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Sample records for alloys fracture mechanics

  1. Morphology Evolution on the Fracture Surface and Fracture Mechanisms of Multiphase Nanostructured ZrCu-Base Alloys.

    PubMed

    Qiu, Feng; Zhu, Lin; Zou, Qian; Wang, Lei; Han, Xue; Li, Qiang; Jiang, Qi-Chuan

    2017-03-13

    A multiphase nanostructured ZrCu-base bulk alloy which showed a unique microstructure consisting of sub-micrometer scale Zr₂Cu solid solution, nano-sized twinned plate-like ZrCu martensite (ZrCu (M)), and retained ZrCu (B2) austenite was fabricated by copper mold casting. The observation of periodic morphology evolution on the fracture surface of the multiphase nanostructured ZrCu-base alloys has been reported, which suggested a fluctuant local stress intensity along the crack propagation. It is necessary to investigate the compressive deformation behavior and the fracture mechanism of the multiphase alloy and the relation to the unique microstructures. The results obtained in this study provide a better understanding of the deformation and fracture mechanisms of multiphase hybrid nanostructured ZrCu-based alloys and give guidance on how to improve the ductility/toughness of bulk ZrCu-based alloys.

  2. Mechanisms of Fracture and Creep of Structural Alloys

    DTIC Science & Technology

    1992-03-30

    FRACTURE AND CREEP OF STRUCTURAL ALLOYS D. A. Koss Department of Materials Science and Engineering The Pennsylvania State University University Park , PA...of Materials Science and Engineering REPCrt: N6,8 Penn State University University Park , PA 16802 Report No. 4 9. SPONSORING MON T ORING AGENCY NAMES...Effects of Stress State on Void Linkin [with Andrew Geltmacher, Ph.D. candidate, Dr. Peter Matic, Naval Research Laboratory, and Dr. Mike Stout, Los

  3. Fracture Mechanics

    DTIC Science & Technology

    1974-01-31

    2219 -T851 aluminum (fractures at low stresses). The parameter KF is alloy compact specimens 1 2 and demonstrate consistent a function of specimen...Congress of 20. Walker, E. K., "The Effect of Stress Ratio Applied Mechanics, 1924. During Crack Propagation and Fatigue for 2024-T3 and 7015- T6 Aluminum ...34Stress- Corrosion Cracking in 12. Kaufman, J. G., and Nelson, F. G., "More Ti-6A1-4V Titanium Alloy in Nitrogen Tetroxide," on Specimen Size Effect in 2219

  4. Tensile Deformation and Fracture Mechanism of Bulk Bimodal Ultrafine-Grained Al-Mg Alloy

    NASA Astrophysics Data System (ADS)

    Lee, Zonghoon; Radmilovic, Velimir; Ahn, Byungmin; Lavernia, Enrique J.; Nutt, Steven R.

    2010-04-01

    The tensile fractures of ultrafine-grained (UFG) Al-Mg alloy with a bimodal grain size were investigated at the micro- and macroscale using transmission electron microscopy (TEM), scanning electron microscopy (SEM) equipped with focused ion beam (FIB), and optical microscopy. The nanoscale voids and crack behaviors near the tensile fracture surfaces were revealed in various scale ranges and provided the evidence to determine the underlying tensile deformation and fracture mechanisms associated with the bulk bimodal metals. The bimodal grain structures exhibit unusual deformation and fracture mechanisms similar to ductile-phase toughening of brittle materials. The ductile coarse grains in the UFG matrix effectively impede propagation of microcracks, resulting in enhanced ductility and toughness while retaining high strength. In view of the observations collected, we propose a descriptive model for tensile deformation and fracture of bimodal UFG metals.

  5. Influence of grain size on the mechanism of fracture of the aluminum alloy V95

    NASA Astrophysics Data System (ADS)

    Petrova, A. N.; Brodova, I. G.; Shirinkina, I. G.; Lyapunova, E. A.; Naimark, O. B.

    2012-07-01

    Mechanical behavior and mechanisms of fracture of the ultrafine-crystalline (UFC) and the coarse-crystalline (CC) aluminum alloy V95 (Al-6.0 Zn-2.3 Mg-2.0 Cu-0.4 Mn (wt %)) manufactured via using severe plastic deformation, namely, by dynamic equal-channel angular pressing (DCAP), have been studied. It has been demonstrated that the UFC material exhibits improved mechanical properties in comparison with the CC analog. A correlation analysis of fracture surfaces and the determination of the Hurst exponent have made it possible to perform a comparative estimation of the uniformity of the fracture structure and of the fractions of ductile and brittle fractures in the samples with the structure-scale characteristics different in value.

  6. Fracture toughness testing and toughening mechanisms of some commercial cobalt-free hardfacing alloys

    SciTech Connect

    Cockeram, B.V.

    1998-04-27

    Hardfacing alloys are weld deposited to provide a wear resistant surface for structural base materials. Commercial low cobalt hardfacing alloys are being evaluated to reduce plant activation levels. Since hardfacing alloys typically must be resistant to cracking to assure adequate in service performance, fracture toughness is a critical material property. Fracture toughness (K{sub IC}) measurements of Fe base, Ni-base, and Co-base hardfacing were performed in accordance with ASTM E399-90 procedure in an effort to identify a tough cobalt-free alternative. Reduced scatter in K{sub IC} data was observed for the Fe base hardfacing, and the 95% lower bound K{sub IC} values were generally higher than the Ni-base Hardfacing alloys. Preliminary crack growth data obtained during precracking indicate that the Ni-base hardfacing possess better fatigue crack growth resistance. However, none of the Fe-base or Ni-base hardfacing have K{sub IC} values that are comparable to the reference Co-base hard facing. The test specimens were machined from thick (0.5 inches) weld deposits, and the microstructures of the test specimens are compared with the more prototypic, thinner deposits. Microstructural and fractographic examinations are used to characterize the fracture mechanisms and delineate the operative toughening mechanisms. Crack deflection and crack bridging toughening mechanisms are shown to be relevant for most of the commercial hardfacing.

  7. Friction Stir-Welded Titanium Alloy Ti-6Al-4V: Microstructure, Mechanical and Fracture Properties

    NASA Astrophysics Data System (ADS)

    Sanders, D. G.; Edwards, P.; Cantrell, A. M.; Gangwar, K.; Ramulu, M.

    2015-05-01

    Friction stir welding (FSW) has been refined to create butt welds from two sheets of Ti-6Al-4V alloy to have an ultra-fine grain size. Weld specimen testing was completed for three different FSW process conditions: As welded, stress relieved, stress relieved and machined, and for the un-welded base material. The investigation includes macrostructure, microstructure, microhardness, tensile property testing, notched bar impact testing, and fracture toughness evaluations. All experiments were conducted in accordance with industry standard testing specifications. The microstructure in the weld nugget was found to consist of refined and distorted grains of alpha in a matrix of transformed beta containing acicular alpha. The enhanced fracture toughness of the welds is a result of increased hardness, which is attributed to an increase in alpha phase, increase in transformed beta in acicular alpha, and grain refinement during the weld process. The noted general trend in mechanical properties from as welded, to stress relieved, to stress relieved and machined conditions exhibited a decrease in ultimate tensile strength, and yield strength with a small increase in ductility and a significant increase in fracture toughness.

  8. Characterization of the Microstructure, Fracture, and Mechanical Properties of Aluminum Alloys 7085-O and 7175-T7452 Hollow Cylinder Extrusions

    NASA Astrophysics Data System (ADS)

    Benoit, Samuel G.; Chalivendra, Vijaya B.; Rice, Matthew A.; Doleski, Robert F.

    2016-09-01

    Microstructural, tensile, and fracture characterizations of cylindrically forged forms of aluminum alloys AA7085-O and AA7175-T7452 were performed. Mechanical and fracture properties were investigated along radial, circumferential, and longitudinal directions to determine directional dependency. American Society for Testing and Materials (ASTM) test methods (ASTM E8-04 and ASTM E1820) were employed for both the tensile and fracture characterizations, respectively. The tensile and fracture properties were related to microstructure in each direction. The strength, elongation at break, and ultimate tensile strength of AA7085-O were higher than those of AA7175-T7452. AA7175-T7452 alloy failed in a brittle manner during fracture studies. AA7085-O outperformed AA7175-T7452 on fracture energy in all of the orientations studied. Smaller grain sizes on the planes normal to circumferential and longitudinal directions showed improvement in both elongation at break and fracture energy values compared to those of radial direction. Scanning electron microscopy images demonstrated cleavage fracture in AA7175-T7452 and transgranular fracture in AA7085-O.

  9. The mechanism of fracture

    SciTech Connect

    Goel, V.S.

    1986-01-01

    In this book eighty-five papers look at fractures. Topics covered are fracture mechanics, fracture mechanisms, evaluating fracture resistance, fracture toughness, predicting crack growth, surface cracking, crack initiation and propagation, weld fractures, engineering applications of fracture mechanics, fracture and failure in nonmetallic materials, dynamic fractures, test techniques, radiation embrittlement, applications of fracture mechanics, design concepts, and creep.

  10. Evaluation of Stress Corrosion Cracking Susceptibility Using Fracture Mechanics Techniques, Part 1. [environmental tests of aluminum alloys, stainless steels, and titanium alloys

    NASA Technical Reports Server (NTRS)

    Sprowls, D. O.; Shumaker, M. B.; Walsh, J. D.; Coursen, J. W.

    1973-01-01

    Stress corrosion cracking (SSC) tests were performed on 13 aluminum alloys, 13 precipitation hardening stainless steels, and two titanium 6Al-4V alloy forgings to compare fracture mechanics techniques with the conventional smooth specimen procedures. Commercially fabricated plate and rolled or forged bars 2 to 2.5-in. thick were tested. Exposures were conducted outdoors in a seacoast atmosphere and in an inland industrial atmosphere to relate the accelerated tests with service type environments. With the fracture mechanics technique tests were made chiefly on bolt loaded fatigue precracked compact tension specimens of the type used for plane-strain fracture toughness tests. Additional tests of the aluminum alloy were performed on ring loaded compact tension specimens and on bolt loaded double cantilever beams. For the smooth specimen procedure 0.125-in. dia. tensile specimens were loaded axially in constant deformation type frames. For both aluminum and steel alloys comparative SCC growth rates obtained from tests of precracked specimens provide an additional useful characterization of the SCC behavior of an alloy.

  11. The Mechanisms of Dispersion Strengthening and Fracture in Al-based XD (TM) Alloys

    NASA Technical Reports Server (NTRS)

    Aiken, R. M., Jr.

    1990-01-01

    The influence of reinforcement size, volume fraction, and matrix deformation behavior on room and elevated temperature strength, and the fracture toughness of metal matrix composites of both pure aluminum and Al(4 percent)Cu(1.5 percent)Mg with 0 to 15 vol percent TiB2 were examined. Higher TiB2 volume fractions increased the tensile yield strength both at room and elevated temperatures, and reduced the elongation to fracture. Tensile tests also indicate that small particles provided a greater increase in strength for a given volume fraction than larger particles, whereas elongation to fracture appeared to be insensitive to reinforcement size. The fracture toughness of the Al(4 percent)Cu(1.5 percent)Mg alloys decreased rapidly with TiB2 additions of 0 to 5 vol percent and more slowly with TiB2 additions of 5 to 15 vol percent. Fracture toughness appears to be independent of TiB2 particle size. The isothermal-aging response of the precipitation strengthened Al(4 percent)Cu(1.5 percent)Mg alloys was not altered by the presence of TiB2.

  12. Dynamic tensile response of Zr-based bulk amorphous alloys: Fracture morphologies and mechanisms

    NASA Astrophysics Data System (ADS)

    Escobedo, J. P.; Gupta, Y. M.

    2010-06-01

    Plate impact experiments were conducted to examine the dynamic tensile response of Zr-based bulk amorphous alloys (BAAs) having a nominal composition of Zr56.7Cu15.3Ni12.5Nb5.0Al10.0Y0.5. The experimental configuration used in our work permitted soft recovery of the samples to allow a careful examination of the fractured samples along with real-time measurements of the sample free-surface velocity (FSV) histories. Tensile loading was preceded by elastic compressive loading to peak stresses in the 3.6 to 6.0 GPa range. Tensile damage in the recovered samples was examined using optical and electron microscopy. The microscopy results showed that the BAA samples exhibit a brittle behavior (as a glass) at the macroscopic level and a ductile behavior (as a metal) at the microscopic level; in addition, corrugations and bumps are observed at the nanoscale. The observed fracture morphologies are related to three key features present in our spall experiments: preceding compressive stress (3.6-6.0 GPa), high tensile loading rate (˜106/s), high mean tensile stress (˜2.3 GPa); and are intrinsically related to the amorphous glassy structure of the BAAs (free volume content). We propose that the compressive stress depletes the free volume content. With increasing compressive stress, the available free volume decreases causing a suppression of shear stresses during tension. Thus, the mean tensile component becomes more dominant at higher stresses. Consequently, the observed surface morphology results from brittle cleavage, causing an increased damage localization in the recovered samples spalled at higher stresses. These observations support the inferences made from measurements of FSV histories. The high tensile loading rate is proposed to be responsible for cracking by multiple shear band propagation and interception, rendering the observed serrated surface morphology. Finally, we proposed that the corrugations are created due to a succession of arrest and propagation of mode

  13. Mechanical characterization and fracture toughness of electroplated cadmium coating of Al -Zn alloy, T6

    NASA Astrophysics Data System (ADS)

    Mohan Kumar, S.; Ravi Kumar, V.; Shashi Kumar, M. E.; Govindaraju, H. K.

    2017-07-01

    Fracture toughness, Hardness and Tensile Strength of the Aluminum alloy 7075-T6 coated with Cadmium with varying thickness of 10µ and 20µ were investigated. Electroplating Cadmium coating process gives excellent corrosion resistance, provides low coefficient of friction which increases the surface hardness of the material. It also provides a uniform and dense coating, in many cases, maintains surface finish as it was before plating. The specimens prepared in line with ASTM E-8M and E-399 standard were subjected to various tests. The results shows thatthe hardness of the EC coted specimens has increased by 10% and increases with increase in thickness, butthe thicker the EC coating, more brittle is the material. The Ultimate Tensile Strength also increased by 5% compared to the uncoated counterpart. There was a steep increase in plain strain fracture toughness with the increase in the coating thickness for the Aluminum 7075-T6 alloy in TL orientation. The crack growth was Unstable due to the strong adhesion between the EC coating and the alloy.

  14. Corrosion fatigue of iron-chromium-nickel alloys: Fracture mechanics, microstructure and chemistry

    SciTech Connect

    Wei, R.P.

    1993-01-25

    Phase transformation and cracking during RT aging of charged, high-purity Fe18Cr12Ni alloy and commerical 304 ss were examined; results show that [epsilon]* (hcp) hydride formed on Fe18Cr12Ni upon charging, and it decomposed rapidly to form first [epsilon] and then [alpha]' martensite. Morphology of fracture surfaces of Fe18Cr12Ni produced by corrosion fatigue in NaCl solutions and in hydrogen was found to be identical. Effort was made to examine the approaches and methodologies used in service life predictions and reliability analyses.

  15. Development and fracture mechanics data for 6Al-6V-2 Sn titanium alloy

    NASA Technical Reports Server (NTRS)

    Fiftal, C. F.; Beck, E. J.

    1974-01-01

    Fracture mechanics properties of 6Al-6V-2Sn titanium in the annealed, solution-treated, and aged condition are presented. Tensile, fracture toughness, cyclic flaw growth, and sustained-load threshold tests were conducted. Both surface flaw and compact tension-specimen geometries were employed. Temperatures and/or environments used were -65 F (220 K) air, ambient, 300 F (422 K) air, and room-temperature air containing 10 and 100% relative humidity.

  16. Corrosion fatigue of iron-chromium-nickel alloys: Fracture mechanics, microstructure and chemistry

    SciTech Connect

    Wei, R.P.

    1992-01-29

    This progress report briefly summarizes the research performed under the referenced grant for the period from 1 December 1990 to 31 December 1991, and contains a cumulative listing of technical presentations and publications dating back to 1 June 1988. Under this grant, a multi-disciplinary research program is undertaken to address certain fundamental issues relating to corrosion fatigue crack growth in structurally important alloys in aqueous environments. The principal goal of the research is to develop and expand the scientific understanding of the processes that control corrosion fatigue crack growth, particularly for ferrous alloys in terms of the controlling mechanical and chemical/electrochemical processes and their interactions with the microstructure. Focus is placed upon the austenitic iron-chromium-nickel (FeCrNi) alloys because of the need to resolve certain mechanistic issues and because of extensive utilization of these alloys in the power generation and chemical industries. Emphasis is given to the growth of short (small) cracks at low growth rates because crack growth in this regime is expected to be more sensitive to changes in external chemical/electrochemical variables.

  17. Spall Fracture Morphologies and Mechanisms of Zr-based Bulk Amorphous Alloys

    NASA Astrophysics Data System (ADS)

    Gupta, Y. M.; Escobedo, J. P.

    2011-06-01

    Plate impact experiments were conducted to examine the dynamic tensile response of Zr-based bulk amorphous alloys (BAAs). Tensile loading was preceded by elastic compressive loading (3.6 to 6.0 GPa). Microscopy results revealed that the BAA samples exhibit brittle behavior (glass like) macroscopically and ductile behavior (metal like) microscopically; corrugations and bumps are observed at the nanoscale. The observed fracture morphologies are related to three key features of our spall experiments and the free volume content of the BAAs. With increasing compressive stress, the available free volume decreases causing a suppression of shear stresses during tension, resulting in brittle cleavage at higher stresses. The high tensile loading rate likely causes cracking by multiple shear band propagation and interception, rendering a serrated surface morphology. Finally, the corrugations are likely created due to a succession of arrest and propagation of mode I cracks. A subsequent dilatation, an effect of the tensile mean stress, caused the corrugations to evolve to bump-type features (10-100 nm). Work supported by DOE/NNSA.

  18. High temperature deformation and fracture mechanisms in a dendritic Ni[sub 3]Al alloy

    SciTech Connect

    Kim, H.K.; Earthman, J.C. . Dept. of Mechanical and Aerospace Engineering)

    1994-03-01

    The mechanisms that control high temperature deformation and rupture were studied in a Ni[sub 3]Al alloy that was thermo-mechanically treated to produce a non-porous dendritic grain structure. Comparisons of data corresponding to the dendritic grain morphology with that for the equiaxed grain structures indicate that the dendritic morphology results in significantly lower creep rates as well as substantially greater times to rupture. Comparison of the data with numerical calculations suggests that this difference in creep strength is due to an inherent resistance to grain boundary sliding by the dendritic grain structure. A constrained cavity growth model was adapted based on microstructural observations to account for cavitation within the dendritic microstructure. The success of the model indicates that rupture time is primarily determined by constrained cavity growth on isolated dendrite boundary segments.

  19. Investigation into the Mechanical Properties and Fracture Behavior of A356 Aluminum Alloy-Based ZrO2-Particle-Reinforced Metal-Matrix Composites

    NASA Astrophysics Data System (ADS)

    Abdizadeh, H.; Baghchesara, M. A.

    2013-11-01

    In the present study, an investigation has been carried out into the influence of ZrO2 content and casting temperature on the mechanical properties and fracture behavior of A356 Al/ZrO2 composites. A356 aluminum alloy matrix composites reinforced with 5, 10 and 15 vol.% ZrO2 were fabricated at 750, 850, and 95 0°C via the stir-casting method. Based on the results obtained, the optimum amount of reinforcement and casting temperature were determined by evaluating the density and mechanical properties of the composites through the use of hardness and tensile tests. The fracture surfaces of composite specimens were also studied to identify the main fracture mechanisms of the composites. The results obtained indicated that all samples fractured due to the interdendritic cracking of the matrix alloy. Reinforcing the Al matrix alloy with ZrO2 particles increased the hardness and ultimate tensile strength of the alloy to the maximum values of 70 BHN and 232 MPa, respectively. The best mechanical properties were obtained for the specimens with 15 vol.% of ZrO2 produced at 75 0°C.

  20. The Joint Strength and Fracture Mechanisms of TC4/TC4 and TA0/TA0 Brazed with Ti-25Cu-15Ni Braze Alloy

    NASA Astrophysics Data System (ADS)

    Zou, Zhihuan; Zeng, Fanhao; Wu, Haobo; Liu, Jian; Li, Yi; Gu, Yi; Yuan, Tiechui; Zhang, Fuqin

    2017-05-01

    In this paper, Ti-25Cu-15Ni (mass ratio) braze alloys were prepared by vacuum arc melting. Additionally, the TA0 pure titanium and TC4 titanium alloy were brazed with the Ti-25Cu-15Ni braze alloy at 960, 980, 1000, 1020, and 1040 °C. The effects of the braze temperature on the tensile strength of the TA0 and TC4 joints and their fracture mechanisms were studied. The maximum tensile strength of the TA0 joints of 219.9 ± 0.1 MPa was achieved at a brazing temperature of 980 °C, and the maximum tensile strength of the TC4 joints of 832.9 ± 0.1 MPa was achieved at the same brazing temperature. These results indicate that their ideal joint strength is comparable. According to the fractography results of the TA0 joints, a mixed fracture morphology is indicated. The TA0 fracture surface is dominated by cleavage fracture with a small contribution from ductile fracture. The TC4 joint fracture arises from cleavage.

  1. Mechanisms of intergranular fracture

    SciTech Connect

    Farkas, D.

    1999-08-01

    The authors present a study of the atomistic mechanisms of crack propagation along grain boundaries in metals and alloys. The failure behavior showing cleavage crack growth and/or crack-tip dislocation emission is demonstrated using atomistic simulations for an embedded-atom model. The simulations follow the quasi-equilibrium growth of a crack as the stress intensity applied increases. Dislocations emitted from crack tips normally blunt the crack and inhibit cleavage, inducing ductile behavior. When the emitted dislocations stay near the crack tip (sessile dislocations), they do blunt the crack but brittle cleavage can occur after the emission of a sufficient number of dislocations. The fracture process occurs as a combination of dislocation emission/micro-cleavage portions that are controlled by the local atomistic structure of the grain boundary. The grain boundary is shown to be a region where dislocation emission is easier, a mechanism that competes with the lower cohesive strength of the boundary region.

  2. A fracture mechanics approach for estimating fatigue crack initiation in carbon and low-alloy steels in LWR coolant environments

    SciTech Connect

    Park, H. B.; Chopra, O. K.

    2000-04-10

    A fracture mechanics approach for elastic-plastic materials has been used to evaluate the effects of light water reactor (LWR) coolant environments on the fatigue lives of carbon and low-alloy steels. The fatigue life of such steel, defined as the number of cycles required to form an engineering-size crack, i.e., 3-mm deep, is considered to be composed of the growth of (a) microstructurally small cracks and (b) mechanically small cracks. The growth of the latter was characterized in terms of {Delta}J and crack growth rate (da/dN) data in air and LWR environments; in water, the growth rates from long crack tests had to be decreased to match the rates from fatigue S-N data. The growth of microstructurally small cracks was expressed by a modified Hobson relationship in air and by a slip dissolution/oxidation model in water. The crack length for transition from a microstructurally small crack to a mechanically small crack was based on studies on small crack growth. The estimated fatigue S-N curves show good agreement with the experimental data for these steels in air and water environments. At low strain amplitudes, the predicted lives in water can be significantly lower than the experimental values.

  3. The Delayed Fracture of Aluminum Alloys.

    DTIC Science & Technology

    1981-01-01

    if necessary and Identify by block number) aluminum alloys, stress - corrosion cracking, oxide film, Auger electron spectroscopy, Auger depth profiling...revere Ide If r ecester’ nd Ientify by block number). b -. ,h 0 unJaInenta mechanZsm of stress - corrosion cracking (SCC) has been studied for high-purity...these specimens is not intergranular. Fracture appears to have originated through pitting corrosion , which caused local stress concentration leading to

  4. Mechanical Properties and Fracture Behaviors of the As-Extruded Mg-5Al-3Ca Alloys Containing Yttrium at Elevated Temperature.

    PubMed

    Son, Hyeon-Taek; Kim, Yong-Ho; Kim, Taek-Soo; Lee, Seong-Hee

    2016-02-01

    Effects of yttrium (Y) addition on mechanical properties and fracture behaviors of the as-extruded Mg-Al-Ca based alloys at elevated temperature were investigated by a tensile test. After hot extrusion, the average grain size was refined by Y addition and eutectic phases were broken down into fine particles. Y addition to Mg-5Al-3Ca based alloy resulted in the improvement of strength and ductility at elevated temperature due to fine grain and suppression of grain growth by formation of thermally stable Al2Y intermetallic compound.

  5. The mechanisms of dispersion strengthening and fracture in Al-based XD(tm) alloys, part 1

    NASA Technical Reports Server (NTRS)

    Aikin, R. M., Jr.

    1990-01-01

    The influence of reinforcement size, volume fraction, and matrix deformation behavior on room and elevated temperature strength; the fracture toughness; and the fatigue crack growth rate of metal matrix composites of Al-4(pct)Cu-1.5(pct)Mg with TiB2 were examined. The influence of reinforcement volume fraction was also examined for pure aluminum with TiB2. Higher TiB2 volume fractions increased the tensile yield strength at both room and elevated temperatures, and reduced the elongation to fracture. Tensile tests also indicate that small particles provided a greater increase in strength for a given volume fraction than larger particles, whereas elongation to fracture appeared to be insensitive to reinforcement size. Interparticle spacing appears to be the factor that controls the strength of these alloys, with the exact nature of the dependence relying on the nature of dislocation slip in the matrix (planar vs. diffuse). The isothermal aging response of the precipitation strengthened Al-4(pct)Cu-1.5(pct)Mg alloys was not accelerated by the presence of TiB2. Cold work prior to artificial aging created additional geometrically necessary dislocations which serve as heterogeneous nucleation sites leading to accelerated aging, a finer precipitate size, and an increase in the strength of the alloy.

  6. Laser Engineered Net Shaping of Nickel-Based Superalloy Inconel 718 Powders onto AISI 4140 Alloy Steel Substrates: Interface Bond and Fracture Failure Mechanism

    PubMed Central

    Kim, Hoyeol; Cong, Weilong; Zhang, Hong-Chao; Liu, Zhichao

    2017-01-01

    As a prospective candidate material for surface coating and repair applications, nickel-based superalloy Inconel 718 (IN718) was deposited on American Iron and Steel Institute (AISI) 4140 alloy steel substrate by laser engineered net shaping (LENS) to investigate the compatibility between two dissimilar materials with a focus on interface bonding and fracture behavior of the hybrid specimens. The results show that the interface between the two dissimilar materials exhibits good metallurgical bonding. Through the tensile test, all the fractures occurred in the as-deposited IN718 section rather than the interface or the substrate, implying that the as-deposited interlayer bond strength is weaker than the interfacial bond strength. From the fractography using scanning electron microscopy (SEM) and energy disperse X-ray spectrometry (EDS), three major factors affecting the tensile fracture failure of the as-deposited part are (i) metallurgical defects such as incompletely melted powder particles, lack-of-fusion porosity, and micropores; (ii) elemental segregation and Laves phase, and (iii) oxide formation. The fracture failure mechanism is a combination of all these factors which are detrimental to the mechanical properties and structural integrity by causing premature fracture failure of the as-deposited IN718. PMID:28772702

  7. Laser Engineered Net Shaping of Nickel-Based Superalloy Inconel 718 Powders onto AISI 4140 Alloy Steel Substrates: Interface Bond and Fracture Failure Mechanism.

    PubMed

    Kim, Hoyeol; Cong, Weilong; Zhang, Hong-Chao; Liu, Zhichao

    2017-03-25

    As a prospective candidate material for surface coating and repair applications, nickel-based superalloy Inconel 718 (IN718) was deposited on American Iron and Steel Institute (AISI) 4140 alloy steel substrate by laser engineered net shaping (LENS) to investigate the compatibility between two dissimilar materials with a focus on interface bonding and fracture behavior of the hybrid specimens. The results show that the interface between the two dissimilar materials exhibits good metallurgical bonding. Through the tensile test, all the fractures occurred in the as-deposited IN718 section rather than the interface or the substrate, implying that the as-deposited interlayer bond strength is weaker than the interfacial bond strength. From the fractography using scanning electron microscopy (SEM) and energy disperse X-ray spectrometry (EDS), three major factors affecting the tensile fracture failure of the as-deposited part are (i) metallurgical defects such as incompletely melted powder particles, lack-of-fusion porosity, and micropores; (ii) elemental segregation and Laves phase, and (iii) oxide formation. The fracture failure mechanism is a combination of all these factors which are detrimental to the mechanical properties and structural integrity by causing premature fracture failure of the as-deposited IN718.

  8. Elevated temperature fracture of RS/PM aluminum alloy 8009

    NASA Technical Reports Server (NTRS)

    Porr, William C., Jr.; Yang, Leng; Gangloff, Richard P.

    1991-01-01

    The fracture behavior of advanced powder metallurgy Al-Fe-V-Si alloy 8009 (previously called FVS0812) is being characterized under monotonic loads, as a function of temperature. Particular attention is focused on contributions to the fracture mechanism from the fine grained dispersoid strengthened microstructure, dissolved solute from rapid solidification, and the moist air environment. Time-dependent crack growth is characterized in advanced aluminum alloys at elevated temperatures with the fracture mechanics approach, and cracking mechanisms are examined with a metallurgical approach. Specific tasks were to obtain standard load crack growth experimental information from a refined testing system; to correlate crack growth kinetics with the j-integral and time dependent C(sub t)(t); and to investigate the intermediate temperature embrittlement of 8009 alloy in order to understand crack growth mechanisms.

  9. The mechanism of fracture

    SciTech Connect

    Goel, V.S.

    1985-01-01

    This book presents the papers given at a conference on the fracture mechanics of metals. Topics considered at the conference included microcrack mechanics, pressurized thermal shock behavior of LWR pressure vessels, stress intensity factors, submerged arc welding, weldments in power plants, pipeline weld quality, natural gas tanks, cast iron for spent nuclear fuel shipping casks, pipe ruptures, physical radiation effects, pressure tubes, hydrogen embrittlement, critical flaw size curves, and the fracture mechanics of steels in turbines of power stations.

  10. Fracture mechanics expert system

    NASA Technical Reports Server (NTRS)

    Powers, E.; Elfer, N.; Casadaban, C.

    1992-01-01

    Attention is given to fracture mechanics, an analytical method used extensively in the National Space Transportation System to conservatively predict the remaining service life of an article when a flaw or a material defect is detected. These analyses are performed on hardware containing material defects that have been detected by various nondestructive inspection techniques. An expert system being developed to streamline the process so that hardware dispositions may be obtained in a timely and consistent manner is discussed. The expert system reduces the potential for errors due to the manual transcription between the various software programs involved in completing a fracture mechanics analysis. NEXPERT Object, the expert system development shell selected for this purpose, allows the various software programs used in fracture mechanics analyses to be accessed and manipulated from the same platform.

  11. Fracture mechanics expert system

    SciTech Connect

    Powers, E.; Elfer, N.; Casadaban, C. )

    1992-01-01

    Attention is given to fracture mechanics, an analytical method used extensively in the National Space Transportation System to conservatively predict the remaining service life of an article when a flaw or a material defect is detected. These analyses are performed on hardware containing material defects that have been detected by various nondestructive inspection techniques. An expert system being developed to streamline the process so that hardware dispositions may be obtained in a timely and consistent manner is discussed. The expert system reduces the potential for errors due to the manual transcription between the various software programs involved in completing a fracture mechanics analysis. NEXPERT Object, the expert system development shell selected for this purpose, allows the various software programs used in fracture mechanics analyses to be accessed and manipulated from the same platform. 7 refs.

  12. Fracture mechanics expert system

    NASA Technical Reports Server (NTRS)

    Powers, E.; Elfer, N.; Casadaban, C.

    1992-01-01

    Attention is given to fracture mechanics, an analytical method used extensively in the National Space Transportation System to conservatively predict the remaining service life of an article when a flaw or a material defect is detected. These analyses are performed on hardware containing material defects that have been detected by various nondestructive inspection techniques. An expert system being developed to streamline the process so that hardware dispositions may be obtained in a timely and consistent manner is discussed. The expert system reduces the potential for errors due to the manual transcription between the various software programs involved in completing a fracture mechanics analysis. NEXPERT Object, the expert system development shell selected for this purpose, allows the various software programs used in fracture mechanics analyses to be accessed and manipulated from the same platform.

  13. Effect of argon purity on mechanical properties, microstructure and fracture mode of commercially pure (cp) Ti and Ti-6Al-4V alloys for ceramometal dental prostheses.

    PubMed

    Bauer, José; Cella, Suelen; Pinto, Marcelo M; Filho, Leonardo E Rodrigues; Reis, Alessandra; Loguercio, Alessandro D

    2009-12-01

    Provision of an inert gas atmosphere with high-purity argon gas is recommended for preventing titanium castings from contamination although the effects of the level of argon purity on the mechanical properties and the clinical performance of Ti castings have not yet been investigated. The purpose of this study was to evaluate the effect of argon purity on the mechanical properties and microstructure of commercially pure (cp) Ti and Ti-6Al-4V alloys. The castings were made using either high-purity and/or industrial argon gas. The ultimate tensile strength (UTS), proportional limit (PL), elongation (EL) and microhardness (VHN) at different depths were evaluated. The microstructure of the alloys was also revealed and the fracture mode was analyzed by scanning electron microscopy. The data from the mechanical tests and hardness were subjected to a two-and three-way ANOVA and Tukey's test (alpha = 0.05). The mean values of mechanical properties were not affected by the argon gas purity. Higher UTS, PL and VHN, and lower EL were observed for Ti-6Al-4V. The microhardness was not influenced by the argon gas purity. The industrial argon gas can be used to cast cp Ti and Ti-6Al-4V.

  14. Effects of alloying elements on mechanical and fracture properties of base metals and simulated heat-affected zones of SA 508 steels

    NASA Astrophysics Data System (ADS)

    Kim, Sangho; Lee, Sunghak; Im, Young-Roc; Lee, Hu-Chul; Oh, Yong Jun; Hong, Jun Hwa

    2001-04-01

    This study was aimed at developing low-alloy steels for nuclear reactor pressure vessels by investigating the effects of alloying elements on mechanical and fracture properties of base metals and heat-affected zones (HAZs). Four steels whose compositions were variations of the composition specification for SA 508 steel (class 3) were fabricated by vacuum-induction melting and heat treatment, and their tensile properties and Charpy impact toughness were evaluated. Microstructural analyses indicated that coarse M3C-type carbides and fine M2C-type carbides were precipitated along lath boundaries and inside laths, respectively. In the steels having decreased carbon content and increased molybdenum content, the amount of fine M2C carbides was greatly increased, while that of coarse M3C carbides was decreased, thereby leading to the improvement of tensile properties and impact toughness. Their simulated HAZs also had sufficient impact toughness after postweld heat treatment (PWHT). These findings suggested that the low-alloy steels with high strength and toughness could be processed by decreasing carbon and manganese contents and by increasing molybdenum content.

  15. Fracture mechanics and parapsychology

    NASA Astrophysics Data System (ADS)

    Cherepanov, G. P.

    2010-08-01

    The problem of postcritical deformation of materials beyond the ultimate strength is considered a division of fracture mechanics. A simple example is used to show the relationship between this problem and parapsychology, which studies phenomena and processes where the causality principle fails. It is shown that the concept of postcritical deformation leads to problems with no solution

  16. Phase Field Fracture Mechanics.

    SciTech Connect

    Robertson, Brett Anthony

    2015-11-01

    For this assignment, a newer technique of fracture mechanics using a phase field approach, will be examined and compared with experimental data for a bend test and a tension test. The software being used is Sierra Solid Mechanics, an implicit/explicit finite element code developed at Sandia National Labs in Albuquerque, New Mexico. The bend test experimental data was also obtained at Sandia Labs while the tension test data was found in a report online from Purdue University.

  17. The effect of microstructure on the fracture toughness of titanium alloys

    NASA Technical Reports Server (NTRS)

    Vanstone, R. H.; Low, J. R., Jr.

    1973-01-01

    The high-strength titanium alloys are widely used in aircraft and aerospace structures due to their high strength to density ratios. In such applications, the fracture toughness rather than the strength is often the factor which requires larger size sections and lower useful payloads. The response of the strength and toughness of titanium alloys was analyzed generally without regard to the fracture mode or the effect of microstructure on the fracture mechanisms. Research on the fracture mechanisms in aluminum alloys and steels showed that the toughness may be improved by decreasing the sizes of inclusions and sub-micron precipitates. An investigation was conducted to study the fracture mechanisms in titanium alloys which may lead to suggestions for the improvement of the fracture toughness without a corresponding loss in strength.

  18. Shear fracture of a rapidly-solidified Al scrap alloy in tension

    SciTech Connect

    Li, D.M.; Bakker, A. . Dept. of Materials Science)

    1994-02-01

    Rapid solidification processing (RSP) has been among important alternatives for improving the performance of Al scrap alloys. While fracture by pure shearing process has long been recognized as a typical failure mode of single crystals, its occurrence in some polycrystalline metals has also been documented in literature. The observations were mostly concentrated on the conventionally processed Al alloys. Partial shear fracture has been found in some cases to relate to delamination/splitting processes as in Al-Li alloys and identified as a toughening mechanism for these alloys. As for Al alloys fabricated using RSP, the shear fracture has not been systematically studied. It is the aim of the present study to investigate the mechanisms of shear fracture in an aluminum scrap alloy with the melt spinning solidification.

  19. Fracture mechanics validity limits

    NASA Technical Reports Server (NTRS)

    Lambert, Dennis M.; Ernst, Hugo A.

    1994-01-01

    Fracture behavior is characteristics of a dramatic loss of strength compared to elastic deformation behavior. Fracture parameters have been developed and exhibit a range within which each is valid for predicting growth. Each is limited by the assumptions made in its development: all are defined within a specific context. For example, the stress intensity parameters, K, and the crack driving force, G, are derived using an assumption of linear elasticity. To use K or G, the zone of plasticity must be small as compared to the physical dimensions of the object being loaded. This insures an elastic response, and in this context, K and G will work well. Rice's J-integral has been used beyond the limits imposed on K and G. J requires an assumption of nonlinear elasticity, which is not characteristic of real material behavior, but is thought to be a reasonable approximation if unloading is kept to a minimum. As well, the constraint cannot change dramatically (typically, the crack extension is limited to ten-percent of the initial remaining ligament length). Rice, et al investigated the properties required of J-type parameters, J(sub x), and showed that the time rate, dJ(sub x)/dt, must not be a function of the crack extension rate, da/dt. Ernst devised the modified-J parameter, J(sub M), that meets this criterion. J(sub M) correlates fracture data to much higher crack growth than does J. Ultimately, a limit of the validity of J(sub M) is anticipated, and this has been estimated to be at a crack extension of about 40-percent of the initial remaining ligament length. None of the various parameters can be expected to describe fracture in an environment of gross plasticity, in which case the process is better described by deformation parameters, e.g., stress and strain. In the current study, various schemes to identify the onset of the plasticity-dominated behavior, i.e., the end of fracture mechanics validity, are presented. Each validity limit parameter is developed in

  20. The effect of hydrogen on the fracture toughness of alloy X-750 at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Symons, Douglas M.

    Ni-Cr-Fe alloys are widely used in pressurized water nuclear reactors (PWR). These alloys are susceptible to stress corrosion cracking (SCC) in PWR environments. There have been numerous mechanisms of crack advance proposed to describe the SCC of the nickel-base alloys in a PWR environment including slip/film rupture/oxidation and hydrogen embrittlement. It has also been suggested that there is not sufficient evidence to implicate hydrogen in the PWR SCC of nickel-base alloys. This program evaluated the effect of hydrogen on the embrittlement of a nickel-base alloy, alloy X-750, at elevated temperatures with a hydrogen concentration typical of what may be developed from the corrosion reaction. Fracture toughness values and the tearing resistance of alloy X-750 were evaluated in hydrogen gas and in air 260°C and 338°C. It was shown that at 260°C and 338°C alloy X-750 was severely embrittled in high pressure hydrogen gas. Further, the fracture morphology changed from predominantly transgranular ductile dimple fracture in air to predominantly intergranular fracture in hydrogen. The fracture morphology in hydrogen was similar to that found for PWR SCC of this material. This work supports a hydrogen-enhanced fracture mechanism contributing to the SCC of nickel-base alloys at elevated temperatures.

  1. Linear elastic fracture mechanics primer

    NASA Technical Reports Server (NTRS)

    Wilson, Christopher D.

    1992-01-01

    This primer is intended to remove the blackbox perception of fracture mechanics computer software by structural engineers. The fundamental concepts of linear elastic fracture mechanics are presented with emphasis on the practical application of fracture mechanics to real problems. Numerous rules of thumb are provided. Recommended texts for additional reading, and a discussion of the significance of fracture mechanics in structural design are given. Griffith's criterion for crack extension, Irwin's elastic stress field near the crack tip, and the influence of small-scale plasticity are discussed. Common stress intensities factor solutions and methods for determining them are included. Fracture toughness and subcritical crack growth are discussed. The application of fracture mechanics to damage tolerance and fracture control is discussed. Several example problems and a practice set of problems are given.

  2. Fracture testing and performance of beryllium copper alloy C 17510

    SciTech Connect

    Murray, H.A.; Zatz, I.J. . Plasma Physics Lab.); Ratka, J.O. )

    1992-01-01

    A series of test programs was undertaken on copper beryllium alloy C 17510 for several variations in material process and chemistry. These variations in C 17510 were primarily optimized for combinations of strength and conductivity. While originally intended for use as cyclically loaded high-field, high-strength conductors in fusion energy research, material testing of C 17510 has indicated that it is an attractive and economical alternative for a host of other structural, mechanical and electrical applications. ASTM tests performed on three variations of C 17510 alloys included both J-integral and plane strain fracture toughness testing (E813, E399) and fatigue crack growth rate tests (E647), as well as verifying tensile, hardness, Charpy, and other well defined mechanical properties. Fracture testing was performed at both room and liquid nitrogen temperatures, which bound the thermal environment anticipated for the fusion components being designed. Fatigue crack propagation stress ratios ranged from nominal zero to minus one at each temperature.

  3. Fracture testing and performance of beryllium copper alloy C 17510

    SciTech Connect

    Murray, H.A.; Zatz, I.J.; Ratka, J.O.

    1992-12-01

    A series of test programs was undertaken on copper beryllium alloy C 17510 for several variations in material process and chemistry. These variations in C 17510 were primarily optimized for combinations of strength and conductivity. While originally intended for use as cyclically loaded high-field, high-strength conductors in fusion energy research, material testing of C 17510 has indicated that it is an attractive and economical alternative for a host of other structural, mechanical and electrical applications. ASTM tests performed on three variations of C 17510 alloys included both J-integral and plane strain fracture toughness testing (E813, E399) and fatigue crack growth rate tests (E647), as well as verifying tensile, hardness, Charpy, and other well defined mechanical properties. Fracture testing was performed at both room and liquid nitrogen temperatures, which bound the thermal environment anticipated for the fusion components being designed. Fatigue crack propagation stress ratios ranged from nominal zero to minus one at each temperature.

  4. Fracture Mechanisms in Iron and Nickel Aluminides

    DTIC Science & Technology

    1988-08-15

    ITmc rE co"i 41 ) 0) Final Report I Contract N00014-84-K-0276 FRACTURE MECHANISMS IN IRON AND NICKEL ALUMINIDES covering the period 1/3/84 - 31/5/88...THIS PAGE ABSTRACT -he high cycle fatigue ( HCF ) resistance of several boron-doped Ni3AI alloys has been determined over a range of test temperatures...were transgranular in the Ni-rich alloys and intergranular or interdendritic in Ni-26%A).. HCF lives decreased sharply at temperatures above 500dC

  5. The effect of alloy composition on the mechanism of stress corrosion cracking of titanium alloys in aqueous environments

    NASA Technical Reports Server (NTRS)

    Boyd, J. D.; Williams, D. N.; Wood, R. A.; Jaffee, R. I.

    1972-01-01

    The effects of alloy composition on the aqueous stress corrosion of titanium alloys were studied with emphasis on determining the interrelations among composition, phase structure, and deformation and fracture properties of the alpha phase in alpha-beta alloys. Accomplishments summarized include the effects of alloy composition on susceptibility, and metallurgical mechanisms of stress-corrosion cracking.

  6. Aluminum Alloy 7068 Mechanical Characterization

    DTIC Science & Technology

    2009-08-01

    strength of 99 ksi (2). The commonly specified material properties for extruded 7068 aluminum are shown in table 1, along with 7050 and 7075 aluminum ...alloys for comparison (3). Table 1. Mechanical property comparison of high-strength aluminum alloys. Property Alloy 7068 7075 7050 Elastic... Aluminum Alloy 7068 Mechanical Characterization by Michael Minnicino, David Gray, and Paul Moy ARL-TR-4913 August 2009

  7. Fracture behavior of nickel-based alloys in water

    SciTech Connect

    Mills, W.J.; Brown, C.M.

    1999-08-01

    The cracking resistance of Alloy 600, Alloy 690 and their welds, EN82H and EN52, was characterized by conducting J{sub IC} tests in air and hydrogenated water. All test materials displayed excellent toughness in air and high temperature water, but Alloy 690 and the two welds were severely embrittled in low temperature water. In 54 C water with 150 cc H{sub 2}/kg H{sub 2}O, J{sub IC} values were typically 70% to 95% lower than their air counterparts. The toughness degradation was associated with a fracture mechanism transition from microvoid coalescence to intergranular fracture. Comparison of the cracking response in water with that for hydrogen-precharged specimens tested in air demonstrated that susceptibility to low temperature cracking is due to hydrogen embrittlement of grain boundaries. The effects of water temperature, hydrogen content and loading rate on low temperature crack propagation were studied. In addition, testing of specimens containing natural weld defects and as-machined notches was performed to determine if low temperature cracking can initiate at these features. Unlike the other materials, Alloy 600 is not susceptible to low temperature cracking as the toughness in 54 C water remained high and a microvoid coalescence mechanism was operative in both air and water.

  8. Small Crack Growth and Fatigue Life Predictions for High-Strength Aluminium Alloys. Part 1; Experimental and Fracture Mechanics Analysis

    NASA Technical Reports Server (NTRS)

    Wu, X. R.; Newman, J. C.; Zhao, W.; Swain, M. H.; Ding, C. F.; Phillips, E. P.

    1998-01-01

    The small crack effect was investigated in two high-strength aluminium alloys: 7075-T6 bare and LC9cs clad alloy. Both experimental and analytical investigations were conducted to study crack initiation and growth of small cracks. In the experimental program, fatigue tests, small crack and large crack tests A,ere conducted under constant amplitude and Mini-TWIST spectrum loading conditions. A pronounced small crack effect was observed in both materials, especially for the negative stress ratios. For all loading conditions, most of the fatigue life of the SENT specimens was shown to be crack propagation from initial material defects or from the cladding layer. In the analysis program, three-dimensional finite element and A weight function methods were used to determine stress intensity factors and to develop SIF equations for surface and corner cracks at the notch in the SENT specimens. A plastisity-induced crack-closure model was used to correlate small and large crack data, and to make fatigue life predictions, Predicted crack-growth rates and fatigue lives agreed well with experiments. A total fatigue life prediction method for the aluminum alloys was developed and demonstrated using the crack-closure model.

  9. Mechanics of Hydraulic Fractures

    NASA Astrophysics Data System (ADS)

    Detournay, Emmanuel

    2016-01-01

    Hydraulic fractures represent a particular class of tensile fractures that propagate in solid media under pre-existing compressive stresses as a result of internal pressurization by an injected viscous fluid. The main application of engineered hydraulic fractures is the stimulation of oil and gas wells to increase production. Several physical processes affect the propagation of these fractures, including the flow of viscous fluid, creation of solid surfaces, and leak-off of fracturing fluid. The interplay and the competition between these processes lead to multiple length scales and timescales in the system, which reveal the shifting influence of the far-field stress, viscous dissipation, fracture energy, and leak-off as the fracture propagates.

  10. EBSD and Nanoindentation-Correlated Study of Delamination Fracture in Al-Li Alloy 2090

    NASA Technical Reports Server (NTRS)

    Tayon, Wesley A.; Crooks, Roy E.; Domack, Marcia S.; Wagner, John A.; Elmustafa, A. A.

    2008-01-01

    Al-Li alloys offer attractive combinations of high strength and low density. However, a tendency for delamination fracture has limited their use. A better understanding of the delamination mechanisms may identify methods to control delaminations through processing modifications. A combination of new techniques has been used to evaluate delamination fracture in Al-Li alloys. Both high quality electron backscattered diffraction (EBSD) information and valid nanoindentation measurements were obtained from fractured test specimens. Correlations were drawn between nano-scale hardness variations and local texture along delaminating boundaries. Intriguing findings were observed for delamination fracture through the combined analysis of grain orientation, Taylor factor, and kernel average misorientation.

  11. Mechanical alloying of brittle materials

    NASA Astrophysics Data System (ADS)

    Davis, R. M.; McDermott, B.; Koch, C. C.

    1988-12-01

    Mechanical alloying by high energy ball milling has been observed in systems with nominally brittle components. The phases formed by mechanical alloying of brittle components include solid solutions (Si + Ge → SiGe solid solution), intermetallic compounds (Mn + Bi → MnBi), and amorphous alloys (NiZr2 + Ni11Zr9 → amorphous Ni50Zr50). A key feature of possible mechanisms for mechanical alloying of brittle components is the temperature of the powders during milling. Experiments and a computer model of the kinetics of mechanical alloying were carried out in order to esti-mate the temperature effect. Temperature rises in typical powder alloys during milling in a SPEX mill were estimated to be ≤350 K using the kinetic parameters determined from the computer model. The tempering response of fresh martensite in an Fe-1.2 wt pct C alloy during milling was consistent with the maximum results of the computer model, yielding temperatures in the pow-ders of ≤575 K i.e., ΔT ≤ 300 K). Thermal activation was required for mechanical alloying of Si and Ge powder. No alloying occurred when the milling vial was cooled by liquid nitrogen. The pos-sible mechanisms responsible for material transfer during mechanical alloying of brittle components are considered.

  12. Mechanisms of Plastic and Fracture Instabilities for Alloy Development of Fusion Materials. Final Project Report for period July 15, 1998 - July 14, 2003

    SciTech Connect

    Ghoniem, N. M.

    2003-07-14

    The main objective of this research was to develop new computational tools for the simulation and analysis of plasticity and fracture mechanisms of fusion materials, and to assist in planning and assessment of corresponding radiation experiments.

  13. Effect of Rolling on High-Cycle Fatigue and Fracture of an Al - Mg - Sc Alloy

    NASA Astrophysics Data System (ADS)

    Zhemchuzhnikova, D. A.; Petrov, A. P.; Eremeev, N. V.; Eremeev, V. V.; Kaibyshev, R. O.

    2016-07-01

    The tensile strength and fatigue properties of alloy 1575 of the Al - Mg - Sc system are studied after hot deformation (at 360°C) and subsequent cold rolling with different reduction ratios. The effect of the deformed structure on the properties and mechanisms of fracture of the alloy under cyclic tests is determined.

  14. Relationship between Fracture Toughness and Tensile Properties of A357 Cast Aluminum Alloy

    NASA Astrophysics Data System (ADS)

    Alexopoulos, N. D.; Tiryakioğlu, M.

    2009-03-01

    The fracture-related mechanical properties of the A357 cast aluminum alloy, namely, elongation to fracture, tensile strain energy density (tensile toughness), strain-hardening exponent, and plane strain fracture toughness were investigated. Correlations between these properties have been established for 25 different artificial aging heat-treatment conditions and for five minor variations in chemical composition. Empirical relationships between the strain energy density and both the tensile elongation to fracture and the strain-hardening exponent have been developed. Analysis of the fracture surfaces indicated that the fracture mechanism of the investigated specimens varies according to the artificial aging conditions. Moreover, empirical relationships between the fracture toughness and strain energy density and between fracture toughness and strain-hardening exponent have been developed; these can be used to estimate the plane strain fracture toughness of A357 as a function of yield strength and tensile toughness.

  15. A statistical model for cleavage fracture of low alloy steel

    SciTech Connect

    Chen, J.H.; Wang, G.Z.; Wang, H.J.

    1996-10-01

    A new statistical model for cleavage fracture of the low alloy steel is proposed. This model is based on a recently suggested physical model and takes account of the effect of the preceding loading processes. This statistical model satisfactorily describes the failure probability distribution of 42 precracked specimens fractured at various loads at a test temperature of {minus}100 C. The micromechanisms of cleavage fracture of low alloy steel are also further discussed.

  16. Relationship between fracture toughness, fracture path, and microstructure of 7050 aluminum alloy. Part 1: Quantitative characterization

    SciTech Connect

    Deshpande, N.U.; Gokhale, A.M.; Denzer, D.K.; Liu, J.

    1998-04-01

    The fracture toughness of Al-Zn-Mg-Cu-based 7XXX aluminum alloys decreases with an increase in the extent of recrystallization. In this contribution, the fracture path of plane-strain fracture-toughness specimens of 7050 alloy (a typical alloy of the 7XXX series) is quantitatively characterized as a function of degree of recrystallization, specimen orientation, and aging condition. The fracture path is quantitatively correlated to fracture toughness, and the bulk microstructural attributes estimated via sterological analysis. In the companion article, these quantitative data are used to develop and verify a multiple-fracture micromechanism-based model that relates the fracture toughness to a number of microstructural parameters of the partially recrystallized alloy plate.

  17. Electronics reliability fracture mechanics. Volume 2: Fracture mechanics

    NASA Astrophysics Data System (ADS)

    Kallis, J.; Duncan, L.; Buechler, D.; Backes, P.; Sandkulla, D.

    1992-05-01

    This is the second of two volumes. The other volume (WL-TR-92-3015) is 'Causes of Failures of Shop Replaceable Units and Hybrid Microcircuits.' The objective of the Electronics Reliability Fracture Mechanics (ERFM) program was to develop and demonstrate a life prediction technique for electronic assemblies, when subjected to environmental stresses of vibration and thermal cycling, based upon the mechanical properties of the materials and packaging configurations which make up an electronic system. The application of fracture mechanics to microscale phenomena in electronic assemblies was a pioneering research effort. The small scale made the experiments very difficult; for example, the 1-mil-diameter bond wires in microelectronic devices are 1/3 the diameter of a human hair. A number of issues had to be resolved to determine whether a fracture mechanics modelling approach is correct for the selected failures; specifically, the following two issues had to be resolved: What fraction of the lifetime is spent in crack initiation? Are macro fracture mechanics techniques, used in large structures such as bridges, applicable to the tiny structures in electronic equipment? The following structural failure mechanisms were selected for modelling: bondwire fracture from mechanical cycling; bondwire fracture from thermal (power) cycling; plated through hole (PTH) fracture from thermal cycling. The bondwire fracture test specimens were A1-1 percent Si wires, representative of wires used in the parts in the modules selected for detailed investigation in this program (see Vol. 1 of this report); 1-mil-diameter wires were tested in this program. The PTH test specimens were sections of 14-layer printed wiring boards of the type used.

  18. [Relationship between mechanical properties and amounts of casting porosities in tensile-test fracture surface of Au-Pd-Ag-Cu alloy (author's transl)].

    PubMed

    Ohno, H; Miyakawa, O; Watanabe, K; Siokawa, N

    1978-04-01

    One hundred and thirty-nine tensile-test specimens of Au-Pd-Ag-Cu alloy were cast in various casting conditions. The specimens were subjected age-hardening heat-treatment. The casting porosities and the nonmetallic inclusions in the surface of a tensile-test fracture of cast specimens were observed and analyzed by use of Electron Probe X-ray Microanalyzer (EPMA). The polosity ratio that is the area ratio of the porosities to the fracture surface was determined. Studies were quantitatively made on the effect of the porosity ratio on the tensile strength and the elongation. Furthermore, the effect of the casting conditions on the tensile strength was investigated. The main results were summarized as follows; The tensile strength decreased only slightly within about 15% of the porosity ratio and remarkably with an increase in its ratio in the range from about 15% to 50%. The elongation, however, decreased considerably in the presence of the porosities of only a few per cent. Aspects of the decrease curves on the tensile strength and the elongation were represented in the shape of an inverse S-type and hyperbolic curve with an increase in the porosity ratio, respectively. With an increase in the porosity ratio, the shapes of the tensile-test specimens at the fracture part and load-elongation curves in the tensile-tests were shown as a brittle fracture. However, the result observed by a scanning electron microscope revealed that the fracture surfaces without the porosities showed mostly "dimple pattern" suggesting a characteristic figure of a ductile fracture. The nonmetallic inclusions in the fracture surfaces were identified as SiO2 (quartz) which was derived from an ingredient of an investment by comparing the inclusion with the reference standards on the characteristic X-ray O Kalpha spectra by EPMA. The microstructures observed by a light microscope showed a coarse structure with the high temperature casting conditions. However, the results of a scanning

  19. Corrosion fatigue of iron-chromium-nickel alloys: Fracture mechanics, microstructure and chemistry. Progress report, January 1, 1992--December 31, 1992

    SciTech Connect

    Wei, R.P.

    1993-01-25

    Phase transformation and cracking during RT aging of charged, high-purity Fe18Cr12Ni alloy and commerical 304 ss were examined; results show that {epsilon}* (hcp) hydride formed on Fe18Cr12Ni upon charging, and it decomposed rapidly to form first {epsilon} and then {alpha}` martensite. Morphology of fracture surfaces of Fe18Cr12Ni produced by corrosion fatigue in NaCl solutions and in hydrogen was found to be identical. Effort was made to examine the approaches and methodologies used in service life predictions and reliability analyses.

  20. Geometrically Frustrated Fracture Mechanics

    NASA Astrophysics Data System (ADS)

    Mitchell, Noah; Koning, Vinzenz; Vitelli, Vincenzo; Irvine, William T. M.

    2015-03-01

    When a flat elastic sheet is forced to conform to a surface with Gaussian curvature, stresses arise in the sheet. The mismatch between initial and final metrics gives rise to new fracture behavior which cannot be achieved by boundary loading alone. Using experiments of PDMS sheets frustrated on 3D-printed surfaces and a linearized analytical model, we demonstrate the ability of curvature to govern the sheets' fracture phenomenology. In this talk, we first show that curvature can both stimulate and suppress fracture initiation, depending on the position and orientation of the initial slit. Secondly, we show that curvature can steer the path of a crack as it propagates through the material. Lastly, the curvature can arrest cracks which would otherwise continue to propagate.

  1. The effect of microstructure on the fracture toughness of titanium alloys

    NASA Technical Reports Server (NTRS)

    Vanstone, R. H.; Low, J. R., Jr.; Shannon, J. L., Jr.

    1974-01-01

    The microstructure of the alpha titanium alloy Ti-5Al-2.5Sn and the metastable beta titanium alloy Beta 3 was examined. The material was from normal and extra low interstitial grade plates which were either air-cooled or furnace-cooled from an annealing treatment. Beta 3 was studied in alpha-aged and omega-aged plates which were heat treated to similar strength levels. Tensile and plane strain fracture toughness tests were conducted at room temperature on the alpha-aged material. The microstructure and fracture mechanisms of alloys were studied using optical metallography, electron microscopy, microprobe analyses, and texture pole figures. Future experiments are described.

  2. Deformation and fracture of thin sheet aluminum-lithium alloys: The effect of cryogenic temperatures

    NASA Technical Reports Server (NTRS)

    Wagner, John A.; Gangloff, Richard P.

    1990-01-01

    The objective is to characterize the fracture behavior and to define the fracture mechanisms for new Al-Li-Cu alloys, with emphasis on the role of indium additions and cryogenic temperatures. Three alloys were investigated in rolled product form: 2090 baseline and 2090 + indium produced by Reynolds Metals, and commercial AA 2090-T81 produced by Alcoa. The experimental 2090 + In alloy exhibited increases in hardness and ultimate strength, but no change in tensile yield strength, compared to the baseline 2090 composition in the unstretched T6 condition. The reason for this behavior is not understood. Based on hardness and preliminary Kahn Tear fracture experiments, a nominally peak-aged condition was employed for detailed fracture studies. Crack initiation and growth fracture toughness were examined as a function of stress state and microstructure using J(delta a) methods applied to precracked compact tension specimens in the LT orientation. To date, J(delta a) experiments have been limited to 23 C. Alcoa 2090-T81 exhibited the highest toughness regardless of stress state. Fracture was accompanied by extensive delamination associated with high angle grain boundaries normal to the fatigue precrack surface and progressed microscopically by a transgranular shear mechanism. In contrast the two peak-aged Reynolds alloys had lower toughness and fracture was intersubgranular without substantial delamination. The influences of cryogenic temperature, microstructure, boundary precipitate structure, and deformation mode in governing the competing fracture mechanisms will be determined in future experiments. Results contribute to the development of predictive micromechanical models for fracture modes in Al-Li alloys, and to fracture resistant materials.

  3. Some recent theoretical and experimental developments in fracture mechanics

    NASA Technical Reports Server (NTRS)

    Liebowitz, H.; Eftis, J.; Hones, D. L.

    1978-01-01

    Recent theoretical and experimental developments in four distinct areas of fracture mechanics research are described. These are as follows: experimental comparisons of different nonlinear fracture toughness measures, including the nonlinear energy, R curve, COD and J integral methods; the singular elastic crack-tip stress and displacement equations and the validity of the proposition of their general adequacy as indicated, for example, by the biaxially loaded infinite sheet with a flat crack; the thermodynamic nature of surface energy induced by propagating cracks in relation to a general continuum thermodynamic description of brittle fracture; and analytical and experimental aspects of Mode II fracture, with experimental data for certain aluminum, steel and titanium alloys.

  4. Fracture testing and performance of beryllium copper alloy C17510

    SciTech Connect

    Murray, H.A.; Zatz, I.J.

    1994-05-01

    When a literature search and discussion with manufacturers revealed that there was virtually no existing data related to the fracture properties and behavior of copper beryllium alloy C17510, a series of test programs was undertaken to ascertain this information for several variations in material processing and chemistry. These variations in C17510 were primarily optimized for combinations of strength and conductivity. While originally intended for use as cyclically loaded high-field, high-strength conductors in fusion energy research, material testing of C17510 has indicated that it is an attractive and economical alternative for a host of other structural, mechanical and electrical applications. ASTM tests performed on three variations of C17510 alloys included both J-integral and plane strain fracture toughness testing and fatigue crack growth rate tests, as well as verifying tensile, hardness, Charpy, and other well defined mechanical properties. Fracture testing was performed at both room and liquid nitrogen temperatures, which bound the thermal environment anticipated for the fusion components being designed. Fatigue crack propagation stress ratios ranged from nominal zero to minus one at each temperature. In order to confirm the test results, duplicate and independent test programs were awarded to separate facilities with appropriate test experience, whenever possible. The primary goal of the test program, to determine and bound the fracture toughness and Paris constants for C17510,was accomplished. In addition, a wealth of information was accumulated pertaining to crack growth characteristics, effects of directionality and potential testing pitfalls. The paper discusses the test program and its findings in detail.

  5. Microstructure and Mechanical Behavior of High-Entropy Alloys

    NASA Astrophysics Data System (ADS)

    Licavoli, Joseph J.; Gao, Michael C.; Sears, John S.; Jablonski, Paul D.; Hawk, Jeffrey A.

    2015-10-01

    High-entropy alloys (HEAs) have generated interest in recent years due to their unique positioning within the alloy world. By incorporating a number of elements in high proportion, usually of equal atomic percent, they have high configurational entropy, and thus, they hold the promise of interesting and useful properties such as enhanced strength and alloy stability. The present study investigates the mechanical behavior, fracture characteristics, and microstructure of two single-phase FCC HEAs CoCrFeNi and CoCrFeNiMn with some detailed attention given to melting, homogenization, and thermo-mechanical processing. Ingots approaching 8 kg in mass were made by vacuum induction melting to avoid the extrinsic factors inherent to small-scale laboratory button samples. A computationally based homogenization heat treatment was given to both alloys in order to eliminate any solidification segregation. The alloys were then fabricated in the usual way (forging, followed by hot rolling) with typical thermo-mechanical processing parameters employed. Transmission electron microscopy was subsequently used to assess the single-phase nature of the alloys prior to mechanical testing. Tensile specimens (ASTM E8) were prepared with tensile mechanical properties obtained from room temperature through 800 °C. Material from the gage section of selected tensile specimens was extracted to document room and elevated temperature deformation within the HEAs. Fracture surfaces were also examined to note fracture failure modes. The tensile behavior and selected tensile properties were compared with results in the literature for similar alloys.

  6. Fracture resistance and fatigue crack growth characteristics of two Al-Cu-Mg-Zr alloys

    NASA Technical Reports Server (NTRS)

    Sarkar, Bhaskar; Lisagor, W. B.

    1992-01-01

    The dependence of strength, fracture resistance, and fatigue crack growth rate on the aging conditions of two alloy compositions based on Al-3.7Cu-1.85Mg-0.2Mn is investigated. Mechanical properties were evaluated in two heat treatment conditions and in two orientations (longitudinal and transverse). Compact tension specimens were used to determine fatigue crack growth characteristics and fracture resistance. The aging response was monitored on coupons using hardness measurements determined with a standard Rockwell hardness tester. Fracture resistance is found to increase with increasing yield strength during artificial aging of age-hardenable 2124-Zr alloys processed by powder metallurgy techniques. Fatigue crack growth rate increases with increasing strength. It is argued that these changes are related to deformation modes of the alloys; a homogeneous deformation mode tends to increase fracture resistance and to decrease the resistance to the fatigue crack propagation rate.

  7. Fracture resistance and fatigue crack growth characteristics of two Al-Cu-Mg-Zr alloys

    SciTech Connect

    Sarkar, B.; Lisagor, W.B. NASA, Langley Research Center, Hampton, VI )

    1992-01-01

    The dependence of strength, fracture resistance, and fatigue crack growth rate on the aging conditions of two alloy compositions based on Al-3.7Cu-1.85Mg-0.2Mn is investigated. Mechanical properties were evaluated in two heat treatment conditions and in two orientations (longitudinal and transverse). Compact tension specimens were used to determine fatigue crack growth characteristics and fracture resistance. The aging response was monitored on coupons using hardness measurements determined with a standard Rockwell hardness tester. Fracture resistance is found to increase with increasing yield strength during artificial aging of age-hardenable 2124-Zr alloys processed by powder metallurgy techniques. Fatigue crack growth rate increases with increasing strength. It is argued that these changes are related to deformation modes of the alloys; a homogeneous deformation mode tends to increase fracture resistance and to decrease the resistance to the fatigue crack propagation rate. 12 refs.

  8. Fracture resistance and fatigue crack growth characteristics of two Al-Cu-Mg-Zr alloys

    NASA Technical Reports Server (NTRS)

    Sarkar, Bhaskar; Lisagor, W. B.

    1992-01-01

    The dependence of strength, fracture resistance, and fatigue crack growth rate on the aging conditions of two alloy compositions based on Al-3.7Cu-1.85Mg-0.2Mn is investigated. Mechanical properties were evaluated in two heat treatment conditions and in two orientations (longitudinal and transverse). Compact tension specimens were used to determine fatigue crack growth characteristics and fracture resistance. The aging response was monitored on coupons using hardness measurements determined with a standard Rockwell hardness tester. Fracture resistance is found to increase with increasing yield strength during artificial aging of age-hardenable 2124-Zr alloys processed by powder metallurgy techniques. Fatigue crack growth rate increases with increasing strength. It is argued that these changes are related to deformation modes of the alloys; a homogeneous deformation mode tends to increase fracture resistance and to decrease the resistance to the fatigue crack propagation rate.

  9. Microstructure and Fracture Behavior of Tungsten Heavy Alloys

    SciTech Connect

    Sunwoo, A

    2003-06-01

    The 93% W-5.6% Ni-1.4% Fe and 93.1% W-4.7% Ni-2.2% Co alloys (WHA) provided by Army Research Laboratory (ARL), Aberdeen are characterized to determine the effects of matrix alloying and swaging on the microstructure and fracture behavior. The W particles are oblong with respect to the swaging direction. The microstructure of the W-Ni-Fe alloy reveals good cohesive bonding between W particles, but there is W-matrix interface separation and matrix alloy cracking. The microstructure of the W-Ni-Co alloy reveals regions of good cohesive bonding between W particles, but also regions where some wetting has not occurred by the liquid. No evidence was observed of matrix alloy cracking. The fracture characteristic of WHA is dominantly cleavage of W particles.

  10. Modelling the graphite fracture mechanisms

    SciTech Connect

    Jacquemoud, C.; Marie, S.; Nedelec, M.

    2012-07-01

    In order to define a design criterion for graphite components, it is important to identify the physical phenomena responsible for the graphite fracture, to include them in a more effective modelling. In a first step, a large panel of experiments have been realised in order to build up an important database; results of tensile tests, 3 and 4 point bending tests on smooth and notched specimens have been analysed and have demonstrated an important geometry related effects on the behavior up to fracture. Then, first simulations with an elastic or an elastoplastic bilinear constitutive law have not made it possible to simulate the experimental fracture stress variations with the specimen geometry, the fracture mechanisms of the graphite being at the microstructural scale. That is the reason why a specific F.E. model of the graphite structure has been developed in which every graphite grain has been meshed independently, the crack initiation along the basal plane of the particles as well as the crack propagation and coalescence have been modelled too. This specific model has been used to test two different approaches for fracture initiation: a critical stress criterion and two criteria of fracture mechanic type. They are all based on crystallographic considerations as a global critical stress criterion gave unsatisfactory results. The criteria of fracture mechanic type being extremely unstable and unable to represent the graphite global behaviour up to the final collapse, the critical stress criterion has been preferred to predict the results of the large range of available experiments, on both smooth and notched specimens. In so doing, the experimental observations have been correctly simulated: the geometry related effects on the experimental fracture stress dispersion, the specimen volume effects on the macroscopic fracture stress and the crack propagation at a constant stress intensity factor. In addition, the parameters of the criterion have been related to

  11. Corrosion fatigue of iron-chromium-nickel alloys: Fracture mechanics, microstructure and chemistry. Progress report, December 1, 1990--December 31, 1992

    SciTech Connect

    Wei, R.P.

    1992-01-29

    This progress report briefly summarizes the research performed under the referenced grant for the period from 1 December 1990 to 31 December 1991, and contains a cumulative listing of technical presentations and publications dating back to 1 June 1988. Under this grant, a multi-disciplinary research program is undertaken to address certain fundamental issues relating to corrosion fatigue crack growth in structurally important alloys in aqueous environments. The principal goal of the research is to develop and expand the scientific understanding of the processes that control corrosion fatigue crack growth, particularly for ferrous alloys in terms of the controlling mechanical and chemical/electrochemical processes and their interactions with the microstructure. Focus is placed upon the austenitic iron-chromium-nickel (FeCrNi) alloys because of the need to resolve certain mechanistic issues and because of extensive utilization of these alloys in the power generation and chemical industries. Emphasis is given to the growth of short (small) cracks at low growth rates because crack growth in this regime is expected to be more sensitive to changes in external chemical/electrochemical variables.

  12. Fracture mechanics of cellular glass

    NASA Technical Reports Server (NTRS)

    Zwissler, J. G.; Adams, M. A.

    1981-01-01

    The fracture mechanics of cellular glasses (for the structural substrate of mirrored glass for solr concentrator reflecting panels) are discussed. Commercial and developmental cellular glasses were tested and analyzed using standard testing techniques and models developed from linear fracture mechanics. Two models describing the fracture behavior of these materials were developed. Slow crack growth behavior in cellular glass was found to be more complex than that encountered in dense glasses or ceramics. The crack velocity was found to be strongly dependent upon water vapor transport to the tip of the moving crack. The existence of a static fatigue limit was not conclusively established, however, it is speculated that slow crack growth behavior in Region 1 may be slower, by orders of magnitude, than that found in dense glasses.

  13. An investigation of plastic fracture in aluminum alloys

    NASA Technical Reports Server (NTRS)

    Low, J. R., Jr.; Vanstone, R. H.; Merchant, R. H.

    1972-01-01

    The brittle fracture of many high strength alloys such as steel, titanium, and aluminum was shown to occur by a process called plastic fracture. According to this process microscopic voids form at impurity particles, then grow and coalesce to cause the final rupture. To further understand the role of impurities, four aluminum alloys were investigated: 2024-T851, 2124-T851, 7075-T7351 and 7079-T651. Fractography, quantitative metallography, and microprobe studies assessed the roles of various impurity particles relative to these alloys.

  14. Mechanically Alloyed High Entropy Composite

    NASA Astrophysics Data System (ADS)

    Popescu, G.; Adrian, M. M.; Csaki, I.; Popescu, C. A.; Mitrică, D.; Vasile, S.; Carcea, I.

    2016-08-01

    In the last years high entropy alloys have been investigated due to their high hardness, high temperature stability and unusual properties that make these alloys to have significant interest. In comparison with traditional alloys that are based on two or three major elements, this new generation alloys consists at least of 5 principal elements, with the concentration between 5 and 35 at.%. The present paper reports synthesis of high entropy alloys (HEA) and high entropy composites (HEC) synthesized by mechanical alloying (MA). The equiatomic AlCrFeNiMn matrix was used for creating the HEA matrix, starting from elemental powders and as reinforcing material for composites was used pure graphite. The mechanical alloying process was carried out at different duration, in a high energy planetary ball mill, under argon atmosphere. The elemental powders alloying began after '5 hours of milling and was complete after 40 hours. The mechanical alloyed matrix and composite was pressed and heat treated under argon protection. The elemental powers were investigated for physical - technological properties, and by X-ray diffraction and scanning electron microscopy. Phase pressing operation was realized with a hydraulic press and the applied pressure was progressive. The sintering process was carried out at 850°C for 2 h. The X-ray diffraction revealed that the MA process resulted in solid solutions formation and also revealed body- centred cubic (BCC) and face-centred cubic (FCC) structures with average grain size around 40 nm. In addition, nanoscale particles were highlighted by scanning electron microscopy, as well as the homogeneity of the chemical composition of the matrix and composite that was confirmed by EDX microanalysis. It was noted that HEA matrix and HEA composites were processed with a high degree of compaction and with a quite large capacity of mixed powder densification (around 70%).

  15. Delayed fracture of Ni-Ti superelastic alloys in acidic and neutral fluoride solutions.

    PubMed

    Yokoyama, Ken'ichi; Kaneko, Kazuyuki; Moriyama, Keiji; Asaoka, Kenzo; Sakai, Jun'ichi; Nagumo, Michihiko

    2004-04-01

    Hydrogen-related degradation of the mechanical properties of a Ni-Ti superelastic alloy has been examined by means of delayed fracture tests in acidic and neutral fluoride solutions and hydrogen thermal desorption analysis. Delayed fracture took place in both solutions; the time to fracture was shorter in the acidic solutions than in the neutral solutions with the same fluoride concentration. The time to fracture was reduced in both solutions when applied stress exceeded the critical stress for martensite transformation. In the acidic solutions, Ni-Ti superelastic alloy underwent general corrosion and absorbed substantial amounts of hydrogen. Fractographic features suggested that the delayed fracture in the acidic solutions was attributable to hydrogen embrittlement, whereas in the neutral solutions, a different fracture mode appeared associated with localized corrosion only in the vicinity of the fracture initiation area. In the neutral solutions, the amount of absorbed hydrogen was much less than that in the acidic solutions, and the delayed fracture was likely to be induced by active path corrosion accompanying hydrogen absorption. The results of the present study imply that the hydrogen-related degradation of performance of Ni-Ti superelastic alloys occurs in the presence of fluoride.

  16. Fracture mechanics and corrosion fatigue.

    NASA Technical Reports Server (NTRS)

    Mcevily, A. J.; Wei, R. P.

    1972-01-01

    Review of the current state-of-the-art in fracture mechanics, particularly in relation to the study of problems in environment-enhanced fatigue crack growth. The usefulness of this approach in developing understanding of the mechanisms for environmental embrittlement and its engineering utility are discussed. After a brief review of the evolution of the fracture mechanics approach and the study of environmental effects on the fatigue behavior of materials, a study is made of the response of materials to fatigue and corrosion fatigue, the modeling of the mechanisms of the fatigue process is considered, and the application of knowledge of fatigue crack growth to the prediction of the high cycle life of unnotched specimens is illustrated.

  17. 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.

  18. Machining characteristics and fracture morphologies in a copper-beryllium (Cu-2Be) alloy

    NASA Astrophysics Data System (ADS)

    Sudhakar, K. V.; Cisneros, J. C.; Cervantes, Hector; Pineda, Cosme Gomez

    2006-02-01

    The technology of materials removal is improved greatly by the introduction of advanced cutting tools like cubic boron nitride, ceramics, polycrystalline diamond and the more recent whisker-reinforced materials. In this paper, the influence of cutting temperature on machinability, mechanical properties, microstructure, and fracture morphology of Cu-2Be alloy using a polycrystalline diamond cutter is investigated. The information on machining, microstructure, and fracture morphology of Cu-2Be alloy are very useful to understand their fabrication characteristics and the basic mechanisms of its deformation and fracture. The machinability (in terms of surface finish) of Cu-2Be alloy is evaluated as a function of cutting temperature, resulting from wet and dry cutting. Machining is carried out on a Hardinge Cobra 42 CNC machine (Hardinge Inc., Elmira, NY), and the machining parameters used—cutting speed, depth of cut, and feed rate—are kept constant during both wet and dry cutting. The machined surface finish on Cu-2Be alloy is measured using a surface finish analyzer (Surftest 401, series 178) technique. The machined specimens are examined for their strength and hardness properties using a standard Universal Testing Machine and Rockwell hardness tester, respectively. Wet cutting (using coolants) produced a smooth surface finish when compared with dry cutting of the Cu-2Be alloy. The machined specimens are examined for their microstructural features using a Nikon optical microscope. The specimens are etched using a suitable etchant solution for revealing such microstructure constituents as grain size, phase proportions, and the possible overheated areas (especially in dry cutting). The fractured surfaces from the tensile and impact toughness tests are investigated for their fracture morphologies (dry and wet cutting) using a microprocessor-controlled scanning electron microscope (Jeol Model JSM 5910 LV). A detailed analysis is also made to understand and interpret

  19. Fracture mechanics parameters for small fatigue cracks

    NASA Technical Reports Server (NTRS)

    Newman, J. C., Jr.

    1992-01-01

    This paper presents a review of some common small-crack test specimens, the underlying causes of the small-crack effect, and the fracture-mechanics parameters that have been used to correlate or predict their growth behavior. This review concentrates on continuum mechanics concepts and on the nonlinear behavior of small cracks. The paper reviews some stress-intensity factor solutions for small-crack test specimens and develops some simple elastic-plastic J integral and cyclic J integral expressions that include the influence of crack-closure. These parameters were applied to small-crack growth data on two aluminum alloys, and a fatigue life prediction methodology is demonstrated. For these materials, the crack-closure transient from the plastic wake was found to be the major factor in causing the small-crack effect.

  20. A nonlinear high temperature fracture mechanics basis for strainrange partitioning

    NASA Technical Reports Server (NTRS)

    Kitamura, Takayuki; Halford, Gary R.

    1989-01-01

    A direct link was established between Strainrange Partitioning (SRP) and high temperature fracture mechanics by deriving the general SRP inelastic strain range versus cyclic life relationships from high temperature, nonlinear, fracture mechanics considerations. The derived SRP life relationships are in reasonable agreement based on the experience of the SRP behavior of many high temperature alloys. In addition, fracture mechanics has served as a basis for derivation of the Ductility-Normalized SRP life equations, as well as for examination of SRP relations that are applicable to thermal fatigue life prediction. Areas of additional links between nonlinear fracture mechanics and SRP were identified for future exploration. These include effects of multiaxiality as well as low strain, nominally elastic, long life creep fatigue interaction.

  1. In-Situ Fracture Observation and Fracture Toughness Analysis of Zr-Based Amorphous Alloys Containing Ductile Dendrites

    NASA Astrophysics Data System (ADS)

    Jeon, Changwoo; Kim, Choongnyun Paul; Lee, Sunghak

    2012-10-01

    Effects of dendrite size on fracture properties of Zr-based amorphous alloys containing ductile β dendrites were explained by directly observing microfracture processes using an in-situ loading stage installed inside a scanning electron microscope (SEM) chamber. Three amorphous alloy plates having different thicknesses were fabricated by varying cooling rates after vacuum arc melting. The effective size of β dendrites was varied from 14.7 to 30.1 μm in the alloy plates, while their volume fraction was almost constant. According to microfracture observation of the alloy containing fine β dendrites, shear bands initiated at the amorphous matrix were connected with the notch tip as they were deepened through dendrites, which led to abrupt crack propagation. In the alloy containing coarser β dendrites, shear bands were initiated at the amorphous matrix to form a crack near the notch tip region and were expanded over large matrix areas. The crack propagation was frequently blocked by β dendrites, and many shear bands are formed near or in front of the propagating crack, thereby resulting in stable crack growth, which could be confirmed by the fracture resistance curve ( R-curve) behavior. This increase in fracture resistance with increasing crack length could be explained by mechanisms of blocking of crack growth, multiple shear band formation, and crack blunting.

  2. Analysis of the flow property of aluminum alloy AA6016 based on the fracture morphology using the hydroforming technology

    NASA Astrophysics Data System (ADS)

    Lang, Lihui; Zhang, Quanda; Sun, Zhiying; Wang, Yao

    2017-09-01

    In this paper, the hydraulic bulging experiments were respectively carried out using AA6016-T4 aluminum alloy and AA6016-O aluminum alloy, and the deformation properties and fracture mechanism of aluminum alloy under the conditions of thermal and hydraulic were analyzed. Firstly, the aluminum alloy AA6016 was dealt with two kinds of heat treatment systems such as solid solution heat treatment adding natural ageing and full annealing, then the aluminum alloy such as AA6016-T4 and AA6016-O were obtained. In the same working environment, the two kinds of materials were used in the process of hydraulic bulging experiments, according to the observation and measurement of the deformation sizes of grid circles and material thicknesses near the fracture region, the flow properties and development trend of fracture defect of the materials were analyzed comprehensively from the perspective of qualitative analysis and quantitative analysis; Secondly, the two kinds of materials were sampled in different regions of the fracture area and the microstructure morphology of the fracture was observed by the scanning electron microscope (SEM). The influence laws of the heat treatment systems on the fracture defect of the aluminum alloy under the condition of the liquid pressure were studied preliminarily by observing the distribution characteristics of the fracture microstructure morphology of dimple. At the same time, the experimental research on the ordinary stamping forming process of AA6016-O was carried out and the influence law of different forming process on the fracture defect of the aluminum alloy material was studied by observing the distribution of the fracture microstructure morphology; Finally, the development process of the fracture defect of aluminum alloy sheet was described theoretically from the view of the stress state.

  3. Modelling of Local Necking and Fracture in Aluminium Alloys

    NASA Astrophysics Data System (ADS)

    Achani, D.; Eriksson, M.; Hopperstad, O. S.; Lademo, O.-G.

    2007-05-01

    Non-linear Finite Element simulations are extensively used in forming and crashworthiness studies of automotive components and structures in which fracture need to be controlled. For thin-walled ductile materials, the fracture-related phenomena that must be properly represented are thinning instability, ductile fracture and through-thickness shear instability. Proper representation of the fracture process relies on the accuracy of constitutive and fracture models and their parameters that need to be calibrated through well defined experiments. The present study focuses on local necking and fracture which is of high industrial importance, and uses a phenomenological criterion for modelling fracture in aluminium alloys. As an accurate description of plastic anisotropy is important, advanced phenomenological constitutive equations based on the yield criterion YLD2000/YLD2003 are used. Uniaxial tensile tests and disc compression tests are performed for identification of the constitutive model parameters. Ductile fracture is described by the Cockcroft-Latham fracture criterion and an in-plane shear tests is performed to identify the fracture parameter. The reason is that in a well designed in-plane shear test no thinning instability should occur and it thus gives more direct information about the phenomenon of ductile fracture. Numerical simulations have been performed using a user-defined material model implemented in the general-purpose non-linear FE code LS-DYNA. The applicability of the model is demonstrated by correlating the predicted and experimental response in the in-plane shear tests and additional plane strain tension tests.

  4. Corrosion fatigue of iron-chromium-nickel alloys: Fracture mechanics, microstructure and chemistry. Final technical report, June 1, 1988--November 30, 1993

    SciTech Connect

    Wei, R.P.

    1994-01-05

    A multi-disciplinary research program was undertaken to address certain fundamental issues relating to corrosion fatigue crack growth in structurally important alloys in aqueous solutions. Focus was placed on austenitic iron-chromium-nickel alloys.

  5. Investigation of Mechanical Properties and Fracture Simulation of Solution-Treated AA 5754

    NASA Astrophysics Data System (ADS)

    Kumar, Pankaj; Singh, Akhilendra

    2017-06-01

    In this work, mechanical properties and fracture toughness of as-received and solution-treated aluminum alloy 5754 (AA 5754) are experimentally evaluated. Solution heat treatment of the alloy is performed at 530 °C for 2 h, and then, quenching is done in water. Yield strength, ultimate tensile strength, impact toughness, hardness, fatigue life, brittle fracture toughness (K_{Ic} ) and ductile fracture toughness (J_{Ic} ) are evaluated for as-received and solution-treated alloy. Extended finite element method has been used for the simulation of tensile and fracture behavior of material. Heaviside function and asymptotic crack tip enrichment functions are used for modelling of the crack in the geometry. Ramberg-Osgood material model coupled with fracture energy is used to simulate the crack propagation. Fracture surfaces obtained from various mechanical tests are characterized by scanning electron microscopy.

  6. Fracture toughness of Alloy 600 and EN82H weld in air and water

    SciTech Connect

    Mills, W.J.; Brown, C.M.

    1999-06-01

    The fracture toughness of Alloy 600 and its weld, EN82H, was characterized in 54 C to 338 C air and hydrogenated water. Elastic-plastic J{sub IC} testing was performed due to the inherent high toughness of these materials. Alloy 600 exhibited excellent fracture toughness under all test conditions. While EN82H welds displayed excellent toughness in air and high temperature water, a dramatic toughness degradation occurred in water at temperatures below 149 C. Comparison of the cracking response in low temperature water with that for hydrogen-precharged specimens tested in air demonstrated that the loss in toughness is due to a hydrogen-induced intergranular cracking mechanism. At loading rates about approx. 1000 MPa {radical}m/h, the toughness in low temperature water is improved because there is insufficient time for hydrogen to embrittle grain boundaries. Electron fractographic examinations were performed to correlate macroscopic properties with key microstructural features and operative fracture mechanisms.

  7. The effect of hydrogen on the fracture toughness of alloy X-750

    NASA Astrophysics Data System (ADS)

    Symons, Douglas M.; Thompson, Anthony W.

    1997-03-01

    The effect of hydrogen on the fracture toughness behavior of a nickel-base superalloy, Alloy X-750, in the solutionized and aged condition was investigated. Notched bend specimens were tested to determine if the fracture process was stress or strain controlled. The fracture was observed to initiate at a distance between the location of maximum stress and maximum strain, suggesting that fracture required both a critical stress and strain. The effect of hydrogen was further investigated and modeled using fracture toughness testing and fractographic examination. The fracture toughness of the non-charged specimen was 147 MPasqrt m . Charging with hydrogen decreased the fracture toughness, K lc, to 52 MPasqrt m at a rapid loading rate and further decreased the toughness to 42 MPasqrt m for a slow loading rate. This is consistent with the rate-limiting step forthe embrittlement process being hydrogen diffusion. The fracture morphology for the hydrogen-charged specimens was intergranular ductile dimple, while the fracture morphology of noncharged specimens was a mixture of large transgranular dimples and fine intergranular dimples. The intergranular failure mechanism in Alloy X-750 was a microvoid initiation process at grain boundary carbides followed by void growth and coalescence. One role of hydrogen was to reduce the void initiation strain for the fine intergranular carbides. Hydrogen may have also increased the rate of void growth. The conditions ahead of a crack satisfy the critical stress criterion at a much lower applied stress intensity factor than for the critical fracture strain criterion. A model based on a critical fracture strain criterion is shown to predict the fracture behavior.

  8. (Fracture mechanics of inhomogeneous materials)

    SciTech Connect

    Bass, B.R.

    1990-10-01

    Discussions were held with Japanese researchers concerning (1) the Elastic-Plastic Fracture Mechanics in Inhomogeneous Materials and Structures (EPI) Program, and (2) ongoing large-scale pressurized- thermal-shock (PTS) experiments in Japan. In the EPI Program, major activities in the current fiscal year include round-robin analyses of measured data from inhomogeneous base metal/weld metal compact- tension (CT) specimens fabricated from welded plates of A533 grade B class 1 steel. The round-robin task involves participants from nine research organizations in Japan and is scheduled for completion by the end of 1990. Additional experiments will be performed on crack growth in inhomogeneous CT specimens and three-point bend (3PB) specimens 10 mm thick. The data will be compared with that generated previously from 19-mm-thick-specimens. A new type of inhomogeneous surface-cracked specimen will be tested this year, with ratio of crack depth to surface length (a/c) satisfying 0.2 {le} (a/c) {le} 0. 8 and using a 3PB type of applied load. Plans are under way to fabricate a new welded plate of A533 grade B class 1 steel (from a different heat than that currently being tested) in order to provide an expanded fracture-toughness data base. Other topics concerning fracture-prevention issues in reactor pressure vessels were discussed with each of the host organizations, including an overview of ongoing work in the Heavy-Section Steel Technology (HSST) Program.

  9. Cleavage fracture in high strength low alloy weld metal

    SciTech Connect

    Bose, W.W.; Bowen, P.; Strangwood, M.

    1996-12-31

    The present investigation gives an evaluation of the effect of microstructure on the cleavage fracture process of High Strength Low Alloy (HSLA) multipass weld metals. With additions of alloying elements, such as Ti, Ni, Mo and Cr, the microstructure of C-Mn weld metal changes from the classical composition, i.e., allotriomorphic ferrite with acicular ferrite and Widmanstaetten ferrite, to bainite and low carbon martensite. Although the physical metallurgy of some HSLA weld metals has been studied before, more work is necessary to correlate the effect of the microstructure on the fracture behavior of such weld metals. In this work detailed microstructural analysis was carried out using optical and electron (SEM and TEM) microscopy. Single edge notched (SEN) bend testpieces were used to assess the cleavage fracture stress, {sigma}{sub F}. Inclusions beneath the notch surface were identified as the crack initiators of unstable cleavage fracture. From the size of such inclusions and the value of tensile stress predicted at the initiation site, the effective surface energy for cleavage was calculated using a modified Griffth energy balance for a penny shape crack. The results suggest that even though inclusions initiate cleavage fracture, the local microstructure may play an important role in the fracture process of these weld metals. The implications of these observations for a quantitative theory of the cleavage fracture of ferritic steels is discussed.

  10. Numerical Analysis in Fracture Mechanics.

    DTIC Science & Technology

    1983-01-20

    in the following. A. 2-D Elastic-Plastic Crack Problem In 1975, ASTh Committee E24.01.09 undertook a task to compare numerical solutions to elastic...Penalty Function and Superposition Method", Fracture Mechanics, 12th Symposium, ed. by P. C. Paris, ASTh SIP 700, p. 439, 1980. [44) Barsoum, R...Landes, J. A. Begley and G. A. Clarke, ASTh SIP 668, p. 65, 1979. [46) Benzley, S., "Nonlinear Calculations With a Quadratic Quarter-point Crack Tip

  11. Review of cryogenic mechanical and thermal properties of Al-Li alloys and Alloy 2219

    SciTech Connect

    Simon, N.J.; Drexler, E.S.; Reed, R.P.

    1991-12-01

    The review of cryogenic mechanical and thermal properties presented here is part of a broader National Institute of Standards and Technology (NIST) program to assess new high-strength Al-Li alloys for use in the cryogenic tankage of the Advanced Launch System (ALS). The purpose of the NIST program has been to assess the relative suitability of high-strength Al-Li alloys and alloy 2219 for use in ALS cryogenic tanks. In the report, the cryogenic data on Al-Li alloys 8090, 2090, WL049, and Al alloy 2219 have been summarized. Properties covered in the survey are tensile strength, yield strength, elongation, fracture toughness, elastic constants, specific heat, thermal conductivity, and thermal expansion.

  12. Fracture mechanics of cellular glass

    SciTech Connect

    Zwissler, J.G.; Adams, M.A.

    1981-02-01

    Cellular glasses are prime candidate materials for the structural substrate of mirrored glass for solar concentrator reflecting panels. These materials are brittle, however, and susceptible to mechanical failure from slow crack growth caused by a stress corrosion mechanism. The results are detailed of one part of a program established to develop improved cellular glasses and to characterize the behavior of these and commercially available materials. Commercial and developmental cellular glasses were tested and analyzed using standard testing techniques and models developed from linear fracture mechanics. Two models describing the fracture behavior of these materials are developed. Slow crack growth behavior in cellular glass was found to be more complex than that encountered in dense glasses or ceramics. The crack velocity was found to be strongly dependent upon water vapor transport to the tip of the moving crack. The existence of a static fatigue limit was not conclusively established, however, it is speculated that slow crack growth behavior in Region I may be slower, by orders of magnitude, than that found in dense glasses.

  13. Mechanical Coal-Face Fracturer

    NASA Technical Reports Server (NTRS)

    Collins, E. R., Jr.

    1984-01-01

    Radial points on proposed drill bit take advantage of natural fracture planes of coal. Radial fracture points retracted during drilling and impacted by piston to fracture coal once drilling halts. Group of bits attached to array of pneumatic drivers to fracture large areas of coal face.

  14. Resistance to fracture, fatigue, and stress-corrosion of Al-Cu-Li-Zr alloys. Final report, 1 July 1981-28 February 1985

    SciTech Connect

    Vasudevan, A.K.; Malcolm, R.C.; Fricke, W.G.; Rioja, R.J.

    1985-02-19

    This investigation was undertaken to characterize the role of composition/microstructure on the mechanical behavior of Al-Cu-Li-Zr alloys. This characterization is intended to serve as a baseline data for alloy development work directed at improving the mechanical properties of Al-Li alloys. The report summarizes the results on fracture, fatigue and stress corrosion behavior of Al-Cu-Li-Zr alloys.

  15. Microstructure-fracture toughness relationship of vanadium alloy/stainless steel brazed joints

    NASA Astrophysics Data System (ADS)

    Gan, Y. X.; Aglan, H. A.; Steward, R. V.; Chin, B. A.; Grossbeck, M. L.

    2001-11-01

    In this work, brazing V-5Ti-5Cr to 304 stainless steel (SS 304) using Au-18Ni alloy as filler material was conducted under high vacuum condition. Sessile drop technique was used to determine the wettability of filler alloy to the stainless steel and the vanadium alloy substrates upon which the relationship between the contact angles with time was obtained. Tensile tests were performed on unnotched and notched specimens to demonstrate the overloading behavior and the fracture toughness of the base materials and the brazed joint. Fracture surface was examined for both the V-5Ti-5Cr and the joint to identify the failure mechanisms under static loadings. It was found that the Au-18Ni filler material exhibited good wettability with the SS 304 and V-5Ti-5Cr. The ultimate tensile strength of the brazed joint reached 245 MPa. The strain to failure was about 1.3%. Young's modulus was about 351 GPa. The fracture toughness ( KIc) of this joint was 19.1 MPa √ m. The fracture surface of the joint showed well brazed area with good wettability and proper amount of residual filler material which came from the solidification of residual liquid filler alloy of Au-Ni. The failure of the joint occurred along the interface of the vanadium/filler under static load.

  16. Fracture characteristics of structural aerospace alloys containing deep surface flaws. [aluminum-titanium alloys

    NASA Technical Reports Server (NTRS)

    Masters, J. N.; Bixler, W. D.; Finger, R. W.

    1973-01-01

    Conditions controlling the growth and fracture of deep surface flaws in aerospace alloys were investigated. Static fracture tests were performed on 7075-T651 and 2219-T87 aluminum, and 6Ai-4V STA titanium . Cyclic flaw growth tests were performed on the two latter alloys, and sustain load tests were performed on the titanium alloy. Both the cyclic and the sustain load tests were performed with and without a prior proof overload cycle to investigate possible growth retardation effects. Variables included in all test series were thickness, flaw depth-to-thickness ratio, and flaw shape. Results were analyzed and compared with previously developed data to determine the limits of applicability of available modified linear elastic fracture solutions.

  17. Compendium of fracture mechanics problems

    NASA Technical Reports Server (NTRS)

    Stallworth, R.; Wilson, C.; Meyers, C.

    1990-01-01

    Fracture mechanics analysis results are presented from the following structures/components analyzed at Marshall Space Flight Center (MSFC) between 1982 and 1989: space shuttle main engine (SSME), Hubble Space Telescope (HST), external tank attach ring, B-1 stand LOX inner tank, and solid rocket booster (SRB). Results from the SSME high pressure fuel turbopump (HPFTP) second stage blade parametric analysis determine a critical flaw size for a wide variety of stress intensity values. The engine 0212 failure analysis was a time dependent fracture life assessment. Results indicated that the disk ruptured due to an overspeed condition. Results also indicated that very small flaws in the curvic coupling area could propagate and lead to failure under normal operating conditions. It was strongly recommended that a nondestructive evaluation inspection schedule be implemented. The main ring of the HST, scheduled to launch in 1990, was analyzed by safe-life and fail-safe analyses. First safe-life inspection criteria curves for the ring inner and outer skins and the fore and aft channels were derived. Afterwards the skins and channels were determined to be fail-safe by analysis. A conservative safe-life analysis was done on the 270 redesign external tank attach ring. Results from the analysis were used to determine the nondestructive evaluation technique required.

  18. Temperature effects on the deformation and fracture of Al-Li-Cu-In alloys

    NASA Technical Reports Server (NTRS)

    Wagner, John A.; Gangloff, Richard P.

    1991-01-01

    The crack initiation and growth fracture resistance of Al-Cu-Li and Al-Cu-Li-In alloys were characterized and optimized for cryogenic tank applications. Presently, the effects of stress state and temperature is being determined on the fracture toughness and fracture mechanisms of commercially available Vintage 3 2090-T81 and experimental 2090+In-T6. Precracked J-integral specimens of both alloys were tested at ambient and cryogenic temperatures in the plane stress and plane strain conditions. Considering ambient temperature, results showed that 2090-T81 exhibited the highest toughness in both plane strain and plane stress conditions. For the plane strain condition, reasonable crack initiation and growth toughness of 1090-T81 are associated with a significant amount of delamination and transgranular fracture. Plane stress toughnesses were higher and fracture was characterized by shear cracking with minimal delaminations. In comparisons, the fracture behavior of 2090+In-T6 is significantly degraded by subgrain boundary precipitation. Toughness is low and characterized by intersubgranular fracture with no delamination in the plane stress or plane strain conditions. Intersubgranular cracking is a low energy event which presumably occurs prior to the onset of slip band cracking. Copious grain boundary precipitation is atypical of commercially available 2090. At cryogenic temperatures, both alloys exhibit increased yield strength, toughness, and amount of delamination and shear cracking. The change in fracture mode of 2090+In-T6 from intersubgranular cracking at ambient temperature to a combination of intersubgranular cracking, shear cracking, and delamination at cryogenic temperature is the subject of further investigation.

  19. In-Situ Fracture Observation and Fracture Toughness Analysis of Ni-Mn-Ga-Fe Ferromagnetic Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Euh, Kwangjun; Lee, Jung-Moo; Nam, Duk-Hyun; Lee, Sunghak

    2011-12-01

    The fracture property improvement of Ni-Mn-Ga-Fe ferromagnetic shape memory alloys containing ductile γ particles was explained by direct observation of microfracture processes using an in-situ loading stage installed inside a scanning electron microscope (SEM) chamber. The Ni-Mn-Ga-Fe alloys contained a considerable amount of γ particles in β grains after the homogenization treatment at 1073 K to 1373 K (800 °C to 1100 °C). With increasing homogenization temperature, γ particles were coarsened and distributed homogeneously along β grain boundaries as well as inside β grains. According to the in-situ microfracture observation, γ particles effectively acted as blocking sites of crack propagation and provided the stable crack growth, which could be confirmed by the R-curve analysis. The increase in fracture resistance with increasing crack length improved overall fracture properties of the Ni-Mn-Ga-Fe alloys. This improvement could be explained by mechanisms of blocking of crack propagation and crack blunting and bridging.

  20. Entablature: fracture types and mechanisms

    NASA Astrophysics Data System (ADS)

    Forbes, A. E. S.; Blake, S.; Tuffen, H.

    2014-05-01

    Entablature is the term used to describe zones or tiers of irregular jointing in basaltic lava flows. It is thought to form when water from rivers dammed by the lava inundates the lava flow surface, and during lava-meltwater interaction in subglacial settings. A number of different fracture types are described in entablature outcrops from the Búrfell lava and older lava flows in Þjórsárdalur, southwest Iceland. These are: striae-bearing, column-bounding fractures and pseudopillow fracture systems that themselves consist of two different fracture types—master fractures with dimpled surface textures and subsidiary fractures with curved striae. The interaction of pseudopillow fracture systems and columnar jointing in the entablature produces the chevron fracture patterns that are commonly observed in entablature. Cube-jointing is a more densely fractured version of entablature, which likely forms when more coolant enters the hot lava. The entablature tiers display closely spaced striae and dendritic crystal shapes which indicate rapid cooling. Master fracture surfaces show a thin band with an evolved composition at the fracture surface; mineral textures in this band also show evidence of quenching of this material. This is interpreted as gas-driven filter pressing of late-stage residual melt that is drawn into an area of low pressure immediately preceding or during master fracture formation by ductile extensional fracture of hot, partially crystallised lava. This melt is then quenched by an influx of water and/or steam when the master fracture fully opens. Our findings suggest that master fractures are the main conduit for coolant entering the lava flow during entablature formation.

  1. Thermal Mechanical Processing Effects on Microstructure Evolution and Mechanical Properties of the Sintered Ti-22Al-25Nb Alloy.

    PubMed

    Wang, Yuanxin; Lu, Zhen; Zhang, Kaifeng; Zhang, Dalin

    2016-03-11

    This work illustrates the effect of thermal mechanical processing parameters on the microstructure and mechanical properties of the Ti-22Al-25Nb alloy prepared by reactive sintering with element powders, consisting of O, B2 and Ti₃Al phases. Tensile and plane strain fracture toughness tests were carried out at room temperature to understand the mechanical behavior of the alloys and its correlation with the microstructural features characterized by scanning and transmission electron microscopy. The results show that the increased tensile strength (from 340 to 500 MPa) and elongation (from 3.6% to 4.2%) is due to the presence of lamellar O/B2 colony and needle-like O phase in B2 matrix in the as-processed Ti-22Al-25Nb alloys, as compared to the coarse lath O adjacent to B2 in the sintered alloys. Changes in morphologies of O phase improve the fracture toughness (KIC) of the sintered alloys from 7 to 15 MPa·m(-1/2). Additionally, the fracture mechanism shifts from cleavage fracture in the as-sintered alloys to quasi-cleavage fracture in the as-processed alloys.

  2. Thermal Mechanical Processing Effects on Microstructure Evolution and Mechanical Properties of the Sintered Ti-22Al-25Nb Alloy

    PubMed Central

    Wang, Yuanxin; Lu, Zhen; Zhang, Kaifeng; Zhang, Dalin

    2016-01-01

    This work illustrates the effect of thermal mechanical processing parameters on the microstructure and mechanical properties of the Ti-22Al-25Nb alloy prepared by reactive sintering with element powders, consisting of O, B2 and Ti3Al phases. Tensile and plane strain fracture toughness tests were carried out at room temperature to understand the mechanical behavior of the alloys and its correlation with the microstructural features characterized by scanning and transmission electron microscopy. The results show that the increased tensile strength (from 340 to 500 MPa) and elongation (from 3.6% to 4.2%) is due to the presence of lamellar O/B2 colony and needle-like O phase in B2 matrix in the as-processed Ti-22Al-25Nb alloys, as compared to the coarse lath O adjacent to B2 in the sintered alloys. Changes in morphologies of O phase improve the fracture toughness (KIC) of the sintered alloys from 7 to 15 MPa·m−1/2. Additionally, the fracture mechanism shifts from cleavage fracture in the as-sintered alloys to quasi-cleavage fracture in the as-processed alloys. PMID:28773315

  3. Special Features of Fracture of a Solid-State Titanium Alloy - Nickel - Stainless Steel Joint

    NASA Astrophysics Data System (ADS)

    Khazgaliev, R. G.; Mukhametrakhimov, M. Kh.; Imaev, M. F.; Shayakhmetov, R. U.; Mulyukov, R. R.

    2015-10-01

    Microstructure, nanohardness, and special features of fracture of three-phase titanium alloy and stainless steel joint through a nanostructural nickel foil are investigated. Uniformly distributed microcracks are observed in Ti2Ni and TiN3 layers joined at temperatures above T = 700°C, whereas no microcracks are observed in the TiNi layer. This suggests that the reason for microcracking is an anomalously large change in the linear expansion coefficient of the TiNi layer during austenitic-martensitic transformation. Specimens subjected to mechanical tests at T = 20°C are fractured along different layers of the material, namely, in the central part of the specimen they are fractured along the Ti2Тi/TiNi interface, whereas at the edge they are fractured along the TiNi/TiNi3 interface.

  4. Fracture healing: mechanisms and interventions

    PubMed Central

    Einhorn, Thomas A.; Gerstenfeld, Louis C.

    2015-01-01

    Fractures are the most common large-organ, traumatic injuries to humans. The repair of bone fractures is a postnatal regenerative process that recapitulates many of the ontological events of embryonic skeletal development. Although fracture repair usually restores the damaged skeletal organ to its pre-injury cellular composition, structure and biomechanical function, about 10% of fractures will not heal normally. This article reviews the developmental progression of fracture healing at the tissue, cellular and molecular levels. Innate and adaptive immune processes are discussed as a component of the injury response, as are environmental factors, such as the extent of injury to the bone and surrounding tissue, fixation and the contribution of vascular tissues. We also present strategies for fracture treatment that have been tested in animal models and in clinical trials or case series. The biophysical and biological basis of the molecular actions of various therapeutic approaches, including recombinant human bone morphogenetic proteins and parathyroid hormone therapy, are also discussed. PMID:25266456

  5. Elastic plastic fracture mechanics methodology for surface cracks

    NASA Technical Reports Server (NTRS)

    Ernst, Hugo A.; Lambert, D. M.

    1994-01-01

    The Elastic Plastic Fracture Mechanics Methodology has evolved significantly in the last several years. Nevertheless, some of these concepts need to be extended further before the whole methodology can be safely applied to structural parts. Specifically, there is a need to include the effect of constraint in the characterization of material resistance to crack growth and also to extend these methods to the case of 3D defects. As a consequence, this project was started as a 36 month research program with the general objective of developing an elastic plastic fracture mechanics methodology to assess the structural reliability of pressure vessels and other parts of interest to NASA which may contain flaws. The project is divided into three tasks that deal with (1) constraint and thickness effects, (2) three-dimensional cracks, and (3) the Leak-Before-Burst (LBB) criterion. This report period (March 1994 to August 1994) is a continuation of attempts to characterize three dimensional aspects of fracture present in 'two dimensional' or planar configuration specimens (Chapter Two), especially, the determination of, and use of, crack face separation data. Also, included, are a variety of fracture resistance testing results (J(m)R-curve format) and a discussion regarding two materials of NASA interest (6061-T651 Aluminum alloy and 1N718-STA1 nickel-base super alloy) involving a bases for like constraint in terms of ligament dimensions, and their comparison to the resulting J(m)R-curves (Chapter Two).

  6. Relation between the fracture laws and the fatigue life of a surface-hardened pseudo-α titanium alloy

    NASA Astrophysics Data System (ADS)

    Bagmutov, V. P.; Vodop'yanov, V. I.; Zakharov, I. N.; Denisevich, D. S.

    2016-07-01

    The laws of fracture and fatigue life of the PT-3V pseudo-α titanium alloy subjected to surface hardening using electromechanical, ultrasonic, and combined treatment are studied. Fracture mechanisms and the structures of crack nucleation and growth zones are described using the results of metallographic and fractographic analysis of samples after fatigue tests. It is shown that the existence of a thin hardened layer on the sample surface changes the crack nucleation time and the state of fracture surface in the crack nucleation zone. This surface is characterized by signs of brittle or ductile fracture, which substantially affects the fatigue life of the sample.

  7. A fracture-resistant high-entropy alloy for cryogenic applications.

    PubMed

    Gludovatz, Bernd; Hohenwarter, Anton; Catoor, Dhiraj; Chang, Edwin H; George, Easo P; Ritchie, Robert O

    2014-09-05

    High-entropy alloys are equiatomic, multi-element systems that can crystallize as a single phase, despite containing multiple elements with different crystal structures. A rationale for this is that the configurational entropy contribution to the total free energy in alloys with five or more major elements may stabilize the solid-solution state relative to multiphase microstructures. We examined a five-element high-entropy alloy, CrMnFeCoNi, which forms a single-phase face-centered cubic solid solution, and found it to have exceptional damage tolerance with tensile strengths above 1 GPa and fracture toughness values exceeding 200 MPa·m(1/2). Furthermore, its mechanical properties actually improve at cryogenic temperatures; we attribute this to a transition from planar-slip dislocation activity at room temperature to deformation by mechanical nanotwinning with decreasing temperature, which results in continuous steady strain hardening.

  8. Fracture toughness of an Al-Li-Cu-In alloy

    NASA Technical Reports Server (NTRS)

    Wagner, John A.; Gangloff, Richard P.

    1992-01-01

    The crack initiation and growth fracture toughness of select AL-Li-Cu alloy variants are characterized and elucidated. Conventionally processed plates form large DC cast ingots are investigated to eliminate the variation in microstructure associated with laboratory scale and SPF-processed material. Fracture resistance is characterized using the J-integral method to establish crack initiation and growth behavior at 25 and -185 C. It is shown that state-of-the-art 2090-T81 has superior toughness compared to 2090 + In-T6 at both test temperatures, with the low toughness of 2090 + In-T6 associated with intersubgranular fracture attributed to a high density of subboundary precipitates.

  9. Fracture toughness of an Al-Li-Cu-In alloy

    NASA Technical Reports Server (NTRS)

    Wagner, John A.; Gangloff, Richard P.

    1992-01-01

    The crack initiation and growth fracture toughness of select AL-Li-Cu alloy variants are characterized and elucidated. Conventionally processed plates form large DC cast ingots are investigated to eliminate the variation in microstructure associated with laboratory scale and SPF-processed material. Fracture resistance is characterized using the J-integral method to establish crack initiation and growth behavior at 25 and -185 C. It is shown that state-of-the-art 2090-T81 has superior toughness compared to 2090 + In-T6 at both test temperatures, with the low toughness of 2090 + In-T6 associated with intersubgranular fracture attributed to a high density of subboundary precipitates.

  10. Finite element methods in fracture mechanics

    NASA Technical Reports Server (NTRS)

    Liebowitz, H.; Moyer, E. T., Jr.

    1989-01-01

    Finite-element methodology specific to the analysis of fracture mechanics problems is reviewed. Primary emphasis is on the important algorithmic developments which have enhanced the numerical modeling of fracture processes. Methodologies to address elastostatic problems in two and three dimensions, elastodynamic problems, elastoplastic problems, special considerations for three-dimensional nonlinear problems, and the modeling of stable crack growth are reviewed. In addition, the future needs of the fracture community are discussed and open questions are identified.

  11. Equations For Selected Fracture-Mechanics Parameters

    NASA Technical Reports Server (NTRS)

    Bubsey, Raymond T.; Orange, Thomas W.; Pierce, William S.; Shannon, John L., Jr.

    1994-01-01

    Equations describing crack-mouth-opening displacements, stress-intensity factors, and related fracture-mechanics parameters of chevron-notched short bar and rod specimens presented in report. Equations in forms suitable for determining fracture toughnesses from maximum loads, for determining crack-extension-resistance curves, and for setting sensitivities of testing instruments. Useful in facilitating testing and interpretation of data from tests of brittle metals, ceramics, and glasses, formed into chevron-notched specimens for fracture testing according to concepts.

  12. Fracture mechanisms and fracture control in composite structures

    NASA Astrophysics Data System (ADS)

    Kim, Wone-Chul

    Four basic failure modes--delamination, delamination buckling of composite sandwich panels, first-ply failure in cross-ply laminates, and compression failure--are analyzed using linear elastic fracture mechanics (LEFM) and the J-integral method. Structural failures, including those at the micromechanical level, are investigated with the aid of the models developed, and the critical strains for crack propagation for each mode are obtained. In the structural fracture analyses area, the fracture control schemes for delamination in a composite rib stiffener and delamination buckling in composite sandwich panels subjected to in-plane compression are determined. The critical fracture strains were predicted with the aid of LEFM for delamination and the J-integral method for delamination buckling. The use of toughened matrix systems has been recommended for improved damage tolerant design for delamination crack propagation. An experimental study was conducted to determine the onset of delamination buckling in composite sandwich panel containing flaws. The critical fracture loads computed using the proposed theoretical model and a numerical computational scheme closely followed the experimental measurements made on sandwich panel specimens of graphite/epoxy faceskins and aluminum honeycomb core with varying faceskin thicknesses and core sizes. Micromechanical models of fracture in composites are explored to predict transverse cracking of cross-ply laminates and compression fracture of unidirectional composites. A modified shear lag model which takes into account the important role of interlaminar shear zones between the 0 degree and 90 degree piles in cross-ply laminate is proposed and criteria for transverse cracking have been developed. For compressive failure of unidirectional composites, pre-existing defects play an important role. Using anisotropic elasticity, the stress state around a defect under a remotely applied compressive load is obtained. The experimentally

  13. Microstructures and Mechanical Properties of Binary Al-Zn Alloys Fabricated by Casting and Heat Treatment

    NASA Astrophysics Data System (ADS)

    Zhou, W. B.; Teng, G. B.; Liu, C. Y.; Qi, H. Q.; Huang, H. F.; Chen, Y.; Jiang, H. J.

    2017-08-01

    Binary Al-Zn alloys with different Zn contents were fabricated by casting and heat treatment. Analysis of mechanical properties showed that the hardness and tensile strength of Al-Zn alloys increased with increased Zn content, with the post-heat treatment hardness and ultimate tensile strength of Al-49Zn alloy reaching as high as 152 HV and 330 MPa, respectively. Meanwhile, the plasticity and toughness of Al-Zn alloys decreased with increased Zn content. Solid-solution strengthening was the main strengthening mechanism for Al-Zn alloys, and Orowan strengthening was also observed in Al-49Zn alloy. The fracture mode of Al-20Zn and Al-35Zn alloys was ductile, whereas Al-20Zn alloy showed good impact toughness. This work provided a basis for further improving the cast component design of the Al-Zn-X system.

  14. Fracture mechanism of a thermal barrier coating

    NASA Astrophysics Data System (ADS)

    Samoilenko, V. M.; Ravilov, R. G.; Drevnyak, V. V.; Petrova, M. A.

    2016-06-01

    The fracture mechanism of the thermal barrier coating of gas turbine blades is studied. The causes of the fracture of the ceramic layer are discussed and the possible ways to increase the fatigue life of the thermal barrier coating are considered.

  15. Fracture mechanics evaluation of GaAs

    NASA Technical Reports Server (NTRS)

    Chen, C. P.

    1984-01-01

    A data base of mechanical and fracture properties for GaAs was generated. The data for single crystal GaAs will be used to design reusable GaAs solar modules. Database information includes; (1) physical property characterizations; (2) fracture behavior evaluations; and (3) strength of cells determined as a function of cell processing and material parameters.

  16. Effect of electropulsing treatment on microstructure and tensile fracture behavior of aged Mg-9Al-1Zn alloy strip

    NASA Astrophysics Data System (ADS)

    Jiang, Yanbin; Tang, Guoyi; Shek, Chanhung; Zhu, Yaohua

    2009-11-01

    The effect of electropulsing treatment (EPT) on the microstructure, mechanical properties, and tensile fracture behavior of aged Mg-9Al-1Zn alloy strip at room temperature was investigated. The results indicated that EPT accelerated the spheroidizing and dissolution of β phase tremendously in the aged Mg-9Al-1Zn alloy strip. The EPT-induced microstructural change resulted in remarkably increasing elongation to failure, remained tensile strength unchanged. A mechanism for rapid spheroidizing and dissolution process of β phase during EPT was proposed based on the reduction of nucleation thermodynamic barrier and enhancement of atomic diffusion. Fracture analysis showed that with increase in frequency of EPT transgranular dimple fracture becomes predominant instead of the quasicleavage fracture.

  17. Ductility and fracture in B2 FeAl alloys. Ph.D. Thesis Final Report

    NASA Technical Reports Server (NTRS)

    Crimp, Martin A.

    1987-01-01

    The mechanical behavior of B2FeAl alloys was studied. Stoichiometric Fe-50Al exhibits totally brittle behavior while iron-rich Fe-40Al yields and displays about 3% total strain. This change in behavior results from large decreases in the yield strength with iron-rich deviations from stoichiometry while the fracture stress remains essentially constant. Single crystal studies show that these yield strength decreases are directly related to decreases in the critical resolved shear stress for a group of zone axes /111/ set of (110) planes slip. This behavior is rationalized in terms of the decrease in antiphase boundary energy with decreasing aluminum content. The addition of boron results in improvements in the mechanical behavior of alloys on the iron-rich side of stoichiometry. These improvements are increased brittle fracture stresses of near-stoichiometric alloys, and enhanced ductility of up to 6% in Fe-40Al. These effects were attributed to increased grain boundary adhesion as reflected by changes in fracture mode from intergranular to transgranular failure. The increases in yield strength, which are observed in both polycrystals and single crystals, result from the quenching in of large numbers of thermal vacancies. Hall-Petch plots show that the cooling rate effects are a direct result of changes in the Hall-Petch intercept/lattice resistance flow.

  18. A new fracturing mechanism for granular media

    NASA Astrophysics Data System (ADS)

    Bessinger, Brad A.; Liu, Zhong; Cook, Neville G. W.; Myer, Larry R.

    Borehole breakout experiments are performed on sintered glass bead bricks and a new microscale fracturing mechanism is described that results in a macroscopic fracture plane oriented perpendicular to the uniaxial compressive loading stress. Scanning Electron Microscopy (SEM) is used to inspect the fracture surfaces and it is found that fracture propagation occurs through a process of grain debonding and ejection from the sample. A two-dimensional boundary integral simulation models the effect of grain removal on subsequent fracturing by reducing the Young's modulus of failed grains, thereby allowing the compressive loading stress to be transferred to adjoining grains and grain contacts. It is found that this stress concentration is sufficient to induce additional grain failure and macroscopic fracture growth perpendicular to the applied load.

  19. Fatigue and Fracture of a Bulk Nanocrystalline NiFe Alloy

    NASA Astrophysics Data System (ADS)

    Yang, Y.; Imasogie, B.; Fan, G. J.; Liaw, Peter K.; Soboyejo, W. O.

    2008-05-01

    This article presents the results of an experimental study of fracture and fatigue in a nanostructured (an average grain size of ˜23 nm) bulk Ni-18 wt pct Fe alloy that was produced using a pulsed electrodeposition technique. The fracture behavior of the alloy is investigated using fracture resistance experiments, while the fatigue behavior is studied in fatigue crack growth experiments. The alloy exhibits limited toughening as the crack initiates at a fracture toughness of about 25 {text{MPa}}{sqrt {text{m}} } and propagates with a slight increase to a plateau value of about 30 {text{MPa}}{sqrt {text{m}} } . The limited toughening arises from the slight increase in the crack-tip plastic-deformation zone at the early crack growth and ligament bridging due to the microcrack formation ahead of the tip of the main crack. In contrast with a flat fatigue-crack wake, a wavy crack wake was observed under monotonic loading. This trend is attributed to the following: (a) nanovoid coalescence at grain boundaries, (b) microcrack formation by joining nanovoids, and (c) the linking of microcracks with the main crack through the fracture of inclined bridging ligaments. The fractured surface is shown to contain ductile dimple structures with average diameters of ˜100 nm. Focused-ion-beam (FIB) methods are also used to study fatigue-crack growth. These results show that fatigue crack growth occurs by the coalescence of nanovoids that form ahead of the crack tip. The observed mechanisms of fatigue crack growth are shown to be consistent with the results of prior atomistic simulations.

  20. The kinetics of composite particle formation during mechanical alloying

    NASA Technical Reports Server (NTRS)

    Aikin, B. J. M.; Courtney, T. H.

    1993-01-01

    The kinetics of composite particle formation during attritor milling of insoluble binary elemental powders have been examined. The effects of processing conditions (i.e., mill power, temperature, and charge ratio) on these kinetics were studied. Particle size distributions and fractions of elemental and composite particles were determined as functions of milling time and processing conditions. This allowed the deduction of phenomenological rate constants describing the propensity for fracture and welding during processing. For the mill-operating conditions investigated, the number of particles in the mill generally decreased with milling time, indicating a greater tendency for particle welding than fracture. Moreover, a bimodal size distribution is often obtained as a result of preferential welding. Copper and chromium 'alloy' primarily by encapsulation of Cr particles within Cu. This form of alloying also occurs in Cu-Nb alloys processed at low mill power and/or for short milling times. For other conditions, however, Cu-Nb alloys develop a lamellar morphology characteristic of mechanically alloyed two-phase ductile metals. Increasing mill power or charge (ball-to-powder weight) ratio (CR) increases the rate of composite particle formation.

  1. Characterization of Fracture and Fatigue Behavior of 7050 Aluminum Alloy Ultra-thick Plate

    NASA Astrophysics Data System (ADS)

    Wei, Lili; Pan, Qinglin; Wang, Yilin; Feng, Lei; Huang, Hongfeng

    2013-09-01

    The microstructure, mechanical property, fracture toughness, and fatigue behavior of 7050 aluminum alloy pre-stretched ultra-thick plate were investigated by means of optical microscopy, scanning electron microscopy, transmission electron microscopy, tensile test, fracture toughness test, and high-cycle fatigue test. The results showed that the microstructure of the ultra-thick plate consisted of recrystallized grains, subgrains, constituent particles, precipitated phases, and precipitate-free zone. Mechanical tests indicated that anisotropy of fracture toughness existed in L-T, T-L, and S-T orientation. Fractographic features suggested that this anisotropy was significant due to the difference of recrystallized grain on different metallographic planes. Compared to 7050 aluminum alloy plate in less thickness, the ultra-thick plate showed deterioration on fracture toughness due to the increase of recrystallized grains but improvement on fatigue property ascribed to the less densely populated particles. Fractographic observations showed that fatigue initiation of this ultra-thick plate was primarily related to the constituent particles and promoted by increase of the stress amplitude.

  2. Fracture mechanics; Proceedings of the 22nd National Symposium, Atlanta, GA, June 26-28, 1990. Vols. 1 & 2

    NASA Technical Reports Server (NTRS)

    Ernst, Hugo A. (Editor); Saxena, Ashok (Editor); Mcdowell, David L. (Editor); Atluri, Satya N. (Editor); Newman, James C., Jr. (Editor); Raju, Ivatury S. (Editor); Epstein, Jonathan S. (Editor)

    1992-01-01

    Current research on fracture mechanics is reviewed, focusing on ductile fracture; high-temperature and time-dependent fracture; 3D problems; interface fracture; microstructural aspects of fatigue and fracture; and fracture predictions and applications. Particular attention is given to the determination and comparison of crack resistance curves from wide plates and fracture mechanics specimens; a relationship between R-curves in contained and uncontained yield; the creep crack growth behavior of titanium alloy Ti-6242; a crack growth response in three heat resistant materials at elevated temperature; a crack-surface-contact model for determining effective-stress-intensity factors; interfacial dislocations in anisotropic bimaterials; an effect of intergranular crack branching on fracture toughness evaluation; the fracture toughness behavior of exservice chromium-molybdenum steels; the application of fracture mechanics to assess the significance of proof loading; and a load ratio method for estimating crack extension.

  3. Fracture mechanics; Proceedings of the 22nd National Symposium, Atlanta, GA, June 26-28, 1990. Vols. 1 & 2

    NASA Technical Reports Server (NTRS)

    Ernst, Hugo A. (Editor); Saxena, Ashok (Editor); Mcdowell, David L. (Editor); Atluri, Satya N. (Editor); Newman, James C., Jr. (Editor); Raju, Ivatury S. (Editor); Epstein, Jonathan S. (Editor)

    1992-01-01

    Current research on fracture mechanics is reviewed, focusing on ductile fracture; high-temperature and time-dependent fracture; 3D problems; interface fracture; microstructural aspects of fatigue and fracture; and fracture predictions and applications. Particular attention is given to the determination and comparison of crack resistance curves from wide plates and fracture mechanics specimens; a relationship between R-curves in contained and uncontained yield; the creep crack growth behavior of titanium alloy Ti-6242; a crack growth response in three heat resistant materials at elevated temperature; a crack-surface-contact model for determining effective-stress-intensity factors; interfacial dislocations in anisotropic bimaterials; an effect of intergranular crack branching on fracture toughness evaluation; the fracture toughness behavior of exservice chromium-molybdenum steels; the application of fracture mechanics to assess the significance of proof loading; and a load ratio method for estimating crack extension.

  4. Relationship between fracture toughness, fracture path, and microstructure of 7050 aluminum alloy. Part 2: Multiple micromechanisms-based fracture toughness model

    SciTech Connect

    Gokhale, A.M.; Deshpande, N.U.; Denzer, D.K.; Liu, J.

    1998-04-01

    A multiple micromechanisms-based model is developed to quantitatively relate the fracture toughness of partially recrystallized 7XXX aluminum alloys to their fracture surface morphology. The model is verified using the experimental data on partially recrystallized 7050 alloy reported in the companion article. It is then used to obtain a quantitative relationship between the fracture toughness and microstructural attributes. The model relates fracture toughness to microstructural parameters such as degree of recrystallization, grain size of recrystallized grains, thickness of recrystallized regions, total surface area of the constituent particles per unit volume, and microstructural anisotropy. The model predicts the changes in the fracture toughness with the specimen orientation.

  5. Fracture mechanism of borated stainless steel

    SciTech Connect

    He, J.Y.; Soliman, S.E.; Baratta, A.J.; Balliett, T.A.

    2000-05-01

    The mechanical properties and fracture mechanism of irradiated and unirradiated boron containing Type 304 stainless steel are studied. Four different batches with different boron weight percentages are used. One of these batches was manufactured by a conventional wrought technique, while the others were manufactured by a powder metallurgy technique. The irradiated specimens were subjected to a fluence level of 5 x 10{sup 19} or 1 {times} 10{sup 21} n/m{sup 2}. The mechanical and fracture tests were performed at temperatures of 233, 298, and 533 K. No significant effects on the mechanical properties or fracture behavior were observed as a result of neutron irradiation and/or temperature. The ductility and toughness of the borated steel were found to decrease with increasing boron content. The effect of boride on void nucleation and linkage was found to play an important role in the fracture behavior of borated steel.

  6. Fracture Mechanics of Delamination. Initiation and Growth.

    DTIC Science & Technology

    1982-01-01

    transverse cracking, delamina- tion, x- radiography , fracture mechanics, strain energy release rate, finite element, initiation and growth criteria...Battelle Columbus Laboratories, Metals and Ceramics Information Center, 505 King Avenue, Columbus, OH 43201. . . .1 Bell Aerospace Company, Buffalo , NY

  7. Electronics Reliability Fracture Mechanics, Volume 2. Fracture Mechanics

    DTIC Science & Technology

    1992-05-01

    8217 I I I I I ) , I, , COOOO SwRI Foil Data Soxeno cnid Antolovich 𔃻 -4 -- Ishi and "ukawa [11]u10 0, C 10- 5- -442 U -7 2 4 2 4 8 a 10 1011 AK (ks...Saxena and S.D. Antolovich , "Low Cycle Fatigue, Fatigue Crack Propagation and Substructures in a Series of Polycrystalline Cu-Al Alloys," Met. Trans. A

  8. Mechanical alloying of biocompatible Co-28Cr-6Mo alloy.

    PubMed

    Sánchez-De Jesús, F; Bolarín-Miró, A M; Torres-Villaseñor, G; Cortés-Escobedo, C A; Betancourt-Cantera, J A

    2010-07-01

    We report on an alternative route for the synthesis of crystalline Co-28Cr-6Mo alloy, which could be used for surgical implants. Co, Cr and Mo elemental powders, mixed in an adequate weight relation according to ISO Standard 58342-4 (ISO, 1996), were used for the mechanical alloying (MA) of nano-structured Co-alloy. The process was carried out at room temperature in a shaker mixer mill using hardened steel balls and vials as milling media, with a 1:8 ball:powder weight ratio. Crystalline structure characterization of milled powders was carried out by X-ray diffraction in order to analyze the phase transformations as a function of milling time. The aim of this work was to evaluate the alloying mechanism involved in the mechanical alloying of Co-28Cr-6Mo alloy. The evolution of the phase transformations with milling time is reported for each mixture. Results showed that the resultant alloy is a Co-alpha solid solution, successfully obtained by mechanical alloying after a total of 10 h of milling time: first Cr and Mo are mechanically prealloyed for 7 h, and then Co is mixed in for 3 h. In addition, different methods of premixing were studied. The particle size of the powders is reduced with increasing milling time, reaching about 5 mum at 10 h; a longer time promotes the formation of aggregates. The morphology and crystal structure of milled powders as a function of milling time were analyzed by scanning electron microscopy and XR diffraction.

  9. Fracture-mechanics studies of cementitious composites

    SciTech Connect

    Jenq, Y.S.

    1987-01-01

    Attempts have been made to apply fracture mechanics to concrete. However, the experimentally observed fracture parameters for concrete were found to be dependent on specimen size. This thesis first addresses studies of size effect on fracture parameters. Following the size-effect studies, applications of the fracture mechanics to concrete and steel-fiber-reinforced concrete are developed. An experimental program is first designed to investigate the factors that cause the size-effect on the fracture parameters used for concrete. The fracture parameters studied are critical stress intensity factor, critical strain energy release rate, critical crack tip opening displacement and fracture energy. The pre-critical stable crack growth is found to be the major factor that causes the size effect on the conventional critical stress intensity factor. Based on the observation of experimental results, the critical stress intensity factor and critical crack-tip opening displacement are proposed as the two basic fracture parameters. A theoretical model is developed for steel-fiber-reinforced concrete. Based on the studies of plain concrete, the contribution of the matrix in steel-fiber-reinforced concrete can be characterized using the proposed model.

  10. Recent advances in the synthesis of alloy phases by mechanical alloying/milling

    NASA Astrophysics Data System (ADS)

    Suryanarayana, C.

    1996-08-01

    Mechanical alloying (MA) is a solid-state powder processing technique involving repeated welding, fracturing, and rewelding of powder particles in a high-energy ball mill. Originally developed to produce oxide-dispersion strengthened nickel- and iron-base superalloys, MA has now been shown to be capable of synthesizing a number of alloy phases—equilibrium and supersaturated solid solutions, stable and metastable crystalline and quasicrystalline intermediate phases, and amorphous alloys. Recent advances in these areas and also on disordering of ordered intermetallics and displacement reactions have been critically reviewed. Wherever possible, comparisons have been made on the product phases obtained by MA and by rapid solidification processing, another non-equilibrium processing technique.

  11. The Origin of Fracture in the I-ECAP of AZ31B Magnesium Alloy

    NASA Astrophysics Data System (ADS)

    Gzyl, Michal; Rosochowski, Andrzej; Boczkal, Sonia; Qarni, Muhammad Jawad

    2015-11-01

    Magnesium alloys are very promising materials for weight-saving structural applications due to their low density, comparing to other metals and alloys currently used. However, they usually suffer from a limited formability at room temperature and low strength. In order to overcome those issues, processes of severe plastic deformation (SPD) can be utilized to improve mechanical properties, but processing parameters need to be selected with care to avoid fracture, very often observed for those alloys during forming. In the current work, the AZ31B magnesium alloy was subjected to SPD by incremental equal-channel angular pressing (I-ECAP) at temperatures varying from 398 K to 525 K (125 °C to 250 °C) to determine the window of allowable processing parameters. The effects of initial grain size and billet rotation scheme on the occurrence of fracture during I-ECAP were investigated. The initial grain size ranged from 1.5 to 40 µm and the I-ECAP routes tested were A, BC, and C. Microstructures of the processed billets were characterized before and after I-ECAP. It was found that a fine-grained and homogenous microstructure was required to avoid fracture at low temperatures. Strain localization arising from a stress relaxation within recrystallized regions, namely twins and fine-grained zones, was shown to be responsible for the generation of microcracks. Based on the I-ECAP experiments and available literature data for ECAP, a power law between the initial grain size and processing conditions, described by a Zener-Hollomon parameter, has been proposed. Finally, processing by various routes at 473 K (200 °C) revealed that route A was less prone to fracture than routes BC and C.

  12. A Hierarchical Approach to Fracture Mechanics

    NASA Technical Reports Server (NTRS)

    Saether, Erik; Taasan, Shlomo

    2004-01-01

    Recent research conducted under NASA LaRC's Creativity and Innovation Program has led to the development of an initial approach for a hierarchical fracture mechanics. This methodology unites failure mechanisms occurring at different length scales and provides a framework for a physics-based theory of fracture. At the nanoscale, parametric molecular dynamic simulations are used to compute the energy associated with atomic level failure mechanisms. This information is used in a mesoscale percolation model of defect coalescence to obtain statistics of fracture paths and energies through Monte Carlo simulations. The mathematical structure of predicted crack paths is described using concepts of fractal geometry. The non-integer fractal dimension relates geometric and energy measures between meso- and macroscales. For illustration, a fractal-based continuum strain energy release rate is derived for inter- and transgranular fracture in polycrystalline metals.

  13. Mechanical Properties of Particulate Reinforced Aluminium Alloy Matrix Composite

    SciTech Connect

    Sayuti, M.; Sulaiman, S.; Baharudin, B. T. H. T.; Arifin, M. K. A.; Suraya, S.; Vijayaram, T. R.

    2011-01-17

    This paper discusses the mechanical properties of Titanium Carbide (TiC) particulate reinforced aluminium-silicon alloy matrix composite. TiC particulate reinforced LM6 alloy matrix composites were fabricated by carbon dioxide sand molding process with different particulate weight fraction. Tensile strength, hardness and microstructure studies were conducted to determine the maximum load, tensile strength, modulus of elasticity and fracture surface analysis have been performed to characterize the morphological aspects of the test samples after tensile testing. Hardness values are measured for the TiC reinforced LM6 alloy composites and it has been found that it gradually increases with increased addition of the reinforcement phase. The tensile strength of the composites increased with the increase percentage of TiC particulate.

  14. Mechanical Properties of Particulate Reinforced Aluminium Alloy Matrix Composite

    NASA Astrophysics Data System (ADS)

    Sayuti, M.; Sulaiman, S.; Baharudin, B. T. H. T.; Arifin, M. K. A.; Suraya, S.; Vijayaram, T. R.

    2011-01-01

    This paper discusses the mechanical properties of Titanium Carbide (TiC) particulate reinforced aluminium-silicon alloy matrix composite. TiC particulate reinforced LM6 alloy matrix composites were fabricated by carbon dioxide sand molding process with different particulate weight fraction. Tensile strength, hardness and microstructure studies were conducted to determine the maximum load, tensile strength, modulus of elasticity and fracture surface analysis have been performed to characterize the morphological aspects of the test samples after tensile testing. Hardness values are measured for the TiC reinforced LM6 alloy composites and it has been found that it gradually increases with increased addition of the reinforcement phase. The tensile strength of the composites increased with the increase percentage of TiC particulate.

  15. The effect of thermal treatment on the fracture properties of alloy X-750 in aqueous environments

    SciTech Connect

    Ballinger, R.; Elliott, C.S.; Hwang, I.S.; Prybylowski, J.

    1993-05-01

    Alloy X-750 is a high strength, age hardenable nickel-base alloy used in light water nuclear reactors. The excellent corrosion resistance and high temperature strength of alloy X-750 make it suitable for use in a variety of structure components in both pressurized water reactors and boiling water reactors. These applications involve exposure of highly stressed material to aqueous media. Operational stresses are subject to low frequency thermally induced fluctuations and high frequency flow induced fluctuations. In general, alloy X-750 has performed well in light water reactors. However, an economically significant number of components have failed unexpectedly due to localized forms of attack such as corrosion fatigue and stress corrosion cracking. Thermal processing history is known to play a significant role in the fracture properties of alloy X-750 in aqueous environments. While thermal treatments have been developed recently to improve performance, in many cases the reason for improved performance remains unclear. Therefore, identification of the mechanisms responsible for the degradation of fracture properties in aqueous environments is necessary. As a corollary it is necessary to achieve an understanding of how thermal treatment influences microstructure and, in turn, how microstructure influences fracture properties in aqueous environments. This report discusses five thermal treatments which were studied: (1) SA-1 hr at 1093{degree}C, (2) AH - 24 hr at 885{degree}C + 20 hr at 704{degree}C, (3) HTH - 1 hr at 1093{degree}C + 20 hr at 704{degree}C, (4) AHTH - 1 hr at 1093{degree}C + 24 hr at 885{degree}C + 20 hr at 704{degree}C, and (5) HOA - 1 hr at 1093{degree}C + 100 hrs at 760{degree}C. Microstructural characterization of these materials was accomplished through the use of optical microscopy, transmission electron microscopy,scanning transmission electron microscopy, energy dispersive x-ray spectroscopy, and x-ray diffractometry.

  16. The fracture of boron fibre-reinforced 6061 aluminium alloy

    NASA Technical Reports Server (NTRS)

    Wright, M. A.; Welch, D.; Jollay, J.

    1979-01-01

    The fracture of 6061 aluminium alloy reinforced with unidirectional and cross-plied 0/90 deg, 0/90/+ or - 45 deg boron fibres has been investigated. The results have been described in terms of a critical stress intensity, K(Q). Critical stress intensity factors were obtained by substituting the failure stress and the initial crack length into the appropriate expression for K(Q). Values were obtained that depended on the dimensions of the specimens. It was therefore concluded that, for the size of specimen tested, the values of K(Q) did not reflect any basic materials property.

  17. The influence of microstructure and strength on the fracture mode and toughness of 7XXX series aluminum alloys

    NASA Astrophysics Data System (ADS)

    Ludtka, Gerard M.; Laughlin, David E.

    1982-03-01

    The effects of microstructure and strength on the fracture toughness of ultra high strength aluminum alloys have been investigated. For this study three ultra high purity compositions were chosen and fabricated into 1.60 mm (0.063 inches) sheet in a T6 temper providing a range of yield strengths from 496 MPa (72 ksi) to 614 MPa (89 ksi). These alloys differ only in the volume fraction of the fine matrix strengthening precipitates (G. P. ordered + η' ). Fracture toughness data were generated using Kahn-type tear tests, as well as R-curve and J c analyses performed on data from 102 mm wide center cracked tension panel tests. Consistent with previous studies, it has been demonstrated that the toughness decreases as the yield strength is increased by increasing the solute content. Concomitant with this decrease in toughness, a transition in fracture mode was observed from predominantly transgranular dimpled rupture to predominantly intergranular dimpled rupture. Both quantitative fractography and X-ray microanalysis clearly demonstrate that fracture initiation for the two fracture modes occurred by void formation at the Cr-dispersoids ( E-phase). In the case of intergranular fracture, void coalescence was facilitated by the grain boundary η precipitates. The difference in fracture toughness behavior of these alloys has been shown to be dependent on the coarseness of matrix slip and the strength differential between the matrix and precipitate free zone (σM-σPFZ). A new fracture mechanism has been proposed to explain the development of the large amounts of intergranular fracture observed in the low toughness alloys.

  18. Damage Tolerant Design Handbook. A Compilation of Fracture and Crack- Growth Data for High-Strength Alloys. Volume 4

    DTIC Science & Technology

    1983-12-01

    Data on Aluminum , Steel and Titanium Alloys, Data Sent From P. G. Porter of Northrop Corporation, March 1, 1982. 4CO03 2024 -T851 KI. , da/dN 2124 -T851...April 1965). 62311 2024 (ALCLAD)-T3 K. 7075(ALCLAD)-T6 K, Gurin, P. J., "Crack Propagation Tests for Some Aluminum Alloy Materials", LR 10498...Characteristics of Aluminum Alloy Cylinders Under Internal Pressure". Engineering Fracture Mechanics, 4 (1) 51-63 (March 1972). 82880 2024 -T851 KIc 2219-T851

  19. Mechanical properties of cast Ti-6Al-4V-XCu alloys.

    PubMed

    Aoki, T; Okafor, I C I; Watanabe, I; Hattori, M; Oda, Y; Okabe, T

    2004-11-01

    The mechanical properties of Ti-6Al-4V-XCu (1, 4 and 10 wt% Cu) alloys were examined. The castings for each alloy were made in a centrifugal titanium casting machine. Two shapes of specimens were used: a dumbbell (20 mm gauge length x 2.8 mm diameter) for mechanical property studies, and a flat slab (2 mm x 10 mm x 10 mm) for metallography, microhardness determination and X-ray diffractometry. Tensile strength, yield strength, modulus of elasticity, elongation and microhardness were evaluated. After tensile testing, the fracture surfaces were observed using scanning electron microscopy. The tensile strengths of the quaternary alloys decreased from 1016 MPa for the 1% Cu alloy to 387 MPa for the 10% Cu alloy. Elongation decreased with an increase in the copper content. The 1% Cu alloy exhibited elongation similar to Ti-6Al-4V without copper (3.0%). The results also indicated that the copper additions increased the bulk hardness of the quaternary alloy. In particular, the 10% Cu alloy had the highest hardness and underwent the most brittle fracture. The mechanical properties of cast Ti-6Al-4V alloy with 1 and 4% Cu were well within the values for existing dental casting non-precious alloys.

  20. Fracture toughness and corrosion resistance of semisolid AlSi5 alloy

    SciTech Connect

    Pola, A.; Montesano, L.; Gelfi, M.; Roberti, R.

    2011-05-04

    The aim of this work was to investigate fracture toughness and corrosion resistance of semisolid AlSi5 castings, compared to samples obtained from conventional casting operations. In order to have a semisolid microstructure, the melt alloy was treated by means of ultrasound during solidification and then poured into permanent moulds. Mechanical properties of semisolid and conventional castings were compared by means of ultimate tensile strength (R{sub m}), yield stress (Rp{sub 02}) and hardness (HV) measurements. Fracture mechanics tests were carried out on Single Edge Notched Bend (SENB) specimens, machined from castings, and pre-cracked by fatigue. These tests were performed to determine the effect of the microstructure on the J-Integral resistance (J-R) behavior and to deeply understand the ductile fracture behaviour of semisolid parts. The J-Integral versus spaced crack extension (J-{Delta}a) curves showed an improved resistance of the semisolid microstructure, due to the higher ductility. Finally, the corrosion behaviour of semisolid samples was compared to that of castings coming from solidification of fully liquid alloy by means of electrochemical potentiodynamic polarization tests. It was observed that the globular microstructure offers better quality, in terms of higher mechanical properties, as a consequence of a more uniform distribution of the solute.

  1. Fracture toughness and corrosion resistance of semisolid AlSi5 alloy

    NASA Astrophysics Data System (ADS)

    Pola, A.; Montesano, L.; Gelfi, M.; Roberti, R.

    2011-05-01

    The aim of this work was to investigate fracture toughness and corrosion resistance of semisolid AlSi5 castings, compared to samples obtained from conventional casting operations. In order to have a semisolid microstructure, the melt alloy was treated by means of ultrasound during solidification and then poured into permanent moulds. Mechanical properties of semisolid and conventional castings were compared by means of ultimate tensile strength (Rm), yield stress (Rp02) and hardness (HV) measurements. Fracture mechanics tests were carried out on Single Edge Notched Bend (SENB) specimens, machined from castings, and pre-cracked by fatigue. These tests were performed to determine the effect of the microstructure on the J-Integral resistance (J-R) behavior and to deeply understand the ductile fracture behaviour of semisolid parts. The J-Integral versus spaced crack extension (J-Δa) curves showed an improved resistance of the semisolid microstructure, due to the higher ductility. Finally, the corrosion behaviour of semisolid samples was compared to that of castings coming from solidification of fully liquid alloy by means of electrochemical potentiodynamic polarization tests. It was observed that the globular microstructure offers better quality, in terms of higher mechanical properties, as a consequence of a more uniform distribution of the solute.

  2. Fracture mechanics of snow avalanches

    NASA Astrophysics Data System (ADS)

    Åström, J. A.; Timonen, J.

    2001-07-01

    Dense snow avalanches are analyzed by modeling the snow slab as an elastic and brittle plate, attached by static friction to the underlying ground. The grade of heterogeneity in the local fracture (slip) thresholds, and the ratio of the average substrate slip threshold to the average slab fracture threshold, are the decisive parameters for avalanche dynamics. For a strong pack of snow there appears a stable precursor of local slips when the frictional contacts are weakened (equivalent to rising temperature), which eventually trigger a catastrophic crack growth that suddenly releases the entire slab. In the opposite limit of very high slip thresholds, the slab simply melts when the temperature is increased. In the intermediate regime, and for a homogeneous slab, the model display features typical of real snow avalanches. The model also suggests an explanation to why avalanches are impossible to forecast reliably based on precursor observations. This explanation may as well be applicable to other catastrophic rupture phenomena such as earthquakes.

  3. Fracture mechanics of snow avalanches.

    PubMed

    Aström, J A; Timonen, J

    2001-07-01

    Dense snow avalanches are analyzed by modeling the snow slab as an elastic and brittle plate, attached by static friction to the underlying ground. The grade of heterogeneity in the local fracture (slip) thresholds, and the ratio of the average substrate slip threshold to the average slab fracture threshold, are the decisive parameters for avalanche dynamics. For a strong pack of snow there appears a stable precursor of local slips when the frictional contacts are weakened (equivalent to rising temperature), which eventually trigger a catastrophic crack growth that suddenly releases the entire slab. In the opposite limit of very high slip thresholds, the slab simply melts when the temperature is increased. In the intermediate regime, and for a homogeneous slab, the model display features typical of real snow avalanches. The model also suggests an explanation to why avalanches are impossible to forecast reliably based on precursor observations. This explanation may as well be applicable to other catastrophic rupture phenomena such as earthquakes.

  4. Interrelation of material microstructure, ultrasonic factors, and fracture toughness of two phase titanium alloy

    NASA Technical Reports Server (NTRS)

    Vary, A.; Hull, D. R.

    1982-01-01

    The pivotal role of an alpha-beta phase microstructure in governing fracture toughness in a titanium alloy, Ti-662, is demonstrated. The interrelation of microstructure and fracture toughness is demonstrated using ultrasonic measurement techniques originally developed for nondestructive evaluation and material property characterization. It is shown that the findings determined from ultrasonic measurements agree with conclusions based on metallurgical, metallographic, and fractographic observations concerning the importance of alpha-beta morphology in controlling fracture toughness in two phase titanium alloys.

  5. Fracture mechanisms of a 2124 aluminum

    NASA Astrophysics Data System (ADS)

    Kim, Young-Hwan; Lee, Sunghak; Kim, Nack J.

    1992-09-01

    This study was aimed at investigating the effects of microstructure on the fracture behavior of a 2124 aluminum composite reinforced with SiC whiskers. Particular emphasis was placed on the role of matrix intermetallic particles, inhomogeneous distribution of whiskers, and whisker breakage in the fracture process. Various tests were conducted on the composite to identify the micromechanical processes that were involved in microvoid or microcrack formation. Detailed microstructural analyses showed that the aluminum matrix contained a significant amount of coarse manganese-containing particles of various sizes which could have been formed during composite processing. In situ scanning electron microscope (SEM) fracture study of the crack initiation and propagation processes clearly showed that these coarse particles fractured prior to matrix/whisker decohesion or whisker breakage, suggesting that the manganese-containing par- ticles significantly accelerated crack initiation in the 2124 Al-SiCw composite. For a better ma- trix alloy for use in the composite, it is suggested that microalloying elements must be monitored to prevent the formation of the coarse intermetallic particles.

  6. Metallurgical and mechanical properties of thorium-doped Ir-0. 3% W alloys

    SciTech Connect

    Liu, C.T.; Inouye, H.; Schaffhauser, A.C.

    1980-04-01

    Metallurgical and mechanical properties of Ir-0.3% W alloys have been studied as a function of thorium concentration in the range 0 to 1000 ppM by weight. The solubility limit of thorium in Ir-0.3% W is below 30 ppM. Above this limit, the excess thorium reacts with iridium to form second-phase particles. Thorium additions raise the recrystallization temperature and effectively retard grain growth at high temperatures. Tensile tests at 650/sup 0/C show that the alloy without thorium additions (undoped alloy) fractured by grainboundary (GB) separation, while the alloys doped with less than 500 ppM thorium failed mainly by transgranular fracture at 650/sup 0/C. Intergranular fracture in the doped alloys is suppressed by GB segregation of thorium, which improves the mechanical properties of the boundary. The impact properties of the alloys were correlated with test temperature, grain size, and heat treatment. The impact ductility increases with test temperature and decreases with grain size. For a given grain size, particularly in the fine-grain size range, the thorium-doped alloys are much more ductile and resistant to GB fracture. All of these results can be correlated on the basis of stress concentration on GBs by using a dislocation pileup model.

  7. Effect of Heat Treatment, Pre-stress and Surface Hardening on Fracture Toughness of Micro-Alloyed Steel

    NASA Astrophysics Data System (ADS)

    Nag Chaudhury, Joydeb

    2014-01-01

    Micro-alloyed steels are being increasingly accepted by industry in various fields of application and are available with a wide variety of microstructures. Extensive literature is available on their microstructure-property relationships. The superior mechanical properties of micro-alloyed steels are caused by fine-grained microstructures and precipitation of micro-alloying elements such as V, Ti and Nb that led to an improvement in yield strength, in the product of tensile strength and total elongation and in Charpy V-notch impact energy as well. The microstructural changes caused by heat treatment or residual stress state caused by surface hardening or mechanical means may influence the fracture toughness of these micro-alloyed steels. It is in this context that the present work begins with experimental determination of quasi-static initiation fracture toughness ( J 1c) of low carbon (0.19%) micro-alloyed steel in as-rolled condition without any heat treatment. The study further explores the effect of normalizing, shot-peening and cyaniding followed by shot-peening on fracture toughness of as-rolled steel under study. The normalizing heat treatment, shot-peening and cyaniding followed by shot-peening—each indicates a positive influence on initiation fracture toughness. Results, when compared, show that cyaniding followed by shot-peening have led to a 2.7 times increase in J 1c. Cyaniding followed by shot-peening may therefore be considered as having the most positive influence on initiation fracture toughness in as-rolled condition for the type of micro-alloyed steel under study. Although initiation fracture toughness is in general known to decrease with increase in yield strength in LEFM arena, the micro-alloyed steel under study when normalized displayed simultaneous improvement in yield strength and J 1c. All these observed effects of normalizing, shot-peening and cyaniding on initiation fracture toughness (elastic-plastic fracture mechanics) were explained

  8. Mechanical properties of neutron-irradiated model and commercial FeCrAl alloys

    NASA Astrophysics Data System (ADS)

    Field, Kevin G.; Briggs, Samuel A.; Sridharan, Kumar; Howard, Richard H.; Yamamoto, Yukinori

    2017-06-01

    The development and understanding of the mechanical properties of neutron-irradiated FeCrAl alloys is increasingly a critical need as these alloys continue to become more mature for nuclear reactor applications. This study focuses on the mechanical properties of model FeCrAl alloys and of a commercial FeCrAl alloy neutron-irradiated to up to 13.8 displacements per atom (dpa) at irradiation temperatures between 320 and 382 °C. Tensile tests were completed at room temperature and at 320 °C, and a subset of fractured tensile specimens was examined by scanning electron microscopy. Results showed typical radiation hardening and embrittlement indicative of high chromium ferritic alloys with strong chromium composition dependencies at lower doses. At and above 7.0 dpa, the mechanical properties saturated for both the commercial and model FeCrAl alloys, although brittle cleavage fracture was observed at the highest dose in the model FeCrAl alloy with the highest chromium content (18 wt %). The results suggest the composition and microstructure of FeCrAl alloys plays a critical role in the mechanical response of FeCrAl alloys irradiated near temperatures relevant to light water reactors.

  9. Applications of memory alloy stent in vertebral fractures

    PubMed Central

    Yimin, Yang; Zhi, Zhang; ZhiWei, Ren; Wei, Ma; Jha, Rajiv Kumar

    2014-01-01

    Background The aim of this study was to evaluate the feasibility of treating vertebral compression fractures using an autonomously developed nitinol memory alloy vertebral stent. Material/Methods Thoracolumbar vertebral specimens from adult human cadavers were made into models of compression fractures. The models were divided into group A, which received percutaneous kyphoplasty (PKP), balloon dilation, and nitinol memory alloy vertebral stent implantation (PKP + nitinol stent group); group B, which received percutaneous vertebroplasty (PVP) and direct implantation of a nitinol memory alloy vertebral stent (PVP + nitinol stent group); and group C, which received PKP, balloon dilation, and bone cement vertebroplasty (PKP + polymethylmethacrylate (PMMA) group). Vertebral heights were measured before and after the surgery and the water bath incubation to compare the impact of the 3 different surgical approaches on reducing vertebral compression. Results The 3 surgical groups could all significantly restore the heights of compressed vertebral bodies. The vertebral heights of the PKP + nitinol stent group, PVP + nitinol stent group, and PKP + PMMA group were changed from the preoperative levels of (1.59±0.08) cm, (1.68±0.08) cm, and (1.66±0.11) cm to the postoperative levels of (2.00±0.09) cm, (1.87±0.04) cm, and (1.99±0.09) cm, respectively. After the water bath, the vertebral heights of each group were changed to (2.10±0.07) cm, (1.98±0.09) cm, and (2.00±0.10) cm, respectively. Pairwise comparison of the differences between the preoperative and postoperative vertebral heights showed that group A and group B differed significantly (P=0.000); group B and group C differed significantly (P=0.003); and group A and group C had no significant difference (P=0.172). Pairwise comparison of the differences in the vertebral heights before and after the water bath showed that group A and group C differed significantly (P=0.000); group B and group C differed significantly

  10. Effects of Be and Fe content on plane strain fracture toughness in A357 alloys

    SciTech Connect

    Tan, Y.H.; Lee, S.L.; Lin, Y.L.

    1995-11-01

    The effect of Be and Fe content on the plane strain fracture toughness K{sub IC} of aluminum-based A357 alloys is investigated. The fracture behavior of A357 alloys has been evaluated as a function of both the magnitude and morphology of iron-bearing compounds and silicon particles. Addition of Be is beneficial for tensile properties and fracture toughness in the case of alloys containing intermediate (0.07 pct) and higher (0.15 pct) Fe levels. On the other hand, Be added to alloys containing the lower Fe (0.01 pct) level appears detrimental to tensile strength, but the quality index, notch-yield ratio (NYR), and plane strain fracture toughness were improved. Fractographic analysis reveals that crack extension of A357 alloys occurs mainly in an intergranular fracture mode. The fracture processes are initiated by void nucleation at iron-bearing compounds or irregularly shaped eutectic silicon particles as a result of their cracking and decohesion from the matrix. Then, void growth and coalescence result in growth of the main crack by shear-linkage-induced breakdown of submicron-strengthening particles. The effect of Be on increasing K{sub IC} is more apparent in the higher Fe alloys than in the lower Fe alloys. Superior toughness obtained by microstructural control has also been achieved in the intermediate and higher Fe levels of Be-containing alloys, with values equal to those obtained in alloys of lower Fe content.

  11. Effects of be and fe content on plane strain fracture toughness in A357 alloys

    NASA Astrophysics Data System (ADS)

    Tan, Yen-Hung; Lee, Sheng-Long; Lin, Yu-Lom

    1995-11-01

    The effect of Be and Fe content on the plane strain fracture toughness K IC of aluminum-based A357 alloys is investigated. The fracture behavior of A357 alloys has been evaluated as a function of both the magnitude and morphology of iron-bearing compounds and silicon particles. Addition of Be is beneficial for tensile properties and fracture toughness in the case of alloys containing intermediate (0.07 pct) and higher (0.15 pct) Fe levels. On the other hand, Be added to alloys containing the lower Fe (0.01 pct) level appears detrimental to tensile strength, but the quality index, notch-yield ratio (NYR), and plane strain fracture toughness were improved. Fractographic analysis reveals that crack extension of A357 alloys occurs mainly in an intergranular fracture mode. The fracture processes are initiated by void nucleation at iron-bearing compounds or irregularly shaped eutectic silicon particles as a result of their cracking and decohesion from the matrix. Then, void growth and coalescence result in growth of the main crack by shear-linkage-induced breakdown of submicronstrengthening particles. The effect of Be on increasing K IC is more apparent in the higher Fe alloys than in the lower Fe alloys. Superior toughness obtained by microstructural control has also been achieved in the intermediate and higher Fe levels of Be-containing alloys, with values equal to those obtained in alloys of lower Fe content.

  12. Mechanical properties of laser welded aluminum alloys

    SciTech Connect

    Douglass, D.M.; Mazumder, J.

    1996-12-31

    The demand for lighter weight vehicles has prompted accelerated development in processing aluminum alloys for automobile structural applications. One of the current research initiatives centers on laser beam welding of aluminum alloys. Autogenous butt welds have been performed on Al 3003, 5754, 6111, and 6061-T6 plates with a 6 kW CO2 laser. For 6061, tensile data indicate about 60% of the base metal strength was attained in the as-welded condition, with a brittle fracture occurring through the weld. A post-weld heat treatment to the T6 condition resulted in a recovery of original ultimate tensile strengths, although these also failed in the weld. Hardness measurements of the post-weld T6 reveal a uniform hardness across the HAZ and fusion zone that is comparable to the original hardness. All 3003 welds fractured in the parent material in a ductile fashion. A high quality bead was consistently achieved with the 3003 alloy, whereas the other alloys demonstrated bead irregularities. SEM photographs reveal large, spherical pores, suggesting that they were formed by gas entrapment rather than by shrinkage.

  13. Microstructure Evolution and Mechanical Properties of Severely Plastically Deformed (SPD) Aluminum Alloys

    DTIC Science & Technology

    2007-05-31

    TITLE AND SUBTITLE 5a. CONTRACT NUMBER Microstructure Evolution and Mechanical Properties of Severely Plastically Deformed (SPD) Aluminum Alloys 5b...modeling study has been carried out to characterize the structure and mechanical properties of severely plastically deformed (SPD) aluminum and its...these routes is the expectation that since the fracture toughness of precipitation hardened aluminum alloys is known to be degraded by grain boundary

  14. Rabotnov damageparameter and description of delayed fracture: Results, current status, application to fracture mechanics, and prospects

    NASA Astrophysics Data System (ADS)

    Stepanova, L. V.; Igonin, S. A.

    2015-03-01

    This paper presents a review of studies of delayed fracture and fracture mechanics problems in which the hypotheses and ideas of Yu. N. Rabotnov and L. M. Kachanov on the mechanisms of delayed fracture under creep conditions are extended to describe fracture processes using scalar and tensor measures of damage. The results of current research in the theory of elasticity, the mathematical theory of plasticity and creep, the mechanics of composites, and linear and nonlinear fracture mechanics, with material damage taken into account.

  15. EBSD characterization of low temperature deformation mechanisms in modern alloys

    NASA Astrophysics Data System (ADS)

    Kozmel, Thomas S., II

    For structural applications, grain refinement has been shown to enhance mechanical properties such as strength, fatigue resistance, and fracture toughness. Through control of the thermos-mechanical processing parameters, dynamic recrystallization mechanisms were used to produce microstructures consisting of sub-micron grains in 9310 steel, 4140 steel, and Ti-6Al-4V. In both 9310 and 4140 steel, the distribution of carbides throughout the microstructure affected the ability of the material to dynamically recrystallize and determined the size of the dynamically recrystallized grains. Processing the materials at lower temperatures and higher strain rates resulted in finer dynamically recrystallized grains. Microstructural process models that can be used to estimate the resulting microstructure based on the processing parameters were developed for both 9310 and 4140 steel. Heat treatment studies performed on 9310 steel showed that the sub-micron grain size obtained during deformation could not be retained due to the low equilibrium volume fraction of carbides. Commercially available aluminum alloys were investigated to explain their high strain rate deformation behavior. Alloys such as 2139, 2519, 5083, and 7039 exhibit strain softening after an ultimate strength is reached, followed by a rapid degradation of mechanical properties after a critical strain level has been reached. Microstructural analysis showed that the formation of shear bands typically preceded this rapid degradation in properties. Shear band boundary misorientations increased as a function of equivalent strain in all cases. Precipitation behavior was found to greatly influence the microstructural response of the alloys. Additionally, precipitation strengthened alloys were found to exhibit similar flow stress behavior, whereas solid solution strengthened alloys exhibited lower flow stresses but higher ductility during dynamic loading. Schmid factor maps demonstrated that shear band formation behavior

  16. Comparison of fracture behavior for low-swelling ferritic and austenitic alloys irradiated in the Fast Flux Test Facility (FFTF) to 180 DPA. Revision 1

    SciTech Connect

    Huang, F.H.

    1992-02-01

    Fracture toughness testing was conducted to investigate the radiation embrittlement of high-nickel superalloys, modified austenitic steels and ferritic steels. These materials have been experimentally proven to possess excellent resistance to void swelling after high neutron exposures. In addition to swelling resistance, post-irradiation fracture resistance is another important criterion for reactor material selection. By means of fracture mechanics techniques the fracture behavior of those highly irradiated alloys was characterized in terms of irradiation and test conditions. Precipitation-strengthened alloys failed by channel fracture with very low postirradiation ductility. The fracture toughness of titanium-modified austenitic stainless steel D9 deteriorates with increasing fluence to about 100 displacement per atom (dpa), the fluence level at which brittle fracture appears to occur. Ferritic steels such as HT9 are the most promising candidate materials for fast and fusion reactor applications. The upper-shelf fracture toughness of alloy HT9 remained adequate after irradiation to 180 dpa although its ductile- brittle transition temperature (DBTT) shift by low temperature irradiation rendered the material susceptible to brittle fracture at room temperature. Understanding the fracture characteristics under various irradiation and test conditions helps reduce the potential for brittle fracture by permitting appropriate measure to be taken.

  17. Comparison of fracture behavior for low-swelling ferritic and austenitic alloys irradiated in the Fast Flux Test Facility (FFTF) to 180 DPA

    SciTech Connect

    Huang, F.H.

    1992-02-01

    Fracture toughness testing was conducted to investigate the radiation embrittlement of high-nickel superalloys, modified austenitic steels and ferritic steels. These materials have been experimentally proven to possess excellent resistance to void swelling after high neutron exposures. In addition to swelling resistance, post-irradiation fracture resistance is another important criterion for reactor material selection. By means of fracture mechanics techniques the fracture behavior of those highly irradiated alloys was characterized in terms of irradiation and test conditions. Precipitation-strengthened alloys failed by channel fracture with very low postirradiation ductility. The fracture toughness of titanium-modified austenitic stainless steel D9 deteriorates with increasing fluence to about 100 displacement per atom (dpa), the fluence level at which brittle fracture appears to occur. Ferritic steels such as HT9 are the most promising candidate materials for fast and fusion reactor applications. The upper-shelf fracture toughness of alloy HT9 remained adequate after irradiation to 180 dpa although its ductile- brittle transition temperature (DBTT) shift by low temperature irradiation rendered the material susceptible to brittle fracture at room temperature. Understanding the fracture characteristics under various irradiation and test conditions helps reduce the potential for brittle fracture by permitting appropriate measure to be taken.

  18. Effects of aging condition on the fracture toughness of 2XXX and 7XXX series aluminum alloy composites

    NASA Technical Reports Server (NTRS)

    Manoharan, M.; Lewandowski, J. J.

    1989-01-01

    Results are presented on the effects of matrix aging condition (i.e., matrix temper) on the fracture toughness of 2XXX and 7XXX Al matrix alloys reinforced with SiC particulates, and the results are compared with the mechanical behavior. Fracture toughness testing was conducted on fatigue precracked bend specimens, and fracture surfaces were examined using SEM. Results revealed dramatic differences in the effect of matrix microstructure on the fracture properties of the two composite series. In the 7XXX material, the toughness values decreased from the underaged (UA) condition to the overaged (OA) condition by approximately 40 percent, while in the 2XXX series composite, the effect of matrix microstructure was marginal. In the 7XXX series composites, a transition in fracture mode from particle cracking (in UA) to matrix and linear-interface failure (in OA) was observed, while the 2XXX series composite failed predominantly by particle cracking.

  19. Fracture mechanics SCC testing of weldments

    SciTech Connect

    Dietzel, W.; Daum, K.H.; Strieder, K.; Kocak, M.

    1994-12-31

    Stress corrosion cracking (SCC) studies of shielded metal arc (SMAW) weld joints of a C-Mn steel were performed using a fracture mechanics based test technique. The specimens contained multipass ferritic weldments with two nitrogen contents and were tested in the As-Welded (AW) condition. Fatigue precracked compact tension (CT) specimens with the cracks in the weld metals were subjected to slow rising displacement rates in the order of 1 {mu}m/h, measured in the load lines of the specimens. The tests were conducted at room temperature in ASTM substitute ocean water under conditions of hydrogen charging (cathodic polarization at {minus}900 mV vs Ag/AgCl, de-aerated solution). Results obtained in these tests in terms of CTOD-R curves are compared with corresponding data obtained in standardized fracture mechanics tests performed in laboratory air. The aim of this work was to assess the feasibility of a rising displacement type of test for SCC testing of weldments. It was also intended to compare the influences of the nitrogen content on the fracture behavior of these welds in air and under conditions of environmentally assisted cracking by using fracture mechanics concepts. The evaluation of the rising displacement SCC tests shows that differences in the fracture behavior observed for testing in laboratory air which could be attributed to the effect of nitrogen are almost completely overridden by the influence of die corrosive environment. Investigations of the fracture surfaces show that the uptake of hydrogen from the aqueous environment in both cases led to a strong embrittlement which is responsible for the decrease in fracture toughness.

  20. Microstructural effects on the tensile and fracture behavior of aluminum casting alloys A356/357

    NASA Astrophysics Data System (ADS)

    Wang, Q. G.

    2003-12-01

    The tensile properties and fracture behavior of cast aluminum alloys A356 and A357 strongly depend on secondary dendrite arm spacing (SDAS), Mg content, and, in particular, the size and shape of eutectic silicon particles and Fe-rich intermetallics. In the unmodified alloys, increasing the cooling rate during solidification refines both the dendrites and eutectic particles and increases ductility. Strontium modification reduces the size and aspect ratio of the eutectic silicon particles, leading to a fairly constant particle size and aspect ratio over the range of SDAS studied. In comparison with the unmodified alloys, the Sr-modified alloys show higher ductility, particularly the A356 alloy, but slightly lower yield strength. In the microstructures with large SDAS (>50 µm), the ductility of the Sr-modified alloys does not continuously decrease with SDAS as it does in the unmodified alloy. Increasing Mg content increases both the matrix strength and eutectic particle size. This decreases ductility in both the Sr-modified and unmodified alloys. The A356/357 alloys with large and elongated particles show higher strain hardening and, thus, have a higher damage accumulation rate by particle cracking. Compared to A356, the increased volume fraction and size of the Fe-rich intermetallics ( π phase) in the A357 alloy are responsible for the lower ductility, especially in the Sr-modified alloy. In alloys with large SDAS (>50 µm), final fracture occurs along the cell boundaries, and the fracture mode is transgranular. In the small SDAS (<30 µm) alloys, final fracture tends to concentrate along grain boundaries. The transition from transgranular to intergranular fracture mode is accompanied by an increase in the ductility of the alloys.

  1. A fracture-mechanics-based approach to fracture control in biomedical devices manufactured from superelastic Nitinol tube.

    PubMed

    Robertson, S W; Ritchie, R O

    2008-01-01

    Several key fracture-mechanics parameters associated with the onset of subcritical and critical cracking, specifically the fracture toughness, crack-resistance curve, and fatigue threshold, have recently been reported for the superelastic alloy Nitinol, in the product form of the thin-walled tube that is used to manufacture several biomedical devices, most notably endovascular stents. In this study, we use these critical parameters to construct simple decision criteria for assessing the quantitative effect of crack-like defects in such Nitinol devices with respect to their resistance to failure by deformation or fracture. The criteria are based on the (equivalent) crack-initiation fracture toughness and fatigue threshold stress-intensity range, together with the general yield strength and fatigue endurance strength, and are used to construct a basis for design against single-event (overload) failures as well as for time-/cycle-delayed failures associated with fatigue.

  2. Shape-Memory-Alloy Release Mechanism

    NASA Technical Reports Server (NTRS)

    Mckinnis, Darin

    1993-01-01

    Release-nut mechanism activated by electric current applied to shape-memory alloy. Separates attached objects quickly by remote control. Does not create hazard or cause damage. Shape-memory release-nut mechanism unaffected by moisture or vacuum. Requires sustained current lasting 5 seconds or longer, and insensitive to electromagnetic interference. Mechanism can be reused.

  3. Shape-Memory-Alloy Release Mechanism

    NASA Technical Reports Server (NTRS)

    Mckinnis, Darin

    1993-01-01

    Release-nut mechanism activated by electric current applied to shape-memory alloy. Separates attached objects quickly by remote control. Does not create hazard or cause damage. Shape-memory release-nut mechanism unaffected by moisture or vacuum. Requires sustained current lasting 5 seconds or longer, and insensitive to electromagnetic interference. Mechanism can be reused.

  4. Mechanical properties of neutron-irradiated model and commercial FeCrAl alloys

    DOE PAGES

    Field, Kevin G.; Briggs, Samuel A.; Sridharan, Kumar; ...

    2017-03-28

    The development and understanding of the mechanical properties of neutron-irradiated FeCrAl alloys is increasingly a critical need as these alloys continue to become more mature for nuclear reactor applications. This study focuses on the mechanical properties of model FeCrAl alloys and of a commercial FeCrAl alloy neutron-irradiated to up to 13.8 displacements per atom (dpa) at irradiation temperatures between 320 and 382 °C. Tensile tests were completed at room temperature and at 320 °C, and a subset of fractured tensile specimens was examined by scanning electron microscopy. Results showed typical radiation hardening and embrittlement indicative of high chromium ferritic alloysmore » with strong chromium composition dependencies at lower doses. At and above 7.0 dpa, the mechanical properties saturated for both the commercial and model FeCrAl alloys, although brittle cleavage fracture was observed at the highest dose in the model FeCrAl alloy with the highest chromium content (18 wt %). Finally, the results suggest the composition and microstructure of FeCrAl alloys plays a critical role in the mechanical response of FeCrAl alloys irradiated near temperatures relevant to light water reactors.« less

  5. Metallurgical characterization of the fracture of several high strength aluminum alloys

    NASA Technical Reports Server (NTRS)

    Bhandarkar, M. D.; Lisagor, W. B.

    1977-01-01

    The fracture behavior for structural aluminum alloys (2024, 6061, 7075, and 7178) was examined in selected heat treatments. The investigation included tensile, shear, and precracked notch-bend specimens fractured at ambient temperature under monotonic loading. Specimens were obtained from thin sheets and thick plates and were tested in longitudinal and transverse orientations at different strain rates. Microstructures of alloys were examined using the optical microscope and the scanning electron microscope with associated energy dispersive X ray chemical analysis. Several different types of second phase particles, some not reported by other investigators, were identified in the alloys. Fracture morphology was related to microstructural variables, test variables, and type of commercial product. Specimen orientation examined in the present investigation had little effect on fracture morphology. Test strain rate changes resulted in some change in shear fracture morphology, but not in fracture morphology of tensile specimens.

  6. Effects of irradiation to 4 dpa at 390 C on the fracture toughness of vanadium alloys

    SciTech Connect

    Gruber, E.E.; Galvin, T.M.; Chopra, O.K.

    1998-09-01

    Fracture toughness J-R curve tests were conducted at room temperature on disk-shaped compact-tension DC(T) specimens of three vanadium alloys having a nominal composition of V-4Cr-4Ti. The alloys in the nonirradiated condition showed high fracture toughness; J{sub IC} could not be determined but is expected to be above 600 kJ/m{sup 2}. The alloys showed very poor fracture toughness after irradiation to 4 dpa at 390 C, e.g., J{sub IC} values of {approx}10 kJ/m{sup 2} or lower.

  7. Synthesis of molybdenum disilicide by mechanical alloying

    SciTech Connect

    Schwarz, R.B.; Srinivasan, S.R.; Petrovic, J.J.; Maggiore, C.J.

    1991-01-01

    We have used mechanical alloying (MA), a high-energy ball-milling process, to prepare MoSi{sub 2} and MoSi{sub 2}-based alloys starting from mixtures of the pure elements. This synthesis route has the potential for preparing oxygen-free MoSi{sub 2} and the flexibility for close control of second-phase additions. MA, first developed for producing oxide-dispersions in Ni-based superalloys, takes advantage of the atomic-level mixing accomplished by the intense mechanical working of the alloy constituents. All the alloying reactions during the process occur in the solid-state. This technique is thus well-suited for synthesizing high melting point materials such as MoSi{sub 2}. The product of the MA process is a highly homogeneous and fine-grained powder. Its purity is determined by the purity of the starting materials and possible impurities introduced during processing. However, a careful control of the MA process enables a minimization of the impurities. We also report here the consolidation of the mechanically alloyed powder and the characterization of the MoSi{sub 2} alloys by optical and transmission electron microscopy, x-ray diffraction, and mechanical property measurements. 21 refs., 9 figs.

  8. Deformation and fracture of a particle-reinforced aluminum alloy composite: Part I. Experiments

    NASA Astrophysics Data System (ADS)

    Pandey, A. B.; Majumdar, B. S.; Miracle, D. B.

    2000-03-01

    Mechanical tests were performed on a powder-metallurgically processed 7093/SiC/15p discontinuously reinforced aluminum (DRA) composite in different heat-treatment conditions, to determine the influence of matrix characteristics on the composite response. The work-hardening exponent and the strain to failure varied inversely to the strength, similar to monolithic Al alloys, and this dependence was independent of the dominant damage mode. The damage consisted of SiC particle cracks, interface and near-interface debonds, and matrix rupture inside intense slip bands. Fracture surfaces revealed particle fracture-dominated damage for most of the heat-treatment conditions, including an overaged (OA) condition that exhibited a combination of precipitates at the interface and a precipitate-free zone (PFZ) in the immediate vicinity. In the highly OA conditions and in a 450°C as-rolled condition, when the composite strength became less than 400 MPa, near-interface matrix rupture became dominant. A combination of a relatively weak matrix and a weak zone around the particle likely contributed to this damage mode over that of particle fracture. Fracture-toughness tests show that it is important to maintain a proper geometry and testing procedure to obtain valid fracture-toughness data. Overaged microstructures did reveal a recovery of fracture toughness as compared to the peak-aged (PA) condition, unlike the lack of toughness recovery reported earlier for a similar 7XXX (Al-Zn-Cu-Mg)—based DRA. The PA material exhibited extensive localization of damage and plasticity. The low toughness of the DRA in this PA condition is explored in detail, using fractography and metallography. The damage and fracture micromechanisms formed the basis for modeling the strength, elongation, toughness, and damage, which are described in Part II of this work.

  9. Trace element effects on ductility and fracture of Ni-Cr-Ce alloys

    NASA Astrophysics Data System (ADS)

    Cosandey, F.; Kandra, J.

    1987-07-01

    The effect of trace additions of Ce, ranging from Oto 180 at. ppm, on the tensile behavior of a Ni-20Cr alloy is presented. For alloys without Ce a transition from ductile transgranular to brittle intergranular fracture mode is observed at high temperatures and for low strain-rate tests. Additions of Ce suppress this transition with a resulting increase in ductility. Maximum effects are observed for temperature and strain rate values where fracture in Ce-free alloys occurs via grain boundary cavitation. The reduced cavitation rate of Ce-containing alloys is suggested to be the result of an increase in both interfacial energy and grain boundary mobility.

  10. Mechanical properties of oxide dispersion strengthened (ODS) molybdenum alloys

    SciTech Connect

    Bianco, R.; Buckman, R.W. Jr.

    1998-03-01

    Oxide dispersion strengthened molybdenum, Mo-ODS, developed by a proprietary powder metallurgy process, exhibits a creep rupture life at 0.65T{sub m} (1,600 C) of three to five orders of magnitude greater than unalloyed molybdenum, while maintaining ductile fracture behavior at temperatures significantly below room temperature. In comparison, the creep rupture life of the Mo-50Re solid solution strengthened alloy at 1,600 C is only an order of magnitude greater than unalloyed molybdenum. The results of microstructural characterization and thermal stability and mechanical property testing are discussed.

  11. Ambient- to elevated-temperature fracture and fatigue properties of Mo-Si-B alloys: Role of microstructure

    NASA Astrophysics Data System (ADS)

    Kruzic, J. J.; Schneibel, J. H.; Ritchie, R. O.

    2005-09-01

    Ambient- to elevated-temperature fracture and fatigue-crack growth results are presented for five Mo-Mo3Si-Mo5SiB2-containing α-Mo matrix (17 to 49 vol pct) alloys, which are compared to results for intermetallic-matrix alloys with similar compositions. By increasing the α-Mo volume fraction, ductility, or microstructural coarseness, or by using a continuous α-Mo matrix, it was found that improved fracture and fatigue properties are achieved by promoting the active toughening mechanisms, specifically crack trapping and crack bridging by the α-Mo phase. Crack-initiation fracture toughness values increased from 5 to 12 MPa√m with increasing α-Mo content from 17 to 49 vol pct, and fracture toughness values rose with crack extension, ranging from 8.5 to 21 MPa√m at ambient temperatures. Fatigue thresholds benefited similarly from more α-Mo phase, and the fracture and fatigue resistance was improved for all alloys tested at 1300 °C, the latter effects being attributed to improved ductility of the α-Mo phase at elevated temperatures.

  12. A Study On Critical Thinning In Thin-walled Tube Bending Of Al-Alloy 5052O Via Coupled Ductile Fracture Criteria

    SciTech Connect

    Li Heng; Yang He; Zhan Mei

    2010-06-15

    Thin-walled tube bending(TWTB) method of Al-alloy tube has attracted wide applications in aerospace, aviation and automobile,etc. While, under in-plane double tensile stress states at the extrados of bending tube, the over-thinning induced ductile fracture is one dominant defect in Al-alloy tube bending. The main objective of this study is to predict the critical wall-thinning of Al-alloy tube bending by coupling two ductile fracture criteria(DFCs) into FE simulation. The DFCs include Continuum Damage Mechanics(CDM)-based model and GTN porous model. Through the uniaxial tensile test of the curved specimen, the basic material properties of the Al-alloy 5052O tube is obtained; via the inverse problem solution, the damage parameters of both the two fracture criteria are interatively determined. Thus the application study of the above DFCs in the TWTB is performed, and the more reasonable one is selected to obtain the critical thinning of Al-alloy tube in bending. The virtual damage initiation and evolution (when and where the ductile fracture occurs) in TWTB are investigated, and the fracture mechanisms of the voided Al-alloy tube in tube bending are consequently discussed.

  13. Crack branching in carbon steel. Fracture mechanisms

    NASA Astrophysics Data System (ADS)

    Syromyatnikova, A. S.; Alekseev, A. A.; Levin, A. I.; Lyglaev, A. V.

    2010-04-01

    The fracture surfaces of pressure vessels made of carbon steel that form during crack branching propagation are examined by fractography. Crack branching is found to occur at a crack velocity higher than a certain critical value V > V c . In this case, the material volume that is involved in fracture and depends on the elastoplastic properties of the material and the sample width has no time to dissipate the energy released upon crack motion via the damage mechanisms intrinsic in the material under given deformation conditions (in our case, via cracking according to intragranular cleavage).

  14. Size Effects in Linear Elastic Fracture Mechanics

    DTIC Science & Technology

    1988-01-01

    Recent Theoretical and Experimental Developments in Fracture Mechanics", Fracture 1977, 1 (1977) 695-723. 40 S. Mindess and J. S. Nadeau," Effect of Notch...0.4 1.42 b 2.0 0.80 b Mindess and Nadeau [40], 1.0 3.98 0.86 b Mortar, 3PB 8.03 0.80 b 12.0 0.82 b 16.0 0.84 b 20.0 0.83 b Concrete, 3PB 1.0 3.54 1.08

  15. A review of fracture mechanics life technology

    NASA Technical Reports Server (NTRS)

    Besuner, P. M.; Harris, D. O.; Thomas, J. M.

    1986-01-01

    Lifetime prediction technology for structural components subjected to cyclic loads is examined. The central objectives of the project are: (1) to report the current state of the art, and (2) recommend future development of fracture mechanics-based analytical tools for modeling subcritical fatigue crack growth in structures. Of special interest is the ability to apply these tools to practical engineering problems and the developmental steps necessary to bring vital technologies to this stage. The authors conducted a survey of published literature and numerous discussions with experts in the field of fracture mechanics life technology. One of the key points made is that fracture mechanics analyses of crack growth often involve consideration of fatigue and fracture under extreme conditions. Therefore, inaccuracies in predicting component lifetime will be dominated by inaccuracies in environment and fatigue crack growth relations, stress intensity factor solutions, and methods used to model given loads and stresses. Suggestions made for reducing these inaccuracies include development of improved models of subcritical crack growth, research efforts aimed at better characterizing residual and assembly stresses that can be introduced during fabrication, and more widespread and uniform use of the best existing methods.

  16. An Experimental Evaluation of Material Properties and Fracture Simulation of Cryorolled 7075 Al Alloy

    NASA Astrophysics Data System (ADS)

    Das, Prosenjit; Singh, I. V.; Jayaganthan, R.

    2012-07-01

    This work presents an experimental evaluation of yield strength, tensile strength, and impact toughness of 7075 Al alloy. The extended finite element method (XFEM) has been chosen for quasi-static crack growth simulations using Charpy impact energy as the crack growth criterion for both Bulk and ultrafine-grained (UFG) 7075 Al alloy. The 7075 Al alloy is rolled for different thickness reductions (40 and 70%) at cryogenic (liquid nitrogen) temperature, and its mechanical properties are studied by performing the tensile and Charpy impact testing. The microstructural characterization of the alloy was carried out using field emission scanning electron microscopy (FE-SEM). The rolling of the Al alloy at cryogenic temperature suppresses dynamic recovery, and dislocation cells formed during processing, transformed into fully formed ultrafine-grains (600 nm) at 70% thickness reduction. The impact energy used as the crack growth criterion under quasi-static loading condition based on the Griffith energy concept. The elastic-plastic ductile fracture simulations are performed by XFEM using ABAQUS Software (Version 6.9). For crack modeling, two different types of functions are used to model a crack based on partition of unity concept. A discontinuous function is used to model the portion behind the crack tip, whereas crack tip is modeled by near-tip asymptotic functions. This permits the crack is to be represented explicitly without meshing the crack surfaces, thus crack propagation simulations can be carried out without a need of re-meshing. Strain energy release and stress distribution ahead of the crack tip is found for some practical crack problems. The numerical examples indicate a significant improvement in crack growth properties of UFG 7075 Al alloy as compared to its bulk form due to an effective grain refinement.

  17. Cryogenic Fracture Toughness Evaluation of an Investment Cast Aluminum-Beryllium Alloy for Structural Applications

    NASA Technical Reports Server (NTRS)

    Gamwell, Wayne; McGill, Preston

    2006-01-01

    This document is a viewgraph presentation that details the fracture toughness of Aluminum-Beryllium Alloy for use in structures at cryogenic temperatures. Graphs and charts are presented in the presentation

  18. Mechanical properties of martensitic alloy AISI 422

    SciTech Connect

    Hamilton, M.L. ); Huang, F.H.; Hu, Wan-Liang )

    1992-06-01

    HT9 is a martensitic stainless steel that has been considered for structural applications in liquid metal reactors (LMRs) as well as in fusion reactors. AISI 422 is a commercially available martensitic stainless steel that closely resembles HT9, and was studied briefly under the auspices of the US LMR program. Previously unpublished tensile, fracture toughness and charpy impact data on AISI 422 were re-examined for potential insights into the consequences of the compositional differences between the two alloys, particularly with respect to current questions concerning the origin of the radiation-induced embrittlement observed in HT9.

  19. Mechanical properties of martensitic alloy AISI 422

    SciTech Connect

    Huang, F.H.; Hu, W.L. ); Hamilton, M.L. )

    1992-09-01

    HT9 is a martensitic stainless steel that has been considered for structural applications in liquid metal reactors (LMRs) as well as in fusion reactors. AISI 422 is a commercially available martensitic stainless steel that closely resembles HT9, and was studied briefly under the auspices of the US LMR program. Previously unpublished tensile, fracture toughness and charpy impact data on AISI 422 were reexamined for potential insights into the consequences of the compositional differences between the two alloys, particularly with respect to current questions concerning the origin of the radiation-induced embrittlement observed in HT9. 8 refs, 8 figs.

  20. Applications of advanced fracture mechanics to fuselage

    NASA Astrophysics Data System (ADS)

    Kanninen, M. F.; O'Donoghue, P. E.; Green, S. T.; Leung, C. P.; Roy, S.; Burnside, O. H.

    Multi-site damage (MSD) in the form of cracking at rivet holes in lap splice joints has been identified as a serious threat to the integrity of commercial aircraft nearing their design life targets. Consequently, to assure the safety of aircraft that have accumulated large numbers of flights, flight hours and years in service requires requires inspection procedures that are based on the possibility that MSD may be present. For inspections of aircraft components to be properly focused on me defect sizes that are critical for structural integrity, fracture analyses are needed. The current methods are essentially those of linear elastic fracture mechanics (LEFM) which are strictly valid only for cracks that extend in a quasi-static manner under small-scale crack tip plasticity conditions. While LEFM is very likely to be appropriate for subcritical crack growth, quantifying the conditions for fracture instability and subsequent propagation may require advanced fracture mechanics techniques. The specific focus in this paper was to identify the conditions in which inelastic-dynamic effects occur in (1) the linking up Of local damage in a lap splice joint to form a major crack, and (2) large-scale fuselage failure by a rapidly occurring fluid structure interaction process.

  1. Hexaferrite magnetic materials prepared by mechanical alloying

    NASA Astrophysics Data System (ADS)

    Ding, J.; Maurice, D.; Miao, W. F.; McCormick, P. G.; Street, R.

    1995-02-01

    The structure and properties of hexaferrites in the form of MFe 12O 19 with M = Ba, Sr and Pb prepared by mechanical alloying and heat treatment have been studied. Coercivities of 6-7 kOe were measured for Ba- and Sr-hexaferrite powders. The high values of coercivities have been associated with small particle sizes (˜ 0.1 μm) resulting from the mechanical alloying and subsequent heat treatment. High-coercivity anisotropic samples have been synthesized using hot-pressing, with remanences of 70-75% of the saturation magnetisation being obtained.

  2. Effect of laser peening with different energies on fatigue fracture evolution of 6061-T6 aluminum alloy

    NASA Astrophysics Data System (ADS)

    Sheng, J.; Huang, S.; Zhou, J. Z.; Lu, J. Z.; Xu, S. Q.; Zhang, H. F.

    2016-03-01

    To deeply understand the effect of laser peening (LP) with different laser pulse energies on 6061-T6 aluminum alloy, the fatigue fracture morphologies evolution process at various fatigue crack growth (FCG) stages and the corresponding strengthen mechanism were investigated. At the initial stage of FCG, more fatigue micro-cliffs were found after LP, while the fatigue striation spacing simultaneously reduced. A "stop-continue" phenomenon of crack propagation was discovered for laser peened samples. The fatigue striation spacing at the middle stage of FCG increased significantly while compared with that at the initial stage, in addition, the fatigue striation spacing decreased with an increase in laser pulse energy. Fracture morphologies in transition region of laser peened samples exhibit a mixing fracture characteristic of striations and dimples. The laser peened sample with laser pulse energy of 7 J presents more circuitous growing paths. Due to the complex stress state induced by LP, dimples with different sizes appeared in the final fracture region.

  3. Deformation and Fracture of P/M Titanium Alloys.

    DTIC Science & Technology

    1983-11-15

    provides to the graduate students involved. In the past fiscal year the program has supported: Roy Bourcier, Ph.D., August 1983; Barbara Lograsso, Ph.D...with Barbara Lograsso, Ph.D. candidate] The use of hot isostatic pressing (HIP) to compact both powders and castings to full density has been a...of Fracture. 16. F. A. McClintock , Journal of Applied Mechanics, 35, (1968) 363-371. 17. J. R. Rice and D. M. Tracey, Journal of the Mechanics and

  4. An investigation into the effects of hydrogen on the fracture and deformation of Alloy X-750

    SciTech Connect

    Symons, Douglas M.

    1994-11-01

    this study investigated the effect of hydrogen on the fracture of a nickel-base superalloy, Alloy X-750 in the solution treated and aged (HTH) condition. The effect of hydrogen was examined through tensile testing and fracture toughness testing incorporating observations from scanning electron microscopy and light microscopy.

  5. Fracture testing of large-scale thin-sheet aluminum alloy

    NASA Astrophysics Data System (ADS)

    Dewit, Roland; Fields, Richard J.; Low, Samuel R., III; Harne, Donald E.; Foecke, Tim

    1995-05-01

    A series of fracture tests on large-scale, pre-cracked, aluminum alloy panel was carried out to examine and to characterize the process by which cracks propagate and link up in this material. Extended grips and test fixtures were specially designed to enable the panel specimens to be loaded in tension in a 1780-kN-capacity universal testing machine. Using existing information, a test matrix was set up to explore regions of failure controlled by fracture mechanics, with additional tests near the boundary between plastic collapse and fracture. In addition, a variety of multiple site damage (MSD) configurations were included to distinguish between various proposed linkage mechanisms. All tests but one used anti-buckling guides. The data were analyzed by two different procedures: (1) the plastic zone model based on the residual strength diagram; and (2) the R-curve. The first three tests were used to determine the basic material properties, and these results were then used in the analysis of the subsequent tests with MSD cracks.

  6. Fracture toughness of Alloy 690 and EN52 weld in air and water

    SciTech Connect

    Brown, C.M.; Mills, W.J.

    1999-06-01

    The effect of low and high temperature water with high hydrogen on the fracture toughness of Alloy 690 and its weld, EN52, was characterized using elastic-plastic J{sub IC} methodology. While both materials display excellent fracture resistance in air and elevated temperature (>93 C) water, a dramatic degradation in toughness is observed in 54 C water. The loss of toughness is associated with a hydrogen-induced intergranular cracking mechanism where hydrogen is picked up from the water. Comparison of the cracking behavior in low temperature water with that for hydrogen-precharged specimens tested in air indicates that the critical local hydrogen content required to cause low temperature embrittlement is on the order of 120 to 160 ppm. Loading rate studies show that the cracking resistance is significantly improved at rates above ca. 1000 MPa{radical}m/h because there is insufficient time to produce grain boundary embrittlement. Electron fractographic examinations were performed to correlate cracking behavior with microstructural features and operative fracture mechanics.

  7. Fracture behavior of reinforced aluminum alloy matrix composites using thermal imaging tools

    NASA Astrophysics Data System (ADS)

    Avdelidis, N. P.; Exarchos, D.; Vazquez, P.; Ibarra-Castanedo, C.; Sfarra, S.; Maldague, X. P. V.; Matikas, T. E.

    2016-05-01

    In this work the influence of the microstructure at the vicinity of the interface on the fracture behavior of particulate-reinforced aluminum alloy matrix composites (Al/SiCp composites) is studied by using thermographic tools. In particular, infrared thermography was used to monitor the plane crack propagation behavior of the materials. The deformation of solid materials is almost always accompanied by heat release. When the material becomes deformed or is damaged and fractured, a part of the energy necessary to initiate and propagate the damage is transformed in an irreversible way into heat. The thermal camera detects the heat wave, generated by the thermo-mechanical coupling and the intrinsic dissipated energy during mechanical loading of the sample. By using an adapted detector, thermography records the two dimensional "temperature" field as it results from the infrared radiation emitted by the object. The principal advantage of infrared thermography is its noncontact, non-destructive character. This methodology is being applied to characterise the fracture behavior of the particulate composites. Infrared thermography is being used to monitor the plane crack propagation behavior of such materials. Furthermore, an innovative approach to use microscopic measurements using IR microscopic lenses was attempted, in order to enable smaller features (in the micro scale) to be imaged with accuracy and assurance.

  8. Stress Concentration and Fracture at Inter-variant Boundaries in an Al-Li Alloy

    NASA Technical Reports Server (NTRS)

    Crooks, Roy; Tayon, Wes; Domack, Marcia; Wagner, John; Beaudoin, Armand

    2009-01-01

    Delamination fracture has limited the use of lightweight Al-Li alloys. Studies of secondary, delamination cracks in alloy 2090, L-T fracture toughness samples showed grain boundary failure between variants of the brass texture component. Although the adjacent texture variants, designated B(sub s1) and B(sub s2), behave similarly during rolling, their plastic responses to mechanical tests can be quite different. EBSD data from through-thickness scans were used to generate Taylor factor maps. When a combined boundary normal and shear tensor was used in the calculation, the delaminating grains showed the greatest Taylor Factor differences of any grain pairs. Kernel Average Misorientation (KAM) maps also showed damage accumulation on one side of the interface. Both of these are consistent with poor slip accommodation from a crystallographically softer grain to a harder one. Transmission electron microscopy was used to confirm the EBSD observations and to show the role of slip bands in the development of large, interfacial stress concentrations. A viewgraph presentation accompanies the provided abstract.

  9. Mechanical Properties of Low Density Alloys at Cryogenic Temperatures

    NASA Astrophysics Data System (ADS)

    Jiao, X. D.; Li, L. F.; Liu, H. J.; Yang, K.

    2006-03-01

    Low-density alloys include aluminum alloys, titanium alloys and magnesium alloys. Aluminum alloys and titanium alloys have been widely investigated and used as structural materials for cryogenic applications because of their light weight and good low-temperature mechanical properties. For aerospace applications, persistent efforts are being devoted to reducing weight and improving performance. Magnesium alloys are the lightest structural alloys among those mentioned above. Therefore, it is necessary to pay attention to magnesium alloys and to investigate their behaviors at cryogenic temperatures. In this paper, we have investigated the mechanical properties and microstructures of some magnesium alloys at cryogenic temperatures. Experimental results on both titanium and magnesium alloys are taken into account in considering these materials for space application.

  10. Mechanical Properties of Low Density Alloys at Cryogenic Temperatures

    SciTech Connect

    Jiao, X. D.; Liu, H. J.; Li, L. F.; Yang, K.

    2006-03-31

    Low-density alloys include aluminum alloys, titanium alloys and magnesium alloys. Aluminum alloys and titanium alloys have been widely investigated and used as structural materials for cryogenic applications because of their light weight and good low-temperature mechanical properties.For aerospace applications, persistent efforts are being devoted to reducing weight and improving performance. Magnesium alloys are the lightest structural alloys among those mentioned above. Therefore, it is necessary to pay attention to magnesium alloys and to investigate their behaviors at cryogenic temperatures. In this paper, we have investigated the mechanical properties and microstructures of some magnesium alloys at cryogenic temperatures. Experimental results on both titanium and magnesium alloys are taken into account in considering these materials for space application.

  11. Interpretation of Fracture Toughness and R-Curve Behavior by Direct Observation of Microfracture Process in Ti-Based Dendrite-Containing Amorphous Alloys

    NASA Astrophysics Data System (ADS)

    Jeon, Changwoo; Kim, Choongnyun Paul; Kim, Hyoung Seop; Lee, Sunghak

    2015-04-01

    Fracture properties of Ti-based amorphous alloys containing ductile β dendrites were explained by directly observing microfracture processes. Three Ti-based amorphous alloys were fabricated by adding Ti, Zr, V, Ni, Al, and Be into a Ti-6Al-4V alloy by a vacuum arc melting method. The effective sizes of dendrites varied from 63 to 104 μm, while their volume fractions were almost constant within the range from 74 to 76 pct. The observation of the microfracture of the alloy containing coarse dendrites revealed that a microcrack initiated at the amorphous matrix of the notch tip and propagated along the amorphous matrix. In the alloy containing fine dendrites, the crack propagation was frequently blocked by dendrites, and many deformation bands were formed near or in front of the propagating crack, thereby resulting in a zig-zag fracture path. Crack initiation toughness was almost the same at 35 to 36 MPa√m within error ranges in the three alloys because it was heavily affected by the stress applied to the specimen at the time of crack initiation at the crack tip as well as strength levels of the alloys. According to the R-curve behavior, however, the best overall fracture properties in the alloy containing fine dendrites were explained by mechanisms of blocking of the crack growth and crack blunting and deformation band formation at dendrites.

  12. The radiation swelling effect on fracture properties and fracture mechanisms of irradiated austenitic steels. Part I. Ductility and fracture toughness

    NASA Astrophysics Data System (ADS)

    Margolin, B.; Sorokin, A.; Shvetsova, V.; Minkin, A.; Potapova, V.; Smirnov, V.

    2016-11-01

    The radiation swelling effect on the fracture properties of irradiated austenitic steels under static loading has been studied and analyzed from the mechanical and physical viewpoints. Experimental data on the stress-strain curves, fracture strain, fracture toughness and fracture mechanisms have been represented for austenitic steel of 18Cr-10Ni-Ti grade (Russian analog of AISI 321 steel) irradiated up to neutron dose of 150 dpa with various swelling. Some phenomena in mechanical behaviour of irradiated austenitic steels have been revealed and explained as follows: a sharp decrease of fracture toughness with swelling growth; untypical large increase of fracture toughness with decrease of the test temperature; some increase of fracture toughness after preliminary cyclic loading. Role of channel deformation and channel fracture has been clarified in the properties of irradiated austenitic steel and different tendencies to channel deformation have been shown and explained for the same austenitic steel irradiated at different temperatures and neutron doses.

  13. Dislocation Substructures Formed After Fracture of Deformed Polycrystalline Cu-Al Alloys

    NASA Astrophysics Data System (ADS)

    Koneva, N. A.; Trishkina, L. I.; Cherkasova, T. V.

    2017-08-01

    The paper deals with the dislocation substructure of polycrystalline FCC alloys modified by plastic deformation at a distance from the area of the specimen fracture. Observations are performed using the transmission electron microscopy. Cu-Al alloys with grain size ranging from 10 to 240 μm are studied in this paper. The parameters of the dislocation substructure are measured and their variation is determined by the increasing distance from the fracture area. It is shown how the grain size influences these processes. The different dislocation substructures which determine the specimen fracture at a mesocscale level are found herein.

  14. Numerical Fracture Analysis of Cryogenically Treated Alloy Steel Weldments

    NASA Astrophysics Data System (ADS)

    Rasool Mohideen, S.; Thamizhmanii, S.; Fatah, M. M. Muhammed Abdul; Saidin, W. Najmuddin W.

    2016-02-01

    Cryogenic treatment is being used commercially in the industries in the last two decades for improving the life of many engineering component such as bearings and cutting tools. Though their influence in improving the wear resistance of tool materials is well established, the effect of treatment on weldments is not much investigated. In the present work, a two dimensional finite element analysis was carried out on the compact tension specimen model for simulating the treatment process and to study the fracture behaviour. The weldments were modelled by thermo- mechanical coupled field analysis for simulating he temperature distribution in the model during weld pool cooling and introducing thermal stresses due to uneven contraction and cooling. The model was subjected to cryogenic treatment by adopting radiation effect. The fracture analysis was carried out using Rice's J- Integral approach. The analysis produced a similar outcome of experimental results i.e. Increase in the fracture toughness of the specimen after cryogenic treatment in the heat affected zone of weldment.

  15. Mechanical Alloying for Making Thermoelectric Compounds

    NASA Technical Reports Server (NTRS)

    Huang, Chen-Kuo; Fleurial, Jean-Pierre; Snyder, Jeffrey; Blair, Richard; May, Andrew

    2007-01-01

    An economical room-temperature mechanical alloying process has been shown to be an effective means of making a homogeneous powder that can be hot-pressed to synthesize a thermoelectric material having reproducible chemical composition. The synthesis of a given material consists of the room temperature thermomechanical-alloying process followed b y a hot-pressing process. Relative to synthesis of nominally the same material by a traditional process that includes hot melting, this s ynthesis is simpler and yields a material having superior thermoelect ric properties.

  16. Study of Fatigue and Fracture Behavior of Cr-Based Alloys and Intermetallic Materials

    SciTech Connect

    He, YH

    2001-01-31

    The microhardness, and tensile and fracture-toughness properties of drop-cast and directionally-solidified Cr-9.25 at.% (atomic percent) Ta alloys have been investigated. Directional solidification was found to soften the alloy, which could be related to the development of equilibrium and aligned microstructures. It was observed that the tensile properties of the Cr-Ta alloys at room and elevated temperatures could be improved by obtaining aligned microstructures. The directionally-solidified alloy also showed increased fracture toughness at room temperature. This trend is mainly associated with crack deflection and the formation of shear ribs in the samples with aligned microstructures. The sample with better-aligned lamellar exhibits greater fracture toughness.

  17. Directionally Solidified NiAl-Based Alloys Studied for Improved Elevated-Temperature Strength and Room-Temperature Fracture Toughness

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. Daniel; Raj, Sai V.; Locci, Ivan E.; Salem, Jonathan A.

    2000-01-01

    Efforts are underway to replace superalloys used in the hot sections of gas turbine engines with materials possessing better mechanical and physical properties. Alloys based on the intermetallic NiAl have demonstrated potential; however, they generally suffer from low fracture resistance (toughness) at room temperature and from poor strength at elevated temperatures. Directional solidification of NiAl alloyed with both Cr and Mo has yielded materials with useful toughness and elevated-temperature strength values. The intermetallic alloy NiAl has been proposed as an advanced material to extend the maximum operational temperature of gas turbine engines by several hundred degrees centigrade. This intermetallic alloy displays a lower density (approximately 30-percent less) and a higher thermal conductivity (4 to 8 times greater) than conventional superalloys as well as good high-temperature oxidation resistance. Unfortunately, unalloyed NiAl has poor elevated temperature strength (approximately 50 MPa at 1027 C) and low room-temperature fracture toughness (about 5 MPa). Directionally solidified NiAl eutectic alloys are known to possess a combination of high elevated-temperature strength and good room-temperature fracture toughness. Research has demonstrated that a NiAl matrix containing a uniform distribution of very thin Cr plates alloyed with Mo possessed both increased fracture toughness and elevated-temperature creep strength. Although attractive properties were obtained, these alloys were formed at low growth rates (greater than 19 mm/hr), which are considered to be economically unviable. Hence, an investigation was warranted of the strength and toughness behavior of NiAl-(Cr,Mo) directionally solidified at faster growth rates. If the mechanical properties did not deteriorate with increased growth rates, directional solidification could offer an economical means to produce NiAl-based alloys commercially for gas turbine engines. An investigation at the NASA Glenn

  18. The fracture resistance of 1420 and 1421 Al-Mg-Li alloys

    SciTech Connect

    Birt, M.J.; Hafley, R.A.; Wagner, J.A.; Lisagor, W.B. )

    1993-04-15

    Aluminum-magnesium-lithium alloy 1420 was developed in the form USSR as a lightweight, weldable, corrosion resistant alloy for aerospace applications. The alloy is primarily strengthened upon aging by the homogeneous precipitation of metastable [delta][prime] (Al[sub 3]Li). The equilibrium T-phase (Al[sub 2]MgLi) also precipitated during aging on grain boundaries and dislocations but does not contribute to strength and can have deleterious effects on fracture toughness. The addition of scandium, which refines the ingot grain structure, led to the evolution of alloy 1421 which exhibits higher strength and superior weldability compared to the earlier 1420 alloy. Zirconium is added to both alloys and forms a coherent precipitate, [beta][prime] (Al[sub 3]Zr), which acts as a recrystallization inhibitor. The fracture resistance of alloys 1420 and 1421 in the T6 temper has been examined by R-curve determination and the observed behavior has been compared with Al alloy, 2219-T87. The center-cracked (M(T)) sheet panels tested in this study were of sufficient width to produce stable crack growth to a [Delta]a of [approximately] 25 mm and the R-curves that were generated allowed for a comparison to be made of the stable crack growth resistance between the alloys in accordance with ASTM E561-86. The data presented are part of an extensive collaborative test program involving both private industry and government laboratories to evaluate the 1420 and 1421 alloys.

  19. Mechanical properties of low tantalum alloys

    NASA Technical Reports Server (NTRS)

    Kortovich, C. S.

    1982-01-01

    The mechanical property behavior of equiaxed cast B-1900 + Hf alloy as a function of tantalum content was studied. Tensile and stress rupture characterization was conducted on cast to size test bars containing tantalum at the 4.3% (standard level), 2.2% and 0% levels. Casting parameters were selected to duplicate conditions used to prepare test specimens for master metal heat qualification. The mechanical property results as well as results of microstructural/phase analysis of failed test bars are presented.

  20. Hot environment effects on alloy mechanical properties

    NASA Technical Reports Server (NTRS)

    Davidson, J. M.; Aning, K.; Tien, J. K.

    1976-01-01

    Prolonged high temperature performance of structural alloys requires joint attention to both corrosion and mechanical properties, and to their possible interactions. In this interpretive review paper, we provide a systematic compaction of theories and key observations on corrosion-mechanical properties interactions, from early single crystal work in the 1930s to recent studies on superalloys in nonoxidizing, oxidizing and hot corrosive environments. Particular attention is paid to environmental effects on creep, stress rupture and fatigue properties.

  1. Hydrogen pickup mechanism of zirconium alloys

    NASA Astrophysics Data System (ADS)

    Couet, Adrien

    Although the optimization of zirconium based alloys has led to significant improvements in hydrogen pickup and corrosion resistance, the mechanisms by which such alloy improvements occur are still not well understood. In an effort to understand such mechanisms, a systematic study of the alloy effect on hydrogen pickup is conducted, using advanced characterization techniques to rationalize precise measurements of hydrogen pickup. The hydrogen pick-up fraction is accurately measured for a specially designed set of commercial and model alloys to investigate the effects of alloying elements, microstructure and corrosion kinetics on hydrogen uptake. Two different techniques to measure hydrogen concentrations were used: a destructive technique, Vacuum Hot Extraction, and a non-destructive one, Cold Neutron Prompt Gamma Activation Analysis. The results indicate that hydrogen pickup varies not only from alloy to alloy but also during the corrosion process for a given alloy. For instance Zircaloy type alloys show high hydrogen pickup fraction and sub-parabolic oxidation kinetics whereas ZrNb alloys show lower hydrogen pickup fraction and close to parabolic oxidation kinetics. Hypothesis is made that hydrogen pickup result from the need to balance charge during the corrosion reaction, such that the pickup of hydrogen is directly related to (and indivisible of) the corrosion mechanism and decreases when the rate of electron transport or oxide electronic conductivity sigmao xe through the protective oxide increases. According to this hypothesis, alloying elements (either in solid solution or in precipitates) embedded in the oxide as well as space charge variations in the oxide would impact the hydrogen pick-up fraction by modifying sigmaox e, which drives oxidation and hydriding kinetics. Dedicated experiments and modelling were performed to assess and validate these hypotheses. In-situ electrochemical impedance spectroscopy (EIS) experiments were performed on Zircaloy-4 tubes

  2. Magnetic properties of metastable Fe Pd alloys by mechanical alloying

    NASA Astrophysics Data System (ADS)

    Yabe, Hiromasa; O'Handley, Robert C.; Kuji, Toshiro

    2007-03-01

    Metastable Fe-Pd powder samples with various Pd content were synthesized by mechanical alloying. Their fundamental properties, i.e., structure, magnetization and coercive fore are discussed. The saturation magnetizations of the metastable Fe-Pd powders gradually decreases with increasing Pd content. The coercive forces observed in as-milled samples are all less than 40 Oe. However, some of the heat-treated samples, notably, Pd content around 55 at% with L1 0 structure, shows Hc up to 1589 Oe.

  3. Deformation and fracture of a directionally solidified NiAl-28Cr-6Mo eutectic alloy

    NASA Technical Reports Server (NTRS)

    Chen, X. F.; Johnson, D. R.; Noebe, R. D.; Oliver, B. F.

    1995-01-01

    A directionally solidified alloy based on the NiAl-(Cr, Mo) eutectic was examined by transmission and scanning electron microscopy to characterize the microstructure and room temperature deformation and fracture behavior. The microstructure consisted of a lamellar morphology with a group of zone axes (111) growth direction for both the NiAl and (Cr, Mo) phases. The interphase boundary between the eutectic phases was semicoherent and composed of a well-defined dislocation network. In addition, a fine array of coherent NiAl precipitates was dispersed throughout the (Cr, Mo) phase. The eutectic morphology was stable at 1300 K with only coarsening of the NiAl precipitates occurring after heat treatment for 1.8 ks (500 h). Fracture of the aligned eutectic is characterized primarily by a crack bridging/renucleation mechanism and is controlled by the strength of the semicoherent interface between the two phases. However, contributions to the toughness of the eutectic may arise from plastic deformation of the NiAl phase and the geometry associated with the fracture surface.

  4. Deformation and fracture of a directionally solidified NiAl-28Cr-6Mo eutectic alloy

    SciTech Connect

    Chen, X.F.; Johnson, D.R.; Noebe, R.D.; Oliver, B.F.

    1995-05-01

    A directionally solidified alloy based on the NiAl-(Cr, Mo) eutectic was examined by transmission and scanning electron microscopy to characterize the microstructure and room temperature deformation and fracture behavior. The microstructure consisted of a lamellar morphology with a group of zone axes (111) growth direction for both the NiAl and (Cr, Mo) phases. The interphase boundary between the eutectic phases was semicoherent and composed of a well-defined dislocation network. In addition, a fine array of coherent NiAl precipitates was dispersed throughout the (Cr, Mo) phase. The eutectic morphology was stable at 1300 K with only coarsening of the NiAl precipitates occurring after heat treatment for 1.8 ks (500 h). Fracture of the aligned eutectic is characterized primarily by a crack bridging/renucleation mechanism and is controlled by the strength of the semicoherent interface between the two phases. However, contributions to the toughness of the eutectic may arise from plastic deformation of the NiAl phase and the geometry associated with the fracture surface.

  5. A comparative assessment of the fracture toughness behavior of ferritic-martensitic steels and nanostructured ferritic alloys

    NASA Astrophysics Data System (ADS)

    Byun, Thak Sang; Hoelzer, David T.; Kim, Jeoung Han; Maloy, Stuart A.

    2017-02-01

    The Fe-Cr alloys with ultrafine microstructures are primary candidate materials for advanced nuclear reactor components because of their excellent high temperature strength and high resistance to radiation-induced damage such as embrittlement and swelling. Mainly two types of Fe-Cr alloys have been developed for the high temperature reactor applications: the quenched and tempered ferritic-martensitic (FM) steels hardened primarily by ultrafine laths and carbonitrides and the powder metallurgy-based nanostructured ferritic alloys (NFAs) by nanograin structure and nanoclusters. This study aims at elucidating the differences and similarities in the temperature and strength dependences of fracture toughness in the Fe-Cr alloys to provide a comparative assessment of their high-temperature structural performance. The KJQ versus yield stress plots confirmed that the fracture toughness was inversely proportional to yield strength. It was found, however, that the toughness data for some NFAs were outside the band of the integrated dataset at given strength level, which indicates either a significant improvement or deterioration in mechanical properties due to fundamental changes in deformation and fracture mechanisms. When compared to the behavior of NFAs, the FM steels have shown much less strength dependence and formed narrow fracture toughness data bands at a significantly lower strength region. It appeared that at high temperatures ≥600 °C the NFAs cannot retain the nanostructure advantage of high strength and high toughness either by high-temperature embrittlement or by excessive loss of strength. Irradiation studies have revealed, however, that the NFAs have much stronger radiation resistance than tempered martensitic steels, such as lower radiation-induced swelling, finer helium bubble formation, lower irradiation creep rate and reduced low temperature embrittlement.

  6. A comparative assessment of the fracture toughness behavior of ferritic-martensitic steels and nanostructured ferritic alloys

    DOE PAGES

    Byun, Thak Sang; Hoelzer, David T.; Kim, Jeoung Han; ...

    2016-12-07

    The Fe-Cr alloys with ultrafine microstructures are primary candidate materials for advanced nuclear reactor components because of their excellent high temperature strength and high resistance to radiation-induced damage such as embrittlement and swelling. Mainly two types of Fe-Cr alloys have been developed for the high temperature reactor applications: the quenched and tempered ferritic-martensitic (FM) steels hardened primarily by ultrafine laths and carbonitrides and the powder metallurgy-based nanostructured ferritic alloys (NFAs) by nanograin structure and nanoclusters. This paper aims at elucidating the differences and similarities in the temperature and strength dependences of fracture toughness in the Fe-Cr alloys to provide amore » comparative assessment of their high-temperature structural performance. The KJQ versus yield stress plots confirmed that the fracture toughness was inversely proportional to yield strength. It was found, however, that the toughness data for some NFAs were outside the band of the integrated dataset at given strength level, which indicates either a significant improvement or deterioration in mechanical properties due to fundamental changes in deformation and fracture mechanisms. When compared to the behavior of NFAs, the FM steels have shown much less strength dependence and formed narrow fracture toughness data bands at a significantly lower strength region. It appeared that at high temperatures ≥600 °C the NFAs cannot retain the nanostructure advantage of high strength and high toughness either by high-temperature embrittlement or by excessive loss of strength. Finally, irradiation studies have revealed, however, that the NFAs have much stronger radiation resistance than tempered martensitic steels, such as lower radiation-induced swelling, finer helium bubble formation, lower irradiation creep rate and reduced low temperature embrittlement.« less

  7. A comparative assessment of the fracture toughness behavior of ferritic-martensitic steels and nanostructured ferritic alloys

    SciTech Connect

    Byun, Thak Sang; Hoelzer, David T.; Kim, Jeoung Han; Maloy, Stuart A.

    2016-12-07

    The Fe-Cr alloys with ultrafine microstructures are primary candidate materials for advanced nuclear reactor components because of their excellent high temperature strength and high resistance to radiation-induced damage such as embrittlement and swelling. Mainly two types of Fe-Cr alloys have been developed for the high temperature reactor applications: the quenched and tempered ferritic-martensitic (FM) steels hardened primarily by ultrafine laths and carbonitrides and the powder metallurgy-based nanostructured ferritic alloys (NFAs) by nanograin structure and nanoclusters. This paper aims at elucidating the differences and similarities in the temperature and strength dependences of fracture toughness in the Fe-Cr alloys to provide a comparative assessment of their high-temperature structural performance. The KJQ versus yield stress plots confirmed that the fracture toughness was inversely proportional to yield strength. It was found, however, that the toughness data for some NFAs were outside the band of the integrated dataset at given strength level, which indicates either a significant improvement or deterioration in mechanical properties due to fundamental changes in deformation and fracture mechanisms. When compared to the behavior of NFAs, the FM steels have shown much less strength dependence and formed narrow fracture toughness data bands at a significantly lower strength region. It appeared that at high temperatures ≥600 °C the NFAs cannot retain the nanostructure advantage of high strength and high toughness either by high-temperature embrittlement or by excessive loss of strength. Finally, irradiation studies have revealed, however, that the NFAs have much stronger radiation resistance than tempered martensitic steels, such as lower radiation-induced swelling, finer helium bubble formation, lower irradiation creep rate and reduced low temperature embrittlement.

  8. Comparison of the Effect of Individual and Combined Zr and Mn Additions on the Fracture Behavior of Al-Cu-Li Alloy AA2198 Rolled Sheet

    NASA Astrophysics Data System (ADS)

    Tsivoulas, Dimitrios; Prangnell, Philip B.

    2013-11-01

    The effect of individual and combined addition of dispersoid-forming alloying elements Zr and Mn on the fracture behavior of the Al-Cu-Li alloy 2198 has been investigated by the Kahn tear test. Overall, the standard baseline 2198 alloy containing only Zr exhibited the best performance, while the alloy with the combined presence of Zr and Mn was slightly inferior. The lowest properties were seen for a Zr-free 2198-0.4Mn alloy variant. In the T351 temper fracture initiated at coarse constituent particles that formed large cavities and microvoid sheets linked the initial sites of void growth. In the Mn-containing alloys microvoids clearly nucleated at the coarser Al20Cu2Mn3 dispersoids within the microstructure, while this was not identifiable for the finer coherent Al3Zr dispersoids. However, this difference in the mechanism of cavity linkage had little effect on the overall toughness of the materials, which was more closely related to the effect of Mn and Zr on the level of recrystallization. Extended artificial aging promoted grain boundary decohesion due to the precipitation of high densities of T1 particles on GBs and favored a cleavage fracture mode. Particle decohesive fracture was also promoted by T1 precipitation on the Mn dispersoids.

  9. Experiments and FEM simulations of fracture behaviors for ADC12 aluminum alloy under impact load

    NASA Astrophysics Data System (ADS)

    Hu, Yumei; Xiao, Yue; Jin, Xiaoqing; Zheng, Haoran; Zhou, Yinge; Shao, Jinhua

    2016-11-01

    Using the combination of experiment and simulation, the fracture behavior of the brittle metal named ADC12 aluminum alloy was studied. Five typical experiments were carried out on this material, with responding data collected on different stress states and dynamic strain rates. Fractographs revealed that the morphologies of fractured specimen under several rates showed different results, indicating that the fracture was predominantly a brittle one in nature. Simulations of the fracture processes of those specimens were conducted by Finite Element Method, whilst consistency was observed between simulations and experiments. In simulation, the Johnson- Cook model was chosen to describe the damage development and to predict the failure using parameters determined from those experimental data. Subsequently, an ADC12 engine mount bracket crashing simulation was conducted and the results indicated good agreement with the experiments. The accordance showed that our research can provide an accurate description for the deforming and fracture processes of the studied alloy.

  10. Enhancement of Impact Toughness by Delamination Fracture in a Low-Alloy High-Strength Steel with Al Alloying

    NASA Astrophysics Data System (ADS)

    Sun, Junjie; Jiang, Tao; Liu, Hongji; Guo, Shengwu; Liu, Yongning

    2016-12-01

    The effect of delamination toughening of martensitic steel was investigated both at room and low temperatures [253 K and 233 K (-20 °C and -40 °C)]. Two low-alloy martensitic steels with and without Al alloying were both prepared. Layered structure with white band and black matrix was observed in Al alloyed steel, while a homogeneous microstructure was displayed in the steel without Al. Both steels achieved high strength (tensile strength over 1600 MPa) and good ductility (elongation over 11 pct), but they displayed stark contrasts on impact fracture mode and Charpy impact energy. Delamination fracture occurred in Al alloyed steel and the impact energies were significantly increased both at room temperature (from 75 to 138 J, i.e., nearly improved up to 2 times) and low temperatures [from 47.9 to 71.3 J at 233 K (-40 °C)] compared with the one without Al. Alloying with Al promotes the segregation of Cr, Mn, Si and C elements to form a network structure, which is martensite with higher carbon content and higher hardness than that of the matrix. And this network structure evolved into a band structure during the hot rolling process. The difference of yield stress between the band structure and the matrix gives rise to a delamination fracture during the impact test, which increases the toughness greatly.

  11. In vitro mechanical integrity of hydroxyapatite coated magnesium alloy.

    PubMed

    Kannan, M Bobby; Orr, Lynnley

    2011-08-01

    The mechanical integrity of resorbable implants during service, especially in load bearing orthopaedic applications, is critical. The high degradation rate of resorbable magnesium and magnesium-based implants in body fluid may potentially cause premature in-service failure. In this study, a magnesium alloy (AZ91) was potentiostatically coated with hydroxyapatite at different cathodic voltages in an attempt to enhance the mechanical integrity. The mechanical integrity of the uncoated and hydroxyapatite coated alloys was evaluated after in vitro testing of the coated samples in simulated body fluid (SBF). The uncoated alloy showed 40% loss in the mechanical strength after five days exposure to SBF. However, the hydroxyapatite coated alloy exposed to SBF showed 20% improvement in the mechanical strength as compared to that of the uncoated alloy. The alloy coated potentiostatically at -2 V performed better than the -3 V coated alloy. The cross-sectional analysis of the coatings revealed relatively uniform coating thickness for the -2 V coated alloy, whereas the -3 V coated alloy exhibited areas of uneven coating. This can be attributed to the increase in hydrogen evolution on the alloy during -3 V coating as compared to -2 V coating. The scanning electron micrographs of the in vitro tested alloy revealed that hydroxyapatite coating significantly reduced the localized corrosion of the alloy, which is critical for better in-service mechanical integrity. Thus, the study suggests that the in vitro mechanical integrity of resorbable magnesium-based alloy can be improved by potentiostatic hydroxyapatite coating.

  12. Correlation of microstructure and fracture toughness in high-chromium white iron hardfacing alloys

    SciTech Connect

    Lee, S.; Choo, S.H.; Kim, N.J.; Baek, E.R.; Ahn, S.

    1996-12-01

    A correlation is made of microstructure and fracture toughness in hypereutectic high-chromium white iron hardfacing alloys. In order to investigate the matrix effect of these alloys, in particular, four different matrices such as pearlite, austenite, and a mixture of pearlite and austenite were employed by changing the ratio of Mn/Si, while the total volume fraction of carbides was fixed. The hardfacing alloys were deposited twice on a mild steel plate by the self-shielding flux-cored arc-welding method. Fracture toughness was increased by increasing the volume fraction of austenite in the matrix, whereas hardness and abrasion resistance were nearly constant. In situ observation of the fracture process showed that cracks initiated at large primary carbides tended to be blocked at the austenitic matrix. This suggested that fracture toughness was controlled mainly by the amount of austenite in the matrix, thereby yielding the better toughness in the hardfacing alloy having the austenitic matrix. Considering both abrasion resistance and fracture toughness, therefore, the austenitic matrix was preferred for the high-chromium white iron hardfacing alloys.

  13. Correlation of microstructure and fracture toughness in high-chromium white iron hardfacing alloys

    NASA Astrophysics Data System (ADS)

    Lee, Sunghak; Choo, Seong-Hun; Kim, Nack J.; Baek, Eung-Ryul; Ahn, Sangho

    1996-12-01

    A correlation is made of microstructure and fracture toughness in hypereutectic high-chromium white iron hardfacing alloys. In order to investigate the matrix effect of these alloys, in particular, four different matrices such as pearlite, austenite, and a mixture of pearlite and austenite were employed by changing the ratio of Mn/Si, while the total volume fraction of carbides was fixed. The hardfacing alloys were deposited twice on a mild steel plate by the self-shielding flux-cored arc-welding method. Fracture toughness was increased by increasing the volume fraction of austenite in the matrix, whereas hardness and abrasion resistance were nearly constant. In situ observation of the fracture process showed that cracks initiated at large primary carbides tended to be blocked at the austenitic matrix. This suggested that fracture toughness was controlled mainly by the amount of austenite in the matrix, thereby yielding the better toughness in the hardfacing alloy having the austenitic matrix. Considering both abrasion resistance and fracture toughness, therefore, the austenitic matrix was preferred for the high-chromium white iron hardfacing alloys.

  14. Analogy between fluid cavitation and fracture mechanics

    NASA Technical Reports Server (NTRS)

    Hendricks, R. C.; Mullen, R. L.; Braun, M. J.

    1983-01-01

    When the stresses imposed on a fluid are sufficiently large, rupture or cavitation can occur. Such conditions can exist in many two-phase flow applications, such as the choked flows, which can occur in seals and bearings. Nonspherical bubbles with large aspect ratios have been observed in fluids under rapid acceleration and high shear fields. These bubbles are geometrically similar to fracture surface patterns (Griffith crack model) existing in solids. Analogies between crack growth in solid and fluid cavitation are proposed and supported by analysis and observation (photographs). Healing phenomena (void condensation), well accepted in fluid mechanics, have been observed in some polymers and hypothesized in solid mechanics. By drawing on the strengths of the theories of solid mechanics and cavitation, a more complete unified theory can be developed.

  15. Effects of Ca and Ce Addition on Tensile and Fracture Properties in Squeeze Cast AT42(Mg-4Al-2Sn) Magnesium Alloys

    NASA Astrophysics Data System (ADS)

    Do, Jeonghyeon; Kim, Byeongho; Park, Yongho; Park, Ikmin; Lee, Sunghak

    2012-08-01

    The effects of the addition of Ca and Ce to the AT42(Mg-4Al-2Sn) alloy on the microstructural modification and deformation, as well as the fracture mechanisms of squeeze cast magnesium alloys, were investigated in this study. Microstructural analyses indicated that the AT42 alloy contained Mg17Al12 and Mg2Sn particles precipitated along cell boundaries, whereas long, needle-shaped CaMgSn particles were precipitated additionally in the AT42-0.5Ca and AT42-1Ca alloys. In the AT42-1Ca-0.5Ce and AT42-1Ca-1Ce alloys containing Al11Ce3 particles as well as Mg17Al12, Mg2Sn, and CaMgSn particles, the overall distribution of precipitates was homogeneously modified considerably as the solidification cell size was refined. According to the observation of deformation and the fracture processes of the AT42-1Ca alloys, the fracture proceeded mainly along cracked, needle-shaped CaMgSn particles at a relatively low stress-intensity factor level. However, in the AT42-1Ca-1Ce alloys, the deformation and fracture proceeded into cells rather than into cell boundaries as twins were developed actively inside cells, although few microcracks were initiated at the precipitates. Thus, the AT42-1Ca-1Ce alloy had the highest strength, ductility, and fracture toughness simultaneously because of the increase in the volume fraction of hard precipitates and the development of many twins in the Mg matrix.

  16. Fracture of Sn-Ag-Cu Solder Joints on Cu Substrates. II: Fracture Mechanism Map

    NASA Astrophysics Data System (ADS)

    Kumar, P.; Huang, Z.; Dutta, I.; Sidhu, R.; Renavikar, M.; Mahajan, R.

    2012-02-01

    A methodology to construct fracture mechanism maps for Sn-3.8%Ag-0.7%Cu (SAC387) solder joints attached to Cu substrates has been developed. The map, which delineates the operative mechanisms of fracture along with corresponding joint fracture toughness values, is plotted in a space described by two microstructure-dependent parameters, with the abscissa describing the interfacial intermetallic compound (IMC) and the ordinate representing the strain-rate-dependent solder yield strength. The plot space encompasses the three major mechanisms by which joints fail, namely (i) cohesive fracture of solder, (ii) cleavage fracture of interfacial intermetallic compounds (IMC), and (iii) fracture of the solder-IMC interface. Line contours of constant fracture toughness values, as well as constant fraction of each of the above mechanisms, are indicated on the plots. The plots are generated by experimentally quantifying the dependence of the operative fracture mechanism(s) on the two microstructure-dependent parameters (IMC geometry and solder yield strength) as functions of strain rate, reflow parameters, and post-reflow aging. Separate maps are presented for nominally mode I and equi-mixed mode loading conditions (loading angle ϕ = 0° and 45°, respectively). The maps allow rapid assessment of the operative fracture mechanism(s) along with estimation of the expected joint fracture toughness value for a given loading condition (strain rate and loading angle) and joint microstructure without conducting actual tests, and may serve as a tool for both prediction and microstructure design.

  17. Laser micromachining for fatigue and fracture mechanics applications

    NASA Astrophysics Data System (ADS)

    Gupta, M. C.; Li, B.; Gadag, S.; Chou, K. C.

    2010-04-01

    A laser micromachining (LMM) method to initiate flaws for fatigue and fracture mechanics applications is successfully demonstrated. Dynamic response of moving energy pulses during LMM of titanium alloy (Ti-3.5Al-2.5V) was numerically simulated by an integrated energy approach using temperature-dependent thermophysical properties and 3D heat transfer code. Stress and strain analyses were performed for a titanium tube of 9.53 mm outer diameter (OD) and 0.81 mm wall thickness (WT) with a 0.23 mm deep and 1.83-mm-long longitudinal laser micro-machined notch, using nonlinear finite element analysis (FEA). For comparison, an electric-discharge-machined (EDM) notched tube with the same notch profile as the laser-prepared tube was also investigated. The calculated hoop stress and strain amplitudes at the notch root of the EDM-prepared tube were approximately 64% and 63% of the stress and strain amplitudes in the laser-prepared tube, respectively, when two tubes were subjected to inner pressures for R ratio of 0.03 and Δ P=45, 50, and 55 MPa. Fatigue life due to crack initiation process can be minimized using LMM method. The described LMM method is, therefore, more appropriate than EDM for accomplishing flaw formation to study fatigue and fracture behavior of various materials.

  18. References and conference proceedings towards the understanding of fracture mechanics

    NASA Technical Reports Server (NTRS)

    Toor, P. M.; Hudson, C. M.

    1986-01-01

    A list of books, reports, periodicals, and conference proceedings, as well as individual papers, centered on specific aspects of fracture phenomenon has been compiled by the ASTM Committee E-24 on Fracture Testing. A list of basic references includes the articles on the development of fracture toughness, evaluation of stress intensity factors, fatigue crack growth, fracture testing, fracture of brittle materials, and fractography. Special attention is given to the references on application of fracture mechanics to new designs and on reevaluation of failed designs, many of them concerned with naval and aircraft structures.

  19. Microstructure and Room-Temperature Mechanical Properties of FeCrMoVTi x High-Entropy Alloys

    NASA Astrophysics Data System (ADS)

    Guo, Jun; Huang, Xuefei; Huang, Weigang

    2017-07-01

    FeCrMoVTi x ( x values represent the molar ratio, where x = 0, 0.5, 1.0, 1.5, and 2.0) high-entropy alloys were prepared by a vacuum arc melting method. The effects of Ti element on the microstructure and room-temperature mechanical properties of the as-cast FeCrMoVTi x alloys were investigated. The results show that the prepared alloys exhibited typical dendritic microstructure and the size of the microstructure became fine with increasing Ti content. The FeCrMoV alloy exhibited a single body-centered cubic structure (BCC1) and the alloys prepared with Ti element exhibited BCC1 + BCC2 mixed structure. The new BCC2 phase is considered as (Fe, Ti)-rich phase and was distributed in the dendrite region. With the increase of Ti content, the volume fraction of the BCC2 phase increased and its shape changed from a long strip to a network. For the FeCrMoV alloy, the fracture strength, plastic strain, and hardness reached as high as 2231 MPa, 28.2%, and 720 HV, respectively. The maximum hardness of 887 HV was obtained in the FeCrMoVTi alloy. However, the fracture strength, yield stress, and plastic strain of the alloys decreased continuously as Ti content increased. In the room-temperature compressive test, the alloys showed typical brittle fracture characteristics.

  20. The effect of copper, chromium, and zirconium on the microstructure and mechanical properties of Al-Zn-Mg-Cu alloys

    NASA Technical Reports Server (NTRS)

    Wagner, John A.; Shenoy, R. N.

    1991-01-01

    The present study evaluates the effect of the systematic variation of copper, chromium, and zirconium contents on the microstructure and mechanical properties of a 7000-type aluminum alloy. Fracture toughness and tensile properties are evaluated for each alloy in both the peak aging, T8, and the overaging, T73, conditions. Results show that dimpled rupture essentially characterize the fracture process in these alloys. In the T8 condition, a significant loss of toughness is observed for alloys containing 2.5 pct Cu due to the increase in the quantity of Al-Cu-Mg-rich S-phase particles. An examination of T8 alloys at constant Cu levels shows that Zr-bearing alloys exhibit higher strength and toughness than the Cr-bearing alloys. In the T73 condition, Cr-bearing alloys are inherently tougher than Zr-bearing alloys. A void nucleation and growth mechanism accounts for the loss of toughness in these alloys with increasing copper content.

  1. The effect of copper, chromium, and zirconium on the microstructure and mechanical properties of Al-Zn-Mg-Cu alloys

    NASA Technical Reports Server (NTRS)

    Wagner, John A.; Shenoy, R. N.

    1991-01-01

    The present study evaluates the effect of the systematic variation of copper, chromium, and zirconium contents on the microstructure and mechanical properties of a 7000-type aluminum alloy. Fracture toughness and tensile properties are evaluated for each alloy in both the peak aging, T8, and the overaging, T73, conditions. Results show that dimpled rupture essentially characterize the fracture process in these alloys. In the T8 condition, a significant loss of toughness is observed for alloys containing 2.5 pct Cu due to the increase in the quantity of Al-Cu-Mg-rich S-phase particles. An examination of T8 alloys at constant Cu levels shows that Zr-bearing alloys exhibit higher strength and toughness than the Cr-bearing alloys. In the T73 condition, Cr-bearing alloys are inherently tougher than Zr-bearing alloys. A void nucleation and growth mechanism accounts for the loss of toughness in these alloys with increasing copper content.

  2. In vitro degradation and mechanical integrity of calcium-containing magnesium alloys in modified-simulated body fluid.

    PubMed

    Kannan, M Bobby; Raman, R K Singh

    2008-05-01

    The successful applications of magnesium-based alloys as degradable orthopaedic implants are mainly inhibited due to their high degradation rates in physiological environment and consequent loss in the mechanical integrity. This study examines the degradation behaviour and the mechanical integrity of calcium-containing magnesium alloys using electrochemical techniques and slow strain rate test (SSRT) method, respectively, in modified-simulated body fluid (m-SBF). Potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) results showed that calcium addition enhances the general and pitting corrosion resistances of magnesium alloys significantly. The corrosion current was significantly lower in AZ91Ca alloy than that in AZ91 alloy. Furthermore, AZ91Ca alloy exhibited a five-fold increase in the surface film resistance than AZ91 alloy. The SSRT results showed that the ultimate tensile strength and elongation to fracture of AZ91Ca alloy in m-SBF decreased only marginally (approximately 15% and 20%, respectively) in comparison with these properties in air. The fracture morphologies of the failed samples are discussed in the paper. The in vitro study suggests that calcium-containing magnesium alloys to be a promising candidate for their applications in degradable orthopaedic implants, and it is worthwhile to further investigate the in vivo corrosion behaviour of these alloys.

  3. Fracture behavior of large-scale thin-sheet aluminum alloy

    NASA Technical Reports Server (NTRS)

    Dewit, Roland; Fields, Richard J.; Mordfin, Leonard; Low, Samuel R.; Harne, Donald

    1994-01-01

    A series of fracture tests on large-scale, pre-cracked, aluminum alloy panels is being carried out to examine and to characterize the process by which cracks propagate and link up in this material. Extended grips and test fixtures were specially designed to enable the panel specimens to be loaded in tension, in a 1780-kN-capacity universal testing machine. Twelve panel specimens, each consisting of a single sheet of bare 2024-T3 aluminum alloy, 3988 mm high, 2286 mm wide, and 1.016 mm thick are being fabricated with simulated through-cracks oriented horizontally at mid-height. Using existing information, a test matrix has been set up that explores regions of failure that are controlled by fracture mechanics, with additional tests near the boundary between plastic collapse and fracture. In addition, a variety of multiple site damage (MSD) configurations have been included to distinguish between various proposed linkage mechanisms. All tests but one use anti-buckling guides. At this writing seven specimens have been tested. Three were fabricated with a single central crack, three others had multiple cracks on each side of the central crack, and one had a single crack but no anti-buckling guides. Each fracture event was recorded on film, video, computer, magnetic tape, and occasionally optical microscopy. The visual showed the crack tip with a load meter in the field of view, using motion picture film for one tip and SVHS video tape for the other. The computer recorded the output of the testing machine load cell, the stroke, and twelve strain gages at 1.5 second intervals. A wideband FM magnetic tape recorder was used to record data from the same sources. The data were analyzed by two different procedures: (1) the plastic zone model based on the residual strength diagram; and (2) the R-curve. The first three tests were used to determine the basic material properties, and these results were then used in the analysis of the two subsequent tests with MSD cracks. There is

  4. Osteoimmune Mechanisms of Segmental Bone Fracture Healing and Therapy

    DTIC Science & Technology

    2016-09-01

    it is essential to understand additional mechanisms that play a crucial role in bone healing through participation of cells other than osteoblasts...osteoclasts and their respective progenitors. Bone fractures heal with overlapping phases of inflammation, cell proliferation, and bone remodeling...fracture healing. During fracture repair, there is an abundant infiltration of immune cells at the fracture site that not only mediate the inflammatory

  5. Mechanical properties of 50Molybdenum-50Rhenium alloys and their assembly by spinal muscular atrophy

    NASA Astrophysics Data System (ADS)

    Xu, Jianhui

    This study is concerned with the deformation and fracture behaviors, especially strain-rate effect on plasticity in tensile tests, of two 50Mo-50Re alloys at strain rates ranging from 10-6 s-1 to 1 s-1 at room temperature in air. Metallographic observations of the 50Mo-50Re alloys before and after tensile deformation were conducted to understand the relationships among mechanical properties, microstructure and strain rate in these alloys. Understanding the strain-rate effect on mechanical properties of 50Mo-50Re alloys is important for optimizing forming operations, especially sheet forming, of these alloys, which are often used in cathode and aerospace applications. An anomalous strain-rate effect on ductility was observed in the 50Mo-50Re alloys. Ductility was significantly increased by increasing the strain rate from 10-6 s-1 to 1 s-1 in the fully-recrystallized and recovery heat-treated 50Mo-50Re alloys in tension at room temperature. At a low strain rate, fracture was predominantly brittle, while it was more ductile at higher stain rates. At a low strain rate, secondary cracks initiated at grain boundaries and triple junctions were observed in these alloys, which suggested that significant stress concentration was generated by tensile plastic deformation in the vicinity of grain boundaries, especially triple junctions. Electron backscatter diffraction experiments revealed that there was strain concentration at grain boundaries and their triple junctions during tensile deformation in these alloys. The decrease in ductility at low strain rates in the alloys was related to the possible interaction between dislocations and trace interstitial atoms (e.g., H, O, N and C) picked up during production of these alloys. This dissertation also reports the research efforts made to optimize small-scale resistance spot welding (SSRSW) of refractory alloy 50Mo-50Re thin sheet by adjusting seven important welding parameters, including hold time, electrode material, electrode

  6. Mechanics of fracture - Fundamentals and some recent developments

    NASA Technical Reports Server (NTRS)

    Liebowitz, H.; Subramonian, N.; Lee, J. D.

    1979-01-01

    An overview is presented of the fundamental aspects of and recent developments in fracture mechanics. Reference is made to linear elastic fracture mechanics including the state of stresses and displacements in the vicinity of cracks, effects of crack geometry and orientation on stress intensity factors, energy balance of Griffith, Irwin's stress intensity concept, and linear elastic fracture mechanics testing for fracture toughness. Other aspects of this paper include the non-linear behavior of materials and their influence on fracture mechanics parameters, consideration of viscoelasticity and plasticity, non-linear fracture toughness parameters as C.O.D., R-curve and J-integral, and a non-linear energy method, proposed by Liebowitz. Finite element methods applied to fracture mechanics problems are indicated. Also, consideration has been given to slow crack growth, dynamic effects on K(IC), Sih's criterion for fracture, Lee and Liebowitz's criterion relating crack growth with plastic energy, and applications of fracture mechanics to aircraft design. Suggestions are offered for future research efforts to be undertaken in fracture mechanics.

  7. Patterns and perspectives in applied fracture mechanics

    SciTech Connect

    Merkle, J.G.

    1994-12-31

    This lecture begins with a overview of applied fracture mechanics pertinent to safety of pressure vessels. It then progresses to a chronological panorama of experimental and analytical results. To be useful and dependable in safety analysis of real structures, new analysis developments must be physically realistic, which means that they must accurately describe physical cause and effect. Consequently, before mathematical modeling can begin, cause and effect must be established from experimental data. This can be difficult and time consuming, but worth the effort. Accordingly, the theme of this paper is that the search for patterns is constant and vital. This theme is illustrated by the development of small, single-specimen, fracture toughness testing techniques. It is also illustrated by the development, based on two different published large-strain, elastic-plastic, three-dimensional finite-element analyses, of a hypothesis concerning three-dimensional loss of constraint. When a generalization of Irwin`s thickness-normalized plastic-zone parameter, reaches a value close to 2{pi}, the through-thickness contraction strain at the apex of the near-tip logarithmic-spiral slip-line region becomes the dominant negative strain accommodating crack opening. Because slip lines passing from the midplane to the stress-free side surfaces do not have to curve, once these slip lines are established, stresses near the crack tip are only elevated by strain hardening and constraint becomes significantly relaxed. This hypothesis, based on published three-dimensional elastic-plastic analyses, provides a potentially valuable means for gaining additional insight into constraint effects on fracture toughness by considering the roles played by the plastic strains as well as the stresses that develop near a crack tip.

  8. Patterns and perspectives in applied fracture mechanics

    NASA Astrophysics Data System (ADS)

    Merkle, John G.; Reuter, Walter G.; Underwood, John H.; Newman, James C., Jr.

    This lecture begins with a overview of applied fracture mechanics pertinent to safety of pressure vessels. It then progresses to a chronological panorama of experimental and analytical results. To be useful and dependable in safety analysis of real structures, new analysis developments must be physically realistic, which means that they must accurately describe physical cause and effect. Consequently, before mathematical modeling can begin, cause and effect must be established from experimental data. This can be difficult and time consuming, but worth the effort. Accordingly, the theme of this paper is that the search for patterns is constant and vital. This theme is illustrated by the development of small, single-specimen, fracture toughness testing techniques. It is also illustrated by the development, based on two different published large-strain, elastic-plastic, three-dimensional finite-element analyses, of a hypothesis concerning three-dimensional loss of constraint. When a generalization of Irwin's thickness-normalized plastic-zone parameter reaches a value close to 2 pi, the through-thickness contraction strain at the apex of the near-tip logarithmic-spiral slip-line region becomes the dominant negative strain accommodating crack opening. Because slip lines passing from the midplane to the stress-free side surfaces do not have to curve, once these slip lines are established, stresses near the crack tip are only elevated by strain hardening and constraint becomes significantly relaxed. This hypothesis, based on published three-dimensional elastic-plastic analyses, provides a potentially valuable means for gaining additional insight into constraint effects on fracture toughness by considering the roles played by the plastic strains as well as the stresses that develop near a crack tip.

  9. Mechanical and Wear Properties of Sb- and Y-Added Mg-9Al-1Zn (AZ91) Alloy

    NASA Astrophysics Data System (ADS)

    Boby, Arun; Srinivasan, A.; Pillai, U. T. S.; Pai, B. C.

    2015-09-01

    This paper studies the effect of Sb and Y additions on the microstructure and mechanical properties of the AZ91 alloy. The results indicate that the Sb and Y additions lead to the formation of Mg3Sb2 and Al2Y phases. These phases modify the morphology of the β-Mg17Al12 phase, and hence refine the microstructure. The effects of Sb and Y additions on the aging behavior have also been investigated. Aging of the AZ91 alloy results in the formation of continuous and discontinuous types of precipitates. Whereas Sb and Y additions to AZ91 alloy suppresses the formation of discontinuous precipitate. The paper also reports the mechanical properties of as-cast and aged Sb-added AZ91-xY alloys for room and high temperatures. The optimum tensile properties are obtained with the alloy having the combined addition of 0.5 wt pct Sb and 0.6 wt pct Y. The fracture surface of AZ91-0.5Sb-0.6Y alloy reveals more quasi-cleavage type of failure with a cleavage fracture than the base alloy. At HT, the AZ91-0.5Sb-0.6Y alloy displays more cleavage facets connected with tearing ridges and shallow dimples than AZ91 alloy. Furthermore, it observed the improvement in wear resistance through the addition of Y. The worn surface reveals abrasion, oxidation, delamination, and plastic deformation wear mechanisms.

  10. Fatigue fracture mechanism maps for a type 304 stainless steel

    NASA Astrophysics Data System (ADS)

    Kimura, M.; Yamaguchi, K.; Hayakawa, M.; Kobayashi, K.; Takeuchi, E.; Matsuoka, S.

    2004-04-01

    Fatigue fracture mechanism maps at room temperature and 573 K for a type 304 stainless steel were constructed by correlating the crack propagation rate with information obtained on the fracture surface. Depending on the crack propagation rate, ranging from 1 × 10-6 to 1 × 10-11 m/cycle, three types of fracture surfaces were observed. One was a striation region; the second was a “featureless” fracture region, which appeared rough under scanning electron microscope (SEM) observation; and the third was crystallographic fracture region, which appeared smooth under SEM observation. The area fractions and the indexes of the fracture surfaces were quantified and identified by the etch-pit method. From the results, crack initiation and propagation mechanisms were cleared and fatigue fracture mechanism maps were constructed. The maps may be useful for investigating the cause of the fatigue failure accident of structures made of type 304 steels.

  11. Mechanisms for fast flow in unsaturated fractured rock

    SciTech Connect

    Tokunaga, Tetsu K.; Wan, Jiamin

    1998-03-01

    Although fractures in rock are well-recognized as pathways for fast percolation of water, the possibility that fast flow could occur along unsaturated fracture pathways is commonly not considered in vadose zone hydrology. In this study, two mechanisms for fast flow along unsaturated fractures were investigated, film flow and surface zone flow. The importance of fracture surface roughness was demonstrated through experiments conducted on ceramic blocks having simple surface topographies. Those experiments showed that film flow on fracture surfaces is largely due to flow along continuous surface channels which become water-filled at near-zero matric (capillary) potentials. The second mechanism, surface zone flow, is important when the permeability of the rock along fractures (fracture skin) is significantly greater than that of the bulk rock matrix. Surface zone fast flow was demonstrated through water imbibition (sorptivity) experiments. These mechanisms help explain observations of rapid solute transport in unsaturated subsurface environments.

  12. Intergranular fracture in some precipitation-hardened aluminum alloys at low temperatures

    SciTech Connect

    Kuramoto, S.; Itoh, G.; Kanno, M.

    1996-10-01

    Intergranular fracture at low temperatures from room temperature down to 4.2 K has been studied in some precipitation-hardened aluminum alloys. Microscopic appearance of intergranular facets is revealed to be greatly affected by the microstructure adjacent to the grain boundaries (GBs). When large precipitates on GBs and wide precipitation-free zones (PFZs) are present, coalescence of microvoids initiated at the GB precipitates causes the intergranular fracture with dimples. This fracture process is found to be unaffected by deformation temperature. On the other hand, in the presence of fine precipitates on GBs and narrow PFZs, matrix slip localization exerts significant influence on the fracture behavior. At low temperatures, large stress concentration at GBs leads to intergranular fracture, forming sharp ledges on the fracture surfaces, while at room temperature, the dynamic recovery process is thought to relax such stress concentration, resulting in a transgranular ductile rupture.

  13. Metallurgical Mechanisms Controlling Mechanical Properties of Aluminum Alloy 2219 Produced by Electron Beam Freeform Fabrication

    NASA Technical Reports Server (NTRS)

    Domack, Marcia S.; Tainger, Karen M.

    2006-01-01

    The electron beam freeform fabrication (EBF3) layer-additive manufacturing process has been developed to directly fabricate complex geometry components. EBF3 introduces metal wire into a molten pool created on the surface of a substrate by a focused electron beam. Part geometry is achieved by translating the substrate with respect to the beam to build the part one layer at a time. Tensile properties demonstrated for electron beam deposited aluminum and titanium alloys are comparable to wrought products, although the microstructures of the deposits exhibit cast features. Understanding the metallurgical mechanisms controlling mechanical properties is essential to maximizing application of the EBF3 process. Tensile mechanical properties and microstructures were examined for aluminum alloy 2219 fabricated over a range of EBF3 process variables. Unique microstructures were observed within the deposited layers and at interlayer boundaries, which varied within the deposit height due to microstructural evolution associated with the complex thermal history experienced during subsequent layer deposition. Microstructures exhibited irregularly shaped grains with interior dendritic structures, described based on overall grain size, morphology, distribution, and dendrite spacing, and were correlated with deposition parameters. Fracture features were compared with microstructural elements to define fracture paths and aid in definition of basic processing-microstructure-property correlations.

  14. Metallurgical Mechanisms Controlling Mechanical Properties of Aluminum Alloy 2219 Produced By Electron Beam Freeform Fabrication

    NASA Technical Reports Server (NTRS)

    Domack, Marcia S.; Taminger, Karen M. B.; Begley, Matthew

    2006-01-01

    The electron beam freeform fabrication (EBF3) layer-additive manufacturing process has been developed to directly fabricate complex geometry components. EBF3 introduces metal wire into a molten pool created on the surface of a substrate by a focused electron beam. Part geometry is achieved by translating the substrate with respect to the beam to build the part one layer at a time. Tensile properties have been demonstrated for electron beam deposited aluminum and titanium alloys that are comparable to wrought products, although the microstructures of the deposits exhibit features more typical of cast material. Understanding the metallurgical mechanisms controlling mechanical properties is essential to maximizing application of the EBF3 process. In the current study, mechanical properties and resulting microstructures were examined for aluminum alloy 2219 fabricated over a range of EBF3 process variables. Material performance was evaluated based on tensile properties and results were compared with properties of Al 2219 wrought products. Unique microstructures were observed within the deposited layers and at interlayer boundaries, which varied within the deposit height due to microstructural evolution associated with the complex thermal history experienced during subsequent layer deposition. Microstructures exhibited irregularly shaped grains, typically with interior dendritic structures, which were described based on overall grain size, morphology, distribution, and dendrite spacing, and were correlated with deposition parameters. Fracture features were compared with microstructural elements to define fracture paths and aid in definition of basic processing-microstructure-property correlations.

  15. Investigation of the plastic fracture of high-strength aluminum alloys

    NASA Technical Reports Server (NTRS)

    Van Stone, R. H.; Merchant, R. H.; Low, J. R., Jr.

    1974-01-01

    In a study of plastic fracture in five high-strength aluminum alloys (2014, 2024, 2124, 7075, and 7079), it has been shown that fracture toughness is affected primarily by the size and volume fraction of the larger (2 to 10 microms) second-phase particles. Certain of these particles crack at small plastic strains, nucleating voids which, with further plastic strain, coalesce to cause fracture. Not all second-phase particles crack at small plastic strains, and qualitative analysis of those which are primarily responsible for void nucleation shows that they contain iron or silicon or both. This result suggests that a reduction in the iron and silicon impurity content of the alloys should improve fracture toughness without loss of strength.

  16. Investigation of the plastic fracture of high-strength aluminum alloys

    NASA Technical Reports Server (NTRS)

    Van Stone, R. H.; Merchant, R. H.; Low, J. R., Jr.

    1974-01-01

    In a study of plastic fracture in five high-strength aluminum alloys (2014, 2024, 2124, 7075, and 7079), it has been shown that fracture toughness is affected primarily by the size and volume fraction of the larger (2 to 10 microms) second-phase particles. Certain of these particles crack at small plastic strains, nucleating voids which, with further plastic strain, coalesce to cause fracture. Not all second-phase particles crack at small plastic strains, and qualitative analysis of those which are primarily responsible for void nucleation shows that they contain iron or silicon or both. This result suggests that a reduction in the iron and silicon impurity content of the alloys should improve fracture toughness without loss of strength.

  17. Correlation of microstructure with the wear resistance and fracture toughness of white cast iron alloys

    NASA Astrophysics Data System (ADS)

    Filipovic, M.; Kamberovic, Z.; Korac, M.; Gavrilovski, M.

    2013-05-01

    The objective of this investigation was to set down (on the basis of the results obtained by the examination of white cast iron alloys with different contents of alloying elements) a correlation between chemical composition and microstructure, on one hand, and the properties relevant for this group of materials, i.e., wear resistance and fracture toughness, on the other. Experimental results indicate that the volume fraction of the eutectic carbide phase (M3C or M7C3) have an important influence on the wear resistance of white iron alloys under low-stress abrasion conditions. Besides, the martensitic or martensite-austenitic matrix microstructure more adequately reinforced the eutectic carbides, minimizing cracking and removal during wear, than did the austenitic matrix. The secondary carbides which precipitate in the matrix regions of high chromium iron also influence the abrasion behaviour. The results of fracture toughness tests show that the dynamic fracture toughness in white irons is determined mainly by the properties of the matrix. The high chromium iron containing 1.19 wt% V in the as-cast condition, showed the greater fracture toughness when compared to other experimental alloys. The higher toughness was attributed to strengthening during fracture, since very fine secondary carbide particles were present mainly in an austenitic matrix.

  18. Effect of Alloying Elements in Hot-Rolled Metastable β-Titanium Alloys. Part II: Mechanical Properties

    NASA Astrophysics Data System (ADS)

    Manda, Premkumar; Chakkingal, Uday; Singh, A. K.

    2016-07-01

    This paper describes the tensile properties, flow and work-hardening behavior of four metastable β-titanium alloys Ti-5Al-5Mo-5V-3Cr (A1), Ti-5Al-3.5Mo-7.2V-3Cr (A2), Ti-5Al-5Mo-8.6V-1.5Cr (A3), and Ti-5Al-3.5Mo-5V-3.94Cr (A4) in α+β hot-rolled condition. The decreasing order of average strength parameters ( σ YS and σ UTS) is A4, A2, A1, and A3. The maximum strength observed in alloy A4 is due to the presence of highest wt. fraction of Cr. The elongation is the maximum and minimum in alloys A3 and A4, respectively. These alloys display moderate to high percent in-plane anisotropy ( A IP) and reasonably low anisotropic index ( δ) values. Both the A IP and δ values are maximum and minimum in alloys A1 and A3, respectively. The yield locus plots also exhibit the presence of anisotropy due to relatively large differences in yield strength values along tension and compression directions. The flow behavior of alloys A1, A2, and A4 follows Swift equation, while the alloy A3 displays best fit with Holloman equation. The presence of prestrain ( ɛ 0) in hot-rolled materials before tensile testing has an important bearing on the flow curves of A1, A2, and A4 alloys. The instantaneous work-hardening rate curves of the alloys A1, A2, and A3 exhibit all the three typical stages (stage I, stage II, and stage III) in RD samples, while the alloy A4 shows the presence of only stage I and stage III. The 45 deg to RD and TD samples of alloys A1, A2, and A4 display only stage I. The stages I and III as well as I and II are present in alloy A3 in 45 deg to RD and TD samples, respectively. Dislocation-controlled strain hardening occurs in all the three stages of these alloys in the absence of stress-induced martensitic transformation (α″) and twinning. Slip is the predominant deformation mechanism during tensile testing. Three types of slip lines, i.e., planar, wavy, and intersecting have been observed close to fracture surfaces of post tensile-tested specimens.

  19. The Delayed Fracture of Aluminum Alloys, End of Year Report.

    DTIC Science & Technology

    1982-03-01

    these commercial alloys is not significantly influenced by the composition of the oxide. In these 7 alloys, the insoluble constituent particles...boundary microstructure, but not to oxide film composition . Accession For 14TTS ’& DTIC T’B ju-tific i ’ Distributon/ Availability Codns *Avi! anl/or * I...Mg-free film for commercial 7 alloys. This latter work was undertaken to further elucidate the effect of film composition on SCC initiation and to

  20. Mechanisms affecting swelling in alloys with precipitates

    SciTech Connect

    Mansur, L.K.; Haynes, M.R.; Lee, E.H.

    1980-01-01

    In alloys under irradiation many mechanisms exist that couple phase instability to cavity swelling. These are compounded with the more familiar mechanisms associated with point defect behavior and the evolution of microstructure. The mechanisms may be classified according to three modes of operation. Some affect cavity swelling directly by cavity-precipitate particle association, others operate indirectly by precipitate-induced changes in sinks other than cavities and finally there are mechanisms that are mediated by precipitate-induced changes in the host matrix. The physics of one mechanism of each type is developed in detail and the results compared where possible to experimental measurements. In particular, we develop the theory necessary to treat the effects on swelling of precipitation-induced changes in overall sink density; precipitation-induced changes in point defect trapping by solute depletion and creation of precipitate particle-matrix interfacial trap sites.

  1. Investigation of Microstructural Factors that Cause Low Fracture Toughness in Silicon Carbide Whisker/Al Alloy Composites

    DTIC Science & Technology

    1988-10-01

    TOUGHNESS IN SILICON CARBIDE WHISKER/Al ALLOY COMPOSITES oSubmittLJ to: Office of Naval Research 800 N. Quincy Street Arlington, VA 22217-5000...September 30, 1988 INVESTIGATION OF MICROSTRUCTURAL FACTORS THAT CAUSE LOW FRACTURE TOUGHNESS IN SILICON CARBIDE WHISKER/Al ALLOY COMPOSITES Submitted...Investigation of Microstructural Factors that Cause Low Fracture Toughness in Silicon Carbide Whisker/Al Alloy Composites .12 PERSONAL AUTHOR(S) F. E. Wawner

  2. Mechanical stratigraphic controls on natural fracture spacing and penetration

    NASA Astrophysics Data System (ADS)

    McGinnis, Ronald N.; Ferrill, David A.; Morris, Alan P.; Smart, Kevin J.; Lehrmann, Daniel

    2017-02-01

    Fine-grained low permeability sedimentary rocks, such as shale and mudrock, have drawn attention as unconventional hydrocarbon reservoirs. Fracturing - both natural and induced - is extremely important for increasing permeability in otherwise low-permeability rock. We analyze natural extension fracture networks within a complete measured outcrop section of the Ernst Member of the Boquillas Formation in Big Bend National Park, west Texas. Results of bed-center, dip-parallel scanline surveys demonstrate nearly identical fracture strikes and slight variation in dip between mudrock, chalk, and limestone beds. Fracture spacing tends to increase proportional to bed thickness in limestone and chalk beds; however, dramatic differences in fracture spacing are observed in mudrock. A direct relationship is observed between fracture spacing/thickness ratio and rock competence. Vertical fracture penetrations measured from the middle of chalk and limestone beds generally extend to and often beyond bed boundaries into the vertically adjacent mudrock beds. In contrast, fractures in the mudrock beds rarely penetrate beyond the bed boundaries into the adjacent carbonate beds. Consequently, natural bed-perpendicular fracture connectivity through the mechanically layered sequence generally is poor. Fracture connectivity strongly influences permeability architecture, and fracture prediction should consider thin bed-scale control on fracture heights and the strong lithologic control on fracture spacing.

  3. [Bone fracture and the healing mechanisms. The mechanical stress for fracture healing in view of distraction osteogenesis].

    PubMed

    Yukata, Kiminori; Takahashi, Mitsuhiko; Yasui, Natsuo

    2009-05-01

    It is generally accepted that moderate mechanical stress influences the course of fracture healing. A flexible fixation of the fractured site can induce fracture callus formation, whereas an unstable fixation can lead to a nonunion. The relationship between mechanical stress and the process of bone regeneration or healing remains incompletely understood. Distraction osteogenesis is a surgical technique that, using appropriate mechanical tension-stress, does not break the callus but rather it stimulates and maintains osteogenesis. The common principles of distraction osteogenesis are osteotomy and slow progressive distraction by an external fixation device. Interest in bone regeneration associated with mechanical stress might lead to better understanding of the fracture healing process.

  4. Microstructural and Mechanical Characterization of Zr Modified 2014 Aluminium Alloy

    DTIC Science & Technology

    2007-11-02

    heated using an induction furnace; the temperature stabilisation time was 6 min. -The gauge section of samples was a solid cylinder with a length (L) of...torsion tests - Fatigue tests -Fracture observations Introduction -Aluminium sheets require a good attitude to the cold metal forming. -Al-Cu-Mg alloys...precipitation occurring during hot deformation or heat treatment Introduction -The precipitation sequence for 2014 Al alloys has been extensively

  5. Controlled release of vancomycin from thin sol-gel films on titanium alloy fracture plate material.

    PubMed

    Radin, Shula; Ducheyne, Paul

    2007-03-01

    Risk of infection is considerable in open fractures and its management is challenging, especially when fracture fixation material is used. Thus, it may be desirable to use a device from which antibiotics can be released in a controlled way. Room temperature processed silica sol-gels are novel, resorbable and biocompatible, controlled release materials. Vancomycin, a potent antibiotic used in treating osteomyelitis, can be released from silica sol-gels. Herein, we describe the synthesis of thin, resorbable, controlled release bactericidal sol-gel films on a Ti-alloy substrate and determine the effect of processing parameters on its degradation and vancomycin release. A close correlation between release and degradation rates suggests that film degradation is the main mechanism underlying the control of release. Using a multi-layer process and various concentrations of vancomycin, released concentrations exceed the minimal inhibitory concentration (MIC) of vancomycin against Staphylococcus aureus. The findings enable the tailoring of release and degradation properties of the films to therapeutic needs by controlling sol-gel processing parameters. Given the bactericidal properties of released vancomycin, and the biocompatibility of the sol-gel films, the present data suggest great promise to prevent and treat bone infections in a clinical setting.

  6. Tensile deformation and fracture properties of a 14YWT nanostructured ferritic alloy

    SciTech Connect

    Alam, M. Ershadul; Pal, Soupitak; Fields, Kirk; Maloy, S. A.; Hoelzer, David T.; Odette, George R.

    2016-08-13

    Here, a new larger heat of a 14YWT nanostructured ferritic alloy (NFA), FCRD NFA-1, was synthesized by ball milling FeO and argon atomized Fe-14Cr-3W-0.4Ti-0.2Y (wt%) powders, followed by hot extrusion, annealing and cross rolling to produce an ≈10 mm-thick plate. NFA-1 contains a bimodal size distribution of pancake-shaped, mostly very fine scale, grains. The as-processed plate also contains a large population of microcracks running parallel to its broad surfaces. The small grains and large concentration of Y–Ti–O nano-oxides (NOs) result in high strength up to 800 °C. The uniform and total elongations range from ≈1–8%, and ≈10–24%, respectively. The strength decreases more rapidly above ≈400 °C and deformation transitions to largely viscoplastic creep by ≈600 °C. While the local fracture mechanism is generally ductile-dimple microvoid nucleation, growth and coalescence, perhaps the most notable feature of tensile deformation behavior of NFA-1 is the occurrence of periodic delamination, manifested as fissures on the fracture surfaces.

  7. Tensile deformation and fracture properties of a 14YWT nanostructured ferritic alloy

    DOE PAGES

    Alam, M. Ershadul; Pal, Soupitak; Fields, Kirk; ...

    2016-08-13

    Here, a new larger heat of a 14YWT nanostructured ferritic alloy (NFA), FCRD NFA-1, was synthesized by ball milling FeO and argon atomized Fe-14Cr-3W-0.4Ti-0.2Y (wt%) powders, followed by hot extrusion, annealing and cross rolling to produce an ≈10 mm-thick plate. NFA-1 contains a bimodal size distribution of pancake-shaped, mostly very fine scale, grains. The as-processed plate also contains a large population of microcracks running parallel to its broad surfaces. The small grains and large concentration of Y–Ti–O nano-oxides (NOs) result in high strength up to 800 °C. The uniform and total elongations range from ≈1–8%, and ≈10–24%, respectively. The strengthmore » decreases more rapidly above ≈400 °C and deformation transitions to largely viscoplastic creep by ≈600 °C. While the local fracture mechanism is generally ductile-dimple microvoid nucleation, growth and coalescence, perhaps the most notable feature of tensile deformation behavior of NFA-1 is the occurrence of periodic delamination, manifested as fissures on the fracture surfaces.« less

  8. Tensile deformation and fracture properties of a 14YWT nanostructured ferritic alloy

    SciTech Connect

    Alam, M. Ershadul; Pal, Soupitak; Fields, Kirk; Maloy, S. A.; Hoelzer, David T.; Odette, George R.

    2016-08-13

    Here, a new larger heat of a 14YWT nanostructured ferritic alloy (NFA), FCRD NFA-1, was synthesized by ball milling FeO and argon atomized Fe-14Cr-3W-0.4Ti-0.2Y (wt%) powders, followed by hot extrusion, annealing and cross rolling to produce an ≈10 mm-thick plate. NFA-1 contains a bimodal size distribution of pancake-shaped, mostly very fine scale, grains. The as-processed plate also contains a large population of microcracks running parallel to its broad surfaces. The small grains and large concentration of Y–Ti–O nano-oxides (NOs) result in high strength up to 800 °C. The uniform and total elongations range from ≈1–8%, and ≈10–24%, respectively. The strength decreases more rapidly above ≈400 °C and deformation transitions to largely viscoplastic creep by ≈600 °C. While the local fracture mechanism is generally ductile-dimple microvoid nucleation, growth and coalescence, perhaps the most notable feature of tensile deformation behavior of NFA-1 is the occurrence of periodic delamination, manifested as fissures on the fracture surfaces.

  9. Mechanical properties of semiconductors and their alloys

    NASA Astrophysics Data System (ADS)

    Sher, A.; Berding, M. A.; Paxton, A. T.; Krishnamurthy, S.; Chen, A.-B.

    1992-02-01

    A wide range of subjects have been treated in this contract. We have devoted time to the development and applications of two first principles computational methods: one, the full-potential linear muffin tin orbital (FP-LMTO) method is somewhat mature and highly accurate, while the other, linear combination of atomic orbitals (LCAO), is less accurate but more flexible and is easily incorporated into the other calculations we have in place, e.g., surface Green's function methods and CPA. Tight binding has also been used. These methods have been applied to solve a host of mechanical-property problems including elastic constants, cleavage energies, sublimation energies, interactions between surface atoms relating to their surface order-disorder state and growth theory, surface segregation, bulk order-disorder theory and phase stability, the effect of dislocations on electronic transport and electro-optic properties of semiconductors, the Ni-Al intermetallic phase diagram, planar fault energies in L12 alloys, high-performance structural metal alloy design, and a contribution to understanding the Jones theory of metal alloying. Many of these subjects have been brought to publishable conclusions. Whenever possible, we have presented our detailed results in the form of preprints and reprints, with only brief summaries of the work given here. In instances where the research is incomplete, we have given somewhat longer expositions.

  10. Subtask 12D3: Fracture properties of V-5Cr-5Ti Alloy

    SciTech Connect

    Li, H.; Hamilton, M.L.; Jones, R.H.

    1995-03-01

    The purpose of this research is to investigate the effect of heat treatment on microstructure and fracture toughness of a V-5Cr-5Ti alloy in the range -50-100{degrees}C. Fracture toughness and impact tests were performed on a V-5Cr-5Ti alloy. Specimens annealed at 1125{degrees}C for 1 h and furnace cooled in a vacuum of 1.33 x 10{sup -5} Pa were brittle at room temperature (RT) and experienced a mixture of intergranular and cleavage fracture. Fracture toughness (J{sub IQ}) at RT was 52 kJ/m{sup 2} and the impact fracture energy (IFE) was 6 J. The IFE at -100{degrees}C was only 1 J. While specimens exhibited high fracture toughness at 100{degrees}C (J{sub IQ} is 485 kj/m{sup 2}), fracture was a mixture of dimple and intergranular failure, with intergranular fracture making up 40% of the total fracture surface. The ductile to brittle transition temperature (DBTT) was estimated to be about 20{degrees}C. When some specimens were given an additional annealing at 890{degrees}C for 24 h, they became very ductile at RT and fractured by microvoid coalescence. The J{sub IQ} value increased from 52 kJ/m{sup 2} to {approximately}1100 kJ/m{sup 2}. The impact test failed to fracture specimens at RT due to a large amount of plastic deformation. 7 refs., 1 fig., 6 tabs.

  11. Fracture toughness of copper-base alloys for ITER applications: A preliminary report

    SciTech Connect

    Alexander, D.J.; Zinkle, S.J.; Rowcliffe, A.F.

    1997-04-01

    Oxide-dispersion strengthened copper alloys and a precipitation-hardened copper-nickel-beryllium alloy showed a significant reduction in toughness at elevated temperature (250{degrees}C). This decrease in toughness was much larger than would be expected from the relatively modest changes in the tensile properties over the same temperature range. However, a copper-chromium-zirconium alloy strengthened by precipitation showed only a small decrease in toughness at the higher temperatures. The embrittled alloys showed a transition in fracture mode, from transgranular microvoid coalescence at room temperature to intergranular with localized ductility at high temperatures. The Cu-Cr-Zr alloy maintained the ductile microvoid coalescence failure mode at all test temperatures.

  12. Microstructure and mechanical properties of Ti-15Zr alloy used as dental implant material.

    PubMed

    Medvedev, Alexander E; Molotnikov, Andrey; Lapovok, Rimma; Zeller, Rolf; Berner, Simon; Habersetzer, Philippe; Dalla Torre, Florian

    2016-09-01

    Ti-Zr alloys have recently started to receive a considerable amount of attention as promising materials for dental applications. This work compares mechanical properties of a new Ti-15Zr alloy to those of commercially pure titanium Grade4 in two surface conditions - machined and modified by sand-blasting and etching (SLA). As a result of significantly smaller grain size in the initial condition (1-2µm), the strength of Ti-15Zr alloy was found to be 10-15% higher than that of Grade4 titanium without reduction in the tensile elongation or compromising the fracture toughness. The fatigue endurance limit of the alloy was increased by around 30% (560MPa vs. 435MPa and 500MPa vs. 380MPa for machined and SLA-treated surfaces, respectively). Additional implant fatigue tests showed enhanced fatigue performance of Ti-15Zr over Ti-Grade4.

  13. Prediction of Failure Due to Thermal Aging, Corrosion and Environmental Fracture in Amorphous and Titanium Alloys

    SciTech Connect

    Farmer, J C

    2003-04-15

    DARPA is exploring a number of advanced materials for military applications, including amorphous metals and titanium-based alloys. Equipment made from these materials can undergo degradation due to thermal aging, uniform corrosion, pitting, crevice corrosion, denting, stress corrosion cracking, corrosion fatigue, hydrogen induced cracking and microbial influenced corrosion. Amorphous alloys have exceptional resistance to corrosion, due in part to the absence of grain boundaries, but can undergo crystallization and other phase instabilities during heating and welding. Titanium alloys are extremely corrosion resistant due to the formation of a tenacious passive film of titanium oxide, but is prone to hydrogen absorption in crevices, and hydrogen induced cracking after hydrogen absorption. Accurate predictions of equipment reliability, necessary for strategic planning, requires integrated models that account for all relevant modes of attack, and that can make probabilistic predictions. Once developed, model parameters must be determined experimentally, and the validity of models must be established through careful laboratory and field tests. Such validation testing requires state-of-the-art surface analytical techniques, as well as electrochemical and fracture mechanics tests. The interaction between those processes that perturb the local environment on a surface and those that alter metallurgical condition must be integrated in predictive models. The material and environment come together to drive various modes of corrosive attack (Figure 1). Models must be supported through comprehensive materials testing capabilities. Such capabilities are available at LLNL and include: the Long Term Corrosion Test Facility (LTCTF) where large numbers of standard samples can be exposed to realistic test media at several temperature levels; a reverse DC machine that can be used to monitor the propagation of stress corrosion cracking (SCC) in situ; and banks of potentiostats with

  14. Deformation and Fracture Behavior of Metallic Glassy Alloys and Glassy-Crystal Composites

    NASA Astrophysics Data System (ADS)

    Louzguine-Luzgin, D. V.; Vinogradov, A.; Li, S.; Kawashima, A.; Xie, G.; Yavari, A. R.; Inoue, A.

    2011-06-01

    The present work demonstrates the deformation behavior of Zr-Cu-Ni-Al bulk glassy alloys and Zr-Ni-Cu-Al-Pd glassy foils as well as Ni-Cu-Ti-Zr bulk crystal-glassy composites. Fracture of Zr60Cu16Ni14Al10 and Zr64.13Ni10.12Cu15.75Al10 bulk glassy alloys is featured by nearly equal fraction areas of cleavage-like and vein-type relief. The observed pattern of alternating cleavage-like and vein-type patterns illustrates a result of dynamically self-organizing shear propagation at the final catastrophic stage. The deformation behavior of Zr64.13Ni10.12Cu15.75Al10 alloy has also been tested at LN2 temperature. The strength of the sample decreases with temperature, and no clear serrated flow typical for bulk glassy samples tested at room temperature is observed in the case of the samples tested at LN2 temperature. We also studied the deformation behavior of Zr-Ni-Cu-Al-Pd glassy foils thinned to electron transparency in situ in tension in a transmission electron microscope. We also present a Ni-Cu-Ti-Zr crystal-glassy composite material having a superior strength paired with a considerable ductility exceeding 10 pct. The metastable cP2 crystalline phase promotes a strain-induced martensitic transformation leading to pseudoelastic behavior as well as enhanced plasticity at room temperature. Underlying mechanisms of plastic deformation are discussed in terms of the interplay between the dislocation slip in the crystalline phase and the shear deformation in the glassy matrix.

  15. Fatigue studies of high-palladium dental casting alloys: Part I. Fatigue limits and fracture characteristics.

    PubMed

    Li, D; Brantley, W A; Mitchell, J C; Daehn, G S; Monaghan, P; Papazoglou, E

    2002-04-01

    The fatigue limits and fracture characteristics for a Pd-Cu-Ga alloy and a Pd-Ga alloy were studied. The alloys were cast into tensile test bars with gauge diameter of 3 mm and gauge length of 15 mm, and the surfaces of the castings were neither air-abraded nor polished after removal from the investment. Specimens were prepared from all-new metal (not previously melted), a combination of 50% new metal and 50% old metal (previously melted one time) and 100% old metal. The cast bars were subjected to heat treatment simulating the complete firing cycles for dental porcelain, and fatigued in air at room temperature under uniaxial tension-compression stress at 10 Hz and a ratio of tensile stress amplitude to compressive stress amplitude (R-ratio) of -1. The alloy microstructures and fracture surfaces were examined with a scanning electron microscope (SEM). Results showed that the fatigue limits at 2 x 10(6)cycles of the Pd-Cu-Ga and Pd-Ga alloys were approximately 0.20 and 0.15 of their 0.1% yield strength (YS) in tension, respectively. The fatigue resistance for specimens from both alloys containing 50% old metal and 50% new metal was comparable to that of specimens containing all-new metal, although this decreased dramatically for Pd-Cu-Ga alloy specimens containing all-old metal. The fatigue resistance of the Pd-Cu-Ga alloy subjected to heat treatment simulating the porcelain firing cycles was not adversely affected by remnants of the original as-cast dendritic microstructure that remained in the relatively large test specimens. A longer heat treatment than recommended by the manufacturer for the porcelain firing cycles is needed to completely eliminate the as-cast dendritic structure in these specimens. The Pd-Cu-Ga alloy exhibited superior fatigue resistance to the Pd-Ga alloy, which has an equiaxed-grain microstructure and lower yield strength.

  16. RESEARCH ON THE BASIC NATURE OF STRESS CORROSION FOR VARIOUS STRUCTURAL ALLOYS AT ROOM AND ELEVATED TEMPERATURE,

    DTIC Science & Technology

    LIFE), GRAIN STRUCTURES(METALLURGY), FRACTURE(MECHANICS), TENSILE PROPERTIES , HEAT TREATMENT, TEMPERATURE, SEA WATER, CHLORIDES, SHEETS, STEEL, MOLYBDENUM ALLOYS, VANADIUM ALLOYS, ENVIRONMENTAL TESTS, MICROSTRUCTURE.

  17. Solution-adaptive finite element method in computational fracture mechanics

    NASA Technical Reports Server (NTRS)

    Min, J. B.; Bass, J. M.; Spradley, L. W.

    1993-01-01

    Some recent results obtained using solution-adaptive finite element method in linear elastic two-dimensional fracture mechanics problems are presented. The focus is on the basic issue of adaptive finite element method for validating the applications of new methodology to fracture mechanics problems by computing demonstration problems and comparing the stress intensity factors to analytical results.

  18. Elastic - Plastic Fracture Mechanics. A Critical Review. Part 1

    DTIC Science & Technology

    1990-04-01

    STATE UNIVERSITY OF NEW YORK MICS COMMITTEE MARITIME COLLE GE Dr. William Sandberg Dr. W. R. Porter AMERICAN IRON AND STEEL INSTITUTE WELDING RESEARCH... welded steel structures. Fundamental concepts and underlying assumptions are described. Standardized test methods and recent developments are reviewed...fracture mechanics, as applied to welded steel structures. First, the fundamental concepts and underlying assumptions of fracture mechanics are described

  19. 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

  20. Hydrogen embrittlement and fracture toughness of a titanium alloy with surface modification by hard coatings

    NASA Astrophysics Data System (ADS)

    Lee, S.-C.; Ho, W.-Y.; Huang, C.-C.; Meletis, E. I.; Liu, Y.

    1996-02-01

    The effect of hydrogen embrittlement on the fracture toughness of a titanium alloy with different surface modifications was investigated. Disk- shaped compact- tension specimens were first coated with different .hard films and then hydrogen charged by an electrochemical method. Glow discharge optical spectrometry (GDOS), scanning electron microscopy (SEM), and x- ray diffractometry (XRD) were applied to analyze the surface characteristics. The results revealed that fracture toughness of the as- received titanium alloy decreased with the increase of hydrogen charging time. Fracture toughness of the alloy after plasma nitriding or ion implantation, which produced a TiN x layer, decreased as well, but to a lesser extent after cathodic charging. The best result obtained was for the alloy coated with a CrN film where fracture toughness was sustained even after hydrogen charging for 144 h. Obviously, the CrN film acted as a better barrier to retard hydrogen permeation, but it was at the sacrifice of the CrN film itself.

  1. Dynamic fracture behavior of Ti-6Al-4V alloy with various stabilities of [beta] phase

    SciTech Connect

    Akmoulin, I.A.; Niinomi, M.; Kobayashi, T. . Dept. of Production Systems Engineering)

    1994-08-01

    The effect of stability of the body-centered cubic (bcc) [beta] phase on the dynamic fracture behavior of Ti-6Al-4V alloy at room temperature and 77 K has been studied. The presence of a highly unstable [beta] phase in the quenched alloy leads to a decrease in both the dynamic fracture toughness and the crack propagation energy, and this decrease becomes more pronounced when test temperature is reduced to 77 K. Somewhat improved fracture characteristics were obtained by applying anneal procedure to receive a fully stable [beta] phase. The highest fracture toughness as well as the greatest crack propagation resistance were observed in the air-cooled grade, where the lattice parameter of the bcc phase was intermediate between those pertaining to quenched and annealed Ti-6Al-4V alloys. The effect is attributed to the vanadium content in the [beta] phase, which is sufficiently high to suppress deformation-induced transformation. On the other hand, the V content should be low enough to retard ductile-brittle transition, typical for the bcc metals at cryogenic temperatures. As a result, marked toughening can be achieved, so that the lowest application temperature of high-strength titanium alloys containing the bcc phase can be decreased significantly.

  2. Fractographic analysis of the low energy fracture of an aluminum alloy

    NASA Technical Reports Server (NTRS)

    Tanaka, J.; Pampillo, C. A.; Low, J. R., Jr.

    1972-01-01

    A study of the fracture process in a high strength aluminum alloy, 2014T6, was undertaken to identify the void nucleating particles in this material, to determine their composition, and to suggest means by which they might be eliminated without loss of strength.

  3. Fluid driven fracture mechanics in highly anisotropic shale: a laboratory study with application to hydraulic fracturing

    NASA Astrophysics Data System (ADS)

    Gehne, Stephan; Benson, Philip; Koor, Nick; Enfield, Mark

    2017-04-01

    The finding of considerable volumes of hydrocarbon resources within tight sedimentary rock formations in the UK led to focused attention on the fundamental fracture properties of low permeability rock types and hydraulic fracturing. Despite much research in these fields, there remains a scarcity of available experimental data concerning the fracture mechanics of fluid driven fracturing and the fracture properties of anisotropic, low permeability rock types. In this study, hydraulic fracturing is simulated in a controlled laboratory environment to track fracture nucleation (location) and propagation (velocity) in space and time and assess how environmental factors and rock properties influence the fracture process and the developing fracture network. Here we report data on employing fluid overpressure to generate a permeable network of micro tensile fractures in a highly anisotropic shale ( 50% P-wave velocity anisotropy). Experiments are carried out in a triaxial deformation apparatus using cylindrical samples. The bedding planes are orientated either parallel or normal to the major principal stress direction (σ1). A newly developed technique, using a steel guide arrangement to direct pressurised fluid into a sealed section of an axially drilled conduit, allows the pore fluid to contact the rock directly and to initiate tensile fractures from the pre-defined zone inside the sample. Acoustic Emission location is used to record and map the nucleation and development of the micro-fracture network. Indirect tensile strength measurements at atmospheric pressure show a high tensile strength anisotropy ( 60%) of the shale. Depending on the relative bedding orientation within the stress field, we find that fluid induced fractures in the sample propagate in two of the three principal fracture orientations: Divider and Short-Transverse. The fracture progresses parallel to the bedding plane (Short-Transverse orientation) if the bedding plane is aligned (parallel) with the

  4. Cryogenic mechanical properties of low density superplastic aluminum alloys

    SciTech Connect

    Verzasconi, S.L.

    1989-05-01

    Two alloy systems, mainly Al-Li-Cu and Al-Mg-Sc, were studied in this work. Both of these systems have been shown to be superplastically formable in the conditions chosen, and both provide a significant density reduction over a currently used aluminum cryogenic fuel tankage material, 2219. The Al-Mg-Sc alloy provides over 50 percent of the density reduction of 2090 over 2219. In addition to lower density, Al-Li alloys have a higher elastic modulus (stiffness) than conventional aerospace alloys. The main purpose of this work is to characterize the cryogenic strength and toughness of several Al-Cu-Li and Al-Mg-Sc alloys. In addition, the microstructures and fracture surfaces are characterized and related to these properties where possible. 43 refs.

  5. Gunshot induced indirect femoral fracture: mechanism of injury and fracture morphology.

    PubMed

    Kieser, David C; Carr, D J; Leclair, S C J; Horsfall, I; Theis, J C; Swain, M V; Kieser, J A

    2013-12-01

    Indirect ballistic fractures occur when a projectile passes close to, but not contacting, the bone. The mechanism of how these fractures occur is not yet proven, but recently the acoustic shockwave has been excluded as a cause. The objective of this study is to determine whether the expanding temporary cavity, the collapse of this cavity or its oscillation causes these fractures. In addition, we describe the fracture morphology and biomechanical causes of this injury. 40 fresh deer femora were strain gauged and embedded in ballistic gelatin before being shot with four different projectiles with varying distances off the bone. Pressure recordings, chronographs and radar allowed assessment of local pressures and energy transfer. High-speed video allowed the temporal relationship between the temporary cavity and fracture formation to be analysed, while sample dissection allowed the fracture morphology to be described. The fractures produced were consistently wedge-shaped and caused by the expansion of the temporary cavity, flexing the bone beyond its yield point, causing tension failure on the cortex opposite the expanding temporary cavity and a compression wedge on the side of the cavity. Local pressure was not predictive of fracture formation but the energy transfer to the gelatin block was predictive. Indirect fractures are caused by the expansion of the temporary cavity and relate to the proximity of this cavity to the bone. Fractures occur from flexion of the bone and classically display wedge-shaped fracture patterns with the apex of the wedge pointing away from the expanding cavity.

  6. An electrochemical investigation of mechanical alloying of MgNi-based hydrogen storage alloys

    NASA Astrophysics Data System (ADS)

    Jiang, Jian-Jun; Gasik, Michael

    The electrochemical properties of amorphous MgNi-based hydrogen storage alloys synthesized by mechanical alloying (MA) were evaluated. The results show that these amorphous Mg 50Ni 50 alloys exhibit a higher discharge capacity and relatively good rate capacity at a suitable grinding time while their cycle life is very poor. In order to improve the cycle life, the surface of the amorphous Mg 50Ni 50 alloy was coated with Ti, Al and Zr in Spex 8000 mill/mixer and the coating effects were further investigated. Based on experimental results, two kinds of MgNi-based amorphous alloys are designed by substituting part of Mg in MgNi-based alloys by suitable elements. These alloys are then composed of four components. Thus, the cycle life of electrodes consisting of these quaternary amorphous alloys is greatly improved.

  7. Processing and Composition Effects on the Fracture Behavior of Spray-Formed 7XXX Series Al Alloys

    NASA Astrophysics Data System (ADS)

    Sharma, M. M.; Ziemian, C. W.; Eden, T. J.

    2010-12-01

    The fracture properties of high-strength spray-formed Al alloys were investigated, with consideration of the effects of elemental additions such as zinc, manganese, and chromium and the influence of the addition of SiC particulate. Fracture resistance values between 13.6 and 25.6 MPa (m)1/2 were obtained for the monolithic alloys in the T6 and T7 conditions, respectively. The alloys with SiC particulate compared well and achieved fracture resistance values between 18.7 and 25.6 MPa (m)1/2. The spray-formed materials exhibited a loss in fracture resistance ( K I) compared to ingot metallurgy 7075 alloys but had an improved performance compared to high-solute powder metallurgy alloys of similar composition. Characterization of the fracture surfaces indicated a predominantly intergranular decohesion, possibly facilitated by the presence of incoherent particles at the grain boundary regions and by the large strength differential between the matrix and precipitate zone. It is believed that at the slip band-grain boundary intersection, particularly in the presence of large dispersoids and/or inclusions, microvoid nucleation would be significantly enhanced. Differences in fracture surfaces between the alloys in the T6 and T7 condition were observed and are attributed to inhomogeneous slip distribution, which results in strain localization at grain boundaries. The best overall combination of fracture resistance properties were obtained for alloys with minimum amounts of chromium and manganese additions.

  8. Evaluation of Microstructure and Mechanical Properties of Nano-Y2O3-Dispersed Ferritic Alloy Synthesized by Mechanical Alloying and Consolidated by High-Pressure Sintering

    NASA Astrophysics Data System (ADS)

    Karak, Swapan Kumar; Dutta Majumdar, J.; Witczak, Zbigniew; Lojkowski, Witold; Ciupiński, Łukasz; Kurzydłowski, K. J.; Manna, Indranil

    2013-06-01

    In this study, an attempt has been made to synthesize 1.0 wt pct nano-Y2O3-dispersed ferritic alloys with nominal compositions: 83.0 Fe-13.5 Cr-2.0 Al-0.5 Ti (alloy A), 79.0 Fe-17.5 Cr-2.0 Al-0.5 Ti (alloy B), 75.0 Fe-21.5 Cr-2.0 Al-0.5 Ti (alloy C), and 71.0 Fe-25.5 Cr-2.0 Al-0.5 Ti (alloy D) steels (all in wt pct) by solid-state mechanical alloying route and consolidation the milled powder by high-pressure sintering at 873 K, 1073 K, and 1273 K (600°C, 800°C, and 1000°C) using 8 GPa uniaxial pressure for 3 minutes. Subsequently, an extensive effort has been undertaken to characterize the microstructural and phase evolution by X-ray diffraction, scanning and transmission electron microscopy, and energy dispersive spectroscopy. Mechanical properties including hardness, compressive strength, Young's modulus, and fracture toughness were determined using micro/nano-indentation unit and universal testing machine. The present ferritic alloys record extraordinary levels of compressive strength (from 1150 to 2550 MPa), Young's modulus (from 200 to 240 GPa), indentation fracture toughness (from 3.6 to 15.4 MPa√m), and hardness (from13.5 to 18.5 GPa) and measure up to 1.5 through 2 times greater strength but with a lower density (~7.4 Mg/m3) than other oxide dispersion-strengthened ferritic steels (<1200 MPa) or tungsten-based alloys (<2200 MPa). Besides superior mechanical strength, the novelty of these alloys lies in the unique microstructure comprising uniform distribution of either nanometric (~10 nm) oxide (Y2Ti2O7/Y2TiO5 or un-reacted Y2O3) or intermetallic (Fe11TiY and Al9.22Cr2.78Y) particles' ferritic matrix useful for grain boundary pinning and creep resistance.

  9. Mixed-mode Mechanism of Hydraulic Fracture Segmentation

    NASA Astrophysics Data System (ADS)

    Hurt, R. S.; Germanovich, L.; Wu, R.

    2006-12-01

    Mixed-mode I+III loading is one of the primary causes of fracture front segmentation. Although such segmented fractures have been observed both in nature and laboratory, we are not aware of direct laboratory experiments on the mode III mechanism of segmentation of hydraulically induced fractures. In this work, we developed a laboratory technique and a theoretical model for studying not only the effect of mode III loading on the onset of hydraulic fracture segmentation, but also the effect of segmentation on the subsequent growth of hydraulic fractures. In quasi-brittle materials, even a small mode III component may cause fracture segmentation due to a tensile stress field induced near the fracture front [Rice, 1968]. Previously, this has been confirmed in experiments with non-hydraulic fractures [Knauss, 1970; Cooke and Pollard, 1996]. In one occasion, quasi-hydraulic fractures propagated in fast, uncontrollable manner [Sommer, 1969]. This is why, we focused on controlled hydraulic fractures with a rather small KIII/KI ratio (1-10 %). For mixed mode I+III experiments, we used transparent, cylindrical PMMA samples with circular internal fractures perpendicular to the sample axis. Fracture orientation was controlled by thermoelastic stresses induced in each sample by preheating it before creating a fracture. In order to apply mode III loading to the initial fracture, a constant torque was applied to the specimen while fluid was injected into the fracture at a constant rate to pressurize it and to induce mode I loading. The velocity of fracture propagation was constrained by controlling the rate of fluid injection. In spite of a small magnitude of the mode III component, we observed segmented fracture fronts in all tested samples. The segments had similar dimensions and shape elongated around the perimeter of the initial fracture. When the fractures were further pressurized by injecting additional fluid into the sample, second-order segments developed along the fronts

  10. Micromechanics-Based Damage Analysis of Fracture in Ti5553 Alloy with Application to Bolted Sectors

    NASA Astrophysics Data System (ADS)

    Bettaieb, Mohamed Ben; Van Hoof, Thibaut; Minnebo, Hans; Pardoen, Thomas; Dufour, Philippe; Jacques, Pascal J.; Habraken, Anne Marie

    2015-03-01

    A physics-based, uncoupled damage model is calibrated using cylindrical notched round tensile specimens made of Ti5553 and Ti-6Al-4V alloys. The fracture strain of Ti5553 is lower than for Ti-6Al-4V in the full range of stress triaxiality. This lower ductility originates from a higher volume fraction of damage sites. By proper heat treatment, the fracture strain of Ti5553 increases by almost a factor of two, as a result of a larger damage nucleation stress. This result proves the potential for further optimization of the damage resistance of the Ti5553 alloy. The damage model is combined with an elastoviscoplastic law in order to predict failure in a wide range of loading conditions. In particular, a specific application involving bolted sectors is addressed in order to determine the potential of replacing the Ti-6Al-4V by the Ti5553 alloy.

  11. Relationships of slip morphology, microcracking, and fracture resistance in a lamellar TiAl-alloy

    SciTech Connect

    Chan, K.S. ); Kim, Y.W. . Materials Research Div.)

    1994-06-01

    The fracture resistance of a lamellar TiAl-alloy was investigated by J-testing under various displacement rates at ambient temperature. Possible relationships between slip morphology, microcracking, and fracture toughness were studied via optical electron microscopy and scanning electron microscopy (SEM). The results indicated that the lamellar TiAl-alloy exhibited a resistance-curve fracture behavior that was relatively rate insensitive in air at ambient temperature. Both interlamellar and translamellar deformation lines were observed in the crack-tip region and in the crack-wake ligaments. Theoretical analyses suggested that the interlamellar deformation lines were likely due to [l brace]111[r brace][110] easy slip, and the translamellar deformation lines were probably produced by both [l brace]111[r brace][110] easy slip and [l brace]111[r brace][11[bar 2

  12. Mechanical Properties of Gradient Structure Mg Alloy

    NASA Astrophysics Data System (ADS)

    Chen, Hongliang; Yang, Jiang; Zhou, Hao; Moering, Jordan; Yin, Zhe; Gong, Yulan; Zhao, KunYu

    2017-09-01

    In this work, a surface mechanical attrition treatment (SMAT) process was applied to AZ31B magnesium alloy at room temperature. This method produced a gradient structure on the treated AZ31B, in which the grains of the topmost layer are refined to nanoscale sizes. A combination of nanocrystallites at the surface and coarse-grains in the center are the main features of this structure. This structure results in an excellent combination of both strength and ductility. The highest yield strength for the 30 minutes SMAT AZ31B samples increased to 249 ± 5 MPa and the uniform elongation decreased to 9.3 ± 0.8 pct, whereas the original yield strength was only 147 ± 4 MPa and the uniform elongation was 15.4 ± 1.1 pct. Microstructural observations, stress relaxation tests, and hardness tests were used to verify the results. Additionally, there is a specific volume fraction of gradient structure to achieve the best mechanical performance, which is shown to be in the range of 9.3 to 14 pct for the AZ31B alloy.

  13. Mechanical Properties of Gradient Structure Mg Alloy

    NASA Astrophysics Data System (ADS)

    Chen, Hongliang; Yang, Jiang; Zhou, Hao; Moering, Jordan; Yin, Zhe; Gong, Yulan; Zhao, KunYu

    2017-07-01

    In this work, a surface mechanical attrition treatment (SMAT) process was applied to AZ31B magnesium alloy at room temperature. This method produced a gradient structure on the treated AZ31B, in which the grains of the topmost layer are refined to nanoscale sizes. A combination of nanocrystallites at the surface and coarse-grains in the center are the main features of this structure. This structure results in an excellent combination of both strength and ductility. The highest yield strength for the 30 minutes SMAT AZ31B samples increased to 249 ± 5 MPa and the uniform elongation decreased to 9.3 ± 0.8 pct, whereas the original yield strength was only 147 ± 4 MPa and the uniform elongation was 15.4 ± 1.1 pct. Microstructural observations, stress relaxation tests, and hardness tests were used to verify the results. Additionally, there is a specific volume fraction of gradient structure to achieve the best mechanical performance, which is shown to be in the range of 9.3 to 14 pct for the AZ31B alloy.

  14. Breakdown of Continuum Fracture Mechanics at the Nanoscale

    PubMed Central

    Shimada, Takahiro; Ouchi, Kenji; Chihara, Yuu; Kitamura, Takayuki

    2015-01-01

    Materials fail by the nucleation and propagation of a crack, the critical condition of which is quantitatively described by fracture mechanics that uses an intensity of singular stress field characteristically formed near the crack-tip. However, the continuum assumption basing fracture mechanics obscures the prediction of failure of materials at the nanoscale due to discreteness of atoms. Here, we demonstrate the ultimate dimensional limit of fracture mechanics at the nanoscale, where only a small number of atoms are included in a singular field of continuum stress formed near a crack tip. Surprisingly, a singular stress field of only several nanometers still governs fracture as successfully as that at the macroscale, whereas both the stress intensity factor and the energy release rate fail to describe fracture below a critically confined singular field of 2–3 nm, i.e., breakdown of fracture mechanics within the framework of the continuum theory. We further propose an energy-based theory that explicitly accounts for the discrete nature of atoms, and demonstrate that our theory not only successfully describes fracture even below the critical size but also seamlessly connects the atomic to macroscales. It thus provides a more universal fracture criterion, and novel atomistic insights into fracture. PMID:25716684

  15. Compressive fracture morphology and mechanism of metallic glass

    NASA Astrophysics Data System (ADS)

    Qu, R. T.; Zhang, Z. F.

    2013-11-01

    We quantitatively investigated the fracture morphologies of Zr52.5Cu17.9Ni14.6Al10Ti5 and Pd78Cu6Si16 metallic glasses (MGs) under compression. The characteristic features of the compressive fracture morphology were captured, and the shear vein patterns were found to be not a one-to-one correspondence between two opposing fracture surfaces in an identical sample. This finding experimentally confirms that the compressive failure behaves in a fracture mode of pure shear (mode II). Quantitative measurements show that a ˜1 μm thickness layer with materials not only inside but also adjacent to the major shear band contributes to the formation of shear vein patterns. The critical shear strain to break a shear band was found to be more than 105% and higher in more ductile MGs under compression than tension. Estimation on the temperature rise at the fracture moment indicates that only ˜5% of the total elastic energy stored in the sample converts into the heat required for melting the layer to form the vein patterns. The mode II fracture toughness was also estimated based on the quantitative measurements of shear vein pattern and found larger than the mode I fracture toughness. Finally, the deformation and fracture mechanisms of MGs under tension and compression were compared and discussed. These results may improve the understanding on the fracture behaviors and mechanisms of MGs and may provide instructions on future design for ductile MGs with high resistance for fracture.

  16. Identification of modes of fracture in a 2618-T6 aluminum alloy using stereophotogrammetry

    SciTech Connect

    Salas Zamarripa, A.; Mata, M.P. Guerrero; Morales, M. Castillo; Beber-Solano, T.P.

    2011-12-15

    The identification and the development of a quantification technique of the modes of fracture in fatigue fracture surfaces of a 2618-T6 aluminum alloy were developed during this research. Fatigue tests at room and high temperature (230 Degree-Sign C) were carried out to be able to compare the microscopic fractographic features developed by this material under these testing conditions. The overall observations by scanning electron microscopy (SEM) of the fracture surfaces showed a mixture of transgranular and ductile intergranular fracture. The ductile intergranular fracture contribution appears to be more significant at room temperature than at 230 Degree-Sign C. A quantitative methodology was developed to identify and to measure the contribution of these microscopic fractographic features. The technique consisted of a combination of stereophotogrammetry and image analysis. Stereo-pairs were randomly taken along the crack paths and were then analyzed using the profile module of MeX software. The analysis involved the 3-D surface reconstruction, the trace of primary profile lines in both vertical and horizontal directions within the stereo-pair area, the measurements of the contribution of the modes of fracture in each profile, and finally, the calculation of the average contribution in each stereo-pair. The technique results confirmed a higher contribution of ductile intergranular fracture at room temperature than at 230 Degree-Sign C. Moreover, there was no indication of a direct relationship between this contribution and the strain amplitudes range applied during the fatigue testing. - Highlights: Black-Right-Pointing-Pointer Stereophotogrammetry and image analysis as a measuring tool of modes of fracture in fatigue fracture surfaces. Black-Right-Pointing-Pointer A mixture of ductile intergranular and transgranular fracture was identified at room temperature and 230 Degree-Sign C testing. Black-Right-Pointing-Pointer Development of a quantitative methodology to

  17. Mechanistic Study of Delamination Fracture in Al-Li Alloy C458 (2099)

    NASA Technical Reports Server (NTRS)

    Tayon, W. A.; Crooks, R. E.; Domack, M. S.; Wagner, J. A.; Beaudoin, A. J.; McDonald, R. J.

    2009-01-01

    Delamination fracture has limited the use of lightweight Al-Li alloys. In the present study, electron backscattered diffraction (EBSD) methods were used to characterize crack paths in Al-Li alloy C458 (2099). Secondary delamination cracks in fracture toughness samples showed a pronounced tendency for fracture between grain variants of the same deformation texture component. These results were analyzed by EBSD mapping methods and simulated with finite element analyses. Simulation procedures include a description of material anisotropy, local grain orientations, and fracture utilizing crystal plasticity and cohesive zone elements. Taylor factors computed for each grain orientation subjected to normal and shear stresses indicated that grain pairs with the largest Taylor factor differences were adjacent to boundaries that failed by delamination. Examination of matching delamination fracture surface pairs revealed pronounced slip bands in only one of the grains bordering the delamination. These results, along with EBSD studies, plasticity simulations, and Auger electron spectroscopy observations support a hypothesis that delamination fracture occurs due to poor slip accommodation along boundaries between grains with greatly differing plastic response.

  18. The relationship between observed stress corrosion cracking fracture morphology and microstructure in Alloy 600

    SciTech Connect

    Symons, D.M.; Burke, M.G.; Foster, J.P.

    1997-12-31

    Microstructure is known to influence the stress corrosion cracking (SCC) behavior of Alloy 600 in both hydrogenated water and steam environments. This study evaluated the relative SCC response of a single heat of Alloy 600 as a function of microstructure in a hydrogenated doped-steam environment. The 400 C doped-steam environment was selected for the SCC tests to accelerate cracking. The material was evaluated in three conditions: (1) as-received (2) as-annealed, and (3) as-annealed + 26% deformation. Microstructural characterization was performed using analytical electron microscopy (AEM) techniques for the evaluation of carbide type and morphology, and general structure. Constant displacement (bolt-loaded) compact tension specimens were used to induce SCC. The as-annealed and as-annealed plus cold worked samples had two fracture morphologies: a rough intergranular SCC fracture morphology and a smooth intergranular fracture morphology. The SCC fracture in the as-received specimens was characterized by a classic intergranular morphology at low magnification, consistent with the microstructural evaluation of cross-sectional metallographic samples. More detailed examination revealed a pseudo-intergranular fracture morphology. This pseudo-intergranular morphology appears to be comprised of very fine cleavage-like microfacets. These observations may assist in understanding the difference in SCC fracture morphologies as reported in the open literature.

  19. Fracture analysis of cast pure Ti and Ti-6Al-4V alloy for dental use.

    PubMed

    Kim, K H; Choi, M Y; Kishi, T

    1997-01-01

    The fracture behavior of cast two types of pure Ti and Ti-6Al-4V alloy was understood by acoustic emission (AE) analysis during a fracture toughness test. Specimens for test were cast by the lost wax method using a specially designed Ti casting machine of pressure-different method for dental use. A fatigue crack was inserted from the machined notch tip into the body of a specimen in the range of 0.45-0.55 a/W. Acoustic emission signals released during the fracture toughness test were detected by two sensors attached to both ends of the specimen. Then the signals were recorded and analysed by the PAC 3000/3104 system. From the early stage of the fracture toughness test, AE signals started to be released in all types of specimens tested. A reaction layer with the investment materials of about 50-100 microns was thought to be the result of the AE release from an early stage of the fracture toughness test. A microfracture behavior of the cast pure Ti and Ti alloys was proposed based on the results obtained from the AE releasing pattern and fracture surface findings.

  20. Deformation mechanisms to ameliorate the mechanical properties of novel TRIP/TWIP Co-Cr-Mo-(Cu) ultrafine eutectic alloys.

    PubMed

    Kim, J T; Hong, S H; Park, H J; Kim, Y S; Suh, J Y; Lee, J K; Park, J M; Maity, T; Eckert, J; Kim, K B

    2017-01-09

    In the present study, the microstructural evolution and the modulation of the mechanical properties have been investigated for a Co-Cr-Mo (CCM) ternary eutectic alloy by addition of a small amount of copper (0.5 and 1 at.%). The microstructural observations reveal a distinct dissimilarity in the eutectic structure such as a broken lamellar structure and a well-aligned lamellar structure and an increasing volume fraction of Co lamellae as increasing amount of copper addition. This microstructural evolution leads to improved plasticity from 1% to 10% without the typical tradeoff between the overall strength and compressive plasticity. Moreover, investigation of the fractured samples indicates that the CCMCu alloy exhibits higher plastic deformability and combinatorial mechanisms for improved plastic behavior. The improved plasticity of CCMCu alloys originates from several deformation mechanisms; i) slip, ii) deformation twinning, iii) strain-induced transformation and iv) shear banding. These results reveal that the mechanical properties of eutectic alloys in the Co-Cr-Mo system can be ameliorated by micro-alloying such as Cu addition.

  1. Deformation mechanisms to ameliorate the mechanical properties of novel TRIP/TWIP Co-Cr-Mo-(Cu) ultrafine eutectic alloys

    PubMed Central

    Kim, J. T.; Hong, S. H.; Park, H. J.; Kim, Y. S.; Suh, J. Y.; Lee, J. K.; Park, J. M.; Maity, T.; Eckert, J.; Kim, K. B.

    2017-01-01

    In the present study, the microstructural evolution and the modulation of the mechanical properties have been investigated for a Co-Cr-Mo (CCM) ternary eutectic alloy by addition of a small amount of copper (0.5 and 1 at.%). The microstructural observations reveal a distinct dissimilarity in the eutectic structure such as a broken lamellar structure and a well-aligned lamellar structure and an increasing volume fraction of Co lamellae as increasing amount of copper addition. This microstructural evolution leads to improved plasticity from 1% to 10% without the typical tradeoff between the overall strength and compressive plasticity. Moreover, investigation of the fractured samples indicates that the CCMCu alloy exhibits higher plastic deformability and combinatorial mechanisms for improved plastic behavior. The improved plasticity of CCMCu alloys originates from several deformation mechanisms; i) slip, ii) deformation twinning, iii) strain-induced transformation and iv) shear banding. These results reveal that the mechanical properties of eutectic alloys in the Co-Cr-Mo system can be ameliorated by micro-alloying such as Cu addition. PMID:28067248

  2. Deformation mechanisms to ameliorate the mechanical properties of novel TRIP/TWIP Co-Cr-Mo-(Cu) ultrafine eutectic alloys

    NASA Astrophysics Data System (ADS)

    Kim, J. T.; Hong, S. H.; Park, H. J.; Kim, Y. S.; Suh, J. Y.; Lee, J. K.; Park, J. M.; Maity, T.; Eckert, J.; Kim, K. B.

    2017-01-01

    In the present study, the microstructural evolution and the modulation of the mechanical properties have been investigated for a Co-Cr-Mo (CCM) ternary eutectic alloy by addition of a small amount of copper (0.5 and 1 at.%). The microstructural observations reveal a distinct dissimilarity in the eutectic structure such as a broken lamellar structure and a well-aligned lamellar structure and an increasing volume fraction of Co lamellae as increasing amount of copper addition. This microstructural evolution leads to improved plasticity from 1% to 10% without the typical tradeoff between the overall strength and compressive plasticity. Moreover, investigation of the fractured samples indicates that the CCMCu alloy exhibits higher plastic deformability and combinatorial mechanisms for improved plastic behavior. The improved plasticity of CCMCu alloys originates from several deformation mechanisms; i) slip, ii) deformation twinning, iii) strain-induced transformation and iv) shear banding. These results reveal that the mechanical properties of eutectic alloys in the Co-Cr-Mo system can be ameliorated by micro-alloying such as Cu addition.

  3. Integration of NDE Reliability and Fracture Mechanics

    SciTech Connect

    Becker, F. L.; Doctor, S. R.; Heas!er, P. G.; Morris, C. J.; Pitman, S. G.; Selby, G. P.; Simonen, F. A.

    1981-03-01

    The Pacific Northwest Laboratory is conducting a four-phase program for measuring and evaluating the effectiveness and reliability of in-service inspection (lSI} performed on the primary system piping welds of commercial light water reactors (LWRs). Phase I of the program is complete. A survey was made of the state of practice for ultrasonic rsr of LWR primary system piping welds. Fracture mechanics calculations were made to establish required nondestrutive testing sensitivities. In general, it was found that fatigue flaws less than 25% of wall thickness would not grow to failure within an inspection interval of 10 years. However, in some cases failure could occur considerably faster. Statistical methods for predicting and measuring the effectiveness and reliability of lSI were developed and will be applied in the "Round Robin Inspections" of Phase II. Methods were also developed for the production of flaws typical of those found in service. Samples fabricated by these methods wilI be used in Phase II to test inspection effectiveness and reliability. Measurements were made of the influence of flaw characteristics {i.e., roughness, tightness, and orientation) on inspection reliability. These measurernents, as well as the predictions of a statistical model for inspection reliability, indicate that current reporting and recording sensitivities are inadequate.

  4. An evaluation of the fatigue crack growth and fracture toughness properties of beryllium-copper alloy CDA172

    NASA Technical Reports Server (NTRS)

    Forman, Royce G.; Henkener, Julie A.

    1990-01-01

    A series of fracture mechanics tests, using the Be-Cu alloy CDA172 in the round rod product form, was conducted in a lab air environment at room temperature. Tensile data is presented in both the L and C directions and K sub Ic data in both the C-R and C-L orientations. Fracture toughness values were derived from M(T) (center cracked), PS(T) (surface cracked) and CC01 (corner cracked) specimens of varying thickness. Fatigue crack growth data were obtained for the C-R orientation at stress ratio of 0.1, 0.4, and 0.7 and for the C-L orientation at stress ratios of 0.1, 0.3, 0.4, and 0.7.

  5. Progress report on the influence of test temperature and grain boundary chemistry on the fracture behavior of ITER copper alloys

    SciTech Connect

    Li, M.; Stubbins, J.F.; Edwards, D.J.

    1998-09-01

    This collaborative study was initiated to determine mechanical properties at elevated temperatures of various copper alloys by University of Illinois and Pacific Northwestern National Lab (PNNL) with support of OMG Americas, Inc. and Brush Wellman, Inc. This report includes current experimental results on notch tensile tests and pre-cracked bend bar tests on these materials at room temperature, 200 and 300 C. The elevated temperature tests were performed in vacuum and indicate that a decrease in fracture resistance with increasing temperature, as seen in previous investigations. While the causes for the decreases in fracture resistance are still not clear, the current results indicate that environmental effects are likely less important in the process than formerly assumed.

  6. Fracture Mechanics for Composites: State of the Art and Challenges

    NASA Technical Reports Server (NTRS)

    Krueger, Ronald; Krueger, Ronald

    2006-01-01

    Interlaminar fracture mechanics has proven useful for characterizing the onset of delaminations in composites and has been used with limited success primarily to investigate onset in fracture toughness specimens and laboratory size coupon type specimens. Future acceptance of the methodology by industry and certification authorities however, requires the successful demonstration of the methodology on the structural level. In this paper, the state-of-the-art in fracture toughness characterization, and interlaminar fracture mechanics analysis tools are described. To demonstrate the application on the structural level, a panel was selected which is reinforced with stringers. Full implementation of interlaminar fracture mechanics in design however remains a challenge and requires a continuing development effort of codes to calculate energy release rates and advancements in delamination onset and growth criteria under mixed mode conditions.

  7. The effect of hot isostatic pressing on crack initiation, fatigue, and mechanical properties of two cast aluminum alloys

    NASA Astrophysics Data System (ADS)

    Rich, T. P.; Orbison, J. G.; Duncan, R. S.; Olivero, P. G.; Peterec, R. H.

    1999-06-01

    This article presents the results of an experimental materials testing program on the effect of hot isostatic pressing (HIP) on the crack initiation, fatigue, and mechanical properties of two cast aluminum alloys: AMS 4220 and 4225. These alloys are often used in castings for high temperature applications. Standard tensile and instrumented Charpy impact tests were performed at room and elevated temperatures. The resulting data quantify improvements in ultimate tensile strength, ductility, and Charpy impact toughness from the HIP process while indicating little change in yield strength for both alloys. In addition standard fracture mechanics fatigue tests along with a set of unique fatigue crack initiation tests were performed on the alloys. Hot isostatic pressing was shown to produce a significant increase in cycles to crack initiation for AMS 4225, while no change was evident in traditional da/dN fatigue crack growth. The data permits comparisons of the two alloys both with and without the HIP process.

  8. Development of a Brazing Alloy for the Mechanically Alloyed High Temperature Sheet Material INCOLOY Alloy MA 956.

    DTIC Science & Technology

    1981-09-01

    well established that joining these alloys by conventional fusion welding techniques has presented problems, especially in achieving good quality high...temperature joint properties, mainly because of agglomeration of the dispersoid in the weld bead. Brazing, diffusion bonding and transient liquid...produced mechanically alloyed iron based sheet material, INQ)LOY alloy MA956, has excellent high temperature strength and corrosion resistance and has

  9. Deformation and fracture of aluminum-lithium alloys: The effect of dissolved hydrogen

    NASA Technical Reports Server (NTRS)

    Rivet, F. C.; Swanson, R. E.

    1990-01-01

    The effects of dissolved hydrogen on the mechanical properties of 2090 and 2219 alloys are studied. The work done during this semi-annual period consists of the hydrogen charging study and some preliminary mechanical tests. Prior to SIMS analysis, several potentiostatic and galvanostatic experiments were performed for various times (going from 10 minutes to several hours) in the cathodic zone, and for the two aqueous solutions: 0.04N of HCl and 0.1N NaOH both combined with a small amount of As2O3. A study of the surface damage was conducted in parallel with the charging experiments. Those tests were performed to choose the best charging conditions without surface damage. Disk rupture tests and tensile tests are part of the study designed to investigate the effect of temperature, surface roughness, strain rate, and environment on the fracture behavior. The importance of the roughness and environment were shown using the disk rupture test as well as the importance of the strain rate under hydrogen environment. The tensile tests, without hydrogen effects, have not shown significant differences between low and room temperature.

  10. A comparison of fracture behavior of low alloy steel with different sizes of carbide particles

    SciTech Connect

    Wang, G.Z.; Chen, J.H.

    1996-07-01

    The fracture behaviors of low alloy steels with similar grain sizes but different sizes of carbide particles were investigated using precracked and notched specimens. The results indicate that in precracked specimens (COD), steel with coarser carbide particles has a lower toughness than steel with finer carbide particles over a temperature range from {minus}196 C to {minus}90 C. However, in notched specimens (four-point bending (4PB) and Charpy V), these two steels shows similar toughness at low temperature where specimens are fractured by cleavage without fibrous cracking. In the transition temperature range, the steel with coarser carbide particles conversely shows a little higher toughness due to the longer extension length of the fibrous crack. This phenomenon indicates that in precracked specimens, the second-phase particles play a leading role in cleavage fracture, while in notched specimens, the grain size dominates the fracture behavior.

  11. Mechanical Properties of High Strength Al-Mg Alloy Sheet

    NASA Astrophysics Data System (ADS)

    Choi, Bong-Jae; Hong, Kyung-Eui; Kim, Young-Jig

    The aim of this research is to develop the high strength Al alloy sheet for the automotive body. For the fabrication Al-Mg alloy sheet, the composition of alloying elements was designed by the properties database and CALPHAD (Calculation Phase Diagram) approach which can predict the phases during solidification using thermodynamic database. Al-Mg alloys were designed using CALPHAD approach according to the high content of Mg with minor alloying elements. After phase predictions by CALPHAD, designed Al-Mg alloys were manufactured. Addition of Mg in Al melts were protected by dry air/Sulphur hexafluoride (SF6) mixture gas which can control the severe Mg ignition and oxidation. After rolling procedure of manufactured Al-Mg alloys, mechanical properties were examined with the variation of the heat treatment conditions.

  12. Mixed mode fracture characterization of hydroxylapatite-titanium alloy interface.

    PubMed

    Mann, K A; Edidin, A A; Kinoshita, R K; Manley, M T

    1994-01-01

    Cantilever beam and four-point bend specimen geometries were used to experimentally determine the critical energy release rates for a plasma sprayed hydroxylapatite-titanium alloy (HA-Ti alloy) interface. A locus of energy release rates as a function of crack tip phase angle was determined where a 0 degree phase angle represented tensile opening (mode I) loading and a 90 degree phase angle represented in-plane shear (mode II) loading. Energy release rates were found to increase substantially with an increase in phase angle. An energy release rate of 0.108 N/mm was determined for a phase angle of 0 degrees (mode I). Energy release rates of 0.221, 0.686, and 1.212 N/mm were determined for phase angles of 66 degrees, 69 degrees, and 72 degrees, respectively. The experimental data was matched to a phenomenological model for which crack propagation depended on mode I loading alone indicating that crack propagation at the Ha-Ti alloy interface is dominated by the mode I loading component. Therefore, regions of HA coated implants that experience compressive or shear loading across the HA-Ti alloy interface may be much less likely to debond than regions that experience tensile loading.

  13. Mechanical Properties and Deformation Mechanisms of Mg-Gd-Y-Zr Alloy at Cryogenic and Elevated Temperatures

    NASA Astrophysics Data System (ADS)

    Chen, Bin; Zheng, Jing-Xu; Yang, Chao-Ming; Chen, Yi-Xin; Cao, San-Chen; Zhao, Zhi-Xian; Li, Xiao-Ling; Lu, Chen

    2017-02-01

    In this study, mechanical properties and deformation mechanisms of Mg-Gd-Y-Zr alloy at temperatures ranging from 77 K to 523 K have been investigated. The effects of temperature on the mechanical properties, deformation mechanism, and fracture mechanism are discussed. The results show that the strengths of alloy decrease gradually while the elongations increase progressively with increasing temperature. The maximum ultimate tensile strength of the alloy as high as 442 MPa is obtained at 77 K. As the temperature increases from 77 K to 523 K, the ultimate tensile strength of the alloy decreases from 442 MPa to 254 MPa and the elongations increase from 6.3% to 28.9% gradually. The study verifies that the deformation at 77 K is predominated by basal slip and {10bar{1}2} {10bar{1}2} < {10bar{1}1} rangle . < {10bar{1}1} rangle deformation twinning system. At 223 K, lots of twins emerge primarily at grain boundaries. At 373 K, all dislocations are proved to be < a> dislocations. At 523 K, although basal slip is still the dominant deformation mechanism, non-basal slip systems also become activate.

  14. Effects of Al3(Sc,Zr) and Shear Band Formation on the Tensile Properties and Fracture Behavior of Al-Mg-Sc-Zr Alloy

    NASA Astrophysics Data System (ADS)

    Huang, Hongfeng; Jiang, Feng; Zhou, Jiang; Wei, Lili; Qu, Jiping; Liu, Lele

    2015-11-01

    The mechanical properties and microstructures of Al-6Mg-0.25Sc-0.1Zr alloy (wt.%) during annealing were investigated by means of uniaxial tensile testing, optical microscope, scanning electron microscope, transmission electron microscope, and high-resolution transmission electron microscope. The results show that a large number of micro and grain-scale shear bands form in this alloy after cold rolling. As the tensile-loading force rises, strain softening would generate in shear bands, resulting in the occurrence of shear banding fracture in cold-rolled Al-Mg-Sc-Zr alloys. Recrystallization takes place preferentially in shear bands during annealing. Due to the formation of coarse-grain bands constructed by new subgrains, recrystallization softening tends to occur in these regions. During low-temperature annealing, recrystallization is inhibited by nano-scale Al3(Sc,Zr) precipitates which exert significant coherency strengthening and modulus hardening. However, the strengthening effect of Al3(Sc,Zr) decreases with the increasing of particle diameter at elevated annealing temperature. The mechanical properties of the recrystallized Al-Mg-Sc-Zr alloy decrease to a minimum level, and the fracture plane exhibits pure ductile fracture characteristics.

  15. Mechanically alloyed Ni-base alloys for heat-resistant applications

    SciTech Connect

    Wilson, R.K.; Fischer, J.J.

    1995-12-31

    INCONEL alloys MA 754 and MA 758 are nickel-base oxide dispersion-strengthened (ODS) alloys made by mechanical alloying (MA). Commercial use of Ma Ni-base alloys to date has been predominantly in aerospace applications of alloy MA 754 as turbine engine vanes. Both alloys are suitable for industrial heat treating components and other heat resistant alloy applications. Field trials and commercial experience in such applications of MA alloys are being gained while high temperature property characterization and new product form development continue. Hot isostatic pressing (HIP) is the standard consolidation method for billets from which large bar and plate are produced for industrial applications of MA. This paper describes production of standard mill shapes from HIP billets, and it presents information on current and potential uses of MA alloys in applications such as: skid rails for use in high temperature walking beam furnaces, heat treating furnace components, components for handling molten glass, and furnace tubes. The paper includes comparison of the properties obtained in alloy MA 754 (20% Cr) and alloy MA 758 (30% Cr).

  16. Microstructure, fracture characteristics, and tensile properties of two tungsten heavy alloys. Final report, January 1992-March 1993

    SciTech Connect

    Kennedy, E.W.

    1995-11-01

    The influence of microstructure on fracture behavior and tensile properties was investigated for two tungsten heavy alloys (93W-4.9Ni-2.1Fe and 91W-6Ni-3Co by weight-percentage) that are suitable materiai candidates for use as kinetic energy penetrators. Both alloys were evaluated in swaged and aged conditions. For comparable levels of swaging and aging, the W-Ni-Co alloy exhibited increased tensile strength and ductility compared to the W-Ni-Fe material. The W-Ni-Co alloy had a smaller average W grain size and a larger percentage of W in the matrix. Fracture surfaces of failed uniaxial tensile specimens tested at quasi-static and low-to-medium strain rates were characterized using scanning electron microscopy. The results indicate a strong relationship between microstructure, fracture behavior, and tensile properties as a function of alloy composition and strain rate.

  17. Effect of Sb on the microstructure and mechanical properties of AZ91 magnesium alloy

    NASA Astrophysics Data System (ADS)

    Wang, Qudong; Chen, Wenzhou; Ding, Wenjiang; Zhu, Yanping; Mabuchi, M.

    2001-03-01

    Effects of Sb addition on the microstructure, mechanical properties, and fracture behaviors of AZ91 magnesium alloy, as well as the sensitivity to section thickness of the structure and mechanical properties, have been studied. The results show that when Sb is added into the AZ91 alloy, the grain is refined, the Mg17Al12 phase is refined and granulated, and a new Mg3Sb2 phase is formed and becomes coarse needle-shaped as Sb content increases. The room-temperature tensile strength, elongation, and impact toughness increase first, and then decrease with increasing Sb content. The study on sensitivity to section thickness shows that, when composition is constant, the room-temperature tensile strength and elongation increase with the reduction of section thickness; when section thickness is constant, the room-temperature tensile strength and elongation increase first, and then decrease with increasing Sb content. Additionally, the Sb addition improves the tensile strength of the AZ91 alloy at 100°C and 150°C. The room-temperature tensile and impact fractographs of the AZ91 alloy show intergranular fracture. With increasing Sb content, the tearing deformation zones on the both fractographs enlarge at first, and then diminish, which is consistent with the change of tensile strength, elongation, and impact toughness increasing first, and then reducing with increasing Sb content.

  18. The effect of hydrogen on the fracture of alloy x-750

    NASA Astrophysics Data System (ADS)

    Symons, Douglas M.; Thompson, Anthony W.

    1996-01-01

    The effect of hydrogen on the fracture of a nickel-base superalloy, alloy X-750, was investigated in the HTH condition. The effect of hydrogen was examined through tensile testing incorporating observations from scanning electron microscopy and light microscopy. The ductility at 25 °C, as measured by elongation to failure for tensile specimens, was reduced from 21 pct for noncharged specimens to 7.3 pct for 5.7 ppm hydrogen and to 3.5 pct for 65 ppm hydrogen. The elongation to failure was a function of the strain rate and test temperature. For hydrogen-charged specimens, the elongation decreased as the strain rate decreased at a constant temperature, while for a constant strain rate and varying temperature, there was a maximum in embrittlement near 25 °C and no embrittlement at -196 °C. For the noncharged specimens, the elongation monotonically increased as temperature increased, while there was no noticeable effect of strain rate. Prestraining prior to charging dramatically decreased elongation after hydrogen charging. When the strain rate was increased on the prestrained specimens, more plastic deformation was observed prior to failure. Failure did not occur until the flow stress was reached, supporting the proposition that plasticity is required for failure. The intergranular failure mechanism in alloy X-750 was a microvoid initiation process at grain boundary carbides followed by void growth and coalescence. The void initiation strain, as determined from tensile data and from sectioning unfractured specimens, was observed to be much lower in the hydrogen-charged specimens as compared to noncharged specimens. The reduced ductility may be explained by either a reduction of the interfacial strength of the carbide-matrix interface or a local hydrogen pressure at the carbide-matrix interface.

  19. Molecular-dynamics simulation of mechanical alloying for the Al50Ti50 alloy

    NASA Astrophysics Data System (ADS)

    Lu, J.; Szpunar, J. A.

    1993-07-01

    The structural ordering development during mechanical alloying of the Al50Ti50 alloy was investigated by using molecular-dynamics computer simulations. Random external forces with both random orientations and magnitudes were used to simulate the mechanical alloying processes and pseudopotential was used as a model for the interaction between the atoms. The results indicate that the final nonequilibrium phase obtained through simulation of mechanical alloying is an amorphous state which can be formed experimentally in the laboratory. The transformation from crystals to amorphous state may locally be a first-order-like phase transition, but statistically it is a gradual phase transition due to the characteristics of random external forces which help atoms to overcome their energetic barrier during the mechanical alloying. This means that the transformation occurs in random sites and is discontinuous.

  20. The Features of Fracture Behavior of an Aluminum-Magnesium Alloy AMg6 Under High-Rate Straining

    NASA Astrophysics Data System (ADS)

    Skripnyak, N. V.

    2015-09-01

    The results of investigation of fracture dynamics of rolled sheet specimens of an AMg6 alloy are presented for the range of strain rates from 10-3 to 103 s-1. It is found out that the presence of nanostructured surface layers on the thin AMg6 rolled sheets results in improved strength characteristics within the above range of strain rates. A modified model of a deforming medium is proposed to describe the plastic flow and fracture of the AMg6 alloy.

  1. Processing and Properties of Mechanical Alloyed Al93Fe3Cr2Ti2 Alloys

    DTIC Science & Technology

    2004-10-01

    Nanomaterials, Aluminum Alloys ABSTRACT Nanostructured A193Fe3Ti2Cr2 alloys were prepared via mechanical alloying (MA) starting from elemental powders...2Cr2 . The aluminum powder had a purity of 99.5 wt% with a mean particle size of 70 ^rn, while the corresponding values for iron, chromium and...increases. 2) All aluminum reflections exhibit broadening even after only 2-hours of milling, indicating the grain size reduction and possibly the

  2. Prior deformation effects on creep and fracture in inconel alloy X-750

    NASA Astrophysics Data System (ADS)

    Pandey, M. C.; Mukherjee, A. K.; Taplin, D. M. R.

    1984-07-01

    Creep fracture process in Inconel alloy X-750 can be modified by room-temperature prestraining. It has been observed that fracture in the prestrained specimens occurred due to growth and interlinkage of the prenucleated voids whereas failure occurred by plastic instability in the non-prestrained specimens. Creep ductility and the times-to-rupture are found to decrease progressively with room-temperature prestraining, but there is no marked influence on the minimum creep rate. This is explained in terms of two compcting processes: a weakening effect caused by prenucleation of grain boundary voids and a hardening effect due to generation of dislocations due to the prestraining.

  3. Grain boundary segregation and hydrogen-induced fracture in 7050 aluminium alloy

    SciTech Connect

    Song, R.G.; Tseng, M.K.; Zhang, B.J.; Liu, J.; Jin, Z.H.; Shin, K.S.

    1996-08-01

    The relationships between grain boundary segregation and crack growth of stress corrosion and corrosion fatigue in 7050 aluminium alloy have been investigated under various aging conditions; the effects of grain boundary segregation on intergranular fracture work have been calculated using a quasichemical approach. The results show that the hydrogen content at the crack tip and the crack growth rate increase with the concentration of solid solution Mg on increasing grain boundary; both Mg and H segregation induce the intergranular fracture work to decrease. Mg segregation accelerates H enriching and crack propagation. It is indicated that a Mg-H interaction occurs in the processes of corrosion fatigue as well as stress corrosion.

  4. Damage and fracture loci for a dual-phase steel and a high-strength low-alloyed steel: Revealing the different plastic localization-damage-ductile fracture pattern

    NASA Astrophysics Data System (ADS)

    Lian, Junhe; Münstermann, Sebastian; Bleck, Wolfgang

    2016-10-01

    The ductile fracture locus has been developed in the recent years as a relevant tool to predict the ductile fracture and assess the structure safety. In the various developed models, the occurrence of the final fracture or the initiation of the fracture is considered as the critical phase of deformation for materials or structures. However, in the application of high-strength steels, the damage onset and evolution are of significant importance in the forming processes, as they are naturally interacting with the plastic localization and ductile fracture and eventually creating various possible failure patterns. The present study contributes to a demonstration of the differences of these features in different steels by quantitatively comparing the material parameters of a hybrid damage mechanics model. A dual-phase steel sheet (DP600) and a high-strength low-alloy steel plate (S355J2+N), which show very different relation patterns between damage and fracture, are investigated. The aim of this study is to compare the plastic localization, damage and fracture loci of them and reveal the differences in their localization-damage initiation-ductile fracture patterns. The reasons for the observed different patterns are discussed and it is concluded that the microstructural features are ultimately contributing to the different patterns and the criteria for evaluating the cold formability of these steels shall be varied depending on their failure patterns.

  5. Thermo-Mechanical Processing Parameters for the INCONEL ALLOY 740

    SciTech Connect

    Ludtka, G.M.; Smith, G.

    2007-11-19

    In 2000, a Cooperative Research and Development Agreement (CRADA) was undertaken between the Oak Ridge National Laboratory (ORNL) and the Special Metals Corporation (SMC) to determine the mechanical property response of the IN740 alloy to help establish thermo-mechanical processing parameters for the use of this alloy in supercritical and ultra-critical boiler tubes with the potential for other end uses. SMC had developed an alloy, commercially known as INCONEL alloy 740, which exhibited various beneficial physical, mechanical, and chemical properties. As part of SMC's on-going efforts to optimize this alloy for targeted boiler applications there was a need to develop an understanding of the thermo-mechanical response of the material, characterize the resulting microstructure from this processing, and possibly, utilize models to develop the appropriate processing scheme for this product.

  6. Mechanical properties and microstructure of copper alloys and copper alloy-stainless steel laminates for fusion reactor high heat flux applications

    NASA Astrophysics Data System (ADS)

    Leedy, Kevin Daniel

    plate showed the best overall mechanical properties of the studied bi-metallic bonded panels. Bond properties were nominally inferior to constituent bulk material properties and fracture toughness values, in particular, were quite low for all bonded laminates. Delamination near the copper alloy-stainless steel interface was the dominate failure mode in the bi-metallic panels. The joining processes caused microstructural alterations in the bond interfacial regions including: microporosity, new precipitate formation, existing precipitate morphology changes and interdiffusion of constituent elements.

  7. Adaptive Finite-Element Computation In Fracture Mechanics

    NASA Technical Reports Server (NTRS)

    Min, J. B.; Bass, J. M.; Spradley, L. W.

    1995-01-01

    Report discusses recent progress in use of solution-adaptive finite-element computational methods to solve two-dimensional problems in linear elastic fracture mechanics. Method also shown extensible to three-dimensional problems.

  8. Fracture mechanics /Dryden Lecture/. [aerospace structural design applications

    NASA Technical Reports Server (NTRS)

    Hardrath, H. F.

    1974-01-01

    A historical outline of the engineering discipline of fracture mechanics is presented, and current analytical procedures are summarized. The current status of the discipline is assessed, and engineering applications are discussed, along with recommended directions for future study.

  9. Effects of Solidification Thermal Parameters on Microstructure and Mechanical Properties of Sn-Bi Solder Alloys

    NASA Astrophysics Data System (ADS)

    Silva, Bismarck Luiz; da Silva, Vítor Covre Evangelista; Garcia, Amauri; Spinelli, José Eduardo

    2017-03-01

    Samples extracted along the length of directionally solidified (DS) castings of three Sn- xBi alloys ( x = 34 wt.%Bi, 52 wt.%Bi and 58 wt.%Bi) were first evaluated metallographically and then subjected to scanning electron microscopy and energy-dispersive x-ray spectroscopy analyses. The characteristic length scale of both eutectic and dendritic phases forming the microstructure were determined and correlated with solidification thermal parameters (growth rate V, and cooling rate Ṫ). Tensile and Vickers hardness tests were performed to allow strength and ductility to be discussed as a function of both microstructure features and alloy solute content. The tertiary dendrite arm spacings along the length of the DS Sn-52 wt.%Bi alloy casting are shown to be lower than those obtained for the Sn-34 wt.%Bi alloy casting. The results of mechanical tests show that, with the decrease in the alloy Bi content, both tensile strength and hardness are improved. This is shown to be mainly attributed to the higher density of Bi precipitates decorating the Sn-rich dendrites, which are finer than the equivalent phase developed for the Sn-52 wt.%Bi alloy. However, the ductility is shown to be significantly improved for specimens associated with regions of more refined microstructure of the Sn-52 wt.%Bi alloy DS casting. A microstructure combining much branched dendrites, fine Bi particles within the β-Sn dendritic matrix and an important proportion of very fine eutectic formed by alternate Bi-rich and Sn-rich phase, seems to be conducive to this higher ductility. In this case, the fracture surface is shown to be more finely broken with presence of dimples for this particular condition, i.e., characteristic of a ductile fracture mode.

  10. Wetting and Mechanical Performance of Zirconia Brazed with Silver/Copper Oxide and Silver/Vanadium Oxide Alloys

    SciTech Connect

    Sinnamon, Kathleen E.; Meier, Alan; Joshi, Vineet V.

    2014-12-01

    The wetting behavior and mechanical strength of silver/copper oxide and silver/vanadium oxide braze alloys were investigated for both magnesia-stabilized and yttria-stabilized (Mg-PSZ and Y-TZP) transformation toughened zirconia substrates. The temperatures investigated were 1000 to 1100°C, with oxide additions of 1 to 10 weight percent V2O5 or CuO, and hold times of 0.9 to 3.6 ks. Increasing either the isothermal hold temperature or time had a distinctly negative effect on the joint strength. The maximum strengths for both braze alloys were obtained for 5 wt. % oxide additions at 1050°C with a hold time of 0.9 ks. The Mg-PSZ/Ag-CuO system exhibited a average fracture strength of 255 MPa (45% of the reported monolithic strength), and the Y-TZP/Ag-CuO system had an average fracture strength of 540 MPa (30% of the reported monolithic strength). The fracture strengths were lower for the Ag-V2O5 braze alloys, with fracture strengths of approximately 180 MPa (30% of the monolithic strength) for Mg-PSZ versus approximately 160 MPa (10% of the monolithic strength) for Y-TZP. No interfacial products were observed in low magnification SEM analysis for the brazing alloys containing V2O5 additions, while there were interfacial products present for brazes prepared with CuO additions in the braze alloy.

  11. The debonding and fracture of Si particles during the fatigue of a cast Al-Si alloy

    SciTech Connect

    Gall, K.; Yang, N.; Horstemeyer, M.; McDowell, D.L.; Fan, J.

    1999-12-01

    Constant-amplitude high-cycle fatigue tests ({sigma}{sub max} = 133 MPa, {sigma}{sub max}/{sigma}{sub y} = 0.55, and R = 0.1) were conducted on a cylindrical samples machined from a cast A356-T6 aluminum plate: The fracture surface of the sample with the smallest fatigue-crack nucleating defect was examined using a scanning electron microscope (SEM). For low crack-tip driving forces (fatigue-crack growth rates of da/dN {lt} 1 x 10{sup {minus}7} m/cycle), the authors discovered that a small semicircular surface fatigue crack propagated primarily through the Al-1% Si dendrite cells. The silicon particles in the eutectic remained intact and served as barriers at low fatigue-crack propagation rates. when the semicircular fatigue crack inevitably crossed the three-dimensional Al-Si eutectic network, it propagated primarily along the interface between the silicon particles and the Al-1% Si matrix. Furthermore, nearly all of the silicon particles were progressively debonded by the fatigue cracks propagating at low rates, with the exception of elongated particles with a major axis perpendicular to the crack plane, which were fractured. As the fatigue cracks grew with a high crack-tip driving force (fatigue-crack growth rates of da/dN {gt} 1 x 10{sup {minus}6} m/cycle), silicon particles ahead of the crack tip were fractured, and the crack subsequently propagated through the weakest distribution of prefractured particles in the Al-Si eutectic. Only small rounded silicon particles were observed to debond while the fatigue crack grew at high rates. Using fracture-surface markings and fracture mechanics, a macroscopic measure of the maximum critical driving force between particle debonding vs fracture during fatigue-crack growth was calculated to be approximately K{sub max}{sup tr} {approx} 6.0 MPa {radical}m for the present cast A356 alloy.

  12. Application of fracture mechanics to graphite under complex stress conditions

    NASA Technical Reports Server (NTRS)

    Yahr, G. T.; Valachovic, R. S.

    1974-01-01

    The purpose of this study was to examine the applicability of linear-elastic fracture mechanics to graphite under multiaxial stress conditions. The specimens were thick-walled graphite cylinders with flat heads which were internally pressurized. Two series of specimens were used. The first series had complete circumferential notches machined diagonally into the head-cylinder juncture region, while the second series was unnotched. The methods of linear-elastic fracture mechanics and a finite-element analysis were used to predict pressures to cause fracture for both notched and unnotched specimens.

  13. Effect of nano-additives on microstructure, mechanical properties and wear behaviour of Fe⿿Cr⿿B hardfacing alloy

    NASA Astrophysics Data System (ADS)

    Gou, Junfeng; Lu, Pengpeng; Wang, You; Liu, Saiyue; Zou, Zhiwei

    2016-01-01

    Fe⿿Cr⿿B hardfacing alloys with different nano-additives content were investigated. The effects of nano-additives on the microstructures of hardfacing alloy were studied by using optical microscope, scanning electron microscope, X-ray diffractometer. The hardness and the fracture toughness of hardfacing alloys were measured, respectively. The sliding wear tests were carried out using a ball-on-disc tribometer. The experimental results showed that primary carbide of hardfacing alloys was refined and its distribution became uniform with content of nano-additives increased. The hardfacing alloys are composed of Cr7C3, Fe7C3, α-Fe and Fe2B according to the results of X-ray diffraction. The hardness of hardfacing alloys increased linearly with the increase of nano-additives. The hardness of the hardfacing alloy with 1.5 wt.% nano-additives increased 54.8% than that of the hardfacing alloy without nano-additives and reached to 1011HV. The KIC of the hardfacing alloy with 0.65 wt.% nano-additives was 15.4 MPam1/2, which reached a maximum. The value increased 57.1% than that of the hardfacing alloy without nano-additives. The wear rates of the hardfacing layer with 0.65 wt.% and 1.0 wt.% nano-additives decreased about 88% than that of the hardfacing layer without nano-additives. The main wear mechanism was adhesion wear.

  14. Oxidation mechanisms for alloys in single-oxidant gases

    SciTech Connect

    Whittle, D.P.

    1981-03-01

    Scales formed on alloys invariably contain the alloy constituents in a ratio different from that in the alloy, owing to the differing thermodynamic tendencies of the alloy components to react with the oxidant and to differences in diffusion rates in scale and alloy phases. This complex interrelationship between transport rates and the thermodynamics of the alloy-oxidant system can be analyzed using multicomponent diffusion theory when transport-controlled growth of single or multi-layered scales occurs. In particular, the superimposition of the diffusion data on an isothermal section of the appropriate phase diagram indicates the likely morphologies of the reaction products, including the sequence of phases found in the scale, the occurrence of internal oxidation and the development of an irregular metal/scale interface. The scale morphologies on alloys are also time-dependent: there is an initial transient stage, a steady state period, and a final breakdown, the latter often related to mechanical influences such as scale adherence, spallation, thermal or mechanical stresses and void formation. Mechanical influences have a more devastating effect in alloy oxidation due to the changes in alloy surface composition during the steady state period.

  15. Ship Fracture Mechanisms Investigation. Part 1

    DTIC Science & Technology

    1987-01-01

    the spar deck, but is belcw the nominal yield for mild steel of 32,000 psi. 3-13 Initiation Site Arrest Down- Toward Ship’s bottom Up- Toward Figure 3...hatch. The deck material in the vicinity of fracture was 46mm (1.81 inch)"EH33" normalized steel . Description of the Circumstances at the Time of...finally installing "CS" normalized steel doubler plate over the existing deck plate at the hatch corners. This repair fractured in the spring of 1976

  16. Dynamic Strength and Edge Effects at Spall Fracture for Titanium Alloys of Varying Oxygen Content

    NASA Astrophysics Data System (ADS)

    Razorenov, Sergey; Kanel, Gennady; Utkin, Alexander; Bogach, Andrey; Burkins, Matthew; Gooch, William

    1999-06-01

    The two objectives of this paper were to study the system of engineering criteria of fracture and fragmentation, including the energy criterion for separation of a spall element, and to study the influence of oxygen content in Ti-6Al-4V alloy on the resistance to plastic deformation and fracture. In the experiments, the peak shock stress was varied from 4 to 75 GPa with the load duration from 10-7 s to 10-5 s. The VISAR free-surface velocity measurements show a growth by 20im t of alloys with increasing oxygen content from 0.105l trength value. Within experimental uncertainty, the specific energy of spall element separation is practically the same for all three types of samples tested.

  17. Influence of hydrogen on deformation and fracture processes in high-strength aluminum alloys

    SciTech Connect

    Bond, G.M.; Robertson, I.M.; Birnbaum, H.K.

    1987-09-01

    Hydrogen-enhanced fracture of age hardened 7050 and 7075 alloys has been studied by an in situ environmental cell TEM deformation technique. The effects of both gaseous and solute hydrogen were investigated. The effects of high-fugacity gaseous hydrogen atmospheres on the behavior of dislocations and crack tips in these alloys were monitored by video recording of dynamic events. It is concluded that hydrogen enhances dislocation mobility and reduces the flow stress. Fracture in hydrogen was similar to that observed in vacuum except that it occurred at lower stresses due to hydrogen-enhanced dislocation mobility. Large silicon- and iron-rich precipitates influenced cracking in cathodically precharged specimens as a result of hydrogen accumulation in their vicinity.

  18. Nondestructive determination of mechanical properties. [aluminum alloys

    NASA Technical Reports Server (NTRS)

    Schneider, E.; Chu, S. L.; Salma, K.

    1984-01-01

    Aluminum alloys of types 1100, 3003, 5052, 6061, and 2024 were used to study the sensitivity of the acousto-elastic constant to changes in the microstructure. Results show that there is a strong relationship between the acousto-elastic constants and the yield strength and hardness. This relationship depends on whether the alloy is strain hardened or precipitation hardened. In strain hardened alloys, the constants increase as the amount of solid solution is decreased, while the behavior is the opposite in precipitation hardened alloys.

  19. Determination of design allowable properties. Fracture of 2219-T87 aluminum alloy

    NASA Technical Reports Server (NTRS)

    Engstrom, W. L.

    1972-01-01

    A literature survey was conducted to provide a comprehensive report of available valid data on tensile properties, fracture toughness, fatigue crack propagation, and sustained load behavior of 2219-T87 aluminum alloy base metal and weldments, as applicable to manned spacecraft tankage. Most of the data found were from tests conducted at room temperature, -320 F and -423 F. Data are presented in graphical and tabular form, and areas in which data are lacking are established.

  20. Microstructure and mechanical properties of thermoelectric nanostructured n-type silicon-germanium alloys synthesized employing spark plasma sintering

    SciTech Connect

    Bathula, Sivaiah; Gahtori, Bhasker; Tripathy, S. K.; Tyagi, Kriti; Srivastava, A. K.; Dhar, Ajay; Jayasimhadri, M.

    2014-08-11

    Owing to their high thermoelectric (TE) figure-of-merit, nanostructured Si{sub 80}Ge{sub 20} alloys are evolving as a potential replacement for their bulk counterparts in designing efficient radio-isotope TE generators. However, as the mechanical properties of these alloys are equally important in order to avoid in-service catastrophic failure of their TE modules, we report the strength, hardness, fracture toughness, and thermal shock resistance of nanostructured n-type Si{sub 80}Ge{sub 20} alloys synthesized employing spark plasma sintering of mechanically alloyed nanopowders of its constituent elements. These mechanical properties show a significant enhancement, which has been correlated with the microstructural features at nano-scale, delineated by transmission electron microscopy.

  1. Production of Cu-Al-Ni Shape Memory Alloys by Mechanical Alloy

    SciTech Connect

    Goegebakan, Musa; Soguksu, Ali Kemal; Uzun, Orhan; Dogan, Ali

    2007-04-23

    The mechanical alloying technique has been used to produce shape memory Cu83Al13Ni4 alloy. The structure and thermal properties were examined by using scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The morphology of the surface suggests the presence of martensite.

  2. Fracture Mechanics for Structural Adhesive Bonds

    DTIC Science & Technology

    1977-10-01

    51 24 Magnified fracture surface photographs for specimen 52 CLS-I 25 Pure mode I sustained-load crack grouth 54 26 Pure mode ! SCC Data in 3 27CK...the technical and economic feasibility of primary adhesively bonded structure. The Air Force aircraft structural integrity program document MEI-STD

  3. Elastic-plastic fracture mechanics technology

    NASA Technical Reports Server (NTRS)

    Newman, J. C., Jr. (Editor); Loss, F. J. (Editor)

    1985-01-01

    Among the topics discussed are: fracture analysis methods evaluation; instability prediction using the K sub R-curve approach; and the deformation failure assessment diagram. Consideration is also given to: instability prediction based on the modified J, J sub M-resistance curve approach; and stable crack growth and instability prediction on the V by means of the V sub R-curve method.

  4. Amorphous powders of Al-Hf prepared by mechanical alloying

    SciTech Connect

    Schwarz, R.B.; Hannigan, J.W.; Sheinberg, H.; Tiainen, T.

    1988-01-01

    We synthesized amorphous Al/sub 50/Hf/sub 50/ alloy powder by mechanically alloying an equimolar mixture of crystalline powders of Al and Hf using hexane as a dispersant. We characterized the powder as a function of mechanical-alloying time by scanning electron microscopy, x-ray diffraction, and differential scanning calorimetry. Amorphous Al/sub 50/Hf/sub 50/ powder heated at 10 K s/sup /minus/1/ crystallizes polymorphously at 1003 K into orthorhombic AlHf (CrB-type structure). During mechanical alloying, some hexane decomposes and hydrogen and carbon are incorporated into the amorphous alloy powder. The hydrogen can be removed by annealing the powder by hot pressing at a temperature approximately 30 K below the crystallization temperature. The amorphous compacts have a diamond pyramidal hardness of 1025 DPH. 24 refs., 7 figs., 1 tab.

  5. Fracture mechanics for delamination problems in composite materials

    NASA Technical Reports Server (NTRS)

    Wang, S. S.

    1983-01-01

    A fracture mechanics approach to the well-known delamination problem in composite materials is presented. Based on the theory of anisotropic laminate elasticity and interlaminar fracture mechanics concepts, the composite delamination problem is formulated and solved. The exact order of the delamination crack-tip stress singularity is determined. Asymptotic stress and displacement fields for an interlaminar crack are obtained. Fracture mechanics parameters such as mixed-mode stress intensity factors, KI, KII, KIII, and the energy release rate, G, for composite delamination problems are defined. To illustrate the fundamental nature of the delamination crack behavior, solutions for edge-delaminated graphite-epoxy composites under uniform axial extension are presented. Effects of fiber orientation, ply thickness, and delamination length on the interlaminar fracture are examined.

  6. Work of fracture of a composite resin: fracture-toughening mechanisms.

    PubMed

    Baudin, Carmen; Osorio, Raquel; Toledano, Manuel; de Aza, Salvador

    2009-06-01

    The aim of this work was to investigate those mechanical parameters able to describe the fracture behavior of dental composite resins. A commercially available fine-particle micro-hybrid resin composite was used. Classical parameters as Young's modulus, strength distribution, and critical stress intensity factor were considered. Strength values were determined using the diametrical compression of discs test and for the critical stress intensity factor both unstable and controlled fracture tests were used. Controlled fracture tests allowed determining the work of fracture. Microstructure was studied by optical and field emission scanning electron microscopy. The obtained properties have been Young's modulus, 17.7 +/- 0.6 GPa; Weibull modulus, m = 14 (upper and lower limits for 90% confidence: 17 and 10); characteristic strength 51 MPa (upper and lower limits for 90% confidence: 53 and 49 MPa); critical stress intensity factor in mode I, K(IC) = 1.3 +/- 0.1 and work of fracture, gamma(wof) = 8-9 J/m(2). Pores and bubbles formed during the packing of the composite were identified as critical defects in the tested specimens. Crack deflection and branching have been identified as toughening mechanisms. Classical mechanical parameters (Young's modulus, hardness...) are not able to efficiently predict the major clinical failure mode of composite resins by fatigue. Work of fracture analysis, which is dependant on microstructural parameters such as particle size and shape, have to be included when testing mechanical properties of dental composite resins in future research studies. 2008 Wiley Periodicals, Inc.

  7. In Vitro Fracture of Human Cortical Bone: Local Fracture Criteria and Toughening Mechanisms

    SciTech Connect

    Nalla, R; Stolken, J; Kinney, J; Ritchie, R

    2004-08-18

    A micro-mechanistic understanding of bone fracture that encompasses how cracks interact with the underlying microstructure and defines their local failure mode is lacking, despite extensive research on the response of bone to a variety of factors like aging, loading, and/or disease. Micro-mechanical models for fracture incorporating such local failure criteria have been widely developed for metallic and ceramic materials systems; however, few such deliberations have been undertaken for the fracture of bone. In fact, although the fracture event in mineralized tissues such as bone is commonly believed to be locally strain controlled, until recently there has been little experimental evidence to support this widely held belief. In the present study, a series of in vitro experiments involving a double-notch bend test geometry are performed in order to shed further light on the nature of the local cracking events that precede catastrophic fracture in bone and to define their relationship to the microstructure. Specifically, crack-microstructure interactions are examined to determine the salient toughening mechanisms in human cortical bone and to characterize how these may affect the anisotropy in fracture properties. Based on preliminary micro-mechanical models of these processes, in particular crack deflection and uncracked ligament bridging, the relative importance of these toughening mechanisms is established.

  8. Fracture of Ni-Ti superelastic alloy under sustained tensile load in physiological saline solution containing hydrogen peroxide.

    PubMed

    Yokoyama, Ken'ichi; Ogawa, Toshio; Fujita, Atsushi; Asaoka, Kenzo; Sakai, Jun'ichi

    2007-09-01

    The fracture of Ni-Ti superelastic alloy has been investigated by a sustained tensile-loading test in physiological saline solution containing hydrogen peroxide (0.15M NaCl + 0.3M H(2)O(2)). The fracture always occurs when the applied stress exceeds the critical stress for martensite transformation. In contrast, under a low applied stress, the fracture does not always occur within 1000 h. The fracture is probably mainly caused by localized corrosion associated with the preferential dissolution of nickel ions. In 0.3M H(2)O(2) solution without NaCl, the fracture does not occur even under a high applied stress. The results of the present study imply that one reason for the fracture of the Ni-Ti superelastic alloy in vivo is localized corrosion due to the synergistic effects of hydrogen peroxide and sodium chloride under applied stress.

  9. Material properties and fracture mechanics in relation to ceramic machining

    SciTech Connect

    Griffith, L.V.

    1993-12-02

    Material removal rate, surface finish, and subsurface damage are largely governed by fracture mechanics and plastic deformation, when ceramics are machined using abrasive methods. A great deal of work was published on the fracture mechanics of ceramics in the late 1970s and early 1980s, although this work has never resulted in a comprehensive model of the fixed abrasive grinding process. However, a recently published model describes many of the most important features of the loose abrasive machining process, for example depth of damage, surface roughness, and material removal rate. Many of the relations in the loose abrasive machining model can be readily discerned from fracture mechanics models, in terms of material properties. By understanding the mechanisms of material removal, from a material properties perspective, we can better estimate how one material will machine in relation to another. Although the fracture mechanics models may have been developed for loose abrasive machining, the principles of crack initiation and propagation are equally valuable for fixed abrasive machining. This report provides a brief review of fracture in brittle materials, the stress distribution induced by abrasives, critical indenter loads, the extension of cracks, and the relation of the fracture process to material removal.

  10. Metallic Reinforcement of Direct Squeeze Die Casting Aluminum Alloys for Improved Strength and Fracture Resistance

    SciTech Connect

    D. Schwam: J.F. Wallace: Y. Zhu: J.W. Ki

    2004-10-01

    The utilization of aluminum die casting as enclosures where internal equipment is rotating inside of the casting and could fracture requires a strong housing to restrain the fractured parts. A typical example would be a supercharger. In case of a failure, unless adequately contained, fractured parts could injure people operating the equipment. A number of potential reinforcement materials were investigated. The initial work was conducted in sand molds to create experimental conditions that promote prolonged contact of the reinforcing material with molten aluminum. Bonding of Aluminum bronze, Cast iron, and Ni-resist inserts with various electroplated coatings and surface treatments were analyzed. Also toughening of A354 aluminum cast alloy by steel and stainless steel wire mesh with various conditions was analyzed. A practical approach to reinforcement of die cast aluminum components is to use a reinforcing steel preform. Such performs can be fabricated from steel wire mesh or perforated metal sheet by stamping or deep drawing. A hemispherical, dome shaped casting was selected in this investigation. A deep drawing die was used to fabricate the reinforcing performs. The tendency of aluminum cast enclosures to fracture could be significantly reduced by installing a wire mesh of austenitic stainless steel or a punched austenitic stainless steel sheet within the casting. The use of reinforcements made of austenitic stainless steel wire mesh or punched austenitic stainless steel sheet provided marked improvement in reducing the fragmentation of the casting. The best strengthening was obtained with austenitic stainless steel wire and with a punched stainless steel sheet without annealing this material. Somewhat lower results were obtained with the annealed punched stainless steel sheet. When the annealed 1020 steel wire mesh was used, the results were only slightly improved because of the lower mechanical properties of this unalloyed steel. The lowest results were

  11. Low melting temperature alloy deployment mechanism and recent experiments

    NASA Technical Reports Server (NTRS)

    Madden, M. J.

    1993-01-01

    This paper describes the concept of a low melting temperature alloy deployment mechanism, U.S. Patent 4,842,106. It begins with a brief history of conventional dimethyl-silicone fluid damped mechanisms. Design fundamentals of the new melting alloy mechanism are then introduced. Benefits of the new over the old are compared and contrasted. Recent experiments and lessons learned complete this paper.

  12. Mechanical and interfacial characterization of laser welded Co-Cr alloy with different joint configurations

    PubMed Central

    Kokolis, John; Chakmakchi, Makdad; Theocharopoulos, Antonios; Prombonas, Anthony

    2015-01-01

    PURPOSE The mechanical and interfacial characterization of laser welded Co-Cr alloy with two different joint designs. MATERIALS AND METHODS Dumbbell cast specimens (n=30) were divided into 3 groups (R, I, K, n=10). Group R consisted of intact specimens, group I of specimens sectioned with a straight cut, and group K of specimens with a 45° bevel made at the one welding edge. The microstructure and the elemental distributions of alloy and welding regions were examined by an SEM/EDX analysis and then specimens were loaded in tension up to fracture. The tensile strength (TS) and elongation (ε) were determined and statistically compared among groups employing 1-way ANOVA, SNK multiple comparison test (α=.05) and Weibull analysis where Weibull modulus m and characteristic strength σο were identified. Fractured surfaces were imaged by a SEM. RESULTS SEM/EDX analysis showed that cast alloy consists of two phases with differences in mean atomic number contrast, while no mean atomic number was identified for welded regions. EDX analysis revealed an increased Cr and Mo content at the alloy-joint interface. All mechanical properties of group I (TS, ε, m and σο) were found inferior to R while group K showed intermediated values without significant differences to R and I, apart from elongation with group R. The fractured surfaces of all groups showed extensive dendritic pattern although with a finer structure in the case of welded groups. CONCLUSION The K shape joint configuration should be preferred over the I, as it demonstrates improved mechanical strength and survival probability. PMID:25722836

  13. Effect of heat treatment on the fracture and structure of tin-indium solder alloy

    NASA Astrophysics Data System (ADS)

    Shalaby, R. M.; El-Sayed, M.

    2005-01-01

    The effect of heat treatment on the structure, hardness, and electrical resistivity of the crystalline Sn100-x In-x (x=10 wt.%) solder alloy is studied. The structures of as-casted and heat-treated alloys have been investigated by means of a X-ray diffraction technique. Using X-ray analysis a crystalline beta-Sn and an In phase are detected. The amount of the crystalline phases increases upon increasing the annealing temperature. It is found that the fracture is delayed from 8.6 kg/mm(2) at 50 s and 100 g at room temperature to 4 kg/mm(2) at 90 s and 100 g at 423 K. Differential thermal analysis was used to investigate the melting characteristics of the alloy (m.p. similar to 214 degrees C). The resistivity is also determined for samples thermally and non-thermally treated.

  14. Weldable aluminum alloy has improved mechanical properties

    NASA Technical Reports Server (NTRS)

    Westerlund, R. W.

    1966-01-01

    Weldable aluminum alloy has good resistance to stress-corrosion cracking, shows unchanged strength and formability after storage at room temperature, and can be pre-aged, stretched, and aged. Since toxic fumes of cadmium oxide are evolved when the new alloy is welded, adequate ventilation must be provided.

  15. Analysis of Fracture Mechanism for Al-Mg/SiCp Composite Materials

    NASA Astrophysics Data System (ADS)

    Maleque, M. A.; Adebisi, A. A.; Izzati, N.

    2017-03-01

    The present study aims to examine the fracture mechnism of silicon carbide particle (SiCp) reinforced aluminium matrix composite (AMC) material with 1 wt% addition of magnesium is fabricated using the stir casting process. The aluminium composite (Al-Mg/SiCp) is investigated for fatigue life and impact strength considering reinforcement weight fraction and influence of temperature on fracture toughness. The fabricated composite was tested using fatigue testing machine and charpy impact tester. Fractographic observations were evaluated with the scanning electron microscopy (SEM) on the fracture surface. It was found that increasing the SiCp weight fraction increased the fatigue life of the composite. Moreover, the 20 wt% SiCp Al-Mg composite attained the highest number of cycle and fatigue life compared to other variations. The mechanism responsible for the phenomena includes load transfer from the Al matrix alloy phase to the high strength and stiffness of the incorporated SiCp. The temperature variation influenced the impact strength of the composite and improved fracture toughness is achieved at 150 °C. It can be concluded from this study that reinforcement weight fraction and temperature affects the fracture behavior of the composites.

  16. The effect of alloying elements on the microstructural development and mechanical properties of multiphase nickel-rich nickel-aluminum alloys

    NASA Astrophysics Data System (ADS)

    Abdo, Zafir Abdo Mohamed

    2000-11-01

    The research work presented in this study is devoted towards examining bulk multiphase nickel-rich alloys derived from the intermetallic compound beta-NiAl. The microstructural development and structure - property relationship of nickel-rich NiAl alloys with different alloying element additions is considered. Additions of chromium, chromium plus titanium, copper as well as higher order additions to nickel-rich NiAl alloys are investigated. The general theme of this research is to produce bulk alloys with fixed compositions and investigate their microstructural stability with respect to high temperature treatments as well as their room temperature mechanical behavior. Many high temperature industrial applications can benefit from these studies. Examples include diffusion coating of nickel-base superalloys, joining of NiAl and nickel bearing substrate and the future application of NiAl alloys in high temperature structural applications. In this work, Cr is selected as an alloying element due to the ability of Cr to enhance the room temperature fracture toughness and ductility of NiAl. The possibility of producing a beta - gamma/gamma ' mixture in high aluminum content Ni-Al-Cr alloys is investigated. The effect of Cr content and high temperature heat treatment on the stability a beta - gamma/gamma' mixture is studied. The precipitation of various morphologies of the A2 type alpha-Cr phase and their effect on the stability of the produced microstructure is evaluated. The formation of an intradendritic L10 type martensite and the precipitation of gamma' from the martensitic regions as a result of high temperature aging treatments is studied. The intent of alloying NiAl with Cr and Ti is to produce microstructures with the potential for combined improved low temperature ductility and high temperature creep resistance. The role of Ti levels in the stability of a beta/beta ' two phase mixture is discussed. The mechanisms of beta ' decomposition as a result of high

  17. Spall fracture and strength of uranium, plutonium and their alloys under shock wave loading

    NASA Astrophysics Data System (ADS)

    Golubev, Vladimir

    2015-06-01

    Numerous results on studying the spall fracture phenomenon of uranium, two its alloys with molybdenum and zirconium, plutonium and its alloy with gallium under shock wave loading are presented in the paper. The majority of tests were conducted with the samples in the form of disks 4mm in thickness. They were loaded by the impact of aluminum plates 4mm thick through a copper screen serving as the cover or bottom part of a special container. The initial temperature of samples was changed in the range of -196 - 800 C degree for uranium and 40 - 315 C degree for plutonium. The character of spall failure of materials and the degree of damage for all tested samples were observed on the longitudinal metallographic sections of recovered samples. For a concrete test temperature, the impact velocity was sequentially changed and therefore the loading conditions corresponding to the consecutive transition from microdamage nucleation up to complete macroscopic spall fracture were determined. Numerical calculations of the conditions of shock wave loading and spall fracture of samples were performed in the elastoplastic approach. Several two- and three-dimensional effects of loading were taken into account. Some results obtained under conditions of intensive impulse irradiation and intensive explosive loading are presented too. The rather complete analysis and comparison of obtained results with the data of other researchers on the spall fracture of examined materials were conducted.

  18. Test environments and mechanical properties of Zr-base bulk amorphous alloys

    SciTech Connect

    Liu, C.T.; Heatherly, L.; Easton, D.S.

    1998-07-01

    The mechanical properties of two Zr-base bulk amorphous alloys (BAA), Zr-10Al-30Cu-5Ni (BAA-10) and Zr-10Al-5Ti-17.9Cu-14.6Ni (BAA-11), were studied by both tensile and compressive tests at room temperature in various test environments. The BAA ingots up to 7 mm in diameter were successfully produced by both arc melting and drop casting and induction melting and injection casting. The BAA specimens deformed mainly elastically, followed by catastrophic failure along shear bands. Examination of the fracture region revealed ductile fracture features resulting from a substantial increase in temperature, which was attributable to the conversion of the stored elastic strain energy to heat. Surprisingly, liquid droplets located at major shear-band cracks adjacent to the fracture section were observed, indicating the occurrence of local melting during fracture. The angle orientation of shear bands, shear-band cracks, and fracture surfaces relative to the stress axis is quite different for BAA specimens tested in tension and compression. This suggests that both shear stress and normal stress may play a role in developing shear bands during plastic deformation. The tensile properties of BAAs were found to be insensitive to the test environment at room temperature. However, the reaction of BAAs with distilled water and heavy water was detected by laser desorption mass spectrometry (LDMS). These results suggest that moisture-induced hydrogen embrittlement in BAAs may be masked by catastrophic fracture following shear bands.

  19. Elastic-plastic fracture mechanics of compact bone

    NASA Astrophysics Data System (ADS)

    Yan, Jiahau

    Bone is a composite composed mainly of organics, minerals and water. Most studies on the fracture toughness of bone have been conducted at room temperature. Considering that the body temperature of animals is higher than room temperature, and that bone has a high volumetric percentage of organics (generally, 35--50%), the effect of temperature on fracture toughness of bone should be studied. Single-edged V-shaped notched (SEVN) specimens were prepared to measure the fracture toughness of bovine femur and manatee rib in water at 0, 10, 23, 37 and 50°C. The fracture toughness of bovine femur and manatee rib were found to decrease from 7.0 to 4.3 MPa·m1/2 and from 5.5 to 4.1 MPa·m1/2, respectively, over a temperature range of 50°C. The decreases were attributed to inability of the organics to sustain greater stresses at higher temperatures. We studied the effects of water and organics on fracture toughness of bone using water-free and organics-free SEVN specimens at 23°C. Water-free and organics-free specimens were obtained by placing fresh bone specimen in a furnace at different temperatures. Water and organics significantly affected the fracture toughness of bone. Fracture toughness of the water-free specimens was 44.7% (bovine femur) and 32.4% (manatee rib) less than that of fresh-bone specimens. Fracture toughness of the organics-free specimens was 92.7% (bovine femur) and 91.5% (manatee rib) less than that of fresh bone specimens. Linear Elastic Fracture Mechanics (LEFM) is widely used to study bone. However, bone often has small to moderate scale yielding during testing. We used J integral, an elastic-plastic fracture-mechanics parameter, to study the fracture process of bone. The J integral of bovine femur increased from 6.3 KJ/mm2 at 23°C to 6.7 KJ/mm2 at 37°C. Although the fracture toughness of bovine bone decreases as the temperature increases, the J integral results show a contrary trend. The energy spent in advancing the crack beyond the linear

  20. Environment enhanced fatigue crack propagation in metals: Inputs to fracture mechanics life prediction models

    NASA Technical Reports Server (NTRS)

    Gangloff, Richard P.; Kim, Sang-Shik

    1993-01-01

    This report is a critical review of both environment-enhanced fatigue crack propagation data and the predictive capabilities of crack growth rate models. This information provides the necessary foundation for incorporating environmental effects in NASA FLAGRO and will better enable predictions of aerospace component fatigue lives. The review presents extensive literature data on 'stress corrosion cracking and corrosion fatigue.' The linear elastic fracture mechanics approach, based on stress intensity range (Delta(K)) similitude with microscopic crack propagation threshold and growth rates, provides a basis for these data. Results are presented showing enhanced growth rates for gases (viz., H2 and H2O) and electrolytes (e.g. NaCl and H2O) in aerospace alloys including: C-Mn and heat treated alloy steels, aluminum alloys, nickel-based superalloys, and titanium alloys. Environment causes purely time-dependent accelerated fatigue crack growth above the monotonic load cracking threshold (KIEAC) and promotes cycle-time dependent cracking below (KIEAC). These phenomenon are discussed in terms of hydrogen embrittlement, dissolution, and film rupture crack tip damage mechanisms.

  1. Mechanical Property Evaluation of Aluminum Alloy 7010-T73651

    DTIC Science & Technology

    1980-07-01

    is intended to improve stress corrosion cracking resistance. Except for a slightly higher copper content, the two alloys, 7010 and 7050 , are similar...sensitive; the room temperature threshold for stress corrosion cracking in a 3.5% Wt. NaCl solution was determined to be in excess of 70 percent of the...Orientation Tensile Tests 4 3 Compact Type Specimen Configurations Used for Fracture Toughness (KIC), Threshold for Stress Corrosion Cracking (KISCC

  2. Multiescalar studies of fracturing mechanisms in fluvial-lacustrine basins

    NASA Astrophysics Data System (ADS)

    Carreon-Freyre, D.; Cerca, M.; Hidalgo, C.; Hernandez-Marin, M.

    2007-05-01

    Fracturing of clayey fluvial and lacustrine deposits has become a major problem in several cities of central Mexico. The available data reveals the coexistence of several factors determining fracturing at different scales. As main factors we analyze the variation in compressibility of sediments causing differential deformation and withdrawal of groundwater causing a drop in pore pressure. Compressibility depends on consolidation, a term that in soil mechanics refers to the expulsion of interstitial water, and provokes volume decrease and land subsidence. Although major volume decrease occurs in the vertical scale, consolidation of silty clayey materials generates also horizontal tensile stresses. Considering that this factor can be determining to the generation of fractures, the deformational conditions of clayey, silty and sandy sequences is analyzed integrating their stratigraphy and mechanical characteristics. A particular emphasis is made in the mineralogical heterogeneity of the clay fraction that can be related to compressibility variations and can generate micro-fracturing by differential deformation. As study case we analyze the mechanical and geological properties of two sedimentary sequences with contrasting hydraulic and mechanical behavior. Our results show that the paleoenvironmental history of sediments can be used to determine a specific type of fracturing. Thus, the fracturing in fluvial lacustrine deposits is not a random phenomenon but is highly dependent of the geological properties of materials.

  3. The Mechanics of Long Bone Fractures.

    DTIC Science & Technology

    1981-01-31

    frequently at the rapid loading rates, indi- cating the relationship of fracture to energy dissipation, since crack formation is an energy...plotted in Figure 15. It can be seen that for angles as large as 100 the error is small. ERROR DUE TC fNCUNATfON OF SCANN NO PLANE TO :_ONGOTUD!NA!_ BONE...aspects. Flying Personnel Research Committee, FPRC/1166, 1961. 10. Lovejoy, C.O., and Barton, T.J.: A simple, rapid method of obtaining geometrical

  4. An investigation on quench cracking behavior of superalloy Udimet 720LI using a fracture mechanics approach

    SciTech Connect

    Mao, J.; Keefer, V.L.; Chang, K.M.; Furrer, D.

    2000-04-01

    Quench cracking can be a serious problem in the heat treatment of high strength superalloys. A new fracture mechanics approach, quench cracking toughness (K{sub Q}), was introduced to evaluate the on-cooling quench cracking resistance of superalloy Udimet 720LI. A fully automatic computer controlled data acquisition and processing system was set up to track the on-cooling quenching process and to simulate the quench cracking. The influences of grain size, cooling rate, solution temperature, and alloy processing routes on quench cracking resistance were investigated. Research results indicate that quench cracking revealed a typical brittle and intergranular failure at high temperatures, which causes a lower quench cracking toughness in comparison to fracture toughness at room temperature. Fine grain structures show the higher quench cracking resistance and lower failure temperatures than intermediate grain structures at the same cooling rates. Moreover, higher cooling rate results in lower cracking toughness under the same grain size structures. In comparison of processing routes, powder metallurgy (PM) alloys show higher cracking resistance than cast and wrought (CW) alloys for fine grain structures at the same cooling rates. However, for immediate grain structure, there is no obvious difference of K{sub Q} between the two processing route in this study.

  5. Microstructure and Mechanical Properties of Ultra-Fine Grain Al-Zr Alloy Fabricated by Mechanical Alloying Process.

    PubMed

    Kim, Chung Seok; Kim, Il-Ho

    2015-08-01

    The ultra-fine grain Al-4Zr alloy has been successfully fabricated by a mechanical alloying process. The intermetallic Al3Zr phases strongly enhance the mechanical properties of Al-based alloy and prevent grain growth of alloy. The phase stability and transformation during mechanical alloying process have been investigated. The ultra-fine grain alloy has been successfully obtained. The thin film of Al-4Zr alloy has been observed by a transmission electron microscope. The equivalent grain size of as-milling specimen is 55 nm. After milling process, the specimens were heat treated at 350 °C to 650 °C. The equivalent grain size of heat treated specimens were 80 nm at 350 °C and 130 nm at 650 °C. Some of Zr atoms were dissolved into the Al matrix and most of them reacted with hydrogen produced by decomposition of PCA to form ZrH2 during mechanical alloying process. These ZrH2 hydrides decomposed gradually after the heat treatment. Stable A13Zr with a D023 structure was formed by heat treatment at temperature of 550 °C.

  6. Adhesive fracture mechanics. [stress analysis for bond line interface

    NASA Technical Reports Server (NTRS)

    Bennett, S. J.; Devries, K. L.; Williams, M. L.

    1974-01-01

    In studies of fracture mechanics the adhesive fracture energy is regarded as a fundamental property of the adhesive system. It is pointed out that the value of the adhesive fracture energy depends on surface preparation, curing conditions, and absorbed monolayers. A test method reported makes use of a disk whose peripheral part is bonded to a substrate material. Pressure is injected into the unbonded central part of the disk. At a certain critical pressure value adhesive failure can be observed. A numerical stress analysis involving arbitrary geometries is conducted.

  7. Advances in the fracture mechanics of cortical bone.

    PubMed

    Bonfield, W

    1987-01-01

    As cortical bone is a semi-brittle solid, its fracture is dependent not only on the magnitude of the applied stress, but also on the nature of any intrinsic or introduced cracks. Consequently a variety of fracture mechanics techniques have been utilised to evaluate the fracture toughness of cortical bone, including the single edge notched, centre notched cylindrical and compact tension methods, and values have been established for the critical stress intensity factor (Kc) and the critical strain energy release rate (Gc). The Kc and Gc values obtained depend on the orientation of the cortical bone, as well as on bone density, the velocity of crack propagation and specimen geometry. The significance of these fracture mechanics parameters for cortical bone is critically reviewed.

  8. Interaction of hydraulic and buckling mechanisms in blowout fractures.

    PubMed

    Nagasao, Tomohisa; Miyamoto, Junpei; Jiang, Hua; Tamaki, Tamotsu; Kaneko, Tsuyoshi

    2010-04-01

    The etiology of blowout fractures is generally attributed to 2 mechanisms--increase in the pressure of the orbital contents (the hydraulic mechanism) and direct transmission of impacts on the orbital walls (the buckling mechanism). The present study aims to elucidate whether or not an interaction exists between these 2 mechanisms. We performed a simulation experiment using 10 Computer-Aided-Design skull models. We applied destructive energy to the orbits of the 10 models in 3 different ways. First, to simulate pure hydraulic mechanism, energy was applied solely on the internal walls of the orbit. Second, to simulate pure buckling mechanism, energy was applied solely on the inferior rim of the orbit. Third, to simulate the combined effect of the hydraulic and buckling mechanisms, energy was applied both on the internal wall of the orbit and inferior rim of the orbit. After applying the energy, we calculated the areas of the regions where fracture occurred in the models. Thereafter, we compared the areas among the 3 energy application patterns. When the hydraulic and buckling mechanisms work simultaneously, fracture occurs on wider areas of the orbital walls than when each of these mechanisms works separately. The hydraulic and buckling mechanisms interact, enhancing each other's effect. This information should be taken into consideration when we examine patients in whom blowout fracture is suspected.

  9. Mechanical properties of amorphous LixSi alloys: a reactive force field study

    NASA Astrophysics Data System (ADS)

    Fan, Feifei; Huang, Shan; Yang, Hui; Raju, Muralikrishna; Datta, Dibakar; Shenoy, Vivek B.; van Duin, Adri C. T.; Zhang, Sulin; Zhu, Ting

    2013-10-01

    Silicon is a high-capacity anode material for lithium-ion batteries. Electrochemical cycling of Si electrodes usually produces amorphous LixSi (a-LixSi) alloys at room temperature. Despite intensive investigation of the electrochemical behaviors of a-LixSi alloys, their mechanical properties and underlying atomistic mechanisms remain largely unexplored. Here we perform molecular dynamics simulations to characterize the mechanical properties of a-LixSi with a newly developed reactive force field (ReaxFF). We compute the yield and fracture strengths of a-LixSi alloys under a variety of chemomechanical loading conditions, including the constrained thin-film lithiation, biaxial compression, uniaxial tension and compression. Effects of loading sequence and stress state are investigated to correlate the mechanical responses with the dominant atomic bonding, featuring a transition from the covalent to the metallic glass characteristics with increasing Li concentration. The results provide mechanistic insights for interpreting experiments, understanding properties and designing new experiments on a-LixSi alloys, which are essential to the development of durable Si electrodes for high-performance lithium-ion batteries.

  10. Mechanical behavior of monocrystalline aluminum-lithium alloy at low temperatures

    SciTech Connect

    Wang, Z.G.; Liu, W.; Xu, Y.B.; Zhang, T.Y.; Zhang, Y. . State Key Lab. for Fatigue and Fracture of Materials)

    1994-12-01

    Investigations have indicated that at low temperature aluminum- lithium alloys display improved toughness and an improved strength-toughness relationship. The yield strength, ultimate tensile strength, elongation and the fracture toughness increase with decreasing temperatures. Several mechanisms have been proposed to explain this most striking feature. Webster claimed that low melting point impurities, such as sodium and potassium, are responsible for the improvement of mechanical properties in Al-Li alloys at low temperatures. However, Venkateswara Rao et al. indicated that the increased delamination at low temperatures can increase the degree of in-plane crack deflection, resulting in toughening of the alloys. On the basis of their own results, Xu and coworker pointed out that the improvement of tensile and fatigue properties at liquid nitrogen temperatures is also presumably attributable to the delamination. Therefore, the mechanisms responsible for the variation in mechanical properties with temperature are not currently well-understood. In order to elucidate the real situation, single crystals of a binary aluminum-lithium alloy were adopted in the present study. This paper is devoted to the description of the behavior of the load-displacement curves and the associated slip traces on the sample surfaces.

  11. Evaluation of the mechanical properties of electroslag refined iron alloys

    NASA Technical Reports Server (NTRS)

    Bhat, G. K.

    1976-01-01

    Nitronic 40 (21Cr-6N-9Mn), HY-130, 9Ni-4Co, and D-6 alloys were prepared and evaluated in the form of 15.2 mm thick plates. Smooth bar tensile tests, double-edge sharp notch fracture toughness tests Charpy V-notch impact tests were conducted on appropriate heat treated specimens of the four steel plates at 22 C, -50 C, -100 C, -150 C, and -196 C. Similar material characterization, including metallographic evaluation studies on air melt and vacuum arc melt grades of same four alloy steels were conducted for comparative purposes. A cost analysis of manufacturing plates of air melt, electroslag remelt and vacuum arc remelt grades was performed. The results of both material characterization and cost analyses pointed out certain special benefits of electroslag processing iron base alloys.

  12. On the Role of Dimensionless Elastic Fracture Mechanics.

    DTIC Science & Technology

    1985-07-03

    34.’ . . . .- . . - . . . - ... - . .. . . . . . -8-.V 6. B.M. Wundt , "A Unified Interpretation of Room Temperature Strength of Notched...Fracture mechanics technology applied to heavy section steel structures. Proc. Second Int. Conf. Fracture, Brighton, U.K., 825-850 (1969). J.G. Williams ...207s (1948). D.H. Winne and B.M. Wundt , Application of the Griffith-Irwin theory of crack propagation to the bursting behavior of disks, including

  13. Mechanical testing - In situ fracture device for Auger electron spectroscopy

    NASA Technical Reports Server (NTRS)

    Moorhead, R. D.

    1976-01-01

    An in situ fracture device for Auger spectroscopy is described. The device is designed to handle small tensile specimens or small double-cantilever beam specimens and is fully instrumented with load and displacement transducers so that quantitative stress-strain measurements can be made directly. Some initial test results for specimens made from 4130 and 1020 steel are presented. Results indicate that impurity segregation at interfaces other than grain boundary may play a significant role in the mechanism of ductile fracture.

  14. Characterization methods of bone-implant-interfaces of bioresorbable and titanium implants by fracture mechanical means.

    PubMed

    Tschegg, E K; Lindtner, R A; Doblhoff-Dier, V; Stanzl-Tschegg, S E; Holzlechner, G; Castellani, C; Imwinkelried, T; Weinberg, A

    2011-07-01

    Bioresorbable materials for implants have become increasingly researched over the last years. The bone-implant-interfaces of three different implant materials, namely a new bioresorbable magnesium alloy, a new self-reinforced polymer implant and a conventional titanium alloy, were tested using various methods: push-out tests, SEM and EDX analyses as well as surface analyses based on stereoscopic 3D pictures were conducted. The fracture energy is proposed as a very significant reference value for characterizing the mechanical performance of a bone-implant system. By using a video-extensometer system instead of, as is commonly done, tracking the movement of the crosshead in the push-out tests, the accuracy of measurement could be increased. Copyright © 2010 Elsevier Ltd. All rights reserved.

  15. Modeling elastic tensile fractures in snow using nonlocal damage mechanics

    NASA Astrophysics Data System (ADS)

    Borstad, C. P.; McClung, D. M.

    2011-12-01

    The initiation and propagation of tensile fractures in snow and ice are fundamental to numerous important physical processes in the cryosphere, from iceberg calving to ice shelf rift propagation to slab avalanche release. The heterogeneous nature of snow and ice, their proximity to the melting temperature, and the varied governing timescales typically lead to nonlinear fracture behavior which does not follow the predictions of Linear Elastic Fracture Mechanics (LEFM). Furthermore, traditional fracture mechanics is formally inapplicable for predicting crack initiation in the absence of a pre-existing flaw or stress concentration. An alternative to fracture mechanics is continuum damage mechanics, which accounts for the material degradation associated with cracking in a numerically efficient framework. However, damage models which are formulated locally (e.g. stress and strain are defined as point properties) suffer from mesh-sensitive crack trajectories, spurious localization of damage and improper fracture energy dissipation with mesh refinement. Nonlocal formulations of damage, which smear the effects of the material heterogeneity over an intrinsic length scale related to the material microstructure, overcome these difficulties and lead to numerically efficient and mesh-objective simulations of the tensile failure of heterogeneous materials. We present the results of numerical simulations of tensile fracture initiation and propagation in cohesive snow using a nonlocal damage model. Seventeen beam bending experiments, both notched and unnotched, were conducted using blocks of cohesive dry snow extracted from an alpine snowpack. Material properties and fracture parameters were calculated from the experimental data using beam theory and quasi-brittle fracture mechanics. Using these parameters, a nonlocal isotropic damage model was applied to two-dimensional finite element meshes of the same scale as the experiments. The model was capable of simulating the propagation

  16. Microstructure and magnetic properties of mechanically alloyed FeSiBAlNi (Nb) high entropy alloys

    NASA Astrophysics Data System (ADS)

    Wang, Jian; Zheng, Zhou; Xu, Jing; Wang, Yan

    2014-04-01

    In this paper, the effects of milling duration and composition on the microstructure and magnetic properties of equi-atomic FeSiBAlNi and FeSiBAlNiNb high entropy alloys during mechanical alloying have been investigated using X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, transmission electron microscopy and alternating gradient magnetometry. The amorphous high entropy alloys have been successfully fabricated using the mechanical alloying method. The results show that the Nb addition prolongs the milling time for the formation of the fully FeSiBAlNi amorphous phase and decreases the glass forming ability. However, FeSiBAlNiNb amorphous high entropy alloy has the higher thermal stability and heat resisting properties. Moreover, the as-milled FeSiBAlNi(Nb) powders are soft-magnetic materials indicated by their low coercivity. The saturation magnetization of the as-milled FeSiBAlNi(Nb) powders decreases with prolonging of the milling time and shows the lowest value when the amorphous high entropy alloys are formed. It suggests that the as-milled products with solid solution phases show the better soft-magnetic properties than those with fully amorphous phases. The Nb addition does not improve the soft-magnetic properties of the FeSiBAlNi high entropy alloys. Rather, both amorphous high entropy alloys have similar soft-magnetic properties after a long milling time.

  17. RSRM nozzle actuator bracket/lug fracture mechanics qualification test

    NASA Technical Reports Server (NTRS)

    Kelley, Peggy

    1993-01-01

    This is the final report for the actuator bracket/lug fracture mechanics qualification test. The test plan (CTP-0071) outlined a two-phase test program designed to answer questions about the fracture criticality of the redesigned solid rocket motor (RSRM) nozzle actuator bracket. An analysis conducted using the NASA/FLAGRO fracture mechanics computer program indicated that the actuator bracket might be a fracture critical component. In the NASA/FLAGRO analysis, a simple lug model was used to represent the actuator bracket. It was calculated that the bracket would fracture if subjected to an actuator stall load in the presence of a 0.10 in. corner crack at the actuator attachment hole. The 0.10 in. crack size corresponds to the nondestructive inspection detectability limit for the actuator bracket. The inspection method used is the dye penetrant method. The actuator stall load (103,424 lb) is the maximum load which the actuator bracket is required to withstand during motor operation. This testing was designed to establish the accuracy of the analytical model and to directly determine whether the actuator bracket is capable of meeting fracture mechanics safe-life requirements.

  18. Toughness of carbon nanotubes conforms to classic fracture mechanics

    PubMed Central

    Yang, Lin; Greenfeld, Israel; Wagner, H. Daniel

    2016-01-01

    Defects in crystalline structure are commonly believed to degrade the ideal strength of carbon nanotubes. However, the fracture mechanisms induced by such defects, as well as the validity of solid mechanics theories at the nanoscale, are still under debate. We show that the fracture toughness of single-walled nanotubes (SWNTs) conforms to the classic theory of fracture mechanics, even for the smallest possible vacancy defect (~2 Å). By simulating tension of SWNTs containing common types of defects, we demonstrate how stress concentration at the defect boundary leads to brittle (unstable) fracturing at a relatively low strain, degrading the ideal strength of SWNTs by up to 60%. We find that, owing to the SWNT’s truss-like structure, defects at this scale are not sharp and stress concentrations are finite and low. Moreover, stress concentration, a geometric property at the macroscale, is interrelated with the SWNT fracture toughness, a material property. The resulting SWNT fracture toughness is 2.7 MPa m0.5, typical of moderately brittle materials and applicable also to graphene. PMID:26989774

  19. Toughness of carbon nanotubes conforms to classic fracture mechanics.

    PubMed

    Yang, Lin; Greenfeld, Israel; Wagner, H Daniel

    2016-02-01

    Defects in crystalline structure are commonly believed to degrade the ideal strength of carbon nanotubes. However, the fracture mechanisms induced by such defects, as well as the validity of solid mechanics theories at the nanoscale, are still under debate. We show that the fracture toughness of single-walled nanotubes (SWNTs) conforms to the classic theory of fracture mechanics, even for the smallest possible vacancy defect (~2 Å). By simulating tension of SWNTs containing common types of defects, we demonstrate how stress concentration at the defect boundary leads to brittle (unstable) fracturing at a relatively low strain, degrading the ideal strength of SWNTs by up to 60%. We find that, owing to the SWNT's truss-like structure, defects at this scale are not sharp and stress concentrations are finite and low. Moreover, stress concentration, a geometric property at the macroscale, is interrelated with the SWNT fracture toughness, a material property. The resulting SWNT fracture toughness is 2.7 MPa m(0.5), typical of moderately brittle materials and applicable also to graphene.

  20. Theoretical Analysis of the Mechanism of Fracture Network Propagation with Stimulated Reservoir Volume (SRV) Fracturing in Tight Oil Reservoirs.

    PubMed

    Su, Yuliang; Ren, Long; Meng, Fankun; Xu, Chen; Wang, Wendong

    2015-01-01

    Stimulated reservoir volume (SRV) fracturing in tight oil reservoirs often induces complex fracture-network growth, which has a fundamentally different formation mechanism from traditional planar bi-winged fracturing. To reveal the mechanism of fracture network propagation, this paper employs a modified displacement discontinuity method (DDM), mechanical mechanism analysis and initiation and propagation criteria for the theoretical model of fracture network propagation and its derivation. A reasonable solution of the theoretical model for a tight oil reservoir is obtained and verified by a numerical discrete method. Through theoretical calculation and computer programming, the variation rules of formation stress fields, hydraulic fracture propagation patterns (FPP) and branch fracture propagation angles and pressures are analyzed. The results show that during the process of fracture propagation, the initial orientation of the principal stress deflects, and the stress fields at the fracture tips change dramatically in the region surrounding the fracture. Whether the ideal fracture network can be produced depends on the geological conditions and on the engineering treatments. This study has both theoretical significance and practical application value by contributing to a better understanding of fracture network propagation mechanisms in unconventional oil/gas reservoirs and to the improvement of the science and design efficiency of reservoir fracturing.

  1. Theoretical Analysis of the Mechanism of Fracture Network Propagation with Stimulated Reservoir Volume (SRV) Fracturing in Tight Oil Reservoirs

    PubMed Central

    Su, Yuliang; Ren, Long; Meng, Fankun; Xu, Chen; Wang, Wendong

    2015-01-01

    Stimulated reservoir volume (SRV) fracturing in tight oil reservoirs often induces complex fracture-network growth, which has a fundamentally different formation mechanism from traditional planar bi-winged fracturing. To reveal the mechanism of fracture network propagation, this paper employs a modified displacement discontinuity method (DDM), mechanical mechanism analysis and initiation and propagation criteria for the theoretical model of fracture network propagation and its derivation. A reasonable solution of the theoretical model for a tight oil reservoir is obtained and verified by a numerical discrete method. Through theoretical calculation and computer programming, the variation rules of formation stress fields, hydraulic fracture propagation patterns (FPP) and branch fracture propagation angles and pressures are analyzed. The results show that during the process of fracture propagation, the initial orientation of the principal stress deflects, and the stress fields at the fracture tips change dramatically in the region surrounding the fracture. Whether the ideal fracture network can be produced depends on the geological conditions and on the engineering treatments. This study has both theoretical significance and practical application value by contributing to a better understanding of fracture network propagation mechanisms in unconventional oil/gas reservoirs and to the improvement of the science and design efficiency of reservoir fracturing. PMID:25966285

  2. Deformation and fracture behavior of composite structured Ti-Nb-Al-Co(-Ni) alloys

    SciTech Connect

    Okulov, I. V. Marr, T.; Schultz, L.; Eckert, J.; Kühn, U.; Freudenberger, J.; Oertel, C.-G.; Skrotzki, W.

    2014-02-17

    Tensile ductility of the Ti-based composites, which consist of a β-Ti phase surrounded by ultrafine structured intermetallics, is tunable through the control of intermetallics. The two Ti-based alloys studied exhibit similar compressive yield strength (about 1000 MPa) and strain (about 35%–40%) but show a distinct difference in their tensile plasticity. The alloy Ti{sub 71.8}Nb{sub 14.1}Ni{sub 7.4}Al{sub 6.7} fractures at the yield stress while the alloy Ti{sub 71.8}Nb{sub 14.1}Co{sub 7.4}Al{sub 6.7} exhibits about 4.5% of tensile plastic deformation. To clarify the effect of microstructure on the deformation behavior of these alloys, tensile tests were carried out in the scanning electron microscope. It is shown that the distribution as well as the type of intermetallics affects the tensile ductility of the alloys.

  3. Processing effects on the mechanical properties of tungsten heavy alloys

    NASA Technical Reports Server (NTRS)

    Kishi, Toshihito; German, R. M.

    1990-01-01

    Tungsten heavy alloys exhibit significant mechanical property sensitivities to the fabrication variables. These sensitivities are illustrated in this examination of vacuum sintering and the effects of composition, sintering temperature, and sintering time on the mechanical properties of tungsten heavy alloys. Measurements were conducted to assess the density, strength, hardness, and elongation dependencies. A detrimental aspect of vacuum sintering is matrix phase evaporation, although vacuum sintering does eliminate the need for postsintering heat treatments.

  4. Facial fractures with concomitant open globe injury: mechanisms and fracture patterns associated with blindness.

    PubMed

    Vaca, Elbert E; Mundinger, Gerhard S; Kelamis, Joseph A; Dorafshar, Amir H; Christy, Michael R; Manson, Paul N; Rodriguez, Eduardo D

    2013-06-01

    Treatment of facial fractures in the setting of open-globe injuries poses a management dilemma because of the often disparate treatment priorities of multidisciplinary trauma teams and the lack of prognostic data regarding visual outcomes. Patients in the University of Maryland Shock Trauma Registry sustaining facial fractures with concomitant open-globe injuries from January of 1998 to August of 2010 were identified. Odds ratios were calculated to identify demographic and clinical variables associated with blindness, and multivariate regression analysis was performed. A total of 99 patients were identified with 105 open-globe injuries. Seventy-nine percent of injuries were blinding, whereas 4.8 percent of globes achieved a final visual acuity greater than or equal to 20/400. Blindness was associated with penetrating injury, increasing number of facial fractures, zygomaticomaxillary complex fracture, admission Glasgow Coma Scale score less than or equal to 8, and globe injury spanning all three eye zones. Fracture repair was performed more frequently (62.5 percent) and more quickly (average time to fracture repair, 4.5 days) in cases of primary globe enucleation/evisceration when compared with complete (21.2 percent; 8 days; p=0.35) or incomplete (42.9 percent; 11 days; p=0.058) primary globe repair. Penetrating injury mechanism and zone of eye injury appear to be better indicators of visual prognosis than facial fracture patterns. Given the high rates of blindness, secondary enucleation, and delay of fracture repair in patients that were not primarily enucleated, the authors recommend that orbital fracture repair not be delayed in the hopes of eventual visual recovery in cases of high-velocity projectile trauma. Risk, III.

  5. Mechanical Behaviour of Light Metal Alloys at High Strain Rates. Computer Simulation on Mesoscale Levels

    NASA Astrophysics Data System (ADS)

    Skripnyak, Vladimir; Skripnyak, Evgeniya; Meyer, Lothar W.; Herzig, Norman; Skripnyak, Nataliya

    2012-02-01

    Researches of the last years have allowed to establish that the laws of deformation and fracture of bulk ultrafine-grained and coarse-grained materials are various both in static and in dynamic loading conditions. Development of adequate constitutive equations for the description of mechanical behavior of bulk ultrafine-grained materials at intensive dynamic influences is complicated in consequence of insufficient knowledge about general rules of inelastic deformation and nucleation and growth of cracks. Multi-scale computational model was used for the investigation of deformation and fracture of bulk structured aluminum and magnesium alloys under stress pulse loadings on mesoscale level. The increment of plastic deformation is defined by the sum of the increments caused by a nucleation and gliding of dislocations, the twinning, meso-blocks movement, and grain boundary sliding. The model takes into account the influence on mechanical properties of alloys an average grains size, grain sizes distribution of and concentration of precipitates. It was obtained the nucleation and gliding of dislocations caused the high attenuation rate of the elastic precursor of ultrafine-grained alloys than in coarse grained counterparts.

  6. Microstructure and mechanical properties of P/M (powder metallurgy) Fe sub 3 Al alloys

    SciTech Connect

    Knibloe, J.R.; Wright, R.N. ); Sikka, V.K. )

    1990-01-01

    Alloys based on Fe{sub 3}Al have an equilibrium DO{sub 3} structure at low temperatures and transform to a B2 structure above about 550{degree}C. The influence of different rates of quenching from the B2 region to room temperature on the microstructure and mechanical properties of powder metallurgy (P/M) alloys with two different Cr contents has been examined. By optimizing the processing to maximize the amount of B2 order, room temperature ductility approaching 20% has been achieved although the fracture mode is primarily brittle cleavage. The refined microstructure resulting from P/M processing contributes to enhanced yield strength compared to ingot processed materials with similar ductility. Increasing the Cr content from 2 to 5% has little effect on mechanical properties. 8 refs., 12 figs., 2 tabs.

  7. Critical analysis of alloy 600 stress corrosion cracking mechanisms in primary water

    SciTech Connect

    Rios, R. |; Noel, D.; Bouvier, O. de; Magnin, T.

    1995-04-01

    In order to study the mechanisms involved in the stress-corrosion cracking (SCC) of Alloy 600 in primary water, the influence of the relevance of physicochemical and metallurgical parameters was assessed: hydrogen and oxygen overpressures, microstructure, and local chemical composition. The obtained results show that, even if the dissolution/oxidation seems to be the first and necessary step responsible for crack initiation and if hydrogen effects can also be involved in cracking, neither a dissolution/oxidation model nor a hydrogen model appears sufficient to account for cracking. Moreover, fractographic examinations performed on specimens` fracture surfaces lead to the fact that attention should be paid to a cleavage like microcracking mechanism involving interactions between corrosion and plasticity at the vicinity of grain boundaries. A corrosion-enhanced plasticity model is proposed to describe the intergranular and transgranular cracking in Alloy 600.

  8. Enhancement of Apoptosis by Titanium Alloy Internal Fixations during Microwave Treatments for Fractures: An Animal Study

    PubMed Central

    Zhang, Lina; Ye, Dongmei; Feng, Xianxuan; Fu, Tengfei; Bai, Yuehong

    2015-01-01

    Objective Microwaves are used in one method of physical therapy and can increase muscle tissue temperature which is useful for improving muscle, tendon and bone injuries. In the study, we sought to determine whether titanium alloy internal fixations influence apoptosis in tissues subjected to microwave treatments at 2,450 MHz and 40 W during the healing of fractures because this issue is not yet fully understood. Methods In this study, titanium alloy internal fixations were used to treat 3.0-mm transverse osteotomies in the middle of New Zealand rabbits’ femurs. After the operation, 30-day microwave treatments were applied to the 3.0 mm transverse osteotomies 3 days after the operation. The changes in the temperatures of the muscle tissues in front of the implants or the 3.0 mm transverse osteotomies were measured during the microwave treatments. To characterize the effects of titanium alloy internal fixations on apoptosis in the muscles after microwave treatment, we performed TUNEL assays, fluorescent real-time (quantitative) PCR, western blotting analyses, reactive oxygen species (ROS) detection and transmission electron microscopy examinations. Results The temperatures were markedly increased in the animals with the titanium alloy implants. Apoptosis in the muscle cells of the implanted group was significantly more extensive than that in the non-implanted control group at different time points. Transmission electron microscopy examinations of the skeletal muscles of the implanted groups revealed muscular mitochondrial swelling, vacuolization. ROS, Bax and Hsp70 were up-regulated, and Bcl-2 was down-regulated in the implanted group. Conclusion Our results suggest that titanium alloy internal fixations caused greater muscular tissue cell apoptosis following 2,450 MHz, 40 W microwave treatments in this rabbit femur fracture models. PMID:26132082

  9. Super High Strength Aluminum Alloy Processed by Mechanical Alloying and Hot Extrusion

    NASA Astrophysics Data System (ADS)

    Zheng, Ruixiao; Yang, Han; Wang, Zengjie; Wen, Shizhen; Liu, Tong; Ma, Chaoli

    Nanostructure strengthened aluminum alloy was prepared by powder metallurgic technology. The rapid solidification Al-Cu-Mg alloy powder was used in this study. To obtain nanostructure, the commercial powder was intensely milled under certain ball milling conditions. The milled powder was compacted first by cold isostatic pressing (CIP) at a compressive pressure of 300MPa, and then extruded at selected temperature for several times to obtain near full density material. Microstructure and mechanical properties of the extruded alloy were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and mechanical tests. It is revealed that the compressive strength of extruded alloy is higher than 800MPa. The strengthening mechanism associated with the nanostructure is discussed.

  10. Hydrogen storage properties of lithium silicon alloy synthesized by mechanical alloying

    NASA Astrophysics Data System (ADS)

    Doi, Koichi; Hino, Satoshi; Miyaoka, Hiroki; Ichikawa, Takayuki; Kojima, Yoshitsugu

    A lithium silicon alloy was synthesized by mechanical alloying method. Hydrogen storage properties of this Li-Si-H system were studied. During hydrogenation of the lithium silicon alloy, lithium atom was extracted from the alloy and lithium hydride was generated. Equilibrium hydrogen pressures for desorption and absorption reactions were measured in a temperature range from 400 to 500 °C to investigate the thermodynamic characteristics of the system, which can reversibly store 5.4 mass% hydrogen with smaller reaction enthalpy than simple metal Li. Li absorbing alloys, which have been widely studied as a negative electrode material for Li ion rechargeable batteries, can be used as hydrogen storage materials with high hydrogen capacity.

  11. Giant magnetoresistance of Co-Ni-Cu alloys produced by mechanical alloying

    NASA Astrophysics Data System (ADS)

    Zhang, Y. Q.; Zhang, Z. D.; Xiao, Q. F.; Geng, D. Y.; Zhao, X. G.; Zhang, W. S.; You, C. Y.

    2003-05-01

    The structure, magnetic properties and magnetoresistance (MR) effect of Co20NixCu80-x alloys produced by mechanical alloying and subsequent annealing have been investigated. After milling for 5 h, a supersaturated solid solution forms for all the alloys. Co20NixCu80-x alloys annealed at 973 K for 30 min segregated into two-phases of fcc-Co and fcc-Cu. The maximum value for MR ratio, at room temperature is 4.7% at a field of 1.2 T, and at 5 K is 15% at a field of 2 T for Co20Cu80 annealed at 718 K for 30 min. The MR ratio of Co-Ni-Cu alloys decreases monotonically with increasing Ni content. The MR and its dependence on particle size are discussed.

  12. Fracture mechanics life analytical methods verification testing

    NASA Technical Reports Server (NTRS)

    Favenesi, J. A.; Clemons, T. G.; Riddell, W. T.; Ingraffea, A. R.; Wawrzynek, P. A.

    1994-01-01

    The objective was to evaluate NASCRAC (trademark) version 2.0, a second generation fracture analysis code, for verification and validity. NASCRAC was evaluated using a combination of comparisons to the literature, closed-form solutions, numerical analyses, and tests. Several limitations and minor errors were detected. Additionally, a number of major flaws were discovered. These major flaws were generally due to application of a specific method or theory, not due to programming logic. Results are presented for the following program capabilities: K versus a, J versus a, crack opening area, life calculation due to fatigue crack growth, tolerable crack size, proof test logic, tearing instability, creep crack growth, crack transitioning, crack retardation due to overloads, and elastic-plastic stress redistribution. It is concluded that the code is an acceptable fracture tool for K solutions of simplified geometries, for a limited number of J and crack opening area solutions, and for fatigue crack propagation with the Paris equation and constant amplitude loads when the Paris equation is applicable.

  13. A study on electromigration-inducing intergranular fracture of fine silver alloy wires

    NASA Astrophysics Data System (ADS)

    Hsueh, Hao-Wen; Hung, Fei-Yi; Lui, Truan-Sheng

    2017-01-01

    In this study, Pd-coated Cu, Ag (purity = 4 N), and Ag alloy (Ag-8Au-3Pd) wires were employed to measure the tensile properties during current stressing using the so-called dynamic current tensile (DCT) test. Both the tensile strength and elongation of the wires decreased dramatically in the DCT test, particularly of the Ag-based wires, and the fracture morphology of the Cu-based and Ag-based wires was ductile fracture and intergranular fracture, respectively. Compared to the Cu-based wires, electromigration occurred more easily in the Ag-based wires, and it always generated voids and cracks at the grain boundaries; therefore, the fracture morphology of the Ag-based wires was intergranular fracture owing to the weakened grain boundary. Further, the results indicated that the Ag-based wires could not carry a higher current density than the Cu-based wires, primarily because their extremely low strength and elongation in current stressing might cause serious reliability problems.

  14. MECHANICAL BEHAVIOR OF MOLYBDENUM DISILICIDE-BASED ALLOYS

    SciTech Connect

    A. MISRA; A. SHARIF; ET AL

    2000-12-01

    We have investigated the mechanical behavior of the following single-phase polycrystalline alloys with the MoSi{sub 2} body-center tetragonal structure: MoSi{sub 2} alloyed with {approximately}2.5 at.% Re, MoSi{sub 2} alloyed with 2 at.% Al, MoSi{sub 2} alloyed with 1 at.% Nb, and MoSi{sub 2} alloyed with 1 at.% Re and 2 at.% Al. Several anomalies in the mechanical behavior of alloyed materials were observed. For example, (1) addition of only {approximately}2.5 at. % Re results in an order of magnitude increase in compressive strength at 1600 C, (2) additions of Nb and Al cause solution softening at near-ambient temperatures, and (3) quaternary MoSi{sub 2}-Re-Al alloys show strengthening at elevated temperatures and reduction in flow stress with enhanced plasticity at near-ambient temperatures in compression. The mechanisms of anomalous solution hardening and softening are discussed.

  15. Effects of nitrogen addition on microstructure and mechanical behavior of biomedical Co-Cr-Mo alloys.

    PubMed

    Yamanaka, Kenta; Mori, Manami; Chiba, Akihiko

    2014-01-01

    In the present study, the microstructures and tensile deformation behaviors of biomedical Co-29Cr-6Mo (wt%) alloys containing different concentrations of nitrogen (0-0.24wt%) were systematically investigated. As the nitrogen concentration increased, the volume fraction of athermal ε martensite decreased, because nanoprecipitates hindered the formation of stacking faults (SFs) by acting as obstacles to Shockley partial dislocation formation, and athermal ε martensite usually forms through the regular overlapping of SFs. The formation of the athermal ε martensite was completely suppressed when the nitrogen concentration exceeded 0.10wt%, resulting in a simultaneous improvement in the strength and ductility of the alloys. It was found that the glide of the Shockley partial dislocations and the strain-induced γ (fcc)→ε (hcp) martensitic transformation (SIMT) operated as the primary deformation mechanisms. However, adding nitrogen reduced the work hardening by suppressing the formation of the SFs and preventing the SIMT from taking place. This resulted in an intrinsic decrease in the tensile ductility of the alloys. It is also shown that all the alloys exhibited premature fractures owing to the SIMT. The formation of annealing twins in the γ grains is found to be enhanced by nitrogen addition and to promote the SIMT, resulting in a reduction in the elongation-to-failure due to nitrogen addition. These results should aid in the design of alloys that contain nitrogen.

  16. Structure and mechanical properties of as-cast Ti-5Nb-xFe alloys

    SciTech Connect

    Hsu, Hsueh-Chuan; Hsu, Shih-Kuang; Wu, Shih-Ching; Lee, Chih-Jhan; Ho, Wen-Fu

    2010-09-15

    In this study, as-cast Ti-5Nb and a series of Ti-5Nb-xFe alloys were investigated and compared with commercially pure titanium (c.p. Ti) in order to determine their structure and mechanical properties. The series of Ti-5Nb-xFe alloys contained an iron content ranging from 1 to 5 mass% and were prepared by using a commercial arc-melting vacuum-pressure casting system. Additionally, X-ray diffraction (XRD) for phase analysis was conducted with a diffractometer, and three-point bending tests were performed to evaluate the mechanical properties of all specimens. The fractured surfaces were observed by using scanning electron microscopy (SEM). The experimental results indicated that these alloys possessed a range of different structures and mechanical properties dependent upon the various additions of Fe. With an addition of 1 mass% Fe, retention of the metastable {beta} phase began. However, when 4 mass% Fe or greater was added, the {beta} phase was entirely retained with a bcc crystal structure. Moreover, the {omega} phase was only detected in the Ti-5Nb-2Fe, Ti-5Nb-3Fe and Ti-5Nb-4Fe alloys. The largest quantity of {omega} phase and the highest bending modulus were found in the Ti-5Nb-3Fe alloy. The Ti-5Nb-2Fe alloy had the lowest bending modulus, which was lower than that of c.p. Ti by 20%. This alloy exhibited the highest bending strength/modulus ratio of 26.7, which was higher than that of c.p. Ti by 214%, and of the Ti-5Nb alloy (14.4 ) by 85%. Additionally, the elastically recoverable angles of the ductile Ti-5Nb-1Fe (19.9{sup o}) and Ti-5Nb-5Fe (29.5{sup o}) alloys were greater than that of c.p. Ti (2.7{sup o}) by as much as 637% and 993%, respectively. Furthermore, the preliminary cell culturing results revealed that the Ti-5Nb-xFe alloys were not only biocompatible, but also supported cell attachment.

  17. [HAND FRACTURES IN CHILDREN - CAUSES AND MECHANISMS OF INJURY].

    PubMed

    Antabak, Anko; Barišić, Branimir; Andabak, Matej; Papeš, Dino; Romić, Ivan; Fuchs, Nino; Luetić, Tomislav

    2015-01-01

    Hand is extremely exposed to various loads and traumas of everyday tasks and activities, resulting in fist fractures being fairly common injuries. The most common mechanism of injury is a direct blow. This retrospective study analyzed the data on 274 children admitted for hand fractures at Clinical Hospital Center Zagreb in the period from 2006 to 2014. The study included 76 girls (28%) and 198 boys (72%). The average patient age was 11.9 years and most were between 10 and 13 years of age. Phalangeal fractures accounted for 80%, metacarpal fractures for 17%, and carpal fractures for 3% of all injuries. Most commonly injuries occurred during recreation (4 1%), at home (37%), at school (18%) and in the street (4%). Direct blow was the major cause of injury (76%), and 24% were caused by fall. Injuries during sport activities are the most common cause of the hand fractures in pediatric population and direct blow is the main mechanism of injury. The peak incidence is at the age of 10-13 years in boys and girls, so prevention should be aimed at this age group. Preventive actions should be focused on injuries that tend to occur in parks, schools and during sport activities.

  18. Mechanical properties and grindability of experimental Ti-Au alloys.

    PubMed

    Takahashi, Masatoshi; Kikuchi, Masafumi; Okuno, Osamu

    2004-06-01

    Experimental Ti-Au alloys (5, 10, 20 and 40 mass% Au) were made. Mechanical properties and grindability of the castings of the Ti-Au alloys were examined. As the concentration of gold increased to 20%, the yield strength and the tensile strength of the Ti-Au alloys became higher without markedly deteriorating their ductility. This higher strength can be explained by the solid-solution strengthening of the a titanium. The Ti-40%Au alloy became brittle because the intermetallic compound Ti3Au precipitated intensively near the grain boundaries. There was no significant difference in the grinding rate and grinding ratio among all the Ti-Au alloys and the pure titanium at any speed.

  19. Relating Cohesive Zone Model to Linear Elastic Fracture Mechanics

    NASA Technical Reports Server (NTRS)

    Wang, John T.

    2010-01-01

    The conditions required for a cohesive zone model (CZM) to predict a failure load of a cracked structure similar to that obtained by a linear elastic fracture mechanics (LEFM) analysis are investigated in this paper. This study clarifies why many different phenomenological cohesive laws can produce similar fracture predictions. Analytical results for five cohesive zone models are obtained, using five different cohesive laws that have the same cohesive work rate (CWR-area under the traction-separation curve) but different maximum tractions. The effect of the maximum traction on the predicted cohesive zone length and the remote applied load at fracture is presented. Similar to the small scale yielding condition for an LEFM analysis to be valid. the cohesive zone length also needs to be much smaller than the crack length. This is a necessary condition for a CZM to obtain a fracture prediction equivalent to an LEFM result.

  20. Statistical fracture mechanics approach to the strength of brittle rock

    SciTech Connect

    Ratigan, J.L.

    1981-06-01

    Statistical fracture mechanics concepts used in the past for rock are critically reviewed and modifications are proposed which are warranted by (1) increased understanding of fracture provided by modern fracture mechanics and (2) laboratory test data both from the literature and from this research. Over 600 direct and indirect tension tests have been performed on three different rock types; Stripa Granite, Sierra White Granite and Carrara Marble. In several instances assumptions which are common in the literature were found to be invalid. A three parameter statistical fracture mechanics model with Mode I critical strain energy release rate as the variant is presented. Methodologies for evaluating the parameters in this model as well as the more commonly employed two parameter models are discussed. The experimental results and analysis of this research indicate that surfacially distributed flaws, rather than volumetrically distributed flaws are responsible for rupture in many testing situations. For several of the rock types tested, anisotropy (both in apparent tensile strength and size effect) precludes the use of contemporary statistical fracture mechanics models.

  1. Fracture mechanics criteria for turbine engine hot section components

    NASA Technical Reports Server (NTRS)

    Meyers, G. J.

    1982-01-01

    The application of several fracture mechanics data correlation parameters to predicting the crack propagation life of turbine engine hot section components was evaluated. An engine survey was conducted to determine the locations where conventional fracture mechanics approaches may not be adequate to characterize cracking behavior. Both linear and nonlinear fracture mechanics analyses of a cracked annular combustor liner configuration were performed. Isothermal and variable temperature crack propagation tests were performed on Hastelloy X combustor liner material. The crack growth data was reduced using the stress intensity factor, the strain intensity factor, the J integral, crack opening displacement, and Tomkins' model. The parameter which showed the most effectiveness in correlation high temperature and variable temperature Hastelloy X crack growth data was crack opening displacement.

  2. Fracture Toughness and Fatigue Crack Growth Behavior of As-Cast High-Entropy Alloys

    NASA Astrophysics Data System (ADS)

    Seifi, Mohsen; Li, Dongyue; Yong, Zhang; Liaw, Peter K.; Lewandowski, John J.

    2015-08-01

    The fracture toughness and fatigue crack growth behavior of two as-vacuum arc cast high-entropy alloys (HEAs) (Al0.2CrFeNiTi0.2 and AlCrFeNi2Cu) were determined. A microstructure examination of both HEA alloys revealed a two-phase structure consisting of body-centered cubic (bcc) and face-centered cubic (fcc) phases. The notched and fatigue precracked toughness values were in the range of those reported in the literature for two-phase alloys but significantly less than recent reports on a single phase fcc-HEA that was deformation processed. Fatigue crack growth experiments revealed high fatigue thresholds that decreased significantly with an increase in load ratio, while Paris law slopes exhibited metallic-like behavior at low R with significant increases at high R. Fracture surface examinations revealed combinations of brittle and ductile/dimpled regions at overload, with some evidence of fatigue striations in the Paris law regime.

  3. Environment assisted degradation mechanisms in aluminum-lithium alloys

    NASA Technical Reports Server (NTRS)

    Gangloff, Richard P.; Stoner, Glenn E.; Swanson, Robert E.

    1988-01-01

    Section 1 of this report records the progress achieved on NASA-LaRC Grant NAG-1-745 (Environment Assisted Degradation Mechanisms in Al-Li Alloys), and is based on research conducted during the period April 1 to November 30, 1987. A discussion of work proposed for the project's second year is included. Section 2 provides an overview of the need for research on the mechanisms of environmental-mechanical degradation of advanced aerospace alloys based on aluminum and lithium. This research is to provide NASA with the basis necessary to permit metallurgical optimization of alloy performance and engineering design with respect to damage tolerance, long term durability and reliability. Section 3 reports on damage localization mechanisms in aqueous chloride corrosion fatigue of aluminum-lithium alloys. Section 4 reports on progress made on measurements and mechanisms of localized aqueous corrosion in aluminum-lithium alloys. Section 5 provides a detailed technical proposal for research on environmental degradation of Al-Li alloys, and the effect of hydrogen in this.

  4. The Mechanical Strength of Si Foams in the Mushy Zone during Solidification of Al-Si Alloys.

    PubMed

    Lim, Jeon Taik; Youn, Ji Won; Seo, Seok Yong; Kim, Ki Young; Kim, Suk Jun

    2017-03-24

    The mechanical strength of an Al-30% Si alloy in the mushy zone was estimated by using a novel centrifugation apparatus. In the apparatus, the alloy melt was partially solidified, forming a porous structure made of primary Si platelets (Si foam) while cooling. Subsequently, pressure generated by centrifugal force pushed the liquid phase out of the foam. The estimated mechanical strength of the Si foam in the temperature range 850-993 K was very low (62 kPa to 81 kPa). This is about two orders of magnitude lower than the mechanical strength at room temperature as measured by compressive tests. When the centrifugal stress was higher than the mechanical strength of the foam, the foam fractured, and the primary Si crystallites were extracted along with the Al-rich melt. Therefore, to maximize the centrifugal separation efficiency of the Al-30% Si alloy, the centrifugal stress should be in the range of 62-81 kPa.

  5. Mechanical transport in two-dimensional networks of fractures

    SciTech Connect

    Endo, H.K.

    1984-04-01

    The objectives of this research are to evaluate directional mechanical transport parameters for anisotropic fracture systems, and to determine if fracture systems behave like equivalent porous media. The tracer experiments used to measure directional tortuosity, longitudinal geometric dispersivity, and hydraulic effective porosity are conducted with a uniform flow field and measurements are made from the fluid flowing within a test section where linear length of travel is constant. Since fluid flow and mechanical transport are coupled processes, the directional variations of specific discharge and hydraulic effective porosity are measured in regions with constant hydraulic gradients to evaluate porous medium equivalence for the two processes, respectively. If the fracture region behaves like an equivalent porous medium, the system has the following stable properties: (1) specific discharge is uniform in any direction and can be predicted from a permeability tensor; and (2) hydraulic effective porosity is directionally stable. Fracture systems with two parallel sets of continuous fractures satisfy criterion 1. However, in these systems hydraulic effective porosity is directionally dependent, and thus, criterion 2 is violated. Thus, for some fracture systems, fluid flow can be predicted using porous media assumptions, but it may not be possible to predict transport using porous media assumptions. Two discontinuous fracture systems were studied which satisfied both criteria. Hydraulic effective porosity for both systems has a value between rock effective porosity and total porosity. A length-density analysis (LDS) of Canadian fracture data shows that porous media equivalence for fluid flow and transport is likely when systems have narrow aperture distributions. 54 references, 90 figures, 7 tables.

  6. Interface Effects on the Fracture Mechanism of a High-Toughness Aluminum-Composite Laminate

    NASA Astrophysics Data System (ADS)

    Cepeda-Jiménez, C. M.; Pozuelo, M.; García-Infanta, J. M.; Ruano, O. A.; Carreño, F.

    2009-01-01

    The microstructure and the mechanical properties of a multilayer composite laminate based on aluminum 7075 and 2024 alloys produced by hot roll bonding were examined. The composite laminate has been tested at room temperature under Charpy-impact tests, three-point bend tests, and shear tests on the interfaces. The toughness of the post-rolling tempered and T6-treated composite laminate, measured by impact- absorbed energy in the crack-arrester orientation, was more than 20 times higher than that of the monolithic Al 7075 alloy and 7 times higher than that of Al 2024 alloy. The outstanding toughness increase of the composite laminate in the post-rolling tempered and T6-treated condition is mainly due to the mechanism of “interface predelamination.” By this fracture mechanism, the interfaces are debonded before the main crack reaches them, warranting delamination in all interfaces. Therefore, delamination and crack renucleation in every layer are responsible for the improvement in toughness.

  7. Amorphous phase formation in mechanically alloyed iron-based systems

    NASA Astrophysics Data System (ADS)

    Sharma, Satyajeet

    Bulk metallic glasses have interesting combination of physical, chemical, mechanical, and magnetic properties which make them attractive for a variety of applications. Consequently there has been a lot of interest in understanding the structure and properties of these materials. More varied applications can be sought if one understands the reasons for glass formation and the methods to control them. The glass-forming ability (GFA) of alloys can be substantially increased by a proper selection of alloying elements and the chemical composition of the alloy. High GFA will enable in obtaining large section thickness of amorphous alloys. Ability to produce glassy alloys in larger section thicknesses enables exploitation of these advanced materials for a variety of different applications. The technique of mechanical alloying (MA) is a powerful non-equilibrium processing technique and is known to produce glassy (or amorphous) alloys in several alloy systems. Metallic amorphous alloys have been produced by MA starting from either blended elemental metal powders or pre-alloyed powders. Subsequently, these amorphous alloy powders could be consolidated to full density in the temperature range between the glass transition and crystallization temperatures, where the amorphous phase has a very low viscosity. This Dissertation focuses on identifying the various Fe-based multicomponent alloy systems that can be amorphized using the MA technique, studying the GFA of alloys with emphasis on improving it, and also on analyzing the effect of extended milling time on the constitution of the amorphous alloy powder produced at earlier times. The Dissertation contains seven chapters, where the lead chapter deals with the background, history and introduction to bulk metallic glasses. The following four chapters are the published/to be published work, where the criterion for predicting glass formation, effect of Niobium addition on glass-forming ability (GFA), lattice contraction on

  8. Crack Tip Plasticity in Dynamic Fracture Mechanics.

    DTIC Science & Technology

    1978-04-01

    0.1. Ant.r.d) ~IIIi. . • ~~~~• ~~~~~~~~~~~~~~~~ ~~~ . - ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ - 1 CRACK TIP PLASTICITY IN DYNANI C FRACTU ...force——from the material’s fracture property——the resistance. The material property represents the energy dissipated ~n flow into the crack tip and...the flow stress varied - arbitrarily along the length of the strip yield zone. The flow stress val- ues were assigned in accord with a known strain

  9. Deformation and fracture of low alloy steels at high temperature

    SciTech Connect

    Marriott, D.L.; Stubbins, J.F.; Leckie, F.A.; Muddle, B.

    1988-12-01

    This project formed part of the initiative in the AR TD program to characterize high temperature, time-dependent damage processes in low alloy steels, for use in the construction of coal-gasification plant. This project was broadly aimed at adding to the knowledge base for this bainitic form of 2.25Cr 1Mo steel, as it related to time-dependent performance at elevated temperature. Its original intention was to obtain information in specific grades of 2.25Cr 1Mo steel, in particular those containing reduced residual elements and microalloyed modifications, which were being considered as candidate materials at the time. This objective was subsequently modified, in the course of the contract period, to a more generic study of bainitic steel, using the 2.25Cr 1Mo material as a representative of the class. The main thrust of the project was directed initially at the detrimental effect of cyclic loading on creep resistance and manifesting itself in an apparently severe creep-fatigue interaction. Three subtasks were eventually identified. These are: a study of the evolution of microstructural changes in bainitic materials during steady load creep and under constant amplitude cyclic deformation, investigation of the effect of cyclic softening on the fatigue and creep strength of complex geometries, focusing on circumferentially notched bars, and investigation of the influence of environment as a possible cause of observed fatigue/elevated temperature interaction through its effects on crack initiation and propagation, using EDM notched specimens tested in air and vacuum. Results are discussed. 24 refs., 40 figs., 5 tabs.

  10. A Novel Cu-10Zn-1.5Ni-0.34Si Alloy with Excellent Mechanical Property Through Precipitation Hardening

    NASA Astrophysics Data System (ADS)

    Chen, Wei; Wang, Mingpu; Li, Zhou; Dong, Qiyi; Jia, Yanlin; Xiao, Zhu; Zhang, Rui; Yu, Hongchun

    2016-11-01

    A novel Cu-10Zn-1.5Ni-0.34Si alloy was designed to replace the expensive tin-phosphor bronze in this paper. The alloy had better comprehensive mechanical properties than traditional C5191 alloy. The aged Cu-10Zn-1.5Ni-0.34Si alloy had a hardness of 220 HV, electrical conductivity of 28.5% IACS, tensile strength of 650 MPa, yield strength of 575 MPa and elongation of 13%. Ni2Si precipitates formed during aging, and the crystal orientation relationship between matrix and precipitates was: (001)α//(001)δ, and [110]α//[100]δ. Ductile fracture surface with deep cavities was found in the alloy. Solid solution strengthening, deformation strengthening and precipitation strengthening were found to be core strengthening mechanisms in the alloy.

  11. Fracture mechanics of delamination defects in multilayer dielectric coatings.

    PubMed

    Liddell, H P H; Mehrotra, K; Lambropoulos, J C; Jacobs, S D

    2013-11-10

    During the fabrication of multilayer-dielectric (MLD) thin-film-coated optics, such as the diffraction gratings used in OMEGA EP's pulse compressors, acid piranha cleaning can lead to the formation of chemically induced delamination defects. We investigate the causes of these defects and describe a mechanism for the deformation and failure of the MLD coating in response to hydrogen peroxide in the cleaning solution. A fracture mechanics model is developed and used to calculate the crack path that maximizes the energy-release rate, which is found to be consistent with the characteristic fracture pattern observed in MLD coating delamination defects.

  12. Equine cortical bone exhibits rising R-curve fracture mechanics.

    PubMed

    Malik, C L; Stover, S M; Martin, R B; Gibeling, J C

    2003-02-01

    Previous studies of the fracture properties of cortical bone have suggested that the fracture toughness increases with crack length, which is indicative of rising R-curve behavior. Based on this indirect evidence and the similarity of bone to ceramic matrix composites, we hypothesized that bone would exhibit rising R-curve behavior in the transverse orientation and that the characteristics of the R-curves would be regionally dependent within the cortex due to variations in bone microstructure and toughening mechanisms. To test these hypotheses, we conducted R-curve experiments on specimens from equine third metacarpal bones using standard fracture mechanics testing methods. Compact type specimens from the dorsal and lateral regions in the middle of the diaphysis were oriented for crack propagation transverse to the longitudinal axis of the bone. The test results demonstrate that equine cortical bone exhibits rising R-curve behavior during transverse crack propagation as hypothesized. Statistical analyses of the crack growth initiation toughness, K0, the peak toughness, Kpeak, and the crack extension at peak toughness, deltaa, revealed significant regional differences in these characteristics. Specifically, the lateral cortex displayed higher crack growth initiation and peak toughnesses. The dorsal cortex exhibited greater crack extension at the peak of crack growth resistance. Scanning electron microscopy revealed osteon pullout on fracture surfaces from the dorsal cortex and but not in the lateral cortex. Taken together, the significant differences in R-curves and the SEM fractography indicate that the fracture mechanisms acting in equine cortical bone are regionally dependent.

  13. Mechanical Properties of Aluminum-alloy Rivets

    NASA Technical Reports Server (NTRS)

    Brueggeman, Wm C

    1936-01-01

    The development of metal construction for aircraft has created a need for accurate and detailed information regarding the strength of riveted joints in aluminum-alloy structures. To obtain this information the National Bureau of Standards in cooperation with the National Advisory Committee for Aeronautics is investigating the strength of riveted joints in aluminum alloys. The strength of riveted joints may be influenced by the form of the head, the ratio of the rivet diameter to the sheet thickness, the driving stress, and other factors. This note gives the results of tests to develop the riveting technique for test specimens and to determine the effects of these factors.

  14. Tungsten solution kinetics and amorphization of nickel in mechanically alloyed Ni-W alloys

    NASA Technical Reports Server (NTRS)

    Aning, A. O.; Wang, Z.; Courtney, T. H.

    1993-01-01

    The kinetics of solution of W, and the subsequent amorphization of Ni, in mechanically alloyed Ni-W alloys has been investigated. As W is a highly abrasive material in the energy intensive devices used for mechanical alloying, we studied the above reactions in different mills. One used hardened steel balls as the grinding media, and the other Al2O3. Abrasion is common to both mills, but Fe wear debris from the hardened steel enters into solution in the Ni rich phases whereas Al2O3 debris is present as small dispersoids. The kinetics of W solution and those of subsequent amorphization do not appear strongly affected by the Fe in solution or the Al2O3 dispersoid. Tungsten dissolves in crystalline Ni in amounts in excess of the equilibrium solubility during alloying. Amorphization of the Ni phase occurs if the W content in this phase exceeds ca. 28 at. pct.

  15. Tungsten solution kinetics and amorphization of nickel in mechanically alloyed Ni-W alloys

    NASA Technical Reports Server (NTRS)

    Aning, A. O.; Wang, Z.; Courtney, T. H.

    1993-01-01

    The kinetics of solution of W, and the subsequent amorphization of Ni, in mechanically alloyed Ni-W alloys has been investigated. As W is a highly abrasive material in the energy intensive devices used for mechanical alloying, we studied the above reactions in different mills. One used hardened steel balls as the grinding media, and the other Al2O3. Abrasion is common to both mills, but Fe wear debris from the hardened steel enters into solution in the Ni rich phases whereas Al2O3 debris is present as small dispersoids. The kinetics of W solution and those of subsequent amorphization do not appear strongly affected by the Fe in solution or the Al2O3 dispersoid. Tungsten dissolves in crystalline Ni in amounts in excess of the equilibrium solubility during alloying. Amorphization of the Ni phase occurs if the W content in this phase exceeds ca. 28 at. pct.

  16. Phase transformation and magnetic properties of Nd-Fe-V-Nb alloys prepared by mechanical alloying

    NASA Astrophysics Data System (ADS)

    Cui, B. Z.; Sun, X. K.; Sui, Y. C.; Geng, D. Y.; Zhang, Z. D.

    2002-09-01

    The phase transformation and magnetic properties of the NdFe 11.35- xV xNb 0.65 ( x=0-1.35) alloys prepared by mechanical alloying (MA) have been studied. Phases of 2:17, 1:7 and 1:12 are formed in the as-annealed alloys with x=0, 0.3-0.7 and 1.0-1.35, respectively. With increasing V content in the NdFe 11.35- xV xNb 0.65 ( x=0.3-0.7) alloys, the Curie temperatures of the matrix 1:7 phases monotonically increase. Upon nitrogenation, with increasing V content, the intrinsic coercivity μ0Hc of the nitrided alloys monotonically increases. The increase becomes sharp at x=1.0 due to the formation of a great amount of Nd(Fe, V) 12N δ. The remanence Jr and the maximum magnetic energy product (BH) max of the nitrided alloys monotonically decrease with increasing V content. The 1:12 phases are formed in all the NdFe 11- xNb xV 1 ( x=0, 0.3, 0.65, 1.0) alloys annealed at 850 oC for 20 min. With increasing Nb content, the crystallization of the 1:12 phase is improved and the relative volume fraction of the 1:12 phase tends to be higher. While μ0Hc of the nitrided alloys monotonically increase, and Jr and (BH) max of the nitrided alloys monotonically decrease. With increasing Nb content in the nitrided alloys, the average grain size of α-Fe decrease while the nitrogen content increases.

  17. Microstructural effects on the deformation and fracture of the alloy Ti-25Al-10Nb-3B-1Mo. Final report, 1 July 1988-15 December 1992

    SciTech Connect

    Ward, C.H.

    1992-12-01

    The effects of microstructure and temperature on tensile and fracture behavior were explored for the titanium aluminide alloy Ti-25Al-lONb-3V-lMo (atomic percent). Three microstructures were selected for this study in an attempt to determine the role of the individual microstructural constituents. the three microstructures studied were an alpha-2 + beta processed microstructure with a fine Widmanstaetten microstructure, a beta processed microstructure with a fine Widmanstaetten microstructure, and a beta processed microstructure with a coarse Widmanstaetten microstructure. Tensile testing of both round and flat specimens was conducted in vacuum at elevated temperature and in air at room and elevated temperatures. Extensive fractography and specimen sectioning were used to study tensile deformation and the effects of environment on this alloy. Room temperature fracture toughness testing using compact tension specimens was conducted. Elevated temperature toughness testing was performed using J-bend bar specimens in an air environment. Again, extensive fractography and specimen sectioning were used to study the elevated temperature toughening mechanisms of this alloy.... Titanium, Titanium aluminide, Intermetallic, Fracture toughness, Tensile behavior, Fractography environmental interaction.

  18. Dynamic strength and edge effects at spall fracture for titanium alloys of varying oxygen content

    NASA Astrophysics Data System (ADS)

    Razorenov, S. V.; Kanel, G. I.; Utkin, A. V.; Bogach, A. A.; Burkins, M.; Gooch, W. A.

    2000-04-01

    The results of VISAR free-surface velocity measurements for Ti-6Al-4V alloys with different oxygen content and the HEL, the spall strength, the spall fracture energy data are presented. The peak shock stress was varied from 4 to 75 GPa, the load duration from ˜10-7 s to ˜10-5 s. The Hugoniot elastic limit grows by ˜20% with increasing the oxygen content from 0.105% up to 0.24%. The alloy with the largest oxygen content exhibits also a greatest viscosity. The measurements have not revealed a notable variations in the spall strength magnitudes as a function of the oxygen content. The specific energy of spall element separation is practically the same for the all three types of samples tested.

  19. Correlation of stress-wave-emission characteristics with fracture aluminum alloys

    NASA Technical Reports Server (NTRS)

    Hartbower, C. E.; Reuter, W. G.; Morais, C. F.; Crimmins, P. P.

    1972-01-01

    A study to correlate stress wave emission characteristics with fracture in welded and unwelded aluminum alloys tested at room and cryogenic temperature is reported. The stress wave emission characteristics investigated were those which serve to presage crack instability; viz., a marked increase in:(1) signal amplitude; (2) signal repetition rate; and (3) the slope of cumulative count plotted versus load. The alloys were 7075-T73, 2219-T87 and 2014-T651, welded with MIG and TIG using 2319 and 4043 filler wire. The testing was done with both unnotched and part-through-crack (PTC) tension specimens and with 18-in.-dia subscale pressure vessels. In the latter testing, a real time, acoustic emission, triangulation system was used to locate the source of each stress wave emission. With such a system, multiple emissions from a given location were correlated with defects found by conventional nondestructive inspection.

  20. Peculiarities of fracture in submicrocrystalline Al-Mg-Mn alloy under impact compression

    NASA Astrophysics Data System (ADS)

    Petrova, A. N.; Brodova, I. G.; Razorenov, S. V.

    2017-05-01

    The method of nondestructive X-ray computed tomography (CT) has been used to study the structure of A5083 (magnesium- and manganese-doped aluminum) alloy samples upon impact compression. The initial samples had an average grain size of 600 nm and submicrocrystalline (SMC) structure formed by dynamic equal-channel angular pressing. Three-dimensional CT images of local fracture regions were obtained and the degree of material damage was estimated by calculating the average and maximum size of discontinuities (pores and microcracks) in various cross sections. The techniques of transmission and scanning electron microscopy were used to trace evolution of the SMC structure of impact-compressed alloy and determine the morphological characteristics of spallation surfaces and other defects.

  1. Mechanical anisotropy of a gamma titanium aluminide alloy after hot extrusion

    SciTech Connect

    Oehring, M.; Lorenz, U.; Niefanger, R.; Appel, F.; Brokmeier, H.G.; Wagner, R.; Clemens, H.; Eberhardt, N.

    1999-07-01

    By hot extrusion below and above the {alpha} transus temperature equiaxed and predominantly lamellar microstructures were obtained in a Ti aluminide alloy. In order to examine a possible orientation dependence of mechanical properties the flow stress, the activation parameters of plastic deformation and the fracture toughness were determined parallel and perpendicular to the extrusion direction at room temperature and 700 C. The observed anisotropy in these properties may be mainly attributed to anisotropies in the microstructures, in particular to a preferential alignment of lamellae in lamellar microstructures.

  2. Role of surfaces and interfaces in controlling the mechanical properties of metallic alloys.

    PubMed

    Lee, Won-Jong; Chia, Wen-Jui; Wang, Jinliu; Chen, Yanfeng; Vaynman, Semyon; Fine, Morris E; Chung, Yip-Wah

    2010-11-02

    This article explores the subtle effects of surfaces and interfaces on the mechanical properties of bulk metallic alloys using three examples: environmental effects on fatigue life, hydrogen embrittlement effects on the ductility of intermetallics, and the role of coherent precipitates in the toughness of steels. It is demonstrated that the marked degradation of the fatigue life of metals is due to the strong chemisorption of adsorbates on exposed slip steps that are formed during fatigue deformation. These adsorbates reduce the reversibility of slip, thus accelerating fatigue damage in a chemically active gas environment. For certain intermetallic alloys such as Ni(3)Al and Ni(3)Fe, the ductility depends on the ambient gas composition and the atomic ordering in these alloys, both of which govern the complex surface chemical reactions taking place in the vicinity of crack tips. Finally, it is shown that local stresses at a coherent precipitate-matrix interface can activate dislocation motion at low temperatures, thus improving the fracture toughness of bulk alloys such as steels at cryogenic temperatures. These examples illustrate the complex interplay between surface chemistry and mechanics, often yielding unexpected results.

  3. Investigation of the fracture mechanics of boride composites

    NASA Technical Reports Server (NTRS)

    Kaufman, L.; Clougherty, E. V.; Nesor, H.

    1971-01-01

    Fracture energies of WC-6Co, Boride 5 (ZrB2+SiC), Boride 8(ZrB2+SiC+C) and Boride 8-M2(ZrB2+SiC+C) were measured by slow bend and impact tests of notched charpy bars. Cobalt bonded tungsten carbide exhibited impact energies of 0.76 ft-lb or 73.9 in-lb/square inch. Boride 5 and the Boride 8 exhibit impact energies one third and one quarter of that observed for WC-6Co comparing favorably with measurements for SiC and Si3N4. Slow bend-notched bar-fracture energies for WC-6Co were near 2.6 in-lb/square inch or 1/20 the impact energies. Slow bend energies for Boride 8-M2, Boride 8 and Boride 5 were 58%, 42% and 25% of the value observed for WC-6Co. Fractograph showed differences for WC-6Co where slow bend testing resulted in smooth transgranular cleavage while samples broken by impact exhibited intergranular failures. By contrast the boride fractures showed no distinction based on testing method. Fabrication studies were conducted to effect alteration of the boride composites by alloying and introduction of graphite cloth.

  4. Fracture mechanisms of retrieved titanium screw thread in dental implant.

    PubMed

    Yokoyama, Ken'ichi; Ichikawa, Tetsuo; Murakami, Hiroki; Miyamoto, Youji; Asaoka, Kenzo

    2002-06-01

    Titanium and its alloy are increasingly attracting attention for use as biomaterials. However, delayed fracture of titanium dental implants has been reported, and factors affecting the acceleration of corrosion and fatigue have to be determined. The fractured surface of a retrieved titanium screw and metallurgical structures of a dental implant system were analyzed. The outer surface of the retrieved screw had a structure different from that of the as-received screw. It was confirmed that a shear crack initiated at the root of the thread and propagated into the inner section of the screw. Gas chromatography revealed that the retrieved screw had absorbed a higher amount of hydrogen than the as-received sample. The grain structure of a titanium screw, immersed in a solution known to induce hydrogen absorption, showed features similar to those of the retrieved screw. It was concluded that titanium in a biological environment absorbs hydrogen and this may be the reason for delayed fracture of a titanium implant.

  5. Kinetics and fracture behavior under cycle loading of an Al-Cu-Mg-Ag alloy

    NASA Astrophysics Data System (ADS)

    Gazizov, M. R.; Kaibyshev, R. O.

    2016-07-01

    The behavior of aluminum alloy AA2139 subjected to T6 treatment, including solution treatment and artificial aging, has been studied using cyclic loading with a constant total strain amplitude. Upon low-cyclic fatigue in the range of total strain amplitudes ɛac of 0.4-1.0%, the cyclic behavior of the AA2139-T6 alloy is determined by the processes that occur under the conditions of predominance of the elastic deformation over plastic deformation. The AA2139 alloy exhibits stability to cyclic loading without significant softening. The stress-strained state of the alloy upon cyclic loading can be described by the Hollomon equation with the cyclic strength coefficient K' and the cyclic strain-hardening exponent n' equal to 641 MPa and 0.066, respectively. The dependence of the number of cycles to fracture on the loading amplitude and its components (amplitudes of the plastic and elastic deformation) is described by a Basquin-Manson-Coffin equation with the parameters σ'/ E = 0.014, b =-0.123, ɛ'f= 178.65, and c =-1.677.

  6. Measurements of residual stress in fracture mechanics coupons

    SciTech Connect

    Prime, Michael B; Hill, Michael R; Nav Dalen, John E

    2010-01-01

    This paper describes measurements of residual stress in coupons used for fracture mechanics testing. The primary objective of the measurements is to quantify the distribution of residual stress acting to open (and/or close) the crack across the crack plane. The slitting method and the contour method are two destructive residual stress measurement methods particularly capable of addressing that objective, and these were applied to measure residual stress in a set of identically prepared compact tension (C(T)) coupons. Comparison of the results of the two measurement methods provides some useful observations. Results from fracture mechanics tests of residual stress bearing coupons and fracture analysis, based on linear superposition of applied and residual stresses, show consistent behavior of coupons having various levels of residual stress.

  7. Fracture mechanics evaluation for at typical PWR primary coolant pipe

    SciTech Connect

    Tanaka, T.; Shimizu, S.; Ogata, Y.

    1997-04-01

    For the primary coolant piping of PWRs in Japan, cast duplex stainless steel which is excellent in terms of strength, corrosion resistance, and weldability has conventionally been used. The cast duplex stainless steel contains the ferrite phase in the austenite matrix and thermal aging after long term service is known to change its material characteristics. It is considered appropriate to apply the methodology of elastic plastic fracture mechanics for an evaluation of the integrity of the primary coolant piping after thermal aging. Therefore we evaluated the integrity of the primary coolant piping for an initial PWR plant in Japan by means of elastic plastic fracture mechanics. The evaluation results show that the crack will not grow into an unstable fracture and the integrity of the piping will be secured, even when such through wall crack length is assumed to equal the fatigue crack growth length for a service period of up to 60 years.

  8. Failure mechanism characterization of platinum alloy

    NASA Technical Reports Server (NTRS)

    Rosen, J. M.; Mcfarlen, W. T.

    1986-01-01

    This article describes procedures and results of testing performed on a platinum/10-percent rhodium, thin-wall tubular product. The purpose of the testing was to develop exemplar SEM fractographs to be used to characterize failures under various environmental conditions. Conditions evaluated for the platinum alloys included high temperature, hydrogen environment, braze metal contamination, and cyclic loading.

  9. Mathematical modeling of mechanical properties of metals and alloys at large strains

    NASA Astrophysics Data System (ADS)

    Agal'tsov, V. I.; Vladimirov, S. A.; Degtyarev, V. P.

    2007-02-01

    We discuss problems in mathematical modeling of the mechanical behavior of metals and alloys at large strains. Attention is mainly paid to the analysis of the stress-strain state of specimens and structural fragments made of highly plastic materials with the effect of stability loss under tensile stresses taken into account. We discuss the methods for determining the true property diagram at strains exceeding the ultimate uniform strain. We process experimental data and determine the true property diagrams for AMg6, AMg6M, and 1201 aluminum alloys and BrKh08 alloy. To calculate the load-carrying capacity of structural members, one often uses the conventional ultimate strength σ b accepted in regulations as a material characteristic. But it follows from the method for experimentally determining this characteristic that it depends on the properties of the specimen viewed as a structure. As a result, a formal use of fracture criteria recommended in regulations leads to a discrepancy between design and experimental values of fracture loads. Nowadays, the finite element method is widely used in practical strength analysis. This method permits one to study the elastoplastic strained state of geometrically complicated structures in detail, take into account physical nonlinearity at large strains, determine damage boundaries, and improve experimental methodology. The wide capabilities of this method allow one to use test results more completely.

  10. Aging effects on the fracture toughness of SiC whisker reinforced 2XXX aluminum alloys

    NASA Technical Reports Server (NTRS)

    Ratnaparkhi, P. L.; Rack, H. J.

    1989-01-01

    The effect of aging (at 150 C) time on the fracture toughness behavior of a 2XXX alloy (Al-3.55Cu-1.29Mg-0.01Fe-trace Mn) reinforced with 5 vol pct F-8 SiC whiskers was investigated by measuring hardness and electrical conductivity followed by fracture toughness tests on center-cracked specimens. The ageing time-hardening response plots showed that, independent of whisker orientation, the initial rapid increase in hardness was followed by a more gradual increase, with a broad hardness peak between 32 and 128 hrs of aging. Coincident with the hardness changes, the electrical conductivity initially decreased, reached a minimum, and then increased at aging times beyond 32 hrs. Examination by SEM indicated that the initial increase in hardness and decrease in conductivity was due to the GPB zone formation, while the subsequent increase in electrical conductivity and decrease in hardness (overaging) was due to S nucleation and growth.

  11. Aging effects on the fracture toughness of SiC whisker reinforced 2XXX aluminum alloys

    NASA Technical Reports Server (NTRS)

    Ratnaparkhi, P. L.; Rack, H. J.

    1989-01-01

    The effect of aging (at 150 C) time on the fracture toughness behavior of a 2XXX alloy (Al-3.55Cu-1.29Mg-0.01Fe-trace Mn) reinforced with 5 vol pct F-8 SiC whiskers was investigated by measuring hardness and electrical conductivity followed by fracture toughness tests on center-cracked specimens. The ageing time-hardening response plots showed that, independent of whisker orientation, the initial rapid increase in hardness was followed by a more gradual increase, with a broad hardness peak between 32 and 128 hrs of aging. Coincident with the hardness changes, the electrical conductivity initially decreased, reached a minimum, and then increased at aging times beyond 32 hrs. Examination by SEM indicated that the initial increase in hardness and decrease in conductivity was due to the GPB zone formation, while the subsequent increase in electrical conductivity and decrease in hardness (overaging) was due to S nucleation and growth.

  12. A compendium of sources of fracture toughness and fatigue crack growth data for metallic alloys. II

    NASA Technical Reports Server (NTRS)

    Hudson, C. M.; Seward, S. K.

    1982-01-01

    A compendium is presented of sources for metallic alloy fracture toughness and fatigue crack growth data, which concentrates on technical reports as the primary source of references and updates the previous Hudson and Seward (1978) compendium references on technical journals. Where available, the accession numbers which are used as code numbers for the ordering of the reports from their publishers are given. The sources of these reports include the AIAA Technical Information Service, the Defense Technical Information Center, the National Technical Information Service, and NASA.

  13. Estimating plane strain fracture toughness of high strength aluminum alloys from crack arrest toughness

    NASA Technical Reports Server (NTRS)

    Dorward, R. C.; Hasse, K. R.

    1977-01-01

    A comparison is made between fracture toughness KIc as measured by recommended ASTM procedures and crack arrest toughness KIa as measured on more than 100 bolt-loaded double-cantilever beam (DCB) specimens from 7075, 7050, and 7049 alloy plates. Close agreement was found between the two values, KIa being on the average less than KIc over a specified range. This indicates that a simplified test based on a bolt-loaded DCB specimen could be used for quality control, lot release, and screening purposes. Measurements of crack length and specimen deflection are all that are required. The specimens do not have to be fatigue precracked, nor is a tensile machine needed.

  14. The mechanics of brittle fracture and faulting on Venus

    NASA Astrophysics Data System (ADS)

    Koenig, Elissa I.

    The surface of Venus exhibits all types of brittle fracture and faulting at all scales. The fractures often exhibit characteristic patterns indicative of the mechanical processes responsible for their formation. In this dissertation I investigate two types of fracture patterns: (1) radial fracture systems related to the emplacement of subsurface dikes, and (2) secondary fractures associated with strike-slip faulting. This work combines detailed structural mapping based on Magellan data with two- and three-dimensional boundary element models of fracture processes to explain the observed deformation and place it in the framework of global tectonics on Venus. I describe two radial fracture systems and compare their geometry to analytical models of dike emplacement from a central magma chamber to constrain the stress fields acting at the time of their formation. Two-dimensional numerical models were implemented to consider the effects of dike initiation, propagation, and interaction. I propose that the stress perturbation around a dike can control the spacing between dikes, and the magnitude of this perturbation is related to the three-dimensional dike shape. Using three-dimensional boundary element models of the stress field around a tabular dike, I determine the relationship between dike aspect ratio (height/length) and spacing. Dike spacing increases as the aspect ratio increases; this relationship is used to infer the height of subsurface dikes. For the analysis of secondary fractures associated with strike-slip faulting, I investigate the spatial and temporal relationships between a ridge belt and an extensive fracture system along the belt boundary in Lavinia Planitia, Venus. I propose that the fractures formed as the result of right-lateral shear localized along the ridge belt, which acted as a pre-existing weak zone hundreds of kilometers long. First-order models of the ridge belt as a crack-like fault plane indicate that the localization and orientation of the

  15. The effects of artificial aging on the microstructure and fracture toughness of Al-Cu-Li alloy 2195

    SciTech Connect

    Chen, P.S.; Kuruvilla, A.K.; Malone, T.W.; Stanton, W.P.

    1998-10-01

    Aluminum-lithium alloys have shown promise for aerospace applications, and National Aeronautics and Space Administration (NASA) has selected the aluminum-lithium Alloy 2195 for the main structural alloy of the super light weight tank (SLWT) for the space shuttle. This alloy has significantly higher strength than conventional 2xxx alloys (such as 2219) at both ambient and cryogenic temperatures. If properly processed and heat treated, this alloy can display higher fracture toughness at cryogenic temperature than at ambient temperature. However, the properties of production materials have shown greater variation than those of other established alloys, as is the case with any new alloy that is being transitioned to a demanding application. A multistep heating-rate controlled (MSRC) aging treatment has been developed that can improve the cryogenic fracture toughness of aluminum-lithium Alloy 2195. At the same levels of yield strength (YS), this treatment results in considerably higher fracture toughness than that found in Alloy 2195, which has received conventional (isothermal) aging. Transmission electron microscopy revealed that the new treatment greatly reduces the size and density of subgrain-boundary T{sub 1} precipitates. In addition, it promotes T{sub 1} and {theta}{double_prime} nucleation, resulting in a fine and dense distribution of precipitate particles in the matrix. The MSRC aging treatment consists of (a) aging at 127 C (260 F) for 5 h, (b) heating continuously from 127 C (260 F) to 135 C (275 F) at a rate of 0.556 C/h (1 F/h), (c) holding at 135 C (275 F) for 5 h, (d) heating continuously from 135 to 143 C (275 to 290 F) at a rate of 0.556 C/h (1 F/h), and (e) holding at 143 C (290 F) for 25 h to obtain a near peak-aged condition.

  16. Mechanical properties of dental Ti-Ag alloys with 22.5, 25, 27.5, and 30 mass% Ag.

    PubMed

    Takahashi, Masatoshi; Kikuchi, Masafumi; Takada, Yukyo

    2015-01-01

    The mechanical properties -tensile strength, yield strength, elongation after fracture, Vickers hardness, and Young's modulus-and the phases of Ti-Ag alloys were investigated, as prepared with 22.5, 25, 27.5, and 30 mass% Ag. The tensile strength, yield strength, hardness, and Young's modulus of the alloys increase with their Ag content up to 25 mass%, but their breaking elongation decreases. These changes in the mechanical properties are attributed to solid-solution strengthening of the α-titanium phase, to Ti2Ag precipitation, and to the formation of eutectic structures composed of α+Ti2Ag. The addition of Ag, at 25 mass% in particular, improves the mechanical properties of these alloys, making them suitable for high strength dental prostheses, such as implantretained superstructures and narrow-diameter implants.

  17. The effect of electric discharge machined notches on the fracture toughness of several structural alloys

    SciTech Connect

    Joyce, J.A.; Link, R.E.

    1993-09-01

    Recent computational studies of the stress and strain fields at the tip of very sharp notches have shown that the stress and strain fields are very weakly dependent on the initial geometry of the notch once the notch has been blunted to a radius that is 6 to 10 times the initial root radius. It follows that if the fracture toughness of a material is sufficiently high so that fracture initiation does not occur in a specimen until the crack-tip opening displacement (CTOD) reaches a value from 6 to 10 times the size of the initial notch tip diameter, then the fracture toughness will be independent of whether a fatigue crack or a machined notch served as the initial crack. In this experimental program the fracture toughness (J{sub Ic} and J resistance (J-R) curve, and CTOD) for several structure alloys was measured using specimens with conventional fatigue cracks and with EDM machined notches. The results of this program have shown, in fact, that most structural materials do not achieve initiation CTOD values on the order of 6 to 10 times the radius of even the smallest EDM notch tip presently achievable. It is found furthermore that tougher materials do not seem to be less dependent on the type of notch tip present. Some materials are shown to be much more dependent on the type of notch tip used, but no simple pattern is found that relates this observed dependence to the material strength toughness, or strain hardening rate.

  18. Investigation of the fracture mechanics of boride composites

    NASA Technical Reports Server (NTRS)

    Clougherty, E. V.; Pober, R. L.; Kaufman, L.

    1972-01-01

    Significant results were obtained in fabrication studies of the role of metallic additives of Zr, Ti, Ni, Fe and Cr on the densification of ZrB2. All elemental additions lower the processing temperatures required to effect full densification of ZrB2. Each addition effects enhanced densification by a clearly distinguishable and different mechanism and the resulting fabricated materials are different. A significant improvement in strength and fracture toughness was obtained for the ZrB2/Ti composition. Mechanical characterization studies for the ZrB2/SiC/C composites and the new ZrB2/Metal materials produced data relevant to the effect of impacting load on measured impact energies, a specimen configuration for which controlled fracture could occur in a suitably hard testing apparatus, and fracture strength data. Controlled fracture--indicative of measurable fracture toughness--was obtained for the ZrB2-SiC-C composite, and a ZrB2/Ti composite fabricated from ZrB2 with an addition of 30 weight per cent Ti. The increased strength and toughness of the ZrB2/Ti composite is consistent with the presence of a significantly large amount of a fine grained acicular phase formed by reaction of Ti with ZrB2 during processing.

  19. Indentation creep of nanocrystalline Cu-TiC alloys prepared by mechanical alloying

    SciTech Connect

    Shen, B.L.; Itoi, T.; Yamasaki, T.; Ogino, Y.

    2000-04-01

    In recent years, nanocrystalline materials have attracted much attention in materials research because they behave differently from conventional materials. For example, the nanocrystalline materials exhibit enhanced mechanical properties, such as high strength and hardness. The present study was performed to investigate the indentation creep mechanism of nanocrystalline Cu-TiC alloys which were prepared by HIP (Hot Isostatic Press) processing of MA (Mechanical Alloying) powders and hot rolling afterwards. As these materials have high densities and high structural stability, the authors could investigate creep behavior at wide temperature ranges below 0.5Tm (Tm is the melting temperature of copper).

  20. Mechanical properties of Mo-Si-B alloys fabricated by using core-shell powder with dispersion of yttria nanoparticles

    NASA Astrophysics Data System (ADS)

    Byun, Jong Min; Bang, Su-Ryong; Choi, Won June; Kim, Min Sang; Noh, Goo Won; Kim, Young Do

    2017-01-01

    In recent years, refractory materials with excellent high-temperature properties have been in the spotlight as a next generation's high-temperature materials. Among these, Mo-Si-B alloys composed of two intermetallic compound phases (Mo5SiB2 and Mo3Si) and a ductile α-Mo phase have shown an outstanding thermal properties. However, due to the brittleness of the intermetallic compound phases, Mo-Si-B alloys were restricted to apply for the structural materials. So, to enhance the mechanical properties of Mo-Si-B alloys, many efforts to add rare-earth oxide particles in the Mo-Si-B alloy were performed to induce the improvement of strength and fracture toughness. In this study, to investigate the effect of adding nano-sized Y2O3 particles in Mo-Si-B alloy, a core-shell powder consisting of intermetallic compound phases as the core and nano-sized α-Mo and Y2O3 particles surrounding the core was fabricated. Then pressureless sintering was carried out at 1400 °C for 3 h, and the mechanical properties of sintered bodies with different amounts of Y2O3 particles were evaluated by Vickers hardness and 3-point bending test. Vickers hardness was improved by dispersed Y2O3 particles in the Mo-Si-B alloy. Especially, Mo-3Si-1B-1.5Y2O3 alloy had the highest value, 589 Hv. The fracture toughness was measured using Mo-3Si-1B-1.5Y2O3 alloy and the value indicated as 13.5 MPa·√m.

  1. The physical metallurgy of mechanically-alloyed, dispersion-strengthened Al-Li-Mg and Al-Li-Cu alloys

    NASA Technical Reports Server (NTRS)

    Gilman, P. S.

    1984-01-01

    Powder processing of Al-Li-Mg and Al-Li-Cu alloys by mechanical alloying (MA) is described, with a discussion of physical and mechanical properties of early experimental alloys of these compositions. The experimental samples were mechanically alloyed in a Szegvari attritor, extruded at 343 and 427 C, and some were solution-treated at 520 and 566 C and naturally, as well as artificially, aged at 170, 190, and 210 C for times of up to 1000 hours. All alloys exhibited maximum hardness after being aged at 170 C; lower hardness corresponds to the solution treatment at 566 C than to that at 520 C. A comparison with ingot metallurgy alloys of the same composition shows the MA material to be stronger and more ductile. It is also noted that properly aged MA alloys can develop a better combination of yield strength and notched toughness at lower alloying levels.

  2. Investigating enhanced mechanical properties in dual-phase Fe-Ga-Tb alloys

    PubMed Central

    Meng, Chongzheng; Wang, Hui; Wu, Yuye; Liu, Jinghua; Jiang, Chengbao

    2016-01-01

    Dual-phase (Fe83Ga17)100−xTbx alloys with 0 ≤ x ≤ 1 were synthesized by arc melting and homogenization treatment. The microstructures and the corresponding mechanical properties were systematically investigated. The chemical composition of the body centered cubic matrix is Fe83Ga17. The monoclinic second phase was composed of meltable precipitates with approximate composition Fe57Ga33Tb10. The nano-hardness of matrix and precipitates were 2.55 ± 0.17 GPa and 6.81 ± 1.03 GPa, respectively. Both the ultimate tensile strength (UTS) and fracture strain (ε) of the alloys were improved by the precipitates for x ≤ 0.2 alloys, but the strain decreases significantly at higher values of x. As potential structural-functional materials, the best mechanical properties obtained were a UTS of 595 ± 10 MPa and an ε of 3.5 ± 0.1%, four-fold and seven-fold improvements compared with the un-doped alloy. The mechanism for these anomalous changes of mechanical properties was attributed to the dispersed precipitates and semi-coherent interfaces, which serve as strong obstacles to dislocation motion and reduce the stress concentration at the grain boundaries. A sizeable improvement of magnetostriction induced by the precipitates in the range 0 ≤ x ≤ 0.2 was discovered and an optimal value of 150 ± 5 ppm is found, over three times higher than that of the un-doped alloy. PMID:27694839

  3. Investigating enhanced mechanical properties in dual-phase Fe-Ga-Tb alloys.

    PubMed

    Meng, Chongzheng; Wang, Hui; Wu, Yuye; Liu, Jinghua; Jiang, Chengbao

    2016-10-03

    Dual-phase (Fe83Ga17)100-xTbx alloys with 0 ≤ x ≤ 1 were synthesized by arc melting and homogenization treatment. The microstructures and the corresponding mechanical properties were systematically investigated. The chemical composition of the body centered cubic matrix is Fe83Ga17. The monoclinic second phase was composed of meltable precipitates with approximate composition Fe57Ga33Tb10. The nano-hardness of matrix and precipitates were 2.55 ± 0.17 GPa and 6.81 ± 1.03 GPa, respectively. Both the ultimate tensile strength (UTS) and fracture strain (ε) of the alloys were improved by the precipitates for x ≤ 0.2 alloys, but the strain decreases significantly at higher values of x. As potential structural-functional materials, the best mechanical properties obtained were a UTS of 595 ± 10 MPa and an ε of 3.5 ± 0.1%, four-fold and seven-fold improvements compared with the un-doped alloy. The mechanism for these anomalous changes of mechanical properties was attributed to the dispersed precipitates and semi-coherent interfaces, which serve as strong obstacles to dislocation motion and reduce the stress concentration at the grain boundaries. A sizeable improvement of magnetostriction induced by the precipitates in the range 0 ≤ x ≤ 0.2 was discovered and an optimal value of 150 ± 5 ppm is found, over three times higher than that of the un-doped alloy.

  4. Investigating enhanced mechanical properties in dual-phase Fe-Ga-Tb alloys

    NASA Astrophysics Data System (ADS)

    Meng, Chongzheng; Wang, Hui; Wu, Yuye; Liu, Jinghua; Jiang, Chengbao

    2016-10-01

    Dual-phase (Fe83Ga17)100‑xTbx alloys with 0 ≤ x ≤ 1 were synthesized by arc melting and homogenization treatment. The microstructures and the corresponding mechanical properties were systematically investigated. The chemical composition of the body centered cubic matrix is Fe83Ga17. The monoclinic second phase was composed of meltable precipitates with approximate composition Fe57Ga33Tb10. The nano-hardness of matrix and precipitates were 2.55 ± 0.17 GPa and 6.81 ± 1.03 GPa, respectively. Both the ultimate tensile strength (UTS) and fracture strain (ε) of the alloys were improved by the precipitates for x ≤ 0.2 alloys, but the strain decreases significantly at higher values of x. As potential structural-functional materials, the best mechanical properties obtained were a UTS of 595 ± 10 MPa and an ε of 3.5 ± 0.1%, four-fold and seven-fold improvements compared with the un-doped alloy. The mechanism for these anomalous changes of mechanical properties was attributed to the dispersed precipitates and semi-coherent interfaces, which serve as strong obstacles to dislocation motion and reduce the stress concentration at the grain boundaries. A sizeable improvement of magnetostriction induced by the precipitates in the range 0 ≤ x ≤ 0.2 was discovered and an optimal value of 150 ± 5 ppm is found, over three times higher than that of the un-doped alloy.

  5. Preparation of Fe-Ni-Based Metal-Metalloid Amorphous Alloys by Mechanical Alloying and Mechanical Grinding Methods

    NASA Astrophysics Data System (ADS)

    Miura, Harumatsu; Isa, Shigeteru; Omuro, Keisuke

    1990-02-01

    Using a high energy ball mill, alloys of Fe40Ni40P14B6 and Fe40Ni40B20 were synthesized from crystalline, elemental iron and nickel metals and iron-metalloid alloys such as Fe-B and Fe-P by mechanical alloying (MA). Powders of the Fe40Ni40P14B6 alloy were also prepared from the cast ingot products by mechanical grinding (MG). Each of the MA and MG powder products showed a halo pattern typical of amorphous materials in the X-ray diffraction trace, and the crystallization enthalpy of the Fe40Ni40P14B6 MA powder, measured by differential scanning calorimetry, was almost the same as that of the melt-quenched sample of the same composition.

  6. Fracture mechanics applied to the machining of brittle materials

    SciTech Connect

    Hiatt, G.D.; Strenkowski, J.S.

    1988-12-01

    Research has begun on incorporating fracture mechanics into a model of the orthogonal cutting of brittle materials. Residual stresses are calculated for the machined material by a combination of Eulerian and Lagrangian finite element models and then used in the calculation of stress intensity factors by the Green`s Function Method.

  7. Mechanical Properties and Corrosion Characteristics of Thermally Aged Alloy 22

    SciTech Connect

    Rebak, R B; Crook, P

    2002-05-30

    Alloy 22 (UNS N06022) is a candidate material for the external wall of the high level nuclear waste containers for the potential repository site at Yucca Mountain. In the mill-annealed (MA) condition, Alloy 22 is a single face centered cubic phase. When exposed to temperatures on the order of 600 C and above for times higher than 1 h, this alloy may develop secondary phases that reduce its mechanical toughness and corrosion resistance. The objective of this work was to age Alloy 22 at temperatures between 482 C and 760 C for times between 0.25 h and 6,000 h and to study the mechanical and corrosion performance of the resulting material. Aging was carried out using wrought specimens as well as gas tungsten arc welded (GTAW) specimens. Mechanical and corrosion testing was carried out using ASTM standards. Results show-that the higher the aging temperature and the longer the aging time, the lower the impact toughness of the aged material and the lower its corrosion resistance. However, extrapolating both mechanical and corrosion laboratory data predicts that Alloy 22 will remain corrosion resistant and mechanically robust for the projected lifetime of the waste container.

  8. Probabilistic fracture mechanics and optimum fracture control of the solid rocket motor case of the shuttle

    NASA Technical Reports Server (NTRS)

    Hanagud, S.; Uppaluri, B.

    1977-01-01

    Development of a procedure for the reliability analysis of the solid rocket motor case of the space shuttle is described. The analysis is based on probabilistic fracture mechanics and consideration of a probability distribution for the initial flaw sizes. The reliability analysis can be used to select design variables, such as the thickness of the SRM case, projected design life and proof factor, on the basis of minimum expected cost and specified reliability bounds. Effects of fracture control plans such as the non-destructive inspections and the material erosion between missions can also be considered in the developed methodology for selection of design variables. The reliability-based procedure can be easily modified to consider other similar structures and different fracture control plans.

  9. Effect of extrusion ratio on microstructure and mechanical properties of Mg-Nd-Zn-Zr alloys prepared by a solid recycling process

    SciTech Connect

    Wen Lihua Ji Zesheng; Li Xiaoliang

    2008-11-15

    Microstructures and room temperature mechanical properties of Mg-2.4Nd-0.6Zn-0.6Zr alloys prepared by a solid recycling process with different extrusion ratios were studied. The tensile properties of the materials were evaluated for the magnesium alloys in as-extruded and extruded-T6 conditions. With increasing extrusion ratio, the tensile strength and elongation to failure increases. The heat treatment results in a significant increase in tensile yield strength and ultimate tensile strength because of dispersive particles or fine precipitates. Moreover, the ductility decreases from as-extruded condition to extruded-T6 condition. The morphology of the fracture surfaces was examined by employing scanning electron microscope. The fracture mode is a mix mechanism with brittle fracture and gliding fracture.

  10. Influences of Hydrogen Micropores and Intermetallic Particles on Fracture Behaviors of Al-Zn-Mg-Cu Aluminum Alloys

    NASA Astrophysics Data System (ADS)

    Su, Hang; Yoshimura, Takuro; Toda, Hiroyuki; Bhuiyan, Md. Shahnewaz; Uesugi, Kentaro; Takeuchi, Akihisa; Sakaguchi, Nobuhito; Watanabe, Yoshio

    2016-12-01

    The combined effects of hydrogen micropores and intermetallic particles on the voids initiation and growth behavior of Al-Zn-Mg-Cu aluminum alloys during deformation and fracture are investigated with the help of the high-resolution X-ray tomography. It is interesting to note that the high-hydrogen concentration induced by an EDM cutting process results in the initiation of quasi-cleavage fracture near surface. With the increase of strain, the quasi-cleavage fracture is gradually replaced by dimple fracture. Voids initiation related to the dimple fracture is caused by both intermetallic particles fracture and interfacial debonding between particles and matrix. The nucleation of hydrogen micropores on intermetallic particles accelerates the voids initiation. The existence of triaxial stress ahead of the tip of a quasi-cleavage crack enhances growth rate for both hydrogen micropores and voids.

  11. Analysis of Deformation Damage and Fracture of 7050 Aluminum Alloy During Double Shear Based on Experiment and Simulation

    NASA Astrophysics Data System (ADS)

    Chen, Han; Li, Fuguo; Cao, Jun; Li, Jinghui; Wang, Qianru; Li, Weina

    2017-03-01

    Based on the finite element simulation and experimental analysis, this paper mainly studies the deformation damage and fracture of 7050-H112 aluminum alloy during double shear based on the elastic strain energy density. The analyses of deformation damage and fracture for ends-free and ends-constrained specimens in complex stress and strain states have been carried out. The different stress and strain states which are characterized by stress triaxiality and strain Lode parameter have important effects on damage and fracture according to the simulation and experimental results. The final fracture is mainly caused by tensile stress both for specimens with ends free and ends constraint. Meanwhile, the shear planes are mainly in a state of shear strain when fracture occurs according to the analysis of stress triaxiality and strain Lode parameter. Three characteristic areas (radiation area, fiber area and shear lips) are observed from fracture morphology and account for different proportions on fracture surface for ends-free and ends-constrained specimens. The simulated results on the damage evolution and fracture from finite element method (FEM) are in good agreement with the experimental ones. Besides, there are competitive relations between ductile fracture and brittle fracture during the process of fracture in this paper.

  12. Analysis of Deformation Damage and Fracture of 7050 Aluminum Alloy During Double Shear Based on Experiment and Simulation

    NASA Astrophysics Data System (ADS)

    Chen, Han; Li, Fuguo; Cao, Jun; Li, Jinghui; Wang, Qianru; Li, Weina

    2017-02-01

    Based on the finite element simulation and experimental analysis, this paper mainly studies the deformation damage and fracture of 7050-H112 aluminum alloy during double shear based on the elastic strain energy density. The analyses of deformation damage and fracture for ends-free and ends-constrained specimens in complex stress and strain states have been carried out. The different stress and strain states which are characterized by stress triaxiality and strain Lode parameter have important effects on damage and fracture according to the simulation and experimental results. The final fracture is mainly caused by tensile stress both for specimens with ends free and ends constraint. Meanwhile, the shear planes are mainly in a state of shear strain when fracture occurs according to the analysis of stress triaxiality and strain Lode parameter. Three characteristic areas (radiation area, fiber area and shear lips) are observed from fracture morphology and account for different proportions on fracture surface for ends-free and ends-constrained specimens. The simulated results on the damage evolution and fracture from finite element method (FEM) are in good agreement with the experimental ones. Besides, there are competitive relations between ductile fracture and brittle fracture during the process of fracture in this paper.

  13. A Fracture Analysis of Ti-10Mo-8V-1Fe-3.5Al Alloy Screws during Assembly.

    PubMed

    Zhang, Weifang; Huang, Yuanxing; Dai, Wei; Jin, Xiaoshuai; Yin, Chang

    2016-10-19

    Titanium screws have properties that make them ideal for applications that require both a high strength-to-weight ratio and corrosion resistance, such as fastener applications for aviation and aerospace. The fracture behavior of Ti-10Mo-8V-1Fe-3.5Al (TB3) alloy screws during assembly was explored. Besides visual examination, other experimental techniques used for the investigation are as follows: (1) fracture characteristics and damage morphology via scanning electron microscopy (SEM); (2) chemical constituents via energy dispersive spectroscopy (EDS) and hydrogen concentration testing; (3) metallographic observation; (4) stress durability embrittlement testing; and (5) torsion simulation testing. Results show that the fracture mode of the screws is brittle. There is no obvious relation to hydrogen-induced brittle. The main reason for the fracture of titanium alloy screws is internal defects, around which oxygen content is high, increasing brittleness. The internal defects of screws result from grain boundary cracking caused by hot forging.

  14. A Fracture Analysis of Ti-10Mo-8V-1Fe-3.5Al Alloy Screws during Assembly

    PubMed Central

    Zhang, Weifang; Huang, Yuanxing; Dai, Wei; Jin, Xiaoshuai; Yin, Chang

    2016-01-01

    Titanium screws have properties that make them ideal for applications that require both a high strength-to-weight ratio and corrosion resistance, such as fastener applications for aviation and aerospace. The fracture behavior of Ti-10Mo-8V-1Fe-3.5Al (TB3) alloy screws during assembly was explored. Besides visual examination, other experimental techniques used for the investigation are as follows: (1) fracture characteristics and damage morphology via scanning electron microscopy (SEM); (2) chemical constituents via energy dispersive spectroscopy (EDS) and hydrogen concentration testing; (3) metallographic observation; (4) stress durability embrittlement testing; and (5) torsion simulation testing. Results show that the fracture mode of the screws is brittle. There is no obvious relation to hydrogen-induced brittle. The main reason for the fracture of titanium alloy screws is internal defects, around which oxygen content is high, increasing brittleness. The internal defects of screws result from grain boundary cracking caused by hot forging. PMID:28773971

  15. Effect of heat treatment on microstructure and fracture toughness of a V-5Cr-5Ti alloy

    SciTech Connect

    Li, H.; Hamilton, M.L.; Jones, R.H.

    1995-04-01

    The purpose of this research is to investigate the effect of heat treatment on microstructure and fracture toughness in the range of {minus}50 to 100{degrees}C for a V-5Cr-5Ti alloy. Fracture toughness and impact tests were performed on a V-5Cr-5Ti alloy. Specimens annealed at 1125{degree}C for 1 h and furnace cooled in a vacuum of 1.33 x 10{sup {minus}5} Pa were brittle at room temperature and experienced a mixture of intergranular and cleavage fracture. The ductile to brittle transition temperature was estimated to be about 20{degree}C. When some specimens were given an additional annealing at 890{degree}C for 24 h, they became very ductile at room temperature and fractured by microvoid coalescence.

  16. Effect of heat treatment on the fracture behaviour of directionally solidified (gamma/gamma-prime)-alpha alloy

    NASA Technical Reports Server (NTRS)

    Sriramamurthy, A. M.; Tewari, S. N.

    1987-01-01

    An investigation is conducted into the influence of various heat treatments on the work of fracture and its relation to microstructure for a directionally solidified Ni-33Mo-5.7Al (wt pct) (gamma/gamma-prime)-alpha alloy. The jagged crack propagation observed is due to delamination of the ligaments and associated plastic deformation. Fracture behavior is examined with respect to alloy microstructures and load-deflection curves. The four heat-treatment conditions considered are: (1) as-directionally solidified, (2) solutionized, (3) directionally solidified and thermally cycled, and (4) solutionized and thermally cycled.

  17. Effect of heat treatments on mechanical properties and damage evolution of thixoformed aluminium alloys

    SciTech Connect

    Cavaliere, P. . E-mail: pasquale.cavaliere@unile.it; Cerri, E.; Leo, P.

    2005-07-15

    In the present work, the effects of heat treatments on mechanical properties, microstructure evolution and damage resulting from plastic deformation of thixoformed A319 and A356 aluminium alloys, are studied. The thixoforming process can lead to the production of components that are characterized by very good mechanical properties and low porosity with a globular microstructure which is fine and uniform. The mechanical properties can be further improved through heat treatments such as T5 and T6. The prime factor influencing the damage in the alloys belonging to the Al-Si system is represented by decohesion of silicon particles resulting from the stress concentration at the particle-matrix interfaces. A statistical analysis of fractured particles after tensile tests in the as-cast and as-treated condition has been carried out in the present work; optical and scanning electron microscopy techniques have been used to characterize the microstructure and fracture surfaces of the specimens and the results are fully presented.

  18. Unique Mechanism of Chance Fracture in a Young Adult Male

    PubMed Central

    Birch, Aaron; Walsh, Ryan; Devita, Diane

    2013-01-01

    Since the first description of the Chance fracture in 1948, there have been few case reports of unique mechanisms causing this classical flexion-extension injury to the spine in motor vehicle accidents, sports injury, and falls. To our knowledge, this injury has not been reported from a fall with the mechanistic forces acting laterally on the spine and with spinal support in place. We present a 21-year-old male who slid down a flight of stairs onto his side wearing a heavy mountaineering style backpack, subsequently sustaining a Chance fracture of his first lumbar vertebrae. PMID:23599852

  19. Unique mechanism of chance fracture in a young adult male.

    PubMed

    Birch, Aaron; Walsh, Ryan; Devita, Diane

    2013-03-01

    Since the first description of the Chance fracture in 1948, there have been few case reports of unique mechanisms causing this classical flexion-extension injury to the spine in motor vehicle accidents, sports injury, and falls. To our knowledge, this injury has not been reported from a fall with the mechanistic forces acting laterally on the spine and with spinal support in place. We present a 21-year-old male who slid down a flight of stairs onto his side wearing a heavy mountaineering style backpack, subsequently sustaining a Chance fracture of his first lumbar vertebrae.

  20. Pediatric Facial Fractures: Interpersonal Violence as a Mechanism of Injury.

    PubMed

    Hoppe, Ian C; Kordahi, Anthony M; Lee, Edward S; Granick, Mark S

    2015-07-01

    Interpersonal violence is a relatively infrequent cause of injury to the craniofacial skeleton in the pediatric population. The presentation of fractures as a result of different causes varies dramatically and can have a direct impact on management. The current study compares facial fractures in a pediatric population as a result of interpersonal violence with other mechanisms of injury. A retrospective review of all of the facial fractures at a level 1 trauma center in an urban environment was performed for the years 2000 to 2012. Patients ≤18 years were included. Patient demographics were collected, as well as location of fractures, concomitant injuries, services consulted, and surgical management strategies. Patients were placed into 2 groups, those sustaining an injury as a result of interpersonal violence and all others. A significance value of 5% was used. During this period, there were 3147 facial fractures treated at our institution, 353 of which were in pediatric patients. Upon further review, 68 patients were excluded because of insufficient data for analysis, leaving 285 patients for review. There were 124 (43.5%) patients identified as sustaining a fracture as a result of interpersonal violence. Those sustaining a fracture as a result of interpersonal violence were statistically (P < 0.05) more likely to be boys and to have sustained a fracture of the mandible. The most common services consulted for this group of patients was plastic surgery and oral and maxillofacial surgery. This group of patients was statistically (P < 0.05) more likely to be admitted specifically for management of a facial fracture and statistically (P < 0.05) more likely to be treated operatively with rigid internal fixation. Those sustaining a fracture as a result of interpersonal violence were significantly less likely to have other systemic injuries such as spinal fractures, intracranial fractures, long bone fractures, and pelvic/thoracic fractures. This group was

  1. Approaches for mechanical joining of 7xxx series aluminum alloys

    NASA Astrophysics Data System (ADS)

    Jäckel, M.; Grimm, T.; Landgrebe, D.

    2016-10-01

    This paper shows a numerical and experimental analysis of the different problems occurring during or after the conventional self-pierce riveting with semi-tubular and solid rivets of the high strength aluminum alloy EN AW-7021 T4. Furthermore this paper describes different pre-process methods by which the fracture in the high strength aluminum, caused by the self-pierce riveting processes, can be prevented and proper joining results are achieved. On this basis, the different approaches are compared regarding joint strength.

  2. Aluminum Alloying Effects on Lattice Types, Microstructures, and Mechanical Behavior of High-Entropy Alloys Systems

    NASA Astrophysics Data System (ADS)

    Tang, Zhi; Gao, Michael C.; Diao, Haoyan; Yang, Tengfei; Liu, Junpeng; Zuo, Tingting; Zhang, Yong; Lu, Zhaoping; Cheng, Yongqiang; Zhang, Yanwen; Dahmen, Karin A.; Liaw, Peter K.; Egami, Takeshi

    2013-12-01

    The crystal lattice type is one of the dominant factors for controlling the mechanical behavior of high-entropy alloys (HEAs). For example, the yield strength at room temperature varies from 300 MPa for the face-centered-cubic (fcc) structured alloys, such as the CoCrCuFeNiTi x system, to about 3,000 MPa for the body-centered-cubic (bcc) structured alloys, such as the AlCoCrFeNiTi x system. The values of Vickers hardness range from 100 to 900, depending on lattice types and microstructures. As in conventional alloys with one or two principal elements, the addition of minor alloying elements to HEAs can further alter their mechanical properties, such as strength, plasticity, hardness, etc. Excessive alloying may even result in the change of lattice types of HEAs. In this report, we first review alloying effects on lattice types and properties of HEAs in five Al-containing HEA systems: Al x CoCrCuFeNi, Al x CoCrFeNi, Al x CrFe1.5MnNi0.5, Al x CoCrFeNiTi, and Al x CrCuFeNi2. It is found that Al acts as a strong bcc stabilizer, and its addition enhances the strength of the alloy at the cost of reduced ductility. The origins of such effects are then qualitatively discussed from the viewpoints of lattice-strain energies and electronic bonds. Quantification of the interaction between Al and 3 d transition metals in fcc, bcc, and intermetallic compounds is illustrated in the thermodynamic modeling using the CALculation of PHAse Diagram method.

  3. Mechanisms of defect complex formation and environmental-assisted fracture behavior of iron aluminides

    SciTech Connect

    Cooper, B.R.; Muratov, L.S.; Kang, B.S.J.; Li, K.Z.

    1997-12-01

    Iron aluminide has excellent corrosion resistance in high-temperature oxidizing-sulfidizing environments; however, there are problems at room and medium temperature with hydrogen embrittlement as related to exposure to moisture. In this research, a coordinated computational modeling/experimental study of mechanisms related to environmental-assisted fracture behavior of selected iron aluminides is being undertaken. The modeling and the experimental work will connect at the level of coordinated understanding of the mechanisms for hydrogen penetration and for loss of strength and susceptibility to fracture. The focus of the modeling component at this point is on the challenging question of accurately predicting the iron vacancy formation energy in Fe{sub 3}A{ell} and the subsequent tendency, if present, for vacancy clustering. The authors have successfully performed, on an ab initio basis, the first calculation of the vacancy formation energy in Fe{sub 3}A{ell}. These calculations include lattice relaxation effects which are quite large. This has significant implications for vacancy clustering effects with consequences to be explored for hydrogen diffusion. The experimental work at this stage has focused on the relationship of the choice and concentration of additives to the improvement of resistance to hydrogen embrittlement and hence to the fracture behavior. For this reason, comparative crack growth tests of FA-186, FA-187, and FA-189 iron aluminides (all with basic composition of Fe-28A{ell}-5Cr, at % with micro-alloying additives of Zr, C or B) under, air, oxygen, or water environment have been performed. These tests showed that the alloys are susceptible to room temperature hydrogen embrittlement in both B2 and DO{sub 3} conditions. Test results indicated that FA-187, and FA-189 are intrinsically more brittle than FA-186.

  4. The fracture properties and toughening mechanisms of bone and dentin

    NASA Astrophysics Data System (ADS)

    Koester, Kurt John

    The mechanical properties of bone and dentin and in particular their fracture properties, are the subject of intense research. The relevance of these properties is increasing as our population ages and fracture incidence impacts the lives of a greater portion of the population. A robust framework is needed to understand the fracture properties of bone and dentin to guide researchers as they attempt to characterize the effects of aging, disease, and pharmaceutical treatments on the properties of these mineralized tissues. In the present work, this framework is provided and applied to human bone, human dentin, and animal bone. In situ electron microscopy was also used to identify the salient toughening mechanisms in bone and dentin. It was found that bone and dentin are extrinsically toughened materials and consequently their fracture properties are best characterized utilizing a crack-growth resistance approach. A description of the different mechanical measurements commonly employed when using small animal models (rats and mice) to evaluate the influence of drug therapies on bone fragility is provided. A study where these properties were measured for a large population of wild-type rats and mice was also conducted. Given my findings, it was determined that for the most complete understanding of small animal bone it was necessary to measure strength and toughness. Strength measurements probe the flaw distribution and toughness measurements to evaluate the resistance to facture in the presence of a single dominant worst-case flaw.

  5. Mechanical Properties of Iron Alumininides Intermetallic Alloy with Molybdenum Addition

    SciTech Connect

    Zuhailawati, H.; Fauzi, M. N. A.

    2010-03-11

    In this work, FeAl-based alloys with and without molybdenum addition were fabricated by sintering of mechanically alloyed powders in order to investigate the effect of molybdenum on iron aluminide mechanical properties. Bulk samples were prepared by mechanical alloying for 4 hours, pressing at 360 MPa and sintering at 1000 deg. C for 2 hours. The specimens were tested in compression at room temperature using Instron machine. The phase identification and microstructure of the consolidated material was examined by x-ray diffraction and scanning electron microscope correspondingly. Results show that 2.5 wt%Mo addition significantly increased the ultimate stress and ultimate strain in compressive mode due to solid solution hardening. However, the addition of Mo more than 2.5 wt% was accompanied by a reduction in both properties caused by the presence of Mo-rich precipitate particles.

  6. Cryogenic Fracture Toughness Improvement for the Super Lightweight Tank's Main Structural Alloy

    NASA Technical Reports Server (NTRS)

    Chen, P. S.; Stanton, W. P.

    2002-01-01

    Marshall Space Flight Center has developed a two-step (TS) artificial aging technique that can significantly enhance cryogenic fracture toughness and resistance to stress corrosion cracking (SCC) in aluminum-copper-lithium alloy 2195. The new TS aging treatment consists of exposures at 132 C (270 F)/20 hr + 138 C (280 F)/42 hr, which can be readily applied to flight hardware production. TS aging achieves the same yield strength levels as conventional aging, while providing much improved ductility in the short transverse direction. After TS aging, five previously rejected lots of alloy 2195 (lots 950M029B, 960M030F, 960M030J, 960M030K, and 960M030L) passed simulated service testing for use in the super lightweight tank program. Each lot exhibited higher fracture toughness at cryogenic temperature than at ambient temperature. Their SCC resistance was also enhanced. All SCC specimens passed the minimum 10-day requirement in 3.5-percent sodium chloride alternate immersion at a stress of 45 ksi. The SCC lives ranged from 57 to 83 days, with an average of 70 days.

  7. Cryogenic Fracture Toughness Evaluation of an Investment Cast Al-Be Alloy for Structural Applications

    NASA Technical Reports Server (NTRS)

    Gamwell, W. R.; McGill, P. B.

    2006-01-01

    Aluminum-Beryllium metal matrix composite materials are useful due to their desirable performance characteristics for aerospace applications. Desirable characteristics of this material includes light-weight, dimensional stability, stiffness, good vibration damping characteristics, low coefficient of thermal expansion, and workability, This material is 3.5 times stiffer and 22% lighter than conventional aluminum alloys. electro-optical systems, advanced sensor and guidance components for flight and satellite systems, components for light-weight high-performance aircraft engines, and structural components for helicopters. Aluminum-beryllium materials are now available in the form of near net shape investment castings. In this materials properties characterization study, the cryogenic tensile and fracture properties of an investment casting alloy, Beralcast 363, were determined. Tensile testing was performed at 21 C (70 F), -73.3 C (-100 F), -195.5 C (-320 F) and -252.8 C (-423 F), and fracture (K(sub lc) and da/dN) testing was performed at -73.3 C (-100 F), -195.5 C (-320 F) and -252.8 C (-423 F). Their use is attractive for weight critical structural applications such as advanced

  8. Cryogenic Fracture Toughness Evaluation of an Investment Cast Al-Be Alloy for Structural Applications

    NASA Technical Reports Server (NTRS)

    Gamwell, W. R.; McGill, P. B.

    2006-01-01

    Aluminum-Beryllium metal matrix composite materials are useful due to their desirable performance characteristics for aerospace applications. Desirable characteristics of this material includes light-weight, dimensional stability, stiffness, good vibration damping characteristics, low coefficient of thermal expansion, and workability, This material is 3.5 times stiffer and 22% lighter than conventional aluminum alloys. electro-optical systems, advanced sensor and guidance components for flight and satellite systems, components for light-weight high-performance aircraft engines, and structural components for helicopters. Aluminum-beryllium materials are now available in the form of near net shape investment castings. In this materials properties characterization study, the cryogenic tensile and fracture properties of an investment casting alloy, Beralcast 363, were determined. Tensile testing was performed at 21 C (70 F), -73.3 C (-100 F), -195.5 C (-320 F) and -252.8 C (-423 F), and fracture (K(sub lc) and da/dN) testing was performed at -73.3 C (-100 F), -195.5 C (-320 F) and -252.8 C (-423 F). Their use is attractive for weight critical structural applications such as advanced

  9. The microstructure and fracture behavior of the dissimilar alloy 690-SUS 304L joint with various Nb addition

    NASA Astrophysics Data System (ADS)

    Lee, H. T.; Jeng, S. L.; Kuo, T. Y.

    2003-05-01

    This study investigates the microstructure and fracture behavior of dissimilar weldments of alloy 690 and SUS 304L for various additions of niobium (0.1, 1.03, 2.49, and 3.35 wt pct) in the flux. With identical parameters and procedures, weldments were butt welded by the shielding metal arc welding (SMAW) process using three layers, with each layer being deposited in a single pass. The results indicate that the microstructure of the fusion zone was primarily dendritic and that the contents of Ni, Cr, and Fe within this zone remain relatively constant and resemble alloy 690. With Nb addition, it is noted that the microstructure changes from a cellular to columnar dendrite and equiaxed dendrite. Meanwhile, the dendrite arm spacing reduces and the secondary arms grow longer. Moreover, the composition of the interdendritic phase, whose precipitate volume percentage increases from 5 to 25 pct, changes from Al-Ti-O to Nb rich. The spread of the interdendritic phase is less in the root bead than in the cap bead due to the greater influence of base metal dilution in this region. Mechanical tests indicate that Nb addition increases the average hardness of the weldment and reduces its elongation prior to rupture. However, the tensile strength is essentially unchanged by Nb addition. It is found that the average hardness of the root bead is generally lower than the cap bead, and that the tensile specimens all rupture in the fusion zone, with the fracture surfaces exhibiting ductile features. It is noted that the cap bead tends to rupture interdendritically with increasing Nb addition. Finally, fractography shows that the dimples in the root become larger and shallower with Nb addition and are rich with an interdendritic phase.

  10. The effect of scandium addition on microstructure and mechanical properties of Al–Si–Mg alloy: A multi-refinement modifier

    SciTech Connect

    Xu, Cong; Xiao, Wenlong; Hanada, Shuji; Yamagata, Hiroshi; Ma, Chaoli

    2015-12-15

    Effect of scandium (Sc) additions on the microstructure, mechanical properties and fracture behavior of Al–Si–Mg casting alloy (F357) were systematically investigated. It was found that Sc addition caused a multi-refining efficiency on the microstructure of as-cast F357 alloy, including refinement of grains and secondary dendrite arm spacing (SDAS), modification of eutectic Si and harmless disposal of β-Al{sub 5}FeSi phase. Subsequent T6 heat treatment had further induced the complete spheroidization of eutectic Si and precipitation of fine secondary Al{sub 3}Sc dispersoids in the Sc modified alloys. Thus the mechanical properties, especially the ductility, were significantly enhanced by the addition of Sc combined with the heat treatment. The highest ultimate tensile strength, yield strength and elongation were achieved in 0.8 wt.% Sc modified F357 alloy combined with T6 heat treatment. Furthermore, fractographic examinations indicated that the ductile fracture mechanism served as a dominate role in the modified alloys due to the formation of fine, deep and uniformly distributed dimples. - Highlights: • Detailed characterization of the multi-refining microstructure of Sc modified F357 alloy was performed. • The multi-refinement was proposed to refine grain and SDAS, modify eutectic Si and β-phase. • Sc modifier combined with T6 treatment is effective in improving tensile properties. • Modification of eutectic Si in F357 alloy with Sc is consistent with the IIT mechanism.

  11. Hydraulic Fracture Extending into Network in Shale: Reviewing Influence Factors and Their Mechanism

    PubMed Central

    Ren, Lan; Zhao, Jinzhou; Hu, Yongquan

    2014-01-01

    Hydraulic fracture in shale reservoir presents complex network propagation, which has essential difference with traditional plane biwing fracture at forming mechanism. Based on the research results of experiments, field fracturing practice, theory analysis, and numerical simulation, the influence factors and their mechanism of hydraulic fracture extending into network in shale have been systematically analyzed and discussed. Research results show that the fracture propagation in shale reservoir is influenced by the geological and the engineering factors, which includes rock mineral composition, rock mechanical properties, horizontal stress field, natural fractures, treating net pressure, fracturing fluid viscosity, and fracturing scale. This study has important theoretical value and practical significance to understand fracture network propagation mechanism in shale reservoir and contributes to improving the science and efficiency of shale reservoir fracturing design. PMID:25032240

  12. Hydraulic fracture extending into network in shale: reviewing influence factors and their mechanism.

    PubMed

    Ren, Lan; Zhao, Jinzhou; Hu, Yongquan

    2014-01-01

    Hydraulic fracture in shale reservoir presents complex network propagation, which has essential difference with traditional plane biwing fracture at forming mechanism. Based on the research results of experiments, field fracturing practice, theory analysis, and numerical simulation, the influence factors and their mechanism of hydraulic fracture extending into network in shale have been systematically analyzed and discussed. Research results show that the fracture propagation in shale reservoir is influenced by the geological and the engineering factors, which includes rock mineral composition, rock mechanical properties, horizontal stress field, natural fractures, treating net pressure, fracturing fluid viscosity, and fracturing scale. This study has important theoretical value and practical significance to understand fracture network propagation mechanism in shale reservoir and contributes to improving the science and efficiency of shale reservoir fracturing design.

  13. Physical and mechanical modelling of neutron irradiation effect on ductile fracture. Part 1. Prediction of fracture strain and fracture toughness of austenitic steels

    NASA Astrophysics Data System (ADS)

    Margolin, Boris; Sorokin, Alexander; Smirnov, Valeriy; Potapova, Vera

    2014-09-01

    A physical-and-mechanical model of ductile fracture has been developed to predict fracture toughness and fracture strain of irradiated austenitic steels taking into account stress-state triaxiality and radiation swelling. The model is based on criterion of plastic collapse of a material unit cell controlled by strain hardening of a material and criterion of voids coalescence due to channel shearing of voids. The model takes into account deformation voids nucleation and growth of deformation and vacancy voids. For justification of the model experimental data on fracture strain and fracture toughness of austenitic steel 18Cr-10Ni-Ti grade irradiated up to maximal dose 150 dpa with various swelling were used. Experimental data on fracture strain and fracture toughness were compared with the results predicted by the model. It has been shown that for prediction of the swelling effect on fracture toughness the dependence of process zone size on swelling should be taken into account.

  14. Processing and Characterization of Mechanically Alloyed NiAl-Based Alloys

    DTIC Science & Technology

    1994-07-20

    34 69OSW *MN. VU e ffo Qm .’so~ W&84" ow" ftawm pl "-wtvý a " M Wc rmsa I. XUR On GELs"NW REORT oIt3.RPOT rVPE AND CAT93 CoVWau July 20, 1994 ’ Fin l Report...SUPPUMWRNTY MOTUS 12a. OMT-U.IOUI AVAIAAJT STAT1[MET 13. OGTFM-1NO Co Unlimited WLA8ETRACT (Mainuna 2O00nw m Mechanical alloying of powders followed by hot...present materials result from their unique microstructure. = 14• TIS. M OF PAGES Mechanical Alloying, NiAl-Aluminides, Intermetallics Strength

  15. A new fracture assessment approach coupling HR-pQCT imaging and fracture mechanics-based finite element modeling.

    PubMed

    Ural, Ani; Bruno, Peter; Zhou, Bin; Shi, X Tony; Guo, X Edward

    2013-04-26

    A new fracture assessment approach that combines HR-pQCT imaging with fracture mechanics-based finite element modeling was developed to evaluate distal radius fracture load. Twenty distal radius images obtained from postmenopausal women (fracture, n=10; nonfracture, n=10) were processed to obtain a cortical and a whole bone model for each subject. The geometrical properties of each model were evaluated and the corresponding fracture load was determined under realistic fall conditions using cohesive finite element modeling. The results showed that the whole bone fracture load can be estimated based on the cortical fracture load for nonfracture (R(2)=0.58, p=0.01) and pooled data (R(2)=0.48, p<0.001) but not for the fracture group. The portion of the whole bone fracture load carried by the cortical bone increased with increasing cortical fracture load (R(2)≥0.5, p<0.05) indicating that a more robust cortical bone carries a larger percentage of whole bone fracture load. Cortical thickness was found to be the best predictor of both cortical and whole bone fracture load for all groups (R(2) range: 0.49-0.96, p<0.02) with the exception of fracture group whole bone fracture load showing the predictive capability of cortical geometrical properties in determining whole bone fracture load. Fracture group whole bone fracture load was correlated with trabecular thickness (R(2)=0.4, p<0.05) whereas the nonfracture and the pooled group did not show any correlation with the trabecular parameters. In summary, this study introduced a new modeling approach that coupled HR-pQCT imaging with fracture mechanics-based finite element simulations, incorporated fracture toughness and realistic fall loading conditions in the models, and showed the significant contribution of the cortical compartment to the overall fracture load of bone. Our results provide more insight into the fracture process in bone and may lead to improved fracture load predictions. Copyright © 2013 Elsevier Ltd. All

  16. A NEW FRACTURE ASSESSMENT APPROACH COUPLING HR-pQCT IMAGING AND FRACTURE MECHANICS-BASED FINITE ELEMENT MODELING

    PubMed Central

    Ural, Ani; Bruno, Peter; Zhou, Bin; Shi, X. Tony; Guo, X. Edward

    2013-01-01

    A new fracture assessment approach that combines HR-pQCT imaging with fracture mechanics-based finite element modeling was developed to evaluate distal radius fracture load. Twenty distal radius images obtained from postmenopausal women (fracture, n = 10; nonfracture, n = 10) were processed to obtain a cortical and a whole bone model for each subject. The geometrical properties of each model were evaluated and the corresponding fracture load was determined under realistic fall conditions using cohesive finite element modeling. The results showed that the whole bone fracture load can be estimated based on the cortical fracture load for nonfracture (R2 = 0.58, p = 0.01) and pooled data (R2 = 0.48, p < 0.001) but not for the fracture group. The portion of the whole bone fracture load carried by the cortical bone increased with increasing cortical fracture load (R2 ≥ 0.5, p < 0.05) indicating that a more robust cortical bone carries a larger percentage of whole bone fracture load. Cortical thickness was found to be the best predictor of both cortical and whole bone fracture load for all groups (R2 range: 0.49–0.96, p < 0.02) with the exception of fracture group whole bone fracture load showing the predictive capability of cortical geometrical properties in determining whole bone fracture load. Fracture group whole bone fracture load was correlated with trabecular thickness (R2 = 0.4, p < 0.05) whereas the nonfracture and the pooled group did not show any correlation with the trabecular parameters. In summary, this study introduced a new modeling approach that coupled HR-pQCT imaging with fracture mechanics-based finite element simulations, incorporated fracture toughness and realistic fall loading conditions in the models, and showed the significant contribution of the cortical compartment to the overall fracture load of bone. Our results provide more insight into the fracture process in bone and may lead to improved fracture load predictions. PMID:23497802

  17. Re Effects on Phase Stability and Mechanical Properties of MoSS+Mo3Si+Mo5SiB2 alloys

    SciTech Connect

    Yang, Ying; Bei, Hongbin; George, Easo P; Tiley, Jaimie

    2013-01-01

    Because of their high melting points and good oxidation resistance Mo-Si-B alloys are of interest as potential ultrahigh-temperature structural materials. But their major drawbacks are poor ductility and fracture toughness at room temperature. Since alloying with Re has been suggested as a possible solution, we investigate here the effects of Re additions on the microstructure and mechanical properties of a ternary alloy with the composition Mo-12.5Si-8.5B (at.%). This alloy has a three-phase microstructure consisting of Mo solid-solution (MoSS), Mo3Si, and Mo5SiB2 and our results show that up to 8.4 at.% Re can be added to it without changing its microstructure or forming any brittle phase at 1600 C. Three-point bend tests using chevron-notched specimens showed that Re did not improve fracture toughness of the three-phase alloy. Nanoindentation performed on the MoSS phase in the three-phase alloy showed that Re increases Young s modulus, but does not lower hardness as in some Mo solid solution alloys. Based on our thermodynamic calculations and microstructural analyses, the lack of a Re softening effect is attributed to the increased Si levels in the Re-containing MoSS phase since Si is known to increase its hardness. This lack of softening is possibly why there is no Re-induced improvement in fracture toughness.

  18. Fracture mechanics analysis of composite microcracking - Experimental results in fatigue

    NASA Technical Reports Server (NTRS)

    Nairn, J. A.; Liu, S.

    1990-01-01

    The Nairn (1989) variational mechanics analysis, which yields the energy release rate of a microcrack's formation between two existing microcracks, has proven useful in the fracture mechanics interpretation of cross-ply laminates' microcracking. Attention is presently given to the application of this energy release rate analysis to a fracture mechanics-based interpretation of microcrack formation during fatigue loading, for the case of fatigue experiments on three layups of Avimid K/IM6 laminates and four layups of Fiberite 934/T300 laminates. The single master Paris-law plot onto which the data from all layups of a given material system fall is claimed to offer a complete characterization of that system's microcrack-formation resistance during fatigue loading.

  19. The role of dispersoids in maintaining the corrosion resistance of mechanically alloyed oxide dispersion strengthened alloys

    SciTech Connect

    Cama, H.; Hughes, T.A.

    1995-05-15

    Amongst the various commercial mechanically alloyed (MA) oxide dispersion strengthened (ODS) alloys available, ferritic alloys are most suitable for use at temperatures exceeding 1,100 C, since {gamma}{prime} particle dissolution results in the loss of strength of nickel based MA ODS alloys. In commercial MA ODS alloys, yttria particles are commonly added in the starting powers, and it is well known that they are not retained in the final product because they react with aluminum and oxygen present in the system during thermomechanical processing and form mixed (Y,Al) oxide particles. In this paper the role of (Y,Al) oxide particles in maintaining the overall aluminum concentration in the matrix necessary to repair the outer oxide scale is discussed. It is well known that during exposure in air, aluminum is lost from the bulk of MA ODS alloys to the growth of a surface alumina film. The extent of aluminum lost is dependent on the section thickness and can significantly affect the volume fraction of the aluminum rich dispersoids. Coarsening of the dispersoids at temperatures up to 1,200 C in the thick MA 956 bar occurs without significant aluminum loss, while their volume fraction increases continuously. However, coarsening of the dispersoids in the thinner ODM 751 tube at 1,200 and 1,300 C is accompanied by dissolution of the dispersoid particles in order to maintain the aluminum concentration in the matrix.

  20. Mechanical alloying of ODS tungsten heavy alloys and microstructure development of intermetallic compounds

    NASA Astrophysics Data System (ADS)

    Chen, Chun-Liang; Huang, Chun-Lin

    2013-09-01

    Oxide dispersion strengthened tungsten heavy alloys have been used in a wide variety of industrial and military applications due to their high density, strength and stiffness. These alloys have been produced by mechanical alloying, which can provide uniform distribution of nano-oxide particles and an extremely fine grain structure, resulting in the reduction of the sintering temperature. However, the high-energy ball-milling process could introduce iron contamination from the vial and milling media during the procedure. In this study, the W-Ni-Y2O3 alloy was investigated as a function of milling time. The results show that the increase of the Fe/Ni ratio has a significant influence on the microstructural development and material properties. The XRD data reveal considerable solid solubility extension in these powders. The tungsten carbide and iron rich intermetallic compounds were formed after long milling times, which can change the relative density and hardness of the alloy. It is essential that we understand the role of intermetallic phases in the ODS tungsten heavy alloy which determine the material properties and the control of microstructural development.

  1. Al-Li alloy AA2198's very high cycle fatigue crack initiation mechanism and its fatigue thermal effect

    NASA Astrophysics Data System (ADS)

    Xu, Luopeng; Cao, Xiaojian; Chen, Yu; Wang, Qingyuan

    2015-10-01

    AA2198 alloy is one of the third generation Al-Li alloys which have low density, high elastic modulus, high specific strength and specific stiffness. Compared With the previous two generation Al-Li alloys, the third generation alloys have much improved in alloys strength, corrosion resistance and weldable characteristic. For these advantages, the third generation Al-Li alloys are used as aircraft structures, such as C919 aviation airplane manufactured by China and Russia next generation aviation airplane--MS-21. As we know, the aircraft structures are usually subjected to more than 108 cycles fatigue life during 20-30 years of service, however, there is few reported paper about the third generation Al-Li alloys' very high cycle fatigue(VHCF) which is more than 108 cycles fatigue. The VHCF experiment of AA2198 have been carried out. The two different initiation mechanisms of fatigue fracture have been found in VHCF. The cracks can initiate from the interior of the testing material with lower stress amplitude and more than 108 cycles fatigue life, or from the surface or subsurface of material which is the dominant reason of fatigue failures. During the experiment, the infrared technology is used to monitor the VHCF thermal effect. With the increase of the stress, the temperature of sample is also rising up, increasing about 15 °C for every 10Mpa. The theoretical thermal analysis is also carried out.

  2. Baseline Fracture Toughness and CGR testing of alloys X-750 and XM-19 (EPRI Phase I)

    SciTech Connect

    J. H. Jackson; S. P. Teysseyre

    2012-02-01

    The Advanced Test Reactor National Scientific User Facility (ATR NSUF) and Electric Power Research Institute (EPRI) formed an agreement to test representative alloys used as reactor structural materials as a pilot program toward establishing guidelines for future ATR NSUF research programs. This report contains results from the portion of this program established as Phase I (of three phases) that entails baseline fracture toughness, stress corrosion cracking (SCC), and tensile testing of selected materials for comparison to similar tests conducted at GE Global Research. The intent of this Phase I research program is to determine baseline properties for the materials of interest prior to irradiation, and to ensure comparability between laboratories using similar testing techniques, prior to applying these techniques to the same materials after having been irradiated at the Advanced Test Reactor (ATR). The materials chosen for this research are the nickel based super alloy X-750, and nitrogen strengthened austenitic stainless steel XM-19. A spare core shroud upper support bracket of alloy X-750 was purchased by EPRI from Southern Co. and a section of XM-19 plate was purchased by EPRI from GE-Hitachi. These materials were sectioned at GE Global Research and provided to INL.

  3. Baseline Fracture Toughness and CGR testing of alloys X-750 and XM-19 (EPRI Phase I)

    SciTech Connect

    J. H. Jackson; S. P. Teysseyre

    2012-10-01

    The Advanced Test Reactor National Scientific User Facility (ATR NSUF) and Electric Power Research Institute (EPRI) formed an agreement to test representative alloys used as reactor structural materials as a pilot program toward establishing guidelines for future ATR NSUF research programs. This report contains results from the portion of this program established as Phase I (of three phases) that entails baseline fracture toughness, stress corrosion cracking (SCC), and tensile testing of selected materials for comparison to similar tests conducted at GE Global Research. The intent of this Phase I research program is to determine baseline properties for the materials of interest prior to irradiation, and to ensure comparability between laboratories using similar testing techniques, prior to applying these techniques to the same materials after having been irradiated at the Advanced Test Reactor (ATR). The materials chosen for this research are the nickel based super alloy X-750, and nitrogen strengthened austenitic stainless steel XM-19. A spare core shroud upper support bracket of alloy X-750 was purchased by EPRI from Southern Co. and a section of XM-19 plate was purchased by EPRI from GE-Hitachi. These materials were sectioned at GE Global Research and provided to INL.

  4. Fracture of porcelain-veneered gold-alloy and zirconia molar crowns using a modified test set-up

    PubMed Central

    Larsson, Christel; Drazic, Marko; Nilsson, Eddie; Vult von Steyern, Per

    2015-01-01

    Abstract Objective: The main aim of this study was to compare fracture load and fracture mode of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) and metal-ceramic (MC) molar crowns using a modified test set-up to produce fractures similar to those seen in vivo, i.e. fractures of the veneering material rather than complete fractures. Materials and methods: 13 high-noble-alloy MC and 13 Y-TZP molar crowns veneered with porcelain were manufactured. The crowns were artificially aged before final load to fracture. Load was applied using a 7 mm diameter steel ball exerting force on the cusps with stresses directed toward the core-veneer interface. Fracture surface analysis was performed using light- and scanning electron microscopy. Results: The test design produced fractures of the veneering material rather than complete fractures. MC crowns withstood significantly (p > 0.001) higher loads (mean 2155 N) than Y-TZP (mean 1505 N) crowns, yet both endure loads sufficient for predictable clinical use. Fracture mode differed between MC and Y-TZP. MC crowns exhibited fractures involving the core-veneer interface but without core exposure. One Y-TZP crown suffered a complete fracture, all others except one displayed fractures of the veneering material involving the core-veneer interface with core exposure. Conclusions: The test set-up produces fractures similar to those found in vivo and may be useful to evaluate the core-veneer interface of different material systems, both metals and ceramics. The study confirms suggestions from previous studies of a weaker core-veneer bond for Y-TZP compared to MC crowns. PMID:28642899

  5. Mechanical properties of cast Ti-Hf alloys.

    PubMed

    Sato, Hideki; Kikuchi, Masafumi; Komatsu, Masashi; Okuno, Osamu; Okabe, Toru

    2005-02-15

    This study examined the mechanical properties of a series of Ti-Hf alloys. Titanium alloys with 10 to 40 mass % Hf were made with titanium and hafnium sponge in an argon-arc melting furnace. Specimens cast into magnesia-based investment molds were tested for yield strength, tensile strength, percentage elongation, and modulus of elasticity. Vickers microhardness was determined at 25 to 600 microm from the cast surface. X-ray diffractometry was also performed. Commercially pure Ti (CP Ti) and pure Ti prepared from titanium sponge were used as controls. The data (n = 5) were analyzed with a one-way ANOVA and the Student-Newman-Keuls test (alpha = 0.05). The diffraction peaks of all the metals matched those for alpha Ti; no beta phase peaks were found. Alloys with Hf > or = 25% had significantly (p < 0.05) higher yield and tensile strength compared to the CP Ti and pure Ti. There were no significant differences (p > 0.05) in elongation among all the Ti-Hf alloys and CP Ti, whereas the elongation of alloys with Hf > or = 30% was significantly (p < 0.05) lower than that of the pure Ti. The cast Ti-Hf alloys tested can be considered viable alternatives to CP Ti because they were stronger than CP Ti and had similar elongation.

  6. Structural and magnetic properties of nanocrystalline Fe-Co-Ni alloy processed by mechanical alloying

    NASA Astrophysics Data System (ADS)

    Raanaei, Hossein; Eskandari, Hossein; Mohammad-Hosseini, Vahid

    2016-01-01

    In this present work, a nanostructured iron-cobalt-nickel alloy with Fe50Co30Ni20 composition has been processed by mechanical alloying. The structural and magnetic properties have been investigated by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and vibrating sample magnetometer. It is shown that the crystallize size reaches to about 18.7 nm after 32 h milling time. A remarkable decrease in coercivity after 16 h milling time and also a continuous increase in remanent magnetization during the mechanical alloying process are observed. Heat treatment of the samples milled at 32 and 48 h demonstrates the crystalline constituent elements and also Fe3O4 crystalline phase.

  7. Fracture control methods for space vehicles. Volume 2: Assessment of fracture mechanics technology for space shuttle applications

    NASA Technical Reports Server (NTRS)

    Ehret, R. M.

    1974-01-01

    The concepts explored in a state of the art review of those engineering fracture mechanics considered most applicable to the space shuttle vehicle include fracture toughness, precritical flaw growth, failure mechanisms, inspection methods (including proof test logic), and crack growth predictive analysis techniques.

  8. Deformation and fracture of Macadamia nuts Part 2: Microstructure and fracture mechanics analysis of nutshell

    NASA Astrophysics Data System (ADS)

    Wang, Chun-Hui; Mai, Yiu-Wing

    A study of the microstructure and mechanical properties of Macadamia nutshells subjected to various heat treatments is given in Part 2 of this paper. It is found that the nutshell has a three-dimensional, close-packed, cell structure. The cells have a diameter to length ratio of about 1 to 3, and the orientation of the cells is reasonably isotropic with no apparent variation with either position or direction. The material behaves in a very brittle manner under tension and compression. Based on the elastic stress analysis of a nut under diametrical compression and the mechanical properties of the shell, it is shown that cracks that cause the final fracture are initiated from the inner surface beneath the loading point. A theoretical model is proposed and predictions of the fracture load for Macadamia nuts are in good agreement with experimental results.

  9. Direct Studies of Fracture Mechanisms in Metals at Highest Magnification.

    DTIC Science & Technology

    1982-05-01

    or even high purity and therefore will deform before and after void initiation according to recog- nized mechanisms of workhardening in pure metals...discussion it is clear that in precipitation hardened alloys material between voids must suffer extensive plastic deformation during neck formation and the...motion of dislocation groups and their specific behavior during plastic deformation to rupture at record- ing speeds of 30 frames per second. In order

  10. Fundamental Mechanisms of Tensile Fracture in Aluminum Sheet Unidirectionally Reinforced with Boron Filament. Ph.D. Thesis - Virginia Polytechnic Inst.

    NASA Technical Reports Server (NTRS)

    Herring, H. W.

    1971-01-01

    Results are presented from an experimental research effort to gain a more complete understanding of the physics of tensile fracture in unidirectionally reinforced B-Al composite sheet. By varying the degree of filament degradation resulting from fabrication, composite specimens were produced which failed in tension by the cumulative mode, the noncumulative mode, or by any desired combination of the two modes. Radiographic and acoustic emission techniques were combined to identify and physically describe a previously unrecognized fundamental fracture mechanism which was responsible for the noncumulative mode. The tensile strength of the composite was found to be severely limited by the noncumulative mechanism which involved the initiation and sustenance of a chain reaction of filament fractures at a relatively low stress level followed by ductile fracture of the matrix. The minimum average filament stress required for initiation of the fracture mechanism was shown to be approximately 170 ksi, and appeared to be independent of filament diameter, number of filament layers, and the identity of the matrix alloy.

  11. Observation and prediction of the deformation and fracture of shape memory alloys

    NASA Astrophysics Data System (ADS)

    Creuziger, Adam

    This thesis explores the deformation and fracture behavior of two common shape memory alloys (SMAs), CuAlNi and NiTi. Millimeter, micrometer and nanometer scale features are observed and compared with crystallographic theory of martensite (CTM) predictions and finite element models. Observed fracture behavior, in conjunction with theory and modeling, shed light on the fracture behavior and deformation in shape memory materials. The in plane and out of plane deformations are quantitatively measured and compared with good agreement to predictions from the CTM. For deformation where the stress state was unknown, predicted martensite plates correlated well with observed features. When the stress state could be calculated using finite element analysis (FEA), an available work criterion was used to predict which type of martensite plate would form; with good agreement in arbitrarily oriented, notched CuAlNi samples. The out of plane deformation caused during transformation was quantitatively investigated and agrees well with the average strain of twinned martensite. Using a FEA model of a tapered martensite, the effect of boundary conditions on the out of plane deformation angle was explored. Some limitations on the available work criterion were found. The direction of the out of plane deformation near the notch is consistently such that the area directly ahead of the notch sinks downward. This effect, and the wide martensite plates observed after fracture occurs, indicate the role boundary conditions have on the transformation observed. These effects are not taken into account in the current available work criterion. In single crystal NiTi, the available work criterion was not predictive of the deformations observed in uniaxial tension or in notched samples. However, available work predictions were useful in predicting the fracture properties of notched single crystal NiTi samples, a capability not previously demonstrated. Investigation into the grain boundary fracture

  12. Mechanism for Corrosion Prevention by a Mechanical Plating of Uniform Zinc-Iron Alloy

    NASA Astrophysics Data System (ADS)

    Kasai, Naoya; Kaku, Yoshihiko; Okazaki, Shinji; Hirai, Kuninori

    2016-11-01

    In situ electrochemical monitoring with a three-electrode cell was applied to investigate the anti-corrosion properties of a mechanical zinc-iron alloy plating. Several electron probe microanalyses were also conducted to identify the chemical elements in the plating. The results indicated the formation of a Zn-Fe intermetallic compound, which allowed a mechanism for corrosion prevention to be proposed. In the proposed mechanism, Zn(OH)2 plays a significant role in the corrosion prevention of steel alloys.

  13. Quantitative Integration of Ndt with Probabilistic Fracture Mechanics for the Assessment of Fracture Risk in Pipelines

    NASA Astrophysics Data System (ADS)

    Kurz, J. H.; Cioclov, D.; Dobmann, G.; Boller, C.

    2010-02-01

    In the context of probabilistic paradigm of fracture risk assessment in structural components a computer simulation rationale is presented which has at the base the integration of Quantitative Non-destructive Inspection and Probabilistic Fracture Mechanics. In this study the static failure under static loading is assessed in the format known as Failure Assessment Diagram (FAD). The fracture risk is evaluated in probabilistic terms. The superposed probabilistic pattern over the deterministic one is implemented via Monte-Carlo sampling. The probabilistic fracture simulation yields a more informative analysis in terms of probability of failure. The ability to simulate the influence of the quality and reliability of non-destructive inspection (NDI) is an important feature of this approach. It is achieved by integrating, algorithmically, probabilistic FAD analysis and the Probability of Detection (POD). The POD information can only be applied in a probabilistic analysis and leads to a refinement of the assessment. By this means, it can be ascertained the decrease of probability of failure when POD-characterized NDI is applied. Therefore, this procedure can be used as a tool for inspection based life time conceptions. In this paper results of sensitivity analyses are presented with the aim to outline, in terms of non-failure probabilities, the benefits of applying NDI, in various qualities, in comparison with the situation when NDI is lacking. A better substantiation is enabled of both the component reliability management and the costs-effectiveness of NDI timing.

  14. Dynamic fracture behavior of Ti-6Al-4V alloy with various stabilities of βphase

    NASA Astrophysics Data System (ADS)

    Akmoulin, I. A.; Niinomi, M.; Kobayashi, T.

    1994-08-01

    The effect of stability of the body-centered cubic (bcc) β phase on the dynamic fracture behavior of Ti-6Al-4V alloy at room temperature and 77 K has been studied. The presence of a highly unstable β phase in the quenched alloy leads to a decrease in both the dynamic fracture toughness and the crack propagation energy, and this decrease bccomes more pronounced when test temperature is reduced to 77 K. Somewhat improved fracture characteristics were obtained by applying anneal procedure to receive a fully stable β phase. The highest fracture toughness as well as the greatest crack propagation resistance were observed in the air-cooled grade, where the lattice parameter of the bcc phase was intermediate between those pertaining to quenched and annealed Ti-6Al-4V alloys. The effect is attributed to the vanadium content in the β phase, which is sufficiently high to suppress deformation-induced transformation. On the other hand, the V content should be low enough to retard ductile-brittle transition, typical for the bcc metals at cryogenic temperatures. As a result, marked toughening can be achieved, so that the lowest application temperature of high-strength titanium alloys containing the bcc phase can be decreased significantly.

  15. Extrinsic fracture mechanisms in two laminated metal composites

    SciTech Connect

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

    1994-11-29

    The crack growth behavior and fracture toughness of two laminated metal composites (6090/SiC/25p laminated with 5182 and ultrahigh-carbon steel laminated with brass) have been studied in both ``crack arrester`` and ``crack divider`` orientations. The mechanisms of crack growth were analyzed and extrinsic toughening mechanisms were found to contribute significantly to the toughness. The influence of laminate architecture (layer thickness and component volume function), component material properties and residual stress on these mechanisms and the resulting crack growth resistance are discussed.

  16. [Bone fracture and the healing mechanisms. Pathophysiology and classification of osteoporotic fractures].

    PubMed

    Kishimoto, Hideaki

    2009-05-01

    Bone provides momentary strength and fatigue strength, and bone strength decreases with age. In elderly men and women with fragile bones osteoporotic fractures frequently occur. Fragility fracture occurs as a consequence of the decrease in momentary strength, and fragility fracture is one of the pathological fractures. In patients with the decrease in fatigue strength, insufficiency fractures frequently occurs. Insufficiency fracture is the same term as stress or fatigue fracture.

  17. Fatigue limits and SEM/TEM observations of fracture characteristics for three Pd-Ag dental casting alloys.

    PubMed

    Li, Dongfa; Brantley, William A; Guo, Wenhua; Clark, William A T; Alapati, Satish B; Heshmati, Reza H; Daehn, Glenn S

    2007-01-01

    The fatigue limits and fracture characteristics for three Pd-Ag dental casting alloys (Super Star, Heraeus Kulzer; Rx 91, Pentron; W-1, Ivoclar Vivadent) were studied. Specimens meeting the dimensions for ADA Specifications No. 5 and 38, and having the as-cast surface condition, were subjected to heat treatment simulating dental porcelain firing cycles and fatigued in air at room temperature under uniaxial tension-compression at 10 Hz. A ratio of compressive stress amplitude to tensile stress amplitude (R-ratio) of -1 was used. Alloy microstructures and fracture surfaces were examined with a scanning electron microscope and a transmission electron microscope. Fatigue limits for the three alloys had low values of approximately 15% of the yield strength for 0.2% permanent tensile strain. Complex fracture surfaces with characteristic striations were observed for all three fatigued alloys. Planar slip of dislocations occurred in the Pd solid solution matrix, along with dislocation-precipitate interactions and dislocation networks in the interfaces between the precipitates and surrounding matrix. Twinning occurred in the Pd solid solution matrix of Rx 91, and within discontinuous precipitates in Super Star and Rx 91. The low fatigue limits for these alloys are attributed to their complex microstructures and perhaps to casting defects.

  18. The influence of heat treatment on the high-stress abrasion resistance and fracture toughness of alloy white cast irons

    NASA Astrophysics Data System (ADS)

    Sare, I. R.; Arnold, B. K.

    1995-07-01

    The influence of a range of austenitizing and subcritical (tempering) heat treatments on the high-stress abrasion resistance and fracture toughness of four commercially significant grades of alloy white cast iron was investigated. Complementing an earlier study[1] on the influence of a more limited range of heat treatments on the gouging abrasion performance of the same alloys, the results showed that the effect of austenitizing temperature on high-stress abrasion pin test weight loss differed for each alloy. With increasing austenitizing temperature, these results ranged from a substantial improvement in wear performance and retention of hardness through to vir-tually no change in wear performance and substantial falls in hardness. Fracture toughness, however, increased markedly in all alloys with increasing austenitizing temperature. Tempering treatments in the range 400 °C to 600 °C, following hardening at the austenitizing temperature used commonly in industrial practice for each alloy, produced significant changes in both hard-ness and wear performance, but negligible changes in fracture toughness. Most importantly, the data showed that selection of the correct temperature for subcritical heat treatment to reduce the retained austenite content for applications involving repeated impact loading is critical if abrasion resistance is not to suffer.

  19. Mechanical Characterization and Corrosion Testing of X608 Al Alloy

    SciTech Connect

    Prabhakaran, Ramprashad; Choi, Jung-Pyung; Stephens, Elizabeth V.; Catalini, David; Lavender, Curt A.; Rohatgi, Aashish

    2016-02-07

    This paper describes the mechanical characterization and corrosion testing of X608 Al alloy that is being considered for A-pillar covers for heavy-duty truck applications. Recently, PNNL developed a thermo-mechanical process to stamp A-pillar covers at room temperature using this alloy, and the full-size prototype was successfully stamped by a tier-1 supplier. This study was conducted to obtain additional important information related to the newly developed forming process, and to further improve its mechanical properties. The solutionization temperature, pre-strain and paint-bake heat-treatment were found to influence the alloy’s fabricability and mechanical properties. Natural aging effect on the formability was investigated by limiting dome height (LDH) tests. Preliminary corrosion experiments showed that the employed thermo-mechanical treatments did not significantly affect the corrosion behavior of Al X608.

  20. Mechanical Stability and Reversible Fracture of Vault Particles

    PubMed Central

    Llauró, Aida; Guerra, Pablo; Irigoyen, Nerea; Rodríguez, José F.; Verdaguer, Núria; de Pablo, Pedro J.

    2014-01-01

    Vaults are the largest ribonucleoprotein particles found in eukaryotic cells, with an unclear cellular function and promising applications as vehicles for drug delivery. In this article, we examine the local stiffness of individual vaults and probe their structural stability with atomic force microscopy under physiological conditions. Our data show that the barrel, the central part of the vault, governs both the stiffness and mechanical strength of these particles. In addition, we induce single-protein fractures in the barrel shell and monitor their temporal evolution. Our high-resolution atomic force microscopy topographies show that these fractures occur along the contacts between two major vault proteins and disappear over time. This unprecedented systematic self-healing mechanism, which enables these particles to reversibly adapt to certain geometric constraints, might help vaults safely pass through the nuclear pore complex and potentiate their role as self-reparable nanocontainers. PMID:24507609

  1. Discrete fracture patterns of virus shells reveal mechanical building blocks.

    PubMed

    Ivanovska, Irena L; Miranda, Roberto; Carrascosa, Jose L; Wuite, Gijs J L; Schmidt, Christoph F

    2011-08-02

    Viral shells are self-assembled protein nanocontainers with remarkable material properties. They combine simplicity of construction with toughness and complex functionality. These properties make them interesting for bionanotechnology. To date we know little about how virus structure determines assembly pathways and shell mechanics. We have here used atomic force microscopy to study structural failure of the shells of the bacteriophage Φ29. We observed rigidity patterns following the symmetry of the capsid proteins. Under prolonged force exertion, we observed fracture along well-defined lines of the 2D crystal lattice. The mechanically most stable building block of the shells was a trimer. Our approach of "reverse engineering" the virus shells thus made it possible to identify stable structural intermediates. Such stable intermediates point to a hierarchy of interactions among equal building blocks correlated with distinct next-neighbor interactions. The results also demonstrate that concepts from macroscopic materials science, such as fracture, can be usefully employed in molecular engineering.

  2. Mechanical alloying Ti[sub 50]Al[sub 50] in nitrogen atmosphere

    SciTech Connect

    Wang, K.Y.; Chen, G.L.; Wang, J.G. )

    1994-07-01

    Titanium aluminides ([gamma]-TiAl or [alpha][sub 2]-Ti[sub 3]Al) are very useful structural materials for application in the aerospace industry owing to their low density, high specific strength and modulus, and good oxidation and corrosion resistance, at least up to 800 C. However, their use has been limited because of a poor ductility and fracture toughness at room temperature. To improve these properties, TiAl compound was recently made as a composite material containing a secondary phase such as boride, carbide, oxide or nitride or refinement of crystalline by inert gas condensation or mechanical alloying. Itsukaichi et al. reported the mechanical alloying of Al-Ti systems, where the amorphous phase was obtained for the Ti[sub 50]Al[sub 50] system after milling of 1,000h in Ar atmosphere. Suryanarayana et al. also reported that the amorphous phase could be obtained after milling for 25h of a Ti-50 at. % Al system and adding a surfactant such as hexane during mechanical alloying. Ogino et al. reported MA of Ti[sub 0.50]Al[sub 0.50] in N[sub 2] gas. The results obtained show that the diffraction peaks broadened at an intermediate stage of milling and thereafter the powder transformed into a cubic nitride (Ti[sub 0.50]Al[sub 0.50])N. But they have not confirmed the formation of an amorphous phase. In this paper, the authors prepared an amorphous Ti-Al phase through mechanical alloying in N[sub 2] gas; thermal behaviors of the amorphous phase were also investigated.

  3. Dynamic Fracture Initiation Toughness at Elevated Temperatures With Application to the New Generation of Titanium Aluminide Alloys. Chapter 8

    NASA Technical Reports Server (NTRS)

    Shazly, Mostafa; Prakash, Vikas; Draper, Susan; Shukla, Arun (Editor)

    2006-01-01

    Recently, a new generation of titanium aluminide alloy, named Gamma-Met PX, has been developed with better rolling and post-rolling characteristics. I'revious work on this alloy has shown the material to have higher strengths at room and elevated temperatures when compared with other gamma titanium aluminides. In particular, this new alloy has shown increased ductility at elevated temperatures under both quasi-static and high strain rate uniaxial compressive loading. However, its high strain rate tensile ductility at room and elevated temperatures is limited to approx. 1%. In the present chapter, results of a study to investigate the effects of loading rate and test temperature on the dynamic fracture initiation toughness in Gamma-Met PX are presented. Modified split Hopkinson pressure bar was used along with high-speed photography to determine the crack initiation time. Three-point bend dynamic fracture experiments were conducted at impact speeds of approx. 1 m/s and tests temperatures of up-to 1200 C. The results show that thc dynamic fracture initiation toughness decreases with increasing test temperatures beyond 600 C. Furthermore, thc effect of long time high temperature air exposure on the fracture toughness was investigated. The dynamic fracture initiation toughness was found to decrease with increasing exposure time. The reasons behind this drop are analyzed and discussed.

  4. Mechanical Properties of the TiAl IRIS Alloy

    NASA Astrophysics Data System (ADS)

    Voisin, Thomas; Monchoux, Jean-Philippe; Thomas, Marc; Deshayes, Christophe; Couret, Alain

    2016-12-01

    This paper presents a study of the mechanical properties at room and high temperature of the boron and tungsten containing IRIS alloy (Ti-48Al-2W-0.08B at. pct). This alloy was densified by Spark Plasma Sintering (SPS). The resultant microstructure consists of small lamellar colonies surrounded by γ regions containing B2 precipitates. Tensile tests are performed from room temperature to 1273 K (1000 °C). Creep properties are determined at 973 K (700 °C)/300 MPa, 1023 K (750 °C)/120 MPa, and 1023 K (750 °C)/200 MPa. The tensile strength and the creep resistance at high temperature are found to be very high compared to the data reported in the current literature while a plastic elongation of 1.6 pct is preserved at room temperature. A grain size dependence of both ductility and strength is highlighted at room temperature. The deformation mechanisms are studied by post-mortem analyses on deformed samples and by in situ straining experiments, both performed in a transmission electron microscope. In particular, a low mobility of non-screw segments of dislocations at room temperature and the activation of a mixed-climb mechanism during creep have been identified. The mechanical properties of this IRIS alloy processed by SPS are compared to those of other TiAl alloys developed for high-temperature structural applications as well as to those of similar tungsten containing alloys obtained by more conventional processing techniques. Finally, the relationships between mechanical properties and microstructural features together with the elementary deformation mechanisms are discussed.

  5. Stress Fracture Etiology as Dependent on Mechanically Induced Fluid Flow

    DTIC Science & Technology

    2004-08-01

    Martin, M . B. Schaffler, and C. H . Turner. Bone microdamage and skeletal fragility in osteoporotic and stress fractures. J.Bone Miner.Res. 12:6...ulnae (Adams et al., 1995). Endosteal and periosteal were labeled weekly using tetracycline solution (15 ing- new bone formation, as well as...Transport mechanism operating Huiskes, R.. Weinans, H ., Grootenboer, H.J., Dalstra, M ., Fudala. B., between blood supply and osteocytes in long bones

  6. Micro and Macro Mechanics of Fracture in Ceramics.

    DTIC Science & Technology

    1982-10-30

    originates from resistant second phase particles in the path of a propagating crack. The crack tends to bow between the particles, causing the stress...increases until the fracture toughness of the particle is reached, whereupon crack advance ensues. The penetrability (or resistance ) of the second phase... resistance interfaces. Crack deflection has been associated with improved mechanical properties; I-3 however, the specific quantitative relation between the

  7. A case study in technology utilization: Fracture mechanics

    NASA Technical Reports Server (NTRS)

    1972-01-01

    This review of NASA contributions to the technology of fracture mechanics illustrates a fundamental role of the Space Agency in a single technical area. While primarily pursuing its goal of minimizing the weight of flight hardware, NASA engineers have generated innovations having broad impact in nonaerospace communities. A review is given of how these specific NASA innovations are communicated to the technical community outside the Space Agency, and current application areas are outlined.

  8. Flow and fracture behavior of aluminum alloy 6082-T6 at different tensile strain rates and triaxialities.

    PubMed

    Chen, Xuanzhen; Peng, Yong; Peng, Shan; Yao, Song; Chen, Chao; Xu, Ping

    2017-01-01

    This study aims to investigate the flow and fracture behavior of aluminum alloy 6082-T6 (AA6082-T6) at different strain rates and triaxialities. Two groups of Charpy impact tests were carried out to further investigate its dynamic impact fracture property. A series of tensile tests and numerical simulations based on finite element analysis (FEA) were performed. Experimental data on smooth specimens under various strain rates ranging from 0.0001~3400 s-1 shows that AA6082-T6 is rather insensitive to strain rates in general. However, clear rate sensitivity was observed in the range of 0.001~1 s-1 while such a characteristic is counteracted by the adiabatic heating of specimens under high strain rates. A Johnson-Cook constitutive model was proposed based on tensile tests at different strain rates. In this study, the average stress triaxiality and equivalent plastic strain at facture obtained from numerical simulations were used for the calibration of J-C fracture model. Both of the J-C constitutive model and fracture model were employed in numerical simulations and the results was compared with experimental results. The calibrated J-C fracture model exhibits higher accuracy than the J-C fracture model obtained by the common method in predicting the fracture behavior of AA6082-T6. Finally, the Scanning Electron Microscope (SEM) of fractured specimens with different initial stress triaxialities were analyzed. The magnified fractographs indicate that high initial stress triaxiality likely results in dimple fracture.

  9. Flow and fracture behavior of aluminum alloy 6082-T6 at different tensile strain rates and triaxialities

    PubMed Central

    Chen, Xuanzhen; Peng, Shan; Yao, Song; Chen, Chao; Xu, Ping

    2017-01-01

    This study aims to investigate the flow and fracture behavior of aluminum alloy 6082-T6 (AA6082-T6) at different strain rates and triaxialities. Two groups of Charpy impact tests were carried out to further investigate its dynamic impact fracture property. A series of tensile tests and numerical simulations based on finite element analysis (FEA) were performed. Experimental data on smooth specimens under various strain rates ranging from 0.0001~3400 s-1 shows that AA6082-T6 is rather insensitive to strain rates in general. However, clear rate sensitivity was observed in the range of 0.001~1 s-1 while such a characteristic is counteracted by the adiabatic heating of specimens under high strain rates. A Johnson-Cook constitutive model was proposed based on tensile tests at different strain rates. In this study, the average stress triaxiality and equivalent plastic strain at facture obtained from numerical simulations were used for the calibration of J-C fracture model. Both of the J-C constitutive model and fracture model were employed in numerical simulations and the results was compared with experimental results. The calibrated J-C fracture model exhibits higher accuracy than the J-C fracture model obtained by the common method in predicting the fracture behavior of AA6082-T6. Finally, the Scanning Electron Microscope (SEM) of fractured specimens with different initial stress triaxialities were analyzed. The magnified fractographs indicate that high initial stress triaxiality likely results in dimple fracture. PMID:28759617

  10. Wide-range displacement expressions for standard fracture mechanics specimens

    NASA Technical Reports Server (NTRS)

    Kapp, J. A.; Gross, B.; Leger, G. S.

    1985-01-01

    Wide-range algebraic expressions for the displacement of cracked fracture mechanics specimens are developed. For each specimen two equations are given: one for the displacement as a function of crack length, the other for crack length as a function of displacement. All the specimens that appear in ASTM Test for Plane-Strain Fracture Toughness of Metallic Materials (E 399) are represented in addition to the crack mouth displacement for a pure bending specimen. For the compact tension sample and the disk-shaped compact tension sample, the displacement at the crack mouth and at the load line are both considered. Only the crack mouth displacements for the arc-shaped tension samples are presented. The agreement between the displacements or crack lengths predicted by the various equations and the corresponding numerical data from which they were developed are nominally about 3 percent or better. These expressions should be useful in all types of fracture testing including fracture toughness, K-resistance, and fatigue crack growth.

  11. Results of fracture mechanics tests on PNC SUS 304 plate

    SciTech Connect

    Mills, W.J.; James, L.A.; Blackburn, L.D.

    1985-08-01

    PNC provided SUS 304 plate to be irradiated in FFTF at about 400/sup 0/C to a target fluence of 5 x 10/sup 21/ n/cm/sup 2/ (E > 0.1 MeV). The actual irradiation included two basically different exposure levels to assure that information would be available for the exposure of interest. After irradiation, tensile properties, fatigue-crack growth rates and J-integral fracture toughness response were determined. These same properties were also measured for the unirradiated material so radiation damage effects could be characterized. This report presents the results of this program. It is expected that these results would be applicable for detailed fracture analysis of reactor components. Recent advances in elastic-plastic fracture mechanics enable reasonably accurate predictions of failure conditions for flawed stainless steel components. Extensive research has focused on the development of J-integral-based engineering approach for assessing the load carrying capacity of low-strength, high-toughness structural materials. Furthermore, Kanninen, et al., have demonstrated that J-integral concepts can accurately predict the fracture response for full-scale cracked structures manufactured from Type 304 stainless steel.

  12. Mechanisms of extraocular muscle injury in orbital fractures.

    PubMed

    Iliff, N; Manson, P N; Katz, J; Rever, L; Yaremchuk, M

    1999-03-01

    The gross and microscopic events that occur after orbital blowout fractures were evaluated to assess the mechanisms of diplopia and muscle injury. Intramuscular and intraorbital pressures were evaluated in experimental animals, in cadavers, and at the time of orbital fracture explorations for repair of orbital fractures in humans. Histologic and circulatory changes, muscle pressure recordings, and operative observations were evaluated. Creation of a compartment syndrome was evaluated to include a histologic evaluation of the orbital fibrous sheath network for the extraocular muscles and the intramuscular vasculature. These experiments and observations do not support the role of a compartment syndrome in ocular motility disturbances because (1) intramuscular pressures were subcritical in both humans and animals; (2) no limiting fascial compartment could be demonstrated; and (3) microangiograms and histologic evaluations did not confirm areas of compartmental ischemic necrosis. Muscle contusion, scarring within and around the orbital fibrous sheath network, nerve contusion, and incarceration within fractures remain the probable causes of diplopia, with the most likely explanations being muscle contusion and fibrosis or incarceration involving the muscular fascial network.

  13. Wide-range displacement expressions for standard fracture mechanics specimens

    NASA Technical Reports Server (NTRS)

    Kapp, J. A.; Gross, B.; Leger, G. S.

    1985-01-01

    Wide-range algebraic expressions for the displacement of cracked fracture mechanics specimens are developed. For each specimen two equations are given: one for the displacement as a function of crack length, the other for crack length as a function of displacement. All the specimens that appear in ASTM Test for Plane-Strain Fracture Toughness of Metallic Materials (E 399) are represented in addition to the crack mouth displacement for a pure bending specimen. For the compact tension sample and the disk-shaped compact tension sample, the displacement at the crack mouth and at the load line are both considered. Only the crack mouth displacements for the arc-shaped tension samples are presented. The agreement between the displacements or crack lengths predicted by the various equations and the corresponding numerical data from which they were developed are nominally about 3 percent or better. These expressions should be useful in all types of fracture testing including fracture toughness, K-resistance, and fatigue crack growth.

  14. Decomposition of equilibrium interphase boundary in substitutional alloys upon mechanical alloying

    NASA Astrophysics Data System (ADS)

    Gapontsev, V. L.; Seleznev, V. D.; Gapontsev, A. V.

    2017-07-01

    The vacancy-flux-induced decomposition of an interphase boundary in substitutional alloys has been considered. The interphase boundary decomposition has been described using the nonequilibrium thermodynamics approach, which considers a heterogeneous system to be continuous medium, including the interphase boundary. A hypothesis of local equilibrium in the thermodynamics of a continuous medium has been substituted for a more general hypothesis that takes into account the nonlocal dependence of thermodynamic forces and fluxes on order parameters. The interpretation of the formation of spatial composition modulations during the mechanical alloying of pure metallic Cu-Co, Cu-Fe, and Fe-Cr-Sn powder mixtures has been given.

  15. State-of-the-art report on piping fracture mechanics

    SciTech Connect

    Wilkowski, G.M.; Olson, R.J.; Scott, P.M.

    1998-01-01

    This report is an in-depth summary of the state-of-the-art in nuclear piping fracture mechanics. It represents the culmination of 20 years of work done primarily in the US, but also attempts to include important aspects from other international efforts. Although the focus of this work was for the nuclear industry, the technology is also applicable in many cases to fossil plants, petrochemical/refinery plants, and the oil and gas industry. In compiling this detailed summary report, all of the equations and details of the analysis procedure or experimental results are not necessarily included. Rather, the report describes the important aspects and limitations, tells the reader where he can go for further information, and more importantly, describes the accuracy of the models. Nevertheless, the report still contains over 150 equations and over 400 references. The main sections of this report describe: (1) the evolution of piping fracture mechanics history relative to the developments of the nuclear industry, (2) technical developments in stress analyses, material property aspects, and fracture mechanics analyses, (3) unresolved issues and technically evolving areas, and (4) a summary of conclusions of major developments to date.

  16. Aluminum alloys for ALS cryogenic tanks: Comparative measurements of cryogenic mechanical properties of Al-Li alloys and alloy 2219, February 1993

    SciTech Connect

    Reed, R.P.; Purtscher, P.T.; Simon, N.J.; McColskey, J.D.; Walsh, R.P.

    1993-02-01

    Tensile and fracture toughness were obtained at cryogenic temperatures to compare the Al-Li alloys 8090, 2090, and WL049, and alloy 2219 in various tempers and specimen orientations. The strongest alloy at very low temperatures is WL049-T851, which is about 10 percent stronger than 2090-T81. Both alloys are considerably stronger than 2219-T87. Alloy 2090-T81 is tougher (about 50 percent) than WL049-T851 at low temperatures; the higher toughness is attributed to the presence of fewer constituent particles and the tendency to delaminate at low temperatures. The delamination divides the moving crack, thus separating it into smaller regions where plane stress (rather than plane strain) conditions are conducive to increased toughness.

  17. Fracture and Stress Evolution on Europa: New Insights Into Fracture Interpretation and Ice Thickness Estimates Using Fracture Mechanics Analyses

    NASA Technical Reports Server (NTRS)

    Kattenhorn, Simon

    2004-01-01

    The work completed during the funding period has provided many important insights into fracturing behavior in Europa's ice shell. It has been determined that fracturing through time is likely to have been controlled by the effects of nonsynchronous rotation stresses and that as much as 720 deg of said rotation may have occurred during the visible geologic history. It has been determined that there are at least two distinct styles of strike-slip faulting and that their mutual evolutionary styles are likely to have been different, with one involving a significant dilational component during shear motion. It has been determined that secondary fracturing in perturbed stress fields adjacent to older structures such as faults is a prevalent process on Europa. It has been determined that cycloidal ridges are likely to experience shear stresses along the existing segment portions as they propagate, which affects propagation direction and ultimately induces tailcracking at the segment tip than then initiates a new cycle of cycloid segment growth. Finally, it has been established that mechanical methods (e.g., flexure analysis) can be used to determine the elastic thickness of the ice shell, which, although probably only several km thick, is likely to be spatially variable, being thinner under bands but thicker under ridged plains terrain.

  18. Mechanical biocompatibilities of titanium alloys for biomedical applications.

    PubMed

    Niinomi, Mitsuo

    2008-01-01

    Young's modulus as well as tensile strength, ductility, fatigue life, fretting fatigue life, wear properties, functionalities, etc., should be adjusted to levels that are suitable for structural biomaterials used in implants that replace hard tissue. These factors may be collectively referred to as mechanical biocompatibilities. In this paper, the following are described with regard to biomedical applications of titanium alloys: the Young's modulus, wear properties, notch fatigue strength, fatigue behaviour on relation to ageing treatment, improvement of fatigue strength, fatigue crack propagation resistance and ductility by the deformation-induced martensitic transformation of the unstable beta phase, and multifunctional deformation behaviours of titanium alloys.

  19. Mechanical Properties and Microstructure of AZ31 Magnesium Alloy Tubes

    NASA Astrophysics Data System (ADS)

    Luo, Alan A.; Sachdev, Anil K.

    Magnesium alloys are increasingly being used in automotive industry for weight reduction and fuel economy improvement. Extruded tubular sections provide further opportunities in mass-efficient designs of automotive structural and interior applications. In this paper, microstructural evaluation indicates that twinning is the predominant deformation mechanism for magnesium alloys at room and moderate temperatures. Dynamic recrystallization is observed at temperatures as low as 150°C, leading to the formation of fine grains as a "necklace" at prior grain boundaries. These new grains cause strain localization and instability due to a loss in strain hardening, and result in failure by cavitation.

  20. Elasto-plastic fracture mechanics of crack growth in soil

    NASA Astrophysics Data System (ADS)

    Hallett, P. D.; Newson, T. A.

    2003-04-01

    A predominant variable in soil structure formation and degradation is crack propagation. Empirical models exist to predict fracture but these do not describe the underlying physical processes. Theoretical fracture mechanics models have been applied to soil, but most are not applicable when soil is in a wet, plastic state. Since the onset of crack formation in soil tends to occur in this condition, physically sound elasto-plastic fracture mechanics approaches are long overdue. We address this weakness by applying a new elasto-plastic fracture mechanics approach to describe crack formation in plastic soil. Samples are fractured using a deep-notch (modified 4-point) bend test, with data on load transmission, sample bending, crack growth, and crack mouth opening collected to assess the crack opening angle (COA), the crack tip opening angle (CTOA) and the plastic energy dissipation rate (Dpl). These are all material properties that can be used directly to predict and describe crack propagation. CTOA will be used to discuss the results here, although a full description of the other parameters will be provided in the conference presentation. It provides a powerful parameter for describing soil cracking since CTOA is induced by soil shrinkage (an easily measured parameter) and can be used to describe elasto-plastic fracture in finite element modelling packages. The test variables we have studied to date are clay platelet orientation, soil texture, clay mineralogy, and pore water salinity. All samples were formed by consolidating a soil slurry with a 120 kPa vertical stress. Tests on pure kaolinite showed that platelet orientation did not affect CTOA which was 0.23 ± 0.02 for both conditions. Soil texture did have a marked influence, however, with silica sand:kaolinite mixes of 20:80 and 40:60 reducing CTOA to 0.14 ± 0.02 and 0.12 ± 0.01 respectively. These lower values of CTOA indicate that less strain is required to induce fracture when the amount of clay is lowered