Abstract: It is particularly important to determine the lap length of the mesh according to the damage size of the composite laminate, and the appropriate lap length can effectively improve the strength of the laminate and extend the service life. Through numerical simulation and experimental verification, the effect of the lap length of the mesh on the vibration characteristics of the repair laminate under the effect of hygrothermal was studied. Based on the first-order shear deformation theory (FSDT) and Hamilton’s principle, the constitutive equation and the free vibration control equation of laminates under hygrothermal effect are derived. The double-sided stepped repair laminate model was established by ABAQUS software, and the vibration characteristics of the patch repair laminate and the complete board using p of 8 mm, 10 mm, 12.7 mm, 14 mm, 16 mm and 18 mm respectively were analyzed under the coupling action of different temperatures, moisture contents and hygrothermal. The results show that when the temperature T is 300~320.15 K and the lap length (p) is 12.7 mm, the thermal stability and stiffness recovery effect of the laminate are better; when the moisture content C is 0%~0.158% and the p-value is 14 mm, the wet stability and stiffness recovery effect of the laminate are better. Under the coupling of hygrothermal, the natural frequency changes greatly by using a patch with a small lap length, and the use of a patch with an excessive lap length will expand the repair area and reduce the remaining stiffness of the laminate. The closer the p-value is to the repair configuration of 12.7~14 mm, the smaller the influence of hygrothermal effect on the natural frequency, and the better the moist heat stability and repair effect of the laminate.

Key words: lap length, composite laminates, ladder digging and repair, hygrothermal effect, vibration characteristics, natural frequency