Location of Repository

Crack growth resistance in nuclear graphite

By Shahed Fazluddin


R-curve behaviour is often used for evaluating crack growth resistance in quasibrittle materials but few studies have focused on polycrystalline graphite. In this study, R-curve behaviour in three commercial grade nuclear graphites, of\ud varying structure and properties, is compared using an optical method, a theoretical compliance method, and, a potential drop (PD) technique to measure crack length. Two graphites are coarse-grained and the third a fine grained graphite. Both 3-point bend and compact tension specimens are used.\ud \ud The fine-grain graphite shows lowest resistance, with the coarse-grained materials displaying similar R-curves. The compliance method is simplest but assumes the material is linear elastic, producing similar R-curves to the optical\ud method. The PID method seriously underestimates the crack length due to crack face bridging, causing the R-curves to show a falling behaviour. The shortfall in the PID measurements presents a novel way of physically measuring\ud the bridging zone length. The graphites display similar variation in the apparent bridging zone length despite the difference in grain size.\ud \ud Higher resistance in the coarser material results from increased crack path deflection, coupled with stronger grain bridging traction within the bridging zone.\ud The bridging zone length is longer in compact tension specimens than in 3-point bend specimens, explaining partly why higher fracture energy is recorded in compact tension. In oxidised graphite, the crack growth resistance reduces but the coarser materials still show useful resistance. The fine-grain graphite shows a tendency toward flat R-curve behaviour with increasing oxidation. The mechanisms responsible for toughening in non-oxidised graphite prevail in oxidised material but diminish with increasing porosity and loss of binder phase.\ud \ud A preliminary study of the nano-indentation behaviour of the nuclear graphites reveals a similar response in all the materials. Anelastic hysteresis in the loadunload\ud response is found with little residual deformation. There is also evidence of a creep effect during the dwell period at the maximum load. Comparison of the average indentation modulus with the bulk flexural and sonic modulus indicates that the nano-indentation technique is unable to sense bulk\ud modulus changes such as occur with oxidation or the forming process. Instead, the method is susceptible to localised structural inhomogeneities.\ud \u

Publisher: Institute for Materials Research (Leeds)
Year: 2002
OAI identifier: oai:etheses.whiterose.ac.uk:879

Suggested articles



  1. (1995). A doi
  2. (1956). A Method for determining the Degree of Orientation of Graphite. doi
  3. (1998). A New Technique for Pre-cracking Ceramic Specimens in Fatigue and Fracture.
  4. (1977). A Simplified Method for Measuring Plane Strain Fracture Toughness. doi
  5. (1990). Acoustic Emmission for Polycrystalline Graphite under Compressive Loading. doi
  6. (2000). Alum ina-m ullite-zi rcon ia Composites obtained by Reaction Sintering, Part 11: R-curve Behaviour.
  7. (2000). Alumina-mullite-zirconia Composites obtained by Reaction Sintering, Part 1: Microstructure & Mechanical behaviour.
  8. (1980). An AC Potential System for Crack Length Measurement.
  9. (1976). Analysis of Coherence, Strain, Thermal Vibration and Preferred Orientation doi
  10. (1985). Analysis of the Potential Drop Technique for Crack Length Measurement in a Chevron-notched Specimen. doi
  11. (1962). Analysis of the Stress-Strain relationships in Reactor Grade Graphite. doi
  12. (1992). Application of ACPD Technique to the determination of R-curves of Tough Ferritic Steels.
  13. (1988). Brittle Fracture Behaviour of Ceramics. doi
  14. C1421-1999, Determination of Fracture Toughness of Advanced Ceramics at Ambient Temperature. doi
  15. C611-1984, Electrical Resistivity of Manufactured Carbon and Graphite Articles at Room Temperature. doi
  16. (1990). Changes in Mechanical Properties of Graphites Parallel and Perpendicular to Compressive Prestress. doi
  17. (1995). Congress on Ceramics,
  18. (1984). Crack Growth Resistance in Microcracking Brittle Materials. doi
  19. (2002). Crack Growth Resistance in Nuclear Graphites. doi
  20. (1999). Critical Examination of the Fundamental Relations used in the Analysis of Nanoindentation Data. doi
  21. (1995). Deformation & Fracture in the Frontal Process Zone & Crack-face Contact Region of Polycrystalline Graphite.
  22. (1973). Deformation in Polycrystalline Graphite.
  23. (1988). Determination of Crack Bridging Forces in Alumina. doi
  24. (1950). Determination of Crystallite Size with the XRay Spectrometer. doi
  25. (1989). Dimensionless Load-Displacement Relation and its Application to Crack Propagation Problems. doi
  26. (1965). Direct Measurement of Fracture Energies of Brittle Heterogeneous Materials. doi
  27. (1983). Dynamic Fracture Toughness of Reaction-bonded Silicon-nitride. doi
  28. E399-1990, Standard Test Method for Plane-Strain Fracture Toughness of Metallic Materials. ASTM Standard E647-91, Measurement of Fatigue Crack Growth Rates.
  29. (1980). Effect of Errors in the Geometric and Electrical Measurements on Crack Length Monitoring by the Potential Drop Technique.
  30. (1983). Effect of Specimen Type on the Measured Values of Fracture Toughness of Brittle Ceramics.
  31. (1987). Elastic Analysis of some Punch Problems for a Layered Medium. doi
  32. (1961). Elastic Recovery of Conical Indentations. doi
  33. (1956). Elements of XRD.
  34. (1990). Elevated-Temperature R-curve Behaviour of a Polycrystalline Alumina. doi
  35. (2002). Enhanced Crack-bridging by Unbonded Inclusions in a Brittle Matrix. doi
  36. (1977). Experimental Determination of Fracture Mechanics Stress- Intensity Calibration doi
  37. (1997). Fabrication, Microstructure and Properties of Unidirectional C-fibre Re-inforced SiC Dual-matrix Composites. doi
  38. (2002). Fracture Characterisation of C/C Composites.
  39. (1989). Fracture Characteristics of Coarse-grained Ceramics.
  40. (1975). Fracture in Brittle Solids. doi
  41. (1967). Fracture in Polycrystalline Graphite. doi
  42. (1988). Fracture Mechanics of Refractory Materials.
  43. (1984). Fracture Mechanics,
  44. (1977). Fracture of Polycrystalline Graphite.
  45. (2000). Fracture Property Changes in Polycrystalline Graphite with Irradiation and Oxidation.
  46. (1992). Fracture Toughness and Brittleness of Ceramic Materials.
  47. (1980). Fracture Toughness Determination of A1203 using Four-point Bend Specimens with Straight-th rough and Chevronnotches. doi
  48. (1993). Fracture Toughness Testing of Brittle Materials. doi
  49. (1992). Generality of the Relationship among Contact Stiffness, Contact Area, and Elastic Modulus during Indentation. doi
  50. (1950). Geometrical Factors affecting Contours of X-ray Spectrometer Maxima. doi
  51. (1986). Graphical Methods for determining the Non-linear Fracture Parameters of Silica and Graphite Refractory Composites. doi
  52. (1984). Graphite and ParaCrystalline Carbon (Chapter 6). In Process Mineralogy of Ceramic Materials.
  53. (1997). In Introduction to Carbon Technologies: Chapter 12: Manufacture of Carbon Anodes.
  54. (1997). In Introduction to Carbon Technologies: Chapter 2: Activated Carbons.
  55. (1986). Interpreting Data from Depth-Sensing Instruments. doi
  56. (1985). Introduction to Fracture Mechanics, doi
  57. (2001). Investigation of Creep Behaviour under Load during Indentation Experiments and its influence on Hardness and Modulus. doi
  58. (2000). Investigation of the Relation between Position within Coater and Pyrolitic Carbon Characteristics using Nano-indentation. doi
  59. (1965). journal of the Serbian Chemical Society.
  60. (1980). Measurement of Crack Length and Data in Corrosion Fatigue.
  61. (1980). Measurement of Crack Length at Elevated Temperatures using the DC Potential Drop Technique.
  62. (1975). Mechanical Behaviour Model for Graphite. ASTM STP 605: Properties Related to Fracture Toughness, doi
  63. (1999). Mechanical Properties of C/C-composite Components determined using Nano-indentation.
  64. (1982). Memory Effect of Crack Resistance during Slow Crack Growth in Notched A1203 Bend Specimens. doi
  65. (1996). Modelling of Disorder and XRD in Coal-based Graphitic Carbons. doi
  66. (1970). Modern Aspects of Graphite Technology.
  67. (1997). Nano-indentation Behaviour of a 2-D C/C Composite for Nuclear Applications. doi
  68. (2000). Nanoindetation Behaviour of Mesophase-de rived Carbon and Graphite Materials. Abstracts (Vol. 1), ist World Conference on Carbon,
  69. (1999). New Procedure for Evaluating Material Resistance Curves under Static Loading Conditions by Applying the Potential Drop Method.
  70. (1962). Nuclear Graphite. doi
  71. (1998). Okada A doi
  72. (1997). On the initial unloading slope in Indentation of Elastic-Plastic Solids by an Indenter with an Axisymmetric Profile. doi
  73. (1992). Optical and Crystallographic Structure of Pitch Cokes. doi
  74. (1981). Oxidation Effects on CTE and Thermal Shock Fracture Initiation in Polycrystalline Graphites. doi
  75. (1968). Physical Properties of Graphite.
  76. (1995). Potential Drop Methods for Crack Characterisation. Materials World,
  77. (1988). R-curve Behaviour of a Polycrystalline Graphite: Microcracking and Grain Bridging in the Wake Region. doi
  78. (1965). Relation between Load and Penetration in the Axisymmetric Boussinesq Problem for a Punch of Arbitrary Profile. doi
  79. (1993). Relations between Structural Parameters obtained by Powder XRD of various Carbon Materials. doi
  80. (1986). Relationship between Microstructure and Elastic Modulus Reduction in Thermally and Radiolytically Corroded Nuclear Graphite. doi
  81. (1989). Section 1.2: Testing of Engineering Ceramics: Methods for determination of density and porosity.
  82. (1986). Sensitivity of the Potential Drop Technique for Crack Length Measurement in a Chevron-notched Specimen. doi
  83. (1983). Simple Velocity Gauge for measuring Crack Growth. doi
  84. (1981). Simultaneous Determination of Shear and Young's Moduli in Composites. doi
  85. (2000). Slow Crack-growth Behaviour in Alumina Ceramics. doi
  86. (2001). Some Aspects of Deformation and Fracture in Carbons.
  87. (1986). Studies of Fracture in Nuclear Graphite.
  88. (1980). The DC Electrical Potential Drop Method for Crack Length Measurement.
  89. (1996). The Detection and Measurement of Crack Growth during Ductile Fracture.
  90. (1971). The Effect of Prestressing on the Thermal Expansion and Young's Modulus of Graphite. doi
  91. (1986). The Fracture of Polygranular Graphites. doi
  92. (2002). The R-curve Behaviour of Alumina-SiC-Graphite Refractory Composites by Different Methodologies,
  93. (1951). The Structure of Graphitic Carbons. doi
  94. (1980). The use of Analogue & Mapping Techniques with Particular Reference to Detection of Short Cracks.
  95. (1992). Work of Fracture of Brittle Materials with Microcracking and Crack Bridging. doi

To submit an update or takedown request for this paper, please submit an Update/Correction/Removal Request.