Accuracy of strain measurement systems on a non-isotropic material and its uncertainty on finite element analysis

Abstract

The application of strain gauges as recommended by the ASTM standards provides accurate strain measurements in isotropic materials. However, their use in composite materials becomes more challenging due to their anisotropic nature. In this study, we hypothesized that the use of the distributed sensing system and the three-dimensional digital image correlation, which can average strain along a line and surface, respectively, may account for strain variability in composite materials. This study shows an investigation on the mechanical properties of unidirectional, cross-ply, and angle-ply carbon-epoxy specimens using strain gauges, distributed sensing system, and digital image correlation. The Bhattacharyya distance method was used to provide a preliminary evaluation of the closeness of the three different measurement techniques while the B-basis statistical method was used to analyze the experimental data in order to obtain a more conservative and reliable material parameter compared to the conventional averaged value, recommended by ASTM standards. Finally, a finite element model was created in Ansys Workbench™ as a means of evaluating the implication of a single point strain gauges measurement, versus a line or a surface strain measurement. The finite element analysis investigation was performed at a laminae level using the measured experimental elastic modulus and at a lamina–lamina level in which the elastic modulus of the unidirectional case was used as input in all the laminate configurations. The former analysis showed good agreement between the finite element analysis and all the strain measurement systems with an averaged percentage difference below 5%. The latter analysis showed a higher discrepancy in the measured percentage difference. A comparison between the finite element analysis and the strain gauges measurements showed an overall percentage difference between the range of 10% and 26%. Distributed sensing system and three-dimensional digital image correlation measurements provided an overall percentage difference below 10% for all the specimen configurations with a maximum percentage difference recorded for the longitudinal angle-ply case of approximately 9%.

Ultrasonic inspection of thin composite laminates

“…Each section was then assigned material properties using the stiffness matrix definition, which depended on the individual plies orientation relative to the global reference. The material properties used, sourced from [13], are shown in Table 1. In contrast to the approach used during the ASTM™ block study, the water path part itself was moved as a whole along the surface of the inspected region.…”

Investigation of the Crack Propagation in the Graphene/Synthetic Rubber Nanocomposite Materials with DIC Technique

“…Investigating the local performance of the material in the area near the crack tip can explain the fracture resistance properties of this material. The amplitude of vertical strain at the crack tip and its effect on the area around the crack are two factors used to explain the crack propagation tendency [4,[35][36][37]. These two factors can be implemented utilizing the full-field displacement distribution acquired from the DIC technique [13,38].…”

Transient Strain Monitoring of Weldments Using Distributed Fiber Optic System

“…Martinez-Bueno et al made use of Rayleigh backscattering technology to instrument and validate a Finite Element Model (FEM) of a composite wing of an Unmanned Aerial Vehicle (UAV) [19]. In [20], Baldassarre et al demonstrated the accuracy of the FODSS with respect to discrete singlepoint measurements such as strain gauges and surface strain measurement technology such as DIC. The author concluded that for anisotropic materials, surface strain measurements such as DIC showed that they were more accurate than a single point or line measurement technique.…”