Jalaj Kumar

Acoustic Emission During Tensile Deformation of Smooth and Notched Specimens of Near Alpha Titanium Alloy

Acoustic emission (AE) generated during tensile deformation of smooth and notched specimens of near Alpha titanium alloy have been studied. A few tests carried out with both types of specimens were also interrupted in order to correlate with the damage mechanism. The results have shown higher acoustic emission during yielding and reduced AE at higher strain level in the smooth specimen. A peak in the root mean square (RMS) voltage at higher strain was associated with the initiation of microcrack. In the notched specimen, localized deformation at the notch tip gives rise to detectable AE in the region prior to macroscopic yielding and gives intense AE at lower strain compared to net section yielding. This is characterized by peak amplitude distribution of hits in which majority of the hits are shifted to lower amplitudes in notched specimens as compared to the smooth specimen. The AE results have been supported by microstructural investigations.

Evolution of Damage in Near α IMI-834 Titanium Alloy Under Monotonic Loading Condition: A Continuum Damage Mechanics Approach

In the present work, a continuum damage mechanics model, based on Lemaitre’s concept of equivalent stress hypothesis (1986, “Local Approach to Fracture ,” Eng. Fract. Mech., 25, pp. 523–537), has been applied to study the evolution of damage under monotonic loading condition in a near α IMI-834 titanium alloy, used for aeroengine components in compressor module. The damage model parameters have been experimentally identified by in situ measurement of damage during monotonic deformation using alternating current potential drop technique. The damage model has been applied to predict damage evolution in an axisymmetrically notched specimen using finite element analysis. A reasonably good agreement has been observed between numerically simulated and experimentally measured damage behaviors. Damage micromechanisms operative in this alloy have also been identified which show multiple damage events.

Acoustic emission studies for characterization of fatigue crack growth behavior in HSLA steel

Abstract High strength low alloy (HSLA) steels are a group of low carbon steels and used in oil and gas pipelines, automotive components, offshore structures and shipbuilding. Fatigue crack growth (FCG) characteristics of a HSLA steel have been studied at two different stress ratios (R = 0.3 and 0.5). Acoustic emission (AE) signals generated during the FCG tests have been used to understand the FCG processes. The AE signals were captured by mounting two piezoelectric sensors on compact tension specimens in liner location configuration. The AE generated in stage II of the linear Paris region of FCG has been attributed to the presence of two sub-stages with two different slopes. The AE generated at higher values of stress intensity factor is found to be useful to identify the transition from stage II to stage III of the FCG. AE location analysis has provided support for increased damage at the crack tip for higher stress ratio. The peak stress intensity (Kmax) values at the crack tip have shown good correlation with the transitions from stage IIa to stage IIb and stage II to stage III of the FCG for the two stress ratios.

Creep–Fatigue Interactions in Ti-6Al-4V Alloy at Ambient Temperature

Abstract In the present investigation, creep–fatigue interaction was studied in an alpha–beta titanium alloy Ti-6Al-4V at ambient temperature. Stress controlled low cycle fatigue tests were conducted with and without hold times. The hold times were introduced to simulate creep phenomenon. The creep damage was found to be responsible for a large reduction in life of the sample tested with hold time.

Observation of Etch-Pits and LAGB Configurations During Ambient Creep of Ti-6Al-4V Alloy

The present work describes the microstructural features of alloy Ti-6Al-4V during constant stress creep at ambient temperature. Samples tested at 800 and 900 MPa stress levels exhibit the presence of etch-pits and/or voids. The ambient creep strain increases with an increase in applied stress due to higher strain rate sensitivity at higher stresses. A high density of low-angle grain boundaries is noticed in and around etch-pits in the creep-tested specimens due to occurrence of slip. The inverse pole figure obtained by EBSD indicates prismatic texture as the main deformation component in the creep-tested specimens.