INFLUENCE OF GEOMETRY RECOVERY ON STRESS STATE OF OPTIMIZED PARTS

2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Boštjan Harl ◽  
Jožef Predan ◽  
Marko Kegl ◽  
Dejan Dinevski
Keyword(s):  
Topology Optimization ◽  
Stress Field ◽  
Fatigue Crack Initiation ◽  
Stress Fields ◽  
Typical Result ◽  
Production Environment ◽  
Stress Concentrations ◽  
Triangulated Surface ◽  
Load Carrying ◽  
Insight Into

This paper discusses the influence of geometry recovery on actual stress fields within load-carrying parts that have to be reconstructed from the resulting surfaces obtained by topology optimization procedures. A typical result of a topology optimization process is a triangulated surface which represents the boundary of the optimized part. In a production environment, this triangulated surface is mostly used to reconstruct a proper CAD model of the optimized part. This process is by far not automated and may require significant skills and efforts. Unfortunately, it also unavoidably introduces variations in the geometry of the optimized part. Although visually these variations might seem to be rather minor, they may very quickly introduce significant stress field variations. These variations may result in harmful locally increased stress levels and even significant stress concentrations. To get more insight into these phenomena, the topology of a quasi-two-dimensional example part is optimized. The resulting geometry is then reconstructed with various levels of precision. For the obtained geometries, the stress fields are studied numerically. It is shown that stress field variations are indeed such that they may influence significantly the probability of fatigue crack initiation and consequently the service life of the part. Obviously, the geometry recovery after topology optimization should be done very carefully, especially if the part will be subject to cyclic loading during operation.

DESIGN OF STRUCTURAL PARTS BY USING MODERN SIMULATION PROCEDURES

2017 ◽  
Vol 4 (1) ◽  
Author(s):  
Boštjan Harl ◽  
Jožef Predan ◽  
Marko Kegl ◽  
Dejan Dinevski
Keyword(s):  
Topology Optimization ◽  
Stress Fields ◽  
Lattice Structures ◽  
The Finite Element Method ◽  
Optimization Software ◽  
And Topology ◽  
Load Carrying ◽  
Domain Configuration ◽  
Structural Parts ◽  
Manufacturing Technologies

This paper discusses modern simulation procedures used in design of structural load-carrying parts that are based on the Finite Element Method. The specific focus of the paper is the topology optimization usage within the context of two currently very interesting topics: configuration and optimization of lattice structures and modern additive manufacturing technologies. Both types of structures are presented together with their limits as well as their potentials for optimization. The discussion is illustrated by two numerical examples and experimentally obtained results. In the examples, a simple beam with three points load is optimized regarding to the different topology setups. The stress fields for different loaded optimized versions of structures are presented and the solutions are discussed and compared to the results of the experiment. A standalone topology optimization software CAESS ProTOp is used for the domain configuration and topology optimization in both examples.

INFLUENCE OF BOUNDARY CONDITIONS VARIATION ON TOPOLOGY OPTIMIZATION OF LOAD-CARRYING PARTS

2018 ◽  
Vol 5 (1) ◽  
Author(s):  
Boštjan Harl ◽  
Marko Kegl ◽  
Jožef Predan ◽  
Dejan Dinevski
Keyword(s):  
Topology Optimization ◽  
Boundary Conditions ◽  
Applied Load ◽  
Stress Fields ◽  
Normal Operation ◽  
Practical Application ◽  
Design Procedures ◽  
Correct Formulation ◽  
Load Carrying ◽  
Definition Of

The paper discusses the problem of boundary conditions formulation in FEA-based design procedures of load-carrying parts driven by topology optimization. The emphasis is on the correct formulation of boundary conditions and the definition of corresponding load cases so that topology optimization will deliver a usable design. It demonstrates that inadequate preparation of load cases may lead to a result that seems to be reasonable, but may behave badly in practical application due to possible lack of robustness and reliability. To illustrate this, an example study is performed for a load-carrying bracket that is fastened by four screws. Namely, in such situations it may quickly happen that one or more screws become at least slightly loose. This changes the stress fields in the part dramatically. If this is not captured correctly in the applied load cases, this means that the topology optimizer will deliver some design that might be extremely sensitive to a loose-screw situation. Such a design may fail very quickly during normal operation.

Level set topology optimization of load carrying battery packs

2021 ◽  
Vol 177 ◽  
pp. 121570
Author(s):  
Sandilya Kambampati ◽  
Justin S. Gray ◽  
H. Alicia Kim
Keyword(s):  
Topology Optimization ◽  
Level Set ◽  
Load Carrying ◽  
Battery Packs

Assessment of the Effect of Pitting Corrosion on Fatigue Crack Initiation in Hydro Turbine Shaft

2013 ◽  
Vol 633 ◽  
pp. 186-196 ◽  
Author(s):  
Radivoje Mitrovic ◽  
Dejan Momcilovic ◽  
Ivana Atanasovska
Keyword(s):  
Pitting Corrosion ◽  
Fatigue Crack Initiation ◽  
Fatigue Loading ◽  
Critical Distance ◽  
Life Assessment ◽  
Stress Concentrations ◽  
Hydro Power ◽  
Turbine Shaft ◽  
Improved Design ◽  
Material Length

Energy efficiency is a key issue worldwide, and not confined solely to the realm of engineers. Past failures of mechanical power system components must be examined carefully in order to minimise future occurrences and increase energy efficiencies. Improved design procedures have been highly sought by engineers and researchers over the past few decades. The latest verified method with strong application potential within the power industry is that of the Theory of Critical Distances (TCD). TCD is not one method, but a group of methods that have a common feature; the use of a characteristic material length parameter, the critical distance L, for calculating the influence of notch-like stress raisers under static and fatigue loading. A case study from a hydro power plant turbine shaft was chosen to illustrate the development of this methodology. The paper illustrates the application of TCD to the fatigue life assessment of a turbine shaft with stress concentrations due to pitting corrosion.

Design Optimisation of a Ferritic Ring Weld Specimen Using FE Modelling

2009 ◽  
Author(s):  
Christopher M. Gill ◽  
Paul Hurrell ◽  
John Francis ◽  
Mark Turski
Keyword(s):  
Heat Treatment ◽  
Residual Stress ◽  
Finite Element ◽  
Neutron Diffraction ◽  
Stress Field ◽  
Finite Element Modelling ◽  
Post Weld Heat Treatment ◽  
Stress Fields ◽  
Element Modelling ◽  
Weld Heat

This paper describes the design optimisation of an SA508 ferritic steel ring weld specimen using FE modelling techniques. The aim was to experimentally and analytically study the effect of post weld heat treatment upon a triaxial residual stress field. Welding highly constrained geometries, such as those found in some pressure vessel joints, can lead to the formation of highly triaxial stress fields. It is thought that application of post weld heat treatments will not fully relax hydrostatic stress fields. Therefore a ferritic multi-pass ring weld specimen was designed and optimised, using 2D finite element modelling, to generate a high magnitude triaxial stress field. The specimen thickness and weld-prep geometry was optimised to produce a large hydrostatic stress field and still allow efficient use of neutron diffraction to measure the residual stress. This paper reports the development of the test specimen geometry and compares the results of welding FE analysis and neutron diffraction measurements. Welding residual stresses were experimentally determined using neutron diffraction; both before post weld heat treatment. Three dimensional moving heat source weld finite element modelling has been used to predict the residual stresses generated by the welding process used. Finite element modelling examined the effect of phase transformation upon the residual stress field produced by welding. The relaxation of welding stresses by creep during post weld heat treatment has also been modelled. Comparisons between the modelled and measured as-welded residual stress profiles are presented. This work allows discussion of the effect of post weld heat treatment of triaxial stress fields and determines if finite element modelling is capable of correctly predicting the stress relaxation.

scholarly journals Local stress fields in solids estimated by acoustical emission method

2021 ◽  
Vol 2103 (1) ◽  
pp. 012064
Author(s):  
V L Hilarov ◽  
E E Damaskinskaya
Keyword(s):  
Time Series ◽  
Acoustic Emission ◽  
Stress Field ◽  
Estimation Method ◽  
Local Stress ◽  
Stress Fields ◽  
Emission Method ◽  
Macroscopic Fracture ◽  
Stress Estimation ◽  
Kinetic Concept

Abstract Based on the Zhurkov’s kinetic concept of solids’ fracture a local internal stress estimation method is introduced. Stress field is computed from the time series of acoustic emission intervals between successive signals. For the case of two structurally different materials the time evolution of these stresses is examined. It is shown that temporal changes of these stresses’ accumulation law may serve as a precursor of incoming macroscopic fracture.

Temperature and Residual Stress Fields in an Austenitic Circumferential Pipe Weld

2002 ◽  
Author(s):  
Ruthard Bonn ◽  
Klaus Metzner ◽  
H. Kockelmann ◽  
E. Roos ◽  
L. Stumpfrock
Keyword(s):  
Residual Stress ◽  
Numerical Calculation ◽  
Stress Field ◽  
Quantitative Determination ◽  
Welding Residual Stress ◽  
Stress Fields ◽  
Residual Stress Field ◽  
Circumferential Welds ◽  
The Impact

The main target of a research programme “experimental and numerical analyses on the residual stress field in the area of circumferential welds in austenitic pipe welds”, sponsored by Technische Vereinigung der Großkraftwerksbetreiber e. V. (VGB) and carried out at MPA Stuttgart, was the validation of the numerical calculation for the quantitative determination of residual stress fields in austenitic circumferential pipe welds. In addition, the influence of operational stresses as well as the impact of the pressure test on the residual stress state had to be examined. By using the TIG orbital welding technique, circumferential welds (Material X 10 CrNiNb 18 9 (1.4550, corresponding to TP 347) were produced (geometric dimensions 255.4 mm I.D. × 8.8 mm wall) with welding boundary conditions and weld parameters (number of weld layers and weld built-up, seam volume, heat input) which are representative for pipings in power plants. Deformation and temperature measurements accompanying the welding, as well as the experimentally determined (X-ray diffraction) welding residual stress distribution, served as the basis for the verification of numeric temperature and residual stress field calculations. The material model on which the calculations were founded was developed by experimental weld simulations in the thermo-mechanical test rig GLEEBLE 2000 for the determination of the material behaviour at different temperatures and elasto-plastic deformation. The numeric calculations were carried out with the Finite Element program ABAQUS. The comparison of the calculation results with the experimental findings confirms the proven validation of the developed numerical calculation models for the quantitative determination of residual stresses in austenitic circumferential pipings. The investigation gives a well-founded insight into the complex thermo-mechanical processes during welding, not known to this extent from literature previously.

Finite element modeling of guyed back spars in cable logging

2004 ◽  
Vol 34 (4) ◽  
pp. 817-828 ◽  
Author(s):  
Albert Saravi ◽  
C Kevin Lyons
Keyword(s):  
Finite Element ◽  
Normal Stress ◽  
Cross Section ◽  
A Priori ◽  
Element Model ◽  
Transverse Cross Section ◽  
Stress Fields ◽  
Stress Concentrations ◽  
Maximum Normal Stress ◽  
Tree Method

In this study a finite element model of a back spar system was developed with three guylines opposing the skyline strap tension. In this paper the allowable skyline strap tension is the tension in the skyline strap that results in the maximum normal stress on a transverse cross section of the tree being equal to an assumed allowable stress. An iterative routine was developed to find the allowable skyline strap tension, and this routine was found to converge rapidly from initial values that were below and above the allowable skyline strap tension. Two algorithms were developed for finding the maximum normal stress on a transverse cross section of a tree, method 1 and method 2. If the plane that the tree displaced in was known a priori, then method 2 could be used, and it was found to be less sensitive to mesh coarseness. If the plane that the tree displaced in was not known a priori, then method 1 had to be used with a less coarse mesh. It was found that the stress concentrations due to simplified cable connections were not significant for rigging configurations that allowed a larger rigging point displacement. The rigging configurations that allowed larger rigging point displacements have stress fields that are dominated by bending, while for rigging configurations that allow only small rigging point displacements, the stress fields are dominated by axial compression.

Comparison between Pile-Up Singularities and Stress Fields Induced by Thin Slip Bands. Application to the Prediction of Grain Boundary Microcrack Nucleation

2013 ◽  
Vol 592-593 ◽  
pp. 61-66
Author(s):  
Maxime Sauzay ◽  
Mohamed Ould Moussa
Keyword(s):  
Slip Band ◽  
Tensile Deformation ◽  
Finite Thickness ◽  
Local Stress ◽  
Stress Fields ◽  
Stress Concentrations ◽  
Griffith Criterion ◽  
Slip Bands ◽  
Pile Up ◽  
Microcrack Initiation

Slip localization is widely observed in metallic polycrystals after tensile deformation, cyclic deformation or pre-irradiation followed by tensile deformation. Such strong deformation localized in thin slip bands induces local stress concentrations in the quasi-elastic matrix around, at the intersections between slip bands (SBs) and grain boundaries (GBs) where microcrack initiation is often observed. Since the work of Stroh, such stress fields have been mostly modeled using the dislocation pile-up theory which leads to stress singularities similar to the LEFM ones. The Griffith criterion has then been widely applied, leading usually to strong underestimations of the macroscopic stress to GB crack initiation. In fact, slip band thickness is finite: 20nm-1000nm depending on material, temperature and loading conditions. Then, many slip planes are plastically activated through the thickness, and not only one single atomic plane. To evaluate more realistic stress fields, numerous crystalline finite element (FE) computations have been carried out using microstructure inputs (slip band aspect ratio, crystal and GB orientation...). A strong influence of slip band thickness close to the slip band corner has been highlighted, which is not accounted for by the pile-up theory. But far away, the thickness has a negligible effect and the predicted stress fields are close to the one predicted by the pile-up theory. Closed-form expressions are deduced from the numerous FE computation results allowing a straightforward prediction of GB stress fields. Slip band plasticity parameters, such as length and thickness, as well as crystal orientation, GB plane and remote stress are taken into account. The dependence with respect to the various parameters can be understood in the framework of matching expansions usually applied to cracks with V notches of finite thickness. As the exponent of the GB stress close-field is only about one-half of the pile-up or LEFM crack one, the Griffith criterion may not be used for GB microcrack prediction in case of finite thickness. That is why finite crack fracture mechanics is used together with both energy and stress criteria. Taking into account SB finite thickness, t>0, leads to predicted remote stresses to GB microcrack initiation three to six times lower than the ones predicted using the to pile-up theory, in agreement with experimental data.

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