Issue 50

N. A. Fountas et alii, Frattura ed Integrità Strutturale, 50 (2019) 584-594; DOI: 10.3221/IGF-ESIS.50.49 590 Ra ( μ m) = 9.3 - 0.004 n - 3.1 f - 2.5 a +29.1 f 2 +1.56 a 2 +0.005 nf - 0.00002 na - 3.5 fa (2) Rt ( μ m) = 75.3 - 0.032 n - 103 f - 35.3 a +210 f 2 +13.5 a 2 +0.051 nf + 0.006 na - 3.5 fa (3) Fc (N) = 69.7 - 0.022 n – 612 f +195 a +1283 f 2 - 53.4 a 2 +0.135 nf – 65 fa (4) To test whether the data predicted by regression models are well-fitted or not, the coefficient of determination R 2 has been calculated for each model. These values have been found to be equal to 97.29 %, 96.76 % and 99.44 % for Ra , Rt and Fc respectively. In other words the correlation coefficients for Ra , Rt and Fc are 0.97, 0.96 and 0.99 respectively. Hence, the data predicted by the developed models for each quality characteristic (output) are well-fitted. In order to gra- phically examine the adequacy of the models, correlation plots were produced. From Fig.7, it is evident that the models developed for fitting the experimental results corresponding to Ra , Rt and Fc are both significant and adequate whilst, simultaneously, they are capable of providing outputs in very good agreement with experimental results. (a) (b) (c) Figure 7 : Comparison of experimental and predicted results for: (a) Ra, (b) Rt and (c) Fc . M ULTI - RESPONSE OPTIMIZATION USING THE GREY WOLF ALGORITHM eta-heuristic optimization techniques have drawn the researchers’ interest over the last two decades. Such tech- niques are Genetic Algorithms (GAs) [23], Ant Colony Optimization (ACO) [24], and Particle Swarm Optimi- zation (PSO) [25]. In addition to the huge number of theoretical works, such techniques have been applied in various engineering fields. The reason why such algorithms have become very popular in terms of their implementation to engineering problem-solving lies on four main reasons, simplicity; flexibility; derivation-free mechanism; and local optima avoidance. In general, meta-heuristic algorithms are quite simple in their application since they have been mostly inspired by simple concepts. The inspirations mimic physical phenomena like animals’ behavior, or evolutionary concepts. This simplic- ity allows for simulating several natural ideas, proposing novel meta-heuristics, hybridizing two or more meta-heuristics, or 18 16 14 12 10 8 6 4 2 9 8 7 6 5 4 3 2 1 Number of experiment Surface roughness, Ra (μm) Ra (μm) exp. Ra (μm) model 18 16 14 12 10 8 6 4 2 45 40 35 30 25 20 15 10 Number of experiment Surface roughness, Rt (μm) Rt (μm) exp. Rt (μm) model 18 16 14 12 10 8 6 4 2 200 180 160 140 120 100 80 60 Number of experiment Main cutting force, Fc (N) Fc (N) exp. Fc (N) model M