Dynamic mechanical analysis was performed on the aryl-aliphatic copolyamides, based on lactam-12 sequences, a tere- or iso-phthalic moiety, and a 3,3＇-dimethyldicyclohexylmethane unit in regular order, whose dielectric relaxation, C-13 NMR and H-2 NMR investigations are reported in the preceding papers of this series. It demonstrates the existence of three secondary relaxations, gamma, beta and omega, which occur in the temperature and frequency ranges where similar secondary relaxations are observed by dielectric relaxation. Comparison of the results obtained in the present paper with those derived from the whole set of experiments carried out on these materials leads to a precise description of the local motions that are responsible for the observed secondary relaxations. (C) 2000 Elsevier Science Ltd. All rights reserved.