Sensor assemblies, units and methods are provided to determine crack development of components of interest associated with a monitored structure. According to preferred embodiments, a sample sensor bolt is provided having a shank with a threaded end, the sensor bolt being formed of a material serving as a surrogate of the material forming a component of interest associated with the monitored structure. A frame surrounds the shank of the sensor bolt and has fluid ports therein to allow fluid to contact an exposed portion of the sensor bolt shank in registry therewith. A load cell is operatively connected to the sensor bolt. A preload nut is threaded onto the threaded end of the sensor bolt shank and contacts an end of the frame so as to place the sensor bolt under an initial tensile stress. Crack formation within the sensor bolt shank caused by fluid acting upon the exposed portion thereof responsively relieves the initial tensile stress of the sensor bolt which is thereby sensed by the load cell, whereby crack formation in the shank can be used to sense the propensity for crack development in the component of interest associated with the monitored structure.