Nucleation and development of plasticity in nanocrystalline BCC iron under shear loading

The features of the nucleation and development of plasticity in nanocrystalline iron with BCC lattice under shear were studied. The mechanisms of plastic deformation playing the main role in the development of structural rearrangements during loading were revealed. It was shown that the development of plasticity can be conditionally divided into several stages. The first stage of plasticity development is associated with the formation and propagation of dislocations and twins. At the second stage, intraganular slip and intergranular sliding begin to make the main contribution to plastic deformation. These processes initiate a change in the shape of the grains. At large shear, the deformation behavior of the sample is governed by the migration of the interfaces. Not only grain boundaries migrate but also twin ones do. As a result of migration processes, the grain sizes of the nanocrystalline sample are enlarged.

Download Full-text

Influence of grain size on mechanisms of plastic deformation and yield stress

Uspihi materialoznavstva ◽

10.15407/materials2020.01.026 ◽

2020 ◽

Vol 2020 (1) ◽

pp. 26-32

Author(s):

K. M. Borysovska ◽

◽

Y.M. Podrezov ◽

S.O. Firstov ◽

◽

...

Keyword(s):

Plastic Deformation ◽

Grain Size ◽

Yield Strength ◽

Plastic Flow ◽

Major Influence ◽

Entire Cross Section ◽

Physical Yield ◽

Grain Sizes ◽

20 Nm ◽

Mechanisms Of Plastic Deformation

The influence of grain size on the physical yield strength of the polycrystal is considered by the method of cellular automata. The physical yield strength of the polycrystal in this model is defined as the stress at which, the plastic deformation covers the entire cross section of the sample from one edge to another. Three mechanisms of plastic deformation are considered. The first one is an initiation of plastic flow from grain to grain by dislocation pile-ups. The second one is plastic flow in different grains independently of each other under the action of external stress and the third one is intergranular slippage. Computer simulations have shown that at large grain sizes (d > 200 nm) deformation propagates from grain to grain by initiating dislocations pile-ups, since in this case pile-ups are quite powerful and have a large effect on neighboring grains. At average values of grain size (20 nm <d <200 nm) plastic deformation occurs in the grains independently of each other, and the external strain give a major influence on plastic deformation. With further reduction of the grain sizes (d <20 nm) the main mechanism of deformation is intergranular slippage. because in grains of this size are quite large image stresses that do not allow large dislocation clusters. In small grains the image forces are quite large to prevent large dislocation pile-ups formation, but the mass and volume of grain are quite small to turn or slip its under the action of external stresses. In accordance with these mechanisms, on the calculated dependence of the physical yield strength vs grain size, there are three areas with different angles of inclination in logarithmic coordinates. Keywords: yield point, grain size, Hall―Petch low.

Download Full-text

Defect Structure Parameters of Deformed Polycrystals on Micro- and Mesolevel of Grain Sizes

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.1013.1 ◽

2014 ◽

Vol 1013 ◽

pp. 1-6

Author(s):

Eduard Kozlov ◽

Natal'ya Popova ◽

Marina Fedorischeva ◽

Nina Koneva

Keyword(s):

Plastic Deformation ◽

Size Effect ◽

Defect Structure ◽

Structure Parameters ◽

Scalar Density ◽

Grain Sizes ◽

Different Types ◽

Closed Structure ◽

Mechanisms Of Plastic Deformation

In the paper we consider the size effect of the closed structural formations as the function of accumulation of scalar density dislocations and their components under plastic deformation. The focus is on the role of interfaces of different types. The sizes are determined and the various parameters of the structure defining the micro-and mesolevel are identified at the development of the mechanisms of plastic deformation. The role of statistically stored dislocations (SSD) and geometrically necessary dislocations (GND) in the formation of the defect structure of the material is examined. It has been established that the smaller the size of the closed structure, the greater the GND part and the smaller the SSD component. The work is based on the TEM research of the structure of deformed materials.

Download Full-text

Finite Element Modeling of Self-Loosening of Bolted Joints

Analysis of Bolted Joints ◽

10.1115/pvp2004-2618 ◽

2004 ◽

Cited By ~ 6

Author(s):

Ming Zhang ◽

Yanyao Jiang ◽

Chu-Hwa Lee

Keyword(s):

Finite Element ◽

Contact Pressure ◽

Bending Moment ◽

Shear Loading ◽

Transverse Load ◽

Fe Model ◽

Bolted Joint ◽

Cyclic Bending ◽

Second Stage ◽

Cyclic Bending Moment

A three-dimensional finite element (FE) model with the consideration of the helix angle of the threads was developed to simulate the second stage self-loosening of a bolted joint. The second stage self-loosening refers to the graduate reduction in clamping force due to the back-off of the nut. The simulations were conducted for two plates jointed by a bolt and a nut and the joint was subjected to transverse or shear loading. An M12×1.75 bolt was used. The application of the preload was simulated by using an orthogonal temperature expansion method. FE simulations were conducted for several loading conditions with different preloads and relative displacements between the two clamped plates. It was found that due to the application of the cyclic transverse load, micro-slip occurred between the contacting surfaces of the engaged threads of the bolt and the nut. In addition, a cyclic bending moment was introduced on the bolted joint. The cyclic bending moment resulted in an oscillation of the contact pressure on the contacting surfaces of the engaged threads. The micro-slip between the engaged threads and the variation of the contact pressure were identified to be the major mechanisms responsible for the self-loosening of a bolted joint. Simplified finite element models were developed that confirmed the mechanisms discovered. The major self-loosening behavior of a bolted joint can be properly reproduced with the FE model developed. The results obtained agree quantitatively with the experimental observations.

Download Full-text

Structural mechanisms of plastic deformation of amorphous alloys containing crystalline nanoparticles

Bulletin of the Russian Academy of Sciences Physics ◽

10.3103/s1062873807120106 ◽

2007 ◽

Vol 71 (12) ◽

pp. 1702-1707 ◽

Cited By ~ 5

Author(s):

A. M. Glezer ◽

S. E. Manaenkov ◽

I. E. Permyakova

Keyword(s):

Plastic Deformation ◽

Amorphous Alloys ◽

Structural Mechanisms ◽

Mechanisms Of Plastic Deformation

Download Full-text

Order-disorder phenomena in α -brass - III. Influence of plastic deformation

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1960.0157 ◽

1960 ◽

Vol 257 (1290) ◽

pp. 363-385 ◽

Cited By ~ 21

Keyword(s):

Plastic Deformation ◽

Cold Work ◽

Stored Energy ◽

High Concentration ◽

Complex Behaviour ◽

Second Stage ◽

Third Stage ◽

Anneal Hardening ◽

Two Stages ◽

Degree Of Order

The evolution of stored energy during heating for specimens of deformed α-brass is quite different from that previously observed for pure metals; the stored energy is much larger and at least three stages of evolution exist. These have been studied for deformation in torsion and tension and the results correlated with measurements of electrical resistivity, density and hardness. The large release of energy in the first two stages is attributed mainly to the return of order destroyed by plastic deformation; the degree of disorder after heavy cold work is much greater than after quenching (part II). However, slight deformation (10% tension) increases the degree of order slightly. The first stage of energy release, below 120 °C, is probably due to rapid reordering assisted by vacancies created during deformation. The second stage represents the bulk of the reordering and some recovery involving rearrangement and annihilation of dislocations. The deformed specimens are probably strain-aged and thus recovery is accompanied by the dispersal of atmospheres of zinc which increases resistivity and decreases density, to some extent counteracting the effects of recovery. The balance of these three processes in stage 2 causes complex behaviour, the magnitude and even the sign of some changes in properties varies with the deformation. Reordering is complete before the beginning of the third stage of further recovery and recrystallization, in which dispersal of atmospheres is again important. Comparison of measurements of energy, resistivity and density suggests that the high concentration of stacking faults contributes to the resistivity. Anneal hardening is observed for the higher deformations and the maximum hardness coincides with the maximum degree of order.

Download Full-text

The Processing of Ultrafine-Grained Materials Using High-Pressure Torsion

Materials Science Forum ◽

10.4028/www.scientific.net/msf.558-559.1283 ◽

2007 ◽

Vol 558-559 ◽

pp. 1283-1294 ◽

Cited By ~ 1

Author(s):

Cheng Xu ◽

Z. Horita ◽

Terence G. Langdon

Keyword(s):

Plastic Deformation ◽

Grain Size ◽

High Pressure ◽

High Pressure Torsion ◽

Metallic Materials ◽

Grain Sizes ◽

Ultrafine Grained ◽

Wide Range ◽

Ultrafine Grained Materials ◽

Thin Disks

It is now well-established that processing through the application of severe plastic deformation (SPD) leads to a significant reduction in the grain size of a wide range of metallic materials. This paper examines the fabrication of ultrafine-grained materials using high-pressure torsion (HPT) where this process is attractive because it leads to exceptional grain refinement with grain sizes that often lie in the nanometer or submicrometer ranges. Two aspects of HPT are examined. First, processing by HPT is usually confined to samples in the form of very thin disks but recent experiments demonstrate the potential for extending HPT also to bulk samples. Second, since the strains imposed in HPT vary with the distance from the center of the disk, it is important to examine the development of inhomogeneities in disk samples processed by HPT.

Download Full-text

Small-Scale Plastic Deformation of Nanocrystalline High Entropy Alloy

Entropy ◽

10.3390/e20110889 ◽

2018 ◽

Vol 20 (11) ◽

pp. 889 ◽

Cited By ~ 6

Author(s):

Sanghita Mridha ◽

Mageshwari Komarasamy ◽

Sanjit Bhowmick ◽

Rajiv Mishra ◽

Sundeep Mukherjee

Keyword(s):

Plastic Deformation ◽

Rate Sensitivity ◽

Small Scale ◽

High Entropy Alloy ◽

Compression Tests ◽

High Entropy ◽

Grain Sizes ◽

Plastic Deformation Behavior ◽

High Strain Rate Sensitivity ◽

Widespread Interest

High entropy alloys (HEAs) have attracted widespread interest due to their unique properties at many different length-scales. Here, we report the fabrication of nanocrystalline (NC) Al0.1CoCrFeNi high entropy alloy and subsequent small-scale plastic deformation behavior via nano-pillar compression tests. Exceptional strength was realized for the NC HEA compared to pure Ni of similar grain sizes. Grain boundary mediated deformation mechanisms led to high strain rate sensitivity of flow stress in the nanocrystalline HEA.

Download Full-text

An Experimental Study of Self-Loosening of Bolted Joints

Journal of Mechanical Design ◽

10.1115/1.1767814 ◽

2004 ◽

Vol 126 (5) ◽

pp. 925-931 ◽

Cited By ~ 43

Author(s):

Yanyao Jiang ◽

Ming Zhang ◽

Tae-Won Park ◽

Chu-Hwa Lee

Keyword(s):

Endurance Limit ◽

Early Stage ◽

Fatigue Curve ◽

Relative Displacement ◽

Shear Loading ◽

Bolted Joints ◽

Second Stage ◽

Controlling Parameter ◽

Cyclic Plastic Deformation ◽

The Relationship

The self-loosening process of a bolted joint consists of two distinct stages. The early stage of self-loosening is due to the cyclic plastic deformation of the materials. The second stage of self-loosening is characterized by the backing off of the nut. The current work is concentrated on an experimental investigation of the second stage self-loosening. Over one hundred bolted joints with M12×1.75 bolts and nuts were experimentally tested using a specially designed testing apparatus. The experiments mimicked two plates jointed by a bolt and a nut and were subjected to cyclic transverse shear loading. During an experiment, the relative displacement between the two clamped plates, denoted by δ, was a controlling parameter. For a given preload, the relationship between, Δδ/2, the amplitude of the relative displacement between the two clamped plates, and, NL, the number of loading cycles to loosening followed a pattern similar to a fatigue curve. There existed an endurance limit below which self-loosening would not persist. A larger preload resulted in a larger endurance limit. However, a large preload increased the possibility for the bolt to fail in fatigue. The results suggest that the use of a regular nut is superior to the use of a flange nut in terms of self-loosening resistance.

Download Full-text