifetime extension of the structure. A portable/in-situ stress-strain microprobe system was developed to evaluate nondestructively in situ the integrity of metallic components [including base metal, welds, and heat-affected zones (HAZs)] The microprobe system utilizes an innovative automated ball indentation (ABI) technique to determine several key mechanical properties (yield strength, true-stress/true-plastic-strain curve, strain-hardening exponent, Lüders strain, elastic modulus, and an estimate of the local fracture toughness). This paper presents ABI test results from several metallic samples. The microprobe system was used successfully to nondestructively test in-situ a circumferentially welded Type 347 stainless steel pipe. Four V-blocks were used to mou...
Instrumented indentation test for hardness and materials parameter from millinewtons to kilonewtons
2002
The ISO/DIS 14577 Metallic materials - Instrumented indentation test for hardness and materials parameters Part 1-3 (IIT) concerns test forces up to 30 kN. The paper reports on IIT at test forces ranging from 0.002 N to 1000 N on non magnetizable steel X8 CrMnN 18- 18 (1.386) with well polished surface using Vickers indenter and four hardness machines of different design (Nano Indenter XP, Fischerscope H 100, Zwick Z005 with Universal hardness head and a laboratory four-column set up materials testing machine) according to the standard. Using mostly identical test parameters the results of the different machines are almost in good agreement. Estimated small differences are caused by the different uncertainties of the used machines and by different methods of mathematical analysis of the detected raw data.
Journal of Materials Research, 2009
Instrumented indentation tests have been widely adopted for elastic modulus determination. Recently, a number of indentation-based methods for plastic properties characterization have been proposed, and rigorous verification is absolutely necessary for their wide application. In view of the advantages of spherical indentation compared with conical indentation in determining plastic properties, this study mainly concerns verification of spherical indentation methods. Five convenient and simple models were selected for this purpose, and numerical experiments for a wide range of materials are carried out to identify their accuracy and sensitivity characteristics. The verification results show that four of these five methods can give relatively accurate and stable results within a certain material domain, which is defined as their validity range and has been summarized for each method.