Materials Science Forum Vols. 575-578

Abstract: In this paper, based on the analysis of coupled action of temperature, phase transformation and stress, the phase transformation condition and equation related to the thermal physical properties are discussed, and the transient temperature distribution of a Cr12 steel cylinder workpiece during gas quenching was obtained by solving the governing equations with a nonlinear boundary. According to the theories of thermal non-elasticity, computational mechanics and phase transformation, a new constitutive equation considering effects of phase transformation with a nonlinear surface heat transfer coefficient is proposed and is solved by means of finite element method (FEM). The thermal stress field is obtained and a way of simulating the technology of the heat treatment by computer is explored.

Abstract: Fiberglass continuous strand mat(CSM)/poly(urethane-isocyanurate) composites were formed by SRIM process, treated under different conditions and then characterized based on dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) ,transmission electron microscopy (TEM) and the mechanical property tests. The results show that the mechanical properties of the composites could be increased with improving the degree of microphase separation. At a given temperature (120°C), the degree of microphase separation is the highest for 4h and decreases gradually with prolonging treatment time. For a given time (4h), the well microphase-separated morphology is obtained and the degree of microphase mixing is increased at 120°C and 140°C treatments, respectively. The degree of microphase separation of the composites decreases with enhancing the temperature to 140°C.

Abstract: Welding is a main processing way in the manufacture of steel bridges. Welding deformation is one of the main influencing factors on the quality of steel bridges, which relates to the effect of material mechanical behavior and welding techniques. The welding distortion is considered to be a result from the inherent strain after welding, which dependent on the highest temperature reached and the constraint at each point. 16Mnq is a common structural steel used in railway steel bridges. Thus, the paper addresses the high-temperature mechanical behavior of 16Mnq through a series of experiments under various peak temperatures and constant constraint conditions. Relationships between temperature, constraint and strain at high temperatures were discussed. The yielding phenomenon based on high temperature occurs under a certain condition of both constraint and temperature, and this phenomenon had significant influence on the inherent strain. The results are significant to understand thermal-mechanical behavior of material and to predict the inherent strain under constant constraint conditions during heat circulates of welding.

Abstract: New dense and porous ceramics are developed using two formulation approaches. These are ceramics with remarkable content of mullite, corundum and ZrO2 - tetragonal and monoclinic in crystalline phase and porous (average size of pores up to 150-350μm) spinel-enstatite/forsterite ceramics. To promote the phase development by high-temperature synthesis of these ceramics the mineral raw materials – illite clay and illite clay together with dolomite are used. Bulk density for mullite (corundum) – zirconia ceramics is increased by equal addition of illite clay (8.2 wt.%) as well as ZrO2 and especially ZrO2 +Y2O3 to starting mullite mixtures. Contrary the addition of different kind and amount of illite clay together with dolomite trends to formation of spinel – enstatite (forsterite) ceramics and decrease the bulk density to the value up to 0.35 g/cm3. The XRD results indicate that ZrO2 monoclinic/tetragonal incorporation in mullite (corundum) structure realizes through the liquid phase. Development of the spinel MgAl2O4 and enstatite MgSiO3 crystalline phases along with the sufficient amount of glassy phase in microstructure and even distributed pores are proper for spinel-enstatite (forsterite) ceramic samples.

Abstract: The development of a new composite that is compounded of natural fibres and of a low price polymer, such as HDPE or PP, began in the last decade of the past century. While this is a rather new material no attempts have been made to analytically describe and simulate mechanical properties of this material. There is also a great lack of knowledge in describing fine tuned processing parameters. Therefore, in the first part of this article micromechanical approach based upon Generalised Method of Cells (GMC) is introduced to simulate properties of injection moulded wood-plastic composite compounded of polypropylene (PP) or polystyrene (PS) and of wood or cellulose short fibres. Materials have first been scanned with an optical and electron microscope to determine average fibre properties and their scatter. These values are then used to determine elastic and plastic response of the composite alongside with its tensile strength and maximum elongation, where the Tsai-Hill failure criterion has been used. The results of the simulation are then compared to experimental data in order to evaluate practical usage of this method. The second part of the article is focused on the simulation of injection moulding where test specimens were injected and the search for optimum injection parameters was performed. Various mechanical and rheological tests were performed and in addition practical industrial products were injected to observe the impact of various natural fibres on the filling of the mould cavity. Every experiment and process was then compared to the numerical simulation in order to evaluate applicability of numerical simulations under real conditions. On the basis of these experiments detailed mould design guidelines are given.

Abstract: High-energy synchrotron diffraction offers great potential for experimental study of recrystallization kinetics. A fine experimental design to study the recrystallization mechanism of Interstitial Free (IF) steel was implemented in this work. In-situ annealing process of cold-rolled IF steel with 80% reduction was observed using high-energy X-ray diffraction. Results show that, the diffraction intensity of {001}<110> and {112}<110> belong to α-fiber texture component decreased with the annealing temperature increased while {111}<110> did nearly not change and {111}<112> increased; the FMTH decreasing and d-space changing with annealing temperature increasing indicated that the residual stress relaxed completely during recovery.

Abstract: Microstructure and properties of plasma immersion ion implantation and deposition diamond-like carbon (DLC) films on bearing steel substrate were studied. Raman spectroscopy analysis indicates that PIII&D DLC consists of a mixture of amorphous and crystalline phases, with a variable ratio of sp2/sp3 carbon bonds, and the sp3 bonds content more than 10%. The nanohardness (H) and the elastic modulus (E) of DLC films measurement indicate that the maximum H (E) value is 40GPa (430GPa). The corrosion polarization curves prove that the corrosion resistance of DLC samples is much better than that of substrate. The friction and wear behaviors and rolling contact fatigue (RCF) life of these samples show that the friction coefficient decrease from 0.87 to 0.2; the L10 , L50 , La and L life of treated sample increases by 9.1, 3.2, 2.5 and 2.4 times, respectively. The RCF life scatter extent of treated samples is improved significantly.

Abstract: Processing of a large number of novel steel types, such as DP, TRIP, CP and TWIP, and high-strength low-carbon bainitic and martensitic DQ-T steels, have been developed based on physical simulation and modelling studies. Among stainless steels, guidelines for processing of ultra-fine grained austenitic stainless steels have been created. Physical simulation has been used by employing a Gleeble thermo-mechanical simulator to reveal the phenomena occurring in the hot rolling stage (the flow resistance, recrystallization kinetics and microstructure evolution), and in the cooling stage (CCT diagrams) for carbon steels and in short-term annealing of cold rolled metastable austenitic steels. Connecting these data with microstructures examined in optical and electron microscopes and resultant mechanical properties have improved the understanding on complex phenomena occurring in the processing of these steels and the role of numerous process variables in the optimization of enhanced mechanical properties.