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

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

Application of fracture-mechanics for weld integrity assessment

The structural integrity assessment of a weld joint by conventional techniques is inadequate, because of unavoidable defects in the weld composite. The stress situation in a component having a defect is quite different from that of a homogeneous material. The significance of fracture mechanics to deal with such integrity assessments is brought out. A brief review on the basic formulations in the application of fracture mechanics is followed by established guidelines for evaluating the integrity of engineering components containing crack-like defects

Assessing the Impact of Misclassification Error on an Epidemiological Association between Two Helminthic Infections

Hookworm, roundworm, and whipworm are collectively known as soil-transmitted helminths. These worms are prevalent in most of the developing countries along with another parasitic infection called schistosomiasis. The tests commonly used to detect infection with these worms are less than 100% accurate. This leads to misclassification of infection status since these tests cannot always correctly indentify infection. We conducted an epidemiological study where such a test, the Kato-Katz technique, was used. In our study we tried to show how misclassification error can influence the association between soil-transmitted helminth infection and schistosomiasis in humans. We used a statistical technique to calculate epidemiological measures of association after correcting for the inaccuracy of the test. Our results show that there is a major difference between epidemiological measures of association before and after the correction of the inaccuracy of the test. After correction of the inaccuracy of the test, soil-transmitted helminth infection was found to be associated with increased risk of acquiring schistosomiasis. This has major public health implications since effective control of one worm can lead to reduction in the occurrence of another and help to reduce the overall burden of worm infection in affected regions

Use of expert system software for life monitoring of power plant components

Life management of primarily high temperature components in power/process plants is a very involved task. Various components in a running power plant are subjected to different loading cycles, temperature, pressure and environmental conditions. The dependence of running power plant on various components as well as interdependence of various components on each other adds to the enormity of the task and requires different maintenance/ repair/ replacement schedules. A systematic and smooth functioning of the plant necessitates a step-by-step analysisfor each components based on its operating parameters, material. In present days, various commercial softwares are used for life monitoring, deciding different schedules in these plants. In the present paper an effort has been made to show the use ofALIAS (Advanced Life Assessment System) and its effectiveness in handling problems related to plant life monitoring, risk analysis, preparing maintenance/repair/replacement schedules

Synthesis, characterization and biological studies of S- benzyl-b-N-(benzoyl)dithiocarbazate and its metal complexes

S-Benzyl-b-N-(benzoyl) dithiocarbazate (SBNBODTC) a new disubstituted dithio-carbazate oxygen–sulfur (OS) donor ligand derived from reaction of S-benzyl dithiocarbazate with benzoyl chloride, formed bischelated complexes of general formula [M(OS)2] where M is Cu2+, Ni2+, Cd2+, Co2+ or Pb2+ and OS is a uninegative bidentate ligand. The ligand and its metal complexes have been characterized by a variety of physico-chemical techniques. S-benzyl-b-N-(benzoyl) dithiocarbazate crystallized with Z0 = 2 in its thione form in cis–cis conformation, with the N–N bond adopting a cis geometry with respect to C@S, while the S-benzyl group adopts a cis geometry with respect to the thione sulfur atom across the C–S bond.SBNBODTC, Cu(OS)2, Ni(OS)2 and Pb(OS)2 display marked cytotoxicity against HL-60 (human myeloid leukemia)while Cd(OS)2 and Co(OS)2 are moderately cytotoxic. The compounds showed moderate but selective activity towards targeted pathogens

Bis{(Z)-[(E)-2-(pyridin-2-ylmethylidene)hydrazin-1-ylidene][(pyridin-2-yl) methylsulfanyl]methanethiolato}nickel(II)

The title compound, [Ni(C13H11N4S 2)2], was obtained by the reaction of S-2- picolyldithiocarbazate and pyridine-2-carbaldehyde with nickel(II) acetate. The NiII atom is located on a twofold rotation axis and is bonded to four N atoms at distances of 2.037 (8) and 2.109 (9) Å, and to two S atoms at a distance of 2.406 (3) Å, leading to a distorted octahedral coordination. The angle between the mean planes of the coordinating moieties of the two symmetry-related tridentate ligands is 83.3 (2)°. In the crystal, complex molecules are linked by weak C - H⋯S hydrogen bonds, π-π interactions between the pyridine rings [centroid-centroid distance = 3.775 (9) Å] and C - H⋯π interactions. The hydrogen-bonding interactions lead to the formation of layers parallel to (010); π-π interactions link these layers into a three-dimensional network