BEHAVIOR OF PLASTIC DEFORMATION AND CRACK PROPAGATION ON FULLY LAMELLAR GAMMA-TiAl ALLOY

Practical residual strain field around the microcrack tip of fully lamellar γ- TiAl alloy was estimate the by digital image correlation (DIC) technology with in-situ SEM observation. And the macro plastic deformation before fracture of such low ductility alloys was observed. The results showed that the size of plastic zone around microcrack tip was 2 ~ 10µ m which was much more smaller than the calculated value by fracture mechanics. During the magnified observation on the plastic deformation region, a series of microcracks were observed in the specimen without macro cracking. Furthermore, the size of distribution region of the microcracks were in the same order of magnitude with the calculated plastic zone near primary crack tip which just reflected the comprehensive effect of microcracks and the plastic deformation on the tips of them.

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Experimental and Numerical Study on Plastic Zone Variation ahead of Fatigue Crack Tip

MATEC Web of Conferences ◽

10.1051/matecconf/201816506004 ◽

2018 ◽

Vol 165 ◽

pp. 06004

Author(s):

Zhang Wei ◽

Zhou Daoqing ◽

Cai Liang

Keyword(s):

Plastic Deformation ◽

Fatigue Crack ◽

Plastic Zone ◽

Crack Growth ◽

Crack Tip ◽

Image Correlation ◽

In Situ Observation ◽

Crack Growth Behaviour ◽

Single Overload

The plastic deformation ahead of crack tip is of great significance to analysis of the fatigue crack growth behaviour. Using the in-situ microscopy experiment technique, the variation of strain field in the vicinity of crack tip is investigated within load cycles at the small time scale. The contours of plastic zones are measured through the in-situ observation and digital image correlation (DIC). Finite element method (FEM) is also used to simulate the plasticity ahead of the crack tip. Furthermore, the numerical studies are extended to the single overload case to analyse the effect of large plastic zone on the subsequent crack growth. The evolution of residual stress is extracted by FEM simulation to explore the influence of plastic deformation before, during and after the single overload applied on the following crack propagation. Based on the FEM analysis, a model is proposed to approximate the size of the overload effect zone. Finally, some experimental data and numerical simulations are employed to validate this model.

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Methodology for in situ stress intensity factor determination on cracked structures by digital image correlation

International Journal of Structural Integrity ◽

10.1108/17579861011099178 ◽

2010 ◽

Vol 1 (4) ◽

pp. 344-357 ◽

Cited By ~ 3

Author(s):

V. Richter‐Trummer ◽

P.M.G.P. Moreira ◽

S.D. Pastrama ◽

M.A.P. Vaz ◽

P.M.S.T. de Castro

Keyword(s):

Stress Intensity Factor ◽

Stress Intensity ◽

Digital Image Correlation ◽

Intensity Factor ◽

Digital Image ◽

Strain Field ◽

Image Correlation ◽

Content Type ◽

Cracked Structures

PurposeThe purpose of this paper is to develop a methodology for in situ stress intensity factor (SIF) determination that can be used for the analysis of cracked structures. The technique is based on digital image correlation (DIC) combined with an overdetermined algorithm.Design/methodology/approachThe linear overdeterministic algorithm for calculating the SIF based on stress values around the crack tip is applied to a strain field obtained by DIC.FindingsAs long as the image quality is sufficiently high, a good accuracy can be obtained for the measured SIF. The crack tip can be automatically detected based on the same strain field. The use of the strain field instead of the displacement field, eliminates problems related to the rigid body motion of the analysed structure.Practical implicationsIn future works, based on the applied techniques, the SIF of complex cracked plane stress structures can be accurately determined in real engineering applications.Originality/valueThe paper demonstrates application of known techniques, refined for other applications, also the use of stress field for SIF overdeterministic calculations.

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Study of Metal Seal of Coiled Tubing Wellhead Hanging Device

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.628.133 ◽

2014 ◽

Vol 628 ◽

pp. 133-136

Author(s):

Xian Yong Zhang ◽

Wei Guo Ma

Keyword(s):

Plastic Deformation ◽

Finite Element Method Analysis ◽

Clearance Ratio ◽

Deformation Region ◽

Coiled Tubing ◽

Metal Seal ◽

Excitation Force ◽

Initial Clearance ◽

Plastic Deformation Region ◽

Method Analysis

A U-shaped metal seal in coiled tubing wellhead hanging device was designed, the metal seal material is brass(H59, H70). The contact stress of sealing interface was analyzed by finite element method analysis, the U-shaped seal has elastic-plastic deformation after excitation force applied, and the plastic deformation region concentrated in contact areas. The influence of U-shaped metal seal initial clearance on sealing effect was presented, the reasonable initial clearance ratio region are 0.8 to 0.9. Excitation forces in different excitation angles were calculated, the reasonable excitation angle region are 15° to 20°. Metal seal overcomes the defects of conventional rubber elastomers, that ensure the safety of wellhead hanging device construction, also improve the service life.

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In situ observation of fracture process of a TiAl alloy with fully lamellar microstructure

Scripta Metallurgica et Materialia ◽

10.1016/0956-716x(95)00239-r ◽

1995 ◽

Vol 32 (10) ◽

pp. 1579-1584 ◽

Cited By ~ 1

Author(s):

Cheng Jin ◽

Jianguo Wang ◽

Wenjue Chen

Keyword(s):

Fracture Process ◽

Tial Alloy ◽

Lamellar Microstructure ◽

In Situ Observation ◽

Fully Lamellar

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Martensite decay in micropitted gears

Proceedings of the Institution of Mechanical Engineers Part J Journal of Engineering Tribology ◽

10.1243/135065005x9790 ◽

2005 ◽

Vol 219 (2) ◽

pp. 77-83 ◽

Cited By ~ 27

Author(s):

A Oila ◽

B. A. Shaw ◽

C. J. Aylott ◽

S. J. Bull

Keyword(s):

Plastic Deformation ◽

Phase Transformations ◽

Deformation Region ◽

Metallographic Examination ◽

Microstructural Constituent ◽

Initiation And Propagation ◽

New Type ◽

Plastic Deformation Region

Metallographic examination performed on a number of micropitted gears has revealed microstructural features similar to those reported in the literature in fatigued bearings, namely, dark etching regions and white etching bands. In addition, a new type of fatigue-induced microstructural constituent was observed close to the surface below asperities referred to as the plastic deformation region. Finally, it is shown that the initiation and propagation of cracks leading to the formation of micropits are related to the phase transformations mentioned previously.

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In situ fracture observations of distinct interface types within a fully lamellar intermetallic TiAl alloy

Journal of Materials Research ◽

10.1557/s43578-020-00088-z ◽

2021 ◽

Author(s):

Michael Burtscher ◽

Markus Alfreider ◽

Klemens Schmuck ◽

Helmut Clemens ◽

Svea Mayer ◽

...

Keyword(s):

Tial Alloy ◽

Fully Lamellar

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Glues Make Gummy Metals Easy to Cut

Volume 2: Processes; Materials ◽

10.1115/msec2019-2922 ◽

2019 ◽

Author(s):

Anirudh Udupa ◽

Tatsuya Sugihara ◽

James B. Mann

Keyword(s):

Plastic Deformation ◽

Cutting Forces ◽

Defect Density ◽

Deformation Mode ◽

Flow Mode ◽

Force Measurements ◽

Low Friction ◽

Machining Processes ◽

Order Of Magnitude

Abstract Metals such as Cu, Al, Ni, Ta and stainless steels, despite their softness and ductility, are considered difficult to machine. This is due to large cutting forces and corresponding formation of a very thick chip during cutting and hence these metals are referred to as “gummy”. Their poor machinability of these materials arises because of an unsteady and highly redundant mode of plastic deformation referred to as sinuous flow. The prevailing plastic deformation mode during machining can be overcome by the application of certain coatings and chemical media on the un-deformed free surface of the workpiece ahead of the cutting process. Using in-situ imaging and concurrent force measurements we present two different mechanochemical routes through which these media can improve machinability. The first route, which requires chemicals that adhere to the metal surface, such as glues and inks, improves cutting by inducing a change in the local plastic deformation mode — from sinuous flow to one characterized by periodic fracture or segmented flow. The second route, which requires chemicals that can react with the workpiece to form a low-friction layer, changes the sinuous flow mode to a smooth, laminar one. Both routes decrease cutting forces by more than 50% with order of magnitude improvement in surface texture as characterized by measured roughness and defect density. The results suggest a broad range of opportunities for improving performance of machining processes for many difficult-to-cut gummy metals.

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In Situ Measurements for Plastic Zone Ahead of Crack Tip and Continuous Strain Variation under Cyclic Loading Using Digital Image Correlation Method

Metals ◽

10.3390/met10020273 ◽

2020 ◽

Vol 10 (2) ◽

pp. 273 ◽

Cited By ~ 5

Author(s):

Yan Zhao ◽

Dianyin Hu ◽

Meng Zhang ◽

Wei Dai ◽

Weifang Zhang

Keyword(s):

Digital Image Correlation ◽

Plastic Zone ◽

Crack Propagation ◽

Digital Image ◽

Crack Tip ◽

Experimental Results ◽

Image Correlation ◽

Specimen Preparation ◽

Strain Variation

Fatigue crack is one of the most common damage forms for aeronautical aluminum alloy. With crack propagation, the strain fields of the whole object surface and plastic zone (PZ) ahead of the crack tip are changing continuously. For most metallic materials, the behavior of PZ around the crack tip and continuous strain variation play a vital role in crack propagation. In this work, the “continuous” strain information at and in front of the crack tip on the specimen surface was obtained quantitatively and the PZ size ahead of crack tip was in situ measured quantitatively with crack propagation by using the digital image correlation (DIC) method, which overcomes the difficulty for the in situ measurement of mechanical variables. Moreover, the method of specimen preparation was simplified by using a white matt paint with strong adhesion, but also resulted in a higher resolution being shown, even for such a large area. Furthermore, the experimental results of the PZ size from the proposed method had good agreement with the theoretical values, which overcomes the limitation that the conventional approaches only consider the quasi-static crack. Finally, the continuous strain variation behavior was analyzed from the experimental results in detail with the consideration of crack propagation.

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