N132-101 TITLE: Thick Composite Crack Analysis

TECHNOLOGY AREAS: Air Platform, Materials/Processes

ACQUISITION PROGRAM: PMA 276

OBJECTIVE: Develop methods within the realm of peridynamic theory to improve damage prediction and growth in thick composite parts for improving design and life predictions in rotary wing applications.

DESCRIPTION: Fiber-reinforced polymer (FRP) laminated composites exhibit directional stiffness and strength properties, and offer different fabrication architecture; thus, enabling advanced design concepts, structural tailoring, multi-functional features, and performance enhancements. Therefore, composites are an important part of vehicle structures and continue to replace traditional metal parts with increasing frequency. Considering their high specific strength and stiffness (relative to metals) they are attractive for aerospace applications. However, composites are inherently anisotropic and non-homogenous, and the strength and stiffness properties of the constituents (fiber and matrix) are extremely different. Strength of FRP composite laminates depends on fiber directions, type of fibers and resins, number of layers, stacking sequence, type of loading, environmental conditions, and random variation of material and strength properties due to manufacturing. The nature of damage initiation and its progression creates more complicated internal loading than would be experienced in traditional, metal parts. Their failure involves a progressive series of events with discrete failure modes such as matrix cracking, fiber-matrix shear, fiber breakage, and delamination. The presence of such failure modes results in stiffness degradation; thus, leading to load redistribution among the layers and constituents. Accurate computation of load redistribution and prediction of failure modes are critical to realistic simulation of composite laminate strength predictions.

In primary load path structures made from composite, damage must be closely monitored to ensure the safety and integrity of the vehicle. Advanced analysis tools are being developed to better model and predict the damage initiation and propagation experienced in laminated composites. As the Navy continues to incorporate more composite structure, accurate damage prediction using analytical methods continues to be an area where improvement is needed. Traditional finite element analysis (FEA) is inherently limited for predicting failure modes especially in fiber-reinforced composites without resorting to external criteria to guide the failure progression.

An alternative to traditional FEA is the peridynamic theory; it is a nonlocal extension of classical continuum mechanics that is based on integral-differential equations involving time and spatial coordinates. The peridynamic equation of motion contrasts with that of classical theory continuum mechanics, which is based on partial differential equations. Peridynamic theory has the capability to handle multi-scale modeling for both length and time, and address discontinuities and non-linearity. The peridynamic theory has the potential to serve as a basic model across all scales avoiding the difficulties inherent to multi-model coupling in addition to the ability to efficiently link with many microscale models including molecular dynamics.

Flexible analysis tools that better assess the effects of damage (impact, environment, fatigue) would be valuable to help predict life and improve design in rotary wing applications. The primary area of interest is rotor components that have been subjected to dynamic loading.

PHASE I: Develop an analytical method within the realm of peridynamic theory for predicting damage initiation and propagation in thick composite parts. Demonstrate the feasibility of the technology by performing analysis on a simulated thick laminate rotor component, subjected to high cycle loading.

PHASE II: Develop the methodology into a prototype analysis tool. Initiate validation through component testing.

PHASE III: Complete verification and validation. Transition the developed technology to appropriate platforms or end users.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: As composites make up a more significant portion of vehicular structure, the need for analysis and prediction tools will also increase. Commercial customers will demand more reliable and robust methods for ensuring the safety of their products. Better analytical understanding of damage initiation and propagation could also spur the development of new manufacturing methods to better suit the needs of users and their structural applications. The ability to model and simulate composite materials for strength prediction can reduce the time and cost for material testing and characterization; thus, provide the opportunity to use advanced material systems on critical military and commercial equipment in a timely manner.

REFERENCES:
1. Reddy, J.N. (2004). Mechanics of Laminated Composite Plates and Shells: Theory and Analysis. 2nd ed. Boca Raton: CRC.

2. Rao, B.N., & S. Rahman.(2001). A Coupled Meshless-finite Element Method for Fracture Analysis of Cracks. Int. Journal of Pressure Vessels and Piping, Vol. 78, pp. 647-657.

3. Xu, J., Askari, A., Weckner, O. & Silling, S. (2008). Peridynamic Analysis of Impact Damage in Composite Laminates. Journal of Aerospace Engineering, Vol. 21, pp. 187-194.

4. Kilic, B., Agwai, A. & Madenci, E. (2009). Peridynamic Theory for Progressive Damage Prediction in Centre-Cracked Composite Laminates. Composite Structures, Vol. 90, pp. 141-151.

5. Kilic, B., & Madenci, E. (2010). Coupling of Peridynamic Theory and Finite Element Method. Journal of Mechanics of Materials and Structures, Vol. 5, pp. 707�733.

6. Agwai, A. Guven, I. & Madenci, E. (2011). Predicting Crack Propagation with Peridynamics: A Comparative Study. International Journal of Fracture, Vol. 171, pp. 65-78.

7. Oterkus, E., Madenci, E., Weckner, O., Silling, S., Bogert, P. & Tessler, A. (2012). Combined finite element and peridynamic analyses for predicting failure in a stiffened composite curved panel with a central slot. Composite Structures, Vol. 94, pp. 839-850.

8. Oterkus, E. & Madenci, E. (2012). Peridynamic Analysis of Fiber Reinforced Composite Materials. Journal of Mechanics of Materials and Structures, Vol. 7, pp. 45-84.

KEYWORDS: Thick Composites; Structural Composites; Damage Prediction; Composite Damage; Delamination; Damage Growth

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