N.C. Santhi Srinivas

Effect of Ultrasonic Shot Peening on Surface Microstructure and Fatigue Behavior of Structural Alloys

Fatigue resistance of structural materials is considered as one of the most important factors in design of structural components for integrity, efficiency and safe functioning under repeated mechanical/thermal loading. Fatigue resistance of structural alloys is characterized in terms of appropriate parameters based on high cycle/low cycle fatigue loading. Fatigue life comprises of two components, number of cycles for crack initiation and for crack propagation. While there is dominant role of the process of crack initiation in high cycle fatigue, low cycle fatigue is controlled by crack propagation. Invariably, fatigue cracks initiate from the surface and surface modification has been used for enhancement of fatigue life, delaying the process of crack initiation. Inducement of compressive residual stress in surface region through shot peening has been one of the most widely used conventional process of enhancing high cycle fatigue life. This paper presents the effect of surface grain refinement, using the novel technique of ultrasonic shot peening, on enhancement of fatigue life of structural alloys at low stress/strain.

Optimization of USSP duration for enhanced corrosion resistance of AA7075

HighlightsUSSP treatment resulted in grain refinement near the surface region.Sample treated for 15 s exhibited superior corrosion properties.The passive layer mainly constituted Al(OH)3 with Al2O3.Pitting was mainly associated with the cathodic second phase precipitates. ABSTRACT This investigation was carried out following our earlier work on the effect of ultrasonic shot peening (USSP) on corrosion resistance of the 7075 aluminium alloy in 3.5 wt% NaCl solution to optimize the duration of USSP. The samples not treated with USSP and different samples treated with USSP were subjected to potentiodynamic polarization and electrochemical impedance spectroscopy. Among the specimens USSP treated from 5 to 30 s, the one USSP treated for 15 s (USSP 15) was found to exhibit highest corrosion potential (Ecorr) and lowest corrosion current density (icorr). Corrosion products were characterized by Scanning Electron Microscopy (SEM) and X‐ray Photoelectron Spectroscopy (XPS). Scanning Kelvin Probe Force Microscopy (SKPFM) was used to measure the surface free potential. The enhanced corrosion resistance of the USSP 15 sample was found to be due to combined effect of surface nanostructure of the matrix, homogeneity and refinement of second phase precipitates. There was enhancement in formation of adherent passive layer in the USSP15 specimen.

Effect of Ratcheting on Tensile Behavior of Zircaloy-2 at Room Temperature

Asymmetric cyclic loading, known as ratcheting fatigue, causes accumulation of cyclic plastic strain and reduces fatigue life of components. This investigation was undertaken to examine the effect of pre-ratcheting on tensile properties of the Zircaloy-2. Stress controlled fatigue tests were performed at room temperature (RT) for 200 cycles with different combinations of the parameters: mean stress (σm), stress amplitude (σa) and stress rate (

Dynamic strain ageing, deformation, and fracture behavior of modified 9Cr–1Mo steel

\dot{\sigma }

Effect of surface Nanostructuring on LCF behavior of aluminum alloy 2014

σ˙). Tensile properties of these samples were evaluated at room temperature. There was marked increase in the yield strength but there was far less effect on the tensile strength. The ductility was reduced due to prior ratcheting. The results have been discussed in terms of work hardening under different combinations of the ratcheting parameters.