Fatigue Damage Mechanism of Titanium in Inert Environments

2012 ◽  
Vol 225 ◽  
pp. 225-229
Author(s):  
Nur Ismarrubie Zahari ◽  
H. Yussof ◽  
M. Sugano
Keyword(s):  
Fatigue Strength ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Fatigue Damage ◽  
Thin Plate ◽  
Fatigue Behavior ◽  
Fatigue Cracks ◽  
Damage Mechanism ◽  
Lattice Defects ◽  
Argon Gas

The fatigue damage of titanium has been studied on thin plate specimens subjected to alternating plane bending in argon gas. Fatigue strength in argon gas at Nf = 108 cycles was obtained to be 102 MPa. Fatigue behavior of titanium in argon gas has been attributed to the degradation of grain boundary cohesion with argon gas atoms/molecules. Fatigue cracks were propagated partly in intergranular mode. It has been plausible that argon gas atoms/molecules could penetrate into the distorted regions close to grain boundary through lattice defects and degrade grain boundary cohesion. Grain boundaries have been preferentially damaged in argon gas. The results in argon gas have been compared with those obtained in vacuum and in air.

scholarly journals Fatigue Behavior of Non-Optimized Laser-Cut Medical Grade Ti-6Al-4V-ELI Sheets and the Effects of Mechanical Post-Processing

Metals ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 843 ◽  
Author(s):  
André Reck ◽  
André Till Zeuner ◽  
Martina Zimmermann
Keyword(s):  
Surface Roughness ◽  
Fatigue Strength ◽  
Surface Quality ◽  
Laser Cutting ◽  
Fatigue Behavior ◽  
Fatigue Cracks ◽  
Surface Condition ◽  
Mechanical Polishing ◽  
Fatigue Properties ◽  
Post Processing

The study presented investigates the fatigue strength of the (α+β) Ti-6Al-4V-ELI titanium alloy processed by laser cutting with and without mechanical post-processing. The surface quality and possible notch effects as a consequence of non-optimized intermediate cutting parameters are characterized and evaluated. The microstructural changes in the heat-affected zone (HAZ) are documented in detail and compared to samples with a mechanically post-processed (barrel grinding, mechanical polishing) surface condition. The obtained results show a significant increase (≈50%) in fatigue strength due to mechanical post-processing correlating with decreased surface roughness and minimized notch effects when compared to the surface quality of the non-optimized laser cutting. The martensitic α’-phase is detected in the HAZ with the formation of distinctive zones compared to the initial equiaxial α+β microstructure. The HAZ could be removed up to 50% by means of barrel grinding and up to 100% through mechanical polishing. A fracture analysis revealed that the fatigue cracks always initiate on the laser-cut edges in the as-cut surface condition, which could be assigned to an irregular macro and micro-notch relief. However, the typical characteristics of the non-optimized laser cutting process (melting drops and significant higher surface roughness) lead to early fatigue failure. The fatigue cracks solely started from the micro-notches of the surface relief and not from the dross. As a consequence, the fatigue properties are dominated by these notches, which lead to significant scatter, as well as decreased fatigue strength compared to the surface conditions with mechanical finishing and better surface quality. With optimized laser-cutting conditions, HAZ will be minimized, and surface roughness strongly decreased, which will lead to significantly improved fatigue strength.

scholarly journals Improvement of trawler hull structure under condition of ensuring fatigue strength

2021 ◽  
Vol 4 (7(112)) ◽  
pp. 50-59
Author(s):  
Leontii Korostylov ◽  
Dmytro Lytvynenko ◽  
Hryhorii Sharun ◽  
Ihor Davydov
Keyword(s):  
Fatigue Strength ◽  
Fatigue Damage ◽  
Hot Spot ◽  
Fatigue Cracks ◽  
Bending Moment ◽  
Theoretical Method ◽  
Corrosive Wear ◽  
Hot Spot Stress ◽  
Hull Structure ◽  
Internal Forces

The structure of the hull of the project 1288 trawler in a region of fore hold was improved to ensure fatigue strength of assemblies of the intersection of main frames with the second bottom. To this end, a study of the fatigue strength of these assemblies was carried out for the original side structure and two versions of its modernization. Values of internal forces at the points of appearance of fatigue cracks in the compartment have been determined for three design versions of the side. It was found that the greatest forces act in the middle of the fore half of the compartment. Calculations of parameters of the long-term distribution of magnitudes of ranges of total equivalent operating stresses according to the Weibull law in the points of occurrence of fatigue cracks for different design versions of the side grillage have been performed. These parameters were determined for the middle of the fore hold of the vessel and for the areas in which maximum values of bending moment ranges are in effect with and without corrosive wear. Values of total fatigue damage and durability of the studied assemblies were determined. Calculations were carried out by nominal stress method, hot spot stress method, and experimental and theoretical method. It was shown that in order to ensure fatigue strength of the assembly under consideration, it is necessary to extend the intermediate frames of the original version of the side structure to the level of the second bottom fixing them to the deck. It is also necessary to attach a cargo platform to the side thus reducing the frame span. As a result, the level of fatigue damage over 25 years of operation will decrease by about 3.5 times. As it was found, approximate consideration of the slamming effect does not significantly increase the amount of fatigue damage to the assembly. The results of the development of recommendations for modernization of the side structure can be implemented both on ships of the 1288 project and on other ships with a transverse side framing system.

Effects of Microstructures on the Mechanical Properties of Dilute Al-Si Alloys

2007 ◽  
Vol 345-346 ◽  
pp. 821-824
Author(s):  
Keiyu Nakagawa ◽  
Teruto Kanadani
Keyword(s):  
Fatigue Strength ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Aging Time ◽  
Fracture Elongation ◽  
Micro Cracks ◽  
Hand Fracture ◽  
Stress Cycles ◽  
Effects Of Aging ◽  
The Relationship

In this paper, we investigated effects of aging at 473K on the relationship between microstructure in the vicinity of the grain boundaries and fatigue strength for Al-1.2%Si alloy. Results obtained show the following features. (1) As aging time, tA increase, the tensile strength (σB) and 0.2% proof stress (σ0.2) increase slowly, but gradually decrease after reaching a maximum at around 18 ks. On the other hand, fracture elongation shows an opposite trend, suggesting that at aging times above 18ks, over aging occurs. (2) The fatigue strength lowers with increasing aging time, however, when the aging time is more than 18 ks at 473K, the fatigue strength remains almost the same. (3) When the aging time is more than 6 ks, grain boundary precipitates with a size greater than several 10s of nm are observed. (4) When the aging time is 18 ks, an accumulation of dislocations are observed at the grain boundaries and in the vicinity of grain boundary precipitates, and dislocations increase with the number of stress cycles. (5) When the aging time is more than 6 ks, the fatigue fracture surface is mainly intergranular. These results suggest that reduction of fatigue strength results from propagation of micro-cracks which are initiated at the large precipitates on the grain boundaries.

Fully Reversed Electric Fatigue Behavior of a Piezoelectric Composite Actuator

2008 ◽  
Author(s):  
Sung-Choong Woo ◽  
Nam Seo Goo
Keyword(s):  
Fatigue Damage ◽  
Fatigue Behavior ◽  
Damage Mechanism ◽  
Ceramic Layer ◽  
Piezoelectric Composite ◽  
Transgranular Fracture ◽  
Intergranular Cracking ◽  
Composite Actuator ◽  
Electric Fatigue ◽  
Pzt Ceramic

The aim of this study is to investigate fully reversed electric fatigue behavior of a piezoelectric composite actuator (PCA). For that purpose, fatigue tests with different loading conditions have been conducted and the performance degradation has been monitored. During a preset number of loading cycles, non-destructive acoustic emission (AE) tests were used for monitoring the damage evolution in real time. The displacement-cycle curves were obtained in fully reversed cyclic bending loading. The microstructures and fracture surfaces of PCA were examined to reveal their fatigue damage mechanism. The results indicated that the AE technique was applicable to fatigue damage assessment in the piezoelectric composite actuator. It was shown that the initial damage mechanism of PCAs under fully reversed electric cyclic loading originated from the transgranular fracture in the PZT ceramic layer; with increasing cycles, local intergranular cracking initiated and the either developed onto the surface of the PZT ceramic layer or propagated into the internal layer, which were some different depending on the drive frequencies and the lay-up sequence of the PCA.

Fatigue Behavior of Type 316L Stainless Steel Coated with Plasma-Sprayed Alumina in Corrosive Environment

1998 ◽  
Author(s):  
H. Kisuki ◽  
M. Sugano ◽  
T. Oshima ◽  
Y. Nasu ◽  
K. Okazaki ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Fatigue Strength ◽  
Plasma Spraying ◽  
Early Stage ◽  
Fatigue Behavior ◽  
Fatigue Cracks ◽  
Fatigue Properties ◽  
Crack Growth Behavior ◽  
Grit Blasting ◽  
Plasma Sprayed

Abstract Fatigue properties of the Al2O3 plasma-sprayed SUS316L stainless steel rod specimens coated on different spraying conditions have been studied in a physiological saline solution (0.9 % NaCl solution) to evaluate the potential of surgical implant application. Fatigue tests were conducted in push-pull loading at the stress ratio of R = -1, and frequency of 2 Hz. Microstructure related with fatigue damage was examined by SEM and TEM. The fatigue strength of Al2O3 plasma-sprayed metals significantly depended on spraying conditions: the effects of spraying on fatigue strength decreased with increasing the applied stress amplitude. As-blasted specimens were higher in fatigue strength than Al2O3 plasma-sprayed specimens. It was found that the plasma spraying had significant effects on fatigue crack growth behavior in the early stage of crack propagation. Fatigue cracks preferentially originated from dents that had been caused on the substrata metal surface subjected to grit-blasting. These results are discussed with both the compressive residual stresses due to the grit blasting which was carried out prior to plasma spraying and the corrosion-resistance of the alumina deposit.

Improvement of Fatigue Crack Growth Resistance by Serrated Grain Boundary at High Temperature

1991 ◽  
Vol 113 (1) ◽  
pp. 9-14 ◽  
Author(s):  
Hiroshi lizuka ◽  
Manabu Tanaka ◽  
Fumio Ashihara
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Crack Growth ◽  
Growth Rates ◽  
Fatigue Cracks ◽  
Crack Growth Resistance ◽  
Fatigue Crack Growth Resistance ◽  
Crack Growth Rates

Effects of serrated grain boundaries on the improvement of fatigue-crack growth resistance were investigated using austenitic 21Cr-4Ni-9Mn heat-resisting steel at 973K in air. Grain boundaries were serrated by grain-boundary reaction precipitates. The crack-growth rates were considerably decreased in the specimens with the serrated grain boundaries. The fatigue cracks were largely deflected by the serrated grain boundaries, and brittle intergranular fracture was retarded. The improvement of the crack-growth resistance was obtained especially under the conditions of low crack-growth rates of less than 30 μm/cycle. The widths and the heights of the deflected portions of the cracks were in the range from about a few μm to 30 μm.

Study on Bending Ultrasonic Fatigue Behavior of Sinter-Hardened Fe-2Cu-2Ni-1Mo-1C Materials Prepared by Warm Compaction

2010 ◽  
Vol 638-642 ◽  
pp. 1848-1853 ◽  
Author(s):  
Zhi Yu Xiao ◽  
Ling Zhou ◽  
Yuan Xun Shen ◽  
Tungwai Leo Ngai ◽  
Yuan Yuan Li
Keyword(s):  
Fatigue Strength ◽  
Crack Propagation ◽  
Fatigue Testing ◽  
Fatigue Behavior ◽  
Fatigue Cracks ◽  
Bending Fatigue ◽  
Warm Compaction ◽  
Ultrasonic Fatigue ◽  
Number Of Cycles ◽  
Rupture Mode

Bending fatigue behavior of a sinter-hardened high density (7.4 g/cm3) Fe-2Cu-2Ni-1Mo-1C material fabricated by die-wall lubricated warm compaction of partially-diffuse alloyed powder was studied by bending ultrasonic fatigue testing. Results showed that fatigue strength decreases continuously with the increasing number of cycles. The fatigue failure yet occurs in the regime of exceeding 107 cycles and exhibits no traditional horizontal plateau between 106 and 107 cycles. Fatigue strength was 194 MPa, 239 MPa and 293 MPa at 108, 107 and 106 cycles respectively. Scanning electron microscopy revealed that cracks initiated from large pores on the surface and from pore clusters near the sub-surface. The fatigue cracks initiated both at single and multiple sites. Crack propagation was mainly in a trans-crystalline rupture mode. Fatigue striation and cleavage plane were observed in the crack propagation region and dimples were observed in the fracture zones.

Recent x-ray diffraction studies of metal fatigue in Japan

1975 ◽  
Vol 10 (1) ◽  
pp. 32-41 ◽  
Author(s):  
K Tanaka
Keyword(s):  
Residual Stress ◽  
Fatigue Strength ◽  
Fatigue Damage ◽  
Fatigue Cracks ◽  
Stress And Strain ◽  
Metal Fatigue ◽  
X Ray Diffraction ◽  
X Ray ◽  
Future Developments ◽  
Non Destructive

This paper describes results of several recent studies, carried out in Japan, on metal-fatigue problems using X-ray diffraction techniques. The subjects covered are the effect of residual stress on fatigue strength, non-destructive detection of fatigue damage from information supplied by X-ray diffraction, and X-ray microbeam analysis of stress and strain near the tips of fatigue cracks and fracture surfaces. The usefulness of the X-ray approach to fatigue problems is emphasized and possible future developments are suggested.

scholarly journals Mechanism of Precipitate Microstructure Affecting Fatigue Behavior of 7020 Aluminum Alloy

Materials ◽  
2020 ◽  
Vol 13 (15) ◽  
pp. 3248 ◽  
Author(s):  
Zhaojun Shan ◽  
Shengdan Liu ◽  
Lingying Ye ◽  
Yiran Li ◽  
Chunhua He ◽  
...  
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Crack ◽  
Fatigue Strength ◽  
Fatigue Behavior ◽  
Fatigue Cracks ◽  
Aged Alloy ◽  
Soft Matrix ◽  
Crack Propagation Resistance ◽  
Boundary Precipitate ◽  
Peak Aged

The effect of different precipitate microstructures obtained by different heat treatments on fatigue behavior of 7020 aluminum alloy was investigated. The fine Guinier Preston I (GPI) zones in the under-aged alloy can be repeatedly sheared by dislocations produced in cyclic loading, making the fatigue crack initiate difficultly and fatigue crack path propagate tortuously. Fatigue strength and fatigue crack propagation resistance of the alloy with shearable precipitates are much higher than those of the alloy with unshearable precipitates. The peak-aged alloy with continuous grain boundary precipitate (GBP) and narrow precipitate free zone (PFZ) is prone to initiate fatigue cracks and reduce fatigue strength. With the growth of unshearable precipitates, the fatigue strength of the alloy firstly increases and then decreases. Precipitates with moderate size in the over-aged alloy improve the roughness-induced crack closure (RICC) effect. Soft matrix with appropriate width between the precipitates can promote the slip reversibility and relax the crack tip stress. The fatigue strength of the moderately over-aged alloy reaches to 122.1 MPa at 107 cycles of loading, and the fatigue crack growth rate (FCGR) is 35.6% slower than that of the peak-aged alloy at ΔK of 10 MPa·m1/2.

Sensitivity to Fatigue Cracks Initiation of Symmetrical Tilt Grain Boundaries in Pure Copper Bicrystals in 1M NaNO2 Solution

2007 ◽  
Vol 561-565 ◽  
pp. 2415-2418
Author(s):  
Hiroyuki Miyamoto ◽  
K. Kuroda ◽  
Takura Mimaki
Keyword(s):  
Plastic Strain ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Fatigue Cracks ◽  
Pure Copper ◽  
Large Angle ◽  
Compression Tests ◽  
High Susceptibility ◽  
Axial Tension ◽  
Pile Up

Sensitivity to corrosion fatigue (CF) crack initiation has been investigated in a series of pure copper bicrystals with a symmetrical <110>-tilt grain boundary. Tests were performed by axial tension-compression tests in 1M NaNO2 solutions. The small-angle tilt bicrystals fractured in both intergranular and transgranular manners accompanied by a large amount of plastic strain to fracture while the large-angle bicrystals fractured in almost intergranular manner with a smaller plastic strain. Susceptibility to CF cracks increases with increasing misorientation. It seems that effect of grain boundaries structures, i.e., Σ-values is small in this experiment. Stress concentration generated by the pile-up of trapped dislocations at the grain boundary could account for the high susceptibility of the intergranular cracks in large-angle grain boundaries

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