Performance analysis of the multiwalled carbon nanotubes electroless coating over 7075-T6 aluminum specimens subjected to variable amplitude loading cases

The designs and improvements in the damage tolerance field for engineering constructions subjected to variable amplitude loading are crucial research topic in the modern technology. In the present work, the combined impact for nickel-multiwalled carbon nanotubes coating with the variable amplitude loading on the fatigue crack growth performance has been investigated in the 7075-T6 aluminum specimens. Electroless plating technique was used to coat the adopted aluminum specimens. Six conditions of the variable amplitude loading were applied individually on the coated and un-coated aluminum specimens. Multifunctional fatigue equipment integrated with high magnification camera and a computer software was utilized to applying the fatigue loading conditions and measuring crack lengths. FESEM and EDXRF techniques were adopted to examine the topography, modification in composition of chemicals and quality of the nano-coated specimens' surfaces. Numerical modeling used an effective algorithm contains Fortran and ABAQUS software has been utilized in order to validate the measured results. The extracted results indicated that there is an enhancement of 62.2 % in the full width failure of the nano-coated specimens in comparison with the un-coated specimens. A single overload condition led to a significant retardation in crack growth and it rates (reach to 27300 delayed cycles) as compared with constant amplitude and other loading. Utilizing the nano-coating over aluminum specimens resulted in decrease the intensity of the retardation of crack growth rates in comparison with that in un-coated specimens for all loading conditions. The behavior similarity of the crack propagation and its path are the main findings of the results' validations that extracted from numerical modeling and fatigue testing.