Fatigue design in the presence of stress concentrations

2003 ◽  
Vol 38 (5) ◽  
pp. 443-452 ◽  
Author(s):  
L Susmel ◽  
D Taylor
Keyword(s):  
High Cycle Fatigue ◽  
Great Majority ◽  
Fatigue Behaviour ◽  
Critical Distance ◽  
Cycle Fatigue ◽  
Stress Concentrations ◽  
Element Analysis ◽  
Distance Method ◽  
Linear Elastic ◽  
Experimental Values

This paper reports a comparative study of some recent methods developed for the estimation of high-cycle fatigue behaviour of components containing stress concentrations. It begins by reviewing some existing methods for the prediction of fatigue limits: the stress-life method, linear elastic fracture mechanics, the Kitagawa-Takahashi and Atzori-Lazzarin approaches and the method of Smith and Miller. Two new methods are described which have been developed during the last few years: the crack modelling method (CMM) and the critical distance method (CDM). These methods were tested by comparing their predictions with experimental data using a large database of 88 different notch geometries and materials. Notches were divided into three types: blunt, sharp and short. The CDM was found to be very successful for all types of notch, giving predictions within 20 per cent of experimental values in the great majority of cases. The CMM encountered difficulties with short notches; correction factors were developed to overcome this problem. Both methods can be used very easily in conjunction with finite element analysis, making them more useful than previous methods for the prediction of high-cycle fatigue in engineering components.

Notch Fatigue and Fracture Mechanics of Austempered Ductile Irons

2010 ◽  
Vol 457 ◽  
pp. 181-186 ◽  
Author(s):  
Bruno Atzori ◽  
Franco Bonollo ◽  
Giovanni Meneghetti
Keyword(s):  
Fatigue Strength ◽  
Fracture Mechanics ◽  
High Cycle Fatigue ◽  
Peak Stress ◽  
Fatigue Behaviour ◽  
Cycle Fatigue ◽  
Elastic Peak ◽  
Linear Elastic ◽  
Design Engineers ◽  
Notch Tip

In this paper the fatigue characterization of an austempered ductile iron (ADI) is presented. The aim of the work is to provide design engineers involved in fatigue assessments with an engineering tool suitable to deal with notches of different severity. Classically, U-notches are divided into blunt notches and sharp notches. The former are characterized by large notch tip radii such that the high cycle fatigue strength is controlled by the elastic peak stress, i.e. by the elastic stress concentration factor. The latter are characterized by reduced notch tip radii such that the effective stress which controls the high cycle fatigue strength is significantly lower than the elastic peak stress and their behaviour become similar to that of a crack having the same length. Blunt notches are assessed according to the classical Notch Mechanics principles, while sharp notches are treated with the Linear Elastic Fracture Mechanics approach. After presenting the classical Frost diagram which highlights the different fatigue behaviour of sharp and blunt notches, fatigue test results generated from notches of different severity are presented as well as a synthesis in a diagram able to account for short cracks/notches, long cracks, sharp notches and blunt notches.

Fatigue Failure Analysis Using the Theory of Critical Distance

2011 ◽  
Vol 462-463 ◽  
pp. 663-667 ◽  
Author(s):  
Ruslizam Daud ◽  
Ahmad Kamal Ariffin ◽  
Shahrum Abdullah ◽  
Al Emran Ismail
Keyword(s):  
Stress Concentration ◽  
Fatigue Failure ◽  
Notch Root ◽  
High Stress ◽  
Critical Distance ◽  
Future Research ◽  
Element Analysis ◽  
Linear Elastic ◽  
The Finite Element Analysis ◽  
Elastic Fracture

This paper explores the initial potential of theory of critical distance (TCD) which offers essential fatigue failure prediction in engineering components. The intention is to find the most appropriate TCD approach for a case of multiple stress concentration features in future research. The TCD is based on critical distance from notch root and represents the extension of linear elastic fracture mechanics (LEFM) principles. The approach is allowing possibilities for fatigue limit prediction based on localized stress concentration, which are characterized by high stress gradients. Using the finite element analysis (FEA) results and some data from literature, TCD applications is illustrated by a case study on engineering components in different geometrical notch radius. Further applications of TCD to various kinds of engineering problems are discussed.

The Effect of Foreign Object Damage on Compressor Blade High Cycle Fatigue Strength

2017 ◽  
Author(s):  
Benjamin Hanschke ◽  
Thomas Klauke ◽  
Arnold Kühhorn
Keyword(s):  
Fatigue Strength ◽  
Service Sector ◽  
High Cycle Fatigue ◽  
Compressor Blade ◽  
Foreign Object ◽  
Cycle Fatigue ◽  
Stress Concentrations ◽  
Foreign Object Damage ◽  
Input Parameters ◽  
Aero Engines

For a considerable amount of time blade integrated disks (blisks) are established as a standard component of high pressure compressors (HPCs) in aero engines. Due to the steady requirement to increase the efficiency of modern HPCs, blade profiles get thinned out and aerodynamic stage loading increases. Ever since, aerofoil design has to balance structural and aerodynamic requirements. One particularity of aero engines is the possibility to ingest different kinds of debris during operation and some of those particles are hard enough to seriously damage the aerofoil. Lately, a growing number of blisk-equipped aero engines entered service and the question of foreign object damage (FOD) sensitivity relating to compressor blade high cycle fatigue (HCF) has emerged. Correct prediction of fatigue strength drop due to a FOD provides a huge chance for cost cutting in the service sector as on-wing repairs (e.g. borescope blending) are much more convenient than the replacement of whole blisks and corresponding engine strips. The aim of this paper is to identify critical FOD-areas of a modern HPC stage and to analyze the effects of stress concentrations — caused by FOD — on the fatigue strength. A process chain has been developed, that automatically creates damaged geometries, meshes the parts and analyses the fatigue strength. Amplitude frequency strength (af-strength) has been chosen as fatigue strength indicator owing to the fact, that amplitudes and frequencies of blade vibrations are commonly measured either by blade tip timing or strain gauges. Furthermore, static and dynamic stress concentrations in damaged geometries compared to the reference design were computed. A random variation of input parameters was performed, such as the radial damage position at blade leading edge and damage diameter. Based on results of the different samples, correlations of input parameters and the fatigue strength drop have been investigated. Evaluation shows a significant mode dependence of critical blade areas with a large scatter between drops in fatigue strength visible for mode to mode comparison. Keeping in mind the necessity of fast response times in the in-service sector, FOD sensitivity computations could be performed for all blade rows of the HPC — including the analysis of possible borescope blending geometries — in the design stage. Finally, the actual amplitude frequency levels (af-levels) of the modes excited during operation have to be appropriately taken into consideration. For example, a pronounced af-strength drop due to a FOD may not be critical for safe engine operations because the observed mode is excited by small af-levels during operation. Hence, the endurance ratio — a quotient of af-level and af-strength — is used as assessment criterion.

scholarly journals Effect of Sandblasting on Low and High-Cycle Fatigue Behaviour after Mechanical Cutting of a Twinning-Induced Plasticity Steel

2018 ◽  
Vol 165 ◽  
pp. 18002
Author(s):  
Antoni Lara ◽  
Mercè Roca ◽  
Sergi Parareda ◽  
Núria Cuadrado ◽  
Jessica Calvo ◽  
...  
Keyword(s):  
High Cycle Fatigue ◽  
Twip Steel ◽  
Low Cycle Fatigue ◽  
Load Ratio ◽  
Fatigue Behaviour ◽  
Cycle Fatigue ◽  
High Manganese ◽  
Amplitude Control ◽  
Cut Edge ◽  
Mechanical Cutting

In the last years, car bodies are increasingly made with new advanced high-strength steels, for both lightweighting and safety purposes. Among these new steels, high-manganese or TWIP steels exhibit a promising combination of strength and toughness, arising from the austenitic structure, strengthened by C, and from the twinning induced plasticity effect. Mechanical cutting such as punching or shearing is widely used for the manufacturing of car body components. This method is known to bring about a very clear plastic deformation and therefore causes a significant increase of mechanical stress and micro-hardness in the zone adjacent to the cut edge. To improve the cut edge quality, surface treatments, such as sandblasting, are often used. This surface treatment generates a compressive residual stress layer in the subsurface region. The monotonic tensile properties and deformation mechanisms of these steels have been extensively studied, as well as the effect of grain size and distribution and chemical composition on fatigue behaviour; however, there is not so much documentation about the fatigue performance of these steels cut using different strategies. Thus, the aim of this work is to analyse the fatigue behaviour of a TWIP steel after mechanical cutting with and without sandblasting in Low and High-Cycle Fatigue regimes. The fatigue behaviour has been determined at room temperature with tensile samples tested with a load ratio of 0.1 and load amplitude control to analyse High-Cycle Fatigue behaviour; and a load ratio of -1 and strain amplitude control to determine the Low-Cycle Fatigue behaviour. Samples were cut by shearing with a clearance value of 5%. Afterwards, a part of the cut specimens were manually blasted using glass microspheres of 40 to 95 microns of diameter as abrasive media. The results show a beneficial effect of the sandblasting process in fatigue behaviour in both regimes, load amplitude control (HCF) and strain amplitude control (LCF) tests, when these magnitudes are low, while no significant differences are observed with higher amplitudes. low-cycle fatigue, high-cycle fatigue, mechanical cutting, sandblasting, high manganese steel, TWIP steel

scholarly journals Influence of defects on the very high cycle fatigue behaviour of forged aeronautic titanium alloy

2014 ◽  
Vol 12 ◽  
pp. 10004
Author(s):  
Alexander Nikitin ◽  
Thierry Palin-Luc ◽  
Andrey Shanyavskiy ◽  
Claude Bathias
Keyword(s):  
Titanium Alloy ◽  
High Cycle Fatigue ◽  
Fatigue Behaviour ◽  
Cycle Fatigue ◽  
Very High Cycle Fatigue ◽  
Very High
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