Search

Fatigue tests were conducted to investigate the effects of mean stress, stress range, and deck thickness on crack growth and fatigue failure of the deck‐rib welded joint. According to the experimental results, a fatigue failure criterion and a fatigue evaluation method for deck‐rib welded joints, which consider mean stress effect, was proposed. The results indicated that the stress range remains the dominating factor, but the influence of mean stress cannot be ignored. It was proposed that the crack length reaching approximately 150 mm and the depth reaching around 70% deck thickness can be taken as the fatigue failure criterion, while increase in mean stress would reduce the critical crack length but increase the critical crack depth. Besides, multiple cracks will weaken the fatigue strength. It is recommended to use Walker method and the FAT 71 curve with enhancement factor f−1=1.3$$ f\left(-1\right)=1.3 $$ to evaluate the fatigue strength under symmetrical stress cycle. [ABSTRACT FROM AUTHOR]

The desire to use additively manufactured (AM) parts to ensure the availability of military aircraft, and to build limited‐life unmanned aerial vehicles (drones), coupled with the United States Air Force (USAF) approach to the airworthiness certification of AM parts has focused attention on durability analysis/assessment, and hence on the growth of small cracks in AM parts. Previous studies have shown that laser powder fusion built (LPBF) Scalmalloy® has: i) A yield stress and an ultimate strength that are greater than that of AA2024‐T3 and comparable to that of AA7075‐T6; ii) A resistance to crack growth that is better than that of AA7075‐T6 and comparable to that of AA2024‐T3. However, since the ability to predict the durability of a part is essential for its airworthiness certification, the present paper illustrates how to perform a linear elastic fracture mechanics (LEFM)‐based durability assessment of Boeing Space, Intelligence and Weapon System (BSIWS) LPBF Scalmalloy®. The durability study includes specimens with both machined surfaces and surfaces left in the as‐built condition. As a result, it would appear that BISWS AM LPBF Scalmalloy® is an ideal candidate for building limited‐life AM replacement parts for fixed and rotary wing aircraft and drones. [ABSTRACT FROM AUTHOR]

Significant interest and developments in phase-field fracture modeling have emerged. It approximates fracture continuously using a length-scale parameter, accurately simulating fracture initiation and crack propagation in brittle materials like Polymethyl Methacrylate (PMMA) with nonlinear elasticity. This study proposes a phase-field approach for simulating PMMA fracture behavior using ABAQUS with a nonlinear elastic material model (UMAT) and a three-layered element composition (UEL). The staggered approach sequentially solves displacements and phase-field variables. Numerical results are validated against experiments considering various geometries, stress concentrators, and pre-cracks. The computational approach accurately predicts fracture initiation and crack growth in complex patterns and diverse loading conditions. [ABSTRACT FROM AUTHOR]

ABSTRACT In this study, molecular dynamics (MD) simulations were employed to investigate the crack propagation behavior of single‐crystal titanium with various crystal orientations under cyclic loading. The analysis demonstrates that each crack model displays temporary cyclic hardening and predominant cyclic softening characteristics. The orientation of crack propagation primarily impacts the characteristics of the softening stage, with less influence on the initial hardening stage. A notable orientation correlation is evident in the mechanism of crack propagation, characterized by the presence of various slip modes and deformation twinning (DT) systems. The crack tip deformation behavior obtained from the simulation aligns with the theoretical predictions of linear elastic fracture mechanics (LEFM). The crack growth rate (CGR) and ΔJ for different crack models show good correlation, and both the crack propagation direction and crack plane orientation affect the characteristics of the ΔJ–da/dN curves. [ABSTRACT FROM AUTHOR]

Resurfacing a moderately deteriorated Portland cement concrete (PCC) pavement with asphalt concrete (AC) layers is considered an efficient rehabilitation practice. However, reflective cracks may develop shortly after resurfacing because of discontinuities (e.g. joints and cracks) in existing PCC pavement. In this paper, a new accelerated full-scale testing approach was developed to study reflective crack growth in AC overlays. Two hydraulic actuators were used to simulate a moving dual-tire assembly with a loading rate of more than five-thousand-wheel passes per hour. A load cycle consists of three steps, simulating a tire approaching, moving across, and leaving a PCC discontinuity. Experiments were conducted to compare the reflective crack behaviour of two overlay configurations. Both test sections were fully cracked in less than an hour. The initiation and propagation of reflective cracks were explicitly documented using crack detectors in conjunction with a camera. The proposed full-scale testing protocol offers a repeatable and efficient approach to systematically investigate the effects of various overlay configurations, thus enabling the identification of optimal design against reflective cracking. [ABSTRACT FROM AUTHOR]

A multi-scale fractographic analysis was performed to a tensile test specimen according to ASTM D638-I additively manufactured by stereolithography with inherent bottom layers. The asymmetric shape of the sample created a rather complex failure analysis case with varying mode I/mode III crack propagation regimes. Performed multi-scaled approach revealed interconnected 3D formation mechanisms of common fractographic features for the first time on additively manufactured UV-cured resins by stereolithography. Both root cause of failure and damage propagation mechanisms were directly correlated with solid building blocks (BB). Printing grids whose shape is pre-defined during manufacturing appeared on the fracture surfaces in the pre-set dimensions. More strikingly, the river pattern formations were found to be the means of communication between different BBs along different material planes. The measured fractal dimension of river patterns was 1.76 which was almost valid in every point on the fracture surface, which provided a pathway for more sophisticated 3D SEM scanning efforts that may pave way to property mapping. A framework fractographic discussion is provided for further research activities on material/printer development along with mechanical testing. [ABSTRACT FROM AUTHOR]

High and very high cycle fatigue tests were performed to examine the microstructure and fracture mechanism of GH4169 superalloy in combination with techniques including electron‐backscatter diffraction (EBSD). Fractographic analysis revealed that surface failures are induced by surface flaws, whereas internal failures are caused by pores, facets, and inclusions. The three‐dimensional observation shows that fracture surfaces exhibit an irregular texture due to crystallographic mismatch of grains and plastic deformation at the crack tip. Based on EBSD analysis, Euler angles exhibited a complex geometry of grain orientation at the crack tip area, hindering crack propagation as evidenced by lower values of the Schmid factor and misorientation at the crack tip. Furthermore, the threshold values of small and long cracks decrease, whereas the transformation sizes from small to long crack growth increase from surface to internal failure. Finally, a novel microstructure defect‐based life prediction model is established, and the predicted results demonstrate a close resemblance to experimental outcomes. [ABSTRACT FROM AUTHOR]

Delayed fracture occurs when cracks grow subcritically prior to achieving KIC. Glass science research in this area has focused almost exclusively on non ion‐exchanged glasses. In this study, an ion‐exchange strengthened aluminosilicate glass was intentionally damaged to measure delayed fracture behavior. Damage was applied both pre and post ion‐exchange and the role of heat‐treatments was investigated. It was found that the delayed fracture likelihood was reduced for samples that were heat‐treated in an environment containing water vapor. An increase in the static fatigue limit was measured for increasing temperature and it was hypothesized that crack toughening takes place during the heat‐treatment due to a water‐assisted stress relaxation mechanism. [ABSTRACT FROM AUTHOR]

The fracture behavior of bi-material made of Ni-Cr-B-Si hardfacing alloy deposited over SS316LN substrate was evaluated under quasi-static and dynamic loads. The crack growth started from notch made on the deposit side and progress toward the substrate deposit interface under both loading conditions was monitored. The displacement rate in quasi-static loading and the loading rate for dynamic loading varied and crack propagation was studied. It was observed that the crack was deflected at the interface and not penetrated to the substrate, irrespective of loading conditions. The reason for crack deflection at the interface was analyzed using the energy-based method. It is shown that the ratio of fracture toughness of the interface to that of the substrate (0.044) is lower than the ratio of energy release rate for the deflecting crack to that of the penetrating crack (0.235). Thus, this material combination satisfies the condition for crack deflection rather than penetration. The fracture toughness of the interface was estimated as ~ 68 MPa m1/2 and it falls between that of hardfacing alloy and SS316LN base metal. Optical and SEM examinations were conducted to corroborate the crack path deviations during crack growth. Results suggest that isolated cracks might be present on hardfaced coatings on critical components for which such cracks are usually not permitted. It may be allowed in preference to repair of these cracks, which is difficult and significantly increases the risk of additional cracks forming on the deposits because of the high susceptibility of the hardfacing alloy to cracking. [ABSTRACT FROM AUTHOR]

In this study, the fatigue crack initiation and growth behaviors of an additively manufactured (AM) Ti-6AI-4V alloy were investigated, and its prospect for fatigue applications was evaluated. The AM specimens were first fabricated by selective laser melting (SLM) and then underwent a cycle of annealing at 800 °C for 2 h and hot isostatic pressing (HIP) treatment at 920 °C/150 MPa/3 h followed by surface machining. Prefabricated spherical defects with different diameters (1.0 mm and 2.0 mm) were introduced to examine the efficacy of HIP treatment for eliminating the built defects. Both fracture morphology and microstructure were characterized to reveal the failure mechanism of these tested specimens. The results suggest that both the fatigue lives and fatigue crack growth resistances of most SLM+HIP-processed specimens are much higher than those of traditional wrought material, thus highlighting that the AM Ti-6AI-4V alloy can be a better candidate for future fatigue applications. However, due to the large variability in fatigue performance, the current SLM+HIP-processed Ti-6Al-4V alloy still cannot meet the demand for high safety and reliability. [ABSTRACT FROM AUTHOR]

Polymethyl methacrylate (PMMA) is an ideal material used in underwater transparent structures such as submersible windows and the fully-transparent pressure chamber of the sightseeing submersibles. The failure of PMMA structures usually come from small crack-like defects. In this paper, the fatigue crack growth experiments were carried out on PMMA materials with different thicknesses (B = 3, 6, 12 mm) and stress ratios (R = 0.1, 0.3) as well as plane strain fracture toughness test for unstable crack propagation conditions. Thickness effect and dwell time effect are experimentally investigated in addition to load ratio effect. The applicability of an improved crack growth rate model on PMMA material is validated by test results. The application of this model for prediction of crack growth rates can greatly save experimental time under different working conditions and can be applied in fatigue assessment of full-transparent structures under random loading. [ABSTRACT FROM AUTHOR]

ABSTRACT Nickel‐aluminum bronze (NAB) is extensively utilized across various industries, particularly marine applications due to its exceptional corrosion resistance. The mechanical properties of NAB are highly dynamic, and influenced by factors such as manufacturing processes, operating environments, and microstructure. This variability introduces complexities and challenges in addressing fatigue, the most common failure mode in metals. This review offers a thorough examination of the fatigue properties of NAB in both their conventionally fabricated and additively manufactured (AM) forms. This review explains the mechanisms that modulate fatigue in NAB by analyzing the existing literature and identifying critical factors such as microstructure, defects, and processing parameters. The goal is to improve the comprehension and dependability of NAB by contrasting the fatigue resistance of cast and AM NAB. The ultimate objective of this comprehensive examination is to predict and reduce component failures, thereby extending the service life and performance of NAB components in demanding environments. [ABSTRACT FROM AUTHOR]

The simulation of crack growth and estimation of fatigue life in engineering structures containing cracks and notches is very complex. The complexity can be simplified by making suitable assumptions based on the experimental observations. The present investigation is aimed to address these aspects. The effect of notch length (a1) and notch offset distance (H) on fatigue crack growth of a crack having length a0 and Paris crack growth parameters under three-point bending constant amplitude loading was investigated. Significant shielding effects on the crack growth rate have been observed for a1 ≤ 0.6a0 and H ≤ 6 mm. It was found that the shielding effects gradually reduced to 18.67 % for a1 > 0.6a0 and H > 6 mm. The effect of offset secondary machined notch was found negligible for a1 = a0 and H ≥ 10 mm. About 50% reduction in fatigue life as compared to a single crack of length a0 = 10 mm was seen for a1 ≤ 6 mm and H ≤ 8 mm. The shielding effect due to the presence of a notch was discussed on the basis of stress intensity factors and von Mises stresses computed by the finite element method. [ABSTRACT FROM AUTHOR]

In this study, the progress of surface crack and high cycle fatigue of the surface piercing propellers (SPPs) are investigated numerically using the finite element method. The cyclic load is calculated from the hydrodynamic pressure on the blade by simulating the fluid around the blade using the computational fluid dynamics software STAR-CCM+. The initial cracks are assumed to be created near the blade root. The fatigue life is calculated from the Paris-Erdogan equation. The results show that the crack close to the root has a shorter life and the stresses at the crack front depend on the blade-water interaction duration. [ABSTRACT FROM AUTHOR]

Presently, Functionally Graded Materials (FGMs) are extensively utilised in several industrial sectors, and the modelling of their mechanical behaviour is consistently advancing. Most studies investigate the impact of layers on the mechanical characteristics, resulting in a discontinuity in the material. In the present study, the extended Finite Element Method (XFEM) technique is used to analyse the damage in a Metal/Ceramic plate (FGM-Al/SiC) with a circular central notch. The plate is subjected to a uniaxial tensile force. The maximum stress criterion was employed for fracture initiation and the energy criterion for its propagation and evolution. The FGM (Al/SiC) structure is graded based on its thickness using a modified power law. The plastic characteristics of the structure were estimated using the Tamura-Tomota-Ozawa (TTO) model in a user-defined field variables (USDFLD) subroutine. Validation of the numerical model in the form of a stress-strain curve with the findings of the experimental tests was established following a mesh sensitivity investigation and demonstrated good convergence. The influence of the notch dimensions and gradation exponent on the structural response and damage development was also explored. Additionally, force-displacement curves were employed to display the data, highlighting the fracture propagation pattern within the FGM structure.

Aviation aircraft will be subjected to a large number of complex random vibration loads during service， and its structure is prone to vibration fatigue，which leads to damage or even failure，which can cause serious losses. The stress intensity factor（SIF）solution method for cracked beams under random vibration loading is investigated，and a time-domain method based on Hudson's theory is proposed to estimate the vibration fatigue crack growth life by combining with the Paris formula. The theoretical analysis and vibration fatigue test are conducted on a typical cantilever beam as an object. The results show that the life prediction results of the proposed time-domain method based on the Hudson's theory is better than that of the experimental estimation results，which can verify that the method can effectively describe the random vibration crack growth behavior.

AerMet 100 steel is a new type of double-hardened high-strength steel, which is often used as landing gear material in amphibious aircraft. In the present paper, the corrosion fatigue behavior and mechanism of AerMet 100 high-strength steel in a 3.5% NaCl solution was studied by stress-controlled fatigue tests and a series of subsequent characterizations of the fracture surface, microstructure, and cracks. The results indicated that the fatigue life of AerMet 100 high-strength steel decreased with a decrease in the stress level in a 3.5% NaCl solution, satisfying the relationship lgN = −2.69 × 10−3 σ + 6.49. The corrosion fatigue crack usually initiated from the corrosion pit and propagated across the martensitic flat noodles. Meanwhile, the corrosion fatigue crack tip was filled with Cr2O3, Fe2O3, and amorphous material; it propagated in the transgranular mode by a slip dissolution mechanism. This study provides some engineering significant for the fatigue performance of AerMet 100 steel in a 3.5% NaCl solution. [ABSTRACT FROM AUTHOR]

This document presents a program developed by Amin Houari from the University of Boumerdes for predicting damage in notched functionally graded materials (FGMs) plates using the extended finite element method (XFEM). The program is written in the USDFLD subroutine and includes variables and dimensions. It reads the X coordinate and assigns it to the first field variable. The program provides a computational simulation for analyzing the behavior of FGMs and predicting damage in notched structures. [Extracted from the article]

In this work, we study the combinational effects of UV irradiation, functionalized graphene (FG) sheets, and organic solvents on the crack evolution in PMMA/FG composites. The UV irradiation leads to the scission of polymer chains in the PMMA/FG composites with the FG sheets hindering the scission of polymer chains. The evolutions of surface cracks and the pre-formed crack in the PMMA/FG composites depend on the diffusion of organic solvents. The increase of Hansen solubility distance (HSD) with the solvent follows the order of cyclohexanol, 2EA, and 1-butanol sequence. The solvent with a smaller HSD diffuses faster in polymer, producing larger tensile stress to cause the nucleation and growth of cracks. The density of surface cracks and the length of the pre-formed crack decrease with increasing the FG fraction and HSD and increase with increasing the UV dose. The activation energy and heat of mixing for the growth of surface cracks increase with the FG fraction and HSD and decrease with increasing the UV dose. The activation energy for the growth of the pre-formed crack increases with increasing the FG fraction and HSD and decreases with increasing the UV dose. The activation energy for the inculcation period of the growth of the pre-formed crack has an opposite trend to the activation energy for the growth of the pre-formed crack versus the FG fraction, HSD, and UV dose. The experimental results show that the evolutions of surface cracks and the pre-formed crack follow the scaling law describing the diffusion of organic solvents in solids. [ABSTRACT FROM AUTHOR]

The effect of a laser beam on the development of cracks in an AL-6061 aluminum plate at various aspect ratios of 1:1, 1:1.5, and 1:2 was investigated in this study. The investigation adopted two clamping types: Clamped-Free-Clamped-Free and Simply-Free-Simply-Free, and supported the plate with a 5 mm crack length. The study aimed to investigate the duration it takes for cracks to propagate when subjected to the impact dynamic load after being exposed to 500 watts of laser power. Compared to the plate with an aspect ratio of 1:2 and the CFCF clamping type that was not subjected to the laser beam, the numerical results showed a 36% increase while increasing by 37% in the experimental results. Furthermore, compared to the plate that was not exposed to the laser beam and had the same boundary conditions, the clamping SFSF type of aluminum plate under dynamic load showed an increase in the number of beats that are required for crack growth of 29% according to experimental results and 28% according to numerical results. The results presented show that clamping conditions have a significant impact on the growth of cracks in the plate. It was found that a crack requires more beats to grow in a crack with an aspect ratio of 1:1 than in a crack with an aspect ratio of 1:1.5, which is larger than the aspect ratio of 1:2. Furthermore, the plate with the CFCF clamping type requires fewer pulses for the crack to grow than the plate with the SFSF clamping type. The heat of a laser beam altered the microstructure of an aluminum plate, generating residual stresses and increasing its surface hardness, thereby enhancing its crack resistance and failure resistance properties. The SEM images showed how the laser beam affected the microstructure of the sample's surface, enhancing its resistance to crack growth compared with the aluminum plate's surface, which was not exposed to the laser beam, and appears smoother. [ABSTRACT FROM AUTHOR]

In order to prevent the body from overheating, a corresponding thermal protection device is usually designed on the inner wall of the combustion chamber. The working environment of this thermal protection device is very harsh, and it needs to withstand internal and external pressure loads and thermal radiation loads of the combustion chamber, especially at the connection between the cylinder and the support parts, the force is harsher. In order to avoid engine damage, causing unnecessary losses. In this article, the thermal–mechanical coupling analysis of the heat shield is carried out by finite element method to analyze the thermal stress and mechanical stress. According to the finite element simulation results, the initial cracks are inserted, respectively, at the stress concentration. Using linear elastic fracture mechanics and Forman–Newman–de Koning models, the crack growth lifetimes of cracks at different locations were calculated. The results of the study show that comparing the initial cracks at different locations, the cracks on the side near the edge of the heat shield have the largest reduction in crack growth life of 64.4% and the critical crack length of 52.0%. The linear superposition of thermal and mechanical stresses under different working conditions has different degrees of nonlinear effects on the crack growth life and critical crack length. The research work in this article can provide a basis for the evaluation of fatigue crack growth life of heat shield and can also provide a reference for engine maintenance. [ABSTRACT FROM AUTHOR]

Archard’s wear law encounters challenges in accurately predicting wear damage and volumes, particularly in complex situations like asperity–asperity collisions. A modified model is proposed and validated, showcasing its ability to predict wear in adhesive contacts with better accuracy than the original Archard’s wear law. The model introduces an improved wear coefficient linked to deformation energy, creating a spatially varying relationship between wear volume and load and imparting a non-linear characteristic to the problem. The improved wear model is coupled with the Boundary Element Method (BEM), assuming that the interacting surfaces are semi-infinite and flat. The deformation energy is calculated from the normal contact pressure and displacements, which are the common outputs of BEM. By relying solely on these outputs, the model can efficiently predict the correct shape and volume of the adhesive wear particle, without resorting to large and often slow models. An important observation is that the wear coefficient is expected to increase based on the accumulated deformation energy along the direction of frictional force. This approach enhances the model’s capability to capture complex wear mechanisms, providing a more accurate representation of real-world scenarios. [ABSTRACT FROM AUTHOR]

In this paper, we propose a new approach for numerically simulating the growth of cracks in unidirectional composite materials, termed extended isogeometric analysis, evaluating the maximum stress intensity factor and T-stress. To validate our approach, we used a small anisotropic plate with two edge cracks, beginning with formulating the governing equations based on the energy integral method, Stroh's Formula, and the Elastic Law describing the behaviour of anisotropic materials, while considering boundary conditions and initial states. A MATLAB code was developed to solve these equations numerically and to post-process the tensile stress and the stress intensity factor (SIF) in the first mode. The results for the SIF closely match those obtained using the extended finite element method (X-FEM), with a discrepancy of only 0.0021 Pa·m0.5. This finding underscores the credibility of our approach. The extended finite element method has demonstrated robustness in predicting crack propagation in composite materials in recent years, leading to its adoption by several widely used software packages in various industries. [ABSTRACT FROM AUTHOR]

Crack growth tests of 316LN stainless steel under load‐controlled and strain‐controlled thermo‐mechanical fatigue (TMF) loadings at the temperature range of 350°C ~ 550°C were conducted. Moreover, the isothermal fatigue (IF) crack growth tests at the maximum temperature of 550°C were performed for comparison. The differences in IF and TMF crack propagation behavior under different loading conditions were thoroughly discussed, and the underlying mechanisms were revealed by a comprehensive characterization of the deformation state of the crack tip region using digital image correlation (DIC) and electron backscatter diffraction (EBSD) methods. Furthermore, it was found that the EBSD characterization was simply based on a single plane made it difficult to evaluate the complex crack growth behavior. In addition, the limitations of the classical parameter of stress intensity factor under TMF loading were presented. Highlights: TMF crack growth behavior of 316LN steel under load‐ and strain‐controlled modes were studied.TMF crack growth rate was higher than that in the isothermal fatigue test at the maximum temperature.The crack growth rate under load‐controlled tests was lower than that in the strain‐controlled tests.Plastic deformation at the crack tip was characterized by DIC and multi‐layer EBSD methods. [ABSTRACT FROM AUTHOR]

While the variational phase-field model has been widely used in modeling fracturing in porous media, it poses a challenge when applying high confining pressures on a model because the relatively large deformation induced by the confining pressures might cause undesired crack nucleation when the strain decomposition scheme are used, which is not consistent with engineering observations. This study proposes a two-step strategy to incorporate in situ stresses into phase-field modeling of hydraulic fractures, addressing the limitations of previous approaches in capturing realistic fracture initiation and propagation under high confinement. A micromechanics-based hydromechanical phase-field model is presented first, and the proposed two-step strategy is investigated with different strain decomposition schemes: isotropic, volumetric–deviatoric, and no-tension models. Two numerical examples show that the two-step strategy effectively achieves a desired initial state with geostatic stresses and zero strain, allowing for accurate simulations even in the presence of complex natural fractures. The efficiency of the proposed two-step strategy for incorporating in situ stresses is highlighted, and the challenges associated with capturing stiffness recovery and shear fracture nucleation under high confinement using strain-based models are discussed. [ABSTRACT FROM AUTHOR]

Crack growth analysis of aircraft fuselage panels is one of the important tasks of aircraft damage tolerance design. In this paper, the crack growth behavior and residual strength characteristics of the internal pressure panel of the aircraft fuselage with longitudinal cracks were analyzed from two aspects: damage tolerance experiment and finite element simulation. A horizontal self-balancing test device was used to apply internal pressure load to the fuselage panel to analyze the damage tolerance characteristics of the panel. Based on the finite element method, the stress field distribution at the crack tip of the fuselage panel under internal pressure load was simulated. And the analysis results of the equivalent stress intensity factor and crack growth of different crack lengths were calculated based on the fracture mechanics theory. The comparison between the crack growth results and the test results validates the feasibility of the analysis method. This serves a as a valuable reference for conducting damage tolerance analysis on aircraft fuselage panels subjected to internal pressure loads.

The longevity of polymer-based sealant and jointing products, including elastomers, significantly depends on the level of exposure to sunlight and joint movement. These factors are particularly crucial in the application of polymers in construction due to their susceptibility to degradation under environmental conditions. For instance, diurnal cycles of contraction and dilation, arising from daily temperature fluctuations, impose significant stress on sealants and joints, impacting their durability over time. The elastic nature of polymeric sealants enables them to endure these cyclic mechanical loads. Athough there is considerable information on sealant durability obtained from laboratory accelerated aging, there is limited knowledge about the effect of climatic factors using historical and projected weather data on the durability and expected service life of these products. This study employed the Shephard crack growth model to predict the performance of sealants in a Canadian context; the crack growth and time-to-failure of hypothetical silicone sealants were investigated across 564 locations, for which historical climate data were obtained from 1998 to 2017, including gridded reanalysis data for the period of 1836–2015. The historical climate data were classified into four climate categories, and crack growth was estimated based on historical climatic data within the valid range for the Shephard model, revealing that locations in colder climates with lower levels of precipitation typically exhibit higher cumulative crack growth. The impact of climatic variation and environmental stressors on the longevity of sealants in the context of climate change was also investigated using future projected data. [ABSTRACT FROM AUTHOR]

Crack propagation in ceramic matrix composites is very difficult to observe and to quantify. To investigate crack formation in all‐oxide ceramic composites, single edge notched bending tests were performed including loading‐unloading cycles and online monitoring of surface deformation using digital image correlation. The crack length was calculated by the compliance method with the crack opening displacement determined optically using digital image correlation. Obtained crack length values were found to be too small considering the sample geometry. Secondly, surface strain monitoring was used to investigate the crack growth. Analysis of cyclic force‐crack opening displacement curves and the results from strain monitoring indicated no major crack growth for loads below maximum force but still a moderately decay of force after onset of cracking. Graphical analysis of the surfaces of broken samples showed crack flank lengths ranging from 3 to 6 mm. Due to highly individual crack deflection mechanisms throughout the thickness of the oxide ceramic composites, deviations between front and back of specimens are found. The results demonstrate the necessity to use individual crack length measurements of each specimen for quantitative fracture mechanical evaluation. Strain monitoring during testing was shown to be a valuable tool for online crack path investigation. [ABSTRACT FROM AUTHOR]

In this research, A zone‐based failure risk assessment (FRA) method of fatigue crack growth (FCG) caused by initial defects in the FGH96 alloy turbine disc is developed. Firstly, the initial defects distribution in the FGH96 alloy turbine disc is calculated based on the defect data. Subsequently, a probabilistic short FCG life model is established, taking into account the dispersion in grain size. Meanwhile, a probabilistic long FCG life model is established, incorporating the life dispersion factor. To calculate the Stress Intensity Factor (SIF) at any position of the disc, the general weight function method and the rectangular plate model are established. Finally, the zoning process is established, enabling a FRA that considers the FCG due to initial defects. The results indicate that the number of cycles corresponding to a 0.13% failure probability of the turbine disc is 7150, and the percentage of failures in each zone is analyzed. [ABSTRACT FROM AUTHOR]

Fatigue refers to the progressive and localized structural damage that occurs when a material is subjected to repeated loading and unloading, typically at levels below its ultimate strength. Several failure mechanisms have been observed in practical scenarios, encompassing high-cycle, low-cycle, thermal, surface, corrosion, and fretting fatigue. Fatigue, connected to the failure of numerous engineered products, stands out as a prevalent cause of structural failure in service. Conducting research on the advancement and application of fatigue analysis technologies is crucial because fatigue analysis plays a critical role in determining the service life of components and mitigating the risk of failure. This study compiles data from a wide range of sources and offers a thorough summary of the state of fatigue analysis. It focuses on the effects of different parameters, including hardness, temperature, residual stresses, and hardfacing, on the fatigue life of different materials and their alloys. The fatigue life of alloys is typically high at low temperatures, but it is significantly reduced at high temperatures or under high-stress conditions. One of the main causes of lower fatigue life is residual stress. High-temperature conditions and hardfacing processes cause the development of tensile residual stresses, which in turn decreases fatigue life. But, if the hardness of the material significantly increases due to hardfacing, then the fatigue life also increases. This manuscript focuses on reviewing the research on fatigue-life prediction methods, shortcomings, and recommendations. [ABSTRACT FROM AUTHOR]

Copyright of Polymer Materials Science & Engineering is the property of Sichuan University, Polymer Research Institute and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

(1) Modeling and characterization of ductile fracture in metals is still a challenging task in the field of computational mechanics. Experimental testing offers specific responses in the form of crack-mouth (CMOD) and crack-tip (CTOD) opening displacement related to applied force or crack growth. The main aim of this paper is to develop a phase-field-based Finite Element Method (FEM) implementation for modeling of ductile fracture in stainless steel. (2) A Phase-Field Damage Model (PFDM) was coupled with von Mises plasticity and a work-densities-based criterion was employed, with a threshold to propose a new relationship between critical fracture energy and critical total strain value. In addition, the threshold value of potential internal energy—which controls damage evolution—is defined from the critical fracture energy. (3) The material properties of AISI 316L steel are determined by a uniaxial tensile test and the Compact Tension (CT) specimen crack growth test. The PFDM model is validated against the experimental results obtained in the fracture toughness characterization test, with the simulation results being within 8% of the experimental measurements. (4) The novel implementation offers the possibility for better control of the ductile behavior of metallic materials and damage initiation, evolution, and propagation. [ABSTRACT FROM AUTHOR]

The prediction of spalling failure evolution in the lifespan of aeroengine bearings is crucial for en-suring the safe return of aircrafts after such failures occur. This study examines the spalling failure evolution process in bearings by integrating the proposed spalling region contact stress analysis model with the multi-directional subsurface crack extension analysis model. The results elucidate the general pattern of spalling expansion. Utilizing this methodology, the fatigue spalling fault evolution in bearings is thoroughly analyzed. Additionally, a two-dimensional model has been developed to simulate and analyze crack propagation in the critical direction of the spalling region, significantly enhancing the model's computational efficiency. [ABSTRACT FROM AUTHOR]

Taking compressor impeller with pressure ratio less than 3 as research object, a prediction method of residual life of compressor impeller was proposed. Considering the action of "inertial" load centrifugal force, finite element method (FEM) technology and sub-model technology were used to comprehensively analyze the mechanical quantities, such as blade stress, and the hot spot stress location of compressor impeller was determined. Crack orientation was determined according to maximum principal stress criterion. The linear elastic fracture mechanics (LEFM) based on FEM and Forman-Newman-de Koning (FNK) model were used to investigate the whole process of crack growth, including stable growth and instability growth stages. The crack growth law and residual life of impeller at different rotate speeds were given. The results show that with the increase of rotate speed, the stress intensity factor (SIF) of initial crack front increases in a quadratic power law, the critical length decreases linearly, and the residual life decreases nonlinearly. The crack grows along the height of blade and then fractures after a deflection of about 90 degrees to the outer edge of blade. The obvious deflection of crack is the sign of crack transition from stable growth stage to instability growth stage. The life of crack in the instability growth stage can be neglected compared with that in the stable growth stage. The analysis method proposed in this article can provide a basis for the damage tolerance evaluation of compressor impeller, and can also provide a reference for maintenance work. [ABSTRACT FROM AUTHOR]

Aero‐disk is a key component of aero‐engine. Due to its complex working conditions, aero‐disk is prone to structural failures. Therefore, it is essential to analyze the reliability and importance input variables of aero‐disk. In this paper, a framework of aero‐disk reliability analysis and global sensitivity analysis (GSA) was established. First, the hazardous regions of aero‐disk were determined by finite element analysis, and the limit state function of aero‐disk was defined by the life interference model. Then D‐Vine model was utilized to establish the correlation model for aero‐disk hazardous regions to evaluate the reliability of aero‐disk. In addition, two GSA methods based on Copula and space partition were proposed to identify important input random variables considering underlying correlation, and the accuracy of the proposed method was verified by two examples. Finally, the proposed method was applied to the GSA of aero‐disk. The results show that the established framework fills in the gap of uncertainty analysis of aero‐disk, which can be extended to other engineering fields. The proposed GSA methods have both high efficiency and accuracy and can realize multi‐dimensional GSA when the correlation of input variables is considered. [ABSTRACT FROM AUTHOR]

The high strength, corrosion resistant, and nonmagnetic characteristics of glass fibre reinforced polymer (GFRP) bars make these bars suitable for use as reinforcement in concrete structures exposed to aggressive environments. This article presents an experimental study on the flexural behaviour of hybrid (SGFRP) concrete beams reinforced with steel and GFRP bars. Six concrete beams measuring 150 × 200 × 2200 mm were fabricated, two of which were normal reinforced concrete (RC) beams and four of which were reinforced with either a hybrid combination of steel and GFRP bars or GFRP bars only. An accelerated corrosion test using the electro-chemical corrosion method was conducted on the RC and hybrid beams until cracks appeared on the beam surface due to steel bar corrosion. Subsequently, a four-point bending test was conducted on the corroded beams until point of failure to assess the flexural behaviour of the corroded SGFRP concrete beams. The experimental results demonstrate that corroded and non-corroded SGFRP beams exhibit similar flexural behaviour and highlight the role of GFRP bars in distributing flexural cracks and in increasing beam load-bearing capacity. In addition, a simple model was proposed based on the obtained experimental results to predict the load-carrying capacities and load–deflection curves of corroded SGFRP concrete beams. [ABSTRACT FROM AUTHOR]

This work presents an analysis of the effect of ball indentation on fatigue crack growth. The main objective is to assess the effectiveness of indentation, particularly its influence on the J-integral, as a fracture criterion governing fracture toughness. Using the finite element method in Abaqus 6.14, we analyzed the residual stresses induced by indentation at different positions along the predicted line of crack propagation and calculated the J-integral. The results highlight that indentation at the crack tip position significantly reduces the J-integral compared to non-indented structures, demonstrating its potential to extend the lifespan of cracked components by delaying crack propagation. The findings underscore the practical application of ball indentation as a viable technique to retard crack growth, contributing to the longevity of cracked components and, consequently, structural integrity. This analysis revealed a crack propagation retardation gain of up to 56%. [ABSTRACT FROM AUTHOR]