Theses and Dissertations at Montana State University (MSU)
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Item Impacts of species protections on wind turbine development: evidence from golden eagle protection policies(Montana State University - Bozeman, College of Agriculture, 2023) O'Brien, Brock Daniel; Chairperson, Graduate Committee: Diane CharltonAs demand for wind energy grows, policymakers face tradeoffs between wind turbine development and wildlife species protections. This is particularly relevant for golden eagles, which have a habitat that overlaps areas of high wind energy development potential. Golden eagle protections, such as the Bald and Golden Eagle Protection Act (BGEPA), therefore potentially conflict with wind energy development goals. Policymakers face a lack of information regarding the existence and size of potential impacts of species protections on wind development. To approach this issue, I employ a difference-in-differences research design exploiting variation in BGEPA enforcement over time and geographic variation in golden eagle exposure to identify the impacts of species protections on wind development in resource-rich areas. I find that counties with high golden eagle exposure experienced declines in expected wind turbine capacity additions of 3.78 megawatts during the enforcement period, suggesting a total of 420 megawatts of foregone wind energy. This electricity generation loss has an estimated value of $56 to $142 million annually. Existing golden eagle valuation methods suggest significant economic gains from wind turbine expansion, although these estimations arguably apply only to marginal wildlife impacts and should be applied with caution. These results emphasize that the value of foregone renewable energy is an often-overlooked component of species protection policy discussions, and that effective conservation measures and funding are necessary both for the futures of many species and for renewable technology deployment.Item Development of surface preparation procedure recommendations for wind turbine blade field repairs(Montana State University - Bozeman, College of Engineering, 2022) Lusty, Ariel Francis; Chairperson, Graduate Committee: Douglas S. CairnsWind turbine blades necessitate reliable field repairs. However, the effects of current wind turbine field repair surface preparation techniques were not well- documented. Poorly informed surface preparation procedures lead to poor quality repairs, so surface preparation procedure recommendations for wind turbine blade field repairs were developed. The effectiveness of current surface preparation techniques, the effects of contaminants, and alternative techniques were evaluated. Current surface preparation techniques involve using solvent wiping to remove contamination. Results indicated that solvent wiping does not significantly affect bond strengths, but solvents can gel resin surfaces. Measuring the changes in bond strengths due to contamination from composite dust and hydraulic oil with time indicated that contamination diffusion effects along bond lines were negligible, but that composite dust and hydraulic oil diminished bond strengths. Contaminants should thus be removed from bond line surfaces prior to repairs. The goal of considering alternative techniques was to increase and equalize the surface energy of repair surfaces using plasma or sizing. There were significant drops in contact angles on composite surfaces treated with plasma, so plasma treatments should continue to be considered for composite surface preparation methods. To examine sizing effects, sizing was applied to scarfed surfaces and specimens were tested in tension. Applying sizing to tapered surfaces prior to scarf repairs did not affect scarf tension ultimate stress values, failure modes, or failure surface elemental composition. In addition, there was a stiffness reduction in the scarfed specimens compared to unscarfed specimens, indicating that the scarf tension repair did not fully restore the composite plate's original properties. Scarf tension experiments were simulated using finite element analysis and results had good agreement between the experiments and the model. The surface preparation recommendation is to test whichever surface preparation methods and adhesive-substrate combinations are used for a repair prior to implementation in the field. Implementing testing of surface preparation methods with adhesive-substrate combinations into surface preparation procedures will decrease lifetime costs and increase energy production for wind turbines, which will ultimately reduce reliance on fossil fuels for societal energy needs.Item Combining acoustic emission and guided ultrasonic waves for global property prediction and structural health monitoring of glass fiber composites(Montana State University - Bozeman, College of Engineering, 2018) Murdy, Paul; Chairperson, Graduate Committee: David A. MillerSince the turn of the century, wind turbines have been rapidly growing in size and are projected to continue growing as the technology develops. These increases in size have led to increased failure rates of the glass fiber composite turbine blades. Because of this, it is of utmost importance to understand failure mechanisms in glass fiber composites and investigate new approaches to predicting failures. This has led to advancements in structural health monitoring of large composites structures by applying sophisticated sensing technologies, in attempts to evaluate material damage states and predict structural failures before they occur. This research has taken a novel approach to apply multiple ultrasonic monitoring techniques, in the form of acoustic emission and guided ultrasonic waves, simultaneously to the mechanical testing of glass fiber reinforced composite laminates. Testing of the composite laminates was conducted in the form of increasing load-unload-reload static tension tests and tension-tension fatigue tests, to measure modulus degradation of the laminates while applying the monitoring techniques. Acoustic emission was used to detect damage events that occurred within laminates in real-time and guided ultrasonic waves were applied periodically to the laminates to observe changes in wave propagation and relate back to damage severity within the laminates. Furthermore, the acoustic emission and guided ultrasonic wave datasets were combined and used to train multivariate regression models to predict modulus degradation of the laminates tested, with no prior knowledge of the laminates' loading histories. Overall, the predictive models were able to make good predictions and showed the potential for combining multiple monitoring techniques into singular systems and statistical predictive models. This research has shown that the combination of the two measurement techniques can be implemented for more accurate and reliable monitoring of large composite structures than the techniques used individually, with minimal additional hardware. Ultimately, this research has paved the way for a new form of smart structural health monitoring, with superior predictive capabilities, which will benefit the renewable energy through reducing maintenance and repair costs and mitigating the risk of wind turbine blade failures.Item Experimentation and finite element analysis of repairs on composite laminates and sandwich beam structures(Montana State University - Bozeman, College of Engineering, 2018) Ibitoye, Oluwafemi Ayodele; Chairperson, Graduate Committee: Douglas S. CairnsComposites like other engineering materials suffer damage due to mishandling, manufacturing defects and under design. Once they are damaged, an available option may be to restore them to working condition. This work investigated the characteristics of repairs done on wind turbine grade fiber reinforced composite laminates and sandwich beams. Two layups ([0] 2 and [45/-45/0/-45/45]) were investigated with varied forms of repair (infusion bonded, adhesive bonded, infusion with overply) conducted on them. Repaired laminate specimens and repaired sandwich beams were subjected to static tensile loads and four-point flexure respectively. Three-dimensional finite element models augmented with cohesive traction separation relationship were used to analyze bond behavior and compare with experimental observation. Strain data was collected using the process of digital image correlation. Results showed that repairs certainly reduced the stress concentration around regions of damage up to certain strain levels. Similarity in debond behavior was also observed between laminates and sandwich beams of similar ply orientation. Differences were noted in the debond behavior of the two different layups ([0] 2 and [45/-45/0/-45/45]) that were repaired and tested. The observations provided conclusions that could help improve the repair effectiveness of composites.Item Influence of fabric architecture on damage progression as evidenced by acoustic emission(Montana State University - Bozeman, College of Engineering, 2016) Lolatte, Austin James; Chairperson, Graduate Committee: David A. MillerFabric reinforced polymer matrix composites are integral structural materials used in wind turbine blades. Wind turbines are expected to increase in size and utilization as global focus turns toward power generation utilizing renewable sources. How these materials change properties due to damage accumulated are important to the future of wind energy. They feature damage mechanisms that are unique from any other engineering material. These factors are now driving innovation for design and manufacturing of the blades. This has led to investigation in characterizing the mechanical behavior of the composites. These composites were manufactured using unidirectional and biaxial fiber layups from three fabrics composed of an epoxy matrix and glass fibers. The effect of the architecture of the fibers on damage progression was determined with acoustic emission sensors that were attached linearly to capture elastic waves emitted by damage mechanisms inside the samples during testing. The critical data extracted from the elastic waveforms include the peak frequency and absolute energy released by the samples and how they are associated with the strength of the samples. A static loading scenario was determined to be the optimal testing method. The use of AE measurements proved to be an invaluable tool to determine how the damage progression of composite materials lead to failure for some, while not being accurate for others. Results found that simple architecture differences for the same fibers have drastic effects on damage progression. However, the energy measurements proved to be imperfect with current technology and application; improvement will be necessary for AE instruments to be a viable tool for energy measurement in the future. AE provides a unique analysis that can identify and characterize damage related to fabric composition. The frequency content provides a consistent method of identifying damage mechanisms between varying materials. Optimal architecture and layup can be determined with the help of AE. Correlating acoustic energy to actual energy dissipated still has potential as a valuable tool if improvement in sensor technology can be achieved. Ultimately, a foundation for correlating mechanical properties of the materials and damage progression to fabric architecture and layup using AE tools was created.Item Investigation of the effect of in-plane fiber waviness in composite materials through multiple scales of testing and finite element modeling(Montana State University - Bozeman, College of Engineering, 2015) Lerman, Michael William; Chairperson, Graduate Committee: Douglas S. CairnsDefects in materials can reduce strengths and lifetimes of manufactured parts. The number of possible defects increase with the complexity inherent in composite materials. The wind industry uses composite wind turbine blades in which the manufacturing process induces a number of defects. In order for the wind industry to continue sustainable expansion, the effects of defects must be better understood. In-plane (IP) fiber waviness is the focus of this work. The three main parts of this work include testing on the coupon level, modeling on the coupon level, and testing of beams in four-point bending (with and without defects). The coupon level testing includes partial IP waves, similar to those in manufactured parts, rather than full width IP waves. This allows investigation into complex interactions and varying failure mechanisms caused by the fiber misalignment gradient. Partial waves are also modeled to both validate testing as well as to increase robustness of a previously developed progressive damage modeling method. Lastly, a sandwich beam test specimen for testing in 4-point bending is developed to investigate the effects of fiber waviness in both tension and compression when loaded in flexure.Item Characterization and energy analysis of fiber reinforced polymer composites by acoustic emission analysis(Montana State University - Bozeman, College of Engineering, 2014) Schuster, Michael Francis; Chairperson, Graduate Committee: David A. MillerFabric reinforced polymer matrix composites are an integral structural material used in wind turbine blades. Wind turbines are expected to experience growth both in physical size and utilization as the focus of power generation shifts towards utilizing renewable sources more efficiently. Even current generation blades are experiencing reliability concerns. These factors are now driving improvements in design and manufacture of wind turbine blades. With this, progress in characterizing the mechanical behavior of materials is necessary. Composite materials possess unique damage mechanisms due to their constituent materials and these require further study. Composite materials were manufactured into four layups from four fabrics and an epoxy matrix. Acoustic emission sensors were applied in a linear locating arrangement to capture elastic waves from damage mechanisms during a tensile test. Data critical to this work that was extracted from the elastic waveforms include peak frequency and absolute energy. A static loading scenario was used to characterize the materials and their damage progression while an LUR loading scenario was used to correlate absolute energy to dissipated strain energy. Results of the material characterization found that a greater range of frequencies, thus damage mechanisms, were observed for increasingly complex fabric architectures. The observed frequency and energy data provided valuable information on the interaction of the various constituent materials. Attempts at obtaining an accurate and consistent correlation value were not successful with the LUR tests. However, total accumulated energy emerged as a consistent metric of equal value between static and LUR tests that shows promise of being an indicator of coupon damage state. Acoustic emission was found to provide a unique analysis that can identify and characterize damage and fabric composition in composite materials. The frequency content provides a consistent method of identifying damage mechanisms between varying materials. Correlating acoustic energy to strain energy dissipated appears to be more complex than is developed here but the concept does hold merit and requires further study. An applicable database of AE characteristics of the materials was created that will be of great use for future more complex sub-structure component testing.Item Mixed mode delamination of glass fiber/polymer matrix composite materials(Montana State University - Bozeman, College of Engineering, 2003) Agastra, Pancasatya; Chairperson, Graduate Committee: John F. MandellItem Design, analysis and testing of a wind turbine blade substructure(Montana State University - Bozeman, College of Engineering, 1995) Combs, David WrightItem High cycle longitudinal and transverse figure of unidirectional glass/polyester composites(Montana State University - Bozeman, College of Engineering, 1995) Wei, Guangxu
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