scholarly journals A Comparison of Macroscopic Fracture Surface and Crack Growth Rate of Ti-6Al-4V

2010 ◽  
Vol 97-101 ◽  
pp. 687-690 ◽  
Author(s):  
Khalil Farhangdoost ◽  
S. Rahnama
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Crack Growth Rate ◽  
Fracture Surface ◽  
Crack Growth ◽  
Transition Region ◽  
Stress Intensity Range ◽  
Effective Stress Intensity Range ◽  
Macroscopic Fracture

A comparison between crack growth rate (da/dN) vs. effective stress intensity range factor (ΔKeff) curve behavior and microscopic and macroscopic fracture surface of commercial Ti-6Al-4V alloy are presented. Three different regimes are correlated with characteristics measured on the fracture surfaces. Three regions can be observed in which part I is rough and darker than others parts known as pre-transition, part II is smooth and light known as transition region and part III is a little darker than part II known as post-transition region. In the present investigation the correlation of fatigue crack growth rate for Ti-6Al-4V and microstructure of fracture surface has been presented.

Some Applications of Fractal Fracture Mechanics to Describe the Fatigue Behaviour of Materials

2008 ◽  
Vol 378-379 ◽  
pp. 355-370 ◽  
Author(s):  
Andrea Carpinteri ◽  
Andrea Spagnoli ◽  
Sabrina Vantadori
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Limit ◽  
Threshold Stress ◽  
Threshold Stress Intensity ◽  
Stress Intensity Range

As is well-known, fatigue limit, threshold stress intensity range and fatigue crack growth rate are influenced by the specimen or structure size. Limited information on size effect is available in the literature. In the present paper, by employing some concepts of fractal geometry, new definitions of fatigue limit, fracture energy and stress intensity factor, based on physical dimensions different from the classical ones, are discussed. Then, size-dependent laws for fatigue limit, threshold stress intensity range and fatigue crack growth rate are proposed. Some experimental results are examined in order to show how to apply such theoretical scaling laws.

Long Fatigue Cracks — Microstructural Effects and Crack Closure

MRS Bulletin ◽  
1989 ◽  
Vol 14 (8) ◽  
pp. 25-36 ◽  
Author(s):  
P.K. Liaw
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Crack Growth Rate ◽  
Load Ratio ◽  
Stress Intensity Range ◽  
Intensity Range

Fracture mechanics technology is an effective tool for characterizing the rates of fatigue crack propagation. Generally, fatigue crack growth rate (da/dN) in each loading cycle can be presented as a function of stress intensity range (ΔK), where ΔK = Kmax — Kmin, Kmax and Kmin are the maximum and the minimum stress intensities, respectively. A typical fatigue crack growth rate curve of da/dN versus ΔK can be divided into three regimes, i.e., Stage I (near-threshold), Stage II (Paris), and Stage III (fast) crack growth regions, as shown in Figure 1.Depending on the region of crack growth, fatigue crack growth behavior can be sensitive to microstructure, environment, and loading conditions [e.g., R (load) ratio = Kmin / Kmax]. In the nearthreshold region, fatigue crack growth rates are very slow, ranging from approximately 10−10 to 10−8 m/cycle. In this region, the fatigue crack growth rate curve eventually reaches a threshold stress intensity range, ΔKth, below which the crack would not grow or grow at an extremely slow rate. Typically, the value of ΔKth is operationally defined as the stress intensity range which gives a corresponding crack growth rate of 10−10 m/cycle. In the nearthreshold region, the influence of microstructure, environment, and load ratio on the rates of crack propagation is very significant.

Fatigue Crack Growth of Alloy 7050-T7451 Plate in L-S Orientation

2012 ◽  
Vol 525-526 ◽  
pp. 221-224
Author(s):  
Rui Bao ◽  
Xiao Chen Zhao ◽  
Ting Zhang ◽  
Jian Yu Zhang
Keyword(s):  
Growth Rate ◽  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Crack Growth Rate ◽  
Crack Growth ◽  
Growth Characteristics ◽  
Stress Intensity Factor Range ◽  
Constant Amplitude ◽  
Stress Ratios

Experiments have been conducted to investigate the crack growth characteristics of 7050-T7451 aluminium plate in L-S orientation. Two loading conditions are selected, i.e. constant amplitude and constant stress intensity factor range (ΔK). The effects of ΔK-levels and stress ratios (R) on crack splitting are studied. Test data shows that crack splitting could result in the reverse of crack growth rate trend with the increasing R ratio at high ΔK-level. The appearance of crack splitting depends on both ΔK and R.

Estimation of Applied Stress at Fatigue Cracks of a Single Crystal Superalloy

2020 ◽  
Author(s):  
Daisuke Kobayashi ◽  
Katsuhiro Takama ◽  
Tomihiko Ikeda
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Fracture Surface ◽  
Single Crystal ◽  
Crack Growth ◽  
Applied Stress ◽  
Fatigue Crack Growth Rate ◽  
Single Crystal Superalloy

Abstract Needless to say, it is important to estimate the stress applied to a material when conducting failure analysis. In recent years, a material assessment method using electron back-scatter diffraction (EBSD) has been developed. It has been reported that a characteristic misorientation distribution corresponding to the fracture mode is seen in cross-sectional EBSD observation near the fracture surface of a Ni-based superalloy. Furthermore, the authors discovered EBSD striations on the crack cross-section, which is formed with each fatigue crack growth during a turbine shut-down process. This was discovered in misorientation analysis on a single-crystal superalloy blade used in a commercial land-based gas turbine. Since Ni-based superalloys have high deformation resistance, they do not undergo enough ductile deformation to form striations at the crack tip on the fracture surface during fatigue crack growth, and, as a result, striations corresponding to cyclic loadings are rarely observed in fractography. Even in such a Ni-based superalloy with brittle crack growth, the fatigue crack growth rate and the applied stress can be estimated by measuring EBSD striation spacing in misorientation analysis. However, a practical problem in assessment is that the resolution limit fixed with field emission scanning electron microscopes (FE-SEM) determine the range in which crack growth rate can be assessed. Hence, it is difficult to clearly discriminate the EBSD striations when the fatigue crack growth rate is too low, such as in the low stress intensity factor range (ΔK) region. The applied stress can be calculated from ΔK. Therefore, in this paper, in order to estimate the applied stress during fatigue crack growth, we focused on estimating ΔK by measuring the plastic zone size along the crack growth.

Fatigue Crack Growth Rate Curve for Nickel Based Alloys in PWR Environment

2007 ◽  
Author(s):  
Yuichiro Nomura ◽  
Katsumi Sakaguchi ◽  
Hiroshi Kanasaki
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Stainless Steels ◽  
Stress Ratio ◽  
Austenitic Stainless Steels ◽  
Rising Time

Japanese reference fatigue crack growth rate (FCGR) curves for ferrite and austenitic stainless steels in light water reactor environments are prescribed in JSME S NA1-2004. However, similar reference FCGR curve for nickel-based alloys for pressurized water reactors (PWR) are not prescribed. In order to propose reference FCGR curve for nickel-based alloys, under high stress ratio and low rising time, the effect of the welding method, the effect of specimen orientation and low stress intensity range fatigue crack propagation tests of nickel-based alloys 600, 132 and 82 weld metals were conducted as part of the Environmental Fatigue Test (EFT) projects of Japan Nuclear Energy Safety Organization (JNES). The results show that the effect of heat, welding methods, specimen orientations and environmental water conditions on the FCGR was not significant for Alloys 600, 132 and 82. The FCGR increased with increase of stress ratio, and cyclic loading frequency. According to the procedure for determining the reference FCGR curve of austenitic stainless steels in PWR environment of nickel-based alloys is proposed based on the reference data and the results of this study. The reference FCGR curve for nickel-based alloys in PWR environment are determined as a function of stress intensity factor range, temperature, load rising time and stress ratio.

scholarly journals Corrosion Fatigue Crack Growth Studies on Pressure Vessel and Piping Steels in Water Environment

2017 ◽  
Vol 62 (3) ◽  
pp. 1857-1862 ◽  
Author(s):  
N.M. Mathew ◽  
S. Vishnuvardhan ◽  
G. Raghava ◽  
A.S. Santhi
Keyword(s):  
Growth Rate ◽  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Crack Growth Rate ◽  
Crack Growth ◽  
Water Environment ◽  
Stress Intensity Factor Range ◽  
Corrosion Fatigue Crack ◽  
Corrosion Fatigue Crack Growth

Abstract Corrosion fatigue crack growth studies were conducted on eccentrically-loaded single edge notch tension specimens made of SA 333 Gr. 6 and SA 516 Gr. 70 carbon steels in water environment. The experiments were conducted using a ±250 kN capacity Universal Testing Machine under constant amplitude sinusoidal loading at a test frequency of 0.50 Hz and stress ratio of 0.1. The fabrication of test specimens and the experiments were carried out based on ASTM E 647 and ASTM E 1820. The crack initiation and growth were monitored and images were captured by using a digital camera at regular intervals of fatigue cycles. By using these images, the length of crack was measured. The tests were terminated when the uncracked portion of the specimens was insufficient to take further load. Crack growth rate and stress intensity factor range values were evaluated at incremental values of loading cycles and crack length. Using the crack growth rate vs. stress intensity factor range plots, best fit curves following power law in the form of Paris’ equation were obtained.

Study on Fatigue Crack Growth Behavior of Zr702/TA2/Q345R Composite Plate With a Through-Wall Crack and a Crack Normal to Interface for SENT Specimen

2019 ◽  
Author(s):  
Binbin Zhou ◽  
Changyu Zhou ◽  
Xiaohua He
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Composite Plate ◽  
Homogeneous Material ◽  
Crack Growth Behavior ◽  
Strength Material

Abstract In this paper, the fatigue crack growth behavior of Zr702/TA2/Q345R composite plate with a through-wall crack and a crack normal to interface for SENT specimen are studied. For the through-wall crack, the mutual interference in fatigue crack growth rate is found. The crack growth rate of the through-wall crack on both sides in Zr702/TA2/Q345R composite plate depends on the difference of stress intensity factors amplitude caused by the different positions of crack tips on both sides and the crack growth rate in corresponding homogeneous material. For the crack normal to interface, two crack propagation directions are taken into account. When crack initiates from the lower strength material side, the crack growth rate decreases to the minimum before crack penetrates the interface. After crack penetrates the interface, crack growth rate accelerates continuously. When crack initiates from the higher strength material side, the fatigue crack growth rate generally increases with the crack length. For both crack forms, all experiment results demonstrate that the crack growth rate is dependent on the competition of the stress intensity factor amplitude, the crack growth rate in corresponding homogeneous material and the interface strength. Besides, finite element results show that elastic mismatch results in a significantly change in the distribution of stress intensity factor amplitude.

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