Mode I fracture of beech-adhesive bondline at three different temperatures

Single edge-notched three-point bending tests (SEN-TPB) for mode I were utilized to experimentally evaluate fracture properties of adhesive bondlines in European beech (Fagus Sylvatica L.). The bondline was examined at two anatomical planes with TR and RT orientation and at control and two elevated temperatures (70 degrees C and 140 degrees C). Among epoxy (EPI), melamine-urea formaldehyde (MUF), and polyurethane (PUR) adhesives, the highest average critical energy G(c) with 0.80 N/mm and fracture energy G(f) with 1079.4 N/mm were obtained for EPI in the TR plane and under standard climate conditions (20 degrees C/65% relative humidity), followed by MUF (G(c) = 0.50 N/mm and G(f) = 620 N/mm) and PUR (G(c) = 0.25 N/mm and G(f) = 290.9 N/mm), respectively. PUR was least effected by elevated temperature, and no significant differences for G(c) and G(f) between TR and RT bondline orientations were found for MUF and PUR treated at 20 degrees C/65% relative humidity while comparisons between other factors varied significantly. Treatment of specimens at elevated temperatures resulted in reduced fracture performance regardless of wood grain orientation or the adhesive system.

Automated summary

Single edge-notched three-point bending tests were used to evaluate the fracture properties of adhesive bondlines in European beech. The results showed that epoxy adhesive had the highest fracture performance under standard climate conditions, and elevated temperatures resulted in reduced fracture performance.