Theses and Dissertations at Montana State University (MSU)
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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 Fiberglass composite tensile fatigue resistance : fiber surface damage analysis and fatigue resistant fiber coating(Montana State University - Bozeman, College of Engineering, 1996) Bian, JinhuaItem 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 Surface modification of E-glass fibers with radio frequency plasma polymerization and its effect on fatigue resistance of composites(Montana State University - Bozeman, College of Engineering, 1996) Fang, DongruiItem Fatigue of E-glass fiber reinforced composite materials and substructures(Montana State University - Bozeman, College of Engineering, 1999) Samborsky, Daniel DavidItem 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 Integration of actuators and sensors into composite structures(Montana State University - Bozeman, College of Engineering, 2009) Ehresman, Jonathan David; Chairperson, Graduate Committee: Douglas S. CairnsThe need for more efficient wind turbine blades is growing in our society. One step in accomplishing this task would be to make wind turbines blades into smart structures. A smart structure is one that incorporates sensors, complete control systems, and active control devices, in order to shed, or redistribute the load placed on the structure. For wind turbine blades this means changing the shape of the blade profile as it encounters different wind conditions. In order to have active control surfaces functioning on wind turbine blades, the existing blades would have to be retrofitted, and the new blades being manufactured would have to be redesigned. There are different control surfaces to consider: gurney flaps and false wall flaps are two that can perturb the boundary layer across the low pressure side of the wing. A flat plate and blade section test bed will be manufactured in order to gather empirical data from wind tunnel testing. For actuation of the control surface there are many choices: electrical, hydraulic, pneumatic, and electro-hydrostatic. These actuator types will be investigated under a set of criterion to determine the best one for turbine blade application. Sensors will be investigated with respect to their use in sensing strain, temperature, acceleration, humidity, and delamination. Sensors are also used for health monitoring. This helps engineers design under a damage tolerant philosophy as opposed to a safe life structure philosophy. These sensors will be placed into laminates and different surface treatments will be reviewed to find the best configuration for each sensor. The sensor will be cleaned with isopropyl alcohol, dipped in a 20% by mass solution of nitric acid, and submerged in a 20% by mass solution of nitric acid for 10 seconds. Detailed surface images will be taken of sensors with different surface treatments in order to better understand the bonding between the sensor and laminate. These images indicate that submerging the sensors into 20% by mass solution of nitric acid is the best surface treatment.