scholarly journals Seawater Effect on Fatigue Behaviour of Notched Carbon/Epoxy Laminates

2021 ◽  
Vol 11 (24) ◽  
pp. 11939
Author(s):  
Ricardo Branco ◽  
Paulo N. B. Reis ◽  
Maria A. Neto ◽  
José D. Costa ◽  
Ana M. Amaro
Keyword(s):  
Water Absorption ◽  
Stress Ratio ◽  
Stress Amplitude ◽  
Rectangular Cross Section ◽  
Fatigue Behavior ◽  
Failure Mechanisms ◽  
Fatigue Behaviour ◽  
Fatigue Tests ◽  
Artificial Seawater ◽  
Microscopy Technique

This paper studies the effect of seawater immersion on the fatigue behavior of notched carbon/epoxy laminates. Rectangular cross-section specimens with a central hole were immersed in natural and artificial seawater for different immersion times (0, 30 and 60 days), being the water absorption rate evaluated over time. After that, fatigue tests were performed under uniaxial cyclic loading using a stress ratio equal to 0.1. After the tests, the optical microscopy technique allowed the examination of the failure micro-mechanisms at the fracture surfaces. The results showed that saturation appeared before 30 days of immersion and that water absorption rates were similar for natural and artificial seawater. The S–N curves showed that the seawater immersion affects the fatigue strength, but there were no relevant effects associated with the type of seawater. Moreover, it was also clear that fatigue life was similar for long lives, close to 1 million cycles, regardless of the immersion time or the type of seawater. On the contrary, for short lives, near 10 thousand cycles, the stress amplitude of dry laminates was 1.2 higher than those immersed in seawater. The failure mechanisms were similar for all conditions, evidencing the fracture of axially aligned fibres and longitudinal delamination between layers.

Orientation Dependence on Fatigue Fracture Behavior of Pure Mg Single Crystals

2018 ◽  
Vol 941 ◽  
pp. 1507-1510
Author(s):  
Yuta Kido ◽  
Akinobu Nakamura ◽  
Masayuki Tsushida ◽  
Hiromoto Kitahara ◽  
Shinji Ando
Keyword(s):  
Single Crystals ◽  
Fracture Behavior ◽  
Room Temperature ◽  
Stress Ratio ◽  
Stress Amplitude ◽  
Fatigue Behavior ◽  
Orientation Dependence ◽  
Fatigue Tests ◽  
Crystal Orientations ◽  
Fatigue Fracture Behavior

It is well known that magnesium (Mg) shows anisotropic fatigue behavior. However, the fatigue mechanisms have yet to be elucidated. The relationships between crystal orientations and crack initiation behavior in Mg single crystals were investigated by uniaxial tension-compression fatigue tests. Three types of round-bar specimens were prepared. The lording direction of AD, BC and EF specimen were [110], [100] and [0001], respectively. Fatigue tests were carried out with the stress ratio R=-1 and the frequency of 10Hz at room temperature in laboratory air. At stress amplitude (σa) over 40 MPa, fatigue lives of BC specimen and EF specimen were the longest and shortest. However, at σa =20 MPa, the fatigue life of all specimens were almost the same. It was found that fatigue lives of Mg single crystals strongly depend on crystal orientations and stress.

scholarly journals Influence of Shot Peening on the Isothermal Fatigue Behavior of the Gamma Titanium Aluminide Ti-48Al-2Cr-2Nb at 750 °C

Metals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 1083
Author(s):  
Christoph Breuner ◽  
Stefan Guth ◽  
Elias Gall ◽  
Radosław Swadźba ◽  
Jens Gibmeier ◽  
...  
Keyword(s):  
Residual Stresses ◽  
Shot Peening ◽  
Elevated Temperatures ◽  
Stress Amplitude ◽  
Negative Impact ◽  
Fatigue Behavior ◽  
Surface Hardness ◽  
Fatigue Tests ◽  
Positive Effects ◽  
Isothermal Fatigue

One possibility to improve the fatigue life and strength of metallic materials is shot peening. However, at elevated temperatures, the induced residual stresses may relax. To investigate the influence of shot peening on high-temperature fatigue behavior, isothermal fatigue tests were conducted on shot-peened and untreated samples of gamma TiAl 48-2-2 at 750 °C in air. The shot-peened material was characterized using EBSD, microhardness, and residual stress analyses. Shot peening leads to a significant increase in surface hardness and high compressive residual stresses near the surface. Both effects may have a positive influence on lifetime. However, it also leads to surface notches and tensile residual stresses in the bulk material with a negative impact on cyclic lifetime. During fully reversed uniaxial tension-compression fatigue tests (R = −1) at a stress amplitude of 260 MPa, the positive effects dominate, and the fatigue lifetime increases. At a lower stress amplitude of 230 MPa, the negative effect of internal tensile residual stresses dominates, and the lifetime decreases. Shot peening leads to a transition from surface to volume crack initiation if the surface is not damaged by the shots.

Effects of Residual Stresses on the High Cycle Fatigue Behavior of Ti-6Al-4V

2010 ◽  
Author(s):  
Yu-Jia Li ◽  
Fu-Zhen Xuan ◽  
Zheng-Dong Wang ◽  
Shan-Tung Tu
Keyword(s):  
Residual Stress ◽  
Fatigue Limit ◽  
Stress Ratio ◽  
Fatigue Behavior ◽  
Fatigue Tests ◽  
X Ray Diffraction ◽  
Surface Residual Stress ◽  
Manufacturing Techniques ◽  
Stress Ratios ◽  
Effect Of Surface

Axial force-controlled fatigue tests are conducted at various stress ratios (R) on Ti-6Al-4V specimens prepared by two different manufacturing techniques (hard turning plus polishing with and without vacuum stress relieve anneal carried out after polishing). Residual stress is measured by using X-ray diffraction. Results indicate that the surface compressive residual stress lead to an increase of fatigue limit at a given life and stress ratio. This effect decreases with increasing stress ratio R. At R = 0.6, the effect of surface residual stress on fatigue limit fades away. In addition, the location of crack initiation shifts from surface to interior when the stress ratio changes from −1 to 0.6.

High-Cycle Fatigue Behavior of Type 4340 Steel Pressurized Blocks Including Mean Stress Effect

2019 ◽  
Author(s):  
Elie A. Badr ◽  
Joanne Ishak
Keyword(s):  
Stress Ratio ◽  
Fatigue Behavior ◽  
Fatigue Loading ◽  
Fatigue Tests ◽  
Ultimate Stress ◽  
Stress Effect ◽  
Mean Stress ◽  
Test Results ◽  
Linear Correction ◽  
The Mean

Abstract Mean stress effects in pressurized steel blocks were examined under constant amplitude fatigue loading. The tests were performed to provide experimental data needed to study the effect of mean stress on fatigue lives of subject specimen, and to substantiate the use of analytical expressions to account for the mean stress. The mean stress was the result of subjecting the specimens to an autofrettage pressure which induced compressive residual stresses at the crossbore intersection of the specimens. Fatigue tests were carried out under both tensile and compressive mean stress levels. Test results were compared to several mean stress accounting relationships such as the Smith-Watson Topper, Bergmann and Seeger, modified Goodman, Gerber and Soderberg. Test results indicated that the modified Goodman equation is favorable in accounting for the effect of both tensile and compressive mean stresses on fatigue life (up to a compressive mean stress to ultimate stress ratio of −0.2). The behavior under compressive mean stress to ultimate stress ratio of less than −0.2 indicated that a linear correction relationship was required.

Effects of chromic acid anodizing on fatigue behavior of 7050 T7451 aluminum alloy

2021 ◽  
Vol 63 (9) ◽  
pp. 805-810
Author(s):  
Çağrı İlhan ◽  
Rıza Gürbüz
Keyword(s):  
Aluminum Alloy ◽  
Stress Ratio ◽  
Chromic Acid ◽  
Fatigue Behavior ◽  
Fatigue Tests ◽  
Constant Amplitude ◽  
Aluminum Oxide Layer ◽  
Fatigue Life Reduction ◽  
Selection Of ◽  
Scanning Electron

Abstract The effect of chromic acid anodizing (CAA) surface treatment on 7050 T7451 aluminum alloy was presented in this study in terms of fatigue behavior. CAA is a treatment against corrosion by producing aluminum oxide layer (Al2O3) at the surface. However, fatigue performance of 7050 T7451 is affected by the coating. In this study, eight different CAA processes were examined with regard to etching stage of pre-treatments by using an alkaline etchant and/or acid etchants with various immersion times. Optical microscopic examinations were applied in order to determine pitting characteristics for the selection of CAA process parameters before fatigue tests. A CAA process was selected among eight processes in terms of pitting characteristics in order to apply fatigue specimens. Four fatigue test groups were determined to investigate bare condition of 7050 T7451 and sub-stages of the CAA particularly. Constant amplitude axial fatigue tests were conducted on specimens at 91 Hz at stress ratio (R) -1 until run-out criteria, which was 106 cycles. Fatigue life reduction was determined due to pretreatments of CAA. Fracture surfaces of the specimens were examined by scanning electron microscope (SEM) to investigate morphology and crack initiation sites.

Low Cycle and Multiaxial Fatigue Behavior of Three Al-Mg-Si Alloys

2014 ◽  
Vol 891-892 ◽  
pp. 1335-1340
Author(s):  
Denise F. Laurito-Nascimento ◽  
Ana Márcia Barbosa da Silva Antunes ◽  
Carlos Antonio Reis Pereira Baptista ◽  
José Célio Dias ◽  
Angelo Souza
Keyword(s):  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Fatigue Behaviour ◽  
Fatigue Tests ◽  
Multiaxial Fatigue ◽  
Damping Capacity ◽  
Reliability Engineering ◽  
Principal Stresses ◽  
Engineering Structures ◽  
6Xxx Series

Al-Mg-Si alloys (6xxx series) are medium strength structural alloys, with good corrosion resistance, good weldability and high damping capacity. They represent a high volumetric fraction of extruded aluminium alloys which are produced for commercial use and have been increasingly applied in the automotive industry. For structural materials, the fatigue strength is the most important factor to ensure a long-term reliability. Engineering structures such as aircrafts and automobiles usually undergo complex multiaxial loadings, which lead to changes of the principal stresses and strains directions in components during a loading cycle. In this study, fatigue tests were performed in three Al-Mg-Si alloys, namely AA 6005, AA 6351 and AA 6063, tempered and aged for the T6 condition. A comparative study was undertaken by assessing their Low Cycle Fatigue (LCF) properties and multiaxial fatigue behaviour using round smooth specimens. Strain-controlled fully reversed axial loadings and distinct combinations of axial-torsional fully reversed stress cycles, including in-phase and 90o out-of-phase loadings were adopted for the tests. The collected data are discussed in relation to some well-known multiaxial fatigue models.

Investigation Into Cumulative Damage Rules to Predict Fretting Fatigue Life of Ti-6Al-4V Under Two-Level Block Loading Condition1

2003 ◽  
Vol 125 (3) ◽  
pp. 315-323 ◽  
Author(s):  
O. Jin ◽  
H. Lee ◽  
S. Mall
Keyword(s):  
Stress Amplitude ◽  
Fatigue Behavior ◽  
Fretting Fatigue ◽  
Fatigue Tests ◽  
Cumulative Damage ◽  
Order Effects ◽  
Block Loading ◽  
Crack Growth Rates ◽  
Damage Rule ◽  
Repeated Block

The effects of variable amplitude loading on fretting fatigue behavior of titanium alloy, Ti-6Al-4V were examined. Fretting fatigue tests were carried out under constant stress amplitude and three different two-level block loading conditions: high-low (Hi-Lo), low-high (Lo-Hi), and repeated block of high and low stress amplitudes. The damage fractions and fretting fatigue lives were estimated by linear and non-linear cumulative damage rules. Damage curve analysis (DCA) and double linear damage rule (DLDR) were capable to account for the loading order effects in Hi-Lo and Lo-Hi loadings. In addition, the predictions by DCA and DLDR were better than that by linear damage rule (LDR). Besides its simplicity of implementation, LDR was also capable of estimating failure lives reasonably well. Repeated two-level block loading resulted in shorter lives and lower fretting fatigue limit compared to those under constant amplitude loading. The degree of reduction in fretting fatigue lives and fatigue strength depended on the ratio of cycles at lower stress amplitude to that at higher stress amplitude. Fracture surface of specimens subjected to Hi-Lo and repeated block loading showed the clear evidence of change in stress amplitude of applied load. Especially, the repeated two-level block loading resulted in characteristic markers which reflected change in crack growth rates corresponding to different stress amplitudes.

Effect of Stress Ratio and Loading Mode on High Cycle Fatigue Properties of Extruded Magnesium Alloys

2014 ◽  
Vol 891-892 ◽  
pp. 557-562
Author(s):  
Kazuaki Shiozawa ◽  
Atsushi Ikeda ◽  
Tsuyoshi Fukumori
Keyword(s):  
Magnesium Alloys ◽  
Stress Ratio ◽  
High Cycle Fatigue ◽  
Stress Amplitude ◽  
Fatigue Crack Initiation ◽  
High Stress ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Loading Mode ◽  
Amplitude Level

The aim of this study is to discuss an effect of stress ratio and loading mode on high cycle fatigue performances of extruded magnesium alloys. Axial loading fatigue tests under three conditions of stress ratio, R, of 0, -1 and-1.5, and also rotating bending fatigue tests have been performed in laboratory air at room temperature using hourglass shaped specimens of AZ31, AZ61, AZ80 and T5-treated AZ80 alloy. From the experimental results, some materials showed a specific stepwise S-N curve on which two knees appear. The shape of S-N diagram depended on a kind of tested materials, applied stress ratio and loading mode. It was suggested from the detail observation of fracture surface that fatigue crack initiation mechanism changed from a twin-induced failure mode at high stress amplitude level to a slip-induced one at low stress amplitude level. This transition was determined with the relation between the minimum stress during a fatigue cycle and the compressive yield stress at which deformation twin occurs.

scholarly journals Effects of Surface Softening on the Mechanical Properties of an AISI 316L Stainless Steel under Cyclic Loading

Metals ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1788
Author(s):  
Tiehui Fang ◽  
Feng Cai
Keyword(s):  
Stainless Steel ◽  
316L Stainless Steel ◽  
Stress Amplitude ◽  
Fatigue Behavior ◽  
High Stress ◽  
Sample Surface ◽  
Fatigue Tests ◽  
Aisi 316L ◽  
Homogeneous Sample ◽  
Aisi 316L Stainless Steel

The effects of surface softening on fatigue behavior of AISI 316L stainless steel were investigated. Using cold-rolling and electromagnetic induction heating treatment, a gradient structure was fabricated on AISI 316L stainless steel within which the grain size decreased exponentially from micrometers to nanometers to mimic the surface softening. Stress-controlled fatigue tests were applied to both the gradient and homogeneous structures. Compared with the homogeneous sample, surface softening had no evident effect on fatigue behavior when the stress amplitude was greater than 400 MPa, but significantly deteriorated the fatigue behavior at stress amplitude ≤400 MPa. At high-stress amplitude, fatigue behavior is dominated by crack propagation. When the stress amplitude is lowered, strength reduction and stress concentration caused by surface softening accelerate crack initiation and propagation, resulting in an inferior fatigue behavior.

Fatigue Tests and Design of Offshore Tubular Joints

1983 ◽  
Vol 105 (2) ◽  
pp. 189-194
Author(s):  
D. Dutta ◽  
F. Mang
Keyword(s):  
Stress Ratio ◽  
Design Method ◽  
Fatigue Behavior ◽  
Load Cycle ◽  
Fatigue Tests ◽  
Post Weld Heat Treatment ◽  
Small Scale ◽  
Plate Test ◽  
Tubular Joints ◽  
Stress Load

The AWS-X “hotspot stress-load cycle” curve used at present for designing tubular joints is based mainly on the fillet-welded plate test data and some more data from small-scale tests on tubular joints, which were available in the early 1970s. A review of further tests carried out in the recent years, including those by the authors, leads to the conclusion that the influence of the diameter and thickness of the tubes plays a significant role in the joint fatigue behavior. Hence, they must be taken into consideration while designing tubular joints accurately and more economically. A modified design method is proposed here with design curves for four diameter values. Further, the results of fatigue tests on K-type joints investigating the effect of stress ratio R and of post-weld heat treatment on the joint fatigue strength are described in this paper.

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