Effect of the Size of Polymer—Fiber Joints on the Change in Adhesive Strength under Various External Influences: Part 1. Scale Dependence of the Adhesive Strength of Fiber—Thermosetting Binder Joints under Normal Conditions

Abstract

An analysis of scale dependences of the force F required to shear the fiber relative to the polymer layer and the adhesive strength τ of fiber—thermosetting binder joints shows that a wide variation in the bond area S is possible only using fibers with a diameter d ≥ 100 μm; if d ≤ 10–15 μm, the F–S and τ–S dependences can currently only be measured for large bonding areas. Below the glass transition temperature of the adhesive pair components, with an increase in area S (in any system), the F–S dependence is described by a monotonically increasing curve tending to saturation, while the τ–S dependence is described by a monotonically nonlinearly decreasing curve. An analysis of τ–S curves allows us to introduce the concept of local adhesive strength as a characteristic of adhesive pair and to formulate the conditions for the failure of joints, as well as the conditions for constructing the composite strength—adhesive strength and binder strength—adhesive strength correlation curves.