Strain measurement of polymer materials by digital image correlation combined with finite-element analysis

Compliant Mechanism-Based Sensor for Large Strain Measurements Employing Fiber Optics

We propose a sensor design for measurement of large strains where direct application of a fiber optic strain gauge is impossible due to the stiffness mismatch between the optical fiber and the structure under test. The sensor design is based on a rhombus type compliant mechanism, which functions to attenuate input strain and transfer it to the ends of the sensing beam with the mounted optical strain gauge. We developed an analytical model of the sensor, which allows us to relate actuation forces, input displacement/strain, and output strain. The analytical model was verified with the finite element analysis and validated against an experimental prototype. The prototype sensor was able to handle input strains exceeding ±2.5 × 10⁵ µε. Potential application areas of the proposed sensor include compliant elastomeric structures, wearables, and soft robotics.

Thermal, morphological, rheological and deformation under mechanical loading analyses of recycled polyethylene terephthalates

This study aims at determining the mechanical deformation behavior of recycled poly (ethylene terephthalate) (r-PET) with digital image correlation (DIC) and finite element method (FEM), and to investigate the morphological, thermal, and rheological properties of r-PETs. Waste bottles were collected in trash bins and granulated with a cutter. Neat PET (n-PET) was also was used to determine accurately the changes in the properties of r-PET. PET test samples were obtained by injection molding at 260, 265, 270, and 275 °C. DIC and FEM were conducted to detect the deformation behavior of the PETs under mechanical loading. The data showed that the behavior of n-PETs and r-PETs were similar, and the stress distribution was found to densify in various areas for both PETs. The mechanical properties generally increased with increasing processing temperature, the best mechanical properties being obtained for thPETs processed at 275 °C. Scanning electron microscopy (SEM) analysis showed that the morphology of all the PETs were similar. Thermal stability was also found to be similar. The rheological moduli of n-PET processed at 260 °C were the highest, while processing r-PET at 275 °C improved its rheological properties.