# Optical Analysis of the Impact Transmission in Steel Sheet Arrays with Bolted-Type Points
## 1 Introduction  
Inspection techniques by means of instrumentation are limited when mapping a complete region as it could be expensive; however, optical metrology is a non-invasive inspection way to obtain different physical parameters. They can withstand local- and whole-field measures with the same experimental set-up [1]. Digital image correlation (DIC) is one of the optical techniques that has applications in different fields. It is a computerized procedure that couples images obtained through a camera and the mathematical outset of correlating them to obtain a physical quantitative variable. It is an outstanding system since [PERSON] and [PERSON] exhibited a method based on the inverse Fourier transform of the phase difference between two images [2]. DIC has served for mechanical measurements, such as for evaluating the heterogeneous strain field in a multiaxial testing machine [3]. By means of a Vic-2D system, the authors achieved two-dimensional strain maps of an entire planar specimen surface [4]. Laser speckles were used to evaluate the displacement field, validated on virtual and real tests [5]. Displacement and strain fields on a large area were performed by means of 3D DIC. The impacts were performed with a gelatin cylinder of 1.5 kg [6]. In addition, in-plane displacement was applied using laser speckles to understand the external force-pulse response. Impacts were subjected to a brick coupled to a table. In this research, a sum of harmonic and damped waves was used to fit and compare with the experimental result [7]. Then, the authors normalized the action-reaction impact by means of a pendulum. The collision response was modeled with an equivalent damped mass-spring system [8]. Finally, an approximation to a modeled wing was handled, in which impacts were subjected to a rigid body, but reactions were measured in an embedded bar. Results were modeled with a damped oscillator with linear and harmonic excitation [9]. In the structural field, DIC has a wide variety of functions as it has evolved to offer high quality, definition, low costs, and easy usability, and it can be implemented with different time and metric scales [10]. This technique is worth evaluating the structural health by providing practical approaches that can be used to identify damage before inservice failures [11]. Talking in the same direction, two reviews about utilizing DIC as atechnique to monitor structural health were written, in which the authors declare that it is a reliable and effective technique to measure whole-field strain in any type of material, turning into a really valuable technique to control the structural health [12; 13]. This technique has an approach to structural displacement measurement. It was evaluated using a charge-coupled-device camera that offers the skill of measuring a large number of points [14]. Other applications were developed by calculating the strain in friction stir-weld samples, in which samples were submitted to uniaxial tensile loads, and the strain evaluation by means of sub-pixel DIC was performed [15]. Recent advances in DIC set the importance of strain measurements within the bond line of an adhesive [16]; to evaluate acceleration, displacements, strain, and strain rate during impact tests [17], to determine the damage and deformation characteristics of rock-like samples [18]; to monitor the Great Belt Bridge [19]; to measure local displacement in hybrid joints [20]; to characterize the structural dynamics of a composite material [21]; and to determine the stress-strain properties of wood samples subjected to tensile tests [22]. It is necessary to mention a crucial part of a structure: the structural joints. Rivets are often used in the fuselage of airplanes, screws and nuts are spent in mechanical and electrical mechanisms, and welding is seen in electrical plates and structural forges, to mention some of the most common ones.