The influence of GNP and nano-silica additives on fatigue life and crack initiation phase of Al-GFRP bonded lap joints subjected to four-point bending

2021 ◽  
Vol 207 ◽  
pp. 108589
Author(s):  
Pedram Zamani ◽  
Abdolrahman Jaamialahmadi ◽  
Lucas F.M. da Silva
Keyword(s):  
Fatigue Life ◽  
Crack Initiation ◽  
Lap Joints ◽  
Nano Silica ◽  
Initiation Phase ◽  
Four Point Bending

An investigation on fatigue life evaluation and crack initiation of Al-GFRP bonded lap joints under four-point bending

2019 ◽  
Vol 229 ◽  
pp. 111433 ◽  
Author(s):  
Pedram Zamani ◽  
Abdolrahman Jaamialahmadi ◽  
Lucas F.M. da Silva ◽  
Khalil Farhangdoost
Keyword(s):  
Fatigue Life ◽  
Crack Initiation ◽  
Lap Joints ◽  
Four Point Bending ◽  
Life Evaluation ◽  
Fatigue Life Evaluation

scholarly journals Random Load Fatigue Damage Accumulation in Mild Steel

1973 ◽  
Vol 187 (1) ◽  
pp. 285-293 ◽  
Author(s):  
B. C. Fisher ◽  
F. Sherratt
Keyword(s):  
Fatigue Life ◽  
Crack Initiation ◽  
Crack Detection ◽  
High Sensitivity ◽  
Optical Microscope ◽  
Random Loading ◽  
Random Load ◽  
Initiation Phase ◽  
Fatigue Damage Accumulation ◽  
Probability Density Distributions

Using high-sensitivity eddy-current crack detection, quantitative division of fatigue life into two stages has been achieved for a variety of random and constant amplitude loading conditions. The divisions adopted were: Stage A, microcrack initiation and propagation, and Stage B, macrocrack propagation. The results of specimen sectioning and optical microscope work show that this behaviour is physically compatible with the observations of Forsyth (1)‡. It is established under random loading that for a given specimen configuration, the proportion of time spent in stage A behaviour for a given fatigue life remains unaltered for changes in the waveform irregularity factor. This statement applies to two series of tests for loading waveforms of unaltered fundamental p.s.d. (power spectral density) shapes and Gaussian amplitude probability density distributions. It is suggested that the signal maximum peak/r.m.s. ratio is a significant factor in determining the proportion of life spent in crack initiation. Cumulative damage predictions are made using Miner's hypothesis on a basis of positive peak stresses to failure for stage A and stage B lives, and overall fatigue life. The results confirm that Miner seriously underestimates the damage contribution at low stresses on fatigue life as a whole, and also for the crack initiation phase of life.

Fatigue and Fretting of Self-Piercing Riveted Joints

Manufacturing ◽  
2002 ◽  
Author(s):  
K. Iyer ◽  
F. L. Brittman ◽  
S. J. Hu ◽  
P. C. Wang ◽  
D. B. Hayden ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Crack Initiation ◽  
Fatigue Cracks ◽  
Three Dimensional ◽  
Lap Joints ◽  
Experimental Program ◽  
Thick Sheet ◽  
Element Analysis ◽  
Tension Tests ◽  
Three Dimensional Finite Element

The fatigue life and fretting characteristics of aluminum alloy 5754-O self-piercing riveted lap joints have been investigated experimentally and analytically. The experimental program involves a set of 27 cyclic tension tests on three different joints consisting of either 1 mm, 2 mm or 3 mm-thick sheet specimens. In most cases (85%), fatigue cracks are found to initiate on the faying surface of the upper sheet, adjacent to the hole, and at an angular location that lies on the sheet loading axis towards the loading end. Three-dimensional finite element analysis of the three joints has also been performed. Computed distributions of local stresses and rivet-sheet slips are interpreted in terms of experimental observations of fatigue life, crack initiation location and fretting damage observations. Significantly, the calculations provide a rationale for the surprising crack initiation location.

scholarly journals Random Load Fatigue Damage Accumulation in Mild Steel

1973 ◽  
Vol 187 (1) ◽  
pp. 285-293 ◽  
Author(s):  
B. C. Fisher ◽  
F. Sherratt
Keyword(s):  
Fatigue Life ◽  
Crack Initiation ◽  
Crack Detection ◽  
High Sensitivity ◽  
Optical Microscope ◽  
Random Loading ◽  
Random Load ◽  
Initiation Phase ◽  
Fatigue Damage Accumulation ◽  
Probability Density Distributions

Using high-sensitivity eddy-current crack detection, quantitative division of fatigue life into two stages has been achieved for a variety of random and constant amplitude loading conditions. The divisions adopted were: Stage A, microcrack initiation and propagation, and Stage B, macrocrack propagation. The results of specimen sectioning and optical microscope work show that this behaviour is physically compatible with the observations of Forsyth (1)‡. It is established under random loading that for a given specimen configuration, the proportion of time spent in stage A behaviour for a given fatigue life remains unaltered for changes in the waveform irregularity factor. This statement applies to two series of tests for loading waveforms of unaltered fundamental p.s.d. (power spectral density) shapes and Gaussian amplitude probability density distributions. It is suggested that the signal maximum peak/r.m.s. ratio is a significant factor in determining the proportion of life spent in crack initiation. Cumulative damage predictions are made using Miner's hypothesis on a basis of positive peak stresses to failure for stage A and stage B lives, and overall fatigue life. The results confirm that Miner seriously underestimates the damage contribution at low stresses on fatigue life as a whole, and also for the crack initiation phase of life.

Influence of Interference and Clamping on Fretting Fatigue in Single Rivet-Row Lap Joints

2000 ◽  
Vol 123 (4) ◽  
pp. 686-698 ◽  
Author(s):  
K. Iyer ◽  
C. A. Rubin ◽  
G. T. Hahn
Keyword(s):  
Crack Initiation ◽  
Three Dimensional ◽  
Fretting Fatigue ◽  
Cyclic Stress ◽  
Lap Joints ◽  
Element Analysis ◽  
Out Of Plane ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element ◽  
Fretting Damage

Primary fretting fatigue variables such as contact pressure, slip amplitude and bulk cyclic stresses, at and near the contact interface between the rivet shank and panel hole in a single rivet-row, 7075-T6 aluminum alloy lap joint are presented. Three-dimensional finite element analysis is applied to evaluate these and the effects of interference and clamping stresses on the values of the primary variables and other overall measures of fretting damage. Two rivet geometries, non-countersunk and countersunk, are considered. Comparison with previous evaluations of the fretting conditions in similar but two-dimensional connections indicates that out-of-plane movements and attending effects can have a significant impact on the fatigue life of riveted connections. Variations of the cyclic stress range and other proponents of crack initiation are found to peak at distinct locations along the hole-shank interface, making it possible to predict crack initiation locations and design for extended life.

Design of crack arrestors for ultra high grade gas transmission pipelines: simulation of crack initiation, propagation and arrest

2011 ◽  
Vol 2 (2) ◽  
pp. 307-319
Author(s):  
F. Van den Abeele ◽  
M. Di Biagio ◽  
L. Amlung
Keyword(s):  
Crack Initiation ◽  
Crack Propagation ◽  
Large Scale ◽  
Large Diameter ◽  
Pipe Material ◽  
High Grade ◽  
Gas Pipelines ◽  
Ductile Crack ◽  
Reinforced Plastics ◽  
Four Point Bending

One of the major challenges in the design of ultra high grade (X100) gas pipelines is the identification of areliable crack propagation strategy. Recent research results have shown that the newly developed highstrength and large diameter gas pipelines, when operated at severe conditions, may not be able to arrest arunning ductile crack through pipe material properties. Hence, the use of crack arrestors is required in thedesign of safe and reliable pipeline systems.A conventional crack arrestor can be a high toughness pipe insert, or a local joint with higher wall thickness.According to experimental results of full-scale burst tests, composite crack arrestors are one of the mostpromising technologies. Such crack arrestors are made of fibre reinforced plastics which provide the pipewith an additional hoop constraint. In this paper, numerical tools to simulate crack initiation, propagationand arrest in composite crack arrestors are introduced.First, the in-use behaviour of composite crack arrestors is evaluated by means of large scale tensile testsand four point bending experiments. The ability of different stress based orthotropic failure measures topredict the onset of material degradation is compared. Then, computational fracture mechanics is applied tosimulate ductile crack propagation in high pressure gas pipelines, and the corresponding crack growth inthe composite arrestor. The combination of numerical simulation and experimental research allows derivingdesign guidelines for composite crack arrestors.

Modeling the Fatigue Damage Evolution in Welded Joints

2017 ◽  
Author(s):  
Zbigniew Mikulski ◽  
Vidar Hellum ◽  
Tom Lassen
Keyword(s):  
Crack Initiation ◽  
Crack Growth ◽  
Fatigue Damage ◽  
Damage Evolution ◽  
Threshold Value ◽  
Phase Model ◽  
Two Phase ◽  
Initiation Phase ◽  
Weld Toe ◽  
Small Cracks

The present paper presents a two-phase model for the fatigue damage evolution in welded steel joints. The argument for choosing a two-phase model is that crack initiation and subsequent crack propagation involve different damage mechanisms and should be treated separately. The crack initiation phase is defined as the number of cycles to reach a crack depth of 0.1 mm. This phase is modelled based on the Dang Van multiaxial stress approach. Both a multiaxial stress situation introduced by the acting loads and the presence of the multiaxial welding residual stresses are accounted for. The local notch effect at the weld toe becomes very important and the irregular weld toe geometry is characterized by extreme value statistics for the weld toe angle and radius. The subsequent crack growth is based in classical fracture based on the Paris law including the effect of the Stress Intensity Factor Range (SIFR) threshold value. The unique fatigue crack growth rate curve suggested by Huang, Moan and Cui is adopted. This approach keeps the growth rate parameters C and m constant whereas an effective SIFR is calculated for the actual stress range and loading ratio. The model is developed and verified based on fatigue crack growth data from fillet welded joints where cracks are emanating from the weld toe. For this test series measured crack depths below 0.1 mm are available. The two-phase model was in addition calibrated to fit the life prediction in the rule based S-N curve designated category 71 (or class F). A supplementary S-N curve is obtained by the Random Fatigue Limit Method (RFLM). The test results and the fitted model demonstrated that the crack initiation phase in welded joins is significant and cannot be ignored. The results obtained by the Dang Van approach for the initiation phase are promising but the modelling is not yet completed. The fracture mechanics model for the propagation phase gives good agreement with measured crack growth. However, it seems that the prediction of crack retardation based on a threshold value for the SIFR gives a fatigue limit that is overly optimistic for small cracks at the weld toe. The threshold value has been determined based on tests with rather large central cracks in plates. The validity for applying this threshold value for small cracks at the weld toe is questioned. As the present two-phase model is based on applied mechanics for both phases the parameters that have an influence on the fatigue damage evolution are directly entering into the model. Any change in these parameters can then be explicitly taken into account in logical and rational manner for fatigue life predictions. This not the case with the rule based S-N curves that are based on pure statistical treatment of the bulk fatigue life.

Fatigue Behavior of Circumferentially Notched Round Bars of Austenitic Stainless Steel Under Torsional and Axial Loads

2010 ◽  
Author(s):  
Masao Itatani ◽  
Keisuke Tanaka ◽  
Isao Ohkawa ◽  
Takehisa Yamada ◽  
Toshiyuki Saito
Keyword(s):  
Fatigue Life ◽  
Stress Concentration ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Fatigue Behavior ◽  
Fatigue Crack Initiation ◽  
Static Tension ◽  
Cyclic Torsion ◽  
Cyclic Tension ◽  
Crack Initiation Life

Fatigue tests of smooth and notched round bars of austenitic stainless steels SUS316NG and SUS316L were conducted under cyclic tension and cyclic torsion with and without static tension. Fatigue strength under fully reversed (R=−1) cyclic tension once increased with increasing stress concentration factor up to Kt=1.5, but it decreased from Kt=1.5 to 2.5. Fatigue life increased with increasing stress concentration under pure cyclic torsion, while it decreased with increasing stress concentration under cyclic torsion with static tension. From the measurement of fatigue crack initiation and propagation lives using electric potential drop method, it was found that the crack initiation life decreased with increasing stress concentration and the crack propagation life increased with increasing stress concentration under pure cyclic torsion. Under cyclic torsion with static tension, the crack initiation life also decreased with increasing stress concentration but the crack propagation life decreased or not changed with increasing stress concentration then the total fatigue life of sharper notched specimen decreased. It was also found that the fatigue life of smooth specimen under cyclic torsion with static tension was longer than that under pure cyclic torsion. This behavior could be explained based on the cyclic strain hardening under non-proportional loading and the difference in crack path with and without static tension.

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