Analysis On The Strength And Parameter Sensitivity Of Fiber Composite Hybrid Joint Structure

Because of its advantages of strong design,light weight,and so on,composite materials have been widely used in defense and military and other related industries.The widespread application of large-scale structures has also made the composite connection structure an inevitable research focus.In this paper,the composite H-shaped sandwich joints as the main research object,in three connection modes and under three conditions of the impact of stress,damage distribution and failure mode of mechanical properties such as in-depth analysis;and then study the geometric size parameters and connection parameters.The influence law on the joints will provide guidance for the optimization of the design and carrying capacity of composite materials in engineering practice.The main work is as follows:First,the main developments of composite materials and hybrid connection structures at home and abroad were thoroughly studied.It was found that the strength,failure modes,and other aspects of the connection structure were changed when various factors such as aperture,pre-tightening force,lamination sequence,and proportion were changed.There are different laws of influence,so it is of great scientific value to study the influence of various parameters on the mechanical properties of composite materials.Secondly,the development of the Hashin failure criterion is mainly introduced.At the same time,the specific formulas of the Hashin criterion in the form of stress and strain in 2D and 3D are described.Then,the damage variable is built into the stiffness attenuation matrix,so that iterative convergence continues until it is determined that the joint is completely ineffective,and the subroutine flow chart is given;finally,the parameterized modeling method is used to complete the composite single-nail double-shear joint.Processing work,using the Hashin criterion to damage the joint check,and the corresponding tensile experiments,it is found that the two results are in good agreement,thus verifying the accuracy of the criteria used and the parametric modeling.Then,for the three types of composite H-shaped sandwich joints under different conditions of analysis,we can find that the tensile damage is the main damage under the tensile conditions,and the compression damage is under the compression and bending conditions.Under tensile and bending conditions,the strength of the mixed joints is greater than that of the simple joints and the bolted joints;however,due to the early failure of the adhesive layer under compression conditions,the load transfer function of the H joints is partially deactivated and its strength is reduced.It is lower than screwed but still higher than glued.At the same time,the failure modes and hazardous areas of joints under different working conditions and connection types are also summarized.Next,we mainly study the influence of two geometric dimension parameters on the stress level factor of H-type sandwich joints.The results show that the increase of web height directly increases the moment of inertia of the joint and the load size,which makes it possible to work in tension and compression.The stress levels of the joints of the joints will obviously increase,but the stress under bending conditions will decrease.The increase of the web thickness will cause the stress of the joint parts to decrease,and the S13 and S33 of the adhesive layer are insensitive to the changes of the two dimensional parameters.Finally,the effect of three connection parameters on the strength and damage distribution of H-shaped mixed joints was investigated.It was found that the increase in thickness and end-to-end distance of the adhesive layer can increase the joint strength,but After a certain degree,there is no longer any improvement;however,the increase in the screw hole radius makes the stress concentration on the H-type joint more obvious,which also results in a significant decrease in strength.The results of the two-parameter change and the single parameter can also be confirmed.At the same time,it can be seen that the sensitivity of the aperture and the end-to-end distance is much stronger than the thickness of the adhesive layer,which indirectly indicates that the bolted form in the mixed joint is more important than the adhesive effect.