NUMERICAL SOLUTION OF FLUID-STRUCTURE INTERACTION IN LIQUID-FILLED PIPES BY METHOD OF CHARACTERISTICS

Fluid-structure interaction (FSI) is essentially a dynamic phenomenon and always exists in fluid-filled pipe system. The four-equation model, which has been proved to be effective to describe and predict the phenomenon of FSI due to friction coupling and Poisson coupling being taken into account, is utilized to describe the FSI of fluid-filled pipe system. Terse compatibility equations are educed by the method of characteristics (MOC) to describe the fluid-filled pipe system. To shorten computing time needed to get the solutions under the condition of keeping accuracy requirement, two steps are adopted, firstly the time step Δt and divided number of the straight pipe are optimized, sec-ondly the mesh spacing Δz close to boundary is subdivided in several submeshes automatically ac-cording to the speed gradient of fluid. The mathematical model and arithmetic are validated by com-parisons between simulation solutions of two straight pipe systems and experiment known from lit-erature.     

Passive Compliance Control of a Weld Inspection Manipulator for Intersecting Pipes

To inspect the welded joint of intersecting pipes in a nuclear power station, a weld inspection manipulator with a passive compliant end-effector was designed and manufactured, and a corresponding control strategy was realized based on a simple novel geometric method. The manipulator was composed of five observable articulations in series. The first three are controllable active articulations driven by servo motors and the other two are uncontrollable passive articulations preloaded by torsion springs. All of them were measured by rotary encoders. The geometrical analysis indicated that passive articulations could be controlled indirectly by adjusting the active articulations. The inverse kinematics question was resolved by the geometrical method in order to determine the relationship between the active articulation variables and the required position force of the end-effector. Then a method of cascaded position-force control was presented and a Matlab simulation was made to verify its validity. The simulation result proved that the control algorithm was of rapid convergence with high precision. To evaluate the quality of inspection, scanning experiments are implemented, which proved that the inspection task was successfully finished. The outcome of this study would provide an automatic manipulator for the welded joint inspection of numerous intersecting pipes in a nuclear power station.     

Investigation into use of side delaminations in interlaminar fracture mechanics

Abstract

Weft knitted glass fibre (GF) fabric reinforced poly(ethylene terephthalate) (PET) composite sheets were manufactured by hot pressing of stacked plain knitted fabric layers. The knits were produced from a commingled yarn containing 70 wt-% (≈50 vol.-%) GF. The reinforcing knits were stretched in the wale direction at various ratios prior to consolidation. The PET matrix of the composite was either amorphous or semicrystalline. The static mechanical performance of the knitted GF–PET composite sheets was studied in tension, compression, and flexure. Measurements were carried out on speci mens in both wale and course directions of the reinforcing knit in order to assess the structural anisotropy. The inherent anisotropy of the unstretched knit was well reflected in the strength data: the response in the wale direction was superior to that measured in the course direction. The mechanical anisotropy increased with increasing stretching of the knit. The dynamic perforation impact behaviour of the composites was determined by instrumented falling weight impact tests. The static and particularly the dynamic performance of the composites with amorphous PET was superior to that of the semicrystalline version.     

Thermal degradation kinetics of 6FDA/durene diamine/pPDA copolyimides

Abstract

Aromatic copolyimides have been synthesised from 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) with various mol-% of 2,3,5,6-tetramethyl-1,4-phenylene diamine (durene diamine (DDA)) and 1,4-phenylene diamine (pPDA) in N -methyl-2-pyrrolidone (NMP). Copolyimides were characterised by inherent viscosity, GPC, DSC, DMA, XRD, and TGA. Inherent viscosity and molecular weight increased with increase in DDA content in copolyimides. This was attributed to higher basicity of DDA than pPDA, which resulted in higher reactivity towards dianhydride. They were found to be soluble in all common solvents except CCl₄ and methanol. The glass transition temperature T _g of these amorphous copolymers increased with increase in DDA content; T _gs determined by DSC and DMA were comparable and T _g calculated using the Fox equation was compared with the experimental value. Thermal degradation of these copolyimides was found to follow second order kinetics in air. The activation energy E _a for the thermal degradation of these copolyimides in air was determined by both the Coats-Redfern and Chang methods and the result was comparable. Both Ea and ln A were found to decrease with increase in DDA content; CO₂ and trace amounts of CHF₃ were the decomposition products. The mechanism of thermal degradation is unique and is not affected by a change in the copolymer composition because all copolyimides display the kinetic compensation effect.     

Natural rubber–cassava starch foam by compression moulding

Abstract

The foaming processes of mixtures of cassava starch–water and cassava starch–natural rubber latex blends have been carried out by compression moulding. The appropriate conditions under which to produce expanded foam are as follows: a temperature of 150°C, 10·8 MPa pressure, and a 2 min moulding time. For the foam from the cassava starch with water as a blowing agent, it was found that water levels in the range of 150–200% by weight of the dry starch gave good conditions for foaming. The resulting foamed material has a uniform closed cell structure. Regarding blending of cassava starch with natural rubber, the natural rubber could not be dispersed in the gelatinised starch when blended at a temperature of 70°C. To stabilise and prevent the coagulation of natural rubber in the blending process, Nonidet P40, a nonionic surfactant, was used. A suitable amount of Nonidet P40 was 1·5% by weight of natural rubber latex. The compressive stress and the storage modulus of the foam obtained increased (42–233%) with increasing natural rubber content owing to the high elasticity of the natural rubber and its promotion of more elasticity to the foams. When 2–5% of benzoyl peroxide by weight of natural rubber was added to the rubber latex, the compressive stress of the foam was further increased (20–118%) owing to vulcanisation of the natural rubber. Furthermore, an addition of 15–30% of calcium carbonate by weight of the dry starch of the blends was found to increase the compressive stress and storage modulus of the foams (69–148%) and the hardness and brittleness of the foams.     

Establishing long-term behaviour of underground pressureless polyolefin materials

Abstract

This paper addresses the difficult problem of predicting service life in pressureless underground plastics pipes applications. Lifetime in such applications is generally determined by thermooxidative behaviour, which is governed principally by the type and amount of two classes of stabiliser: primary antioxidants and thio-synergistics. Ageing studies in water at 95°C have indicated that, for polypropylene (PP), mechanical performance is not influenced by exposure for up to six months (longer term trials are in progress). Despite this, aging in water can have a significant effect on the thermoxidative life of PP, by extracting antioxidant additives. As in pressurised pipe applications, determination of the combined effects of oxygen and water extraction is key to useful predictions of durability. In an attempt to improve life assessment, polypropylene plaques have been aged in contact with water at 95°C to determine the fitting parameters for Fickian diffusion. The residual stabiliser was measured directly by high-performance liquid chromatography (HPLC) and indirectly, using oven aging. Parameters have been determined for three phenolic primary antioxidants widely used in polyolefin pipes. Direct analysis by HPLC was found to give much lower scatter and hence is proposed as the more reliable method. A methodology is proposed to predict the lifetime of polyolefin pipe materials for underground sewerage applications avoiding the need to make tests on pipes.