Repeatable and controllable notch and pre-crack sharpening via continuous-wave laser for fracture toughness of epoxy resin/MWCNTs nanocomposites: Fabrication, preparation, and characterization

In this work, a repeatable, controllable, non-contact, cost-effective, and fast method of producing notches and pre-cracks for the accurate measurement of the fracture toughness test of epoxy resin composites is suggested. The fabrication of the notches and pre-cracks for the fracture toughness test of a 5052-epoxy resin and 5052epoxy resin/0.1, 0.5, and 1.0 wt% MWCNTs nanocomposites were done using a steel razor blade method and a laser ablation method. A continuous-wave CO2 laser with a power of 150 W, a wavelength of 1064 nm, a spot size of 100 mu m for the Gaussian beam, and a focusing distance of 50 mm in atmospheric conditions was applied. The fracture toughness results of the laser ablation and the steel razor blade methods were compared. The created notches and sharp pre-cracks had the highest accuracy and reproducibility with no plastic deformation ahead of the pre-cracking tip compared to other similar investigations. The radius of the pre-cracking tips in the as-prepared samples with the laser method was less than approximately 5 mu m. The average values of the fracture toughness of an epoxy resin and epoxy resin/0.1, 0.5, and 1.0 wt% MWCNTs nanocomposites with sharpened pre-cracks produced by the laser method were 0.826 +/- 0.005, 1.10 +/- 0.025, 1.23 +/- 0.025, and 1.09 +/- 0.015 MPa m1/2, respectively. The obtained fracture toughness values of the laser method were repeatable with an error accuracy of less than +/- 0.005 and corresponded to the ISO and ASTM standards.

Automated summary

This work proposes a repeatable, controllable, non-contact, cost-effective, and fast method for measuring the fracture toughness of epoxy resin composites. The notches and pre-cracks for the fracture toughness test were fabricated using a steel razor blade method and a laser ablation method. The results of the laser ablation method were found to have the highest accuracy and reproducibility, with pre-cracking tips that exhibited no plastic deformation. The fracture toughness values obtained by the laser method were in accordance with ISO and ASTM standards, demonstrating their repeatability and accuracy.