In this research,we introduce an innovative approach that combines the Continuum Damage Mechanics-Finite Element Method(CDM-FEM)with the Particle Swarm Optimization(PSO)-based technique,to predict the Medium-Low-Cycle...In this research,we introduce an innovative approach that combines the Continuum Damage Mechanics-Finite Element Method(CDM-FEM)with the Particle Swarm Optimization(PSO)-based technique,to predict the Medium-Low-Cycle Fatigue(MLCF)life of perforated structures.First,fatigue tests are carried out on three center-perforated structures,aiming to assess their fatigue life under various strengthening conditions.These tests reveal significant variations in fatigue life,accompanied by an examination of crack initiation through the analysis of fatigue fracture surfaces.Second,an innovative fatigue life prediction methodology is applied to perforated structures,which not only forecasts the initiation of fatigue cracks but also traces the progression of damage within these structures.It leverages an elastoplastic constitutive model integrated with damage and a damage evolution model under cyclic loads.The accuracy of this approach is validated by comparison with test results,falling within the three times error band.Finally,we explore the impact of various strengthening techniques,including cross-sectional reinforcement and cold expansion,on the fatigue life and damage evolution of these structures.This is achieved through an in-depth comparative analysis of both experimental data and computational predictions,which provides valuable insights into the behavior of perforated structures under fatigue conditions in practical applications.展开更多
A time-domain method, based on linear velocity potential theory, is presented to study the interaction between narrow-banded random waves and perforated structures. A simple relation is derived to estimate the jet len...A time-domain method, based on linear velocity potential theory, is presented to study the interaction between narrow-banded random waves and perforated structures. A simple relation is derived to estimate the jet length of flows through the perforated wall. The reflection coefficient of narrow banded random waves from perforated structures is calculated by assuming a Rayleigh distribution of the heights of incident random waves. For reflection of narrow-banded waves from a single-chamber perforated breakwater, a comparison of the predicted and measured reflection coefficients shows that the method presented in this paper can provide a prediction better than that of regular waves. Numerical results are also reported on the reflection of narrow-banded waves from multi-chamber perforated breakwaters.展开更多
Porous structures are highly preferred for bone regeneration and high tissue in-growth.In present work,electrical discharge drilling(EDD),a thermal erosion process was used to produce through holes in Mg-alloys to fab...Porous structures are highly preferred for bone regeneration and high tissue in-growth.In present work,electrical discharge drilling(EDD),a thermal erosion process was used to produce through holes in Mg-alloys to fabricate perforated structure similar to open cell porous structure in extruded AZ31.Apatite formation and weight loss study was conducted for 7 days,14 days and 21 days after immersion tests in SBF solution.The perforated structure in AZ31 with 26 through micro-holes provides 72%increase in surface area but with marginally 4%higher weight loss as compare to non-perforated structure.Comparing perforated and non-perforated samples of Mg-alloy,it was well observed that perforated structure forms high volume of apatite as compared to non-perforated structure.Scanning electron microscopic(SEM)study revealed that in perforated structure,drilled holes retain their circularity after 21 days of immersion test and distinct corrosion phenomenon occur at localized sites.展开更多
Acoustic structure study always is the academic research interest. Diffusion ab？sorbing structure（DiflFsorber） has good research value because it has both diflFusion property and sound absorption property. Quadrati...Acoustic structure study always is the academic research interest. Diffusion ab？sorbing structure（DiflFsorber） has good research value because it has both diflFusion property and sound absorption property. Quadratic residue diffusers（QRD） structure which had good diffusion property was combined with the perforated panel which had good sound absorption property in this study. According to standard AES-4id-2001, the diffusion experiments were carried out to study QRD structure and ones composited with perforated-panels which had1 mm-thickness and perforated percentage of 3%, 5%, 8% respectively. The polar coordinate diagrams of different structure were analyzed to derive the diffusion coefficients. Results showed that the composite structure still had good diffusion performance in the frequency range from100 Hz to 800 Hz. The reflection sound energy of composite structure reduced obviously in the perforated panel resonance frequency range where there was about 2 dB reduction averagely.The study result can provide the reference for the design and development of diifsorber.展开更多
Perforated structures are widely employed in MEMS devices for dissipation control,energy absorption,and performance optimization.Among these,the damping weakening effect is particularly intriguing,attracting considera...Perforated structures are widely employed in MEMS devices for dissipation control,energy absorption,and performance optimization.Among these,the damping weakening effect is particularly intriguing,attracting considerable attention and widespread application.Evaluating the impact of perforations on damping is crucial for enhancing the performance of MEMS devices.This paper investigates the damping tuning mechanisms of perforations and presents two theoretical models for accurately predicting viscous damping.The two models exhibit unique advantages under high and low perforation ratios,respectively.Both models account for complex boundary conditions and various hole geometries,including cylindrical,conical,prismatic,and trapezoidal holes.Modeling and simulations demonstrate the complementarity of the two models,enabling accurate viscous damping predictions across nearly all perforation ratios.Subsequently,the theoretical models are validated through a series of vibration tests on perforated oscillators,with errors consistently controlled within 10%.Experimental results demonstrate that perforations can easily achieve a damping reduction of more than one order of magnitude.Moreover,compared to normal cylindrical holes,trapezoidal holes are found to achieve superior damping reduction with a smaller sacrifice in surface area,which holds great potential for capacitive,acoustic,and optical MEMS devices.This work lays the foundation for viscous damping design and optimization of MEMS device dynamics,creating new applications.展开更多
基金support from the National Natural Science Foundation of China(No.12472072)the Fundamental Research Funds for the Central Universities,China.
文摘In this research,we introduce an innovative approach that combines the Continuum Damage Mechanics-Finite Element Method(CDM-FEM)with the Particle Swarm Optimization(PSO)-based technique,to predict the Medium-Low-Cycle Fatigue(MLCF)life of perforated structures.First,fatigue tests are carried out on three center-perforated structures,aiming to assess their fatigue life under various strengthening conditions.These tests reveal significant variations in fatigue life,accompanied by an examination of crack initiation through the analysis of fatigue fracture surfaces.Second,an innovative fatigue life prediction methodology is applied to perforated structures,which not only forecasts the initiation of fatigue cracks but also traces the progression of damage within these structures.It leverages an elastoplastic constitutive model integrated with damage and a damage evolution model under cyclic loads.The accuracy of this approach is validated by comparison with test results,falling within the three times error band.Finally,we explore the impact of various strengthening techniques,including cross-sectional reinforcement and cold expansion,on the fatigue life and damage evolution of these structures.This is achieved through an in-depth comparative analysis of both experimental data and computational predictions,which provides valuable insights into the behavior of perforated structures under fatigue conditions in practical applications.
基金The project partially supported by the Hong Kong Research Grant Council (DAG03/04.EG39, DAG04/05.EG32)
文摘A time-domain method, based on linear velocity potential theory, is presented to study the interaction between narrow-banded random waves and perforated structures. A simple relation is derived to estimate the jet length of flows through the perforated wall. The reflection coefficient of narrow banded random waves from perforated structures is calculated by assuming a Rayleigh distribution of the heights of incident random waves. For reflection of narrow-banded waves from a single-chamber perforated breakwater, a comparison of the predicted and measured reflection coefficients shows that the method presented in this paper can provide a prediction better than that of regular waves. Numerical results are also reported on the reflection of narrow-banded waves from multi-chamber perforated breakwaters.
文摘Porous structures are highly preferred for bone regeneration and high tissue in-growth.In present work,electrical discharge drilling(EDD),a thermal erosion process was used to produce through holes in Mg-alloys to fabricate perforated structure similar to open cell porous structure in extruded AZ31.Apatite formation and weight loss study was conducted for 7 days,14 days and 21 days after immersion tests in SBF solution.The perforated structure in AZ31 with 26 through micro-holes provides 72%increase in surface area but with marginally 4%higher weight loss as compare to non-perforated structure.Comparing perforated and non-perforated samples of Mg-alloy,it was well observed that perforated structure forms high volume of apatite as compared to non-perforated structure.Scanning electron microscopic(SEM)study revealed that in perforated structure,drilled holes retain their circularity after 21 days of immersion test and distinct corrosion phenomenon occur at localized sites.
基金supported by the National Natural Science Foundation of China(11004133)open project of China communication and transportation industry key laboratory of environmental technology
文摘Acoustic structure study always is the academic research interest. Diffusion ab？sorbing structure（DiflFsorber） has good research value because it has both diflFusion property and sound absorption property. Quadratic residue diffusers（QRD） structure which had good diffusion property was combined with the perforated panel which had good sound absorption property in this study. According to standard AES-4id-2001, the diffusion experiments were carried out to study QRD structure and ones composited with perforated-panels which had1 mm-thickness and perforated percentage of 3%, 5%, 8% respectively. The polar coordinate diagrams of different structure were analyzed to derive the diffusion coefficients. Results showed that the composite structure still had good diffusion performance in the frequency range from100 Hz to 800 Hz. The reflection sound energy of composite structure reduced obviously in the perforated panel resonance frequency range where there was about 2 dB reduction averagely.The study result can provide the reference for the design and development of diifsorber.
基金supported by National Natural Science Foundation of China(62004166)Natural Science Foundation of Ningbo(202003N4062)+1 种基金Natural Science Foundation of Zhejiang Province(LY23F040002)Aeronautical Science Foundation of China(20230008053003).
文摘Perforated structures are widely employed in MEMS devices for dissipation control,energy absorption,and performance optimization.Among these,the damping weakening effect is particularly intriguing,attracting considerable attention and widespread application.Evaluating the impact of perforations on damping is crucial for enhancing the performance of MEMS devices.This paper investigates the damping tuning mechanisms of perforations and presents two theoretical models for accurately predicting viscous damping.The two models exhibit unique advantages under high and low perforation ratios,respectively.Both models account for complex boundary conditions and various hole geometries,including cylindrical,conical,prismatic,and trapezoidal holes.Modeling and simulations demonstrate the complementarity of the two models,enabling accurate viscous damping predictions across nearly all perforation ratios.Subsequently,the theoretical models are validated through a series of vibration tests on perforated oscillators,with errors consistently controlled within 10%.Experimental results demonstrate that perforations can easily achieve a damping reduction of more than one order of magnitude.Moreover,compared to normal cylindrical holes,trapezoidal holes are found to achieve superior damping reduction with a smaller sacrifice in surface area,which holds great potential for capacitive,acoustic,and optical MEMS devices.This work lays the foundation for viscous damping design and optimization of MEMS device dynamics,creating new applications.
