APPLYING DIGITAL IMAGE CORRELATION TO CHARACTERIZE ADVANCED COMPOSITE MANUFACTURING PROCESSES AND MATERIALS

Ensuring quality control within manufacturing is a vital necessity to the industry as it reduces waste, minimize cost, and provides a trusted product to the customer. Quality control is performed through inspection techniques that not only support the production line but assist the research and development of future materials and products. The advanced composite manufacturing field is a growing industry with large-scale polymer composite additive manufacturing and advanced discontinuous reinforced composites. Each has their own material property inspection requirements such as detection of residual warpage for the additive print process, fiber orientation for discontinuous composites, and thermal expansion measurements for all composites. This research outlines novel approaches and newly developed inspection techniques utilizing digital image correlation (DIC) to measure material properties of composites.

DIC is an optical metrology method which provides full-field position and strain measurements while also being non-invasive. Three novel alterations of DIC are used to characterize composite manufactured structures and components. The three applications are (1) in-situ monitoring of thermal residual warpage of composite large-scale additive manufacturing (LSAM), (2) measuring relative fiber orientation within reinforced composites, and (3) local coefficient of thermal expansion (CTE) measurements.

This research found the natural rough surface of the LSAM composite material replicates a speckle pattern suitable for the DIC correlation algorithm with a minimal 3.57% error. This enables DIC to monitor the print process in-situ without painting a speckle pattern. Additionally, DIC combined with a local heating method accurately measured the fiber orientation, achieving 2.5° ± 1.5° accuracy for a continuous unidirectional reinforced composite. The inspection of a discontinuous reinforced composite resulted in an error range from 2.2% to 24.1% when compared to the standardize radiography method. Finally, DIC also measured the coefficient of thermal expansion (CTE) when paired with an infrared camera to monitor the change in temperature. The presence of boundary conditions during locally heating reduced CTE values by 44.9% to 297.0% compared to the standardized method. A correction factor was developed to relate the DIC results to the standardized method.