Cruciform specimens biaxial extension performance relationship to constitutive identification

TL;DR

This paper develops optimized cruciform specimen shapes for biaxial extension tests, improving stress uniformity and parameter identification through in silico design and experimental validation.

Contribution

It introduces new cruciform specimen geometries optimized via computational methods and validated experimentally for better constitutive parameter fitting in biaxial tests.

Findings

New specimen shapes outperform existing ones in biaxial tests.

Full field strain measurements enable efficient parameter fitting.

Small gauge areas improve approximation to ideal behavior.

Abstract

Main desired features of biaxial tests are: uniformity of stresses and strains; high strain levels in gauge areas; reliable constitutive parameters identification. Despite cruciform specimen suitability to modern tensile devices, standard testing techniques are still debated because of difficulties in matching these demands. This work aims at providing rational performance objectives and efficient cruciform specimens shapes in view of constitutive parameter fitting. Objective performance is evaluated along particular lines lying on principal directions in equibiaxial tensile tests. A rich specimen profile geometry is purposely optimized in silico by varying cost function and material compressibility. Experimental tests, monitored via digital image correlation, are carried out for validation. New shapes are designed and tested in a biaxial tensile apparatus and show to perform better than existing ones. Parameter fitting is efficiently performed by only exploiting full field strain measurements along lines. Small gauge areas and small fillet radii cruciform specimens get closer to the ideal behavior. For constitutive parameters identification in two-dimensional tensile experiments, data analysis on gauge lines deformation suffices.