Investigation of adhesive properties and core geometry effect on natural vibration behavior of honeycomb composites under pretension

Honeycomb composite materials are preferred in areas where lightness and stiffness are important from the aviation sector to the energy sector. In this study, with the help of finite element method in honeycomb composite material; the effect of selected parameters and prestress on natural frequencies were investigated as a result of gravitational prestressed / non-prestressed and thermal expansion prestressed / non-prestressed analyzes. Selected parameters; geometry parameters (core width, core height, topology), thermal expansion coefficient of adhesive material and modulus of young's modulus of adhesive material. As it is known, vibrations on the structures can have destructive effects even at small loads, especially if they are at the same frequency with natural frequencies. As a result of the analysis, it was determined that prestressing has an effect on natural frequencies. However, due to the high rigidity and lightness of the material in question, the effect caused by gravitational prestressing was determined to be negligible in the parameter range we investigated. As a result of thermal expansion prestressing; it is generally determined that it decreases the initial natural frequency values but the change effect on other mode frequencies is very low. It has been determined that stiffness decreases as the value of the core width parameter increases and stiffness increases as the value of the core height parameter increases. As a result of the increase of core width parameter value, it was determined that the main mode frequency value was transferred to lower frequency value and 100 mode frequencies examined were moved to a narrow frequency range (Acceptance: the natural frequency values that affect more than 5% of the total mass are called the main mode). As the value of the topology parameter increased, it was determined that the main mode frequency was moved to a lower frequency value and the 100 mode frequencies examined were moved to a narrow frequency range. As the value of core height parameter increased, it was determined that 100 mode frequencies examined were carried to a narrow frequency range. However, it has been determined that the main mode frequency values are increased or decreased according to the direction of freedom. Therefore, there is no general interpretation of the main mode frequency change. As a result of the increase in the young's modulus of the epoxy material, it was determined that the frequency values of the main mode were generally increased slightly. Increasing coefficient of thermal expansion of epoxy material did not change natural frequencies. When the young's modulus and thermal expansion coefficient parameters of the epoxy material are examined in the results of thermal expansion prestressed / non-prestressed analysis; it was determined that the main mode frequency value increased with a small amount by pretension effect.