The high strain rate fiber direction tensile response of Ultra High Molecular Weight Polyethylene (UHMWPE) composites is of interest in applications where impact damage may occur. This response varies substantially with strain rate. However, physical testing of these composites is difficult at strain rates above 10^-1/s. A Monte Carlo simulation of composite tensile strength is constructed to estimate the tensile behavior of these composites. Load redistribution in the vicinity of fiber breaks varies according to fiber and matrix properties, which are in turn strain rate dependent. The distribution of fiber strengths is obtained from single fiber tests at strain rates ranging from 10^-4/s to 10^-1/s and shifted using the time-Temperature Superposition Principle (tTSP) to strain rates of 10^-4/s to 10^6/s. Other fiber properties are obtained from the same tests, but are assumed to be deterministic. Matrix properties are also assumed to be deterministic and are obtained from mechanical testing of neat matrix material samples. Simulation results are compared to experimental data for unidirectional lamina at strain rates up to 10^-1/s. Above 10^-1/s, simulation results are compared to experimental data shifted using tTSP. Similarly, through-thickness shear response of UHMWPE composites is of interest to support computational modeling of impact damage. In this study, punch shear testing of UHMWPE composites is conducted to determine shear properties. Two test fixtures, one allowing, and one preventing backplane curvature are used in conjunction with finite element modeling to investigate the stress state under punch shear loading and the resulting shear strength of the composite. / Ph. D.

The objective of this dissertation centers on gaining a better understanding of the structure - property - performance relations of nickel and copper through the advanced multiscale theoretical framework and integrated computational methods. The goal of this dissertation also includes to combine material science and computational mechanics to acquire a transformative understanding of how the different crystal orientations, size scales, and penetration velocities affect plastic deformation and damage behavior of metallic materials during high strain rate (> 103s-1) processes. A multiscale computational framework for understanding plasticity and shearing mechanisms of metallic materials during the high rate process was developed, which for the first time reveals micromechanical insights on how different crystal orientations, size scales, and penetration velocities affect the atomistic simulations which render structure property information for plasticity, shearing and damage mechanisms. The contributions of this dissertation include: (1) Comprehensive understanding of the plasticity and shearing mechanisms between the nickel penetrator and copper target under high strain rates (2) Development of a multiscale study of a nickel penetrator striking a copper plate by employing macroscale simulations and atomistic simulations to better understand the micromechanisms. (3) An essential description of how different crystal orientations, size scales, and strain rates affect the plasticity and shearing mechanisms.

In this thesis, the dynamic structural response of six scaled flexural masonry walls to scaled blast loading is experimentally investigated. These walls have been tested in at an open range with charge masses ranging from 5 kg to 25 kg of Pentex-D explosive material with a TNT equivalency of 1.2, and with a constant stand-off distance of 5 m throughout testing. The field properties of the blast wave, which includes the reflected and free field pressures, were recorded. Additionally, the displacement response histories of the wall over the blast test were recorded and the post-blast damage was documented. This study puts forth several potential models for the analysis of the experimental data. The experimentally obtained blast characteristics were compared to predictions of the Kingery and Bulmash (K-B) model. The strain rates used during the study are equivalent to those developed by a number of studies for the materials used in the construction of the specimens. The results obtained through the experimental program are compared to those from a variety of single degree of freedom models, ranging from simplified linear relationships to complex stress-strain relations accounting for the effects that arise because of the increased strain rate due to blast testing. The simplified model assumes a constant stiffness, mass, and triangular pressure profile to determine the peak deflection of the specimen during an experimental test. The bilinear and nonlinear models are based on the discretization of the wall sections into a number of layers, and using strain-rate dependent, stress-strain relations of the constituent materials to generate stresses within the layers. These stresses then iv form the basis of the resistance function to determine the structural response of the test specimens. In this study, the effect of higher modes of vibration on the test specimens is not included. The bilinear and nonlinear models are then implemented to develop Pressure-Impulse (P-I) diagrams, and the effect of the strain rate on P-I diagrams is investigated. The P-I are then available to be implemented into the recent blast code for reinforced masonry flexural walls. The fitted results of the recorded experimental blast pressure parameters are shown to be adequately approximated by the software ConWep in terms of the peak pressure and specific impulse. Comparing the K-B model, which forms the theoretical basis of ConWep, to the raw pressure profile data obtained from the experimental testing, a significant variations is found in the pressure data while significant scatter is found in the impulse. The analytical results show that increasing the nonlinearity of the material accounts for; the response predicted by the single degree of freedom model more closely relates to the response of the specimens. In addition, strain rate effects have a significant impact on the potential level of protection (LOP) provided by masonry flexural walls, as it has a noticeable effect on the curves of the P-I diagram. / Thesis / Master of Applied Science (MASc)

In this work, Slow Strain Rate Test (SSRT) testing, Light Optical Microscopy (LOM) and Scanning Electron Microscopy (SEM) were used to study the effect of microstructure, corrosive environments and cathodic polarisation on stress corrosion cracking (SCC) of two grades of high strength steels, Type A and Type B. Type A is manufactured by quench and tempered (Q&T) method. Type B, a normalize steel was used as reference. This study also supports electrochemical polarisation resistance method as an effective testing technique for measuring the uniform corrosion rate. SSRT samples were chosen from base metal, weld metal and Heat Affected Zone (HAZ). SSRT tests were performed at room temperature under Open Circuit Potential (OCP) and cathodic polarisation using 4 mA/cm2 in 1 wt% and 3.5 wt% NaCl solutions. From the obtained corrosion rate measurements performed in 1 wt% and 3.5 wt% NaCl solutions it was observed that increased chloride concentration and dissolved oxygen content enhanced the uniform corrosion for all tested materials. Moreover, the obtained results from SSRT tests demonstrate that both Q&T and normalized steels were not susceptible to SCC in certain strain rate (1×10-6 s-1) in 1 wt% and 3.5 wt% NaCl solutions under OCP condition. It was confirmed by a ductile fracture mode and high reduction in area. The weld metal of Type A with acicular ferrite (AF), pro-eutectoid (PF) and bainite microstructure showed higher susceptibility to hydrogen assisted stress corrosion cracking compared to base metal and HAZ. In addition, typical brittle intergranular cracking with small reduction in area was observed on the fracture surface of the Type A due to hydrogen charging.

No description available.

Friction stir welding (FSW) of HSLA steel commonly produces a hard zone (HZ) on the advancing side (AS) of the weld. Despite its detrimental effects on weld toughness, the mechanisms of its formation have not been thoroughly investigated and are not well understood. This paper investigates the various mechanisms in FSW believed to affect the weld HZ, namely: strain, strain-rate, peak temperature and cooling rate. Gleeble tests indicate that strain and strain rate have negligible effects on weld HZ with cooling rate and peak temperature as dominant effects. Jominy tests resulted in cooling rate having 270% greater influence than peak temperature on the formation of lath ferrite microstructures similar to what is observed in the HZ of FSW X65. Comparing weld HZ microstructures to Jominy tests, it is estimated that cooling rates on the AS of the weld are at least 150°C/s higher than the retreating side. Reducing the cooling rate on the AS will likely lead to an improved microstructure at the weld HZ.

The inland waterway system in the United States is fundamental to the transportation system as a whole and the success of the nation’s economy. Barge transportation in these waterways levitates congestion on the highway system and is beneficial when comparing barge transportation to other modes of freight transportation in measures of capacity, congestion, emissions, and safety. Unavoidably, the highway system intersects with the waterways, resulting in the risk of vessels collision into bridge structures. Particularly for barge impact, the literature is questioning the accuracy and oversimplification of the current design specifications. The impact problem was investigated in this research using three-dimensional finite-element analyses. To investigate the collision of a barge into a bridge pier, a range of material models are first investigated through simulating a drop-hammer impact onto a reinforced concrete beam. A detailed model of a jumbo hopper barge is then developed, with particular detail in the bow. The barge model is examined for its response to impact into rigid piers of different size and shape. RC piers, having different shape and boundary conditions, are impacted by the barge model and assessed using selected metrics. The final part of the research examines the response of an existing bridge pier subject to an impact by a chemical transporter barge that frequently travels in the waterway.

Mitigation of the blast risk associated with terrorist attacks and accidental explosions threatening critical infrastructure has become a topic of great interest in the civil engineering community, both in Canada and abroad. One method of mitigating blast risk is to retrofit vulnerable structures to resist the impulsive effects of blast loading. A comprehensive re-search program has been undertaken to develop fibre reinforced polymer (FRP) retrofit methodologies for structural and non-structural elements, specifically reinforced concrete slabs and walls, subjected to blast loading. The results of this investigation are equally valid for flexure dominant reinforced concrete beams subject to blast effects. The objective of the research program was to generate a large volume of research data for the development of blast-resistant design guidelines for externally bonded FRP retrofit systems. A combined experimental and analytical investigation was performed to achieve the objectives of the program. The experimental program involved the construction and simulated blast testing of a total of thirteen reinforced concrete wall and slab specimens divided into five companion sets. These specimens were subjected to a total of sixty simulated explosions generated at the University of Ottawa Shock Tube Testing Facility. Companion sets were designed to study one- and two-way bending, as well as the performance of specimens with simply-supported and fully-fixed boundary conditions. The majority of the specimens were retrofitted with externally bonded carbon fibre reinforced polymer (CFRP) sheets to improve overall load-deformation characteristics. Specimens within each companion set were subjected to progressively increasing pressure-impulse combinations to study component behaviour from elastic response up to inelastic component failure. The blast performance of companion as-built and retrofitted specimens was quantified in terms of measured load-deformation characteristics, and observed member behaviour throughout all stages of response. The results show that externally bonded FRP retrofits are an effective retrofit technique to improve the blast resistance of reinforced concrete structures, provided that debonding of the composite from the concrete substrate is prevented. The test results also indicate that FRP retrofitted reinforced concrete structures may survive initial inbound displacements, only to failure by moment reversals during the negative displacement phase. The experimental test data was used to verify analytical techniques to model the behaviour of reinforced concrete walls and slabs subjected to blast loading. The force-deformation characteristics of one-way wall strips were established using inelastic sectional and member analyses. The force-deformation characteristics of two-way slab plates were established using commonly accepted design approximations. The response of all specimens was computed by explicit solution of the single degree of freedom dynamic equation of motion. An equivalent static force procedure was used to analyze the response of CFRP retrofitted specimens which remained elastic after testing. The predicted maximum displacements and time-to-maximum displacements were compared against experimental results. The analysis indicates that the modelling procedures accurately describe the response characteristics of both retrofitted and unretrofitted specimens observed during the experiment.

The application of polymers in robust engineering designs is on the rise due to their excellent mechanical properties such as high fracture toughness, specific strength, durability, as well as, thermal and chemical resistances. Implementation of some advanced polymeric solids is limited due to the lack of available mechanical properties. In order for these materials to endure strenuous engineering designs it is vital to investigate their response in multiple loading rates and conditions. In this thesis, the mechanical response of polyethermide (PEI) is characterized under quasi-static, high strain rate, and multiple impact conditions. Standard tension, torsion, and compression experiments are performed in order to distinguish the multi-regime response of PEI. The effects of physical ageing and rejuvenation on the quasi-static mechanical response are investigated. The strain softening regime resulting from strain localization is eliminated by thermal and mechanical rejuvenation, and the advantages of these processes are discussed. The dynamic fracture toughness of the material in response to notched impact via Charpy impact test is evaluated. The high strain-rate response of PEI to uniaxial compression is evaluated at rates exceeding 104/s via miniaturized Split Hopkinson Pressure Bar (MSHPB), and compared to the quasi-static case to determine strain-rate sensitivity. The elastic response of the aged material to multiple loading conditions are correlated using the Ramberg-Osgood equation, while the elastoplastic response of rejuvenated PEI is correlated using a both the Ramberg-Osgood equation and a novel model. The strain-rate sensitivity of the strength is found to be nominally bilinear and transition strains are modeled using the Ree-Erying formulation. Finally, multiple impact experiments are performed on PEI using the MSHPB and a model is proposed to quantify damage as a result of collision.

As technology is developing in all automotive companies, car body designers have also investigated new materials such as composite and aluminum alloys. Designing modern car structures has also created various challenges in the production process, including formability limitations. The main purpose of this research work was to develop a test setup for an open-hole uniaxial tensile test and investigate the effect of the cutting tool on the shearing edge quality of the series 6000 aluminum alloy and materials formability as a result. To approach this significant issue, detecting the onset of necking and forming limit curves FLC using 3D digital image correlations (DIC) capabilities were studied. Two methods based on strain rate for evaluating the instability through 3D DIC and Matlab were applied. Eighteen specimens in rolling, transverse, and diagonal directions were investigated. Although the results of the tensile test machine are close for all tests, due to 3D DIC limitations, detecting the onset of necking was hard to obtain.