02-28-2013, 12:27 PM
The operating pressure and shape for the Grendel was partially derived with one eye on the use of a polymer casing. It has several attributes where it is similar to a steel case in behavior. While such a move would preclude the move towards a hotter loading as discussed in the military section of this forum it is quite possible with the current set up.
The challenges facing the use of polymers in a case are now primarily bullet retention and a clean release. Obturation is fine but some work is required as pressures rise above 24,000 psi.The interaction of the case with a hot chamber has been addressed successfully if one cares to dig enough but this seems to evade the current efforts except one.
Reloading is not possible.
In the examination of an FEA model I think you will find that the construction of the support structure and the constraints thereof are the biggest challenges. The system should all exist in the elastic regime except the case which does exhibit plastic behavior so your model should be able to account for both. For those interested the simple version is to examine the relative hoop expansion of the dissimilar materials as a compound thick cylinder problem. Very crude but enlightening.
The challenges facing the use of polymers in a case are now primarily bullet retention and a clean release. Obturation is fine but some work is required as pressures rise above 24,000 psi.The interaction of the case with a hot chamber has been addressed successfully if one cares to dig enough but this seems to evade the current efforts except one.
Reloading is not possible.
In the examination of an FEA model I think you will find that the construction of the support structure and the constraints thereof are the biggest challenges. The system should all exist in the elastic regime except the case which does exhibit plastic behavior so your model should be able to account for both. For those interested the simple version is to examine the relative hoop expansion of the dissimilar materials as a compound thick cylinder problem. Very crude but enlightening.