Material Response and Continuum Relations; or From Microscales to Macroscales

1984 ◽  
Vol 106 (4) ◽  
pp. 286-289 ◽  
Author(s):  
D. C. Drucker
Keyword(s):  
Plastic Deformation ◽  
Shear Stress ◽  
Aluminum Alloys ◽  
Single Crystals ◽  
Continuum Mechanics ◽  
Stress Strain ◽  
Material Response ◽  
Macroscopic Behavior ◽  
Macroscopic Stress ◽  
Structural Metals

Brief qualitative assessments are presented of a few approaches to macroscopic stress-strain relations for structural metals, alloys, and composites and some remarks are made about fracture. Ignoring the scale and applying continuum mechanics to the microstructure lies at one extreme, the dislocation scale treatment of single crystals and simple polycrystals at another. When, as for structural aluminum alloys, the shear stress required for continuing plastic deformation is so much higher than for the constituent single crystals, it seems unlikely that the latter approach is able to exhibit the salient features of macroscopic behavior.

scholarly journals The critical shear stress of mercury single crystals

1937 ◽  
Vol 163 (912) ◽  
pp. 34-53 ◽  
Keyword(s):  
Plastic Deformation ◽  
Shear Stress ◽  
Melting Point ◽  
Single Crystal ◽  
Single Crystals ◽  
Critical Shear Stress ◽  
Impurity Content ◽  
Thermal Agitation ◽  
Plastic Yield ◽  
Metal Single Crystals

The influence of very small quantities of impurity on the critical shear stress of metal single crystals has an important bearing on the mechanism of their plastic deformation. For investigations in this field, mercury is a very suitable metal: its impurity content can easily be reduced to an extremely low level (Hulett 1911) and it contains no dissolved gases (Hulett 1911). Also, as first pointed out by Andrade (1914), single crystal wires of this metal can be prepared without difficulty. The low melting point of mercury (-38∙8° C.) is far from being a disadvantage. The crystals can be maintained at -60° C., and at a temperature so near the melting point the thermal agitation may be expected to accentuate phenomena not observable at lower temperatures, if such agitation plays the important part in the mechanism of glide ascribed to it (Taylor 1934; Polanyi 1934; Orowan 1934). As a possible instance of this, the experiments to be described have revealed the existence of a preliminary “set” preceding the true plastic yield. Widely differing forms of slip band have also been observed, and are described elsewhere (Greenland 1937). It is hoped that these results will throw further light on the mechanism of glide.

Derivation of Polycrystal Creep Properties From the Creep Data of Single Crystals

1977 ◽  
Vol 44 (1) ◽  
pp. 73-78 ◽  
Author(s):  
T. H. Lin ◽  
C. L. Yu ◽  
G. J. Weng
Keyword(s):  
Single Crystals ◽  
Creep Deformation ◽  
Tensile Loading ◽  
Present Theory ◽  
Sole Source ◽  
Stress And Strain ◽  
Creep Data ◽  
Stress Strain ◽  
Macroscopic Stress ◽  
Additional Constant

A method developed for calculating the polycrystal stress-strain-time relation from the creep data of single crystals is shown. Slip is considered to be the sole source of creep deformation. This method satisfies, throughout the aggregate, both the condition of equilibrium and that of continuity of displacement as well as the creep characteristics of single crystals. A very large three-dimensional region is assumed to be filled with innumerable identical cubic blocks, each of which consists of 64 cube-shaped crystals of different orientations. This region is assumed to be embedded in an infinite elastic isotropic medium. This infinite medium is subject to a uniform loading. The average stress and strain of a cubic block at the center of the region is taken to represent the macroscopic stress and strain of the polycrystal. This method is self-consistent and considers the heterogeneous interaction effect of the creep deformation of all slid crystals. The macroscopic stress-strain-time relations of the polycrystal were calculated for three tensile loadings, one radial loading, and two nonradial loadings of combined tension and torsion. The numerical results given by the present theory agree well with those predicted by the so-called “Mechanical Equation of State.” The creep strain components calculated by the present theory for the case of a constant tensile loading followed by an additional constant tensile loading are found to be considerably higher than those predicted by von Mises and Tresca’s theories. These results agree well qualitatively with experimental results.

The Effects of Strain Rate and Thickness on the Response of Thin Layers of Solder Loaded in Pure Shear

1997 ◽  
Vol 119 (2) ◽  
pp. 81-84 ◽  
Author(s):  
A. Gilat ◽  
K. Krishna
Keyword(s):  
Plastic Deformation ◽  
Shear Stress ◽  
Strain Rate ◽  
Mechanical Response ◽  
Pure Shear ◽  
Strain Curve ◽  
Thin Layers ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Stress And Deformation

A new configuration for testing thin layers of solder is introduced and employed to study the effects of strain rate and thickness on the mechanical response of eutectic Sn-Pb solder. The solder in the test is loaded under a well defined state of pure shear stress. The stress and deformation in the solder are measured very accurately to produce a reliable stress-strain curve. The results show that both the stress needed for plastic deformation and ductility increase with increasing strain rate.

Plastic Deformations in Single Crystals of FePd with the L10 Structure

2008 ◽  
Vol 1128 ◽  
Author(s):  
Katsushi Tanaka ◽  
Wang Chen ◽  
Kyosuke Kishida ◽  
Norihiko L. Okamoto ◽  
Haruyuki Inui
Keyword(s):  
Plastic Deformation ◽  
Shear Stress ◽  
Temperature Dependence ◽  
Single Crystals ◽  
Yield Stress ◽  
Room Temperature ◽  
Positive Temperature ◽  
Plastic Deformations ◽  
L10 Structure ◽  
Critical Resolved Shear Stress

AbstractCompressive deformations of L10-ordered single crystals of FePd have been investigated from room temperature to 873 K. The critical resolved shear stress for superlattice dislocations is hard to determine resulting from buckling that occurs after a small amount of conventional plastic deformation. The CRSS for superlattice dislocations determined from yield stress is significantly larger than that of ordinary dislocations. The CRSS for octahedral glide of ordinary and superlattice dislocations are virtually independent of the temperature, and the positive temperature dependence of the yield stress is not observed for both, ordinary and superlattice dislocations, by the present experiments.

Mechanical behavior assessment of sucrose using nanoindentation

2007 ◽  
Vol 22 (7) ◽  
pp. 2037-2045 ◽  
Author(s):  
K.J. Ramos ◽  
D.F. Bahr
Keyword(s):  
Experimental Study ◽  
Plastic Deformation ◽  
Shear Stress ◽  
Elastic Modulus ◽  
Slip System ◽  
Single Crystals ◽  
Maximum Shear Stress ◽  
Model Material ◽  
Instrumented Indentation ◽  
Plastic Properties

An experimental study of the elastic and plastic properties of sucrose single crystals, which can be considered to be a model material for both pharmaceutical excipients and explosives, has been carried out using nanoindentation. Instrumented indentation was used to characterize the properties of both habit and cleavage planes on the (100) and (001) orientations; the elastic modulus on the (100) is 38 GPa, while the modulus on the (001) is 33 GPa. The hardness of sucrose is approximately 1.5 GPa. Nanoindentation enables assessment of the onset of plastic deformation on cleaved surfaces, and a maximum shear stress of 1 GPa can be supported prior to plastic deformation. The deformation in this material is crystallographically dependent, with pileup around residual indentation impressions showing evidence of preferential slip system activity.

Plastic Deformation of Ni3Nb Single Crystals

1998 ◽  
Vol 552 ◽  
Author(s):  
Kouji Hagihara ◽  
Takayoshi Nakano ◽  
Yukichi Umakoshi
Keyword(s):  
Plastic Deformation ◽  
Shear Stress ◽  
Single Crystals ◽  
Crystal Orientation ◽  
Strengthening Mechanism ◽  
Orientation Dependence ◽  
Slip Model ◽  
Compression Tests ◽  
Increasing Temperature ◽  
Critical Resolved Shear Stress

ABSTRACTTemperature dependence of yield stress and operative slip system in Ni3Nb single crystals with the DOa structure was investigated in comparison with that in an analogous L12 structure. Compression tests were performed at temperatures between 20 °C and 1200 °C for specimens with loading axes perpendicular to (110), (331) and (270).(010)[100] slip was operative for three orientations, while (010)[001] slip for (331) and {211} <10 7 13> twin for (270) orientations were observed, depending on deformation temperature. The critical resolved shear stress (CRSS) for the (010)[100] slip anomaly increased with increasing temperature showing a maximum peak between 400 °C and 800 °C depending on crystal orientation. The CRSS showed orientation dependence and no significant strain rate dependence in the temperature range for anomalous strengthening. The [100] dislocations with a screw character were aligned on the straight when the anomalous strengthening occurred. The anomalous strengthening mechanism for (010)[100] slip in Ni3Nb single crystals is discussed on the basis of a cross slip model which has been widely accepted for some L12-type compounds.

scholarly journals On the inhomogeneity of plastic deformation in the crystals of an aggregate

1948 ◽  
Vol 193 (1032) ◽  
pp. 89-97 ◽  
Keyword(s):  
Plastic Deformation ◽  
Grain Boundaries ◽  
Single Crystals ◽  
Tensile Deformation ◽  
Strain Curve ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
X Ray

The variation of plastic deformation in aluminium specimens consisting of large crystals has been determined by measuring elongation and hardness at various points after tensile deformation. The deformation varied from grain to grain, and also within each grain the deformation near the boundary was greater or smaller than at the centre according to whether the neighbour was more or less deformed, i. e. there is not necessarily inhibition of slip near grain boundaries. These results were supported by metallographic and X-ray observations. Their importance with respect to the calculation of the stress-strain curve of aggregates from those of single crystals is discussed. It is suggested that a mechanism other than slip operates near the grain boundaries during deformation, and even within the crystals during large extensions.

Investigation of shock-wave deformation history from recovered structure

1986 ◽  
Vol 44 ◽  
pp. 434-435
Author(s):  
M.A. Mogilevsky ◽  
L.S. Bushnev
Keyword(s):  
Shock Wave ◽  
Plastic Deformation ◽  
Dislocation Density ◽  
Shock Waves ◽  
Shock Front ◽  
Single Crystals ◽  
Residual Deformation ◽  
Deformation Structure ◽  
Deformation History ◽  
Deformation Velocity

Single crystals of Al were loaded by 15 to 40 GPa shock waves at 77 K with a pulse duration of 1.0 to 0.5 μs and a residual deformation of ∼1%. The analysis of deformation structure peculiarities allows the deformation history to be re-established.After a 20 to 40 GPa loading the dislocation density in the recovered samples was about 1010 cm-2. By measuring the thickness of the 40 GPa shock front in Al, a plastic deformation velocity of 1.07 x 108 s-1 is obtained, from where the moving dislocation density at the front is 7 x 1010 cm-2. A very small part of dislocations moves during the whole time of compression, i.e. a total dislocation density at the front must be in excess of this value by one or two orders. Consequently, due to extremely high stresses, at the front there exists a very unstable structure which is rearranged later with a noticeable decrease in dislocation density.

Sign in / Sign up

Export Citation Format

Share Document