Directional property machine

Paper made on a paper machine exhibits quite different properties in the x and y directions (the machine and cross machine directions), an example of which is a difference in stiffness which can be demonstrated by plotting the specific elastic stiffness in the x-y plane as a function of the machine direction and cross machine direction co-ordinates in the form of a polar diagram (Figure 4.7). 

In most processes for the manufacture of paper, the fibres may align themselves in a preferred direction. In machine-made paper, the orientation is particularly marked, as the fibres are oriented in the direction in which the web is moving, the machine direction (MD). The MD of a piece of paper is of particular importance in determining the properties of a piece of paper. The direction across the paper at right angles to the MD is called the cross direction (CD). When paper is made from pulp, the smallest particles will penetrate furthest into the paper as the water drains through it. So for this and several... 

The aforementioned specimen with a penny-shaped crack and similar specimens facilitate simple and straightforward measurements of Ki, at least in principle. They are impractical, however, for a number of good reasons. These necessarily large specimens are inefficient with respect to the amount of material and the loading capacity of the testing machine that would be required. They may not reflect the actual microstructure and property of the size of material of interest, and cannot discern directional properties of the materials. 

Note that the method of making the plastic sample and the test specimen can have significant effect on the measured values of the properties of the material. Test specimens may be molded directly or machined from samples which have been compression molded, injection molded, or extruded. Each processing method involves a range of variables, such as melt temperature, mold or die temperature, and shear rate, which influence the properties of the material. 

Woven reinforcement material constructed is by interlacing fibers, yarns, or filaments to form such fabric patterns as basket, plain, harness, satin, leno weaves, scrim, etc. These different weaving patterns are used to provide different processing and/or directional properties. There are filling threads that represent threads in the so-called machine direction warp threads represent those in the transverse direction or at 90° to the filling threads. 

MD, machine direction TD, transverse direction Property, measured at 50% RH, 23°C Tensile strength, max., MPa Non-std modulus, MPa Elongation to break, %... 

Directionally reinforced molding compound (XMC) contains continuous reinforcements (up to 70 wt%) arranged in an X pattern with some chopped fibers and the final product has strong directional properties in the continuous fiber direction. XMC can be made on almost any filament winding machine as shown in Fig. 3.11. 

Fluoropolymers produce a transparent film fabricated in thin gauges ranging typically from 0.012 mm to 0.040 mm thickness. The film is produced by stretching an extruded sheet or tube in two orthogonal directions—the machine direction and the transverse direction. Stretching is carried out at a temperature below the melting point of the polymer and results in a partial orientation of polymer molecules in the direction of stretch. In principle, biaxially oriented film is isotropic—its properties are the same in both the machine and transverse directions. In practice, film produced by the tenter process tends to be more highly oriented in the machine direction whereas the blown process produces a film that is more nearly isotropic. 

Biaxial Orientation. Many polymer films require orientation to achieve commercially acceptable performance (10). Orientation may be uniaxial (generally in the machine direction [MD]) or biaxial where the web is stretched or oriented in the two perpendicular planar axes. The biaxial orientation may be balanced or unbalanced depending on use, but most preferably is balanced. Further, this balance of properties may relate particularly to tensile properties, tear properties, optical birefringence, thermal shrinkage, or a combination of properties. A balanced film should be anisotropic, although this is difficult to achieve across the web of a flat oriented film. 

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