Physical interpretation of delamination growth in multidirectional composite laminates under mode I cyclic loading using acoustic emission

• Grant number: 19/18570-4
• Support type: Scholarships abroad - Research Internship - Master's degree
• Effective date (Start): June 07, 2020
• Effective date (End): December 05, 2020
• Field of knowledge: Engineering - Materials and Metallurgical Engineering - Nonmetallic Materials
• Principal researcher: Herman Jacobus Cornelis Voorwald
• Grantee: Roberto Ferreira Motta Junior
• Supervisor abroad: Reyndert Christiaan Alderliesten
• Home Institution: Faculdade de Engenharia (FEG). Universidade Estadual Paulista (UNESP). Campus de Guaratinguetá. Guaratinguetá , SP, Brazil
• Research place: Delft University of Technology (TU Delft), Netherlands
• Associated to the scholarship: 19/00846-3 - Relation between interlaminar damage extension and fibre orientation with acoustic signal: quasi-static and cyclic loading, BP.MS

Abstract

Composite laminates have been widely employed in aeronautics and aerospace industry as a consequence of its high stiffness and strength in combination with a low specific weight. However, due to the anisotropic nature of composites, this material presents low strength to out-of-plane stresses, which make them vulnerable to delamination. Among all damage types in composites, delamination is the most severe and recurrent, reducing the material strength and stiffness, which may lead to structural failure. Aircraft structures are constantly under cyclic loading and considering that fatigue is a major cause for delamination growth, the understanding of fatigue behaviour is a primary design concern. Hence, numerous fatigue crack growth (FCG) models for composites have been developed in the last decades, nevertheless, none of them presents a satisfactory explanation of the underlying physical phenomenon. This leads to overdesigned structures resulting in increasing weight as a consequence of no-growth design philosophy. Besides, only unidirectional composites were evaluated for most of the FCG models developed so far, neglecting the influence of fibre orientation with respect to crack propagation. Aiming to understand the underlying physics of crack propagation in multidirectional composite laminates under mode I cyclic loading, this research will conduct fatigue tests according to ASTM D6115-97 in double cantilever beam (DCB) specimens with four different lay-ups. Therefore, four different crack propagation interfaces will be evaluated (0°/0°, 30°/-30°, 45°/-45°, 60°/-60°), enabling the assessment of the fibre direction influence over crack propagation. Moreover, the influence of R-ratio (energy ratios) will be assessed, and the capability of acoustic emission (AE) quantifying physical damage during fatigue crack propagation will be evaluated. (AU)