Induced Stress Distribution Research Articles

Noninvasive in vivo determination of residual strains and stresses.

Vascular growth and remodeling during embryonic development are associated with blood flow and pressure induced stress distribution, in which residual strains and stresses play a central role. Residual strains are typically measured by performing in vitro tests on the excised vascular tissue. In this paper, we investigated the possibility of estimating residual strains and stresses using physiological pressure-radius data obtained through in vivo noninvasive measurement techniques, such as optical coherence tomography or ultrasound modalities. This analytical approach first tested with in vitro results using experimental data sets for three different arteries such as rabbit carotid artery, rabbit thoracic artery, and human carotid artery based on Fung's pseudostrain energy function and Delfino's exponential strain energy function (SEF). We also examined residual strains and stresses in the human swine iliac artery using the in vivo experimental ultrasound data sets corresponding to the systolic-to-diastolic region only. This allowed computation of the in vivo residual stress information for loading and unloading states separately. Residual strain parameters as well as the material parameters were successfully computed with high accuracy, where the relative errors are introduced in the range of 0-7.5%. Corresponding residual stress distributions demonstrated global errors all in acceptable ranges. A slight discrepancy was observed in the computed reduced axial force. Results of computations performed based on in vivo experimental data obtained from loading and unloading states of the artery exhibited alterations in material properties and residual strain parameters as well. Emerging noninvasive measurement techniques combined with the present analytical approach can be used to estimate residual strains and stresses in vascular tissues as a precursor for growth estimates. This approach is also validated with a finite element model of a general two-layered artery, where the material remodeling states and residual strain generation are investigated.

Effect of core ceramic grinding on fracture behaviour of bilayered lithium disilicate glass–ceramic under two loading schemes

ObjectivesThe purpose of this in vitro study was to evaluate the effect of core ceramic grinding on the fracture behaviour of bilayered lithium disilicate glass–ceramic (LDG) under two loading schemes. MethodsInterfacial surfaces of sandblasted LDG disks (A) were ground with 220 (B), 500 (C) and 1200 (D) grit silicon carbide (SiC) sandpapers, respectively. Surface roughness and topographic analysis were performed using a profilometer and a scanning electron microscopy (SEM), and then underwent retesting after veneer firing. Biaxial fracture strength (σf) and Weibull modulus (m) were calculated either with core in tension (subgroup t) or in compression (subgroup c). Failure modes were observed by SEM, and loading induced stress distribution was simulated and analyzed by finite element analysis. Statistical data analysis was performed using Kruskal–Wallis, one-way ANOVA, and paired test at a significance level of 0.05. ResultsAs the grits size of SiC increased, LDG surface roughness decreased from group A to D (p<0.001), which remained unchanged after veneer firing. No difference in σf (p=0.41 for subgroups At–Dt; p=0.11 for subgroups Ac–Dc), m values as well as failure modes was found among four subgroups for both loading schemes. Specimens in subgroup t showed higher σf (p<0.001) and m values than subgroup c. Stress distribution between loading schemes did not differ from each other. Cracks, as the dominant failure mode initiated from bottom tensile surface. No sign of interfacial cracking or delamination was observed for all groups. ConclusionsTechnician grinding changed surface topography of LDG ceramic material, but was not detrimental to the bilayered system strength after veneer application. LDG bilayered system was more sensitive to fracture when loaded with veneer porcelain in tension. Clinical significanceWithin the limitations of the simulated grinding applied, it is concluded that veneer porcelain can be applied directly after technician grinding of LDG ceramic as it has no detrimental effect on the strength of bilayered structures. The connector areas of LDG fixed dental prosthesis are more sensitive to fracture compared with single crowns, and should be fabricated with more caution.

Molecular dynamics simulation of heat conduction in Si nano-films induced by ultrafast laser heating

Molecular dynamics simulations are carried out to study the thermal and mechanical phenomena of heat conduction induced by ultrafast laser heating of nanoscale Si films. A distribution of internal heat source obeying Beer–Lambda law is applied to model the laser energy deposition in the film and to calculate the induced temperature and stress distributions. Thermal waves are observed from the local temperature temporal variations and spatial distributions. The developments of averaged static pressure and local displacement in the film show a consistent periodicity. The time evolutions of both the local pressure and net heat flux fluctuate strongly, but show similar trends between these two local physical quantities, demonstrating a close relationship between the stress and the net heat flow.

Estimation of the iron loss in deep-sea permanent magnet motors considering seawater compressive stress.

Deep-sea permanent magnet motor equipped with fluid compensated pressure-tolerant system is compressed by the high pressure fluid both outside and inside. The induced stress distribution in stator core is significantly different from that in land type motor. Its effect on the magnetic properties of stator core is important for deep-sea motor designers but seldom reported. In this paper, the stress distribution in stator core, regarding the seawater compressive stress, is calculated by 2D finite element method (FEM). The effect of compressive stress on magnetic properties of electrical steel sheet, that is, permeability, BH curves, and BW curves, is also measured. Then, based on the measured magnetic properties and calculated stress distribution, the stator iron loss is estimated by stress-electromagnetics-coupling FEM. At last the estimation is verified by experiment. Both the calculated and measured results show that stator iron loss increases obviously with the seawater compressive stress.

Geotechnical investigations and preliminary support design for the Geçilmez tunnel: A case study along the Black Sea coastal highway, Giresun, northern Turkey

This study encompasses geotechnical investigations, stability assessments and design of the preliminary support systems for the Geçilmez tunnel which is constructed in Giresun for the improvement of the highway along the Black Sea coast. During the study, a detailed geological map of the study area was prepared and the geotechnical characteristics of the rock masses were determined. The rock mass classification of the tunnel grounds was performed by utilizing the RMR method, Q system, NATM and the Geological Strength Index (GSI) classification which was followed by performing a geotechnical investigation along the tunnel grounds in order to obtain the geotechnical parameters for the stability analyses of the portals and of the tunnel. Lugeon (water pressure) tests were performed in order to determine the permeability of the rock mass along the tunnel. The appropriate geotechnical parameters were utilized in order to perform rock slope stability kinematic and limit equilibrium analyses at the portals of the tunnel. Empirical preliminary tunnel support systems according to the RMR method, Q-system and NATM were determined. The structurally controlled instabilities within the tunnel sections were identified and the required preliminary tunnel support systems were determined to overcome these instabilities. Regarding the structurally controlled rock failures along the probable weak zones and lineaments (i.e., inactive probable faults or shear zones) during tunneling, wedge stability analysis was utilized to determine the potential wedge failures that could possibly occur during tunneling and to apply the necessary support systems for stabilizing any wedge failure in the tunnel. The induced stress distributions and deformations in the rock mass surrounding the tunnel grounds was investigated and the interaction of the support systems with the rock mass was analyzed by using numerical (finite element) modeling. In the finite element analyses it was assumed that the rock mass behaved as a fractured rock mass since the tunnel grounds were moderate to highly jointed. The objective of the numerical modeling was to check the validity of the empirical preliminary tunnel support requirements and also to compare the results with those obtained through assuming structurally controlled failures during tunneling. The performance of the preliminary tunnel support was also validated on the basis of thrust–moment interaction analyses. The results of the structurally controlled failure analyses, numerical analyses and thrust–moment analyses were compared in an attempt to determine the preliminary tunnel support systems to stabilize the Geçilmez tunnel.

The Effect of Dental Implant Design on Bone Induced Stress Distribution and Implant Displacement

implants have a great role in changing treatment concepts to edentulous ridges. This paper presents a finite element analysis evaluation of the effect of implant design on the stress distribution induced in bone surrounding the implant and on the micro displacement of the implant of a full arch screw retained cantilevered fixed mandibular restoration, in case of immediate loading. Twelve models were simulated, all composed of four identical interforaminal dental implants and a cantilever overdenture. Two design parameters (the implant diameter and taper) were tested while keeping all other parameters fixed. The simulated 12 implants have 3.2, 3.7, 4.7 and 6 mm diameter with 0, 2 and 5 degrees tapering respectively. Vertical and oblique loads were applied on the right premolar and first molar under model restrain. Results revealed that, increasing implant diameter leads to decreased bone induced stresses and also decreased implant micro displacement and so leading to better initial stability. On the contrary, increasing implant tapering increased bone induced stresses and also increased implant micro displacement.

Nanograting Orientation Influence on Stress Induced by Femtosecond Laser in Fused Silica

Under certain conditions, femtosecond lasers can be used to introduce self-organized nanogratings in the bulk of fused silica. Here, we report that the nanogratings orientation influences the induced stress distribution around laser affected zones.

Adaptive Control of Aircraft Wing Flutter by Stress-Induced Stiffness Modification

Lightweight unoccupied air vehicles (UAVs) with wide wingspans are especially vulnerable to dynamic instability. Such instability can be contained by using mass and stiffness balancing and the shape and attitude of the aircraft in flight. Passive methods and pilot-operated devices such as dampers, ailerons, flaps, and other actuators, are currently used. Also, ongoing attempts exist to develop self-adaptive controls by using piezoelectric and other devices. The present work is concerned with controlling aerodynamic flutter by using stress-induced elements in selected structural components of the aircraft wing. A scheme has been developed to determine the “optimal” locations for such elements to be activated, in real time, to contain the dynamic instability or flutter condition. Various stress-induced stiffening schemes have been developed to modify the frequency response of aircraft wings by shifting the critical flutter speed to safe levels. Results and conclusions include the identification of the optimal location and type of the stress-induced elements and the magnitude and distribution of induced stress for best results with the least expense of energy during actuation.

A numerical study of the thermally induced stress distribution in a rotating hollow disc heated by a moving heat source acting on one of the side surfaces

This study presents the effects of a moving heat source (MHS) on a rotating hollow steel disc heated from its one side surface under stagnant ambient conditions. As the disc rotates around the z-axis with a constant angular speed Ω, the heat source moves along from one radial segment to the next radial segment in the radial direction on the processed surface at the end of each revolution of the disc. Three-dimensional (3D) numerical calculations are performed individually for a wide range of thermal conductivity λ of steel and for different Ωs. In order to obtain the thermal stress per heat flux intensity q0, it is assumed that the thermo-physical properties of the disc do not change with temperature. The maximum effective thermal stress ratio varies in the range of 22–134 °C depending on λ and Ω. While the MHS passes from one radial segment to the next radial segment, it causes an additional steeping of the effective thermal stress. However, when the values of λ and Ω are increased, the maximum effective thermal stress ratio can be reduced by a considerable amount.

Transient Temperature and Thermal Stress Distributions in a Hollow Disk Subjected to a Moving Uniform Heat Source

This study presents numerical analyses of transient temperature and thermally induced stress distributions in a stationary hollow steel disk partially heated by a moving uniform heat source from its outer surface under stagnant ambient conditions. The moving heat source applied on a certain angular segment of the processed surface rotates with a constant angular speed (ω). The peak levels of the temperature gradients and the thermal stress ratios at the heated segments do not rise very much after 2–3 cycles. When the value of ω is increased, the maximum effective thermal stress ratio can be decreased in a considerable amount.

Sensitivity of proximal femoral stiffness and areal bone mineral density to changes in bone geometry and density

Areal bone mineral density (aBMD) is the most common surrogate measurement for assessing the bone strength of the proximal femur associated with osteoporosis. Additional factors, however, contribute to the overall strength of the proximal femur, primarily the anatomical geometry. Finite element analysis (FEA) is an effective and widely used computer-based simulation technique for modelling mechanical loading of various engineering structures, providing predictions of displacement and induced stress distribution due to the applied load. FEA is therefore inherently dependent upon both density and anatomical geometry. FEA may be performed on both three-dimensional and two-dimensional models of the proximal femur derived from radiographic images, from which the mechanical stiffness may be predicted. It is examined whether the outcome measures of two-dimensional FEA, two-dimensional, finite element analysis of X-ray images (FEXI), and three-dimensional FEA computed stiffness values of the proximal femur are more sensitive than aBMD to changes in trabecular bone density and femur geometry. It is assumed that if an outcome measure follows known trends with changes in density and geometric parameters, then an increased sensitivity will be indicative of an improved prediction of bone strength. All three outcome measures increased non-linearly with trabecular bone density, increased linearly with cortical shell thickness and neck width, decreased linearly with neck length, and were relatively insensitive to neck-shaft angle. For femoral head radius, aBMD was relatively insensitive, with two-dimensional FEXI and three-dimensional FEA demonstrating a non-linear increase and decrease in sensitivity respectively. For neck anteversion, aBMD decreased non-linearly, whereas both two-dimensional FEXI and three-dimensional FEA demonstrated a parabolic-type relationship, with the maximum stiffness being achieved at an angle of approximately 15 degrees. Multi-parameter analysis showed that all three outcome measures demonstrated their highest sensitivity to a change in cortical thickness. When changes in all input parameters were considered simultaneously, three and two-dimensional FEA had statistically equal sensitivities (0.41 +/- 0.20 and 0.42 +/- 0.16 respectively, p = ns) that were significantly higher than the sensitivity of aBMD (0.24 +/- 0.07; p = 0.014 and 0.002 for three-dimensional and two-dimensional FEA respectively). This simulation study suggests that since mechanical integrity and FEA are inherently dependent on anatomical geometry, FEXI stiffness, being derived from conventional two-dimensional radiographic images, may provide an improvement in the prediction of bone strength of the proximal femur than currently provided by aBMD.

Thermomechanical Properties of Functionally Graded Al-SiC&lt;sub&gt;p&lt;/sub&gt; Composites

A theoretical model is applied to the analysis of thermomechanical properties of Al-SiCp FGMs in this study. Functionally graded Al-SiCp composites (Al-SiCp FGMs) consisted with 10 layers gradually changing volume fractions of Al and SiCp were fabricated using the pressureless infiltration technique. Al-SiCp FGMs plates of total thickness of 3mm, 5mm and 7mm with fairly uniform distribution and compositional gradient of SiCp reinforcement in the Al matrix throughout the thickness was successfully fabricated. The curvature of Al-SiCp FGM plates was measured to check the internal stress distribution predicted via a theoretical model for the analysis of thermomechanical deformation. The evolution of curvature and also internal stresses in response to temperature variations could be predicted for the different combinations of geometric thickness of FGM plates. Theoretical prediction of thermally induced stress distribution makes it possible to design FGM structures without any critical failure during the usage of them.

05/01319 Numerical solutions of transient conjugate heat transfer and thermally induced stress distribution in a heated and rotating hollow disk

05/01319 Numerical solutions of transient conjugate heat transfer and thermally induced stress distribution in a heated and rotating hollow disk

Transient temperature and thermally induced stress distributions in a partly-circumferentially heated cylindrical workpiece

This paper presents the numerical solutions of the transient temperature and thermally induced stress distributions in a partly-circumferentially heated cylindrical hollow workpiece (steel) with conjugate heat transfer. Outer surface of the workpiece is heated partly-circumferentially heat flux as its remainder outer surface is circumferentially cooled with fluid (water). Three phenomena have been considered as; (1) conduction inside the cylinder, (2) convection from the cylinder surface to the surrounding fluid, and (3) thermal stress produced by high temperature gradient inside the cylinder. The governing flow and energy equations have been solved numerically by using a control volume approach. The PHOENICS 3.2 and HEATING7 computer codes have been used for the numerical evaluation. The transient calculations have been performed individually for four fluid inlet velocities, ui = 0.005, 0.01, 0.015 and 0.020 m/s, until the system attains steady-state. The results of this study clearly demonstrate that the temperature contours in the low inlet velocity cases are more near to a symmetric case with respect to the y = 0 plane than that in the high inlet velocity cases, and the increment of the inlet velocity exponentially reduces the temperatures and thermally induced stresses in the workpiece. The effective thermal stress differences occurring in the workpiece can be significantly reduced by the high fluid inlet velocity.

Numerical solutions of transient temperature and thermally induced stress distributions in a solid disk heated with radially periodic expanding and contracting ring heat flux

Thermal stresses are taken into consideration as important phenomena in many manufacturing processes and design applications. Moreover, moving heat source is frequently encountered in these processes. The aim of this study is to analyze the numerical solutions of transient temperature and thermally induced stress distributions in a solid steel disk heated with radially periodic expanding and contracting ring heat flux under stagnant ambient conditions. It was assumed that the ring heat flux per unit area at the each ring surface was uniform. The applied heat transfer rate, Q, regularly increases from 3.14 to 311 W and then decreases to 3.14 W in one period depending on the area of heated ring. The FLUENT 5.3 program was chosen as computer code to calculate these numerical solutions. Furthermore, a computer program, applying the SIMPSON integration method to the obtained temperature distributions from the heat transfer calculations, has been developed to calculate numerically the governing thermal stress distributions. The calculations were performed individually for a wide range of thermal conductivity, from 20 to 60 W/m K stepped by 5 W/m K and in addition 43 W/m K, and for the various ring heat flux expansion and contraction speeds, from 0.0005 to 0.001 m/s stepped by 0.0001 m/s, under transient conditions. The temperature and thermal stress distributions were obtained as per the moving ring heat flux per unit area, q 0. Due to the fact that the maximum temperatures distribution profiles peak at the first and last rings while they increase linearly with the process time, the maximum thermal stress ratio profiles also vary quasi-periodically by peaking at that rings. Furthermore, the thermal stress ratio profiles at the processed surface peak at the heated ring except the first ring and they are repeated with a time interval of one period by almost not changing the peaked shapes of themselves. These obtained results would be useful for similar process using the steels considered in this study.

Numerical solutions of transient conjugate heat transfer and thermally induced stress distribution in a heated and rotating hollow disk

Numerical solutions of transient conjugate heat transfer and thermally induced stress distribution in a heated and rotating hollow disk

Numerical solutions of transient conjugate heat transfer and thermally induced stress distribution in a heated and rotating hollow disk

Abstract Thermally induced stresses are taken into consideration as important phenomena in many manufacturing processes and design applications. Stress analysis is subsequently performed using the temperatures derived in the thermal analysis. The aim of this study is to calculate the transient temperature and thermally induced stress distributions in a rotating hollow disk, which is subjected to a thermal process by keeping its temperature within a certain desired interval for a certain time. The disk considered for this purpose was uniformly heated from the inner and bottom surfaces in cases A and B, respectively, and cooled from the top and outer surfaces with water. The heat flux applied on the surface was regularly increased and decreased depending on the maximum temperature of the disk during the thermal process to keep the maximum temperature of the disk within a certain desired interval (the temperature controlled heating case). In this heat flux regulating process, values of the heat transfer rate, Q , were selected as 1257 and 125.7 W for the high and low heat flux cases, respectively. The calculations were performed individually for various coolant velocities, U c =0.1,0.2,…,0.5 m/s under transient conditions. In the temperature controlled heating case, the maximum temperature and thermal stress profiles continue as periodic curves with logarithmically increasing periods in case A and a constant period in case B after the maximum temperature value reaches the desired upper temperature limit (100 °C). In the cases of U c =0.2–0.5 m/s of case B, since the maximum temperature levels do not exceed the desired upper temperature limit, the maximum temperature and thermal stress profiles increase logarithmically until the system reaches steady state. The effective stress ratio profiles at the bottom surface are higher with respect to those at other planes in the axial direction, and their maximum values vary in the range of 0.044–0.22 as parallel to the relevant temperature profiles. The results of this study clearly demonstrate the numerical solutions of transient temperature and thermally induced stress distributions in the considered disk.

Spherical cavity expansion in densifying material

When subjected to sufficiently large compressive stresses, amorphous silica glass densifies permanently. Such densification is facilitated by shear stresses. It also exhibits some unique features upon grinding, which are associated with the plastic behavior of amorphous silica under constrained compression. To describe the effect of densification, a constitutive law proposed by Lambropoulos et al. [J. Am. Ceram. Soc. 79, 1441 (1996)] is used to model plastic deformation of silica. A densification parameter is introduced as a material parameter. Analytic solution of cavity expansion is presented here for this constitutive law. Both associated and nonassociated flow theories are studied. The range of values of the densification parameter for amorphous silica is estimated. For amorphous silica, the cavity expansion model shows that, based on the induced stress distribution, densification contributes to lower removal rate and less subsurface damage.

Coupling length scales for multiscale atomistics-continuum simulations: atomistically induced stress distributions in Si/Si3N4 nanopixels.

A hybrid molecular-dynamics (MD) and finite-element simulation approach is used to study stress distributions in silicon/silicon-nitride nanopixels. The hybrid approach provides atomistic description near the interface and continuum description deep into the substrate, increasing the accessible length scales and greatly reducing the computational cost. The results of the hybrid simulation are in good agreement with full multimillion-atom MD simulations: atomic structures at the lattice-mismatched interface between amorphous silicon nitride and silicon induce inhomogeneous stress patterns in the substrate that cannot be reproduced by a continuum approach alone.

Flow induced stress distribution on wall of blast furnace hearth

The flow induced shear stress on the wall of a blast furnace hearth has been computed by solving the Navier–Stokes and Darcy flow equations in the hearth numerically. The Navier–Stokes equations are utilised to compute the flow field in the coke free zone while the Darcy flow equations are utilised for the flow of liquid metal in the coke packed porous zone, known as the deadman. The shape of the deadman was taken to be hemispherical and it was simulated to be porous in nature. The taphole was placed through a block of refractory material through which the metal was allowed to flow out of the hearth. From the resulting flow field the shear stresses on the side wall of the hearth were computed as a function of the length and size of the taphole when the hearth was filled with liquid metal. It has been found that the peak stress value at the bottom plane, midplane (halfway between the bottom and the taphole exit plane), and at the plane of the taphole reduces significantly compared with the case of having no taphole block at all. However, the effect of the size of the taphole on the wall shear stress was not found to be very significant. It was also found that the peak stress decreases with an increase in the taphole length and the location of the peak stress shifts slightly in the increasing direction of θ. Such an arrangement of placement of the block does not produce any more peak stress anywhere in the azimuthal direction at a particular plane; rather, it helps to smooth out the peaks in the stresses arising due to fluid flow. The reasons for mechanical erosion inside the hearth are complicated. However, flow induced shear stresses play a very important role in initiating and aggravating the amount of erosion along with other factors. This has provided the main motivation to compute the flow induced shear stress on the inside wall of the hearth and study the effect of various parameters on it in the present work.