Influence of fabric architecture on damage progression as evidenced by acoustic emission

Abstract

Fabric reinforced polymer matrix composites are integral structural materials used in wind turbine blades. Wind turbines are expected to increase in size and utilization as global focus turns toward power generation utilizing renewable sources. How these materials change properties due to damage accumulated are important to the future of wind energy. They feature damage mechanisms that are unique from any other engineering material. These factors are now driving innovation for design and manufacturing of the blades. This has led to investigation in characterizing the mechanical behavior of the composites. These composites were manufactured using unidirectional and biaxial fiber layups from three fabrics composed of an epoxy matrix and glass fibers. The effect of the architecture of the fibers on damage progression was determined with acoustic emission sensors that were attached linearly to capture elastic waves emitted by damage mechanisms inside the samples during testing. The critical data extracted from the elastic waveforms include the peak frequency and absolute energy released by the samples and how they are associated with the strength of the samples. A static loading scenario was determined to be the optimal testing method. The use of AE measurements proved to be an invaluable tool to determine how the damage progression of composite materials lead to failure for some, while not being accurate for others. Results found that simple architecture differences for the same fibers have drastic effects on damage progression. However, the energy measurements proved to be imperfect with current technology and application; improvement will be necessary for AE instruments to be a viable tool for energy measurement in the future. AE provides a unique analysis that can identify and characterize damage related to fabric composition. The frequency content provides a consistent method of identifying damage mechanisms between varying materials. Optimal architecture and layup can be determined with the help of AE. Correlating acoustic energy to actual energy dissipated still has potential as a valuable tool if improvement in sensor technology can be achieved. Ultimately, a foundation for correlating mechanical properties of the materials and damage progression to fabric architecture and layup using AE tools was created.