Mechanical deformations in a graphene-reinforced cellulose sample

Abstract

The ever-increasing requirements of product quality and reliability demand more efficient measuring and test methods that must be online, nondestructive, wholefield and without contact. Optical methods seem to be ideal for such purposes. The interferometric technique of ESPSI (Electronic Speckle Pattern Shearing Interferometry), or Shearography, is a coherent-optical measuring and test method that is similar to holographic interferometry. However, this method displays many advantages for industrial applications, due to its relative insensitivity to environmental disturbances. Shearography measures the gradient of the deformation, not the deformation itself as holography does. Consequently, shearography measures strain information directly. Based on the above, Shearography was adapted for the surface strain measurement in graphene-reinforced composite materials; the information was evaluated at each point from our sample observed area. Defect inspections with shearography on fiber-reinforced plastics parts, widely used in aircrafts, ships, chemical and oil and gas industries, are often performed outside of the lab. An optical system capable of measuring the strain fields in and out of plane was developed based on electronic speckle interferometry. The obtained interferogram images were processed using the phase-stepping technique. A specific specimen geometry and an optical arrangement based on the Michelson interferometer are proposed to measure the deformation along two orthogonal axes due to sensibility in and out of plane. The advantages of the system include its high sensitivity and stability. The experimental setup and approach for estimating the strain fields was validated using a membrane based on polylactic acid reinforced with cellulose microcrystalline as sample with and without graphene.