Effect of Thermal Treatment on CFRP Parts Before and After Adhesive Bonding

Numerous non-destructive techniques are being investigated for assuring quality of the adhesive bonds.The research presented here is focused on non-destructive assessment of carbon fibre reinforced polymer(CFRP)parts.The surface condition directly influences the performance of adhesive bonds.The structural joints should ensure safe usage of a structure.However,some modifications of the surface may lead to weak bond that cannot carry the desired load.This is why there is a search for methods of surface assessment before bonding.Moreover,reliable techniques are required to allow to verify the integrity of the adhesive bond after manufacturing or bonded repair.We focus on the laser induced fluorescence(LIF)method for assessing the surface state.The LIF is a noncontact measurement method.In the context of adhesive bond assessment the electromechanical impedance(EMI)method is studied.The EMI uses surface bonded piezoelectric sensors for excitation and sensing.The investigated samples were made of CFRP layers.The samples were treated at elevated temperatures.The influence of the thermal treatment was studied using LIF.The thermal treatment at 220℃could be clearly distinguishedrom the rest of the considered samples.The thermally treated plates were bonded to untreated plate and then they were measured with the EMI method to study the influence of the treatment on the adhesive bond.The changes of EMI spectra were significant for the treatment at 280 ℃ and for some thermally treated samples that were later contaminated with de-icing fluid.     

Full Wavefield Analysis for Damage Assessment in Composite Materials

In this paper damage assessment based on guided elastic wave propagation phenomenon is presented.Guided waves are generated by piezoelectric transducer and registered by scanning laser doppler vibrometer(SLDV).Signal processing is based on the analysis of full wavefield measurements gathered from dense mesh of measurement points spanned over area of investigated samples.Full wavefield measurement approach allows creation of animations presenting the guided wave propagation in the structure.Moreover such approach is suitable for analysis of interaction of guided waves with discontinuities located in structure.In the research attention is paid especially on analysis of phenomenon of S0/A0′guided wave mode conversion due to interaction with investigated discontinuities-teflon inserts and impact damage.The presented work is related to glass fibre reinforced polymer(GFRP)samples.In the research,auxiliary non-destructive testing(NDT)method is also utilized.The aim of this method is to indicate the depth of discontinuity,and to prove that delamination was created in the case of impact damage.Auxiliary method is based on terahertz spectroscopy(THz)where the analysis of propagation of electromagnetic waves in the terahertz band is conducted.THz spectroscopy method can be utilized for damage assessment in the dielectric materials like GFRP.