Fatigue Characteristic and Dislocation Substructure of A356 Casting Alloy under Multi-Axial Cyclic Loadings

2011 ◽  
Vol 306-307 ◽  
pp. 489-495 ◽  
Author(s):  
De Feng Mo ◽  
Guo Qiu He ◽  
Da Fu Liu ◽  
Zheng Yu Zhu
Keyword(s):  
Fatigue Life ◽  
Fatigue Failure ◽  
Low Cycle Fatigue ◽  
Cyclic Hardening ◽  
Fatigue Tests ◽  
Loading Path ◽  
Loading Paths ◽  
Casting Alloys ◽  
The Difference ◽  
Additional Hardening

Mechanical fatigue tests were conducted on specimens of A356-T6 casting alloys under multi-axial cyclic loadings with 5 loading paths (proportional, circular, square, diamond, and ellipse path). Optical microscopy and TEM were used to examine both undeformed and fatigue failure specimens. It is shown that undeformed material has coarse microstructure with low density of dislocation. Under every loading path, cyclic hardening dominates the whole fatigue process. Additional hardening is found in this casting material, but the rate and extent of cyclic hardening and additional hardening are quite dependent on particular loading paths. Various dislocation substructures are observed in the specimens including specimens fatigued to 20 cycles and fatigue failure specimens. While these dislocation substructures are determined by the moving ability of dislocation and interactions between dislocation and particles. Low cycle fatigue life is sensitive to the difference of loading paths, and the fatigue life increases as the extent of cyclic hardening decreases.

Multiaxial Fatigue of 6061-T6 Aluminum Alloy under Corrosive Environment

2016 ◽  
Vol 853 ◽  
pp. 77-82
Author(s):  
Xu Chen ◽  
Rui Si Xing ◽  
Xiao Peng Liu
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Life ◽  
Stress Amplitude ◽  
Low Cycle Fatigue ◽  
Cyclic Hardening ◽  
Cyclic Softening ◽  
Fatigue Tests ◽  
Plastic Strain Amplitude ◽  
Multiaxial Fatigue ◽  
Corrosive Environment

Aluminium alloys are widely used in the fields of automobile, machinery and naval construction. To investigate the effect of non-proportional loadings and corrosive environment on the fatigue resistance of 6061-T6 aluminum alloy, a set of uniaxial and multiaxial low cycle fatigue tests were carried out. Firstly, the results of uniaxial tests showed that the alloy exhibited cyclic hardening then cyclic softening. With the increase of stress amplitude the cyclic softening became pronounced. The increasing of plastic deformation was basically cyclically stable with small plastic strain amplitude accumulation when the stress amplitude was lower than 200MPa ,while it was increasing rapidly when the stress amplitude was higher than 220MPa. Secondly, it was observed that non-proportional cycle additional hardening of 6061-T6 aluminum alloy was little. While the fatigue life was badly affected by the loading paths. Thirdly ,the fatigue corrosion interactions were also talked about in details by performing the tests under the same loading conditions with corrosive environment. The experiment proved that the seawater corrosion has huge impact on fatigue life under pH 3. Finally, a multi-axial fatigue life prediction model was used to predict the fatigue life with or without the corrosive environment which showed a good agreement with experimental data.

Low-Cycle Fatigue of Nickel-Based Superalloy Hastelloy X at Elevated Temperatures

2001 ◽  
Author(s):  
Lijia Chen ◽  
Peter K. Liaw ◽  
Robert L. McDaniels ◽  
James W. Blust ◽  
Paul F. Browning ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Stress Relaxation ◽  
Test Temperature ◽  
Low Cycle Fatigue ◽  
Hold Time ◽  
Cyclic Hardening ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Hastelloy X ◽  
Nickel Based Superalloy

The fully-reversed total strain-controlled low-cycle fatigue tests with and without hold times, as well as stress-relaxation tests, were conducted at 816°C and 927°C in laboratory air on a nickel-based superalloy, HASTELLOY X. The influence of temperatures and hold times on low-cycle fatigue behavior of the alloy was investigated. At both temperatures of 816°C and 927°C, the alloy exhibited initial cyclic hardening, followed by a saturated cyclic stress response or cyclic softening under low-cycle fatigue without hold times. For low-cycle fatigue tests with hold times, however, the alloy showed either cyclic hardening or cyclic stability, which is closely related to the test temperature and the duration of the hold time. It was also observed that the low-cycle fatigue life of the alloy considerably decreased due to the introduction of strain hold times. Generally, a longer hold time would result in a greater reduction in the fatigue life. However, for the tests without hold times, the test temperature seems to have little influence on the fatigue life of the alloy at the test temperatures used in this investigation. The stress relaxation tests show that at the beginning of strain hold, the stress drops very quickly and then decreases very slowly with prolonging time. In addition, the fracture surfaces of the fatigued specimens were observed using scanning electron microscopy to determine the crack initiation and propagation modes. The fatigue life was predicted by the frequency modified tensile hysteresis energy method. The predicted lives were found to be in good agreement with the experiment results.

Comparative Study of the Additional Hardening Effects of Three Structural Steels

2006 ◽  
Vol 514-516 ◽  
pp. 534-538
Author(s):  
Luís G. Reis ◽  
Bin Li ◽  
Manuel de Freitas
Keyword(s):  
Low Cycle Fatigue ◽  
Testing Machine ◽  
Great Influence ◽  
Structural Steels ◽  
Loading Path ◽  
Multiaxial Loading ◽  
Cycle Fatigue ◽  
Proportional Loading ◽  
Loading Paths ◽  
Additional Hardening

For a safe and reliable design of components, it is needed to study the effects of multiaxial loading and particularly the non-proportional loadings on the fatigue damage. The objective of this paper is to evaluate and compare the additional hardening effects of proportional and non-proportional loading paths. Low-cycle fatigue behaviour of three structural steels: CK45 (ferritic-perlitic microstructure) normalized steel, 42CrMo4 (bainitic microstructure) quenched and tempered steel and stainless steel (austenitic microstructure) X10CrNiS 18 9 are studied under different proportional and non-proportional loading paths and different levels. A series of tests of biaxial low-cycle fatigue composed of tension/compression with static or cyclic torsion were carried out on a biaxial servo-hydraulic testing machine Instron 8088. The experiments showed that the three materials studied have very different additional hardening behaviour, under multiaxial cyclic loading paths. The local cyclic stress/strain states are influenced by the multiaxial loading paths due to interactions between the normal stress and shear stress during cyclic plastic deformation. The microstructure is an important key and has a great influence on the additional hardening. The additional hardening effect is dependent of the loading path and also the intensity of the loading.

scholarly journals Fatigue Testing of Wearable Sensing Technologies: Issues and Opportunities

Materials ◽  
2021 ◽  
Vol 14 (15) ◽  
pp. 4070
Author(s):  
Andrea Karen Persons ◽  
John E. Ball ◽  
Charles Freeman ◽  
David M. Macias ◽  
Chartrisa LaShan Simpson ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Prediction Models ◽  
Fatigue Testing ◽  
Low Cycle Fatigue ◽  
Wearable Sensors ◽  
Fatigue Tests ◽  
Proof Of Concept ◽  
Cycle Fatigue ◽  
Wearable Sensing ◽  
Failure Data

Standards for the fatigue testing of wearable sensing technologies are lacking. The majority of published fatigue tests for wearable sensors are performed on proof-of-concept stretch sensors fabricated from a variety of materials. Due to their flexibility and stretchability, polymers are often used in the fabrication of wearable sensors. Other materials, including textiles, carbon nanotubes, graphene, and conductive metals or inks, may be used in conjunction with polymers to fabricate wearable sensors. Depending on the combination of the materials used, the fatigue behaviors of wearable sensors can vary. Additionally, fatigue testing methodologies for the sensors also vary, with most tests focusing only on the low-cycle fatigue (LCF) regime, and few sensors are cycled until failure or runout are achieved. Fatigue life predictions of wearable sensors are also lacking. These issues make direct comparisons of wearable sensors difficult. To facilitate direct comparisons of wearable sensors and to move proof-of-concept sensors from “bench to bedside,” fatigue testing standards should be established. Further, both high-cycle fatigue (HCF) and failure data are needed to determine the appropriateness in the use, modification, development, and validation of fatigue life prediction models and to further the understanding of how cracks initiate and propagate in wearable sensing technologies.

An Investigation of Cyclic Transient Behavior and Implications on Fatigue Life Estimates

1997 ◽  
Vol 119 (2) ◽  
pp. 161-170 ◽  
Author(s):  
Yanyao Jiang ◽  
Peter Kurath
Keyword(s):  
Stainless Steel ◽  
Fatigue Life ◽  
Cyclic Hardening ◽  
Transient Behavior ◽  
Fatigue Tests ◽  
304 Stainless Steel ◽  
Deformation History ◽  
Life Estimation ◽  
Fatigue Life Estimation ◽  
Track Deformation

Current research focuses on proportional cyclic hardening and non-Massing behaviors. The interaction of these two hardenings can result in the traditionally observed overall softening, hardening or mixed behavior exhibited for fully reversed strain controlled fatigue tests. Proportional experiments were conducted with five materials, 304 stainless steel, normalized 1070 and 1045 steels, and 7075-T6 and 6061-T6 aluminum alloys. All the materials display similar trends, but the 304 stainless steel shows the most pronounced transient behavior and will be discussed in detail. Existing algorithms for this behavior are evaluated in light of the recent experiments, and refinements to the Armstrong-Frederick class of incremental plasticity models are proposed. Modifications implemented are more extensive than the traditional variation of yield stress, and a traditional strain based memory surface is utilized to track deformation history. Implications of the deformation characteristics with regard to fatigue life estimation, especially variable amplitude loading, will be examined. The high-low step loading is utilized to illustrate the effect of transient deformation on fatigue life estimation procedures, and their relationship to the observed and modeled deformation.

Improving Fatigue Life of Riveted Joints by Rivet Hole Sizing

2014 ◽  
Vol 598 ◽  
pp. 141-146
Author(s):  
Adam Lipski ◽  
Zbigniew Lis
Keyword(s):  
Fatigue Life ◽  
Fold Increase ◽  
Fatigue Tests ◽  
Aviation Industry ◽  
Lap Joint ◽  
Riveted Joints ◽  
Riveting Process ◽  
The Difference ◽  
Structural Connection ◽  
The Impact

The aim of this paper is to assess the impact of the rivet hole sizing process on the fatigue life based on the example of the structural connections characteristic for riveted joints used in aviation industry. Test specimens reflected the structural connection consisting in a riveted lap joint of an airplane plating stiffened with a T-bar. Connected plates and the T-bar are made of D16CzATW aluminum alloy. 3 mm diameter oval head solid rivets for aviation-related purposes were made of PA24 aluminum. During fatigue tests, individual specimens with non-sized holes and with sized holes were subjected to uniaxial, one-sided, fixed-amplitude loading (R = 0). It can be concluded from the fatigue life comparison that introduction of an additional operation in the riveting process, i.e. the hole sizing, results in significant, about two-fold increase of the fatigue life of the riveted structural connection, even at slight sizing degree. The difference of the specimen damage nature was observed between specimens with sized and non-sized holes.

Low-Cycle Fatigue Life of Continuously Cyclic-Hardening Material

2020 ◽  
Author(s):  
Zhong Zhang ◽  
Xijia Wu
Keyword(s):  
Fatigue Life ◽  
Plastic Strain ◽  
Root Mean Square ◽  
Low Cycle Fatigue ◽  
Cyclic Hardening ◽  
Mean Square ◽  
Cycle Fatigue ◽  
Fatigue Crack Nucleation ◽  
Hardening Material ◽  
Plastic Strain Range

Abstract A general fatigue life equation is derived by modifying the Tanaka-Mura-Wu dislocation pile-up model for variable strain-amplitude fatigue processes, where the fatigue crack nucleation life is expressed in terms of the root mean square of plastic strain range. Low-cycle fatigue tests were conducted on an austenitic stainless steel. at 400°C and 600°C, the material exhibits continuously cyclic-hardening behaviour. The root mean square of plastic strain ranges is evaluated from the experimental data for each test condition at strain rates ranging from 0.0002/s to 0.02/s. The variable-amplitude Tanaka-Mura-Wu model is found to be in good agreement with the LCF data, which effectively proves Miner’s rule on the stored plastic strain energy basis.

Evaluation of the Heat Treatment Role for Light Aluminum Alloys Subjected to Creep and Low Cycle Fatigue

2010 ◽  
Vol 638-642 ◽  
pp. 455-460 ◽  
Author(s):  
A. Rutecka ◽  
L. Dietrich ◽  
Zbigniew L. Kowalewski
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Low Cycle Fatigue ◽  
Numerical Models ◽  
Cyclic Hardening ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Lower Stress ◽  
Creep Tests ◽  
Different Temperatures

The AlSi8Cu3 and AlSi7MgCu0.5 cast aluminium alloys of different composition and heat treatment were investigated to verify their applicability as cylinder heads in the car engines [1]. Creep tests under the step-increased stresses at different temperatures, and low cycle fatigue (LCF) tests for a range of strain amplitudes and temperatures were carried out. The results exhibit a significant influence of the heat treatment on the mechanical properties of the AlSi8Cu3 and AlSi7MgCu0.5. An interesting fact is that the properties strongly depend on the type of quenching. Lower creep resistance (higher strain rates) and lower stress response during fatigue tests were observed for the air quenched materials in comparison to those in the water quenched. Cyclic hardening/softening were also observed during the LCF tests due to the heat treatment applied. The mechanical properties determined during the tests can be used to identify new constitutive equations and to verify existing numerical models.

scholarly journals Impact of Temperature on Low-Cycle Fatigue Characteristics of the HR6W Alloy

Materials ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 6741
Author(s):  
Grzegorz Junak ◽  
Anżelina Marek ◽  
Michał Paduchowicz
Keyword(s):  
Fatigue Life ◽  
Room Temperature ◽  
Low Cycle Fatigue ◽  
Fatigue Tests ◽  
Total Strain ◽  
Cycle Fatigue ◽  
Fatigue Characteristics

This paper presents the results of tests conducted on the HR6W (23Cr-45Ni-6W-Nb-Ti-B) alloy under low-cycle fatigue at room temperature and at 650 °C. Fatigue tests were carried out at constant values of the total strain ranges. The alloy under low-cycle fatigue showed cyclic strengthening both at room temperature and at 650 °C. The degree of HR6W strengthening described by coefficient n’ was higher at higher temperatures. At the same time, its fatigue life Nf at room temperature was, depending on the range of total strain adopted in the tests, several times higher than observed at 650 °C.

Low Cycle Fatigue Properties of FGH720Li Superalloy

2021 ◽  
Vol 1035 ◽  
pp. 292-296
Author(s):  
Zi Chao Peng ◽  
Jun Ying Sheng ◽  
Xu Qing Wang ◽  
Yue Tang
Keyword(s):  
Fatigue Life ◽  
Powder Metallurgy ◽  
Applied Stress ◽  
Low Cycle Fatigue ◽  
Influencing Factor ◽  
Fatigue Tests ◽  
Fatigue Properties ◽  
Nickel Base Superalloy ◽  
Loading Frequency ◽  
Cycle Fatigue

Low cycle fatigue (LCF) properties of a powder metallurgy(PM) nickel base superalloy FGH720Li were systematically studied in this work, including smooth LCF and notched LCF tested at various temperatures and different stress. The relationship between the fatigue life and applied stress was analyzed both for smooth fatigue and notch fatigue tests. The effects of loading frequency and stress ratio on LCF behavior were also studied. As an important influencing factor of the fatigue life in powder metallurgy superalloy, the effect of inclusions on LCF life was also investigated. The results showed that the fatigue properties of FGH720Li alloy was excellent, when tested at the temperature of 450°C and applied stress of 1230MPa, the fatigue life could exceed 5×104 cycles. When tested at 650°C and 1150MPa, the average fatigue life was still beyond 2×105 cycles.

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