Digital image correlation is an experimental optical non-contact full field displacement and strain evaluation method based on the surface subsets tracking with photo cameras, digital images processing, and numerical computation. However, the full field of strain computation is a challenging problem, mainly because the displacement field to be differentiated is not continuous, individual subsets are tracked by the optical digital image correlation system. Moreover, the numerical differentiation can also amplify the noise of the displacement field inducing thus strain errors when the displacement data are poor. The peridynamics theory (which equations are cast in terms of spatial integrals of displacements, instead of spatial derivatives in the classical continuum mechanics) based algorithm is considered in this study and applied for the experimental digital image correlation displacement field to analyze possible peridynamic differentiation method advantages. A strains convergence analysis between the digital image correlation and peridynamic differentiation methods is done in this study. The integro-differential strain calculation as an alternative method is validated against digital image correlation and finite element simulation strain fields. It is also shown that the digital image correlation, a noisy displacement field, still provides an accurate and low level noise strain evaluation based on the proposed method.

The possibility of using the Digital Image Correlation (DIC) technique, along with Lamb wave analysis, was investigated in this study for damage detection and characterization of polymer carbon fiber (CFRP) composites with the help of numerical modeling. The finite element model (FEM) of the composite specimen with artificial damage was developed in ANSYS and validated by the results of full-field DIC strain measurements. A quantitative analysis of the damage detection capabilities of DIC structure surface strain measurements in the context of different defect sizes, depths, and orientation angles relative to the loading direction was conducted. For Lamb wave analysis, a 2D spatial-temporal spectrum analysis and FEM using ABAQUS software were conducted to investigate the interaction of Lamb waves with the different defects. It was demonstrated that the FEM updating procedure could be used to characterize damage shape and size from the composite structure surface strain field from DIC. DIC defect detection capabilities for different loadings are demonstrated for the CFRP composite. For the identification of any composite defect, its characterization, and possible further monitoring, a methodology based on initial Lamb wave analysis followed by DIC testing is proposed.

The non-local theory of peridynamics, based on integral equation of motion, offers a computation alternative for materials with discontinuities. In this study, the peridynamic material model parameters are calibrated using full field Digital Image Correlation measurements applied to simple tensile test experiments, circumventing thus the need for more challenging test setups/methods for the determination of the peridynamic material parameters (especially the critical stretch failure parameter). A two stage algorithm in the optimization software LS-Opt together with a MATLAB stage for performing the peridynamic simulation and an Excel stage for defining the outputs of the simulation are implemented to minimize the differences between the peridynamic model and experimental results. The material model parameters determined based on the simple test setup and the calibration procedure proposed here can then be used for modeling more challenging geometries and load cases in peridynamics.

Numerical fatigue process modelling is complex and still an open task. Discontinuity caused by fatigue cracks requires special finite element techniques based on additional parameters, the selection of which has a strong effect on the simulation results. Moreover, the calculation of fatigue life according to empirical material coefficients (e.g., Paris law) does not explain the process, and coefficients should be set from experimental testing, which is not always possible. A new nonlocal continuum mechanics formulation without spatial derivative of coordinates, namely, peridynamics (PD), which was created 20 y ago, provides new opportunities for modelling discontinuities, such as fatigue cracks. The fatigue process can be better described by using the atomistic approach-based kinetic theory of fracture (KTF), which includes the process temperature, maximum and minimum stresses, and loading frequency in its differential fatigue damage equation. Standard 316L stainless steel specimens are tested, and then the KTF-PD fatigue simulation is run in this study. In-house MATLAB code, calibrated from the material S‒N curve, is used for the KTF-PD simulation. A novel KTF equation based on the cycle stress‒strain hysteresis loop is proposed and applied to predict fatigue life. The simulation results are compared with the experimental results, and good agreement is observed for both symmetric and asymmetric cyclic loading.

Numerical fatigue process modelling is complex and still open task. Discontinuity caused by the fatigue crack requires special finite element techniques based on additional parameters, which selection has a strong effect on simulation results. Moreover, fatigue life calculation according to empirical material coefficients (e. g., Paris law) does not explain the process and coefficients should be set from experimental testing, which is not always possible. New non-local continuum mechanics formulation without spatial derivatives of coordinates – peridynamics (PD), created 20 years ago, brings new opportunities modelling discontinuities, such as fatigue crack. The fatigue process can be better described by using the atomistic approach based kinetic theory of fracture (KTF), which includes the process temperature, maximum and minimum stress, and the loading frequency in its differential fatigue damage equation. Standard 316L stainless steel specimens are tested, and then the KTF-PD fatigue simulation is run in this study. The in-house MATLAB code, calibrated from the material S-N curve, is used for the KTF-PD simulation. A novel KTF equation based on the cycle stress-strain hysteresis loop is proposed and applied to predict the fatigue life. The simulation results are compared with the experimental results, and good agreement is observed for both symmetric and asymmetric cyclic loading.

Interlaminar failure of bonded composite structures is quite often. Nowadays there is a lot of lightweight high reliability carbon or glass fiber (CFRP or GFRP) reinforced polymer composite constructions with bonded carbon or glass fiber rods. In order to better understand the delamination processes of the rods, analytical equations were analyzed. Later, mode I interlaminar failure experiments with CFRP rods 3x3 mm were performed and fracture toughness G_IC = 135 J/m² was found. According to the analytic equations, experiment and values, given literature, finite element model (FEM) of the bonded carbon fiber rods was created in software LS-Dyna. Most of the differences between experimental and simulated force-displacement curves are not higher than 6 % what validates the FEM of the bonded CFRP rods. Also, additional methods, such as peridynamics of the bond area of the rods were analyzed. Offered finite element approach of the bonded CFRP rods is very useful for FEM creation to design and evaluate high reliability CFRP or GFRP constructions.