Progresses in Fracture and Strength of Materials and Structures

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Authors: Xiao Peng Li, He Li, Qing Kai Han, Jie Liu, Bang Chun Wen
Abstract: Vibratory pile driver-extractor is broadly applied in civil constructions, but the friction vibration theory and dynamic characteristics of friction vibration are not studied well. In this paper, the vibration friction characteristics and dynamics of pile driving process are studied based on nonlinear dynamics and friction theory. A dynamic model of system is established firstly, and then nonlinear dynamic principle and working process are studied in details. The simulation results can provide useful guidance for both vibration friction research in engineering and design in the development of such machines.
Authors: Yuan Bin Zhang, Hui Luo, Guo Fan Wang
Abstract: The microstructure and wear-resistance of the welding deposited metal of Fe-Ti-Nb-V-C and Fe-Cr-W-Mo-C alloy system (with American MG700 as example) are studyed by using SEM , TEM and MM200 wear testing machine. It is revealed that Ti and Nb promote the formation of dispersed MC type carbide granules, while the carbides of Cr and W or Mo tend to precipitate along grain boundary. The formation of MC carbide granules depletes the carbon content in the matrix, and then low carbon martensite matrix can be achieved. The hard and tough matrix and the granular carbides improve the wear-resistance of the deposited metal. But excessive Ti and Nb induce the formation of bigger granules with sharp corner and result too soft matrix, then the wear-resistance decrease. As to the Fe-Cr-W-Mo-C alloy system, network carbides and high carbon martensite matrix make the deposited metal very brittle. During wearing process, the propagating of microcrack in the matrix induces lots of scraps flake off, which decrease the wear-resistance of the deposited metal. The deposited metal of Fe-0.64Ti-1.18Nb-2.18V-1.43Cr-0.97C alloy system in current study achieve the best wear-resistance.
Authors: Yun Peng, Xi De Li, Wen Kui
Abstract: In Microelectromechanical System (MEMS), the capillary force plays an important role owing to the strong capillary force often makes the suspended or moving structures in MEMS adhere to contact the substrate, which lead to the failure of the devices. This paper presents experimental and theoretical results that characterize the capillary adhesion of micro-cantilevers by means of capillary actuation. Micro-cantilever beams were loaded at various locations along the freestanding portion of the beam using the capillary force and the deflections of the beams were real-time and in-situ measured with micro speckle interferometry. The mechanical stability and adhesion of micro-cantilever under capillary forces were examined and the deflecting configurations of the beams and the relationship of the magnitude of the capillary force to the size of the specimen were presented.
Authors: Mik Hail Pak, Choon Yeol Lee, Young Suck Chai
Abstract: Fracture toughness calculation by Movable Cellular Automata (MCA) method is demonstrated in this study in order to verify the validity of application of MCA method to the fracture problems. Two different geometries: edge-cracked strip and center cracked plate tension specimen have been considered to simulate numerically, which make place in real experiments. Soda-Lime silica glass for brittle material, AISI 1040 Steel and Aluminum Alloy 2024 for ductile materials were used, respectively. Fulfillment of basic principles of fracture mechanics has been checked. In MCA method, special fracture criterion is used to describe the process of crack propagation and critical stress and displacement was obtained, which are used as input data for evaluating the fracture toughness. In comparisons with table data, the results showed the sufficient agreement, which states the facility of the MCA method in application to the fracture problems.
Authors: Lei Gong, Lin Mao Qian, Zhong Rong Zhou
Abstract: By using an atomic force microscopy, the friction behavior of a NiTi shape memory alloy is investigated under various temperatures in vacuum environment. Under wearless condition at low loads, the adhesion-dominated friction of NiTi is almost temperature independent. However, while scratch mark appears after friction at high loads, the plough-dominated friction force is found to decrease with the increaase in temperature. Based on a simple contact analysis, the temperature dependent friction behavior of NiTi at high loads may be mainly attributed to the thermoelastic phase transition in NiTi. While temperature increases from 26~100°C, the tensile phase transition stress of NiTi increases from 412~964 MPa, which induces ~27% magnitude decrease in the contact area between the diamond tip and NiTi. It further results in the decrease in the plough-dominated friction force on NiTi.
Authors: Zhi Xin Han, Bing Liu, Jin Xia Du, Shao Feng Wang
Abstract: The vibration motion and the sliding ratio of the gear system were analyzed. It was revealed that the system vibration may make the meshing point at the middle of the tooth surface move in reciprocating motion and therefore may increase relative-sliding and the abrasion between two tooth surfaces meshed. So it can be concluded that the abrasion may result in the system vibration.
Authors: Takashi Murakami, T. Inoue, H. Shimura, Shinya Sasaki, Miki Nakano
Abstract: In this study, Fe-2.0Si-4.6C (mass%) gray cast iron disk specimens with three different matrix phases were coated with MoS2 using pressure spraying, and the friction and wear properties of the specimens were investigated against AISI52100 steel and polytetrafluoroethylene balls under the lubrication of oil using an Optimol SRV friction tester. When AISI52100 steel balls were used as the paired material, all of the MoS2-coated gray cast iron specimens showed lower friction coefficients and higher wear resistance than the non-coated disk specimens. On the other hand, MoS2-coated gray cast iron specimens exhibited higher friction coefficients than non-coated disk specimens for the most part, when polytetrafluoroethylene balls were used as the paired material.
Authors: Zeng Min Shi, Yong Zheng, Wen Jun Liu
Abstract: Ti(C, N)-based cermet cutting tools were prepared by vacuum sintering and tested in dry machining of normalized medium carbon steel (AISI1045) at various combinations of cutting speed (Vc), feed rate (f), and depth of cut (ap). And the wear mechanism was investigated in detail using scanning electron microscopy (SEM) and electron-probe microanalysis (EPMA). Comparing to the cemented carbide YT15 and cermet TN20, the newly fabricated cermet tools exhibited better performance and higher wear resistance. For Ti(C, N)-based cermet tools, the wear mechanism was predominantly controlled by the flank wear under all cutting condition. It was found that the removal of the ceramic grain and abrasive wear were the main source of tools failure. In addition, adhesion and oxidation were also observed.
Authors: Xiao Wang, Jian Li, Wei Chen, Lan Cai, Jian Ying Zhu
Abstract: Fabricating surfaces with controlled micro-geometry may be an effective approach to improved tribological performance. In this paper, the effect of laser surface micro-mesh texturing on the tribological performance is investigated theoretically with numerical solution of EHL point contact. In the theoretical model, the Reynolds equation is used as the governing equation. Well controlled micro-mesh texturing is described in film thickness equation. By Full Multi-Grid (FMG) method, the solutions of film thickness profile and pressure distribution map are present over a wide range of texturing parameters. The influence of width, depth and orientation of mesh texturing on the friction coefficient is analyzed. Result shows that, the film thickness profile and pressure distribution are sensitive to the parameters of micro-mesh texturing. The curve result of friction coefficient under two load conditions indicated that the parameters of mesh are key factor for texturing design. Solutions demonstrate the ability of numerical simulation on the design and optimization of surface mesh texturing.
Authors: Shi Bo Wang, Shi Rong Ge
Abstract: The friction and wear behavior of nylon1010 composites filled with different proportions of ZnOw in reciprocating sliding against GCr15 steel ball under dry friction condition were studied. The worn surface and wear particles were then examined with SEM. The elastic modulus, nano-hardness and ball indentation hardness of composites increased with the content of ZnOw. The coefficients of friction of composites decreased lightly, which changed from 0.36 and 0.26 of nylon matrix to 0.30 and 0.22 of composites at 0.04 m/s and 0.08m/s sliding velocity, respectively. The anti-wear property of composites was improved with large extent. The typical wear mechanism of nylon matrix is adhesion and micro-melting. However, peeling of surface layer appears owing to fatigue for composites. Roll-shaped wear debris were produced for pure nylon, while flake-like debris for nylon composites.

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