Fracture Initiation Research Articles

An Alternative Finite Element Formulation to Predict Ductile Fracture in Highly Deformable Materials

Abstract An alternative finite element formulation to predict ductile damage and fracture in highly deformable materials is presented. For this purpose, a finite-strain elastoplastic model based on the Gurson–Tvergaard–Needleman (GTN) formulation is employed, in which the level of damage is described by the void volume fraction (or porosity). The model accounts for large strains, associative plasticity, and isotropic hardening, as well as void nucleation, coalescence, and material failure. To avoid severe damage localization, a nonlocal enrichment is adopted, resulting in a mixed finite element whose degrees-of-freedom are the current positions and nonlocal porosity at the nodes. In this work, 2D triangular elements of linear-order and plane-stress conditions are used. Two systems of equations have to be solved: the global variables system, involving the degrees-of-freedom; and the internal variables system, including the damage and plastic variables. To this end, a new numerical strategy has been developed, in which the change in material stiffness due to the evolution of internal variables is embedded in the consistent tangent operator regarding the global system. The performance of the proposed formulation is assessed by three numerical examples involving large elastoplastic strains and ductile fracture. Results confirm that the present formulation is capable of reproducing fracture initiation and evolution, as well as necking instability. Convergence analysis is also performed to evaluate the effect of mesh refinement on the mechanical response. In addition, it is demonstrated that the nonlocal parameter alleviates damage localization, providing smoother porosity fields.

Ayurvedic Management of Osteoporosis W.S.R. to Asthikshaya- A Pilot Study

Osteoporosis is marked by a substantial decrease in bone mass and a deterioration of the microarchitecture of bone tissue, which increases the risk of fractures. This condition often goes unnoticed until a fracture occurs, which is why it is often referred to as a "silent disease". Asthikshaya is an Ayurvedic term that refers to the depletion, degeneration, or weakening of Asthi Dhatu (bone tissue). It occurs when there is an insufficient formation or nourishment of the Asthi Dhatu, leading to a decrease in bone density and strength. This condition can manifest as bone weakness, brittle nails and teeth, hair loss, joint pain, and a greater risk of fractures or bone-related disorders, such as osteoporosis. Worldwide, an osteoporotic fracture happens every three seconds, significantly impacting individuals and disrupting their lives. By the age of 50, the probability of sustaining a fracture is one in three for women and one in five for men. The incidence of hip fractures in women is greater than the combined risk of breast, ovarian, and uterine cancers, while for men, the risk of hip fractures exceeds that of prostate cancer. Alarmingly, about 50% of individuals who experience an initial osteoporotic fracture will suffer additional fractures, with the risk escalating with each subsequent incident. In the present clinical study, 15 clinically proven patients of Osteoporosis were treated with Asthiposhtika Vati to evaluate its therapeutic effectiveness. Ayurvedic parameters (Lakshanas) of Asthikshaya were used as subjective parameters to assess the effectiveness of the drug. Statistical analysis was conducted using the t-test, and the results were encouraging, indicating that Asthiposhtika Vati (Anubhoot yoga) is effective in managing osteoporosis, thereby exploring various aspects of this clinical condition.

Hydrogen Embrittlement of Galvanized Press-Hardened Steels: A Review

Press-hardened steels (PHS), as an alternative to traditional steels and aluminum alloys, combine great mechanical performance with low manufacturing costs. PHS are martensitic steels with ultimate tensile strength (UTS) up to 2000 MPa. These steels are commonly coated with zinc-based coatings (PHS GI) consisting of multiple Zn–Fe phases to enhance corrosion resistance. However, similar to all high-strength steels, PHS are known for their elevated susceptibility to hydrogen embrittlement (HE). Absorption of atomic hydrogen into the steel lattice can lead to a transition from a ductile to a brittle fracture mechanism and decrease the stress necessary for fracture initiation. This review examines the microstructure of PHS GI with a focus on how the manufacturing process influences key parameters of the coating. The material’s susceptibility to HE is discussed in the following sections, along with the potential for hydrogen introduction through corrosion in atmospheric environments. The relationship between the content of hydrogen and its effects on fracture behavior is discussed, along with the corrosion behavior of PHS GI. The potential areas for future research and development of PHS GI with increased HE resistance are proposed.

Influence of nano‐silica particles on fracture features of recycled aggregate concrete using boundary effect method: Experiments and prediction models

AbstractThe aim of this investigation is to assess the impact of using nano‐silica (Na) at varying weight percentages of 0%, 1.5%, 3%, 4.5%, and 6% as partial cement substitute on fracture parameters of recycled aggregate concrete (RAC). A servo‐controlled testing system was employed to carry out three‐point flexure tests on 90 notched beams. Boundary effect method was used in order to interpret the fracture features. The results illustrate that adding Na increases the size‐independent fracture energy, fracture toughness and initial fracture energy of RAC by 29%, 32%, and 24% compared to that without Na, respectively. The maximum values of these parameters occur at 4.5% Na. The reference crack length () decreases from 6% to 22% by adding 1.5% to 6% Na. This shows that the RAC gets more brittle by the addition of Na. Moreover, the RAC behavior moves towards linear elastic fracture mechanics criteria by adding Na. Finally, according to the mechanical properties and test variables, multivariable models were suggested for prediction of the fracture parameters of the RAC containing Na. The models predictions were compared with experimental findings of the previous research.

Micro-fracture mechanism of microwave induced fracturing of basalt based on a novel Electromagnetic–Thermal–Mechanical coupling model

Microwave-assisted rock fracturing is recognized for its efficiency, energy savings, and environmental benefits. Investigating microscopic mechanisms of microwave-induced rock fracturing is essential for predicting the weakening effect on rock. A coupled Electromagnetic–Thermal–Mechanical model based on FEM–DEM was established to describe the response of rock under microwave irradiation. This model employs interpolation algorithms and mineral lattices randomization algorithms to establish a 2D cross-sectional representation of rock. A discrete element calculation method is proposed to synchronize computational time with the experimental time. The model can simulate the multi-physical field response of different rocks under various conditions, making it an effective tool for studying microwave-induced rock fracturing. The effectiveness of the numerical model was validated through open-end microwave-induced fracturing experiments on basalt. Additionally, the study elucidates the micro-fracture mechanism of basalt under microwave irradiation. The results indicate that the direction of crack propagation is influenced by microwave power and boundary effects. The patterns of fracture development between minerals are summarized as follows: Initial fractures primarily result from the rapid heating of microwave-absorbing minerals like enstatite,creating a significant temperature gradient. With increased heating time, heat transfers to highly expansive minerals such as olivine, causing fractures due to localized thermal expansion.

A multi-linear constitutive relation considering the temperature effect on quasi-static mode I delamination in UD/MD laminates

In this study, a multi-linear constitutive relation taking into account temperature and fiber bridging is proposed for characterizing delamination behavior in composite laminates under various temperature conditions. An approach combining analytical solution and J-integral is also established for determining the cohesive parameters in the multi-linear constitutive relation. To validate the proposed constitutive relation, mode I quasi-static delamination experiments of unidirectional (UD) and multidirectional (MD) carbon/bismaleimide laminates are carried out at 25 ℃ (room temperature), 80 °C and 130 ℃. The experimental results show that the increasing temperature resulted in a monotonic increase in the fracture toughness of the UD laminates while affect the fracture toughness of MD laminates slightly. A FE model is established with the implementation of the proposed multi-linear constitutive relation using UMAT subroutine. Good agreements between the experimental and simulated results demonstrate the validity of the proposed constitutive relation, with the relative difference of peak load between predicted and experimental values less than 8.2 % and the relative difference of initial and steady-state fracture toughness between predicted and tested results less than 15 %. This study provides the possibility to numerically study the temperature effect on the delamination behavior of laminates and has promising applications in the damage tolerance design of composite structures.

Use of medialized trochanteric-entry intramedullary nail to improve alignment in proximal femur nonunions.

Proximal femur shaft nonunion is a challenging problem, often occurring after malreduction that results in postoperative malalignment and decreased healing potential. Correction of malalignment is critical to achieving osseous union. Here we present a novel technique for treating proximal femur nonunions with varus malalignment using an intramedullary nail inserted through a medialized trochanteric entry point. Patients who underwent a proximal femur shaft (subtrochanteric or proximal third shaft) nonunion operation at a single level 1 academic referral centre by two attending surgeons between 1/1/2014 and 1/1/2022 were identified. Radiographic imaging was reviewed to determine initial fracture classification and calculation of coronal plane alignment (CPA), which was measured on preoperative, immediate postoperative, and final follow-up radiographs. Postoperative complications, reoperations, infections, and osseous union were also collected. Twenty-one patients with a mean age of 49.9 years (66% male) were identified. Mean preoperative CPA was 125.6 degrees, immediate postoperative mean CPA was 132.6 degrees, and mean final follow-up CPA was 131.5 degrees. Mean change in CPA from immediate postoperative films to final follow-up was a decrease of 0.4 degrees. 17 patients had follow up for a minimum of 12 months or until osseous union, and all achieved union without any major complications. Exchange nailing with an antegrade trochanteric entry nail through a medialized trochanteric starting point is a safe and effective technique in the treatment of proximal femur nonunions. This technique results in improved postoperative alignment that is sustained throughout the postoperative course, and may lead to increased rates of osseous union.

Role of molecular damage in crack initiation mechanisms of tough elastomers

Tough soft materials such as multiple network elastomers (MNE) or filled elastomers are typically stretchable and include significant energy dissipation mechanisms that prevent or delay crack growth. Yet most studies and fracture models focus on steady-state propagation and damage is assumed to be decoupled from the local stress and strain fields near the crack tip. We report an in situ spatial-temporally resolved 3D measurement of molecular damage in mechanophore-labeled MNE just before a crack propagates. This technique, complemented by digital image correlation, allows us to compare the spatial distribution of both damage and deformation in single network (SN) elastomers and in MNE. Compared to SN, MNE have a wide-spread damage in front of the crack and, surprisingly, delocalize strain concentration. A continuum model, where damage distribution is fully coupled to the crack tip fields, is proposed to explain these results. Additional measurements of time-dependent molecular damage during fixed grips relaxation in the presence of a crack reveal that the less localized damage distribution delays fracture initiation. The observations and exploratory modeling reveal the dynamic fracture mechanism of MNE, providing guidance for rational design of high-performance tough elastomers.

Comprehensive Investigation of Factors Affecting Acid Fracture Propagation with Natural Fracture

Acid fracturing is a crucial stimulation technique to enhance hydrocarbon recovery in carbonate reservoirs. However, the interaction between acid fractures and natural fractures remains complex due to the combined effects of mechanical, chemical, and fluid flow processes. This study extends a previously developed hydro-mechano-reactive flow coupled model to analyze these interactions, focusing on the influence of acid dissolution. The model incorporates reservoir heterogeneity and simulates various scenarios, including different stress differences, approaching angles, injection rates, and acid concentrations. Numerical simulations reveal distinct propagation modes for acid and hydraulic fractures, highlighting the significant influence of acid dissolution on fracture behavior. Results show that hydraulic fractures are more likely to cross natural fractures, whereas acid fractures tend to be arrested due to wormhole formation. Increasing stress differences and approaching angles promote fracture crossing, while lower angles favor diversion into natural fractures. Higher injection rates facilitate fracture crossing by increasing pressure accumulation, but excessive acid concentrations hinder fracture initiation due to enhanced wormhole formation. The study demonstrates the importance of tailoring fracturing treatments to specific reservoir conditions, optimizing parameters to enhance fracture propagation and reservoir stimulation. These findings contribute to a deeper understanding of fracture mechanics in heterogeneous reservoirs and offer practical implications for improving the efficiency of hydraulic fracturing operations in unconventional reservoirs.

Refracturing Time Optimization Considering the Effect of Induced Stress by Pressure Depletion in the Shale Reservoir

Refracturing is an important technology for tapping remaining oil and gas areas and enhancing recovery in old oilfields. However, a complete and detailed refracturing timing optimization scheme has not yet been proposed. In this paper, based on the finite volume method and the embedded discrete fracture model, a new coupled fluid flow/geomechanics pore-elastic-fractured reservoir model is developed. The COMSOL 3.5 commercial software was used to verify the accuracy of our model, and by studying the influence of matrix permeability, initial stress difference, cluster spacing, and fracture half-length on the orientation of maximum horizontal stress, a timing optimization method for refracturing is proposed. The results of this paper show that the principle of optimizing the refracturing timing is to avoid the time window where the percentage of Type I (Type I indicates that stress inversion has occurred, 0∘≤α≤20∘; Type II indicates that the turning degree is strong, 20∘<α≤70∘; and Type III indicates less stress reorientation, 70∘<α≤90∘) stress reorientation area is relatively large, so that the fractures can extend perpendicular to the horizontal wellbore. At the same time, the simulation results show that with the increase in production time, the percentage of Type I and Type II increases first and then decreases, while the percentage of Type III decreases first and then increases. When the reservoir permeability, stress difference, and cluster spacing are larger, the two types of refracturing measures can be implemented earlier. But, with the increase in fracture half-length, the timing of refracturing Method I is earlier, and the timing of refracturing Method II is later. The research results of this paper are of great significance to the perfection of the refracturing theory and the optimization of refracturing design.

Field experiments and main understanding of shale oil hydraulic fracturing

To understand the key processes of hydraulic fracturing in shale oil reservoirs, such as artificial fracture initiation and extension, proppant transportation and settlement, and the influencing factors of post-fracture production, many hydraulic fracturing field tests have been conducted in the United States. Examples include the ConocoPhillips tests and the National Hydraulic Fracturing Experiment. The results have promoted the innovation and development of fracturing technology. A good correlation exists between lithological changes and the roughness of artificial fractures. Although numerous artificial cracks are created, the number that can provide oil and gas seepage is relatively small, determined by the effectiveness of these cracks. The settlement of proppants in actual geological formations involves factors such as geology, lithology, fractures, and stress. The pressure data indicate that when the reservoir pressure drops below the bubble point pressure, the decline in production sharply increases. The key variables affecting shale oil well production include the horizontal well position, well spacing, horizontal section length, and sand addition intensity. These technologies are suitable for the adaptive process of China’s terrestrial shale oil fracturing, promoting the development and rapid increase of shale oil production.

Effect of Occlusal and Axial Thickness on the Fracture Load of Implant-Supported Monolithic Zirconia Crowns.

To evaluate the fracture load of monolithic zirconia crowns with implant screw holes, focusing on variations in occlusal and axial thicknesses, and to assess the interaction between these variables. Six different prostheses were designed using CAD software, varying in occlusal thickness (0.5 mm, 1.0 mm) and axial thickness (0.4 mm, 0.8 mm, 1.2 mm) based on the height and thickness differences of the titanium implant abutment. Twelve specimens per design were created by milling zirconia blocks and titanium abutments. These specimens were cemented with resin and subjected to thermomechanical aging (50 N, 200,000 cycles, 5°C-55°C, 30 seconds dwell time) using a chewing simulator. Static loading was applied using a universal testing machine at a rate of 0.5 mm/min until fracture occurred, and the load value (N) at the moment of the initial fracture was recorded. Fracture pattern and surface analyses were performed. Statistical analyses included two-way analysis of variance, Tukey HSD test, multiple regression analysis, and Fisher's exact test. Both occlusal and axial thicknesses significantly influenced the fracture load (P < .05), with a significant interaction between them (P < .05). An occlusal thickness of 1.0 mm exhibited a significantly higher fracture load compared to 0.5 mm (P < .05). An axial thickness of 1.2 mm showed a significantly higher fracture load compared to 0.4 mm and 0.8 mm (P < .05). The difference in axial thickness between 0.8 mm and 1.2 mm had a more substantial impact on fracture load than the difference in occlusal thickness between 0.5 mm and 1.0 mm (P < .05). Fractographic analysis showed that the thin axial wall exhibited twist hackles without involvement of the crown margin, whereas the thick axial wall exhibited no hackles and a more catastrophic failure involving the crown margin. For monolithic zirconia crowns with implant screw holes, when sufficient occlusal thickness cannot be achieved, an axial thickness of at least 1.2 mm is recommended to ensure higher fracture resistance.

Test-and-FE-based method for obtaining complete stress-strain curves of structural steels including fracture

Ductile fracture is a common limit state of frameworks of steel structures and can be predicted by incorporating models for fracture initiation and propagation in finite element (FE) analyses. However, accurate prediction of fracture relies on unique fracture parameters for a given material, requiring precise predictions of fracture strain and stress states obtained through coupon tests and accompanying FE data analysis. In recent decades, various methods have been proposed to predict ductile fracture initiation, including various design geometries of coupons, test setups and FE analyses, which may lead to inconsistent fracture strains and stress states. Hence, there is a need for proposing a standard procedure for the design, test and accompanying FE-based calibration of fracture parameters, as pursued in this paper. Given that ductile fracture initiates under significant plastic strain, a constitutive model for the full strain range is required, as also proposed in this paper. Moreover, to reduce the experimental and data analytical efforts, an empirical method is proposed that uses only a small number of coupon tests to calibrate the fracture parameters. The method encompasses three levels wherein one, two, or three coupon tests are required. All in all, the paper presents a methodology for determining the full-range true stress-strain curve and the initiation of fracture, including a new post-necking constitutive model and methods for determining the free parameters of the post-necking and fracture initiation models. While applied to steel in this paper, the proposed methodology is potentially also applicable to other metals.

A retrospective review of revision and re-revision patella osteosynthesis performed for failure of fixation of initial comminuted fracture patterns: very high complication rates.

Literature on revision osteosynthesis for failed patella fracture fixation is extremely limited. This study reviews the treatment options and outcomes for revision and re-revision osteosynthesis at a Level 1 Trauma Center. All patella revision osteosynthesis between January 2021 and March 2024 were identified using Current Procedural Terminology (CPT) codes at a single tertiary care academic centre. Medical records, operative reports and radiographs were reviewed to collect details regarding patient demographics, initial injury and fracture management, indications for revision surgery, revision construct, post-operative weight bearing and range of motion restrictions, and outcomes. The primary outcome was major failure defined as loss of fixation or further surgery for non-union or infection. Ten patients underwent revision osteosynthesis for failed fixation. All fractures were initially comminuted fracture patterns (AO/OTA 34-C3), with nine (90%) initially treated with a 2.7mm patella-specific variable angle (VA) locking plate (Synthes, Paoli, PA). Half (n=5) of the patients were revised with the same patella specific plate and half with an all suture transosseous fibertape tension band (Arthrex, Naples, FL). Additional fixation in the form of bony augmentation was performed in 20% (n=2) of cases and soft tissue augmentation in 70% (n=7). There was a 70% (n=7) major failure rate, mostly due to loss of inferior pole fixation. There were four re-revision procedures performed with surgical fixation. Two of these subsequently developed infection, one united and the other had no radiographic signs of union and was lost to follow-up, but was without complication. Regardless of the chosen fixation construct, revision osteosynthesis for failed fixation of initial comminuted fracture patterns has an extremely high rate of failure. Complications increase with further revision surgery.

Initiation Pressure and Fracture Path of Near-Field Symmetric Pre-cut Hydraulic Fracturing

Initiation Pressure and Fracture Path of Near-Field Symmetric Pre-cut Hydraulic Fracturing

Fracture toughness of alkali-activated concrete subjected to aggressive environment

This study investigates the fracture toughness of alkali-activated granulated blast-furnace slag (GBFS)-based geopolymer concrete (GPC), non-activated slag cement concrete, and ordinary Portland cement (OPC) concrete in acidic, alkaline, and chloride solutions over six months. A total of 580 centrally straight-notched Brazilian disc (CSNBD) specimens were cast to assess pure mode-I (0°), pure mode-II (28.7°), and mixed-mode (15° and 45°) fractures under these conditions. Microstructural analyses (SEM) were performed to evaluate microstructural changes after six months of exposure. Results showed that GPC exhibited the lowest initial fracture toughness but the smallest reduction (7 %-11 % depending on the mode) across all environments, with slag cement concrete and OPC experiencing reductions of 11 %-14 % and 14 %-21 %, respectively, in acidic conditions. In alkaline environments, GPC showed a 3 %-6 % decrease in fracture toughness, while OPC and slag cement concrete showed reductions of 6 %-13 %. The gradient boosting regressor accurately predicted the failure load of CSNBD specimens, achieving an R² score of 0.948. Finally, SHAP sensitivity analysis identified concrete type, exposure time, and environment as critical input features, consistent with experimental results.

Study on Near-Wellbore Fracture Initiation and Propagation with Fixed-Plane Perforation in Horizontal Well for Unconventional Reservoirs

At present, in the process of volume fracturing for a tight reservoir, employing the spiral perforation method to induce the fracture propagation direction would always obtain an unsatisfactory effect, which causes the deflection and tortuosity of hydraulic fractures. Therefore, researchers presented the fixed-plane perforation method for enhancing the effect on volume fracturing. In this paper, the three-dimensional discrete lattice method is used to study the initiation and propagation law of horizontal well fixed-plane perforation in unconventional reservoirs under two different stress states. The results show that it is more suitable to use fixed-plane perforation for reducing the initiation pressure. When employing the fixed-plane perforation method, fracture always initiates in the perforation plane, presents as an irregular fan-shaped failure surface, and then propagates along the wellbore. The initiation pressure is highly correlated to the phasing angle between adjacent perforations under different conditions, and the rate of increase in the initiation pressure decreases by around 1.59~6.38% when the phasing angle reaches 30°. The fracturing pressure is inversely correlated with the diameter and tunnel length of the perforations and the horizontal stress difference. When the diameter increases to 17 mm, the tunnel length increases to 25 cm or the horizontal stress difference reaches 8 MPa. These results reveal an insignificant effect of the above parameters on the initiation pressure.

Geological and Engineering Integration Fracturing Design and Optimization Study of Liushagang Formation in Weixinan Sag

The Weixinan Sag in the Beibuwan Basin is rich in shale oil resources. However, the reservoirs exhibit rapid phase changes, strong compartmentalization, thin individual layers, and high-frequency vertical variations in the thin interbedded sandstone and mudstone. These factors can restrict the height of hydraulic fracture propagation. Additionally, the low-porosity and low-permeability shale oil reservoirs face challenges such as low production rates and rapid decline. To address these issues, the Plannar3D full 3D fracturing model was used to simulate hydraulic fracture propagation and to study the main controlling factors for fracture propagation in the second member of the Liushagang Formation. Based on the concept of geological–engineering integration, a sweet spot evaluation was conducted to identify reservoirs with relatively better brittleness, reservoir properties, and oil content as the fracturing targets for horizontal wells. The UFM model was then applied to optimize fracturing parameters. This study indicates that the matrix-type oil shale has a high clay mineral content, resulting in a low Young’s modulus and poor brittleness. This makes hydraulic fracture propagation difficult and leads to less effective reservoir stimulation. In contrast, hydraulic fractures propagate more easily in high-brittleness interlayer-type oil shale. Therefore, it is recommended to prioritize the extraction of shale oil from interlayer-type oil shale reservoirs. The difference in interlayer stress is identified as the primary controlling factor for cross-layer fracture propagation in the study area. Based on the concept of geological–engineering integration, a sweet spot evaluation standard was established for the second member of the Liushagang Formation, considering both reservoir quality and engineering quality. Four sweet spot zones of interlayer-type oil shale reservoirs were identified according to this evaluation standard. To achieve uniform fracture initiation, a differentiated segment and cluster design was implemented for certain high-angle sections of well WZ11-6-5d. Interlayer-type oil shale was selected as the fracturing target, and the UFM was used for hydraulic fracture propagation simulation. Fracturing parameters were optimized with a focus on hydraulic fracture characteristics and the estimated ultimate recovery (EUR). The optimization results were as follows: a single-stage length of 50 m, cluster spacing of 15 m, pump injection rate of 10 m3/min, fluid intensity of 25 m3/m, and proppant intensity of 3.5 t/m. The application of these optimized fracturing parameters in field operations resulted in successful fracturing and the achievement of industrial oil flow.

Quasi-static and fatigue performance of Ti-6Al-4V triply periodic minimal surface scaffolds manufactured via laser powder bed fusion for hard-tissue engineering

Additive manufacturing of Triply Periodic Minimum Surface scaffolds offers a promising solution for bone defect restoration and an alternative to traditional implants in hard tissue engineering. This study investigates the quasi-static and tension-compression cyclic properties of laser powder bed fusion-produced Ti6Al4V lattice-based architectures, specifically gyroid and diamond scaffold geometries. The scaffolds were designed to emulate the mechanical properties of bones, with pore sizes (650–1000 μm) suitable for tissue engineering, and porosities ranging from to 30–60 %. The quasi-static tensile properties of the stiffness and yield strength were characterized experimentally and validated numerically using the finite-element method. The results showed that the stiffness and tensile strength of the scaffolds were comparable to those of cortical bone, reducing the risk of scaffold failure. The influence of post-processing by heat treatment and hot isostatic pressing resulted in an increased fatigue limit and ductility compared with non-treated materials reported in the literature. Fractography analysis revealed that fatigue fracture initiation occurred at the outer surface of the skeleton structures, where the maximum tensile stress was concentrated. These findings support the assumption that the designed scaffolds accurately replicate the mechanical and fatigue characteristics of cortical bone, offering suitable alternatives for bone replacement and orthopedic implants.

Sensitivity Analysis of Depth-Controlled Oriented Perforation in Horizontal Wells Based on the 3D Lattice Method

The main method used to exploit unconventional oil and gas reservoirs involves multi-cluster perforation combined with hydraulic fracturing in horizontal wells. However, as the use of this technology has expanded, challenges like reduced perforation efficiency and elevated fracture initiation pressure have surfaced. The depth-controlled oriented perforation technique helps achieve uniform fracture initiation, enhance efficiency, and lower initiation pressure. In this study, a hydraulic fracturing fluid–solid coupling model at the perforation scale was established using the 3D lattice method to compare the near-wellbore fracture morphologies of depth-controlled oriented perforation, spiral perforation, and oriented perforation. Additionally, this study analyzes the effects of injection rate, reservoir elastic modulus, and horizontal stress difference on the fracture morphology and initiation pressure of depth-controlled oriented perforation. This study clarifies the applicability of depth-controlled oriented perforation in different types of reservoirs for the first time. The results indicate that intermediate fractures between spiral and oriented perforations are hindered, while depth-controlled oriented perforation ensures uniform fracture initiation. In the injection rate range of 0.144 to 0.360 L/min, an increase in injection rate accelerates the rise of fluid pressure within the perforations, leading to an increase in fracture initiation pressure. Therefore, excessively high injection rates are unfavorable for fracture initiation. Through depth-controlled oriented perforation, long and singular fractures can be formed in reservoirs with significant horizontal stress differences and high elastic moduli.