## 1 Introduction
Since IET is non-destructive, the method is suitable for testing at different temperatures (see, e.g., Brebels [13]). IET was selected for the current study because of these advantages. Standard IET uses analytical and empirical formulas to derive the elastic properties from measured vibration quantities. Unfortunately, there are no formulas available for freely suspended orthotropic plates. In 1986, [PERSON] [14] demonstrated the possibility of replacing standard IET formulas with special-purpose finite element (FE) models. He used a mixed numerical experimental technique (MNET) for the identification of the engineering constants. The engineering constants in the numerical model were iteratively tuned in such a way that computed resonance frequencies match the measured values. The resulting identification method, called the Resonalyer procedure, can simultaneously identify the four engineering constants of an orthotropic material from measured resonance frequencies of a test plate by IET. Validation of the results obtained by the Resonalyer procedure was presented in several publications [15; 16; 17]. [PERSON] [18] presented an extension of the Resonalyer procedure including the identification of the damping part of complex orthotropic engineering constants. During previous decades, various authors have presented related MNET approaches for the identification of orthotropic elastic constants [19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36]. Most authors have agreed that testing freely suspended samples provides better agreement with the numerical model than other types of boundary conditions. Clamping or simply supporting samples influences the damping behavior especially. Some studies worked with a large series of resonance  
Figure 2: Decaying sinusoidal time domain signal after impulse excitation. frequencies on freely suspended test plates without special requirements for the aspect ratio of the test plates. However, these large series of frequencies on test plates with an arbitrary aspect ratio poses several problems. First, EMA or OMA are necessary to couple the measured frequencies with the correct sequence of computed resonance frequencies. Secondly, higher vibration modes are influenced more by transverse shear deformation, making thin plate theory increasingly inaccurate. Adapting a thick plate theory, on the other hand, requires knowledge of the transverse shear modulus, which is difficult to identify. The potential to run more complex numerical models on faster computers opened the way to develop more elaborate material identification methods. Among others, [PERSON] [21] and [PERSON] [23] used thick plate models in which the transverse shear modulus was estimated using an empirical formula. [PERSON] [25] presented mixed numerical experimental techniques for the identification of layered materials and laminates. EMA and OMA are the most applied methods in numerical experimental procedures for the identification of engineering constants. They both need the measurement of modal shapes associated with resonance frequencies. Non-contact EMA and EMO require laser scanners. This is difficult to execute with temperature control. The Resonalyser procedure needs only resonance frequencies and damping ratios, which can be solved with IET and allows easier temperature control. An early attempt to include the temperature dependency of the engineering constants of thin orthotropic plates was published by [PERSON] in 2010 [37]. He used IET with manual excitation of the test samples in a temperature-controlled cavity. The Resonalyser procedure was used for the identification of the elastic engineering constants. In a more recent paper, [PERSON] et al. [38] investigated the dynamic behavior of several carbon-fiber-epoxy laminated composite plates at different temperatures, using OMA. The modal contributions were selected as a function of the targeted frequency.