Theses and Dissertations at Montana State University (MSU)
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/733
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Item Fatigue of skin-stiffener intersections in composite wind turbine blade structures(Montana State University - Bozeman, College of Engineering, 2000) Morehead, Robert B.Item Modeling of in-plane and interlaminar fatigue behavior of glass and carbon fiber composite materials(Montana State University - Bozeman, College of Engineering, 2007) Wilson, Timothy James; Chairperson, Graduate Committee: Douglas S. CairnsThis thesis presents the results of a modeling study of the fatigue behavior of fiberglass and carbon fiber reinforced epoxy composite materials intended primarily for wind turbine blades. The modeling effort is based on recent experimental results for infused glass fiber laminates typical of current blades, and hybrid carbon prepreg laminates of potential interest for future blades. There are two focus areas: in-plane performance represented by stress-life (S-N) curves, and out-of-plane ply delamination at details including ply drops and joints, based on fracture mechanics. In-plane fatigue models for both the mean performance and a statistically fit model with a 95/95 confidence limit were developed for three laminates, each representative of lower cost materials with applications in the wind turbine industry. These include polyester and epoxy resin infused glass fabrics and a hybrid carbon prepreg; two of the materials were tested in the axial and transverse directions. Models were adapted for the S-N results at several uniaxial loading conditions, including special treatment of the time dependence at high loads.Item Fatigue performance of macro-fiber piezoelectric composite actuator with respect to variable beam geometry(Montana State University - Bozeman, College of Engineering, 2012) Rosatti, Lyric Michael; Chairperson, Graduate Committee: David A. MillerThis study is an investigation into the reliability and performance over the lifetime of the piezoelectric fiber composite, macro fiber composite (MFC), with respect to variable beam geometry. MFC's are a class of smart structure utilizing the piezoelectric effect. The MFC is a thin flexible composite system that can be laminated to surfaces or embedded in classic composite structures for actuation and sensing. These piezocomposite structures are rectangular patches made of Lead-Zirconium-Titinate (PZT) piezoceramic fibers, copper-clad polyimide film, and epoxy. MFC's were originally developed at NASA Langley Research Center and are now commercially available from a single manufacturer. In this study, lifespan and performance were characterized by using the MFC as an actuator to impart deflection in a substrate. This structure is referred to as a Unimorph. The beam geometry affects the bending stiffness of the beam, and thus affects the reaction of the MFC. The only free geometrical dimension in this study was beam height. The unimorph was actuated cyclically by an electrical field of 3E+6 volts per micron at a frequency of 3750 Hz. Expected cycles to failure was 10 9 cycles. The test specimens consisted of cantilevered A2 tool steel beams, with six discrete beam heights, and an MFC patch laminated to one surface by a two-part epoxy. Beam tip displacement measurements were taken using a laser displacement sensor as an indication of cyclical performance over time. The beams were cycled until failure or 10 9 cycles for all beam geometries. The results of the experiment indicate a severe drop off in life with an increase of work energy out of the system. This is a function of the ratio of beam stiffness to MFC stiffness. After a break-in period of less than 250E+6 cycles, no significant degradation in operational performance was indicated by the recorded tip displacement despite an immense amount of crack propagation in the piezoceramic fibers. The results of this testing can be used in designing piezoelectric actuators and as a basis for further study of MFC's.Item Internal damage characterization for composite materials under biaxial loading configuration(Montana State University - Bozeman, College of Engineering, 2007) Smith, Jay David; Chairperson, Graduate Committee: Douglas S. CairnsThis thesis contains the results of a composite material database developed for fiber glass laminates using test data from the in-plane loader (IPL). The IPL is a unique multi-axial test machine developed at Montana State University. The research was completed with the aim to improve the reliability of composite materials, namely fiber glass for use in wind turbine blades. An energy method was used to characterize strain-induced damage in fiber glass coupons. The energy dissipated by internal failure mechanisms was employed as a metric of internal damage. Thus, by means of a deconvolution procedure data from the IPL was used to obtain a dissipated energy density function. The dissipated energy density function was utilized to characterize the behavior of fiber glass between the onset of damage through ultimate material failure. Two cases studies were used to evaluate the current capabilities of the dissipated energy density function created from IPL data.