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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)

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