William W Predebon - Profile on Academia.edu (original) (raw)
Papers by William W Predebon
A Generalized Analysis of Thermal and Mechanical Loads in Inertial Confinement Reactors
Journal of Thermal Stresses, 1980
ABSTRACT An analysis of thermal and mechanical loads acting on an inertial confinement fusion (or... more ABSTRACT An analysis of thermal and mechanical loads acting on an inertial confinement fusion (or fusion/fission) reactor is presented. It is shown that, as a result of the pulsed mode of operation, quasi-steady-state temperatures and stresses can be separated into static and dynamic components. Numerical results are presented for a specific design of a spherical fusion/fission reactor with a lithium-wetted wall. For the purpose of scaling, materials selection, and fatigue damage assessment, approximate formulas for temperatures and stresses are also given.
Unsteady Flow in a Tube With Prescribed Discharge
Journal of Applied Mechanics, 1969
A vacuum hot pressed alumina material having small, isometric grains; a uniform distribution ther... more A vacuum hot pressed alumina material having small, isometric grains; a uniform distribution thereof; relatively low, predominantly transgranular porosity; and a density approaching the theoretical density of pure alumina produced by vacuum hot pressing alumina powder which contains at least 98.0% alumina, is substantially free of any sintering aids or any other additives, and has a median particle size less than about 3 microns, in a vacuum hot press operated at a temperature of at least about 1350° C. and a pressure of at least 28 MPa (3500 PSI) for a sintering period of at least 1.5 hours. The vacuum hot pressed alumina material also has compressive strength, flexural strength, impact strength, and wear resistance superior to that for most conventional sintered alumina materials.https://digitalcommons.mtu.edu/patents/1072/thumbnail.jp
1996 Annual Conference Proceedings
This paper presents a case study of a teaching assistants (TA's) training program in the Departme... more This paper presents a case study of a teaching assistants (TA's) training program in the Department of Mechanical Engineering and Engineering Mechanics at Michigan Technological University. This training program may be unique in that it is designed to achieve dual objectives: to improve the quality of undergraduate instruction by graduate TA's and to develop leadership skills in graduate students for their professional growth. The second objective was deemed necessary to provide the TA's who do not intend to pursue a teaching profession with an incentive to accept a very demanding program. The program consists of approximately fifteen hours spent during an orientation session given a week before the beginning of the academic year and another fifteen hours in weekly sessions distributed throughout the first quarter of the academic year. The topics covered during the orientation session include: learning styles, cognition theory, human development theory, diversity, and techniques for organization and presentation. The weekly seminar consists of discussions on just-in-time topics such as preparing quizzes, dealing with difficult students, and evaluating students. TA's are also asked to give mock presentations which are video-taped and analyzed in private at a later time. Throughout the training, various communication and interpersonal skills are emphasized and demonstrated. An analysis of teaching evaluations conducted before and after the training shows a marked improvement in the performance of TA's. Also, survey results showed that the TA's in the program are satisfied with the support and nurturing they have received for teaching and for their professional development. This TA training program has recently been presented to the entire campus as a model program.
1996 Annual Conference Proceedings
Traditional new faculty orientations focus on university services, fringe benefits, and research ... more Traditional new faculty orientations focus on university services, fringe benefits, and research activities. If teaching is discussed at all, it is minimal. The orientation workshop and seminar series presented in this paper has a new look. The emphasis is on teaching. Topics discussed include: how to be a successful and happy faculty member, the Michigan Technological University (MTU) student body, total student development, university learning centers, and preparing for the first day. The orientation is followed by weekly seminars throughout the year. The weekly seminars, particularly in the fall, discuss just in time topics such as preparing for quizzes and exams, dealing with marginal student performance, student evaluations, classroom assessment, grading, active vs. passive learning, reflective teaching, etc. The orientation is directed at new faculty, i.e., faculty at the university for three years or less. The weekly seminar series includes more experienced teachers as well. The goal is to encourage an exchange of ideas about teaching between new and experienced professors. The orientation and seminar series were initiated for the first time in Fall of 1995. The attendance, participation, and response has been very good. The evaluation and feedback from faculty in attendance has been encouraging.
International Conference on Engineering Education August 6 -- 10, 2001 Oslo, Norway FROM THE CLASSROOMTO THE BOARDROOM
The response of a high purity alumina to plate-impact testing
AIP Conference Proceedings, 1994
ABSTRACT Alumina disks which were vacuum hot pressed from a 99.99% pure Al2O3 powd... more ABSTRACT Alumina disks which were vacuum hot pressed from a 99.99% pure Al2O3 powder were subjected to flyer-plate impact testing. VISAR techniques were used to measure rear surface velocities. The Hugoniot elastic limit (HEL) for this alumina was 11.9 GPa. At a precompression of three times the HEL, a remarkably high spall strength of 1.2 GPa was observed. However, a negligible spall strength was found when the alumina was shocked to approximately 1.3 times the HEL. These results indicate that the spall strength of pure polycrystalline alumina goes through a transition, first decreasing in value near the HEL and then increasing again above the HEL. In other flyer-plate impact tests, manganin stress gauges were used to measure the decay of the HEL with specimen thickness. The HELL for this alumina decreases slightly when the thickness of the specimen was increased but stabilized for specimens thicker than about 9 mm.
Scripta Metallurgica, 1988
“An International Industry/University/Collaboration” Norsk Hydro/Michigan Tech/NTNU, C. L. White, W. W. Predebon, E. Wathne, and P. K. Larsen, pp. 6D2-7 -- 6D2-10 in the Proceedings of the International Conference on Engineering Education, 6-10 August, 2001, Oslo, Norway
The dependence of yield strength on lamellar termination density in Co-CoAl eutectic alloys
Acta Metallurgica, 1985
ABSTRACT The compressive yield strength of directionally solidified Co-CoAl eutectic alloys was m... more ABSTRACT The compressive yield strength of directionally solidified Co-CoAl eutectic alloys was measured in specimens containing a range of lamellar termination densities but at approximately a constant interlamellar spacing. The yield strength was found to decrease as the transverse lamellar termination density increased. A linear dependence of yield strength on the distance between the terminations is observed provided the spacing between terminations is less than 500 μ. For spacings greater than this, the yield strength is approximately constant. These observations are attributed to a relaxation in constraint on deformation between the two phases due to the initiation of enhanced slip in the vicinity of the terminations.RésuméNous avons mesuré la limite élastique en compression d'alliages eutectiques Co-CoAl solidifiés uni direction ellement dans des échantillons présentant une gamme de densités de terminaisons de lamelles, mais dont l'espacement interlamellaire était approximativement constant. La limite élastique diminuait lorsque la densité de terminaisons lamellaires transverses augmentait. Nous avons observé une variation linéaire de la limite élastique en fonction de la distance entre les terminaisons à condition que l'espacement entre les terminaisons soit inférieur à 500μm. Pour les espacement supérieurs, la limite élastique est approximativement constante. Nous attribuons ces observations à une relaxation de la contrainte de déformation entre les deux phases due au début d'un glissement favorisé au voisinage des terminaisons.ZusammenfassungDie Flieβspannung von gerichtet erstarrten eutektischen Co-CoAl-Legierungen wurde im Druckversuch gemessen. Die Legierungen enthielten verschiedene Dichten an Lamellenenden, jedoch in näherungsweise gleichem Abstand zwischen den Lamellen. Die Flieβspannung sank mit ansteigender transversaler Dichte der Lamellenenden. Die Flieβspannung hing linear vom Abstand zwischen den Enden ab, wenn dieser Abstand unter 500 μm lag. Oberhalb dieser Grenze bleibt die Flieβspannung näherungsweise konstant. Diese Befunde werden einer Erleichterung in den Einschränkungen der Verformung zugeschrieben, die zwischen den beiden Phasen durch verstärkte Gleitung an den Enden bedingt wird.
The fracture toughness of a high-strength alumina: compact tension versus indentation fracture techniques
Journal of Materials Science Letters, 1994
ABSTRACT The indentation fracture method is widely used for assessing the fracture toughness of c... more ABSTRACT The indentation fracture method is widely used for assessing the fracture toughness of ceramic materials. In one technique, the surface traces of cracks formed about a Vickers microhardness indentation are measured, and the toughness value is determined knowing the applied load as well as the hardness and elastic modulus of the material (Vickers indentation technique) [1-3]. In a second method, the Vickers indentation forms the critical flaw on the surface of a three- or four-point bend specimen. Two applications of the method are then possible: the fracture toughness value is calculated knowing the load used to produce the flaw and the fracture stress of the indented bar [4] or by actually measuring the flaw size and shape after fracturing the bar at a known stress [5] (indentation strength technique). The former procedure has the advantage in that no direct measurement of the flaw is required.
Journal of Materials Science, 1993
The effect of growth defects known as lamellar terminations on the yielding and fracture behaviou... more The effect of growth defects known as lamellar terminations on the yielding and fracture behaviour of Co-CoAl eutectic single crystals was studied using tensile tests and finiteelement modelling. The yield strength and strain to fracture were found to decrease with increasing termination density. Observations of deformed surfaces and serial sectioning experiments on fractured tensile specimens revealed that crack initiation during the fracture process was enhanced by the presence of lamellar terminations. The fracture surfaces were found to have a staircase-type appearance, which indicated that the final fracture process was discontinuous with a step-wise propagation from one CoAl lamella to adjacent CoAl lamellae. A computer simulation was conducted to determine the stress distributions about lamellar terminations in model microstructures, since the experimental results suggested that the lamellar terminations behaved as stress concentrations in the microstructure. The finite-element calculation confirmed that lamellar terminations can influence the yielding process; the stress at which the first slip system was activated was found to decrease with increasing termination density.
Elastic-Plastic Analysis of Directionally Solidified Lamellar Eutectic Composites
Journal of Engineering Materials and Technology, 1987
Yielding in a crystal structure occurs with plastic slip on preferential planes. It is similar to... more Yielding in a crystal structure occurs with plastic slip on preferential planes. It is similar to yielding on maximum shear planes in an isotropic continuum, but in this case the slip is anisotropic. The anisotropic slip is described by 24 piecewise, continuous yield functions, also known as the generalized Schmid’s law for FCC crystals. The plastic strain increment for any one slip mechanism is assumed given by the potential flow law of plasticity. However, there are combined slip situations where two or more slip mechanisms are activated simultaneously. In this paper, the plastic strains for all the possible intersections in FCC crystals are derived, i.e., for intersections of two, four, and eight yield surfaces of compatible stress states. A strain hardening modulus H′ is included by defining an equivalent shear stress τ and an equivalent plastic shear strain γp for each slip system. The analysis is programmed for finite-element solution on the computer, by defining a strain “vec...
Dynamic launch process of performed fragments
Journal of Applied Physics, 1988
It is shown through numerical simulations that the gap between performed fragments closes during ... more It is shown through numerical simulations that the gap between performed fragments closes during explosive launch, trapping the detonation products until radial expansion of the fragments is sufficient to separate the fragments. Circumferential strains from the numerical calculations are in good agreement with the plastic strains from recovered fragments. Additionally, considerable insights into the dynamics of the explosive launch process
ZAMM - Zeitschrift für Angewandte Mathematik und Mechanik, 1972
Unter Verwendung dea H enc k yachen Verzerrungsmufies im E'alle der Isotropie und eines Pseudo-Sp... more Unter Verwendung dea H enc k yachen Verzerrungsmufies im E'alle der Isotropie und eines Pseudo-SpannungstetMors im nichtiaotropen Fall wird die StoJwelle in einem hyperelastischen dfedium in rein raumlicher Weise formuliert, um auj dime Weise die Entropieanderung in schwachen StoJen zu erhalten. Using the H e n c k y strain-measure in the case of isotropy and a pseudo-stress tensor for nonisotropic case. the pnper gices a complete spatial formulation of the shockwave i n a hyperelastic medium. This formulution is used to obtain entropy changes for weak shocks. ~J I H onpenenema M~M~H~H H I I ~HTPOIIMM B cna6b1x m a w a x $op~ynup yeTcH WCTO rrpocTpaircT-BennbiM cnoco60~ ygapHasi Bonna B csepxynpyrofi cpene, npmeena A~F I cnygaa M B O T~V~M H ~e p y neQopMaum reH K M a nnn H~M B O T~O I I H O I ' O caysari rice~no~e113op nanpuwemm.
Computational Mechanics, 1991
Most continuum descriptions of damage evolution generally require history-dependent material vari... more Most continuum descriptions of damage evolution generally require history-dependent material variables. The Lagrangian formulation of the continuum equations is the natural coordinate system for tracking material-history quantities. In numerical simulations of dynamic events such as in penetration and perforation of target plates by projectiles, the Lagrangian mesh can become severely compressed and distorted which effectively terminates advancing the solution in time. On the other hand, the Eulerian formulation, with its fixed coordinate system, does not suffer from mesh distortion. However, Eulerian descriptions usually follow only what crosses cell boundaries, and instead of computing the time history of material particles, they describe the average instantaneous state of a material in a computational zone. This paper describes the inclusion and evaluation of the history of equivalent plastic strain, which is a representative measure of damage, as an internal state variable within an Eulerian numerical framework. The formulation and method of advection of the equivalent plastic strain are described, and the results for two example problems are discussed and comparisons are made with the results of Lagrangian calculations.
BFREADCOMPLEUTINFORM 1. REPORT NUMBER 2' GOVT ACCESSION NO,-I RECIPIENT'S CATALOG NUMBER HIMI Mwo... more BFREADCOMPLEUTINFORM 1. REPORT NUMBER 2' GOVT ACCESSION NO,-I RECIPIENT'S CATALOG NUMBER HIMI Mwo rainkdum Ilcpurt No, 2790'__________________ 4. TITLE (AmidSubrIrll) S.TVPo ¶O REPORT & PERIOD COVERIrD N I MSI 1X~-IAIZI HADI),MOI)II NGl C rOMPI ,T 7'AI1 AUTB. CONTRACT OR GRANT NUMBER(a) Charles h, Andcrson5 7'1AMP AND ADDRESS 10. PROGRAM ELEMENT, PROJECT, TASK(A&WOR UIT NUMBERS UISA B~allisti1c Research Labhoratorie losA=& KU Abordoen Proving (, round, MID 21(005 1,612f41 ii, CONT ROLLING OFFICE NAME AND ADDRESS tIP Army Mateor ie Dievo 1opilont 1; Read iness, ((mimand OCTW 1077) 5001 i s enhowor Avenue IHUSRO`"IS Aloxandthia, VA 22333 5. iT MNIORNGAGENCY NAME & ADDRESS(Pt different from Contro~llin 0gW,.o) 16.SIFCURITY CL.AV a thIs p IS.DCASSIFICATIN ONRDING IS. DISTRIBUTION STATEMENT (at this Report) Approved fn' o public release; distribution unlimited.) D C1 7. DISTRIBUTION STATEMENT (otf he ebeftct itered In bfok 20, idIfforopefrIIom Report) IS. SUPPLEMENTARY NOTES Sulwi? Isreds In terim In emoz-an dum Reoer t No, 233 dated ,Junoc 197d. I9. KEY WORDS (Continue on roer**. side it neceusary anid IdentIty, by block number) H emp C omputat.ionis Wa rhead Modeling Rad iographice t oehn iques Velocity voctor predictions Eixplosive testing SAM-I1) Liner effects Anti-alirerm ft watrhcads Geometri cal variat ions Preformed fragments Froaumnt recovery' test ing 20. ABSTRACT (CoiIInuo on roverer side It nec*eewy aid identify by block number) (k I b) A comiputat ionail warhead modeling capability has boon developed wh ich models tho effcets of warhead length to diameter ratio, end confinement variation, cxplosivc material and initiation posture, and internal cavity shape and material. These effocts ore modeled with a. time-dependent, two-dimensional, Lagrangian finitedifference computer code, integrally modified to include fragment separation (or fragmentation for continuous warheads) and subsequent explosive ga' leakage between fragments.-.. / DO D I'jMA" 1473 EDITION OF I NOY 65 It O@%OLtTE
Impact Response of Polymeric Materials at Varying Depths of Penetration
Instrumented Impact Testing of Plastics and Composite Materials
17. DISTRIBUTION STATEMENT (of the aberact entered In Block 20, If different fom Roport) Ill. SUP... more 17. DISTRIBUTION STATEMENT (of the aberact entered In Block 20, If different fom Roport) Ill. SUPPLEMENTARY NOTES IS. KEY WORDS (Contin,. on revere elde if neceeoeary end identify by block #ltmber) Fragment at ion Finite-Difference Codes Fragment Velocity Predictions ABSTRACT (Continue on re .. ee olte If necesea end Identify by block n.ebe.) Calculational techniques for, predicting warhead performance based upon the * fragment velocity distribution are presented and compared with experimental data. A simple technique is shown to be inadequate fbr many practical configurations. For accurate distributions, a two-dimensional, time-dependent, finite-difference code is shown to be adequate. As an integral part of this , code, a model for the effects of casing fragmentation and explosive gas leakage has been included.
1997 Annual Conference Proceedings
The objective of the program described in this paper is to help under-represented minority studen... more The objective of the program described in this paper is to help under-represented minority students (African-American, American Indian, Hispanic, and Upper Peninsula Women) to be successful in a number of fundamental engineering courses during their sophomore year and make a smooth transition to the junior and senior level courses in engineering design and analysis. Michigan Technological University (MTU) already has an Engineering Learning Center (ELC) which is dedicated to achieving this objective for all students. However, it was hypothesized that the ELC, where students are coached by fellow students on several gateway courses such as Statics, Dynamics, and Mechanics of Materials, has the potential to be more effective as a means of helping minority students be successful if more ELC coaches were the minority students themselves. Consequently, eleven minority students were recruited and were given extensive training on learning and coaching skills over a course of two quarters. The training included sessions on diversity in learning styles, studying skills, problem solving skills, interpersonal skills, intrapersonal skills, and techniques for promoting motivation. All recruits successfully completed the training program and, subsequently, worked as ELC coaches. This program is in its second year and, while a quantitative assessment of the program cannot be made at this stage, anecdotal evidence indicates a need to sustain this program.
A Generalized Analysis of Thermal and Mechanical Loads in Inertial Confinement Reactors
Journal of Thermal Stresses, 1980
ABSTRACT An analysis of thermal and mechanical loads acting on an inertial confinement fusion (or... more ABSTRACT An analysis of thermal and mechanical loads acting on an inertial confinement fusion (or fusion/fission) reactor is presented. It is shown that, as a result of the pulsed mode of operation, quasi-steady-state temperatures and stresses can be separated into static and dynamic components. Numerical results are presented for a specific design of a spherical fusion/fission reactor with a lithium-wetted wall. For the purpose of scaling, materials selection, and fatigue damage assessment, approximate formulas for temperatures and stresses are also given.
Unsteady Flow in a Tube With Prescribed Discharge
Journal of Applied Mechanics, 1969
A vacuum hot pressed alumina material having small, isometric grains; a uniform distribution ther... more A vacuum hot pressed alumina material having small, isometric grains; a uniform distribution thereof; relatively low, predominantly transgranular porosity; and a density approaching the theoretical density of pure alumina produced by vacuum hot pressing alumina powder which contains at least 98.0% alumina, is substantially free of any sintering aids or any other additives, and has a median particle size less than about 3 microns, in a vacuum hot press operated at a temperature of at least about 1350° C. and a pressure of at least 28 MPa (3500 PSI) for a sintering period of at least 1.5 hours. The vacuum hot pressed alumina material also has compressive strength, flexural strength, impact strength, and wear resistance superior to that for most conventional sintered alumina materials.https://digitalcommons.mtu.edu/patents/1072/thumbnail.jp
1996 Annual Conference Proceedings
This paper presents a case study of a teaching assistants (TA's) training program in the Departme... more This paper presents a case study of a teaching assistants (TA's) training program in the Department of Mechanical Engineering and Engineering Mechanics at Michigan Technological University. This training program may be unique in that it is designed to achieve dual objectives: to improve the quality of undergraduate instruction by graduate TA's and to develop leadership skills in graduate students for their professional growth. The second objective was deemed necessary to provide the TA's who do not intend to pursue a teaching profession with an incentive to accept a very demanding program. The program consists of approximately fifteen hours spent during an orientation session given a week before the beginning of the academic year and another fifteen hours in weekly sessions distributed throughout the first quarter of the academic year. The topics covered during the orientation session include: learning styles, cognition theory, human development theory, diversity, and techniques for organization and presentation. The weekly seminar consists of discussions on just-in-time topics such as preparing quizzes, dealing with difficult students, and evaluating students. TA's are also asked to give mock presentations which are video-taped and analyzed in private at a later time. Throughout the training, various communication and interpersonal skills are emphasized and demonstrated. An analysis of teaching evaluations conducted before and after the training shows a marked improvement in the performance of TA's. Also, survey results showed that the TA's in the program are satisfied with the support and nurturing they have received for teaching and for their professional development. This TA training program has recently been presented to the entire campus as a model program.
1996 Annual Conference Proceedings
Traditional new faculty orientations focus on university services, fringe benefits, and research ... more Traditional new faculty orientations focus on university services, fringe benefits, and research activities. If teaching is discussed at all, it is minimal. The orientation workshop and seminar series presented in this paper has a new look. The emphasis is on teaching. Topics discussed include: how to be a successful and happy faculty member, the Michigan Technological University (MTU) student body, total student development, university learning centers, and preparing for the first day. The orientation is followed by weekly seminars throughout the year. The weekly seminars, particularly in the fall, discuss just in time topics such as preparing for quizzes and exams, dealing with marginal student performance, student evaluations, classroom assessment, grading, active vs. passive learning, reflective teaching, etc. The orientation is directed at new faculty, i.e., faculty at the university for three years or less. The weekly seminar series includes more experienced teachers as well. The goal is to encourage an exchange of ideas about teaching between new and experienced professors. The orientation and seminar series were initiated for the first time in Fall of 1995. The attendance, participation, and response has been very good. The evaluation and feedback from faculty in attendance has been encouraging.
International Conference on Engineering Education August 6 -- 10, 2001 Oslo, Norway FROM THE CLASSROOMTO THE BOARDROOM
The response of a high purity alumina to plate-impact testing
AIP Conference Proceedings, 1994
ABSTRACT Alumina disks which were vacuum hot pressed from a 99.99% pure Al2O3 powd... more ABSTRACT Alumina disks which were vacuum hot pressed from a 99.99% pure Al2O3 powder were subjected to flyer-plate impact testing. VISAR techniques were used to measure rear surface velocities. The Hugoniot elastic limit (HEL) for this alumina was 11.9 GPa. At a precompression of three times the HEL, a remarkably high spall strength of 1.2 GPa was observed. However, a negligible spall strength was found when the alumina was shocked to approximately 1.3 times the HEL. These results indicate that the spall strength of pure polycrystalline alumina goes through a transition, first decreasing in value near the HEL and then increasing again above the HEL. In other flyer-plate impact tests, manganin stress gauges were used to measure the decay of the HEL with specimen thickness. The HELL for this alumina decreases slightly when the thickness of the specimen was increased but stabilized for specimens thicker than about 9 mm.
Scripta Metallurgica, 1988
“An International Industry/University/Collaboration” Norsk Hydro/Michigan Tech/NTNU, C. L. White, W. W. Predebon, E. Wathne, and P. K. Larsen, pp. 6D2-7 -- 6D2-10 in the Proceedings of the International Conference on Engineering Education, 6-10 August, 2001, Oslo, Norway
The dependence of yield strength on lamellar termination density in Co-CoAl eutectic alloys
Acta Metallurgica, 1985
ABSTRACT The compressive yield strength of directionally solidified Co-CoAl eutectic alloys was m... more ABSTRACT The compressive yield strength of directionally solidified Co-CoAl eutectic alloys was measured in specimens containing a range of lamellar termination densities but at approximately a constant interlamellar spacing. The yield strength was found to decrease as the transverse lamellar termination density increased. A linear dependence of yield strength on the distance between the terminations is observed provided the spacing between terminations is less than 500 μ. For spacings greater than this, the yield strength is approximately constant. These observations are attributed to a relaxation in constraint on deformation between the two phases due to the initiation of enhanced slip in the vicinity of the terminations.RésuméNous avons mesuré la limite élastique en compression d'alliages eutectiques Co-CoAl solidifiés uni direction ellement dans des échantillons présentant une gamme de densités de terminaisons de lamelles, mais dont l'espacement interlamellaire était approximativement constant. La limite élastique diminuait lorsque la densité de terminaisons lamellaires transverses augmentait. Nous avons observé une variation linéaire de la limite élastique en fonction de la distance entre les terminaisons à condition que l'espacement entre les terminaisons soit inférieur à 500μm. Pour les espacement supérieurs, la limite élastique est approximativement constante. Nous attribuons ces observations à une relaxation de la contrainte de déformation entre les deux phases due au début d'un glissement favorisé au voisinage des terminaisons.ZusammenfassungDie Flieβspannung von gerichtet erstarrten eutektischen Co-CoAl-Legierungen wurde im Druckversuch gemessen. Die Legierungen enthielten verschiedene Dichten an Lamellenenden, jedoch in näherungsweise gleichem Abstand zwischen den Lamellen. Die Flieβspannung sank mit ansteigender transversaler Dichte der Lamellenenden. Die Flieβspannung hing linear vom Abstand zwischen den Enden ab, wenn dieser Abstand unter 500 μm lag. Oberhalb dieser Grenze bleibt die Flieβspannung näherungsweise konstant. Diese Befunde werden einer Erleichterung in den Einschränkungen der Verformung zugeschrieben, die zwischen den beiden Phasen durch verstärkte Gleitung an den Enden bedingt wird.
The fracture toughness of a high-strength alumina: compact tension versus indentation fracture techniques
Journal of Materials Science Letters, 1994
ABSTRACT The indentation fracture method is widely used for assessing the fracture toughness of c... more ABSTRACT The indentation fracture method is widely used for assessing the fracture toughness of ceramic materials. In one technique, the surface traces of cracks formed about a Vickers microhardness indentation are measured, and the toughness value is determined knowing the applied load as well as the hardness and elastic modulus of the material (Vickers indentation technique) [1-3]. In a second method, the Vickers indentation forms the critical flaw on the surface of a three- or four-point bend specimen. Two applications of the method are then possible: the fracture toughness value is calculated knowing the load used to produce the flaw and the fracture stress of the indented bar [4] or by actually measuring the flaw size and shape after fracturing the bar at a known stress [5] (indentation strength technique). The former procedure has the advantage in that no direct measurement of the flaw is required.
Journal of Materials Science, 1993
The effect of growth defects known as lamellar terminations on the yielding and fracture behaviou... more The effect of growth defects known as lamellar terminations on the yielding and fracture behaviour of Co-CoAl eutectic single crystals was studied using tensile tests and finiteelement modelling. The yield strength and strain to fracture were found to decrease with increasing termination density. Observations of deformed surfaces and serial sectioning experiments on fractured tensile specimens revealed that crack initiation during the fracture process was enhanced by the presence of lamellar terminations. The fracture surfaces were found to have a staircase-type appearance, which indicated that the final fracture process was discontinuous with a step-wise propagation from one CoAl lamella to adjacent CoAl lamellae. A computer simulation was conducted to determine the stress distributions about lamellar terminations in model microstructures, since the experimental results suggested that the lamellar terminations behaved as stress concentrations in the microstructure. The finite-element calculation confirmed that lamellar terminations can influence the yielding process; the stress at which the first slip system was activated was found to decrease with increasing termination density.
Elastic-Plastic Analysis of Directionally Solidified Lamellar Eutectic Composites
Journal of Engineering Materials and Technology, 1987
Yielding in a crystal structure occurs with plastic slip on preferential planes. It is similar to... more Yielding in a crystal structure occurs with plastic slip on preferential planes. It is similar to yielding on maximum shear planes in an isotropic continuum, but in this case the slip is anisotropic. The anisotropic slip is described by 24 piecewise, continuous yield functions, also known as the generalized Schmid’s law for FCC crystals. The plastic strain increment for any one slip mechanism is assumed given by the potential flow law of plasticity. However, there are combined slip situations where two or more slip mechanisms are activated simultaneously. In this paper, the plastic strains for all the possible intersections in FCC crystals are derived, i.e., for intersections of two, four, and eight yield surfaces of compatible stress states. A strain hardening modulus H′ is included by defining an equivalent shear stress τ and an equivalent plastic shear strain γp for each slip system. The analysis is programmed for finite-element solution on the computer, by defining a strain “vec...
Dynamic launch process of performed fragments
Journal of Applied Physics, 1988
It is shown through numerical simulations that the gap between performed fragments closes during ... more It is shown through numerical simulations that the gap between performed fragments closes during explosive launch, trapping the detonation products until radial expansion of the fragments is sufficient to separate the fragments. Circumferential strains from the numerical calculations are in good agreement with the plastic strains from recovered fragments. Additionally, considerable insights into the dynamics of the explosive launch process
ZAMM - Zeitschrift für Angewandte Mathematik und Mechanik, 1972
Unter Verwendung dea H enc k yachen Verzerrungsmufies im E'alle der Isotropie und eines Pseudo-Sp... more Unter Verwendung dea H enc k yachen Verzerrungsmufies im E'alle der Isotropie und eines Pseudo-SpannungstetMors im nichtiaotropen Fall wird die StoJwelle in einem hyperelastischen dfedium in rein raumlicher Weise formuliert, um auj dime Weise die Entropieanderung in schwachen StoJen zu erhalten. Using the H e n c k y strain-measure in the case of isotropy and a pseudo-stress tensor for nonisotropic case. the pnper gices a complete spatial formulation of the shockwave i n a hyperelastic medium. This formulution is used to obtain entropy changes for weak shocks. ~J I H onpenenema M~M~H~H H I I ~HTPOIIMM B cna6b1x m a w a x $op~ynup yeTcH WCTO rrpocTpaircT-BennbiM cnoco60~ ygapHasi Bonna B csepxynpyrofi cpene, npmeena A~F I cnygaa M B O T~V~M H ~e p y neQopMaum reH K M a nnn H~M B O T~O I I H O I ' O caysari rice~no~e113op nanpuwemm.
Computational Mechanics, 1991
Most continuum descriptions of damage evolution generally require history-dependent material vari... more Most continuum descriptions of damage evolution generally require history-dependent material variables. The Lagrangian formulation of the continuum equations is the natural coordinate system for tracking material-history quantities. In numerical simulations of dynamic events such as in penetration and perforation of target plates by projectiles, the Lagrangian mesh can become severely compressed and distorted which effectively terminates advancing the solution in time. On the other hand, the Eulerian formulation, with its fixed coordinate system, does not suffer from mesh distortion. However, Eulerian descriptions usually follow only what crosses cell boundaries, and instead of computing the time history of material particles, they describe the average instantaneous state of a material in a computational zone. This paper describes the inclusion and evaluation of the history of equivalent plastic strain, which is a representative measure of damage, as an internal state variable within an Eulerian numerical framework. The formulation and method of advection of the equivalent plastic strain are described, and the results for two example problems are discussed and comparisons are made with the results of Lagrangian calculations.
BFREADCOMPLEUTINFORM 1. REPORT NUMBER 2' GOVT ACCESSION NO,-I RECIPIENT'S CATALOG NUMBER HIMI Mwo... more BFREADCOMPLEUTINFORM 1. REPORT NUMBER 2' GOVT ACCESSION NO,-I RECIPIENT'S CATALOG NUMBER HIMI Mwo rainkdum Ilcpurt No, 2790'__________________ 4. TITLE (AmidSubrIrll) S.TVPo ¶O REPORT & PERIOD COVERIrD N I MSI 1X~-IAIZI HADI),MOI)II NGl C rOMPI ,T 7'AI1 AUTB. CONTRACT OR GRANT NUMBER(a) Charles h, Andcrson5 7'1AMP AND ADDRESS 10. PROGRAM ELEMENT, PROJECT, TASK(A&WOR UIT NUMBERS UISA B~allisti1c Research Labhoratorie losA=& KU Abordoen Proving (, round, MID 21(005 1,612f41 ii, CONT ROLLING OFFICE NAME AND ADDRESS tIP Army Mateor ie Dievo 1opilont 1; Read iness, ((mimand OCTW 1077) 5001 i s enhowor Avenue IHUSRO`"IS Aloxandthia, VA 22333 5. iT MNIORNGAGENCY NAME & ADDRESS(Pt different from Contro~llin 0gW,.o) 16.SIFCURITY CL.AV a thIs p IS.DCASSIFICATIN ONRDING IS. DISTRIBUTION STATEMENT (at this Report) Approved fn' o public release; distribution unlimited.) D C1 7. DISTRIBUTION STATEMENT (otf he ebeftct itered In bfok 20, idIfforopefrIIom Report) IS. SUPPLEMENTARY NOTES Sulwi? Isreds In terim In emoz-an dum Reoer t No, 233 dated ,Junoc 197d. I9. KEY WORDS (Continue on roer**. side it neceusary anid IdentIty, by block number) H emp C omputat.ionis Wa rhead Modeling Rad iographice t oehn iques Velocity voctor predictions Eixplosive testing SAM-I1) Liner effects Anti-alirerm ft watrhcads Geometri cal variat ions Preformed fragments Froaumnt recovery' test ing 20. ABSTRACT (CoiIInuo on roverer side It nec*eewy aid identify by block number) (k I b) A comiputat ionail warhead modeling capability has boon developed wh ich models tho effcets of warhead length to diameter ratio, end confinement variation, cxplosivc material and initiation posture, and internal cavity shape and material. These effocts ore modeled with a. time-dependent, two-dimensional, Lagrangian finitedifference computer code, integrally modified to include fragment separation (or fragmentation for continuous warheads) and subsequent explosive ga' leakage between fragments.-.. / DO D I'jMA" 1473 EDITION OF I NOY 65 It O@%OLtTE
Impact Response of Polymeric Materials at Varying Depths of Penetration
Instrumented Impact Testing of Plastics and Composite Materials
17. DISTRIBUTION STATEMENT (of the aberact entered In Block 20, If different fom Roport) Ill. SUP... more 17. DISTRIBUTION STATEMENT (of the aberact entered In Block 20, If different fom Roport) Ill. SUPPLEMENTARY NOTES IS. KEY WORDS (Contin,. on revere elde if neceeoeary end identify by block #ltmber) Fragment at ion Finite-Difference Codes Fragment Velocity Predictions ABSTRACT (Continue on re .. ee olte If necesea end Identify by block n.ebe.) Calculational techniques for, predicting warhead performance based upon the * fragment velocity distribution are presented and compared with experimental data. A simple technique is shown to be inadequate fbr many practical configurations. For accurate distributions, a two-dimensional, time-dependent, finite-difference code is shown to be adequate. As an integral part of this , code, a model for the effects of casing fragmentation and explosive gas leakage has been included.
1997 Annual Conference Proceedings
The objective of the program described in this paper is to help under-represented minority studen... more The objective of the program described in this paper is to help under-represented minority students (African-American, American Indian, Hispanic, and Upper Peninsula Women) to be successful in a number of fundamental engineering courses during their sophomore year and make a smooth transition to the junior and senior level courses in engineering design and analysis. Michigan Technological University (MTU) already has an Engineering Learning Center (ELC) which is dedicated to achieving this objective for all students. However, it was hypothesized that the ELC, where students are coached by fellow students on several gateway courses such as Statics, Dynamics, and Mechanics of Materials, has the potential to be more effective as a means of helping minority students be successful if more ELC coaches were the minority students themselves. Consequently, eleven minority students were recruited and were given extensive training on learning and coaching skills over a course of two quarters. The training included sessions on diversity in learning styles, studying skills, problem solving skills, interpersonal skills, intrapersonal skills, and techniques for promoting motivation. All recruits successfully completed the training program and, subsequently, worked as ELC coaches. This program is in its second year and, while a quantitative assessment of the program cannot be made at this stage, anecdotal evidence indicates a need to sustain this program.