<p>Electro-magnetic mass drivers (EMD) are linear payload accelerators at the forefront of multi-physics technology that find uses in weaponry, low orbit satellite insertion, plasma propulsion system for spacecraft, electro-magnetic aircraft launch catapults, impact phenomena \&amp; terminal ballistics in material science, and fuel pellet injection in nuclear fusion reactors. In a homopolar type EMD, the accelerating track comprises a uniform width passage formed by clamping two electrically conductive rails in an electrically insulating housing using bolts. Bolts are pre-loaded with force $F$ to pre-stress the EMD assembly and minimize the change in passage width (or rail separation) during operation. The entire assembly is similar to a bolted T-shaped joint consisting of a dissimilar material sandwiched between clamping plates (flanges) subjected to tensile loading. The difference is that unlike in a bolted T-joint, where the joint strength is independent of load path, load path in the case of EMD is desired to route through rails to achieve maximum stiffness against deflection. The tensile load originates from the rails' internal faces and travels to bolts through clamping plates. Housing material is not subjected to this tensile loading. It is desired that bolt pre-load takes the same path in reverse order to counteract the tensile load.&nbsp; Instead, it is observed that a significant portion of bolt pre-load resides in housing alone which necessitates high bolt number $N$ and a higher bolt pre-load. This issue has not been addressed in any literature concerned with the design and calculation of strength and stiffness of bolted EMD. This study is designed to characterize load path in initial clamping state and that in operation as a function of housing height $H$ and clamp separation distance $S$. It is observed that a favorable load path is achieved and stiffness increases as $H/S$ decreases.. Furthermore, the line of action of forces in clamping plates is analyzed. It is seen that a decrease in $H/S$ causes an increase in bending of clamp plates. For an analytical understanding, clamping plates are approximated as beams, and the primary mode of failure is identified as bending while the shear effect is negligible and ignored. The shape of clamping plates is altered in anticipation of the expected load path, and material is aligned in load path direction to reduce the bending effect of loading. This is achieved by preemptively angling the beam and shortening its span. Since the material is stiffer in tensile loading than in bending, shape-optimized clamping plates provide improved stiffness and ease of assembly. The analysis and design method proposed in this paper provides a theoretical basis for designing ultra-stiff and lightweight EMD.</p>

Load Path Analysis and Design for Stiffness of Bolted Electro-Magnetic Mass Drivers

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.