a b s t r a c tThis paper presents a hybrid procedure for mechanical characterization of hyper-elastic materials based on moiré, finite element analysis and global optimization. The characterization process is absolutely general because does not require any assumption on specimen geometry, loading or/and boundary conditions. The novel experimental approach followed in this research relies on a proper combination of intrinsic moiré and projection moiré which allows 3D displacement components to be measured simultaneously and independently using always the same experimental setup and just one single camera. In order to properly compare experimental data and finite element predictions, 3D displacement information encoded in moiré patterns which are relative to the deformed configuration taken by the specimen are expressed in the reference system of the unloaded state.A global optimization algorithm based on multi-level and multi-point simulated annealing which keeps memory of all best records generated in the optimization is used in order to find the unknown material properties through the minimization of the X functional built by summing over the differences between displacements measured experimentally and those predicted numerically.Feasibility, efficiency and robustness of the proposed methodology are demonstrated for both isotropic and anisotropic specimens subject to increasing pressure loads: a natural rubber membrane and a glutaraldehyde treated bovine pericardium patch, respectively. Remarkably, the results of the characterization process are in very good agreement with target data independently determined. For the isotropic specimen, the maximum error on hyper-elastic constants is less than 1% and the residual error on displacements is less than 3.5%. For the anisotropic specimen, the maximum error on material properties is about 3.5% while the residual error on displacements is less than 3%. The identification process fails or becomes less reliable if ''local" displacement values are considered.
This paper describes an hybrid procedure for mechanical characterization of biological membranes. The in-plane displacement field of a glutaraldehyde treated bovine pericardium patch obtained with an equi-biaxial tension test is measured with intrinsic moiré and then compared with finite element predictions. Preliminary analysis of moiré patterns observed in the experiments justifies the assumption of the constitutive model based on transversely isotropic hyperelasticity. In order to determine the 16 hyperelastic constants included in the constitutive model and the fiber orientation, the difference Ω between displacement values measured with moiré and their counterpart determined numerically is minimized by means of multi-level and multi-point simulated annealing. Results clearly demonstrate the efficiency of the identification procedure presented in this research: in fact, residual difference between experimental data and numerical values of in-plane displacements is less than 2%. In order to validate the entire identification process, another experimental test is conducted by inflating the same specimen. Out-of-plane displacements, now measured with projection moiré, are compared with predictions of a new finite element model reproducing the experimental test. The 16 hyper-elastic constants previously determined are given in input to the inflation test FE model. Remarkably, experimental and numerical results are again in excellent agreement: maximum percent error on w-displacement is less than 3%.
This study analyzes the effect of porcelain veneer restoration on the structural response of a maxillary incisor. Tooth deformation is evaluated, prior to and after restoration, by the synergic use of Phase‐Shifting Electronic Speckle Pattern Interferometry (PS‐ESPI) and 3D finite element (FE) analyses. The intact maxillary incisor and the porcelain veneer restored tooth are subject to flexural load. Displacement fields are measured with Phase‐Shifting Electronic Speckle Pattern Interferometry. Experimental tests are simulated with 3D FE analyses tuning materials parameters via an optimisation‐based inverse procedure. ESPI measurements indicate that the restoration design under study produced deformations very similar to those of the intact tooth under load. FE results show sharp changes in displacement and stress 1 mm above the cement–enamel junction on the facial side of the restored tooth. Severe stress concentration (about 50% increase with respect to natural tooth) appears at the interface between veneer restoration and intact enamel and dentine tissues. This confirms the hypothesis that veneer restorations can amplify the effect of occlusal loading on the loss of dental hard tissue in the tooth cervical region.
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