Effects of layer quantities and stacking sequences on L-shape composite manufacturing qualities in using OOA(out-of-autoclave)prepregs were studied.The mechanisms of air evacuated in 5 kinds of lay-ups were revealed b...Effects of layer quantities and stacking sequences on L-shape composite manufacturing qualities in using OOA(out-of-autoclave)prepregs were studied.The mechanisms of air evacuated in 5 kinds of lay-ups were revealed by image analysis of cut surfaces and thickness measurements.Results show that air in OOA prepregs is evacuated in two ways.Most of the air is forced out of layers directly by vacuum before air accesses in prepregs closed.Very little entrapped air moves perpendicularly to outer layers under hydrostatic resin pressure.When a laminate contains less than 16 layers,voids can hardly be found in layers.When a laminate contains more than 16 layers,voids cannot be expelled completely during the window of vertical movement.As for stacking sequences,the synergetic effect of slip function and nest function determines the thickness and voids content of laminates.Results show that the average of single layer thickness of unidirectional layers is the lowest,and the average of single layer thickness of quasi-isotropic layers is the highest.The voids content of quasi isotropic is the highest,which is consistent with the theoretical analysis.展开更多
This study focuses on the insert-injection molding process. The thermoset composite inserts in this study were carbon fiber/epoxy (CF/Epoxy) prepreg sheets. The injected molded part was glass fiber contained phenolic ...This study focuses on the insert-injection molding process. The thermoset composite inserts in this study were carbon fiber/epoxy (CF/Epoxy) prepreg sheets. The injected molded part was glass fiber contained phenolic resin (GF/PF). The CF/Epoxy was placed in the mold cavity prior to injecting GF/PF onto the inserted injection molded CF/Epoxy specimens. The role of adhesion between the inserted part and injected resin on the mechanical properties was evaluated by 3 point bending and impact tests. In addition, the effect of prepreg orientation on the mechanical properties of the prepreg inserted-injection molding system was investigated. It was found that the prepreg with unidirectional orientation significantly improved flexural and impact strength of the inserted injection molding composites, providing better support and resistance to bending and impact loading. The main failure modes of the specimens were structural and adhesive failure.展开更多
A new isothermally based cure kinetic model for the prepreg was presented using an industrially supplied prepreg rather than neat resin.The matrix resin was bismaleimide(BMI)resin,and the reinforcement was carbon fibe...A new isothermally based cure kinetic model for the prepreg was presented using an industrially supplied prepreg rather than neat resin.The matrix resin was bismaleimide(BMI)resin,and the reinforcement was carbon fiber T700-12S.A series of isothermal Differential Scanning Calorimetry(DSC)tests were performed and analyzed by the proposed nth-order reaction model.An increase in the cure rate was observed at the higher temper-ature in both neat and prepreg.After reaching the peak value,the cure rate of resin dropped off faster in prepreg,resulting in a lower average value of the ultimate heat of reaction.The presence of carbon fiber was found to significantly impact the curing behavior of the resin,leading to significant changes from the neat resin kinetic parameters.The carbon fibers imposed restrictions on the molecular mobility of reactive species,reduced the extent of polymeri-zation within the system and did not change the cure mechanism of resin.展开更多
With the growing needs of prepreg tapes for the automated fiber placement(AFP),the deviation-rectifying of prepreg in slitting process was investigated on a self-developed 16-tow prepreg slitting and winding machine.T...With the growing needs of prepreg tapes for the automated fiber placement(AFP),the deviation-rectifying of prepreg in slitting process was investigated on a self-developed 16-tow prepreg slitting and winding machine.The process of slitting and rewinding of prepreg tape was introduced,and the reason of prepreg tape deviation in slitting process was analyzed.In order to ensure the quality of the narrow prepreg slits,the application of the fuzzy PID algorithm in a closed-loop control system was discussed.A fuzzy PID algorithm was designed by combining fuzzy rules and PID controller.By applying it to precise deviation-rectifying control strategy,the automatic control of rectification could be achieved with accuracy of 0.1 mm,which satisfies the requirement of the prepreg tape both in slitting quality and layup quality for AFP.展开更多
Marking arbitrary three-dimensional(3D) target curves on given objects with curved surface is required in many industrial fields, such as fabric prepreg placement in composite material part fabrication, product assemb...Marking arbitrary three-dimensional(3D) target curves on given objects with curved surface is required in many industrial fields, such as fabric prepreg placement in composite material part fabrication, product assembly, surface painting for decoration, etc. A shortcut to the solution of this intractable problem is proposed by utilizing a galvanometric laser scanner(GLS) with the aid of a camera. Without using the existing tedious GLS calibration procedures,the proposed method directly establishes a mapping between the 3D coordinates of the laser spots on the object surface and the control voltages of the scanner. A single-hidden layer feedforward neural network(SLFN) is employed to model the mapping. By projecting a dense grid of laser spots on the object to be marked and simultaneously taking only one image, the SLFN model is trained in minutes via a linear solving mechanism. Experiments demonstrate that the trained SLFN model has a good generalization performance for marking 3D target curves. The 3D laser marking errors on experimental objects are less than 0.5 mm. The proposed method is especially suitable for on-site use and can be conveniently extended to multiple GLSs for marking large complex objects.展开更多
From 1980’s decade,the introduction of carbon composite materials in structural applications has been consistently increased in the successive generations of civil aircraft from Single Aisle to Middle-long Range to a...From 1980’s decade,the introduction of carbon composite materials in structural applications has been consistently increased in the successive generations of civil aircraft from Single Aisle to Middle-long Range to achieve a culminant point with more than 50%in structure weight in recent commercial civil aircraft.This evolution,done through successive iterations,has been possible by combining in the same time the improvement of intrinsic composite material performances and its transformation into prepreg production technologies together with the development of new manufacturing process for material lay-up automation at composite shop-floor manufacturer of aircraft composite parts.New challenges are still coming to continuously develop materials and technologies in order to pursue the production more cost-effective composite parts.Associated to higher aircraft production rate for single aisle,new challenges may force material and aircraft designers and producers to furthermore drive new products and processes introduction and new ways of transformation within in next decade of composite aircraft designs.We propose to illustrate these trends using past and recent developments and our return of experience from Hexcel on Civil Aircraft programs.展开更多
βray online monitoring technique for resin content measurement has been developed, which is characterized by simple operation, short measuring time, and high measuring accuracy. It has been used to measure the resin ...βray online monitoring technique for resin content measurement has been developed, which is characterized by simple operation, short measuring time, and high measuring accuracy. It has been used to measure the resin content of pregreg tapes during manufacturing of them. This paper gives the measuring results. Meanwhile, the effects of the deviation of the βray monitoring system itself and the variation of the release paper on the measuring accuracy have been analyzed and discussed.展开更多
In the field of highly integrated printed circuit board （PCB）, the heat resistant substrate with low water absorption is very important material. To get the resin composition for the high functional substrate materi...In the field of highly integrated printed circuit board （PCB）, the heat resistant substrate with low water absorption is very important material. To get the resin composition for the high functional substrate material with low moisture absorption and high glass transition temperature （Tg） simultaneously, a fluorenyl ＂Cardo＂ epoxy was incorporated into novolac cyanate ester resin. As an optimum curing agent for the fiuorenyl epoxy, methyl nadic anhydride （MNA） was selected. Silica powders as fillers were added into the resin composition. The partial replacement of the cyanate ester resin with the fluorenyl epoxy could reduce the moisture absorption with keeping high glass transition temperature over 300 ℃. The laminate, which was fabricated from prepregs made with 40 wt% silica-filled resin composition and glass fabric, showed high Tg of 317 ℃ and low moisture absorption of 0.57%.展开更多
In this work, flexural properties and failure behavior of unidirectional (UD) carbon fiber reinforced polyamide 6 (CF/Nylon 6) and epoxy resin (CF/ Epoxy) laminates were investigated through three-point bending test. ...In this work, flexural properties and failure behavior of unidirectional (UD) carbon fiber reinforced polyamide 6 (CF/Nylon 6) and epoxy resin (CF/ Epoxy) laminates were investigated through three-point bending test. The mechanical properties and failure behavior of 0 and 90 degree CF/Nylon 6 and CF/Epoxy laminates were discussed based on the fiber volume fraction, fiber distribution, void content, interfacial properties, transversal tensile strength and fracture toughness. The effects of fiber volume fraction, fiber distribution, void content and their hybrid effect on the flexural properties were investigated. Step-by-step observation and scanning electron microscope observation of laminates after flexural tests were employed to analyze the fracture process.展开更多
In this study, a novel bio-based thermosetting system has been developed from epoxy resin （EP）, with rosin-sourced anhydrides （maleopimaric acid, RAM） as curing agent and imidazole type latent catalyst （two amino...In this study, a novel bio-based thermosetting system has been developed from epoxy resin （EP）, with rosin-sourced anhydrides （maleopimaric acid, RAM） as curing agent and imidazole type latent catalyst （two amino imidazole salt complex, IMA）, to be used as matrix for hot-melt prepreg curing at mid-temperature. For comparison, the epoxy resin system with petroleum sourced hardener methylhexahydrophthalicanhydride （MHHPA） was also examined. The curing behaviour and mechanism were investigated by non-isothermal differential scanning calorimeter （DSC） analysis and Fourier transform infrared （FTIR） spectra. The results showed that the curing course of bio-based epoxy resin system containing RAM included two stages, which were the reaction between the free carboxyl group of RAM and oxirane ring under the acceleration of IMA, and the main reaction attributed to the reaction between anhydride and oxirane. According to Kissinger method, the reaction activation energy （E,） of two stages were 68.9 and 86.5kJmo1-1, respectively. The Eo of EP/MHHPA and EP/IMA resin system were 81.04 and 77.9kJmol-I. The processing property of EP/RAM/IMA system, i.e. the relationship between viscosity-temperature-time, was characterized by cone-plate viscometer aim to decide the processing parameter ofprepreg preparation. The effect of RAM content on mechanical performance and dynamic mechanical property was investigated. Noteworthily, compared with the laminates with EP/MHHPA as matrix, the laminates with RAM as hardeners achieved a 44%, 73% and 70℃ increase in bending strength, bending modulus and the glass transition temperature, respectively, due to the bulky hydrogenated phenanthrene ring structure incorporated into the cross-linking networks. When the fiber volume fraction reached 47%, the mechanical property of the laminates prepared with hot melt prepreg was superior or comparable to that of composites with pure petroleum sourced matrix. RAM as cross-linking agent of epoxy resin holds a great potential to satisfy the requirement of composites such as structure and secondary structure parts preparation.展开更多
Co-cured vacuum assisted resin infusion process(co-VARI process),which combined vacuum assisted resin infusion(VARI)with prepreg vacuum bag only process(VBO),was adopted to fabricate T-shaped stiffened skin with non-c...Co-cured vacuum assisted resin infusion process(co-VARI process),which combined vacuum assisted resin infusion(VARI)with prepreg vacuum bag only process(VBO),was adopted to fabricate T-shaped stiffened skin with non-crimp fabric(NCF)stiffener and prepreg skin.During compaction stage of co-VARI process,prepreg resin impregnated fiber fabric under elevated temperature and vacuum pressure.This phenomenon was characterized by fluorescent micrographs with different holding temperature and time.Its influences on processing quality and mechanical performance for co-VARI stiffened skin with different filler materials at triangular region were further analyzed by optical micrographs and pull-off test,respectively.The results show that increasing holding temperature and prolonging holding time can promote prepreg resin impregnation in fiber fabric.Moderate prepreg resin impregnation is favorable to reduce resin rich region and increase fiber volume fraction at prepreg-fabric interface.Moreover,prepreg resin impregnation effect plays significant roles on pull-off performance for co-VARI stiffened skin with fabric filler but has negligible influences on specimens with prepreg filler.In addition,compared with stiffened skin with fabric filler,superior processing quality and pull-off performances are achieved for co-VARI stiffened skin with prepreg core filler.These results are helpful to optimize processing procedures and fabricate composite structure by coVARI process.展开更多
Objective:Increasing evidences have shown that prepregnancy maternal weight and gestational weight gain(GWG)may associate with offspring’s neurodevelopment.However,the effects of prepregnancy maternal overweight,obes...Objective:Increasing evidences have shown that prepregnancy maternal weight and gestational weight gain(GWG)may associate with offspring’s neurodevelopment.However,the effects of prepregnancy maternal overweight,obesity,and excessive GWG on offspring’s intelligence remain controversial.This meta-analysis aimed to re-assess the association between prepregnancy body mass index(BMI),GWG,and children’s intelligence.Methods:We systematically searched multiple databases,including PubMed,EMBASE,Cochrane Library,and Ovid Medline,from their inception through February 2021.Studies assessing the association between prepregnancy BMI or GWG and children’s intelligence were further screened manually before final inclusion.Cohorts that analyzed the association between prepregnancy BMI or GWG and intelligence of offspring were included,and we used the Mantel-Haenszel fixed-effects method to compute the weighted mean difference(WMD)and 95%confidence interval(CI)of each study.Results:A total of 12 articles were included in this systematic review,while six of them in the meta-analysis.There was a significant full-scale IQ reduction in children born from overweight and obese mothers,with WMDs of-3.08(95%CI:-4.02,-2.14)and-4.91(95%CI:-6.40,-3.42),respectively.Compared with control group,the WMDs for performance and verbal intelligence quotient(IQ)were decreased in overweight and obesity groups.However,we observed no association between children’s full-scale IQ and excessive GWG with WMD of-0.14(95%CI:-0.92,0.65).Conclusions:Women’s prepregnancy overweight and obesity adversely associate with children’s intelligence but no association with excessive GWG.Our study suggests that further researches focusing on the effect of prepregnancy maternal health on offspring’s intelligence development are needed.展开更多
Hydrogen-powered aircraft,as a cutting-edge exploration of clean-energy air transportation,impose more stringent requirements for lightweight hydrogen storage due to the limitations of aircraft weight and volume.Compo...Hydrogen-powered aircraft,as a cutting-edge exploration of clean-energy air transportation,impose more stringent requirements for lightweight hydrogen storage due to the limitations of aircraft weight and volume.Composite hydrogen storage cylinders have become one of the preferred solutions for hydrogen storage systems in hydrogen-powered aircraft due to their light weight and high strength.However,during the automated placement of high-stiffness thermoplastic composites(T700/PEEK),fibers may buckle or break in the head section.As the head radius decreases,the overlap of adjacent tows increases,resulting in an increase in the thickness of the polar pores,which is contrary to the light-weighting requirements.To solve this problem,this paper derives the trajectory algorithm as a manufacturing process limitation when thermoplastic fiber bundles are laid without wrinkles,provides a definition of the overlap rate between adjacent fibers,and the effect of different ellipsoid ratios of head profile changes on the overlap of fiber bundles is investigated.The larger the ellipsoid ratio of the prolate ellipsoid is,the smaller the overlap of gaps generated by neighboring fiber bundles is,and the overlap at the pole holes is also smaller,while the change of the oblate ellipsoid is not significant.The prolate ellipsoid has greater application and research value than the oblate ellipsoid in terms of processability,which is of great research significance for the design and fabrication of thermoplastic composite hydrogen storage cylinders for hydrogen-powered aircraft.展开更多
文摘Effects of layer quantities and stacking sequences on L-shape composite manufacturing qualities in using OOA(out-of-autoclave)prepregs were studied.The mechanisms of air evacuated in 5 kinds of lay-ups were revealed by image analysis of cut surfaces and thickness measurements.Results show that air in OOA prepregs is evacuated in two ways.Most of the air is forced out of layers directly by vacuum before air accesses in prepregs closed.Very little entrapped air moves perpendicularly to outer layers under hydrostatic resin pressure.When a laminate contains less than 16 layers,voids can hardly be found in layers.When a laminate contains more than 16 layers,voids cannot be expelled completely during the window of vertical movement.As for stacking sequences,the synergetic effect of slip function and nest function determines the thickness and voids content of laminates.Results show that the average of single layer thickness of unidirectional layers is the lowest,and the average of single layer thickness of quasi-isotropic layers is the highest.The voids content of quasi isotropic is the highest,which is consistent with the theoretical analysis.
文摘This study focuses on the insert-injection molding process. The thermoset composite inserts in this study were carbon fiber/epoxy (CF/Epoxy) prepreg sheets. The injected molded part was glass fiber contained phenolic resin (GF/PF). The CF/Epoxy was placed in the mold cavity prior to injecting GF/PF onto the inserted injection molded CF/Epoxy specimens. The role of adhesion between the inserted part and injected resin on the mechanical properties was evaluated by 3 point bending and impact tests. In addition, the effect of prepreg orientation on the mechanical properties of the prepreg inserted-injection molding system was investigated. It was found that the prepreg with unidirectional orientation significantly improved flexural and impact strength of the inserted injection molding composites, providing better support and resistance to bending and impact loading. The main failure modes of the specimens were structural and adhesive failure.
文摘A new isothermally based cure kinetic model for the prepreg was presented using an industrially supplied prepreg rather than neat resin.The matrix resin was bismaleimide(BMI)resin,and the reinforcement was carbon fiber T700-12S.A series of isothermal Differential Scanning Calorimetry(DSC)tests were performed and analyzed by the proposed nth-order reaction model.An increase in the cure rate was observed at the higher temper-ature in both neat and prepreg.After reaching the peak value,the cure rate of resin dropped off faster in prepreg,resulting in a lower average value of the ultimate heat of reaction.The presence of carbon fiber was found to significantly impact the curing behavior of the resin,leading to significant changes from the neat resin kinetic parameters.The carbon fibers imposed restrictions on the molecular mobility of reactive species,reduced the extent of polymeri-zation within the system and did not change the cure mechanism of resin.
基金financially supported by the National Basic Research Program of China(973Program)the Priority Academic Program Development of Jiangsu Higher Education Institutionsthe Fundamental Research Funds for the Central Universities ( No. 3082615NS2015056)
文摘With the growing needs of prepreg tapes for the automated fiber placement(AFP),the deviation-rectifying of prepreg in slitting process was investigated on a self-developed 16-tow prepreg slitting and winding machine.The process of slitting and rewinding of prepreg tape was introduced,and the reason of prepreg tape deviation in slitting process was analyzed.In order to ensure the quality of the narrow prepreg slits,the application of the fuzzy PID algorithm in a closed-loop control system was discussed.A fuzzy PID algorithm was designed by combining fuzzy rules and PID controller.By applying it to precise deviation-rectifying control strategy,the automatic control of rectification could be achieved with accuracy of 0.1 mm,which satisfies the requirement of the prepreg tape both in slitting quality and layup quality for AFP.
基金partly supported by the National Natural Science Foundation of China (No. 51575276)
文摘Marking arbitrary three-dimensional(3D) target curves on given objects with curved surface is required in many industrial fields, such as fabric prepreg placement in composite material part fabrication, product assembly, surface painting for decoration, etc. A shortcut to the solution of this intractable problem is proposed by utilizing a galvanometric laser scanner(GLS) with the aid of a camera. Without using the existing tedious GLS calibration procedures,the proposed method directly establishes a mapping between the 3D coordinates of the laser spots on the object surface and the control voltages of the scanner. A single-hidden layer feedforward neural network(SLFN) is employed to model the mapping. By projecting a dense grid of laser spots on the object to be marked and simultaneously taking only one image, the SLFN model is trained in minutes via a linear solving mechanism. Experiments demonstrate that the trained SLFN model has a good generalization performance for marking 3D target curves. The 3D laser marking errors on experimental objects are less than 0.5 mm. The proposed method is especially suitable for on-site use and can be conveniently extended to multiple GLSs for marking large complex objects.
文摘From 1980’s decade,the introduction of carbon composite materials in structural applications has been consistently increased in the successive generations of civil aircraft from Single Aisle to Middle-long Range to achieve a culminant point with more than 50%in structure weight in recent commercial civil aircraft.This evolution,done through successive iterations,has been possible by combining in the same time the improvement of intrinsic composite material performances and its transformation into prepreg production technologies together with the development of new manufacturing process for material lay-up automation at composite shop-floor manufacturer of aircraft composite parts.New challenges are still coming to continuously develop materials and technologies in order to pursue the production more cost-effective composite parts.Associated to higher aircraft production rate for single aisle,new challenges may force material and aircraft designers and producers to furthermore drive new products and processes introduction and new ways of transformation within in next decade of composite aircraft designs.We propose to illustrate these trends using past and recent developments and our return of experience from Hexcel on Civil Aircraft programs.
文摘βray online monitoring technique for resin content measurement has been developed, which is characterized by simple operation, short measuring time, and high measuring accuracy. It has been used to measure the resin content of pregreg tapes during manufacturing of them. This paper gives the measuring results. Meanwhile, the effects of the deviation of the βray monitoring system itself and the variation of the release paper on the measuring accuracy have been analyzed and discussed.
文摘In the field of highly integrated printed circuit board （PCB）, the heat resistant substrate with low water absorption is very important material. To get the resin composition for the high functional substrate material with low moisture absorption and high glass transition temperature （Tg） simultaneously, a fluorenyl ＂Cardo＂ epoxy was incorporated into novolac cyanate ester resin. As an optimum curing agent for the fiuorenyl epoxy, methyl nadic anhydride （MNA） was selected. Silica powders as fillers were added into the resin composition. The partial replacement of the cyanate ester resin with the fluorenyl epoxy could reduce the moisture absorption with keeping high glass transition temperature over 300 ℃. The laminate, which was fabricated from prepregs made with 40 wt% silica-filled resin composition and glass fabric, showed high Tg of 317 ℃ and low moisture absorption of 0.57%.
文摘In this work, flexural properties and failure behavior of unidirectional (UD) carbon fiber reinforced polyamide 6 (CF/Nylon 6) and epoxy resin (CF/ Epoxy) laminates were investigated through three-point bending test. The mechanical properties and failure behavior of 0 and 90 degree CF/Nylon 6 and CF/Epoxy laminates were discussed based on the fiber volume fraction, fiber distribution, void content, interfacial properties, transversal tensile strength and fracture toughness. The effects of fiber volume fraction, fiber distribution, void content and their hybrid effect on the flexural properties were investigated. Step-by-step observation and scanning electron microscope observation of laminates after flexural tests were employed to analyze the fracture process.
基金supported by the China-EU co-funded project ECO-COMPASS(Grant No.MJ2015-HG-103)
文摘In this study, a novel bio-based thermosetting system has been developed from epoxy resin （EP）, with rosin-sourced anhydrides （maleopimaric acid, RAM） as curing agent and imidazole type latent catalyst （two amino imidazole salt complex, IMA）, to be used as matrix for hot-melt prepreg curing at mid-temperature. For comparison, the epoxy resin system with petroleum sourced hardener methylhexahydrophthalicanhydride （MHHPA） was also examined. The curing behaviour and mechanism were investigated by non-isothermal differential scanning calorimeter （DSC） analysis and Fourier transform infrared （FTIR） spectra. The results showed that the curing course of bio-based epoxy resin system containing RAM included two stages, which were the reaction between the free carboxyl group of RAM and oxirane ring under the acceleration of IMA, and the main reaction attributed to the reaction between anhydride and oxirane. According to Kissinger method, the reaction activation energy （E,） of two stages were 68.9 and 86.5kJmo1-1, respectively. The Eo of EP/MHHPA and EP/IMA resin system were 81.04 and 77.9kJmol-I. The processing property of EP/RAM/IMA system, i.e. the relationship between viscosity-temperature-time, was characterized by cone-plate viscometer aim to decide the processing parameter ofprepreg preparation. The effect of RAM content on mechanical performance and dynamic mechanical property was investigated. Noteworthily, compared with the laminates with EP/MHHPA as matrix, the laminates with RAM as hardeners achieved a 44%, 73% and 70℃ increase in bending strength, bending modulus and the glass transition temperature, respectively, due to the bulky hydrogenated phenanthrene ring structure incorporated into the cross-linking networks. When the fiber volume fraction reached 47%, the mechanical property of the laminates prepared with hot melt prepreg was superior or comparable to that of composites with pure petroleum sourced matrix. RAM as cross-linking agent of epoxy resin holds a great potential to satisfy the requirement of composites such as structure and secondary structure parts preparation.
文摘Co-cured vacuum assisted resin infusion process(co-VARI process),which combined vacuum assisted resin infusion(VARI)with prepreg vacuum bag only process(VBO),was adopted to fabricate T-shaped stiffened skin with non-crimp fabric(NCF)stiffener and prepreg skin.During compaction stage of co-VARI process,prepreg resin impregnated fiber fabric under elevated temperature and vacuum pressure.This phenomenon was characterized by fluorescent micrographs with different holding temperature and time.Its influences on processing quality and mechanical performance for co-VARI stiffened skin with different filler materials at triangular region were further analyzed by optical micrographs and pull-off test,respectively.The results show that increasing holding temperature and prolonging holding time can promote prepreg resin impregnation in fiber fabric.Moderate prepreg resin impregnation is favorable to reduce resin rich region and increase fiber volume fraction at prepreg-fabric interface.Moreover,prepreg resin impregnation effect plays significant roles on pull-off performance for co-VARI stiffened skin with fabric filler but has negligible influences on specimens with prepreg filler.In addition,compared with stiffened skin with fabric filler,superior processing quality and pull-off performances are achieved for co-VARI stiffened skin with prepreg core filler.These results are helpful to optimize processing procedures and fabricate composite structure by coVARI process.
基金Program of Shanghai Academic Research Leader(20XD1424100)Shanghai Hospital Development Center(SHDC12018X17)+1 种基金Shanghai Municipal Health Commission(201840210)Science and Technology Commission of Shanghai Municipality(18410711800)。
文摘Objective:Increasing evidences have shown that prepregnancy maternal weight and gestational weight gain(GWG)may associate with offspring’s neurodevelopment.However,the effects of prepregnancy maternal overweight,obesity,and excessive GWG on offspring’s intelligence remain controversial.This meta-analysis aimed to re-assess the association between prepregnancy body mass index(BMI),GWG,and children’s intelligence.Methods:We systematically searched multiple databases,including PubMed,EMBASE,Cochrane Library,and Ovid Medline,from their inception through February 2021.Studies assessing the association between prepregnancy BMI or GWG and children’s intelligence were further screened manually before final inclusion.Cohorts that analyzed the association between prepregnancy BMI or GWG and intelligence of offspring were included,and we used the Mantel-Haenszel fixed-effects method to compute the weighted mean difference(WMD)and 95%confidence interval(CI)of each study.Results:A total of 12 articles were included in this systematic review,while six of them in the meta-analysis.There was a significant full-scale IQ reduction in children born from overweight and obese mothers,with WMDs of-3.08(95%CI:-4.02,-2.14)and-4.91(95%CI:-6.40,-3.42),respectively.Compared with control group,the WMDs for performance and verbal intelligence quotient(IQ)were decreased in overweight and obesity groups.However,we observed no association between children’s full-scale IQ and excessive GWG with WMD of-0.14(95%CI:-0.92,0.65).Conclusions:Women’s prepregnancy overweight and obesity adversely associate with children’s intelligence but no association with excessive GWG.Our study suggests that further researches focusing on the effect of prepregnancy maternal health on offspring’s intelligence development are needed.
基金This work was supported by Special Funds of 2023 Jiangsu Provincial Science and Technology Plan(First Batch of Innovation Capacity Building Plan)[No.ZAG23009].
文摘Hydrogen-powered aircraft,as a cutting-edge exploration of clean-energy air transportation,impose more stringent requirements for lightweight hydrogen storage due to the limitations of aircraft weight and volume.Composite hydrogen storage cylinders have become one of the preferred solutions for hydrogen storage systems in hydrogen-powered aircraft due to their light weight and high strength.However,during the automated placement of high-stiffness thermoplastic composites(T700/PEEK),fibers may buckle or break in the head section.As the head radius decreases,the overlap of adjacent tows increases,resulting in an increase in the thickness of the polar pores,which is contrary to the light-weighting requirements.To solve this problem,this paper derives the trajectory algorithm as a manufacturing process limitation when thermoplastic fiber bundles are laid without wrinkles,provides a definition of the overlap rate between adjacent fibers,and the effect of different ellipsoid ratios of head profile changes on the overlap of fiber bundles is investigated.The larger the ellipsoid ratio of the prolate ellipsoid is,the smaller the overlap of gaps generated by neighboring fiber bundles is,and the overlap at the pole holes is also smaller,while the change of the oblate ellipsoid is not significant.The prolate ellipsoid has greater application and research value than the oblate ellipsoid in terms of processability,which is of great research significance for the design and fabrication of thermoplastic composite hydrogen storage cylinders for hydrogen-powered aircraft.
