Evaluation On Fatigue Damage Of Guyed Mast's Ear-plate

Guyed masts consist of a slender shaft and inclined pre-stressed guys of multi-stories which have the characters of great height, relatively small cross-section. Under the excitation of the natural wind ,guyed masts may happen large amplitude of vibration ,the fatigue failure is one of the important failure forms. In recent years ,it is often seen that the high truss structure espically the guyde masts under wind load has been damaged. Many mast accident reports also show that the accident was accused by structural instability or structural components stress exceed the ultimate strength which may induce fatigue damage, particularly in the shaft chord and Guy connected with the shaft,so the ear-plate's fatigue life prediction is very important to the life of the entire guyed mast. Because of the complex random wind loading and the guyed mast's nonlinear dynamic characteristics ,which caused the ear plate's stess is very complicated, and the coherent literatures about the ear-plate's fatigue problem are not much.In order to obtain more precise stress time-domaine curve of the gusset plate , we divide the cordelle into a number of cable element and the chord into beam element, and then establish the mast structure's nonlinear model. The model is imposed the simulated wind-load at the time of 0.1s,and then open the large deformation options, select the Newton-Raphson iterative method and set Newmark-βtime integration parameters, and then the mast structure's stress-time curve under different wind load can be obtained by the time-domain nonlinear analysis.As the role of random wind load, the guyed mast's ear-plate's node stress is always changing, that is to say, stress rate change with the time-history, so the ear-plate's fatigue failure is amplitude fatigue. So this paper will evaluation the ear-plate's fatigue failure of the crack initiation phase. In order to analyze the fatigue problem, we must solve the following problems:(1)Find the crack initiation phase 's fatigue model which can describes the mast structure's ear-plate's fatigue problem in the amplitude load. (2)According to the characteristic of unfixed critical damage plane under amplitude multiaxial fatigue loads, how to find the critical damage plane to forecast amplitude multiaxial fatigue life is extremely important.According to pull ears's local size structure and stress,we estabilsh the local entities model by SOLD45 element. Making the cordelle strain time-domain curve which can be got by Mast structure's nonlinear dynamic analysis as load, mean while taking the cordelle angular changes into account,we can get the ear-plate's dangerous point's strain time-domain curve under cyclic loading. Through coordinate transformation we can got all nodes's stress component and strain component in any material plane,and fix the critical damage plane of each time by the method of maximum shear strain plane. According to the characteristic of unfixed critical damage plane under amplitude multiaxial fatigue loads,and then weighted mean the weight coefficient which can be fixed by the material damage degree of the current plane ,so the critical damage plane can be difined as weighted average maximum shear strain plane. Then cycle count the positive and shear stress of the critical damage plane by the method of multiaxial cycle counting method (even rainflow counting) .By the△ε_eq-N line life estimation model calculate the fatigue damage of a single cycle on the critical damage plane .Although the ear-plate in complex multiaxis non-proportional loading stress, its random load series of fatigue load almost all in high-cycle fatigue areas yet, so we can still ues the Miner theorem to accumulate the fatigue damage of each cycle and predict the fatigue life.According to this study can see that the non-proportional multiaxial fatigue theory to analyze the mast structure of the ear-plate's fatigue damage is closer to the ear-plate's complex stress under random wind load;mean while the critical injury parameters which is used in the△ε_eq-N line not only suitable for proportional loading, but also for non-proportional loading can be more theoretical and practical significance.