We describe a novel mechanism for the synthesis of a stable high-entropy alloy powder from an otherwise immiscible Mg-Ti rich metallic mixture by employing high-energy mechanical milling.The presented methodology expe...We describe a novel mechanism for the synthesis of a stable high-entropy alloy powder from an otherwise immiscible Mg-Ti rich metallic mixture by employing high-energy mechanical milling.The presented methodology expedites the synthesis of amorphous alloy powder by strategically injecting entropic disorder through the inclusion of multi-principal elements in the alloy composition.Predictions from first principles and materials theory corroborate the results from microscopic characterizations that reveal a transition of the amorphous phase from a precursor intermetallic structure.This transformation,characterized by the emergence of antisite disorder,lattice expansion,and the presence of nanograin boundaries,signifies a departure from the precursor intermetallic structure.Additionally,this phase transformation is accelerated by the presence of multiple principal elements that induce severe lattice distortion and a higher configurational entropy.The atomic size mismatch of the dissimilar elements present in the alloy produces a stable amorphous phase that resists reverting to an ordered lattice even on annealing.展开更多
An accurate estimation of wind loads on telecommunication towers is crucial for design,as well as for perform-ing reliability,resilience,and risk assessments.In particular,drag coefficient and interference factor are ...An accurate estimation of wind loads on telecommunication towers is crucial for design,as well as for perform-ing reliability,resilience,and risk assessments.In particular,drag coefficient and interference factor are the most significant factors for wind load computations.Wind tunnel tests and computational fluid dynamics(CFD)are the most appropriate methods to estimate these parameters.While wind tunnel tests are generally preferred in practice,they require dedicated facilities and personnel,and can be expensive if multiple configurations of tower panels and antennas need to be tested under various wind directions(e.g.,fragility curve development for system resilience analysis).This paper provides a simple,robust,and easily accessible CFD protocol with widespread applicability,offering a practical solution in situations where wind tunnel testing is not feasible,such as complex tower configurations or cases where the cost of running experiments for all the tower-antennas configurations is prohibitively high.Different turbulence models,structural and fluid boundary conditions and mesh types are tested to provide a streamlined CFD modeling strategy that shows good convergence and balances accuracy,computational time,and robustness.The protocol is calibrated and validated with experimental studies available in the literature.To demonstrate the capabilities of the protocol,three lattice tower panels and antennas with different configurations are analyzed as examples.The protocol successfully estimates the drag and lateral wind loads and their coefficients under different wind directions.Noticeable differences are observed between the esti-mated wind loads with this protocol and those computed by a simple linear superposition used in most practical applications,indicating the importance of tower-antenna interaction.Also,as expected,the wind loads recom-mended by design codes overestimate the simulated results.More importantly,the telecommunication design codes inadequately identify the most favorable wind directions that are associated with the lowest wind loads,while the results of the proposed protocol align with observations from experimental studies.This information may be used to select the tower orientation before construction.The findings of this study are of importance for the telecommunication industry,which seeks reliable results with minimal computational efforts.In addition,it enhances the fragility analysis of telecommunication towers under strong winds,and the portfolio risk and resilience assessment of telecommunication systems.展开更多
建立了线路板(PCB)测试中变形对应的二维图形变换模型,使用正态和W e ibu ll分布统计模型处理数据,成功用于针床式在线测试仪(B ed-of-na ils T esting F ix ture)可靠性定量评估,并由定量实测结果分析了针床测试仪对准误差的类型、大...建立了线路板(PCB)测试中变形对应的二维图形变换模型,使用正态和W e ibu ll分布统计模型处理数据,成功用于针床式在线测试仪(B ed-of-na ils T esting F ix ture)可靠性定量评估,并由定量实测结果分析了针床测试仪对准误差的类型、大小及产生原因。展开更多
Accurate estimates of ductility demands on buckling-restrained braced frames(BRBFs)are crucial to performance-based design of BRBFs.An analytical study on the seismic behavior of BRBFs has been conducted at the ATLSS ...Accurate estimates of ductility demands on buckling-restrained braced frames(BRBFs)are crucial to performance-based design of BRBFs.An analytical study on the seismic behavior of BRBFs has been conducted at the ATLSS Center,Lehigh University to prepare for an upcoming experimental program.The analysis program DRAIN-2DX was used to model a one-bay,four-story prototype BRBF including material and geometric nonlinearities.The buckling- restrained brace(BRB)model incorporates both isotropic and kinematic hardening.Nonlinear static pushover and time- history analyses were performed on the prototype BRBF.Performance objectives for the BRBs were defined and used to evaluate the time-history analysis results.Particular emphasis was placed on global ductility demands and ductility demands on the BRBs.These demands were compared with anticipated ductility capacities.The analysis results,along with results from similar previous studies,are used to evaluate the BRBF design provisions that have been recommended for codification in the United States.The results show that BRB maximum ductility demands can be as high as 20 to 25.These demands significantly exceed those anticipated by the BRBF recommended provisions.Results from the static pushover and time- history analyses are used to demonstrate why the ductility demands exceed those anticipated by the recommended provisions. The BRB qualification testing protocol contained in the BRBF recommended provisions is shown to be inadequate because it requires only a maximum ductility demand of at most 7.5.Modifications to the testing protocol are recommended.展开更多
基金supported in part by the National Science Foundation(NSF)award#CMMI-1944040。
文摘We describe a novel mechanism for the synthesis of a stable high-entropy alloy powder from an otherwise immiscible Mg-Ti rich metallic mixture by employing high-energy mechanical milling.The presented methodology expedites the synthesis of amorphous alloy powder by strategically injecting entropic disorder through the inclusion of multi-principal elements in the alloy composition.Predictions from first principles and materials theory corroborate the results from microscopic characterizations that reveal a transition of the amorphous phase from a precursor intermetallic structure.This transformation,characterized by the emergence of antisite disorder,lattice expansion,and the presence of nanograin boundaries,signifies a departure from the precursor intermetallic structure.Additionally,this phase transformation is accelerated by the presence of multiple principal elements that induce severe lattice distortion and a higher configurational entropy.The atomic size mismatch of the dissimilar elements present in the alloy produces a stable amorphous phase that resists reverting to an ordered lattice even on annealing.
基金support from the Pennsylvania Department of Community&Economic Development(DCED)through grant PIT-19-02 and of Lehigh University through the“Research Futures:Major Program Development”the“Research Fu-tures:Special Seed Funding Opportunity”grants are gratefully acknowl-edged.
文摘An accurate estimation of wind loads on telecommunication towers is crucial for design,as well as for perform-ing reliability,resilience,and risk assessments.In particular,drag coefficient and interference factor are the most significant factors for wind load computations.Wind tunnel tests and computational fluid dynamics(CFD)are the most appropriate methods to estimate these parameters.While wind tunnel tests are generally preferred in practice,they require dedicated facilities and personnel,and can be expensive if multiple configurations of tower panels and antennas need to be tested under various wind directions(e.g.,fragility curve development for system resilience analysis).This paper provides a simple,robust,and easily accessible CFD protocol with widespread applicability,offering a practical solution in situations where wind tunnel testing is not feasible,such as complex tower configurations or cases where the cost of running experiments for all the tower-antennas configurations is prohibitively high.Different turbulence models,structural and fluid boundary conditions and mesh types are tested to provide a streamlined CFD modeling strategy that shows good convergence and balances accuracy,computational time,and robustness.The protocol is calibrated and validated with experimental studies available in the literature.To demonstrate the capabilities of the protocol,three lattice tower panels and antennas with different configurations are analyzed as examples.The protocol successfully estimates the drag and lateral wind loads and their coefficients under different wind directions.Noticeable differences are observed between the esti-mated wind loads with this protocol and those computed by a simple linear superposition used in most practical applications,indicating the importance of tower-antenna interaction.Also,as expected,the wind loads recom-mended by design codes overestimate the simulated results.More importantly,the telecommunication design codes inadequately identify the most favorable wind directions that are associated with the lowest wind loads,while the results of the proposed protocol align with observations from experimental studies.This information may be used to select the tower orientation before construction.The findings of this study are of importance for the telecommunication industry,which seeks reliable results with minimal computational efforts.In addition,it enhances the fragility analysis of telecommunication towers under strong winds,and the portfolio risk and resilience assessment of telecommunication systems.
文摘Accurate estimates of ductility demands on buckling-restrained braced frames(BRBFs)are crucial to performance-based design of BRBFs.An analytical study on the seismic behavior of BRBFs has been conducted at the ATLSS Center,Lehigh University to prepare for an upcoming experimental program.The analysis program DRAIN-2DX was used to model a one-bay,four-story prototype BRBF including material and geometric nonlinearities.The buckling- restrained brace(BRB)model incorporates both isotropic and kinematic hardening.Nonlinear static pushover and time- history analyses were performed on the prototype BRBF.Performance objectives for the BRBs were defined and used to evaluate the time-history analysis results.Particular emphasis was placed on global ductility demands and ductility demands on the BRBs.These demands were compared with anticipated ductility capacities.The analysis results,along with results from similar previous studies,are used to evaluate the BRBF design provisions that have been recommended for codification in the United States.The results show that BRB maximum ductility demands can be as high as 20 to 25.These demands significantly exceed those anticipated by the BRBF recommended provisions.Results from the static pushover and time- history analyses are used to demonstrate why the ductility demands exceed those anticipated by the recommended provisions. The BRB qualification testing protocol contained in the BRBF recommended provisions is shown to be inadequate because it requires only a maximum ductility demand of at most 7.5.Modifications to the testing protocol are recommended.
