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This study examines the influence of micro-particles derived from
Urtica dioica
L. (nettle) fibres on the mechanical behaviour of struc
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tural epoxy adhesive joints. Short-fibre filler (diameter < 100
µm,
length < 500
µm) characterised by noticeable porosity and morpho
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logical heterogeneity was added to the epoxy matrix in various con
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centrations (0.25–1.00
wt.%). Static tests revealed that the optimum
strength, deformability, and cohesion of the joints were achieved at
0.50
wt.%, resulting in up to a 20% increase in strength compared to
the reference epoxy. Higher filler contents led to poorer dispersion,
increased heterogeneity, and reduced mechanical properties. Under
cyclic loading (low-cycle fatigue), joints with higher filler content
exhibited significantly shorter fatigue life, with premature failure often
occurring early in testing—joints with pure epoxy or with 0.25
wt.%
filler demonstrated better stability and fatigue resistance. Scanning
electron microscopy analysis confirmed delamination at both the
adhesive–adherent interface and within the adhesive layer under
cyclic stress, for components subjected to cyclic loading, pure epoxy
or epoxy modified with up to 0.25
wt.% natural nettle filler appears to
be the most effective solution. The findings highlight the potential of
bio-based fillers to enhance sustainable structural adhesive system.
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