## 1 Introduction  
As a result of their superiority in stiffness, impact and corrosion resistivities, as well as being lightweight, reinforced thermoplastic composite materials gain profound advantages over metallic alloys especially in aerospace industries. Unlike their metallic counterparts, reinforced composite materials can be tailored to meet a desired structural performance taking fiber orientation or ply stacking sequences as design variables. [PERSON] et al. [1] discussed this possibility with the least-weight design objective constrained to mechanical, geometrical, and technological requirements. Nevertheless, these privileges come with defect-free forming challenges. Regardless of the advancements in forming technology, manufacturing defect-free composite structures is not yet realized, and hence, the advantages could not be fully exercised. [PERSON] et al. [2] discussed the influence of defects on mechanical performance. Based on their virtual testing framework, defects such as fiber misalignment significantly influence the mechanical response of the composite structure. Various physical experiments and computer simulations have been done over the years [3; 4; 5; 6], though the objective of suppressing forming defects still remains unachieved. [PERSON] et al. [7] studied the influence of micro-voids on the mechanical properties of plain weave carbon/epoxy composite. They reported that the stiffness of the defective composite laminate reduces compared to its theoretical value. [PERSON] et al. [8] studied the limitations and challenges of manufacturing impact resistant composite structures. To enhance the impact resistance of composite structures, interleaf layers are inserted between adjacent composite plies. This induces forming defects in composite structures. A comprehensive review on the manufacturing defects and their effects on the mechanical performance of fiber reinforced composite materials was given by [PERSON] et al. [9]. In their report, it was indicated that, despite many years of research on the formation and effects of defects in composite structures, no mature predictive tools are realized yet. As long as manufacturing a completely defect-free composite structure is unlikely, to prevent a catastrophic in-service failure of this structure, a post-manufacturing defect detection mechanism has to be developed. In this realm, detection mechanisms have been developed over the years. A case study on wrinkle detection mechanisms reported by [PERSON] et al. [10] depicted both the challenges and essentiality of commonly used detection mechanisms. A feasibility study on a damage detecting fabric sensor for draped composite structures was presented by [PERSON] et al. [11]. [PERSON] et al. [12] developed an analytical model and analyzed the influence of out-of-plane wrinkle defects on the mechanical properties of fiber reinforced composite laminates. Their report showed that out-of-plane wrinkle defects drastically affect the shear moduli and Poisson's ratios of composite laminates. Fiber reinforced composite structures can be manufactured through different methods that range from tedious hand-layup to fast and automated fiber placing (AFP) technology. Even with advanced manufacturing technology like AFP, forming defects exist [13; 14]. Another commonly known forming technique is press forming, which is used for fast composite structure production especially for aircraft components. Sikken stiffener type, landing gear, door, and rear pressure bulkhead aircraft components are some examples of components manufactured using press forming. [PERSON] et al. [15], using their hot-stamping system, reported the influence of forming temperature on the incursion of defects. During press forming, adjacent plies of composite laminate have to slip over each other to conform to a mold geometry. Resistance to this slippage results in fiber misalignment, buckling, and wrinkling, thereby degrading the advantages of composite materials.