CAX技术在纤维复合机构研制过程中的应用

纤维复合结构在非高技术领域的应用日渐广泛.现在并不是只有诸如飞机制造、船舶制造和赛车运动这一类众所周知的应用领域采用这种引人注目的材料.本文将阐述如何借助三维CAD系统("Catia"V5)模拟层合结构从设计到制造的整个研制过程.重点论述复杂的壳结构,同时也考虑集成在"Catia"V5中的"第三方"产品以支持整个研制过程.     

Hollow Poly(3‐hydroxybutyrate) Fibers Produced by Melt Spinning

Native and nucleated PHB has been melt‐spun and the properties of the resulting fibers have been investigated. Biocompatible nucleating agents such as HAP and THY were compared to BN as a reference material. DSC was used to investigate the non‐isothermal crystallization kinetics as a function of processing temperature and cooling rate. It was found that particularly the choice of process temperature can ensure sufficient primary crystallization of native PHB: heating not higher than 10–15 K above the melting temperature induced a favorable crystallization behavior of native PHB. Thus, melt spinning at low process temperatures without additives was demonstrated to be the key to the formation of well‐defined hollow PHB fibers.

     

A Viscoelastic Analysis of the Creep Behaviour of a Chopped Strand Mat E-Glass Fibre Reinforced Vinylester Resin

The viscoelastic response of a chopped strand mat E-glass fibre reinforced vinylester resin has been studied over a wide range of applied stress levels. At low applied stress levels, the material exhibited a linear viscoelastic response well represented by Schapery's power law model with constant C and n terms. At higher stresses nonlinear behaviour was observed which apparently is caused by the multiplicity of complex local phenomena associated with and preceding damage development (plastic deformation of the matrix, interfacial slippage, fiber-matrix debonding). The limits of linear viscoelastic behaviour and of damage initiation – about 0.48% strain or 42 MPa – coincide for this material. However, for successful modelisation of uniaxial creep strain in the nonlinear range a modified power law is proposed which uses stress-dependent creep parameters C and n.     

Ultimate Load Capacities of Plane and Axisymmetric Headed Anchors

A finite-element-based linear elastic fracture mechanics analysis of the pullout of headed anchors is presented. The anchor is modeled as a vertically loaded crack of diameter c, embedded at a depth d, with a rigid upper surface, and traction-free lower surface. The fracture toughness and Poisson's ratio of the surrounding matrix are KIc and ν, respectively. For selected values of d∕c, the mode-I stress intensity factor is calculated for each increment of the crack growth, which emanates from the edge of the anchor, and follows the direction of zero mode-II stress intensity factor. The stress intensity factors are used to calculate the ultimate load Pu, which is written as Pu = g(d∕c, ν)d3∕2KIc. For ν = 0.2 and relatively large values of d∕c, g = 2.8 for axisymmetric anchors and g = 1.2 for plane strain anchors.     

Investigation of wind turbine wake superposition models using Reynolds‐averaged Navier‐Stokes simulations

It is well accepted that the wakes created by upstream turbines significantly impact on the power production and fatigue loading of downstream turbines and that this phenomenon affects wind farm performance. Improving the understanding of wake effects and overall efficiency is critical for the optimisation of layout and operation of increasingly large wind farms. In the present work, the NREL 5‐MW reference turbine was simulated using blade element embedded Reynolds‐averaged Navier‐Stokes computations in sheared onset flow at three spatial configurations of two turbines at and above rated flow speed to evaluate the effects of wakes on turbine performance and subsequent wake development. Wake recovery downstream of the rearward turbine was enhanced due to the increased turbulence intensity in the wake, although in cases where the downstream turbine was laterally offset from the upstream turbine this resulted in relatively slower recovery. Three widely used wake superposition models were evaluated and compared with the simulated flow‐field data. It was found that when the freestream hub‐height flow speed was at the rated flow speed, the best performing wake superposition model varied depending according to the turbine array layout. However, above rated flow speed where the wake recovery distance is reduced, it was found that linear superposition of single turbine velocity deficits was the best performing model for all three spatial layouts studied.     

Extracting angles of attack from blade‐resolved rotor CFD simulations

The distribution of the angles of attack over the span of a rotor blade, together with blade element theory, provides a useful framework to understand forces, performance and other fluid dynamic phenomena of axial‐flow rotors. However, the angle of attack is not straightforward to define for a three‐dimensional rotor, where the flow is perturbed by the blade circulation, shed vorticity and wake development. This paper evaluates six methods to extract the angles of attack from blade‐resolved CFD simulations of axial‐flow turbines. Simulations of two different rotors are presented: a low solidity rotor designed for wind and a higher solidity rotor designed for tidal stream energy conversion. Of the analysed methods, five were obtained from the literature and are tested in terms of their internal parameters. The remaining method is named the streamtube analysis method (SAM) and is presented as an improvement on analysis methods that azimuthally average the flow data on the rotor plane, referred to as azimuthal averaging techniques (AATs). The SAM method accounts for the expansion of the streamtubes in flow‐field velocity sampling and exhibits improved convergence on the internal parameters compared with AAT. The six methods are benchmarked in terms of the angles of attack, axial induction factors and the local lift and drag coefficients, identifying that most perform well and converge with each other despite the different underlying assumptions or modelling approaches. However, given the limitations and inherent dependency on internal parameters, the line averaging and SAM are suggested for general flow analysis application.     

Effects of thermal stressing on saturated vegetable oils and isolated triacylglycerols ‐ product analysis by MALDI‐TOF mass spectrometry,NMR and IR spectroscopy

It is well‐known that triacylglycerols in vegetable oils undergo slow oxidative modifications upon storage particularly at elevated temperatures. This has been shown primarily for oils with unsaturated fatty acid residues that are most sensitive towards oxidation. Saturated oils, however, were by far less investigated. In the present study saturated oils (coconut oil) as well as isolated triacylglycerols were exposed to defined thermal stressing and the resulting products were investigated in dependence on temperature and the heating period. Matrix‐assisted laser desorption and ionization spectrometry, ¹³C and ³¹P nuclear magnetic resonance spectroscopy and infrared spectroscopy were used for the characterization of the native as well as the thermally stressed oil samples. These methods were used since they provide both, fast and reliable information on oil composition and can be performed faster than other more established methods. We found that the degradation mechanism of saturated fatty acids is completely different from unsaturated fatty acids. Whereas unsaturated oils are primarily depleted under the cleavage of the double bonds, saturated oils undergo a conversion of one methylene group into a carbonyl group. This was independently demonstrated by all applied methods for the triacylglycerols as well as for the free fatty acids derived after saponification.     

Influence of the Metal Ions Cr3+, Fe3+, Ni2+ and Cu2+ on the Stability and Oxygen Consumption of Acrylic and Methacrylic Acid

For the safe and trouble‐free operation of a manufacturing plant and the safe storage of acrylic, as well as methacrylic monomers, it is important to know the polymerization stability as a function of the process parameters (temperature, oxygen concentration, and impurities, e.g., metal ions). Contamination with metal ions can be caused by the corrosion of steel units. Therefore, the influence of the metal ions Cr³⁺, Fe³⁺, Ni²⁺ and Cu²⁺ in the concentration range of 0–10 ppm (g g^–1) on the polymerization behavior and the oxygen consumption of acrylic and methacrylic acid were examined in this work. It was shown that Cr³⁺, Ni²⁺, and Cu²⁺ ions extend the inhibition period of acrylic acid (AA) and methacrylic acid (MAA) and reduce the O₂ consumption. Fe³⁺ ions, however, cause a decrease of the inhibition period and in the case of AA an increase of the O₂ consumption, which leads, in the end, to a faster unintentional polymerization. Therefore, alloys which contain iron should be avoided as far as possible in the construction of AA plants. Fe³⁺‐ions show the opposite influence towards MAA, here the presence of Fe³⁺ shows a stabilizing effect.