The stiffness of graphite-graphite joints: Ultrasonic investigation and modelling

Large assemblies of graphite blocks are a feature of many nuclear reactors, and the seismic response of these assemblies are determined by the blocks’ static and dynamic behavior. The load-deflection relationship of these blocks can be influenced by surface roughness effects and is dependent on the nature of the interface between blocks. Ultrasonic reflection coefficient measurements are used to investigate the stiffness distribution of this interface under various loading conditions. A quasi-static model of the interface was adopted, allowing the interfacial stiffness to be measured as a function of applied load, sound frequency, surface roughness and graphite composition, for which issues of high attenuation and granular scattering were addressed and overcome. This method was also used to study the distribution of the load across large face areas. Cyclical loading of the graphite-graphite interface has also been carried out—giving information on the elastic/plastic nature of the contact and an insight i...