Evaluation of Overloading and Crack Closure Effects on Fatigue Crack Growth in an Aircraft 7075-T7351 Al-Alloy

2013 ◽  
Vol 577-578 ◽  
pp. 325-328
Author(s):  
Ivo Černý ◽  
Dagmar Mikulová
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Closure ◽  
Mouth Opening ◽  
Crack Mouth Opening Displacement ◽  
Stress Intensity Factor Range ◽  
Al Alloy ◽  
Opening Displacement ◽  
Al 7075

Al 7075 alloy is a high strength material usually used for highly stressed components in lightweight structures, typically in aircraft, aerospace and defence applications. It can be applied in different heat treatment conditions, but the T7351 temper state is most widely used because of improved stress-corrosion cracking resistance. An investigation of effects of overloads on fatigue crack growth (FCG) and retardation in Al 7075-T7351 alloy was carried out. FCG rates were measured at load asymmetry R = Fmin / Fmax = 0.1, in quite wide region of growth between 10-8 and 10-5 m/cycle (stress intensity factor range ΔK between 6 and 40 MPa m1/2). Retardation effects of overloads of the magnitudes 2.7-times and 3.0-times of the maximum load in the constant range fatigue loading were significant. Crack mouth opening displacement was evaluated at numerous stages of crack growth including pre-cracking with so called load shedding method. The overloads resulted in substantial crack closure effects, which, however, did not occur immediately after the overloading, but after further fatigue crack extension. Results are discussed considering both theoretically and experimentally estimated plastic zone size and considering crack closure issues recently published in the literature

Fatigue Crack Growth Behaviour of AISI 50100 Precipitation Hardened Steel after Welding

2012 ◽  
Vol 570 ◽  
pp. 9-14
Author(s):  
Amir Sultan ◽  
Riffat Asim Pasha ◽  
Sayyid Masood Ur Rehman Shah ◽  
Haris Ali ◽  
Asim Zulfiqar
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Crack Growth Rate ◽  
Mouth Opening ◽  
Crack Mouth Opening Displacement ◽  
Width Ratio ◽  
Crack Growth Behaviour

Single-edged notched tension (SENT) specimen is used to study the fatigue crack growth rate (FCGR) behavior of AISI 50100 steel using MTS 810. Calibration tests are run to get plots of crack mouth opening displacement (CMOD) vs. Load and CMOD vs. Crack length to width ratio with the known crack lengths. FCGR of welded and un-welded specimens are plotted against stress intensity range to show the effect of welding on fatigue crack growth rate of AISI 50100 steel, initial results of the experimentation are presented.

Crack Closure and Propagation Studies to Determine the Effects of Simple Load Interaction

1992 ◽  
Vol 114 (3) ◽  
pp. 229-236 ◽  
Author(s):  
Satish Chand
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Closure ◽  
Transient Behavior ◽  
Al Alloy ◽  
Block Loading ◽  
Notched Specimens ◽  
Single Overload ◽  
Growth Experiments

Crack closure and fatigue crack growth experiments were performed on centrally notched specimens of 6063-T6 Al-alloy under single overload and block loading conditions. Using crack closure data, values of effective stress range ratio (U) were found. Assuming that the crack closure phenomenon is responsible for transient behavior of fatigue crack growth rate (FCGR), the FCGR behavior during load interaction was predicted using a constant amplitude crack propagation description in conjunction with the experimentally measured U-values. On comparing predicted FCGR with those found experimentally, it was observed that the predicted FCGR always agrees with the trend of experimental FCGR behavior and provides either exact or conservative estimates of the FCGR.

Effects of Crack Closure on the Fatigue Crack Growth Rates of Ferritic Steels Subjected to Severe Reversing Loads

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
Kisaburo Azuma ◽  
Shinjiro Hidaka ◽  
Yasuhiro Yamazaki
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Closure ◽  
Growth Rates ◽  
Stress Intensity Factor Range ◽  
Low Alloy Steels ◽  
Closure Model ◽  
Alloy Steels ◽  
Crack Growth Rates

Abstract Low-alloy steels are extensively used in pressure boundary components of nuclear power plants. The structural integrity of the components made of low-alloy steels can be evaluated by the flaw evaluation procedure provided by Section XI of the ASME Boiler and Pressure Vessel Code. According to the Code, the stress intensity factor range ΔK can be used to determine the fatigue crack growth rates of the material. However, it has been reported that the fatigue crack growth rate under severe reversing loads is also strongly influenced by crack closure behavior. This paper discusses the relation between applied stresses and the fatigue crack growth rate for cracks in low-alloy steels exposed to air. Compressive-tensile cyclic loadings are applied to center-notched plates to obtain the fatigue crack growth curves. The test data demonstrate that effective stress intensity factor range predicted by our closure model described the crack growth property more accurately. A comparison among crack closure models indicates that our crack closure model is suitable to predict the crack growth rates when low constraint conditions are assumed at the crack tip due to severe reversing loads.

Fatigue Crack Growth for Ferritic Steel Under Negative Stress Ratio

2018 ◽  
Author(s):  
Yoshihito Yamaguchi ◽  
Kunio Hasegawa ◽  
Yinsheng Li
Keyword(s):  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Intensity Factor ◽  
Crack Growth ◽  
Applied Stress ◽  
Crack Closure ◽  
Stress Ratio ◽  
Stress Intensity Factor Range

Crack closure during fatigue crack growth is an important phenomenon for predicting fatigue crack growth amount. Many experimental data show that fatigue cracks close at not only negative loads but also positive loads during constant amplitude loading cycles, depending on applied stress levels. The Appendix A-4300 in the ASME Code Section XI provides two equations of fatigue crack growth rates expressed by stress intensity factor range for ferritic steels under negative stress ratio. The boundary of two fatigue crack growth rates is classified by the magnitude of applied stress intensity factor range with the consideration of crack closure. The objective of this paper is to investigate the influence of the magnitude of the stress intensity factor range on crack closure. Fatigue tests have been performed on ferritic steel specimens in air environment at room and high temperatures. Crack closures were obtained as a parameter of stress ratio. It was found that crack closure occurs at a smaller applied stress intensity factor range than the definition given by the Appendix A-4300.

scholarly journals Fatigue Crack Growth from Notches: A Numerical Analysis

2020 ◽  
Vol 10 (12) ◽  
pp. 4174 ◽  
Author(s):  
Micael Borges ◽  
Manuel Caldas ◽  
Fernando Antunes ◽  
Ricardo Branco ◽  
Pedro Prates
Keyword(s):  
Fatigue Crack ◽  
Stress State ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Closure ◽  
Numerical Approach ◽  
Crack Tip Opening Displacement ◽  
Notch Radius ◽  
Opening Displacement ◽  
Global Trends

A numerical approach based on plastic crack tip opening displacement (CTOD) was followed to study fatigue crack growth (FCG) from notches. The identification of fundamental mechanisms was made considering notched and unnotched models, with and without contact of crack flanks. Different parameters were studied, namely, notch radius, crack length, stress state, and material. The notch increases the plastic CTOD, and therefore fatigue crack growth rate, da/dN, as expected. The reduction of notch radius increases da/dN but reduces the notch affected zone. Ahead of the notch affected zone, da/dN increases linearly with crack growth, with a rate that increases linearly with the plastic CTOD. The crack closure phenomenon has a dramatic effect under plane stress conditions but a limited effect on plane strain conditions. In the former case, the contact of crack flanks reduces substantially the effect of notch radius and the size of the notch affected zone. These trends are associated with the increase of crack closure level with notch radius. The material does not affect the global trends, but the reduction of yield stress increases the level of plastic deformation and therefore da/dN. The effect of material, and also of stress state, is mainly associated with crack closure.

scholarly journals Study on the Influence of the Gurson–Tvergaard–Needleman Damage Model on the Fatigue Crack Growth Rate

Metals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 1183
Author(s):  
Edmundo R. Sérgio ◽  
Fernando V. Antunes ◽  
Diogo M. Neto ◽  
Micael F. Borges
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Plastic Strain ◽  
Crack Growth ◽  
Damage Model ◽  
Crack Tip ◽  
Strength Parameter ◽  
Stress Intensity Factor Range

The fatigue crack growth (FCG) process is usually accessed through the stress intensity factor range, ΔK, which has some limitations. The cumulative plastic strain at the crack tip has provided results in good agreement with the experimental observations. Also, it allows understanding the crack tip phenomena leading to FCG. Plastic deformation inevitably leads to micro-porosity occurrence and damage accumulation, which can be evaluated with a damage model, such as Gurson–Tvergaard–Needleman (GTN). This study aims to access the influence of the GTN parameters, related to growth and nucleation of micro-voids, on the predicted crack growth rate. The results show the connection between the porosity values and the crack closure level. Although the effect of the porosity on the plastic strain, the predicted effect of the initial porosity on the predicted crack growth rate is small. The sensitivity analysis identified the nucleation amplitude and Tvergaard’s loss of strength parameter as the main factors, whose variation leads to larger changes in the crack growth rate.

Finite Element Simulation of Stable Fatigue Crack Growth Using Critical CTOD Determined by Preliminary Finite Element Analysis

2014 ◽  
Vol 891-892 ◽  
pp. 1675-1680
Author(s):  
Seok Jae Chu ◽  
Cong Hao Liu
Keyword(s):  
Finite Element ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Finite Element Simulation ◽  
Crack Growth ◽  
Crack Tip ◽  
Stress Intensity Factor Range ◽  
Crack Tip Opening Displacement ◽  
Element Analysis ◽  
Element Simulation

Finite element simulation of stable fatigue crack growth using critical crack tip opening displacement (CTOD) was done. In the preliminary finite element simulation without crack growth, the critical CTOD was determined by monitoring the ratio between the displacement increments at the nodes above the crack tip and behind the crack tip in the neighborhood of the crack tip. The critical CTOD was determined as the vertical displacement at the node on the crack surface just behind the crack tip at the maximum ratio. In the main finite element simulation with crack growth, the crack growth rate with respect to the effective stress intensity factor range considering crack closure yielded more consistent result. The exponents m in the Paris law were determined.

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