Fractal Analysis of Microstructural and Fractograpghic Images for Evaluation of Materials

Materials have hierarchically organized complex structures at different length scales. Quantitative description of material behaviour is dependent on four fundamental length scales [1], which are of concern to materials scientists. These are (1) nano scale, 1-103 nm, (2)micro scale, 1-10 3 μm, (3) macro scale, 1-103mm, and (4) global size scale, 1-106 m. While the nano scale corresponds to, often, highly ordered atomic structures, the global size scale relates geophysical phenomena and large man made engineering structures. Micro scale and macro scale correspond to size of material samples used in laboratories, for designing and for fabrication of miniature to small machineries

Advances in computer-aided crack length measurement during fatigue crack growth testing

The accurate measurement of crack length is one of the most important aspect of fatigue crack growth rate (FCGR) testing. Of the various methods available for crack length measurement, compliance technique is very popular due to the facilities it provides for easy automation. In the compliance technique, compliance crack length (CCL) rela-tions are used for correlating the compliance, computed from measurements of displacements & loads during fatigue cycling, to the crack length contained in the specimen. CCL relations are specific not only to the specimen geometry, but also to the location on the specimen body at which displacements are measured. This specificness is not very conducive to the experimentalist as it introduces errors in the measured crack length if the location of displacement measurement is not accurately maintained. With variations in specimen geometry and size, the accu-rate positioning of displacement measurement transducers is not an easy task. In order to provide greater flexi-bility in the use of the compliance technique, a new scheme has been proposed in this paper. Modelling the defo-rmation of a fracture mechanics specimen during fatigue cycling as rotation of two rigid hinge about a hringe point, the relationship between the location of the hinge-point with crack length has been established using finite element analysis for the single-edge notched three point bend specimen. Further -an iterative method has been developed which can be implemented in the background software for on-line crack length measurement. It has been shown that the iterative method converges rapidly to give the crack length with high accuracy

Compliance crack length relations for the four-point bend specimen

Compliance crack length relations for the four-point bend specimen geometry have not been reported in the literature in spite of this geometry being one of the popularly used specimens for fatigue crack growth studies. An effort has been made in the present work to fill this gap. Accordingly, the finite element technique was employed to simulate loading and calculate displacements at various locations in a four-point bend specimen. The load-displacement data thus obtained were processed to yield compliance crack length relations. These relations were employed to calculate the crack length during fatigue testing of four-point bend specimens in which the crack length was also measured by optical means. A good correlation was observed between the predicted crack length and that measured optically

Analysis of damage in high strength steels

In continuum damage mechanics (CDM) approach, damage accumulation takes place through void initiation, growth and coalescence. In this study, a Bayesian Neural Network based model has been developed to calculate the complex relationship between the extent of damage accumulation and its influencing parameters for a variety of high strength low alloy steels. The model has been applied to confirm that the predictions are reasonable

Microstructural damage evaluation in Ni-based superalloy gas turbine blades by fractal analysis

Ni-based superalloys are used as turbine disc and blade material in which creep, fatigue and creep-fatigue are the important damage mechanisms. Mechanical properties of these alloys depend upon the amounts of gamma-gamma-prime present in the microstructure as well as precipitation of carbides along the grain boundaries. The distribution of gamma-prime depends on the chemical composition, operating temperature and the length of service exposure. During service exposure, as damage accumulates progressively, the morphological characteristics of microstructure change which needs to be assessed using metallographic technique. Conventionally, the extent of damage resulting in deterioration of mechanical properties is quantified by hardness measurement. The variation in hardness is correlated with the morphological features in the metalographic images by identifying precipitation of carbides, presence of cuboidal gamma-prime and the structural changes that occur in the matrix. In this paper, we report fractal dimensions of the insitu metallographic images which can correlate the progressive damage accumulation at various locations of the blades

Modelling of Crack-tip Blunting using Finite Element Method (FEM) (GAP-0088)

For determination of fracture toughness in engineering structural materials, the standard procedure specifies the generation of a crack growth resistance curve (R curve) experimentally and identification of the critical toughness parameter by the intersection of an offset to a blunting line on the R curve. The use of a theoretical blunting line, as proposed in the standards, often gives conservative fracture toughness values particularly in high toughness materials. In this project, through finite element simulation of standard fracture mechanics test specimen, the crack blunting process in ductile materials is proposed to be investigated. From the load-displacement data generated by FEM, the crack tip opening displacement (CTOD) as well as J, an energy parameter of elastic plastic fracture mechanics, and Δa, the crack extension, accompanying the blunting process have been calculated. The effect of variation of material properties like Young’s modulus, E, yield stress, σy and strain hardening parameter, n, on the shape and slope of the blunting line has been established. The numerically obtained blunting line has been validated using experimental results. Important conclusions drawn from this investigation are the following ♦ the blunting line is mildly sensitive to the level of flow stress, with the inflection occurring at a lower flow stress and with reduced sharpness as the flow stress is increased. The blunting line slope is higher in low strength materials. ♦ the nature of the blunting line is greatly dependent with the work hardening capacity of the material, with the overall slope of the blunting line increases with increased hardening behaviour. ♦ the crack tip profile is elliptical not semicircular. For the low strain hardening materials the major axis is more than the minor axis i.e. CTOD2*da

Lead content in new decorative paints in India

The paint industry in India is broadly classified into two categories: organized sector and unorganized sector. Multinational and big Indian companies form the organized sector, whereas the small- and medium-scale industries which produce paints for the local market form the unorganized sector. The present study was undertaken to determine the level of lead in decorative paints in India. A total of 148 paint samples sourced from four organized sector companies and six unorganized sector companies were analyzed for the total lead content. Results of this study reveal that 39 % of the total paints tested (n = 148) contain lead more than 300 ppm, the voluntary limit prescribed by Bureau of Indian Standards, BIS (IS 15489:2011), and 45 % of the tested paints contain lead more than 90 ppm, the US limit. Further analysis of the data indicates that only 5 % of the tested paints manufactured by organized sector companies contain lead more than 300 ppm (n = 91), whereas 93 % of the tested paints manufactured by unorganized sector companies contain lead more than 300 ppm (n = 57). Comparison with earlier reported data suggests that while organized sector companies are gradually abandoning the use of leadbased compounds in their paints, the unorganized sector companies are still adding lead based compounds intentionally in their paints despite the potential health hazards associated with it. The maximum concentration of lead obtained was 80,350 ppm in one of the paints manufactured by an unorganized sector company. The presence of high concentration of lead in yellow and green color paints indicates that color can be a predictor of lead content in decorative paints

Design and Development of Soil Moisture Based Automatic Irrigation System in Nepal

A prototype soil moisture based an automated irrigation system were developed at National Maize Research Program in 2018 to study the water requirement of drought tolerant crop genotype. The irrigation system has been controlled by Arduino UNO as a micro controller. The instant soil moisture data were collected either in Excel format or graphical format using internet of things through the programming of Global System for Mobile Communication: Subscriber Identity Module (GSM:SIM card) of Nepal Telecom. The developed automated irrigation system has found maintained the predetermined threshold soil moisture. This automated irrigation system has been developed to make applicable for drip irrigation system which has operated at low water pressure maintained by 1.5² professional-grade solenoid valve. The introduction of this automated irrigation system has developed the base for Nepalese agricultural scientist in designing and promoting irrigation technology to make Nepalese agricultural more sustainable, mechanized and productive

Proficiency Testfor Proximate Analysis of Coal: Determination of Moisture, Ash, Volatile Matter and Total Sulfur

Proficiency test (PT) is an important way of meeting the requirements of NABL accreditation (ISO/IEC 17025) in the areas of chemical testing. It provides laboratories with an objective means of assessing and demonstrating the reliability of data they produce. In this study, 18 laboratories interested in the ultimate analysis of coal participated in a proficiency test conducted by CSIR-National Metallurgical Laboratory, Jamshedpur in collaboration with CSIR-National Physical Laboratory, New Delhi in 2011-12. The participating Iaboratories used classical and instrumental methods of analysis to determine moisture, ash, volatile matter and total sulfur in a homogenized coal sample. This paper reports the analytical results and statistical evaluation of the results using z-score

Development of fracture mechanics expression by finite element analysis

With the extensive usage of fracture mechanics in the design, quality control and integrity assessment of engineering components, it is imperative that fracture mechanics expressions, which relate the stress intensity factor and compliance to the geometry of the cracked configuration, be developed. In this endeavour, the finite element method can be extremely useful. The paper discusses the use of finite element analysis for the development of fracture mechanics expressions, and illustrates the usage with some recent work carried out by the authors at NML