Interlaminar Shear Behavior of Laminated Carbon Fiber Reinforced Plastic from Microscale Strain Distributions Measured by Sampling Moiré Technique

Abstract

In this article, the interlaminar shear behavior of a [±45°]4s laminated carbon fiber reinforced plastic (CFRP) specimen is investigated, by utilizing microscale strain mapping in a wide field of view. A three-point bending device is developed under a laser scanning microscope, and the full-field strain distributions, including normal, shear and principal strains on the cross section of CFRP, in a three-point bending test, are measured using a developed sampling Moiré technique. The microscale shear strain concentrations at interfaces between each two adjacent layers were successfully detected and found to be positive-negative alternately distributed before damage occurrence. The 45° layers slipped to the right relative to the −45° layers, visualized from the revised Moiré phases, and shear strain distributions of the angle-ply CFRP under different loads. The absolute values of the shear strain at interfaces gradually rose with the increase of the bending load, and the sudden decrease of the shear strain peak value implied the occurrence of interlaminar damage. The evolution of the shear strain concentrations is useful in the quantitative evaluation of the potential interlaminar shear failure.

Measurement of microscopic strain distributions of CFRP laminates with fiber discontinuities by sampling moiré method

“…This might have occurred due to the grid fabrication defects caused by fibers in the back surface, thus causing some nonuniform grid sizes and spaces. As Wang et al [36] explained, the strain measurement accuracy of the used moiré method depends on the pitch accuracy of the fabricated specimen grid. Even though the grid fabricated by the photolithography technique seems to be suitable for the microscopic deformation measurement based on the results obtained in this study, the noise can be reduced more if the grid quality is improved.…”

“…In recent years, the moiré technique has attracted considerable attention and has been applied to the deformation measurement of various materials. Ever since the moiré technique was first reported in 1948 [31], various moiré methods have been successively developed for in-plane and out-of-plane deformation measurements [18,[32][33][34][35][36][37]. A study by Yoneyama et al [32] applied the Virtual Fields Method in combination with moiré interferometry to identify the through-thickness material properties of CFRP.…”

“…The displacement can be accurately measured from a single-shot grid image using a spatial phase-shifting technique. Wang et al (2019) showed some applications of the sampling moiré method in the microscopic strain measurement of CFRP laminates [36], where the interlaminar shear behavior of an angle-ply-laminated CFRP specimen was investigated. In this study, a recently developed sampling moiré method based on previous developments by Wang et al [18,33,35] and Ri et al [34] was applied to measure the existing strain around the resin pocket due to fiber discontinuity in unidirectional (UD) CFRP laminates.…”

Robust Polymer Planar Bragg Grating Sensors Embedded in Commercial-Grade Composites

“…However, their true mechanical behavior cannot be fully represented by classical theories. For example, under bending, the resulting flexural behavior of a CFRP laminate is influenced by various additional effects, such as interlaminar shear stresses, which again, are highly dependent on the employed fiber orientations [3][4][5]. Additionally, in comparison to classical materials, composites tend to behave inherently different in excess load situations.…”

Carbon Fiber Reinforced Polymers

“…Wang et al [ 15 ] investigated the interlaminar shear behavior of CFRP specimens by microscale strain mapping. A three-point bending device was developed under a laser scanning microscope, and the full-field strain distributions, including normal, shear and principal strains on the cross section of CFRP, in a three-point bending test, were measured using a developed sampling Moiré technique.…”