Optimization of Epoxy Resin Mixing Ratios on the Strength of Glass Fiber-Reinforced Composite Joints

Abstract:

Glass fiber-reinforced composites (GFRC) are widely used in structural applications due to their high strength-to-weight ratio and excellent fatigue resistance. Nevertheless, the mechanical integrity of adhesive joints remains a critical challenge in composite structural engineering. This study aims to investigate the influence of varying epoxy resin mixing ratios on the lap shear strength of glass fiber-reinforced composite joints. Two experimental schemes were conducted by varying the resin-to-hardener composition in the range of 10:50 to 70:50 (by weight). Single-lap joint specimens were fabricated and tested in accordance with ASTM D5868-95. The results demonstrated that a resin-to-hardener ratio of 50:50 yielded the maximum lap shear strength, reaching 5.71 MPa for resin system A and 5.28 MPa for resin system B. This ratio indicated a stoichiometric balance between epoxy groups and active amine groups, resulting in optimal curing with maximum cross-linking density. Deviations from this optimal ratio, either due to excess or deficiency of one component, led to a significant reduction in joint strength, as indicated by brittle fracture or weak adhesive bonding. These findings highlight the importance of precise control over epoxy adhesive formulations to ensure reliable mechanical performance in composite structures. The implications of this research contribute to the development of more durable and efficient adhesive systems, particularly for GFRC applications in the automotive, aerospace, and marine industries.

• Periodical: Materials Science Forum (Volume 1189)
• Pages: 43-51
• DOI: https://doi.org/10.4028/p-pyKrl2
• Online since: May 2026
• Authors: Sugiyanto Sugiyanto*, Sarjito Sarjito, Rois Fatoni
• Keywords: Adhesive Joints, Epoxy Resin, Glass Fiber, Mixing Ratio, Shear Strength

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