Turkish Aerospace Industries

About: Turkish Aerospace Industries is a based out in . It is known for research contribution in the topics: Finite element method & Nonlinear system. The organization has 237 authors who have published 241 publications receiving 1461 citations. The organization is also known as: TUSAS & TUSAŞ.

Mechanistic force modeling for milling of unidirectional carbon fiber reinforced polymer laminates

Abstract: Carbon fiber reinforced polymer (CFRP) usage in the aerospace industry has been steadily increasing due to its superior material properties such as high strength, low weight, high resistance to corrosion, and a low thermal expansion coefficient. In addition, CFRP parts are produced near-net-shape, a process that eliminates rough machining operations. However, machining operations such as drilling, side milling, and slotting are still necessary to give the CFRP parts their final shape. A majority of the studies on machining of CFRP laminates are on drilling. The number of studies on milling of CFRPs is quite limited. In this study, a mechanistic cutting force model for milling CFRPs is proposed based on experimentally collected cutting force data during slot milling of unidirectional CFRP laminates using two different polycrystalline diamond cutters. Cutting force coefficients in radial and tangential directions are calculated as a function of fiber cutting angle. The relationship is represented with simple sine functions. The mechanistic model is shown to be capable of predicting cutting forces during milling of multidirectional CFRP laminates. The experimental milling force measurements and predicted milling forces agree well with each other. Surface milling experiments were also conducted to investigate the relationship between milling forces and surface quality. Some suggestions on surface milling of CFRP laminates are given based on these observations.

Online, automatic, near‐real time estimation of GPS‐TEC: IONOLAB‐TEC

Abstract: [1] The variability of space weather can best be captured using total electron content (TEC), which corresponds to total number of electrons on a ray path. The dual-frequency ground based GPS receivers provide a cost-effective means for monitoring TEC. Computation of TEC for a single GPS station is a challenge due to various unknowns and ambiguities such as inter-frequency receiver bias and satellite bias, choice of mapping function, and peak height of ionosphere for ionospheric piercing point. In this study, IONOLAB group introduces a robust, automatic, online computation routine near-real time TEC, IONOLAB-TEC, for IGS and/or EUREF stations from www.ionolab.org. The user can choose online one station or multiple stations, date or dates for the computation. The IONOLAB-TEC values can be compared with TEC estimates from IGS analysis centers. The output can be obtained either in graphical form, or IONOLAB-TEC estimates can be provided in an excel file. The service is easy to use with a graphical user interface. This unique and original space weather application is provided online, and IONOLAB-TEC estimates are downloaded automatically to the user defined directories under user defined filenames.

Experimental and computational study of the damage process in CFRP composite beams under low-velocity impact

Abstract: Damage process in composites subjected to low-velocity impact is investigated both experimentally and numerically. Drop-weight impact experiments are carried out, in which a model unidirectional [ 0 5 / 90 3 ] s CFRP laminate beam is impacted by a cylindrical head creating an almost uniform two-dimensional loading condition. Initiation and progression of damage, consisting of matrix cracks and delamination, are visualized in real-time via ultra-high-speed camera at rates up to 60,000 fps and the sequence of failure events are clearly captured. Evolution of dynamic strain fields in the laminate is then quantified by a Digital Image Correlation (DIC) analysis and the resulting final failure patterns are characterized by a digital microscope. In the computational part, a three-dimensional finite element analysis is performed using ABAQUS/Explicit to simulate the experiments. In these simulations, the intraply matrix damage in the middle 90° layers is modeled using a Continuum Damage Mechanics (CDM) based composite failure theory with LaRC04 initiation criterion and implemented via a user-written VUMAT subroutine. Delamination is modeled using cohesive interface elements that are introduced between the 0°/90° interfaces. Damage initiation time, location and the interaction of failure modes are compared with the experimental data. Real-time observations of the sequentially occurring diagonal matrix cracking followed by dynamic delaminations are made. In addition to the major diagonal matrix cracks, existence of multiple diagonal micro-matrix cracks near the upper interface are shown which are also predicted by the simulations. Finally, experimentally obtained real-time strain field values, failure mechanisms and the failure sequence are shown to be in good agreement with the simulations. We believe that the elaborate experimental results presented here for an idealized composite layup can serve as a benchmark test case to validate composite and interface damage modeling methods.