Optical method of caustics applied in viscoelastic fracture analysis

The optical method of caustics is developed here to study the fracture of viscoelastic materials. By adopting a distribution of viscoelastic stress fields near the crack tip, the method of caustics is used to determine the viscoelastic fracture parameters from the caustic patterns near the crack tip. Two viscoelastic materials are studied. These are PMMA and ternary composites of HDPE/POE-g-MA/CaCO3. The transmitted and reflective methods of caustics are performed separately to investigate viscoelastic fracture behaviors. The stress intensity factors (SIFs) versus time is determined by a series of shadow spot patterns combined with viscoelastic parameters evaluated by creep tests. In order to understand the viscoelastic fracture mechanisms of HDPE/POE-g-MA/CaCO3 composites, their fracture surfaces are observed by a Scanning Electron Microscope (SEM). The results indicate that the method of caustics can be used to characterize the fracture behaviors of viscoelastic materials and further to optimize the design of polymer composites.

Research highlights
► Optical method of caustics is developed to study the viscoelastic fracture by adopting the distribution of viscoelastic stress field near a crack tip.
► The transmitted and reflective viscoelastic methods of caustics are introduced separately to study the viscoelastic fracture for transparent or non-transparent materials.
► Viscoelastic fracture parameters can be determined by caustic patterns.
► This method can be used to characterize the fracture properties of viscoelastic materials.