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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. [ABSTRACT FROM AUTHOR]

Non-destructive evaluation is essential for the safe and uninterrupted operation of pressure vessels. This study reports on infrared thermography-based online hydrotesting of three AISI type 304 stainless steel pressure vessels with simulated defects of 1.8 mm, 2.2 mm and 2.5 mm depths. The surface temperature rise of the defect and defect-free regions are remotely monitored using an infrared camera. It is observed that the temperature rise of the defect region is much higher compared to that of the defect-free regions and the normalised temperature difference monotonically increases with defect depth due to the higher stress concentration-induced faster rate of deformation. The rate of increase of the normalised temperature difference rapidly increases with defect depth and the rate is found to be linearly correlated with the normalised stress difference between the defect and defect-free regions. The ring-like hot-spot observed in the defect regions in the infrared images, prior to failure, corresponds to the circular morphology of the fabricated defects, and the circumference of the circular defects is identified as the most probable location for crack initiation. Contrast enhancement of the acquired infrared images is achieved using image processing algorithms. This study shows that infrared thermography can be effectively used for online monitoring of growing defects during hydrotesting of pressure vessels. [ABSTRACT FROM AUTHOR]

Tool temperature is one of the major life-limiting factors for micro-end cutting tools. Therefore, monitoring of the cutting tool temperature during the milling process is very useful. Here, we use infrared thermography for online monitoring of the cutting tool temperature during the micro-end milling of two different workpieces, aluminium alloy Al6061 and AISI 4340 steel, and the effects of milling parameters such as spindle speed, feed rate and depth of cut on the tool temperature are systematically studied. Our study shows that the tool temperature increases with increasing spindle speed and feed rate because of a larger amount of frictional heat generated at the interface between the tool and the workpiece. The maximum increase in tool temperature in the case of the aluminium alloy workpiece is found to be 1.18 times lower than that of the steel workpiece, which is attributed to the larger thermal diffusivity of the aluminium alloy and the reduced frictional heat generation due to the lower hardness and shear strength compared to the steel workpiece. Two-way analysis of variance is used to evaluate the relative importance of the various milling parameters in tool temperature increase. It is observed that spindle speed is the most significant factor that influences the tool temperature, whereas feed rate is found to have a less significant influence. The workpiece temperature is simultaneously measured using a K-type thermocouple and a calibration curve between the tool and the workpiece temperatures is obtained, which is used for estimation of the workpiece temperature using infrared thermography. The material removal rate is calculated for various process input conditions, which will be useful to increase the material removal rate and to avoid temperature-induced tool damage. The advantage of using infrared thermography is that the temperature distribution of the micro-end milling tool and workpiece can be mapped. [ABSTRACT FROM AUTHOR]