Tensile strength, also known as uniform separation strength or normal tensile strength, refers to the tensile force per unit area that an adhesive can withstand when it fails under tensile stress. Its unit is expressed in megapascals (MPa).
Since the stress distribution under tension is much more uniform than that under shear, the tensile strength of most adhesives is significantly higher than their shear strength. In actual testing, when the specimen is subjected to external forces, the adhesive tends to deform more than the adherend. Additionally, due to the eccentricity (misalignment) of the applied external force, shear stress is likely to occur, and transverse compression may also arise. Therefore, mixed-mode failure (simultaneous occurrence of multiple failure modes) may happen when the specimen breaks.
If the length of the specimen is increased and the bonded area is reduced, the impact of peeling during breakage can be minimized, resulting in more uniform stress distribution. The effects of elastic modulus, adhesive layer thickness, test temperature, and loading rate on tensile strength are basically similar to their effects on shear strength.