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Open Access

ARTICLE

Numerical Modeling and Static Contact Analysis for a Bioinspired Rigid-Soft Fingertip

Jiafeng Liu1,2, Junhao He1, Binbin Deng1, Jie Sun1, Chenyu Shi1,3, Shunhang Liang1, Zicong Zhou1,4, Guangsheng Feng1, Jie Zhang1,*
1 School of Mechanics and Construction Engineering, Jinan University, Guangzhou, China
2 Department of Engineering Mechanics, Tsinghua University, Beijing, China
3 School of Aeronautics and Astronautics, Zhejiang University, Hangzhou, China
4 CAS Key Laboratory of Mechanical Behavior and Design of Materials, University of Science and Technology of China, Hefei, China
* Corresponding Author: Jie Zhang. Email: email

Computers, Materials & Continua https://doi.org/10.32604/cmc.2026.083128

Received 30 March 2026; Accepted 10 June 2026; Published online 07 July 2026

Abstract

The ability to achieve sufficient grasping force while maintaining conformal contact with objects is highly attractive for bio-inspired flexible robotic hands and grippers. In this paper, a flexible robotic hand design is developed inspired by the human hand, where the fingers have an embedded rigid phalanx wrapped in soft silicone rubber materials. A rigid-soft numerical model is developed to investigate the static contact behavior of a fingertip with a rigid flat using finite element (FE) analysis. The Ogden constitutive model is adopted to characterize the hyper-elastic behavior of the silicone rubber material and its parameters are determined by uniaxial tensile and compression experiments. The FE numerical model is validated against experimental contact radius measurements, indicating that the classical Hertz contact theory becomes inadequate for large-deformation rigid-soft contact, and the presence of an internal rigid core has a great impact on the contact behavior. It is observed that when the normal force is small, the maximum stresses occur near the contact area. As the normal force increases, the location of the maximum stresses gradually migrates to the interface between the soft tissue and the rigid bone, indicating that the interfacial stress should be considered in the fingertip design. A parametric study is further conducted to systematically evaluate the effects of contact angle, friction coefficient, and rigid bone size on the contact force-deformation relationship and the resulting stress distribution along the rigid-soft interface. The simulations show that, within a certain parameter range, the contact angle and the friction coefficient slightly affect the interfacial stress distribution, while the structural size has a significant effect. The interfacial stresses exhibit a U-shaped dependence on the rigid bone size, with optimal stress minimization achieved at a bone-to-fingertip radius ratio between 3/8 and 1/2 for the present rigid flat contact configuration. These findings provide novel insights into the fingertip contact behavior and can further inspire the design of the flexible manipulators.

Keywords

Soft fingertip; rigid-soft model; contact analysis; finite element analysis; experimental validation

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