Plastic deformation processing drawing

Drawing is a plastic deformation process in which the cross-sectional area of a part is reduced by the contemporary action of a pulling force and a converging die. 

Plasticity. Slip, the gliding motion of full planes of atoms or partial planes, called dislocation, allows for the deformation processing of polycrystalline metals (forging, extrusion, rolling, swaging, and drawing). Slip occurs much more readily across close-packed planes in close-packed directions. 

As discussed in Sect. 3.2, once a mature fibril is created, further thickening occurs by a viscoplastic drawing mechanism which involves intense plastic deformation at the craze/bulk interface [32], Instead of using a non-Newtonian formulation as in [32] or a formulation based on Eyring s model [45], but on the basis of a preliminary study of the process [36], the craze thickening is described with a similar expression as the viscoplastic strain rate for the bulk in Eq. 3 as [20]... 

Figure 5.2 Schematic of wire drawing process for metals. The process exploits the ability of metals to undergo large scale plastic deformation. The material is pulled through a conical die that forces a reduction in the diameter. A variety of shapes, round, hexagon, square, etc. can be drawn.

It was considered initially that because there is no net tensile stress in a hydrostatic extrusion process it might be possible to impose very large plastic deformations without incurring fracture. It was indeed shown that Rj, of 30 can be imposed in polyethylene comparable to the draw ratios of 30 adiieved in a tensile drawing process, and that both processes are limited by the strain hardening behaviour of the material, which is determined solely by the total plastic strain imposed. This led to an important... 

It has been shown that fracture is a very complex process and the fracture performance depends on both the initiation and the propagation of a defect [6-10] in the material. Under impact, most polymers break in very distinct manners. Several types of fracture have been identified depending on the amount of plastic deformation at the crack tip and the stability of crack propagation. For each type, an appropriate analysis has been developed to determine the impact fracture energy of the material. These methods have also been verified in various plastics [11,12]. The different fracture behaviors in most polymers are illustrated in Figure 27.1, which shows a schematic drawing of the load-deflection diagram of Charpy tests on HIPS [13] under an impact velocity of 2 m/s at various temperatures. 

Studies of craze microstructure and the surrounding displacements of crazes have established that the only parts around a craze that undergo plastic deformation are concentrated into a process zone at the tip of the craze, and into a fringing layer all around the entire craze body. In the process zone craze matter is generated by one of the two processes discussed above, and fibrils are necked down to the final extension ratio. In the fringing layer, additions are made to craze fibrils by drawing polymer out of half space. Outside the idetifiable parts of a craze, the solid polymer remains entirely elastic while inside the craze body the fully drawn fibers carry the required craze tractions purely elastically in their orientation hardened state at the... 

On the basis of plastic deformation visible at 2% extension, the original draw direction being contracted while the thickness of the sheet remained unchanged, the non-linearity at 0 = 90° was attributed to a slip mechanism involving rigid body rotation. This process occurred in conjunction with the linear mechanism associated with unordered r ons. Again c/c shear should be negligible. 

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