Highlights from the 2013 National Science Foundation Workshop on “Durability of
Polymers and Polymeric Composites: Current Challenges and Future Prospects”,
March 6th-7th, 2013,
Hyatt Hotel, Monterey, CA, USA
Anastasia Muliana and Valeria La Saponara
Polymers and polymeric composites are widely used in many engineering applications and have become
increasingly popular for advanced structural systems. This is because they are lightweight and strong, it is
easy to adjust their properties for certain applications, and they have high corrosion resistances and
relatively low processing costs. Figure 1 illustrates several examples of applications of polymers and
polymeric composites. There have been vast developments of polymers and polymeric composites for
aerospace and civil applications for the past 50 years, recent advances have been made in biomedical
industries for various implants and prostheses (Joachim Kohn, Nature Materials 3, 745 – 747, 2004).
Another promising application is in off-shore industry since the use of lightweight composite risers will
reduce platform weight which will be the advantages for deep water drilling (U.S. Minerals Management
Service, Gulf of Mexico Region, Offshore Information, October 1999). However, there are many
challenging and unresolved scientific issues, which are related to their long-term performance, that
engineers face in using polymer and polymeric composites in the above applications. The issues are
mostly associated with limited knowledge in the life performance and durability of polymers and
polymeric composites.
The goal of this NSF workshop, supported by the Programs of Structural Materials and Mechanics and
Mechanics of Materials (with respective Program Managers Dr. Grace Hsuan and Dr. Martin Dunn) of
the National Science Foundation (NSF) Civil, Mechanical and Manufacturing Innovation Division, which
was part of the workshop on Service Life Predictions of Polymeric Materials, organized by Dr.
Christopher White from the Materials and Structural Systems Division Engineering Laboratory, National
Institute of Standards and Technology (NIST), is to bring the US research community together to share
the recent developments in the modeling and experimental understanding of the degradation and life
prediction of polymeric and polymeric composite structures under various mechanical loading and
environmental conditions. More importantly, the workshop aims at creating a discussion forum to analyze
what we, as the research community, have seen in the current approaches in predicting life performance
and durability of polymeric structures and should do in the scientific fundamentals - basic science and
engineering level to further enhance our understanding on the mechanisms that lead to continuous
changes in the properties and performance of such structures. Table 1 lists the participants of this NSF
workshop. This meeting opens opportunities for US researchers in academia to collaborate with
researchers from national laboratories and industry partners (from NIST participants), for further
enhancing current methods in predicting life performance and degradation in polymers, which is expected
to have tremendous impact in resolving current durability issues in many engineering applications.
Another goal of this workshop is to engage graduate students with the field of durability of polymeric
composites, through a poster competition (see Table 2). This will provide a unique opportunity for
students to present their works, networking with their peers and other engineers and researchers.
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Figure 1 From top left figures, clockwise: Airbus A380 has utilized various forms of polymeric
composites for several aircraft components, namely carbon fiber reinforced polymer (CFRP), glass
(GFRP), hybrid that consists C-GFRP, and also GFRP + aluminum layers (Glare). Glass fiber composites
are also used for bridges exposed to harsh environments and for retrofitting concrete structures from
impact loading and corrosion protection. Several prostheses and implants have considered polymers and
polymeric composites since the properties of these materials can be tailored to match the ones of human
tissues.
Table 1. Information on technical presentations of the NSF workshop
Presenter (affiliation)
K. Liechti
(Univ. Texas- Austin)
J. Qi
(Univ. ColoradoBoulder)
K.R. Rajagopal
(Texas A&M)
J. M. Caruthers
(Purdue Univ.)
S. Keten
(Northwestern Univ.)
K. Pochiraju
(Stevens Inst. of
Title
Shear modified Free Volume Concepts for Nonlinear Viscoelastic Behavior of
Polymers
Photo-mechanics of Polymer Structural Alteration due to Light Irradiation
Modeling the Non-linear Response of Polymeric Solids Undergoing
Microstructural Changes Due to the Diffusion of Solids
Development of Constitutive Models for the Long-term Performance of Glassy
Polymers
Solvent and Confinement Effects on the Thermomechanical Behavior of
Amorphous Polymers
Thermo-mechanical Effects in Polymeric Composites, Modeling/experiment
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Technology)
A. Muliana
(Texas A&M)
C. Bakis
(Pennsylvania
State Univ.)
G. Yun
(Akron Univ.)
V. La Saponara
(Univ. CaliforniaDavis)
B. R. Loyola
(Sandia National
Laboratories)
Coupled Heat Conduction and Thermo-viscoelastic Analyses of Polymeric
Composites
Externally Bonded FRP Strengthening: Effects of Elevated Temperatures and
Sustained Loads
Stochastic Characterization for Micromechanical Properties of Polymer Matrix
A Study on the Impact of Aerospace Fluids on the Durability of FiberReinforced Composite Structures
Time Dependency of Electrical Properties of MWCNT/PVDF Films Subjected
to Temperature Cycling
Table 2. Graduate students attending NSF workshop and poster competition
Name
MMR Chowdury
Affiliation
Tuskegee University
Qi Ge
University of ColoradoBoulder
Kai Yu
University of ColoradoBoulder
Mehdi Karevan
Georgia Institute of
Technology
Jianyong Liang
Stevens Institute of
Technology
University of Miami
Seyedreza
Mohammadizadeh
Reza Rahimi
University of Akron
Miranda Rudolph
University of CaliforniaDavis
Georgia Institute of
Technology
Matthew Smith
Wil Srubar
Stanford University
Hua Zhu
University of MissouriColumbia
Title
Durability Study of Low Velocity Impact
Responses of Conventional and Nanophased
CFRP Composites Exposed to Seawater
Finite Deformation Thermomechanical
Constitutive Modeling and Numerical
Implementation of Triple Shape Polymeric
Composites Due to Dual Thermal Transitions
General Design Considerations for the
Thermally Triggered SMP Composites with
Internal Heating
Mechanical and Electrical Characteristics of
Exfoliated Graphite Nanoplatelets/Polyamide12
Multifunctional Polymer Nanocomposites
Processed by Selective Laser Sintering
Damage Evolution due to Thermal Oxidation
of Laminated Polymeric Matrix Composites
A-FEM That Is 100+ Time Faster Than X-FEM
in Simulating Arbitrary Cracking Problems in
Solids
Development of Full-field Strain Sensor using
Mechanoluminescence Materials
Durability prognosis of polymeric composite
wind turbine blades
Solution Processing of Vertically Aligned
Polymer Nanotubes for Thermal Interface and
Multi-functional Applications
Improving the Hygrothermal Durability
Performance of Lignocellulose-Biopolymer
Composite Materials via Chemical Modification
Study of the dynamic response of novel
laminated glass using transparent glass fiberreinforced composite interlayer
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Current Progress and Priorities
Current research on the behaviors of polymers and polymeric composites investigates modeling
mechanical response, thermal-diffusion transport, and chemical reactions of polymers both at the
continuum and atomistic scales. Stochastic constitutive models and statistical mechanics approaches that
incorporate fluctuations at the nano and/or molecular scales have been considered in order to bridge the
molecular motions of polymers to the overall responses at the continuum scale. Available models that
describe performance of polymers and polymeric composites and various solution methods (both
analytical and computational) have incorporated the viscoelastic response of polymers and the effects of
coupled mechanical and non-mechanical stimuli, such as light irradiation, diffusion of various solvents,
changes in temperatures, oxidation, etc. It is understood that the macroscopic performance of polymers
depends strongly on the changes in the micro-molecular arrangements of the polymers in response to the
external stimuli, and also processing conditions, such as curing time and temperature. Initiations and
evolutions of damage and degradation in materials are currently linked to localized stresses/strains due to
variations in the material microstructure, such as inclusions, pores, defects, microcracks, etc. Moreover,
materials and structures undergo continuous changes in their properties and characteristics with time, and
these changes can be accelerated or decelerated with exposures to various external stimuli. Current efforts
in understanding these continuous time-dependent changes in polymers and polymer composites that
could lead to degradation, healing, and aging of the materials have been limited. There have been several
models/attempts to predict long-term response of polymers and polymeric composites through the use of
accelerated time-dependent methods, which may or may not be appropriate to the structure under study.
However, predicting aging and understanding life performance of polymers remain challenges.
To enhance the understanding of the overall performance of polymers and to bridge the response of
materials at various scales, micromechanics and multi-scale modeling have been considered. Current
advances in micro-mechanics and multi-scale modeling have been on predicting mechanical responses of
composites under short-term loading condition. The main issue with multi-scale modeling is that,
currently, little is understood about the right interaction and transition of the response across various
geometrical and time scales, and the coupling between the mechanical and non-mechanical responses of
the materials. In addition, multi-scale modeling is generally computationally expensive, which hinders its
usage in designing devices and large scale structures.
Several issues have been identified, with participants from academia, research labs, and industries, related
to current challenges in understanding life performance of polymers and polymer composites:
1) Disengagement between researchers in the fields of chemistry and mechanics. Chemists would
typically focus on understanding the chemical properties and performance of the polymers at the
molecular level, with an intention to develop polymers with certain functional behaviors, such as high
temperature resistance, enhanced toughness and ductility, high strength, good damping capability, etc.
Mechanicians, with theoretical, experimental, or computational mechanics background, often concern
with predicting or understanding the bulk mechanical and physical properties of polymers. This is
usually done by formulating models based on some approximations and parameters, with an intention
to predict performance of certain polymers under certain loading conditions in order to support design
of structures made of these materials. Most of the times, these approximations and parameters
incorporate only the external stimuli, in which the polymers are subjected to, but neglect the
information regarding the chemistry and changes in the molecular structures of the polymers.
2) Many of theoretical and experimental studies on understanding performance of polymers and
polymeric composites have been done under predefined conditions at the laboratory and at a
relatively short period, while during their service polymer based structures are subjected to rather
complex loading conditions over long period. The laboratory and service conditions would be
completely different; however, limited resources and time would prevent scientists/engineers to
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simulate real life service conditions. This leads to impediments in designing reliable devices and
structures with a predictable life span.
3) Scientists and engineers working in production typically do not work together in analyzing and
designing devices and structures. Simple models with approximations and idealizations are often
necessary in design, but the question is: how simple do they need to be? Engineers need to have
informations on when the simple model fails and how should we go from here. This requires the
engineers to have fundamental and practical knowledge about the subjects in both mechanics and
chemistry aspects.
4) From the industry standpoint, there is urgency in manufacturing materials and launching the products.
It is of course more desirable to put the products into market with detailed understanding on their
expected overall performance, which requires comprehensive analyses and rigorous models. This,
however, is not always the case, as rigorous models and systematic understanding would take time,
and the production and launch of a product requires timely decisions.
5) An ideal situation would be if chemists, physicists, mathematicians, and engineers were collaborating.
This is not always possible because of different language, mindsets and training. Collaboration from
different expertise is ideal but not necessarily realistic.
6) Under real life loading conditions, polymers and polymeric composites often experience complex
behaviors, viscoelastic, plastic, aging, healing, etc. Many research works in these topics emphasize on
linear and elastic responses, especially during the design of devices and structures, where
simplification of problems are often desired and complexity is often avoided. One of the reasons for
this is that there has been a small effort given on teaching nonlinear and complex behaviors in the
undergraduate and graduate mechanics courses, and mechanics students have little exposures on the
polymer chemistry. Likewise, many chemistry students might focus only on the chemical aspects of
the polymers and neglect the potential engineering problems that the polymers can experience while
in service. This lack of cross pollination between different fields would prevent students, future
scientists and engineers, to think of and approach problems beyond their comfort level of knowledge.
Several inputs from participants on the next realistic steps to bridge the knowledge gaps in durability of
polymers are as follows. It is necessary to link the chemistry or polymers to constitutive modeling in
order to better predict life performance of polymers. Rigorous models that are capable of incorporating
continuous changes in the properties and performance of polymers (for example, ultra-sensitive oxygen
uptake) under various conditions are needed. It is also important to develop analytical/numerical tools
based on rigorous models that can be used by engineers and manufacturers for designing and predicting
performance of polymers and polymeric structures. In order to promote fundamental research that bridges
chemistry and mechanics fields, support is needed from funding agencies, so that research works in these
two fields with different priorities and directions can be streamlined towards achieving certain goals. It is
important to train students to be open-minded to other scientific fields, and to introduce them to
multidisciplinary studies, while focusing on their core subjects.
Future Directions
Polymers and polymeric composites have become materials of choice in many engineering applications,
and the use of these materials also opens many opportunities for cutting edge engineering and technology
such as in biomedical and off-shore industries. However, the durability and reliability issues of these
materials are still not well understood, which has an impediment in the design of devices and structures
made of polymers. As stated above, rigorous models that include all possible aspects related to the
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performance of polymers and polymer composites and collaborations among experts from various fields
are desirable, but the efforts might not be practical and realistic. We to some extent need to have some
approximations and simplifications in assessing performances of devices and structures.
In order to address the durability and reliability issues of polymers and polymeric composites, it is
important to emphasize on the performance of polymeric based materials and structures under various
external stimuli, both mechanical and non-mechanical effects. Failures in materials and structures are not
necessarily due to mechanical loading only. Exposure to non-mechanical stimuli can significantly
contribute to degradation in the materials and failures of the structures. It is also necessary to have close
collaborations between chemists and mechanicians in order to understand the mechano-chemistry
behaviors of polymers and polymeric composites when they are subjected to various stimuli that mimic
real life conditions. This would help the chemists in developing polymers for certain engineering
applications as they have information on the various histories of external stimuli that could cause changes
in the chemical structures of these materials, and the mechanicians would have information on how
changes in the chemical structures of polymers would affect the overall mechanical performance of the
polymeric based materials. For example, under impact and cyclic loadings, polymers could generate
significant amount of heat, thus increasing their body temperatures, and temperature changes would
influence the mechanical performance of polymers. Chemists might design polymers with high damping
capability, and information on potential high temperature changes during service would really be useful
for them to enhance their polymer designs. Likewise, if mechanicians have information on the mechanochemistry behaviors of materials during their service, it will help them in better predicting failures and
understanding durability of the materials.
It is also important for engineers, who design devices and structures, to have some knowledge on the
mechano-chemistry behaviors of polymers and polymeric composites, which would help them in
assessing degradation of the structures during service and predicting life of the structures. For this
purpose, it is necessary to expose undergraduate and graduate students in mechanics to some knowledge
on polymer chemistry which gives the information about the effect of the chemical structures on the
mechanical properties of materials. Students in chemistry should also be familiar with some engineering
aspects in order to provide useful information on the expected overall performance of the polymers.
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