EAGER: Investigating the Use of Spiral Cracking Pattern in Fracture Characterization of Soft Adhesive Materials

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This EArly-concept Grant for Exploratory Research (EAGER) project will investigate a novel method of fracture characterization of soft adhesive materials through spiral cracking patterns that can form on these materials when they are attached to a stiff substrate. Application of traditional fracture testing methods in fracture assessment of soft materials is quite challenging due to poor repeatability as well as large creep deformations that occurs during the test. The research outcome of this project could enable a paradigm shift in fracture behavior characterization of soft adhesive materials. Moreover, the research will provide understanding of cracking in film/substrate systems, which is essential in designing crack-resistant coatings. Knowledge created through this research will empower researchers to precisely interpret cracking patterns in important applications areas, such as thermal barrier coatings, reflective coatings in optical applications, modern high-performance ceramics (e.g. turbine blades in jet engines), micro-electro-mechanical systems (MEMS), and medicine. Other potential benefits to the US economy and society include manufacturing of durable and high-performance fracture resistant materials, such as paint, epoxies, and hydrocarbon polymers. The primary objective of this EAGER project is to effectively utilize spiral cracking pattern as a powerful diagnostic tool to obtain valuable information about the composition and fracture behavior of soft adhesive materials. An innovative integrated approach coupling acoustic emissions (AE) technique with Digital Image Analysis (DIA) will be explored: (1) to determine the precise 3D geometry of spiral cracks; (2) to find the best mathematical model to represent the cracking patterns; and (3) to measure the AE-based fracture energy of the material. Multi-sensor AE source-location approach will be used to provide real-time accurate visualization of the 3D geometry of fracture process zone along the spiral crack path. Finally, quantitative assessment of mud (channeling) cracking patterns, morphology of cracks, and statistical analysis of shape and size of fragmentation will be explored. The relationship between fracture energies from spiral and mud crackings will be thoroughly investigated to predict the mud cracking patterns in thin films using the spiral cracking-based fracture energy of the material.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.