Abstract
A methodology for the life extension of an X-Ray target was developed. X-Ray tube targets are rotating axisymmetric multi-component components used in X-Ray tubes of medical equipment. An X-Ray target is subjected to extreme cyclic thermal loading conditions based on the imaging system requirements. A very complex, time dependent stress state is present in such targets because of the combination of processing and utilization. Residual stresses are present following initial target assembly and heat treatment required to establish and maintain the high vacuum required in the X-Ray tube. In addition, cyclic stresses arise from the imaging protocols. The factors controlling these stresses include the thermal expansion coefficients of the various materials, the temperature distributions and the geometry of the components. The proposed methodology for the life extension of an X-Ray target included the development of an integrated thermal and structural axisymmetric finite element model. The combined thermal structural model was initially used to evaluate the severity of the various thermal protocols a target is subjected to. The structural analysis was carried out in the plastic regime, since typical stresses exceeded the yield stress of the materials used. Design of experiment (DOE) studies were carried out in order to evaluate the influence of geometric quantities on the resultant temperature distribution and thermal stresses. Tolerances of geometric quantities were applied to reflect manufacturing inaccuracies. An optimal design was selected for which the equivalent plastic strains were minimized. The effect of the manufacturing tolerances on the optimal solution was also examined.
