Fatigue Life Prediction of Microstructures

2012 ◽  
Author(s):  
Gustavo M. Castelluccio ◽  
David L. McDowell
Keyword(s):  
Grain Size ◽  
Life Prediction ◽  
High Cycle Fatigue ◽  
Crack Formation ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Modeling Framework ◽  
Small Cracks ◽  
Engineering Alloys ◽  
Bimodal Grain Size

The formation and early growth of fatigue cracks in the high cycle fatigue regime is influenced by microstructuctural features such as grain size and morphological and crystallographic texture. However, most fatigue models do not predict the influence of the microstructure on early stages of crack formation, or they employ parameters that should be calibrated with experimental data from specimens with microstructures of interest. These post facto strategies are adequate to characterize materials, but they are not fully appropriate to aid in the design of fatigue-resistant engineering alloys. This paper presents a modeling framework that facilitates relative assessment of fatigue resistance among different microstructures. The scheme employs finite element simulations that explicitly render the microstructure and a methodology that estimates transgranular fatigue growth for microstructurally small cracks on a grain-by-grain basis, including consideration of growth within grains (embedded analytically) and stress redistribution as the cracks extend. The methodology is implemented using a crystal plasticity algorithm in ABAQUS and calibrated to study fatigue crack initiation of a bimodal grain size distribution found in RR1000 powder processed Ni-base superalloys for turbine disk applications.

Micromechanics of an Extrusion in High-Cycle Fatigue With Creep

1990 ◽  
Vol 57 (4) ◽  
pp. 815-820 ◽  
Author(s):  
T. H. Lin ◽  
S. R. Lin ◽  
X. Q. Wu
Keyword(s):  
Crack Initiation ◽  
Tensile Strain ◽  
High Cycle Fatigue ◽  
Elevated Temperatures ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Tensor Component ◽  
Shear Stresses ◽  
Cycle Fatigue ◽  
Thin Slice

Extrusions and intrusions often are sites of fatigue cracks. The extent of extrusions is important in fatigue crack initiation. Metals often are subject to fatigue loadings at elevated temperatures. At temperatures below one half of the melting temperature slip is the main mechanism of inelastic deformation. In this study, an aluminum polycrystal loaded in this temperature range is considered. A most favorably oriented crystal located at a free surface of a f.c.c. polycrystal subject to creep under cyclic tension and compression of high-cycle fatigue is considered. An extrusion in this crystal is shown to be produced by a positive slip in one thin slice “P” and a negative slip in a closely located slice “Q”. An initial tensile strain εααI in the thin slice “R” sandwiched between P and Q causes a positive initial shear stress ταβI in P and a negative one in Q. It is shown that the extrusion growth causes a tensile strain in R, which can activate a second slip system giving a creep strain with a tensor component εαα. It has the same effect as the initial strain εααI in causing this difference in shear stresses in P and Q and gives much additional extrusion growth. The extent of intrusion and extrusion is important in this study of crack initiation.

scholarly journals Interactions between geometrical defects and microstructure during high cycle fatigue of polycrystalline aluminium with different grain sizes

2018 ◽  
Vol 165 ◽  
pp. 14004
Author(s):  
Benoît Bracquart ◽  
Charles Mareau ◽  
Nicolas Saintier ◽  
Franck Morel
Keyword(s):  
Grain Size ◽  
Fatigue Crack ◽  
Crack Initiation ◽  
High Cycle Fatigue ◽  
Fatigue Behavior ◽  
Fatigue Crack Initiation ◽  
Cycle Fatigue ◽  
Grain Sizes ◽  
Average Grain Size ◽  
Geometrical Defects

In this work, the influence of the geometrical defect size on the high cycle fatigue behavior of polycrystalline aluminium with different grain sizes is investigated, to better understand the role of internal length scales. Two sizes of grains and defect are used: 100 μm and 1000 μm, the grain size being controlled with thermomechanical treatments. Fully reversed stress-controlled fatigue tests are then carried out. According to fatigue test results, surface crack initiation is delayed when the grain size is reduced, while an approximation of the fatigue limit shows that it is not much influenced by the average grain size. The relative defect diameter (compared to the grain size) seems to be the leading parameter influencing fatigue crack initiation from a defect. Finally, Electron BackScattered Diffraction (EBSD) maps are collected for specimens with large grains and small defects. Fatigue crack initiation from a defect is found to be strongly impacted by the crystallographic orientation of the surrounding grain, crack initiation preferably occurring in crystals being favorably oriented for plastic slip.

The effect of corrosion location relative to local stresses on the fatigue life of geometrically-complex, galvanically corroded AA7075-T6

CORROSION ◽  
10.5006/3908 ◽  
2021 ◽  
Author(s):  
Carly Cocke ◽  
Rebecca Marshall ◽  
Charles Sprinkle ◽  
Adam Goff ◽  
Robert Kelly ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Stress Field ◽  
Crack Formation ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
High Stress ◽  
Corrosion Damage ◽  
Relative Impact ◽  
Fastener Hole ◽  
Macro Scale

Aluminum components used in aerospace structures are commonly coupled with stainless-steel fasteners. These through-hole geometries on the aluminum substrate cause a concentrated stress field. The high-stresses at the fastener sites can preferentially initiate coating damage allowing for moisture ingress which can lead to the formation of a galvanic couple between the aluminum alloy and the stainless-steel fastener. Corrosion damage is known to favorably initiate fatigue cracks thus severely reducing the total life of the component. This work aims to understand the relative impact and interaction of fastener hole geometry induced stress concentrations and corrosion damage on the fatigue crack initiation behavior. Specifically, by imparting various levels of corrosion severities at different locations within the macro-scale stress field, the relative impact of each on the initiation process can be determined. This work demonstrated a dominant role of the macro-scale stress field on the crack formation location. Specifically, crack formation was found to preferentially occur at high stress regions in lieu of forming at lower stress regions, regardless of corrosion severity. Critically, the findings of this work will inform the means by which coatings are evaluated and will serve as a controlled validation of experiments for fracture mechanics modeling.

Simulation and Prediction Method of the Fatigue Cracks Life for Remanufacturing Shaft Parts

2014 ◽  
Vol 684 ◽  
pp. 291-296
Author(s):  
Yan Feng ◽  
Shou Xu Song ◽  
Qing Di Ke
Keyword(s):  
Fatigue Life ◽  
Life Prediction ◽  
Crack Formation ◽  
Fatigue Cracks ◽  
Prediction Method ◽  
Service Condition ◽  
Simulation Method ◽  
Element Analysis ◽  
Relationship Of ◽  
The Relationship

Combining the method of finite element analysis with fatigue life prediction, fatigue cracks on the shaft parts is analyzed with cyclic loading. Analyzing the shafts with different sizes of cracks in different locations, a simulation modal is established. Informed by analytical and numerical simulation method, the crack formation and propagation life could be calculated. With considering the relationship of "Frequency - crack - fatigue life - remanufacturing ", the remanufacturability of the shaft parts might be evaluated based on service condition. And in this paper, a more convenient way to detecting and predicting the fatigue cracks on shaft parts is given.

scholarly journals Experimental Study on Forged TC4 Titanium Alloy Fatigue Properties under Three-Point Bending and Life Prediction

Materials ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5329
Author(s):  
Bohan Wang ◽  
Li Cheng ◽  
Dongchun Li
Keyword(s):  
Titanium Alloy ◽  
Life Prediction ◽  
High Cycle Fatigue ◽  
Fatigue Cracks ◽  
Fracture Morphology ◽  
Fatigue Tests ◽  
Fatigue Properties ◽  
Cycle Fatigue ◽  
Three Point Bending ◽  
Tc4 Titanium Alloy

Ultrasonic fatigue tests of TC4 titanium alloy equiaxed I, II and bimodal I, II obtained by different forging processes were carried out in the range from 105 to 109 cycles using 20 kHz three-point bending. The results showed that the S-N curves had different shapes, there was no traditional fatigue limit, and the bimodal I had the best comprehensive fatigue performance. The fracture morphology was analyzed by SEM, and it was found that the fatigue cracks originated from the surface or subsurface facets, showing a transgranular quasi-cleavage fracture mechanism. EDS analysis showed that the facets were formed by the cleavage of primary α grains, and the fatigue cracks originated from the primary α grain preferred textures, rather than the primary α grain clusters. From the microstructure perspective, the reasons for better equiaxed high-cycle-fatigue properties and better bimodal ultra-high-cycle-fatigue properties were analyzed. The bimodal I fatigue life prediction based on energy was also completed, and the prediction curve was basically consistent with the experimental data.

Research on high cycle fatigue damage characterization of FV520B steel based on the nonlinear Lamb wave

2021 ◽  
pp. 030932472110384
Author(s):  
Pengfei Wang ◽  
Qiwen Zhou ◽  
Bingbing Chen ◽  
Sanlong Zheng ◽  
Chao Wang ◽  
...  
Keyword(s):  
Fatigue Damage ◽  
Room Temperature ◽  
High Cycle Fatigue ◽  
Lamb Waves ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
High Strength ◽  
Cycle Fatigue ◽  
Initial Stage

In this study, high-strength steel FV520B sheets were subjected to high-cycle tensile-tension fatigue experiments at room temperature in order to obtain fatigue-damaged specimens. Then Lamb waves were used to perform nonlinear ultrasonic testing on them to obtain the normalized relative nonlinear coefficients, β′/ β0. The corresponding relationship between β′/ β0 and the percentage of fatigue life was obtained. Finally, the microstructural changes of the damaged samples were observed by a scanning electron microscope in order to explore the correlation mechanism between β′/ β0 and the degree of micro-defects and fatigue damage. The experimental results showed that as the number of fatigue cycles increased, β′/ β0 first slowly rose, then quickly rose to reach a peak, and finally declined, which was consistent with the generation and propagation of dislocations and cracks during fatigue damage. As the length and number of microcracks increased, β′/ β0 also increased, especially in the initial stage of fatigue crack initiation. β′/ β0 was very sensitive to the size of fatigue cracks, so the change of β′/ β0 can be used to detect the degree of early fatigue damage of the material.

scholarly journals Fatigue life research of welded joints in railway girder

2020 ◽  
Vol 7 (2) ◽  
Author(s):  
Kirill Zhunev ◽  
Jurij Murovannyj ◽  
Andrey Yashnov
Keyword(s):  
Fatigue Life ◽  
Welded Joints ◽  
High Cycle Fatigue ◽  
Crack Formation ◽  
Fatigue Cracks ◽  
Moving Load ◽  
Moving Loads ◽  
Reliable Prediction ◽  
Strain Monitoring ◽  
Complex Tensor

Progressive crack formation in welded joints of railway girders requires a reliable prediction of the fatigue life. It was found that the most common fatigue cracks are T-9 and T-10, which are formed in welded joints of vertical stiffeners to the beam web. The service life calculation of such joints, according to guideline, shows overestimated results. To reduce the error, the operational features of these joints were investigated under a moving loads. Stress-strain monitoring was carried out with the help of a small-sized automated tensometric complex «Tensor-MS». In total, 13 trussed and solid-web girders were investigated. As a result, it was found that the beam web near the welded ends of stiffeners subjected to bending deformations, but fatigue curves, obtained under tensile-compressive, are used to calculate the durability of such joints. To increase the reliability of fatigue calculation, laboratory tests were carried out for a high-cycle fatigue of welded specimens, simulating joints with T-9, T-10 cracks. The design and materials of laboratory specimens were assigned similarly to that of the main beams or the floor beams. Analysis of the actual stresses under the moving load revealed the necessary loading conditions for laboratory specimens. Totally, 42 laboratory samples were tested for bending. As a result of the tests, fatigue curves of welded joints were obtained. The results show a decrease in the joints durability by 20–50 % in comparison with the samples tested in tensile-compressive. In addition, as a result of the tests, the dependences of the fatigue cracks growth rate on the maximum cycle stresses were obtained.

Sign in / Sign up

Export Citation Format

Share Document