Title: Experimental and Numerical Study on Defects and Repair of Automated Fiber Placement Features

Authors: Waruna Seneviratne, John Tomblin, Mohamed Shafie

DOI: 10.33599/nasampe/s.21.0626

Abstract: In the fabrication of complex aerospace structures, Automated Fiber Placement (AFP) has been considered to be one of the most advanced manufacturing methods. The primary feature of AFP fabrication method lies in the tow-by-tow/course-by-course placement of composite material using a robotic fiber placement head. While in the fabrication process, very fine tolerances are set to manage gaps and spacing in between fiber tows and courses; machine and operator errors along with part geometry limitations introduce AFP gap/overlap features within the construction. By understanding the effects due to these gaps and features, a better judgement of the process induced defect and the structural integrity of the part can be predetermined. In cases were gaps or missing tows are present within a composite layup, the local feature region becomes a resin rich area during the curing phase. This leads to intrinsic stress concentration due to the resin properties and the local fiber discontinuity. In this current study, such gap features are studied and a missing-tow repair-configuration during the manufacturing process has been evaluated in its effectiveness in dispersing the stress concentration. The repair configuration will be of a case where the gap is only detected after a subsequent ply is placed on top of the missing-tow. The main focus was to establish methods for developing knockdowns and design allowable which can be incorporated in the presence of such features. The knockdown effects were compared with pristine configurations of un-notched and open-hole test specimens under planar loading. Strength knockdown predications were also obtained using high fidelity finite element models to serve as a tool for comparison with test data. B-Spline analysis method (BSAM) developed under the Air Force Research Laboratories (AFRL) was used to predict failure strengths as well as to identify matrix crack/delamination propagation regions.

References: 1. Seneviratne, W., Tomblin, J., Shafie, M., Perera, S. and Smith, G., “Automated Fiber Placement (AFP) – Effects of Features and Defects.” Proceedings of the American Society for Composites Thirty-Fourth Technical Conference, Atlanta, GA, Sept. 23-25, 2019. American Society for Composites. DOI: 10.12783/asc34/31280. 2. ASTM Standard D5766/5766M-11, 2018, “Standard Test Method for Open-Hole Tensile Strength of Polymer Matrix Composite Laminates.” ASTM International, West Conshohocken, PA, 2018. DOI: 10.1520/D5766_D5766M-11R18. 3. ASTM Standard D3039/3039M-17, 2017, “Standard Test Method for Tensile Properties of Polymer Matrix Composite Materials.” ASTM International, West Conshohocken, PA, 2017. DOI: 10.1520/D3039_D3039M-17. 4. ASTM Standard D6484/6484M-14, 2014, “Standard Test Method for Open-Hole Compressive Strength of Polymer Matrix Composite Laminates.” ASTM International, West Conshohocken, PA, 2014. DOI: 10.1520/D6484_D6484M-14. 5. Ataş, A., Hodzic, A. and Soutis, C., “Strength Prediction of Bolted Joints in Cross-Ply Laminates Based on Subcritical Damage Modelling.” Proceedings of the 15th European Conference on Composite Materials, Venice, June 24-28, 2012. European Conference on Composite Materials. 6. Heimbs, S., S. Heller, P. Middendorf, F. Hähnel, and J. Weiße. "Low velocity impact on CFRP plates with compressive preload: test and modelling." International Journal of Impact Engineering 36(10-11) (2009): 1182-1193. DOI: 10.1016/j.ijimpeng.2009.04.006 7. NCAMP Material datasheet, “Solvay Cytec Cycom 5320-1 T650 Unitape Qualification Materials Property Data Report”, CAM-RP-2013-002 Rev A, National Institute for Aviation Research (NIAR), Wichita State University, Wichita, KS. 8. Iarve,E.V, Mollenhauer,D, and R Kim "Mesh-independent modeling and moiré interferometry studies of damage accumulation in open-hole composite laminates." Mechanics of Composite Materials 40(5) (2004): 419-426. DOI: 10.1023/B:MOCM.0000047232.60559.27 9. Iarve, E. V., and D. H. Mollenhauer. "Mesh-independent matrix cracking and delamination modeling in advanced composite materials." Numerical Modelling of Failure in Advanced Composite Materials. Woodhead Publishing, 2015. 227-264. DOI: 10.1016/B978-0-08-100332-9.00009-8 10. Mollenhauer, D., et al. "Simulation of discrete damage in composite overheight compact tension specimens." Composites Part A: Applied Science and Manufacturing 43(10) (2012): 1667-1679. DOI: 10.1016/j.compositesa.2011.10.020 11. Turon, A., et al. "A damage model for the simulation of delamination in advanced composites under variable-mode loading." Mechanics of materials 38(11) (2006): 1072-1089. DOI : 10.1016/j.mechmat.2005.10.003 12. Iarve, E. V., et al. "Strength prediction in composites with stress concentrations: classical Weibull and critical failure volume methods with micromechanical considerations." Journal of materials science 41(20) (2006): 6610-6621. DOI: 10.1007/s10853-006-0200-y 13. Maimí, P, et al. "A continuum damage model for composite laminates: Part I–Constitutive model" Mechanics of Materials 39(10)(2007):897-908. DOI: 10.1016/j.mechmat.2007.03.005 14. Maimí, P., et al. "A continuum damage model for composite laminates: Part II–Computational implementation and validation." Mechanics of Materials 39(10) (2007): 909-919. DOI: 10.1016/j.mechmat.2007.03.006 15. Pinho, S. T., et al. "Failure models and criteria for FRP under in-plane or three-dimensional stress states including shear non-linearity.", NASA/TM-2005-213530, Hampton, VA, 2005. 16. Mollenhauer, et al.,” United States Air Force Investigation and Evaluation of Composite Scarf Repairs”, NATO AVT Bonded Joint Specialist Meeting Proceedings STO-MP-AVT-266, 2018. 17. Iarve, E., Mollenhauer, D., Breitzman, T., Hoos, K., and Swindeman M., “Initiation and Propagation of Fiber Failure in Composite Laminates”, 19th International Conference on Composite Materials, Montreal, Canada, Jul 28- Aug 2, 2013

Conference: SAMPE NEXUS 2021

Publication Date: 2021/06/29

SKU: TP21-0000000626

Pages: 15

Price: FREE