Evaluation of Fatigue Data Through Miniature Specimen Test Techniques
19 Nov 2015-
TL;DR: In this article, the authors present the results of cyclic ball indentation test method as well as cyclic small punch test method that is used to generate the fatigue data at different stress levels.
Abstract: Fatigue properties of materials is an important input while estimating the residual life of critical components. Fatigue data (stress vs. cycles or strain vs. cycles or fatigue crack growth rate data) are used to predict the residual life. One of the shortcomings of this method is that it relies on data generated from virgin material or surveilance coupons which have been exposed to the harsh environment over a period of time. Often the quantity of material available for fatigue data is small and being probabilistic in nature, fatigue data requires multiple specimens to be tested at any given stress/strain levels. This has prompted us to develop test procedures to determine the fatigue data of materials from small volume of material. In this paper, we present the results of cyclic ball indentation test method as well as cyclic small punch test method that is used to generate the fatigue data at different stress levels. There are several fine details relating to these test technique — viz., establishing a equivalent damage criteria for failure life with standard LCF/HCF test specimens. Apart from this, several variables that influence the testing process needs to be considered.This paper briefly reviews the viability of using miniature specimen test techniques, particularly cyclic ball indentation and cyclic small punch testing for extracting the fatigue data, based on the author’s previous work. It is shown that, both the test techniques are capable of detecting and quantifying the prior fatigue damage in the materials.Copyright © 2015 by ASME
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TL;DR: The Small Punch Test (SPT) is an evolving small specimen test technique which has the potential to extract the mechanical properties from small volume specimens as discussed by the authors. But, the validity of these correlations have to be examined, as these are developed from a specified set of materials and testing conditions.
Abstract: Small Punch Test (SPT) is an evolving small specimen test technique which has the potential to extract the mechanical properties from small volume specimens. This test method is used to determine the in situ mechanical properties of components in service for measuring the structural integrity and residual life. The pre-requisite for using this test is to establish correlations between SPT and conventional tests in priori. A number of correlations have been developed between traditional tests and SPT results for determining mechanical properties. The validity of these correlations have to be examined, as these are developed from a specified set of materials and testing conditions. To evaluate SPT and the developed correlations, it is crucial to understand the fundamentals of this test method, the different regimes of deformation experienced by the specimen and its sensitivity for various testing parameters. The attempt of this work is to relook the SPT as a whole and its potential to measure the different mechanical properties. This work lists the various SPT configurations, materials used in literature and the correlations developed. In addition, the influence of test parameters on SPT response, the viability of empirical or analytical relations used to extract mechanical properties and the general issues in SPT is discussed.
27 citations
TL;DR: In this article, Small Punch Creep (SPC) test has been used as an alternative technique for the remaining life calculation of in-service components functioning at high temperature and harsh ambience, since the extraction of conventional full scale specimens from the components in service impairs its integrity.
Abstract: Small punch creep (SPC) test has an important role in the remaining life calculation of in-service components functioning at high temperature and harsh ambience. Since the extraction of conventional full scale specimens from the components in service impairs its integrity, SPC test can be used as an alternative technique. This test method requires very thin disc similar to those needed for transmission electron microscopy (~ 3 mm diameter and 0.5 mm thick). The pre-requisite to employ this test technique is to establish correlations between uniaxial creep and SPC tests in priori. The purpose and scope of this work is to present briefly the principle of SPC testing method in comparison with uniaxial creep test. The differences in terms of specimen geometry and deformation process have been clearly brought out. The correlations developed by several researchers for determining the creep properties from SPC test along with uniaxial creep results for comparison is presented. The contributions by several authors in the direction of numerical simulation and fractography of SPC test is also briefed.
10 citations
TL;DR: Small specimen mechanical testing is an exciting and rapidly developing field in which fundamental deformation behaviours can be observed from experiments performed on comparatively small amounts of data as discussed by the authors, which can be found in this paper.
Abstract: Small specimen mechanical testing is an exciting and rapidly developing field in which fundamental deformation behaviours can be observed from experiments performed on comparatively small amounts o...
8 citations
Cites methods from "Evaluation of Fatigue Data Through ..."
...An ABI test was determined to be suitable to indicate fatigue damage for a set of various metallic materials, but not to quantify it.(61) Ratcheting was investigated using a wire specimen (Figure 13) made from stainless steel, and it was determined that ratcheting strain rate decreased when the number of cycles increased and the wire specimen had a strong memory of previous loading history....
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References
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TL;DR: In this paper, a Miniaturized Disk Bend Test (MDT) is proposed to extract post-irradiation mechanical behavior information from disk-shaped specimens no larger than those used for Transmission Electron Microscopy.
Abstract: A Miniaturized Disk Bend Test capable of extracting postirradiation mechanical behavior information from disk-shaped specimens no larger than those used for Transmission Electron Microscopy is currently being developed. Finite element analysis is performed to convert the experimentally measured load-deflection data into useful engineering information. Since neutron irradiation costs scale with specimen volume, successful development of miniaturized mechanical property tests could provide significant savings in irradiation testing costs for nuclear materials used in fusion and other nuclear technologies. In addition, it may be possible to provide mechanical behavior information which is not ordinarily obtainable due to space limitations in irradiation experiments.
319 citations
TL;DR: In this paper, the authors used finite element modeling to study the development of pile-up during indentation with a rigid sphere as it relates to the measurement of mechanical properties by load and depth sensing indentation.
Abstract: Finite element modeling has been used to study the development of pile-up during indentation with a rigid sphere as it relates to the measurement of mechanical properties by load and depth sensing indentation. A wide range of materials with different elastic moduli, yield stresses, strain-hardening exponents, and friction coefficients were examined. Results show that during a significant portion of the spherical indentation process, the amount of pile-up cannot be related solely to the strain-hardening exponent, as is often assumed. Rather, after initially sinking-in at small depths of penetration, the pile-up for many materials evolves and increases gradually as the indenter is driven into the material. Even when deformation enters the fully developed plastic stage, the pile-up geometry continues to change in manner that can significantly affect the contact area. It is also shown that contact friction affects the pile-up geometry, and that the pile-up heights before and after the indenter is unloaded can be quite different. Implications for the measurement of mechanical properties by load and depth sensing indentation methods are discussed.
254 citations
TL;DR: A wide array of specimen geometries and test techniques have now been developed as discussed by the authors, and the purpose of this paper is to review these techniques and examine their status, problems, and potential for future applications.
Abstract: Small specimen test technology has evolved out of the necessity to develop and monitor materials proposed for or used in nuclear power generation systems. Development of materials for improved cladding and in-core structures for fission reactors and assessment of core materials and pressure vessel steels already under irradiation necessitated the use of specimens which fit into existing irradiation space or which could be extracted from irradiated structures, such as cladding or ducts. Interest in simulating neutron irradiation by light and heavy ion irradiation led to the development of thin foil and wire geometry specimens. Further, interest in developing materials for fusion reactors has added additional constraints on specimen sizes associated with available irradiation volumes in existing and proposed high-energy neutron irradiation facilities. Consequently, a wide array of specimen geometries and test techniques has now been developed. It is the purpose of this paper to review these techniques and examine their status, problems, and potential for future applications.
162 citations
TL;DR: In this article, a small-punch test technique was used to evaluate the flow properties of 1Cr-0.5Mo steel and 18Cr-9Ni stainless steel.
Abstract: The small punch (SP) test technique is an attractive method for evaluating mechanical behavior in materials where only small volumes of materials are available. An SP-test machine was developed where miniature disc specimens 5 and 3 mm in diameter and with thickness ranging between 50 to 400 µm can be investigated. For two materials, a 1Cr-0.5Mo low alloy steel and an 18Cr-9Ni austenitic stainless steel, the stress-strain flow curve was assessed and compared with that in tensile tests. The yield strength was determined from the SP-test by analyzing the initial elastic deformation with help of classical plate bending theory. The effective flow properties in the biaxial stress state were evaluated through analytical modelling of the stretching deformation. Good agreement between the uniaxial and biaxial flow properties was found for the 1Cr-0.5Mo steel and acceptable agreement for the 18Cr-9Ni steel.
35 citations
TL;DR: In this article, a portable/in situ stress-strain microprobe (SSM) system was used to measure true-stress/true-plastic-strain behavior of several metallic materials, welds, and their heat-affected-zones (HAZs) in various metallurgical and damage conditions.
Abstract: A novel portable/in situ Stress-Strain Microprobe (SSM) system was used to measure true-stress/true-plastic-strain ({sigma}{sub t}-{epsilon}{sub p}) behavior of several metallic materials, welds, and their heat-affected-zones (HAZs) in various metallurgical and damage conditions. The SSM system utilized an automated ball indentation (ABI) technique to measure elastic modulus, yield strength, {sigma}{sub t}-{epsilon}{sub p} curve, strength coefficient, strain-hardening-exponent (uniform ductility), and to estimate fracture toughness (from the ABI-measured flow properties) in carbon steels, stainless steels, nickel alloys, aluminum alloys, titanium alloys, zirconium alloys, etc. Numerous ABI tests were also conducted on several nuclear pressure vessel steels (NPVSs) in the unirradiated, neutron irradiated, and post-irradiated thermally-annealed conditions. For all these test materials and conditions, the ABI-derived results were in good agreement with those from conventional standard test methods. Furthermore, the nondestructive ABI test results rigorously indicated the various levels of neutron-embrittlement damage and the percentage of ductility recovery following thermal annealing of the NPVS specimens. In situ/nondestructive structural applications of the SSM system and its ABI technique have been demonstrated by testing a circumferentially welded stainless steel pipe and a full-thickness section of a nuclear pressure vessel (using 90{degrees}V-blocks and magnetic mounts for temporary attachment of the SSM testing head to the pipe andmore » the steel section, respectively). All SSM localized tests were computer-controlled and conducted in less than 2 minutes per ABI test; depending on the desired strain rate. Example test results on metallic structural components and samples are presented in this paper. 21 refs., 5 figs., 1 tab.« less
26 citations