ABSTRACT
At the end of this chapter you should be able to:
• understand the construction and principle of operation of an electrical resistance strain gauge, including temperature and pressure compensation and null and deflection methods
• understand the principle of operation of the Wheatstone bridge • understand foil gauge and foil gauge type of electrical resistance strain gauge, including advantages and
disadvantages and gauge materials • appreciate different types of gauge adhesives, including cellulose acetates, epoxy resins, cyanoacrylates
and Norton-Rockide • understand some methods of water-proofing • understand combined bending and torsion of circular section shafts, developing formulae for M and T • understand combined bending and axial strains and full bridge for measuring M • appreciate photoelasticity, birefringence, circularly polarised light, experimental photoelasticity, material
fringe value, stress trajectories, three-dimensional photoelasticity • understand Moire fringes, brittle lacquer techniques • appreciate semi-conductor and acoustical strain gauges • appreciate the use of lacquers to determine experimental strains
than that caused by external loadings. To overcome this deficiency, it is necessary to attach another strain gauge (called a ‘dummy’ gauge) to a piece of material with the same properties as the structure itself, and to subject this piece of material to the same temperature changes as the structure, but not to ‘constrain’ the ‘dummy’ gauge, or allow it to undergo any external loading.
