###### Abstract
Monofunctional electrical and tensile properties of injection-molded multiwalled carbon nanotubes (MWCNT) reinforced polyamide 66 hybrid composites were investigated in which the chopped carbon fiber of different lengths and the MWCNTs were added to nylon 6,6 [10]. The monofunctional electrical conductivity test was completed on the same test coupons before the tensile testing [10]. While the test results depicted the excellent electrical properties due to the addition of fillers with a limitation in mechanical properties improvement, this study did not address the multifunctional coupled flexural-eletrical properties of the 3D printed continuous carbon fiber composites [10]. Multi-functional composites were manufactured, which involved introducing carbon nanotubes (CNTs) into carbon fiber wet-laid composites as functional nano-fillers for improved electrical, thermal, and mechanical performance [11]. Polyamide 6 (PA6) short fiber was introduced into carbon fiber and CNT mixture to improve bonding between CNTs and the carbon fiber [11]. While the addition of CNT to the carbon fiber nonwoven and the electrical conductivity were observed to be directly proportional to each other and a slight decrease in tensile strength, this paper did not address the coupled multifunctional flexural-electrical properties of the 3D printed continuous carbon fiber composites [11]. There are no current solutions to certify multifunctional carbon fiber composite structures for an aircraft. Existing manufacturing techniques from the unintentional composites material system to support the coupled multifunctional carbon fiber composites have not been investigated. The maturation of existing manufacturing techniques for implementation into the aircraft and its certification tests are needed. Due to the infancy of the existing AM techniques and processes, those technologies are not used in aerospace applications. The multifunctional carbon fiber composites are not implemented on a large commercial scale in aircraft, unmanned aircraft systems (UAS), and spacecraft. Limited studies are available in the literature on the use of the AM technologies and the multifunctional evaluations of multifunctional composites. The existing regulatory frameworks, policies, guidance, and industry consensus standards pertain to monofunctional material systems. An experimental investigation was performed for the assessment of electro-flexure response of the conductive natural fiber hybrid composites that were made up of laminates of jute and flax fibers [12]. Test coupons were tested to undergo flexural loading for the electrical and bending responses [12]. Four-point circumferential probe method was utilized for measuring electrical response exerted by flexural loading of the test coupons [12]. Varying carbon fiber lengths and carbon fiber densities were used for comparative assessment of flexural performance, and deformation detection revealed that an increase of carbon fibers decreased the flexural strength and increased the flexural strain at break for all composites of carbon fiber length of 150 \(\upmu\)m [12]. While the concurrent electro-flexure response was conducted on the traditionally manufactured solid laminate composites, the coupled multifunctional properties of additively manufactured multifunctional composites are not addressed to date [12]. Certification requirements for composite aircraft are separate for assessing the monofunctional properties (e.g., electrical, thermal, structural, etc.). Those monofunctional properties are known as unifunctional material system properties. Three-point bend testing was conducted on traditionally fabricated multifunctional carbon nanotubes, enhanced structural composites for improved toughness, and damage monitoring. Reinforcement effects of the multifunctional carbon nanotubes enhanced structural composites were structurally investigated via tensile and three-point bend testing, which led to significant improvement of stress and strain at failure [13].