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Tamil Nadu, India
Tamil Nadu, India

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Ahiri B.B.,NDED | Sarkar A.,Thermography Section RTS and Smart Materials Section SMARTS | Agavathiappan S.,NDED | Agesha A.,NDED | And 4 more authors.
Insight: Non-Destructive Testing and Condition Monitoring | Year: 2016

Infrared thermography is employed for online temperature measurement during high-cycle fatigue testing of nickelaluminium bronze (NAB) samples with inherent casting defects. NAB is a widely-used material for marine applications due to its high corrosion resistance and good mechanical strength. It is observed that the temperature of the samples increased during fatigue cycling due to conversion of work done to heat. The crack initiation time is estimated from the variation of sample temperature as a function of the number of fatigue cycles and it is observed that for defect-free samples approximately 90% of the fatigue life is consumed in crack initiation, whereas for samples with large volumetric internal defects or smaller defects close to the surface, crack initiation occurs much earlier. The location of the fatigue crack is identified from the acquired infrared images and the zone surrounding the crack tip appears as a hot-spot due to the localised high temperature originating from intense plastic deformation at the crack tip. The crack propagation path is visually mapped from the infrared images by tracking changes in the hot-spot locations during progressive cyclic loading. The crack propagation rate and the stress intensity factor are evaluated from the infrared images and a linear increase in the rate of crack propagation with a change in the stress intensity factor is observed on a log-log scale during stage II stable crack growth, which is in accordance with the Paris Law. The results suggest that a priori identification of the probable zone of failure is possible using the infrared thermography technique. © 2016 The British Institute of Non-Destructive Testing.

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