Slip, twinning, and fracture at a grain boundary in the L12 ordered structure—AΣ = 9 tilt boundary

1988 ◽  
Vol 3 (5) ◽  
pp. 848-855 ◽  
Author(s):  
M. H. Yoo ◽  
A. H. King
Keyword(s):  
Intergranular Fracture ◽  
Local Stress ◽  
Boundary Region ◽  
Anisotropic Elasticity ◽  
Tilt Boundary ◽  
Microplastic Deformation ◽  
Ordered Structure ◽  
Local Stress Concentration ◽  
Boron Segregation

The role of interaction between slip dislocations and a Σ = 9 tilt boundary in localized microplastic deformation, cleavage, or intergranular fracture in the Li2 ordered structure has been analyzed by using the anisotropic elasticity theory of dislocations and fracture. Screw superpartials cross slip easily at the boundary onto the (1$\overline 1$1) and the (001) planes at low and high temperatures, respectively. Transmission of primary slip dislocations onto the conjugate slip system occurs with a certain degree of difficulty, which is eased by localized disordering. When the transmission is impeded, cleavage fracture on the ($\overline 1$11) plane is predicted to occur, not intergranular fracture, unless a symmetric double pileup occurs simultaneously. Absorption (or emission) of superpartials occurs only when the boundary region is disordered. Slip initiation from pre-existing sources near the boundary can occur under the local stress concentration. Implications of the present result on the inherent brittleness of grain boundaries in Ni3 Al and its improvement by boron segregation are discussed.

Grain boundary structure intergranular fracture and the role of segregants as embrittling agents

1980 ◽  
Vol 295 (1413) ◽  
pp. 165-165 ◽  
Keyword(s):  
Grain Boundary ◽  
Intergranular Fracture ◽  
Boundary Region ◽  
Boundary Structure ◽  
Orientation Relation ◽  
Substantial Evidence ◽  
Grain Boundary Structure ◽  
Different Types

There is substantial evidence, from studies of annealed and crept aluminium, which indicates that once a dislocation has entered the boundary region between two grains it dissociates to form several grain boundary dislocations of Burgers vectors determined by the orientation relation between the grains. Subsequent behaviour depends on boundary structure, the dissociation products remaining bunched together in certain boundaries and moving apart in others, indicative of a friction type stress active in the boundary. A simple classification of the different types of boundary, where friction stresses were either high or low, into coincidence and non-coincidence boundaries, however, was not possible.

Solid Solution Effects and Deformation Micros trueture of Shock-Loaded Iron Manganese Alloys

1970 ◽  
Vol 28 ◽  
pp. 420-421
Author(s):  
A. Christou ◽  
J. V. Foltz ◽  
N. Brown
Keyword(s):  
Solid Solution ◽  
Shock Loading ◽  
High Strain ◽  
Local Stress ◽  
Strain Rates ◽  
Local Stress Concentration ◽  
Bcc Metals ◽  
Manganese Alloys ◽  
Iron Manganese ◽  
Transmission Microscope

In general, all BCC transition metals have been observed to twin under appropriate conditions. At the present time various experimental reports of solid solution effects on BCC metals have been made. Indications are that solid solution effects are important in the formation of twins. The formation of twins in metals and alloys may be explained in terms of dislocation mechanisms. It has been suggested that twins are nucleated by the achievement of local stress-concentration of the order of 15 to 45 times the applied stress. Prietner and Leslie have found that twins in BCC metals are nucleated at intersections of (110) and (112) or (112) and (112) type of planes.In this paper, observations are reported of a transmission microscope study of the iron manganese series under conditions in which twins both were and were not formed. High strain rates produced by shock loading provided the appropriate deformation conditions. The workhardening mechanisms of one alloy (Fe - 7.37 wt% Mn) were studied in detail.

Determination of DC06+ZE Sheet Crack Cause

2016 ◽  
Vol 368 ◽  
pp. 121-125
Author(s):  
Pavel Kejzlar ◽  
Tomáš Pilvousek ◽  
Michal Tregler
Keyword(s):  
Stress Concentration ◽  
Tensile Stress ◽  
Deep Drawing ◽  
Crack Formation ◽  
Local Stress ◽  
Local Deformation ◽  
Local Stress Concentration ◽  
Bcc Lattice ◽  
Hard Particles

The present work deals with determination of the cause of crack occurring in a part of car body manufactured from deep-drawing sheet. UHR-SEM, EDS, EBSD and measurement of microhardness were used for evaluation of the structure, local deformation and crack formation mechanism. A material analysis discovered foreign particles in the material. These particles were identified as MgAl2O4 with BCC lattice. The occurrence of these hard particles led to local stress concentration, decrease in mechanical strength and sheet breach due to tensile stress during deformation.

Permeability Improvement Technology of Directional Hydraulic Fracturing in Low Permeability

2014 ◽  
Vol 599-601 ◽  
pp. 385-390 ◽  
Author(s):  
Xue Xi Chen ◽  
Rui Qing Bi ◽  
Wen Guang Jin ◽  
Yong Xu
Keyword(s):  
Stress Concentration ◽  
Hydraulic Fracturing ◽  
Maximum Concentration ◽  
Local Stress ◽  
Field Application ◽  
Low Permeability ◽  
Pressure Relief ◽  
Local Stress Concentration ◽  
Directional Hydraulic Fracturing ◽  
Better Than

According to the conventional fracturing could easily lead to the local stress concentration of coal, the effect of pressure relief and permeability improvement is not ideal. The mechanism of directional hydraulic fracturing is analyzed and the parameters such as the layout of directional hole, the fracturing hole sealing, the minimum cracking pressure are discussed, then the field application tests are carried out. The results show that the directional hydraulic fracturing effect is better than that of ordinary fracturing hole and the maximum concentration and the average drainage scalar is respectively 3.75 times and 4 times of the ordinary hole pumping gas fracturing effects. The effect of permeability improvement is remarkable.

Effect of Coal Loading Conditions on Structural Characteristics of LFTS

2019 ◽  
Author(s):  
Hiroaki Eto ◽  
Koji Iizuka ◽  
Ryo Nishigochi ◽  
Tomoki Ikoma ◽  
Yasuhiro Aida ◽  
...  
Keyword(s):  
Stress Concentration ◽  
Loading Condition ◽  
Local Stress ◽  
Asia Pacific ◽  
Linear Potential ◽  
Detailed Model ◽  
Local Stress Concentration ◽  
East Kalimantan ◽  
Wave Response ◽  
Bulk Carriers

Abstract Indonesia is a main country supplying coal in the Asia-Pacific region, it is important to ensure a stable coal supply to Japan. Because the topography of the seabed near East Kalimantan Island, Indonesia’s main coal production area, is shallow, it is difficult for bulk carriers to reach the coast. Therefore, Large-Scale Floating Coal Transshipment Station (LFTS) was proposed, which will be used as a relay base between coal-barging barges from land and bulk carriers offshore. Installing an LFTS offshore from East Kalimantan is expected to improve coal transport productivity. LFTS can store coal equivalent to five times the capacity of one bulk carrier (total 500,000T), and can accommodate 2 bulk carriers at the same time during offloading. The scale of LFTS is 590m × 160m. The LFTS has a flat spread and the elastic behavior becomes the dominant Structure. The upper part of the LFTS is different rigidity partly because the partition wall to be loaded by dividing the coal into each quality is provided. Loaded coal not only changes the draft of the LFTS but also greatly deforms the LFTS and is expected to cause local stress concentration on the structural members. Therefore, this paper investigates wave response characteristics and stress characteristics with the coal loading of the LFTS, and then evaluation of structural strength by limit state design method. In this study, linear potential theory and the finite element method (FEM) were used to analyze the static hydroelastic motion under various coal loading condition and wave response of LFTS. And, to grasp the local stress concentration occurring inside the LFTS by using the response results, a detailed model modeling a complicated internal structure was prepared. Zooming analysis which is a method of giving the deformation result by the whole model of LFTS as forced displacement to the local detailed model was carried out. As a result, depending on the coal loading condition and wave conditions, it became clear that LFTS will be in a tough situation.

High Resolution 3D Reconstruction of an Atherosclorotic Plaque by a Combination of Histology and 3D Ultrasound

2009 ◽  
Author(s):  
Ahsan Choudhury ◽  
Michael Luppi ◽  
Warren Hopkins ◽  
Hao Gao ◽  
Saroj Das ◽  
...  
Keyword(s):  
3D Reconstruction ◽  
Stress Analysis ◽  
Plaque Rupture ◽  
Local Stress ◽  
3D Ultrasound ◽  
Plaque Morphology ◽  
Local Stress Concentration ◽  
Arterial Plaque ◽  
Cerebral Ischemic ◽  
Ischemic Attack

The sudden rupture of a vulnerable arterial plaque is a major cause of cerebral ischemic attack. Triggering of sudden rupture is a result of unfavourable plaque morphology, and is also a result of local stress concentration acting on the plaque. Computational stress analysis on a realistic plaque model is an important tool to assess the vulnerability of plaque rupture. However, the accuracy of the stress analysis is heavily dependent on the accuracy of the 3D reconstruction of the plaque geometry. The derivation of accurate vessel geometries from medical imaging has proved to be difficult due to limited image spatial resolution (at about 0.3mm in-plane) and the lack of contrast between the plaque components.

scholarly journals Role of Internal Stress in the Early-Stage Nucleation of Amorphous Calcium Carbonate Gels

2020 ◽  
Vol 10 (12) ◽  
pp. 4359 ◽  
Author(s):  
Qi Zhou ◽  
Tao Du ◽  
Lijie Guo ◽  
Gaurav Sant ◽  
Mathieu Bauchy
Keyword(s):  
Molecular Dynamics ◽  
Calcium Carbonate ◽  
Driving Force ◽  
Early Stage ◽  
Local Stress ◽  
Amorphous Calcium Carbonate ◽  
Local Coordination ◽  
Dynamics Simulations ◽  
Over Time

Although calcium carbonate (CaCO3) precipitation plays an important role in nature, its mechanism remains only partially understood. Further understanding the atomic driving force behind the CaCO3 precipitation could be key to facilitate the capture, immobilization, and utilization of CO2 by mineralization. Here, based on molecular dynamics simulations, we investigate the mechanism of the early-stage nucleation of an amorphous calcium carbonate gel. We show that the gelation reaction manifests itself by the formation of some calcium carbonate clusters that grow over time. Interestingly, we demonstrate that the gelation reaction is driven by the existence of some competing local molecular stresses within the Ca and C precursors, which progressively get released upon gelation. This internal molecular stress is found to originate from the significantly different local coordination environments exhibited by Ca and C atoms. These results highlight the key role played by the local stress acting within the atomic network in governing gelation reactions.

Analysis for Fracture Behavior of Compactor Grinding Tooth Forging Die Based on Finite Element Method

2011 ◽  
Vol 189-193 ◽  
pp. 2491-2494
Author(s):  
Yong Shao ◽  
Ji Zhou ◽  
Ping Yi Guo
Keyword(s):  
Fracture Behavior ◽  
Local Stress ◽  
Maximum Load ◽  
Local Stress Concentration ◽  
Forging Process ◽  
Stress Changes ◽  
Fracture Behaviors ◽  
Plastic Analysis ◽  
Die Stress ◽  
Forging Die

For forging die fracture behaviors during the actual forging process of compactor grinding tooth, the fully forging process has been simulated based on FEM. Die stress changes and distributions were analyzed in details through two related simulation processes. The maximum load acting on the die which type is ideal rigid body predicted firstly. Then, the die stress can be obtained by the elastic-plastic analysis when the die bears maximum load. Results show that Local stress concentration beyond ultimate strength of material causes the fracture of lower die.

Sign in / Sign up

Export Citation Format

Share Document