Goddard Space Flight Center (MD)
The purpose of this project was to determine the effects of cryogenic temperatures and thermocycling on five different lead/tin solder alloys. The knowledge gained from this project will aid engineers at the NASA Goddard Space Flight Center in developing a heat switch to be used on the ASTRO-E satellite. Test samples to be soldered were made, consisting of metal plugs made out of brass and stainless steel, and copper rings. The ends of the plugs were pressed into the rings and the parts were then dipped into molten solder. Half of the soldered samples were thermocycled 100 times by dipping them into liquid nitrogen and then heating the samples back up to room temperature. Finally, all the samples underwent tensile pull tests performed by an Instron machine. Half of all the samples were tested at room temperature and half were tested while submerged in liquid nitrogen. Load displacement graphs were plotted for each sample and the load each sample failed at was recorded. From analyzing the data, it could be seen that test temperature and lead content in the solder effected the mode of failure of each sample: ductile or brittle fracture. All of the solders tested at room temperature failed by plastic deformation, while most of the solders tested in liquid nitrogen failed by brittle fracture. Only two solders, those with the highest lead content, retained their ductility while being tested in liquid nitrogen. Also, by analyzing the results it was determined that themocycling 100 cycles had no effect on the mode of failure or the shear strength of the samples. The substrate metal, brass or stainless steel, also had no effect on the shear strength of the solders.
Worcester Polytechnic Institute
Major Qualifying Project
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