Three dimensional finite element simulations of ductile to brittle failure mode transition in glassy amorphous polymers
Brunda Kattekola (IIT Kanpur), Sumit Basu (Indian Institute of Technology)
Crack initiation and growth: methods, applications, and challenges
Tue 9:00 - 10:30
Sayles Auditorium
Polycarbonate (PC) is a commercially important example of a ductile glassy amorphous polymer. Fracture toughness of PC, though generally higher relative to other polymers of its type, is sensitively affected by various geometric and material factors. For example, molecular weight, ageing time, specimen thickness, notch radius, loading rate etc are known to affect the toughness. In this work, we perform 3D Finite Element simulations on single edge notched tensile (SENT) specimen to study the ductile to brittle transition in PC. We particularly focus on simulating the failure mode transition involving a switch in the mode of fracture from shear band dominated plastic flow at the notch tip to crazing with decrease in notch radius and increase in specimen thickness In the first part of the work, we validated and calibrated constitutive model for PC. During this process, extensive tensile and compression experiments were conducted on PC to determine the model parameters. Further experiments and simulations were conducted on SENT specimens with a range of thicknesses and notch tip radii to study the failure mode. A simple criterion involving critical mean stress (of 70 MPa) and opening stress (of 400 MPa) was used to differentiate the brittle mode from the ductile failure in simulations. It is seen that the size and shape of the plastic zone varies with notch tip radius and thickness of the specimen. In thick specimens with sharp notches, the mid-plane experienced high mean stress which points to brittle failure at the center of the specimen. However, the thin specimens mostly satisfied the ductile failure criterion and showed weak variation of the stress along the thickness direction. We further construct a failure map for commercial PC in thickness-notch tip plane, where a critical value of the ratio of the thickness to the notch tip radius of 25.5 separated the brittle zone from the ductile in the failure map.