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.

Effects of Dynamic Ion Mixing Coating Condition for Fatigue Properties of Stainless Steel with TiN Film

2007 ◽  
Vol 353-358 ◽  
pp. 1875-1878 ◽  
Author(s):  
Satoshi Fukui ◽  
Riichi Murakami ◽  
Daisuke Yonekura
Keyword(s):  
Stress Intensity Factor ◽  
Stainless Steel ◽  
Stress Intensity ◽  
Fatigue Strength ◽  
Intensity Factor ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Fatigue Properties ◽  
Stress Intensity Factor Range ◽  
Tin Film

Four point bending fatigue tests were carried out using martensitic stainless steel with TiN film deposited at five different deposition rates by dynamic ion mixing process in order to investigate the influence of deposition rate on the fatigue strength. As a result, the fatigue limit clearly increased by the deposition at appropriate conditions. However, the deposition by other conditions resulted in the degradation of fatigue strength. This is caused by the decrease of threshold stress intensity factor after TiN deposition and the difference of defect distribution in the film. In addition, the crack propagation rate was increased in low stress intensity factor range by the deposition of TiN film.

Crack-Propagation Rate in 7075-T6 Plates Under Cyclic Tensile and Transverse Shear Loadings

1969 ◽  
Vol 91 (4) ◽  
pp. 764-769 ◽  
Author(s):  
Soushiro Iida ◽  
A. S. Kobayashi
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Propagation ◽  
Sliding Mode ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Opening Mode ◽  
Direct Stiffness ◽  
Maximum Opening

Crack-propagation rate in 7075-T6 tension plates was determined for central cracks initially oriented in 45, 60, and 90 deg, to the width direction of the tension plates which were loaded cyclically. Opening and sliding mode of stress-intensity factors, K1 and K2, were determined by the method of direct stiffness for curved cracks generated from these initially slanted cracks. Crack-propagation rates, Δa/ΔN, were then plotted against the maximum opening mode of stress-intensity factor, K1, in the presence of sliding mode of stress-intensity factor, K2. Comparison between the corresponding crack-propagation rate in control specimens without K2 showed that the propagation rate is definitely increased in the presence of K2.

Experimental Determination of the Crack Tip Stress Intensity Factor in Integrally Stiffened Panels

2016 ◽  
Vol 1135 ◽  
pp. 112-127
Author(s):  
Carlos E. Chaves ◽  
Caio Magno de Assunção
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Propagation ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Experimental Information ◽  
Image Correlation ◽  
Manufacturing Cost ◽  
Stiffened Panels

Integral structures offer large benefits in terms of manufacturing cost, but suffer from a lower degree of fail safety when compared to built-up structures. In order to achieve an improvement on the fatigue crack propagation (FCP), crack containment features (also known as crenellations) have been used on these structures. The source of the FCP improvement is the stress intensity factor (K) modification due to the geometry change. In the current study, an analysis about means of estimating K from the experimental information, and also to verify the K behavior while the crack propagates was performed. The study tested two AA 7475 panels, one with crenellations and another without. As the crack propagates, the K values were estimated in two forms, based on the crack propagation rate and by using a digital image correlation (DIC) system, coupled with strain gages. Based on DIC system, it was possible to evaluate the K estimation, the singularity dominated zone size and the K increase, as long as the crack propagated, for both test specimens. A comparison between the two methods was also made, and finally the use of a DIC system as a tool for estimating the K parameter was discussed.

Crack Propagation in a Gun Barrel Due to the Firing Thermo-Mechanical Stresses

2003 ◽  
Vol 125 (3) ◽  
pp. 293-298 ◽  
Author(s):  
Eric Petitpas ◽  
B. Campion
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Residual Stresses ◽  
Crack Propagation ◽  
Internal Surface ◽  
Mechanical Stresses ◽  
Stress Intensity Factor Range ◽  
Plastic Behavior ◽  
Gun Barrel

The thermo-mechanical effects of firing induce very considerable stresses on the internal surface of the gun barrels. Consequently, micro-cracks appear very soon in the life of the tube. So it is important to control the propagation of these cracks. For more than 10 years, modeling has been used by Giat-Industries to understand and to control this phenomenon. This paper focuses on the study of short crack propagation kinetics during firings. Two-dimensional modeling taking into consideration the residual stresses from a hydraulic autofrettage and the thermo-mechanical stresses due to the successive firings is presented. The cyclic plastic behavior of the material is taken into consideration. This makes it possible to observe the effect of loss of the residual stresses at the surface due to the firings. Cracks of increasing length are introduced in the model to calculate the stress intensity factor. An innovative point is the modeling of the contact between the crack lips in order to take into account the effect of crack closing during cooling. Indeed the effective stress intensity factor range is calculated using this model for numerous crack lengths. A classic Paris law is then used to predict the crack propagation kinetics. Sensitivity analysis has been carried out using this model; in particular, the effect of autofrettage on crack propagation is analyzed as well as the effect of the use of lower-strength steels.

Fatigue Life Prediction of Ship Welded Materials

2005 ◽  
Vol 297-300 ◽  
pp. 743-749
Author(s):  
Min Koo Han ◽  
Mamidala Ramulu
Keyword(s):  
Residual Stress ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Residual Stresses ◽  
Crack Propagation ◽  
Crack Closure ◽  
Fatigue Cracks ◽  
Welding Process ◽  
Weld Toe

Fatigue crack propagation life of weld toe crack through residual stress field was estimated using Elber's crack closure concept. Propagation of weld toe crack is heavily influenced by residual stresses caused by the welding process, so it is essential to take into account the effect of residual stresses on the propagation life of a weld toe crack. Fatigue cracks at transverse and longitudinal weld toe was studied, these two cases represent the typical weld joints in ship structures. Numerical and experimental studies are performed for both cases. Residual stresses near the welding area were estimated through a nonlinear thermo-elasto-plastic finite element method and the residual stress intensity factor with Glinka's weight function method. Effective stress intensity factor was calculated using the Newman-Forman-de Koning-Henriksen equation, which is based on the Dugdale strip yield model in estimating the crack closure level, U, at different stress ratios. Calculated crack propagation life coincided well with experimental results.

Numerical Analysis of Crack Propagation in Cyclic-Loaded Structures

1967 ◽  
Vol 89 (3) ◽  
pp. 459-463 ◽  
Author(s):  
R. G. Forman ◽  
V. E. Kearney ◽  
R. M. Engle
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Propagation ◽  
Crack Extension ◽  
Load Ratio ◽  
Stress Intensity Factor Range ◽  
Time To Failure ◽  
Excellent Correlation ◽  
Extensive Experimental Data

An improved theory is proposed for the crack-growth analysis of cyclic-loaded structures. The theory assumes that the crack tip stress-intensity-factor range, ΔK, is the controlling variable for analyzing crack-extension rates. The new theory, however, takes into account the load ratio, R, and the instability when the stress-intensity factor approaches the fracture toughness of the material, Kc. Excellent correlation is found between the theory and extensive experimental data. A computer program has been developed using the new theory to analyze the crack propagation and time to failure for cyclic-loaded structures.

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