In order to avoid brittle fracture failure, a ductile engineered cementitious composite （ECC） was attempted in steel/concrete connection zones to replace normal concrete. The influence of the ECC material ductility ...In order to avoid brittle fracture failure, a ductile engineered cementitious composite （ECC） was attempted in steel/concrete connection zones to replace normal concrete. The influence of the ECC material ductility on connection failure modes and structural performance was investigated via the pushout test of stud/ECC connection, the pullout test of two-dimensional anchor bolt/ECC connection and the finite element modeling （FEM）. The experimental results suggest that the micromechanically designed ECC with a tensile ductility 300 times that of normal concrete switches the brittle fracture failure mode to a ductile one in steel connection zones. This modification in material behavior leads to higher load carrying capacity and structural ductility, which is also confirmed in FEM investigation. The enhancement in structural response through material ductility engineering is expected to be applicable to a wide range of engineering structures where steel and concrete come into contact.展开更多
The effect of steel corrosion on the behavior of bond between steel and the surrounding concrete was investigated. Pullout tests were carried out to demonstrate bond stress-slip response for reinforcing steel bars of ...The effect of steel corrosion on the behavior of bond between steel and the surrounding concrete was investigated. Pullout tests were carried out to demonstrate bond stress-slip response for reinforcing steel bars of a series of corrosion level. Specimens either confined or unconfined were investigated for evaluation of the effect of confinement on bond strength and failure mode. Also, the tests were analyzed using nonlinear finite element analysis. It was shown that for both confined and unconfined steel bars, bond strength generally decreases as the corrosion level increases when corrosion level is relatively high. Confinement was demonstrated to provide excellent means to conteract bond loss for corroded reinforcing steel bars. It was shown that unconfined specimens generally split at a small slip with a large crack width and result in splitting failure while confined specimens contribute to a small crack width and generally cause a pullout failure. The analysis results agree reasonably well with the experiments.展开更多
Sintering shrinkage, compressive strength, bending strength, metallurgical morphology, microstructure and chemical composition diffusion of hydroxyapatite-316L stainless steel(HA-316L SS) composites were investigated....Sintering shrinkage, compressive strength, bending strength, metallurgical morphology, microstructure and chemical composition diffusion of hydroxyapatite-316L stainless steel(HA-316L SS) composites were investigated. The results show that the sintering shrinkage of HA-316L SS composites decreases from 27.38% to 8.87% for cylinder sample or from 27.18% to 8.62% for cuboid sample with decreasing the volume ratio of HA to 316L SS, which leads to higher sintering activity of HA compared with that of 316L SS. The compressive strength of HA-316L SS composites changes just like parabolic curve (245.3→126.3→202.8 MPa) with reducing the volume ratio of HA to 316L SS. Bending strength increases from 86.3MPa to 124. 2 MPa with increasing the content of 316L SS. Furthermore, comprehensive mechanical properties of 1.0∶3.0 (volume ratio of HA to 316L SS) composite are optimal with compressive strength and bending strength equal to 202.8 MPa and 124.2 MPa, respectively. The (microstructure) and metallurgical structure vary regularly with the volume ratio of HA to 316L SS. Some chemical reaction takes place at the interface of the composites during sintering.展开更多
Based on the manufacturing method now used in our country,caused low bear- ing capacity in the bolt-end,which is a potential danger in the bolt supporting tunnel and a waste of money,and presented the new type strong ...Based on the manufacturing method now used in our country,caused low bear- ing capacity in the bolt-end,which is a potential danger in the bolt supporting tunnel and a waste of money,and presented the new type strong steel big-end bolt can solve this problem.Analyzed the active state of the end of bolt by ANSYS,we can know that it is very disadvantage when bolt bore eccentric load.Contrasted with the different that com- mon bolt and big-end bolt when they bore the same loading.The common bolt is bigger than the big-end bolt in stress value.Study on the processing technic of the new type of the strong steel big-end bolt,the new metal big-end bolt was produced by heat processing over big-end bolt and upset.From the microscopic examination on bolt metal,it is con- cluded that heat processing on the bolt-end refines the crystal grain of the metal material, which not only increase its extension but improve its property.Moreover the strength ability of the bolt material can be exerted completely.展开更多
This paper demonstrates the possibility of combining both glass and carbon FRP （Fibre Reinforced Polymer） composite materials with a low-cost construction material （i.e. concrete） in a hybrid system that brings hi...This paper demonstrates the possibility of combining both glass and carbon FRP （Fibre Reinforced Polymer） composite materials with a low-cost construction material （i.e. concrete） in a hybrid system that brings higher performance levels to the design of lightweight, corrosion resistant, yet inexpensive beams providing acceptable structural properties. The objective of the research is to investigate the behaviour of a hybrid composite section under flexure. The hybrid section consists of a top concrete slab, Glass Fibre Reinforced Polymer （GFRP） beam section and Carbon Fibre Reinforced Polymer （CFRP） laminate on the extreme underside. This maximizes the benefits of each material, that is： high tensile strength of CFRP, compressive strength and low cost of concrete, light weight and lower cost of GFRP, and high corrosion resistance of all components. Three beam samples were manufactured and tested to failure while monitoring deflections and strains. By adding CFRP layers under the concrete-GFRP composite beam increases the bending strength and reduces the deflection. The most important factor in the proposed strengthening technique of GFRP-concrete composite beams by using CFRP is the adhesive material that bonds the CFRP to the GFRP. Any weakness in CFRP-GFRP bond may cause brittle failure of the beam. The study results indicate the benefits of using hybrid FRP-concrete beams to increase flexural load carrying capacity and beam stiffness and provide a numerical model that can be further developed to model more advanced material arrangements in the future. The outcome of this research provides information for both designers and researchers in the field of FRP composites.展开更多
The mechanical peratures and cooling rates properties and microstructure of as-cast Nb-Ti microalloyed steel at different tern- are investigated in this paper. The III brittle zone （700--900~C） is revealed. The redu...The mechanical peratures and cooling rates properties and microstructure of as-cast Nb-Ti microalloyed steel at different tern- are investigated in this paper. The III brittle zone （700--900~C） is revealed. The reduction of the hot ductility is due to the film-like proeutectoid ferrite or the Nb（C, N） precipitates along the austenitic grain boundaries. In the temperature range of 850 1000~C, with the increase of the cooling rate, the hot ductility decreases. However, in the range of 650--850 ~C, the appearance of large volume fractions of ferrite on austenite grain boundaries minimizes the effect of cooling rate on hot ductility. When the cooling rate is 10 ℃/s, austenite transforms more quickly to ferrite and at a lower temperature a larger amount of ferrite nucleates and precipitates in the grain, which leads to a sharper improvement in the hot ductility at 650 ℃.展开更多
基金The National Natural Science Foundation of China(No. 51008071)the Natural Science Foundation fo Jiangsu Province(No. BK2010413)Teaching & Research Excellence Grant for Young Faculty Members at Southeast University,the US National Science Foundation (No. CMS-0223971,CMS-0329416)
文摘In order to avoid brittle fracture failure, a ductile engineered cementitious composite （ECC） was attempted in steel/concrete connection zones to replace normal concrete. The influence of the ECC material ductility on connection failure modes and structural performance was investigated via the pushout test of stud/ECC connection, the pullout test of two-dimensional anchor bolt/ECC connection and the finite element modeling （FEM）. The experimental results suggest that the micromechanically designed ECC with a tensile ductility 300 times that of normal concrete switches the brittle fracture failure mode to a ductile one in steel connection zones. This modification in material behavior leads to higher load carrying capacity and structural ductility, which is also confirmed in FEM investigation. The enhancement in structural response through material ductility engineering is expected to be applicable to a wide range of engineering structures where steel and concrete come into contact.
文摘The effect of steel corrosion on the behavior of bond between steel and the surrounding concrete was investigated. Pullout tests were carried out to demonstrate bond stress-slip response for reinforcing steel bars of a series of corrosion level. Specimens either confined or unconfined were investigated for evaluation of the effect of confinement on bond strength and failure mode. Also, the tests were analyzed using nonlinear finite element analysis. It was shown that for both confined and unconfined steel bars, bond strength generally decreases as the corrosion level increases when corrosion level is relatively high. Confinement was demonstrated to provide excellent means to conteract bond loss for corroded reinforcing steel bars. It was shown that unconfined specimens generally split at a small slip with a large crack width and result in splitting failure while confined specimens contribute to a small crack width and generally cause a pullout failure. The analysis results agree reasonably well with the experiments.
文摘Sintering shrinkage, compressive strength, bending strength, metallurgical morphology, microstructure and chemical composition diffusion of hydroxyapatite-316L stainless steel(HA-316L SS) composites were investigated. The results show that the sintering shrinkage of HA-316L SS composites decreases from 27.38% to 8.87% for cylinder sample or from 27.18% to 8.62% for cuboid sample with decreasing the volume ratio of HA to 316L SS, which leads to higher sintering activity of HA compared with that of 316L SS. The compressive strength of HA-316L SS composites changes just like parabolic curve (245.3→126.3→202.8 MPa) with reducing the volume ratio of HA to 316L SS. Bending strength increases from 86.3MPa to 124. 2 MPa with increasing the content of 316L SS. Furthermore, comprehensive mechanical properties of 1.0∶3.0 (volume ratio of HA to 316L SS) composite are optimal with compressive strength and bending strength equal to 202.8 MPa and 124.2 MPa, respectively. The (microstructure) and metallurgical structure vary regularly with the volume ratio of HA to 316L SS. Some chemical reaction takes place at the interface of the composites during sintering.
文摘Based on the manufacturing method now used in our country,caused low bear- ing capacity in the bolt-end,which is a potential danger in the bolt supporting tunnel and a waste of money,and presented the new type strong steel big-end bolt can solve this problem.Analyzed the active state of the end of bolt by ANSYS,we can know that it is very disadvantage when bolt bore eccentric load.Contrasted with the different that com- mon bolt and big-end bolt when they bore the same loading.The common bolt is bigger than the big-end bolt in stress value.Study on the processing technic of the new type of the strong steel big-end bolt,the new metal big-end bolt was produced by heat processing over big-end bolt and upset.From the microscopic examination on bolt metal,it is con- cluded that heat processing on the bolt-end refines the crystal grain of the metal material, which not only increase its extension but improve its property.Moreover the strength ability of the bolt material can be exerted completely.
文摘This paper demonstrates the possibility of combining both glass and carbon FRP （Fibre Reinforced Polymer） composite materials with a low-cost construction material （i.e. concrete） in a hybrid system that brings higher performance levels to the design of lightweight, corrosion resistant, yet inexpensive beams providing acceptable structural properties. The objective of the research is to investigate the behaviour of a hybrid composite section under flexure. The hybrid section consists of a top concrete slab, Glass Fibre Reinforced Polymer （GFRP） beam section and Carbon Fibre Reinforced Polymer （CFRP） laminate on the extreme underside. This maximizes the benefits of each material, that is： high tensile strength of CFRP, compressive strength and low cost of concrete, light weight and lower cost of GFRP, and high corrosion resistance of all components. Three beam samples were manufactured and tested to failure while monitoring deflections and strains. By adding CFRP layers under the concrete-GFRP composite beam increases the bending strength and reduces the deflection. The most important factor in the proposed strengthening technique of GFRP-concrete composite beams by using CFRP is the adhesive material that bonds the CFRP to the GFRP. Any weakness in CFRP-GFRP bond may cause brittle failure of the beam. The study results indicate the benefits of using hybrid FRP-concrete beams to increase flexural load carrying capacity and beam stiffness and provide a numerical model that can be further developed to model more advanced material arrangements in the future. The outcome of this research provides information for both designers and researchers in the field of FRP composites.
文摘The mechanical peratures and cooling rates properties and microstructure of as-cast Nb-Ti microalloyed steel at different tern- are investigated in this paper. The III brittle zone （700--900~C） is revealed. The reduction of the hot ductility is due to the film-like proeutectoid ferrite or the Nb（C, N） precipitates along the austenitic grain boundaries. In the temperature range of 850 1000~C, with the increase of the cooling rate, the hot ductility decreases. However, in the range of 650--850 ~C, the appearance of large volume fractions of ferrite on austenite grain boundaries minimizes the effect of cooling rate on hot ductility. When the cooling rate is 10 ℃/s, austenite transforms more quickly to ferrite and at a lower temperature a larger amount of ferrite nucleates and precipitates in the grain, which leads to a sharper improvement in the hot ductility at 650 ℃.
