scholarly journals Influence of testing and tempering temperatures on fatigue behaviour, life and crack initiation mechanisms in a 5%Cr martensitic steel

2010 ◽  
Vol 2 (1) ◽  
pp. 427-439 ◽  
Author(s):  
D. Delagnes ◽  
F. Rézaï-Aria ◽  
C. Levaillant
Keyword(s):  
Crack Initiation ◽  
Martensitic Steel ◽  
Fatigue Behaviour

Fatigue Behaviour of the Novel Titanium Alloys TIMETAL® 407 and TIMETAL® 412

2021 ◽  
Author(s):  
◽  
William Davey
Keyword(s):  
Crack Initiation ◽  
Titanium Alloys ◽  
Low Cycle Fatigue ◽  
Fatigue Crack Initiation ◽  
Charpy Impact ◽  
Fatigue Behaviour ◽  
High Energy ◽  
Process Window ◽  
Cycle Fatigue ◽  
The Impact

TIMETAL®407 (Ti-407) is a medium strength (~650MPa 0.2%YS) titanium alloy, recently developed by TIMET, in conjunction with Rolls-Royce plc for use in applications requiring high energy absorption at impact. Preliminary Charpy Impact (V notch) testing showed Ti-407 to absorb nearly twice the impact energy of Ti-6-4 and exhibit more than 2.5 times the lateral expansion. Further initial testing suggested the high cycle fatigue (HCF) run out stress of Ti-407 matches that of Ti-6-4 and other high strength alpha-beta titanium alloys. Ti-407 displayed more than double the tool life than that of Ti-6-4. The reduction in tool wear supports lower forces required for faster, more efficient machining. Compared to Ti-6-4, the relatively low elevated temperature flow stress, greater malleability and wide process window should allow Ti-407 to be processed with fewer reheats, while exhibiting reduced surface cracking and giving a consistently good surface finish. Optimised Ti-407 manufacturing processes should allow parts to be formed closer to net shape giving higher yields and requiring less machining to the components finished size. This project has evaluated HCF, as well as low cycle fatigue (LCF) and dwell fatigue crack initiation mechanisms in Ti-407, to clarify the effects of alloy chemistry, microstructural morphology and scale, and crystallographic texture. A derivative of Ti-407, Ti-412 (~750MPa 0.2%YS) was also tested towards the end of the project and helped to further elucidate understanding of the fatigue characteristics of the two alloys. Of interest was the strong HCF response displayed relative to the monotonic tensile strength. As well as the investigation into the crack initiation mechanisms, an assessment of crack propagation across a range of microstructural conditions was carried out on Ti-407 material.

Contact Fatigue Life Investigations and Wear Mechanisms of Different Case Hardened and Nidrided Steels

2014 ◽  
Vol 604 ◽  
pp. 51-54
Author(s):  
Andreas Trausmuth ◽  
Istvan Godor ◽  
Alexander Dietrich
Keyword(s):  
Crack Initiation ◽  
Rolling Contact Fatigue ◽  
Point Contact ◽  
Contact Fatigue ◽  
Compound Layer ◽  
Fatigue Behaviour ◽  
Rolling Contact ◽  
Contact Fatigue Life ◽  
Nitrided Surface ◽  
Lower Contact

The present work examines experimentally the local damage evolution and compares the differences in fatigue behaviour of case-hardened and plasma nitrided layers under rolling contact fatigue (RCF). The RCF experiments are accompanied by damage assessments. In order to assess experimentally the extreme conditions of point contact, the experiments are performed on a ball-on-rod (BoR) test rig. Results showed that nitrided surface get more important to RCF at lower contact pressure due to the comparable thin nitration depth, whereas at high contact stress the crack initiation starts on the surface of the compound layer and crack grow further in the diffusion layer. The carburised layer of case-hardened surfaces do not show any surface crack initiation.

scholarly journals Environmentally assisted cracking of T91 ferritic-martensitic steel in heavy liquid metals

2020 ◽  
Vol 38 (2) ◽  
pp. 183-194 ◽  
Author(s):  
Anna Hojná ◽  
Patricie Halodová ◽  
Michal Chocholoušek ◽  
Zbyněk Špirit ◽  
Lucia Rozumová
Keyword(s):  
Crack Initiation ◽  
Martensitic Steel ◽  
Liquid Metals ◽  
High Stress ◽  
Flow Speed ◽  
Heavy Liquid ◽  
Extension Rate ◽  
Oxygen Control ◽  
Environmentally Assisted Cracking ◽  
Static Conditions

AbstractIn order to advance material development for future nuclear systems, an insight into the cracking conditions of T91 ferritic-martensitic steel in heavy liquid metals (HLM) is provided. The paper critically reviews previous experimental data and summarizes them with new results. The new testing of T91 steel was performed in contact with slow flow and static HLM to study crack initiation, especially in liquid PbBi eutectic at 300°–350°C and Pb at 400°C with about 1 × 10−6 wt.% of oxygen. Pre-stressed coupons were exposed to the liquid metals for up to 2000 h. Constant extension rate tests (CERTs) were performed in the liquid metals to accelerate cracking development. Under static conditions, the testing resulted in oxidation without any crack observation. Under the CERT ones, the T91 steel showed a tendency to crack initiation in PbBi, while in Pb, cracks were not initiated even when the oxide layer was broken. Moreover, the environmentally assisted crack initiated at the maximum load and continued to grow under further loading without unstable failure. Both previous and new data have confirmed that high stress and plastic strain are pre-conditions for the environmentally assisted cracking of T91 in static HLM. It indicates that in the systems utilizing continuous oxygen control of HLM, the LME/EAC of the T91 could develop only in the beyond design load conditions. Further testing is necessary to address the HLM flow speed effect.

Numerical modelling of fatigue crack initiation of martensitic steel

2010 ◽  
Vol 41 (5) ◽  
pp. 823-829 ◽  
Author(s):  
S. Glodež ◽  
N. Jezernik ◽  
J. Kramberger ◽  
T. Lassen
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Numerical Modelling ◽  
Martensitic Steel ◽  
Fatigue Crack Initiation

Thermal and Mechanical Fatigue Loading: Mechanisms of Crack Initiation and Crack Growth

2014 ◽  
Author(s):  
Stefan Utz ◽  
Ewa Soppa ◽  
Christopher Kohler ◽  
Xaver Schuler ◽  
Horst Silcher
Keyword(s):  
Stainless Steel ◽  
Cyclic Loading ◽  
Austenitic Stainless Steel ◽  
Crack Initiation ◽  
Crack Growth ◽  
Mechanical Loading ◽  
Room Temperature ◽  
Fatigue Behaviour ◽  
Stress And Strain ◽  
Micro Cracks

The present contribution is focused on the experimental investigations and numerical simulations of the deformation behaviour and crack development in the austenitic stainless steel X6CrNiNb18-10 (AISI–347) under thermal and mechanical cyclic loading in HCF and LCF regimes. The main objective of this research is the understanding of the basic mechanisms of fatigue damage and development of simulation methods, which can be applied further in safety evaluations of nuclear power plant components. In this context the modelling of crack initiation and crack growth inside the material structure induced by varying thermal or mechanical loads are of particular interest. The mechanisms of crack initiation depend among other things on the art of loading, microstructure, material properties and temperature. The Nb-stabilized austenitic stainless steel in the solution-annealed condition was chosen for the investigations. Experiments with two kinds of cyclic loading — pure thermal and pure mechanical — were carried out and simulated. The fatigue behaviour of the steel X6CrNiNb18-10 under thermal loading was studied within the framework of the joint research project [1]. Interrupted thermal cyclic tests in the temperature range of 150 °C to 300 °C combined with non-destructive residual stress measurements (XRD) and various microscopic investigations, e.g. in SEM, were used to study the effects of thermal cyclic loading on the material. This thermal cyclic loading leads to thermal induced stresses and strains. As a result intrusions and extrusions appear inside the grains (at the surface), at which micro-cracks arise and evolve to a dominant crack. Finally, these micro-cracks cause continuous and significant decrease of residual stresses. The fatigue behaviour of the steel X6CrNiNb18-10 under mechanical loading at room temperature was studied in the framework of the research project [2]. With a combination of interrupted LCF tests and EBSD measurements the deformation induced transformation of a fcc austenite into a bcc α′-martensite was observed in different stages of the specimen lifetime. The plastic zones develop at the crack tips, in which stress and strain amplitudes are much higher than the nominal loading, and enable martensitic transformation in the surrounding of the crack tip. The consequence of this is that cracks grow in the “martensitic tunnels”. The short and long crack growth behaviours of the steel X6CrNiNb18-10 under mechanical loading at room temperature and T = 288 °C were studied for different loading parameters. Moreover, the R-ratio was modified in order to study the effect of crack closure at the crack tip for long cracks. Several FE-models of specimens with different geometries and microstructures were created and cyclically loaded according to the experimental boundary conditions. A plastic constitutive law based on a Chaboche type model was implemented as a user subroutine in the FE software ABAQUS. The corresponding material parameters were identified using uniaxial LCF tests of X6CrNiNb18-10 with different strain amplitudes and at different temperatures. These calculations aimed in the estimation of stress and strain distributions in the critical areas in which the crack initiation was expected.

scholarly journals Fatigue behaviour of corrosion pits in X65 steel pipelines

2018 ◽  
Vol 233 (5) ◽  
pp. 1771-1782 ◽  
Author(s):  
Farnoosh Farhad ◽  
Xiang Zhang ◽  
David Smyth-Boyle
Keyword(s):  
Finite Element ◽  
Crack Initiation ◽  
Stress Ratio ◽  
Fatigue Crack Initiation ◽  
Local Stress ◽  
Fatigue Behaviour ◽  
Stress And Strain ◽  
Element Analysis ◽  
X65 Steel ◽  
Corrosion Pits

Corrosion pits are a form of geometrical discontinuity that lead to stress and strain concentration in engineering components, resulting in crack initiation under service loading conditions and ultimately fracture and failure. Initiation and propagation of cracks in offshore pipelines can lead to loss of containment and environmental and commercial impacts. In order to prevent such failures, tools to predict the structural integrity of pipelines need to be improved. This work investigates the fatigue behaviour of corrosion pits in API-5L X65 grade steel pipeline utilising numerical and analytical methods. Firstly, load-controlled fatigue tests were carried out on smooth X65 steel samples to establish S–N data. Secondly, local stress–strain behaviour at corrosion pits and its effect on fatigue crack initiation were investigated using elastic-plastic finite element analysis of samples containing a single corrosion pit under cyclic loading. Analysis of stabilised stress–strain hysteresis loops at corrosion pits showed that the local stress ratio at the pit changes from 0.1 to −0.4 while the applied stress amplitude increases with the same stress ratio of 0.1. Analytical methods were also used to predict the local maximum stress and strain at the pit, which showed a similar local stress ratio to the finite element analysis result but lower stress and strain ranges. Finally, fatigue crack initiation life was predicted using the combination of finite element stress and strain analysis and the Smith–Watson–Topper strain–life approach. An advantage of this method for life estimation is that this approach considers the local stress and strains at corrosion pits rather than applied stress.

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