Study of crack initiation or damage in very high cycle fatigue using ultrasonic fatigue test and microstructure analysis

We reviewed the research and developments in the field of fatigue failure, focusing on very-high cycle fatigue (VHCF) of metals, alloys, and steels. We also discussed ultrasonic fatigue testing, historical relevance, major testing principles, and equipment. The VHCF behavior of Al, Mg, Ni, Ti, and various types of steels were analyzed. Furthermore, we highlighted the major defects, crack initiation sites, fatigue models, and simulation studies to understand the crack development in VHCF regimes. Finally, we reviewed the details regarding various issues and challenges in the field of VHCF for engineering metals and identified future directions in this area.

Download Full-text

Effect of shot peening on very high cycle fatigue of 2024-T351 aluminium alloy

Materials Express ◽

10.1166/mex.2020.1722 ◽

2020 ◽

Vol 10 (7) ◽

pp. 1032-1039

Author(s):

Renhui Tian ◽

Jiangfeng Dong ◽

Yongjie Liu ◽

Qingyuan Wang ◽

Yunrong Luo

Keyword(s):

Fracture Surface ◽

Crack Initiation ◽

Shot Peening ◽

High Cycle Fatigue ◽

Fatigue Tests ◽

Cycle Fatigue ◽

Very High Cycle Fatigue ◽

Fatigue Strength Improvement ◽

Ultrasonic Fatigue ◽

Very High

To investigate the influence of shot peening (SP) on very high cycle fatigue (VHCF) performance of 2024-T351, the specimens with three surface conditions were performed under ultrasonic fatigue tests: mechanicallypolished without peening (NP), ceramic shot peening (SP1), steel and glass mixed shot peening (SP2). The roughness, microhardness, residual stress, fractography measurement and scanning electron microscopy (SEM) were applied before fatigue test to characterize the effective layer induced by the peening treatment. For the failed specimens, the fracture surface were analysed using SEM to study the mechanisms of fatigue crack propagation. In addition, the fatigue life curve in ultra-high cycle region continuously decreased in the three series of specimens. However, the experimental results revealed that fatigue strength improvement resulting from shot peening treatment was negligible in very high cycle regime. Furthermore, the stress intensity factor for the surface crack initiation (SCI) and interior crack initiation (ICI) was discussed based on quantitative analysis on the fracture surface. The average values of ΔKfish-eye for NP, SP1 and SP2 specimens are about 2.22, 1.48 and 1.61 MPa · m1/2, respectively.

Download Full-text

Very High Cycle Fatigue Investigations on the Fatigue Strength of Additive Manufactured and Conventionally Wrought Inconel 718 at 873 K

Metals ◽

10.3390/met11111682 ◽

2021 ◽

Vol 11 (11) ◽

pp. 1682

Author(s):

Alexander Schmiedel ◽

Christina Burkhardt ◽

Sebastian Henkel ◽

Anja Weidner ◽

Horst Biermann

Keyword(s):

Crack Initiation ◽

Inconel 718 ◽

High Cycle Fatigue ◽

Fatigue Testing ◽

Reference Conditions ◽

Cycle Fatigue ◽

Very High Cycle Fatigue ◽

Ultrasonic Fatigue ◽

Fine Grained Structure ◽

Very High

The fatigue lives of additively manufactured (AM) Inconel 718 (IN718) produced by selective electron beam melting and conventional wrought material as reference conditions were studied in the very high cycle fatigue regime under fully reversed loading (R = −1) at the elevated temperature of 873 K using an ultrasonic fatigue testing system. The fatigue lives of the AM material were significantly reduced compared to the wrought material, which is discussed in relation to the microstructure and a fractographical analysis. The additively manufactured material showed large columnar grains with a favoured orientation to the building direction and porosity, whereas the wrought material showed a fine-grained structure with no significant texture, but had Nb- and Ti-rich non-metallic inclusions. Crystallographic crack initiation as well as crack initiation from the surface or internal defects were observed for the AM and the wrought IN718, respectively.

Download Full-text

The influential factors on very high cycle fatigue testing results

MATEC Web of Conferences ◽

10.1051/matecconf/201816520002 ◽

2018 ◽

Vol 165 ◽

pp. 20002 ◽

Cited By ~ 1

Author(s):

PENG Wen-jie ◽

XUE Huan ◽

GE rui ◽

PENG zhou

Keyword(s):

Fatigue Test ◽

High Cycle Fatigue ◽

Fatigue Testing ◽

Inclusion Size ◽

Influential Factors ◽

Test Results ◽

Cycle Fatigue ◽

Very High Cycle Fatigue ◽

Ultrasonic Fatigue ◽

Very High

When the fatigue cycle is extended from high cycle (105~107) to very high cycle (107~109), the fatigue testing results will be more sensitive to the influential factors such as specimen size, specimen surface roughness and the inclusion size. The influential factors on the very high cycle fatigue testing results are investigated in the present paper. Firstly, the design and control method for ultrasonic fatigue test were introduced for several specimen shapes. The effect of the shape, size and the surface roughness of specimen on the ultrasonic fatigue test results are investigated. Meanwhile, the effect of test frequency and the size of the inclusion on the fatigue test results are also investigated. It is concluded that: 1. the test results of specimen with different shape and size differ with each other, due to the risk volume is different. 2. There is a critical roughness for the specimen, depending on the hardness of tested metallic material. A larger roughness than the critical one will lead to a premature fracture. 3. The frequency effect is obvious for the low strength steel, however, is prone to vanish for the very high strength steel. 4. The very high cycle fatigue will be more sensitive to the inclusion size as the strength increases and the S/N curve character is strongly related to the size of the inclusion.

Download Full-text

Usability of Ultrasonic Frequency Testing for Rapid Generation of High and Very High Cycle Fatigue Data

Materials ◽

10.3390/ma14092245 ◽

2021 ◽

Vol 14 (9) ◽

pp. 2245

Author(s):

Michael Fitzka ◽

Bernd M. Schönbauer ◽

Robert K. Rhein ◽

Niloofar Sanaei ◽

Shahab Zekriardehani ◽

...

Keyword(s):

Strain Rate ◽

High Cycle Fatigue ◽

Fatigue Properties ◽

Ultrasonic Frequency ◽

Cycle Fatigue ◽

Reinforced Polymer ◽

Very High Cycle Fatigue ◽

Ultrasonic Fatigue ◽

Fibre Reinforced Polymer ◽

Very High

Ultrasonic fatigue testing is an increasingly used method to study the high cycle fatigue (HCF) and very high cycle fatigue (VHCF) properties of materials. Specimens are cycled at an ultrasonic frequency, which leads to a drastic reduction of testing times. This work focused on summarising the current understanding, based on literature data and original work, whether and how fatigue properties measured with ultrasonic and conventional equipment are comparable. Aluminium alloys are not strain-rate sensitive. A weaker influence of air humidity at ultrasonic frequencies may lead to prolonged lifetimes in some alloys, and tests in high humidity or distilled water can better approximate environmental conditions at low frequencies. High-strength steels are insensitive to the cycling frequency. Strain rate sensitivity of ferrite causes prolonged lifetimes in those steels that show crack initiation in the ferritic phase. Austenitic stainless steels are less prone to frequency effects. Fatigue properties of titanium alloys and nickel alloys are insensitive to testing frequency. Limited data for magnesium alloys and graphite suggest no frequency influence. Ultrasonic fatigue tests of a glass fibre-reinforced polymer delivered comparable lifetimes to servo-hydraulic tests, suggesting that high-frequency testing is, in principle, applicable to fibre-reinforced polymer composites. The use of equipment with closed-loop control of vibration amplitude and resonance frequency is strongly advised since this guarantees high accuracy and reproducibility of ultrasonic tests. Pulsed loading and appropriate cooling serve to avoid specimen heating.

Download Full-text