84 T. Kosta and J. O. Mares Jr. typically calibrated to define single valued parameters which lose the capability to capture the statistical distribution of the interface properties throughout the bulk material. Alternatively, experiments such as those by Gent and Park [5] and proposed by Lauke [6, 7] explicitly study the delamination of a single particle within a binder matrix. Specifically, Gent and Park [5] examined the delamination of a glass sphere within an optically transparent binder material under an applied tensile load and observed the onset of debonding at the interface as well as additional features such as the cavitation or crazing of the binder near the particle-binder interface. The stress states within the binder material which generated the debond event were analytically determined and noted as the critical debonding stress. This critical debonding stress was noted to serve as an indicator of the strength of adhesion between the particle and the binder material. In this work we extend the methodology introduced by Gent and Park [5] to incorporate the Digital Image Correlation (DIC) technique to quantify the strain fields of the binder material near an embedded glass bead through a debonding event. This method can serve as a basis to collect a statistically relevant set of debonding information for a coupled binder and particle system of interest. The data acquired with this technique allows for enhanced validation of modeling approached to ensure proper capture of the salient physics. 11.2 Experimental Methods 11.2.1 Sample Fabrication To allow for the inference of the strain state of the binder material during a debonding event, standard tensile test samples were constructed of a transparent matrix material with a single spherical particle inclusion surrounded by a plane of fine tracking particles. Rectangular dog-bone tensile samples with a cross section approximately 9 mm by 12 mm were constructed from Sylgard 184 in a layered approach in order to properly embed a spherical glass particle which serves as the inclusion, as well as a plane of tracking particles for use in DIC. Dow Corning Sylgard 184 silicone elastomer was used for the binder material and was mixed in a 10:1 base to curative ratio by mass for all samples. The highly transparent nature of the material allowed for the observation of particles and debonding within the sample throughout the experiment. An initial layer of Sylgard 184 was poured into a dog-bone shaped mold to a height of approximately 6.35 mm and cured at 100 ◦C for 30 min. A thin layer of binder was then applied to the partially cured surface, and a spherical glass particle was placed in the middle of the sample such that the thin layer of binder was level with the midplane of the particle. In order to allow for suitable observation of the delamination event, glass particles with a nominal diameter of 0.65 mm were selected from a lot of 3 M hollow glass microspheres. The sample was then cured for an additional 30 min at 100 ◦C. A thin layer of a mixture of Cospheric 27–32 μm black paramagnetic polyethylene microspheres and Sylgard 184 was then applied to the surface of the new cure layer to serve as the DIC speckle pattern, and the mold was then filled to the full mold height of 12.70 mm. The sample was then cured at 100 ◦C for 30 min. The sample was released from the mold and excess binder was trimmed. The sample construction process is summarized in Fig. 11.1, and a notional diagram of the fully constructed sample is presented in Fig. 11.2. The quality of the placement of the spherical glass particle and the surrounding plane of tracking particles were evaluated with the use of a Zeiss Discovery V12 stereoscope. The glass particles were examined to ensure their placement at the midplane through the thickness of the dog-bone test article, as well as at the mid-location of the sample in the front view. As the success of the strain field measurement using DIC is highly dependent upon the quality of the application of the Fig. 11.1 Illustration of the layered approach to construct dog-bone samples of Sylgard 184 with an embedded spherical glass particle and pattern of tracking particles
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