Analysis On Stress Intensity Factor And Ultimate Bearing Capacity Of Cracked Plates Repaired With CFRP

Under the operating conditions of the ship,due to the complex and changeable environmental loads,the hull structure is often subjected to alternating loads,and the hull structure is prone to crack initiation.After the crack initiation,the bearing capacity of the structure will decrease significantly,and even fracture occurs.Therefore,remedial measures must be taken to improve the safety of the hull structure.Carbon fiber reinforced polymer(CFRP)has the characteristics of high strength,light weight and good durability.It has been widely used in the structural repair of ships,aviation,construction and other fields.Therefore,it is of great practical significance to use CFRP to repair the cracked structure of the hull.In this thesis,the simplified mechanical derivation model of CFRP double-sided repair cracked plate and ABAQUS finite element method are used to study the CFRP double-sided repair cracked plate.The stress intensity factor and ultimate load of the repaired cracked plate are analyzed,and the patch is optimized.The specific research contents and results are as follows:(1)The theoretical method of stress intensity factor calculation and finite element comparison verification.The theoretical method and finite element method are used to calculate the stress intensity factor of the CFRP repair center through the type I crack plate.The error between the theoretical method calculation results and the finite element method calculation results is within the acceptable range of 10 %.It is verified that the ABAQUS finite element calculation of the stress intensity factor of the CFRP repair crack plate is accurate and reliable.(2)Stress intensity factor analysis of CFRP repair model without debonding.The finite element software ABAQUS was used to calculate the stress intensity factors of CFRP repair center-through mode I crack plate,center-through oblique crack plate,center-through mode I crack stiffened plate and center-through oblique crack stiffened plate,and the shear stress distribution of the adhesive layer of the model was analyzed.The stress intensity factor increases with the increase of crack half length,and the stress intensity factor decreases after repair.The shear stress at the end of the adhesive layer is the largest,so the first place to fail is the debonding of the adhesive layer at the end of the patch repair.(3)The ultimate bearing capacity analysis of CFRP repair model with debonding.The ultimate load of CFRP repaired plate with center penetrating mode I crack and oblique crack plate and CFRP repaired stiffened plate with center penetrating mode I crack were calculated by ABAQUS,and the influence of CFRP patch parameters on the ultimate load was analyzed.After repair,the ultimate load of the cracked plate increases obviously,and the ultimate bearing capacity of the cracked structure is obviously improved.The debonding failure of adhesive layer directly affects the ultimate load of the repaired cracked plate,and the debonding of adhesive layer first occurs at the end of CFRP.When the length of CFRP patch increases to the critical length of CFRP patch,the ultimate load no longer increases.(4)When the length and width of CFRP patch reach the optimal repair size,the repair effect is the best.The thicker the patch,the smaller the thickness of the adhesive layer,the better the repair effect.When the patch width(short axis)is the same as the crack plate width,the patch length / width(long axis / short axis)is greater than or equal to 1,the repair effect is the best,and the rectangular patch repair effect is better than the elliptical patch repair.For CFRP repaired mode I cracked plate,when the angle between the fiber direction of the patch and the crack is 90°,the stress intensity factor is the smallest and the repair effect is the best.For CFRP repaired inclined crack plate,when the angle between the fiber direction of the patch and the inclined crack is 45° to 60°,the repair effect is the best.