scholarly journals Set-up of a Generalized Dataset for Crack-Closure-Mechanisms of Cast Steel

2021 ◽  
Vol 5 (4) ◽  
pp. 84-88
Author(s):  
Michael Horvath ◽  
Matthias Oberreiter ◽  
Michael Stoschka ◽  
Martin Leitner
Keyword(s):  
Crack Propagation ◽  
Crack Growth ◽  
Crack Closure ◽  
Cast Steel ◽  
Crack Propagation Rate ◽  
Crack Growth Resistance ◽  
Stress Intensity Factor Range ◽  
Resistance Curve ◽  
Stress Ratios ◽  
The Impact

In components, crack propagation is subjected to crack-closure-mechanisms which affect the build-up of the relevant threshold stress intensity factor range during cyclic loading. As structural parts are exposed to service loads incorporating a variety of load ratios, a significant change of the long-crack threshold value occurs, leading to a severe stress ratio dependency of crack-closure-mechanisms. Thus, an extensive number of crack propagation experiments is required to gain statistically proven fracture mechanical parameters describing the build-up of closure effects as crack growth resistance curves.The article presents a generalized dataset to assess the formation of crack-closure-mechanisms of cast steel G21Mn5+N. Numerous crack propagation experiments utilizing single edge notched bending (SENB) sample geometries are conducted, incorporating alternate to tumescent stress ratios. The statistically derived, generalized crack growth resistance curve features the impact of closure effects on the crack propagation rate in a uniform manner. To extend the dataset to arbitrary load ratios, the long-crack threshold approach according to Newman is invoked. The generalized dataset for the cast steel G21Mn5+N is validated by analytical fracture mechanical calculations for the utilized SENB-sample geometries. Incorporating a modified NASGRO equation, a sound correlation of analytical and experimental crack propagation rates is observed. Moreover, the derived master crack propagation resistance curve is implemented as a user-defined script into a numerical crack growth calculation tool and supports a local, node--based numerical crack propagation study as demonstrated for a representative SENB-sample. Concluding, the derived dataset facilitates the calculation of fatigue life of crack-affected cast steel components subjected to arbitrary stress ratios.

Further Insights on the Relationship Between J and CTOD for SE(B) and SE(T) Specimens Including Ductile Crack Propagation

2015 ◽  
Author(s):  
Diego F. B. Sarzosa ◽  
Claudio Ruggieri
Keyword(s):  
Crack Propagation ◽  
Crack Growth ◽  
Growth Analysis ◽  
Crack Tip ◽  
Crack Growth Resistance ◽  
J Integral ◽  
Resistance Curve ◽  
Ductile Crack ◽  
Crack Growth Resistance Curve ◽  
The Relationship

In structural assessment procedures the crack driving force is usually estimated numerically based on the J -Integral definition because its determination is well established in many finite element codes. The nuclear industry has extensive fracture toughness data expressed in terms of J-Integral and huge experience with its applications and limitations. On the other hand, material fracture toughness is typically measured by Crack Tip Opening Displacement (CTOD) parameter using the hinge plastic model or double clip gauge technique. The parameter CTOD has a wide acceptance in the Oil and Gas Industry (OGI). Also, the OGI has a lot of past data expressed in terms of CTOD and the people involved are very familiar with this parameter. Furthermore, the CTOD parameter is based on the physical deformation of the crack faces and can be visualized and understood in an easy way. There is a unique relationship between J and CTOD beyond the validity limits of Linear Elastic Fracture Mechanics (LEFM) for stationary cracks. However, if ductile crack propagation occurs, the crack tip deformation profile and stress-strain fields ahead of the crack tip will change significantly when compared to the static case. Thus, the stable crack propagation may change the well established relationship between J and CTOD for stationary cracks compromising the construction of resistance curves J-Δa from CTOD-Δa data or vice versa. This investigation is a complementary study on the relationship between J-Integral and CTOD under ductile crack propagation of a previous work. The theoretical definition of CTOD using the 90° method and the empirical expression used in the standard ASTM E1820 are analyzed under stable crack growth. Plane-strain finite element computations including stationary and growth analysis are conducted for 3P SE(B) and clamped SE(T) specimens having different notch length to specimen width ratios in the range of 0.1–0.5. For the growth analysis, the models are loaded to levels of J consistent to a crack growth resistance curve representative of a typical pipeline steel. A computational cell methodology to model Mode I crack extension in ductile materials is utilized to describe the evolution of J with a. Laboratory testing of an API 5L X70 steel at room temperature using standard, deeply cracked C(T) specimens is used to measure the crack growth resistance curve for the material and to calibrate the key cell parameter defined by the initial void fraction, f 0. The presented results provide additional understanding of the effects of ductile crack growth on the relationship between J-Integral and CTOD for standard and non-standard fracture specimens. Specific procedures for evaluation of CTOD-R curves using SE(T) and SE(B) specimens with direct application to structural integrity assessment and defect analysis in pipelines and risers will be proposed, yielding accurate and robust relations between J-Integral and CTOD.

Fatigue Properties for Micro-Sized Ni-P Amorphous Alloy Specimens

1999 ◽  
Vol 605 ◽  
Author(s):  
S. Maekawa ◽  
K. Takashima ◽  
M. Shimojo ◽  
Y Higo ◽  
M. V Swain
Keyword(s):  
Fatigue Crack ◽  
Amorphous Alloy ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Stress Ratio ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Stress Intensity Factor Range ◽  
Fatigue Crack Propagation Rate ◽  
Stress Ratios

AbstractFatigue crack propagation tests at different stress ratios of 0.1 and 0.5 have been performed on microsized Ni-P amorphous alloy specimens to investigate the influence of stress ratio in the crack growth properties of microsized materials. The specimens tested were cantileverbeam-type with dimensions of 10 × 12 × 50 νm3 prepared by focused ion beam machining. Notches with a depth of 3 [m were introduced in all specimens. The entire set of fatigue tests as performed using a newly developed fatigue testing machine in air at room temperature. Fine stripes deduced to be striations were observed on the fatigue fracture surface. Careful measurements of the striation spacings were made. Fatigue crack propagation rate, that is striation spacing, is plotted as a function stress intensity factor range. Fatigue crack propagation rate at stress-ratios of 0.1 and 0.5 in microsized Ni-P amorphous alloy specimens are given by da/dN ∼ 1.3 × 10−8 ΔK;1.16 and da/dN ∼ 3.7 × 10−8 ΔK0.5, respectively. At a given ΔK, crack propagation rate at a stress ratio of 0.5 was higher than that at 0.1. It is considered that a decrease in crack propagation rate at stress ratio of 0.1 is due to adecrease in effective stress intensity factor range ΔKeff, by the effect of crack closure.

scholarly journals Prediction of Fatigue Crack Growth in Metallic Specimens under Constant Amplitude Loading Using Virtual Crack Closure and Forman Model

Metals ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 977
Author(s):  
Sanjin Krscanski ◽  
Josip Brnic
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Propagation ◽  
Crack Closure ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Stress Intensity Factor Range ◽  
Small Scale ◽  
Plastic Dissipation

This paper considers the applicability of virtual crack closure technique (VCCT) for calculation of stress intensity factor range for crack propagation in standard metal specimen geometries with sharp through thickness cracks. To determine crack propagation rate and fatigue lifetime of a dynamically loaded metallic specimen, in addition to VCCT, standard Forman model was used. Values of stress intensity factor (SIF) ranges ΔK for various crack lengths were calculated by VCCT and used in conjunction with material parameters available from several research papers. VCCT was chosen as a method of choice for the calculation of stress intensity factor of a crack as it is simple and relatively straightforward to implement. It is relatively easy for implementation on top of any finite element (FE) code and it does not require the use of any special finite elements. It is usually utilized for fracture analysis of brittle materials when plastic dissipation is negligible, i.e., plastic dissipation belongs to small-scale yielding due to low load on a structural element. Obtained results showed that the application of VCCT yields good results. Results for crack propagation rate and total lifetime for three test cases were compared to available experimental data and showed satisfactory correlation.

Application of the R-Curve Concept to Fatigue Crack Growth

1978 ◽  
Vol 100 (4) ◽  
pp. 416-420 ◽  
Author(s):  
D. P. Wilhem ◽  
M. M. Ratwani
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Extension ◽  
Stress Ratio ◽  
Cyclic Stress ◽  
Crack Growth Resistance ◽  
Resistance Curve ◽  
Cyclic Stress Ratio ◽  
Wide Range

Crack growth resistance for both static (rising load) and for cyclic fatigue crack growth has been shown to be a continuous function over a range of 0.1 μm to 10 cm in crack extension for 2024-T3 aluminum. Crack growth resistance to each fatigue cycle of crack extension is shown to approach the materials ordinary undirectional static crack resistance value when the cyclic stress ratio is zero. The fatigue crack extension is averaged over many cycles and is correlated with the maximum value of the crack tip stress intensity, Kmax. A linear plot of crack growth resistance for fatigue and static loading data shows similar effects of thickness, stress ratio, and other parameters. The effect of cyclic stress ratio on crack growth resistance for 2219 aluminum indicates the magnitude of differences in resistance when plotted to a linear scale. Prediction of many of these trends is possible using one of several available crack growth data correlating techniques. It appears that a unique resistance curve, dependent on material, crack orientation, thickness, and stress/physical environment, can be developed for crack extensions as small as 0.076 μm (3 μ inches). This wide range, crack growth resistance curve is seen of immense potential for use in both fatigue and fracture studies.

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.

scholarly journals Fatigue Crack Growth Behaviour and Role of Roughness-Induced Crack Closure in CP Ti: Stress Amplitude Dependence

Metals ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1656
Author(s):  
Mansur Ahmed ◽  
Md. Saiful Islam ◽  
Shuo Yin ◽  
Richard Coull ◽  
Dariusz Rozumek
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Crack Growth ◽  
Crack Closure ◽  
Fatigue Cracks ◽  
Propagation Mechanism ◽  
Amplitude Dependence ◽  
Crack Growth Behaviour ◽  
Crack Propagation Mechanism ◽  
Cp Ti

This paper investigated the fatigue crack propagation mechanism of CP Ti at various stress amplitudes (175, 200, 227 MPa). One single crack at 175 MPa and three main cracks via sub-crack coalescence at 227 MPa were found to be responsible for fatigue failure. Crack deflection and crack branching that cause roughness-induced crack closure (RICC) appeared at all studied stress amplitudes; hence, RICC at various stages of crack propagation (100, 300 and 500 µm) could be quantitatively calculated. Noticeably, a lower RICC at higher stress amplitudes (227 MPa) for fatigue cracks longer than 100 µm was found than for those at 175 MPa. This caused the variation in crack growth rates in the studied conditions.

Prestrain Influence on Fatigue Crack Propagation in a 304L Stainless Steel

2009 ◽  
Author(s):  
Kokleang Vor ◽  
Catherine Gardin ◽  
Christine Sarrazin-Baudoux ◽  
Jean Petit ◽  
Claude Amzallag
Keyword(s):  
Growth Rate ◽  
Stainless Steel ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Crack Propagation ◽  
Crack Closure ◽  
Threshold Region ◽  
304L Stainless Steel

The scope of this study is to investigate the effect of tensile prestrain on crack growth behavior in a 304L stainless steel. Fatigue crack propagation tests were performed on single-edge notched tension (SENT) raw specimens (0% of prestrain) and on prestrained specimens (2% and 10%). On one hand, it is found that the different levels of prestrain exhibit no significant influence on crack propagation in the high range of Stress Intensity Factor (SIF), where there is no detectable crack closure. On the other hand, a clear effect of prestrain on crack growth rate can be observed in the near threshold region where closure is detected. Thus, it can be concluded that the prestrain mainly affects the crack growth rate through its influence on the crack closure.

Study on the Influence of Crack Growth Behavior on Fatigue Life in Simulated Reactor Coolant Environment of Different Temperature

2020 ◽  
Author(s):  
Tatsuru Misawa ◽  
Takanori Kitada ◽  
Takao Nakamura
Keyword(s):  
High Temperature ◽  
Fatigue Life ◽  
Crack Propagation ◽  
Crack Growth ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Growth Behavior ◽  
Crack Growth Behavior ◽  
Reactor Coolant ◽  
Different Temperatures

Abstract It has been clarified that the fatigue life is decreased in the fatigue test of high-temperature and high-pressure water that simulates PWR reactor coolant environment compared to that in the atmosphere. Temperature, strain rates, dissolved oxygen concentration, etc. affect the decrease of fatigue life. The influence of crack growth behavior on the fatigue life of Type 316 austenitic stainless steel [1] in simulated PWR reactor coolant environment of different temperatures was investigated in this study. Fatigue tests were conducted under different temperatures (200°C and 325°C) in a simulated PWR reactor coolant environment with interrupting, and cracks generated on the specimen surface were observed with two-step replica method. From the results of observation, the influence of crack growth behavior in different temperatures on the fatigue life was clarified. As a result, it was confirmed that the decrease of the fatigue life due to high temperature is mainly caused by the acceleration of crack propagation rate in the depth direction by the increase of crack coalescence frequency due to the increase of crack initiation number and crack propagation rate in the length direction.

Sign in / Sign up

Export Citation Format

Share Document