Study on mechanism of circumferential cracks in cold-region tunnels

There exists frost damage in cold-region tunnels. The circumferential cracks affect the function of tunnels. Using three-dimensional finite element method, the authors analyzed the mechanism of circumferential cracks in cold-region tunnels It is proved that the internal thermal stress in lining exceeds the tensile strength of concrete, which is the direct cause for circumferential cracks occurring. The laws of thermal stress in lining induced by parameters such as temperature drop, horizontal drag coefficient and length of lining are analyzed. The conclusions are valuable to the design and construction of cold-region tunnels considering the thermal stress.

DAMAGE TOLERANCE AND FATIGUE LIFE ESTIMATION FOR PIPE/ROD BAR STRUCTURE

The damage tolerance for pipe/rod bar in the auxiliary power units （APUs） support system is studied. The main objective is to study whether planes can safely land when the fatigue crack appears on the bar. Firstly, the stress intensity factors （K~） of two bar structures are computed, and the iso-stress intensity factor （iso-Kl） model is presented. The model uses the finite element model （FEM） instead of the parameters of material to com- pute the crack propagation. Then, the general relations between Kt vs crack size are obtained for different mate- rials, inner to outer diameter ratios （D^n/Dout） and external crack propagation angles （0）. Finally, the FEM anal- ysis results are input to the ANSYS parametric design language（ANSYS-APDL） software. And the fatigue life of damaged bar is estimated under the condition of loading spectrum.

Sanders＇ Mid-long Cylindrical Shell Theory and its Application to Ocean Engineering Structures

The cylindrical shell is one of the main structural parts in ocean engineering structures.These cylinders are mostly of medium length,which means that the radius of the cross section is significantly smaller than the length of the cylindrical shell.From the viewpoint of the shell theory,they belong to the mid-long cylindrical shell category.To solve mechanical problems on this kind of structure,especially a cracked cylindrical shell,analysis based on shell theory is necessary.At present the generally used solving system for the mid-long cylindrical shell is too complicated,difficult to solve,and inapplicable to engineering.This paper introduced the Sanders' mid-long cylindrical shell theory which reduces the difficulty of the solution process,and will be suitable for solving problems with complicated boundary conditions.On this basis,the engineering applications of this theory were discussed in conjunction with the problem of a mid-long cylindrical shell having a circumferential crack.The solution process is simple,and the closed form solution can usually be found.In practical engineering applications,it gives satisfactory precision.

Effects of Crack Opening Angle and External Loads on Reliability of Welded Pipe with Circumferential Crack

The reliability of welded pressure pipe with circumferential surface crack was calculated by using 3D stochastic finite element method.This method has overcome the shortcomings of conservative results in safety assessment with deterministic fracture mechanics method.The calculation of reliability was based on 3D elasticplastic stochastic finite element program which was developed by ourselves.The effects of variables such as fracture toughness,bending moment and depth of the circumferential surface crack on the structure reliability were also discussed.The calculation results indicate that the crack opening angle has certain effect on the reliability of the welded pipe.When the mean value of bending moment is 10kN·m,with the crack opening angle increasing from 30°to 180°,the failure probability of the welded pipe changes from 3.8379×10-8to 3.6943×10-6.When the mean value of bending moment is 15kN·m,with the crack opening angle increasing from 30°to 180°,the failure probability of the welded pipe changes from 3.986 5×10-6to 1.936 7×10-3.The bending moment has great effect on the reliability of the welded pipe.When the mean value of moment is changed from 10 to 15 kN·m,the failure probability of the welded pipe increases dramatically for the same circumferential crack opening angle.Regardless of changing of moment,the pipe has higher reliability if the crack opening angle is less than 60°.The method has put forward a new way for safety assessment of welded pipe with circumferential surface crack.