Fatigue & Fracture of Engineering Materials & Structures最新文献

The TC4 titanium (Ti) alloy has been widely utilized in various industries such as aerospace and shipbuilding, owing to its numerous advantages. Its exceptional properties have made it a material of choice for applications requiring high performance and reliability. The total weld thickness was 140 mm, and microstructures and high-cycle fatigue properties were investigated at three different layers within the 140-mm section. Experimental results show that the overlap area at two weld roots has the highest microhardness and largest nonuniformity of the overall joints, so the area is found to have the poorest high-cycle fatigue properties. The microstructures in every layer of the weld metal of the joints were analyzed to determine the causes of the poor fatigue properties in the overlapping area at the weld roots. Significant amounts of α′ acicular microstructure are present in the weld metal of joints, while the overlap area at weld roots contains more α′ acicular microstructure with a finer size. Compared with other layers, the weld metal and base metal in Layer 2 (overlap area) have the largest microhardness gradient, where the stress concentration is more serious in the fatigue experimental process. Heat dissipation conditions was a critical factor for the inhomogeneity of microstructure and mechanical properties along the thickness direction of 140-mm double-sided electron beam welding joint. Fatigue damage (micropore) is formed at β phases in priority, and fatigue cracks propagate via series connection of micropores, indicative of transgranular ductile cracks.

In ultrasonic fatigue tests, the VHCF properties can be determined in a reasonable time. Nevertheless, the high frequency can affect the fatigue behavior for some materials. This study investigated the fatigue capability of 34CrNiMo6 and 42CrMo4 steels, both of which find widespread applications in several mechanical components. These steels were carried out for conventional and ultrasonic fatigue tests under fully reversed testing conditions. A microplasticity strain amplitude was calculated, indicating an order of magnitude decreases around 10–100, when compared with the experimental results from low-frequency tests. Cyclic strain rates were estimated for each steel and correlated with the number of cycles to failure. A conversion constant was obtained by fitting a curve to convert the high frequency results into theoretical results at low frequency. The experimental and predicted results were evaluated. The results proved the relevance of the strain rate in frequency effect. The converted results showed strong agreement with the experimental results in low-frequency tests for the steels being studied.

In this study, precision-bearing samples were tested on bearing test bench under light load condition for different time periods. Surface morphologies of damage bearing samples were characterized from two aspects (2D and 3D) by various methods. Numerous micropits can be observed on surfaces of raceways and steel balls. Combing with surface damage morphologies and thickness of oil films, it can be speculated that main formation mechanism of micropits is that the surface asperities puncture the oil film firstly and then squeezed into surface in contact with it. Potential effect of vibration during the formation process of micropits had been found by repetitive experiments on RCF test machine. Micropits can form more easily under higher vibration values. Surface microcracks can initiate and propagate with the synergistic effects of repeated plastic deformation and oxide-assisted.

This study aims to promote the resource utilization of solid waste in asphalt pavements and improve its fatigue performance. For this, phosphogypsum whisker (PSW) was used as a substitute filler to prepare asphalt mixture. Through pavement performance tests and four-point bending test, the effects of different filler types and substitution ratios on the pavement performance and fatigue performance of asphalt mixtures were investigated. On this basis, the phenomenological method was used to further construct the fatigue performance prediction model. The results indicate that PSW can effectively enhance the high temperature performance and moisture stability of the mixtures but has an adverse effect on low temperature performance. Additionally, the enhancement effect of PSW on pavement performance is more significant than PC42.5 cement (PCC). Both PSW and PCC can enhance the fatigue performance of the mixtures, with PSW exhibiting a more pronounced effect, and the incorporation of substitute fillers helps to curb the degradation trend in fatigue performance. Comparative studies indicate that the error rate of prediction model for various mixtures is significantly below 5%, with low volatility in the prediction results. Furthermore, the variance analysis results reveal that strain has a more pronounced impact on the fatigue performance of the mixtures.

This paper investigates the ability of the self-heating method to characterize the fatigue behavior of 316L stainless steel produced by Laser Powder Bed Fusion. Nearly dense cylinders are built vertically using various process parameters corresponding to various volumetric energy densities. Fatigue specimens are then machined from these cylinders and polished. Fully reversed tension–compression fatigue tests (R = −1) are conducted. The self-heating method is used for the estimation of the fatigue limits. These fatigue limits are compared to results obtained from S-N curves in the high cycle regime. Whatever the set of process parameters, the self-heating curves show three distinct domains of heat dissipation. Thanks to microstructure analysis, fractographic observations, and correlations with S–N curves, these domains can be closely linked to damage mechanisms associated or not with defects.