Abstract: Apparatus and a method for indicating static stress including residual stress in an object utilize the stress dependence of the specific heat of an object by scanning the surface of the object with a pulsed laser light source and measuring the resulting temperature changes by means of an infra red detector to provide stress information. A common scanning system including a beam splitter enables the pulsed light output to the object and the received infra red radiation to be scanned simultaneously. The optical paths of the light and infra red through the scanning system are made different so that the infra red sensor does not respond to any hot spot in the scanning system. A further laser source provides three spaced beams which are transmitted through the beam splitter so as to impinge on the surface of the object at points surrounding the instantaneous point of inspection.

Abstract: Apparatus and method for indicating stress in an object comprising viewing the temperature variation of part of the surface of the object as it is stressed. An infra-red detector detects small changes of temperature and the stress may be applied by natural loading or by cyclic stressing imposed by a vibrator.