Determination of the symmetries of an experimentally determined stiffness tensor; application to acoustic measurements

TL;DR

This paper presents a method to determine the symmetry properties of an experimentally obtained stiffness tensor, especially when the symmetry is unknown, using ultrasonic measurements and a concept of tensor distance to symmetry classes.

Contribution

It introduces a comprehensive approach combining ultrasonic measurements, visual symmetry analysis, and tensor distance metrics to identify material symmetries without prior assumptions.

Findings

Method effectively identifies symmetries in raw stiffness tensors.

Visual tools help interpret quasi-symmetries from ultrasonic data.

Nearest symmetric tensor can be computed for any given symmetry class.

Abstract

For most materials, the symmetry group is known a priori and deduced from the realization process. This allows many simplifications for the measurements of the stiffness tensor. We deal here with the case where the symmetry is a priori unknown, as for biological or geological materials, or when the process makes the material symmetry axis uncertain (some composites, monocrystals). The measurements are then more complicated and the raw stiffness tensor obtained does not exhibit any symmetry in the Voigt's matricial form, as it is expressed in the arbitrarily chosen specimen's base. A complete ultrasonic measurement of the stiffness tensor from redundant measurements is proposed. In a second time, we show how to make a plane symmetry pole figure able to give visual information about the quasi-symmetries of a raw stiffness tensor determined by any measurement method. Finally we introduce the concept of distance from a raw stiffness tensor to one of the eight symmetry classes available for a stiffness tensor. The method provides the nearest tensor (to the raw stiffness tensor) possessing a chosen symmetry class, with its associated natural symmetry base.