TRIP-assisted multiphase steels exhibit an excellent balance of strength and ductility, which makes them very attractive for the automotive industry. These remarkable mechanical properties can be attributed mainly to the continuous transformation of retained austenite into martensite during straining (TRansformation Induced Plasticity). The aim of this thesis was to clarify the interaction between the hot rolling conditions, the formation of microstructure, and the resulting mechanical properties. Various rolling simulation techniques were employed to determine how the composite microstructure is formed during the various steps of multi-stage thermomechanical processing. The interaction between deformation and phase transformation is highlighted, particularly from the viewpoint of the transformation texture.

<p align='justify'>This thesis is devoted to the micromechanical study of the size-dependent strengthening in Transformation Induced Plasticity (TRIP) steels. Such grades of advanced high-strength steels are compelling for the automotive industry, due to their improved mechanical properties. Among others, they combine a good strength versus ductility balance. In this context, many research works have been carried out to study these grades of steels. In particular, from a numerical point of view, earlier studies within the framework of classical plasticity do not properly reproduce the strengthening levels characterizing TRIP steels and obtained experimentally.</p> <p align='justify'>In this study, the strain gradient plasticity theory presented by Fleck and Hutchinson (2001) is chosen to account for the strengthening effect resulting from the phase transformation. A two-dimensional embedded cell model of a simplified microstructure composed of small cylindrical metastable austenitic inclusions, partially undergoing the phase transformation, within a ferritic matrix is used.</p> <p align='justify'>First, the single-parameter version of the strain gradient plasticity theory under small strain assumption is used for the simulations. The impact of the higher order boundary conditions is assessed. It is shown that, when the plastic flow is unconstrained at the elasto-plastic boundaries, the transformation strain has no significant impact on the overall strengthening. The strengthening is essentially coming from the composite effect with a marked inclusion size effect resulting from the appearance during deformation of new boundaries (at the interface between parent and product phases) constraining the plastic flow.</p> <p align='justify'>Second, the multi-parameter version of the strain gradient plasticity theory, incorporating separately the rotational and extensional gradients in the formulation, is employed under small strain assumption. The effect of the plastic strain gradients resulting from the transformation strain is better captured. In particular, the results show a significant influence of the shear component of the transformation strain. An implicit confinement effect is revealed at the elasto-plastic boundaries which is partly responsible for the transformation strain effect. Size effects on the overall strengthening are also revealed, due to a combined size dependent effect of the transformation strain and of the evolving composite structure.</p><p align='justify'>Third, the extension of the strain gradient plasticity theory to a finite strain description is applied. A significant effect of the transformation strain is obtained with the multi-parameter version of the theory as well as an optimal austenite grain size improving the damage resistance of the martensite, in agreement with the typical grain size of the current TRIP-assisted steels (Jacques et al., 2007).</p>

Traffic assignment is the last step in the conventional four-step transportation planning model, following trip generation, trip distribution, and mode choice. It concerns selection of routes between origins and destinations on the traffic network. Traditional traffic assignment methods do not consider trip chaining behavior. Since commuters always make daily trips in the form of trip chains, meaning a traveler’s trips are sequentially made with spatial correlation, it makes sense to develop models to feature this trip chaining behavior. Network performance in congested areas depends not only on the total daily traffic volume but also on the trip distribution over the course of a day. Therefore, this research makes an effort to propose a network traffic assignment framework featuring commuters’ trip chaining behavior. Travelers make decisions on their departure time and route choices under a capacity-constrained network. The modeling framework sequentially consists of an activity origin-destination (OD) choice model and a dynamic user equilibrium (DUE) traffic assignment model. A heuristic algorithm in an iterative process is proposed. A solution tells commuters’ daily travel patterns and departure distributions. Finally, a numerical test on a simple transportation network with simulation data is provided. In the numerical test, sensitivity analysis is additionally conducted on modeling parameters.

Allt fler kunder söker sig i dag till så kallade tredjepartskanaler på internet för att boka hotell. En tredjepartskanal är en hemsida som samlar ett flertal hotell som kunden kan jämföra och välja mellan. I anslutning till dessa internetbaserade tredjepartskanaler finns vanligtvis kommentarsfält där kunder som tidigare bott på hotellen kan dela med sig av sin upplevelse genom kommentarer, det vill säga word-of-mouth. Dessa kommentarer har enligt forskning stor inverkan på kommande kunders köpbeslut, vilket motiverar en studie som undersöker hotells kunskap och arbete med word-of-mouth. Detta undersöks genom en kvalitativ fallstudie av svenska hotell. Undersökningen visar att kunskapen på flera håll är begränsad och att det operativa arbetet med word-of-mouth i många fall kan förbättras.

Most e orts on High Temperature Shape Memory Alloys (HTSMAs), have focused on improving their work characteristics by thermomechanical treatment methods. However, the in uence of transformation induced plasticity (TRIP) and viscoplasticity during actuation has not been studied. The objective of this dissertation work was to study the in uence of plasticity and viscoplasticity on the transformation characteristics that occur during two common actuation-loading paths in TiPdNi HTSMAs. Thermomechanical tests were conducted along di erent loading paths. The changes in the transformation temperature, actuation strain and irrecoverable strain during the tests were monitored. Transmission Electron Microscopy (TEM) studies were also conducted on select test specimens to understand the underlying microstructural changes. The study revealed that plasticity, which occurs during certain actuation load paths, alters the transformation temperatures and/or the actuation strain depending on the loading path chosen. The increase in the transformation temperature and the irrecoverable strain at the end of the loading path indicated that the rate independent irrecoverable strain results in the generation of localized internal stresses. The increased transformation temperatures were mapped with an equivalent stress (which corresponds to an internal stress) using the as-received material's transformation phase diagram. A trend for the equivalent internal stress as a function of the applied stress and accumulated plastic strain was established. Such a function can be implemented into thermomechanical models to more accurately capture the behavior of HTSMAs during cyclic actuation. On the contrary, although the viscoplastic strain generated during the course of constant stress thermal actuation could signi cantly reduce actuation strain depending on the heating/cooling rate. Additional thermomechanical and microstructural tests revealed no signi cant change in the transformation behavior after creep tests on HTSMAs. Comparing the thermomechanical test results and TEM micrographs from di erent cases, it was concluded that creep does not alter the transformation behavior in the HTSMAs, and any change in the transformation behavior can be attributed to the retained martensite which together with TRIP contributes to the rate independent irrecoverable strain. As a consequence, a decrease in the volume fraction of the martensite contributing towards the transformation must be considered in the modeling.

Transformation Induced Plasticity (TRIP) steels have both high strength and high ductility. Retained austenite in the microstructure, upon straining, transforms to martensite and this absorbs energy and improves the work hardening of the steel, giving improved elongation. The transformation can be either stress-assisted or strain-induced and the initiation and the mechanism depend on the composition of, the size and shape of, and the phases surrounding, the austenite grains. It is important to understand the relationship between these variables and the properties of the TRIP steel. The aim of this work was to determine how the microstructure of the TRIP steel affects the transformation. Four experimental microstructures were developed, containing austenite grains with different sizes, shapes, and surrounding phases. The Fine microstructure had thin elongated austenite laths between fine bainitic ferrite laths, the Coarse microstructure had elongated austenite grains between coarser bainitic ferrite laths, the Equiaxed microstructure had equiaxed austenite grains in a matrix of equiaxed ferrite and the Acicular microstructure had elongated austenite grains surrounded by recovered ferrite laths. Tensile tests were performed and detailed characterization, using neutron diffraction, was done of samples with the four microstructures. The variation in the amount of austenite during deformation was measured. The tensile tests revealed that the microstructures had different mechanical properties and different transformation behaviours. Fine had the lowest elongation and the highest strength. Acicular and Equiaxed had good elongation but lower strength. Coarse had intermediate strength and Equiaxed had sustained work hardening. The transformation in Fine and Coarse was minimal. Coarse had some slow, steady transformation, but Fine may have had none. The transformation in Equiaxed was larger. It started quickly and then slowed at higher strains. The austenite in Acicular transformed steadily. The predominant mechanism of transformation was stress-assisted transformation, with strain-induced transformation occurring only in Equiaxed. The results of this work showed that the influence of the surrounding phases on the stability of the austenite is significant. The differences in the transformation behaviour of the four microstructures seemed to be due more to the surrounding phases than the grain size or the composition, although both these factors also played a role. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2007-12-14 13:35:07.248

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Purpose The purpose of the paper is to understand how crucial of importance is e-WOM within the French tourism industry with a focus on trip retailers – travel agencies and tour-operators – by observing and analyzing how they encourage and manage e-WOM.   Methodology The paper uses deductive approach with a triangulation method based on a qualitative research through 24 semi-structured telephone interviews and a quantitative research through the behavior analysis of 112 trip retailers on online communities. Findings It was found that the French trip retailers encourage e-WOM by primarily joining and using online communities via posting pictures and special offers at least twice a week on social networks. Besides, among those that collect and manage positive and negative comments, they mainly do it on Facebook by rather adopting a non-defensive attitude. Managerial implications The authors suggest trip retailers not use as many online communities they can but regularly be active on the one(s) they choose to use. Moreover, responding not only to negative but also to positive e-WOM may be a strategy that paid off since few trip retailers take it into consideration. Regarding the management of negative e-WOM, the authors recommend against deleting non-eulogistic comments and reply publicly within 24 hours.   Limitations This study was limited to French trip retailers and cannot consequently be generalised for all international trip retailers. Additionally, the specific sector trip retailers work with has not been taken into consideration. Moreover, even if trip retailers have been classified within four categories, no deeply correlation has been studied between the size and their online activity.   Further research suggestions Future research is needed to possibly confirm and subsequently generalise the findings of this paper to the overall tourism industry in France. Moreover, it is necessary to compare what trip retailers think to do and what they really do on the web and determine a degree of relevance. Furthermore, due to the constantly growing interest for online communities by tourism professionals, an updated study of that one should be conducted during the next five years and results compared. It would be finally also interesting to measure the impact of e-WOM on online communication strategies   Article classification Qualitative and quantitative studies

Trip chaining and mode choice are two important travel behavior decisions in activity-based travel demand modeling system. The hierarchy of these two decisions influences models predictive capability and policy sensitivity. This thesis is aimed at investigating the hierarchical relationship between these decisions and also the effects of socio-demographic characteristics on them. Structural Equation Modeling (SEM) technique is used for this investigation. A six week travel diary data collected in Thurgau, Switzerland in 2003 is used for model estimation. Model estimation results show that for work-tour, trip chain and mode choice decisions are simultaneous and it remains consistent across the six weeks. For weekdays non-work tour, mode choice precedes trip chain whereas for weekends non-work tour trip chain precedes mode choice. The investigation of the effect of a number of socio-demographic characteristics on trip chaining and mode choice behaviors is also found useful for better understanding of these behaviors. / Transportation Engineering

Industries, such as the automotive industry, aim to increase the reliability of their products to match the demands and assure the safety of their clients. The proposition of a third generation advanced high strength steel is introduced in this study. The ideas surrounding the behavior of transformation induced plasticity (TRIP) steels and particle reinforced composites are combined and investigated. A finite element model (FEM) is created to investigate the effects of dispersed ceramic particles with varying parameters throughout a TRIP steel microstructure and identify key mechanisms responsible for achieving simultaneous enhancements in strength and ductility. The ceramic material utilized and volume fraction of the ceramic particles dispersed throughout the representative volume element (RVE) are the two varying parameters investigated in this study. Through observing the equivalent plastic strain (PEEQ) distribution at different strain levels up to 100%, evidence of failure controlled by strain localization throughout the ferrite matrix is more prevalent through the softer, austenitic microstructures with 5% or less ceramic particle inclusions. On the other hand, the presence of the hard martensite constituents, or 10% volume fraction of ceramics in an austenitic structure, proposed that failure would engender due to void nucleation at the harder constituent/ferrite interfaces. These voids will then grow and coalesce throughout the microstructure, resulting in a crack. The increased addition of ceramic inclusions also illustrates a simultaneous enhancement in the ultimate tensile strength and ultimate strain in all microstructures. Tensile strength increases by a total of 18% with 10% volume ceramic particles in a TRIP steel microstructure. Between utilizing silicon carbide, cementite, zirconia and aluminum oxide ceramic particles, the microstructure that illustrated the most optimal enhanced performance in strength and ductility was the 10% volume fraction aluminum oxide particle reinforced TRIP steel composite.