• Hajikazemi, Mohammad
• Van Paepegem, Wim
• Sommer, Josef
• Baere, Ives De

Abstract

Ply cracking is typically the first ply level damage mode in composite laminates under static and fatigue tensile loading. Ply cracks do not usually cause the final failure of a laminate, but may significantly degrade the effective properties of the composite and serve as a source for other damage modes initiation. However, the in-situ experimental detection and quantification of this damage mode is a challenging task specially under fatigue loading conditions without stopping the test. This work is focused on detection of ply cracking and calculation of crack density [1] in multidirectional symmetric composite laminates. The main objective of this work is to study whether the DIC technique [2] is reliable for automated crack detection and functional in calculation of crack density. Therefore, digital image correlation with 2D-DIC and 3D-DIC setups (Figure 1) at the edge and top surfaces of [02/902]s, [02/452]s and [902/02]s glass/epoxy laminates is utilized to detect crack density under uniaxial quasi-static and fatigue loading conditions. For fatigue, the maximum cyclic tensile stress of 90% of the first crack initiation stress, obtained from quasi-static tests, with load ratio σmin/σmax=0.1, frequency of 5 Hz and up to 200,000 cycles, is considered. An optimization analysis is implemented to evaluate the resolution and the standard uncertainty in DIC strain and displacement measurements. Next, a comparison is established between the discontinuities in both strain and displacement fields for crack detection. Consequently, the displacement field has proved to deliver better and more accurate results than strain fields in crack density calculation. The results obtained from DIC analysis are compared and validated by microscopic images which are acquired after performing each test (Figure 2). The study of the results shows that the developed DIC methodology are suited for automated crack detection in fatigue and quasi-static loadings, and as such extract the evolution of crack density vs. number of cycles.

Topics

• density
• impedance spectroscopy
• surface
• glass
• glass
• crack
• fatigue
• composite