The research presented in this article focuses on a 9-m CX-100 wind turbine blade, designed by a team led by Sandia National Laboratories and manufactured by TPI Composites Inc. The key difference between the 9-m blade and baseline CX-100 blades is that this blade contains fabric wave defects of controlled geometry inserted at specified locations along the blade length. The defect blade was tested at the National Wind Technology Center at the National Renewable Energy Laboratory using a schedule of cycles at increasing load level until failure was detected. Researchers used digital image correlation, shearography, acoustic emission, fiber-optic strain sensing, thermal imaging, and piezoelectric sensing as structural health monitoring techniques. This article provides a comparison of the sensing results of these different structural health monitoring approaches to detect the defects and track the resultant damage from the initial fatigue cycle to final failure.
A fatigue test of a wind turbine blade was conducted a t the National Renewable Energy Laboratory in the fall of 1994. Acoustic emission monitoring of the test was performed, starting with the second loading level. The acoustic emission data indicated that this load exceeded the strength of the blade. From the first cycle a t the new load, an oil can type of deformation occurred in two areas of the upper skin of the blade. One of these was near the blade root and the other was about the middle of the tested portion of the blade. The emission monitoring indicated that no damage was taking place in the area near the root, but in the deforming area near the middle of the blade, damage occurred from the first cycles a t the higher Ioad. The test was stopped after approximately one day and the blade was declared destroyed, although no gross damage had occurred. Several weeks later the test was resumed, to be continued until gross damage occurred. The upper skin tofe approximately one half hour after the cycling was restarted.
The technology of acoustic emission (AE) testing has been advanced and used at Sandia for the past 40 years. AE has been used on structures including pressure vessels, fire bottles, wind turbines, gas wells, nuclear weapons, and solar collectors. This monograph begins with background topics in acoustics and instrumentation and then focuses on current acoustic emission technology. It covers the overall design and system setups for a test, with a wind turbine blade as the object. Test analysis is discussed with an emphasis on source location. Three test examples are presented, two on experimental wind turbine blades and one on aircraft fire extinguisher bottles. Finally, the code for a FORTRAN source location program is given as an example of a working analysis program. Throughout the document, the stress is on actual testing of real structures, not on laboratory experiments.
Prepared by Sandia National Laboratories Albuquerque, New Mexlco 87185 and Livermore, California 94550 for the United States Department of Energy under Contract DE-AC04-94AL85000 Approved for public release; distribution is unlimited.
The effects of hydrostatic pressure between 0 and 22 kbar on the elastic constants of SrTiO3 were measured at 295°K. All constants increased linearly with pressure in this range. The pressure derivatives of the adiabatic constants dCij/dP are: 10.21±0.15, 3.51±0.15, and 1.24±0.05 for C11, C12, and C44, respectively. These pressure derivatives, in conjunction with the recent second-harmonic generation results of Mackey and Arnold, allow us to determine the complete set of third-order elastic constants. The results, in units of 1012 dyn/cm2, are: C111=−49.6±4.3, C112=−7.7±1.6, C123=+0.2±4.3, C144=−8.1±2.4, C166=−3.0±1.2, and C456=0.9±2.7. Combined with the temperature derivatives of the (second-order) elastic constants at constant pressure, the pressure results allow a determination of the explicit volume and temperature dependences of these constants. In addition, the present results allow us to calculate the acoustic mode Grüneisen parameters, an approximate value of the limiting Grüneisen constant, γ0=1.52, and the coefficients of the polynominal and logarithmic (Murnaghan) forms of the high-pressure equation of state of SrTiO3.
A 9 meter TX-100 wind turbine blade, developed under a Sandia National Laboratories R&D program, was recently fatigue tested to blade failure at the National Renewable Energy Laboratories, National Wind Technology Center. The fatigue test provided an opportunity to exercise a number of structural health monitoring (SHM) techniques and nondestructive testing (NDT) systems. The SHM systems were provided by teams from NASA Kennedy Space Center, Purdue University and Virginia Tech (VT). The NASA and VT impedance-based SHM systems used separate but similar arrays of Smart Material macro-fiber composite actuators and sensors. Their actuator activation techniques were different. The Purdue SHM setup consisted of several arrays of PCB accelerometers and exercised a variety of passive and active SHM techniques, including virtual and restoring force methods. A commercial off-the-shelf Physical Acoustics Corporation acoustic emission (AE) NDT system gathered blade AE data throughout the test. At a fatigue cycle rate around 1.2 Hertz, and after more than 4,000,000 fatigue cycles, the blade was diagnostically and visibly failing at the blade spar cap termination point at 4.5 meters. For safety reasons, the test was stopped just before the blade completely failed. This paper provides an overview of the SHM and NDT system setups, and some test results.
Longitudinal and shear velocities have been measured as a function of temperature in polycrystalline samples of ScH1.99, YH1.93, and ErH1.81. From these measurements values of the limiting Debye temperature, θ0, the bulk modulus, Young's modulus, the shear modulus, and Poisson's ratio are calculated.
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