Research On Strength Of Composite/Steel Mechanical Joint On Ship

Composite materials have been widely used in the marine industry,especially in ship superstructures because of their high specific strength,specific stiffness and excellent designability.Nowadays,in order to reduce the weight of the whole structure,the main hull is constructed by traditional steel,and the superstructure is made of composite materials.Due to the great difference between steel and composite materials,welded joints can not be used.The structural forms of this connection area are mostly mechanical joints,and typical connection joints are available in L-type and π-type.The L-joint is fixed on the steel deck directly by bolts.The water tightness and strength of the deck are destroyed by opening holes on the deck,and the stress concentration is easy to occur at the joint corner.The π-type joint is to place the composite plate in two parallel flat steels which is connected by bolts.It mainly depends on the shear load of bolts.The opening area is easy to be destroyed,thereby causing bolt looseness or partial structural damage to cause the connection structure to fail.Therefore,in this paper,the experimental and simulation studies on the mechanical connection of the two glass fiber reinforced composites(hereinafter referred to as "composites")are carried out.At the same time,a new type of L-connector and reinforcement scheme are designed.The joints were tested and verified by finite element analysis.The results show that the strengthened L-shaped joints have higher joint strength than the original L-type and π-type joints and have strong practicability.The specific contents of this paper are as follows:(1)For composite single-bolt connections,structural geometric parameters such as end-to-diameter ratio,width-to-diameter ratio,bolt-hole fit clearance,contact friction factor and bolt pre-tightening force will affect the failure mode and strength of the connections.According to the progressive damage theory of composite materials,the effects of these factors on the failure mode and strength of single-bolt connections are analyzed by finite element method in this paper.(2)The mechanical connection structures of composite superstructure and deck are mostly π-type joints.Based on this connection structure,the ultimate bearing capacity and corresponding failure modes of single-bolt and double-bolt π-type joints under tensile load are studied by experiment and finite element simulation,and the effects of geometric parameters such as end-diameter ratio and width-diameter ratio on the strength of the joints are analyzed.(3)In view of the disadvantages of L-type and π-type joints,a new type of L-type joints is designed.In this paper,the ultimate bearing capacity of this new type of L-joint under tension load is studied by the combination of experiment and finite element simulation.Based on the failure mode of the joint,a local strengthening scheme is designed and verified by experiment and finite element simulation.The results show that the ultimate load-bearing capacity of the strengthened L-joint is greatly improved.