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<p>In recent years, manufacturers have increasingly embraced sustainable practices by employing eco-friendly, recycled, and recyclable materials along with greener production processes. Adhesive bonding has become a preferred method for joining composites, as it forms strong joints without disrupting structural continuity, unlike fasteners such as rivets and screws that cause fibre-matrix discontinuities and stress concentrations. Aerospace and automotive industries have also begun integrating natural fibres due to their low weight, renewability, and reduced environmental impact. However, studies involving failure modes in bonded joints of these structures are still minimal. This study presents crack propagation Resistance curves (R-curves) under Mode I loading using Double Cantilever Beam (DCB) tests according to ASTM D5528 and D3433, manufactured with castor oil polyurethane matrix as adhesive. Three configurations were evaluated: Metal Substrate Bonded Joints (MSBJ) with secondary bonding; jute fibre Composite Substrate Bonded Joints (CSBJ) also with secondary bonding; and Delamination Failure (DF) specimens, where the interface was generated during curing in a co-curing process. The Compliance-Based Beam Method (CBBM) for <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(G_{Ic}\)</EquationSource> </InlineEquation> was compared with J-integral <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(J_{Ic}\)</EquationSource> </InlineEquation> evaluation, as specimens may display inelastic response. Results revealed that the Fracture Process Zone (FPZ) was smaller for metallic substrates than for natural fibre composites. Fractographic analysis by Scanning Electron Microscopy (SEM) showed cohesive failure in all specimens. Despite sharing the same interface constituent, MSBJ and DF exhibited higher average critical SERR values (<InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(1.11\pm 0.23\)</EquationSource> </InlineEquation> and <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(1.12\pm 0.29\)</EquationSource> </InlineEquation> kJ/m<InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(^2\)</EquationSource> </InlineEquation>) compared to CSBJ (<InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(0.53\pm 0.13\)</EquationSource> </InlineEquation> <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(\mathrm{kJ/m}^2\)</EquationSource> </InlineEquation>) using CBBM. This work contributes to the development of bonded joints through a fully renewable composite system with both natural fibres and matrix under Mode I interlaminar fracture. Furthermore, comparison of data reduction schemes for R-curve values reinforces the methodology and provides experimental data applicable to numerical models for sustainable joints.</p>

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Mode I energy release rate for bio-based bonded joints using metallic and natural fibre substrates

  • 期刊论文

  • 发表日期：

    2026年2月11日

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  • Rudolf Kniess Ronchi,
  • Felipe Ruivo Fuga,
  • Carlos Vinícios Opelt,
  • Ricardo De Medeiros

摘要

In recent years, manufacturers have increasingly embraced sustainable practices by employing eco-friendly, recycled, and recyclable materials along with greener production processes. Adhesive bonding has become a preferred method for joining composites, as it forms strong joints without disrupting structural continuity, unlike fasteners such as rivets and screws that cause fibre-matrix discontinuities and stress concentrations. Aerospace and automotive industries have also begun integrating natural fibres due to their low weight, renewability, and reduced environmental impact. However, studies involving failure modes in bonded joints of these structures are still minimal. This study presents crack propagation Resistance curves (R-curves) under Mode I loading using Double Cantilever Beam (DCB) tests according to ASTM D5528 and D3433, manufactured with castor oil polyurethane matrix as adhesive. Three configurations were evaluated: Metal Substrate Bonded Joints (MSBJ) with secondary bonding; jute fibre Composite Substrate Bonded Joints (CSBJ) also with secondary bonding; and Delamination Failure (DF) specimens, where the interface was generated during curing in a co-curing process. The Compliance-Based Beam Method (CBBM) for \(G_{Ic}\) was compared with J-integral \(J_{Ic}\) evaluation, as specimens may display inelastic response. Results revealed that the Fracture Process Zone (FPZ) was smaller for metallic substrates than for natural fibre composites. Fractographic analysis by Scanning Electron Microscopy (SEM) showed cohesive failure in all specimens. Despite sharing the same interface constituent, MSBJ and DF exhibited higher average critical SERR values ( \(1.11\pm 0.23\) and \(1.12\pm 0.29\) kJ/m \(^2\) ) compared to CSBJ ( \(0.53\pm 0.13\) \(\mathrm{kJ/m}^2\) ) using CBBM. This work contributes to the development of bonded joints through a fully renewable composite system with both natural fibres and matrix under Mode I interlaminar fracture. Furthermore, comparison of data reduction schemes for R-curve values reinforces the methodology and provides experimental data applicable to numerical models for sustainable joints.