The strength and the failure mechanisms of notched composite materials are of considerable importance in several industrial applications where joints and bolts are unavoidable. They become the main concern when notched composite components are subjected to repeated cyclic loadings. To enhance the fatigue life of composite materials, research efforts were also dedicated to the toughening mechanisms of resin systems. Thermoset systems were modified to overcome their brittle nature by a second phase consisting of nano- or micro- sized fillers (such as nanotubes, nano-fibres, nano-particles, etc.). To this purpose, the family of hybrid nano/micro enhanced resin systems has been extended exploiting microfibrils cellulose (MFC). Cellulose is the most abundant natural homo-polymer and one of the most promising renewable and environmentally friendly resources. The aim of this experimental study was to contribute on the understanding the effect of hybrid microfibrils cellulose epoxy resin (MFC content 0.3% of the resin weight) on the tensile fatigue performance of open hole carbon textile composites. This comprehensive study had three steps. The first dealt with the pre-fatigue quasi-static tensile behavior to measure the relevant mechanical properties, and understanding the damage modes initiation and development around the hole by digital image correlation (DIC) and scanning electron microscope (SEM) observations. The second aimed to detect the effect of the hybrid microfibrils cellulose epoxy resin on the fatigue life diagram of the open hole textile composite by tensile-tensile cyclic loading. Moreover, in this step, the damage development during cyclic loading was observed by DIC, SEM and X-ray micro-CT. Finally, the third step was dedicated to post-fatigue quasi-static tensile behavior, after one million cycles, to assess the retention of the tensile strength and the distribution of the damage comparing to the pre-fatigue quasi-static results. The MFC hybridization of the matrix improved the damage tolerance of the open hole carbon textile composite leading to the extension of the fatigue life. The enhanced performance was mainly connected to the bridging effect of cellulose microfibrils preventing or delaying the cracks propagation in the matrix and along the fiber-matrix interface.

FATIGUE BEHAVIOUR OF OPEN HOLE CARBON TEXTILE COMPOSITE WITH MICROFIBRILS CELLULOSE MODIFIED EPOXY

Carvelli V.;
2022-01-01

Abstract

The strength and the failure mechanisms of notched composite materials are of considerable importance in several industrial applications where joints and bolts are unavoidable. They become the main concern when notched composite components are subjected to repeated cyclic loadings. To enhance the fatigue life of composite materials, research efforts were also dedicated to the toughening mechanisms of resin systems. Thermoset systems were modified to overcome their brittle nature by a second phase consisting of nano- or micro- sized fillers (such as nanotubes, nano-fibres, nano-particles, etc.). To this purpose, the family of hybrid nano/micro enhanced resin systems has been extended exploiting microfibrils cellulose (MFC). Cellulose is the most abundant natural homo-polymer and one of the most promising renewable and environmentally friendly resources. The aim of this experimental study was to contribute on the understanding the effect of hybrid microfibrils cellulose epoxy resin (MFC content 0.3% of the resin weight) on the tensile fatigue performance of open hole carbon textile composites. This comprehensive study had three steps. The first dealt with the pre-fatigue quasi-static tensile behavior to measure the relevant mechanical properties, and understanding the damage modes initiation and development around the hole by digital image correlation (DIC) and scanning electron microscope (SEM) observations. The second aimed to detect the effect of the hybrid microfibrils cellulose epoxy resin on the fatigue life diagram of the open hole textile composite by tensile-tensile cyclic loading. Moreover, in this step, the damage development during cyclic loading was observed by DIC, SEM and X-ray micro-CT. Finally, the third step was dedicated to post-fatigue quasi-static tensile behavior, after one million cycles, to assess the retention of the tensile strength and the distribution of the damage comparing to the pre-fatigue quasi-static results. The MFC hybridization of the matrix improved the damage tolerance of the open hole carbon textile composite leading to the extension of the fatigue life. The enhanced performance was mainly connected to the bridging effect of cellulose microfibrils preventing or delaying the cracks propagation in the matrix and along the fiber-matrix interface.
2022
microfibrils cellulose, carbon textile composites, open hole, fatigue,
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11311/1224191
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