Development of multi-physics numerical simulation model to investigate thermo-mechanical fatigue crack propagation in an autofrettaged gun barrel

In this research,a detailed multi-physics study has been carried out by numerically simulating a solid fractured gun barrel for 20 thermo-mechanical cycles.The numerical model is based on thermal effects,mechanical stress fields and fatigue crack mechanics.Elastic-plastic material data of modified AISI 4340 at temperatures ranging from 25 to 1200℃and at strain rates of 4,16,32 and 48 s^(-1) was acquired from high-temperature compression tests.This was used as material property data in the simulation model.The boundary conditions applied are kept similar to the working gun barrel during continuous firing.A methodology has been provided to define thermo-mechanically active surface-to-surface type interface between the crack faces for a better approximation of stresses at the crack tip.Comparison of results from non-autofrettaged and autofrettaged simulation models provide useful information about the evolution of strains and stresses in the barrel at different points under combined thermo-mechanical loading cycles in both cases.The effect of thermal fatigue under already induced compressive yield due to autofrettage and the progressive degradation of the accumulated stresses due to thermo-mechanical cyclic loads on the internal surface of the gun barrel(mimicking the continuous firing scenario)has been analyzed.Comparison between energy release rate at tips of varying crack lengths due to cyclic thermo-mechanical loading in the non-autofrettaged and autofrettaged gun has been carried out.

Numerical simulation of thermo-mechanical fatigue properties for particulate reinforced composites

In this paper, a two dimensional Voronoi cell element, formulated with creep, thermal and plastic strain, is applied for the numerical simulation of thermo-mechanical fatigue behavior for particulate reinforced composites. The relation between mechanical fatigue phases and thermal fatigue phases influences the thermo-mechanical fatigue behavior and cyclic creep damage. The topological features of micro-structure in particulate reinforced composites, such as the orientation, depth-width ratio, distribution and volume fraction of inclusions, have a great influence on thermo-mechanical behavior. Some related conclusions are obtained by examples of numerical simulation.

Review on structural fatigue of NiTi shape memory alloys:Pure mechanical and thermo-mechanical ones

Structural fatigue of NiTi shape memory alloys is a key issue that should be solved in order to promote their engineering applications and utilize their unique shape memory effect and super-elasticity more sufficiently. In this paper, the latest progresses made in experimental and theoretical analyses for the structural fatigue features of NiTi shape memory alloys are reviewed. First, macroscopic experimental observations to the pure mechanical and thermo-mechanical fatigue features of the alloys are summarized; then the state-of-arts in the mechanism analysis of fatigue rupture are addressed; further, advances in the construction of fatigue failure models are provided; finally, summary and future topics are outlined.

Cyclic deformation behaviors of Ti-46Al-2Cr-2Nb-0.15B alloy during thermo-mechanical fatigue tests

Thermo-mechanical fatigue tests were carried out on the gamma-TiAl alloy in the temperature range of 500-800℃ under mechanical strain control m order to evaluate its cyclic deformation behaviors at elevated temperature. Cyclic deformation curves, stress-strain hysteresis loops under different temperature--strain cycles were analyzed and dislocation configurations were also observed by TEM. The mechanisms of cyclic hardening or softening during thermo-mechanical fatigue （TMF） tests were also discussed. Results showed that thermo-mechanical fatigue lives largely depended on the applied mechanical strain amplitudes, applied types of strain and temperature. On the hysteresis loops appeared two apparent asymmetries： one was zero asymmetry and the other was tensile and compressive asymmetry. Dislocations configuration and slip behaviors were contributed to cyclic hardening or cyclic softening.

CHARACTERIZATION OF THERMO-MECHANICAL FATIGUE PROPERTIES FOR PARTICULATE REINFORCED COMPOSITES

A Voronoi cell dement, formulated with creep, thermal and plastic strain was applied for investigation of thermo-mechanical fatigue behavior for particulate reinforced composites. Under the in-phase fatigue loading, the maximum of tensile deformation at the maximum given loading are larger than that at the same maximum under the out-phase fatigue. The stiffness decreases nonlinearly with the increasing of the phase angle, which results in increasing of the area of fatigue loop curve and the decrease in fatigue life. The spatially centralizing of inclusions results in decreasing of the plastic strain amplitude and the area of fatigue loop curve, which will also reduce the consumption of single-circle plastic strain energy and prolong the fatigue life.

Thermo-mechanical fatigue behavior of nickel-base powder metallurgy superalloy FGH96 under tension-tension loading

Thermo-mechanical fatigue （TMF） behavior of FGH96, a nickel-base powder metallurgy superalloy, has been studied under tension-tension loading at the temperature range from 550 to 720 ℃. The results show that TMF fracture mode is intergranular for the in-phase （IP）, but transgranular cleavage-like for the out-of-phase （OP） samples. The total content of Al, Ti and Nb in the γ＇ phases for the IP or OP samples and the partitioning ratio of γ＇/γin these elements for the IP samples are relatively higher at the lower strain amplitude, which is consistent with the case of the γ＇ size that is larger at the lower strain amplitude, the lattice parameter misfit is negative and the absolute value is lower at the lower strain amplitude that is correlative with the change of the γ＇ morphology. The deformation at the lower strain amplitude is mainly dominated by the dislocation lines and dislocation pairs in the matrix channels, at the higher strain amplitude dominated by the large numbers of superlattice stacking faults within the γ＇ phases.

Novel Crystallization Behaviors of Zr-Based Metallic Glass Under Thermo-Mechanical Coupled Fatigue Loading Condition

Novel crystallization behaviors of Zr55Cu30Al10Ni5 bulk metallic glass are investigated. On the one hand, mixed oxides, including CuO, CuAlO2, CuA12O4 and ZrO2, show sequential oxidation process determined by coupling effects of specific cyclic load and temperature. On the other hand, at a temperature (100℃) by far lower than Tg of 412 ℃, under cyclic loading condition, non-oxidized binary alloy CuZr2 is precipitated;the thermo-mechanical coupled effects of temperature below Tg, and fatigue accumulation on the non-oxidized crystallization behaviors are revealed. Meanwhile, at a constant temperature of 400 ℃, by comparing among the XRD patterns, respectively, obtained from tensile, creep and fatigue fractures, the dominating effect of cyclic load on the generation of non-oxidized CuZr2 is verified. Furthermore, the crystallization behavior of amorphous phases under cyclic loading condition is observed through TEM micrograph and diffraction pattern at 100℃.

基于改进BP神经网络的焦炭塔热机械疲劳剩余寿命预测

焦炭塔热机械疲劳剩余寿命的分析对于保证焦炭塔的正常运行、防止事故的发生有着十分重要的意义。结合人工神经网络技术,提出了根据有限的材料热机械疲劳试验结果,用改进的BP神经网络预测焦炭塔热机械疲劳剩余寿命的方法,编制了相应的程序,并在实际应用中证明了此方法的有效性。这为研究焦炭塔热机械疲劳剩余寿命提供了一种新的方法。

840 kN大吨位悬式绝缘子振动疲劳性能测试及分析

为减轻串重,简化金具,研发840 kN大吨位绝缘子已成为迫切需要解决的问题。840 kN大吨位绝缘子为国内外首次研发,为了确定其长期机械疲劳性能,总结以往经验,设计了一套有效的技术方法,能够量化考核大吨位绝缘子机械性能。依据所提出的试验方法,确定了试验参数、设计了合适的试验装置。对7个厂家共10种型号的420 kN和840 kN悬式绝缘子进行了振动疲劳试验,考核了840 kN绝缘子的振动疲劳极限及残余机械强度,并与420 kN绝缘子的相关性能进行了对比。依据试验结果,得到了840 kN绝缘子机械疲劳性能的设计薄弱点及其振动疲劳特性,证明了840 kN绝缘子的振动疲劳性能不低于420 kN绝缘子。相关研究结果为840 kN大吨位绝缘子振动疲劳检测提供了思路,也为其工程推广应用提供了技术支撑。