Stress Relaxation Modelling

Modern gas turbine bolts experience severe operational conditions due to high temperatures and elevated axial stresses, generated by the tightening couple applied during the turbine assembly. In such conditions the relaxation of the initial stress due to viscous phenomena has to be taken into account in order to guarantee the proper operation of the turbine. Relaxation modelling can either be based on strain controlled relaxation tests or load controlled creep tests. Both solutions present difficulties: relaxation tests entail critical experimental issues, whereas creep tests may not be significant for the given strain controlled operational condition of a gas turbine bolt. Some of these problems will be described in the paper and solutions will be provided. The performances of several models for stress relaxation quantification will be compared, highlighting advantages and disadvantages of each approach. In particular, great emphasis will be given to those aspects which are relevant for bolt design or tightening load calculation. For instance, some important requirements are: firstly, the possibility to implement the given model easily in finite element calculations; secondly, the possibility to accurately calculate the relaxation in the second life of a serviced bolt after re-tightening; lastly, the possibility to reduce as much as possible the time required for the experimental tests. In order to evaluate the coefficients of the different models considered in the study, creep tests were performed at 450°C and 475°C with applied stresses producing a strain ε = 1% in a time range of 1000–10000h and stress relaxation tests were performed at the same temperatures with initial strain in the range of 0.2%. After some stress relaxation, the specimens were reloaded at the initial stress several times in order to simulate the aforesaid service conditions of bolts. In the paper it will be shown how a valid model, capable of predicting the stress relaxation with acceptable accuracy, can be fed either by creep or relaxation tests, provided that the experimental tests and the related data elaboration are conducted with the proper methodology. This scenario provides the engineer responsible for material model creation with a remarkable flexibility, essential to fulfill the requirements of modern GT design, in terms of accuracy, promptness of data collection and possibility of FEM implementation.

Different Techniques to Mitigate Partial Shading in Photovoltaic Panels

Energies ◽

10.3390/en14133863 ◽

2021 ◽

Vol 14 (13) ◽

pp. 3863

Author(s):

Tiago Alves ◽

João Paulo N. Torres ◽

Ricardo A. Marques Lameirinhas ◽

Carlos A. F. Fernandes

Keyword(s):

Cell Model ◽

Research Work ◽

Experimental Tests ◽

Operating Conditions ◽

Pv System ◽

Partial Shading ◽

System Architectures ◽

Pv Systems ◽

Pv Panel

The effect of partial shading in photovoltaic (PV) panels is one of the biggest problems regarding power losses in PV systems. When the irradiance pattern throughout a PV panel is inequal, some cells with the possibility of higher power production will produce less and start to deteriorate. The objective of this research work is to present, test and discuss different techniques to help mitigate partial shading in PV panels, observing and commenting the advantages and disadvantages for different PV technologies under different operating conditions. The motivation is to contribute with research, simulation, and experimental work. Several state-of-the-artsolutions to the problem will be presented: different topologies in the interconnection of the panels; different PV system architectures, and also introducing new solution hypotheses, such as different cell interconnections topologies. Alongside, benefits and limitations will be discussed. To obtain actual results, the simulation work was conducted by creating MATLAB/Simulink models for each different technique tested, all centered around the 1M5P PV cell model. The several techniques tested will also take into account different patterns and sizes of partial shading, different PV panel technologies, different values of source irradiation, and different PV array sizes. The results will be discussed and validated by experimental tests.

Numerical Evaluation of Structural Safety of Linear Actuator for Flap Control of Aircraft Based on Airworthiness Standard

Aerospace ◽

10.3390/aerospace8040104 ◽

2021 ◽

Vol 8 (4) ◽

pp. 104

Author(s):

Dong-Hyeop Kim ◽

Young-Cheol Kim ◽

Sang-Woo Kim

Keyword(s):

Numerical Analysis ◽

Analytical Method ◽

Safety Evaluation ◽

Experimental Tests ◽

Structural Safety ◽

Linear Actuator ◽

The Finite Element Method ◽

Margin Of Safety ◽

Verification Methodology ◽

Airworthiness standards of Korea recommend verifying structural safety by experimental tests and analytical methods, owing to the development of analysis technology. In this study, we propose a methodology to verify the structural safety of aircraft components based on airworthiness requirements using an analytical method. The structural safety and fatigue integrity of a linear actuator for flap control of aircraft was evaluated through numerical analysis. The static and fatigue analyses for the given loads obtained from the multibody dynamics analysis were performed using the finite element method. Subsequently, the margin of safety and vulnerable area were acquired and the feasibility of the structural safety evaluation using the analytical method was confirmed. The proposed numerical analysis method in this study can be adopted as an analytical verification methodology for the airworthiness standards of civilian aircraft in Korea.

Numerical Experiments in Using Voronoi Cell Finite Elements for Topology Optimization

Volume 5: 35th Design Automation Conference, Parts A and B ◽

10.1115/detc2009-87460 ◽

2009 ◽

Author(s):

James M. Gibert ◽

Georges M. Fadel

Keyword(s):

Topology Optimization ◽

Isotropic Material ◽

Numerical Experiments ◽

Voronoi Cell ◽

Material Model ◽

Topological Optimization ◽

Compliance Minimization ◽

Design Variables ◽

Standard Linear

This paper provides two separate methodologies for implementing the Voronoi Cell Finite Element Method (VCFEM) in topological optimization. Both exploit two characteristics of VCFEM. The first approach utilizes the property that a hole or inclusion can be placed in the element: the design variables for the topology optimization are sizes of the hole. In the second approach, we note that VCFEM may mesh the design domain as n sided polygons. We restrict our attention to hexagonal meshes of the domain while applying Solid Isotropic Material Penalization (SIMP) material model. Researchers have shown that hexagonal meshes are not subject to the checker boarding problem commonly associated with standard linear quad and triangle elements. We present several examples to illustrate the efficacy of the methods in compliance minimization as well as discuss the advantages and disadvantages of each method.

Effect of Cure State on Stress Relaxation in 3501-6 Epoxy Resin

Journal of Engineering Materials and Technology ◽

10.1115/1.2812254 ◽

1997 ◽

Vol 119 (3) ◽

pp. 262-265 ◽

Cited By ~ 7

Author(s):

S. R. White ◽

A. B. Hartman

Keyword(s):

Stress Relaxation ◽

Epoxy Resin ◽

Creep Compliance ◽

Numerical Technique ◽

Matrix Material ◽

Relaxation Modulus ◽

Master Curves ◽

Creep Tests ◽

Three Point Bending ◽

Direct Inversion

Little experimental work has been done to characterize how the viscoelastic properties of composite material matrix resins develop during cure. In this paper, the results of a series of creep tests carried out on 3501–6 epoxy resin, a common epoxy matrix material for graphite/epoxy composites, at several different cure states is reported. Beam specimens were isothermally cured at increasing cure temperatures to obtain a range of degrees of cure from 0.66 to 0.99. These specimens were then tested in three-point bending to obtain creep compliance over a wide temperature range. The master curves and shift functions for each degree of cure case were obtained by time-temperature superposition. A numerical technique and direct inversion were used to calculate the stress relaxation modulus master curves from the creep compliance master curves. Direct inversion was shown to be adequate for fully cured specimens, however it underpredicts the relaxation modulus and the transition for partially cured specimens. Correlations with experimental stress relaxation data from Kim and White (1996) showed that reasonably accurate results can be obtained by creep testing followed by numerical conversion using the Hopkins-Hamming method.

Thermal Decomposition of Vulcanized Structures of Deformed Vulcanizates Containing Various Accelerators

Rubber Chemistry and Technology ◽

10.5254/1.3539858 ◽

1953 ◽

Vol 26 (4) ◽

pp. 759-763 ◽

Cited By ~ 4

Author(s):

B. Dogadkin ◽

Z. Tarasova

Keyword(s):

Stress Relaxation ◽

Physical And Mechanical Properties ◽

Heat Stability ◽

Chemical Bonds ◽

Structural Elements ◽

Specific Chemical ◽

Vulcanized Rubber ◽

Different Temperatures ◽

Chemical Groups ◽

Abstract According to the hypotheses developed by the authors, vulcanized rubber is a system in which the molecular chains are united by local molecular and chemical bonds of varying intensity. The concentration, distribution, and strength of these bonds determine the principal physical and mechanical properties of the vulcanizates. Consequently the study of the structure of the vulcanizate is of primary practical value. The explanation of the nature of the bonds in a vulcanizate by chemical methods is very difficult, mainly because of the impossibility of distinguishing the specific chemical groups which enter into the composition of the different molecular chains from those bonds between the chains which are responsible for the development of spatial structures. From this view point, the thermo-mechanical method described below, which is based on the study of stress relaxation at different temperatures, is of great significance. As was shown by Dogadkin and Reznikovskii˘, the delayed stress relaxation in a vulcanizate at temperatures up to 70° C is caused by rupture of the local intermolecular bonds and the regrouping of the structural elements of the polymeric chains without destruction of the chemical bonds between them. Accordingly, after some time at these temperatures, a practically balanced stress is established, which depends on the number of the stronger bonds remaining. At temperatures above 70° C, rupture of the chemical bonds between the chains takes place; its speed increases with decrease of the energy activating the rupture of the given type of bond. Particularly in the case of sulfur vulcanizates, we can assume that the following types of bonds exist between the chains of the rubber: (1) —C—C—, which develop as a result of the polymerizationprocesses; (2) —C—S—C— monosulfide; (3) —C—S—S—C— disulfide, and (4) —C—Sn—C— polysulfide, formed as a result of the direct participation of the vulcanizing agent, sulfur, in the process of joining of the molecular chains. The energy of these chains can be estimated as 62.7 kcal, per mole for C—C, 54.5 kcal. per mole for C—S, and 27.5 kcal. per mole for the —S—S bond. Naturally, the heat stability of a vulcanizate will depend on which of the indicated types of bonds predominates.

The United States Navy “Standard Day” for Marine Gas Turbines

Volume 1: Aircraft Engine; Fans and Blowers; Marine; Honors and Awards ◽

10.1115/gt2017-64048 ◽

2017 ◽

Author(s):

John Hartranft ◽

Bruce Thompson ◽

Dan Groghan

Keyword(s):

United States ◽

Gas Turbine ◽

United States Navy ◽

Gas Turbines ◽

The United States ◽

Industrial Applications ◽

Jet Engines ◽

Jet Engine ◽

Power Capability

Following the successful development of aircraft jet engines during World War II (WWII), the United States Navy began exploring the advantages of gas turbine engines for ship and boat propulsion. Early development soon focused on aircraft derivative (aero derivative) gas turbines for use in the United States Navy (USN) Fleet rather than engines developed specifically for marine and industrial applications due to poor results from a few of the early marine and industrial developments. Some of the new commercial jet engine powered aircraft that had emerged at the time were the Boeing 707 and the Douglas DC-8. It was from these early aircraft engine successes (both commercial and military) that engine cores such as the JT4-FT4 and others became available for USN ship and boat programs. The task of adapting the jet engine to the marine environment turned out to be a substantial task because USN ships were operated in a completely different environment than that of aircraft which caused different forms of turbine corrosion than that seen in aircraft jet engines. Furthermore, shipboard engines were expected to perform tens of thousands of hours before overhaul compared with a few thousand hours mean time between overhaul usually experienced in aircraft applications. To address the concerns of shipboard applications, standards were created for marine gas turbine shipboard qualification and installation. One of those standards was the development of a USN Standard Day for gas turbines. This paper addresses the topic of a Navy Standard Day as it relates to the introduction of marine gas turbines into the United States Navy Fleet and why it differs from other rating approaches. Lastly, this paper will address examples of issues encountered with early requirements and whether current requirements for the Navy Standard Day should be changed. Concerning other rating approaches, the paper will also address the issue of using an International Organization for Standardization, that is, an International Standard Day. It is important to address an ISO STD DAY because many original equipment manufacturers and commercial operators prefer to rate their aero derivative gas turbines based on an ISO STD DAY with no losses. The argument is that the ISO approach fully utilizes the power capability of the engine. This paper will discuss the advantages and disadvantages of the ISO STD DAY approach and how the USN STD DAY approach has benefitted the USN. For the future, with the advance of engine controllers and electronics, utilizing some of the features of an ISO STD DAY approach may be possible while maintaining the advantages of the USN STD DAY.

Determination of the classification-based tactics for treating meniscus lesions in children

Russian Journal of Pediatric Surgery ◽

10.18821/1560-9510-2020-24-3-194-197 ◽

2020 ◽

Vol 24 (3) ◽

pp. 194-197

Author(s):

Daria D. Pavlova ◽

S. M. Sharkov ◽

M. A. Petrov ◽

E. M. Krainova

Keyword(s):

Modern Literature ◽

New Approaches ◽

Current Trends ◽

Meniscus Lesions ◽

New approaches to the treatment of meniscus lesions is currently a hot topic in traumatology and orthopedics. Meniscus resection and suture issues are widely discussed and studied in modern literature. Current trends in the care of meniscus pathologies are aimed to restore the structure of the damaged segment by stitching it using various techniques. A classification scale plays an important role in the treatment of any disease because it allows to uniformly describe the main criteria of pathology and to define a treatment tactics. The given review describes modern classifications of meniscus lesions with their advantages and disadvantages.

Volume 2: Coal, Biomass and Alternative Fuels; Combustion and Fuels; Oil and Gas Applications; Cycle Innovations ◽

Industrial Gas Turbine Uprates: Tips, Tricks and Traps

10.1115/97-gt-409 ◽

1997 ◽

Author(s):

T. L. Ragland

Keyword(s):

Gas Turbine ◽

Output Power ◽

Gas Turbines ◽

Customer Value ◽

Low Cost ◽

Pressure Ratio ◽

Original Design ◽

Industrial Gas Turbine ◽

Cycle Efficiency

After industrial gas turbines have been in production for some amount of time, there is often an opportunity to improve or “uprate” the engine’s output power or cycle efficiency or both. In most cases, the manufacturer would like to provide these uprates without compromising the proven reliability and durability of the product. Further, the manufacturer would like the development of this “Uprate” to be low cost, low risk and result in an improvement in “customer value” over that of the original design. This paper describes several options available for enhancing the performance of an existing industrial gas turbine engine and discusses the implications for each option. Advantages and disadvantages of each option are given along with considerations that should be taken into account in selecting one option over another. Specific options discussed include dimensional scaling, improving component efficiencies, increasing massflow, compressor zero staging, increasing firing temperature (thermal uprate), adding a recuperator, increasing cycle pressure ratio, and converting to a single shaft design. The implications on output power, cycle efficiency, off-design performance engine life or time between overhaul (TBO), engine cost, development time and cost, auxiliary requirements and product support issues are discussed. Several examples are provided where these options have been successfully implemented in industrial gas turbine engines.

The Method for Product Design Selection with Incomplete Linguistic Weight Information Based on Quality Function Deployment in a Fuzzy Environment

Mathematical Problems in Engineering ◽

10.1155/2013/943218 ◽

2013 ◽

Vol 2013 ◽

pp. 1-10 ◽

Cited By ~ 3

Author(s):

Ming Li

Keyword(s):

Product Design ◽

Quality Function Deployment ◽

Design Development ◽

Quality Function ◽

Fuzzy Environment ◽

Design Requirements ◽

Design Selection ◽

The Given ◽

The Relationship

The selection of a design for the given product is a critical problem in product design development. Focuses of the designers and customers on the design are not identical. In order to bridge the gap and provide a more relaxing way to select the design, a new method based on quality function deployment (QFD) is proposed. In such a method, customers are required to give their linguistic preferences on the design with respect to the customer requirements (CRs). In the rating of the weight of CRs, they are allowed to provide incomplete linguistic weight information and the objective optimization model is proposed to derive the exact linguistic weight information. Designers are required to rate the correlation between design requirements (DRs) and the relationship between the CRs and DRs to construct the house of quality. Opinions given by the customers are translated into the opinions with respect to the DRs based on the QFD. Afterwards, the priorities of the designs and design requirements are determined. The assessment results not only show the contribution of each design requirement to the customer satisfaction but also show the advantages and disadvantages of each design from the designers’ perspective clearly and directly. An example is provided to validate the applicability of the proposed method.

Change in Creep Deformation of PST Crystals with Different Stress Axes

MRS Proceedings ◽

10.1557/proc-980-0980-ii05-06 ◽

2006 ◽

Vol 980 ◽

Author(s):

Xiaohua Min ◽

Eisaku Sakurada ◽

Masao Takeyama ◽

Takashi Matsuo

Keyword(s):

Creep Rate ◽

Slip System ◽

Initial Stress ◽

Creep Deformation ◽

Strain Curve ◽

Stage I ◽

Stress Axis ◽

Creep Tests ◽

Transient Stage ◽

Stereographic Triangle

AbstractBased on our analysis of a lot of creep rate-strain curves of PST crystals with the different angles between the lamellar plate and the stress axis, designated as ø, it was confirmed that the creep rate and the creep deformation manner strongly depend on the ø. It was supposed that the predominant creep deformation using γ plate during the transient stage is derived by the fully suppression of the operation of another slip systems not parallel to γ plate through α2 plate. It was also confirmed that the initial stress axes of the PST crystals within the standard stereographic triangle move for the [001]-[111] line, and then turn their directions for [111] pole during the transient stage. This moving manner of the stress axis indicated that the first slip system of [101](111) continues to the area near the [001]-[111] line in the standard stereographic triangle, and then, the second slip system of [110](111) operates. By comparing this moving manner to the creep rate-strain curve, it is suggested that the first slip system of [101](111) operates during the Stage I where the light decrease in the creep rate remains, after that, the second slip system of [110](111) appears and leads to steep decrease in the creep rate. This stage was designated as the Stage II. According to this conception, it is supposed that the strain at the end of the Stage I is directly correlated with the angle from the initial stress axis to the [001]-[111] line in the standard stereographic triangle. In this study, this supposition was confirmed by conducting the creep tests at 1148 K/68.6 MPa using two PST crystals with ø of 31° and 34°. The initial stress axis of the PST crystal with ø of 31° locates nearer to the [001]-[-111] line than that of the PST crystal with ø of 34°. The strain at the end of the Stage I of the PST crystal with ø of 31° is half that of the PST crystal with ø of 34°. By analyzing the inverse pole figures of the creep interrupted PST crystals, it was confirmed that the angle from the initial stress axis to the [001]-[111] line is correlated with the strain of the transient stage.