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Sample records for fracture toughness reference

  1. Reference point indentation is not indicative of whole mouse bone measures of stress intensity fracture toughness

    PubMed Central

    Carriero, Alessandra; Bruse, Jan L.; Oldknow, Karla J.; Millán, José Luis; Farquharson, Colin; Shefelbine, Sandra J.

    2014-01-01

    Bone fragility is a concern for aged and diseased bone. Measuring bone toughness and understanding fracture properties of the bone are critical for predicting fracture risk associated with age and disease and for preclinical testing of therapies. A reference point indentation technique (BioDent) has recently been developed to determine bone's resistance to fracture in a minimally invasive way by measuring the indentation distance increase (IDI) between the first and last indentations over cyclic indentations in the same position. In this study, we investigate the relationship between fracture toughness KC and reference point indentation parameters (i.e. IDI, total indentation distance (TID) and creep indentation distance (CID)) in bones from 38 mice from six types (C57Bl/6, Balb, oim/oim, oim/+, Phospho1−/− and Phospho1 wild type counterpart). These mice bone are models of healthy and diseased bone spanning a range of fracture toughness from very brittle (oim/oim) to ductile (Phospho1−/−). Left femora were dissected, notched and tested in 3-point bending until complete failure. Contralateral femora were dissected and indented in 10 sites of their anterior and posterior shaft surface over 10 indentation cycles. IDI, TID and CID were measured. Results from this study suggest that reference point indentation parameters are not indicative of stress intensity fracture toughness in mouse bone. In particular, the IDI values at the anterior mid-diaphysis across mouse types overlapped, making it difficult to discern differences between mouse types, despite having extreme differences in stress intensity based toughness measures. When more locations of indentation were considered, the normalised IDIs could distinguish between mouse types. Future studies should investigate the relationship of the reference point indentation parameters for mouse bone in other material properties of the bone tissue in order to determine their use for measuring bone quality. PMID:25280470

  2. Dynamic fracture toughness

    NASA Technical Reports Server (NTRS)

    Kobayashi, A. S.; Ramulu, M.; Dadkhah, M. S.; Yang, K.-H.; Kang, B. S. J.

    1986-01-01

    Dynamic fracture toughness versus crack velocity relations of Homalite-100, polycarbonate, hardened 4340 steel and reaction bonded silicon nitride are reviewed and discrepancies with published data and their probable causes are discussed. Data scatter in published data are attributed in part to the observed fluctuations in crack velocities. The results reaffirmed our previous conclusion that the dynamic fracture toughness versus crack velocity relation is specimen dependent and that the dynamic arrest stress intensity factor is not a unique material property.

  3. Fracture toughness curve shift method

    SciTech Connect

    Nanstad, R.K.; Sokolov, M.A.; McCabe, D.E.

    1995-10-01

    The purpose of this task is to examine the technical basis for the currently accepted methods for shifting fracture toughness curves to account for irradiation damage, and to work through national codes and standards bodies to revise those methods, if a change is warranted. During this reporting period, data from all the relevant HSSI Programs were acquired and stored in a database and evaluated. The results from that evaluation have been prepared in a draft letter report and are summarized here. A method employing Weibull statistics was applied to analyze fracture toughness properties of unirradiated and irradiated pressure vessel steels. Application of the concept of a master curve for irradiated materials was examined and used to measure shifts of fracture toughness transition curves. It was shown that the maximum likelihood approach gave good estimations of the reference temperature, T{sub o}, determined by rank method and could be used for analyzing of data sets where application of the rank method did not prove to be feasible. It was shown that, on average, the fracture toughness shifts generally exceeded the Charpy 41-J shifts; a linear least-squares fit to the data set yielded a slope of 1.15. The observed dissimilarity was analyzed by taking into account differences in effects of irradiation on Charpy impact and fracture toughness properties. Based on these comparisons, a procedure to adjust Charpy 41-J shifts for achieving a more reliable correlation with the fracture toughness shifts was evaluated. An adjustment consists of multiplying the 41-J energy level by the ratio of unirradiated to irradiated Charpy upper shelves to determine an irradiated transition temperature, and then subtracting the unirradiated transition temperature determined at 41 J. For LUS welds, however, an unirradiated level of 20 J (15 ft-1b) was used for the corresponding adjustment for irradiated material.

  4. Increasing Metal Fracture Toughness

    NASA Technical Reports Server (NTRS)

    Lawing, P. L.; Wood, W. H.; Sandefur, P. G. J.

    1982-01-01

    In technique developed at Langley Research Center several thin sheets of metal are diffusion-brazed together in vacuum furnace to create thick piece of metal that retains much of fracture toughness of its thin components. Technique is expected to make many of high-strength stainless steels, not currently suitable, usable at cryogenic temperatures.

  5. Fracture toughness of anisotropic graphites

    SciTech Connect

    Kennedy, C.R.; Kehne, M.T.

    1985-01-01

    Fracture toughness measurements have been made at 0, 30, 45, 60, and 90/sup 0/ from the extrusion axis on a reasonably anisotropic graphite, grade AGOT. It was found that the fracture toughness did not vary appreciably with orientation. An observed variation in strength was found to be the result of defect orientation.

  6. Test-Free Fracture Toughness

    NASA Technical Reports Server (NTRS)

    Minnetyan, Levon; Chamis, Christos C. (Technical Monitor)

    2003-01-01

    Computational simulation results can give the prediction of damage growth and progression and fracture toughness of composite structures. The experimental data from literature provide environmental effects on the fracture behavior of metallic or fiber composite structures. However, the traditional experimental methods to analyze the influence of the imposed conditions are expensive and time consuming. This research used the CODSTRAN code to model the temperature effects, scaling effects and the loading effects of fiberbraided composite specimens with and without fiber-optic sensors on the damage initiation and energy release rates. The load-displacement relationship and fracture toughness assessment approach is compared with the test results from literature and it is verified that the computational simulation, with the use of established material modeling and finite element modules, adequately tracks the changes of fracture toughness and subsequent fracture propagation for any fiberbraided composite structure due to the change of fiber orientations, presence of large diameter optical fibers, and any loading conditions.

  7. Fracture toughness testing data. A bibliography

    NASA Technical Reports Server (NTRS)

    Carpenter, J. L., Jr.; Moya, N.; Stuhrke, W. F.

    1975-01-01

    This bibliography is comprised of approximately 800 reference citations related to the mechanics of failure in aerospace structures. Most of the references are for documents that include fracture toughness testing data and its application or documents on the availability and usefulness of fracture mechanics analysis methodology. The bibliography represents a search of the literature published in the period April 1962 through April 1974 and is largely limited to documents published in the United States.

  8. Fracture toughness anisotropy in shale

    NASA Astrophysics Data System (ADS)

    Chandler, Michael R.; Meredith, Philip G.; Brantut, Nicolas; Crawford, Brian R.

    2016-03-01

    The use of hydraulic fracturing to recover shale gas has focused attention on the fundamental fracture properties of gas-bearing shales, but there remains a paucity of available experimental data on their mechanical and physical properties. Such shales are strongly anisotropic, so that their fracture propagation trajectories depend on the interaction between their anisotropic mechanical properties and the anisotropic in situ stress field in the shallow crust. Here we report fracture toughness measurements on Mancos shale determined in all three principal fracture orientations: Divider, Short Transverse, and Arrester, using a modified short-rod methodology. Experimental results for a range of other sedimentary and carbonate rocks are also reported for comparison purposes. Significant anisotropy is observed in shale fracture toughness measurements at ambient conditions, with values, as high as 0.72 MPa m1/2 where the crack plane is normal to the bedding, and values as low as 0.21 MPa m1/2 where the crack plane is parallel to the bedding. For cracks propagating nonparallel to bedding, we observe a tendency for deviation toward the bedding-parallel orientation. Applying a maximum energy release rate criterion, we determined the conditions under which such deviations are more or less likely to occur under more generalized mixed-mode loading conditions. We find for Mancos shale that the fracture should deviate toward the plane with lowest toughness regardless of the loading conditions.

  9. Fracture toughness of polyimide films

    NASA Technical Reports Server (NTRS)

    Hinkley, J. A.; Mings, S. L.

    1989-01-01

    Two aromatic polyimides and an aromatic polyamide-imide were tested in single edge notched tension. Fracture toughnesses, normalized to 25 micron film thickness ranged from 1.65 to 5.4 MPa m sup 1/2. LARC-TPI, a thermoplastic polyimide, showed evidence of crazing ahead of a growing crack whereas the other materials formed a shear yielded zone.

  10. Test-Free Fracture Toughness

    NASA Technical Reports Server (NTRS)

    Minnetyan, Levon; Chamis, Christos C. (Technical Monitor)

    2003-01-01

    Computational simulation results can give the prediction of damage growth and progression and fracture toughness of composite structures. The experimental data from literature provide environmental effects on the fracture behavior of metallic or fiber composite structures. However, the traditional experimental methods to analyze the influence of the imposed conditions are expensive and time consuming. This research used the CODSTRAN code to model the temperature effects, scaling effects and the loading effects of fiber/braided composite specimens with and without fiber-optic sensors on the damage initiation and energy release rates. The load-displacement relationship and fracture toughness assessment approach is compared with the test results from literature and it is verified that the computational simulation, with the use of established material modeling and finite element modules, adequately tracks the changes of fracture toughness and subsequent fracture propagation for any fiber/braided composite structure due to the change of fiber orientations, presence of large diameter optical fibers, and any loading conditions.

  11. Hydrogen fracture toughness tester completion

    SciTech Connect

    Morgan, Michael J.

    2015-09-30

    The Hydrogen Fracture Toughness Tester (HFTT) is a mechanical testing machine designed for conducting fracture mechanics tests on materials in high-pressure hydrogen gas. The tester is needed for evaluating the effects of hydrogen on the cracking properties of tritium reservoir materials. It consists of an Instron Model 8862 Electromechanical Test Frame; an Autoclave Engineering Pressure Vessel, an Electric Potential Drop Crack Length Measurement System, associated computer control and data acquisition systems, and a high-pressure hydrogen gas manifold and handling system.

  12. Identifying Novel Clinical Surrogates to Assess Human Bone Fracture Toughness.

    PubMed

    Granke, Mathilde; Makowski, Alexander J; Uppuganti, Sasidhar; Does, Mark D; Nyman, Jeffry S

    2015-07-01

    Fracture risk does not solely depend on strength but also on fracture toughness; ie, the ability of bone material to resist crack initiation and propagation. Because resistance to crack growth largely depends on bone properties at the tissue level, including collagen characteristics, current X-ray based assessment tools may not be suitable to identify age-related, disease-related, or treatment-related changes in fracture toughness. To identify useful clinical surrogates that could improve the assessment of fracture resistance, we investigated the potential of (1)H nuclear magnetic resonance spectroscopy (NMR) and reference point indentation (RPI) to explain age-related variance in fracture toughness. Harvested from cadaveric femurs (62 human donors), single-edge notched beam (SENB) specimens of cortical bone underwent fracture toughness testing (R-curve method). NMR-derived bound water showed the strongest correlation with fracture toughness properties (r = 0.63 for crack initiation, r = 0.35 for crack growth, and r = 0.45 for overall fracture toughness; p < 0.01). Multivariate analyses indicated that the age-related decrease in different fracture toughness properties were best explained by a combination of NMR properties including pore water and RPI-derived tissue stiffness with age as a significant covariate (adjusted R(2)  = 53.3%, 23.9%, and 35.2% for crack initiation, crack growth, and overall toughness, respectively; p < 0.001). These findings reflect the existence of many contributors to fracture toughness and emphasize the utility of a multimodal assessment of fracture resistance. Exploring the mechanistic origin of fracture toughness, glycation-mediated nonenzymatic collagen crosslinks and intracortical porosity are possible determinants of bone fracture toughness and could explain the sensitivity of NMR to changes in fracture toughness. Assuming fracture toughness is clinically important to the ability of bone to resist fracture

  13. Identifying novel clinical surrogates to assess human bone fracture toughness

    PubMed Central

    Granke, Mathilde; Makowski, Alexander J; Uppuganti, Sasidhar; Does, Mark D; Nyman, Jeffry S

    2015-01-01

    Fracture risk does not solely depend on strength but also on fracture toughness, i.e. the ability of bone material to resist crack initiation and propagation. Because resistance to crack growth largely depends on bone properties at the tissue level including collagen characteristics, current X-ray based assessment tools may not be suitable to identify age-, disease-, or treatment-related changes in fracture toughness. To identify useful clinical surrogates that could improve the assessment of fracture resistance, we investigated the potential of 1H nuclear magnetic resonance spectroscopy (NMR) and reference point indentation (RPI) to explain age-related variance in fracture toughness. Harvested from cadaveric femurs (62 human donors), single-edge notched beam (SENB) specimens of cortical bone underwent fracture toughness testing (R-curve method). NMR-derived bound water showed the strongest correlation with fracture toughness properties (r=0.63 for crack initiation, r=0.35 for crack growth, and r=0.45 for overall fracture toughness; p<0.01). Multivariate analyses indicated that the age-related decrease in different fracture toughness properties were best explained by a combination of NMR properties including pore water and RPI-derived tissue stiffness with age as a significant covariate (adjusted R2 = 53.3%, 23.9%, and 35.2% for crack initiation, crack growth, and overall toughness, respectively; p<0.001). These findings reflect the existence of many contributors to fracture toughness and emphasize the utility of a multimodal assessment of fracture resistance. Exploring the mechanistic origin of fracture toughness, glycation-mediated, non-enzymatic collagen crosslinks and intra-cortical porosity are possible determinants of bone fracture toughness and could explain the sensitivity of NMR to changes in fracture toughness. Assuming fracture toughness is clinically important to the ability of bone to resist fracture, our results suggest that improvements in fracture

  14. Fracture toughness testing of polymer matrix composites

    NASA Technical Reports Server (NTRS)

    Grady, Joseph E.

    1992-01-01

    A review of the interlaminar fracture indicates that a standard specimen geometry is needed to obtain consistent fracture toughness measurements in polymer matrix composites. In general, the variability of measured toughness values increases as the toughness of the material increases. This variability could be caused by incorrect sizing of test specimens and/or inconsistent data reduction procedures. A standard data reduction procedure is therefore needed as well, particularly for the tougher materials. Little work has been reported on the effects of fiber orientation, fiber architecture, fiber surface treatment or interlaminar fracture toughness, and the mechanisms by which the fibers increase fracture toughness are not well understood. The little data that is available indicates that woven fiber reinforcement and fiber sizings can significantly increase interlaminar fracture toughness.

  15. TRITIUM EFFECTS ON WELDMENT FRACTURE TOUGHNESS

    SciTech Connect

    Morgan, M; Michael Tosten, M; Scott West, S

    2006-07-17

    The effects of tritium on the fracture toughness properties of Type 304L stainless steel and its weldments were measured. Fracture toughness data are needed for assessing tritium reservoir structural integrity. This report provides data from J-Integral fracture toughness tests on unexposed and tritium-exposed weldments. The effect of tritium on weldment toughness has not been measured until now. The data include tests on tritium-exposed weldments after aging for up to three years to measure the effect of increasing decay helium concentration on toughness. The results indicate that Type 304L stainless steel weldments have high fracture toughness and are resistant to tritium aging effects on toughness. For unexposed alloys, weldment fracture toughness was higher than base metal toughness. Tritium-exposed-and-aged base metals and weldments had lower toughness values than unexposed ones but still retained good toughness properties. In both base metals and weldments there was an initial reduction in fracture toughness after tritium exposure but little change in fracture toughness values with increasing helium content in the range tested. Fracture modes occurred by the dimpled rupture process in unexposed and tritium-exposed steels and welds. This corroborates further the resistance of Type 304L steel to tritium embrittlement. This report fulfills the requirements for the FY06 Level 3 milestone, TSR15.3 ''Issue summary report for tritium reservoir material aging studies'' for the Enhanced Surveillance Campaign (ESC). The milestone was in support of ESC L2-1866 Milestone-''Complete an annual Enhanced Surveillance stockpile aging assessment report to support the annual assessment process''.

  16. iTOUGH2 Command Reference

    SciTech Connect

    Finsterle, Stefan

    2002-06-18

    iTOUGH2 is a program for parameter estimation, sensitivity analysis, and uncertainty propagation analysis. It is based on the TOUGH2 simulator for non-isothermal multiphase flow in fractured and porous media. This report contains a detailed description of all iTOUGH2 commands.

  17. Fracture toughness of hot-pressed beryllium

    NASA Technical Reports Server (NTRS)

    Lemon, D. D.; Brown, W. F., Jr.

    1985-01-01

    This paper presents the results of an investigation into the fracture toughness, sustained-load flaw growth, and fatigue-crack propagation resistance of S200E hot-pressed beryllium at room temperature. It also reviews the literature pertaining to the influence of various factors on the fracture toughness of hot-pressed beryllium determined using fatigue-cracked specimens.

  18. Fracture toughness testing data: A technology survey

    NASA Technical Reports Server (NTRS)

    Stuhrke, W. F.; Carpenter, J. L., Jr.

    1975-01-01

    Technical abstracts for about 90 significant documents relating to fracture toughness testing for various structural materials including information on plane strain and the developing areas of mixed mode and plane stress test conditions are presented. An overview of the state-of-the-art represented in the documents that have been abstracted is included. The abstracts in the report are mostly for publications in the period April 1962 through April 1974. The purpose of this report is to provide, in quick reference form, a dependable source for current information in the subject field.

  19. Fracture Toughness of Functionally Graded Steels

    NASA Astrophysics Data System (ADS)

    Nazari, Ali; Mohandesi, Jamshid Aghazadeh; Riahi, Shadi

    2012-04-01

    In this study, fracture toughness of functionally graded steels in both crack divider and crack arrester configurations has been studied. Spot-welded plain carbon steel and austenitic stainless steel with different thicknesses and arrangements were used as electrodes of electroslag remelting to produce functionally graded steels. Fracture toughness of the specimens in crack divider configuration was found to depend on the arrangements of the primary electrodes' pieces together with the type of the containing phases. In crack arrester configuration, the fracture toughness was found to depend on the crack tip position and the distance of the crack tip with respect to the bainitic or martensitic intermediate layers.

  20. Fracture toughness testing of polymer matrix composites

    NASA Technical Reports Server (NTRS)

    Grady, Joseph E.

    1992-01-01

    The experimental techniques and associated data analysis methods used to measure the resistance to interlaminar fracture, or 'fracture toughness', of polymer matrix composite materials are described. A review in the use of energy techniques to characterize fracture behavior in elastic solids is given. An overview is presented of the types of approaches employed in the design of delamination-resistant composite materials.

  1. Fracture Toughness Properties of Gd123 Superconducting Bulks

    NASA Astrophysics Data System (ADS)

    Fujimoto, H.; Murakami, A.

    Fracture toughness properties of melt growth GdBa2Cu3Ox (Gd123) large single domain superconducting bulks with Ag2O of 10 wt% and Pt of 0.5 wt%; 45 mm in diameter and 25 mm in thickness with low void density were evaluated at 77 K through flexural tests of specimens cut from the bulks, and compared to those of a conventional Gd123 with voids. The densified Gd123 bulks were prepared with a seeding and temperature gradient method; first melt processed in oxygen, then crystal growth in air; two-step regulated atmosphere heat treatment. The plane strain fracture toughness, KIC was obtained by the three point flexure test of the specimens with through precrack, referring to the single edge pre-cracked beam (SEPB) method, according to the JIS-R-1607, Testing Methods for Fracture Toughness of High Performance Ceramics. The results show that the fracture toughness of the densified Gd123 bulk with low void density was higher than that of the standard Gd123 bulk with voids, as well as the flexural strength previously reported. We also compared the fracture toughness of as-grown bulks with that of annealed bulks. The relation between the microstructure and the fracture toughness of the Gd123 bulk was clearly shown.

  2. Survey of fracture toughness test methods

    NASA Technical Reports Server (NTRS)

    Brown, W. F., Jr.; Jones, M. H.; Srawley, J. E.

    1968-01-01

    Comprehensive survey presents current methods of fracture toughness testing that are based on linear elastic fracture mechanics. General principles of the basic two dimensional crack stress field model are discussed in relation to real three dimensional specimens. Methods of test instrumentation and procedure are described.

  3. On the fracture toughness of advanced materials

    SciTech Connect

    Launey, Maximilien E.; Ritchie, Robert O.

    2008-11-24

    Few engineering materials are limited by their strength; rather they are limited by their resistance to fracture or fracture toughness. It is not by accident that most critical structures, such as bridges, ships, nuclear pressure vessels and so forth, are manufactured from materials that are comparatively low in strength but high in toughness. Indeed, in many classes of materials, strength and toughness are almost mutually exclusive. In the first instance, such resistance to fracture is a function of bonding and crystal structure (or lack thereof), but can be developed through the design of appropriate nano/microstructures. However, the creation of tough microstructures in structural materials, i.e., metals, polymers, ceramics and their composites, is invariably a compromise between resistance to intrinsic damage mechanisms ahead of the tip of a crack (intrinsic toughening) and the formation of crack-tip shielding mechanisms which principally act behind the tip to reduce the effective 'crack-driving force' (extrinsic toughening). Intrinsic toughening is essentially an inherent property of a specific microstructure; it is the dominant form of toughening in ductile (e.g., metallic) materials. However, for most brittle (e.g., ceramic) solids, and this includes many biological materials, it is largely ineffective and toughening conversely must be developed extrinsically, by such shielding mechanisms as crack bridging. From a fracture mechanics perspective, this results in toughening in the form of rising resistance-curve behavior where the fracture resistance actually increases with crack extension. The implication of this is that in many biological and high-strength advanced materials, toughness is developed primarily during crack growth and not for crack initiation. This is an important realization yet is still rarely reflected in the way that toughness is measured, which is invariably involves the use of single-value (crack-initiation) parameters such as the

  4. The shear fracture toughness, KIIc, of graphite

    DOE PAGESBeta

    Burchell, Timothy D.; Erdman, III, Donald L.

    2015-11-05

    In this study, the critical shear stress intensity factor, KIIc, here-in referred to as the shear fracture toughness, KIIc (MPa m), of two grades of graphite are reported. The range of specimen volumes was selected to elucidate any specimen size effect, but smaller volume specimen tests were largely unsuccessful, shear failure did not occur between the notches as expected. This was probably due to the specimen geometry causing the shear fracture stress to exceed the compressive failure stress. In subsequent testing the specimen geometry was altered to reduce the compressive footprint and the notches (slits) made deeper to reduce themore » specimen's ligament length. Additionally, we added the collection of Acoustic Emission (AE) during testing to assist with the identification of the shear fracture load. The means of KIIc from large specimens for PCEA and NBG-18 are 2.26 MPa m with an SD of 0.37 MPa m and 2.20 MPa m with an SD of 0.53 MPa m, respectively. The value of KIIc for both graphite grades was similar, although the scatter was large. In this work we found the ratio of KIIc/KIc ≈ 1.6. .« less

  5. Dynamic fracture toughness determined using molecular dynamics

    SciTech Connect

    Swadener, J. G.; Baskes, M. I.; Nastasi, Michael Anthony,

    2004-01-01

    Molecular dynamics (MD) simulations of fracture in crystalline silicon are conducted in order to determine the dynamic fracture toughness. The MD simulations show how the potential energy released during fracture is partitioned into surface energy, energy stored in defects and kinetic energy. First, the MD fracture simulations are shown to produce brittle fracture and be in reasonable agreement with experimental results. Then dynamic hcture toughness is calculated as the sum of the surface energy and the energy stored as defects directly from the MD models. Models oriented to produce fracture on either (111) or (101) planes are used. For the (101) fracture orientation, equilibrium crack speeds of greater than 80% of the Rayleigh wave speed are obtained. Crack speeds initially show a steep increase with increasing energy release rate followed by a much more gradual increase. No plateau in crack speed is observed for static energy release rates up to 20 J/m{sup 2}. At the point where the change in crack speed behavior occur, the dynamic fracture toughness (J{sub d}) is still within 10% of two times the surface energy (2{gamma}{sub 0}) and changing very slowly. From these MD simulations, it appears that the change in crack speed behavior is due to a change in the kinetic energy generation during dynamic fracture. In addition, MD simulations of facture in silicon with defects were conducted. The addition of defects increases the inelastic dissipation and the energy stored in defects.

  6. Large fracture toughness boron-epoxy composites

    NASA Technical Reports Server (NTRS)

    Atkins, A. G.

    1975-01-01

    The high tensile strengths of strong interfacial bonding may be combined with the large fracture toughness of weak interfacial bonding in brittle fiber/brittle matrix composites by intermittently coating the filaments before layup so as to have random alternate weak and strong regions. Appropriate coating materials enable Cook-Gordon Mode I interfacial debonding to take place, which produces very long pull-out lengths with an associated large contribution to toughness. Unidirectional boron-epoxy composites have been so made which have toughnesses greater than 200 kJ/sq m while retaining rule of mixtures tensile strengths. Similar trends have been observed for crossply layups.

  7. Fracture toughness of fibrous composite materials

    NASA Technical Reports Server (NTRS)

    Poe, C. C., Jr.

    1984-01-01

    Laminates with various proportions of 0 deg, 45 deg, and 90 deg plies were fabricated from T300/5208 and T300/BP-907 graphite/epoxy prepreg tape material. The fracture toughness of each laminate orientation or lay-up was determined by testing center-cracked specimens, and it was also predicted with the general fracture-toughness parameter. The predictions were good except when crack-tip splitting was large, at which time the toughness and strengths tended to be underpredicted. By using predictions, a parametric study was also made of factors that influence fracture toughness. Fiber and matrix properties as well as lay-up were investigated. Without crack-tip splitting, fracture toughness increases in proportion to fiber strength and fiber volume fraction, increases linearly with E(22)/E(11), is largest when the modulus for non-0 deg fibers is greater than that of 0 deg fibers, and is smallest for 0(m)/90(p)(s) lay-ups. (The E(11) and E(22) are Young's moduli of the lamina parallel to and normal to the direction of the fibers, respectively). For a given proportion of 0 deg plies, the most notch-sensitive lay-ups are 0(m)/90(p)(s) and the least sensitive are 0(m)/45(n)(s) and alpha(s). Notch sensitivity increases with the proportion of 0 deg plies and decreases with alpha. Strong, tough matrix materials, which inhibit crack-tip splitting, generally lead to minimum fracture toughness.

  8. Fracture Toughness Prediction for MWCNT Reinforced Ceramics

    SciTech Connect

    Henager, Charles H.; Nguyen, Ba Nghiep

    2013-09-01

    This report describes the development of a micromechanics model to predict fracture toughness of multiwall carbon nanotube (MWCNT) reinforced ceramic composites to guide future experimental work for this project. The modeling work described in this report includes (i) prediction of elastic properties, (ii) development of a mechanistic damage model accounting for matrix cracking to predict the composite nonlinear stress/strain response to tensile loading to failure, and (iii) application of this damage model in a modified boundary layer (MBL) analysis using ABAQUS to predict fracture toughness and crack resistance behavior (R-curves) for ceramic materials containing MWCNTs at various volume fractions.

  9. 10 CFR Appendix G to Part 50 - Fracture Toughness Requirements

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 10 Energy 1 2012-01-01 2012-01-01 false Fracture Toughness Requirements G Appendix G to Part 50 Energy NUCLEAR REGULATORY COMMISSION DOMESTIC LICENSING OF PRODUCTION AND UTILIZATION FACILITIES Pt. 50, App. G Appendix G to Part 50—Fracture Toughness Requirements I. Introduction and scope. II. Definitions. III. Fracture toughness tests....

  10. 10 CFR Appendix G to Part 50 - Fracture Toughness Requirements

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 10 Energy 1 2013-01-01 2013-01-01 false Fracture Toughness Requirements G Appendix G to Part 50 Energy NUCLEAR REGULATORY COMMISSION DOMESTIC LICENSING OF PRODUCTION AND UTILIZATION FACILITIES Pt. 50, App. G Appendix G to Part 50—Fracture Toughness Requirements I. Introduction and scope. II. Definitions. III. Fracture toughness tests....

  11. 10 CFR Appendix G to Part 50 - Fracture Toughness Requirements

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 10 Energy 1 2014-01-01 2014-01-01 false Fracture Toughness Requirements G Appendix G to Part 50 Energy NUCLEAR REGULATORY COMMISSION DOMESTIC LICENSING OF PRODUCTION AND UTILIZATION FACILITIES Pt. 50, App. G Appendix G to Part 50—Fracture Toughness Requirements I. Introduction and scope. II. Definitions. III. Fracture toughness tests....

  12. 10 CFR Appendix G to Part 50 - Fracture Toughness Requirements

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 10 Energy 1 2011-01-01 2011-01-01 false Fracture Toughness Requirements G Appendix G to Part 50 Energy NUCLEAR REGULATORY COMMISSION DOMESTIC LICENSING OF PRODUCTION AND UTILIZATION FACILITIES Pt. 50, App. G Appendix G to Part 50—Fracture Toughness Requirements I. Introduction and scope. II. Definitions. III. Fracture toughness tests....

  13. 10 CFR Appendix G to Part 50 - Fracture Toughness Requirements

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 10 Energy 1 2010-01-01 2010-01-01 false Fracture Toughness Requirements G Appendix G to Part 50 Energy NUCLEAR REGULATORY COMMISSION DOMESTIC LICENSING OF PRODUCTION AND UTILIZATION FACILITIES Pt. 50, App. G Appendix G to Part 50—Fracture Toughness Requirements I. Introduction and scope. II. Definitions. III. Fracture toughness tests....

  14. The fracture toughness of soft tissues.

    PubMed

    Taylor, David; O'Mara, Niamh; Ryan, Eoin; Takaza, Michael; Simms, Ciaran

    2012-02-01

    Fracture toughness is important for any material, but to date there have been few investigations of this mechanical property in soft mammalian tissues. This paper presents new data on porcine muscle tissue and a detailed analysis of all previous work. The conclusion is that, in most cases, fracture toughness has not in fact been measured for these tissues. Reanalysis of the previous work shows that failure of the test specimens generally occurred at the material's ultimate strength, implying that no information about toughness can be obtained from the results. This finding applied to work on cartilage, artificial neocartilage, muscle and the TMJ disc. Our own data, which was also found to be invalid, gave measured fracture toughness values which were highly variable and showed a strong dependence on the crack growth increment. The net-section failure stress and failure energy were relatively constant in large specimens, independent of crack length, whilst for smaller specimens they showed a strong size effect. These findings are explained by the fact that the process zone size, estimated here using the critical distance parameter L, was similar to, or larger than, critical specimen dimensions (crack length and specimen width). Whilst this analysis casts doubt on much of the published literature, a useful finding is that soft tissues are highly tolerant of defects, able to withstand the presence of cracks several millimetres in length without significant loss of strength. PMID:22301183

  15. Measuring the Real Fracture Toughness of Ceramics: ASTM C 1421

    NASA Astrophysics Data System (ADS)

    Salem, Jonathan; Quinn, George; Jenkins, Michael

    ASTM C 1421 "Standard Test Methods for Determination of Fracture Toughness of Advanced Ceramics at Ambient Temperature" is a high-quality, technicallyrigorous, full-consensus standard that may have finally answered the question, "What is the 'real' fracture toughness of ceramics?" This document was eight years in the actual standardization process (although an estimated two decades of preparation work may have preceded the actual standardization process). Three different types of notch/crack geometries are employed in flexure beams: single edge precracked beam (SEPB); chevron-notched beam (CNB), and surface crack in flexure (SCF). Extensive experimental, analytical, and numerical evaluations were conducted in order to mitigate interferences that frequently lower the accuracy of fracture toughness test results. Several round robins (e.g. Versailles Advanced Materials and Standards {VAMAS}) verified and validated the choice of dimensions and test parameters included in the standard. In addition, the standard reference material NIST SRM 2100 was developed and can be used in concert with ASTM C 1421 to validate a fracture toughness test setup or test protocol.

  16. Veins improve fracture toughness of insect wings.

    PubMed

    Dirks, Jan-Henning; Taylor, David

    2012-01-01

    During the lifetime of a flying insect, its wings are subjected to mechanical forces and deformations for millions of cycles. Defects in the micrometre thin membranes or veins may reduce the insect's flight performance. How do insects prevent crack related material failure in their wings and what role does the characteristic vein pattern play? Fracture toughness is a parameter, which characterises a material's resistance to crack propagation. Our results show that, compared to other body parts, the hind wing membrane of the migratory locust S. gregaria itself is not exceptionally tough (1.04±0.25 MPa√m). However, the cross veins increase the wing's toughness by 50% by acting as barriers to crack propagation. Using fracture mechanics, we show that the morphological spacing of most wing veins matches the critical crack length of the material (1132 µm). This finding directly demonstrates how the biomechanical properties and the morphology of locust wings are functionally correlated in locusts, providing a mechanically 'optimal' solution with high toughness and low weight. The vein pattern found in insect wings thus might inspire the design of more durable and lightweight artificial 'venous' wings for micro-air-vehicles. Using the vein spacing as indicator, our approach might also provide a basis to estimate the wing properties of endangered or extinct insect species. PMID:22927966

  17. Interlaminar fracture toughness of thermoplastic composites

    NASA Technical Reports Server (NTRS)

    Hinkley, J. A.; Johnston, N. J.; Obrien, T. K.

    1988-01-01

    Edge delamination tension and double cantilever beam tests were used to characterize the interlaminar fracture toughness of continuous graphite-fiber composites made from experimental thermoplastic polyimides and a model thermoplastic. Residual thermal stresses, known to be significant in materials processed at high temperatures, were included in the edge delamination calculations. In the model thermoplastic system (polycarbonate matrix), surface properties of the graphite fiber were shown to be significant. Critical strain energy release rates for two different fibers having similar nominal tensile properties differed by 30 to 60 percent. The reason for the difference is not clear. Interlaminar toughness values for the thermoplastic polyimide composites (LARC-TPI and polyimidesulfone) were 3 to 4 in-lb/sq in. Scanning electron micrographs of the EDT fracture surfaces suggest poor fiber/matrix bonding. Residual thermal stresses account for up to 32 percent of the strain energy release in composites made from these high-temperature resins.

  18. Fracture toughness and crack growth of Zerodur

    NASA Technical Reports Server (NTRS)

    Viens, Michael J.

    1990-01-01

    The fracture toughness and crack growth parameters of Zerodur, a low expansion glass ceramic material, were determined. The fracture toughness was determined using indentation techniques and was found to be 0.9 MPa x m(sup 1/2). The crack growth parameters were determined using indented biaxial specimens subjected to static and dynamic loading in an aqueous environment. The crack growth parameters n and 1n(B) were found to be 30.7 and -6.837, respectively. The crack growth parameters were also determined using indented biaxial specimens subjected to dynamic loading in an ambient 50 percent relative humidity environment. The crack growth parameters n and 1n(B) at 50 percent relative humidity were found to be 59.3 and -17.51, respectively.

  19. Interlaminar fracture toughness of thermoplastic composites

    NASA Technical Reports Server (NTRS)

    Hinkley, Jeffrey A.; Johnston, Norman J.; O'Brien, T. Kevin

    1989-01-01

    Edge delamination tension and double cantilever beam tests were used to characterize the interlaminar fracture toughness of continuous graphite-fiber composites made from experimental thermoplastic polyimides and a model thermoplastic. Residual thermal stresses, known to be significant in materials processed at high temperatures, were included in the edge delamination calculations. In the model thermoplastic system (polycarbonate matrix), surface properties of the graphite fiber were shown to be significant. Cricital strain energy release rates for two different fibers having similar nominal tensile properties differed by 30 to 60 percent. The reason for the difference is not clear. Interlaminar toughness values for the thermoplastic polyimide composites (LARC-TPI and polyimidesulfone) were 3 to 4 in-lb/sq in. Scanning electron micrographs of the EDT fracture surfaces suggest poor fiber/matrix bonding. Residual thermal stresses account for up to 32 percent of the strain energy release in composites made from these high-temperature resins.

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

    SciTech Connect

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

    1997-07-01

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

  1. Determining Ductile Fracture Toughness in Metals

    SciTech Connect

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

    2014-01-01

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

  2. Interphase effect on intralaminar fracture toughness

    SciTech Connect

    Hrivnak, J.A.; Dagastine, R.R.; McCullough, R.L.

    1996-12-31

    In fiber reinforced thermoset composites there is a growing body of experimental evidence which has pointed to a region at the fiber/matrix boundary with properties that differ from the fiber or matrix. This region extends beyond the two dimensional interface at the fiber/matrix boundary to have a finite thickness with chemical and structural property gradients. This leads to the concept of an interphase region. The interphase has a large effect on the thermal and mechanical properties of the composite such as fracture toughness, glass transition temperature and the coefficient of thermal expansion. Understanding the interphase region becomes crucial to tailoring a composite to a desired set of properties.

  3. Dynamic Fracture Initiation Toughness of ASTM A533, Grade B Steel Plate

    SciTech Connect

    Graham, S.M.; Link, R.E.

    1999-05-01

    The dynamic fracture toughness of an ASTM A533, Grade B steel plate was determined at several temperatures in the ductile-brittle transition region. Crack-tip loading rates ranged from approximately 10(sup3) to 10(sup5) MPa m/s. The fracture toughness was shown to decrease with increased loading rate. The dynamic fracture toughness was compared with results from previous investigations, and it was shown that the decrease in toughness due to increased loading rate at the highest test temperature was not as severe as reported in previous investigations. It was also shown that the reference temperature. T(sub0) was better index of the fracture toughness vs. temperature relationship than the nil-ductility temperature, RT(subNDT), for this material.

  4. Reactor Material Program Fracture Toughness of Type 304 Stainless Steel

    SciTech Connect

    Awadalla, N.G.

    2001-03-28

    This report describes the experimental procedure for Type 304 Stainless Steel fracture toughness measurements and the application of results. Typical toughness values are given based on the completed test program for the Reactor Materials Program (RMP). Test specimen size effects and limitations of the applicability in the fracture mechanics methodology are outlined as well as a brief discussion on irradiation effects.

  5. Fracture toughness of Cu-Sn intermetallic thin films

    NASA Astrophysics Data System (ADS)

    Balakrisnan, B.; Chum, C. C.; Li, M.; Chen, Z.; Cahyadi, T.

    2003-03-01

    Intermetallic compounds (IMCs) are formed as a result of interaction between solder and metallization to form joints in electronic packaging. These joints provide mechanical and electrical contacts between components. The knowledge of fracture strength of the IMCs will facilitate predicting the overall joint property, as it is more disposed to failure at the joint compared to the solder because of its brittle characteristics. The salient feature of this paper is the measurement of the fracture toughness and the critical energy-release rate of Cu3Sn and Cu6Sn5 intermetallic thin films, which is the result of the interaction between Sn from the solder and Cu from the metallization. To achieve the objective, a controlled buckling test was used. A buckling test in the current work refers to one that displays large transverse displacement caused by axial compressive loading on a slender beam. The stress and strain along the beam can be easily calculated by the applied displacement. Fracture-toughness values of Cu3Sn and Cu6Sn5 are 2.85 MPa √m ± 0.17 MPa √m and 2.36 MPa √m ± 0.15 MPa √m, respectively. Corresponding critical energy-release rate values are 65.5 J/m2 ± 8.0 J/m2 and 55.9 J/m2 ± 7.3 J/m2, respectively. The values obtained were much higher than the ones measured in bulk intermetallic samples but correlated well with those values obtained from conventional fracture-toughness specimens when fracture was confined within the intermetallic layers. Hence, the controlled buckling test is a promising fast and effective way to elucidate mechanical properties of thin films.

  6. Fracture Toughness in Advanced Monolithic Ceramics - SEPB Versus SEVENB Methods

    NASA Technical Reports Server (NTRS)

    Choi, S. R.; Gyekenyesi, J. P.

    2005-01-01

    Fracture toughness of a total of 13 advanced monolithic ceramics including silicon nitrides, silicon carbide, aluminas, and glass ceramic was determined at ambient temperature by using both single edge precracked beam (SEPB) and single edge v-notched beam (SEVNB) methods. Relatively good agreement in fracture toughness between the two methods was observed for advanced ceramics with flat R-curves; whereas, poor agreement in fracture toughness was seen for materials with rising R-curves. The discrepancy in fracture toughness between the two methods was due to stable crack growth with crack closure forces acting in the wake region of cracks even in SEVNB test specimens. The effect of discrepancy in fracture toughness was analyzed in terms of microstructural feature (grain size and shape), toughening exponent, and stable crack growth determined using back-face strain gaging.

  7. Laser notching ceramics for reliable fracture toughness testing

    SciTech Connect

    Barth, Holly D.; Elmer, John W.; Freeman, Dennis C.; Schaefer, Ronald D.; Derkach, Oleg; Gallegos, Gilbert F.

    2015-09-19

    A new method for notching ceramics was developed using a picosecond laser for fracture toughness testing of alumina samples. The test geometry incorporated a single-edge-V-notch that was notched using picosecond laser micromachining. This method has been used in the past for cutting ceramics, and is known to remove material with little to no thermal effect on the surrounding material matrix. This study showed that laser-assisted-machining for fracture toughness testing of ceramics was reliable, quick, and cost effective. In order to assess the laser notched single-edge-V-notch beam method, fracture toughness results were compared to results from other more traditional methods, specifically surface-crack in flexure and the chevron notch bend tests. Lastly, the results showed that picosecond laser notching produced precise notches in post-failure measurements, and that the measured fracture toughness results showed improved consistency compared to traditional fracture toughness methods.

  8. Laser notching ceramics for reliable fracture toughness testing

    DOE PAGESBeta

    Barth, Holly D.; Elmer, John W.; Freeman, Dennis C.; Schaefer, Ronald D.; Derkach, Oleg; Gallegos, Gilbert F.

    2015-09-19

    A new method for notching ceramics was developed using a picosecond laser for fracture toughness testing of alumina samples. The test geometry incorporated a single-edge-V-notch that was notched using picosecond laser micromachining. This method has been used in the past for cutting ceramics, and is known to remove material with little to no thermal effect on the surrounding material matrix. This study showed that laser-assisted-machining for fracture toughness testing of ceramics was reliable, quick, and cost effective. In order to assess the laser notched single-edge-V-notch beam method, fracture toughness results were compared to results from other more traditional methods, specificallymore » surface-crack in flexure and the chevron notch bend tests. Lastly, the results showed that picosecond laser notching produced precise notches in post-failure measurements, and that the measured fracture toughness results showed improved consistency compared to traditional fracture toughness methods.« less

  9. Fracture toughness for copper oxide superconductors

    DOEpatents

    Goretta, K.C.; Kullberg, M.L.

    1993-04-13

    An oxide-based strengthening and toughening agent, such as tetragonal ZrO[sub 2] particles, has been added to copper oxide superconductors, such as superconducting YBa[sub 2]Cu[sub 3]O[sub x] (123) to improve its fracture toughness (K[sub IC]). A sol-gel coating which is non-reactive with the superconductor, such as Y[sub 2]BaCuO[sub 5] (211) on the ZrO[sub 2] particles minimized the deleterious reactions between the superconductor and the toughening agent dispersed therethrough. Addition of 20 mole percent ZrO[sub 2] coated with 211 yielded a 123 composite with a K[sub IC] of 4.5 MPa(m)[sup 0.5].

  10. Fracture toughness for copper oxide superconductors

    DOEpatents

    Goretta, Kenneth C.; Kullberg, Marc L.

    1993-01-01

    An oxide-based strengthening and toughening agent, such as tetragonal Zro.sub.2 particles, has been added to copper oxide superconductors, such as superconducting YBa.sub.2 Cu.sub.3 O.sub.x (123) to improve its fracture toughness (K.sub.IC). A sol-gel coating which is non-reactive with the superconductor, such as Y.sub.2 BaCuO.sub.5 (211) on the ZrO.sub.2 particles minimized the deleterious reactions between the superconductor and the toughening agent dispersed therethrough. Addition of 20 mole percent ZrO.sub.2 coated with 211 yielded a 123 composite with a K.sub.IC of 4.5 MPa(m).sup.0.5.

  11. Fracture toughness testing of Linde 1092 reactor vessel welds in the transition range using Charpy-sized specimens

    SciTech Connect

    Pavinich, W.A.; Yoon, K.K.; Hour, K.Y.; Hoffman, C.L.

    1999-10-01

    The present reference toughness method for predicting the change in fracture toughness can provide over estimates of these values because of uncertainties in initial RT{sub NDT} and shift correlations. It would be preferable to directly measure fracture toughness. However, until recently, no standard method was available to characterize fracture toughness in the transition range. ASTM E08 has developed a draft standard that shows promise for providing lower bound transition range fracture toughness using the master curve approach. This method has been successfully implemented using 1T compact fracture specimens. Combustion Engineering reactor vessel surveillance programs do not have compact fracture specimens. Therefore, the CE Owners Group developed a program to validate the master curve method for Charpy-sized and reconstituted Charpy-sized specimens for future application on irradiated specimens. This method was validated for Linde 1092 welds using unirradiated Charpy-sized and reconstituted Charpy-sized specimens by comparison of results with those from compact fracture specimens.

  12. Fracture toughness of advanced ceramics at room temperature

    NASA Technical Reports Server (NTRS)

    Quinn, George D.; Salem, Jonathan; Bar-On, Isa; Cho, Kyu; Foley, Michael; Fang, HO

    1992-01-01

    Results of round-robin fracture toughness tests on advanced ceramics are reported. A gas-pressure silicon nitride and a zirconia-toughened alumina were tested using three test methods: indentation fracture, indentation strength, and single-edge precracked beam. The latter two methods have produced consistent results. The interpretation of fracture toughness test results for the zirconia alumina composite is shown to be complicated by R-curve and environmentally assisted crack growth phenomena.

  13. Tritium Effects on Fracture Toughness of Stainless Steel Weldments

    SciTech Connect

    MORGAN, MICHAEL; CHAPMAN, G. K.; TOSTEN, M. H.; WEST, S. L.

    2005-05-12

    The effects of tritium on the fracture toughness properties of Type 304L and Type 21-6-9 stainless steel weldments were measured. Weldments were tritium-charged-and-aged and then tested in order to measure the effect of the increasing decay helium content on toughness. The results were compared to uncharged and hydrogen-charged samples. For unexposed weldments having 8-12 volume percent retained delta ferrite, fracture toughness was higher than base metal toughness. At higher levels of weld ferrite, the fracture toughness decreased to values below that of the base metal. Hydrogen-charged and tritium-charged weldments had lower toughness values than similarly charged base metals and toughness decreased further with increasing weld ferrite content. The effect of decay helium content was inconclusive because of tritium off-gassing losses during handling, storage and testing. Fracture modes were dominated by the dimpled rupture process in unexposed weldments. In hydrogen and tritium-exposed weldments, the fracture modes depended on the weld ferrite content. At high ferrite contents, hydrogen-induced transgranular fracture of the weld ferrite phase was observed.

  14. Bone Fragility Beyond Strength and Mineral Density: Raman Spectroscopy Predicts Femoral Fracture Toughness in a Murine Model of Rheumatoid Arthritis

    PubMed Central

    Inzana, Jason A.; Maher, Jason R.; Takahata, Masahiko; Schwarz, Edward M.; Berger, Andrew J.; Awad, Hani A.

    2012-01-01

    Clinical prediction of bone fracture risk primarily relies on measures of bone mineral density (BMD). BMD is strongly correlated with bone strength, but strength is independent of fracture toughness, which refers to the bone’s resistance to crack initiation and propagation. In that sense, fracture toughness is more relevant to assessing fragility-related fracture risk, independent of trauma. We hypothesized that bone biochemistry, determined by Raman spectroscopy, predicts bone fracture toughness better than BMD. This hypothesis was tested in tumor necrosis factor-transgenic mice (TNF-tg), which develop inflammatory-erosive arthritis and osteoporosis. The left femurs of TNF-tg and wild type (WT) littermates were measured with Raman spectroscopy and micro-computed tomography. Fracture toughness was assessed by cutting a sharp notch into the anterior surface of the femoral mid-diaphysis and propagating the crack under 3 point bending. Femoral fracture toughness of TNF-tg mice was significantly reduced compared to WT controls (p=0.04). A Raman spectrum-based prediction model of fracture toughness was generated by partial least squares regression (PLSR). Raman spectrum PLSR analysis produced strong predictions of fracture toughness, while BMD was not significantly correlated and produced very weak predictions. Raman spectral components associated with mineralization quality and bone collagen were strongly leveraged in predicting fracture toughness, reiterating the limitations of mineralization density alone. PMID:23261243

  15. 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.

  16. EFFECT OF TRITIUM AND DECAY HELIUM ON WELDMENT FRACTURE TOUGHNESS

    SciTech Connect

    Morgan, M; Scott West, S; Michael Tosten, M

    2006-09-26

    The fracture toughness data collected in this study are needed to assess the long-term effects of tritium and its decay product on tritium reservoirs. The results show that tritium and decay helium have negative effects on the fracture toughness properties of stainless steel and its weldments. The data and report from this study has been included in a material property database for use in tritium reservoir modeling efforts like the Technology Investment Program ''Lifecycle Engineering for Tritium Reservoirs''. A number of conclusions can be drawn from the data: (1) For unexposed Type 304L stainless steel, the fracture toughness of weldments was two to three times higher than the base metal toughness. (2) Tritium exposure lowered the fracture toughness properties of both base metals and weldments. This was characterized by lower J{sub Q} values and lower J-da curves. (3) Tritium-exposed-and-aged base metals and weldments had lower fracture toughness values than unexposed ones but still retained good toughness properties.

  17. Correlations between ultrasonic and fracture toughness factors in metallic materials

    NASA Technical Reports Server (NTRS)

    Vary, A.

    1978-01-01

    A heuristic mathematical basis is proposed for the experimental correlations found between ultrasonic propagation factors and fracture toughness factors in metallic materials. A crack extension model is proposed wherein spontaneous stress (elastic) waves produced during microcracking are instrumental in promoting the onset of unstable crack extension. Material microstructural factors involved in this process are measurable by ultrasonic probing. Experimental results indicate that ultrasonic attenuation and velocity measurements will produce significant correlations with fracture toughness properties and also yield strength.

  18. Correlations between ultrasonic and fracture toughness factors in metallic materials

    NASA Technical Reports Server (NTRS)

    Vary, A.

    1978-01-01

    A heuristic mathematical basis was proposed for the experimental correlations found between ultrasonic propagation factors and fracture toughness factors in metallic materials. A crack extension model was developed wherein spontaneous stress (elastic) waves produced during microcracking are instrumental in promoting the onset of unstable crack extension. Material microstructural factors involved in the process are measurable by ultrasonic probing. Experimental results indicate that ultrasonic attenuation and velocity measurements will produce significant correlations with fracture toughness properties and also yield strength.

  19. Critical Fracture Toughness Measurements of an Antarctic Ice Core

    NASA Astrophysics Data System (ADS)

    Christmann, Julia; Müller, Ralf; Webber, Kyle; Isaia, Daniel; Schader, Florian; Kippstuhl, Sepp; Freitag, Johannes; Humbert, Angelika

    2014-05-01

    Fracture toughness is a material parameter describing the resistance of a pre-existing defect in a body to further crack extension. The fracture toughness of glacial ice as a function of density is important for modeling efforts aspire to predict calving behavior. In the presented experiments this fracture toughness is measured using an ice core from Kohnen Station, Dronning Maud Land, Antarctica. The samples were sawed in an ice lab at the Alfred Wegener Institute in Bremerhaven at -20°C and had the dimensions of standard test samples with thickness 14 mm, width 28 mm and length 126 mm. The samples originate from a depth of 94.6 m to 96 m. The grain size of the samples was also identified. The grain size was found to be rather uniform. The critical fracture toughness is determined in a four-point bending approach using single edge V-notch beam samples. The initial notch length was around 2.5 mm and was prepared using a drilling machine. The experimental setup was designed at the Institute of Materials Science at Darmstadt. In this setup the force increases linearly, until the maximum force is reached, where the specific sample fractures. This procedure was done in an ice lab with a temperature of -15°C. The equations to calculate the fracture toughness for pure bending are derived from an elastic stress analysis and are given as a standard test method to detect the fracture toughness. An X-ray computer tomography (CT scanner) was used to determine the ice core densities. The tests cover densities from 843 kg m-3 to 871 kg m-3. Thereby the influence of the fracture toughness on the density was analyzed and compared to previous investigations of this material parameter. Finally the dependence of the measured toughness on thickness, width, and position in the core cross-section was investigated.

  20. A parametric study of fracture toughness of fibrous composite materials

    NASA Technical Reports Server (NTRS)

    Poe, C. C., Jr.

    1987-01-01

    Impacts to fibrous composite laminates by objects with low velocities can break fibers giving crack-like damage. The damage may not extend completely through a thick laminate. The tension strength of these damage laminates is reduced much like that of cracked metals. The fracture toughness depends on fiber and matrix properties, fiber orientations, and stacking sequence. Accordingly, a parametric study was made to determine how fiber and matrix properties and fiber orientations affect fracture toughness and notch sensitivity. The values of fracture toughness were predicted from the elastic constants of the laminate and the failing strain of the fibers using a general fracture toughness parameter developed previously. For a variety of laminates, values of fracture toughness from tests of center-cracked specimens and values of residual strength from tests of thick laminates with surface cracks were compared to the predictions to give credibility to the study. In contrast to the usual behavior of metals, it is shown that both ultimate tensile strength and fracture toughness of composites can be increased without increasing notch sensitivity.

  1. Fracture toughness of metallic glasses: annealing-induced embrittlement.

    PubMed

    Rycroft, Chris H; Bouchbinder, Eran

    2012-11-01

    Quantitative understanding of the fracture toughness of metallic glasses, including the associated ductile-to-brittle (embrittlement) transitions, is not yet available. Here, we use a simple model of plastic deformation in glasses, coupled to an advanced Eulerian level set formulation for solving complex free-boundary problems, to calculate the fracture toughness of metallic glasses as a function of the degree of structural relaxation corresponding to different annealing times near the glass temperature. Our main result indicates the existence of an elastoplastic crack tip instability for sufficiently relaxed glasses, resulting in a marked drop in the toughness, which we interpret as annealing-induced embrittlement transition similar to experimental observations. PMID:23215386

  2. Fracture toughness of oxide-dispersion strengthened copper

    SciTech Connect

    Alexander, D.J.

    1996-10-01

    The fracture toughness of an oxide-dispersion strengthened copper alloy AL-15 has been examined at room temperature and 250{degrees}C, in air and in vacuum (< 10{sup {minus}6} torr). Increasing test temperature causes a significant decrease in the fracture toughness of this material, in either air or vacuum environments. In addition, specimens oriented in the T-L orientation (crack growth parallel to the extrusion direction) show significantly lower toughness than those in the L-T orientation (crack growth perpendicular to the extrusion direction).

  3. Evaluation and significance of fracture toughness in ceramic materials

    SciTech Connect

    Mutoh, Y.

    1995-12-31

    Fracture toughness tests of several ceramic materials were carried out according to the various test methods, that is the Bridge indentation (BI, SEPB), Fatigue precrack (FP), Controlled surface flaw (CSF), Chevron notch (CN) and Indentation fracture (IF) methods. Mutual comparison of the test results was made to discuss the validity and applicability of each test method. Significance of the apparent fracture toughness with stable crack growth was discussed. The intrinsic fracture toughness can be obtained by the CSF method, in which a small surface crack is used. At high temperatures, since nonlinear deformation due to softening of glass phase and stable crack growth occur, nonlinear fracture mechanics approach should be applied. J{sub IC}-value is successfully evaluated according to the R-curve method.

  4. Dynamic fracture toughness evaluation by measurement of CTOD

    SciTech Connect

    Sharpe, W.N. Jr.; Douglas, A.S.; Shapiro, J.M.

    1988-02-01

    Quantification of the dynamic fracture toughness of structural materials is essential to a wide range of problems-from nuclear accidents to ordnance applications. However, the difficulties associated with accurate measurements of crack under dynamic loading are considerable. Thus there are no standardized procedures and few reliable results. A systematic study of the dynamic fracture toughness of SAE-01 tool steel, 4340 and HY100 steels, and a tungsten are described using the Interferometric Strain/Displacement Gage (ISDG) system which has very high frequency resolution. The ISDG system is used to measure the crack tip opening displacement (CTOD) 100 microns behind a fatigue crack tip in a three-point bend specimen. Static measurements on similar specimens serve to calibrate the method and ensure consistency with the accepted procedures for static fracture toughness testing. Finite element analyses are used to obtain full field information at the point of initiation and to assess the material characteristics which lead to changes in toughness with loading rate. The major advantage of the method is that information is obtained very close to the crack tip, so that stress wave loading effects are accounted for. Results show that 4340 steel, which is strain-rate insensitive, has no significant change in toughness with loading rate. Measurable toughness dependence on loading rate is found for HY-100 and tungsten, which are approximately 15 percent tougher under dynamic conditions. The SAE-01 tool steel shows a significant increase (50 percent) in fracture toughness for dynamic over static loading.

  5. Interfacial fracture toughness of alumina/niobium systems

    SciTech Connect

    Stout, M.G. ); O'Dowd, N.P.; Shih, C.F. . Div. of Engineering)

    1991-01-01

    The interfacial fracture toughness of an alumina/niobium composite has been measured as a function of phase angle. The interface was formed by solid-state bonding bulk Coor's AD-999 fine-grain alumina with a commercial purity niobium at 1600{degrees}C for 0.5 hr under a pressure of 10.5 MPa. The alumina/niobium system has a number of features which makes it ideal for an investigation of interfacial fracture toughness. From HREM data we estimate that the width of the interface is no more than 10 atomic planes. Furthermore the thermal expansion coefficients of the two materials differ by less than 5% so residual stresses due to the bonding process are small. Using symmetric and asymmetric four point bend specimens we have measured the fracture toughness of homogenous alumina and that of the alumina/niobium bimaterial in combinations of in-plane shear and tension. The fracture toughness of the homogenous alumina is relatively insensitive to the loading phase. The measured fracture toughness K{sub c} of the interface, however, depended strongly on phase angle. We were unable to obtain valid alumina/niobium interfacial toughness data at negative phase angles as the fracture initiates in the alumina and not at the interface. In symmetric bending at a phase angle {approx}5{degrees}, we measured a nominal interface toughness of 4.0 MPa{radical}m, comparable to the homogeneous alumina. We found that the toughness increased with loading phase angle to a value of K{sub c} {approx} 9 MPa{radical}m at a phase between 25{degrees} and 40{degrees}. Preliminary calculations and experiments suggest that this effect is due to an asymmetric stress distribution, with respect to the interface, and plastic deformation in the niobium. 12 refs., 9 figs., 1 tab.

  6. Semi-interpenetrating polymer network's of polyimides: Fracture toughness

    NASA Technical Reports Server (NTRS)

    Hansen, Marion Glenn

    1988-01-01

    The objective was to improve the fracture toughness of the PMR-15 thermosetting polyimide by co-disolving LaRC-TPI, a thermoplastic polyimide. The co-solvation of a thermoplastic into a thermoset produces an interpenetration of the thermoplastic polymer into the thermoset polyimide network. A second research program was planned around the concept that to improve the fracture toughness of a thermoset polyimide polymer, the molecular weight between crosslink points would be an important macromolecular topological parameter in producing a fracture toughened semi-IPN polyimide.

  7. 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.

  8. Fracture toughness of ultrashort pulse-bonded fused silica

    NASA Astrophysics Data System (ADS)

    Richter, S.; Naumann, F.; Zimmermann, F.; Tünnermann, A.; Nolte, S.

    2016-02-01

    We determined the bond interface strength of ultrashort pulse laser-welded fused silica for different processing parameters. To this end, we used a high repetition rate ultrashort pulse laser system to inscribe parallel welding lines with a specific V-shaped design into optically contacted fused silica samples. Afterward, we applied a micro-chevron test to measure the fracture toughness and surface energy of the laser-inscribed welding seams. We analyzed the influence of different processing parameters such as laser repetition rate and line separation on the fracture toughness and fracture surface energy. Welding the entire surface a fracture toughness of 0.71 {MPa} {m}^{1/2}, about 90 % of the pristine bulk material ({≈ } 0.8 {MPa} {m}^{1/2}), is obtained.

  9. 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.

  10. Fracture toughness of steel-fiber-reinforced bone cement.

    PubMed

    Kotha, S P; Li, C; Schmid, S R; Mason, J J

    2004-09-01

    Fractures in the bone-cement mantle (polymethyl methacrylate) have been linked to the failure of cemented total joint prostheses. The heat generated by the curing bone cement has also been implicated in the necrosis of surrounding bone tissue, leading to loosening of the implants. The addition of reinforcements may improve the fracture properties of bone cement and decrease the peak temperatures during curing. This study investigates the changes in the fracture properties and the temperatures generated in the ASTM F451 tests by the addition of 316L stainless steel fibers to bone cement. The influence of filler volume fraction (5-15% by volume) and aspect ratios (19, 46, 57) on the fracture toughness of the acrylic bone cement was assessed. Increasing the volume fraction of the steel fibers resulted in significant increases in the fracture toughness of the steel-fiber-reinforced composite. Fracture-toughness increases of up to 2.63 times the control values were obtained with the use of steel-fiber reinforcements. No clear trend in the fracture toughness was discerned for increasing aspect ratios of the reinforcements. There is a decrease in the peak temperatures reached during the curing of the steel-fiber-reinforced bone cement, though the decrease is too small to be clinically relevant. Large increases in the fatigue life of acrylic bone cement were also obtained by the addition of steel fibers. These results indicate that the use of steel fibers may enhance the durability of cemented joint prostheses. PMID:15293326

  11. Measurement of the toughness of bone: A tutorial with special reference to small animal studies✩

    PubMed Central

    Ritchie, R.O.; Koester, K.J.; Ionova, S.; Yao, W.; Lane, N.E.; Ager, J.W.

    2013-01-01

    Quantitative assessment of the strength and toughness of bone has become an integral part of many biological and bioengineering studies on the structural properties of bone and their degradation due to aging, disease and therapeutic treatment. Whereas the biomechanical techniques for characterizing bone strength are well documented, few studies have focused on the theory, methodology, and various experimental procedures for evaluating the fracture toughness of bone, i.e., its resistance to fracture, with particular reference to whole bone testing in small animal studies. In this tutorial, we consider the many techniques for evaluating toughness and assess their specific relevance and application to the mechanical testing of small animal bones. Parallel experimental studies on wild-type rat and mouse femurs are used to evaluate the utility of these techniques and specifically to determine the coefficient of variation of the measured toughness values. PMID:18647665

  12. The fracture toughness of cancellous bone.

    PubMed

    Cook, R B; Zioupos, P

    2009-09-18

    The mechanical capacity and integrity of cancellous bone is crucial in osteoporosis, a condition which is set to become more prevalent with increasing lifespan and population sizes. The fracture toughness (FT) of cancellous bone has never been examined before and the conditions associated with the growth of a major crack through the lattice of cancellous bone, a cellular solid, may improve our understanding for structural integrity of this material. The aim of this study is to provide (i) basic data on cancellous bone FT and (ii) the experimental support for the hypothesis of Gibson, L.J., Ashby, M.F. [1997a. Chapter 10: Wood. In: Cellular Solids: Structure and Properties, second ed. Cambridge University Press, pp. 387-428; Gibson, L.J., Ashby, M.F., 1997b. Chapter 11: Cancellous Bone. In: Cellular Solids: Structure and Properties, second ed. Cambridge University Press, pp. 429-52] that the FT of cancellous bone tissue is governed by the density of the tissue to a power function of between one and two. 294 SENB and 121 DC(T) specimen were manufactured from 45 human femoral heads, 37 osteoporotic and 8 osteoarthritic, as well as 19 equine thoracic vertebrae. The samples were manufactured in two groups: the first aligned with the trabecular structure (A( parallel)), the second orientated at 90 degrees to the main trabecular orientation (A( perpendicular)). The samples were tested in either tensile or bending mode to provide values of the stress intensity factor (K). The results which were obtained show a strong and significant link between the density of the cancellous bone tissue and that the critical stress intensity values are governed by the density of the tissue to a power function of between 1 and 2 (K(Q) vs. apparent density: A( perpendicular)=1.58, A( parallel)=1.6). Our results provide some fundamental values for the critical stress intensity factor for cancellous bone and also support the previous hypothesis as set by Gibson, L.J., Ashby, M.F., 1997a

  13. Fracture toughness of polybutadiene at cryogenic temperatures. Technical report

    SciTech Connect

    Burford, R.P.

    1983-04-01

    An estimate of fracture toughness of crosslined polybutadiene rubber at -180 degrees C has been made using the double torsin method. By using suitable specimen dimensions and strain rates, controlled crack propagatin can be achieved, together with a constant compliance to crack length ratio. Strain energy release rated for this polymer, crosslinked with either dicumyl peroxide or sulphur, were found to be an order of magnitude higher than for linear, glassy thermoplastics. Crazing is considered to contribute to the high toughness observed.

  14. Effects of radiation on the interlaminar fracture toughness of a graphite/epoxy composite

    SciTech Connect

    Funk, J.G.; Sykes, G.F.

    1986-01-01

    An experimental study is made of the effect of electron irradiation (10 to the 10th rad), simulating a 30-year geosynchronous orbit exposure, on the fracture toughness of a graphite/epoxy composite, T300/934. The double cantilever beam (DBC) test is used to determine Mode I (peel) critical strain energy release rate and the edge delamination tension (EDT) test is used to determine mixed Mode I and II (peel and shear) critical strain energy release rate. It is found that the electron interaction of the epoxy matrix material enhances the fracture toughness properties of the composite and that the test temperature has a significant effect on the fracture toughness of both baseline and irradiated material. 13 references.

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

    SciTech Connect

    Wagner, J.A.; Gangloff, R.P. Virginia, University, Charlottesville )

    1992-06-01

    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. 21 refs.

  16. 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.

  17. A joint fracture toughness evaluation of hot-pressed beryllium

    NASA Technical Reports Server (NTRS)

    Conrad, H.; Sargent, G. A.; Brown, W. F., Jr.

    1977-01-01

    Fracture toughness tests at room temperature were made on three-point bend specimens cut from hot-pressed beryllium obtained from two suppliers. The test specimens had dimensions conforming to ASTM fracture toughness standard E399-72. A total of 42 specimens were machined from each batch of material. Six specimens from each batch were then distributed to seven independent laboratories for testing. The test data from the laboratories were collected and analyzed for differences between the laboratories and the two batches of material. It is concluded that ASTM 399-72 can be used as a valid test procedure for determining the fracture toughness of beryllium, providing that Kf(max) in fatigue cracking could be up to 80 percent of the K(0) value.

  18. Fracture behavior of 9Cr nanostructured ferritic alloy with improved fracture toughness

    NASA Astrophysics Data System (ADS)

    Byun, Thak Sang; Yoon, Ji Hyun; Wee, Sung Hun; Hoelzer, David T.; Maloy, Stuart A.

    2014-06-01

    Nanostructured ferritic alloys (NFAs) have been considered as primary candidate materials for both fission and fusion reactors because of their excellent creep and irradiation resistances. It has been shown that high temperature fracture toughness could be significantly improved by appropriate thermo-mechanical treatments (TMTs). This article focuses on the static fracture behaviors of newly developed 9Cr NFAs with improved toughness. Optimal TMTs resulted in high fracture toughness at room temperature (>250 MPa √m) and in retaining higher than 100 MPa √m over a wide temperature range of 22-700 °C. Significant differences were found in fracture surfaces and fracture resistance (J-R) curves after different TMTs. Unique fracture surface features such as shallow nanoscale facets decorated with shear lips and flake-like grains were observed in high toughness specimens.

  19. Fracture toughness and strength of 96% alumina

    SciTech Connect

    Price, D.B.; Chinn, R.E.; McNerney, K.R.; Brog, T.K.; Kim, C.Y.; Krutyholowa, M.W.; Chen, N.W.; Haun, M.J.

    1997-05-01

    There exists a need to understand the controlling factors that simultaneously impact strength and toughness in 96% alumina. The enhancement of both strength and toughness enables designers to extend the use limits and reliability for structural ceramics. This article presents mechanical property results from a group study examining the use of different alkaline-earth aluminosilicate intergranular compositions containing magnesium, calcium and strontium oxides (RO) in 96% alumina. Principal results address trends in indentation strength toughness and modulus of rupture. Trends in the data are presented relative to existing theories of thermal expansion mismatch toughening, grain-bridging crack-wake effect and crack deflection mechanisms. Strength is addressed in terms of strength after indentation, crack growth of indentation flaws and Weibull characterization for the strength distribution.

  20. A 3-Dimensional discrete fracture network generator to examine fracture-matrix interaction using TOUGH2

    SciTech Connect

    Ito, Kazumasa; Yongkoo, Seol

    2003-04-09

    Water fluxes in unsaturated, fractured rock involve the physical processes occurring at fracture-matrix interfaces within fracture networks. Modeling these water fluxes using a discrete fracture network model is a complicated effort. Existing preprocessors for TOUGH2 are not suitable to generate grids for fracture networks with various orientations and inclinations. There are several 3-D discrete-fracture-network simulators for flow and transport, but most of them do not capture fracture-matrix interaction. We have developed a new 3-D discrete-fracture-network mesh generator, FRACMESH, to provide TOUGH2 with information about the fracture network configuration and fracture-matrix interactions. FRACMESH transforms a discrete fracture network into a 3 dimensional uniform mesh, in which fractures are considered as elements with unique rock material properties and connected to surrounding matrix elements. Using FRACMESH, individual fractures may have uniform or random aperture distributions to consider heterogeneity. Fracture element volumes and interfacial areas are calculated from fracture geometry within individual elements. By using FRACMESH and TOUGH2, fractures with various inclinations and orientations, and fracture-matrix interaction, can be incorporated. In this paper, results of flow and transport simulations in a fractured rock block utilizing FRACMESH are presented.

  1. The interlaminar fracture toughness of woven graphite/epoxy composites

    NASA Technical Reports Server (NTRS)

    Funk, Joan G.; Deaton, Jerry W.

    1989-01-01

    The interlaminar fracture toughness of 2-D graphite/epoxy woven composites was determined as a function of stacking sequence, thickness, and weave pattern. Plain, oxford, 5-harness satin, and 8-harness satin weaves of T300/934 material were evaluated by the double cantilever beam test. The fabric material had a G (sub Ic) ranging from 2 to 8 times greater than 0 degrees unidirectional T300/934 tape material. The interlaminar fracture toughness of a particular weave style was dependent on whether the stacking sequence was symmetric or asymmetric and, in some cases, on the fabric orientation.

  2. An innovative technique for evaluating fracture toughness of graphite materials

    NASA Astrophysics Data System (ADS)

    Wang, Jy-An John; Liu, Ken C.

    2008-10-01

    Spiral notch torsion fracture toughness test (SNTT) was developed recently to measure the intrinsic fracture toughness ( KIC) of structural materials. The SNTT system operates by applying pure torsion to uniform cylindrical specimens with a notch line that spirals around the specimen at a 45° pitch. The KIC values are obtained with the aid of a three-dimensional finite-element computer code, TOR3D-KIC. The SNTT method is uniquely suitable for testing a wide variety of materials used extensively in pressure vessel and piping structural components and weldments, including others such as ceramics, their composites, and concrete.

  3. Small punch testing for fracture toughness measurement. Final report

    SciTech Connect

    Foulds, J.R.; Woytowitz, P.J.; Parnell, T.K.

    1995-06-01

    The fracture toughness of the material of an operating power plant structural component affects the flaw tolerance of the component. A lower toughness implies a lower flaw tolerance, and generally results in an increased concern for component integrity and higher operation and maintenance costs. Often, the material fracture toughness is unknown because it was never specified or measured, or because service conditions have resulted in its degradation to an unknown extent. Examples of in- service degradation include temper embrittlement of steam turbine rotor low alloy steels exposed to elevated temperatures and neutron irradiation embrittlement of nuclear reactor pressure vessel steels. Conventional test methods for measuring toughness require the removal of large material samples from the in-service component, which is generally impractical. However, the recent development of miniature sample removal systems and the small punch test technique (which utilizes non-standard, miniature specimens of 0.5 mm or 0.020 in. thickness) now provides a convenient, practical, and virtually nondestructive means of evaluating the material of an in-service component for toughness and related mechanical properties. The small punch test method follows an approach that is based on the continuum material toughness concept wherein the criterion for fracture is defined and measured via the continuum stress-strain deformation properties of the material. The procedure specifically involves computing the {open_quotes}local{close_quotes} strain energy density accumulated at the location and time of crack initiation in the small punch test specimen using large-strain finite element analysis. Since the procedure also includes estimation of the material uniaxial tensile stress-strain behavior from the small punch load-displacement curve, both the fracture toughness and the uniaxial tensile behavior are determined from a single small punch test.

  4. On the development of a new fracture toughness procedure

    NASA Astrophysics Data System (ADS)

    Bernard, M.; Provan, J. W.

    1989-05-01

    The present ASTM test procedure for plane strain fracture toughness is time consuming, expensive, includes specimen thickness requirements, and provides no assurance of a valid K(sub IC). An attempt to circumvent the thickness limitations and to develop a simple, inexpensive method to determine plane strain fracture toughness is reported. A novel disc-shaped specimen geometry was investigated for the determination of the plane strain fracture toughness of metallic materials. The specimen has an axisymmetric notch on its upper face, is clamped on its periphery and is uniformly and perpendicularly loaded around the notch. The frozen stress photoelasticity method was applied to Araldite specimens with fatigue precracked notches to determine the stress intensity factors and the fracture mode. One configuration was retained and using the crack profile from the test, a finite element study was performed to determine the compliance of the specimen geometry. Finally, the fracture toughness of aluminium Al7075-T651 was determined by applying the critical load obtained from rupture tests.

  5. Fractal model for estimating fracture toughness of carbon nanotube reinforced aluminum oxide

    SciTech Connect

    Rishabh, Abhishek; Joshi, Milind R.; Balani, Kantesh

    2010-06-15

    The current work focuses on predicting the fracture toughness of Al{sub 2}O{sub 3} ceramic matrix composites using a modified Mandelbrot's fractal approach. The first step confirms that the experimental fracture toughness values fluctuate within the fracture toughness range predicted as per the modified fractal approach. Additionally, the secondary reinforcements [such as carbon nanotubes (CNTs)] have shown to enhance the fracture toughness of Al{sub 2}O{sub 3}. Conventional fractural toughness evaluation via fractal approach underestimates the fracture toughness by considering the shortest crack path. Hence, the modified Mandelbrot's fractal approach considers the crack propagation along the CNT semicircumferential surface (three-dimensional crack path propagation) for achieving an improved fracture toughness estimation of Al{sub 2}O{sub 3}-CNT composite. The estimations obtained in the current approach range within 4% error regime of the experimentally measured fracture toughness values of the Al{sub 2}O{sub 3}-CNT composite.

  6. Dynamic fracture toughnesses of reaction-bonded silicon nitride

    NASA Technical Reports Server (NTRS)

    Kobayashi, A. S.; Emery, A. F.; Liaw, B. M.

    1983-01-01

    The room-temperature dynamic fracture response of reaction-bonded silicon nitride is investigated using a hybrid experimental-numerical procedure. In this procedure, experimentally determined crack velocities are utilized to drive a dynamic finite-element code or dynamic finite-difference code in its generation mode in order to extract numerically the dynamic stress intensity factor of the fracturing specimen. Results show that the dynamic fracture toughness vs crack velocity relations of the two reaction-bonded silicon nitrides do not follow the general trend in those relations of brittle polymers and steel. A definite slow crack velocity during the initial phase of dynamic crack propagation is observed in reaction-bonded silicon nitride, which results in a nonunique dynamic fracture toughness vs crack velocity relation. In addition, it is found that a propagating crack will continue to propagate under a static stress intensity factor substantially lower than K(IC).

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

    SciTech Connect

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

    1994-05-01

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

  8. 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

  9. 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. PMID:26989774

  10. The feasibility of ranking material fracture toughness by ultrasonic attenuation measurements

    NASA Technical Reports Server (NTRS)

    Vary, A.

    1975-01-01

    A preliminary study was conducted to assess the feasibility of ultrasonically ranking material fracture toughness. Specimens of two grades of maraging steel for which fracture toughness values were measured were subjected to ultrasonic probing. The slope of the attenuation coefficient versus frequency curve was empirically correlated with the plane strain fracture toughness value for each grade of steel.

  11. The feasibility of ranking material fracture toughness by ultrasonic attenuation measurements

    NASA Technical Reports Server (NTRS)

    Vary, A.

    1975-01-01

    A preliminary study was conducted to assess the feasibility of ultrasonically ranking material fracture toughness. Specimens of two grades of maraging steel for which fracture toughness values were measured were subjected to ultrasonic probing. The slope of the attenuation coefficient vs frequency curve was empirically correlated with the plane strain fracture toughness value for each grade of steel.

  12. On the in vitro fracture toughness of human dentin

    SciTech Connect

    Imbeni, V.; Nalla, R.K.; Bosi, C.; Kinney, J.H.; Ritchie, R.O.

    2002-02-05

    The in vitro fracture toughness of human dention has been reported to be of the order of 3 MPa sqrt m. This result, however is based on a single study for a single orientation, and furthermore involves notched, rather than fatigue precracked, test samples.

  13. Effects of direct and indirect bleach on dentin fracture toughness.

    PubMed

    Tam, L E; Noroozi, A

    2007-12-01

    There are concerns that tooth-whitening procedures irreversibly damage tooth structure. We investigated the hypothesis that dental bleaches significantly affect dentin structural integrity. The objective was to evaluate the effects of peroxide bleaches on dentin fracture toughness. Compact test specimens, composed of human dentin, were used (n = 10/group). Bleach (16% or 10% carbamide peroxide or 3% hydrogen peroxide) or control material, containing 0.1% sodium fluoride, was applied directly or indirectly to dentin through enamel (6 hrs/day) for 2 or 8 weeks. Fracture toughness results were analyzed by ANOVA and Fisher's LSD test (p < 0.05). There were significant decreases in mean fracture toughness after two- and eight-week direct (19-34% and 61-68%, respectively) and indirect (up to 17% and 37%, respectively) bleach application. The in vitro reduction in dentin fracture toughness caused by the application of peroxide bleaches was greater for the direct application method, longer application time, and higher bleach concentration. PMID:18037654

  14. Size and Geometry Effects on Rock Fracture Toughness: Mode I Fracture

    NASA Astrophysics Data System (ADS)

    Ayatollahi, M. R.; Akbardoost, J.

    2014-03-01

    In this paper, the effects of specimen size and geometry on the apparent mode I fracture toughness ( K c) of an Iranian white marble (Neyriz) are studied. A number of fracture tests were conducted on center-cracked circular disk (CCCD) specimens with different radii to investigate the size effects on K c. The experimental results demonstrate that the apparent fracture toughness increases in bigger specimens. In order to explain the experimental results, the modified maximum tangential stress (MMTS) criterion is used, where higher order terms of the Williams' series expansion are included in the maximum tangential stress criterion. It is shown that the MMTS criterion provides good estimates for the apparent fracture toughness of Neyriz marble, obtained from fracture tests of edge-cracked triangular specimens. It is, therefore, concluded that the proposed criterion is able to account for the size and geometry effects on the fracture resistance of rocks simultaneously.

  15. Fracture Behavior of Silica- and Rubber-Nanoparticle-Toughed Epoxies

    NASA Astrophysics Data System (ADS)

    Labak, Amelia K.

    Particle-toughened crosslinked epoxies are popular materials for a variety of applications, including the microelectronics industry. For this application, the properties of these materials, such as a high fracture toughness and a low coefficient of thermal expansion, are highly appealing. In order to achieve these properties, inorganic particles are often added into the matrix. For this study, both inorganic and organic particles-toughened epoxies are investigated in the hopes of finding an optimized system. In particular, in this study, micron-sized silica and nano-sized rubbery block copolymers are added to an amine-cured epoxy matrix. A series of rubber-only and silica-only systems are investigated for their contribution to the fracture toughness. Then, a series of hybrid systems are investigated. The hypothesis is that the rubber will contribute toughness through rubber particle cavitation and matrix void growth and the silica will contribute toughness through crack pinning and bridging and particle debonding. In the hybrid systems, these mechanisms will take place at a different scale. Therefore, the nanoscale mechanisms of the rubber will be able to function at the same time as the micron sized mechanisms of the silica and the resultant toughness will be synergistically higher. The results from this study show an interesting contribution from the rubber particles both in the rubber-only systems and the hybrid system. Ultimately, there was a marked increase in the fracture toughness of the hybrid systems, although not synergistic. This increase indicates that it would be possible to create an optimized hybrid system from the combined addition of these particles.

  16. Fracture toughness of experimental dental composites aged in ethanol.

    PubMed

    Ferracane, J L; Berge, H X

    1995-07-01

    Fracture toughness (KIc) is an intrinsic property which may be related to the ability of a restorative material to resist fracture and abrasion. This property may change for a dental composite restorative due to the effects of various oral solvents. The hypothesis to be tested was that aging in ethanol would cause a reduction in the fracture toughness of dental composites, and that the extent of this reduction might be dependent upon certain compositional variables. The fracture toughnesses of three series of experimental composites with various degrees of conversion, filler volume, and percent of silane-treated fillers were compared after the composites were aged for periods of one month and six months in 75% ethanol/water, a solvent which serves as a food-simulating liquid. An unfilled Bis-GMA/TEGDMA resin served as the control. All composites, with the exception of one subjected to a post-light-curing heat treatment, experienced a significant reduction (from 30 to 56%) in KIc after being aged in 75% ethanol for six months. A similar reduction in KIc of 58% for the unfilled resin suggested that the reduction for the composites was due to a weakening of the resin matrix, which facilitated crack propagation. A simultaneous reduction in microhardness was also demonstrated. One month of aging in ethanol also produced large reductions in KIc for specimens with insufficient cure and minimal filler volume, suggesting that the properties of the resin matrix predominated for these composites.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:7560394

  17. Fracture toughness of SiC/Al metal matrix composite

    NASA Technical Reports Server (NTRS)

    Flom, Yury; Parker, B. H.; Chu, H. P.

    1989-01-01

    An experimental study was conducted to evaluate fracture toughness of SiC/Al metal matrix composite (MMC). The material was a 12.7 mm thick extrusion of 6061-T6 aluminum alloy with 40 v/o SiC particulates. Specimen configuration and test procedure conformed to ASTM E399 Standard for compact specimens. It was found that special procedures were necessary to obtain fatigue cracks of controlled lengths in the preparation of precracked specimens for the MMC material. Fatigue loading with both minimum and maximum loads in compression was used to start the precrack. The initial precracking would stop by self-arrest. Afterwards, the precrack could be safely extended to the desired length by additional cyclic tensile loading. Test results met practically all the E399 criteria for the calculation of plane strain fracture toughness of the material. A valid K sub IC value of the SiC/Al composite was established as K sub IC = 8.9 MPa square root of m. The threshold stress intensity under which crack would cease to grow in the material was estimated as delta K sub th = 2MPa square root of m for R = 0.09 using the fatigue precracking data. Fractographic examinations show that failure occurred by the micromechanism involved with plastic deformation although the specimens broke by brittle fracture. The effect of precracking by cyclic loading in compression on fracture toughness is included in the discussion.

  18. HYDROGEN EFFECTS ON THE FRACTURE TOUGHNESS PROPERTIES OF FORGED STAINLESS STEELS

    SciTech Connect

    Morgan, M

    2008-03-28

    The effect of hydrogen on the fracture toughness properties of Types 304L, 316L and 21-6-9 forged stainless steels was investigated. Fracture toughness samples were fabricated from forward-extruded forgings. Samples were uniformly saturated with hydrogen after exposure to hydrogen gas at 34 MPa or 69 and 623 K prior to testing. The fracture toughness properties were characterized by measuring the J-R behavior at ambient temperature in air. The results show that the hydrogen-charged steels have fracture toughness values that were about 50-60% of the values measured for the unexposed steels. The reduction in fracture toughness was accompanied by a change in fracture appearance. Both uncharged and hydrogen-charged samples failed by microvoid nucleation and coalescence, but the fracture surfaces of the hydrogen-charged steels had smaller microvoids. Type 316L stainless steel had the highest fracture toughness properties and the greatest resistance to hydrogen degradation.

  19. A new basis for the determination of fracture toughness

    NASA Technical Reports Server (NTRS)

    Banerjee, S.

    1979-01-01

    A study is presented which shows that the growth of the plastic zone and the constraint in a compact tension specimen depends significantly on specimen width. The analysis permits the estimation of the contribution of the growth of plastic zone to the deviation from linearity. The contribution of the crack growth to the deviation from linearity is evaluated from the analysis of a typical R-curve data. A combination of these two analyses enables one to define a very simple procedure for the determination of fracture toughness. The fracture toughness is defined as the stress intensity value at which the crack extension starts. The good agreement between analytical results and experimental KQ and KIC values determined over a wide range of thicknesses, widths, and materials justifies the proposed procedures. The KIC determined according to this procedure is independent of specimen width and such a procedure enhances the range of applicability of the K concept to a wider combination of configurations and materials.

  20. Fracture toughness of brittle materials determined with chevron notch specimens

    NASA Technical Reports Server (NTRS)

    Shannon, J. L., Jr.; Bubsey, R. T.; Pierce, W. S.; Munz, D.

    1981-01-01

    Short bar, short rod, and four-point-bend chevron-notch specimens were used to determine the plane strain fracture toughness of hot-pressed silicon nitride and sintered aluminum oxide brittle ceramics. The unique advantages of this specimen type are: (1) the production of a sharp natural crack during the early stage of test loading, so that no precracking is required, and (2) the load passes through a maximum at a constant, material-independent crack length-to-width ratio for a specific geometry, so that no post-test crack measurement is required. The plane strain fracture toughness is proportional to the maximum test load and functions of the specimen geometry and elastic compliance. Although results obtained for silicon nitride are in good mutual agreement and relatively free of geometry and size effects, aluminum oxide results were affected in both these respects by the rising crack growth resistance curve of the material.

  1. Fracture toughness evaluations of TP304 stainless steel pipes

    SciTech Connect

    Rudland, D.L.; Brust, F.W.; Wilkowski, G.M.

    1997-02-01

    In the IPIRG-1 program, the J-R curve calculated for a 16-inch nominal diameter, Schedule 100 TP304 stainless steel (DP2-A8) surface-cracked pipe experiment (Experiment 1.3-3) was considerably lower than the quasi-static, monotonic J-R curve calculated from a C(T) specimen (A8-12a). The results from several related investigations conducted to determine the cause of the observed toughness difference are: (1) chemical analyses on sections of Pipe DP2-A8 from several surface-cracked pipe and material property specimen fracture surfaces indicate that there are two distinct heats of material within Pipe DP2-A8 that differ in chemical composition; (2) SEN(T) specimen experimental results indicate that the toughness of a surface-cracked specimen is highly dependent on the depth of the initial crack, in addition, the J-R curves from the SEN(T) specimens closely match the J-R curve from the surface-cracked pipe experiment; (3) C(T) experimental results suggest that there is a large difference in the quasi-static, monotonic toughness between the two heats of DP2-A8, as well as a toughness degradation in the lower toughness heat of material (DP2-A8II) when loaded with a dynamic, cyclic (R = {minus}0.3) loading history.

  2. Measurement of fracture toughness of an ice core from Antarctica

    NASA Astrophysics Data System (ADS)

    Christmann, J.; Müller, R.; Webber, K. G.; Isaia, D.; Schader, F. H.; Kipfstuhl, S.; Freitag, J.; Humbert, A.

    2014-09-01

    The critical fracture toughness is a material parameter describing the resistance of a cracked body to further crack extension. It is an important parameter to simulate and predict the break-up behaviour of ice shelves from calving of single icebergs to the disintegration of entire ice shelves over a wide range of length scales. The fracture toughness values are calculated with equations that are derived from an elastic stress analysis. Additionally, an X-ray computer tomography (CT scanner) was used to identify the density as a function of depth. The critical fracture toughness of 91 Antarctic inland ice samples with densities between 840 to 870 kg m-3 has been determined by applying a four-point-bending technique on single edge v-notched beam samples. The examined ice core was drilled 70 m north of Kohnen Station, Dronnning Maud Land (75°00' S, 00°04' E, 2882 m). Supplementary data are available at doi:10.1594/PANGAEA.835321.

  3. On the study of crack-initiation fracture toughness of fiber glass asphalt shingles

    SciTech Connect

    Shiao, M.L.

    1999-07-01

    The fracture behavior of fiber glass asphalt shingles was examined by measuring their J-integral fracture toughness at crack initiation. The corresponding fracture mechanisms were also studied by in situ fracture observation and by scanning electron microscopy. The applicability of using J-integral fracture toughness to characterize asphalt shingles was discussed and its relationships to other mechanical properties was established. The results indicated that the fracture toughness at crack initiation can be accurately measured for fiber glass shingles and the values may be used to characterize their cracking resistance. Fracture toughness measured from various shingle samples was found to correlate to the shingle's tensile toughness and to its tear strength. Preliminary results on fracture mechanisms suggested that failure in the asphalt coatings by micro-cavitation may be the controlling event leading to crack advance. The importance of the glass fiber mat on a shingle's resistance to fracture was also discussed.

  4. The development of in situ fracture toughness evaluation techniques in hydrogen environment

    SciTech Connect

    Wang, Jy-An John; Ren, Fei; Tan, Ting; Liu, Ken C

    2014-01-01

    Fracture behavior and fracture toughness are of great interest regarding reliability of hydrogen pipelines and storage tanks, however, many conventional fracture testing techniques are difficult to be realized under the presence of hydrogen, in addition to the inherited specimen size effect. Thus it is desired to develop novel in situ fracture toughness evaluation techniques to study the fracture behavior of structural materials in hydrogen environments. In this study, a torsional fixture was developed to utilize an emerging fracture testing technique, Spiral Notch Torsion Test (SNTT). The in situ testing results indicated that the exposure to H2 significantly reduces the fracture toughness of 4340 high strength steels by up to 50 percent. Furthermore, SNTT tests conducted in air demonstrated a significant fracture toughness reduction in samples subject to simulated welding heat treatment using Gleeble, which illustrated the effect of welding on the fracture toughness of this material.

  5. Fracture toughness testing for the MC3478/79 retaining nut

    SciTech Connect

    Merten, C.W.

    1986-11-30

    A subsize, three-point bend specimen was developed for determining the fracture toughness of the maraging 350 steel used in the MC3478/79 retaining nuts. A comparison of test conditions and results with criteria for fracture toughness testing indicated that a valid value for K/sub Ic/ was obtained. Using the subsize test specimen, four heat-treating processes were evaluated. Scanning electron microscopy studies were performed in an attempt to correlate fracture surface appearance to fracture toughness. These studies suggested that as fracture toughness increases, the tendency toward quasi-cleavage decreases and dimple size increases.

  6. Interlaminar shear fracture toughness and fatigue thresholds for composite materials

    NASA Technical Reports Server (NTRS)

    O'Brien, T. Kevin; Murri, Gretchen B.; Salpekar, Satish A.

    1989-01-01

    Static and cyclic end notched flexure tests were conducted on a graphite epoxy, a glass epoxy, and graphite thermoplastic to determine their interlaminar shear fracture toughness and fatigue thresholds for delamination in terms of limiting values of the mode II strain energy release rate, G-II, for delamination growth. The influence of precracking and data reduction schemes are discussed. Finite element analysis indicated that the beam theory calculation for G-II with the transverse shear contribution included was reasonably accurate over the entire range of crack lengths. Cyclic loading significantly reduced the critical G-II for delamination. A threshold value of the maximum cyclic G-II below which no delamination occurred after one million cycles was identified for each material. Also, residual static toughness tests were conducted on glass epoxy specimens that had undergone one million cycles without delamination. A linear mixed-mode delamination criteria was used to characterize the static toughness of several composite materials; however, a total G threshold criterion appears to characterize the fatigue delamination durability of composite materials with a wide range of static toughness.

  7. Interlaminar shear fracture toughness and fatigue thresholds for composite materials

    NASA Technical Reports Server (NTRS)

    Obrien, T. Kevin; Murri, Gretchen B.; Salpekar, Satish A.

    1987-01-01

    Static and cyclic end notched flexure tests were conducted on a graphite epoxy, a glass epoxy, and graphite thermoplastic to determine their interlaminar shear fracture toughness and fatigue thresholds for delamination in terms of limiting values of the mode II strain energy release rate, G-II, for delamination growth. The influence of precracking and data reduction schemes are discussed. Finite element analysis indicated that the beam theory calculation for G-II with the transverse shear contribution included was reasonably accurate over the entire range of crack lengths. Cyclic loading significantly reduced the critical G-II for delamination. A threshold value of the maximum cyclic G-II below which no delamination occurred after one million cycles was identified for each material. Also, residual static toughness tests were conducted on glass epoxy specimens that had undergone one million cycles without delamination. A linear mixed-mode delamination criteria was used to characterize the static toughness of several composite materials; however, a total G threshold criterion appears to characterize the fatigue delamination durability of composite materials with a wide range of static toughness.

  8. Experimental Determination of the Fracture Toughness and Brittleness of the Mancos Shale, Utah.

    NASA Astrophysics Data System (ADS)

    Chandler, Mike; Meredith, Phil; Crawford, Brian

    2013-04-01

    non-linearity. This produces hysteresis during cyclic loading, allowing for the calculation of a brittleness coefficient using the residual displacement after successive loading cycles. This can then be used to define a brittleness corrected Fracture Toughness, KIcc. We report anisotropic KIcc values and a variety of supporting measurements made on the Mancos Shale in the three principle Mode-I crack orientations (Arrester, Divider and Short-Transverse) using a modified Short-Rod sample geometry. The Mancos is an Upper Cretaceous shale from western Colorado and eastern Utah with a relatively high siliclastic content for a gas target formation. The Short-Rod methodology involves the propagation of a crack through a triangular ligament in a chevron-notched cylindrical sample [3]. A very substantial anisotropy is observed in the loading curves and KIcc values for the three crack orientations, with the Divider orientation having KIcc values 25% higher than the other orientations. The measured brittleness for these Mancos shales is in the range 1.5-2.1; higher than for any other rocks we have found in the literature. This implies that the material is extremely non-linear. Increases in KIcc with increasing confining pressure are also investigated, as Shale Gas reservoirs occur at depths where confining pressure may be as high as 35MPa and temperature as high as 100oC. References [1] C.A. Green, P. Styles & B.J. Baptie, "Preese Hall Shale Gas Fracturing", Review & Recommendations for Induced Seismic Mitigation, 2012. [2] N.R. Warpinski & M.B. Smith, "Rock Mechanics and Fracture Geometry", Recent advances in Hydraulic Fracturing, SPE Monograms, Vol. 12, pp. 57-80, 1990. [3] F. Ouchterlony, "International Society for Rock Mechanics Commision on Testing Methods: Suggested Methods for Determining the Fracture Toughness of Rock", International Journal of Rock Mechanics and Mining Science & Geomechanics Abstracts, Vol. 25, 1988.

  9. 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.

  10. Effect of environment on fracture toughness of 96 wt pct alumina

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Tikare, Veena; Salem, Jonathan A.

    1993-01-01

    An effort is made to deepen understanding of environmental effects on the fracture toughness of an alumina composition that contains a residual glassy phase, by ascertaining the fracture toughness under atmospheric conditions in such varied environments as air distilled water, silicone oil, and liquid nitrogen. Fracture toughness was determined via the single-edge-precracked beam technique. Weibull strength parameters are compared for polished specimens tested both in air and silicone environments.

  11. Master Curve and Conventional Fracture Toughness of Modified 9Cr-1Mo Steel

    SciTech Connect

    Ji-Hyun, Yoon; Sung-Ho, Kim; Bong-Sang, Lee; Woo-Seog, Ryu; Jonghwa, Chang

    2006-07-01

    Modified 9Cr-1Mo steel is a primary candidate material for reactor pressure vessel of Very High Temperature Gas-Cooled Reactor (VHTR) in Korean Nuclear Hydrogen Development and Demonstration (NHDD) program. In this study, T0 reference temperature, J-R fracture resistance and Charpy impact properties were evaluated for commercial Grade 91 steel as preliminary tests for the selection of the RPV material for VHTR. The fracture toughness of the modified 9Cr-1Mo steel was compared with those of SA508-Gr.3. The objective of this study was to obtain pre-irradiation fracture toughness properties of modified 9Cr-1Mo steel as reference data for the radiation effects investigation. The results are as follows. Charpy impact properties of the modified 9Cr-1Mo steel were similar to those of SA508-Gr.3. T0 reference temperatures were measured as -67.7 deg C and -72.4 deg C from the tests with standard PCVN (pre-cracked Charpy V-notch) and half sized PCVN specimens respectively, which were similar to results for SA508-Gr.3. The K{sub Jc} values of modified 9Cr-1Mo with test temperatures are successfully expressed with the Master Curve. The J-R fracture resistance of modified 9Cr-1Mo steel at room temperature was almost the same as that of SA508-Gr.3. On the other hand it was a little bit higher at an elevated temperature. (authors)

  12. In situ tensile fracture toughness of surficial cohesive marine sediments

    NASA Astrophysics Data System (ADS)

    Johnson, Bruce D.; Barry, Mark A.; Boudreau, Bernard P.; Jumars, Peter A.; Dorgan, Kelly M.

    2012-02-01

    This study reports the first in situ measurements of tensile fracture toughness, K IC, of soft, surficial, cohesive marine sediments. A newly developed probe continuously measures the stress required to cause tensile failure in sediments to depths of up to 1 m. Probe measurements are in agreement with standard laboratory methods of K IC measurements in both potter's clay and natural sediments. The data comprise in situ depth profiles from three field sites in Nova Scotia, Canada. Measured K IC at two muddy sites (median grain size of 23-50 μm) range from near zero at the sediment surface to >1,800 Pa m1/2 at 0.2 m depth. These profiles also appear to identify the bioturbated/mixed depth. K IC for a sandy site (>90% sand) is an order of magnitude lower than for the muddy sediments, and reflects the lack of cohesion/adhesion. A comparison of K IC, median grain size, and porosity in muddy sediments indicates that consolidation increases fracture strength, whereas inclusion of sand causes weakening; thus, sand-bearing layers can be easily identified in K IC profiles. K IC and vane-measured shear strength correlate strongly, which suggests that the vane measurements should perhaps be interpreted as shear fracture toughness, rather than shear strength. Comparison of in situ probe-measured values with K IC of soils and gelatin shows that sediments have a K IC range intermediate between denser compacted soils and softer, elastic gelatin.

  13. Determination of dynamic fracture toughness using a new experimental technique

    NASA Astrophysics Data System (ADS)

    Cady, Carl M.; Liu, Cheng; Lovato, Manuel L.

    2015-09-01

    In other studies dynamic fracture toughness has been measured using Charpy impact and modified Hopkinson Bar techniques. In this paper results will be shown for the measurement of fracture toughness using a new test geometry. The crack propagation velocities range from ˜0.15 mm/s to 2.5 m/s. Digital image correlation (DIC) will be the technique used to measure both the strain and the crack growth rates. The boundary of the crack is determined using the correlation coefficient generated during image analysis and with interframe timing the crack growth rate and crack opening can be determined. A comparison of static and dynamic loading experiments will be made for brittle polymeric materials. The analysis technique presented by Sammis et al. [1] is a semi-empirical solution, however, additional Linear Elastic Fracture Mechanics analysis of the strain fields generated as part of the DIC analysis allow for the more commonly used method resembling the crack tip opening displacement (CTOD) experiment. It should be noted that this technique was developed because limited amounts of material were available and crack growth rates were to fast for a standard CTOD method.

  14. Absolute surface energies, fracture toughness, and cracking in nitrides

    NASA Astrophysics Data System (ADS)

    Dreyer, Cyrus E.; Janotti, Anderson; van de Walle, Chris G.

    2014-03-01

    Growth of high quality single crystals and epitaxial layers of GaN is critical for producing high-efficiency optoelectronic and power electronic devices. One of the fundamental material properties that govern growth of single crystals is the absolute surface energy of the crystallographic planes. Knowledge of these energies is required to understand and optimize growth rates of different facets in GaN, and provide fracture toughnesses for brittle fracture. By means of hybrid functional calculations, we have determined absolute surface energies for the non-polar {11-20} a and {10-10} m planes, and approximated values for polar (0001) + c and (000-1) - c planes in wurtzite GaN. For all surfaces, we consider low-energy bare and hydrogenated reconstructions under a variety of conditions relevant to experimental growth techniques. We find that the energies of the m and a planes are similar, and constant over the range of conditions studied. In contrast, the energies of the polar planes are strongly condition dependent. Even so, we find that the + c polar plane is systematically lower in energy than the - c plane. We have used our surface energies to determine brittle fracture toughnesses in AlN and GaN, as well as the critical thickness for cracking of AlGaN on GaN.

  15. Fracture toughness studies of rubber-toughened polycarbonate

    SciTech Connect

    Kim, S.W.

    1993-01-01

    Polycarbonate was toughened with preformed core/shell particles. The fracture toughness at different toughener levels and temperatures was measured according to a J-integral procedure using compact tension test specimens. An extensive critique of the J-integral procedures was made and compared in this study. The fracture toughness J[sub IC] of unmodified polycarbonate in Mode I is 2.68 kJ/m[sup 2] at a crosshead speed of 5.08 mm/min with the specimen thickness ranging from 3.175 to 9.525 mm, at temperatures ranging from [minus]20 to 23[degrees]C. Under the same conditions, the J[sub IC] of rubber-toughened polycarbonates were 4.88, 5.68, 7.70, and 7.46 kJ/m[sup 2], at toughener levels of 2.5, 5, 7.5, and 10 parts, respectively, by weight per hundred parts (phr) of polycarbonate. The maximum toughness was realized at 7.5 phr of toughener and began to decrease at 10 phr. Tensile stress-strain curves indicated that the modulus is retained at all toughener levels. The ultimate stress and strain, however, steadily decreased. Fracture surfaces of test specimens were examined by scanning electron microscope (SEM) and analyzed to elucidate the toughening mechanism. This indicated polycarbonate deforms through shear-yielding with or without the second phase. The fracture surface of broken tensile bars showed limited cavity volume compared to the compact tension specimens. The reason for this appears to be the higher crack speed accompanying fracture in the bars. The failure mechanism and the degree of toughening from the rubbery domains are different in the compact tension specimen and tensile bar specimen: with the compact tension specimens, dilatational deformation involving cavitation is dominant. The cavitation is initiated by interfacial debonding around the particles. In this, shear-yielding is limited. In the fracture of the tensile bar specimens, shear-yielding is dominant with limited dilatational deformation involving cavitation.

  16. Double Cantilever Beam Fracture Toughness Testing of Several Composite Materials

    NASA Technical Reports Server (NTRS)

    Kessler, Jeff A.; Adams, Donald F.

    1992-01-01

    Double-cantilever beam fracture toughness tests were performed by the Composite Materials Research Group on several different unidirectional composite materials provided by NASA Langley Research Center. The composite materials consisted of Hercules IM-7 carbon fiber and various matrix resin formulations. Multiple formulations of four different families of matrix resins were tested: LaRC - ITPI, LaRC - IA, RPT46T, and RP67/RP55. Report presents the materials tested and pertinent details supplied by NASA. For each material, three replicate specimens were tested. Multiple crack extensions were performed on each replicate.

  17. Monitoring crack extension in fracture toughness tests by ultrasonics

    NASA Technical Reports Server (NTRS)

    Klima, S. J.; Fisher, D. M.; Buzzard, R. J.

    1975-01-01

    An ultrasonic method was used to observe the onset of crack extension and to monitor continued crack growth in fracture toughness specimens during three point bend tests. A 20 MHz transducer was used with commercially available equipment to detect average crack extension less than 0.09 mm. The material tested was a 300-grade maraging steel in the annealed condition. A crack extension resistance curve was developed to demonstrate the usefulness of the ultrasonic method for minimizing the number of tests required to generate such curves.

  18. Monitoring crack extension in fracture toughness tests by ultrasonics

    NASA Technical Reports Server (NTRS)

    Klima, S. J.; Fisher, D. M.; Buzzard, R. J.

    1976-01-01

    An ultrasonic method was used to observe the onset of crack extension and to monitor continued crack growth in fracture toughness specimens during three-point bend tests. A 20-MHz transducer was used with commercially available equipment to detect average crack extension less than 0.09 mm. The material tested was a 300-grade maraging steel in the annealed condition. A crack extension resistance curve was developed to demonstrate the usefulness of the ultrasonic method for minimizing the number of tests required to generate such curves.

  19. On the feasibility of quantitative ultrasonic determination of fracture toughness: A literature review

    NASA Technical Reports Server (NTRS)

    Fu, L. S.

    1980-01-01

    The three main topics covered are: (1) fracture toughness and microstructure, (2) quantitative ultrasonic and microstructure; and (3) scattering and related mathematical methods. Literature in these areas is reviewed to give insight to the search of a theoretical foundation for quantitative ultrasonic measurement of fracture toughness. The literature review shows that fracture toughness is inherently related to the microstructure and in particular, it depends upon the spacing of inclusions or second particles and the aspect ratio of second phase particles. There are indications that ultrasonic velocity attenuation measurements can be used to determine fracture toughness. The leads to a review of the mathematical models available in solving boundary value problems related to microstructural factors that govern facture toughness and wave motion. A framework towards the theoretical study for the quantitative determination of fracture toughness is described and suggestions for future research are proposed.

  20. Fracture Toughness Testing of ASTM A285 Steel for Fracture Analysis of Savannah River Site Storage Tanks

    SciTech Connect

    Subramanian, K.H.

    2001-05-15

    The fracture toughness properties of A285 steels are being measured at specific material and test conditions for application to elastic-plastic fracture mechanics analysis of storage tanks at the Department of Energy Savannah River Site.

  1. Fracture mechanics characterization of welds: Fatigue life analysis of notches at welds: J(sub Ic) fracture toughness tests for weld metal

    NASA Astrophysics Data System (ADS)

    Underwood, John H.

    1995-03-01

    In this report two methods of fracture analysis of welds will be emphasized, one addressing fatigue life testing and analysis of notches at welds, and the other addressing the final fracture of the welded component and the fracture toughness tests used to characterize final fracture. These fatigue and fracture methods will be described by referring to recent work from the technical literature and from the U.S. Army Armament Research, Development, and Engineering Center, primarily fracture case study and fracture test method development investigations. A brief general summary will be given of fatigue and fracture methods and concepts that have application to welded structures. Specific fatigue crack initiation tests and analysis methods will be presented, using example results from a welded stainless steel box beam of a cannon carriage. Recent improvements and simplifications in J.integral fracture toughness tests will be described, particularly those related to welds. Fracture toughness measurements for various stainless steel weld metals and heat treatments will also be described.

  2. 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.

  3. 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.

  4. TRITIUM AGING EFFECTS ON THE FRACTURE TOUGHNESS PROPERTIES OF FORGED STAINLESS STEEL

    SciTech Connect

    Morgan, M

    2008-04-14

    The fracture toughness properties of Type 21-6-9 stainless steel were measured for forgings in the unexposed, hydrogen-exposed, and tritium-exposed-and-aged conditions. Fracture toughness samples were cut from conventionally-forged and high-energy-rate-forged forward-extruded cylinders and mechanically tested at room temperature using ASTM fracture-toughness testing procedures. Some of the samples were exposed to either hydrogen or tritium gas (340 MPa, 623 K) prior to testing. Tritium-exposed samples were aged for up to seven years and tested periodically in order to measure the effect on fracture toughness of {sup 3}He from radioactive tritium decay. The results show that hydrogen-exposed and tritium-exposed samples had lower fracture- toughness values than unexposed samples and that fracture toughness decreased with increasing decay {sup 3}He content. Forged steels were more resistant to the embrittling effects of tritium and decay {sup 3}He than annealed steels, although their fracture-toughness properties depended on the degree of sensitization that occurred during processing. The fracture process was dominated by microvoid nucleation, growth and coalescence; however, the size and spacing of microvoids on the fracture surfaces were affected by hydrogen and tritium with the lowest-toughness samples having the smallest microvoids and finest spacing.

  5. A single fracture toughness parameter for fibrous composite laminates

    NASA Technical Reports Server (NTRS)

    Poe, C. C., Jr.

    1981-01-01

    A general fracture toughness parameter Qc was previously derived and verified to be a material constant, independent of layup, for centrally cracked boron aluminum composite specimens. The specimens were made with various proportions of 0 and + or - 45 degree plies. A limited amount of data indicated that the ratio Qc/epsilon tuf' where epsilon tuf is the ultimate tensile strain of the fibers, might be a constant for all composite laminates, regardless of material and layup. In that case, a single value of Qc/epsilon tuf could be used to predict the fracture toughness of all fibrous composite laminates from only the elastic constants and epsilon tuf. Values of Qc/epsilon tuf were calculated for centrally cracked specimens made from graphite/polyimide, graphite/epoxy, E glass/epoxy, boron/epoxy, and S glass graphite/epoxy materials with numerous layups. Within ordinary scatter, the data indicate that Qc/epsilon tuf is a constant for all laminates that did not split extensively at the crack tips or have other deviate failure modes.

  6. Gas pressure sintering of silicon nitride to optimize fracture toughness

    SciTech Connect

    Tiegs, T.N.; Nunn, S.D.; Beavers, T.M.; Menchhofer, P.A.; Barker, D.L.; Coffey, D.W.

    1995-06-01

    Gas-pressure sintering (GPS) can be used to densify silicon nitride containing a wide variety of sintering additives. Parameters affecting the sintering behavior include densification temperature, densification time, grain growth temperature, grain growth time and heating rates. The Si{sub 3}N{sub 4}-6% Y{sub 2}O{sub 3}-2% A1{sub 2}O{sub 3} samples sintered to high densities at all conditions used in the present study, whereas the Si{sub 3}N{sub 4}-Sr{sub 2}La{sub 4}Yb{sub 4}(SiO{sub 4}){sub 6}O{sub 2} samples required the highest temperatures and longest times to achieve densities {ge}98 % T. D. The main effect on the fracture toughness for Si{sub 3}N{sub 4}-6% Y{sub 2}O{sub 3}-2% A1{sub 2}O{sub 3} samples was the use of a lower densification temperature, which was 1900C in the present study. For the Si{sub 3}N{sub 4}-Sr{sub 2}La{sub 4}Yb{sub 4}SiO4{sub 4}){sub 6}O{sub 2} composition, fracture toughness was sensitive to and improved by a slower heating rate (10c/min), a lower densification temperature (1900`), a higher grain growth temperature (2000C), and a longer grain growth time (2 h).

  7. Deformation and fracture toughness in high-performance polymers

    SciTech Connect

    Pater, R.H.; Soucek, M.D.; Jang, B.Z.

    1993-12-31

    A systematic study was made of 10 principal high-performance thermoplastics and two semiinterpenetrating polymer networks (semi-IPNs). The fundamental tendency to undergo localized crazing or shear banding, as opposed to a more diffuse homogeneous shear-yielding deformation, was evaluated. Amorphous thermoplastics exhibited crazing as the primary mode of deformation. In contrast, semi-crystalline materials displayed both crazing and shear banding. Increasing the crystallinity increased diffuse shear yielding at the expense of craze growth. Another effect was an enlargement of the deformation zone. Some ordered polymers showed only diffuse shear yielding, whereas others displayed a combination of weak crazes and diffuse shear yielding. For a semi-IPN, increasing the degree of cross-linking decreased crazing, deformation zone size, and fracture toughness of an amorphous thermoplastic. Thus, crystallinity acts like cross-linking in reducing crazing, but, exerts the opposite effect on changing the size of the deformation zone. These results suggest that the reduction in fracture toughness by crystallinity is mainly due to decreased crazing, whereas reduction by cross-linking arises from both decreased crazing and diminished deformation zone. 43 refs., 42 figs., 1 tab.

  8. 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.

  9. Fracture toughness of thick section dissimilar electron beam weld joints

    SciTech Connect

    Kocak, M.; Junghans, E.

    1994-12-31

    Microstructural investigations as well as crack tip opening displacement (CTOD) fracture toughness test based on elastic-plastic fracture mechanics were performed on single pass, full penetration similar and dissimilar electron beam (EB) welds of 40 mm thick 316L type austenitic steel and high alloyed fine tempered martensitic 9Cr 1Mo Nb V (P91 -ASTM A213) steel. The latter modified steel has been developed to fill up the gap between 12Cr steel and austenitic stainless steels with respect to the high temperature properties and better weldability. Furthermore, it shows a small thermal expansion coefficient and is not susceptible to stress corrosion cracking like the austenitic steel. The weldment properties were evaluated by microstructural analysis, microhardness, Charpy V- notch impact, and by newly developed flat microtensile specimens (0.5 mm thick). The dissimilar EB weld metal and HAZ of P91 steel has been shown to be microstructurally and mechanically distinct from both austenitic and martenistic parent metals. The use of microsized rectangular tensile specimens provides unique solution to the problem of the mechanical property determination of the narrow EB weld joint. The HAZ of the 9Cr1Mo steel exhibits extremely poor CTOD toughness properties in as-welded condition at room temperature. The CTOD values obtained were believed to be represent the intrinsic property of this zone, since the distance of the crack tip to the austenitic steel part was too large to receive a stress relaxation effect from low strength side on the crack tip (by accommodating the applied strains in the high toughness, lower strength 316L plate).

  10. Characterization of tensile strength and fracture toughness of nuclear graphite NBG-18 using subsize specimens

    NASA Astrophysics Data System (ADS)

    Yoon, J. H.; Byun, T. S.; Strizak, J. P.; Snead, L. L.

    2011-05-01

    The mechanical properties of NBG-18 nuclear grade graphite were characterized using small specimen test techniques and statistical treatment on the test results. New fracture strength and toughness test techniques were developed to use subsize cylindrical specimens with glued heads and to reuse their broken halves. Three sets of subsize cylindrical specimens of different sizes were tested to obtain tensile fracture strength and fracture toughness. The mean fracture strength decreased as the specimen size increased. The fracture strength data indicate that in the given diameter range the size effect is not significant and much smaller than that predicted by the Weibull moduli estimated for individual specimen groups of the Weibull distribution. Further, no noticeable size effect existed in the fracture toughness data. The mean values of the fracture toughness datasets were in a narrow range of 1.21-1.26 MPa√m.

  11. Assessments of Fracture Toughness of Monolithic Ceramics-SEPB Versus SEVNB Methods

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Gyekenyesi, John P.

    2006-01-01

    Fracture toughness of a total of 13 advanced monolithic ceramics including silicon nitrides, silicon carbide, aluminas, and glass ceramic was determined at ambient temperature by using both single edge precracked beam (SEPB) and single edge v-notched beam (SEVNB) methods. Relatively good agreement in fracture toughness between the two methods was observed for advanced ceramics with flat R-curves; whereas, poor agreement in fracture toughness was seen for materials with rising R-curves. The discrepancy in fracture toughness between the two methods was due to stable crack growth with crack closure forces acting in the wake region of cracks even in SEVNB test specimens. The effect of discrepancy in fracture toughness was analyzed in terms of microstructural feature (grain size and shape), toughening exponent in R-curve, and stable crack growth determined using back-face strain gaging.

  12. Mode II Interlaminar Fracture Toughness and Fatigue Characterization of a Graphite Epoxy Composite Material

    NASA Technical Reports Server (NTRS)

    O'Brien, T. Kevin; Johnston, William M.; Toland, Gregory J.

    2010-01-01

    Mode II interlaminar fracture toughness and delamination onset and growth characterization data were generated for IM7/8552 graphite epoxy composite materials from two suppliers for use in fracture mechanics analyses. Both the fracture toughness testing and the fatigue testing were conducted using the End-notched Flexure (ENF) test. The ENF test for mode II fracture toughness is currently under review by ASTM as a potential standard test method. This current draft ASTM protocol was used as a guide to conduct the tests on the IM7/8552 material. This report summarizes the test approach, methods, procedures and results of this characterization effort.

  13. Effects of constraint on upper shelf fracture toughness

    SciTech Connect

    Joyce, J.A.; Link, R.E.

    1995-12-31

    The upper shelf fracture toughness and tearing resistance of two structural steels, HY-100 and ASTM A533, Gr. B, were determined over a wide range of applied constraint. The constraint conditions were varied by changes in specimen geometry and loading mode. Bend specimens with shallow and deep cracks, compact specimens, and single and double edge notched tension specimens were used in this study. A rotation correction was developed for the single edge notch tension specimen which greatly improved the behavior of the J-R curves determined using this specimen. The experimental results were used to investigate the applicability of the Q and T stress parameters to the correlation of upper shelf initiation toughness, J{sub Ic}, and tearing resistance, T{sub mat}. The J-Q and J-T stress loci, and corresponding plots of material tearing resistance plotted against Q and T, were developed and compared with the expectations of the O`Dowd and Shih and the Betegon and Hancock analyses. The principle conclusions of this work are that J{sub Ic} does not appear to be dependent on T stress or Q while the material tearing resistance, T{sub mat}, is dependent on T stress and Q, with the tearing modulus increasing as constraint decreases.

  14. 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.

  15. Fracture toughness and crack-resistance curve behavior in metallic glass-matrix composites

    SciTech Connect

    Launey, Maximilien E.; Hofmann, Douglas C.; Suh, Jin-Yo; Kozachkov, Henry; Johnson, William L.; Ritchie, Robert O.

    2009-05-26

    Nonlinear-elastic fracture mechanics methods are used to assess the fracture toughness of bulk metallic glass (BMG) composites; results are compared with similar measurements for other monolithic and composite BMG alloys. Mechanistically, plastic shielding gives rise to characteristic resistance?curve behavior where the fracture resistance increases with crack extension. Specifically, confinement of damage by second?phase dendrites is shown to result in enhancement of the toughness by nearly an order of magnitude relative to unreinforced glass.

  16. Application of fracture toughness scaling models to the ductile-to- brittle transition

    SciTech Connect

    Link, R.E.; Joyce, J.A.

    1996-01-01

    An experimental investigation of fracture toughness in the ductile-brittle transition range was conducted. A large number of ASTM A533, Grade B steel, bend and tension specimens with varying crack lengths were tested throughout the transition region. Cleavage fracture toughness scaling models were utilized to correct the data for the loss of constraint in short crack specimens and tension geometries. The toughness scaling models were effective in reducing the scatter in the data, but tended to over-correct the results for the short crack bend specimens. A proposed ASTM Test Practice for Fracture Toughness in the Transition Range, which employs a master curve concept, was applied to the results. The proposed master curve over predicted the fracture toughness in the mid-transition and a modified master curve was developed that more accurately modeled the transition behavior of the material. Finally, the modified master curve and the fracture toughness scaling models were combined to predict the as-measured fracture toughness of the short crack bend and the tension specimens. It was shown that when the scaling models over correct the data for loss of constraint, they can also lead to non-conservative estimates of the increase in toughness for low constraint geometries.

  17. Biaxial loading effects on fracture toughness of reactor pressure vessel steel

    SciTech Connect

    McAfee, W.J.; Bass, B.R.; Bryson, J.W. Jr.; Pennell, W.E.

    1995-03-01

    The preliminary phases of a program to develop and evaluate fracture methodologies for assessing crack-tip constraint effects on fracture toughness of reactor pressure vessel (RPV) steels have been completed by the Heavy-Section Steel Technology (HSST) Program. Objectives were to investigate effect of biaxial loading on fracture toughness, quantify this effect through existing stress-based, dual-parameter, fracture-toughness correlations, or propose and verify alternate correlations. A cruciform beam specimen with 2-D, shallow, through-thickness flaw and a special loading fixture was designed and fabricated. Tests were performed using biaxial loading ratios of 0:1 (uniaxial), 0.6:1, and 1:1 (equi-biaxial). Critical fracture-toughness values were calculated for each test. Biaxial loading of 0.6:1 resulted in a reduction in the lower bound fracture toughness of {approximately}12% as compared to that from the uniaxial tests. The biaxial loading of 1:1 yielded two subsets of toughness values; one agreed well with the uniaxial data, while one was reduced by {approximately}43% when compared to the uniaxial data. Results were evaluated using J-Q theory and Dodds-Anderson (D-A) micromechanical scaling model. The D-A model predicted no biaxial effect, while the J-Q method gave inconclusive results. When applied to the 1:1 biaxial data, these constraint methodologies failed to predict the observed reduction in fracture toughness obtained in one experiment. A strain-based constraint methodology that considers the relationship between applied biaxial load, the plastic zone width in the crack plane, and fracture toughness was formulated and applied successfully to the data. Evaluation of this dual-parameter strain-based model led to the conclusion that it has the capability of representing fracture behavior of RPV steels in the transition region, including the effects of out-of-plane loading on fracture toughness. This report is designated as HSST Report No. 150.

  18. Improving fracture toughness of dental nanocomposites by interface engineering and micromechanics

    PubMed Central

    Chan, K.S.; Lee, Y-D; Nicolella, D. P.; Furman, B. R.; Wellinghoff, S.; Rawls, H.R.

    2007-01-01

    The fracture toughness of dental nanocomposites fabricated by various methods of mixing, silanization, and loadings of nanoparticles had been characterized using fatigue-precracked compact-tension specimens. The fracture mechanisms near the crack tip were characterized using atomic force microscopy (AFM), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The near-tip fracture processes in the nanocomposties were identified to involve several sequences of fracture events, including: (1) particle bridging, (2) debonding at the poles of particle/matrix interface, and (3) crack deflection around the particles. Analytical and finite-element methods were utilized to model the observed sequences of fracture events to identify the source of fracture toughness in the dental nanocomposites. Theoretical results indicated that silanization and nanoparticle loadings improved the fracture toughness of dental nanocomposites by a factor of 2 to 3 through a combination of enhanced interface toughness by silanization, crack deflection, as well as crack bridging. A further increase in the fracture toughness of the nanocomposites can be achieved by increasing the fracture toughness of the matrix, nano-filled particles, or the interface. PMID:18670579

  19. Estimation of fracture toughness of cast stainless steels during thermal aging in LWR systems

    SciTech Connect

    Chopra, O.K. )

    1991-06-01

    A procedure and correlations are presented for predicting the change in fracture toughness of cast stainless steel components due to thermal aging during service in light water rectors (LWRs) at 280--330{degrees}C (535--625{degrees}F). The fracture toughness J-R curve and Charpy-impact energy of aged cast stainless steels are estimated from known mineral in formation. Fracture toughness of a specific cast stainless steel is estimated from the extent and kinetics of thermal embrittlement. The extent of thermal embrittlement is characterized by the room-temperature normalized'' Charpy-impact energy. A correlation for the extent of embrittlement at saturation,'' i.e., the minimum impact energy that would be achieved for the material after long-term aging, is given in terms of a material parameter, {Phi}, which is determined from the chemical composition. The fracture toughness J-R curve for the material is then obtained from correlations between room-temperature Charpy-impact energy and fracture toughness parameters. Fracture toughness as a function of time and temperature of reactor service is estimated from the kinetics of thermal embrittlement, which is determined from chemical composition. A common lower-bound'' J-R curve for cast stainless steels with unknown chemical composition is also defined for a given material specification, ferrite content, and temperature. Examples for estimating impact strength and fracture toughness of cast stainless steel components during reactor service are describes. 24 refs., 39 figs., 2 tabs.

  20. Biaxial loading and shallow-flaw effects on crack-tip constraint and fracture-toughness

    SciTech Connect

    Pennell, W.E.; Bass, B.R.; Bryson, J.W.; McAfee, W.J.; Theiss, T.J.; Rao, M.C.

    1993-12-01

    Uniaxial tests of single-edged notched bend (SENB) specimens with both deep- and shallow-flaws have shown elevated fracture-toughness for the shallow flaws. The elevation in fracture-toughness for shallow flaws has been shown to be the result of reduced constraint at the crack-tip. Biaxial loading has the potential to increase constraint at the crack-tip and thereby reduce some of the shallow-flaw, fracture-toughness elevation. Biaxial fracture-toughness tests have shown that the shallow-flaw, fracture-toughness elevation is reduced but not eliminated by biaxial loading. Dual-parameter, fracture-toughness correlations have been proposed to reflect the effect of crack-tip constraint on fracture-toughness. Test results from the uniaxial and biaxial tests were analyzed using the dual-parameter technology. Discrepancies between analysis results and cleavage initiation site data from fractographic examinations indicate that the analysis models are in need of further refinement. Addition of a precleavage, ductile-tearing element to the analysis model has the potential to resolve the noted discrepancies.

  1. 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.

  2. Fracture Toughness of Advanced Structural Ceramics: Applying ASTM C1421

    DOE PAGESBeta

    Swab, Jeffrey J.; Tice, Jason; Wereszczak, Andrew A.; Kraft, Reuben H.

    2014-11-03

    The three methods of determining the quasi-static Mode I fracture toughness (KIc) (surface crack in flexure – SC, single-edge precracked beam – PB, and chevron notched beam – VB) found in ASTM C1421 were applied to a variety of advanced ceramic materials. All three methods produced valid and comparable KIc values for the Al2O3, SiC, Si3N4 and SiAlON ceramics examined. However, not all methods could successfully be applied to B4C, ZrO2 and WC ceramics due to a variety of material factors. The coarse-grained microstructure of one B4C hindered the ability to observe and measure the precracks generated in the SCmore » and PB methods while the transformation toughening in the ZrO2 prevented the formation of the SC and PB precracks and thus made it impossible to use either method on this ceramic. The high strength and elastic modulus of the WC made it impossible to achieve stable crack growth using the VB method because the specimen stored a tremendous amount of energy prior to fracture. Even though these methods have passed the rigors of the standardization process there are still some issues to be resolved when the methods are applied to certain classes of ceramics. We recommend that at least two of these methods be employed to determine the KIc, especially when a new or unfamiliar ceramic is being evaluated.« less

  3. Acoustic Emission Methodology to Evaluate the Fracture Toughness in Heat Treated AISI D2 Tool Steel

    NASA Astrophysics Data System (ADS)

    Mostafavi, Sajad; Fotouhi, Mohamad; Motasemi, Abed; Ahmadi, Mehdi; Sindi, Cevat Teymuri

    2012-10-01

    In this article, fracture toughness behavior of tool steel was investigated using Acoustic Emission (AE) monitoring. Fracture toughness ( K IC) values of a specific tool steel was determined by applying various approaches based on conventional AE parameters, such as Acoustic Emission Cumulative Count (AECC), Acoustic Emission Energy Rate (AEER), and the combination of mechanical characteristics and AE information called sentry function. The critical fracture toughness values during crack propagation were achieved by means of relationship between the integral of the sentry function and cumulative fracture toughness (KICUM). Specimens were selected from AISI D2 cold-work tool steel and were heat treated at four different tempering conditions (300, 450, 525, and 575 °C). The results achieved through AE approaches were then compared with a methodology proposed by compact specimen testing according to ASTM standard E399. It was concluded that AE information was an efficient method to investigate fracture characteristics.

  4. Effects of Heating Rate on Microstructure and Fracture Toughness of Railway Wheel Steel

    NASA Astrophysics Data System (ADS)

    Ren, Xuechong; Qi, Ji; Gao, Jianyu; Wen, Lei; Jiang, Bo; Chen, Gang; Zhao, Hai

    2016-02-01

    The microstructure and fracture toughness K IC (or K Q) of railway wheel steel with 0.53 wt pct C were studied under various heating rates. The effects of the heating rate on the grain size and the relation between the grain size and the fracture toughness were discussed. The results show that rapid heating not only refines the grains but can also result in more homogeneous grains. The cleavage fracture toughness strongly relates to the grains with larger size. It can be observed that under different heating rates, the fracture toughness K Q increases with decreasing average diameter of the top 5 pct grains D 5. K Q (MPa m1/2) = 194.3-29.8 ln( D 5) when D 5 is in the range of 30 to 73 μm. This result can be interpreted by the cleavage fracture critical event, which is grain-sized crack propagation controlled.

  5. 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.

  6. The fracture toughness of borides formed on boronized cold work tool steels

    SciTech Connect

    Sen, Ugur; Sen, Saduman

    2003-06-15

    In this study, the fracture toughness of boride layers of two borided cold work tool steels have been investigated. Boriding was carried out in a salt bath consisting of borax, boric acid, ferro-silicon and aluminum. Boriding was performed at 850 and 950 deg. C for 2 to 7 h. The presence of boride phases were determined by X-ray diffraction (XRD) analysis. Hardness and fracture toughness of borides were measured via Vickers indenter. Increasing of boriding time and temperature leads to reduction of fracture toughness of borides. Metallographic examination showed that boride layer formed on cold work tool steels was compact and smooth.

  7. Fracture toughness testing of core from the Cambro-Ordovician Section on the Oak Ridge Reservation

    SciTech Connect

    Lemiszki, P.J.; Landes, J.D.

    1996-10-01

    The modified ring test was used to determine the mode I fracture toughness of bedrock cores from the DOE Oak Ridge Reservation in east Tennessee. Low porosity sandstones, limestones, and dolostones from the lower part of the Paleozoic section in Copper Creek and Whiteoak Mountain thrust sheets were sampled. In general, the average mode I fracture toughness decreases from sandstone, dolostone, and limestone. The fracture toughness of the limestones varies between rock units, which is related to different sedimentologic characteristics. Quality of results was evaluated by testing cores of Berea Sandstone and Indiana Limestone, which produced results similar to published results.

  8. Effect of microstructure and notch root radius on fracture toughness of an aluminum metal matrix composite

    NASA Technical Reports Server (NTRS)

    Manoharan, M.; Lewandowski, J. J.

    1989-01-01

    Recent results on the effects of matrix aging condition (matrix temper) and notch root radius on the measured fracture toughness of a SiC particulate reinforced aluminum alloy are reviewed. Stress intensity factors at catastrophic fracture were obtained for both underaged and overaged composites reveal. The linear relation found between apparent fracture toughness and the square root of the notch root radius implies a linear dependence of the crack opening displacement on the notch root radius. The results suggest a strain controlled fracture process, and indicate that there are differences in the fracture micromechanisms of the two aging conditions.

  9. FRACTURE TOUGHNESS OF 9Cr-1MoV AND THERMALLY AGED ALLOY 617 FOR ADVANCED REACTOR APPLICATIONS

    SciTech Connect

    Nanstad, Randy K; Sokolov, Mikhail A; Chen, Xiang

    2012-01-01

    Nickel-base Alloy 617 is being considered as a structural material for application in the secondary heat exchanger of the New Generation Nuclear Plant, a very high temperature gas-cooled reactor. Thermal aging of Alloy 617 plate and welds is being performed with tensile, Charpy impact, and fracture toughness tests conducted at temperatures to 950 C. Results of testing for thermal aging to 5,300 h have been obtained and are presented; varying effects of thermal aging temperature and time on fracture toughness are observed. The 9Cr-1MoV (Grade 91) ferritic steel is a candidate for structural applications in the sodium fast reactor. Fracture toughness testing of unaged Grade 91 steel has been performed to evaluate specimen size effects in preparation for future testing of the material in the thermally aged condition. Results for material in the mill-annealed and heat treated conditions are presented and show that this heat of Grade 91 steel does not indicate a small specimen bias on the fracture toughness Master Curve reference temperature.

  10. Influence of crack depth on the fracture toughness of reactor pressure vessel steel

    SciTech Connect

    Theiss, T.J.; Bryson, J.W.

    1991-01-01

    The Heavy Section Steel Technology Program (HSST) at Oak Ridge National Laboratory (ORNL) is investigating the influence of flaw depth on the fracture toughness of reactor pressure vessel (RPV) steel. Recently, it has been shown that, in notched beam testing, shallow cracks tend to exhibit an elevated toughness as a result of a loss of constraint at the crack tip. The loss of constraint takes place when interaction occurs between the elastic-plastic crack-tip stress field and the specimen surface nearest the crack tip. An increased shallow-crack fracture toughness is of interest to the nuclear industry because probabilistic fracture-mechanics evaluations show that shallow flaws play a dominant role in the probability of vessel failure during postulated pressurized-thermal-shock (PTS) events. Tests have been performed on beam specimens loaded in 3-point bending using unirradiated reactor pressure vessel material (A533 B). Testing has been conducted using specimens with a constant beam depth (W = 94 mm) and within the lower transition region of the toughness curve for A533 B. Test results indicate a significantly higher fracture toughness associated with the shallow flaw specimens compared to the fracture toughness determined using deep-crack (a/W = 0.5) specimens. Test data also show little influence of thickness on the fracture toughness for the current test temperature ({minus}60{degree}C). 21 refs., 5 figs., 3 tabs.

  11. Simplified data reduction methods for the ECT test for mode 3 interlaminar fracture toughness

    NASA Technical Reports Server (NTRS)

    Li, Jian; Obrien, T. Kevin

    1995-01-01

    Simplified expressions for the parameter controlling the load point compliance and strain energy release rate were obtained for the Edge Crack Torsion (ECT) specimen for mode 3 interlaminar fracture toughness. Data reduction methods for mode 3 toughness based on the present analysis are proposed. The effect of the transverse shear modulus, G(sub 23), on mode 3 interlaminar fracture toughness characterization was evaluated. Parameters influenced by the transverse shear modulus were identified. Analytical results indicate that a higher value of G(sub 23) results in a low load point compliance and lower mode 3 toughness estimation. The effect of G(sub 23) on the mode 3 toughness using the ECT specimen is negligible when an appropriate initial delamination length is chosen. A conservative estimation of mode 3 toughness can be obtained by assuming G(sub 23) = G(sub 12) for any initial delamination length.

  12. Fracture Toughness Determination of Cracked Chevron Notched Brazilian Disc Rock Specimen via Griffith Energy Criterion Incorporating Realistic Fracture Profiles

    NASA Astrophysics Data System (ADS)

    Xu, Yuan; Dai, Feng; Zhao, Tao; Xu, Nu-wen; Liu, Yi

    2016-08-01

    The cracked chevron notched Brazilian disc (CCNBD) specimen has been suggested by the International Society for Rock Mechanics to measure the mode I fracture toughness of rocks, and has been widely adopted in laboratory tests. Nevertheless, a certain discrepancy has been observed in results when compared with those derived from methods using straight through cracked specimens, which might be due to the fact that the fracture profiles of rock specimens cannot match the straight through crack front as assumed in the measuring principle. In this study, the progressive fracturing of the CCNBD specimen is numerically investigated using the discrete element method (DEM), aiming to evaluate the impact of the realistic cracking profiles on the mode I fracture toughness measurements. The obtained results validate the curved fracture fronts throughout the fracture process, as reported in the literature. The fracture toughness is subsequently determined via the proposed G-method originated from Griffith's energy theory, in which the evolution of the realistic fracture profile as well as the accumulated fracture energy is quantified by DEM simulation. A comparison between the numerical tests and the experimental results derived from both the CCNBD and the semi-circular bend (SCB) specimens verifies that the G-method incorporating realistic fracture profiles can contribute to narrowing down the gap between the fracture toughness values measured via the CCNBD and the SCB method.

  13. Indentation fracture toughness of sintered silicon carbide in the Palmqvist crack regime

    NASA Technical Reports Server (NTRS)

    Li, Zhuang; Ghosh, Asish; Kobayashi, Albert S.; Bradt, Richard C.

    1989-01-01

    The fracture toughness of a sintered dense alpha-SiC was estimated by the Vickers indentation microfracture method in the low-load Palmqvist crack regime. It was observed that the use of simultaneously obtained Vickers hardnesses does not yield reliable fracture toughness values, nor does application of the median-crack-derived equations. It is necessary to utilize a load-independent, crack-free hardness value with this toughness estimation method. Although several of the curve-fitting equations yield similar toughnesses, it is concluded for the Palmqvist crack system in this alpha-SiC that the Niihara-Morena-Hasselman (1982) equation is the only one which yields fracture toughness values in agreement with conventional measurement techniques.

  14. Fracture toughness of irradiated candidate materials for ITER first wall/blanket structures: Summary report

    SciTech Connect

    Alexander, D.J.; Pawel, J.E.; Grossbeck, M.L.; Rowcliffe, A.F.

    1996-04-01

    Disk compact specimens of candidate materials for first wall/blanket structures in ITER have been irradiated to damage levels of about 3 dpa at nominal irradiation temperatures of either 90 250{degrees}C. These specimens have been tested over a temperature range from 20 to 250{degrees}C to determine J-integral values and tearing moduli. The results show that irradiation at these temperatures reduces the fracture toughness of austenic stainless steels, but the toughness remains quite high. The toughness decreases as the temperature increases. Irradiation at 250{degrees}C is more damaging that at 90{degrees}C, causing larger decreases in the fracture toughness. The ferritic-martensitic steels HT-9 and F82H show significantly greater reductions in fracture toughness that the austenitic stainless steels.

  15. Fracture toughness determination of ceramic and resin-based dental composites.

    PubMed

    Kvam, K

    1992-01-01

    A new method has been developed for Klc determinations of brittle materials with precracks introduced by indentations. A reference glass, five ceramic materials, and one resin-based composite were tested. Knoop hardness indentations were made with a load of 49 N in a line from edge to edge vertical to the long axis on one surface of four-point flexure bars, to make a continuous crack under the indentations. Five specimens of each material were fractured in a four-point bend test with the line of indentations placed in the zone of constant and maximum tensile stress. Separate unfractured specimens were ground and polished to expose and measure the preformed continuous crack. The mean of six crack-depth measurements was used together with the fracture load and the dimensions of the bend specimens to calculate the fracture toughness, Klc of each material. The determined Klc value (x +/- SD) for the reference glass was 0.81 +/- .24 MPa m1/2 and corresponds to previous studies. The resin-based composite material, Silux Plus, had a value of 1.04 +/- 0.14 MPa m1/2. The Klc values (MPa m1/2) were 0.94 +/- 0.31 for Dicor, 1.41 +/- 0.18 for Cerestore, 1.50 +/- 0.29 for NBK-1000, 1.60 +/- 0.17 for Vitadur-N and 2.14 +/- 0.14 for Hi-Ceram. Hi-Ceram had significantly higher Klc values than the other materials. The new method seemed to be of value in determining the fracture toughness of non-metallic dental materials. PMID:1550892

  16. Modeling fracture toughness of functionally graded steels in crack divider configuration

    NASA Astrophysics Data System (ADS)

    Aghazadeh Mohandesi, J.; Nazari, A.; Vishkasogheh, Mehdi Hamid; Abedi, Mohammad

    2010-10-01

    Fracture toughness of functionally graded steels in crack divider configuration has been modeled. By utilizing plain carbon and austenitic stainless steel slices with various thicknesses and arrangements as electroslag remelting electrodes, functionally graded steels were produced. The fracture toughness of the functionally graded steels was found to depend on the type, volume fraction and position of the phases present. According to the area under the stress-strain curve of each layer in the functionally graded composites, a mathematical model has been presented for fracture toughness prediction using the rule of mixtures. In addition, the fracture toughness of the composites has been simulated by the 3D dynamic finite element method. There is good agreement between experimental results and those acquired from the numerical and mathematical models.

  17. Effect of Elevated Temperature and Loading Rate on Delamination Fracture Toughness

    NASA Technical Reports Server (NTRS)

    Reeder, J. R.; Allen, D. H.; Bradley, W. L.

    2003-01-01

    The effects of temperature and loading rate on delamination growth were studied. The delamination fracture toughness of IM7/K3B was measured at 149 C, 177 C, and 204 C. At each temperature the tests were performed with a variety of loading rates so that the delamination initiated over the range of time from 0.5 sec to 24 hrs. The double cantilever beam (DCB) test was used to measure fracture toughness. The results showed that the delamination resistance is a complicated function of both time and temperature with the effect of temperature either increasing or decreasing the fracture toughness depending on the time scale. The results also showed that the fracture toughness changed by as much as a factor of three as the time scale changed over the five orders of magnitude tested.

  18. 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

  19. Fracture toughness of titanium–cement interfaces: effects of fibers and loading angles

    PubMed Central

    Khandaker, Morshed; Utsaha, Khatri Chhetri; Morris, Tracy

    2014-01-01

    Ideal implant–cement or implant–bone interfaces are required for implant fixation and the filling of tissue defects created by disease. Micron- to nanosize osseointegrated features, such as surface roughness, fibers, porosity, and particles, have been fused with implants for improving the osseointegration of an implant with the host tissue in orthopedics and dentistry. The effects of fibers and loading angles on the interface fracture toughness of implant–cement specimens with and without fibers at the interface are not yet known. Such studies are important for the design of a long-lasting implant for orthopedic applications. The goal of this study was to improve the fracture toughness of an implant–cement interface by deposition of micron- to nanosize fibers on an implant surface. There were two objectives in the study: 1) to evaluate the influence of fibers on the fracture toughness of implant–cement interfaces with and without fibers at the interfaces, and 2) to evaluate the influence of loading angles on implant–cement interfaces with and without fibers at the interfaces. This study used titanium as the implant, poly(methyl methacrylate) (PMMA) as cement, and polycaprolactone (PCL) as fiber materials. An electrospinning unit was fabricated for the deposition of PCL unidirectional fibers on titanium (Ti) plates. The Evex tensile test stage was used to determine the interface fracture toughness (KC) of Ti–PMMA with and without PCL fibers at 0°, 45°, and 90° loading angles, referred to in this article as tension, mixed, and shear tests. The study did not find any significant interaction between fiber and loading angles (P>0.05), although there was a significant difference in the KC means of Ti–PMMA samples for the loading angles (P<0.05). The study also found a significant difference in the KC means of Ti–PMMA samples with and without fibers (P<0.05). The results showed that the addition of the micron- to nanosize PCL fibers on Ti improved the

  20. Fracture Toughness of Advanced Structural Ceramics: Applying ASTM C1421

    SciTech Connect

    Swab, Jeffrey J.; Tice, Jason; Wereszczak, Andrew A.; Kraft, Reuben H.

    2014-11-03

    The three methods of determining the quasi-static Mode I fracture toughness (KIc) (surface crack in flexure – SC, single-edge precracked beam – PB, and chevron notched beam – VB) found in ASTM C1421 were applied to a variety of advanced ceramic materials. All three methods produced valid and comparable KIc values for the Al2O3, SiC, Si3N4 and SiAlON ceramics examined. However, not all methods could successfully be applied to B4C, ZrO2 and WC ceramics due to a variety of material factors. The coarse-grained microstructure of one B4C hindered the ability to observe and measure the precracks generated in the SC and PB methods while the transformation toughening in the ZrO2 prevented the formation of the SC and PB precracks and thus made it impossible to use either method on this ceramic. The high strength and elastic modulus of the WC made it impossible to achieve stable crack growth using the VB method because the specimen stored a tremendous amount of energy prior to fracture. Even though these methods have passed the rigors of the standardization process there are still some issues to be resolved when the methods are applied to certain classes of ceramics. We recommend that at least two of these methods be employed to determine the KIc, especially when a new or unfamiliar ceramic is being evaluated.

  1. Improved fracture toughness corrosion-resistant bearing material

    NASA Technical Reports Server (NTRS)

    Bamberger, E. N.; Nahm, A. H.

    1986-01-01

    A development program was performed to establish whether a corrosion-resistant bearing material, such as a 14Cr steel, could be modified to allow carburization, thereby providing the excellent fracture toughness characteristics feasible with this process. The alloy selected for investigation was AMS 5749. Several modifications were made including the addition of a small amount of nickel for austenite stabilization. While some promising results were achieved, the primary objective of an acceptable combination of case hardness and microstructure was not attained. Because the high chromium content presents a serious problem in achieving a viable carburizing cycle, a number of experimental steels having lower chromium contents (8 to 12%) were produced in laboratory quantities and evaluated. The results were basically the same as those initially obtained with the modified AMS 5749. Corrosion tests were performed on AMS 5749, AISI M50, and 52100 bearing steels as well as some of the lower chromium steels. These tests showed that a reduced chromium level (10 to 12%) provided essentially the same corrosion protection as the 14Cr steels.

  2. Fracture toughness of brittle materials determined with chevron notch specimens

    NASA Technical Reports Server (NTRS)

    Shannon, J. L., Jr.; Bursey, R. T.; Munz, D.; Pierce, W. S.

    1980-01-01

    The use of chevron-notch specimens for determining the plane strain fracture toughness (K sub Ic) of brittle materials is discussed. Three chevron-notch specimens were investigated: short bar, short rod, and four-point-bend. The dimensionless stress intensity coefficient used in computing K sub Ic is derived for the short bar specimen from the superposition of ligament-dependent and ligament-independent solutions for the straight through crack, and also from experimental compliance calibrations. Coefficients for the four-point-bend specimen were developed by the same superposition procedure, and with additional refinement using the slice model of Bluhm. Short rod specimen stress intensity coefficients were determined only by experimental compliance calibration. Performance of the three chevron-notch specimens and their stress intensity factor relations were evaluated by tests on hot-pressed silicon nitride and sintered aluminum oxide. Results obtained with the short bar and the four-point-bend specimens on silicon nitride are in good agreement and relatively free of specimen geometry and size effects within the range investigated. Results on aluminum oxide were affected by specimen size and chevron-notch geometry, believed due to a rising crack growth resistance curve for the material. Only the results for the short bar specimen are presented in detail.

  3. Microstructural effects on fracture toughness of polycrystalline ceramics in combined mode I and mode II loading

    NASA Technical Reports Server (NTRS)

    Singh, D.; Shetty, D. K.

    1988-01-01

    Fracture toughness of polycrystalline alumina and ceria partially-stabilized tetragonal zirconia (CeO2-TZP) ceramics were assessed in combined mode I and mode II loading using precracked disk specimens in diametral compression. Stress states ranging from pure mode I, combined mode I and mode II, and pure mode II were obtained by aligning the center crack at specific angles relative to the loading diameter. The resulting mixed-mode fracture toughness envelope showed significant deviation to higher fracture toughness in mode II relative to the predictions of the linear elastic fracture mechanics theory. Critical comparison with corresponding results on soda-lime glass and fracture surface observations showed that crack surface resistance arising from grain interlocking and abrasion was the main source of the increased fracture toughness in mode II loading of the polycrystalline ceramics. The normalized fracture toughness for pure mode II loading, (KII/KIc), increased with increasing grain size for the CeO2-TZP ceramics. Quantitative fractography confirmed an increased percentage of transgranular fracture of the grains in mode II loading.

  4. Fracture toughness of plasma-sprayed thermal barrier ceramics: Influence of processing, microstructure, and thermal aging

    SciTech Connect

    Dwivedi, Gopal; Viswanathan, Vaishak; Sampath, Sanjay; Shyam, Amit; Lara-Curzio, Edgar

    2014-06-09

    Fracture toughness has become one of the dominant design parameters that dictates the selection of materials and their microstructure to obtain durable thermal barrier coatings (TBCs). Much progress has been made in characterizing the fracture toughness of relevant TBC compositions in bulk form, and it has become apparent that this property is significantly affected by process-induced microstructural defects. In this investigation, a systematic study of the influence of coating microstructure on the fracture toughness of atmospheric plasma sprayed (APS) TBCs has been carried out. Yttria partially stabilized zirconia (YSZ) coatings were fabricated under different spray process conditions inducing different levels of porosity and interfacial defects. Fracture toughness was measured on free standing coatings in as-processed and thermally aged conditions using the double torsion technique. Results indicate significant variance in fracture toughness among coatings with different microstructures including changes induced by thermal aging. Comparative studies were also conducted on an alternative TBC composition, Gd2Zr2O7 (GDZ), which as anticipated shows significantly lower fracture toughness compared to YSZ. Furthermore, the results from these studies not only point towards a need for process and microstructure optimization for enhanced TBC performance but also a framework for establishing performance metrics for promising new TBC compositions.

  5. Fracture toughness of plasma-sprayed thermal barrier ceramics: Influence of processing, microstructure, and thermal aging

    DOE PAGESBeta

    Dwivedi, Gopal; Viswanathan, Vaishak; Sampath, Sanjay; Shyam, Amit; Lara-Curzio, Edgar

    2014-06-09

    Fracture toughness has become one of the dominant design parameters that dictates the selection of materials and their microstructure to obtain durable thermal barrier coatings (TBCs). Much progress has been made in characterizing the fracture toughness of relevant TBC compositions in bulk form, and it has become apparent that this property is significantly affected by process-induced microstructural defects. In this investigation, a systematic study of the influence of coating microstructure on the fracture toughness of atmospheric plasma sprayed (APS) TBCs has been carried out. Yttria partially stabilized zirconia (YSZ) coatings were fabricated under different spray process conditions inducing different levelsmore » of porosity and interfacial defects. Fracture toughness was measured on free standing coatings in as-processed and thermally aged conditions using the double torsion technique. Results indicate significant variance in fracture toughness among coatings with different microstructures including changes induced by thermal aging. Comparative studies were also conducted on an alternative TBC composition, Gd2Zr2O7 (GDZ), which as anticipated shows significantly lower fracture toughness compared to YSZ. Furthermore, the results from these studies not only point towards a need for process and microstructure optimization for enhanced TBC performance but also a framework for establishing performance metrics for promising new TBC compositions.« less

  6. The effects of specimen geometry and size on the fracture toughness of nuclear graphites

    SciTech Connect

    Romanoski, G.R.; Burchell, T.D.

    1991-01-01

    In a joint Oak Ridge National Laboratory (ORNL)/Japan Atomic Energy Research Institute (JAERI) study, various fracture toughness techniques were applied to Toyo Tanso grade IG-110 graphite to establish if specimen geometry influences on fracture toughness. The test geometries investigated were: compact tension (CT), disc compact tension (DCT), short rod (SR), chevron-notched short-red (CNSR), cylindrical bend specimen (BS), and centrally slotted disc (CSD). Specimen geometries which allow slow crack propagation, such as the CNSR and CT, yielded higher fracture toughness values than those where fracture is very rapid, e.g., the CSD. In a further ORNL study, the CNSR specimen geometry was selected to investigate the effect of specimen size on fracture toughness. Three specimen sizes and three grades of graphite were examined: Great Lakes Carbon grade H-451, Stackpole grade 2020, and Toyo Tanso grade IG-110. Grade H-451 was the toughest graphite, while Stackpole 2020 was the least tough. Fracture toughness increased with increasing specimen size for all graphites tested. This result was attributed to rising R-curve behavior. 13 refs., 8 figs., 3 tabs.

  7. Microstructure and Origin of Hot-Work Tool Steel Fracture Toughness Deviation

    NASA Astrophysics Data System (ADS)

    Podgornik, Bojan; Leskovšek, Vojteh

    2013-12-01

    Dies and tools used in hot metal forming are exposed to elevated temperatures and high contact pressures, and therefore to wear and fatigue. Fracture toughness is thus one of the main material properties used when selecting and optimizing heat treatment of tools. However, fracture toughness data alone is not sufficient and need to be supported by other material properties and features. The aim of the present research work was to correlate fracture toughness properties of hot-work tool steel, especially its variation to the local microstructure, microhardness, and composition and to establish methodology for proper evaluation of tool steel's fracture toughness. Research was performed on H11-type hot-work tool steel specimens, heat treated under the same conditions but displaying greatly different fracture toughness. Results show that the presence of any weak point, either in a form of non-metallic inclusions and/or large undissolved eutectic carbide clusters, located in the region of positive segregation with high microhardness will lead to considerable reduction in fracture toughness.

  8. Biaxial loading and shallow-flaw effects on crack-tip constraint and fracture-toughness

    SciTech Connect

    Pennell, W.E.; Bass, B.R.; Bryson, J.W.; McAfee, W.J.; Theiss, T.J.; Rao, M.C.

    1994-04-01

    Uniaxial tests of single-edged notched bend (SENB) specimens with both deep- and shallow-flaws have shown elevated fracturetoughness for the shallow flaws. The elevation in fracture-toughness for shallow flaws has been shown to be the result of reduced constraint at the crack-tip. Biaxial loading has the potential to increase constraint at the crack-tip and thereby reduce some of the shallow-flaw, fracture-toughness elevation. Biaxial fracture-toughness tests have shown that the shallow-flaw, fracture-toughness elevation is reduced but not eliminated by biaxial loading. Dual-parameter, fracture-toughness correlations have been proposed to reflect the effect of crack-tip constraint on fracture-toughness. Test results from the uniaxial and biaxial tests were analyzed using the dual-parameter technology. Discrepancies between analysis results and cleavage initiation site data from fractographic examinations indicate that the analysis models are in need of further refinement. Addition of a precleavage, ductile-tearing element to the analysis model has the potential to resolve the noted discrepancies.

  9. Fracture toughness and fracture behavior of SA508-III steel at different temperatures

    NASA Astrophysics Data System (ADS)

    Liu, Jia-hua; Wang, Lei; Liu, Yang; Song, Xiu; Luo, Jiong; Yuan, Dan

    2014-12-01

    The fracture toughness of SA508-III steel was studied in the temperature range from room temperature to 320°C using the J-integral method. The fracture behavior of the steel was also investigated. It was found that the conditional fracture toughness ( J Q) of the steel first decreased and then increased with increasing test temperature. The maximum and minimum values of J Q were 517.4 kJ/m2 at 25°C and 304.5 kJ/m2 at 180°C, respectively. Dynamic strain aging (DSA) was also observed to occur when the temperature exceeded 260°C with a certain strain rate. Both the dislocation density and the number of small dislocation cells effectively increased because of the occurrence of DSA; as a consequence, crack propagation was more strongly inhibited in the steel. Simultaneously, an increasing number of fine carbides precipitated under high stress at temperatures greater than 260°C. Thus, the deformation resistance of the steel was improved and the J Q was enhanced.

  10. Microstructure and fracture toughness of Mn-stabilized cubic titanium trialuminide

    NASA Astrophysics Data System (ADS)

    Zbroniec, Leszek Ireneusz

    This thesis project is related to the fracture toughness aspects of the mechanical behavior of the selected Mn-modified cubic Ll2 titanium trialuminicles. Fracture toughness was evaluated using two specimen types: Single-Edge-Precracked-Beam (SEPB) and Chevron-Notched-Beam (CNB). The material tested was in cast, homogenized and HIP-ed condition. In the preliminary stage of the project due to lack of the ASTM Standard for fracture toughness testing of the chevron-notched specimens in bending the analyses of the CNB configuration were done to establish the optimal chevron notch dimensions. Two types of alloys were investigated: (a) boron-free and boron doped low-Mn (9at.% Mn), as well as (b) boron-free and boron-doped high-Mn (14at.% Mn). Toughness was investigated in the temperature range from room temperature to 1000°C and was calculated from the maximum load. It has been found that toughness of coarse-grained "base" 9Mn-25Ti alloy exhibits a broad peak at the 200--500°C temperature range and then decreases with increasing temperature, reaching its room temperature value at 10000°C. However, the work of fracture (gammaWOF) and the stress intensity factor calculated from it (KIWOF) increases continuously with increasing temperature. Also the fracture mode dependence on temperature has been established. To understand the effect of environment on the fracture toughness of coarse-grained "base", boron-free 9Mn-25Ti alloy, the tests were carried out in vacuum (˜1.3 x 10-5 Pa), argon, oxygen, water and liquid nitrogen. It has been shown that fracture toughness at ambient temperature is not affected by the environments containing moisture (water vapor). It seems that at ambient temperatures these materials are completely immune to the water-vapor hydrogen embrittlement and their cause of brittleness is other than environment. To explore the influence of the grain size on fracture toughness the fracture toughness tests were also performed on the dynamically

  11. The effect of temperature on the fracture toughness of Weldalite(TM) 049

    NASA Technical Reports Server (NTRS)

    Lach, Cynthia L.; Gangloff, Richard P.

    1991-01-01

    The uncertain effect of temperature is characterized on the deformation and fracture behavior of Weldalite(TM) 049 from cryogenic to elevated temperatures. Fracture resistance is measured and the determination of fracture mechanisms emphasized, including slip plane cracking, high angle boundary delamination, subgrain boundary cracking, and microvoid coalescence. Microstructure is controlled to produce either predominantly T(sub 1) or T(sub 1) + delta (after Blankenship and Starke) and to examine the effect of dislocation-precipitate interaction on fracture toughness.

  12. Factors influencing the Mode I interlaminar fracture toughness of a rubber toughened thermoplastic matrix composite

    NASA Technical Reports Server (NTRS)

    Parker, D. S.; Yee, A. F.

    1989-01-01

    The use of a rubber modified thermoplastic resin has been investigated as a method to improve the Mode I interlaminar fracture toughness of a unidirectional continuous carbon fiber composite. Test results show that the improvement in the fracture toughness is less than expected due to rubber particle agglomeration, solvent and molding induced crystallization of the matrix and poor fiber/matrix adhesion. The plastic zone in composites utilizing tough matrices can extend well beyond a single interfibrillar spacing. However, the development of the plastic zone is limited due to the failure of the fiber/matrix interface. In order to fully evaluate the potential of tough composites using toughened matrices, any improvement made in the matrix toughness must be coupled with improvements in the fiber/matrix adhesion.

  13. Fracture toughness of irradiated candidate materials for ITER first wall/blanket structures

    SciTech Connect

    Alexander, D.J.; Pawel, J.E.; Grossbeck, M.L.; Rowcliffe, A.F.; Shiba, Kiyoyuki

    1994-12-31

    Disk compact specimens of candidate materials for first wall/blanket structures in ITER have been irradiated to damage levels of about 3 dpa at nominal irradiation temperatures of either 90 or 250{degrees}C. These specimens have been tested over a temperature range from 20 to 250{degrees}C to determine J-integral values and tearing moduli. The results show that irradiation at these temperatures reduces the fracture toughness of austenitic stainless steels, but the toughness remains quite high. The toughness decreases as the test temperature increases. Irradiation at 250{degrees}C is more damaging than at 90{degrees}C, causing larger decreases in the fracture toughness. Ferritic-martensitic steels are embrittled by the irradiation, and show the lowest toughness at room temperature.

  14. Ab initio-based fracture toughness estimates and transgranular traction-separation modelling of zirconium hydrides

    NASA Astrophysics Data System (ADS)

    Olsson, P. A. T.; Kese, K.; Kroon, M.; Alvarez Holston, A.-M.

    2015-06-01

    In this work we report the results of an ab initio study of the transgranular fracture toughness and cleavage of brittle zirconium hydrides. We use the Griffith-Irwin relation to assess the fracture toughness using calculated surface energy and estimated isotropic Voigt-Reuss-Hill averages of the elastic constants. The calculated fracture toughness values are found to concur well with experimental data, which implies that fracture is dominated by cleavage failure. To investigate the cleavage energetics, we model the decohesion process. To describe the interplanar interaction we adopt Rose’s universal binding energy relation, which is found to reproduce the behaviour accurately. The modelling shows that the work of fracture and ductility decreases with increasing hydrogen content.

  15. THE EFFECT OF STRAIN RATE ON FRACTURE TOUGHNESS OF HUMAN CORTICAL BONE: A FINITE ELEMENT STUDY

    PubMed Central

    Ural, Ani; Zioupos, Peter; Buchanan, Drew; Vashishth, Deepak

    2011-01-01

    Evaluating the mechanical response of bone under high loading rates is crucial to understanding fractures in traumatic accidents or falls. In the current study, a computational approach based on cohesive finite element modeling was employed to evaluate the effect of strain rate on fracture toughness of human cortical bone. Two-dimensional compact tension specimen models were simulated to evaluate the change in initiation and propagation fracture toughness with increasing strain rate (range: 0.08 to 18 s−1). In addition, the effect of porosity in combination with strain rate was assessed using three-dimensional models of microcomputed tomography-based compact tension specimens. The simulation results showed that bone’s resistance against the propagation of fracture decreased sharply with increase in strain rates up to 1 s−1 and attained an almost constant value for strain rates larger than 1 s−1. On the other hand, initiation fracture toughness exhibited a more gradual decrease throughout the strain rates. There was a significant positive correlation between the experimentally measured number of microcracks and the fracture toughness found in the simulations. Furthermore, the simulation results showed that the amount of porosity did not affect the way initiation fracture toughness decreased with increasing strain rates, whereas it exacerbated the same strain rate effect when propagation fracture toughness was considered. These results suggest that strain rates associated with falls lead to a dramatic reduction in bone’s resistance against crack propagation. The compromised fracture resistance of bone at loads exceeding normal activities indicates a sharp reduction and/or absence of toughening mechanisms in bone during high strain conditions associated with traumatic fracture. PMID:21783112

  16. The development of in situ fracture toughness evaluation techniques in hydrogen environment

    SciTech Connect

    Wang, John Jy-An; Ren, Fei; Tan, Tin; Liu, Ken

    2014-12-19

    Reliability of hydrogen pipelines and storage tanks is significantly influenced by the mechanical performance of the structural materials exposed in the hydrogen environment. Fracture behavior and fracture toughness are of specific interest since they are relevant to many catastrophic failures. However, many conventional fracture testing techniques are difficult to be realized under the presence of hydrogen. Thus it is desired to develop novel in situ techniques to study the fracture behavior of structural materials in hydrogen environments. In this study, special testing apparatus were designed to facilitate in situ fracture testing in H2. A torsional fixture was developed to utilize an emerging fracture testing technique, Spiral Notch Torsion Test (SNTT). The design concepts will be discussed. Preliminary in situ testing results indicated that the exposure to H2 significantly reduces the fracture toughness of 4340 high strength steels by up to 50 percent. Furthermore, SNTT tests conducted in air demonstrated a significant fracture toughness reduction in samples subject to simulated welding heat treatment using Gleeble, which illustrated the effect of welding on the fracture toughness of this material.

  17. The development of in situ fracture toughness evaluation techniques in hydrogen environment

    DOE PAGESBeta

    Wang, John Jy-An; Ren, Fei; Tan, Tin; Liu, Ken

    2014-12-19

    Reliability of hydrogen pipelines and storage tanks is significantly influenced by the mechanical performance of the structural materials exposed in the hydrogen environment. Fracture behavior and fracture toughness are of specific interest since they are relevant to many catastrophic failures. However, many conventional fracture testing techniques are difficult to be realized under the presence of hydrogen. Thus it is desired to develop novel in situ techniques to study the fracture behavior of structural materials in hydrogen environments. In this study, special testing apparatus were designed to facilitate in situ fracture testing in H2. A torsional fixture was developed to utilizemore » an emerging fracture testing technique, Spiral Notch Torsion Test (SNTT). The design concepts will be discussed. Preliminary in situ testing results indicated that the exposure to H2 significantly reduces the fracture toughness of 4340 high strength steels by up to 50 percent. Furthermore, SNTT tests conducted in air demonstrated a significant fracture toughness reduction in samples subject to simulated welding heat treatment using Gleeble, which illustrated the effect of welding on the fracture toughness of this material.« less

  18. Fracture and fracture toughness of nanopolycrystalline metals produced by severe plastic deformation

    PubMed Central

    Hohenwarter, A.; Pippan, R.

    2015-01-01

    The knowledge of the fracture of bulk metallic materials developed in the last 50 years is mostly based on materials having grain sizes, d, in the range of some micrometres up to several hundred micrometres regarding the possibilities of classical metallurgical methods. Nowadays, novel techniques provide access to much smaller grain sizes, where severe plastic deformation (SPD) is one of the most significant techniques. This opens the door to extend basic research in fracture mechanics to the nanocrystalline (NC) grain size regime. From the technological point of view, there is also the necessity to evaluate standard fracture mechanics data of these new materials, such as the fracture toughness, in order to allow their implementation in engineering applications. Here, an overview of recent results on the fracture behaviour of several different ultrafine-grained (d<1 μm) and NC (d<100 nm) metals and alloys covering examples of body- and face-centred cubic structures produced by SPD will be given. PMID:25713459

  19. Effect of tritium and decay helium on the fracture toughness properties of stainless steel weldments

    SciTech Connect

    Morgan, M. J.; West, S.; Tosten, M. H.

    2008-07-15

    J-Integral fracture toughness tests were conducted on tritium-exposed-and- aged Types 304L and 21-6-9 stainless steel weldments in order to measure the combined effects of tritium and its decay product, helium-3 on the fracture toughness properties. Initially, weldments have fracture toughness values about three times higher than base-metal values. Delta-ferrite phase in the weld microstructure improved toughness provided no tritium was present in the microstructure. After a tritium-exposure-and-aging treatment that resulted in {approx}1400 atomic parts per million (appm) dissolved tritium, both weldments and base metals had their fracture toughness values reduced to about the same level. The tritium effect was greater in weldments (67 % reduction vs. 37% reduction) largely because the ductile discontinuous delta-ferrite phase was embrittled by tritium and decay helium. For both base metals and weldments, fracture toughness values decreased with increasing decay helium content in the range tested (50-800 appm). (authors)

  20. TRITIUM AND DECAY HELIUM EFFECTS ON THE FRACTURE TOUGHNESS PROPERTIES OF STAINLESS STEEL WELDMENTS

    SciTech Connect

    Morgan, M; Scott West, S; Michael Tosten, M

    2007-08-31

    J-Integral fracture toughness tests were conducted on tritium-exposed-and-aged Types 304L and 21-6-9 stainless steel weldments in order to measure the combined effects of tritium and its decay product, helium-3 on the fracture toughness properties. Initially, weldments have fracture toughness values about three times higher than base-metal values. Delta-ferrite phase in the weld microstructure improved toughness provided no tritium was present in the microstructure. After a tritium-exposure-and-aging treatment that resulted in {approx}1400 atomic parts per million (appm) dissolved tritium, both weldments and base metals had their fracture toughness values reduced to about the same level. The tritium effect was greater in weldments (67 % reduction vs. 37% reduction) largely because the ductile discontinuous delta-ferrite interfaces were embrittled by tritium and decay helium. Fracture toughness values decreased for both base metals and weldments with increasing decay helium content in the range tested (50-200 appm).

  1. Fracture Toughness Measurements and Assessment of Thin Walled Conduit Alloys in a Cicc Application

    NASA Astrophysics Data System (ADS)

    Walsh, R. P.; Han, K.; Toplosky, V. J.

    2008-03-01

    The Series-Connected Hybrid Magnets under construction at the NHMFL use Cable-in-Conduct-Conductor (CICC) technology. The 4 K mechanical properties of the conduit are extremely important to the performance and reliability of the magnets. We have measured tensile and fracture toughness of two candidate conduit alloys (Haynes 242 and modified 316LN) in various metallurgical states, with emphasis on the final state of production. To assess the material in its final production state, non-standard specimens are removed directly from the round-corner rectangular conduit and tested after exposure to a simulated Nb3Sn reaction heat treatment. Non-standard middle-tension (MT) fracture toughness specimens enable toughness evaluation of the base metal, welds and weld/base transitional region in the as-fabricated conduit with final dimensions not suitable for conventional fracture toughness specimens. Although fracture toughness tests of the thin walled conduit fail to meet ASTM test validity requirements they provide a qualitative evaluation and estimate of the fracture toughness of the conduit and the welds.

  2. FRACTURE TOUGHNESS MEASUREMENTS AND ASSESSMENT OF THIN WALLED CONDUIT ALLOYS IN A CICC APPLICATION

    SciTech Connect

    Walsh, R. P.; Han, K.; Toplosky, V. J.

    2008-03-03

    The Series-Connected Hybrid Magnets under construction at the NHMFL use Cable-in-Conduct-Conductor (CICC) technology. The 4 K mechanical properties of the conduit are extremely important to the performance and reliability of the magnets. We have measured tensile and fracture toughness of two candidate conduit alloys (Haynes 242 and modified 316LN) in various metallurgical states, with emphasis on the final state of production. To assess the material in its final production state, non-standard specimens are removed directly from the round-corner rectangular conduit and tested after exposure to a simulated Nb{sub 3}Sn reaction heat treatment. Non-standard middle-tension (MT) fracture toughness specimens enable toughness evaluation of the base metal, welds and weld/base transitional region in the as-fabricated conduit with final dimensions not suitable for conventional fracture toughness specimens. Although fracture toughness tests of the thin walled conduit fail to meet ASTM test validity requirements they provide a qualitative evaluation and estimate of the fracture toughness of the conduit and the welds.

  3. Fracture-tough, corrosion-resistant bearing steels

    NASA Technical Reports Server (NTRS)

    Olson, Gregory B.

    1990-01-01

    The fundamental principles allowing design of stainless bearing steels with enhanced toughness and stress corrosion resistance has involved both investigation of basic phenomena in model alloys and evaluation of a prototype bearing steel based on a conceptual design exercise. Progress in model studies has included a scanning Auger microprobe (SAM) study of the kinetics of interfacial segregation of embrittling impurities which compete with the kinetics of alloy carbide precipitation in secondary hardening steels. These results can define minimum allowable carbide precipitation rates and/or maximum allowable free impurity contents in these ultrahigh strength steels. Characterization of the prototype bearing steel designed to combine precipitated austenite transformation toughening with secondary hardening shows good agreement between predicted and observed solution treatment response including the nature of the high temperature carbides. An approximate equilibrium constraint applied in the preliminary design calculations to maintain a high martensitic temperature proved inadequate, and the solution treated alloy remained fully austenitic down to liquid nitrogen temperature rather than transforming above 200 C. The alloy can be martensitically transformed by cryogenic deformation, and material so processed will be studied further to test predicted carbide and austenite precipitation behavior. A mechanistically-based martensitic kinetic model was developed and parameters are being evaluated from available kinetic data to allow precise control of martensitic temperatures of high alloy steels in future designs. Preliminary calculations incorporating the prototype stability results suggest that the transformation-toughened secondary-hardening martensitic-stainless design concept is still viable, but may require lowering Cr content to 9 wt. pct. and adding 0.5 to 1.0 wt. pct. Al. An alternative design approach based on strain-induced martensitic transformation during

  4. Effects of tensile loading on upper shelf fracture toughness

    SciTech Connect

    Joyce, J.A.; Link, R.E.

    1994-03-01

    Constraint has been an important consideration in fracture mechanics from the earliest work that was done to develop the 1974 version of the ASTM Standard E399. O`Dowd and Shih (1991) have proposed that the difference in crack tip stress fields can be quantified in terms of a field quantity that they have call Q. The Q quantity is a function of J, the crack shape and size, the structural geometry, mode of loading and on the level of deformation and can only be calculated from a high resolution elastic-plastic computational analysis. A similar, simpler, but more controversial approach has been suggested by Betegon and Hancock (1991), who use the non-singular term of the elastic, crack singularity solution, called the T-Stress, as a measure of elastic-plastic crack tip constraint. The objective of this work is to develop some upper shelf, elastic-plastic experimental results to attempt to investigate the applicability of the Q and T stress parameters to the correlation of upper shelf initiation toughness and J resistance curves. The first objective was to obtain upper shelf J resistance curves, J{sub Ic}, and tearing resistance results for a range of applied constraint. The J-Q and J-T stress loci were developed and compared with the expectations of the O`Dowd and Shih and the Betegon and Hancock analyses. Constraint was varied by changing the crack length and also by changing the mode of loading from bending to predominantly tensile. The principle conclusions of this work are that J{sub Ic} does not appear to be dependent on T stress or Q while the material tearing resistance is dependent on T stress and Q, with the tearing modulus increasing as constraint decreases.

  5. Dependence of fracture toughness of molybdenum laser welds on processing parameters and in-situ oxygen gettering

    SciTech Connect

    Pope, L.E.; Jellison, J.L.

    1980-01-01

    Fracture toughness properties have been determined for laser welds in different grades of molybdenum. The fracture toughness of welds in sintered molybdenum was consistently less than the fracture toughness of welds in vacuum arc remelted molybdenum. These differences cannot be attributed to oxygen content, since the oxygen level was nominally the same for all grades of molybdenum examined in this program. Alloy additions of titanium by means of physically deposited coatings significantly improved the fracture toughness of welds in sintered molybdenum, whereas titanium additions to welds in vacuum arc remelted molybdenum decreased the fracture toughness slightly. Pulsed laser welds exhibited fine columnar structures and, in the case of sintered molybdenum, superior fracture toughness when compared with continuous wave laser welds. 6 figures, 3 tables.

  6. The effect of strain rate on fracture toughness of human cortical bone: a finite element study.

    PubMed

    Ural, Ani; Zioupos, Peter; Buchanan, Drew; Vashishth, Deepak

    2011-10-01

    Evaluating the mechanical response of bone under high loading rates is crucial to understanding fractures in traumatic accidents or falls. In the current study, a computational approach based on cohesive finite element modeling was employed to evaluate the effect of strain rate on fracture toughness of human cortical bone. Two-dimensional compact tension specimen models were simulated to evaluate the change in initiation and propagation fracture toughness with increasing strain rate (range: 0.08-18 s(-1)). In addition, the effect of porosity in combination with strain rate was assessed using three-dimensional models of micro-computed tomography-based compact tension specimens. The simulation results showed that bone's resistance against the propagation of a crack decreased sharply with increase in strain rates up to 1 s(-1) and attained an almost constant value for strain rates larger than 1 s(-1). On the other hand, initiation fracture toughness exhibited a more gradual decrease throughout the strain rates. There was a significant positive correlation between the experimentally measured number of microcracks and the fracture toughness found in the simulations. Furthermore, the simulation results showed that the amount of porosity did not affect the way initiation fracture toughness decreased with increasing strain rates, whereas it exacerbated the same strain rate effect when propagation fracture toughness was considered. These results suggest that strain rates associated with falls lead to a dramatic reduction in bone's resistance against crack propagation. The compromised fracture resistance of bone at loads exceeding normal activities indicates a sharp reduction and/or absence of toughening mechanisms in bone during high strain conditions associated with traumatic fracture. PMID:21783112

  7. Mechanical properties and fracture toughness of rail steels and thermite welds at low temperature

    NASA Astrophysics Data System (ADS)

    Wang, Yuan-qing; Zhou, Hui; Shi, Yong-jiu; Feng, Bao-rui

    2012-05-01

    Brittle fracture occurs frequently in rails and thermite welded joints, which intimidates the security and reliability of railway service. Railways in cold regions, such as Qinghai-Tibet Railway, make the problem of brittle fracture in rails even worse. A series of tests such as uniaxial tensile tests, Charpy impact tests, and three-point bending tests were carried out at low temperature to investigate the mechanical properties and fracture toughness of U71Mn and U75V rail steels and their thermite welds. Fracture micromechanisms were analyzed by scanning electron microscopy (SEM) on the fracture surfaces of the tested specimens. The ductility indices (percentage elongation after fracture and percentage reduction of area) and the toughness indices (Charpy impact energy A k and plane-strain fracture toughness K IC) of the two kinds of rail steels and the corresponding thermite welds all decrease as the temperature decreases. The thermite welds are more critical to fracture than the rail steel base metals, as indicated by a higher yield-to-ultimate ratio and a much lower Charpy impact energy. U71Mn rail steel is relatively higher in toughness than U75V, as demonstrated by larger A k and K IC values. Therefore, U71Mn rail steel and the corresponding thermite weld are recommended in railway construction and maintenance in cold regions.

  8. Significance of locally intensified strain aging to the fracture toughness of welded steel structures

    SciTech Connect

    Dawes, M.G.

    1995-12-31

    A review of past studies shows that tests on specimens notched after welding can give overestimates of the fracture toughness that occurs at the tips of flaws present during welding. This situation results from locally intensified straining and aging embrittlement (LISAE), which has been shown to trigger low stress brittle fractures in both notched and welded wide plate tension tests, and welded structures in service. Although the relative susceptibilities of steels to strain aging embrittlement are sometimes assessed by testing bulk strained and aged samples, the results of such tests may be optimistic. A summary is given of work to develop a fracture toughness test method for LISAE. The new test will give increased confidence and accuracy in fracture assessments, be of use in selecting tough materials, and aid the development of materials that are resistant to LISAE.

  9. Fracture toughness of irradiated Zr-2.5Nb pressure tube from Indian PHWR

    NASA Astrophysics Data System (ADS)

    Shah, Priti Kotak; Dubey, J. S.; Shriwastaw, R. S.; Dhotre, M. P.; Bhandekar, A.; Pandit, K. M.; Anantharaman, S.; Singh, R. N.; Chakravartty, J. K.

    2015-03-01

    Fracture toughness of irradiated Zr-2.5Nb alloy pressure tube, fabricated by the cold pilgering and stress relieving route, was evaluated using disk compact tension type specimens. These specimens were punched out from the irradiated pressure tube (S-07), which was in service for about 8 effective full power years of reactor operation in the Kakrapar Atomic Power Station-2 (KAPS-2). The tests were carried out remotely inside a lead shielded enclosure. Crack growth during the test was measured using the direct current potential drop technique. The irradiated pressure tube showed low fracture toughness at 25 °C. The fracture toughness increased with increase in temperature up to 250 °C but was practically unaffected with further increase in temperature up to 300 °C. This paper discusses the fracture behavior of irradiated Indian pressure tube material and compares it with other data available.

  10. Fracture toughness evaluation of fusion reactor structural steels at low temperatures by small punch tests

    NASA Astrophysics Data System (ADS)

    Misawa, T.; Nagata, S.; Aoki, N.; Ishizaka, J.; Hamaguchi, Y.

    1989-12-01

    A small punch (SP) test using miniaturized specimens has been performed for cryogenic austenitic steels at 4.2, 77 and 293 K to evaluate fracture toughness in a fusion material program. An SP testing cryostat for load versus deflection curve measurements has been successfully constructed. A universal relationship between valid fracture toughness, JIC, and equivalent fracture strain, ¯ge qf, for austenitic steels at different test temperatures has been confirmed and empirical parameters for that relation have been determined using a linear regression model. A linear correlation between valid JIC and ¯ge qf has been clarified for austenitic steels at low temperatures, where the regression coefficient is found to be 845 kJ/m 2. Using the results of the SP test above room temperature, a new attempt at statistical analysis has been proposed to estimate the relative change in fracture toughness due to neutron irradiation.

  11. Extrapolation of Fracture Toughness Data for HT9 Irradiated at 360-390°C

    SciTech Connect

    Gelles, David S.; Kurtz, Richard J.

    2007-05-01

    Following irradiation in the FFTF-AC01 test at 360°C to 5.5 x 1022 n/cm2, two HT9 samples tested at 30°C were measured to have fracture toughness levels of 28.2 and 31.9 MPa m1/2, respectively, whereas a third identical specimen tested at 205°C gave 126 MPa m1/2. Based on testing of notched tensile specimens from the same irradiation test, the low toughness was a result of brittle fracture. A similar low level of toughness has also been demonstrated in HT9 following irradiation at 250°C and therefore such behavior is reproducible. Using ASTM Standard E1921-02, which characterizes the fracture toughness of ferritic steels that experience onset of cleavage cracking at instabilities, it is shown that these data can be analyzed by a Master Curve approach, and that the trend of the fracture toughness over a wider range of temperatures can be estimated. Master Curve analysis demonstrates that toughness will remain low over a wide range of temperatures near 30°C, but will degrade only slightly when temperatures drop to –10°C.

  12. Process development for 9Cr nanostructured ferritic alloy (NFA) with high fracture toughness

    NASA Astrophysics Data System (ADS)

    Byun, Thak Sang; Yoon, Ji Hyun; Hoelzer, David T.; Lee, Yong Bok; Kang, Suk Hoon; Maloy, Stuart A.

    2014-06-01

    This article is to summarize the process development and key characterization results for the newly-developed Fe-9Cr based nanostructured ferritic alloys (NFAs) with high fracture toughness. One of the major drawbacks from pursuing ultra-high strength in the past development of NFAs is poor fracture toughness at high temperatures although a high fracture toughness is essential to prevent cracking during manufacturing and to mitigate or delay irradiation-induced embrittlement in irradiation environments. A study on fracture mechanism using the NFA 14YWT found that the low-energy grain boundary decohesion in fracture process at a high temperature (>200 °C) resulted in low fracture toughness. Lately, efforts have been devoted to explore an integrated process to enhance grain bonding. Two base materials were produced through mechanical milling and hot extrusion and designated as 9YWTV-PM1 and 9YWTV-PM2. Isothermal annealing (IA) and controlled rolling (CR) treatments in two phase region were used to enhance diffusion across the interfaces and boundaries. The PM2 alloy after CR treatments showed high fracture toughness (KJQ) at represented temperatures: 240-280 MPa √m at room temperature and 160-220 MPa √m at 500 °C, which indicates that the goal of 100 MPa √m over possible nuclear application temperature range has been well achieved. Furthermore, it is also confirmed by comparison that the CR treatments on 9YWTV-PM2 result in high fracture toughness similar to or higher than those of the conventional ferritic-martensitic steels such as HT9 and NF616.

  13. Correlations among ultrasonic propagation factors and fracture toughness properties of metallic materials

    NASA Technical Reports Server (NTRS)

    Vary, A.

    1976-01-01

    Empirical evidence was developed to show that a close relation exists among fracture toughness, yield strength, and ultrasonic attenuation properties of metallic materials. The evidence was obtained by ultrasonic probing of specimens of two maraging steels and a titanium alloy. It was concluded that nondestructive ultrasonic methods can be used to indirectly evaluate fracture-related material properties. The results suggest that these nondestructive ultrasonic measurements can also serve as an adjunct to destructive testing, measurement, and analysis of fracture properties.

  14. Fracture toughness of stoichiometric, non-stoichiometric and ternary-alloyed Al{sub 2}Ti

    SciTech Connect

    Ma, J.C.; Lukitsch, M.J.; Ambrow, C.E.; Benci, J.E.

    1997-12-31

    Polycrystalline stoichiometric Al{sub 2}Ti was produced via casting or powder metallurgy and further processed yielding material in six conditions. The fracture toughness of the six material conditions was determined from the critical load to initiate cracks with a Vickers indenter. The results show a strong dependence on material condition. Powder processed Al{sub 2}Ti exhibits the highest fracture toughness value among the material conditions studied. Polycrystalline non-stoichiometric Al{sub 2{+-}y}Ti{sub 1{+-}y} and ternary-alloyed Al{sub 2}Ti + X were prepared in as-cast and cast and annealed conditions. Each material condition exhibited a multiphase microstructure. The composition of the phases present in each alloy was analyzed with SEM/EDS. Fracture toughness values of cast and annealed stoichiometric and non-stoichiometric binary alloys are 20--30% greater than as-cast stoichiometric Al{sub 2}Ti. For the ternary alloys, the fracture toughness values show a strong dependence on the ternary element used and heat treatment condition. The fracture toughness values of three hot forged ternary alloys were also determined.

  15. The shear fracture toughness, KIIc, of graphite

    SciTech Connect

    Burchell, Timothy D.; Erdman, III, Donald L.

    2015-11-05

    In this study, the critical shear stress intensity factor, KIIc, here-in referred to as the shear fracture toughness, KIIc (MPa m), of two grades of graphite are reported. The range of specimen volumes was selected to elucidate any specimen size effect, but smaller volume specimen tests were largely unsuccessful, shear failure did not occur between the notches as expected. This was probably due to the specimen geometry causing the shear fracture stress to exceed the compressive failure stress. In subsequent testing the specimen geometry was altered to reduce the compressive footprint and the notches (slits) made deeper to reduce the specimen's ligament length. Additionally, we added the collection of Acoustic Emission (AE) during testing to assist with the identification of the shear fracture load. The means of KIIc from large specimens for PCEA and NBG-18 are 2.26 MPa m with an SD of 0.37 MPa m and 2.20 MPa m with an SD of 0.53 MPa m, respectively. The value of KIIc for both graphite grades was similar, although the scatter was large. In this work we found the ratio of KIIc/KIc ≈ 1.6. .

  16. Fiber reinforced solids possessing great fracture toughness: The role of interfacial strength

    NASA Technical Reports Server (NTRS)

    Atkins, A. G.

    1974-01-01

    The high tensile strength characteristic of strong interfacial filament/matrix bonding can be combined with the high fracture toughness of weak interfacial bonding, when the filaments are arranged to have alternate sections of high and low shear stress (and low and high toughness). Such weak and strong areas can be achieved by appropriate intermittent coating of the fibers. An analysis is presented for toughness and strength which demonstrates, in broad terms, the effects of varying the coating parameters of concern. Results show that the toughness of interfaces is an important parameter, differences in which may not be shown up in terms of interfacial strength. Some observations are made upon methods of measuring the components of toughness in composites.

  17. On the distance criterion for failure at the tips of cracks, minimum fracture toughness, and non-dimensional toughness parameters

    NASA Astrophysics Data System (ADS)

    Neville, D. J.

    T HE PRESENT paper describes a distance criterion for failure at the tips of cracks in materials showing plasticity which, for stress-controlled cleavage on the lower shelf of toughness, is based on consideration of plasticity local to individual crack-initiation sites rather than on the distance from the remote crack tip to a crack-initiation site. For the upper shelf, consideration is of conditions local to voids, but the thermodynamic balance determining the moment of failure is for the macrocrack rather than microcracks, and a criterion of strain is used rather than a criterion of stress. This new criterion of distance or critical distance leads to a good description of temperature-dependent changes in toughness, on the lower shelf where failure is caused by stress-controlled cleavage and on the upper shelf where fracture runs by a strain-controlled ductile mechanism as well as in the region of transition in between, and always on the basis that these changes are due to temperature-dependent changes in yield strength and Young's modulus. A non-dimensional toughness parameter is observed. The present work is in agreement with many accepted ideas about fracture. The significance of the self-similarity of the distributions of stress and strain at the tips of cracks and the over-riding importance of crack-opening displacement in the determination of conditions for propagation are emphasised.

  18. A fractographic study of the edge-sliding mode in fracture toughness testing

    NASA Technical Reports Server (NTRS)

    Jones, D. L.; Chisholm, D. B.

    1976-01-01

    A fractographic study of Mode II fracture surfaces has been conducted for the purpose of identifying the microstructural mechanisms responsible for fracture in the edge-sliding mode. A compact shear (CS) specimen was employed to generate the fracture surfaces and also to establish Mode II fracture toughness values for Ti-6Al-4V, A533-B steel, and several aluminum alloys. In all tests, one of the two edge cracks sustained complete Mode II fracture while the other exhibited only a limited amount of subcritical crack growth. Mode II fracture surfaces, which were unique in appearance, have been examined by optical and scanning electron microscopy. It was determined that shear (or parabolic) microvoid coalescence was the dominant mechanism for Mode II fracture. It was also established that most of the surface abrasions were created by the relative sliding of the fracture surfaces during unstable fracture rather than the crack initiation process.

  19. An Improved Approach to Fracture Toughness Assessment of Brittle Coating on Ductile Substrate Systems under Indentation

    NASA Astrophysics Data System (ADS)

    Demidova, Natalia V.

    Fracture toughness is an important material property that determines the structural integrity of a component with pre-existing or service-generated flaws. In the present research, an indentation-based method and the associated fracture mechanics model are proposed for fracture toughness assessment of brittle coating/ductile substrate systems. The proposed models consider well-developed radial/median cracks generated under sharp indentation, despite that the crack formation process may have gone through crack initiation and propagation phases. For generality, the geometry of a well-developed crack is assumed to be semi-elliptical in shape. The driving force of the crack is considered to stem from the residual plastic zone expansion under the indenter, as well as the far-field Boussinesq (elastic) stress. Three well-defined configurations are studied. For the first configuration, a crack with a depth of less than 7% of the coating thickness is considered. In this case, the problem is treated as the one for the monolithic material with the coating material properties. For the second configuration, a crack that runs deeper than 7% of the coating thickness but is still within the coating layer is analyzed. In this case, the composite hardness is introduced into the analysis to account for the influence of the substrate material properties; and furthermore, an interface correction factor is proposed to take into account the presence of the coating/substrate interface and its influence on the stress intensity factor of the well-developed elliptical cracks. For the third configuration, a crack penetrating into the substrate is considered. In this case, based on the condition of deformation compatibility across the coating/substrate interface, the bulk modulus for the coating/substrate system is introduced into the analysis. A series of indentation tests are conducted on a WC/10Co/4Cr coating/1080 low carbon steel substrate specimen, which is a brittle coating on a ductile

  20. Effect of WC/Co coherency phase boundaries on Fracture toughness of the nanocrystalline cemented carbides

    PubMed Central

    Xie, Hongxian; Song, Xiaoyan; Yin, Fuxing; Zhang, Yongguang

    2016-01-01

    The effect of coherency WC/Co phase boundaries on the fracture toughness of the nanocrystalline WC-Co cemented carbides is studied by MD simulation method. The simulation results show that the nanocrystalline WC-Co cemented carbides with coherency WC/Co phase boundaries has higher fracture toughness than that without coherency WC/Co phase boundaries. Moreover, the mechanism of why coherency WC/Co phase boundaries can improve the fracture toughness of the nanocrystalline cemented carbides is also investigated. It is found the fact that the separation energy of the coherent WC/Co phase boundary is larger than that of the incoherent WC/Co phase boundaries is the main reason for this excellent mechanical property. PMID:27485922

  1. Effect of WC/Co coherency phase boundaries on Fracture toughness of the nanocrystalline cemented carbides

    NASA Astrophysics Data System (ADS)

    Xie, Hongxian; Song, Xiaoyan; Yin, Fuxing; Zhang, Yongguang

    2016-08-01

    The effect of coherency WC/Co phase boundaries on the fracture toughness of the nanocrystalline WC-Co cemented carbides is studied by MD simulation method. The simulation results show that the nanocrystalline WC-Co cemented carbides with coherency WC/Co phase boundaries has higher fracture toughness than that without coherency WC/Co phase boundaries. Moreover, the mechanism of why coherency WC/Co phase boundaries can improve the fracture toughness of the nanocrystalline cemented carbides is also investigated. It is found the fact that the separation energy of the coherent WC/Co phase boundary is larger than that of the incoherent WC/Co phase boundaries is the main reason for this excellent mechanical property.

  2. Development of plane strain fracture toughness test for ceramics using Chevron notched specimens

    NASA Technical Reports Server (NTRS)

    Bubsey, R. T.; Shannon, J. L., Jr.; Munz, D.

    1983-01-01

    Chevron-notched four-point-bend and short-bar specimens have been used to determine the fracture toughness of sintered aluminum oxide and hot-pressed silicon nitride ceramics. The fracture toughness for Si3N4 is found to be essentially independent of the specimen size and chevron notch configuration, with values ranging from 4.6 to 4.9 MNm exp -3/2. In contrast, significant specimen size and notch geometry effects have been observed for Al2O3, with the fracture toughness ranging from 3.1 to 4.7 MNm exp -3/2. These effects are attributed to a rising crack growth resistance curve for the Al2O3 tested.

  3. Strength, Fracture Toughness, Fatigue, and Standardization Issues of Free-standing Thermal Barrier Coatings

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Zhu, Dong-Ming; Miller, Robert A.

    2003-01-01

    Strength, fracture toughness and fatigue behavior of free-standing thick thermal barrier coatings of plasma-sprayed ZrO2-8wt % Y2O3 were determined at ambient and elevated temperatures in an attempt to establish a database for design. Strength, in conjunction with deformation (stress-strain behavior), was evaluated in tension (uniaxial and trans-thickness), compression, and uniaxial and biaxial flexure; fracture toughness was determined in various load conditions including mode I, mode II, and mixed modes I and II; fatigue or slow crack growth behavior was estimated in cyclic tension and dynamic flexure loading. Effect of sintering was quantified through approaches using strength, fracture toughness, and modulus (constitutive relations) measurements. Standardization issues on test methodology also was presented with a special regard to material's unique constitutive relations.

  4. The effects of radiation on the interlaminar fracture toughness of a graphite/epoxy composite

    NASA Technical Reports Server (NTRS)

    Funk, J. G.; Sykes, G. F.

    1986-01-01

    An experimental study is made of the effect of electron irradiation (10 to the 10th rad), simulating a 30-year geosynchronous orbit exposure, on the fracture toughness of a graphite/epoxy composite, T300/934. The double cantilever beam (DBC) test is used to determine Mode I (peel) critical strain energy release rate and the edge delamination tension (EDT) test is used to determine mixed Mode I and II (peel and shear) critical strain energy release rate. It is found that the electron interaction of the epoxy matrix material enhances the fracture toughness properties of the composite and that the test temperature has a significant effect on the fracture toughness of both baseline and irradiated material.

  5. Dynamic fracture-toughness evaluation by measurement of CTOD (Crack Tip Opening Displacement). Interim report

    SciTech Connect

    Sharpe, W.N.; Douglas, A.S.; Shapiro, J.M.

    1988-03-15

    Quantification of the dynamic fracture toughness of structural materials is essential to a wide range of problems - from nuclear accidents to ordnance applications. However, the difficulties associated with accurate measurements of cracks under dynamic loading are considerable. Thus there are no standardized procedures and few reliable results. This work describes a systematic study of the dynamic fracture toughness of SAE-01 tool steel, 4340 and HY100 steels and a tungsten, using the ISDG (Interferometric Strain/Displacement Gage) system which has very-high-frequency resolution. The major advantage of the method is that information is obtained very close to the crack tip, so that stress wave loading effects are accounted for. A detailed error analysis gives an uncertainty of -10% to +20% in the determination of fracture toughness, which compares with + or - 20% for published work.

  6. The importance of fracture toughness in ultrafine and nanocrystalline bulk materials

    PubMed Central

    Pippan, R.; Hohenwarter, A.

    2016-01-01

    ABSTRACT The suitability of high-strength ultrafine and nanocrystalline materials processed by severe plastic deformation methods and aimed to be used for structural applications will strongly depend on their resistance against crack growth. In this contribution some general available findings on the damage tolerance of this material class will be summarized. Particularly, the occurrence of a pronounced fracture anisotropy will be in the center of discussion. In addition, the great potential of this generated anisotropy to obtain high-strength materials with exceptionally high fracture toughness in specific loading and crack growth directions will be enlightened. IMPACT STATEMENT Severely plastically deformed materials are reviewed in light of their damage tolerance. The frequently observed toughness anisotropy allows unprecedented fracture toughness – strength combinations. PMID:27570712

  7. Recommendations for the determination of valid mode II fracture toughnesses K{sub IIc}

    SciTech Connect

    Hiese, W.; Kalthoff, J.F.

    1999-07-01

    From a discussion of the sizes of the plastic zones at the tip of a crack under shear (Mode II) and tensile (Mode I) conditions of loading, hypotheses on specimen size requirements are derived for determining valid values of the shear fracture toughness K{sub IIc}. The following conclusions are drawn: The minimum specimen thickness for a K{sub IIc} test can be smaller, but the minimum in-plane specimen dimensions should be larger than for a K{sub Ic} test. For verification of these hypotheses, Mode II and additionally Mode I fracture toughnesses were determined for the aluminum alloy 7075 and the tool steel 90 MnCrV 8. Measurements were performed with specimens of different sizes with respect to the size of the crack tip plastic zones. The obtained data are in good agreement with the derived criteria for measuring Mode II fracture toughnesses K{sub IIc} and confirm their validity.

  8. Moisture-heat effects on unidirectional composite laminates fracture toughness and fatigue crack growth

    NASA Astrophysics Data System (ADS)

    Zhang, Fusheng; Pzinz, R.; Zichy, J. H.

    1993-04-01

    The heat-moisture effect on interlaminar fracture toughness of T300/914C graphite/epoxy unidirectional composite laminates is investigated under mode I opening loading witb DCB specimen. The fracture toughness in moisture-heat conditioning increases, and the glass transition temperature decreases. SEM fractographs revealed no discernible difference in the fracture surface morphology of moisture-heat and dry conditioned specimens. No fiber bridging occurs in the testing. Delamination fatigue crack growth experiments are carried out on T300/914C graphite/epoxy unidirectional laminates. It is found that the mode I cyclic crack growth rate yields a power low relationship between da/dN and the maximum cyclic strain energy release rate. The crack growth rate of the moisture-heat conditioned specimen is lower than that of the dry conditioned. The environmental effects are explained on the basis of fractography and fracture mechanisms and fracture mechanics.

  9. Fracture capacity of HFIR vessel with random crack size and toughness

    SciTech Connect

    Chang, S.J.

    1994-09-01

    The probability of fracture versus a range of applied hoop stresses along the High Flux Isotope Reactor vessel is obtained as an estimate of its fracture capacity. Both the crack size and the fracture toughness are assumed to be random variables and subject to assumed distribution functions. Possible hoop stress is based on the numerical solution of the vessel response by applying a point pressure-pulse at the center of the fluid volume within the vessel. Both the fluid-structure interaction and radiation embrittlement are taken into consideration. Elastic fracture mechanics is used throughout the analysis. The probability function of fracture for a single crack due to either a variable crack depth or a variable toughness is derived. Both the variable crack size and the variable toughness are assumed to follow known distributions. The probability of vessel fracture with multiple number of cracks is then obtained as a function of the applied hoop stress. The probability of fracture function is, then, extended to include different levels of confidence and variability. It, therefore, enables one to estimate the high confidence and low probability fracture capacity of the reactor vessel under a range of accident loading conditions.

  10. A moving-load controlled-displacement fracture-toughness testing machine

    NASA Astrophysics Data System (ADS)

    Pujari, V. K.; Finnie, I.; Hauser, F. E.

    1981-06-01

    A testing procedure using a moving-load controlled-displacement fracture-toughness testing machine is described. It provides simple means for studying fracture-toughness gradients in structural materials caused by varying thickness, heat-treatment variations, mechanical working gradients, welding, and different corrosive environments. The energy-release rate at the onset of crack propagation and the plane-strain fracture toughness can be measured directly without compliance calibration or stress-intensity evaluation. Specimens made of 7075-76 aluminum-alloy were used in the testing, both at constant and linearly varying net-section thickness. The large number of fracture-toughness points obtained allowed the probability distribution of toughness values to be studied with the curve showing a normal distribution. It is concluded that the strain-energy release-rate expression derived for this system is independent of crack length and the specimen geometry is simple. Furthermore, the technique of controlled crack propagation (discrete jump) provides a large number of data points along the specimen length.

  11. A Proposal for the Maximum KIC for Use in ASME Code Flaw and Fracture Toughness Evaluations

    SciTech Connect

    Kirk, Mark; Stevens, Gary; Erickson, Marjorie A; Yin, Shengjun

    2011-01-01

    Nonmandatory Appendices A [1] and G [2] of Section XI of the ASME Code use the KIc curve (indexed to the material reference transition temperature, RTNDT) in reactor pressure vessel (RPV) flaw evaluations, and for the purpose of establishing RPV pressure-temperature (P-T) limits. Neither of these appendices places an upper-limit on the KIc value that may be used in these assessments. Over the years, it has often been suggested by some of the members of the ASME Section XI Code committees that are responsible for maintaining Appendices A and G that there is a practical upper limit of 200 ksi in (220 MPa m) [4]. This upper limit is not well recognized by all users of the ASME Code, is not explicitly documented within the Code itself, and the one source known to the authors where it is defended [4] relies on data that is either in error, or is less than 220 MPa m. However, as part of the NRC/industry pressurized thermal shock (PTS) re-evaluation effort, empirical models were developed that propose common temperature dependencies for all ferritic steels operating on the upper shelf. These models relate the fracture toughness properties in the transition regime to those on the upper shelf and, combined with data for a wide variety of RPV steels and welds on which they are based, suggest that the practical upper limit of 220 MPa m exceeds the upper shelf fracture toughness of most RPV steels by a considerable amount, especially for irradiated steels. In this paper, available models and data are used to propose upper bound limits of applicability on the KIc curve for use in ASME Code, Section XI, Nonmandatory Appendices A and G evaluations that are consistent with available data for RPV steels.

  12. Increased fracture toughness of graphite-epoxy composites through intermittent interlaminar bonding. [Mylar interlayer

    NASA Technical Reports Server (NTRS)

    Felbeck, D. K.; Jea, L. C.

    1980-01-01

    Intermittent interlaminar bonding, which can lead to a large increase in the fracture surface area, was achieved through the introduction of thin perforated Mylar between the layers of a multi-layer continuous-filament graphite-epoxy composite. For the best optimum condition included in this study, fracture toughness was increased from about 100 kJ/sq m for untreated specimens to an average of about 500 kJ/sq m, while tensile strength dropped from 500 MPa to 400 MPa, and elastic modulus remained the same at about 75 GPa. An approximate analysis is presented to explain the observed improvement in toughness.

  13. Identification of Fracture Toughness for Discrete Damage Mechanics Analysis of Glass-Epoxy Laminates

    NASA Astrophysics Data System (ADS)

    Barbero, E. J.; Cosso, F. A.; Martinez, X.

    2014-08-01

    A methodology for determination of the intralaminar fracture toughness is presented, based on fitting discrete damage mechanics (DDM) model predictions to available experimental data. DDM is constitutive model that, when incorporated into commercial finite element software via user material subroutines, is able to predict intralaminar transverse and shear damage initiation and evolution in terms of the fracture toughness of the composite. The applicability of the DDM model is studied by comparison to available experimental data for Glass-Epoxy laminates. Sensitivity of the DDM model to h- and p-refinement is studied. Also, the effect of in-situ correction of strength is highlighted.

  14. Simplified composite micromechanics equations for strength, fracture toughness and environmental effects

    NASA Technical Reports Server (NTRS)

    Chamis, C. C.

    1984-01-01

    A unified set of composite micromechanics equations of simple form is summarized and described. This unified set includes composite micromechanics equations for predicting: (1) ply in-plane uniaxial strengths; (2) through-the-thickness strength (interlaminar and flexural); (3) in-plane fracture toughness; (4) in-plane impact resistance; and (5) through-the-thickness (interlaminar and flexural) impact resistance. Equations are also included for predicting the hygrothermal effects on strength, fracture toughness and impact resistance. Several numerical examples are worked out to illustrate the ease of use of the various composite micromechanics equations.

  15. Fracture toughness measurements on a glass bonded sodalite high-level waste form.

    SciTech Connect

    DiSanto, T.; Goff, K. M.; Johnson, S. G.; O'Holleran, T. P.

    1999-05-19

    The electrometallurgical treatment of metallic spent nuclear fuel produces two high-level waste streams; cladding hulls and chloride salt. Argonne National Laboratory is developing a glass bonded sodalite waste form to immobilize the salt waste stream. The waste form consists of 75 Vol.% crystalline sodalite (containing the salt) with 25 Vol.% of an ''intergranular'' glassy phase. Microindentation fracture toughness measurements were performed on representative samples of this material using a Vickers indenter. Palmqvist cracking was confirmed by post-indentation polishing of a test sample. Young's modulus was measured by an acoustic technique. Fracture toughness, microhardness, and Young's modulus values are reported, along with results from scanning electron microscopy studies.

  16. Recommendations for the shallow-crack fracture toughness testing task within the HSST (Heavy-Section Steel Technology) Program

    SciTech Connect

    Theiss, T.J. )

    1990-09-01

    Recommendations for Heavy-Section Steel Technology Program's investigation into the influence of crack depth on the fracture toughness of a steel prototypic of those in a reactor pressure vessel are included in this report. The motivation for this investigation lies in the fact that probabilistic fracture mechanics evaluations show that shallow flaws play a dominant role in the likelihood of vessel failure, and shallow-flaw specimens have exhibited an elevated toughness compared with conventional deep-notch fracture toughness specimens. Accordingly, the actual margin of safety of vessels may be greater than that predicted using existing deep-notch fracture-toughness results. The primary goal of the shallow-crack project is to investigate the influence of crack depth on fracture toughness under conditions prototypic of a reactor vessel. A limited data base of fracture toughness values will be assembled using a beam specimen of prototypic reactor vessel material and with a depth of 100 mm (4 in.). This will permit comparison of fracture-toughness data from deep-cracked and shallow-crack specimens, and this will be done for several test temperatures. Fracture-toughness data will be expressed in terms of the stress-intensity factor and crack-tip-opening displacement. Results of this investigation are expected to improve the understanding of shallow-flaw behavior in pressure vessels, thereby providing more realistic information for application to the pressurized-thermal shock issues. 33 refs., 17 figs.

  17. The effect of crack instability/stability on fracture toughness of brittle materials

    SciTech Connect

    Baratta, F.I.

    1997-12-31

    This paper summarizes three recent experimental works coauthored by the present author regarding the effect of crack instability/stability on fracture toughness, and also includes the necessary formulae for predicting stability. Two recent works have shown that unstable crack extension resulted in apparent increases in fracture toughness compared to that determined during stable crack growth. In the first investigation a quasi-brittle polymer, polymethylmethacrylate, was examined. In the second, a more brittle metallic material, tungsten, was tested. In both cases the transition from unstable to stable behavior was predicted based on stability analyses. The third investigation was conducted on a truly brittle ceramic material, hot pressed silicon nitride. These three papers showed that fracture toughness test results conducted on brittle materials vary according to whether the material fractures in an unstable or stable manner. Suggestions for achieving this important yet difficult phenomenon of stable crack growth, which is necessary when determining the fracture toughness variation occurring during unstable/stable crack advance, are presented, as well as recommendations for further research.

  18. Evaluation of Fracture Toughness of Tantalum Carbide Ceramic Layer: A Vickers Indentation Method

    NASA Astrophysics Data System (ADS)

    Song, Ke; Xu, Yunhua; Zhao, Nana; Zhong, Lisheng; Shang, Zhao; Shen, Liuliu; Wang, Juan

    2016-06-01

    A tantalum carbide (TaC) ceramic layer was produced on gray cast iron matrix by in situ technique comprising a casting process and a subsequent heat treatment at 1135 °C for 45 min. Indentation fracture toughness in TaC ceramic layer was determined by the Vickers indentation test for various loads. A Niihara approach was chosen to assess the fracture toughness of TaC ceramic layer under condition of the Palmqvist mode in the experiment. The results reveal that K IC evaluation of TaC ceramic layer by the Vickers indentation method strongly depends on the selection of crack system and K IC equations. The critical indentation load for Vickers crack initiation in TaC ceramic layer lies between 1 and 2 N and the cracks show typical intergranular fracture characteristics. Indentation fracture toughness calculated by the indentation method is independent of the indentation load on the specimen. The fracture toughness of TaC ceramic layer is 6.63 ± 0.34 MPa m1/2, and the toughening mechanism is mainly crack deflection.

  19. Crack growth rates and fracture toughness of irradiated austenitic stainless steels in BWR environments.

    SciTech Connect

    Chopra, O. K.; Shack, W. J.

    2008-01-21

    In light water reactors, austenitic stainless steels (SSs) are used extensively as structural alloys in reactor core internal components because of their high strength, ductility, and fracture toughness. However, exposure to high levels of neutron irradiation for extended periods degrades the fracture properties of these steels by changing the material microstructure (e.g., radiation hardening) and microchemistry (e.g., radiation-induced segregation). Experimental data are presented on the fracture toughness and crack growth rates (CGRs) of wrought and cast austenitic SSs, including weld heat-affected-zone materials, that were irradiated to fluence levels as high as {approx} 2x 10{sup 21} n/cm{sup 2} (E > 1 MeV) ({approx} 3 dpa) in a light water reactor at 288-300 C. The results are compared with the data available in the literature. The effects of material composition, irradiation dose, and water chemistry on CGRs under cyclic and stress corrosion cracking conditions were determined. A superposition model was used to represent the cyclic CGRs of austenitic SSs. The effects of neutron irradiation on the fracture toughness of these steels, as well as the effects of material and irradiation conditions and test temperature, have been evaluated. A fracture toughness trend curve that bounds the existing data has been defined. The synergistic effects of thermal and radiation embrittlement of cast austenitic SS internal components have also been evaluated.

  20. Evaluation of Fracture Toughness of Tantalum Carbide Ceramic Layer: A Vickers Indentation Method

    NASA Astrophysics Data System (ADS)

    Song, Ke; Xu, Yunhua; Zhao, Nana; Zhong, Lisheng; Shang, Zhao; Shen, Liuliu; Wang, Juan

    2016-07-01

    A tantalum carbide (TaC) ceramic layer was produced on gray cast iron matrix by in situ technique comprising a casting process and a subsequent heat treatment at 1135 °C for 45 min. Indentation fracture toughness in TaC ceramic layer was determined by the Vickers indentation test for various loads. A Niihara approach was chosen to assess the fracture toughness of TaC ceramic layer under condition of the Palmqvist mode in the experiment. The results reveal that K IC evaluation of TaC ceramic layer by the Vickers indentation method strongly depends on the selection of crack system and K IC equations. The critical indentation load for Vickers crack initiation in TaC ceramic layer lies between 1 and 2 N and the cracks show typical intergranular fracture characteristics. Indentation fracture toughness calculated by the indentation method is independent of the indentation load on the specimen. The fracture toughness of TaC ceramic layer is 6.63 ± 0.34 MPa m1/2, and the toughening mechanism is mainly crack deflection.

  1. Strength and Fracture Toughness of Solid Oxide Fuel Cell Electrolyte Material Improved

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P.; Choi, Sung R.

    2002-01-01

    Solid oxide fuel cells (SOFC) are being developed for various applications in the automobile, power-generation, and aeronautics industries. Recently, the NASA Glenn Research Center has been exploring the possibility of using SOFC's for aeropropulsion under its Zero Carbon Dioxide Emission Technology (ZCET) Program. 10-mol% yttriastabilized zirconia (10YSZ) is a very good anionic conductor at high temperatures and is, therefore, used as an oxygen solid electrolyte in SOFC. However, it has a high thermal expansion coefficient, low thermal shock resistance, low fracture toughness, and poor mechanical strength. For aeronautic applications, the thin ceramic electrolyte membrane of the SOFC needs to be strong and tough. Therefore, we have been investigating the possibility of enhancing the strength and fracture toughness of the 10YSZ electrolyte without degrading its electrical conductivity to an appreciable extent. We recently demonstrated that the addition of alumina to zirconia electrolyte increases its strength as well as its fracture toughness. Zirconia-alumina composites containing 0 to 30 mol% of alumina were fabricated by hot pressing. The hot pressing procedure was developed and various hot pressing parameters were optimized, resulting in dense, crackfree panels of composite materials. Cubic zirconia and a-alumina were the only phases detected, indicating that there was no chemical reaction between the constituents during hot pressing at elevated temperatures. Flexure strength sf and fracture toughness K(sub IC) of the various zirconia-alumina composites were measured at room temperature as well as at 1000 C in air. Both properties showed systematic improvement with increased alumina addition at room temperature and at 1000 C. Use of these modified electrolytes with improved strength and fracture toughness should prolong the life and enhance the performance of SOFC in aeronautics and other applications.

  2. Notch Fracture Toughness of Glasses: Dependence on Rate, Age, and Geometry

    NASA Astrophysics Data System (ADS)

    Vasoya, Manish; Rycroft, Chris H.; Bouchbinder, Eran

    2016-08-01

    Understanding the fracture toughness (resistance) of glasses is a fundamental problem of prime theoretical and practical importance. Here we theoretically study its dependence on the loading rate, the age (history) of the glass, and the notch radius ρ . Reduced-dimensionality analysis suggests that the notch fracture toughness results from a competition between the initial, age- and history-dependent, plastic relaxation time scale τ0pl and an effective loading time scale τext(K˙ I,ρ ) , where K˙ I is the tensile stress-intensity-factor rate. The toughness is predicted to scale with √{ρ } independently of ξ ≡τext/τ0pl for ξ ≪1 , to scale as T √{ρ }log (ξ ) for ξ ≫1 (related to thermal activation, where T is the temperature), and to feature a nonmonotonic behavior in the crossover region ξ ˜O (1 ) (related to plastic yielding dynamics). These predictions are verified using 2D computations, providing a unified picture of the notch fracture toughness of glasses. The theory highlights the importance of time-scale competition and far-from-steady-state elasto-viscoplastic dynamics for understanding the toughness and shows that the latter varies quite significantly with the glass age (history) and applied loading rate. Experimental support for bulk metallic glasses is presented, and possible implications for applications are discussed.

  3. Adhesion and interfacial fracture toughness between hard and soft materials

    NASA Astrophysics Data System (ADS)

    Rahbar, Nima; Wolf, Kurt; Orana, Argjenta; Fennimore, Roy; Zong, Zong; Meng, Juan; Papandreou, George; Maryanoff, Cynthia; Soboyejo, Wole

    2008-11-01

    This paper presents the results of a combined experimental and theoretical study of adhesion between hard and soft layers that are relevant to medical devices such as drug-eluting stents and semiconductor applications. Brazil disk specimens were used to measure the interfacial fracture energies between model parylene C and 316L stainless steel over a wide range of mode mixities. The trends in the overall fracture energies are predicted using a combination of adhesion theories and fracture mechanics concepts. The measured interfacial fracture energies are shown to be in good agreement with the predictions.

  4. Temperature dependence of fracture toughness in HT9 steel neutron-irradiated up to 145 dpa

    SciTech Connect

    Baek, Jong-Hyuk; Byun, Thak Sang; Maloy, S; Toloczko, M

    2014-01-01

    The temperature dependence of fracture toughness in HT9 steel irradiated to high doses was investigated using miniature three-point bend (TPB) fracture specimens. These specimens were from the ACO-3 fuel duct wall of the Fast Flux Test Facility (FFTF), in which irradiation doses were in the range of 3.2 144.8 dpa and irradiation temperatures in the range of 380.4 502.6 oC. A miniature specimen reuse technique has been established for this investigation: the specimens used were the tested halves of miniature Charpy impact specimens (~13 3 4 mm) with diamond-saw cut in the middle. The fatigue precracking for specimens and fracture resistance (J-R) tests were carried out in a MTS servo-hydraulic testing machine with a vacuum furnace following the standard procedure described in the ASTM Standard E 1820-09. For each of five irradiated and one archive conditions, 7 to 9 J-R tests were performed at selected temperatures ranging from 22 C to 600 C. The fracture toughness of the irradiated HT9 steel was strongly dependent on irradiation temperatures rather than irradiation dose. When the irradiation temperature was below about 430 C, the fracture toughness of irradiated HT9 increased with test temperature, reached an upper shelf of 180 200 MPa m at 350 450 C and then decreased with test temperature. When the irradiation temperature 430 C, the fracture toughness was nearly unchanged until about 450 C and decreased with test temperature in higher temperature range. Similar test temperature dependence was observed for the archive material although the highest toughness values are lower after irradiation. Ductile stable crack growth occurred except for a few cases where both the irradiation temperature and test temperature are relatively low.

  5. Fatigue crack growth characteristics and fracture toughness of {gamma}-TiAl base alloy sheet material

    SciTech Connect

    Behr, R.; Wanner, A.; Clemens, H.; Glatz, W.

    1995-07-01

    Room temperature tension-tension fatigue crack growth experiments were performed on single edge notch specimens of Ti-48Al-2Cr sheet materials produced on industrial scale with different microstructures ranging from near gamma to fully lamellar. Crack extension was monitored using a travelling optical microscope and a DC potential method. Crack paths and fracture surfaces were investigated by SEM. Fracture toughness data were determined by monotonic loading of previously fatigued samples.

  6. Effect of hydride orientation on fracture toughness of Zircaloy-4 cladding

    NASA Astrophysics Data System (ADS)

    Hsu, Hsiao-Hung; Tsay, Leu-Wen

    2011-01-01

    Hydrogen embrittlement is one of the major degradation mechanisms for high burnup fuel cladding during reactor service and spent fuel dry storage, which is related to the hydrogen concentration, morphology and orientation of zirconium hydrides. In this work, the J-integral values for X-specimens with different hydride orientations are measured to evaluate the fracture toughness of Zircaloy-4 (Zry-4) cladding. The toughness values for Zry-4 cladding with various percentages of radial hydrides are much smaller than those with circumferential hydrides only in the same hydrogen content level at 25 °C. The fractograghic features reveal that the crack path is influenced by the orientation of zirconium hydride. Moreover, the fracture toughness measurements for X-specimens at 300 °C are not sensitive to a variation in hydride orientation but to hydrogen concentration.

  7. The effect of mixed mode precracking on the mode 1 fracture toughness of composite laminates

    NASA Technical Reports Server (NTRS)

    Shankar, Prashanth; Bascom, Williard D.; Nairn, John A.

    1993-01-01

    We subjected double cantilever beam specimens from four different composite materials to mixed-mode precracking. Three different precracking mode 1 to mode 2 ratios were used--1 to 4, 1 to 1, and 4 to 1. Following precracking the specimens were tested for mode I fracture toughness. The mixed-mode precracking often influenced the mode 1 toughness and its influence persisted for as much as 60 mm of mode 1 crack growth. We tested composites with untoughened matrices, composites with rubber-toughened matrices, and composites with interlayer toughening. Depending on material type and precracking mode ratio, the precracking could cause either a significant increase or a significant decrease in the mode 1 fracture toughness.

  8. Results of ASTM round robin testing for mode 1 interlaminar fracture toughness of composite materials

    NASA Technical Reports Server (NTRS)

    Obrien, T. Kevin; Martin, Roderick H.

    1992-01-01

    The results are summarized of several interlaboratory 'round robin' test programs for measuring the mode 1 interlaminar fracture toughness of advanced fiber reinforced composite materials. Double Cantilever Beam (DCB) tests were conducted by participants in ASTM committee D30 on High Modulus Fibers and their Composites and by representatives of the European Group on Fracture (EGF) and the Japanese Industrial Standards Group (JIS). DCB tests were performed on three AS4 carbon fiber reinforced composite materials: AS4/3501-6 with a brittle epoxy matrix; AS4/BP907 with a tough epoxy matrix; and AS4/PEEK with a tough thermoplastic matrix. Difficulties encountered in manufacturing panels, as well as conducting the tests are discussed. Critical issues that developed during the course of the testing are highlighted. Results of the round robin testing used to determine the precision of the ASTM DCB test standard are summarized.

  9. Influence of specimen size/type on the fracture toughness of five irradiated RPV materials

    SciTech Connect

    Sokolov, Mikhail A; Lucon, Enrico

    2015-01-01

    The Heavy-Section Steel Irradiation (HSSI) Program had previously irradiated five reactor pressure vessel (RPV) steels/welds at fast neutron fluxes of about 4 to 8 x 1011 n/cm2/s (>1 MeV) to fluences from 0.5 to 3.4 1019 n/cm2 and at 288 °C. The unirradiated fracture toughness tests were performed by Oak Ridge National Laboratory with 12.7-mm and 25.4-mm thick (0.5T and 1T) compact specimens, while the HSSI Program provided tensile and 5 x 10-mm three-point bend specimens to SCK-CEN for irradiation in the in-pile section of the Belgian Reactor BR2 at fluxes > 1013 n/cm2/s and subsequent testing by SCK-CEN. The BR2 irradiations were conducted at about 2 and 4 x 1013 n/cm2/s with irradiation temperature between 295 °C and 300 °C (water temperature), and to fluences between 6 and 10 x 1019n/cm2. The irradiation-induced shifts of the Master Curve reference temperatures, ΔT0, for most of the materials deviated from the embrittlement correlations much more than expected, motivating the testing of 5 x 10-mm three-point bend specimens of all five materials in the unirradiated condition to eliminate specimen size and geometry as a variable. Tests of the unirradiated small bend specimens resulted in Master Curve reference temperatures, T0, 25 °C to 53 °C lower than those from the larger compact specimens, meaning that the irradiation-induced reference temperature shifts, ΔT0, were larger than the initial measurements, resulting in much improved agreement between the measured and predicted fracture toughness shifts.

  10. Heat Treatment Effect on Fracture Toughness of F82H Irradiated in HFIR

    SciTech Connect

    Stoller, Roger E; Sokolov, Mikhail A; Tanigawa, Hiroyasu; Hirose, Takanori; Odette, G.R.; Okubo, N.; Jitsukawa, Shiro; Sawai, T.

    2011-01-01

    Irradiation hardening and fracture toughness of reduced-activation ferritic/martensitic steel F82H after irradiation were investigated with a focus on changing the fracture toughness transition temperature as a result of several heat treatments. The specimens were standard F82H-IEA (IEA), F82H-IEA with several heat treatments (Mod1 series) and a heat of F82H (Mod3) containing 0.1 % tantalum. The specimens were irradiated up to 20 dpa at 300oC in the High Flux Isotope Reactor under a collaborative research program between JAEA/US-DOE. The results of hardness tests showed that irradiation hardening of IEA was comparable with that of Mod3. However, the fracture toughness-transition temperature of Mod3 was lower than that of IEA. The transition temperature of Mod1 was also lower than that of the IEA heat. These results suggest that optimization of specifications on the heat treatment condition and modification of the minor alloying elements seem to be effective to reduce the fracture toughness-transition temperature after irradiation.

  11. 75 FR 10410 - Alternate Fracture Toughness Requirements for Protection Against Pressurized Thermal Shock Events...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-03-08

    ..., 2010 (75 FR 5495). The February 3, 2010 document corrected a final rule published on January 4, 2010 (75 FR 13), that amends the NRC's regulations to provide alternate fracture toughness requirements for... document published on February 3, 2010 (75 FR 5495). Therefore, the NRC finds that notice and...

  12. 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.

  13. Fracture Toughness Properties of Savannah River Site Storage Tank ASTM A285 Low Carbon Steel

    SciTech Connect

    Subramanian, K.H.

    2002-05-22

    A materials test program was developed to measure mechanical properties of ASTM A285 Grade B low carbon steel for application to structural and flaw stability analysis of storage tanks at the Department of Energy (DOE) Savannah River Site (SRS). Under this plan, fracture toughness and tensile testing are being performed at conditions that are representative of storage tank

  14. 75 FR 5495 - Alternate Fracture Toughness Requirements for Protection Against Pressurized Thermal Shock Events...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-02-03

    ... (75 FR 13), that amends the NRC's regulations to provide alternate fracture toughness requirements for....Lesar@nrc.gov . SUPPLEMENTARY INFORMATION: In FR doc. E9-31146, published on January 4, 2010, make the... relevant material group given in Table 5. TR03FE10.008 where: m is the slope of a plot of all of the...

  15. Microstructure and Fracture Toughness of FeNiCr-TiC Composite Produced by Thermite Reaction

    NASA Astrophysics Data System (ADS)

    Xi, Wenjun; Shi, Chaoliang

    The microstructures of the FeNiCr-TiC composite produced by the rapid solidification thermite process were investigated using X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The effects of aging treatment on the microstructure and fracture toughness of the composite were examined. Results showed that the FeNiCr-TiC composite was composed of ferrite (α-FeNiCr), TiC and NiAl (β phase). TiC particles in the matrix were in the shape of polygon and uniformly distributed, and their size was less than 3 µm. The β phase was coherent with the ferrite matrix, and its average size was about 50 nm. The fracture toughness of composite was 22 MPa·m1/2 without aging. When the aging temperature was below 600°C, the fracture toughness of the composite had higher plateau values and reached the maximum of 32 MPa·m1/2 at aging temperature 500°C due to the precipitation of NiAl phase on the nanometer scale. The fracture toughness decreased rapidly aged at 650°C, and then kept homology value in the range of 700 to 900°C, which was attributed to the precipitation of needle-shaped carbide (Cr/Fe)7C3 at the grain boundaries.

  16. THE IMPORTANCE OF MICROSTRUCTURAL VARIATIONS ON THE FRACTURE TOUGHNESS OF HUMAN DENTIN

    PubMed Central

    Ivancik, J.; Arola, D.

    2012-01-01

    The crack growth resistance of human dentin was characterized as a function of relative distance from the DEJ and the corresponding microstructure. Compact tension specimens were prepared from the coronal dentin of caries-free 3rd molars. The specimens were sectioned from either the outer, middle or inner dentin. Stable crack extension was achieved under Mode I quasi-static loading, with the crack oriented in-plane with the tubules, and the crack growth resistance was characterized in terms of the initiation (Ko), growth (Kg) and plateau (Kp) toughness. A hybrid approach was also used to quantify the contribution of dominant mechanisms to the overall toughness. Results showed that human dentin exhibits increasing crack growth resistance with crack extension in all regions, and that the fracture toughness of inner dentin (2.2±0.5 MPa•m0.5) was significantly lower than that of middle (2.7±0.2 MPa•m0.5) and outer regions (3.4±0.3 MPa•m0.5). Extrinsic toughening, composed mostly of crack bridging, was estimated to cause an average increase in the fracture energy of 26% in all three regions. Based on these findings, dental restorations extended into deep dentin are much more likely to cause tooth fracture due to the greater potential for introduction of flaws and decrease in fracture toughness with depth. PMID:23131531

  17. Aspects of the Fracture Toughness of Carbon Nanotube Modified Epoxy Polymer Composites

    NASA Astrophysics Data System (ADS)

    Mirjalili, Vahid

    Epoxy resins used in fibre reinforced composites exhibit a brittle fracture behaviour, because they show no sign of damage prior to a catastrophic failure. Rubbery materials and micro-particles have been added to epoxy resins to improve their fracture toughness, which reduces strength and elastic properties. In this research, carbon nanotubes (CNTs) are investigated as a potential toughening agent for epoxy resins and carbon fibre reinforced composites, which can also enhance strength and elastic properties. More specifically, the toughening mechanisms of CNTs are investigated theoretically and experimentally. The effect of aligned and randomly oriented carbon nanotubes (CNTs) on the fracture toughness of polymers was modelled using Elastic Plastic Fracture Mechanics. Toughening from CNT pull-out and rupture were considered, depending on the CNTs critical length. The model was used to identify the effect of CNTs geometrical and mechanical properties on the fracture toughness of CNT-modified epoxies. The modelling results showed that a uniform dispersion and alignment of a high volume fraction of CNTs normal to the crack growth plane would lead to the maximum fracture toughness enhancement. To achieve a uniform dispersion, the effect of processing on the dispersion of single walled and multi walled CNTs in epoxy resins was investigated. An instrumented optical microscope with a hot stage was used to quantify the evolution of the CNT dispersion during cure. The results showed that the reduction of the resin viscosity at temperatures greater than 100 °C caused an irreversible re-agglomeration of the CNTs in the matrix. The dispersion quality was then directly correlated to the fracture toughness of the modified resin. It was shown that the fine tuning of the ratio of epoxy resin, curing agent and CNT content was paramount to the improvement of the base resin fracture toughness. For the epoxy resin (MY0510 from Hexcel), an improvement of 38% was achieved with 0.3 wt

  18. A novel pillar indentation splitting test for measuring fracture toughness of thin ceramic coatings

    SciTech Connect

    Sebastiani, Marco; Johanns, K. E.; Herbert, Erik G.; Carassiti, Fabio; Pharr, George Mathews

    2014-05-16

    Fracture toughness is an important material property that plays a role in determining the in-service mechanical performance and adhesion of thin ceramic films. Unfortunately, measuring thin film fracture toughness is affected by influences from the substrate and the large residual stresses that can exist in the films. In this paper, we explore a promising new technique that potentially overcomes these problems based on nanoindentation testing of micro-pillars produced by focused ion beam milling of the films. By making the pillar diameter approximately equal to its length, the residual stress in the pillar’s upper portion is almost fully relaxed, and when indented with a sharp Berkovich indenter, the pillars fracture by splitting at reproducible loads that are readily quantified by a sudden displacement excursion in the load displacement behavior. Cohesive finite element simulations are used to analyze and develop, for a given material, a simple relation between the critical load at failure, pillar radius, and fracture toughness. The main novel aspect of this work is that neither crack geometries nor crack sizes need to be measured post test. Furthermore, the residual stress can be measured at the same time with toughness, by comparing the indentation results from the stress-free pillars and the as-deposited film. The method is tested on three different hard coatings formed by physical vapor deposition: titanium nitride, chromium nitride, and a CrAlN/Si3N4 nanocomposite. Results compare well to independently measured values of fracture toughness for the three brittle films. The technique offers several benefits over existing methods.

  19. Dependence of Fracture Toughness on Crystallographic Orientation in Single-Crystalline Cubic (β) Silicon Carbide

    SciTech Connect

    Pharr, M.; Katoh, Y.; Bei, H.

    2006-01-01

    Along with other desirable properties, the ability of silicon carbide (SiC) to retain high strength after elevated temperature exposures to neutron irradiation renders it potentially applicable in fusion and advanced fission reactors. However, properties of the material such as room temperature fracture toughness must be thoroughly characterized prior to such practical applications. The objective of this work is to investigate the dependence of fracture toughness on crystallographic orientation for single-crystalline β-SiC. X-ray diffraction was first performed on the samples to determine the orientation of the crystal. Nanoindentation was used to determine a hardness of 39.1 and 35.2 GPa and elastic modulus of 474 and 446 GPa for the single-crystalline and polycrystalline samples, respectively. Additionally, crack lengths and indentation diagonals were measured via a Vickers micro-hardness indenter under a load of 100 gf for different crystallographic orientations with indentation diagonals aligned along fundamental cleavage planes. Upon examination of propagation direction of cracks, the cracks usually did not initiate and propagate from the corners of the indentation where the stresses are concentrated but instead from the indentation sides. Such cracks clearly moved along the {1 1 0} family of planes (previously determined to be preferred cleavage plane), demonstrating that the fracture toughness of SiC is comparatively so much lower along this set of planes that the lower energy required to cleave along this plane overpowers the stress-concentration at indentation corners. Additionally, fracture toughness in the <1 1 0> direction was 1.84 MPa·m1/2, lower than the 3.46 MPa·m1/2 measured for polycrystalline SiC (which can serve as an average of a spectrum of orientations), further demonstrating that single-crystalline β-SiC has a strong fracture toughness anisotropy.

  20. A novel pillar indentation splitting test for measuring fracture toughness of thin ceramic coatings

    DOE PAGESBeta

    Sebastiani, Marco; Johanns, K. E.; Herbert, Erik G.; Carassiti, Fabio; Pharr, George Mathews

    2014-05-16

    Fracture toughness is an important material property that plays a role in determining the in-service mechanical performance and adhesion of thin ceramic films. Unfortunately, measuring thin film fracture toughness is affected by influences from the substrate and the large residual stresses that can exist in the films. In this paper, we explore a promising new technique that potentially overcomes these problems based on nanoindentation testing of micro-pillars produced by focused ion beam milling of the films. By making the pillar diameter approximately equal to its length, the residual stress in the pillar’s upper portion is almost fully relaxed, and whenmore » indented with a sharp Berkovich indenter, the pillars fracture by splitting at reproducible loads that are readily quantified by a sudden displacement excursion in the load displacement behavior. Cohesive finite element simulations are used to analyze and develop, for a given material, a simple relation between the critical load at failure, pillar radius, and fracture toughness. The main novel aspect of this work is that neither crack geometries nor crack sizes need to be measured post test. Furthermore, the residual stress can be measured at the same time with toughness, by comparing the indentation results from the stress-free pillars and the as-deposited film. The method is tested on three different hard coatings formed by physical vapor deposition: titanium nitride, chromium nitride, and a CrAlN/Si3N4 nanocomposite. Results compare well to independently measured values of fracture toughness for the three brittle films. The technique offers several benefits over existing methods.« less

  1. Impact of surface finishes on the flexural strength and fracture toughness of In-Ceram Zirconia.

    PubMed

    Manawi, Manal; Ozcan, Mutlu; Madina, Manal; Cura, Cenk; Valandro, Luiz Felipe

    2012-01-01

    Dental restorations made of zirconia are usually selectively adjusted chairside to eliminate occlusal or internal interferences that can impair the mechanical properties of ceramic framework material. Effects of polishing procedures on zirconia after chipping or simply glazing the monolithic zirconia restorations are not known. This study evaluated the effects of different surface treatment procedures--namely, glazing or grinding, finishing, and polishing regimens--on the flexural strength and fracture toughness of a zirconia core material. Forty zirconia specimens were prepared and divided into two main groups (n = 20) according to the type of surface treatment (glazed or ground, finished, and polished). Each group was further divided into two subgroups (n = 10) according to type of mechanical test (flexural strength and fracture toughness). The roughness measurements were performed before mechanical testing. Qualitative evaluation of representative specimens of each subgroup was performed using SEM. The surface roughness mean (μm; ± standard deviations) recorded for the glazed specimens (0.94 ± 0.2) was significantly lower than that of the finished and polished group (3.01 ± 0.1) (P < 0.05). The glazed zirconia showed significantly higher flexural strength (385.4 ± 45.4 MPa) and fracture toughness (6.07 ± 1 MPa.m½) values than the ground, finished, polished zirconia (302.4 ± 47.6 MPa and 2.14 ± 0.5 MPa.m½) (P = 0.002 and P < 0.001 for flexural strength and fracture toughness, respectively). A smooth topographic pattern after glazing could not be obtained after finishing and polishing. Grinding, finishing, and polishing markedly decreased the flexural strength and fracture toughness of zirconia compared to the glazed groups. PMID:22414507

  2. A novel pillar indentation splitting test for measuring fracture toughness of thin ceramic coatings

    NASA Astrophysics Data System (ADS)

    Sebastiani, M.; Johanns, K. E.; Herbert, E. G.; Carassiti, F.; Pharr, G. M.

    2015-06-01

    The fracture toughness of thin ceramic films is an important material property that plays a role in determining the in-service mechanical performance and adhesion of this important class of engineering materials. Unfortunately, measurement of thin film fracture toughness is affected by influences from the substrate and the large residual stresses that can exist in the films. In this paper, we explore a promising new technique that potentially overcomes these issues based on nanoindentation testing of micro-pillars produced by focused ion beam milling of the films. By making the pillar diameter approximately equal to its length, the residual stress in the upper portion of the pillar is almost fully relaxed, and when indented with a sharp Berkovich indenter, the pillars fracture by splitting at reproducible loads that are readily quantified by a sudden displacement excursion in the load displacement behaviour. Cohesive finite element simulations are used for analysis and development of a simple relationship between the critical load at failure, pillar radius and fracture toughness for a given material. The main novel aspect of this work is that neither crack geometries nor crack sizes need to be measured post test. In addition, the residual stress can be measured at the same time with toughness, by comparison of the indentation results obtained on the stress-free pillars and the as-deposited film. The method is tested on three different hard coatings created by physical vapour deposition, namely titanium nitride, chromium nitride and a CrAlN/Si3N4 nanocomposite. Results compare well to independently measured values of fracture toughness for the three brittle films. The technique offers several benefits over existing methods.

  3. Effect of Mixed-Mode Ratio on Cryogenic Interlaminar Fracture Toughness of Woven Fabric Glass/Epoxy Laminates

    SciTech Connect

    Shindo, Y.; Horiguchi, K.; Kumagai, S.; Shinohe, D.

    2004-06-28

    This paper summarizes the results of an experimental and analytical study conducted to investigate the effect of mixed-mode ratio on the cryogenic interlaminar fracture toughness of woven fabric glass/epoxy laminates. Interlaminar fracture tests were performed and a three-dimensional finite element analysis was carried out to obtain critical strain energy release rates. The cryogenic interlaminar fracture toughness increased upon the introduction of the mode II component.

  4. HYDROGEN EFFECTS ON FRACTURE TOUGHNESS OF TYPE 316L STAINLESS STEEL FROM 175 K TO 425 K

    SciTech Connect

    Morgan, M; Glenn Chapman, G

    2009-05-04

    The effects of hydrogen on the fracture-toughness properties of Type 316L stainless steel from 175 K to 425 K were measured. Fracture-toughness samples were fabricated from Type 316L stainless steel forgings and hydrogen-charged with hydrogen at 34 MPa and 623 K for two weeks prior to testing. The effect of hydrogen on the J-Integral vs. crack extension behavior was measured at various temperatures by fracturing non-charged and hydrogen-charged samples in an environmental chamber. Hydrogen-charged steels had lower toughness values than non-charged ones, but still retained good toughness properties. The fracture-toughness values of hydrogen-charged samples tested near ambient temperature were about 70% of non-charged values. For hydrogen-charged samples tested at 225 K and 425 K, the fracture-toughness values were 50% of the non-charged values. In all cases, fracture occurred by microvoid nucleation and coalescence, although the hydrogen-charged samples had smaller and more closely spaced microvoids. The results suggest that hydrogen effects on toughness are greater at 225 K than they are at ambient temperature because of strain-induced martensite formation. At 425 K, the hydrogen effects on toughness are greater than they are at ambient temperature because of the higher mobility of hydrogen.

  5. Fracture fragility of HFIR vessel caused by random crack size or random toughness

    SciTech Connect

    Chang, Shih-Jung; Proctor, L.D.

    1993-11-01

    This report discuses the probability of fracture (fracture fragility) versus a range of applied hoop stresses along the HFIR vessel which is obtained as an estimate of its fracture capacity. Both the crack size and the fracture toughness are assumed to be random variables that follow given distribution functions. Possible hoop stress is based on the numerical solution of the vessel response by applying a point pressure-pulse it the center of the fluid volume within the vessel. Both the fluid-structure interaction and radiation embrittlement are taken into consideration. Elastic fracture mechanics is used throughout the analysis. The probability of vessel fracture for a single crack caused by either a variable crack depth or a variable toughness is first derived. Then the probability of fracture with multiple number of cracks is obtained. The probability of fracture is further extended to include different levels of confidence and variability. It, therefore, enables one to estimate the high confidence and low probability capacity accident load.

  6. Analysis of fracture toughness of explosion-hardened martensitic steel

    NASA Astrophysics Data System (ADS)

    Moskvitina, L. V.

    2015-10-01

    In this work we study a shift of the following nonlinear states: tempering + abatement + 10 GPa shock loading + welding thermocycle. As a result the self-organized HAZ metal structure with elements of self-similarity on different scales is found. The fractal analysis shows how formed defects affect the HAZ metal hardness of 14H2GMR steel with the martensitic structure of static fracture. The statistical analysis of stereometric parameters of fracture shows a higher energy intensity of static fracture in specimens treated by explosion. The multifractal analysis reveals hardness of the grid dislocation structure induced by explosion in the air-hardening zone. The homogeneity of the dislocation structure related to carbides increases the resistance of HAZ metal of static fracture.

  7. Fracture Toughness of Veneering Ceramics for Fused to Metal (PFM) and Zirconia Dental Restorative Materials

    PubMed Central

    Quinn, Janet B.; Quinn, George D.; Sundar, Veeraraghaven

    2010-01-01

    Veneering ceramics designed to be used with modern zirconia framework restorations have been reported to fracture occasionally in vivo. The fracture toughness of such veneering ceramics was measured and compared to that of conventional feldspathic porcelain veneering ceramics for metal framework restorations. The fracture toughness of the leucite free veneer was measured to be 0.73 MPa m ± 0.02 MPa m, which is less than that for the porcelain fused to metal (PFM) veneering ceramic: 1.10 MPa ± 0.2 MPa. (Uncertainties are one standard deviation unless otherwise noted.) The surface crack in flexure (SCF) method was suitable for both materials, but precrack identification was difficult for the leucite containing feldspathic porcelain PFM veneer. PMID:21833158

  8. Fracture toughness/Young's modulus correlation for low-density fibrous silica bodies

    NASA Technical Reports Server (NTRS)

    Green, D. J.

    1983-01-01

    Fracture toughness and static Young's modulus were measured for the low-density silic fiber materials used as tiles in the thermal protection system of the Space Shuttle. The fracture behavior was found to be in excellent agreement with a previously formulated micromechanical model and allowed both (density) classes of tile material to be correlated to a single function. A similar correlation was also found between strength and Young's modulus, which is the basis of a nondestructive evaluation test for these materials. It was shown that the value of Young's modulus determined from a dynamic test can be substantially greater than that determined in a static mechanical test. This effect must be taken into account in the correlation. Finally, it was also determined that these materials have significant variations in Kc, both within and between production units, so that the strength variability in these materials is dependent on both fracture toughness and flaw-size variations.

  9. Temperature dependence of fracture toughness of the cubic (L1{sub 2}) titanium trialuminides

    SciTech Connect

    Varin, R.A.; Zbroniec, L.

    1997-12-31

    Fracture toughness vs. temperature of the cubic (L1{sub 2}), Mn- modified titanium trialuminide (based on Al{sub 3}Ti) was investigated in air at the temperature range up to 1,000 C. Toughness calculated from the maximum load exhibits a broad peak (K{sub Q} {approx} 7--10 MPam{sup 0.5}) at the 200--500 C temperature range and then decreases with increasing temperature, reaching a room temperature value of {approximately}4.5 MPam{sup 0.5} at 1,000 C. However, the work of fracture ({gamma}{sub WOF}, J/m{sup 2}) and the stress intensity factor calculated from it (K{sub 1WOF}) increases continuously with increasing temperature. Fracture modes exhibit a gradual transition from transgranular cleavage at room temperature to predominantly intergranular failure at the 800--1,000 C range.

  10. The effects of neutron irradiation on fracture toughness of austenitic stainless steels.

    SciTech Connect

    Chopra, O. K.; Gruber, E. E.; Shack, W. J.

    1999-05-21

    Austenitic stainless steels are used extensively as structural alloys in reactor pressure vessel internal components because of their superior fracture toughness properties. However, exposure to high levels of neutron irradiation for extended periods leads to significant reduction in the fracture resistance of these steels. This paper presents results of fracture toughness J-R curve tests on four heats of Type 304 stainless steel that were irradiated to fluence levels of {approx}0.3 and 0.9 x 10{sup 21} n cm{sup {minus}2} (E >1 MeV) at {approx}288 C in a helium environment in the Halden heavy water boiling reactor. The tests were performed on 1/4-T compact tension specimens in air at 288 C; crack extensions were determined by both DC potential and elastic unloading compliance techniques.