Damage initiation and evolution during monotonic cooling of laminated composites

The objective of this work is to develop a methodology to predict matrix damage initiation and evolution in laminated composites subjected to monotonic cooling using discrete damage mechanics and a careful characterization of the required temperature-dependent material properties. Since prediction of thermo-mechanical damage requires precise knowledge of the temperature-dependent properties of the material, back-calculation of fiber and matrix properties from different sources is included. The proposed methodology is flexible, in that it can be adapted to the availability of experimental data. A compilation of literature data is developed to estimate the properties of several fiber and matrix systems. Prediction of lamina and laminate temperature-dependent properties are compared with available data. Furthermore, temperature-dependent fracture toughness of four material systems are estimated from available crack density data. For the material systems studied, it is found that temperature-independent fracture toughness is satisfactory for prediction of damage initiation, evolution, and saturation.

Damage Initiation and Evolution of Panicum Miliaceum Seeds Under Compression

Panicum Miliaceum (common millet) is an ancient crop and spread widely across the world. The high survivability and adaptability of this species is attributed to the unique structure of the seedcoat. Recently, it was found the seedcoat has a fascinating complex microstructure with star-shaped epidermis cells, articulated together via wavy suture interfaces, to form a compact jigsaw puzzle-like layer. To explore the damage initiation and evolution during quasi-static uniaxial compression, finite element simulations were performed for full seeds, and single seedcoat and kernels. A parametric study was conducted for the seedcoat and kernel to explore the relationship between material properties and damage. The material properties of the seedcoat and kernel were obtained by nanoindentation testing. A Hashin progressive damage material model was used to capture damage evolution of the seedcoat, combined with a damage plasticity model for the kernel. The simulation results show the capabilities in modeling the damage of seeds.