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Damage Analysis for Mixed Mode Crack Initiation
Full text linkThe paper presents a numerical simulation for mixed mode crack initiation based on the concepts of damage mechanics. A model with two scalar damage variables is introduced for characterization of damage in a material element. Then a tangent modulus tensor is derived for damage-coupled constitutive equations. A failure criterion is developed with the concept of damage accumulation not only to identify the location of damaged element where the crack initiation angle but also to determine the critical load for mixed mode fracture. The damage model developed is incorporated in a general-purpose finite element program ABAQUA through its UMAT subroutine. The finite element program is then used to perform numerical simulation for pre-cracked specimens under monotonic tensile loading. The thin plates are made of aluminum alloy and particulate composite embedded with a crack of inclined angle β = 0°, 30°, 45° and 60° for mixed mode fracture analysis. The predicted crack initiation loads and the angles of crack initiation agree well with the test results
Implicit Boundary Conditions for Direct Simulation Monte Carlo Method in MEMS Flow Predictions
Full text linkA simple implicit treatment for the low speed inflow and outflow boundary conditions for the direct simulation Monte Carlo (DSMC) of the flows in microelectromechanical systems (MEMS) is proposed. The local mean flow velocity, temperature, and number density near the subsonic boundaries were used to determine the number of molecules entering the computational domain and their corresponding velocities at every sample average step. The proposed boundary conditions were validated against micro-Poiseuille flows and micro-Couette flows. The results were compared with analytical solutions derived from the Navier-Stokes equations using first-order and second order slip-boundary conditions. The results show that the implicit treatment of the subsonic flow boundaries is robust and appropriate for use in the DSMC of the flows in MEMS