Journal articles on the topic 'Residual fracture opening'
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1
Bortolan Neto, Luiz, Aditya Khanna, and Andrei Kotousov. "A new approach to evaluate the performance of partially propped hydraulic fractures." APPEA Journal 53, no. 1 (2013): 355. http://dx.doi.org/10.1071/aj12030.
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A new approach for evaluating the performance of hydraulic fractures that are partially packed with proppant (propping agent) particles is presented. The residual opening of the partially propped fracture is determined as a function of the initial fracture geometry, the propped length of the fracture, the compressive rock stresses, the elastic properties of the rock, and the compressibility of the proppant pack. A mathematical model for fluid flow towards the fracture is developed, which incorporates the effects of the residual opening profile of the fracture and the high conductivity of the unpropped fracture length. The residual opening profile of the fracture is calculated for a particular case where the proppant pack is nearly rigid and there is no closure of the fracture faces due to the confining (compressive) stresses. A sensitivity study is performed to demonstrate the dependence of the well productivity index on the propped length of the fracture, the proppant pack permeability, and the dimensionless fracture conductivity. The sensitivity study suggests that the residual opening of a fracture has a significant impact on production, and that partially propped fractures can be more productive than fully propped fractures. Application of this new approach can lead to economic benefits.
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Zhang, Rui, Zhou Dao Lu, and Jiang Tao Yu. "Determination of Residual Fracture Toughness of Post-Fire Concrete." Advanced Materials Research 712-715 (June 2013): 1062–66. http://dx.doi.org/10.4028/www.scientific.net/amr.712-715.1062.
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Determination of double-K fracture parameter using both analytical and weight function method is carried out in present research. In calculating the cohesive fracture toughness, two situations are divided at critical load. Wedge-splitting tests with ten temperatures varying from 20oC to 600oC are implemented. The complete load-crack opening displacement curves are obtained from which the initial and critical fracture toughness could be calculated experimentally. The validation of double-K fracture model to the post-fire concrete specimens is proved. Meanwhile the weight function method agrees well with the analytical method.
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Krstić, Vladimir D. "Unified Model for Fracture of Brittle Solids." Key Engineering Materials 280-283 (February 2007): 1739–44. http://dx.doi.org/10.4028/www.scientific.net/kem.280-283.1739.
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A unified model for fracture of brittle solid based on crack opening displacement is presented. The model allows the prediction of elastic and fracture response of brittle materials containing spherical and cylindrical pores and polycrystalline solids containing anisotropic residual stresses. The analysis can also be used to predict spontaneous cracking and fracture of two phase systems possessing mismatch stresses.
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Chen, Qingyang, Anjing Tang, and Zhoudao Lu. "Toughness Calculation of Postfire Normal Concrete." Advances in Materials Science and Engineering 2014 (2014): 1–8. http://dx.doi.org/10.1155/2014/452763.
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Fracture tests of postfire normal concrete with ten temperatures up to 600°C are implemented. Residual fracture toughness using analytical method is determined. Two situations are divided at critical load when calculating the cohesive fracture toughness. The initial and critical fracture toughness could be calculated from the complete load-crack opening displacement curves. Finally, the validation of double-Kfracture model to the postfire concrete specimens is proved.
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Bian, J., and Zx Ge. "Material Test on Strain Fracture and Crack Opening Displacement Based on Digital Image Correlation Method." Archives of Civil Engineering 62, no. 3 (September 1, 2016): 3–22. http://dx.doi.org/10.1515/ace-2015-0079.
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Abstract As a machining technology, welding can cause serious accidents by overloading or operation mistakes. Through analyzing the causes of various welding accidents, we found that the major cause for damage imposed after welding parts are loaded is the fracture of materials. Therefore, studying the influence of welding residual stress on the fracture property of materials is of great significance. This paper applied the digital image correlation technique to study the fracture property of welding parts under the influence of welding residual stress. In addition, standard parts and welding parts were selected to carry out a contrast experiment. Room temperature tensile tests were performed on both standard parts and test pieces after residual stress measurement. Using displacement field and strain field data obtained through VIC-2D software, the stress intensity factor around the crack tip of each specimen under the conditions of small load was calculated and corresponding analysis was carried out.
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Dong, P., and F. W. Brust. "Welding Residual Stresses and Effects on Fracture in Pressure Vessel and Piping Components: A Millennium Review and Beyond." Journal of Pressure Vessel Technology 122, no. 3 (April 10, 2000): 329–38. http://dx.doi.org/10.1115/1.556189.
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In this paper, the recent advances in weld residual stress modeling procedures are first reviewed within the context of pressure vessel and piping applications. A typical pipe girth weld was then used as an example to highlight some of the critical issues in weld residual stress prediction, measurement, and residual stress effects on various aspects of fracture behaviors from stress intensity factor solutions for a growing crack to crack-opening displacement calculations for leak-before-break assessment. Finally, the future needs in improved fracture mechanics procedures by incorporating the rapidly expanding knowledge on weld residual stresses are summarized with respect to pressure vessel and piping applications. [S0094-9930(00)02103-X]
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Chen, Jing, and Zhoudao Lu. "Crack Extension Resistance of Normal-Strength Concrete Subjected to Elevated Temperatures." Advances in Materials Science and Engineering 2014 (2014): 1–12. http://dx.doi.org/10.1155/2014/683756.
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Determination of the residual crack extension resistance curves (KR-curves) associated with cohesive force distribution on fictitious crack zone of complete fracture process is implemented in present research. The cohesive force distributes according to bilinear softening traction-separation law proposed by Petersson. Totally ten temperatures varying from 20°C to 600°C and the specimen size of230×200×200 mm with initial-notch depth ratios 0.4 are considered. The load-crack mouth opening displacement curves (P-CMOD) of postfire specimens are obtained by wedge-splitting method from which the stress intensity factor curves (K-curves) are calculated. In each temperature, with the distribution of cohesive force along the fracture process zone, the residual fracture toughnessKR(Δa) increases with increasing crack lengthΔa, whereas theKR-curves decrease with increasing temperaturesTmfor the thermal damage induced. The stability analysis on crack propagation demonstrates that when the residualKR-curve is higher thanK-curve, the crack propagates steadily; otherwise, the crack propagates unsteadily.
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Khanna, Aditya, Luiz Bortolan Neto, and Andrei Kotousov. "Effect of residual opening on the inflow performance of a hydraulic fracture." International Journal of Engineering Science 74 (January 2014): 80–90. http://dx.doi.org/10.1016/j.ijengsci.2013.08.012.
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Lee, Jung Suk, Kwang Ho Kim, Jae Hwan Han, and Dong Il Kwon. "Evaluation of Mechanical and Fracture Characteristics Using Instrumented Indentation Technique." Materials Science Forum 539-543 (March 2007): 2210–15. http://dx.doi.org/10.4028/www.scientific.net/msf.539-543.2210.
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The material characterization on the weak points of the structural systems is essential to evaluate safety accurately. However, general material characterization methods such as uniaxial tensile test and CTOD (crack tip opening displacement) test are destructive, therefore, it cannot be applied to the system in use. To overcome this problem, the material characterization using instrumented indentation technique was developed. However, current researches on instrumented indentation technique focus on the hardness measurement. The evaluation of flow property, residual stress and fracture toughness using instrumented indentation technique is not sufficiently performed. In this paper, we introduce the evaluation method of the flow property, the residual stress near the weldment and the fracture toughness developed from damage mechanics. The algorithm of flow property evaluation, the residual stress evaluation model and the fracture toughness model by using indentation were verified comparing with the experimental results.
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Lu, Zhou Dao, and Neng You. "Determination of Double-G Fracture Parameters of Post-Fire Concrete." Advanced Materials Research 746 (August 2013): 348–51. http://dx.doi.org/10.4028/www.scientific.net/amr.746.348.
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Double-G fracture model was recently proposed based on the conception of energy release rate to describe the fracture behaviour on cracked concrete. Two fracture parameters, i.e., the initiation fracture energy releaseGIciniand the unstable fracture energy releaseGIcun, are termed to distinguish the different crack propagation stages undergoing during the whole fracture process in concrete. In present work, following the Double-G fracture model at ambient temperature, the residual Double-G fracture parameters of post-fire concrete is elaborately introduced. Totally ten temperatures varying from 20oC to 600oC and the specimens size of 230×200×200 mm with initial-notch depth ratios 0.4 were considered. Wedge-splitting method is adopted to measure the loadcrack mouth opening displacement curves (PCMOD) and double-G fracture parameters are experimentally determined.
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He, Xin, Ross Larsen, Fangliang Chen, and Huiming Yin. "Residual Stress and Opening-Mode Fracture Analysis of Multilayered Structures Subjected to Thermal Loading." Journal of Engineering Mechanics 145, no. 3 (March 2019): 04019010. http://dx.doi.org/10.1061/(asce)em.1943-7889.0001579.
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Saruta, Wakiko, Toshiyuki Takahashi, Toshihiro Kumabe, Manabu Minami, Ryo Kanematsu, Hiroya Shimauchi Ohtaki, Ryotaro Otsuka, and Junya Hanakita. "Transdural reduction of a bone fragment protruding into the spinal canal during surgical treatment of lumbar burst fracture: A case report." Surgical Neurology International 12 (August 16, 2021): 406. http://dx.doi.org/10.25259/sni_611_2021.
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Background: There have been many reports on the clinical, radiographic, and surgical management of thoracolumbar burst fractures attributed to high-energy trauma. Interestingly, few reports have described how to extract bone fragments associated with these injuries protruding into the spinal canal contributing to significant neurological deficits. Methods: An 18-year-old male presented with a severe L3-level paraparesis (i.e., loss of motor/sensory function below L3 lower extremity hyporeflexia, and sphincter dysfunction: American Spinal Injury Association [ASIA] Impairment Scale B) following a high-speed crash. The computed tomography and magnetic resonance studies revealed a L3 burst fracture with bone fragments protruding into the spinal canal causing marked cauda equina compression. Following a L3-L4 laminectomy, and opening of the dorsal dura, the bone fragments were ventrally impacted into the fractured L3 vertebral body a pedicle/screw L1-L5 fusion was then completed. Results: One month later, the patient recovered to an ASIA Scale of C, (i.e., residual proximal 3/5 and distal 2/5 motor deficits, with partial sensory sparing). Conclusion: Transdural ventral impaction of protruded bone fragments attributed to high speed lumbar burst fractures contributing to significant cauda equina compression can be safely/effectively accomplished.
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Pieszka, Daniel, Karel Kubečka, and Ivan Kološ. "Post-Cracking Steel Fiber Reinforced Concrete Slabs with Subsoil Interaction." Advanced Materials Research 1020 (October 2014): 210–14. http://dx.doi.org/10.4028/www.scientific.net/amr.1020.210.
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The aim of the paper is to investigate the flexural behavior and property changes of concrete structures reinforced by steel fibers (SFRC) and to use the results for carrying capacity assessment of SFRC post-cracked slab on ground structure with subsoil interaction effect. Because the national codes cover neither design nor assessment of SFRC structures the investigation is generally based on the nonlinear fracture mechanics models to establish the stress-crack opening and load-crack mouth opening displacement relationship. Then the flexural tensile strength and residual flexural tensile strength of the post-cracked SFRC structure is determined with respect to subsoil interaction.
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CHANG, KYONG-HO, and CHIN-HYUNG LEE. "J-INTEGRAL FOR A 3-D INTERFACE CRACK CONFIGURATION IN WELDS OF DISSIMILAR STEELS." International Journal of Modern Physics B 20, no. 25n27 (October 30, 2006): 4201–6. http://dx.doi.org/10.1142/s0217979206041094.
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In this study, path-independent values of the J-integral in the finite element context for an arbitrary three-dimensional interface crack configuration in welds of dissimilar steels are presented. For the fracture mechanics analysis of an interface crack in welds of dissimilar steels, residual stress analysis and fracture analysis must be performed sequentially. In the analysis of cracked bodies containing residual stress, the usual domain integral formation results in path-dependent values of the J-integral. And unlike cracks in homogeneous materials, an interface crack in welds of dissimilar steels always induces both opening and shearing modes of stress in the vicinity of the crack tip. Therefore, this paper discusses modifications of the conventional J-integral that yield path independence in the presence of residual stress and the total J values which can characterize the severity of an interface crack tip in welds of dissimilar steels. A finite element method which can evaluate the J-integral for an interface crack in three-dimensional residual stress bearing bodies is developed using the modified J-integral definition and total J values. The situation when residual stresses only are present is studied as is the case when mechanical stresses are applied in conjunction with a residual stress field.
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Brown, Michael. "The mechanism of melt extraction from lower continental crust of orogens." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 95, no. 1-2 (March 2004): 35–48. http://dx.doi.org/10.1017/s0263593300000900.
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ABSTRACTMelt extraction is a process with a length scale that spans many orders of magnitude. Studies of residual migmatites and granulites suggest that melt has migrated from grain boundaries to networks of leucosome-filled structures to steeply inclined cylindrical or tabular granites inferred to have infilled ascent conduits. For example, in anatectic rocks from southern Brittany, France, during decompression-induced biotite-breakdown melting, melt is inferred to have been expressed from foliation-parallel structures analogous to compaction bands to dilation and shear bands, based on location of residual leucosome, and from this network of structures to ascent conduits, preserved as dykes of granite. The leucosome-filled deformation band network is elongated parallel to a sub-horizontal lineation, suggesting that mesoscale melt flow was focused primarily in the plane of the foliation along the lineation to developing dilatant transverse structures. The leucosome network connects with petrographic continuity to granite in dykes; however, the orientation of dykes discordant to fabric anisotropy suggests that their formation was controlled by stress, which indicates that the process is a fracture phenomenon. Blunt fracture tips and zigzag propagation paths indicate that the dykes represent ductile opening-mode fractures; these are postulated to have formed by coalescence of melt pockets. The structures record a transition from accumulation to draining; quantitative volume fluxes are calculated and presented for the generalised extraction process. The anatectic system may have converged to a critical state at some combination of melt fraction and melt distribution that enabled formation of ductile opening-mode fractures, but fractal distribution of inferred mesoscale melt-filled structures has not been demonstrated; this may reflect the inherent anisotropy and/or residual nature of the drained source. Melt extraction has been modelled as a self-organised critical phenomenon, but the mechanism of extraction is not described and the relationship between these models and the spatial and temporal granularity of lower continental crust is not addressed. Self-organised critical phenomena are driven systems involving ‘avalanches’ with a fractal frequency-size distribution; thus, the distribution of melt batch sizes might be expected to be fractal, but this has not yet been demonstrated in nature.
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Grinys, Audrius, Henrikas Sivilevičius, Darius Pupeikis, and Ernestas Ivanauskas. "FRACTURE OF CONCRETE CONTAINING CRUMB RUBBER." Journal of Civil Engineering and Management 19, no. 3 (June 14, 2013): 447–55. http://dx.doi.org/10.3846/13923730.2013.782335.
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Every year, colossal amounts of used and non-biodegradable rubber tyres are accumulated in the world. Experience shows that the most efficient way to increase the concrete fracture energy G F (N/m) is to use metal or polypropylene fibres. The optimal content of fibre increases concrete resistance to stress (especially tensile stress under bending force). Concrete fracture is not brittle; concrete continues deforming after maximum stresses and is able to resist certain stresses, there is no abrupt decrease in loading. The research has proved that crumb rubber can be used in concretes as an alternative to metal and polypropylene fibres. The investigation has found that rubber waste additives, through their specific properties can partly take up tensile stresses in concrete and make the concrete fracture more plastic; besides, such concrete requires a significantly higher fracture energy and concrete samples can withstand much higher residual strength at 500 µm crack mouth opening displacement (CMOD) and deflection.
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Sakaida, Yoshihisa, and Shotaro Mori. "Two-Dimensional Mapping of Crack-Face Bridging Stresses in Alumina Using Synchrotron Micro X-Ray Beam." Materials Science Forum 571-572 (March 2008): 243–48. http://dx.doi.org/10.4028/www.scientific.net/msf.571-572.243.
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In order to understand an effect of crack-face bridging stress field of alumina ceramics on its fracture toughness, local residual stress distribution due to crack face grain bridging behind the crack tip was measured using synchrotron x-ray beam at SPring-8 in Japan. The SEPB (Single Edge Precracked Beam) specimens of two types of polycrystalline Al2O3 were used for stress measurement; one was pressureless sintered Al2O3 (AL1) and the other was hot-press sintered Al2O3 (TAL). Pop-in precracks were introduced by bridge-indentation method. Before residual stress mapping, the SEPB specimens were unloaded from a constant applied load to zero using four points bending device. Two-dimensional residual stress field was mapped by scanning a micro X-ray beam of 50×50 μm2 with the scanning interval of 12.5 or 25 μm. As a result, in the case of AL1 having conventional fracture toughness and strength, the compressive residual stresses due to crack-face bridging were only observed in the close vicinity of crack tip. On the other hand, in the case of TAL having higher fracture toughness and strength, the compressive residual stresses were widely distributed behind the crack tip. Larger compressive stress was locally generated along the crack path at interlocked grains. The compressive bridging stresses distributed behind the crack tip were found to enlarge with a decrease in the crack opening displacement against a constant applied stress intensity factor, Kapp. It was concluded that the difference in residual stress fields behind crack tip was attributed to the differences in its microstructure and microcrack propagation behavior, such as deflections and interlocked grains.
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Ma, Tian Hui, Chun An Tang, Lian Chong Li, Zheng Zhao Liang, and Yong Bin Zhang. "Numerical Simulation on Fracture Formation on Surfaces of Bi-Layered Columnar Materials." Advanced Materials Research 446-449 (January 2012): 2929–33. http://dx.doi.org/10.4028/www.scientific.net/amr.446-449.2929.
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Parallel fracture formation on surfaces of bi-layered columnar materials like growing tree trunk has been previously studied numerically. In this paper, numerical results of a continuous transition from parallel to polygonal fracture patterns with principal stress ratio provides the clear convincing theoretical explanation for fracture spacing. We perform three-dimensional simulations of fracture growth in a bi-layered columnar model with an embedded heterogeneous layer under inner radial expansion and terminal tension by finite element approach. As a result of this expansion, the bark stretches until it reaches its limit of deformation and cracks. A novel numerical code, 3D Realistic Failure Process Analysis code (abbreviated as RFPA3D) is used to obtain numerical solutions. In this numerical code, the heterogeneity of materials is taken into account by assigning different properties to the individual elements according to statistical distribution function. Elastic-brittle constitutive relation with residual strength for elements and a Mohr-Coulomb criterion with a tensile cut-off are adopted so that the elements may fail either in shear or in tension. The discontinuity feature of the initiated crack is automatically induced by using degraded stiffness approach when the tensile strain of the failed elements reaching a certain value. Numerical results of a continuous transition from parallel to polygonal fracture patterns with principal stress ratio are obtained by varying simulation parameters, the thickness of the material layer. We find that, except for further opening of existing fractures after they are well-developed (saturation), new fractures may also initiate and propagate along the interface between layers, which may serve as another mechanism to accommodate additional strain for fracture saturated layers.
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Ding, Yao, and Yu-Lei Bai. "Fracture Properties and Softening Curves of Steel Fiber-Reinforced Slag-Based Geopolymer Mortar and Concrete." Materials 11, no. 8 (August 15, 2018): 1445. http://dx.doi.org/10.3390/ma11081445.
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Adding short steel fibers into slag-based geopolymer mortar and concrete is an effective method to enhance their mechanical properties. The fracture properties of steel fiber-reinforced slag-based geopolymer concrete/mortar (SGC/SGM) and unreinforced control samples were compared through three-point bending (TPB) tests. The influences of steel fiber volume contents (1.0%, 1.5% and 2.0%) on the fracture properties of SGC and SGM were studied. Load-midspan deflection (P-δ) curves and load-crack mouth opening displacement (P-CMOD) curves of the tested beams were recorded. The compressive and splitting tensile strengths were also tested. The fracture energy, flexural strength parameters, and fracture toughness of steel fiber-reinforced SGC and SGM were calculated and analyzed. The softening curves of steel fiber-reinforced SGC and SGM were determined using inverse analysis. The experimental results show that the splitting tensile strength, fracture energy, and fracture toughness are significantly enhanced with fiber incorporation. A strong correlation between the equivalent and residual flexural strengths is also observed. In addition, the trilinear strain-softening curves obtained by inverse analysis predict well of the load-displacement curves recorded from TPB tests.
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Harhaji, Vladimir, Ivica Lalic, Miodrag Vranjes, Milena Mikic, and Vladimir Djan. "Isolated avulsion fracture of the fibular head." Vojnosanitetski pregled 77, no. 5 (2020): 545–48. http://dx.doi.org/10.2298/vsp171024103h.
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Introduction. Rupture of lateral collateral ligament of the knee is most often joined with other ligament ruptures. Isolated rupture of this ligament is rare and there are few papers about treatment options and results. Here we reported a case of isolated lateral collateral ligament rupture and the treatment outcome. Case report. A patient, 22 years old male, injured his left knee while playing American football. While landing on the outstretched left leg, he felt a sudden pain in his knee. The patient could not continue the competition. Initial orthopedic examination revealed lateral opening and further diagnostic procedure (magnetic resonance imaging) revealed isolated grade III rupture of lateral collateral ligament with avulsion fracture of the fibular head, and distension of anterior and posterior cruciate ligaments. Patient was surgically treated with metal sutures passed through conjoined tendon and proximal fibula. Postoperatively patient worn above knee cast for 6 weeks and after that he was included in rehabilitation. Three and six years after this injury, the patient has still been professional football player with no symptoms and no clinical instability of the knee despite radiological and computed tomography verified pseudoarthrosis of the fractured fibular head fragment. Conclusion. Early diagnostic and absence of additional injuries of the knee leads to a faster and full functional recovery of patients with isolated avulsion fracture of the fibular head, while surgical treatment provides knee stability with no residual ligament instability during sports activities.
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Špaková, Jana, and Ján Dusza. "Comparison of R-Curve Behavior of Si3N4 Measured by Indentation Method and Single-Edge V-Notched Beam Technique (SEVNB)." Key Engineering Materials 409 (March 2009): 308–12. http://dx.doi.org/10.4028/www.scientific.net/kem.409.308.
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Study compare R-curve behaviour of silicon nitride obtained using Vickers indented beam specimens and single edge V-notched beam (SEVNB). R-curve measurement realized by Vickers indented beam was reported by Krause. Crack growth using single edge V-notched beam was observed in situ. The indentation experiments, in comparison with SEVNB method revealed higher R-curve values (KR=3.3 – 4.8 MPa.m1/2). The discrepancy in the R-curve results is attributed to inaccuracy related to the determination of indentation toughness. The indentation fracture toughness may include the aspects of crack opening behaviour, residual indentation stress intensity.
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Fan, Menglong, Chuanyong Chen, Haijun Xuan, Hailong Qin, Mingmin Qu, Songyi Shi, Zhongnan Bi, and Weirong Hong. "Effect of Residual Stress Induced by Different Cooling Methods in Heat Treatment on the Fatigue Crack Propagation Behaviour of GH4169 Disc." Materials 15, no. 15 (July 28, 2022): 5228. http://dx.doi.org/10.3390/ma15155228.
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In this study, the effects of residual stress induced by three different cooling methods during heat treatment on the crack propagation behaviour of the GH4169 disc were investigated. Different levels of stress fields were induced to the specially designed discs by using air cooling (AC), air jetting cooling (AJC) and water quenching (WQ) methods and were quantitated by numerical simulation. These discs were then subjected to prefabricated cracking, and crack propagation tests were conducted on a spin tester with two load spectrums. Crack growth behaviour was depicted via the surface replica technique and fracture morphology. Regarding the linear superposition of residual stress and centrifugal force, the crack propagation behaviour of different discs was simulated using the FRANC3D software. AJC and WQ introduced compressive residual stress (−259 MPa and −109 MPa, respectively) into the disc compared with the AC method (about −1.5 MPa). The AJC method increases the crack propagation life of the disc by introducing residual compressive stress into the area near the surface of the central hole to inhibit the opening of the crack surface. When the fatigue load was low, this inhibition effect was more significant.
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Baldi, Andrea, Allegra Comba, Riccardo Michelotto Tempesta, Massimo Carossa, Gabriel Kalil Rocha Pereira, Luiz Felipe Valandro, Gaetano Paolone, Alessandro Vichi, Cecilia Goracci, and Nicola Scotti. "External Marginal Gap Variation and Residual Fracture Resistance of Composite and Lithium-Silicate CAD/CAM Overlays after Cyclic Fatigue over Endodontically-Treated Molars." Polymers 13, no. 17 (September 4, 2021): 3002. http://dx.doi.org/10.3390/polym13173002.
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The purpose of this in vitro study was to evaluate the external marginal gap variation with a 3D quantitative method and the residual fracture resistance after cyclic fatigue in endodontically treated molars restored with overlays of different materials, with and without fiber posts-supported buildups. Forty-eight human maxillary molars were selected, endodontically treated, prepared with standardized MOD cavities and randomly allocated into 6 study groups considering the “core strategy” (build-up with composite resin; build-up with composite resin supported by a fiber post); and the “restorative material” of the indirect adhesive overlay (GrandioBlocks, Voco; Cerasmart, GC; CeltraDuo, Dentsply). All procedures were executed according with manufacturers guidelines. Micro-CT analysis prior and after cyclic fatigue were executed, followed by scanning electron microscope analysis and fracture resistance test. The Two-Way ANOVA analysis showed that interfacial gap progression was significantly influenced by the “core strategy” (p < 0.01) but not of “restorative material” (p = 0.59). Concerning fracture resistance, “restorative material” was statistically significant (p < 0.01), while “core strategy” (p = 0.63) and the interaction (p = 0.84) were not. In conclusion, the fiber post presence within the build-up promoted a lower interfacial gap opening after fatigue, evaluated through micro-CT scans. In terms of fracture resistance, teeth restored with Cerasmart and Celtra Duo were statistically similar, but superior to GrandioBlocks.
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Wang, Xueli, Dongpo Wang, Lianshuang Dai, Caiyan Deng, Chengning Li, Yanjun Wang, and Ke Shen. "Effect of Post-Weld Heat Treatment on Microstructure and Fracture Toughness of X80 Pipeline Steel Welded Joint." Materials 15, no. 19 (September 25, 2022): 6646. http://dx.doi.org/10.3390/ma15196646.
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In the current study, post-weld heat treatment (PWHT 580 °C) was used for an X80 pipeline steel-welded joint, and the fracture toughness of the welded joint was investigated using a crack tip opening displacement (CTOD) test. The relationship between microstructure evolution and fracture toughness is also discussed in this study. The results showed that the weld center mainly consisted of acicular ferrite (AF). The subcritical heat-affected zone (SCHAZ) consisted of a large amount of fine polygonal ferrite and some AF, and it maintained the rolling state of the base metal. The microstructure of the coarse-grained heat-affected zone (CGHAZ) was composed of granular bainite (GB) and M/A constituents, the latter of which decreased after the PWHT. The CTOD values of the weld center were in the range of 0.18–0.27 mm, while those of the CGHAZ were in the range of 0.02–0.65 mm. A brittle fracture occurred in the CGHAZ for both the as-welded and PWHT samples; the CTOD values were 0.042 mm and 0.026 mm, respectively. The CTOD values of the SCHAZ’s location were in the range of 0.8–0.9 mm. The PWHT did not deteriorate the microstructure of the CGHAZ and had little influence on the fracture toughness of the X80 pipeline steel-welded joint; it ensured the fracture toughness of the welded joints and reduced the welding residual stress.
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Jung, Yeon-Gil, Antonia Pajares, and Brian R. Lawn. "Effect of oxide and nitride films on strength of silicon: A study using controlled small-scale flaws." Journal of Materials Research 19, no. 12 (December 1, 2004): 3569–75. http://dx.doi.org/10.1557/jmr.2004.0454.
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Strength properties of silicon substrates containing dense oxide and nitride surface films are investigated using nanoindentations to introduce small flaws of predetermined scale. The indentation flaws provide favored sites for failure in subsequent flexure loading, even in the subthreshold region for indentations without visible corner cracking, confirming that microflaws generated within the indentation zone act as effective crack sources in the substrate. Deposition of the oxide films increases the strength while the nitride films diminish it at any given indentation load. The strength shifts are attributed primarily to the presence of residual compressive stress in the oxide, tensile stress in the nitride. A fracture mechanics formulation based on a previous analysis for monolithic substrates is here adapted to allow for a superposed crack closing or opening stress-intensity factor term associated with the residual stresses. Allowance is also made in the mechanics for the influence of the film on effective hardness and modulus of the substrate. The formulation accounts for the basic strength shifts and enables evaluation of the magnitude of the residual stresses. The results quantify the susceptibility of basic device materials to damage from small-scale contacts and impacts.
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Hu, Dongyuan, Xvfeng Zhang, Xiaoling Liu, Zhen Qin, Li Hu, Chris Rudd, and Xiaosu Yi. "Study on Toughness Improvement of a Rosin-Sourced Epoxy Matrix Composite for Green Aerospace Application." Journal of Composites Science 4, no. 4 (November 10, 2020): 168. http://dx.doi.org/10.3390/jcs4040168.
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A high temperature epoxy resin was formulated by using a rosin-sourced anhydride-type curing agent, i.e., maleopimaric acid (RAM), and a two-component epoxy consisting of an E51-type epoxy and a solid phenolic epoxy to form a bio-sourced green matrix resin. The glass transition temperature of the final resin was 238 °C Carbon fiber composite prepreg and was manufactured and laminated into composite specimens. Interleaving Toughening Technology (ITT) was applied to the laminates by using Polyamide interleaf veils. The interlaminar fracture toughness and compression after impact (CAI) strength were investigated and showed that the opening Mode I interlaminar fracture toughness GIC and the Mode II interlaminar fracture toughness GIIC of the specimens with interleaves were significantly improved from 227.51 J/m2 to 509.22 J/m2 and 1064.3 J/m2 to 1510.8 J/m2, respectively. Correspondingly, the drop-weight impact test shows that the interleaves reduced the impact damage area from 20.9% to 11.3% of the total area, and the CAI residual strength was increased from 144 MPa to 191 MPa. Meanwhile, mechanical tests showed that the in-plane properties of the interleaved laminates were slightly reduced due to carbon fiber volume fraction reduction. In conclusion, the high glass transition temperature, fracture toughness and CAI behaviour make the green resin matrix composite a potential candidate for aerospace applications.
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Dar, N. U., E. M. Qureshi, A. M. Malik, M. M. I. Hammouda, and R. A. Azeem. "Analysis of circumferentially welded thin-walled cylinders to study the effects of tack weld orientations and joint root opening on residual stress fields." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 223, no. 5 (May 1, 2009): 1037–49. http://dx.doi.org/10.1243/09544062jmes1191.
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In recent years, the demand for resilient welded structures with excellent in-service load-bearing capacity has been growing rapidly. The operating conditions (thermal and/or structural loads) are becoming more stringent, putting immense pressure on welding engineers to secure excellent quality welded structures. The local, non-uniform heating and subsequent cooling during the welding processes cause complex thermal stress—strain fields to develop, which finally leads to residual stresses, distortions, and their adverse consequences. Residual stresses are of prime concern to industries producing weld-integrated structures around the globe because of their obvious potential to cause dimensional instability in welded structures, and contribute to premature fracture/failure along with significant reduction in fatigue strength and in-service performance of welded structures. Arc welding with single or multiple weld runs is an appropriate and cost-effective joining method to produce high-strength structures in these industries. Multi-field interaction in arc welding makes it a complex manufacturing process. A number of geometric and process parameters contribute significant stress levels in arc-welded structures. In the present analysis, parametric studies have been conducted for the effects of a critical geometric parameter (i.e. tack weld) on the corresponding residual stress fields in circumferentially welded thin-walled cylinders. Tack weld offers considerable resistance to the shrinkage, and the orientation and size of tacks can altogether alter stress patterns within the weldments. Hence, a critical analysis for the effects of tack weld orientation is desirable.
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Kutin, Marina, Ivana Vasovic, Mirko Maksimovic, and Marko Ristic. "Prediction of Residual Life Assesment Using Thermography and Crack Growth Analysis." Applied Mechanics and Materials 157-158 (February 2012): 202–9. http://dx.doi.org/10.4028/www.scientific.net/amm.157-158.202.
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The most important characteristics for service safety of complex metal structures are those describing crack initiation and growth caused by static or dynamic, variable loading. Crack initiation and growth is subject of numerous investigations by different methods. The paper shows the possibility of applying infrared thermography to the problems of fracture mechanics. The main aim of testing was to qualitative relate the temperature changes of the spacemen measured by infrared thermography with the evaluation of fatigue cracks in steel specimen. Based on the distribution of temperature on the surface of the sample, during the action of force, the spread of plastic zones and crack tip are determined. The increase of temperature produced by the plastic deformation at the crack tip has been measured by infrared camera Thermal CAM SC640, FLIR Systems. SE(B) specimens were tested in three-point bending (TPB), following the procedures of ASTM E1820, on electrical mechanical testing machine with crack tip opening displacement (CTOD) control, at room temperature. Numerical simulation of stress distribution on the same model under same condition is presented, too. The results showed that thermography is a method suitable for monitoring and prediction of crack initiation and growth, as well as critical stress in elastic and elastic-plastic deformations. Fatigue crack growth behaviour of cracked TPB specimen made of S355 J2 G3 steel using Paris relation is considered.
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Mekayarajjananonth, Trakol, Nattinee Chitcharus, Sheldon Winkler, and Meredith C. Bogert. "The Effect of Fiber Dowel Heights in Resin Composite Cores on Restoration Failures of Endodontically Treated Teeth." Journal of Oral Implantology 35, no. 2 (April 1, 2009): 63–69. http://dx.doi.org/10.1563/1548-1336-35.2.63.
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Abstract In vitro and in vivo testing suggest that fiber posts may reduce the incidence of root fractures of endodontically treated teeth. The purpose of this in vitro study was to compare the effect of fiber post height in resin composite cores on the fracture resistance of endodontically treated teeth. Forty maxillary central incisors were randomly divided into 2 control groups (Groups 1 and 2) of 5 teeth each, and 3 experimental groups (Groups 3, 4, and 5) of 10 teeth each. The teeth in Group 1 had their opening restored with composite resin, the teeth in Group 2 were restored with quartz fiber posts without resin composite cores, and the teeth in Groups 3, 4, and 5 were restored with quartz fiber posts of 2, 4, and 6 mm high, respectively, in 6-mm resin composite cores. Ceramic crowns were fabricated for the specimens. Specimens were positioned in a mounting device and aligned at a 130-degree angle to the long axis of each tooth. A universal testing machine was used to apply constant load at a crosshead speed of 0.5 mm/min until failure occurred. The highest fracture load and mode of failure of each specimen was recorded. The highest fracture resistance force was observed in Group 2 (290.38 ± 48.45 N) and decreased, respectively, in Group 1 (238.98 ± 26.26 N), Group 5 (228.35 ± 58.79 N), Group 4 (221.43 ± 38.74 N), and Group 3 (199.05 ± 58.00 N). According to one-way analysis of variance (ANOVA) and Duncan's test (P ≤ .05), there was no statistically significant increase in the force from Group 3 to Group 5, and the force in Group 2 was significantly higher than that of the experimental groups. There was no statistical significance difference in force among the experimental groups, and the amount of residual tooth structure was found to be the critical factor in fracture resistance. The results suggest that endodontically treated teeth should be restored with the longest possible post height while preserving maximum tooth structure.
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Parker, A. P., S. N. Endersby, T. J. Bond, J. H. Underwood, S. L. Lee, and J. Higgins. "Stress Concentration, Stress Intensity, and Fatigue Lifetime Calculations in Autofrettaged Tubes Containing Axial Perforations Within the Wall." Journal of Pressure Vessel Technology 119, no. 4 (November 1, 1997): 488–93. http://dx.doi.org/10.1115/1.2842334.
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Elastic, elastic-plastic and experimental stress analyses, and fatigue lifetime predictions are presented for thick cylinders containing multiple, axial holes within the wall. The holes are generally semi-elliptical (including semi-circular), and the cylinders are autofrettaged after introduction of the holes and are subsequently subjected to cyclic pressurization of the bore. Two potentially critical failure locations are identified; a fracture-mechanics based design methodology is proposed; elastic and elastic-plastic finite element (FE) analyses are undertaken. The elastic FE analysis predicts hoop stresses at the bore resulting from internal pressurization which are some 7 percent higher than those for the equivalent plain tube. For a given hole size and location and for nominal overstrains of 40 percent or greater, the residual compressive stress at the bore is reduced by approximately 15 percent below the value for a plain tube of the same radius ratio. Two experimental investigations are reported, one based upon X-ray diffraction, to measure residual stresses and stress gradients, and the other based upon radial tube slitting, to measure opening angle. They confirm most features of the residual stress profiles predicted from FE analysis with the exception of high compressive residual stresses and stress gradients immediately adjacent to the hole boundaries. Appropriate use of the residual stress information permits prediction of tube lifetimes for cracks emanating from the bore and from the hole. For the geometry and loading under consideration, the more critical location is predicted to be the hole boundary, the lifetime for failures originating from this point being some 60 percent of the lifetime for cracks originating at the bore.
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Bencardino, Francesco. "Mechanical Parameters and Post-Cracking Behaviour of HPFRC according to Three-Point and Four-Point Bending Test." Advances in Civil Engineering 2013 (2013): 1–9. http://dx.doi.org/10.1155/2013/179712.
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High performance fibre reinforced concrete (HPFRC) is a modern structural material with a high potential and with an increasing number of structural applications. Structural design of HPFRC elements is based on the post-cracking residual strength provided by fibre reinforcement, and for structural use, a minimum mechanical performance of HPFRC must be guaranteed. To optimize the performance of HPFRC in structural members, it is necessary to establish the mechanical properties and the post-cracking and fracture behaviour in a univocal and reliable way. The best test methodology to evaluate the post-cracking and toughness properties of HPFRC is the beam bending test. Two different types of configurations are proposed: the three-point and the four-point bending tests. The overall focus of this paper is to evaluate the mechanical properties and the post-cracking and fracture behaviour of HPFRC, using the two different standard test procedures. To achieve these aims, plain and fibre concrete specimens were tested. All the test specimens were extensively instrumented to establish the strength properties, crack tip and crack mouth opening displacement, and post-cracking behaviour. The results of the two types of bending tests were critically analysed and compared to identify and highlight the differing effects of the bending load configurations on the mechanical parameters of HPFRC material.
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Koren, Zvi, and Igor Ravve. "Full-azimuth subsurface angle domain wavefield decomposition and imaging Part I: Directional and reflection image gathers." GEOPHYSICS 76, no. 1 (January 2011): S1—S13. http://dx.doi.org/10.1190/1.3511352.
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We present a new subsurface angle-domain seismic imaging system for generating and extracting high-resolution information about subsurface angle-dependent reflectivity. The system enables geophysicists to use all recorded seismic data in a continuous fashion directly in the subsurface local angle domain (LAD), resulting in two complementary, full-azimuth, common-image-angle gather systems: directional and reflection. The complete set of information from both types of angle gathers leads to accurate, high-resolution, reliable velocity model determination and reservoir characterization. The directional angle decomposition enables the implementation of specular and diffraction imaging in real 3D isotropic/anisotropic geological models, leading to simultaneous emphasis on continuous structural surfaces and discontinuous objects such as faults and small-scale fractures. Structural attributes at each subsurface point, e.g., dip, azimuth and continuity, can be derived directly from the directional anglegathers. The reflection-angle gathers display reflectivity as a function of the opening angle and opening azimuth. These gathers are most meaningful in the vicinity of actual local reflecting surfaces, where the reflection angles are measured with respect to the derived background specular direction. The reflection-angle gathers are used for automatic picking of full-azimuth angle-domain residual moveouts (RMO) which, together with the derived background orientations of the subsurface reflection horizons, provide a complete set of input data to isotropic/anisotropic tomography. The full-azimuth, angle-dependent amplitude variations are used for reliable and accurate amplitude versus angle and azimuth (AVAZ) analysis and reservoir characterization. The proposed system is most effective for imaging and analysis below complex structures, such as subsalt and subbasalt, high-velocity carbonate rocks, shallow low-velocity gas pockets, and others. In addition, it enables accurate azimuthal anisotropic imaging and analysis, providing optimal solutions for fracture detection and reservoir characterization.
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Blazy, Julia, Łukasz Drobiec, and Paweł Wolka. "Flexural Tensile Strength of Concrete with Synthetic Fibers." Materials 14, no. 16 (August 7, 2021): 4428. http://dx.doi.org/10.3390/ma14164428.
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Fiber reinforcement is currently most often used in floors, railway sleepers, prefabricated structural elements such as slabs, beams and tanks, and in small architecture elements. Designing elements or structures made of fiber-reinforced concrete requires knowledge of its basic mechanical parameters. In the case of concretes with metallic fibers, the literature can find many tests and standard guidelines regarding compressive, flexural, tensile strength and fracture energy. The properties of concretes with non-metallic fibers are slightly less recognized, especially concretes with new types of polymer fibers. Additionally, the lack of standardized methods of testing concrete with polymer fibers make their application much more difficult. In the article, the possibility of using the EN 14651 standard to assess the flexural tensile strength of concrete with the addition of 2.0 and 3.0 kg/m3 of synthetic fibers with different geometry and form was presented. There was a 5.5–13.5% increase in the flexural tensile strength depending on the mixture type. Moreover, in the case of fiber-reinforced concretes, the ductility was enhanced and the samples were characterized by significant residual flexural tensile strengths. Additionally, from the workability tests it was concluded that after the incorporation of fibers, the consistency class decreased by one, two or three. Nevertheless, the compressive strengths of concrete with and without fibers were very similar to each other, and varied from 58.05 to 61.31 MPa. Moreover, it was concluded that results obtained from three-point bending tests significantly differed from empirical formulas for the calculation of the flexural tensile strength of fiber-reinforced concretes with dispersed steel fibers present in the literature. As a result, the new formula determined by the authors was proposed for concrete with polymer fibers with a nominal fiber content ≤1.0% and slenderness of up to 200. It must be mentioned that the formula gave a very good agreement with studies presented in different literature positions. In addition, an attempt was made to evaluate the strengths of tested mixes in accordance with the Model Code 2010. However, it occurred that the proposed fiber-reinforced concrete mixtures would not be able to replace traditional reinforcement in a form of steel bars. Furthermore, in uniaxial tensile tests, it was not possible to determine the σ–w graphs, and received results for maximum tensile strength did not show the clear influence of fibers incorporation on concrete. Then, the fracture energy enhancement (from about 16 to 22 times) and dependencies: crack mouth opening displacement–deflection; crack mouth opening displacement–crack tip opening displacement; and crack tip opening displacement–deflection were analyzed. Finally, the results from flexural tensile tests were compared with measurements of the surface displacement field obtained through the Digital Image Correlation technique. It was concluded that this technique can be successfully used to determine the crack mouth and crack tip opening displacements with very high accuracy.
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Ni, Xinhua, Yunwei Fu, Xiequan Liu, and Long Zhang. "Strength prediction of composite ceramic under the non-ellipsoidal particles bridging." World Journal of Engineering 13, no. 1 (February 8, 2016): 12–17. http://dx.doi.org/10.1108/wje-02-2016-003.
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Purpose This paper aims to promote a strength model for TiC-TiB2 composite ceramic with non-ellipsoidal particles bridging. Based on the microstructure of TiC-TiB2 composite ceramic, equivalent average residual stress under particles interaction is calculated with the interact direct derivative estimate. Supposing the crack opening displacement keeps ellipsoidal under the TiB2 particles bridging, crack growth resistance curve is obtained. Design/methodology/approach Composite strength under R-cure with crack unstable propagation is calculated. Based on this model, influences of particles volume fraction, shape, size and other parameters on strength are analyzed. Findings Results indicated that calculated values are consistent to the tested data. Crack growth resistance increases with crack propagation and TiB2 volume fraction. The TiB2 particle does not pull-out entirely even ceramic fracture. Ceramic strength increases with the TiB2 particle volume fraction, the ratio of platelet diameter and thickness, and it reduces with particle thickness. Originality/value Supposing the crack open displacement keeps ellipsoidal under the TiB2 particles bridging, crack growth resistance curve is obtained.
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Novokreshchennykh, Dmitrii V., and Aleksei V. Raspopov. "WAYS OF IMPROVING THE FORMATION HYDRAULIC FRACTURING EFFECTIVENESS IN CARBONATE DEPOSITS OF FIELDS OF THE REPUBLIC OF KOMI AND NENETS AUTONOMOUS OKRUG." Вестник Пермского национального исследовательского политехнического университета. Геология. Нефтегазовое и горное дело 20, no. 2 (June 2020): 175–81. http://dx.doi.org/10.15593/2224-9923/2020.2.7.
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The study presents an overview of the formation hydraulic fracturing application in carbonate deposits of fields of the Republic of Komi and Nenets Autonomous Okrug. The formation hydraulic fracturing technology has become widely used in carbonate reservoirs since 2012, with over three hundred well jobs performed. A significant share of residual recoverable reserves in carbonate deposits needs to be withdrawn; production rates need to be increased, inter alia, by way of the formation hydraulic fracturing. In the conditions of gradual deterioration of porosity and permeability of candidate wells, maintaining a steady level of technological effectiveness of hydraulic fracturing is ensured by implementing new technologies and optimizing standard processes. The hydraulic fracturing implementation issues are inextricably connected to the main issues of oilfield developments and specific structural features of carbonate reservoirs. Taking into account the specific structural features of carbonate reservoirs and existing development issues, the main objectives of the formation hydraulic fracturing have been determined: fracture conductivity increase; horizontal and vertical sweep increase; reduction of uncontrolled leakage of fracturing fluid; reduction of fracture height in conditions of adjacent water- and gas-saturated interbeds. Presently, a number of technologies has been successfully adapted and is used at the Republic of Komi and Nenets Autonomous Okrug sites. Due to the implementation of the integral approach to selection of the hydraulic fracturing technology modifications, taking into account the existing oilfield development issues and structural peculiarities of carbonate reservoirs, the reliable effectiveness of the method has been ensured in the conditions of deteriorating candidate wells; the technology application range has been extended. The study suggests expanding the range of the existing laboratory analyses to include such aspects as determination of stress intensity factor – fracture resistance and Biot’s poroelastic parameter, study of leakage rate dynamics in regard to various fracturing fluids, depending on the reservoir properties of core samples at given gradients, determination of dependence of proppants dynamic transfer on rheological properties of fracturing fluids and their filtration rates for various degrees of fracture model opening.
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Roslee, Rodeano. "EFFECTS OF PHYSICAL AND MECHANICAL PROPERTIES OF RESIDUAL SOIL ON SLIDING AREA AT BUNDU TUHAN, SABAH, MALAYSIA." Geological Behavior 4, no. 1 (March 4, 2020): 18–25. http://dx.doi.org/10.26480/gbr.01.2020.18.25.
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The study of the earth mass movement has long been regarded as one of the most important and interesting aspect of engineering geology and geotechnical engineering, which the designers and planners from the private and public sectors address when implementing the initial stage of urban and rural development projects. This involves highways and infrastructures construction and land use planning among the others. Failure to appreciate the problems relating to mass movements of earth material could lead to damage of man made structures and even the loss of lives. These studies focused on the mass movement in Bundu Tuhan to Kundasang highway area approximately 84 km to 96 km from Kota Kinabalu city, Sabah, one of the most vulnerable to mass movements occurrence in west coast of Sabah. It is bounded by longitude line E 116o 31.592’ to E 116o 36.183’ and latitude line N 06o 00.269’ to N 05o 57.610’. The main objectives of this study are; 1) to map and locate the landslides in the study area; and 2) to study the mechanism and the influence of geological factors causing the mass movement. Geology of the study area and its surrounding is hosted mainly by three sedimentary rock formations: Trusmadi Formation (Palaeocene to Eocene age), Crocker Formation (Late Eocene to Early Miocene age) and Pinousuk Gravel (Upper Pleistocene to Holocene age). These three geologic formations dissected by numerous geological lineaments structural produced by a complex tectonic history of multi phase folding and thrust, normal and reverse faulting. These tectonic setting reduce the physical and mechanical properties of the soil and produced intensive displacement in substrata resulting in intensive high degree of weathering processes. The weathered materials are weak and cause sinking, subsidence and sliding due to high pore pressure subjected by both shallow and deep groundwater. Evaluation 10 boreholes data in study area indicated that the groundwater table in study area is shallow and range 1.9 meter to about 11.3 meters. The groundwater in study area fluctuate drastically even within short period. Sand and gravel layer with variable thickness defined the major shallow aquifers within the top weathered materials while the highly fracture sedimentary rocks defined the major deep aquifers. Most of the aquifer within top unconsolidated weathered material is under unconfined condition. Most of significant aquifers within the sedimentary rocks are sandstones. The sandstones generally fracture and contain coarse sediments, which increase the permeability. Geologic and geotechnic evaluation of the study area indicates that the mass movement take place when slope materials are no longer able to resist the force of gravity. These decrease the shear resistance resulting mass movement, which is due to internal and external factors. Internal factors involve some change in either physical or chemical properties of the rock and soil. External factors involve increase of shear stress on slope, which usually involves a form of disturbance that is induced by man. The triggering mechanism in the study area most likely involves heavy rainfall causing water saturation of the slope material and loss of cohesion along rapture planes. The sheared shale, bedding and fault planes, and opening fractures are all structural weaknesses, which acting as pathways for water seepage, hastening the weakening and eventual mass movement in the study area. Development planning has to consider these hazards in order to counter their effect. An environmental management program should be implemented to prevent these losses. Geological and geotechnical studies will play a vital role in ground stability assessment that critical in public safety.
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Bortolan Neto, Luiz, and Andrei Kotousov. "On the residual opening of hydraulic fractures." International Journal of Fracture 181, no. 1 (March 20, 2013): 127–37. http://dx.doi.org/10.1007/s10704-013-9828-1.
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Molokov, K. A., V. V. Novikov, and A. P. German. "Analytical model for assessing fatigue limit of welded joints of ferritic-pearlitic steels." Advanced Engineering Research 20, no. 3 (October 5, 2020): 225–34. http://dx.doi.org/10.23947/2687-1653-2020-20-3-225-234.
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Introduction. Microdefects and zones with stress concentration in welded joints cause fatigue macrocracks. Such damage is potentially dangerous, especially if the fatigue life of the structure is almost exhausted. In this case, the crack size is close to the critical value, and it is crucial to determine its length. The paper considers the development of an engineering analytical model for assessing the critical crack length and endurance limit of welded joints with the formed grain in the structure of ferrite-pearlitic steels after welding. Materials and Methods. The theory and methods of fracture mechanics at the mesoscale are used. A simple analytical dependence is obtained, which provides determining the critical dimensions of a macrocrack for ferrite-pearlite steels without using the Griffiths formula. . The calculation results of the critical crack lengths of various steels depending on their yield strength are presented. An analytical dependence of the endurance limit calculation for the most dangerous symmetric loading cycle, according to the standard set of mechanical characteristics and the average grain diameter of ferrite-pearlite steel, is presented. Results. Structural deformation analysis of the crack propagation process has been performed. On its basis, an engineering technique for assessing the endurance limit is developed. A mathematical model that enables to calculate the endurance limit and the critical crack length in the components of welded assemblies of large-sized facilities, considering periodic loads of a symmetrical cycle, is developed. Using this model, it is possible to estimate the degree of metal sensitivity to the original characteristics (yield stress, Poisson's ratio, grain diameter, relative constriction, Young's modulus, power-law hardening coefficient, etc.).Discussion and Conclusion. Under stresses corresponding to the steel endurance limit, the critical crack opening rates of the tip and edges approach each other. Energetically, this moment approximately corresponds to the transition of the crack to an unstable state. The accumulation of one-sided plastic deformations causes the limiting state of plasticity of the region adjacent to the crack tip and its avalanche-like or sharply accelerated motion. This critical area is interrelated with the grain diameter of the material, the characteristic of critical plasticity and the critical opening at the crack tip at the fatigue limit. The proposed analytical dependences can be used to assess the residual life and the fatigue limit of welded structures, the influence of various factors on the fatigue limit of welded joints of ferrite-pearlitic steels used in mechanical engineering, shipbuilding, pipeline transport, etc
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Bortolan Neto, Luiz, and Andrei Kotousov. "Residual opening of hydraulic fractures filled with compressible proppant." International Journal of Rock Mechanics and Mining Sciences 61 (July 2013): 223–30. http://dx.doi.org/10.1016/j.ijrmms.2013.02.012.
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Bortolan Neto, Luiz, and Andrei Kotousov. "Residual opening of hydraulically stimulated fractures filled with granular particles." Journal of Petroleum Science and Engineering 100 (December 2012): 24–29. http://dx.doi.org/10.1016/j.petrol.2012.11.014.
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Khanna, Aditya, Hao Luong, Andrei Kotousov, Giang D. Nguyen, and L. R. Francis Rose. "Residual opening of hydraulic fractures created using the channel fracturing technique." International Journal of Rock Mechanics and Mining Sciences 100 (December 2017): 124–37. http://dx.doi.org/10.1016/j.ijrmms.2017.10.023.
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Koren, Zvi, and Igor Ravve. "Azimuthally dependent anisotropic velocity model update." GEOPHYSICS 79, no. 2 (March 1, 2014): C27—C53. http://dx.doi.org/10.1190/geo2013-0178.1.
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We consider a case where a 3D depth migration has been performed in the local angle domain (LAD) using rich-azimuth seismic data (e.g., conventional land surveys). The subsurface geologic model is characterized by considerable azimuthally anisotropic velocity variations. The background velocity field used for the migration can consist of azimuthally independent, e.g., vertical transverse isotropy, and/or azimuthally dependent (e.g., orthorhombic), velocity layers. The resulting 3D full-azimuth reflection angle gathers generated by the LAD migration represent in situ high-resolution amplitude preserved reflectivities associated with opening angles between incident and reflected slowness vectors in the specular directions. Residual moveouts (RMOs) automatically picked on these 3D image gathers along major horizons can indicate considerable residual periodic azimuthal variations. This situation is typical in depth imaging applied to unconventional shale plays, where the background velocity model doesn’t yet account for the aligned stress/fracture systems that exist in some of the target layers. We use the azimuthally dependent, phase-angle RMOs to update the interval parameters of the background model, accounting for the azimuthal anisotropy effect. Until now, this problem was mainly treated in the unmigrated time-offset domain, which is limited in describing the actual in situ changes of the velocity field with azimuths. The subsurface full-azimuth phase-angle domain RMOs provide better physical parameters to analyze the in situ azimuthal variations of the anisotropic media. Our method is grounded in a newly derived generalized Dix-based theory, where locally the background and updated models are assumed to be 1D anisotropic velocity models. At each lateral location, the orthorhombic axis [Formula: see text] points in the vertical direction across all layers, but the azimuthal orientations of the orthorhombic layers change from layer to layer. An effective model for such a layered structure (background or updated) is represented by a single layer with a vertical time identical to that of the whole package, effective fast and slow normal moveout (NMO) velocities, and an effective azimuthal orientation of the slow NMO velocity. Our approach begins with computation of these effective parameters for the background model and conversion of the high-resolution RMOs into a dense set of updated, effective, azimuthally dependent NMO velocities, which are then converted into three effective parameters of the updated model. Next, we apply a generalized Dix-based inversion approach to estimate the local NMO parameters for each updated layer. Finally, we convert the local parameters into interval azimuthally varying anisotropic model parameters (e.g., TTI, orthorhombic, or tilted orthorhombic) within each layer. The 1D Dix-based approach presented in this work should not be considered an alternative to more accurate 3D global inversion approaches, such as global anisotropic tomography. However, the proposed method can be effectively used for moderately laterally varying models, and some of the principal physical rules derived for the 1D model can be further used to improve the formulation and geophysical constraints applied to 3D global inversion methods.
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Willems, Luc, André Pouclet, and Jean-Paul Vicat. "Existence of karsts into silicated non-carbonated crystalline rocks in Sahelian and Equatorial Africa, hydrogeological implications." Bulletin de la Société Géologique de France 173, no. 4 (July 1, 2002): 337–45. http://dx.doi.org/10.2113/173.4.337.
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Abstract Various cavities studied in western Niger and South Cameroon show the existence of important karstic phenomena into metagabbros and gneisses. These large-sized caves resulted from generalized dissolution of silicate formations in spite of their low solubility. Karstification is produced by deep hydrous transfer along lithological discontinuities and fracture net works. The existence of such caves has major implications in geomorphology, under either Sahelian and Equatorial climate, and in hydrogeology and water supply, particularly in the Sahel area. Introduction. – Since a few decades, several karst-like morphologies are described in non-carbonated rocks (sandstones, quartzites, schistes, gneisses…) [Wray, 1997 ; Vicat and Willems, 1998 ; Willems, 2000]. The cave of Guéssédoundou in West Niger seems to be due to a large dissolution of metagabbros. The cave of Mfoula, South Cameroon, attests for the same process in gneisses. This forms proof that big holes may exist deeper in the substratum even of non-carbonated silicate rocks. Their size and number could mainly influence the landscape and the hydrogeology, especially in the Sahelian areas. Guéssédoundou, a cave into metagabbros in West Niger. – The site of Guéssédoundou is located 70 km south-west of Niamey (fig. 1). The cave is opened at the top of a small hill, inside in NNE-SSW elongated pit (fig. 2 ; pl. I A). The hole, 3 to 4 m deep and 20 m large, has vertical walls and contains numerous sub-metric angular blocks. A cave, a few meters deep, comes out the south wall. Bedrocks consist of metagabbros of the Makalondi greenstone belt, a belt of the Palaeoproterozoic Birimian Formations of the West Africa craton [Pouclet et al., 1990]. The rock has a common granular texture with plagioclases, partly converted in albite and clinozoisite, and pyroxenes pseudomorphosed in actinote and chlorite. It is rather fairly altered. Chemical composition is mafic and poorly alkaline (tabl. I). A weak E-W schistosity generated with the epizonal thermometamorphism. The site depression was created along a N010o shear zone where rocks suffered important fracturation and fluid transfers, as shown by its silification and ferruginisation. The absence of human activity traces and the disposition of the angular blocks attest that the pit is natural and was due to the collapse of the roof of a vast cavity whose current cave is only the residual prolongation. To the vertical walls of the depression and at the cave entry, pluridecimetric hemispheric hollows are observed (pl. I B). Smooth morphology and position of these hollows sheltered within the depression dismiss the assumptions of formation by mechanical erosion. In return, these features are typical shape of dissolution processes observed into limestone karstic caves. That kind of process must be invoked to explain the opening of the Guéssédoundou cave, in the total lack of desagregation materials. Dissolution of metagabbro occurred during hydrous transfer, which was probably guided by numerous fractures of the shear zone. Additional observations have been done in the Sirba Valley, where similar metabasite rocks constitute the substratum, with sudden sinking of doline-like depressions and evidence of deep cavities by core logging [Willems et al., 1993, 1996]. It is concluded that karstic phenomena may exist even in silica-aluminous rocks of crystalline terrains, such as the greenstones of a Precambrian craton. Mfoula a cave into gneisses in South Cameroon. – The cave of Mfoula is located 80 km north-east of Yaoundé (fig. 3). It is the second largest cave of Cameroon, more than 5,000 m3, with a large opening in the lower flank of a deep valley (pl. I C). The cavity is about 60 m long, 30 m large and 5 to 12 m high (fig. 4; pl. I D). It is hollowed in orthogneisses belonging to the Pan-African Yaoundé nappe. Rocks exhibit subhorizontal foliation in two superposed lithological facies: the lower part is made of amphibole- and garnet-bearing layered gneisses, and the upper part, of more massive granulitic gneisses. Average composition is silico-aluminous and moderately alkaline (tabl. I). The cave is made of different chambers separated by sub-cylindrical pillars. The ceiling of the main chamber, 6 m in diameter, is dome-shaped with a smooth surface (D, fig. 4). The walls have also a smooth aspect decorated with many hemispherical hollows. The floor is flat according to the rock foliation. They are very few rock debris and detrital fragments and no traces of mechanical erosion and transport. The general inner morphology is amazingly similar to that of a limestone cave. The only way to generate such a cavity is to dissolve the rock by water transfer. To test the effect of the dissolution process, we analysed a clayey residual sampled in an horizontal fracture of the floor (tabl. I). Alteration begins by plagioclases in producing clay minerals and in disagregating the rock. However, there is no more clay and sand material. That means all the silicate minerals must have been eliminated. Dissolution of silicates is a known process in sandstone and quartzite caves. It may work as well in gneisses. To fasten the chemical action, we may consider an additional microbial chemolitotrophe activity. The activity of bacteria colonies is known in various rocks and depths, mainly in the aquifer [Sinclair and Ghiorse, 1989 ; Stevens and McKinley, 1995]. The formation of the Mfoula cave is summarized as follow (fig. 5). Meteoric water is drained down along sub-vertical fractures and then along horizontal discontinuities of the foliation, particularly in case of lithological variations. Chemical and biological dissolution is working. Lateral transfers linked to the aquifer oscillations caused widening of the caves. Dissolved products are transported by the vertical drains. Regressive erosion of the valley, linked to the epeirogenic upwelling due to the volcano-tectonic activity of the Cameroon Line, makes the cavities come into sight at the valley flanks. Discussion and conclusion. – The two examples of the Guéssédoundou and Mfoula caves evidence the reality of the karsts in non-carbonated silicated rocks. The karst term is used to design ≫ any features of the classical karst morphology (caves, dolines, lapies…) where dissolution plays the main genetical action ≫ [Willems, 2000]. Our observations indicate that (i) the karst genesis may have occurred into any kind of rocks, and (ii) the cave formation is not directly dependent of the present climate. These facts have major consequences to hydrogeological investigations, especially for water supply in Sahelian and sub-desertic countries. Some measurements of water transfer speed across either sedimentary pelitic strata of the Continental terminal or igneous rocks of the substratum in West Niger [Estèves and Lenoir, 1996 ; Ousmane et al., 1984] proved that supplying of aquifers in these silico-aluminous rocks may be as fast as in a karstic limestone. That means the West Niger substratum is highly invaded by a karstic net and may hidden a lot of discontinuous aquifers. The existence of this karst system can be easily shown by morphological observations, the same that are done in karstic limestone regions (abnormally suspended dry valleys, collapses, dolines…). Clearly, this must be the guide for any search of water, even in desertic areas where limestones are absent.
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Kosior-Kazberuk, Marta, Julita Krassowska, and Carolina Piña Ramírez. "Post cracking behaviour of fibre reinforced concrete with mineral wool fibers residues." MATEC Web of Conferences 174 (2018): 02016. http://dx.doi.org/10.1051/matecconf/201817402016.
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The research concerns the feasibility of recycling fibers from mineral wool residues from construction and demolition waste, by incorporating them into a fine grained concrete. All the specimens of concrete with various types of fibers have been subjected to the mechanical tests of flexural and compressive strength. Also the pre-cracking and postcracking softening behaviour of concrete with fiber residues has been investigated. The flexural load-CMOD and load-deflection relationships, obtained in three-point bending test, have been used to determine the fracture parameters: fracture energy, critical stress intensity factor, critical crack tip opening displacement, critical effective crack length. It was verified that the incorporation of mineral residues to a cement concrete is a viable alternative for their recycling; the new composites analyzed maintain adequate mechanical properties for different application.
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Salvati, Enrico, Cyril Besnard, Robert A. Harper, Thomas Moxham, Richard M. Shelton, Gabriel Landini, and Alexander M. Korsunsky. "Crack Tip Stress Field Analysis of Crack Surface Contact and Opening during In Situ Wedge Loading of Human Enamel." Key Engineering Materials 827 (December 2019): 85–91. http://dx.doi.org/10.4028/www.scientific.net/kem.827.85.
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Shallow cracks are often observed in dental enamel, however do not normally lead to deep fractures. Previous work has highlighted the toughening mechanisms that operate in enamel during crack propagation, but very little is known about the deformation and stress fields arising around the propagating cracks during realistic loading conditions. This work aims to elucidate how the stresses are distributed within human dental enamel when a pre-existing crack is subjected to opening and surface contact with in situ indentation. We present a synchrotron-based insitu analysis coupled with a linear elastic finite element method simulation. The experimental reconstructed stress fields identified a prominent residual stress within the enamel, accompanied by a visible pattern that appeared clearly associated with its underlying microstructure. The numerical modelling of the stress field and discerning of surface contact and crack opening caused by the indentation was subsequently possible, even if in this study the influence of the anisotropy induced by the presence of features at a smaller scale was neglected. The implications of these findings and directions for future research are discussed.
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Carvalho, Caroline Gomes, João Victor Frazão Câmara, and Paulo Sérgio da Silva Santos. "The positive impact of dental care on the patient's quality of life after cancer treatment: a case report." Research, Society and Development 9, no. 9 (September 1, 2020): e650997639. http://dx.doi.org/10.33448/rsd-v9i9.7639.
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Objective: To report the case of a patient after cancer treatment and evaluate the impact of oral health on quality of life, through the Oral Health Impact Profile (OHIP-14) before, during, and after dental treatment. Methodology: A patient after antineoplastic treatment attended the clinic specialized. In all consultations, OHIP-14 was applied. Case report: A 68-year-old man diagnosed with keratinizing squamous cell carcinoma of the larynx (T3N0MX), undergoing chemotherapy and adjuvant radiotherapy (2878.2 Grays) and vertical partial laryngectomy surgery without ganglionic emptying. After CT, he complained of tooth loss and discomfort in the tongue after radiotherapy. Ex-drinker for 5 years, ex-smoker for 6 months, but alcoholic for> 10 years and smoker <50 years. Side effects of antineoplastic treatment included labial dryness, hyposalivation, dental fractures, residual roots, changes in swallowing, pain during mouth opening, and cervical movement. The results OHIP-14 was medium (17.85), weak (3.52), weak (2.84) and null impact of oral health on quality of life in the initial consultation, throughout the dental treatment, at the end of dental treatment and 1 year and 2 months after dental treatment, respectively. There was a high impact on psychological discomfort (3.55), medium on psychological disability (1.6), and functional limitation (2.04), in 2015, 2017, and 2018, respectively. Conclusion: The performance of the dentist on the late oral effects of chemotherapy and radiotherapy had a positive impact on improving the quality of life after cancer treatment, with the help of the multidisciplinary team.
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Maľa, M., V. Greif, and M. Ondrášik. "Pore structure evolution in andesite rocks induced by freeze–thaw cycles examined by non-destructive methods." Scientific Reports 12, no. 1 (May 19, 2022). http://dx.doi.org/10.1038/s41598-022-12437-5.
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AbstractIn this paper, we compare the values of petrophysical properties before and after 100 freeze–thaw (F–T) cycles, as well as recorded length change behaviour and temperature development on a vacuum-saturated fractured andesite rock sample taken from the Babina Quarry in Slovakia using a specially-constructed thermodilatometer, VLAP 04, equipped with two HIRT-LVDT sensors. We also used non-destructive visualization of the rock pore network by µCT imaging in order to study the development of the pore structure and fracture network in pyroxene andesites during the freeze–thaw process. The results show that the andesite rock samples, due to good fabric cohesion, low porosity, and low pore interconnection, showed good resistance against frost-induced damage. However, it must be stated that the main process causing disintegration of this type of rock is fracture opening, which is caused by internal stresses induced by water–ice phase transition. The overall residual strain recorded after 100 F–T cycles was not significant, however, the increase of 31 pp in volume of the fracture showed us that repeated freezing and thawing can lead to long term deterioration in terms of subcritical crack growth in brittle-elastic solids like pyroxene-andesite rocks.
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Seko, Yusuke, Yasuhito Imai, Masaki Mitsuya, Noritake Oguchi, and Fumiyoshi Minami. "Application of Weibull Stress Criterion to Brittle Fracture Assessment of Heat-Affected Zone-Notched Welds With Residual Stress." Journal of Pressure Vessel Technology 138, no. 2 (October 15, 2015). http://dx.doi.org/10.1115/1.4031662.
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A constraint loss correction procedure using the Weibull stress criterion is specified in ISO 27306. However, this standard is applicable only to structural steel components with defects, not to welded joints. Therefore, we propose a method for estimating the brittle fracture limit of a weld with a notch in the heat-affected zone (HAZ) and residual stress based on the Weibull stress criterion. Three-point bending (3PB) tests and wide-plate (WP) tension tests of HAZ-notched welds made of 780-MPa class high-strength steel were conducted at −40 °C. The minimum critical crack tip opening displacement (CTOD) of the WP specimen fracturing at the coarse-grained region of the HAZ (CGHAZ) was approximately four times that of the 3PB specimen. Then, the effects of specimen geometry, residual stress, crack-front shape, and HAZ microstructure classification on the Weibull stress were investigated by using a finite element analysis (FEA). The results of these analyses showed that the specimen geometry, the welding residual stress, and HAZ microstructure affect the Weibull stress of HAZ-notched welds as crack driving force. Based on above results, the CTOD–Weibull stress curves for 3PB and WP specimens fracturing at CGHAZ were calculated by using an FEA. It was confirmed that the brittle fracture limit of an HAZ-notched weld with residual stress could be predicted from the Weibull stress criterion because predicted critical CTOD of WP specimens obtained by Weibull stress included experimental critical CTOD of WP specimens.
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Wei, Xiangyang, Hehua Zhu, Qing Chen, J. Woody Ju, Zhiguo Yan, and Yi Shen. "A micromechanical crack bridging model considering the slip-softening interface with the residual shear stress for SFRCC." International Journal of Damage Mechanics, October 10, 2022, 105678952211280. http://dx.doi.org/10.1177/10567895221128057.
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Characterizing the bond properties of the steel fiber/matrix interface plays an important role in describing the crack bridging effect in steel fiber-reinforced cementitious composites (SFRCC). In this paper, a new interface law considering the residual shear stress is proposed to interpret the slip-softening effects of the steel fiber/matrix interface. Accordingly, a micromechanical crack bridging model for SFRCC is formulated by combining the single steel fiber pullout model with the image analysis-based fiber orientation distribution. Comparisons with the experimental data and the existing models show that the proposed model can well predict SFRCC’s tensile softening behavior. Meanwhile, the decrease rate of the bridging stress, the composite fracture energy, the peak bridging stress and the corresponding peak crack opening displacement (COD) are employed to quantitatively evaluate the crack bridging curves. Finally, the effects of the residual shear stress ratio, the interfacial softening coefficient and the fiber orientation distribution on the crack bridging relation are discussed with the proposed framework.
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Cheung, Jason Pui Yin, Kam Yim Sze, Kenneth Man Chee Cheung, and Teng Zhang. "The first magnetically controlled growing rod (MCGR) in the world – lessons learned and how the identified complications helped to develop the implant in the past decade: case report." BMC Musculoskeletal Disorders 22, no. 1 (April 1, 2021). http://dx.doi.org/10.1186/s12891-021-04181-0.
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Abstract Background The first magnetically controlled growing rod (MCGR) was implanted in 2009. Since then multiple complications have been identified that have helped drive the development of the MCGR and its surgery. The aim of this report is to illustrate how identified complications in the first MCGR helped with developments in the past decade and to report a unique failure mechanism with stud fracture close to the barrel opening. Case presentation A 5-year old girl with a scoliosis of 58.5 degrees at T1–9 and 72.8 degrees at T9-L4 had a single MCGR inserted and anchored at T3–4 and L3–4. At postoperative 13 months the MCGR was noted to have lost of distraction between lengthening episodes due to unrestricted turning of the internal magnet. To prevent further loss of distraction, an external magnet was placed outside the skin to prevent the magnet from turning back. The overall balance was suboptimal and after the rod was fully distracted, proximal junctional kyphosis occurred. Subsequently, the MCGR was modified with an internal keeper plate to prevent loss of distraction and a dual set of these rods were implanted when the patient was 9 years old. Extension proximally to C7-T1 was done to manage the proximal junctional kyphosis. Her spinal balance improved and distractions continued. She subsequently developed add-on below and the piston rod was not aligned with the actuator. The lumbar spine was also observed to have autofusion. She subsequently had final fusion surgery performed at the age of 15 from C7-L4 leaving a residual tilt below to avoid fusion to the pelvis. The final extracted rod on the left side indicated the “crooked rod sign” on X-ray and rod dissections revealed a new failure mechanism of stud fracture close to the barrel opening. Body fluids and tissue may infiltrate the rod despite no obvious deformation or fractures resulting in hastened wearing of the threads. Conclusions There are various complications associated with MCGRs that are related to rod design and surgical inexperience. Repeated rod stalling is not recommended with potential stud fracture and “crooked rod sign”. Rotor stalling and thread wearing which indicates rod failure still require solutions.