Disordered Nanoparticle Packings under Local Stress Exhibit Avalanche-Like, Environmentally Dependent Plastic Deformation

Nano Letters ◽  
2018 ◽  
Vol 18 (9) ◽  
pp. 5418-5425 ◽  
Author(s):  
Joel A. Lefever ◽  
Jason P. Mulderrig ◽  
Jyo Lyn Hor ◽  
Daeyeon Lee ◽  
Robert W. Carpick
Keyword(s):  
Plastic Deformation ◽  
Local Stress

scholarly journals Effect of plastic deformation on the evolution of wear and local stress fields in fretting

2016 ◽  
Vol 82 ◽  
pp. 1-8 ◽  
Author(s):  
Zupan Hu ◽  
Wei Lu ◽  
M.D. Thouless ◽  
J.R. Barber
Keyword(s):  
Plastic Deformation ◽  
Local Stress ◽  
Stress Fields

Stochastic Mesoscale Modeling of Elastic-Plastic Deformation

1999 ◽  
Vol 578 ◽  
Author(s):  
A. Staroselsky ◽  
V.V. Bulatov
Keyword(s):  
Plastic Deformation ◽  
Stress Distribution ◽  
Local Stress ◽  
State Theory ◽  
Crystallographic Structure ◽  
Crystallographic Slip ◽  
Structural Levels ◽  
Considerable Detail ◽  
New Phase ◽  
Nucleation And Growth Mechanism

AbstractPlastic response of a solid under stress depends on its crystallographic structure and morphology. Two of the major mechanisms of plasticity in metals are crystallographic slip and twinning. The purpose of this work is to analyze the influence of local stress distribution on slip and twin nucleation and propagation and to examine how this behavior depends on the interaction among slips, twins, and grain boundaries. We formulate a simple model in which slip and twin systems are defined at appropriate angles to each other. Plastic flow is treated as a Markovian stochastic process consisting of a series of local inelastic transformations (LITs) in the representative volume elements (RVE). The probabilities of LITs per unit time are defined in the framework of transition-state theory. By varying the types of allowed LITs and/or the scale of RVE, plastic deformation is modeled at different structural levels, from a small volume of single crystal to the aggregate response of an isotropic polycrystalline solid. An important feature of this model is that evolution of the internal stress distribution is traced explicitly throughout the simulation run. This allows us to examine conditions of slip and twinning in considerable detail. In particular, we observe that twinning occurs through a nucleation-and-growth mechanism whose rate is controlled by the size of the critical nucleus of the new phase.

scholarly journals Improved incrementally affine method for viscoelastic-viscoplastic composite by utilizing an adaptive scheme

2021 ◽  
Author(s):  
Jiyoung Jung ◽  
Youngsoo Kim ◽  
Sangryun Lee ◽  
Issam Doghri ◽  
Seunghwa Ryu
Keyword(s):  
Plastic Deformation ◽  
Mechanical Response ◽  
Mean Field ◽  
Complex Loading ◽  
Local Stress ◽  
Yield Reduction ◽  
Adaptive Scheme ◽  
The Matrix ◽  
Particulate Reinforced ◽  
Affine Scheme

We propose a micromechanics-based mean-field homogenization scheme for the viscoelastic-viscoplastic particulate-reinforced composite which is applicable to predict its mechanical response under complex loading conditions. We apply a formulation based on an incrementally affine scheme by using algorithmic tangent operators, while adaptively adjusting the strain of each constituent at every step of the loading process to ensure the consistency of the accumulated strain state and the concentration tensor. We name the method adaptive incrementally affine method. Despite mathematically rigorous derivation, the method has some errors in plastic deformation regime. We propose an assumption for better prediction which dropping out the affine strain and affine stress in adaptive scheme. We show that the adaptive incrementally affine scheme is able to predict the viscoelastic response very well. Still, it is inevitable that the plastic deformation of the composite is initiated earlier than our mean-field theoretical prediction because of the local stress concentration near the particulate. Hence, we propose a yield reduction method that enforces the earlier initiation of the plastic deformation in the matrix phase when obtaining an effective mechanical response. We show that the predictions from the adaptive incrementally affine scheme adjusted with the yield reduction match well with various numerical simulations on particulate-reinforced composites considering viscoelastic, elastic-viscoplastic, and viscoelastic-viscoplastic matrices under uniaxial, cyclic, and bi-axial loadings.

scholarly journals Analysis and Characterization on Dynamic Recrystallization in Casting AZ31 Mg Alloys Under Plane Strain Compression

Materials ◽  
2020 ◽  
Vol 13 (3) ◽  
pp. 522
Author(s):  
Li Xu ◽  
Minghua Xiang ◽  
Jun Wang ◽  
Jun Zhang ◽  
Chenning Wang ◽  
...  
Keyword(s):  
Plastic Deformation ◽  
Dynamic Recrystallization ◽  
Strain Rate ◽  
Plane Strain ◽  
Rate Sensitivity ◽  
Local Stress ◽  
Plane Strain Compression ◽  
Mg Alloys ◽  
Coarse Grained ◽  
Compression Tests

Studies on twinning, twin-induced dynamic recrystallization (TDRX), and their temperature and strain rate dependences are of considerable significance to the ultimate strength and plastic formability of the coarse-grained Mg alloys during severe plastic deformation. Plane strain compression tests were conducted on the parallelepiped samples of casting AZ31 Mg alloys. The twinning and recrystallization behaviors close to and away from the crack boundaries were characterized using electron backscatter diffraction. The results show: (1) with increasing strain rate for tests, the extension twin proliferates significantly. Due to the local stress concentration, the TDRX is more active in the area close to the crack tip and exhibits the positive strain-rate sensitivity as twinning; (2) the TDRX is not only stress-favored but also closely links to the temperature. However, the TDRX is not utterly proportional to the temperature. Compared to 400 °C, 300 °C is more beneficial to the TDRX, achieving the higher strength and plastic deformability. The main reason is that the higher strain-hardening rate and flow stress at the higher strain rate and lower temperature motivates the transformation from twinning to the fine twin-walled grains more efficiently, and the stress-favored TDRX is crucial to refine grains and continue plastic deformation for the casting Mg alloys with coarse grains.

Damages Caused by Projectile Impact

2016 ◽  
Vol 689 ◽  
pp. 29-33
Author(s):  
Adnan I.O. Zaid
Keyword(s):  
Plastic Deformation ◽  
Phase Transformation ◽  
Impact Velocity ◽  
Incident Angle ◽  
Shear Bands ◽  
Local Stress ◽  
Target Thickness ◽  
Target Plate ◽  
Reflected Waves ◽  
Plug Formation

Impact conditions involve velocities below the sonic speed, which is normally of the order few hundreds up to few thousands m/s. The implications of impact depend on projectile and target materials, impact velocity, incident angle and the mass and shape of the projectile impacting head. The superimposition of progressing and reflected waves can lead to local stress levels that exceed the material’s strength, thus causing cracks and / or fracture at significant velocities. At low impact velocities, plastic deformation normally prevails. With increasing velocities the projectile will leave a hole in the target. With decreasing target thickness, the effects range from perforation, via internal cracks, and finally to plug formation. In this paper, the damages caused by impact which include: perforation, plugs formation and their fracture, metallurgical changes e.g. shear bands, twinning, recrystallization and phase transformation and fractures both in the projectile and the target plate are presented and discussed.

Grain boundary segregation and intergranular fracture in molybdenum

1980 ◽  
Vol 370 (1743) ◽  
pp. 431-458 ◽  
Keyword(s):  
Plastic Deformation ◽  
Grain Boundaries ◽  
Cross Sections ◽  
Boundary Segregation ◽  
Crack Tip ◽  
Local Stress ◽  
Intergranular Brittleness ◽  
Solubility Of Oxygen ◽  
Carbon Additions ◽  
Work Of Fracture

The refractory group VIA metals generally exhibit intergranular brittleness when they are in the recrystallized condition. This causes severe problems in their fabrication and places major limitations on their practical application. The phenomenon, generally referred to as recrystallization embrittlement, results in large increases in the ductile-to-brittle transition temperature and a change in fracture mode in the lower shelf regime from cleavage to intergranular with a significant decrease in ductility. The embrittlement is widely considered to be associated with interstitial impurities but there have been few systematic studies to elucidate their effects. The present paper reports results from a systematic study of segregation and intergranular embrittlement in binary molybdenum-oxygen and ternary molybdenum-oxygen-carbon alloys. The experiments were carried out on ‘bamboo’ specimens containing a series of identical single grain boundaries traversing their cross-sections. Measurements have been made of the activation energy for oxygen segregation to grain boundaries in the binary molybdenum-oxygen alloys. The influence of carbon additions on the level of oxygen segregation has also been determined. In addition, the influence of oxygen segregation on the energy to fracture has been studied and this has involved quantitative measurements of the work of fracture and the contribution made by plastic deformation. Results from metallographic studies are also presented, showing the effects of segregation on fracture surface topography and dislocation structures immediately adjacent to the fracture surfaces. In discussing the results we consider the thermodynamics of oxygen segregation to grain boundaries and the role played by carbon in inhibiting segregation. It is proposed that carbon either increases the effective solubility of oxygen in molybdenum or acts as a trap for oxygen atoms. In either case the effect is to reduce the driving force for segregation. We also consider the influence of segregation on the work of fracture and show that the reduction in oxygen segregation resulting from the addition of carbon produces small increases in fracture energy. This increases the local stress to propagate a crack sufficiently to promote plastic deformation which blunts the crack tip. The consequent change in geometry reduces the stress concentration at the crack tip, thereby resulting in a large increase in the applied fracture stress and the work to fracture.

Plastic Deformation of a Laminated Plate With a Hole

1980 ◽  
Vol 47 (4) ◽  
pp. 827-832 ◽  
Author(s):  
Y. A. Bahei-El-Din ◽  
G. J. Dvorak
Keyword(s):  
Plastic Deformation ◽  
Circular Hole ◽  
Metal Matrix ◽  
Matrix Material ◽  
Local Stress ◽  
Elastic Fibers ◽  
Plastic Behavior ◽  
Laminated Plate ◽  
Plastic Yielding ◽  
Metal Matrix Composite Material

The elastic-plastic behavior of a (0/90) symmetric FP-Al plate containing a circular hole is investigated using the finite-element method. Of principal concern are plastic yielding at the circular hole and fracture of the plate caused by failure of the fiber at the hole. The results illustrate the significance of plasticity in deformation of metal-matrix composites. The behavior of the laminated plate is compared with that of a geometrically similar plate made of an unreinforced matrix material, for uniaxial loading/unloading/reloading sequences. The comparison reveals significant differences in the role of plastic deformation in these two materials. Specifically, plastic yielding in the matrix of the laminated plate at the circular hole leads to a substantial increase in the local stress concentration in the elastic fibers adjacent to the hole boundary. Also, it is found that the fiber reinforcement causes a large increase in the stiffness and strength of the composite, but only a minor elevation of its yield strength. Therefore, to take advantage of the mechanical properties of the metal matrix composite material, it is necessary to admit working loads which exceed its elastic limit.

Investigation of Relationship between Material Flow Direction and Local Stress Field in Plastic Deformation

2008 ◽  
Vol 575-578 ◽  
pp. 489-494 ◽  
Author(s):  
Ji Zhang ◽  
Zhu Bin He ◽  
Shi Jian Yuan
Keyword(s):  
Plastic Deformation ◽  
Stress Field ◽  
Material Flow ◽  
Flow Direction ◽  
Stress Gradient ◽  
Local Stress ◽  
Movement Direction ◽  
Mean Stress ◽  
Gradient Direction ◽  
Local Stress Field

The maximum mean stress gradient direction in typical plane strain and axisymmetrical plastic deformation problems was calculated by numerical method to investigate relationships between material flow direction and related local stress field. Good agreement was found between the movement direction in the deforming bodies and the maximum mean stress gradient direction of the related local mean stress field. This agreement was also found in typical 3-D problems by numerical simulation and visualization.

Sem Examinations of Glass Knives

1970 ◽  
Vol 28 ◽  
pp. 282-283
Author(s):  
J. Temple Black
Keyword(s):  
Plastic Deformation ◽  
Tensile Loading ◽  
Resultant Force ◽  
Stress Concentrations ◽  
Edge Chipping ◽  
Surface Flaws ◽  
Edge Defects ◽  
Microscopic Surface

There are two types of edge defects common to glass knives as typically prepared for microtomy purposes: 1) striations and 2) edge chipping. The former is a function of the free breaking process while edge chipping results from usage or bumping of the edge. Because glass has no well defined planes in its structure, it should be highly resistant to plastic deformation of any sort, including tensile loading. In practice, prevention of microscopic surface flaws is impossible. The surface flaws produce stress concentrations so that tensile strengths in glass are typically 10-20 kpsi and vary only slightly with composition. If glass can be kept in compression, wherein failure is literally unknown (1), it will remain intact for long periods of time. Forces acting on the tool in microtomy produce a resultant force that acts to keep the edge in compression.

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.

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