| Abstract [eng] |
Aerospace composite structures are usually bonded using two-component adhesives. These adhesives require high temperatures to cure, so traditional heating methods, such as autoclaving, are used. However, these methods have several major drawbacks that limit their applicability in the aerospace sector: the equipment is energy-intensive and too expensive for the production of large structures. Therefore, the goal of this final project is to develop an innovative method for bonding composite parts using localised heating to cure an epoxy adhesive. For this study, the single-lap joint type was chosen due to its wide applicability in aircraft structures. The experiments were conducted with six groups of specimens: a control group (abbreviated KG) (adhesive without fillers), a NAP group (non-woven carbon fiber, abbreviated NAP), and four groups of multi-walled carbon nanotube (MWCNT) specimens with different MWCNT loadings in the adhesive (0.25, 0.50, 0.75, and 1.00 wt %). An electrical system controlled by an Arduino Mega 2560 Rev3 microcontroller was developed for localised heating, managing the supply of electric current to each sample according to a specified heating cycle. Measurements of electrical resistivity showed that the alignment of MWCNTs in the adhesive is more effective at lower MWCNT loadings, particularly at 0.25 wt % and 0.5 wt %, where the average resistance of the samples decreased by 94.88 % and 97.95 %, respectively. At higher MWCNT loadings, where a greater number of electrically conductive networks are already formed, the change in resistance after MWCNT alignment is less significant. Thermographic analysis results showed that the higher the MWCNT loading in the sample, the more uniform the temperature distribution is over the entire joint area. The most uniform temperature distribution was observed in the NAP sample due to the isotropic electrical and thermal conductivity of the NAP fiber used throughout the joint. The results of tensile tests showed that lower MWCNT loadings (0.25 wt % and 0.5 wt %) strengthened the adhesive used in the joints (9.66 MPa and 10.16 MPa, respectively). In contrast, higher MWCNT loadings deteriorated the mechanical properties of the joint (0.75 wt % – 9.01 MPa; 1.00 wt % – 8.61 MPa). SEM analysis showed that at higher MWCNT loadings, the mechanical properties of the joint decreased due to an increased number of voids, MWCNT agglomerates, and increased brittleness of the adhesive. Finite element analysis showed that with increasing MWCNT loading, the model temperature decreased and became more uniform, particularly in the case of randomly dispersed MWCNTs. At a 1.00 wt % MWCNT loading, the difference between the average temperatures of randomly dispersed and aligned MWCNTs in the RVE model was 2.23%, increasing to 4.98% at a 0.25 wt % loading. FEA analysis showed that MWCNT alignment leads to more efficient heat generation, resulting in higher average and maximum temperatures. |
