Mode I quasi–static and fatigue delamination characterisation of polymer composites for wind turbine blade applications

Abstract

Ambitious electricity generation targets from renewable sources set by many governments have lead to the rapid growth of the wind energy industry over the last two decades. The need for larger wind turbine blades for increasing energy generation has considerably increased the demand and use of high performance composites in wind turbine applications, mainly in blades. A common type of failure in composite materials is delamination of adjacent layers, which can occur either due to manufacturing inconsistencies or due to in service loads. Understanding and characterising delamination is very important in order to implement damage tolerant design methodologies. The present research work focuses on the assessment of the delamination behaviour of composites for wind turbine applications. Several composite systems were tested and their fracture toughness and fatigue delamination propagation behaviour under mode I (peeling) loading conditions were evaluated. Quasi–static tests were performed and delamination initiation values were evaluated. Fatigue delamination growth rate curves (da/dN versus G _Imax) were also produced. The carbon/epoxy and glass/epoxy material systems tested were compared in terms of resin type, fibre type and interfacial characteristics.     

Influence of Prior Deformation on The Sensitisation of AISI Type 304 Stainless Steel and Applicability of EPR Technique

Abstract

The influence of prior plastic deformation on the degree of sensitisation (DOS) of AISI 304 stainless steel has been studied for various levels of cold work ranging from 0 to 25% using the ASTM standard A262 practices A and E, and the electrochemical potentiokinetic reactivation (EPR) technique. Peak current density and reactivation charge density were determined from single loop EPR experiments and the ratio of the peak current during reactivation to that during activation was determined from double loop EPR experiments. The feasibility of using these techniques for determining the DOS in cold worked samples was examined. The reproducibility of the EPR results is rather poor. There appears to be no well defined systematic trend between the degree of cold work and the DOS as estimated from the EPR parameters. EPR parameters were found to be dependent on the temperature of aging and the degree of prior cold work. Threshold values above which a sample can be treated as sensitised cannot therefore be determined from EPR tests without being confirmed independently by conventional ASTM standard methods.     

Condition monitoring and prognosis of utility scale wind turbines

Abstract

The state of the art in condition monitoring in wind turbines, and related technologies currently applied in practice and under development for aerospace applications, are reviewed. Condition monitoring systems estimate the current condition of a machine from sensor measurements, whereas prognosis systems give a probabilistic forecast of the future condition of the machine under the projected usage conditions. Current condition monitoring practice in wind turbine rotors involves tracking rotor imbalance, aerodynamic asymmetry, surface roughness and overall performance and offline and online measurements of stress and strain. Related technologies for monitoring of load history and fatigue crack growth in aircraft structures are evaluated for their applicability to wind turbine blades. Similarly, condition monitoring practice in wind turbines is compared with monitoring and prognosis in helicopter gearboxes. The state of the art in condition monitoring of electronic controls, power electronics and towers is also evaluated and compared with the state of the art in aerospace. Based on these comparisons, technology needs and future challenges for the development of condition monitoring and prognosis for large wind machines, both onshore and offshore, are summarised.     

A review of materials degradation in utility scale wind turbines

Abstract

This paper presents a comprehensive review of the state of knowledge of materials used in the major wind turbine components of both land based and offshore wind turbines. The paper is divided into the following seven major sections: utility scale wind turbine design overview; current state of wind turbine technology; review of degradation of materials used in wind turbines; a summary of materials degradation service experience; condition monitoring overview; review of materials based research and development for wind turbines; a summary of missing knowledge and future materials challenges. The review points out that the most important degradation mechanism is fatigue which limits the life, reliability and performance of current wind turbines. As even larger machines are built in the future, with pressures to cut weight and cost, continued materials research and development, as summarised in this paper, is warranted. This critical assessment and review of materials based degradation should be of interest to a wide range of technical energy specialists including those from manufacturers, research and development centres, end users (i.e. electric power generation companies) and financiers and insurers.     

基于WEB的嵌入式机电设备管理软件的设计与开发

本文主要讨论嵌入式机电设备利用WINDWEBSERVER进行设备接口开发,以及管理系统软件结构开发中的关键技术,介绍了机电设备管理系统应用软件的设计与开发。     

The simulation and error analysis of raindrop size distribution obtained by micro rain radar

Observation of raindrop size distribution( DSD) with a vertically pointing micro rain radar( MRR) has important significance in the precipitation measurement field. The Mie scattering of large particle,vertical wind and air turbulence have great influences on the retrieval of DSD measured by MRR. This paper simulates the process of how three factors affect the inversion of DSD and the calculation of other precipitation parameters,then makes the errors analysis. Because the wavelength of MRR is 12.5mm,M ie theory is more suitable for the precipitation particle than Rayleigh approximation,w hich may cause the underestimation of number density of small droplets and the overestimation of that in middle field. The vertical wind results in inaccurate estimation of particle terminal velocity,so the diameter is measured with some errors by empirical relationship,w hich affects the calculating accuracy of radar reflectivity and rain rate. Air turbulence can broaden the pow er spectral density,of which the impact on the inversion of DSD are concentrated in small droplets field. Then the measured data from MRR is analyzed and the results prove the impacts of those factors. Finally,according to the analysis and application limits,the prospect of the future research trend of particle size distribution is conducted.     

A wind turbine battery charger for Africa

The principal objective of the project was to examine the proposition that a wind turbine rated at about 500 watts could be manufactured in Zimbabwe and that it could operate cost-effectively in the low-windspeed conditions characteristic of that country.The results from the test programme between 12 July and 1 November 1996 show that the turbine produced 392 kWh at an average of 106 kWh per month, 134W mean. This output is the equivalent of nineteen 50-watt PV panels at that site. The equivalent cost was 20% of the PV alternative, with a Foreign currency requirement of less than 5%.The project has been a practical demonstration of the potential for linking specialist external design expertise with indigenous industrial capacity. The outcome is a locally-manufactured product for both the domestic and export markets, capable of competing in one of the fastest growing sectors of the renewable energy industry.     

感受风的速度

接到约稿的通知,正忙得不可开交。第二天下午四点半,一档大型户外特别节目就要开始录制,我担任这个访谈节目的主持人,还有好些案头工作没有完成,加加班吧。“有班加是幸福的”,每次在疲惫之中总是给自己这样的鼓励。这种疯狂的工作状态虽然辛苦,但至少说明生活是充实的。     

Statistical analysis of metastable pitting events on carbon steel

Abstract

The metastable pitting behaviour of galvanically coupled and potentiostatically controlled A516–70 carbon steel in a chloride containing solution has been statistically analysed. It is shown that the pitting activity, indicated by the pit initiation rate, depends on immersion time, applied potential, and chloride concentration. There is a strong correlation among the pitting events at a high pitting activity, where the metastable pitting events follow non-Poissonian behaviour and a previous pit has an influence on subsequent pitting events. When the pitting activity decreases, the correlation decreases and approaches the Poisson distribution.