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Book Size Geometry and Material Effects in Fracture Toughness Testing of Irradiated Zr 2 5Nb Pressure Tube Material

Download or read book Size Geometry and Material Effects in Fracture Toughness Testing of Irradiated Zr 2 5Nb Pressure Tube Material written by RSW Shewfelt and published by . This book was released on 2000 with total page 21 pages. Available in PDF, EPUB and Kindle. Book excerpt: The effect of initial crack size on the crack growth resistance (J-R) curves determined from burst tests on irradiated Zr-2.5Nb pressure tubes has been studied and the results compared with those obtained from matched curved compact specimens. The study used sections from three different tubes representative of material of low, intermediate, and high toughness. In each case a series of burst tests was conducted at 250°C with different starting crack sizes (from 35 to 85 mm) followed by small specimen testing. The toughness was characterized by means of deformation J-R curves using the d-c potential drop method to measure stable crack growth. Fractographic studies were also conducted in support of the J-R curve results.

Book Link Between Results of Small and Large Scale Toughness Tests on Irradiated Zr 2 5Nb Pressure Tube Material

Download or read book Link Between Results of Small and Large Scale Toughness Tests on Irradiated Zr 2 5Nb Pressure Tube Material written by PH. Davies and published by . This book was released on 1996 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt: The link between the results of small- (curved compact) and large-scale (burst) toughness tests on irradiated Zr-2.5Nb pressure tube material was investigated using material from tubes of different toughness values. Comparison between the crack growth resistance (deformation J-R) curves from the small- and large-scale specimens reveals the material dependence of geometry effects and shows that the crack-tip constraint in the compact specimen is generally higher than that in the burst specimen. For higher toughness material, the crack-extension region over which there is good correspondence between the J-R curves from the small- and large-scale specimens is in agreement with current knowledge of validity requirements for J-controlled crack growth of bend-type specimens. Fractographic studies were conducted and the results shown to be consistent with the observed geometry effects, a larger proportion of highly constrained, flat fracture being produced with the small bend-type specimens than with the burst tests. The results are discussed using a volume-controlled fracture model for bend-type specimens in which it is assumed that the toughness is governed by the development of the plastic zone associated with an intermediate-constraint, transition region between the central, flat-fracture zone and surfaceshear or slant-fracture zone. Applying scaling factors from the volume-controlled fracture model, good agreement is obtained between scaled values of the maximum pressure/load toughness from the small- and large-scale tests over a range of normalized plastic zone size of 0.4 to 1.

Book Fracture toughness of hydrided zr 2 5nb pressure tube material irradiated in the NRU test reactor

Download or read book Fracture toughness of hydrided zr 2 5nb pressure tube material irradiated in the NRU test reactor written by P. H. Davies and published by . This book was released on 1995 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: A study was completed on hydrided specimens of zr-2.5 nb pressure tube material irradiated in the nru test reactor to fluences up to 5 x 10 sup(24) n.m. sup(-2). material with three different mixed hydride morphologies (m1, m2 and m3 with hydrogen concentrations in the range of 42 to 61 wt ppm, 62 to 75 wt ppm and 183 to 216 wt ppm, respectively, and hydride continuity coefficients (hccs) in the range 0.1 to 0.3) was supplied by ontario hydro technologies for irradiation. the morphologies consisted of mixed hydrides of different orientations (m1/m2) as well as predominantly circumferential hydrides (m3). the joint effect of irradiation and zirconium hydride significantly reduces the toughness of the material at all test temperatures up to the operating temperature range, 240 degrees c, and results in an increased incidence of discontinuous crack growth (crack jumping) and unstable fracture. after irradiation the transition temperature for upper shelf fracture behaviour is above 240 degrees c for all three hydride morphologies. the reduction in the maximum load toughness, k sub(ml), at 240 degrees c is about 30 mpa square root of m due to irradiation and up to a further 18 mpa square root of m (m2) and 22 mpa square root of m (m3) due to the zirconium hydride. fractographic evidence is presented which shows that the increased incidence of discontinuous crack growth and unstable fracture after irradiation is due not only to an increase in the number of hydride sites activated close to the radial-axial plane but also to changes in the ability of the remaining material to arrest the crack. in particular, material containing a high concentration of microsegregated species (zr-cl-c complex) promotes unstable fracture due to the reduced area and width of dimpled rupture zones (between fissures) available for crack arrest.

Book Radial fracture toughness of irradiated zr 2 5nb pressure tube material

Download or read book Radial fracture toughness of irradiated zr 2 5nb pressure tube material written by D. D. Himbeault and published by . This book was released on 1995 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Book Effect of Irradiation on the Fracture Properties of Zr 2 5Nb Pressure Tubes at the End of Design Life

Download or read book Effect of Irradiation on the Fracture Properties of Zr 2 5Nb Pressure Tubes at the End of Design Life written by S. St Lawrence and published by . This book was released on 2005 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt: To determine the fracture properties of Zr-2.5Nb pressure tubes irradiated until the end of design life, cantilever beam, curved compact toughness, and transverse tensile samples were prepared from a typical pressure tube and irradiated in the high flux reactor OSIRIS at CEA, Saclay, France. Experiments were conducted on two batches of samples mounted in two irradiation inserts. Each insert held sixteen samples of each type of specimen. The first insert was irradiated to a fluence corresponding to approximately half of the design life in a CANDU3 reactor. The experimental results were reported in [1]. Samples in the second insert were irradiated for 10.5 years in OSIRIS and received a maximum neutron fluence of 2.61 x 1026 n/m2 (E > 1 MeV), being equivalent to 2.98 x 1026 n/m2 (E > 1 MeV) in a CANDU reactor, i.e., corresponding to ~30 years operation in CANDU reactors at 80 % capacity factor. The present report describes the results of tensile, fracture toughness, and Delayed Hydride Cracking (DHC) tests and XRD microstructure analysis from the second batch of specimens. A continuous and gradual evolution in tensile, fracture, DHC properties, and dislocation densities is demonstrated without any evidence of a sudden change following the initial transitient at very low fluence. In the whole high fluence range, there is a very slow rate of increase in c-component dislocation density, strength, and DHC velocity and a slow reduction in elongation and Nb concentration in the ?-phase. The a-type dislocation density and fracture toughness remain approximately constant. The results from the second insert of specimens confirm that, following the initial transient at very low fluence, there is little further change in the fracture properties of Zr-2.5Nb pressure tube material. Therefore, material properties behave in a stable and predicable manner to the end of a 30 years design life for CANDU reactor pressure tubes.

Book Fracture Toughness Evaluation of Heat Treated Zr 2 5Nb Pressure Tubes

Download or read book Fracture Toughness Evaluation of Heat Treated Zr 2 5Nb Pressure Tubes written by T. Asada and published by . This book was released on 1991 with total page 19 pages. Available in PDF, EPUB and Kindle. Book excerpt: Tests of full-size pressure tubes and compact tension specimens having several widths are carried out with emphasis on the size effect on the fracture toughness of the pressure tube material, which is made of heat-treated Zr-2.5Nb. The hydrogen concentration of the specimens ranges from 10 to 400 ppm, and the test temperature from room temperature to 573 K.

Book Effect of Long Term Irradiation on the Fracture Properties of Zr 2 5Nb Pressure Tubes

Download or read book Effect of Long Term Irradiation on the Fracture Properties of Zr 2 5Nb Pressure Tubes written by S. Sagat and published by . This book was released on 2000 with total page 17 pages. Available in PDF, EPUB and Kindle. Book excerpt: Results from fracture toughness and tensile and delayed hydride cracking (DHC) tests on Zr-2.5Nb pressure tubes removed from CANDU power reactors in the 1970s and 80s for surveillance showed considerable scatter. At that time, the cause of the scatter was unknown and prediction of fracture toughness to the end of the design life of a CANDU reactor using the surveillance data was difficult. To eliminate the heat-to-heat variability and to determine end-of-life mechanical properties, a program was undertaken to irradiate, in a high-flux reactor, fracture toughness, DHC, and transverse tensile specimens from a single "typical" pressure tube. Two inserts were placed in the OSIRIS reactor at CEA, Saclay, in 1988. Each insert held 16 of each type of specimen. The first insert, ERABLE 1, was designed so that half the specimens could be replaced at intervals and the properties could be measured as a function of fluence. All the specimens would be removed after a total fluence of 15 x 1025 n . m-2, E > 1 MeV. The second insert, ERABLE 2, was designed to run without interruption to a fluence of 30 x 1025 n . m-2, the fluence corresponding to 30 years' operation of a CANDU reactor at 90% capacity factor. The irradiation temperature was chosen to be 250°C, the inlet temperature of early CANDU reactors. The irradiation of ERABLE 1 has been completed and sets of specimens have been removed and tested with maximum fluences of approximately 0.7, 1.7, 2.8, 12, and 17 x 1025 n . m-2, E > 1 MeV. X-ray and TEM examinations have been performed on the material from fractured specimens to characterize the irradiation damage. Results showed that there is, initially, a large change in the mechanical properties before a fluence of 0.6 x 1025 n . m-2, E > 1 MeV (corresponding to an initial rapid increase in a-type dislocation density), followed by a gradual change. As expected, the fracture toughness decreased with fluence, whereas the yield strength, UTS, and DHC crack velocities all increased. Z-ray analysis showed that, although the a-type dislocation density remained constant after the initial increase, the number of c-component dislocations showed a steady increase, agreeing with the behavior seen in the mechanical specimens. Because the flux in OSIRIS is different from that in a CANDU reactor, specimens were also irradiated in NRU, a heavy water moderated test reactor with approximately the same flux as a CANDU reactor, to fluences of 0.3, 0.6, and 1.0 x 1025 n.m-2, E > 1 MeV for comparison. These initial results show that, once past the initial transient, one can have confidence that there will be little further degradation with fluence, with the results from the NRU specimens being similar to those from OSIRIS.

Book Stress Triaxiality in Zr 2 5Nb Pressure Tube Materials

Download or read book Stress Triaxiality in Zr 2 5Nb Pressure Tube Materials written by B. W. Leitch and published by . This book was released on 2009 with total page 18 pages. Available in PDF, EPUB and Kindle. Book excerpt: The crack growth resistance of irradiated Zr-2.5Nb pressure tubes is controlled by the initiation of voids and their subsequent growth and coalescence. The presence of particles that contribute to void nucleation is determined by the operating conditions/history of the pressure tube and by the concentration of pre-existing species, which is a function of the manufacturing process. The susceptibility of the pressure tubes to void nucleation is determined by the number and distribution of particles, the deformation properties of the matrix, and the stress state at the crack tip. The effect of irradiation on zirconium material is to increase the yield stress but to reduce the work hardening ability of the matrix and to promote strain localization, which, in turn, leads to void nucleation. Void nucleation is also enhanced by high values of stress triaxiality at or near the crack tip. For irradiated pressure tube material, both small-scale curved compact tension specimens and large-scale burst test sections are used to characterize the crack growth resistance. However, the measured fracture toughness can depend on the specimen geometry due to differences in constraint. The present investigation uses three-dimensional finite element analyses to characterize stress triaxiality at the crack tip in these different specimen geometries. Results of the numerical analyses are compared to the experimental evidence that provide qualitative evidence of differences in stress triaxiality at the crack tip for different specimen geometries.

Book Constraint Effects in Testing Different Curved Geometries of Zr 2 5Nb Pressure Tube Material

Download or read book Constraint Effects in Testing Different Curved Geometries of Zr 2 5Nb Pressure Tube Material written by PH. Davies and published by . This book was released on 1995 with total page 33 pages. Available in PDF, EPUB and Kindle. Book excerpt: Constraint effects in testing different curved geometries of Zr-2.5Nb pressure tube material have been studied with the aim of understanding discrepancies between toughness (critical crack length) values obtained from small specimens and burst tests. Crack growth resistance or deformation J-R curves were obtained on unirradiated pressure tube material at room temperature using small 17 and 34 mm wide curved compact specimens, 60 mm wide curved centre cracked specimens and burst test specimens.

Book Effects of Hydride Morphology on Zr 2 5Nb Fracture Toughness

Download or read book Effects of Hydride Morphology on Zr 2 5Nb Fracture Toughness written by AC. Wallace and published by . This book was released on 1989 with total page 23 pages. Available in PDF, EPUB and Kindle. Book excerpt: The effects of hydride morphology on the axial fracture toughness of cold-worked Zr-2.5Nb pressure tube material have been determined between room temperature and 240°C. Tests were performed on small compact tension specimens machined from samples of material prepared with different morphologies and hydrogen concentrations. The morphologies were characterized by a parameter referrred to as the hydride continuity coefficient (HCC), which provides a measure of the extent to which hydrides are oriented in the axial-radial plane of the pressure tube. Hydrides in this orientation are known to be detrimental to the fracture properties of the tube. Fracture toughness was characterized by a J-R curve technique, from which it is possible to estimate the maximum stable size of a through-wall axial crack for typical reactor operating conditions. Material with HCC values greater than 0.5 exhibited low toughness from room temperature to 240°C, at which temperature there was an abrupt transition to an upper shelf toughness value. As HCC decreases, the transition to upper shelf toughness occurs more gradually and is complete at a lower temperature.

Book Correlation Between Irradiated and Unirradiated Fracture Toughness of Zr 2 5Nb Pressure Tubes

Download or read book Correlation Between Irradiated and Unirradiated Fracture Toughness of Zr 2 5Nb Pressure Tubes written by CK. Chow and published by . This book was released on 1994 with total page 33 pages. Available in PDF, EPUB and Kindle. Book excerpt: Three coordinated research programs were undertaken on the fracture toughness of Zr-2.5Nb pressure tubes to determine relationships between irradiated and unirradiated values, the effect of long-term irradiation, and the causes of the variation in toughness. The present paper describes results from these programs and their implications.