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Research Papers

Virtual Testing for Advanced Aerospace Composites: Advances and Future Needs

[+] Author and Article Information
Q. D. Yang1

Department of Mechanical and Aerospace Engineering, University of Miami, Coral Gables, FL 33124qdyang@miami.edu

Brian N. Cox

 Teledyne Scientific Company, 1049 Camino Dos Rios, Thousand Oaks, CA 91360

X. J. Fang, Z. Q. Zhou

Department of Mechanical and Aerospace Engineering, University of Miami, Coral Gables, FL 33124

It has been shown (Song et al. , 2006), that this method is equivalent to the extended finite element method (XFEM) in which a discontinuity in the displacement field is introduced by enrichment of the shape functions with the Heaviside step function (e.g., Wells and Sluys, 2001 and Moës and Belytschko, 2002).

1

Corresponding author.

J. Eng. Mater. Technol 133(1), 011002 (Nov 23, 2010) (6 pages) doi:10.1115/1.4002637 History: Received February 03, 2010; Revised July 15, 2010; Published November 23, 2010; Online November 23, 2010

In this paper, the conceptual, experimental, and computational challenges associated with virtual testing have been discussed and recent advances that address these challenges have been summarized. The promising capability of augmented finite element method based numerical platform for carry out structural level, subply scale, and microscopic single-fiber level analyses with explicit consideration of arbitrary cracking has been demonstrated through a hierarchical simulation-based analysis of a double-notched tension test reported in the literature. The simulation can account for the nonlinear coupling among all major damage modes relevant at different scales. Thus, it offers a complete picture of how microdamage processes interact with each other to eventually form a catastrophic major crack responsible for structural failure. In the exercise of virtual testing, such information is key to guide the design of discovery experiments to inform and calibrate models of the evolution processes. Urgent questions derived from this exercise are: How can we assure that damage models address all important mechanisms, how can we calibrate the material properties embedded in the models, and what constitutes sufficient validation of model predictions? The virtual test definition must include real tests that are designed in such a way as to be rich in the information needed to inform models and must also include model-based analyses of the tests that are required to acquire the information. Model-based analysis of tests must be undertaken and information-rich tests must be defined, taking proper account of the limitations of experimental methods and the stochastic nature of sublaminar and microscopic phenomena.

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Figures

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Figure 5

A-FEM simulated progressive failure of a microscopic representative volume element with explicit consideration of matrix cracking, fiber/matrix debonding, and randomly located fibers. The five nominal stress versus separation curves are different runs with randomly assigned fiber organizations. The inset shows the multiple cohesive damage in matrix and the final cracking path of connected microcracks in matrix and fiber/matrix interfaces.

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Figure 4

(a) A (0/90/0) laminate with a tunneling crack that is accompanied by four delamination cracks (15) and (b) a numerically determined boundary between the tunneling-without-delamination and tunneling-with-delamination modes on σ̂/E¯2−ΓII/ΓI plane

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Figure 3

(a) Image taken immediately before specimen failure with clearly coupled splitting cracks, intraply transverse cracks, and wedge-shaped delamination zones, (b) predicted damages closely follow the experimentally observed damage pattern, (c) comparison of measured and predicted load-displacement data, and (d) comparison of splitting crack length as a function of applied stress

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Figure 2

(a) An A-FEM with double nodes traversed by an intraelement cohesive crack. This element can be treated by defining two mathematical elements (b) and (c); each has the same geometrical dimension of the A-FEM but with different physical material domains for stiffness integration (9).

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Figure 1

Paradigm of a virtual test system: Component shape and architecture (1) and continuum material behavior (2) suffice for predicting macrobehavior (3). Knowledge of crack types (4) and fracture data (5) generate cohesive fracture model (6), which allows prediction of crack evolution (7). Validation to this scale is made against crack observations (8). 3D images of fiber distributions (9) allow prediction of matrix distribution (10). When this is combined with morphological data (11), probability distributions can be stated for different defect types (12), leading to predictions of stochastic failure events at the microscale (13). Trends in interface strength can be computed by atomistic theory (14) and their effect on macrobehavior predicted up through the hierarchy, allowing validation against engineering data. This simplified example of strength modeling has an analog in predicting temperature distributions with Biot numbers serving as the linking constitutive laws between scales instead of cohesive laws.

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