In this study, two full-size concrete wails were tested and analyzed to demonstrate the effectiveness of a chemically reactive enamel （CRE） coating in improving their mechanical behavior under blast loading： one wi...In this study, two full-size concrete wails were tested and analyzed to demonstrate the effectiveness of a chemically reactive enamel （CRE） coating in improving their mechanical behavior under blast loading： one with CRE-coated rebar and the other with uncoated rebar. Each wall was subjected in sequence to four explosive loads with equivalent 2, 4, 6-trinitrotoluene （TNT） charge weights of 1.82, 4.54, 13.6, and 20.4 kg. A finite element model of each wall under a close-in blast load was developed and validated with pressure and strain measurements, and used to predict rebar stresses and concrete surface sWain distributions of the wall. The test results and visual inspections consistently indicated that, compared with the barrier wall with uncoated reinforcement, the wall with CRE-coated rebar has fewer concrete cracks on the front and back faces, more effective stress transfers from concrete to steel rebar, and stronger connections with its concrete base. The concrete surface strain distributions predicted by the model under various loading conditions are in good agreement with the crack patterns observed during the tests.展开更多
Dragline excavators are closed-loop mining manipulators that operate using a rigid multilink framework and rope and rigging system,which constitute its front-end assembly.The arrangements of dragline front-end assembl...Dragline excavators are closed-loop mining manipulators that operate using a rigid multilink framework and rope and rigging system,which constitute its front-end assembly.The arrangements of dragline front-end assembly provide the necessary motion of the dragline bucket within its operating radius.The assembly resembles a five-link closed kinematic chain that has two independent generalized coordinates of drag and hoist ropes and one dependent generalized coordinate of dump rope.Previous models failed to represent the actual closed loop of dragline front-end assembly,nor did they describe the maneuverability of dragline ropes under imposed geometric constraints.Therefore,a three degrees of freedom kinematic model of the dragline front-end is developed using the concept of generalized speeds.It contains all relevant configuration and kinematic constraint conditions to perform complete digging and swinging cycles.The model also uses three inputs of hoist and drag ropes linear and a rotational displacement of swinging along their trajectories.The inverse kinematics is resolved using a feedforward displacement algorithm coupled with the Newton-Raphson method to accurately estimate the trajectories of the ropes.The trajectories are solved only during the digging phase and the singularity was eliminated using Baumgarte's stabilization technique(BST),with appropriate inequality constraint equations.It is shown that the feedforward displacement algorithm can produce accurate trajectories without the need to manually solve the inverse kinematics from the geometry.The research findings are well in agreement with the dragline real operational limits and they contribute to the efficiency and the reduction in machine downtime due to better control strategies of the dragline cycles.展开更多
基金Project supported by the National Natural Science Foundation of China （Nos. 51379186 and 51522905）, the Zhejiang Provincial Natural Science Foundation of China （No. LR15E090001）, and the Leonard Wood Institute under Award （No. LWI61009）, USA
文摘In this study, two full-size concrete wails were tested and analyzed to demonstrate the effectiveness of a chemically reactive enamel （CRE） coating in improving their mechanical behavior under blast loading： one with CRE-coated rebar and the other with uncoated rebar. Each wall was subjected in sequence to four explosive loads with equivalent 2, 4, 6-trinitrotoluene （TNT） charge weights of 1.82, 4.54, 13.6, and 20.4 kg. A finite element model of each wall under a close-in blast load was developed and validated with pressure and strain measurements, and used to predict rebar stresses and concrete surface sWain distributions of the wall. The test results and visual inspections consistently indicated that, compared with the barrier wall with uncoated reinforcement, the wall with CRE-coated rebar has fewer concrete cracks on the front and back faces, more effective stress transfers from concrete to steel rebar, and stronger connections with its concrete base. The concrete surface strain distributions predicted by the model under various loading conditions are in good agreement with the crack patterns observed during the tests.
基金The funding from the Robert H.Quenon Endowment at Missouri S&T for this research is also greatly acknowledged.
文摘Dragline excavators are closed-loop mining manipulators that operate using a rigid multilink framework and rope and rigging system,which constitute its front-end assembly.The arrangements of dragline front-end assembly provide the necessary motion of the dragline bucket within its operating radius.The assembly resembles a five-link closed kinematic chain that has two independent generalized coordinates of drag and hoist ropes and one dependent generalized coordinate of dump rope.Previous models failed to represent the actual closed loop of dragline front-end assembly,nor did they describe the maneuverability of dragline ropes under imposed geometric constraints.Therefore,a three degrees of freedom kinematic model of the dragline front-end is developed using the concept of generalized speeds.It contains all relevant configuration and kinematic constraint conditions to perform complete digging and swinging cycles.The model also uses three inputs of hoist and drag ropes linear and a rotational displacement of swinging along their trajectories.The inverse kinematics is resolved using a feedforward displacement algorithm coupled with the Newton-Raphson method to accurately estimate the trajectories of the ropes.The trajectories are solved only during the digging phase and the singularity was eliminated using Baumgarte's stabilization technique(BST),with appropriate inequality constraint equations.It is shown that the feedforward displacement algorithm can produce accurate trajectories without the need to manually solve the inverse kinematics from the geometry.The research findings are well in agreement with the dragline real operational limits and they contribute to the efficiency and the reduction in machine downtime due to better control strategies of the dragline cycles.
