Annex VII - Co-operative program on development, evaluation and standardization of methods for testing mechanical properties of nanomaterials for application in automotive industries

Annex Objectives:
This annex aims to develop measurement methods using Instrumented Indentation Test (IIT) and
atomic force microscopes (AFM) to quantify the influence of nanoparticles used in reinforcing
nanocomposites to achieve quality control.

Annex Participants:
Dr. Michael Griepentrog, BAM, Germany (resigned due to health issues)
Dr. Stephen Hsu, GWU, USA (acting chair)
Dr. Guanglu, National Center for Nanoscience and Technology, China
Dr. Chen, SICCAS, China
Dr. Michel Dumolin, Materials and Processes, Canada
Dr. Florence Perrin-Sarazin, Institute Industrial Materials, Canada
Dr. Chanmin Su, VEECO, USA
Dr. Gregory F. Meyers, Dow Chemical Company, USA
Dr. Alan Brewin, NPL, UK
Dr. Sidney Cohen, Weizmann Institute, Israel

Significance and Impact
Nanocomposites are low cost, strong and flexible materials with very high potential impact on
many industries and sectors. Successful quality control methodology for nanocomposites in the
transportation technologies could accelerate light weighting, introduce multifunctional properties
from control systems to crash-worthiness body structures at low cost. The materials being
studied in this annex is clay nanoparticle infiltrated polymer composites. Test methods and
property prediction based on measurement is the goal. If successful, it would remove one of the
major barriers for its wide-spread use in cars and trucks, resulting in significant weight reduction
and fuel economy improvements.

Technical Program and structure
Subtask 1: mini-round robin study between BAM and GWU to develop test methods
Subtask 2: send test procedures to selected laboratories for beta testing to validate the write-ups
Subtask 3: distribute samples and conduct round robin tests
Subtask 4: develop precision statements and issue standardized test methods.

Annex accomplishments
At BAM special methods for testing visco-elastic properties (loss and storage modulus) using
dynamic methods have been evaluated successfully. But these methods are not generally
available for all users of IIT. The influence of temperature and humidity on the measured values
of mechanical properties of polymers, especially Polyamide was investigated by BAM. It was
shown, that repeatable results can only be achieved if temperature and humidity are kept strictly
constant. The ability to maintain strict control of temperature and humidity is not generally
available in every laboratory.

Developing and evaluating testing methods following additional properties of composite
polymers have to take into account of: mechanical properties of the particles in the composite,
size and shape, concentration and distribution of the particles in the composite, and the nature,
magnitude of the bonding forces between the particles and the matrix material. For IIT, the
volume deformed under pressure is measured and the result should reflect the combined stiffness
of the composite. At BAM, using the intended clay particle infiltrated composite sample,
location specific values have been obtained.

At GWU, a mapping technique using frequency modulated AFM mapping technique was
developed to overcome the sample inhomogeneity problem. But since the nanoparticles are
distributed somewhat randomly in the matrix, representative sample surface cannot be obtained.
Thin cross-sectioning of the polymer composite to generate test specimens often cause surface
damage and nanoparticle pull-outs. For two years, BAM and GWU searched for sample
preparation technique. The solution was found using a cryogenic microtome with diamond blade
to prepare indentation samples. But such instrument is expensive and not widely available by the
participating laboratories.

Many issues, such as using stiff cantilevers, blunt tips, mapping technique, and modeling to
determine the nanoparticle contribution to the global properties from individual particles were
eventually resolved to a level that can yield meaningful interpretations but still fall short of a user
friendly, simple test procedure to yield critical control parameter for quality control.
Both BAM and GWU have drafted and revised test procedures using IIT and AFM for such
measurement. But the round robin study, after some discussions with participants, was deemed
impractical to reach the desired objectives due to technical barriers to achieve a precision
statement. The results and the current situation will be presented to the ExCo for consideration
and decision.