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Sample records for ductility

  1. Austempered Ductile Iron Machining

    NASA Astrophysics Data System (ADS)

    Pilc, Jozef; Šajgalík, Michal; Holubják, Jozef; Piešová, Marianna; Zaušková, Lucia; Babík, Ondrej; Kuždák, Viktor; Rákoci, Jozef

    2015-12-01

    This article deals with the machining of cast iron. In industrial practice, Austempered Ductile Iron began to be used relatively recently. ADI is ductile iron that has gone through austempering to get improved properties, among which we can include strength, wear resistance or noise damping. This specific material is defined also by other properties, such as high elasticity, ductility and endurance against tenigue, which are the properties, that considerably make the tooling characteristic worse.

  2. Ductile transplutonium metal alloys

    DOEpatents

    Conner, W.V.

    1981-10-09

    Alloys of Ce with transplutonium metals such as Am, Cm, Bk and Cf have properties making them highly suitable as souces of the transplutonium element, e.g., for use in radiation detector technology or as radiation sources. The alloys are ductile, homogeneous, easy to prepare and have a fairly high density.

  3. Ductile transplutonium metal alloys

    DOEpatents

    Conner, William V.

    1983-01-01

    Alloys of Ce with transplutonium metals such as Am, Cm, Bk and Cf have properties making them highly suitable as sources of the transplutonium element, e.g., for use in radiation detector technology or as radiation sources. The alloys are ductile, homogeneous, easy to prepare and have a fairly high density.

  4. Ductile crystalline-amorphous nanolaminates.

    PubMed

    Wang, Yinmin; Li, Ju; Hamza, Alex V; Barbee, Troy W

    2007-07-01

    It is known that the room-temperature plastic deformation of bulk metallic glasses is compromised by strain softening and shear localization, resulting in near-zero tensile ductility. The incorporation of metallic glasses into engineering materials, therefore, is often accompanied by complete brittleness or an apparent loss of useful tensile ductility. Here we report the observation of an exceptional tensile ductility in crystalline copper/copper-zirconium glass nanolaminates. These nanocrystalline-amorphous nanolaminates exhibit a high flow stress of 1.09 +/- 0.02 GPa, a nearly elastic-perfectly plastic behavior without necking, and a tensile elongation to failure of 13.8 +/- 1.7%, which is six to eight times higher than that typically observed in conventional crystalline-crystalline nanolaminates (<2%) and most other nanocrystalline materials. Transmission electron microscopy and atomistic simulations demonstrate that shear banding instability no longer afflicts the 5- to 10-nm-thick nanolaminate glassy layers during tensile deformation, which also act as high-capacity sinks for dislocations, enabling absorption of free volume and free energy transported by the dislocations; the amorphous-crystal interfaces exhibit unique inelastic shear (slip) transfer characteristics, fundamentally different from those of grain boundaries. Nanoscale metallic glass layers therefore may offer great benefits in engineering the plasticity of crystalline materials and opening new avenues for improving their strength and ductility. PMID:17592136

  5. Ductile crystalline–amorphous nanolaminates

    PubMed Central

    Wang, Yinmin; Li, Ju; Hamza, Alex V.; Barbee, Troy W.

    2007-01-01

    It is known that the room-temperature plastic deformation of bulk metallic glasses is compromised by strain softening and shear localization, resulting in near-zero tensile ductility. The incorporation of metallic glasses into engineering materials, therefore, is often accompanied by complete brittleness or an apparent loss of useful tensile ductility. Here we report the observation of an exceptional tensile ductility in crystalline copper/copper–zirconium glass nanolaminates. These nanocrystalline–amorphous nanolaminates exhibit a high flow stress of 1.09 ± 0.02 GPa, a nearly elastic-perfectly plastic behavior without necking, and a tensile elongation to failure of 13.8 ± 1.7%, which is six to eight times higher than that typically observed in conventional crystalline–crystalline nanolaminates (<2%) and most other nanocrystalline materials. Transmission electron microscopy and atomistic simulations demonstrate that shear banding instability no longer afflicts the 5- to 10-nm-thick nanolaminate glassy layers during tensile deformation, which also act as high-capacity sinks for dislocations, enabling absorption of free volume and free energy transported by the dislocations; the amorphous–crystal interfaces exhibit unique inelastic shear (slip) transfer characteristics, fundamentally different from those of grain boundaries. Nanoscale metallic glass layers therefore may offer great benefits in engineering the plasticity of crystalline materials and opening new avenues for improving their strength and ductility. PMID:17592136

  6. Ductile extension in alpine Corsica

    NASA Astrophysics Data System (ADS)

    Jolivet, Laurent; Dubois, Roland; Fournier, Marc; Goffé, Bruno; Michard, André; Jourdan, Claudie

    1990-10-01

    Ductile deformation in high-pressure (P)-low temperature (T) conditions due to the westward thrusting of oceanic material onto a continental basement in alpine Corsica is overprinted by a late deformation event with a reverse shear sense (eastward) that took place in less severe P-T conditions. We show that the late deformation can be linked to extension during rifting and spreading of the Liguro Provençal basin from late Oligocene to late-middle Miocene time. Major compressive thrust contacts were reactivated as ductile normal faults and, in some units, only a penetrative eastward shear can be observed. This extension following the thickening of the crust brought tectonic units which underwent very different P- T conditions during the earlier stage into close contact. The Balagne nappe, which shows neither significant ductile deformation nor metamorphism, directly overlies the high-P units. The extensional deformation is distributed through the entire thickness of the nappe stack but is more important along the major thrust contacts, which localize the strain. The geometry of the crustal extension is controlled by that of the early compressive thrusts. The latest structures are east-dipping brittle normal faults which bound the early to middle Miocene Saint Florent half graben.

  7. Wear resistance of ductile irons

    SciTech Connect

    Lerner, Y.S. )

    1994-06-01

    This study was undertaken to evaluate the wear resistance of different grades of ductile iron as alternatives to high-tensile-strength alloyed and inoculated gray irons and bronzes for machine-tool and high-pressure hydraulic components. Special test methods were employed to simulate typical conditions of reciprocating sliding wear with and without abrasive-contaminated lubricant for machine and press guideways. Quantitative relationships were established among wear rate, microstructure and microhardness of structural constituents, and nodule size of ductile iron. The frictional wear resistance of ductile iron as a bearing material was tested with hardened steel shafts using standard test techniques under continuous rotating movement with lubricant. Lubricant sliding wear tests on specimens and components for hydraulic equipment and apparatus were carried out on a special rig with reciprocating motion, simulating the working conditions in a piston/cylindrical unit in a pressure range from 5 to 32 MPa. Rig and field tests on machine-tool components and units and on hydraulic parts have confirmed the test data.

  8. Intrinsic ductility of glassy solids

    NASA Astrophysics Data System (ADS)

    Shi, Yunfeng; Luo, Jian; Yuan, Fenglin; Huang, Liping

    2014-01-01

    Glasses are usually brittle, seriously limiting their practical usage. Recently, the intrinsic ductility of glass was found to increase with the Poisson's ratio (v), with a sharp brittle-to-ductile (BTD) transition at vBTD = 0.31-0.32. Such a correlation between far-from-equilibrium fracture and near-equilibrium elasticity is unexpected and not understood. Molecular dynamics simulations, on three families of glasses (metallic glasses, amorphous silicon, and silica) with controlled bonding, processing, and testing conditions, show that glasses with low covalency and high structural disorder have high v and ductility, and vice versa. The BTD transitions triggered by the aforementioned causes in each system correspond to a unified vBTD value, which increases with its average coordination number (CN). The vBTD-CN relation can be comprehended by recognizing v as a measure of covalency and disorder, and the BTD transition as a competition between shear and cleavage. Our results provide guidelines for developing new recipes and processes for tough glasses.

  9. What drives polymer glasses ductile?

    NASA Astrophysics Data System (ADS)

    Wang, Shi-Qing; Cheng, Shiwang; Li, Xiaoxiao; Lin, Panpan; Liu, Jianning

    2015-03-01

    The presentation aims to explore an important question in polymer physics: what makes polymer glasses of high molecular weight ductile? Upon deformation, load-bearing strands (LBS) emerge along the direction of the stress. Chain tension builds up in LBS due to the displacement of LBS. Segments that do not belong to LBS sequentially get activated by the LBS in the order of their proximity to LBS. If the chain network breaks down before driving the glass into a state of global plasticity, crazing and brittle fracture takes place instead of yielding and macroscopic plastic deformation. Fast deformation assures that chain pullout does not have time to materialize. Global plasticity also takes time to develop. Thus, the outcome is dictated by which process takes place first. In light of the recently proposed molecular model for yielding and brittle-ductile transition of polymer glasses, we present different examples from experiment to illustrate the importance to understand the interplay between short-ranged intersegmental interactions and long-ranged intrachain networking. NSF-DMR (EAGER- 1444859)

  10. Ductile failure X-prize.

    SciTech Connect

    Cox, James V.; Wellman, Gerald William; Emery, John M.; Ostien, Jakob T.; Foster, John T.; Cordova, Theresa Elena; Crenshaw, Thomas B.; Mota, Alejandro; Bishop, Joseph E.; Silling, Stewart Andrew; Littlewood, David John; Foulk, James W., III; Dowding, Kevin J.; Dion, Kristin; Boyce, Brad Lee; Robbins, Joshua H.; Spencer, Benjamin Whiting

    2011-09-01

    Fracture or tearing of ductile metals is a pervasive engineering concern, yet accurate prediction of the critical conditions of fracture remains elusive. Sandia National Laboratories has been developing and implementing several new modeling methodologies to address problems in fracture, including both new physical models and new numerical schemes. The present study provides a double-blind quantitative assessment of several computational capabilities including tearing parameters embedded in a conventional finite element code, localization elements, extended finite elements (XFEM), and peridynamics. For this assessment, each of four teams reported blind predictions for three challenge problems spanning crack initiation and crack propagation. After predictions had been reported, the predictions were compared to experimentally observed behavior. The metal alloys for these three problems were aluminum alloy 2024-T3 and precipitation hardened stainless steel PH13-8Mo H950. The predictive accuracies of the various methods are demonstrated, and the potential sources of error are discussed.

  11. Transformation plasticity in ductile solids

    SciTech Connect

    Olson, G.B.

    1993-02-01

    Research has addressed the role of martensitic transformation plasticity in the enhancement of toughness in high-strength austenitic steels, and the enhancement of formability in multiphase low-alloy sheet steels. In the austenitic steels, optimal processing conditions have been established to achieve a significant increase in strength level, in order to investigate the interaction of strain-induced transformation with the microvoid nucleation and shear localization mechanisms operating at ultrahigh strength levels. The stress-state dependence of transformation and fracture mechanisms has been investigated in model alloys, comparing behavior in uniaxial tension and blunt-notch tension specimens. A numerical constitutive model for transformation plasticity has been reformulated to allow a more thorough analysis of transformation/fracture interactions. Processing of a new low alloy steel composition has been optimized to stabilize retained austenite by isothermal bainitic transformation after intercritical annealing. Preliminary results show a good correlation of uniform ductility with the austenite amount and stability.

  12. 'Work-Hardenable' Ductile Bulk Metallic Glass

    SciTech Connect

    Das, Jayanta; Eckert, Juergen; Tang Meibo; Wang Weihua; Kim, Ki Buem; Baier, Falko; Theissmann, Ralf

    2005-05-27

    Usually, monolithic bulk metallic glasses undergo inhomogeneous plastic deformation and exhibit poor ductility (<1%) at room temperature. We present a new class of bulk metallic glass, which exhibits high strength of up to 2265 MPa together with extensive 'work hardening' and large ductility of 18%. Significant increase in the flow stress was observed during deformation. The 'work-hardening' capability and ductility of this class of metallic glass is attributed to a unique structure correlated with atomic-scale inhomogeneity, leading to an inherent capability of extensive shear band formation, interactions, and multiplication of shear bands.

  13. Ductile fracture processes in 7075 aluminum

    SciTech Connect

    You, C.P. ); Thompson, A.W. ); Bernstein, I.M. )

    1995-02-01

    The ductile fracture of 7075 aluminum was examined as a function of aging condition, from underaged to overaged. Notched specimens allowed the triaxiality of stress to be varied. Increasing triaxiality, which was due to increasing notch acuity, decreased ductility and increased nucleation of voids, in accord with expectations from ductile fracture models. Overaged material, which is generally resistant to environmental damage, was not susceptible to hydrogen embrittlement even with high triaxiality, but void sizes were increased by hydrogen. That increase suggested that void growth rates may be assisted by hydrogen in overaged 7075 aluminum.

  14. Weldable ductile molybdenum alloy development

    SciTech Connect

    Cockeram, B. V.; Ohriner, Evan Keith; Byun, Thak Sang; Schneibel, Joachim H; Miller, Michael K; Snead, Lance Lewis

    2008-01-01

    Molybdenum and its alloys are attractive structural materials for high-temperature applications. However, various practical issues have limited its use. One concern relates to the loss of ductility occurring in the heat-affected weld zone caused by segregation of oxygen to grain boundaries. In this study, a series of arc melted molybdenum alloys have been produced containing controlled additions of B, C, Zr, and Al. These alloys were characterized with respect to their tensile properties, smooth bend properties, and impact energy for both the base metal and welds. These alloys were compared with a very high purity low carbon arc cast molybdenum reference. For discussion purposes the alloys produced are separated into two categories: Mo Al B alloys, and Mo Zr B alloys. The properties of Mo Zr B alloy welds containing higher carbon levels exhibited slight improvement over unalloyed molybdenum, though the base-metal properties for all Mo Zr B alloys were somewhat inconsistent with properties better, or worse, than unalloyed molybdenum. A Mo Al B alloy exhibited the best DBTT values for welds, and the base metal properties were comparable to or slightly better than unalloyed molybdenum. The Mo Al B alloy contained a low volume fraction of second-phase particles, with segregation of boron and carbon to grain boundaries believed to displace oxygen resulting in improved weld properties. The volume fractions of second-phase particles are higher for the Mo Zr B alloys, and these alloys were prone to brittle fracture. It is also noted that these Mo Zr B alloys exhibited segregation of zirconium, boron and carbon to the grain boundaries.

  15. Ductility enhancement of iron-aluminide alloys

    SciTech Connect

    Sikka, V.K. )

    1991-07-01

    Iron aluminides based on Fe{sub 3}Al are ordered intermetallic alloys that offer good oxidation resistance, excellent sulfidation resistance, and low material cost. These materials also conserve strategic elements such as chromium and have a lower density than stainless steels. However, limited ductility at ambient temperature and a sharp drop in strength above 600C have been major deterrents to their acceptance for structural applications. This paper presents results on iron aluminides with room-temperature elongations of 15 to 20%. Ductility values were improved by a combination of thermomechanical processing and heat-treatment control. This method of ductility improvement has been demonstrated for a range of compositions. The data presented in this paper suggest that the Fe{sub 3}Al-based compositions tested are sensitive to environmental effects. The environment of concern is moisture in air that reacts with aluminum to form hydrogen at the metal surface. The hydrogen produced is adsorbed and absorbed in the specimens during plastic strain and results in low room-temperature ductilities. Results showed that the use of highly elongated grains produced by warm working increases ductility. A special heat treatment produces an additional improvement in ductility.

  16. 49 CFR 192.277 - Ductile iron pipe.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 49 Transportation 3 2011-10-01 2011-10-01 false Ductile iron pipe. 192.277 Section 192.277 Transportation Other Regulations Relating to Transportation (Continued) PIPELINE AND HAZARDOUS MATERIALS SAFETY... Ductile iron pipe. (a) Ductile iron pipe may not be joined by threaded joints. (b) Ductile iron pipe...

  17. 49 CFR 192.277 - Ductile iron pipe.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 49 Transportation 3 2012-10-01 2012-10-01 false Ductile iron pipe. 192.277 Section 192.277 Transportation Other Regulations Relating to Transportation (Continued) PIPELINE AND HAZARDOUS MATERIALS SAFETY... Ductile iron pipe. (a) Ductile iron pipe may not be joined by threaded joints. (b) Ductile iron pipe...

  18. 49 CFR 192.277 - Ductile iron pipe.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 49 Transportation 3 2013-10-01 2013-10-01 false Ductile iron pipe. 192.277 Section 192.277 Transportation Other Regulations Relating to Transportation (Continued) PIPELINE AND HAZARDOUS MATERIALS SAFETY... Ductile iron pipe. (a) Ductile iron pipe may not be joined by threaded joints. (b) Ductile iron pipe...

  19. 49 CFR 192.277 - Ductile iron pipe.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 49 Transportation 3 2010-10-01 2010-10-01 false Ductile iron pipe. 192.277 Section 192.277 Transportation Other Regulations Relating to Transportation (Continued) PIPELINE AND HAZARDOUS MATERIALS SAFETY... Ductile iron pipe. (a) Ductile iron pipe may not be joined by threaded joints. (b) Ductile iron pipe...

  20. 49 CFR 192.277 - Ductile iron pipe.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 49 Transportation 3 2014-10-01 2014-10-01 false Ductile iron pipe. 192.277 Section 192.277 Transportation Other Regulations Relating to Transportation (Continued) PIPELINE AND HAZARDOUS MATERIALS SAFETY... Ductile iron pipe. (a) Ductile iron pipe may not be joined by threaded joints. (b) Ductile iron pipe...

  1. Prospects for Ductility and Toughness Enhancement of Nial by Ductile Phase Reinforcement

    NASA Technical Reports Server (NTRS)

    Noebe, R. D.; Ritzert, F. J.; Misra, A.; Gibala, R.

    1991-01-01

    The use of NiAl as a structural material has been hindered by the fact that this ordered intermetallic does not exhibit significant tensile ductility or toughness at room temperature. A critical review of the operative flow and fracture mechanisms in monolithic NiAl has thus established the need for ductile phase toughening in this order system. Progress in ductile phase reinforced intermetallic systems in general and specifically NiAl-based materials has been reviewed. In addition, further clarification of the primary mechanisms involved in the flow and fracture of ductile phase reinforced alloys has evolved from ongoing investigations of several model NiAl-based materials. The mechanical behavior of these model directionally-solidified alloys (Ni-30Al and Ni-30Fe-20Al) are discussed. Finally, the prospects for developing a ductile phase toughened NiAl-based alloy and the shortcomings presently inherent in these systems are analyzed.

  2. Phase-field modeling of ductile fracture

    NASA Astrophysics Data System (ADS)

    Ambati, M.; Gerasimov, T.; De Lorenzis, L.

    2015-05-01

    Phase-field modeling of brittle fracture in elastic solids is a well-established framework that overcomes the limitations of the classical Griffith theory in the prediction of crack nucleation and in the identification of complicated crack paths including branching and merging. We propose a novel phase-field model for ductile fracture of elasto-plastic solids in the quasi-static kinematically linear regime. The formulation is shown to capture the entire range of behavior of a ductile material exhibiting -plasticity, encompassing plasticization, crack initiation, propagation and failure. Several examples demonstrate the ability of the model to reproduce some important phenomenological features of ductile fracture as reported in the experimental literature.

  3. Bend ductility of tungsten heavy alloys

    SciTech Connect

    Gurwell, W.E.; Garnich, M.R.; Dudder, G.B.; Lavender, C.A.

    1992-11-01

    A bend ductility test is used to indicate the formability of tungsten heavy alloys sheet. The primary test bends a notchless Charpy impact specimen to a bend angle of approximately 100C. This can be augmented by a bend-completion test. Finite element modeling as well as strain-gaged bend specimens elucidate the strain distribution in the specimen as a function of material thickness and bend angle. The bend ductilities of 70%W, 807.W and 90%W alloys are characterized. As expected, decreasing thickness or tungsten content enhances bend ductility. Oxidation is not detrimental; therefore, controlled atmosphere is not required for cooling. The potentially detrimental effects of mechanical working (e.g., rolling, roller-leveling, grit blasting, and peening) and machining (e.g., cutting and sanding) are illustrated.

  4. Material Characterization for Ductile Fracture Prediction

    NASA Technical Reports Server (NTRS)

    Hill, Michael R.

    2000-01-01

    The research summarized in this document provides valuable information for structural health evaluation of NASA infrastructure. Specifically, material properties are reported which will enable calibration of ductile fracture prediction methods for three high-toughness metallic materials and one aluminum alloy which can be found in various NASA facilities. The task of investigating these materials has also served to validate an overall methodology for ductile fracture prediction is currently being employed at NASA. In facilitating the ability to incorporate various materials into the prediction scheme, we have provided data to enable demonstration of the overall generality of the approach.

  5. Ductile aluminide alloys for high temperature applications

    SciTech Connect

    Liu, C.T.; Stiegler, J.O.

    1986-09-16

    An alloy is described consisting essentially of sufficient nickel and aluminum to form Ni/sub 3/A1, an amount of boron sufficient to promote ductility in the alloy and 0.3 to 1.5 atomic percent of an element selected from the group consisting of hafnium and zirconium. The alloy further including 6 to 12 atomic percent iron.

  6. Nanostructuring and ductility of crystals under compression

    NASA Astrophysics Data System (ADS)

    Magomedov, M. N.

    2016-05-01

    Nanostructuring of crystals into domains under uniform compression, the ductility of a solid nanostructure under pressure, and the bimodal distribution of domain size are explained based on the dependence of the surface energy and surface pressure on the shape, size, and density of a nanocrystal.

  7. Ductile mandrel and parting compound facilitate tube drawing

    NASA Technical Reports Server (NTRS)

    Burt, W. R., Jr.; Mayfield, R. M.; Polakowski, N. H.

    1966-01-01

    Refractory tubing is warm drawn over a solid ductile mandrel with a powder parting compound packed between mandrel and the tubes inner surface. This method applies also to the coextrusion of a billet and a ductile mandrel.

  8. OVERALL VIEW OF SOUTHERN DUCTILE'S PATTERN REPAIR SHOP, SHOWING A ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    OVERALL VIEW OF SOUTHERN DUCTILE'S PATTERN REPAIR SHOP, SHOWING A SPANISH-MADE FORADIA BORING MACHINE IN THE FOREGROUND. - Southern Ductile Casting Company, Mold Making, 2217 Carolina Avenue, Bessemer, Jefferson County, AL

  9. Calculation Method of Lateral Strengths and Ductility Factors of Constructions with Shear Walls of Different Ductility

    SciTech Connect

    Yamaguchi, Nobuyoshi; Nakao, Masato; Murakami, Masahide; Miyazawa, Kenji

    2008-07-08

    For seismic design, ductility-related force modification factors are named R factor in Uniform Building Code of U.S, q factor in Euro Code 8 and Ds (inverse of R) factor in Japanese Building Code. These ductility-related force modification factors for each type of shear elements are appeared in those codes. Some constructions use various types of shear walls that have different ductility, especially for their retrofit or re-strengthening. In these cases, engineers puzzle the decision of force modification factors of the constructions. Solving this problem, new method to calculate lateral strengths of stories for simple shear wall systems is proposed and named 'Stiffness--Potential Energy Addition Method' in this paper. This method uses two design lateral strengths for each type of shear walls in damage limit state and safety limit state. Two lateral strengths of stories in both limit states are calculated from these two design lateral strengths for each type of shear walls in both limit states. Calculated strengths have the same quality as values obtained by strength addition method using many steps of load-deformation data of shear walls. The new method to calculate ductility factors is also proposed in this paper. This method is based on the new method to calculate lateral strengths of stories. This method can solve the problem to obtain ductility factors of stories with shear walls of different ductility.

  10. Ductility of a continuous fiber reinforced aluminum matrix composite

    NASA Technical Reports Server (NTRS)

    Jansson, S.; Leckie, Frederick A.

    1991-01-01

    The transverse properties of an aluminum alloy metal matrix composite reinforced by continuous alumina fibers have been investigated. The composite is subjected to both mechanical and cyclic thermal loading. The ductility can vary by an order of magnitude according to the operating conditions. For high mechanical and low thermal loading the ductility is small, for low mechanical and high thermal loading the ductility is an order of magnitude higher. Experiments on a beam in bending confirm that the ductility is strongly dependent on the loading conditions. The observations suggest a means of utilizing the inherent ductility of the matrix.

  11. Coupled thermal stress simulations of ductile tearing

    DOE PAGESBeta

    Neilsen, Michael K.; Dion, Kristin

    2016-03-01

    Predictions for ductile tearing of a geometrically complex Ti-6Al-4V plate were generated using a Unified Creep Plasticity Damage model in fully coupled thermal stress simulations. Uniaxial tension and butterfly shear tests performed at displacement rates of 0.0254 and 25.4 mm/s were also simulated. Results from these simulations revealed that the material temperature increase due to plastic work can have a dramatic effect on material ductility predictions in materials that exhibit little strain hardening. Furthermore, this occurs because the temperature increase causes the apparent hardening of the material to decrease which leads to the initiation of deformation localization and subsequent ductilemore » tearing earlier in the loading process.« less

  12. Designing tensile ductility in metallic glasses

    PubMed Central

    Sarac, Baran; Schroers, Jan

    2013-01-01

    Effectiveness of a second phase in metallic glass heterostructures to improve mechanical properties varies widely. Unfortunately, methods to fabricate such heterostructures like foams and composites do not allow controlled variation of structural features. Here we report a novel strategy, which allows us to vary heterostructural features independently, thereby enabling a systematic and quantitative study. Our approach reveals the optimal microstructural architecture for metallic glass heterostructures to achieve tensile ductility. Critical design aspect is a soft second phase, which is most effective when spacing between the second phase assumes the critical crack length of the metallic glass. This spacing should coincide with the second phase’s size, and beyond, the specific second phase morphology of the heterostructure is crucial. These toughening strategies are only effective in samples that are large compared with the spacing of the second phase. The identified design aspects provide guidance in designing tensile ductility into metallic glasses. PMID:23863967

  13. Designing tensile ductility in metallic glasses.

    PubMed

    Sarac, Baran; Schroers, Jan

    2013-01-01

    Effectiveness of a second phase in metallic glass heterostructures to improve mechanical properties varies widely. Unfortunately, methods to fabricate such heterostructures like foams and composites do not allow controlled variation of structural features. Here we report a novel strategy, which allows us to vary heterostructural features independently, thereby enabling a systematic and quantitative study. Our approach reveals the optimal microstructural architecture for metallic glass heterostructures to achieve tensile ductility. Critical design aspect is a soft second phase, which is most effective when spacing between the second phase assumes the critical crack length of the metallic glass. This spacing should coincide with the second phase's size, and beyond, the specific second phase morphology of the heterostructure is crucial. These toughening strategies are only effective in samples that are large compared with the spacing of the second phase. The identified design aspects provide guidance in designing tensile ductility into metallic glasses. PMID:23863967

  14. A review of macroscopic ductile failure criteria.

    SciTech Connect

    Corona, Edmundo; Reedlunn, Benjamin

    2013-09-01

    The objective of this work was to describe several of the ductile failure criteria com- monly used to solve practical problems. The following failure models were considered: equivalent plastic strain, equivalent plastic strain in tension, maximum shear, Mohr- Coulomb, Wellman's tearing parameter, Johnson-Cook and BCJ MEM. The document presents the main characteristics of each failure model as well as sample failure predic- tions for simple proportional loading stress histories in three dimensions and in plane stress. Plasticity calculations prior to failure were conducted with a simple, linear hardening, J2 plasticity model. The resulting failure envelopes were plotted in prin- cipal stress space and plastic strain space, where the dependence on stress triaxiality and Lode angle are clearly visible. This information may help analysts select a ductile fracture model for a practical problem and help interpret analysis results.

  15. Towards mesh independent simulation of ductile fracture.

    SciTech Connect

    Fang, Huei Eliot; Veilleux, Michael; Emery, John M.; Wellman, Gerald William; Foulk, James W., III

    2010-11-01

    Recent work at Sandia National Laboratories has focused on preparing strong predictive models for the simulation of ductile failure in metals. The focus of this talk is on the development of engineering-ready models that use a phenomenological approach to represent the ductile fracture processes. As such, an empirical tearing parameter that accounts for mean stress effects along the crack front is presented. A critical value of the tearing parameter is used in finite element calculations as the criterion for crack growth. Regularization is achieved with three different methods and the results are compared. In the first method, upon reaching the critical tearing, the stress within a solid element is decayed by uniformly shrinking the yield surface over a user specified amount of strain. This yields mesh-size dependent results. As a second method for regularization, cohesive surface elements are inserted using an automatic remeshing technique. In the third method, strain-localization elements are inserted with the automated remeshing.

  16. Rapid ductile afterslip from coseismic heating

    NASA Astrophysics Data System (ADS)

    Platt, J. D.; Meade, B. J.; Savage, H. M.; Rowe, C. D.

    2015-12-01

    Earthquakes are typically followed by months of afterslip, the total of which is generally an order of magnitude smaller than the seismic slip. The classic model for afterslip envisions seismic slip transferring stress to adjacent regions, driving accelerated stable sliding that expands the rupture area. However, a small proportion of earthquakes exhibit unusually large and rapid afterslip in the hours immediately following rupture. Here we present a new model that bridges the transition from seismic to postseismic deformation and may explain these observations of rapid afterslip. Seismic slip produces a significant temperature rise that slowly diffuses into the surrounding material following the cessation of seismic slip. Any process with strong temperature dependence is more sensitive to this heat transient than to the ambient temperatures present during the interseismic period. Coupling the temperature evolution of a fault to a ductile flow law we model postseismic deformation during the heat transient. Our idea of coseismic heating enhancing ductile flow is supported by field observations of micro-shear zones adjacent to psuedotachylyte veins. Enhanced ductility is largely confined to the zone that deformed seismically, making our model equivalent to rapid afterslip. Combining analytic and numerical methods we solve for the total afterslip in terms of the slip rate and fault strength during seismic slip and the ductile flow parameters. Our results are sensitive to the assumed rheology and deforming zone thickness, and while total afterslip is generally small some plausible parameter ranges predict afterslip comparable to or greater than the seismic slip developing over timescales shorter than an hour. We demonstrate that rapid afterslip can drive significant frictional heating, leading to a thermal runaway instability that produces a near total postseismic stress drop. To conclude we investigate the tsunami magnitude that rapid afterslip could produce.

  17. High strength, high ductility low carbon steel

    DOEpatents

    Koo, Jayoung; Thomas, Gareth

    1978-01-01

    A high strength, high ductility low carbon steel consisting essentially of iron, 0.05-0.15 wt% carbon, and 1-3 wt% silicon. Minor amounts of other constituents may be present. The steel is characterized by a duplex ferrite-martensite microstructure in a fibrous morphology. The microstructure is developed by heat treatment consisting of initial austenitizing treatment followed by annealing in the (.alpha. + .gamma.) range with intermediate quenching.

  18. Preparation of nanostructured materials having improved ductility

    DOEpatents

    Zhao, Yonghao; Zhu, Yuntian T.

    2010-04-20

    A method for preparing a nanostructured aluminum alloy involves heating an aluminum alloy workpiece at temperature sufficient to produce a single phase coarse grained aluminum alloy, then refining the grain size of the workpiece at a temperature at or below room temperature, and then aging the workpiece to precipitate second phase particles in the nanosized grains of the workpiece that increase the ductility without decreasing the strength of the workpiece.

  19. Weldability and hot ductility of iron aluminides

    SciTech Connect

    Ash, D.I.; Edwards, G.R. . Center for Welding and Joining Research); David, S.A. )

    1991-05-01

    The weldability of iron aluminide alloys is discussed. Although readily welded with electron beam (EB) and gas-tungsten arc (GTA) techniques, iron aluminides are sometimes susceptible to cracking during cooling when welded with the GTA welding process. Taken into account are the effects of microstructural instability (grain growth), weld heat input (cooling rate) and environment on the hot ductility of an iron aluminide alloy designated FA-129. 64 refs., 59 figs., 3 tabs.

  20. Microstructural Characterization of Nodular Ductile Iron

    SciTech Connect

    Springer, H K

    2012-01-03

    The objective of this study is to quantify the graphite particle phase in nodular ductile iron (NDI). This study provides the basis for initializing microstructure in direct numerical simulations, as part of developing microstructure-fracture response models. The work presented here is a subset of a PhD dissertation on spall fracture in NDI. NDI is an ideal material for studying the influence of microstructure on ductile fracture because it contains a readily identifiable second-phase particle population, embedded in a ductile metallic matrix, which serves as primary void nucleation sites. Nucleated voids grow and coalesce under continued tensile loading, as part of the micromechanisms of ductile fracture, and lead to macroscopic failure. For this study, we used 2D optical microscopy and quantitative metallography relationships to characterize the volume fraction, size distribution, nearest-neighbor distance, and other higher-order metrics of the graphite particle phase. We found that the volume fraction was {Phi} = 0.115, the average particle diameter was d{sub avg} = 25.9 {mu}m, the Weibull shape and scaling parameters were {beta} = 1.8 and {eta} = 29.1 {mu}m, respectively, the (first) nearest neighbor distance was L{sub nn} = 32.4 {mu}m, the exponential coefficients for volume fraction fluctuations was A{sub {Phi}} = 1.89 and B{sub {Phi}} = -0.59, respectively. Based on reaching a coefficient-of-variation (COV) of 0.01, the representative volume element (RVE) size was determined to be 8.9L{sub nn} (288 {mu}m).

  1. Testing Bonds Between Brittle And Ductile Films

    NASA Technical Reports Server (NTRS)

    Wheeler, Donald R.; Ohsaki, Hiroyuki

    1989-01-01

    Simple uniaxial strain test devised to measure intrinsic shear strength. Brittle film deposited on ductile stubstrate film, and combination stretched until brittle film cracks, then separates from substrate. Dimensions of cracked segments related in known way to tensile strength of brittle film and shear strength of bond between two films. Despite approximations and limitations of technique, tests show it yields semiquantitative measures of bond strengths, independent of mechanical properties of substrates, with results reproducible with plus or minus 6 percent.

  2. Strong, Ductile Rotor For Cryogenic Flowmeters

    NASA Technical Reports Server (NTRS)

    Royals, W. T.

    1993-01-01

    Improved magnetic flowmeter rotor resists cracking at cryogenic temperatures, yet provides adequate signal to magnetic pickup outside flowmeter housing. Consists mostly of stainless-steel alloy 347, which is ductile and strong at low temperatures. Small bead of stainless-steel alloy 410 welded in groove around circumference of round bar of stainless-steel alloy 347; then rotor machined from bar. Tips of rotor blades contain small amounts of magnetic alloy, and passage of tips detected.

  3. Tunable Tensile Ductility in Metallic Glasses

    PubMed Central

    Magagnosc, D. J.; Ehrbar, R.; Kumar, G.; He, M. R.; Schroers, J.; Gianola, D. S.

    2013-01-01

    Widespread adoption of metallic glasses (MGs) in applications motivated by high strength and elasticity combined with plastic-like processing has been stymied by their lack of tensile ductility. One emerging strategy to couple the attractive properties of MGs with resistance to failure by shear localization is to employ sub-micron sample or feature length scales, although conflicting results shroud an atomistic understanding of the responsible mechanisms in uncertainty. Here, we report in situ deformation experiments of directly moulded Pt57.5Cu14.7Ni5.3P22.5 MG nanowires, which show tunable tensile ductility. Initially brittle as-moulded nanowires can be coerced to a distinct glassy state upon irradiation with Ga+ ions, leading to tensile ductility and quasi-homogeneous plastic flow. This behaviour is reversible and the glass returns to a brittle state upon subsequent annealing. Our results suggest a novel mechanism for homogenous plastic flow in nano-scaled MGs and strategies for circumventing the poor damage tolerance that has long plagued MGs.

  4. Ductile damage model with void coalescence

    SciTech Connect

    Tonks, D.L.

    1995-03-01

    A general model for ductile damage in metals is presented. It includes damage induced by shear stress as well as damage caused by volumetric tension. Spallation is included as a special case. Strain induced damage is also treated. Void nucleation and growth are included and give rise to strain rate effects. Strain rate effects also arise in the model through elastic release wave propagation between damage centers. Underlying physics of the model is the nucleation, growth, and coalescence of voids in a plastically flowing solid. Implementation of the model in hydrocodes is discussed.

  5. Ductile Titanium Alloy with Low Poisson's Ratio

    SciTech Connect

    Hao, Y. L.; Li, S. J.; Sun, B. B.; Sui, M. L.; Yang, R.

    2007-05-25

    We report a ductile {beta}-type titanium alloy with body-centered cubic (bcc) crystal structure having a low Poisson's ratio of 0.14. The almost identical ultralow bulk and shear moduli of {approx}24 GPa combined with an ultrahigh strength of {approx}0.9 GPa contribute to easy crystal distortion due to much-weakened chemical bonding of atoms in the crystal, leading to significant elastic softening in tension and elastic hardening in compression. The peculiar elastic and plastic deformation behaviors of the alloy are interpreted as a result of approaching the elastic limit of the bcc crystal under applied stress.

  6. Continuous-Discontinuous Model for Ductile Fracture

    SciTech Connect

    Seabra, Mariana R. R.; Cesar de Sa, Jose M. A.

    2010-06-15

    In this contribution, a continuum-dicontinuum model for ductile failure is presented. The degradation of material properties trough deformation is described by Continuum Damage Mechanics in a non-local integral formulation to avoid mesh dependence. In the final stage of failure, the damaged zone is replaced by a cohesive macro crack and subsequent traction-free macro crack for a more realistic representation of the phenomenon. The inclusion of the discontinuity surfaces is performed by the XFEM and Level Set Method and avoids the spurious damage growth typical of this class of models.

  7. SOUTHERN DUCTILE DOES NOT OWN OR CREATE PATTERNS USED IN ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    SOUTHERN DUCTILE DOES NOT OWN OR CREATE PATTERNS USED IN THEIR MOLDS. AS A JOBBING FOUNDRY MAKING CASTINGS ON AN CONTRACTUAL-ORDER BASIS, THEIR CUSTOMERS PROVIDE, OR CONTRACT FOR PATTERN CONSTRUCTION. SOUTHERN DUCTILE DOES, HOWEVER, PROVIDE REPAIR SERVICES SHOWN AS JOHNNY TIDWELL PREPARES A PLATE, FORM -FITTING TO THEIR MOLDING MACHINES, THAT A PATTERN WILL BE AFFIXED TO. - Southern Ductile Casting Company, Mold Making, 2217 Carolina Avenue, Bessemer, Jefferson County, AL

  8. Impact testing of ductile cast iron: Tension and compression

    SciTech Connect

    Yokoyama, T.; Takata, T.; Sogabe, Y.

    1995-11-01

    Impact tension and compression tests on ferritic ductile cast iron (JIS FCD370) are conducted by means of the split Hopkinson bar technique. Reliable stress-strain relations in tension and compression for ductile cast iron are determined at strain rates of over 10{sup 3}/s. The test results indicate that ductile cast iron shows different strength characteristics in tension and compression under impact loading as well as under quasi-static loading. Microscopic examinations of the post-test specimens reveal that this mechanical behavior is attributed to the presence of spheroidal graphites in a ferritic matrix of ductile cast iron.

  9. Wear resistance properties of austempered ductile iron

    SciTech Connect

    Lerner, Y.S.; Kingsbury, G.R.

    1998-02-01

    A detailed review of wear resistance properties of austempered ductile iron (ADI) was undertaken to examine the potential applications of this material for wear parts, as an alternative to steels, alloyed and white irons, bronzes, and other competitive materials. Two modes of wear were studied: adhesive (frictional) dry sliding and abrasive wear. In the rotating dry sliding tests, wear behavior of the base material (a stationary block) was considered in relationship to countersurface (steel shaft) wear. In this wear mode, the wear rate of ADI was only one-fourth that of pearlitic ductile iron (DI) grade 100-70-03; the wear rates of aluminum bronze and leaded-tin bronze, respectively, were 3.7 and 3.3 times greater than that of ADI. Only quenched DI with a fully martensitic matrix slightly outperformed ADI. No significant difference was observed in the wear of steel shafts running against ADI and quenched DI. The excellent wear performance of ADI and its countersurface, combined with their relatively low friction coefficient, indicate potential for dry sliding wear applications. In the abrasive wear mode, the wear rate of ADI was comparable to that of alloyed hardened AISI 4340 steel, and approximately one-half that of hardened medium-carbon AISI 1050 steel and of white and alloyed cast irons. The excellent wear resistance of ADI may be attributed to the strain-affected transformation of high-carbon austenite to martensite that takes place in the surface layer during the wear tests.

  10. ALTHOUGH SOUTHERN DUCTILE DOES NOT OWN PATTERNS, THEY ARE REQUIRED ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    ALTHOUGH SOUTHERN DUCTILE DOES NOT OWN PATTERNS, THEY ARE REQUIRED TO STORE THEM AND KEEP THEM AVAILABLE FOR THEIR CUSTOMERS ORDERS. THE BARRET/DOUGLAS LIFTING TRUCK IS USED TO REACH AND TRANSPORT PATTERNS. - Southern Ductile Casting Company, Mold Making, 2217 Carolina Avenue, Bessemer, Jefferson County, AL

  11. Study made of ductility limitations of aluminum-silicon alloys

    NASA Technical Reports Server (NTRS)

    Bailey, W. A.; Frederick, S. F.

    1967-01-01

    Study of the relation between microstructure and mechanical properties of aluminum-silicon alloys determines the cause of the variations in properties resulting from differences in solidification rate. It was found that variations in strength are a consequence of variations in ductility and that ductility is inversely proportional to dendrite cell size.

  12. GRINDING ROOM AT SOUTHERN DUCTILE CASTING COMPANY, BESSEMER FOUNDRY SHOWING ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    GRINDING ROOM AT SOUTHERN DUCTILE CASTING COMPANY, BESSEMER FOUNDRY SHOWING WHEELABORATOR THAT IMPALE SHOT AT TUMBLING CASTINGS TO REMOVE EXCESS SURFACE METALS AND SAND; ANNEALING OVENS TO HEAT CERTAIN CASTINGS TO ACHIEVE A DESIRED CHARACTERISTIC; AND GRINDING WHEELS USED TO REMOVE GATES. - Southern Ductile Casting Company, Grinding & Shipping, 2217 Carolina Avenue, Bessemer, Jefferson County, AL

  13. 46 CFR 56.60-15 - Ductile iron.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... (incorporated by reference; see 46 CFR 56.01-2). (b) Ductile iron castings conforming to ASTM A 395... 395 (incorporated by reference, see 46 CFR 56.01-2) may be used within the service restrictions and... 46 Shipping 2 2011-10-01 2011-10-01 false Ductile iron. 56.60-15 Section 56.60-15 Shipping...

  14. 46 CFR 56.60-15 - Ductile iron.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... (incorporated by reference; see 46 CFR 56.01-2). (b) Ductile iron castings conforming to ASTM A 395... 395 (incorporated by reference, see 46 CFR 56.01-2) may be used within the service restrictions and... 46 Shipping 2 2012-10-01 2012-10-01 false Ductile iron. 56.60-15 Section 56.60-15 Shipping...

  15. 46 CFR 56.60-15 - Ductile iron.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... (incorporated by reference; see 46 CFR 56.01-2). (b) Ductile iron castings conforming to ASTM A 395... 395 (incorporated by reference, see 46 CFR 56.01-2) may be used within the service restrictions and... 46 Shipping 2 2014-10-01 2014-10-01 false Ductile iron. 56.60-15 Section 56.60-15 Shipping...

  16. 46 CFR 56.60-15 - Ductile iron.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... (incorporated by reference; see 46 CFR 56.01-2). (b) Ductile iron castings conforming to ASTM A 395... 395 (incorporated by reference, see 46 CFR 56.01-2) may be used within the service restrictions and... 46 Shipping 2 2013-10-01 2013-10-01 false Ductile iron. 56.60-15 Section 56.60-15 Shipping...

  17. 46 CFR 56.60-15 - Ductile iron.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... (incorporated by reference; see 46 CFR 56.01-2). (b) Ductile iron castings conforming to ASTM A 395... 395 (incorporated by reference, see 46 CFR 56.01-2) may be used within the service restrictions and... 46 Shipping 2 2010-10-01 2010-10-01 false Ductile iron. 56.60-15 Section 56.60-15 Shipping...

  18. The nucleation of austenite in ferritic ductile cast iron

    SciTech Connect

    Chou, J.M.; Hon, M.H. ); Lee, J.L. )

    1992-07-01

    Austempered ductile cast iron has recently been receiving increasing attention because of its excellent combination of strength and ductility. Since the austenitization process has a significant influence on the mechanical properties of austempered ductile cast iron, several investigations on the nucleation sites of austenite and diffusion paths of carbon from spheroidal graphite have been reported in ferritic ductile cast iron. However, agreement on this subject has not ben reached. The purpose of this paper is to study the preferential nucleation sites of austenite during austenitization at two austenitizing temperatures in ferritic ductile cast iron. An attempt was made to understand the reasons which give rise to preferential austenite nucleation sites. The carbon diffusion paths from spheroidal graphite were also investigated.

  19. Causes of the hot ductility drops of steels

    NASA Astrophysics Data System (ADS)

    Kolbasnikov, N. G.; Matveev, M. A.; Mishin, V. V.; Mishnev, P. A.; Nikonov, S. V.

    2014-09-01

    The effect of conditions of continuous casting and hot rolling of steel on the high-temperature ductility of a microalloyed pipe steel of strength class Kh42 and 17G1S-U steel is studied. A Gleeble-3800 thermomechanical facility is used to perform physical modeling of the hot ductility of steel. The temperature dependence of the hot ductility of steel is determined under various slab cooling conditions in a continuous caster and during hot rolling. The ductility drops of iron and steels is found to be mainly caused by an increase in the elastic modulus near the temperatures of the polymorphic transformation caused by first- and secondorder phase transformations (polymorphic and magnetic transformations, respectively). Structural factors, such as the grain size, excess-phase inclusions located along initial grain boundaries, and interstitial impurities, lead to an additional decrease in the ductility.

  20. Recommendations for ductile and brittle failure design criteria for ductile cast iron spent-fuel shipping containers

    SciTech Connect

    Schwartz, M.W.

    1984-04-01

    This report presents recommendations for establishing design and acceptance criteria for the ductile cast iron to be used for fabricating spent-fuel shipping casks. These recommendations address design criteria for preventing ductile failure, and acceptance criteria for preventing brittle fracture, based upon drop testing a flawed prototype cask.

  1. Hot Ductility Behavior of an 8 Pct Cr Roller Steel

    NASA Astrophysics Data System (ADS)

    Wang, Zhenhua; Sun, Shuhua; Shi, Zhongping; Wang, Bo; Fu, Wantang

    2015-04-01

    The hot ductility of an 8 pct Cr roller steel was determined between 1173 K and 1473 K (900 °C and 1200 °C) at strain rates of 0.01 to 10 s-1 through tensile testing. The fracture morphology was observed using scanning electron microscopy, and the microstructure was examined through optical microscopy and transmission electron microscopy. The dependence of the hot ductility behavior on the deformation conditions, grain size, and precipitation was analyzed. The relationship between the reduction in area and the natural logarithm of the Zener-Hollomon parameter (ln Z) was found to be a second-order polynomial. When ln Z was greater than 40 s-1, the hot ductility was poor and fracture was mainly caused by incompatible deformation between the grains. When ln Z was between 32 and 40 s-1, the hot ductility was excellent and the main fracture mechanism was void linking. When ln Z was below 32 s-1, the hot ductility was poor and fracture was mainly caused by grain boundary sliding. A fine grain structure is beneficial for homogenous deformation and dynamic recrystallization, which induces better hot ductility. The effect of M7C3 carbide particles dispersed in the matrix on the hot ductility was small. The grain growth kinetics in the 8 pct Cr steel were obtained between 1373 K and 1473 K (1100 °C and 1200 °C). Finally, optimized preheating and forging procedures for 8 pct Cr steel rollers are provided.

  2. Creep deformation characteristics of ductile discontinuous fiber reinforced composites

    SciTech Connect

    Biner, S.B.

    1993-10-01

    Role of material parameters and geometric parameters of ductile reinforcing phase on the creep deformation behavior of 20% discontinuously reinforced composite was numerically investigated including debonding and pull-out mechanisms. Results indicate that for rigidly bonded interfaces, the creep rate of the composite is not significantly influenced by the material properties and geometric parameters of the ductile reinforcing phase due to development of large hydrostatic stress and constrained deformation in the reinforcement. For debonding interfaces, the geometric parameters of the reinforcing phase are important; however, event with very weak interfacial behavior low composite creep rates can be achieved by suitable selection of the geometric parameters of the ductile reinforcing phase.

  3. High-temperature ductility of electro-deposited nickel

    NASA Technical Reports Server (NTRS)

    Dini, J. W.; Johnson, H. R.

    1977-01-01

    Work done during the past several months on high temperature ductility of electrodeposited nickel is summarized. Data are presented which show that earlier measurements made at NASA-Langley erred on the low side, that strain rate has a marked influence on high temperature ductility, and that codeposition of a small amount of manganese helps to improve high temperature ductility. Influences of a number of other factors on nickel properties were also investigated. They included plating solution temperature, current density, agitation, and elimination of the wetting agent from the plating solution. Repair of a large nozzle section by nickel plating is described.

  4. Carbon content of austenite in austempered ductile iron

    SciTech Connect

    Chang, L.C.

    1998-06-05

    The development of austempered ductile iron (ADI) is a major achievement in cast iron technology. The austempering heat treatment enables the ductile cast iron containing mainly strong bainitic ferrite and ductile carbon-enriched austenite, with some martensite transforms from austenite during cooling down to room temperature. A key factor controlling the stability of the retained austenite can be evaluated soundly using the thermodynamics principles. It is the purpose here to demonstrate that the data of ADI from numerous sources have a similar trend.

  5. Experimental aspects of an investigation of macroscopic ductile failure criteria

    SciTech Connect

    Soo Hoo, M.S.; Benzley, S.E.; Priddy, T.G.

    1981-03-01

    Experimental results for the ductile failure of 7075-T651 aluminum are presented. Four separate shapes were tested to investigate the importance that macroscopic effective shear stress, hydrostatic stress, and plastic strain play in describing ductile failure of materials. The specimens used were: thin wall torsion tubes to create a state of pure shear, uniform hollow tubes to create a state of uniaxial stress; hour-glass shaped hollow tubes to create a state of biaxial stress; and notched round bars to create a state of triaxial stress. Two proposed ductile failure criteria are discussed in conjunction with the experimental results presented.

  6. Determining Ductile Fracture Toughness in Metals

    SciTech Connect

    Chen, Xiang; Nanstad, Randy K; Sokolov, Mikhail A; Manneschmidt, Eric T

    2014-01-01

    Ductile fracture toughness determination, such as the J-integral versus crack growth resistance (J-R) curve, is a useful tool for evaluating material structural integrity in the presence of pre-existing defects. The J-R curve represents a way to calculate the work (energy) per unit fracture surface area needed to drive the crack growth. A typical J-R curve is shown in Fig. 1 from which the material fracture toughness near the initiation of stable crack growth (Jq) can be derived. In addition, tearing modulus (TR), representing the material resistance to stable crack growth, can be calculated based on the slope of the J-R curve between two exclusion lines (red dashed lines in Fig. 1). Since the introduction of the J-R curve, extensive efforts have been continuously devoted to develop simplified and reliable methods for determining the material J-R curve. This article briefly reviews three widely-used J-R curve test methods in metals, i.e. elastic unloading compliance (EUC), normalization, and direct current potential drop (DCPD). The main difference in these methods relates to the determination of the crack size. More details of performing the J-R curve determination can be found in ASTM standard E1820-11.

  7. Ultrahigh Ductility, High-Carbon Martensitic Steel

    NASA Astrophysics Data System (ADS)

    Qin, Shengwei; Liu, Yu; Hao, Qingguo; Zuo, Xunwei; Rong, Yonghua; Chen, Nailu

    2016-07-01

    Based on the proposed design idea of the anti-transformation-induced plasticity effect, both the additions of the Nb element and pretreatment of the normalization process as a novel quenching-partitioning-tempering (Q-P-T) were designed for Fe-0.63C-1.52Mn-1.49Si-0.62Cr-0.036Nb hot-rolled steel. This high-carbon Q-P-T martensitic steel exhibits a tensile strength of 1890 MPa and elongation of 29 pct accompanied by the excellent product of tensile and elongation of 55 GPa pct. The origin of ultrahigh ductility for high-carbon Q-P-T martensitic steel is revealed from two aspects: one is the softening of martensitic matrix due to both the depletion of carbon in the matensitic matrix during the Q-P-T process by partitioning of carbon from supersaturated martensite to retained austenite and the reduction of the dislocation density in a martensitic matrix by dislocation absorption by retained austenite effect during deformation, which significantly enhances the deformation ability of martensitic matrix; another is the high mechanical stability of considerable carbon-enriched retained austenite, which effectively reduces the formation of brittle twin-type martensite. This work verifies the correctness of the design idea of the anti-TRIP effect and makes the third-generation advanced high-strength steels extend to the field of high-carbon steels from low- and medium-carbon steels.

  8. Retention of ductility in high-strength steels

    NASA Technical Reports Server (NTRS)

    Parker, E. R.; Zackay, V. F.

    1969-01-01

    To produce high strength alloy steel with retention of ductility, include tempering, cooling and subsequent tempering. Five parameters for optimum results are pretempering temperature, amount of strain, strain rate, temperature during strain, and retempering temperature.

  9. INTERIOR VIEW WITH CASTING MACHINE AND A 20' DUCTILE IRON ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    INTERIOR VIEW WITH CASTING MACHINE AND A 20' DUCTILE IRON PIPE BEING EXTRACTED USING PIPE PULLERS. - McWane Cast Iron Pipe Company, Pipe Casting Area, 1201 Vanderbilt Road, Birmingham, Jefferson County, AL

  10. INTERIOR VIEW WITH CASTING MACHINE AND A 4" DUCTILE IRON ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    INTERIOR VIEW WITH CASTING MACHINE AND A 4" DUCTILE IRON PIPE BEING EXTRACTED FROM CASTING MACHINE - McWane Cast Iron Pipe Company, Pipe Casting Area, 1201 Vanderbilt Road, Birmingham, Jefferson County, AL

  11. INTERIOR VIEW OF CASTING MACHINE WITH 4' DUCTILE IRON PIPE ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    INTERIOR VIEW OF CASTING MACHINE WITH 4' DUCTILE IRON PIPE BEING WEIGHED ON SCALES AT CASTING MACHINE. - McWane Cast Iron Pipe Company, Pipe Casting Area, 1201 Vanderbilt Road, Birmingham, Jefferson County, AL

  12. INTERIOR VIEW WITH CASTING MACHINE AND A 4' DUCTILE IRON ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    INTERIOR VIEW WITH CASTING MACHINE AND A 4' DUCTILE IRON PIPE BEING CENTRIFUGALLY CAST, AS OPERATOR WATCHES TO ENSURE QUALITY. - McWane Cast Iron Pipe Company, Pipe Casting Area, 1201 Vanderbilt Road, Birmingham, Jefferson County, AL

  13. Ductile alloy and process for preparing composite superconducting wire

    DOEpatents

    Verhoeven, J.D.; Finnemore, D.K.; Gibson, E.D.; Ostenson, J.E.

    An alloy for the commercial production of ductile superconducting wire is prepared by melting together copper and at least 15 weight percent niobium under non-oxygen-contaminating conditions, and rapidly cooling the melt to form a ductile composite consisting of discrete, randomly distributed and oriented dendritic-shaped particles of niobium in a copper matrix. As the wire is worked, the dendritic particles are realigned parallel to the longitudinal axis and when drawn form a plurality of very fine ductile superconductors in a ductile copper matrix. The drawn wire may be tin coated and wound into magnets or the like before diffusing the tin into the wire to react with the niobium. Impurities such as aluminum or gallium may be added to improve upper critical field characteristics.

  14. Ductile alloy and process for preparing composite superconducting wire

    DOEpatents

    Verhoeven, John D.; Finnemore, Douglas K.; Gibson, Edwin D.; Ostenson, Jerome E.

    1983-03-29

    An alloy for the commercial production of ductile superconducting wire is prepared by melting together copper and at least 15 weight percent niobium under non-oxygen-contaminating conditions, and rapidly cooling the melt to form a ductile composite consisting of discrete, randomly distributed and orientated dendritic-shaped particles of niobium in a copper matrix. As the wire is worked, the dendritric particles are realigned parallel to the longitudinal axis and when drawn form a plurality of very fine ductile superconductors in a ductile copper matrix. The drawn wire may be tin coated and wound into magnets or the like before diffusing the tin into the wire to react with the niobium. Impurities such as aluminum or gallium may be added to improve upper critical field characteristics.

  15. Method of making sintered ductile intermetallic-bonded ceramic composites

    DOEpatents

    Plucknett, Kevin; Tiegs, Terry N.; Becher, Paul F.

    1999-01-01

    A method of making an intermetallic-bonded ceramic composite involves combining a particulate brittle intermetallic precursor with a particulate reactant metal and a particulate ceramic to form a mixture and heating the mixture in a non-oxidizing atmosphere at a sufficient temperature and for a sufficient time to react the brittle intermetallic precursor and the reactant metal to form a ductile intermetallic and sinter the mixture to form a ductile intermetallic-bonded ceramic composite.

  16. Method of making sintered ductile intermetallic-bonded ceramic composites

    DOEpatents

    Plucknett, K.; Tiegs, T.N.; Becher, P.F.

    1999-05-18

    A method of making an intermetallic-bonded ceramic composite involves combining a particulate brittle intermetallic precursor with a particulate reactant metal and a particulate ceramic to form a mixture and heating the mixture in a non-oxidizing atmosphere at a sufficient temperature and for a sufficient time to react the brittle intermetallic precursor and the reactant metal to form a ductile intermetallic and sinter the mixture to form a ductile intermetallic-bonded ceramic composite. 2 figs.

  17. Ductile flow by water-assisted cataclasis

    NASA Astrophysics Data System (ADS)

    den Brok, Bas

    2003-04-01

    In the presence of water otherwise brittle materials may deform macroscopically ductile by water-assisted cataclastic creep. This is possible as long as (i) solubility is high enough, so that stress-corrosion can occur, and (ii) local stress is low enough, to that fracturing remains subcritical. Water-assisted cataclastic creep (WACC) may play an important role in the middle and lower continental crust where mineral solubilities are high and stresses low. WACC is a poorly understood deformation process. Experiments were performed on very soluble brittle salts (Na-chlorate; K-alum) to study microstructure development by WACC. The experiments were carried out at room temperature and atmospheric pressure in a small see-through vessel. In this way the cataclastic deformation process could be studied "in-situ" under the microscope. Crystals were loaded in the presence of saturated salt solution. It appeared that originally straight mineral surfaces were instable when kept under stress. Grooves (or channels) slowly developed in the surface by local dissolution. These grooves behave like so-called Grinfeld instabilities. They develop because the energy of a grooved surface under stress is lower than the energy of a straight surface under stress. The grooves may deepen and turn into subcritical cracks when local stress further increases. These cracks propagate slowly. They propagate parallel to sigma1 but also at an angle and even perpendicular to sigma1, often following crystallographically controlled directions. The fractures mostly change direction while propagating, locally making turns of more than 180 degrees. Irregular fracture fragments thus develop. The fractures may migrate sideways (as with grain bounday migration) probably by solution-redeposition driven by differences in stress between both sides of the fracture. Thus the shape of the fragments changes. The size of the fracture fragments seems to be controlled by the distance of the grooves, which decreases

  18. From brittle to ductile: a structure dependent ductility of diamond nanothread.

    PubMed

    Zhan, Haifei; Zhang, Gang; Tan, Vincent B C; Cheng, Yuan; Bell, John M; Zhang, Yong-Wei; Gu, Yuantong

    2016-06-01

    As a potential building block for the next generation of devices/multifunctional materials that are spreading in almost every technology sector, one-dimensional (1D) carbon nanomaterial has received intensive research interests. Recently, a new ultra-thin diamond nanothread (DNT) has joined this palette, which is a 1D structure with poly-benzene sections connected by Stone-Wales (SW) transformation defects. Using large-scale molecular dynamics simulations, we found that this sp(3) bonded DNT can transition from brittle to ductile behaviour by varying the length of the poly-benzene sections, suggesting that DNT possesses entirely different mechanical responses than other 1D carbon allotropes. Analogously, the SW defects behave like a grain boundary that interrupts the consistency of the poly-benzene sections. For a DNT with a fixed length, the yield strength fluctuates in the vicinity of a certain value and is independent of the "grain size". On the other hand, both yield strength and yield strain show a clear dependence on the total length of DNT, which is due to the fact that the failure of the DNT is dominated by the SW defects. Its highly tunable ductility together with its ultra-light density and high Young's modulus makes diamond nanothread ideal for the creation of extremely strong three-dimensional nano-architectures. PMID:27181833

  19. Numerical modeling of ductile tearing effects on cleavage fracture toughness

    SciTech Connect

    Dodds, R.H. Jr.; Tang, M.; Anderson, T.L.

    1994-05-01

    Experimental studies demonstrate a significant effect of specimen size, a/W ratio and prior ductile tearing on cleavage fracture toughness values (J{sub c}) measured in the ductile-to-brittle transition region of ferritic materials. In the lower-transition region, cleavage fracture often occurs under conditions of large-scale yielding but without prior ductile crack extension. The increased toughness develops when plastic zones formed at the crack tip interact with nearby specimen surfaces which relaxes crack-tip constraint (stress triaxiality). In the mid-to-upper transition region, small amounts of ductile crack extension (often < 1-2 mm) routinely precede termination of the J-{Delta}a curve by brittle fracture. Large-scale yielding, coupled with small amounts of ductile tearing, magnifies the impact of small variations in microscale material properties on the macroscopic fracture toughness which contributes to the large amount scatter observed in measured J{sub c}-values. Previous work by the authors described a micromechanics fracture model to correct measured J{sub c}-values for the mechanistic effects of large-scale yielding. This new work extends the model to also include the influence of ductile crack extension prior to cleavage. The paper explores development of the new model, provides necessary graphs and procedures for its application and demonstrates the effects of the model on fracture data sets for two pressure vessel steels (A533B and A515).

  20. 49 CFR 192.373 - Service lines: Cast iron and ductile iron.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 49 Transportation 3 2012-10-01 2012-10-01 false Service lines: Cast iron and ductile iron. 192.373... Regulators, and Service Lines § 192.373 Service lines: Cast iron and ductile iron. (a) Cast or ductile iron... cast iron pipe or ductile iron pipe is installed for use as a service line, the part of the...

  1. 49 CFR 192.373 - Service lines: Cast iron and ductile iron.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 49 Transportation 3 2013-10-01 2013-10-01 false Service lines: Cast iron and ductile iron. 192.373... Regulators, and Service Lines § 192.373 Service lines: Cast iron and ductile iron. (a) Cast or ductile iron... cast iron pipe or ductile iron pipe is installed for use as a service line, the part of the...

  2. 49 CFR 192.373 - Service lines: Cast iron and ductile iron.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 49 Transportation 3 2014-10-01 2014-10-01 false Service lines: Cast iron and ductile iron. 192.373... Regulators, and Service Lines § 192.373 Service lines: Cast iron and ductile iron. (a) Cast or ductile iron... cast iron pipe or ductile iron pipe is installed for use as a service line, the part of the...

  3. 49 CFR 192.373 - Service lines: Cast iron and ductile iron.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 49 Transportation 3 2010-10-01 2010-10-01 false Service lines: Cast iron and ductile iron. 192.373... Regulators, and Service Lines § 192.373 Service lines: Cast iron and ductile iron. (a) Cast or ductile iron... cast iron pipe or ductile iron pipe is installed for use as a service line, the part of the...

  4. 49 CFR 192.373 - Service lines: Cast iron and ductile iron.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 49 Transportation 3 2011-10-01 2011-10-01 false Service lines: Cast iron and ductile iron. 192.373... Regulators, and Service Lines § 192.373 Service lines: Cast iron and ductile iron. (a) Cast or ductile iron... cast iron pipe or ductile iron pipe is installed for use as a service line, the part of the...

  5. Theory of nonequilibrium segregation in an Fe-Mn-Ni ternary alloy and a ductile-brittle-ductile transition

    SciTech Connect

    Heo, N.H.

    1996-07-01

    In an Fe-8Mn-7Ni ternary alloy, age-hardened by coherently formed face-centered tetragonal MnNi intermetallic compounds within the matrix, a modeling based on a regular solution model is performed to formulate the nonequilibrium grain boundary segregation behaviors of the alloying elements, followed by a ductile-brittle-ductile transition in the alloy. An equation is derived representing the segregation kinetics. It is confirmed from the calculations that the segregation behaviors of the elements are directly controlled by the precipitation reaction in the matrix. The nonequilibrium segregation behaviors are characterized by time-temperature diagrams, which show maximum segregation levels of the elements in an intermediate aging time and temperature range. The calculated results explain theoretically and semiquantitatively the relationship between the nonequilibrium segregation of the elements and the ductile-brittle-ductile transition.

  6. Ductile iron data base: correlations between microstructure and fracture toughness: Background document for draft ASTM ductile iron specification

    SciTech Connect

    McConnell, P.; Lombrozo, P.

    1987-02-01

    A computer data base was generated to relate ductile iron fracture toughness with microstructural parameters, chemistry, and mechanical properties. Such relationships are considered necessary before a ductile iron material specification can be generated for spent nuclear fuel containers. Although scatter exists in the available data and more data are desirable, tentative conclusions can be drawn. In particular, ductile iron with high ferrite content (>80%) and spherical graphite nodules shows relatively high fracture toughness values suggesting its suitability for use in spent nuclear fuel casks. A material specification based upon nodule count (or the inversely related nodule spacing) may ensure a minimum fracture toughness in ductile iron. Increasing nodule spacing (decreasing count) increases the fracture toughness. Other relationships between mechanical properties and microstructure/chemistry are evaluated.

  7. Mechanical Characterization of Nodular Ductile Iron

    SciTech Connect

    Springer, H K

    2012-01-03

    The objective of this study is to characterize the strength and fracture response of nodular ductile iron (NDI) and its underlying ferritic matrix phase. Quasistatic and split Hopkinson pressure bar (SHPB) compression tests were performed on NDI and a model material for the NDI matrix phase (Fe-Si alloy). Smooth and notch round bar (NRB) samples were loaded in tension until fracture to determine strain-at-failure with varying stress triaxiality. Multiple tests were performed on each small and large smooth bar samples to obtain fracture statistics with sample size. Fracture statistics are important for initializing simulations of fragmentation events. Johnson-Cook strength models were developed for the NDI and the Fe-Si alloy. NDI strength model parameters are: A = 525 MPa, B = 650 MPa, n = 0.6, and C = 0.0205. The average SHPB experimental strain-rate of 2312/s was used for the reference strain-rate in this model. Fe-Si alloy strength model parameters are: A=560 MPa, B = 625 MPa, n = 0.5, and C = 0.02. The average SHPB experimental strain-rate of 2850/s was used for the reference strain-rate in this model. A Johnson-Cook failure model was developed for NDI with model parameters: D{sub 1} = 0.029, D{sub 2} = 0.44, D{sub 3} = -1.5, and D{sub 4} = D{sub 5} = 0. An exponential relationship was developed for the elongation-at-failure statistics as a function of length-scale with model parameters: S{sub f1} = 0.108, S{sub f2} = -0.00169, and L{sub m} = 32.4 {mu}m. NDI strength and failure models, including failure statistics, will be used in continuum-scale simulations of explosively-driven ring fragmentation. The Fe-Si alloy strength model will be used in mesoscale simulations of spall fracture in NDI, where the NDI matrix phase is captured explicitly.

  8. From brittle to ductile: a structure dependent ductility of diamond nanothread

    NASA Astrophysics Data System (ADS)

    Zhan, Haifei; Zhang, Gang; Tan, Vincent B. C.; Cheng, Yuan; Bell, John M.; Zhang, Yong-Wei; Gu, Yuantong

    2016-05-01

    As a potential building block for the next generation of devices/multifunctional materials that are spreading in almost every technology sector, one-dimensional (1D) carbon nanomaterial has received intensive research interests. Recently, a new ultra-thin diamond nanothread (DNT) has joined this palette, which is a 1D structure with poly-benzene sections connected by Stone-Wales (SW) transformation defects. Using large-scale molecular dynamics simulations, we found that this sp3 bonded DNT can transition from brittle to ductile behaviour by varying the length of the poly-benzene sections, suggesting that DNT possesses entirely different mechanical responses than other 1D carbon allotropes. Analogously, the SW defects behave like a grain boundary that interrupts the consistency of the poly-benzene sections. For a DNT with a fixed length, the yield strength fluctuates in the vicinity of a certain value and is independent of the ``grain size''. On the other hand, both yield strength and yield strain show a clear dependence on the total length of DNT, which is due to the fact that the failure of the DNT is dominated by the SW defects. Its highly tunable ductility together with its ultra-light density and high Young's modulus makes diamond nanothread ideal for the creation of extremely strong three-dimensional nano-architectures.As a potential building block for the next generation of devices/multifunctional materials that are spreading in almost every technology sector, one-dimensional (1D) carbon nanomaterial has received intensive research interests. Recently, a new ultra-thin diamond nanothread (DNT) has joined this palette, which is a 1D structure with poly-benzene sections connected by Stone-Wales (SW) transformation defects. Using large-scale molecular dynamics simulations, we found that this sp3 bonded DNT can transition from brittle to ductile behaviour by varying the length of the poly-benzene sections, suggesting that DNT possesses entirely different

  9. An investigation of the mechanical damping of ductile iron

    SciTech Connect

    Carpenter, S.H.; Stuch, T.E.; Salzbrenner, R.

    1995-11-01

    Ductile iron has been suggested as a candidate material for a number of practical applications, including turbine casings, automotive components, and transportation and storage casks for hazardous and radioactive materials. The applications require the enhanced ductility resulting from the presence of spherical graphite nodules in the ductile ferrite iron matrix. Proper design of such components requires a knowledge of the mechanical properties, including how energy is absorbed and dissipated (mechanical damping) by the test material. This article is a study of the mechanical damping of a series of well-characterized ductile iron materials (four separate materials) as a function of strain amplitude, temperature over the range of {minus}100 C to + 100 C, and magnetic field. The major sources of damping were found to be dislocation motion in the graphite phase and magnetomechanical damping in the ferrite phase. The magnitude of the magnetomechanical damping was much larger than that due to dislocation motion. An additional goal of the investigation was to determine if any correlation existed between the measured mechanical damping and the fracture toughness of the ductile iron materials; no correlation was found.

  10. Ductile electroactive biodegradable hyperbranched polylactide copolymers enhancing myoblast differentiation.

    PubMed

    Xie, Meihua; Wang, Ling; Guo, Baolin; Wang, Zhong; Chen, Y Eugene; Ma, Peter X

    2015-12-01

    Myotube formation is crucial to restoring muscular functions, and biomaterials that enhance the myoblast differentiation into myotubes are highly desirable for muscular repair. Here, we report the synthesis of electroactive, ductile, and degradable copolymers and their application in enhancing the differentiation of myoblasts to myotubes. A hyperbranched ductile polylactide (HPLA) was synthesized and then copolymerized with aniline tetramer (AT) to produce a series of electroactive, ductile and degradable copolymers (HPLAAT). The HPLA and HPLAAT showed excellent ductility with strain to failure from 158.9% to 42.7% and modulus from 265.2 to 758.2 MPa. The high electroactivity of the HPLAAT was confirmed by UV spectrometer and cyclic voltammogram measurements. These HPLAAT polymers also showed improved thermal stability and controlled biodegradation rate compared to HPLA. Importantly, when applying these polymers for myotube formation, the HPLAAT significantly improved the proliferation of C2C12 myoblasts in vitro compared to HPLA. Furthermore, these polymers greatly promoted myogenic differentiation of C2C12 cells as measured by quantitative analysis of myotube number, length, diameter, maturation index, and gene expression of MyoD and TNNT. Together, our study shows that these electroactive, ductile and degradable HPLAAT copolymers represent significantly improved biomaterials for muscle tissue engineering compared to HPLA. PMID:26335860

  11. Impact of ductility on hydraulic fracturing in shales

    NASA Astrophysics Data System (ADS)

    MacMinn, Chris; Auton, Lucy

    2016-04-01

    Hydraulic fracturing is a method for extracting natural gas and oil from low-permeability rocks such as shale via the high-pressure injection of fluid into the bulk of the rock. The goal is to initiate and propagate fractures that will provide hydraulic access deeper into the reservoir, enabling gas or oil to be collected from a larger region of the rock. Fracture is the tensile failure of a brittle material upon reaching a threshold tensile stress, but some shales have a high clay content and may yield plastically before fracturing. Plastic deformation is the shear failure of a ductile material, during which stress relaxes through irreversible rearrangements of the particles of the material. Here, we investigate the impact of the ductility of shales on hydraulic fracturing. We first consider a simple, axisymmetric model for radially outward fluid injection from a wellbore into a ductile porous rock. We use this model to show that plastic deformation greatly reduces the maximum tensile stress, and that this maximum stress does not always occur at the wellbore. We then complement these results with laboratory experiments in an analogue system, and with numerical simulations based on the discrete element method (DEM), both of which suggest that ductile failure can indeed dramatically change the resulting deformation pattern. These results imply that hydraulic fracturing may fail in ductile rocks, or that the required injection rate for fracking may be much larger than the rate predicted from models that assume purely elastic mechanical behavior.

  12. TEM investigation of ductile iron alloyed with vanadium.

    PubMed

    Dymek, S; Blicharski, M; Morgiel, J; Fraś, E

    2010-03-01

    This article presents results of the processing and microstructure evolution of ductile cast iron, modified by an addition of vanadium. The ductile iron was austenitized closed to the solidus (1095 degrees C) for 100 h, cooled down to 640 degrees C and held on at this temperature for 16 h. The heat treatment led to the dissolution of primary vanadium-rich carbides and their subsequent re-precipitation in a more dispersed form. The result of mechanical tests indicated that addition of vanadium and an appropriate heat treatment makes age hardening of ductile iron feasible. The precipitation processes as well as the effect of Si content on the alloy microstructure were examined by scanning and transmission electron microscopy. It was shown that adjacent to uniformly spread out vanadium-rich carbides with an average size of 50 nm, a dispersoid composed of extremely small approximately 1 nm precipitates was also revealed. PMID:20500418

  13. Hot Ductility of the 17-4 PH Stainless Steels

    NASA Astrophysics Data System (ADS)

    Herrera Lara, V.; Guerra Fuentes, L.; Covarrubias Alvarado, O.; Salinas Rodriguez, A.; Garcia Sanchez, E.

    2016-03-01

    The mechanisms of loss of hot ductility and the mechanical behavior of 17-4 PH alloys were investigated using hot tensile testing at temperatures between 700 and 1100 °C and strain rates of 10-4, 10-2, and 10-1 s-1. Scanning electron microscopy was used in conjunction with the results of the tensile tests to find the temperature region of loss of ductility and correlate it with cracking observed during processing by hot upsetting prior to ring rolling. It is reported that 17-4 PH alloys lose ductility in a temperature range around 900 °C near to the duplex austenite + ferrite phase field. Furthermore, it is found that niobium carbides precipitated at austenite/ferrite interfaces and grain boundaries have a pronounced effect on the mechanical behavior of the alloy during high-temperature deformation.

  14. Representing ductile damage with the dual domain material point method

    SciTech Connect

    Long, C. C.; Zhang, D. Z.; Bronkhorst, C. A.; Gray, III, G. T.

    2015-12-14

    In this study, we incorporate a ductile damage material model into a computational framework based on the Dual Domain Material Point (DDMP) method. As an example, simulations of a flyer plate experiment involving ductile void growth and material failure are performed. The results are compared with experiments performed on high purity tantalum. We also compare the numerical results obtained from the DDMP method with those obtained from the traditional Material Point Method (MPM). Effects of an overstress model, artificial viscosity, and physical viscosity are investigated. Our results show that a physical bulk viscosity and overstress model are important in this impact and failure problem, while physical shear viscosity and artificial shock viscosity have negligible effects. A simple numerical procedure with guaranteed convergence is introduced to solve for the equilibrium plastic state from the ductile damage model.

  15. Representing ductile damage with the dual domain material point method

    DOE PAGESBeta

    Long, C. C.; Zhang, D. Z.; Bronkhorst, C. A.; Gray, III, G. T.

    2015-12-14

    In this study, we incorporate a ductile damage material model into a computational framework based on the Dual Domain Material Point (DDMP) method. As an example, simulations of a flyer plate experiment involving ductile void growth and material failure are performed. The results are compared with experiments performed on high purity tantalum. We also compare the numerical results obtained from the DDMP method with those obtained from the traditional Material Point Method (MPM). Effects of an overstress model, artificial viscosity, and physical viscosity are investigated. Our results show that a physical bulk viscosity and overstress model are important in thismore » impact and failure problem, while physical shear viscosity and artificial shock viscosity have negligible effects. A simple numerical procedure with guaranteed convergence is introduced to solve for the equilibrium plastic state from the ductile damage model.« less

  16. Meshfree simulations of thermo-mechanical ductile fracture

    NASA Astrophysics Data System (ADS)

    Simkins, D. C.; Li, S.

    2006-08-01

    In this work, a meshfree method is used to simulate thermo-mechanical ductile fracture under finite deformation. A Galerkin meshfree formulation incorporating the Johnson-Cook damage model is implemented in numerical computations. We are interested in the simulation of thermo-mechanical effects on ductile fracture under large scale yielding. A rate form adiabatic split is proposed in the constitutive update. Meshfree techniques, such as the visibility criterion, are used to modify the particle connectivity based on evolving crack surface morphology. The numerical results have shown that the proposed meshfree algorithm works well, the meshfree crack adaptivity and re-interpolation procedure is versatile in numerical simulations, and it enables us to predict thermo-mechanical effects on ductile fracture.

  17. Brittle to Ductile Transition in Densified Silica Glass

    PubMed Central

    Yuan, Fenglin; Huang, Liping

    2014-01-01

    Current understanding of the brittleness of glass is limited by our poor understanding and control over the microscopic structure. In this study, we used a pressure quenching route to tune the structure of silica glass in a controllable manner, and observed a systematic increase in ductility in samples quenched under increasingly higher pressure. The brittle to ductile transition in densified silica glass can be attributed to the critical role of 5-fold Si coordination defects (bonded to 5 O neighbors) in facilitating shear deformation and in dissipating energy by converting back to the 4-fold coordination state during deformation. As an archetypal glass former and one of the most abundant minerals in the Earth's crest, a fundamental understanding of the microscopic structure underpinning the ductility of silica glass will not only pave the way toward rational design of strong glasses, but also advance our knowledge of the geological processes in the Earth's interior. PMID:24849328

  18. Brittle and ductile friction and the physics of tectonic tremor

    USGS Publications Warehouse

    Daub, E.G.; Shelly, D.R.; Guyer, R.A.; Johnson, P.A.

    2011-01-01

    Observations of nonvolcanic tremor provide a unique window into the mechanisms of deformation and failure in the lower crust. At increasing depths, rock deformation gradually transitions from brittle, where earthquakes occur, to ductile, with tremor occurring in the transitional region. The physics of deformation in the transition region remain poorly constrained, limiting our basic understanding of tremor and its relation to earthquakes. We combine field and laboratory observations with a physical friction model comprised of brittle and ductile components, and use the model to provide constraints on the friction and stress state in the lower crust. A phase diagram is constructed that characterizes under what conditions all faulting behaviors occur, including earthquakes, tremor, silent transient slip, and steady sliding. Our results show that tremor occurs over a range of ductile and brittle frictional strengths, and advances our understanding of the physical conditions at which tremor and earthquakes take place. Copyright ?? 2011 by the American Geophysical Union.

  19. Ductile Faults Control Seismogenic Movement on Oceanic Transforms

    NASA Astrophysics Data System (ADS)

    Lister, G. S.; Tkalcic, H.; Forster, M. A.; McClusky, S.

    2014-12-01

    Structural Geology is about 3D geometry and the symphony of kinematically-coordinated movement. In this case we discuss patterns of violent relative displacement inferred from focal plane data for earthquakes. Systematic stereographic analysis of centroid moment tensor data often shows well-defined orientation groups in scatterplots of fault plane normals and associated slip line vectors. These allow important geodynamic inferences, e.g., we can show that ductile faults control the geometry of oceanic transforms, and that normal fault earthquakes on spreading ridges are usually skewed with respect to adjacent transform faults. To explain this asymmetry requires finite rock strength, but it also means that it is not brittle failure that controls the orientation of oceanic transforms. This asymmetry also requires formation of tilt block geometries reminiscent of Basin-and-Range-style continental extension, systematic offset of earthquake hypocentres from the spreading ridge, and a general complexity in magma-fault interactions that is far beyond what might be expected if ocean-floor spreading is the result of dilating tension-mode fractures in dyke swarms. The role of ductile faulting should be given special mention because mostly it is argued that brittle faults are responsible for earthquakes. Yet many other examples of ductile faults in operation can be inferred, e.g., ductile faults associated with slab drop-off, where slab boudinage leads to extensional ductile faults and seismic activity driven by the pulling away of a relict slab, e.g., beneath the Hindu Kush. Another example might be found by close examination of the tectonic significance of the lowermost of the double (or paired) seismic zones such as can be seen in cross-sections of the subducting slab beneath Japan. The lowermost of the paired seismic zones may mark the locus of aseismic ductile shears or detachments formed by slumping of gigantic sheets of rock attempting to slide down the face of

  20. Analysis of nucleation modelling in ductile cast iron

    NASA Astrophysics Data System (ADS)

    Moumeni, E.; Tutum, C. C.; Tiedje, N. S.; Hattel, J. H.

    2012-01-01

    Heterogeneous nucleation of nodular graphite at inclusions in ductile iron during eutectic solidification has been investigated. The experimental part of this work deals with casting of ductile iron samples with two different inoculants in four different thicknesses. Chemical analysis, metallographic investigation and thermal analysis of the specimens have been carried out. A numerical model has been implemented and the results (i.e. cooling curve, cooling rate, nodule count and solid fraction) have shown a good agreement with experimental studies; following this, inoculation parameters in the model have been studied and discussed.

  1. VIEW OF INTERIOR OF SOUTHERN DUCTILE CASTING COMPANY, CENTERVILLE FOUNDRY ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    VIEW OF INTERIOR OF SOUTHERN DUCTILE CASTING COMPANY, CENTERVILLE FOUNDRY SHOWING MOLD MAKING WITH PNEWMATIC JOLT SQUEEZE COPE AND DRAG MOLDING MACHINES THAT INDIVIDUALLY MADE EITHER A COPE OR DRAG AND A SMALL WHEELED MATCHPLATE JOLT-SQUEEZE MACHINE THAT COMPRESSED AN ENTIRE MOLD AT A SINGLE TIME USING A DOUBLE-SIDED PATTERN (MATCHPLATE). ALSO SHOWN ARE RAILED PALLET CAR CONVEYORS THAT CARRIED COMPLETED MOLDS FROM MOLDING MACHINES TO POURING AREAS WHERE WORKERS USED SMALL OVERHEAD CRANE TO LIFT JACKETS AND WEIGHTS ONTO THE MOLDS TO HOLD THEM TOGETHER WHILE POURING. - Southern Ductile Casting Company, Centerville Foundry, 101 Airport Road, Centreville, Bibb County, AL

  2. Defect assessment procedure based on ductile tearing process

    NASA Astrophysics Data System (ADS)

    Wei, Yang

    1987-11-01

    Strain hardening, crack growth resistance and nonuniform load distribution have significant effects on the ductile tearing process. A defect assessment procedure incorporating with the above features is proposed in the present paper, with the final appearance of “design curves” to facilitate engineering applications.

  3. How plasticizer makes a ductile polymer glass brittle?

    NASA Astrophysics Data System (ADS)

    Zhao, Yue; Li, Xiaoxiao; Wang, Shi-Qing

    During uniaxial extension, a polymer glass of high molecular weight is ductile at high temperatures (still below Tg) and turns brittle when the temperature is sufficiently lowered. Incorporation of small-molecular additives to polymer glasses can speed up segmental relaxation considerably. The effect of such plasticization should be to make the polymers more ductile. We examined the effect of blending a few weight percent of either triphenyl phosphate (TPP) or a mineral oil to a commercial-grade PS and PMMA. Our Instron tests show that the plasticized PS is less ductile. Specifically, at 70 oC, the original PS is ductile at an extensional rate of 0.02 s-1 whereas the PS with 4 wt. % TPP turns brittle. Mechanical spectroscopic measurements show that the alpha relaxation time is shortened by more than two orders of magnitude with 4 wt. % TPP. On the other hand, such anomalous behavior did not occur in PMMA. We need to go beyond the conventional description to rationalize these results This work is supported, in part, by a NSF Grant (DMR-EAGER-1444859).

  4. Wear Performance of Cu-Alloyed Austempered Ductile Iron

    NASA Astrophysics Data System (ADS)

    Batra, Uma; Batra, Nimish; Sharma, J. D.

    2013-04-01

    An investigation was carried out to examine the influence of structural and mechanical properties on wear behavior of austempered ductile iron (ADI). Ductile iron (DI) samples were austenitized at 900 °C for 60 min and subsequently austempered for 60 min at three temperatures: 270, 330, and 380 °C. Microstructures of the as-cast DI and ADIs were characterized using optical and scanning microscopy, respectively. The structural parameters, volume fraction of austenite, carbon content of austenite, and ferrite particle size were determined using x-ray diffraction technique. Mechanical properties including Vicker's hardness, 0.2% proof strength, ultimate tensile strength, ductility, and strain hardening coefficient were determined. Wear tests were carried out under dry sliding conditions using pin-on-disk machine with a linear speed of 2.4 m/s. Normal load and sliding distance were 45 N and 1.7 × 104 m, respectively. ADI developed at higher austempering temperature has large amounts of austenite, which contribute toward improvement in the wear resistance through stress-induced martensitic transformation, and strain hardening of austenite. Wear rate was found to depend on 0.2% proof strength, ductility, austenite content, and its carbon content. Study of worn surfaces and nature of wear debris revealed that the fine ausferrite structure in ADIs undergoes oxidational wear, but the coarse ausferrite structure undergoes adhesion, delamination, and mild abrasion too.

  5. IRON TEEMING FROM CUPOLA (UPPER RIGHT CORNER) DUCTILE IRON LADLE ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    IRON TEEMING FROM CUPOLA (UPPER RIGHT CORNER) DUCTILE IRON LADLE MOVING DOWN TRACK IN PREPARATION FOR DISTRIBUTION TO DE LAVAUD MACHINES. - United States Pipe & Foundry Company Plant, Melting & Treatment Areas, 2023 St. Louis Avenue at I-20/59, Bessemer, Jefferson County, AL

  6. IRON TEEMING FROM CUPOLA (UPPER RIGHT CORNER) DUCTILE IRON LADLE ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    IRON TEEMING FROM CUPOLA (UPPER RIGHT CORNER) DUCTILE IRON LADLE MOVING DOWN TRACK IN PREPARATION FOR DISTRIBUTION TO DE LAVAUD MACHINES, LADLE TRANSFER CRANE ON FAR LEFT. - United States Pipe & Foundry Company Plant, Melting & Treatment Areas, 2023 St. Louis Avenue at I-20/59, Bessemer, Jefferson County, AL

  7. Thermo-Mechanical Processing and Properties of a Ductile Iron

    SciTech Connect

    Syn, C.K.; Lesuer, R.R.; Sherby, O.D.

    1997-07-14

    Thermo-mechanical processing of ductile irons is a potential method for enhancing their mechanical properties. A ductile cast iron containing 3.6% C, 2.6% Si and 0.045% Mg was continuously hot-and-warm rolled or one-step press-forged from a temperature in the austenite range (900{degrees}C-1100{degrees}C) to a temperature below the A, temperature. Various amounts of reduction were used (from 60% to more than 90%) followed by a short heat ent at 600`C. The heat ent lead to a structure of fine graphite in a matrix of ferrite and carbides. The hot-and- warm worked materials developed a pearlitic microstructure while the press-forged material developed a spheroidite-like carbide microstructure in the matrix. Cementite-denuded ferrite zones were developed around graphite stringers in the hot-and-warm worked materials, but such zones were absent in the press-forged material. Tensile properties including tensile strength and total elongation were measured along the direction parallel and transverse to the rolling direction and along the direction transverse to the press-forging direction. The tensile ductility and strength both increased with a decrease in the amount of hot-and-warm working. The press- forged materials showed higher strength (645 MPa) than the hot-and-warrn worked materials (575 MPa) when compared at the same ductility level (22% elongation).

  8. Improving the low temperature ductility of NiAl

    NASA Technical Reports Server (NTRS)

    Guha, Sumit; Munroe, Paul R.; Baker, Ian

    1989-01-01

    As part of a study aimed at developing a ductile NiAl-based alloy, ingots of Ni-Fe-Al alloys were cast and hot extruded to rods. The purpose of the iron additions was two-fold viz; to produce a change in the slip vector from 001 to 111 line and, in one alloy, to add a L1(2)-structured ductile second phase. Extruded Ni-20Al-30Fe was two-phase, containing a pro-eutectic B2 phase in a fine lamellar structure of B2+L1(2) phases. Room temperature tensile testing of both single extruded and double extruded alloys resulted in 8-percent and 22-percent plastic elongation and yield stresses of 850 and 760 MPa, respectively. Fracture in both cases occurred by ductile tearing of the eutectic and transgranular cleavage of the proeutectic phase at 1350 MPa. The ductility in double extruded condition is higher than that reported earlier in rapidly solidified wires by Inoue et al. (1984). By comparison, extruded single-phase B2-structured Ni-30Al-20Fe exhibited a fracture strength of 780 MPa, no plasticity, and a mixture of intergranular fracture and transgranular cleavage. This is contrast to earlier work by Inoue et al. where a yield stress of 400 MPa, 5 percent plastic strain, and a mixture of dimple and intergranular fracture was reported.

  9. Ductile-regime turning of germanium and silicon

    NASA Technical Reports Server (NTRS)

    Blake, Peter N.; Scattergood, Ronald O.

    1989-01-01

    Single-point diamond turning of silicon and germanium was investigated in order to clarify the role of cutting depth in coaxing a ductile chip formation in normally brittle substances. Experiments based on the rapid withdrawal of the tool from the workpiece have shown that microfracture damage is a function of the effective depth of cut (as opposed to the nominal cutting depth). In essence, damage created by the leading edge of the tool is removed several revolutions later by lower sections of the tool edge, where the effective cutting depth is less. It appears that a truly ductile cutting response can be achieved only when the effective cutting depth, or critical chip thickness, is less than about 20 nm. Factors such as tool rake angle are significant in that they will affect the actual value of the critical chip thickness for transition from brittle to ductile response. It is concluded that the critical chip thickness is an excellent parameter for measuring the effects of machining conditions on the ductility of the cut and for designing tool-workpiece geometry in both turning and grinding.

  10. Impact of ductility on hydraulic fracturing in shales

    NASA Astrophysics Data System (ADS)

    Auton, Lucy; MacMinn, Chris

    2015-11-01

    Hydraulic fracturing is a method for extracting natural gas and oil from low-permeability rocks such as shale via the injection of fluid at high pressure. This creates fractures in the rock, providing hydraulic access deeper into the reservoir and enabling gas to be collected from a larger region of the rock. Fracture is the tensile failure of a brittle material upon reaching a threshold tensile stress, but some shales have a high clay content and may yield plastically before fracturing. Plastic deformation is the shear failure of a ductile material, during which stress relaxes through irreversible rearrangements of the particles of the material. Here, we investigate the impact of the ductility of shales on hydraulic fracturing. We consider a simple, axisymmetric model for radially outward fluid injection from a wellbore into a ductile porous rock. We solve the model semi-analytically at steady state, and numerically in general. We find that plastic deformation greatly reduces the maximum tensile stress, and that this maximum stress does not always occur at the wellbore. These results imply that hydraulic fracturing may fail in ductile rocks, or that the required injection rate for fracking may be much larger than the rate predicted from purely elastic models.

  11. Brittle-to-Ductile Transition in Metallic Glass Nanowires.

    PubMed

    Şopu, D; Foroughi, A; Stoica, M; Eckert, J

    2016-07-13

    When reducing the size of metallic glass samples down to the nanoscale regime, experimental studies on the plasticity under uniaxial tension show a wide range of failure modes ranging from brittle to ductile ones. Simulations on the deformation behavior of nanoscaled metallic glasses report an unusual extended strain softening and are not able to reproduce the brittle-like fracture deformation as found in experiments. Using large-scale molecular dynamics simulations we provide an atomistic understanding of the deformation mechanisms of metallic glass nanowires and differentiate the extrinsic size effects and aspect ratio contribution to plasticity. A model for predicting the critical nanowire aspect ratio for the ductile-to-brittle transition is developed. Furthermore, the structure of brittle nanowires can be tuned to a softer phase characterized by a defective short-range order and an excess free volume upon systematic structural rejuvenation, leading to enhanced tensile ductility. The presented results shed light on the fundamental deformation mechanisms of nanoscaled metallic glasses and demarcate ductile and catastrophic failure. PMID:27248329

  12. Ductility of a dental Ag-Pd-Cu-Au alloy.

    PubMed

    Syverud, M; Herø, H

    1984-02-01

    A silver-palladium type of dental alloy for fixed restorations has been investigated with regard to the ability of the material to be plastically deformed in uniaxial tensile testing after two different age-hardening treatments. A certain degree of ductility is required for the burnishing of the margins. Aged to peak hardness at 350 degrees C after solid-solution annealing at 900 degrees C, the material was found to be brittle owing to a reaction zone along the grain boundaries, promoting an intergranular fracture. When the age-hardening temperature was lowered to 275 degrees C, a less pronounced reaction zone along the grain boundaries could be observed. The accompanying mechanical properties after precipitation hardening at 275 degrees C are probably an acceptable compromise between mechanical strength and ductility. Small particles along grain boundaries and brittleness were also found after solid-solution annealing at 900 degrees C and quenching. It is suggested that the improved ductility after subsequent aging at 275 degrees C is due to a coarsening of these small particles. In the as-cast condition the alloy was softer and more ductile than in the age-hardened state. PMID:6585123

  13. Heat treatment procedure to increase ductility of degraded nickel alloy

    NASA Technical Reports Server (NTRS)

    Prager, M.

    1968-01-01

    Tests demonstrate the room temperature ductility of degraded Rene 41 can be increased to acceptable values by solution heat treatment at a temperature of 2050 degrees to 2150 degrees F /1 to 2 hours/ and cooling through a controlled temperature range followed by normal aging in air /16 hours at 1400 degrees F/.

  14. Displacement–length scaling of brittle faults in ductile shear

    PubMed Central

    Grasemann, Bernhard; Exner, Ulrike; Tschegg, Cornelius

    2011-01-01

    Within a low-grade ductile shear zone, we investigated exceptionally well exposed brittle faults, which accumulated antithetic slip and rotated into the shearing direction. The foliation planes of the mylonitic host rock intersect the faults approximately at their centre and exhibit ductile reverse drag. Three types of brittle faults can be distinguished: (i) Faults developing on pre-existing K-feldspar/mica veins that are oblique to the shear direction. These faults have triclinic flanking structures. (ii) Wing cracks opening as mode I fractures at the tips of the triclinic flanking structures, perpendicular to the shear direction. These cracks are reactivated as faults with antithetic shear, extend from the parent K-feldspar/mica veins and form a complex linked flanking structure system. (iii) Joints forming perpendicular to the shearing direction are deformed to form monoclinic flanking structures. Triclinic and monoclinic flanking structures record elliptical displacement–distance profiles with steep displacement gradients at the fault tips by ductile flow in the host rocks, resulting in reverse drag of the foliation planes. These structures record one of the greatest maximum displacement/length ratios reported from natural fault structures. These exceptionally high ratios can be explained by localized antithetic displacement along brittle slip surfaces, which did not propagate during their rotation during surrounding ductile flow. PMID:26806996

  15. DUCTILE URANIUM FUEL FOR NUCLEAR REACTORS AND METHOD OF MAKING

    DOEpatents

    Zegler, S.T.

    1963-11-01

    The fabrication process for a ductile nuclear fuel alloy consisting of uranium, fissium, and from 0.25 to 1.0 wt% of silicon or aluminum or from 0.25 to 2 wt% of titanium or yttrium is presented. (AEC)

  16. Micromechanics based simulation of ductile fracture in structural steels

    NASA Astrophysics Data System (ADS)

    Yellavajjala, Ravi Kiran

    The broader aim of this research is to develop fundamental understanding of ductile fracture process in structural steels, propose robust computational models to quantify the associated damage, and provide numerical tools to simplify the implementation of these computational models into general finite element framework. Mechanical testing on different geometries of test specimens made of ASTM A992 steels is conducted to experimentally characterize the ductile fracture at different stress states under monotonic and ultra-low cycle fatigue (ULCF) loading. Scanning electron microscopy studies of the fractured surfaces is conducted to decipher the underlying microscopic damage mechanisms that cause fracture in ASTM A992 steels. Detailed micromechanical analyses for monotonic and cyclic loading are conducted to understand the influence of stress triaxiality and Lode parameter on the void growth phase of ductile fracture. Based on monotonic analyses, an uncoupled micromechanical void growth model is proposed to predict ductile fracture. This model is then incorporated in to finite element program as a weakly coupled model to simulate the loss of load carrying capacity in the post microvoid coalescence regime for high triaxialities. Based on the cyclic analyses, an uncoupled micromechanics based cyclic void growth model is developed to predict the ULCF life of ASTM A992 steels subjected to high stress triaxialities. Furthermore, a computational fracture locus for ASTM A992 steels is developed and incorporated in to finite element program as an uncoupled ductile fracture model. This model can be used to predict the ductile fracture initiation under monotonic loading in a wide range of triaxiality and Lode parameters. Finally, a coupled microvoid elongation and dilation based continuum damage model is proposed, implemented, calibrated and validated. This model is capable of simulating the local softening caused by the various phases of ductile fracture process under

  17. Thermomechanical coupling and dynamic strain ageing in ductile fracture

    NASA Astrophysics Data System (ADS)

    Delafosse, David

    1995-01-01

    This work is concerned with plastic deformation at the tip of a ductile tearing crack during propagation. Two kinds of effects are investigated: the thermomechanical coupling at the tip of a mobile ductile crack, and the influence of Dynamic Strain Aging (DSA) on ductile fracture. Three alloys are studied: a nickel based superalloy (N18), a soft carbon steel, and an Al-Li light alloy (2091). The experimental study of the thermo mechanical coupling effects by means of infrared thermography stresses the importance of plastic dissipation in the energy balance of ductile fracture. Numerical simulations involving plastic deformation as the only dissipation mechanism account for the main part of the measured heating. The effects of DSA on ductile tearing are investigated in the 2091 Al-Li alloy. Based on the strain rate/temperature dependence predicted by the standard model of DSA, an experimental procedure is set up for this purpose. Three main effects are evidenced. A maximum in tearing resistance is shown to be associated with the minimum of strain rate sensitivity. Through a simple model, this peak in tearing resistance is attributed to an increase in plastic dissipation as the strain rate sensitivity is decreased. Heterogenous plastic deformation is observed in the crack tip plastic zone. Comparison with uniaxial testing allows us to identify the observed strain heterogeneities as Portevin-Le Chatelier instabilities in the crack tip plastic zone. We perform a simplified numerical analysis of the effect of strain localization on crack tip screening. Finally, small crack propagation instabilities appear at temperatures slightly above that of the tearing resistance peak. These are interpreted as resulting from a positive feed-back between the local heating at the tip of a moving crack and the decrease in tearing resistance with increasing temperature.

  18. 49 CFR 192.489 - Remedial measures: Cast iron and ductile iron pipelines.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 49 Transportation 3 2011-10-01 2011-10-01 false Remedial measures: Cast iron and ductile iron... for Corrosion Control § 192.489 Remedial measures: Cast iron and ductile iron pipelines. (a) General graphitization. Each segment of cast iron or ductile iron pipe on which general graphitization is found to...

  19. 49 CFR 192.489 - Remedial measures: Cast iron and ductile iron pipelines.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 49 Transportation 3 2010-10-01 2010-10-01 false Remedial measures: Cast iron and ductile iron... for Corrosion Control § 192.489 Remedial measures: Cast iron and ductile iron pipelines. (a) General graphitization. Each segment of cast iron or ductile iron pipe on which general graphitization is found to...

  20. 49 CFR 192.489 - Remedial measures: Cast iron and ductile iron pipelines.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 49 Transportation 3 2012-10-01 2012-10-01 false Remedial measures: Cast iron and ductile iron... for Corrosion Control § 192.489 Remedial measures: Cast iron and ductile iron pipelines. (a) General graphitization. Each segment of cast iron or ductile iron pipe on which general graphitization is found to...

  1. 49 CFR 192.489 - Remedial measures: Cast iron and ductile iron pipelines.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 49 Transportation 3 2014-10-01 2014-10-01 false Remedial measures: Cast iron and ductile iron... for Corrosion Control § 192.489 Remedial measures: Cast iron and ductile iron pipelines. (a) General graphitization. Each segment of cast iron or ductile iron pipe on which general graphitization is found to...

  2. 49 CFR 192.489 - Remedial measures: Cast iron and ductile iron pipelines.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 49 Transportation 3 2013-10-01 2013-10-01 false Remedial measures: Cast iron and ductile iron... for Corrosion Control § 192.489 Remedial measures: Cast iron and ductile iron pipelines. (a) General graphitization. Each segment of cast iron or ductile iron pipe on which general graphitization is found to...

  3. Ductile-brittle-ductile transition and grain boundary segregation of Mn and Ni in an Fe-6Mn-12Ni alloy

    SciTech Connect

    Heo, N.H.

    1996-05-15

    Recently, Heo and Lee reported a ductile-brittle-ductile (DBD) transition in an Fe-8Mn-7Ni ternary alloy, which was caused by manganese segregation to the grain boundaries and its desegregation into the matrix. More recently Heo theoretically analyzed the nonequilibrium segregation behaviors of the elements in the Fe-8Mn-7Ni alloy. The aim of the present study is to investigate whether other Fe-6Mn-12Ni ternary alloy also shows the ductile-brittle-ductile transition, and is additionally to ascertain whether calculated results are consistent with experimental data. The study encompasses experimental procedures and a modeling based on the previous research. A general discussion will show that such an approach allows a comprehensive understanding of the ductile-brittle-ductile transition in the Fe-Mn-Ni ternary alloys.

  4. Simulations of ductile flow in brittle material processing

    SciTech Connect

    Luh, M.H.; Strenkowski, J.S.

    1988-12-01

    Research is continuing on the effects of thermal properties of the cutting tool and workpiece on the overall temperature distribution. Using an Eulerian finite element model, diamond and steel tools cutting aluminum have been simulated at various, speeds, and depths of cut. The relative magnitude of the thermal conductivity of the tool and the workpiece is believed to be a primary factor in the resulting temperature distribution in the workpiece. This effect is demonstrated in the change of maximum surface temperatures for diamond on aluminum vs. steel on aluminum. As a preliminary step toward the study of ductile flow in brittle materials, the relative thermal conductivities of diamond on polycarbonate is simulated. In this case, the maximum temperature shifts from the rake face of the tool to the surface of the machined workpiece, thus promoting ductile flow in the workpiece surface.

  5. Prediction of Microstructure in High-Strength Ductile Forging Parts

    SciTech Connect

    Urban, M.; Back, A.; Hirt, G.; Keul, C.; Bleck, W.

    2010-06-15

    Governmental, environmental and economic demands call for lighter, stiffer and at the same time cheaper products in the vehicle industry. Especially safety relevant parts have to be stiff and at the same time ductile. The strategy of this project was to improve the mechanical properties of forging steel alloys by employing a high-strength and ductile bainitic microstructure in the parts while maintaining cost effective process chains to reach these goals for high stressed forged parts. Therefore, a new steel alloy combined with an optimized process chain has been developed. To optimize the process chain with a minimum of expensive experiments, a numerical approach was developed to predict the microstructure of the steel alloy after the process chain based on FEM simulations of the forging and cooling combined with deformation-time-temperature-transformation-diagrams.

  6. Influence of microstructure on fracture toughness of austempered ductile iron

    SciTech Connect

    Rao, P.P.; Putatunda, S.K.

    1997-07-01

    An investigation was carried out to examine the influence of microstructure on the plane strain fracture toughness of austempered ductile iron. Austempered ductile iron (ADI) alloyed with nickel, copper, and molybdenum was austenitized and subsequently austempered over a range of temperatures to produce different microstructures. The microstructures were characterized through optical microscopy and X-ray diffraction. Plane strain fracture toughness of all these materials was determined and was correlated with the microstructure. The results of the present investigation indicate that the lower bainitic microstructure results in higher fracture toughness than upper bainitic microstructure. Both volume fraction of retained austenite and its carbon content influence the fracture toughness. The retained austenite content of 25 vol pct was found to provide the optimum fracture toughness. It was further concluded that the carbon content of the retained austenite should be as high as possible to improve fracture toughness.

  7. Microstructure of thin-wall ductile iron castings

    SciTech Connect

    Dogan, Omer N.; Schrems, Karol K.; Hawk, Jeffrey A.; Druschitz, A.P.

    2001-10-01

    The automotive industry is seeking to replace current car parts made of aluminum and iron castings with thin wall (down to 2 mm) iron castings to reduce the cost and weight of automobiles. The mechanical properties of thin wall ductile iron castings are affected strongly by the thickness of the castings. The thinner castings cool at a faster rate, and microstructural features that form during solidification, and subsequently, transform in the solid state, are strongly dependent on a geometrical parameter related to the ratio of surface area-to-volume of the casting. As this ratio becomes larger, castings cool faster. As a result, the nodule count on the observation plane of the specimens increases dramatically (>2000 nodules/mm2 in most specimens), i.e. as the thickness of castings decreases. Also, the matrix of the thin walled ductile iron castings becomes more ferritic as the ratio of surface area-to-volume decreases.

  8. Enhancement of Strength and Ductility in Bulk Nanocrystalline Metals

    SciTech Connect

    Nieh, T; Schuh, C A; Caturla, M J; Hodge, A M

    2004-02-17

    The purpose of this project is to develop a robust scientific and technological framework for the design of high-strength and -ductility nanocrystalline materials for applications of technical importance to the Laboratory. The project couples theory and experiments with an emphasis on materials of macroscopic dimensions (mm to cm) that are composed of nanoscale (<100 nm) grains. There are four major tasks: (1) synthesize nanocrystalline materials with grain size in the 5- to 100-nm range; (2) conduct experimental studies to probe mechanisms of mechanical deformation and failure; (3) use large-scale simulation modeling technologies to provide insight to deformation mechanisms that may not be observable experimentally; and (4) check the results obtained from modeling, comparing experimental observations with results obtained from atomistic and dislocation-based simulations. This project supports efforts within the Stockpile Stewardship Program (SSP) to understand and predict properties of metals such as strength and ductility.

  9. The effect of yield strength and ductility to fatigue damage

    NASA Technical Reports Server (NTRS)

    Yeh, H. Y.

    1973-01-01

    The cumulative damage of aluminium alloys with different yield strength and various ductility due to seismic loads was studied. The responses of an idealized beam with a centered mass at one end and fixed at the other end to El Centro's and Taft's earthquakes are computed by assuming that the alloys are perfectly elastoplastic materials and by using numerical technique. Consequently, the corresponding residual plastic strain can be obtained from the stress-strain relationship. The revised Palmgren-Miner cumulative damage theorem is utilized to calculate the fatigue damage. The numerical results show that in certain cases, the high ductility materials are more resistant to seismic loads than the high yield strength materials. The results also show that if a structure collapse during the earthquake, the collapse always occurs in the very early stage.

  10. A Study of Solder Alloy Ductility for Cryogenic Applications

    NASA Technical Reports Server (NTRS)

    Lupinacci, A.; Shapiro, A. A.; Suh, J-O.; Minor, A. M.

    2013-01-01

    For aerospace applications it is important to understand the mechanical performance of components at the extreme temperature conditions seen in service. For solder alloys used in microelectronics, cryogenic temperatures can prove problematic. At low temperatures Sn-based solders undergo a ductile to brittle transition that leads to brittle cracks, which can result in catastrophic failure of electronic components, assemblies and spacecraft payloads. As industrial processes begin to move away from Pb-Sn solder, it is even more critical to characterize the behavior of alternative Sn-based solders. Here we report on initial investigations using a modified Charpy test apparatus to characterize the ductile to brittle transformation temperature of nine different solder systems.

  11. Tensile Fracture of Ductile Materials. M.S. Thesis

    NASA Technical Reports Server (NTRS)

    Pai, D. M.

    1984-01-01

    For brittle materials, circular voids play an important role relative to fracture, intensifing both tensile and compressive stresses. A maximum intensified tensile stress failure criterion applies quite well to brittle materials. An attempt was made to explore the possibility of extending the approach to the tensile fracture of ductile materials. The three dimensional voids that exist in reality are modelled by circular holes in sheet metal. Mathematical relationships are sought between the shape and size of the hole, after the material is plastically deformed, and the amount of deformation induced. Then, the effect of hole shape, size and orientation on the mechanical properties is considered experimentally. The presence of the voids does not affect the ultimate tensile strength of the ductile materials because plastic flow wipes out the stress intensification caused by them. However, the shape and orientation of the defect is found to play an important role in affecting the strain at fracture.

  12. Ductile damage prediction in sheet and bulk metal forming

    NASA Astrophysics Data System (ADS)

    Badreddine, Houssem; Labergère, Carl; Saanouni, Khemais

    2016-04-01

    This paper is dedicated to the presentation of an advanced 3D numerical methodology for virtual sheet and/or bulk metal forming simulation to predict the anisotropic ductile defects occurrence. First, the detailed formulation of thermodynamically-consistent fully coupled and fully anisotropic constitutive equations is given. The proposed constitutive equations account for the main material nonlinearities as the anisotropic plastic flow, the mixed isotropic and kinematic hardening and the anisotropic ductile damage under large inelastic strains. Second, the related numerical aspects required to solve the initial and boundary value problem (IBVP) are very briefly presented in the framework of the 3D finite element method. The global resolution schemes as well as the local integration schemes of the fully coupled constitutive equations are briefly discussed. Finally, some typical examples of sheet and bulk metal forming processes are numerically simulated using the proposed numerical methodology.

  13. Flash Joule heating for ductilization of metallic glasses

    PubMed Central

    Okulov, I. V.; Soldatov, I. V.; Sarmanova, M. F.; Kaban, I.; Gemming, T.; Edström, K.; Eckert, J.

    2015-01-01

    Metallic glasses (MGs) inherit their amorphous structure from the liquid state, which predetermines their ability to withstand high loads approaching the theoretical limit. However, the absence of slip systems makes them very sensitive to the type of loading and extremely brittle in tension. The latter can be improved by precipitation of ductile crystals, which suppress a catastrophic propagation of shear bands in a glassy matrix. Here we report a novel approach to obtain MG-matrix composites with tensile ductility by flash Joule heating applied to Cu47.5Zr47.5Al5 (at.%) metallic glass. This homogeneous, volumetric and controllable rapid heat treatment allows achieving uniformly distributed metastable B2 CuZr crystals in the glassy matrix. It results in a significant tensile strain of 6.8±0.5%. Moreover, optimized adjustment of the heat-treatment conditions enables tuning of microstructure to achieve desired mechanical properties. PMID:26219864

  14. Ductile mode electrochemical oxidation assisted micromachining for glassy carbon

    NASA Astrophysics Data System (ADS)

    Nam, Eunseok; Lee, Chan-Young; Jun, Martin B. G.; Min, Byung-Kwon

    2015-04-01

    Recently, a new mechanical machining process using electrochemical oxidation was reported. Electrochemical oxidation assisted micromachining was applied to the machining of glassy carbon. The material removal process of the electrochemical oxidation assisted micromachining consists of repeated cycles of oxidation followed by removal of the oxide layer. In this paper, we experimentally investigate and compare the critical chip thickness for ductile mode cutting in mechanical machining and electrochemical oxidation assisted micromachining of glassy carbon. The theoretical critical chip thickness is calculated for mechanical machining of glassy carbon and experimentally verified. The effect of electrochemical oxidation on the critical chip thickness for ductile mode micromachining is also studied for glassy carbon. It is found that the critical chip thickness is increased for the electrochemical oxidation assisted micromachining.

  15. Microstructural evolution and ductile phase toughening in brazed joints

    NASA Astrophysics Data System (ADS)

    Philips, Noah Robinson

    In typical brazed joints, melting point depressants degrade the structural robustness by concentrating as brittle phases into continuous seams along the centerline. The objective of this dissertation is to sufficiently understand the mechanisms governing the microstructure of a typical braze that approaches for modifying the fabrication to eliminate brittleness can be identified and demonstrated. A characterization of a quaternary braze (Nicrobraze 31) used for stainless steel bonds, containing P and Si melting point depressants, reveals that the thermochemical interactions governing the microstructure include dissolution/reprecipitation, solid-state diffusion, and solidification. It is shown that the Si can be incorporated into a solid solution gamma-Ni(Fe, Si) phase that forms by reprecipitation. A fracture toughness test for intermediate toughness materials is developed to quantify the performance of brazed joints. The test configuration is a wedge driven DCB (Double Cantilever Beam), with design guided by analytical solutions for the energy release rate and compliance. The fracture resistance of a typical braze joint is found to be significantly greater than that for the intermetallic constituents. Approximately half of the toughening is attributed to plastic stretch of the ductile phase within the eutectic. The remainder is attributed to dissipation within a plastic zone that forms in the primary gamma-Ni(Fe, Si) regions. Heat treatments are presented that use ductile phase toughening to mitigate the effect of brittle intermetallics in a Ni-based braze alloy. The development of this beneficial microstructure is based on an understanding of the transient dissolution and isothermal solidification phenomena. By rapid cooling after a short brazing time, gamma-Ni(Fe, Si) is redistributed to the midline where it disrupts the intermetallics and forms a network of ductile ligaments upon fracture. Reinforcement by the modified ductile phase nearly doubles the toughness

  16. Numerical modelling of the solidification of ductile iron

    NASA Astrophysics Data System (ADS)

    Liu, J.; Elliott, R.

    1998-01-01

    Numerical calculations are presented describing the solidification of a ductile iron based on the Stefanescu macroscopic heat transfer-microscopic solidification kinetic model but using a different kinetic model than that used by Stefanescu. The results show that the kinetic model used influences the recalescence behaviour predicted by the modelling. Cooling curves calculated with the present model show reasonable agreement with experimentally measured cooling curves for four different cooling rates.

  17. Fluid-Assisted Shear Failure Within a Ductile Shear Zone

    NASA Astrophysics Data System (ADS)

    Kirkpatrick, J. D.; Compton, K.; Holk, G. J.

    2015-12-01

    Exhumed shear zones often contain folded and/or dynamically recrystallized structures such as veins and pseudotachylytes that record contemporaneous brittle and ductile deformation representing mixed bulk rheology. Here, we constrain the conditions that promote the transitions between ductile and brittle deformation by investigating quartz veins with shear offsets in the Saddlebag Lake shear zone in the central Sierra Nevada, California. Mesozoic metasedimentary rocks within the shear zone contain transposed bedding, strong cleavage, dextrally rotated porphyroclasts, and a steep mineral lineation, which together suggest an overall transpressive kinematic regime for the ductile deformation. Foliation sub-parallel veins are one subset of the veins in the shear zone. They have observed horizontal trace lengths of up to around 5 meters, though most are obscured by limited exposure, and displacements range from ~3-30 mm, with 1-5 mm of opening. Foliation sub-parallel veins are folded with the foliation and quartz microstructures and fluid inclusion thermobarometry measurements from vein samples indicate temperatures during vein formation by fracture were between 300-680°C. Quartz δ18O values (+5.9 to +16.5) suggest extended fluid-rock interaction that involved magmatic (δ18O ~ +8 to +10) and meteoric (δ18O down to -1) fluids. Foliation sub-parallel veins are most abundant in relatively massive, quartz-rich rocks where they are boudinaged, indicating they were rigid inclusions after formation. Based on the orientation and spatial distribution of the veins, we infer that they formed under high differential stress with pore pressures sufficiently high for the rocks to be critically stressed for shear failure along mechanically weak foliation planes. These observations suggest high pore pressures and mechanical heterogeneity at a variety of scales are necessary conditions for nucleation of shear fractures within ductile shear zones.

  18. Modeling the strength and ductility of magnesium alloys containing nanotwins

    SciTech Connect

    Gorti, Sarma B; Radhakrishnan, Balasubramaniam

    2013-01-01

    Magnesium alloys have been receiving much attention recently as potential lightweight alternatives to steel for automotive and other applications, but the poor formability of these alloys at low temperatures has limited their widespread adoption for automotive applications. Recent work with face centered cubic (FCC) materials has shown that introduction of twins at the nanometer scale in ultra-fine grained FCC polycrystals can provide significant increase in strength with a simultaneous improvement in ductility. This objective of this work is to explore the feasibility of extending this concept to hexagonal close packed (HCP) materials, with particular focus on using this approach to increase both strength and ductility of magnesium alloys. A crystal plasticity based finite element (CPFE) model is used to study the effect of varying the crystallographic texture and the spacing between the nanoscale twins on the strength and ductility of HCP polycrystals. Deformation of the material is assumed to occur by crystallographic slip, and in addition to the basal and prismatic slip systems, slip is also assumed to occur on the {1 0 -1 1} planes that are associated with compression twins in these materials. The slip system strength of the pyramidal systems containing the nanotwins is assumed to be much lower than the strength of the other systems, which is assumed to scale with the spacing between the nanotwins. The CPFE model is used to compute the stress-strain response for different microstrucrutral parameters, and a criterion based on a critical slip system shear strain and a critical hydrostatic stress is used to compute the limiting strength and ductility, with the ultimate goal of identifying the texture and nanotwin spacing that can lead to the optimum values for these parameters.

  19. Nano-modification to improve the ductility of cementitious composites

    SciTech Connect

    Yeşilmen, Seda; Al-Najjar, Yazin; Balav, Mohammad Hatam; Şahmaran, Mustafa; Yıldırım, Gürkan; Lachemi, Mohamed

    2015-10-15

    Effect of nano-sized mineral additions on ductility of engineered cementitious composites (ECC) containing high volumes of fly ash was investigated at different hydration degrees. Various properties of ECC mixtures with different mineral additions were compared in terms of microstructural properties of matrix, fiber-matrix interface, and fiber surface to assess improvements in ductility. Microstructural characterization was made by measuring pore size distributions through mercury intrusion porosimetry (MIP). Hydration characteristics were assessed using thermogravimetric analysis/differential thermal analysis (TGA/DTA), and fiber-matrix interface and fiber surface characteristics were assessed using scanning electron microscopy (SEM) through a period of 90 days. Moreover, compressive and flexural strength developments were monitored for the same period. Test results confirmed that mineral additions could significantly improve both flexural strength and ductility of ECC, especially at early ages. Cheaper Nano-CaCO{sub 3} was more effective compared to nano-silica. However, the crystal structure of CaCO{sub 3} played a very important role in the range of expected improvements.

  20. Nanodomained Nickel Unite Nanocrystal Strength with Coarse-Grain Ductility

    PubMed Central

    Wu, Xiaolei; Yuan, Fuping; Yang, Muxin; Jiang, Ping; Zhang, Chuanxin; Chen, Liu; Wei, Yueguang; Ma, Evan

    2015-01-01

    Conventional metals are routinely hardened by grain refinement or by cold working with the expense of their ductility. Recent nanostructuring strategies have attempted to evade this strength versus ductility trade-off, but the paradox persists. It has never been possible to combine the strength reachable in nanocrystalline metals with the large uniform tensile elongation characteristic of coarse-grained metals. Here a defect engineering strategy on the nanoscale is architected to approach this ultimate combination. For Nickel, spread-out nanoscale domains (average 7 nm in diameter) were produced during electrodeposition, occupying only ~2.4% of the total volume. Yet the resulting Ni achieves a yield strength approaching 1.3 GPa, on par with the strength for nanocrystalline Ni with uniform grains. Simultaneously, the material exhibits a uniform elongation as large as ~30%, at the same level of ductile face-centered-cubic metals. Electron microscopy observations and molecular dynamics simulations demonstrate that the nanoscale domains effectively block dislocations, akin to the role of precipitates for Orowan hardening. In the meantime, the abundant domain boundaries provide dislocation sources and trapping sites of running dislocations for dislocation multiplication, and the ample space in the grain interior allows dislocation storage; a pronounced strain-hardening rate is therefore sustained to enable large uniform elongation. PMID:26122728

  1. Constrained molecular dynamics for quantifying intrinsic ductility versus brittleness

    NASA Astrophysics Data System (ADS)

    Tanguy, D.

    2007-10-01

    Evaluating the critical load levels for intrinsic ductility and brittle propagation is a first, but necessary, step for modeling semibrittle crack propagation. In the most general case, the calculations have to be fully atomistic because the details of the crack tip structure cannot be captured by continuum mechanics. In this paper, we present a method to explore ductile and brittle configurations, within the same force field, giving a quantitative estimate of the proximity of a transition from intrinsic ductility to brittleness. The shear localization is characterized by a centrosymmetry criterion evaluated on each atom in the vicinity of the crack tip. This provides an efficient order parameter to track the nucleation and propagation of dislocations. We show that it can be used as a holonomic constraint within molecular dynamics simulations, giving a precise control over plasticity during crack propagation. The equations of motion are derived and applied to crack propagation in the [112¯] direction of an fcc crystal loaded in mode I along [111]. The critical loads for dislocation emission and for brittle propagation are computed. The key point is that the generalized forces of constraint are not dissipative. Therefore, they do not spoil the critical elastic energy release rates (the Griffith criterion is preserved). As an example of the possibilities of the method, the response of blunted tips is investigated for three configurations: a slab of vacancies, an elliptical hole, and a circular hole. Brittle propagation by an alternative mechanism to cleavage, called “vacancy injection,” is reported.

  2. The development and validation of a ductile fracture analysis model

    SciTech Connect

    Kanninen, M.F.; Morrow, T.B.; Grant, T.S.

    1994-05-01

    The ultimate objective of this research is a user-oriented methodology that can be used by gas transmission company engineers for assessing the risk of ductile fracture propagation in the full range of design and operating conditions anticipated for their gas transmission pipeline system. A thoroughly validated procedure is therefore required that encompasses the full range of pipe diameters, operating pressures, pipe steels and rich gas compositions (RGCs) used by North American gas transmission companies. The final result could be incorporated into a user friendly PC-based code that would allow engineering assessment of safety margins for pipeline design and operation to be determined. Towards this objective, this report describes two specific tasks that were undertaken to advance the model development. Parametric calculations of crack tip pressure vs. wave speed were completed that bound the full range of (RGCs) decompression. The results were used in parametric ductile fracture computations, conducted to proclude an interpolating formula for the computation of the upper bound crack driving force for RGCs, supplementing the formula developed previously for methane. The results of the research completed to date can be used for a new pipeline design; or to calculate the critical pressure for an existing pipeline above which any rupture could lead to long propagating fracture. For either application, the ductile fracture resistance of candidate or existing line pipe steel can be determined using the procedures given in App. B.

  3. Nanodomained Nickel Unite Nanocrystal Strength with Coarse-Grain Ductility

    NASA Astrophysics Data System (ADS)

    Wu, Xiaolei; Yuan, Fuping; Yang, Muxin; Jiang, Ping; Zhang, Chuanxin; Chen, Liu; Wei, Yueguang; Ma, Evan

    2015-06-01

    Conventional metals are routinely hardened by grain refinement or by cold working with the expense of their ductility. Recent nanostructuring strategies have attempted to evade this strength versus ductility trade-off, but the paradox persists. It has never been possible to combine the strength reachable in nanocrystalline metals with the large uniform tensile elongation characteristic of coarse-grained metals. Here a defect engineering strategy on the nanoscale is architected to approach this ultimate combination. For Nickel, spread-out nanoscale domains (average 7 nm in diameter) were produced during electrodeposition, occupying only ~2.4% of the total volume. Yet the resulting Ni achieves a yield strength approaching 1.3 GPa, on par with the strength for nanocrystalline Ni with uniform grains. Simultaneously, the material exhibits a uniform elongation as large as ~30%, at the same level of ductile face-centered-cubic metals. Electron microscopy observations and molecular dynamics simulations demonstrate that the nanoscale domains effectively block dislocations, akin to the role of precipitates for Orowan hardening. In the meantime, the abundant domain boundaries provide dislocation sources and trapping sites of running dislocations for dislocation multiplication, and the ample space in the grain interior allows dislocation storage; a pronounced strain-hardening rate is therefore sustained to enable large uniform elongation.

  4. Superior austempered ductile iron (ADI) properties achieved by prior hot isostatic pressing (HIP)

    SciTech Connect

    LaGoy, J.L.; Widmer, R.; Zick, D.H.

    1996-12-31

    Ductile iron obtained from different foundries and cast by dissimilar methods has been successfully hot isostatically pressed (HIPed) before austempering to achieve substantially higher ductilities, without significant detriment to other properties, than those reached by austempering along. HIP was attempted to solve different mechanical deficiencies in austempered ductile iron (ADI) such as the lack of ductility in higher strength grades, inconsistent mechanical properties, and service life limitations. A variety of HIP temperatures were analyzed from near the austenitizing region up to within 56 C (100 F) of the melting point of ductile iron. Microporosity was eliminated by HIP at all temperatures, and subsequent austempering revealed a uniform ADI microstructure. HIP proved successful with both unencapsulated castings and those enclosed within steel canisters. Additional benefits caused by HIP processing of ductile iron castings without the austempering treatment include a significant decrease in mechanical property data scatter, high hardness at reasonable ductility levels, and a substantially reduced scrap rate.

  5. Predictive Process Optimization for Fracture Ductility in Automotive TRIP Steels

    NASA Astrophysics Data System (ADS)

    Gong, Jiadong

    In light of the emerging challenges in the automotive industry of meeting new energy-saving and environment-friendly requirements imposed by both the government and the society, the auto makers have been working relentlessly to reduce the weight of automobiles. While steel makers pushed out a variety of novel Advanced High Strength Steels (AHSS) to serve this market with new needs, TRIP (Transformation Induced Plasticity) steels is one of the most promising materials for auto-body due to its exceptional combination of strength and formability. However, current commercial automotive TRIP steels demonstrate relatively low hole-expansion (HE) capability, which is critical in stretch forming of various auto parts. This shortcoming on ductility has been causing fracture issues in the forming process and limits the wider applications of this steel. The kinetic theory of martensitic transformations and associated transformation plasticity is applied to the optimization of transformation stability for enhanced mechanical properties in a class of high strength galvannealed TRIP steel. This research leverages newly developed characterization and simulation capabilities, supporting computational design of high-performance steels exploiting optimized transformation plasticity for desired mechanical behaviors, especially for the hole-expansion ductility. The microstructure of the automotive TRIP sheet steels was investigated, using advanced tomographic characterization including nanoscale Local Electrode Atom Probe (LEAP) microanalysis. The microstructural basis of austenite stability, the austenite carbon concentration in particular, was quantified and correlated with measured fracture ductility through transformation plasticity constitutive laws. Plastic flow stability for enhanced local fracture ductility at high strength is sought to maintain high hole-expansion ductility, through quantifying the optimal stability and the heat-treatment process to achieve it. An additional

  6. 49 CFR 192.487 - Remedial measures: Distribution lines other than cast iron or ductile iron lines.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... cast iron or ductile iron lines. 192.487 Section 192.487 Transportation Other Regulations Relating to... iron or ductile iron lines. (a) General corrosion. Except for cast iron or ductile iron pipe, each... the purpose of this paragraph. (b) Localized corrosion pitting. Except for cast iron or ductile...

  7. 49 CFR 192.487 - Remedial measures: Distribution lines other than cast iron or ductile iron lines.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... cast iron or ductile iron lines. 192.487 Section 192.487 Transportation Other Regulations Relating to... iron or ductile iron lines. (a) General corrosion. Except for cast iron or ductile iron pipe, each... the purpose of this paragraph. (b) Localized corrosion pitting. Except for cast iron or ductile...

  8. 49 CFR 192.487 - Remedial measures: Distribution lines other than cast iron or ductile iron lines.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... cast iron or ductile iron lines. 192.487 Section 192.487 Transportation Other Regulations Relating to... iron or ductile iron lines. (a) General corrosion. Except for cast iron or ductile iron pipe, each... the purpose of this paragraph. (b) Localized corrosion pitting. Except for cast iron or ductile...

  9. 49 CFR 192.487 - Remedial measures: Distribution lines other than cast iron or ductile iron lines.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... cast iron or ductile iron lines. 192.487 Section 192.487 Transportation Other Regulations Relating to... iron or ductile iron lines. (a) General corrosion. Except for cast iron or ductile iron pipe, each... the purpose of this paragraph. (b) Localized corrosion pitting. Except for cast iron or ductile...

  10. 49 CFR 192.487 - Remedial measures: Distribution lines other than cast iron or ductile iron lines.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... cast iron or ductile iron lines. 192.487 Section 192.487 Transportation Other Regulations Relating to... iron or ductile iron lines. (a) General corrosion. Except for cast iron or ductile iron pipe, each... the purpose of this paragraph. (b) Localized corrosion pitting. Except for cast iron or ductile...

  11. Validity assessment of ductile fracture criteria in cold forming

    SciTech Connect

    Shabara, M.A.; El-Domiaty, A.A.; Kandil, A.

    1996-08-01

    This paper describes the assessment of various empirical and semiempirical ductile fracture criteria to determine their ability to predict the occurrence of fracture in metalforming processes. The criteria assessed are reformulated such that each is expressed in terms of mostly nondimensional material-dependent quantities and constants. The constants in each criterion are determined using data from published experimental results on cold upsetting of aluminum and steel specimens. The limit strain or the forming limit corresponding to each criterion is then determined and compared with the experimental data. There is clearly good agreement between theory and experiment for several criteria, but the predictions of other criteria fall far from experimental results.

  12. Ductile damage modeling based on void coalescence and percolation theories

    SciTech Connect

    Tonks, D.L.; Zurek, A.K.; Thissell, W.R.

    1995-09-01

    A general model for ductile damage in metals is presented. It includes damage induced by shear stress as well as damage caused by volumetric tension. Spallation is included as a special case. Strain induced damage is also treated. Void nucleation and growth are included, and give rise to strain rate effects. Strain rate effects also arise in the model through elastic release wave propagation between damage centers. The underlying physics of the model is the nucleation, growth, and coalescence of voids in a plastically flowing solid. The model is intended for hydrocode based computer simulation. An experimental program is underway to validate the model.

  13. Microstructure and fracture of alloyed austempered ductile iron

    SciTech Connect

    Eric, Olivera; Rajnovic, Dragan; Zec, Slavica; Sidjanin, Leposava; Jovanovic, Milan T. . E-mail: tmsj@ptt.yu

    2006-12-15

    An investigation has been conducted on two austempered ductile irons alloyed with Cu and Cu + Ni, austenitized at 900 deg. C and austempered at 350 deg. C. The microstructure and fracture mode developed through these treatments have been identified by means of light and scanning electron microscopy and X-ray diffraction analysis. Impact energy measurements were performed on un-notched Charpy specimens. The maximum value of retained austenite volume fraction observed in the material alloyed with Cu + Ni was higher than in that alloyed with Cu austenitized and austempered under the same conditions. This led to the material alloyed with Cu + Ni having higher impact energy and substantial plastic deformation.

  14. A model for the graphite formation in ductile

    NASA Astrophysics Data System (ADS)

    Skaland, T.; Grong, Ø.; Grong, T.

    1993-10-01

    In the present investigation, mathematical models have been developed to quantify the extent of carbon diffusion occurring in ductile cast iron during cooling from the eutectic temperature. Computer calculations show that small variations in the cooling conditions may significantly alter the number density and size distribution of graphite nodules in the iron matrix, in agreement with experimental observations. This makes it difficult to compare microstructure data from various section size materials without allowing for differences in the kinetic strength of the thermal cycles with respect to carbon diffusion.

  15. Modeling ductile dynamic fracture with ABAQUS/explicit

    SciTech Connect

    Anderson, C.A.; Turner, C.

    1996-05-01

    This paper illustrates the use of advanced constitutive models in ABAQUS/Explicit together with highly focused finite element meshes to simulate the propagation of a fracture in a ductile medium. A double edge-cracked specimen under far field dynamic tensile loading is analyzed, and shows both rectilinear motion or unstable oscillatory motion of the crack depending on the material property constraints. Results are also presented for a simulation of ASTM`s standard fracture test E399. Comparisons of ABAQUS/Explicit results with experiments or other analytical/numerical results are made.

  16. Using ductile iron pipe for penstocks: A new option

    SciTech Connect

    Hurless, R.C.

    1996-04-01

    When choosing the type of material for the penstock at a new project or when repairing or replacing pipe at existing plants, it may pay off to take a look at ductile iron pipe. This type of pipe was used at the Wailuku River hydro project, resulting in a more corrosion resistant, durable, and cost-effective penstock. This article reviews the planning and decision-making that went into this effort, including: (1) material properties, (2) testing, (3) performance under negative pressure conditions, (4) pressure rating, (5) corrosion resistance, (6) seismic effects, (7) installation problems, and (8) economic considerations.

  17. Design of ductile bulk metallic glasses by adding ''soft'' atoms

    SciTech Connect

    Zheng, N.; Pauly, S.; Calin, M.; Gemming, T.; Qu, R. T.; Zhang, Z. F.; Eckert, J.

    2012-04-02

    We propose a strategy for the design of ductile bulk metallic glasses (BMGs) through minor substitution using relatively large atoms, which make the bonding nature become more metallic and with it less shear resistant. Such a locally modified structure results in topological heterogeneity, which appears to be crucial for achieving enhanced plasticity. This strategy is verified for Ti-Zr-Cu-Pd glassy alloys, in which Cu was replaced by In, and seems to be extendable to other BMG systems. The atomic-scale heterogeneity in BMGs is somewhat analog to defects in crystalline alloys and helps to improve the overall plasticity of BMGs.

  18. On Key Factors Influencing Ductile Fractures of Dual Phase (DP) Steels

    SciTech Connect

    Sun, Xin; Choi, Kyoo Sil; Soulami, Ayoub; Liu, Wenning N.; Khaleel, Mohammad A.

    2009-11-25

    In this paper, we examine the key factors influencing ductile failure of various grades of dual phase (DP) steels using the microstructure-based modeling approach. Various microstructure-based finite element models are generated based on the actual microstructures of DP steels with different martensite volume fractions. These models are, then, used to investigate the influence of ductility of the constituent ferrite phase and also the influence of voids introduced in the ferrite phase on the overall ductility of DP steels. It is found that with volume fraction of martensite in the microstructure less than 15%, the overall ductility of the DP steels strongly depends on the ductility of the ferrite matrix, hence pre-existing micro voids in the microstructure significantly reduce the overall ductility of the steel. When the volume fraction of martensite is above 15%, the preexisting voids in the ferrite matrix does not significantly reduce the overall ductility of the DP steels, and the overall ductility is more influenced by the mechanical property disparity between the two phases. The applicability of the phase inhomogeneity driven ductile failure of DP steels is then discussed based on the obtained computational results for various grades of DP steels, and the experimentally obtained scanning electron microscopy (SEM) pictures of the corresponding grades of DP steels near fracture surface are used as evidence for result validations.

  19. Nitrogen Impurity Gettering in Oxide Dispersion Ductilized Chromium

    SciTech Connect

    Brady, Michael P; Anderson, Ian M; Weaver, Mark; Meyer III, Harry M; Walker, Larry R; Miller, Michael K; Larson, David James; Wright, Ian G; Sikka, Vinod K; Rar, Andrei; Pharr, George Mathews; Keiser, James R; Walls, Claudia Alexandra

    2003-01-01

    Work by Scruggs in the 1960s demonstrated that tensile ductility could be achieved at room temperature in powder metallurgically-produced Cr alloyed with MgO. During consolidation, much of the MgO converted to the MgCr{sub 2}O{sub 4} spinel phase, which was hypothesized to getter nitrogen from the Cr, rendering it ductile. We have duplicated this effect, achieving room temperature tensile elongations of 4% for hot-pressed Cr-6MgO-(0-1)Ti (wt.%) and 10% for hot-pressed and extruded Cr-6MgO-0.75Ti. Direct incorporation of nitrogen into the MgCr{sub 2}O{sub 4} phase was not detected; however, impurities, particularly nitrogen and sulfur, were observed to segregate to and/or precipitate at interfaces between the MgO/MgCr{sub 2}O{sub 4} phases and the Cr matrix. Exploratory studies of other non-spinel forming oxide dispersions (La{sub 2}O{sub 3}, TiO{sub 2} and Y{sub 2}O{sub 3}) showed a similar pattern of impurity segregation/precipitation, suggesting that there is nothing unique about spinel dispersions in Cr with regards to impurities. However, none of these other dispersions resulted in similar levels of tensile elongation.

  20. On probabilistic aspects in the dynamic degradation of ductile materials

    NASA Astrophysics Data System (ADS)

    Roy, Gilles; Trumel, Hervé; Hild, Francois; Pellegrini, Yves-Patrick; Denoual, Christophe

    2009-06-01

    Dynamic loadings produce high stress waves leading to the spallation of ductile materials such as aluminium, copper, magnesium or tantalum [1-3]. The main mechanism used to explain the change in the number of cavities with the stress rate is nucleation inhibition, induced by the growth of already nucleated cavities [4]. The dependence of the spall strength and critical time with the loading rate is investigated in the framework of a probabilistic model [4]. The present approach, which explains previous experimental findings on the strain rate dependence of the spall strength, is applied to analyze experimental data on tantalum [5]. [3pt] References: [1] Meyers M.A., Aimone C. T., 1983, ``Dynamic Fracture (Spalling) of Metals'', Prog. Mater. Sci., 18(1),pp. 1-96 [2] Curran D.R., Seaman L., Shockey D.A., 1987, ``Dynamic Fracture of Solids'', Phys. Rep., 147, pp. 253-388 [3] Grady D.E., 1988, ``The Spall Strength of Condensed Matter'', J. Mech. Phys. Sol., 36(3), pp. 353-384 [4] Trumel H., Hild F., Roy G., Pellegrini Y.-P., Denoual C., submitted to J. Mech. Phys. Sol., 2008. [5] Roy G., 2003, ``Vers une modelisation approfondie de l'endommagement dynamique ductile. Investigation experimentale d'une nuance de tantale et developpements theoriques'', Ph.D. Thesis, Poitiers University, France

  1. Microalloying ultrafine grained Al alloys with enhanced ductility.

    PubMed

    Jiang, L; Li, J K; Cheng, P M; Liu, G; Wang, R H; Chen, B A; Zhang, J Y; Sun, J; Yang, M X; Yang, G

    2014-01-01

    Bulk ultrafine grained (UFG)/nanocrystal metals possess exceptional strength but normally poor ductility and thermal stability, which hinder their practical applications especially in high-temperature environments. Through microalloying strategy that enables the control of grains and precipitations in nanostructured regime, here we design and successfully produce a highly microstructure-stable UFG Al-Cu-Sc alloy with ~275% increment in ductility and simultaneously ~50% enhancement in yield strength compared with its Sc-free counterpart. Although the precipitations in UFG alloys are usually preferentially occurred at grain boundaries even at room temperature, minor Sc addition into the UFG Al-Cu alloys is found to effectively stabilize the as-processed microstructure, strongly suppress the θ-Al2Cu phase precipitation at grain boundary, and remarkably promote the θ'-Al2Cu nanoparticles dispersed in the grain interior in artificial aging. A similar microalloying strategy is expected to be equally effective for other UFG heat-treatable alloys. PMID:24398915

  2. Microalloying Ultrafine Grained Al Alloys with Enhanced Ductility

    PubMed Central

    Jiang, L.; Li, J. K.; Cheng, P. M.; Liu, G.; Wang, R. H.; Chen, B. A.; Zhang, J. Y.; Sun, J.; Yang, M. X.; Yang, G.

    2014-01-01

    Bulk ultrafine grained (UFG)/nanocrystal metals possess exceptional strength but normally poor ductility and thermal stability, which hinder their practical applications especially in high-temperature environments. Through microalloying strategy that enables the control of grains and precipitations in nanostructured regime, here we design and successfully produce a highly microstructure-stable UFG Al-Cu-Sc alloy with ~275% increment in ductility and simultaneously ~50% enhancement in yield strength compared with its Sc-free counterpart. Although the precipitations in UFG alloys are usually preferentially occurred at grain boundaries even at room temperature, minor Sc addition into the UFG Al-Cu alloys is found to effectively stabilize the as-processed microstructure, strongly suppress the θ-Al2Cu phase precipitation at grain boundary, and remarkably promote the θ′-Al2Cu nanoparticles dispersed in the grain interior in artificial aging. A similar microalloying strategy is expected to be equally effective for other UFG heat-treatable alloys. PMID:24398915

  3. Ductile-Phase-Toughened Tungsten for Plasma-Facing Materials

    NASA Astrophysics Data System (ADS)

    Cunningham, Kevin Hawkins

    A variety of processing approaches were employed to fabricate ductile-phase-toughened (DPT) tungsten (W) composites. Mechanical testing and analytical modeling were used to guide composite development. This work provides a basis for further development of W composites to be used in structural divertor components of future fusion reactors. W wire was tested in tension, showing significant ductility and strength. Coatings of copper (Cu) or tungsten carbide (WC) were applied to the W wire via electrodeposition and carburization, respectively. Composites were fabricated using spark plasma sintering (SPS) to consolidate W powders together with each type of coated W wire. DPT behavior, e.g. crack arrest and crack bridging, was not observed in three-point bend testing of the sintered composites. A laminate was fabricated by hot pressing W and Cu foils together with W wires, and subsequently tested in tension. This laminate was bonded via hot pressing to thick W plate as a reinforcing layer, and the composite was tested in three-point bending. Crack arrest was observed along with some fiber pullout, but significant transverse cracking in the W plate confounded further fracture toughness analysis. The fracture toughness of thin W plate was measured in three-point bending. W plates were brazed with Cu foils to form a laminate. Crack arrest and crack bridging were observed in three-point bend tests of the laminate, and fracture resistance curves were successfully calculated for this DPT composite. An analytical model of crack bridging was developed using the basis described by Chao in previous work by the group. The model uses the specimen geometry, matrix properties, and the stress-displacement function of a ductile reinforcement ("bridging law") to calculate the fracture resistance curve (R-curve) and load-displacement curve (P-D curve) for any test specimen geometry. The code was also implemented to estimate the bridging law of an arbitrary composite using R-curve data

  4. Significance of grain sliding mechanisms for ductile deformation of rocks

    NASA Astrophysics Data System (ADS)

    Dimanov, A.; Bourcier, M.; Gaye, A.; Héripré, E.; Bornert, M.; Raphanel, J.; Ludwig, W.

    2013-12-01

    Ductile shear zones at depth present polyphase and heterogeneous rocks and multi-scale strain localization patterns. Most strain concentrates in ultramylonitic layers, which exhibit microstructural signatures of several concomitant deformation mechanisms. The latter are either active in volume (dislocation creep), or in the vicinity and along interfaces (grain sliding and solution mass transfer). Because their chronology of appearance and interactions are unclear, inference of the overall rheology seems illusory. We have therefore characterized over a decade the rheology of synthetic lower crustal materials with different compositions and fluid contents, and for various microstructures. Non-Newtonian flow clearly related to dominant dislocation creep. Conversely, Newtonian behavior involved grain sliding mechanisms, but crystal plasticity could be identified as well. In order to clarify the respective roles of these mechanisms we underwent a multi-scale investigation of the ductile deformation of rock analog synthetic halite with controlled microstructures. The mechanical tests were combined with in-situ optical microscopy, scanning electron microscopy and X ray computed tomography, allowing for digital image correlation (DIC) techniques and retrieval of full strain field. Crystal plasticity dominated, as evidenced by physical slip lines and DIC computed slip bands. Crystal orientation mapping allowed to identify strongly active easy glide {110} <110> systems. But, all other slip systems were observed as well, and especially near interfaces, where their activity is necessary to accommodate for the plastic strain incompatibilities between neighboring grains. We also evidenced grain boundary sliding (GBS), which clearly occurred as a secondary, but necessary, accommodation mechanism. The DIC technique allowed the quantification of the relative contribution of each mechanism. The amount of GBS clearly increased with decreasing grain size. Finite element (FE) modeling

  5. Tensile properties of austempered ductile iron under thermomechanical treatment

    SciTech Connect

    Achary, J.

    2000-02-01

    A new processing method was investigated for improving the strength and elongation of austempered ductile iron (ADI) by grain refinement of parent austenite using thermomechanical treatment. The material was deformed at the austenitization temperature by single and multipass rolling before the austempering treatment. The effects of the amount of deformation, austenitization temperature, austempering temperatures, reaustenitization, and secondary deformation on the tensile properties were studied. The properties obtained using the method were compared with those of the ASTM standards. The effect of deformation on the graphite shape was also studied. Tensile strength/yield strength/elongation values were found to increase with increasing austenite deformation up to 40% and then to start decreasing. Tensile strength/yield strength and elongation values of 1,700 MPa/1,300 MPa/5% and 1,350 MPa/920 MPa/15% can be achieved with this method in the ranges of variables studied.

  6. Ductile fracture of cylindrical vessels containing a large flaw

    NASA Technical Reports Server (NTRS)

    Erdogan, F.; Irwin, G. R.; Ratwani, M.

    1976-01-01

    The fracture process in pressurized cylindrical vessels containing a relatively large flaw is considered. The flaw is assumed to be a part-through or through meridional crack. The flaw geometry, the yield behavior of the material, and the internal pressure are assumed to be such that in the neighborhood of the flaw the cylinder wall undergoes large-scale plastic deformations. Thus, the problem falls outside the range of applicability of conventional brittle fracture theories. To study the problem, plasticity considerations are introduced into the shell theory through the assumptions of fully-yielded net ligaments using a plastic strip model. Then a ductile fracture criterion is developed which is based on the concept of net ligament plastic instability. A limited verification is attempted by comparing the theoretical predictions with some existing experimental results.

  7. Multi-scale simulation of ductile iron casting

    NASA Astrophysics Data System (ADS)

    Kubo, J.

    2015-06-01

    It has been well known that addition of rare earth elements was indispensable for production of ductile cast iron. The addition reduces solidification shrinkage. However there are still ambiguities in understanding the mechanism and predicting the casting defects. A possible explanation for the reduction of shrinkage is that the addition of rare earth promotes expansion of castings due to the graphite formation, which is related to cooling rate. In this study, the effect of rare earth addition was considered as a function of cooling rate and solidification shrinkage rate was determined by the macro-scale simulation. In the meso-scale and the micro-scale simulations, distribution of graphite nodules was compared with the experimental results. The multi-scale simulation result well reproduced the experimental results.

  8. Nondestructive characterization of ductile cast iron by magnetic adaptive testing

    NASA Astrophysics Data System (ADS)

    Vertesy, G.; Uchimoto, T.; Tomáš, I.; Takagi, T.

    2010-10-01

    This paper reports correlation of magnetic descriptors with Brinell hardness and conductivity of ductile cast iron, aiming to develop a novel nondestructive method by magnetic adaptive testing. Four series of cast iron staircase-shaped samples were investigated by this method, where different cooling rates of samples during casting resulted in different structures of each sample. The flat samples were magnetized by an attached yoke, and sensitive descriptors were obtained from a proper evaluation, based on the measurements of series of magnetic minor hysteresis loops, without magnetic saturation of the samples. Results of the nondestructive magnetic tests were compared with destructive mechanical measurements of Brinell hardness and conductivity and good correlation was found between them.

  9. A model for ductile metal friction at high velocities

    NASA Astrophysics Data System (ADS)

    Hammerberg, J. E.; Ravelo, R. J.; Germann, T. C.

    We describe a meso-macro scale model for the frictional force at ductile metal interfaces for high velocities and large compressions. The model incorporates the micro-mesoscopic growth and refinement of material microstructure in a highly strained region at the sliding interface and incorporates both rate dependent plasticity and thermal conduction. The model compares favorably with recent large scale (1.8 billion atom) simulations to 50 ns of 3-dimensional polycrystalline 13-50 nm grain size Al-Al interfaces at pressures of 15 GPa using the SPaSM NonEquilibrium Molecular Dynamics (NEMD) simulation code. This work was performed under the auspices of the U.S. Dept. of Energy under Contract DE-AC52-06NA25396. The support of the LANL ASC-PEM program is gratefully acknowledged.

  10. Numerical method for shear bands in ductile metal with inclusions

    SciTech Connect

    Plohr, Jee Yeon N; Plohr, Bradley J

    2010-01-01

    A numerical method for mesoscale simulation of high strain-rate loading of ductile metal containing inclusions is described. Because of small-scale inhomogeneities, such a composite material is prone to localized shear deformation (adiabatic shear bands). The modeling framework is the Generalized Method of Cells of Paley and Aboudi [Mech. Materials, vol. 14, pp. /27-139, 1992], which ensures that the micromechanical response of the material is reflected in the behavior of the composite at the mesoscale. To calculate the effective plastic strain rate when shear bands are present, the analytic and numerical analysis of shear bands by Glimm, Plohr, and Sharp [Mech. Materials, vol. 24, pp. 31-41, 1996] is adapted and extended.

  11. Development of New Cryocooler Regenerator Materials-Ductile Intermetallic Compounds

    SciTech Connect

    K.A. Gschneidner; A.O. Pecharsky; V.K. Pecharsky

    2004-09-30

    The volumetric heat capacities of a number of binary and ternary Er- and Tm-based intermetallic compounds, which exhibited substantial ductilities, were measured from {approx}3 to {approx}350 K. They have the RM stoichiometry (where R = Er or Tm, and M is a main group or transition metal) and crystallize in the CsCl-type structure. The heat capacities of the Tm-based compounds are in general larger than the corresponding Er-based materials. Many of them have heat capacities which are significantly larger than those of the low temperature (<15 K) prototype cryocooler regenerator materials HoCu{sub 2}, Er{sub 3}Ni and ErNi. Utilization of the new materials as regenerators in the various cryocoolers should improve the performance of these refrigeration units for cooling below 15 K.

  12. Ductile tungsten-nickel alloy and method for making same

    DOEpatents

    Snyder, Jr., William B.

    1976-01-01

    The present invention is directed to a ductile, high-density tungsten-nickel alloy which possesses a tensile strength in the range of 100,000 to 140,000 psi and a tensile elongation of 3.1 to 16.5 percent in 1 inch at 25.degree.C. This alloy is prepared by the steps of liquid phase sintering a mixture of tungsten-0.5 to 10.0 weight percent nickel, heat treating the alloy at a temperature above the ordering temperature of approximately 970.degree.C. to stabilize the matrix phase, and thereafter rapidly quenching the alloy in a suitable liquid to maintain the matrix phase in a metastable, face-centered cubic, solid- solution of tungsten in nickel.

  13. The Brittle-Ductile Transition - A Self-Consistent Approach.

    NASA Astrophysics Data System (ADS)

    Hobbs, B.; Regenauer-Lieb, K.; Ord, A.; Yuen, D. A.

    2006-12-01

    The brittle-ductile transition (BDT) in the Earth is commonly viewed as a switch between two different constitutive behaviors, plastic and viscous, and is represented in models by various formulations. We show that thermal-mechanical coupling leads to a self consistent view where the BDT emerges naturally within one constitutive framework once a critical temperature is attained. Viscous folding occurs above this temperature and brittle fracturing below. Seismic activity is maximised at the BDT. Orogenesis emerges as a thermal-mechanical decoupling near the BDT during flexing of the lithosphere with the development of "crocodile" -like structures, fold-nappe systems and far-travelled thrust sheets. For quartz- feldspar composite materials this transition lies in a critical range of 500 K to 580 K.

  14. Microstructure of thin-wall ductile iron castings

    SciTech Connect

    Dogan, Omer N.; Schrems, Karol K.; Hawk, Jeffrey A.

    2003-01-01

    Step plate castings with section thicknesses of 1.5 mm to 6 mm and individual (single) castings with section thicknesses of 2 mm to 6 mm were produced using a ductile iron chemistry. Microstructures of these thin wall ductal iron castings were characterized quantitatively using an image analyzer. Matrix structure (amount of pearlite, ferrite, and massive carbides) and graphite structure (volume fraction, nodule size, nodule content, and nodularity) were investigated as a function of section thickness. Pearlite content, nodule count, and nodularity increased with decreasing section thickness, whereas the nodule size decreased. Nodule content exceeded 2000 nodules per mm{sup 2} at the thinnest sections. Statistical analysis was performed to investigate the effect of casting parameters on the microstructure.

  15. Ductile-to-brittle transition in spallation of metallic glasses

    SciTech Connect

    Huang, X.; Ling, Z.; Dai, L. H.

    2014-10-14

    In this paper, the spallation behavior of a binary metallic glass Cu{sub 50}Zr{sub 50} is investigated with molecular dynamics simulations. With increasing the impact velocity, micro-voids induced by tensile pulses become smaller and more concentrated. The phenomenon suggests a ductile-to-brittle transition during the spallation process. Further investigation indicates that the transition is controlled by the interaction between void nucleation and growth, which can be regarded as a competition between tension transformation zones (TTZs) and shear transformation zones (STZs) at atomic scale. As impact velocities become higher, the stress amplitude and temperature rise in the spall region increase and micro-structures of the material become more unstable. Therefore, TTZs are prone to activation in metallic glasses, leading to a brittle behavior during the spallation process.

  16. Bending Fatigue Strength of Austempered Ductile Iron Spur Gears

    NASA Astrophysics Data System (ADS)

    Yamanaka, Masashi; Tamura, Ryo; Inoue, Katsumi; Narita, Yukihito

    This paper deals with an experimental evaluation of bending fatigue strength for austempered ductile iron (ADI) spur gears. The module is 2.5 and the number of teeth is 26 in the test gears. The material of the test gears corresponds to Japan Industrial Standard (JIS) FCAD1100-15. Some gears are processed by one of two types of fine particle bombarding (FPB). The surface roughness is slightly increased by FPB. The obtained strengths are 623 MPa for the as-austempered gears, and 1011 and 1085 MPa for the gears after FPB. The strength is expressed by the fillet stress level, which is calculated by FEM. The strength of a gear with the same dimensions made of carburized SCr420H alloy steel is 1205 MPa, and the strength of the ADI gear is approximately half that of the carburized steel gear. The FPB process has a significant effect on the ADI gear, improving its strength by 62-74%.

  17. Microstructural evolution in the HAZ of Inconel 718 and correlation with the hot ductility test

    NASA Technical Reports Server (NTRS)

    Thompson, R. G.; Genculu, S.

    1983-01-01

    The nickel-base alloy 718 was evaluated to study the role of preweld heat treatment in reducing or eliminating heat-affected zone hot cracking. Three heat treatments were studied using the Gleeble hot ductility test. A modified hot ductility test was also used to follow the evolution of microstructure during simulated welding thermal cycles. The microstructural evolution was correlated with the hot ductility data in order to evaluate the mechanism of hot cracking in alloy 718. The correlation of hot ductility with microstructure showed that recrystallization, grain growth, and dissolution of precipitates did not in themselves cause any loss of ductility during cooling. Ductility loss during cooling was not initiated until the constitutional liquation of NbC particles was observed in the microstructure. Laves-type phases were found precipitated in the solidified grain boundaries but were not found to correlate with any ductility loss parameter. Mechanisms are reviewed which help to explain how heat treatment controls the hot crack susceptibility of alloy 718 as measured in the hot ductility test.

  18. Ductile Binder Phase For Use With Almgb14 And Other Hard Ceramic Materials

    DOEpatents

    Cook, Bruce A.; Russell, Alan; Harringa, Joel

    2005-07-26

    This invention relates to a ductile binder phase for use with AlMgB14 and other hard materials. The ductile binder phase, a cobalt-manganese alloy, is used in appropriate quantities to tailor good hardness and reasonable fracture toughness for hard materials so they can be used suitably in industrial machining and grinding applications.

  19. Ductility Characterization of U-6Nb and Ta-W Alloys

    SciTech Connect

    Sun, T; Cervantes, O

    2006-09-15

    We have previously evaluated the ductility behaviors of U-6Nb and pure Ta. One important observation was that both alloys have very stable necking ductility independent of test conditions. In contrast, uniform ductility varied significantly depending upon strain rates and temperatures. In general, higher strain rate and lower temperature reduce the uniform ductility. Using literature data, we have developed two dynamic ductility models to predict the ductility behaviors of pure-Ta and water-quenched U-6Nb respectively under extreme conditions. In this study we further evaluate the aging effect on U-6Nb and the W-addition effect on Ta. For U-6Nb, the objective is to determine whether or not the ductility degradation by low-temperature aging mostly measured in quasi-static condition can still be observed under dynamic loading (high strain rate) condition. For Ta-W alloys, the focus is to identify the key control parameter so that the optimal condition of high-strength/high-ductility of Ta-10W can be achieved for certain defense-related applications.

  20. High post-irradiation ductility thermomechanical treatment for precipitation strengthened austenitic alloys

    DOEpatents

    Laidler, James J.; Borisch, Ronald R.; Korenko, Michael K.

    1982-01-01

    A method for improving the post-irradiation ductility is described which prises a solution heat treatment following which the materials are cold worked. They are included to demonstrate the beneficial effect of this treatment on the swelling resistance and the ductility of these austenitic precipitation hardenable alloys.

  1. Boudinage and folding as an energy instability in ductile deformation

    NASA Astrophysics Data System (ADS)

    Peters, Max; Herwegh, Marco; Paesold, Martin K.; Poulet, Thomas; Regenauer-Lieb, Klaus; Veveakis, Manolis

    2016-05-01

    We present a theory for the onset of localization in layered rate- and temperature-sensitive rocks, in which energy-related mechanical bifurcations lead to localized dissipation patterns in the transient deformation regime. The implementation of the coupled thermomechanical 2-D finite element model comprises an elastic and rate-dependent von Mises plastic rheology. The underlying system of equations is solved in a three-layer pure shear box, for constant velocity and isothermal boundary conditions. To examine the transition from stable to localized creep, we study how material instabilities are related to energy bifurcations, which arise independently of the sign of the stress conditions imposed on opposite boundaries, whether in compression or extension. The onset of localization is controlled by a critical amount of dissipation, termed Gruntfest number, when dissipative work by temperature-sensitive creep translated into heat overcomes the diffusive capacity of the layer. Through an additional mathematical bifurcation analysis using constant stress boundary conditions, we verify that boudinage and folding develop at the same critical Gruntfest number. Since the critical material parameters and boundary conditions for both structures to develop are found to coincide, the initiation of localized deformation in strong layered media within a weaker matrix can be captured by a unified theory for localization in ductile materials. In this energy framework, neither intrinsic nor extrinsic material weaknesses are required, because the nucleation process of strain localization arises out of steady state conditions. This finding allows us to describe boudinage and folding structures as the same energy attractor of ductile deformation.

  2. Development of ductile high-strength chromium alloys, phase 2

    NASA Technical Reports Server (NTRS)

    Filippi, A. M.

    1973-01-01

    Strength and ductility were evaluated for chromium alloys dispersion hardened with the putative TaC, TaB, CbC, and CbB compounds. TaC and TaB proved to be the most potent strengtheners, but when combined, their effect far outweighed that produced individually. Tests at 1422 K (2100 F) on an alloy containing these two compounds at the combined level of 0.5 m/o revealed a 495 MN/sq m (70 ksi) tensile strength for wrought material, and a 100 hour rupture strength of 208 MN/sq m (30 ksi) when solution annealed and aged to maximize creep resistance. These levels of high temperature strength greatly exceed that reported for any other chromium-base alloy. The ductile-to-brittle transition temperature (DBTT) of the two phase strengthened alloy occurred at approximately 588 K (600 F) when heat treated to optimize creep strength and was not improved by fabrication to produce a wrought and recovered microstructure. The lowest DBTT measured on any of the alloys investigated was 422 K (300 F). Strengthening phases actually formed in Cr-Ta-B and Cr-Cb-B compositions are probable M2CrB2 (M=Ta or Cb) compounds of tetragonal crystal structure. The likely habit relationship between these compounds and chromium is postulated. Cube habit coherency was identified for TaC precipitation in chromium by electron microscopy. In another study, the maximum solubility of carbon in chromium was indicated to lie between 3/4 and 1 a/o and that of boron to be 1/2 a/o.

  3. Highly ductile UV-shielding polymer composites with boron nitride nanospheres as fillers

    NASA Astrophysics Data System (ADS)

    Fu, Yuqiao; Huang, Yan; Meng, Wenjun; Wang, Zifeng; Bando, Yoshio; Golberg, Dmitri; Tang, Chengchun; Zhi, Chunyi

    2015-03-01

    Polymer composites with enhanced mechanical, thermal or optical performance usually suffer from poor ductility induced by confined mobility of polymer chains. Herein, highly ductile UV-shielding polymer composites are successfully fabricated. Boron nitride (BN) materials, with a wide band gap of around ∼6.0 eV, are used as fillers to achieve the remarkably improved UV-shielding performance of a polymer matrix. In addition, it is found that spherical morphology BN as a filler can keep the excellent ductility of the composites. For a comparison, it is demonstrated that traditional fillers, including conventional BN powders can achieve the similar UV-shielding performance but dramatically decrease the composite ductility. The mechanism behind this phenomenon is believed to be lubricant effects of BN nanospheres for sliding of polymer chains, which is in consistent with the thermal analyses. This study provides a new design to fabricate UV-shielding composite films with well-preserved ductility.

  4. Ductile-to-brittle transition of oxidised Zircaloy-4 and E110 claddings

    NASA Astrophysics Data System (ADS)

    Hózer, Zoltán; Győri, Csaba; Matus, Lajos; Horváth, Márta

    2008-02-01

    The ductile-to-brittle transition of the claddings of PWR and VVER nuclear fuel rods has been investigated in ring compression tests performed at room temperature with Zircaloy-4 and E110 samples oxidised in high temperature steam. These experiments were evaluated on the basis of the form of load-displacement curves. The ductile samples were characterised by a horizontal ductile plateau after the elastic deformation, while in the case of the brittle samples the ductile plateau was missing. The ductility limits of both alloys were expressed in terms of oxidation time and cladding temperature. From this, a numerical procedure was derived for the simulation of Zr cladding embrittlement during loss-of-coolant accidents. The results indicated a faster embrittlement of the E110 alloy than that of the Zircaloy-4 under identical conditions. The new approach is proposed as an alternative of the 17% ECR criterion to evaluate cladding embrittlement in design basis accident (DBA) scenarios.

  5. A new insight into ductile fracture of ultrafine-grained Al-Mg alloys

    PubMed Central

    Yu, Hailiang; Tieu, A. Kiet; Lu, Cheng; Liu, Xiong; Liu, Mao; Godbole, Ajit; Kong, Charlie; Qin, Qinghua

    2015-01-01

    It is well known that when coarse-grained metals undergo severe plastic deformation to be transformed into nano-grained metals, their ductility is reduced. However, there are no ductile fracture criteria developed based on grain refinement. In this paper, we propose a new relationship between ductile fracture and grain refinement during deformation, considering factors besides void nucleation and growth. Ultrafine-grained Al-Mg alloy sheets were fabricated using different rolling techniques at room and cryogenic temperatures. It is proposed for the first time that features of the microstructure near the fracture surface can be used to explain the ductile fracture post necking directly. We found that as grains are refined to a nano size which approaches the theoretical minimum achievable value, the material becomes brittle at the shear band zone. This may explain the tendency for ductile fracture in metals under plastic deformation. PMID:25851228

  6. Kinetic Ductility and Force-Spike Resistance of Proteins from Single-Molecule Force Spectroscopy.

    PubMed

    Cossio, Pilar; Hummer, Gerhard; Szabo, Attila

    2016-08-23

    Ductile materials can absorb spikes in mechanical force, whereas brittle ones fail catastrophically. Here we develop a theory to quantify the kinetic ductility of single molecules from force spectroscopy experiments, relating force-spike resistance to the differential responses of the intact protein and the unfolding transition state to an applied mechanical force. We introduce a class of unistable one-dimensional potential surfaces that encompass previous models as special cases and continuously cover the entire range from ductile to brittle. Compact analytic expressions for force-dependent rates and rupture-force distributions allow us to analyze force-clamp and force-ramp pulling experiments. We find that the force-transmitting protein domains of filamin and titin are kinetically ductile when pulled from their two termini, making them resistant to force spikes. For the mechanostable muscle protein titin, a highly ductile model reconciles data over 10 orders of magnitude in force loading rate from experiment and simulation. PMID:27558726

  7. Ductility demands on buckling-restrained braced frames under earthquake loading

    NASA Astrophysics Data System (ADS)

    Fahnestock, Larry A.; Sause, Richard; Ricles, James M.; Lu, Le-Wu

    2003-12-01

    Accurate estimates of ductility demands on buckling-restrained braced frames (BRBFs) are crucial to performance-based design of BRBFs. An analytical study on the seismic behavior of BRBFs has been conducted at the ATLSS Center, Lehigh University to prepare for an upcoming experimental program. The analysis program DRAIN-2DX was used to model a one-bay, four-story prototype BRBF including material and geometric nonlinearities. The buckling-restrained brace (BRB) model incorporates both isotropic and kinematic hardening. Nonlinear static pushover and time-history analyses were performed on the prototype BRBF. Performance objectives for the BRBs were defined and used to evaluate the time-history analysis results. Particular emphasis was placed on global ductility demands and ductility demands on the BRBs. These demands were compared with anticipated ductility capacities. The analysis results, along with results from similar previous studies, are used to evaluate the BRBF design provisions that have been recommended for codification in the United States. The results show that BRB maximum ductility demands can be as high as 20 to 25. These demands significantly exceed those anticipated by the BRBF recommended provisions. Results from the static pushover and time-history analyses are used to demonstrate why the ductility demands exceed those anticipated by the recommended provisions. The BRB qualification testing protocol contained in the BRBF recommended provisions is shown to be inadequate because it requires only a maximum ductility demand of at most 7.5. Modifications to the testing protocol are recommended.

  8. Ductile Deformation of Dehydrating Serpentinite Evidenced by Acoustic Signal Monitoring

    NASA Astrophysics Data System (ADS)

    Gasc, J.; Hilairet, N.; Wang, Y.; Schubnel, A. J.

    2012-12-01

    Serpentinite dehydration is believed to be responsible for triggering earthquakes at intermediate depths (i.e., 60-300 km) in subduction zones. Based on experimental results, some authors have proposed mechanisms that explain how brittle deformation can occur despite high pressure and temperature conditions [1]. However, reproducing microseismicity in the laboratory associated with the deformation of dehydrating serpentinite remains challenging. A recent study showed that, even for fast dehydration kinetics, ductile deformation could take place rather than brittle faulting in the sample [2]. This latter study was conducted in a multi-anvil apparatus without the ability to control differential stress during dehydration. We have since conducted controlled deformation experiments in the deformation-DIA (D-DIA) on natural serpentinite samples at sector 13 (GSECARS) of the APS. Monochromatic radiation was used with both a 2D MAR-CCD detector and a CCD camera to determine the stress and the strain of the sample during the deformation process [3]. In addition, an Acoustic Emission (AE) recording setup was used to monitor the microseismicity from the sample, using piezo-ceramic transducers glued on the basal truncation of the anvils. The use of six independent transducers allows locating the AEs and calculating the corresponding focal mechanisms. The samples were deformed at strain rates of 10-5-10-4 s-1 under confining pressures of 3-5 GPa. Dehydration was triggered during the deformation by heating the samples at rates ranging from 5 to 60 K/min. Before the onset of the dehydration, X-ray diffraction data showed that the serpentinite sustained ~1 GPa of stress which plummeted when dehydration occurred. Although AEs were recorded during the compression and decompression stages, no AEs ever accompanied this stress drop, suggesting ductile deformation of the samples. Hence, unlike many previous studies, no evidence for fluid embrittlement and anticrack generation was found

  9. Hot Ductility Behavior of Boron Containing Microalloyed Steels with Varying Manganese Contents

    NASA Astrophysics Data System (ADS)

    Brune, Tobias; Senk, Dieter; Walpot, Raphael; Steenken, Bernhard

    2015-02-01

    The hot ductility is measured for six different steel grades with different microalloying elements and with varying manganese contents using the hot tensile test machine with melting/solidification unit at the Department of Ferrous Metallurgy RWTH Aachen University. To identify the influence of manganese on hot ductility, tests are performed with varying the manganese content from 0.7 to 18.2 wt pct, a high manganese steel. Additionally, the effect of different cooling and strain rates is analyzed by changing the particular rate for selected samples in the minima. To investigate and detect the cause of cracking during testing, the fracture surfaces in the ductility minima are considered with scanning electron microscope-energy dispersive X-ray spectroscopy. Thermodynamic modeling is conducted on basis of the commercial software ThermoCalc©. A sharp decrease of the hot ductility is recognizable at 1398 K (1125 °C), at only 0.7 wt pct manganese because of the low manganese to sulfur ratio. The grades with a Mn content up to 1.9 wt pct show a good ductility with minimal ductility loss. In comparison, the steel grade with 18.2 wt pct has a poor hot ductility. Because of the formation of complex precipitates, where several alloying elements are involved, the influence of boron on hot ductility is not fully clarified. By increasing the cooling rate, the reduction of area values are shifted to smaller values. For high test temperatures, these measured values are decreased for lower strain rates. Thereby, an early drop of the ductility is noticeable for the high temperatures around 1373 K (1100 °C).

  10. Japan Beyond-Brittle Project (JBBP) for Development of EGS Reservoirs in Ductile Zones

    NASA Astrophysics Data System (ADS)

    Asanuma, H.; Muraoka, H.; Tsuchiya, N.; Ito, H.

    2012-12-01

    EGS (Enhanced Geothermal System) geothermal has been identified as a most promising method of geothermal development because of its potential applicability to a much wider range of sites, many of which have previously been considered to be unsuitable for geothermal development. Meanwhile, some critical problems with EGS technologies have been experimentally identified, such as low recovery of injected water, difficulties in establishing universal design/development methodologies, and the occurrence of induced seismicity, suggesting that there may be limitations in realizing EGS in earthquake-prone compression tectonic zones. We propose a new concept of engineered geothermal development where reservoirs are created in ductile basement. This potentially has a number of advantages including: (a) simpler design and control of the reservoir, (b) nearly full recovery of injected water, (c) sustainable production, (d) lower cost when developed in relatively shallower ductile zones in compression tectonic settings, (e) large potential quantities of energy extraction from widely distributed ductile zones, (f) the establishment of a universal design/development methodology, and (g) suppression of felt earthquakes from/around the reservoirs. To further assess the potential of EGS reservoir development in ductile zones we have initiated the "Japan Beyond-Brittle Project (JBBP)". It is intended that the first few years of the JBBP will be spent in basic scientific investigation and necessary technology development, including studies on rock mechanics in the brittle/ductile regime, characterization of ductile rock masses, development of modeling methodologies/technologies, and investigations of induced/triggered earthquakes. We expect to drill a deep experimental borehole that will penetrate the ductile zone in northeast Japan after basic studies are completed. The feasibility of EGS reservoir development in the ductile zone will then be assessed through observations and

  11. Quantification of damage evolution for a micromechanical model of ductile fracture in spallation of tantalum

    SciTech Connect

    Zurek, A.K.; Thissell, W.R.; Tonks, D.L.; Hixon, R.; Addessio, F.

    1997-05-01

    The authors present quantification of micromechanical features such as voids that comprise the ductile fracture obtained under uniaxial strain condition in a spall test of commercial purity tantalum. Two evolutionary parameters of ductile fracture void formation are quantified: (i) the void volume fraction (porosity) and its distribution with respect to the distance from the main spall fracture plane, and (ii) void diameter distribution. The results complement the discussion of the implications of void clustering and linking for micromechanical modeling of ductile fracture as presented in a paper by D. L. Tonks et al. in this volume.

  12. Tuning ideal tensile strengths and intrinsic ductility of bcc refractory alloys.

    PubMed

    Qi, Liang; Chrzan, D C

    2014-03-21

    An important theoretical ductility criterion for group V and VI metal-based refractory alloys in body-centered cubic (bcc) lattices is the mechanical failure mode of their perfect crystals under tension along the weakest direction [100]. Pure Mo and W fail by cleavage and are deemed intrinsically brittle. However, first-principles calculations show that alloying with group IV or V transition metals can transform these materials into ones that display intrinsically ductile behavior, failing in shear under [100] tension. Remarkably, this transition can be understood as an electron filling effect with the intrinsically ductile response the manifestation of a Jahn-Teller distortion. PMID:24702389

  13. Integrated modeling and heat treatment simulation of austempered ductile iron

    NASA Astrophysics Data System (ADS)

    Hepp, E.; Hurevich, V.; Schäfer, W.

    2012-07-01

    The integrated modeling and simulation of the casting and heat treatment processes for producing austempered ductile iron (ADI) castings is presented. The focus is on describing different models to simulate the austenitization, quenching and austempering steps during ADI heat treatment. The starting point for the heat treatment simulation is the simulated microstructure after solidification and cooling. The austenitization model considers the transformation of the initial ferrite-pearlite matrix into austenite as well as the dissolution of graphite in austenite to attain a uniform carbon distribution. The quenching model is based on measured CCT diagrams. Measurements have been carried out to obtain these diagrams for different alloys with varying Cu, Ni and Mo contents. The austempering model includes nucleation and growth kinetics of the ADI matrix. The model of ADI nucleation is based on experimental measurements made for varied Cu, Ni, Mo contents and austempering temperatures. The ADI kinetic model uses a diffusion controlled approach to model the growth. The models have been integrated in a tool for casting process simulation. Results are shown for the optimization of the heat treatment process of a planetary carrier casting.

  14. Wear behavior of bainite ductile cast iron under impact load

    NASA Astrophysics Data System (ADS)

    Sun, Ting; Song, Ren-bo; Yang, Fu-qiang; Wu, Chun-jing

    2014-09-01

    The dry impact wear behavior of bainite ductile cast iron was evaluated under three different impact loads for 30000 cycles. The strain-hardening effects beneath the contact surfaces were analyzed according to the surfaces' micro-hardness profiles. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to observe the worn surfaces. The results indicated that the material with the highest hardness was the one continuously cooled at 20°C, which exhibited the lowest wear rate under each set of test conditions. The hardness of the worn surface and the thickness of the hardened layer increased with the increases in impact load and in the number of test cycles. The better wear performance of the sample cooled at 20°C is attributed to its finer microstructure and superior mechanical properties. All the samples underwent the transformation induced plasticity (TRIP) phenomenon after impact wear, as revealed by the fact that small amounts of retained austenite were detected by XRD.

  15. An analysis of ductile rupture modes at a crack tip

    NASA Astrophysics Data System (ADS)

    Needleman, A.; Tvergaard, V.

    A N ELASTIC-VISCOPLASTIC model of a ductile, porous solid is used to study the influence of the nucleation and growth of micro-voids in the material near the tip of a crack. Conditions of small scale yielding are assumed, and the numerical analyses of the stress and strain fields are based on finite strain theory, so that crack tip blunting is fully accounted for. An array of large inclusions or inclusion colonies, with a relatively low strength, results in large voids near the crack tip at a rather early stage, whereas small second phase particles in the matrix material between the inclusions require large strains before cavities nucleate. Various distributions of the large inclusions, and various critical strains for nucleation of the small scale voids between the inclusions, are considered. Localization of plastic flow plays an important role in determining the failure path between the crack tip and the nearest larger void, and the path is strongly sensitive to the distribution of the large inclusions. Values of the J-integral and the crack opening displacement at fracture initiation are estimated, together with values of the tearing modulus during crack growth, and these values are related to experimental results.

  16. Neutron Diffraction Studies of Intercritically Austempered Ductile Irons

    SciTech Connect

    Druschitz, Alan; Aristizabal, Ricardo; Druschitz, Edward; Hubbard, Camden R; Watkins, Thomas R

    2011-01-01

    Neutron diffraction is a powerful tool that can be used to identify the phases present and to measure the spacing of the atomic planes in a material. Thus, the residual stresses can be determined within a component and/or the phases present. New intercritically austempered irons rely on the unique properties of the austenite phase present in their microstructures. If these materials are to see widespread use, methods to verify the quality (behavior consistency) of these materials and to provide guidance for further optimization will be needed. Neutron diffraction studies were performed at the second generation neutron residual stress facility (NRSF2) at the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory on a variety of intercritically austempered irons. For similar materials, such as TRIP steels, the strengthening mechanism involves the transformation of metastable austenite to martensite during deformation. For the intercritically austempered ductile irons two different deformation/strengthening mechanisms, phase transformation and slip, dependent upon the iron chemistry, were observed. Lattice strain and phase fraction data as a function of applied stress are presented.

  17. Thermoelastic-plastic flow and ductile fracture in solids

    SciTech Connect

    Tonks, D.L.

    1985-01-01

    The main aim of these lectures is to develop the theory of elastic-plastic flow in solids, with application to a particular class of processes, namely those in which the dissipation of plastic work cannot be neglected. Examples of such processes are highspeed impact phenomena and cratering, shock compression, often shock release as well, and explosive deformation and welding. An important part of the development is to include the anisotropic elastic properties of a solid, and for this reason the theory applies to solids in general. On the other hand, it is possible that some of the results will have limited validity for nonmetals. The secondary aim of the lectures is to develop a general framework for ductile fracture, and describe the current practice in the field. Our theory is incremental in nature and suitable for integrating along a process in small timesteps as is done in ''hydrodynamic'' computer programs. A notational conflict arose, because in continuum mechanics the extensive quantities are taken per unit mass, while in thermodynamics they are usually per unit volume. The continuum mechanics normalization, i.e., per unit mass, is used throughout, with the result that uncommon factors of density show up in the thermodynamic equations.

  18. Ultrahigh strength and ductility of metallic nanolayered composites

    SciTech Connect

    Mara, Nathan Allan; Bhattacharyya, Dhriti; Dickerson, Pat; Hoagland, Richard; Misra, Amit

    2009-01-01

    In recent years, the high strength of nanomaterials has gathered much interest in the materials community. Nanomaterials (polycrystalline and composites) have already been used, largely by the semiconductor community, as critical length scales for chip design have decreased to tens of nanometers. However, to ensure reliability of nanomaterials in almost any application, the mechanisms underlying their structural integrity must be well understood. For these materials to be put into service on a broader scale, not only should their strength be considered, but also ductility, toughness, formability, and fatigue resistance. While some progress has been made into constructing models for the deformation mechanisms governing these behaviors, the body of experimental knowledge is still limited, especially when length scales drop below 10 nanometers. This work produces stress-strain curves for nanolaminate composites with individual layer thickness of 40 nm and 5 run. Nanolaminate composites fabricated via magnetron sputtering comprised of alternating 5 nm thick Cu and Nb multilayers (two relatively soft metals) exhibit strengths on par with hardened tool steel and deformability in compression in excess of 25% [1]. The deformability of nanoscale composites is found to be limited by the onset of geometric instability, rather than due to intrinsic material behavior.

  19. Quantifying Damage Accumulation During Ductile Plastic Deformation Using Synchrotron Radiation

    SciTech Connect

    Suter, Robert M.; Rollett, Anthony D.

    2015-08-15

    Under this grant, we have developed and demonstrated the ability of near-field High Energy Diffraction Microscopy (nf-HEDM) to map crystal orientation fields over three dimensions in deformed polycrystalline materials. Experimental work was performed at the Advanced Photon Source (APS) at beamline 1-ID. Applications of this new capability to ductile deformation of copper and zirconium samples were demonstrated as was the comparison of the experimental observations to computational plasticity models using a fast Fourier transform based algorithm that is able to handle the large experimental data sets. No such spatially resolved, direct comparison between measured and computed microstructure evolutions had previously been possible. The impact of this work is reflected in numerous publications and presentations as well as in the investments by DOE and DOD laboratories of millions of dollars in applying the technique, developing sophisticated new hardware that allows the technique to be applied to a wide variety of materials and materials problems, and in the use of the technique by other researchers. In essence, the grant facilitated the development of a new form of three dimensional microscopy and its application to technologically critical states of polycrystalline materials that are used throughout the U.S. and world economies. On-going collaborative work is further optimizing experimental and computational facilities at the APS and is pursuing expanded facilities.

  20. Review on symmetric structures in ductile shear zones

    NASA Astrophysics Data System (ADS)

    Mukherjee, Soumyajit

    2016-07-01

    Symmetric structures in ductile shear zones range widely in shapes and geneses. Matrix rheology, its flow pattern, its competency contrast with the clast, degree of slip of the clast, shear intensity and its variation across shear zone and deformation temperature, and degree of confinement of clast in shear zones affects (independently) the degree of symmetry of objects. Kinematic vorticity number is one of the parameters that govern tail geometry across clasts. For example, symmetric and nearly straight tails develop if the clast-matrix system underwent dominantly a pure shear/compression. Prolonged deformation and concomitant recrystallization can significantly change the degree of symmetry of clasts. Angular relation between two shear zones or between a shear zone and anisotropy determines fundamentally the degree of symmetry of lozenges. Symmetry of boudinaged clasts too depends on competency contrast between the matrix and clast in some cases, and on the degrees of slip of inter-boudin surfaces and pure shear. Parasitic folds and post-tectonic veins are usually symmetric.

  1. Thermomechanical Fatigue of Ductile Cast Iron and Its Life Prediction

    NASA Astrophysics Data System (ADS)

    Wu, Xijia; Quan, Guangchun; MacNeil, Ryan; Zhang, Zhong; Liu, Xiaoyang; Sloss, Clayton

    2015-06-01

    Thermomechanical fatigue (TMF) behaviors of ductile cast iron (DCI) were investigated under out-of-phase (OP), in-phase (IP), and constrained strain-control conditions with temperature hold in various temperature ranges: 573 K to 1073 K, 723 K to 1073 K, and 433 K to 873 K (300 °C to 800 °C, 450 °C to 800 °C, and 160 °C to 600 °C). The integrated creep-fatigue theory (ICFT) model was incorporated into the finite element method to simulate the hysteresis behavior and predict the TMF life of DCI under those test conditions. With the consideration of four deformation/damage mechanisms: (i) plasticity-induced fatigue, (ii) intergranular embrittlement, (iii) creep, and (iv) oxidation, as revealed from the previous study on low cycle fatigue of the material, the model delineates the contributions of these physical mechanisms in the asymmetrical hysteresis behavior and the damage accumulation process leading to final TMF failure. This study shows that the ICFT model can simulate the stress-strain response and life of DCI under complex TMF loading profiles (OP and IP, and constrained with temperature hold).

  2. Ductility enhancement in NiAl (B2)-base alloys by microstructural control

    NASA Astrophysics Data System (ADS)

    Ishida, K.; Kainuma, R.; Ueno, N.; Nishizawa, T.

    1991-02-01

    An attempt to improve ductility of NiAl (B2)-base alloys has been made by the addition of alloying elements and the control of microstructure. It has been found that a small amount of fcc γ phase formed by the addition of Fe, Co, and Cr has a drastic effect not only on the hot workability but also on the tensile ductility at room temperature. The enhancement in ductility is mainly due to the modification of Β-phase grains by the coexistence of γ phase. The effect of alloying elements on the hot forming ability is strongly related to the phase equilibria and partition behavior among γ, γ' (L12 structure), and Β phases in the Ni-Al-X alloy systems. The ductility-enhancement method shows promise for expanding the practical application of nickel aluminide.

  3. Ordered iron aluminide alloys having an improved room-temperature ductility and method thereof

    SciTech Connect

    Sikka, V.K.

    1992-01-28

    This patent describes a method for improving the room temperature ductility and high temperature strength of iron aluminide intermetallic alloys. It comprises: thermomechanically working of the alloys ; heating the alloys; and rapidly cooling the alloys.

  4. Work-Hardening Induced Tensile Ductility of Bulk Metallic Glasses via High-Pressure Torsion

    NASA Astrophysics Data System (ADS)

    Joo, Soo-Hyun; Pi, Dong-Hai; Setyawan, Albertus Deny Heri; Kato, Hidemi; Janecek, Milos; Kim, Yong Chan; Lee, Sunghak; Kim, Hyoung Seop

    2015-04-01

    The mechanical properties of engineering materials are key for ensuring safety and reliability. However, the plastic deformation of BMGs is confined to narrow regions in shear bands, which usually result in limited ductilities and catastrophic failures at low homologous temperatures. The quasi-brittle failure and lack of tensile ductility undercut the potential applications of BMGs. In this report, we present clear tensile ductility in a Zr-based BMG via a high-pressure torsion (HPT) process. Enhanced tensile ductility and work-hardening behavior after the HPT process were investigated, focusing on the microstructure, particularly the changed free volume, which affects deformation mechanisms (i.e., initiation, propagation, and obstruction of shear bands). Our results provide insights into the basic functions of hydrostatic pressure and shear strain in the microstructure and mechanical properties of HPT-processed BMGs.

  5. Alternating brittle and ductile response of coherent twin boundaries in nanotwinned metals

    SciTech Connect

    Sinha, Tanushree; Kulkarni, Yashashree

    2014-11-14

    Nanotwinned metals have opened exciting avenues for the design of high strength and high ductility materials. In this work, we investigate crack propagation along coherent twin boundaries in nanotwinned metals using molecular dynamics. Our simulations reveal that alternating twin boundaries exhibit intrinsic brittleness and ductility owing to the opposite crystallographic orientations of the adjoining twins. This is a startling consequence of the directional anisotropy of an atomically sharp crack along a twin boundary that favors cleavage in one direction and dislocation emission from the crack tip in the opposite direction. We further find that a blunt crack exhibits ductility in all cases albeit with very distinct deformation mechanisms and yield strength associated with intrinsically brittle and ductile coherent twin boundaries.

  6. Ductile electroless Ni-P coating onto flexible printed circuit board

    NASA Astrophysics Data System (ADS)

    Wang, Wenchang; Zhang, Weiwei; Wang, Yurong; Mitsuzak, Naotoshi; Chen, Zhidong

    2016-03-01

    In this study, a ductile electroless Ni-P coating on the flexible printed circuit board (FPCB) was prepared in an acidic nickel plating bath. The addition of dipropylamine (DPA) in electroless plating not only improves the ductility of the Ni-P coating, but also enhances the corrosion resistance. The further analysis reveals that the ductility improvement and enhancement of corrosion resistance for the Ni-P coating may be due to the fact that the addition of DPA significantly refines the volume of columnar nodule and reduce the porosity, thus leading to the released internal stress. In addition, it was found that the nodule within the Ni-P coating grew into a columnar structure, which may be also contribute to the improvement of ductility.

  7. Grain-boundary contamination and ductility loss in boron-doped Ni3Al

    NASA Astrophysics Data System (ADS)

    Takeyama, M.; Liu, C. T.

    1989-10-01

    The effect of heat treatment on ductility loss in a boron-doped Ni3Al was studied by tensile tests of alloy specimens exposed to contaminated environments. Specimens heat-treated extensively in evacuated quartz capsules at 1323 K exhibit only 3.3 pct ductility at 1033 K, whereas a previous study reported a tensile ductility of about 24 pet for specimens heat-treated in a high vacuum system. Aluminum oxide and silicon-contaminated regions were observed at and near external surfaces of capsule-annealed specimens. The reactions occurring during heat treatment are interpreted in terms of thermodynamics. An Auger electron spectroscopy study revealed oxygen penetration along grain boundaries during capsule annealing. Although the surface oxide layer and silicon contamination both contribute to some reductions in ductility, the major cause for embrittlement comes from oxygen penetration along grain boundaries.

  8. Numerical simulations of interfacial debonding in ductile-phase reinforced intermetallic matrix composites

    SciTech Connect

    Henshall, G.A.; Zywicz, E.; Strum, M.J.

    1993-08-10

    The fracture toughness of brittle intermetallic compounds can be improved by ductile-phase reinforcements. Effectiveness of the ductile phase in bridging cracks, and therefore increasing, the composite toughness, is known qualitatively to depend upon the extent of debonding, between the two phases. Numerical crack-growth simulations are used here to provide semi-quantitative predictions of the influence of interfacial debonding on the macroscopic stress-displacement behavior and, hence, the fracture toughness of an idealized Pb/glass composite. The interfacial toughness required to cause debonding, characterized by a constant critical energy release rate, is varied parametrically. As expected, higher interfacial toughness results in less interphase debonding, higher composite strength, and greater ductile-phase constraint. Consequently, the increase in ductile-phase triaxiality can potentially accelerate internal void formation and growth or facilitate cleavage fracture, either of which would likely decrease the toughness of the composite.

  9. An investigation into the role of adhesion in the erosion of ductile metals

    NASA Technical Reports Server (NTRS)

    Brainard, W. A.; Salik, J.

    1980-01-01

    Existing theories of erosion of ductile metals based on cutting and deformation mechanisms predict no material removal at normal incidence which is contradictory to experience. Thus, other mechanisms may be involved. The possible role of adhesive material transfer during erosion is investigated by both single particle impingement experiments and erosion by streams of particles. Examination of the rebounding particles as well as the eroded surface yields evidence of a significant adhesive mechanism for the ductile metals investigated.

  10. An investigation into the role of adhesion in the erosion of ductile metals

    NASA Technical Reports Server (NTRS)

    Brainard, W. A.; Salik, J.

    1980-01-01

    Existing theories of erosion of ductile metals based on cutting and deformation mechanisms predict no material removal at normal incidence which is contradictory to experience. Thus, other mechanisms may be involved. The possible role of adhesive material transfer during erosion is investigated by both single-particle impingement experiments and erosion by streams of particles. Examination of the rebounding particles as well as the eroded surfaces yields evidence of a significant adhesive mechanism for the ductile metals investigated.

  11. Atomistic Simulation of Brittle to Ductile Transition in GaN Nanotubes

    SciTech Connect

    Wang, Zhiguo; Zu, Xiaotao; Gao, Fei; Weber, William J.

    2006-12-11

    Molecular dynamics methods with a Stillinger-Weber potential have been used to investigate the mechanical properties of wurtzite-type single crystalline GaN nanotubes under applied tensile stresses. At lower temperatures, the nanotubes show brittle properties; whereas at higher temperatures, they behave as ductile materials. The brittle to ductile transition (BDT) is systemically investigated, and the corresponding transition temperatures have been determined in GaN. The BDT temperature generally increases with increasing thickness of nanotubes and strain rate.

  12. Modeling Shear Instabilities With Block Sliders: Brittle and Ductile

    NASA Astrophysics Data System (ADS)

    Riedel, M. R.

    2003-12-01

    Block slider-type models have been succesfully used for almost 35 years to describe the spatio-temporal development of shear instabilities in the brittle crust (Burridge & Knopoff, 1967; Olami et al., 1992). More recently, increasing attention is paid on the extension of the classical Burridge-Knopoff model (based on a pure Mohr-Coulomb rheology) with a viscous component, either to include depth-dependent properties into the model or aiming at a more accurate description of fore- and aftershock sequences of a main earthquake event (e.g. Hainzl et al., 1999). On the other hand, viscous feedback mechanisms of various types have become an increasingly attractive mechanism for the generation of intermediate-depth and deep-focus earthquakes in the ductile mantle lithosphere (e.g. Wiens & Snider, 2001). Heat generated during viscous deformation provides a positive feedback to creep and eventually faulting under high pressure (Karato et al., 2001, Bercovici & Karato, 2003). The present paper discusses the specific properties of block slider-type models that are extended with a viscous component and compare their behaviour with the pure brittle ("classical") case. Block slider-type models for ductile instabilities are numerically much less demanding than solutions based on the corresponding, thermal-mechanically coupled, continuum equations. They allow for the inclusion of possible non-equilibrium effects associated with mineral phase transformations in a subducting slab (kinetic overshoot, grainsize reduction, latent heat release) in a straightforward manner. They may therefore serve as an effective tool to study the coupling of viscous heating, temperature-dependent viscosity and brittle stress transfer that are thought to cause the specific spatial-temporal clustering of intermediate-depth and deep-focus eartquakes. References D. Bercovici and S. Karato "Theoretical Analysis of Shear Localization in the Lithosphere", in: Reviews in Mineralogy and Geochemistry 51, eds. S

  13. A mechanism-based approach to modeling ductile fracture.

    SciTech Connect

    Bammann, Douglas J.; Hammi, Youssef; Antoun, Bonnie R.; Klein, Patrick A.; Foulk, James W., III; McFadden, Sam X.

    2004-01-01

    Ductile fracture in metals has been observed to result from the nucleation, growth, and coalescence of voids. The evolution of this damage is inherently history dependent, affected by how time-varying stresses drive the formation of defect structures in the material. At some critically damaged state, the softening response of the material leads to strain localization across a surface that, under continued loading, becomes the faces of a crack in the material. Modeling localization of strain requires introduction of a length scale to make the energy dissipated in the localized zone well-defined. In this work, a cohesive zone approach is used to describe the post-bifurcation evolution of material within the localized zone. The relations are developed within a thermodynamically consistent framework that incorporates temperature and rate-dependent evolution relationships motivated by dislocation mechanics. As such, we do not prescribe the evolution of tractions with opening displacements across the localized zone a priori. The evolution of tractions is itself an outcome of the solution of particular, initial boundary value problems. The stress and internal state of the material at the point of bifurcation provides the initial conditions for the subsequent evolution of the cohesive zone. The models we develop are motivated by in-situ scanning electron microscopy of three-point bending experiments using 6061-T6 aluminum and 304L stainless steel, The in situ observations of the initiation and evolution of fracture zones reveal the scale over which the failure mechanisms act. In addition, these observations are essential for motivating the micromechanically-based models of the decohesion process that incorporate the effects of loading mode mixity, temperature, and loading rate. The response of these new cohesive zone relations is demonstrated by modeling the three-point bending configuration used for the experiments. In addition, we survey other methods with the potential

  14. The effect of alloy elements on the microstructure and properties of austempered ductile irons

    SciTech Connect

    Lin, B.Y.; Chen, E.T.; Lei, T.S.

    1995-05-01

    Ductile cast iron has already demonstrated excellent mechanical properties. If given proper austempering, it can exhibit even more outstanding characteristics. The process of austempering for ductile cast iron is similar to steel, and requires an adequate completely, and then rapidly quenching the austenitizing temperature allowing the matrix of ductile iron to be austenitized completely, and then rapidly quenching the austenitized ductile iron down to 300 C--400 C. Caution is required to prevent austenite from transforming into proeutectoid ferrite or pearlite. Finally, the ductile iron must be kept in an isothermal condition for a proper length of time. Many kinds of experimental techniques such as quantitative metallography, magnetic change, dilatometry, X-ray diffraction, electrical resistivity change etc., may be used to measure the phase transformation during the austempering of ductile irons. However, the method of measuring the change of electrical resistivity, not only provides continuous and complete data, but also the time to start and to finish for both stages of the reaction can be significantly determined. In this paper, the effect of alloy elements on the microstructure and property of ADI was investigated. First, the specimens containing Mn, Cu, Ni and Mo were made separately, then a PC-controlled vacuum heat treating system was used for the heat treatments.

  15. Effects of Pore Distributions on Ductility of Thin-Walled High Pressure Die-Cast Magnesium

    SciTech Connect

    Choi, Kyoo Sil; Li, Dongsheng; Sun, Xin; Li, Mei; Allison, John

    2013-06-01

    In this paper, a microstructure-based three-dimensional (3D) finite element modeling method is adopted to investigate the effects of porosity in thin-walled high pressure die-cast (HPDC) Magnesium alloys on their ductility. For this purpose, the cross-sections of AM60 casting samples are first examined using optical microscope and X-ray tomography to obtain the general information on the pore distribution features. The experimentally observed pore distribution features are then used to generate a series of synthetic microstructure-based 3D finite element models with different pore volume fractions and pore distribution features. Shear and ductile damage models are adopted in the finite element analyses to induce the fracture by element removal, leading to the prediction of ductility. The results in this study show that the ductility monotonically decreases as the pore volume fraction increases and that the effect of ‘skin region’ on the ductility is noticeable under the condition of same local pore volume fraction in the center region of the sample and its existence can be beneficial for the improvement of ductility. The further synthetic microstructure-based 3D finite element analyses are planned to investigate the effects of pore size and pore size distribution.

  16. Pin-On-Disc Characterization of Brass/Ferritic and Pearlitic Ductile Iron Rubbing Pair

    NASA Astrophysics Data System (ADS)

    Çetin, Melik

    2011-04-01

    Wear behaviour of special brass produced through two different methods (centrifugal and sand casting) was investigated. The wear tests were carried out at sliding velocities of 0.2 ms-1, 0.3 ms-1, 0.4 ms-1 and 0.5 ms-1 and under 10 N, 20 N, and 40 N variable loads. The sliding distance was 600 m for all the tests. A pin-on-disc device with round specimen inserts was used to conduct friction and wear tests in which the friction coefficient, the contact temperature and the linear wear of the tribo-pairs were continuously recorded against sliding distance. Two different materials were used as the counterparts, namely ferritic ductile iron equivalent to GGG40 and pearlitic ductile iron equivalent to GGG60. The microstructures and wear scars of the brass specimens were examined by optical, scanning electron microscopy (SEM) and X-ray microanalyses by EDAX. A correlation between hardness and wear volume rate was established for the investigated centrifugally cast and sand cast brass specimens. The volume rate of specimens produced by sand casting method was generally found to be higher than those of centrifugally cast specimens. Ferritic ductile counterpart led to higher wear volume rate than pearlitic ductile counterpart for the both specimens. Severe abrasive wear scars were observed for the sand cast specimens/ferritic ductile iron pair. However, severe adhesive wear took place for the centrifugally cast specimen/pearlitic ductile iron pair.

  17. Seismic Rheological Model and Reflection Coefficients of the Brittle-Ductile Transition

    NASA Astrophysics Data System (ADS)

    Carcione, José M.; Poletto, Flavio

    2013-12-01

    It is well established that the upper—cooler—part of the crust is brittle, while deeper zones present ductile behaviour. In some cases, this brittle-ductile transition is a single seismic reflector with an associated reflection coefficient. We first develop a stress-strain relation including the effects of crust anisotropy, seismic attenuation and ductility in which deformation takes place by shear plastic flow. Viscoelastic anisotropy is based on the eigenstrain model and the Zener and Burgers mechanical models are used to model the effects of seismic attenuation, velocity dispersion, and steady-state creep flow, respectively. The stiffness components of the brittle and ductile media depend on stress and temperature through the shear viscosity, which is obtained by the Arrhenius equation and the octahedral stress criterion. The P- and S-wave velocities decrease as depth and temperature increase due to the geothermal gradient, an effect which is more pronounced for shear waves. We then obtain the reflection and transmission coefficients of a single brittle-ductile interface and of a ductile thin layer. The PP scattering coefficient has a Brewster angle (a sign change) in both cases, and there is substantial PS conversion at intermediate angles. The PP coefficient is sensitive to the layer thickness, unlike the SS coefficient. Thick layers have a well-defined Brewster angle and show higher reflection amplitudes. Finally, we compute synthetic seismograms in a homogeneous medium as a function of temperature.

  18. Effect of foundation flexibility on ductility reduction factors for R/C stack-like structures

    NASA Astrophysics Data System (ADS)

    Halabian, Amir M.; Kabiri, Shabnam

    2011-06-01

    The most important parameter used to determine force reduction factors in force-based design procedures adopted in the current seismic codes is the structural ductility. For a structure supported on a flexible foundation, the ductility factor could be affected by foundation compliances. The ductility factors given in the current codes are mostly assigned ignoring the effect of SSI and therefore the objective of this research is to assess the significance of SSI phenomenon on ductility factors of stack-like structures. The deformed configuration of stack-like structures is idealized as an assemblage of beam elements considering nonlinear moment-curvature relations, while a linear sway-rocking model was implemented to model the supporting soil. Using a set of artificial records, repeated linear and nonlinear analyses were performed by gradually increasing the intensity of acceleration to a level where the first yielding of steel in linear and nonlinear analyses is observed and a level corresponding to the stack collapse in the nonlinear analysis. The difference between inelastic and elastic resistance in terms of displacement ductility factors has been quantified. The results indicate that foundation flexibility can decrease the ductility of the system and neglecting this phenomenon may lead to erroneous conclusions in the prediction of the seismic performance of flexibly-supported R/C stack-like structures.

  19. Steady crack growth through ductile metals: Computational studies

    NASA Astrophysics Data System (ADS)

    Sobotka, James C.

    This thesis examines the crack-front response during sustained ductile tearing in structural metals at quasistatic rates using high resolution finite element computations. At load levels approaching the steady-growth regime, well-established computational methods that model material damage break down numerically as vanishingly small load increments produce increasingly large amounts of crack extension. The computational model adopted here determines the deformation history of a steadily advancing crack directly without the need for a priori (transient) analysis that considers blunting of the pre-existing stationary crack and subsequent growth through the associated initial plastic zone. Crack extension occurs at the remotely applied, fixed loading without the need for a local growth criteria. This numerical scheme utilizes a streamline integration technique to determine the elastic-plastic fields, generalized from a two-dimensional to a fully three-dimensional setting and implemented within mixed Matlab/C++/F-90 based software. Modifications of the conventional finite element formulation lead to an efficient procedure -- readily parallelized -- and determine the invariant near-front fields, representative of steady-state growth, on a fixed mesh in a boundary-layer framework. In the small-scale yielding regime, the crack front does not sense the existence of remote boundaries, and computational results retain a strong transferability among various geometric configurations where near-front, plastic deformation remains entirely enclosed by the surrounding linear-elastic material. The global stress intensity factor (KI ) and imposed T-stress fully specify displacement constraints along the far-field boundary, and in a three-dimensional setting, the panel thickness reflects the only natural length scale. The initial studies in this work consider steady crack advance within the small-scale yielding context under plane-strain conditions and mode I loading. These analyses

  20. Comparison of High-Temperature Properties and Thermal Shock Resistance of Austempered Ductile Irons (ADI) with Those of Pearlitic Ductile Cast Irons

    NASA Astrophysics Data System (ADS)

    Ajabshiri, Mehrdad; Sharafi, Shahriar; Moeini, Alireza

    2012-01-01

    High-temperature strength and thermal shock resistance of austempered ductile iron (ADI) in high temperatures because of instability of ausferrite phase has been less interest. The aim of this study is to investigate the tensile properties of ADI and pearlitic ductile cast iron by using the short-time tensile test in high temperatures. Tensile test was conducted in temperatures of 298 K, 673 K, 873 K, and 1073 K (25 °C, 400 °C, 600 °C, and 800 °C). Thermal shock test also was conducted by using the molten lead bath at 1273 K (1000 °C). In this experiment, samples of pearlitic ductile cast iron and ADI were divided in two groups; that after immersing in the molten lead bath for 25 seconds, one group was cooled in the air and other one was quenched in the water. Results showed that strength and thermal shock resistance of ADI samples are higher than those of the pearlitic ductile cast iron.

  1. Nonequilibrium grain-boundary segregation and ductile-brittle-ductile transition in Fe-Mn-Ni-Ti age-hardening alloy

    SciTech Connect

    Heo, N.H.

    1996-10-01

    Nonequilibrium segregation kinetics of alloying elements and a ductile-brittle-ductile transition behavior have been investigated in an Fe-8.4Mn-7.4Ni-1.7Ti alloy. The alloy experienced a ductile-brittle-ductile (DBD) transition during isothermal aging. In the brittle region, the alloy showed a decrease in intergranular fracture strength and a subsequent increase with aging time. This is due to the segregation of titanium to the grain boundaries and its desegregation into the matrix. The intergranular fracture strength was higher on the zero tensile elongation finish curve than on the start curve. This is because the grain-boundary segregation level of titanium is relatively lower on the finish curve. The lowest intergranular fracture strength increased with increasing aging temperature, which was attributed to a lower grain-boundary segregation level of titanium at higher temperature. Manganese caused an overall reduction in intergranular fracture strength and, as a result, the delayed occurrence of the zero tensile elongation (ZTE) finish curve in a temperature and long-time plot.

  2. Possible transient creep events in a brittle-ductile continental crust: observations, experiments and potential models.

    NASA Astrophysics Data System (ADS)

    Lavier, Luc

    2016-04-01

    In a given tectonic province and over thousands to millions of years, slip on faults is believed to be constant and approximately equal to the local tectonic rate in agreement with rigid plate tectonic theory. In this model the ductile lower crust flows in response to this steady plate motion. Moreover brittle and ductile behaviors interact only at a sharp boundary defined as the brittle ductile transition (BDT). However in the continental lithosphere brittle and ductile behavior may coexist over a large range of pressure and temperature conditions for different mineral compositions. This generates heterogeneities in the brittle and ductile crust that are often ignored in models of shear zones. We hypothesize that the interaction between brittle (elastic) and ductile (viscous) behavior may cause deviations from steady-state slip and generates transient creep events on shear zones that release many meters of creep over years to thousands of years marked by a single period of tectonic activity followed by quiescence. We present a set of numerical and analytical models, analogue experiments as well as some observations in nature that may support this hypothesis. In this presentation we extend an analytic formulation to model creep events within shear zones at the transition between brittle and ductile behavior in the crust. We assume that creep events are triggered by a set of interconnected fractures modeled as propagating dislocations. The amount of connectivity controls the nature and the intensity of the transient creep events. The shear zone behaves as a forced damped oscillator that can release strain accumulated during jammed/locked periods. The creep can be over-, critically-, or under-damped. The time scale of the events may vary between seconds to thousands of years depending on the viscous, elastic and plastic (fractures) properties of the shear zone.

  3. Two brittle ductile transitions in subduction wedges, as revealed by topography

    NASA Astrophysics Data System (ADS)

    Thissen, C.; Brandon, M. T.

    2013-12-01

    Subduction wedges contain two brittle ductile transitions. One transition occurs within the wedge interior, and a second transition occurs along the decollement. The decollement typically has faster strain rates, which suggests that the brittle ductile transition along the decollement will be more rearward (deeper) than the transition within the interior. However, the presence of distinct rheologies or other factors such as pore fluid pressure along the decollement may reverse the order of the brittle-ductile transitions. We adopt a solution by Williams et al., (1994) to invert for these brittle ductile transitions using the wedge surface topography. At present, this model does not include an s point or sediment loading atop the wedge. The Hellenic wedge, however, as exposed in Crete presents an ideal setting to test these ideas. We find that the broad high of the Mediterranean ridge represents the coulomb frictional part of the Hellenic wedge. The rollover in topography north of the ridge results from curvature of the down going plate, creating a negative alpha depression in the vicinity of the Strabo, Pliny, and Ionian 'troughs' south of Crete. A steep topographic rise out of these troughs and subsequent flattening reflects the brittle ductile transition at depth in both the decollement and the wedge interior. Crete exposes the high-pressure viscous core of the wedge, and pressure solution textures provide additional evidence for viscous deformation in the rearward part of the wedge. The location of the decollement brittle ductile transition has been previously poorly constrained, and Crete has never experienced a subduction zone earthquake in recorded history. Williams, C. A., et al., (1994). Effect of the brittle ductile transition on the topography of compressive mountain belts on Earth and Venus. Journal of Geophysical Research Solid Earth

  4. Microstructures and Mechanical Properties of a Wear-Resistant Alloyed Ductile Iron Austempered at Various Temperatures

    NASA Astrophysics Data System (ADS)

    Cui, Junjun; Chen, Liqing

    2015-08-01

    To further improve the mechanical performance of a new type of alloyed bainitic wear-resistant ductile iron, the effects of the various austempering temperatures have been investigated on microstructure and mechanical behaviors of alloyed ductile iron Fe-3.50C-1.95Si-3.58Ni-0.71Cu-0.92Mo-0.65Cr-0.36Mn (in weight percent). This alloyed ductile iron were firstly austenitized at 1123 K (850 °C) for 1 hour and then austempered in a salt bath at 548 K, 573 K, and 598 K (275 °C, 300 °C, and 325 °C) for 2 hours according to time-temperature-transformation diagram calculated by JMatPro software. The microstructures of austempered wear-resistant ductile irons consist of matrix of dark needle-like ferrite plus bright etching austenite and some amount of martensite and some dispersed graphite nodules. With increasing the austempering temperature, the amount of ferrite decreases in austempered ductile iron, while the amount of austenite and carbon content of austenite increases. There is a gradual decrease in hardness and increase in compressive strength with increasing austempering temperature. The increased austenite content and coarsened austenite and ferrite can lead to a hardness decrease as austempering temperature is increased. The increased compressive strength can be attributed to a decreased amount of martensitic transformation. The alloyed ductile iron behaves rather well wear resistance when the austempering is carried out at 598 K (325 °C) for 2 hours. Under the condition of wear test by dry sand/rubber wheel, the wear mechanisms of austempered ductile irons are both micro-cutting and plastic deformation.

  5. Hot Ductility Characterization of Sanicro-28 Super-Austenitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Mirzaei, A.; Zarei-Hanzaki, A.; Abedi, H. R.

    2016-05-01

    The hot ductility behavior of a super-austenitic stainless steel has been studied using tensile testing method in the temperature range from 1073 K to 1373 K (800 °C to 1100 °C) under the strain rates of 0.1, 0.01, and 0.001 s-1. The hot compression tests were also performed at the same deformation condition to identify the activated restoration mechanisms. At lower temperatures [ i.e., 1073 K and 1173 K (800 °C and 900 °C)], the serration of initial grain boundaries confirms the occurrence of dynamic recovery as the predominant restoration process. However, in the course of applied deformation, the initial microstructure is recrystallized at higher temperatures [ i.e., 1273 K and 1373 K (1000 °C and 1100 °C)]. In this respect, annealing the twin boundaries could well stimulate the recrystallization kinetic through initiation new annealing twins on prior annealing twin boundaries. The hot tensile results show that there is a general trend of increasing ductility by temperature. However, two regions of ductility drop are recognized at 1273 K and 1373 K (1000°C)/0.1s-1 and (1100°C)/0.01s-1. The ductility variations at different conditions of temperature and strain rate are discussed in terms of simultaneous activation of grain boundary sliding and restoration processes. The observed ductility troughs are attributed to the occurrence of grain boundary sliding and the resulting R-type and W-type cracks. The occurrence of dynamic recrystallization is also considered as the main factor increasing the ductility at higher temperatures. The enhanced ductility is primarily originated from the post-uniform elongation behavior, which is directly associated with the strain rate sensitivity of the experimental material.

  6. Microtopography for Ductile Fracture Process Characterization - Part 1: Theory and Methodology

    SciTech Connect

    Lloyd, Wilson Randolph

    2003-02-01

    The mechanics of ductile fracture is receiving increased focus as the importance of integrity of structures constructed from ductile materials is increasing. The non-linear, irreversible mechanical response of ductile materials makes generalized models of ductile cracking very difficult to develop. Therefore, research and testing of ductile fracture have taken a path leading to deformation-based parameters such as crack tip opening displacement (CTOD) and crack tip opening angle (CTOA). Constrained by conventional test techniques and instrumentation, physical values (e.g. crack mouth opening displacement, CMOD, and CTOA angles) are measured on the test specimen exterior and a single through-thickness "average" interior value is inferred. Because of three-dimensional issues such as crack curvature, constraint variation, and material inhomogeneity, inference of average parameter values may introduce errors. The microtopography methodology described here measures and maps three-dimensional fracture surfaces. The analyses of these data provide direct extraction of the parameters of interest at any location within the specimen interior, and at any desired increment of crack opening or extension. A single test specimen can provide all necessary information for the analysis of a particular material and geometry combination.

  7. Ductile grinding of silicon carbide as a production method for reflective optics

    SciTech Connect

    Kahl, W.K.

    1993-11-01

    Ductile regime grinding or shear-mode grinding is an enabling technology that is finding application in the optics manufacturing industry. By definition, ductile removal occurs when the scale of machining is conducted below a material-dependent critical dimension or chip size. Much of the interest in ductile grinding resides in manufacturing glass optics, which experience brittle-ductile transition at {approximately}10 nm. Silicon carbide has a critical dimension that is on the order of 100--200 nm, making it a more attractive candidate for the technology. Preliminary results from an on-axis chemical vapor deposited (CVD) SiC sphere (f/14) indicate 317 {Angstrom} surface roughness and 0.96 wave P-V figure were achieved with this manufacturing method. Surface finish, interferometric measured figure and BRDF scatter results are presented from ductile regime grinding of 40 and 75 mm flats of CVD silicon carbide, bare reaction bonded SiC (RBSiC) and uniaxial hot-pressed SiC (HPSiC).

  8. Influence of testing environment on the room temperature ductility of FeAl alloys

    NASA Technical Reports Server (NTRS)

    Gaydosh, D. J.; Nathal, M. V.

    1990-01-01

    The effects of testing atmospheres (air, O2, N2, and vacuum) on the room-temperature ductility of Fe-40Al, Fe-40Al-0.5B, and Fe-50Al alloys were investigated. The results confirmed the decrease in room-temperature ductility of Fe-rich FeAl alloys by the interaction of the aluminide with water vapor, reported previously by Liu et al. (1989). The highest ductilities were measured in the atmosphere with the lowest moisture levels, i.e., in vacuum. It was found that significant ductility is still restricted to Fe-rich alloys (Fe-40Al), as the Fe-50Al alloy remained brittle under all testing conditions. It was also found that slow cooling after annealing was beneficial, and the effect was additive to the environmental effect. The highest ductility measurements in this study were 9 percent elongation in furnace-cooled Fe-40Al and in Fe-40Al-0.5B, when tested in vacuum.

  9. Effect of Boron Precipitation Behavior on the Hot Ductility of Boron Containing Steel

    NASA Astrophysics Data System (ADS)

    Cho, Kyung Chul; Mun, Dong Jun; Kim, Jin Young; Park, Joong Kil; Lee, Jae Sang; Koo, Yang Mo

    2010-04-01

    The effect of boron (B) precipitation behavior on the hot ductility of B containing steel was investigated. Hot ductility of B containing steel was sensitive to the cooling rate (CR) in the range of 1 to 20 K/s (1 to 20 °C/s), whereas that of B-free steel showed little change with CR. Increased CR causes deepening and widening of the ductility trough in B containing steel. Particle tracking autoradiography (PTA) analysis and transmission electron microscope (TEM) image of the samples show that boron nitride (BN) particles form along prior austenite grain boundaries, and that as CR increases, these particles become smaller and more numerous. This increase in the number of small BN precipitates may promote intergranular fracture, leading to a decrease in hot ductility in the lower austenite temperature region (1173 to 1273 K (900 to 1000 °C)). Furthermore, the formation of filmlike ferrite at ~1123 K (850 °C) causes a decrease in the hot ductility of this steel regardless of B addition and CR.

  10. Influence of cerium additions on high-temperature-impact ductility and fracture behavior of iridium alloys

    SciTech Connect

    Gubbi, A.N.; Zee, R.H.; George, E.P.; Ohriner, E.K.

    1997-10-01

    Radioisotope thermoelectric generators (RTGs), used for supplying electric power to interplanetary space missions, utilize the energy liberated due to decay of the radioisotope fuel. The material used for cladding the fuel pellets is an iridium-based alloy developed at Oak Ridge National Laboratory, which contains nominally 0.3 wt pct W, 60 wppm Th, and 50 wppm Al, generally known as DOP-26. High-temperature tensile impact testing was carried out on Ir + 0.3 wt pct W alloys doped with cerium and thorium individually, and with cerium and thorium together. Impact ductility was evaluated as a function of grain size and test temperature. Cerium by itself was not as effective as thorium in improving the grain boundary cohesion, even though it segregated more strongly than thorium to the grain boundaries. This lower grain boundary cohesion was responsible for lower impact ductility and higher brittle-to-ductile transition temperature of cerium-doped alloys compared to those of the thorium- or thorium plus cerium-doped alloys. Reduction in thorium content by a factor of 5 (from 50 to 10 appm) in the bulk did not result in any significant reduction in high-temperature impact ductility or an increase in the brittle-to-ductile transition temperature as long as sufficient cerium was added to provide grain refinement. Grain boundary strengths of thorium- and thorium plus cerium-doped alloys were almost identical.

  11. Analytical prediction of the location of ductility dip cracking in the trans-varestraint test

    SciTech Connect

    Singh, I.; Kroenke, W.; Cola, M.

    1997-05-01

    Some NiCrFe weld metals exhibit decreased ductility over a temperature range known as the {open_quotes}ductility dip{close_quotes} temperature (DDT) range. Ductility dip cracking (DDT) is a phenomenon which occurs in a zone bounded by the DDT range on its sides and a threshold plastic strain on its bottom as shown in figure 1. Figure 1 illustrates how ductility varies as weld metal cools from the solidus temperature for materials with and without a ductility dip. The purpose of this work is to demonstrate the ability to predict the location of the DDC in a Trans-Varestraint Test (TVT) for a specimen machined from a weld deposited EN52 plate. The DDC predictions require a combination of Trans-Varestraint testing and finite element analysis. The test provides the threshold value of externally applied nominal strain below which DDC does not occur. The analysis provides the corresponding threshold local or peak strain. The threshold local plastic strain level and the DDT range are used to predict the location of the DDC. The ultimate purpose of this work is to evaluate susceptibility of highly constrained, component welds to DDC. Test results for Trans-Varestraint Testing for a weld deposited EN52 plate are reported in reference. The ability to predict the location of the DDC in the Trans-Varestraint Test using the techniques reported herein is demonstrated by showing good comparison between the analytical results and the test data.

  12. Evading the strength–ductility trade-off dilemma in steel through gradient hierarchical nanotwins

    PubMed Central

    Wei, Yujie; Li, Yongqiang; Zhu, Lianchun; Liu, Yao; Lei, Xianqi; Wang, Gang; Wu, Yanxin; Mi, Zhenli; Liu, Jiabin; Wang, Hongtao; Gao, Huajian

    2014-01-01

    The strength–ductility trade-off has been a long-standing dilemma in materials science. This has limited the potential of many structural materials, steels in particular. Here we report a way of enhancing the strength of twinning-induced plasticity steel at no ductility trade-off. After applying torsion to cylindrical twinning-induced plasticity steel samples to generate a gradient nanotwinned structure along the radial direction, we find that the yielding strength of the material can be doubled at no reduction in ductility. It is shown that this evasion of strength–ductility trade-off is due to the formation of a gradient hierarchical nanotwinned structure during pre-torsion and subsequent tensile deformation. A series of finite element simulations based on crystal plasticity are performed to understand why the gradient twin structure can cause strengthening and ductility retention, and how sequential torsion and tension lead to the observed hierarchical nanotwinned structure through activation of different twinning systems. PMID:24686581

  13. Ductility improvement of direct-cast gamma TiAl-based alloy sheet

    SciTech Connect

    Hanamura, Toshihiro; Hashimoto, Keizo

    1997-12-31

    For improving the room temperature tensile ductility of direct-cast gamma TiAl sheets without affecting their high-temperature strength, direct sheet casting with TiB{sub 2} particle dispersion is employed and conducted. The TiB{sub 2} addition and rapid cooling results in the formation of a fine equiaxed grain microstructure with an average grain size of {approximately}10{micro}m, contributing to the increase in the room temperature ductility to 2.1% with the high-temperature tensile strength kept at about 200 MPa. This improvement of room-temperature ductility is attributable to the following fact. The high oxygen content of this material, about 2,500 wt.ppm, is not harmful to the tensile ductility when the oxygen is in the solid solution of the {alpha}{sub 2} lamellar phase or in oxide particles, which are fine enough not to cause brittleness to the matrix. From these findings, a principle is proposed that oxygen is not harmful to the ductility of gamma TiAl when its microstructure containing oxygen is fine enough.

  14. Modeling of ductile deformation in anisotropic rocks with slip surfaces

    NASA Astrophysics Data System (ADS)

    Dabrowski, Marcin

    2013-04-01

    Flanking structures and sheath folds can develop in layered rocks due to flow perturbation around slip surfaces in shear zones (Exner and Dabrowski, 2010; Reber et al., submitted). Mechanical anisotropy of the host rock has been shown to play a major role in determining the slip rate and the flow pattern around it (Kocher and Mancktelow, 2006; Fletcher, 2011). In addition, anisotropic fluids such as ductile foliated rocks have a 'memory' of deformation due to evolving microstructure. For example, the rotation of a rigid circular inclusion embedded in a layered host in layer-parallel shear results in the structural reorganization around it, which leads to the modification of the flow pattern in the host and in consequence to a massive reduction of the inclusion rotation rate (Dabrowski and Schmid, 2011). Willis (1964) derived an analytical elastic solution for an elliptical inclusion in a homogeneous anisotropic matrix subject to a uniform load in the far field. The solution can be reduced to the case of an incompressible viscous medium. The case of an arbitrarily oriented inviscid slit under shear parallel to the principal axis of anisotropy can be obtained by reducing it even further. Although derived for the initial state of homogeneous planar anisotropy, the solution provides useful insights into the large deformation behavior of the system. In this study, I will use different models and numerical modeling techniques to assess the impact of mechanical anisotropy and structural development on the perturbing flow around an inviscid slit (slip surface) embedded in a host comprising discrete isotropic layers in layer-parallel simple shear. In the limit of thin layers (the number of layers intercepting the slit tends to infinity), the host is modeled as an anisotropic fluid. The anisotropic viscosity is determined by the bulk anisotropic viscosity of the layered system. The layering is initially planar or equivalently the anisotropy is initially homogeneous. Both non

  15. Laser beam welding of new ultra-high strength and supra-ductile steels

    NASA Astrophysics Data System (ADS)

    Dahmen, Martin

    2015-03-01

    Ultra-high strength and supra-ductile are entering fields of new applications. Those materials are excellent candidates for modern light-weight construction and functional integration. As ultra-high strength steels the stainless martensitic grade 1.4034 and the bainitic steel UNS 53835 are investigated. For the supra-ductile steels stand two high austenitic steels with 18 and 28 % manganese. As there are no processing windows an approach from the metallurgical base on is required. Adjusting the weld microstructure the Q+P and the QT steels require weld heat treatment. The HSD steel is weldable without. Due to their applications the ultra-high strength steels are welded in as-rolled and strengthened condition. Also the reaction of the weld on hot stamping is reflected for the martensitic grades. The supra-ductile steels are welded as solution annealed and work hardened by 50%. The results show the general suitability for laser beam welding.

  16. Ductility and impact resistance of P/M molybdenum-rhenium alloys

    SciTech Connect

    Leichtfried, Gerhard; Schneibel, Joachim H; Heilmaier, M.

    2006-01-01

    Mo-Re alloys containing between 5 and 47.5 wt pct Re were fabricated from Mo and Mo-Re powders by sintering and hot radial forging. The mechanical properties of as-forged, stress-relieved, and recrystallized specimens were examined. Up to a concentration of 41 wt pct Re, the Charpy ductile-to-brittle transition temperature decreased monotonically with increasing rhenium concentration. Consistent with this, bend angles for fracture at T = -100 C increased monotonically with increasing rhenium concentration. Between 10 and 41 wt pct rhenium, the room-temperature tensile ductility of recrystallized Mo-Re remained nearly constant with values on the order of 35 to 45 pct. This result differs from the low ductility values observed previously by Lundberg (1997) for compositions on either side of Mo-13 wt pct Re.

  17. Texture Modification and Ductility Enhancement in Mg Alloy Through Friction Stir Processing

    SciTech Connect

    Yu, Zhenzhen; Feng, Zhili; Choo, Hahn; Vogel, Sven

    2011-01-01

    The correlation between friction stir processing parameters, i.e., rotation and travel rates of the processing tool, the texture modification and ductility enhancement of an Mg alloy AZ31B was investigated. With the systematic changes in processing parameters as represented by a Zener-Hollomon parameter input, a transition of different crystallographic texture was observed through neutron diffraction measurement, which correlated well with the changes in deformation and recrystallization mechanism activated during the FSP. The variation in the texture leads to dramatic changes in the strength and ductility in the stir zone of the processed Mg plate. A maximum of three-fold increase in the ductility was achieved in the Mg alloy through FSP when the Zener-Hollomon parameter exceeds a critical value, which is associated with low rotation speed and high travel speed processing conditions.

  18. A coupled ductile fracture phase-field model for crystal plasticity

    NASA Astrophysics Data System (ADS)

    Hernandez Padilla, Carlos Alberto; Markert, Bernd

    2015-08-01

    Nowadays crack initiation and evolution play a key role in the design of mechanical components. In the past few decades, several numerical approaches have been developed with the objective to predict these phenomena. The objective of this work is to present a simplified, nonetheless representative phenomenological model to predict the crack evolution of ductile fracture in single crystals. The proposed numerical approach is carried out by merging a conventional elasto-plastic crystal plasticity model and a phase-field model modified to predict ductile fracture. A two-dimensional initial boundary value problem of ductile fracture is introduced considering a single-crystal setup and Nickel-base superalloy material properties. The model is implemented into the finite element context subjected to a quasi-static uniaxial tension test. The results are then qualitatively analyzed and briefly compared to current benchmark results in the literature.

  19. Transition temperature and fracture mode of as-castand austempered ductile iron.

    PubMed

    Rajnovic, D; Eric, O; Sidjanin, L

    2008-12-01

    The ductile to brittle transition temperature is a very important criterion that is used for selection of materials in some applications, especially in low-temperature conditions. For that reason, in this paper transition temperature of as-cast and austempered copper and copper-nickel alloyed ductile iron (DI) in the temperature interval from -196 to +150 degrees C have been investigated. The microstructures of DIs and ADIs were examined by light microscope, whereas the fractured surfaces were observed by scanning electron microscope. The ADI materials have higher impact energies compared with DIs in an as-cast condition. In addition, the transition curves for ADIs are shifted towards lower temperatures. The fracture mode of Dls is influenced by a dominantly pearlitic matrix, exhibiting mostly brittle fracture through all temperatures of testing. By contrast, with decrease of temperature, the fracture mode for ADI materials changes gradually from fully ductile to fully brittle. PMID:19094047

  20. A Study on Fracture Locus of St12 Steel And Implementation Ductile Damage Criteria

    NASA Astrophysics Data System (ADS)

    Khataei, Mohammad; Poursina, Mehrdad; Kadkhodaei, Mahmoud

    2010-06-01

    In a metal forming process, the state of stress is one of the most important parameters on forming and behavior of the material. According to ductile damage criteria, the magnitudes of fracture strain for various stress triaxiality values should be determined for prediction of the place and time of ductile fracture. In this paper, the magnitudes of fracture strain of St12 steel is measured using several tensile tests on notched samples. Johnson-Cook equation for fracture strain as a function of stress triaxiality is calibrated for St12 steel, using the obtained experimental data. The accuracy of this function is achieved by comparison of the FEM results with experimental data which are achieved during simple tension and Erichsen tests. The simulation results have shown that the ductile damage model is a suitable criterion for prediction of fracture in St12 steel. In addition, notched samples tensile tests are suitable for calibration of Johnson-Cook equation for St12 steel.

  1. Studying the Enhanced Ductility of Bimodal Nanocrystalline Copper Using a Coarse-Grained Model

    NASA Astrophysics Data System (ADS)

    Gao, Guo-Jie Jason; Wang, Yun-Jiang; Ogata, Shigenobu

    Viewing a bimodal configuration of nanocrystalline copper as composed of soft grains containing stiff cores, we proposed a coarse-grained model with systematically tunable stiffness of grains to study the enhanced ductility of bimodal nanocrystalline copper [Y. Wang, M. Chen, F. Zhou, and E. Ma, Nature 419 (2002) 912]. Using molecular dynamics simulations, we shear our model quasistatically. Our results not only qualitatively confirms that a bimodal configuration could behave more ductile than a monomodal one but also predicts there exists a range of ratio of soft/stiff domains that best minimizes shear localization. Moreover, our model indicates that a bimodal configuration could sometimes exacerbate shear localization and therefore jeopardize ductility if the ratio of soft/stiff domains is not properly chosen. This may explain why some experimental results are hard to be reproduced.

  2. Neutron irradiation effects on the ductile-brittle transition of ferritic/martensitic steels

    SciTech Connect

    Klueh, R.L.; Alexander, D.J.

    1997-08-01

    Ferritic/martensitic steels such as the conventional 9Cr-1MoVNb (Fe-9Cr-1Mo-0.25V-0.06Nb-0.1C) and 12Cr-1MoVW (Fe-12Cr-1Mo-0.25V-0.5W-0.5Ni-0.2C) steels have been considered potential structural materials for future fusion power plants. The major obstacle to their use is embrittlement caused by neutron irradiation. Observations on this irradiation embrittlement is reviewed. Below 425-450{degrees}C, neutron irradiation hardens the steels. Hardening reduces ductility, but the major effect is an increase in the ductile-brittle transition temperature (DBTT) and a decrease in the upper-shelf energy, as measured by a Charpy impact test. After irradiation, DBTT values can increase to well above room temperature, thus increasing the chances of brittle rather than ductile fracture.

  3. Strength and ductility improvement of ultrafine-grained tungsten produced by equal-channel angular pressing

    NASA Astrophysics Data System (ADS)

    Hao, T.; Fan, Z. Q.; Zhang, T.; Luo, G. N.; Wang, X. P.; Liu, C. S.; Fang, Q. F.

    2014-12-01

    In this study, equal-channel angular pressing (ECAP) was employed to refine the grain size of tungsten at relatively low temperatures. The small punch (SP) test results show that the ultrafine-grained tungsten appears an evident improvement in both strength and ductility compared with primary coarse-grained tungsten. The analysis results from SP test data indicate that the ductile-to-brittle transition temperature (DBTT) of the ultrafine-grained tungsten decrease to 386 °C and 322 °C due to the ECAP processing at 800 °C and 950 °C, respectively. The reason of the improvement in both strength and ductility of the ultrafine-grained tungsten produced by ECAP is discussed.

  4. Heterogeneous lamella structure unites ultrafine-grain strength with coarse-grain ductility

    PubMed Central

    Wu, Xiaolei; Yang, Muxin; Yuan, Fuping; Wu, Guilin; Wei, Yujie; Huang, Xiaoxu; Zhu, Yuntian

    2015-01-01

    Grain refinement can make conventional metals several times stronger, but this comes at dramatic loss of ductility. Here we report a heterogeneous lamella structure in Ti produced by asymmetric rolling and partial recrystallization that can produce an unprecedented property combination: as strong as ultrafine-grained metal and at the same time as ductile as conventional coarse-grained metal. It also has higher strain hardening than coarse-grained Ti, which was hitherto believed impossible. The heterogeneous lamella structure is characterized with soft micrograined lamellae embedded in hard ultrafine-grained lamella matrix. The unusual high strength is obtained with the assistance of high back stress developed from heterogeneous yielding, whereas the high ductility is attributed to back-stress hardening and dislocation hardening. The process discovered here is amenable to large-scale industrial production at low cost, and might be applicable to other metal systems. PMID:26554017

  5. Strength, fracture, and fatigue behavior of advanced high-temperature intermetallics reinforced with ductile phases

    NASA Astrophysics Data System (ADS)

    Soboyejo, W. O.; Rao, K. T. Venkateswara; Sastry, S. M. L.; Ritchie, R. O.

    1993-03-01

    The results of recent studies on the fatigue and fracture behavior of extruded Ti-48A1 + 20 vol pct TiNb and hot-isostatically pressed (“hipped”) MoSi2 + 20 vol pct Nb are presented (compositions in atomic percent unless stated otherwise). The effects of ductile phase reinforcement of Ti-48A1 and MoSi2 on the micromechanisms of fracture under monotonie and cyclic loading are elucidated. Micromechanics models are applied to the prediction of crack-tip shielding components, and the effects of temperature on tensile/compressive/flexure strengths are discussed. Ductile phase toughening under monotonie loading conditions is shown to be associated with lower fatigue crack growth resistance. The lower fatigue resistance is attributed to the absence of crack-tip shielding, higher crack opening displacements, and the effects of inelastic strains that are developed in ductile phase-reinforced composites under cyclic loading conditions.

  6. Heterogeneous lamella structure unites ultrafine-grain strength with coarse-grain ductility.

    PubMed

    Wu, Xiaolei; Yang, Muxin; Yuan, Fuping; Wu, Guilin; Wei, Yujie; Huang, Xiaoxu; Zhu, Yuntian

    2015-11-24

    Grain refinement can make conventional metals several times stronger, but this comes at dramatic loss of ductility. Here we report a heterogeneous lamella structure in Ti produced by asymmetric rolling and partial recrystallization that can produce an unprecedented property combination: as strong as ultrafine-grained metal and at the same time as ductile as conventional coarse-grained metal. It also has higher strain hardening than coarse-grained Ti, which was hitherto believed impossible. The heterogeneous lamella structure is characterized with soft micrograined lamellae embedded in hard ultrafine-grained lamella matrix. The unusual high strength is obtained with the assistance of high back stress developed from heterogeneous yielding, whereas the high ductility is attributed to back-stress hardening and dislocation hardening. The process discovered here is amenable to large-scale industrial production at low cost, and might be applicable to other metal systems. PMID:26554017

  7. Metallurgical evaluation of factors influencing the ductility of aged T-111

    NASA Technical Reports Server (NTRS)

    Gold, R. E.

    1972-01-01

    The metallurgical factors influencing the ductility of T-111 (Ta-8W-2Hf) alloy following long-time exposures of GTA welds and tubing in the temperature range 982 C (1800 F) through 1316 C (2400 F) were evaluated by means of scanning and transmission electron microscopy, Auger electron emission spectroscopy, and optical metallographic procedures. No classical aging response occurs in the alloy over the temperature range studied. The ductility impairment implied by previous investigations is not the result of microstructural response of the alloy to thermal exposures. Intergranular failure in the GTA sheet welds appears the result of random contamination by silicon, potassium, and/or fluorine at the grain boundaries of the fusion zones. Exposure to lithium at high temperatures had no adverse effects on the ductility of T-111 tubing. These materials were, however, sensitive to post-age handling and testing procedures.

  8. Ductility and strength reduction factors for degrading structures considering cumulative damage.

    PubMed

    Bojórquez, Edén; Ruiz, Sonia E; Reyes-Salazar, Alfredo; Bojórquez, Juan

    2014-01-01

    The effect of cumulative damage on the strength requirements of degrading structures is assessed through the evaluation of the target ductility and corresponding strength reduction factors of simple degrading structures. While the reduction on ductility is established through the use of Park and Ang index, the suggestions given by Bojórquez and Rivera are used to model the degradation of the structural properties of the simple systems. Target ductilities and their corresponding reduced strength reduction factors are established for five sets of ground motions; most of them are recorded in California. The results given in this paper provide insight into all relevant parameters that should be considered during seismic design of earthquake-resistant structures. Finally, some recommendations to evaluate the effect of cumulative damage on seismic design are suggested. PMID:24883410

  9. Ductility and Strength Reduction Factors for Degrading Structures Considering Cumulative Damage

    PubMed Central

    Bojórquez, Edén; Ruiz, Sonia E.; Reyes-Salazar, Alfredo; Bojórquez, Juan

    2014-01-01

    The effect of cumulative damage on the strength requirements of degrading structures is assessed through the evaluation of the target ductility and corresponding strength reduction factors of simple degrading structures. While the reduction on ductility is established through the use of Park and Ang index, the suggestions given by Bojórquez and Rivera are used to model the degradation of the structural properties of the simple systems. Target ductilities and their corresponding reduced strength reduction factors are established for five sets of ground motions; most of them are recorded in California. The results given in this paper provide insight into all relevant parameters that should be considered during seismic design of earthquake-resistant structures. Finally, some recommendations to evaluate the effect of cumulative damage on seismic design are suggested. PMID:24883410

  10. The Nature of the Tensile Fracture in Austempered Ductile Iron with Dual Matrix Microstructure

    NASA Astrophysics Data System (ADS)

    Kilicli, Volkan; Erdogan, Mehmet

    2010-02-01

    The tensile fracture characteristics of austempered ductile irons with dual matrix structures and different ausferrite volume fractions have been studied for an unalloyed ductile cast iron containing (in wt.%) 3.50 C, 2.63 Si, 0.318 Mn, and 0.047 Mg. Specimens were intercritically austenitized (partially austenitized) in two phase region (α + γ) at various temperatures for 20 min and then quenched into a salt bath held at austempering temperature of 365 °C for various times and then air cooled to room temperature to obtain various ausferrite volume fractions. Conventionally austempered specimens with fully ausferritic matrix and unalloyed as-cast specimens having fully ferritic structures were also tested for comparison. In dual matrix structures, results showed that the volume fraction of proeutectoid ferrite, new (epitaxial) ferrite, and ausferrite [bainitic ferrite + high-carbon austenite (stabilized or transformed austenite)] can be controlled to influence the strength and ductility. Generally, microvoids nucleation is initiated at the interface between the graphite nodules and the surrounding ferritic structure and at the grain boundary junctions in the fully ferritic microstructure. Debonding of the graphite nodules from the surrounding matrix structure was evident. The continuity of the ausferritic structure along the intercellular boundaries plays an important role in determining the fracture behavior of austempered ductile iron with different ausferrite volume fractions. The different fracture mechanisms correspond to the different levels of ausferrite volume fractions. With increasing continuity of the ausferritic structure, fracture pattern changed from ductile to moderate ductile nature. On the other hand, in the conventionally austempered samples with a fully ausferritic structure, the fracture mode was a mixture of quasi-cleavage and a dimple pattern. Microvoid coalescence was the dominant form of fracture in all structures.

  11. Ductility Enhancement of Molybdenum Phase by Nano-sizedd Oxide Dispersions

    SciTech Connect

    Bruce Kang

    2008-07-31

    The present research is focused on ductility enhancement of molybdenum (Mo) alloys by adding nano-sized oxide particles to the alloy system. The research approach includes: (1) determination of microscopic mechanisms responsible for the macroscopic ductility enhancement effects through atomistic modeling of the metal-ceramic interface; (2) subsequent computer simulation-aided optimization of composition and nanoparticle size of the dispersion for improved performance; (3) synthesis and characterization of nanoparticle dispersion following the guidance from atomistic computational modeling analyses (e.g., by processing a small sample of Mo alloy for evaluation); and (4) experimental testing of the mechanical properties to determine optimal ductility enhancement.Through atomistic modeling and electronic structure analysis using full-potential linearized muffin-tin orbital (FP-LMTO) techniques, research to date has been performed on a number of selected chromium (Cr) systems containing nitrogen (N) and/or magnesium oxide (MgO) impurities. The emphasis has been on determining the properties of the valence electrons and the characteristics of the chemical bonds they formed. It was found that the brittle/ductile behavior of this transitional metal system is controlled by the relative population of valence charges: bonds formed by s valence electrons yield metallic, ductile behavior, whereas bonds formed by d valence electrons lead to covalent, brittle behavior. The presence of valence bands from impurities also affects the metal bonding, thereby explaining the detrimental and beneficial effects induced by the inclusion of N impurities and MgO dispersions. These understandings are useful for optimizing ductility enhancement effects on the dispersion materials.

  12. The Pennsbury-Concord shear zone: A deformed ductile thrust, central Appalachian Piedmont

    SciTech Connect

    Solar, G.S.; Hill, M.L. . Dept. of Geology)

    1993-03-01

    The contact between the Baltimore Gneiss and the Wissahickon Group in southeastern Pennsylvania is a ductile shear zone. The contact extends from just west of Pennsbury to just east of Concord, Pennsylvania. The strike of the shear zone contact varies along its length from a general orientation of N60--65E in the west to N75--80E near Concord and then to N30E adjacent to the Rosemont Shear Zone. Microstructural analysis reveals deformation in units on both sides of the contact that is characterized by plastic deformation mechanisms associated with depths below the brittle-ductile transition. Retrograde metamorphism and grain-size reduction as well as continuity across the zone indicate that this deformation was later than the metamorphism of the individual units. The contact has experienced at least two phases of deformation. The early phase was ductile thrusting juxtaposing the Wissahickon Group gneiss on top of the Precambrian Baltimore Gneiss and producing a high temperature pervasive planar and linear fabric. This fabric is most preserved in the west where foliation is shallowly dipping with a lineation trending S54E and plunging 35[degree] to the SE. The later phase was characterized by transposition of the ductile thrust fabric to a more strike-parallel orientation. Along the contact zone to the east, strike of the foliation gradually changes 10--15[degree], dip becomes steeper and the orientation of lineation changes to S85E with plunge of 17[degree] to the east. The deformation of the contact therefore confirms that the ductile thrusting is earlier than the major transcurrent shearing of the Appalachian Piedmont. Named the Pennsbury-Concord Zone, this deformed ductile thrust could be a root zone of brittle thrust faulting to the west in the fold-and-thrust-belt of central PA.

  13. How melt stretching affect the brittle-ductile transition temperature of polymer glasses

    NASA Astrophysics Data System (ADS)

    Cheng, Shiwang; Wang, Shi-Qing

    2013-03-01

    Upon increasing temperature a brittle polymer glass can turn ductile. PMMA is a good example. For a while this brittle-ductile transition (BDT) was thought to be determined by the emergence of a secondary relaxation....1-3 On the other hand, it has been known for a long time...4-6 that predeformation in the melt state (e.g., melt stretching) can also make brittle glasses behave in a ductile manner. This transformation has recently received a satisfactory explanation based on a picture of structural hybrid for polymer glasses....7 It appears that BDT is dictated by the relative mechanical characteristics of the primary structure (due to the van der Waals bonds) and the chain network. The present work, based on conventional Instron tensile extension tests and DMA tests, shows that melt stretching does not alter the secondary relaxation behavior of PMMA and PC yet can turn them the brittle PMMA ductile and the ductile PC brittle. Moreover, sufficient melt stretching makes the brittle PS ductile although it does not produce any secondary relaxation process..1. Monnerie, L.; Laupretre, F.; Halary, J. L. Adv. Polym. Sci2005, 187, 35-213. 2. Monnerie, L.; Halary, J. L.; Kausch, H. Adv. Polym. Sci2005, 187, 215-364. 3. Wu, S. J. Appl. Polym. Sci.1992, 46, (4), 619-624. 4. Vincent, P. I. Polymer1960, 1, (0), 425-444. 5. Harris, J. S.; Ward, I. M. J. Mater. Sci.1970, 5, (7), 573-579. 6. Ender, D. H.; Andrews, R. D. J. Appl. Phys.1965, 36, (10), 3057-3062. 7. Zartman, G. D.; Cheng, S.; Li, X.; Lin, F.; Becker, M. L.; Wang, S.-Q. Macromolecules2012, 45, (16), 6719-6732.

  14. Ultrafine-grained titanium of high interstitial contents with a good combination of strength and ductility

    NASA Astrophysics Data System (ADS)

    Xu, W.; Wu, X.; Sadedin, D.; Wellwood, G.; Xia, K.

    2008-01-01

    A dehydrided Ti powder of very high oxygen content was successfully consolidated using back pressure equal channel angular processing into a fully dense bulk ultrafine-grained Ti showing apparent compressive ductility as well as high true yield and ultimate strengths of 1350 and 1780MPa, respectively. Interstitial solid solution strengthening contributed to the majority of the increase in strength with additional contribution from ultrafine grains. Significantly, the material also exhibited much improved ductility for such a high interstitial content, thanks probably to the nonequilibrium grain boundaries and bimodal grain structure introduced during severe plastic deformation.

  15. Percolation, wave propagation, and void link up effects in ductile fracture

    SciTech Connect

    Tonks, D.L.

    1994-02-01

    This work investigates the time evolution and spatial morphology of ductile damage based on void growth and coalecence. The size enhancement of damage cluster growth, as well as wave speed limiting of growth, are treated microscopically. Simplified 2D plane strain simulations using individual voids are done with uniaxial stress and explained with a probabilistic theory. At low strain rate, fracture occurs by long, localized cracks. At high strain rates, widespread, random damage breaks the system. The Voronoi tessellation of voids can be used to map out the spatial network of still solid material in 3D ductile fracture. Using it, the spallation porosity is calculated based on percolation theory.

  16. Influence of hydrostatic pressure on the ductility of copper as a function of its initial state

    NASA Astrophysics Data System (ADS)

    Egorov, S. A.

    2016-03-01

    The influence of hydrostatic pressure in the interval 0-250 MPa on the deformation properties of copper versus its initial state is studied. After liquid nitrogen storage, the torsion strain to fracture is found to increase when the pressure rises to 200 MPa. As the pressure rises further and reaches 250 MPa, the torsion strain to fracture drops. Preliminary torsion to a strain of 5% in opposition to torsion under pressure makes the pressure dependence of the ultimate strain linear. If the prestrain equals 25%, a rise in the pressure to 150MPa increases the ductility of the material. A further increase in the pressure to 250 MPa changes the ductility insignificantly.

  17. Ordered iron aluminide alloys having an improved room-temperature ductility and method thereof

    DOEpatents

    Sikka, Vinod K.

    1992-01-01

    A process is disclosed for improving the room temperature ductility and strength of iron aluminide intermetallic alloys. The process involves thermomechanically working an iron aluminide alloy by means which produce an elongated grain structure. The worked alloy is then heated at a temperature in the range of about 650.degree. C. to about 800.degree. C. to produce a B2-type crystal structure. The alloy is rapidly cooled in a moisture free atmosphere to retain the B2-type crystal structure at room temperature, thus providing an alloy having improved room temperature ductility and strength.

  18. Theoretical investigation on improving the ductility of Rh3V by ternary addition

    NASA Astrophysics Data System (ADS)

    Manjula, M.; Sundareswari, M.; Jayalakshmi, D. S.; Viswanathan, E.

    2015-06-01

    The band structure calculations are performed on the intermetallic compounds Rh3V and Rh3Vx(Al)1-x by Full Potential Linearized Augmented Plane Wave(FP-LAPW) method. Total energies are calculated as a function of volume and fitted to Birch-Murnaughan equation of state to find the lattice parameter and the other ground state properties. The ductility of these compounds has been analyzed using Cauchy's Pressure, Pugh Rule and Poisson's ratio. From this study we observed that Rh3V is brittle while its alloy Rh3V0.875Al0.125 is ductile. Electron density plots are illustrated and compared.

  19. Transformation plasticity in ductile solids. Final report, August 1, 1988--November 30, 1995

    SciTech Connect

    Olson, G.B.

    1996-09-01

    Throughout history, the development of stronger materials has enabled the realization of countless technological advances. Unfortunately, any increase in strength is rarely achieved without concomitant decreases in toughness and ductility: a fact which severely limits the utility of materials such as ultrahigh-strength alloy steels. Typical precipitation-strengthened stainless steels have very little toughness at high strength levels. In the last decade, however, several investigators have reported exceptionally large fracture toughness values in high-strength precipitation-hardened metastable austenitic steels. This remarkable achievement is directly attributable to the process of transformation toughening. This report describes studies on tranformations and enhancement of plane-strain ductility in high strength steels.

  20. Development and Testing of a Linear Polarization Resistance Corrosion Rate Probe for Ductile Iron Pipe (Web Report 4361)

    EPA Science Inventory

    The North American water and wastewater community has hundreds of millions of feet of ductile iron pipe in service. Only a portion of the inventory has any form of external corrosion control. Ductile iron pipe, in certain environments, is subject to external corrosion.Linear Pola...

  1. Effects of Sample Geometry and Loading Rate onTensile Ductility of TRIP800 Steel

    SciTech Connect

    Sun, Xin; Soulami, Ayoub; Choi, Kyoo Sil; Guzman, O.; Chen, Weinong W.

    2012-04-15

    The effects of sample geometry and loading rate on the tensile ductility of a commercial grade Transformation Induced Plasticity (TRIP) steel are examined in this paper. Quasistatic tensile tests were performed for the 1.2mm gauge TRIP800 steel sheets with two geometries: sub-sized ASTM E-8 and a custom designed miniature tensile sample. Sample geometry effects on post-uniform elongation are discussed together with other experimental data reported in the open literature. Further discussions on the effects of sample geometry are cast in the context of mesh-size dependent ductility in finite element-based engineering simulations. The quasi-static tensile curve for the miniature sample is then compared with the split Hopkinson bar results at the loading rates of 1700-S-1 and 2650-S-1 with the same sample design. In contrary to the typical strain rate sensitivity results for mild steel where the dynamic strength increase at high strain rate usually occurs at the price of ductility reduction, our results show that the TRIP800 under examination has positive strain rate sensitivity on both strength and ductility. Images of the deformation process captured by high speed camera together with scanning electron microscopy (SEM) near the fracture zone are also used to elucidate the different deformation modes at different loading rates.

  2. Local Plastic-Strain Heterogeneities and Their Impact on the Ductility of Mg

    NASA Astrophysics Data System (ADS)

    Martin, Guilhem; Sinclair, Chad W.; Poole, Warren J.; Azizi-Alizamini, Hamid

    2015-08-01

    Microscale plastic strain heterogeneity can arise in polycrystalline Mg and its alloys in a variety of different ways. In this article, we illustrate how microscale digital image correction based on scanning electron microscope images can reveal this plastic heterogeneity in commercially pure polycrystalline Mg and how such observations provide insight into plasticity, damage, and ductility.

  3. Effect of Cooling Rate on Microstructure and Mechanical Properties of Thin-Walled Ductile Iron Castings

    NASA Astrophysics Data System (ADS)

    Górny, Marcin; Tyrała, Edward

    2013-01-01

    This article addresses the effect of cooling rate on microstructure and mechanical properties as determined by changing molding media and section size. The research was conducted for thin-walled iron castings with 2-5-mm wall thickness and for the reference casting with 13-mm wall thickness, using different molding materials (silica sand and insulating sand "LDASC") to achieve various cooling rates. Thermal analysis was performed to determine the real cooling rate at the beginning of the graphite eutectic solidification. In general, it was found that the predictions based on theoretical analysis of the solidification process of ductile iron are in good agreement with the experimental outcomes. Finally, the present study provides insights into the effect of cooling rate on the graphite nodule count, the ferrite fraction and mechanical properties of thin-walled ductile iron castings. The study shows that the cooling rate of thin-walled castings varies in a wide range (80-15 °C/s) when changing the wall thickness from 2 to 5 mm, accompanied by significantly changing the mechanical properties of ductile iron. The cooling rate can be effectively reduced by applying an insulating sand to obtain the desired properties of thin-walled castings practically in the whole range of ductile iron grades in accordance with the ASTM Standard.

  4. The Mechanism of High Ductility for Novel High-Carbon Quenching-Partitioning-Tempering Martensitic Steel

    NASA Astrophysics Data System (ADS)

    Qin, Shengwei; Liu, Yu; Hao, Qingguo; Wang, Ying; Chen, Nailu; Zuo, Xunwei; Rong, Yonghua

    2015-09-01

    In this article, a novel quenching-partitioning-tempering (Q-P-T) process was applied to treat Fe-0.6C-1.5Mn-1.5Si-0.6Cr-0.05Nb hot-rolled high-carbon steel and the microstructures including retained austenite fraction and the average dislocation densities in both martensite and retained austenite were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, respectively. The Q-P-T steel exhibits high strength (1950 MPa) and elongation (12.4 pct). Comparing with the steel treated by traditional quenching and tempering (Q&T) process, the mechanism of high ductility for high-carbon Q-P-T steel is revealed as follows. Much more retained austenite existing in Q-P-T steel than in Q&T one remarkably enhances the ductility by the following two effects: the dislocation absorption by retained austenite effect and the transformation-induced plasticity effect. Besides, lower dislocation density in martensite matrix produced by Q-P-T process plays an important role in the improvement of ductility. However, some thin plates of twin-type martensite embedded in dislocation-type martensite matrix in high-carbon Q-P-T steel affect the further improvement of ductility.

  5. Statistical analysis of the mechanical properties of thin walled ductile iron castings

    SciTech Connect

    Schrems, Karol K.; Hawk, Jeffrey A.; Dogan, Omer N.; Druschitz, A.P.

    2003-01-01

    Ductile iron castings have long been used in the automotive market. Ductile iron is inexpensive to produce and has desirable fracture resistance and mechanical properties. However, the weight of ductile iron is driving an effort to reduce wall thickness in order to increase fuel economy. Traditionally, cast iron has been cast into thick, bulky shapes. Reducing the section size of cast iron can be done, but pushes foundry practice into new areas. A consortium of foundries, foundry suppliers, and automotive manufacturers has been pursuing the use of thin walled ductile cast iron. This paper investigates the mechanical behavior of three experimental heats of thin-wall castings in order to evaluate property trends and limits. Castings as thin as 1.7 mm (0.07 in) have been successfully cast. The study was designed to investigate the effects of thickness and different casting heats on the dependent variables of ultimate tensile strength, yield strength, elongation-to-failure, reduction in area, and hardness. The ultimate tensile strength of the castings is found to increase as the casting thickness decreases. Conversely, the elongation-to-failure is found to decrease as the casting thickness decreases. Heat-to-heat differences were found, but they were usually within the scatter of the data.

  6. Atomistic aspects of ductile responses of cubic silicon carbide during nanometric cutting

    PubMed Central

    2011-01-01

    Cubic silicon carbide (SiC) is an extremely hard and brittle material having unique blend of material properties which makes it suitable candidate for microelectromechanical systems and nanoelectromechanical systems applications. Although, SiC can be machined in ductile regime at nanoscale through single-point diamond turning process, the root cause of the ductile response of SiC has not been understood yet which impedes significant exploitation of this ceramic material. In this paper, molecular dynamics simulation has been carried out to investigate the atomistic aspects of ductile response of SiC during nanometric cutting process. Simulation results show that cubic SiC undergoes sp3-sp2 order-disorder transition resulting in the formation of SiC-graphene-like substance with a growth rate dependent on the cutting conditions. The disorder transition of SiC causes the ductile response during its nanometric cutting operations. It was further found out that the continuous abrasive action between the diamond tool and SiC causes simultaneous sp3-sp2 order-disorder transition of diamond tool which results in graphitization of diamond and consequent tool wear. PMID:22078069

  7. A meshfree continuous-discontinuous approach for the ductile fracture modeling in explicit dynamics analysis

    NASA Astrophysics Data System (ADS)

    Wu, C. T.; Ma, N.; Takada, K.; Okada, H.

    2016-09-01

    This paper presents a combined continuous-discontinuous modeling technique for the dynamic ductile fracture analysis using an interactive particle enrichment algorithm and a strain-morphed nonlocal meshfree method. The strain-morphed nonlocal meshfree method is a nodel-integrated meshfree method which was recently proposed for the analysis of elastic-damage induced strain localization problems. In this paper, the strain-morphed nonlocal meshfree formulation is extended to the elastic-plastic-damage materials for the ductile fracture analysis. When the ductile material is fully degraded, the interactive particle enrichment scheme is introduced in the strain-morphed nonlocal meshfree formulation that permits a continuous-to-discontinuous failure modeling. The essence of the interactive particle enrichment algorithm is a particle insertion-deletion scheme that produces a visibility criterion for the description of a traction-free crack and leads to a better presentation of the ductile fracture process. Several numerical benchmarks are examined using the explicit dynamics analysis to demonstrate the effectiveness and accuracy of the proposed method.

  8. Significantly Increasing the Ductility of High Performance Polymer Semiconductors through Polymer Blending.

    PubMed

    Scott, Joshua I; Xue, Xiao; Wang, Ming; Kline, R Joseph; Hoffman, Benjamin C; Dougherty, Daniel; Zhou, Chuanzhen; Bazan, Guillermo; O'Connor, Brendan T

    2016-06-01

    Polymer semiconductors based on donor-acceptor monomers have recently resulted in significant gains in field effect mobility in organic thin film transistors (OTFTs). These polymers incorporate fused aromatic rings and have been designed to have stiff planar backbones, resulting in strong intermolecular interactions, which subsequently result in stiff and brittle films. The complex synthesis typically required for these materials may also result in increased production costs. Thus, the development of methods to improve mechanical plasticity while lowering material consumption during fabrication will significantly improve opportunities for adoption in flexible and stretchable electronics. To achieve these goals, we consider blending a brittle donor-acceptor polymer, poly[4-(4,4-dihexadecyl-4H-cyclopenta[1,2-b:5,4-b']dithiophen-2-yl)-alt-[1,2,5]thiadiazolo[3,4-c]pyridine] (PCDTPT), with ductile poly(3-hexylthiophene). We found that the ductility of the blend films is significantly improved compared to that of neat PCDTPT films, and when the blend film is employed in an OTFT, the performance is largely maintained. The ability to maintain charge transport character is due to vertical segregation within the blend, while the improved ductility is due to intermixing of the polymers throughout the film thickness. Importantly, the application of large strains to the ductile films is shown to orient both polymers, which further increases charge carrier mobility. These results highlight a processing approach to achieve high performance polymer OTFTs that are electrically and mechanically optimized. PMID:27200458

  9. 49 CFR 192.369 - Service lines: Connections to cast iron or ductile iron mains.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 49 Transportation 3 2012-10-01 2012-10-01 false Service lines: Connections to cast iron or ductile iron mains. 192.369 Section 192.369 Transportation Other Regulations Relating to Transportation... Customer Meters, Service Regulators, and Service Lines § 192.369 Service lines: Connections to cast iron...

  10. 49 CFR 192.369 - Service lines: Connections to cast iron or ductile iron mains.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 49 Transportation 3 2014-10-01 2014-10-01 false Service lines: Connections to cast iron or ductile iron mains. 192.369 Section 192.369 Transportation Other Regulations Relating to Transportation... Customer Meters, Service Regulators, and Service Lines § 192.369 Service lines: Connections to cast iron...

  11. 49 CFR 192.369 - Service lines: Connections to cast iron or ductile iron mains.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 49 Transportation 3 2010-10-01 2010-10-01 false Service lines: Connections to cast iron or ductile iron mains. 192.369 Section 192.369 Transportation Other Regulations Relating to Transportation... Customer Meters, Service Regulators, and Service Lines § 192.369 Service lines: Connections to cast iron...

  12. 49 CFR 192.369 - Service lines: Connections to cast iron or ductile iron mains.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 49 Transportation 3 2011-10-01 2011-10-01 false Service lines: Connections to cast iron or ductile iron mains. 192.369 Section 192.369 Transportation Other Regulations Relating to Transportation... Customer Meters, Service Regulators, and Service Lines § 192.369 Service lines: Connections to cast iron...

  13. 49 CFR 192.369 - Service lines: Connections to cast iron or ductile iron mains.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 49 Transportation 3 2013-10-01 2013-10-01 false Service lines: Connections to cast iron or ductile iron mains. 192.369 Section 192.369 Transportation Other Regulations Relating to Transportation... Customer Meters, Service Regulators, and Service Lines § 192.369 Service lines: Connections to cast iron...

  14. Brittle versus ductile deformation as the main control of the deep fluid circulation in continental crust

    NASA Astrophysics Data System (ADS)

    Violay, Marie; Madonna, Claudio; Burg, Jean-Pierre

    2016-04-01

    The Japan Beyond-Brittle Project (JBBP) and the Taupo Volcanic Zone-Deep geothermal drilling project in New Zealand (TVZ-DGDP) proposed a new concept of engineered geothermal development where reservoirs are created in ductile rocks. This system has several advantages including (1) a simpler design and control of the reservoir due to homogeneous rock properties and stress states in the ductile domain ,(2) possible extraction of supercritical fluids (3) less probability for induced earthquakes. However, it is at present unknwon what and how porosity and permeability can be engineered in such environments. It has been proposed that the magmatic chamber is surrounded by a hot and ductile carapace through which heat transfer is conductive because the plastic behaviour of the rock will close possible fluid pathways. Further outward, as temperature declines, the rock will encounter the brittle-ductile transition with a concomitant increase in porosity and permeability. The thickness of the conduction-dominated, ductile boundary zone between the magmatic chamber and the convecting geothermal fluid directly determines the rate of heat transfer. To examine the brittle to ductile transition in the context of the Japanese crust, we conducted deformation experiments on very-fine-grain granite in conventional servocontrolled, gas-medium triaxial apparatus (from Paterson instrument). Temperature ranged from 600° C to 1100° C and effective confining pressure from 100 to 150 MPa. Dilatancy was measured during deformation. The method consisted in monitoring the volume of pore fluid that flows into or out of the sample at constant pore pressure. Permeability was measured under static conditions by transient pressure pulse method. Mechanical and micro-structural observations at experimental constant strain rate of 10‑5 s‑1 indicated that the granite was brittle and dilatant up to 900 ° C. At higher temperatures the deformation mode becomes macroscopically ductile, i

  15. Ductility Enhancement of Molybdenum Phase by Nano-sized Oxide Dispersions

    SciTech Connect

    Kang, Bruce

    2008-07-18

    The objective of this research is to understand and to remedy the impurity effects for room-temperature ductility enhancement of molybdenum (Mo) based alloys by the inclusion of nano-sized metal oxide dispersions. This research combines theoretical, computational, and experimental efforts. The results will help to formulate systematic strategies in searching for better composed Mo-based alloys with optimal mechanical properties. For this project, majority of the research effort was directed to atomistic modeling to identify the mechanisms responsible for the oxygen embrittling and ductility enhancement based on fundamental electronic structure analysis. Through first principles molecular dynamics simulations, it was found that the embrittling impurity species were attracted to the metal oxide interface, consistent with previous experiments. Further investigation on the electronic structures reveals that the presence of embrittling species degrades the quality of the metallic chemical bonds in the hosting matrix in a number of ways, the latter providing the source of ductility. For example, the spatial flexibility of the bonds is reduced, and localization of the impurity states occurs to pin the dislocation flow. Rice’s criterion has been invoked to explain the connections of electronic structure and mechanical properties. It was also found that when impurity species become attracted to the metal oxide interface, some of the detrimental effects are alleviated, thus explaining the observed ductility enhancement effects. These understandings help to develop predictive capabilities to facilitate the design and optimization of Mo and other high temperature alloys (e.g. ODS alloys) for fossil energy materials applications. Based on the theoretical and computational studies, the experimental work includes the preparation of Mo powders mixed with candidate nano-sized metal oxides, which were then vacuum hot-pressed to make the Mo alloys. Several powder mixing methods

  16. Slip transfer across fault discontinuities within granitic rock at the brittle-ductile transition

    NASA Astrophysics Data System (ADS)

    Nevitt, J. M.; Pollard, D. D.; Warren, J. M.

    2011-12-01

    Fault mechanics are strongly influenced by discontinuities in fault geometry and constitutive differences between the brittle and ductile regions of the lithosphere. This project uses field observations, laboratory analysis and numerical modeling to investigate deformational processes within a contractional step at the brittle-ductile transition, and in particular, how slip is transferred between faults via ductile deformation across the step. The Bear Creek field area (central Sierra Nevada, CA) is comprised of late Cretaceous biotite-hornblende granodiorite and experienced a period of faulting at the brittle-ductile transition. Abundant echelon faults in Bear Creek, some of which were seismically active, provide many textbook examples of contractional steps, which are characterized by well-developed ductile fabrics. The occurrence of hydrothermal alteration halos and hydrothermal minerals in fracture fill documents the presence of water, which we suggest played a weakening role in the constitutive behavior of the granodiorite. Furthermore, the mechanism that accomplishes slip transfer in contractional steps appears to be related to water-enhanced ductile deformation. We focus our investigation on Outcrop SG10, which features a 10cm thick aplite dike that is offset 0.45m through a contractional step between two sub-parallel left-lateral faults. Within the step, the aplite undergoes dramatic thinning (stretch ~1/10) and the granodiorite is characterized by a well-developed mylonitic foliation, in which quartz and biotite plastically flow around larger grains of feldspars, hornblende and opaque minerals. Electron backscatter diffraction (EBSD) analysis gives a more quantitative depiction of the active micromechanics and reveals how slip is accommodated at the crystal scale throughout the step. We use Abaqus, a commercial finite element software, to test several constitutive laws that may account for the deformation observed both macro- and microscopically throughout

  17. Microscopic dynamics perspective on the relationship between Poisson's ratio and ductility of metallic glasses

    NASA Astrophysics Data System (ADS)

    Ngai, K. L.; Wang, Li-Min; Liu, Riping; Wang, W. H.

    2014-01-01

    In metallic glasses a clear correlation had been established between plasticity or ductility with the Poisson's ratio νPoisson and alternatively the ratio of the elastic bulk modulus to the shear modulus, K/G. Such a correlation between these two macroscopic mechanical properties is intriguing and is challenging to explain from the dynamics on a microscopic level. A recent experimental study has found a connection of ductility to the secondary β-relaxation in metallic glasses. The strain rate and temperature dependencies of the ductile-brittle transition are similar to the reciprocal of the secondary β-relaxation time, τβ. Moreover, metallic glass is more ductile if the relaxation strength of the β-relaxation is larger and τβ is shorter. The findings indicate the β-relaxation is related to and instrumental for ductility. On the other hand, K/G or νPoisson is related to the effective Debye-Waller factor (i.e., the non-ergodicity parameter), f0, characterizing the dynamics of a structural unit inside a cage formed by other units, and manifested as the nearly constant loss shown in the frequency dependent susceptibility. We make the connection of f0 to the non-exponentiality parameter n in the Kohlrausch stretched exponential correlation function of the structural α-relaxation function, φ (t) = exp [ { - ( {t/{τ _α }})^{1 - n} }]. This connection follows from the fact that both f0 and n are determined by the inter-particle potential, and 1/f0 or (1 - f0) and n both increase with anharmonicity of the potential. A well tested result from the Coupling Model is used to show that τβ is completely determined by τα and n. From the string of relations, (i) K/G or νPoisson with 1/f0 or (1 - f0), (ii) 1/f0 or (1 - f0) with n, and (iii) τα and n with τβ, we arrive at the desired relation between K/G or νPoisson and τβ. On combining this relation with that between ductility and τβ, we have finally an explanation of the empirical correlation between

  18. Ductility contrast induced by silicification in pelitic schist of the Ryoke metamorphic belt, Japan

    NASA Astrophysics Data System (ADS)

    Mateen, Tayyaba; Yamamoto, Hiroshi; Rehman, Hafiz Ur; Terabayashi, Masaru

    2015-11-01

    Contrasting ductility is recognized in the rocks of Cretaceous Ryoke metamorphic belt in Iwakuni area, southwest Japan. Pelitic schist is ubiquitous in the region and differences in mineral assemblages mark increase in metamorphic grade. The area has been graded as chlorite-biotite zone in the north progressing into biotite- and muscovite-cordierite zones in the south. Pelitic schist near the boundary between the biotite- and muscovite-cordierite zones has undergone partial silicification to form whitish silicified schist layers which contain two types of quartz veins: those parallel to foliation in the host rock are called schistosity-concordant veins, and those inclined to host rock foliation, schistosity-discordant veins. In this study we examined the quartz structure in the silicified schist and in both types of veins to understand the ductility contrast induced by the silicification process. Crystallographic orientations of quartz in the veins and silicified schist rocks were studied using the Scanning Electron Microscopy (SEM) based Electron Back Scatter Diffraction (EBSD) technique. Quartz c-axis orientations in the silicified schist are nearly random, demonstrating an absence of post-silicification ductile deformation. Quartz grains in the schistosity-concordant veins have preferred c-axis orientations perpendicular to the schistosity indicating ductile shortening. In contrast, schistosity-discordant veins display distinct quartz c-axis fabric than that found in the schistosity-concordant veins. This is because the two types of host rocks exhibit a difference in ductility during deformation. The presence of deformed quartz veins in the undeformed silicified schist indicates transformation of the ductile pelitic schist into the brittle silicified schist at mid-crustal levels where these rocks originate, hence forming contrasting rock layers. Schistosity-concordant veins in the biotite-rich pelitic schist deformed with its host rock in a ductile manner while

  19. Mechanical behavior and brittle-ductile transition of high-chromium martensitic steel

    NASA Astrophysics Data System (ADS)

    Odnobokova, M. V.; Kipelova, A. Yu.; Belyakov, A. N.; Kaibyshev, R. O.

    2016-04-01

    The article presents data on the static tensile tests and dynamic impact-toughness tests of a highchromium martensitic 10Kh9V1M1FBR steel (0.12 wt % C, 9.8 wt % Cr, 0.93 wt % W, 1.01 wt % Mo, 0.2 wt % V, 0.05 wt % Nb, 0.05 wt % N, 0.003 wt % B, 0.36 wt % Mn, 0.2 wt % Ni, 0.06 wt % Si, 0.01 wt % P, 0.008 wt % S, 0.02 wt % Cu, 0.1 wt % Co, 0.015 wt % Al, and the remainder is Fe) in the temperature range from 20 to-196°C. In the case of static loading, a reduction in the temperature leads to an increase in the strength characteristics; upon a drop in the temperature from 20 to-100°C, the plasticity also increases. This is connected with the fact that the ductile fracture remains the basic mechanism down to cryogenic temperatures. The brittle-ductile transition related to the transition from ductile intragranular fracture to quasibrittle one is observed at-45°C. The steel exhibits high impact toughness to the temperature of-60°C ( KCV -60 = 95 J/cm2), at which the fraction of the ductile component in fracture is equal to 20%. At 80°C, the impact toughness decreases down to critical values (30 J/cm2), which correlates with the decrease in the fraction of the ductile component on the fracture surface down to 1%. The further decrease in the impact toughness down to 10 J/cm2 at-196°C is related to the transition from intragranular to intergranular brittle fracture.

  20. Evaluation of static and dynamic fracture toughness in ductile cast iron

    SciTech Connect

    Kobayashi, Toshiro; Yamada, Shinya . Dept. of Production Systems Engineering)

    1994-11-01

    Ductile cast irons have been explored as a cask (container for spent nuclear fuel) material because of their low cost and good formability. The cask, which is a huge casting with 400-mm thickness and 100-Mg weight, envelops the nuclear material. Therefore, the fracture toughness of cask must be evaluated not only under the static loading condition but also under the dynamic loading condition to ensure its safety against an accident during the transport. In this article, crack extension behavior and fracture toughness of ductile cast iron were examined by three-point bend tests, where various detection methods of crack initiation under static and dynamic loading conditions were adopted. Loading on the specimens was interrupted at various displacement points, and the final fracture surfaces of the specimen were observed via scanning electron microscopy (SEM). Crack-tip opening displacement (CTOD) obtained under the dynamic loading conditions was smaller than that under the static loading condition in ferritic ductile cast iron, and CTOD additionally decreased with increasing pearlite content in the matrix. The relationship between J([Delta]C) obtained by the compliance changing rate method and J(R) established by the intersection of the crack extension resistance curve and the theoretical blunting line varied with pearlite content. The average value of J([Delta]C) and J(R), that is J(mid), was proposed to define the fracture toughness of ductile cast iron; J(mid) was considered to be a reasonable measure for the fracture toughness of ductile cast iron, irrespective of loading condition and the pearlite content in the matrix.

  1. Metastable high-entropy dual-phase alloys overcome the strength-ductility trade-off.

    PubMed

    Li, Zhiming; Pradeep, Konda Gokuldoss; Deng, Yun; Raabe, Dierk; Tasan, Cemal Cem

    2016-06-01

    Metals have been mankind's most essential materials for thousands of years; however, their use is affected by ecological and economical concerns. Alloys with higher strength and ductility could alleviate some of these concerns by reducing weight and improving energy efficiency. However, most metallurgical mechanisms for increasing strength lead to ductility loss, an effect referred to as the strength-ductility trade-off. Here we present a metastability-engineering strategy in which we design nanostructured, bulk high-entropy alloys with multiple compositionally equivalent high-entropy phases. High-entropy alloys were originally proposed to benefit from phase stabilization through entropy maximization. Yet here, motivated by recent work that relaxes the strict restrictions on high-entropy alloy compositions by demonstrating the weakness of this connection, the concept is overturned. We decrease phase stability to achieve two key benefits: interface hardening due to a dual-phase microstructure (resulting from reduced thermal stability of the high-temperature phase); and transformation-induced hardening (resulting from the reduced mechanical stability of the room-temperature phase). This combines the best of two worlds: extensive hardening due to the decreased phase stability known from advanced steels and massive solid-solution strengthening of high-entropy alloys. In our transformation-induced plasticity-assisted, dual-phase high-entropy alloy (TRIP-DP-HEA), these two contributions lead respectively to enhanced trans-grain and inter-grain slip resistance, and hence, increased strength. Moreover, the increased strain hardening capacity that is enabled by dislocation hardening of the stable phase and transformation-induced hardening of the metastable phase produces increased ductility. This combined increase in strength and ductility distinguishes the TRIP-DP-HEA alloy from other recently developed structural materials. This metastability-engineering strategy should

  2. Metastable high-entropy dual-phase alloys overcome the strength–ductility trade-off

    NASA Astrophysics Data System (ADS)

    Li, Zhiming; Pradeep, Konda Gokuldoss; Deng, Yun; Raabe, Dierk; Tasan, Cemal Cem

    2016-06-01

    Metals have been mankind’s most essential materials for thousands of years; however, their use is affected by ecological and economical concerns. Alloys with higher strength and ductility could alleviate some of these concerns by reducing weight and improving energy efficiency. However, most metallurgical mechanisms for increasing strength lead to ductility loss, an effect referred to as the strength–ductility trade-off. Here we present a metastability-engineering strategy in which we design nanostructured, bulk high-entropy alloys with multiple compositionally equivalent high-entropy phases. High-entropy alloys were originally proposed to benefit from phase stabilization through entropy maximization. Yet here, motivated by recent work that relaxes the strict restrictions on high-entropy alloy compositions by demonstrating the weakness of this connection, the concept is overturned. We decrease phase stability to achieve two key benefits: interface hardening due to a dual-phase microstructure (resulting from reduced thermal stability of the high-temperature phase); and transformation-induced hardening (resulting from the reduced mechanical stability of the room-temperature phase). This combines the best of two worlds: extensive hardening due to the decreased phase stability known from advanced steels and massive solid-solution strengthening of high-entropy alloys. In our transformation-induced plasticity-assisted, dual-phase high-entropy alloy (TRIP-DP-HEA), these two contributions lead respectively to enhanced trans-grain and inter-grain slip resistance, and hence, increased strength. Moreover, the increased strain hardening capacity that is enabled by dislocation hardening of the stable phase and transformation-induced hardening of the metastable phase produces increased ductility. This combined increase in strength and ductility distinguishes the TRIP-DP-HEA alloy from other recently developed structural materials. This metastability-engineering strategy

  3. A diffraction based study of the deformation mechanisms in anomalously ductile B2 intermetallics

    NASA Astrophysics Data System (ADS)

    Mulay, Rupalee Prashant

    For many decades, the brittle nature of most intermetallic compounds (e.g. NiAl) has been the limiting factor in their practical application. Many B2 (CsCl prototypical structure) intermetallics are known to exhibit slip on the <001>{110} slip mode, which provides only 3 independent slip systems and, hence, is unable to satisfy the von Mises (a.k.a. Taylor) criterion for polycrystalline ductility. As a result, inherent polycrystalline ductility is unexpected. Recent discovery of a number of ductile B2 intermetallics has raised questions about possible violation of the von Mises criterion by these alloys. These ductile intermetallic compounds are MR (metal (M) combined with a rare earth metal or group IV refractory metal (R)) alloys and are stoichiometric, ordered compounds. Single crystal slip trace analyses have only identified the presence of <100>{011} or <100>{010} slip systems. More than 100 other B2 MR compounds are known to exist and many of them have already been shown to be ductile (e.g., CuY, AgY, CuDy, CoZr, CoTi, etc.). Furthermore, these alloys exhibit a large Bauschinger effect. The present work uses several diffraction based techniques including electron back scattered diffraction (EBSD), X-ray diffraction (XRD) and in-situ neutron diffraction; in conjunction with scanning electron microscopy (SEM), transmission electron microscopy (TEM), mechanical testing, and crystal plasticity modeling, to elucidate the reason for ductility in select B2 alloys, explore the spread of this ductility over the B2 family, and understand the Bauschinger effect in these alloys. Several possible explanations (e.g., slip of <111> dislocations, strong texture, phase transformations and twinning) for the anomalous ductility were explored. An X-ray diffraction based analysis ruled out texture, phase purity and departure from order as explanations for the anomalous ductility in MR alloys. In-situ neutron diffraction and post deformation SEM, EBSD, and TEM were unable to

  4. Parametric study of irradiation effects on the ductile damage and flow stress behavior in ferritic-martensitic steels

    NASA Astrophysics Data System (ADS)

    Chakraborty, Pritam; Biner, S. Bulent

    2015-10-01

    Ferritic-martensitic steels are currently being considered as structural materials in fusion and Gen-IV nuclear reactors. These materials are expected to experience high dose radiation, which can increase their ductile to brittle transition temperature and susceptibility to failure during operation. Hence, to estimate the safe operational life of the reactors, precise evaluation of the ductile to brittle transition temperatures of ferritic-martensitic steels is necessary. Owing to the scarcity of irradiated samples, particularly at high dose levels, micro-mechanistic models are being employed to predict the shifts in the ductile to brittle transition temperatures. These models consider the ductile damage evolution, in the form of nucleation, growth and coalescence of voids; and the brittle fracture, in the form of probabilistic cleavage initiation, to estimate the influence of irradiation on the ductile to brittle transition temperature. However, the assessment of irradiation dependent material parameters is challenging and influences the accuracy of these models. In the present study, the effects of irradiation on the overall flow stress and ductile damage behavior of two ferritic-martensitic steels is parametrically investigated. The results indicate that the ductile damage model parameters are mostly insensitive to irradiation levels at higher dose levels though the resulting flow stress behavior varies significantly.

  5. Progressive deformation structures associated with ductile thrusts in the Moine Nappe, Sutherland, N. Scotland

    NASA Astrophysics Data System (ADS)

    Holdsworth, Robert E.

    In the deeper parts of mountain belts, polyphase structural sequences observed at outcrop-scale can arise due either to overprinting of regionally distinct deformation phases (e.g. reworking, changes in orogenic boundary conditions), or to localized controls that bring about transient changes in the patterns of ductile flow. These are unlikely to be mutually exclusive processes, and examples from Scotland demonstrate that, once regionally separate events are delimited using radiometric evidence, it is possible to isolate complex deformation sequences arising due to local controls. In the western Moine Nappe of Sutherland, the dominant structures were formed during Caledonian ductile thrusting towards the WNW, whilst earlier (?Precambrian) phases are relatively minor in importance. Two groups of Caledonian folds and fabrics are recognized in many exposures: main phase ( D2) structures which are broadly contemporaneous with ductile thrust fabrics, and later secondary phase ( F3) folds. The latter can be divided into two geometric groups: sheath-fold types which formed initially as WNW-overturned buckles subsequently modified by ductile shearing; and asymmetric types, which are commonly open folds apparently formed with axes close or sub-parallel to the thrust transport direction. Secondary structures show a close spatial association with high strain zones along ductile thrusts, and can be shown to have formed during the later stages of thrusting in certain critical exposures. I propose that they may form due to strain perturbations resulting from variations in the relative rates of ductile flow within the mylonites. Where differential shearing occurs due to flow-normal perturbations, wrench-related asymmetric fold types may form. In contrast, secondary sheath-fold structures may result from localized compression phases caused by flow-parallel perturbations. Local flow-perturbation models may be appropriate in situations where the distribution of later structures is

  6. Antiformal closure in ductile and brittle-ductile in fold-and-thrust belt tranverse zones, Moine Thrust Belt, NW Scotland

    NASA Astrophysics Data System (ADS)

    Leslie, G.; Krabbendam, M.

    2009-04-01

    Abrupt lateral changes in thrust geometry occur in many mountain-building fold-and-thrust belts. Such changes in architecture are referred to as so-called transverse zones, and are commonly thought to be related to kinematic responses to irregularities generated across pre-existing, sometimes re-activated, basement faults. In many cases however the causative structure is concealed, either by distal parts of the thrust belt or the foreland basin. Sharp lateral changes in the structural geometry of ductile thrust stacks are less widely studied and reported. In NW Scotland, the classic Caledonian WNW-vergent Moine Thrust Belt exposes excellent examples of the structural architecture in such transverse zones, both in kilometre-scale thick monolithic (meta-)sandstone packages subject to ductile deformation, and in much thinner heterolithic packages subject to brittle-ductile deformation. In both cases the amplitude of the antiformal disturbance associated with the transverse zone is much greater than amplitude of any irregularity identified in the basement below. In Neoproterozoic Moine rocks in the hanging wall of the Moine Thrust, a large-scale lateral culmination wall forms a component part of the Oykel Transverse Zone (OTZ), a kilometre-scale thick constrictional ductile shear zone striking sub-parallel to the WNW-directed thrust transport direction. The OTZ forms the SW limit of the Cassley Culmination. ESE-plunging mullions are an integral part of the fabric of the transverse zone and were generated by constriction sub-parallel to the WNW-directed thrust transport direction. Main folds and fabrics in the transverse zone hanging-wall are folded by main folds and fabrics in the footwall, demonstrating the overall foreland-propagating record of ductile deformation as the Cassley Culmination grew. Constriction and mullion development are attributed to differential, transtensional movement across the transverse zone during the later stages of culmination development

  7. Implications of radiation-induced reductions in ductility to the design of austenitic stainless steel structures

    SciTech Connect

    Lucas, G.E.; Billone, M.; Pawel, J.E.; Hamilton, M.L.

    1995-12-31

    In the dose and temperature range anticipated for ITER, austenitic stainless steels exhibit significant hardening with a concomitant loss in work hardening and uniform elongation. However, significant post-necking ductility may still be retained. When uniform elongation (e{sub u}) is well defined in terms of a plastic instability criterion, e{sub u} is found to sustain reasonably high values out to about 7 dpa in the temperature range 250-350 C, beyond which it decreases to about 0.3% for 316LN. This loss of ductility has significant implications to fracture toughness and the onset of new failure modes associated with hear instability. However, the retention of a significant reduction in area at failure following irradiation indicates a less severe degradation of low-cycle fatigue life in agreement with a limited amount of data obtained to date. Suggestions are made for incorporating these results into design criteria and future testing programs.

  8. The potential for ductility enhancement from surface and interface dislocation sources in NiAl

    NASA Technical Reports Server (NTRS)

    Noebe, R. D.; Bowman, R. R.; Kim, J. T.; Larsen, M.; Gibala, R.

    1990-01-01

    Limited ductility and toughness of NiAl and related aluminides near room temperature pose major problems in their potential application as structural materials. An analysis of these problems is presented as part of a review of the flow and fracture behavior of binary NiAl. Following this discussion is a demonstration that conditions of elastic and plastic constraint associated with phase boundaries afforded by surface films, internal lamellae, or precipitates may introduce sufficient densities of mobile dislocations to enhance the ductility of NiAl-based materials by significant amounts. Examples of this behavior are presented for several model materials, including 001- and 123-oriented single crystals of oxide-coated NiAl, directionally solidified beta-gamma-prime (Ni70Al30) and beta-gamma (Ni50Fe30Al20) in situ composites, and several NiAl/precipitate systems. The nature of the resulting dislocation substructures and the effects of several materials variables are described.

  9. Effect of alloying on electronic structure, strength and ductility characteristics of nickel aluminide

    NASA Astrophysics Data System (ADS)

    Kovalev, A. I.; Barskaya, R. A.; Wainstein, D. L.

    2003-06-01

    The possibility of production of alloyed NiAl intermetallic compound having satisfactory processing ductility at room temperature has been investigated. The samples were made by extrusion of sintered powder blanks. The effect of Fe, Cr, Co, Mo, B and La doping on mechanical properties of nickel aluminide was investigated. Alloying has a beneficial effect on decrease of the ductile-brittle transition temperature and micro-mechanism of fracture. The doping of nickel aluminide by Fe (2 at.%), Mo (2 at.%) and Co(2 at.%) was studied by valence band XPS and plasmon losses electron spectroscopy. The shift of the Fermi level ( EF) and variation of density of conduction electrons - neff were found in doped NiAl. The results show good correlation between EFneff and micro-hardness of alloyed NiAl intermetallic.

  10. Smart fiber-reinforced polymer rods featuring improved ductility and health monitoring capabilities

    NASA Astrophysics Data System (ADS)

    Belarbi, Abdeldjelil; Watkins, Steve E.; Chandrashekhara, K.; Corra, Josh; Konz, Bethany

    2001-06-01

    The strain-measuring capability of fiber optic strain gages in fiber-reinforced polymer (FRP) rebars was investigated for failure-inducing loads. Fiber optic interferometric sensors were embedded in a pultruded carbon fiber core and then another layer of carbon fibers were filament wound around the core to form a shell. Pultrusion and filament winding techniques protect the fiber optic strain gages from the concrete environment while providing a secure bond to the core and additional ductility to the overall FRP rebar. Tests of coupon FRP rebar and of FRP-rebar-reinforced concrete beams show that the fiber optic strain gages can read internal strain through failure and can duplicate data from conventional linear variable differential transformers and electrical resistance strain gages. Also, the shell of the FRP rebar inside the concrete beams failed before the rebar core providing pseudo-ductility.

  11. Numerical simulation of damage evolution for ductile materials and mechanical properties study

    NASA Astrophysics Data System (ADS)

    El Amri, A.; Hanafi, I.; Haddou, M. E. Y.; Khamlichi, A.

    2015-12-01

    This paper presents results of a numerical modelling of ductile fracture and failure of elements made of 5182H111 aluminium alloys subjected to dynamic traction. The analysis was performed using Johnson-Cook model based on ABAQUS software. The modelling difficulty related to prediction of ductile fracture mainly arises because there is a tremendous span of length scales from the structural problem to the micro-mechanics problem governing the material separation process. This study has been used the experimental results to calibrate a simple crack propagation criteria for shell elements of which one has often been used in practical analyses. The performance of the proposed model is in general good and it is believed that the presented results and experimental-numerical calibration procedure can be of use in practical finite-element simulations.

  12. Multi-Response Optimization of Carbidic Austempered Ductile Iron Production Parameters using Taguchi Method

    NASA Astrophysics Data System (ADS)

    Dhanapal, P.; Mohamed Nazirudeen, S. S.; Chandrasekar, A.

    2012-04-01

    Carbide Austempered Ductile Iron (CADI) is the family of ductile iron containing wear resistance alloy carbides in the ausferrite matrix. This CADI is manufactured by selecting and characterizing the proper material composition through the melting route done. In an effort to arrive the optimal production parameters of multi responses, Taguchi method and Grey relational analysis have been applied. To analyze the effect of production parameters on the mechanical properties signal-to-noise ratio and Grey relational grade have been calculated based on the design of experiments. An analysis of variance was calculated to find the amount of contribution of factors on mechanical properties and their significance. The analytical results of Taguchi method were compared with the experimental values, and it shows that both are identical.

  13. Flow of mantle fluids through the ductile lower crust: Heliumisotope trends

    SciTech Connect

    Kennedy, B. Mack; van Soest, Matthijs C.

    2007-10-07

    Heat and mass are injected into the shallow crust when mantle fluids are able to flow through the ductile lower crust. Minimum 3He/4He ratios in surface fluids from the northern Basin and Range province, western North America increase systematically from low, crustal values in the east to high, mantle values in the west, a regional trend that correlates with the rates of active crustal deformation. The highest ratios occur where the extension and shear strain rates are greatest. The correspondence of helium isotope ratios and active trans-tensional deformation indicates a deformation enhanced permeability and that mantle fluids can penetrate the ductile lithosphere in regions even where there is no significant magmatism. Superimposed on the regional trend are local, high-{sup 3}He/{sup 4}He anomalies signifying hidden magmatic activity and/or deep fluid production with locally enhanced permeability, identifying zones with high resource potential, particularly for geothermal energy development.

  14. Linking Nanoscales and Dislocation Shielding to the Ductile-Brittle Transition of Silicon

    NASA Astrophysics Data System (ADS)

    Hintsala, Eric; Teresi, Claire; Gerberich, William W.

    2016-06-01

    The ductile-brittle transition of nano/microscale silicon is explored at low-temperature, high stress conditions. A pathway to eventual mechanism maps describing this ductile-brittle transition behavior using sample size, strain rate, and temperature is outlined. First, a discussion of variables controlling the BDT in silicon is given and discussed in the context of development of eventual modeling that could simultaneously incorporate all their effects. For description of energy dissipation by dislocation nucleation from a crack tip, three critical input parameters are identified: the effective stress, activation volume, and activation energy for dislocation motion. These are discussed individually relating to the controlling variables for the BDT. Lastly, possibilities for measuring these parameters experimentally are also described.

  15. Influence of casting size and graphite nodule refinement on fracture toughness of austempered ductile iron

    SciTech Connect

    Lee, S.C.; Hsu, C.H.; Chang, C.C.; Feng, H.P.

    1998-10-01

    Casting size affects the solidification cooling rate and microstructure of casting materials. Graphite nodules existing in the structure of ductile iron are an inherent and inert second phase that cannot be modified in subsequent heat-treatment processing. The matrix and the fineness of the second phase undoubtedly have some impact on the fracture toughness of the as-cast material, as does the subsequent heat treatment, as it alters the microstructure. This research applied austempering heat treatment to ductile iron of different section sizes and graphite nodule finenesses. The influence of these variables on the plane strain fracture toughness (K{sub IC}) of the castings so treated was compared to that of the as-cast state. Metallography, scanning electron microscopy (SEM), and X-ray diffraction analysis were performed to correlate the properties attained to the microstructural observation.

  16. The morphology of solidification of thin-section ductile iron castings

    SciTech Connect

    Yeung, C.F.; Zhao, H.; Lee, W.B.

    1998-04-01

    The morphology of solidified structures of thin-section ductile iron castings has been investigated by color metallographic techniques. Primary austenitic dendrites were observed to be formed over the whole section of castings when the wall thickness was less than 14mm. The dendrites were thin and long, and the length and the number of dendrites depended on the solidification rate or the wall thickness of the casting. Growth of the dendritic arms was directional, being perpendicular to the surface of castings and along the wall thickness. Interdendrite segregation of Si and Mn is found to occur in thin-section ductile iron castings, as revealed by both color metallography and energy dispersive X-ray microanalysis. The segregation is more pronounced toward the center of castings.

  17. Theoretical investigation on improving the ductility of Rh{sub 3}V by ternary addition

    SciTech Connect

    Manjula, M.; Sundareswari, M. Jayalakshmi, D. S.; Viswanathan, E.

    2015-06-24

    The band structure calculations are performed on the intermetallic compounds Rh{sub 3}V and Rh{sub 3}V{sub x}(Al){sub 1-x} by Full Potential Linearized Augmented Plane Wave(FP-LAPW) method. Total energies are calculated as a function of volume and fitted to Birch-Murnaughan equation of state to find the lattice parameter and the other ground state properties. The ductility of these compounds has been analyzed using Cauchy’s Pressure, Pugh Rule and Poisson’s ratio. From this study we observed that Rh{sub 3}V is brittle while its alloy Rh{sub 3}V{sub 0.875}Al{sub 0.125} is ductile. Electron density plots are illustrated and compared.

  18. Production and Machining of Thin Wall Gray and Ductile Cast Iron

    SciTech Connect

    Fleischman, E.H.; Li, H.; Griffin, R.; Bates, C.E.; Eleftheriou, E.

    2000-11-03

    The University of Alabama at Birmingham, in cooperation with the American Foundry Society, companies across North America, with support from the U.S. Department of Energy, is conducting a project to develop an understanding of the factors that control the machinability of cast gray and ductile iron. Differences of as much as 500% have been found in machinability have been observed at the same strength. The most machinable irons were those with a high cell counts and few carbonitride inclusions. Additions of tin and copper can be added to both gray and ductile iron to stabilize the pearlite, but excessive additions (above those required to produce the desired pearlite content) degrade the machinability.

  19. The abrasion and impact-abrasion behavior of austempered ductile irons

    SciTech Connect

    Hawk, Jeffrey A.; Dogan, Omer N.; Lerner, Y.S.

    1998-01-01

    Austempering of ductile irons has led to a new class of irons, Austempered Ductile Irons (ADIs), with improved mechanical strength and fracture toughness lacking in gray cast irons. Laboratory wear tests have been used to evaluate the abrasive and impact-abrasive wear behavior of a suite of ADIs. The use of high-stress, two-body abrasion, low-stress, three-body abrasion, and impact-abrasion tests provides a clear picture of the abrasive wear behavior of the ADIs and the mechanisms of material removal. When combined with hardness measurements, fracture toughness and a knowledge of the microstructure of the ADIs, the overall performance can be assessed relative to more wear resistant materials such as martensitic steels and high-chromium white cast irons

  20. Ductility of metal alloys with grain size distribution in a wide range of strain rates

    NASA Astrophysics Data System (ADS)

    Skripnyak, Vladimir V.; Skripnyak, Nataliya V.; Skripnyak, Evgeniya G.

    Ductility of ultrafine grained (UFG) metal alloys with a distribution of grain size was investigated in wide loading conditions by numerical simulation. The multiscale models with a unimodal and a bimodal grain size distributions were developed using the data of structure research of hexagonal close packed and face center cubic UFG alloys. Macroscopic fracture is considered as a result of the formation of percolation clusters of damage at the mesoscopic level. The critical fracture strain of UFG alloys on the mesoscale level depends on the relative volumes of coarse grains. The nucleation of damages at quasi-static and dynamic loading is associated with strain localization in UFG partial volumes with bimodal grain size distribution. The concentration of damages arise in the vicinity of the boundaries of coarse and ultrafine grains. The occurrence of a bimodal grain size distributions causes the increase of UFG alloys' ductility, but decrease of their tensile strength. Linkoping University, Sweden.

  1. Flow of mantle fluids through the ductile lower crust: helium isotope trends.

    PubMed

    Kennedy, B Mack; van Soest, Matthijs C

    2007-11-30

    Heat and mass are injected into the shallow crust when mantle fluids are able to flow through the ductile lower crust. Minimum 3He/4He ratios in surface fluids from the northern Basin and Range Province, western North America, increase systematically from low crustal values in the east to high mantle values in the west, a regional trend that correlates with the rates of active crustal deformation. The highest ratios occur where the extension and shear strain rates are greatest. The correspondence of helium isotope ratios and active transtensional deformation indicates a deformation-enhanced permeability and that mantle fluids can penetrate the ductile lithosphere, even in regions where there is no substantial magmatism. Superimposed on the regional trend are local, high 3He/4He anomalies indicating hidden magmatic activity and/or deep fluid production with locally enhanced permeability, identifying zones with high resource potential, particularly for geothermal energy development. PMID:18048684

  2. Cumulative-strain-damage model of ductile fracture: simulation and prediction of engineering fracture tests

    SciTech Connect

    Wilkins, M.L.; Streit, R.D.; Reaugh, J.E.

    1980-10-03

    A cumulative-strain-damage criterion is used to predict the initiation and propagation of fracture in ductile materials. The model is consistent with a model of ductile rupture that involves void growth and coalescence. Two- and three-dimensional finite difference computer codes, which use incremental-plasticity theory to describe large strains with rotation, are used to trace the history of damage in a material due to external forces. Fracture begins when the damage exceeds a critical value over a critical distance and proceeds as the critical-damage state is reached elsewhere. This unified approach to failure prediction can be applied to an arbitrary geometry if the material behavior has been adequately characterized. The damage function must be calibrated for a particular material using various material property tests. The fracture toughness of 6061-T651 aluminum is predicted.

  3. A Unified Cohesive Zone Approach to Model Ductile Brittle Transition in Reactor Pressure Vessel Steels

    SciTech Connect

    Pritam Chakraborty; S. Bulent Biner

    2014-08-01

    In this study, a unified cohesive zone model has been proposed to predict, Ductile to Brittle Transition, DBT, in Reactor Pressure Vessel, RPV, steels. A general procedure is described to obtain the Cohesive Zone Model, CZM, parameters for the different temperatures and fracture probabilities. In order to establish the full master-curve, the procedure requires three calibration points with one at the upper-shelf for ductile fracture and two for the fracture probabilities, Pf, of 5% and 95% at the lower-shelf. In the current study, these calibrations were carried out by utilizing the experimental fracture toughness values and flow curves. After the calibration procedure, the simulations of fracture behavior (ranging from completely unstable to stable crack extension behavior) in one inch thick compact tension specimens at different temperatures yielded values that were comparable to the experimental fracture toughness values, indicating the viability of such unified modeling approach.

  4. RECENT PROGRESS IN THE DEVELOPMENT OF DUCTILE-PHASE TOUGHENED TUNGSTEN FOR PLASMA-FACING MATERIALS

    SciTech Connect

    Henager, Charles H.; Kurtz, Richard J.; Roosendaal, Timothy J.; Borlaug, Brennan A.; Setyawan, Wahyu; Wagner, Karla B.; Odette, G Robert; Cunningham, Kevin; Fields, Kirk A.; Gragg, David; Zok, Frank W.

    2014-09-30

    A promising approach to increasing fracture toughness and decreasing the DBTT of a W-alloy is by ductile-phase toughening (DPT) [1-3]. In this method, a ductile phase is included in a brittle matrix to prevent fracture propagation by crack bridging. To examine the prospect of DPT, W-Cu three-point bend samples were deformed at several strain rates and temperatures. Data from these tests is used for the calibration of a dynamic crack-bridging model that can effectively predict elevated temperature crack growth in W-composites. The development and initial testing of a Cu-ligament bridging model based on a micromechanical flow stress model of Cu is discussed. Good agreement with the 3-point bend testing data is demonstrated along with future plans to improve the model.

  5. Strength and ductility with {10͞11} - {10͞12} double twinning in a magnesium alloy.

    PubMed

    Lentz, M; Risse, M; Schaefer, N; Reimers, W; Beyerlein, I J

    2016-01-01

    Based on their high specific strength and stiffness, magnesium alloys are attractive for lightweight applications in aerospace and transportation, where weight saving is crucial for the reduction of carbon dioxide emissions. Unfortunately, the ductility of magnesium alloys is usually limited. It is thought that one reason for the lack of ductility is that the development of - double twins (DTW) cause premature failure of magnesium alloys. Here we show with a magnesium alloy containing 4 wt% lithium, that the same impressively large compression failure strains can be achieved with DTWs as without. The DTWs form stably across the microstructure and continuously throughout straining, forming three-dimensional intra-granular networks, a potential strengthening mechanism. We rationalize that relatively easier slip characteristic of this alloy plastically relaxed the localized stress concentrations that DTWs can generate. This result may provide key insight and an alternative perspective towards designing formable and strong magnesium alloys. PMID:27040648

  6. Manipulating the interfacial structure of nanomaterials to achieve a unique combination of strength and ductility

    NASA Astrophysics Data System (ADS)

    Khalajhedayati, Amirhossein; Pan, Zhiliang; Rupert, Timothy J.

    2016-02-01

    The control of interfaces in engineered nanostructured materials has met limited success compared with that which has evolved in natural materials, where hierarchical structures with distinct interfacial states are often found. Such interface control could mitigate common limitations of engineering nanomaterials. For example, nanostructured metals exhibit extremely high strength, but this benefit comes at the expense of other important properties like ductility. Here, we report a technique for combining nanostructuring with recent advances capable of tuning interface structure, a complementary materials design strategy that allows for unprecedented property combinations. Copper-based alloys with both grain sizes in the nanometre range and distinct grain boundary structural features are created, using segregating dopants and a processing route that favours the formation of amorphous intergranular films. The mechanical behaviour of these alloys shows that the trade-off between strength and ductility typically observed for metallic materials is successfully avoided here.

  7. Manipulating the interfacial structure of nanomaterials to achieve a unique combination of strength and ductility.

    PubMed

    Khalajhedayati, Amirhossein; Pan, Zhiliang; Rupert, Timothy J

    2016-01-01

    The control of interfaces in engineered nanostructured materials has met limited success compared with that which has evolved in natural materials, where hierarchical structures with distinct interfacial states are often found. Such interface control could mitigate common limitations of engineering nanomaterials. For example, nanostructured metals exhibit extremely high strength, but this benefit comes at the expense of other important properties like ductility. Here, we report a technique for combining nanostructuring with recent advances capable of tuning interface structure, a complementary materials design strategy that allows for unprecedented property combinations. Copper-based alloys with both grain sizes in the nanometre range and distinct grain boundary structural features are created, using segregating dopants and a processing route that favours the formation of amorphous intergranular films. The mechanical behaviour of these alloys shows that the trade-off between strength and ductility typically observed for metallic materials is successfully avoided here. PMID:26887444

  8. Brittle-to-ductile transition of lithiated silicon electrodes: Crazing to stable nanopore growth

    SciTech Connect

    Wang, Haoran; Chew, Huck Beng; Wang, Xueju; Xia, Shuman

    2015-09-14

    Using first principle calculations, we uncover the underlying mechanisms explaining the brittle-to-ductile transition of Li{sub x}Si electrodes in lithium ion batteries with increasing Li content. We show that plasticity initiates at x = ∼ 0.5 with the formation of a craze-like network of nanopores separated by Si–Si bonds, while subsequent failure is still brittle-like with the breaking of Si–Si bonds. Transition to ductile behavior occurs at x ⩾ 1 due to the increased density of highly stretchable Li–Li bonds, which delays nanopore formation and stabilizes nanopore growth. Collapse of the nanopores during unloading of the Li{sub x}Si alloys leads to significant strain recovery.

  9. Effect of prestraining on the brittle-to-ductile transition of NiAl single crystals

    SciTech Connect

    Shrivastava, S.; Ebrahimi, F.

    1997-12-31

    The brittle-to-ductile transition (BDT) has been established for NiAl single crystals as evaluated by fracture toughness testing and also the effects of prestraining on the brittle-to-ductile transition temperature (BDTT) have been investigated. Specimens were prestrained to a 10% plastic strain level at 200 C under tension prior to toughness testing. The BDT of the prestrained specimens was compared to that of the as homogenized specimens. The results have revealed the occurrence of two competing effects upon prestraining: (1) an increase in dislocation sources causing a difficulty in micro-crack initiation and resulting in an increase in toughness at low temperatures, and (2) an increase in the flow stress resulting in an increase in BDT temperature. The crack initiation and propagation mechanisms were also analyzed and have been discussed.

  10. Ductile-brittle transition behavior of tungsten under shock loading conditions

    SciTech Connect

    Lassila, D.H.; Gray, G.T. III

    1993-02-01

    In an effort to characterize the ductile-brittle transition behavior of warm forged tungsten under shock loading conditions, we have performed shock/soft-recovery experiments at 22 and 4000 C. Results at 22 C indicate that shock (19 GPa) induced strains appear to be accommodated by fracture processes, i.e. there were no indications of shock induced plastic deformation and the test sample was reduced to rubble. At 400 C, the test sample was recovered intact and the shock induced plasticity caused deformation banding and an increase in the dislocation density of the material. For reasons unclear, almost no change in the post shock mechanical behavior was observed, despite the significant changes in the microstructure. The results of these experiments demonstrate the principal of a ductile-brittle transition behavior of tungsten under uniaxial shock loading conditions and indicate that explosively driven deformation of tungsten of this material will result in pulverization due to shock loading.

  11. Ductile fracture of pipes and cylindrical containers with a circumferential flaw

    SciTech Connect

    Erdogan, F.; Delale, F.

    1981-05-01

    The problem of ductile fracture of a pipe or cylindrical container having a relatively long and deep circumferential part-through crack or through a crack and subjected to a uniform axial membrane load in the crack region is discussed. After describing the evolution of the ductile fracture process, first the results of the elasticity solution for the circumferentially cracked cylindrical shell based on the Reissner's Transverse Shear Theory are presented. The elastic-plastic part-through crack problem then is considered. In the analysis the plastic deformations are approximated by a perfectly plastic layer similar to the conventional Dugdale model. The load carrying capacity of the cylinder is estimated in various ways by using the crack opening stretch along the leading edge of the crack as the critical load factor. 20 references.

  12. Brittle-to-ductile transition of lithiated silicon electrodes: Crazing to stable nanopore growth.

    PubMed

    Wang, Haoran; Wang, Xueju; Xia, Shuman; Chew, Huck Beng

    2015-09-14

    Using first principle calculations, we uncover the underlying mechanisms explaining the brittle-to-ductile transition of LixSi electrodes in lithium ion batteries with increasing Li content. We show that plasticity initiates at x = ∼ 0.5 with the formation of a craze-like network of nanopores separated by Si-Si bonds, while subsequent failure is still brittle-like with the breaking of Si-Si bonds. Transition to ductile behavior occurs at x ⩾ 1 due to the increased density of highly stretchable Li-Li bonds, which delays nanopore formation and stabilizes nanopore growth. Collapse of the nanopores during unloading of the LixSi alloys leads to significant strain recovery. PMID:26374052

  13. Brittle-to-ductile transition of lithiated silicon electrodes: Crazing to stable nanopore growth

    NASA Astrophysics Data System (ADS)

    Wang, Haoran; Wang, Xueju; Xia, Shuman; Chew, Huck Beng

    2015-09-01

    Using first principle calculations, we uncover the underlying mechanisms explaining the brittle-to-ductile transition of LixSi electrodes in lithium ion batteries with increasing Li content. We show that plasticity initiates at x = ˜ 0.5 with the formation of a craze-like network of nanopores separated by Si-Si bonds, while subsequent failure is still brittle-like with the breaking of Si-Si bonds. Transition to ductile behavior occurs at x ⩾ 1 due to the increased density of highly stretchable Li-Li bonds, which delays nanopore formation and stabilizes nanopore growth. Collapse of the nanopores during unloading of the LixSi alloys leads to significant strain recovery.

  14. On the limit of surface integrity of alumina by ductile-mode grinding

    SciTech Connect

    Zarudi, I.; Zhang, L.C.

    2000-01-01

    This paper investigates both experimentally and theoretically the subsurface damage in alumina by ductile-mode grinding. It was found that the distribution of the fractured area on a ground mirror surface, with the Rms roughness in the range from 30 nm to 90 nm, depends on not only the grinding conditions but also the pores in the bulk material. Surface pit formation is the result of interaction of abrasive grains of the grinding wheel with pores. Thus the surface quality achievable by ductile-mode grinding is limited by the initial microstructure of a material. The investigation shows that median and radial cracks do not appear and hence are not the cause of fracture as usually thought.

  15. Superior Tensile Ductility in Bulk Metallic Glass with Gradient Amorphous Structure

    PubMed Central

    Wang, Q.; Yang, Y.; Jiang, H.; Liu, C. T.; Ruan, H. H.; Lu, J.

    2014-01-01

    Over centuries, structural glasses have been deemed as a strong yet inherently ‘brittle’ material due to their lack of tensile ductility. However, here we report bulk metallic glasses exhibiting both a high strength of ~2 GPa and an unprecedented tensile elongation of 2–4% at room temperature. Our experiments have demonstrated that intense structural evolution can be triggered in theses glasses by the carefully controlled surface mechanical attrition treatment, leading to the formation of gradient amorphous microstructures across the sample thickness. As a result, the engineered amorphous microstructures effectively promote multiple shear banding while delay cavitation in the bulk metallic glass, thus resulting in superior tensile ductility. The outcome of our research uncovers an unusual work-hardening mechanism in monolithic bulk metallic glasses and demonstrates a promising yet low-cost strategy suitable for producing large-sized, ultra-strong and stretchable structural glasses. PMID:24755683

  16. Manipulating the interfacial structure of nanomaterials to achieve a unique combination of strength and ductility

    PubMed Central

    Khalajhedayati, Amirhossein; Pan, Zhiliang; Rupert, Timothy J.

    2016-01-01

    The control of interfaces in engineered nanostructured materials has met limited success compared with that which has evolved in natural materials, where hierarchical structures with distinct interfacial states are often found. Such interface control could mitigate common limitations of engineering nanomaterials. For example, nanostructured metals exhibit extremely high strength, but this benefit comes at the expense of other important properties like ductility. Here, we report a technique for combining nanostructuring with recent advances capable of tuning interface structure, a complementary materials design strategy that allows for unprecedented property combinations. Copper-based alloys with both grain sizes in the nanometre range and distinct grain boundary structural features are created, using segregating dopants and a processing route that favours the formation of amorphous intergranular films. The mechanical behaviour of these alloys shows that the trade-off between strength and ductility typically observed for metallic materials is successfully avoided here. PMID:26887444

  17. Bifurcation and neck formation as a precursor to ductile fracture during high rate extension

    SciTech Connect

    Freund, L.B.; Soerensen, N.J.

    1997-12-31

    A block of ductile material, typically a segment of a plate or shell, being deformed homogeneously in simple plane strain extension commonly undergoes a bifurcation in deformation mode to nonuniform straining in the advanced stages of plastic flow. The focus here is on the influence of material inertia on the bifurcation process, particularly on the formation of diffuse necks as precursors to dynamic ductile fracture. The issue is considered from two points of view, first within the context of the theory of bifurcation of rate-independent, incrementally linear materials and then in terms of the complete numerical solution of a boundary value problem for an elastic-viscoplastic material. It is found that inertia favors the formation of relatively short wavelength necks as observed in shaped charge break-up and dynamic fragmentation.

  18. Numerical and experimental study of the ductile failure of 7075-T651 aluminum

    SciTech Connect

    Benzley, S.E.; Soo Hoo, M.S.; Priddy, T.G.

    1981-05-01

    A combined experimental/numerical analysis has been performed on the nonlinear response and ductile failure of 7075-T651 aluminum. The different specimen shapes which were tested and analyzed produced: (1) pure shear; (2) uniaxial; (3) biaxial; and (4) triaxial states of stress in an axisymmetric geometry. Experiments performed on these specimens were subsequently analyzed with large strain finite element calculations. The calculations closely modelled experimental behavior. The calculated stresses and strains were then used to study ductile multiaxial failure criteria for monotonic loading configurations. This study concludes that the strain at which 7075-T651 aluminum fails is dependent upon the existing triaxial stress field, the higher the triaxiality, the smaller the effective plastic strain at failure. The relationship between strain at failure and the degree of triaxiality is given by the failure criteria.

  19. In-Situ Studies of Intercritically Austempered Ductile Iron Using Neutron Diffraction

    SciTech Connect

    Druschitz, Alan; Aristizabal, Ricardo; Druschitz, Edward; Hubbard, Camden R; Watkins, Thomas R; Walker, Larry R; Ostrander, M

    2012-01-01

    Intercritically austempered ductile irons hold promise for applications requiring fatigue durability, excellent castability, low production energy requirements, reduced greenhouse gas emissions and excellent machinability. In the present study, four different ductile iron alloys, containing manganese and nickel as the primary austenite-stabilizing elements, were heat treated to obtain different quantities of austenite in the final microstructure. This paper reports the microstructures and phases present in these alloys. Further, lattice strains and diffraction elastic constants in various crystallographic directions and the transformation characteristics of the austenite as a function of applied stress were determined using in-situ loading with neutron diffraction at the second generation Neutron Residual Stress Facility (NRSF2) at the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory (ORNL).

  20. High strength and high ductility behavior of 6061-T6 alloy after laser shock processing

    NASA Astrophysics Data System (ADS)

    Gencalp Irizalp, Simge; Saklakoglu, Nursen

    2016-02-01

    The plastic deformation behavior of 6061-T6 alloy which was subjected to severe plastic deformation (SPD) at high strain rates during laser shock processing (LSP) was researched. In LSP-treated materials, the near surface microstructural change was examined by TEM and fracture surfaces after tensile testing were examined by SEM. An increase in strength of metallic materials brings about the decrease in ductility. In this study, the results showed that LSP-treated 6061-T6 alloy exhibited both high strength and high ductility. TEM observation showed that stacking fault (SF) ribbon enlarged, deformation twins formed and twin boundary increased in LSP-treated 6061-T6 alloy. This observation was an indication of stacking fault energy (SFE) decrease. Work hardening capability was recovered after LSP impacts.

  1. Rhenium Alloys as Ductile Substrates for Diamond Thin-Film Electrodes.

    PubMed

    Halpern, Jeffrey M; Martin, Heidi B

    2014-02-01

    Molybdenum-rhenium (Mo/Re) and tungsten-rhenium (W/Re) alloys were investigated as substrates for thin-film, polycrystalline boron-doped diamond electrodes. Traditional, carbide-forming metal substrates adhere strongly to diamond but lose their ductility during exposure to the high-temperature (1000°C) diamond, chemical vapor deposition environment. Boron-doped semi-metallic diamond was selectively deposited for up to 20 hours on one end of Mo/Re (47.5/52.5 wt.%) and W/Re (75/25 wt.%) alloy wires. Conformal diamond films on the alloys displayed grain sizes and Raman signatures similar to films grown on tungsten; in all cases, the morphology and Raman spectra were consistent with well-faceted, microcrystalline diamond with minimal sp(2) carbon content. Cyclic voltammograms of dopamine in phosphate-buffered saline (PBS) showed the wide window and low baseline current of high-quality diamond electrodes. In addition, the films showed consistently well-defined, dopamine electrochemical redox activity. The Mo/Re substrate regions that were uncoated but still exposed to the diamond-growth environment remained substantially more flexible than tungsten in a bend-to-fracture rotation test, bending to the test maximum of 90° and not fracturing. The W/Re substrates fractured after a 27° bend, and the tungsten fractured after a 21° bend. Brittle, transgranular cleavage fracture surfaces were observed for tungsten and W/Re. A tension-induced fracture of the Mo/Re after the prior bend test showed a dimple fracture with a visible ductile core. Overall, the Mo/Re and W/Re alloys were suitable substrates for diamond growth. The Mo/Re alloy remained significantly more ductile than traditional tungsten substrates after diamond growth, and thus may be an attractive metal substrate for more ductile, thin-film diamond electrodes. PMID:25404788

  2. Effect of low temperatures on charpy impact toughness of austempered ductile irons

    NASA Astrophysics Data System (ADS)

    Riabov, Mikhail V.; Lerner, Yury S.; Fahmy, Mohammed F.

    2002-10-01

    Impact properties of standard American Society for Testing Materials (ASTM) grades of austempered ductile iron (ADI) were evaluated at subzero temperatures in unnotched and V-notched conditions and compared with ferritic and pearlitic grades of ductile irons (DIs). It was determined that there is a decrease in impact toughness for all ADI grades when there is a decrease in content of retained austenite and a decrease in test temperature, from room temperature (RT) to -60 °C. However, the difference in impact toughness values was not so noticeable for low retained austenite containing grade 5 ADI at both room and subzero temperatures as it was for ADI grade 1. Furthermore, the difference in impact toughness values of V-notched specimens of ADI grades 1 and 5 tested at -40 °C was minimal. The impact behaviors of ADI grade 5 and ferritic DI were found to be more stable than those of ADI grades 1, 2, 3, and 4 and pearlitic DI when the testing temperature was decreased. The impact toughness of ferritic DI was higher than that of ADI grades 1 and 2 at both -40 °C and -60 °C. The impact properties of ADI grades 4 and 5 were found to be higher than that of pearlitic DI at both -40 °C and -60 °C. The scanning electron microscopy (SEM) study of fracture surfaces revealed mixed ductile and quasicleavage rupture morphology types in all ADI samples tested at both -40 °C and -60 °C. With decreasing content of retained austenite and ductility, the number of quasicleavage facets increased from ADI grade 1-5. It was also found that fracture morphology of ADI did not experience significant changes when the testing temperature decreased. Evaluation of the bending angle was used to support impact-testing data. Designers and users of ADI castings may use the data developed in this research as a reference.

  3. Evidence for fluid flow in ductile shear zones, Granite Wash Mountains, Maria fold and thrust belt

    SciTech Connect

    Marin, B.A.; Mosher, S. . Dept. of Geological Sciences)

    1993-04-01

    Synkinematic fluids that accompanied Mesozoic (D2) deformation in the Granite Wash Mountains, eastern Maria fold and thrust belt, had profound effects on the metamorphic mineralogy and deformation mechanisms of Paleozoic metsedimentary rocks. The D2 thrusts are discrete brittle faults that commonly bound highly sheared, ductilely deformed rocks. These low-angle faults cross cut a vertical section of Paleozoic and Mesozoic supracrustal rocks that were multiply repeated and upturned by earlier Mesozoic deformation, D1. Kinematic analysis of a series of these ductile shear zones has confirmed that the dominant sense of motion during thrusting was to the SW, however, some isolated kinematic indicators and indicators along the lowest zone suggest NE-thrusting. Microstructures in samples collected both within D2 ductile shear zones and outside D2 zones show fluids played an important role in D2 deformation. The abundant evidence for fluids along D2 ductile shear zones includes: quartz veins in the Kaibab Fm (a dolomitic marble), zones of metasomatic alteration ( bleached'' zones) within D2 zones, an increase in the abundance of metamorphic minerals within D2 zones, and the presence of synkinematic wollastonite in silicones limestones of the Redwall Fm. The most dramatic and significant effect of synkinematic fluids in on the style of deformation mechanisms operating during thrusting. Evidence for intracrystalline plastic deformation and rotational recrystallization is not well-developed: instead, microstructures are dominated by migrational recrystallization fabrics. In some samples, quartz grain boundaries have migrated over a preexisting foliation defined by aligned micas, indicating that grain boundaries were highly mobile. Fluid-enhanced grain boundary mobility has allowed internally deformed grains or parts of grains to be consumed rapidly with no or little record of the deformation left behind.

  4. Rhenium Alloys as Ductile Substrates for Diamond Thin-Film Electrodes

    PubMed Central

    Halpern, Jeffrey M.; Martin, Heidi B.

    2014-01-01

    Molybdenum-rhenium (Mo/Re) and tungsten-rhenium (W/Re) alloys were investigated as substrates for thin-film, polycrystalline boron-doped diamond electrodes. Traditional, carbide-forming metal substrates adhere strongly to diamond but lose their ductility during exposure to the high-temperature (1000°C) diamond, chemical vapor deposition environment. Boron-doped semi-metallic diamond was selectively deposited for up to 20 hours on one end of Mo/Re (47.5/52.5 wt.%) and W/Re (75/25 wt.%) alloy wires. Conformal diamond films on the alloys displayed grain sizes and Raman signatures similar to films grown on tungsten; in all cases, the morphology and Raman spectra were consistent with well-faceted, microcrystalline diamond with minimal sp2 carbon content. Cyclic voltammograms of dopamine in phosphate-buffered saline (PBS) showed the wide window and low baseline current of high-quality diamond electrodes. In addition, the films showed consistently well-defined, dopamine electrochemical redox activity. The Mo/Re substrate regions that were uncoated but still exposed to the diamond-growth environment remained substantially more flexible than tungsten in a bend-to-fracture rotation test, bending to the test maximum of 90° and not fracturing. The W/Re substrates fractured after a 27° bend, and the tungsten fractured after a 21° bend. Brittle, transgranular cleavage fracture surfaces were observed for tungsten and W/Re. A tension-induced fracture of the Mo/Re after the prior bend test showed a dimple fracture with a visible ductile core. Overall, the Mo/Re and W/Re alloys were suitable substrates for diamond growth. The Mo/Re alloy remained significantly more ductile than traditional tungsten substrates after diamond growth, and thus may be an attractive metal substrate for more ductile, thin-film diamond electrodes. PMID:25404788

  5. A study of stress-rupture and ductility properties of thin laminae composites

    NASA Technical Reports Server (NTRS)

    Hoffman, C. A.; Weeton, J. W.

    1974-01-01

    It is shown that, by rolling, tungsten-tantalum laminar composites can be reduced in thickness as much as 90 to 1, with a resulting improvement in strength of nearly 66%. Further reductions in laminar thickness are believed to be possible with further increases in the strength of the composite material. The rolled tungsten-tantalum laminar material shows also a remarkable low-temperature ductility, sustaining a 3-T bend at room temperature without incurring macrodamage.

  6. The relationship between constraint and ductile fracture initiation as defined by micromechanical analyses

    SciTech Connect

    Panontin, T.L.; Sheppard, S.D.

    1995-12-31

    The overall objective of this study is to provide a proven methodology to allow the transfer of ductile fracture initiation properties measured in standard laboratory specimens to large, complex, flawed structures. A significant part of this work involved specifically addressing the effects of constrain on transferability under large scale yielding conditions. The approach taken was to quantify constrain effects through micromechanical fracture models coupled with finite element generated crack tip stress-strain fields to identify the local condition corresponding to fracture initiation. Detailed finite element models predicted the influence of specimen geometry, loading mode, and material flow properties on the crack tip fields. The ability of two local, ductile fracture models (the Rice and Tracey void growth model (VGM) and the stress-modified, critical strain (SMCS) criterion of Mackenzie et al. and Hancock and Cowling) to predict fracture initiation were investigated. Predictions were made using experimentally verified, two- and three-dimensional, finite strain, large deformation, finite element analyses. Two, high toughness pressure vessel steels were investigated: A516 Gr70, a ferritic, carbon-manganese mild steel demonstrating high hardening behavior, and HY-80, a martensitic, high strength low alloy (HSLA) steel possessing medium hardening ability. Experimental verification of the ductile fracture initiation predictions was performed in a variety of crack geometries possessing a range of a/w ratios from 0.15 to 0.70 and experiencing a range of load conditions from three point bending to nearly pure tension. The predicted constrain dependence of global ductile fracture parameters in the two materials is shown.

  7. Experiments on buoyancy-driven crack around the brittle-ductile transition

    NASA Astrophysics Data System (ADS)

    Sumita, Ikuro; Ota, Yukari

    2011-04-01

    We report the results of laboratory experiments exploring how a buoyancy-driven liquid-filled crack migrates within a viscoelastic medium whose rheology is around the brittle-ductile transition. To model such medium, we use a low concentration agar, which has a small yield stress and a large yield strain (deformation) when it fractures. We find that around the transition, the fluid migrates as a hybrid of a diapir (head) and a dyke (tail). Here the diapir is a bulged crack in which fracturing occurs at its tip and closes at its tail to form a dyke. A small amount of fluid is left along its trail and the fluid decelerates with time. We study how the shape and velocity of a constant volume fluid change as two control parameters are varied; the agar concentration ( C) and the density difference Δρ between the fluid and the agar. Under a fixed Δρ, as C decreases the medium becomes ductile, and the trajectory and shape of the fluid changes from a linearly migrating dyke to a meandering or a bifurcating dyke, and finally to a diapir-dyke hybrid. In this transition, the shape of the crack tip viewed from above, changes from blade-like to a cusped-ellipse. A similar transition is also observed when Δρ increases under a fixed C, which can be interpreted using a force balance between the buoyancy and the yield stress. Our experiments indicate that cracks around the brittle-ductile transition deviates from those in an elastic medium by several ways, such as the relaxation of the crack bulge, slower deceleration rate, and velocity becoming insensitive to medium rheology. Our experiments suggest that the fluid migrates as a diapir-dyke hybrid around the brittle-ductile transition and that fluid migration of various styles can coexist at the same depth, if they have different buoyancy.

  8. Machinable, Thin-Walled, Gray and Ductile Iron Casting Production, Phase III

    SciTech Connect

    Charles Bates; Hanjun Li; Robin Griffin

    2003-12-08

    This report presents the results of research conducted to determine the effects of normal and abnormal processing and compositional variations on machinability (tool wear rate) of gray and ductile iron. The procedures developed allow precise tool wear measurements to be made and interpreted in terms of microstructures and compositions. Accurate data allows the most efficient ways for improving machinability to be determined without sacrificing properties of the irons.

  9. Multi-Objective Optimization of a Wrought Magnesium Alloy for High Strength and Ductility

    SciTech Connect

    Radhakrishnan, Balasubramaniam; Gorti, Sarma B; Patton, Robert M; Simunovic, Srdjan

    2013-01-01

    An optimization technique is coupled with crystal plasticity based finite element (CPFE) computations to aid the microstructural design of a wrought magnesium alloy for improved strength and ductility. The initial microstructure consists of a collection of sub-micron sized grains containing deformation twins. The variables used in the simulations are crystallographic texture, and twin spacing within the grains. It is assumed that plastic deformation occurs mainly by dislocation slip on two sets of slip systems classified as hard and soft modes. The hard modes are those slip systems that are inclined to the twin planes and the soft mode consists of dislocation glide along the twin plane. The CPFE code calculates the stress-strain response of the microstructure as a function of the microstructural parameters and the length-scale of the features. A failure criterion based on a critical shear strain and a critical hydrostatic stress is used to define ductility. The optimization is based on the sequential generation of an initial population defined by the texture and twin spacing variables. The CPFE code and the optimizer are coupled in parallel so that new generations are created and analyzed dynamically. In each successive generation, microstructures that satisfy at least 90% of the mean strength and mean ductility in the current generation are retained. Multiple generation runs based on the above procedure are carried out in order to obtain maximum strength-ductility combinations. The implications of the computations for the design of a wrought magnesium alloy are discussed. Research sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U. S. Department of Energy.

  10. Designing metallic glass matrix composites with high toughness and tensile ductility.

    PubMed

    Hofmann, Douglas C; Suh, Jin-Yoo; Wiest, Aaron; Duan, Gang; Lind, Mary-Laura; Demetriou, Marios D; Johnson, William L

    2008-02-28

    The selection and design of modern high-performance structural engineering materials is driven by optimizing combinations of mechanical properties such as strength, ductility, toughness, elasticity and requirements for predictable and graceful (non-catastrophic) failure in service. Highly processable bulk metallic glasses (BMGs) are a new class of engineering materials and have attracted significant technological interest. Although many BMGs exhibit high strength and show substantial fracture toughness, they lack ductility and fail in an apparently brittle manner in unconstrained loading geometries. For instance, some BMGs exhibit significant plastic deformation in compression or bending tests, but all exhibit negligible plasticity (<0.5% strain) in uniaxial tension. To overcome brittle failure in tension, BMG-matrix composites have been introduced. The inhomogeneous microstructure with isolated dendrites in a BMG matrix stabilizes the glass against the catastrophic failure associated with unlimited extension of a shear band and results in enhanced global plasticity and more graceful failure. Tensile strengths of approximately 1 GPa, tensile ductility of approximately 2-3 per cent, and an enhanced mode I fracture toughness of K(1C) approximately 40 MPa m(1/2) were reported. Building on this approach, we have developed 'designed composites' by matching fundamental mechanical and microstructural length scales. Here, we report titanium-zirconium-based BMG composites with room-temperature tensile ductility exceeding 10 per cent, yield strengths of 1.2-1.5 GPa, K(1C) up to approximately 170 MPa m(1/2), and fracture energies for crack propagation as high as G(1C) approximately 340 kJ m(-2). The K(1C) and G(1C) values equal or surpass those achievable in the toughest titanium or steel alloys, placing BMG composites among the toughest known materials. PMID:18305540

  11. Effect of grain orientation on ductility in a nanocrystalline Ni-Fe alloy

    SciTech Connect

    Li, Hongqi; Misra, Amit; Liaw, Peter K; Choo, Hahn

    2008-01-01

    The influence of columnar grain geometry on mechanical property was studied in an electrodeposited nanocrystalline Ni-Fe alloy. The compressive results show that the strength is independent of grain orientation. However, the plastic strain increased remarkably when the loading axis is parallel to the direction of grain columns, which is due to the enhanced grain boundary and dislocation activities. The significance of the current study is that a new strategy was developed to improve the ductility of nanocrystalline materials.

  12. The influence of strain rate and hydrogen on the plane-strain ductility of Zircaloy cladding

    SciTech Connect

    Link, T.M.; Motta, A.T.; Koss, D.A.

    1998-03-01

    The authors studied the ductility of unirradiated Zircaloy-4 cladding under loading conditions prototypical of those found in reactivity-initiated accidents (RIA), i.e.: near plane-strain deformation in the hoop direction (transverse to the cladding axis) at room temperature and 300 C and high strain rates. To conduct these studies, they developed a specimen configuration in which near plane-strain deformation is achieved in the gage section, and a testing methodology that allows one to determine both the limit strain at the onset of localized necking and the fracture strain. The experiments indicate that there is little effect of strain rate (10{sup {minus}3} to 10{sup 2} s{sup {minus}1}) on the ductility of unhydrided Zircaloy tubing deformed under near plane-strain conditions at either room temperature or 300 C. Preliminary experiments on cladding containing 190 ppm hydrogen show only a small loss of fracture strain but no clear effect on limit strain. The experiments also indicate that there is a significant loss of Zircaloy ductility when surface flaws are present in the form of thickness imperfections.

  13. In-situ ductile metal/bulk metallic glass matrix composites formed by chemical partitioning

    DOEpatents

    Kim, Choong Paul; Hays, Charles C.; Johnson, William L.

    2004-03-23

    A composite metal object comprises ductile crystalline metal particles in an amorphous metal matrix. An alloy is heated above its liquidus temperature. Upon cooling from the high temperature melt, the alloy chemically partitions, forming dendrites in the melt. Upon cooling the remaining liquid below the glass transition temperature it freezes to the amorphous state, producing a two-phase microstructure containing crystalline particles in an amorphous metal matrix. The ductile metal particles have a size in the range of from 0.1 to 15 micrometers and spacing in the range of from 0.1 to 20 micrometers. Preferably, the particle size is in the range of from 0.5 to 8 micrometers and spacing is in the range of from 1 to 10 micrometers. The volume proportion of particles is in the range of from 5 to 50% and preferably 15 to 35%. Differential cooling can produce oriented dendrites of ductile metal phase in an amorphous matrix. Examples are given in the Zr--Ti--Cu--Ni--Be alloy bulk glass forming system with added niobium.

  14. In-situ ductile metal/bulk metallic glass matrix composites formed by chemical partitioning

    DOEpatents

    Kim, Choong Paul; Hays, Charles C.; Johnson, William L.

    2007-07-17

    A composite metal object comprises ductile crystalline metal particles in an amorphous metal matrix. An alloy is heated above its liquidus temperature. Upon cooling from the high temperature melt, the alloy chemically partitions, forming dendrites in the melt. Upon cooling the remaining liquid below the glass transition temperature it freezes to the amorphous state, producing a two-phase microstructure containing crystalline particles in an amorphous metal matrix. The ductile metal particles have a size in the range of from 0.1 to 15 micrometers and spacing in the range of from 0.1 to 20 micrometers. Preferably, the particle size is in the range of from 0.5 to 8 micrometers and spacing is in the range of from 1 to 10 micrometers. The volume proportion of particles is in the range of from 5 to 50% and preferably 15 to 35%. Differential cooling can produce oriented dendrites of ductile metal phase in an amorphous matrix. Examples are given in the Zr--Ti--Cu--Ni--Be alloy bulk glass forming system with added niobium.

  15. Predicting Ductility and Failure Modes of TRIP Steels under Different Loading Conditions

    SciTech Connect

    Choi, Kyoo Sil; Liu, Wenning N.; Sun, Xin; Khaleel, Mohammad A.

    2010-06-12

    We study the ultimate ductility and failure modes of a TRIP (TRansformation-Induced Plasticity) 800 steel under different loading conditions with an advanced micromechanics-based finite element analysis. The representative volume element (RVE) for the TRIP800 under examination is developed based on an actual microstructure obtained from scanning electron microscopy (SEM). The evolution of retained austenite during deformation process and the mechanical properties of the constituent phases of the TRIP800 steel are obtained from the synchrotron-based in-situ high-energy X-ray diffraction (HEXRD) experiments and a self-consistent (SC) model. The ductile failure of the TRIP800 under different loading conditions is predicted in the form of plastic strain localization without any prescribed failure criteria for the individual phases. Comparisons of the computational results with experimental measurements suggest that the microstructure-based finite element analysis can well capture the overall macroscopic behavior of the TRIP800 steel under different loading conditions. The methodology described in this study may be extended for studying the ultimate ductile failure mechanisms of TRIP steels as well as the effects of the various processing parameters on the macroscopic behaviors of TRIP steels.

  16. Computer simulation of strength and ductility of nanotwin-strengthened coarse-grained metals

    NASA Astrophysics Data System (ADS)

    Guo, X.; Ji, R.; Weng, G. J.; Zhu, L. L.; Lu, J.

    2014-10-01

    The superior strength-ductility combination in nanotwin (NT)-strengthened metals has provided a new potential for optimizing the mechanical properties of coarse-grained (CG) metals. In this paper computer simulations based on the mechanism-based strain gradient plasticity and the Johnson-Cook failure criterion have been carried out to uncover the critical factors that serve to provide this dual function. Our results indicate that both the distribution characteristics of the NT regions and the constitutive relations of the NT phase can have a significant impact on the strength and ductility of the CG Cu strengthened by the NT regions. In particular, twin spacing, distribution characteristics such as arrangement, shape and orientation, together with volume fraction of the NT regions, can all have significant effects. Along the way, we also discovered that microcrack initiation, coalescence and deflection constituted the entire failure process. Significant insights into the morphology of NT regions that could deliver superior strength and ductility combination for CG metals have been established.

  17. Experimental investigation of stress and strain fields in a ductile matrix surrounding an elastic inclusion

    SciTech Connect

    Nugent, E.E.; Calhoun, R.B.; Mortensen, A.

    2000-04-19

    A method for measuring stress and strain distributions within a ductile material deforming by dislocational slip is developed. The method exploits the transparency and room-temperature ductility of silver chloride, and combines the techniques of photoelasticity and marker tracking. This method is used to investigate the deformation of an elasto-plastic ductile matrix surrounding an isolated stiff fiber, the grain size of the material being slightly smaller than the fiber length. The data are compared to predictions of finite element calculations which take the matrix to be an isotropic elasto-plastic von Mises continuum. It is found that this model does not fully capture all of the features of the experimental data. Data suggest that the cause for observed discrepancies is the strong influence exerted by grain boundaries and grain orientation on the distribution of stress and strain within the matrix. A comparison is also made between the data and predictions of the Eshelby equivalent inclusion calculation, to show that a far higher level of discrepancy results than with the finite element calculations; this is caused by the fact that the Eshelby equivalent inclusion calculation is essentially elastic and thus allows significant stress concentrations.

  18. Towards an analysis of leak-before-break assessments in the ductile tearing regime

    SciTech Connect

    Parfitt, V.R.

    1991-12-31

    This paper presents the elastic-plastic fracture analysis of a typical semi-elliptical axial surface flaw growing to a thru-thickness flaw and assessing the leak-before break situation in a pressure vessel subject to pressure. The paper first discusses the semi-elliptical flaw J-integral solution and the thru-thickness flaw solution as modified herein. Then a review is presented of the three ductile tearing stability fracture analysis methods based on the fully plastic J-integral solution; (1) the crack driving force diagram, (2) the tearing modulus diagram, and (3) the failure assessment diagram. These methods are then used to determine the factors of safety to initiation of ductile tearing as the crack grows. Factors of safety based on either pressure alone or crack size alone are illustrated. An illustration is given of a leak-before-break solution discussing the semi-elliptical flaw growing to a thru-thickness flaw in the vessel. The paper concludes with a discussion of additional effort needed to better characterize leak-before-break solutions in the ductile tearing regime.

  19. A cross-shear deformation for optimizing the strength and ductility of AZ31 magnesium alloys

    PubMed Central

    Hamad, Kotiba; Ko, Young Gun

    2016-01-01

    Magnesium alloys have recently attracted great interest due their lightweight and high specific strength. However, because of their hexagonal close-packed structure, they have few active slip systems, resulting in poor ductility and high mechanical anisotropy at room temperature. In the present work, we used a cross-shear deformation imposed by a differential speed rolling (DSR) technique to improve the room temperature strength and ductility of AZ31 magnesium alloy sheets. To introduce the cross-shear deformation, the sheets were rotated 180° around their longitudinal axis between the adjacent passes of DSR. The sheets of the AZ31 alloy subjected to the cross-shear deformation showed a uniform fine microstructure (1.2 ± 0.1 μm) with weak basal textures. The fabricated sheets showed a simultaneous high ultimate tensile strength and elongation-to-failure, i.e., ~333 MPa and ~21%, respectively. These were explained based on the structural features evolved due to the cross-shear deformation by DSR. The high strength was attributed to the uniform fine microstructure, whereas the high ductility was explained based on the basal texture weakening. PMID:27406685

  20. Effect of Ductile Agents on the Dynamic Behavior of SiC3D Network Composites

    NASA Astrophysics Data System (ADS)

    Zhu, Jingbo; Wang, Yangwei; Wang, Fuchi; Fan, Qunbo

    2016-07-01

    Co-continuous SiC ceramic composites using pure aluminum, epoxy, and polyurethane (PU) as ductile agents were developed. The dynamic mechanical behavior and failure mechanisms were investigated experimentally using the split Hopkinson pressure bar (SHPB) method and computationally by finite element (FE) simulations. The results show that the SiC3D/Al composite has the best overall performance in comparison with SiC3D/epoxy and SiC3D/PU composites. FE simulations are generally consistent with experimental data. These simulations provide valuable help in predicting mechanical strength and in interpreting the experimental results and failure mechanisms. They may be combined with micrographs for fracture characterizations of the composites. We found that interactions between the SiC phase and ductile agents under dynamic compression in the SHPB method are complex, and that interfacial condition is an important parameter that determines the mechanical response of SiC3D composites with a characteristic interlocking structure during dynamic compression. However, the effect of the mechanical properties of ductile agents on dynamic behavior of the composites is a second consideration in the production of the composites.

  1. A cross-shear deformation for optimizing the strength and ductility of AZ31 magnesium alloys.

    PubMed

    Hamad, Kotiba; Ko, Young Gun

    2016-01-01

    Magnesium alloys have recently attracted great interest due their lightweight and high specific strength. However, because of their hexagonal close-packed structure, they have few active slip systems, resulting in poor ductility and high mechanical anisotropy at room temperature. In the present work, we used a cross-shear deformation imposed by a differential speed rolling (DSR) technique to improve the room temperature strength and ductility of AZ31 magnesium alloy sheets. To introduce the cross-shear deformation, the sheets were rotated 180° around their longitudinal axis between the adjacent passes of DSR. The sheets of the AZ31 alloy subjected to the cross-shear deformation showed a uniform fine microstructure (1.2 ± 0.1 μm) with weak basal textures. The fabricated sheets showed a simultaneous high ultimate tensile strength and elongation-to-failure, i.e., ~333 MPa and ~21%, respectively. These were explained based on the structural features evolved due to the cross-shear deformation by DSR. The high strength was attributed to the uniform fine microstructure, whereas the high ductility was explained based on the basal texture weakening. PMID:27406685

  2. A cross-shear deformation for optimizing the strength and ductility of AZ31 magnesium alloys

    NASA Astrophysics Data System (ADS)

    Hamad, Kotiba; Ko, Young Gun

    2016-07-01

    Magnesium alloys have recently attracted great interest due their lightweight and high specific strength. However, because of their hexagonal close-packed structure, they have few active slip systems, resulting in poor ductility and high mechanical anisotropy at room temperature. In the present work, we used a cross-shear deformation imposed by a differential speed rolling (DSR) technique to improve the room temperature strength and ductility of AZ31 magnesium alloy sheets. To introduce the cross-shear deformation, the sheets were rotated 180° around their longitudinal axis between the adjacent passes of DSR. The sheets of the AZ31 alloy subjected to the cross-shear deformation showed a uniform fine microstructure (1.2 ± 0.1 μm) with weak basal textures. The fabricated sheets showed a simultaneous high ultimate tensile strength and elongation-to-failure, i.e., ~333 MPa and ~21%, respectively. These were explained based on the structural features evolved due to the cross-shear deformation by DSR. The high strength was attributed to the uniform fine microstructure, whereas the high ductility was explained based on the basal texture weakening.

  3. Study of mechanical, physical, and corrosion behavior of 0.5% cobalt alloyed austempered ductile iron

    NASA Astrophysics Data System (ADS)

    Abdullah, Bulan; Jaffar, Ahmed; Alias, Siti Khadijah; Ramli, Abdullah; Izham, Mohd Faizul

    2010-03-01

    Objectives: The purpose of this research was to determine the mechanical properties and corrosion behavior of 0.5% Co-DI before and after heat treatment and compare with commercial ductile iron. Methods: Molten metal of newly developed ductile iron which alloyed with 0.5% Cobalt produced through CO2 sand casting method. The specimens then performed preheat to 500°C in an hour then oil quenched. Specimens then performed annealing to 900°C in half an hour before oil quenched again. 500°C, 600°C and 700°C austempering temperature had been selected subjected to the specimens in half an hour before cooled to room temperature. The tests involved are microstructure analysis which included nodule count and phase analysis, polarization test, spectrometer test, density test, tensile test (ASTM E 8M), hardness test and impact test (ASTM A327) on as cast and austempered specimen. Results: 0.5% Cobalt alloyed austempered ductile iron with 500°C austempered temperature is the optimum temperature for 0.5% Co-ADI. It's not only increase the nodule count in the content, but also improve the mechanical properties such as impact toughness and tensile strength. Corrosion rate of 0.5% Co-DI also improved compare to unalloyed DI.

  4. Study of mechanical, physical, and corrosion behavior of 0.5% cobalt alloyed austempered ductile iron

    NASA Astrophysics Data System (ADS)

    Abdullah, Bulan; Jaffar, Ahmed; Alias, Siti Khadijah; Ramli, Abdullah; Izham, Mohd Faizul

    2009-12-01

    Objectives: The purpose of this research was to determine the mechanical properties and corrosion behavior of 0.5% Co-DI before and after heat treatment and compare with commercial ductile iron. Methods: Molten metal of newly developed ductile iron which alloyed with 0.5% Cobalt produced through CO2 sand casting method. The specimens then performed preheat to 500°C in an hour then oil quenched. Specimens then performed annealing to 900°C in half an hour before oil quenched again. 500°C, 600°C and 700°C austempering temperature had been selected subjected to the specimens in half an hour before cooled to room temperature. The tests involved are microstructure analysis which included nodule count and phase analysis, polarization test, spectrometer test, density test, tensile test (ASTM E 8M), hardness test and impact test (ASTM A327) on as cast and austempered specimen. Results: 0.5% Cobalt alloyed austempered ductile iron with 500°C austempered temperature is the optimum temperature for 0.5% Co-ADI. It's not only increase the nodule count in the content, but also improve the mechanical properties such as impact toughness and tensile strength. Corrosion rate of 0.5% Co-DI also improved compare to unalloyed DI.

  5. Effect of matrix structure on the impact properties of an alloyed ductile iron

    SciTech Connect

    Toktas, Guelcan . E-mail: gzeytin@balikesir.edu.tr; Tayanc, Mustafa; Toktas, Alaaddin

    2006-12-15

    An investigation was performed to examine the influence of the matrix structure on the impact properties of a 1.03% Cu, 1.25% Ni and 0.18% Mo pearlitic ductile iron. Specimens were first homogenized at 925 deg. C for 7 h and a fully ferritic structure was obtained in all ductile iron samples. Then, various heat treatments were applied to the homogenized specimens in order to obtain pearlitic/ferritic, pearlitic, tempered martensitic, lower and upper ausferritic matrix structures. The unnotched charpy impact specimens were tested at temperatures between - 80 deg. C and + 100 deg. C; the tensile properties (ultimate tensile strength, 0.2% yield strength and elongation) and the hardnesses of the matrix structures were investigated at room temperature. The microstructures and the fracture surfaces of the impact specimens tested at room temperature were also investigated by optical and scanning electron microscope. The results showed that the best impact properties were obtained for the ferritic matrix structure that had the lowest hardness, yield and tensile strength. Ductile iron with a lower ausferritic matrix had the best combination of ultimate tensile strength, percent elongation and impact energies of all structures.

  6. Tempering rapidly solidified ductile cast iron by pulsed laser beam reprocessing

    SciTech Connect

    Wang, H.M. . Dept. of Materials Science and Engineering); Bergmann, H.W. . Materials Science Dept.)

    1994-08-15

    During laser surface rapid remelting of cast irons, the melt pool solidifies rapidly and metastably (i.e. according to the metastable Fe-Fe[sub 3]C system) producing an ultra-fine ledeburite hard surface which is much more abrasion resistant than the original substrate. Previous literature mainly focused on remelting various grey and ductile irons with high power CO[sub 2] lasers for improved wear resistance and other surface properties, and on studying the physical metallurgy of laser remelted surfaces. Unfortunately, the unstable nature and rapid tempering behavior of the rapidly solidified ledeburite were generally neglected, although some publications mentioned the tempering phenomenon during successive overlap remelting. In this paper, a laser remelted ductile case iron surface was tempered by rapid pulsed laser beam reprocessing. The rapidly solidified ductile iron was found to be rapidly graphitized, as a result, a layer of Fe-base alloy containing ultra-fine graphite particles was produced. The unusual rapid graphitization phenomenon was preliminarily discussed.

  7. Specimen preparation by ion beam slope cutting for characterization of ductile damage by scanning electron microscopy.

    PubMed

    Besserer, Hans-Bernward; Gerstein, Gregory; Maier, Hans Jürgen; Nürnberger, Florian

    2016-04-01

    To investigate ductile damage in parts made by cold sheet-bulk metal forming a suited specimen preparation is required to observe the microstructure and defects such as voids by electron microscopy. By means of ion beam slope cutting both a targeted material removal can be applied and mechanical or thermal influences during preparation avoided. In combination with scanning electron microscopy this method allows to examine voids in the submicron range and thus to analyze early stages of ductile damage. In addition, a relief structure is formed by the selectivity of the ion bombardment, which depends on grain orientation and microstructural defects. The formation of these relief structures is studied using scanning electron microscopy and electron backscatter diffraction and the use of this side effect to interpret the microstructural mechanisms of voids formation by plastic deformation is discussed. A comprehensive investigation of the suitability of ion beam milling to analyze ductile damage is given at the examples of a ferritic deep drawing steel and a dual phase steel. Microsc. Res. Tech. 79:321-327, 2016. © 2016 Wiley Periodicals, Inc. PMID:26854331

  8. Ru/Al Multilayers Integrate Maximum Energy Density and Ductility for Reactive Materials

    NASA Astrophysics Data System (ADS)

    Woll, K.; Bergamaschi, A.; Avchachov, K.; Djurabekova, F.; Gier, S.; Pauly, C.; Leibenguth, P.; Wagner, C.; Nordlund, K.; Mücklich, F.

    2016-01-01

    Established and already commercialized energetic materials, such as those based on Ni/Al for joining, lack the adequate combination of high energy density and ductile reaction products. To join components, this combination is required for mechanically reliable bonds. In addition to the improvement of existing technologies, expansion into new fields of application can also be anticipated which triggers the search for improved materials. Here, we present a comprehensive characterization of the key parameters that enables us to classify the Ru/Al system as new reactive material among other energetic systems. We finally found that Ru/Al exhibits the unusual integration of high energy density and ductility. For example, we measured reaction front velocities up to 10.9 (±0.33) ms-1 and peak reaction temperatures of about 2000 °C indicating the elevated energy density. To our knowledge, such high temperatures have never been reported in experiments for metallic multilayers. In situ experiments show the synthesis of a single-phase B2-RuAl microstructure ensuring improved ductility. Molecular dynamics simulations corroborate the transformation behavior to RuAl. This study fundamentally characterizes a Ru/Al system and demonstrates its enhanced properties fulfilling the identification requirements of a novel nanoscaled energetic material.

  9. Ductility Enhancement of Post-Northridge Connections by Multilongitudinal Voids in the Beam Web

    PubMed Central

    Celikag, Murude; Hedayat, Amir A.

    2013-01-01

    Since the earthquakes in Northridge and Kobe in 1994 and 1995, respectively, many investigations have been carried out towards improving the strength and ductility of steel beam to column pre- and post-Northridge connections. In order to achieve these objectives, recent researches are mainly focused on three principles: reducing the beam section to improve the beam ductility, adding different kinds of slit damper to beam and column flanges to absorb and dissipate the input earthquake energy in the connection and strengthening the connection area using additional elements such as rib plates, cover plates, and flange plates to keep the plastic hinges away from the column face. This paper presents a reduced beam section approach via the introduction of multilongitudinal voids (MLV) in the beam web for various beam depths varying from 450 mm to 912 mm. ANSYS finite element program was used to simulate the three different sizes of SAC sections: SAC3, SAC5, and SAC7. Results showed an improvement in the connection ductility since the input energy was dissipated uniformly along the beam length and the total rotation of the connection was over four percent radian. PMID:24311977

  10. Ru/Al Multilayers Integrate Maximum Energy Density and Ductility for Reactive Materials

    PubMed Central

    Woll, K.; Bergamaschi, A.; Avchachov, K.; Djurabekova, F.; Gier, S.; Pauly, C.; Leibenguth, P.; Wagner, C.; Nordlund, K.; Mücklich, F.

    2016-01-01

    Established and already commercialized energetic materials, such as those based on Ni/Al for joining, lack the adequate combination of high energy density and ductile reaction products. To join components, this combination is required for mechanically reliable bonds. In addition to the improvement of existing technologies, expansion into new fields of application can also be anticipated which triggers the search for improved materials. Here, we present a comprehensive characterization of the key parameters that enables us to classify the Ru/Al system as new reactive material among other energetic systems. We finally found that Ru/Al exhibits the unusual integration of high energy density and ductility. For example, we measured reaction front velocities up to 10.9 (±0.33) ms−1 and peak reaction temperatures of about 2000 °C indicating the elevated energy density. To our knowledge, such high temperatures have never been reported in experiments for metallic multilayers. In situ experiments show the synthesis of a single-phase B2-RuAl microstructure ensuring improved ductility. Molecular dynamics simulations corroborate the transformation behavior to RuAl. This study fundamentally characterizes a Ru/Al system and demonstrates its enhanced properties fulfilling the identification requirements of a novel nanoscaled energetic material. PMID:26822309

  11. Effects of rolling on the ductility of 80% tungsten heavy alloy

    SciTech Connect

    Lavender, C.A.; Gurwell, W.E.

    1992-11-01

    Relations between transverse tensile ductility and rolling and annealing schedules were investigated for solid-state sintered and annealed 80%W8%Ni-2%Fe heavy alloy rolled at 900C or 1150C with varying reductions between anneals at either 1150C or 1400C. Final anneals and a solution heat treatment were employed prior to tensile testing. Metallographic and fractographic analyses were performed to determine relations between microstructure and physical properties. Multiple 1400C intermediate anneals with a maximum 60% rolling reduction produced higher transverse tensile elongations than rolled with a higher final reduction, 86%. Tensile elongation differences were attributed to the recrystallized intra-particle W grain sizes achieved during the final anneal. Materials given a maximum of 60% reduction before final anneal had fewer intra-particle W grains and therefore higher ductilities. For materials rolled at 900C or 1150C, no differences in transverse tensile elongation were observed. 1150C intermediate anneals had consistently lower ductility. 900C rolling produced slightly higher elongations than 1150C rolling, but only when the material was annealed at 1455C. Tensile yield and ultimate strengths did not vary greatly with rolling and intermediate annealing conditions. The edge cracking correlated with observed lateral spread and the material softness.

  12. The ductile-brittle size transition of iron aluminide ligaments in an FeAl/TiC composite

    SciTech Connect

    Subramanian, R.; Schneibel, J.H.

    1998-08-10

    The fracture surfaces of FeAl/TiC composites containing 70 vol% TiC were investigated. Since thin iron aluminide ligaments in the composites fractured in a ductile manner, whereas thicker ones fractured by cleavage, a systematic correlation of the fracture mode to the ligament thickness was performed. The results clearly show that FeAl ligaments thicker than about 1--2 {micro}m fracture by cleavage and those smaller in size fracture predominantly in a ductile manner. The ductile failure mode is attributed to the limited dislocation pile-up distance available for very thin ligaments, which prevents high stresses from building up and eliminates cleavage fracture. It is also shown that the ductile-brittle transition size is controlled by alloying and/or heat treatment. No significant dependence of the fracture toughness on the fracture mode would be found.

  13. Deformation mechanisms of NiAl cyclicly deformed near the brittle-to-ductile transformation temperature

    NASA Technical Reports Server (NTRS)

    Antolovich, Stephen D.; Saxena, Ashok; Cullers, Cheryl

    1992-01-01

    One of the ongoing challenges of the aerospace industry is to develop more efficient turbine engines. Greater efficiency entails reduced specific strength and larger temperature gradients, the latter of which means higher operating temperatures and increased thermal conductivity. Continued development of nickel-based superalloys has provided steady increases in engine efficiency and the limits of superalloys have probably not been realized. However, other material systems are under intense investigation for possible use in high temperature engines. Ceramic, intermetallic, and various composite systems are being explored in an effort to exploit the much higher melting temperatures of these systems. NiAl is considered a potential alternative to conventional superalloys due to its excellent oxidation resistance, low density, and high melting temperature. The fact that NiAl is the most common coating for current superalloy turbine blades is a tribute to its oxidation resistance. Its density is one-third that of typical superalloys and in most temperature ranges its thermal conductivity is twice that of common superalloys. Despite these many advantages, NiAl requires more investigation before it is ready to be used in engines. Binary NiAl in general has poor high-temperature strength and low-temperature ductility. On-going research in alloy design continues to make improvements in the high-temperature strength of NiAl. The factors controlling low temperature ductility have been identified in the last few years. Small, but reproducible ductility can now be achieved at room temperature through careful control of chemical purity and processing. But the mechanisms controlling the transition from brittle to ductile behavior are not fully understood. Research in the area of fatigue deformation can aid the development of the NiAl system in two ways. Fatigue properties must be documented and optimized before NiAl can be applied to engineering systems. More importantly though

  14. Hot Ductility and Deformation Behavior of C-Mn/Nb-Microalloyed Steel Related to Cracking During Continuous Casting

    NASA Astrophysics Data System (ADS)

    Lanjewar, H. A.; Tripathi, Pranavkumar; Singhai, M.; Patra, P. K.

    2014-10-01

    Hot ductility studies have been performed on C-Mn and C-Mn-Nb steels with an approach to simulate the effect of cooling conditions experienced by steel in secondary cooling zone during continuous casting. Thermal oscillations prior to tensile straining deteriorate hot ductility of steel by deepening and widening the hot ductility trough. C-Mn steels are found to exhibit ductility troughs in three distinct zones whereas C-Mn-Nb steel shows drop in ductility only at low temperature in the vicinity of ferrite transformation temperatures. Start of ferrite transformation in steels causes yield ratio to increase while work hardening rates and strength coefficient decrease with decrease in test temperature in presence of thermal oscillation prior to tensile testing. Inhibition of recrystallization due to build-up of AlN particles along with the presence of MnS particles in structure and low work hardening rates causes embrittlement of steel in austenitic range. Alloying elements enhancing work hardening rates in austenitic range can be promoted to improve hot ductility. The presence of low melting phase saturated with impurities along the austenitic grain boundaries causes intergranular fracture at high temperature in C-Mn steels.

  15. Role of matrix/reinforcement interfaces in the fracture toughness of brittle materials toughened by ductile reinforcements

    NASA Astrophysics Data System (ADS)

    Xiao, L.; Abbaschian, R.

    1992-10-01

    Crack interactions with ductile reinforcements, especially behavior of a crack tip at the interface, have been studied using MoSi2 composites reinforced with Nb foils. Effects of fracture energy of interfaces on toughness of the composites have also been investigated. Variation of interfacial bonding was achieved by depositing an oxide coating or by the development of a reaction prod- uct layer between the reinforcement and matrix. Toughness was measured using bend tests on chevron-notched specimens. It has been established that as a crack interacts with a ductile re- inforcement, three mechanisms compcte: interfacial debonding, multiple matrix fracture, and direct crack propagation through the reinforcement. Decohesion length at the matrix/reinforcement interface depends on the predominant mechanism. Furthermore, the results add to the evidence that the extent to which interfacial bonding is conducive to toughness of the composites depends on the criterion used to describe the toughness and that ductility of the ductile reinforcement is also an important factor in controlling toughness of the composites. Loss of ductility of the ductile reinforcement due to inappropriate processing could result in little improvement in tough- ness of the composites.

  16. The Influence of the Induced Ferrite and Precipitates of Ti-bearing Steel on the Ductility of Continuous Casting Slab

    NASA Astrophysics Data System (ADS)

    Qian, Guoyu; Cheng, Guoguang; Hou, Zibing

    2015-11-01

    In order to investigate the loss of the ductility of Ti-bearing ship plate steel under 1000 °C, where the ductility begins to reduce rapidly, so the hot ductility of Ti-bearing ship plate steel has been obtained using the Gleeble 1500 thermal-mechanical simulator and also the studies about the effect of grain boundary ferrite films and precipitates containing Ti on the ductility has been carried out. The result showed that the TiN particles precipitating at 950 °C with a larger size and smaller volume fraction cannot effectively suppress the occurrence of recrystallization and the ductility still retains at a high level, although R.A. value presents a certain degree of decline compared with 1000 °C. A large number of smaller Ti(C,N) particles precipitate at 900 °C and can induce the formation of a very small amount of fine grain boundary ferrite, which deteriorates the adhesion strength of the grain boundary, so the R.A. value rapidly reduces to less than 50%. When the temperature falls to close Ae3 (827 °C), the amount of the grain boundary ferrite films increase due to the ferrite phase transformation, but the ferrite film thickness becomes more uneven at the same time, which results in the increase of strain concentration and plays a leading role in causing the decrease of ductility, so the R.A. value has been kept less than 40% as the temperature cooling to 800 °C from 850 °C. When the temperature further decreases, the ductility starts to recover due to the increase of average ferrite film thickness to a greater degree which greatly reduces the strain concentration of the grain boundary.

  17. Effect of austempering time on mechanical properties of a low manganese austempered ductile iron

    SciTech Connect

    Putatunda, S.K.; Gadicherla, P.K.

    2000-04-01

    An investigation was carried out to examine the influence of austempering time on the resultant microstructure and the room-temperature mechanical properties of an unalloyed and low manganese ductile cast iron with initially ferritic as-cast structure. The effect of austempering time on the plane strain fracture toughness of this material was also studied. Compact tension and round cylindrical tensile specimens were prepared from unalloyed ductile cast iron with low manganese content and with a ferritic as-cast (solidified) structure. These specimens were then austempered in the upper (371 C) and lower (260 C) bainitic temperature ranges for different time periods, ranging from 30 min. to 3 h. Microstructural features such as type of bainite and the volume fraction of ferrite and austenite and its carbon content were evaluated by X-ray diffraction to examine the influence of microstructure on the mechanical properties and fracture toughness of this material. The results of the present investigation indicate that for this low manganese austempered ductile iron (ADI), upper ausferritic microstructures exhibit higher fracture toughness than lower ausferritic microstructures. Yield and tensile strength of the material was found to increase with an increase in austempering time in a lower bainitic temperature range, whereas in the upper bainitic temperature range, time has no significant effect on the mechanical properties. A retained austenite content between 30 to 35% was found to provide optimum fracture toughness. Fracture toughness was found to increase with the parameter (X{gamma}C{gamma}/d){sup 1/2}, where X{gamma} is the volume fraction of austenite, C{gamma} is the carbon content of the austenite, and d is the mean free path of dislocation motion in ferrite.

  18. Effect of initial microstructure on the activation energy of second stage during austempering of ductile iron

    SciTech Connect

    Campos-Cambranis, R.E.; Narvaez Hernandez, L.; Cisneros-Guerrero, M.M.; Perez-Lopez, M.J.

    1998-03-13

    The good balance among mechanical properties of austempered ductile irons (ADI) mainly depends on the matrix microstructure, which basically consists of acicular ferrite and carbon-enriched austenite. This structure is produced by isothermal transformation of the austenite over the temperature range of 523 to 673 K. It is well accepted that during the isothermal holding, the transformation takes place in two stages. In the first stage, the austenite decomposes into acicular ferrite and carbon-enriched austenite. When the austenite is transformed at temperatures higher than 623 K, the acicular ferrite is free of carbides; at temperatures below 623 K, besides the formation of the acicular ferrite and austenite, precipitation of carbides takes place over the plates of the acicular ferrite. The mixture of ferrite and austenite is known as ausferrite being the responsible for the good mechanical properties of ADI. In this work, the ausferrite obtained above and below 623 K will be termed high and low temperature ausferrite respectively. Although ausferrite does not transform at room temperature, it is not a thermodynamically stable structure. Consequently, if the isothermal holding is extended, or if ADI is heated at high temperatures (523 to 800 K), the second stage of the austempering reaction will occur. During this stage, the carbon rich austenite will decompose into ferrite and carbides. In order to establish the maximum working temperature of ADI, it is necessary to characterize the thermal stability of ausferrite microstructure, since once stage II takes place, the mechanical properties, in particular ductility and toughness, are adversely affected. In the present work the influence of previous ausferrite microstructure (that obtained during first stage) of an alloyed ductile iron (0.6%Ni, 0.15%Mo) on the empirical activation energy of stage II is studied.

  19. Structural Evidence for Fluid-Assisted Shear Failure within a Ductile Shear Zone

    NASA Astrophysics Data System (ADS)

    Compton, K.; Kirkpatrick, J. D.

    2014-12-01

    Recent observations of seismic slip occurring below the seismogenic zone of large fault zones have emphasized the significance of coeval ductile and brittle processes at high temperatures. We present observations of a shear zone contained within the Saddlebag Lake pendant of the eastern Sierra Nevada, CA, where Triassic and Jurassic metavolcanics and metasediments are highly strained in a high-temperature shear zone. Transposed bedding and cleavage that define a flattening fabric, dextrally rotated porphyroclasts, and a steep, pervasive lineation together suggest an overall transpressive kinematic regime for the ductile deformation. The high-strain rocks exhibit multiple episodes of vein formation, indicating a prolonged migration of hydrothermal fluids throughout the system. Crosscutting relationships and mineral assemblages define discrete sets of differently oriented veins. The veins form by fracture, but many veins are folded and boudinaged, showing synkinematic brittle and ductile deformation. We document foliation-parallel quartz veins that show shear displacement from the geometry of pull-apart structures and offsets of earlier veins. Synkinematic equilibrium mineral assemblages within the host rock and dynamic recrystallization of the quartz veins show they formed at temperatures around 400 to 500°C. The shear fractures have horizontal trace lengths of up to a few meters and displacements range from 2-3 mm to ~3 cm, with 1-5 mm of opening. Assuming the observed offset in the fractures occurred in a single event, these measurements are consistent with stress drops of 1 to 10 MPa. We interpret these observations to show that the veins formed as a result of high pore fluid pressure that caused shear failure at low effective stresses. Because foliated rocks are mechanically anisotropic, the foliation provided planes of weakness for failure with a preferred orientation. Evidence for shear failure occurring within crystal-plastic shear zones at high temperatures

  20. Linear Elastic and Cohesive Fracture Analysis to Model Hydraulic Fracture in Brittle and Ductile Rocks

    NASA Astrophysics Data System (ADS)

    Yao, Yao

    2012-05-01

    Hydraulic fracturing technology is being widely used within the oil and gas industry for both waste injection and unconventional gas production wells. It is essential to predict the behavior of hydraulic fractures accurately based on understanding the fundamental mechanism(s). The prevailing approach for hydraulic fracture modeling continues to rely on computational methods based on Linear Elastic Fracture Mechanics (LEFM). Generally, these methods give reasonable predictions for hard rock hydraulic fracture processes, but still have inherent limitations, especially when fluid injection is performed in soft rock/sand or other non-conventional formations. These methods typically give very conservative predictions on fracture geometry and inaccurate estimation of required fracture pressure. One of the reasons the LEFM-based methods fail to give accurate predictions for these materials is that the fracture process zone ahead of the crack tip and softening effect should not be neglected in ductile rock fracture analysis. A 3D pore pressure cohesive zone model has been developed and applied to predict hydraulic fracturing under fluid injection. The cohesive zone method is a numerical tool developed to model crack initiation and growth in quasi-brittle materials considering the material softening effect. The pore pressure cohesive zone model has been applied to investigate the hydraulic fracture with different rock properties. The hydraulic fracture predictions of a three-layer water injection case have been compared using the pore pressure cohesive zone model with revised parameters, LEFM-based pseudo 3D model, a Perkins-Kern-Nordgren (PKN) model, and an analytical solution. Based on the size of the fracture process zone and its effect on crack extension in ductile rock, the fundamental mechanical difference of LEFM and cohesive fracture mechanics-based methods is discussed. An effective fracture toughness method has been proposed to consider the fracture process zone

  1. Late Cretaceous ductile deformation, metamorphism and plutonism in the Piute Mountains, eastern Mojave Desert

    SciTech Connect

    Fletcher, J.M.; Karlstrom, K.E. )

    1990-01-10

    Late Cretaceous deformation in the Piute Mountains involved ductile thrusting on a network of anastomosing northeast and southwest directed shear zones. The shear zones often separate Proterozoic lithologies with strong competency contrasts, suggesting that Proterozoic crustal anisotropies were important in controlling the geometry of the shear zone network. Shear zones now divide the crust into wedge- and lozenge-shaped blocks. The Piute Mountains can be separated into two kinematic domains, each characterized by a dominant sense of shear. Thrusting in the southwest directed kinematic domain ended at 85 {plus minus} 7 Ma, the age of the late synkinematic East Piute pluton. Thrusting in the northeast directed kinematic domain could have lasted until 74 {plus minus} 3 Ma, the age of the Lazy Daisy pluton. Postthrusting northwest-southeast shortening produced a second generation of upright open folds with a northeast striking subvertical crenulation cleavage. F{sub 2} strain increases toward the south and is concentrated around the margins of the Lazy Daisy pluton. This deformation was synchronous with pluton emplacement. Lake Cretaceous peak metamorphism outlasted all ductile deformation. Peak metamorphic grade increases from upper greenschist facies in the north to upper amphibolite facies as the Lazy Daisy pluton is approached. Temperature and pressure of approximately 450 C and 2.5-4.0 kbar were achieved during ductile thrusting. Temperatures of 500-540 C existed at the onset of upright open folding, and peak temperatures as high as 620 C near the Lazy Daisy pluton occurred after F{sub 2} upright folding. All penetrative deformation ended before 72-71 Ma, by which time the area had cooled to below 300 C.

  2. Brittle intermetallic compound makes ultrastrong low-density steel with large ductility.

    PubMed

    Kim, Sang-Heon; Kim, Hansoo; Kim, Nack J

    2015-02-01

    Although steel has been the workhorse of the automotive industry since the 1920s, the share by weight of steel and iron in an average light vehicle is now gradually decreasing, from 68.1 per cent in 1995 to 60.1 per cent in 2011 (refs 1, 2). This has been driven by the low strength-to-weight ratio (specific strength) of iron and steel, and the desire to improve such mechanical properties with other materials. Recently, high-aluminium low-density steels have been actively studied as a means of increasing the specific strength of an alloy by reducing its density. But with increasing aluminium content a problem is encountered: brittle intermetallic compounds can form in the resulting alloys, leading to poor ductility. Here we show that an FeAl-type brittle but hard intermetallic compound (B2) can be effectively used as a strengthening second phase in high-aluminium low-density steel, while alleviating its harmful effect on ductility by controlling its morphology and dispersion. The specific tensile strength and ductility of the developed steel improve on those of the lightest and strongest metallic materials known, titanium alloys. We found that alloying of nickel catalyses the precipitation of nanometre-sized B2 particles in the face-centred cubic matrix of high-aluminium low-density steel during heat treatment of cold-rolled sheet steel. Our results demonstrate how intermetallic compounds can be harnessed in the alloy design of lightweight steels for structural applications and others. PMID:25652998

  3. An investigation of the mineral in ductile and brittle cortical mouse bone.

    PubMed

    Rodriguez-Florez, Naiara; Garcia-Tunon, Esther; Mukadam, Quresh; Saiz, Eduardo; Oldknow, Karla J; Farquharson, Colin; Millán, José Luis; Boyde, Alan; Shefelbine, Sandra J

    2015-05-01

    Bone is a strong and tough material composed of apatite mineral, organic matter, and water. Changes in composition and organization of these building blocks affect bone's mechanical integrity. Skeletal disorders often affect bone's mineral phase, either by variations in the collagen or directly altering mineralization. The aim of the current study was to explore the differences in the mineral of brittle and ductile cortical bone at the mineral (nm) and tissue (µm) levels using two mouse phenotypes. Osteogenesis imperfecta model, oim(-/-) , mice have a defect in the collagen, which leads to brittle bone; PHOSPHO1 mutants, Phospho1(-/-) , have ductile bone resulting from altered mineralization. Oim(-/-) and Phospho1(-/-) were compared with their respective wild-type controls. Femora were defatted and ground to powder to measure average mineral crystal size using X-ray diffraction (XRD) and to monitor the bulk mineral to matrix ratio via thermogravimetric analysis (TGA). XRD scans were run after TGA for phase identification to assess the fractions of hydroxyapatite and β-tricalcium phosphate. Tibiae were embedded to measure elastic properties with nanoindentation and the extent of mineralization with backscattered electron microscopy (BSE SEM). Results revealed that although both pathology models had extremely different whole-bone mechanics, they both had smaller apatite crystals, lower bulk mineral to matrix ratio, and showed more thermal conversion to β-tricalcium phosphate than their wild types, indicating deviations from stoichiometric hydroxyapatite in the original mineral. In contrast, the degree of mineralization of bone matrix was different for each strain: brittle oim(-/-) were hypermineralized, whereas ductile Phospho1(-/-) were hypomineralized. Despite differences in the mineralization, nanoscale alterations in the mineral were associated with reduced tissue elastic moduli in both pathologies. Results indicated that alterations from normal crystal size

  4. Role of fluid overpressures in crustal strength and the form of the brittle-ductile transition

    NASA Astrophysics Data System (ADS)

    Suppe, J.

    2014-12-01

    The classic crustal strength-depth model of Brace and Kolhstedt (1980) (see figure) based on experimental rock mechanics depends in the brittle regime on the critical assumption of linearly increasing hydrostatic pore-fluid pressures. This leads to a predicted linearly increasing brittle strength that is well established based on deep borehole stress measurements in crystalline crust. In contrast, fluid overpressures are widely documented in orogenic belts based on borehole data, seismic velocity analysis and analysis of veins, in some cases showing complex fault-valve pressure fluctuations between lithostatic and hydrostatic. Typical observed overpressure-depth relationships predict a brittle crustal strength that is approximately constant with depth in contrast with the classic model. This constant-strength behavior below the fluid-retention depth (ZFRD in figure) has been confirmed using deep borehole stress and fluid-pressure measurements (Suppe, 2014). Recent ductile-plastic modeling of disequilibrium compaction suggests that pressure solution promotes further increases in overpressure and weakening, promoting a very prolonged low-strength brittle-ductile transition. Overpressured conditions can be inferred to exist over a substantial fraction of crustal thickness, spanning the brittle-ductile transition, in several tectonic environments, most straightforwardly in shale-rich clastic sedimentary basins built to sea level on oceanic or highly thinned continental crust such as the US Gulf Coast and Niger Delta. These thick accumulations commonly deform into shale-rich plate boundary mountain belts (e.g. Bangladesh/Miyanmar, Makran, Trinidad/Barbados, Gulf of Alaska, southern Taiwan and New Zealand). There is deep geophysical evidence for near lithostatic pore-fluid pressures existing to depths of 20-30km based on Vp, Vs, Vp/Vs and Q observations. We present active examples from Taiwan and New Zealand, combining borehole data and seismic tomography.

  5. Brittle intermetallic compound makes ultrastrong low-density steel with large ductility

    NASA Astrophysics Data System (ADS)

    Kim, Sang-Heon; Kim, Hansoo; Kim, Nack J.

    2015-02-01

    Although steel has been the workhorse of the automotive industry since the 1920s, the share by weight of steel and iron in an average light vehicle is now gradually decreasing, from 68.1 per cent in 1995 to 60.1 per cent in 2011 (refs 1, 2). This has been driven by the low strength-to-weight ratio (specific strength) of iron and steel, and the desire to improve such mechanical properties with other materials. Recently, high-aluminium low-density steels have been actively studied as a means of increasing the specific strength of an alloy by reducing its density. But with increasing aluminium content a problem is encountered: brittle intermetallic compounds can form in the resulting alloys, leading to poor ductility. Here we show that an FeAl-type brittle but hard intermetallic compound (B2) can be effectively used as a strengthening second phase in high-aluminium low-density steel, while alleviating its harmful effect on ductility by controlling its morphology and dispersion. The specific tensile strength and ductility of the developed steel improve on those of the lightest and strongest metallic materials known, titanium alloys. We found that alloying of nickel catalyses the precipitation of nanometre-sized B2 particles in the face-centred cubic matrix of high-aluminium low-density steel during heat treatment of cold-rolled sheet steel. Our results demonstrate how intermetallic compounds can be harnessed in the alloy design of lightweight steels for structural applications and others.

  6. Strain localization in carbonate rocks experimentally deformed in the ductile field

    NASA Astrophysics Data System (ADS)

    Rybacki, E.; Morales, L. F. G.; Dresen, G.

    2012-04-01

    The deformation of rocks in the Earth's crust is often localized, varying from brittle fault gauges in shallow environments to mylonites in ductile shear zones at greater depth. A number of theoretical, experimental, and field studies focused on the evolution and extend of brittle fault zones, but little is known so far about initiation of ductile shear zones. Strain localization in rocks deforming at high temperature and pressure may be induced by several physical, chemical, or structurally-related mechanisms. We performed simple and pure shear deformation experiments on carbonate rocks containing structural inhomogenities in the ductile deformation regime. The results may help to gain insight into the evolution of high temperature shear zones. As starting material we used cylindrical samples of coarse-grained Carrara marble containing one or two 1 mm thin artificially prepared sheets of fine-grained Solnhofen limestone, which act as soft inclusions under the applied experimental conditions. Length and diameter of the investigated solid and hollow cylinders were 10-20 mm and 10-15 mm, respectively. Samples were deformed in a Paterson-type gas deformation apparatus at 900° C temperature and confining pressures of 300 and 400 MPa. Three samples were deformed in axial compression at a bulk strain rate of 8x10-5 s-1to axial strains between 0.02 and 0.21 and 15 samples were twisted in torsion at a bulk shear strain rate of 2x10-4 s-1 to shear strains between 0.01 and 3.74. At low strain, specimens deformed axially and in torsion show minor strain hardening that is replaced by strain weakening at shear strains in excess of about 0.2. Peak shear stress at the imposed condition is about 20 MPa. Strain localized strongly within the weak inclusions as indicated by inhomogeneous bending of initially straight strain markers on sample jackets. Maximum strain concentration within inclusions with respect to the adjacent matrix was between 4 and 40, depending on total strain and

  7. Stiffness, strength, and ductility of nanoscale thin films and membranes: a combined wrinkling-cracking methodology.

    PubMed

    Chung, Jun Young; Lee, Jung-Hyun; Beers, Kathryn L; Stafford, Christopher M

    2011-08-10

    We establish and validate a measurement method based on wrinkling-cracking phenomena that allows unambiguous measurements of three fundamental mechanical properties in nanoscale thin film geometries, including elastic modulus, strength, and fracture strain. In addition to polymer and metal thin films, the method is applied to the active nanolayers of a composite reverse osmosis membrane before and after chlorination, illustrating the ability to detect a ductile-to-brittle transition in these materials indicative of "embrittlement", a behavior that impairs long-term durability and is detrimental to membrane performance. PMID:21761850

  8. Impurity effects on high-temperature tensile ductility of iridium alloys at high strain rate

    SciTech Connect

    McKamey, C.G.; George, E.P.; Lee, E.H.; Ohriner, E.K.; Heatherly, L.; Cohron, J.W.

    1999-12-17

    The current study was undertaken to determine what effects, if any, larger amounts of certain impurities (Al,Cr,Fe,Ni, and Si) might have on the physical metallurgy and mechanical properties of the DOP-26 iridium alloy. This report summarizes the effects of these impurities on grain growth behavior and high-temperature high-strain-rate tensile ductility. Comparisons are made to the grain growth behavior and high-strain-rate tensile properties of the DOP-26 alloy without intentional impurity additions.

  9. High velocity properties of the dynamic frictional force between ductile metals

    SciTech Connect

    Hammerberg, James Edward; Hollan, Brad L; Germann, Timothy C; Ravelo, Ramon J

    2010-01-01

    The high velocity properties of the tangential frictional force between ductile metal interfaces seen in large-scale NonEquilibrium Molecular Dynamics (NEMD) simulations are characterized by interesting scaling behavior. In many cases a power law decrease in the frictional force with increasing velocity is observed at high velocities. We discuss the velocity dependence of the high velocity branch of the tangential force in terms of structural transformation and ultimate transition, at the highest velocities, to confined fluid behavior characterized by a critical strain rate. The particular case of an Al/Al interface is discussed.

  10. Understanding the changes in ductility and Poisson's ratio of metallic glasses during annealing from microscopic dynamics

    SciTech Connect

    Wang, Z.; Ngai, K. L.; Wang, W. H.

    2015-07-21

    In the paper K. L. Ngai et al., [J. Chem. 140, 044511 (2014)], the empirical correlation of ductility with the Poisson's ratio, ν{sub Poisson}, found in metallic glasses was theoretically explained by microscopic dynamic processes which link on the one hand ductility, and on the other hand the Poisson's ratio. Specifically, the dynamic processes are the primitive relaxation in the Coupling Model which is the precursor of the Johari–Goldstein β-relaxation, and the caged atoms dynamics characterized by the effective Debye–Waller factor f{sub 0} or equivalently the nearly constant loss (NCL) in susceptibility. All these processes and the parameters characterizing them are accessible experimentally except f{sub 0} or the NCL of caged atoms; thus, so far, the experimental verification of the explanation of the correlation between ductility and Poisson's ratio is incomplete. In the experimental part of this paper, we report dynamic mechanical measurement of the NCL of the metallic glass La{sub 60}Ni{sub 15}Al{sub 25} as-cast, and the changes by annealing at temperature below T{sub g}. The observed monotonic decrease of the NCL with aging time, reflecting the corresponding increase of f{sub 0}, correlates with the decrease of ν{sub Poisson}. This is important observation because such measurements, not made before, provide the missing link in confirming by experiment the explanation of the correlation of ductility with ν{sub Poisson}. On aging the metallic glass, also observed in the isochronal loss spectra is the shift of the β-relaxation to higher temperatures and reduction of the relaxation strength. These concomitant changes of the β-relaxation and NCL are the root cause of embrittlement by aging the metallic glass. The NCL of caged atoms is terminated by the onset of the primitive relaxation in the Coupling Model, which is generally supported by experiments. From this relation, the monotonic decrease of the NCL with aging time is caused by the slowing down

  11. Ductile to brittle transition in dynamic fracture of brittle bulk metallic glass

    SciTech Connect

    Wang, G.; Han, Y. N.; Han, B. S.; Wang, W. H.; Xu, X. H.; Ke, F. J.

    2008-05-01

    We report an unusual transition from a locally ductile to a pure brittle fracture in the dynamic fracture of brittle Mg{sub 65}Cu{sub 20}Gd{sub 10} bulk metallic glass. The fractographic evolution from a dimple structure to a periodic corrugation pattern and then to the mirror zone along the crack propagation direction during the dynamic fracture process is discussed within the framework of the meniscus instability of the fracture process zone. This work might provide an important clue in understanding of the energy dissipation mechanism for dynamic crack propagation in brittle glassy materials.

  12. Simultaneous enhancement of toughness, ductility, and strength of nanocrystalline ceramics at high strain-rates

    SciTech Connect

    Mo Yifei; Szlufarska, Izabela

    2007-04-30

    Molecular dynamics simulations of tensile testing have been performed on nc-SiC. Reduction of grain size promotes simultaneous enhancement of ductility, toughness, and strength. nc-SiC fails by intergranular fracture preceded by atomic level necking. Conventionally, high strain-rate deformations of ceramics are limited by diffusion time scales, since diffusion prevents premature cavitation and failure. The authors report a nondiffusional mechanism for suppressing premature cavitation, which is based on unconstrained plastic flow at grain boundaries. Based on the composite's rule of mixture, they estimate Young's modulus of random high-angle grain boundaries in nc-SiC to be about 130 GPa.

  13. A damage mechanics based approach for developing a quantitative understanding of ductile fracture.

    SciTech Connect

    Thissell, W. R.; Tonks, D. L.; Schwartz, D. S.

    2004-01-01

    A self-consistent damage mechanics approach for describing ductile fracture is introduced. This approach consists of damage quantification of incipiently failed specimens resulting from well-controlled and diagnosed experiments that span a wide parameter space of stress triaxiality, strain rate, and equivalent plastic strain. Numerical simulations are performed of these experiments using damage constitutive models and the simulation predictions are compared with the experimental measurements and post-mortem damage quantification, with the goal of developing, validating, and calibrating the damage constitutive models. New developments are described, such as the coupling between void and deformation bands.

  14. Ultraprecision, high stiffness CNC grinding machines for ductile mode grinding of brittle materials

    NASA Astrophysics Data System (ADS)

    McKeown, Patrick A.; Carlisle, Keith; Shore, Paul; Read, R. F.

    1990-10-01

    Under certain controlled conditions it is now possible to machine brittle materials such as glasses and ceramics using single or multi-point diamond tools (grinding), so that material is removed by plastic flow, leaving crack-free surfaces. This process is called 'shear' or 'ductile' mode grinding. It represents a major breakthrough in modern manufacturing engineering since it promises to enable: - complex optical components, both transmission and reflecting to be generated by advanced CNC machines with very little (or even zero) subsequent polishing. - complex shaped components such as turbine blades, nozzle guide vanes, etc. to be finish machined after near net shape forming, to high precision in advanced ceramics such as silicon nitride, without inducing micro-cracking and thus lowering ultimate rupture strength and fatigue life. Ductile mode "damage free" grinding occurs when the volume of materials stressed by each grit of the grinding wheel is small enough to yield rather than exhibit brittle fracture, i.e. cracking. In practice, this means maintaining the undeformed chip thickness to below the ductile-brittle transition value; this varies from material to material but is generally in the order of 0.1 pm or 100 nm, (hence the term "nanogrinding" is sometimes used) . Thus the critical factors for operating successfully in the ductile regime are machine system accuracy and dynamic stiffness between each grit and the workpiece. In detail this means: (i) High precision 'truing' of the diamond grits, together with dressing of the wheel bond to ensure adequate ' openness'; (ii) Design and build of the grinding wheel spindle with very high dynamic stiffness; error motions, radial and axial, must be considerably less than 100 nfl. (iii) Design and build of the workpiece carriage motion system with very high dynamic stiffness; error motions, linear or rotary, must be well within 100 nm. (iv) Smooth, rumble-free, high-stiffness servo-drives controlling the motions

  15. Novel alpha-zirconium phosphonates for the reinforcement of ductile thermoplastics

    NASA Astrophysics Data System (ADS)

    Furman, Benjamin R.

    2007-12-01

    Ductile thermoplastics are useful additives for providing fracture toughness to brittle thermosetting polymers; however, this toughening is usually accompanied by a significant decrease in elastic modulus. Therefore, alpha-zirconium phosphonates (ZrP) were developed and investigated as reinforcing nano-scale fillers that increase the yield strength and elastic modulus of a polyester thermoplastic without causing a reduction in its ductility. ZrP materials are synthetic layered compounds that are imbued with targeted organic surface functionalities and whose structural development can be carefully controlled in the laboratory. Ether-terminal alkyl ZrP materials were designed and synthesized, using a conventional ZrF62--mediated preparation, with the intent of developing strong dipole-dipole interactions between the layer surfaces and polyester macromolecules. Additionally, a general method for using lamellar lyotropic liquid crystals (LLC's) as supramolecular templates for alkyl ZrP was evaluated, whose products showed promising similarity to the conventionally prepared materials. The LLC-forming characteristics of several organophosphonate preparations were determined, showing improved mesophase stability with mixed amphiphiles and preparation with R4N + counterions. A mixed-surface octyl/methoxyundecyl ZrP was produced and combined with polycaprolactone (PCL) and polymethylmethacrylate (PMMA) in concentrations up to 50% (w/w). The mechanical properties of the ZrP/PCL nanocomposite were evaluated by tensile, flexural, and dynamic mechanical testing methods. Nanocomposites containing 5% (w/w) ZrP showed significant increases in tensile yield stress and elastic modulus without suffering any loss of ductility versus the unfilled polymer. Layer delamination from the ZrP tactoids was minimal and did not occur through an intercalative mechanism. Higher ZrP loadings resulted in the agglomeration of tactoids, leading to defect structures and loss of strength and ductility

  16. Hot Ductility Behaviors in the Weld Heat-Affected Zone of Nitrogen-Alloyed Fe-18Cr-10Mn Austenitic Stainless Steels

    NASA Astrophysics Data System (ADS)

    Moon, Joonoh; Lee, Tae-Ho; Hong, Hyun-Uk

    2015-04-01

    Hot ductility behaviors in the weld heat-affected zone (HAZ) of nitrogen-alloyed Fe-18Cr-10Mn austenitic stainless steels with different nitrogen contents were evaluated through hot tension tests using Gleeble simulator. The results of Gleeble simulations indicated that hot ductility in the HAZs deteriorated due to the formation of δ-ferrite and intergranular Cr2N particles. In addition, the amount of hot ductility degradation was strongly affected by the fraction of δ-ferrite.

  17. Three Dimensional Forming Simulation of the Shielded Slot Plate for the MCFC Using a Ductile Fracture Criterion

    NASA Astrophysics Data System (ADS)

    Lee, C. H.; Yang, D. Y.; Lee, S. R.; Chang, I. G.; Lee, T. W.

    2011-08-01

    The shielded slot plate, which has a sheared corrugated trapezoidal pattern, is a component of the metallic bipolar plate for the molten carbonate fuel cell (MCFC). In order to increase the efficiency of the fuel cell, the unit cell of the shielded slot plate should have a relatively large upper area. Additionally, defects from the forming process should be minimized. In order to simulate the slitting process, whereby sheared corrugated patterns are formed, ductile fracture criteria based on the histories of stress and strain are employed. The user material subroutine VUMAT is employed for implementation of the material and ductile fracture criteria in the commercial FEM software ABAQUS. The variables of the ductile fracture criteria were determined by comparing the simulation results and the experimental results of the tension test and the shearing test. Parametric studies were conducted to determine the critical value of the ductile fracture criterion. Employing these ductile fracture criteria, the three dimensional forming process of the shielded slot plate was numerically simulated. The effects of the slitting process in the forming process of the shielded slot plate were analyzed through a FEM simulation and experimental studies. Finally, experiments involving microscopic and macroscopic observations were conducted to verify the numerical simulations of the 3-step forming process.

  18. Ductile, Brittle Failure Characteristics as Determined by the State of the Material and the Imposed State of Stress

    SciTech Connect

    Christensen, R M

    2004-02-05

    A method is developed for determining whether a particular mode of failure is expected to be of ductile type or brittle type depending upon both the state of the material and the particular state of stressing the isotropic material to failure. The state of the material is determined by two specific failure properties and a newly formulated failure theory. The ductile versus brittle criterion then involves the state of the material specification and the mean normal stress part of the imposed stress state. Several examples are given for different stress states and a spectrum of materials types. Closely related to the failure mode types are the orientations of the associated failure surfaces. The resulting failure surface angle predictions are compared with those from the Coulomb-Mohr failure criterion. In uniaxial tension, only the present method correctly predicts the octahedral failure angle at the ductile limit, and also shows a distinct failure mode transition from ductile type to brittle type as the state of the material changes. The explicit D-B criterion and the related failure surface orientation methodology are intended to provide a refinement and generalization of the ductile-brittle transition viewed only as a state property to also include a dependence upon the type of stress state taken to failure.

  19. Evaluation of varying ductile fracture criteria for 42CrMo steel by compressions at different temperatures and strain rates.

    PubMed

    Quan, Guo-zheng; Luo, Gui-chang; Mao, An; Liang, Jian-ting; Wu, Dong-sen

    2014-01-01

    Fracturing by ductile damage occurs quite naturally in metal forming processes, and ductile fracture of strain-softening alloy, here 42CrMo steel, cannot be evaluated through simple procedures such as tension testing. Under these circumstances, it is very significant and economical to find a way to evaluate the ductile fracture criteria (DFC) and identify the relationships between damage evolution and deformation conditions. Under the guidance of the Cockcroft-Latham fracture criteria, an innovative approach involving hot compression tests, numerical simulations, and mathematic computations provides mutual support to evaluate ductile damage cumulating process and DFC diagram along with deformation conditions, which has not been expounded by Cockcroft and Latham. The results show that the maximum damage value appears in the region of upsetting drum, while the minimal value appears in the middle region. Furthermore, DFC of 42CrMo steel at temperature range of 1123~1348 K and strain rate of 0.01~10 s(-1) are not constant but change in a range of 0.160~0.226; thus, they have been defined as varying ductile fracture criteria (VDFC) and characterized by a function of temperature and strain rate. In bulk forming operations, VDFC help technicians to choose suitable process parameters and avoid the occurrence of fracture. PMID:24592175

  20. Post Quench Ductility Evaluation of Zircaloy-4 and Select Iron Alloys under Design Basis and Extended LOCA Conditions

    SciTech Connect

    Yan, Yong; Keiser, James R; Terrani, Kurt A; Bell, Gary L; Snead, Lance

    2014-01-01

    Oxidation experiments were conducted at 1200 C in flowing steam with tubing specimens of Zircaloy-4, 317, 347 stainless steels, and the commercial FeCrAl alloy APMT. The purpose was to determine the oxidation behavior and post quench ductility of these alloys under postulated loss-of-coolant accident conditions. The parabolic rate constant for Zircaloy-4 tubing samples at 1200 were determined to be k = 2.173 107 g2/cm4/s C, in excellent agreement with the Cathcart-Pawel correlation. The APMT alloy experienced the slowest oxidation rate among all materials examined in this work. The ductility of post quenched samples was evaluated by ring compression tests at 135 C. For Zircaloy-4, the ductile to brittle transition occurs at an equivalent cladding reacted (ECR) of 19.3%. SS-347 was still ductile after being oxidized for 2400 s (CP-ECR 50%), but the maximum load was reduced significantly owing to the metal layer thickness reduction. No ductility decrease was observed for the post-quenched APMT samples oxidized up to four hours.

  1. Evaluation of Varying Ductile Fracture Criteria for 42CrMo Steel by Compressions at Different Temperatures and Strain Rates

    PubMed Central

    Quan, Guo-zheng; Luo, Gui-chang; Mao, An; Liang, Jian-ting; Wu, Dong-sen

    2014-01-01

    Fracturing by ductile damage occurs quite naturally in metal forming processes, and ductile fracture of strain-softening alloy, here 42CrMo steel, cannot be evaluated through simple procedures such as tension testing. Under these circumstances, it is very significant and economical to find a way to evaluate the ductile fracture criteria (DFC) and identify the relationships between damage evolution and deformation conditions. Under the guidance of the Cockcroft-Latham fracture criteria, an innovative approach involving hot compression tests, numerical simulations, and mathematic computations provides mutual support to evaluate ductile damage cumulating process and DFC diagram along with deformation conditions, which has not been expounded by Cockcroft and Latham. The results show that the maximum damage value appears in the region of upsetting drum, while the minimal value appears in the middle region. Furthermore, DFC of 42CrMo steel at temperature range of 1123~1348 K and strain rate of 0.01~10 s−1 are not constant but change in a range of 0.160~0.226; thus, they have been defined as varying ductile fracture criteria (VDFC) and characterized by a function of temperature and strain rate. In bulk forming operations, VDFC help technicians to choose suitable process parameters and avoid the occurrence of fracture. PMID:24592175

  2. Microstructure control in iron aluminides by phase decomposition or by mechanical alloying for improved strength and ductility

    SciTech Connect

    Morris, D.G.; Gunther, S.

    1997-12-31

    The iron aluminides based on Fe{sub 3}Al or FeAl being developed for intermediate temperature applications suffer from mediocre room temperature strength and ductility and poor high temperature tensile and creep strength. Attempts to overcome these problems have been restricted by the limited possibilities of structure modification by, for example, precipitation of stable strengthening particles. The present study examines two approached to obtaining two-phase mixtures for improved strength and ductility: by adjusting chemical compositions such that two-phase order-disorder ({alpha}-{alpha}{double_prime}) mixtures are obtained, and by mechanical alloying. Two-phase {alpha}-{alpha}{double_prime} mixtures are obtained by heat treatment of Fe-Al alloys with Al content near 20--24% and in ternary Fe-Al-Si alloys with suitably adjusted Al and Si contents. Microstructures of such alloys can be modified during heat treatments by ordering, precipitation or decomposition, and two-phase mixtures similar to those in the {gamma}-{gamma}{prime} superalloys obtained. Such two-phase alloys show good high temperature tensile and creep strength with some indication of reasonable ductility and reduced environmental sensitivity. Mechanical alloying can easily produce Fe-Al alloys of fine grain size reinforced with stable oxide particles. These structures lead to high room temperature strength with some ductility; controlled recrystallization can significantly modify both strength and ductility.

  3. Ductile Damage and Fatigue Behavior of Semi-Finished Tailored Blanks for Sheet-Bulk Metal Forming Processes

    NASA Astrophysics Data System (ADS)

    Besserer, Hans-Bernward; Hildenbrand, Philipp; Gerstein, Gregory; Rodman, Dmytro; Nürnberger, Florian; Merklein, Marion; Maier, Hans Jürgen

    2016-03-01

    To produce parts from sheet metal with thickened functional elements, bulk forming operations can be employed. For this new process class, the term sheet-bulk metal forming has been established recently. Since sheet-bulk metal forming processes such as orbital forming generates triaxial stress and strain states, ductile damage is induced in the form of voids in the microstructure. Typical parts will experience cyclic loads during service, and thus, the influence of ductile damage on the fatigue life of parts manufactured by orbital forming is of interest. Both the formation and growth of voids were characterized following this forming process and then compared to the as-received condition of the ferritic deep drawing steel DC04 chosen for this study. Subsequent to the forming operation, the specimens were fatigued and the evolution of ductile damage and the rearrangement of the dislocation networks occurring during cyclic loading were determined. It was shown, that despite an increased ductile damage due to the forming process, the induced strain hardening has a positive effect on the fatigue life of the material. However, by analyzing the fatigued specimens a development of the ductile damage by an increasing number of voids and a change in the void shape were detected.

  4. Ductile Fracture Prediction in Rotational Incremental Forming for Magnesium Alloy Sheets Using Combined Kinematic/Isotropic Hardening Model

    NASA Astrophysics Data System (ADS)

    Nguyen, Duc-Toan; Park, Jin-Gee; Kim, Young-Suk

    2010-08-01

    To predict the ductile fracture of a magnesium alloy sheet when using rotational incremental forming, a combined kinematic and isotropic hardening law is implemented and evaluated from the histories of the ductile fracture value ( I) using a finite element analysis. Here, the criterion for a ductile fracture, as developed by Oyane ( J. Mech. Work. Technol., 1980, vol. 4, pp. 65-81), is applied via a user material based on a finite element analysis. To simulate the effect of the large amount of heat generation at elements in the contact area due to the friction energy of the rotational tool-specimen interface on the equivalent stress-strain evolution in incremental forming, the Johnson-Cook (JC) model was applied and the results compared with equivalent stress-strain curves obtained from tensile tests at elevated temperatures. The finite element (FE) simulation results for a ductile fracture were compared with the experimental results for a (80 mm × 80 mm × 25 mm) square shape with a 45 and 60 deg wall angle, respectively, and a (80 mm × 80 mm × 20 mm) square shape with a 70 deg wall angle. The trends of the FE simulation results agreed quite well with the experimental results. Finally, the effects of the process parameters, i.e., the tool down-step and tool radius, on the ductile fracture value and FLC at fracture (FLCF) were also investigated using the FE simulation results.

  5. X-ray diffraction study of the phase purity, order, and texture of ductile B2 intermetallics

    SciTech Connect

    Mulay, Rupalee; Wollmershauser, J.A. A.; Heisel, M A; Bei, Hongbin; Russell, A M; Agnew, S R

    2010-01-01

    Representatives (AgY, CuY, AgEr, CuDy, MgY and MgCe) of the newly discovered family of ductile stoichiometric B2 intermetallic (metal-rare-earth element, MR) compounds were characterized by X-ray diffraction, to determine if their anomalous ductility is related to an exceptional level of phase purity, lack of chemical ordering or a strong crystallographic texture. Brittle NiAl served as an anti-type in this study. We found that all of the rare-earth compounds, except MgY, have a significant volume fraction (-5-20vol.%) of second phases (M{sub 2}R intermetallics and R{sub 2}O{sub 3} oxides), which has not been reported in previous studies of these materials. The most ductile of observed MR compounds, AgY, is highly ordered. A moderate texture was observed in AgY, which may explain its higher ductility (using polycrystal modeling) as compared to other MR compounds. However, the intrinsic polycrystalline ductility of these compounds in the randomly textured state (like that observed in CuY) still has no specific, definitive explanation.

  6. Effects of prior ductile tearing on cleavage fracture toughness in the transition region

    NASA Astrophysics Data System (ADS)

    Dodds, R. H., Jr.; Tang, M.; Anderson, T. L.

    1993-12-01

    Previous work by the authors described a micromechanics fracture model to correct measured J sub c-values for the mechanistic effects of large-scale yielding. This new work extends the model to also include the influence of ductile crack extension prior to cleavage. Ductile crack extensions of 10-15 times the initial crack tip opening displacement at initiation are considered in plane-strain, finite element computations. The finite element results demonstrate a significant elevation in crack-tip constraint due to macroscopic 'sharpening' of the extending tip relative to the-blunt tip at the initiation of growth. However this effect is offset partially by the additional plastic deformation associated with the increased applied J required to grow the crack. The initial a/W ratio, tearing modulus, strain hardening exponent and specimen size interact in a complex manner to define the evolving near-tip conditions for cleavage fracture. The paper explores development of the new model, provides necessary graphs and procedures for its application and demonstrates the effects of the model on fracture data sets for two pressure vessel steels (A533B and A515).

  7. An investigation of the loss of ductility in hydrogen charged beta-Ti alloys

    NASA Technical Reports Server (NTRS)

    Robertson, Ian M.

    1995-01-01

    The high strength, low density, and good corrosion resistance of Ti-based alloys make them candidate materials for a number of applications in the aerospace industry. A major limitation in the use of these alloys in the advanced hypersonic flight vehicle program is their susceptibility to hydrogen embrittlement. This study focuses on the hydrogen sensitivity of TIMETAL 21S beta-Ti alloy. The material received was in the form of grip-ends of failed tensile test samples which had been exposed to different charging conditions (combinations of hydrogen pressure and temperature). The samples received, the charging conditions, and their fracture mode are discussed. It can be seen that the fracture behavior changes from ductile to brittle with increasing hydrogen content, but the transition in behavior occurs for a small increase in hydrogen concentration. The aim of this program was to assess the microstructural differences between the ductile and brittle alloys to ascertain the embrittlement mechanism. A range of tools which included x-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used.

  8. Development of ductile Fe{sub 3}Al-based aluminides

    SciTech Connect

    McKamey, C.G.; Sikka, V.K.; Goodwin, G.M.

    1993-07-01

    Iron aluminides based on Fe{sub 3}Al are of interest because of their excellent oxidation and corrosion resistance, especially in sulfur-bearing atmospheres. Work at ORNL has centered on developing Fe{sub 3}Al-based alloys with improved ambient temperature ductilities and increased strengths at temperatures of 600--700C. Ambient temperature brittleness in this system is not ``inherent,`` but is caused by atomic hydrogen which is produced by an environmental reaction between aluminum in the alloy and water vapor in the atmosphere. Great strides have been made in understanding this embrittlement Phenomenon, and the production of alloys with room temperature ductilities of over 10% and tensile yield strengths at 600C of as high as 500 MPa is now possible through modifications in alloy composition and control of thermomechanical processing techniques. Creep rupture lifes of over 200 h at 593C (1100{degrees}F) and 207 MPa (30 ksi) can also be produced through control of alloy composition and microstructure. This paper summarizes our present efforts to improve the tensile and creep rupture properties and gives the status of efforts to commercialize Fe{sub 3}Al-based alloy compositions.

  9. Origin of Shear Stability and Compressive Ductility Enhancement of Metallic Glasses by Metal Coating

    PubMed Central

    Sun, B. A.; Chen, S. H.; Lu, Y. M.; Zhu, Z. G.; Zhao, Y. L.; Yang, Y.; Chan, K. C.; Liu, C. T.

    2016-01-01

    Metallic glasses (MGs) are notorious for the poor macroscopic ductility and to overcome the weakness various intrinsic and extrinsic strategies have been proposed in past decades. Among them, the metal coating is regarded as a flexible and facile approach, yet the physical origin is poorly understood due to the complex nature of shear banding process. Here, we studied the origin of ductile enhancement in the Cu-coating both experimentally and theoretically. By examining serrated shear events and their stability of MGs, we revealed that the thin coating layer plays a key role in stopping the final catastrophic failure of MGs by slowing down shear band dynamics and thus retarding its attainment to a critical instable state. The mechanical analysis on interplay between the coating layer and shear banding process showed the enhanced shear stability mainly comes from the lateral tension of coating layer induced by the surface shear step and the bonding between the coating layer and MGs rather than the layer thickness is found to play a key role in contributing to the shear stability. PMID:27271435

  10. Ductile deformations of opposite vergence in the eastern part of the Guerrero Terrane (SW Mexico)

    NASA Astrophysics Data System (ADS)

    Salinas-Prieto, J. C.; Monod, O.; Faure, M.

    2000-10-01

    The Teloloapan volcanic arc in SW Mexico represents the easternmost unit of the Guerrero Terrane. It is overthrust by the Arcelia volcanic unit and is thrust over the Guerrero-Morelos carbonate platform. These major structures result from two closely related tectonic events: first, an eastward verging, ductile deformation (D1) characterized by an axial-plane schistosity (S1) supporting an E-W trending mineral stretching lineation (L1) and associated with synschistose isoclinal, curvilinear folds (F1). Numerous kinematic indicators such as asymmetrical pressure-shadows, porphyroclast systems, and micro-shear bands (S-C structures) indicate a top-to-the-east shear along L1. This first deformation was followed by another ductile event (D2) that produced a crenulation cleavage (S2) associated with westward overturned folds (F2), hence showing that the vergence of D2 is opposite to that of D1. Regionally, both D1 and D2 deformations have been identified east and west of the Teloloapan unit, in the Arcelia volcanic rocks as well as in the Mexcala flysch of Late Cretaceous age overlying the Guerrero-Morelos platform. This implies that all three units were deformed and thrust simultaneously, during the Late Cretaceous or Paleocene, prior to the deposition of the overlying, undeformed Eocene red beds of the Balsas group.

  11. Masonry Infilling Effect On Seismic Vulnerability and Performance Level of High Ductility RC Frames

    SciTech Connect

    Ghalehnovi, M.; Shahraki, H.

    2008-07-08

    In last years researchers preferred behavior-based design of structure to force-based one for designing and construction of the earthquake-resistance structures, this method is named performance based designing. The main goal of this method is designing of structure members for a certain performance or behavior. On the other hand in most of buildings, load bearing frames are infilled with masonry materials which leads to considerable changes in mechanical properties of frames. But usually infilling wall's effect has been ignored in nonlinear analysis of structures because of complication of the problem and lack of simple logical solution. As a result lateral stiffness, strength, ductility and performance of the structure will be computed with less accuracy. In this paper by use of Smooth hysteretic model for masonry infillings, some high ductile RC frames (4, 8 stories including 1, 2 and 3 spans) designed according to Iranian code are considered. They have been analyzed by nonlinear dynamic method in two states, with and without infilling. Then their performance has been determined with criteria of ATC 40 and compared with recommended performance in Iranian seismic code (standard No. 2800)

  12. Origin of Shear Stability and Compressive Ductility Enhancement of Metallic Glasses by Metal Coating.

    PubMed

    Sun, B A; Chen, S H; Lu, Y M; Zhu, Z G; Zhao, Y L; Yang, Y; Chan, K C; Liu, C T

    2016-01-01

    Metallic glasses (MGs) are notorious for the poor macroscopic ductility and to overcome the weakness various intrinsic and extrinsic strategies have been proposed in past decades. Among them, the metal coating is regarded as a flexible and facile approach, yet the physical origin is poorly understood due to the complex nature of shear banding process. Here, we studied the origin of ductile enhancement in the Cu-coating both experimentally and theoretically. By examining serrated shear events and their stability of MGs, we revealed that the thin coating layer plays a key role in stopping the final catastrophic failure of MGs by slowing down shear band dynamics and thus retarding its attainment to a critical instable state. The mechanical analysis on interplay between the coating layer and shear banding process showed the enhanced shear stability mainly comes from the lateral tension of coating layer induced by the surface shear step and the bonding between the coating layer and MGs rather than the layer thickness is found to play a key role in contributing to the shear stability. PMID:27271435

  13. Gradient twinned 304 stainless steels for high strength and high ductility

    DOE PAGESBeta

    Chen, Aiying; Liu, Jiabin; Wang, Hongtao; Lu, Jian; Wang, Y. Morris

    2016-04-23

    Gradient materials often have attractive mechanical properties that outperform uniform microstructure counterparts. It remains a difficult task to investigate and compare the performance of various gradient microstructures due to the difficulty of fabrication, the wide range of length scales involved, and their respective volume percentage variations. We have investigated four types of gradient microstructures in 304 stainless steels that utilize submicrotwins, nanotwins, nanocrystalline-, ultrafine- and coarse-grains as building blocks. Tensile tests reveal that the gradient microstructure consisting of submicrotwins and nanotwins has a persistent and stable work hardening rate and yields an impressive combination of high strength and high ductility,more » leading to a toughness that is nearly 50% higher than that of the coarse-grained counterpart. Ex- and in-situ transmission electron microscopy indicates that nanoscale and submicroscale twins help to suppress and limit martensitic phase transformation via the confinement of martensite within the twin lamellar. Twinning and detwinning remain active during tensile deformation and contribute to the work hardening behavior. We discuss the advantageous properties of using submicrotwins as the main load carrier and nanotwins as the strengthening layers over those coarse and nanocrystalline grains. Furthermore, our work uncovers a new gradient design strategy to help metals and alloys achieve high strength and high ductility.« less

  14. Radiation-Induced Helium Nanobubbles Enhance Ductility in Submicron-Sized Single-Crystalline Copper.

    PubMed

    Ding, Ming-Shuai; Du, Jun-Ping; Wan, Liang; Ogata, Shigenobu; Tian, Lin; Ma, Evan; Han, Wei-Zhong; Li, Ju; Shan, Zhi-Wei

    2016-07-13

    The workability and ductility of metals usually degrade with exposure to irradiation, hence the phrase "radiation damage". Here, we found that helium (He) radiation can actually enhance the room-temperature deformability of submicron-sized copper. In particular, Cu single crystals with diameter of 100-300 nm and containing numerous pressurized sub-10 nm He bubbles become stronger, more stable in plastic flow and ductile in tension, compared to fully dense samples of the same dimensions that tend to display plastic instability (strain bursts). The sub-10 nm He bubbles are seen to be dislocation sources as well as shearable obstacles, which promote dislocation storage and reduce dislocation mean free path, thus contributing to more homogeneous and stable plasticity. Failure happens abruptly only after significant bubble coalescence. The current findings can be explained in light of Weibull statistics of failure and the beneficial effects of bubbles on plasticity. These results shed light on plasticity and damage developments in metals and could open new avenues for making mechanically robust nano- and microstructures by ion beam processing and He bubble engineering. PMID:27249672

  15. Evolution of Microstructures During Austempering of Ductile Irons Alloyed with Manganese and Copper

    NASA Astrophysics Data System (ADS)

    Dasgupta, Ranjan Kumar; Mondal, Dipak Kumar; Chakrabarti, Ajit Kumar

    2013-03-01

    The influences of relatively high manganese (0.45 through 1.0 wt pct) and copper (0.56 through 1.13 wt pct) contents on microstructure development and phase transformation in three austempered ductile irons have been studied. The experimental ductile irons alloyed with copper and manganese are found to be practically free from intercellular manganese segregation. This suggests that the positive segregation of manganese is largely neutralized by the negative segregation of copper when these alloying elements are added in appropriate proportions. The drop in unreacted austenite volume (UAV) with increasing austempering temperature and time is quite significant in irons alloyed with copper and manganese. The ausferrite morphology also undergoes a transition from lenticular to feathery appearance of increasing coarseness with the increasing austempering temperature and time. SEM micrographs of the austempered samples from the base alloy containing manganese only, as well as copper plus manganese-alloyed irons, clearly reveal the presence of some martensite along with retained austenite and ferrite. X-ray diffraction analysis also confirms the presence of these phases. SEM examination further reveals the presence of twinned martensite in the copper plus manganese-alloyed samples. The possibility of strain-induced transformation of austenite to martensite during austempering heat treatment is suggested.

  16. Creep and rupture of an ODS alloy with high stress rupture ductility. [Oxide Dispersion Strengthened

    NASA Technical Reports Server (NTRS)

    Mcalarney, M. E.; Arsons, R. M.; Howson, T. E.; Tien, J. K.; Baranow, S.

    1982-01-01

    The creep and stress rupture properties of an oxide (Y2O3) dispersion strengthened nickel-base alloy, which also is strengthened by gamma-prime precipitates, was studied at 760 and 1093 C. At both temperatures, the alloy YDNiCrAl exhibits unusually high stress rupture ductility as measured by both elongation and reduction in area. Failure was transgranular, and different modes of failure were observed including crystallographic fracture at intermediate temperatures and tearing or necking almost to a chisel point at higher temperatures. While the rupture ductility was high, the creep strength of the alloy was low relative to conventional gamma prime strengthened superalloys in the intermediate temperature range and to ODS alloys in the higher temperature range. These findings are discussed with respect to the alloy composition; the strengthening oxide phases, which are inhomogeneously dispersed; the grain morphology, which is coarse and elongated and exhibits many included grains; and the second phase inclusion particles occurring at grain boundaries and in the matrix. The creep properties, in particular the high stress dependencies and high creep activation energies measured, are discussed with respect to the resisting stress model of creep in particle strengthened alloys.

  17. Modeling of damage in ductile cast iron - The effect of including plasticity in the graphite nodules

    NASA Astrophysics Data System (ADS)

    Andriollo, T.; Thorborg, J.; Tiedje, N. S.; Hattel, J.

    2015-06-01

    In the present paper a micro-mechanical model for investigating the stress-strain relation of ductile cast iron subjected to simple loading conditions is presented. The model is based on a unit cell containing a single spherical graphite nodule embedded in a uniform ferritic matrix, under the assumption of infinitesimal strains and plane-stress conditions. Despite the latter being a limitation with respect to full 3D models, it allows a direct comparison with experimental investigations of damage evolution on the surface of ductile cast iron components, where the stress state is biaxial in nature. In contrast to previous works on the subject, the material behaviour in both matrix and nodule is assumed to be elasto-plastic, described by the classical J2-flow theory of plasticity, and damage evolution in the matrix is taken into account via Lemaitre's isotropic model. The effects of residual stresses due to the cooling process during manufacturing are also considered. Numerical solutions are obtained using an in-house developed finite element code; proper comparison with literature in the field is given.

  18. PREDICTION OF CHARACTERISTIC LENGTH AND FRACTURE TOUGHNESS IN DUCTILE-BRITTLE TRANSITION

    SciTech Connect

    Lam, P

    2008-04-15

    Finite element method was used to analyze the three-point bend experimental data of A533B-1 pressure vessel steel obtained by Sherry, Lidbury, and Beardsmore [1] from -160 to -45 C within the ductile-brittle transition regime. As many researchers have shown, the failure stress ({sigma}{sub f}) of the material could be approximated as a constant. The characteristic length, or the critical distance (r{sub c}) from the crack tip, at which {sigma}{sub f} is reached, is shown to be temperature dependent based on the crack tip stress field calculated by the finite element method. With the J-A{sub 2} two-parameter constraint theory in fracture mechanics, the fracture toughness (J{sub C} or K{sub JC}) can be expressed as a function of the constraint level (A{sub 2}) and the critical distance r{sub c}. This relationship is used to predict the fracture toughness of A533B-1 in the ductile-brittle transition regime with a constant {sigma}{sub f} and a set of temperature-dependent r{sub c}. It can be shown that the prediction agrees well with the test data for wide range of constraint levels from shallow cracks (a/W= 0.075) to deep cracks (a/W= 0.5), where a is the crack length and W is the specimen width.

  19. A micro-model for eutectoid phase transformations in as-cast ductile iron

    SciTech Connect

    Vijayaraghavan, R.; Bradley, F.J.

    1999-11-05

    As ductile iron is cooled below the eutectoid temperature range, there are two branches available for decomposition of the eutectoid austenite: the stable eutectoid reaction (ferrite reaction) in which ferrite and graphite are the product phases and the metastable eutectoid reaction (pearlite reaction) leading to pearlite formation. The following sections describe mathematical formulation and calibration of a semi-empirical micro-model to simulate solid-state transformations in as-cast ductile iron. A comprehensive set of data and experimental results obtained from laboratory experiments in conjunction with an optimization methodology has been used to calibrate the micro-model. The experimental results consisted of cooling curve and microstructure characterization data obtained from a series of heats conducted as a part of industry sponsored research aimed at developing thermal analysis based methodologies for process control in foundries. Four different types of thermal analysis cups were poured. As the principal objective in this work is to develop a model to predict microstructure evolution, heat transfer in the thermal analysis cups is simulated using a simple lumped system volume element model in which the temperature is a function of time only.

  20. A process model for the microstructure evolution in ductile cast iron. Part 1: The model

    SciTech Connect

    Onsoeien, M.I.; Gundersen, O.; Grong, O.; Skaland, T.

    1999-04-01

    In the present investigation, the multiple phase changes occurring during solidification and subsequent cooling of near-eutectic ductile cast iron have been modeled using the internal state variable approach. According to this formalism, the microstructure evolution is captured mathematically in terms of differential variation of the primary state variables with time for each of the relevant mechanisms. Separate response equations have then been developed to convert the current values of the state variables into equivalent volume fractions of constituent phases utilizing the constraints provided by the phase diagram. The results may conveniently be represented in the form of C curves and process diagrams to illuminate how changes in alloy composition, graphite nucleation potential, and thermal program affect the microstructure evolution at various stages of the process. The model can readily be implemented in a dedicated numerical code for the thermal field in real castings and used as a guiding tool in design of new treatment alloys for ductile cast irons. An illustration of this is given in an accompanying article (Part 2).

  1. Burst Ductility of Zirconium Clads: The Defining Role of Residual Stress

    NASA Astrophysics Data System (ADS)

    Kumar, Gulshan; Kanjarla, A. K.; Lodh, Arijit; Singh, Jaiveer; Singh, Ramesh; Srivastava, D.; Dey, G. K.; Saibaba, N.; Doherty, R. D.; Samajdar, Indradev

    2016-05-01

    Closed end burst tests, using room temperature water as pressurizing medium, were performed on a number of industrially produced zirconium (Zr) clads. A total of 31 samples were selected based on observed differences in burst ductility. The latter was represented as total circumferential elongation or TCE. The selected samples, with a range of TCE values (5 to 35 pct), did not show any correlation with mechanical properties along axial direction, microstructural parameters, crystallographic textures, and outer tube-surface normal (σ 11) and shear (τ 13) components of the residual stress matrix. TCEs, however, had a clear correlation with hydrostatic residual stress (P h), as estimated from tri-axial stress analysis on the outer tube surface. Estimated P h also scaled with measured normal stress (σ 33) at the tube cross section. An elastic-plastic finite element model with ductile damage failure criterion was developed to understand the burst mechanism of zirconium clads. Experimentally measured P h gradients were imposed on a solid element continuum finite element (FE) simulation to mimic the residual stresses present prior to pressurization. Trends in experimental TCEs were also brought out with computationally efficient shell element-based FE simulations imposing the outer tube-surface P h values. Suitable components of the residual stress matrix thus determined the burst performance of the Zr clads.

  2. Ductility of Advanced High-Strength Steel in the Presence of a Sheared Edge

    NASA Astrophysics Data System (ADS)

    Ruggles, Tim; Cluff, Stephen; Miles, Michael; Fullwood, David; Daniels, Craig; Avila, Alex; Chen, Ming

    2016-07-01

    The ductility of dual-phase (DP) 980 and transformation-induced plasticity (TRIP) assisted bainitic ferritic (TBF) 980 steels was studied in the presence of a sheared edge. Specimens were tested in uniaxial tension in a standard test frame as well as in situ in the scanning electron microscope (SEM). Incremental tensile straining was done in the SEM with images taken at each strain increment. Then digital image correlation (DIC) was used to compute the effective strain at the level of the individual phases in the microstructure. Shear banding across multiple phases was seen in strained TBF specimens, while the DP specimens exhibited more of a patchwork strain pattern, with high strains concentrated in ferrite and low strains observed in the martensite. Two-point statistics were applied to the strain data from the DIC work and the corresponding microstructure images to evaluate the effect of phase hardness on localization and fracture. It was observed that the DP 980 material had a greater tendency for localization around hard phases compared to the TBF 980. This at least partially explains the greater ductility of the TBF material, especially in specimens where a sheared edge was present.

  3. Lithospheric extension near Lake Mead, Nevada - A model for ductile flow in the lower crust

    NASA Technical Reports Server (NTRS)

    Kruse, Sarah; Mcnutt, Marcia; Phipps-Morgan, Jason; Royden, Leigh

    1991-01-01

    Small variations in gravity anomalies and topographic elevation observed in areas that have undergone highly variable amounts of upper crustal thinning can be satisfactorily explained by ductile flow of lower crustal material under the proper conditions. The boundary between the unextended Colorado Plateau and a strongly extended domain in the Basin and Range Province in the Lake Mead (Nevada) region is examined. Finite element modeling of Newtonian flow and power law creep shows that flow over the length scale of the eastern Basin and Range (500) km or more) corresponding to upper crustal extension by a factor of 1.4-3 over 10 million years requires effective viscosities less than 10 to the 18th - 10 to the 20th Pa s for ductile channels 10-25 km thick. Modeling suggests that these effective viscosities may be sustained by lower crustal material deforming at laboratory-derived power law creep rates. The longer-scale flow may require elevated crustal temperatures (more than 700 C), depending on the composition and material properties assumed. Under the boundary conditions assumed in this study the linear viscous flow models yield a satisfactory approximation to deformation by power law creep. This work suggests that flow in the lower crust may be a viable mechanism for producing small variations in total crustal thickness between strongly extended and less extended regions, and thereby explaining the relative uniformity in gravity and topography between such regions.

  4. Lithospheric extension near Lake Mead, Nevada - A model for ductile flow in the lower crust

    NASA Astrophysics Data System (ADS)

    Kruse, Sarah; McNutt, Marcia; Phipps-Morgan, Jason; Royden, Leigh

    1991-03-01

    Small variations in gravity anomalies and topographic elevation observed in areas that have undergone highly variable amounts of upper crustal thinning can be satisfactorily explained by ductile flow of lower crustal material under the proper conditions. The boundary between the unextended Colorado Plateau and a strongly extended domain in the Basin and Range Province in the Lake Mead (Nevada) region is examined. Finite element modeling of Newtonian flow and power law creep shows that flow over the length scale of the eastern Basin and Range (500) km or more) corresponding to upper crustal extension by a factor of 1.4-3 over 10 million years requires effective viscosities less than 10 to the 18th - 10 to the 20th Pa s for ductile channels 10-25 km thick. Modeling suggests that these effective viscosities may be sustained by lower crustal material deforming at laboratory-derived power law creep rates. The longer-scale flow may require elevated crustal temperatures (more than 700 C), depending on the composition and material properties assumed. Under the boundary conditions assumed in this study the linear viscous flow models yield a satisfactory approximation to deformation by power law creep. This work suggests that flow in the lower crust may be a viable mechanism for producing small variations in total crustal thickness between strongly extended and less extended regions, and thereby explaining the relative uniformity in gravity and topography between such regions.

  5. Element-wise algorithm for modeling ductile fracture with the Rousselier yield function

    NASA Astrophysics Data System (ADS)

    Areias, P.; Dias-da-Costa, D.; Sargado, J. M.; Rabczuk, T.

    2013-12-01

    Within the theme of ductile fracture in metals, we propose an algorithm for FEM-based computational fracture based on edge rotations and smoothing of complementarity conditions. Rotation axes are the crack front nodes in surface discretizations and each rotated edge affects the position of only one or two nodes. Modified edge positions correspond to the predicted crack path. To represent softening, porous plasticity in the form of the Rousselier yield function is used. The finite strain integration algorithm makes use of a consistent updated Lagrangian formulation which makes use of polar decomposition between each increment. Constitutive updating is based on the implicit integration of a regularized non-smooth problem. The proposed alternative is advantageous when compared with enriched elements that can be significantly different than classical FEM elements and still pose challenges for ductile fracture or large amplitude sliding. For history-dependent materials, there are still some transfer of relevant quantities between meshes. However, diffusion of results is more limited than with tip or full remeshing. To illustrate the advantages of our approach, fracture examples making use of the Rousselier yield function are presented. The Ma-Sutton crack path criterion is employed. Traditional fracture benchmarks and newly proposed verification tests are solved. These were found to be very good in terms of crack path and load/displacement accuracy.

  6. The effect of cyclic loading during ductile tearing on the fracture resistance of nuclear pipe steels

    SciTech Connect

    Rudland, D.L.; Brust, F.

    1997-12-01

    As part of the First International Piping and Integrity Research Group (IPIRG-1) program, a series of 152.4-mm (6-in.)-diameter Schedule 120, A106 Grade B carbon steel and TP304 stainless steel cyclic through-wall crack (TWC) pipe tests were conducted at 288 C (550 F). The conclusion reached from these experiments was that fully reversed loading decreases the ductile tearing resistance of nuclear pipe steels. As part of the Second International Piping and Integrity Research Group (IPIRG-2) program, a series of cyclically loaded compact tension [C(T)] tests were conducted to determine if this effect is present in laboratory specimens and whether these small-scale results can be used to predict larger through-wall crack pipe behavior. The specimens wee run in displacement control using several cyclic displacement increments and stress ratios. It was found that as the stress ratio was decreased, i.e., the amount of compressive plasticity is increased, the ductile tearing resistance of the material decreased. Fractographic analysis was performed on several C(T) specimens to determine the cyclic degradation mechanism. It was found that crack tip sharpening and void flattening were observed and could be the mechanisms that contributed to the cyclic degradation. In addition to the laboratory tests, finite element analyses were performed on a cyclic C(T) specimen to verify the ASTM E 1152 procedure used and to calculate the cyclic J-R curves.

  7. Ductility of Advanced High-Strength Steel in the Presence of a Sheared Edge

    NASA Astrophysics Data System (ADS)

    Ruggles, Tim; Cluff, Stephen; Miles, Michael; Fullwood, David; Daniels, Craig; Avila, Alex; Chen, Ming

    2016-05-01

    The ductility of dual-phase (DP) 980 and transformation-induced plasticity (TRIP) assisted bainitic ferritic (TBF) 980 steels was studied in the presence of a sheared edge. Specimens were tested in uniaxial tension in a standard test frame as well as in situ in the scanning electron microscope (SEM). Incremental tensile straining was done in the SEM with images taken at each strain increment. Then digital image correlation (DIC) was used to compute the effective strain at the level of the individual phases in the microstructure. Shear banding across multiple phases was seen in strained TBF specimens, while the DP specimens exhibited more of a patchwork strain pattern, with high strains concentrated in ferrite and low strains observed in the martensite. Two-point statistics were applied to the strain data from the DIC work and the corresponding microstructure images to evaluate the effect of phase hardness on localization and fracture. It was observed that the DP 980 material had a greater tendency for localization around hard phases compared to the TBF 980. This at least partially explains the greater ductility of the TBF material, especially in specimens where a sheared edge was present.

  8. Effect of Tempering Temperature and Time on Strength and Hardness of Ductile Cast Iron

    NASA Astrophysics Data System (ADS)

    Kumar, R.; Behera, R. K.; Sen, S.

    2015-02-01

    The effects of tempering temperature and time on the mechanical properties of ductile cast iron is investigated in the current work. The specimens were austenitized at 900°C for 120 minutes and then quenched in mineral oil at room temperature. Immediately after quenching the specimens were tempered at 400°C and 200°C for 60min, 90min, and 120min. In the tempering temperature range of 200°C-400°C, there is sudden increase in impact strength, ductility and toughness of the materials, as the temperature and time increase. The UTS drops initially, and hardness of materials will depends on amount of phase of martensitic and retained austenitic and graphite nodules. In this work alloying elements also effected the microstructure of the specimen. And due to increase tempering time the amount of martensitic phase will decrease and retained austenitic phase will increase, retained austenitic phase is softer then martensitic so hardness will decrease.

  9. Ductile opening-mode fracture by pore growth and coalescence during combustion alteration of siliceous mudstone

    NASA Astrophysics Data System (ADS)

    Eichhubl, Peter; Aydin, Atilla

    2003-01-01

    Opening-mode fractures with blunt tips and large maximum apertures are characteristic of clinker that formed by combustion alteration of siliceous mudstone. These fractures are inferred to result from pore growth and coalescence, with initially circular pores inherited from the diatomaceous protolith. Circular pores grow preferentially in an en-échelon arrangement and coalesce to elongate pores and blunt-tipped fractures by thinning and rupture of bridges between pores. Coalescence of overlapping en-échelon pores causes fracture propagation in a zig-zag path that is considered indicative of significant inelastic deformation outside the immediate vicinity of the fracture tips. This process of fracture formation by void growth and coalescence is inferred to result from solution mass transfer and possible bulk melt movement during partial melting of clinker. Chemical mass transfer provides a mechanism for extensive inelastic deformation in the surrounding host rock concurrent with fracturing that is considered characteristic of ductile fracture. The preferred elongation of coalescing pores and local rupture of pore bridges is explained by a tensile sintering stress due to the thermodynamic tendency of the system for energy minimization of solid and liquid surfaces. It is suggested that ductile fracture processes that are accompanied by extensive inelastic deformation lead to opening-mode fractures with large apertures in a variety of crustal settings including metamorphic and magmatic systems as well as in reactive diagenetic environments, thus affecting fracture-controlled transfer of heat and mass and the rheology of the Earth's crust.

  10. Study on the cutting mechanism and the brittle ductile transition model of isotropic pyrolyric graphite

    NASA Astrophysics Data System (ADS)

    Wang, Minghai; Wang, Hujun; Liu, Zhonghai

    2010-12-01

    Isotropic pyrolyric graphite (IPG) is a new kind of brittle material, it can be used for sealing the aero-engine turbine shaft and the ethylene high-temperature equipment. It not only has the general advantages of ordinal carbonaceous materials such as high temperature resistance, lubrication and abrasion resistance, but also has the advantages of impermeability and machinability that carbon/carbon composite doesn't have. Therefore, it has broad prospects for development. Mechanism of brittle-ductile transition of IPG is the foundation of precision cutting while the plastic deformation of IPG is the essential and the most important mechanical behavior of precision cutting. Using the theory of strain gradient, the mechanism of this material removal during the precision cutting is analyzed. The critical cutting thickness of IPG is calculated for the first time. Furthermore, the cutting process parameters such as cutting depth, feed rate which corresponding to the scale of brittle-ductile transition deformation of IPG are calculated. In the end, based on the theory of micromechanics, the deformation behaviors of IPG such as brittle fracture, plastic deformation and mutual transformation process are all simulated under the Sih.G.C fracture criterion. The condition of the simulation is that the material under the pressure-shear loading conditions .The result shows that the best angle during the IPG precision cutting is -30°. The theoretical analysis and the simulation result are validated by precision cutting experiments.

  11. Study on the cutting mechanism and the brittle ductile transition model of isotropic pyrolyric graphite

    NASA Astrophysics Data System (ADS)

    Wang, Minghai; Wang, Hujun; Liu, Zhonghai

    2011-05-01

    Isotropic pyrolyric graphite (IPG) is a new kind of brittle material, it can be used for sealing the aero-engine turbine shaft and the ethylene high-temperature equipment. It not only has the general advantages of ordinal carbonaceous materials such as high temperature resistance, lubrication and abrasion resistance, but also has the advantages of impermeability and machinability that carbon/carbon composite doesn't have. Therefore, it has broad prospects for development. Mechanism of brittle-ductile transition of IPG is the foundation of precision cutting while the plastic deformation of IPG is the essential and the most important mechanical behavior of precision cutting. Using the theory of strain gradient, the mechanism of this material removal during the precision cutting is analyzed. The critical cutting thickness of IPG is calculated for the first time. Furthermore, the cutting process parameters such as cutting depth, feed rate which corresponding to the scale of brittle-ductile transition deformation of IPG are calculated. In the end, based on the theory of micromechanics, the deformation behaviors of IPG such as brittle fracture, plastic deformation and mutual transformation process are all simulated under the Sih.G.C fracture criterion. The condition of the simulation is that the material under the pressure-shear loading conditions .The result shows that the best angle during the IPG precision cutting is -30°. The theoretical analysis and the simulation result are validated by precision cutting experiments.

  12. Burst Ductility of Zirconium Clads: The Defining Role of Residual Stress

    NASA Astrophysics Data System (ADS)

    Kumar, Gulshan; Kanjarla, A. K.; Lodh, Arijit; Singh, Jaiveer; Singh, Ramesh; Srivastava, D.; Dey, G. K.; Saibaba, N.; Doherty, R. D.; Samajdar, Indradev

    2016-08-01

    Closed end burst tests, using room temperature water as pressurizing medium, were performed on a number of industrially produced zirconium (Zr) clads. A total of 31 samples were selected based on observed differences in burst ductility. The latter was represented as total circumferential elongation or TCE. The selected samples, with a range of TCE values (5 to 35 pct), did not show any correlation with mechanical properties along axial direction, microstructural parameters, crystallographic textures, and outer tube-surface normal ( σ 11) and shear ( τ 13) components of the residual stress matrix. TCEs, however, had a clear correlation with hydrostatic residual stress ( P h), as estimated from tri-axial stress analysis on the outer tube surface. Estimated P h also scaled with measured normal stress ( σ 33) at the tube cross section. An elastic-plastic finite element model with ductile damage failure criterion was developed to understand the burst mechanism of zirconium clads. Experimentally measured P h gradients were imposed on a solid element continuum finite element (FE) simulation to mimic the residual stresses present prior to pressurization. Trends in experimental TCEs were also brought out with computationally efficient shell element-based FE simulations imposing the outer tube-surface P h values. Suitable components of the residual stress matrix thus determined the burst performance of the Zr clads.

  13. Brittle and Ductile Behavior in Deep-Seated Landslides: Learning from the Vajont Experience

    NASA Astrophysics Data System (ADS)

    Paronuzzi, Paolo; Bolla, Alberto; Rigo, Elia

    2016-06-01

    This paper analyzes the mechanical behavior of the unstable Mt. Toc slope before the 1963 catastrophic collapse, considering both the measured data (surface displacements and microseismicity) and the updated geological model of the prehistoric rockslide. From February 1960 up to 9 October 1963, the unstable mass behaved as a brittle-ductile `mechanical system,' characterized by remarkable microseismicity as well as by considerable surface displacements (up to 4-5 m). Recorded microshocks were the result of progressive rock fracturing of distinct resisting stiff parts made up of intact rock (indentations, undulations, and rock bridges). The main resisting stiff part was a large rock indentation located at the NE extremity of the unstable mass that acted as a mechanical constraint during the whole 1960-1963 period, inducing a progressive rototranslation toward the NE. This large constraint failed in autumn 1960, when an overall slope failure took place, as emphasized by the occurrence of the large perimetrical crack in the upper slope. In this circumstance, the collapse was inhibited by a reblocking phenomenon of the unstable mass that had been previously destabilized by the first reservoir filling. Progressive failure of localized intact rock parts progressively propagated westwards as a consequence of the two further filling-drawdown cycles of the reservoir (1962 and 1963). The characteristic brittle-ductile behavior of the Vajont landslide was made possible by the presence of a very thick (40-50 m) and highly deformable shear zone underlying the upper rigid rock mass (100-120 m thick).

  14. Origin of Shear Stability and Compressive Ductility Enhancement of Metallic Glasses by Metal Coating

    NASA Astrophysics Data System (ADS)

    Sun, B. A.; Chen, S. H.; Lu, Y. M.; Zhu, Z. G.; Zhao, Y. L.; Yang, Y.; Chan, K. C.; Liu, C. T.

    2016-06-01

    Metallic glasses (MGs) are notorious for the poor macroscopic ductility and to overcome the weakness various intrinsic and extrinsic strategies have been proposed in past decades. Among them, the metal coating is regarded as a flexible and facile approach, yet the physical origin is poorly understood due to the complex nature of shear banding process. Here, we studied the origin of ductile enhancement in the Cu-coating both experimentally and theoretically. By examining serrated shear events and their stability of MGs, we revealed that the thin coating layer plays a key role in stopping the final catastrophic failure of MGs by slowing down shear band dynamics and thus retarding its attainment to a critical instable state. The mechanical analysis on interplay between the coating layer and shear banding process showed the enhanced shear stability mainly comes from the lateral tension of coating layer induced by the surface shear step and the bonding between the coating layer and MGs rather than the layer thickness is found to play a key role in contributing to the shear stability.

  15. Reliability model for ductile hybrid FRP rebar using randomly dispersed chopped fibers

    NASA Astrophysics Data System (ADS)

    Behnam, Bashar Ramzi

    Fiber reinforced polymer composites or simply FRP composites have become more attractive to civil engineers in the last two decades due to their unique mechanical properties. However, there are many obstacles such as low elasticity modulus, non-ductile behavior, high cost of the fibers, high manufacturing costs, and absence of rigorous characterization of the uncertainties of the mechanical properties that restrict the use of these composites. However, when FRP composites are used to develop reinforcing rebars in concrete structural members to replace the conventional steel, a huge benefit can be achieved since FRP materials don't corrode. Two FRP rebar models are proposed that make use of multiple types of fibers to achieve ductility, and chopped fibers are used to reduce the manufacturing costs. In order to reach the most optimum fractional volume of each type of fiber, to minimize the cost of the proposed rebars, and to achieve a safe design by considering uncertainties in the materials and geometry of sections, appropriate material resistance factors have been developed, and a Reliability Based Design Optimization (RBDO), has been conducted for the proposed schemes.

  16. Dislocation creation and void nucleation in FCC ductile metals under tensile loading: A general microscopic picture

    PubMed Central

    Pang, Wei-Wei; Zhang, Ping; Zhang, Guang-Cai; Xu, Ai-Guo; Zhao, Xian-Geng

    2014-01-01

    Numerous theoretical and experimental efforts have been paid to describe and understand the dislocation and void nucleation processes that are fundamental for dynamic fracture modeling of strained metals. To date an essential physical picture on the self-organized atomic collective motions during dislocation creation, as well as the essential mechanisms for the void nucleation obscured by the extreme diversity in structural configurations around the void nucleation core, is still severely lacking in literature. Here, we depict the origin of dislocation creation and void nucleation during uniaxial high strain rate tensile processes in face-centered-cubic (FCC) ductile metals. We find that the dislocations are created through three distinguished stages: (i) Flattened octahedral structures (FOSs) are randomly activated by thermal fluctuations; (ii) The double-layer defect clusters are formed by self-organized stacking of FOSs on the close-packed plane; (iii) The stacking faults are formed and the Shockley partial dislocations are created from the double-layer defect clusters. Whereas, the void nucleation is shown to follow a two-stage description. We demonstrate that our findings on the origin of dislocation creation and void nucleation are universal for a variety of FCC ductile metals with low stacking fault energies. PMID:25382029

  17. Strain modeling of attachment zones developed between brittle and ductile crust at wrenching plate boundaries

    NASA Astrophysics Data System (ADS)

    Teyssier, C.; Tikoff, B.; Weber, J.

    2001-12-01

    Using strain modeling we analyze the ductile deformation beneath rigid upper crustal blocks that rotate and translate in wrench zones. We define the zone of deformation as an "attachment zone" and assume strain continuity between the wrench shearing in the ductile crust and the horizontal shearing induced by the rotation/translation of rigid blocks. For reasonable amounts of rotation/translation of rigid blocks and reasonable thicknesses of attachment zones, the orientation and shape of the finite strain ellipsoids within attachment zones are calculated, and the orientation of planar and linear fabrics are predicted. Attachment zones beneath rotating blocks should display radiating foliation and concentric lineations; if rotation of rigid blocks is driven from below, deformation in the attachment zone is dominated by the wrench component, altering significantly the radiating and concentric patterns of foliation and lineation. Attachment zones beneath translating blocks display a wide range of foliation orientations, with steep foliations below the central part of rigid blocks, and gently dipping foliations toward the margins. Below the upper crustal strike-slip faults, foliation is shallowly dipping, strain intensity is maximum, and there is an abrupt reversal of sense of shear across a presumed discontinuity. The linear belt of greenschist-grade metamorphic rocks in Trinidad's Northern Ranges and eastern Venezuela's Paria Peninsula is a candidate for an exhumed attachment zone developed beneath translating upper crustal blocks during Neogene highly oblique convergence between the Caribbean and South America plates.

  18. Prevention of ductility loss in hydrogen-charged steel by gamma-ray irradiation

    SciTech Connect

    Miki, T.; Ikeya, M.; Touge, M.

    1984-11-01

    Hydrogen is known as a constituent which degrades the mechanical properties of metals and alloys, particularly their ductility. The degradation of mechanical properties, called hydrogen embrittlement, is a serious problem in metals and alloys under a hydrogen environment, e.g., pickling, welding, plating, etc. Although many researches have been made to clarify the nature and the mechanism of hydrogen embrittlement in steels (1), little has been reported on the method of prevention of hydrogen embrittlement except for works by Pressouyre and Bernstein (2,3). They showed that the susceptibility of ferrous alloys to hydrogen embrittlement is reduced by addition of titanium. Recently, we found that hydrogen in stainless steels is outgassed upon exposure to ionizing radiation (4-7). Therefore, hydrogen embrittlement in steels is expected to be influenced by ionizing radiation. This study was undertaken to determine the extent of prevension of hydrogen embrittlement by examining the effect of gammairradiation on the ductility in a low carbon steel electrolytically charged with hydrogen.

  19. Deformation mechanisms of NiAl cyclicly deformed near the brittle-to-ductile transition temperature

    NASA Technical Reports Server (NTRS)

    Cullers, Cheryl L.; Antolovich, Stephen D.

    1993-01-01

    The intermetallic compound NiAl is one of many advanced materials which is being scrutinized for possible use in high temperature, structural applications. Stoichiometric NiAl has a high melting temperature, excellent oxidation resistance, and good thermal conductivity. Past research has concentrated on improving monotonic properties. The encouraging results obtained on binary and micro-alloyed NiAl over the past ten years have led to the broadening of NiAl experimental programs. The purpose of this research project was to determine the low cycle fatigue properties and dislocation mechanisms of stoichiometric NiAl at temperatures near the monotonic brittle-to-ductile transition. The fatigue properties were found to change only slightly in the temperature range of 600 to 700 K; a temperature range over which monotonic ductility and fracture strength increase markedly. The shape of the cyclic hardening curves coincided with the changes observed in the dislocation structures. The evolution of dislocation structures did not appear to change with temperature.

  20. Reducing deformation anisotropy to achieve ultrahigh strength and ductility in Mg at the nanoscale.

    PubMed

    Yu, Qian; Qi, Liang; Mishra, Raja K; Li, Ju; Minor, Andrew M

    2013-08-13

    In mechanical deformation of crystalline materials, the critical resolved shear stress (CRSS; τCRSS) is the stress required to initiate movement of dislocations on a specific plane. In plastically anisotropic materials, such as Mg, τCRSS for different slip systems differs greatly, leading to relatively poor ductility and formability. However, τCRSS for all slip systems increases as the physical dimension of the sample decreases to approach eventually the ideal shear stresses of a material, which are much less anisotropic. Therefore, as the size of a sample gets smaller, the yield stress increases and τCRSS anisotropy decreases. Here, we use in situ transmission electron microscopy mechanical testing and atomistic simulations to demonstrate that τCRSS anisotropy can be significantly reduced in nanoscale Mg single crystals, where extremely high stresses (∼2 GPa) activate multiple deformation modes, resulting in a change from basal slip-dominated plasticity to a more homogeneous plasticity. Consequently, an abrupt and dramatic size-induced "brittle-to-ductile" transition occurs around 100 nm. This nanoscale change in the CRSS anisotropy demonstrates the powerful effect of size-related deformation mechanisms and should be a general feature in plastically anisotropic materials. PMID:23904487

  1. Experimental observation of dynamic ductile damage development under various triaxiality conditions

    NASA Astrophysics Data System (ADS)

    Pillon, Laurianne; Adolf, Lise-Marie

    2015-06-01

    Fracture in ductile materials finds its origin in microscopic mechanisms: the nucleation of voids that grow and coalesce in order to form a crack. The most popular of these models, proposed by Gurson, aims at describing the damage development with respect to the plastic behavior of porous material. The Gurson model has been extended by Perrin to describe damage evolution in ductile viscoplastic porous materials. The Gurson-Perrin model (GPm) allows representing damage development with respect to the stress triaxiality and strain-rate conditions. We propose a new experimental design able to test and validate the GPm under various dynamic conditions and for different triaxiality levels. The experimental project will be detailed. A notch is drawn in the Cu cylindrical target where damage develops and the local failure occurs. A variation of the notch radius enables a variation in the triaxiality level. Three notch radii have been tested. Observations with numerical cameras allow following the shape of the notch, a characteristic of damage development. Several PDV measurements have been performed around the target. A first analysis of this experimental process will be shown and comparisons with numerical simulations will be presented.

  2. Development of extremely ductile lead-free Sn-Al solders for futuristic electronic packaging applications

    NASA Astrophysics Data System (ADS)

    Alam, Md Ershadul; Gupta, Manoj

    2014-03-01

    In the present study, new lead-free Sn-Al solders are developed incorporating varying amount of Al (0.4 and 0.6% by weight) into pure Sn using disintegrated melt deposition technique. Solder samples were then subsequently extruded at room temperature and characterized. Microstructural characterization studies revealed equiaxed grain morphology, minimal porosity, reasonably uniform distribution of Al particles and good Sn-Al interfacial integrity. Melting temperature of Sn-0.6Al (228°C) was found to be close to the eutectic Sn-0.7Cu (227°C) solders. Microhardness was increased with increasing amount of Al in pure Sn. Room temperature tensile test results revealed that newly developed Sn-0.6Al solders exhibited significant improvement in 0.2% yield strength (˜67%), ultimate tensile strength (˜18%) and ductility (˜123%) when compared to commercial Sn-0.7Cu solder. Ductility was improved about 222%, 263% and 81% when compared to commercially available Sn-3.5Ag-0.7Cu, Sn-3.5Ag and Sn-37Pb solders, respectively without compromising strength.

  3. An Improved Approach to Fracture Toughness Assessment of Brittle Coating on Ductile Substrate Systems under Indentation

    NASA Astrophysics Data System (ADS)

    Demidova, Natalia V.

    Fracture toughness is an important material property that determines the structural integrity of a component with pre-existing or service-generated flaws. In the present research, an indentation-based method and the associated fracture mechanics model are proposed for fracture toughness assessment of brittle coating/ductile substrate systems. The proposed models consider well-developed radial/median cracks generated under sharp indentation, despite that the crack formation process may have gone through crack initiation and propagation phases. For generality, the geometry of a well-developed crack is assumed to be semi-elliptical in shape. The driving force of the crack is considered to stem from the residual plastic zone expansion under the indenter, as well as the far-field Boussinesq (elastic) stress. Three well-defined configurations are studied. For the first configuration, a crack with a depth of less than 7% of the coating thickness is considered. In this case, the problem is treated as the one for the monolithic material with the coating material properties. For the second configuration, a crack that runs deeper than 7% of the coating thickness but is still within the coating layer is analyzed. In this case, the composite hardness is introduced into the analysis to account for the influence of the substrate material properties; and furthermore, an interface correction factor is proposed to take into account the presence of the coating/substrate interface and its influence on the stress intensity factor of the well-developed elliptical cracks. For the third configuration, a crack penetrating into the substrate is considered. In this case, based on the condition of deformation compatibility across the coating/substrate interface, the bulk modulus for the coating/substrate system is introduced into the analysis. A series of indentation tests are conducted on a WC/10Co/4Cr coating/1080 low carbon steel substrate specimen, which is a brittle coating on a ductile

  4. Simulation of seismic waves in the brittle-ductile transition (BDT) using a Burgers model

    NASA Astrophysics Data System (ADS)

    Poletto, Flavio; Farina, Biancamaria; Carcione, José Maria

    2014-05-01

    The seismic characterization of the brittle-ductile transition (BDT) in the Earth's crust is of great importance for the study of high-enthalpy geothermal fields in the proximity of magmatic zones. It is well known that the BDT can be viewed as the transition between zones with viscoelastic and plastic behavior, i.e., the transition between the upper, cooler, brittle crustal zone, and the deeper ductile zone. Depending on stress and temperature conditions, the BDT behavior is basically determined by the viscosity of the crustal rocks, which acts as a key factor. In situ shear stress and temperature are related to shear viscosity and steady-state creep flow through the Arrhenius equation, and deviatory stress by octahedral stress criterion. We present a numerical approach to simulate the propagation of P-S and SH seismic waves in a 2D model of the heterogeneous Earth's crust. The full-waveform simulation code is based on a Burgers mechanical model (Carcione, 2007), which enables us to describe both the seismic attenuation effects and the steady-state creep flow (Carcione and Poletto, 2013; Carcione et al. 2013). The differential equations of motion are calculated for the Burgers model, and recast in the velocity-stress formulation. Equations are solved in the time domain using memory variables. The approach uses a direct method based on the Runge-Kutta technique, and the Fourier pseudo-spectral methods, for time integration and for spatial derivation, respectively. In this simulation we assume isotropic models. To test the code, the signals generated by the full-waveform simulation algorithm are compared with success to analytic solutions obtained with different shear viscosities. Moreover, synthetic results are calculated to simulate surface and VSP seismograms in a realistic rheological model with a dramatic temperature change, to study the observability of BDT by seismic reflection methods. The medium corresponds to a selected rheology of the Iceland scenario

  5. Investigation of Ductile Damage in DP980 Steel Sheets Using Mechanical Tests and X-ray Micro-Tomography

    NASA Astrophysics Data System (ADS)

    Mishra, A.; Leguen, C.; Thuillier, S.; Maire, E.

    2011-05-01

    This study is part of a broader research project on the prediction of formability limits in bending on radius of the order of the sheet thickness, based on ductile damage. As a first step, ductile damage in DP980 steel sheet was investigated by means of micro-tomography and mechanical testing, including tensile and simple shear tests. The local strain in tension was measured with a digital image correlation device up to rupture, on macroscopic samples of standard dimensions. Moreover, interrupted tensile tests on smaller specimen were also performed, in order to analyze the void distribution by X-ray micro-tomography. The final aim is to perform numerical simulation of the tests, with Gurson-Tvergaard-Needleman model, to take into account the influence of ductile damage on the mechanical behavior. A fair description of the void volume fraction was obtained as well as the stress level, in the case of small-size specimen.

  6. Abrasive wear behavior of a brittle matrix (MoSi2) composite reinforced with a ductile phase (Nb)

    SciTech Connect

    Alman, David E.; Hawk, Jeffrey A.

    2001-10-01

    The toughness of a variety of brittle ceramic and intermetallic matrices has been improved through the incorporation of ductile metallic reinforcements. In these composites resistance to catastrophic failure of the matrix is derived through a combination of mechanisms, including matrix crack bridging, matrix crack defection and rupturing of the ductile phase. The degree to which these mechanisms operate is a function of composite microstructure. In general, the ductile phase is softer than the matrix phase. This may have unique implications when the materials are subjected to a wear environment, whether intentional or not. Hence, it is important to understand the wear behavior of these new materials. MoSi2–Nb was selected as a model composite system, in part because of the wide body of open literature regarding this system. The influences of abrasive wear environment and the composite microstructure (Nb reinforcement size, shape and volume fraction) on the wear resistance of the composites are reported.

  7. Simultaneously Enhancing the Ductility and Strength in a Hierarchical and Multiphase Nanolaminated TiZrAlV

    NASA Astrophysics Data System (ADS)

    Shi, Yindong; Wang, Lina; Wu, Chunxia

    2015-12-01

    High strength and ductility are the prerequisite for structural materials for wide applications. Here, a simultaneous enhancement of both the ductility and strength is reported in a hierarchical and multiphase nanolaminated (HMN) TiZrAlV prepared via thermomechanical processing treatments. An excellent combination of high ultimate tensile strength of σb ~ 1550 MPa and good elongation to failure of ɛf ~ 8.0% is obtained in an appropriate HMN structure that consists of nanoscale α″ martensites, submicroscale α plates, and large microscale primary αp grains, much better than that (σb ~ 1440 MPa, ɛf ~ 3.6%) of its coarse-laminated counterpart without primary αp grains. The present study is significant for the enhancement of strength and ductility of engineering materials via the design of hierarchical-laminated structure.

  8. Postweld solution annealing effects on the ductility of ni-co-cr-base alloy gas tungsten arc welds

    NASA Astrophysics Data System (ADS)

    Lim, C.-S.; Baek, K.-K.

    1996-12-01

    The welding characteristics of a commercial wrought alloy with a nominal composition of Ni-29Co-28Cr-2.75Si were investigated. Gas tungsten arc weldments with filler metal matching the chemistry of the alloy were found to have limited room-temperature ductility in the as-welded condition. Since welding is the main fabrication method of this alloy, the welding and postweld heat treatment (PWHT) characteristics were examined to provide guidelines for fabrication in the field. Metallographic evaluation revealed that the weld metal was characterized by the distribution of a continuous eutectic phase consisting primarily of (Si,Ti)xNiy The continuous eutectic phase in the as-welded deposit, which caused poor ductility of the welds, was successfully reduced or removed with proper PWHT. The PWHT is necessary if cold forming of a weldment is required after welding or if adequate joint ductility is a design requirement. The recommended PWHT temperature is 1050 °C.

  9. A New Ductility Exhaustion Model for High Temperature Low Cycle Fatigue Life Prediction of Turbine Disk Alloys

    NASA Astrophysics Data System (ADS)

    Zhu, Shun-Peng; Huang, Hong-Zhong; Li, Haiqing; Sun, Rui; Zuo, Ming J.

    2011-06-01

    Based on ductility exhaustion theory and the generalized energy-based damage parameter, a new viscosity-based life prediction model is introduced to account for the mean strain/stress effects in the low cycle fatigue regime. The loading waveform parameters and cyclic hardening effects are also incorporated within this model. It is assumed that damage accrues by means of viscous flow and ductility consumption is only related to plastic strain and creep strain under high temperature low cycle fatigue conditions. In the developed model, dynamic viscosity is used to describe the flow behavior. This model provides a better prediction of Superalloy GH4133's fatigue behavior when compared to Goswami's ductility model and the generalized damage parameter. Under non-zero mean strain conditions, moreover, the proposed model provides more accurate predictions of Superalloy GH4133's fatigue behavior than that with zero mean strains.

  10. Phase-field modelling of ductile fracture: a variational gradient-extended plasticity-damage theory and its micromorphic regularization.

    PubMed

    Miehe, C; Teichtmeister, S; Aldakheel, F

    2016-04-28

    This work outlines a novel variational-based theory for the phase-field modelling of ductile fracture in elastic-plastic solids undergoing large strains. The phase-field approach regularizes sharp crack surfaces within a pure continuum setting by a specific gradient damage modelling. It is linked to a formulation of gradient plasticity at finite strains. The framework includes two independent length scales which regularize both the plastic response as well as the crack discontinuities. This ensures that the damage zones of ductile fracture are inside of plastic zones, and guarantees on the computational side a mesh objectivity in post-critical ranges. PMID:27002069

  11. Enhancing tensile ductility of a particulate-reinforced aluminum MMC by lamination with Mg-9% Li alloy

    SciTech Connect

    Syn, C.K.; Lesuer, D.R.; Sherby, O.D.

    1995-05-01

    A laminated metal composite has been made by press bonding alternating layers of a particulate-reinforced aluminum MMC, 6090/SiC/25p, and a Mg-9%Li alloy. The mechanical properties including tensile ductility were evaluated. The tensile ductility of the Al MMC was found to increase from 3.5% to 11.5%. In contrast to other laminates based on ultrahigh carbon, steel, the laminate of this study and other Al MMC laminates exhibited tensile yield strengths that did not follow the rule of averages. This is attributed to interlayer reaction products developed during processing of the Al MMC laminates.

  12. Effects of Non-metallic Inclusions on Hot Ductility of High Manganese TWIP Steels Containing Different Aluminum Contents

    NASA Astrophysics Data System (ADS)

    Wang, Yu-Nan; Yang, Jian; Wang, Rui-Zhi; Xin, Xiu-Ling; Xu, Long-Yun

    2016-06-01

    The characteristics of inclusions in Fe-16Mn- xAl-0.6C ( x = 0.002, 0.033, 0.54, 2.10 mass pct) steels have been investigated and their effects on hot ductility of the high manganese TWIP steels have been discussed. Ductility is very poor in the steel containing 0.54 mass pct aluminum, which is lower than 20 pct in the temperature range of 873 K to 1473 K (600 °C to 1200 °C). For the steels containing 0.002 and 2.10 mass pct aluminum, ductility is higher than 40 pct in the same temperature range. The hot ductility of steel containing 0.033 mass pct aluminum is higher than 30 pct throughout the temperature range under examination. With increasing aluminum content, the main inclusions in the steels change along the route of MnO/(MnO + MnS) → MnS/(Al2O3 + MnS) → AlN/(Al2O3 + MnS)/(MgAl2O4 + MnS) → AlN. The thermodynamic results of inclusion types calculated with FactSage software are in agreement with the experimental observation results. The inclusions in the steels containing 0.002 mass pct aluminum do not deteriorate the hot ductility. MnS inclusions whose average size, number density, and volume ratio are 1.12 μm, 15.62 mm-2, and 2.51 × 10-6 in the steel containing 0.033 mass pct aluminum reduce the ductility. In the steel containing 0.54 mass pct aluminum, AlN inclusions whose average size, number density, and volume ratio are 0.878 μm, 16.28 mm-2 and 2.82 × 10-6 can precipitate at the austenite grain boundaries, prevent dynamic recrystallization and deteriorate the hot ductility. On the contrary, in the steel containing 2.10 mass pct aluminum, the average size, number density and volume ratio of AlN inclusions change to 2.418 μm, 35.95 mm-2, and 2.55 × 10-5. They precipitate in the matrix, which do not inhibit dynamic recrystallization and thereby do not lead to poor hot ductility.

  13. The role of fluids on the brittle-ductile transition in the crust

    NASA Astrophysics Data System (ADS)

    Hirth, Greg; Beeler, Nick

    2015-04-01

    To characterize stress and deformation style at the base of the seismogenic zone we investigate how the mechanical properties of fluid-rock systems respond to variations in temperature and strain rate. The role of fluids on the processes responsible for the brittle-ductile transition in quartz-rich rocks has not been explored at experimental conditions where the kinetic competition between microcracking and viscous flow is similar to that expected in the Earth. Our initial analysis of this competition suggests that the effective pressure law for sliding friction should not work as effectively near the brittle-ductile transition (BDT) as it does at shallow conditions. Our motivation comes from three observations. First, extrapolation of quartzite flow laws indicates the brittle-ductile transition (BDT) occurs at ~300 °C at geologic strain rates for conditions where fault strength is controlled by a coefficient of friction of ~0.6 with a hydrostatic pore-fluid pressure gradient. Second, we suggest that the preservation of relatively high stress microstructures indicates that the effective stress law must sometimes evolve rapidly near the BDT. There is abundant evidence for the presence of fluids during viscous deformation of mylonites (e.g., recrystallization and redistribution of micas, dissolution and reprecipitation of quartz). The relatively high viscous stresses inferred from these microstructures are incompatible with the standard effective stress relationship. A similar "paradox" is evident at experimental conditions where viscous creep is studied in the laboratory. In this case, the presence of fluid (which should produce low effective stress) does not promote localized brittle failure, even though these experiments are conducted under undrained conditions. Third, experiments on partially molten rocks illustrate viscous creep behavior during both drained compaction and undrained triaxial deformation tests, even though the melt pressure approaches or equals

  14. AN INVESTIGATION OF THE MINERAL IN DUCTILE AND BRITTLE CORTICAL MOUSE BONE

    PubMed Central

    Rodriguez-Florez, Naiara; Garcia-Tunon, Esther; Mukadam, Quresh; Saiz, Eduardo; Oldknow, Karla J.; Farquharson, Colin; Millán, José Luis; Boyde, Alan; Shefelbine, Sandra J.

    2015-01-01

    Bone is a strong and tough material composed of apatite mineral, organic matter and water. Changes in composition and organization of these building blocks affect bone’s mechanical integrity. Skeletal disorders often affect bone’s mineral phase, either by variations in the collagen or directly altering mineralization. The aim of the current study was to explore the differences in the mineral of brittle and ductile cortical bone at the mineral (nm) and tissue (µm) levels using two mouse phenotypes. Osteogenesis imperfecta murine (oim−/−) mice were used to model brittle bone; PHOSPHO1 mutants (Phospho1−/−) had ductile bone. They were compared to their respective wild-type controls. Femora were defatted and ground to powder to measure average mineral crystal size using X-ray diffraction (XRD), and to monitor the bulk mineral to matrix ratio via thermogravimetric analysis (TGA). XRD scans were run after TGA for phase identification, to assess the fractions of hydroxyapatite and β-tricalcium phosphate. Tibiae were embedded to measure elastic properties with nanoindentation and the extent of mineralization with backscattered electron microscopy (qbSEM). Interestingly, the mineral of brittle oim−/− and ductile Phospho1−/− bones had many similar characteristics. Both pathology models had smaller apatite crystals, lower mineral to matrix ratio, and showed more thermal conversion to β-tricalcium phosphate than their wild-types, indicating deviations from stoichiometric hydroxyapatite in the original mineral. The degree of mineralization of the bone matrix was different for each strain: oim−/− were hypermineralized, while Phospho1−/− were hypomineralized. However, alterations in the mineral were associated with reduced tissue elastic moduli in both pathologies. Results revealed that despite having extremely different whole bone mechanics, the mineral of oim−/− and Phospho1−/− has several similar trends at smaller length scales. This

  15. Mechanical behavior of low porosity carbonate rock: from brittle creep to ductile creep

    NASA Astrophysics Data System (ADS)

    Nicolas, A.; Fortin, J.; Gueguen, Y.

    2013-12-01

    Mechanical compaction and associated porosity reduction play an important role in the diagenesis of porous rocks. They may also affect reservoir rocks during hydrocarbon production, as the pore pressure field is modified. This inelastic compaction can lead to subsidence, cause casing failure, trigger earthquake, or change the fluid transport properties. In addition, inelastic deformation can be time - dependent. In particular, brittle creep phenomena have been deeply investigated since the 90s, especially in sandstones. However knowledge of carbonates behavior is still insufficient. In this experimental study, we focus on the mechanical behavior of a low porosity (9%) white Tavel (France) carbonate rock (>98% calcite) at P-Q conditions beyond the elastic domain. It has been shown that in sandstones composed of quartz, cracks are developing under these conditions. However, in carbonates, calcite minerals can meanwhile also exhibit microplasticity. The samples were deformed in the triaxial cell of the Ecole Normale Superieure de Paris at effective confining pressures ranging from 35 MPa to 85 MPa and room temperature. Experiments were carried on dry and water saturated samples to explore the role played by the pore fluids. Time dependency was investigated by a creep steps methodology: at each step, differential stress was increased rapidly and kept constant for at least 24h. During these steps elastic wave velocities (P and S) and permeability were measured continuously. Our results show two different creep behaviors: (1) brittle creep is observed at low confining pressures, whereas (2) ductile creep is observed at higher confining pressures. These two creep behaviors have a different signature in term of elastic wave velocities and permeability changes. Indeed, in the brittle domain, the primary creep is associated with a decrease of elastic wave velocities and an increase of permeability, and no secondary creep is observed. In the ductile domain, the primary creep

  16. Numerical Optimization of the Method of Cooling of a Massive Casting of Ductile Cast-Iron

    NASA Astrophysics Data System (ADS)

    Dobrovska, Jana; Kavicka, Frantisek; Stransky, Karel; Sekanina, Bohumil; Stetina, Josef

    2010-06-01

    The numerical models of the temperature field of solidifying castings, according to various authors, have been observing two main goals—directed solidification as the basic assumption for the healthiness of a casting and the optimization of the technology while maintaining the optimal product properties. The achievement of these goals is conditioned by the ability to analyze and, successively, to control the effect of the deciding factors, which either characterize the process or accompany it. An original application of ANSYS simulated the forming of the temperature field of a massive casting from ductile cast-iron during the application various methods of its cooling using steel chills. The numerical model managed to optimize more than one method of cooling but, in addition to that, provided serious results for the successive model of structural and chemical heterogeneity, and so it also contributes to influencing the pouring structure. The file containing the acquired results from both models, as well as from their organic unification, brings new and, simultaneously, remarkable findings of causal relationships between the structural and chemical heterogeneity (i.e. between the sizes of the spheroids of graphite, the cells, density of the spheroids of graphite, etc.) and the local solidification time in any point of the casting. The determined relations therefore enable the prediction of the face density of the spheroids of graphite in dependence on the local solidification time. The calculated temperature field of a two-ton 500×500×1000 mm casting of ductile cast-iron with various methods of cooling has successfully been compared with temperatures obtained experimentally. The casting was cast in sand mould. The calculated model of the kinetics of the temperature field of the casting was verified during casting with temperature measurements in selected points. This has created a tool for the optimization of the structure with an even distribution of the

  17. Welding of nickel-base superalloys having a nil-ductility range

    NASA Technical Reports Server (NTRS)

    Smashey, Russell W. (Inventor); Kelly, Thomas J. (Inventor); Snyder, John H. (Inventor); Sheranko, Ronald L. (Inventor)

    1999-01-01

    An article made of a nickel-base superalloy having a nil-ductility range from the solidus temperature of the alloy to about 600.degree. F. below the solidus temperature is welded, as for example in the weld repair of surface cracks, by removing foreign matter from the area to be welded, first stress relieving the article, adjusting the temperature of the article to a welding temperature of from about 1800.degree. F. to about 2100.degree. F., welding a preselected area in an inert atmosphere at the welding temperature, and second stress relieving the article. Welding is preferably accomplished by striking an arc in the preselected area so as to locally melt the alloy in the preselected area, providing a filler metal having the same composition as the nickel-based superalloy of the article, and feeding the filler metal into the arc so that the filler metal is melted and fused with the article to form a weldment upon solidification.

  18. Bulk metallic glass composite with good tensile ductility, high strength and large elastic strain limit

    PubMed Central

    Wu, Fu-Fa; Chan, K. C.; Jiang, Song-Shan; Chen, Shun-Hua; Wang, Gang

    2014-01-01

    Bulk metallic glasses exhibit high strength and large elastic strain limit but have no tensile ductility. However, bulk metallic glass composites reinforced by in-situ dendrites possess significantly improved toughness but at the expense of high strength and large elastic strain limit. Here, we report a bulk metallic glass composite with strong strain-hardening capability and large elastic strain limit. It was found that, by plastic predeformation, the bulk metallic glass composite can exhibit both a large elastic strain limit and high strength under tension. These unique elastic mechanical properties are attributed to the reversible B2↔B19′ phase transformation and the plastic-predeformation-induced complicated stress state in the metallic glass matrix and the second phase. These findings are significant for the design and application of bulk metallic glass composites with excellent mechanical properties. PMID:24931632

  19. Experimental and continuum plasticity aspects of the brittleness and ductility of bicrystal interfacial fracture

    NASA Astrophysics Data System (ADS)

    Kysar, Jeffrey William

    1998-12-01

    The philosophical basis of this work is to gain a better understanding of the issues which determine the brittleness and ductility of materials. One approach to the question, pioneered by Rice and Thomson, has been to characterize a material in terms of its intrinsic brittleness and ductility based on a competition between dislocation emission and cleavage failure at a crack tip. To test this hypothesis, Beltz and Wang constructed a copper/sapphire bicrystal which exhibits a directional dependence of fracture when loaded in four-point bending and reported that the observed directional dependence can be rationalized on the basis of dislocation nucleation at the crack tips. In the present work we independently repeat the Beltz and Wang experiments in an effort to quantify them and to compare the results to finite element simulation. In the process we show that the observed directional dependence of fracture is opposite to that predicted on the basis of dislocation nucleation at the crack tip. One goal of the present work is to experimentally characterize the directional dependence of fracture. A specially designed crack opening interferometer and an Atomic Force Microscope are used to measure the crack opening displacement profile. General features of crack growth are also observed directly through the transparent sapphire. Another main thrust of this work is to use continuum plasticity in an attempt to explain the directional dependence of fracture. To that end we model the copper/sapphire specimen with the finite element technique while accounting for the full elastic-plastic anisotropy of the single copper crystal. The experimental results show that both cracks propagate in a quasistatic manner at a fixed crack tip angle opening, at least away from the crack tip. The experimentally observed brittle crack has an opening approximately one-half that of the ductile crack. Further, atomic force microscopy measurements show that the near tip crack opening displacement

  20. Anti-friction Coating for Drilling of Green Austempered Ductile Iron (ADI) grade

    NASA Astrophysics Data System (ADS)

    Meena, A.; El Mansori, M.; Ghidossi, P.; Mkaddem, A.

    2011-05-01

    In this paper the anti-friction performance of two types of coating, post-coated coating and PVD-TiAlN coating were investigated when drilling green austempered ductile iron (ADI) grade. The green ADI grade is produced by a new processing technology known as continuous casting-heat treatment process. The effect of coatings on tool wear and surface finish of the holes when drilling using coolant were reported. Results showed that the tool with post-coated coating has higher anti-friction properties as compared to PVD-TiAlN coating in terms of tool wear and surface roughness. Results also showed that there is a formation of preventive aluminum oxide layer during machining for both types of coating.

  1. Core/shell structural transformation and brittle-to-ductile transition in nanowires

    NASA Astrophysics Data System (ADS)

    Yuan, Zaoshi; Nomura, Ken-ichi; Nakano, Aiichiro

    2012-04-01

    Nanowires (NWs) exhibit thermo-mechanical properties that are distinct from their bulk properties, and their understanding is critical for the reliability, manufacturability, and optimization of a wide range of devices consisting of NWs. Here, molecular-dynamics simulation reveals a rich size-temperature "phase diagram" for the mechanical response of a zinc-oxide NW under tension. For smaller diameters and higher temperatures, transitions are found from brittle cleavage to structural transformation-mediated brittle cleavage to ductile failure. Atomistic mechanisms of the unique nano-thermo-mechanical behavior are elucidated as a consequence of surface-structural relaxation, which in particular predicts spontaneous formation of a core/shell structure under tension. The nano-thermo-mechanical phase diagram resolves controversies between previous experiments and theory, and the predicted "intrinsic" core/shell structure may find device applications.

  2. Metamorphic core complexes: Expression of crustal extension by ductile-brittle shearing of the geologic column

    NASA Technical Reports Server (NTRS)

    Davis, G. H.

    1985-01-01

    Metamorphic core complexes and detachment fault terranes in the American Southwest are products of stretching of continental crust in the Tertiary. The physical and geometric properties of the structures, fault rocks, and contact relationships that developed as a consequence of the extension are especially well displayed in southeastern Arizona. The structures and fault rocks, as a system, reflect a ductile-through-brittle continuum of deformation, with individual structures and faults rocks showing remarkably coordinated strain and displacement patterns. Careful mapping and analysis of the structural system has led to the realization that strain and displacement were partitioned across a host of structures, through a spectrum of scales, in rocks of progressively changing rheology. By integrating observations made in different parts of the extensional system, especially at different inferred depth levels, it has been possible to construct a descriptive/kinematic model of the progressive deformation that achieved continental crustal extension in general, and the development of metamorphic core complexes in particular.

  3. Strength Development of High-Strength Ductile Concrete Incorporating Metakaolin and PVA Fibers

    PubMed Central

    Nuruddin, Muhammad Fadhil; Shafiq, Nasir

    2014-01-01

    The mechanical properties of high-strength ductile concrete (HSDC) have been investigated using Metakaolin (MK) as the cement replacing material and PVA fibers. Total twenty-seven (27) mixes of concrete have been examined with varying content of MK and PVA fibers. It has been found that the coarser type PVA fibers provide strengths competitive to control or higher than control. Concrete with coarser type PVA fibers has also refined microstructure, but the microstructure has been undergone with the increase in aspect ratio of fibers. The microstructure of concrete with MK has also more refined and packing of material is much better with MK. PVA fibers not only give higher stiffness but also showed the deflection hardening response. Toughness Index of HSDC reflects the improvement in flexural toughness over the plain concrete and the maximum toughness indices have been observed with 10% MK and 2% volume fraction of PVA fibers. PMID:24707202

  4. Effects of Antimony and Wall Thickness on Graphite Morphology in Ductile Iron Castings

    NASA Astrophysics Data System (ADS)

    Glavas, Zoran; Strkalj, Anita; Maldini, Kresimir

    2016-05-01

    Effects of Sb additions on the graphite morphology of ductile iron castings in different wall thicknesses (3, 12, 25, 38, 50, 75, and 100 mm) were analyzed in this paper. In the wall thicknesses of 3, 12, and 25 mm, low contents of rare earth (RE) elements showed a beneficial effect on nodule count and nodularity. Nodularity >80 pct and a high nodule count were achieved without the addition of Sb. In the wall thicknesses of 38, 50, 75, and 100 mm, nodularity >80 pct was not achieved without the use of the chill or proper content of Sb. Excess of RE elements was neutralized with the addition of proper amount of Sb to the wall thickness. Addition of 0.01 wt pct Sb (ratio of RE/Sb = 0.34, ratio of RE/SE = 0.105) was sufficient to achieve nodularity >80 pct in the wall thicknesses of 38, 50, 75, and 100 mm.

  5. On the brittle-ductile behavior of iron meteorites - New experimental constraints

    NASA Technical Reports Server (NTRS)

    Matsui, T.; Schultz, P. H.

    1984-01-01

    Impact trials were performed at the NASA vertical gun range to study low-temperature brittle-ductile transitions in meteoritic, steel and iron targets. The trials were performed to enhance the data base underlying the concept of formation of planetesimals in collisional coagulation. Impact velocities of 1.6-5.5 km/sec were used, as were temperatures from 100-300 K. Spallation was observed in the tests with meteorite samples, even at room temperature, and brittleness was enhanced at temperature below 200 C. Net mass losses were induced at the higher impact velocities. It is suggested that iron meteorite agglomerations could form in the inner solar region during nebular condensation, but would not form in farther-out regions such as the asteroid belt. The protoplanets could have an iron core, with metallicity decreasing with radius from the core, which may have happened with the earth.

  6. Fatigue of Austempered Ductile Iron with Two Strength Grades in Very High Cycle Regime

    NASA Astrophysics Data System (ADS)

    Zhang, Jiwang; Li, Wei; Song, Qingpeng; Zhang, Ning; Lu, Liantao

    2016-03-01

    In this study, Austempered ductile irons (ADIs) with two different strength grades were produced and the fatigue properties were measured at 109 cycles. The results show that the S-N curves give a typical step-wise shape and there is no fatigue limit in the very high cycle fatigue regime. The two grades ADI have the similar fracture behaviors and fatigue failure can initiate from defects at specimen surface and subsurface zone. On the fracture surfaces of some specimens, the `granular-bright-facet' area with rich carbon distribution is observed in the vicinity of the defect. The microstructure affects the crack behaviors at the early propagation stage. The ADI with upper and lower bainite shows higher fatigue strength compared with the ADI with coarse upper bainite.

  7. Numerical Simulation of Austempering Heat Treatment of a Ductile Cast Iron

    NASA Astrophysics Data System (ADS)

    Boccardo, Adrián D.; Dardati, Patricia M.; Celentano, Diego J.; Godoy, Luis A.; Górny, Marcin; Tyrała, Edward

    2016-02-01

    This paper presents a coupled thermo-mechanical-metallurgical formulation to predict the dimensional changes and microstructure of a ductile cast iron part as a consequence of an austempering heat process. To take into account the different complex phenomena which are present in the process, the stress-strain law and plastic evolution equations are defined within the context of the associate rate-independent thermo-plasticity theory. The metallurgical model considers the reverse eutectoid, ausferritic, and martensitic transformations using macro- and micro-models. The resulting model is solved using the finite element method. The performance of this model is evaluated by comparison with experimental results of a dilatometric test. The results indicate that both the experimental evolution of deformation and temperature are well represented by the numerical model.

  8. Strength development of high-strength ductile concrete incorporating Metakaolin and PVA fibers.

    PubMed

    Nuruddin, Muhammad Fadhil; Khan, Sadaqat Ullah; Shafiq, Nasir; Ayub, Tehmina

    2014-01-01

    The mechanical properties of high-strength ductile concrete (HSDC) have been investigated using Metakaolin (MK) as the cement replacing material and PVA fibers. Total twenty-seven (27) mixes of concrete have been examined with varying content of MK and PVA fibers. It has been found that the coarser type PVA fibers provide strengths competitive to control or higher than control. Concrete with coarser type PVA fibers has also refined microstructure, but the microstructure has been undergone with the increase in aspect ratio of fibers. The microstructure of concrete with MK has also more refined and packing of material is much better with MK. PVA fibers not only give higher stiffness but also showed the deflection hardening response. Toughness Index of HSDC reflects the improvement in flexural toughness over the plain concrete and the maximum toughness indices have been observed with 10% MK and 2% volume fraction of PVA fibers. PMID:24707202

  9. Investigating the Brittle Ductile Transition Zone Using Southern California Seismicity and the SCEC Community Fault Model

    NASA Astrophysics Data System (ADS)

    Hauksson, E.; Shearer, P.; Lin, G.

    2008-12-01

    The depth to the brittle-ductile transition zone depends on crustal parameters such as rock type, temperature, fluid pressure, and strain rate. We analyze the relocated background seismicity (1981-2005) in southern California to identify features that may be associated with rupture patterns near the brittle-ductile transition zone in past major earthquakes. The bulk of this seismicity is aftershocks that decay with time since the occurrence of the mainshock. We focus our analysis on the seismicity associated with the 1987 Mw6.6 Superstition Hills, 1992 Mw6.1 Joshua Tree, 1992 Mw7.3 Landers, 1994 Mw6.7 Northridge, and 1999 Mw7.1 Hector Mine earthquakes. Both observational and modeling studies suggest that the coseismic stress changes from major earthquakes should cause a sudden increase in the strain rate in the vicinity of the brittle-ductile transition zone at the time of the mainshock. For instance, the average depth of seismicity after the 1992 Mw7.3 Landers earthquake became ~2 km deeper as compared to before the mainshock. Apparently, the stress redistribution due to the mainshock faulting caused a strain-rate dependent downward displacement of the brittle-ductile transition. We have also determined the changes in the mean and maximum depths of seismicity for these southern California mainshocks. At the time of the mainshocks, the mean depth of seismicity exhibits a transient change of about 1 to 2 km by decaying to a new deeper depth, except for the Superstition Hills earthquake, where the seismicity depth remained unchanged. Similarly, the D95% (the depth above which 95% of the earthquakes occur) and D5% (the average depth of the deepest 5% of the earthquakes) behave like the mean depth, with a rapid transient and subsequent returning to the same depth or a slightly shallower depth. Only the thrust-faulting Northridge sequence exhibits a deep cluster that is separate from the main aftershock zone, which is predicted by geodynamic the thrust-fault models. We

  10. RECENT PROGRESS OF CRACK BRIDGING MODELING OF DUCTILE-PHASE-TOUGHENED W-CU COMPOSITES

    SciTech Connect

    Setyawan, Wahyu; Henager, Charles H.; Wagner, Karla B.; Roosendaal, Timothy J.; Borlaug, Brennan A.; Kurtz, Richard J.; Odette, G Robert; Cunningham, Kevin; Zok, Frank W.

    2015-04-16

    A crack bridging model using calculated Cu stress-strain curves has been developed to study the toughening of W-Cu composites. A strengthening factor and necking parameters have been added to the model for the ductile-phase bridges to incorporate constraint effects at small bridge sizes. Parametric studies are performed to investigate the effect of these parameters. The calculated maximum applied stress intensity, aKmax, to induce a 1-mm stable crack is compared to the experimental stress intensity at peak load, Kpeak. Without bridge necking, increasing the strengthening factor improves the agreement between aKmax and Kpeak when plotted vs. logarithm of the displacement rate. Improvement can also be achieved by allowing necking with a larger failure strain. While the slope is better matched with this latter approach, the calculated value of aKmax is significantly larger than Kpeak.

  11. Microstructural study of surface melted and chromium surface alloyed ductile iron

    NASA Astrophysics Data System (ADS)

    Sohi, M. Heydarzadeh; Ebrahimi, M.; Ghasemi, H. M.; Shahripour, A.

    2012-07-01

    In this study, ductile iron was surface melted and chromium surface alloyed via pre-placing of ferrochromium powder with different thicknesses and subsequently surface melting by tungsten inert gas (TIG) process. Optical and scanning electron microscopy, as well as micro-hardness testing and X-ray diffraction analysis were used for characterization of the treated samples. Surface melting and chromium surface alloying resulted in formation of ledeburitic structure and high chromium white cast iron in the treated layers, respectively. It was also noticed that hardness of the treated layers was considerably higher than that of the base material. Increasing thickness of ferrochromium layer increased the amount of M7C3 carbides and hardness of the alloyed layer.

  12. Cow-eye microstructure evolution of laser pulse processed for ductile iron

    NASA Astrophysics Data System (ADS)

    Ba, Fahai; Gan, Cuihua; Yu, Gang

    2003-04-01

    Pulsed laser beam with lattice distribution was used to modify surface processing for ductile iron. The microstructures around the graphite were observed using OM, and Nanoindentation and micro-hardness of that measured from surface to inner of sample. The result shows that the graphite ball has an important effect on cow-eye microstructure evolution either in light molten area or in phase change hardened are. It is not true that assuming the material is uniform during laser rapid heating and fast cooling for the graphite ball as a dependant composition phase. The microstructures of cow-eye is made up of fine remnant austenite in light molten area, and consisted of martensite and bainite in laser modified are. The cow-eye microstructure has a transformation from martensite and bainite to pearlite with the distance increasing from surfce. At last, the microstructure evolution of cow-eye has been discussed.

  13. A phase-field model for ductile fracture at finite strains and its experimental verification

    NASA Astrophysics Data System (ADS)

    Ambati, Marreddy; Kruse, Roland; De Lorenzis, Laura

    2016-01-01

    In this paper, a phase-field model for ductile fracture previously proposed in the kinematically linear regime is extended to the three-dimensional finite strain setting, and its predictions are qualitatively and quantitatively compared with several experimental results, both from ad-hoc tests carried out by the authors and from the available literature. The proposed model is based on the physical assumption that fracture occurs when a scalar measure of the accumulated plastic strain reaches a critical value, and such assumption is introduced through the dependency of the phase-field degradation function on this scalar measure. The proposed model is able to capture the experimentally observed sequence of elasto-plastic deformation, necking and fracture phenomena in flat specimens; the occurrence of cup-and-cone fracture patterns in axisymmetric specimens; the role played by notches and by their size on the measured displacement at fracture; and the sequence of distinct cracking events observed in more complex specimens.

  14. Assessing the elastic properties and ductility of Fe-Cr-Al alloys from ab initio calculations

    NASA Astrophysics Data System (ADS)

    Nurmi, E.; Wang, G.; Kokko, K.; Vitos, L.

    2016-01-01

    Fe-Al is one of the best corrosion resistant alloys at high temperatures. The flip side of Al addition to Fe is the deterioration of the mechanical properties. This problem can be solved by adding a suitable amount of third alloying component. In the present work, we use ab initio calculations based on density functional theory to study the elastic properties of Fe?Cr?Al? alloys for Al and Cr contents up to 20 at.%. We assess the ductility as a function of chemistry by making use of the semi-empirical correlations between the elastic parameters and mechanical properties. In particular, we derive the bulk modulus to shear modulus ratio and the Cauchy pressure and monitor their trends in terms of chemical composition. The present findings are contrasted with the previously established oxidation resistance of Fe-Cr-Al alloys.

  15. Plasticity and an Inverse Brittle-to-Ductile Transition in Strontium Titanate

    SciTech Connect

    Gumbsch, P.; Taeri-Baghbadrani, S.; Brunner, D.; Sigle, W.; Ruehle, M.

    2001-08-20

    The use of ceramic materials is often restricted by a transition from ductile behavior to brittle fracture with decreasing temperature. For example, strontium titanate (SrTiO{sub 3} ) is known to be extremely fragile and brittle below 1300 K. It is therefore surprising to find that SrTiO{sub 3} single crystals can be deformed in compression below 1050 K again. Extensive plastic deformation up to 7% strain at low yield stresses of the order of only 120 MPa is possible at room temperature. Low temperature plasticity is carried by the same <110>{l_brace}1{bar 1} 0{r_brace} dislocations as the high temperature deformation along the <001> axis. From this we conclude that these dislocations must exist in two different core configurations.

  16. Rate dependent response and failure of a ductile epoxy and carbon fiber reinforced epoxy composite

    SciTech Connect

    Brown, Eric N; Rae, Philip J; Dattelbaum, Dana M; Stahl, David B

    2010-01-01

    An extensive characterization suite has been performed on the response and failure of a ductile epoxy 55A and uniaxial carbon fiber reinforced epoxy composite of IM7 fibers in 55A resin from the quasistatic to shock regime. The quasistatic and intermediate strain rate response, including elastic modulus, yield and failure have are characterized by quasistatic, SHPB, and DMA measurements as a function of fiber orientation and temperature. The high strain rate shock effect of fiber orientation in the composite and response of the pure resin are presented for plate impact experiments. It has previously been shown that at lower impact velocities the shock velocity is strongly dependent on fiber orientation but at higher impact velocity the in-plane and through thickness Hugoniots converge. The current results are compared with previous studies of the shock response of carbon fiber composites with more conventional brittle epoxy matrices. The spall response of the composite is measured and compared with quasistatic fracture toughness measurements.

  17. High-strength carbon nanotube fibre-like ribbon with high ductility and high electrical conductivity.

    PubMed

    Wang, J N; Luo, X G; Wu, T; Chen, Y

    2014-01-01

    Macroscopic fibres made up of carbon nanotubes exhibit properties far below theoretical predictions and even much lower than those for conventional carbon fibres. Here we report improvements of mechanical and electrical properties by more than one order of magnitude by pressurized rolling. Our carbon nanotubes self-assemble to a hollow macroscopic cylinder in a tube reactor operated at high temperature and then condense in water or ethanol to form a fibre, which is continually spooled in an open-air environment. This initial fibre is densified by rolling under pressure, leading to a combination of high tensile strength (3.76-5.53 GPa), high tensile ductility (8-13%) and high electrical conductivity ((1.82-2.24) × 10(4) S cm(-1)). Our study therefore demonstrates strategies for future performance maximization and the very considerable potential of carbon nanotube assemblies for high-end uses. PMID:24964266

  18. Seismic performance and global ductility of RC frames rehabilitated with retrofitted joints by CFRP laminates

    NASA Astrophysics Data System (ADS)

    Fakharifar, M.; Sharbatdar, M. K.; Lin, Z.; Dalvand, A.; Sivandi-Pour, A.; Chen, G.

    2014-03-01

    This paper presents a new FRP retrofitting scheme to strengthen local beam-column joints in reinforced concrete (RC) frames. The new retrofitting scheme was proposed following a preliminary study of four different existing retrofitting schemes. A numerical simulation was conducted to evaluate the effectiveness of FRP-strengthened reinforced concrete frames by bridging behavior of local joints to the whole structure. Local confinement effects due to varying retrofitting schemes in the joints were simulated in the frame model. The seismic behavior factor was used to evaluate the seismic performance of the strengthened RC frames. The results demonstrated that the new proposed retrofitting scheme was robust and promising, and finite element analysis appropriately captured the strength and global ductility of the frame due to upgrading of the local joints.

  19. Numerical simulation of fine blanking process using fully coupled advanced constitutive equations with ductile damage

    NASA Astrophysics Data System (ADS)

    Labergere, C.; Saanouni, K.; Benafia, S.; Galmiche, J.; Sulaiman, H.

    2013-05-01

    This paper presents the modelling and adaptive numerical simulation of the fine blanking process. Thermodynamically-consistent constitutive equations, strongly coupled with ductile damage, together with specific boundary conditions (particular command of forces on blank holder and counterpunch) are presented. This model is implemented into ABAQUS/EXPLICIT using the Vumat user subroutine and connected with an adaptive 2D remeshing procedure. The different material parameters are identified for the steel S600MC using experimental tensile tests conducted until the final fracture. A parametric study aiming to examine the sensitivity of the process parameters (die radius, clearance die/punch) to the punch force and fracture surfaces topology (convex zone, sheared zone, fracture zone and the burr).

  20. Influence of microstructure refinement on strength, ductility and toughness of TiAl alloys

    SciTech Connect

    Morris, M.A.; Leboeuf, M.

    1997-12-31

    Different Ti-Al alloys with grain sizes ranging from 7 {micro}m to 320 nm have been prepared by consolidation of atomized and mechanically milled powders of nominal composition Ti-48Al-2Mn-2Nb and containing carbon additions. The materials obtained consist of equiaxed {gamma} grains containing a distribution of {alpha}{sub 2} phase mostly along grain or powder boundaries. The high flow strength and low fracture toughness obtained from these materials have been correlated to the fine scale of the microstructure and the transfer of slip across adjacent {gamma} grains. The existence of stress concentrations at boundaries between {gamma} grains leads to emission of curved dislocations and twins. The low mobility of emitted dislocations is responsible for the lack of tensile ductility in these alloys which fail by microcrack formation at grain boundaries.

  1. Coeval brittle and ductile structures associated with extreme deformation partitioning in a multilayer sequence

    NASA Astrophysics Data System (ADS)

    Druguet, Elena; Alsop, G. Ian; Carreras, Jordi

    2009-05-01

    An investigation on the effects of a strong rheological contrast in the deformation of layered anisotropic rocks is presented. The study focuses on the geometric and kinematic analysis of complex structures developed within and adjacent to a thin marble-metapsammite multilayer unit from the Cap de Creus tectonometamorphic belt (NE Spain). Zones of high ductile strain localise in the marble layers, which exhibit complex folds, whereas metapsammites show mostly brittle (boudinage) structures. These structures strongly contrast with coeval retrogressive discrete shear zones developed in the surrounding migmatitic schists. The extreme strain partitioning is due to the rheological contrast between different lithological layers. In addition, the specific orientation of this multilayer unit induces a reversal of local kinematics with regard to bulk kinematics. Consequently, caution should be exercised when interpreting regional tectonics in highly partitioned domains associated with rheological heterogeneities.

  2. Effects of Antimony and Wall Thickness on Graphite Morphology in Ductile Iron Castings

    NASA Astrophysics Data System (ADS)

    Glavas, Zoran; Strkalj, Anita; Maldini, Kresimir

    2016-08-01

    Effects of Sb additions on the graphite morphology of ductile iron castings in different wall thicknesses (3, 12, 25, 38, 50, 75, and 100 mm) were analyzed in this paper. In the wall thicknesses of 3, 12, and 25 mm, low contents of rare earth (RE) elements showed a beneficial effect on nodule count and nodularity. Nodularity >80 pct and a high nodule count were achieved without the addition of Sb. In the wall thicknesses of 38, 50, 75, and 100 mm, nodularity >80 pct was not achieved without the use of the chill or proper content of Sb. Excess of RE elements was neutralized with the addition of proper amount of Sb to the wall thickness. Addition of 0.01 wt pct Sb (ratio of RE/Sb = 0.34, ratio of RE/SE = 0.105) was sufficient to achieve nodularity >80 pct in the wall thicknesses of 38, 50, 75, and 100 mm.

  3. Bulk evaluation of ductile damage development using high resolution tomography and laminography

    NASA Astrophysics Data System (ADS)

    Maire, Eric; Morgeneyer, Thilo; Landron, Caroline; Adrien, Jerome; Helfen, Lukas

    2012-04-01

    Ductile fracture of metals is accompanied at the microscopic scale with the appearance of damage, in the form of small cavities. Damage progress is divided into three distinct and consecutive phases: initiation, growth and coalescence. This article illustrates the use of three-dimensional nondestructive imaging to study this damage development. Two techniques, mainly based on the attenuation of X-rays are now used for this type of studies at high resolution: tomography and laminography. The interest of laminography is that samples with larger dimensions (in the form of sheets) than the conventional tomography ones can be used. Examples of images obtained with the two techniques, as well as quantification using X-ray tomography, are presented.

  4. Transformation plasticity in ductile solids. Annual progress report, June 1, 1992--May 31, 1993

    SciTech Connect

    Olson, G.B.

    1993-02-01

    Research has addressed the role of martensitic transformation plasticity in the enhancement of toughness in high-strength austenitic steels, and the enhancement of formability in multiphase low-alloy sheet steels. In the austenitic steels, optimal processing conditions have been established to achieve a significant increase in strength level, in order to investigate the interaction of strain-induced transformation with the microvoid nucleation and shear localization mechanisms operating at ultrahigh strength levels. The stress-state dependence of transformation and fracture mechanisms has been investigated in model alloys, comparing behavior in uniaxial tension and blunt-notch tension specimens. A numerical constitutive model for transformation plasticity has been reformulated to allow a more thorough analysis of transformation/fracture interactions. Processing of a new low alloy steel composition has been optimized to stabilize retained austenite by isothermal bainitic transformation after intercritical annealing. Preliminary results show a good correlation of uniform ductility with the austenite amount and stability.

  5. Effects of long-term aging on ductility and microstructure of Cb and Mo alloys

    NASA Technical Reports Server (NTRS)

    Stephens, J. R.

    1977-01-01

    A program was conducted to determine if aging embrittlement occurs in columbium-base alloys C-103, Cb-1Zr, and Cb-752 or in a molybdenum alloy, Mo-TZM. Results showed that aging embrittlement does not occur in C-103, Cb-1Zr, or Mo-TZM during long-term (1000 hour) aging at temperatures in the range of 700-1025 C. In comparison, aging embrittlement occurred in the Cb-752 alloy after similar aging at 900 C. A critical combination of the solute additions W and Zr led to Zr segregation at grain boundaries during long-term aging which subsequently resulted in embrittlement as indicated by an increase in the ductile-brittle transition temperature from below -196 C to about -150 C.

  6. A nonlinear CDM model for ductile failure analysis of steel bridge columns under cyclic loading

    NASA Astrophysics Data System (ADS)

    Nguyen Van Do, Vuong; Lee, Chin-Hyung; Chang, Kyong-Ho

    2014-06-01

    A nonlinear cyclic plasticity damage model for ductile metals, which is able to take large deformation effects into consideration, has been developed using a new damage dissipation potential formulation in order to predict the cyclic inelastic behavior of steel bridge piers. The cyclic constitutive equations that employ the combined isotropic-kinematic hardening rule for plastic deformation is incorporated into the damage mechanics in conjunction with the large strain formulation. The damage growth law is based on the experimental observations that the evolution of microvoids results in nonlinear damage accumulation with plastic deformation. The damage model parameters and the procedure for their identification are presented. The proposed model has been validated and successfully applied to thin-walled steel bridge tubular columns subjected to alternating lateral displacements to evaluate the seismic performance.

  7. The exponential flow law applied to necking and folding of a ductile layer

    NASA Astrophysics Data System (ADS)

    Schmalholz, Stefan M.; Fletcher, Raymond C.

    2011-01-01

    The uniaxial exponential law, ?, has been applied to experimental results for steady-state creep, including that of wet and dry olivine, pyroxenite and carbonates, at a deviatoric stress greater than ˜100 MPa. Such stress levels likely occur in the upper-mantle lithosphere and middle crust. In a layered rock, in layer-parallel extension or shortening, high deviatoric stress can occur in the stiffest layers, for example, a dolomite layer in fine-grained marble. Under assumptions of isotropy and incompressibility, the uniaxial law yields ? where J2=sijsij/2 is an invariant of the deviatoric stress tensor, sij. Linearization about a homogeneous basic-state of flow yields equations identical in form to those obtained for the familiar power law. This establishes expressions for an effective viscosity, ? and stress exponent, ?, where ? is an invariant of the basic-state deformation rate, ?. These results allow application of existing analytical folding and necking solutions for a rock layer of power-law fluid to a rock layer with an exponential flow law. The effective stress exponent for the exponential flow law increases with decreasing temperature, through the dependence of C on the latter and, weakly, with increasing deformation rate. For dry olivine, effective stress exponents are between 10 and 30 for temperatures between 400 and 600°C with little dependence on deformation rate. Finite element simulations employing full non-linear forms of the flow laws show that large strain necking is nearly identical for power law and exponential flow laws. The results suggest that the instability in necking and folding in ductile rock layers can be considerably stronger than inferred from results based on flow laws representing diffusion and dislocation creep. The large values of the effective stress exponent, ne > ˜15, that may be attained for exponential flow laws can account for observed outcrop-scale ductile necking.

  8. Response and representation of ductile damage under varying shock loading conditions in tantalum

    NASA Astrophysics Data System (ADS)

    Bronkhorst, C. A.; Gray, G. T.; Addessio, F. L.; Livescu, V.; Bourne, N. K.; McDonald, S. A.; Withers, P. J.

    2016-02-01

    The response of polycrystalline metals, which possess adequate mechanisms for plastic deformation under extreme loading conditions, is often accompanied by the formation of pores within the structure of the material. This large deformation process is broadly identified as progressive with nucleation, growth, coalescence, and failure the physical path taken over very short periods of time. These are well known to be complex processes strongly influenced by microstructure, loading path, and the loading profile, which remains a significant challenge to represent and predict numerically. In the current study, the influence of loading path on the damage evolution in high-purity tantalum is presented. Tantalum samples were shock loaded to three different peak shock stresses using both symmetric impact, and two different composite flyer plate configurations such that upon unloading the three samples displayed nearly identical "pull-back" signals as measured via rear-surface velocimetry. While the "pull-back" signals observed were found to be similar in magnitude, the sample loaded to the highest peak stress nucleated a connected field of ductile fracture which resulted in complete separation, while the two lower peak stresses resulted in incipient damage. The damage evolution in the "soft" recovered tantalum samples was quantified using optical metallography, electron-back-scatter diffraction, and tomography. These experiments are examined numerically through the use of a model for shock-induced porosity evolution during damage. The model is shown to describe the response of the tantalum reasonably well under strongly loaded conditions but less well in the nucleation dominated regime. Numerical results are also presented as a function of computational mesh density and discussed in the context of improved representation of the influence of material structure upon macro-scale models of ductile damage.

  9. Rapid theory-guided prototyping of ductile Mg alloys: from binary to multi-component materials

    NASA Astrophysics Data System (ADS)

    Pei, Zongrui; Friák, Martin; Sandlöbes, Stefanie; Nazarov, Roman; Svendsen, Bob; Raabe, Dierk; Neugebauer, Jörg

    2015-09-01

    In order to identify a method allowing for a fast solute assessment without lengthy ab initio calculations, we analyze correlations and anti-correlation between the {{{I}}}1 stacking fault energies ({{{I}}}1SFEs), which were shown to be related to the macroscopic ductility in Mg alloys, and five material parameters of 18 different elemental solutes. Our analysis reveals that the atomic volume V of pure solutes, their electronegativity ν and bulk modulus B are either linearly or logarithmically related to the {{{I}}}1 SFE. Comparing the impact of solutes with that of yttrium (that increases the ductility in Mg) we propose a single numerical quantity (called yttrium similarity index, YSI) that is based on these inter-relations. Subsequently, we evaluate this new figure of merit for 76 elements from the periodic table of elements in search for solutes reducing the {{{I}}}1 SFE. Limiting ourselves first to binary Mg alloys, we hardly find any alternative solutes providing similar {{{I}}}1{SFE} reduction as that due to rare-earth (RE) additions. Therefore, we extended our search to ternary Mg alloys. Assuming that the physical properties of solute combinations can be represented by their average values, 2850 solute combinations were checked and 133 solute pairs (not including any RE elements) have been found to have a YSI larger than 0.85. Quantum-mechanical calculations have been subsequently performed for 11 solute pairs with YSIs higher than 0.95 and they were all found to reduce the {{{I}}}1{SFE} in excellent agreement with the predictions based on the YSI.

  10. Analysis Of Ductile Crack Growth In Pipe Test In STYLE Project

    SciTech Connect

    Yin, Shengjun; Williams, Paul T; Klasky, Hilda B; Bass, Bennett Richard

    2012-01-01

    The Oak Ridge National Laboratory (ORNL) is conducting structural analyses, both deterministic and probabilistic, to simulate a large scale mock-up experiment planned within the European Network for Structural Integrity for Lifetime Management non-RPV Components (STYLE). The paper summarizes current ORNL analyses of STYLE s Mock-up3 experiment to simulate/evaluate ductile crack growth in a cladded ferritic pipe. Deterministic analyses of the large-scale bending test of ferritic surge pipe, with an internal circumferential crack, are simulated with a number of local micromechanical approaches, such as Gurson-Tvergaard-Needleman (GTN) model and cohesive-zone model. Both WARP 3D and ABAQUS general purpose finite element programs are being used to predict the failure load and the failure mode, i.e. ductile tearing or net-section collapse, as part of the pre-test phase of the project. Companion probabilistic analyses of the experiment are utilizing the ORNL developed open-source Structural Integrity Assessment Modular - Probabilistic Fracture Mechanics (SIAM-PFM) framework. SIAM-PFM contains engineering assessment methodology such as the tearing instability (J-T analysis) module developed for inner surface cracks under bending load. The driving force J-integral estimations are based on the SC.ENG1 or SC.ENG2 models. The J-A2 methodology is used to transfer (constraint-adjust) J-R curve material data from standard test specimens to the Mock-up3 experiment configuration. The probabilistic results of the Mock-Up3 experiment obtained from SIAM-PFM will be compared to those generated using the deterministic finite element modeling approach. The objective of the probabilistic analysis is to provide uncertainty bounds that will assist in assessing the more detailed 3D finite-element solutions and to also assess the level of confidence that can be placed in the best-estimate finite-element solutions.

  11. Optimization of strength and ductility in nanotwinned ultrafine grained Ag: twin density and grain orientations

    DOE PAGESBeta

    Ott, R. T.; Geng, J.; Besser, M. F.; Kramer, M. J.; Wang, Y. M.; Park, E. S.; LeSar, R.; King, A. H.

    2015-06-27

    Nanotwinned ultrafine grained Ag thick films with different twin densities and orientations have been synthesized by magnetron sputtering with a wide-range of deposition rates. The twin boundary (TB) spacings and orientations as well as the grain size for the different deposition conditions have been characterized by both synchrotron X-ray scattering and transmission electron microscopy (TEM). Structural characterization combined with uniaxial tensile tests of the free-standing films reveals a large increase in the yield strength for films deposited at high deposition rates without any accompanying change in the TB spacing – a behavior that is in contrast with what has beenmore » reported in the literature. We find that films deposited at lower deposition rates exhibit more randomly oriented grains with a lower overall twin density (averaged over all the grains) than the more heavily twinned grains with strong <111> fiber texture in the films deposited at higher deposition rates. The TB spacing in the twinned grains, however, does not show any significant dependence on the deposition rate. The dependence of the strength and ductility on the twin density and orientations can be described by two different soft deformation modes: 1) untwinned grains and 2) nanowinned grains that are not oriented with <111> along the growth direction. The untwinned grains provide relatively low resistance to slip, and thus decreased strength, while the nanotwinned grains that are not oriented with <111> along the growth direction are softer than nanotwinned grains that are oriented with <111> along the growth direction. We reveal that an ultrafine-grained (150-200 nm) structure consisting of a mixture of nanotwinned (~ 8-12 nm spacing) and untwined grains yields the best combination of high strength and uniform tensile ductility.« less

  12. Secondary Al-Si-Mg High-pressure Die Casting Alloys with Enhanced Ductility

    NASA Astrophysics Data System (ADS)

    Bösch, Dominik; Pogatscher, Stefan; Hummel, Marc; Fragner, Werner; Uggowitzer, Peter J.; Göken, Mathias; Höppel, Heinz Werner

    2015-03-01

    Al-Si-Mg-based secondary cast alloys are attractive candidates for thin-walled high-pressure die castings for applications in the transport industry. The present study investigates the effect of manganese additions at high cooling rates on microstructure, mechanical properties, and on the dominating fracture mechanisms of alloy AlSi10Mg with an elevated iron concentration. Systematic variations of the Mn content from 0.20 to 0.85 wt pct at a constant Fe content of 0.55 wt pct illustrate the key changes in type, phase fraction, and shape of the Fe-containing intermetallic phases, and the corresponding influence on the alloy's ductility. For high-pressure die casting (HPDC), an optimal range of the Mn content between 0.40 and 0.60 wt pct, equivalent to a Mn/Fe ratio of approximately 1, has been identified. At these Mn and Fe contents, the high cooling rates obtained in HPDC result in the formation of fine and homogeneously distributed α-Al15(Fe,Mn)3Si2 phase, and crack initiation is transferred from AlFeSi intermetallics to eutectic silicon. The study interprets the microstructure-property relationship in the light of thermodynamic calculations which reveal a significant increase in undercooling of the α-Al15(Fe,Mn)3Si2 phase with increased Mn content. It concludes that the interdependence of the well-defined Mn/Fe ratio and the high cooling rate in HPDC can generate superior ductility in secondary AlSi10Mg cast alloys.

  13. Chemical composition and structural identification of eutectic carbide in 1 pct Mn ductile iron

    NASA Astrophysics Data System (ADS)

    Ahmadabadi, M. Nili; Niyama, E.; Tanino, M.; Abe, T.; Ohide, T.

    1994-05-01

    Manganese, which may be used in ductile cast iron as a potent hardenability promoter, segregates in the intercellular region. This segregation becomes more severe as a consequence of poor inoculation, low cooling rate, or increasing of nominal Mn content in the alloy. In severely Mn-segregated regions, Mn eutectic carbide may be formed, which has a deteriorating effect on the mechanical properties of casting. In this study, a 1 Pct Mn ductile iron was used to investigate the chemical composition and crystal structure of the Mn eutectic carbide by electron microscopy (scanning and transmission), X-ray, and an electron probe microanalyzer (EPMA). Transmission electron microscope (TEM) and X-ray studies show that the crystal structure of carbide is orthorhombic with lattice parameters of a = 14.825, b = 11.415, and c = 8.880 (Å). The concentrations of Mn, Si, and Cr in carbide, analyzed by scanning electron microscope-energy-dispersive X-ray spectrometer (SEM-EDX) and transmission electron microscope-energy-dispersive X-ray spectrometer (TEM-EDX), were 5.0 to 7.0, 0.5 to 2.8 and 1.5 to 2.2 (wt Pct), respectively. The ratio of Fe plus other metal atoms to C was calculated from EPMA experiments to be 2.5-2.9. It was shown that by diminishing Mn segregation, precipitated eutectic carbide can be reduced. It is expected that this can be achieved by reducing nominal content of Mn or by increasing nodule count.

  14. Influence of coolant on ductile mode processing of binderless nanocrystalline tungsten carbide through ultraprecision diamond turning

    NASA Astrophysics Data System (ADS)

    Doetz, Marius; Dambon, Olaf; Klocke, Fritz; Fähnle, Oliver

    2015-08-01

    Molds made of tungsten carbide are typically used for the replicative mass production of glass lenses by precision glass molding. Consequently an ultra-precision grinding process with a subsequent fresh-feed polishing operation is conventionally applied. These processes are time consuming and have a relatively low reproducibility. An alternative manufacturing technology, with a high predictability and efficiency, which additionally allows a higher geometrical flexibility, is the single point diamond turning technique (SPDT). However, the extreme hardness and the chemical properties of tungsten carbide lead to significant tool wear and therefore the impossibility of machining the work pieces in an economical way. One approach to enlarge the tool life is to affect the contact zone between tool and work piece by the use of special cutting fluids. This publication emphasizes on the most recent investigations and results in direct machining of nano-grained tungsten carbide with mono crystal diamonds under the influence of various kinds of cutting fluids. Therefore basic ruling experiments on binderless nano grained tungsten carbide were performed, where the tool performed a linear movement with a steadily increasing depth of cut. As the ductile cutting mechanism is a prerequisite for the optical manufacturing of tungsten carbide these experiments serve the purpose for establish the influence of different cutting fluid characteristics on the cutting performance of mono crystal diamonds. Eventually it is shown that by adjusting the coolant fluid it is possible to significantly shift the transition point from ductile to brittle removal to larger depths of cut eventually enabling a SPDT of binderless tungsten carbide molds.

  15. Strain localization in ductile rocks: A comparison of natural and simulated pinch-and-swell structures

    NASA Astrophysics Data System (ADS)

    Peters, Max; Berger, Alfons; Herwegh, Marco; Regenauer-Lieb, Klaus

    2016-06-01

    We study pinch-and-swell structures in order to uncover the onset of strain localization and the change of deformation mechanisms in layered ductile rocks. To this end, boudinaged monomineralic veins embedded in an ultramylonitic matrix are analyzed quantitatively. The swells are built up by relatively undeformed original calcite grains, showing twinning and minor subgrain rotation recrystallization (SGR). Combined with progressive formation of high-angle misorientations between grains, indicative of SGR, severe grain size reduction defines the transition to the pinches. Accordingly, dynamically recrystallized grains have a strong crystallographic preferred orientation (CPO). Toward the necks, further grain size reduction, increasingly random misorientations, nucleation of new grains, and a loss of the CPO occur. We postulate that this microstructure marks the transition from dislocation to diffusion creep induced by strain localization. We confirm that the development of boudins is insensitive to original grain sizes and single-crystal orientations. In order to test these microstructural interpretations, a self-consistent numerical grain size evolution is implemented, based on thermo-mechanical principles, end-member flow laws and microphysical processes. Applying constant velocity and isothermal boundary conditions to a 3-layer finite element pure shear box, pinch-and-swell structures emerge out of the homogeneous layer through grain size softening at a critical state. Viscosity weakening due to elevated strain rates and dissipated heat from grain size reduction promotes strain rate weakening until a critical grain size is reached. At this point, a switch from dislocation to diffusion creep occurs. This state locks in at local steady states and is microstructurally expressed in pinches and swells, respectively. Thus, boudinage is identified as an energy attractor, identifying the high-energy steady state of an extending layered structure. We conclude from the

  16. Optimization of strength and ductility in nanotwinned ultrafine grained Ag: twin density and grain orientations

    SciTech Connect

    Ott, R. T.; Geng, J.; Besser, M. F.; Kramer, M. J.; Wang, Y. M.; Park, E. S.; LeSar, R.; King, A. H.

    2015-06-27

    Nanotwinned ultrafine grained Ag thick films with different twin densities and orientations have been synthesized by magnetron sputtering with a wide-range of deposition rates. The twin boundary (TB) spacings and orientations as well as the grain size for the different deposition conditions have been characterized by both synchrotron X-ray scattering and transmission electron microscopy (TEM). Structural characterization combined with uniaxial tensile tests of the free-standing films reveals a large increase in the yield strength for films deposited at high deposition rates without any accompanying change in the TB spacing – a behavior that is in contrast with what has been reported in the literature. We find that films deposited at lower deposition rates exhibit more randomly oriented grains with a lower overall twin density (averaged over all the grains) than the more heavily twinned grains with strong <111> fiber texture in the films deposited at higher deposition rates. The TB spacing in the twinned grains, however, does not show any significant dependence on the deposition rate. The dependence of the strength and ductility on the twin density and orientations can be described by two different soft deformation modes: 1) untwinned grains and 2) nanowinned grains that are not oriented with <111> along the growth direction. The untwinned grains provide relatively low resistance to slip, and thus decreased strength, while the nanotwinned grains that are not oriented with <111> along the growth direction are softer than nanotwinned grains that are oriented with <111> along the growth direction. We reveal that an ultrafine-grained (150-200 nm) structure consisting of a mixture of nanotwinned (~ 8-12 nm spacing) and untwined grains yields the best combination of high strength and uniform tensile ductility.

  17. Effect of numerical parameters on characterizing the hardening behavior of ductile uniaxial tension specimens.

    SciTech Connect

    Cordova, Theresa Elena; Dion, Kristin; Laing, John Robert; Corona, Edmundo; Breivik, Nicole L.; Wellman, Gerald William; Shelton, Timothy R.

    2010-11-01

    Many problems of practical importance involve ductile materials that undergo very large strains, in many cases to the point of failure. Examples include structures subjected to impact or blast loads, energy absorbing devices subjected to significant crushing, cold-forming manufacturing processes and others. One of the most fundamental pieces of data that is required in the analysis of this kind of problems is the fit of the uniaxial stress-strain curve of the material. A series of experiments where mild steel plates were punctured with a conical indenter provided a motivation to characterize the true stress-strain curve until the point of failure of this material, which displayed significant ductility. The hardening curve was obtained using a finite element model of the tensile specimens that included a geometric imperfection in the form of a small reduction in the specimen width to initiate necking. An automated procedure iteratively adjusted the true stress-strain curve fit used as input until the predicted engineering stress-strain curve matched experimental measurements. Whereas the fitting is relatively trivial prior to reaching the ultimate engineering stress, the fit of the softening part of the engineering stress-stain curve is highly dependent on the finite element parameters such as element formulation and initial geometry. Results by two hexahedral elements are compared. The first is a standard, under-integrated, uniform-strain element with hourglass control. The second is a modified selectively-reduced-integration element. In addition, the effects of element size, aspect ratio and hourglass control characteristics are investigated. The effect of adaptively refining the mesh based on the aspect ratio of the deformed elements is also considered. The results of the study indicate that for the plate puncture problem, characterizing the material with the same element formulation and size as used in the plate models is beneficial. On the other hand, using

  18. Response and representation of ductile damage under varying shock loading conditions in tantalum

    DOE PAGESBeta

    Bronkhorst, C. A.; Gray, III, G. T.; Addessio, F. L.; Livescu, V.; Bourne, N. K.; MacDonald, S. A.; Withers, P. J.

    2016-02-28

    The response of polycrystalline metals, which possess adequate mechanisms for plastic deformation under extreme loading conditions, is often accompanied by the formation of pores within the structure of the material. This large deformation process is broadly identified as progressive with nucleation, growth, coalescence, and failure the physical path taken over very short periods of time. These are well known to be complex processes strongly influenced by microstructure, loading path, and the loading profile, which remains a significant challenge to represent and predict numerically. In the current study, the influence of loading path on the damage evolution in high-purity tantalum ismore » presented. Tantalum samples were shock loaded to three different peak shock stresses using both symmetric impact, and two different composite flyer plate configurations such that upon unloading the three samples displayed nearly identical “pull-back” signals as measured via rear-surface velocimetry. While the “pull-back” signals observed were found to be similar in magnitude, the sample loaded to the highest peak stress nucleated a connected field of ductile fracture which resulted in complete separation, while the two lower peak stresses resulted in incipient damage. The damage evolution in the “soft” recovered tantalum samples was quantified using optical metallography, electron-back-scatter diffraction, and tomography. These experiments are examined numerically through the use of a model for shock-induced porosity evolution during damage. The model is shown to describe the response of the tantalum reasonably well under strongly loaded conditions but less well in the nucleation dominated regime. As a result, numerical results are also presented as a function of computational mesh density and discussed in the context of improved representation of the influence of material structure upon macro-scale models of ductile damage.« less

  19. Modelling of the effect of precipitates on work-hardening, ductility and impact behaviour of ferritic-martensitic Cr steels

    NASA Astrophysics Data System (ADS)

    Preininger, D.

    2002-12-01

    The effect of precipitates on work-hardening, tensile ductility and impact behaviour of carbon and high nitrogen martensitic 7-12Cr as well as particle strengthened ODS-(9-13)Cr steels have been analysed by models. A minimum of work-hardening and uniform strain generally appears around 600 °C at onset of dislocation recovery. Pronounced precipitation by increasing nitrogen and carbon content or additionally of fine Y 2O 3-particles distinctly increases work-hardening and uniform ductility. These, however, decrease with increasing strengthening but do not reach a visible level above 1500 MPa for ODS-steels at 20 °C. Minima of total elongation and fracture strain additionally appear in carbon and nitrogen martensitic steels around 300 °C where dynamic strain ageing occurs. Fracture strain and ductile upper shelf energy of Charpy tests in accordance with model predictions also decrease with increasing yield strength more strongly for ODS-steels due to their enhanced work-hardening and localized deformation. The strength-induced increase of ductile-to-brittle transition temperatures of ODS-steels is comparable to that observed by irradiation defect strengthening.

  20. Ductility Evaluation of As-Hydrided and Hydride Reoriented Zircaloy-4 Cladding under Simulated Dry-Storage Condition

    SciTech Connect

    Yan, Yong; Plummer, Lee K; Ray, Holly B; Cook, Tyler S; Bilheux, Hassina Z

    2014-01-01

    Pre-storage drying-transfer operations and early stage storage expose cladding to higher temperatures and much higher pressure-induced tensile hoop stresses relative to normal operation in-reactor and pool storage under these conditions. Radial hydrides could precipitate during slow cooling and provide an additional embrittlement mechanism as the cladding temperature decreases below the ductile-to-brittle transition temperature. As a means of simulating this behavior, unirradiated hydrided Zircaloy-4 samples were fabricated by a gas charging method to levels that encompass the range of hydrogen concentrations observed in current used fuel. Mechanical testing was carried out by the ring compression test (RCT) method at various temperatures to evaluate the sample s ductility for both as-hydrided and post-hydride reorientation treated specimens. As-hydrided samples with higher hydrogen concentration (>800 ppm) resulted in lower strain before fracture and reduced maximum load. Increasing RCT temperatures resulted in increased ductility of the as-hydrided cladding. A systematic radial hydride treatment was conducted at various pressures and temperatures for the hydrided samples with H content around 200 ppm. Following the radial hydride treatment, RCTs on the hydride reoriented samples were conducted and exhibited lower ductility compared to as-hydrided samples.

  1. Standard specification for ferritic ductile iron pressure-retaining castings for use at elevated temperatures. ASTM standard

    SciTech Connect

    1998-10-01

    This specification is under the jurisdiction of ASTM Committee A-4 on Iron Castings and is the direct responsibility of Subcommittee A04.02 on Malleable and Ductile Iron Castings. Current edition approved Jul. 10, 1998. Published October 1998. Originally published as A 395-55T. Last previous edition was A 395-88(1993).

  2. Study of the isothermal transformation of ductile iron with 0.5% Cu by electrical resistance measurement

    SciTech Connect

    Lin, B.Y.; Chen, E.T.; Lei, T.S.

    1995-10-01

    A computer-controlled system for measuring electrical resistance has been developed and used to study the isothermal transformation of austenite in a ductile iron (3.31% C, 3.12% Si, 0.22% mn, 0.55% Cu). The ability of the technique to follow the isothermal decomposition of austenite was established by measurements on an AISI 4340 steel. The times at which the austenite decomposed to primary ferrite, pearlite, and bainite were accurately detected. In the ductile iron, the formation of pearlite and of bainite was easily detected, and an isothermal transformation diagram was constructed from the results. The temperature range for the formation of bainite is especially important in producing austempered ductile iron (ADI) and was mapped. An initial stage of decomposition of austenite to ferrite and high-carbon austenite is followed by a time delay; then the high-carbon austenite decomposes to bainite. The formation of ADI requires austempering to a structure of ferrite and high-carbon austenite, then quenching to retain this structure, thus avoiding the formation of bainite. This is achieved by isothermal transformation into the time-delay region. For the ductile iron studied here, this time region was about 2.6 h at 400 C and increased to 277 h at 300 C.

  3. Ductile-brittle transition behavior of V-4Cr-4Ti irradiated in the dynamic helium charging experiment

    SciTech Connect

    Chung, H.M.; Nowicki, L.J.; Busch, D.E.

    1995-04-01

    The objective of this work is to determine the effect of simultaneous displacement damage and dynamically charged helium on the ductile-brittle transition behavior of V-4Cr-4Ti specimens irradiated to 18-31 dpa at 425-600{degrees}C in the Dynamic Helium Charging Experiment (DHCE).

  4. Extraordinary high ductility/strength of the interface designed bulk W-ZrC alloy plate at relatively low temperature

    PubMed Central

    Xie, Z. M.; Liu, R.; Miao, S.; Yang, X. D.; Zhang, T.; Wang, X. P.; Fang, Q. F.; Liu, C. S.; Luo, G. N.; Lian, Y. Y.; Liu, X.

    2015-01-01

    The refractory tungsten alloys with high ductility/strength/plasticity are highly desirable for a wide range of critical applications. Here we report an interface design strategy that achieves 8.5 mm thick W-0.5 wt. %ZrC alloy plates with a flexural strength of 2.5 GPa and a strain of 3% at room temperature (RT) and ductile-to-brittle transition temperature of about 100 °C. The tensile strength is about 991 MPa at RT and 582 MPa at 500 °C, as well as total elongation is about 1.1% at RT and as large as 41% at 500 °C, respectively. In addition, the W-ZrC alloy plate can sustain 3.3 MJ/m2 thermal load without any cracks. This processing route offers the special coherent interfaces of grain/phase boundaries (GB/PBs) and the diminishing O impurity at GBs, which significantly strengthens GB/PBs and thereby enhances the ductility/strength/plasticity of W alloy. The design thought can be used in the future to prepare new alloys with higher ductility/strength. PMID:26531172

  5. Improvement in Abrasion Wear Resistance and Microstructural Changes with Deep Cryogenic Treatment of Austempered Ductile Cast Iron (ADI)

    NASA Astrophysics Data System (ADS)

    Šolić, Sanja; Godec, Matjaž; Schauperl, Zdravko; Donik, Črtomir

    2016-07-01

    The application of a deep cryogenic treatment during the heat-treatment processes for different types of steels has demonstrated a significant influence on their mechanical and tribological properties. A great deal of research was conducted on steels, as well as on other kinds of materials, such as hard metal, gray cast iron, aluminum, aluminum alloys, etc., but not on austempered ductile iron (ADI). In this research the influence of a deep cryogenic treatment on the microstructure and abrasive wear resistance of austempered ductile iron was investigated. The ductile cast iron was austempered at the upper ausferritic temperature, deep cryogenically treated, and afterwards tempered at two different temperatures. The abrasion wear resistance was tested using the standard ASTM G65 method. The microstructure was characterized using optical microscopy, field-emission scanning electron microscopy, electron back-scattered diffraction, and X-ray diffraction in order to define the microstructural changes that influenced the properties of the ADI. The obtained results show that the deep cryogenic treatment, in combination with different tempering temperatures, affects the matrix microstructure of the austempered ductile iron, which leads to an increase in both the abrasion wear resistance and the hardness.

  6. Extraordinary high ductility/strength of the interface designed bulk W-ZrC alloy plate at relatively low temperature

    NASA Astrophysics Data System (ADS)

    Xie, Z. M.; Liu, R.; Miao, S.; Yang, X. D.; Zhang, T.; Wang, X. P.; Fang, Q. F.; Liu, C. S.; Luo, G. N.; Lian, Y. Y.; Liu, X.

    2015-11-01

    The refractory tungsten alloys with high ductility/strength/plasticity are highly desirable for a wide range of critical applications. Here we report an interface design strategy that achieves 8.5 mm thick W-0.5 wt. %ZrC alloy plates with a flexural strength of 2.5 GPa and a strain of 3% at room temperature (RT) and ductile-to-brittle transition temperature of about 100 °C. The tensile strength is about 991 MPa at RT and 582 MPa at 500 °C, as well as total elongation is about 1.1% at RT and as large as 41% at 500 °C, respectively. In addition, the W-ZrC alloy plate can sustain 3.3 MJ/m2 thermal load without any cracks. This processing route offers the special coherent interfaces of grain/phase boundaries (GB/PBs) and the diminishing O impurity at GBs, which significantly strengthens GB/PBs and thereby enhances the ductility/strength/plasticity of W alloy. The design thought can be used in the future to prepare new alloys with higher ductility/strength.

  7. Simulation of seismic waves at the earth's crust (brittle-ductile transition) based on the Burgers model

    NASA Astrophysics Data System (ADS)

    Carcione, J. M.; Poletto, F.; Farina, B.; Craglietto, A.

    2014-09-01

    The earth's crust presents two dissimilar rheological behaviors depending on the in situ stress-temperature conditions. The upper, cooler part is brittle, while deeper zones are ductile. Seismic waves may reveal the presence of the transition but a proper characterization is required. We first obtain a stress-strain relation, including the effects of shear seismic attenuation and ductility due to shear deformations and plastic flow. The anelastic behavior is based on the Burgers mechanical model to describe the effects of seismic attenuation and steady-state creep flow. The shear Lamé constant of the brittle and ductile media depends on the in situ stress and temperature through the shear viscosity, which is obtained by the Arrhenius equation and the octahedral stress criterion. The P and S wave velocities decrease as depth and temperature increase due to the geothermal gradient, an effect which is more pronounced for shear waves. We then obtain the P-S and SH equations of motion recast in the velocity-stress formulation, including memory variables to avoid the computation of time convolutions. The equations correspond to isotropic anelastic and inhomogeneous media and are solved by a direct grid method based on the Runge-Kutta time stepping technique and the Fourier pseudospectral method. The algorithm is tested with success against known analytical solutions for different shear viscosities. A realistic example illustrates the computation of surface and reverse-VSP synthetic seismograms in the presence of an abrupt brittle-ductile transition.

  8. Simulation of seismic waves at the Earth crust (brittle-ductile transition) based on the Burgers model

    NASA Astrophysics Data System (ADS)

    Carcione, J. M.; Poletto, F.; Farina, B.; Craglietto, A.

    2014-06-01

    The Earth crust presents two dissimilar rheological behaviours depending on the in-situ stress-temperature conditions. The upper, cooler, part is brittle while deeper zones are ductile. Seismic waves may reveal the presence of the transition but a proper characterization is required. We first obtain a stress-strain relation including the effects of shear seismic attenuation and ductility due to shear deformations and plastic flow. The anelastic behaviour is based on the Burgers mechanical model to describe the effects of seismic attenuation and steady-state creep flow. The shear Lamé constant of the brittle and ductile media depends on the in-situ stress and temperature through the shear viscosity, which is obtained by the Arrhenius equation and the octahedral stress criterion. The P- and S-wave velocities decrease as depth and temperature increase due to the geothermal gradient, an effect which is more pronounced for shear waves. We then obtain the P-S and SH equations of motion recast in the velocity-stress formulation, including memory variables to avoid the computation of time convolutions. The equations correspond to isotropic anelastic and inhomogeneous media and are solved by a direct grid method based on the Runge-Kutta time stepping technique and the Fourier pseudospectral method. The algorithm is tested with success against known analytical solutions for different shear viscosities. A realistic example illustrates the computation of surface and reverse-VSP synthetic seismograms in the presence of an abrupt brittle-ductile transition.

  9. The Strain-Hardening Behavior of Partially Austenitized and the Austempered Ductile Irons with Dual Matrix Structures

    NASA Astrophysics Data System (ADS)

    Kilicli, Volkan; Erdogan, Mehmet

    2008-04-01

    In the current study, an unalloyed ductile iron containing 3.50 C wt.%, 2.63 Si wt.%, 0.318 Mn wt.%, and 0.047 Mg wt.% was intercritically austenitized (partially austenitized) in two-phase regions (α + γ) at different temperatures for 20 min and then was quenched into salt bath held at austempering temperature of 365 °C for various times to obtain different ausferrite plus proeutectoid ferrite volume fractions. Fine and coarse dual matrix structures (DMS) were obtained from two different starting conditions. Some specimens were also conventionally austempered from 900 °C for comparison. The results showed that a structure having proeutectoid ferrite plus ausferrite (bainitic ferrite + high-carbon austenite (retained or stabilized austenite)) has been developed. Both of the specimens with ˜75% ausferrite volume fraction (coarse structure) and the specimen with ˜82% ausferrite volume fraction (fine structure) exhibited the best combination of high strength and ductility compared to the pearlitic grades, but their ductility is slightly lower than the ferritic grades. These materials also satisfy the requirements for the strength of the quenched and tempered grades and their ductility is superior to this grade. The correlation between the strain-hardening rates of the various austempered ductile iron (ADI) with DMS and conventionally heat-treated ADI microstructures as a function of strain was conducted by inspection of the respective tensile curves. For this purpose, the Crussard-Jaoul (C-J) analysis was employed. The test results also indicate that strain-hardening behavior of ADI with dual matrix is influenced by the variations in the volume fractions of the phases, and their morphologies, the degree of ausferrite connectivity and the interaction intensities between the carbon atoms and the dislocations in the matrix. The ADI with DMS generally exhibited low strain-hardening rates compared to the conventionally ADI.

  10. Probing the Statistical Validity of the Ductile-to-Brittle Transition in Metallic Nanowires Using GPU Computing.

    PubMed

    French, William R; Pervaje, Amulya K; Santos, Andrew P; Iacovella, Christopher R; Cummings, Peter T

    2013-12-10

    We perform a large-scale statistical analysis (>2000 independent simulations) of the elongation and rupture of gold nanowires, probing the validity and scope of the recently proposed ductile-to-brittle transition that occurs with increasing nanowire length [Wu et al. Nano Lett. 2012, 12, 910-914]. To facilitate a high-throughput simulation approach, we implement the second-moment approximation to the tight-binding (TB-SMA) potential within HOOMD-Blue, a molecular dynamics package which runs on massively parallel graphics processing units (GPUs). In a statistical sense, we find that the nanowires obey the ductile-to-brittle model quite well; however, we observe several unexpected features from the simulations that build on our understanding of the ductile-to-brittle transition. First, occasional failure behavior is observed that qualitatively differs from that predicted by the model prediction; this is attributed to stochastic thermal motion of the Au atoms and occurs at temperatures as low as 10 K. In addition, we also find that the ductile-to-brittle model, which was developed using classical dislocation theory, holds for nanowires as small as 3 nm in diameter. Finally, we demonstrate that the nanowire critical length is higher at 298 K relative to 10 K, a result that is not predicted by the ductile-to-brittle model. These results offer practical design strategies for adjusting nanowire failure and structure and also demonstrate that GPU computing is an excellent tool for studies requiring a large number of independent trajectories in order to fully characterize a system's behavior. PMID:26592289

  11. Effect of Temperature Reversion on Hot Ductility and Flow Stress-Strain Curves of C-Mn Continuously Cast Steels

    NASA Astrophysics Data System (ADS)

    Dong, Zhihua; Li, Wei; Long, Mujun; Gui, Lintao; Chen, Dengfu; Huang, Yunwei; Vitos, Levente

    2015-08-01

    The influence of temperature reversion in secondary cooling and its reversion rate on hot ductility and flow stress-strain curve of C-Mn steel has been investigated. Tensile specimens were cooled at various regimes. One cooling regime involved cooling at a constant rate of 100 °C min-1 to the test temperature, while the others involved temperature reversion processes at three different reversion rates before deformation. After hot tensile test, the evolution of mechanical properties of steel was analyzed at various scales by means of microstructure observation, ab initio prediction, and thermodynamic calculation. Results indicated that the temperature reversion in secondary cooling led to hot ductility trough occurring at higher temperature with greater depth. With increasing temperature reversion rate, the low temperature end of ductility trough extended toward lower temperature, leading to wider hot ductility trough with slightly reducing depth. Microstructure examinations indicated that the intergranular fracture related to the thin film-like ferrite and (Fe,Mn)S particles did not changed with varying cooling regimes; however, the Widmanstatten ferrite surrounding austenite grains resulted from the temperature reversion process seriously deteriorated the ductility. In addition, after the temperature reversion in secondary cooling, the peak stress on the flow curve slightly declined and the peak of strain to peak stress occurred at higher temperature. With increasing temperature reversion rate, the strain to peak stress slightly increased, while the peak stress showed little variation. The evolution of plastic modulus and strain to peak stress of austenite with varying temperature was in line with the theoretical prediction on Fe.

  12. The Border Ranges shear zone, Glacier Bay National Park, Alaska: An example of an ancient brittle-ductile transition zone

    SciTech Connect

    Smart, K.J. . Dept. of Geological Sciences)

    1992-01-01

    The Border Ranges fault system in southern Alaska forms the tectonic boundary between the Peninsular-Alexander-Wrangellia (PAW) composite terrane and the Chugach terrane. In Glacier Bay National Park, the Border Ranges fault system is a north-northwest trending, 10 kilometer wide zone of ductile shear zones and brittle faults hereafter referred to as the Border Ranges shear zone. Three-dimensional strain analyses of plagioclase lathes in the foliated calc-alkaline plutons reveals a strong flattening fabric with the plane of maximum flattening (XY-plane) oriented northwest-southeast and dipping steeply to the southwest. The distribution and shapes of sub-elliptical mafic enclaves in the calc-alkaline plutons show a similarly oriented flattening fabric. Coeval brittle and ductile deformational processes are indicated by: (1) ductile shear zones narrowing to brittle faults at the outcrop scale; and (2) undulose quartz with subgrain development, kinked biotite, twinned and undulose feldspar, and fractured and twinned hornblende often within a single thin-section. Amphibole geobarometry indicates that two of the calc-alkaline plutons deformed by the shear zone crystallized at pressures of approximately 3 kilobars equivalent to 10 to 12 kilometers depth. Metamorphic mineral assemblages within the mylonites indicate deformation under lower greenschist facies conditions (300--400 C). The shear zone may represent a snapshot of the brittle-ductile transition of an ancient convergent-transform plate boundary. As such, this unique exposure may be an ancient analogue for the brittle-ductile transition of the present day San Andreas fault system.

  13. Quartz Rheology - A Multidisciplinary Analysis of a Fossil Brittle-ductile Shear Array in the Central Southern Alps, New Zealand

    NASA Astrophysics Data System (ADS)

    Grigull, S.; Little, T. A.; Ellis, S.

    2006-12-01

    An exhumed fossil brittle-ductile shear array in the central Southern Alps, New Zealand, provides a natural laboratory for the investigation of the rheological behaviour of natural quartz under mid-lower crustal levels during transiently high stresses that are related to the upramping of the Pacific plate onto the Alpine Fault and followed by a stress drop. At depths >20 km, temperatures of 450-500° C, fluctuating fluid pressures of 310 MPa to 560 MPa (near lithostatic) and minimum strain rates of ~10^{-13 s-1, quartzofeldspathic wall rocks were faulted brittlely, presumably by aseismic stable sliding. Where brittle fault tips encounter older quartz veins embedded in the wall rocks, they terminate into shear zones in the quartz veins, deforming them brittlely and/or ductilely. Some embedded quartz veins deformed entirely ductilely to finite shear strains of 5-15. Despite these high strains and despite the smooth, coherent and ductile nature of the shearing of the veins, most of the ductilely sheared quartz veins show randomised or poorly developed CPO patterns. Most of the brittle faults are infilled by quartz-calcite veins indicating their role as conduits of fluids during deformation. We evaluate geological field observations such as deformed vein shape, scaling relationships between vein thickness and ductility and vein thickness distribution density and spacing of the brittle faults. Using finite element modelling, we simulate the observed vein structures in order to derive one or more flow laws that can explain the observed deformation for these naturally deformed quartz veins within the available time constraints and within the constraints of the known physical conditions. Two-dimensional models were set up and initially deformed to small finite strains in order to gain insight into the observed scaling relationship between the vein thickness and the proportional fraction of ductile creep strain (i. e. ductility of the quartz veins). The results show that

  14. The effect of segregation on the austemper transformation and toughness of ductile irons

    NASA Astrophysics Data System (ADS)

    Lin, B. Y.; Chen, E. T.; Lei, T. S.

    1998-06-01

    The effect of segregation of alloying elements on the phase transformation of ductile iron during austempering was investigated. Four heats, each containing 0.4%Mn, 1% Cu, 1.5% Ni, or 0.4% Mo (wt%) separately, were melted; then three different sizes of casting bars (3,15, and 75 mm diameter) were poured from each heat. The distribution and the degree of segregation of certain elements were quantitatively analyzed using an electron microprobe. A personal computer (PC)-controlled heat treating system was used to measure electrical resistivity, and the information on resistivity variations was used to analyze the effect of segregation on phase transformations during austempering. Also, Charpy impact and Rockwell hardness tests were performed to determine the effect of segregation on properties. Results of the electron microprobe analysis showed that the degree of segregation of alloy elements increases with an increase in diameter of the casting bars (i.e., an increase of solidification time of castings). The degree of segregation of alloy elements, represented by segregation ratio (SR) (the maximum concentration of element in cell divided by the minimum concentration of element in cell), varied linearly with the casting modulus (M) (volume of casting divided by surface area of casting). Regarding the segregating tendency among alloy elements, positive segregating elements Mn and Mo showed more segregation than the negative segregating elements Si, Cu, and Ni. In addition, segregation of Mo was more significant than Mn, and that for Cu was greater than Ni and Si. Between the time of finishing the first stage and beginning the second stage of bainite reaction in ductile irons, there is a significant “processing window,” At;, for austempering to obtain optimum mechanical properties. From the electrical resistivity data, it was observed that the austempering temperature plays a major role in the processing window. There was a narrow window at 400 ‡C but a larger

  15. Dating the longevity of ductile shear zones: Insight from 40Ar/39Ar in situ analyses

    NASA Astrophysics Data System (ADS)

    Schneider, Susanne; Hammerschmidt, Konrad; Rosenberg, Claudio L.

    2013-05-01

    We attempt to improve temporal constraints on the longevity and the termination of ductile shear zones by performing texturally-controlled in situ 40Ar/39Ar analyses of pre-kinematic muscovite, biotite and K-feldspars, of syn-kinematic phengite and K-feldspar, and of post-kinematic phengite within the same samples of sinistral shear zones from the western Tauern Window (Eastern Alps). Additionally two samples were dated by the Rb/Sr method (microsampling). Relative sequences of mineral formation based on microstructural, cross-cutting relationships were confirmed by in situ 40Ar/39Ar analyses, showing that syn-kinematic minerals are, in general, younger than pre-kinematic minerals and older or of equal age than the post-kinematic minerals of the same sample. From the rim to the core of the western Tauern Window syn-kinematic phengite and K-feldspar reveal a set of formation ages varying between 33 and 15 Ma for the northernmost and peripheral shear zone (Ahorn Shear Zone), between 24 and 12 Ma for the intermediate shear zone network (Tuxer Shear Zones), and between 20 and 7 Ma for the southernmost and central shear zone (Greiner Shear Zone). The age variation of syn-kinematic phengite and K-feldspar analyses is larger than the analytical error of each age obtained. In addition, isochron calculations of the syn-kinematic minerals reveal atmospheric-like 40Ar/36Ar intercepts. Therefore, the obtained age values of the syn-kinematic minerals are interpreted as formation ages which date increments of a long lasting deformation period. The time range of deformation of each shear zone system is bracketed by the oldest and youngest formation ages of syn-kinematic phengite and K-feldspar. Post-kinematic phengite laths show the youngest formation ages and overlap with the youngest syn-kinematic formation ages. This relationship indicates that post-kinematic growth occurred immediately after syn-kinematic mineral formation at the end of ductile sinistral shear. Hence, the

  16. The Relationship Between Constraint and Ductile Fracture Initiation as Defined by Micromechanical Analyses

    NASA Technical Reports Server (NTRS)

    Panontin, Tina L.; Sheppard, Sheri D.

    1994-01-01

    The use of small laboratory specimens to predict the integrity of large, complex structures relies on the validity of single parameter fracture mechanics. Unfortunately, the constraint loss associated with large scale yielding, whether in a laboratory specimen because of its small size or in a structure because it contains shallow flaws loaded in tension, can cause the breakdown of classical fracture mechanics and the loss of transferability of critical, global fracture parameters. Although the issue of constraint loss can be eliminated by testing actual structural configurations, such an approach can be prohibitively costly. Hence, a methodology that can correct global fracture parameters for constraint effects is desirable. This research uses micromechanical analyses to define the relationship between global, ductile fracture initiation parameters and constraint in two specimen geometries (SECT and SECB with varying a/w ratios) and one structural geometry (circumferentially cracked pipe). Two local fracture criteria corresponding to ductile fracture micromechanisms are evaluated: a constraint-modified, critical strain criterion for void coalescence proposed by Hancock and Cowling and a critical void ratio criterion for void growth based on the Rice and Tracey model. Crack initiation is assumed to occur when the critical value in each case is reached over some critical length. The primary material of interest is A516-70, a high-hardening pressure vessel steel sensitive to constraint; however, a low-hardening structural steel that is less sensitive to constraint is also being studied. Critical values of local fracture parameters are obtained by numerical analysis and experimental testing of circumferentially notched tensile specimens of varying constraint (e.g., notch radius). These parameters are then used in conjunction with large strain, large deformation, two- and three-dimensional finite element analyses of the geometries listed above to predict crack

  17. The effect of grain refinement on the room-temperature ductility of as-cast Fe{sub 3}Al-based alloys

    SciTech Connect

    Viswanathan, S.; Andleigh, V.K.; McKamey, C.G.

    1995-08-01

    Fe{sub 3}Al-based alloys exhibit poor room-temperature ductility in the as-cast condition. In this study, the effect of grain refinement of the as-cast alloy on room-temperature ductility was investigated. Small melts of Fe-28 at. % Al-5 at. % Cr were inoculated with various alloying additions and cast into a 50- x 30- x 30-mm graphite mold. The resulting ingots were examined metallographically for evidence of grain refinement, and three-point bend tests were conducted on samples to assess the effect on room-temperature ductility. Ductility was assumed to correlate with the strain corresponding to the maximum stress obtained in the bend test. The results showed that titanium was extremely effective in grain refinement, although it severely embrittled the alloy in contents exceeding 1%. Boron additions strengthened the alloy significantly, while carbon additions reduced both the strength and ductility. The best ductility was found in an alloy containing titanium, boron, and carbon. In order to verify the results of the grain refinement study, vacuum-induction melts of selected compositions were prepared and cast into a larger 25- x 150- x 100-mm graphite mold. Tensile specimens were machined from the ingots, and specimens were tested at room temperature. The results of the tensile tests agreed with the results of the grain refinement study; in addition, the addition of molybdenum was found to significantly increase room-temperature tensile ductility over that of the base alloy.

  18. Ductile fracture toughness of modified A 302 grade B plate materials. Volume 2

    SciTech Connect

    McCabe, D.E.; Manneschmidt, E.T.; Swain, R.L.

    1997-02-01

    The objective of this work was to develop ductile fracture toughness data in the form of J-R curves for modified A 302 grade B plate materials typical of those used in fabricating reactor pressure vessels. A previous experimental study at Materials Engineering Associates (MEA) on one particular heat of A 302 grade B plate showed decreasing J-R curves with increased specimen thickness. This characteristic has not been observed in numerous tests made on the more recent production materials of A 533 grade B and A 508 class 2 pressure vessel steels. It was unknown if the departure from norm for the MEA material was a generic characteristic for all heats of A 302 grade B steels or just unique to that one particular plate. Seven heats of modified A 302 grade B steel and one heat of vintage A 533 grade B steel were provided to this project by the General Electric Company of San Jose, California. All plates were tested for chemical content, tensile properties, Charpy transition temperature curves, drop-weight nil-ductility transition (NDT) temperature, and J-R curves. Tensile tests were made in the three principal orientations and at four temperatures, ranging from room temperature to 550{degrees}F (288{degrees}C). Charpy V-notch transition temperature curves were obtained in longitudinal, transverse, and short transverse orientations. J-R curves were made using four specimen sizes (1/2T, IT, 2T, and 4T). None of the seven heats of modified A 302 grade showed size effects of any consequence on the J-R curve behavior. Crack orientation effects were present, but none were severe enough to be reported as atypical. A test temperature increase from 180 to 550{degrees}F (82 to 288{degrees}C) produced the usual loss in J-R curve fracture toughness. Generic J-R curves and mathematical curve fits to the same were generated to represent each heat of material. This volume is a compilation of all data developed.

  19. Mechanical and Microstructural Evolution of Ductile Shear Zones: Implications for the Deep Structure of Lithospheric Faults

    NASA Astrophysics Data System (ADS)

    Platt, J. P.; Behr, W. M.

    2010-12-01

    We offer three new concepts that help place constraints on the mechanics and width of plate-boundary shear zones below the brittle-ductile transition. 1. Lithospheric shear zones operate at approximately constant stress at any given depth (temperature). This is because shear zones form by microstructural changes that cause weakening and hence strain localization. These changes occur when the ambient stress reaches the yield strength σy of intact rock. As a result, the cumulative width w of shear zones reaches a value such that they can accommodate plate motion at a flow stress equal to σy. 2. Exhuming shear zones preserve a record of the stress-temperature profile through the deforming crust. Increasing strain localization as the rocks cool, and quenching of the microstructure outside the narrowing shear zone, allow preservation of the microstructure and mineral chemistry at various stages in their evolution. If the flow stress in the shear zone at any depth is a measure of the yield strength of the surrounding rock, we can use this information to construct strength-depth profiles through the lithosphere. 3. Dislocation creep causes dynamic recrystallization and grainsize reduction. This may result in a switch to grainsize-sensitive creep, which is the main cause of weakening and strain localization in shear zones. At constant strain-rate, this results in a stress drop, which may be followed by grain growth, preventing a permanent switch in mechanism. If shear zones operate at constant stress, however, dislocation density in the deforming grains remains the same after the switch, so that dynamic recrystallization and grain-boundary migration driven by dislocation strain energy continue at the same rate as before. This inhibits grain growth driven by surface energy, so that the deformation mechanism switch is permanent. We calculate shear zone widths at depth in the lithosphere based on these concepts. We use a stress-temperature profile obtained from the Whipple

  20. Analytical and Experimental Nanomechanical Approaches to Understanding the Ductile-to-Brittle Transition

    NASA Astrophysics Data System (ADS)

    Hintsala, Eric Daniel

    This dissertation presents progress towards understanding the ductile-to-brittle transition (DBT) using a mixture of nanomechanical experiments and an analytical model. The key concept is dislocation shielding of crack tips, which is occurs due to a dislocation back stress. In order to properly evaluate the role of these interactions, in-situ experiments are ideal by reducing the number of interacting dislocations and allowing direct observation of cracking behavior and the dislocations themselves. First, in-situ transmission electron microscope (TEM) compression experiments of plasma-synthesized silicon nanocubes (NCs) are presented which shows plastic strains greater than 50% in a semi-brittle material. The mechanical properties are discussed and plasticity mechanisms are identified using post-mortem imaging with a combination of dark field and high-resolution imaging. This observations help to develop a back stress model which is used to fit the hardening regime. This represents the first study of its kind where back stresses are used in a discrete manner to match hardening rates. However, the important measurable quantities for evaluating the DBT include fracture toughness values and energetic activation parameters for cracking and plasticity. In order to do this, a new method for doing in-situ fracture experiments is explored. This method is pre-notched three point bending experiments, which were fabricated by focused ion beam (FIB) milling. Two different materials are evaluated: a model ductile material, Nitronic 50, an austenitic steel alloy, and a model brittle material, silicon. These experiments are performed in-situ scanning electron microscope (SEM) and TEM and explore different aspects including electron backscatter diffraction (EBSD) to track deformation in SEM scale experiments, pre-notching using a converged TEM beam to produce sharper notches better replicating natural cracks, etching procedures to reduce residual FIB damage and elevated