Octavian Knoll

Bio: Octavian Knoll is an academic researcher. The author has contributed to research in topics: Digital image correlation & Strain gauge. The author has co-authored 1 publications.

Strain Acquisition Framework and Novel Bending Evaluation Formulation for Compression-Loaded Composites Using Digital Image Correlation.

Abstract: Consistent and reproducible data are key for material characterization. This work presents digital image correlation (DIC) strain acquisition guidelines for compression-loaded carbon fiber composites. Additionally, a novel bending criterion is formulated which builds up on the DIC strain data so that it is able to completely replace state-of-the-art tactile strain devices. These guidelines are derived from a custom test setup that simultaneously investigates the front and side view of the specimen. They reflect both an observation and post-processing standpoint. It is found that the DIC-based strain progress matches closely with state-of-the-art strain gauges up to failure initiation. The new bending evaluation criterion allows the bending state—and therefore, the validity of the compression test—to be monitored analogously to the methodology defined in the standards. Furthermore, the new bending criterion eliminates a specific bending mode, caused by an offset of clamps, which cannot be detected by the traditional strain gauge-based monitoring approach.

Experimental and Numerical Study on the Bending Behavior of Satin-Woven SiCf/SiC Composites

Abstract: The present research intends to explore the progressive failure in the case of five-harness SiCf/SiC satin-woven sheet composites consisting of twelve layers using a combination of numerical and experimental methods. For derivation and characterization of the bending behavior, a three-point bending procedure was used under conditions of atmospheric temperature. A charge-coupled device (CCD) camera was used to monitor the initiation and evolution of the failures. Variations in the strain fields were quantified following the digital image correlation (DIC) approach, whereas the resultant failure markings were elucidated by conducting microscopic assessments. The 3D finite element modeling (FEM) of the experiment was accomplished via ABAQUS/Explicit, thereby reproducing the material performance. A 3D-modified theory of the Tsai-Wu failure initiation was executed by exploiting the VUMAT subroutine. The evolutionary rule was used to study the complementary failure. A cohesive zone element of the composite interlayer was utilized to mimic the intra-deformation interfacial damage. The DIC-based experimental values of the strain fields agreed favorably with the numerical computations and the strength value error was less than 10%. An in-depth investigation was performed concerning the advantage of the 3D modeling approach to study the applicability of the method for the foreseeable distribution of the complex field parameters (e.g., progressive failure deposition and free edge effect) inside the critical specimen section.