Materials Sciences and Applications, 2011, 2, 1730-1740 doi:10.4236/msa.2011.212231 Published Online December 2011 (http://www.SciRP.org/journal/msa) Copyright © 2011 SciRes. MSA Fatigue Failure of Notched Specimen—A Strain-Life Approach Bikash Joadder, Jagabandhu Shit, Sanjib Acharyya * , Sankar Dhar Department of Mechanical Engineering, Jadavpur University, Kolkata, India. E-mail: * skacharyya@mech.jdvu.ac Received July 22 nd , 2011; revised September 9 th , 2011; accepted November 15 th , 2011. ABSTRACT Failure cycles of notched round specimens under strain controlled cyclic loading are predicted using strain—life rela- tions obtained from experiment for plain fatigue round specimens. For notched specimens, maximum strain occurs at notch root and is different from applied controlled strain. The maximum strain is computed by appropriate Finite ele- ment analysis using the FE software ABAQUS. FE model and material parameters are validated by comparing the FE results and experimental results of LCF tests of round specimens. This value of maximum strain is used for prediction of failure cycles. Prediction is compared with the experimental results. The results show good matching. Keywords: Strain-Life Equation, Failure Cycle, Notched Specimen, LCF, Cyclic Plasticity 1. Introduction Fatigue has become progressively more relevant for tech- nological development in automobiles, aircraft, com- pressors, pumps, turbines, etc., subject to repeated load- ing and vibration. Today it is often stated that fatigue accounts for at least 90 percent of all service failures due to mechanical causes [1]. A fatigue failure is particularly insidious because it occurs without any obvious warning. Therefore methodology for fatigue failure prediction is of immense importance in industry and practice. One of the popular age old stress based method for predicting fa- tigue failure is based on S-N curve which was later on modified to consider the effect of mean stress, effect of low amplitude spikes in load spectra and statistical nature of fatigue. Using Miner’s rule [2] the method can be ap- plied for cumulative load cycles to assess the cumulative damage. But all these application is valid for High cycle fatigue where the stress and strain do not exceed the elas- tic limit. For low-cycle fatigue conditions where the stress is high enough to create plastic deformation, fatigue failure results from cyclic strain rather than from cyclic stress. Low-cycle fatigue is usually characterised by the Coffin-Manson relation [3-6], best described by the material relation between plastic strain amplitude and life which is known as strain life curve. An important use of the strain-life curve is to predict the life for crack initia- tion at notches in machine parts where the nominal stresses are elastic but the local stresses and strains at the root of a notch are inelastic. Neuber [7] proposed a sim- ple function of nominal stress remotely measured from the notch, which can be used to predict failure at the notch. Basquin [8,9] observed that Stress-Life data could be modeled using a power relationship, which results in a straight line on a log-log plot. This observation corre- sponds to elastic material behavior in the strain-life ap- proach. Later the aproaches suggested by Basquin and Coffin-Manson are combined together to develop the strain life curve applicable over the whole regim (HCF and LCF). A. H. Noroozi, G. Glinka, S. Lambert [10] developed unified two-parameter fatigue crack growth driving force model to account for the residual stress and subsequently the stress ratio effect on fatigue crack growth. Ostash, Panasyuk and Kostyk [11] modelled fatigue fracture of materials as a process of initiation of a macrocrack of a particular length (material constant), which is success- sively repeated (step-by-step) during its growth and the ‘local stress range vs. macrocrack initiation period rela- tionship for notched specimens, might be applied to the determination of the ‘macrocrack growth rate, da/dN, vs. effective stress intensity factor range relationship. A fatigue crack growth model under constant ampli- tude loading has been developed by Pandey and Chand [12] considering energy balance during crack growth. Plastic energy dissipated during growth of a crack within