Associateship opportunity leads To understanding of composite materials, properties

  • Published
  • By Tim Anderl
  • Air Force Reserch Laboratory
WRIGHT-PATTERSON AIR FORCE BASE --  Although National Research Council (NRC) Associate Dr. Brent Volk imagined pursuing a career in academia following receipt of his PhD from Texas A&M in 2010, a chance meeting with an Air Force scientist turned into an opportunity Dr. Volk never before considered.

"I met Dr. Jeffery Baur at a conference in 2010 and we had a really good discussion about the research we were hoping to do in the future," Dr. Volk explained.

Dr. Baur, an NRC mentor and research leader from the Air Force Research Laboratory Materials and Manufacturing Directorate's Structural Materials Division, and Dr. Volk continued discussions following the conference and Dr. Baur suggested that an NRC project researching composite materials and properties could provide an opportunity for their continued collaboration. Dr. Volk arrived at AFRL to begin the project, "Three-Dimensional Modeling of Polymer Matrix Composites with Tailored Interfaces in Response to Fast Strain Rates and Extreme Temperature Gradients," in October 2012.

During his NRC tenure, Volk developed a computational framework to investigate the effects of modifying the interfacial region in carbon fiber/polymer matrix composites when exposed to large temperature gradients. It is expected that this modeling framework will allow scientists to predict the response of current composite materials, and help in the design of new composite materials.

"The new composite materials could possibly include tailored nanoscale interfaces," Dr. Volk said. "For example, those with carbon nanotubes between the polymer matrix and the fiber tows. Dependent on the desired application, we're predicting that tailoring the interface will provide tunable thermal conductivity and subsequently promote or delay the onset of ablation without penalty in the mechanical properties."

"In simple terms, we're developing a computational perspective on how composite materials will behave with different thermal gradients, and answering the question of whether the interface can help address various thermal challenges."

This research endeavor holds significance for Air Force applications, allowing scientists and engineers to improve the properties, strength and weight of materials, determine appropriate processing and manufacturing processes, and even predict how materials will behave during flight.

"There is also some applicability of this research in composite machining as well as in exploring the use of lasers for additive manufacturing of composites," Dr. Volk added.

Dr. Volk's research was executed in a multi-scale manner where the representative volume element ranged from a single 7.5um fiber in a polymer matrix to a plain-weave composite. Through an integrated computational materials science and engineering (ICMSE) approach, the research led to an experiment in which a single carbon fiber was embedded in a polymer resin, and resistively and laser heated to observe the effects of the interface region. According to Dr. Volk, ongoing computational efforts are aimed at predicting the effects of modifying the thickness, conductivity, and absorption coefficients of the interface region.

"At the plain-weave scale, I leveraged an AFRL-developed textile code, Virtual Textile Morphology Suite (VTMS), to create realistic, virtual microstructure by simulating the boundary conditions and compaction method used during the processing of the composite," Dr. Volk added. "By developing a Python code, the tows created in VTMS are translated into Abaqus, a commercially available finite element software, in which the polymer matrix unit cell is formed around the tow geometries and the thermomechanical loading conditions are simulated. The sensitivity of the resulting effective material properties on the tow dimensions highlights the necessity to have accurate computational microstructures when performing the thermomechanical finite element analyses.

"To better predict the final geometries of composite parts, I performed thermomechanical modeling to predict the residual stresses of the parts subjected to different cure cycles, thermomechanical boundary conditions, experimental calibrations and material models," he added.

Without the NRC associateship Dr. Volk admitted that he'd probably never have experienced AFRL. Today, his research on scientific and technological challenges that are relevant to national interests is a source of tremendous patriotism and pride, he said.

"I've had the benefit of working on multiple projects with collaborators from a broad range of backgrounds in support of a larger Integrated Product Team," Dr. Volk explained. "And having a mentor like Dr. Baur was also extremely rewarding. I could tell he had a vested interest in my success and future, and wanted to help me position myself for whatever I chose to do next."

Dr. Volk answered his "what next" question when he made the decision to become a government civilian with AFRL's Structural Materials Division in early 2014.