Studies of microwaves applications for adhesive, weld joint and NDT technique

One of the most important areas of the application of industrial microwave processing for materials processing is curing polymers and polymer based composites. This research effort has been made to fast process and assesses the joining of thermoplastic substrates. Polycarbonate and Acrylic sheet substrates were chosen. Two adhesives were selected, namely the C-245 General Purpose Epoxy Adhesive and Toughened Acrylic Adhesive respectively in order to provide heterogenous bonging. Teflon jig and wooden clamp jig were designed and used to assist the adhesive joining process. Single lap shear joints were prepared for characterisation to ASTM procedures. Adherend were prepared and the joining process was performed in the Variable Frequency Microwave Furnace (VFMF). Curing was input with various power levels and irradiation duration. Inside the cavity of the VFMF, a temperature senor probe was used to automatically monitor the temperature level of the load. Operational parameters, such as temperature and power levels, were recorded and saved as a file on the CPU unit. Tensile testing was performed on the all adhesive joints using Instron Machine and the tensile bond strength (Stage I) was calibrate and recorded. Another set sample (Stage II) was performed again, but the tensile testing measurements were performed after six months since the bonding was performed. These two sets of data has recorded and further studied. Scanning Electron Microscopy (SEM), photostress analysis using a polariscope, and infrared spectroscopy analysis were performed on selected fractured joints to explore the detailed fractured surface characteristics and stress distribution of the tested to destruction joints. Results show the average of both set of the bond strength and the different percentage deviations from the parent material strength. In general, stage II seemed to yield weaker bond strength. This provided a strong indication that the microwave curing bonding strength is time (duration) sensitive. The polariscope results showed an even stress distribution and the bond strength being close to the parent material strength. Towards the end of the thesis, a new NDT (non-destructive testing) methodoloty is demonstrated based on the microwave characterisation technique. This form of quality testing can prove to be a new evaluation tool for assessing bond integrity using the same processing and quality testing facilities, ie the VFMF. In summary, this thesis presents the results of many adhesive bonded experimental studies as well as a new methodology for evaluating bonded joints. Together with the new findings about the duration sensitivity of the microwave curing process and NDT technique, the associated limitatioins are outlined. The recommendations arising from the research outcomes suggest ways for extending the work of this research studies and suggest further developments for enhancing the capabilities and applications of the techniques.