Quantitative visualisation of the continuous whole-field stress evolution in complex pore structures using photoelastic testing and 3D printing methods.

Providing a quantitative description of the whole-field stress evolution in complex structures subjected to continuous loading processes using traditional photoelastic approaches is a significant challenge because of the difficulties with fabricating complex structures, identifying the stress distribution and evolution, and unwrapping isochromatic phase maps. To overcome the challenges, we proposed a novel method to quantify the continuous whole-field stress evolution in a complex porous structure that was fabricated with 3D printing technology. The stress fringes were identified by analysing a series of continuous frames extracted from a video recording of the fringe changes and determining the valleys of the light intensity change curve over the entire loading process. The experimental data were compared with the numerical results of the complex model with identical pore geometries, physical properties, and loading conditions to evaluate the accuracy and effectiveness of the method. In principle, the applicability of the reported method for identifying and unwrapping the continuous whole-field stress is not affected by the complexity of a structure.

Expanding the "Magic Triangle" of Reinforced Rubber Using a Supramolecular Filler Strategy.

A strategy for optimizing the rolling resistance, wet skid and cut resistance of reinforced rubber simultaneously using a supramolecular filler is demonstrated. A ß-alanine trimer-grafted Styrene Butadiene Rubber (A3-SBR) pristine polymer was designed and mechanically mixed with commercially available styrene butadiene rubber to help the dispersion of a ß-alanine trimer (A3) supramolecular filler in the rubber matrix. To increase the miscibility of A3-SBR with other rubber components during mechanical mixing, the pristine polymer was saturated with ethanol before mixing. The mixture was vulcanized using a conventional rubber processing method. The morphology of the assembles of the A3 supramolecular filler in the rubber matrix was studied by Differential Scanning Calorimetry (DSC) and Transmission Electron Microscopy (TEM). The Differential Scanning Calorimetry study showed that the melting temperature of ß-sheet crystals in the vulcanizates was around 179 °C and was broad. The melting temperature was similar to that of the pristine polymer, and the broad melting peak likely suggests that the size of the crystals is not uniform. The Transmission Electron Microscopy study revealed that after mixing the pristine polymer with SBR, some ß-sheet crystals were rod-like with several tens of nanometers and some ß-sheet crystals were particulate with low aspect ratios. Tensile testing with pre-cut specimens showed that the vulcanizate containing A3-SBR was more cut-resistant than the one that did not contain A3-SBR, especially at a large cut size. The rolling resistance and wet skid were predicted by dynamic mechanical analysis (DMA). DMA tests showed that the vulcanizates containing A3-SBR were significantly less hysteretic at 60 °C and more hysteretic at 0 °C based on loss factor. Overall, the "magic triangle" was expanded by optimizing the rolling resistance, wet-skid, and cut resistance simultaneously using a ß-alanine trimer supramolecular filler. The Payne effect also became less severe after introducing the ß-alanine trimer supramolecular filler into the system.

Visualization method for stress-field evolution during rapid crack propagation using 3D printing and photoelastic testing techniques.

Quantitative visualization and characterization of stress-field evolution during fracture rapid growth is critical for understanding the mechanisms that govern the deformation and failure of solids in various engineering applications. However, the direct capture and accurate characterization of a rapidly-changing stress field during crack propagation remains a challenge. We report an experimental method to quantitatively visualize and characterize rapid evolution of the stress-field during crack propagation in a transparent disc model containing a penetrating fusiform crack. Three-dimensional (3D) printing technology and a stress-sensitive photopolymer resin were adopted to produce the disc model and to alleviate the residual processing stress that usually blurs the dynamic stress field due to overlap. A photoelastic testing system that synchronized a high-speed digital camera and a pulsed laser with a nanosecond full width at half maximum (FWHM) was used to capture the rapid evolution of the stress field in the vicinity of crack tips. The results show that the proposed method is suitable to directly visualize and quantitatively characterize the stress-field evolution during crack rapid propagation. It is proved that the crack propagation velocity is strongly governed by the stress field around the crack tips.