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Negative and positive Poynting effects in tendon under simple shear
C S Moreira1, F S Araújo2, L C S Nunes3
1Department of Mechanical Engineering (MECAN), Universidade do Estado do Rio de Janeiro - UERJ, Rua Fonseca Telles 121, São Cristóvão, 20940-903, Rio de Janeiro, RJ, Brazil.
Journal of the Mechanical Behavior of Biomedical Materials
|November 18, 2025
Summary
Shear forces in tendons were measured, revealing that shear stress is proportional to shear, with no strain-stiffening. Normal stresses, influenced by random fiber networks, are key to understanding tendon mechanics and injury treatment.
Area of Science:
- Biomechanics
- Materials Science
Background:
- Shear load transfer is vital for tendon function, preventing injury by redistributing internal loads.
- Understanding tendon stress states is crucial for comprehending load transfer mechanisms.
Purpose of the Study:
- To investigate normal and shear stresses in tendons under simple shear.
- To analyze the influence of shear force applied parallel to fascicles and collagen fibers.
- To explore the role of random fiber networks in tendon mechanics.
Main Methods:
- Simultaneous measurement of normal and shear forces and shear deformation in tendon samples.
- Application of a straightforward model to describe tendon normal and shear behavior.
- Simultaneous fitting of expressions to measured normal and shear stresses.
Main Results:
- Tendon shear behavior showed no strain-stiffening; shear stress was proportional to shear.
- Compressive and tensile normal stresses (Poynting effects) were observed.
- Random fiber networks influenced tensile normal stress, but not compressive normal stress within a certain range.
Conclusions:
- Random fiber networks significantly impact normal stress states in tendons during simple shear.
- The findings offer insights into tendon injury mechanisms and biomimetic material design.
- Understanding these mechanics can inform better treatments for tendon injuries.
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