# Characterization of Shear Strain on PDMS: Numerical and Experimental Approaches  
[PERSON]  
1 Instituto Politecnico de Braganca (IPB), 5300-253 Braganca, Portugal; [EMAIL_ADDRESS] (A.S.); [EMAIL_ADDRESS] (E.M.); [EMAIL_ADDRESS] (C.B.) 2 Centro Federal de Educacao Tecnologica Celso Suckow da Fonseca campus Angra dos Reis (CEFET/RJ), Angra dos Reis 23953-030, Rio de Janeiro, Brazil
[PERSON] et al. [11] carried out studies on flexible PDMS models to study the interaction between fluids (blood analog) and the structure of the intracranial aneurysm. From this study, it was found that the displacement value on the channel wall was very low, thus showing the need to determine values for shear and tensile tests for small deformations. Therefore, there is a need to study and characterize the mechanical behavior of PDMS under shear stress action and, in this sense, research work has been developed [16; 17] that refers to the implementation of tensile tests on simple lap joints associated with digital image correlation (DIC) as well as the determination of their shear modulus [18]. To characterize the mechanical behavior of a material when it is subject to a shear loading, it is usually required to perform shear tests. Typically, shear tests were implemented using specimens that are fixed in two holding grips and incremental displacement values are applied in one of the holding grips. Usually, the main objective of this test is to determine the shear strength, which corresponds to the maximum shear stress that the material can withstand before rupture. However, in the study of materials with high elasticity, as in the case of the hyperelastic materials, there is a great interest in understanding how its deformation occurs when subjected to shear forces. In this case, it is necessary to accompany the deformation during the test before breaking visually. Experimental optical techniques are an interesting alternative. These techniques have the advantage of accessing displacement and strain fields, are non-contact techniques, have high resolution and can use white light or laser illumination. Optical methods, such as DIC [19], geometric or interferometric Moire [20], and speckle or holographic interferometry [21], are available with resolution up to the laser wavelength. Despite high resolution of all interferometric techniques, image decorrelation for high deformation values frequently occurs. This phenomenon usually occurs in tests of hyperelastic materials, as such, they are inadequate for studying these materials. In contrast, DIC allows the measurement of displacement and strain fields for high deformation values. The experimental characterization of the mechanical behavior of hyperelastic materials, when subjected to the action of shear forces, has the advantage of allowing more accurate and realistic results; however, its implementation requires laboratory facilities and costly equipment. On the other hand, there has been an exponential growth in the use of numerical tools based on the finite element method (FEM) [22; 23]. The appearance of computational tools applied to hyperelastic materials is due to lower costs of the method and the increase in the calculation capacity of the computers. For numerical simulation with hyperelastic materials, it is necessary to use constitutive models that are adequate to the material under study and tensile tests (uni or biaxial) are usually required to better characterize this material [24]. Considering the advantages of each approach, both experimental and numerical, some researchers have developed hybrid methods that use experimental information in numerical simulations [25]. The purpose of this work is to characterize the mechanical behavior of PDMS through an experimental method using 3D DIC and comparing it with four different numerical constitutive models. For this, two models with varying thicknesses of simple lap joints with PDMS were developed, and the results of the experimental tests were compared with the numerical simulation.