scholarly journals Effect of Surface Mechanical Attrition Treatment on the very high cycle fatigue behavior of TC11

2018 ◽  
Vol 165 ◽  
pp. 09001
Author(s):  
Tao Gao ◽  
Zhidan Sun ◽  
Hongqian Xue ◽  
Delphine Retraint
Keyword(s):  
Titanium Alloy ◽  
Fatigue Strength ◽  
Crack Initiation ◽  
High Cycle Fatigue ◽  
Surface Mechanical Attrition Treatment ◽  
Cycle Fatigue ◽  
Very High Cycle Fatigue ◽  
Mechanical Attrition ◽  
Before And After ◽  
Very High

As an important engine component material, TC11 (Ti-6.5Al-3.5Mo-1.5Zr-0.3Si) titanium alloy is subjected to high frequency cyclic loading and its failure occurs beyond 109 cycles. It is thus essential to investigate the very high cycle fatigue (VHCF) behavior of this alloy. Surface Mechanical Attrition Treatment (SMAT) is a promising surface treatment technique to improve fatigue strength by modifying the surface microstructure. Therefore, it is important to understand the fatigue damage and failure process of SMATed titanium alloy in the VHCF regime. In this work, VHCF tests of TC11 before and after SMAT under fully reversed loading were conducted at room temperature by using an ultrasonic fatigue testing machine at a frequency of 20 kHz. The preliminary results seem to indicate that SMAT can reduce fatigue strength and fatigue life of TC11. Fracture surface analysis of the specimens before and after SMAT was performed using scanning electron microscope (SEM) to investigate the mechanisms of crack initiation and propagation. Particular attention was paid to fatigue crack initiation sites. The effect of SMAT on damage mechanism of SMATed TC11 in the VHCF regime was discussed.

scholarly journals Properties of the Fine Granular Area and Postulated Models for Its Formation during Very High Cycle Fatigue—A Review

2020 ◽  
Vol 10 (23) ◽  
pp. 8475
Author(s):  
Jan Patrick Sippel ◽  
Eberhard Kerscher
Keyword(s):  
Fatigue Strength ◽  
Crack Initiation ◽  
Crack Growth ◽  
High Performance ◽  
High Cycle Fatigue ◽  
The Other ◽  
Cycle Fatigue ◽  
Very High Cycle Fatigue ◽  
Open Questions ◽  
Very High

Understanding the mechanisms leading to very high cycle fatigue is necessary to make predictions about the behavior under various conditions and to ensure safe design over the whole lifetime of high-performance components. It is further vital for the development of possible measures to increase the very high cycle fatigue strength. This review therefore intends to give an overview of the properties of the fine granular area that have been observed so far. Furthermore, the existing models to describe the early crack initiation and crack growth within the very high cycle fatigue regime are outlined and the models are evaluated on the basis of the identified fine granular area properties. The aim is to provide an overview of the models that can already be considered refuted and to specify the respective open questions regarding the other individual models.

scholarly journals Effect of LCF Pre-Damage on Very High Cycle Fatigue Behavior of TC21 Titanium Alloy

2017 ◽  
Author(s):  
Nie Baohua ◽  
Zhao Zihua ◽  
Ouyang Yongzhong ◽  
Chen Dongchu ◽  
Chen Hong ◽  
...  
Keyword(s):  
Titanium Alloy ◽  
Crack Initiation ◽  
High Cycle Fatigue ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Fatigue Crack Initiation ◽  
Mechanism Analysis ◽  
Cycle Fatigue ◽  
Very High Cycle Fatigue ◽  
Very High

The effect of low cycle fatigue (LCF) pre-damage on the subsequent very high cycle fatigue (VHCF) behavior is investigated in TC21 titanium alloy. LCF pre-damage is applied under 1.8% strain amplitude up to various fractions of the expected life and subsequent VHCF properties are determined using ultrasonic fatigue tests. Results show that 5% of LCF pre-damage insignificantly affects the VHCF limit due to the absent of pre-crack, but decreases the subsequent fatigue crack initiation life estimated by Pairs’ law. Pre-cracks introduced by 10% and 20% of LCF pre-damage significantly reduce the subsequent VHCF limits. The crack initiation site shifts from subsurface-induced fracture for undamaged and 5% of LCF pre-damage specimens to surface pre-crack for 10% and 20% of LCF pre-damage specimens in very high cycle region. The fracture mechanism analysis indicate that LCF pre-crack will re-start to propagate under subsequently low stress amplitude when stress intensity factor of pre-crack is larger than its threshold. Furthermore, the predicted fatigue limits based on EI Haddad model for the LCF pre-damage specimens well agree with the experimental results.

scholarly journals Defect induced cracking and modeling of fatigue strength for an additively manufactured Ti-6Al-4V alloy in very high cycle fatigue regime

2021 ◽  
Author(s):  
Weiqian Chi ◽  
Wenjing Wang ◽  
Chengqi Sun
Keyword(s):  
Fatigue Strength ◽  
Crack Initiation ◽  
High Cycle Fatigue ◽  
Surface Defects ◽  
Fatigue Crack Initiation ◽  
Projection Area ◽  
Cycle Fatigue ◽  
Very High Cycle Fatigue ◽  
Artificial Surface ◽  
Very High

Additively manufactured (AM) alloy usually inevitably contains defects during the manufacturing processor or service process. Defects, as a harmful factor, could significantly reduce the fatigue performance of materials. This paper shows that the location and introduced form of defects play an important role in high cycle and very high cycle fatigue (VHCF) behavior of selective laser melting Ti-6Al-4V alloy. S-N curve descends linearly for internal defects induced failure. While for artificial surface defects induced failure, S-N curve descends at first and then exhibits a plateau region feature. We also observed competition of interior crack initiation with the fine granular area feature in VHCF regime. The paper indicates that only the size or the stress intensity factor range of the defect is not an appropriate parameter describing the effect of defects on the fatigue crack initiation. Finally, the effect of artificial surface defects on high cycle and VHCF strength is modeled, i.e. the fatigue strength   σ, fatigue life  N and defect size area (square root of projection area of defect perpendicular to principal stress direction) is expressed as  σ = CN ( area)  for  N and  σ = CN ( area)  for  N≥N, where  C,  a and  n are constants, N is the number of cycles at the knee point.

scholarly journals Defect induced cracking and modeling of fatigue strength for an additively manufactured Ti-6Al-4V alloy in very high cycle fatigue regime

2021 ◽  
Author(s):  
Weiqian Chi ◽  
Wenjing Wang ◽  
Chengqi Sun
Keyword(s):  
Fatigue Life ◽  
Fatigue Strength ◽  
Crack Initiation ◽  
Surface Defect ◽  
High Cycle Fatigue ◽  
Projection Area ◽  
Cycle Fatigue ◽  
Very High Cycle Fatigue ◽  
Artificial Surface ◽  
Very High

Additively manufactured (AM) alloy usually inevitably contains defects during manufacturing processor in service. Defects, as a harmful factor, could significantly reduce the fatigue performance of materials. This paper shows that the location and introduced form of defects play an important role in high cycle and very high cycle fatigue (VHCF) behavior of selective laser melting Ti-6Al-4V alloy. The fatigue life descends linearly with stress amplitude for interior defect induced failure. While for artificial surface defect induced failure, the fatigue life descends at first, and then exhibits a plateau region feature. We also observed competition of interior crack initiation with fine granular area feature in VHCF regime. The paper indicates that only the size or the stress intensity factor range of the defect is not an appropriate parameter describing the effect of defect on the fatigue crack initiation. Finally, the effect of artificial surface defect on high cycle and VHCF strength is modeled, i.e. the fatigue strength  σ, fatigue life  N and defect size ( area)  (square root of projection area of defect perpendicular to principal stress direction) is expressed as  σ= CN( area) for  N0 and  σ= CN ( area) for  N≥N , where  C,  a and  n are constants, N  is the number of cycles at the knee point.

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