13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- A Pipeline Approach to Developing Virtual Tests for Composite Materials Brian Cox1,*, Hrishikesh Bale2, Matthew Blacklock3, Bao-Chan Do4, Renaud Rinaldi3, Robert Ritchie2, Qingda Yang4, Frank Zok3, and David Marshall1 1 Teledyne Scientific Co LLC, Thousand Oaks, CA 91360, USA 2 University of California, Berkeley, CA 94720, USA 3 University of California, Santa Barbara, CA 93106, USA 4 University of Miami, Coral Gables, FL 33124, USA * Corresponding author: bcox@teledyne.com Abstract A multi-disciplinary project combines experiments and theory to build high-fidelity virtual tests of composite materials. The virtual test is assembled via a “pipeline” running through a number of collaborating institutions. Key experimental challenges are acquiring 3D data that reveal the random microstructure and damage events at high temperatures in the interior of the composite with very high resolution (~ 1 μm). Key theoretical challenges include representing the stochastic characteristics of the 3D microstructure, modeling the failure events that evolve within it, and developing efficient methods for executing large ensembles of stochastic virtual tests. To begin, 3D images of 3D woven ceramic composites are captured by x-ray μCT on a synchrotron beamline. The statistics of the shape and positioning of the fiber tows in the 3D architecture are used to calibrate a generator that creates virtual specimens that are individually distinct but share the statistical characteristics of measured specimens. Failure of the virtual specimens is simulated by advanced computational methods, revealing the complete failure sequence of multiple interacting crack types. Validation of the analytical methods is performed by comparing with data captured at 1500°C and above, using digital image correlation or μCT to track damage evolution. Keywords virtual test, stochastic, high temperature, ceramic, textile 1. Introduction One role of a virtual test, as its name suggests, is to replace a real engineering test by a computer simulation. Ideally, the simulation would predict engineering properties ab initio with sufficient fidelity that the real test becomes unnecessary. More realistically, a virtual test calibrated by a few real tests will reduce the matrix of real tests needed to ensure safe use of a material, perhaps by an order of magnitude or more [1]. Of equal interest is the possibility that a virtual test can function as a tool for optimizing material design [1-5]. Indeed, a virtual test can yield much richer information about the correlation between the microstructure of a material and its performance than is easily available from experiments: in the virtual test, we have full knowledge of the microstructure and its effect on the details of failure mechanisms, whereas in the real test, such effects are often concealed in the interior of the specimen. Virtual tests are of special value for high temperature materials, e.g., the current generation of integral textile ceramic matrix composites [6] with potential use temperatures ranging up to 1500ºC. While mechanisms of failure in composites that act at room temperature can be determined quite readily either by modern 3D imaging or by destructive sectioning following interruption of tests, mechanisms acting at high temperatures are much more difficult to probe. The virtual test offers the possibility of probing details of damage mechanisms for different temperature and loading histories using simulations coupled to relatively simple surface observations on real specimens. Nevertheless, advancing test methods applicable to high temperatures remains critical: the proven fidelity of a virtual test can never exceed the ability to identify the mechanisms that must be
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