Theses and Dissertations at Montana State University (MSU)
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Item Effect of process variables on the uncured handleability and formability of stretch broken carbon fiber(Montana State University - Bozeman, The Graduate School, 2022) Rezaul, Riad Morshed; Chairperson, Graduate Committee: Cecily A. RyanCarbon fiber is a high-performance reinforcing material used extensively in aerospace composites. Although carbon fiber is used in both continuous and discontinuous form, the continuous carbon fiber is limited by its inability to stretch due to its low strain to failure during manufacturing structures with complex geometries. Stretch broken carbon fiber (SBCF) is a type of discontinuous and aligned carbon fiber which has the potential to solve this limitation of inextensibility of its continuous counterpart. The discontinuous nature of SBCF enhances its stretchability making this material a prime candidate for manufacturing parts with complex curvatures. SBCF is generated by stretching the fibers using a pair of differentially driven rollers, which breaks the fibers at their intrinsic flaws. Although SBCF can be stretched due to being discontinuous, it compromises the tensile strength due to the lack of fiber continuity. Therefore, a polymeric coating known as sizing is applied to the SBCF to reconstruct its tensile strength. In the context of SBCF production, sizing serves two important functions. Firstly, sizing provides uncured carbon fiber the desired handleability and back-tension ability. Secondly, sizing enhances the formability of SBCF, which is a defined as the ease at which a material can be formed into a desired shape without failure. The goal of this work is to investigate the effect of process variables on the generation of stretch broken carbon fiber with consistent and repeatable material properties. The stretch broken carbon fiber research group at Montana State University (MSU) has developed a stretch breaking machine known as 'Bobcat' to generate single tow MSU SBCF. The noteworthy process variables related to MSU SBCF production includes sizing deposition on the tow, stretch ratio, nip force, line speed, fiber length distribution, and tow tenacity. Target amount of sizing deposition on MSU SBCF tow was achieved by choosing an appropriate sizing bath. A temperature-controlled tow tenacity result suggests that MSU SBCF possesses adequate handleability, back-tension ability and formability. MSU SBCF also shows a narrow fiber length distribution and relatively short mean fiber length which indicate improved formability. Reproducibility of these results were observed in the replicate batches of MSU SBCF. Suitable stretch ratio and nip force regimes were identified to optimize MSU SBCF production.Item Using a beam theory model to quantify metatarsal bone stress during running(Montana State University - Bozeman, College of Education, Health & Human Development, 2023) McKibben, Kaitlyn Marie; Chairperson, Graduate Committee: James N. Becker; This is a manuscript style paper that includes co-authored chapters.Running is a common fitness activity that is associated with a high incidence of overuse injuries, including metatarsal stress fractures. One contributor to stress injury is repetitive loading of the metatarsals without adequate recovery time and experiencing larger volumes and magnitudes of bone loading may increase injury risk. Thus, quantifying metatarsal loads can be beneficial to understanding injury risk. However, it is currently difficult to estimate bone stress in clinical settings and unclear how bone stress changes following a long run. Therefore, the purpose of this thesis was to 1) characterize changes in metatarsal bone stress before and after the completion of a long-distance run, and 2) suggest a clinically feasible method for estimating metatarsal bone stress. Study 1 involved 21 healthy long-distance runners who ran 25% of their average weekly mileage on an instrumented treadmill. Foot kinematics, ground reaction forces, and in-shoe plantar pressures were collected at the beginning and end of the run and a mathematical model was used to estimate bone stresses and bending moments for all five metatarsals. Plantar stress, dorsal stress, and midshaft bending moments in the second and third metatarsals were greater after the completion of the run. This is consequential for injury risk because the second and third metatarsals are the most susceptible to stress fracture development. In study 2, seventeen runners ran barefoot across a force plate overlaid with a plantar pressure mat while foot kinematics were recorded. The same mathematical model of the metatarsals was used to estimate third metatarsal bone stresses and bending moments, and linear regressions determined whether force or pressure beneath the metatarsal predicted bone loads. A model containing head and base pressure differentials and force beneath the metatarsal head was the best predictor of bone loading, indicating that the use of plantar pressure measurements as a surrogate measure of bone stress could be a time and cost-effective method for estimating bone stress in clinical settings. Moving forward, elucidating how metatarsal bone stress changes over the course of a long run and finding more accessible ways to quantify bone stress could help alleviate injury risk.Item Development and characterization of a split Hopkinson pressure bar for testing high shock accelerometers(Montana State University - Bozeman, College of Engineering, 2022) Berg, Charlotte Katherine; Chairperson, Graduate Committee: David A. MillerExtreme environments pose significant challenges in the aerospace and defense fields. Prior to equipment deployment, dynamic testing is often conducted to identify potential failure points from high shock. Accelerometers are vital sensors for characterizing system response to transient inputs, such as impact and vibration, faced by atmospheric reentry vehicles or explosive protection equipment. However, accurate data collection is often inhibited by sensor damage or nonlinear response to dynamic inputs. A controlled experimental system capable of recreating extreme conditions is needed to assess sensor limitations and design options prior to full-scale structural testing. Conventionally built for high strain-rate material testing, a Split Hopkinson Pressure Bar uses colinear elastic bar impact to produce high energy, short-duration stress waves. Material samples are sandwiched between elastic bars and dynamic properties are derived from stress waves reflected by or transmitted through the sample. In this work, a modified Hopkinson Pressure Bar was developed to assess accelerometer response to high-energy, dynamic inputs. The modified system consists of a gas gun that propels a short steel striker into a longer steel incident bar, producing a nondispersive stress wave. A single-axis Endevco 7270 piezoresistive accelerometer is mounted on a fly-away structure aligned with the incident bar. The stress wave that reaches the accelerometer creates a shock impulse of similar magnitude and frequency as an explosive test. The Hopkinson Pressure Bar was characterized with a range of input configurations and produces acceleration pulses with amplitudes up to 100,000 g and durations of 0.2 ms. Strain signals were compared to accelerometer output in two mounting configurations over a range of shock levels. There was good agreement between strain-derived acceleration and peak accelerometer accelerations. Experimental system capabilities and limitations are presented alongside current challenges and directions for future research. The setup developed for this research increases sensor and material testing capabilities under extreme environmental conditions.Item Developing bio-inspired methodologies for encoding angular position from strain(Montana State University - Bozeman, College of Engineering, 2020) Lange, Christopher William; Chairperson, Graduate Committee: Mark JankauskiAs mechanical systems rely more on closed-loop control, the sensors which supply feedback information are essential. Additionally, in systems where sensor function is critical, sensor redundancy is important to retain functionality if one or more sensors fail. Redundancy can be achieved through multiple high-fidelity sensors which measure the same type of information, such as gyroscopes or accelerometers. However, multiple high-fidelity sensors can increase cost significantly. This thesis explores the potential to replace or augment the functionality of angular position sensors using strain measurements. Strain gauges are already used in system health monitoring systems. By utilizing these already implemented sensors to measure angular position, we can remove the additional cost of redundant angular position sensors. However, for complex systems, the mapping between strain and angular position is unclear. By incorporating reduced order, physics-based models into machine learning techniques, we can efficiently transform high-order strain data into angular position. To demonstrate the potential of using alternative sensing methods, we developed a reduced order model of a parametrically excited flexible pendulum. Inspiration for this simplified system comes from insect halteres, which are small sensory organs evolved from insect hind wings which provide rapid information about body rotation. The parametrically excited flexible pendulum allows a single axis of rotation and single direction of flexibility to be paired, and their relationship studied. By varying parameters within the model such as pendulum length and modulus as well as parametric excitation amplitude and frequency, the Gaussian process regression learning can be optimized to reduce training time and increase untrained prediction accuracy. Inputs of strain and parametric excitation position along with their respective first and second derivatives are then analyzed to determine which inputs are interrelated and therefore un-necessary, thus reducing the input required. This provides the essential first steps towards using machine learning to implement multiple sensor, deformation based, multi axial angular position sensing in complex systems.Item Developing a load acquisition system for a multiaxial test frame(Montana State University - Bozeman, College of Engineering, 2019) Carpenter, Aaron James; Chairperson, Graduate Committee: David A. MillerMaterial testing has traditionally been completed by using a uniaxial load frame which isolates a single stress component. Engineers however, design components for applications in a multi-axial world to withstand stress in multiple directions. The In-Plane Loader (IPL) at Montana State University expands the realm of material testing to three degrees of freedom within a two-dimensional plane. Applications of the IPL include composite material testing and experimental validation of constitutive models in multiple axes. The multi-axial test frame has been in place at MSU for several years. One of the primary challenges associated with the IPL is its ability to accurately measure multi-axial load components. The purpose of this work was to develop and validate an updated multi-axial load acquisition system for the IPL. The procedure included design, manufacture, implementation, and validation of the system. Validating the system in multiple axes required isolating single stress components along each of the planar axes. Tension tests were completed to isolate the vertical component, and shear tests were completed to isolate the horizontal component. Each of the results were compared to results of standardized test procedures designed to isolate their respective stress components. Digital image correlation was implemented as a non-contact method of measuring displacement for the testing procedures. The data collected in this study provides confidence in the ability to measure multi-axial loading in combination with digital image correlation to expand the capabilities of multi-axial testing. The system provides the ability to study load dependent failure of materials as well as displacement dependent failure. The information presented provides an understanding of challenges associated with multi-axial testing which hopes to assist in the development of future multi-axial test frames.Item In-plane shear behavior of geosynthetics from bias biaxial tests using digital image correlation(Montana State University - Bozeman, College of Engineering, 2019) Schultz, Emily Christine; Chairperson, Graduate Committee: Steven PerkinsGeosynthetics are polymeric membranes used for structural reinforcement of soils in a variety of roadway and foundation applications, many of which create biaxial loading on the geosynthetic. Orthotropic linear elastic models have been used to represent geosynthetic behavior at working load levels for engineering design purposes. Typically, the models rely on index parameters obtained from test methods that do not represent the biaxial field loading conditions. Proper calibration of these models requires load-strain data obtained from tests that have controlled stress and strain boundaries such as biaxial tension tests. Previously at Montana State University, Haselton (2018) successfully used a custom biaxial device to perform biaxial tension tests on cruciform shaped geosynthetic specimens, producing a partial set of resilient elastic constants for two woven geotextiles and six biaxial geogrids. To complete the set of elastic constants by determination of the in-plane shear modulus, another mode of loading was necessary. Literature from biaxial shear tests of architectural membranes suggested cutting the cruciform shaped samples with the principal material directions on a 45-degree bias, which causes the sample to shear when the cruciform axes are unequally loaded. This test mode was successfully implemented with the existing biaxial device to determine the resilient in-plane shear modulus using an orthotropic linear elastic model. Full-field strain measurements were captured using digital imaging correlation (DIC) software available at Montana State University. DIC was shown to produce equivalent strain measurements to the mechanical instrumentation (LVDTs) used by Haselton, enabling a combined dataset. The full-field DIC strain measurements were then used to validate Haselton's assumption regarding the region of uniform strain and to identify the region of uniform strain for data collection in this thesis. DIC also showed reasonably pure biaxial tension in the cruciform samples, validating the elastic constant derivations for both Haselton and this thesis.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 A photoelastic investigation of three-dimensional contact stresses(Montana State University - Bozeman, College of Engineering, 1968) Schafer, Douglas CraigItem Analysis for three-dimensional pipe structures by group relaxation(Montana State University - Bozeman, College of Engineering, 1949) Bassar, NicholasItem Numerical analysis for rectangular slabs under hydrostatic pressure(Montana State University - Bozeman, College of Engineering, 1952) Bozzay, Joseph
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