Papers by Keyword: Thermal Expansion

Abstract: High speed transmission table is wildly used in industry and the demand is increased recently. High speed ball-screw device is a major component in the system. High speed transmission brings high friction and causes serious thermal displacement, especially in vertical transmission situation. Because the external load is become axial load applied on nut directly. Friction and wear became heavier on contact areas between ball and raceways, preload in ball-screw will thus be decreased speedily with operating time. The decrease of preload is also affect thermal rising rate and thermal displacement.The work of this paper is to establish a thermal elastic-viscous hydrodynamic lubrication (EHL) analysing model for friction calculation. Contact and friction forces of each contact area varying with operating conditions of ball-screw can be obtained as boundary conditions of FEM model, and theoretical results were well confirmed with surface temperature and displacement of screw. The aim of the study is useful in understanding thermal effect for a preloaded double nut ball-screw in vertical transmission.

Abstract: The paper introduces the possibility to replace the “wet alloy”, used for sprinkler-triggering within automatic fire protection systems, with a shape memory alloy (SMA) type. The idea of the present application is based on the thermoelastic reversible martensitic transformation, governing SMA functioning, which has completely reversible character, and enables the occurrence of two-way shape memory effect (TWSME) after the application of a thermomechanical treatment called “training”. For this purpose a commercial NiTi rod, which was martensitic at room temperature, was subjected to thermal analysis tests, performed by differential scanning calorimetry (DSC) and dilatometry. Martensite (M) reversion to parent phase (A), during heating, was emphasized by an endothermic peak on the DSC thermogram and by a length shrinkage, on the dilatogram. The capacity to develop TWSME was revealed by the change in displacement-temperature variation, with increasing the number of training cycles. This stabilized fully reversible behavior recommends NiTi rods as executive elements of a new concept of resettable sprinkler for fire protection.

Abstract: In this work, AZ91D composite reinforced with M40 fiber was prepared by pressure impregnation method. Expansion behaviors of M40/AZ91D composite were studied with thermal expansion instrument in 25-150 °C and 25-150 °C temperature ranges of internal heat circulation, and then analyzed the influence law of hysteresis, residual strain and coefficient of thermal expansion (CTE) by different temperature change rate. The results revealed that residual stress and strain in process of pressure impregnation would lead to strain hysteresis and residual strain of composite in thermal cycling. At the same time, the CTE of the composites decreased with the increase of cycle times. Residual strain of the composite went up with the rise of temperature changed rate of the thermal cycling and CTE decreased with temperature change rate ascending in the 25-150°C temperature range. The CTE of the composites decreased with the increase of temperature during the heating process, which cut down with the increase of temperature in process of heating and cooling in the 25-495°C temperature range.

Abstract: Graphite has attracted both academia and researchers due to its outstanding properties such as having strength 200 times stronger than steel, great efficiency of heat and electricity conduction, low cost and also facile fabrication. In this study, two facile approaches of producing nanosize graphite were performed; thermal expansion and sonication. Graphite that was produced are used as reinforcement in epoxy composite for adhesive applications. In order to determine the mechanical properties of the composite, tensile test was performed using Dumbbell shape of sample. The outcome of the test shows that 1 wt% of expanded graphite produce the highest value of Young Modulus which is 18 MPa. It was also found that adding more expanded graphite increased the ductility of composite by lowering epoxy brittleness. As for adhesive testing, double cantilever beam was used using Universal Testing Machine where the result shows that 1 wt% of expanded graphite demonstrates the highest value of adhesive toughness which is 9398 J/m2. The result of porosity-density indicates that porosity of composites will affect the mechanical properties. From the overall results, it is conclude that smaller weight percentage of expanded graphite produces better composite while for sonication process shows no difference at all. Thus demonstrates that time of dispersion does not give significant effect on the maximum load and stress of the composites.

Abstract: The fabrication and thermal physical properties contain thermal conductivity (TC) and coefficient of thermal expansion (CTE) using 40%、50%、60% vol% β-SiC particle reinforced Al composite for electronic packaging respectively have been analyzed. The composites were produced by ball milling and pressing method. The composite which fabricated by tri-sized β-SiC particle with a weight ratio of 17:7:1,vol% of 50% and 60%.The dense and morphology were investigated. The relationship between volume fraction of β-SiC particle and thermal physical properties was discussed. Changed the volume fraction of β-SiC particle will led to a decreasing or increasing of TC and CTE. It found that values of TC and CTE were achieved their maximum balance when using tri-sized β-SiC particle of 160μm ,125μm as well as 38μm with a weight ratio of 17:7:1 and 50%vol of β-SiC particle reinforcing.

Abstract: Highly porous cordierite ceramic by using of talcum, kaolinite and γ-alumina was obtained by method of slip casting of concentrated suspension. Additives of amorphous silica and non-stabilized zirconia in the amount of 5 wt% were used. Sintering temperature of dried samples was in range of 1250 – 1450°C. All the samples contain crystalline phases of cordierite, mullite and corundum but, depending on the additives, as a result of sintering in addition forms spinel, cristobalite or zircon (ZrSiO₄). Porosity of obtained materials changes in large scale from 42 to 59 per cent; it is influenced by both sintering temperature and composition. Compressive strength increases with the addition of zirconia. In comparison, compressive strength of samples without additives or with silica additive does not exceed 3.5 MPa. The increase of coefficient of thermal expansion depends both on the composition and sintering temperature. ZrO₂ additive increases the coefficient of thermal expansion considerably.

Abstract: Metastable β titanium alloy Ti-15Mo was investigated in this study. In-situ electrical resistance and thermal expansion measurements conducted on solution treated material revealed influence of ongoing phase transitions on measured properties. The monotonicity of the dependence of electrical resistance on temperature changes at 225, 365 and 560 °C The thermal expansion deviates from linearity between 305 and 580 °C.

Abstract: Abstract. The negative expansion observed at low temperatures in specific crystallographic directions of complex structures with anisotropic interactions is explained by microscopic analysis within the tight-binding, quasi-harmonic approximation of lattice dynamics. The results agree with measurements on multilayer sandwiches of transition-metal dichalcogenides, high-temperature superconductors and relevant nanostructures including the carbon-based nanotubes.

Abstract: Series of the mixed cobaltites-ferrites RCo_1−xFe_xO₃ (x = 0.1–0.9) and cobaltites-chromites RCo_0.5Cr_0.5O₃ (R = Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er) with the orthorhombic perovskite structure (space group Pbnm) have been prepared from stoichiometric amounts of rare earth oxides, Co₃O₄, Fe₂O₃ and Cr₂O₃ by solid-state reaction in air at 1473–1573 K. In situ high-temperature X-ray synchrotron powder diffraction revealed anomalous lattice expansion of both series, which is reflected in a sigmoidal dependence of the unit cell dimensions and in abnormal anisotropic increase of the thermal expansion coefficients (TEC). Depending on the composition, several broad maxima in the temperature range of 500−1000 K are observed, which are evidently connected with the transitions of Co³⁺ cations to the higher spin states. The observed anomalies in the mixed cobaltites-ferrites and cobaltites-chromites are less pronounced compared with the corresponding “pure” cobaltites.

Abstract: Microdamage, viscoplastic and viscoelastic strain development in 90-layers of cross-ply laminates subjected to tensile loading is studied on unsymmetrical GF/EP laminates measuring the thermal curvature change. All three phenomena partially compensate for the effect of the thermal mismatch reducing the residual stress (specimen curvature). The viscoplastic strain contribution to curvature change is the largest whereas the effect of transient viscoelasticity is the smallest. Damage is included in the analysis through its effect on the effective transverse modulus of the 90-layer.