Multiaxial processing

Different extrusion profile processes can be used such as a robotic profile. A robot delivers the hot melt over or around a substrate. This robotic extrusion process can uses a flexible, heated, high-pressure hose that is connected to the extruder s die exit. The hot melt travels through the hose. At the end of the hose is a nozzle the tip of this nozzle is, in effect the actual profile die. A computer-regulated multiaxis robot controls the positioning of the profile nozzle die. The nozzle/die is guided by the robot to deposit the profile s hot melt on, as an example, a substrate that is on a multi-station rotating table supporting other substrates to be covered. 

ESC is mostly a surface-initiated failure of multiaxially stressed polymers in contact with surface-active substances. These surface-active substances do not cause chemical degradation of the polymer, but rather accelerate the process of macroscopic brittle-crack failure. Crazing and cracking may occur when a polymer under multiaxial stresses is in contact with a medium. A combination of external and/or internal stresses in a component may be involved. 

On the other hand, plastic deformation by grinding or shot peening produces maCrostresses that are accurately measurable by x-rays, as shown by excellent agreement between x-ray and dissection measurements. Figure 16-11 shows an example. Deformation by these processes appears to be multiaxial, rather than uniaxial, and pseudo-macrostress is accordingly absent. 

Fig. 15.9. Multiwafer batch processing chamber, showing 13-wafer process disk and multiaxis tilt capability...

Criteria 2, 5, and 6 are generally used for yielding, or the onset of plastic deformation, whereas criteria 1,3, and 4 are used for fracture. The maximum shearing stress (or Tresca [3]) criterion is generally not true for multiaxial loading, but is widely used because of its simplicity. The distortion energy and octahedral shearing stress criteria (or von Mises criterion [4]) have been found to be more accurate. None of the failure criteria works very well. Their inadequacy is attributed, in part, to the presence of cracks, and of their dominance, in the failure process. 

PS or copolymers are used extensively in injection blow molding. Tough and craze-resistant PS containers have been made by multiaxially oriented injection-molded parisons (238). This process permits the design of blow-molded objects with a high degree of controlled orientation, independent of blow ratio or shape. 

While lab tests often employ simple uniaxial loads, rubber components in service commonly experience states that combine loads from multiple directions. Such loads are said to be multiaxial. Fracture and fatigue processes occurring under such loads are governed by the same general principles as for uniaxial loads, but additional consideration must be made to account for the way in which local effects on crack precursors depend on orientation. 

The structure and orientation of the reinforcing fibers in the matrix system are essential for the mechanical properties of the work-piece. The choice of a particular architecture is dependent on multiple factors like drapeabiUty of the fabric, geometry/shape of the workpiece, mechanical requirements, and manufacturing process. Compraients made of unidirectional layers (laminates) are showing the best mechanical properties since the fibers are completely stretched (no undulation). Usually the single layers of a laminate are showing different fiber orientations. This causes anisotropic material behavior in the planar direction. The structure of a multiaxial layered laminate is shown in Fig. 2. 

This section will describe the process and machinery for making multiaxially oriented film from LCP. As summarized in section 2, the extruded LCP melt can be oriented through axial and transverse shear forces. Now, we will consider the use of stretching, or elongational forces, to improve and control the orientation. 

Films made from LCP and LCP-thermoplastic blends have been made using the blown film process [6,10,11,15-17], combined with a counter-rotating die. This process provides for multiaxial orientation of the LCP through controlled shear forces in the die prior to extrusion from the lips. Then, after extrusion from the die, the semi-molten LCP film tube is simultaneously stretched in the longitudinal (machine) direction and the circumferential (transverse) direction. The die shear and stretching were discussed previously in section 3. 

M.S. Greenfield, A.D. Ronemus, R.L. Void, R.R. Void, P.E. Ellis, T.E. Raidy, Deuterium quadrupole-echo NMR spectroscopy. III. Practical aspects of lineshape calculations for multiaxis rotational processes,. Magn. Reson. 72 (1987) 89—107. 

Processing of thermoplastic materials often leads to parts that are partially oriented. In these operations the materials undergo large multiaxial deformations, which remain as frozen in stresses once the material is cooled under its glass transition. (31,32). 

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