Fracture Surface Research Articles

Conditions for the local arrest of a hydraulic fracture by a region of larger toughness

Abstract We investigate the conditions for the local arrest of a hydraulic fracture encountering a region of larger toughness. The propagation of a hydraulic fracture strongly depends on the ratio between the energy dissipated in the creation of new fracture surfaces and the energy dissipated in viscous flow. Because this ratio evolves during propagation, a hydraulic fracture can exhibit different behaviors when encountering the same toughness heterogeneity. The fracture can be locally arrested or its velocity only reduced. When viscous fluid flow dissipation dominates, a larger increase of fracture toughness is required to locally arrest the fracture. In the framework of linear hydraulic fracture mechanics, we determine the conditions under which a region of higher fracture toughness is capable of arresting a propagating hydraulic fracture. In particular, we obtain a relation for the minimum increase of fracture toughness required to locally arrest a fracture as a function of the dimensionless ratio of the dissipated energies (viscous versus fracture) when the fracture has just reached the heterogeneity. We obtain relations for the full parametric space covering both toughness and viscous-dominated regimes. Fully coupled numerical simulations of hydraulic fracture growth confirm the scaling relations.

Evaluation of Phase Transformation on Boron Decorated Sn-1.5Ag-0.7 Cu Joined Cu Pillar for Packaging Connection

Abstract The microstructure transformation, mechanical properties, and fracture behavior of boron (B) decorated tin (Sn)-1.5%Ag-0.7%copper (Cu) (SAC157) solder joints with Cu pillars were analyzed. Three concentrations of B (0.015%, 0.020%, and 0.025%) were evenly mixed into the SAC157 solders. The addition of B refined the primary β-Sn phase and transformed the eutectic phase Ag3Sn from a plate-like structure to a dense stripe configuration. During high-temperature storage, coarse intermetallic compounds (IMCs) that extruded into the primary β-Sn in SAC157 solder were observed, and the growth of IMCs was inhibited by B-pinning boundary motion. Furthermore, the B additive simultaneously increased hardness and improved ductility by reducing grain size. In shear strength tests, the SAC157 solder exhibited a brittle fracture surface with a shorter displacement of 0.78 mm, compared to 1.2 mm of elongation in B-decorated SAC157 solders, which displayed ductile properties characterized by a dimpled fracture surface. In conclusion, B particles acted as heterogeneous nucleation sites, effectively refining the grain structure, inhibiting the growth of the eutectic phase, and simultaneously enhancing ductility without compromising hardness.

Precise Replication of Complex Rock Fracture Surfaces Combining 3D Printing, Mold-and-Cast, and Statistical Analysis

Precise Replication of Complex Rock Fracture Surfaces Combining 3D Printing, Mold-and-Cast, and Statistical Analysis

Elastic Wave Propagation Through Cylinders with Fluid-Filled Fractures Using the Discontinuous Galerkin Method

Accurately modeling fractures in wave-propagation simulations is challenging due to their small scale relative to other features. While equivalent-media models can approximate fracture-induced anisotropy, they fail to capture their discrete influence on wave propagation. To address this limitation, the Interior-Penalty Discontinuous Galerkin Method (IP-DGM) can be adapted to incorporate the Linear-Slip Model (LSM) to represent fractures explicitly. In this study, we apply IP-DGM to elastic wave propagation in fractured cylindrical domains using realistic fracture compliances obtained from laboratory experiments (using ultrasonic-pulse transmission) to simulate the effects of fluid-filled fractures. We analyze how fracture spacing and fluid type influence P- and S-wave behavior, focusing on amplitude attenuation and wave-front delays. Our numerical results align with experimental and theoretical predictions, demonstrating that higher-density fluids enhance wave transmission, reducing the impedance contrast and improving coupling across fracture surfaces. These findings highlight the capability of IP-DGM to accurately model wave propagation in realistic fractured and saturated media, providing a valuable tool for seismic monitoring in fractured reservoirs and other applications where fluid-filled fractures are prevalent.

A Generic Fracture Conductivity Model for Partially Propped Fracture Networks with Proppant Embedment and Proppant Pack Deformation

Hydraulic fracturing involving proppant injection is currently the most effective technology to stimulate tight, unconventional reservoirs. The conductivity offered by the created propped and unpropped fracture segments is directly linked to the well deliverability. The accurate modeling of the fracture network conductivity is key to well performance prediction. Unlike most previous studies that have focused on the single-fracture conductivity, a comprehensive fracture network conductivity model was developed by incorporating more complex rock and proppant deformation mechanisms and integrating the conductivity of different propped and unpropped fracture segments through hydraulic–electric analogies. Specifically, for propped fracture segments, the proppant pack permeability was described by simultaneously considering the viscous shear from fracture walls, stress sensitivity, and multiple- or single-proppant-layer placement, while the dynamic width was controlled through proppant pack compaction and proppant embedment. In unpropped fracture segments, as self-supported fracture surface deformation changes the fracture compressibility, the stress-dependent compressibility was utilized to depict the dynamic width. The developed propped and unpropped fracture conductivity models were separately verified against experimental measurement data. Through the hydraulic–electric analogies, a new partially propped fracture network conductivity model was established. For propped fracture segments, an increase in the proppant pack compressibility significantly reduced the fracture conductivity, particularly under high-stress conditions. A larger initial propped fracture aperture offered higher fracture conductivity under identical stress conditions. For single-layer propped fractures, a decrease in the fracture surface elastic modulus from 15 GPa to 10 GPa slightly reduced the fracture conductivity due to greater proppant embedment. For unpropped fractures, a larger compressibility reduction rate (lower fracture compressibility) led to better fracture conductivity maintenance. The fracture network conductivity was dominated by the unpropped fracture segment conductivity when the unpropped length reached 45.5% of the total fracture network length.

Assessment of large-scale heterogeneity due to toughness variations in a multipass weld: brittle failure mechanisms and modeling

The fracture surfaces of 49 SE(B) toughness tests performed on five different geometries, were carefully investigated by SEM imaging and cross-section analysis. The specimens were extracted from a large multi-pass weld in T-S orientation. The failure characteristics were associated with three distinctly different zones of the weld. Transgranular fracture occurred primarily in the reheated zone and in the as-welded zone with a dendritic microstructure inclined relative to the crack plane. With a dendritic microstructure aligned with the crack plane intergranular fracture occurred. The toughness of the as-welded zone with a low inclination angle, was significantly lower than that obtained in the other two weld zones. Due to the relatively large size of the zones compared to the fracture process zones of the tests, it is appropriate to characterize the failure behavior as large-scale heterogeneity. Weakest-link modeling may be applied locally in each weld zone, giving rise to three different sets of model parameters. A new calibration technique is introduced and used to fit a local weakest-link model to the toughness distribution curves of the individual zones.

Flexural Behavior of Blended Slurry-Infiltrated Fibrous Concrete Boards Made with Hybrid fibers and Nano Slag

High volume fraction of fibers with notable improvements in strength, durability, ductility, and toughness are the main fundamental advantages of slurry infiltrated fibrous concrete (SIFCON). The experimental study presented in this work examines the flexural behavior of composite boards made of SIFCON. It also looks into the effect of hybrid fiber reinforcement on toughness and strength characteristics, as well as the addition of binary and ternary blends of SIFCON under flexural loading. Thirty boards measuring an effective span of 300 mm, width of 150 mm and 25 mm thickness were cast and tested at 28 days in order to examine the toughness, flexural strength, load-deformation and microstructural analysis characteristics. Various volume fractions of steel and plastic fibers of (8+0, 7+1, 6+2, 5+3, and 4+4%) respectively were used. After that, the specimens were divided into two groups: binary (cement+ micro silica) and ternary (cement+ micro silica+ nano slag). Also, a SEM test was used to track microstructural features of fractured surfaces. The results showed that adding nanomaterials clearly enhanced the microstructure's density and decreased the number of pores in the SIFCON boards that were created. Moreover, the steel fiber demonstrated a 40% increase in flexural strength compared to the hybrid fiber system composed of 4% steel fiber and 4% plastic fiber in the binary blend. In the ternary blend, this difference was reduced to 34%. Additionally, the incorporation of nano slag enhanced the strength properties of the produced SIFCON mixes by up to 22% in the ternary blends.

A centroid iterative method for fitting the femoral neck axis in rotational osteotomy: a finite element analysis and biomechanical investigation

Abstract The femoral neck axis (FNA) is an important reference in femoral neck rotational osteotomy, which is a hip preservation procedure. The purpose of this study was to propose a method for determining the FNA with high accuracy and reliability and to evaluate the effect of FNA determination accuracy on the stress and strain distribution in the proximal femur. Femoral computed tomography data from 50 patients were reconstructed, and the FNA was fitted by the centroid iterative method. The fitting accuracy was evaluated in terms of the distance between the femoral head centre and the FNA. The reliability was assessed by intraclass correlation coefficient (ICC). Stress–strain distributions of the native femur model and rotational osteotomy models with accurate FNA and deviated FNA were simulated by finite element analysis and digital image correlation methods. The distance between the femoral head centre and the FNA was 1.24 ± 0.35 mm. The intra- and interobserver reliability was high, with ICC values of 0.960 and 0.924, respectively. The maximum von Mises stress was 25.76 MPa, 50.82 MPa, and 93.24 MPa for the native femur model, accurate FNA model, and deviated FNA model, respectively. The finite element strain distributions were linearly correlated with digital image correlation results. The centroid iterative method for FNA fitting has high accuracy and reliability. Accurate determination of the FNA reduces stress concentration in the proximal femur and decreases the risk of subsequent fracture and non-union of the osteotomy surface.

Experimental investigation on vibration characteristics and damping factor of coir fiber reinforced polyester composite material

This research aimed to investigate the composite material composed of polyester with randomly oriented short coir fibers with a length of 10 mm and varying weight percentages from 5 to 20%. The composite material was fabricated by the hand layup method. The tensile strength, flexural strength, hardness, impact strength, free vibration analysis, and damping characteristics were studied; the SEM images were used to analyze the fractured surface of the composite specimens. The current empirical study identified a conspicuous association between the gradual escalation in fiber content for the natural frequency and the damping attributes of the composite material. The test results showed that the composite with 15% coir fibers worked best for several studies examining characteristics over a wide range of temperatures and frequencies. Coir-based composite material yields a natural frequency of 61,862 Hz and a maximum damping ratio (ζ) of 0.29592, indicating enhanced rigidity and vibration absorption capabilities. The damping factor (tan δ) reached a notably low value of 0.360 at a 10 Hz frequency with 15 wt.% fiber content, demonstrating improved energy dissipation. The results show that polyester composites containing 15% wt.% coir fibers have the best mechanical and damping properties, making them a sustainable choice for industrial uses that need to reduce vibrations.

Reprocessing of natural and artificial UV aged acrylonitrile-butadiene-styrene

In the present study, the influence of reprocessing of aged acrylonitrile-butadiene-styrene (ABS) was investigated on the mechanical properties, melt flow index and morphology. Virgin ABS granules were injection molded into the shapes of the tensile, flexural and impact samples to determine the mechanical, rheological and morphological properties. Then, samples were exposed to two controlled environments, namely artificial accelerated ageing in a QUV chamber (simulating outdoor weathering with alternating cycles of ultraviolet (UV) light and moisture at controlled elevated temperature) for up to 15 days and natural ageing in Gebze (Turkey) for up to 1 year between February 2019 and February 2020 to determine the effect of a long-term outdoor exposure on the properties. After these weathering stages, naturally and UV aged samples were ground and the ground samples were blended with virgin ABS polymer at different ratios (25%, 50% and 75% by weight). The mixed materials were molded again to fabricate test samples and then characterized. In conclusion, in current work, the mechanical, rheological and morphological properties of virgin, aged in outdoors for 12 months, aged in UV chamber for 15 days and blends of virgin-aged ABS were investigated. Both natural and UV ageing caused aesthetical changes. Results showed that the tensile strength, elongation at break, flexural strength, deflection and impact strength reduced after 12 months exposure to natural ageing and 15 days exposure to UV ageing. However, MFI increased after 12 months exposure to natural ageing and 15 days exposure to UV ageing. An increment in the tensile strength, elongation at break, flexural strength and deflection was found with the incorporation of virgin ABS to 12 months naturally aged and 15 days UV aged samples. It was seen that the natural ageing, UV ageing and the reprocessing did not cause a significant change in the morphology of fractured surfaces.

Experimental and Numerical Investigation of Constant-Amplitude Fatigue Performance in Welded Joints of Steel Tubular Flange Connections for Steel Structures

Welded joints of tubular flange connections (TFCs) for steel structures are prone to cumulative fatigue breakdown under oscillatory loading regimes. This study investigates the constant-amplitude fatigue performance of these welded connections through combined experimental testing and finite element analysis. Seven tubular flange connection specimens were subjected to constant-amplitude fatigue tests, and the nominal stress range approach was employed to establish S-N curves for the TFC welds, which were then compared with existing design codes. Stress concentration behavior at the weld toe was analyzed using ABAQUS finite element software. Macro- and micro-scale examinations of fatigue fracture surfaces were conducted to elucidate the fatigue crack mechanisms. The results demonstrate an allowable stress range of 82.41 MPa at a 2-million-cycle fatigue strength, exceeding the specifications of current fatigue design codes. The finite element analysis shows that there is a significant stress concentration at the weld toe of the steel tube–flange weld, and the uneven stress distribution in the circumferential direction of the weld makes this position more prone to fatigue failure, which is consistent with the experimental phenomena. The derived fatigue design method for TFCs provides practical guidance for engineering applications.

Experimental study on the long-term conductivity of self-support fracture in deep shale reservoirs

Reservoir modification fracturing technology is one of the key technologies for the effective development of deep shale gas reservoirs. But the low initial production and fast decreasing after fracturing deep shale gas wells restrict the efficient development of deep shale gas. Many stratification fracture surfaces and tensile fracture surfaces were prepared by using a high-precision 3D morphological scanner and carving machine. How the flat fracture surfaces’ long-term hydraulic conductivity was affected by temperature and closure pressure was investigated. Additionally, the influence of closure stress and fracture surface type on the long-term hydraulic conductivity of self-supported fracture surfaces was examined by using a self-developed high-temperature and high-pressure fracture conductivity tester. The patterns of change and main control factors of the long-term hydraulic conductivity of fractures in deep shale reservoirs are aimed to be clarified. The results of the study show that the long-term flow infiltration capacity of self-supported fracture surface was affected by the closure stress and temperature. In experiments examining the impact of closure stress on the long-term infiltration capacity of flat plate cracks, there remains a pattern in the infiltration capacity. Initially, the crack infiltration capacity decreases relatively quickly before 20 h. This rapid decrease slows down as time progresses from 20 to 50 h. Beyond 50 h, the infiltration capacity of the cracks essentially stabilizes. When comparing the results under the same proppant conditions, it’s clear that a higher closure stress leads to a more rapid decrease in crack infiltration capacity. Furthermore, the final stable infiltration capacity of cracks in the experimental group subjected to large closure stress is notably smaller compared to that of the group with small closure stress. This indicates that closure stress plays a significant role in determining the long-term infiltration performance of flat plate fractures. In the experiments of supported cracks and self-supported cracks, the higher the temperature, the smaller the inflow capacity, and the decrease is gradually reduced; the conductivity of self-supported cracks decreases rapidly, and at 20 h, the inflow capacity decreases to about 1% of the initial value. Under the same conditions, the infiltration capacity of stratification fracture surface is higher than that of tensioned crack surface. The results of this paper can provide certain reference significance for the design and construction of oilfield site fracturing, and then provide certain contribution to the improvement of oil and gas recovery.

Research on the Impact Toughness of 3D-Printed CoCrMo Alloy Components Based on Fractal Theory

In order to obtain high-performance 3D printed parts, this study focuses on the key performance indicator of impact toughness. The parametric modeling software Rhino 6 is used to design impact specimens, and the laser selective melting equipment DiMetal-100, independently developed by the South China University of Technology, is used to manufacture impact specimens. Subsequently, the CoCrMo alloy parts were annealed using an MXQ1600-40 box-type atmosphere furnace and subjected to impact testing using a cantilever beam impact testing machine XJV-22. Fractal theory was applied to analyze the fractal behavior of the resulting impact fracture surfaces. The research results indicate that the 3D-printed impact specimens exhibited excellent surface quality, characterized by brightness, low roughness, and the absence of significant defects such as warping or deformation. In terms of annealing treatment, lower annealing temperatures did not improve the impact performance of SLM-formed CoCrMo alloy parts but instead led to a decrease in toughness. While increasing the annealing temperature can improve toughness to some extent, the effect is limited. Furthermore, the relationship between impact energy and heat treatment temperature exhibits a U-shaped trend. The fractal dimension analysis shows that the parts annealed in a 1200 °C furnace have the highest fractal dimension and better toughness performance. This study introduces a novel approach by comprehensively integrating advanced 3D printing technology, annealing processes, and fractal theory analysis to systematically investigate the influence of annealing temperature on the impact properties of 3D-printed CoCrMo alloy parts, thereby establishing a solid foundation for the application of high-performance 3D printed parts.

Fatigue Properties of Methacrylic Adhesive Plexus MA300.

This study investigates the fatigue durability of Plexus MA300 methacrylic adhesive, which is employed in structural joints of metals, plastics, and composites. Cast adhesive specimens were subjected to cyclic tensile loads at a frequency of 5 Hz with a stress ratio R = 0.1. Six load levels were tested. Hysteresis loops were recorded during testing and analyzed in detail. Significant differences in fatigue fracture characteristics were observed depending on load level. Specimens subjected to high loads exhibited a characteristic radial structure with a distinct crack initiation point, whereas specimens tested at lower loads showed more uniform, matte fracture surfaces. Hysteresis loop analysis revealed phenomena typical for polymers: creep and damping causing energy dissipation. Various fatigue approaches were compared: stress-based, strain-based, energy-based, and stiffness-based. The highest coefficient of determination (R²) was obtained for the model based on strain energy density, indicating its superior utility in predicting the fatigue life of the tested adhesive. The obtained results contribute to the understanding of the fatigue behavior of methacrylic adhesives and provide practical data for structural joint design involving this material class.

Effect of Ni Content and Tempering Temperature on Hydrogen Embrittlement of SA372 Steels for Pressure Vessel

This study investigates the influence of grain boundary characteristics on hydrogen embrittlement in SA372 steels by varying Ni content and tempering temperature. Microstructural characteristics and mechanical properties were analyzed to understand hydrogen trapping behavior, followed by an in-situ slow strain-rate test (SSRT) to assess hydrogen embrittlement resistance and hydrogen-induced fracture behavior. A higher tempering temperature reduces the density of reversible hydrogen trap sites, such as dislocations, thereby decreasing the steel’s resistance to hydrogen embrittlement. However, key factors influencing hydrogen trapping, including lattice sites, dislocations, grain size, and tensile strength, remained unchanged regardless of Ni content. Consequently, the hydrogen content measured through thermal desorption analysis (TDA) was also consistent. The fraction of Σ3 grain boundaries was the only factor that increased with higher Ni content, indicating a potential role in hydrogen embrittlement. The SSRT results demonstrated that at elevated tempering temperatures, higher Ni content reduced hydrogen embrittlement resistance, leading to intergranular fractures on the fracture surface. This reduction in resistance was attributed to hydrogen accumulation along prior austenite grain boundaries, facilitated by dislocation pile-ups and its diffusion along Σ3 grain boundaries. At lower tempering temperatures, however, the effect of Ni content on hydrogen embrittlement resistance was less significant, as intergranular fractures were primarily associated with high dislocation density rather than Σ3 grain boundaries.

Strengthening Mechanism of Cold-Rolled Co-Based Super Alloy for Diaphragm Valves under Room Temperature Tensile Loading

Cold-rolled Co-Cr-Ni alloy (Elgiloy) and Co-Ni-Cr alloy (SPRON 510) can be considered for diaphragm valve materials in gas valve systems. In this study, the effect of direct aging (DA) heat treatment on the tensile properties of Co-based alloys was investigated and the influence of microstructural changes on the tensile behavior was examined. The Co-Cr-Ni Elgiloy alloy exhibited a hexagonal close packed (HCP) phase formation through strain induced martensite transformation (SIMT) in both as-rolled and DA conditions, promoting finer grains due to increased sub-structured and recrystallized grains. In contrast, the Co-Ni-Cr SPRON 510 alloy showed a face centered cubic (FCC) single phase with a higher precipitates fraction and dislocation density. Both Co-based alloys showed improved hardness and strength after DA treatment, with the Co-Cr-Ni alloy demonstrating higher tensile strength and the Co-Ni-Cr alloy exhibiting higher yield strength and elongation. The Co-Cr-Ni alloy revealed fine shallow dimples and cleavage fracture mode, while Co-Ni-Cr showed larger dimples and river patterns on tensile fracture surfaces. The Co-Cr-Ni alloy’s deformation behavior was dominated by active SIMT due to low stacking fault energy (SFE), while the Co-Ni-Cr alloy primarily formed deformation twins due to higher SFE. The high tensile strength of the Co-Cr-Ni alloy was dominated by hardening effects due to a relatively fine grain size and SIMT behavior, while the high yield strength of the Co-Ni-Cr alloy was dominated by deformation twin, dislocation density, Taylor factor and high precipitate fraction.

Microstructure and Mechanical Properties of Dual‐Phase FeCoCrNiAl0.6 High Entropy Alloys Prepared by Laser Directed Energy Deposition

Recently, dual‐phase high‐entropy alloys with excellent strength–ductility combination have attracted widespread attention in the scientific community. Herein, three dense and crack‐free dual‐phase FeCoCrNiAl0.6 high entropy alloys (HEAs) were successfully prepared by laser directed energy deposition (LDED) via adjusting laser scanning speed. The alloys printed have formed fine columnar face‐centered cubic (FCC) dendrites and woven mesh body‐centered cubic (BCC) interdendrites. The BCC phase is further composed of nanoscale A2 and B2 phases formed by spinodal decomposition. As the laser scanning speed increased from 5 mm s−1 to 9 mm s−1, the fraction of FCC phase increased from 56.9 to 70.5%, and the size of FCC dendrites refined. The sample printed at 9 mm s−1 with an average grain size of 3.9 μm showed a comprehensive mechanical property, namely, a high yield stress and ultimate tensile stress (712.0 and 1121.9 MPa) and a total elongation of 16.5%. The fracture surface changed from a cleavage‐type facet to ductile dimples as the laser scanning speed increased. Based on the microstructures of base materials, it can be concluded that the fine microstructure and soft FCC phase can prevent the initiation and propagation of microcracks and, thereafter, alleviate the brittle failure.

Effects of process parameters on dynamic and static load capacity of EN AW-2024-T3 aluminum alloy joints prepared by friction stir welding

This study investigates the impact of friction-stir welding (FSW) process parameters on the mechanical performance and fracture behavior of EN AW-2024-T3 aluminum alloy joints. A series of static and dynamic mechanical tests were conducted on six welded samples, revealing that the joint strength and fracture characteristics are highly sensitive to FSW parameters, particularly tool rotational rate, pin length, and traverse speed. Sample III, which exhibited the optimal combination of parameters, achieved the highest static load capacity, reaching 98.5% of the raw material's strength. Dynamic testing further confirmed Sample III's superior performance, with the highest recorded load capacity and significant energy absorption, as evidenced by ductile fracture features and high surface roughness. In contrast, Sample V, characterized by an excessive pin length, showed the lowest static and dynamic strength, along with a brittle fracture mode. The surface topography and SEM analysis of fracture surfaces indicated that optimized FSW conditions promote a ductile fracture mode, enhancing joint toughness under dynamic loading. These findings underscore the critical role of process parameter optimization in improving the mechanical properties and fracture resistance of FSW aluminum joints, making them more suitable for applications subjected to static and dynamic loading.

Failure process and fracture surface analysis of aluminum-steel tubular joints fabricated by magnetic pulse crimping under fatigue loading

Failure process and fracture surface analysis of aluminum-steel tubular joints fabricated by magnetic pulse crimping under fatigue loading

Quantitative characterization of fracture surfaces of granite specimens under triaxial extension using SEM and deep learning

Quantitative characterization of fracture surfaces of granite specimens under triaxial extension using SEM and deep learning