Deformation of Poly-l-lactid acid (PLLA) under Uniaxial Tension and Plane-Strain Compression

The ability of PLLA, either amorphous or semicrystalline, to plastic deformation to large strain was investigated in a wide temperature range (Td = 70–140 °C). Active deformation mechanisms have been identified and compared for two different deformation modes—uniaxial drawing and plane-strain compression. The initially amorphous PLLA was capable of significant deformation in both tension and plane-strain compression. In contrast, the samples of crystallized PLLA were found brittle in tensile, whereas they proved to be ductile and capable of high-strain deformation when deformed in plane-strain compression. The main deformation mechanism identified in amorphous PLLA was the orientation of chains due to plastic flow, followed by strain-induced crystallization occurring at the true strain above e = 0.5. The oriented chains in amorphous phase were then transformed into oriented mesophase and/or oriented crystals. An upper temperature limit for mesophase formation was found below Td = 90 °C. The amount of mesophase formed in this process did not exceed 5 wt.%. An additional mesophase fraction was generated at high strains from crystals damaged by severe deformation. After the formation of the crystalline phase, further deformation followed the mechanisms characteristic for the semicrystalline polymer. Interlamellar slip supported by crystallographic chain slip has been identified as the major deformation mechanism in semicrystalline PLLA. It was found that the contribution of crystallographic slip increased notably with the increase in the deformation temperature. The most probable active crystallographic slip systems were (010)[001], (100)[001] or (110)[001] slip systems operating along the chain direction. At high temperatures (Td = 115–140 °C), the α→β crystal transformation was additionally observed, leading to the formation of a small fraction of β crystals.

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Deformation Mechanisms of Isotactic Poly-1-Butene and Its Copolymers Deformed by Plane-Strain Compression and Tension

Crystals ◽

10.3390/cryst9040194 ◽

2019 ◽

Vol 9 (4) ◽

pp. 194 ◽

Cited By ~ 1

Author(s):

Zbigniew Bartczak ◽

Magdalena Grala ◽

Alina Vozniak

Keyword(s):

Plane Strain ◽

Deformation Mechanism ◽

Flow Direction ◽

True Strain ◽

Fiber Texture ◽

Plane Strain Compression ◽

Deformation Mechanisms ◽

Random Copolymers ◽

Pole Figures ◽

Angle Scattering

The deformation-induced crystalline texture of isotactic poly-1-butene and its random copolymers with ethylene, developing during plane-strain compression and uniaxial tension, was investigated with X-Ray pole figures, supported by small-angle scattering (SAXS) and thermal analysis (DSC). The crystallographic (100)[001] chain slip was identified as the primary deformation mechanism, active in both compression and tension, supported by the transverse slip system and interlamellar shear. At the true strain around 0.8, lamellae fragmentation and partial destruction of the crystalline phase due to slip localization was observed, much heavier in tension than in plane-strain compression. That fragmentation brought an acceleration of the slip, which ultimately led to a common fiber texture in tensile samples, with the chain direction oriented preferentially along the drawing (flow) direction. Slightly more complicated crystal texture, reflecting triaxiality of the stress field, still with the chain direction preferentially oriented near the flow direction, was observed in compression. Additional deformation mechanism was observed at low strain in the plane-strain compression, which was either interlamellar shear operating in amorphous layers and supported by crystallographic slips or the simultaneous (110)[110] transverse slip operating on a pair of (110) planes. It was concluded that deformation proceeded similarly in both studied deformation modes, with practically the same deformation mechanisms engaged. Then, the plane-strain compression, proceeding homogeneously and preventing cavitation, seems more suitable for studies of the real deformation behavior, not obscured by any unwanted side-effects.

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Formation Process of Texture in AZ80 Alloy during High Temperature Plane Strain Compression Deformation

Materials Science Forum ◽

10.4028/www.scientific.net/msf.702-703.340 ◽

2011 ◽

Vol 702-703 ◽

pp. 340-343

Author(s):

Jinuk Kim ◽

Kazuto Okayasu ◽

Hiroshi Fukutomi

Keyword(s):

Plane Strain ◽

Formation Process ◽

True Strain ◽

Extrusion Direction ◽

Fiber Texture ◽

Plane Strain Compression ◽

Compression Direction ◽

Compression Deformation ◽

Pole Figures ◽

Az80 Alloy

Formation process of textures in AZ80 is investigated on polycrystal specimens with different initial textures by plane strain compression deformation at 673 K and 723 K with strain rates between 5.0×10-4s-1 and 5.0×10-2s-1. Three kinds of specimens were taken out from the extruded bars with (direction of the extrusion) fiber texture by changing the geometrical relationship with the extrusion direction. In the case of the specimen having parallel to the compression direction before deformation, the initial fiber texture gradually transformed into several orientations with increasing strain at 723K with a strain rate of 5.0×10-2s-1. oriented grains, which was not seen in the pole figures before deformation appeared after the deformation up to -1.0 in true strain. The other two kinds of specimens have compression directions perpendicular to direction. The textures after deformation of these two kinds of specimens also consisted of several components. Some of them are common among the three kinds of specimens and the others are retained components of the initial texture.

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Local Textures in Deformed and Recrystallized Aluminium Crystal

Textures and Microstructures ◽

10.1155/tsm.20.141 ◽

1993 ◽

Vol 20 (1-4) ◽

pp. 141-154 ◽

Cited By ~ 2

Author(s):

A. Akef ◽

J. H. Driver

Keyword(s):

Single Crystals ◽

Plane Strain ◽

Crystal Orientation ◽

Recrystallization Texture ◽

True Strain ◽

Plane Strain Compression ◽

Deformation Bands ◽

Transition Band ◽

Complete Recrystallization

The recrystallization mechanisms in deformed aluminium single crystals have been investigated by SEM microdiffraction techniques (ECP and EBSP). Aluminium crystals of (001)(uv0) and (001)[011-] orientations were deformed in plane strain compression to a true strain of ~1 to develop different deformation microstructures. Transition bands separating deformation bands were formed by orientation splitting in the (001)(uv0) crystals, but were not observed in the (001)[011-] crystal.During annealing at 250°C and 400°C, recrystallization nuclei are developed in both the deformed matrix and along transition bands. Matrix nucleation appears to occur by a subgrain coalescence mechanism according to which the new grains are misoriented 15-30° from the average as-deformed material. Transition band nucleation gives an orientation spread 20-30° around the original, undeformed crystal orientation. A well-defined cube recrystallization texture is obtained at 400°C after complete recrystallization of the initial cube crystal.

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Experimental and Numerical Study of Texture Evolution and Anisotropic Plastic Deformation of Pure Magnesium under Various Strain Paths

Advances in Materials Science and Engineering ◽

10.1155/2018/2867281 ◽

2018 ◽

Vol 2018 ◽

pp. 1-12

Author(s):

Hamad F. Alharbi ◽

Monis Luqman ◽

Ehab El-Danaf ◽

Nabeel H. Alharthi

Keyword(s):

Strain Hardening ◽

Uniaxial Tension ◽

Plane Strain ◽

Texture Evolution ◽

Plane Strain Compression ◽

Pure Magnesium ◽

Deformation Mechanisms ◽

Slip Systems ◽

Simple Compression ◽

Strain Paths

The deformation behavior and texture evolution of pure magnesium were investigated during plane strain compression, simple compression, and uniaxial tension at room temperature. The distinctive stages in the measured anisotropic stress-strain responses and numerically computed strain-hardening rates were correlated with texture and deformation mechanisms. More specifically, in plane strain compression and simple compression, the onset of tensile twins and the accompanying texture-hardening effect were associated with the initial high strain-hardening rates observed in specimens loaded in directions perpendicular to the crystallographic c-axis in most of the grains. The subsequent drop in strain-hardening rates in these samples was correlated with the exhaustion of tensile twins and the activation of pyramidal <c+a> slip systems. The falling strain-hardening rates were observed in simple compression and plane strain compression with loading directions parallel to the c-axis where the second pyramidal <c+a> slip systems were the only slip families that can accommodate deformation. For uniaxial tension with the basal plane parallel to the tensile axis, the prismatic <a> and second pyramidal <c+a> slips are the main deformation mechanisms. The predicted relative slip and twin activities from the crystal plasticity simulations clearly showed the effect of texture on the type of activated deformation mechanisms.

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