On the tearing of a polymer film

Abstract

The Post-Yielding Fracture Mechanics explains the fracture behaviour of a precracked films and thin sheets that show fully-yielded state at the crack tip during the fracture. The Essential Work of Fracture method (EWF) has been used for this type of fracture characterization. Two parameters are involved in EWF: the specific work of fracture, we, where is described the real fracture process area, and the non-specific work of fracture, wp, which is related to the rest of phenomenons that occur in the fracture. The use of videoextensometers during the test, has permited to record the deformation and the crack opening displacement when the test has carried out. Afterwards, images has been analysed to acquire the most suitable value of deformation, avoiding wrong calculations due to viscoelasticity energy. In this work, the fracture of a 0.6 mm thick PETG film was studied using the DDENT specimen by a relationship between EWF and J-Integral in the J – Δa curve. This new representation has been used in order to determine the crack initiation, displacement and stress initiation. The evaluation has discovered that the specific essential work of fracture, we, is equal to a fracture initiation value, JIC . At the same time, it has been calculated the new method which relate the plastic term, β · wp, and the crack initiation stress, 𝜎𝑖 . La mecànica de fractura Post-cedència explica el comportament de films i plaques fines pre – entallades, que mostren un complet estat de cedència a la punta de la entalla durant la fractura. El mètode del Treball Essencial de Fractura (EWF) és utilitzat per caracteritzar aquest tipus de fractura. Hi ha dos paràmetres implicats en el EWF: el treball específic de fractura, we, on el procés es descriu la àrea de procés real de fractura, i el treball no-específic de fractura, wp, el qual està relacionat amb la resta de fenòmens que ocorren en la fractura.