Role of TiO2 nanoparticles as particulate fillers in epoxy adhesives: Toughening mechanisms vs. agglomeration effects under fatigue loading

Akbarzadeh, Pooria

doi:10.22104/jpst.2026.8463.1299

Role of TiO₂ nanoparticles as particulate fillers in epoxy adhesives: Toughening mechanisms vs. agglomeration effects under fatigue loading

Document Type : Research Article

Author

Pooria Akbarzadeh

Department of Mechanical Engineering, University of Sistan and Baluchestan, Zahedan, Iran

10.22104/jpst.2026.8463.1299

Abstract

Incorporating particulate metal-oxide nano-fillers into brittle epoxy matrices effectively modifies fracture toughness; however, structural endurance is fundamentally governed by the competition between effective nanoparticle dispersion and localized agglomeration. This study investigates the micro-mechanical behavior, toughening mechanisms, and agglomeration effects of TiO₂ nanoparticles incorporated into a structural epoxy adhesive at 0.50, 1.0, and 3.0 wt% loading fractions. Glass/epoxy double-lap joints were fabricated and subjected to quasi-static tensile and tension-tension cyclic fatigue testing (R = 0.1, 4 Hz) to evaluate these particulate systems. The results indicate that optimal dispersion at 1.0 wt% yields the best average performance, achieving the highest mean static failure load (8.44 kN) and maximum characteristic fatigue life (η = 37,857 cycles). Micro-mechanical analysis suggests this optimal fraction enhances fatigue resistance through energy-dissipating mechanisms, predominantly crack pinning and deflection. Conversely, 3.0 wt% loading severely degrades static and fatigue behavior, which is attributed to significant nanoparticle agglomeration, forming rigid clusters that act as localized stress concentrators and promote premature microcrack coalescence. Since direct microscopic characterization of the filler dispersion was not performed, these toughening and agglomeration mechanisms are inferred from the mechanical responses and fracture behavior. Furthermore, Weibull analysis exposed a crucial reliability crossover linked to filler distribution: while 1.0 wt% exhibited the highest average fatigue life, the more uniform distribution at 0.5 wt% minimized statistical scatter. This rendered it the safest conservative formulation at a 90 % reliability level (B₁₀ life). These findings underscore that harnessing the full potential of particulate fillers requires balancing active micro-mechanical toughening with conservative statistical reliability.

Graphical Abstract

Role of TiO2 nanoparticles as particulate fillers in epoxy adhesives: Toughening mechanisms vs. agglomeration effects under fatigue loading

Highlights

TiO₂ nanoparticles improved the static and fatigue performance of epoxy adhesives.
Weibull analysis shows a reliability crossover between 0.5 and 1.0 wt% TiO₂.
While 1.0 wt% gave the highest mean life, 0.5 wt% showed the best B₁₀ reliability.
3.0 wt% TiO₂ reduced life, likely due to agglomeration and stress concentration.
Crack pinning and deflection are the main toughening mechanisms at 1.0 wt% TiO₂.

Keywords

Composite double-lap joints

TiO₂ nanoparticles

Fatigue life reliability

Weibull statistical analysis

Nanoparticle agglomeration

Subjects

Particle Science and Technology

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