Faculty Publications

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    Influence of heat treatment on near-threshold fatigue crack growth behavior of high strength aluminum alloy 7010
    (Springer Science and Business Media Deutschland GmbH, 2020) Nandana, M.S.; Udaya, B.K.; Manjunatha, C.M.
    In this study, aluminum alloy 7010 was subjected to three different ageing treatments i.e., peak ageing (T6), over ageing (T7451) and retrogression and re-ageing (RRA) to study the influence of precipitate microstructure on the fatigue crack growth rate (FCGR) behavior. The microstructural modifications were studied by using TEM to examine the change in size and morphology of the precipitates. The size of the precipitates in the matrix range from 16-20nm in T7451, 5-6nm in RRA and 2-3nm in T6 alloys, respectively. The FCGR tests were performed on standard compact tension (CT) specimens as per ASTM E647 standard in a computer controlled servo-hydraulic test machine with applied stress ratio, R = 0.1 and loading frequency of 10 Hz. The crack growth was measured by adopting compliance technique using a CMOD gauge attached to the CT specimen. The fatigue crack growth rate was higher in T7451 and lowest in RRA treated alloy. The RRA treated alloy showed higher (formula presented) compared to T7451 and T6 treated alloys. The measured (formula presented) was 11.1, 10.3 and (formula presented) in RRA, T6 and T7451 alloys, respectively. In the near-threshold regime, the RRA treated alloy exhibited nearly 2-3 times reduction in the crack growth rate compared to the T6 alloy. The growth rate in the RRA alloy was one order lower than that of the T7451 condition. The surface roughness of RRA treated alloy was more pronounced. The reduction in FCGR observed in RRA alloy was correlated to partial crack closure due to tortuous crack path and partially due to increased spacing between the matrix precipitates. The reduction in near-threshold FCGR and increase in (formula presented) is expected to benefit the damage tolerant capability of the aircraft structural components under service loads. © Springer Nature Switzerland AG 2020.
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    Structural health monitoring capabilities in ceramic-carbon nanocomposites
    (2014) Inam, F.; Badekai Ramachandra, B.R.; Vo, T.; Daoush, W.M.
    A novel method for analysing structural health of alumina nanocomposites filled with graphene nanoplatelets (GNP), carbon nanotubes (CNTs) and carbon black nano-particles (CB) is presented. All nanocomposites were prepared using novel colloidal processing and then by Spark Plasma Sintering. Good homogeneous dispersion was observed for all carbon filled materials. Nanocomposite bars were indented to produce sub-surface damage. Change in electrical conductivities were analysed after indentation to understand structural damage. For correlating change in electrical conductivity and indentation damage and understanding damage tolerance, mechanical properties were compared. Because of the systematically induced indentation damage, a sharp decrease of 86% was observed in the electrical conductivity of CNT nanocomposite as compared to 69% and 27% in the electrical conductivities of GNP nanocomposites and CB nanocomposites respectively. CNTs impart superior damage sensing capability in alumina nanocomposites, in comparison to GNP and CB, due to their fibrous nature, high aspect ratio and high electrical conductivity. © 2013 Elsevier Ltd and Techna Group S.r.l.
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    Damage Tolerance Capability of Retrogression and Re-aged 7010 Aluminum Alloy Under FALSTAFF Loading
    (Springer, 2020) Nandana, M.S.; Bhat, K.U.; Manjunatha, C.M.
    The present work deals with the damage tolerance characteristics of high strength aluminum alloy tempered in T6 and reversion condition. The fatigue experiments were carried out by applying a service simulating load spectrum, i.e., standard mini FALSTAFF loading. The crack propagation speed was found to be lower and the total crack propagation life was longer by 22% for reversion-treated alloy. The crack growth was also predicted to be using two parameter crack driving force approach. The fatigue data of these treated alloys under constant amplitude loading at various stress ratios were analyzed to obtain crack growth law. The predicted crack growth behavior was conservative and followed similar trend in both the alloys as observed in experiments. Predicted results of reversion-treated alloy also showed longer crack growth life. The modified microstructure after reversion treatment was attributed for the observed improvement in damage tolerance capability. © 2020, The Indian Institute of Metals - IIM.