scholarly journals Fatigue Behavior of Al 7075-T6 Plates Repaired with Composite Patch under the Effect of Overload

Metals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 2025
Author(s):  
Bel Abbes Bachir Bouiadjra ◽  
S. M. A. K. Mohammed ◽  
Faycal Benyahia ◽  
Abdulmohsen Albedah
Keyword(s):  
Crack Growth ◽  
Fatigue Behavior ◽  
Adhesive Layer ◽  
Fatigue Tests ◽  
Thin Plates ◽  
Composite Patch ◽  
Al 7075 ◽  
Number Of Cycles ◽  
Aluminum Alloy 7075 ◽  
Cycles To Failure

Repair of aeronautical structures by composite patch bonding has shown its effectiveness in several studies during the last few decades. This repair technique leads to a retardation in the propagation of repaired cracks via load bridging across the patch throughout the adhesive layer, interfacing it with the repaired structure. The purpose of this study is to analyze the behavior of patch-repaired cracks present in thin plates made of aluminum alloy 7075-T6 and subjected to a single tensile overload. The sequence of application of overload on the fatigue behavior was also studied. Fatigue tests were conducted on Al 7075-T6 notched specimens where crack growth and number of cycles to failure were monitored for different patching/overload scenarios. A detailed fractographic study was performed on failed specimens to analyze the micromechanical behavior of the crack growth related to each scenario. The obtained results showed that the application of the overload before bonding the patch leads to an almost infinite fatigue life of the repaired plates.

Unification proposals for fatigue crack propagation laws

2017 ◽  
Vol 13 (2) ◽  
pp. 262-283 ◽  
Author(s):  
Vladimir Kobelev
Keyword(s):  
Differential Equation ◽  
Crack Propagation ◽  
Crack Length ◽  
Closed Form ◽  
Crack Growth ◽  
Stress Ratio ◽  
Elementary Functions ◽  
Content Type ◽  
Number Of Cycles ◽  
Cycles To Failure

Purpose The purpose of this paper is to propose the new dependences of cycles to failure for a given initial crack length upon the stress amplitude in the linear fracture approach. The anticipated unified propagation function describes the infinitesimal crack-length growths per increasing number of load cycles, supposing that the load ratio remains constant over the load history. Two unification functions with different number of fitting parameters are proposed. On one hand, the closed-form analytical solutions facilitate the universal fitting of the constants of the fatigue law over all stages of fatigue. On the other hand, the closed-form solution eases the application of the fatigue law, because the solution of nonlinear differential equation turns out to be dispensable. The main advantage of the proposed functions is the possibility of having closed-form analytical solutions for the unified crack growth law. Moreover, the mean stress dependence is the immediate consequence of the proposed law. The corresponding formulas for crack length over the number of cycles are derived. Design/methodology/approach In this paper, the method of representation of crack propagation functions through appropriate elementary functions is employed. The choice of the elementary functions is motivated by the phenomenological data and covers a broad region of possible parameters. With the introduced crack propagation functions, differential equations describing the crack propagation are solved rigorously. Findings The resulting closed-form solutions allow the evaluation of crack propagation histories on one hand, and the effects of stress ratio on crack propagation on the other hand. The explicit formulas for crack length over the number of cycles are derived. Research limitations/implications In this paper, linear fracture mechanics approach is assumed. Practical implications Shortening of evaluation time for fatigue crack growth. Simplification of the computer codes due to the elimination of solution of differential equation. Standardization of experiments for crack growth. Originality/value This paper introduces the closed-form analytical expression for crack length over number of cycles. The new function that expresses the damage growth per cycle is also introduced. This function allows closed-form analytical solution for crack length. The solution expresses the number of cycles to failure as the function of the initial size of the crack and eliminates the solution of the nonlinear ordinary differential equation of the first order. The different common expressions, which account for the influence of the stress ratio, are immediately applicable.

scholarly journals Mechanical Fatigue of Bovine Cortical Bone Using Ground Reaction Force Waveforms in Running

2018 ◽  
Vol 140 (3) ◽  
Author(s):  
Lindsay L. Loundagin ◽  
Tannin A. Schmidt ◽  
W. Brent Edwards
Keyword(s):  
Cortical Bone ◽  
Stress Fracture ◽  
Ground Reaction Force ◽  
Fatigue Behavior ◽  
Reaction Force ◽  
High Impact ◽  
Loading Rates ◽  
Mechanical Fatigue ◽  
Number Of Cycles ◽  
Cycles To Failure

Stress fractures are a common overuse injury among runners associated with the mechanical fatigue of bone. Several in vivo biomechanical studies have investigated specific characteristics of the vertical ground reaction force (vGRF) in heel-toe running and have observed an association between increased loading rate during impact and individuals with a history of stress fracture. The purpose of this study was to examine the fatigue behavior of cortical bone using vGRF-like loading profiles, including those that had been decomposed into their respective impact and active phase components. Thirty-eight cylindrical cortical bone samples were extracted from bovine tibiae and femora. Hydrated samples were fatigue tested at room temperature in zero compression under load control using either a raw (n = 10), active (n = 10), low impact (n = 10), or high impact (n = 8) vGRF profile. The number of cycles to failure was quantified and the test was terminated if the sample survived 105 cycles. Fatigue life was significantly greater for both impact groups compared to the active (p < 0.001) and raw (p < 0.001) groups, with all low impact samples and 6 of 8 high impact samples surviving 105 cycles. The mean (± SD) number of cycles to failure for the active and raw groups was 12,133±11,704 and 16,552±29,612, respectively. The results suggest that loading rates associated with the impact phase of a typical vGRF in running have little influence on the mechanical fatigue behavior of bone relative to loading magnitude, warranting further investigation of the mechanism by which increased loading rates are associated with stress fracture.

Development of Predictive Models for Fatigue Crack Growth in Rails

2011 ◽  
Vol 488-489 ◽  
pp. 13-16
Author(s):  
Antonio De Iorio ◽  
Marzio Grasso ◽  
George Kotsikos ◽  
F. Penta ◽  
G. P. Pucillo
Keyword(s):  
Crack Growth ◽  
Fatigue Behavior ◽  
Service Condition ◽  
Fatigue Tests ◽  
Analytical Models ◽  
The Finite Element Method ◽  
Stress Concentrations ◽  
Initiation Point ◽  
Fatigue Failures ◽  
The Web

Fatigue failures of rails often occur at the rail foot, since the geometry of this zone gives rise to stress concentrations under service loads or defects during rail manufacture and installation. In this paper, the fatigue behavior of cracks at the web/foot region of a rail is analyzed numerically. Analytical models in the literature for a semi-elliptical surface crack in a finite plate assume that the geometry of the front remains semi-elliptical during the whole propagation phase and the ellipse axes do not undergo translations or rotations. Fatigue tests show that this is not the case for such cracks in rails. A predictive model for crack growth has been developed by assuming an initial small crack at one probable initiation point between the web and foot of the rail in reference to a service condition loading. SIF values have been estimated by means of the finite element method and the plastic radius correction. The results attained were compared with crack growth experimental data.

Effect of Roller-Working on Fatigue Strength Improvement of Notched Structural Stainless Steel

2006 ◽  
Vol 306-308 ◽  
pp. 151-156
Author(s):  
Priyo Tri Iswanto ◽  
Shinichi Nishida ◽  
Nobusuke Hattori ◽  
Yuji Kawakami
Keyword(s):  
Plastic Deformation ◽  
Stainless Steel ◽  
Fatigue Limit ◽  
Fatigue Behavior ◽  
Fatigue Tests ◽  
Mean Stress ◽  
Increase With Increase ◽  
Fatigue Strength Improvement ◽  
Rolled Specimen ◽  
Number Of Cycles

In order to study the effect of plastic deformation on fatigue behaviors of plastically deformed specimen, bending fatigue tests had been performed on notched deformed stainless steel specimens. Also pulsating fatigue tests were done on notched non-deformed specimens to evaluate the influence of mean stress on fatigue behavior of notched non-deformed specimens. The result showed that according to increase of deformation value, the fatigue limits of these specimens also significantly increase. Fatigue limit of rolled specimen does not linearly increase with increase in plastic deformation value. Based on fatigue limit diagram, the effect of compressive residual stress on fatigue limit improvement of stainless steel is higher than that of work-hardening. In case of non-deformed specimen, when the compressive mean stress increases, the fatigue limit and the number of cycles to failure increase. In case of tensile mean stress, this kind of mean stress decreases the fatigue limit.

Combination of Cyclic Fatigue Testing and Materials Characterisation to Investigate Ageing of Elastomers

2017 ◽  
Vol 44 (4) ◽  
pp. 1-8 ◽  
Author(s):  
T. Kroth ◽  
D. Lellinger ◽  
I. Alig ◽  
M. Wallmichrath
Keyword(s):  
Fatigue Life ◽  
Molecular Mass ◽  
Fatigue Testing ◽  
Cyclic Fatigue ◽  
Chain Scission ◽  
Thermal Ageing ◽  
Fatigue Tests ◽  
Additive Package ◽  
Number Of Cycles ◽  
Cycles To Failure

Cyclic fatigue testing and elastomer characterisation were combined to study changes in material properties and network structure of elastomers during thermal ageing. Natural rubber containing a typical additive package with carbon black was studied as a model material. The samples were aged at different temperatures in air or under a nitrogen atmosphere. The fatigue life in number of cycles to failure (S-N curves) was determined from force- and displacement-controlled fatigue tests on tensile bar specimens after different thermal ageing times. Changes in mechanical properties and crosslink density were studied by tensile tests, dynamic mechanical analysis, stress relaxation experiments, compression set measurements, swelling measurements and solid-state NMR. Changes in network density during thermal ageing are related to the interplay between the formation of new crosslinks and chain scission. The average molecular mass of the network chains was found to be a suitable parameter for comparing different characterisation methods. An initial decrease in the molecular mass between two crosslinking points due to post-curing is followed by an increase due to chain scission. A similar trend was found for fatigue life in number of cycles to failure (N) in force-controlled fatigue tests: an increase in N for short ageing times is followed by a decrease after longer ageing times.

Optimization of composite patch repair for maximum stability of crack growth in an aluminum plate

2016 ◽  
Vol 231 (20) ◽  
pp. 3690-3701
Author(s):  
B Talebi ◽  
A Abedian
Keyword(s):  
Finite Element ◽  
Crack Growth ◽  
Cohesive Zone Model ◽  
Adhesive Layer ◽  
Patch Repair ◽  
Aluminum Plate ◽  
Uniaxial Tensile ◽  
Zone Model ◽  
Composite Patch ◽  
The Stability

In this paper, the configuration parameters of pre-designed composite patch repair are optimized with the aim of achieving the highest level of stability of crack growth in aluminum in the presence of some constraints such as weight, load sustainability, shear stress in the adhesive layer and maximum stress in the patch. For this purpose, the patch is modeled in full scale by ABAQUS, a commercial finite element code. The crack growth process is simulated with the extended finite element method under uniaxial tensile loading, and the Cohesive Zone Model is used to model the progressive damage in the adhesive of the composite patch repair. Also, sensitivity analysis is performed on the configuration parameters and it is shown that three parameters, i.e. width, stiffness ratio, and height of the patch are more important. Nonlinear fracture mechanics concepts have been used in calculating the stability of crack in the cracked aluminum plate. The results show that optimization based on the method proposed in this paper causes the stability of crack growth to increase by 21% while the patch weight is reduced by 52%.

A Multi-Station Rolling/Sliding Tribotester for Knee Bearing Materials

2004 ◽  
Vol 126 (2) ◽  
pp. 380-385 ◽  
Author(s):  
Douglas W. Van Citters ◽  
Francis E. Kennedy ◽  
John H. Currier ◽  
John P. Collier ◽  
Thomas D. Nichols
Keyword(s):  
Material Properties ◽  
Normal Load ◽  
Fatigue Behavior ◽  
Water Environment ◽  
Fatigue Tests ◽  
Test Environment ◽  
Normal Contact ◽  
Bearing Materials ◽  
Number Of Cycles

Total joint replacements traditionally employ ultra high molecular weight polyethylene (UHMWPE) as a bearing material due to its desirable material properties and biocompatibility. Failure of these polyethylene bearings can lead to expensive and risky revision surgery, necessitating a better understanding of UHMWPE’s tribological properties. A six-station rolling/sliding machine was developed to study the behavior of accelerated-aged UHMWPE in cylinder-on-cylinder contact. The normal load and sliding/rolling ratio in the oscillatory contacts can be controlled separately for each test station, as can the liquid test environment. Fatigue tests were run on the machine with UHMWPE versus cobalt-chrome cylinders in a distilled water environment at normal contact pressures of approximately 20 MPa. All specimens failed by subsurface cracking during tribotesting on the machine, and the failures were similar to those that occur in-vivo. The fatigue behavior of the polymer was analyzed to determine its relationship to oxidation and stress state in the rolling/sliding cylinder. At the 20 MPa test load, the number of cycles to fatigue failure by subsurface cracking was inversely proportional to the oxidation level. Analysis of the stress levels through the bulk of the polyethylene specimens and their relationship to the material properties provide insight as to why cracks initiate and propagate subsurface.

Experimental fatigue behavior of carbon/flax hybrid composites under tensile loading

2020 ◽  
pp. 002199832095490
Author(s):  
Mariem Ben Ameur ◽  
Abderrahim El Mahi ◽  
Jean-Luc Rebiere ◽  
Moez Beyaoui ◽  
Moez Abdennadher ◽  
...  
Keyword(s):  
Volume Fraction ◽  
Hybrid Composites ◽  
Fatigue Behavior ◽  
Damping Ratio ◽  
Hysteresis Loops ◽  
Tensile Loading ◽  
Fatigue Tests ◽  
Dissipated Energy ◽  
Fiber Volume ◽  
Number Of Cycles

The aim of the present study is to investigate the mechanical behavior of carbon/flax hybrid composites under static and fatigue tensile loading. The failure characteristics and parameters used in the fatigue tests were deduced from the static ones. The effect of the applied stress level, hybridization and stacking sequences on the stiffness, hysteresis loops, dissipated energy and damping, were studied for a various number of cycles during fatigue tests. The Wohler S-N curves were constructed to investigate the effect of hybridization on the fatigue behavior. The results obtained show that the fatigue performance as well as the fatigue resistance increase with the increase of the volume fraction of carbon fiber. Nevertheless, the damping ratio and the fatigue life increase with the increase of the flax fiber volume fraction.

Fatigue Tests on Aluminum Specimens Subjected to Constant and Random Amplitude Loadings

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Morteza Rahimi Abkenar ◽  
David P. Kihl ◽  
Majid T. Manzari
Keyword(s):  
Fatigue Life ◽  
Aluminum Alloys ◽  
Cyclic Stress ◽  
Fatigue Tests ◽  
Test Results ◽  
Number Of Cycles ◽  
Mechanical Devices ◽  
Cycles To Failure ◽  
Amplitude Versus ◽  
Weight Structures

Increasing interest in using aluminum as the structural component of light-weight structures, mechanical devices, and ships necessitates further investigations on fatigue life of aluminum alloys. The investigation reported here focuses on characterizing the performance of cruciform-shaped weldments made of 5083 aluminum alloys in thickness of 9.53 mm (3/8 in.) under constant, random, and bilevel amplitude loadings. The results are presented as S/N curves that show cyclic stress amplitude versus the number of cycles to failure. Statistical procedures show good agreements between test results and predicted fatigue life of aluminum weldments. Moreover, the results are compared to the results obtained from previous experiments on aluminum specimens with thicknesses of 12.7 mm (1/2 in.) and 6.35 mm (1/4 in.).

scholarly journals An Updated Review of the Fatigue Behavior of Components Coated with Thin Hard Corrosion-Resistant Coatings

2014 ◽  
Vol 8 (1) ◽  
pp. 87-98 ◽  
Author(s):  
Sergio Baragetti ◽  
Francesco Villa
Keyword(s):  
Numerical Models ◽  
Fatigue Behavior ◽  
Hard Coatings ◽  
Current Application ◽  
Current State ◽  
Numerical Characterization ◽  
Number Of Cycles ◽  
Corrosion Resistant Coatings ◽  
Cycles To Failure

In the present manuscript, an extended review on the state of the art on the experimental and numerical characterization of the fatigue behavior of Physically Vapor Deposited (PVD) and Chemically Vapor Deposited (CVD) thin hard coatings is presented. The current application and development fields of PVD and CVD treatments are analysed, focusing on the advantages granted by the adoption of these coatings for corrosion protection on various materials and components. The most recent experimental research results related to the fatigue behavior of PVD and CVD coated specimens are reported. Fatigue strength values are presented for various coating processes on different substrates, including hard steel as well as aluminium and titanium light alloys. Corrosion fatigue effects on coated specimens are presented where available, in order to evaluate the coating effectiveness in aggressive environments. An overview on the current state of development of theoretical and numerical models for the characterization of coated components and for the maximum number of cycles to failure is proposed to the reader.

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