The ductile-brittle transition(DBT)of poly (phenylene ether ketone)due to long-term retaining at temperature of 200℃ has been studied by tensile experiment

scanning electron microscopy and differential scanning calorimetry measurements. The DBT can be considered as competition between fracture mechanisms of crazing and that of shear yielding.It is found that the DBT of PEK-C due to long-term retaining at 200℃ occurs at about 589 retaining hours.It is shown from tensile experiment that the deaging phenomena was observed

and it only depends on the shear deformation and has intrinsic relationship with DBT.