Effect of Low Cycle Fatigue Predamage on Very High Cycle Fatigue Behavior of TC21 Titanium Alloy

Nie, Baohua; Zhang, Zhao; Ouyang, Yong-Zhong; Chen, Dongchu; Chen, Hong; Sun, Haibo; Shu, Liu

doi:10.3390/ma10121384

Cited by 15 publications

(8 citation statements)

References 24 publications

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“…Titanium alloys are widely used for aeronautical structures because of their high specific strength, toughness, and damage tolerance [1]. Due to the very high vibration frequency of aeronautical structures, their fatigue failure occurs in the very high cycle fatigue (VHCF, i.e., more than 10 7 cycles) regime, and fatigue cracks are inclined to initiate at the subsurface of high strength titanium alloys [2,3]. In practice, notches in aeronautical structures are a common problem resulting from the sharp change of a complex geometry, such as a screw thread, groove, scratch, and foreign object damage (FOD).…”

Section: Introductionmentioning

confidence: 99%

Notch Effect on the Fatigue Behavior of a TC21 Titanium Alloy in Very High Cycle Regime

et al. 2018

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The very high cycle fatigue (VHCF) property of TC21 titanium alloy blunt-notched specimens were investigated by using an ultrasonic fatigue test machine with a frequency of 20 kHz. S–N of blunt-notched specimens illustrated a continuous decrease characteristic with a horizontal line over the 105–109 cycle regimes. However, the fatigue life showed a large scatter for blunt-notched specimens. Blunt-notch significantly reduced the fatigue property in the high cycle and very high cycle regimes compared with that of smooth specimens. The crack initiation modes for blunt-notched specimens in the very high cycle regime can be divided into three types: (i) surface initiation, (ii) subsurface with flat facet, and (iii) subsurface with “facet + fine granular area”. The crack initiation mechanism of blunt-notched specimens is discussed in view of the interaction of notch stress gradient distribution and heterogeneous microstructure. Furthermore, the fatigue limit model based on the theory of critical distance (TCD) was modified for the very high cycle regime, and the scatter of the fatigue property of the blunt-notched specimens were well predicted by using this model.

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Section: Introductionmentioning

confidence: 99%

Notch Effect on the Fatigue Behavior of a TC21 Titanium Alloy in Very High Cycle Regime

et al. 2018

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“…Accelerated testing is usually conducted in the medium stress range. The hyperbolic sine stress term of Equation (5) in the medium range can be redefined as…”

Section: Parametric Accelerated Life Testing Of Mechanical Systemsmentioning

confidence: 99%

“…However, in this instance, there had been no proper testing methods for the failures of the mechanical product detected in field [1][2][3]. Repeated loads or overloading due to daily usage may cause structural failure in a product and reduce its lifetime [4,5]. Many engineers think such possibilities can be assessed by: (1) mathematical modeling using Newtonian methods, (2) assessing the time response of the system for dynamic loads, (3) utilizing the rain-flow counting method [6,7], or (4) estimating system damage using the Palmgren-Miner's rule [8].…”

Section: Introductionmentioning

confidence: 99%

Improving the Reliability of Mechanical Components That Have Failed in the Field Due to Repetitive Stress

Woo¹,

O’Neal

2019

Metals

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To improve the reliability of mechanical parts that have failed in the field, a reliability methodology for parametric accelerated life testing (ALT) is proposed. It consists of: (1) a parametric ALT plan, (2) a load analysis, (3) a tailored series of parametric ALTs with action plans, and (4) an evaluation of the final designs to ensure the design requirements are satisfied. This parametric ALT should help an engineer reproduce the fractured or failed parts in a product subjectedto repetitive loading and correct the faulty designs. As a test case, the helix upper dispenser of a refrigerator ice-maker fractured in field was studied. Using a load analysis, we discerned that the helix upper dispenser fracture was due to repetitive loads and a faulty design with a 2 mm gap between the blade dispenser and the helix upper dispenser. During the first and second ALTs, the fracture in the helix upper dispenser was reproduced. The failure modes and mechanisms found were similar to those of the failed sample in field. As an action plan, the design of the helix upper dispenser was modified by eliminating the 2 mm gap and adding enforced ribs. In the third ALT there were no problems. After three rounds of parametric ALTs, the reliability of the helix upper dispenser was guaranteed as a 10-year life with an accumulated failure rate of 1%.

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Section: Introductionmentioning

confidence: 99%

“…Throughout their ultra-long time service, the components are subjected to cyclic load with high frequency and low amplitude, thus the very high cycle fatigue (VHCF) of titanium alloy has been drawing world wide attention [2,3]. Fatigue failure in high strength titanium alloys occurs beyond the conventional fatigue limit of 10 7 cycles, and the stress-number of cycles to failure (S-N) curves exhibit a step-wise shape [2] or a decreasing shape [4]. Another important characteristic of these titanium alloys is that the crack initiation site shifts from the surface-induced fracture at low cycle regimes to a subsurface-induced fracture at very high cycle regimes [5], which may be responsible for the variability of the fatigue properties and the step-wise shape of the S-N curve.…”

Section: Introductionmentioning

confidence: 99%

Effect of Basketweave Microstructure on Very High Cycle Fatigue Behavior of TC21 Titanium Alloy

Nie

Zhang

Chen

et al. 2018

Metals

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This paper discusses the effect of basketweave microstructure on the very high cycle fatigue behavior of TC21 titanium alloy. Ultrasonic fatigue tests at 20 kHz are done on a very high cycle fatigue (VHCF) property of the alloys with 60 µm and 40 µm basketweave size, respectively. Results show that the alloys illustrate step-wise S-N characteristics over the 10 5 -10 9 cycle regimes and that fatigue fracture in both of the alloys occur beyond the conventional fatigue limit of 10 7 cycles. Subsurface crack initiation occurs at low stress amplitude. A fine granular area (FGA) is observed along the α lamella at the subsurface crack initiation site. The mechanism for the subsurface crack initiation is revealed using layer-by-layer-polishing, due to the micro-voids that are introduced at the granular α phase. The colony of α lamella is due to the local stress concentrated between them under the cyclic load. The stress intensity factor range at the FGA front is regarded as the threshold value controlling the internal crack propagation. Furthermore, the effect of the baseketweave size on the very high cycle fatigue limits of the TC21 titanium alloy is evaluated based on the Murakami model, which is consistent with the experimental results. The fatigue life of TC21 titanium alloy is well predicted using the energy-based crack nucleation life model.

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Effect of Low Cycle Fatigue Predamage on Very High Cycle Fatigue Behavior of TC21 Titanium Alloy

Cited by 15 publications

References 24 publications

Notch Effect on the Fatigue Behavior of a TC21 Titanium Alloy in Very High Cycle Regime

Notch Effect on the Fatigue Behavior of a TC21 Titanium Alloy in Very High Cycle Regime

Improving the Reliability of Mechanical Components That Have Failed in the Field Due to Repetitive Stress

Effect of Basketweave Microstructure on Very High Cycle Fatigue Behavior of TC21 Titanium Alloy

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