Comparative Study of Models on Confinement of Concrete Cylinders with Fiber-Reinforced Polymer Composites

The use of fiber-reinforced polymer (FRP) composites for strengthening and/or rehabilitation of concrete structures is gaining increasing popularity in the civil engineering community. One of the most attractive applications of FRP materials is their use as confining devices for concrete columns, which may result in remarkable increases of strength and ductility as indicated by numerous published experimental results. Despite a large research effort, a proper analytical tool to predict the behavior of FRP-confined concrete has not yet been established. Most of the available models are empirical in nature and have been calibrated against their own sets of experimental data. On the other hand, the experimental results available in the literature encompass a wide range of values of the significant variables. The objective of this work is a systematic assessment of the performance of the existing models on confinement of concrete columns with FRP materials. The study is conducted in the following steps: the experimental data on confinement of concrete cylinders with FRP available in the technical literature are classified according to the values of the significant variables; the existing empirical and analytical models are reviewed, pointing out their distinct features; the whole set of available experimental results is compared with the whole set of analytical models; and strengths and weaknesses of the various models are analyzed. Finally, a new equation is proposed to evaluate the axial strain at peak stress of FRP-confined concrete cylinders.     

增容树脂对SBS改性沥青性能的影响

采用光学显微镜、熔体流动速率仪、动态力学分析仪和沥青基本性能测试，研究了增容树脂（T）对SBS分散及改性效果的影响。结果表明：SBS/沥青共混物加入增容树脂（T）后，光学显微镜相片中SBS颗料消失；动态粘弹谱中低温侧（PB链段）的玻璃化温度从-55℃升至-43.8℃，这些表明加入增容树脂（T）能改善SBS在沥青中的分散，树脂与PB链段有较好的相互作用。在改性沥青中加入增容树脂（T）后对软化点、针入度影响不大，而延度显著增大。     

INFLUENCE OF Al ON DUCTILITY IMPROVEMENT BY B IN Ni_3Al ALLOYS

The “order-disorder” model was adopted to calculate the lattice vacancies related to the com- position change in Ni_3Al alloys.A great deal of vacancies,i.e.,the non-stoichiometric vacan- cies,may exist in the Ni_3Al alloys containing Al over stoichiometry,i.e.25 at.-%.This was confirmed by the positron annihilation technique.Therefore,the influence of Al content on the enhancing behaviour of B towards the ductility of Ni_3Al alloys can be understood by the interaction of non-stoiehiometric vacancies and B atoms.     

冶炼工艺对0Cr15Ni25WMoTi2NbAl合金力学性能的影响

研究了真空感应 电渣和非真空感应 电渣两种工艺冶炼的0Cr1 5Ni2 5WMoTi2NbAl合金的杂质元素含量、组织与性能。因真空感应冶炼过程中晶界偏聚元素Pb得到了有效挥发 ,减轻了晶界的弱化效应 ,因而该合金中高温塑性、持久强度均不同程度提高。随着中温形变速率的降低 (拉伸、大应力持久、小应力持久 ) ,两工艺合金的晶界弱化效应加剧。未发现两者的基本组织以及晶界沉淀相的种类、数量、形貌和分布有明显差异。     

A new Cu–Hf–Al ternary bulk metallic glass with high glass forming ability and ductility

We have discovered a new Cu-based bulk metallic glass (BMG). Although of a simple Cu₄₉Hf₄₂Al₉ ternary composition, the as-cast alloy is a monolithic, uniform BMG with a critical diameter as large as 10 mm. The width of the supercooled liquid region ΔT_x and the reduced glass transition temperature T_rg for this glass are 85 K and 0.62, respectively. In addition to its high glass-forming ability and high density of 11 g/cc, this BMG exhibits high ductility with a compressive plastic strain of 11–13%, making it a good candidate for applications as well as for studies of deformation behavior of Cu-based BMGs.     

Predicting whether a material is ductile or brittle

In this paper we discuss the various models that have been used to predict whether a material will tend to be ductile or brittle. The most widely used is the Pugh ratio, $G/K$, but we also examine the Cauchy pressure as defined by Pettifor, a combined criterion proposed by Niu, the Rice and Thomson model, the Rice model, and the Zhou-Carlsson-Thomson model. We argue that no simple model that works on the basis of simple relations of bulk polycrystalline properties can represent the failure mode of different materials, particularly where geometric effects occur, such as small sample sizes. Instead the processes of flow and fracture must be considered in detail for each material structure, in particular the effects of crystal structure on these processes.     

Ductility of FRP plated flexural members

The design of reinforced concrete (RC) flexural members such as beams, slabs and columns is intrinsically based on the inherent ductility of the member. In reinforced concrete beams and slabs, ductility is generally achieved by using ‘under-reinforced’ sections and generally governed by the neutral axis depth parameter k_u which requires ultimate failure by concrete crushing at a specified strain ε_c. As the plates of fibre reinforced polymer (FRP) plated RC beams can fracture or debond before the concrete crushes at ε_c, the k_u approach is not directly applicable. Hence, new fundamental approaches and a deeper understanding of ductility are required which are the subjects of this paper.     

Fracture and microstructure of open cell aluminum foam

SEM and EDS measurements were used to scrutinize the microstructure of Duocel open cell 6101 aluminum foam in relation to its fracture properties. In-situ SEM tensile tests on the open cell aluminum foam were performed to investigate the different fracture modes of struts and Aramis/Digital Image Correlation software was used to map the strain in individual struts. Observations during tensile tests showed that the microstructure of the struts has a great influence on the fracture behaviour of the foam. In particular AlFeSi-precipitates, which are due to the casting of the 6101 aluminum alloy, and the morphology of the foam alters the fracture mode of the struts in the foam from transgranular to intergranular. Less energy is needed for intergranular fracture of struts and the strain to failure of the foam is decreased due to weak individual struts.     

Effectiveness of Composites in Earthquake Damage Repair of Reinforced Concrete Flared Columns

A method to utilize fiber composites for rapid repair of earthquake damaged flared columns was developed. Two 0.4-scale reinforced concrete columns that had been tested to failure in previous research were used. Both columns had been subjected to slow cyclic loads and had failed due to low-cycle fatigue of the longitudinal bars. To repair the columns, the damaged concrete in and around the plastic hinge was removed and the steel bars were straightened. Low-shrinkage, high-strength concrete grout was placed in the column afterward. The broken longitudinal bars were not replaced. Rather, glass and carbon fiber reinforced polymer (FRP) sheets with fibers running in the axial direction of the column were added to provide flexural strength to the columns. Additionally, glass FRP sheets with horizontal fibers were attached on the column to provide confinement and shear strength. Cyclic tests of the repaired columns indicated that the method to restore the strength was effective. Analysis using conventional constitutive relationships led to a close estimate of the lateral load response of the models.