Improved Simulation of Damage Propagation Can Lead to Better, Cheaper CFRPs

Owing to their low weight, durability, and mechanical performance, carbon-fiber-reinforced plastic (CFRP) laminates are being incorporated into state-of-the-art aerospace, transportation, and construction applications. However, designing CFRP laminates can be very time consuming. Engineers must run multiple strength tests to benchmark CFRP specimens whenever they adjust a given design. This drives up the cost of the final product and hinders applications of CFRPs in a wider range of fields.

Against this backdrop, researchers Dr. Chenyu Wang, a former PhD student at the Graduate School of Sophia University, and Professor Toshio Nagashima from Sophia University developed a novel method to conduct numerical simulations of damage propagation in CFRP laminates. Their findings were published online in volume 316 of the journal Composite Structures, on April 13, 2023.

The researcher duo based their approach on a quasi-3D version of the extend finite element method (XFEM). In FEM, a structure or material is divided into small sub-regions known as elements, followed by the solving of physical equations for each element to determine the overall response of the system. The “extend” version, which has been used in this study, adds functions that capture local effects around discontinuities, enabling more accurate modeling of damage propagation in the form of crack growth.

Notably, since CFRP laminates are made of stacked layers of material, modeling them as flat two-dimensional planes would fail to capture anomalies such as delamination. A three-dimensional FEM simulation, meanwhile, would be computationally intensive and complex to set up. To overcome these issues, the researchers took a balanced approach. They first modeled the desired CFRP laminate as a 2D structure composed of quadrilateral finite elements and marked the position where cracks might occur. Then, they projected this structure in the thickness direction, while the models used to simulate delamination and matrix crack were automatically generated through their simulation system. This strategy made the computations manageable and the modeling to simulate CFRP damage easier and more efficient.

To verify the validity of their approach, the researchers ran simulations of three different strength and damage propagation tests on CFRP laminates and compared their results with the experimental data reported in other studies. The first was an open-hole tension test, in which a CFRP laminate with a circular hole in the middle was pulled from one end while the other end was anchored. The second was a quasi-static indentation (QSI) test, where a hard semi-sphere was pressed slowly and steadily against a CFRP laminate. Lastly, the third test was the compression-after-impact test, in which the damaged specimens from the QSI test were subjected to a compressive force to assess their integrity and damage tolerance.

Overall, the results of the proposed simulation method agreed well with the experimental data, outperforming the existing quasi-3D XFEM-based techniques. Confident about the potential of the novel approach, Dr. Wang remarked: “The applications of composite materials such as CFRP will become more extensive and efficient if the results of this study are utilized in related fields.”

Widespread adoption of CFRPs is also likely to have important environmental implications. “In the future, if the damage of composite materials can be predicted more efficiently and accurately via numerical simulations, their cost will decrease. If these lightweight and high-strength materials are further applied in transportation, it will have a positive impact on energy savings and environmental protection,” added Dr. Wang.