Phase III - Pressure Load Increase

From Initial Contact Of Case And Chamber To Maximum Radial Displacement Of The Case

The case and chamber deflect together radially as a combined unit having variable stiffness.
Stiffness varies with radial displacement because the case is usually deforming plastically.
Temperature of the case inside wall surface and internal chamber pressure peak at nearly the same time.
The average case temperature is relatively low but temperature begins to contribute to reducing the load carried by the case.
The thermal gradient through the case wall is greatest during this phase.
The chamber reaches its maximum radial excursion.

The thermal gradient (growth) tends to reduce the average strain in the case wall. The maximum hoop strain, at the outer radius will be increased slightly over that produced by the gas pressure loading alone, because the thermal growth of the case pushes against the chamber. However, the average strain in the case is less with the thermal effects than without.