Thermoelastic Conditions Research Articles

Optomechanical design and analysis of lens assembly for space application

This study illustrates how commercial off-the-shelf optics may be employed in space exploration cameras. The most frequent loads on optical systems are self-weight, which is caused by gravitational orientations, vibration, and temperature ranges, which is caused by exposure to quickly changing temperatures ranging from extremely cold to very hot and during launch. This study describes the modulation transfer function (MTF) performance of the selected lens assembly, followed by a top-down method to disassemble the optical parts of the commercial lens housing. The lens enclosure was designed and modelled by retaining the interelement lengths determined from physical measurement. The performance of the lens barrel and optical elements have also been validated in ANSYS using a quasi-static loading and thermoelastic condition. As a post-performance assessment owing to stress and vibrations during satellite launch, a tilt-separation simulation was conducted. As a result of this research, it has been demonstrated that optomechanical design of commercial lens assembly is feasible for use in space application camera systems.

Selecting a Coating for Ceramic End Mill Based on the Stress-Strain Behavior of its Cutting Edge. Part 1

A coating for a Si3N4 ceramic end mill was selected based on the analysis of the results of numerical simulation of the stress-strain behavior of its cutting edge. It was found that the TiC coating is more effective than TiN coating, and reduces the temperature and stresses of the cutting edge of the mill under the transient thermoelastic conditions. This is critical for reducing the intensity of micro-chipping of ceramic material during operation.

The Influence of High-Power Microwave Signal Transmission on the Thermoelastic Condition of a Waveguide

The interdisciplinary problem on the influence of power loss of microwave signals transmitted by waveguides on their thermoelastic condition is considered. The estimation of the temperature field is carried out based on the developed mathematical model with the differential equation of the thermal balance of the waveguide, which takes into account the different conditions of its operation and which is solved using the finite difference method using the program developed.

Thermo-Mechanical and Structural Performances of Automobile Disc Brakes: A Review of Numerical and Experimental Studies

Disc brake system is one of the most critical components in a vehicle, which is always exposed to nonlinear transient thermoelastic conditions. Optimal design of a brake system to suit the heat transfer, weight and packing requirements is an ongoing challenge. Substantial researches have been carried out and are underway, in order to address the diverse issues related to thermal, mechanical and structural performances of automobile disc brakes. With the extensive application of numerical tools and techniques, the analyses involved became easier and effective. The present article provides an exhaustive review of the numerical and experimental studies reported so far, on the analysis and design of solid and ventilated disc brakes. The directions for future works are also described. The review reveals that, there is enough scope for extended research for realizing optimal design of disc brake system by truly emulating all the relevant practical situations.

Inline temperature compensation for dimensional metrology of polymer parts in a production environment based on 3D thermomechanical analysis

In the present work a new method for thermal compensation in dimensional metrology of polymer parts in a production environment based on 3D thermomechanical simulations is developed. A fixture for measuring the length dimension of a classical polymer part is placed in a production environment and equipped with sensors in terms of thermocouples for temperature measurements of the part and the fixture and a contact probe for measuring the dimension. A 3D thermomechanical model is developed in ABAQUS, emulating the thermoelastic conditions of the polymer part when placed in the fixture. Knowledge from classical heat transfer and elasticity theory is then applied to derive a more generic, yet simple expression for the compensation from the transient 3D temperature and displacement fields, based on dimensionless values, which makes applicable for a wide range of initial and surrounding conditions found in a production environment. The developed expression is then used for length compensation on 24 samples measured inline ten minutes after production. The results reveals a significant improvement in capturing the transient behavior of the part with a reduced error from 13 μm to 3 μm, applying the developed formula instead of using more classical 1D standard thermal compensation.

Optimization of Pressure Vessel Under Thermo-Elastic Condition

In this work, a pressure vessel under thermo-elastic condition is modeled which is useful for industries like refineries, power plant etc. The combined effect of internal pressure and steady-state temperature gradient is considered. A pressure vessel problem is formulated to minimize its total cost subjected to the constraints that can ensure safe design. The problem is solved using elitist Genetic Algorithm (GA). Further, simulations on stress against thickness are carried out, which reveal that the maximum shear stress gets reduced up to a certain thickness. After that, it starts increasing due to an increase in the compressive hoop/circumferential stress under thermo-elastic condition. The bi-objective optimization problem is then formulated by minimizing the total cost and the maximum shear stress simultaneously. The bi-objective problem is solved using elitist non-dominated sorting genetic algorithm. The cost effective to the safe trade-off solutions are generated. These approximate Pareto-optimal solutions are evolved in two clusters in which the solution from one of the clusters is more preferable for practical and feasible pressure vessel design. The post-optimization analysis of results suggests that the bi-objective optimization study offers more valuable insight of the problem than the single-objective optimization.

Second Order Two-Scale Method for Composite Plate with 3-D Periodic Configuration under Condition of Coupled Thermoelasticity

In this paper, we give a second-order two-scale (SOTS) computational method for composite plate with 3-D periodic configuration under condition of coupled thermoelasticity by means of construction way. Based on the Reissner-Mindlin deformation pattern and integral projection operator of temperature, the homogenization solution is obtained. The SOTS's approximate solution is constructed by the cell functions and the homogenization solution. A set of numerical results are demonstrated for predicting the effective parameters, the displacement and temperature of composite plate. It shows that SOTS's method can capture the 3-D local behaviors caused by 3-D micro-structures well.

Effect of a TiC Coating on the Stress-Strain State of a Plate of a High-Density Nitride Ceramic Under Nonsteady Thermoelastic Conditions

An original method is presented to obtain relations which describe how the thickness and thermal conductivity of a TiC coating are related to the temperatures, displacements, and stresses in a nitride ceramic plate under nonsteady thermoelastic conditions. It is shown that the stress-strain state of parts made of high-density ceramics can be controlled under such conditions by the application of coatings.

Second-Order Two-Scale Analysis Method for the Quasi-Periodic Structure of Composite Materials under Condition of Coupled Thermo-Elasticity

The second-order two-scale asymptotic expansions of the increment of temperature and the displacement for the quasi-periodic structure of composite materials under coupled thermo-elasticity condition are derived formally in this paper. The characteristic of the asymptotic model is the coupling between macroscopic scale and microscopic scale. Numerical examples including different coefficients are presented illustrating the efficiency and stability of the computational strategy. They show that the expansions to the second terms are necessary to obtain the thermal and mechanical behavior precisely, and the local and global oscillation of the increment of temperature and displacement are dependent on the microscopic and macroscopic part of the coefficients respectively.

Multi-scale FE computation for the structures of composite materials with small periodic configuration under condition of coupled thermoelasticity

In this paper, the multi-scale computational method for a structure of composite materials with a small periodic configuration under the coupled thermoelasticity condition is presented. The two-scale asymptotic (TSA) expression of the displacement and the increment of temperature for composite materials with a small periodic configuration under the condition of thermoelasticity are briefly shown at first, then the multi-scale finite element algorithms based on TSA are discussed. Finally the numerical results evaluated by the multi-scale computational method are shown. It demonstrates that the basic configuration and the increment of temperature strongly influence the local strains and local stresses inside a basic cell.

Multi-scale analysis for the structure of composite materials with small periodic configuration under condition of coupled thermoelasticity

In this paper, the multi-scale computational method for a structure of composite materials with a small periodic configuration under the coupled thermoelasticity condition is presented.The two-scale asymptotic (TSA) expression of the displacement and the increment of temperature for composite materials with a small periodic configuration under the condition of thermoelasticity are briefly shown at first, then the multi-scale finite element algorithms based on TSA are discussed. Finally the numerical results evaluated by the multi-scale computational method are shown. It demonstrates that the basic configuration and the increment of temperature strongly influence the local strains and local stresses inside a basic cell.

Analysis of spurious bulk waves in ball surface wave device

We analyzed the acoustic waves propagating in a sphere to establish a useful guideline for the design of NDE apparatus and ball surface acoustic wave (SAW) device exploiting the diffraction-free propagation of SAW on a sphere. First, we calculated the laser-generated acoustic displacements both under ablation condition and under thermoelastic condition and verified experimentally the validity of the calculation. Next, the acoustic waves excited by out-of-plane stress and those excited by in-plane stress were compared. The results showed that when the out-of-plane stress was applied, the relative amplitudes of the bulk waves to that of the SAW were larger and the number of bulk waves was larger than that when the in-plane stress was applied, while the SAW had similar waveforms in each case. The ratio of the relative amplitude of the bulk waves for the out-of-plane stress and the in-plane stress was 3.1:1 at φ 1=90° and 1.67:1 at φ 1=0°. The large amplitude for the out-of-plane stress can be explained by wide directivities of bulk waves. Consequently, we found that it is necessary for ball SAW device to select a piezoelectric material and form of interdigital transducer so that the in-plane stress becomes dominant.

THERMOELASTIC PROBLEM OF UNIFORM HEAT FLOW DISTURBED BY A FLAT TOROIDAL CRACK IN A TRANSVERSELY ISOTROPIC MEDIUM

The thermoelastic problem of uniform heat flow disturbed by a flat toroidal crack in a transversely isotropic medium is investigated using the method of Hankel transforms. The three-part mixed thermoelastic boundary conditions are satisfied using the tech niques of triple integral equations and multiplying factors. The stress intensity factors at the inner and outer crack tips are obtained in exact expressions as the products of a dimensional quantity and nondimensional functions. The fracture transition of a flat toroidal crack to a penny-shaped crack and to a two-dimensional line crack is studied at different values of the ratio of the inner crack radius to the outer crack radius.

Collinear cracks in a layered half-plane with a graded nonhomogeneous interfacial zone – Part I: Mechanical response

The problem of collinear cracks embedded in a layered half-plane is investigated. The medium consists of a surface layer and a semi-infinite substrate bonded through an interfacial zone with graded properties. The interfacial zone is treated as a nonhomogeneous layer and its elastic modulus is assumed to vary continuously in thickness direction. Three collinear cracks of different length exist, one in each one of the constituent materials perpendicular to the nominal interfaces. A system of singular integral equations applicable under both the mechanical and transient thermal loading conditions is derived. Part I of the paper addresses the details that lead to the derivation of the integral equations and the cracking behavior in the layered medium subjected to mechanical loading. As a result, the values of stress intensity factors are presented as functions of geometric and material parameters of the problem. In Part II, under the uncoupled, quasi-static thermoelastic condition, the response of collinear cracks to thermal shock loading is considered.

温度変化を受ける異種接合材のＪ積分値におよぼす中間層の影響

In this paper, the J-integral for an interfacial crack by thermal stress that developed during the cooling of the dissimilar material joint is studied. The thermoelastic analysis of J-integral for the bonded joint with an insert layer is performed using the finite element method. The effect of insert layer on the J-integral under the thermoelastic condition is discussed. It is found that the J-integral have three types of variation with an increase of insert layer thickness. The variations of J-integral with an increase of insert layer thickness are dominated by the nondimensional parameter (αC-αB)/(αA-αB) that expressed the relation in magnitude of coefficients of linear expansion and the ratio of Young's modulus (EA/EC). As a result, it is possible to predict the variation of J-integral with an increase of insert layer thickness by using these dominant parameters.

Generating acoustic waves by laser: theoretical and experimental study of the emission source

A laser pulse incident on a material may generate acoustic waves by means of two different phenomena: by thermal expansion at low incident power density (thermoelastic effect); and by vaporizing surface material at high incident power density (ablation effect). A synthesis of various theoretical models representing the acoustic displacements generated by a point laser impact is given, and then validated by interferometer measurements of ultrasonic displacements generated both under ablation conditions and under thermoelastic conditions.

Crystallography and morphology studies of Fe-Pt martensites: Lenticular to thin plate transition and thin plate morphologies

Ordering of austenitic Fe-Pt alloys near the composition Fe 3Pt results in a progressive change from a non-thermoelastic to a thermoelastic martensitic transformation. Along with this change in transformation kinetics the martensite morphology was investigated in detail, using Fe-23, 24 and 25 at.% Pt alloys. The martensite morphology was found to change from a lenticular to a thin plate type depending mainly upon the martensite formation temperature, at early stages of the transition from non-thermoelastic to thermoelastic behavior. Thin plate martensite exhibits a wide range of thermal hysteresis (from 150 to 20°C) and only this morphology exhibits thermoelastic transformation. Thin plate martensite was examined as to crystallographic aspects, and the observed martensite morphologies are explained in terms of a combination of fundamental pairs of variants. As the transformation approaches the thermoelastic condition, the co-operative nucleation of the four variants in a plate group increases and the transformed region exhibits a well organized pattern.

The thermoelastic condition of a body with a heat-liberating inclusion

The thermoelastic condition of a body with a heat-liberating inclusion