This study analyzes the relationship between fracture toughness and the fracture surface fractal dimension for a set of twenty-four CT-type AISI 4340 steel specimens heat treated to a variety of tensile strengths. Spe...This study analyzes the relationship between fracture toughness and the fracture surface fractal dimension for a set of twenty-four CT-type AISI 4340 steel specimens heat treated to a variety of tensile strengths. Specimens were tested in accordance with ASTM E 399. Their respective fracture surfaces were plated, polished, photographed under an SEM in BSE mode and measured according to the Richardson method to obtain fractal dimensions. For brittle materials the limited results are consistent with previous literature: increasing fractal dimension with increasing toughness. For partially or fully ductile materials the results indicate a decrease in fractal dimension with an increase in fracture toughness. The data are modeled using a variation of the function applied to ceramics. Fracture in a ductile mode is characterized by the formation of dimples which exhibit fractal characteristics. The results are discussed in terms of the micromechanisms of fracture.展开更多
Blockchains have been around for more than ten years,and since 2015,a plethora of systems have been launched to target more flexible use cases.More recently,several enterprise blockchain systems,such as Consensys Quor...Blockchains have been around for more than ten years,and since 2015,a plethora of systems have been launched to target more flexible use cases.More recently,several enterprise blockchain systems,such as Consensys Quorum and Hyperledger Fabric,have been launched to make blockchain simpler to apply in complex organizational configurations.In this paper,we identify a specific Department of Defense use case,extrapolate requirements,and perform a thorough assessment of the different layers of the blockchain stack to identify the existing state of the art and undertake a gap analysis of the technology for this context.We describe a platform that meets many of these challenges and show how we architected,designed,and implemented a solution for this use case for deployment at NAVAIR.This solution connects transactions from two separate blockchain systems,Consensys Quorum and Hyperledger Fabric,by using a graph-based approach that preserves privacy while enabling full transparency across the military and supplier networks.展开更多
This study presents the development of computationally efficient coupling of Navier–Stokes Computational Fluid Dynamics(CFD)with a helicopter flight dynamics model with the ultimate goal of real-time simulation of ai...This study presents the development of computationally efficient coupling of Navier–Stokes Computational Fluid Dynamics(CFD)with a helicopter flight dynamics model with the ultimate goal of real-time simulation of airwake effects in the helicopter/ship Dynamic Interface(DI).The flight dynamics model is free to move within a computational domain,where the main rotor forces are converted to source terms in the momentum equations of the CFD solution using an actuator disk model.Simultaneously,the CFD solver calculates induced velocities that are fed back to the simulation and affect the aerodynamic loads in the flight dynamics.The CFD solver models the inflow,ground effect and interactional aerodynamics in the flight dynamics simulation,and these calculations can be coupled with the solution of the external flow(e.g.,ship airwake effects).The simulation framework for fully-coupled pilot-in-the-loop(PIL)flight dynamics/CFD is demonstrated for a simplified shedding wake.Initial tests were performed with 0.38 million structured grid cells running on 352 processors and showed near-real-time performance.Improvements to the coupling interface are described that allow the simulation run at near-real-time execution speeds on currently available computing platforms.Improvements in computing hardware are expected to allow real-time simulations.展开更多
文摘This study analyzes the relationship between fracture toughness and the fracture surface fractal dimension for a set of twenty-four CT-type AISI 4340 steel specimens heat treated to a variety of tensile strengths. Specimens were tested in accordance with ASTM E 399. Their respective fracture surfaces were plated, polished, photographed under an SEM in BSE mode and measured according to the Richardson method to obtain fractal dimensions. For brittle materials the limited results are consistent with previous literature: increasing fractal dimension with increasing toughness. For partially or fully ductile materials the results indicate a decrease in fractal dimension with an increase in fracture toughness. The data are modeled using a variation of the function applied to ceramics. Fracture in a ductile mode is characterized by the formation of dimples which exhibit fractal characteristics. The results are discussed in terms of the micromechanisms of fracture.
基金funding from a Phase Ⅱ SBIR grant(Contract No.N68335-20-C-0302)for the VIPART project(PO,Dr Manivannan Venkat)to support NAVAIR.
文摘Blockchains have been around for more than ten years,and since 2015,a plethora of systems have been launched to target more flexible use cases.More recently,several enterprise blockchain systems,such as Consensys Quorum and Hyperledger Fabric,have been launched to make blockchain simpler to apply in complex organizational configurations.In this paper,we identify a specific Department of Defense use case,extrapolate requirements,and perform a thorough assessment of the different layers of the blockchain stack to identify the existing state of the art and undertake a gap analysis of the technology for this context.We describe a platform that meets many of these challenges and show how we architected,designed,and implemented a solution for this use case for deployment at NAVAIR.This solution connects transactions from two separate blockchain systems,Consensys Quorum and Hyperledger Fabric,by using a graph-based approach that preserves privacy while enabling full transparency across the military and supplier networks.
基金the Office of Naval Research,ONR,under Grant/Contract numbers N00014-14-C-0020(PSU)and N00014-13-C-0456(CRAFT Tech).
文摘This study presents the development of computationally efficient coupling of Navier–Stokes Computational Fluid Dynamics(CFD)with a helicopter flight dynamics model with the ultimate goal of real-time simulation of airwake effects in the helicopter/ship Dynamic Interface(DI).The flight dynamics model is free to move within a computational domain,where the main rotor forces are converted to source terms in the momentum equations of the CFD solution using an actuator disk model.Simultaneously,the CFD solver calculates induced velocities that are fed back to the simulation and affect the aerodynamic loads in the flight dynamics.The CFD solver models the inflow,ground effect and interactional aerodynamics in the flight dynamics simulation,and these calculations can be coupled with the solution of the external flow(e.g.,ship airwake effects).The simulation framework for fully-coupled pilot-in-the-loop(PIL)flight dynamics/CFD is demonstrated for a simplified shedding wake.Initial tests were performed with 0.38 million structured grid cells running on 352 processors and showed near-real-time performance.Improvements to the coupling interface are described that allow the simulation run at near-real-time execution speeds on currently available computing platforms.Improvements in computing hardware are expected to allow real-time simulations.
