## 2 DIC Methodology Evolution--The History Review
### 2D-DIC  
_From Early Research Till Today_  
The next stage of optical method development was to the formulation of the main principles for digitally recording images containing measurement data. In addition, algorithms for analyzing digital images and extracting data with high precision were proposed [11].  
Among authors who worked on computer-based image processing techniques were [PERSON] and [PERSON] in 1982 [23], who proposed to use to ultrasonic waves and their reflection before and after loading, thus obtaining full-field digital \"images\". In addition, the idea of \"matching process\" was presented, using continuum mechanics concepts to indicate deformations in small areas.  
An important step towards developing the optical method, known today as 2D-digital image correlation (2D-DIC) was made by [PERSON] et al. in 1983 [24]. They developed main numerical equations and experimentally confirmed the feasibility to use this technique in engineering issues. [PERSON] et al. in later work (1986 [25]) also proposed using gradient search methods in order to increase the accuracy of subset-matching. Among the authors who studied the possibility of DIC for various engineering issues are [PERSON] et al. [26] and [PERSON] et al. [27]. Thus, it was shown that the correlation technique provides reliable accuracy for planar translations, rotations and deformations of solid bodies [26; 27]. During the 1980s, scientific interest in DIC methodology rapidly increased, and theoretical approaches and procedures were validated, updated and modified. [PERSON] et al. [28] in 1989 combined X-ray radiography and the DIC-method in order to measure internal deformation in composite material and study transverse strain fields [11]. The 1990s was the decade of scientific research on the possibility to measure surface deformations in planar components. For example, cracking processes were studied by [PERSON] et al. [29] in term of stress intensity factor determination. In addition, the use of image correlation enables tracking the local crack tip plastic zone, caused by \"three-dimensional effects\" [30].  
Further development of the method was conducted by [PERSON] [31] and [PERSON] et al. [32], who researched the stress-strain state with the use of DIC at high temperature. In addition, according to [11], this period could be characterized by increased interest in DIC to study fracture performance in various materials: metals [33; 34; 35], plastics [36; 37], wood [38] and ceramics [39]. Among the later works are articles by [PERSON] and [PERSON] [40; 41], where the concrete was studied and works [42; 43], which provided detailed investigations of composites.  
Since 2000, the DIC technique has extended to a wide range of engineering issues and tasks. Thus, a great number of research works were conducted, dedicated to improving the matching process accuracy during image recognition. For example, higher order spline interpolation functions were proposed by [PERSON] et al. in [44]. The same assumptions and propositions were made by [PERSON] and [PERSON] [45], as well as by [PERSON] and [PERSON] [46]. Authors in [45; 46] noted the applicability of quadratic shape functions for study of non-uniform strain fields [11]. In addition, the investigation of [PERSON] et al. [47; 48] focused on development of \"extended 2D-DIC\", the methodology combining the analytical FEM model and high-precision results, obtained with the use of image correlation Simultaneously, another area of scientific interest of this period included studies of mechanical properties of materials: elastic [49; 50] and hyperelastic properties [51], as well as the properties on a microscale [52].