Chapter 4
Advances on the Constitutive Characterization of Composites via Multiaxial Robotic Testing and Design Optimization


The research areas of mutiaxial robotic testing and design optimization have been recently utilized for the purpose of data-driven constitutive characterization of anisotropic material systems. This effort has been enabled by both the progress in the areas of computers and information in engineering as well as the progress in computational automation. Although our efforts have begun three decades ago, in this chapter we are presenting our progress on this synergistic combination of technologies developed in the last five years. Specifically, in this chapter we are reporting on the first successful implementation of our evolving methodology that recently was completed with the first industrial rate campaign of experiments for this purpose. This methodology is motivated by the data-driven requirements of employing design optimization principles for determining the constitutive behavior of composite materials as described in our recent work [1, 2]. Traditionally, the determination of the constitutive characterization of composite materials has been achieved through conventional uniaxial tests, mainly aiming for the estimation of the elastic properties. Typically, extraction of these properties, involve uniaxial tests conducted with specimens mounted on uniaxial testing machines, where the major orthotropic axis of any given specimen is angled relative to the loading direction. In addition, specimens are designed such that a homogeneous state of strain is developed over a well-defined area, which is required for the purpose of measuring stresses and strains through the measurement of the respective reaction forces and displacement [3, 4]. Consequently, the use of uniaxial testing machines imposes requirements of using multiple specimens, griping fixtures, and multiple experiments without the option of studying mutltiaxial effects. The requirement of a homogeneous state of strain frequently imposes restrictions on the sizes and shapes of specimens to be tested. These requirements result in increased cost and time, and to inefficient characterization processes. To address these issues and to extend characterization to multiaxial state of strain in both the linear and non-linear regimes, multi-degree of freedom automated mechatronic testing machines, which are capable of loading specimens multiaxially, in conjunction with energy-based inverse characterization methodologies, were introduced at the Naval Research Laboratory (NRL) [5–7]. This development was the first of its kind and has continued through the present [8–10].

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