Applied Mechanics and Materials Vol. 697

Abstract: Four Ti (C,N)-based cermets with Cr₃C₂ content of 0.3%, 0.6%, 0.9% and 1.2 % in mass ratio were sintered in vacuum at 1430oC, 1450oC, 1465oC and 1480oC. The mechanical properties of the specimens were determinted and microstructures were observed using the scanning electron microscope (SEM) to study the effect of Cr₃C₂ content on mechanical properties and microstructure. The results show that the four Ti (C,N)-based cermets sintered at 1465oC have the best overall mechanical properties; and among them, the cermet with 0.6% Cr₃C₂ has the best overall mechanical properties, i.e. transverse rupture strength (TRS) 1967MPa, hardness 1556HV and fracture toughness (K_IC) 9.5MPa.m^1/2. With the increase of Cr₃C₂ content, the black core volume fraction firstly increases and then decreases, the white core decreases in a progressive and continuous manner, the rim phase firstly increases and then decreases, the binder phase firstly decreases and then increases.

Abstract: In all process based in powder and in particular in the rotational moulding process, the major physical phenomenon during the flow of the powders is the sintering and grains growth. The sintering is the formation of only one particle starting from two or many particles under the effect of the temperature and the forces of surface tension. We interest in this study in particular at the mechanism of Polyvinylidene fluoride (PVDF) sintering. The results of this study can enable us to maximize our knowledge about sintering mechanism and enable us to determine parameters such as the speed of sintering for the optimization of the process.

Abstract: In this research, new progressive fatigue damage models are established to calculate the fatigue life and simulate damage process of composite pin joints. The proposed models based on residual strength and residual stiffness of unidirectional laminates, have three parameters to present the different damage state, which can accurately describe the growth process of fatigue damage propagation by the mathematical method. The fatigue damage models combining with stress analysis, failure analysis, and material property degradation process, can predict the fatigue life, damage state and residual material properties of composite structures under arbitrary loading conditions. Using the models, composite pin joints with different stacking sequence are analyzed, fatigue life and damage quantification are concluded simultaneously. The proposed models and the process of analysis provide a way to solve the fatigue durability of composite structures.

Abstract: Due to its excellent performance, carbon fiber-reinforced plastics (CFRP) have been widely applied in industrial applications. The phenomenon of delamination can readily occur when drilling CFRP composites, which affects the quality of drilling holes. To effectively control the generation of processing defects, this paper focused on the analysis of the thrust force and the delamination factor. The delamination analysis was performed using graphs of the spindle speed, feed rate and drill diameter as independent parameters. The results suggest that there was a positive correlation between the delamination factor F_d and the thrust force F_z. The delamination factor decreases with increases in the spindle speed and increases with increases in the feed rate or with increases in the drill diameter. Based on the experimental data, this paper established a formula model of the delamination factor F_d, which would promote the further study of drilling CFRP composites.

Abstract: Melt holding time has important influences on the modification effect of Sr modified AS31 alloy. Effects of different melt holding time (30min, 60min, 90min and 120min) at 700°C on as cast microstructure and tensile properties both at ambient temperature and elevated temperature of Sr-modified AS31 alloy were studied. There exist polyhedral shape, fine fibers shape and a few Chinese script Mg2Si particles in Sr-modified AS31 alloys. And the average grain size is smallest in Sr-modified AS31 alloys with holding time at 700°C for 30min. The ultimate strength, yield strength and elongation at both ambient temperature and 150°C decrease gradually when the melt holding time increases from 30min to 120min. In the process of smelting of Sr-modified AS31. The burning loss of Sr element becomes more serious with the prolongation of melt holding time, which contributes to the modification effect reducing.

Abstract: An extruded ZK60 magnesium alloy was subjected to artificial aging at 180 oC for an investigation of the effect of aging time on its precipitation behavior and mechanical properties. Uniaxial tensile tests were conducted to obtain the mechanical properties. Optical microscopy and transmission electron microscopy (TEM) were employed to observe microstructure change before and after aging treatment. It is shown that, both tensile yield strength and ultimate tensile strength increases with aging time. The fracture elongation after aging for 20 h reaches up to 21.0%, and the yield strength increases to 269.5 MPa, 19.4% higher than that of extruded specimens (un-aged), showing a good match of strength and ductility. Three newly-formed precipitates were observed after aging for over 20 h, among which particulate and dispersive precipitates should be responsible for the good combination of strength and ductility.

Abstract: As an environment-protecting waterborne coating, the cathodic electrodeposite coating has wide applications prospects.The self-crosslinked acrylate grafted epoxy resins for cathodal electrophoretic coating were synthesized by grafting acrylic polymer onto epoxy resin . This epoxy-acrylic copolymer both have high modulus, high-strength ,excellent chemical resistance and corrosion resistance of epoxy resin, and both have the light-acrylic resin fullness, good weather resistance and other characteristics of acrylic resin,which are widely used in the automotive, building materials, home appliances and other fields.The electrophoretic coating is an extremely complex process. The effects of the parameters of electrophoretic technology on the properties of paint films were studied systemically.The results show that the electrophoretic paint with better appearance and propeties can be made when voltage was about 90V,the solid share was 16%,pH was 5.8and electrophoresis time was 2-3min.

Abstract: Metal aluminum surface can be corroded easily in acid and alkaline environment. Inspired by the self-cleaning lotus leaf, the development of superhydrophobic metal surfaces to prevent metals from corroding is enjoying tremendous popularity amongst scientists and engineers. In this work, superhydrophobic surface was obtained on aluminum foils via a facile neutral sol solution immersion process and post-modification in ethanol solution of heptadecafluoro-1,1,2,2-tetradecyl trimethoxysilane (FAS-17) solution through a hydrothermal synthesis technique. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and water contact angle measurement are used to investigate the morphologies, microstructures, chemical compositions and wettability of the produced films on aluminum substrates. The results indicated that the superhydrophobic surface, configured of a rough labyrinth structure with convexity and notch, has robust hydrophobility, which had a static water contact angle of 165.6 ± 2.8° and a water roll-off angle of <1°, exhibited long-term durability and stability in air. The present research work provides a new strategy for the simple preparation superhydrophobic films on aluminum foil for practical industrial applications.

Abstract: The characteristics including surface morphology, phase constitution, thickness and the corrosion resistance of the porously anodic films prepared in the sulfuric electrolyte with different additives at 35°C were investigated by SEM, EDS, XRD and electrochemical polarization method in this paper. The additives are organic acids, polyhydric alcohols and rare earth (REE) salts. A porous anodic film with about 20 nm holes in diameter can be obtained by additives into the sulfuric electrolyte. The main chemical compositions of the anodic films are Al, O elements, and a small amount of S. The film after boiling water sealing is composed of boehmite (Al₂O₃·H₂O) and alumina (Al₂O₃) phases. The compactness and the thickness of the anodic films can be improved by the coupling effect of the additives, which increases the corrosion resistance of the film. The effect of additives on morphologies and corrosion resistance is discussed.

Abstract: The characterization in microstructure, morphology and oxidation behavior of three iron-based coatings by Supersonic Arc Spraying (HVAS), were investigated by XRD, FESEM, EDS and thermal exposure in furnace in this paper. It is indicated that the three coatings are typical layer and compact structure. The coatings are composed of Fe (s.s) phase and kinds of ferric oxides, chrome carbides and/ or intermetallic phase distributing along the interface of lamellar layers. More Cr and Ti, Al elements can alternate the diameter and morphologies of the holes, resulting from the formation of oxides, carbides and intermetallic phase. The results indicate that SXTiAlC coating shows the most excellent oxidation resistance with 2.70 mg·cm^-2 in mass gain, while that are 88.08 mg·cm^-2 and 16.64 mg·cm^-2 after 100 h thermal exposure at 800°C for LX88A and SXHCrA coatings, respectively. The oxidation behavior is discussed.