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Andrew E Lovejoy

Publications and source records attributed to Andrew E Lovejoy.

23 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Manufacturing Trials of Integrally Stiffened Panels for Flight Applications

Reduced weight is an ever-increasing demand within the aerospace industry, and non-traditional means of achieving this demand are increasingly being considered. There is also a desire to reduce the manual labor involved in attaching thousands of parts together with rivets and other fasteners. Using advanced stiffener concepts can avoid the weight of fasteners and streamline fabrication by reducing the part count, while still providing the mandatory strength requirements for flight certification. Described herein is a set of manufacturing trials that were completed at NASA Langley Research Center to investigate the feasibility of various integrated stiffener concepts. Fully composite stiffeners that can be integrated or attached by other means, either through bonding or interleaving them within the skin, can remove the fasteners and still maintain a rapid manufacturing rate. This study contains these advanced stiffener concepts, and the lessons learned and design iterations that resulted from the series of manufacturing trials. Each set of trials was completed with an end goal of using tow-steered integral stiffeners for flight structure in composite aircraft wings.

Composite↗
NASA NTRSDate not supplied

Manufacturing Trials of Integrally Stiffened Composite Panels Using Automated Fiber Placement

Commercial aircraft structures are frequently manufactured from carbon-epoxy materials because of their weight and stiffness advantages compared to metallic materials. Wing cover panels are regularly manufactured using an automated fiber placement (AFP) process, but current design and manufacturing methodologies do not fully take advantage of the opportunities afforded by AFP. Design and manufacturing studies were undertaken at the NASA Langley Research Center at the Integrated Structural Assembly of Advanced Composites (ISAAC) facility to quantify manufacturing benefits and limitations associated with AFP to create structurally efficient integral stiffeners as an alternative to bonded or mechanically fastened stiffeners. This methodology could save weight and remove failure mechanisms by reducing the need for rivets and bonding materials since the stiffener plies are interleaved within the skin plies. The use of AFP with integral stiffeners can open the design space, but a fundamental, systematic evaluation of manufacturing limitations is necessary. Manufacturing trials are described herein, where considered manufacturing variables included stiffener location, stiffener course staggering, stiffener widths, stiffener intersections, and material thicknesses for both the skin and stiffener plies. The manufacturing process and lessons learned from each trial are described, including the most successful current design which contains staggered stiffeners, non-traditional laminate angles, and a combination of multiple material thicknesses within the same laminate.

Composite manufacturing↗
NASA NTRSDate not supplied

Improvements to Stitching Controls for Manufacturing Advanced Stitched Composites

Stitched composites have been extensively studied and have been shown to have benefits over unstitched composites for stiffened structures, including improved damage tolerance, reduced weight, and fewer fasteners. These benefits make stitched composites attractive from a performance perspective, however, the nature of stitching the preforms prior to infusion includes additional manufacturing steps and equipment compared to conventional resin infusion. Stitching of composite material structures at NASA Langley Research Center (LaRC) is performed at the Integrated Structural Assembly of Advanced Composites (ISAAC) facility using control algorithms developed by the lead author. Two deficiencies have been identified in the current control algorithms, and mitigations for these deficiencies were developed within the Hi-Rate Composite Aircraft Manufacturing (HiCAM) project and are presented herein. First, decoupling stitch translation and rotation takes more time for stitching since two robot operation control steps are executed for each stitch. Therefore, a method was developed to determine when to decouple the translation and rotation for stitching, which reduces stitch time by decoupling the operation control steps only when necessary to execute the stitch properly. Second, a correction to the sideslip stitching approach that eliminates a significant portion of the pre- and post-stitching activities was developed. The developed method adjusts the sideslip stitch angle based on the rotations of previous stitches to ensure that the width of the stitching seam remains constant along its length. Constant seam width eliminates observed overlap of the insertion and catcher thread portions for highly curved paths, which maintains the desired uniformity of through-the-thickness architecture along the seam and eliminates the local degradation of properties where the insertion needle is too close to, or crosses, the catcher needle portion of the seam.

stitching↗