# The Key Role of Laser Ultrasonics in the Context of Sustainable Production in an I 4.0 Value Chain
###### Abstract  
The advancement of laser ultrasonics has increased rapidly in recent years, providing applications for materials characterization as well as for industrial utilization, as a quality control device. The wide-ranging capabilities for high-temperature in-situ analysis of a variety of microstructural characteristics offers a multitude of possibilities for usage in R&D. To date, this is the only known method that has been successfully deployed for in-situ materials characterization, as well as in the harsh environment of the metalworking industry. Combined with the enablers, introduced by the fourth industrial revolution, and the conjunction of a laser ultrasonic system with a Smart Production Lab, it has great potential to contribute to lower rejection rates, better recyclability, and consequently to a more sustainable production. In this review, the potential for systemic sustainability is explained throughout a part of the value chain, in the context of Industry 4.0. In addition, the integration of the methodology into a miniaturized Smart Production Lab is demonstrated, with the intention of incorporating it as a substantial part of the creation of a digital twin. Such a lab is designed to serve as an interface between laboratory and industry, in order to reveal the possibilities of digital transformation, Industry 4.0, and the application of highly flexible systems such as the laser-ultrasonic system for companies. laser ultrasonics; in-situ material testing; quality control; I 4.0; real-time monitoring; Smart Production Lab +
Footnote †: journal: Applied Sciences  
forward them to a superordinate system. Additional in-line Quality Inspection Systems, investigating the component for deviations (e.g., geometry, cracks, voids, etc.) between or during the processing steps would allow the defects to be corrected in further process steps. A significant innovation therefore, would be the implementation of a Digital Model (DM), a Digital Shadow (DS), or even a Digital Twin (DT) [13; 14]. The latter one is able to detect deviations in real time, on the basis of simultaneously performed calculations, usually with the usage of finite element analysis (FEA), proposing appropriate measures for subsequent process routes, to eliminate the error or to remove the defective component [15]. In the aerospace industry, in addition to non-destructive testing of any safety-relevant component, a simulation of the manufacturing process with an integrated microstructure model is often required in order to predict the resulting microstructure prevailing in a component in advance, in order to be able to estimate mechanical properties [16; 17; 18; 19]. For the purpose of creating a valid microstructure model of a material, an extensive amount of material parameters is required to be able to describe the essential microstructural changes during thermal and thermomechanical treatments [20; 21; 22]. Traditionally, experiments are carried out in a thermomechanical treatment simulator (TMTS) to determine the material parameters for static, dynamic, and metadynamic recrystallization (RX) and recovery phenomena, as well as for primary and secondary grain growth at different temperatures, strains and strain rates for different time steps. The analysis is subsequently carried out by an ex-situ analysis of the microstructural evolution i.e., by optical evaluation methods [23; 24; 25]. Accordingly, the generation of a set of material parameters for a valid microstructure model takes an average of three years. As this is the most common development scenario, it is abundantly evident that it is time-, material-, and resource-intensive. Obviously, this is contrary to the actual development plan, both governmental and self-imposed by the industry, which is to emphasize sustainability and responsible CO\({}_{2}\)-saving production [26; 27; 28]. Therefore, alternative methods to detect microstructural changes in real-time, in-situ, and also at high temperatures, under the respective manufacturing conditions, are intensively investigated.