Papers by Keyword: Bonding Mechanism

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Authors: Chun Ming Wei, Hui Su, Qiang Zhao, Chun Li Bi
Abstract: The quality of construction joint is significantly influenced by the precision in the concrete placement. In order to obtain the mechanical properties of horizontal construction joints surface, a comprehensive research was conducted. The research focused on the tensile capacity and seismic behavior of construction joints surface. According the tests failure characteristics, four kinds of cracking model of construction joints zone were formed. Test results indicated that bond materials could increase displacement ductility more than 10%~30%. And the clamping action provided by bond materials was so good that failure didn’t occur at the construction joint itself, but in the concrete adjacent to it. Axial compressive force is advantageous for the shear capacity of construction joint interface.
Authors: T. Hussain
Abstract: Cold gas dynamic spraying (CGDS) is a relatively new branch of surface engineering that involves modification of the surface of substrates to provide specific engineering advantages, which the substrate alone cannot provide. Cold spraying, as a metal deposition technique, involves spraying of typically 10-40 μm particles which are accelerated by a propellant gas to 300-1200 m/s at a temperature well below the melting point of material, and upon impact deform and adhere to the substrate. The deposition process in cold spraying occurs in a solid state which results in reduced oxidation and absence of phase changes; whereas, in thermal spraying deposition occurs of molten or semi molten particles. Over the last decade the interest in cold spraying has increased substantially. Considerable effort has been invested in process developments and optimization of coatings like copper. However, bonding in cold spraying is still a matter of some debate. The most prevalent theory is that when a particle travels at a minimum required velocity the particle deforms at a very high strain rate upon impact and during this deformation thermal softening dominates over work hardening in impact zone and a material jet is produced. This material jet removes oxides from the surface of the materials and the metal-to-metal contact is established between the freshly exposed surfaces. However, precisely how this high strain rate deformation behaviour of material promotes bonding is still unclear and requires further investigations. This article provides a comprehensive review of the current theories of bonding in cold spraying based on numerical modelling of impact and experimental work. The numerical modelling of the impact section reviews adiabatic shear instability phenomena, critical velocity, critical particle diameter, window of deposition of particles, particle impact on various substrates and the role of adhesion and rebound energy. The review of the experimental section describes the shear lip formation, crater formation on the substrates, role of surface oxides, characterization of bond formation, role of substrate preparations, coating build up mechanisms and contributions of mechanical and metallurgical components in bonding. Cold spraying of copper and aluminium has been widely explored in the last decade, now it is of growing interest to the scientific and engineering communities to explore the potential of titanium and its alloys. Titanium and its alloys are widely utilized in many demanding environments such as aerospace, petrochemical, biomedical etc. Titanium components are very expensive to manufacture because of the costly extraction process of titanium and their difficult to machine properties. Therefore, additive manufacturing from powder and repair of titanium components are of great interest to the aerospace industry using technologies such as cold gas spraying. Titanium coating as a barrier layer has a great potential for corrosion resistant applications. Cold spraying has a great potential to produce oxygen-sensitive materials, such as titanium, without significant chemical degradation of the powder. In-flight oxidation of materials can be avoided to a great extent in cold spraying unlike thermal spraying. This review article provides a critical overview of deposition efficiency of titanium powder particles, critical velocity, bond strength, porosity, microhardness, microstructural features including microstrain and residual stress, mechanical properties reported by various research groups. A summary of the competitor warm sprayed titanium coating is also presented in this article.
Authors: Lu Xia, You Shou Zhang, Jin Huang
Abstract: Adding B-ion additive or Mg-ion additive to Al-phosphate binder to get different binders, and viscosity of Al-phosphate binders and dry strength of their no-bake sand were tested, bonding mechanism among sands of Al-phosphate no-bake sand was discussed by SEM and EDS. Results indicate that Mg-ion additive can increase binder’s viscosity and dry strength of its no-bake sand more obviously than B-ion additive, adding Mg-ion additive and B-ion additive simultaneously is more obvious. Location crack produced is changed from sand surface to binding bridge inner while adding Mg-ion additive and B-ion additive simultaneously ,and fracture mode is changed from adhesive fracture mainly to cohesive fracture mainly, dry strength is improved from 0.86MPa to 2.38MPa.
Authors: Li Ying Tang, Fei Chen, Xin Zhang, Chun Ming Zhang, Qiang Shen, Lian Meng Zhang
Abstract: Boron (B) has great potential to be the primary fuel in energetic systems for its high heating values per unit volume and mass. The existence of B2O3 layer on its surface holding the combustion of B back has limited its extensive utilization. Adding magnesium (Mg) into B can improve its poor combustion performance according to the previous research. A new technique, cryomilling, was employed to prepare Mg and B (Mg/B) composite powders. The powders were cryomilled with a ball-to-powder ratio (BPR) of 80: 1(w/w) and an impeller rotation speed of 400 rpm, 500 rpm and 600 rpm. The cryomilling time is 5 h, 6 h and 7 h. A small amount of ferrum (Fe) is introduced into the powders in spite that the main phases are Mg and B. The effects of cryomilling parameters, such as cryomilling time and rotation speed on Mg/B composite powders were investigated. The results show the amount of active Mg and B is over 80%. The bonding mechanism during the process is analogous to mechanical alloy.
Authors: Siri Marthe Arbo, Ida Westermann, Bjørn Holmedal
Abstract: In tri-layered Cold Roll Bonded (CRB) composite sheets of dissimilar metals, uneven thickness reduction of the different layers have been observed. This has been explained by the difference in yield strength/flow stress of the metals. The aim of this research was to study if these observations also depend on different parameters such as stacking sequence and initial sheet thickness, as opposed to only material properties. Hence, tri-layered CRB composite sheets consisting of AA6082 and IF-steel were produced with two different stacking sequences, St/Al/St vs Al/St/Al. Two different layer thicknesses of the intermediate layer were used. Rolling was performed in a single pass achieving approximately 55-65% total thickness reduction. Comparisons between the samples are given, focusing on the reduction of thickness achieved in each layer, the roll bonded interface characteristics and the bond strength of the joints. The overall thickness reduction achieved in each layer was found to be similar for both metals in both stacking sequences for the considered material combination. The stacking sequence is statistically found not to have any effect on the bond strength of the joints. The thickness of the intermediate layer does not significantly affect the overall bond strength of the composite sheet for both stacking sequences. These findings are opposed to earlier results found in the literature.
Authors: A.T.J. Van Helvoort, K.M. Knowles, J.A. Fernie
Authors: Bing Hua Mo, Zhong Ning Guo, Yuan Bo Li, Chang Liu
Abstract: Resistance microwelding is an important microjoining process used in the fabrication of microelectronics, MEMS and medical devices. However, the process is infeasible in the situation of terminating insulated copper wire to metal sheet due to the hindrance of the insulation coating in common opposed configuration. To address this problem, a revised electrode configuration is used. The effect of main process parameters (welding current, weld time and electrode force) were investigated by detailed mechanical testing and metallurgical examinations. A bonding mechanism with several main process stages (wire cold collapse, coating melting and withdrawing, and solid-state bonding) was proposed.
Authors: Frank Gaertner, Tobias Schmidt, Heinrich Kreye
Abstract: Cold spraying is a fairly new coating technique, which within the last decade attracted serious attention of research groups and spray companies. As compared to thermal spraying, the low process temperatures in cold spraying result in unique coating properties, which promise new applications. Since particles impact with high kinetic energy in the solid state, new concepts to describe coating formation are requested to enable the full potential of this new technology. The present contribution gives a brief review of current models concerning bonding, supplying a description of the most influential spray parameters and consequences for new developments. With respect to spray forming by cold cold spraying, microstructures and thick, further machineable structures are presented.
Authors: Wei Peng, Tao Gao, C.Y. Yao, X.L. Yuan
Authors: Qiang Wang, Ming Xing Zhang
Abstract: Cold spray (CS) is an emerging revolutionary technology for deposition of metal or composite powders at a low temperature. High quality deposits can be produced without heating related defects, such as oxidation, phase transformation and residual tensile stress due to the shrinkage during fast cooling. The present contribution demonstrates the state of the art of CS process. Since nozzle is a key component in the CS equipment to prompt the efficiency of particle acceleration, the progress of its design is summarized. Major issues regarding to the successful adhesion of particles and corresponding interaction with substrates and existing deposits are discussed, in terms of numerical simulation and experimental observation. Current implemented CS applications are presented, and potential industrial applications are discussed. Keywords: cold spray; coatings; rapid manufacturing; particle impact; bonding mechanism; nozzle design
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