Fiber-matrix debonding behaviour using in-situ electron and light microscopy during mechanical testing
Topic(s) : Experimental techniques
Co-authors :
Lode DAELEMANS (BELGIUM), Olivier VERSCHATSE (BELGIUM), Mehdi NIKFOROOZ (BELGIUM), Karen DE CLERCK , Wim VAN PAEPEGEM (BELGIUM)Abstract :
Our research focuses on a novel analysis of fiber-matrix interface debonding in glass/epoxy and carbon/epoxy composite materials by integrating in-situ electron microscopy (SEM) and light microscopy techniques during mechanical testing of small-scale specimens. The specimens can be feasibly produced for a wide range of materials, while the in-situ microscopy allows for the observation and analysis of the debonding process with a high level of detail. The ability to observe these interactions in real-time offers a powerful tool for material scientists and engineers. Our method aims to enhance understanding of microscale debonding behavior and to provide quantified data suitable for integration into micromechanical finite element models.
The in-situ SEM measurements are accompanied by microscale Digital Image Correlation (DIC) to acquire full-field strain measurements on polished sides of composite specimens. For this purpose, we developed a novel speckling technique tunable for a SEM magnification range of 500 – 5000x, easily applicable to various composite materials. Via the developed SEM-DIC method, the strain distribution around fibers is visualized during debonding. The use of various sample types, with differing fiber types and volumes, demonstrated both the potential and limitations of this framework for studying composites at the microscale.
Since in-situ SEM measurements are limited to surface observations (typically visualization of a specimen edge), we also employed in-situ (polarized) optical microscopy to analyze the debonding over the full interface length using optimized cruciform-shaped specimens containing a single fiber. In these tests, the fiber-matrix interface is loaded under normal conditions, in contrast to traditional methods such as microdroplet testing, where the interface is loaded in shear. The test method was verified using fiber types known for their differing bonding behaviors with epoxy resin. A series of tests on two different sized fibers showcased the usefulness of the in-situ optical microscopy method as debond initiation and propagation could be mapped. This approach yielded greater insights into the debonding process and enabled the quantification of the onset and propagation stress levels of debonding.
The in-situ SEM measurements are accompanied by microscale Digital Image Correlation (DIC) to acquire full-field strain measurements on polished sides of composite specimens. For this purpose, we developed a novel speckling technique tunable for a SEM magnification range of 500 – 5000x, easily applicable to various composite materials. Via the developed SEM-DIC method, the strain distribution around fibers is visualized during debonding. The use of various sample types, with differing fiber types and volumes, demonstrated both the potential and limitations of this framework for studying composites at the microscale.
Since in-situ SEM measurements are limited to surface observations (typically visualization of a specimen edge), we also employed in-situ (polarized) optical microscopy to analyze the debonding over the full interface length using optimized cruciform-shaped specimens containing a single fiber. In these tests, the fiber-matrix interface is loaded under normal conditions, in contrast to traditional methods such as microdroplet testing, where the interface is loaded in shear. The test method was verified using fiber types known for their differing bonding behaviors with epoxy resin. A series of tests on two different sized fibers showcased the usefulness of the in-situ optical microscopy method as debond initiation and propagation could be mapped. This approach yielded greater insights into the debonding process and enabled the quantification of the onset and propagation stress levels of debonding.