In this work, we have undertaken to analyze the adhesive joints in polymeric beams particularly those of polymethylmethacrylate (PMMA). Ultra-thin joints in PMMA it having uniform and tapered cross-sections were introduced by joining the pieces using 1, 2- dichloroethane (DCE). The property of the joint was varied using two modifiers, dioctylphthalate (DOP) plasticiser and non-solvent cyclohexane (CH). Transverse flexural waves in the beam were generated by impacting the beam function of time was measured at a given location. The acceleration at a given point on the beam is assumed to be formed by superposition of forward wave, wave coming from the ends of the beam and that of the wave emerging from the joint. The flexural response, so generated, is found to have a region where the information (i. e. %DOP content) concerning the nature of the joint is coded. It was shown that, for rectangular beam, the FFT of this portion is linearly correlated with the %DOP for smaller frequencies. In order to carry out more controlled experiments, studies were made using a calibrated impact hammer and it was found that striking with this hammer is a multiple impact process. However, in a short time (4 millisecond) there is only one impact for which the acceleration versus time data at a given location on the beam was collected. The peak value of this flexural response is found to decrease with the modifier content. Using optimal search technique employing genetic algorithm, the flexural wave, corresponding to the joint was separated. It is shown that for a tapered beam, the FFT amplitudes of the waves reflected and transmitted through the joint are related to the content of the modifier in it. The amplitude ratio of the magnitude of the second lowest frequency after and before joint increase with the modifier content and is more sensitive to the variation in the amount of the CH in joint. The ultimate joint strength of the PMMA beam was also determined using a universal testing machine as per ASTM standards and the failure strength is found to decrease monotonically with the amount of DOP in the joint. Similar tests were conducted for the beams having uniform cross section and identical conclusions were arrived at. It appears that the technique proposed in this work can be successfully used to characterize the mechanical properties of the joint.
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