Equivalent Stress Increase Research Articles

Investigation on the transient rolling contact behaviour of corrugated rail considering material work hardening

The process of work hardening in the corrugation zone of the steel rail results in an uneven distribution of hardness, with higher hardness in the corrugation troughs and lower hardness in the corrugation crests. To study the influence of hardness on the rolling contact behavior of the wheel-rail at corrugation zone, a three-dimensional wheel-rail transient rolling contact finite element model is established based on the measured corrugation and hardness distribution of the rail to reveal the influence of the non-uniform distribution of hardness at corrugation zone on the wheel-rail contact state and the wear and fatigue of the rail surface. The results indicate that: (1) work hardening in the corrugation zone leads to an increase in equivalent stress and strain within the contact patch between the wheel and rail. However, due to the increase in yield strength, plastic deformation and residual strain are somewhat reduced; (2) The uneven distribution of hardness in the corrugation zone results in an elevation of longitudinal shear strain between the wheel and rail, which may initiate tangential fatigue cracks and spalling of the steel rail surface; (3) the wear on the rail surface is large near the wave crest and small near the wave trough, work hardening will change the wear difference between the wave crest and wave trough while reducing the wear, resulting in the “peak shaving and valley filling” phenomenon developing faster in the early wave wear period and slower in the later period.

Investigation of Structural Strength and Fatigue Life of Rotor System of a Vertical Axial-Flow Pump under Full Operating Conditions

Axial-flow pumps consider both the conventional pump mode and the pump as turbine (PAT) mode operation and put forward higher requirements for long-term operation stability and structural strength; therefore, it is of great engineering significance to evaluate the structural strength and fatigue life of the rotor under full operating conditions. In this study, based on computational fluid dynamics and the one-way fluid-structure interaction algorithm, the structural strength and fatigue life of the rotor system of a large vertical axial-flow pump under full operating conditions were evaluated and studied. The results show that blade deformation and equivalent stress are generally higher in the PAT mode than in the pump mode. The maximum deformation in both modes occurs at the tip of the blade, while the area of stress concentration is at the root of the blade. Both the deformation and the equivalent stress increase with increasing flow rate. The minimum safety factor occurs at the blade root in both modes, and the safety factor in the PAT mode is relatively smaller than that in pump mode. Therefore, when designing and manufacturing axial flow pumps for turbine duties, priority should be given to material strength at the blade root during PAT mode operation to ensure safe and stable operation. The aim of this study is to provide technical references and theoretical foundations for evaluating the service cycle of axial-flow pumps and the influence on pump life under different operation modes.

Design optimization of sleeve finger splint model using Finite Element Analysis

One of the rehabilitation alternatives for fingers injuries is to use a finger splint. Some existing finger splint models still use excessive material, and the size is not appropriate. The purpose of this study was to propose a customized sleeve finger splint model with a conical shape along with the finger surface from the proximal phalanges to the distal phalanges. Design optimization using topology optimization was carried out to reduce mass and volume while maintaining the stress strength of the model. The stages of the method in this research were modeling design, preprocessing analysis, topology optimization, and postprocessing analysis. Topology optimization design was set with 70% mass in response constraint. The analysis results showed a significant reduction in the model mass of 42.18%, from 6.78 grams to 3.92 grams. Meanwhile, the maximum equivalent stress increased slightly by 3.42%, from 8.12 MPa to 8.4 MPa. Even though there was an increase in equivalent stress after topology optimization, the sleeve finger splint model was still categorized as safe, with a safety factor of 3.39.

Nano-scale machining of polycrystalline coppers - effects of grain size and machining parameters

In this study, a comprehensive investigation on nano-scale machining of polycrystalline copper structures is carried out by molecular dynamics (MD) simulation. Simulation cases are constructed to study the impacts of grain size, as well as various machining parameters. Six polycrystalline copper structures are produced, which have the corresponding equivalent grain sizes of 5.32, 6.70, 8.44, 13.40, 14.75, and 16.88 nm, respectively. Three levels of depth of cut, machining speed, and tool rake angle are also considered. The results show that greater cutting forces are required in nano-scale polycrystalline machining with the increase of depth of cut, machining speed, and the use of the negative tool rake angles. The distributions of equivalent stress are consistent with the cutting force trends. Moreover, it is discovered that in the grain size range of 5.32 to 14.75 nm, the cutting forces and equivalent stress increase with the increase of grain size for the nano-structured copper, while the trends reserve after the grain size becomes even higher. This discovery confirms the existence of both the regular Hall–Petch relation and the inverse Hall–Petch relation in polycrystalline machining, and the existence of a threshold grain size allows one of the two relations to become dominant. The dislocation-grain boundary interaction shows that the resistance of the grain boundary to dislocation movement is the fundamental mechanism of the Hall–Petch relation, while grain boundary diffusion and movement is the reason of the inverse Hall–Petch relation.

Hot workability and models for flow stress of NIMONIC 115 Ni-base superalloy

The hot workability of the nickel-base alloy NIMONIC 115 has been investigated by means of torsion testing in extended ranges of strain rate (0.01–1 s −1) and temperature (1140–1180 °C). The flow curves have shown, in general, an increase in equivalent stress up to a peak value followed by a softening until rupture. At 1140 °C, for strain rates varying between 0.01 and 1 s −1, the peak in flow stress is followed by a marked softening up to a steady state condition which can be attributed to the occurrence of dynamic recrystallisation. The hot ductility vs. true temperature, occurring during torsion tests, has been analysed. Flow behaviour of NIMONIC 115 alloy vs. process parameters has been modelled by means of an equation relating the hyperbolic sine of flow stress to the temperature-modified strain rate. The results have been analysed and discussed.