scholarly journals Fatigue size effect due to defects in an AA7050 alloy

2018 ◽  
Vol 165 ◽  
pp. 14015 ◽  
Author(s):  
Foued Abroug ◽  
Etienne Pessard ◽  
Guénaël Germain ◽  
Franck Morel
Keyword(s):  
Size Effect ◽  
Scale Effect ◽  
Surface Defects ◽  
Probabilistic Approach ◽  
Fatigue Crack Initiation ◽  
Size Difference ◽  
Weakest Link ◽  
Fatigue Design ◽  
Artificial Surface ◽  
Crack Initiation Criterion

One objective of this project is to propose a fatigue design approach that is able to account for a large range of machining surface defects and different component sizes and geometries. Due to the huge size difference between a typical fatigue specimen and large aircraft components it was first necessary to confirm if a size effect can indeed be observed. This was done by introducing different numbers of artificial surface defects on smooth specimens. The material investigated is a 7050 Aluminium alloy (Al Zn6CuMgZr). Plane bending specimens both without and with artificial hemispherical surface defects were tested. The number of defects was varied from 1 to 44 defects per specimen and the defect size ranged from 60 μm to 800 μm in diameter. The test results allow the characterization of both the defect effect and scale effect on the fatigue response of the material. A probabilistic approach based on the weakest link concept together with a proper fatigue crack initiation criterion is used to account for the stress distribution and the size of the highly stressed volume. Predictions using FE simulations show a good agreement with experimental results and illustrate the importance of taking the scale effect into account in HCF.

scholarly journals Defect induced cracking and modeling of fatigue strength for an additively manufactured Ti-6Al-4V alloy in very high cycle fatigue regime

2021 ◽  
Author(s):  
Weiqian Chi ◽  
Wenjing Wang ◽  
Chengqi Sun
Keyword(s):  
Fatigue Strength ◽  
Crack Initiation ◽  
High Cycle Fatigue ◽  
Surface Defects ◽  
Fatigue Crack Initiation ◽  
Projection Area ◽  
Cycle Fatigue ◽  
Very High Cycle Fatigue ◽  
Artificial Surface ◽  
Very High

Additively manufactured (AM) alloy usually inevitably contains defects during the manufacturing processor or service process. Defects, as a harmful factor, could significantly reduce the fatigue performance of materials. This paper shows that the location and introduced form of defects play an important role in high cycle and very high cycle fatigue (VHCF) behavior of selective laser melting Ti-6Al-4V alloy. S-N curve descends linearly for internal defects induced failure. While for artificial surface defects induced failure, S-N curve descends at first and then exhibits a plateau region feature. We also observed competition of interior crack initiation with the fine granular area feature in VHCF regime. The paper indicates that only the size or the stress intensity factor range of the defect is not an appropriate parameter describing the effect of defects on the fatigue crack initiation. Finally, the effect of artificial surface defects on high cycle and VHCF strength is modeled, i.e. the fatigue strength   σ, fatigue life  N and defect size area (square root of projection area of defect perpendicular to principal stress direction) is expressed as  σ = CN ( area)  for  N and  σ = CN ( area)  for  N≥N, where  C,  a and  n are constants, N is the number of cycles at the knee point.

scholarly journals DEPENDENCE OF CREEP FAILURE PROBABILITY ON THE SIZE OF METALLIC SPECIMENS

2013 ◽  
Vol 7 (3) ◽  
pp. 166-169
Author(s):  
Krzysztof Nowak
Keyword(s):  
Size Effect ◽  
Scale Effect ◽  
Failure Probability ◽  
Experimental Verification ◽  
Experimental Analysis ◽  
Numerical Models ◽  
Creep Failure ◽  
Weakest Link ◽  
Link Model

Abstract The occurrence of statistical size effect is considered for damage in creep conditions. The numerical and experimental analysis have been performed. The obtained results are ambiguous. Numerical models confirm the scale effect which can be statistical or deterministic one. But this effect has no experimental verification. It may suggest that the weakest link model cannot be applied in creep conditions. Explanation of this needs further investigations

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.

Influence of Inner Surface Defects on the Fatigue Strength of Pipe Subjected to Cyclic Internal Pressure

1978 ◽  
Vol 100 (4) ◽  
pp. 360-368
Author(s):  
Y. Yazaki ◽  
S. Hashirizaki ◽  
S. Nishida ◽  
C. Urashima
Keyword(s):  
Fatigue Strength ◽  
Internal Pressure ◽  
Test Specimen ◽  
Surface Defects ◽  
Fatigue Crack Initiation ◽  
Internal Surface ◽  
Fatigue Tests ◽  
Inner Surface ◽  
Surface Notch ◽  
Medium Diameter

Cyclic internal oil pressure fatigue tests were carried out on medium-diameter ERW pipes of API 5LX - X60 in an attempt to determine the influence of surface defects on the fatigue strength. Experimental factors investigated were the depth and location of internal surface notch in relation to the axis of pipe. The specimen was subjected to cyclic internal pressure, the cyclic rate being 0.3–0.5 Hz. During the test, Acoustic Emission (AE) techniques were applied to detect the fatigue crack initiation. Along with the aforementioned fatigue tests, pulsating tension fatigue tests were carried out on specimens with the same surface notches as the cyclic internal pressure fatigue test specimen.

Reassessing the atomic size effect on glass forming ability: Effect of atomic size difference on thermodynamics and kinetics

2016 ◽  
Vol 69 ◽  
pp. 123-127 ◽  
Author(s):  
Hyung-Seop Han ◽  
Nayoung Park ◽  
Jin-Yoo Suh ◽  
Ho-Seok Nam ◽  
Hyun-Kwang Seok ◽  
...  
Keyword(s):  
Size Effect ◽  
Glass Forming Ability ◽  
Size Difference ◽  
Atomic Size ◽  
Glass Forming ◽  
Thermodynamics And Kinetics ◽  
Atomic Size Difference

Fatigue Life Prediction of Vortex Reducer Based on Stress Gradient

2018 ◽  
Author(s):  
Yanbin Luo ◽  
Yanrong Wang ◽  
Bo Zhong ◽  
Jiazhe Zhao ◽  
Xiaojie Zhang
Keyword(s):  
Fatigue Life ◽  
Size Effect ◽  
Stress Gradient ◽  
Fatigue Crack Initiation ◽  
High Stress ◽  
Stress Effect ◽  
Mean Stress ◽  
Notched Specimens ◽  
Life Model ◽  
The Mean

The effects of stress gradient and size effect on fatigue life are investigated based on the distributions of stress at notch root of the notched specimens of GH4169 alloy. The relationship between the life of the notched specimens and the smooth specimens is correlated by introducing the stress gradient effect factor, and a new life model of predicting the notched specimens based on the Walker modification for the mean stress effect is established. In order to improve the prediction precision of life model with the equation parameters having a definite physical significance, the relationships among fatigue parameters, monotonic ultimate tensile strength and reduction of area are established. Three-dimensional elastic finite element (FE) analysis of a vortex reducer is carried out to obtain the data of stress and strain for predicting its life. The results show that there is a high-stress gradient at the edge of the air holes of the vortex reducer, and it is thus a dangerous point for fatigue crack initiation. The prediction result of the vortex reducer is more reasonable if the mean stress, stress gradient and size effect are considered comprehensively. The developed life model can reflect the effects of many factors well, especially the stress concentration. The life of the notched specimens predicted by this model give a high estimation precision, and the prediction life data mainly fall into the scatter band of factor 2.

scholarly journals Fatigue strength characterization of Al-Si cast material incorporating statistical size effect

2018 ◽  
Vol 165 ◽  
pp. 14002 ◽  
Author(s):  
Roman Aigner ◽  
Martin Leitner ◽  
Michael Stoschka
Keyword(s):  
Size Effect ◽  
Extreme Value Distribution ◽  
Ct Scanning ◽  
Element Analysis ◽  
Cast Material ◽  
Stressed Volume ◽  
Alloy Casting ◽  
Weakest Link ◽  
Testing Region ◽  
Strength Characterization

Cast aluminium components may exhibit material imperfections such as shrinkage and gas pores, or oxide inclusions. Therefore, the fatigue resistance is significantly influenced by the size and location of these inhomogenities. In this work, two different specimen geometries are manufactured from varying positions of an Al-Si-Cu alloy casting. The specimen geometries are designed by means of shape optimization based on a finite element analysis and exhibit different highly-stressed volumes. The numerically optimized specimen curvature enforces a notch factor of only two percent. To enable the evaluation of a statistical size effect, the length of the constant testing region and hence, the size of the highly-stressed volume varies by a ratio of one to ten between the two specimen geometries. Furthermore, the location of the crack initiation is dominated by the comparably greatest defects in this highly-stressed volume, which is also known as Weibull’s weakest link model. The crack initiating defect sizes are evaluated by means of light microscopy and modern scanning electron microscope methods. Finally, the statistical size effect is analysed based on the extreme value distribution of the occurring defects, whereby the size and location of the pores is non-destructively obtained by computed tomography (CT) scanning. This elaborated procedure facilitates a size-effect based methodology to study the defect distribution and the associated local fatigue life of CPS casted Al-Si lightweight components.

Studies on the grinding force, size effect, surface texture, and mechanism of material removal in the grinding of AA6061-TiB2/ZrB2 in situ composite

2019 ◽  
Vol 2 (2) ◽  
pp. 152-166
Author(s):  
A. Mahamani
Keyword(s):  
Size Effect ◽  
Surface Integrity ◽  
Material Removal ◽  
Surface Defects ◽  
Aluminum Matrix ◽  
Grinding Force ◽  
Aluminum Matrix Composites ◽  
Matrix Composites ◽  
Grinding Conditions

Machining and conversion of aluminum matrix composites into a desired shape with accuracy has been a challenge for many years. Grinding is a process aimed at achieving better-quality surface finish along with reasonable rate of material removal. The present article describes the influence of operating parameters on the tangential grinding force, size effect, and surface integrity in the grinding of in situ aluminum matrix composites using various grinding wheels. The material removal mechanism of the in situ composite under different grinding conditions is established. Experimental results show that the grinding operating parameters have significant influence on the tangential grinding force, size effect, surface integrity, and material removal. Scanning electron and atomic force microscopy findings indicate presence of numerous surface defects on the grounded surface under all grinding conditions. Diamond grinding wheel outperformed the CBN and Al2O3 wheels by requiring lower grinding force and specific grinding energy and generating lower surface defects. Surface defects, including grinding striation, delamination, and ridge formation are unavoidable under all machining conditions. However, the aforementioned surface defects indicate the ductile mode of material removal at all experimental conditions. Undeformed chip thickness under various grinding conditions plays a significant role in material removal and surface generation. These findings help to understand the mechanism of material removal in machining of in situ composites under various grinding conditions, which helps in attaining the economic production rate without compromising the surface integrity.

Fatigue design of railway wheels: a probabilistic approach

2014 ◽  
Vol 37 (10) ◽  
pp. 1136-1145 ◽  
Author(s):  
C. Roux ◽  
X. Lorang ◽  
H. Maitournam ◽  
M. L. Nguyen-Tajan
Keyword(s):  
Probabilistic Approach ◽  
Fatigue Design ◽  
Railway Wheels
Sign in / Sign up

Export Citation Format

Share Document