Chapter 11 Characterization of Interface Debonding Behavior Utilizing an Embedded Digital Image Correlation Scheme Tomislav Kosta and Jesus O. Mares Jr. Abstract We present an in situ Digital Image Correlation (DIC) technique to characterize the interface debond behavior in a Sylgard 184-based particulate composite under quasi-static tensile loading. We construct tensile specimens with a single 650 μm glass bead inclusion at the center of the sample along with an embedded DIC speckle pattern at the midplane to enable measurement of the strain field in the region surrounding the embedded glass bead. The planar nature of the speckle pattern paired with the transparent binder allows for measurement of the sub-surface strain with simple camera diagnostics. Symmetry of the tensile specimen enables straightforward interpretation of the results. By capturing the evolution of the strain field from the unloaded state up to, and through, the delamination, we obtain a rich data set describing the debond process. Through repetition of the experiment, the debond behavior can be described in a statistically meaningful manner. This approach allows for calibration of a targeted constitutive model and serves as a tool to probe the effect of material or surface modification to promote adhesion. Keywords Sylgard 184 · Interfaces · Interface debonding · Interface delamination · DIC 11.1 Introduction The mechanical properties of composite materials depend on both the properties of the individual components as well as the properties of the interfaces between those components, particularly in the context of material strength. Depending on the filler volume fraction, the interface debond strength can have a significant influence on the strength of the composite. We refer to the interface debond as the mechanical separation of two separate components in a composite material, or delamination. The interface debonding strength (or adhesion strength) becomes particularly important for the development of high fidelity computational models to simulate events in which strength and flow properties play a role. However, accurate statistical representation of the delamination occurring within composite materials under mechanical loading is difficult to achieve due to the technical challenges in the characterization of the interface properties. Several standardized test methods exist for the measurement of adhesion of a simple binary material system; however these tests are poorly suited for quantitative assessment of the interface debonding strength in composite materials. Tests such as the pull [1], peel [2], and blister test [3] provide a means of quantifying the debonding process; however, the stress states of the materials in these experiments are non-ideal and complicate the interpretation of the effective properties associated with delamination. These tests tend to produce data which is highly dependent upon the specific geometry of the debonding process, proving difficult to characterize the general interface properties. Additionally, due to required sample geometries, these tests are not well-suited to examine particulate bulk composites, making them difficult to apply to many material systems of interest. Several methods have been developed to investigate the effective interface debonding strength by examining the fracture of particulate bulk composites. For example, Tan et al. [4] have integrated digital image correlation (DIC) into a modeI fracture test of a composite sample to provide targeted data for cohesive zone element model parameterization. These experiments provide direct results for model calibration; however, the delamination properties that dominate the delamination occurring at individual particle-binder interfaces are heavily integrated through this approach. The resultant models are T. Kosta ( ) · J. O. Mares Jr. United States Air Force Research Laboratory, Munitions Directorate, Eglin AFB, FL, USA e-mail: tomislav.kosta@us.af.mil; jesus.mares.2@us.af.mil © The Society for Experimental Mechanics, Inc. 2021 M.-T. Lin et al. (eds.), Advancement of Optical Methods & Digital Image Correlation in Experimental Mechanics, Conference Proceedings of the Society for Experimental Mechanics Series, https://doi.org/10.1007/978-3-030-59773-3_11 83
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