# Prediction of the Tensile Load of Drilled CFRP by Artificial Neural Network
## 1 Introduction  
Composite materials can be defined as materials obtained by combining more than one material with one another without chemical interaction and dissolution to obtain the desired mechanical property. Composite materials improve rigidity, strength, corrosion resistance, electrical resistance, tribological properties, weight, wear resistance of the materials [1]. Along with the developing technology, traditional materials such as metal and ceramics are insufficient and cumbersome for the production of new products [2]. Composite materials can be an alternative to traditional materials. Especially since the 1960s, the use of composites has increased dramatically in parallel with the development of technology. For example, the Boeing DC-9 aircraft, which is produced in 1965, contains less than 5% by weight of composites. However, the Boeing A380 aircraft which was produced in 2012, contains 53% by weight of composite [3]. For another example, the Lamboghini Sesto Elemento contains 80% by weight of composite. Carbon fiber reinforced plastic (CFRP) is the most known composite material [4]. CFRP requires machining for assembly integration [5]. The drilling is the most used machining method for CFRP. However, some problems have been encountered in the drilling of CFRP [6]. Delamination, tool wear, and bad surface roughness are some of these problems [7]. Tensile strength is adversely affected by these problems. These problems are the root of most part rejections [8]. This indicates how important it is to drill composite materials to the correct parameters. Researchers have focused on optimization of the defects caused by drilling. A literature study is given below. [PERSON] et al. [9] found out the decrease in tensile strength caused by delamination. They have researched the decrease in tensile strength using a finite element method model. In their paper, cohesive elements and the damage mechanics model were applied to determine the decrease of strength caused by drilling-induced delamination. They noted that he delamination induced by drilling decreases the tensile strength of composite and up to about 15% of the strength decreases with the increase of the delamination factor. [PERSON] and [PERSON] [10] compared the strength of composite that was produced in drilled holes and molded-in holes. Their study has shown that the strength of specimens with drilled-holes exhibited failure strengths lower than those with molded-in holes. When the hole diameter decreased, the maximum stress increased but the difference between tensile strength of the composite with drilled holes and molded-in holes increased from 15 to 25%. [PERSON] et al. [11] researched the influence of drilling parameters on natural fiber reinforced plastics (NFRP) composite. They used natural fiber such as banana, hemp, jute and vakka in their study. They determined that cutting speed is the most effective drilling parameter on the strength of NFRP. They recommended a medium cutting speed and low feed rate speed to minimize the loss of tensile strength of NFRP. [PERSON] et al. [12] researched the influence of drilling conditions on the strength of flax fiber reinforced polymer composite using the Taguchi method. Their study showed that the influence of drill bit type was negligible and that lowest feed rate and highest spindle speed caused minimum loss of strength of composite. [PERSON] et al. [13] evaluated tensile strength of the composite by using a neural network depending on drilling parameters. The experiments were carried out with 4 different tool geometries (8 facets, 4 facet, Parabolic and Jodrill), 3 levels of feed rate and 3 levels of spindle speed. They introduced an artificial neural network (ANN) model for the tensile strength of the composite in their study. They confirmed the experimental data with the ANN model. Most researchers have focused on the effects of drilling parameters on delamination, cutting force and surface roughness. However, few researchers have investigated the reduction of strength due to drilling parameters.