Carbon fiber prepreg tack characterization for automated fiber placement Nicholas J. Albertson 1, Brian W. Grimsley 2 1 NASA LARSS Summer Intern, Mechanical Engineering, Duke University, 2 LARSS Mentor, Advanced Materials and Processing Branch, NASA Langley Objective To contribute to the ACP process model development by examining the effects of temperature and humidity on the tack of commercially available aerospace prepreg. Additionally, a profilometer will be used to measure the material surface roughness to determine if there is any correlation with the measured tack values. References 1.) Designfax.net; 2.) Mtorres.es 3.) Dubois, O. et al, 2009; 4.) Beakou, A. et al, fiber/torresfiberlayup Introduction Automatic Fiber Placement (AFP) is a recently adopted technology in the aerospace industry. It is an automated method for manufacturing carbon fiber composites for applications where the structures are large and complex, or where traditional hand lay-up techniques are not suitable. Figure 2: An AFP machine depositing strips of prepreg onto a mold [2] Robotic placement heads are used to deposit strips of prepreg, or thin sheets of carbon fiber that have been pre-impregnated with a bonding matrix, such as an epoxy resin. Figure 1: AFP used to manufacture the fuselage of the Boeing Dreamliner [1] An AFP process model which accurately predicts process defects will significantly reduce the trial and error fabrication effort required to meet production certification of aerospace composite structures. NASA has recently partnered with the aerospace industry in the Advanced Composites Project (ACP) to develop AFP process models which can predict part quality based on the physical interaction of the AFP processing parameters such as placement speed, orientation, and lay-up environment. Discussion Methods This study is concerned with developing the testing process and proof of concept. Future steps include performing significantly more baseline probe-tack testing to explore the effects of all test variables on the characteristic tack of the prepreg. This data will be analyzed and results will be included in the ACP process model to determine ideal manufacturing conditions for AFP carbon fiber products. The results from this prepreg tack characterization study will contribute to the development of reliable AFP process models. This will result in a decrease in the current trial and error development process required to meet production certification of composite structure on aerospace vehicles. Figure 3: Instron 5448 Microtester (left), FRT Profilometer (right) The probe tack test is a method for quantitatively measuring the tack of pressure sensitive adhesives (i.e. tape), and has been adopted for carbon fiber prepreg. A 10 mm diameter probe was designed and machined for an Instron ® 5848 Microtester mechanical test frame using a 100N load cell. Additionally, the test frame has a heating chamber attachment which allows temperature control between room temperature and 65°C. A testing profile was developed that controlled the contact rate, contact force, contact time, and debonding rate. The initial values for these variables were obtained from the literature [3,4]. The quantitative tack measurement is reported as the max tensile force and the apparent modulus, which is calculated from the stress vs. extension data. The surface roughness data is obtained using an FRT ® laser profilometer, and is reported as a characteristic length. Figure 3: A characteristic probe tack test result (left); a prepreg sample undergoing the probe tack test (above) Figure 4: A characteristic profilometry result (right); a prepreg sample showing the 10mm square test region (above)