K.V. Sudhakar

ANN back-propagation prediction model for fracture toughness in microalloy steel

Fracture toughness of microalloy steel was evaluated as per ASTM E399 standard. Artificial neural network back-propagation model was developed to predict the behavior of fracture toughness and tensile strength as a function of microstructure. Both fracture toughness and tensile strength were found to increase with the increase in martensite content in a dual phase microstructure of microalloy steel. The primary objective of the ANN Back-propagation (BP) prediction model was to validate and extend the application of microalloy steels for various engineering applications. ANN training model was found to be in good agreement with the experimental results. The ANN training model has been used to predict the best/optimum toughness properties in terms of intercritical annealing temperature and martensite content. This can be used as a practical tool for predicting the fracture toughness in other series of steels comprising dual-phase microstructures and also to optimize strength and ductility properties.

Prediction of corrosion-fatigue behavior of DP steel through artificial neural network

Abstract Corrosion–fatigue crack growth (da/dN) of dual phase (DP) steel was analyzed using an artificial neural network (ANN) based model. The training data consisted of corrosion–fatigue crack growth rates at varying stress intensity ranges (ΔK) for martensite contents between 32 and 76%. The ANN model exhibited excellent comparison with the experimental results. Since a large number of variables are used during training the model, it will provide a reliable and useful predictor for corrosion–fatigue crack growth (FCG) in DP steels.

Fatigue behavior of a high density powder metallurgy steel

Abstract Rotating bending fatigue tests were carried out on a high density Fe–2%Ni based powder metallurgy steel at 50 Hz frequency and at room temperature. The material was subjected to high cycle fatigue to evaluate endurance/fatigue limit and its influence on heat treatment/microstructure. The fractured fatigue surfaces were examined using scanning electron microscope to study the mechanism/s associated with crack propagation. Optical microscopy was carried out to characterize the microstructures resulting from different heat treatments. The microstructure was observed to have an influence on endurance/fatigue limit. As-sintered material exhibited the lowest endurance/fatigue limit when compared with the material in the hardened and tempered condition. Electron microscopy studies demonstrated the mechanism/s of crack linking and/or interconnection of pores characterizing the crack propagation. It has been observed that, by carefully designing the heat treatment the high density powder metallurgy steel can be beneficially used in fatigue loaded components.

Micromechanics of fracture in extrusion die punch

Abstract Die punches which fractured during extrusion of steel billets were investigated to assess the possible causes for premature failure. Visual examination and hardness measurements were carried out to support the evidence for failure. Detailed metallurgical investigation (optical and electron microscopy) of fractured die punches demonstrated the presence of cleavage and/or quasi cleavage fracture features typical of a brittle mode of fracture. It was observed that there was a need to evaluate the fracture toughness property of the material and the judgement based solely on hardness values seemed inadequate.

Failure analysis of an automobile valve spring

Abstract This paper presents the failure analysis of an automobile valve spring which failed in service. The fractured surfaces as well as the surface of the spring material close to the fractured surface were examined in a scanning electron microscope at suitable magnifications. Optical microscopy was performed to evaluate the basic microstructure of the as-received material. Detailed electron microscopic studies have indicated that the failure was due to the presence of non-metallic inclusions near the surface of the spring material.

Failure analysis of automobile bimetal bearings

Abstract This paper presents the failure analysis of automobile bimetal bearings (α+β type brass) which failed during storage before final assembly. The exposed surfaces/defective areas of the material were examined in a scanning electron microscope. Optical microscopy was also carried out to characterize the basic microstructure of the bimetal. Detailed electron and optical microscopic studies have conclusively demonstrated that the failure was due to the mechanism of stress corrosion cracking.

Investigation of fracture in a K12 tongue component

Abstract A series of failures of K12 tongue components occurred, which are used in automobile seat belts. Scanning electron microscopic studies of the fracture surface indicated that premature fracture of the component was due to the presence of microshrinkage and interdendritic porosity in the material. This paper presents the detailed microscopic analysis of the raw material as well as the finished product of the tongue components to ascertain the actual cause/s for failure.