A review on the drilling of CFRP/Ti stacks: Machining characteristics, damage mechanisms and suppression strategies at stack interface

ANN Based Estimation of the Defects Severity at the Drilling of GFRP/Ti Multilayered Composite Structure

“…Unfortunately, when drilling the structure under consideration, it is very difficult to use a support tightly pressed against the back side of the wall being drilled, since the strict requirement of alignment forces drilling of both coaxial holes in one drill pass, and the closed box-shaped design of the spar will make it difficult to install any supports. The dependences obtained qualitatively fully correspond to the results of the studies cited above [10][11][12][13]17,18,20,29,42] both in terms of the nature and value of the degree of delamination at the entry and exit of drills from holes, and in terms of the dependence of these defects on the drill geometry and drilling modes. However, a complete quantitative comparison of the results obtained in the work with the results of the cited studies is impossible and illegal due to the significant difference in the properties of the processed materials.…”

“…A large and ever-expanding variety of composite materials, composite/metal layered structures required for machining significantly complicates the development of a system for classifying and ranking the machinability of such structures [2,3,15,29], an analogue of which is currently developed for metal alloys and is being continuously improved [22,53]. The creation of such a system, which requires the efforts of specialists from many countries, will require the implementation of huge amounts of research using not only the most modern scientific methods, but also means for detecting and assessing the degree of defects, suitable for real production conditions.…”

“…Despite the fact that in many works, e.g. [2,3,6,8,13,15,29,43,48], it is indicated that the amount of delamination decreases with increasing cutting speed, its upper limit was restricted due to elevated temperature, which was established experimentally. Based on the recommendations of these works and our own experience gained in the industrial manufacture of spars, a variation interval of 7.5-19 m/min was adopted for the cutting speed, and 0.2-0.8 mm/rev for feed rate.…”

“…The delamination measurements were carried out using a computer system for digital processing and analysis of the optical microscopic images recorded on the front and back sides of the drilled samples. In accordance with the generally accepted methodology (see review papers [2,15,29]), the amount of delamination was taken as half the difference between the maximum diameter Dmax of the circle circumscribed around the layered area and the nominal diameter D of the hole. In Figure 3, this value is represented by the letter d.…”

“…Studies of the conditions for the occurrence and development of the described defects using the most modern experimental equipment, including, optical and Scanning Electron Microscopy (SEM), Raman and Fourier-Transform Infrared (FTIR) spectroscopy; reconstruction of the temperature field by using high sensitive thermocouples integrated inside the specimens with multi-sensorial data acquisition system, thermal analysis, high precision mechanical testing according the required ASTM standards, are presented in works [11,16,[29][30][31][32][33][34][35][36][37][38][39]. Their results made it possible to study in detail the thermal effects in polymer matrices, to propose methods for reducing their influence by introducing some fillers, and to reduce unwanted deformations due to the rational choice of process modes.…”