Roll-over shape of a prosthetic foot: a finite element evaluation and experimental validation
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ORIGINAL ARTICLE
Roll-over shape of a prosthetic foot: a finite element evaluation and experimental validation Thirunindravur Mannan Balaramakrishnan 1 & Sundararajan Natarajan 1
&
Sujatha Srinivasan 1
Received: 10 August 2019 / Accepted: 25 June 2020 # International Federation for Medical and Biological Engineering 2020
Abstract Prosthetic feet have generally been designed experimentally by adopting a trial-and-error technique. The objective of this research is to introduce a novel numerical approach for the a priori evaluation of the roll-over shape (ROS) of a prosthetic foot for application in its systematic design and development. The ROS was achieved numerically by employing a non-linear finite element model incorporating the augmented Lagrangian and multi-point constraint contact formulations, a hyperelastic material model and a higher-order strain definition. The Ottobock Solid Ankle Cushion Heel (SACH) foot was chosen to experimentally validate the numerical model. The geometry of the foot was evaluated from optical scans, and the material properties were obtained from uniaxial tensile, shear and volumetric compression tests. A new setup was designed for an improved experimental determination of the ROS, with the inclusion of an extended moment arm and variable loading. Error analysis of the radius of curvature of the ROS between the numerical and experimental results showed the percentage error to be 7.52%, thereby establishing the validity of the model. A numerical design model of this kind can be utilised to vary the input design parameters to arrive at a prosthetic foot with specified performance characteristics effectively and economically. Keywords Finite element analysis . Gait . Artificial limbs . Foot . Walking
1 Introduction A prosthetic foot should biomimic the functions of the human ankle–foot complex. From a technical standpoint, this implies that a prosthesis must ideally be able to facilitate the kinematics, kinetics, muscle activation patterns and metabolic cost of conventional human walking in amputee gait. On the contrary, researchers have found that unilateral amputations lead to bilateral asymmetries in the ground reaction force [1], stance phase ankle flexion [2], muscle activation patterns [3] and step length [4] between the residual limb and the contralateral limb in amputee gait. The vertical excursion of the centre of mass of the amputee has also been reported to show variations between the limbs during the stance phase [5], and the overall walking speed has been stated to decrease in amputee walking [6]. Hence, the goal of enhancing the functionality of a * Sundararajan Natarajan [email protected] 1
TTK Center for Rehabilitation Research and Device Development (R2D2), Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai, Tamil Nadu 600036, India
prosthetic foot continues to present challenges in achieving improved amputee gait characteristics. Several methods have been adopted to characterise a prosthetic foot to improve its functionality
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