Design of Triaxial Tests with Polymer Matrix Composites

Area of Science:

• Materials Science
• Mechanical Engineering
• Composite Materials

Background:

• Multiaxial testing offers realistic failure modes for composites under complex loads but faces challenges in equipment, experimental design, and result interpretation.
• A six-actuator triaxial testing machine enables simultaneous, synchronized axial loading in three dimensions, providing a framework for advanced composite testing.

Purpose of the Study:

• To numerically design a triaxial experiment for a polymer-based composite using finite element method (FEM).
• To characterize the triaxial response of a polymer-based composite with apparent isotropic behavior.
• To identify loading scenarios that may lead to composite failure under triaxial stress states.

Main Methods:

• Finite Element Method (FEM) was employed to define a triaxial specimen geometry for homogeneous stress and strain states.
• A novel fixing system was proposed to replicate numerical boundary conditions in experimental setups.
• Analytical and FEM virtual testing procedures were developed to determine the full strain tensor in the triaxially loaded region.

Main Results:

• FEM simulations identified stress concentrations in the uniaxially loaded arms of the specimen, predicting experimental failure in these regions.
• The study proposes using hydrostatic and deviatoric strain tensor components to assess composite susceptibility to triaxial failure.
• Loading scenarios with higher deviatoric strain components were identified as more likely to cause damage.

Conclusions:

• The designed triaxial tests, while not precisely determining triaxial strength, are valuable for observing composite behavior before failure.
• The proposed methodology allows for adequate characterization of the triaxial response of polymer-based composites.
• This research contributes to understanding composite material behavior under complex, multiaxial loading conditions.