Digital Repository, ECF14, Cracow 2002

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Influence of Pre-Exposition and Pre-Loading on the Environmental Stress Cracking of a PBT/PBA Co-Poly(Ester Ester)

Last modified: 2013-02-10


Previous research showed Environmental Stress Cracking (ESC), i.e. mutualintensification of the destructive effect of loading and environment, of a chemical nature ofpoly(butylene terephthalate)/poly(butylene adipate) (PBT/PBA) copoly(ester ester) in waterand phosphoric acid solution at 353 K. The ESC was studied by means of constant-loadtime-to-failure (TTF) experiments performed on sharply notched tensile specimens. In mostpractical situations the application of stress and initial contact with a potential ESC fluiddo not coincide. It is known that in the case of physical ESC the order of loading as well asimmersion and the time in between can influence the severity of attack. To investigate if thisis also the case with chemical ESC of PBT/PBA in water and phosphoric acid solution, theinteraction between environment and deformation is tested by means of exposition orloading before the actual ESC testing (TTF tests in environment). The tests are performedat 2.5 MPa, within the stress range where chemical ESC occurs. Previous research [1]without pre-exposition and pre-loading showed a heavy reduction in the TTF, indicating anacceleration of the ESC, due to the presence of acid. Also a lifetime inversion region isfound (longer TTF for higher load) indicating competition between crack growth andblunting mechanisms. These results, in combination with the results of the pre-expositionand pre-loading experiments described in this paper, lead to the hypothesis that earlymechanical loading causes crack tip blunting and local strain hardening due to orientation,resulting in a TTF increase. Accordingly, early chemical exposition, especially expositionto acid solution, reduces the favourable effect of blunting and orientation resulting in adecrease of TTF.

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