Twenty-one square concrete columns were constructed and tested. The testing results indicate that bonded carbon fiber reinforced plastics(CFRP) sheets can be used to increase the strength and improve the serviceabilit...Twenty-one square concrete columns were constructed and tested. The testing results indicate that bonded carbon fiber reinforced plastics(CFRP) sheets can be used to increase the strength and improve the serviceability of damaged concrete columns at low temperatures. The failure of the specimens,in most cases,takes place within the middle half of the columns. And the failure of strengthened columns is sudden and explosive. The CFRP sheets increase both the axial load capacity and the ultimate concrete compressive strain of the columns. The ultimate loads of strengthened columns at-10,0 and 10 ℃ increase averagely by 9.09%,6.63% and 17.83%,respectively,as compared with those of the control specimens. The axial compressive strength of strengthened columns is related to the curing temperatures. The improvement of axial compressive strength decreases with reducing temperature,and when the temperature drops to a certain value,the improvement increases with falling temperature.展开更多
The frictional resistance and machining quality when cutting carbon fiber reinforced plastics (CFRP) laminates are associated with tribological behavior of tool materials. In the present study, the tribological proper...The frictional resistance and machining quality when cutting carbon fiber reinforced plastics (CFRP) laminates are associated with tribological behavior of tool materials. In the present study, the tribological properties of three types of monolayer microcrystalline diamond (MCD) coatings, nanocrystalline diamond (NCD) coatings and dual-layer MCD/NCD coatings sliding against CFRP are investigated under dry lubricated conditions using the rotational friction tester. The coefficients of friction (COF), wear rate and worn surfaces of the contacted surfaces are analyzed for the MCD-CFRP, NCD-CFRP and MCD/NCD-CFRP contacting pairs. The results show that compared with the monolayer MCD and NCD, the bilayer of MCD/NCD coating displays the lowest COF with the value of ~0.13, it is 42% and 55% of the values for MCD and NCD coatings. Due to the rough surfaces of MCD, the wear debris of CFRP on MCD samples exhibits the plowing effect. While for the NCD and MCD/NCD samples, the wear fragments display the planar shapes. The wear rate of CFRP against MCD is more than twice that of CFRP against NCD, due to the excellent loading capacity. While the wear rate of CFRP against MCD/NCD is about twice than that of CFRP-NCD pairs. The bilayer of MCD/NCD combines the excellent advantages of high hardness of MCD and the smooth surface of NCD. It shows the broad application potential for the bilayer coatings.展开更多
Formation of entrance and exit defects in coarse pitch orbital drilling(CPOD)of carbon fiber reinforced plastic(CFRP)plates was investigated.Deep observation on entrance and exit morphology shows tear and burr are typ...Formation of entrance and exit defects in coarse pitch orbital drilling(CPOD)of carbon fiber reinforced plastic(CFRP)plates was investigated.Deep observation on entrance and exit morphology shows tear and burr are typical defects.Meanwhile,tear is more obvious than burr,and more entrance tears emerge than exit tears.As one of the major causes of entrance and exit defects in CPOD,cutting forces were substaintially studied by contrast experiments.Then,the effect of cutting parameters on entrance and exit tear was qualitatively analyzed through a single factor test.Experiment results indicate that the variation of rotation speed has little influence on entrance and exit tear.Increasing tangential feed per tooth can enlarge entrance tear,but bring little effect on exit tear.By increasing axial feed pitch,the hole entrance and exit show severe tear.When revolution radius grows bigger and bigger,entrance and exit tear firstly decreases,and then increases.Finally,the models of tear and delamination during CPOD of CFRP were established,the formation mechanisms of entrance and exit defects were revealed,and the control strategies were accordingly put forward.展开更多
The testing of thirteen reinforced concrete (RC) beams strengthened by epoxy-bonded glass fiber reinforced plastic plate (GFRP) shows that the RC beam and the GFRP plate with epoxy bonding on it can work fairly we...The testing of thirteen reinforced concrete (RC) beams strengthened by epoxy-bonded glass fiber reinforced plastic plate (GFRP) shows that the RC beam and the GFRP plate with epoxy bonding on it can work fairly well in coordination to each other. But there is relative slipping between RC beam and GFRP plate. And the strain of GFRP and steel rebar of RC beam satisfies the quasi-plane-hypothesis, that is, the strain of longitudinal fiber that parallels to the neutral axis of plated beam within the scope of effective height (h0) of the cross section is in direct proportion to the distance from the fiber to the neutral axis. The strain of GFRP and steel rebar satisfies the equation: ε GFRP =Kε steel .展开更多
This study is the investigation of the microstructure of different types of carbon fiber. They were compared with the carbonized and graphitized fibers. Results of structural researches have been presented. It was fou...This study is the investigation of the microstructure of different types of carbon fiber. They were compared with the carbonized and graphitized fibers. Results of structural researches have been presented. It was found that the damage varies from different pollution and the damage of the monofibers. The effect of the pollution of the monofiber was determined.展开更多
Carbon fiber reinforced plastic(CFRP)has been applied in aeronautics,aerospace,automotive and medical industries due to its superior mechanical properties.However,due to its difficult-to-cut characteristic,various dam...Carbon fiber reinforced plastic(CFRP)has been applied in aeronautics,aerospace,automotive and medical industries due to its superior mechanical properties.However,due to its difficult-to-cut characteristic,various damages in twist drilling and chip removal clog in core drilling could happen,inevitably reducing hole quality and hole-manufacturing efficiency.This paper proposes the wave-motion milling(WMM)method for CFRP hole-manufacturing to improve hole quality.This paper presents a motion path model based on the kinematics of the WMM method.The wave-motion cutting mode in WMM was analyzed first.Then,comparison experiments on WMM and conventional helical milling(CHM)of CFRP were carried out under dry conditions.The results showed that the hole surface quality of the CFRP significantly improved with a decrease of 18.1%–36%of Ra value in WMM compared to CHM.WMM exerted a significantly weaker thrust force than that of CHM with a reduction of 12.0%–24.9%and 3%–7.7%for different axial feed per tooth and tangential feed per tooth,respectively.Meanwhile,the hole exit damages significantly decreased in WMM.The average tear length at the hole exit in WMM was reduced by 3.5%–29.5%and 35.5%–44.7%at different axial feed per tooth and tangential feed per tooth,respectively.Moreover,WMM significantly alleviated tool wear.The experimental results suggest that WMM is an effective and promising strategy for CFRP hole-manufacturing.展开更多
In this paper,the influence of some important parameters affecting the flexural behavior of reinforced concrete beams strengthened with one layer of carbon fiber reinforced polymer(CFRP)laminate has been studied.For t...In this paper,the influence of some important parameters affecting the flexural behavior of reinforced concrete beams strengthened with one layer of carbon fiber reinforced polymer(CFRP)laminate has been studied.For this purpose,six reinforced concrete beams were cast and tested in the laboratory.Based on the obtained data,when CFRP laminate is applied to the tension face,too close to the steel rebar,the flexural strength of the strengthened beam is reduced.In general,the performance of the beam strengthened with one wide CFRP strip is better than that strengthened with two equivalent narrow strips.Ultimate load capacity of each strengthened beam was calculated based on the method given by the ACI 440.2R and compared with the test one.It is concluded that,to avoid the steel rebar-CFRP laminate interaction effect,the CFRP laminate depth-to-the effective depth ratio(df/d)should not be smaller than about 1.17.展开更多
The application of fiber reinforced plastic(FRP),including carbon FRP and glass FRP,for structural repair and strengthening has grown due to their numerous advantages over conventional materials such as externally bon...The application of fiber reinforced plastic(FRP),including carbon FRP and glass FRP,for structural repair and strengthening has grown due to their numerous advantages over conventional materials such as externally bonded reinforcement(EBR) and near-surface mounted(NSM) strengthening techniques.This paper summarizes the results from 21 reinforced concrete beams strengthened with different methods,including externally-bonded and near-surface mounted FRP,to study the strain coordination of the FRP and steel rebar of the RC beam.Since there is relative slipping between the RC beam and the FRP,the strain of the FRP and steel rebar of the RC beam satisfy the quasi-plane-hypothesis;that is,the strain of the longitudinal fiber that parallels the neutral axis of the plated beam within the scope of the effective height(h 0) of the cross section is in direct proportion to the distance from the fiber to the neutral axis.The strain of the FRP and steel rebar satisfies the equation:ε FRP =βε steel,and the value of β is equal to 1.1-1.3 according to the test results.展开更多
Rehabilitation of existing structures with fiber reinforced plastic(FRP)has been growing in popularity because they offer superior performance in terms of resistance to corrosion and high specific stiffness.The strain...Rehabilitation of existing structures with fiber reinforced plastic(FRP)has been growing in popularity because they offer superior performance in terms of resistance to corrosion and high specific stiffness.The strain coordination results of 34 reinforced concrete beams(four groups)strengthened with different methods were presented including external-bonded or near-surface mounted glass or carbon FRP or helical rib bar in order to study the strain coordination of the strengthening materials and steel rebar of RC beam.Because there is relative slipping between concrete and strengthening materials(SM),the strain of SM and steel rebar of RC beam satisfies the double linear strain distribution assumption,that is,the strain of longitudinal fiber parallel to the neutral axis of plated beam within the scope of effective height(h0)of the cross section is in direct proportion to the distance from the fiber to the neutral axis.The strain of SM and steel rebar satisfies the equation εGCH=βεsteel,where the value of β is equal to 1.1-1.3 according to the test results.展开更多
The earthquake resistant property of reinforced concrete members depends on the interaction between reinforcing bars and surrounding concrete through bond to a large degree. In this paper a general system aimed at dea...The earthquake resistant property of reinforced concrete members depends on the interaction between reinforcing bars and surrounding concrete through bond to a large degree. In this paper a general system aimed at dealing with the failure analysis of reinforced concrete columns strengthened with carbon fiber reinforced plastic (CFRP) sheets including bond slip of the anchored reinforcing bars at the foot of the columns is presented. It is based on the yield design theory with a mixed modeling of the structure, according to which the concrete material is treated as a classical two dimensional continuum, whereas the longitudinal reinforcing bars are regarded as one dimensional rods including bond slip at the foot of the columns. In shear reinforced zones both the shear CFRP sheets and transverse reinforcing bars are incorporated in the analysis through a homogenization procedure and they are only in tension. The approach is then implemented numerically by means of the finite element formulation. The numerical procedure produces accurate estimates for the loading carrying capacity of the shear members taken as an illustrative application by correlation with the experimental results, so the proposed approach is valid.展开更多
The aim of the present paper is to reveal the influence of different fiber orientations on the tool wear evolution and wear mechanism. Side-milling experiments with large-diameter milling tools are conducted. A finite...The aim of the present paper is to reveal the influence of different fiber orientations on the tool wear evolution and wear mechanism. Side-milling experiments with large-diameter milling tools are conducted. A finite element(FE) cutting model of carbon fiber reinforced plastics(CFRP)is established to get insight into the cutting stress status at different wear stages. The results show that different fiber orientations bring about distinct differences in the extent, profile and mechanism of tool wear. Severer wear occurs when cutting 45° and 90° plies, followed by 0°, correspondingly,the least wear is obtained when θ = 135°(θ represents the orientation of fibers). Moreover, the worn profiles of cutting tools when θ = 0° and 45° are waterfall edge, while round edge occurs whenθ = 135° and a combined shape of waterfall and round edge is obtained when θ = 90°. The wear mechanisms under different fiber orientations are strongly dependent on the cutting stress distributions. The evolution of tool wear profile is basically consistent with the stress distribution on the tool surface at different wear stages, and the extent of tool wear is determined by the magnitude of stress on the tool surface. Besides, the worn edges produce an actual negative clearance angle,which decreases the actual cutting thickness and leads to compressing and bending failure of fibers beneath the cutting region as well as low surface qualities.展开更多
为了研究20 W纳秒激光对碳纤维复合材料(CFRP)烧蚀的工艺质量,采用单因素实验方法及光切法进行了理论分析和实验验证,得到了扫描速率、峰值功率、离焦量对材料表面加工质量的影响规律,并对0.5 mm CFRP材料板进行了烧蚀实验。结果表明,...为了研究20 W纳秒激光对碳纤维复合材料(CFRP)烧蚀的工艺质量,采用单因素实验方法及光切法进行了理论分析和实验验证,得到了扫描速率、峰值功率、离焦量对材料表面加工质量的影响规律,并对0.5 mm CFRP材料板进行了烧蚀实验。结果表明,调整激光器的离焦量,让激光的焦点与材料平面在同一高度,可使扫描线宽最小,减少了材料烧蚀的热影响区,提高了激光能量利用率;设定激光扫描速率为220 mm/s和峰值功率为10 W,可得到大小为3.50μm的CFRP最小表面粗糙度平均值,其中粗糙度数据稳定性样本方差最佳,约为0.133μm 2,在此条件下可得到良好的加工表现。此研究为脉冲激光加工CFRP材料工艺研究提供一定参考,并为脉冲激光加工复合材料工艺应用打下了一定的实践基础。展开更多
基金Project(04043076) supported by the Outstanding Youth Foundation for Scientific and Technological Research of Anhui Province, ChinaProject(2007jq1035) supported by the Scientific Research Projects for Young College Teachers of Anhui Province, China
文摘Twenty-one square concrete columns were constructed and tested. The testing results indicate that bonded carbon fiber reinforced plastics(CFRP) sheets can be used to increase the strength and improve the serviceability of damaged concrete columns at low temperatures. The failure of the specimens,in most cases,takes place within the middle half of the columns. And the failure of strengthened columns is sudden and explosive. The CFRP sheets increase both the axial load capacity and the ultimate concrete compressive strain of the columns. The ultimate loads of strengthened columns at-10,0 and 10 ℃ increase averagely by 9.09%,6.63% and 17.83%,respectively,as compared with those of the control specimens. The axial compressive strength of strengthened columns is related to the curing temperatures. The improvement of axial compressive strength decreases with reducing temperature,and when the temperature drops to a certain value,the improvement increases with falling temperature.
文摘The frictional resistance and machining quality when cutting carbon fiber reinforced plastics (CFRP) laminates are associated with tribological behavior of tool materials. In the present study, the tribological properties of three types of monolayer microcrystalline diamond (MCD) coatings, nanocrystalline diamond (NCD) coatings and dual-layer MCD/NCD coatings sliding against CFRP are investigated under dry lubricated conditions using the rotational friction tester. The coefficients of friction (COF), wear rate and worn surfaces of the contacted surfaces are analyzed for the MCD-CFRP, NCD-CFRP and MCD/NCD-CFRP contacting pairs. The results show that compared with the monolayer MCD and NCD, the bilayer of MCD/NCD coating displays the lowest COF with the value of ~0.13, it is 42% and 55% of the values for MCD and NCD coatings. Due to the rough surfaces of MCD, the wear debris of CFRP on MCD samples exhibits the plowing effect. While for the NCD and MCD/NCD samples, the wear fragments display the planar shapes. The wear rate of CFRP against MCD is more than twice that of CFRP against NCD, due to the excellent loading capacity. While the wear rate of CFRP against MCD/NCD is about twice than that of CFRP-NCD pairs. The bilayer of MCD/NCD combines the excellent advantages of high hardness of MCD and the smooth surface of NCD. It shows the broad application potential for the bilayer coatings.
基金supported in part by the Major Project of the Ministry of Science and Technology of China(No.2012ZX04003-031)the Innovation Project of Jiangsu Province(No.2016-05)
文摘Formation of entrance and exit defects in coarse pitch orbital drilling(CPOD)of carbon fiber reinforced plastic(CFRP)plates was investigated.Deep observation on entrance and exit morphology shows tear and burr are typical defects.Meanwhile,tear is more obvious than burr,and more entrance tears emerge than exit tears.As one of the major causes of entrance and exit defects in CPOD,cutting forces were substaintially studied by contrast experiments.Then,the effect of cutting parameters on entrance and exit tear was qualitatively analyzed through a single factor test.Experiment results indicate that the variation of rotation speed has little influence on entrance and exit tear.Increasing tangential feed per tooth can enlarge entrance tear,but bring little effect on exit tear.By increasing axial feed pitch,the hole entrance and exit show severe tear.When revolution radius grows bigger and bigger,entrance and exit tear firstly decreases,and then increases.Finally,the models of tear and delamination during CPOD of CFRP were established,the formation mechanisms of entrance and exit defects were revealed,and the control strategies were accordingly put forward.
基金Sponsored by the Natural Science Foundation of Henan Province(Grant No.004041700).
文摘The testing of thirteen reinforced concrete (RC) beams strengthened by epoxy-bonded glass fiber reinforced plastic plate (GFRP) shows that the RC beam and the GFRP plate with epoxy bonding on it can work fairly well in coordination to each other. But there is relative slipping between RC beam and GFRP plate. And the strain of GFRP and steel rebar of RC beam satisfies the quasi-plane-hypothesis, that is, the strain of longitudinal fiber that parallels to the neutral axis of plated beam within the scope of effective height (h0) of the cross section is in direct proportion to the distance from the fiber to the neutral axis. The strain of GFRP and steel rebar satisfies the equation: ε GFRP =Kε steel .
文摘This study is the investigation of the microstructure of different types of carbon fiber. They were compared with the carbonized and graphitized fibers. Results of structural researches have been presented. It was found that the damage varies from different pollution and the damage of the monofibers. The effect of the pollution of the monofiber was determined.
基金supported by National Natural Science Foundation of China(Grant No.51905024,51905138,51975035 and 91960203).
文摘Carbon fiber reinforced plastic(CFRP)has been applied in aeronautics,aerospace,automotive and medical industries due to its superior mechanical properties.However,due to its difficult-to-cut characteristic,various damages in twist drilling and chip removal clog in core drilling could happen,inevitably reducing hole quality and hole-manufacturing efficiency.This paper proposes the wave-motion milling(WMM)method for CFRP hole-manufacturing to improve hole quality.This paper presents a motion path model based on the kinematics of the WMM method.The wave-motion cutting mode in WMM was analyzed first.Then,comparison experiments on WMM and conventional helical milling(CHM)of CFRP were carried out under dry conditions.The results showed that the hole surface quality of the CFRP significantly improved with a decrease of 18.1%–36%of Ra value in WMM compared to CHM.WMM exerted a significantly weaker thrust force than that of CHM with a reduction of 12.0%–24.9%and 3%–7.7%for different axial feed per tooth and tangential feed per tooth,respectively.Meanwhile,the hole exit damages significantly decreased in WMM.The average tear length at the hole exit in WMM was reduced by 3.5%–29.5%and 35.5%–44.7%at different axial feed per tooth and tangential feed per tooth,respectively.Moreover,WMM significantly alleviated tool wear.The experimental results suggest that WMM is an effective and promising strategy for CFRP hole-manufacturing.
文摘In this paper,the influence of some important parameters affecting the flexural behavior of reinforced concrete beams strengthened with one layer of carbon fiber reinforced polymer(CFRP)laminate has been studied.For this purpose,six reinforced concrete beams were cast and tested in the laboratory.Based on the obtained data,when CFRP laminate is applied to the tension face,too close to the steel rebar,the flexural strength of the strengthened beam is reduced.In general,the performance of the beam strengthened with one wide CFRP strip is better than that strengthened with two equivalent narrow strips.Ultimate load capacity of each strengthened beam was calculated based on the method given by the ACI 440.2R and compared with the test one.It is concluded that,to avoid the steel rebar-CFRP laminate interaction effect,the CFRP laminate depth-to-the effective depth ratio(df/d)should not be smaller than about 1.17.
基金Consultative Program of the Chinese Academy of Engineeringthe foundation for Excellent Young of Hunan Scientific Committee+1 种基金the National Natural Science Foundation of Hunan Provincethe Science and Research Program of Hunan Province
文摘The application of fiber reinforced plastic(FRP),including carbon FRP and glass FRP,for structural repair and strengthening has grown due to their numerous advantages over conventional materials such as externally bonded reinforcement(EBR) and near-surface mounted(NSM) strengthening techniques.This paper summarizes the results from 21 reinforced concrete beams strengthened with different methods,including externally-bonded and near-surface mounted FRP,to study the strain coordination of the FRP and steel rebar of the RC beam.Since there is relative slipping between the RC beam and the FRP,the strain of the FRP and steel rebar of the RC beam satisfy the quasi-plane-hypothesis;that is,the strain of the longitudinal fiber that parallels the neutral axis of the plated beam within the scope of the effective height(h 0) of the cross section is in direct proportion to the distance from the fiber to the neutral axis.The strain of the FRP and steel rebar satisfies the equation:ε FRP =βε steel,and the value of β is equal to 1.1-1.3 according to the test results.
基金Project(11B033)supported by the Foundation for Excellent Young Scholars of Hunan Scientific Committee,ChinaProject(116001)supported by the Consultative Program of the Chinese Academy of Engineering+1 种基金Project(11JJ6040)supported by the National Natural Science Foundation of Hunan Province,ChinaProject(2010GK3198)supported by the Science and Research Program of Hunan Province,China
文摘Rehabilitation of existing structures with fiber reinforced plastic(FRP)has been growing in popularity because they offer superior performance in terms of resistance to corrosion and high specific stiffness.The strain coordination results of 34 reinforced concrete beams(four groups)strengthened with different methods were presented including external-bonded or near-surface mounted glass or carbon FRP or helical rib bar in order to study the strain coordination of the strengthening materials and steel rebar of RC beam.Because there is relative slipping between concrete and strengthening materials(SM),the strain of SM and steel rebar of RC beam satisfies the double linear strain distribution assumption,that is,the strain of longitudinal fiber parallel to the neutral axis of plated beam within the scope of effective height(h0)of the cross section is in direct proportion to the distance from the fiber to the neutral axis.The strain of SM and steel rebar satisfies the equation εGCH=βεsteel,where the value of β is equal to 1.1-1.3 according to the test results.
文摘The earthquake resistant property of reinforced concrete members depends on the interaction between reinforcing bars and surrounding concrete through bond to a large degree. In this paper a general system aimed at dealing with the failure analysis of reinforced concrete columns strengthened with carbon fiber reinforced plastic (CFRP) sheets including bond slip of the anchored reinforcing bars at the foot of the columns is presented. It is based on the yield design theory with a mixed modeling of the structure, according to which the concrete material is treated as a classical two dimensional continuum, whereas the longitudinal reinforcing bars are regarded as one dimensional rods including bond slip at the foot of the columns. In shear reinforced zones both the shear CFRP sheets and transverse reinforcing bars are incorporated in the analysis through a homogenization procedure and they are only in tension. The approach is then implemented numerically by means of the finite element formulation. The numerical procedure produces accurate estimates for the loading carrying capacity of the shear members taken as an illustrative application by correlation with the experimental results, so the proposed approach is valid.
基金supported by the National Natural Science Foundation of China(No.52075380)the Natural Science Foundation of Tianjin(Nos.21JCYBJC00610 and 19JCYBJC19000).
文摘The aim of the present paper is to reveal the influence of different fiber orientations on the tool wear evolution and wear mechanism. Side-milling experiments with large-diameter milling tools are conducted. A finite element(FE) cutting model of carbon fiber reinforced plastics(CFRP)is established to get insight into the cutting stress status at different wear stages. The results show that different fiber orientations bring about distinct differences in the extent, profile and mechanism of tool wear. Severer wear occurs when cutting 45° and 90° plies, followed by 0°, correspondingly,the least wear is obtained when θ = 135°(θ represents the orientation of fibers). Moreover, the worn profiles of cutting tools when θ = 0° and 45° are waterfall edge, while round edge occurs whenθ = 135° and a combined shape of waterfall and round edge is obtained when θ = 90°. The wear mechanisms under different fiber orientations are strongly dependent on the cutting stress distributions. The evolution of tool wear profile is basically consistent with the stress distribution on the tool surface at different wear stages, and the extent of tool wear is determined by the magnitude of stress on the tool surface. Besides, the worn edges produce an actual negative clearance angle,which decreases the actual cutting thickness and leads to compressing and bending failure of fibers beneath the cutting region as well as low surface qualities.