AN EXPERIMENTAL STUDY ON THE FRACTURE BEHAVIOUR OF TOUGHENED RESINS UNDER MIXED MODE LOADS

Improving the fracture toughness of materials particularly by particulate toughening mechanisms is an area that has generated a lot of commercial interest in the recent years. Reports have shown that infusion of particles in the inter-laminar and intra-laminar region improves material performance by several orders of magnitude. However, detailed characterisation of particle induced toughening mechanisms in mixed-mode remains complex and calls further exploration. The sponsoring organization of this project conducts advanced research in developing methodologies that characterize fracture behaviour of particulate toughened polymers. This study has developed a novel, repeatable pre-crack initiation tool that produces a consistent, sharp pre-crack of a specified length, orientation and crack front in a consistent and safe manner. This tool facilitates high through-put characterisation of fracture behaviour in toughened polymers. The Compact Tension Mixed Mode modified (CTMMM) specimen and grips designed in this study provide less constraint at the pin loading points and hence facilitate ‘pure’ mode I, mode II and mixed mode I&II testing. A range of unmodified and particle toughened resins were subjected to fracture testing in these loading modes. Displacement fields around the tip of the crack were determined by 2D Digital Image Correlation (DIC) and fracture parameters were evaluated using in-house software (DICITAC). The combined preparation and testing methodology using 2D DIC and the fracture parameter extraction methods have proved to be an efficient and effective way to screen different resin formulations. Results show that in unmodified and particle-modified resins, the type and concentration of particle (% weight loading) influences fracture toughness of a resin and determines its behaviour in mixed mode I and II. Further, it is shown that strain energy and behaviour of resin modified composites are also influenced by particle weight loading concentrations of the resin systems incorporated in them.