Analysis of crack evolution in fretting fatigue with spherical contact

2009 ◽  
Vol 44 (6) ◽  
pp. 503-515 ◽  
Author(s):  
C Navarro ◽  
S Muñoz ◽  
J Domínguez
Keyword(s):  
Fretting Fatigue ◽  
Fatigue Tests ◽  
Crack Evolution ◽  
Spherical Contact ◽  
Al 7075 ◽  
Growth Laws ◽  
Small Cracks ◽  
Number Of Cycles ◽  
The One ◽  
Theoretical Results

This paper analyses various procedures for predicting crack growth as a function of the number of cycles in fretting fatigue tests with spherical contact. The evolution of the crack is calculated using fracture mechanics starting from an initial defect. Different growth laws are considered, including the behaviour of small cracks, by modifying either the threshold or the effective stress intensity factor value. Theoretical results are compared with those obtained in tests on Al 7075 T651. Results show that, although the final lives predicted by the different laws are similar, the predicted crack evolution does vary, and the most precise law is the one that modifies the growth threshold.

scholarly journals Fretting-Fatigue Analysis of Shot-Peened Al 7075-T651 Test Specimens

Metals ◽  
2019 ◽  
Vol 9 (5) ◽  
pp. 586 ◽  
Author(s):  
Vicente Martín ◽  
Jesús Vázquez ◽  
Carlos Navarro ◽  
Jaime Domínguez
Keyword(s):  
Fatigue Life ◽  
Residual Stresses ◽  
Shot Peening ◽  
Normal Load ◽  
Fretting Fatigue ◽  
Fatigue Tests ◽  
Material Surface ◽  
Tangential Load ◽  
Bulk Stress ◽  
Al 7075

Shot peening is a mechanical treatment that induces several changes in the material: surface roughness, increased hardness close to the surface, and, the most important, compressive residual stresses. This paper analyzes the effect of this treatment on alloy Al 7075-T651 in the case of fretting fatigue with cylindrical contact through the results of 114 fretting fatigue tests. There are three independent loads applied in this type of test: a constant normal load N, pressing the contact pad against the specimen; a cyclic bulk stress σ in the specimen; and a cyclic tangential load Q through the contact. Four specimens at each of 23 different combinations of these three parameters were tested—two specimens without any treatment and two treated with shot peening. The fatigue lives, contact surface, fracture surface, and residual stresses and hardness were studied. Improvement in fatigue life ranged from 3 to 22, depending on fatigue life. The relaxation of residual-stress distribution related to the number of applied cycles was also measured. Finally, another group of specimens treated with shot peening was polished and tested, obtaining similar lives as in the tests with specimens that were shot-peened but not polished.

Fretting fatigue in a spherical contact

2002 ◽  
Vol 37 (6) ◽  
pp. 469-478 ◽  
Author(s):  
C Navarro ◽  
M García ◽  
J Domínguez
Keyword(s):  
Equivalent Stress ◽  
Fretting Fatigue ◽  
Initiation Site ◽  
Fatigue Tests ◽  
Multiaxial Fatigue ◽  
Spherical Contact ◽  
Linear Elastic ◽  
Advantages And Disadvantages ◽  
Elastic Fracture

This article describes different types of tests in fretting fatigue and different geometries for use in testing, comparing mainly cylindrical and spherical contacts and their corresponding advantages and disadvantages. Practical differences can be observed between these two types of tests regarding the alignment of the pads, the level of the loads to be applied, the rigidity in the test rig, the shape of the crack, the localization of the point of initiation of the crack, etc. The loads applied in spherical contact and stress distribution beneath the contact zone are described. As this stress state is multiaxial and non-proportional, the appropriate multiaxial criteria are needed in order to characterize the stress field. An equivalent stress is derived from the criteria and later related to the initiation of the crack. At the same time, with the use of the calculated stresses, a semi-analytical approach using a weight function is described for the determination of the stress intensity factor. The results of a series of fretting fatigue tests have been analysed. The initiation site, the orientation of the crack and, for the tests that did not fail, the length of the crack have been studied using a multiaxial fatigue criterion and linear elastic fracture mechanics (LEFM).

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.

ESTIMATION OF AXIAL FRETTING FATIGUE LIFE AT ELEVATED TEMPERATURES USING CRITICAL DISTANCE THEORY

2018 ◽  
Vol 25 (03) ◽  
pp. 1850067 ◽  
Author(s):  
G. H. MAJZOOBI ◽  
P. AZHDARZADEH
Keyword(s):  
Fatigue Life ◽  
Elevated Temperatures ◽  
Low Cycle Fatigue ◽  
Fretting Fatigue ◽  
Critical Distance ◽  
Fatigue Tests ◽  
Elastic Behavior ◽  
Cycle Fatigue ◽  
Al 7075 ◽  
Special Approach

Fretting fatigue life is traditionally estimated by experiment. The objective of this work is to introduce a special approach for estimation of axial fretting fatigue life at elevated temperatures from plain fatigue test based on the critical distance theory. The method uses Fatemi–Socie parameter as a multiaxial criterion to compute the stress multiaxiality on focus path. This method considers only elastic behavior for materials, and two characteristic diagrams are obtained from plain fatigue tests on two U-shaped and V-shaped notched specimens. The results showed reasonable agreement between the predictions by the proposed method and the experiments for ambient temperature. For elevated temperatures, the results indicated that the predicted fretting fatigue life was considerably overestimated in the low cycle fatigue (LCF) regime and underestimated in the high cycle fatigue (HCF) region with respect to experimental measurements. The reason for such discrepancy is believed to be due to the complex behavior of AL 7075-T6, which exhibits at elevated temperatures because of the problems such as aging, oxidation and reduction of strength.

Effect of Stress Relief Groove Shape on Fretting Fatigue Strength

2007 ◽  
Vol 353-358 ◽  
pp. 856-859 ◽  
Author(s):  
Shunsuke Kataoka ◽  
Chu Sakae ◽  
Masanobu Kubota ◽  
Yoshiyuki Kondo
Keyword(s):  
Fatigue Strength ◽  
Stress Relief ◽  
Groove Depth ◽  
Fretting Fatigue ◽  
Fatigue Tests ◽  
Analysis Model ◽  
Maximum Improvement ◽  
Pressure Concentration ◽  
Small Cracks ◽  
Relief Groove

The objective of this study is to evaluate the effect of stress relief groove on fretting fatigue strength. Fretting fatigue tests and finite element analyses were done. The shape of groove was controlled by groove radius R and tangential angle θ. The depth of groove was specified by R and θ. Fretting fatigue strength was increased with an increase of θ and then it turned into a decrease. The decrease was caused by the transition of failure mode from fretting fatigue at the contact part to plain fatigue at the groove root. The transition was caused by an increase of stress concentration at the groove root with an increase of the groove depth. Therefore, the maximum improvement of fatigue strength was achieved by the largest θ limited by fatigue strength of the groove root. In the analysis, the groove generates high compressive stress field at the contact edge, where small cracks never propagate. Therefore, assumptions to relieve the contact pressure concentration at the contact edge were taken into the analysis model. The values of stress intensity factor ranges for small cracks introduced near the contact edge were almost the same between grooved and non-groove specimens.

scholarly journals Fatigue Properties of AZ31B Magnesium Alloy Processed by Equal-Channel Angular Pressing

Metals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1191
Author(s):  
Ryuichi Yamada ◽  
Shoichiro Yoshihara ◽  
Yasumi Ito
Keyword(s):  
Magnesium Alloy ◽  
Equal Channel Angular Pressing ◽  
Low Cycle Fatigue ◽  
Annealed Sample ◽  
Fatigue Tests ◽  
Fatigue Properties ◽  
Angular Pressing ◽  
Fundamental Research ◽  
Number Of Cycles ◽  
Biodegradable Magnesium

A stent is employed to expand a narrowed tubular organ, such as a blood vessel. However, the persistent presence of a stainless steel stent yields several problems of late thrombosis, restenosis and chronic inflammation reactions. Biodegradable magnesium stents have been introduced to solve these problems. However, magnesium-based alloys suffer from poor ductility and lower than desired fatigue performance. There is still a huge demand for further research on new alloys and stent designs. Then, as fundamental research for this, AZ31 B magnesium alloy has been investigated for the effect of equal-channel angular pressing on the fatigue properties. ECAP was conducted for one pass and eight passes at 300 °C using a die with a channel angle of 90°. An annealed sample and ECAP sample of AZ31 B magnesium alloy were subjected to tensile and fatigue tests. As a result of the tensile test, strength in the ECAP (one pass) sample was higher than in the annealed sample. As a result of the fatigue test, at stress amplitude σa = 100 MPa, the number of cycles to failure was largest in the annealed sample, medium in the ECAP (one pass) sample and lowest in the ECAP (eight passes) sample. It was suggested that the small low cycle fatigue life of the ECAP (eight passes) sample is attributable to severe plastic deformation.

scholarly journals Multi-Stage Cold Forging Process for Manufacturing a High-Strength One-Body Input Shaft

Materials ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 532
Author(s):  
A Jo ◽  
Myeong Jeong ◽  
Sang Lee ◽  
Young Moon ◽  
Sun Hwang
Keyword(s):  
High Strength ◽  
Microstructural Characterization ◽  
Fatigue Tests ◽  
Machining Process ◽  
Cold Forging ◽  
Element Analysis ◽  
Forging Process ◽  
Input Shaft ◽  
Multi Stage ◽  
The One

A multi-stage cold forging process was developed and complemented with finite element analysis (FEA) to manufacture a high-strength one-body input shaft with a long length body and no separate parts. FEA showed that the one-body input shaft was manufactured without any defects or fractures. Experiments, such as tensile, hardness, torsion, and fatigue tests, and microstructural characterization, were performed to compare the properties of the input shaft produced by the proposed method with those produced using the machining process. The ultimate tensile strength showed a 50% increase and the torque showed a 100 Nm increase, confirming that the input shaft manufactured using the proposed process is superior to that processed using the machining process. Thus, this study provides a proof-of-concept for the design and development of a multi-stage cold forging process to manufacture a one-body input shaft with improved mechanical properties and material recovery rate.

Self-Healing and Repairing Concrete Cracks Based on Bio-Mineralization

2014 ◽  
Vol 629-630 ◽  
pp. 494-503 ◽  
Author(s):  
Chun Xiang Qian ◽  
Mian Luo ◽  
Li Fu Ren ◽  
Rui Xing Wang ◽  
Rui Yang Li ◽  
...  
Keyword(s):  
Concrete Surface ◽  
Cellular Respiration ◽  
Self Healing ◽  
Capillary Suction ◽  
Water Permeation ◽  
Carbonate Ions ◽  
Micro Cracks ◽  
Small Cracks ◽  
The Common ◽  
The One

In this paper, three bio-mineralization mechanisms were proposed to repair cement-based materials cracks. The common feature is that the three are all induced by bacterial. A type of bacterial which can decompose urea and release carbonate ions could be applied to repair micro cracks on concrete surface when combining calcium ions. But what need to be noted is that the way of repairing cracks is passive. Some alkaliphilic bacterial spores could be added to concrete when casted and two different types of bacterial were used to realize the function of self-healing. The sources of carbonate ions made them different, the one release carbonate dioxide through its own cellular respiration, the other could transfer carbon dioxide in air to bicarbonate. Coefficient of capillary suction, apparent water permeation coefficient and area repairing rate were applied to characterize the repairing effectiveness. The tests results were that all three bio-mineralization mechanisms showed excellent repair effect to small cracks formed at early ages. When the bacteria were immobilized by ceramsite, the self-healing effect could be improved for the cracks formed at late ages.

Effects of T5 and T6 Heat Treatments Applied to Rheocast A356 Parts for Automotive Applications

2008 ◽  
Vol 141-143 ◽  
pp. 237-242 ◽  
Author(s):  
Mario Rosso ◽  
Ildiko Peter ◽  
R. Villa
Keyword(s):  
Fatigue Behaviour ◽  
Cyclic Stress ◽  
Industrial Applications ◽  
Fatigue Tests ◽  
Controlled Cooling ◽  
Test Analysis ◽  
Heat Treated ◽  
Mechanical Performances ◽  
Semi Solid ◽  
Number Of Cycles

The correlation between the evaluation of the mechanical and of the fatigue behaviour of the rheocast, T5 and T6 heat treated SSM A356 aluminium alloy with respect to the microstructures of the component has been investigated. The study has been carried out on a suspension arm injected in a rheocasting 800 tons plant in Stampal S.p.A. The new rheocasting is a process that allows obtaining the alloys in a semisolid state directly from the liquid state, by controlled cooling of the molten alloys. The resulting microstructures are very fine, free from defects and homogeneous: these characteristics improve the mechanical properties of the alloys and specially the response to cyclic stress, an important issue for a suspension component. After a preliminary tensile test analysis, axial high frequency fatigue tests have been carried out at room temperature on specimen cut out from the suspension arm to determine the Wöhler curve and the number of cycles to failure. The results of this work allow a comparison of the effects of heat treatment process, T5 or T6, on Semi-Solid components for industrial applications in the automotive field. On the basis of these analysis the correlation between microstructure and mechanical performances can be established.

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