A Speckling Technique for DIC on Ultra-Soft, Highly Hydrated Materials

Abstract

Background: Digital image correlation is a useful tool in many engineering disciplines to measure and visualize deformation fields. Noteworthily, its successful application is critically dependent on a high-quality surface speckle pattern. While there are numerous standard techniques to apply such patterns, some materials require special techniques because of their unique surface properties. Objective: The goal of our technical brief is to introduce a speckling technique for ultra-soft and highly hydrated materials for which standard speckling techniques may not be suitable. We chose blood clot as our primary sample material. Methods: We identified polymer granules as an easy, fast, and inexpensive speckling material. To test its efficacy and applicability, we patterned blood clot with a 50:50 mix of black and white granules. Next, we conducted pure shear and mode-I fracture experiments to determine whether these granules produce a high-quality DIC pattern and whether their application alters the material’s behavior. Results: We found that applying a 50:50 mix of black and white granules produced high-quality speckle patterns as evaluated via the mean image gradient and a digital image correlation simulator. Additionally, we found that applying granules to the samples’ surfaces does not alter their material properties as measured via the material’s stiffness, strength, work-to-fracture, and fracture toughness. We confirmed that our technique also works for other ultra-soft and highly hydrated materials by applying it to gelatin. Conclusion: In conclusion, we provide an easy, fast, and inexpensive speckling technique for ultra-soft, highly hydrated materials, such as blood clot and gelatin, which does not alter the materials’ mechanical properties.