*4.2.3.1. By 4-step braiding method*

In the 4-step braiding method, each machine cycle involves four different motions in order to intertwine the longitudinal yarns that are positioned in row and column directions along the cross-section. Braider yarns, on the other hand, are intertwined by braider carriers that move in predetermined paths within the matrix so as to form the fabric. Florentine developed a 3D braided preform that has a layered structure [69]. Yarns are intertwined with each other according to a certain path and are biased such that the width of the fabric is at an angle between 10˚and 70˚. The process involves rectangular layout of individual row/column arrangements in the machine bed. Each individual row has a braider carrier in order to carry out four different cartesian motions (Figure 30).

**Figure 30.** Schematic views of (a) 3D braiding machine and (b) yarn carrier path [69].

Brown developed a 3D circular braided fabric having one set of fiber sets [90]. In order to form the fabric structure, these fiber sets are intertwined with each other. The machine has concentric rings that are attached to a joint axis. Braid carriers are circumferentially mounted to the inside diameter of the ring. The ring is adjusted depending upon the thickness of the fabric. The rings rotate one braid carrier distance depending on a pre-determined path. Then, the braid carriers move in the axial direction. After that, the cycles are repeated in the above sequence. The fabric has ±bias yarn orientation through the thickness of the cylinder wall and cylinder surface at the helical path, as shown in Figure 31.

**Figure 31.** (a) Schematic views of 3D circular braiding machine [90] (b) yarn carrier path [69].
