Abstract
The aim of the present paper is to study the mechanical performance evolution of pinned hybrid glass-flax composite laminates under environment aging conditions. Hybrid glass-flax fibers/epoxy pinned laminates were exposed to salt-spray fog environmental conditions up to 60 days. With the purpose of assessing the relationship between mechanical performances and failure mechanisms at increasing aging time, single lap joints at varying joint geometry (i.e., hole diameter D and hole distance E from free edge) were characterized after 0 days (i.e., unaged samples), 30 days, and 60 days of salt-fog exposition. Based on this approach, the property–structure relationship of the composite laminates was assessed on these critical environmental conditions. In particular, a reduction of failure strength for long-aging-time-aged samples was observed in the range 20–30% compared to unaged one. Due to the natural fiber degradation in a salt-fog environment, premature catastrophic fractures mode due to shear-out and net-tension were found, related to reduced joint fracture strength. This behavior identifies that this type of joint requires a careful design in order to guarantee an effective mechanical stability of the composite hybrid joint under long-term operating conditions in an aggressive environment.
Highlights
Hybrid composite materials were addressed as effective approach to optimize structural design in several industrial fields, such as construction, aerospace or automotive [1,2]
The engineering choice of these materials has shown significant advantages compared to conventional non-hybrid composites [3]
Several research activates highlighted that the engineering design of natural fiber based composite materials is a potentially suitable key factor to guarantee an effective synergy between mechanical performance and green sustainable material [2,4]
Summary
Hybrid composite materials were addressed as effective approach to optimize structural design in several industrial fields, such as construction, aerospace or automotive [1,2]. The engineering choice of these materials has shown significant advantages compared to conventional non-hybrid composites [3]. In such a context, the high mechanical properties of synthetic fibers and the environmental compatibility of natural fibers represent an effective and reliable combination to develop hybrid composite materials with marked performances of sustainability and mechanical/structural effectiveness. Mechanical joint is one of the industrially applied methods to assemble composite structures. Structural joints, often required at the design level, are high stress concentration points that make this region sensitive to Polymers 2020, 12, 40; doi:10.3390/polym12010040 www.mdpi.com/journal/polymers
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