Practical Adhesion Measurement in Adhering Systems: A Phase Boundary Sensitive Test

Abstract

The strength of adhesive bonds is assessed by means of mechanical tests in which an increasing load is applied until failure occurs. This paper describes a three point flexure test using a single adherend/adhesive structure. Contrary to what occurs with usual tests such as single or double lap shear and peel tests, this configuration is sensitive to the adherend surface chemistry variations and adhesive cure conditions and thus allows evaluation of the properties of the adhesive bond joint interphase. Data are presented which demonstrate the flexure test sensitivity to the effects of surface prebonding treatments on interphasial mechanical properties, such as rigidity modulus. Photoelastic isochromatic fringes are recorded simultaneously with flexure test data as a means to monitor stress distribution, failure initiation and crack propagation. This test shows that the stresses are uniformly distributed along the specimen length and remain parallel to the interfacial region and insure failure totally along the adherend/adhesive interface.