*4.4.1. Two-dimensional knitted fabric*

The 2D knitted fabric is produced by mainly two methods, namely, weft knitting and warp knitting. In weft knitting, latch needles are arranged circumferentially in the axial and radial direction of the machine bed. Yarn guiding bars feed the yarns to the axial latch needles mounted on the cylinder. Both axial and radial latch needles interloop the yarns to make 2D circular weft knitted fabric for various composite applications. Figure 40 shows the interloop‐ ing action, 2D glass weft knitted fabric and cylinder section of a 2D circular weft knitting machine [49].

**Figure 40.** (a) Schematic views of 2D weft knitted fabric during formation (b) 2D weft knitted glass fabric (c) 2D weft knitting machine [49, 79].

Warp knitting consists of a yarn feeding unit, multiple yarn guiding bars, multiple axial latch needles, a sinker and a fabric take-up unit. The guide bars are located at the front of the machine. The sinker bar holds the fabric by moving forward while the needle bar starts to rise from knocks-over (holding down action). As the needle bar rises to its full height, the old overlaps open the latches and slip down onto the stems. Then, the sinker bar withdraws in order to enable the overlapping of guide bars (clearing action). The guide bars move to the back of the machine and then make a shogging for the overlap (overlap action). Then the guide bars swing to the front and the yarns wrap into the needle hooks (return swing action). The needle bar moves down in order that the old overlaps contact and close the latches, trapping the new overlaps inside. The sinker bar now starts to move forward (latch closing action). As the needle bar continues to descend, its head passes below the surface of the trick-plate, drawing the new overlap through the old overlap, and as the sinkers advance over the trickplate, the underlap shogging of the guide bar is commenced (knocking-over and underlap action). These knitting actions and the machine are shown in Figure 41 [49, 106].

#### *4.4.2. Three-dimensional knitted fabric*

#### *4.4.2.1. By weft knitting method*

The 3D weft knitting method was developed by Offermann et al. [108]. The weft knitting machine consists of warp and weft feeding, warp yarn guide track, weft yarn carrier, stitch yarn carrier, yarn feeding unit and fabric take-up unit as shown in Figure 42. Two layers of

**Figure 41.** (a) Schematic views of the warp knitting action to form the 2D warp knitted fabric structure using the latch (b) Actual 2D warp knitting machine [36, 49, 107].

warp yarns are laid by warp yarn guide track. Two layers of weft yarns are laid over the warp layers by weft yarn carriers. The stitching yarn locks the warp and weft yarn sets using multiple latch needles in which stitched yarns were structured as weft loops. Simple as well as complex sectional knitted preforms were fabricated by the special take-up device. The critical process parameters are warp and weft densities, stitching density, yarn feeding, and fabric take-up ratios [51, 109].

**Figure 42.** (a) Schematic views of 3D weft knitting methods (b) 3D knitting machine; and (c) weft yarn carrier during knitting [108, 109].
