Fracture Surface Morphology Research Articles

Comprehensive investigation and modeling of pitting corrosion effects on mechanical properties and fatigue performance of steel wires

Steel wires are widely employed in structural engineering due to their robust strength. However, the emergence of pitting corrosion significantly impacts their capacity, fatigue performance, and mechanical traits, with no specific codes addressing this issue. To assess the load-bearing capacity of corroded steel wires, predict their remaining fatigue life, and analyze failure modes, a comprehensive physical test was conducted. Mechanical evaluations of corroded wires were followed by 3D scanning to analyze corrosion attributes and fracture surface morphology. Using fuzzy reliability theory, a model estimated wire capacity under varying corrosion degrees. Subsequent fatigue testing explored performance and developed a predictive residual life model. Investigation results revealed a rapid and gradual decrease in capacity's reliability coefficient. Corroded wire fracture morphologies were classified as typical and multi-source cracks, including subtypes like cracks expanding in the same plane and step-like fractures. All wire types exhibited a cracking threshold exceeding 5.6 MPa·m1/2, with fracture intensity declining as corrosion severity increased. Notably, the model better suited slightly corroded wires, showing up to 30.93 % relative error for severely corroded wires. Enhancing accuracy for the latter entails considering additional factors to refine the model.

ELECTROMAGNETIC PROPERTIES, FORMING LIMIT DIAGRAMS AND FRACTURE TOUGHNESS OF LAMINATED Al/Fe2O3 COMPOSITES

In this study, electrophysical, electromagnetic and mechanical properties, fracture toughness and forming limit diagram (FLD) of Al base composite samples have been studied experimentally. All samples have been fabricated via accumulative roll bonding (ARB) process. To this purpose, AA1060/ Fe2O3 composite strips with thickness of 1 mm have been fabricated with up to eight ARB passes at 300[Formula: see text]C. In this study, magnetic Al/Fe2O3 composites reinforced with 0, 5% and 10 wt.% of Fe2O3 particles have been manufactured via ARB. The microstructure was studied by optical microscopy (OM). Also, by decreasing the thickness of layers at higher number of passes (increasing the plastic strain), the bonding quality among the layers was improved. Scanning electron microscopy (SEM) fracture surface morphology of samples after the tensile test showed that by increasing the passes, the fracture style (mode) converted to shear ductile at higher ARB passes. So, deep dimples shrink slowly and their number and depth decreased relative to the annealed sample. As the criterion of formability, the area under the FLDs dropped sharply after the first pass and then improved by increasing the passes. Results of fracture test have shown that the value of fracture toughness has been enhanced continually to the maximum value of 34.3 MPam[Formula: see text] at the 8th pass.

Direct observation of the fracture behavior of the polyether ketone ketone (PEKK) spherulites

AbstractThis article reports the direct observation of the fracture of individual poly‐ether‐ketone‐ketone (PEKK) spherulites. A single layer of PEKK spherulites was obtained by bonding a PEKK film in‐between two sandblasted Ti alloy plates using an autoclave. The crack of an individual PEKK spherulite was achieved by opening the Ti/PEKK/Ti sandwich using a double cantilever beam test. The fracture morphology of the PEKK spherulite was characterized using scanning electron microscopy and atomic force microscopy. It was found that under tensile stress the crack of the individual spherulite propagates along the middle plane and crosses the nucleation core. This is due to the symmetric radial structure of the spherulite. Moreover, it was found that the fracture surface morphology at the core of the spherulite is strongly influenced by the local crystalline structure, which is anisotropic and determined by the initial nucleation growth direction. As a result, the area fraction experiencing plastic deformation during the fracture of PEKK spherulites at different orientations may vary by an order of 10. Our results show the important role of the initial nucleation growth direction on the mechanical properties of the polymer crystals and may provide a new approach to the design of high‐performance polymer materials with tailored crystalline structures.

Fracture behavior of high-temperature granite subjected to liquid nitrogen cooling: Semi-circular bending test and crack evolution analysis

Liquid nitrogen fracturing is an effective technique for stimulating reservoirs in hot dry rock exploitation. The application of low-temperature liquid nitrogen to high-temperature granite generates thermal stress, thereby altering its mechanical properties and fracture behavior. This study focused on type I fracture characteristics by conducting semi-circular bending tests on high-temperature granite treated with liquid nitrogen. The fracture behavior was analyzed using acoustic emission (AE) and digital image correlation methods. The fractured surface morphology was examined using laser scanning, and fractal theory and tortuosity analysis were employed to assess the fracture surface roughness. Scanning electron microscopy (SEM) provided insight into the impact of liquid nitrogen cooling on fracture characteristics. The findings indicated that treated granite specimens below 150℃ exhibited an increased peak load, fracture toughness, and fracture energy compared to untreated specimens. SEM images revealed isolated microcracks in specimens at 25℃ and 150℃, which effectively passivated pre-existing notches and increased fracture toughness. For granites above 200℃ following liquid nitrogen treatment, P-wave velocity, peak load, fracture toughness, and fracture energy decreased significantly as temperature increased. AE signals were observed earlier for granites at higher temperatures. The length of the fracture process zone increased with temperature, and the crack tip opening displacement exhibited a step-like increase at 600℃ under loading. The fractal dimension of the fracture surface varied with temperature, whereas the tortuosity exhibited a substantial increase with increasing temperature. As the temperature difference increased, an increasing number of microcracks appeared, forming interconnected networks that compromised the rock integrity, ultimately leading to reduced fracture toughness and the development of a rougher failure surface.

Effect of weakening characteristics of mechanical properties of granite under the action of liquid nitrogen

Liquid nitrogen fracturing and hot dry rock geothermal development are both emerging technologies in the field of energy. However, during the extraction of geothermal energy, it can cause the evolution of geological fractures, leading to the diffusion of groundwater and pollutants, thereby causing environmental pollution issues. Currently, geothermal energy has become a focal point in the global development of renewable energy. However, traditional hydraulic fracturing methods used in harnessing geothermal resources suffer from limitations such as limited fracture creation, uncertain initiation points, and environmental pollution. In contrast, liquid nitrogen has emerged as a promising reservoir stimulation technique, exhibiting significant effects on rock fracturing. In this study, we conducted three-point bending tests on granite samples subjected to liquid nitrogen treatment at temperatures of 300°C, with varying numbers of cooling cycles. Changes in fundamental mechanical parameters were analyzed. Additionally, through acoustic emission monitoring, we studied the variations in characteristic parameters of acoustic emissions under different cooling cycle conditions. Furthermore, based on the theory of energy evolution, we analyzed the energy evolution process during sample failure under different cooling cycle conditions. Using a compact scanning electron microscope, we observed changes in the microstructure of granite and analyzed the influence of cooling treatment on its surface characteristics and failure modes, thereby revealing the thermal damage process of granite. Moreover, by employing a non-metallic ultrasonic testing analyzer, we scanned the fracture surface morphology of granite and investigated the variations in fracture surface morphology features and surface roughness parameters caused by cooling treatment. The results indicate that liquid nitrogen cooling treatment can more effectively reduce the mechanical properties of rocks, and this effect is further enhanced at high temperatures. Under the condition of 300°C, after undergoing different cycles of liquid nitrogen cooling, granite will exhibit a more diverse macroscopic and microscopic structural failure characteristics, consistent with the expected formation of fluid flow channels in high-temperature rock formations.

Properties of abaca/epoxy composites modified by activated carbon particles for orthosis application

Abaca fiber (AF), epoxy (EP), and activated carbon particle (ACPs) incorporated composites have been previously studied to improve their mechanical properties. A study on integrating AF and ACPs to reinforce EP has not been done for comparison. The current study investigates the mechanical (tensile and flexural) and physical (water absorption) properties of AF/EP composites with 20 vol% AF modified by ACPs at 1% to 10% levels, and ACPs/EP composite with 20 vol% ACPs. Optical and scanning electron microscopy examined ACPs and the composite’s fracture surface morphologies. X-ray diffraction was used to identify the ACPs’ phase. The results showed that adding 5 vol% ACPs to AF/EP led to an optimum tensile strength of 42.50 MPa, which was slightly lower than AF/EP (43.00 MPa), and an optimum flexural strength of 62.10 MPa, which was slightly higher than AF/EP (60.50 MPa). Besides, adding 20% ACPs to EP resulted in a tensile strength of 31.93 MPa, higher than the previous result of ACPs/EP (26.34 MPa), also by adding 20% ACPs. Introducing ACPs to AF/EP could reduce water absorption in the composite by 6.52%. The measured flexural modulus of AF/EP added with 5 vol% ACPs was selected as the best material used in the simulation of ankle-foot orthosis (AFO) by Autodesk Inventor integrated with ANSYS Workbench 2019 R1. Applying a load of 27 N resulted in a von Misses stress of 54.018 MPa and a deformation of 44.675 mm.

Approach to characterize rock fracture surface: Insight from roughness and fractal dimension

The characterization of rock fracture is essential for revealing and understanding the fracture mechanism. In this research, the fracture of sandstone is characterized from the perspective of the 3D morphology of fracture surface. The 3D morphology is quantified by two fractal dimension (D) calculation methods: cubic covering method (CCM) and surface area method (SAM). The applicability of both methods is verified by two special cases of which one is a 2D plane and another one is a novel surface model with a dimension of 3. However, in actual application, one shortcoming of the CCM rooted in the algorithm is exposed, which introduces a distorted D for the surface with a small degree of undulation. On the contrary, relying on a new algorithm proposed to calculate the fracture surface area, the SAM can completely avoid the distortion problem. Based on the SAM, the 3D morphologies of a series of fracture surfaces of sandstone in the conventional triaxial test are quantified. It is observed that D has a strong correlation with the fracture mechanism. With the transition of failure mechanism from tension fracture to shear fracture, D presents a decreasing trend. The reason underlying this correlation is analyzed. In Discussion, several improved CCMs are introduced, and whether the improvements have solved the distortion problem is assessed. The accuracy of the SAM is also evaluated using the Takagi fractal surfaces.

Experimental investigation on mode I fracture behavior of sandstone after grouting filling under three-point bending

The widespread presence of fissures in natural rock masses poses numerous challenges to the design and construction of rock engineering. As an effective reinforcement method, grouting filling is crucial for maintaining the safety and stability of underground engineering. In this study, a testing and monitoring system was established to perform three-point bending tests on sandstone specimens with a pre-notch after grouting filling utilizing high-definition cameras and the rock mechanics testing machine. Combined with the digital image correlation (DIC) method and 3D scanning technique, the influence of grouting filling type on the mechanical behavior and fracture characteristics of sandstones was investigated. Simultaneously, a novel approach for quantitatively determining crack initiation and propagation was proposed based on the maximum principal strain theory. The results indicated that the peak load of specimens all tends to rise with the increase of filling rate and filling material strength. The fracture toughness and nominal tensile strength initially ascend and then slightly decline when the filling rate goes up, whereas both grow continuously as the filling material strength improves. Increasing the filling rate and filling material strength can decrease the opening degree of the pre-notch and postpone the development of the fracture process zone (FPZ). The crack propagates steadily to a certain length before remarkably increasing as the load rises, while the FPZ length exhibits a growth trend from slow to rapid and subsequently to sluggish. Moreover, the grouting filling effect will also have a pronounced impact on the crack propagation path and fracture surface morphology.

High-Temperature Tensile Behaviour of GTAW Joints of P92 Steel and Alloy 617 for Two Different Fillers.

This study explores the high-temperature (HT) tensile rupture characteristics of a dissimilar gas-tungsten-arc-welded (GTAW) joint between P92 steel and Alloy 617, fabricated using ER62S-B9 and ERNiCrCoMo-1 fillers. The high-temperature tensile tests were performed at elevated temperatures of 550 °C and 650 °C. An optical microscope (OM) and a field emission scanning electron microscope (FESEM) were utilized to characterize the joint. The high-temperature test results indicated that the specimen failed at the P92 base metal/intercritical heat-affected zone (ICHAZ) rather than the weld metal for the ERNiCrCoMo-1(IN617) filler. This finding confirmed the suitability of the joint for use in the Indian advanced ultra-supercritical (A-USC) program. The fracture surface morphology and presence of precipitates were analysed using an SEM equipped with energy dispersive spectroscopy (EDS). The appearance of the dimples and voids confirmed that both welded fillers underwent ductile-dominant fracture. EDS analysis revealed the presence of Cr-rich M23C6 phases, which was confirmed on the fracture surface of the ER62S-B9 weld (P92-weld). The hardness plot was analysed both in the as-welded condition and after the fracture.

Influence of carbon black particle size on fatigue life of rubber compound by varying strain and temperature

AbstractFatigue failure is one of the most critical failure modes in engineering structures. The fracture process proceeds through two major phases: crack nucleation and subsequent crack propagation leading to the ultimate failure. With special reference to rubber products especially tyre, the fatigue crack growth characteristics have been well understood with good approximation by many researchers. But the experimental research on crack nucleation is in the nascent stage. In the present study, we have focused on the role of filler particle size, temperature and strain on crack nucleation and fracture surface morphology of unfilled and carbon black (CB)‐filled natural rubber (NR) compounds. Three different kinds of ASTM grade carbon blacks, namely, N134, N234 and N339 have been used to determine the effect of filler particle size on crack initiation. All compounds have been tested at room temperature (i.e., RT 25°C), 70°C and 100°C with different strain amplitudes (50%, 75%, 100%, and 125%) to understand its effect on damage mechanics. It is observed that at a given strain and temperature, compound with N134 has better fatigue life in comparison to the N234 and N339. It is also found that with increasing temperature, fatigue life is being reduced for all the compounds. Optical microscope and field emission scanning electron microscope (FESEM) along with micro computational tomography (CT) have been utilized to understand the failure mechanism which reveal the presence of initial flaws as filler protrusions that creates micro cracks during fatigue loading and thus leads to crack nucleation.

Lamina Influences on Tensile Strength of Shallow Marine Shales from Upper Ordovician, Western Ordos Basin.

To investigate the influence of the lamina effect on the tensile strength of shallow marine shales and improve the shortcomings of the existing Brazilian standard disc splitting method, the Lamina shale of the Upper Ordovician Wulalik Fm in the western margin of the Ordos Basin was selected as the experimental object. Based on the radial wave velocity anisotropy test, the direction of crustal stress was determined, and standard cores were drilled. The Brazilian standard disc splitting experiment on Lamina shale with different loading angles was designed and carried out. The influence of lamina on the tensile strength of shale was summarized, and an improved calculation method of tensile strength was proposed. The experimental results indicate that the presence of lamina makes the tensile strength of shallow marine shale exhibit significant anisotropy, and the fracture surface morphology of standard discs under different loading angles varies greatly. The overall failure characteristics can be classified into two types: linear and curved. When the loading angle is 0° or 90°, the fracture surface of the disc belongs to tensile failure (linear type), and the traditional splitting method has good applicability. When the loading angle is greater than 0° and less than 90°, the fracture surface of the disc belongs to tensile shear failure (curve type), and traditional splitting methods are not applicable. There is a difference in tensile strength between vertical and horizontal wells, and vertical wells should consider the comprehensive tensile strength of the rock matrix and lamina at a 90° loading angle. Horizontal wells should consider the tensile strength of the weak lamina plane with a loading angle of 0°. The improved Brazilian splitting method solves the problem of the traditional method, calculating lower tensile strength values when the loading angle is greater than 0° and less than 90°. This provides important basic data support for wellbore stability evaluation and reservoir stimulation transformation.

The influence of fracture surface morphology on nonuniform etching in limestone acid fracturing

The success of acid fracturing in tight limestone reservoirs relies on the formation of nonuniform etching on the fracture wall. However, almost all acid fracturing models neglect the effect of fracture surface morphology on nonuniform etching. In this study, a three-dimensional acid fracturing mathematical model is developed to quantify and analyze the influence of rough fracture surface morphology on nonuniform etching for the first time by defining a morphology coefficient to describe the degree of local and overall morphological undulations of the fracture surface from a three-dimensional scale. The model uses the moving mesh partial differential equation (MMPDE) method to describe the flow field and spatial variation in the fracture as the fracture surface is continuously dissolved with the acid during acid fracturing, and the MMPDE moving mesh is coupled with the flow field, mass transfer, acid-rock reaction and fracture width variation. Based on the model, the effects of flow pattern, morphology coefficient, initial fracture width and fracture type on the nonuniform etching are studied. The simulation results demonstrate that the rough fracture surface can disturb the flow field and make the acid distribution more turbulent, which is conducive to the formation of nonuniform etching on the fracture surface. This phenomenon of flow rate differentiation can enhance the acid transfer distance. The local etching degree of the fracture surface decreases with the increase of the morphology coefficient of the area, and the strongly etching areas will appear around it. When the morphology coefficient of the local fracture area is larger than 1.2218, the area can appear obvious strongly etching areas and weakly etching areas after acid etching. The larger the initial fracture width is, the smaller the degree of nonuniform etching on the fracture surface. The prediction model constructed based on multiple linear regression was highly accurate (R2 = 0.9268) for the standard deviation of facture width (StdWidth) after acid etching. The critical value of StdWidth is recommended to be 0.6 as the criterion for judging the nonuniform etching ability. When the nonuniformity of the fracture surface is greater than this value, it is considered that the nonuniform etching ability is strong. In addition, the fracture with shear damage can produce relative sliding distance, which makes the fracture morphology on both sides of the fracture surface unevenly distributed and thus disturbs the flow field, which enhances the degree of nonuniform etching on the fracture surface. As the sliding distance increase, the magnitude of this enhancement also increases gradually. This study proposes a new three-dimensional characterization method for rough fracture surface morphology, solves the issue of mismatching flow field due to dynamic change in fracture width during acid fracturing.

Fracture surface morphology characterization and its influence on plugging performance of granular lost circulation materials

The irregularity and complexity of formation fracture morphology lead to great uncertainty in lost circulation control. At present, the fracture morphology is simplified to be smooth in the process of fracture plugging investigation, thus the influence of fracture surface morphology on the retention behavior and pressure bearing capacity of granular lost circulation materials (LCMs) remains unknown. To fill this gap, the reverse engineering technology was utilized for investigating the influence of fracture surface morphology on plugging performance. In this study, the three-dimensional (3D) reverse reconstruction and quantitative characterization of fracture surface were realized based on the 3D coordinates of real fracture surfaces, which were obtained through the 3D structured light scanning. A new parameter “particle size matching factor” was established to analysis the retention behavior of LCM particles. A new method for fracture plugging experiments was established based on 3D printing technology, which can obtain the structure of the sealing zone in fracture with real morphology. The results show that the irregularity of the real fracture surface leads to the local shrinkage of the flow channels, while provide support force to LCMs, which has an important influence on the plugging performance of LCMs. The larger the “particle size matching factor”, the easier to form retention in fractures. With the increase of Joint Roughness Coefficient (JRC) and fractal dimension, the pressure bearing capacity of the sealing zone is significantly improved. The research results are helpful to more accurately realize the plugging mechanism of granular LCMs, which contributes to improve efficiency of lost circulation control.

Experimental investigation on fracturing effects in hydraulic sand fracturing with acoustic emission and 3d laser scanning

Due to the extremely low permeability of shale reservoirs, large-scale reservoir fracturing is required. Hydraulic fracturing is one of the most important technologies in shale gas exploration and development. In this paper, the acoustic emission energy and the number of location and fracture surface morphology of specimens before and after fracture are studied through hydraulic sand fracturing test. The test results show that: (1) the energy ratio obtained during hydraulic fracturing without proppant is the smallest, and increasing the confining pressure, as well as reducing the displacement and viscosity of the fracturing fluid will cause the energy ratio to decrease. From the perspective of acoustic emission energy, the proppant play an important role in the generation of fractures during hydraulic sand fracturing; (2) when the confining pressure increases, the number of shale specimens before and after rupture is the largest, but the total number of locating events is smaller than the sanding ratio increased; there is no proppant hydraulic fracturing, the number of specimens before and after the rupture is the largest. And the total number reached the minimum, indicating that the proppant can play an important role in the hydraulic sand fracturing test; (3) the sand is relatively large, the specific surface and standard deviation both reach the maximum, indicating that the fracture surface roughness is the largest under the test condition, and the fracturing effect is the best, but the specific surface and standard deviation are the minimum when fracturing without proppant, so indicating that the fracture surface fracturing effect is the worst at this time.

Study on the durability of steel wire under the coupling effects of harsh environment and variable loads

steel wire is regarded as the most important component of cable-stayed bridges, and it has been widely used in practical engineering. Most of the studies only considered the effect of variable loads and chloride corrosion on the durability of steel wires separately. However, few studies have reported their coupling effects. In order to investigate the durability of steel wires considering their coupling effects, A physical test was performed to investigate the corrosion–fatigue performance. After the experiment finished, a tensile device was used to test the mechanical properties of corroded steel wires with different corrosion degrees. Then the corrosion characteristics of different specimens and fracture surface morphology of the steel wires were investigated using a 3D scanner, which was used to analyse the failure mode of each type of steel wires. In addition, a model was proposed to evaluate the reliability of corroded steel wires. Finally, a fatigue test was conducted to explore their fatigue performance and the S-N curve of steel wires with different corrosion degrees was obtained. The results show that the fatigue life of the steel wires is mainly affected by environmental effects when the steel wire at low stress amplitudes. However, as the stress amplitude increases, the fatigue life of it is decided by the stress amplitude. The fracture morphology of the corroded steel wires can be two categories: single-source fracture and multi-source fracture, For the steel wires corroded slightly, cracks often drive from one fatigue source (pit defect). As the corrosion degrees increase, the depth of pits enhances, cracks drive from different fatigue sources. In addition, the propagation zones decrease, and the rupture regions increase, as the steel wires corroded seriously.

Preparation and Characterization for the Thermal Stability and Mechanical Property of PLA and PLA/CF Samples Built by FFF Approach.

Currently, the mechanical performances of polylactic acid (PLA) samples prepared using the fused filament fabrication (FFF) technique are relatively poor. Hence, the carbon fiber (CF) is used to improve the thermal stability and mechanical property of FFF-ed PLA samples in this paper. The crystalline structure, thermal stability, melt flow rate, tensile strength and fractured surface morphology of PLA and PLA/CF samples were investigated with an X-ray diffraction device, differential scanning calorimeter, thermogravimetric analyzer, melt flow rate equipment, universal tensile test machine and scanning electron microscope, respectively. Meanwhile, the reinforcement mechanism of CF on the mechanical property of PLA samples was also analyzed. XRD results revealed that the diffraction peaks intensities of PLA/CF sample were obviously lower than those of PLA sample. TGA and DSC curves illustrated that the initial thermal decomposition temperature, thermal stability and crystallinity of the PLA/CF sample improved significantly. The tensile strength of the PLA/CF sample was 91.58 MPa, which was 42.49% higher than that of the PLA sample. Moreover, SEM images showed that the fractured behavior of the PLA sample varied from brittle fracture to ductile fracture after the introduction of CF. The results concluded the CF is a feasible fiber for enhancing the performances of the PLA sample.

Fracture mechanism of 316L/BNi-2 brazed joints using experiment and microstructure-based model

Compact components are prone to failure at brazed joints. To ensure the reliability of brazed joints, it is vital to have a comprehensive understanding of the fracture mechanism of brazed joints which can be attributed to highly inhomogeneous microstructures and individual phase mechanical properties. This study measured the stress-strain curve of brazed joint micro-zone of 316L austenitic stainless steel with the BNi-2 filler alloy by a tensile testing machine equipped with a CCD camera. The instrumented indentation technique was used to determine the flow properties of individual phases in joints considering the size effect. Representative volume element (RVE) technology was applied to simulate the mechanical behavior of brazed joints, which was in good agreement with the tested. The fracture of brazed joints can be divided into ductile fracture and brittle fracture which includes the decohesion of the interface between the boride and the austenite matrix and the fragmentation of the boride in terms of the analysis of the morphology of cross-section and fracture surface in brazed joints. According to the stress and strain distribution in the brazing micro-zone, the plastic strain localization cause decohesion, and the stress concentration along the loading direction cause boride fragmentation.

Hot Ductility Evolution Mechanism of Titanium‐Bearing Microalloyed Steels

Titanium‐bearing (Ti‐bearing) microalloyed steels have high strength and toughness by grain refinement effect of carbonitride precipitates. However, they can induce surface cracks of continuous casting slab when the Ti alloyed content is high. A microalloyed steel with Ti content (0.10–0.15 wt%) is carried out by thermalmechanical simulator over 600–1350 °C to analyze hot ductility evolution mechanism. Fracture surface morphology, phase transition, and behavior of precipitates of the tensile samples are investigated by experimental detection and thermodynamic calculation. The ductility–temperature curves show that the third brittle temperature range is 600–890 °C, which is mainly attributed to the thin proeutectoid ferrite film and precipitated titanium carbonitride particles, widening the embrittlement temperature ranges through of steel. In addition, the tensile samples at 890–1350 °C have good hot ductility, indicating the dynamic recrystallization of deformed austenite can trigger grain boundaries migration away from cracks and avoid the side effect of the Ti (C,N) particles on hot ductility. The first brittle temperature range of 1350 °C‐melting point is mainly ascribed to the partial melting of the grain boundaries with element segregation of sulfur and phosphorus, and microporosity loose among dendrites.

Micro-scale reconstruction and CFD-DEM simulation of proppant-laden flow in hydraulic fractures

A comprehensive investigation of the dynamical characteristics of proppant-laden flow systems in hydraulic fractures is important for the development of unconventional oil and gas resources. In this paper, we combine the micro-scale reconstruction technique and CFD-DEM method to numerically investigate the mobility and distribution rules of proppant-laden fluid in rough hydraulic fractures. To characterize realistic fracture surface morphology, six synthetic fracture models were assembled based on optical scanning data of real shale from three sets of hydraulic fracturing experiments. In order to accurately simulate the fluid-particle two-phase flow in rough fractures, the lift forces and particle rolling effect are considered in the CFD-DEM model. First, the effectiveness of the used CFD-DEM solver was validated by comparing it to the experimental data. We then examined mechanisms for the typical flow behaviors of proppant particles and fracturing fluid in smooth and rough fractures. Subsequently, the surface area ratio of the synthetic fracture model is adopted to characterize the cross-scale relationship between the micro-scale proppant distribution and fracture’s geometric features induced by the macroscale fracturing parameters (i.e., confining stress, fluid viscosity, flow rate, and sand ratio). Lastly, the parameter effects of the fracturing fluid, proppant particle, and fracture aperture on the dynamic characteristics of particulate flow in the hydraulic fracture are further discussed. In summary, the presented numerical model and findings can help better understand particle transport and distribution in real rock fractures and bridge the connectivity of the micro-scale particle flow and macroscopic fracturing parameter, which is vital for hydraulic fracturing process optimization.

Fracture Characteristics of Super Duplex Stainless Steel after Hot Tensile Testing

This study’s temperature range of hot tensile testing is 1000–1200 °C, which is consistent with ordinary industrial hot working temperatures. The fractography of super duplex stainless steel S32750 after hot tensile testing is investigated with Optical Microscopy and Scanning Electron Microscopy, and Electron Back-scatter Diffraction and Transmission Electron Microscopy study hot deformation behaviors of the necking area. The results reveal that ~1050–1150 °C is the optimal hot working temperature range regarding hot ductility and cracking sensitivity. The micro-voids nucleate at the ferrite-austenite interphase boundaries following the Kurdjumov-Sachs (K-S) or Nishiyama-Wasserman (N-W) orientation relationship at 1000 °C. Therefore, a quasi-cleavage fracture forms along the interphase boundaries. At the temperature range 1050–1150 °C, a uniform distribution of fracture surface is formed, and the highest Reduction in Area appears at 1150 °C. Dynamic phase transformation occurs with the formation of secondary austenite at ferrite grain boundaries at 1200 °C, which results in an intergranular fracture surface morphology.