The use of metal strain gauges and ultrasonic transducers have long been studied in the field of Nondestructive Evaluation (NDE) as a part of structural health monitoring (SHM). Strain gauges use electrical resistance to monitor strains during the loading of a component. Ultrasonic transducers are piezo devices that use a crystal-like sensing element with very low excitation energy that can monitor small strains such as acoustic emissions (AEs). These types of devices have been used to locate the sources of AEs from artificial sources, such as Hsu-Nielsen pencil lead break (PLB) tests, or natural sources such as quasi-static fracture or crack propagation. This type of evaluation has significant advantages over other types of damage inspections such as liquid die penetrant, Blue Light, Eddy Current, or X-ray inspections where visual inspections, large defects, and high levels of user experience are required. The ultrathin silicon membrane (USM) sensor developed by NanoSonic Inc. is a piezoresistive sensor, incorporating the best aspects of a conventional strain gauge and ultrasonic transducer. The sensor can measure both the strain of a component, as well as any acoustic emission that is emitted on the component. To the author's knowledge this is the only sensor capable of simultaneous measurement of these two data types. This paper presents the sensor's ability to be used for quasi-static fracture monitoring. The sensor is first compared to commercial ultrasonic transducers in an unloaded pencil lead break (PLB) test for determining the ability in measuring lamb waves for source location estimation. The NanoSonic USM sensor is further compared to commercial strain gauges and ultrasonic transducers during a PLB test under a tensile load where it is demonstrated the USM sensor yields similar measurements to both commercial sensors. The final test was a quasi-static fracture test, where the NanoSonic USM sensor was able to detect substantially lower energy AEs than the previous test and record the strain history during fracture. This duality of the USM sensor demonstrates an inherent usefulness to NDE and SHM fields. The sensor offers sensing capabilities comparable to commercially available sensors in a smaller package, with less power consumption, at a lower cost. / Master of Science / Nondestructive evaluation (NDE) is a field within structural health monitoring (SHM) that refers to determining any defects within a component that would hinder its performance without modifying its existing condition. This has historically been done by visual inspection by which experienced personnel examine the part for defects. This is inherently flawed as cracking below the surface of a component is common and would not be detected and extensive experience is required to successfully complete this task. Components in hard-to-reach places, with coatings, or that are small also prove challenges to visual inspection. Engineers have developed several new testing methods to combat these flaws. The use of acoustic emission (AE) testing allows sensors, called ultrasonic transducers, to receive and emit sounds at high frequencies to conduct the inspection. This can be done by emitting a sound which is then propagated as a wave along the surface of the component, if the wave hits a defect, it is scattered. A receiving sensor would then receive an unexpected signal, indicating that there is a problem. Furthermore, an array of these sensors can be employed to 'listen' for these surfaces waves that may be emitted during the standard operation of the components. Things like high loads, cracking, and impacts will all be able to be detected. The use of an array of sensors will allow the location of these events. This paper will discuss a new type of sensor, an ultrathin silicon membrane (USM) sensor developed by NanoSonic Inc. This type of sensor can detect high frequencies similar to an ultrasonic transducer, as well as measure large loads that would deform the part, resulting in an event known as strain. The novelty of the NanoSonic USM sensor is its ability to monitor both pieces of information simultaneously, which is believed to be the first to do so in the field. The ability to obtain information on strain and locations of acoustic events within a component during standard operation would be a valuable prospect for the aerospace, civil, and automotive industries.

This master´s thesis deals with the evaluation of fracture behavior of ODS steel MA956 at high temperature range. This behavior was tested by using miniaturized CT specimens, on which were performed experiments to measure of ductile crack growth resistance curves (J-R curves). The value of the fracture toughness was determined from these J-R curves. Fracture properties were consequently evaluated by using fractographic analysis of the fracture surfaces. Structural properties of material was identified by hardness measurement and analyzed by metallographic methods. Results of the measurements show drop of the fracture toughness with respect to the increasing temperature.

This thesis deals with a high temperature testing of fracture toughness and studies the size effect on measured values using miniature size CT specimen. Two types of specimen geometry were manufactured from P91 steel, the standard size and the quarter size specimen. J-R curves were obtained in the temperature range from 23°C to 600°C. No specimen size effect was observed at room temperature tests. The realized experiments together with fractography analysis demonstrated the drop of toughness at 400°C caused by the effect of dynamic strain aging.

The thesis deals with the determination of fracture toughness using compact tension (CT) test specimens at elevated and high temperatures. The experimental material steel P91 designated for application at temperatures 550650°C was used. The fracture toughness in the ductile fracture region of the steel was characterized by the R curve, which characterises the resistance against crack propagation depending on the crack length. The effect of temperature on the R curve at range 23600°C was evaluated. Next the specimen size effect using three sizes of CT specimens at 23°C and the effect of loading rate (2, 0,2 a 0,02 mm/min) at 600°C was examined. The results showed that the temperature has distinct effect on the R-curve, which yields minimal values at 400°C. Only the smallest test specimen size with thickness 6.25mm showed the specimen size effect giving about 10% lower values of toughness comparing to larger specimens. The effect of loading rate was clearly distinguishable. The values of toughness varied about 20% of the toughness value comparing individual loading rate.