1945 ISSN 1229-9197 (print version) ISSN 1875-0052 (electronic version) Fibers and Polymers 2019, Vol.20, No.9, 1945-1957 Multilayered Glass Filament Yarn Surfaces as Sensor Yarn for In-situ Monitoring of Textile-reinforced Thermoplastic Composites Toty Onggar*, Eric Häntzsche, Rolf-Dieter Hund, and Chokri Cherif Institute of Textile Machinery and High Performance Material Technology, Technical University of Dresden, Dresden 01069, Germany (Received January 7, 2019; Revised February 21, 2019; Accepted April 25, 2019) Abstract: High-performance textile filament yarns, more precisely glass filament (GF) yarn, were used as base material for the development of sensor yarns (SY) because GFs offer high tensile strengths and moduli of elasticity in addition to beneficial decomposition temperatures and elongation. The aim of this work was the creation of a multifunctional sensor yarn (MFSY) based of GF. To achieve this aim, a homogeneous, completely coated first (1st) and second (2nd) silver (Ag) layer was built on the GF yarn surface by developing new technologies. The 1st Ag layer monitors damage within the thermoplastic composite globally, whereas the 2nd Ag layer monitors it locally and defects interface damage. Also, there was an insulation layer between two Ag layers, leading to a total of three layers built on the GF surface. Its surface morphology was determined by light and scanning electron microscopy (SEM) to assess Ag layer properties, such as structure, homogeneity, and cracking. For structural analysis, GFs were investigated using a Fourier transform infrared spectrometer (FTIR). The Ag layer thickness was determined after coating and metallization. Textile-physical tests of the GF in terms of tensile strength, elasticity modulus, elongation at break, yarn fineness and electric conductivity, were carried out before and after silvering. Keywords: Glass fiber, Coating, Wet-chemical silvering, Sensor yarn, Multiple layers Introduction There is a growing interest in the industrial use of fiber composites as an alternative to metallic components in vehicle, machine, and plant construction and for sports equipment or medical technology due to increasing demand for lightweight constructions. After preparing the duroplastic and thermoplastic composite, it should be checked for unwanted defects. These undesired defects occur in matrix systems, such as cavities, matrix-accessible regions, residual stress, waviness in the reinforcing structure, and inadequate impregnation of the reinforcing structure with the matrix, etc. While many of these so-called deficiencies are difficult to identify, their effects on the overall structural integrity of the device can be severe. Therefore, to minimize risk, maximize utilization, and successfully apply textile-reinforced composites, it is important to carefully study the critical changes in structural parameters to detect structural damages. Damage in a textile-reinforced composite typically appears as one of three main mechanisms: matrix cracks, delamination, and fracture of reinforcing fibers (Figure 1). It can occur singly, however usually there is a combination of two or three mechanisms, depending on the laminate layout, structural configuration, loading direction, component characteristics, and prevailing environmental conditions [1]. These types of damage are typically caused by continuous *Corresponding author: toty.onggar@tu-dresden.de DOI 10.1007/s12221-019-1237-2 Figure 1. (a) Traverse, (b) longitudinal matrix fracture, and (c) fracture propagation (in the case of poor fiber-matrix bonding) in unidirectional (UD) composite material [1].