Using Micromechanics, Chemistry, Image Analyses, and Modeling to Better Understand Failure in Reinforced Composites

Date & Time: 
Thu, 04/26/2018 - 11:30am
Gale A. Holmes
Materials Science and Engineering Division, NIST
Discovery Park F175

Challenges that impede the wide spread use of fiber reinforced composites in structural applications are optimization of mechanical performance and structural integrity. Given the multi-phase morphology of composites, the interface/interphase (I/I) formed between the fiber and matrix during manufacturing is the controlling feature. The I/I region includes all the volume altered during the fabrication process and reflects the unique chemical composition that creates the adhesive forces between the matrix and fiber. Much has been learned about the I/I during the past 50 years. However, understanding the composition and properties of this region and its relationship to fracture toughness, strength, and stiffness in various failure modes and loading configurations is still an evolving interdisciplinary research topic.

In this presentation three facets of this complex problem will be discussed. These features must be understood to better link the microstructure-property relationships in the I/I region. They are as follows:

  1. The role of reaction kinetics on covalent bond formation in the I/I region of epoxy/amine glass fiber composites and its impact on fiber-fracture morphology.
  2. The use of stress activated mechanophores to probe fiber fracture dynamics and the impact of the stress redistribution process on damage formation.
  3. The role of matrix morphology and fiber-fiber interactions on damage accumulation and time dependent failure in glass fiber composites.

Gale Holmes received a B.S. degree in chemistry from the University of Texas @ Austin in May 1977. He then worked for the Dow Chemical Co in Freeport, Texas as an analytical chemist for 12 years. In August 1989 he left Dow for Texas A&M University to pursue a Ph.D. in Mechanical Engineering. After graduation in August 1994, he was briefly employed at Federal Mogul in Ann Arbor, Michigan before accepting a research position in April 1995 with the National Institute of Standards and Technology. He was the vice-chair and chair of the Gordon Research Conference (GRC) on Composites in 2008 and 2010, respectively. He has received two Department of Commerce Gold Medals (2007, 2010) for his work of the Electronic Passport and Soft Body Armor (SBA). His research interests are ballistic fibers, nano-tailored multi-functional materials, embedded interfaces, composite micromechanics, and time-dependent relaxation phenomena in polymeric systems. On March 16, 2018, it was published that the SBA research helped the Department of Justice secure a $66 million settlement with Toyobo and its U.S. subsidiary for knowingly selling defective body armor to the U.S. government.