Browsing by Subject "Aerospace industry"

Now showing 1 - 5 of 5

Open Access
Comparative analysis of PCD drill designs during drilling of CFRP laminates
(Elsevier, 2015) Karpat, Yiğit; Bahtiyar, O.
As a result of increased use of CFRPs in the aerospace industry, the machining of CFRPs has been studied extensively. The majority of these studies consider drilling of CFRPs, since it is the most common process in the machining of structural parts used in aircraft. It has been shown that drilling process parameters and drill geometry significantly influence the quality of holes. In this study, a systematic approach has been used to compare the influence of drill geometry on process outputs such as drilling forces, torques and tool wear. Custom-made double point angle polycrystalline diamond (PCD) drills from the same manufacturer were used in the experiments. The advantage of this approach is that it eliminates the drill material and edge preparation effects on the experimental measurements, thus helps reveal the influence of drill geometry on the process outputs. The pros and cons of different drill designs are discussed and an appropriate design is identified for the drilling of thick CFRP laminate considered in this study.
Open Access
Energy based investigation of process parameters while drilling carbon fiber reinforced polymers
(Elsevier B.V., 2016) Karpat, Yiğit; Bahtiyar, O.
Carbon fiber reinforced polymers (CFRPs) are widely used in the aerospace industry due to their light weight, high strength, and low thermal conductivity. Drilling is a critical process that affects the quality of CFRP parts. This work studies the influence of process parameters on delamination and tool wear. Polycrystalline diamond helical drills are used in the experiments. It has been shown that drilling energy calculations can be used to set appropriate feed and speed parameters and for increasing drilling performance of CFRPs. The results also indicate the importance of thermal modeling of CFRP laminate for better understanding of the drilling process. © 2016 The Authors.
Open Access
GPS/TEC estimation with IONOLAB method
(IEEE, 2007) Nayir, H.; Arıkan, F.; Arıkan, Orhan; Erol, C. B.
Total Electron Content (TEC) is a key variable to measure the ionospheric characteristics and disturbances. The Global Positioning System (GPS) can be used for TEC estimation making use of the recorded signals at the GPS receiver. Reg-Est method that is developed by F.Arikan, C.B. Erol and O. Arikan can be used to estimate high resolution, robust TEC values combining GPS measurements of 30 s resolution obtained from the satellites which are above the 10° elevation limit. Using this method, it is possible to estimate TEC values for a whole day or a desired time period both for quiet and disturbed days of the ionosphere. Reg-Est provides robust TEC estimates for high-latitude, mid-latitude and equatorial stations. In this study, some important parameters of Reg-Est such as ionospheric thin shell height, weighting function and receiver-satellite biases are investigated. By incorporating the results of the investigation, Reg-Est algorithm is developed into IONOLAB method. Thin shell model height is an important parameter for Single Layer Ionosphere Model (SLIM). In this study, it is shown that IONOLAB provides reliable and robust TEC estimates independent of the choice of the maximum ionization height. Signals from the low elevation satellites are prone to multipath effects. In order to reduce the distortion due to multipath signals, the optimum weighting function is implemented in IONOLAB, minimizing the non-ionospheric noise effects. GPS receivers record both pseudorange and phase data of signals. IONOLAB can input absolute TEC computed from the pseudorange measurements or phase-corrected low-noise TEC. The TEC estimates for both of these inputs are in good accordance with each other. Thus, taking either pseoudorange or phase-corrected measurement data as input, high resolution, robust TEC estimates can be obtained from IONOLAB. Another important parameter for TEC estimation is satellite-receiver instrumental biases. The biases are the frequency dependent delays due to satellite and receiver hardware. In order to compute TEC, satellite and receiver biases should be removed from GPS measurements correctly. However, the proper procedure of how to include them in the TEC computation is generally vaguely defined. IONOLAB suggests a technique for inclusion of the hardware biases obtained from the web for TEC estimates that are consistent with the results from the IGS analysis centers.
Open Access
Milling force modelling of multidirectional carbon fiber reinforced polymer laminates
(Elsevier, 2012) Karpat, Yiğit; Bahtiyar, O.; Deger, B.
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 a polycrystalline diamond cutter. Cutting force coefficients in radial and tangential directions are calculated as a function of fiber cutting angle. The mechanistic model is shown to be capable of predicting cutting forces during milling of multidirectional CFRP laminates and capable of investigating stability of machining. © 2012 The Authors.
Open Access
Synthetic TEC mapping with ordinary and universal kriging
(IEEE, 2007-06) Sayın, I.; Arıkan, F.; Arıkan, Orhan
Spatiotemporal variations in the ionosphere affects the HF and satellite communications and navigation systems. Total Electron Content (TEC) is an important parameter since it can be used to analyze the spatial and temporal variability of the ionosphere. In this study, the performance of the two widely used Kriging algorithms, namely Ordinary Kriging (OrK) and Universal Kriging (UnK), is compared over the synthetic data set. In order to represent various ionospheric states, such as quiet and disturbed days, spatially correlated residual synthetic TEC data with different variances is generated and added to trend functions. Synthetic data sampled with various type of sampling patterns and for a wide range of sampling point numbers. It is observed that for small sampling numbers and with higher variability, OrK gives smaller errors. As the sample number increases, UnK errors decrease faster. For smaller variances in the synthetic surfaces, UnK gives better results. For increasing variance and decreasing range values, usually, the errors increase for both OrK and UnK. © 2007 IEEE.