Study Of The Fracture Strength Of CFRP Laminates After Surface Scratch Damage At Different Ambient Temperatures

Because of its excellent mechanical properties,Carbon Fiber Reinforced Polymer（CFRP）has been widely used in aerospace,rail transportation,vehicle engineering,mechanical equipment,civil engineering and wind power equipment.However,CFRP composites are inevitably subject to surface micro-damage defects caused by external influences during service life,and the resin matrix is subject to high-temperature vitrification and low-temperature embrittlement,so it is necessary to conduct scratch damage tolerance studies on CFRP surfaces under high/low temperature environments.In this paper,three temperature environments,namely ambient（23℃）,low temperature（-60℃）and high temperature（60℃）,were selected to study the fracture performance of CFRP surfaces after scratch damage.A prediction model for the scratch damage tolerance of CFRP surfaces was established based on the boundary effect theory,and a quantification method for the crack tip damage area was proposed to achieve the fracture performance prediction under different temperature fields.（1）In response to the challenge of processing quantitative depth shallow cracks on CFRP surfaces,a method of surface shallow crack prefabrication and crack depth calibration was investigated.Firstly,CFRP laminate specimens were prepared in the laboratory using a hand-glued laminate lay-up and hot press forming process;then,a special tooling that can be connected to an electronic universal testing machine to clamp the blade was designed,and the initial crack was prefabricated by applying pressure load to the blade in a load-controlled manner;finally,the average depth of shallow cracks formed under each pressure load was observed under a metallographic microscope.（2）Based on the boundary effect theory,the fracture strength of CFRP sheets after the appearance of shallow surface cracks at different ambient temperatures was investigated,and the distribution of crack tip damage zones and quantitative evaluation methods were analysed.The fracture characteristics of the crack tip damage zone were observed and analysed by metallographic microscopy,and the optimal values of the parameterβand the fracture parameter C were determined to reflect the distribution range of the crack tip damage zone,and a CFRP surface scratch damage tolerance prediction model was established based on the boundary effect theory.（3）The coupling effect of service environment temperature and shallow surface cracks on the fracture strength of CFRP is investigated.The relationship between temperature and tensile strength is obtained from the test results,and the spatial design surface of fracture strength of CFRP laminates(P_max-T-a₀surface)is drawn by the CFRP surface damage tolerance prediction model to predict the non-linear elastic fracture behaviour of CFRP laminates under different service temperature environments.