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1

Fresh and hardened properties of 3D printable cementitious materials for building and construction

Paul S. C., Tay Y. W. D., Panda B., Tan M. J.

Archives of Civil and Mechanical Engineering

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2018

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Vol. 18, no. 1

311--319

EN

The main advantage of 3D concrete printing (3DCP) is that it can manufacture complex, non-standard geometries and details rapidly using a printer integrated with a pump, hosepipe and nozzle. Sufficient speed is required for efficient and fast construction. The selected printing speed is a function of the size and geometrical complexity of the element to be printed, linked to the pump speed and quality of the extruded concrete material. Since the printing process requires a continuous, high degree of control of the material during printing, high performance building materials are preferred. Also, as no supporting formwork is used for 3DCP, traditional concrete cannot be directly used. From the above discussion, it is postulated that in 3DCP, the fresh properties of the material, printing direction and printing time may have significant effect on the overall load bearing capacity of the printed objects. The layered concrete may create weak joints in the specimens and reduce the load bearing capacity under compressive, tensile and flexural action that requires stress transfer across or along these joints. In this research, the 3D printed specimens are collected in different orientations from large 3DCP objects and tested for mechanical properties. For the materials tested, it is found that the mechanical properties such as compressive and flexural strength of 3D printed specimen are governed by its printing directions.

2

Effects of sintering on Y2O3-doped CeO2

Tavafoghi Jahromi M., Tan M. J.

Journal of Achievements in Materials and Manufacturing Engineering

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2009

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Vol. 34, nr 2

130-136

EN

Purpose: Having high electrical conductivity, Y2O3-doped CeO2 is a good candidate for various high temperature electrochemical devices, such as solid oxide fuel cells and oxygen gas sensor. However, its inferior mechanical properties compared to its competitors, e.g. ZrO2-based electrolytes, has restricted its usage. Design/methodology/approach: The present work evaluates the sintering behavior and mechanical properties of CeO2, and aims to enhance the mechanical properties and sinterability while restricting the grain growth by doping with Y2O3. Findings: The relative density, rather than the Y2O3 concentration, was the most important factor that affected the mechanical properties of CeO2. Increase of density resulted in higher hardness and elastic modulus, and lower the fracture toughness of CeO2. In the optimum condition, the KIC of 5.1 MPa.m1/2, nanohardness of 13.0 GPa, and elastic modulus of 371.5 GPa were obtained for the undoped CeO2 (density = 98.00%) sintered at 1700°C. Research limitations/implications: This study does not include sintering at higher temperatures. It is also worth investigating formation of oxygen vacancy or Ce2O3 material in the Y2O3-doped CeO2. Practical implications: It is noteworthy that in this study, the high temperature calcination of mixed powders is avoided in order to keep yitria as a second phase (not as a solute) in the ceria matrix. This enables yitria to be more effective to suppress the grain growth. Originality/value: The objectives are to improve the mechanical properties and to reveal the effects of various parameters, such as density, grain size, and yitria doping on the nano/micro indentation behavior of ceria material.

3

Cavitation and grain growth during superplastic forming

Tan M. J., Liew K. M., Tan H.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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Vol. 24, nr 1

307-314

EN

Purpose: The purpose of the paper is to study the cavitation and grain growth during superplastic forming. Design/methodology/approach: Superplastic alloys exhibit the extremely large elongation to failure by their high strain rate sensitivity. Cavities have widely been observed during superplastic deformation of metals and alloys and lead to the degradation of material properties such as tensile, creep, fatigue and stress-corrosion behavior. In this work, a finite element method is developed, which considers the grain growth and the effect of material damage. Findings: The effects of material parameters and deformation damage on the superplastic deformation process are numerically analyzed, and the means to control cavitation growth is discussed. The microstructural mechanism of grain growth during superplastic deformation is also studied. A new model considering the grain growth is proposed and applied to conventional superplastic materials. The relationships between the strain, the strain rate, the test temperature, the initial grain size and the grain growth respectively in superplastic materials are discussed. Practical implications: The effect of variation of strain rate sensitivity (in value) on the strain limit of the superplastic deformation is investigated, and the theoretically calculated values are compared with the experimental results. Originality/value: A new microstructure model based on the microstructural mechanism of superplastic deformation has been proposed. This model has been successfully applied to analyze conventional superplastic materials.

4

Analysis of cavitation and its effects on superplastic deformation

Tan M. J., Liew K. M., Tan H.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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Vol. 25, nr 2

7-10

EN

Purpose: To study the effects of cavitation on the superplastic deformation using finite element method. Design/methodology/approach: Using constitutive equations for superplastic deformation, and taking into account the effects of grain growth and cavitation growth, Zn-Al and LY12CZ alloys are used for simulations to show effects of m values, elongation-to-failure values, percentage cavities and effects of imposed hydrostatic pressure during superplastic forming processes. Findings: During superplastic deformation, cavitation damage increases with the increase in strain. For high strain rate sensitivity, necking develops which leads to final fracture; whereas for low strain strain rate sensitivity, the final fracture is due to cavitation growth. Research limitations/implications: The effects of material parameters and deformation damage on the superplastic deformation process are numerically analyzed, and the means to control cavitation growth is discussed. Originality/value: A three dimensional viscoplastic finite element programe, taking into account of microstructural mechanisms, such as test temperature and cavity growth has been developed for superplastic deformation.

5

Superplasticity studies in a beta titanium alloy

Tan M. J., Zhu X. J., Thiruvarudchelvan S., Liew K. M.

Archives of Materials Science and Engineering

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2007

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Vol. 28, nr 12

717-721

EN

Purpose: In the present study, the Superplastic Forming and deformation behavior as well as related mechanisms of this titanium alloy were investigated. Design/methodology/approach: The high temperature deformation of a beta titanium alloy (Ti-15V-3Cr-3Sn-3Al) was studied in this work. Uniaxial tensile tests were carried out at 650, 750, 850 and 950°C with an initial strain rates from 10 -1 s -1 to 10 -4 s -1. The effects of temperatures and initial strain rates on the superplasticity of this alloy were studied. Findings: The studies showed that dynamic recrystallization took place during high temperature deformation and this process not only decrease the average grain size of the alloy but also increase the misorientation angle. Microstructure evolution during high temperature forming as well as related mechanisms were also investigated. Practical implications: The investigation of microstructure of beta titanium alloy as related phenomens during high temperature deformation are important for achieving desired mechanical behavior of the material. Originality/value: The Superplasticity studies in a beta titanium alloy as well as related mechanism are investigated.

6

Microstructure evolution of CP titanium during high temperature deformation

Tan M. J., Zhu X. J.

Archives of Materials Science and Engineering

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2007

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Vol. 28, nr 1

5-11

EN

Purpose: To investigate the superplasticity of commercially pure titanium alloy and microstructure evolution of the alloy during high temperature deformation. Design/methodology/approach: Uniaxial tensile tests were carried out at 600, 750 and 800°C with an initial strain rate from 10 -1 s -1 10 -4 s -1. EBSD technology was used to evaluate the microstructure of the commercially pure titanium alloy deformed at high temperature. Findings: It is found that this titanium alloy does not show good superplasticity at 600-800°C due to the rapid grain growth. Studies also show that the dynamic recrystallization took place at high temperatures. The optimum dynamic recrystallization conditions were found to be at 600°C with an initial strain rate of 0.001/s, attaining the highest volume fraction of fine grains whose average grain size is ≈ 9.7 µm at strain of 80%. This process not only decreases the average grain size of the alloy but also increase the misorientation angle of the grain boundary. Practical implications: The investigations of microstructure of the commercially pure titanium alloy as well as related phenomena during high temperature deformation are important for achieving desired mechanical behavior of the material. Originality/value: The dynamic recrystallization phenomenon of commercially pure titanium alloy as well as related mechanism is investigated.

7

Dynamic recrystallization in commercially pure titanium

Tan M. J., Zhu X. J.

Journal of Achievements in Materials and Manufacturing Engineering

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2006

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Vol. 18, nr 1-2

183--186

EN

Purpose: A study was conducted to investigate the dynamic recrystallization of commercially pure Titanium alloy during high temperature deformation in order to understand it further and enable expansion of its usage. Design/methodology/approach: Uniaxial tensile tests were carried out at 600, 750 and 800°C with different initial strain rates. Microstructure evolution during high temperature tensile testing was studied by using optical microscope and Electron Back Scattered Diffraction. Findings: It is found that this titanium alloys do not show good superplasticity at 600-800°C due to the rapid grain growth. Studies also show that the dynamic recrystallization took place at high temperatures. This process not only decreases the average grain size of the alloy but also increase the misorientation angle of the grain boundary. Practical implications: The investigations of dynamic recrystallization of commercially pure titanium alloy as well as related phenomena are important for achieving desired mechanical behavior of the material. Originality/value: The dynamic recrystallization phenomenon of commercially pure titanium alloy as well as related mechanism is investigated.