Micromechanisms of Deformation and Fracture in a Ti3Al-Nb Alloy

1990 ◽  
Vol 213 ◽  
Author(s):  
A.S. Akkurt ◽  
G. Liu ◽  
G.M. Bond
Keyword(s):  
Crack Propagation ◽  
Material Characterization ◽  
High Stress ◽  
Crack Branching ◽  
In Situ Tem ◽  
Phase Boundaries ◽  
Deformation And Fracture ◽  
Characterization Studies ◽  
Fracture Processes

ABSTRACTThe object of this study has been to gain a greater understanding of deformation and fracture processes in a Ti-24Al-11Nb (at %) alloy. The in-situ TEM deformation technique has been used to observe these processes as they occur. Material characterization studies revealed the existence of three different crystal structures in the material (α2,B2 and orthorhombic (0)). Slip is first initiated in the B2 and 0 phases. Although dislocations are observed in the α2 phase in the deformed material, they are seen only in high-stress regions and only in some laths. While numerous dislocations may be injected into the corresponding grain and phase boundaries, slip does not easily propagate into the α2 phase. Cracks are seen to originate most frequently in the regions transformed fully to α2 laths, and sometimes in the regions that contain α2 laths at prior β grain boundaries. Failure of grain or phase boundaries in the B2 or 0 phases where no α2 is present is not observed. Crack branching in the α2 phase is common, particularly in the vicinity of phase boundaries. Crack propagation in the B2 and 0 phases occurs by plastic thinning, and cracks formed in the α2 lath regions are either stopped in phase boundaries or blunted in the neighboring 0 or B2 grains.

scholarly journals Fracture in Bulk Amorphous Alloys

1998 ◽  
Vol 554 ◽  
Author(s):  
J. A. Horton ◽  
J. L. Wright ◽  
J. H. Schneibel
Keyword(s):  
Crack Propagation ◽  
Crack Growth ◽  
Shear Bands ◽  
Bulk Amorphous Alloy ◽  
In Situ Tem ◽  
X Ray Diffraction ◽  
Transmission Electron ◽  
Crack Tips ◽  
Temperature Fracture

AbstractThe fracture behavior of a Zr-based bulk amorphous alloy, Zr-10 Al-5 Ti-17.9 Cu-14.6Ni (at.%), was examined by transmission electron microscopy (TEM) and x-ray diffraction forany evidence of crystallization preceding crack propagation. No evidence for crystallizationwas found in shear bands in compression specimens or at the fracture surface in tensile specimens.In- situ TEM deformation experiments were performed to more closely examine actualcrack tip regions. During the in-situ deformation experiment, controlled crack growth occurredto the point where the specimen was approximately 20 μm thick at which point uncontrolledcrack growth occurred. No evidence of any crystallization was found at the crack tips or thecrack flanks. Subsequent scanning microscope examination showed that the uncontrolledcrack growth region exhibited ridges and veins that appeared to have resulted from melting. Performing the deformations, both bulk and in-situ TEM, at liquid nitrogen temperatures (LN2) resulted in an increase in the amount of controlled crack growth. The surface roughness of the bulk regions fractured at LN2 temperatures corresponded with the roughness of the crack propagation observed during the in-situ TEM experiment, suggesting that the smooth-appearing room temperature fracture surfaces may also be a result of localized melting.

scholarly journals In situ TEM observations of high-strain-rate deformation and fracture in pure copper

2020 ◽  
Vol 33 ◽  
pp. 10-16
Author(s):  
T. Voisin ◽  
M.D. Grapes ◽  
T.T. Li ◽  
M.K. Santala ◽  
Y. Zhang ◽  
...  
Keyword(s):  
High Strain Rate ◽  
Strain Rate ◽  
High Strain ◽  
Pure Copper ◽  
In Situ Tem ◽  
Deformation And Fracture ◽  
High Strain Rate Deformation

scholarly journals Probing Mobile-point-defect-mediated Nanodomain Evolutions in Ferroelastic-ferroelectrics Under High Stress with In-situ TEM

2020 ◽  
Vol 26 (S2) ◽  
pp. 2418-2419
Author(s):  
Yu Deng ◽  
Jim Ciston ◽  
Karen Bustillo ◽  
Colin Ophus ◽  
Ruopeng Zhang ◽  
...  
Keyword(s):  
Point Defect ◽  
High Stress ◽  
In Situ Tem

scholarly journals Capturing and Micromechanical Analysis of the Crack-Branching Behavior in Welded Joints

Metals ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 1308
Author(s):  
Wenjie Wang ◽  
Jie Yang ◽  
Haofeng Chen ◽  
Qianyu Yang
Keyword(s):  
Crack Propagation ◽  
Welded Joints ◽  
High Stress ◽  
High Strength ◽  
Crack Branching ◽  
Stress Concentrations ◽  
Ductile Materials ◽  
Pulling Forces ◽  
Crack Propagation Process ◽  
Combined Action

During the crack propagation process, the crack-branching behavior makes fracture more unpredictable. However, compared with the crack-branching behavior that occurs in brittle materials or ductile materials under dynamic loading, the branching behavior has been rarely reported in welded joints under quasi-static loading. Understanding the branching criterion or the mechanism governing the bifurcation of a crack in welded joints is still a challenge. In this work, three kinds of crack-branching models that reflect simplified welded joints were designed, and the aim of the present paper is to find and capture the crack-branching behavior in welded joints and to shed light on its branching mechanism. The results show that as long as there is another large enough propagation trend that is different from the original crack propagation direction, then crack-branching behavior occurs. A high strength mismatch that is induced by both the mechanical properties and dimensions of different regions is the key of crack branching in welded joints. Each crack branching is accompanied by three local high stress concentrations at the crack tip. Three pulling forces that are created by the three local high stress concentrations pull the crack, which propagates along with the directions of stress concentrations. Under the combined action of the three pulling forces, crack branching occurs, and two new cracks initiate from the middle of the pulling forces.

Deformation mechanisms at epitaxial semiconductor interfaces studied by in situ TEM

1992 ◽  
Vol 50 (1) ◽  
pp. 248-249
Author(s):  
R. Hull ◽  
J.C. Bean ◽  
F. Ross
Keyword(s):  
Strain Relaxation ◽  
High Stress ◽  
Dislocation Motion ◽  
Dislocation Nucleation ◽  
Deformation Mechanisms ◽  
Dynamic Strain ◽  
In Situ Tem ◽  
Stress Regime ◽  
Semiconductor Interfaces

We have studied deformation mechanisms at epitaxial semiconductor interfaces, primarily in the GexSi1-x/Si and InxGa1-xAs/GaAs systems, by in-situ annealing of metastably strained films in the transmission electron microscope (TEM). This allows direct, real-time, observation and recording of dynamic strain relaxation phenomena such as misfit dislocation nucleation, propagation and interaction mechanisms. This geometry also allows considerable insight into fundamental dislocation physics, as we are able, for example, to accurately quantify dislocation propagation velocities as functions of well-defined effective stresses (in the 108 - 109 pa regime)in the epitaxial layers, and to vary dislocation structure and character by varying the orientation of the epitaxial interface. Comparison with measurements of dislocation velocities in bulk semiconductors and with models of dislocation motion via kink propagation, allows extension of existing measurements and models to the thin film, high stress regime.

Estimation of Salt Rocks’ Long-Term Strength in Natural Conditions

2015 ◽  
Vol 243 ◽  
pp. 11-16
Author(s):  
Alexander A. Baryakh ◽  
Sergey Yu. Lobanov ◽  
Ivan S. Lomakin
Keyword(s):  
Underground Mining ◽  
Term Strength ◽  
New Approach ◽  
In Situ Data ◽  
The Earth ◽  
Deformation And Fracture ◽  
Strength Based ◽  
Fracture Processes

New approach to construction curve of salt rock’s long-term strength based on the diagram’s analysis of the earth surface subsidence growth under the influence of underground mining has been proposed. Performed verification of received estimation showed acceptable fit of mathematical modeling results of interchamber pillars’ deformation and fracture processes with in-situ data.

In-situ TEM study of crack propagation in crystal thinning area and crystal rotation at crack tip in Al

2021 ◽  
pp. 141800
Author(s):  
Kang Yan ◽  
Zhongwei Chen ◽  
Wenjie Lu ◽  
Yanni Zhao ◽  
Wei Le ◽  
...  
Keyword(s):  
Crack Propagation ◽  
Crack Tip ◽  
In Situ Tem ◽  
Crystal Rotation

scholarly journals Challenges and Accomplishments in Mechanical Testing Instrumented by In Situ Techniques: Infrared Thermography, Digital Image Correlation, and Acoustic Emission

2021 ◽  
Vol 11 (15) ◽  
pp. 6718
Author(s):  
Aleksander Sendrowicz ◽  
Aleksander Omholt Myhre ◽  
Seweryn Witold Wierdak ◽  
Alexei Vinogradov
Keyword(s):  
Acoustic Emission ◽  
Digital Image Correlation ◽  
Mechanical Testing ◽  
Digital Image ◽  
Image Correlation ◽  
Deformation And Fracture ◽  
Fracture Of Materials ◽  
Non Destructive ◽  
Fracture Processes

A current trend in mechanical testing technologies is to equip researchers and industrial practitioners with the facilities for non-destructive characterisation of the deformation and fracture processes occurring on different scales. The synergistic effect of such a combination of destructive and non-destructive techniques both widens and deepens existing knowledge in the field of plasticity and fracture of materials and provides the feedback sought to develop new non-destructive testing approaches and in situ monitoring techniques with enhanced reliability, accuracy and a wider scope of applications. The macroscopic standardised mechanical testing is still dominant in the research laboratories and industrial sector worldwide. The present paper reviews multiple challenges commonly faced by experimentalists, aiming at enhancing the capability of conventional mechanical testing by a combination of contemporary infrared thermography (IRT), rapid video imaging (RVI) with non-contact strain mapping possibilities enabled by the digital image correlation (DIC) method, and the acoustic emission (AE) technique providing unbeatable temporal resolution of the stochastic defect dynamics under load. Practical recommendations to address these challenges are outlined. A versatile experimental setup uniting the unique competencies of all named techniques is described alone with the fascinating possibilities it offers for the comprehensive characterisation of damage accumulation during plastic deformation and fracture of materials. The developed toolbox comprising practical hardware and software solutions brings together measuring technologies, data, and processing in a single place. The proposed methodology focuses on the characterisation of the thermodynamics, kinematics and dynamics of the deformation and fracture processes occurring on different spatial and temporal scales. The capacity of the proposed combination is illustrated using preliminary results on the tensile and fatigue behaviour of the fcc Inconel-625 alloy used as a representative example. Dissipative processes occurring in this alloy are assessed through the complex interplay between the released heat, acoustic emission waves, and expended and stored elastic energy.

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