Environmental issues enforce transportation sectors to limit their carbon dioxide emissions in various ways. Automotive manufacturers attempt to reduce carbon dioxide emission by seeking various strategies, e.g., increasing aerodynamic efficiency, using more fuel-efficient engines, reducing friction and wear of transmission systems, and, most importantly, by using lightweight materials and structures. This dissertation is a contribution toward a lightweight design of structures by proposing numerical models suitable for damage prediction of thermoplastic composite materials. In this dissertation, predictive damage models for two different length scales, namely micromechanics, and mesomechanics, were proposed. Micromechanics is used to predict the nonlinear damage behavior of elementary thermoplastic composite ply, while the mesomechanics is used to predict the failure behavior of thermoplastic composite laminates (test coupon or plate scale). For the micromechanics, a representative volume element (RVE) of such materials was rigorously determined using a geometrical two-point probability function and the eigenvalue stabilization of homogenized elastic tensor obtained by Hill-Mandel kinematic homogenization. We proposed a viscoelastic viscoplastic model for the polypropylene matrix to extend the capability of the micromechanics model in predicting the damage behavior of the composite ply at higher rates. At the mesoscale, we improved the classical mesomechanics damage modeling in the off-axis direction by introducing the confinement effect. The pragmatic approach consists of separating the progressive damage into two parts, namely “diffuse damage regime” and “transverse-cracking regime”, were described by two distinct damage parameters. We also enriched the mesomechanics model by proposing a viscoelastic and viscoplastic model to account for the rate-dependent behavior of the thermoplastic composites. We showed that the predictions given by the proposed micromechanics and mesomechanics models were in excellent agreement with the experimental results in terms of the global stress-strain curves, including the linear and nonlinear portion of the response and also the failure point, making it useful virtual testing tools for the design of thermoplastic composites.

No description available.

Research areas within the automotive industry are dedicated to reducing the weight and emissions of vehicles. Through the application of lightweight materials, such as polymers, fuel consumption and production costs can be decreased. Therefore, understanding the mechanical responses and failure mechanisms of these materials is significant to the development and design of vehicular structural components. Experimental tests were performed to capture the time, temperature, and stress state dependence, as well as failure mechanisms and large-strain mechanical responses of polypropylene (PP) and copolymer polypropylene (co-PP). Alongside studying the mechanical responses of PP and co-PP, the deformation mechanisms associated with the ductile and brittle failures were also examined. By applying an Internal State Variable (ISV) model, the mechanical behavior of PP and co-PP under various strain rates and temperatures was predicted. Phenomenological, mechanics based failure criteria were also applied to the model to predict the ductile or brittle failure of the materials.

Thermoplastic welding utilizes a fiber laser to join samples that are clamped together. Laser energy is transferred through the natural sample to the interface with the opaque sample where heat energy creates a weld through conduction and radiation heat transfer modes. The overall goal of this research is to understand the effect of heat source loading on PA6 and PA66 thermoplastic materials from laser through transmission welding that is used to join natural and opaque materials. The welding process is studied through a combination of finite element simulation, experimentation, and design of experiment modeling. The results of temperature profile and melt properties of the material are compared with weld strength and quality to provide welds used in a range of applications from the automotive industry to hermetically sealed medical components. Research of heat source models is used to determine the best representation of the laser energy for laser through transmission welding of thermoplastic materials. The comprehensive objective is to find the best fit of laser parameters to PA6 and PA66 material samples to predict weld quality in the through transmission laser welding process. Results of the research include temperature profile behavior for surface exposure and single pass weld tests, and thermal conductivity verification of PA6 and PA66 through experimentation. Finite element simulations of the experiments provide analysis of temperature dependent properties and time dependent analysis of the laser heat source loading. The Gaussian surface model with penetration variable is determined to be the best representation of the laser through transmission welding of thermoplastic material after completing heat source literature review and analysis. Finally, surface response methods were used to find the most influential parameters in laser through transmission welding, which were the number of laser passes and laser power for PA6 and PA66 materials.

No description available.

Reticulitermids were significantly more likely to discover subterranean baits connected by physical guidelines than freestanding baits under both laboratory and field conditions. In the laboratory, subterranean termites built significantly longer tunnels adjacent to cellulosic guidelines than plastic guidelines. In the field, all guideline materials were equally effective at directing tunneling activity. Reticulitermes spp. workers were tested to determine their preferred substrate temperature. The preferred range for Reticulitermes spp. workers was found to be 18 to 27 degrees C. A laboratory bioassay was performed to determine if Reticulitermes spp. aggregates within thermal shadows. Significantly more Reticulitermes spp. workers aggregated within cool thermal shadows than control areas. In a multiple choice bioassay, mean consumption was higher for paper baits treated with fructose, galactose, glucose, raffinose, sucrose, trehalose and uric acid than for control baits. In a multiple choice bioassay, mean consumption was significantly lower for baits treated with arbutin, and most amino acids than for control baits. In the no-choice bioassay, the amount of paper bait consumed did not differ significantly for any of the treated baits tested and control baits. / Ph. D.

Styrenic block copolymer thermoplastic elastomers are one of the most widely used thermoplastic elastomers (TPEs) today. The focus of this research is to fundamentally understand the structure-processs-property relationships in these materials. Deformation behavior of the block copolymers with cylindrical and lamellar morphologies has been investigated in detail using unique techniques like deformation calorimetry, transmission electron microscopy (TEM), combined in-situ small angle x-ray and wide angle x-ray scattering (SAXS/WAXS). The research involves the study of structural changes that occur at different length scales along with the energetics involved upon deformation. The structural changes in the morphology of these systems on deformation have been investigated using combined SAXS/WAXS setup. Small angle x-ray scattering probed the changes at the nano-scale of polystyrene (PS) cylinders, while wide angle x-ray scattering probed the changes at molecular length scales of the amorphous/crystalline domains of the elastomeric mid-block in these systems. TEM analysis of the crosslinked elastomers (by UV curing) further confirms the interpretation of structural details as obtained from SAXS upon deformation. New structural features at both these length scales have been observed and incorporated into the overall deformation mechanisms of the material. Characteristic structural parameters have been correlated to differences in their mechanical response in the commercially relevant cylindrical block copolymers. Effect of various process conditions and thermal treatments has been investigated. The process conditions affect the structure at both micro-scopic (grain size) and nano-scopic (domain size) length scales. A correlation has been obtained between a mechanical property (elastic modulus) and an easily measurable structural parameter (d-spacing). Effect of various phase transitions such as order-to-order transition has been studied. Selective solvents can preferentially swell one phase of the block copolymer relative to other and thus bring a change in morphology. Such kinetically trapped structures when annealed at higher temperature try to achieve their thermodynamic equilibrium state. Such changes in morphology significantly affect their tensile and hysteretic response. In another work it has been shown that by carefully compounding these styrenic block copolymers having different morphologies, it is possible to completely disrupt the local scale order and remove the grain boundaries present in these materials. Finally, a new test technique has been developed, by modifying an existing Charpy device to test polymeric films at a high strain rate. A custom designed load-cell is used for force measurements which imposes harmonic oscillations on a monotonic loading signal. The data obtained from this device can be used to analyze visco-elastic response of polymeric films at frequencies much higher than the conventional dynamic mechanical analyzer (DMA).

In recent decades, a type of shape memory polymers (SMPs), namely thermoplastic shape memory polyurethane (shape memory TPU, using TPU for short) has drawn considerable attention for its excellent shape memory properties, versatile structure and good mechanical properties. Most recently, shape memory TPU films are envisioned as a replacement for automobile exterior and interior decorative applications in the forms of laminates through in-mold forming (IMF) process. However, for a better dimensional control of laminates during the IMF, the shape memory effect of laminates needs to be controlled such that its behaviour is only noted at the time of damage and is not an instigator of delamination. In order to investigate the shape memory behavior of TPU based laminates after they had experienced normal processing such as by thermoforming, the influence of different properties were examined, including TPU film modulus, substrate used (polypropylene (PP) versus acrylonitrile butadiene styrene (ABS)), ambient temperature and the extent of deep draw, on the recovery behaviour. The study included analyses through both experimental and modelling methods. A novel thermo-mechanical cycling method was proposed to examine the shape memory property of the TPU based laminates under stretching/bending conditions more similar to thermoforming. Recovery based on this method was defined using new terms of angle recovery ratio and recovery rate. The new test examined recovery at 15oC, 45oC and 65oC; these ambient conditions were selected above and below the glass transition temperature of the TPU. Results showed that the final angle recovery ratio and recovery rate of deformed laminates based on a new commercial class of TPU shape memory polymer increased with its modulus from low to high. Substrates of higher modulus (ABS) lowered the final angle recovery ratio and recovery rate achievable for a formed laminate. Furthermore, increasing the ambient temperature increased both the final angle recovery ratios and recovery rates of formed TPU based laminates. As the extent of draw changed from 6 mm to 10mm, the final angle recovery ratios and recovery rates of formed laminates increased for all TPU films but this trend was reversed when the draw further increased beyond 10mm. The laminate system was subsequently modelled using a linear viscoelastic (SLV) constitutive model to analyze the stress-strain relationship between the substrate and TPU film layers during recovery. A model parameter related to stress transfer across the interface of these two polymer layers was fitted to the experimental results with an excellent degree of fit. The model results fitted well with experimental data and showed that the final angle recovery ratios of formed TPU laminates were mainly dependant on the moduli of TPU and substrates layers as well as the stress transfer ratio through the adhesive layer (TR). The influence of the adhesive layer was not a trivial variable in the recovery nature of the laminate. The influence of ambient temperature on the recovery behaviour of laminates was mainly due to the temperature-dependent and time-dependent Young’s modulus and relaxation time of both TPU and substrate layers. Higher relaxation times for the TPU layer or lower relaxation time for the substrate layer yielded a higher recovery rate for the laminate during the first five minutes of recovery. / Thesis / Master of Applied Science (MASc) / Special classes of Polyurethanes exhibit a strong memory of their formed shape, and hence are called shape memory polymers. Films made of these polymers are envisioned as a replacement for decorative applications in automobiles if their forming behaviour is understood. This thesis project looked at how much of that memory was preserved as a laminate after thermoforming by looking at the effect of film stiffness, backing material used (polypropylene (PP) versus acrylonitrile butadiene styrene (ABS)), ambient temperature and the extent of deep draw, using both experimental and modelling methods. Results showed that through using stiffer films, weaker substrates, high ambient temperature or an optimal extent of deep draw, recovery behavior of the shape memory polymer in these laminates can be improved, and vice versa.

Taking advantage of their inherent abrasion resistant, weather resistant, and outstanding mechanical strength, film-grade thermoplastic polyurethanes (TPU) are currently being used as paint protective films but are also being considered for paint replacement within the automotive industry. Special grades of TPU with shape memory behaviour offer an additional feature of self-healing to decorative coatings but there are concerns of shape fixity at service temperatures which are above their glass transition temperature (Tg). In this study, the shape memory behaviour of a developmental TPU film with Tg around room temperature was investigated. In order to understand the shape memory behaviour, the TPU film was laminated to a rigid polymer substrate of either polypropylene (PP) or acrylonitrile butadiene styrene (ABS). Three different acrylic based pressure sensitive adhesives were tested to bond the film to the substrate, namely a commercial high shear strength transfer tape and two solvent based adhesives of high and low shear strength that were manually cast. The influence of the adhesive was given significant attention as a variable of study in this thesis. The characterization of all the polymeric films and substrates was based on a series of thermo-mechanical tests (tensile test, stress relaxation test, DSC and DMA). The adhesives were characterized by lap-shear test, peel test, and parallel plate rheometry. The results of material characterization were used to support the analysis and interpretation of shape memory behaviour. The TPU based laminate was deformed by a matched mold thermoforming process with a pair of arched matched molds. The recovery behaviour of formed samples was quantified with a newly designed measurement method and the results were reported as recovery ratio and recovery rate. During recovery, the surrounding temperature was considered to be an important variable. The recovery behaviour of specimens was investigated in a controlled environment at setpoint temperatures of 15oC, 45oC or 65oC. No shape memory effect was found at 15oC (below TPU’s Tg), and yet both recovery ratio and recovery rate increased with temperature, from 45oC to 65oC (both above the TPU’s Tg). Since the recovery process was related to the elastic response of the hard segment phase within the TPU, the recovery stress was strongly related to strain conditions. By varying the draw depth into the mold from 6 mm, to 10 mm or 12 mm (8.86%, 15.90% or 19.88% strain, respectively), the recovery measurement results showed that the shape memory effect was weaker with lower strain as less recovery stresses were generated in the TPU film. With the draw depth of 10 mm, the highest recovery ratio and recovery rate were observed, and yet an inexplicable decrease in the recovery ratio and recovery rate occurred as the draw depth increased further from 10mm to 12mm. In regards to the influence by a substrate, TPU/PP laminate showed a more significant recovery behaviour than TPU/ABS laminates at both 45oC and 65oC. The elastic modulus of the substrate was found to have a key role on the recovery process; the recovery nature of formed laminate decreased with stiffer substrate. Three adhesives with differing rheological and adhesion properties were tested to bond the TPU film to a substrate. The formed laminates with “strongest” adhesive (transfer tape) in terms of stiffness and adhesion strength showed the highest recovery ratio/rate over laminates made with “weaker” solvent cast adhesives, at both 45oC and 65oC. A finite element analysis (FEA) was employed to simulate the stress transfer within a multilayer structure bonded by a viscoelastic adhesive layer of varying stiffness; the simulated result showed that the relatively low stiffness adhesive could reduce the stress transfer efficiency within layers of a laminate. It suggested that more recovery stresses were transferred from TPU to substrate with a stiffer adhesive layer (transfer tape) and hence increased the recovery ratio and recovery rate. Therefore, adhesive with relatively low stiffness and adhesion strength could be a better choice to reduce the recovery effect of TPU laminate after forming. However, TPU was found to slide at the unsealed edge of formed laminate when the solvent based adhesives were used; the sliding behavior reduced the recovery by releasing stored recovery stress. In the case of HS and LS adhesives at high temperature (65oC), cohesive failure was observed when the edge of specimen was sealed led to a higher bending moment thus increased the recovery ratio over 24 hours investigations. Therefore, adhesives of weaker shear strength do not necessarily overcome the nature of shape recovery by the TPU when formed part shape needs to be preserved. / Thesis / Master of Applied Science (MASc) / Nowadays, smart materials in particular shape-memory polymers have been widely used in the industrial and medical applications. Thermoplastic polyurethane (TPU) is one of the significant shape memory polymer groups. The two-phase morphology of a typical TPU gives a unique shape memory behaviour over a defined temperature range. However, this shape memory effect affects the shape fixity of formed TPU. In this study, a special-grade TPU film was laminated to a rigid polymer substrate using selected pressure sensitive adhesives (PSAs). In order to investigate the effect of adhesive layer on the shape memory behaviour of this TPU based laminate, three PSAs with varying properties were applied. The laminate was thermoformed, quenched and processed in a temperature-controlled chamber with a designed recovery measurement method. The shape memory effect was observed at temperatures above the transition temperature of TPU, and this recovery effect was enhanced at higher temperature. Furthermore, the mechanical property of the substrate material was considered as a key factor on the recovery behaviour of the laminate; the recovery of the formed laminate was restricted with a stiffer substrate. The most significant discovery from the recovery results indicated that the shape memory effect was reduced with the adhesive with relatively low adhesion strength, however, the delamination of the laminate occurs with weaker adhesives.

<p> An electrically conductive thermoplastic composite (ECTPC) consists of electrically conductive filler(s) at a concentration above percolation threshold distributed in an insulating polymer matrix. The high concentration of the filler required to achieve high electrical conductivity for ECTPC is usually accompanied with the deterioration of mechanical properties and a large increase in the viscosity which prevents feasible processing of these materials in common polymer processing equipments such as injection molding machinery. The initial focus of this work was to control these drawbacks by using combinations of conductive fillers namely carbon fiber (CF) and carbon black (CB) to create a hybrid-filler composite. Cyclic olefin copolymer (COC), an amorphous polyolefin, was used as the matrix material. It was found that carbon black and carbon fiber synergistically contribute to the transport of electrons through the matrix. The synergism exists at various filler concentrations including when one of the fillers was present below its percolation threshold, but not at high carbon fiber content. Results showed that where the concentration of CF was several fold higher than carbon black a good trade-off between viscosity and conductivity can be achieved so that the obtained composites can be reasonably processed tn common processing equipment e.g. in an injection molding machine </p> <p> Carbon fiber is preferred to carbon black as it leads to ECTPC with higher electrical conductivity and lower viscosity. However, the high aspect ratio fibers preferentially align in the flow direction leading to ECTPCs which have electrical conductivity several orders of magnitude greater in the in-plane rather than through-plane. We focused on foaming as a strategy to reorient the fibers toward the through-plane direction in foam injection molding. Through a fractional factorial experimental design, the effect of injection rate, melt temperature and mold temperature on electrical conductivity was screened at two levels for foam and nonfoam COC/CF(lO vol%)-CB(2 vol%) injection molded composites. It was found that foaming significantly enhanced the through-plane fiber orientation and through-plane conductivity of the hybrid composite at low injection rate and high melt temperature. The concurrence of the melt flow and bubble growth was considered to be the key mechanism for fiber reorientation while the cell size and shape should not disrupt the conductive path spanning the bulk of the material. </p> <p> The importance of the relative length scale of the fillers on cell size and subsequently, electrical conductivity was investigated by injection molding. Results showed that where the length scale of the filler was comparable to the cell size, as for foamed COC/CF composites, the conductivity considerably decreases with foaming. The drop was greater in the through plane direction and smaller in the in-plane direction for the composites with larger average fiber length. Also smaller cells led to a larger drop in the composite conductivity. It was observed that where the length scale of the filler was much smaller than the cell size as such for COC/CB composites, foaming enhanced the electrical conductivity particularly in the through-plane directions and its effects became more pronounced at lower carbon black concentrations. It was proposed that induced carbon black coagulation by foaming was the main reason for the observed improvement in conductivity. For COC/CF-CB hybrid composites, enhancement in through-plane conductivity, particularly at CB concentration below percolation, via foaming inferred that CB aggregates significantly contributed in improving fiber-fiber contacts. </p> <p> Reorientation of the fibers by foaming was found to be very dependent on processing conditions. High viscosity and fiber- fiber interactions can hinder fiber rotation. The general understanding of the investigation was that fiber reorientation may occur where the cells are much larger than the fibers. In comparison, a series of nonfoam injection molded composites containing CF, CB and CF-CB were foamed in a batch process to avoid flow effects. The insignificant change in fiber orientation with foaming proved that fibers can not rotate by the growth of an adjacent cell in the absence of shear. Also, a large drop in electrical conductivity with foaming as compared to the foam injection molded composites suggested that particle relocalization can not occur in batch foaming. </p> / Thesis / Doctor of Philosophy (PhD)