Projects
Optimization of Steered Fiber Paths for Robotic Automated Fiber Placement (RAFP)
Recent developments in technology and the introduction of composite-heavy aircraft like Boeing 787 and Airbus 350XWB series, has forced CFRP manufacturing for large aerospace structures using RAFP technology. While ensuring faster production and repeatable manufacturing of parts, it also opens a design paradise for an airframe designer to now use non- traditional fiber paths that could be steered based on optimal design for various loading conditions, like minimizing stress concentrations around cutouts or to maximize the buckling loads. This project identified manufacturing parameters and constraints and introduced a novel method to incorporate these technical details in deriving optimized fiber paths for specific design loads.
Effect of defects in Robotic Automated Fiber Placement (RAFP)
Automated composite manufacturing using RAFP comes with some inherent defects, that are identified as manufacturing signatures. These are imperfections caused while the CFRP tows are laid on a tool surface or imperfection during consolidation and curing. These include imperfections like tow misalignment, tow buckling, tow pull up, gaps and fold-over (overlaps). They are closely related to the machine that is used and hence is referred to as manufacturing signature (MS). In this study, a comprehensive testing framework is introduced and specimens with controlled gap and overlap imperfections of varying sizes and distribution were manufactured and tested. Digital image correction (DIC), in situ inspection with edge cameras and post-test microscopy analyses provide a detailed insight into the failure progression and modes.
Buckling tests on RAFP manufactured, optimized, flat panels
Optimal designs proposed for maximizing uniaxial buckling performance of flat composite panels were manufactured using RAFP technology. These panels had repeating overlap regions in each ply that caused local in-built stiffeners causing local local unsymmetry and thereby causing warpage post curing. The curvatures were quantified using co-ordinate measuring machine (CMM) and bespoke fixtures were made to accommodate testing of these curved panels. Buckling tests are conducted to quantify the transition load of the structures under uniform uniaxial edge compression
Double- Double Laminates
Traditional lay-ups in laminated composite structural parts have largely focused on using quasi-isotropic laminates made of permutations of 0°,90° and ±45° laminae. In this study, three different lay-ups of symmetric laminates to compute critical buckling loads under uniaxial in-plane compressive loads is first investigated. An optimization problem is solved to determine the lay-ups that maximize the buckling performance. The resulting laminates are compared against a new class of laminates, referred to as double-double (DD), which have distinctive advantages for thickness tapering and therefore manufacturability. It is concluded that DD laminates, because of their manufacturability advantages, are promising candidates for several aerostructural applications.
Optimal non-homogenous structures using 3D printed plastics
Additive manufacturing modalities open wide possibilities to manufacture monolithic non-homogenous structures to tailor structural properties. It is also taken into consideration that the printed materials have an anisotropic behavior as the print direction is stiffer than the transverse direction. Some of the examples are- optimal distribution of materials of different discrete stiffness to minimize stress concentrations around cutout in flat plates, optimal distribution of stiffness to increase energy absorption in circular honey comb structures under in-plane compressive loading, optimally designed L-bracket under shear loading etc. Further, behavior of these materials are modeled using non-linear viscoelasticity or J2 plasticity models to obtain the load- displacement response.
