Numerical Simulation of Low Cycle Fatigue Behavior of Ti_(2)AlNb Alloy Subcomponents

Many titanium alloy subcomponents are subjected to fatigue loading in aerospace engineering,resulting in fatigue failure.The fatigue behavior of Ti_(2)AlNb alloy subcomponents was investigated based on the Seeger fatigue life theory and the improved Lemaitre damage evolution theory.Firstly,the finite element models of the standard openhole specimen and Y-section subcomponents have been established by ABAQUS.The damage model parameters were determined by fatigue tests,and the reliability of fatigue life simulation results of the Ti_(2)AlNb alloy standard open-hole specimen was verified.Meanwhile,the fatigue life of Ti_(2)AlNb alloy Y-section subcomponents was predicted.Under the same initial conditions,the average error of fatigue life predicted by two different models was 20.6%.Finally,the effects of loading amplitude,temperature,and Y-interface angle on fatigue properties of Ti_(2)AlNb Y-section subcomponents were investigated.These results provide a new idea for evaluating the fatigue life of various Ti_(2)AlNb alloy subcomponents.

Synthesis and characterization of Ba(Co_xNb_(1-x))O_3 nanoparticles by hydrothermal processing

The nanosized Ba(CoxNb1-x)O3(BCN) particles were prepared under high temperature and pressure conditions by precipitation from metal nitrates with aqueous potassium hydroxide. Ba(CoxNb1-x)O3 powders were obtained in the temperature range of 170-210 ℃ for 6 h. The results show that the average size of the synthesized particles increases with increasing reaction temperature. The average size of the synthesized particles is about 10 nm. The crystalline phase of the synthesized particles is found to be Ba(CoxNb1-x)O3. Ceramics derived from the nano BCN powders could achieve high sintering density at a relatively low sintering temperature.

Experimental Investigation on the LCF Behavior Affected by Manufacturing Defects and Creep Damage of One Selective Laser Melting Nickel-Based Superalloy at 815℃

Uniaxial tensile tests and stress-controlled low-cycle fatigue(LCF) and creep-fatigue interaction(CFI) tests of Inconel 625 alloy manufactured by selective laser melting(SLM) were performed at 815℃ in air environments.The microstructure was characterized by optical microscopy and scanning electron microscopy after testing.The results confirmed that significant embrittlement and large scatter in LCF life are resulted from manufacturing defects.The CFI life is decreased sharply to approximately dozens of cycles with the accumulated creep strain;however,the selected dwell time(i.e.,60 s and 300 s)exhibits low sensitivity to the fracture time and elongation to failure.The embrittlement of SLM Inconel 625 was proposed to be due to the low grain uniformity and precipitation of carbides at the grain boundaries.Due to the quality of the SLM process,the accelerated initiation and propagation of fatigue crack are caused by the present unmelted powder particles,which result in the large dispersion of LCF life.Meanwhile,due to the accumulation of creep damage,cracks in the CFI test are initiated along the grain boundaries and then linked together,contributing to a significant decline in fatigue life.