Fatigue & Fracture of Engineering Materials & Structures最新文献

A simulation model was developed to predict the bending fatigue life of carburized spur gears. The crack initiation location and life were estimated using a strain-life approach with a multilayer model, and the crack propagation life was determined using the Paris–Erdoğan equation based on the linear elastic fracture mechanics approach and the separating morphing and adaptive remeshing technology (SMART). The present study investigates the effect of gear design parameters, including the pressure angle, profile shift, and tooth width, on tooth root fracture. The final step in the validation process entailed the use of single-tooth bending fatigue (STBF) experiments to assess the reliability of the simulation results. Consequently, the findings from comprehensive simulation and experimental investigations have demonstrated that augmenting the pressure angle results in substantial enhancements in root crack propagation and fatigue life. The predicted bending fatigue life, crack initiation, and propagation demonstrate a strong correlation with experimental findings.

To identify the fracture initiation position and growth characteristics in heterogeneous rock, we performed in-situ NMR observations to capture fracture propagation and proposed a damage constitutive model considering crack closure to characterize the macroscopic failure behavior of rock. Results reveal that microcrack propagation is earlier in the area with high microcrack density. Fractures initiate from pores and propagate between pores along the direction of maximum compressive stress loading. Fracture propagation tends to coalesce and form a larger fracture cluster in the zone with high microcrack density, showing a remarkable fracture localization. In contrast, a dispersed crack growth occurred in areas with low density. The proposed damage constitutive model considering crack compaction effectively characterizes the rock's prefailure process. These results clarify the mesoscopic fracture propagation within the porous rock considering internal microcrack distribution, which has significant implications for predicting fracture growth within rocks.

Uniaxial compression tests instrumented with acoustic emission and digital image correlation systems were conducted to explore the failure behaviors of unbolted and bolted jointed specimens. The jointed specimens were fabricated by 3D printing with a fixed inclination angle of 45° and five joint roughness coefficients (JRC) values: 2.88, 7.47, 11.86, 15.37, and 19.15. For unbolted jointed specimens, as JRC increased from 2.88 to 19.15, the increments in strength, elastic modulus, and failure strain were 19.99 MPa, 6.95 × 10⁻³, and 0.52 GPa, respectively. Bolting produced a marked increase in failure strain for jointed specimens with JRC = 2.88 and 7.47; the bolting-induced gains in strength, elastic modulus, and failure strain diminished as JRC increased. Both increasing JRC and bolting led to a larger total number of cracks and a stabilization of the b-value. As the JRC increased, the failure mode of jointed specimens shifted from joint sliding to matrix tensile-splitting. Bolting exacerbated joint wear and increases promoted the formation of tensile cracks within the matrix. The bolts in jointed specimens with JRC = 2.88 and 7.47 were sheared off, whereas those in specimens with JRC = 15.37 and 19.15 underwent bending deformation. Higher JRC values increased the ratio of axial to vertical deformation in the bolts.

The surface condition of additively manufactured (AM) parts strongly influences fatigue performance. Laser shock peening (LSP) is an effective surface enhancement method that improves the quality of AM metals by introducing compressive residual stresses (CRSs). In this study, two different metallic alloys, γ-TiAl and IN939, were manufactured using powder bed fusion (PBF) techniques. The γ-TiAl alloy was produced via electron beam melting (PBF-EB), while IN939 was fabricated through laser powder bed fusion (PBF-LB). After fabrication, all specimens were subjected to LSP and then tested under four-point bending fatigue conditions. The results were compared between the as-built and LSP-treated conditions. For the PBF-EB γ-TiAl alloy, a fatigue limit was determined based on the 2 × 10⁶ cycle run-out criterion, and LSP led to a 50.1% increase in the fatigue limit. For the PBF-LB IN939 alloy, because none of the as-built samples reached the run-out cycle threshold, fatigue life comparisons were made at selected normalized stress levels. The LSP-treated specimens showed fatigue life improvements by factors of 1.87 and 3.72 at stress levels of 0.74 and 0.87, respectively. Scanning electron microscopy (SEM) was used to evaluate the fracture surfaces, and the influence of LSP on fatigue behavior was discussed for both alloys.

Fracture toughness measurement using miniature specimens is of great interest in the context of small-section applications, surveillance specimens for in-situ radiation experiments, and for evaluating new alloys with limited volume of availability. In this study, and as part of a broader high-temperature alloy design effort, the fracture toughness of two specialized refractory niobium (Nb) alloys was determined using miniature four-point bend specimens. In particular, the question of how the initial notch length (or depth) affected the toughness of alloys with contrasting deformation behavior (ductile versus brittle) was explored in detail. In general, fracture toughness, as measured by maximum stress intensities at fracture, increased with notch length, reaching a maximum at a₀/W of about 0.3, and then decreasing at large notch lengths. This behavior was found in both ductile and brittle alloys, suggesting that this is an intrinsic size effect arising from the mechanics of deformation of the net-section. A new net-section-based stress analysis is used to model the fracture toughness behavior and explain the notch length dependence of fracture behavior. Based on the net-section stress analysis, it is found that fracture occurred at a constant notch tip stress condition at all notch depths, yet creating a significant variation in fracture toughness with notch length in both brittle and ductile alloys. The implications of the findings on the measurement and interpretation of small specimen fracture toughness are discussed.

Basic mechanical and low-cycle fatigue (LCF) properties of 10CrNi3MoV steel were comprehensively examined by experimental tests at low temperatures in the paper. The variations of yield, tensile strength, and impact values were presented to show their variation tendency. Furthermore, the LCF tests were conducted, and some fatigue indicators under strain-controlled loadings, such as hysteresis loops, cyclic Masing behavior, and fatigue capacity were characterized. Fatigue crack growth (FCG) tests quantitatively revealed the factors of stress ratio and temperature on the FCG resistances. Results show that the decrease of temperature also improves the capacity of basic mechanical properties, crack initiation, and crack growth of the steel, while the impact properties will deteriorate with variation of temperature. The ductile and brittle fracture transition (DBT) behaviors under different loading conditions were also examined. Results demonstrate that the DBT behavior for LCF properties is consistent with that of FCG performance at low temperatures.

The present work investigates the dominant failure mechanisms and crack growth behavior under isothermal and thermomechanical fatigue (TMF), analyzed in terms of energy release rate and phase-field fracture modeling. The test material consisted of single-edge notched tension (SENT) specimens fabricated from the nickel-based heat-resistant alloy XH73M. Experiments were conducted under conditions of pure fatigue, fatigue–creep interaction, and both in-phase and out-of-phase TMF within the temperature range of 230°C to 650°C. Fractographic analysis based on fatigue fracture diagrams and scanning electron microscopy revealed characteristic features of crack propagation processes under thermomechanical loading. The experimental data on initial, current, and critical values of the energy release rate were incorporated into phase-field fracture models to simulate the dominant intergranular and transgranular failure mechanisms in XH73M. Furthermore, the study establishes the limitations of employing conventional degradation functions for modeling cyclic fracture processes at elevated temperatures. Summary: The XH73M alloy tests performed for fatigue, creep–fatigue, in-phase, and out-of-phase TMF. The dominant failure mechanisms for TMF are correlated with the energy release rate. The known equations for phase-field fatigue degradation function have limited capabilities. The XH73M alloy dominant failure mechanisms are modeled by the Voronoi tessellation method.

To address the stochastic characteristics of fatigue damage, this study proposed a Markov chain–based crack propagation prediction model integrating linear elastic fracture mechanics. First, the state transfer process for the rib-to-deck weld was analyzed. Then, the state transfer probability matrix was calculated by analyzing the relationship between the stress intensity factor range and the transfer probability in Paris equation. In the process of calculating the stress intensity factor ranges, the randomness of multiple parameters needs to be considered including initial cracks. Subsequently, the evolution of fatigue states can be derived. After that, the fatigue test of the segment model was conducted to verify the correctness of the proposed model. Finally, the model was applied to evaluate the fatigue state of the rib-to-deck weld of the steel bridge. The results reveal that the proposed model is consistent with the experimental results and provides a probabilistic fatigue life prediction.

This paper presents the fatigue life analysis and experimental study on a broadband non-stationary stochastic process with mean stress. An experimental platform capable of simultaneously applying random vibration loads with mean stress and periodic loads to specimens is first constructed, thereby inducing non-stationarity in the vibration response. Vibration fatigue tests on edge-notched 6063-T6 aluminum alloy specimens verify the influence of both the mean value and non-stationarity of the stochastic process on vibration fatigue life. A novel model is subsequently developed for predicting the fatigue life under broadband non-stationary stochastic processes with mean stress. This model quantitatively accounts for the effects of mean stress, as well as the amplitude and frequency of periodic loads, on vibration fatigue life. The results of the vibration fatigue tests indicate that the proposed model provides accurate fatigue life of the broadband non-stationary stochastic processes with mean stress in the frequency domain.