Determination of the fracture toughness of polybutylene terephthalate (PBT) film by the essential work method: Effect of specimen size and geometry

The fracture behavior of PET films of thicknesses 0.125, 0.175, 0.275, 0.37 5 and 0.5 mm was investigated according to Essential Work of Fracture (EWF) method. Single edge and double edge notched specimens of varying ligament lengths were tested in tension producing load-displacement traces that were typical of ductile failure. A linear relationship was obtained between the total specific work of fracture (w(f)) and ligament length (L). This linea rity was maintained as ligament length exceeded the plastic zone size or on e third of sample width. It was found that while the specific essential wor k of fracture (w(e)) was independent of thickness, the specific non-essenti al work of fracture (beta w(p)) decreased with increasing thickness. It was found also, that work of fracture parameters were independent of the speci men width for the range of thicknesses used in the present study. Neverthel ess, for a sample width of 20 mm, a lower w(e) and a higher beta w(p) value was obtained. Good agreement was found between values of w(e) obtained fro m SENT and those obtained from DENT specimens; the value of beta w(p) was c onsistently higher for SENT specimens.