Modeling Of Steel Componentcrack Propagation And Its Application On Engineering

When designer design members,he must control the working stress of members shall not exceed the allowable stress [σ],according to the static strength design principles they completed a lot of design.But it does not completely avoid the structure damage,when the working stress is less than the allowable stress,structure is also easy to be destroyed.This is because imperfection exits inthe member,it can have the stress concentration at the tip of the crack,the strength of the structure or component is inevitably weakens,under the action of service load,cracks will expand,crack size increase gradually as time growth,and finally the member is destroyed.This paper studies numerical modeling method of fatigue crack extension,provide the basis for choosing finite element modeling parameter of crack body,complete the static and dynamic simulation of fatigue crack,and achieve good results.In this paper,the work is as follows:(1)Introduce shortly the basic theory of fracture mechanics,summarize the regularity of fatigue crack propagation,conclude the method to get the stress intensity factor of the different situations.(2)Due to the stress at the crack tip has the characteristic of singularities,when we use the conventional finite element method to calculate the tablet through crack stress intensity factor,crack tip region use three-dimensional quarter equinoctial isoparametric degenerate singular unit.Based on the conventional Finite Element Method(FEM),several common crack plate(I-crack plate、Ⅱ-crack plate、compound crack plate and collinear crack plate)has carried on the static simulation,respectively solve the stress intensity factor of the crack length under different circumstance.and compare stress intensity factor of the theoretical value eference based on 《Stress Intensity Factor’s Handbook》 to verify the reliability of the method in this paper.Through the rain flow count method for 8 seismic data processing,frame structure of a selected node as an example,simulate crack propagation,and calculate the service life of the frame beam.(3)When the crack length changes,if we uses the modeling method to solve the stress intensity factor,the member should be meshed under every crack length,the workload is huge.This article solve stress intensity factor of certain amount of different crack length,establishing database of stress intensity factor,and then use interpolation method to solve the stress intensity factor of any another crack length.Firstly use slab to demonstrate the correctness of exploiting the interpolation method to solve the stress intensity factor,then use this method to solve the stress intensity factor under different crack length of three-dimension I-beam in real time.(4)This paper uses the Virtual Crack Closure Technique and Extended Finite Element Method to simulate dynamic Crack propagation of cracked plate under different conditions.The principle of Extended Finite Element Method is using the form function to represent interruption,so the form function of discontinuous field can completely be separated with the grid boundaries,so XFEM can deal with crack discontinuous problems and some issues of heterogeneous materials.Finally use Extended Finite Element Method to simulate the three dimensional I-beam crack propagation,the effect is very good.