Computational Methods for Debonding in Composites

72 B.N. Cox et al.
mixed-mode crack are not enough.) A map of the vector displacement field around
an initiating crack would in principle be a sufficient measurement, but the questions
of how to make such a measurement and the accuracy required of it remain very
much open. New experimental methods for measuring very small crack displacements,
e.g., with high-resolution x-ray tomography, are very promising; however,
data acquisition and analysis for such experiments are challenging and yet to be
demonstrated. A simpler prospect may be to use the evolution of the macroscopic
crack shape as the calibrating information, since Fig. 3.4 and similar figures in
[13, 20, 38, 60] suggest that this is an information-rich experiment for determining
p(u). Current research continues to seek a calibration method, validated by testing
the accuracy to which ensuing predictions match fracture experiments.
3.7 Concluding Remarks
A functioning virtual test is a system of theoretical models, specialized laboratory
tests, and engineering field tests, linked by statistical and decision theory tools,
which only when taken in its entirety can satisfy the goal of substituting simulations
for a large fraction of real tests in a material design or material certification procedure.
The virtual test is a rich and complex system, requiring Systems Engineering
and Systems Science governance of activities in a number of disparate research and
engineering disciplines. Prior efforts to develop virtual tests for composite materials
(or other engineering or biological materials) appear not to have addressed the
assembly of the complete structure. Advances in modeling, computation and experimental
techniques over the past two decades make the development of a virtual test
a realistic goal; the major new challenge is achieving the integration of the necessary
disciplines.
This challenge should not be mistaken as merely the need for more experiments
or more modeling. The greatest gaps in the technology of virtual tests lie where
models and experiments should be unified. In particular, theorists are challenged by
(1) the need to participate in the design of new experiments that will yield the information
they need to inform and calibrate models and (2) the need for model-based
methods of inferring data from tests. Experimentalists are challenged by designing
experiments that yield the correct type of information for extending the scope of
models. Higher spatial and temporal resolution and three-dimensional imaging are
of course very useful, but more specifically experiments must be devised that probe
those aspects of materials damage that are critical to formulating and quantifying
models. The skill sets needed to meet these challenges are not necessarily to be
found among current modeling and experimental communities. Other disciplines,
especially statistics, decision theory, and physics, must be brought into the effort.
A virtual test should be a living, continually evolving system. Therefore a key
challenge is to create a structure that can support its maintenance. Both systems
engineering and systems science aspects exist in this challenge, with the whole
integrated by the tools of information science.