The increasing demand for sustainable and environmentally friendly materials has driven research towards the development of green composites.In this work,the flax/polylactic acid(PLA)braided yarns were fabricated by b...The increasing demand for sustainable and environmentally friendly materials has driven research towards the development of green composites.In this work,the flax/polylactic acid(PLA)braided yarns were fabricated by braiding PLA filaments with 4 to 24 spindles on flax yarns.After curing at different temperatures(180℃and 190℃),the core/sheath structural flax/PLA composite yarns were manufactured.According to the results of the tensile test,the flax/PLA composite yarn with 4-spindle PLA yarns as a sheath layer and at a curing temperature of 180℃reached the maximum elastic modulus of about(5.79±0.65)GPa and the maximum tensile strength of about(162.17±18.18)MPa.This flax/PLA composite yarn with good mechanical properties would be suitable for green composites in the automobile manufacturing industry and building materials.展开更多
Preforming process would change yarn angle and yarn orientation,its influence on the material properties and material orientations needs to be considered in the performance analysis.However,most current performance mo...Preforming process would change yarn angle and yarn orientation,its influence on the material properties and material orientations needs to be considered in the performance analysis.However,most current performance models fail to account for the preforming effect.An integrated performance model accounting for the impact of preforming has been developed.In this integrated model,part geometry,yarn angle and orientation after preforming of multiple prepreg layers are predicted by Finite Element Analysis(FEA)using a non-orthogonal constitutive law.Experiments were conducted to validate the preforming simulation for a single dome composites structure made by two prepreg layers with different initial fiber orientations.Performance analysis until failure was then conducted for the single dome structure to validate the integrated performance model.Comparison between simulation and experiment shows that not only the failure mode and failure zone,but also the force-displacement curve during compression process are captured correctly by the performance model,demonstrating the effectiveness of the newly proposed model in accounting for the impact of preforming process.展开更多
A comprehensive study of yarn architecture of two-step rectangle 3D braided composites is presented. Firstly, the braided surface, the shapes of yarns and the intertwining between braider yams and axial yams are analy...A comprehensive study of yarn architecture of two-step rectangle 3D braided composites is presented. Firstly, the braided surface, the shapes of yarns and the intertwining between braider yams and axial yams are analyzed from experimentation. With the microstructure being defined, three levels of unit cell structure are identified, i.e. large unit cell, second unit cell and minimal unit cell. Secondly, based on the minimal unit cell in the interior and on the boundary of the entire cross-section, the deformations of axial yams squashed by braider yams contribute to the increase of the fiber packing factors of axial yams. Finally, the predicted fiber volume fraction of the composites decreases with the increase of linear density of the braider yam and the pitch length. Favorable correlations between the predicted and the experimental results arc found for six groups of the composites.展开更多
The mechanical and strain sensing properties of carbon nanotube composite yarns （CNTs/PDMS） with different weight percent of PDMS were studied. The CNT/PDMS composite yarn was prepared by infiltration method. Pictur...The mechanical and strain sensing properties of carbon nanotube composite yarns （CNTs/PDMS） with different weight percent of PDMS were studied. The CNT/PDMS composite yarn was prepared by infiltration method. Pictures of diameter of CNT composite yarns were obtained though polarized light microscope. Resistance change values of CNT composites under stretching were obtained though the single fiber strength tester and digital multimeter and related mechanical, electrical software. The changes of mechanical properties. electrical properties and sensing pertbrmance of pure and composite CNT yarns were discussed and analyzed. The results showed that the strength of CNT yarn declined after it was composited with PDMS polymer. In addition, the conductivity and sensing performance of CNT yarns improved significantly. The most suitable CNT composite yam occurs at PDMS mass fraction of 1% when strength and sensing properties were all considered.展开更多
The use of maleic anhydride (MA) coupling agent in polypropylene (PP) matrix system is promising technique to enhance the fibre-matrix interface in composite applications. However, most of the previous studies are foc...The use of maleic anhydride (MA) coupling agent in polypropylene (PP) matrix system is promising technique to enhance the fibre-matrix interface in composite applications. However, most of the previous studies are focused on either treatment of the natural fibres or the PP matrix with this coupling agent, which are not commercially viable. In this work, a cost-effective technique “hybrid yarns” was used to manufacture commingled reinforcing flax fibres and MA-grafted PP matrix fibres. Two types of twist-less flax/PP and flax/MAPP hybrid yarns were produced containing 40% flax and 60% matrix fibres by volume. Both PP and MAPP fibres were thermally and rheologically characterised using DSC, MFI, TGA, DTA and capillary rheometer. It is found that the composites manufactured from flax/MAPP blends exhibited 15% higher strength and 25% higher modulus compared to those made of flax/PP. This was due to the improved flax/matrix interface, the higher melt flow rate and lower share viscosity behaviour of the MAPP matrix fibres compared to the standard PP fibres used.展开更多
基金National Natural Science Foundation of China(No.52273054)Shanghai Natural Science Foundation,China(No.20ZR1402200)。
文摘The increasing demand for sustainable and environmentally friendly materials has driven research towards the development of green composites.In this work,the flax/polylactic acid(PLA)braided yarns were fabricated by braiding PLA filaments with 4 to 24 spindles on flax yarns.After curing at different temperatures(180℃and 190℃),the core/sheath structural flax/PLA composite yarns were manufactured.According to the results of the tensile test,the flax/PLA composite yarn with 4-spindle PLA yarns as a sheath layer and at a curing temperature of 180℃reached the maximum elastic modulus of about(5.79±0.65)GPa and the maximum tensile strength of about(162.17±18.18)MPa.This flax/PLA composite yarn with good mechanical properties would be suitable for green composites in the automobile manufacturing industry and building materials.
基金the financial support from the Young Fund of Natural Science Foundation of Shaanxi Province,China(Nos.2020JQ-121 and 2020JQ-701)the Direct Grant for Research,China(No.4055130)from the Chinese University of Hong Kong,China。
文摘Preforming process would change yarn angle and yarn orientation,its influence on the material properties and material orientations needs to be considered in the performance analysis.However,most current performance models fail to account for the preforming effect.An integrated performance model accounting for the impact of preforming has been developed.In this integrated model,part geometry,yarn angle and orientation after preforming of multiple prepreg layers are predicted by Finite Element Analysis(FEA)using a non-orthogonal constitutive law.Experiments were conducted to validate the preforming simulation for a single dome composites structure made by two prepreg layers with different initial fiber orientations.Performance analysis until failure was then conducted for the single dome structure to validate the integrated performance model.Comparison between simulation and experiment shows that not only the failure mode and failure zone,but also the force-displacement curve during compression process are captured correctly by the performance model,demonstrating the effectiveness of the newly proposed model in accounting for the impact of preforming process.
基金This research was funded by Scientific Research Fund of National Ministry of Education (00135)
文摘A comprehensive study of yarn architecture of two-step rectangle 3D braided composites is presented. Firstly, the braided surface, the shapes of yarns and the intertwining between braider yams and axial yams are analyzed from experimentation. With the microstructure being defined, three levels of unit cell structure are identified, i.e. large unit cell, second unit cell and minimal unit cell. Secondly, based on the minimal unit cell in the interior and on the boundary of the entire cross-section, the deformations of axial yams squashed by braider yams contribute to the increase of the fiber packing factors of axial yams. Finally, the predicted fiber volume fraction of the composites decreases with the increase of linear density of the braider yam and the pitch length. Favorable correlations between the predicted and the experimental results arc found for six groups of the composites.
文摘The mechanical and strain sensing properties of carbon nanotube composite yarns （CNTs/PDMS） with different weight percent of PDMS were studied. The CNT/PDMS composite yarn was prepared by infiltration method. Pictures of diameter of CNT composite yarns were obtained though polarized light microscope. Resistance change values of CNT composites under stretching were obtained though the single fiber strength tester and digital multimeter and related mechanical, electrical software. The changes of mechanical properties. electrical properties and sensing pertbrmance of pure and composite CNT yarns were discussed and analyzed. The results showed that the strength of CNT yarn declined after it was composited with PDMS polymer. In addition, the conductivity and sensing performance of CNT yarns improved significantly. The most suitable CNT composite yam occurs at PDMS mass fraction of 1% when strength and sensing properties were all considered.
文摘The use of maleic anhydride (MA) coupling agent in polypropylene (PP) matrix system is promising technique to enhance the fibre-matrix interface in composite applications. However, most of the previous studies are focused on either treatment of the natural fibres or the PP matrix with this coupling agent, which are not commercially viable. In this work, a cost-effective technique “hybrid yarns” was used to manufacture commingled reinforcing flax fibres and MA-grafted PP matrix fibres. Two types of twist-less flax/PP and flax/MAPP hybrid yarns were produced containing 40% flax and 60% matrix fibres by volume. Both PP and MAPP fibres were thermally and rheologically characterised using DSC, MFI, TGA, DTA and capillary rheometer. It is found that the composites manufactured from flax/MAPP blends exhibited 15% higher strength and 25% higher modulus compared to those made of flax/PP. This was due to the improved flax/matrix interface, the higher melt flow rate and lower share viscosity behaviour of the MAPP matrix fibres compared to the standard PP fibres used.
