The purpose of this paper is to establish the rules governing current combat robotics and showcase an idea on how to create a more powerful robot. The robot would use its weapon to spin the rest of its body while having the weapon's gyro forces lift the entire robot and move it a set distance while spinning. Performing both of these actions simultaneously would create a more powerful robot through the use of a more destructive weapon system. Many initial tests were conducted to verify that the electronics and code worked and that the wheels could withstand the significant gyro forces when spinning. Multiple prototype chassis were designed and optimized to better handle the shape and the electronics went through several revisions so that they could be packaged in a cleaner and more space efficient way. A final prototype was designed with the knowledge from the initial tests which was then manufactured and tested to verify that the weapon could rotate the entire robot.

Damage and failure of advanced composite materials and structures are often manifestations of nonlinear deformation that involve multiple mechanisms and their interactions at the constituent length scale. The presence and interactions of inelastic microscale constituents strongly influence the macroscopic damage anisotropy and useful residual life. The mechano-chemical interactions between constituents at the atomistic length scale play a more critical role with nanoengineered composites. Therefore, it is desirable to link composite behavior to specific microscopic constituent properties explicitly and lower length scale features using high-fidelity multiscale modeling techniques.In the research presented in this dissertation, an atomistically-informed multiscale modeling framework is developed to investigate damage evolution and failure in composites with radially-grown carbon nanotube (CNT) architecture. A continuum damage mechanics (CDM) model for the radially-grown CNT interphase region is developed with evolution equations derived using atomistic simulations. The developed model is integrated within a high-fidelity generalized method of cells (HFGMC) micromechanics theory and is used to parametrically investigate the influence of various input micro and nanoscale parameters on the mechanical properties, such as elastic stiffness, strength, and toughness. In addition, the inter-fiber stresses and the onset of damage in the presence of the interphase region are investigated to better understand the energy dissipation mechanisms that attribute to the enhancement in the macroscopic out-of-plane strength and toughness. Note that the HFGMC theory relies heavily on the description of microscale features and requires many internal variables, leading to high computational costs. Therefore, a novel reduced-order model (ROM) is also developed to surrogate full-field nonlinear HFGMC simulations and decrease the computational time and memory requirements of concurrent multiscale simulations significantly. The accurate prediction of composite sandwich materials' thermal stability and durability remains a challenge due to the variability of thermal-related material coefficients at different temperatures and the extensive use of bonded fittings. Consequently, the dissertation also investigates the thermomechanical performance of a complex composite sandwich space structure subject to thermal cycling. Computational finite element (FE) simulations are used to investigate the intrinsic failure mechanisms and damage precursors in honeycomb core composite sandwich structures with adhesively bonded fittings.

In this conference paper, nanoscale material property data and ASTM mode I interlaminar fracture results for three-phase buckypaper samples are presented and analyzed. Vacuum filtration and surfactant-free methods were used to manufacture buckypaper membranes. Epoxy infused buckypaper membranes were placed in front of the crack tip in a stitch bonded carbon fiber polymer matrix composite using a hand layup technique. Peak Force Quantitative Nanomechanical Mapping (PFQNM), using probes with nominal tip radius in the range of 5 to 8 nm were used. PFQNM fully characterized the interphase region between a three-phase sample of carbon monofilament, epoxy resin, and multi-walled carbon nanotube (MWCNT) buckypaper. This experiment captured reproducible nanoscale morphological, viscoelastic, elastic and energy properties of porous MWCNT buckypaper samples. An enlarged interphase region surrounding the CNT buckypaper was found. The buckypaper and epoxy interphase thickness was found to be 50nm, higher than the 10-40nm reported for epoxy and carbon monofilaments. The observed MWCNT structure provides explanation of the increased surface roughness compared to the smooth carbon monofilaments. The increased surface roughness likely improves mechanical interlocking with the epoxy of adjacent lamina. The interphase and subsurface characterization data at the nanoscale level provide explanation for a change in crack propagation toughness. Nanoscale analysis of the buckypaper surface proved the inhomogeneous properties even at the scale of a few square micrometer. The improvement in crack initiation and propagation energy is due to mechanical interlocking, crack path diversion, and the large interphase zone surrounding the buckypaper.

Carbon Fiber Reinforced Polymers (CFRP) are a promising engineering material because of their multifunctionality and desirable mechanical, electrical, and thermal properties. The mechanical and fracture properties of CFRPs rely on effective stress transfer from the bulk matrix to individual carbon fibers. Pristine carbon fibers (CF) are chemically unreactive and smooth, which inhibits stress transfer mechanisms and makes CF susceptible to matrix debonding. Current composite research aims to improve the synergy between the CF and surrounding matrix by engineering the interphase. The composite interphase is characterized by mechanical properties deviating from the fiber and matrix properties. Carbon nanotubes (CNT), graphene nanoplatelets, and other carbon nanofillers have been studied extensively for their interphase-enhancing capabilities.

This dissertation presents the development of structural health monitoring and prognostic health management methodologies for complex structures and systems in the field of mechanical engineering. To overcome various challenges historically associated with complex structures and systems such as complicated sensing mechanisms, noisy information, and large-size datasets, a hybrid monitoring framework comprising of solid mechanics concepts and data mining technologies is developed. In such a framework, the solid mechanics simulations provide additional intuitions to data mining techniques reducing the dependence of accuracy on the training set, while the data mining approaches fuse and interpret information from the targeted system enabling the capability for real-time monitoring with efficient computation.

In the case of structural health monitoring, ultrasonic guided waves are utilized for damage identification and localization in complex composite structures. Signal processing and data mining techniques are integrated into the damage localization framework, and the converted wave modes, which are induced by the thickness variation due to the presence of delamination, are used as damage indicators. This framework has been validated through experiments and has shown sufficient accuracy in locating delamination in X-COR sandwich composites without the need of baseline information. Besides the localization of internal damage, the Gaussian process machine learning technique is integrated with finite element method as an online-offline prediction model to predict crack propagation with overloads under biaxial loading conditions; such a probabilistic prognosis model, with limited number of training examples, has shown increased accuracy over state-of-the-art techniques in predicting crack retardation behaviors induced by overloads. In the case of system level management, a monitoring framework built using a multivariate Gaussian model as basis is developed to evaluate the anomalous condition of commercial aircrafts. This method has been validated using commercial airline data and has shown high sensitivity to variations in aircraft dynamics and pilot operations. Moreover, this framework was also tested on simulated aircraft faults and its feasibility for real-time monitoring was demonstrated with sufficient computation efficiency.

This research is expected to serve as a practical addition to the existing literature while possessing the potential to be adopted in realistic engineering applications.

This experiment analyzed the degradation mechanisms in polymer matrix composite (PMC) samples after more than 50 years of simulated exposure to hygrothermal conditioning. This strong, form-adaptive, lightweight material is suitable for use on critical structures including nuclear powerplants and spacecrafts as primary reinforcers to improve fracture toughness. Current literature regarding PMC material has a poor understanding of its delamination trends and varying interphase properties that determine its overall reliability under extreme weather conditions. This paper will evaluate the long-term impact from exposure to heat and humidity regarding the material’s stiffness and degradation to confirm PMC’s reliability for use in structures that undergo these conditions. To study this phenomenon, aged and unaged PMC samples were analyzed on the nanoscale using PeakForce Quantitative Nanomechanical mode (PF-QNM) of Atomic Force Microscopy with an indentation tip no greater than 10nm in radius. This paper compares this testing method to the results from recent research on other microscopy modes to discuss the validity of the PF-QNM model as it is used for this analysis. The data obtained allowed for analysis of crack propagation and quantification of strength in interphase between the composite’s constituents. This research verifies the testing method for which a comprehensive understanding of the environmental influences on PMC mechanical properties could be achieved.

Multiaxial mechanical fatigue of heterogeneous materials has been a significant cause of concern in the aerospace, civil and automobile industries for decades, limiting the service life of structural components while increasing time and costs associated with inspection and maintenance. Fiber reinforced composites and light-weight aluminum alloys are widely used in aerospace structures that require high specific strength and fatigue resistance. However, studying the fundamental crack growth behavior at the micro- and macroscale as a function of loading history is essential to accurately predict the residual fatigue life of components and achieve damage tolerant designs. The issue of mechanical fatigue can be tackled by developing reliable in-situ damage quantification methodologies and by comprehensively understanding fatigue damage mechanisms under a variety of complex loading conditions. Although a multitude of uniaxial fatigue loading studies have been conducted on light-weight metallic materials and composites, many service failures occur from components being subjected to variable amplitude, mixed-mode multiaxial fatigue loadings. In this research, a systematic approach is undertaken to address the issue of fatigue damage evolution in aerospace materials by:

(i) Comprehensive investigation of micro- and macroscale crack growth behavior in aerospace grade Al 7075 T651 alloy under complex biaxial fatigue loading conditions. The effects of variable amplitude biaxial loading on crack growth characteristics such as crack acceleration and retardation were studied in detail by exclusively analyzing the influence of individual mode-I, mixed-mode and mode-II overload and underload fatigue cycles in an otherwise constant amplitude mode-I baseline load spectrum. The micromechanisms governing crack growth behavior under the complex biaxial loading conditions were identified and correlated with the crack growth behavior and fracture surface morphology through quantitative fractography.

(ii) Development of novel multifunctional nanocomposite materials with improved fatigue resistance and in-situ fatigue damage detection and quantification capabilities. A state-of-the-art processing method was developed for producing sizable carbon nanotube (CNT) membranes for multifunctional composites. The CNT membranes were embedded in glass fiber laminates and in-situ strain sensing and damage quantification was achieved by exploiting the piezoresistive property of the CNT membrane. In addition, improved resistance to fatigue crack growth was observed due to the embedded CNT membrane.

Epoxy resins and composite materials are well characterized in their mechanical properties. However these properties change as the materials age under different conditions, as their microstructure undergoes changes from the absorption or desorption of water. Many of these microstructural changes occur at the interfacial region between where the matrix of the composite meets the reinforcement fiber, but still result in significant effects in the material properties. These effects have been studied and characterized under a variety of conditions by artificially aging samples. The artificial aging process focuses on exposing samples to environmental conditions such as high temperature, UV light, and humidity. While conditions like this are important to study, in real world applications the materials will not be simply resting in a laboratory created environment. In most circumstances, they are subjected to some kind of stress or impact. This report will focus on designing an experiment to analyze aged samples under tensile loading and creating a fixture that will sustain loading while the samples are aged. . The conditions that will be tested are control conditions at standard temperature and humidity in the laboratory, submerged, thermal heating, submerged and heated, and hygrothermal.

Shape Memory Polymers (SMPs) are smart polyurethane thermoplastics that can recover their original shape after undergoing deformation. This shape recovery can be actuated by raising the SMP above its glass transition temperature, Tg. This report outlines a process for repeatedly recycling SMPs using 3D printing. Cubes are printed, broken down into pellets mechanically, and re-extruded into filament. This simulates a recycling iteration that the material would undergo in industry. The samples are recycled 0, 1, 3, and 5 times, then printed into rectangular and dog-bone shapes. These shapes are used to perform dynamic mechanical analysis (DMA) and 3-point bending for shape recovery testing. Samples will also be used for scanning electron microscopy (SEM) to characterize their microstructure.

Seamless carbon fiber reinforced polymer matrix (CFRP) composites are being investigated in many structural applications with the purpose of withstanding the extreme pressures and maintaining stiffness in mechanical systems. This report focuses on: fabrication of CFRP tubes and end caps, the production of a pressurization system to test standards set by Fiber Reinforced Composite (FRC) Pipe and Fittings for Underground Fire Protection Service [1], developing a library for different damage types for seamless composite pipes, and evaluating pre-existing flaws with flash thermography, carrying out hydrostatic testing, and performing nondestructive testing (NDT) to characterize damage induced on the pipes such as cracking, crazing, and fiber breakage. The tasks outlined will be used to develop design guidelines for different combinations of loading systems.