Effects of Defects: Part B—Progressive Damage Modeling of Fiberglass/Epoxy Composite Structures with Manufacturing Induced Flaws Utilizing Cohesive Zone Elements

Abstract

The Effects of Defects is important for the reliability of modern composite wind turbine blades. The DOE has sponsored a comprehensive study to characterize common manufacturing defects and establish damage growth and validation tools to contribute to a wind turbine blade reliability infrastructure. To support this development of a reliability infrastructure, progressive damage modeling of blade representative coupons has been performed. A model has been developed that is combined of both continuum and discrete modeling approaches. A user-defined material subroutine has been created and used with material properties established from experimental testing for the former, while cohesive zone elements were placed between each fiber tow to capture the fracture that occurs in these areas for the latter. Two-dimensional (2D), four-layer coupon level models were generated based on the geometry of the as-tested specimens. Results from this model were compared to the visual damage progression and stress-strain data from in-plane wave tests in tension and compression. While the uniformity of the models resulted in more dramatic changes at failure points, the progression was found to match in these cases, thereby verifying the combined continuum and discrete modeling approach. NomenclatureBRC = Blade Reliability Collaborative MSUCG = Montana State University Composites Group OP = out-of-plane wave IP = in-plane wave CDM = Continuum Damage Model DDM = Discrete Damage Model σ = Stress ε = Strain u = displacement

Effects of Defects: Part B—A Comparison of Progressive Damage Modeling of Fiberglass/Epoxy Composite Structures with Manufacturing Induced Flaws

“…9 This method utilized the same user inputs noted above, including material properties and shear response.…”

“…As such, the decision tree shown in Figure 3 shows the typical logic utilized in a progressive damage model and was utilized in previous CDM efforts performed by the authors which was the foundation for the work presented herein. 4,7,9 Discrete modeling is considered by many to be more consistent with the physical damage of thermosetting polymer reinforced composites. 11 As noted, a continuum approach relies on representing the damage as a change in material properties, whereas, observed damage is typically local failure of the constituents (matrix and/or fiber).…”

“…However, both modeling options have shown promise for modeling composite materiels. 7,9 Continuum modeling derives from the assumption that a material is continuous and fills an entire region of space. 10 From this, it is broken into representative volume elements (RVE) such that constitutive equations relate the RVE to the entire structure.…”

“…Thus, research specific to understand the criticality of defects common to blades is necessary and coupon level, benchmark testing was performed by the MSUCG. [4][5][6][7][8][9] The prior benchmark material testing (BMT) was performed to establish and understand the material properties, failure points and modes, and damage progression of both unflawed and flawed specimens. For example, it was clearly evident that once a flaw was introduced, the material response in the flawed area dominated the overall response in most cases as indicated by the review of digital image correlation data as seen in Figure 2.…”

Recent Industrial Developments of Marine Composites Limit States and Design Approaches on Strength

“…In general, cohesive models currently represent a powerful instrument to investigate the influence of cohesive parameters in small-scale model, while their implementation in largescale design is still far from being achieved due to computational limits. Some promising applications include the analysis of local problems, as well as the numerical characterization of the material capacity to resist against delaminating stresses as reported by Cricrì and Perrella (2017) and Woo et al (2013).…”