## 1 Introduction  
The Reunion des Musees Nationaux-Grand Palais, who has been producing resin reproductions of artworks, aimed to investigate the integrity of the composite materials used to replace original sculptures in historical monuments [1]. These composite materials, mostly known as artificial or engineered stones, consist of a polymer matrix (polyester or epoxy [2]) incorporating rock powder (e.g., marble or slate [3]). These kinds of materialsare experimentally well-known for their good mechanical performance and homogeneity, although few scientific studies on their characteristics have been published in the literature [4; 5; 6; 7; 8; 9; 10]. In order to address mechanical behavior issues, a complete set of properties and characterization of general materials is needed. [PERSON] et al. designed an experiment using classical mechanical tests to expose the effects of both the resin and marble powder percentage on the material properties, as well as to identify a possible correlation between these factors on the performance of marble composite structures [4]. [PERSON] et al. compared three types of engineered stones against limestone and granite in their durability against temperature, assessing thermal ageing and thermal shock effects on each material's flexural strength and Young's modulus [5]. In addition, [PERSON] et al. demonstrated through classical mechanical characterization that plasma treatment induces improvements in all the mechanical properties of marble composite structures [7]. Moreover, in order to propose artificial marble as an alternative material in industrial settings (such as sustainable green composite materials for construction applications [9]), [PERSON] et al. studied the impact of microstructure and showed that the regular interphase resin residues improved mechanical properties [8]. Other techniques, such as Fourier transform infrared spectroscopy, scanning electron microscopy and X-ray diffraction, respectively allow us to study the chemistry of composite formation, reveal the surface features and ascertain the presence of hard phases [10]. Nevertheless, a few studies have analyzed these kinds of materials using ultrasonic methods, such as [6], who used longitudinal and shear ultrasonic wave velocities in order to calculate the values of the acoustic impedance, Poisson's ratio and elastic constants of epoxy resin/marble powder composites. Indeed, ultrasonic techniques [11] are commonly used in the nondestructive testing of materials because they can be employed both in laboratory and in situ conditions to determine and monitor physical and mechanical properties of materials such as wood [12; 13], metals [14; 15], polymer/composites [16; 17; 18] and rocks [19; 20]. Several configurations and instrumentations have been developed for ultrasonic testing, such as contact transducers (bulk, shear and wedge), immersion techniques and laser vibrometry [11]. In the last case, scanning laser Doppler vibrometry is a widely adopted method to measure the out-of-plane vibrational displacements related to the 1D wave propagation of materials for detecting defects or estimating viscoelastic parameters [15]. Recent technological developments have led to performant 3D scanning laser Doppler vibrometers, which give access to both out-of-plane and in-plane vibrational velocity components, which combined with inverse problem approaches, allow for the identification of orthotropic elastic stiffness using 3D guided wavefield data [21]. Likewise, numerical methods, including machine-learning methods (such as clustering of multivariate data series), are also actively used in applications related to material property characterization by means of elastic guided wave propagation phenomena [22]. This study is hereby presented to estimate the mechanical properties of composite materials used in artwork reproduction by means of laser vibrometry. Different polymer/filler composite samples were studied using ultrasonic waves.