The present paper is dedicated to the mechanical and fracture characterisation of a specific earthen material, that is, the shot-earth 772. Although such a material has been recently characterised from a microstructural, chemical and physical point of view, the knowledge of its mechanical and fracture properties (essential for extending its use in construction industry) is still lacking. Such characterisations are here performed both experimentally, through laboratory tests, and numerically, through a FE model. The experimental tests (i.e. flexural, compression and fracture tests) are carried out on shot-earth specimens according to Recommendations available for concrete and a method proposed by some of the present authors, named Modified Two-Parameter Model. The numerical analyses are performed by employing a micromechanical model (implemented in a non-linear 2D FE homemade code), which allows to simulate both flexural and fracture behaviour of the shot-earth examined. Finally, the obtained numerical results are compared with the experimental ones.

An accurate and stable data-driven model is proposed in this work for fatigue life prediction in presence of mean stresses. In the model, multiple independent extreme learning machines are trained using different training data and neural network configurations, and are then combined equally in an ensemble to model the complex correlations between fatigue life, material properties and mechanical responses. Meanwhile, theoretical prediction, as a representation of domain knowledge, is integrated to optimize the data-driven processes of model training and prediction, diversifying the information source of fatigue life modeling. Extensive experimental results covering thirteen metallic materials and a wide range of mean stress levels are collected from the open literature for model training and evaluation. The results demonstrate that the proposed model can achieve high accuracy and good stability [simultaneously](javascript:;), even with a small training dataset, showing great applicability for fatigue life prediction under mean stress loading conditions.

The influence of load ratio on the high and very high cycle fatigue (VHCF) strength of Ck45M steel processed by thermomechanical rolling integrated direct quenching was investigated. Ultrasonic fatigue tests were performed under uniaxial and torsional loading at load ratios of R = −1, 0.05, 0.3 and 0.5 with smooth specimens and specimens containing artificially introduced defects. Up to 2×10 5 cycles, failure originated from surface aluminate inclusions and pits under both loading conditions. The prevailing fracture mechanisms in the VHCF regime were interior crack initiation under uniaxial loading and surface shear crack initiation under torsional loading. The mean-stress sensitivity and the fatigue strength were evaluated using fracture mechanics approaches. Equal fatigue limits for uniaxial and torsional loading were determined considering the size of crack initiating defects and the appropriate threshold condition for Mode-I crack growth. Furthermore, the mean-stress sensitivity is independent of loading condition and can be expressed by σ w R = σ w R = - 1 ∙ 1 - R 2 0.63 and τ w R = τ w R = - 1 ∙ 1 - R 2 0.63 .

The stress ratio ( R) effect, especially at elevated temperatures, is associated with the fatigue crack growth (FCG) prediction in aero-engine hot-end components under complex operation conditions. The FCG experiments with three R were conducted on Ni-based superalloy GH4169 at room temperature (RT), 550 °C, and 700 °C. The results indicate that the R-effect on the FCG of GH4196 is temperature-dependent. Therefore, efforts were made to identify the R-effect at various temperatures to describe the FCG. The concept of the crack-closure or the two-driving-force was examined to quantify the R-effect considering the temperature influence. Fractographic analyses on the fracture surface were performed to discuss the underlying mechanism responsible for the temperature influence. The study can contribute to the R-dependent FCG modeling at various temperatures.

The maximum tangential stress (MTS) criterion is one of the most widely used criteria for predicting the direction of crack extension. The suitability of this criterion is examined under different loading conditions using extended finite element method (XFEM). Experimental and numerical results reported in the literature are considered to evaluate the validity and accuracy of the criterion. The results demonstrate that the MTS criterion evaluated by stress intensity factors (SIF) can accurately predict the direction of crack propagation in specimens under direct tensile loading. This criterion overestimates the angle of crack initiation in the specimen under indirect tensile loading, but underestimates the angle in the specimen subjected to three-point bending. It is concluded that the MTS criterion based on SIF could not accurately predict the direction of the crack initiation, which could, however, be determined properly based on the stress distribution around the crack tip obtained by XFEM numerical models.

The process of fatigue spalling in the rings of ball bearings at durability exceeding 10 8 cycles under in-service loading conditions is analyzed on the basis of fractography and the slices prepared in radial planes of rings. The cracks are shown to originate at subsurface from carbides inherent in the bearing steel or inclusions permissible by sizes for the material. Subsequently, the development of cracks perpendicular to the ring raceway surface takes place similarly as in the VHCF regime with the elliptical “fish-eye” formation. The subsequent crack growth was demonstrated step-by-step up to the ring material fragment separation. The total crack path by alternating stops of propagation and new crack nucleation under conditions of mixed-mode I+II+III mechanisms with the crack branching was discussed. In the final stage, the crack grows towards the ring raceway and either appears on the raceway surface or coalesce with a similar adjacent crack followed by fatigue spalling formation.

The recently developed Edge Tracing (ET) method allows to estimate the radial deformation in axisymmetric tensile specimens via analysis of digital images recorded during the experiments. Images are processed to detect the sample’s contours and therefore, estimate the minimal cross–section diameter. This technique was mainly developed to characterize the elastic–plastic behavior well beyond the necking strain. The aim of this work is to extend the ET method to two case studies. Firstly, the post–necking behavior and failure of a low ductility Al–alloy are investigated. Low ductility alloys tend to fail brutally after reaching the maximum load. The major result is the capture of the sharp load drop which allowed to calibrate parameters of a GTN damage model. Secondly, the anisotropic elastic–plastic behavior of a “vintage” line pipe steel is characterized by a direct measurement of the Lankford coefficient. Assembled experimental data allowed to model the anisotropic plasticity in different loading directions.

Titanium is a versatile biocompatible metal that is desirable in additively manufactured medical implant devices. However, additively manufactured parts have particular microstructures, porosity, residual stress and surface conditions which can have a strong impact on fatigue performance. Implants have an added complexity from the saline operating environment and the associated impact on the safe design life. Equally, direct energy deposition induces a complex thermal history which, if not carefully controlled, can significantly alter the mechanical/material properties of the component. This study investigates the decrease in fatigue life, in an in-vitro body fluid simulation using Ringer’s solution, observed in Ti-6Al-4V specimens extracted from coupons manufactured by directed energy deposition. An interrupted deposition strategy was employed to control build regularity, which appeared to influence certain mechanical properties, including corrosion fatigue life. An ≈50% decrease in fatigue life was observed in Ringer’s solution at 6 Hz loading frequency, clearly important in designing implants.

A multilayer overlay coating system containing an intermediate intermetallic layer (designated 2IML) is an architecture expected to show good fatigue resistance. Experimental characterisation and modelling simulations were carried out to classify the different crack initiation mechanisms occurring during fatigue of this coating system and to reveal how changes in the layer architecture lead to fatigue improvement. Fatigue improvement is achieved by decreasing the IML-Top layer thickness due to the increased surface crack initiation resistance. However subsurface initiation mechanisms inhibit the improvement (dominated by surface initiation mechanism) achieved by locating the IML-Top layer closer to the top surface.

The present-day interest in the use of composite-steel joints in primary marine applications requires an in-depth knowledge of the fatigue performance of thick adhesive joints. This paper reports on experimental tests, quasi-static and fatigue, performed on unaged and aged bi-material double strap joints with thick adhesive bondlines. The specimens are monitored by Digital Image Correlation and Infrared Thermography techniques to evaluate the types and extent of damage that occur in the joint during fatigue loading. The S-N curve of the aged joint is evaluated along with it's fatigue limit. It is found that the unaged specimens fail due to cohesive damage, hackles and disbond at the adhesive-adherend interface and the aged specimens failed due to delamination within the composite. The specimens that survived fatigue loading showed similar residual strength as specimens that were not fatigue loaded.

In order to study the fracture properties of dam concrete under post-peak cyclic loading, wedge splitting tests with three loading rates (0.001 mm/s, 0.01 mm/s, 0.1 mm/s) were performed on notched cubic dam concrete specimens. Meanwhile, the acoustic emission (AE) and digital image correlation (DIC) technologies were used to record the crack propagation process of specimens. Test results show that the fracture of dam concrete has a significant rate effect: with the loading rate increases, the peak load increases, the slope of the post-peak P-CMOD curve gradually decreases and the stiffness degradation of dam concrete becomes more serious. The cumulative AE count shows a step increasing trend and has a Kaiser effect. The Kaiser effect decreases with the post-peak cyclic loading procedure, and with the loading rate increases, the Kaiser effect increases. With the increasing of loading rate, AE energy fluctuates violently and b value fluctuates frequently, indicating the damage of dam concrete becomes more serious. As the loading procedure, the damage of the specimen accumulates gradually, and the strain recovery rate decreases gradually. With the loading rate increases, the strain recovery rate decreases and the permanent crack increases. Based on the fictitious crack model, the effective crack length shows a gradual and steady rising trend. As the loading rate increases, the growth rate of the effective crack length becomes large.

In this study, high-speed ballistic impact tests were conducted on GH4169 alloy samples with the aeroengine compressor blade leading edge feature to simulate the notch-type foreign object damages (FOD). Macroscopic and microscopic characterization of FOD and high cycle fatigue tests were performed to investigate the effect of FOD depth on GH4169 alloy fatigue strength along with numerical analysis using Kitagawa-Takahashi diagram. Results show the incident side of notch-type FOD is relatively smooth, whereas the exit side is rugged. The FOD depth ranges from 0.18mm to 1.33mm, and the fatigue strength of damaged samples is 37.93%~97.04% of the undamaged samples. As FOD depth increases, damage length, material losses and stress concentration coefficient of the FOD increase significantly along with the increasing adiabatic shear bands, micro voids and cracks, resulting in fatigue strength reduction. Numerical analysis indicates that the Kitagawa-Takahashi diagram can provide a basic model for the design of FOD tolerance.

Biaxial (axial and torsional loading) static tests were performed for the first time on EN-GJS-600–3 ductile cast iron tubular specimens obtained reproducing the solidification conditions typical of thick-walled castings. The experimental results were elaborated to determine the yield and fracture loci of the material, which exhibited significant deviations from those predicted by the Von Mises and Mohr-Coulomb criteria usually adopted for steels and grey cast iron, respectively. For this purpose, several alternative criteria proposed in the technical literature, some of them specifically devised for composite materials, have been calibrated and compared to account for the peculiar mechanical properties of this natural composite material.

Fatigue fracture is one of the most common metallic component failure cases in manufacturing industries. The observation on fractography can provide the direct evidence for failure analysis. In this study, an image segmentation method based on Fully Convolutional Networks (FCNs) was proposed to figure out the boundary between fatigue crack propagation and fast fracture regions from optical microscope (OM) fractography images. Furthermore, novel morphing-based data augmentation method was adopted to enable few-shot learning of sample images. The proposed framework can successfully segment two categories, namely the crack propagation and fast fracture regions, thus differentiating the boundary of two regions in one image. The artificial intelligence (AI) assisted fatigue analysis architecture can complete the failure analysis procedure in 0.5 second and prove the feasibility of fatigue failure analysis. The segmentation accuracy of developed network achieves 95.4% for the fatigue crack propagation region, as well as 97.2% for the fast fracture region, which possesses comparable accuracy to the segmentation results using Mask R-CNN Regional Convolutional Neural Network (Mask R-CNN), one state-of-the-art deep learning networks.

Neural network (NN) models have made a significant impact on fatigue-related engineering communities and are expected to increase rapidly soon due to the recent advancements in machine learning and artificial intelligence. A comprehensive review of fatigue modeling methods using NNs is lacking and will help to recognize past achievements and suggest future research directions. Thus, this paper presents a survey of 251 publications between 1990 and July 2021. The NN modeling in fatigue is classified into five applications: fatigue life prediction, fatigue crack, fatigue damage diagnosis, fatigue strength, and fatigue load. A wide range of NN architectures are employed in the literature and are summarized in this review. An overview of important considerations and current limitations for the application of NNs in fatigue is provided. Statistical analysis for the past and the current trend is provided with representative examples. Existing gaps and future research directions are also presented based on the reviewed articles.

The paper discusses various partial solutions used for estimating fatigue life under variable amplitude multiaxial loading in the high-cycle fatigue domain. The concurring effects are treated, and their proposed solutions are commented upon. The major focus is on the categories of the phase shift effect and of cycle counting, and on the scope and quality of data, which support discussed theories. Results of own new experimental data set on specimens from S355 steel are provided. Fatigue life estimates for McDiarmid and Findley multiaxial methods and for two different methods of load path decomposition to cycles are shown to highlight some of the points open for discussion. It is concluded that the available experimental data are not sufficient to substantiate a clear decision to follow a definite algorithm.

This work investigates the influence of temperature on the creep damage behaviors of red sandstone. The samples treated at 25 ℃, 200 ℃, 400 ℃ and 600 ℃ are selected to carry out the uniaxial compression and creep experiments. It is found that temperature has obvious influence on uniaxial compressive strength, Young’s modulus and failure modes of red sandstone. It can be also believed that the temperature can degrade the mechanical behaviors of red sandstone. However, as the temperature increases, the damage value does not always increase, the damage variable has a negative value at 25 ~ 400 ℃. It can be found that the higher the temperature, the larger the effect of loading ratio on the ratio of creep strain to instantaneous strain, that is, temperature reduces the ability of red sandstone to resist creep deformation. Acoustic emission (AE) technology has been also used in the loading process of uniaxial compression and creep tests. It is found that the probability density of AE absolute energy of different samples still satisfies the Gutenberg-Richter law well. In uniaxial compression test, as the temperature increases, the absolute value of the critical index increases exponentially. In the uniaxial creep test, as the loading ratio increases, the absolute value of the critical index first decreases and then increases. When the loading ratio is the same, as the temperature increases, the absolute value of the critical index also increases exponentially.

Using thin-walled cone-pipe welded joints of stainless steels, fatigue tests under bending loads were carried out. The test data were statistically analyzed with the Benard’s approximation, Gaussian, 2P-Weibull, and 3P-Weibull distributions. Stress–life curves at different failure probabilities by a constant strength scatter band model were obtained. The metallographic structures were investigated, and the stress concentration states were analyzed to elucidate the causes of the strengths and scatters. In the high-cycle fatigue regime, the 3P-Weibull distribution was mostly in agreement with the Benard’s approximation, and the coefficient of determination was 0.9642. The microstructure of the weld metal with a high weld opening angle was mainly ferrite phase with 20% austenite distribution. The crack initiation point was close to the weld interface, but the propagation direction was at a right angle, and initially penetrated the heat affected zone of the cone, leading to the high fatigue strength. The stress concentration factors depended on the weld opening angles, indicating the main factor which affected strengths and scatters.