Study On Mechanical Properties Of Epoxy Resin Toughened By PIS/Nanosilica And Its Composites

Carbon fiber/epoxy resin matrix composites(CFRP)has a series of excellent properties such as high modulus,high tensile strength,high toughness,low density and low corrosion sensitivity.It is widely used in aerospace,transportation,and automotive parts.Manufacturing and sporting goods industries.However,in actual application,there are also some defects in the CFRP composites:there is a special three-dimensional network structure inside the matrix epoxy resin,which is brittle,high crosslinking density,and high internal stress,resulting in poor toughness and impact resistance of the composite material.Based on this,the epoxy resin matrix was toughened and modified to improve the bonding strength of the matrix resin and carbon fiber,and the fracture mechanics and failure mechanism of the composite were studied.In this paper,a new type of thermoplastic polyimide and modified nanosilica were synthesized to toughen epoxy resin,and the best toughening method was selected to prepare composite materials with different laminating angles and thickness.The effects of unmodified and modified resin as matrix on the toughness of composites and the effects of ply angle and ply thickness on the mode I and II fracture toughness of composites were tested and compared by two test methods:double cantilever beam test(DCB)and end notch bending test(ENF).The conclusion of the paper is as follows:1.Polyimide(PIS)containing trifluoromethyl group was synthesized by low temperature copolymerization,and was used to modify epoxy resin.The effects of different components of PIS on the properties of epoxy resin were analyzed.The results show that 7.5 wt%of PIS has the most significant toughening effect on the epoxy resin.Compared with the unmodified resin,the fracture stress is increased from 40.4 MPa to 92.3 MPa,which is 128%higher.The fracture toughness(Kic)value increased from 0.86 MPa·m1/2 to 1.56 MPa·m1/2,which also significantly improved the toughness.2.By the methods of chemical modification,the successful grafting reactive functional groups on the nanometer silicon dioxide,and modification of nanometer silicon dioxide to enhance toughening of epoxy resin,the results show that the modified resin system of the tensile stress and strain were significantly increased,while modified nanosilica content is 3 wt%,the fracture stress is 85.2 MPa,the fracture strain of 6.21%,compared with unmodified resin increased by 110.9%and 132.6%respectively.3.The epoxy resin was strengthened and toughened by blending PIS with modified nanosilica,and the tensile fracture properties were measured.The results showed that the tensile stress and strain of the PIS/nanosilica composite reinforced epoxy resin system increased significantly,and the blend system of 7.5 wt%PIS and 3 wt%modified nanosilica showed the largest fracture stress.The value is 106.3 MPa,the breaking strain is 8.50%,which is 163.1%and 218.4%higher than the unmodified resin,and both are higher than the maximum value of each single-component modification.The fracture toughness and SEM of the two-component blend toughened epoxy resin show that the blend system changes the epoxy resin system from brittle fracture to ductile fracture,and the fracture toughness KIC value increases from 0.86 MPa·m1/2 to 1.98 MPa·m1/2.4.Modified and unmodified resins were used as matrix to prepare composites with different ply angles,and their tensile and bending properties were tested.The results show that the composites prepared with modified resin as matrix have better tensile and flexural properties,and their tensile strength and flexural strength are significantly higher than those prepared with unmodified resin as matrix.Among the different lay-up methods,the composite prepared by 0° angle lay-up showed the best tensile strength,and the composite prepared by 450 angle lay-up showed the best bending strength.5.By using unmodified epoxy resin and PIS/nanosilica composite modified epoxy resin as the matrix,composite materials with different lay angles and lay thicknesses were prepared,and their fracture toughness was analyzed through DCB and ENF tests,To explore its toughening mechanism.The results show that the fracture toughness of the composites with PIS/nanosilica modified resin as matrix is significantly higher than that with unmodified resin as matrix.Among the composites prepared by different layup methods,the composite laid at 450 angle shows the largest fracture toughness values of mode Ⅰ and mode Ⅱ.Among the composites with different thickness,the fracture toughness of the composites with the same resin matrix and layup mode does not change significantly,which indicates that the thickness has little effect on the fracture toughness of the composites.