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To capture the stress corrosion cracking (SCC) in metallic materials, a phase‐field framework considering localized plastic deformation and stress states is established. A new function of critical energy release rate is proposed to describe the degradation of cracking resistance of materials in the SCC process. This proposed framework can reproduce SCC results consistent with experimental observations in C‐ring steel SCC tests, especially capturing the directionally characteristic of the cracks. Furthermore, the influences of localized plastic deformation and stress states on the SCC process are studied. This novel phase‐field framework can capture (1) the influences of coupled electricity, mechanics to the SCC mechanisms; (2) the contribution of plastic strain energy as the driving force for the phase‐field; (3) the potential and preferential crack initiation and propagation morphology within the complex stress and strain domain; and (4) the dependence of SCC rate and propagation direction on stress state and localized plastic deformation. Highlights: A phase‐field framework for SCC prediction of elastoplastic materials is established.The novel framework is implemented in finite element model and validated by tests.The framework can capture SCC morphology within the complex stress and strain domain.Influences of stress states and localized plastic deformation on SCC are clarified. [ABSTRACT FROM AUTHOR]

The formation of a stress corrosion crack (SCC) in the canister wall of a dry cask storage system (DCSS) has been identified as a potential issue for the long-term storage of spent nuclear fuel. The presence of a SCC in a storage system could represent a through-wall flow path from the canister interior to the environment. Modern, vertical DCSSs are of particular interest due to the commercial practice of using relatively high helium backfill pressures (up to approximately 800 kPa) in the canister to enhance internal natural convection. This pressure differential offers a comparatively high driving potential for blowdown of any particulates that might be present in the canister in the event of a through-wall SCC. In this study, the rates of gas flow and aerosol transmission of a spent fuel surrogate through an engineered microchannel with dimensions representative of a SCC were evaluated experimentally using coupled mass flow and aerosol analyzers. The microchannel was formed by mating two gauge blocks with a linearly tapering slot orifice nominally 13 μm (0.0005 in.) tall on the upstream side and 25 μm (0.001 in.) tall on the downstream side. The orifice is 12.7 mm (0.500 in.) wide by 8.89 mm (0.350 in.) long (flow length). Surrogate aerosols of cerium oxide (CeO2) were seeded and mixed with either helium or air inside a pressurized tank. The aerosol characteristics were measured immediately upstream and downstream of the simulated SCC at elevated and ambient pressures, respectively. The next iteration of testing involves replacing the engineered microchannel with lab-grown SCCs. Preliminary clean flow testing has been conducted on SCC samples provided by the Electric Power Research Institute. These data sets demonstrate a new capability to characterize SCCs under well-controlled boundary conditions. Preliminary testing efforts are focused on understanding the evolution in both the size and quantity of a hypothetical release of aerosolized spent fuel particles from failed fuel cladding into the canister interior, and ultimately, through a SCC. [ABSTRACT FROM AUTHOR]

The propagation behavior of stress corrosion cracking (SCC) for two CrNiMoV steels in the simulated environment of low-pressure nuclear steam turbine rotor was systematically investigated by microstructural characterizations, electrochemical measurements, slow strain rate tensile tests, and crack growth rate (CGR) measurements. The results showed that both the corrosion susceptibility and stress corrosion susceptibility increased with the increase of localized residual strain, yield strength, and the decrease of grain size. With the higher stress corrosion susceptibility, the SCC CGR of Steel A was higher than Steel B in the corrosive solution at 80 °C, however, at 180 °C the SCC CGR of Steel A was lower than Steel B under the lower applied K. The change of SCC CGR was strongly affected by crack branches, crack deflections and plastic deformation during the SCC propagation, which may have some correlations with the microstructural distribution.

One of the challenges regarding the application of laser polishing in injection mold manufacturing is to eliminate the tensile residual stress on a polished cavity surface without the extra expenses of an annealing vacuum furnace. This study aims to develop a fast laser annealing method using a dual-beam laser system by which a mold cavity can be laser-polished and then laser-annealed. Fourteen mold steel specimens were laser-polished by a dual-beam laser, resulting in a roughness reduction from the initial state, Sa 1.11 μm, to Sa 0.16 μm, a smoother surface finish. A numerical simulation of laser annealing using the current CW laser was implemented to optimize the laser annealing parameters to guide the experiment of CW laser annealing. XRD measurement results showed that the tensile residual stress dropped from an initial 638 MPa to 10 MPa in an annealing cycle time of 40 min at 750 °C; therefore, fatigue cracks or stress corrosion cracks (SCC) on the mold cavity will no longer occur. Confocal microscopy, X-ray diffraction, and scanning electron microscopy were used to obtain the microstructure and phase composition of the microstructures, demonstrate that laser polishing and laser annealing by a dual-beam laser is a fast and effortless technique which can be effectively employed in injection mold manufacturing. [ABSTRACT FROM AUTHOR]

A 5000m3 single deck floating roof crude oil storage tank was found to have a cracked Q345R bottom plate during an open tank inspection. To analyze the cause of the failure, a series of experiments were carried out. The results showed that the chemical composition of the failed crude oil storage tank bottom plate material Q345R had a slight excess of S, V, and Ti which causes the material to form a bainite structure, resulting in a hard and brittle material with poor toughness. Q345R is susceptive to H2S stress corrosion cracking according to SCC test. Based on the working condition investigation, the cracked plate was subjected to the local settlement and H2S contained corrosive medium. With the stress concentration induced by local settlement, the bottom plate cracked. In order to avoid such incidents, Q345R material should be avoided in H2S containing environment, and online monitoring should be carried out regularly to assess the overall condition of the tanks.

• The complex cracking mechanism of the blade of the 54H60 propeller system is investigated. • A mixed-mode fatigue crack propagation analysis is performed. • The structural reliability analysis supports the rapid liberation of the blade with the presence of IGC. Legacy propeller blades made of aluminum alloy are susceptible to fatigue cracking. Once the crack nucleated, it propagates rapidly because of the high rotational speed of the blade. This study uses mixed-mode fatigue crack analysis to understand the out-of-plane interaction of intergranular crack (IGC) and fatigue crack revealed in a U.S. Marine Corp. C-130 crash in 2017. The cracking mechanism is sequential: IGC followed by fatigue cracking, which eventually causes the liberation of the blade. A finite-element-method-based stress analysis elucidates the transition from IGC to fatigue crack. The result showed that the IGC provided enough driving force for the fatigue crack nucleation. A Monte-Carlo-simulation-based risk analysis is performed using the stress and crack growth analyses. The critical plane approach is utilized to determine the equivalent stress intensity factor for the crack growth analysis. The risk analysis results support the rapid liberation of the blade with consideration of large variation in initial crack size. The results also clearly show the necessity of structural risk analysis for planning inspection and maintenance. [ABSTRACT FROM AUTHOR]

A drill collar with material of 0Cr20Mn21Ni2N serviced in a coastal continental shelf oilfield, has cracked and leaked after a short period of working. Failure analysis of drill collar was performed by a series of experiments, including Chemical analysis, Fractographic analysis, Microstructural analysis, Intergranular attack test, Mechanical property, Residual stress test, EBSD analysis of relationship between crack propagation and crystal orientation. The fractographic observations showed crack initiated from the inner surface and extended to outer surface by the mode of inter-granular and quasi-cleavage trans-granular fracture, many branch cracks were produced during its propagation. Serious corrosion morphology was found both on the inner surface of drill collar and fracture surface, and S and Cl were detected in the corrosion products. The above evidence indicates that the cracking failure mode of drill collar can be described as the Stress Corrosion Cracking (SCC) of austenitic stainless steel. The causes of stress corrosion cracks are attributed to three aspects. Firstly, the microstructures of the materials are sensitized seriously, and there are many precipitated phases at grain boundaries, which result in chromium depletion in the grain boundaries and decrease of corrosion resistance of the materials. Secondly, during service the mud water on the inner surface of drill collar is composed of seawater containing chloride and sulfate radical, which provides corrosive environment for materials. Thirdly, the residual tensile stress on the inner surface of the drill collar reaches 112 MPa, which hinders the formation of passive film on the surface of stainless steel and has adverse effect on the corrosion resistance of the material. In addition, the mechanism of crack formation was studied by EBSD. Corrosion pits of inner-surface of drill collar is intergranular corrosion, which first occurs at random grain boundaries with high misorientation angles, rather than at special grain boundaries such as Σ3. SCC crack initiates from the corrosive pit and propagate along the grain boundary first and gradually transit to transgranular growth with Zigzag fracture morphology along {111}〈110〉 slip system, which proves SCC transgranular crack propagation obeys the slip corrosion mechanism. • The failure for stainless steels of Fe-Cr-Mn-N system has been seldom reported by literature. • The failure is attributed to sensitized microstructure, corrosive environment, and residual tensile stress. • The mechanism of SCC formation is also studied, which proves crack propagation obeys the slip corrosion mechanism. [ABSTRACT FROM AUTHOR]

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The purpose of this study is to characterize the features of magnetic flux density perturbation as a result of the variation of conductivity in an equivalent model of the stress-corrosion crack (SCC). By using numerical computation of A-𝜙 method, the magnetic field nearby the inspection target was simulated for an eddy current probe of large rectangular excitation coil and a conductor plate with a modeled SCC. A conductive notch was set in the center of the conductor plate as an equivalent crack model of a real SCC. Different conductivities and crack depths were varied into the equivalent SCC model for analyzing their influences to the distribution of magnetic flux density perturbation above the model plate. Numerical results showed that the distributions of magnetic flux density were suitable to distinguish the difference of the conductivities of the SCC between 0% and 20% of the base material for normal testing frequencies. In addition, it was also found that the profile of distributed conductivity along the crack length can be better represented with the field induced by the excitation current laterally to the crack length. [ABSTRACT FROM AUTHOR]

Disappearance and reappearance of delayed cracks were observed in deep drawing process of SUS304 cylindrical cups under elevated blank holding forces (BHF) of 8~32 kN with nanolubricants containing 1~3 wt% SiO2 concentrations at limiting draw ratio. The widest crack-free BHF range determined experimentally, i.e., 29~31 kN was for 2 wt% SiO2. Delayed cracks were observed below and beyond this BHF range. The frictional force at the flange surfaces slightly increased when entering the crack-free BHF range, as evidenced by the rebound in sidewall thickness, relative intensity of α′-martensite, elongated height, and drawing force beyond 28 kN. The coefficients of friction for each BHF were obtained with finite element simulations. Since residual stresses developed along the outer surface of the cup due to the unbending of the material when the material left the draw die profile, the slight increase in frictional force in the radial direction along the flange surfaces reduced the circumferential tensile residual stress of the cup, particularly at 80% cup height. The elimination of delayed cracks was attributed to the lower tensile residual stress gradient, i.e., lower and higher tensile residual stresses at 80% and 100% cup heights, respectively. However, the excessive increase at 100% cup height was a result of the increase in longitudinal compressive stress at BHF beyond 31 kN due to the stress equilibrium, leading to the reappearance of cracks. The minimum BHF required to eliminate cracks changed minimally with increasing SiO2 concentration. [ABSTRACT FROM AUTHOR]