Maximum Tensile Hoop Stress Research Articles

TRISO burnup-dependent failure analysis in FHRs using BISON

In this study, we perform a study on TRIstructural ISOtropic (TRISO) Silicon Carbide (SiC) layer failure using the BISON fuel performance code. SiC thermomechanical behavior is analyzed during both steady-state and accident scenarios pertaining to a Fluoride-Salt-Cooled High-Temperature Reactor (FHR). A monodimensional single particle model is adapted from a previous analysis and run at 140 mW/particle for 500 days. The maximum burnup reached is 18.49% FIMA. A total of three accident scenarios are simulated at both fresh fuel conditions and following multiple irradiations at 2% FIMA increments up to 18.49% FIMA. The instances include an overcooling transient, a Control Rod Withdrawal (CRW) and a Loss of Forced Cooling Accident (LOFA). SiC hoop stress and failure probability predictions are evaluated for all simulated cases. A consistent tangential compressive stress state is found as a function of burnup for SiC. The maximum compressive hoop stress reaches approximately -400 MPa. The maximum SiC failure probability as a function of burnup is 2⋅10−13% at steady-state and no increases are predicted during transient simulations. It is concluded that the selected accident scenarios, under our modeling assumptions, are not predicted to pose a challenge to SiC integrity due to their relatively slow progression and low temperature increments, for both fresh fuel and at burnup values up to 18.49% FIMA. A 2D model is used, along with XFEM, to simulate a crack in the Inner Pyrolytic Carbon (IPyC). Conservative IPyC failure predictions are obtained with Weibull statistics approximately 38 days after beginning of irradiation. After crack formation, hoop stress concentrations are predicted in SiC using conservative assumptions, with failure probability increasing to 3.3⋅10−4%. 2D BISON simulations of the base irradiation are then carried out to the maximum burnup and transient conditions are subsequently applied. SiC maximum tensile hoop stress is predicted at the time of crack initiation, after which crack expansion reduces the predicted stress magnitude in the material. The results presented in the work are interpreted under the selected modeling assumptions and conclusions are based on a comparison with a parallel analysis on a High-Temperature Gas-Cooled Reactor design to evaluate the effects of power density and burnup on SiC performance.

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.

An exact analytical solution for stress concentrations within layered hollow spheres under compression

The paper presents the exact analytical solution for the stress concentrations within a layered hollow sphere under diametral compression. Numerical results show that the stress distribution within a layered hollow sphere changes drastically along the axis of loading, and the maximum tensile hoop stress may appear at the interface as well as at the internal surface. In general, a harder outer layer leads to a maximum tensile hoop stress in the outer layer near the interface; whereas a softer outer layer leads to a compressive hoop stress at the same location. A thinner outer layer usually results in a higher tensile hoop stress, regardless of the relative stiffness between the layer and the hollow sphere. The hoop stress at the interface also increases with the internal pressure but decreases with the contact size of loading. By changing the relative thickness and mechanical properties of the layered hollow sphere, the present solution not only provides the basis for the design and the fabrication of suitable layered hollow spheres with multiple functions against delamination at the interfaces or tensile cracking at the internal surfaces, but also provides a useful benchmark for the numerical simulations for various advanced multilayered hollow spheres.

An investigation of the critical conditions leading to deintercalation induced fracture in two-phase elastic electrode particles using a moving interphase core-shell model

Phase separation has been widely observed in various energy storage systems, and is known to severely impact mechanical integrity and electrochemical performance in lithium intercalation materials. Core-shell type models have been extensively used for modeling diffusion, phase transformation, deformation, and stress generation in phase changing energy storage materials. The purpose of this work is to present a systematic fracture mechanics analysis of two-phase electrode particles with core-shell structure subject to deintercalation using both numerical and analytical models. Mechanical behavior of the host solid is assumed to follow small deformation linear elasticity, and geometry of the particles is considered to be cylindrical/spherical. A moving interphase model accounting for the effect of solution non-ideality is utilized in combination with the weight function method of fracture mechanics to numerically calculate stress intensity factors (SIFs) for pre-existing cracks at the particle surface. Further, an analytical solution in the limit of small surface fluxes and a semi-analytical solution in the presence of large surface fluxes are also developed for the maximum SIF which could arise for a pre-existing surface crack during a complete deintercalation half-cycle. Implication of the results in terms of prediction of a critical particle size to avoid fracture in two-phase electrode particles is also presented. Numerical results along with their comparison with analytical predictions are presented in terms of the concentration and stress profiles, maximum tensile hoop stress, and maximum SIFs for a range of two-phase regular solid solutions and subject to a broad range of surface deintercalation fluxes. We further examine the results of this work by considering a lithium deintercalation system whose thermodynamic behavior is considerably different from that of a regular solution, and the results found using analytical and numerical models are compared.

Numerical Modeling of Fracture-Resistant Sn Micropillars as Anode for Lithium Ion Batteries

Sn possesses three times higher capacity in comparison to graphite anode (372 mAhg–1) that makes it a promising candidate for enhanced performance Li ion batteries. Contrary to Si, Sn is compliant and ductile in nature and thus is expected to readily relax the Li diffusion-induced stresses. The low melting point of Sn additionally allows for stress relaxations from time-dependent or creep deformations even at room temperature. In this study, numerical modeling is used to reveal the significance of plasticity and creep-based stress relaxations in the Sn working electrode. The maximum elastic tensile hoop stresses for 1 μm micropillar size with 1C charging rate conditions reduces down from ∼1 GPa to ∼200 MPa when Sn is allowed to plastically deform at a yield strength of ∼150 MPa. After experimentally determining the creep response of Sn micropillars, creep deformations are incorporated in numerical modeling to show that the maximum tensile hoop stress is further reduced to ∼0.45 MPa under the same conditio...

Influence of interference fit size on hole deformation and residual stress in hi-lock bolt insertion

The interference fit can improve the fatigue performance of mechanical joints and is widely used in aircraft assembly. In this paper, specimens of lap plates and several interference fit sizes were designed, and then the interference fit hi-lock bolt insertion was carried out in an experimental test. Using the commercial finite element software ABAQUS, a two-dimensional axisymmetric finite element model was established to simulate the bolt insertion process. The finite element model was validated by comparison of experimental results and finite element prediction for insertion force and protuberance height. After the interference fitted bolt insertion, the changing characteristics of the non-uniform hole expansion and protuberance were presented with increases in interference fit size. Under low level of interference fit, the tensile hoop stress was produced mainly on the hole wall, and changed into compressive hoop stress when interference fit size is larger. The maximum tensile hoop stress point on faying surfaces went away from the hole wall with interference fit size increasing.

The influence of CO2 laser local irradiation on the laser damage resistance of fused silica

The influence of CO2 laser local irradiation (CLLI) on the laser damage resistance of fused silica was studied. It is found that CLLI has no evident effect on the laser-induced damage threshold (LIDT) of fused silica when the temperature of irradiation center is low (1139 K). However, the influence of CLLI on LIDT becomes important when the temperature of irradiation center is higher (1638 K). AT first, LIDT decreases with r increasing from zero to rM, where r is the distance to irradiation center, and rM is the distance at which the residual stress-induced phase retardance reaches the maximum. Then, LIDT increases a little when r is larger than rM. The origin of this phenomenon is discussed. Due to the residual stress, re-initiated damage in irradiation region can result in the formation of fractures. The fractures due to the re-initiated damage at irradiation center transport along radial direction firstly, and then transport along the tangential direction near rM. This may be due to the maximum tensile hoop stress and radial stress dependence of radius. Cares should be taken for the optical cleaning when thermal oven annealing is used to eliminate the residual stress. Otherwise, crystallization can be induced by contamination during annealing. The contamination also has negative impact on the light transmission and LIDT.

Microstructural and Residual Stress Development due to Inertia Friction Welding in Ti-6246

A thorough investigation has been performed to assess the microstructural properties, mechanical properties (hardness and elastic modulus), and residual stress development in Ti-6Al-2Sn-4Zr-6Mo (Ti-6246) inertia friction welds in the as-welded and postweld heat-treated conditions. It was evident that the thermomechanical deformation in the weld region occurred above the β transus, forming dynamically recrystallized β grains and precipitating acicular α within the β grains, which resulted in a localized hardness increase. In the heat-affected zone, a ghost microstructure of the base metal formed because of the absence of sufficient time for diffusion, resulting in Mo segregation in the prior primary α plates. Energy-dispersive synchrotron X-ray diffraction and neutron diffraction were used to assess the residual stress development in the three principal directions. The variation in the unstrained lattice parameters across the weld regions was established by imposing a stress balance on the axial stress component in the radial direction. It was found that the maximum stresses occurred in the hoop direction, with significantly lower stresses present in the radial and axial directions. The maximum tensile hoop stresses were located at ~4 mm from the weld centerline and not at the dynamically recrystallized β-rich weld zone. This was associated with the α → β phase transformation and the subsequent acicular α precipitation within the region surrounding the weld centerline.

Thermal and stress analysis in Nd: YAG laser rod with different double end pumping methods

In this work, the finite element analysis has been used to predict the temperature distribution in Nd: YAG laser rod; double end-pumped by two methods Gaussian or top hat beam. The rod is cooled by water passing through annular, which surrounds the active media. The temperature distribution has been used to predict numerically, the nodal displacements, strain and stress based on the principle of virtual work. The main task is to determine the temperature distribution in Nd: YAG laser rod, the subsequent value and location of maximum tensile hoop stress associated with the two types of the double end pumping for different absorption power. Some conclusions are obtained; as the radius pumping ratio increases the location of maximum hoop stress will move toward the periphery and vice-versa. Small reduction is observed in the location of maximum hoop stress when pumping method change from the top-hat beam to Gaussian beam, especially at low radius pumping ratio and high absorption power. Top hat beam end pumping will cause more intense tension hoop stress at the facets of the rod than that of Gaussian beam even the later may produce high center temperature. This work may be important for designer while choosing the type of pumping, maximum produced tensile hoop stress and its location, especially when hoop stress is ultimate.

Inflation and eversion of functionally graded non-linear elastic incompressible circular cylinders

We study axisymmetric radial deformations of a circular cylinder composed of an inhomogeneous Mooney–Rivlin material with the two material parameters varying continuously through the cylinder thickness either by a power law or an affine relation. It is found that for the exponent of the power law function equal to 1, the hoop stress for an internally pressurized cylinder is uniform in the cylinder. One can tailor the gradation of these two material parameters to make the maximum tensile hoop stress occur either on the inner surface or on the outer surface. Also, the stress concentration in a pressurized thick cylinder strongly depends upon the value of the exponent of the power law variation of the two material parameters. For an affine through-the-thickness variation of the two elastic moduli the hoop stress at the point R = R in R ou is nearly the same as that in a cylinder composed of a homogeneous material. Here R in and R ou equal, respectively, the inner and the outer radii of the cylinder in the unstressed reference configuration, and R is the radial coordinate of a point in the reference configuration. The stress distribution in an everted cylinder strongly depends upon its thickness in the reference configuration.

Dynamic response of an elastic sphere under diametral impacts

This paper presents a new analytical solution for an elastic sphere under a double impact load which applies as a Heaviside step function of time along a diameter. The suddenly applied loads are modeled as either uniform or Hertz contact stress and are applied through two patches on two ends of a diameter of the solid sphere. The method of solution uses decomposition theory, in which the final dynamic solution is decomposed into two auxiliary problems: (I) a static solution of the applied loading; and (II) the free vibration of the sphere subject to an initial deformed shape induced by the auxiliary problem I. Time evolutions of the stress field at selected points along the axis of compression agree with the solution by [Jingu, T., Nezu, K., 1985. Transient stress in an elastic sphere under diametrical concentrated impact loads. Bulletin JSME 28 (245), 2553–2561] when contact zone is very small (i.e. case of suddenly applied point loads). If energy loss is allowed at each boundary reflection, our long term solution converges to the static solution. The size and shape of the compressive cones under the applied loads are relatively insensitive to the size of the contact zone, while the magnitude of tensile stress along the axis of compression decreases with the contact area. The maximum tensile hoop stress along the axis of compression always appears at point r/ a = 0.38 and at time of 2.61 T 1 (where 2 T 1 is the time for P-wave traveling across the sphere). Based on wave interference plots, inferred failure patterns are proposed and compared to those observed failure pattern in our double impact test.

Stress Concentration Reduction at a Reinforced Hole Loaded by a Bonded Circular Inclusion

This paper considers analytically the stress concentration in an infinite plane loaded by a circular inclusion, which is bonded to a reinforced hole in the plane. The pulling force of the inclusion is modeled by distributed body force. The infinite plane, the reinforced ring, and the circular inclusion can be of different elastic properties. Airy stress function with body force potential was used to solve the problem analytically. Numerical results show that the maximum tensile hoop stress at the hole boundary in the plane can be reduced to becoming negligible if an optimum stiffness ratio between the plane and the rivet is chosen (normally a harder material for the reinforced ring comparing to the plane is needed). An optimum thickness of the reinforced ring can also be determined to further reduce the hoop stress concentration. Therefore, the results of the present study provide a new theoretical basis for designing a reinforced rivet hole.

Transverse Strength of SCS‐6 Silicon Carbide Fibers

A diametral compression test was used to measure the transverse strength of SCS‐6 SiC fibers before and after heat treatment. Subjecting fibers to diametral compression successfully produced transverse tensile failure in the form of fiber cracking along the same diametral plane in which the compressive load was applied. An analysis of the hoop stress along the diametral plane, in which the effects of the C core were included, showed that there is a large tensile hoop stress concentration in the SiC sheath at the interface between the C core and the SiC sheath, where the stress is 6.3 times greater than the stress present in a solid SiC fiber under identical loading. This high tensile hoop stress concentration promotes crack initiation near the core and significantly limits the capability of these fibers to withstand transverse compressive loading. The maximum tensile hoop stresses, located at the interface between the C core and SiC sheath, at the measured failure loads were 850 MPa for the as‐received SCS‐6 fiber and 1210 MPa for fibers exposed to a 1‐h heat treatment at 1850°C in 138 MPa of Ar.