Tensile Hoop Stress Research Articles

Study on Thermo-Hydro-Mechanical Coupling and the Stability of a Geothermal Wellbore Structure

For processes such as water injection in deep geothermal production, heat transfer and fluid flow are coupled and affect one another, which leads to numerous challenges in wellbore structure safety. Due to complicated wellbore structures, consisting of casing, cement sheaths, and formations under high temperature, pressure, and in situ stress, the effects of thermo-hydro-mechanical (THM) coupling are crucial for the instability control of geothermal wellbores. A THM-coupled model was developed to describe the thermal, fluid, and mechanical behavior of the casing, cement sheath, and geological environment around the geothermal wellbore. The results show that a significant disturbance of effective stress occurred mainly due to the excess pore pressure and temperature changes during cold water injection. The effective stress gradually propagated to the far-field and disrupted the integrity of the wellbore structure. A serious thermal stress concentration occurred at the junction of the cased-hole and open-hole section. When the temperature difference between the injected water and the formation was up to 160 °C, the maximum hoop tensile stress in the granite formation reached up to 43.7 MPa, as high as twice the tensile strength, which may increase the risk of collapse or rupture of the wellbore structure. The tensile radial stress, with a maximum of 31.9 MPa concentrated at the interface between the casing and cement sheath, can cause the debonding of the cementing sheath. This study provides a reference for both the prediction of THM responses and the design of drilling fluid density in geothermal development.

Oxidation of 3D‐printed SiC in air and steam environments

AbstractThe high‐temperature oxidation of additively manufactured and chemically vapor infiltrated (3D‐printed SiC) has been compared to chemical vapor deposited (CVD) SiC. 100‐h isothermal exposures were conducted at 1425° and 1300°C at 1 atm under both dry air and steam environments. A SiC reaction tube was utilized to reduce silica volatility. After steam oxidation at 1425° and 1300°C, on the 3D‐printed SiC surface, which was intrinsically rougher than the CVD surface, scales were 70%–90% thicker at the convex regions compared to concave/flat regions. In the convex regions, large cracks perpendicular to the oxidizing interface were observed. After dry air oxidation, scale thicknesses were comparable between 3D‐printed SiC and CVD SiC, regardless of geometry. Finite element modeling, conducted to elucidate the relationship between SiC geometry and ß‐ to α‐cristobalite transformation stress, determined cristobalite transformation tensile stresses to be on the order of 103 MPa during cool down, assuming a 6 vol% reduction. Compared to flat SiC substrates, tensile transformation stresses were elevated at concave regions and relaxed at convex regions. Combined with specimen mass gain (accounting for the rougher surface) of 3D‐printed SiC being 15%–32% higher for 3D‐printed SiC after 1300°C and 1425°C steam oxidation, the work presented concludes that the increased oxidation of 3D‐printed SiC is primarily caused by tensile hoop stresses driven by oxidation volume expansion. Lastly, the efficacy of the 3D‐printing method is demonstrated through the production of tristructural isotropic imbedded 3D‐printed SiC fuel forms.

Quench characteristics and mechanical responses during quench propagation in rare earth barium copper oxide pancake coils

Quench and mechanical behaviors are critical issues in high temperature superconducting coils. In this paper, the quench characteristics in the rare earth barium copper oxide (REBCO) pancake coil at 4.2 K are analyzed, and a two-dimensional (2D) axisymmetric electro-magneto-thermal model is presented. The effects of the constituent materials, background field, and coil size are analyzed. An elastoplastic mechanical model is used to study the corresponding mechanical responses during the quench propagation. The variations of the temperature and strain in superconducting layers are compared. The results indicate that the radial strain evolutions can reflect the transverse quench propagation and the tensile hoop and radial stresses in superconducting layers increase with the quench propagation. The possible damages are discussed with the consideration of the effects of the background field and coil size. It is concluded that the high background field significantly increases the maximum tensile hoop and radial stresses in quenching coils and local damage may be caused.

The Application of Neutron Diffraction Techniques (NDT) in Measuring Residual Strain-Stresses of Engineering Materials

In order to quantitatively understand the residual strain distributions and benefits of engineering components following special technique treatment, such as Autofrettaging, Hot Isostatic Pressing (HIP) and Dissimilar Material Welding (DMW), the Neutron Diffraction Technique (NDT) has been employed recently to measure residual strain and stress distributions on following three cases of (a) Autofrettaged Aluminum 7075 high pressure vessels; (b) Hot Isostatic Pressed (HIPPED) heavy metals of tungsten clad in tantalum plate and (c) Dissimilar Material Welding (DMW) of 316L austenitic stainless steel and ferritic steel AS508 with Alloy 52 weld filler. This paper reports the recent research findings, including (a) NDT can identify optimal Autofrettage pressure level, by which load bearing capacity of the Autofrettaged pressure vessel increased by 215MPa; (b) NDT is able to reveal residual strains within heavy metals of Tungsten clad in Tantalum plate HIPPED and (c) NDT revealed a maximum residual tensile hoop stress value of about 494MPa in the interface between parent material SA508 and the weld seam. This is vital information for the post weld process and subsequent safe use of the dissimilar materials weld. Other researchers’ successful examples of working with NDT are also briefly reviewed. Future prospective of Engineering Materials Diffractometer (EMD) at CSNS is described too with a view to demonstrating the application and importance of NDT in revealing residual strain-stresses that are inevitable within engineering materials and engineering components following any manufacturing process.

КАЛИБРОВКА МОДЕЛИ КОРРОЗИОННОГО РАСТРЕСКИВАНИЯ ЗАЩИТНОГО СЛОЯ БЕТОНА

The article presents a method for determining the stresses arising in the protective layer of concrete in the presence of a porous zone around the "steel-concrete" interphase medium. It has been shown that radial cracks form and propagate in the concrete surrounding the reinforcement until the ultimate serviceability state, such as chipping or delamination of concrete, occurs. The generated hoop tensile stresses in concrete strongly depend on the ratio of the volume of a unit mass of rust to the volume of iron. Calculated formulas for the pressure applied by corrosion products to the concrete layer are given.

Creep Testing of Thermoplastic Fiber-Reinforced Polymer Composite Tubular Coupons.

Thermoplastic fiber-reinforced polymer composites (TP-FRPC) are gaining popularity in industry owing to characteristics such as fast part fabrication, ductile material properties and high resistance to environmental degradation. However, TP-FRPC are prone to time-dependent deformation effects like creep under sustained loading, which can lead to significant dimensional changes and affect the safe operation of structures. Previous research in this context has focused, mainly, on testing of flat coupons. In this study, a creep testing method for TP-FRPC tubular coupons was developed. Specimens were fabricated using tape winding and subjected to well-defined loading conditions, i.e., pure hoop tensile and pure axial compressive stress. Strain gauges and digital image correlation were both employed for strain measurements and were found to be in good agreement. The evolution of strain rate, Poisson’s ratio and creep compliance were investigated. The prediction of experimental data by the Burgers model and the Findley’s power law model were explored. The research findings suggest that the developed experimental and analysis approach provides valuable information for the design of material systems and structures.

Effects of wait on cement, setting depth, pipe material, and pressure on performance of liner cement

An intact cement sheath between a liner and its host casing is critical for maintaining well integrity. The liner-casing overlap incorporates a cement sheath and a seal assembly that collectively establish a dual barrier system. This type of barrier provides a unique set of hydraulic and mechanical properties that are necessary to isolate fluids and prevent undesired communication between formations, wellbore, and environment. The hydraulic and mechanical integrity of the cement sheath can be compromised as a result of stresses induced by various drilling, completion, intervention, stimulation, production, and injection operations.The assessment of cement sheath integrity in the liner barrier system has been a major concern for both the industry as well as the regulators. The objective of this paper is to study the mechanical integrity and the risk of failure at the casing-cement and cement-liner interfaces. The evaluation was performed for various downhole pressure conditions, cement and pipe properties, wait-on-cement (WOC) intervals, and liner setting depths. Analytically and experimentally validated finite element modelling (FEM) approach was employed in this work. The simulation results indicate that tensile hoop stress generated by pressure loads, is one of the most dominant factors that compromises the cement mechanical integrity. This observation was supported by the radial cracks observed during the experimental pressure tests. This work advances design and performance evaluation guidelines for liner cements. Results presented will assist engineers in predicting cement failure modes and identifying operation limits to consider during a well's life cycle.

Rules of non-superconducting phase particles on crack propagation in YBCO coated conductors fabricated by the IBAD-MOCVD

Cracks caused by tensile stress in YBa2Cu3O7-x-coated conductors (YBCO-CCs) can cause irreversible degradation to their superconducting properties. Understanding the initiation and propagation modes of cracks can assist in preventing conductor failure and enhancing their mechanical properties in further. In this study, we used a chemical etching method and scanning electron microscopy to investigate crack morphology in the YBCO layer of conductors where the protective metal layer had been removed. For YBCO-CCs that experienced no deformation, many non-superconducting phase particles were observed and their grain size distribution corresponded to a Gaussian distribution. Energy dispersive x-ray spectroscopy identified these as Y-Cu-O particles. For the YBCO-CCs that experienced axial tension at 77 K, different propagation modes of cracks in the YBCO layer, including transgranular fracture, branching, deflection and pinning were observed for the first time. Statistical analysis demonstrated that transgranular fracture occurred in ∼ 95% of the crack modes. We analysed the reason for this phenomenon considering the thermal stresses stored inside and around the non-superconducting phase particles. The coefficient of thermal expansion of the Y2Cu2O5 particles is less than that of the YBCO superconducting matrix, and therefore, the hoop tensile stress generated near the boundary of the Y2Cu2O5 particle accelerates the bottom-up propagation of the crack. The other crack propagation modes such as crack branching, deflection, pinning and bridging in the YBCO layer can be considered mechanisms of blocking crack propagation that can increase the fracture toughness of the YBCO layer.

Numerical investigation on stress distribution and evolution in 9Cr/2.25Cr dissimilar welded rotor undergoing welding and heat treatment

Numerical investigation has been employed to analysis stress distribution in 9Cr/2.25Cr dissimilar welded rotor undergoing welding and heat treatment in order to help optimize structural design. The simulated residual stress on inner and outer cylindrical surface has been validated with experimental data. Distribution and evolution of welding residual stress along weld center line through thickness has also been investigated. It is found that expansion due to martensitic phase transformation in cap weld and shrinkage in nominal HAZ determines the distribution of residual stress on outer cylindrical surface. Meanwhile, expansion caused by martensitic phase transformation and bending effect in annular structure is responsible for the evolution and distribution of through-wall residual stress. Distribution and peak value of through-wall welding residual stress remains after the weld height reaches a certain value (it is about 30% thickness from the inner cylindrical surface in this work), which provides a possibility to predict stress distribution with less time. Meanwhile, post weld heat treatment (PWHT) can release residual stress effectively. Hence, more attention has been paid to as-welded residual stress. Compared with 2.25Cr weld filler, 9Cr weld filler induces greater compressive hoop stress in the newly deposited weld metal and decreases the peak value of tensile hoop stress under it because of greater martensitic phase transformation expansion in cooling process and smaller yield stress at low temperatures.

Mechanical Integrity of Conductive Carbon-Black-Filled Aqueous Polymer Binder in Composite Electrode for Lithium-Ion Battery.

The mechanical stability of aqueous binder and conductive composites (BCC) is the basis of the long-term service of composite electrodes in advanced secondary batteries. To evaluate the stress evolution of BCC in composite electrodes during electrochemical operation, we established an electrochemical–mechanical model for multilayer spherical particles that consists of an active material and a solid-electrolyte-interface (SEI)-enclosed BCC. The lithium-diffusion-induced stress distribution was studied in detail by coupling the influence of SEI and the viscoelasticity of inorganic-filler-doped polymeric bonding material. It was found that tensile hoop stress plays a critical role in determining whether a composite electrode is damaged or not—and circumferential cracks may primarily initiate in BCC, rather than in other electrode components. Further, the peak tensile stress of BCC is at the interface with SEI and does not occur at full lithiation due to the relaxation nature of polymer composite. Moreover, mechanical damage would be greatly misled if neglecting the existence of SEI. Finally, the structure integrity of the binder and conductive system can be effectively improved by (1) increasing the carbon black content as much as possible in the context of meeting cell capacity requirements—it is greater than 27% and 50% for sodium alginate and the mixtures of carboxy styrene butadiene latex and sodium carboxymethyl cellulose, respectively, for composite graphite anode; (2) reducing the elastic modulus of SEI to less than that of BCC; (3) decreasing the lithiation rate.

Structural behavior of CFST arch foots under pumping pressure of concrete infills

Prestressed concrete (PC) continuous girder-arch composite bridges, using concrete filled steel tubes (CFST) as the arch ribs to support the PC main girder, have gained their popularity in recently constructed large span bridges. The adoption of CFSTs brings many advantages, such as the concrete infill help to prevent the occurrence of local buckling in steel tubes, while the steel tubes can serve as framework for concrete core and strengthen the encased concrete. In order to achieve the above merits, the arch foots connecting the CFST arch ribs and PC girder are supposed to have sufficient strength and stiffness. However, the extensive use of CFST arch ribs showed that concrete cracking are commonly found at the arch foots. This paper studied the structural behavior of arch foot by employing a comprehensive numerical model. The influence of pumping pressure from concrete infill at construction stage on local stress of the arch foots was presented and discussed. The results indicated that the radial stress produced by pumping pressure at the joint zone squeezed the concrete around the arch foots, which resulted in significant hoop tensile stresses in the surrounding concrete. The outcomes of this study can provide technical support to improve the construction quality and structure stability, and optimize the construction procedures for this type of bridges.

Evaluation of thermomechanical behaviors of UO2-5 vol% Mo nuclear fuel pellets with sandwiched configuration

Deploying high thermal conductive materials as additives to UO2 has been highlighted due to their enhanced thermal performance as a potential candidate of Accident-Tolerant Fuels (ATFs). Herein, we investigate thermomechanical behaviors of UO2 – 5 vol% Mo fuel pellets with a sandwiched configuration where Mo layers are positioned on the top and bottom of a UO2 part. The successfully fabricated sandwich-type UO2 fuel pellets with an inclusion of 5 vol% Mo by using a conventional sintering method exhibit up to 3.0 and 2.5 times higher effective thermal conductivities at 800 °C than standard UO2 and dispersion-type UO2 – 5 vol% Mo fuel pellets, due to the effective heat transfer characteristics in the Light Water Reactor (LWR) fuel. Accordingly, the sandwich-type fuel pellets not only effectively reduce the thermal stress gradients across the pellets, but also significantly decrease the maximum tensile hoop stresses of fuel pellets. Finally, the radial deformation behaviors of the sandwich-type fuel pellets are also investigated under a simulated irradiation condition, showing that an hourglass-shaped deformation of UO2 pellets are considerably mitigated.

Die stress analysis and improvement of the welding valve fastener in multi-stage forging

This study explores the multi-stage cold forming die of a welding valve fastener using simulation software. It is possible to understand the various stress intensities of the die core bore and the corresponding distributions during each forging stage so as to improve the service life of the die. These stresses include radial stress, axial stress, hoop stress, and maximum principal stress, as well as the different types of stresses that could cause different fractures of the die core. Therefore, it is necessary to use different die design methods to improve the fracture issues for different die cores. For example, shrink fit can be used between the die core and die case. By adjusting the size of the shrink fit, tensile hoop stress can be converted into compressive hoop stress, which can avoid the generation of axial cracking of the die during the forging formation. In addition, drastic changes in axial stress caused by the stress concentration on the die core can yield a transverse crack of the die core. Thus adopting preventative measures by split such a stress concentration into two sections reduces the drastic changes in axial stress on that section.

On residual stress analysis and microstructural evolution for stainless steel type 304 spent nuclear fuel canisters weld joint: Numerical and experimental studies

Chloride-induced stress corrosion cracking (CISCC) in the weldments of austenitic stainless steel canisters is one of the primary safety concerns during the dry storage of used nuclear fuel at Independent Spent Fuel Storage Installations in coastal areas. In order to evaluate the CISCC behavior in the canister, a 3D sequentially coupled thermo-mechanical finite element model was built to simulate the residual stresses induced by two intersecting longitudinal and circumferential multi-pass welds in austenitic stainless steel mockup canister. Weld-induced residual stresses from simulation were in good agreement with the experimental measurement results by deep-hole drilling and contour methods. Through-wall high tensile axial and hoop stresses were observed in both the fusion zone and heat affected zone (HAZ) in the longitudinal and circumferential weld, respectively. On the other hand, the microstructure within the weldments of 304 stainless steel mockup was characterized using optical microscopy, scanning electron microscopy, electron back-scattered diffraction and energy dispersive X-ray spectroscopy methods. A few amount of MnS inclusions in both the base metal and HAZ, and a lot of (Mn,Si)xOy inclusions in the fusion zone were found. Meanwhile, there is some α′-martensite in the base metal, while the martensite was reversed in the HAZ. In the fusion zone, there is a lot of δ-ferrite. The martensite reversion phenomenon was also verified by the combination of Feritscope test and thermal simulation, which could predict a martensite reversion temperature as 400C°. The welding residual stresses and microstructure analysis results could offer the instructive information for the prediction of CISCC behavior of the spent nuclear fuel canisters.

Reach and geometry of dynamic gas-driven fractures

Dynamic gas fracturing is a well stimulation technique that is able to create multiple fractures emanating from a wellbore. It operates by pressurizing at rise-times and peak pressures intermediate between conventional hydraulic fracturing and explosive fracturing. Two consecutive processes operate during this fracturing process: (i) generation and propagation of a dynamic stress wave that overpowers the static stress field and creates multiple radial fractures around borehole, followed by (ii) quasi-static pressurization and further extension of those starter-fractures by the expanding gas. Dynamic analysis is first performed to follow the evolution of the stress wave propagating from the borehole. The radial (r) distribution of peak tensile hoop-stress diminishes as 1/rα with the power exponent (α) asymptoting to 2 as the loading rate decreases. This rapid attenuation generally limits the length of the body-wave-generated radial fractures to several borehole radii. The gas-loading of the borehole wall is followed by permeation of the gas pressure into the newly created radial fractures. Linear elastic fracture mechanics (LEFM) perturbation analysis shows that a regular distribution of multiple radial starter-cracks will preferentially propagate the longer cracks at the expense of the shorter cracks – that will arrest and snap-shut. This system naturally selects of the order of six dominant fractures that may grow in unison until the in situ stress field reasserts control as the fractures lengthen. This restricts the maximum number of the dominant fractures to of the order of six at the conclusion of treatment - a common observation in both in situ and laboratory experiments.

Hygrothermal Creep and Stress Redistribution Analysis of Temperature and Moisture Dependent Magneto-Electro-Elastic Hollow Sphere

In this article, the time-dependent stress redistribution analysis of magneto-electro-elastic (MEE) thick-walled sphere subjected to mechanical, electrical, magnetic and uniform temperature gradient as well as moisture concentration gradient is presented. Combining constitutive equations of MEE with stress-strain relations as well as strain-displacement relations results in obtaining a differential equation in which there are the creep strains. At the first step, discounting creep strains in the mentioned equation, an analytical solution for the hygro-thermo-magneto-electro-elastic behavior is achieved at the initial state. After that, the creep stress rates can be achieved by keeping only the creep strains in the differential equation for the steady-state condition. The analysis is done by applying the Prandtl-Reuss equations as well as Norton’s law in creep behavior modeling. Finally, the history of stresses, displacement as well as magnetic and potential field, at any time, is achieved using an iterative method. Results show that the increase in tensile hoop stress resulted from creep progress must be considered in design progress. Also, the effect of hygrothermal loading is more extensive after creep evolution.

Effect of extra-large compound calcium-aluminosilicate inclusions on cracking of camshafts

About one-hundred out of three-hundred camshafts were found to crack in varying degrees after finishing final heat treatment of induction-quenching. The cracked camshafts were made from one steel ingot of same furnace number. The failed camshafts are used in truck diesel engine with six cylinders. Stereomicroscope observation showed that several longitudinal and radial cracks were presented on the external surfaces of journals and cams and the side of journals of camshafts. Numerous extra-large elongated compound inclusions of calcium-aluminosilicate (CaO⋅Al2O3⋅SiO2) along the longitudinal of camshaft were found on the fracture surfaces. Fracture surfaces characteristically “woody” in appearance or lamellar and deep groove fracture topography were confirmed to be associated with inclusion distribution along the longitudinal direction of camshaft. Metallographic examination indicated that the camshaft material had a very low purity, especially in the surface region of camshafts, i.e. crack origin regions. The total index of oxide inclusion of the metallographic samples from the smoothed fracture surfaces was evaluated to be K4 = 181 according to DIN standard, much higher than the specified index, K4 ≤ 30. During induction-quenching process, a hoop tensile thermal stress and a hoop tensile transformation stress would develop on the matrix surrounding the compound inclusion of calcium-aluminosilicate due to the significant difference in the thermal expansion coefficients between them and the volume expansion of matrix in the surface region resulting from the transformation of austenite to martensite. When the superimposed stress of both stresses was greater than the tensile strength of matrix material in the surface region, the micro-cracks along the radial of compound inclusion would develop on the matrix surrounding the compound inclusion to lead to cracking of camshaft.

The effect of peak cladding temperature occurring during interim-dry storage on transport-induced cladding embrittlement

To evaluate transport-induced cladding embrittlement after interim-dry storage, ring compression tests were carried out at room temperature(RT) and 135 °C. The ring compression test specimens were prepared by simulating the interim-dry storage conditions that include four peak cladding temperatures of 250, 300, 350 and 400 °C, two tensile hoop stresses of 80 and 100 MPa, two hydrogen contents of 250 and 500 wt.ppm-H and a cooling rate of 0.3 °C/min. Radial hydride fractions of the ring specimens vary depending on those interim-dry storage conditions. The RT compression tests generated lower offset strains than the 135 °C ones. In addition, the RT and 135 °C compression tests indicate that a higher peak cladding temperature, a higher tensile hoop stress and the lower hydrogen content generated a lower offset strain. Based on the embrittlement criterion of 2.0% offset strain, an allowable peak temperature during the interim-dry storage may be proposed to be less than 350 °C under the tensile hoop stress of 80 MPa at the terminal cool-down temperature of 135 °C.

Effects of current density on fracture behaviors for micron-sized crystalline silicon electrodes

The large volume change during lithiation/delithiation leads the silicon electrodes in lithium-ion batteries to severely degrade the mechanical performance and the silicon electrodes in lithium-ion batteries to further deteriorate electrochemical properties, which limits the commercial applications of silicon electrodes. After several year’s studies, the whole process of fracture for crystalline silicon anodes has been almost understood. However, the relationship between fracture behaviors and the lithiation depth has not been sufficiently studied. In this work, the <i>in-situ</i> observations of morphological changes (e.g., volume expansion, crack initiation, propagation, and debonding of lithiated silicon) during lithiation at the different current densities are reported for silicon micropillars fabricated by standard photolithography and a deep reactive ion etching process. Also, this work focuses on the relative depth of lithiation of silicon electrodes at the moment of crack initiation, which is one of the crucial parameters representing the utilization of active materials with no crack. The results show that the silicon micropillars are broken faster (i.e., crack initiation and pulverization in a shorter lithiation time) and more seriously at a large current density, exhibiting more prominent symmetry of morphology. However, the relative depths of lithiation at the different current densities have just a slight difference (i.e., 18%–22%), when cracks are initiated. Here in this work, a silicon micropillar fracture is confirmed by the optical observation, while the relative depth of lithiation is calculated according to the capacity data recorded by the charge/discharge battery test system. The small fluctuation of the relative depth of lithiation with the large wave of current density can be ascribed to the dominant role of local stress concentration caused by anisotropic volume change in fracture behavior, which is validated by the results obtained by the finite element model (i.e., the depth of lithiation predicted by numerical simulations is ～ 22.6%). Therefore, the relationship between fracture behavior and the lithiation kinetics is established, providing an effective strategy for estimating the utilization of active materials under crack-free operation. With the help of the theoretical mechanics model considering both volume change and concurrent movement of reaction front, the stress state in the lithiated silicon at the moment of crack initiation is given, showing the tensile hoop stress near the reaction front. Consequently, these results suggest that the fracture behaviors depend on the current density, but the position of crack initiation (i.e., the depth of lithiation with no crack) is unrelated to current density (at least in a relatively broad range) for large micron-sized crystalline silicon electrodes, thereby shedding light on the fracture mechanisms and the design of alloy anodes (e.g., size and structure) in lithium-ion batteries.

Effect of power history on pellet-cladding interaction

In this paper, the mechanical pellet-cladding interaction (PCI) is studied under various power histories. We find that the power history significantly affects possible PCI failure. PCI during the thermal transient period of power ramping occurs in such a way that crack-mouth opening increases regardless of when contact is initiated, before or during power ramping. The crack-mouth opening continues to increase further during the thermal steady state (during the power ramp). Conversely, PCI initiated either during the thermal steady-state power ramp or during the normal operation (with no power ramp) leads to decrease in crack-mouth opening. As a consequence, PCI initiated before power ramping or during the transient period of power ramping leads to high local tensile hoop stress. In contrast, PCI initiated during the thermal steady state of power ramping or during the normal operation without power ramping leads to local compressive hoop stress. In the former case, PCI failure near the crack tip might be anticipated (by either brittle failure during the transient power ramp or failure during the steady-state power ramp), whereas in the latter case, it is suppressed.