Fracture Mechanics of Heterogeneous Composites
The increasing application of composite materials due to their ubiquitous advance in terms of mechanical and thermal properties has brought attention to the fracture mechanics of the materials possessing heterogeneity. Recent investigations have focused on the micro- and macro-mechanism of fracture in heterogeneous composites (HCs). In this study, the fracture mechanics of the two HCs: Polymer bonded explosive (PBX) simulant and hot mixed asphalt (HMA) are evaluated on the macroscopic scale. It is an interest of Sandia National Laboratory to examine the fracture resistance of PBXs, particularly those of varying composition and subjected to aging. In this research, a batch of PBX simulants are manufactured in the laboratory environment and the fracture resistance is experimentally investigated. Primarily, a simulant composition of 80 wt.% soda lime glass beads (SLGB) and 20 wt.% high impact Polystyrene 825 (HIPS) is prepared to perform Brazilian disk tests to characterize the tensile and compressive properties. Fracture toughness and energy tests are performed in the semi-circular bending (SCB) configuration on 80, 81, 82, and 83 wt.% SLGB compositions. Digital image correlation (DIC) is performed to record the surface displacements and calculate surface strains during testing. The micromechanical behavior of ductile and brittle fracture is observed using digital microscopy and scanning electron microscopy of the fracture surface. It is found that fracture behavior is heavily depended on the microstructural heterogeneous distribution of particulate polymer matrix, micro-voids/cracks, and interfacial bonding energy. In the consecutive section, a proposal on the thermomechanical behavior of hot mixed asphalt (HMA) at low temperature is presented. There is a need to elucidate the thermomechanical fracture resistance of HMAs employed in the pavement. These materials are highly heterogeneous, with batch-to-batch variations outside of these observed in classic structure materials (such as structural alloys or even concrete). The impact of weather on these materials (HMAs) is one of the primary research focuses of the Southern Plains Transportation Center. On that interest, this proposal is prepared to investigate the thermal stress and thermal mismatch of HMA subjected to cooling. HMA specimens will manufacture according to TxDOT standard. This proposal includes a plan to perform the indirect tensile test and thermal stress restrained specimen test for single edge prismatic specimen on several HMAs at varying temperature to acquire a master curve and low-temperature fracture properties. The application of DIC system will enable us to observe crack initiation, propagation, and nucleation as well as the thermal and mechanical strains, and thermal contraction coefficient within asphalt specimens. This plan of the proposal also includes the integration of Infrared (IR) thermography with DIC in order to observe the thermal mismatch gradient. A method will develop to sync the DIC cameras and the IR cameras to take images of the asphalt specimens simultaneously and then it will post-process using MATLAB software. These approaches of analysis and the series of testing protocols will enable us to investigate the thermomechanical response of HMAs and to achieve a sustainable solution for a better understanding of HMAs complex interactions of fracture mechanics at weather extremes.
Rabbi, Fazle MD., "Fracture Mechanics of Heterogeneous Composites" (2018). ETD Collection for University of Texas, El Paso. AAI10813817.