Determination of residual stresses in amorphous thermoplastic polymers by DMA

The processing of polymers and polymeric materials always leaves some residual stresses in the final product, which can have a positive but usually a negative effect on the properties of the final product. Polycarbonate was injection molded into the mold, which was heated to 50, 60, or 70 degrees C to produce test specimens with different amounts of residual stresses. They were then annealed at various temperatures below T-g to partially remove the stresses or heated to 145 degrees C (above T-g) to completely remove them. Comparison between annealed and as-molded samples showed a strong influence of residual stresses on mechanical properties. Dynamic mechanical analysis (DMA) analysis showed that the loss modulus can be divided into the intrinsic loss modulus, which is a material property, and the residual stress, which can be relaxed at a given temperature. The stress relaxation curve, obtained by subtracting the loss modulus of the annealed sample from the loss modulus of the as-molded sample gives us the ability to estimate the residual stresses that have been or can still be relaxed by heating to a given temperature.

Automated summary

The processing of polymers and polymeric materials leads to residual stresses in the final product, which significantly affect the mechanical properties. Experimental results show that residual stresses can be removed by heating, and they have a strong influence on the mechanical properties.