Abstract

A hybrid multi-output approach which combined the Taguchi method and fuzzy logic was used in this research in order to optimise the mechanical and physical properties of PVC pipes. Eight techological parameters which mostly define the extrusion process were taken into consideration in order to obtain the best possible results for six measurable quality characteristics of PVC pipes. Eighteen experiments with the same number of different parameter value sets were conducted resulting in eighteen various PVC pipe samples. The sample from the second experiment showed the highest value of comprehensive output measure (COM = 0.615), while the lowest COM value (0.359) was noted with the sample no. 13. The results of ANOVA revealed that traction speed is the most significant parameter affecting multiple characteristics with contribution of 28.86%. The optimum combination of factors and their levels is A₁, B₃, C₃, D₂, E₂, F₃, G₃, H₂ – the sample produced at traction speed of 8.8 m/min, nozzle temperature of 211℃, expander doser speed of 23.2 rpm, extruder screw speed of 17.5 rpm, coextruder screw speed of 40.6 rpm, barrel temperature of 178 ℃, extruder mixture doser speed of 28.1 rpm and the coextruder mixture doser speed of 36.4 rpm.

Abstract

Sandwich structures made of composite materials, namely glass fibre/polyester, are widely used in  the naval, ground transportation, aerospace and telecommunication industries. Due to the combination of key factors: the good mechanical properties of this kind of materials together with their low specific weight and their permeability to electromagnetic waves. These structures are often subjected to impulsive loads during its service life. Therefore, in order to obtain a safer structural design, a better knowledge of the impact response must be accomplished. It has been demonstrated that the composition of the skins plays a fundamental role in the behaviour of sandwich structures against high-energy ballistic impacts. The structures studied in this work are composed by two E-glass fibre/polyester skins and a PVC core. With the objective of optimising this kind of structures when they are subjected to high-energy impact, a numerical study in the finite element code Abaqus has been carried out. In this study, the number of plies in the front and rear faces varies in order to find the configuration that presents better ballistic performance. To this aim, a VUMAT subroutine previously developed has been used for the skins. The core has been modeled with the crushable foam constitutive model available in the software Abaqus. The influence of the thickness of the skins can be tested by means of this numerical model. The results obtained show that the residual velocity disminishes the more the number of layers in the rear skin increases.