Sharif Digital Repository

Mechanical failures in most cases originate from the exterior layers of the components. It is considerably effective to apply methods and treatments capable to improve the mechanical properties on component’s surface. Surface nanocrystallization produced by severe plastic deformation (SPD) processes such as severe shot peening (SSP) is increasingly considered in the recent years. However, artificial intelligence systems such as artificial neural network (ANN) as an efficient approach instead of costly and time consuming experiments is widely employed to predict and optimize the science and engineering problems in the last decade. In the present study the application of ANN in predicting of... 

The modified couple stress theory is employed in this paper in order to formulate the size-dependent strain energy release rate of Euler-Bernoulli and Timoshenko notched beams. As a case study, the normalized energy release rate of the aforementioned beams has been developed for three-point bending as a function of the ratio of material length scale parameter to the beam depth. The results of the current model are compared to the experimental data. The good agreement between the present results and the experimental values indicates that the current model can be successfully applied to evaluate size dependent energy release rate of structures  

Shot peening is the most common surface treatment employed to enhance the fatigue performance of structural metallic materials and often carried out after other surface treatments. This paper mainly focuses on the effects of initial conditions of surface such as initial stress filed and hardness profile on shot peening residual stress field. The residual stress distribution induced by shot peening is obtained using Hertzian contact theory and elastic–plastic evaluation after yielding occurred during impingement and rebound of shots. Elastic plastic calculations are performed using different hardening models considering Bauschinger effect. The present model is able to predict redistribution... 

This paper presents an analytical model to predict the residual stress distribution induced by Shot peening. The analytical approach is based on the work of Shen and Atluri (2006) [18] with some modifications. The modifications are related to the elasto-plastic unloading of shot impingements, friction coefficient effect and the fraction of kinetic energy transmitted to the treated material. In order to predict more realistic residual stresses, the elasto-plastic unloading phase of shot impacts is modeled using two nonlinear kinematic hardening models considering the Bauschinger effect. Moreover, the effect of the Coulomb friction between target surface and shots is evaluated. For this... 

Shot peening is one of the most effective surface strengthening treatment technologies in which compressive residual stresses are induced beneath the specimen surface. Effects of various factors on the distribution of residual stress profile induced by shot peening have been investigated by many researchers. However, initial residual stresses are one of the important factors which affect the shot peening residual stress.This study is aimed to present comprehensive numerical and experimental study on the effect of initial residual stresses on the shot peened specimen. Initial residual stresses were induced using a four-point bending rig and grinding. Incremental center hole drilling (ICHD)... 

This study presents the results of failure analysis of a 28 MW gas turbine at the Rei electrical power plant. The gas turbine failed during the shutdown period and near its second natural frequency at 4200 rpm. Initial inspections revealed that the compressor disk of stage 15 was fractured, and all of the stationary and rotary blades of stages 14-18 of the compressor had been detached or broken from the dovetail region of the disks. The fracture roots were investigated by performing finite element modeling and fractography analysis. It was shown that a crack was initiated from the disk edge on its interface with the rotor shaft and was propagated under cyclic loading. As a result of the... 

The effect of mold hardness on the microstructure of ductile iron and the contraction porosity was investigated. Molds with different hardnesses (0.41, 0.48, 0.55, 0.62 MPa) and a sand mold prepared by Co2 method were used. The influence of silicon content on the induced expansion pressure owing to the formation of graphite was also investigated. The contraction during solidification can be compensated by an induced expansion owing to the graphite relief when the hardness of mold increases; therefore, the possibility of achieving a sound product without using any riser increases  

In the present research work the binary NiTi alloys with various compositions in the range of 50.3-51 at.% Ni were used. Samples have been annealed at 850 °C for 15 min and then quenched in water. In order to characterize transformation temperatures and enthalpy changes of the forward and the reverse martensitic transformation, Differential Scanning Calorimetric (DSC) experiments were performed. The enthalpy and entropy changes as a function of Ni atomic content have been thermodynamically investigated. Results show that enthalpy and entropy changes of martensitic transformation decrease when Ni atomic content increases. The variation of enthalpy and entropy of martensitic transformation... 

EEG based biometrics using linear Support Vector Machine (SVM) is proposed in this paper. Human identification using electroencephalographic signal was done in this research. Reliability of most of the biometrics systems is not up to the mark because of the possibility of being faked or duplicated. Here, the brain signatures were used as a possible biometric identifier. A Database for Emotion Analysis using Physiological Signals containing 40 trials from each participant was used. International 10-20 system of EEG electrode placement was employed and data from Cz electrode was taken for this research. Some researches showed nice performance with few subjects. Here, 20 subjects were used from... 

Due to unique properties of NiTi shape memory alloys such as high corrosion resistance, biocompatibility, super elasticity and shape memory behavior, NiTi shape memory alloys are suitable materials for medical applications. Although TiO2 passive layer in these alloys can prevent releasing of nickel to the environment, high nickel content and stability of passive layer in these alloys are very debatable subjects. In this study a NiTi shape memory alloy with nominal composition of 50.7 atom% Ni was investigated by corrosion tests. Electrochemical tests were performed in two physiological environments of Ringer solution and NaCl 0.9% solution. Results indicate that the breakdown potential of... 

During the shut down period, a 32. MW gas turbine experienced a severe failure accompanied by a loud noise near its second natural frequency at 4200. rpm. After opening the turbine casing, it was revealed that the disks of stages 16 and 17 of the compressor had been fractured and all of the stationary and rotary blades of stages 14-18 of the compressor had been detached from the dovetail region of the disks. The degree of damage was such that repairing the compressor was not economical, and thus, the compressor was no longer able to be used. Diagnostic work was carried out using different finite element models and fractography analysis. Analysis showed that multiple cracks had been initiated...