Fracture Surface Research Articles

Short Crack Behavior of an Additively Manufactured Ti–6Al–4V Alloy Under Ultrasonic High Cycle Fatigue Testing

ABSTRACTThe high cycle fatigue (HCF) behaviors of an additively manufactured (AM) Ti–6Al–4V alloy with fully lamellar microstructures processed electron beam powder bed fusion (EB‐PBF) and wire‐fed electron beam directed energy deposition (Sciaky) routes were compared. Ultrasonic fatigue (USF) testing at the stress ratio of R = −1 was applied to monitor the growth of small cracks initiated at surface micronotches. Crack growth rates lower than 10−8 (m/cycle) at ΔK = 6 MPa·m1/2 were measured in samples processed by both methods. The finer α lath thickness (~1 μm) of the Sciaky samples resulted in a slower fatigue crack growth rate than the EB‐PBF samples with coarser laths. The interaction of cracks with the lamellar microstructures was characterized by electron backscatter diffraction. Crack propagation largely followed the lath interfaces in the Sciaky samples, whereas cracks cut across colonies in the EB‐PBF samples. Different fatigue fracture surface characteristics were observed for the EB‐PBF and Sciaky samples.

Investigation of Combined Aging and Mullins Stress Softening of Rubber Nanocomposites

The present study investigated the effects of thermal aging, ultraviolet radiation (UV), and stress softening on the performance properties of rubber modified with Cloisite Na+ or Cloisite 20A. Tensile strength (TS), strain at break (SB), modulus, and the retention coefficient were measured before and after aging. Results showed that TS and SB decreased by about 50% after 7 days of aging for all tested samples due to the breakage of the chemical bonds between rubber and nanoparticles. The modulus at 300% elongation increased by 20%, 15%, and 7% after thermal aging for the unmodified sample, nanocomposites with Cloisite Na+, and Cloisite 20A, respectively. The shape retention coefficient of all samples was not affected by heat, except for the virgin rubber sample, which exhibited a decrease of about 15% under thermal aging. The virgin matrix and nanocomposites showed different values of aging coefficient during thermal aging and UV radiation. The dissipated energy of samples that were aged after stretching was slightly higher than that of samples that were aged after stretching due to the breakdown of the bonds within the nanocomposites. Loading-reloading energy results showed that the level of stress softening was lower when Mullins was applied after the aging of the samples. Differential scanning calorimetry results indicated a slight decrease in Tg1 in the aged and stretched samples and an increase in the temperature of the first endothermic peak due to the addition of nanofillers in the stretched and aged samples. Thermogravimetric analysis revealed that all tested samples exhibited similar thermograms, regardless of their state of stretching or aging. Scanning electron microscopy analysis showed that the fracture surface of the virgin unaged sample was rough with some holes, while it was flatter and less rough after aging.

Enhancing the Self-Healing Efficiency of Ti3AlC2 MAX Phase via Irradiation.

Self-healing materials are highly desirable in the nuclear industry to ensure nuclear security. Although extensive efforts have been devoted to developing self-healing materials in the past half century, very limited successes have been reported for ceramics or metals. Here, we report an intrinsic self-healing material of Ti3AlC2 MAX phase, which exhibits both ceramic and metallic properties, and a strategy for further enhancing the self-healing via irradiation is proposed. Quantitative in situ transmission electron microscopy tensile testing reveals that the fracture strength of 1.58 GPa is achieved on thoroughly fractured Ti3AlC2, corresponding to the self-healing efficiency of 19.8%, which is increased to 28.1% after irradiation. In situ irradiation experiments, atomic-resolution characterizations, and molecular dynamics simulations reveal that spontaneous rebonding of partial atoms on fracture surfaces is responsible for the self-healing, and irradiation-enhanced atomic migration, interplanar spacing increment, and gap-filling contribute to the self-healing enhancement.

Investigating the influence of ferric oxide grade alumino‐silicate cenosphere particulates and heat treatment on the microstructural evolution and mechanical properties of Al6061/ferric oxide alumino‐silicate cenosphere (x weight %) composite

AbstractThe main aim of this investigation is to fabricate aluminum 6061 composites with three different weight percentages of ferric oxide grade alumino silicate cenosphere (1 wt.%, 3 wt.%, and wt.%) by the stir‐casting process. The fabricated cast composite and T6 heat‐treated composite is used to obtain a fundamental understanding of various weight percentages of the cenosphere and the influence of heat treatment on the microstructural changes, mechanical characteristics, the mechanism of fracture, and the interface between the aluminum‐matrix and ferric oxide grade alumino‐silicate cenosphere particulates. Tensile and compressive tests with a constant strain rate (0.5 mm ⋅ min−1) were carried out to study the strength and to find a correlation between the various weight fractions of cenosphere and heat treatment. Investigations of the changes in the microstructure of the aluminum ferric oxide grade alumino silicate cenosphere composite and the fractography of the fracture surface are investigated using optical and scanning electron microscope. X‐ray diffraction was utilized to confirm the results obtained from optical and scanning electron microscope analyses for phase characterization validation. A maximum of 30 % increase in hardness value, 20 % increase in tensile strength value, 33 % increase in maximum compressive strength value, and 2 % increase in elongation values are observed in heat‐treated composite when compared to cast composite.

Fracture analysis under modes I and II of adhesive joints on CFRP in saline environment

This study analyzes the delamination behavior of adhesive joints after exposure to a saline environment for zero, one, and twelve weeks. Delamination was assessed under static and fatigue loading conditions in fracture Modes I and II, with a detailed analysis of fracture surfaces using Scanning Electron Microscopy (SEM) and Backscattered Electron (BSE) detection. The 3D images reveal significant morphological differences in fracture surfaces, showing variations in fatigue lines and the presence of impurities depending on the fracture mode. A probabilistic fatigue life analysis was performed using a Weibull regression model, showing notable changes, especially in Mode I at a high number of cycles. A chemical analysis using EDX and FTIR-ATR complemented the mechanical study, revealing an increase in sodium and chlorine concentrations with prolonged saline exposure. Oxidative degradation was also observed, with carbonyl groups increasing significantly over time, particularly in areas most exposed to the saline mist.

Interphase mechanics vs chemical compatibility: Generating a deformable PA6-carbon fiber interphase

Good interfacial adhesion is typically correlated to obtaining the best tensile/flexural performance for carbon fibre-reinforced composites. The nature or even presence of the interphase, a localized region around the fibre-matrix junction, is often discussed but notoriously difficult to visualize and characterise. Here, a surface-initiated electro-polymerization approach to covalently graft either polyacrylamide or polygylcidyl methacrylate to the carbon fibres was used. This was followed by continuous melt compounding into the polyamide-6 matrix prior to injection moulding. Analysis via X-ray photoelectron spectroscopy (XPS) coupled with topological/visual study through scanning electron microscopy (SEM), showed distinct surface changes after modification and at the composite fracture surface. Additionally, mechanical (tensile, flexural, and tribological characteristics) and thermal (differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA)) investigations were performed. The results showed that the unmodified CF samples exhibit higher tensile and flexural modulus than the modified CF samples. However, the wear rate has been significantly decreased for modified CF samples. SEM of fractured composite surfaces showcased a clear interphase region surrounding the fibre, highlighting the importance of interphase/interphase mechanics in the design of optimal composite interfaces.

Characterization of different size reinforcement effects on microstructural failure mechanism in carbon nanotube-reinforced aluminum composites

In this study, we investigated the effect of reinforcement sizes on the tensile strength and ductility of carbon nanotube (CNT)-reinforced aluminum matrix composites fabricated through ball milling, followed by hot extrusion of a powder encapsulated in an aluminum container. We analyzed the microstructural properties of the samples, including the aluminum grain size, its spatial variation with the alignment of CNT, and CNT length. Nanoindentation test results revealed the spatial variation of hardness and Young’s modulus of composites with small-diameter CNTs, indicating local Al4C3 formation and interlock structure resulting from dislocation accumulation during the fabrication process. This explains dimples of different sizes observed on the fracture surfaces of the samples and the occurrence of CNT pullout. Furthermore, we proposed the failure mechanism of the composites under tensile strain and calculated the failure strain using the Whitehouse–Clyne model. The calculated failure strain agrees well with the experimental values. The high ductility of the composites is attributed to the large grain fracture and rotation of neighboring grains due to the constraint imposed by CNTs.

Mechanical and Tribological Properties of Carbon Fiber Reinforced POM Composite Filled With Maleamidic Acid Treated Carbon Nanotube

ABSTRACTIn order to attain improved mechanical properties of the carbon fiber (CF) reinforced polyoxymethylene (POM) composite, maleamidic acid treated carbon nanotube (CNT) was deposited on carbon fiber. The mechanical properties of composites have been investigated. The tensile strength values of the treated CF/POM composites at all CNT mixing ratios are found to be higher than that of untreated one. The surface morphologies of the fractured surfaces of the composites were recorded using scanning electron microscopy (SEM) to gain information about the fiber–matrix interfacial adhesion in the composites. The friction coefficient of all the CF/POM/CNT composites decrease as the load increases from 10 to 20 N under the same sliding speed of 1000 r/min. XPS results showed that the formation of C–O, C=O, and O–C=O based species give rise to chemical bonds of the CF and the POM.

Green hybrid composites partially reinforced with flax woven fabric and coconut shell waste-based micro-fillers

This research is focused on hybrid green composites using flax woven fabric in which the matrix phase was further reinforced with coconut shell waste-based cellulosic microparticles as fillers. Mesoscale mechanical models were successfully developed to simulate the tensile properties of such hybrid composites based on hybridization of fibers and biobased materials using epoxy resin. S-glass fabrics with plain, twill and biaxial constructions, were used as the outer layers, while plain-woven flax fabric was used as the middle layer. A high level of agreement was observed between the experimental and predicted values. The static tensile tests were followed by cyclic tensile tests, microscopic analysis of fracture surfaces and dynamic mechanical analysis. The influence of the hybrid fabric geometry and combination with biowaste-based micro cellulosic material was observed to significantly influence the tensile properties determined by both experimental and numerical analysis. Dynamic mechanical analysis also validated the quasistatic measurements. A higher storage modulus and loss modulus were registered for the hybrid composites impregnated with a 1 % bio filler-based matrix. The damping factor (tan delta) was lower for the hybrid composites than for the nonhybrid samples and the control samples from the pure matrix. This difference is attributed to the stronger interface between the fibers and the particle-based matrix, which restricts the molecular mobility and increases the stiffness of the composites. Fractographic images were obtained by scanning electron microscopy (SEM) to study the failure modes and mechanisms of the composite samples. The microparticles were uniformly dispersed in the epoxy resin and thus enabled microcracking rather than macrocracks. The failure mainly occurred due to fiber failure, matrix cracking and delamination. Such hybrid composites are useful for exterior and interior components in automotive applications.

Fracture behavior, mechanical properties, and microstructural analysis of vacuum automated GMAW welded dissimilar A353 and A516 steels for pressure vessels

In this study, the performance of the automatic gas metal arc welding (GMAW) process in vacuum for similar and dissimilar joints of A353 and A516 steel plates with different thicknesses was intensively evaluated. Fracture of all vacuum-welded samples occurred in the heat-affected zone (HAZ) of A516 steel, highlighting the significant influence of HAZ microstructure and width on the cryogenic impact energy and strength of these joints. According to microscopic observations and impact tests, the fractures were fully ductile for notches in the weld and A353 HAZ, where dimples were observed on the fracture surfaces and the impact energy exceeded 50 J. This ductile behavior is particularly significant for notches in the weld due to the presence of a vacuum during welding prevents the formation of gas voids and oxide and hydride compounds that are normally the origin of cracks. However, for notches in the A516 HAZ, where the cleavage faces were observed on the fracture surfaces and the impact energy was less than 30 J, the fractures were quite brittle. For dissimilar vacuum-welded samples, the impact energy and fracture type for notches in the weld and A353 HAZ were nearly the same as those in similar A353 joints. However, for notches in the A516 HAZ, the impact energy and fracture type were close to those observed in the A516 joints. Yield strength and ultimate tensile strength (UTS) of A353-A353 non-vacuum-welded samples compared to vacuum-welded samples decreased by more than 78% and 40%, respectively. As well as, yield strengths and UTSs of A516-A516 non-vacuum samples compared to vacuum samples decreased by more than 34% and 4%, respectively. On the other side, the impact samples with a notch position in the weld suffered brittle fracture instead of ductile fracture because their impact energy decreased by about 40%.

XPS analysis of damp heat aged and fractured polymer/glass laminates

Essential for the durability of photovoltaic (PV) modules is the polymeric encapsulant. In addition to the well-established ethylene vinyl acetate copolymers (EVA), polyolefin elastomers (POE) are gaining market relevance. The main objective of this paper was to elucidate the ageing and degradation mechanisms of PV relevant glass laminates based on UV-transparent EVA and POE encapsulants by X-ray photoelectron spectroscopy (XPS).Special focus was given to the polymer/glass interfaces. Therefore, glass laminates were damp heat aged and debonded by monotonic compressive shear testing. Subsequently, the polymer side of the fractured surfaces was characterized by XPS and Fourier-transform infrared spectroscopy (FTIR). The polar EVA encapsulant revealed more pronounced deterioration than the less polar POE material.Significant differences were already discernible after 1kh of damp heat exposure. The diffusion of Na ions from the glass substrate into the polymer matrix and the formation of Na salts at the interface were ascertained for EVA and to a less extent also for POE. While EVA laminates failed primarily close to the interface, but still within the EVA material, glass residues were detected on the fractured POE surfaces indicating interface-near glass corrosion and a fracture path propagating back and forth within POE and glass.

Disclosing Connection Links between Microstructure and Mechanical Performance in Pulsating Current Gas Tungsten Arc Welding of Hastelloy B-2 Superalloy

In this study, welding a Ni-Mo-based superalloy (Hastelloy B-2) was examined in order to characterize the microstructure and mechanical performance of joints along with assessing the effects of current intensity on the microstructure and mechanical responses of different weld zones. The gas tungsten arc welding (GTAW) process was used to weld the samples using ERNiCrMo-2 filler metal. The pulsed current GTAW process was used to weld the superalloy sheets of thickness of 1 mm with background current (Ib) of 20 A and 40 A and peak current (Ip) of 80 A and 60 A. Tensile and Vickers microhardness tests were conducted to evaluate the effect of pulsed current on mechanical properties of the welds along with chemistry and microstructure characterizations. Finally, the fracture surfaces after the tensile test were studied using SEM fractography analysis. The results indicated that increasing Ib and decreasing Ip led to low heat input and high cooling rate resulting in a high thermal gradient. This caused microstructure transition from the columnar dendrites to the coaxial ones in the weld zone; molten metal convection in the fusion zone led to fine grains in the weld zone during welding time. Moreover, a significant decrease in the amount of molybdenum carbides at the interdendritic regions of the weld metal was observed under these conditions. The tensile strength of the weld metal was higher than that of the base metal resulting in the fracture of all welds from the base metal. Additionally, the microhardness results indicated a significant increase for the weld metal compared to both heat-affected zone (HAZ) and base metal. The higher mechanical properties of the weld metal is attributed to the increase in background current and decrease in peak current leading to a fine grain microstructure. Fractography following the tensile test showed a completely ductile fracture.

Achieving balanced mechanical properties in Fe–0.16C plain low-carbon steel by trimodal microstructure and fine cementite

In the present study, for the first time, a trimodal microstructure (including coarse, fine, and ultrafine ferrite grains) was created in plain low-carbon steel by simple thermomechanical processing including intercritical annealing (at 770 °C, 800 °C, and 830 °C), 75% cold rolling, and finally heat treatment at 550 °C. The results showed that martensite with two different morphologies consisting of lath (low-carbon) and plate (high-carbon) were created in the microstructures of 800-75% and 830-75% sheets due to the non-homogeneous distribution of carbon atoms as a result of not using the homogenization treatment. After the final heat treatment, the samples exhibited trimodal grain size distribution of ferrite including coarse grains (larger than 5 micrometers), fine grains (between 1 and 5 micrometers), and ultrafine grains (UFGs) (smaller than 1 micrometer). The formation of ultrafine grains was ascribed to the presence of martensite with lath morphology in the 800-75% and 830-75% samples. The size of cementite particles in the 770-75%-550 sample was larger than the other two samples (800-75%-550 and 830-75%-550) owing to the presence of martensite phase only with plate morphology in 770-75%-550 steel. Unlike the 800-75%-550 sheet, the entire microstructure of the 770-75%-550 and 830-75%-550 samples had not undergone complete recrystallization and several deformed ferrite grains were still visible in the microstructures. The strength and hardness of the heat-treated sheets was larger than that of the as-received steel due to the presence of fine spherical cementite particles and fine ferrite grains in the microstructure of the heat-treated samples. Based on the obtained results, the 800-75%-550 sample revealed the best combination of strength-ductility-toughness due to trimodal microstructure along with the formation of fine spherical cementite particles. The failure mode of all heat-treated samples was ductile and there were both fine and coarse dimples in the fracture surfaces.

Fatigue-induced fracture failure of acrylic-polycarbonate laminated aircraft canopy

The fatigue-induced fracture failure of the aircraft canopy occurred in the poly(methyl methacrylate) (PMMA) layer laminated on polycarbonate (PC) during flight. For more than 24 years, the aircraft had been operated at high altitudes and supersonic flight. To identify the root cause and the mechanism for the formation of the fracture, the fracture surfaces were investigated. The fracture morphologies were characterized using optical microscope (OM) and scanning electron microscope (SEM).In macroscopic observations, the main crack showed a total length of approximately 1.6 m from the front to the right of the crack stop groove when viewed from the front of the canopy. The main crack ran about 0.9 m including partly curved line from the front part to the upper middle one and then reached about 0.7 m in a straight line perpendicular to the right of the crack stop groove. There were two crack ends in the main crack: one was at the lower part of the front, the other was at the right end of the crack stop groove. Numerous macro-cracks visible to the naked eye were distributed only on the front surface of the canopy.In microscopic examination, the voids on the front surface of the outer PMMA layer were formed by the friction heat with air during the supersonic flight. The voids served as the origins, the actual starting point of the crack. The voids slowly grew to macro-cracks vertically or horizontally by the thermal stress during flying at high altitudes. Cracks proceeded in the direction of 90 degrees while being bisected in V-shapes downward from the surface of the PMMA layer with the action of thermal tension. The crack growth represents the typical characteristics of the fatigue crack: multi-origins, ratchet marks, and beach marks. The main crack grew further, forming a slight curved line by connecting adjacent macro-cracks arranged in an almost vertical direction. When crack growth reached a critical point, the catastrophic fracture progressed rapidly from the primary origin of the fatigue crack to both ends due to the action of lateral force. Fast crack zones on both sides showed the same dimple and river patterns.This study explains that the combined and synergistic interaction of the fatigue crack and environmental stresses iteratively occurred on the front surface in the outer PMMA layer of the aircraft canopy due to the continual exposure to high altitudes and supersonic flights, consequently resulting in the fatigue-induced fracture failure.

Characteristics of rock strength failure and identification of hazardous areas in the roof of deep mining stope

The roof of deep mining stopes is notoriously unstable and challenging to manage due to high in-situ stress and deteriorating rock conditions. To address this issue, a comprehensive approach was employed, incorporating indoor physical experiments, numerical simulations, and field tests to investigate the stope roof rock composition characteristics and strength failure modes in the Laoyingshan deep coal mine. The study revealed the distribution characteristics of the high in-situ stress field in this mining area and delineated different levels of hazards in the roof. The results indicate that, under identical lithological conditions, the mineral composition of deep rock formations is complex. Changes in some mineral components and properties were observed, leading to increased expansiveness and water absorption in clay minerals such as sodium montmorillonite and kaolinite within the basic roof layer. In simulated tests of surrounding rock strength in deep mining stopes, as stress levels approached 2 MPa, the damage factor increased, showing a trend of localized concentration. Internal damage began to exhibit noticeable spatial evolutionary expansion patterns and gradual nucleation. When stress exceeded 8 MPa, rocks transitioned from macroscopic fracture surfaces to microscopic fragmentation zones, with a sudden decrease in stiffness degradation values, internal instantaneous collapse, and phenomena akin to “rock burst” under high stress disturbance. In-situ stress testing determined that the stress field in the deep mining zone of Laoyingshan is in a thrust fault stress state, with horizontal stress predominance. The maximum stress direction is predominantly southwest-northeast, with stress magnitude reaching 25.49 MPa. By arranging post-mining and pre-mining borehole observation stations and utilizing image grayscale fracture recognition technology in MATLAB, the roof was classified into four danger levels: “extremely broken,” “broken,” “significant fractures,” and “minor fractures.” Main control measures for coupling grouting in deep-shallow zonation rigidity were proposed based on these classifications.

Synergistic effects of dual reactive compatibilizers for high-performance fully biodegradable polylactic acid/poly (butyleneadipate-co-terephthalate) composites

The PLA-g-(GMA-co-St) graft copolymer (PGS) was prepared using melt-free radical grafting technology, PGS and ESO were simultaneously employed as compatibilizers for the poly (lactic acid)/poly (butylene adipate-co-terephthalate) (PLA/PBAT) blends. The effects of the type and amount of compatibilizers on the properties of the blends were studied. The results reveal that the epoxy groups in PGS and ESO can interact with the terminal groups of PLA and PBAT. The incorporation of either PGS or ESO separately can improve the compatibility between PLA and PBAT to a considerable degree. However, the introduction of both compatibilizers into the PLA/PBAT blends results in a notable shift of the Tg of the two phases, reduces the size of PBAT particles, and makes their dispersion more uniform. This reveals that the dual reactive compatibilizers can achieve a synergistic effect, significantly reducing the interfacial tension between the two phases and facilitating inter-phase dispersion, ultimately forming a more uniform microstructure. Simultaneously, as the amount of ESO added to the blends gradually increases, the vicat softening temperature and complete decomposition temperature of the blends continue to increase, the notched impact strength and elongation at the break of the blend gradually increase and then decrease. When the ESO amount reaches 4 wt%, the performance of each property increases to 88.9 °C, 447.66 °C, 335.16 %, and 23,359.30 J/m2, respectively. At this point, the fracture surface of the blend samples is accompanied by a large-scale plastic deformation. In conclusion, this work represents the first attempt to accomplish synergistic effects via dual reactive compatibilizers. Under the best formulation and processing circumstances, the PLA/PBAT blends greatly increase their overall performance while maintaining biodegradability, hence broadening their application prospects in packaging, agriculture, and disposable tableware.

Experimental investigation on fracture propagation in shale fractured by high-temperature carbon dioxide

The productivity of shale reservoirs was significantly enhanced by the high-temperature CO2 fracturing technique. The injection of high-temperature CO2 into the formation induced rock fracture propagation, creating advantageous pathways for fluid flow. In this research, a self-developed in situ high-temperature convective heat simulation experimental apparatus was employed to systematically conduct simulated experiments on high-temperature CO2 fractured shale under different influencing factors. The experimental results demonstrated that the permeability of CO2 increased as the injection temperature increased. The rock fracture pressure was effectively reduced by high-temperature CO2 fractured shale. Higher complexity was observed in fracture propagation, accompanied by a substantial increase in microcracks and branching fractures. The shale fracture pressure increased with increasing triaxial stress and CO2 injection rate. The confining pressure restricted the further propagation of fractures under relatively high stress conditions, thereby reducing the width and density of fractures, lowering the fracture complexity. Nevertheless, the thermal shock effect of the fluid was exacerbated as the injection rate of high-temperature CO2 increased. The initiation of microcracks was facilitated by the intensification of local thermal stress in shale, inducing multiple curved fractures and forming a more complex fracture network. Compared to horizontal bedding shale, the fracture pressure of vertical bedding shale was relatively higher during high-temperature CO2 fracturing. In addition, the geometric morphology of fracture propagation was more complex, characterized by rougher fracture surfaces, leading to a greater improvement in reservoir reconstruction volume. This research contributed to the optimization of CO2 resource utilization, provided experimental evidence for the application of high-temperature convection fracturing technology in in situ shale conversion projects.

Investigation of the accuracy of multi-input models using deep learning to estimate the tensile shear strength of adhesive joints

The correlation between the fracture surface images and residual tensile shear strength of adhesive joints immersed in water was investigated using deep learning. Multi-input models were used to investigate the effects of input parameters on the estimated strength. Specifically, the immersion time and temperature were added as inputs to the fracture surface image to identify the effects of multiple inputs and the conditions that contribute to the improved estimation accuracy. The estimation results showed that the highest accuracy was obtained when both immersion time and immersion temperature were added as input parameters. The variance in the estimated strength tends to be smaller for each additional parameter. To improve the accuracy of estimation using a multi-input model, approximate trends should be estimated for each input parameter alone. Conversely, the use of input parameters for which the trend cannot be estimated may reduce the estimation accuracy.

Development and performance evaluation of a mechanically triggered release microcapsule based on in-situ polymerization for lost circulation control

Lost circulation is a critical technical challenge in the drilling and production process of underground oil and gas energy. In this study, a mechanically triggered release microcapsule for lost circulation control was designed and prepared with an in-situ polymerization using melamine, urea, formaldehyde, and diglycidyl ether of bisphenol A (healing agent) as raw materials. The structure and properties of the microcapsule were characterized by different techniques. The results show that the healing agent was successfully encapsulated by the resin shell, the median particle size (D50) of the microcapsules is 120.3 μm, and the thermal stability is excellent. The compatibility experiments show that the surface wettability and shear stability of the microcapsules are good in water-based drilling fluid. The compressive strength test reveals that the healing agent in the microcapsule is released and filled in the gap of the plugging zone under the contact pressure. The concentration of microcapsules and the size distribution of rigid particles are critical for the in-situ reinforcement effect. In addition, the fracture plugging performance of the microcapsule was studied. The results show that the pressure-bearing capacity of the plugging zone increases as the irregularity of the fracture surface increases. These findings indicate the microencapsulated healing agent is an effective lost circulation material (LCM), and provide a new technical idea for lost circulation control.

Correction: Image-Based Fracture Surface Defect Characterization Methods for Additively Manufactured Ti-6Al-4V Tested in Fatigue

Correction: Image-Based Fracture Surface Defect Characterization Methods for Additively Manufactured Ti-6Al-4V Tested in Fatigue