Influences of Loading Rates on Stress-Strain Relations of Cured Bulks of Brittle and Ductile Adhesives

Influences of loading rates on the stress-strain relations of cured adhesive were experimentally investigated. A brittle epoxy adhesive and a ductile epoxy adhesive modified with rubber particles were examined. Concave specimens of the cured adhesives were made, and strain gages for very large strain were bonded on the specimens. The specimens were tested in static conditions with a material testing machine and in dynamic condition with a drop-weight impact testing machine. The influences of loading rates on the stress-strain relations of the adhesives were identified. For the brittle adhesive, the modulus was constant in both the static and dynamic conditions, and the tensile strength and total strain increased with the increase of loading rates. For the ductile adhesive, large plastic deformation occurred in the static condition, and the tensile strength was 37 MPa and the total strain was 14%. In contrast, in the condition of high loading rate, the ductile adhesive became brittle, and the ultimate stress increased and the maximum strain decreased.