WATER DIFFUSION IN DOUBLE CANTILEVER BEAM ADHESIVE JOINTS

Abstract

STRUCTURAL ADHESIVES ARE INCREASINGLY BEING USED IN THE AEROSPACE AND AUTOMOTIVE INDUSTRIES. THEY ALLOW FOR LIGHT WEIGHT VEHICLES, FUEL SAVINGS AND REDUCED EMISSIONS. HOWEVER, THE ENVIRONMENTAL DEG-RADATION OF ADHESIVE JOINTS IS A MAJOR SETBACK IN ITS WIDE IMPLEMEN-TATION. MOISTURE DEGRADATION OF ADHESIVE JOINTS INCLUDES PLASTICIZA-TION, ATTACKING OF THE INTERFACE, SWELLING OF THE ADHESIVE AND CONSE-QUENT CREATION OF RESIDUAL STRESSES. THIS MAY LEAD TO REVERSIBLE AND IRREVERSIBLE DAMAGE. IN THIS WORK DOUBLE CANTILEVER BEAM (DCB) SPECIMENS USING TWO DIFFERENT ADHESIVES FOR THE AUTOMOTIVE INDUSTRY WERE SUBJECTED TO TWO DIFFERENT AGEING ENVIRONMENTS. THEY WERE TESTED PERIODICALLY UNTIL THE TOUGHNESS OF THE ADHESIVES STABILIZED, WHICH MEANS THAT THEY WERE FULLY DEGRADED. AN ASSOCIATION WAS MADE BETWEEN THE TOUGHNESS OF THE ADHESIVE AND THE AMOUNT OF WATER THAT IT HAD ABSORBED. THIS WAY IT WAS POSSIBLE TO INDIRECTLY MEASURE THE WATER UPTAKE IN AN ADHESIVE JOINT TAKING INTO ACCOUNT THE WATER UPTAKE PROPERTIES OF THE ADHESIVES STUDIED, WHICH HAD BEEN DETERMINED IN ANOTHER STUDY. IT WAS FOUND THAT DIFFUSION OF WATER INTO THE STUDIED ADHESIVE JOINTS WAS FASTER THAN DIFFUSION THROUGH THE BULK ADHESIVE ALONE. A MODEL THAT TAKES INTO ACCOUNT DIFFUSION THROUGH THE INTERFACE BETWEEN THE ADHESIVE AND THE ADHERENDS WAS PROPOSED.