A constitutive model for fiber-reinforced extrudable fresh cementitious paste

Xiangming Zhou,Zongjin Li 사단법인 한국계산역학회 2011 Computers and Concrete, An International Journal Vol.8 No.4

In this paper, time-continuous constitutive equations for strain rate-dependent materials are presented first, among which those for the overstress and the consistency viscoplastic models are considered. By allowing the stress states to be outside the yield surface, the overstress viscoplastic model directly defines the flow rule for viscoplastic strain rate. In comparison, a rate-dependent yield surface is defined in the consistency viscoplastic model, so that the standard Kuhn-Tucker loading/unloading condition still remains true for rate-dependent plasticity. Based on the formulation of the consistency viscoplasticity, a computational elasto-viscoplastic constitutive model is proposed for the short fiber-reinforced fresh cementitious paste for extrusion purpose. The proposed constitutive model adopts the von-Mises yield criterion, the associated flow rule and nonlinear strain rate-hardening law. It is found that the predicted flow stresses of the extrudable fresh cementitious paste agree well with experimental results. The rate-form constitutive equations are then integrated into an incremental formulation, which is implemented into a numerical framework based on ANSYS/LS-DYNA finite element code. Then, a series of upsetting and ram extrusion processes are simulated. It is found that the predicted forming load-time data are in good agreement with experimental results, suggesting that the proposed constitutive model could describe the elasto-viscoplastic behavior of the short fiber-reinforced extrudable fresh cementitious paste.

Experimental study on white layers in high-speed grinding of AISI52100 hardened steel

Xiangming Huang,Yinghui Ren,Zhixiong Zhou,Hang Xiao 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.3

Ground white layer structure is an untempered martensitic due to grinding heat and plastic deformation. Many researchers have studiedthe formation of white layers at low grinding speed. However, few studies were found on white layer at high grinding speed. Therefore,to minimize white layer, it would be very useful to know the formation of white layer in the high-speed grinding. We performed grindingexperiments using hardened AISI52100 steel with cubic boron nitride (CBN). Grinding force and grinding temperature were onlinemeasured during grinding process. Surface roughness, residual stress and white layer were also examined, respectively. The influence ofgrinding wheel speed on grinding force and surface integrity was analyzed. Formation of white layer was also studied. Experimentalresults show that grinding force and plastic deformation decrease significantly at higher grinding speed. Meanwhile, white layer depthand residual stress value increase with the grinding wheel speed, and residual stress is well correlated with ground white layer depth. White layer during high-speed grinding process results from phase transformation due to grinding heat and rapid cooling, while the plasticdeformation may be ignored for the ground white layer.

Anchorage Effects of Various Steel Fibre Architectures for Concrete Reinforcement

Sadoon Abdallah,Mizi Fan,Xiangming Zhou,Simon Le Geyt 한국콘크리트학회 2016 International Journal of Concrete Structures and M Vol.10 No.3

This paper studies the effects of steel fibre geometry and architecture on the cracking behaviour of steel fibre reinforced concrete (SFRC), with the reinforcements being four types, namely 5DH (Dramix<SUP>®</SUP> hooked-end), 4DH, 3DH-60 and 3DH-35, of various hooked-end steel fibres at the fibre dosage of 40 and 80 kg/㎥. The test results show that the addition of steel fibres have little effect on the workability and compressive strength of SFRC, but the ultimate tensile loads, post-cracking behaviour, residual strength and the fracture energy of SFRC are closely related to the shapes of fibres which all increased with increasing fibre content. Results also revealed that the residual tensile strength is significantly influenced by the anchorage strength rather than the number of the fibres counted on the fracture surface. The 5DH steel fibre reinforced concretes have behaved in a manner of multiple crackings and more ductile compared to 3DH and 4DH ones, and the end-hooks of 4DH and 5DH fibres partially deformed in steel fibre reinforced self-compacting concrete (SFR–SCC). In practice, 5DH fibres should be used for reinforcing high or ultra-high performance matrixes to fully utilize their high mechanical anchorage.

Anchorage Effects of Various Steel Fibre Architectures for Concrete Reinforcement

Abdallah, Sadoon,Fan, Mizi,Zhou, Xiangming,Geyt, Simon Le Korea Concrete Institute 2016 International Journal of Concrete Structures and M Vol.10 No.3

This paper studies the effects of steel fibre geometry and architecture on the cracking behaviour of steel fibre reinforced concrete (SFRC), with the reinforcements being four types, namely 5DH ($Dramix^{(R)}$ hooked-end), 4DH, 3DH-60 and 3DH-35, of various hooked-end steel fibres at the fibre dosage of 40 and $80kg/m^3$. The test results show that the addition of steel fibres have little effect on the workability and compressive strength of SFRC, but the ultimate tensile loads, post-cracking behaviour, residual strength and the fracture energy of SFRC are closely related to the shapes of fibres which all increased with increasing fibre content. Results also revealed that the residual tensile strength is significantly influenced by the anchorage strength rather than the number of the fibres counted on the fracture surface. The 5DH steel fibre reinforced concretes have behaved in a manner of multiple crackings and more ductile compared to 3DH and 4DH ones, and the end-hooks of 4DH and 5DH fibres partially deformed in steel fibre reinforced self-compacting concrete (SFR-SCC). In practice, 5DH fibres should be used for reinforcing high or ultra-high performance matrixes to fully utilize their high mechanical anchorage.

Pull-Out Behaviour of Hooked End Steel Fibres Embedded in Ultra-high Performance Mortar with Various W/B Ratios

Sadoon Abdallah,Mizi Fan,Xiangming Zhou 한국콘크리트학회 2017 International Journal of Concrete Structures and M Vol.11 No.2

This paper presents the fibre-matrix interfacial properties of hooked end steel fibres embedded in ultra-high performance mortars with various water/binder (W/B) ratios. The principle objective was to improve bond behaviour in terms of bond strength by reducing the (W/B) ratio to a minimum. Results show that a decrease in W/B ratio has a significant effect on the bondslip behaviour of both types of 3D fibres, especially when the W/B ratio was reduced from 0.25 to 0.15. Furthermore, the optimization in maximizing pullout load and total pullout work is found to be more prominent for the 3D fibres with a larger diameter than for fibres with a smaller diameter. On the contrary, increasing the embedded length of the 3D fibres did not result in an improvement on the maximum pullout load, but increase in the total pullout work.

Development of a High-Speed and Precision Micro- Spindle for Micro-Cutting

Wei Liu,Zhixiong Zhou,Xiangming Huang,Zhi-Jian He,Yong Du 한국정밀공학회 2014 International Journal of Precision Engineering and Vol. No.

Mechanical micromachining using micro-machine tools is very competitive in manufacturing geometrically complex 3D micro-partsin various engineering materials with advantages of small space, energy-efficient, low equipment production and operation costs. Askey components of micro-machine tools, micro-spindles directly determine the performance of micro-machine tools and theapplication and development of mechanical micromachining technology. This study proposes a novel design concept of the separatelyspindle and tool and one-piece tool/rotor structure for micro-spindles, whose micro-tool can maintain good rotational accuracy athigh rotational speeds. In the principle prototype micro-spindle, an air driven turbine was used as power spindle. The design andoptimization of the micro-spindle were conducted. The fabrication and evaluation of the prototype micro-spindle were presented. Theresults of the principle prototype micro-spindle were analyzed and some efforts for the subsequent micro-spindle were proposed.

Pull-Out Behaviour of Hooked End Steel Fibres Embedded in Ultra-high Performance Mortar with Various W/B Ratios

Abdallah, Sadoon,Fan, Mizi,Zhou, Xiangming Korea Concrete Institute 2017 International Journal of Concrete Structures and M Vol.11 No.2

This paper presents the fibre-matrix interfacial properties of hooked end steel fibres embedded in ultra-high performance mortars with various water/binder (W/B) ratios. The principle objective was to improve bond behaviour in terms of bond strength by reducing the (W/B) ratio to a minimum. Results show that a decrease in W/B ratio has a significant effect on the bond-slip behaviour of both types of 3D fibres, especially when the W/B ratio was reduced from 0.25 to 0.15. Furthermore, the optimization in maximizing pullout load and total pullout work is found to be more prominent for the 3D fibres with a larger diameter than for fibres with a smaller diameter. On the contrary, increasing the embedded length of the 3D fibres did not result in an improvement on the maximum pullout load, but increase in the total pullout work.

Investigation of Grinding Characteristic using Nanofluid Minimum Quantity Lubrication

Cong Mao,Xiaojun Tang,Hongfu Zou,Xiangming Huang,Zhixiong Zhou 한국정밀공학회 2012 International Journal of Precision Engineering and Vol. No.

Conventional grinding fluid is widely used in grinding process, which results in high consumption and impacting the environment. The promising alternative to conventional dry and fluid coolant application is minimum quantity lubrication (MQL). It is known that the cooling and lubrication performance of the grinding fluid is the key technical area for the success application of MQL grinding process. In this study, Water based Al2O3 nanofluid was applied to grinding process with MQL approach for its excellent convection heat transfer and thermal conductivity properties. The grinding characteristics of hardened AISI 52100 steel were investigated and compared with those of wet, dry and pure water MQL grinding. Experimental results show that water based Al2O3 nanofluid MQL grinding can significantly reduce the grinding temperature, decrease the grinding forces, improve the ground surface morphology and reduce the surface roughness in comparison to pure water MQL grinding. Furthermore, the cooling and lubricating mechanism for nanofluid MQL grinding was discussed in detail.

Performances of Concrete Columns with Modular UHPC Permanent Formworks Under Axial Load

Yibo Yang,Baixi Chen,Yong Chen,Huanyang Zhou,Fucai Liu,Xiangming Xie,Junsheng Chen,Wenying Guo,Hengchang Wang 한국콘크리트학회 2023 International Journal of Concrete Structures and M Vol.17 No.5

This research proposed the modular prefabricated permanent formwork system made of ultra-high-performance concrete (UHPC). Two kinds of modular formwork shapes were designed: the flat formwork and the ribbed. The experimental investigation on the axial compression performance of the composite columns that consist of the normal strength concrete (NSC) core and the modular UHPC permanent formwork was demonstrated. Compared with the flat formwork, the ribbed formwork exhibited better bonding with the NSC core. As observed from the test results, the composite column with the ribbed formwork presented a similar axial behavior as the NSC column with a slight improvement in ultimate loads. Therefore, the modular UHPC ribbed permanent formwork could be regarded as the additional cover to the conventional NSC column. In addition, the finite element analysis (FEA) model was also developed to simulate the composite columns numerically. The predicted capacities agreed with the experimental results, which validated the numerical models. The crack pattern estimated by the FEA model revealed that the interaction between the permanent formwork and the inner concrete introduced many tiny cracks to the concrete core. However, as protected by the UHPC permanent formwork, the overall durability of the composite columns can still be enhanced.