# Monitoring the Joint Area of Composite Membrane Materials
## 2 Materials and Methods
### Methods
#### 2.2.3 Embroidery  
As previously mentioned, sensor layouts should be tested under conditions that are as realistic as possible. Hence, the integration of the sensors into the textile carrier structure of the membrane would provide ideal conditions. However, the corresponding manufacturing processes (weaving, coating, etc.) are too inflexible for functional or design tests such as those undertaken within the framework of the current study. Therefore, potential sensor arrangements were embroidered on the surface of commercially available textile membranes. It is assumed that sensor functionality is not negatively affected if the sensor is more strongly integrated into the membrane (sensor is located on the carrier fabric, i.e., under the coating being part of the carrier fabric), whereby enhanced connection to the load-bearing components of the composite is achieved. Embroidery is a technical process closely related to sewing. It is suitable for applying solids to a textile surface. In addition to yarns, this can include beads or sequins in clothing technology. In technical embroidery, electronic components can be attached to a textile or embroidered directly onto a textile surface in the form of conductive yarns. Thus, the textile surface, in this context called embroidery ground, is stitched through with a needle, which guides the embroidery thread through the textile. This aims at achieving a form- and force-fit fixation of the embroidery thread on the textile surface. In manual embroidery, a single thread is guided alternately along the upper and lower side of the embroidery ground to ensure a proper connection; in contrast, in the case of machine embroidery, the double lockstitch is used (see Figure 2). In addition to the needle thread system, a second thread system is used on the opposite side of the embroidery base; this is termed bobbin thread. After stitching through the embroidery ground, needle thread and bobbin thread are crossed, whereby the needle thread is subsequently pulled back to \begin{table}
\begin{tabular}{c c} \hline
**Welding Parameter** & **Value** \\ \hline Welding time [s] & 3 \\ Welding pressure [bar] & 3 \\ Welding power [\% of max *] & 38 \\ Cooling time [s] & 3 \\ Cooling pressure [bar] & 3 \\ \hline \end{tabular} \({}^{*}\)5 kW.  
\end{table} 
Table 2: Applied welding parameters. Figure 1: Schematic of high-frequency (HF) welding. the top again. The two thread systems interlock so that a connection to the embroidery ground is established [22]. If a yarn cannot be used as one of the two embroidery threads, it serves as additional thread on the surface of the embroidery ground. In this case, it is fixed on the surface by means of the embroidery thread systems. As a result, almost any type of thread-like structure, for example cables, can be fixed to a textile surface. Since the additional thread is not part of the actual lockstitch seam, its connection to the surface is less load-bearing compared to directly embroidered threads. The tailored fiber placement (TFP) technology is based on the principle of embroidery including an additional yarn. The greatest advantage of embroidery, in contrast to other textile manufacturing processes, is the almost unlimited freedom of geometry offered in terms of embroidery patterns. This means that even highly complex structures can be created in a short time requiring little effort. All embroidery experiments described below were carried out on a ZSK SGY 0200-650D embroidery machine, equipped with two W-embroidery heads. Textile membrane needles of type Groz-Beckert 34 D/16 \(\times\) 2 TRI/287 D 110 that were suited to the embroidery ground were used. These particular needles are equipped with a special cutting tip, which enables the piercing of relatively firm and thick materials, such as leather or technical membranes. In order to achieve the best possible connection between sensor yarns and membrane, the sensor yarns should be integrated as one of the two embroidery threads rather than as additional thread.