Papers by Keyword: Indentation Test

Abstract: Titanium and its alloys are commonly used for biomedical implants and therefore should have good biocompatibility, suitable levels of strength, fracture toughness, fatigue resistance, and low elastic modulus. Alloying Ti with β-stabilizing elements (Ta, Mo, Nb and V) allows obtaining alloys with elastic modulus closer to that of bone (10-30 GPa), thus minimizing the tendency for stress shielding and bone resorption. A combinatorial method, based on variable composition laser-assisted deposition, has been used for synthesizing Ti-Ta alloys. The alloys were characterized in composition and microstructure by XRD, SEM, and EDS, and mechanical properties were assessed using depth-sensing ultramicroindentation tests. As the Ta content increases from 3 wt% to 36 wt%, the elastic modulus of the alloys decreases from 120 GPa to about 45 Gpa, corresponding to a region formed of the predominant α” (orthorhombic) phase. The lowest value of elastic modulus (45 GPa) was obtained for the Ti-36Ta (wt%) alloy, which is considerably lower than those of commercial Ti alloys currently used (above 110 GPa). Based on these results, volumetric samples of Ti-40Ta alloy were produced by laser deposition, presenting the predominance of the α” (orthorhombic) phase, elastic modulus as (80±12) GPa, and nanohardness as (4.2±0.6) GPa with H_it/E_it equal to 0.052±0.015, which reinforces the viability of using this composition with potential application as a biomaterial.

Abstract: Pile has a textured structure that contains voids and cavities, and the texture hardens with repeated use. It is advantageous to numerically evaluate the hardening characteristics of the pile texture for the development of the products such as towels. Then, the objective of this study is to establish an objective method for evaluating the hardening of the pile due to repeated use. In particular, to determine product specifications, it is necessary to define the conditions under which measurement results are stable. Therefore, for proper design of pile products, objective test methods for repeat use of the pile must be identified. This article reports the effect of repeated indentation testing with a spherical probe on towel samples folded in two to form four layers. A contact theory based on Hertzian theorem is used to evaluate the stiffening of the towel due to repeated indentation. For the properties evaluated in this extended contact theorem, the stiffening behavior is discussed by comparing the changes in the results of 20 repeated tests. In this discussion, the critical times of the indentation test are analyzed to quantify the characteristics of the stiffening behavior of the cotton towels. Analyzing the indentation times shows that critical conditions for the number of tests can be defined.

Abstract: Austenitic stainless steels are widely used due to their resistance to corrosion and to the possibility of using them at temperatures above 600 °C. Plasma nitriding and nitrocarburizing consist of a thermochemical process that introduces nitrogen and nitrogen/carbon, in atomic form, allowing the formation of second phases of these elements with the substrate. These thermochemical treatments of plasma nitriding and nitrocarburizing were performed on austenitic stainless steel AISI 312 at temperatures of 400 °C and 500 °C, obtaining thicknesses of around 12 μm and 24 μm, respectively. Mechanical properties of indentation were obtained using a Hit 300 nanoindenter (Anton Paar), in a load-unload cycle and with a depth of up to 10% of the layer, with Berkovich indenter. The elastic moduli obtained for the nitrided layers were 281 ± 21 GPa (400 °C) and 163 ± 32 GPa (500 °C) and for the nitrocarburized were 214 ± 12 GPa (400 °C) and 169 ± 25 GPa (500 °C). The indentation nanohardness obtained for the nitrided layers were 14.1 ± 1.0 GPa (400 °C) and 3.5 ± 1.2 GPa (500 °C) and for the nitrocarburized layers were 10.8 ± 0.8 GPa (400 °C) and 4.3 ± 1.2 GPa (500 °C). Therefore, these results indicate slightly higher values for the two mechanical properties indentation (elastic modulus and nanohardness) at 400 °C than at 500 °C caused by nitriding compared to nitrocarburizing treatment; however, when considering the percentages of standard deviations, the treatments at 500 °C present much higher values for these properties, as compared to the treatments at 400 °C, a behavior associated with the presence of chromium and iron nitrides.

Abstract: Energy absorbing properties of open-cell carbon foams were evaluated by quasi-static and dynamic compression tests. Though carbon foams show brittle deformation behaviors, they have wide plateau region. The plateau stress linearly increases with increasing the relative density. Furthermore, the strain rate sensitivity is 0.03 and 0.15 at low and high strain rate region, respectively. Indentation tests were performed on cylindrical sample having porosity of 92.3 to 92.8% with different impact speeds. No plateau region is observed and macro cracks occur in the high speed indentation test. The energy absorption efficiency of carbon foams is higher than that of conventional aluminum foams because of their wide plateau regions.

Abstract: In design of the electronic device, FEM analyses considering the creep deformation of solder joints in-situ should be conducted to evaluate the strength reliability. The indentation test is one of effective method to evaluate the creep deformation in microscopic region. However, the result obtained by the indentation test does not coincide with that obtained by the tensile creep test. To solve the problem, the method to determine the suitable area for the indentation test had also been proposed by using the numerical test. To apply the proposed method for the actual indentation test, the homogeneity of specimen should be considered. In this paper, the analyses of the proposed indentation tests were conducted by using the homogeneous and inhomogeneous specimen models of Sn-3.0Ag-0.5Cu. Three types of the deformation behavior were given for the initial phase and the indenter was pushed into in the specimen at the three locations. As a result, it was found that there was not difference in the distribution of the principal stress caused by variation in the indent location. However, the proposed method can successfully determine the reference area except for the case when the deformation behaviors of the constituent phases have a large difference.

Abstract: With the ever-growing demand for further increase in the integration density of semiconductor devices, silicon wafers as the substrates for most devices are required to be extremely flat. In particular, it is strongly required to suppress edge roll-off, which seriously deteriorates the surface flatness near the wafer edge during polishing process in the final stage of the wafer manufacturing. In this study, we investigate the properties of polishing pads required for decreasing edge roll-off and propose the evaluation method of the properties. Polishing experiments with silicon wafers and evaluation tests for polishing pads reveal that the proposed method can estimate the obtained edge surface flatness.

Abstract:

Cemented carbides belong among materials with high hardness and wear resistance even at temperatures around 700 °C. These properties are due to carbide composite structure which is formed mainly of tungsten carbide (WC) in combination with a metal matrix (usually cobalt). A synergistic effect that has a positive impact on the final properties is obtained by the combination of hard carbides and a soft matrix. The high hardness of the cemented carbides is associated with a decrease in fracture toughness which in the case of cutting tools is an important property. It is therefore necessary to measure the value of fracture toughness and thus monitor the state of the material. In practice, the fracture toughness of cemented carbides is usually tested by indentation methods of metallographic samples. Therefore, this work focuses on the comparison and optimization of computational models for determining fracture toughness using indentation methods. Eight types of cemented carbides used for the manufacture of cutting tools were tested. Fracture toughness of selected cemented carbides was measured after heat loading.

Abstract: In this paper, research on a testing method of indentation test proposed by F M Haggag is discussed first, and the experimental testing research on metallic material properties with strain aging is carried out and discussed using indentation test. The authors proposed to use indentation test to measure the properties of metallic materials with strain aging embrittlement based on experimental verification. And it provides a possibility to measure the properties of metallic materials with strain aging using nondestructive testing method.

Abstract: The aim of this study is to show elastic J-integral needed to evaluate the interfacial fracture toughness of bi-material in indentation test. Three dimensional J-integrals along the crack front tip in semi-elliptical crack lying on the interface were analyzed using domain integral technique installed in commercialized finite element code MARC. The J-integral was calculated under several kind of aspect ratio of semi-elliptical cracks. In order to have to evaluate the interfacial fracture toughness from interfacial crack length and indentation load obtained in indentation tests, the analytical formula for two dimensional interfacial crack J-integral under plane stress, which had been introduced by J. R. Rice and G. C. Sih, was modified in reflecting upon the three dimensional effect. Finally, the indentation test was conducted for Aluminum alloy/ PMMA combination sample, and the associated fracture toughness was evaluated.Fig.1 Schematic illustration of indentation testFig.2 Schematic illustration of analysis mode

Abstract: The indentation test is one of the most common techniques for the mechanical characterization of materials. Different tests have been standardized, depending on punch geometry and indentation parameters, and different models have also been set up to predict indentation hardness and to estimate uni-axial mechanical properties for all the geometries (cone, wedge, pyramid, sphere, etc.). A flat-ended cylindrical indentation technique (FIMEC) has been developed by one of the present authors. FIMEC employs a cylindrical punch with diameter ranging from 3.0 to 0.5 mm and gives pressure-penetration curves from which yield stress and elasticity modulus can be determined. The specific characteristics of FIMEC are: 1-the high simplicity of the apparatus; 2-the possibility to get information about the local material properties on a scale large enough to include many grains (data represent bulk characteristics and are not influenced by those factors which dramatically affect micro-and nanoindentation tests); 3-the large versatility in industrial applications such as the control of welding quality, 4-the on-line monitoring of forging or extrusion processes etc.. This paper describes a new algorithm developed to calculate the yield stress from FIMEC curves. To assess the reliability of the method, it has been tested on several metals of known characteristics and the scattering of data with respect those from tensile tests resulted to be within ±7%.