Research On The TA2/PEEK Joints Fracture Toughness Using Regular Surface Micro-pits

One of the predominant concerns in designing,manufacture and application of fibre metal laminates(FMLs)was to optimize the interfacial fracture toughness of metal-polymer joints.It was important to understand the adhesion mechanisms since it will help engineers design failure-resistant interfaces.In this paper,the TA2/PEEK joints were investigated by the processing of lithography,finite element analysis,double cantilever beam(DCB)tests,wetting angle measurement,SEM and orthogonal experiment.Then,the paper has discussed the optimal processing of lithography,the effect of parameters of micro-pits on fracture toughness,wettability and failure mechanism of TA2/PEEK joints.Finally,the results revealed the relation between parameters of micro-pits and failure mechanism of TA2/PEEK joints under mode I loading.Firstly,the regular micro-pits have been fabricated on TA2 surface by lithography.The primary factors,such as surface roughness,coating,baking and etching,were explored to obtain the optimal processing of SUN-1150 P.The results revealed that the coating was conducted at low speed 600 rpm/min with dwell time 5s,and high-speed 4000 rpm/min with dwell time 30 s,and then the specimens were exposed to UV for 40 s.The heating was followed by pre-baking temperature 110? with dwell time of 10 min and post-baking temperature at 90? with dwell time of 30 min.The depth of micro-pits was propotional to etching time when etching time over 30 min.Then,the finite element analysis was applied for evaluation of the effect of parameters of micro-pits on fracture toughness of TA2-PEEK-TA2 joints under model I loading.The reaults suggested that the micro-pits can make the stress redistribute and adjust the maximum value of stress.For rough interface,the micro cracks grew up to macroscopical crack and then propagated along the TA2-PEEK interfacial.In addition,the micro-pits extended the path length for the initial crack development along the bonded joints,thereby promoting energy dissipation.Finally,the DCB test was conducted to study the effect of parameters of micro-pits on fracture toughness of TA2-PEEK joints.The study revealed that TA2 surface roughness was a positive/negative relation to the parameters of micro-pits.The TA2 surface free energy significantly increases with the increase of surface roughness.But,the surface energy is not proportional to the surface roughness.The parameters of micro-pit contributed directly to failure mode transition from adhesive to cohesive or vice versa.The high fracture toughness of TA2-PEEK joint was obtained when the optimal values of the diameter,the ratio of diameter-spacing and diameter-depth were 400 ?m,4:1 and 8:1,respectively.