The development of a numerical modelling approach for carbon bre reinforced plastic energy absorbing structures designed for crash events using Abaqus/CZone is described within this master thesis. Several crash tube series have been designed, manufactured, and tested with a rather unconventional cross-sectional geometry. The squared cross-sectional geometry consisted of "curved" at sections, and double flanges for adhering two halves together. The crash tube halves contain carbon bre epoxy UD laminates, and are manufactured using a hot-press machine. Adjustments for experimental tests were made in the geometry, laminate denition, and impact velocity. Numerical simulations were focused on geometry, laminate definition, impact velocity, flange geometry, material model, laminate thickness, and crush properties. The numerical model consisted of two parts, namely a 3D discrete rigid planar shell as impactor plate without material properties, and a 3D shell crash tube with an imported geometry from Dassault Systems CATIA V5. Material, and cohesive properties were assigned to the crash tube using the Abaqus Ply Fabric material model, and CZone. Mesh seed length was smaller than the critical mesh seed length. An initial clearance between the impactor and crash tube has been implemented within the assembly. Step size was set to 0.05 s, and dynamic explicit step type was selected. General contact was defined using default settings. A qualitative good agreement between numerical and experimental test results is achieved for V100, V500, V600, and V700 series with c.o.v. values for stroke length of 2.2%, 7.0%, 5.3%, and 4.1%,respectively. V500-V700 series are only tested once, whilst the V100 series has been tested five times. The V200 and V300 series with modified geometries achieved c.o.v. values within a complete different order of magnitude for stroke length, namely 14% for V200 series, and 15% for V300 series. Although only three specimens have been tested for the V200, and V300 series, it is not the main reason for this mismatch. The starting deceleration at the linear increasing segment is much lower than observed in experiments, and causes this major difference. Elevated impact velocities for the V1502, and V1503 series tend to have a positive influence on the numerical results, and ensure a higher initial starting deceleration at the linear increasing segment. Numerical results show that increased taper ratios result in decreased decelerations. A flange geometry study showed that implementing a double flange suppresses debonding, and increases the deceleration, as the geometrical stiffness is increased. Not having a flange results in lower decelerations, and larger stroke lengths, as the geometrical cross-section provides less stiffness. A bonded single flange will be debonded, independent of bonding properties, as even extremely high bonding properties have shown direct debonding under impact load. Stiffer laminates result in higher decelerations and shorter stroke lengths. This statement is tested in three different ways, namely by changing the laminate denitions, laminate thickness's, and the crush properties. Three different material models have been tested. Abaqus Ply Fabric has proven to be easiest in usage, and showing a qualitative good agreement with the experimental results. Abaqus Ply Fabric does over predict the stroke length, whereas Hashin, and Tsai-Wu achieve a more accurate stroke length prediction. However, it is safer to over predict the stroke length. No material model is capable of capturing the initial peek decelerations.

Seismic pressures on displacing or rigid retaining or basement walls have been derived based on the original work of Mononobe and Okabe, who used a shake table to calculate dynamic pressures of displacing retaining walls existing in cohesionless soils. Since this original work was done over eighty years ago, the results of Mononobe and Okabe, colloquially known as M-O theory, have been applied to different conditions, including non-displacing basement walls, as well as changes in soil properties. Since the original work of M-O, there have been numerous studies completed to verify the accuracy of the original calculation, most notably the work of Seed and Whitman (1970), Wood (1973), Sitar (Various), and Ostadan (2005). This has resulted in varying opinions for the accuracy of M-O theory, whether it is grossly unconservative or conservative, as well as its effectiveness for situations where the wall does not displace enough to engage active soil conditions. This study examines (3) different wall cases, a cantilever retaining wall, gravity retaining wall, and rigid basement wall, through an implcit finite element analysis, under simple sinusoidal boundary accelerations. The soil is modeled using the Drucker-Prager model for elastic-plastic properties. The dynamic pressure increment is observed for different driving frequencies, with the anticipation that an in-phase and out of phase response between the soil and structure will be achieved, resulting in both lower and higher than M-O pressure values.

The current uses of unmanned aerial vehicles (UAVs) in wildland firefighting center around mapping, scouting, and firing operations. These operations and additional operations are often held back by lack of range and lift capacity of current UAV options. Software design tools were developed in this research to aid in designing a UAV for wildland firefighting. The tools help create a mission profile, estimate the mass of the UAV, select a motor and rotor, select a battery, and generate and analyze a finite element (FE) sector model. These tools leverage parametric analysis and studying existing hardware to create a design. The FE model is generated based on the mission profile, a motor and rotor, and battery as design parameters and a set of design variables. The tools developed for creating a mission profile, estimating mass, selecting a motor and rotor, and selecting a battery successfully aid the preliminary design of an octocopter, hexacopter, and quadcopter. The FE tool was designed around an octocopter's geometry, which leads to complications in generating FE models for a hexacopter or quadcopter. Recommendations were made for altering the FE tool to account for hexacopters and quadcopters. Other recommendations were made to support future work in creating an optimized design of a wildland firefighting UAV. / Master of Science / The use of multirotor UAVs in various industries is rapidly expanding. One industry that currently uses UAVs but is limited in their capabilities is wildland firefighting. Wildland firefighters use UAVs for scouting, mapping, and firing operations. Scouting includes finding road access to the fire, finding water sources, searching for spot fires, and many other applications. Mapping is typically done to understand the size of the fire. Firing operations are conducted to start small, controlled fires to remove fuel from the fires path. However, these operations as well as future applications of UAVs are often limited by the flight time and the lifting capabilities current UAV options offer. Tools were developed in this research to create a preliminary design of a UAV for wildland firefighting. The design parameters and variables of the UAV design are outlined throughout the tools. The tools allow for compiling mission requirements, selecting motors/rotors and a battery to use in the UAV, and a preliminary structural analysis of the UAV design. The preliminary structural analysis includes extracting stresses, strains, and displacements experienced through a simplified mission as well as the natural frequencies of the finite element sector model. The design of octocopters, hexacopters, and quadcopters were explored using the set of design tools. The tools were successfully in selecting components for each style of UAV and at the preliminary structural analysis of the octocopter design. However, the structural analysis was not able to be conducted for the hexacopter and quadcopter design due to geometric conditions in the finite element model.

This thesis discusses plasticity-induced crack closure based finite element simulations of small fatigue cracks in three dimensions utilizing crystal plasticity theory. Previously, modeling has been performed in two dimensions using a double-slip crystal plasticity material model. The goal of this work is to extend that research using a full three-dimensional FCC crystal plasticity material model implementation that accounts for all twelve FCC slip systems. Discussions of Python scripts that were written to perform analyses with the commercial finite element code ABAQUS are given. A detailed description of the modeling methodology is presented along with results for single crystals and bicrystals. The results are compared with finite element and experimental results from the literature. A discussion of preliminary work for the analysis of crack growth around an intermetallic particle is also presented.

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There have been several design models for single plate shear connections in the past 20 years. The current design model states that the bolt shear rupture strength of a connection is a function of the number of bolts and the a-distance, which is the distance from the weld line to the bolt line. The evaluation of this design model demonstrates inconsistent predictions for the strength of the connection. The finite element program ABAQUS was used throughout the research to study single plate shear connections. Finite element analyses included model verification and investigations of parameters, including the effect of a-distance, plate thickness, plate material, and the position of a connection with respect to a beam neutral axis. In addition, double-column bolt connections were studied. The results show that bolt shear rupture strength of a connection is not a function of the a-distance. Plate materials and thicknesses that do not satisfy ductility criteria result in connections with significant horizontal forces at the bolts. This horizontal force reduces the shear strength of a bolt group and creates a moment that must be considered in design. The magnitude of the force depends on the location of the bolt with respect to the beam neutral axis. A new design model for single plate shear connections with bolts in a single column is proposed. It was found that in double-column bolt connections, force redistribution among the bolt columns occurs. Force redistribution does not occur when thick plates are used, resulting in bolts in the outer column (from the support) fracturing while bolts in the inner column resist much less force. Further study is needed for double-column configurations. The study of plate behavior shows that the shear stress distribution when a plate reaches the strain hardening stage is not constant throughout the cross section. A relationship for calculating plate shear yielding strength based on this shear distribution is proposed. / Ph. D.

This dissertation describes the occurrence of pumping-induced earth fissures associated with quaternary faulting using numerical simulations. The Eglington Fault located in Las Vegas valley has been selected as the prototype fault described herein. The finite-element software program ABAQUS is used for the numerical simulations. The Eglington fault area is chosen because it represents one of the best examples displaying the complex relationship between fissuring, faulting and pumping-induced stress. This fault is known to influence both the vertical and horizontal deformation patterns through the accumulation of stress in its vicinity. The result is that fissures are observed on both sides of the fault and in close proximity to the fault plane. In addition to the complex fault-fissure connection, a thick caliche-rich vadose zone with weak mechanical strength allows for the initiation and propagation of fissures. The numerical analysis a) investigates the geometrical and hydromechanical features of the zone of influence surrounding the Eglington Fault; b) identifies the zones of accumulated stress on the surface and at depth that can lead to fissuring; and c) simulates the onset and propagation of tensile-induced fissures. Three-dimensional numerical simulations of this fault indicate that a 100-meter wide fault-zone composed by sand-like material best reproduces the conditions of stress that may lead to fissuring in the vicinity of the fault. Additionally, two-dimensional models reveal that two main mechanisms promote the accumulation of stress in the vicinity of the fault zone: one is the counterclockwise rotation of the unsaturated portion of the fault zone; the other is the differential compaction caused by the difference in the accumulated thickness of compressible layers. Tensile stress is concentrated on the surface in the hanging wall, but maximum shear stress zones are simulated to occur on both sides of the fault at the contact between the saturated aquifer and the vadose zone. A final analysis of the initiation and propagation of tensile-induced fissures demonstrates that fissures commence and propagate only within the vadose zone, and that the propagation path is influenced by the mechanical properties of the medium and the location of the main load, which in this case is pumping. / Ph. D.

Carbon fiber reinforced polymers (CFRP), which can be used to strengthen and repair damaged steel structures, have gained popularity in recent years. On the one hand, CFRP has demonstrated substantial advantages over conventional reinforcing techniques like welding and bolting, such as light weight, high strength, and corrosion resistance. Additionally, the CFRP application process is relatively easy, rapid, and labor-intensive. On the other hand, failure is more likely to happen at the bond interface due to the high strength characteristics of steel and CFRP. Thus, studying the bond behavior and failure mechanism of CFRP strengthened steel structures as well as the variables that are crucial to the bond quality. Prior to implementing these elements in an actual construction, it is necessary to thoroughly study the factors affecting this bond strength. Despite the fact that some theoretical predictive modeling for the strength between steel/CFRP joints under various loading situations has been published, in this work, by using finite element modelling, one may compute the failure loads and effective length of the steel/CFRP specimens quickly, simply and accurately. Additionally, factors affecting these parameters are also investigated in this study. / Master of Science / Structural Steel deteriorates over time. Due to this, engineers are constantly on the look-out for cheap and easy ways to repair and maintain these structures. One of the methods is the use of carbon fibred polymer or CFRP. In the literature, it has been frequently documented that CFRPs can make existing structures stronger. Additionally, CFRP has the advantages of not corroding and prevents the structure from becoming significantly heavier. Due to this high strength of CFRP, the failure occurs at the steel-CFRP interface and thus this bond and the factors affecting this bond needs to be studied. One way to do this is experimental testing and another way is finite element modelling which can give you data that is harder to get using experimental testing. Thus, this study focuses on finite element modelling of these joints and how it can be used for studying these joints.

This thesis introduces an approach for modeling the monotonic and cyclic response of cold-formed steel framing screw-fastened connections in commercial finite element programs. The model proposed and verified herein lays the groundwork for seismic modeling of cold-formed steel (CFS) framing including shear walls, gravity walls, floor and roof diaphragms, and eventually whole building seismic analysis considering individual fastener behavior and CFS structural components modeled with thin-shell elements. An ABAQUS user element (UEL) is written and verified for a nonlinear hysteretic model that can simulate pinching and strength and stiffness degradation consistent with CFS screw-fastened connections. The user element is verified at the connection level, including complex cyclic deformation paths, by comparing to OpenSees connection simulation results. The connection model is employed in ABAQUS shear wall simulations of recent monotonic and cyclic experiments where each screw-fastened connection is represented as a UEL. The experimental and simulation results are consistent for shear wall load-deformation response and cyclic strength and stiffness degradation, confirming the validity of the UEL element and demonstrating that light steel framing performance can be directly studied with simulations as an alternative to experiments. / Master of Science