Conventional Fracture Research Articles

Experiments and modeling of the combined tension-shear ultra-low-cycle fatigue of structural steel sheet regarding loading histories

This paper presents the experimental and modeling studies of the combined tension-shear ultra-low-cycle fatigue (ULCF) of Q345 structural steel sheet with thickness of 8 mm, considering the loading histories and stress state dependencies. Butterfly-shaped cyclic shear specimens, along with fixtures designed for adjustable shear angles, are used to explore ULCF damage evolution subjected to various combinations of shear and normal stress. The cyclic test programs consist of loading cases with shear angles of 0°(CS00), 30°(CS30), and 45°(CS45), all subjected to cyclic loading with constant-deformation-range (CR), varying-deformation-range (VR), and random-deformation (RD). Testing results confirm dependencies on deformation range and stress state. The combined tension-shear ULCF life increases as the deformation range decreases, while the higher triaxiality induced by the increase in shear angle reduces the ULCF life. Subsequently, the cyclic shear-void damage model (CSVDM) is proposed to comprehensively characterize the evolution of combined tension-shear ULCF damage. The kinematic equivalent plastic strain is introduced to determine dependency on plastic deformation histories. A new damage locus related to stress state is proposed to consider the matrix-shear mechanism under plane strain and the void-growth-collapse mechanism under axisymmetric loading. Compared to the conventional stress-weighted ductile fracture model (SWDFM) and the Lode parameter-enhanced cyclic void growth model (LCVGM), the proposed model exhibits advantages in accurately predicting ULCF failure under different loading protocols and shear angles, as indicated by impressively low average errors of 0.92 % for CS00, 2.08 % for CS30, and 1.42 % for CS45 specimens.

The Acoustic Emission Testing in the Evaluation of Fracture Toughness of Brittle Materials.

Evaluating the fracture resistance of dental ceramics is essential for assessing their behavior. This study aimed to validate a custom load-to-fracture test for assessing fracture strength compared to a conventional method. Acoustic emission testing, a non-destructive (ND) lab test, was employed to evaluate the fracture toughness (FT) of brittle materials by capturing sound waves generated by crack formation in failing samples. A total of 130 samples, divided into three types (glass sheets, zirconia sheets, and monolithic zirconia crowns), were tested. The fracture loads were measured using both custom and conventional methods. The mean fracture loads for glass sheets were 650.46 N ± 110.38 (custom) compared to 691.41 N ± 155.92 (conventional). For zirconia sheets, the values were 95.25 N ± 7.78 (custom) vs 112.75 N ± 31.26 (conventional). Monolithic zirconia crowns showed mean fracture loads of 1108.99 N ± 327.89 (custom) compared to 1292.52 N ± 271.42 (conventional). Statistically significant differences were evident in all three types, indicating lower values with custom testing for all samples. The custom testing demonstrated an advantage in identifying cracks at lower loads, thereby enhancing the accuracy of fracture load values. Despite its limitations, the study suggests that the custom setup could be a viable alternative to conventional fracture load testing of brittle materials. However, further testing with more materials is recommended to enhance the results' accuracy and generalizability. The findings indicate that the custom load-to-fracture test can provide more accurate measurements of FT in dental ceramics, which is crucial for predicting their clinical performance and longevity. How to cite this article: Haddad C, Eng JG, Zoghbi AE. The Acoustic Emission Testing in the Evaluation of Fracture Toughness of Brittle Materials. J Contemp Dent Pract 2024;25(7):617-623.

Fatigue crack growth in functionally graded materials using an adaptive phase field method with cycle jump scheme

Functionally graded materials provide versatility in adjusting the volume fractions of constituent materials to meet specific design requirements. However, this customization often introduces mode-mixity at the crack tip, posing challenges in predicting fracture under cyclic loading with discrete approaches and computationally expensive with conventional phase-field fracture models. To address these issues, this paper introduces an adaptive phase-field fracture formulation with cycle jump scheme to elegantly predict fatigue crack nucleation and growth in functionally graded materials. Within this framework, the effective properties at a point are estimated using the Mori–Tanaka homogenization scheme, while the crack growth due to cyclic load is captured by incorporating an additional fatigue degradation parameter. Moreover, the computational efficiency of the proposed framework is improved through an adaptive mesh refinement and explicit cycle jump scheme. The adaptive refinement scheme utilizes an error indicator derived from both the displacement solution and phase-field variable. The adaptive refinement scheme is integrated with efficient quadtree decomposition, which generates a hierarchical mesh structure. Hanging nodes resulting from the quadtree decomposition are efficiently handled using a polygonal finite element method. The proposed framework is validated against experimental and numerical results reported in the literature. Furthermore, we investigate the fatigue crack growth resistance across a broad range of material gradation directions, gaining valuable insights and identifying functionally graded materials with high fatigue resistance.

Enhancing the fracture resistance of additive manufactured polylactic acid via Morse-code-like architecturing

Additively manufactured poly-lactic acid (PLA) suffers from a limited fracture resistance. In this study, a combination of circular hole (dot) and elliptical hole (dash) architectures inspired from the Morse-Code are incorporated into (PLA) through additive manufacturing (AM) to improve their fracture resistance. The circular hole-like (C) features work as crack arrestors and the elliptical hole-like (E) features work as crack deflectors. A combination of simulations and experiments are performed to quantifiably determine the effect of single feature, double features, and other tailored arrangements of these features on the crack driving force and fracture resistance using elastic-plastic fracture mechanics. All the AM architecture systems show a significantly higher fracture resistance compared to the bulk AM PLA. Amongst the various systems tested, both the initiation work of fracture and total work of fracture are found to be the highest for alternative layers of E-C features. A 1172 % increase is observed from initiation to total work of fracture for the EC architecture, which is reflected in the fracture resistance curve (R-curve). This has important applications in the structural integrity and life of biomedical systems made from PLA. The applicability of work of fracture and conventional fracture mechanics for additively manufactured, architected systems with significant crack tip plasticity is also discussed.

Numerical simulation of geothermal reservoir thermal recovery of heterogeneous discrete fracture network-rock matrix system

In contrast to previous methodologies utilizing smooth fractures for predicting production in fractured geothermal reservoirs, this study introduces a novel approach employing a non-uniform rough discrete fracture network model characterized by heterogeneous apertures. Partial differential equations governing dual porosity flow and heat transfer are formulated, followed by a multi-physical field coupling simulation for the reservoir-scale formation model. The investigation focuses on the 50-year production performance of an enhanced geothermal system (EGS) under various parameters. Findings indicate a 15 % increase in production temperature with a 10-degree rise in injection temperature and a 10 % increase when well spacing is halved. Conversely, doubling the injection velocity or increasing the fracture aperture from 2 mm to 5 mm results in a 20 % and 25 % decrease in production temperature, respectively. These results highlight the negative impacts of faster fluid movement and larger fracture apertures on thermal retention. Conventional smooth fracture networks tend to underestimate both production temperature and the operational lifespan of EGS. An effective flow rate is defined, and an empirical prediction model for thermal recovery is established. This study provides valuable insights into the interplay of parameters affecting EGS production performance, serving as a pertinent reference for analyzing the influence of heterogeneous apertures on geothermal reservoirs.

Study on Characteristics of Ultrasound-Assisted Fracture Splitting for AISI 1045 Quenched and Tempered Steel.

Ultrasonic vibration-assisted con-rod fracture splitting (UV-CFS) was used to carry out the fracture experiment of 1045 quenched and tempered steel. The effect of ultrasonic vibration on the fracture properties was studied, the fracture microstructure and the evolution of dislocations near the fracture were analyzed and the microscopic mechanism was analyzed. The results show that in the case of conventional fracture splitting without amplitude, the dimple and the fracture belong to ductile fracture. With the increase in ultrasonic amplitude, the plasticity and pore deformation of the con-rod samples decrease at first and then increase; when the amplitude reaches a certain point, the load required for cracking is reduced to a minimum and the ultrasonic hardening effect is dominant, resulting in a decrease in the plasticity of the sample, a cleavage fracture, a brittle fracture, the minimum pore deformation and high cracking quality. The research results also show that with the increase in ultrasonic amplitude, the fracture dislocation density decreases at first, then increases, and dislocation entanglement and grain breakage appear, then decrease, and multiple dislocation slip trajectories appear. The changes in the dislocation density and microstructure are consistent with the above results.

Data-Driven Dynamic Inversion Method for Complex Fractures in Unconventional Reservoirs

Abstract Hydraulic fracturing is a crucial technology for enhancing the recovery of oil and gas from unconventional reservoirs. Accurately describing fracture morphology is essential for accurately predicting production dynamics. This article proposes a new fracture inversion model based on dynamic data-driven methods, which is different from the conventional linear elastic fracture mechanics model. This method eliminates the need to consider complex mechanical mechanisms, resulting in faster simulation speeds. In the model, the fracture morphology is constrained by combining microseismic data and fracturing construction data, and the fracture tip propagation domain is introduced to characterize the multi-directionality of fracture propagation. The simulated fracture exhibits a multi-branch fracture network morphology, aligning more closely with geological understanding. In addition, the influence of microseismic signal intensity on the direction of fracture propagation is considered in this study. The general stochastic approximation (GSA) algorithm is employed to optimize the direction of fracture propagation. The proposed method is applied to both the single-stage fracturing model and the whole well fracturing model. The research findings indicate that in the single-stage fracturing model, the inverted fracture morphology aligns closely with the microseismic data, with a fitting rate of the fracturing construction curve exceeding 95%, and a microseismic data fitting rate exceeding 93%. In the whole well fracturing model, a total of 18 sections were inverted. The fitting rate between the overall fracture morphology and the microseismic data reached 90%. The simulation only took 5 minutes, demonstrating high computational efficiency and meeting the needs of large-scale engineering fracture simulation. This method can effectively support geological modeling and production dynamic prediction.

Modelling short crack growth under creep-fatigue interaction for different dwell times

The creep-fatigue interaction (CFI) short crack growth behavior of 316H steel under different dwell times at 550℃ was investigated in this work. The dwell time effect of the CFI short crack growth behavior is analyzed systematically, the results revealed that compared to the long cracks, the short cracks is more sensitive to the creep damage effect during the dwell period. Meanwhile, a CTOD-based CFI short crack growth rate predication model is proposed by introducing the creep effect during the dwell time. Compared with conventional fracture mechanics approach, the CTOD-based approach demonstrated a superior capability in providing a unified prediction result for the creep-fatigue interaction in short crack growth rates under different dwell times.

An investigation on fracture toughness predictions from mini-sized uniaxial tensile specimens with global and local approaches

This study provides investigations on whether the fracture toughness can be accurately predicted from mini-sized uniaxial tensile specimens with existing global and local approaches. The critical toughness model, based on classical fracture mechanics, and the energy release rate (ERR) model, based on damage mechanics, were used as the two representative global approaches. While the finite element simulated compact tension (CT) specimen implemented with Gurson-Tvergaard-Needleman model was used as the local approach. Specimen size effect was judged through the viewpoints of stress–strain relationship and damage development. It was proved that the specimen size has no significant influence on stress–strain relationship, and has little influence on damage developments when the thickness reaches 1.0 mm. Fracture toughness predictions were conducted on four metals, including two steels (SA508Gr.3Cl.1 and 18MnMoNbR), one aluminum alloy (6061-T651), and one titanium alloy (TC4). For TC4 exhibiting brittle cleavage features on the fracture surface of CT specimens, neither the global nor the local approach can accurately predict its fracture toughness. For 6061-T651 exhibiting both ductile and brittle features on the fracture surface of CT specimens, there exists significant macroscopic crack propagation at the moment of conventional fracture toughness determination. The existence of significant macroscopic crack is inconsistent with the “equivalent crack” assumption in the ERR model, leading to a failure in its fracture toughness prediction. For two steels following the “equivalent crack” assumption, the ERR model and the local approach yield more accurate predictions (with the maximum error around 10 %) than their critical toughness counterpart (with the maximum error around 30 %).

Characterization and reconstruction of rough fractures based on vector statistics

The characteristics of fracture networks are of great significance for unconventional geo-energy exploitation such as shale oil, shale gas and geo-thermal extraction. Natural fractures and induced fractures after reservoir stimulation control the mechanical properties and fluid flow of the reservoirs. The quantitative characterization and reconstruction of rough fractures are essential for studying the fluid flow and mechanical properties of the reservoirs with complicated fracture networks. Based on vector statistics, a vector statistical method (VSM) for quantitative characterization of rough fractures is proposed and tested using 10 standard joint profiles. Furthermore, the growth vector counting method (counting method) and growth vector probability method (probability method) for single rough fractures in two-dimensional (2D) and three-dimensional (3D) models are proposed. Afterward, a morphology comparison and quantitative evaluation of single rough fractures before and after reconstruction are conducted. When the counting and probability methods are used to reconstruct single rough fractures, the difference in the tortuosity and fractal dimensions of the original and reconstructed fractures are less than 5% and 2.5%, respectively. It implies the counting and probability methods proposed herein can reconstruct rough fractures with approximate statistical characteristics and quantitative characterization parameters. Subsequently, the counting and probability methods for single rough fractures are further developed for 2D and 3D modeling of conventional and rough discrete fracture networks. The results indicate that the growth vector counting and probability methods proposed in this study have significant potential for rough discrete fracture network modeling. In addition, the merits and limitations of the proposed algorithms in modeling discrete fracture network models are discussed.

Differences in the permeability assessment of the fractured reservoir rocks using the conventional and the rough discrete fracture network modeling

Permeability assessment of naturally fractured rocks and fractured rocks after fracturing is critical to the development of oil and gas resources. In this paper, based on the discrete fracture network (DFN) modeling method, the conventional discrete fracture network (C-DFN) and the rough discrete fracture network (R-DFN) models are established. Through the seepage numerical simulation of the fractured rocks under different DFN, the differences in permeability of the fractured rocks under different parameters and their parameter sensitivity are analyzed and discussed. The results show that unconnected and independent fractures in the fracture network may weaken the seepage capacity of the fractured rocks. The fractured rock permeability increases with increase in connectivity and porosity and decreases with increase in maximum branch length and fracture dip. The use of C-DFN to equate the fracture network in the fractured rocks may underestimate the connectivity of the fracture network. For the more realistic R-DFN, the promotion of gas flow by connectivity is dominant when connectivity is high, and the hindrance of gas flow by fracture roughness is dominant when connectivity is low or when it is a single fracture. The permeability of the fractured rocks with R-DFN is more sensitive to the parameters than that of the fractured rocks with C-DFN. The higher the connectivity and porosity of the fractured rocks, the more obvious the difference between the permeability of the fractured rocks evaluated by C-DFN and R-DFN.

Production induced fracture closure of deep shale gas well under thermo-hydro-mechanical conditions

Deep shale gas reservoirs have geological characteristics of high temperature, high pressure, high stress, and inferior ability to pass through fluids. The multi-stage fractured horizontal well is the key to exploiting the deep shale gas reservoir. However, during the production process, the effectiveness of the hydraulic fracture network decreases with the closure of fractures, which accelerates the decline of shale gas production. In this paper, we addressed the problems of unclear fracture closure mechanisms and low accuracy of shale gas production prediction during deep shale gas production. Then we established the fluid–solid–heat coupled model coupling the deformation and fluid flow among the fracture surface, proppant and the shale matrix. When the fluid–solid–heat coupled model was applied to the fracture network, it was well solved by our numerical method named discontinuous discrete fracture method. Compared with the conventional discrete fracture method, the discontinuous discrete fracture method can describe the three-dimensional morphology of the fracture while considering the effect of the change of fracture surface permeation coefficient on the coupled fracture–matrix flow and describing the displacement discontinuity across the fracture. Numerical simulations revealed that the degree of fracture closure increases as the production time proceeds, and the degree of closure of the secondary fractures is higher than that of the primary fractures. Shale creep and proppant embedment both increase the degree of fracture closure. The reduction in fracture surface permeability due to proppant embedment reduces the rate of fluid transfer between matrix and fracture, which has often been overlooked in the past. However, it significantly impacts shale gas production, with calculations showing a 24.7% cumulative three-year yield reduction. This study is helpful to understand the mechanism of hydraulic fracture closure. Therefore, it provides the theoretical guidance for maintaining the long-term effectiveness of hydraulic fractures.

A robust tension-compression asymmetric phase-field fracture model for describing PBX cracking under complex stress states

ABSTRACT The crack behaviors under complex stress states are very important for the safety of polymer-bonded explosives (PBXs) under accidental stimulations, but their accurate description is a challenge. Due to the advances of tracking discontinuities and multi-fields coupling, the phase-field model for complex fracture phenomena is attracting significant interest recently. Conventional phase-field fracture models are tension-compression symmetric or based on volumetric-deviatoric strain energy split, and these conventional phase-field models may lead to unrealistic fracture patterns, which hinders its further application in PBX fracture simulations. In this work, we present an extended, tension-compression asymmetric phase-field fracture model for PBXs, which distinguishes the contributions of tensile and compressive stresses to damage driving energy, and couples the mechanism of mechanical degradation and energy-driving cracking diffusion. We implemented our improved phase-field fracture model into finite element calculations and compared the simulation results with the conventional tension-compression symmetric phase-field fracture model and volumetric-deviatoric strain energy split phase-field fracture model by simulating PBX specimens under static loadings. The results show that our model not only accurately depicts the tensile and compressive cracks, but also describes compression-assisted cracking while suppressing unrealistic damage nucleation caused by small amplitudes of local compressive stresses, making it a very efficient way of describing PBX cracking under complex stress states. This new model is both mathematically and physically concise, and convenient for numerical implementation. Moreover, the novel model can be naturally extended to simulate shock-induced dynamic and/or coupled fracture of PBXs because of its feasibilities for dynamic extension and multi-field coupling.

Assessment of selected biomarkers of bone healing and inflammation among subjects with fracture on traditional and conventional treatment methods

Abstract 
 
 Fractures have significant implications for health. Treatment approaches vary, including traditional and conventional methods. This study in Ekpoma, Nigeria assessed biomarkers in fracture healing through a cross-sectional random sampling. Blood samples from 60 subjects were analyzed for hydroxyproline, creatinine, calcium, alkaline phosphatase, and C-reactive protein. The aim was to evaluate treatment effectiveness and improvement in patient outcomes by monitoring bone remodeling. Statistical analysis utilized is the SPSS software version 21.0 software (SPSS Inc., Chicago, IL, USA). Biochemical marker analysis revealed that serum alkaline phosphatase activity, calcium, and creatinine did not significantly differ between subjects without fractures and those with fractures (p>0.05). However, hydroxyproline levels exhibited a significant difference (p<0.05), with higher values observed in subjects with fractures. Additionally, C-reactive protein levels showed significant variations (p<0.05), indicating increased inflammation in fracture patients. High-sensitive C-reactive protein levels also displayed significant differences (p<0.05). Further analysis comparing male and female subjects without fractures and those with fractures revealed no significant variations in serum alkaline phosphatase, calcium, and creatinine levels (p>0.05). However, hydroxyproline levels demonstrated significant variations (p<0.05) between males and females in the fracture group, suggesting gender-specific differences in bone metabolism. C-reactive protein and High-sensitive C-reactive protein levels exhibited significant variations (p<0.05) between males and females in the fracture group. Furthermore, a comparison between patients on traditional and conventional treatment methods indicated significant variations in serum alkaline phosphatase activity and calcium levels (p<0.05), suggesting distinct effects of the treatment modalities on these markers. However, no significant differences were observed in creatinine, C-reactive protein, and high-sensitive C-reactive protein levels (p>0.05). Traditional and conventional fracture treatment methods may affect biochemical markers differently, with gender-specific variations in hydroxyproline, C-reactive protein, and high-sensitive C-reactive protein levels. Further research is needed to understand the clinical implications and underlying mechanisms of these findings.

Unveiling the microstructure of LES manufactured parts for sustainable productive business

The Light Engineering Sector (LES) is regarded as the bloodline of Bangladesh’s economy for simultaneously creating jobs, poverty alleviation, and strengthening foreign currency reserves by reducing dependency on imported products for local industries. But this promising industry is now facing roadblocks mainly due to poor quality under service loading. Though many new and advanced manufacturing techniques are now available, conventional sand casting is the most widely used manufacturing technique utilized by the local spare parts manufacturer. It is well established that the mechanical properties (strength, toughness) of a material are determined by its microstructure. To date, the microstructure characterization of LES products has not been subject to much scrutiny. Therefore, in this work, an attempt has been made to systematically investigate the microstructure of an LES-manufactured marine propeller using an Optical microscope (OM) and Scanning Electron Microscope (SEM) equipped with Energy Dispersive Spectroscopy (EDS). A locally made marine propeller supplied by ACBD company was used for this study. It was found that the microstructure of both materials mainly consists of pores, needle-shaped particles, and Chinese script-like features embedded in the aluminum matrix. Based on EDS results it may be concluded that the needle-shaped particle is mainly composed of Si and Al. Moreover, the average pore size observed was about 5109.5 μm. Use of horse-and-buggy technology, and lack of knowledge of the casting process such as properties of molding sand, the composition of raw material, overall metallurgical control of the casting process, etc. might have resulted in these casting defects. As the conventional particle fracture mechanism for ductile fracture starts once the maximum load is applied, the presence of pores may exhibit premature growth soon after the beginning of plastic deformation. Therefore, the presence of large pores may exhibit premature growth immediately at the beginning of plastic deformation, thereby drastically reducing the mechanical properties under service loading. In summary, both the government and the private sector should involve themselves in strong and focused dissemination research activities with the support of universities so that suitable modifications and modernization can be adopted in the existing system.

Research on the Development Mechanism of Three Kinds of Cracks in Rock Cutting

In order to study the mechanism of crack propagation in rock cutting, experiments and discrete element numerical simulation of rock cutting at different depths were adopted in this paper. The rock fragmentation can be divided into mini-size fragmentation and normal-size fragmentation from a size viewpoint. The discrete element method (DEM) is used to further investigate the mechanism of normal size fragmentation at different depths and record the process of crack initiation and propagation. Additionally, the paper characterizes the process of crack initiation and examines the representative rock fragmentation. According to the mechanism of crack development, rock fragmentation can be divided into three categories: conventional failure, fracture failure, and damage failure. The fragmentation of three kinds of failure has one common point. To form semi-dislodged rock fragmentation, the macroscopic shear cracks are first formed. Subsequently, the tensile failure at weak places causes fragmentation ejection. Therefore, the mechanism of fragmentation generation in rock cutting is investigated in terms of crack initiation and extension. In this study, the fracture phenomenon of previous rock cutting experiments is reproduced by an experiment, and the failure process is analyzed in detail by the discrete element method, which reveals the essence of producing fragment phenomena and summarizes the fracture phenomenon and damage crack propagation mechanism in rock cutting.

Dynamic and adaptive mesh-based graph neural network framework for simulating displacement and crack fields in phase field models

Fracture is one of the main causes of failure in engineering structures. Phase field methods coupled with adaptive mesh refinement (AMR) techniques have been widely used to model crack propagation due to their ease of implementation and scalability. However, phase field methods can still be computationally demanding making them unfeasible for high-throughput design applications. Machine learning (ML) models such as Graph Neural Networks (GNNs) have shown their ability to emulate complex dynamic problems with speed-ups orders of magnitude faster compared to high-fidelity simulators. In this work, we present a dynamic mesh-based GNN framework for emulating phase field simulations of single-edge crack propagation with AMR for different crack configurations. The developed framework – ADAPTive mesh-based graph neural network (ADAPT-GNN) – exploits the benefits of both ML methods and AMR by describing the graph representation at each time step as the refined mesh itself. Using ADAPT-GNN, we predict the evolution of displacement fields and scalar damage field (or phase field) with good accuracy compared to the conventional phase-field fracture model. We also compute crack stress fields with good accuracy using the predicted displacements and phase field parameter.

An inversion for asymmetric hydraulic fracture growth and fracture opening distribution from tilt measurements

The eigenstrain tensor is defined in terms of the unit vector normal to the fracture plane and the dislocation vector to characterize the fracture geometry and to determine the fracture induced deformation field. Compared to the conventional nonlinear fracture model, the forward fracture model provides a linear relationship between fracture geometry parameters (eigenstrain) and the induced deformation. Therefore, a linear inverse problem needs to be tackled in mapping the fracture geometry by inversion of tilt observations. The fracture orientation and opening distribution of a tensile-dominated hydraulic fracture can be mapped iteratively in a coupled way by using the forward model defined in terms of the dislocation vector. The proposed analysis method is applied to field tilt data collected for monitoring the growth of a hydraulic fracture placed in the preconditioning of a roof rock over a coal longwall panel at a test site. Inversion of the tilt data produces a low fracture dip angle of 6.8°, which agrees with a nearly horizontal fracture orientation confirmed by intersection data collected in offset monitoring boreholes. Tikhonov regularization technique is applied to stabilize the discrete ill-posed inverse problem. The regularized solution provides information on the fracture opening distribution and asymmetric fracture growth. The inversion shows that the fracture grows uniformly and roughly in a radial pattern at early injection times, but grows asymmetrically, preferentially, and consistently to the northwest during later times. The predicted fracture growth agrees with the temperature logging to measure fracture intersections with the offset monitoring boreholes.

Preparation of Cross-Sectional Membrane Samples for Scanning Electron Microscopy Characterizations Using a New Frozen Section Technique.

Characterization of the cross-sectional morphologies of polymeric membranes are critical in understanding the relationship of structure and membrane separation performances. However, preparation of cross-sectional samples with flat surfaces for scanning electron microscopy (SEM) characterizations is challenging due to the toughness of the non-woven fabric support. In this work, a new frozen section technique was developed to prepare the cross-sectional membrane samples. A special mold was self-designed to embed membranes orientationally. The frozen section parameters, including the embedding medium, cryostat working temperature, and sectioning thickness were optimized. The SEM characterizations demonstrated that the frozen section technique, using ultrapure water as the embedding medium at a working temperature of -30 °C and a sectioning thickness of 0.5 µm, was efficient for the preparation of the membrane samples. Three methods of preparation for the cross-sectional polymeric membranes, including the conventional liquid nitrogen cryogenic fracture, the broad ion beam (BIB) polishing, and the frozen section technique were compared, which showed that the modified frozen section method was efficient and low cost. This developed method could not only accelerate the development of membrane technology but also has great potential for applications in preparation of other solid samples.

A review on Simulate Fracture and Ultra-Low Cycle Fatigue in Steel Structures by ABAQUS

In recent years, many advances have been made in fatigue and failure modeling in steel structures. The methods used to simulate failure and fatigue caused by earthquakes in steel structures are based on experimental and semi-empirical methods or conventional fracture mechanics. Semi-empirical methods cannot be generalized to a wide range of structural details, but conventional fracture mechanics can be reliably used only to simulate brittle fractures such as those observed in the Northridge and Kobe earthquakes, where large-scale yielding is absent. Similar to what is described in this paper, physics-based micromodels seek to simulate the fundamental processes of void growth and coalescence and granular shear responsible for very low-cycle fracture and fatigue in structures. These models are relatively free of assumptions about behavior and can be accurately used to simulate fracture and fatigue in a general sense under different conditions. The growth of voids or cracks can cause sudden crack propagation and deterioration of strength on a global scale of structural components. Therefore, these micromodels, relying on fundamental physics, are equally applicable to situations considered as "brittle" or "unbreakable" at the structural or component level. Examples are given to demonstrate the use of one of these models - the Cyclic Void Growth Model (CVGM) - to simulate failure through continuous finite element analyses.