Graphene materials have excellent optical and electrical properties,and in recent years,significant achievements have been made in the chemical improvement and preparation of graphene.This article analyzes the progres...Graphene materials have excellent optical and electrical properties,and in recent years,significant achievements have been made in the chemical improvement and preparation of graphene.This article analyzes the progress in the chemical preparation,chemical modification,surface chemistry,and catalysis of graphene,in order to provide reference for relevant personnel.展开更多
Progressive collapse of building structures under blast and impact loads has attracted great attention all over the world. Progressive collapse analysis is essential for an economic and safe design of building structu...Progressive collapse of building structures under blast and impact loads has attracted great attention all over the world. Progressive collapse analysis is essential for an economic and safe design of building structures against progressive collapse to blast and impact loads. Because of the catastrophic nature of progressive collapse and the potentially high cost of constructing or retrofitting buildings to resist it, it is imperative that the progressive collapse analysis methods be reliable. For engineers, their methodology to carry out progressive collapse evaluation need not only be accurate and concise, but also be easily used and works fast. Thus, many researchers have been spending lots of effort in developing reliable, efficient and straightforward progressive collapse analysis methods recently. In the present paper, current progressive collapse analysis methods available in the literature are reviewed. Their suitability, applicability and reliability are discussed. Our recent proposed new method for progressive collapse analysis of reinforced concrete frames under blast loads is also introduced.展开更多
Based on parameter design language, a program of progressive failure analysis in composite structures is proposed. In this program, the relationship between macro- and micro-mechanics is established and the macro stre...Based on parameter design language, a program of progressive failure analysis in composite structures is proposed. In this program, the relationship between macro- and micro-mechanics is established and the macro stress distribution of the composite structure is calculated by commercial finite element software. According to the macro-stress, the damaged point is found and the micro-stress distribution of representative volume element is calculated by finite-volume direct averaging micromechanics(FVDAM). Compared with the results calculated by failure criterion based on macro-stress field(the maximum stress criteria and Hashin criteria) and micro-stress field(Huang model), it is proven that the failure analysis based on macro- and micro-mechanics model is feasible and efficient.展开更多
Nowadays,with the increasing operational life of ships,the aging effects on their structural behavior need to be investigated precisely.With the corrosive marine environment taken into consideration,one of the importa...Nowadays,with the increasing operational life of ships,the aging effects on their structural behavior need to be investigated precisely.With the corrosive marine environment taken into consideration,one of the important effects of aging that must be studied is thickness degradation.In this paper,with the use of previously proposed equivalent thickness formulations for corroded plates,the progressive collapse analysis software HULLST is enhanced,and then,the effects of different corrosion models of uniform,random,pitting,and tanker pattern types on the ultimate and residual strengths of a floating production,storage,and offloading vessel hull girder are evaluated for the ages of 0 to 25 years.Results reveal that the uniform corrosion and random corrosion models have close outcomes.The value of relative reduction in the ultimate strength of ship hull girder(compared with the intact condition)ranges roughly from 6%for the age of 5 years to 17%for the age of 25 years in the hogging mode.The relative reduction in the ultimate strength ranges from 4%to 16%in the sagging mode.Pitting corrosion and tanker pattern(random)corrosion models lead to higher relative reductions in ultimate strength.The pitting corrosion model leads to a 16%–32%relative reduction in the ultimate strength for the ages of 5–25 years of the ship in either hogging or sagging.The tanker pattern(random)corrosion model leads to a 6%–37%relative reduction in the ultimate strength in the hogging mode and 3%–31%in the sagging mode at ship ages of 5 to 25 years.展开更多
With the considerable applications of ceramic matrix composites(CMC) in aircraft engineering, the design of CMC bolted joint gains paramount attention because of its capacity to to improve load-bearing efficiency of a...With the considerable applications of ceramic matrix composites(CMC) in aircraft engineering, the design of CMC bolted joint gains paramount attention because of its capacity to to improve load-bearing efficiency of aircraft key structure. In this work, a 3 D finite element model was established to predict tensile performance and failure modes of single-lap, single-bolt 2 D C/SiC composite, and superalloy joint, which considers the progressive damage behavior of 2 D woven C/SiC composites. On the basis of the developed progressive damage model, a parametric study was carried out to illustrate the effects of bolt preload and bolt-hole clearance on mechanical behaviors of the hybrid bolted joint. It was found that the increase in the value of bolt preload made the failure load grow first and then drop, and the optimum value of bolt preload 5.00 kN generated 56.47% rise in the initial failure load and 22.83% rise in the final failure load for the bolted joint in comparison with zero preload case. As the clearance increased from 0 to 2.00%, the initial and final failure loads respectively declined by 45.88% and 24.02% for 2.00% bolt-hole clearance relative to the neat-fit case. The loss in failure loads can be reduced to compressive stress concentration around the fastening hole-edge area, leading to the appearance of earlier damages by the introduction of increasing bolt hole clearance.展开更多
Unsupervised and supervised pattern recognition( PR)techniques are used to classify the acoustic emission( AE) data originating from the quasi-isotropic self-reinforced polyethylene composites,in order to identify the...Unsupervised and supervised pattern recognition( PR)techniques are used to classify the acoustic emission( AE) data originating from the quasi-isotropic self-reinforced polyethylene composites,in order to identify the various mechanisms in the multiangle-ply thermoplastic composites. Ultra-high molecular weight polyethylene / low density polyethylene( UHMWPE / LDPE)composites were made and tested under quasi-static tensile load. The failure process was monitored by the AE technique. The collected AE signals were classified by unsupervised and supervised PR techniques, respectively. AE signals were clustered with unsupervised PR scheme automatically and mathematically. While in the supervised PR scheme,the labeled AE data from simple lay-up UHMWPE / LDPE laminates were utilized as the reference data.Comparison was drawn according to the analytical results. Fracture surfaces of the UHMWPE / LDPE specimens were observed by a scanning electron microscope( SEM) for some physical support. By combining both classification results with the observation results,correlations were established between the AE signal classes and their originating damage modes. The comparison between the two classifying schemes showed a good agreement in the main damage modes and their failure process. It indicates both PR techniques are powerful for the complicated thermoplastic composites. Supervised PR scheme can lead to a more precise classification in that a suitable reference data set is input.展开更多
[Objective] One mesoscale system of rainstorm in the warm zone in Nansha area during June 8 and 9 in 2009 was studied.[Method] By dint of routine meteorological observation data,NCEP reanalysis data,FY-2C TBB,and wind...[Objective] One mesoscale system of rainstorm in the warm zone in Nansha area during June 8 and 9 in 2009 was studied.[Method] By dint of routine meteorological observation data,NCEP reanalysis data,FY-2C TBB,and wind line data,etc.,the circulation situation,physics field,and the activity of convection system of mesoscale of one rainstorm in the warm zone of Nansha during June 8 and 9 in 2009 were expounded so as to explore the causes of such rainstorm.[Result] The rainstorm had distinct convection nature,with large precipitation intensity,uneven distribution,and short timeliness.Most precipitation fell in 5 hours.And the rainstorm in the warm zone was directly related to the activity of meso-convective system and was resulted from moderate β scale convection system(Mβcss).The flux field of the high layer of convection layer had fine absorption effect.Coordinating with the southwest and south field at middle and low 500 and 850 hPa in the middle and lower layer to converge around the Zhujiang Delta,it provided unstable condition and humidity for the rainstorm in Nansha area.The advantageous combination of flux in convective layer,vortex and vertical speed field and the sufficient water supply provided dynamic and water vapor guarantee for the generation of rainstorm in the Nansha area.The vertical speed of <-0.3 m/s reflected the beginning of precipitation and the smaller the vertical speed was,the stronger the precipitation intensity became.[Conclusion] It provided reference for the report of rainstorm of such kind in the future.展开更多
This study addresses the effectiveness of a simple stiffness tailoring concept to delay damage initiation, control damage progression, and improve residual strength in tensile-loaded composite plates with a central ci...This study addresses the effectiveness of a simple stiffness tailoring concept to delay damage initiation, control damage progression, and improve residual strength in tensile-loaded composite plates with a central circular cutout. The tailoring concept is to simply reposit all axially oriented (0°) material into regions near the edge of the plate away from the cutout. This tailoring is done in a way so as not to affect the weight of the plate. This accomplishes several beneficial changes in the way that the plate resists loading with no increases in material cost or weight. Lowering the axial stiffness of the laminate surrounding the cutout lowers the stress concentration. Increasing the axial stiffness near edges of the plate attracts loading away from the vicinity of the cutout to further lower stresses in the critical cutout region. This study focuses on in-plane response including damage progression and residual strength as a function of the degree of tailoring and cutout size. Strength and stiffness properties typical of IM7/8551-7 preperg material were assumed and a modified version of the Hashin failure criteria was used to identify the local damage. Results show that tailoring can significantly increase the damage initiation load and the residual strength. In some cases, observed evidence shows that tailoring performs as a damage arrest mechanism.展开更多
Reinforced concrete(RC) load bearing wall is widely used in high-rise and mid-rise buildings. Due to the number of walls in plan and reduction in lateral force portion, this system is not only stronger against earthqu...Reinforced concrete(RC) load bearing wall is widely used in high-rise and mid-rise buildings. Due to the number of walls in plan and reduction in lateral force portion, this system is not only stronger against earthquakes, but also more economical. The effect of progressive collapse caused by removal of load bearing elements, in various positions in plan and stories of the RC load bearing wall system was evaluated by nonlinear dynamic and static analyses. For this purpose, three-dimensional model of 10-story structure was selected. The analysis results indicated stability, strength and stiffness of the RC load-bearing wall system against progressive collapse. It was observed that the most critical condition for removal of load bearing walls was the instantaneous removal of the surrounding walls located at the corners of the building where the sections of the load bearing elements were changed. In this case, the maximum vertical displacement was limited to 6.3 mm and the structure failed after applying the load of 10 times the axial load bored by removed elements. Comparison between the results of the nonlinear dynamic and static analyses demonstrated that the "load factor" parameter was a reasonable criterion to evaluate the progressive collapse potential of the structure.展开更多
The vulnerability of reinforced concrete(RC)building systems to progressive collapse has turned out to be a challenging trouble for professional structural engineers so as to prevent total failure on account of ...The vulnerability of reinforced concrete(RC)building systems to progressive collapse has turned out to be a challenging trouble for professional structural engineers so as to prevent total failure on account of nearby damage.The goal of this paper is to enhance the knowledge of such buildings’behavior underneath several scenarios of misplaced columns at different floor stages,and their capacity for progressive collapse.The homes had been analyzed following the guidelines for progressive collapse evaluation and design organized by means of the general services administration guidelines(GSA).The progressive collapse of a ten story structure subjected to a simplest gravity load is taken into consideration and the column has been eliminated at one place and the spread damage is evaluated.The progressive collapse study has been carried out by way of removing the column at a diagnosed crucial locations(at corner,middle and at interior)as in line with GSA guidelines.Static analysis is done using analysis program ETABS.For each case,the consequences were taken in terms of demand capacity ratio(DCR)at critical section,and as a result the structure has been assessed for it’s susceptible to progressive collapse.The availability of shear wall is made on the component wherein collapse occurred and DCR values are mentioned.After imparting the shear wall to the structure,the progressive collapse of the structure because of accidental load may be controlled in order that the GSA guidelines recommended DCR value would be within the range.展开更多
Given the difficulty in accurately evaluating the fatigue performance of large composite wind turbine blades(referred to as blades),this paper takes the main beam structure of the blade with a rectangular cross-sectio...Given the difficulty in accurately evaluating the fatigue performance of large composite wind turbine blades(referred to as blades),this paper takes the main beam structure of the blade with a rectangular cross-sectionas the simulation object and establishes a composite laminate rectangular beam structure that simultaneouslyincludes the flange,web,and adhesive layer,referred to as the blade main beam sub-structure specimen,throughthe definition of blade sub-structures.This paper examines the progressive damage evolution law of the compositelaminate rectangular beam utilizing an improved 3D Hashin failure criterion,cohesive zone model,B-K failurecriterion,and computer simulation technology.Under static loading,the layup angle of the anti-shear web hasa close relationship with the static load-carrying capacity of the composite laminate rectangular beam;under fatigueloading,the fatigue damage will first occur in the lower flange adhesive area of the whole composite laminaterectangular beam and ultimately result in the fracture failure of the entire structure.These results provide a theoreticalreference and foundation for evaluating and predicting the fatigue performance of the blade main beamstructure and even the full-size blade.展开更多
Based on the strength reduction method and strain-softening model,a method for progressive failure analysis of strain-softening slopes was presented in this paper.The mutation is more pronounced in strain-softening an...Based on the strength reduction method and strain-softening model,a method for progressive failure analysis of strain-softening slopes was presented in this paper.The mutation is more pronounced in strain-softening analysis,and the mutation of displacement at slope crest was taken as critical failure criterion.An engineering example was provided to demonstrate the validity of the present method.This method was applied to a cut slope in an industry site.The results are as follows:(1) The factor of safety and the critical slip surface obtained by the present method are between those by peak and residual strength.The analysis with peak strength would lead to non-conservative results,but that with residual strength tends to be overly conservative.(2) The thickness of the shear zone considering strain-softening behaviour is narrower than that with non-softening analysis.(3) The failure of slope is the process of the initiation,propagation and connection of potential failure surface.The strength parameters are mobilized to a non-uniform degree while progressive failure occurs in the slope.(4) The factor of safety increases with the increase of residual shear strain threshold and elastic modulus.The failure mode of slope changes from shallow slip to deep slip.Poisson's ratio and dilation angle have little effect on the results.展开更多
Ceramic matrix composite(CMC)and superalloy bolted joints are commonly used high temperature connection structures in aerospace and aeronautical fields.In this paper,a finite element model coupled with progressive dam...Ceramic matrix composite(CMC)and superalloy bolted joints are commonly used high temperature connection structures in aerospace and aeronautical fields.In this paper,a finite element model coupled with progressive damage analysis of 2D C/SiC composites and superalloy bolted joint was implemented to simulate the uniaxial tensile loading process by using the ABAQUS finite element software.The parametric effects of raised head bolt on stress distribution,tensile performance,and damage process were studied for the CMC⁃superalloy bolted joint structures.The results showed that the final failure load increased first to the maximum value,and then decreased with the rise of bolt diameter,bolt head diameter,and bolt head thickness,respectively.When the three parameters were 5.0 mm,9.5 mm,and 2.8 mm for the current studied bolt configuration,the joint structure gave the maximum load bearing capacity for the considered parameter ranges.It was also found that around 42%potential improvement in load bearing capacity could be achieved by very small adjustments in bolt parameters of the joints.展开更多
On account of the background of China's "new normal" characterized by slower economic growth, this paper analyses the low-carbon economy status quo in the Beijing-Tianjin-Hebei region and empirically inv...On account of the background of China's "new normal" characterized by slower economic growth, this paper analyses the low-carbon economy status quo in the Beijing-Tianjin-Hebei region and empirically investigates the relationship between carbon dioxide(CO_2) emissions and its various factors for China's Beijing-Tianjin-Hebei region using panel data econometric technique. We find evidence of existence of Environmental Kuznets Curve. Results also show that economic scale, industrial structure, and urbanization rate are crucial factors to promote CO_2emissions. However, technological progress, especially the domestic independent research and development, plays a key role in C0_2 emissions abatement. Next, we further analyze the correlation between each subregion and various factors according to Grey Relation Analysis. Thereby,our findings provide important implications for policymakers in air pollution control and C0_2 emissions reduction for this region.展开更多
In this study, single and interactive effect of three parameters, pH, ferrous and pulp concentration has been investigated by a 2^3 full factorial CCRD (central composite rotatable design) composed of eight factoria...In this study, single and interactive effect of three parameters, pH, ferrous and pulp concentration has been investigated by a 2^3 full factorial CCRD (central composite rotatable design) composed of eight factorial points, six central and six axial points. Initially, "none" mode from transformation subsection was chosen as the default choice for both responses, i.e. %recovery and gram of recovered zinc. Box-Cox plots give the best Lambda for each response (y^Lambda= f (A, B, C .....)) which occur at 1.91 and 2.16 for %recovey and gram of recovered zinc, respectively. A linear (y^1.91 = f (linear)) and a quadratic (y^2. 16= f (quadratic)) equation were suggested by software as the model for %recovery and gram of recovered zinc, respectively. Analysis of variance (ANOVA) for both models shows a high coefficient of determination (R^2). In order to optimize and find the best conditions under which three parameters occur appropriately, optimization was done numerically. Desirability plots indicate properly that the best conditions occur at pH = 1.46, ferrous = 6.67 g/L, %pulp = 7.1 (%w/v), %recovery = 86.5, gram of recovered zinc = 0.63 g and desirability = 0.777. Finally, PRP (progressive route of the process) analysis donates us a proper insight of what is happening during these 30 days. PRP analysis categorizes flasks in two parts, 1- flasks worth economically, 2- flasks with one-time-usable feed materials.展开更多
Altogether 27716 cystic hydatid cases and 445 alveolar hydatid cases slinically diagnosed and surgically treated in China were retrospectively studied.
文摘Graphene materials have excellent optical and electrical properties,and in recent years,significant achievements have been made in the chemical improvement and preparation of graphene.This article analyzes the progress in the chemical preparation,chemical modification,surface chemistry,and catalysis of graphene,in order to provide reference for relevant personnel.
基金Supported by National Natural Science Foundation of China(No.50638030and No.50528808)National Key Technologies R&D Program of China(No.2006BAJ13B02)
文摘Progressive collapse of building structures under blast and impact loads has attracted great attention all over the world. Progressive collapse analysis is essential for an economic and safe design of building structures against progressive collapse to blast and impact loads. Because of the catastrophic nature of progressive collapse and the potentially high cost of constructing or retrofitting buildings to resist it, it is imperative that the progressive collapse analysis methods be reliable. For engineers, their methodology to carry out progressive collapse evaluation need not only be accurate and concise, but also be easily used and works fast. Thus, many researchers have been spending lots of effort in developing reliable, efficient and straightforward progressive collapse analysis methods recently. In the present paper, current progressive collapse analysis methods available in the literature are reviewed. Their suitability, applicability and reliability are discussed. Our recent proposed new method for progressive collapse analysis of reinforced concrete frames under blast loads is also introduced.
基金Project(51075204)supported by the National Natural Science Foundation of ChinaProjects(2012ZB52026,2014ZB52024)supported by the Aeronautical Science Foundation of ChinaProject(NS2014024)supported by the Fundamental Research Funds for the Central Universities,China
文摘Based on parameter design language, a program of progressive failure analysis in composite structures is proposed. In this program, the relationship between macro- and micro-mechanics is established and the macro stress distribution of the composite structure is calculated by commercial finite element software. According to the macro-stress, the damaged point is found and the micro-stress distribution of representative volume element is calculated by finite-volume direct averaging micromechanics(FVDAM). Compared with the results calculated by failure criterion based on macro-stress field(the maximum stress criteria and Hashin criteria) and micro-stress field(Huang model), it is proven that the failure analysis based on macro- and micro-mechanics model is feasible and efficient.
文摘Nowadays,with the increasing operational life of ships,the aging effects on their structural behavior need to be investigated precisely.With the corrosive marine environment taken into consideration,one of the important effects of aging that must be studied is thickness degradation.In this paper,with the use of previously proposed equivalent thickness formulations for corroded plates,the progressive collapse analysis software HULLST is enhanced,and then,the effects of different corrosion models of uniform,random,pitting,and tanker pattern types on the ultimate and residual strengths of a floating production,storage,and offloading vessel hull girder are evaluated for the ages of 0 to 25 years.Results reveal that the uniform corrosion and random corrosion models have close outcomes.The value of relative reduction in the ultimate strength of ship hull girder(compared with the intact condition)ranges roughly from 6%for the age of 5 years to 17%for the age of 25 years in the hogging mode.The relative reduction in the ultimate strength ranges from 4%to 16%in the sagging mode.Pitting corrosion and tanker pattern(random)corrosion models lead to higher relative reductions in ultimate strength.The pitting corrosion model leads to a 16%–32%relative reduction in the ultimate strength for the ages of 5–25 years of the ship in either hogging or sagging.The tanker pattern(random)corrosion model leads to a 6%–37%relative reduction in the ultimate strength in the hogging mode and 3%–31%in the sagging mode at ship ages of 5 to 25 years.
基金Sponsored by the Pre-Research Foundation of Shenyang Aircraft Design and Research Institute,the Aviation Industry Corporation of China(Grant No.JH20128255)the National Defence Basic Research Program(Grant No.JZ20180032)the Pre-Research Foundation of Equipment Development Department of People’s Republic of China Central Military Commission(Grant No.ZJJSN20200001)。
文摘With the considerable applications of ceramic matrix composites(CMC) in aircraft engineering, the design of CMC bolted joint gains paramount attention because of its capacity to to improve load-bearing efficiency of aircraft key structure. In this work, a 3 D finite element model was established to predict tensile performance and failure modes of single-lap, single-bolt 2 D C/SiC composite, and superalloy joint, which considers the progressive damage behavior of 2 D woven C/SiC composites. On the basis of the developed progressive damage model, a parametric study was carried out to illustrate the effects of bolt preload and bolt-hole clearance on mechanical behaviors of the hybrid bolted joint. It was found that the increase in the value of bolt preload made the failure load grow first and then drop, and the optimum value of bolt preload 5.00 kN generated 56.47% rise in the initial failure load and 22.83% rise in the final failure load for the bolted joint in comparison with zero preload case. As the clearance increased from 0 to 2.00%, the initial and final failure loads respectively declined by 45.88% and 24.02% for 2.00% bolt-hole clearance relative to the neat-fit case. The loss in failure loads can be reduced to compressive stress concentration around the fastening hole-edge area, leading to the appearance of earlier damages by the introduction of increasing bolt hole clearance.
基金Scientific Research Foundation of Guangdong Polytechnic,China(No.K2010201)
文摘Unsupervised and supervised pattern recognition( PR)techniques are used to classify the acoustic emission( AE) data originating from the quasi-isotropic self-reinforced polyethylene composites,in order to identify the various mechanisms in the multiangle-ply thermoplastic composites. Ultra-high molecular weight polyethylene / low density polyethylene( UHMWPE / LDPE)composites were made and tested under quasi-static tensile load. The failure process was monitored by the AE technique. The collected AE signals were classified by unsupervised and supervised PR techniques, respectively. AE signals were clustered with unsupervised PR scheme automatically and mathematically. While in the supervised PR scheme,the labeled AE data from simple lay-up UHMWPE / LDPE laminates were utilized as the reference data.Comparison was drawn according to the analytical results. Fracture surfaces of the UHMWPE / LDPE specimens were observed by a scanning electron microscope( SEM) for some physical support. By combining both classification results with the observation results,correlations were established between the AE signal classes and their originating damage modes. The comparison between the two classifying schemes showed a good agreement in the main damage modes and their failure process. It indicates both PR techniques are powerful for the complicated thermoplastic composites. Supervised PR scheme can lead to a more precise classification in that a suitable reference data set is input.
文摘[Objective] One mesoscale system of rainstorm in the warm zone in Nansha area during June 8 and 9 in 2009 was studied.[Method] By dint of routine meteorological observation data,NCEP reanalysis data,FY-2C TBB,and wind line data,etc.,the circulation situation,physics field,and the activity of convection system of mesoscale of one rainstorm in the warm zone of Nansha during June 8 and 9 in 2009 were expounded so as to explore the causes of such rainstorm.[Result] The rainstorm had distinct convection nature,with large precipitation intensity,uneven distribution,and short timeliness.Most precipitation fell in 5 hours.And the rainstorm in the warm zone was directly related to the activity of meso-convective system and was resulted from moderate β scale convection system(Mβcss).The flux field of the high layer of convection layer had fine absorption effect.Coordinating with the southwest and south field at middle and low 500 and 850 hPa in the middle and lower layer to converge around the Zhujiang Delta,it provided unstable condition and humidity for the rainstorm in Nansha area.The advantageous combination of flux in convective layer,vortex and vertical speed field and the sufficient water supply provided dynamic and water vapor guarantee for the generation of rainstorm in the Nansha area.The vertical speed of <-0.3 m/s reflected the beginning of precipitation and the smaller the vertical speed was,the stronger the precipitation intensity became.[Conclusion] It provided reference for the report of rainstorm of such kind in the future.
基金NASA,the State of South Carolina,and Clemson University through the EPSCoR grant 'Development and Enhancement of Research Capability for Aircraft Structures and Materials'.
文摘This study addresses the effectiveness of a simple stiffness tailoring concept to delay damage initiation, control damage progression, and improve residual strength in tensile-loaded composite plates with a central circular cutout. The tailoring concept is to simply reposit all axially oriented (0°) material into regions near the edge of the plate away from the cutout. This tailoring is done in a way so as not to affect the weight of the plate. This accomplishes several beneficial changes in the way that the plate resists loading with no increases in material cost or weight. Lowering the axial stiffness of the laminate surrounding the cutout lowers the stress concentration. Increasing the axial stiffness near edges of the plate attracts loading away from the vicinity of the cutout to further lower stresses in the critical cutout region. This study focuses on in-plane response including damage progression and residual strength as a function of the degree of tailoring and cutout size. Strength and stiffness properties typical of IM7/8551-7 preperg material were assumed and a modified version of the Hashin failure criteria was used to identify the local damage. Results show that tailoring can significantly increase the damage initiation load and the residual strength. In some cases, observed evidence shows that tailoring performs as a damage arrest mechanism.
文摘Reinforced concrete(RC) load bearing wall is widely used in high-rise and mid-rise buildings. Due to the number of walls in plan and reduction in lateral force portion, this system is not only stronger against earthquakes, but also more economical. The effect of progressive collapse caused by removal of load bearing elements, in various positions in plan and stories of the RC load bearing wall system was evaluated by nonlinear dynamic and static analyses. For this purpose, three-dimensional model of 10-story structure was selected. The analysis results indicated stability, strength and stiffness of the RC load-bearing wall system against progressive collapse. It was observed that the most critical condition for removal of load bearing walls was the instantaneous removal of the surrounding walls located at the corners of the building where the sections of the load bearing elements were changed. In this case, the maximum vertical displacement was limited to 6.3 mm and the structure failed after applying the load of 10 times the axial load bored by removed elements. Comparison between the results of the nonlinear dynamic and static analyses demonstrated that the "load factor" parameter was a reasonable criterion to evaluate the progressive collapse potential of the structure.
文摘The vulnerability of reinforced concrete(RC)building systems to progressive collapse has turned out to be a challenging trouble for professional structural engineers so as to prevent total failure on account of nearby damage.The goal of this paper is to enhance the knowledge of such buildings’behavior underneath several scenarios of misplaced columns at different floor stages,and their capacity for progressive collapse.The homes had been analyzed following the guidelines for progressive collapse evaluation and design organized by means of the general services administration guidelines(GSA).The progressive collapse of a ten story structure subjected to a simplest gravity load is taken into consideration and the column has been eliminated at one place and the spread damage is evaluated.The progressive collapse study has been carried out by way of removing the column at a diagnosed crucial locations(at corner,middle and at interior)as in line with GSA guidelines.Static analysis is done using analysis program ETABS.For each case,the consequences were taken in terms of demand capacity ratio(DCR)at critical section,and as a result the structure has been assessed for it’s susceptible to progressive collapse.The availability of shear wall is made on the component wherein collapse occurred and DCR values are mentioned.After imparting the shear wall to the structure,the progressive collapse of the structure because of accidental load may be controlled in order that the GSA guidelines recommended DCR value would be within the range.
基金the Science and Technology Programs of Gansu Province(Grant Nos.21JR1RA248,23YFGA0050)the Young Scholars Science Foundation of Lanzhou Jiaotong University(Grant Nos.2020039,2020017)+2 种基金the Special Funds for Guiding Local Scientific and Technological Development by the Central Government(Grant No.22ZY1QA005)the National Natural Science Foundation of China(Grant No.72361019)the Gansu Provincial Outstanding Graduate Students Innovation Star Program(Grant No.2023CXZX-574).
文摘Given the difficulty in accurately evaluating the fatigue performance of large composite wind turbine blades(referred to as blades),this paper takes the main beam structure of the blade with a rectangular cross-sectionas the simulation object and establishes a composite laminate rectangular beam structure that simultaneouslyincludes the flange,web,and adhesive layer,referred to as the blade main beam sub-structure specimen,throughthe definition of blade sub-structures.This paper examines the progressive damage evolution law of the compositelaminate rectangular beam utilizing an improved 3D Hashin failure criterion,cohesive zone model,B-K failurecriterion,and computer simulation technology.Under static loading,the layup angle of the anti-shear web hasa close relationship with the static load-carrying capacity of the composite laminate rectangular beam;under fatigueloading,the fatigue damage will first occur in the lower flange adhesive area of the whole composite laminaterectangular beam and ultimately result in the fracture failure of the entire structure.These results provide a theoreticalreference and foundation for evaluating and predicting the fatigue performance of the blade main beamstructure and even the full-size blade.
基金Project supported by the National Natural Science Foundation of China (No. 10972238)the Scholarship Award for Excellent Doctoral Student Granted by Ministry of Educationthe Transportation Science and Technology Projects of Hunan Province (No. 201003),China
文摘Based on the strength reduction method and strain-softening model,a method for progressive failure analysis of strain-softening slopes was presented in this paper.The mutation is more pronounced in strain-softening analysis,and the mutation of displacement at slope crest was taken as critical failure criterion.An engineering example was provided to demonstrate the validity of the present method.This method was applied to a cut slope in an industry site.The results are as follows:(1) The factor of safety and the critical slip surface obtained by the present method are between those by peak and residual strength.The analysis with peak strength would lead to non-conservative results,but that with residual strength tends to be overly conservative.(2) The thickness of the shear zone considering strain-softening behaviour is narrower than that with non-softening analysis.(3) The failure of slope is the process of the initiation,propagation and connection of potential failure surface.The strength parameters are mobilized to a non-uniform degree while progressive failure occurs in the slope.(4) The factor of safety increases with the increase of residual shear strain threshold and elastic modulus.The failure mode of slope changes from shallow slip to deep slip.Poisson's ratio and dilation angle have little effect on the results.
基金Sponsored by the Pre⁃Research Foundation of Shenyang Aircraft Design and Research Institute,Aviation Industry Corporation of China(Grant No.JH20128255).
文摘Ceramic matrix composite(CMC)and superalloy bolted joints are commonly used high temperature connection structures in aerospace and aeronautical fields.In this paper,a finite element model coupled with progressive damage analysis of 2D C/SiC composites and superalloy bolted joint was implemented to simulate the uniaxial tensile loading process by using the ABAQUS finite element software.The parametric effects of raised head bolt on stress distribution,tensile performance,and damage process were studied for the CMC⁃superalloy bolted joint structures.The results showed that the final failure load increased first to the maximum value,and then decreased with the rise of bolt diameter,bolt head diameter,and bolt head thickness,respectively.When the three parameters were 5.0 mm,9.5 mm,and 2.8 mm for the current studied bolt configuration,the joint structure gave the maximum load bearing capacity for the considered parameter ranges.It was also found that around 42%potential improvement in load bearing capacity could be achieved by very small adjustments in bolt parameters of the joints.
基金supported by National Social Science Foundation Project of China-A study on the Long-term Mechanism and Policy of Promoting the Construction of Ecological Civilization with Green Technological Innovation in China:[Grant Number 14AJL017]
文摘On account of the background of China's "new normal" characterized by slower economic growth, this paper analyses the low-carbon economy status quo in the Beijing-Tianjin-Hebei region and empirically investigates the relationship between carbon dioxide(CO_2) emissions and its various factors for China's Beijing-Tianjin-Hebei region using panel data econometric technique. We find evidence of existence of Environmental Kuznets Curve. Results also show that economic scale, industrial structure, and urbanization rate are crucial factors to promote CO_2emissions. However, technological progress, especially the domestic independent research and development, plays a key role in C0_2 emissions abatement. Next, we further analyze the correlation between each subregion and various factors according to Grey Relation Analysis. Thereby,our findings provide important implications for policymakers in air pollution control and C0_2 emissions reduction for this region.
文摘In this study, single and interactive effect of three parameters, pH, ferrous and pulp concentration has been investigated by a 2^3 full factorial CCRD (central composite rotatable design) composed of eight factorial points, six central and six axial points. Initially, "none" mode from transformation subsection was chosen as the default choice for both responses, i.e. %recovery and gram of recovered zinc. Box-Cox plots give the best Lambda for each response (y^Lambda= f (A, B, C .....)) which occur at 1.91 and 2.16 for %recovey and gram of recovered zinc, respectively. A linear (y^1.91 = f (linear)) and a quadratic (y^2. 16= f (quadratic)) equation were suggested by software as the model for %recovery and gram of recovered zinc, respectively. Analysis of variance (ANOVA) for both models shows a high coefficient of determination (R^2). In order to optimize and find the best conditions under which three parameters occur appropriately, optimization was done numerically. Desirability plots indicate properly that the best conditions occur at pH = 1.46, ferrous = 6.67 g/L, %pulp = 7.1 (%w/v), %recovery = 86.5, gram of recovered zinc = 0.63 g and desirability = 0.777. Finally, PRP (progressive route of the process) analysis donates us a proper insight of what is happening during these 30 days. PRP analysis categorizes flasks in two parts, 1- flasks worth economically, 2- flasks with one-time-usable feed materials.
文摘Altogether 27716 cystic hydatid cases and 445 alveolar hydatid cases slinically diagnosed and surgically treated in China were retrospectively studied.