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CATHODIC DELAMINATION AT POLYMER/METAL INTERFACES

Kenneth Liechti (), Thomas Mauchien (UT Austin)

Crack initiation and growth: methods, applications, and challenges

Tue 4:20 - 5:40

Sayles Auditorium

The overall objective of this work is to establish the feasibility of modeling the cathodic delamination problem in polymer coated submarine components with a view to developing a more accurate testing standard for Accelerated Life Testing (ALT) and to determining the effectiveness of new approaches for combating cathodic delamination in a quantitative manner. The resistance to cathodic delamination is characterized using a fracture mechanics approach whereby the crack growth rate from a suitably designed specimen is plotted against the corresponding energy release rate, which is viewed as the driving force for cathodic delamination. From a fracture mechanics perspective, cathodic delamination is viewed as environmentally assisted crack growth so that the importance of factors such as galvanic potential, applied electrical potential, transducer materials, elastomeric materials, priming agents, non-conductive coatings, etc. can be considered as well as environmental conditions including temperature, dissolved oxygen level, pH levels, salinity, etc. The paper first describes the mechanical characterization of the polyurea as a nonlinearly viscoelastic material. This is followed by a fracture analysis to characterize the variation of energy release rate with crack length in a strip blister configuration. Cathodic delamination experiments with polyurea on titanium and steel with two different surface treatments (PR-420 and plasma polymerization) were conducted at a series of temperatures. The resulting resistance curves indicated that the polyurea/PR-420/titanium interface had the highest resistance to delamination and temperature accelerated cathodic delamination. Surface analyses are currently underway with a view to providing insights into delamination mechanisms.