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PROBLEMS ASSOCIATED WITH FIBRE-REINFORCEDCOMPOSITES ULTRASONICALLY-ASSISTED DRILLINGCourse: PhD Mechanical EngineeringFacultyofTechnologyPresenter: Sikiru Oluwarotimi ISMAILCo-authors: Dr Hom Nath Dhakal,Dr Ivan Popov.REFERENCES Ismail S.O., Dhakal H.N., Dimla E., Beaugrand J., Popov I. (2016). The effectsof drilling parameters & aspect ratios on delamination & surface roughnessof lignocellulosic HFRP composites. J. of Applied Polymer Science, 133 (7), 1-8, DOI:10.1002/app.42879, published early view/on-line. Speranza V., Sorrentino A., De Santis F., Pantani R.(2014). Characterizationof PCL melt crystallization: Complementary optical micros., DSC&AFMstudies. Scient. World J., 2014, 1-9. Makhdum, F.; Phadnis, V. A.; Roy, A.; Silberschmidt, V. V. (2014). Effect ofultrasonically-assisted drilling on carbon-fibre-reinforced plastic. J. SoundVibration, 333, 5939–5952. Mallick, P. K. (2008). Fibre-reinforcement composites, materials,manufacturing and design. Third edition, CRC Press, Taylor and FrancisGroup, USA, pp. 1- 619.INTRODUCTION Composites, particularly the natural fibre-reinforcedcomposites such as hemp fibre-reinforcedpolymer/polycaprolactone (HFRP/PCL) have becomeattractive materials today with various desirableproperties and applications (Ismail et al., 2015). The ultrasonically-assisted drilling (UAD) hasremarkable advantages over the conventional drilling(CD), especially in achieving high drilling-forcereduction and excellent drilled surface finish. These advantages are contributing factors for thequality of the drilled holes. This study revealed that the benefits of UAD aredifficult to obtain for the drilling of the HFRC/PCL.MATERIALS AND METHODS Materials (workpiece/sample) HFRP/PCL, extruded composite laminate with aspectratios (AR) of 00 (neat), 19, 26, 30 and 38 (Fig. 1.0b). Experimental Methods/Design. L16 42 orthogonal array of Taguchi method (Fig. 1.0a). UD and UAD techniques, using high speed steel (HSS)drill bit.Fig. 1.0: The CD and UAD (machining) experimental set-up and (a) & (b) samples.RESULTS AND DISCUSSIONSFig. 2.0: Poor surface quality and insignificant force reduction during UAD of HFRP/PCL (natural/biodegradable composites with polycaprolactone matrix).(a) CAD drawing(b) HFRP/PCL laminate(a)UADsurface roughness (Ra),up to 13µm after UAD.(b) CDTable 1.0: Drilling Parameters and Conditions.(a) UAD (b) CDUADCD In addition to the expensiveness of set-up,unpredictable results and drill bit chipping effects ofUAD, Figure 2.0a depicts greater poor surface qualityduring UAD when compared with the CD (Fig. 2.0b), evenat variable drilling parameters (Table 1.0) and AR. A huge occurrence of matrix-melting was observed,resulting into poor burnt-chip evacuation, due to the60oC melting temperature of PCL (Speranza et al., 2014),quite lower than 56-90.2°C & 265–290.8°C compositetool interface temperature during CD & UAD respectively(Makhdum et al., 2014), and above 200°C thermaldegradation or decomposition of natural fibres includinghemp fibres (Mallick, 2008).CONCLUSIONS The two observable effects produced a very high averagesurface roughness (Ra), up to 13µm. Evidently, the drilling-induced damage on HFRP/PCLcomposite depends greatly on the compositeconstituents (fibres and matrix) and drilling techniques. Hence, the choice of drilling technique and engineeringapplications of the drilled HFRC/PCL laminates shoulddepend on their responses to these damage, as UADtechniques could not benefit significantly.