Microstructure development of complex phase steels during thermomechanical processing

Population growth and continuous infrastructural development have brought a high demand for private automotive vehicles, which is expected to continue rising in the coming years. As a result, there will be a larger number of vehicles in transit and therefore the probabilities of crash collisions and CO2 emissions into the environment will also increase. For this reason, the technological development of steels for automotive applications is increasingly important. CO2 emissions can be reduced by improving fuel consumption lowering the weight of vehicles. Therefore, automakers are investing in research to develop lighter and stronger automotive components which meet the safety requirements, without increasing production costs. Complex phase (CP) steels have been introduced as candidates to improve steel properties through thermomechanical controlled processing (TMP). This thesis focuses on investigating different TMP schedules in a CP steel composition to evaluate the microstructure evolution and mechanical properties. The potential of the alloying elements has been assessed to develop a stronger steel grade through TMP. The effect of deformation parameters and cooling conditions on the final product was also considered in the analysis. Small specimens of CP steel underwent four-pass TMP routes, simulating deformations conditions during finishing rolling. This was done in a TMP machine under the module of plane strain compression. The TMP routes were designed by defining the critical processing parameters such as transformation temperatures and recrystallization-stop temperature. The TMP explores the influence of the conditioning of the austenite during the finishing rolling and the subsequent development of the microstructure in the run-out table. An extensive characterization was done for the as-received material and the post-processed specimens. The deformation parameters and the cooling strategies led to the development of microstructures corresponding to certain mechanical properties and volume fraction of phases. The higher tensile strength and higher amount of bainite were achieved in the specimen deformed at lower last-pass temperature but higher holding temperature during the step cooling. This generated high dislocation density with deformation bands and therefore high Sv to facilitate transformation products. The heavily deformed and non-recrystallized austenite structure is ideal to create fine-grained products which increase the tensile strength. This is also favourable to start ferrite transformation in a relatively short time. Alloying elements play a key role in the microstructure development through TMP, e.g. Nb addition delays austenite recrystallization, retaining a high Sv. Most of the TMP schedules designed in this work developed the mechanical properties and microstructure to be considered as CP for automotive applications

Integrated microbioreactor arrays for high-throughput experimentation

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.Includes bibliographical references (p. 219-226).Bioprocesses with microbial cells play an important role in producing biopharmaceuticals such as human insulin and human growth hormone, and other products such as amino acids and biopolymers. Because bioprocesses involve the complicated interaction between the genetics of the microorganisms and their chemical and environmental conditions, hundreds or thousands of microbial growth experiments are necessary for to develop and optimize them. In addition, efforts to develop models for bioprocesses also require numerous growth experiments to study microorganism phenotypes. This work describes the design and development of integrated arrays of microbioreactors that can provide the oxygen transfer and control capabilities of a stirred tank bioreactor in a high-throughput format. The devices comprise a novel peristaltic oxygenating mixer and microfluidic injectors, which are fabricated using a process that allows combining multiple scale (100/,m-lcm) and multiple depth (100/im-2mm) structures in a single mold.(cont.) The microbioreactors have a 100/L working volume, a high oxygen transfer rate (kLa ; 0.1s-1), and closed loop control over dissolved oxygen and pH ( 0.1). Overall, the system supports eight simultaneous batch cultures, in two parallel arrays, with two dissolved oxygen thresholds, individual pH set points, and automated near real-time monitoring of optical density, dissolved oxygen concentration, and pH. These capabilities allowed the demonstration of multiple Escherichia coli aerobic fermentations to high cell densities (>13g-dcw/L), with individual bioreactor performance on par with bench scale stirred tank bioreactors. The successful integration of diverse microfluidic devices and optical sensors in a scalable architecture opens a new pathway for continued development of parallel bioreactor systems.by Harry Lee.Ph.D

Contact region fidelity, sensitivity, and control in roll-based soft lithography

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 341-349).Soft lithography is a printing process that uses small features on an elastomeric stamp to transfer micron and sub-micron patterns to a substrate. Translating this lab scale process to a roll-based manufacturing platform allows precise control of the stamp contact region and the potential for large area, high rate surface patterning. In this manner, emerging devices can be produced economically, including flexible displays, distributed sensor networks, transparent conductors, and bio-inspired surfaces. Achieving and maintaining collapse-free contact of the soft stamp features is a necessary condition for printing. In the first part of the thesis, stamp behavior is examined at two length scales. First, microfeature collapse is examined across a range of dimensionless aspect ratios and pattern ratios to determine the collapse mode and the feature stiffness. Second, behavior of roll-mounted stamps is investigated on the macroscopic scale. The results of these analyses, simulations, and experiments show that contact is prohibitively sensitive as the feature scale shrinks to single microns or below. In the second part of the thesis, methods are developed to reduce the contact sensitivity. A compliant stamp architecture is introduced to tune the mechanical response of the stamp. Next, a new process for manufacturing cylindrical stamps is developed that removes limitations of planar stamp templates. The third part of the thesis addresses process control. A parallel kinematic stage is designed to manipulate the height and pitch of a roll over a substrate with submicron precision. A hybrid state-space / classical feedback control approach is used to achieve high bandwidth servo control in the presence of coupling and unmodeled dynamics. Using optical instrumentation, the stamp contact pattern is monitored and can be controlled using camera images as a control variable. Ultimately, a practical method of impedance control is implemented that demonstrates excellent disturbance rejection. The results of this thesis provide models for stamp behavior at the local microscale and the roll-based macroscale. These results illustrate the high sensitivity of contact to displacement disturbances in roll-based lithography, but also provide valuable design insight towards designing stamps and processing machinery that are robust to these inherent disturbances.by Joseph Edward Petrzelka.Ph.D

Measurement of recovery and recrystallisation in interstitial free steels using electromagnetic sensors

Interstitial free (IF) steel is used extensively throughout applications in the automotive, packaging and furniture industries due to its excellent formability and ductility. The manufacturing process ensures excellent material properties for subsequent forming processes are developed through the formation of a fine equi-axed grain structure and crystallographic texture. The annealing process improves the formability of the cold rolled IF sheet, whilst also reducing strength through the recovery and recrystallisation process. After the cold rolling process the grain structure is heavily deformed. During the recovery process the dislocation density is reduced through annihilation and redistribution of dislocations to form sub grains. During the recrystallisation process new grains nucleate and grow into new, strain free, grains. Magnetic properties of ferromagnetic material are known to be affected by microstructural phenomena such as dislocation density, grain boundaries, grain size and texture. It is therefore possible to monitor the recovery and recrystallisation processes using sensors that are responsive to changes in magnetic properties. The purpose of the research completed was to establish whether it would be possible to use electromagnetic (EM) sensors to monitor recovery and recrystallisation processes in-situ during heat treatment, such that EM sensors could then be deployed in a continuous annealing line

Quantification of microstructure during the phase transformation of dynamically cooled steels using the EMspec® sensor

Electromagnetic (EM) sensor signals are sensitive to changes in permeability and resistivity in steel, where both are determined by microstructure, chemical composition and temperature. EM sensors are currently being used in the steel industry to monitor the phase transformation of hot strip on the runout table. However, there are factors still not fully understood when it comes to the EM signal such as relationship between phase fraction transformed at high temperatures and the EM signal. The purpose of this research is to quantitatively relate the EM of zero crossing frequency to microstructure and more specifically phase fraction during transformation of steels at high temperature. The EMspec® industrial EM sensor which is currently used in industrial conditions on the run-out table of a hot strip mill has been installed into a run out table simulator that consists of a furnace and roller run out table. This system has been designed and constructed to allow the EMspec® sensor to be able to monitor various steels through transformation during dynamic cooling on a lab-based scale. A full 3D finite element model of the EMspec® sensor has been developed in a parallel project and is able to use permeability and resistivity values to predict zero crossing frequency. This model has been used in this project to along with measured resistivities and extrapolated permeabilities from the literature to predict zero crossing frequency. The power law was used along with the permeability values, resistivities and phase fraction obtained from dilatometry to predict zero crossing frequency. The EMspec® industrial sensor has been used to monitor the full phase transformation of various carbon steels including mild steels of 3, 6 and 10mm in thickness, a high carbon steel and medium carbon steel. The EMspec® sensor was able to distinguish between the mild steels of different thickness due to their different cooling rates in air and therefore transformation trajectory. The EMspec® sensor was also used to successfully monitor a 2.25 Cr- 1 Mo steel to measure the full transformation to bainite below the Curie temperature. The magnetic transformation of the duplex stainless steel was also monitored by the EMspec® as it cools through the Curie temperature. The EMspec® sensor was shown to be sensitive to the formation of sigma phase as a result of heat treatment of the duplex stainless steel. The sample with higher amount of sigma phase had a lower zero crossing frequency. When relating the ZCF to phase percentage transformed obtained from dilatometry, the 6mm and 10mm mild steels, the high carbon and the 2.25 Cr- 1Mo steel all needed to be approximately 30-40% transformed before an increase in ZCF would occur due to the need for ferromagnetic phase connectivity before permeability significantly increases. This agrees well with the literature for room temperature ferrite fractions however there is room for discrepancies when taking into the temperature difference between a dilatometry sample and a larger sample cooling on the ROT. For the mild steels, the ZCF would peak before dilatometry predicts the steels to be 100% transformed. The modelling data agreed well with the experimental data for steels that consisted of lower permeability phases such as the 2.25Cr-1Mo and high carbon steels. For the 3mm, 6mm and 10mm thick mild steels, the model could not solve for the high permeabilities which may be due to a more refined mesh being required. The model was able to solve for the duplex stainless steel however the modelled data did not agree with the experimental data due to the nature of the calculation of effective permeability. Power law was used however this does not consider the microstructural parameters such as the connectivity of ferrite. The permeabilities at lower phase fractions is higher as a result of this. The work in this project shows that the EMspec® industrial sensor can monitor the full transformation of multiple steels below the Curie temperature and the EMspec® signal can be related quantitatively to phase percentage transformed although the discrepancy between a dilatometry sample and a large sample with inhomogeneity in temperature cannot be ignored

CNC Feed Drive Control

This document serves as the Final Design Report (FDR) for a senior project developed by our team: four senior Mechanical Engineering students and one computer engineering student at California Polytechnic State University, San Luis Obispo (Cal Poly). While the project was completed for, and sponsored by, Professor Simon Xing of Cal Poly, the remainder of the university’s controls professors will be indirectly benefited from this project. Our goal was to design and implement a functional CNC Feed Drive to be used for educational demonstrations and data collection. This document discusses our early product research and benchmark goals, which established constraints for our product design, as well as identifies our design process and conclusions. Through this evaluation of the feed drive form and function, we determined optimal system components - including a DC motor with rotary encoders, a ballscrew, linear bearings, and a load table with screws for fixturing. This FDR also discusses our design progression, beginning with the structural prototype and followed by a description of the final design. This will include the manufacturing steps taken, the front-end and back-end code generated and used to control the system, and the associated user’s manual. Lastly, this report will discuss the test procedures that we derived from the design verification requirements and include an overview of our test results. We conclude with our final acknowledgments, and we wanted to mention that we are extremely grateful to have worked on this project. The team has learned so much throughout the year, and we look forward to handing the prototype over to Professor Xing

41st Aerospace Mechanisms Symposium

The proceedings of the 41st Aerospace Mechanisms Symposium are reported. JPL hosted the conference, which was held in Pasadena Hilton, Pasadena, California on May 16-18, 2012. Lockheed Martin Space Systems cosponsored the symposium. Technology areas covered include gimbals and positioning mechanisms, components such as hinges and motors, CubeSats, tribology, and Mars Science Laboratory mechanisms

NASA Tech Briefs, September 1990

Topics covered include: New Product Ideas; NASA TU Services; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Programs; Mechanics; Machinery; Fabrication Technology; Mathematics and Information Sciences; Life Sciences