Copyright (c) 2010 All rights reserved. http://works.bepress.com/blondon Recent documents in Blair London en-us Sat, 28 Aug 2010 01:31:35 PDT 3600 http://works.bepress.com/blondon/19 http://works.bepress.com/blondon/19 Thu, 26 Aug 2010 17:40:57 PDT Friction stir processing (FSP) 2519-T87 aluminum plate results in enhanced ductility, 25% strain at fracture. However, the yield strength in the FSP zone drops to 175 MPa from ~400 MPa. Actively cooling the plate during FSP increases the yield strength to 185 MPa and decreases ductility to 20% strain at fracture. Thick bending of a plate of the alloy was demonstrated after the surface was subjected to FSP. D. Hilbert Articles http://works.bepress.com/blondon/18 http://works.bepress.com/blondon/18 Thu, 26 Aug 2010 17:40:57 PDT Metallic materials may be joined utilizing a friction stir processing technique. The friction stir processing technique utilizes a shaped, rotating tool to move material from one side of the joint to be welded to the other without liquefying the base material. Blair London Patents http://works.bepress.com/blondon/17 http://works.bepress.com/blondon/17 Thu, 26 Aug 2010 17:40:56 PDT The stir zone (SZ) temperature cycle was measured during the friction stir processing (FSP) of NiAl bronze plates. The FSP was conducted using a tool design with a smooth concave shoulder and a 12.7-mm step-spiral pin. Temperature sensing was accomplished using sheathed thermocouples embedded in the tool path within the plates, while simultaneous optical pyrometry measurements of surface temperatures were also obtained. Peak SZ temperatures were 990 ⁰Cto 1015 ⁰C (0.90 to 0.97 TMelt) and were not affected by preheating to 400⁰C, although the dwell time above 900 ⁰C was increased by the preheating. Thermocouple data suggested little variation in peak temperature across the SZ, although thermocouples initially located on the advancing sides and at the centerlines of the tool traverses were displaced to the retreating sides, precluding direct assessment of the temperature variation across the SZ. Microstructure-based estimates of local peak SZ temperatures have been made on these and on other similarly processed materials. Altogether, the peak-temperature determinations from these different measurement techniques are in close agreement. Sprinivasan Swaminathan Articles http://works.bepress.com/blondon/14 http://works.bepress.com/blondon/14 Thu, 26 Aug 2010 17:40:55 PDT Our titanium aluminide alloy was readily heat treated to a fully lamellar state by holding at 1345C for 1.5 hours and furnace cooling resulting in a grain size of 330 muon m. The yield stress, ultimate stress, and total elongation were 315MPa, 465MPa, and 0.46% respectively. The fully lamellar microstructure shows significant work hardening. No long cracks initiated at R=0.1 and variation max=300MPa with up to 1.4 million cycles. Blair London Articles http://works.bepress.com/blondon/15 http://works.bepress.com/blondon/15 Thu, 26 Aug 2010 17:40:55 PDT A gamma titanium aluminide alloy article, is prepared using a piece of a gamma titanium aluminide alloy having a composition capable of forming alpha, alpha-2, and gamma phases. The alpha transus temperature of the gamma titanium aluminide alloy piece is determined. The gamma titanium aluminide alloy piece is consolidated by hot isostatic pressing at a temperature of from about 50 F. to about 250 F. below the alpha transus temperature and at a pressure of from about 10,000 to about 30,000 pounds per square inch, for a duration of from about 1 to about 20 hours. The piece is heat treated at a temperature of from about 5 F. to about 300 F. below the alpha transus temperature for a time sufficient to refine the microstructure and generate a microstructure comprising from about 10 to about 90 volume percent gamma phase. The step of heat treating is conducted at a temperature of from about 45 F. to about 200 F. above the temperature of the step of hot isostatic pressing. Thomas J. Kelly Patents http://works.bepress.com/blondon/16 http://works.bepress.com/blondon/16 Thu, 26 Aug 2010 17:40:55 PDT No Abstract. R. W. Hayes Articles http://works.bepress.com/blondon/13 http://works.bepress.com/blondon/13 Thu, 26 Aug 2010 17:40:54 PDT No Abstract. D. A. Wheeler Articles http://works.bepress.com/blondon/12 http://works.bepress.com/blondon/12 Thu, 26 Aug 2010 17:40:54 PDT The study of small surface fatigue cracks in AISI 4140 quenched and tempered steel by a nondestructive surface acoustic wave technique is summarized. A novel cantilevered bending, plate-type fatigue specimen is described that is compatible with the acoustic method. Small cracks are initiated from a 25-μm deep surface pit produced by an electrospark machine. The importance of studying these Blair London Articles http://works.bepress.com/blondon/10 http://works.bepress.com/blondon/10 Thu, 26 Aug 2010 17:40:53 PDT Classical ballet technique relies on mastery of the five basic positions of the feet. Every movement in classical ballet goes through one or more of these positions. The positions are practiced in class, used in choreography, and become second nature in performance on stage. Engineering may have a similar context. These engineering “positions” are not just the foundational coursework leading up to an engineering degree such as mathematics, chemistry, or physics. Rather, the positions are aspects of engineering that a practicing engineer routinely does to successfully perform as engineers. The engineering positions discussed are: question, analyze, team, write, and speak. We believe these positions need to be included and practiced in engineering classes because they are the essence of engineering practice and performance. Blair London Conference Proceedings http://works.bepress.com/blondon/11 http://works.bepress.com/blondon/11 Thu, 26 Aug 2010 17:40:53 PDT Classical ballet classes have a universal structure that fosters active in-class learning. This structure creates a safe environment for students to try, fail, be corrected, and succeed. Engineering classes lack a common structure; most learning in engineering occurs outside of class. Engineering classes could move toward adopting a similar structure to ballet to improve in-class learning and mirror engineering culture and practice. The paper describes aspects of ballet class structure and practices that work and how these can apply to engineering classes. A new engineering class session structure is presented following the ballet model where engineering students are motivated to participate and learn during the class. Blair London Conference Proceedings http://works.bepress.com/blondon/8 http://works.bepress.com/blondon/8 Thu, 26 Aug 2010 17:40:52 PDT Six different engineering courses were taught using aspects of the classical ballet instruction model in organization, teaching methods, and learning strategies. There was a strong focus on performance. The courses spanned sophomore to senior levels. Some aspects of the ballet model worked well: setting rules for the Sacred Space for learning, the beginning activity (“stretch”), the overall organization of the class session, communicating the known ideal, including historical background, and using demonstrations. Some aspects did not work (thus far): exams are not yet performances on stage, little practice or rehearsal occurs, little competition between students occurs, asking students questions in class is uncomfortable, and many students do not want to be in class. New ideas presented include “casting” for exams and highlighting the role of repetition in learning. It was deemed worthwhile to apply the performing arts model to foster increased learning during engineering class. Blair London Conference Proceedings http://works.bepress.com/blondon/9 http://works.bepress.com/blondon/9 Thu, 26 Aug 2010 17:40:52 PDT The steady-state creep deformation behavior of a cast two phase gamma TiAl alloy having the composition Ti---48Al---1Nb (at.%) has been studied. Tension creep tests using the stress increment technique (θθ2θ3) were conducted over the temperature range of 704–850°C at constant initial applied stress level of 103.4–241.3 MPa. The activation energy for creep over the temperature and stress regime of this study varied 317.5 kJ/mol (137.8 MPa) up to 341.0 kJ/mol (206.8 MPa) with an average value of 326.4 kJ/mol. This is well within the range of values previously measured for gamma TiAl alloys where creep controlled by volume diffusion has been suggested as rate controlling. The stress exponents meaured were 5.0 at 704°C, 4.9 at 750°C, 4.7 at 800°C and 4.46 at 850°C. Using the activation energy of 326.4 kJ/mol, the temperature compensated steady-state creep rate was plotted against long stress with all temperatures collapsing onto a single line having a slope equal to 4.95. Using conventional creep analysis, this value of the stress exponent can be taken as suggestive of dislocation climb controlled power law creep as the operative deformation mechanism within the stress and temperature regime of the present study. The boundary separating the lamellar grains in two phase gamma TiAl alloys having the duplex microstructure may be a very important aspect of this microstructure with respect to creep deformation resistance. The interlocking γ/α2 laths making up these boundaries are expected to be very resistant to grain boundary sliding which may contribute to creep deformation in the dislocation creep regime. Finally, some previous observations along with a comparison of the creep behavior of the Ti---48Al---1Nb alloy to that of a Tiz.sbnd;50.3Al binary have been discussed in terms of the pre-exponential constant A in the power law creep equation. TiAl alloys having similar stress and temperature dependencies but differing steady-state strain rates over comparable stress-temperature regimes may be rationalized on the basis of differing power law creep constants which may reflect differences in stacking fault energies. R. W. Hayes Articles