Modeling Of Crack Growth In Reinforced Bulkhead Of Civil Aircraft

Reinforced bulkhead is a typical structure in civil aircraft.It is difficult to avoid crack generation in assembly and service.Strength decrease due to crack growth is an important issue for aircraft.Damage tolerance evaluation should be considered in order to ensure that the bulkhead can be met the requirement of regulations.And the crack growth analysis is one of the important content of damage tolerance evaluation.Related to the practical engineering in this paper,the damage tolerance evaluation was studied according to structure type and load condition.Stress intensity factor(SIF)of crack tip is an essential prerequisite for crack growth analysis.The extended finite element method(XFEM)is a new numerical method.During solving the SIF,it can reflect the complicated structure and external load.Now it has been widely used in engineering practice.In this paper,the SIF of crack tip of reinforced bulkhead was calculated by using XFEM in ABAQUS and performed crack growth life analysis as a new approach.Then compared the results with the traditional method.In the same time,the effect of strengthening rib for crack growth life was also studied to provide the basis for structural optimization design.The major contents and achievements are as follows:1)Base on the previous research results,this paper put forward the concrete contents and basic methods of damage tolerance evaluation and crack growth analysis for the bulkhead.The bulkhead structure,design features and main load conditions of civil aircraft fuselage were mentioned systematically in this paper.The concept and process of damage tolerance evaluation of aircraft structures were introduced in detail.The knowledge and difficulty were grasped.And the SIF is the key factor in crack growth analysis.2)Based on ABAQUS,the method using XFEM to calculate the SIF was built.Firstly,According to the model analysis of finite width plate with single edge crack,discussed the variation of SIF value under different load and magnitude in tension and moment load.And compared the results from analytical solution.Secondly,performed analysis for angle with single edge crack.Reached the SIF under different ratio of two edges of angle in tension load.And compared the results from reference.The comparison results showed that this method was feasible and accurate.At the same time,it was clear in modeling method and technique in ABAQUS.3)A new method was proposed to calculate the crack growth life of reinforced bulkhead base on XFEM in ABAQUS.As the initial crack was assumption and the growth path was determined,acquired the relationship between crack length and SIF of crack tip using XFEM in ABAQUS.And prepared the crack growth analysis program based on formula and damage standards to calculate crack growth life.The analysis results showed that the traditional method is conservative,and the crack growth life was low.And the new method could reflect the complicated structure and external load,and the crack growth life was high.4)Study the effect of strengthening rib on the bulkhead web for crack growth life base on XFEM.Set the width and distance from inner edge of reinforced bulkhead as optimize parameter.The SIF of crack tip and crack growth life were obtained by the analysis of the different optimization schemes.The research results showed that the stress in bulkhead was reduced,and crack growth was retrain.At the same time,the influence of the width and distance was studied.Through comparison results to figure out the improvement and provide guidance for the design.