Development of LaSAT and bonding strength evaluation of epoxy adhesive over a wide range of loading rates

ABSTRACT

This study improved laser shock-wave adhesion test (LaSAT) to evaluate the bonding strength of an aluminum alloy/epoxy resin adhesive, since the bonding strength is dependent on loading rate. In this method, strong shock wave due to laser ablation induces interfacial fracture, and the critical stress is computed using numerical simulations of the FEM. To accurately evaluate the bonding strength, the input waveform caused by laser ablation was identified for FEM computation. Such ablation impact (pressure vs. time) and its spatial distribution of ablation impact were experimentally investigated, and this study computed stress-wave propagation in the specimen. It is found that numerical simulation with FEM reproduced well the wave propagation. A wide range of loading rates was achieved by the quasi-static tensile test, split Hopkinson pressure bar (SHPB) test, and LaSAT. As a result, bonding strength exhibited a significant dependence on the strain rate, similar to that of bulk resin materials in general.

KEYWORDS:

• Laser shock-wave adhesion test (LaSAT)
• bonding strength
• epoxy resin adhesive
• loading rate dependency
• split Hopkinson pressure bar (SHPB) test

Acknowledgments

This work is supported by JSPS KAKENHI (grant no. 21H01217) from the Japan Society for the Promotion of Science.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Highlights

1. Bonding strength of an epoxy adhesive under several loading (strain) rates was evaluated.

2. A wide range of strain rates (10⁻³ to 10⁶ s⁻¹) can be achieved using the quasi-static tensile test, split Hopkinson pressure bar test, and laser shock-wave adhesion test.

3. To accurately evaluate bonding strength using LaSAT, an input waveform caused by laser ablation was identified for FEM.

4. Comparison of the LaSAT experiment and numerical simulation with FEM revealed reproducible wave propagation.

5. The thermally cured specimen exhibited a higher bonding strength than the room-temperature-cured specimen.

6. The effect of thermal curing on bonding was observed at wide loading rates.

Additional information

Funding

The work was supported by the Japan Society for the Promotion of Science [21H01217].