Notched Fatigue of Zr-Based Bulk Metallic Glass

2007 ◽  
Vol 345-346 ◽  
pp. 259-262 ◽  
Author(s):  
Yoshikazu Nakai ◽  
Naoki Sei ◽  
Bok Key Kim
Keyword(s):  
Crack Initiation ◽  
Metallic Glass ◽  
Bulk Metallic Glass ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Shear Bands ◽  
Fatigue Tests ◽  
Propagation Mechanism ◽  
Shear Mode ◽  
Crack Propagation Mechanism

In the present study, fatigue tests of sharp-notched Zr-based bulk metallic glass (BGM), were conducted under fully reversed cyclic bending, and the fatigue crack initiation mechanisms were clarified by using AFM. The fracture surface was also observed to examine the crack propagation mechanism. The fatigue notch factor was 2.0, while the elastic stress concentration factor is 2.7. From the macroscopic observations of fractured specimen, either tension mode or shear mode fracture morphologies were observed. Either in smooth specimens or notched specimens, no prodigious sign of crack initiation were observed, i.e., fatigue cracks were initiated from shear bands those were formed just before the crack initiation.

Fatigue Crack Initiation and Growth in Stainless Steel Pipe Welds

2009 ◽  
Author(s):  
D. Green ◽  
R. D. Smith ◽  
J. P. Taggart ◽  
D. Beardsmore ◽  
S. Robinson
Keyword(s):  
Crack Initiation ◽  
Crack Growth ◽  
Thermal Loading ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Cyclic Hardening ◽  
Element Model ◽  
Fatigue Tests ◽  
Welded Pipe ◽  
Pipe Work

Thermal fatigue cracks have been found in austenitic pipe work in many pressurised water reactors, caused by thermal cycling due to the passage of water at different temperatures along the pipe inner surface. The rates of crack initiation and growth for this situation are not well understood because of the stochastic nature of the temperature fluctuations. Therefore, large allowances must be made when assessing the integrity of this pipe work to this failure mechanism. Improved assessment of crack initiation and growth could enable increased plant availability, and better safety cases. A programme of work has been completed consisting of fatigue tests on thick 304L butt-welded pipe specimens, and accompanying predictions of crack initiation and growth. In each test, uniform thermal cycles were generated using a water jet on a small area of the pipe. The magnitude of the cycles differed between the tests. Crack initiation and growth were monitored using a dye penetrant technique, applied to the pipe inner and outer surfaces, together with destructive examination. Crack initiation predictions were made using fatigue data derived from mechanical fatigue tests on the same material as in the pipe specimens. Good predictions were made using a strain-life endurance curve at a temperature corresponding to the average temperature of the metal surface during the thermal cycle. Crack growth predictions were based on an inelastic finite-element model accounting for cyclic hardening, and an enhanced R5 procedure (1) with crack closure taken into account. A linear elastic fracture mechanics definition of a Paris law for crack growth was used, and plastic redistribution effects were included. Predictions were good for all of the experimental scenarios carried out. A further experimental and analytical programme is in hand using the same experimental arrangements, concerning variable amplitude thermal loading.

scholarly journals Mechanism of Fatigue Crack Initiation in Austenitic Stainless Steels in LWR Environments

2002 ◽  
Author(s):  
Omesh K. Chopra
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Stainless Steels ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Austenitic Stainless Steels ◽  
Fracture Morphology ◽  
Fatigue Tests ◽  
Temperature Level ◽  
Metallographic Examination

This paper examines the mechanism of fatigue crack initiation in austenitic stainless steels (SSs) in light water reactor (LWR) coolant environments. The effects of key material and loading variables, such as strain amplitude, strain rate, temperature, level of dissolved oxygen in water, and material heat treatment on the fatigue lives of wrought and cast austenitic SSs in air and LWR environments have been evaluated. The influence of reactor coolant environments on the formation and growth of fatigue cracks in polished smooth SS specimens is discussed. Crack length as a function of fatigue cycles was determined in air and LWR environments. The results indicate that decreased fatigue lives of these steels are caused primarily by the effects of the environment on the growth of cracks <200 μm and, to a lesser extent, on enhanced growth rates of longer cracks. A detailed metallographic examination of fatigue test specimens was performed to characterize the fracture morphology. Exploratory fatigue tests were conducted to enhance our understanding of the effects of surface micropits or minor differences in the surface oxide on fatigue crack initiation.

scholarly journals FATIGUE CRACK INITIATION IN A CARBON BLACK–FILLED NATURAL RUBBER

2016 ◽  
Vol 89 (1) ◽  
pp. 126-141 ◽  
Author(s):  
Bertrand Huneau ◽  
Isaure Masquelier ◽  
Yann Marco ◽  
Vincent Le Saux ◽  
Simon Noizet ◽  
...  
Keyword(s):  
Crack Initiation ◽  
Carbon Black ◽  
Natural Rubber ◽  
Energy Dispersive Spectrometry ◽  
Chemical Nature ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Fatigue Tests ◽  
X Rays ◽  
The Matrix

ABSTRACT A detailed study of the initiation of fatigue cracks in carbon black–filled natural rubber is conducted. Interrupted fatigue tests are performed and fatigued samples are observed with a scanning electron microscope. This procedure first enables the quantification of the morphology, spatial distribution, and evolution of crack initiation sites for different strain levels, which gives some statistical data for each strain level. It also permits analysis of the chemical nature of inclusions inducing crack initiation thanks to energy dispersive spectrometry of X-rays. It is shown that fatigue damage initially occurs generally on carbon black agglomerates or oxides such as ZnO. However, those two types of inclusions correspond to different crack initiation mechanisms, and most of the time, only the initiations on carbon black agglomerates are followed by crack propagation that leads to failure. This difference is probably because carbon black agglomerates have a stronger cohesion than ZnO inclusions and a stronger adhesion to the matrix.

Fatigue Crack Initiation Model of Type 316 Stainless Steel

2016 ◽  
Author(s):  
Terushi Ishizawa ◽  
Takao Nakamura ◽  
Takanori Kitada
Keyword(s):  
Crack Initiation ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Strain Range ◽  
Fatigue Tests ◽  
Statistical Dispersion ◽  
Crack Initiation Life ◽  
Using Data ◽  
Two Parameters ◽  
The Relationship

The fatigue tests under different conditions of strain range were conducted in air and the replica observation of fatigue cracks on specimen surface was also conducted. Using data obtained in fatigue tests, statistical dispersion of crack initiation life was quantified and modeled through an application of two-parameter Weibull distribution. The relationship between strain range and two parameters (s, shape parameter and Η, scale parameter) of crack initiation model was discussed. Thereby, the applicability of crack initiation model for arbitrary strain range was shown. Furthermore, the validation of P-curve applied crack initiation model was conducted by the simulation of fatigue life.

Study on fatigue crack initiation of Zr-based bulk metallic glass with corrosion pits

2018 ◽  
Vol 2018 (0) ◽  
pp. OS0808
Author(s):  
Hirotaka KUWAHARA ◽  
Akira Ueno ◽  
Benjamin GUENNEC ◽  
Yoshihiko YOKOYAMA ◽  
Akiyoshi SAKAIDA ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Metallic Glass ◽  
Bulk Metallic Glass ◽  
Fatigue Crack Initiation ◽  
Corrosion Pits
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