Axial Stress Research Articles

Evaluation and Performance Analysis of Liquefied Petroleum Gas Cylinders

This paper presents the experimental results of the tensile, bending, hardness, hydrostatic testing, and microstructural properties of liquefied petroleum gas cylinders from local sources. The burst pressure and fracture sites were also investigated. In addition, know how LPG cylinders are compliant with ISO 4706 requirements as per standard to get approval and acceptance. The tests were performed on three samples (C1, C2, and C3), and all the tests were according to the specification. Tensile testing was carried out at room temperature (23C°) as per ISO 6892-2016. Tensile test specimens with a gauge length of 50 mm were prepared from the sidewall of cylinders. The equipment used is built up around a 250 KN maximum capacity of (Instron Servo-Hydraulic Testing Machine Model 1332). At the same time, micro-hardness testing was carried out as per ASTM A384. Diamond indenter (pyramid) with a face angle of 136° was used. During testing (1kg) load was applied on the sample with a dwell time of 15 seconds. As for bending tests were carried out in accordance with ISO 7438 for all cylinders to evaluate their welding qualities. The results of microstructural characterization show that the carbon content for all samples averaged ~ 0.067 wt.% and manganese ~ 0.46 wt.% and the microstructure was largely ferritic. The tensile strength of the parent metal showed that LPG gas cylinders recorded high tensile strength of ~ 418 MPa on average, yield strength of ~ 291 MPa on average, a % elongation 26.6 (for parent metal), the tensile strength of ~ 449 MPa as average, yield strength of ~ 314 MPa as average, % elongation 32 (for weld metal) and hardness of ~ 143 (kg/mm2) as average by Vickers scale. Moreover, in the hydrostatic pressure test, the computer controlled electro-hydraulic servo pressure test machine was used. The results of the hydrostatic pressure test were as follows, pressure burst (BP) 103 bar, nominal hoop stress 528 MPa, volumetric expansion 25%, hydrostatic extend ratio 3.9%, sites of failure exist out of welding, and finally no fragmentation observed regarding to fracture types. All samples tested exhibited high resilience to crack propagation which showed ductile fracture after burst and tensile tests.

Mechanical integrity of tubular elements based on strength and fracture criteria during transient CO2 injection

Geological carbon sequestration (GCS) is an essential technology for reducing carbon emissions. Wellbore integrity is crucial to ensure the safety of GCS. During low-temperature carbon dioxide (CO2) injection, the wellbore temperature decreases, causing the tubing and casing to contract, resulting in considerable axial tensile stresses, and making mechanical failure likely. This paper establishes a transient flow model for CO2 injection to predict the temperature and pressure distribution in the wellbore. Then, the strength safety factor of the tubing and casing is calculated using the material strength criteria. Fracture mechanics theory is employed to analyze the risk of crack propagation in defective tubing or casing during CO2 injection. The study indicates that the wellbore temperature near the wellhead is lower as CO2 is injected. Under typical injection conditions, the tubing and casing have high strength safety factors but small crack propagation factors. The stress intensity factor of cracks on the tubing and casing's outer surface is more significant than inner surface defects, posing a higher risk of crack propagation. When the tubing or casing exits a penetrating crack, its propagation safety factor is less than 1, necessitating the avoidance of through-wall cracks. The results guide maintaining wellbore integrity in carbon dioxide geological sequestration engineering.

Finite element (FE) analysis of thermal stress in production process of multi-layer lining ladle

This paper presented the development of the thermo-mechanical coupling model and simulation analysis of a composite refractory layer ladle. The thermomechanical modeling of the ladle was carried out using the Finite Element Method (FEM), taking into account the joints between the slag line bricks as well as the contact between the composite refractory layers. The temperature and thermal stress characteristics of the overall ladle structure under different transit conditions were investigated using the finite element analysis software ANSYS. We also performed a comparative analysis on the improvement effect of thermal stresses by expansion joints of different sizes. The simulation results were validated with previous studies. The results showed that the installation of expansion joints within a suitable range did not significantly change the thermal expansion characteristics of the refractory lining, but it also reduced the thermal stress level of the lining to a large extent. A larger temperature gradient produced higher thermal stresses, and in the direction of the ladle height, the more downward the position of its maximum compressive stress was greater. Under different working conditions, compared with the axial and hoop stress, the radial stress was small in magnitude. Axial stress exhibited a greater degree of sensitivity to pressure variations than hoop stress. The developed thermodynamic model considering the full contact between the bricks and the refractory layer gave us a more complete view of the physical field laws inside the ladle.

Influence of concentration-dependent material properties on the fracture and debonding of electrode particles with core–shell structure

Core–shell electrode particle designs offer a route to improved lithium-ion battery performance. However, they are susceptible to mechanical damage such as fracture and debonding, which can significantly reduce their lifetime. Using a coupled finite element model, we explore the impacts of diffusion-induced stresses on the failure mechanisms of an exemplar system with an NMC811 core and an NMC111 shell. In particular, we systematically compare the implications of assuming constant material properties against using Li concentration-dependent diffusion coefficient and partial molar volume. With constant material properties, our results show that smaller cores with thinner shells avoid debonding and fracture regimes. When factoring in a concentration-dependent partial molar volume, the maximum values of tensile hoop stress in the shell are found to be significantly lower than those predicted with constant properties, reducing the likelihood of fracture. Furthermore, with a concentration-dependent diffusion coefficient, significant barriers to full electrode utilisation are observed due to reduced lithium mobility at high states of lithiation. This provides a possible explanation for the reduced accessible capacity observed in experiments. Shell thickness is found to be the dominant factor in precluding structural integrity once the concentration dependency is accounted for. These findings shed new light on the performance and effective design of core–shell electrode particles.

Failure pressure prediction of high-strength steel pipe bend considering pipe and corrosion geometry

This study examines the influence of pipe bend geometry and corrosion geometry on the failure pressure of high-strength steel pipe bends subjected to internal pressure and axial compressive stress. Finite element analysis determines the impact of bend angle, bending radius, defect depth, defect length, defect spacing, and axial compressive stress on failure pressures. The findings reveal that increasing the bend angle reduces failure pressures significantly, with corrosion defects exacerbating this effect. Increased bending radius increases normalized failure pressure from 0.88 to 0.91 for intrados defects and decreases it from 0.98 to 0.93 for extrados defects. Additionally, single defects cause a slight 2.5–3.0% reduction in normalized failure pressure, while longitudinally and circumferentially aligned defects result in a 13–15% decrease in normalized failure pressure. Defect depth and length also significantly influence the failure pressure, particularly for deeper and longer defects (up to 48.2%). Furthermore, an empirical equation for predicting failure pressures in corroded pipe bends with high accuracy (R2 = 0.99) is developed based on Artificial Neural Network. This enhances pipeline integrity assessment and design practices.

The strain ratio-dependent multiaxial low cycle fatigue behaviour and life prediction of 316L stainless steel based on critical plane at elevated temperature

The study mainly investigates the effect of strain ratio on the multiaxial low cycle fatigue behaviour of 316L at 550 °C. The evolution of both axial and torsional stress amplitude is observed to go through three stages: cyclic hardening, softening and fracture. What's different is that the torsional loading experiences fewer cyclic hardening cycles compared to the axial loading. Regarding the interaction between axial and torsional stresses, it is observed that as the torsional strain increases, the axial deformation response presents a lower peak stress and a higher softening rate, while the torsional peak stress and softening rate hardly changes with the increase of axial strain amplitude. The fracture pattern is obtained through three-dimensional (3D) depth-of-field observation. It is discovered that as the strain ratio increases, the fracture pattern transits from tensile failure mode to shear failure mode. Furthermore, the orientation angle of the fracture surface increases and lies between the critical plane angle of maximum shear strain and maximum normal strain, indicating a mixed failure mode. Additionally, a comparison of nine representative critical plane models reveals that the energy-based models can better predict the multiaxial fatigue life influenced by the strain ratio. Finally, based on the analysis of deformation and failure mechanisms, a normal damage parameter weakening factor (NDWF) is introduced into the KBM-R model, and an improved normal stress component (INSC) is introduced into the Wu-R model. The two modified models well capture the impact of strain ratio and accurately predict the multiaxial fatigue life of both 316L and P92 steel.

Experimental study on damage evolution process, seepage characteristics, and energy response of columnar jointed basalt under true triaxial cyclic loading

The physical response of Columnar Jointed Basalt (CJB) under a stress–seepage coupling field is of great significance for dam safety and oil and gas reservoir evaluation. A true triaxial experimental machine was used for investigating the deformation, damage evolution characteristics, seepage properties, and energy response of the CJB. Before the start of the test, a series of uniaxial compression tests were used to determine the ratio of similar materials, and the cyclic loading test results indicate that: The strength characteristics of CJB decreases slowly and then increases rapidly as the dip angle β varies from 0° to 90° under two loading conditions of the tiered cyclic loading (T–C) and the constant amplitude cyclic loading (CA–C), showing an obvious U–shaped trend, and four different loading stages can be distinguished by characteristic stress. In the yield stage, the stress–strain curve shows an obvious plastic hysteresis loop, there is a strong correlation between the failure modes of the CJB and β of the specimen, the joint surface gradually deteriorates owing to loading and unloading conditions, and structural control failure occurs widely in specimens. The damage evolution process is discussed in combination with the Load–Unloading Response Ratio, and the relative damage amount (Df) is defined by cycle index. The permeability–axial stress relationship of the specimen conforms to the power exponential relationship, and the permeability evolution characteristics are strongly correlated with the degree of damage. The energy response of the CJB were investigated by tress–strain curve, under two loading modes, T–C and CA–C, the cumulative curves of dissipation energy Ed can be fitted by an exponential function and a logarithmic function, respectively. The findings of this research hold immense importance for clarifying the mechanical and seepage properties of CJB under a stress–seepage coupling field.

Analytical determination and numerical validation of the shear factor in annular sector cross sections

In the present study, the shear factor of an annular sector cross section, including the thickness effect, has been analytically determined for the first time. The shear factors depend on the angle of the sector and on the mean radius to thickness ratio. Two approaches were used to determine circumferential and radial shear stresses. The limits of validity of the approach were established, based on the similarity of the shear factors determined from both approaches. The results obtained from the present analytical approach were compared with the results of another analytical approach developed for thin sections. To check the suitability of analytically determined shear factors, unidirectional composite cantilever beams have been analysed by the finite element method, for different cross sections and cantilever lengths. With the material properties and displacement at the cantilever tip known, shear factors were determined and compared with those obtained from the analytical approach. The script used to calculate the shear factors is included as an appendix.

The interfacial behavior of an axisymmetric film bonded to a graded inhomogeneous substrate

With the development of high-tech applications such as thermal barrier coatings, stretchable and flexible electronics, etc, the key film/substrate systems are more commonly involving three-dimensional axisymmetric problems with graded inhomogeneous substrates. In these film/substrate systems, the effects of geometric and material factors of both the films and the substrates on the interfacial behavior are urgently needed to be uncovered. Herein, a novel theoretical axisymmetric model of an elastic film bonded to a graded substrate is proposed and solved by using Hankel integral transformation and orthotropic polynomials. The interfacial shear stress and the corresponding shear stress intensity factor as well as radial stresses and hoop stresses of both the film and the graded substrate are obtained. It is found that the present model works well to predict the interfacial behavior between an axisymmetric film and a graded substrate. Compared with cases with homogeneous substrates, choosing graded substrates can reduce the risk of edge fracture on the surface of the substrate. A film with a smaller elastic modulus and thickness is advantageous for the interface reliability of the film/substrate system under a thermal load. The results should be useful for not only understanding the load transfer mechanism of axisymmetric film/substrate system, but also providing a valuable guidance to optimize film/substrate structures in various practical and potential applications.

Remodeling of Murine Branch Pulmonary Arteries Under Chronic Hypoxia and Short-Term Normoxic Recovery.

Chronic hypoxia plays a central role in diverse pulmonary pathologies, but its effects on longitudinal changes in the biomechanical behavior of proximal pulmonary arteries remain poorly understood. Similarly, effects of normoxic recovery have not been well studied. Here, we report hypoxia-induced changes in composition, vasoactivity, and passive biaxial mechanics in the main branch pulmonary artery of male C57BL/6J mice exposed to 10% FiO2 for 1, 2, or 3 weeks. We observed significant changes in extracellular matrix, and consequently wall mechanics, as early as 1 week of hypoxia. While circumferential stress and stiffness returned toward normal values by 2-3 weeks of hypoxia, area fractions of cytoplasm and thin collagen fibers did not return toward normal until after 1 week of normoxic recovery. By contrast, elastic energy storage and overall distensibility remained reduced after 3 weeks of hypoxia as well as following 1 week of normoxic recovery. While smooth muscle and endothelial cell responses were attenuated under hypoxia, smooth muscle but not endothelial cell responses recovered following 1 week of subsequent normoxia. Collectively, these data suggest that homeostatic processes were unable to preserve or restore overall function, at least over a brief period of normoxic recovery. Longitudinal changes are critical in understanding large pulmonary artery remodeling under hypoxia, and its reversal, and will inform predictive models of vascular adaptation.

Theoretical and Finite Element Analysis of Pressure Vessel

Objectives: This study tests the vessel strength and performance of pressure vessel under Internal pressure, Nozzle loads, and Hydro-test using Ansys APDL, validating design alignment with ASME Section VIII following the Design by rule (Analytical) and Design by Analysis (FEA) accurate elastic analysis approach. Methods: This study employs ASME methods to validate vessel integrity under various loads. Strength is confirmed through analytical formulas and Finite Element Analysis (FEA) using ANSYS APDL, aligned with widely used ASME BPVC codes in the oil and gas industry. The FE model, utilizing hex elements, ensures result accuracy with a minimum of three elements across thickness. Boundary conditions are validated by comparing hoop stress in FEA with analytically calculated values. ASME's computationally efficient elastic analysis, employing a linear approach, includes stress linearization at discontinuity and non-discontinuity locations, verifying vessel design through analysis. Findings: Initial thicknesses for the shell and cone exceeded analytically calculated minimums, affirming vessel structural integrity through ASME's design by rule approach. Finite Element Analysis (FEA) stress analysis at critical points, such as nozzle junctions and other discontinuity areas, validates accuracy through hoop stress checks. Analysis of design and test load cases reveals stress categories well within ASME Sec VIII limits, confirming the vessel's safety and compliance with elastic stress analysis standards. Novelty: This method emerges as a reliable tool for vessel design, ensuring safety and ASME compliance, particularly beneficial for industries like oil and gas. It provides precise guidelines utilizing hex mesh, validates boundary conditions through hoop stress comparison, and comprehensively assesses stress in critical and non-critical zones through elastic stress analysis. Addressing common challenges identified in the literature review, this approach enhances the accuracy and reliability of pressure vessel designs in compliance with ASME standards for design and test loadings. Keywords: Pressure Vessels, Process Industries, Stress, Loads, Pressure, Thermal, Design Validation, ASME, FE analysis

Simplified homogenization technique for nonlinear finite element analysis of in-plane loaded masonry walls

The present investigation focuses on the nonlinear modelling of masonry walls under in-plane loading. To conduct this macro-scale study, a homogenization technique is applied to derive the equivalent secant moduli according to damage and friction sliding at the micro scale level for both bed mortar joint and brick material constituents. In the homogenization process the representative unit cell of masonry panel with a regular arrangement is first defined. Then a simplified kinematical model is proposed to describe the behaviour of the homogenized unit-cell under combined axial and shear stresses. This is based on the cohesive model for pure mode I and II and by allowing for the Coulomb's friction law for bed joint and the scalar damage model is adopted for the brick material. In the first stage, the proposed homogenization technique is verified for various unit cell constituents at micro-scale level. In the second step, this homogenization procedure was incorporated into proposed in-house finite elements software. To achieve this end, a new beam finite element is formulated in the context of the fibre higher order shear deformation theory HSDT. Using the proposed finite elements model, a numerical investigation is conducted to check the validity of the proposed model against the available experimental and numerical investigations. This allowed for the study of the effect of the applied compressive load on the lateral ultimate load.

Mechanical properties of partially bonded rock anchors in squeezing large-deformation soft rock tunnels

Partially bonded rock anchors are crucial structural tunnel support elements whose effectiveness depends on their interactions with the surrounding rock. This study combined laboratory experiments and numerical simulations to examine the mechanical behavior of partially bonded rock anchors under pull-out tests, focusing on the influence of bonded lengths. The axial strain of the anchor body and the vertical strain of the concrete block along the anchor axis were tested using distributed optical fibers. The results indicated that the anchor body stress remained relatively constant in the unbonded sections but gradually decreased as the depth into the bonded section increased. Simultaneously, the significant compressive stress range induced by the rock anchor in the concrete block decreased rapidly as the bonded length increased. Subsequently, the effects of different bonded lengths, unbonded section positions, and bonding combinations on the mechanical behavior and support effectiveness of partially bonded rock anchors in highly stressed soft rock tunnels undergoing substantial deformation were investigated using numerical simulations in ABAQUS. These findings suggest that rock anchors with longer bonded lengths have better control of the rock between the anchors. Simultaneously, the maximum axial stress of rock anchors tended to increase with longer bonded lengths. The rock displacement tended to be obviously larger when the unbonded section was set at the end of the rock anchors compared with when the unbonded section was set in the middle. The rock displacement was larger when the unbonded section was set at the outer end of the rock anchors, indicating that setting unbonded sections near the tunnel wall was detrimental to controlling rock deformation while improving structural safety. Setting one unbonded section near the tunnel wall and another unbonded section in the middle of the rock anchors resulted in excellent structural safety and rock deformation control. Furthermore, fully bonded rock anchors were compared with partially bonded rock anchors based on suitable bonding combinations in the deformation section of Muzhailing Tunnel. The results indicated that the fully bonded rock anchors experienced axial forces exceeding the yielding load in the early stages of support, with noticeable early yielding of the anchor plate. In contrast, the unbonded sections in the partially bonded rock anchors did not yield in either the bonded anchor body or the anchor plate. Partially bonded rock anchors exhibited better overall stability and reliability under high-deformation tunnel conditions.

Damage evolution modeling of CFRP/Al single-lap screw type blind riveted joints during realistic installation process

As studies on the damage behaviors of composites during screw type blind riveting are notably absent, this paper seeks to fill this gap by combining experimental tests and numerical simulation methods. A three-dimensional finite element model was proposed, and the simulation results were obtained and validated by experimental data. The light microscope and scanning electron microscope were used to observe the stress state, axial deformation, damage modes, and damage distribution in two load-bearing regions at the initial contact and after installation. The results demonstrated that the preload showed a four-step “zero -steep rise -decline -steep rise” development during installation. The stress and deformation were concentrated in two circular zones, with the maximum axial stress component and deformation of 321 MPa and 0.046 mm, respectively. In two pressed zones, there were three failure modes, with out-plane matrix crushing being the most severe. In-plane matrix cracking damage is seen at a 45° direction in the first layer, with a damage index of 0.745. In addition, the effect of two geometric parameters of the sleeve on the blind head shape, load-bearing regions, and CFRP damage was investigated. The results would build confidence in reducing CFRP damage and enhancing joint integrity.

A novel stress concentration inspection method for marine oil and gas pipeline based on UNSM

Stress concentration of marine oil and gas pipelines can lead to deformation and cracks, laying out great hidden dangers for safe operation. This paper proposes a novel in-line inspection method for stress concentration based on UNSM (unsaturated magnetization) for oil and gas pipelines. Firstly, the stress concentration inspection mechanism with UNSM is analyzed, and the equivalent magnetic circuit model of the inspection probe is derived. Secondly, the response signal features of axial, radial and complex stresses were investigated parametrically by numerical simulation. Then, quantitative tensile stress inspection was carried out with the UNSM inspection probe. Finally, the pipeline stress state is continuously scanned by the self-developed defect dynamic scanning experimental system. The results show that the UNSM inspection probe can effectively detect the abnormal stress of the pipeline. Meanwhile, the axial tensile, radial compressive stress and complex stress increase the axial permeability of the pipeline, resulting in a negative correlation of characteristic signals. Besides, the signal feature shows the "basin" distribution and decreases gradually with the increase of the lift-off. The above research provides a reference for developing in-line inspection equipment for the abnormal stress of marine pipelines.

The effect of imperfect bonding on stress distribution in fibrous composites

An attempt was made to map the distribution of stress in fibrous composites with imperfect bonding. Two analytical micro-mechanics models were developed. In the first model, the composite was subjected to axial tensile loading, parallel to the fiber direction, and the assumption of iso-strain was employed to derive the control equations. In the second model, the composite was loaded in the direction transverse to the fiber. An iso-stress condition was employed, and Airy stress function was utilized to articulate the stress and displacement equations. An assumption of how the stress is transferred between the matrix and the fiber was introduced in both models. To investigate and validate the models, specimens were fabricated using a carbon plain weave fabric and a geopolymer matrix. Single fiber pullout and three-point bending tests were carried out. The maximum average tensile stress obtained from the three-point bending tests, as well as the mechanical properties of the fiber and geopolymer, served as input for the models. Results indicate that the effect of the level of bonding is very high in the transverse direction while almost negligible in the axial direction. The difference in the maximum value of the axial tensile stress at the fiber-matrix interface was used to calculate the numerical value of the interfacial shear strength, and the numerical result matched the data obtained from the single fiber pullout test.

Mechanics behavior and failure mechanism of the intralayer carbon/glass hybrid rod

AbstractThe carbon/glass hybrid rod exhibits high tensile strength, light weight, and strong corrosion resistance. However, the bottleneck of interlayer splitting exists in the interlayer hybrid rod, severely impeding safe operation. To solve the problem of rod splitting, this paper proposed a new scheme of an intralayer carbon/glass hybrid rod. Based on the material constitutive model, a full‐scale simulation model was developed. The stress distribution and deformation of the hybrid rod were analyzed and the progressive damage mechanism of the hybrid rod was explained. The results indicated that, for the intralayer carbon/glass hybrid rod, (a) the ultimate experimental tensile load witnessed a significant increase, rising by 14.0% from 452.4 to 515.7 kN compared to the interlayer hybrid rod; (b) the numerical model predicted the tensile load of 525.9 kN, with an error of 1.9% compared to the test result, meeting engineering accuracy requirements; (c) the elastic deformation stage saw a 146.7% increase from 280.2 to 691.3 MPa in the maximum axial stress of the carbon‐fiber layer, and a 120% increase from 89.8 to 198.0 MPa in the maximum radial stress of the glass fiber layer as the tensile displacement increased from 0.16 to 0.32 mm. In conclusion, the intralayer carbon/glass hybrid rod proposed in this paper can significantly improve the tensile strength compared to the interlayer hybrid rod, which can accelerate the application of carbon/glass hybrid rods in oil and gas fields.Highlights According to the problem of interlayer splitting in the interlayer carbon/glass hybrid rods, a novel scheme of an intralayer carbon/glass hybrid rod was proposed. Based on the material constitutive model, a full‐scale simulation model of an intralayer carbon/glass hybrid rod was developed to analyze the stress distribution and deformation response under tensile load. The dynamic progressive damage analysis method for intralayer carbon/glass hybrid rods was proposed to reveal the damage evolution mechanism.

Water and mud inrush dynamics process simulation by using coarse-grained CFD-DEM method

Water and mud inrush disaster is a typical fluid-solid coupling problem, and its forecasting and prevention can reduce human and economic losses. In this work, a coarse-grained discrete element method and computational fluid dynamics model based on bonded particles is employed to investigate an inrush disaster happened in Foshan Metro Line 2. It's shown that the current model can simulate beam bending, and the differences from the analytical solution are 7% and 5% in deflection and maximum axial stress. This study also suggests that two-way coupling is in superior agreement with field observation than one-way coupling. The water pressure is highly influential as it increases from 0.15 MPa, 0.25 MPa, 0.35 MPa to 0.45 MPa inrush occurrence time varies from 28.0 s, 11.5 s, 7.5 s to 5.0 s, respectively. The current model is capable of simulating water and mud inrush, and may provide a framework for investigating this disaster in complex engineering scenarios.

Multiphysics Analysis of PLOFC and DLOFC Accidents in the HTGR-TR

High-temperature, gas-cooled reactors (HTGRs) are promising advanced reactor designs. Leveraging passive safety features, higher core outlet temperatures, previous commercial operational experience, and potential coupling with nonelectrical systems, HTGRs present many advantages over traditional light water reactors and other advanced reactor designs. The High-Temperature, Gas-Cooled Test Reactor (HTGR-TR) is a point design developed by Idaho National Laboratory as a response to the need for the expansion of U.S. test reactor capabilities. The HTGR-TR was designed to serve as a test reactor for Generation-IV small modular prismatic block HTGRs and to provide irradiation data, two crucial contributions to the development of advanced reactors. As in any reactor design, it is necessary to understand the behavior of the reactor during accident scenarios to determine the overall safety of the design. Pressurized loss of forced cooling (PLOFC) and depressurized loss of forced cooling (DLOFC) are two accidents that can occur in HTGRs and that present challenges to decay heat removal. In order to understand the behavior of the fuel during these accidents, the resulting mechanical behavior and fission product migration in the fuel are evaluated. Using the HTGR-TR design, which utilizes tristructural isotropic (TRISO) fuel, a multiphysics analysis during the PLOFC and DLOFC transients was performed. This study utilizes neutronics, thermal hydraulics, and fuel performance modeling to analyze the behavior of TRISO particles during steady-state operation and the described transients. This analysis aims to characterize the hoop stress and strain during the transients, as well as predict fission product migration and radiological release. Due to the startup conditions of the HTGR-TR, the silicon carbide (SiC) layer for both of the transients and steady-state conditions are initially in compression for both the hoop stress and strain. The DLOFC transient at the beginning of cycle was the most challenging overall to the fuel, having the closest to tensile behavior and the closest to tensile strain. Because the integrity of the SiC layer was not challenged during any of the transients, the release of 90Sr and 137Cs was found to be negligible. The PLOFC transient at the end of cycle resulted in the largest 110mAg release and subsequent radioactivity increase. However, the increase in radioactivity was minor when compared to typical operating conditions due to the relatively large diffusivity of 110mAg though SiC at normal operating temperatures. Highlights include Neutronics and thermal-hydraulic modeling generating steady-state and transient conditions for use in fuel performance analysis.2. Detailed BISON analysis demonstrating the excellent performance of TRISO fuel during PLOFC and DLOFC transients.3. Fuel behavior showing negligible fission product release.

The athlete's heart: allometric considerations on published papers and relation to cardiovascular variables.

To evaluate the morphology of the "athlete's heart", left ventricular (LV) wall thickness (WT) and end-diastolic internal diameter (LVIDd) at rest were addressed in publications on skiers, rowers, swimmers, cyclists, runners, weightlifters (n = 927), and untrained controls (n = 173) and related to the acute and maximal cardiovascular response to their respective disciplines. Dimensions of the heart at rest and functional variables established during the various sport disciplines were scaled to body weight for comparison among athletes independent of body mass. The two measures of LV were related (r = 0.8; P = 0.04) across athletic disciplines. With allometric scaling to body weight, LVIDd was similar between weightlifters and controls but 7%-15% larger in the other athletic groups, while WT was 9%-24% enlarged in all athletes. The LVIDd was related to stroke volume, oxygen pulse, maximal oxygen uptake, cardiac output, and blood volume (r = ~ 0.9, P < 0.05), while there was no relationship between WT and these variables (P > 0.05). In conclusion, while cardiac enlargement is, in part, essential for the generation of the cardiac output and thus stroke volume needed for competitive endurance exercise, an enlarged WT seems important for the development of the wall tension required for establishing normal arterial pressure in the enlarged LVIDd.