Fracture Appearance Research Articles

Assessment of the impact behavior of CLF-1 steel with Charpy V-notch testing and miniature Charpy V-notch testing

China Low-activation Ferrite steel (CLF-1), as one of the structural materials developed in China for fusion reactors, is a Reduced activation Ferritic/Martensitic (RAFM) steel modeled after the traditional T91 steel (9Cr-1Mo-0.2V-0.08Nb). For fusion reactor materials, the Charpy impact testing is an important method to assess their notch sensitivity. In this study, Charpy impact tests were conducted on CLF-1 steel using Charpy V-notch specimens (CVN) and Miniature Charpy V-notch specimens (Kleinstprobe, KLST) to assess the impact behavior of CLF-1 steel, and data normalization was performed on the KLST specimen. The results show that as the specimen size of CLF-1 steel decreased, the curves of impact absorbed energy, lateral expansion, and shear fracture appearance shifted towards lower temperatures, and the impact absorbed energy significantly decreased. Both the macroscopic and microscopic characteristics of the specimens obtained from the experiments indicated that KLST specimens could achieve the same fracture characteristics as CVN specimens. Additionally, at the same experimental temperature, KLST specimens exhibited a higher proportion of ductile fracture regions.

Microscopic characteristics of peri- and postmortem fracture surfaces

This study investigated if microscopic surface features captured with a scanning electron microscope (SEM) effectively discriminate fracture timing. We hypothesized that microscopic fracture characteristics, including delamination, osteon pullout, and microcracks, may vary as bone elasticity decreases, elucidating perimortem and postmortem events more reliably than macroscopic analyses. Thirty-seven unembalmed, defleshed human femoral shafts from males (n=18) and females (n=2) aged 33–81 years were fractured at experimentally simulated postmortem intervals (PMIs) ranging from 1 to 60 warm weather days (250–40,600 ADH). A gravity convection oven was used to approximate tissue decomposition at 37 C and 27 C, and the resulting heat-time unit (accumulated degree hours, or ADH) was used to examine fractures in elastic/wet versus brittle/dry bone. The bones were fractured with a drop test frame using a three-point bending setup, sensors were used to calculate fracture energy, and high-speed photography documented fracture events. The following data were collected to relate fracture appearance to the biomechanical properties of bone: PMI (postmortem interval) length in ADH, temperature, humidity, collagen percentage, water loss, bone mineral density, cortical bone thickness, fracture energy, age, sex, cause of death, and microscopic fracture feature scores. SEM micrographs were collected from the primary tension zones of each fracture surface, and three microscopic fracture characteristics were scored from a region of interest in the center of the tension zone: percentage of delaminated osteons, percent osteon pullout, and number of microcracks. Multiple linear regression showed that microscopic fracture surface features are strong predictors of ADH (adjusted R-squared=0.67 for the 0 – 40,000 ADH samples; adjusted R-squared=0.92 for the 0–16,000 ADH samples). Osteon pullout is the single best predictor of ADH. Additionally, water loss is the primary driver of bone elasticity changes in low ADH samples, while collagen fibers appear to remain intact until later in the postmortem interval (approximately 40,000 ADH in this study). The results of this study indicate microscopic fracture surface analysis detects the biomechanical effects of decreased elasticity more reliably and with greater sensitivity than macroscopic analysis.

[Translated article] Evaluation, differential diagnosis and treatment of vertebral osteoporosis: How to avoid the occurrence of new fractures

Osteoporosis is a highly prevalent and multifactorial disease whose main manifestation is the appearance of fragility or low-impact fractures. The most frequent locations of osteoporotic fractures occur at the vertebrae, femoral, distal end of the radius and humerus. Osteoporotic vertebral fracture deserves special mention among them due to its prevalence, importance as it often goes unnoticed and medium-long term consequences are: pain, deformity, disability and deterioration in quality of life. In this review we will focus on the classification and initial evaluation of the patient with osteoporosis, estimation of risk factors, laboratory and imaging studies for an adequate assessment using simple radiography, dual densitometry and magnetic resonance imaging. We will also address the main aspects of the differential diagnosis, treatment and prevention of vertebral fragility fracture, briefly reviewing the main therapeutic agents currently used for its prevention and treatment.

Experimental study of the fatigue failure behavior of aluminum alloy 2024-T351 under multiaxial loading

Multiaxial fatigue has been drawing much attention because it is more applicable to engineering practice. In this paper, an experimental study of aluminum alloy (AA) 2024-T351 was carried out under multiaxial loading with an aim to assess the damage evolution process and failure mechanism under in-phase and out-of-phase loadings. Firstly, fatigue life and stress response under multiaxial cyclic loads were obtained, and it found that although there is non-proportional hardening, the fatigue life subjected to proportional loading is significantly shorter than that of under a nonproportional loading, which was tried to be explained by the ductility of the material. Secondly, a detailed analysis of the damage evolution process based on the degradation of the elastic modulus and the fatigue failure process based on the digital image correlation (DIC) method was provided. Next, a micro-analysis of the specimens’ fracture appearance was conducted to obtain the fracture characteristics and found that AA2024-T351 presents a dominant shear fracture mode under proportional loading and a mixed mode of tensile and shear fracture under non-proportional loading. Last but not least, The Fatemi-Socie criterion was modified by considering the material’s ductility and the interaction between normal stress and shear stress acting on the critical plane. The multiaxial life prediction results of the modified FS model for AA2024-T351 in this paper were all within the scatter bands of 3 on life.

Evaluación, diagnóstico diferencial y tratamiento de la osteoporosis vertebral: cómo evitar la aparición de nuevas fracturas

Osteoporosis is a highly prevalent and multifactorial disease whose main manifestation is the appearance of fragility or low-impact fractures. The most frequent locations of osteoporotic fractures occur at the vertebrae, femoral, distal end of the radius and humerus. Osteoporotic vertebral fracture deserves special mention among them due to its prevalence, importance as it often goes unnoticed and medium-long term consequences are: pain, deformity, disability and deterioration in quality of life. In this review we will focus on the classification and initial evaluation of the patient with osteoporosis, estimation of risk factors, laboratory and imaging studies for an adequate assessment using simple radiography, dual densitometry and magnetic resonance imaging. We will also address the main aspects of the differential diagnosis, treatment and prevention of vertebral fragility fracture, briefly reviewing the main therapeutic agents currently used for its prevention and treatment.

Deep Learning-Based Surgical Treatment Recommendation and Nonsurgical Prognosis Status Classification for Scaphoid Fractures by Automated X-ray Image Recognition.

Biomedical information retrieval for diagnosis, treatment and prognosis has been studied for a long time. In particular, image recognition using deep learning has been shown to be very effective for cancers and diseases. In these fields, scaphoid fracture recognition is a hot topic because the appearance of scaphoid fractures is not easy to detect. Although there have been a number of recent studies on this topic, no studies focused their attention on surgical treatment recommendations and nonsurgical prognosis status classification. Indeed, a successful treatment recommendation will assist the doctor in selecting an effective treatment, and the prognosis status classification will help a radiologist recognize the image more efficiently. For these purposes, in this paper, we propose potential solutions through a comprehensive empirical study assessing the effectiveness of recent deep learning techniques on surgical treatment recommendation and nonsurgical prognosis status classification. In the proposed system, the scaphoid is firstly segmented from an unknown X-ray image. Next, for surgical treatment recommendation, the fractures are further filtered and recognized. According to the recognition result, the surgical treatment recommendation is generated. Finally, even without sufficient fracture information, the doctor can still make an effective decision to opt for surgery or not. Moreover, for nonsurgical patients, the current prognosis status of avascular necrosis, non-union and union can be classified. The related experimental results made using a real dataset reveal that the surgical treatment recommendation reached 80% and 86% in accuracy and AUC (Area Under the Curve), respectively, while the nonsurgical prognosis status classification reached 91% and 96%, respectively. Further, the methods using transfer learning and data augmentation can bring out obvious improvements, which, on average, reached 21.9%, 28.9% and 5.6%, 7.8% for surgical treatment recommendations and nonsurgical prognosis image classification, respectively. Based on the experimental results, the recommended methods in this paper are DenseNet169 and ResNet50 for surgical treatment recommendation and nonsurgical prognosis status classification, respectively. We believe that this paper can provide an important reference for future research on surgical treatment recommendation and nonsurgical prognosis classification for scaphoid fractures.

Drilling- and coring-induced artefacts in poorly indurated clays

Macroscopic and microscopic drilling-induced deformation structures were documented in cores of Ypresian Ieper Group and Rupelian Boom Formation clays using macro-polished slabs and polarizing microscopy of thin sections. The cores were recovered in north Belgium from a depth of a few hundred metres by pushing a steel barrel with a cutting shoe into the non-indurated clays that are in a ductile to brittle transition state. The outer border of the clay cores was bent downwards due to the pushing action. The geometry of the drilling-induced fractures can be described as vertically stacked axisymmetrical conical fractures complexed by a general concave and undulating shape, and by fractures splaying from other fractures. At the microscopic scale (2D), the fractures are micro-faults that produce a breccia texture and which consist of thin planes, lines in 2D, of orientated clay minerals. The preferred orientation of these clay minerals in the fractures point to shear movement and explain the shiny appearance of these slickenside-like fractures when viewed in 3D. The micro-faults produce clay domains tilted with respect to each other. Recognizing exclusively drilling-induced structures helps in the selection of cores and core fragments for further laboratory testing, and may be of help in distinguishing them from regional faults or fracture systems in homogeneous clays. Thematic collection: This article is part of the Sustainable geological disposal and containment of radioactive waste collection available at: https://www.lyellcollection.org/topic/collections/radioactive

Experimental study on the dynamic mechanical and progressive fracture behavior of multi-jointed rock mass under repetitive impact loading

The failure of rock masses is often controlled by structural planes, and the study on the dynamic mechanical behavior of multi-jointed rock masses under repetitive dynamic loading is still few. A series of repetitive impact tests on multi-jointed gabbro (MJG) are conducted with the split Hopkinson pressure bar (SHPB) testing apparatus. The effects of repetitive impact and joint inclination angles (α) on the dynamic mechanical behavior of MJG from the perspectives of impact number, stress equilibrium, dynamic mechanical properties, energy evolution, and macro and micro failure modes are deeply investigated. The results show that the joint inclination angle affects the impact resistance of the MJG. Under repetitive impact loadings, the mechanical behavior of the MJG is consistent, with tensile wing cracks initiating from the joint tips and propagating along the loading direction until specimen failure. During this process, cracks propagate along the weakest paths, thereby consuming the energy generated by the impact and preventing the activation of other minor defects. The macroscopic failure of the MJG undergoes four stages: the appearance of white patch, crack coalescence, crack penetration, and fracture, with the final failure mode being splitting. The microscopic formation stage of white patch is divided into microcrack activation and microcrack widening.

Impact Fracture Behaviour of Powder Metallurgy Steels Sintered at Different Temperatures

For powder metallurgy steels prepared through the press-and-sinter route, interparticle bonding is the most decisive feature defining the mechanical properties. It depends on the compacting pressure, but predominantly on the sintering conditions, mainly the sintering temperature. In the present contribution, the progressive strengthening of the sintering necks with increasing temperature is shown by fractography for plain carbon steels as well as alloyed grades. For sintered steels, in contrast to wrought steels, the appearance of cleavage fracture is rather a positive sign, indicating pronounced interparticle strength as attained at high sintering temperatures. At lower temperatures, in contrast, localised failure of the sintering necks typically occurs as ductile rupture, but with rather low consumed energy. Alloy elements with a high oxygen affinity introduced by prealloying retard formation of sound sintering bridges up to temperatures at which carbothermal reduction of the surface oxides becomes possible, while admixing such elements through suitable masteralloys yields attractive interparticle strength already at standard belt furnace temperatures of 1120 °C.

Response characteristics of acoustic emission signal and judgment criteria for different fracture modes

Coal mining is going deeper into the ground, resulting in more intense and frequent mine dynamic disasters. To ensure the early warning of dynamic disasters, it is significant to accurately reveal the differences of acoustic emission (AE) signals generated by rock fractures. This paper focuses on studying how AEs average frequency (AF) and rise angle (RA) change in sandstone during loading, and examines the characteristics of waveform amplitude, energy, and frequency distribution of AE signals from different types of fractures. The findings reveal that the percentage of shear fracture gradually increases with increasing load, and the energy activity of the AE signal is significantly enhanced in the high stress stage. The occurrence of the main fracture was preceded by a large number of low-frequency tensile fracture AE signals, accompanied by a small decrease in RA and a small increase in AF. The spectra of different fracture signals were characterized as “low anomalous F” for shear fractures, “vertical F” for low-frequency tensile fractures, and “high anomalous F” for high-frequency tensile fractures. Their energy distribution in the frequency domain was respectively described as “peak-centered distribution”, “pillar-shaped distribution” and “peak-skewed distribution”. The outcomes of the decomposition and reconstruction from the P- and S-waves reveal that the P wave energy (Ep) dominates in the high-frequency tensile fracture AE signal, while the S wave energy (Es) is greater in the low-frequency tensile fracture and the shear fracture AE signals. The ES/EP threshold value for laboratory discrimination of tensile and shear fracture is 3, as the fracture extends and penetrates, the ES/EP value rises rapidly at the appearance of macroscopic fracture. The findings offer theoretical guidance for monitoring and early warning of coal and rock dynamic hazards as well as revealing the morphology of fracture source.

Dynamic mechanical properties and constitutive model establishment of QSTE420 steel

The uniaxial tensile tests of QSTE420 steel under different strain rates were carried out using an electronic universal material testing machine, a high-speed tensile testing machine and a split Hopkinson tension bar (SHTB) device, the engineering stress-strain curves of steel within the range of 0.001– 1000 s−1 were obtained and the mechanical properties of steel at different strain rates were analyzed. The results show that in the static strain rate range of 10−3– 10−2 s−1, the yield strength and tensile strength of QSTE420 steel exhibit minimal variation, fluctuating between 430– 434 MPa and 507– 515 MPa, respectively; while the uniform elongation and elongation at break remain approximately at 12% and 35%, respectively. In the high strain rate range of 10−1– 103 s−1, both yield strength and tensile strength exhibit a consistent increase in direct correlation with the tensile rate. Specifically, the yield strength increases from 444 to 607 MPa and the tensile strength increases from 523 to 640 MPa as the strain rate escalates from 10−1 to 103 s−1. Moreover, the elongation at break demonstrates a general increasing trend and reaches its peak value of 45.65% at 100 s−1. The morphology of fracture surfaces under different strain rates are observed by Scanning Electron Microscopy (SEM). The fracture appearance analysis reveals numerous dimples in the fracture, indicating a ductile fracture. Furthermore, the comparison demonstrates that steel exhibits enhanced plasticity at a strain rate of 100 s−1. Based on the experimental results, the Johnson-Cook constitutive model was established and modified. The modified Johnson-Cook model exhibits a higher determination coefficient (R2) compared to the original version, signifying an improved fitting accuracy.

Atypical Tibial Fracture Treated with Osteosynthesis Associated with Total Knee Arthroplasty: Case Report.

Bisphosphonates are widely used in the treatment of osteoporosis but predispose the patient to the appearance of atypical fractures. The femoral subtrochanteric region is usually affected, but other bones can be as well. Atypical tibia fractures in patients with severe gonarthrosis is a therapeutic challenge. The present work reports the case of an elderly patient with advanced gonarthrosis who presented atypical tibial fracture. The patient made prolonged use of bisphosphonates for osteoporosis, presenting with pain and functional limitation resulting from gonarthrosis, which progressed to sudden pain in the right tibial metaphysis, preventing ambulation. The radiographs showed bilateral severe arthrosis; marked varism; tibial and femoral medial erosion; and fracture in the proximal third of the right tibial diaphysis. The fracture and arthrosis on the right side were treated by osteosynthesis with blocked plaque and total knee arthroplasty with posterior stabilization and fixed base. After physical rehabilitation, significant improvement of pain and function was reported, independent gait was reacquired and a range of motion of 0 to 100° was reached. After one year, the radiographs showed fracture consolidation and satisfactory alignment of the lower limbs' axes. The coexistence of severe arthrosis and atypical fracture made treatment difficult. However, the result was satisfactory and the approach with simultaneous osteosynthesis and arthroplasty proved to be adequate.

3D spatial fracture behavior of sandstone containing a surface flaw under uniaxial compression

Surface defects are prevalent in natural rock masses, and the newborn cracks that initiate from these defects and significantly affect structural stability usually extend in a three-dimensional (3D) manner. Hence, in this research, a series of uniaxial compression tests were conducted on sandstone specimens containing a surface flaw to examine the effect of nondimensional flaw depth (0, 0.3, 0.5 and 0.75) on the fracture behavior. The crack propagation process was monitored by digital image correlation (DIC) technique, and postmortem microscopic fracture morphology was measured using scanning electron microscope (SEM) method. In addition, the fracture energy evolution and stress intensity factors (SIFs) along the semi-elliptical flaw perimeter were discussed in detail to theoretically interpret the experimental phenomena. The results indicate that the strength decreased by 2.70%, 10.90% and 11.91% for nondimensional surface flaw depths of 0.3, 0.5 and 0.75, respectively, and elastic modulus exhibited a reduction of 3.71%, 10.69% and 3.21%, respectively. Full-field deformation contours demonstrate that crack paths in the front surface of the specimen were totally different from those in the back surface, but the failure pattern tended to be similar to that of specimens containing a penetrated flaw with the increasing flaw depth. The micro appearance of a typical fracture further reveals the complicated stress state (mixed I-II-III mode) under uniaxial compression. For a larger flaw depth, the proportion of releasable elastic strain energy in total input strain energy was improved, while the percentage of dissipated energy was reduced. Based on fracture mechanics, SIFs along the flaw periphery uncover the magnitude of KI, KII and KIII and further the type of initiation crack type. Finally, parametric analysis was carried out to investigate the effects of flaw length and specimen thickness. The difference in crack pattern from surface and penetrated flaw was also discussed in detail.

Predicting the Fracture Propensity of Amorphous Silica Using Molecular Dynamics Simulations and Machine Learning

Amorphous silica (a-SiO2) is a widely used inorganic material. Interestingly, the relationship between the local atomic structures of a-SiO2 and their effects on ductility and fracture is seldom explored. Here, we combine large-scale molecular dynamics simulations and machine learning methods to examine the molecular deformations and fracture mechanisms of a-SiO2. By quenching at high pressures, we demonstrate that densifying a-SiO2 increases the ductility and toughness. Through theoretical analysis and simulation results, we find that changes in local bonding topologies greatly facilitate energy dissipation during plastic deformation, particularly if the coordination numbers decrease. The appearance of fracture can then be accurately located based on the spatial distribution of the atoms. We further observe that the static unstrained structure encodes the propensity for local atomic coordination to change during applied strain, hence a distinct connection can be made between the initial atomic configurations before loading and the final far-from-equilibrium atomic configurations upon fracture. These results are essential for understanding how atomic arrangements strongly influence the mechanical properties and structural features in amorphous solids and will be useful in atomistic design of functional materials.

Assessment of Different Approaches for Measuring Shear Fracture Appearance in Charpy Tests

Abstract Different approaches for establishing shear fracture appearance (SFA) on tested Charpy specimens were assessed and compared, namely (in order of increasing expected accuracy) estimates based on characteristic forces from instrumented Charpy tests, optical measurements using image analysis software, and measurements performed with the aid of a scanning electron microscope. Comparisons between different SFA values for 129 instrumented Charpy tests currently included in the National Institute of Standards and Technology database allowed us to establish the relationships between the different available approaches and formulate recommendations for the revision of the standards ASTM E2298-18, Standard Test Method for Instrumented Impact Testing of Metallic Materials, and ISO 14556:2015, Metallic Materials — Charpy V-Notch Pendulum Impact Test — Instrumented Test Method, which currently provide four empirical correlations that can be used to estimate SFA.

Study on Overburden Structure Characteristics and Fracture Evolution Law in Upward Mining at Kuangou Coal Mine

The development of vertical fractures in the overburden rock below after upward mining of a coal seam can influence the safe mining of both this seam and the seams above. This paper employs the method of physical similarity simulation to experimentally study the overburden structure and fracture evolution law during upward mining of the No. 4 coal seam in Kuangou Coal Mine. The study reveals that the overburden rock of the lower No. 4 coal seam after mining exhibits a typical "three-zone" characteristic, with the caved zone overburden showing a distinct cantilever beam-hinged structure, and the overburden structure of the bending and sinking zone is relatively intact. In the experiment, no significant vertical through-layer fractures were observed during the first five periodic pressures. However, during the 6th to 11th periodic pressure periods, when mining pressure became intense, a total of six vertical through-layer fractures appeared near the coal wall of the working face. These fractures, aligned with the caving angle direction, extended upwards through the No. 3 coal seam located 60m above the No. 4 seam. The overall fracture evolution showed opening during intense mining pressure and gradual closing after the pressure subsided. Two of these vertical through-layer fractures had a larger extension range, eventually reaching the surface. During the upward mining process, the appearance of vertical through-layer fractures did not lead to sliding instability or rapid sinking of the overburden roof. The working face could thus continuously advance. This research has implications for the safe upward mining in similar mines.

Failure analysis on outer tube breaks of a double-sleeve rapid cooling heat exchanger

Failure analysis of a double-sleeve rapid cooling heat exchanger used for ethylene cracking process is presented in this study. The outer tubes of the heat exchanger break four times in succession. The inner tube and the outer tube materials of the heat exchanger are 13CrMo4-5 and SA106Gr.B, respectively. Based on the analysis of fracture appearance, chemical composition, mechanical properties, oxidation products and metallographic microstructure, it is found that short-time local overheating resulted in the four outer tube breaks. The observed pearlite spheroidization of SA106Gr.B indicate the temperature at the break positions exceed the phase transition critical temperature AC1（735℃）. Based on the analysis of the heat transfer process and boiler water circulation, it is found that the heat transfer deterioration of in a single set of double-sleeve, i.e., water is completely converted into superheated saturated steam, is the root cause of short-time local overheating. In view of the above failure mechanism, several countermeasures were proposed including the verification of the circulation ratio to ensure that the heat absorption per unit volume of cooling water is within the threshold value should be conducted in the design process, considering the uneven distribution of cooling water and cracking gas at the inlet and the influence of shock vibration caused by water and cracked gas, an appropriate safety factor should be considered for the design of gap / water volume during operation, as well as promoting the monitoring of vital parameters (e.g., the temperature during operation).

Power Law Creep Behavior Model of Third Generation Lead-Free Alloys Considering Isothermal Aging

Abstract In realistic applications, the solder joint is continually subjected to thermal-mechanical stress due to the difference in the coefficient of thermal expansion between the printed circuit board substrate and the electronic packaging components. Creep and fatigue processes were the most common causes of failure in electronic assemblies. Under isothermal aging, creep deformation becomes more prominent. The aged microstructure was recognized by intermetallic coarsening and the appearance of intergranular fracture generated by dynamic recrystallization in the bulk solder joint. In this study, the influence of Bi content on the creep behaviors of solder joints was investigated under various aging conditions. Three lead-free solder alloys, including SAC305, SAC-3Bi, and SAC-6Bi, are tested at room temperature. For each alloy, preliminary micro-indentation tests were conducted to define three stress levels for distinct aging conditions. After each test, displacement versus time data was gathered. A novel approach based on an empirical model was developed to systematically examine the development of the steady-state creep rate. A power dependency prediction model was developed to investigate the relationship between creep strain rate and stress levels. The steady-state creep rate of SAC305 is significantly higher than that of SAC-Bi alloys owing to the presence of bismuth (Bi) in the solid solution at room temperature. The creep properties showed less variation after 100 h of aging. SAC-Bi alloys showed less coarsening of the intermetallic compounds precipitates after aging than SAC305. In the SAC-Bi solder alloys, combinations of precipitate and solid solution hardening mechanisms were observed, while Ag3Sn particles were the dominant strengthening mechanism in the SAC305 alloy system.

Automatic fracture characterization in CT images of rocks using an ensemble deep learning approach

The presence of fractures in a rock mass can have a substantial influence on its mechanical and hydraulic properties. For many years, computed tomography (CT) scan has been effectively utilized to investigate the internal structures of rock. However, quantitative characterization of fracture based on CT data remains a challenging endeavor due to the inevitable blurry appearance of fractures in CT images, complexity in fracture patterns and the heterogeneity of host rock. In this study, a deep learning-based method is presented for automatically and accurately segmenting rock fractures in CT images, with special consideration for directional ambiguous fractures embedded in heterogeneous backgrounds. Our method involves two stages: (1) fracture detection in the form of minimal bounding boxes using the Faster R-CNN deep learning algorithm, and (2) fracture segmentation inside the detected bounding boxes using the U-Net deep learning algorithm. The detection stage aims to establish spatial constraints for the segmentation process, thereby significantly minimizing undesirable noise and artifacts existing in the background from consideration and consequently improving the segmentation result. In addition, we also develop a system that can automatically extract fracture properties including orientation, length, aperture, and wall roughness of fractures based on detection and segmentation results from our method. Experiments on CT images of fractured coarse-grained granite, fine-grained sandstone, and shale core samples were carried out in an attempt to confirm the applicability of our approach. The comparison between fracture segmentation results and the manually-annotated ground truths shows that our approach can achieve a competitive dice score of up to 0.942 and also outperform other state-of-the-art deep learning approaches including Mask R-CNN and U-Net alone.

Combined loading effect on high cycle fatigue fracture behaviors of a stainless steel welded structure of elbow and socket

In welded structures with complicated geometries and combined loading state, it is crucial to establish the criteria for fatigue failure. High cycle fatigue tests under combined loading states were performed using stainless steel sheets and welded specimens of elbow pipe and socket in this work. The cyclic stress–strain curve of the parent sheet were applied to the characteristics analysis of the welded specimens. Mode I or Mode I + III fatigue fracture occurred at the stress concentration part of the weld, and the crack starting point was different depending on the loading mode. The applied load was divided into bending and torsion for analysis, and the crack initiation was found on the side with the higher equivalent stress converted according to the Gough-Pollard failure criterion. The crack grew almost perpendicularly to the surface of the elbow pipe, and exhibited the appearance of a transgranular fracture. The fatigue limit based on the stress intensity factor (SIF) amplitude calculated by the proposed method using the strain energy release rate remained nearly constant even though the measured surface strain differed greatly. It is possible to predict the fatigue limit and life of similar structures by simplified models.