scholarly journals Experimental and Computational Approach to Fatigue Behavior of Polycrystalline Tantalum

Metals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 416 ◽  
Author(s):  
Damien Colas ◽  
Eric Finot ◽  
Sylvain Flouriot ◽  
Samuel Forest ◽  
Matthieu Mazière ◽  
...  
Keyword(s):  
Free Surface ◽  
Low Cycle Fatigue ◽  
Large Strain ◽  
Fatigue Behavior ◽  
Fatigue Crack Initiation ◽  
Field Measurements ◽  
Test Sample ◽  
Lattice Rotation ◽  
Element Simulation ◽  
Crack Initiation Criterion

This work provides an experimental and computational analysis of low cycle fatigue of a tantalum polycrystalline aggregate. The experimental results include strain field and lattice rotation field measurements at the free surface of a tension–compression test sample after 100, 1000, 2000, and 3000 cycles at ±0.2% overall strain. They reveal the development of strong heterogeneites of strain, plastic slip activity, and surface roughness during cycling. Intergranular and transgranular cracks are observed after 5000 cycles. The Crystal Plasticity Finite Element simulation recording more than 1000 cycles confirms the large strain dispersion at the free surface and shows evidence of strong local ratcheting phenomena occurring in particular at some grain boundaries. The amount of ratcheting plastic strain at each cycle is used as the main ingredient of a new local fatigue crack initiation criterion.

Low Cycle Fatigue Behavior and Mechanism of Newly Developed Advanced Heat Resistant Austenitic Stainless Steels at High Temperature

2014 ◽  
Vol 891-892 ◽  
pp. 377-382 ◽  
Author(s):  
Guo Cai Chai
Keyword(s):  
High Temperature ◽  
Room Temperature ◽  
Low Cycle Fatigue ◽  
Large Strain ◽  
Fatigue Behavior ◽  
Fatigue Crack Initiation ◽  
Electron Back Scatter Diffraction ◽  
Dynamic Strain ◽  
Cycle Fatigue ◽  
Dynamic Strain Ageing

Austenitic stainless steel grade UNS S31035 (Sandvik Sanicro® 25) has been developed for the next generation of 700°C A-USC power plant. This paper will mainly focus on the study of low cycle fatigue behavior and damage mechanisms of the material at room temperature, 600C to 700C by using electron back scatter diffraction and electron channeling contrast image techniques. At room temperature, the material shows a hardening and softening behavior as usual. At high temperature, however, it shows only a cyclic hardening behavior. Dynamic strain ageing can be one of the mechanisms. The damage and fatigue crack initiation mechanisms due to cyclic loading at different temperatures and loading conditions have been identified. The interactions between dislocations or slip bands with grain boundary or twin boundary are the main damage mechanism at low temperature or at high temperature with large strain amplitudes. Strain localization due to dislocation slipping is the main mechanism for the damage in grain.

scholarly journals Effect of LCF Pre-Damage on Very High Cycle Fatigue Behavior of TC21 Titanium Alloy

2017 ◽  
Author(s):  
Nie Baohua ◽  
Zhao Zihua ◽  
Ouyang Yongzhong ◽  
Chen Dongchu ◽  
Chen Hong ◽  
...  
Keyword(s):  
Titanium Alloy ◽  
Crack Initiation ◽  
High Cycle Fatigue ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Fatigue Crack Initiation ◽  
Mechanism Analysis ◽  
Cycle Fatigue ◽  
Very High Cycle Fatigue ◽  
Very High

The effect of low cycle fatigue (LCF) pre-damage on the subsequent very high cycle fatigue (VHCF) behavior is investigated in TC21 titanium alloy. LCF pre-damage is applied under 1.8% strain amplitude up to various fractions of the expected life and subsequent VHCF properties are determined using ultrasonic fatigue tests. Results show that 5% of LCF pre-damage insignificantly affects the VHCF limit due to the absent of pre-crack, but decreases the subsequent fatigue crack initiation life estimated by Pairs’ law. Pre-cracks introduced by 10% and 20% of LCF pre-damage significantly reduce the subsequent VHCF limits. The crack initiation site shifts from subsurface-induced fracture for undamaged and 5% of LCF pre-damage specimens to surface pre-crack for 10% and 20% of LCF pre-damage specimens in very high cycle region. The fracture mechanism analysis indicate that LCF pre-crack will re-start to propagate under subsequently low stress amplitude when stress intensity factor of pre-crack is larger than its threshold. Furthermore, the predicted fatigue limits based on EI Haddad model for the LCF pre-damage specimens well agree with the experimental results.

Comparative Low-Cycle Fatigue Behavior of HAYNES 244 Alloy and Waspaloy

2021 ◽  
Author(s):  
Michael G. Fahrmann
Keyword(s):  
Thermal Loading ◽  
Coefficient Of Thermal Expansion ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Axial Strain ◽  
Fatigue Crack Initiation ◽  
High Strength ◽  
Cyclic Hardening ◽  
Cycle Fatigue ◽  
Softening Behavior

Abstract HAYNES® 244® alloy was chiefly developed to address the need for high-strength, low coefficient of thermal expansion (CTE) alloys for seal rings and cases in advanced gas turbine engines. In addition to these attributes, adequate resistance to low-cycle fatigue (LCF) due to cyclic thermal and mechanical loading during service is critical for such applications. The isothermal LCF performance of commercially produced 0.5” (12.5 mm) thick, fully heat treated plate products of 244 alloy was evaluated by means of axial strain-controlled (R = −1) LCF tests covering total strain ranges up to 1.25 % (without dwells), at temperatures ranging from 800–1400°F (427–760°C). In addition, the comparative LCF performance of Waspaloy, a well-established alloy for turbine cases, was evaluated under selected, nominally identical test conditions. S-N curves were constructed and fitted by the Coffin-Manson equation, allowing the delineation of regimes controlled by the elastic and plastic response of the material. Fracture surfaces were examined in the scanning electron microscope to identify fatigue crack initiation sites and crack propagation modes. Differences between the alloys are discussed in terms of tensile strength and cyclic hardening/softening behavior. Implications for fatigue performance of these alloys under cyclic thermal loading conditions are discussed as well.

Fatigue Life Simulation of a High Pressure Breech System

2006 ◽  
Vol 326-328 ◽  
pp. 1027-1030 ◽  
Author(s):  
Seung Kee Koh ◽  
Eui Gyun Na ◽  
Tae Hyun Baek ◽  
K.J. Kang ◽  
S.T. Ahn ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Crack Initiation ◽  
Stress Analysis ◽  
Structural Integrity ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Fatigue Crack Initiation ◽  
Local Strain ◽  
Fatigue Tests ◽  
Ring Groove

In order to evaluate the structural integrity of the breech system used for a thick-walled cylinder subjected to pulsating high internal pressure, fatigue life simulation of a breech system was performed. A stress analysis of the breech was performed to locate the critical region vulnerable to crack initiation. Low-cycle fatigue behavior of the breech material was investigated to obtain the fatigue crack initiation properties. Elastic-plastic finite element stress analysis resulted in a stress concentration at the breech ring groove root. Strains at the breech ring and block were experimentally measured using strain gages and resulted in similar values compared to the calculated strains. Local strain approach was employed to estimate the fatigue life of the breech system for crack initiation at the groove root of the breech ring. Fatigue tests using simulation specimens were performed and an averaged fatigue life was obtained, showing a very good agreement with the calculated fatigue life within a factor of two.

Low Cycle Fatigue of Electrodeposited Pure Nanocrystalline Metals

2007 ◽  
Vol 561-565 ◽  
pp. 1299-1302 ◽  
Author(s):  
Pasquale Cavaliere
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Fatigue Crack ◽  
Crack Propagation ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Fatigue Crack Initiation ◽  
Size Variation ◽  
Load Ratio ◽  
Cycle Fatigue

The fatigue behavior of metals is strongly governed by the grain size variation. As the tensile strength, the fatigue limit increases with decreasing grain size in the microcrystalline regime. A different trend in mechanical properties has been demonstrated in many papers for metals with ultrafine (< 1 m) and nanocrystalline (< 100 nm) grain size in particular in the yield stress and fatigue crack initiation and growth. The fatigue behavior of electrodeposited nanocrystalline Ni (20 and 40 nm mean grain size) and nanocrystalline Co (20 nm) has been analyzed in the present paper by means of stress controlled tests. The monothonic mechanical properties of the materials were obtained from tensile tests by employing an Instron 5800 machine by measuring the strain with an extensometer up to 2.5% maximum strain. The strain gage specimen dimensions measured 20 mm length and 5 mm width, all the specimens were produced by electro-discharge machining. The low cycle fatigue tests were performed with specimens of the same geometry of the tensile ones in tension-tension with load ratio R=0.25. The fatigue crack propagation experiments were carried out by employing single edge notched specimens measuring 39 mm in length, 9.9 mm in width and with an electro-discharge machined edge-notch of 1 mm. All the endurance fatigue and crack propagation tests were performed at 10 Hz.

Strain Ratio Effect on the Low Cycle Fatigue Behavior and Microstructure of High-Mn Austenitic Alloy Undergoing the Strain-Induced ε-Martensitic Transformation

2018 ◽  
Vol 941 ◽  
pp. 1065-1070
Author(s):  
Ilya Nikulin ◽  
Takahiro Sawaguchi
Keyword(s):  
Martensitic Transformation ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Control Mode ◽  
Total Strain ◽  
Lattice Rotation ◽  
Mean Stress ◽  
Total Strain Amplitude ◽  
Cycle Fatigue ◽  
The Mean

The effect of the strain asymmetry on low-cycle fatigue properties and microstructure of Fe–15Mn–10Cr–8Ni–4Si (in. wt. %) alloy undergoing the strain-induced ε-martensitic transformation (ε-MT) were investigated at strain ratios,R, of-1, -0.2, 0.2 and 0.5 under total strain-control mode with total strain amplitude of 0.01. At studied strain ratios the clear asymmetry in tension and compression stress providing tensile mean stress was observed in alloy deformed atRof-0.2, 0.2 and 0.5. The mean stress rapidly decreases to ~ 100 cycles and remain almost zero until failure. It was found that strain-induced ε-martensitic transformation and lattice rotation of austenite provide cyclic hardening of the studied alloy leading to the mean stress relaxation and provides the stability in hysteresis loops behavior at studiedR. As a consequence, the fatigue life,Nf, of the alloy remains on the level of the alloy deformed by LCF atR, of -1 (NfR=-1=9200 cycles). The details of the fatigue behavior, deformation mechanisms and microstructure evolution of the studied alloy are discussed.

scholarly journals Effect of Local Recrystallized Grains on the Low Cycle Fatigue Behavior of a Nickel-Based Single Crystal Superalloy

Crystals ◽  
2019 ◽  
Vol 9 (6) ◽  
pp. 312 ◽  
Author(s):  
Xianfeng Ma ◽  
Jishen Jiang ◽  
Wenjie Zhang ◽  
Hui-ji Shi ◽  
Jialin Gu
Keyword(s):  
Crack Propagation ◽  
Single Crystal ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Initiation Site ◽  
Single Crystal Superalloy ◽  
Cycle Fatigue ◽  
Intergranular Cracking

This paper aims to understand the effect of local recrystallization (RX) on the low cycle fatigue fracture of a turbine-blade single crystal nickel-based superalloy. The fatigue life of the single crystal superalloy was evidently decreased by local recrystallization. In single crystal specimens, casting porosity is the preferential fatigue crack initiation site, which is followed by crystallographic crack propagation along one or several octahedral slip planes. For all RX specimens, fatigue cracks preferred to initiate from local recrystallized grains and propagated through the recrystallized grains in a transgranular manner, followed by crystallographic crack propagation in the substrate single crystal superalloy. Moreover, fatigue tests indicated that locally recrystallized specimens exhibited temperature dependent fracture modes, i.e., transgranular cracking dominated at 550 °C, whereas intergranular cracking was preferred at 850 °C. Evident oxidation of fracture surfaces and strength degradation of grain boundaries at 850 °C was evidenced by scanning electronic microscopic observations. The present study emphasized the need to evaluate the effect of recrystallization according to the working conditions of turbine components, i.e., the local temperature.

scholarly journals Low-Cycle Fatigue Crack Initiation Simulation and Life Prediction of Powder Superalloy Considering Inclusion-Matrix Interface Debonding

Materials ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 4018
Author(s):  
Shuming Zhang ◽  
Yuanming Xu ◽  
Hao Fu ◽  
Yaowei Wen ◽  
Yibing Wang ◽  
...  
Keyword(s):  
Finite Element ◽  
Crack Initiation ◽  
Life Prediction ◽  
Damage Mechanics ◽  
Low Cycle Fatigue ◽  
Fatigue Crack Initiation ◽  
Fatigue Loading ◽  
Interface Debonding ◽  
Damage Evolution Equation ◽  
Finite Element Software

From the perspective of damage mechanics, the damage parameters were introduced as the characterizing quantity of the decrease in the mechanical properties of powder superalloy material FGH96 under fatigue loading. By deriving a damage evolution equation, a fatigue life prediction model of powder superalloy containing inclusions was constructed based on damage mechanics. The specimens containing elliptical subsurface inclusions and semielliptical surface inclusions were considered. The CONTA172 and TARGE169 elements of finite element software (ANSYS) were used to simulate the interfacial debonding between the inclusions and matrix, and the interface crack initiation life was calculated. Through finite element modeling, the stress field evolution during the interface debonding was traced by simulation. Finally, the effect of the position and shape size of inclusions on interface debonding was explored.

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