Mark S. Oliver Ph.D. Candidate Department of Materials Science and Engineering Stanford University Phone: 650-723-3268 Office: Durand Bldg., Rm. 165 Email: markoliver@stanford.edu

Educational Background

Research

Reliability of Adhesive Interphases in Titanium Graphite Laminates

Structural composite laminates now often consist of both fiber-reinforced polymer and metallic plies.  These hybrid materials are generally referred to as fiber metal laminates (FMLs).  Combining metallic and polymeric materials gives these hybrid laminates many unique physical and mechanical properties that make them especially well suited for use in aerospace structures.  FMLs made of aluminum and either glass or aramid fibers are currently used in the fabrication of aerospace structures.  However, aluminum posses poor high-temperature properties and is not compatible with carbon fiber due to galvanic corrosion.  Thus, there is considerable interest in using titanium-graphite (TiGr) laminates, which consist of titanium alloy foil and a carbon (graphite) fiber reinforced polymer (CFRP).

Many studies of damage in TiGr laminates have identified delamination between the titanium and CFRP layers as a dominant mode of laminate failure.  To address this issue, current state-of-the-art laminates possess complex interphases between the metal and CFRP plies that are engineered to form strong and durable bond.  A schematic of this interphase in shown below.  It consists of a metal oxide layer, a nanostructured metal/silane sol-gel coupling layer (see section below) and a thin structural adhesive film.  Despite the vast improvements in interlaminar adhesion since the inception of TiGr laminates, there are still serious concerns regarding interlaminar reliability, particularly in harsh environmental conditions.

                    Schematic of Hierarchical Layered Structure of TiGr Laminate Interphases

Our research is focused of improving the reliability of adhesive interphases for titanium graphite laminates by investigating the micro and nanoscale mechanisms of interphase degradation and failure.  Our experimental efforts include measuring the resistance of the entire interphase to delamination under a range of loading and environmental conditions as well as using a novel approach to directly measure the adhesion-promoting properties of the sol-gel coupling layer.    

Metal/Epoxysilane Sol-Gel Coupling Layers

Much remains unknown regarding the fundamental processing-nanostructure-property relationships that govern the performance and reliability of the sol-gel layer used to couple the titanium and epoxy resin interface in state-of-the-art TiGr laminates (discussed above).  This aspect of our research is focused on developing an improved understanding of these relationships.  Our motivations are to improve the reliability of TiGr laminate interphases as well as to develop new coupling layers for use in a wide range of technologies where metal oxide/resin adhesion is critical.

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