Experimental and numerical investigation of a composite structure with frame and skin

A composite structure with frame and skin based on cabin structure in a large space telescope is studied in this paper.The frame is composed of longitudinal and transverse beams with hybrid bonded/bolted joints,and the skin is connected to the frame by bolts.Tensile tests are conducted on the structure by a set of test stand.It is observed that residual deformation occurs in the first test of the structure,which is attributed to the relative sliding between the skin and frame because of bolt-hole clearances.The high tightening torque and the increased number of the skin-frame bolts contribute to the high stiffness of the structure.A finite element model(FEM)of this composite structure is established,and the simulation model is verified by the experimental results.The FEM is contrastively analyzed with different frame joints,and it is found that adhesive joining in the hybrid bonded/bolted joints enhances the stiffness of the structure significantly.Given that adhesive plays a leading role in the stiffness of the hybrid joints,Tie contact in FEM is proposed to simulate bonded or hybrid joints when studying the stiffness performance of undamaged structure.

Tensile properties of a composite–metal single-lap hybrid bonded/bolted joint

Hybrid bonded/bolted(HBB) joint has been widely used in engineering practice because it can overcome the potential weakness of pure bonded and pure bolted joints. However, studies on HBB joint are still at the initial stage. In this paper, tensile properties of a composite–metal singlelap HBB joint was investigated experimentally. And a detailed finite element model(FEM) was established to simulate the tensile behavior of the joint. The model was verified by the experimental results. Then the damage propagation and load transfer mechanism were explored based on the FEM. The results show that the HBB joint can provide multi-load transmission paths and resist damage propagation in the adhesive. The HBB joint has higher strength and energy absorption capacity than the pure bonded joint. And the HBB joint has greater initial damage load and tensile stiffness than pure bolted joint. Adhesive fillets can obviously improve the tensile performances of the HBB joint. Lateral stiffness of the joint boundary and testing machine show obvious effects on tensile performances of single-lap hybrid joints.

Tensile properties analysis of CFRP-titanium plate multi-bolt hybrid joints

Hybrid joints have better tensile properties than pure bonded and bolted bolts,and are increasingly used in the aerospace field.Tensile tests are carried out for the Hybrid Bonded/Bolted(HBB)joints of Carbon Fiber Reinforced Polymer(CFRP)laminate and titanium alloy plate under different bolt numbers,and the corresponding load–displacement curves are obtained.At the same time,based on Continuum Damage Mechanics(CDM)theory,which is derived from 3D Hashin failure criteria,and a Cohesive Zone Model(CZM),the tensile strength prediction model of the composite laminate-titanium alloy plate multi-bolted HBB joint was established,and the numerical simulation results were in good agreement with the experimental height,which validate the feasibility of the model.The difference in the bearing capacity of HBB joints under different numbers of bolts is compared and analyzed.On this basis,the influence of inter-bolt distance on the tensile properties of the HBB joints is explored.The results show that the double-nail HBB joints can effectively improve the end warpage and low bearing capacity of the single-nail HBB joints.The tensile failure load of the double-nail HBB joints under the standard lap width(30 mm)is 82.6%higher than that of the single nail,the tensile failure load of the three-bolt HBB joints is 34.1%higher than that of the double nail.For the three-bolt HBB joint,the joint strength is controlled by the adhesive and the external bolt,while the internal bolt is redundant,the hybrid joint can be simplified by reducing the middle bolt.The inter-bolt distance has a great influence on the failure load of the hybrid joint.Increasing the inter-bolt distance can effectively improve the bearing capacity of the structure.