Theses and Dissertations at Montana State University (MSU)
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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 Fiber shape effects on the compressive strength of unidirectional carbon fiber composites: a computational study(Montana State University - Bozeman, College of Engineering, 2020) Clarke, Ryan; Chairperson, Graduate Committee: David A. MillerThe tensile strength tends to be much higher than the compressive strength for carbon fiber reinforced polymer composites because of a change in failure modes. Current research activities are looking at novel precursors for reducing overall costs of carbon fiber production. The potential cost savings in new precursor carbon fiber make it economically feasible to use in large structural components. Some fiber precursors and manufacturing methods produce carbon fibers that have a kidney-shaped cross-section whereas traditional carbon fiber is circular. The aim of this study is to investigate the differences in compressive failure responses between fiber shapes in carbon fiber composites. A finite element micromechanical model was developed in ABAQUS of a single carbon fiber embedded in a square matrix with periodic boundary conditions. Two fiber cross-sectional geometries were examined: circular and kidney shaped. Three factors that affect the compressive failure response of carbon fiber reinforced polymers were investigated. These include fiber misalignment, volume fraction, and multiaxial loading. The results showed negligible differences between the compressive failure response of fibers with different cross-sectional shapes. Compressive strength was shown to have a decaying sensitivity to increasing fiber misalignment. Decreasing the volume fraction did decrease the compressive strength but also increased the compressive failure strain. In addition, adding in-plane shear loads proved detrimental to the compressive load-carrying capacity of a composite structure. This research showed minimizing fiber misalignment in manufacturing processes is only beneficial for high tolerance processes. In addition, decreasing volume fraction could be beneficial for highly flexible structures. Finally, the results demonstrated the need to minimize multiaxial loading for optimal composite compressive response.Item Pilot study of a high capacity ductile seismic holdown for cross laminated timber(Montana State University - Bozeman, College of Engineering, 2019) Nicholas, John Howison; Chairperson, Graduate Committee: Damon FickNew manufactured wood products referred to as mass timber have allowed for greater seismic load capacities than ever before for designing wood structures. The increased capacities could allow for taller wood structures; however, traditional wood connections do not meet the seismic performance needs for new manufactured wood products such as cross laminated timber (CLT). New connection methods must be investigated to allow for the growth of the CLT industry in mid- and high-rise structures. The objective of this research is to develop a wood connection to resist larger uplift forces experienced in CLT structures and provide energy dissipation in seismic events. The connection development was performed through fastener testing using self-drilling dowel fasteners for concealed connections with steel knife plates installed in a wood member. Finite element modeling and testing of reduced section steel plate to provide a ductile response to cyclic loading was performed to determine the feasibility of this connections style. The results of the investigation indicate that reduced section steel plates that limit the connection failure to a desired location in the steel plate could greatly increase the seismic performance of CLT seismic force resisting systems.Item Validation of high strain rate, multiaxial loads using an in-plane loader, digital image correlation, and FEA(Montana State University - Bozeman, College of Engineering, 2018) Stroili, Christopher; Chairperson, Graduate Committee: David A. MillerMontana State University's In-Plane Loader (IPL) is a machine designed to test for mechanical properties at multi-axial states of stress and strain by in-plane translation and rotation. Historically the machine has been used to characterize composite lay-ups, where applying multi-axial loads can better describe anisotropic materials. The IPL testing machine uses Digital Image Correlation (DIC) software and a stereoscopic camera system to measure strains on the surface of the test coupon by tracking a stochastic pattern applied to the gage section. The focus of this work was to test the capabilities beyond quasi-static composites testing, specifically looking to explore the feasibility of testing plastics and metals at strain rates from 10 0 to 10 3 s -1. This work explored the speed and loading capabilities of the IPL and determined a suitable coupon geometry which balances gage section area with material strength. 304 Stainless Steel was tested both on the IPL and in uniaxial tension. Experimental tensile test data was fit to a Johnson Cook strain rate sensitive constitutive model. This constitutive equation was then used with an implicit dynamic finite element analysis (FEA) model. To study the validity of high rate testing of steel in the IPL, strain from the DIC experimental data was compared with the FEA results. While the strains predicted by the FEA model varied from experimental results, a better understanding of the IPL capabilities has been achieved. Moving forward, a series of recommendations have been made so that high strain rate multi-axial testing of metals can be implemented with more robust constitutive models.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 Particle imaging velocimetry data assimilation using least-square finite element methods(Montana State University - Bozeman, College of Engineering, 2016) Rajaraman, Prathish Kumar; Chairperson, Graduate Committee: Jeffrey Heys; T. A. Manteuffel, M. Belohlavek, E. McMahon and Jeffrey J. Heys were co-authors of the article, 'Echocardiograpic particle imaging velocimetry data assimilation with least square finite element methods' in the journal 'Computers & mathematics with applications' which is contained within this thesis.; G. D. Vo, G. Hansen and Jeffrey J. Heys were co-authors of the article, 'Comparison of continuous and discontinuous finite element methods for parabolic differential equations employing implicit time intergation' submitted to the journal 'International journal of numerical methods for heat & fluid flow' which is contained within this thesis.; T. A. Manteuffel, M. Belohlavek and Jeffrey J. Heys were co-authors of the article, 'Combining existing numerical models with data assimilation using weighted least-squares finite element methods' submitted to the journal 'International journal of numerical methods in biomedical engineering' which is contained within this thesis.Recent advancements in the field of echocardiography have introduced various methods to image blood flow in the heart. Of particular interest is the left ventricle of the heart, which pumps oxygenated blood from the lungs out through the aorta. One method for imaging blood flow is injecting FDA-approved micro-bubbles into the left ventricle, and then, using the motion of the microbubbles and the frame rate of the ultrasound scan, the blood velocity can be calculated. In addition to blood velocity, echocardiologists are also interested in calculating pressure gradients and other flow properties, but this is not currently possible because the velocity data obtained is two-dimensional and contains noise. In order to realize the full potential of microbubbles as a tool for determining the pumping efficiency and health of the LV, three-dimensional velocity data is required. Our goal is to assimilate two-dimensional velocity data from ultrasound experiments into a three-dimensional computer model. In order to achieve this objective, a numerical method is needed that can approximate the solution of a system of differential equations and assimilate an arbitrary number of noisy experimental values at arbitrary points within the domain of interests to provide a "most probable" approximate solution that is accordingly influenced by the experimental data. In this thesis we present two different approaches for data assimilation, the first approach is more computationally expensive, but requires only a single step. The second approach uses a two stage data assimilation technique but is computationally less expensive. The motivation for using the least-squares finite element method approach is that it provides many advantages such as the ability to match the numerical solution more closely to more accurate data and less closely to the less accurate data.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 Three dimensional finite element analysis of matrix cracks in multidirectional composite laminates(Montana State University - Bozeman, College of Engineering, 1993) Shrinivas, ModayurItem Numerical analysis of blast loaded civilian structures(Montana State University - Bozeman, College of Engineering, 2000) Lutzenberger, Bert JeffreyItem Fatigue of skin-stiffener intersections in composite wind turbine blade structures(Montana State University - Bozeman, College of Engineering, 2000) Morehead, Robert B.