## 1 Introduction  
Woven carbon fiber reinforced polymer (CFRP) has become attractive to be used for critical load-bearing structures in airplanes, trains, ships, and cars. The woven pattern can improve structural stability since the loads on wrap and weft directions can be held by fibers simultaneously in one lamina [1]. As a consequence, it can increase the damage tolerance of the CFRP structure. Compared to unidirectional CFRP, the manufacturing process of woven CFRP are relatively easy and fast [2]. One of the main challenges to use woven CFRP is the difficulty in detecting structural damages due to intricate patterns and anisotropic properties [3]. The damages need to be detected as early as possible to avoid structural failures during operation. The development of structural health monitoring (SHM) technology for woven CFRP that can detect initial damages needs to be conducted. SHM aims to create a time domain-based structural failure monitoring system that can be used as the basis for establishing a diagnosis or prognosis [4]. SHM has been developed for unidirectional CFRP in the last few decades. The most popular SHM technology uses the piezoresistive behavior of the CFRP to detect the damages [5]. The behavior enables CFRP to be like a strain gauge in which its electrical resistance changes when mechanical strain increases due to exposure of the load. By measuring the electrical resistance alteration, the strain condition in the CFRP can be investigated. Furthermore, the level and type of damages to the CFRP may be determined by analyzing the recorded electrical resistance [6; 7]. Some researchers report that piezoresistive behavior can be measured by a four-wire method [8; 9]. [PERSON] and [PERSON] stated that unidirectional CFRP has positive piezoresistivity in which electrical resistance increases proportionally with the increased mechanical strain [10]. This result is also supported by the findings reported by [PERSON] et al. [11] and [PERSON] et al. [12]. However, different results were obtained by [PERSON] et al. [9; 13] and [PERSON] et al. [14]. By using two probe-wires and four probe-wires methods, they reported that the CFRP had a negative piezoresistivity. Both argued that the positive piezoresistivity that was reported by many researches was previously caused by increased electrical resistance in electrodes, not from the changes in electric resistance in CFRP. [PERSON] and [PERSON] conducted tests with techniques similar to [PERSON] et al. [9; 13] and [PERSON] et al. [14] and produced negative piezoresistivity [8][PERSON] However, they argued that the negative piezoresistivity occurred due to poor surface treatment prior to the electrode [PERSON]. For fine surface treatment, the CFRP has positive piezoresistivity with gauge factor in a range between 2 to 4[PERSON] The latest study was conducted by [PERSON] et al. to find out the effect of contact resistance between CFRP and electrodes to the piezoresistive behavior [15]. They also reported that the roughness of the composite surface attached to the electrodes affects the test results. Thus, these factors need to be considered in testing and application. Furthermore, the use of piezoresistivity can be extended to the development of self-healing technologies, namely the ability of the CFRP to repair the damage to their structures. The concept of self-healing using piezoresistivity has been revealed by [PERSON] et al. by utilizing the Diels-Alder reaction [16; 17]. Unlike like piezoresistive behavior in the unidirectional CFRP that has been investigated intensively, the behavior in woven CFRP still needs to be further clarified. Indeed, the behavior is strongly influenced by various factors and parameters, including the fiber arrangement. The woven pattern might cause nonlinear piezoresistive behavior in line with its mechanical behavior [18; 19]. The relationship between these parameters needs to be revealed for the future implementation and development of SHM technology. In this work, the piezoresistive behavior in plain-woven CFRP is investigated.