The primary objective of this work was to develop a laser source for fundamental investigations in the field of laser – materials interactions. In particular it is supposed to facilitate the study of the influence of the temporal energy distribution such as the interaction between adjacent pulses on ablation processes. Therefore, the aim was to design a laser with a highly flexible and easily controllable temporal energy distribution. The laser to meet these demands is an SBS-laser with optional active mode-locking. The nonlinear reflectivity of the SBS-mirror leads to a passive Q-switching and issues ns-pulse bursts with µs spacing. The pulse train parameters such as pulse duration, pulse spacing, pulse energy and number of pulses within a burst can be individually adjusted by tuning the pump parameters and the starting conditions for the laser. Another feature of the SBS-reflection is phase conjugation, which leads to an excellent beam quality thanks to the compensation of phase distortions. Transverse fundamental mode operation and a beam quality better than 1.4 times diffraction limited can be maintained for average output powers of up to 10 W. In addition to the dynamics on a ns-timescale described above, a defined splitting up of each ns-pulse into a train of ps-pulses can be achieved by additional active mode-locking. This twofold temporal focussing of the intensity leads to single pulse energies of up to 2 mJ at pulse durations of approximately 400 ps which corresponds to a pulse peak power of 5 MW. While the pulse duration is of the same order of magnitude as those of other passively Q-switched lasers with simultaneous mode-locking, the pulse energy and pulse peak power exceeds the values of these systems found in the literature by an order of magnitude. To the best of my knowledge the laser presented here is the first implementation of a self-starting mode-locked SBS-laser oscillator. In order to gain a better understanding and control of the transient output of the laser two complementary numerical models were developed. The first is based on laser rate equations which are solved for each laser mode individually while the mode-locking dynamics are calculated from the resultant transient spectrum. The rate equations consider the mean photon densities in the resonator, therefore the propagation of the light inside the resonator is not properly displayed. The second model, in contrast, introduces a spatial resolution of the resonator and hence the propagation inside the resonator can more accurately be considered. Consequently, a mismatch between the loss modulation frequency and the resonator round trip time can be conceived. The model calculates all dynamics in the time domain and therefore the spectral influences such as the Stokes-shift have to be neglected. Both models achieve an excellent reproduction of the ns-dynamics that are generated by the SBS-Q-switch. Separately, each model fails to reproduce all aspects of the ps-dynamics of the SBS-laser in detail. This can be attributed to the complexity of the numerous physical processes involved in this system. But thanks to their complementary nature they provide a very useful tool for investigating the various influences on the dynamics of the mode-locked SBS-laser individually. These aspects can eventually be recomposed to give a complete picture of the mechanisms which govern the output dynamics. Among the aspects under scrutiny were in particular the start resonator quality which determines the starting condition for the SBS-Q-switch, the modulation depth of the AOM and the phonon lifetime as well as the Brillouin-frequency of the SBS-medium. The numerical simulations and the experiments have opened several doors inviting further investigations and promising a potential for further improvement of the experimental results: The results of the simulations in combination with the experimental results which determined the starting conditions for the simulations leave no doubt that the bandwidth generation can primarily be attributed to the SBS-Stokes-shift during the buildup of the Q-switch pulse. For each resonator round trip, bandwidth is generated by shifting a part of the revolving light in frequency. The magnitude of the frequency shift corresponds to the Brillouin-frequency which is a constant of the SBS material and amounts in the case of SF6 to 240 MHz. The modulation of the AOM merely provides an exchange of population between spectrally adjacent modes and therefore diminishes a modulation in the spectrum. By use of a material with a Brillouin-frequency in the GHz range the bandwidth generation can be considerably accelerated thereby shortening the pulse duration. Also, it was demonstrated that yet another nonlinear effect of the SBS can be exploited: If the phonon lifetime is short compared to the resonator round trip time we obtain a modulation in the SBS-reflectivity that supports the modulation of the AOM. The application of an external optical feedback by a conventional mirror turns out to be an alternative to the AOM in synchronizing the longitudinal resonator modes. The interesting feature about this system is that it is ― although highly complex in the physical processes and the temporal output dynamics ― very simple and inexpensive from a technical point of view. No expensive modulators and no control electronics are necessary. Finally, the numerical models constitute a powerful tool for the investigation of emission dynamics of complex laser systems on arbitrary timescales and can also display the spectral evolution of the laser output. In particular it could be demonstrated that differences in the results of the complementary models vanish for systems of lesser complexity. / Ziel der Arbeit ist die Entwicklung einer Laserstrahlquelle, die zur Untersuchung von Laser-Material-Wechselwirkungen eingesetzt werden soll. Im Mittelpunkt des Interesses steht hierbei der Einfluss der zeitlichen Pulsstruktur des Lasers auf Materialabtragsprozesse. Daraus ergibt sich die Anforderung einer möglichst hohen Flexibilität in der Pulsstruktur des Lasers sowie einer möglichst guten Strahlqualität. Eine gute Strahlqualität zeichnet sich durch eine homogene räumliche Intensitätsverteilung aus und ist Voraussetzung für eine gezielte Energiedeponierung auf dem Material. Diese Anforderungen wurden mit einem SBS-Laser erfüllt. Dabei handelt es sich um einen Laser, der einen SBS-Spiegel verwendet, dessen Reflektivität auf der Streuung des Lichts an Schallwellen beruht, die von dem einfallenden Licht selbst erzeugt werden. Als Resultat hat dieser Spiegel eine Reflektivität, die abhängig von der Energie des eingestrahlten Lichts ist. In einem Laser verwendet führt diese energieabhängige Reflektivität zu einer sogenannten Güteschaltung, die sich in der Ausbildung von kurzen Lichtpulsen mit Dauern von etwa 100 Nanosekunden äußert. Die Abstände zwischen den Pulsen, die Pulsdauern und die Pulsenergien können sehr leicht durch die Randbedingungen, wie etwa die Reflektivität der konventionellen Spiegel des Lasers, gesteuert werden. Durch eine zusätzliche, aktiv herbeigeführte Verlustmodulation im Laserresonator wird eine Aufspaltung der Nanosekundenpulse in eine Reihe von Pulsen mit Dauern von nur noch einigen 100 Pikosekunden erreicht. Diese Technik ist unter dem Begriff Modenkopplung bekannt. Es liegt jetzt also eine doppelte Pulsstruktur vor: Nanosekundenpulse, die sich jeweils aus vielen Pikosekundenpulsen zusammensetzen. Durch diese doppelte zeitliche Bündelung der Ausgangsleistung werden während der Pulse Spitzenleistungen von bis zu 5 MW erreicht. Die Pulsenergien der ps-Pulse erreichen bis zu 2 mJ. Diese Werte liegen um den Faktor 10 über denen vergleichbarer Systeme. Meines Wissens ist dies die erste Umsetzung eines selbsttätigen SBS-Lasers mit zusätzlicher Modenkopplung. Um die verschiedenen Einflüsse auf diese Emissionsdynamik besser verstehen und kontrollieren zu können, wurden zwei Modelle mit komplementären Ansätzen entwickelt, auf deren Basis diese Dynamik durch numerische Simulationen wiedergegeben werden kann. Insbesondere können auf diese Weise auch die Einflüsse von einzelnen Materialparametern isoliert betrachtet werden, was im Experiment im allgemeinen nicht möglich ist. Der SBS-Laser wurde bereits erfolgreich in Laser-Materialbearbeitungsexperimenten eingesetzt. So konnte beispielsweise gezeigt werden, dass sich die Bearbeitungsdauer beim Wendelbohren durch die Verwendung von Pulszügen, also einer Reihe kurz aufeinander folgender Pulse, gegenüber dem Einsatz von Pulsen mit gleichmäßigen Abständen erheblich verbessern lässt.

This thesis is about a behavioural medicine approach in periodontal treatment and oral hygiene self-care. The aim of this thesis was to develop, describe, and evaluate an individually tailored oral health educational program on oral hygiene behaviour and non-surgical periodontal treatment success, and to determine factors of importance for predicting oral hygiene behaviour. Two separate studies, both conducted at a specialist clinic for periodontics in a Swedish county council are described. In the first study, the program was developed and described in two experimental single-case studies with multiple baseline designs (Paper I). The second study was a randomised controlled single-blinded trial [n = 113, mean age 51.2, 53% female] in which, the effectiveness of the program was compared with standard treatment on oral hygiene habits, plaque control, and gingivitis (Paper II), periodontal status (Paper III), and attitudes, subjective norms, and self-efficacy (Paper IV). The tailored oral health educational program included a motivational interviewing method and cognitive behavioural techniques, and the individual tailoring for each participant was based on participants’ thoughts and cognitions, intermediate and long-term goals, and oral health status. Participants in the individually tailored program reported higher frequency of daily interdental cleaning and were more confident about maintaining the attained level of behaviour change, had better oral hygiene, and healthier gingival tissue, particularly interproximally. There was a great reduction in periodontal pocket depth and bleeding on probing scores (BoP) for participants in both programs with a greater reduction in BoP scores in the tailored-treatment group. A lower dental plaque score at treatment start increased the predicted probability of attaining treatment success, and self-efficacy towards interdental cleaning predicted oral hygiene behaviour. These studies demonstrate an individually tailored oral health education program is preferable to standard program as an oral hygiene behaviour change interventions in non-surgical periodontal treatment. / Behavioural medicine perspectives for change and prediction of oral hygiene behaviour

Litteratur som berör begreppet individanpassad undervisning framhåller både positiva samt negativa aspekter, vad beträffar detta arbetssätt. Med denna bakgrund fann vi det intressant att undersöka hur verksamma pedagoger i grundskolans tidiga år, uttrycker sig om individanpassad undervisning. För att studera hur det ser ut i verksamheten, valde vi att använda oss av en kvalitativ metod med intervjuer som teknik för insamlande av data. Det material som samlats in har analyserats och beskrivits med hjälp av teorianknytning. Resultatet visade att tidsrelaterad individualisering är den form som tillämpas mest i undervisningen, men respondenterna poängterar också betydelsen av att anpassa undervisningen till den nivå där eleven befinner sig, det vill säga svårighetsrelaterad individualisering. Respondenterna vidhöll även att denna arbetsform är till fördel för de svagpresterande eleverna, något som skiljer sig från den forskning som framkommit inom området. En annan intressant aspekt som vi kunde urskilja utifrån resultatet, var att det fanns motsättningar mellan pedagoger och forskare huruvida individanpassad undervisning, är en illusion eller verklighet. Ett hinder som respondenterna lyfter fram är att det i dagens skola förekommer stora klasser med bara en pedagog, vilket innebär att det kan vara svårt att få tiden att räcka till för att organisera en individanpassad undervisning. / Literature that contains the concept individual tailored education show both positive and negative aspects, regarding this method. With this background, we found it interesting to examine how active teachers, in the compulsory school, express about individual tailored education. In order to study how it is in the reality, we have chosen to use us of a qualitative method, with interviews for collecting of information. The information that was gathered have then been analyzed and described with the aid of theory connection. The result showed that timerelated individualization is the most common type that teachers applies in their education, but the respondents also points out the importens to adapt the education on the basis of each individual, in another word difficultrelated individualization. The respondents maintained also that this work form is to advantage for the pupils who have difficulties, something that distinguish from research within the area. The study also showed another interesting aspect, namely that there were contradictions between teachers and researchers, whether individual tailored education is an illusion or if it is reality. An obstacle that the respondents points out is that the school of today has big classes with only one teacher, which means that it, according to time, can be difficult to organize individual tailored education.

In an automotive crash event, hot stamped, die quenched martensitic structural components have been shown to provide excellent intrusion resistance. These alloys exhibit only limited ductility, however, which may limit the overall impact performance of the component. The introduction of lower strength and more ductile “tailored” properties within some regions of a hot stamped component has the potential to improve impact performance. One approach being applied to achieving such tailored properties is through locally controlling the cooling rate within the stamping die. The primary motivation for the current work is to understand the role of cooling rate on the as-quenched mechanical response of tailored hot stampings, which has required characterization of the high strain rate mechanical behaviour of tailored hot stamped boron steel. The effect of cooling rate and resulting microstructure on the as-quenched mechanical behavior of USIBOR® 1500P boron steel at strain rates between 10-3 and 103 s-1 was investigated. Specimens quenched at rates above the critical cooling rate (~27 °C/s) exhibited a fully martensitic microstructure with a UTS of ~1,450 MPa. Sub-critical cooling rates, in the range 14°C/s to 50 °C/s, resulted in as-quenched microstructures ranging between bainitic to martensitic, respectively. Tension tests revealed that predominantly bainitic material conditions (14 °C/s cooling rate) exhibited a lower UTS of 816 MPa compared to 1,447 MPa for the fully martensitic material condition (50 °C/s cooling rate) with a corresponding increase in elongation from 0.10 to 0.15 for the bainitic condition. The reduction in area was 70% for the bainitic material condition and 58% for the martensitic material conditions which implied that a tailored region consisting of bainite may be a desirable candidate for implementation within a hot stamped component. The strain rate sensitivity was shown to be moderate for all of the as-quenched material conditions and the measured flow stress curves were used to develop a strain rate sensitive constitutive model, the “Tailored Crash Model (TCM)”. The TCM accurately reproduced the measured flow stress curves as a function of effective plastic strain, strain rate and Vickers hardness (or area fraction of martensite and bainite). The effect of deformation during quenching and the associated shift in the CCT diagram on the subsequent constitutive response was also examined for this material. Specimens were simultaneously quenched and deformed at various cooling rates to achieve a range of as-quenched microstructures that included ferrite in addition to martensite and bainite. Tensile tests conducted on these specimens at strain rates ranging from 0.003 s-1 to ~80 s-1 revealed that the presence of ferrite resulted in an increase in uniform elongation and n-value which increased overall energy absorption for a given hardness level. The strain rate sensitivity was shown to be moderate for all of the as-quenched material conditions and the TCM constitutive model was extended to account for the presence of ferrite. This extended constitutive model, the “Tailored Crash Model II (TCM II)”, has been shown to predict flow stress as a function of effective plastic strain, strain rate and area fraction of martensite, bainite and ferrite. As a validation exercise, uniaxial tension test simulations of specimens extracted from the transition zone of a hot stamped lab-scale B-pillar with tailored properties [1] were performed. The measured hardness distribution along the gauge length of the tensile specimens was used as input for the TCM constitutive model to define the element constitutive response used in the finite element (FE) models. The measured stress versus strain response and strain distribution during loading (measured using digital image correlation) was in excellent agreement with the FE models and thus validated the TCM constitutive model developed in this work. Validation of the TCM II version of the model is left for future work.

Hot forming of boron steels is becoming increasingly popular in the automotive industry due to the demands for weight reduction and increased safety requirements for new vehicles. Hot formed components offer a significant increase in strength over conventional cold-formed steels, which has allowed for reductions in material thickness (and thus weight) while maintaining the same strength. Hot formed components are typically used in structural applications to improve the integrity of the vehicle’s cabin in the event of a collision. It has been suggested, however, that the crash performance of certain hot formed parts may be increased by locally tailoring their mechanical properties to improve their energy absorption. The final microstructure of a hot formed part is driven by the rate at which it is cooled within the tooling during the forming and quenching process. By controlling the cooling rate of the part, it is possible to control the final microstructure, and thus the final mechanical properties. This thesis outlines the experimental and numerical studies that were performed for the hot forming of a lab-scale B-pillar. A hot forming die set was developed which has both heating and cooling capabilities to control the local cooling rate of the blank as it is formed and quenched. The first aspect of this research is to produce a hot formed part which is representative of an industrial component, and then to numerically model the process to predict the final mechanical properties. The second aspect is to produce a hot formed part with tailored mechanical properties, such that there are regions of the part with very high strength (very hard) and other regions with increased ductility (softer). By tailoring the microstructure to meet the performance requirement of a hot formed part, it may be possible to optimize its crash behavior and also reduce the overall weight. Cartridge heaters were installed into sections of the tooling allowing it to reach a maximum temperature of 400°C. Cooling channels are used in other sections to maintain it at approximately room temperature. Experiments were performed on 1.2 mm Usibor® 1500P steel at heated die temperatures ranging from 25°C to 400°C. In the fully cooled region, the Vickers hardness of the blank was measured to be 450 – 475 HV, on average. As the temperature of the heated region was increased, a significant softening trend was observed in the areas of the blank that were in contact with the heated tool. The greatest levels of softening occurred in the 400°C heated die trial. Hardness measurements as low as 234 HV were recorded, which represents a reduction in hardness of 49% compared to the fully cooled trials. Numerical models of the experiments were developed using LS-DYNA and use of its advanced hot forming material model which allows for microstructure and hardness prediction within the final part. The numerical models have shown promising results in terms of predicting the hardness trends as the temperature of the die increases. Thermal expansion of the tooling resulted in local changes in the geometry of the tooling which proved to be problematic during the forming and quenching stages of the process. The expansion caused unexpected changes in the part-die contact, and the resulting microstructures were altered. These thermal expansion issues were addressed in the current work by shimming the tooling; however, in future work the tooling should be designed to account for this expansion at the desired operating temperature.

Urban forests provide environmental, social, and economic benefits to urban residents. These benefits are often overlooked when making spatial and financial distributive decisions in urban areas. The City of Tampa has demonstrated interest in its urban forest resource and estimated its extent and some of the benefits provided. Estimating economic values for benefits that have not been quantified can help to ensure that resources are distributed more efficiently. Five methods to estimate urban forest benefits in the City of Tampa are reviewed, with contingent valuation being the method chosen out of this review process. A mailed, dichotomous choice contingent valuation survey was executed with two points of contact, yielding 107 responses for a 21.4 percent response rate. Despite positively rating the City’s urban forest, the majority of respondents (62.6 percent) were willing to pay for it to increase. The Turnbull distribution-free estimator was used to estimate a lower bound of $3.23 for willingness to pay to increase Tampa’s urban forest resource by 250,000 trees. Willingness to pay was positively associated with income and education. The survey responses also yielded important attitudinal and behavioral information that can help local decision makers increase the efficiency of urban forest distribution, maintenance, and promotion.

Cancer is the leading cause of death in Taiwan. Breast cancer has the highest morbidity rate in females. Early detection in Taiwanese women is hampered by their inadequate knowledge of risk factors, their biased perceptions of mammography and by their low intentions to carry out recommended preventative strategies. Although the Internet has become a powerful tool to disseminate health information, health information offered on the web frequently is not theoretically-based or patient-centered. Effken's (2003) Informatics Research Organizing Model (IROM) and the Transtheoretical Model (TTM) (Prochaska & Diclemente, 1982; Rakowski, Dube, & Goldstein, 1996) were used to guide the design and evaluation of a tailored web-based program aimed at improving effective breast cancer detection in Taiwanese women. This study used a pretest-posttest design to examine the impact of a tailored, web-based educational intervention on Taiwanese women's perceptions of and intentions to obtain mammography, as well as their satisfaction with the website. One hundred twenty eight Taiwanese women were randomly assigned to one of two groups: tailored intervention (TI) or standard intervention (SI). The TI group received tailored educational materials (i.e. tailored messages, case studies, personal testimonies, and mammography information). The SI group received an educational brochure developed by the Bureau of Health Promotion, Department of Health (DOH). A Stage of Adoption of Mammography Question (SAMQ) and Decisional Balance of Mammography Inventory (DBMI) were administered before and after the educational intervention. A Website Users Satisfaction (WUS) and Demographics Inventory (DI) were administered after the intervention. All materials and instruments were delivered and assessed via a website. ANCOVAs, Chi-Square tests and t-tests were utilized to test the hypotheses. Results of the study revealed that the TI group differed significantly from the SI group in terms of perceptions of, and intentions to obtain, mammography, as well as in satisfaction with the website. The results of this study contribute to our knowledge of how a health education website can change women's mammography-related perceptions and intentions if theoretically-based and tailored interventions are emphasized.

Bakalauro darbe analizuojamas pritaikytų programų atitikimas mokinių specialiesiems ugdymosi poreikiams. Teorinėje dalyje nagrinėjama ugdymo individualizavimo samprata, esminiai pritaikytų programų ir ugdymo individualizavimo principai. Empirinėje dalyje nagrinėjama mokiniams, turintiems specialiųjų ugdymosi poreikių, pritaikytų programų kokybė. Tyrimo tikslas – įvertinti pritaikytų programų atitikimą mokinių specialiesiems ugdymosi poreikiams. Uždaviniai: 1) Išanalizuoti mokslinės literatūros šaltinius ir atskleisti ugdymo individualizavimo sampratą, esminius principus; išnagrinėti pritaikytų programų sampratą, ugdymo individualizavimo (mokymo tikslų, mokymo turinio, mokymo metodų ir pasiekimų įvertinimo) ypatumus. 2) Turinio analizės metodu išnagrinėti pritaikytų programų kokybę, įvertinant mokymo tikslų ir turinio, mokymo metodų ir pasiekimų vertinimo atitikimą individualiems mokinių specialiesiems ugdymosi poreikiams. 3) Atskleisti programų pritaikymo kokybės teigiamus aspektus ir tobulintinas sritis. Tyrimo metodai – mokslinės literatūros; kiekybinė turinio analizė. Išnagrinėta 50 pritaikytų programų. Tyrinėjant pritaikytų programų atitikimą mokinių specialiesiems ugdymosi poreikiams, atlikta tokių kiekvienos programos komponentų analizė: 1) Mokinio galių ir specialiųjų ugdymosi poreikių apibūdinimas. 2) Mokymo tikslų formulavimas. 3) Dalyko turinio teminis planavimas. 4) Mokymo metodų ir būdų numatymas. 5) Pažangos ir pasiekimų vertinimas. Empirinio tyrimo išvados 1... [toliau žr. visą tekstą] / The Bachelor`s Degree paper provides the analysis of the conformance of programmes adapted to the students having special educational demands. Theoretical part includes the consideration of education individualization concept, essential principles of the adapted programmes and education individualization. Empirical part provides analysis of quality of programmes adapted to students having special educational demands. Research aim – to evaluate the conformity of the programmes adapted to the students having special educational demands. Tasks: 1) To analyse the scientific literature sources and disclose the concept and essential principles of education individualization; consider the concept of the adapted programmes, peculiarities of education individualization (evaluation of teaching objectives, teaching content, teaching methods and consequences). 2) To analyse the quality of the adapted programmes using the content analysis method, evaluating the conformity of teaching objectives and content, teaching methods and consequences to individual special educational demands of students. 3) To disclose positive aspects of quality of the adapted programmes and the fields to be improved. Research methods – analysis of scientific literature; quantitative content analysis. 50 adapted programmes were analysed. While analysing the conformity of programmes adapted to the students having special educational demands the analysis of the following components of each programme was carried... [to full text]

Hot forming of boron steels is becoming increasingly popular in the automotive industry due to the demands for weight reduction and increased safety requirements for new vehicles. Hot formed components offer a significant increase in strength over conventional cold-formed steels, which has allowed for reductions in material thickness (and thus weight) while maintaining the same strength. Hot formed components are typically used in structural applications to improve the integrity of the vehicle’s cabin in the event of a collision. It has been suggested, however, that the crash performance of certain hot formed parts may be increased by locally tailoring their mechanical properties to improve their energy absorption. The final microstructure of a hot formed part is driven by the rate at which it is cooled within the tooling during the forming and quenching process. By controlling the cooling rate of the part, it is possible to control the final microstructure, and thus the final mechanical properties. This thesis outlines the experimental and numerical studies that were performed for the hot forming of a lab-scale B-pillar. A hot forming die set was developed which has both heating and cooling capabilities to control the local cooling rate of the blank as it is formed and quenched. The first aspect of this research is to produce a hot formed part which is representative of an industrial component, and then to numerically model the process to predict the final mechanical properties. The second aspect is to produce a hot formed part with tailored mechanical properties, such that there are regions of the part with very high strength (very hard) and other regions with increased ductility (softer). By tailoring the microstructure to meet the performance requirement of a hot formed part, it may be possible to optimize its crash behavior and also reduce the overall weight. Cartridge heaters were installed into sections of the tooling allowing it to reach a maximum temperature of 400°C. Cooling channels are used in other sections to maintain it at approximately room temperature. Experiments were performed on 1.2 mm Usibor® 1500P steel at heated die temperatures ranging from 25°C to 400°C. In the fully cooled region, the Vickers hardness of the blank was measured to be 450 – 475 HV, on average. As the temperature of the heated region was increased, a significant softening trend was observed in the areas of the blank that were in contact with the heated tool. The greatest levels of softening occurred in the 400°C heated die trial. Hardness measurements as low as 234 HV were recorded, which represents a reduction in hardness of 49% compared to the fully cooled trials. Numerical models of the experiments were developed using LS-DYNA and use of its advanced hot forming material model which allows for microstructure and hardness prediction within the final part. The numerical models have shown promising results in terms of predicting the hardness trends as the temperature of the die increases. Thermal expansion of the tooling resulted in local changes in the geometry of the tooling which proved to be problematic during the forming and quenching stages of the process. The expansion caused unexpected changes in the part-die contact, and the resulting microstructures were altered. These thermal expansion issues were addressed in the current work by shimming the tooling; however, in future work the tooling should be designed to account for this expansion at the desired operating temperature.

In an automotive crash event, hot stamped, die quenched martensitic structural components have been shown to provide excellent intrusion resistance. These alloys exhibit only limited ductility, however, which may limit the overall impact performance of the component. The introduction of lower strength and more ductile “tailored” properties within some regions of a hot stamped component has the potential to improve impact performance. One approach being applied to achieving such tailored properties is through locally controlling the cooling rate within the stamping die. The primary motivation for the current work is to understand the role of cooling rate on the as-quenched mechanical response of tailored hot stampings, which has required characterization of the high strain rate mechanical behaviour of tailored hot stamped boron steel. The effect of cooling rate and resulting microstructure on the as-quenched mechanical behavior of USIBOR® 1500P boron steel at strain rates between 10-3 and 103 s-1 was investigated. Specimens quenched at rates above the critical cooling rate (~27 °C/s) exhibited a fully martensitic microstructure with a UTS of ~1,450 MPa. Sub-critical cooling rates, in the range 14°C/s to 50 °C/s, resulted in as-quenched microstructures ranging between bainitic to martensitic, respectively. Tension tests revealed that predominantly bainitic material conditions (14 °C/s cooling rate) exhibited a lower UTS of 816 MPa compared to 1,447 MPa for the fully martensitic material condition (50 °C/s cooling rate) with a corresponding increase in elongation from 0.10 to 0.15 for the bainitic condition. The reduction in area was 70% for the bainitic material condition and 58% for the martensitic material conditions which implied that a tailored region consisting of bainite may be a desirable candidate for implementation within a hot stamped component. The strain rate sensitivity was shown to be moderate for all of the as-quenched material conditions and the measured flow stress curves were used to develop a strain rate sensitive constitutive model, the “Tailored Crash Model (TCM)”. The TCM accurately reproduced the measured flow stress curves as a function of effective plastic strain, strain rate and Vickers hardness (or area fraction of martensite and bainite). The effect of deformation during quenching and the associated shift in the CCT diagram on the subsequent constitutive response was also examined for this material. Specimens were simultaneously quenched and deformed at various cooling rates to achieve a range of as-quenched microstructures that included ferrite in addition to martensite and bainite. Tensile tests conducted on these specimens at strain rates ranging from 0.003 s-1 to ~80 s-1 revealed that the presence of ferrite resulted in an increase in uniform elongation and n-value which increased overall energy absorption for a given hardness level. The strain rate sensitivity was shown to be moderate for all of the as-quenched material conditions and the TCM constitutive model was extended to account for the presence of ferrite. This extended constitutive model, the “Tailored Crash Model II (TCM II)”, has been shown to predict flow stress as a function of effective plastic strain, strain rate and area fraction of martensite, bainite and ferrite. As a validation exercise, uniaxial tension test simulations of specimens extracted from the transition zone of a hot stamped lab-scale B-pillar with tailored properties [1] were performed. The measured hardness distribution along the gauge length of the tensile specimens was used as input for the TCM constitutive model to define the element constitutive response used in the finite element (FE) models. The measured stress versus strain response and strain distribution during loading (measured using digital image correlation) was in excellent agreement with the FE models and thus validated the TCM constitutive model developed in this work. Validation of the TCM II version of the model is left for future work.