Measurement and Correlation of Electrical Conductivity of β-Cyclodextrin in Water Solution

The electrical conductivity of 4% β-cyclodextrin in water solution had been measured by electrode method from（323.65~353.65） K at atmospheric pressure. The expe...     

Numerical modelling of small disc creep test

Abstract

The small disc creep test is described. The disc creep curves observed need to be related to the creep properties of the material obtained by conventional testing. This relationship should include a means of assessing the creep damage which is initially present in the material and therefore to an estimate of remanent life. There are difficulties with such correlations and these are shown to be related to an imperfect understanding of the complex nature of the small punch test. This understanding can be improved by suitable physical modelling of the deformation occurring. The present paper describes a suitable finite element model and verifies the model against experimental observations of disc creep tests. The model uses a realistic creep deformation law which includes strain hardening, thermal softening and damage accumulation for 0·5Cr0·5Mo0·25V steel. It is shown that the results obtained from the test are sensitive not only to the initial condition of the specimen but also to the conditions of the test (e.g. the values of frictional forces at the punch/specimen interface). The paper makes suggestions of how the model may be used to optimise the disc creep test.     

Role of Vertical Component of Surface Tension of the Droplet on the Elastic Deformation of PDMS Membrane

Poly(dimethylsiloxane) (PDMS) has been widely used in lab-on-a-chip and micro-total analysis systems (μ-TAS), thus wetting and electrowetting behaviors of PDMS are of great importance in these devices. PDMS is a kind of soft polymer material, so the elastic deformation of PDMS membrane by a droplet cannot be neglected due to the vertical component of the interfacial tension between the liquid and vapor, and this vertical component of liquid–vapor surface tension is also balanced by the stress distribution within the PDMS membrane. Such elastic deformation and stress distribution not only affect the exact measurement of contact angle, but also have influence on the micro-fluidic behavior of the devices. Using ANSYS code, we simulated numerically the elastic deformation and stress distribution of PDMS membrane on a rigid substrate due to the liquid–vapor surface tension. It is found that the vertical elastic deformation of the PDMS membrane is on the order of several tens of nanometers due to the application of a droplet with a diameter of 2.31 mm, which is no longer negligible for lab-on-a-chip and μ-TAS. The vertical elastic deformation increases with the thickness of the PDMS membrane, and there exists a saturated membrane thickness, regarded as a semi-infinite membrane thickness, and the vertical elastic deformation reaches a limiting value when the membrane thickness is equal to or thicker than such saturated thickness.     

Experimental investigation and numerical analysis of compaction behaviour of moulding sand

Abstract

The compaction behaviour of green sand was studied to assess the applicability of the Cooper–Eaton equation under conditions close to those of real foundry operations. The results indicate that the Cooper–Eaton equation describes the behaviour reasonably well, allowing prediction of the pressure required to achieve sand moulds of reasonable density. A corresponding distinct element method numerical simulation was also attempted. The study contributes useful information to the understanding of green sand compaction. It is clear that spherical sand is preferable to improve filling behaviour and that the gap between mould wall and pattern must be sufficiently large to avoid prevent weak sand compaction.     

Compression characteristics of 6Cr21Mn10MoVNbN heat resistant valve alloy at elevated temperatures

Abstract

6Cr21Mn10MoVNbN is a new type of alloy used for heavy duty engines. Thermal simulation, metallography, X-ray diffraction and theoretical analysis have been used to study the deformation behaviour of the alloy at elevated temperatures. By introducing an internal variable parameter, a constitutive equation has been suggested for the dynamic calculation of the stress/strain curve for this alloy based on the Zerrilli–Armstrong equation used for fcc materials. The data calculated using the equation developed agree fairly well with the experimental data. The microstructure of the alloy is found to depend greatly on temperature and strain rate. When the alloy is deformed at 850°C, Cr₂₃C₆ precipitates from the matrix. The lower the strain rate, the more Cr₂₃C₆ precipitated from the matrix. At the same time, the amount of Cr₂₃C₆ decreases with increasing temperature. Between 850 and 1050°C, the amount of NbN in the alloy increases with increasing temperature and reaches a peak at 1050°C. NbN begins to decrease when the temperature gets to 1150°C. At this temperature, carbides and nitrides in the alloy, especially those distributed on the grain boundaries, begin to be dissolved into the matrix in great deal. The microcracks propagate easily along the grain boundaries of the alloy.     

Analytical Solution of the Forward Position Analysis of Parallel Manipulators That Generate 3-RS Structures

In this work the forward position analysis (FPA) of 3-RS structures (R, S, P and C = revolute, spherical, prismatic and cylindrical, respectively) is carried out applying recursively the Sylvester dialytic elimination method. The analytical solution provided in this contribution yields 16 possible poses of the moving platform given the limb lengths of the manipulator and it is applicable to a wide class of parallel manipulators, e.g., the 3-RP*S mechanism, 3-CP*S mechanism, 6–3 Gough–Stewart platforms and 3-RR*S mechanism. A case study is included which consists of solving the FPA of a 3–3 Gough–Stewart platform, also known as an octahedrical mechanism.     

Numerical analysis of particle transport during solidification using models based on stochastic differential equation

Abstract

In the present work, a comprehensive theoretical model is developed to describe the particle transport mechanisms in a solidifying binary melt in the presence of random thermofluidic fluctuations offered by the surrounding fluid medium. The detailed transport phenomena in the particle and bulk phases are coupled together through a stochastic formalism, capturing the physical mechanisms and consequences of complex interparticle interactions and the associated growth and/or dissolution of the crystals. The equation of the motion of the particles is modelled using the theory of stochastic differential equations. Numerical simulation study reveals the statistically randomised nature of the evolution of particle phase, which otherwise cannot be captured from a purely deterministic viewpoint. The mathematical model is also tested by comparing present numerical results with reported experimental observations; a very good agreement can be observed in this regard, thereby establishing the authenticity of the proposed formulation.     

Mould powder consumption of continuous casting operations

Abstract

Mould powder consumption is an important parameter in continuous casting. Previous investigations, involving regression analysis or estimation of powder consumption, have identified the factors controlling powder consumption. However, those data were obtained for casting speeds less than 2 m min ^-1, and some relate to speeds less than 1 m min ^-1. Sumitomo Metal Industries has developed a medium thick high speed continuous casting operation for speeds between 2 and a maximum of 8 m min ^-1. Some of the powder consumption data obtained using the new process could not be explained on the basis of the former investigations: these data are discussed in the present report. The conclusions drawn are: (i) gravity is the main driving force for inflow of liquid powder between mould wall and solidified shell; (ii) to increase the powder consumption per unit strand surface area for speeds of ~8 m min ^-1 is difficult; and (iii) a powder consumption of under 0·1 kg m ^-2 is sufficient when casting at 8 m min ^-1.