Experimental and Numerical Investigation of CO2 Laser Cutting of Carbon/Kevlar Hybrid Composite

Koohi, Kaveh Moghadasi (2020) Experimental and Numerical Investigation of CO2 Laser Cutting of Carbon/Kevlar Hybrid Composite. Masters thesis, Universiti Malaysia Sarawak (UNIMAS).

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Abstract

Carbon/Kevlar hybrid composites are increasingly being utilized in aerospace and automotive industries due to their superior structural (both in fatigue and static conditions) and lightweight characteristics. Laser cutting is an effective way to perform precise cutting of the composites due to its non-contact method. Accordingly, use of powerful lasers in cutting of composites is fairly wide to overcome some challenges concerning anisotropic properties of these materials at the expense of large heat-affected zones (HAZs) and kerf width, and fiber pullout. However, use of low power lasers due to possessing lower beam intensity for cutting fiber reinforced composite is not quite common. The situation becomes more challenging when it comes to cutting hybrid composites owing to constituting more than two dissimilar materials. Additionally, complexities in definition of constituents materials properties of hybrid composites has being led to pay less attention in numerical modelling of laser processing of these types of composites, while numerical modelling offers considerable promise to reduce costs associated with trial-and-error process in laser cutting. Therefore, the aim of this study is to investigate low-power CO2 laser cutting of a synthetic carbon/Kevlar hybrid composite and to introduce a new method of numerical modelling using a novel technique of element deletion during laser movement to achieve kerf characteristics and HAZ. Response surface methodology (RSM) along with Box-Behnken design was employed to understand the interactions between the process parameters such as laser power, cutting speed and standoff distance (SOD), and their effects on the cut quality characteristics including size of HAZ and kerf characteristics. Following this, process parameter optimization was successfully carried out using ANOVA to minimize HAZ and kerf widths in multi-pass scanning. ANOVA shows that medium power level (37.6 W) at maximum level of cutting speed (25 mm/s) and SOD of 51.04 mm are optimum in multi-pass scanning of carbon/Kevlar composite. Based on these parameters, the experimentally optimized kerf characteristics and HAZ were measured less than 10%. Qualitative measurement using scanning electron microscope was performed to evaluate the effects of process parameters and fiber orientation on fiber pullout, HAZ and material decomposition. Difference between the thermal properties of carbon fibers, Kevlar fibers and polymer matrix (epoxy) was found to influence HAZ and kerf widths. Due to limitation of the experiment to measure thermal stresses, numerical simulation utilizing Abaqus was performed to calculate the stresses and damaged area developed in the cutting region. At the same time, element removal of the ablated composite was successfully predicted using temperature dependent Hashin-damage criteria. It was discovered that the temperature gradient around the fibers is inhomogeneous due to higher thermal conductivity of carbon fibers than Kevlar fibers. Additionally, stress profile shows that the stress generally increases with the number of passes. The numerical simulation agrees well with the experimentally measured HAZ and kerf widths. The study is expected to be the first step towards an application of rules for manufacturability of carbon/Kevlar hybrid composite, specifically in aerospace and automobile industries especially in designing high-stiffness and lightweight structures for ailerons, fuselages, landers, rovers, and satellite buses.

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