Computer Simulation of Plastic Deformation of Small Crystals
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COMPUTER SIMULATION OF PLASTIC DEFORMATION OF SMALL CRYSTALS
MASAO DOYAMA The Nishi Tokyo University Uenohara. Kitatsurugun. Yamanashi 409-01 JAPAN
ABSTRACT The deformation of body centered iron whiskers has been simulated. The iron whisker has a very sharp yield stress. Dislocations are created in a small coppe crystal.A higher stress was needed to create the first partial dislocation but less stress to create the second partial dislocation. 1. INTRODUCTION It has been wellknown that the yield stress of whiskers is very high Whiskers are often thought to be and close to the theoretical strength. Some experiments on the ideal single crystals close to perfect crystals. In this paper the plastic stress strain curve have been reported [1]. deformation of small iron whiskers whose axes are [100] and [110] were sim ulated. The plastic deformation of small copper crystals with and without The method of molecular dynamics was used in cracks were also simulated. this study.
2. IRON WHISKERS 2.1. Specimens A needle shape iron whisker containg 2632 atoms was created in a computer. The axis was the [110] direction. This axis is taken to be z axis. The size of the whisker is 8a x 8a x 14a. where a is the lattice parameter. but truncated at the edges as shown in Fig. l. The side faces are (110), A notch was made on one face. The specimen was (110). (001) and (001). A step is taken to be 3 first relaxed 100 steps by molecular dynamics. X 10-1'scc. 2.2. Computational Method were specially Two atom layers at the both ends. "holder region" treated, extended and held at these positions. The tensile deformation of 0.004 was uniformly given in a tensile direction [1111], then the stress was relaxed by the method of molecular dynamics. After each uniform deformation, atoms were relaxed 100 steps by the method of molecular dynamics. Then uniform deformation was given, followed by a relaxation of another hlitachi Super computer S-810 100 steps. This procedure was repeated. at the University of Tokyo was used for the simulation. Mat. Res. Soc. Symp. Proc. Vol. 239. 01992 Materials Research Society
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(1101 [111] (110)
(110)
(0 1) (b)
•' (ri )
(eV)
0.1 0 -0. 1
,
2
_
.
-0.2
26
r (A)
S Fig.l.
Iron specimen A
Fig.2. The effective interaction potential between atoms in iron.
2.3. Interatomic Potential The interatomic potential between i-th and j-th iron atoms in alpha phase was represented by 12] 0 (ri) = -0. 188917(r;j - 1.82709) +41.70192(ri j-2.50849) +0.198294 eV rij is the distance between the i-th and j-th atoms in A. The potential is plotted in Fig. 2. This potential is smoothly truncated at 3.44 A. For this potential the body centered cubic lattice is the most stable. This potential has been used for the calculations of point defects and amorphous iron. 2.4. Results of the Tensile Deformation of Iron Whiskers The total force in the z direction of all the atoms in the "holder" region were calculated. This can be taken as the tensile stress. The tensile stress and the strain was plotted in Fig.3. As seen from the s
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