scholarly journals TEXTURAL FRACTOGRAPHY

2011 ◽  
Vol 21 (4) ◽  
pp. 49 ◽  
Author(s):  
Hynek Lauschmann ◽  
Ondřej Ráček ◽  
Michal Tůma ◽  
Ivan Nedbal
Keyword(s):  
Growth Rate ◽  
Crack Growth Rate ◽  
Random Field ◽  
Crack Growth ◽  
Crack Surface ◽  
Textural Analysis ◽  
Spectral Structure ◽  
Gibbs Random Field ◽  
Growth Crack ◽  
History Of

The reconstitution of the history of a fatigue process is based on the knowledge of any correspondences between the morphology of the crack surface and the velocity of the crack growth (crack growth rate - CGR). The textural fractography is oriented to mezoscopic SEM magnifications (30 to 500x). Images contain complicated textures without distinct borders. The aim is to find any characteristics of this texture, which correlate with CGR. Pre-processing of images is necessary to obtain a homogeneous texture. Three methods of textural analysis have been developed and realized as computational programs: the method based on the spectral structure of the image, the method based on a Gibbs random field (GRF) model, and the method based on the idealization of light objects into a fibre process. In order to extract and analyze the fibre process, special methods - tracing fibres and a database-oriented analysis of a fibre process - have been developed.

Multi-Fractal Features of Fatigue Crack Surfaces in Relation to Crack Growth Rate

2007 ◽  
Vol 567-568 ◽  
pp. 129-132
Author(s):  
Zuzana Sekerešová ◽  
Hynek Lauschmann
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
3D Reconstruction ◽  
Crack Growth ◽  
Crack Surface ◽  
Optical Microscope ◽  
Multilinear Regression ◽  
Sem Images ◽  
Fracture Surfaces

Texture of a fatigue crack surface is strictly related to crack growth rate. Cracks in specimens from aluminum alloy were studied. Two types of information were used: SEM images of fracture surfaces, and 3D reconstructions of fracture surface morphologies. Sets of equidistantly focused images obtained by an optical microscope served as the basis for 3D reconstruction. Multiparametric fractal analysis was applied to characterize crack surfaces. A vector of fractal features represented each image or 3D reconstruction of selected locations of fracture surfaces. For estimating fractal characteristics, the box-counting method in 3D was used in all cases, [1]. Multilinear regression was used to express the relation between crack growth rate and feature vectors, with satisfactory results for both crack surface representations.

scholarly journals Effect of water flow and depth on fatigue crack growth rate of underwater wet welded low carbon steel SS400

2021 ◽  
Vol 11 (1) ◽  
pp. 329-338 ◽  
Author(s):  
E. Surojo ◽  
J. Anindito ◽  
F. Paundra ◽  
A. R. Prabowo ◽  
E. P. Budiana ◽  
...  
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Carbon Steel ◽  
Crack Growth Rate ◽  
Crack Growth ◽  
Water Flow ◽  
Water Depth ◽  
Water Flow Rate ◽  
Low Carbon Steel ◽  
Low Carbon

Abstract Underwater wet welding (UWW) is widely used in repair of offshore constructions and underwater pipelines by the shielded metal arc welding (SMAW) method. They are subjected the dynamic load due to sea water flow. In this condition, they can experience the fatigue failure. This study was aimed to determine the effect of water flow speed (0 m/s, 1 m/s, and 2 m/s) and water depth (2.5 m and 5 m) on the crack growth rate of underwater wet welded low carbon steel SS400. Underwater wet welding processes were conducted using E6013 electrode (RB26) with a diameter of 4 mm, type of negative electrode polarity and constant electric current and welding speed of 90 A and 1.5 mm/s respectively. In air welding process was also conducted for comparison. Compared to in air welded joint, underwater wet welded joints have more weld defects including porosity, incomplete penetration and irregular surface. Fatigue crack growth rate of underwater wet welded joints will decrease as water depth increases and water flow rate decreases. It is represented by Paris's constant, where specimens in air welding, 2.5 m and 5 m water depth have average Paris's constant of 8.16, 7.54 and 5.56 respectively. The increasing water depth will cause the formation of Acicular Ferrite structure which has high fatigue crack resistance. The higher the water flow rate, the higher the welding defects, thereby reducing the fatigue crack resistance.

Fracture and Fatigue Resistance of Ultrafine Grain CuCrZr Alloy Produced ECAP

2006 ◽  
Vol 503-504 ◽  
pp. 811-816 ◽  
Author(s):  
Alexei Vinogradov ◽  
Kazuo Kitagawa ◽  
V.I. Kopylov
Keyword(s):  
Growth Rate ◽  
Crack Growth Rate ◽  
Crack Growth ◽  
Stable Crack Growth ◽  
Ultrafine Grain ◽  
J Integral ◽  
Present Communication ◽  
Angular Pressing ◽  
Fatigue And Fracture ◽  
Anisotropy Of Mechanical Properties

Anisotropy of mechanical properties, fatigue and fracture resistance of precipitation hardened CuCrZr alloy ultrafine (UFG) grained by equal-channel angular pressing (ECAP) is in focus of the present communication. Fracture toughness was estimated in terms of J-integral and the fatigue crack growth rate was quantified. It was found that although the estimated JIC-value appeared lower than that reported in the literature for a reference alloy, the ductility, fracture and crack growth resistance remained satisfactory after ECAP while the tensile strength and fatigue limit improved considerably. The stable crack growth rate did not differ very much for ECAP and reference conventional CuCrZr and no remarkable anisotropy in the stable crack growth was noticed.

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.

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.

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