## 1 Introduction  
Composite materials have revolutionized the way vehicles, construction parts, and consumer goods are designed. They are replacing more and more traditional materials, like steel, wood, and aluminum. Composite materials are utilized successfully in dynamically loaded structures like satellites, military aircraft, expensive cars, boats, sports, and many consumer goods. The success of composites is attributed to their mechanical properties, including a high stiffness-to-weight ratio, high strength-to-weight ratio, and good fatigue resistance. Furthermore, they offer design flexibility, allowing for tailoring of mechanical properties and the creation of new shapes. However, composites also exhibit complex mechanical behavior, posing challenges for design and testing, as discussed by [PERSON] (1986). The elastic material properties of composite components are crucial in determining how these parts deform under static and dynamic loads. Their vibration and acoustic behavior are influenced by the elastic and damping properties. Temperature variations modify the elastic and damping properties of these composite parts. This is especially relevant for modern recyclable thermoplastic composites, studied by, e.g., [PERSON] et al. [PERSON] et al. (2010). Change of resonance frequencies, mode shapes, and the transient response of the structure can affect the functional behavior of vehicles, construction parts, and consumer goods. Understanding the temperature-dependent elastic and damping properties is essential for reliable composite structure design. Orthotropic materials have elastic properties that are symmetrical with respect to a Cartesian coordinate system. Most composites exhibit orthotropic behavior due to stiffer fiber reinforcement compared to the matrix material, which is particularly evident in unidirectionally reinforced layers. Four engineering constants are required to describe the orthotropic in-plane stiffness behavior of thin sheets. In a plane with two perpendicular orthotropic material directions 1 and 2 (see, e.g., Figure 1), the relationship between stresses and strains is given by the stiffness matrix C:  
\[\sigma_{1}^{*}=\mathrm{C}_{1}^{*}\mathrm{\hat{\mathrm{\mathrm{\mathrm{\mathrm{ \mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{\mathrm{ \mathrm{\mathrm  
modulus test is necessary, with the added complication of strain and displacements measurements at elevated temperatures. Dynamic testing methods are indirect methods. The impulse excitation technique (IET) (e.g., ASTM C 1259-98 [9]), experimental modal analysis (EMA) and operational modal analysis (OMA) (e.g., He and [PERSON] [10]), and dynamic measurement analysis (DMA) (e.g., Schalnak [11]) are the most used dynamic methods. Dynamic testing methods are more difficult to understand intuitively but are easier to execute and provide more accurate engineering constants at low stress and strain amplitudes (see, e.g., [PERSON] and Morell [8]). DMA uses forced excitation to measure the elastic and damping properties of composite lamina within a limited frequency range. DMA allows the identification of temperature and frequency dependent elastic and damping properties. DMA is conducted using small beam samples. Peel stresses at the free boundaries, induced by machining the composite beam specimens, can therefore have considerable influence on the test results. EMA, OMA, and IET address this issue with larger test samples. IET is easy to perform and requires less complex equipment than EMA or OMA. Simply tapping the test sample causes a vibration response with low amplitude. This vibration response can be measured with a sensor and is called \"The impulse response function\" (IRF). The IRF is composed of the decaying excited modes of vibration of the test sample (for visualization, see also Figure 2). Resonance frequencies and damping ratios can be extracted from the measured IRF (see, e.g., Heritage [12]).