Characterization of the Effect of Cold Joints and Functional Grading in Stepwise Constructed Tensile Dog Bones with Embedded Digital Image Correlation

Abstract

We present an extension of our previously published work in which we utilized an in situ/embedded Digital Image Correlation (DIC) technique to evaluate the effect of aging on the interface debonding strength in an idealized particulate composite. The idealized composite consists of a single ~650 μm glass bead inclusion at the center of a Sylgard 184 dog bone tensile sample along with an embedded DIC speckle pattern at the mid-plane. The speckle pattern enables the measurement of the strain field in the region surrounding the embedded glass bead while the sample undergoes a tensile load to failure. The measured strain field can then be used in conjunction with the global load measurement to characterize the local stress required to induce a failure at the interface. In previous works we have demonstrated how this approach can be used to characterize interface debonding. Construction of these tensile samples is done in a stepwise fashion with partial cure cycles in order to achieve a reliable in situ/embedded DIC speckle pattern. This stepwise construction introduces two uncertainties into the experiment, namely, cold joints between the casting layers and functional grading of the stiffness properties due to each layer experiencing different curing histories. In this work we present an evaluation of the effect of the cold joints and functional grading by performing tension tests to measure the global stiffness of dog bones of various sample configurations spanning the number of cold joints and the cure cycle history. By comparing the measured stiffness of each sample configuration, the effect of the cold joints and functional grading are determined.