## 1 Introduction  
High strength, high modulus, low elongation, and lightweight synthetic fibers such as high modulus polyethylene (HMPE) and aramid (such as Kevlar) have become promising materials to produce ropes for engineering applications. Recently, applications of these types of synthetic fiber ropes have emerged in robotics, such as tendon-driven [1; 2; 3], active endoscope [4], and artificial muscle [5]. The mechanical properties of synthetic fiber ropes are greatly affected by the construction geometry of the rope twisting or braiding method [6; 7]. Braided synthetic fiber ropes are favored because they are torque balanced and provide high stiffness. Braided synthetic fiber ropes are assembled by interlacing yarns or strands over and under each other, half in the clockwise direction and half in the counterclockwise direction. In recent years, several researchers have studied the mechanical properties of braided composite materials composed of synthetic fibers and epoxy [8; 9; 10; 11; 12; 13]. [PERSON] et al. [8] predicted the longitudinal elastic modulus of braided Kevlar 49/epoxy resin tube by examining the micro-structure \"unit cell\" in the tube, based on classical laminate (plate) theory (CLT/CLPT). The authors also considered the path of undulating strands by assuming a sinusoidal function and performed an experiment to compare with the analytical results from CLT. [PERSON] and [PERSON] [9] estimated the longitudinal elastic modulus of braided tubular composites by considering the unit cell as a curved geometry. They found that the longitudinal elastic modulus decreased when the braided angle of the composite tube increased. In addition, they also considered the unit cell as a plate and compared results from both cases with experimental data. [PERSON] et al. [PERSON] et al. (2010) investigated the effect of changes in the radius of the tube and the angle of the strand during tensile loading on the longitudinal elastic modulus by examining three different unit cells on Kevlar 49/epoxy braided tube. The change in the radius and angle were measured based on 3D digital image correlation (DIC). However, there was a large standard deviation in the radius measurements, possibly due to the shallow focal depth of images and uneven sample surfaces. [PERSON] and [PERSON] [PERSON] and [PERSON] (2010) developed an analytical model for tubular braided composites in which they studied different braided patterns of tubular composites. They applied a volume average stiffness method to predict the elastic modulus of the tubular composites and compared the results with existing models and experiments in the literature. [PERSON] et al. [PERSON] et al. (2011) predicted the longitudinal and shear modulus of 2D tubular braided composites with both rigid epoxy and elastomeric polyurethane resin matrices. They obtained good agreement between the model and experimental data. Recently, [PERSON] and [PERSON] and [PERSON] (2012) developed a software based on a volume average stiffness method to estimate elastic modulus of tubular braided composite. The elastic modulus of braided tubular composites consisting of Kevlar 49/epoxy has been widely predicted based on classical laminate theory (CLT) and a volume average method which considers only a unit cell in the structure and compares the experimental data of tubular braided composite. Previous research [PERSON] et al. (2010); [PERSON] et al. (2010); [PERSON] et al. (2010); [PERSON] et al. (2010); [PERSON] et al. (2010); [PERSON] et al. (2010) determined the modulus of tubular braided composites made of Kevlar 49 and matrix using conventional unit (MPa) and based on cross-sectional area. As noted by [PERSON] et al. [PERSON] et al. (2010), inaccuracy of radius measurement could occur, affecting the elasticity modulus of the braided rope. Moreover, no research has used CLT for synthetic fiber rope without a matrix for the estimation of the longitudinal elastic modulus.