Residual stresses in amorphous polymers

The origin of internal stresses in a polymeric component, subjected to an arbitrary cooling, will be described. The differential volume relaxation arising as a result of the different thermal history suffered by each body point was considered as the primary source of stresses build up. A numerical routine was developed accounting for the simultaneous stress relaxation processes and implemented within an Ansys (R) environment. The volume relaxation kinetics was modelled by using the four-parameter TNM (Tool-Narayanaswamy-Mohynian) phenomenological theory using the PVT (Pressure-Volume-Temperature) data obtained on a polystyrene sample. The numerical algorithm translates the specific volume theoretical predictions at each body point as applied non-mechanical loads acting on the component. Thermorheological complexity emerged due to coupling of volume and stress relaxation phenomena A linear dependence of Poisson's ratio on the tensile relaxation modulus was postulated. A quantitative predictions of time dependent stress distribution was realized for two specific test cases.