bluuebunny/crossref_metadata_2025 huggingface dataset:
Charpy Impact Toughness of Martensitic Steels Irradiated in FFTF: Effect of Heat Treatment
Authors: Klueh RL , Alexander DJ
Published: March 2009

Charpy tests were made on plates of 9Cr-1MoVNb and 12Cr-1MoVW steels given four different normalizing-and-tempering treatments. Onethird-size Charpy specimens from each steel were irradiated to 7.4-8 × 1026 n/m2 (about 34-37 dpa) at 420°C in the Materials Open Test Assembly of the Fast Flux Test Facility. Specimens were also thermally aged to 20000 h at 400°C to determine the effect of aging during irradiation. Previous work on these steels irradiated to 4–5 dpa at 365°C in MOTA were reexamined in light of the new results. The tests indicated that prior austenite grain size, which was varied by different normalizing treatments, had an effect on impact behavior of the 9Cr-1MoVNb but not on the 12Cr-1MoVW. Tempering treatment had relatively little effect on the shift in DBTT for both steels. Conclusions are presented on how heat treatment can be used to optimize properties.
Effects of Neutron Irradiation on the Notch Ductility of 15MnTi Steel
Authors: Aixin YJ , Han RP
Published: March 2009

15MnTi steel as a support plate must withstand both the weight of the reactor core of about 100 tons and dynamic loads at 40°C to 50°C. In this study, the steel was embrittled by the neutron irradiation from the reactor core. The ductile-brittle transition temperature was also increased.

The specimens were taken from base plate, weld metal, and weld heat-affected zone. The specimens were irradiated in a swimming pool reactor (SPR).

The test results included impact energy (αk), reference transition temperature (RTNDT), and transition temperature increase (ΔTcv) of 15MnTi steel under the neutron exposure 1 to 2 × 1018n/cm2(E > 1 MeV). The transition temperature was 6°C and 2°C for base plate and weld metal, respectively, after 1 × 1018n/cm2(E > 1 MeV) at 50°C. The transition temperature increase was 40°C, 41°C, and 32°C for base plate, weld metal, and weld heat-affected zone, respectively, after about 2 × 1018n/cm2(E > 1 MeV) at 50°C.

The data of transition temperature increased on 15MnTi steel after 1 to 6 × 1018n/cm2(E > 1 MeV) at 50°C was summarized. An empirical equation was obtained: T = 32.7 - 1.8 lnϕt + 17.8 ln2ϕt, where ϕt is fast neutron exposure (E > 1 MeV).
The Influence of Specimen Size on Measurement of Thermal or Irradiation Creep in Pressurized Tubes
Authors: Garner FA , Hamilton ML , Puigh RJ , Eiholzer CR , Duncan DR , Toloczko MB , Kumar AS
Published: March 2009

Thin-walled pressurized tubes have been developed for measurement of thermal creep and irradiation creep. Miniaturization of these tubes allows more tests to be conducted in the limited reactor space available and decreases the impact of displacement rate gradients and temperature gradients. Studies conducted on a variety of tube sizes show that, when specimen fabrication history and irradiation conditions are controlled, miniaturization can be successfully achieved and valid data produced.
Tensile Properties of Neutron Irradiated 316Ti and 15-15Ti Steels
Authors: Fissolo A , Lévy V , Séran JL , Maillard A , Royer J , Rabouille O
Published: March 2009

This paper deals with the tensile behavior of CW316Ti and CW15-15Ti Phénix fuel pin cladding. The tension tests were conducted on defueled tubes irradiated up to 115 dpa3 in the 400–640°C temperature range. Test temperature corresponds essentially to irradiation temperature. The results emphasize that, although irradiation induces a reduction of ductility, the failure always occurs with significant plastic deformation, even for the most highly irradiated cladding.

At irradiation temperatures below 560°C, the embrittlement of both steels is correlated to the swelling and thus to the occurrence of irradiation-induced voids; in this case, the failure is transgranular. In the high irradiation temperature range, a marked difference is observed between the two steels when the tests are conducted at the irradiation temperature, since the rupture is essentially intergranular on CW316Ti and transgranular on CW15-15Ti. The tensile properties of the CW15-15Ti cladding are better than those of CW316Ti because it swells less and is less prone to creep-like embrittlement.
Helium-Induced Weld Degradation of HT-9 Steel
Authors: Wang C-A , Lin HT , Grossbeck ML , Chin BA
Published: March 2009

Helium-bearing Sandvik HT-9 ferritic steel was tested for weldability to simulate the welding of structural components of a fusion reactor after irradiation. Helium was introduced into HT-9 steel to 0.3 and 1 atomic parts per million (appm) by tritium doping and decay. Autogenous single pass full penetration welds were produced using a gas tungsten arc (GTA) welding process under laterally constrained conditions. Microscopic examination showed no sign of any weld defect in HT-9 steel containing 0.3 appm helium. However, intergranular micro cracks were observed in the HAZ of HT-9 steel containing 1 appm helium. The microcracking was attributed to helium bubble growth at grain boundaries under the influence of high stresses and temperatures that were present during welding. Mechanical test results showed that both the yield strength (YS) and ultimate tensile strength (UTS) decreased with increasing temperature, while the total elongation increased with increasing temperature for all control and helium-bearing HT-9 steels.
Radiation Creep and Swelling of Austenitic 16Cr-15Ni-3Mo-Nb Steels Irradiated in the Reactor BOR-60 at 350 and 420 C
Authors: Neustroev VS , Shamardin VK
Published: March 2009

Radiation creep and swelling of 16Cr-15Ni-3Mo-Nb steels were studied after irradiation in the BOR-60 reactor at 350 and 420 C up to maximum fluence 11.9*1026 m-2 (E>0.1MeV), i.e. 60 dpa. Pressurized tubes were made of two steels with different carbon content (0.046 and 0.006 w. %). Swelling of the stress-free tubes depends on carbon content. Radiation creep rate depends only upon the stress level and the rate of swelling. Coefficients of swelling and creep interrelation are not sensitive to carbon content and irradiation temperature.
Influence of Aluminum and Titanium on Gas Bubble Microstructure Formation in Nickel Under Helium-Ion Irradiation
Authors: Kalin BA , Chernov II , Kalashnikov AN , Markin AV , Shishkin GN , Korshunov SN
Published: March 2009

The influence of aluminum and titanium on the helium bubble microstructure formation in nickel and its alloys was investigated using transmission electron microscopy (TEM), thermal desorption spectroscopy (TDS), electrical resistance, and microhardness measurements. The helium implantation was carried out at room temperature (cold implantation) and at 750°C (high-temperature implantation) up to dose 5 ∙ 1020 m-2. The materials used were nickel base alloys with aluminum content of 0 to 7.5 wt.% and with titanium content of 0 to 8.3 wt.%. A substantial influence of aluminum and titanium on the helium bubble microstructure parameters has been established. The results are discussed in terms of helium trapping in the solution taking into account the formation of a secondary phase.
Radiation-Induced Solute Segregation and Stress Corrosion Cracking Study of AISI 304 and AISI 304L Stainless Steels
Authors: Liu WJ , Kai JJ , Tsai CH
Published: March 2009

Radiation induced solute segregation (RIS) of chromium, nickel, and minor elements (e.g., Si, P, S, etc.) in the vicinity of grain boundaries and its influences on intergranular stress corrosion cracking (IGSCC) of commercial purity AISI 304 and AISI 304L austenitic stainless steels were investigated in this study. High energy protons were used for producing irradiation environment.

Three millimeter TEM discs and miniature tensile specimens were irradiated at 550°C with 1 and 5 MeV H+ individually to doses of 0.01, 0.1, and 1 dpa respectively. Microstructural evolution and radiation-induced solute segregation were studied by using STEM/EDAX microscopy. Constant extension rate tensile (CERT) under various environments were performed using the irradiated miniature tensile specimens to study the relationship between solute segregation and SCC susceptibility of these materials.

Microstructural examination indicated that void swelling was observed in both 304 stainless steels irradiated specimens at the dose of 0.1 dpa and above. Precipitate analysis found that M23C6 carbides were the major precipitates in the as-received (AR) and sensitized (SAS) specimens. Irradiation enhanced precipitation(M23C6 carbides)along grain boundaries was also observed in irradiated AR specimens. It was found that in the irradiated specimens, both Cr and Fe were depleted and Ni and Si were enriched near the grain boundary areas. Proton irradiation induced the nucleation and growth of ferrite phase(bcc) was observed in AISI 304L stainless steels irradiated at 550°C. The size and density of ferrite increased with increasing fluence, and it is found that many M23C6 carbides formed along the interface of F-matrix and ferrite grains.

CERT test indicated that IGSCC accompanying with TG fracture existed in the irradiated region after 1 dpa irradiation and dimples in the unirradiated region. It is found proton irradiation induced the grain boundary etching and surface slip bands which may in turn affect the CERT results in the sense of initiating intergranular cracks.
Influence of Impurities and Alloying Elements on IASCC in Neutron Irradiated Austenitic Stainless Steels
Authors: Kodama M , Fukuya K , Kayano H
Published: March 2009

Slow strain rate tests (SSRTs) and HNO3/Cr6+ corrosion tests of several types stainless steels irradiated to 5.3×1024n/m2 at about 573K, were conducted to evaluate the correlation between irradiation assisted stress corrosion cracking (IASCC) and radiation induced grain boundary segregation.

All the stainless steels tested failed intergranularly after neutron irradiation. Type 321 and 347 were less susceptible to IASCC than Type 304 and 316. IASCC susceptibility was mitigated by the addition of oversized elements for chromium (for example/ titanium and niobium).

Intergranular corrosion in the HNO3/Cr6+ tests was accelerated due to irradiation in commercial purity (CP) stainless steels, while high purity (HP) stainless steels were immune to corrosion. The occurrence of IASCC in both HP and CP stainless steels indicated that radiation induced impurities enrichment may not be the main contributor to IASCC.

IASCC susceptibility could be correlated to the austenite phase stability and steels of higher austenite phase stability seemed to be less susceptible to IASCC.
The Relationship of Grain Boundary Composition in Irradiated Type 304SS to Neutron Fluence and IASCC
Authors: Jacobs AJ
Published: March 2009

Scanning transmission electron microscopy (STEM) analyses and HNO3/Cr+6 corrosion tests were carried out on irradiated Type 304 (UNS 530400) stainless steel (SS), in an attempt to correlate grain boundary composition with fast neutron fluence (E > 1 MeV) and irradiation-assisted stress corrosion cracking (IASCC) susceptibility. Test coupons originated from boiling water reactor (BWR) internals which had been fabricated from several heats of material. STEM and corrosion test results showed that cracking incidence in a crevice is independent of silicon and phosphorus segregation and chromium depletion, although still dependent on fluence. Grain boundary levels of silicon and phosphorus were influenced most strongly by the bulk values of these elements. In the commercial-purity (CP) heats having relatively high bulk values of silicon and phosphorus, marked segregation of these elements was observed with increasing fluence. The amount of chromium depletion tended to be greater in the CP heats than in a high-purity (HP) heat at higher fluences, and lower in the CP heats at lower fluences.
The Observation and Interpretation of Microstructural Evolution and Swelling in Austenitic Steels Under Irradiation
Authors: Sekimura N , Hamada K , Ishino S
Published: March 2009

Irradiation behavior of model austenitic steels is investigated to establish mechanistic modeling of swelling and other property changes under irradiation. Neutron irradiation experiments were performed using Material Open Test Assembly (MOTA) at 693, 793 and 873 K to 35 to 40 dpa in the Fast Flux Test Facility (FFTF) cycles 10 and 11. Cavity formation and dislocation development were quantitatively estimated to evaluate the effect of temperature history on the microstructural evolution under irradiation in fission reactors. Fine dislocation loops observed in the matrix of the alloys irradiated in cycle 10 were considered to come from the low-temperature irradiation during the reactor shut-down at the end of the cycle. Very few small loops were detected in identical specimens irradiated in FFTF cycle 11 where the reactor power and temperature were simultaneously decreased a short time during the shut-down.
The Role of Nickel and Zinc in Defect Behavior and Microstructural Evolution of Copper Under Electron Irradiation
Authors: Muroga T , Ishimaru E , Yoshida N
Published: March 2009

The effects of nickel and/or zinc addition on microstructural evolution in copper under electron irradiation have been investigated to study possible effects of solid transmutants generated in copper and copper alloys by fusion neutrons. Radiation-induced dislocation density increased with increasing nickel content but was independent of zinc content during 1 MeV electron irradiation. An enrichment of nickel and a depletion of zinc at grain boundaries occurred during irradiation. Measurements of temperature and damage rate dependences of saturated dislocation loop density showed that the interstitials are deeply trapped by nickel clusters forming loop nuclei in alloys containing nickel. It was shown that clusters of nickel as a solid transmutation product can affect strongly the dislocation evolution and related properties of copper and copper alloys by trapping interstitials from relatively initial period of fusion reactor operation. On the other hand, the effects of zinc production seemed to be small, althogh possible interactions with vacancies were suggested.
Mechanical Properties of Induction Brazed Glidcop Al-15
Authors: Lee CK , Chin BA , Zinkle SJ , Wilcox RC
Published: March 2009

An induction brazing process using a silver filler material was developed for the copper alloy GlidCop Al-15. Hardness measurements indicated recrystallization did not occur during brazing. Failure of overlap joints in tensile occurred outside the joint when the overlap to base metal thickness ratio was greater than 1.5. The average unit tensile strength of overlap joints increased with this ratio and became constant at a ratio of 5. The average unit shear strength continued to decrease with an increasing ratio. Fatigue results of unbrazed GlidCop Al-15 were described by a total strain-life curve for both high cycle and low cycle fatigue. Brazed joints were tested only in the elastic strain region. Fatigue strengths of induction and furnace brazed butt joints were about the same but less than that of the cold worked GlidCop Al-15 alloy.
Evolution of Microstructure in Zirconium Alloy Core Components of Nuclear Reactors during Service
Authors: Griffiths M , Chow PCK , Coleman CE , Holt RA , Sagat S , Urbanic VF
Published: March 2009

X-ray diffraction (XRD) and analytical electron microscopy (AEM) have been used to characterise microstructural and microchemical changes produced by neutron irradiation of Zr-2.5Nb, Zircaloy-2 and Zircaloy-4 nuclear reactor core components.

In many cases there is a clear relationship between the radiation damage microstructure and the physical properties of in-service core components. For example, the difference in delayed hydride cracking velocity between the inlet and outlet ends of Zr-2.5Nb pressure tubes in PHWR reactors can be directly correlated with variations in a-dislocation density and β-Zr phase decomposition. For the same tubes, the variation of fracture toughness has the same fluence dependence as dislocation loop density and, in addition, improvements in corrosion behaviour can be linked with decreases in the Nb concentration in the α-Zr matrix due to Nb precipitation during irradiation. For PWR and BWR reactors, the onset of “breakaway” growth in Zircaloy-4 guide tubes can be directly correlated with the appearance of basal plane dislocation loops in the microstructure.
Strain Hardening Parameter Evaluation of Irradiated Zircaloy—2
Authors: Balakrishnan KS , Chatterjee S
Published: March 2009

The strain hardening parameter of irradiated Zircaloy-2, has been evaluated using two empirical equations, namely Hollomon's and Voce's. Room temperature ring tension test data generated on irradiated fuel element cladding tubes as well as the 573 K tension test data obtained on irradiated pressure tubes, were utilised. The cladding tubes were from fuel elements of Tarapur Atomic Power Station (TAPS) that had experienced burnup ranging from 6000 to 15000 MWD/T. The pressure tubes had undergone 3.6 Effective Full Power Years of operation in Rajasthan Atomic Power Station (RAPS). Of the two equations employed for the study, Voce's equation was found to be more suitable for predicting the uniform ductility and ultimate tensile strength values in conformity with experimentally observed results.
Irradiation Growth of Zirconium Alloys
Authors: Yang JC , Ren JY
Published: March 2009

Experimental investigation of irradiation growth on annealed Zircaloy-4 and 20% to 50% cold-worked Zr-2.5wt%Nb specimens with stress relief has been carried out. The specimens are irradiated in a heavy water reactor at 610 K to 4.2 x 1024 n/m2 (E > 1.0 MeV). The growth strains increase linearly with fluence. The saturation of growth is not observed for all specimens. The difference of growth behavior between two kinds of Zircaloy-4 tube may be associated with the content of minor alloying elements and impurities that influence the microstructure evolution under irradiation.

The difference of growth strains of cold-worked Zr-2.5wt%Nb at different temperature of stress relief is related to the grain size and shape and the degree of cold work.
Irradiation-Induced Precipitation in Vanadium-Base Alloys Containing Titanium
Authors: Chung HM , Loomis BA , Smith DL
Published: March 2009

A transmission electron microscopy (TEM) investigation has been conducted on V-Ti, V-Ti-Cr, and V-Ti-Si alloys after neutron-irradiation at 420 and 600°C to fluences up to 114 dpa in the Fast Flux Test Facility (FFTF). Two types of irradiation-induced precipitates were identified, i.e., Ti2O and Ti5Si3, in addition to blocky Ti(O,N,C) that formed by thermal processes during ingot fabrication. Characteristics of the irradiation-induced precipitation were correlated with the swelling and mechanical properties of the irradiated alloys. In specimens where Ti5Si3 precipitation was significant, swelling was negligible. In specimens where Ti2O and Ti5Si3 precipitation was significant, ductility was relatively low.
Fatigue Crack Growth of Neutron Irradiated V-15Cr-5Ti and V-3Ti-1Si
Authors: Witzenburg WV , de Bruyne HJ
Published: March 2009

Compact-tension (CT) specimens of the alloys V-15Cr-5Ti and V-3Ti-1Si were irradiated to 3.8 × 1025n.m-2 (E > 0.1 MeV), corresponding to 4.0 dpa, at the temperatures 500, 600 and 700°C. Some specimens of the alloy V-3Ti-1Si were doped with 100 appm 10B, which during the irradiation was almost entirely transmuted to helium. Following irradiation constant-load-amplitude crack growth was measured at 200°C in air. All tests were performed at one R-ratio of 0.1 and a frequency of 2 Hz. Although both alloys in unirradiated condition showed similar crack growth rates as a function of the stress intensity factor range, the irradiated alloys behaved differently. The fatigue crack growth rate of V-3Ti-1Si irradiated at 500°C was slightly higher, with a lower dependence on the stress intensity factor range, compared to the unirradiated material, while after irradiation at 600 and 700°C the fatigue crack growth rate approached that of the unirradiated material. On the other hand, the alloy V-15Cr-5Ti irradiated at 500 and 600°C showed irregular crack growth and a higher growth rate, indicative of local unstable crack growth. After irradiation at 700°C the fatigue crack growth rate of this alloy also approached that of the unirradiated reference material. Limited data indicate that helium, generated by (n,α)-reaction with 10B, had no effect on the crack growth rate.
Effect of Neutron Irradiation on Thermal Conductivity of Carbon/Carbon Fiber Materials at 400 and 600°C in the Fluence Range 1 × 1022 to 1 × 1024 m-2
Authors: Thiele BA , Binkele L , Koizlik K , Nickel H
Published: March 2009

Because of their low atomic number and excellent thermal conductivity, carbon/ carbon fiber materials are seen as potential candidates for plasma-facing components, such as divertors, in Tokamak fusion devices. In the technology phase of Next European Torus (NET) or International Thermonuclear Experimental Reactor (ITER), the surface of a divertor will operate between 400 and 1000°C, and the materials will accumulate a lifetime neutron fluence equivalent to a dpa damage of 0.1. Low doses of neutron irradiation cause a significant decrease in the thermal conductivity of graphitic materials at low temperatures. To quantify the effect, candidate materials such as fine- and superfine-grained graphites (as reference materials), carbon/carbon fiber composites, and an oriented pyrolytic carbon (PyC) were irradiated at 400 and 600°C up to 0.1 dpa. At this fluence and at 400°C, the thermal conductivity (/) is reduced by 40 to 60%, whereas irradiation at 600°C caused a reduction of the l-values at irradiation temperature by about 20 to 40%. This spread seems to be caused by material differences but could be due to the uncertainties in the measurement and neutron fluence.
Coherency Stress and Transgranular Stress Corrosion Cracking of Cu-18Au Alloy
Authors: Fritz JD , Parks BW , Pickering HW
Published: March 2009

It has been proposed that the lattice mismatch between a dealloyed layer and the substrate alloy may play a role in the transgranular stress corrosion cracking (TSCC) of copper alloys. This investigation uses the single-exposure X-ray technique to measure the residual stress in a dealloyed layer formed by the selective dissolution of copper (Cu) from a copper-gold (Cu-18Au) alloy. The gold-rich dealloyed layer was found to have an average compressive stress of 39.3 MPa, indicative of a lattice mismatch at the alloy/dealloyed layer interface. Polycrystalline specimens of Cu-18Au that were dealloyed and then stressed during anodic polarization to relatively large overpotentials for copper dissolution showed cracking that propagated well into the substrate alloy. The cracking was predominantly transgranular, and the fracture surfaces showed features consistent with a transgranular cleavage mechanism. On the other hand, specimens that were dealloyed and then stressed while polarized to relatively low overpotentials for copper dissolution, formed cracks in the dealloyed layer that were always arrested at the alloy/dealloyed layer interface. Lateral resolution was a fraction of a micrometre (μm), so that it was obvious that within this resolution limit there was no propagation into the bulk alloy. These results suggest that the lattice mismatch by itself is not sufficient to propagate a crack into the substrate alloy. However, results for a wider range of conditions and with improved resolution are now needed to more completely address this issue.
Environmental Acceleration of Fatigue Crack Growth in Reactor Pressure Vessel Materials and Environments
Authors: Van Der Sluys WA , Emanuelson RH
Published: March 2009

This paper presents the results of experiments to determine which variables have the most effect on environmentally assisted cracking (EAC) of reactor pressure vessel steels. Four heats of SA508 and three heats of SA533 were studied in 288°C pressurized water reactor, light water reactor, and boiling water reactor environments. The sulfur content of these materials ranged from 0.004 to 0.025%. The most important variable was found to be the sulfur content and sulfur morphology of the material. A material with a bulk sulfur content greater than 0.010% may be susceptible to EAC. The loading frequency was found to be an important variable. Minor effects of EAC were attributed to the load ratio, ΔK level, and oxygen content of the environment. An experimental method to introduce sulfur directly to the crack tip is described. A time-based method of data interpretation is discussed.
A Mechanics-Based Analysis of Stress-Corrosion Cracking of Line-Pipe Steel in a Carbonate-Bicarbonate Environment
Authors: Leis BN , Walsh WJ
Published: March 2009

A model for stress-corrosion cracking (SCC) crack initiation and early growth has been developed and used to rationalize the SCC susceptibility observed in tapered-tension tests of line-pipe steels that have been tested at a high maximum stress, with a small amplitude load-controlled cyclic component in a carbonate-bicarbonate environment. Results presented here indicated a good correlation between the observed susceptibility and that predicted with the model. The main conclusion is that SCC models can be used to rationalize experimentally observed cracking behavior and as such can be used to identify conditions for cracking or mitigation beyond the scope of the test conditions, including line pipe applications.
Modeling of Sulfide Inclusion Distributions in Relation to the Environmentally Assisted Cracking of Low-Alloy Steels in a Pressurized Water Reactor Environment
Authors: Swan DI , Chapman OJV
Published: March 2009

Work carried out in the recent past by members of the International Cyclic Crack Growth Rate Group (ICCGRG) has demonstrated the close connection between the occurrence of environmentally assisted cracking (EAC) in low-alloy steels in a pressurized water environment and the presence of sulfide inclusions in the steel. Due to the length of time that experimental work can take, coupled with the sometimes poor repeatability of tests, work was undertaken on a computer model of “sulfide particle” distributions and their interaction with a hypothetical crack front.

The model is basically simple in concept, proceeding in the following manner. An array of randomly located spherical particles, each assumed to consist of a large number of subparticles is set up within a matrix. A crack, exposed to a water environment, is then grown through this matrix, particles intercepted by the crack dissolving; this is modeled by the spreading out of subparticles. Additional factors such as the rate of particle dissolution and rate of subparticle loss from the system are also incorporated into the model. The model is set up to calculate the number of subparticles that congregate at the crack tip. The single premise adopted is that greater than a specified number of subparticles at the crack tip is sufficient to bring about EAC.

In the work discussed here, consideration is given to the relative importance of material sulfur content and second-phase particle size. It was found that the latter had a much greater influence on subparticle numbers at the crack tip than the former. From this, it is concluded that the setting of a bounding curve in Section XI of the ASME Code for modern low sulfur steels would depend more on the occurrence of smaller sulfide particles than the lower sulfur content in such steels. Also considered was the variation of the occurrence of EAC with cycling frequency and stress intensity factor range (ΔK). From the boundaries to the EAC regime, data are obtained that can be applied to the setting of upper bounding curves for the ASME Code.
Effects of Stress and Stress History on the Magnitude of the Environmental Attack in Renè 80
Authors: Balsone SJ , Nicholas T , Khobaib M
Published: March 2009

Sustained-load creep tests using smooth, round bar specimens of Renè 80 were conducted at 900°C (1652°F) in two environments, namely, laboratory air and a 90% Na2SO4/10% NaCl molten salt film. Results show approximately a factor-of-two reduction in the rupture life of specimens tested in the molten salt environment. Metallographic examination of the failed specimens showed greater depths of environmental attack in the cross section as stress level increased from 207 to 310 MPa (30 to 45 ksi). Below a “critical” stress level, the depth of environmental attack remains nearly constant. Failure initiated by cracking along oxide-metal interfaces resulting from oxygen penetration and the formation of internal oxide fingers in the substrate material. A periodic unloading/reloading fatigue cycle superimposed on sustained-load creep tests had no effect on rupture lives for specimens tested in laboratory air,and the depth of environmental attack remained constant. However, rupture lives obtained in the molten salt environment were significantly reduced by the periodic fatigue cycle where spallation of the surface oxide layer during cycling was extensive and the depths of hot corrosion attack were greater.
Environmental and Microstructural Influence on Fatigue Propagation of Small Surface Cracks
Authors: Petit J , Zeghloul A
Published: March 2009

The propagation of small surface cracks has been studied on a high-strength aluminum alloy 7075 in peak aged (T651) and overaged (T7351) conditions. Tests were performed at a load ratio R = 0.1 and a frequency of 35 Hz in ambient air and in vacuum. Small crack growth was monitored by mean of replicas. The behavior of small cracks is compared to that of long and short through cracks and discussed on the basis of closure measurements performed on long cracks. A strong influence of environment on small crack growth has been shown which is similar to that observed for through cracks in the low rate range (<10-8 m/cycle). The lower resistance observed in air has been related to water vapor embrittlement as previously shown for long cracks. The influence of microstructure at the scale of grain size has been shown to be large on crystallographic Stage I propagation observed in vacuum on the 7075 T651, but weak on Stage II propagation observed on the 7075 T651 in air and on the 7075 T7351 in both environmental conditions.
Environmentally Induced Fatigue Crack Propagation Under Variations in the Loading Conditions
Authors: Schulte K , Nowack H , Lütjering G
Published: March 2009

In order to evaluate the influence of the environment on the crack retardation behavior under variable loading conditions, high-low block loading tests were performed in vacuum, air, and a 3.5% NaCl (sodium chloride) solution. In an additional test series, variations of the environment from vacuum in the high loading period to air or to 3.5% NaCl solution in the low loading period were performed, and vice versa. These tests, together with an extensive study of the crack surface morphology gave insight into the different fatigue mechanisms induced by the various environments at the crack tip.

A further test series was performed, where the load level was kept constant (constant-amplitude loading) and only the test environment was changed. The results show a variation of the environment from the 3.5% NaCl solution to vacuum causes a retardation in fatigue crack propagation.
Influence of Experimental Variables on the Measurement of Stress Corrosion Cracking Properties of High-Strength Steels
Authors: Judy RW , King WE , Hauser JA , Crooker TW
Published: March 2009

A systematic investigation was undertaken to examine the influence of experimental variables on the measurement of stress corrosion cracking (SCC) properties of two high-strength steels using fracture mechanics test procedures. The properties of interest were the SCC threshold stress-intensity (KISCC) and time-based crack growth rate (da/dt). Two quench-and-tempered alloy steels in the form of rolled plate material were tested. The steel had yield strengths of 965 MPa (140 ksi) and 1207 MPa (175 ksi). The primary experimental variables investigated included: (1) specimen type (bolt-loaded wedge-opening loaded (WOL) and cantilever beam); (2) bulk solution chemistry (3.5% NaCl in distilled water and natural seawater); (3) dissolved oxygen content of the bulk solution; (4) electrode potential (open circuit and -1.0 V versus Ag/AgCl); (5) method of applying cathodic protection (potentiostat and zinc couple; (6) precracking stress-intensity level; (7) initial applied stress-intensity level; and (8) test duration. The effects of these experimental variables on KISCC and da/dt measurement are reported and the implications of these findings on test method development are discussed.
Environmentally Assisted Cracking Behavior of a High-Level Nuclear Waste Container Alloy
Authors: James LA , Duncan DR
Published: March 2009

The environmentally assisted cracking behavior of cast ASTM A27 steel in a simulated groundwater environment was studied using both statically loaded and cyclically loaded specimens. The results show that, compared to other aqueous environments, the groundwater environment is relatively nonaggressive. The nonaggressive nature of this environment is believed to be related to its high pH and low level of dissolved oxygen.
Evaluation of Cavitation-Erosion Resistance of Ion-Plated Titanium Nitride Coating
Authors: Matsumura M , Oka Y , Ebara R , Kobayashi T , Odohira T , Wada T , Hatano M
Published: March 2009

Cavitation-erosion tests of steel, coated with a layer of titanium nitride (TiN) by physical vapor deposition, were conducted using a wall-facing vibratory testing facility and an ultrasonic cavitation-erbsion testing facility based on the ASTM Method for Vibratory Cavitation Erosion Test (G 32-85). The amount of erosion damage to the test specimen was evaluated by various methods. It was confirmed that the erosion resistance of TiN coated steel is superior to steel coated with the same film thickness of electroplated chromium, and of course to uncoated base metal (SUS410J1 stainless steel). It has been also confirmed that chromium-titanium nitride multilayered coating shows the most effective erosion resistance among the tested ion-plated coating specimens. The reasons of this improvement in the erosion resistance of TiN coated materials are as follows. First, the TiN layer did not peel off from the substrate surface, owing to its adhesion strength. Secondly, the erosion resistance of the layer itself was greater than that of the substrate material. In addition, it has been confirmed that this erosion resistance is maintained even after the erosion damage has reached the substrate material, since the residual stress generated by the layer deposition improves the durability of the base metal.
Fatigue of Welded Structural and High-Strength Steel Plate Specimens in Seawater
Authors: Sablok AK , Hartt WH
Published: March 2009

Corrosion fatigue data for three series of experiments involving a butt-welded structural and nine higher strength steels (yield stress, 370 to 750 MPa)—with the latter representing relatively new strengthening technologies such as microalloying, control rolling, thermomechanical control processing, and precipitation hardening—have been evaluated comparatively. Variables in the tests included: (1) the R ratio, (2) the as-welded versus ground and postweld heat-treated conditions, and (3) freely corroding versus cathodically protected conditions, although the nature and duration of the experiments was not conducive to a systematic treatment of these factors. Fatigue life data for the freely corroding specimen experiments reflected an influence of the weld toe geometry and the associated stress-concentration factor for as-welded specimens and of the R ratio for postweld heat-treated ones. On the other hand, no effect of the material strength was apparent. Limited data for the cathodically polarized specimens indicated improvement in fatigue life over that for the freely corroding specimens and for higher strength steels over structural steels.
Corrosion Fatigue Testing of Welded Tubular Joints Under Realistic Service Stress Histories
Authors: Dharmavasan S , Kam JCP , Dover WD
Published: March 2009

Because of the large number of stress cycles experienced by offshore structures in the North Sea, fatigue has become a major design consideration for such structures. Extensive research and testing has therefore been carried out to study the fatigue behavior of offshore structural components, particularly the welded tubular joints.

The laboratory technology for fatigue testing of tubular joints has now progressed to the point where realistic in-service stress history can be used. Crack growth results have been obtained with the use of more realistic load histories, coupled With the effects of the environment.

This paper summarizes some of the progress in the design and simulation philosophy for fatigue testing load histories. The latest crack growth data for welded tubular joints tested under realistic fatigue stress histories, in air and in a corrosive environment, are also presented. In most cases, the crack growth can be predicted reasonably accurately with standard fracture mechanics methodology. However, some unexpected crack growth retardation behavior was also observed, and there is currently no established calculation procedure to predict this phenomenon. Therefore, further studies are required to explain this unusual crack growth feature.
Fracture Toughness Testing of Weld Heat-Affected Zones in Structural Steel
Authors: Fairchild DP
Published: March 2009

Multipass weld HAZs in structural steel exhibit a high level of heterogeneity. High-toughness and low-toughness microstructures can exist within 1 or 2 mm of each other. Low-HAZ crack-tip opening displacement (CTOD) results in some structural steels have been attributed to local brittle zones (LBZs), which exist in the coarse-grain heat-affected zone (HAZ) region (CGHAZ). Fracture initiation in an LBZ occurs by a weak-link process, which is described in this paper. If a particular weld contains LBZs, before a low CTOD result will occur, the precrack must be located close enough to the weak link that the crack-tip process zone can initiate fracture. HAZ CTOD precrack placement for welds containing LBZs is discussed, and the importance of posttest sectioning techniques is also explained. The line fraction of CGHAZ that was sampled by the crack tip was calculated for 485 HAZ CTOD tests (22 structural steels). These data are statistically analyzed to show that for welds containing LBZs, a low CTOD result becomes more probable if the crack samples more CGHAZ.
Study of Methods for CTOD Testing of Weldments
Authors: Machida S , Miyata T , Toyosada M , Hagiwara Y
Published: March 2009

Several precracking methods for crack-tip opening displacement (CTOD) testing of weldments were studied, including as local precompression, reverse bending, and high R-ratio fatigue. The precracking procedure could influence the validity of the precrack shape. However, it was found that an irregular precrack front had little effect on CTOD values of the heat-affected zone (HAZ). Results indicate that the current limitations on the fatigue precrack shape can be relaxed.

CTOD values comparable to those of the standard B × 2B specimen were obtained from the subsidiary B × B specimen with a through-thickness notch of a length-to-specimen-width ratio of 0.5. Hence, it can be possible to use B × B specimens instead of B × 2B specimens in the standard CTOD testing of weldments.

The CTOD test results for weld HAZ were strongly affected by the notch positioning in the welded joint. By analyzing the weld thermal history, HAZ microstructures were classified. Then, it was revealed that CTOD values were closely related to the maximum size of the local brittle zone (LBZ) at the crack tip.
Fracture Toughness of Underwater Wet Welds
Authors: Dexter RJ
Published: March 2009

The wet and wet-backed shielded metal-arc welding (SMAW) process can produce welds suitable for structural applications provided fracture control is considered in the design. Welding procedure qualification tests and fracture toughness tests [the ASTM Test for JIc, a Measure of Fracture Toughness (E 813-87)] were performed on the heat-affected zone (HAZ) and weld metal of wet, wet-backed, and dry fillet and groove welds made with (1) A36 steel and E6013 electrodes, and (2) A516 steel and nickel alloy electrodes. Despite Vickers hardness (HV) measurements exceeding 300 HV [xl.O kgf (HV 1.0)] in the HAZ of the ferritic welds and 400 HV in the HAZ of the austenitic welds, no hydrogen cracking or brittle fracture behavior was observed. Generally, the Charpy tests indicated upper-shelf fracture behavior at -2°C (28°F), and the HAZ was found to be tougher than the weld metal. Crack-tip opening displacement (CTOD) estimates were made using British Standard (BS) 5762, and the CTOD was found to be proportional to J even after large crack extension. The maximum load point values of CTOD and J are compared with the initiation values determined by the procedure of ASTM Test E 813. The fracture toughness of the welds is sufficient to be tolerant of flaws much larger than those allowed under American Welding Society (AWS) specifications.
Fracture Toughness of Manual Metal-Arc and Submerged-Arc Welded Joints in Normalized Carbon-Manganese Steels
Authors: Burget W , Blaue JG
Published: March 2009

This paper shows that, in the temperature transition regime, scatter of weld metal and heat-affected zone toughness values is related to material heterogeneity in the welded joints. Results were obtained from impact testing of V-notched and fatigue-cracked Charpy specimens as well as from static fracture toughness tests on small-scale and full-thickness specimens. Besides material heterogeneity, mechanical heterogeneity is emphasized as having a significant influence on the fracture performance of heat-affected zone specimens.
Towards a Damage Tolerance Philosophy for Composite Materials and Structures
Authors: O'Brien TK
Published: March 2009

A damage-threshold/fail-safety approach is proposed for ensuring that composite structures are both sufficiently durable for economy of operation, and adequately failsafe or damage tolerant for flight safety. Matrix cracks are assumed to exist throughout the off-axis plies. Delamination onset is predicted using strain energy release rate thresholds. Delamination growth is accounted for in one of three ways: either analytically, using delamination growth laws in conjunction with strain energy release rate analyses incorporating delamination resistance curves: experimentally, using measured stiffness loss; or conservatively, assuming delamination onset corresponds to catastrophic delamination growth. Fail safety is assessed by accounting for the accumulation of delaminations through the thickness. A tension fatigue life prediction for composite laminates is presented as a case study to illustrate how this approach may be implemented. Suggestions are made for applying the damage threshold/fail-safety approach to compression fatigue, tension/compression fatigue, and compression strength following low-velocity impact.
Some Observations About Test Specimens and Structural Analysis for Fibrous Composites
Authors: Hart-Smith LJ
Published: March 2009

This paper presents an assessment of various tests conducted to characterize individual fibrous composite laminae in such a way that the strengths and stiffnesses of cross plied laminates made from those laminae can be predicted analytically, without the need to confirm the predictions by testing each and every cross-plied laminate. In the paper, tests for in-plane shear, longitudinal tension and compression, and transverse tension and compression are treated. Both strengths and elastic moduli are covered. Only in the ±45° laminate test are there orthogonal fibers to prevent premature failure from widespread cracking of the resin matrix. All the other tests have fibers in only one direction. The transverse tension tests in particular, but even the fiber-dominated longitudinal tests, are shown to be currently unsatisfactory but could be improved by including appropriate orthogonal fibers. Doing so would prevent any structurally insignificant microcracks in the resin from joining up and causing the specimens to fail catastrophically before completing their task of fully characterizing the laminae. With such revised test data, it is possible to predict the strength of cross-plied structural laminates far more accurately than by tests on unidirectional laminae, as has been done in the past.
Ply-Level Failure Analysis of a Graphite/Epoxy Laminate Under Bearing-Bypass Loading
Authors: Naik RA , Crews JH
Published: March 2009

A combined experimental and analytical study has been conducted to investigate and predict the damage-onset failure modes of a graphite/epoxy laminate subjected to combined bearing and bypass loading. Tests were conducted in a test machine that allowed the bearing-bypass load ratio to be controlled while a single-fastener coupon was loaded to failure in either tension or compression. Test coupons consisted of 16-ply, quasi-isotropic T300/5208 graphite/epoxy laminates with a centrally located 6.35-mm bolt having a clearance fit. Onset failure modes and loads were determined for each test case. The damage-onset modes were studied in detail by sectioning and micrographing the damaged specimens. In addition, some specimens were loaded to ultimate failure. A two-dimensional finite-element analysis was conducted to determine lamina strains around the bolt hole. Damage onset consisted of matrix cracks, delamination, and fiber failures. Stiffness loss appeared to be caused by fiber failures rather than by matrix cracking and delamination. Fiber failures in the 0-deg plies in the net-section tension and net-compression modes followed the matrix cracking direction in the adjacent 45-deg plies. Fiber failures associated with bearing damage were of two different types: compressively loaded fibers in the 0-deg plies failed by crushing, whereas fibers in the 90-deg plies failed in tension. An unusual offset-compression mode was observed for com-pressive bearing-bypass loading in which the specimen failed across its width, along a line offset from the hole. The computed lamina strains in the fiber direction were used in a combined analytical and experimental approach to predict bearing-bypass diagrams for damage onset from a few simple tests.
Mechanics of Instability-Related Delamination Growth
Authors: Whitcomb JD
Published: March 2009

Local buckling of a delaminated group of plies can lead to high interlaminar stresses and delamination growth. The mechanics of instability-related delamination growth (IRDG) had been described previously for the through-width delamination. This paper uses the results of finite-element analyses to gain insight into the mechanics of IRDG for the embedded delamination subjected to either uniaxial or axisymmetric loads. This insight is used to explain the dramatic differences in strain energy release rates observed for the through-width delamination, the axisymmetrically loaded embedded delamination, and the uniaxially loaded embedded delamination.
Understanding and Predicting Sublaminate Damage Mechanisms in Composite Structures
Authors: Armanios EA , Rehfield LW , Weinstein F
Published: March 2009

The resistance to crack growth exhibited by a quasi-isotropic double cracked-lap-shear specimen made of AS4/3502 graphite/epoxy materials was investigated. The factors reported earlier to influence delamination behavior such as fiber bridging, fiber breakage, and curing stresses were examined to assess their effect in the specimen. It was found that the prevalent damage modes for this specimen design were matrix microcracks and delamination. These two modes interact to produce the resistance behavior observed under tensile loading. The quantitative assessment of resistance was based on an engineering intuitive approach. Matrix microcracking was induced by the strain concentration at the crack front. Delamination onset was determined using a fracture mechanics approach based on the total energy release rate and the energy release rate components. When compared with test results, the predictions of the analytical model provide a rational physical explanation of the resistance behavior.