Investigation of the Stress Fields Around a Fatigue Crack in Aluminium Alloy 5091

2008 ◽  
Vol 571-572 ◽  
pp. 119-124 ◽  
Author(s):  
M. Rahman ◽  
Michael E. Fitzpatrick ◽  
Lyndon Edwards ◽  
S. Pratihar ◽  
Matthew J. Peel ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Aluminium Alloy ◽  
Crack Tip ◽  
Fatigue Loading ◽  
Compact Tension ◽  
European Synchrotron Radiation Facility ◽  
Stress Fields ◽  
Small Scale ◽  
X Ray Diffraction ◽  
X Ray

There have been many theoretical studies to predict the stress fields around the tip of a growing fatigue crack. However, until recently the highly-localized, small scale nature of the stresses has meant that direct measurement has not been possible. With the current generation of synchrotron X-ray sources, sub-millimetre sampling dimensions are now possible, and it has become possible to evaluate directly the stresses at the tip of a fatigue crack and to see how the stresses evolve as the result of an overload, for example. In this paper we present results of synchrotron X-ray diffraction analysis of the stress fields around a fatigue crack in aluminium alloy 5091 (Al-Mg-Li-C-O); this is a dispersion-strengthened alloy with a fine grain size, which makes it ideal for such experiments. Compact tension (CT) specimens were prepared with constant amplitude fatigue loading. The energy dispersive X-ray diffraction (EDXRD) technique was used for measuring strains around the crack tip along the mid thickness of the specimen under in-situ loading. The measurement was carried out at the ESRF (European Synchrotron Radiation Facility), Grenoble, France on the ID15A beam line. The experimental crack tip stresses have been compared with the analytical fracture mechanics solution.

scholarly journals The study of redistribution in residual stresses during fatigue crack growth

2021 ◽  
Vol 15 (4) ◽  
pp. 8565-8579
Author(s):  
Mohammad Noghabi ◽  
I. Sattari-far ◽  
H. Hosseini Toudeshky
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Residual Stresses ◽  
Crack Growth ◽  
Crack Tip ◽  
Side Surface ◽  
Fatigue Loading ◽  
Compact Tension ◽  
Fracture Parameter ◽  
Residual Stress Field

Numerical and experimental study was conducted on fatigue crack growth (FCG) of metallic components to investigate the redistribution of mechanical residual stresses during FCG. To this end, the compact tension specimens of an aluminium alloy were used. In addition, mechanical residual stresses were introduced near the crack tip by applying compressive and tensile loads, followed by visually observing the side-surface of the specimens to estimate the crack growth length. In the numerical simulation, cyclic J-integral was used as the crack growth fracture parameter and a good agreement was observed between the numerical and experimental results. The results of the finite element method demonstrated a clear redistribution of mechanical residual stresses during FCG. After a few cycles, the residual stress field around the crack tip reached a lower magnitude value confined in a smaller zone, although this zone was stable during the remaining fatigue process. Finally, present study evaluated the effect of stress ratio, load amplitude, and initial residual stresses level on the redistribution of residual stresses. It was observed that the residual stresses are mainly released during the first steps of fatigue loading.

Applicability of Precracked Charpy Specimens for Determining Fatigue Crack Growth and J-R Properties: Experiments and Assessment of K and J Dominance

2014 ◽  
Author(s):  
Gustavo Henrique B. Donato ◽  
Rodrygo Figueiredo Moço ◽  
Tatiane Rossi Merlo
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Driving Forces ◽  
Crack Tip ◽  
Structural Steels ◽  
Stress Fields ◽  
Small Scale ◽  
Main Challenge

Structural integrity assessments regarding Fatigue Crack Growth (FCG) and fracture phenomena are based on fracture mechanics theoretical background and rely upon the notion that a single parameter (usually K or J, respectively for linear elastic and elastic-plastic fracture mechanics) characterizes the crack-tip stress fields and controls local damage. However, the validity of K/J as crack-tip driving forces representative of local stress fields is only achieved if SSY (Small Scale Yielding) conditions prevail. It means that plasticity ahead of the crack must be small. Current standards (e.g.: ASTM E399, E1820, E647, ISO 12135) impose severe geometrical restrictions for the specimens (minimum thicknesses and crack depths) looking for plane strain (high constraint) conditions and therefore K and J-dominance. The main challenge is that thicknesses and/or planar dimensions of current real structures made of high toughness structural steels are in several cases not enough for the extraction of “valid” C(T), SE(B) or SE(T) specimens. In this context, subsized specimens are of great interest. As an example, Charpy geometries have been investigated during the last decades. This work is concerned about testing high structural steels and investigates the applicability of fatigue-precracked Charpy specimens for determining FCG (da/dN vs. ΔK) and J-R curves. The main issues are: i) verify the feasibility of the experiments in a servohydraulic machine in terms of scatter, control and repeatability; ii) quantify the validity limits of K and J for such reduced geometries. Samples had notches machined by EDM and were precracked reaching a/W=0.25 and a/W=0.45. FCG and J-R tests were successfully conducted with repeatability and refined 3D non-linear FE models were developed to provide compliance solutions and verify K and J dominance. Consequently, mechanical properties from subsized samples could be obtained and compared to data obtained from standardized C(T) specimens made of the same steel. The applicability of precracked Charpy geometry could be investigated, motivating further investigations in the field.

EndoFEM Crack Closure Analysis of AL2024-T3 CCT Specimen Under All Tension Fatigue Loading

2000 ◽  
Vol 16 (4) ◽  
pp. 203-215
Author(s):  
C. F. Lee ◽  
L. T. Hsiao
Keyword(s):  
Fatigue Crack ◽  
Crack Length ◽  
Crack Closure ◽  
Crack Opening ◽  
Crack Tip ◽  
Fatigue Loading ◽  
Cyclic Plasticity ◽  
Small Scale ◽  
Element Analysis ◽  
Element Mesh

ABSTRACTThe endochronic cyclic plasticity with finite element analysis (EndoFEM) is employed to simulate plasticity-induced crack closure phenomenon of Al 2024-T3 CCT specimens under maximum cyclic stress of 80MPa and 0.1 stress ratio (R). Various fatigue crack lengths are generated by a rc dominated-node-released strategy. The suitability of element-mesh planning around crack tip is supported by the real simulations in the decreasing tendencies of crack opening load (Pop) with increased distance behind the crack tip, and the enough elements to reflect the reversed plastic responses at minimum load.EndoFEM results of vertical stress ahead of the crack tip show a typical distribution of small scale yield (SSY) in the realm of fracture mechanics; and Pop/Pmax ratio determined at 1mm behind crack tip is kept constant i.e. Kmax-independent. In these cases, fatigue parameters based on either the far field loading parameter ΔK, the effective ΔK (ΔKeff) with crack closure effect, or the mechanical responses ahead of crack tip (e.g. stress parameter, reversed (plastic) strain at 1mm) are all equivalent and are linearly correlated with the stage II fatigue crack growth (FCP) rate. However, for longer crack length with the ligament bending effect or shorter crack length with the starter notch effect, the Pop/Pmax ratio decreases and changes the SSY stress distribution. This result reduces the usefulness of the above fatigue parameters. As a consequence, a nonlinear correlation of FCP rates with ΔK or ΔKeff are purely empirical. The Kmax-dependent ΔKeff must be considered in the correlation as suggested by the present study of EndoFEM.

Solid-state Thermoelectric Characteristics of NiII, FeII, CoII, and CuII Borohydrides

2021 ◽  
Author(s):  
Isam M. Arafa ◽  
Mazin Y. Shatnawi ◽  
Yousef N. Obeidallah ◽  
Ahmed K. Hijazi ◽  
Yaser A . Yousef
Keyword(s):  
Energy Transport ◽  
Waste Heat ◽  
Mixed Valence ◽  
Small Scale ◽  
X Ray Diffraction ◽  
Promising Candidate ◽  
X Ray ◽  
Cold Pressed ◽  
Thermal Energy Transport ◽  
Body Heat

Abstract Four transition metal borohydrides (MTBHs, MT = Ni, Fe, Co, and Cu) were prepared by sonicating a mixture of the desired MT salt with excess NaBH4 in a nonaqueous DMF/CH3OH media. The process afforded bimetallic (Ni-BH4), trimetallic (Fe-BH4, Co-BH4), and mixed-valence (Cu-H, Cu-BH4) amorphous, ferromagnetic nanoparticles as identified by thermal, ATR-IR, X-Ray diffraction, and magnetic susceptibility techniques. The electrical conductivity (σ) of cold-pressed discs of these MTBHs shows a nonlinear increase while their thermal conductivity (κ) decreases in the temperature range of 303 ≤ T ≤ 373 K. The thermal energy transport occurs through phonon lattice dynamics rather than electronic. The σ/κ ratio shows a nonlinear steep increase from 9.4 to 270 KV-2 in Ni-BH4, while a moderate-weak increase is observed for Fe-BH4, Co-BH4, and Cu-BH4. Accordingly, the corresponding thermoelectric (TE) parameters S, PF, ZT, and η were evaluated. All TE data shows that the bimetallic Ni-BH4 (S, 80 μVK-1; PF, 259 μWm-1K-2; ZT 0.64; η, 2.56%) is a better TE semiconductor than the other three MT-BHs investigated in this study. Our findings show that Ni-BH4 is a promising candidate to exploit low-temperature waste heat from body heat, sunshine, and small domestic devices for small-scale TE applications.

A Simplified Method Study of Aluminium Alloy Fatigue Crack Tip Parameters Computed by Elastic-Plastic Finite Element Model

2010 ◽  
Vol 97-101 ◽  
pp. 2748-2751
Author(s):  
Xin Song ◽  
Jing Zhong Xiang ◽  
Jia Zhen Zhang
Keyword(s):  
Finite Element ◽  
Fatigue Crack ◽  
Aluminium Alloy ◽  
Crack Tip ◽  
Element Model ◽  
Crack Model ◽  
Dynamic Crack ◽  
Elastic Plastic ◽  
Static Crack ◽  
Element Computation

Fatigue crack propagation of aluminium alloy 7049-OA has been studied by non-linear finite element business-oriented software ABAQUS, and elastic-plastic finite element models of static fatigue crack and dynamic fatigue crack of center crack panel (CCP) specimens are also built. Based on the finite element computation results, the differences of stress and crack opening displacement around crack tip of static crack model have been compared with those of dynamic crack model. The compared results showed that the finite element computation results of dynamic crack model can be replaced by the results calculated by the static crack model. Fatigue crack tip parameters of aluminium alloy CCP specimens can be calculated by elastic-plastic finite element model of static crack. This is an effective method to cut down the computation expense and promote the computational efficiency.

scholarly journals Human insulin polymorphism upon ligand binding and pH variation: the case of 4-ethylresorcinol

IUCrJ ◽  
2015 ◽  
Vol 2 (5) ◽  
pp. 534-544 ◽  
Author(s):  
S. Fili ◽  
A. Valmas ◽  
M. Norrman ◽  
G. Schluckebier ◽  
D. Beckers ◽  
...  
Keyword(s):  
Human Insulin ◽  
Organic Ligand ◽  
European Synchrotron Radiation Facility ◽  
X Ray Diffraction ◽  
Ph Variation ◽  
X Ray ◽  
X Ray Crystallography ◽  
Swiss Light Source ◽  
Crystallization Experiments ◽  
Ph Range

This study focuses on the effects of the organic ligand 4-ethylresorcinol on the crystal structure of human insulin using powder X-ray crystallography. For this purpose, systematic crystallization experiments have been conducted in the presence of the organic ligand and zinc ions within the pH range 4.50–8.20, while observing crystallization behaviour around the isoelectric point of insulin. High-throughput crystal screening was performed using a laboratory X-ray diffraction system. The most representative samples were selected for synchrotron X-ray diffraction measurements, which took place at the European Synchrotron Radiation Facility (ESRF) and the Swiss Light Source (SLS). Four different crystalline polymorphs have been identified. Among these, two new phases with monoclinic symmetry have been found, which are targets for the future development of microcrystalline insulin drugs.

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