Reliability Analysis Based on a Nonlinear Fatigue Damage Accumulation Model

A modified nonlinear fatigue damage accumulation model based on the Manson-Halford theory was presented,and the new model was developed for fatigue life prediction under constant and variable amplitude loading, which took the effects of the load interactions and the phenomenon of material's strength degradation into account. The experimental data of the 30 Cr Mn Si A and the LY-12 cz from literature were used to verify the proposed model. And from the good agreement between the experimental data and predicted results,we can see it clear that the proposed method can be applied to predicting fatigue life under different loadings.

Investigating fatigue behavior of gear components with the acoustic emission technique

A novel method is presented to evaluate the complicated fatigue behavior of gears made of20Cr2Ni4 A.Fatigue tests are conducted in a high-frequency push-pull fatigue tester,and acoustic emission（AE）technique is used to acquire metal fatigue signals.After analyzing large number of AE frequency spectrum,we find that：the crack extension can be expressed as the energy of specific frequency band,which is abbreviated as F-energy.To further validate the fatigue behavior,some correlation analysis is applied between F-energy and some AE parameters.Experimental results show that there is significant correlation among the Fenergy,root mean square（RMS）,relative energy,and hits.The findings can be used to validate the effectiveness of the F-energy in predicting fatigue crack propagation and remaining life for parts in-service.F-energy,as a new AE parameter,is first put forward in the area of fatigue crack growth.

PROBABILISTIC MINER’S RULE IN FATIGUE RELIABILITY

Firstly, constant amplitude P-S_a-S_m-N_c surface family is established.Secondly, four basic assumptions, i.e., monotonically increasing, non-coupling, separability andnonintersecting of fatigue damage accumulation are proposed from the viewpoint of both damagemechanics and fracture mechanics. Then the individual isodamage D-S_a-S_m-N surface under constantamplitude loading is constructed and the two-dimensional individual Miner's rule is derived.Consequently, the two-dimensional probabilistic Miner's rule (TPMiner) is established and proved fora population subjected to variable amplitude loading. Finally, with successfully experimentverification, TPMiner proves be to very useful and feasible in fatigue reliability theory.

Multi-Excitation Fatigue Testing for Large Full-Scale Wind Turbine Blade

In order to solve the problem of insufficient exciting force of equipment for large full-scale wind turbine blade fatigue testing,the influence of gravity on the performance of excitation equipment and fatigue damage evaluation of the different positions of wind turbine blades are analyzed.With the multi-excitation loading in the horizontal direction,the actuator force of the excitation equipment does not need to overcome the gravity of the dynamic mass,which directly outputs the exciting force of the system vibration.The excitation efficiency of the equipment is 77%higher than that of the vertical load.The gravity moment of the horizontal loading mode is perpendicular to the loading direction.That is,the mean load in the flapwise direction is zero.The weight of excitation equipment could replace the tuning mass on the condition that the self-weight of equipment is reduced by the multi-excitation mode,which helps the excitation equipment play the comprehensive function of excitation equipment and tuning mass.At the same time,the gravity moment in the edgewise direction will be decreased by 17.0%22.5%under the multi-excitation horizontal loading mode.In the vertical loading mode,the gravity moment is the mean load,which only increases fatigue damage accumulation by 15.6%.By comparing the role of gravity in the excitation equipment and fatigue damage evaluation,the multi-excitation horizontal loading mode has more advantage to performance the exciting force than the contribution of gravity to the fatigue damage accumulation in the vertical loading mode.Through the fatigue testing of multi-excitation horizontal loading,the potential of excitation equipment is explored,and the problem of insufficient exciting force in large full-scale wind turbine blade fatigue testing will be solved.

Fatigue analysis of the bow structure of FPSO

The bow structure of FPSO moored by the single mooring system is rather complicated. There are many potential hot spots in connection parts of structures between the mooring support frame and the forecastle. Mooring forces, which are induced by wave excitation and transferred by the YOKE and the mooring support frame, may cause fatigue damage to the bow structure. Different from direct wave-in duced-forces, the mooring force consists of wave frequency force (WF) and 2nd dr aft low frequency force (LF) [3] , which are represented by two sets of short-term distribution respectively. Based on two sets of short-term distribution of moor ing forces obtained by the model test, the fatigue damage of the bow structure of FPSO is analyzed, with emphasis on two points. One is the procedure and position selection for fatigue check, and the other is the application of new formulae for the calculation of accumulative fatigue damage caused by two sets of short-term distribution of hot spot stress range. From the results distingui shed features of fatigue damage to the FPSO’s bow structure can be observed.