In recent years, the composites industry has experienced a major shift from autoclave to out-of-autoclave (OoA) processing methods. This shift has been motivated by the high capital and operating costs of autoclaves as well as the long cycle times. As the demand for composites in commercial aircraft increases, autoclave processing will not be able to satisfy the required production rates. While there are advantages to OoA processing, a major disadvantage is the increased susceptibility to defect formation due to the absence of compaction pressure provided by an autoclave. Therefore, one major focus of the M. C. Gill Composites Center is defect reduction in composite parts made from OoA prepregs. The Composites Center has access to a wide variety of characterization, fabrication and processing techniques that enable comprehensive analysis of OoA prepregs. Our efforts have led to new insights into defect sources and mitigation strategies. Recent contributions to this field are noted below.
As exemplified by wind turbine blades and components of oil platforms, the use of polymers and polymer composites for civil infrastructure is accelerating. In such applications, long-term durability is critical, as structures are generally expected to provide decades of service with minimal inspection or maintenance. Understanding the effects of aging on the mechanical performance of polymers and polymer composites are essential to mitigation strategies as well as lifetime prediction. The M. C. Gill Composites Center at USC has been actively studying the effects of exposure to aging environments on the mechanical and thermal properties of composite materials. Studies have focused on thermal, oxidative, hygrothermal, and radiation aging effects. Research from this topic has led to several publications in the leading journals of the field; the most recent papers are listed below.
The performance of conventional materials can be enhanced by introducing nano-sized reinforcing phases. This reinforcing phase can be in the form of particles (ceramic particles), sheets (e.g. graphene microsheets), or fibers (e.g. carbon nanotubes). Understanding the mechanism responsible for improved mechanical properties is crucial to further development of processing techniques and improvement of properties. The M.C. Gill Composites Center at USC has extensive experience in studying different aspects of nano-composites, including correlating processing parameters with mechanical properties of such materials. Our group has worked with a range of nano-inclusions, including carbon nanotubes, graphene, and nano-structured aluminum alloys. Below are some of our group’s publications, presenting our recent contributions to the field.
Sandwich structures, consisting of two (frequently composite) face sheets bonded on either side of a low-density core material, display excellent out-of-plane compression and shear properties with very low areal density. For this reason, composite sandwich structures have long appealed to the aerospace industry for use in weight-critical applications. The M.C. Gill Composites Center at USC has experience in studying how material selection, structural design, and manufacturing process parameters affect the mechanical performance of composite sandwich structures. In addition to introducing and characterizing novel core materials, our recent work includes characterizing and predicting quasi-static, dynamic, and vibroacoustic properties as a function of constituent element material properties. Below are some of our group’s most recent publications, describing our contributions to this field.
Creating a material that is lightweight and yet strong is the ultimate goal of many material scientists. Lightweight metals such as aluminum, magnesium, titanium and their alloys are light and tough, resulting in extensive adoption for widespread use in aerospace, automobile, and other industries. The M.C. Gill Composites Center at USC has a broad background in exploring and developing novel processing techniques and unique microstructures for such materials. Two highlights are manufacturing and production of aluminum and syntactic steel foams. Research from this topic has led to publications in the leading journals of the field; the most recent papers are listed below.
High temperature composites and liquid molding
Carbon fiber composites are increasingly used in high-temperature applications, driving the development of new resin systems such as benzoxazines and polyimides. These resins can be used to fabricate fan blades, ducts, or casings for jet and rocket engines, where service temperatures can reach several hundred degrees Celsius. Manufacturing techniques include compression molding and resin transfer molding (RTM). Due to the complex chemistry of these resins, the processing is significantly more challenging than for traditional epoxies. Research at the M.C. Gill Composites Center focuses on comprehensive materials characterization and the development of optimized manufacturing procedures. Through a combination of experiments and modeling, we demonstrate defect formation mechanisms and prevention strategies, and establish process windows and manufacturing guidelines as deliverables for our industrial sponsors.
Acoustics and vibration of composites
Traditionally, strategies for reducing the acoustic energy transmission have fundamentally relied on the principles underlying the Acoustic Mass Law. This law states that transmission loss in a theoretic infinite barrier with zero stiffness is directly proportional to both the frequency of the sound transmitted and aerial density of the acoustic barrier. For weight critical applications, strategies that rely on this principle are untenable. The M.C. Gill Composites Center at USC has recently been investigating alternative strategies for acoustic transmission mitigation including. One such strategy uses an array of membrane-type acoustic metamaterials as an acoustic barrier for narrow-band low-frequency acoustic rejection. We also have experience optimizing the acoustic transmission properties of sandwich structures through the design of a novel core material. The Composite Center boasts significant experience in fabricating, experimentally characterizing, and modeling (analytic and finite element) these structures to determine and improve their vibroacoustic performance. Below are some of our group’s most recent publications, presenting our recent contributions to this field.
Mechanical behavior and failure analysis
The composites industry is always looking to develop novel resin systems and fabric architectures to push the limits of various performance metrics; but before composites incorporating new material systems or processing techniques are deployed, it is important to have a full and reliable understanding of their mechanical properties. Additionally, a complementary understanding of failure mechanisms can inform designers of how to avoid the loading conditions under which failure can be anticipated. The M. C. Gill Composites Center has made considerable investments in developing and maintaining the infrastructure necessary for a full battery of mechanical tests. Our facilities boast four load frames and an impact drop tower, allowing us to conduct quasi-static, dynamic, and fatigue testing. Additional analysis can be conducted using the available light and electron microscopes. Below are some of our group’s most recent publications, highlighting work in which our mechanical testing infrastructure was integral.
Because the study of composite materials requires a cross-disciplinary perspective as well as a wide array of laboratory instrumentation, we recruit members from diverse backgrounds—including physics, chemical engineering, mechanical engineering, and, of course, materials science. This diversity in our infrastructure and the technical breadth of our staff puts us in the unique position to take on a broad range of projects sometimes only tangentially related to our primary areas of focus. Below are our recent publications that reflect that diversity of backgrounds and training.
- J-250 “Adhesion of metallic glass and epoxy in composite-metal bonding”, L. Hamill, and S. Nutt, Composites B (2018) (Download from USC Composites or ScienceDirect)
- J-249 “Galvanic corrosion resistant fiber metallaminates of metallic glass and carbon fiber composites”, L. Hamill, D. Hofmann, and S. Nutt, Adv Engrg Matls (2017) (Download from USC Composites or Wiley)
- J-248 “Chemical Treatment for Dissolution of Amine-Cured Epoxies at Atmospheric Pressure”, Y. Ma, D. Kim, and S. Nutt, PolymDegrad Stab(2017) (Download from USC Composites or ScienceDirect)
- J-246 “Mean Field Homogenization Methods for Strand Composites”, A. Jain, B. Jin,and S. Nutt, Composites B 124 31-39(2017) (Download from USC Composites or ScienceDirect)
- J-237 “Assembly of layered monetite-chitosan nanocomposite and its transition to organized hydroxyapatite: An alternative to bone substitute material”J. Moradian-Oldak,Q.Ruan, D. Liberman, Y. Zhang, D. Ren, Y. Zhang, and S. Nutt, ACS Biomaterials Sci & Engrg 2 1049-58(2016)(Download from USC Composites or ACS)
- J-236 “Amelogenin affects brushite crystal morphology and promotes its phase transformation to monetite” Ren, Dongni;Ruan, Qichao; Tao, Jinhui;Lo, Jonathan;Nutt, Steven;Moradian-Oldak,Janet. Crystal Growth & Design Aug 164981-90 (2016)(Download from USC Composites or Wiley)
- J-234 “All-printed Strain Sensors:Builidng Blocks of the Aircraft Structural Health Monitoring System” Y. Zhang, N. Anderson, S. Bland,S. Nutt, G. Jursich, and Shiv. Hoshi, Sensors and Actuators A, Oct(2016) (Download from USC Composites or ScienceDirect )
- J-233 “The effects of heat treatment on 7075 Al cold spray deposits” M.R. Rokni, C.A. Widener, V.K. Champagne, and S.R. Nutt, Surf Coatings&Tech, Oct (2016)(Download from USC Composites or ScienceDirect) )
- J-229 “The Effect of Processing Parameters on Volatile Release for a Benzoxazine/Epoxy Blended RTM Resin; J. Lo, M. Anders, T. Centea, and S.R. Nutt, Compos. A Feb (2016) (Download from USC Composites or ScienceDirect )
- J-227 “Thermosetting Polymer Based Flexible Synthetic Cement for Successful Zonal Isolation in Thermal Wells-A New Approach” R. Shanbhag, Z. Melrose, S.R. Nutt,M.Cleveland,and R.Keese, Soc Petrol Engrs July(2015)(Download from USC Composites or Soc Petrol Engrs )
- J-225 “Two-Step SPD Processing of a Trimodal Al-Based Nanocomposite”Yuzheng Zhang, S Sabbaghianrad, H. Yang, T.D. Topping, T.G. Langdon, E.J. Lavernia, J.M. Schoenung, and S.R. Nutt, Metall Trans Sept (2015) (Download from USC Composites or Springer)
- J-215 “Amelogenin-Chitosan Matrix for Human Enamel Regrowth: Effects of viscosity and Supersaturation Degree” Q. Ruan, N. Siddiqah, X. Li, S. Nutt, and J. Oldak, Connective Tissue Research, 55 [S1] 150-154 (2014) (Download from USC Composites or Taylor & Francis Online)
- J-211 “Bio-Inspired Impact Resistant Composites” L. Grunenfelder, N. Suksangpanya, C. Slinas, G. Milliron, N. Yaraghi, S. Herrera, I. Evans-Lutterodt, S.R. Nutt, P. Zavattieri, D. Kisailus, Acta Biomaterialia Apr (2014). (Download fromUSC Composites or ScienceDirect)
- J-210 “Effects of Fabric Target Shape and Size on the V50 Ballistic Impact Response of Soft Body Armor Composite Structures” G. Nilakantan and S. Nutt, Compos. Structures 116 661-669(2014) (Download from USC Compositesor ScienceDirect)
- J-208 “Poly(phenylene oxide) modified cyanate ester resin for self-healing” L. Yuan, S. Huang, Y. Hu, A. Gu, G. Liang, G Chen, Y Gao, and, S. Nutt, Polymers for Advanced Technologies (2104) (Download from USC Composites or Wiley)
- J-206 “Effects of Clamping Design on the Ballistic Impact Response of Soft Body Armor” G. Nilakantan and S. Nutt, Compos Structures 108 137-50 (2014) (Download from USC Composites or ScienceDirect)
- J-204 “Blends of Polystyrene and Poly (n-Butyl Methacrylate) Mediated by Perfluorocarbon End Groups” Jingguo Shen, Victoria A. Piunova, Steven Nutt and Thieo E. Hogen-Esch, Polymer 215790-5800 (2013) (Download from USC Composites or ScienceDirect)
- J-203 “Synthesis of poly(urea-formaldehyde) encapsulated dibutyltin dilaurate through the self-catalysis of core materials” L. Yuan, F. Chen, A. Gu, G. Liang, C. Lin, S. Huang, and S. Nutt, Polymer Bulletin Sept (2013) (Download from USC Composites or Springer)
- J-202 “A cyanate ester/microcapsule system with low cure temperature and self-healing” L. Yuan, S. Huang, A. Gu, G. Liang, F. Chen, Y. Hui, and S. Nutt, Compos Sci & Tech 87 (2013) 111-117 (Download from USC Composites or ScienceDirect)
- J-201 “Hypervelocity Impact of Bulk Metallic Glasses and Composites” L. Hamill, S. Roberts, M. Davidson, W.L. Johnson, S. Nutt, and D.C. Hofmann, Adv. Engrg. Matls, 15  1-9 (2013) (Download from USC Composites or Wiley)
- J-197 “An Amelogenin-Chitosan promotes assembly of an enamel-like layer with a dense interface” Q Ruan, Y Zhang, X Yang, S Nutt, and J Moradian-Oldak, Acta Biomaterialia, 9 (2013) 7789-7297 (Download from USC Composites or ScienceDirect)
- J-189 “Investigating Amorphous Metal Composite Architectures as Spacecraft Shielding” M Davidson, S Roberts, G Castro, RP Dillon, A Kunz, H Kozachkov, MD Demetriou, WL Johnson, S Nutt, DC Hofmann, Adv Engrg Matls (2012) (Download from USC Composites or Wiley)
- J-185 “Novel polytphenylene oxide microcapsules filled with epoxy resins” L. Yuan, A Gu, S. Nutt, J. Wu, C. Lin, F. Chen, and G. Liang, Polymers Adv. Tech. 24  81-89 (2012)(Download from USC Composites or Wiley)
- J-175 “Moisture Absorption in Unidirectional Hybrid Composites” E. Barjasteh and S.R. Nutt, Compos. A, 43  (2012) 158-164 (Download from USC Composites or ScienceDirect)
- J-174 “Multifunctional Superhydrophobic Composite Films from a Synergistic Self-Organization Process” H. Lu, and M. Fang, Z. Tang, and S. Nutt J. Mater. Chem. 22 (2012) 109-114. (Download from USC Composites or RSC)