Axial Thermal Loads Research Articles

Energy-Preserving Perturbation Method for Thermally Induced Dynamics in Aerospace Tensegrity Structures

Tensegrity structures are emerging as pivotal components in the assembly of ultralarge modular spacecraft in orbit, primarily due to their exceptional volume-to-mass ratio and robust controllability. During on-orbit operations, given the low damping and high flexibility of tensegrity, its vibration-induced deformations affect the magnitude of the heat flux, presenting a typical force–shape coupling problem. This paper introduces an energy-preserving matrix perturbation solution designed to efficiently and accurately address the thermally induced vibration challenges in tensegrity. This method effectively mitigates the energy dissipation and numerical instability issues. Furthermore, the analysis incorporates the impact of the axial component of heat flux on structural vibration, uncovering the influence mechanism of this often-overlooked slow variable on the dynamic behavior of tensegrity. The proposed method demonstrates a deviation of less than 1% between the thermal response and the results obtained from finite element analysis, while achieving a 70% reduction in computation time. The varying axial thermal load leads to a rapid decrease in system frequency, resulting in divergent thermal vibrations. Additionally, the significant dynamic stress can potentially surpass the structural stress limits. These findings underscore the critical importance of considering such effects in the design and calculation of tensegrity structures for aerospace applications.

Effect of thermal axial load on vibration of cracked single-walled carbon nanotubes modelled as Timoshenko nanobeams using nonlocal theory

ABSTRACT This paper investigates free vibration of cracked single-walled carbon nanotubes modelled as Timoshenko nanobeams under axial thermal load. The main objective of this work is a deep, true, and precise formulation to analyse truly the thermal effects on the Timoshenko nanobeam model. Nonlocal elasticity theory is applied to Timoshenko beam model. It is assumed that a crack divides the beam into two segments. The crack is modelled by a torsional spring connecting the beam segments to each other. The thermal load acts as an axial force on the nanobeam. Galerkin’s method is used to solve the partial differential equation of motion. The effect of the crack location, crack severity, thermal load, and nonlocal parameter on the frequencies are examined. As the crack severity increases, the frequencies decrease except the modes in which the crack locates at one of their nodes. All mode frequencies decrease at the high temperatures and increase at the low temperatures. Increasing the nonlocal parameter causes a reduction in the frequencies at any temperature. The nonlocal parameter effect on the frequencies increases at high or elevated temperatures.

Effect of temperature on dynamic behavior of cracked metallic and composite beam

Euler-Bernoulli beam model is used to analyze the thermal vibration of cracked metallic and laminated composite beam with fully clamped ends. An analytical solution technique is proposed to investigate the natural vibration of cracked beam subjected to axial thermal load. An open and stable crack is considered perpendicular to the beam axis. In this study, three different types of material such as steel, copper and aluminum and their composition are used to analyze the thermal effect on different modes of frequency. The effects of thermal stress on the vibration of cracked metallic and composite fully clamped beam are revealed. The results show that the effect of temperature is significant on the natural frequency of cracked metallic and composite beam.

Structural performance monitoring of buried pipelines using distributed fiber optic sensors

In this study, a method involving the use of distributed fiber optic temperature and strain sensors is presented to quantitatively assess the structural performance for buried pipelines by considering both longitudinal bending load and axial thermal load. The monitoring scheme of distributed strain and temperature sensors is proposed based on the pipeline structural analysis, and the assessment approach is formulated using the distributed monitoring data. The time-spatial variation in the bending strain and temperature of the burial pipelines are monitored using distributed fiber optic sensors. The structural performance of the pipeline is then assessed with the monitored data in conjunction with the pipe parameters and internal pressure. A field application was performed on a buried gas pipeline to investigate the availability of the proposed method and the results from the site application demonstrate that the proposed method effectively assesses the structural performance of the burial pipelines with the distributed strain and temperature data.

Plastic ratchetting of railhead material in the vicinity of insulated rail joints with wheel and thermal loads

A detailed finite element analysis (FEA) was carried out to present a stress analysis of an insulated rail joint IRJ considering a wheel load on the IRJ producing stresses above the shakedown limit of the rail material. A 5mm endpost thickness is considered at the discontinuity in the rail steel which is required to form the 6 bolt IRJ. In addition, an axial pressure load of 165MPa was also considered on the rail faces at the discontinuity in the form of compression (buckling) and tension (pull-apart). A modified Hertzian contact pressure distribution is considered in this simulation. 100 cycles of dynamic wheel load of 174kN were applied to the rail top materials in the vicinity of the IRJ.Residual stress and plastic strain, equivalent plastic strain and permanent deformation of railhead material in the vicinity of IRJ are presented. The strain data depict damage of endpost materials and ratchetting failure of rail ends due to vertical wheel load and axial thermal load. The ratchetting failure modes follow the established trend of decay in the ratchetting rate in successive wheel load cycles. The size of the plastic zone in the railhead materials is also identified.

NITINOL-reinforced plates: Part I. Thermal characteristics

The static and dynamic characteristics of NITINOL-reinforced composite plates are influenced primarily by the temperature distribution inside the composite matrix. Such distribution arises from the electrical heating of NITINOL fibers embedded along the neutral plane of these composite plates. When temperatures are developed above the martensite transformation temperature of the NITINOL fiber, the elastic modulus of the fibers increases approximately fourfold and significant phase recovery forces are generated. Such thermal activation of the NITINOL fibers increases the elastic energy of the fibers and enchances the stiffness of the plates, provided that the phase recovery forces are high enough to compensate for the loss of the modulus of elasticity of the composite and counterbalance the generated thermal loads. Understanding the interaction between the thermal, static and dynamic characteristics of the NITINOL-reinforced plates is essential to tailoring the performance of these plates to match changes in the operating conditions. Such an interaction is influenced primarily by the temperature distribution inside the plates during the activation and de-activation of the NITINOL fibers. In this study, a thermal finite element model is developed to determine steady-state and transient temperature distributions inside NITINOL-reinforced composite plates resulting from different activation strategies of the NITINOL fibers. The theoretical predictions are compared with experimental measurements in order to validate the thermal finite element model. The resulting temperature distribution can be used to determine an average modulus of elasticity of the composite. The average temperature rise above ambient can also be used to compute the axial thermal loading on the composite plate. Such predictions are utilized in computing the static and dynamic characteristics of NITINOL-reinforced plates which are presented in Parts II and III of this paper, respectively.

Mechanical approach to the evaluation of the low temperature threshold of added transmission losses in single-coated optical fibers

An easy-to-use calculation procedure for the evaluation of thermally induced forces in single-coated optical fibers is discussed. The calculations show that the increase in the lateral pressure at the cladding-coating interface adequately reflects the experimentally observed increase in the added transmission losses at low temperatures. The measurements were carried out on loose fibers in a test chamber, where mechanical effects other than the thermally induced shrinkage of the coating were excluded. It is suggested that the thermally induced lateral pressure be used as a tentative criterion of the low temperature threshold of the expected added optical losses in single-coated fibers. The increase in this pressure reflects the increase in the axial thermal loading as well. Single-coated optical fibers can be successfully used in transmission media operated at moderately low temperatures (for instance, in undersea systems) which do not cause large thermally induced forces; otherwise, a dual-coated fiber design should be considered. The final selection of the most feasible coating design must be based on all the material, optical, chemical, technological, mechanical, environmental, and cost considerations. >