Magnetic Force Calculation in Reluctance Force Launcher

To study the clamping device in reluctance force launcher, the Maxwell stress tensor method is extended to contact force calculations. It is generally believed that the Maxwell stress tensor method is only suitable for objects surrounded by air or vacuum. However, in this article, the Maxwell stress tensor applicable to ferromagnetic materials is re-derived, and the classical Maxwell stress tensor is successfully reproduced. Its integral region is determined as the outer surface of the interface between the object and the outside world, which means that the Maxwell stress tensor method can be used for contact force calculations. Subsequently, the Maxwell stress tensor method was used for force studies in the clamping device. The needed clamping force of the clamping device is calculated. The reducing effect of ferromagnetic materials on the clamping force and the effect on the acceleration force of the projectile are analyzed. Finally, based on the determined integral region, the reason why the integral result of Maxwell stress tensor method is related to the integral path is successfully explained, which provides another theoretical basis for the contact force calculation method in this article.