Trivariant Lagrange Factor Polynomial for Discrete Rayleigh Distributed Reliability Analysis of Aeroengine Combustion Chamber Cylinder

2013 ◽  
Vol 10 (1) ◽  
Author(s):  
Chun Nam Wong ◽  
Yang Lu
Keyword(s):  
Combustion Chamber ◽  
Thermal Conditions ◽  
Economic Factors ◽  
Structural Variants ◽  
Temperature Dependent ◽  
Application Range ◽  
Linear Polynomial ◽  
As Stress ◽  
Stress Dependent ◽  
Dependent Probability

In most of the existing stress-strength interference (SSI) models, stress and strength are assumed to be independent structural variants. However, under severe thermal conditions, such as in aeroengine combustion chamber, this assumption may not hold. One structural variant, such as strength, may become unilateral dependent on another variant, such as stress or temperature. In addition, to evaluate the discrete reliability of structures using unilateral dependent structural variants, discrete SSI models were developed using not just linear polynomial or line segments, but higher order polynomials. These models are based on the trivariant Lagrange factor polynomial approach. Normal distributed temperature dependent stress and Rayleigh distributed thermal stress dependent strength are represented by discrete structural variants that possess unilateral dependent probability mean functions. Based on their dependence formulations, the trivariant Lagrange factor polynomial of the discrete SSI model was generated. Applicability of this method was validated by a specific aeroengine combustion chamber cylinder using different molding alloys. Meanwhile the application range of some existing SSI models is extended for interval shifted data. Comparing machinability, reliability, and economic factors, 1Cr11MoV was the most suitable alloy in the design.

SPH Analysis for Transient Thermal Stress of FGMs with Temperature-Dependent Properties

2015 ◽  
Vol 1096 ◽  
pp. 297-301
Author(s):  
Gui Ming Rong ◽  
Hiroyuki Kisu
Keyword(s):  
Thermal Stress ◽  
Thermal Conditions ◽  
Functionally Graded ◽  
Temperature Dependent ◽  
Graded Materials ◽  
Initial Stage ◽  
Particle Hydrodynamics ◽  
Smoothed Particle ◽  
Temperature Dependent Properties ◽  
Transient Thermal

A formulation using the deviatoric stress and the continuity equation is extended to the analysis of the dynamic response of functionally graded materials (FGMs) subjected to a thermal shock by smoothed particle hydrodynamics (SPH), in which temperature dependent properties of materials are considered. Several dynamic thermal stress problems are analyzed to investigate the fluctuation of thermal stress at the initial stage under three types of thermal conditions, with the addition of two kinds of mechanical boundary conditions.

Modelling Semi-Solid Behaviour and Brittle Temperature Range

2019 ◽  
Vol 285 ◽  
pp. 361-366 ◽  
Author(s):  
Khalil Traidi ◽  
Véronique Favier ◽  
Philippe Lestriez ◽  
Karl Debray ◽  
Laurent Langlois ◽  
...  
Keyword(s):  
Solid State ◽  
Material Properties ◽  
Solid Phase ◽  
Thermal Conditions ◽  
Tensile Tests ◽  
Internal Variable ◽  
Temperature Dependent ◽  
Brittle Transition ◽  
Semi Solid ◽  
First Time

In this paper, a new elastic viscoplastic micromechanical modelling is proposed to represent the semi-solid behaviour and predict the ductile-brittle transition of the C38LTT near the solidus. It is based on a viscoplastic modelling previously presented in [1]. The originality of the new model comes from three main enhancements: the transition between the solid state and the semi-solid state was included meaning that the material properties were taken temperature-dependent, the elastic properties was taken into account similarly as [2] and the evolution of the internal variable describing the degree of agglomeration of the solid phase was enhanced. The model was implemented in the commercial software FORGE©. Tensile tests representing the experimental thermal conditions and obtained using a GLEEBLE© machine were simulated. The comparison of the predicted and experimental results shows that, for the first time to our knowledge, the three steps of the load-displacement response and ductile-brittle transition were successfully described.

Evaluate the Importance of Shear Modulus in Dynamic FEM of Flexible Pavement Considering AC Cross-Anisotropy

2016 ◽  
Author(s):  
Mesbah U. Ahmed ◽  
Rafiqul A. Tarefder
Keyword(s):  
Shear Modulus ◽  
Resilient Modulus ◽  
Vertical Plane ◽  
Element Model ◽  
Tire Pressure ◽  
Stress Strain ◽  
Viscoelastic Parameters ◽  
Cross Anisotropy ◽  
As Stress ◽  
Stress Dependent

Goal of this study is to evaluate the effect of shear modulus variation on pavement responses, such as stress-strain, under dynamic load incorporating the AC cross-anisotropy. A dynamic Finite Element Model (FEM) of an instrumented asphalt pavement section on Interstate 40 (I-40) near Albuquerque, New Mexico, is developed in ABAQUS to determine stress-strain under truck tire pressure. Laboratory dynamic modulus tests were conducted on the AC cores to determine the temperature and frequency varying modulus values along both vertical and horizontal directions. The test outcomes are used to produce cross-anisotropic and viscoelastic parameters. Resilient modulus tests are conducted on granular aggregates from base and subbase layer to determine the nonlinear elastic and stress-dependent modulus values. These material parameters are integrated to the FEM through a FORTRAN subroutine via User Defined Material (UMAT) in the ABAQUS. The developed FEM is validated using the pavement deflections and stress-strain data under Falling Weight Deflectometer (FWD) test. The validated dynamic FEM is simulated under the non-uniform vertical tire contact stress. For the parametric study to investigate the effect of shear modulus variation on pavement responses, the validated FEM is simulated by varying the shear modulus in the AC layer. The results show that the variation in shear modulus along a vertical plane barely affects the tensile strain at the bottom of the AC layer and vertical compressive strains in both AC and unbound layers.

scholarly journals Leaf Senescence: The Chloroplast Connection Comes of Age

Plants ◽  
2019 ◽  
Vol 8 (11) ◽  
pp. 495 ◽  
Author(s):  
Martín L. Mayta ◽  
Mohammad-Reza Hajirezaei ◽  
Néstor Carrillo ◽  
Anabella F. Lodeyro
Keyword(s):  
Cell Death ◽  
Leaf Senescence ◽  
Developmental Process ◽  
Reproductive Organs ◽  
Common Thread ◽  
Dependent Cell ◽  
Redox Poise ◽  
Natural Leaf ◽  
As Stress ◽  
Stress Dependent

Leaf senescence is a developmental process critical for plant fitness, which involves genetically controlled cell death and ordered disassembly of macromolecules for reallocating nutrients to juvenile and reproductive organs. While natural leaf senescence is primarily associated with aging, it can also be induced by environmental and nutritional inputs including biotic and abiotic stresses, darkness, phytohormones and oxidants. Reactive oxygen species (ROS) are a common thread in stress-dependent cell death and also increase during leaf senescence. Involvement of chloroplast redox chemistry (including ROS propagation) in modulating cell death is well supported, with photosynthesis playing a crucial role in providing redox-based signals to this process. While chloroplast contribution to senescence received less attention, recent findings indicate that changes in the redox poise of these organelles strongly affect senescence timing and progress. In this review, the involvement of chloroplasts in leaf senescence execution is critically assessed in relation to available evidence and the role played by environmental and developmental cues such as stress and phytohormones. The collected results indicate that chloroplasts could cooperate with other redox sources (e.g., mitochondria) and signaling molecules to initiate the committed steps of leaf senescence for a best use of the recycled nutrients in plant reproduction.

Growth temperature-dependent expression of structural variants of Listeria monocytogenes lipoteichoic acid

Immunobiology ◽  
2011 ◽  
Vol 216 (1-2) ◽  
pp. 24-31 ◽  
Author(s):  
Oliver Dehus ◽  
Markus Pfitzenmaier ◽  
Gunthard Stuebs ◽  
Natalie Fischer ◽  
Wilhelm Schwaeble ◽  
...  
Keyword(s):  
Listeria Monocytogenes ◽  
Growth Temperature ◽  
Lipoteichoic Acid ◽  
Structural Variants ◽  
Temperature Dependent

A Note on the Normalized Approach to Simulating Moisture Diffusion in a Multimaterial System Under Transient Thermal Conditions Using ansys 14 and 14.5

2014 ◽  
Vol 136 (3) ◽  
Author(s):  
Dapeng Liu ◽  
Seungbae Park
Keyword(s):  
Material Property ◽  
Thermal Conditions ◽  
Moisture Diffusion ◽  
Electronic Components ◽  
Current Version ◽  
Temperature Dependent ◽  
Moisture Concentration ◽  
Hygroscopic Swelling ◽  
Packaging Industry ◽  
Transient Thermal

Moisture can have significant effects on the performance and reliability of electronic components. Accurately simulating moisture diffusion is important for designers and manufacturers to obtain a realistic reliability evaluation. Beginning with version 14, ansys is capable of simulating diffusion and related behaviors, such as hygroscopic swelling, with newly developed elements. However, a normalized approach is still required to deal with the discontinuity of concentrations at the material boundaries, and normalization of the moisture concentration in transient thermal conditions is tricky. Case studies have shown that normalizing the moisture concentration with respect to a time- or temperature-dependent material property will lead to erroneous results. This paper re-addresses the issues of performing diffusion simulations under transient thermal conditions and more general anisothermal conditions (temporally and spatially), and suggests an easy-to-use approach to cope with the limitations of the current version for users in the electronic packaging industry.

Stress Versus Temperature Dependence of Activation Energies for Creep

1992 ◽  
Vol 114 (1) ◽  
pp. 46-50 ◽  
Author(s):  
A. D. Freed ◽  
S. V. Raj ◽  
K. P. Walker
Keyword(s):  
Activation Energy ◽  
Free Energy ◽  
Gibbs Free Energy ◽  
Elevated Temperatures ◽  
Lattice Diffusion ◽  
Dislocation Climb ◽  
Temperature Dependent ◽  
Dislocation Glide ◽  
Controlling Mechanism ◽  
Stress Dependent

The activation energy for creep at low stresses and elevated temperatures is associated with lattice diffusion, where the rate controlling mechanism for deformation is dislocation climb. At higher stresses and intermediate temperatures, the rate controlling mechanism changes from dislocation climb to obstacle-controlled dislocation glide. Along with this change in deformation mechanism occurs a change in the activation energy. When the rate controlling mechanism for deformation is obstacle-controlled dislocation glide, it is shown that a temperature-dependent Gibbs free energy does better than a stress-dependent Gibbs free energy in correlating steady-state creep data for both copper and LiF-22mol percent CaF2 hypereutectic salt.

Creep Behavior of an Al2O3-Sic Composite

1988 ◽  
Vol 120 ◽  
Author(s):  
P. Lipetzky ◽  
S. R. Nutt ◽  
P. F. Becher
Keyword(s):  
Deformation Mechanisms ◽  
Alumina Powder ◽  
Creep Data ◽  
Volume Percent ◽  
Temperature Dependent ◽  
Creep Tests ◽  
Sic Whiskers ◽  
Alumina Composite ◽  
Shock Resistance ◽  
Stress Dependent

AbstractThe addition of SiC whiskers to Al2O3 causes significant improvement in mechanical properties, including fracture toughness, thermal shock resistance, and creep resistance. The creep response of a whisker-reinforced alumina composite has been measured using four-point flexural loading at temperatures of 1200 and 1300C. Composites were fabricated by hot-pressing a blend of alumina powder with 33 volume percent SiC whiskers. The creep data showed a stress-dependent stress exponent equal to 1 at low stress levels and ranging from 4–6 at higher stresses. The applied stress at which the transition occurred was temperature dependent and ranged from 50–125 MPa. Mechanisms of creep deformation were determined from TEM observations of specimens prepared from interrupted creep tests. Voids were observed at grain boundary-interface junctions in tensile regions and whiskers within the composite were sometimes oxidized where voids had formed. TEM observations from specific stages of steady state creep reached under different applied loads are presented, and the relative contributions of different deformation mechanisms are discussed.

scholarly journals The Stress-Dependent Dynamics of Saccharomyces cerevisiae tRNA and rRNA Modification Profiles

Genes ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 1344
Author(s):  
Yasemin Yoluç ◽  
Erik van de Logt ◽  
Stefanie Kellner-Kaiser
Keyword(s):  
Isotope Labeling ◽  
Model Organism ◽  
Rna Degradation ◽  
Rna Modification ◽  
Rna Modifications ◽  
Profile Changes ◽  
Stressed Cells ◽  
As Stress ◽  
Stress Dependent ◽  
Internal And External Factors

RNAs are key players in the cell, and to fulfil their functions, they are enzymatically modified. These modifications have been found to be dynamic and dependent on internal and external factors, such as stress. In this study we used nucleic acid isotope labeling coupled mass spectrometry (NAIL-MS) to address the question of which mechanisms allow the dynamic adaptation of RNA modifications during stress in the model organism S. cerevisiae. We found that both tRNA and rRNA transcription is stalled in yeast exposed to stressors such as H2O2, NaAsO2 or methyl methanesulfonate (MMS). From the absence of new transcripts, we concluded that most RNA modification profile changes observed to date are linked to changes happening on the pre-existing RNAs. We confirmed these changes, and we followed the fate of the pre-existing tRNAs and rRNAs during stress recovery. For MMS, we found previously described damage products in tRNA, and in addition, we found evidence for direct base methylation damage of 2′O-ribose methylated nucleosides in rRNA. While we found no evidence for increased RNA degradation after MMS exposure, we observed rapid loss of all methylation damages in all studied RNAs. With NAIL-MS we further established the modification speed in new tRNA and 18S and 25S rRNA from unstressed S. cerevisiae. During stress exposure, the placement of modifications was delayed overall. Only the tRNA modifications 1-methyladenosine and pseudouridine were incorporated as fast in stressed cells as in control cells. Similarly, 2′-O-methyladenosine in both 18S and 25S rRNA was unaffected by the stressor, but all other rRNA modifications were incorporated after a delay. In summary, we present mechanistic insights into stress-dependent RNA modification profiling in S. cerevisiae tRNA and rRNA.

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