Hyperelastic constitutive model parameters identification using optical-based techniques and hybrid optimisation

Abstract

In this paper we propose a new optical-based technique to identify the constitutive relation coefficients of the hyperelastic material using a hybrid optimisation approach. This technique can be used in place of traditional mechanical testing of elastomers for applications that involve inhomogeneous deformation. The purpose of the proposed method is to identify the incompressible hyperelastic material constitutive relation coefficients using a single experiment under different loading cases. The method comprises sample surface 3D reconstruction and uses finite element simulations to replicate the experiments, and uses a hybrid optimisation technique to minimise the error between actual 3D deformations and FE simulation results. The proposed hybrid technique predicts the hyperelastic constitutive relation coefficients more accurately than other optimisation methods. This study introduces a novel approach by employing a subpixel image registration algorithm for 3D reconstruction. The method requires a single experiment with diverse loading cases to accurately determine the coefficients of hyperelastic constitutive relations. The setup is portable and can be accommodated in a small suitcase. For this purpose, an apparatus was constructed comprising a stereoscopic system with eight cameras and a six-degree-of-freedom force-torque sensor to measure the induced forces and torques during the experiments. We identified the constitutive relation coefficients of Ogden N1, Ogden N3, Yeoh, and Arruda-Boyce relations which are commonly used models for silicone materials, using a traditional uniaxial test, optical uniaxial test (experiments performed using a constructed optical system), and inhomogeneous deformations tests. The study demonstrated that the coefficients obtained from inhomogeneous deformation tests provided the most accurate FE predictions. It was also shown that hyperelastic constitutive relation coefficients obtained from traditional uniaxial tests are insufficient to describe the material behaviour when the material undergoes inhomogeneous deformations.

A pneumatic reconfigurable socket for transtibial amputees

“…Material properties were measured, and constitutive laws appropriate to describe the elastomer systematically evaluated as previously described in detail in. 50 In accordance with the findings of our earlier study, we developed an Ogden model (N = 3) with coefficients of μ 1 = 12.1 kPa, μ 2 = 10.8 kPa, μ 3 = À2.8 kPa, α 1 = 3.34, α 2 = 4.08, and α 3 = 5.19. Based on the literature the typical friction coefficient observed between the residual limb and the socket is 0.5 ± 0.1.…”

Remodeling of the Fibula Stump After Transtibial Amputation

“… 10 , 11 However, the data given by the authors concern the formation of the femoral stump in animals and do not touch upon the issues of changes in the structural organisation of bone tissue under load in the prosthesis. Recently, the issues of optical identification of model parameters, 12 fabrication of pneumatic reconfigured sockets for proper stump fit, 13 and characterization of soft tissue features after tibial amputation 14 have been developed, which may in the future affect both bone structure and prosthetic outcomes. The available studies of the peroneal bone tissue after transtibial amputation only state the disturbance of bone formation in the form of acuminosity or club-like shape and phenomena of peroneal nerve neuritis.…”