Abstract: A methods and systems for determining a change in condition of a rock bolt. Some methods may comprise, at a first point in time, propagating shear and longitudinal ultrasonic waves along the rock bolt to measure a first time of flight for each of the shear and longitudinal waves, at a second point in time after the first point in time, propagating shear and longitudinal ultrasonic waves along the rock bolt to measure a second time of flight for each of the shear and longitudinal waves, and using the relative changes of the first and second time of flights, determining the change in condition of the rock bolt section.

Abstract: The disclosure is of a composite lamellar pellicle for producing thermographic patterns by means of liquid crystals which are spread upon an inner sheet and sandwiched between two outer sheets both of which have adequate mechanical strength for normal handling and at least one of which is transparent, all three layers preferably being poor conductors of heat and flexible without being elastic.