Optimization process of sandwich composite pipes by the Taguchi method

In this study, an optimization process for sandwich composite pipes with a sand-filled resin core is carried out based on the Taguchi method. According to the ASTM D2412-02 standard, the stiffness of the composite pipes is measured using parallel plate loading. Three similar pipes with three layers are produced as test specimens at Farassan Manufacturing and Industrial Company. The inner and outer layers of the specimens are made of continuous fibre/resin, while the middle layer is a laminate of continuous E-glass fibre/resin/sand. The test specimens are subjected to quasi-static lateral compression tests using a universal testing machine and their stiffness is determined at a deflection of 5% of the internal diameter. The wall thicknesses of the inner (T1), middle (T2) and outer layer (T3) are then considered as three control factors during optimization. 25 experiments are considered using design of experiments (DoE) and numerically simulated using ABAQUS software. Based on the composite multi-objective SNR, the influence of the layer-thickness factors was ranked as T1, T3, and T2, respectively. In addition, the results showed that the optimal sample is achieved when T1, T2 and T3 are set to 0.7, 2.0 and 2.0 mm, respectively; The finite element model predicted a nominal compressive-load increase of 14.93% at 5% diameter deflection for the optimized configuration. Based on the 1.17% numerical–experimental difference obtained at the same validation point, the estimated improvement ranges from approximately 13.6% to 16.3%. These results show that optimizing the layer thickness ratio using the Taguchi method can significantly improve the structural performance of sandwich composite pipes and provide valuable design guidelines for industrial applications.