Thermal Stress Considerations Research Articles

Correction to: Local Stress Distributions in Fiber-Reinforced Composites with Consideration of thermal Stresses During the Curing Process

Correction to: Local Stress Distributions in Fiber-Reinforced Composites with Consideration of thermal Stresses During the Curing Process

Local Stress Distributions in Fiber-Reinforced Composites with Consideration of Thermal Stresses During the Curing Process

Local Stress Distributions in Fiber-Reinforced Composites with Consideration of Thermal Stresses During the Curing Process

Vibration analysis of rotating thermally-stressed gyroscope, based on modified coupled displacement field method

Free lateral vibration analysis of gyroscope model is studied in this paper. This gyroscope is modeled as a rotating simply-supported beam which is under an initial thermal stress. Thermo-mechanical properties of the beam are mutable with temperature. For the first time beam is supposed to rotate around a fixed axis in which rotational displacement field is expressed as a liner function in terms of combination of axial and lateral displacements. Dynamic-vibration equations of the proposed model are derived based on the Hamilton’s principle. Due to the symmetry of the system, Navier approach is adopted as solution approach. For evaluation, current results are compared with the results available at the technical literature showing high level of accuracy. New results emerged from of this paper imply effects of rotation of the beam and thermal stresses simultaneously upon the dynamic response of beams: different values of lateral velocity factor strongly affect the frequencies of the system; however, axial velocity factor does not play any role. In short, rotation of the beam accompanied by thermal stresses are affecting the dynamic behavior of the beam-type gyroscope remarkably. Consideration of thermal stresses and rotation rates are the most vital factors in the design of a gyroscope.

Investigation Into the Thermal Limitations of Steam Turbines During Start-Up Operation

Liberalized electricity market conditions and concentrating solar power technologies call for increased power plant operational flexibility. Concerning the steam turbine (ST) component, one key aspect of its flexibility is the capability for fast starts. In current practice, turbine start-up limitations are set by consideration of thermal stress and low cycle fatigue. However, the pursuit of faster starts raises the question whether other thermal phenomena can become a limiting factor to the start-up process. Differential expansion (DE) is one of such thermal properties, especially since the design of axial clearances is not included as part of start-up schedule design and because its measurement during operation is often limited or not a possibility at all. The aim of this work is to understand DE behavior with respect to transient operation and to quantify the effect that such operation would have in the design and operation of axial clearances. This was accomplished through the use of a validated thermomechanical model that was used to compare DE behavior for different operating conditions of the machine. These comparisons showed that faster starts do not necessarily imply that wider axial clearances are needed, which means that the thermal flexibility of the studied turbine is not limited by DE. However, for particular locations, it was also obtained that axial rubbing can indeed become a limiting factor in direct relation to start-up operation. The resulting approach presented in this work serves to avoid over-conservative limitations in both design and operation concerning axial clearances.

Comparison of analytical methods for the consideration of thermal stresses in the engineering failure assessment

This paper focuses on a comparison of different analytical methods for engineering failure assessment of components subjected to high thermal loading. The primary goal is to validate the analysis tools available within the FAD methodology and thus reduce the conservatism of the analytical assessment. Two well-known approaches based on the ρ and V factors, which have been established within the R6 code for taking into account the interaction of the primary and secondary stresses, are considered along with a recently developed Vg procedure. The analytical methods are validated on examples of two-dimensional crack geometries by varying the crack size, material strain hardening, and the ratio of the primary to secondary stresses. The accuracy of the analytical methods is judged by comparing the estimated elastic-plastic crack driving force with results of direct finite-element calculations. The traditional FAD approach incorporating the ρ and V factors is concluded to considerably overestimate the crack driving force, whereas the Vg method is shown to yield most accurate predictions.

Scaling laws based metamodels for the selection of the cooling strategy of electromechanical actuators in the early design stages

The integration of electromechanical actuation systems for aerospace applications requires additional thermal stress considerations during the preliminary design, which were not necessary within the hydraulic technology. The favored models during this design phase are simple, continuous and explicit mathematical expressions to enable easy analytical manipulations or implementations in worksheets or optimization loops. The paper shows how such models can be obtained for the desired applications, illustrating the example of a Limited Angle Torque Motor (LATM) with different cooling strategies. The used method for gathering the models is a regression process on data obtained by finite element simulations. The originality of the method stands in the physical insight of the regression function which is based on scaling laws and dimensional analysis. An example of preliminary design of a LATM illustrates the use of the obtained models for the comparison of two possible architectures intended to minimize the mass of the actuator by implementing different cooling strategies.

Constant diurnal temperature regime alters the impact of simulated climate warming on a tropical pseudoscorpion

Recent theory suggests that global warming may be catastrophic for tropical ectotherms. Although most studies addressing temperature effects in ectotherms utilize constant temperatures, Jensen's inequality and thermal stress considerations predict that this approach will underestimate warming effects on species experiencing daily temperature fluctuations in nature. Here, we tested this prediction in a neotropical pseudoscorpion. Nymphs were reared in control and high-temperature treatments under a constant daily temperature regime, and results compared to a companion fluctuating-temperature study. At constant temperature, pseudoscorpions outperformed their fluctuating-temperature counterparts. Individuals were larger, developed faster, and males produced more sperm, and females more embryos. The greatest impact of temperature regime involved short-term, adult exposure, with constant temperature mitigating high-temperature effects on reproductive traits. Our findings demonstrate the importance of realistic temperature regimes in climate warming studies, and suggest that exploitation of microhabitats that dampen temperature oscillations may be critical in avoiding extinction as tropical climates warm.

Investigation of the Interface Parameters of Fiber-Reinforced Composite Materials

Design of the interfacial properties is a significant fundamental issue in the field of composite materials. Much attention has been paid to the improvement of the interface strength, while there has been a little work concerning the mechanical design of the interface for fiber-reinforced polymers (FRPs) in which the fiber is transversely isotropic thanks to its orientation feature. Based on the conception of neutral inclusion and imperfect interface conditions, the interface parameters are obtained for the FRPs by using Kolosov constant. We demonstrate the effect of the thermal residual stresses on the neutrality for FRPs in this paper. If the interface has the properties of design parameters without consideration of thermal stress, the presence of thermal residual stress/strain would break the neutrality in the cases of equal-biaxial tension and pure shear. In particular, the neutral fiber does not exist unless the thermal stress is eliminated in the equal-biaxial tension. In the case of uniaxial tension, the neutral fiber does not exist in absence of thermal stress, while the neutrality would become possible by properly controlling the thermal residual stress. Because the large thermal residual stress will result in the formation of cracks in matrix, a trade-off design is necessary between the neutrality and the initiation of matrix cracking.

Concrete Thermal Stress of Arch Dam in Construction Period of Stability against Sliding of Steep Slope Section

Thermal stress, as one of the most important stress of the arch dam during construction period, strongly influences the sliding stability of the arch dam. To analyze this kind of impact on arch dam sliding stability, numerical modeling of a typical slope dam section from 300-meter-high levels arch dam during construction period was conducted. Based on the rigid body limit equilibrium method, results of the case considering thermal stress as well as those without thermal stress were presented. Detailed comparison with the results of multiple monoliths was also made. In addition, the relevant sliding stability coefficient with the consideration of thermal stress was suggested.

Synthesis of carbon fibre-reinforced, silicon carbide composites by soft-solution approach

The aim of the present work centers on synthesizing and characterizing carbon fibre (Cf) reinforced, silicon carbide matrix composites which are considered to have potential applications in aerospace and automobile industry. A series of composites, namely the Cf-SiC, Cf-(SiC+ZrC), Cf-(SiC+ZrB2), and Cf-(SiC+ZrO2), have been prepared by a proposed soft-solution approach. This approach involves the use of water-soluble precursors of colloidal silica, sucrose, zirconium oxychloride, and boric acid as sources of silica, carbon, zirconia, and boron oxide, respectively to achieve the desired matrices through drying, carbonization and carbothermal reduction. The prepared powders and the composites were characterized by thermal analysis, X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analyses to assess the phase formation and microstructure of the materials, apart from assessment of their tensile properties. The study shows that the soft-solution process yields matrices with finer crystallite sizes, having homogeneous distribution of the constituent phases of either the powders or of the composite matrices. The role of the additional phases on the tensile properties of the composites has been discussed using consideration of thermal stresses at fibre-matrix interface; whereas the role of the carbothermal reduction temperature in determining these properties has been explained using the interfacial characteristics of the fibre-matrix. Addition of ZrO2 in the matrix of SiC has shown to improve the properties of Cf-SiC composites considerably. The results of this investigation unambiguously demonstrate that aqueous solution-based processing can be used for fabrication of these composites in relatively shorter time in an environmental friendly manner without using any expensive equipment. The approach is capable of yielding composites with different phases in the matrix by simple variation of precursor materials and solutions. The small crystallite sizes, fine particle distribution and low carbothermal reduction temperatures are some of the specific merits of the proposed method.

Study on Thermal Stresses the Extreme Temperature in Bridge Deck Pavements Using FEM Analysis

The thermal stresses at the extreme temperatures in bridge deck pavements (BDP) was analyzed in the paper. The sample bridge deck and asphalt concrete pavements were analyzed. The maximum principal and shear stresses in the BDP at the wide range of temperatures were calculated using 3D finite element method. The compared results showed a strong linear correlation between the BDP maximum principal stress and the elastic modulus. This linear relationship also existed between the shear stress and the elastic modulus. From the finite element analysis, it is found that the BDP elastic modulus affects the thermal stress more than the thickness of BDP. With the consideration of thermal stresses of BDP, the thickness of BDP from 6 to 12 cm is recommended for the BDP construction.

Electromagnetic Disruption Effects in the ARIES-RS Tokamak Design

A model of the induced currents and resultant electromagnetic forces and stresses during a disruption event in the ARIES-RS tokamak design is presented. Like many other power reactor concepts, the ARIES-RS has a modular design consisting of toroidally segmented internal structures to limit disruption induced currents and facilitate maintenance. During a disruption, currents driven in these structures cross the large toroidal magnetic field producing substantial electromagnetic forces.To consider these effects, a transient three-dimensional electromagnetic finite element model of the ARIES-RS device was created, implemented by the commercial code ANSYS. The same code was used for dynamic structural analysis.The model includes all major components (the first wall, blankets, divertor plates, stabilizing shells, vacuum vessel, shields) electromagnetically coupled together. The magnets are assumed to remain energized during the disruption. The plasma current decay is prescribed, not coupled with the current in the structure. Halo currents and and vertical displacement events, which may produce larger forces than found in this study, are not considered.The results illuminate important design tradeoffs. For a centered fast plasma current quench, the outboard first wall/blanket modules were found to experience the most severe loading. Current in the sidewalls generate forces that produce large torques on these structures. Supports are needed to react these loads; however, thermal stress considerations drive designs toward a first wall with a compliant support system. Thus, supports needed to reinforce against disruption loads can lower the maximum permissible heat flux on the first wall. Further, electromagnetic pressure on the first wall requires a factor of two reduction in the coolant channel width in some regions, resulting in higher pumping power.Extension of the results to other modular tokamak designs is discussed.Color versions of the figures are available on the world wide web at http://silver.neep.wisc.edu/disrupt or by contacting the authors.

Modeling of the mechanical properties of discontinuous-aligned-fiber composites after thermoforming

Specimens made of unidirectional and bidirectional discontinuous-aligned-fiber (DAF) composite material were elongated to different states of deformation by thermoforming. Tension tests were performed on pre-stretched specimens. The thermoforming behavior was modeled by using the Herschel-Bulkley model. The effect of fiber orientation during thermoforming was described by applying the Jeffrey equation. The combination of both the Herschel-Bulkley model and the Jeffrey equation enabled, under consideration of thermal stresses, the determination of the ultimate tensile strength of thermoformed unidirectional and bidirectional DAF materials. These results correlated well with those of the experimental tensile tests.

Ignition of a condensed substance by a hot plate with consideration of thermal stresses

Ignition of a condensed substance by a hot plate with consideration of thermal stresses

Heat-Sink Structural Design Concepts for a Hypersonic Research Airplane

Hypersonic research aircraft design requires careful consideration of thermal stresses. This paper relates some of the problems in a heat-sink structural design that can be avoided by appropriate selection of design options, including material selection, design concepts, and load paths. Data on several thermal loading conditions are presented on various conventional designs including bulkheads, longerons, fittings, and frames. Results indicate that conventional designs are inadequate and that acceptable designs are possible by incorporating innovative design practices. These include nonintegral pressure compartments, ball-jointed links to distribute applied loads without restraining the thermal expansion, and material selections based on thermal compatibility. Nomenclature E = Young's modulus of elasticity g = acceleration of gravity K = restraining factor k = thermal conductivity A/ = change in length L = length M = Mach number Q = dynamic pressure A T = temperature di f f erence a. — coefficient of thermal expansion a =stress

Concrete Reactor Shield

Report on design and construction of reactor biological shield wall and dome for Consolidated Edison Co's Nuclear Elec Generating Station at Indian Point, NY; study to select type of arch; thermal stress considerations; construction aspects.