Service Life of Nano-enabled Fiber-Reinforced Polymer (NeFRP) Composites Project

This project will develop measurement science to support the development of industry consensus standards for service life prediction of nano-enabled fiber-reinforced polymer  (NeFRP) composites.  Products or industries that will significantly benefit from developments in this area include next-generation composites for manufacturing and infrastructure applications. Predictive models will be developed and validated from improved measurements of performance under interacting environmental stresses such as moisture, temperature, stress, and electrical fields.

Objective: To develop measurement science to support service life prediction of nano-enabled fiber-reinforced polymeric (NeFRP) composites used in manufacturing and infrastructure systems, by FY2015.

What is the new technical idea? The new technical idea is the development and delivery of measurement science and models for service life prediction of nano-enabled fiber-reinforced polymer (NeFRP) structural composites for use in manufacturing and civil infrastructure applications. A NeFRP composite has properties that have been engineered utilizing nano-sized materials to impart multifunctional capabilities such as electrical conductivity, toughness, and reduced environmental impact. These composites have recently emerged as candidate materials for reducing fuel consumption and emissions in conventionally powered vehicles, electric and hybrid vehicles, and commercial aircraft. They not only provide significant strength to weight ratio improvements for vehicle lightweighting, but they impart significant additional functionality such as electrical conductivity and increased barrier properties. Similar high performance, lightweight composite materials and components are critically needed for new construction, repair of existing infrastructure and buildings, and for use in alternative energy technologies such as wind turbines. Often these materials offer superior performance compared to traditional materials, but questions of long term performance present a barrier to more widespread use. The lack of science-based service life prediction tools and standards to quantitatively predict the long-term performance of these advanced materials reduces the ability of customers to quantify the lifetime cost of investing in NeFRP technologies.

External drivers motivating the development of advanced materials for infrastructure and vehicles include (1) the Administration’s Blueprint for a Clean Energy Future^[1], which calls for the development of more efficient cars and trucks by making investments in advanced technologies for vehicles, and (2) the 2008 GAO Report on Physical Infrastructure: Challenges and Investment Options for the Nation's Infrastructure^[2], which specifically call out improving surface transportation and aviation systems as serious infrastructure challenges facing the U.S.

In an advanced structural composite, the fibers (carbon or glass) are the primary load-bearing component and are typically 50 times stronger and 20-150 times stiffer than the matrix polymers. The matrix polymers serve as a binder to maintain the desired fiber orientations and spacings, transmit loads into the fibers, transmit shear loads between fiber plies, and protect the fibers from surface damage and environmental effects. In spite of the important role that the matrix polymer plays, the failure- and temperature-limiting component of advanced composites is the polymer matrix, which tends to have low fracture toughness and is susceptible to weathering effects from UV, temperature, and moisture. The rapid development of nano-manufacturing is providing the impetus for significant improvement in the mechanical and physical properties of conventional FRP materials. A recent approach used to enhance the physical and mechanical properties of the polymer matrix and provide improved composite interlaminar properties involves the addition of nano-sized structure to the surface of reinforcement fibers. Other strategies include the incorporation of engineered nanofillers, such as carbon nanotubes, carbon nanofibers, graphene, cellulose nanofibers, and layered silicates, to the composite matrix system. These NeFRP composites combine the advantages of both fiber-reinforced structural composites and polymer nanocomposites to produce novel materials with improved fracture performance and additional functionalities such as barrier properties, superior electrical conductivity, reduced waste stream constituents, and fire resistance.

However, in a workshop hosted by NIST/CNST entitled “The New Steel?  Enabling the Carbon Nanomaterials Revolution:  Markets, Metrology and Scale-Up”^[3], workshop participants, representing the full spectrum of companies engaged in carbon nanomaterial manufacturing, component production and integration, cited that one of the three significant technical barriers to the widespread implementation of these materials was uncertainty surrounding their lifetime performance. Durability and service life is a critical concern for polymer composites in general, and especially in the extreme environments encountered in aerospace, marine, and space applications.^[4]

NeFRP represents a novel class of engineered materials whose enhanced performance (electrical, mechanical, chemical) is derived from the interaction of engineered nanostructures with both fillers and matrix. This interaction will change with time as the NeFRP degrades from environmental exposure, with the degradation process affecting different performance parameters at different rates. For example, a composite may retain strength and fracture toughness, but electrical conductivity could drop precipitously.  This could lead to  catastrophic failure for a coating that served as the strength and conductive pathway for an airplane wing or windmill airfoil. Stakeholders require new models and test methods to account for the complicated long term performance window of these materials. The development of quantitative service life prediction for NeFRPs is solidly based on the existing polymer composite expertise of the Sustainable Engineered Materials Program.

What is the research plan? The proposed research plan involves three primary thrusts to deliver service life prediction models and measurements for NeFRP:

1. Development of measurement science to characterize the interfacial and bulk mechanical properties of NeFRP composites. We will collaborate with the CNST team that is leading a SERI project on Carbon Nanocomposite Manufacturing: Processing, Properties, Performance (Alex Liddle, team leader) whose goal is to allow stakeholders to engineer composite performance by controlling nanotube growth from the fibers through process quality control during the manufacturing process. The SERI project will develop online microwave characterization of nanotubes grown from glass or carbon fibers and link this measurement to NeFRP composite electrical performance. The SERI team will utilize nanoscale material property characterization via electron microscopy, nanoscale Raman measurements, microwave technique development, and physical models linking nanotube microstructure to electrical conductivity. Mechanical property characterization before and after material degradation is crucial for understanding long term performance and service life prediction but was not within the scope of the original SERI project EL researchers will therefore coordinate mechanical property characterization of NeFRP materials created during the nanomanufacturing process. This characterization will focus on bulk and interfacial property measurements.

   The bulk mechanical properties of NeFRP composites as a function of nanotube microstructure will be characterized through quasi-static tensile, shear, and compression measurements. Interfacial measurements will be characterized at small strain using dynamic mechanical measurements. The interlaminar shear strength will be used to characterize large strain properties in both quasi-static and fatigue environments. The locus of failure (interfacial or within matrix) will be determined through optical and electron microscopy.

2. Characterization of NeFRP durability and service under environmental exposures involving ultraviolet radiation, temperature, moisture, and mechanical loading and service life prediction models. EL researchers will facilitate development of service life prediction models for NeFRP composites by engaging with the SERI team to develop protocols and measurements that enable modeling and prediction of the long-term performance of these materials.  These protocols and measurements will be based on the mechanical property characterization mentioned above and will be conducted in parallel with SERI team measurements using electron microscopy, Raman, and microwave techniques as a function of accelerated exposure conditions.

   Environmental exposure of NeFRP will be carried out on the NIST SPHERE (Simulated Photodegradation via High Energy Radiant Exposure) weathering device, and the morphology and mechanical properties of the selected materials will be assessed as a function of material processing parameters, temperature, relative humidity, and ultraviolet radiation. The capability of nanotube systems to photocatalyze degradation under UV radiation will be determined through electron paramagnetic resonance measurements. In FY 13, the focus will be on identifying preliminary primary modes of failure in preparation for more focused studies in FY 14 and FY 15.

3. Identification of measurement science and standards needs for NeFRP service life prediction. While the SERI project represents an opportunity to engage in service life prediction deliverables in a NIST-wide collaborative effort, it is specific to one NeFRP technology. There are significant efforts involving graphene, silicate-based fillers, and nanocellulose fibers for use in engineered multi-functional composites. Service life prediction problems remain, but must be better defined by stakeholders in terms of national importance, cost reduction, and enhanced performance potential. This third thrust will enable the Sustainable Engineered Materials program to identify the critical measurement science needs that are applicable to the long-term performance aspects of NeFRP and supportive of the current program deliverables.

   A NIST workshop on service life prediction measurement science and standards needs for NeFRP composites will be held to develop interactions with industrial and government stakeholders. The workshop will hold focused discussions with representatives of target sectors – automotive, aerospace, civil infrastructure (bridges, pipes, wind turbines), and manufacturing. The workshop will expand on the roadmap developed in conjunction with the SERI effort to identify stakeholders and stakeholder needs beyond carbon fiber based NeFRP technologies.

[1] Blueprint For a Clean Energy Future, http://www.whitehouse.gov/sites/default/files/blueprint_secure_energy_future.pdf; examples include 80% of electricity from clean and renewable energy sources and raising average fuel economy to 35.5 miles per gallon by 2016.

[2] GAO Report on Physical Infrastructure: Challenges and Investment Options for the Nation's Infrastructure, 2008.  http://www.gao.gov/new.items/d08763t.pdf. 

[3] http://www.nist.gov/cnst/thenewsteel.cfm

[4] Going to Extremes: Meeting the Emerging Demand for Durable Polymer Matrix Composites, Committee on Durability and Life Prediction of Polymer Matrix Composites in Extreme Environments, US National Research Council (2005), http://www.nap.edu/catalog/11424.html