Fatigue & Fracture of Engineering Materials & Structures最新文献

E690 high-strength steel is widely used in ocean engineering due to its excellent properties. However, it is highly susceptible to fracture and failure under the coupled effects of corrosion and fatigue in marine environments. This paper investigates the corrosion fatigue fracture mechanisms through experimental and theoretical analyses. First, a series of corrosion fatigue tests on E690 steel specimens were conducted to study the crack propagation behavior, and the crack growth parameters were fitted using the Paris equation. Second, scanning electron microscopy was employed to analyze the corrosion fracture characteristics of the E690 steel specimens. Lastly, finite element analysis and molecular dynamics simulations were used to examine the crack propagation process and failure mechanisms from multiscales. The results show that under the influence of corrosion, dislocation accumulation at the crack tip leads to a plastic deformation mechanism dominated by dislocations during crack propagation. Furthermore, the combined effects of anodic dissolution and hydrogen embrittlement accelerate crack growth. In dry air conditions, loading frequency has no significant impact on the crack growth rate, whereas, in corrosive environments, the coupling of low frequency and corrosion shortens the corrosion fatigue life.

This study is aimed at clarifying the mechanism of effectively healing fatigue cracks in steel; austenitic stainless steel, SUS304; and hot work tool steel, SKD61, using high-density pulsed current. The results show that the current concentration occurred at the crack tip for SUS304, and crack closure was observed near the fatigue crack tip. On the other hand, crack closure was observed at the notch tip in SKD61. The fatigue crack closure phenomena were verified by finite element analysis, revealing that contact pressure was applied behind the crack tip owing to local bending deformation associated with residual stress near the crack tip. For effective crack healing, it is necessary to bond the interface leveraging compressive stress and Joule heat generated at the crack tip during current application.

Crack initiation in AISI 316 stainless steel has been investigated. Persistent slip bands (PSBs) were characterized using scanning electron microscopy (SEM) and atomic force microscopy (AFM). PSBs on the surface of the material increase the surface roughness and result in crack initiation. EBSD data from near the crack initiation region were used to correlate the global and local misorientations of the grains, plastic deformation, and Schmid factor with the fatigue life of specimens. The crack initiation region was found to have the highest misorientations. The region near crack initiation was found to have more plastic deformation, which was severe in specimens loaded with higher stresses. The kernel average misorientation (KAM) and grain reference orientation deviation (GROD) maps from the EBSD data were investigated for specimens that failed at different fatigue cycles. It was found that the interaction of high dislocation density, substructuring, and misorientation of low-angle grain boundaries in the region of plastic deformation resulted in fatigue crack initiation.

In situ fatigue crack propagation experiment was conducted on laser cladding with coaxial powder feeding (LCPF) K477 under various stress ratios and temperatures. Multiple crack initiation sites were observed by using in situ scanning electron microscopy (SEM). The fatigue short crack growth rate was measured, and the impacts of temperature and stress ratio on this growth rate were analyzed. Based on these experiments, the experimental data were expanded, and three ensemble learning algorithms, that is, random forest (RF), extreme gradient boosting (XGBoost), and light gradient boosting machine (LightGBM), were employed to establish a fatigue short crack growth rate model controlled by multiple parameters. It is indicated that the RF model performs the best, achieving a coefficient of determination (R²) of up to 0.88. The fatigue life predicted by the machine learning (ML) method agrees well with the experimental one.

This paper utilized an in-situ electron microscopy technique along with high-temperature fatigue tests conducted at 298, 573, and 923 K to observe the initiation and propagation of short fatigue cracks (SFC) in the nickel-based superalloy GH4169 and to examine changes in grain boundaries. The study examined how temperature and local microstructure affect the growth behavior of SFC in GH4169, which was fabricated using laser powder bed fusion (LPBF). The growth rate of SFC increased with higher temperature and stress amplitude, while the GH4169 alloy exhibited a combination of intergranular and transgranular fractures. Using the modified Paris model, the SFC growth model with Young's modulus (E) as an independent variable successfully predicted the crack propagation rate under various temperature loading conditions.

To predict the fatigue life of materials under cyclic loading, some research works have used the temperature rise caused by self-heating. The current paper presents a model based on the damage-entropy and self-heating concepts to predict the fatigue life of rubber and rubber composites. To this end, laws of thermodynamics were utilized to relate the material's temperature rise to its damage. The existing entropy-based model was modified to predict the fatigue life of SFRCs by incorporating the concept of damage entropy. The present model, which considers the material's viscoelastic energy, stored energy, and wasted energy and calculates the damage entropy in each loading cycle, was rigorously tested through an extensive experimental program. The experimental results demonstrated the model's accuracy in predicting the fatigue life of rubber and rubber composites at the applied strain below 88%.

Investigating the creep properties of damaged rocks is essential for evaluating the long-term stability of seismically cracked slopes in earthquake-prone regions. In this study, cyclic loading-unloading and step creep loading tests were sequentially performed on metamorphic sandstone, granite, and phyllite. Dissipated energy was introduced to establish the initial damage model, and the effect patterns and mechanisms of initial damage on creep properties were analyzed. The experimental results showed that dissipated energy and the damage variable increased linearly with the number of loading-unloading cycles. The increase in initial damage results in greater creep strain, higher steady-state creep rate, and increased dissipated energy under the same creep loading, while reducing the long-term strength of the rock. Prior loading-unloading promoted the development of microcracks and accelerated the time-dependent deformation of the rock. This study provides a new understanding of the long-term stability of seismically cracked slopes in strong-earthquake mountainous areas.

This study explores the application of laser-assisted cutting (LAC) in FeCoCrNiAl_0.6 high-entropy alloys to address traditional machining challenges and poor surface quality. It systematically analyzes the effects of laser power, scan speed, and spot diameter on surface integrity and fatigue life. Using Abaqus/FE-SAFE simulations and LAC experiments, differences in surface quality and fatigue cycles under various laser parameters are observed. Results show that increasing the spot radius reduces heat accumulation and center temperature. A 1 mm radius yields a center temperature 5.58 times higher than a 7 mm radius and achieves a residual compressive stress of 412 MPa, which decreases to 198 MPa (51.9% reduction) at 7 mm. Larger laser power increases stress and fatigue life positively, while higher scan speeds reduce stress. Fatigue cycles drop by 82.9% as the spot radius increases from 1 to 7 mm, while 25 W power extends fatigue life 4.26 times compared to 10 W.