Deformation rate dependence of the essential and non-essential work of fracture parameters in an amorphous copolyester

The plane stress fracture toughness of an amorphous copolyester (aCOP) was determined at ambient temperature as a function of the deformation rate (v = 1, 10 and 100 mm min(-1)) by the essential work of fracture (EWF) concept using tensile-loaded deeply double-edge notched (DDEN-T) specimens. It was established that both specific essential (w(e)) and non-essential or plastic work of fracture (w,) are composed terms linked to yielding (subscript y) and necking (subscript n), respectively. The essential terms, i.e. w,, and w,,, did not change with increasing v. This indicates that by increasing v no alteration in the initial plane stress conditions occurred. The slopes of regression lines fitted for the w, versus ligament (i.e. beta'w(p,y)) and w(n) versus ligament (beta " w(p,n)) data tended to increase with increasing v. The overall shape parameter of the plastic zone (beta) slightly decreased with the deformation rate. The plastic zone was formed by cold-drawing and not via true plastic deformation as evidenced by annealing-induced (just beyond T-g) shape recovery. (C) 1998 Elsevier Science Ltd. All rights reserved.