Repairing the Ni-based superalloy component remains challenging due to the limited understanding of the role of the defect’s morphology on microstructure and related deformation responses.To address this issue,GH4099...Repairing the Ni-based superalloy component remains challenging due to the limited understanding of the role of the defect’s morphology on microstructure and related deformation responses.To address this issue,GH4099 Ni-based superalloy plate with U-shaped and V-shaped grooves was prepared and repaired by laser-directed energy deposition method using GH4099 powders.Both grooves exhibit three similar regions at the repaired interphase,which are the base metal region with equiaxed grains,repaired region with columnar or elongated equiaxed grains,and a transition region in between.High-temperature gradient in the repaired region induced a high density of substructures,and the repaired region in U-shaped grooves has an even higher temperature gradient due to fewer passes of the melted metal,which induces more metallic carbides in the subgrain boundaries and improves the tensile strength of the repaired samples.However,due to the steep side walls,local vortex might form at the bottom corner of the U-shaped groove,leaving macroscale holes and micro-cracks there.Such defects will decrease the alloy’s ductility.The relationship among groove morphology-macro-and microstructure-mechanical properties is then established,which suggesting the preferred V-shaped groove considering the flatter sidewall and more passes induced near equilibrium microstructure.展开更多
Radial-Additive Friction Stir Repairing(R-AFSR),which has been developed in recent years for the exceeded tolerance hole,is an innovative technology to realize the one-step repairing.Enhancing the repair strength of e...Radial-Additive Friction Stir Repairing(R-AFSR),which has been developed in recent years for the exceeded tolerance hole,is an innovative technology to realize the one-step repairing.Enhancing the repair strength of exceeded tolerance hole is necessary and meaningful from the perspective of suiting more and more wide-scrapped equipment in the industrial field.UltrasonicAssisted R-AFSR(UA-RAFSR)is proposed as a strategy to achieve the 2024 aluminum(Al)alloy repaired hole with high strength.Analyses of microstructure formation indicate that the addition of ultrasonic eliminated the kissing bond and“S”line,refined the grain size,enlarged the interfacial bonding area and enhanced the atomic diffusion.Thus,the mechanical properties of 2024 Al alloy repaired hole were heightened by ultrasonic,and the maximum compressive shear and tensile strengths respectively reached 214.5 MPa and 297.3 MPa,which were 98.6% and 94.0% of those of the standard mechanical hole.The research results confirm that the UA-RAFSR is a powerful technology for the nearly-equal-strength repair of exceeded tolerance hole.展开更多
High-quality repair of damaged Inconel 718(IN718)superalloy components can achieve great economic benefits.However,the directly double aging(DA)treatment by industrial standards,yields an inferior ductility on the rep...High-quality repair of damaged Inconel 718(IN718)superalloy components can achieve great economic benefits.However,the directly double aging(DA)treatment by industrial standards,yields an inferior ductility on the repaired component than that of the wrought base metal.In this work,wrought IN718 components were repaired by laser-directed energy deposition(LDED),a novel tailored heat treatment(THT)schedule consisting of a short-term low-temperature homogenization,and subsequent DA was sub-sequently conducted to strengthen the repaired IN718 alloys.The microstructure evolution and mechan-ical properties of the DA and THT-treated repaired alloys were comparatively investigated.The results indicated that the THT effectively dissolved most of the hard brittle Laves precipitates in the deposition region with only slight coarsening of the grains in the substrate.As compared to the DA sample,the elon-gation of the THT sample increased remarkably by 88%with only a slight reduction of 19.2 MPa in yield stress.Moreover,the strain distribution of the THT sample was overall more even but then destabilized in a narrow abnormal coarsened grain region caused by the static recrystallization.In general,this study breaks through the limitation of the low ductility of the DA-treated repaired IN718 alloys and provides a promising way to further improve the mechanical properties.展开更多
Repairs of corroded high-pressure pipelines are essential for fluids transportation under high pressure.One of the methods used in their repairs is the use of layered composites.The composite used must have the necess...Repairs of corroded high-pressure pipelines are essential for fluids transportation under high pressure.One of the methods used in their repairs is the use of layered composites.The composite used must have the necessary strength.Therefore,the experiments and analytical solutions presented in this paper are performed according to the relevant standards and codes,including ASME PCC-2,ASME B31.8S,ASME B31.4,ISO 24817 and ASME B31.G.In addition,the experimental tests are replicated numerically using the finite element method.Setting the strain gauges at different distances from the defect location,can reduce the nonlinear effects,deformation,and fluctuations due to the high pressure.The direct relationship between the depth of an axial defect and the stress concentration is observed at the inner side edges of the defect.Composite reparation reduces the non-linearities related to the sharp variation of the geometry and a more reliable numerical simulation could be performed.展开更多
Damage caused due to low-velocity impacts in composites leads to substantial deterioration in their residual strength and eventually provokes structural failure.This work presents an experimental investigation on the ...Damage caused due to low-velocity impacts in composites leads to substantial deterioration in their residual strength and eventually provokes structural failure.This work presents an experimental investigation on the effects of different patch and parent laminate stacking sequences on the enhancement of impact strength of Carbon Fiber Reinforced Polymers(CFRP)composites by utilising the adhesively bonded external patch repair technique.Damage evolution study is also performed with the aid of Acoustic Emission(AE).Two different quasi-isotropic configurations were selected for the parent laminate,viz.,[45°/45°/0°/0°]s and[45°/0°/45°/0°]s.Quasi Static Indentation(QSI)test was performed on both the pristine laminates,and damage areas were detected by using the C-scan inspection technique.Damaged laminates were repaired by using a single-sided patch of two different configurations,viz.,[45°/45°/45°/45°]and[45°/0°/0°/45°],and employing a circular plug to fill the damaged hole.Four different combinations of repaired laminates with two configurations of each parent and patch laminate were produced,which were further subjected to the QSI test.The results reveal the effectiveness of the repair method,as all the repaired laminates show higher impact resistance compared to the respective pristine laminates.Patches of[45°/0°/0°/45°]configuration when repaired by taking[45°/45°/0°/0°]s and[45°/0°/45°/0°]s as parents exhibited 68%and 73%higher peak loads,respectively,than the respective pristine laminates.Furthermore,parent and patch of configuration[45°/0°/45°/0°]s and[45°/0°/0°/45°],respectively,attain the highest peak load,whereas[45°/45°/0°/0°]s and[45°/45°/45°/45°]combinations possess the most gradual decrease in the load.展开更多
One of the main factors of laser induced damage is the modulation to incident laser which is caused by the defect in the subsurface of the fused silica. In this work, the repaired damage site irradiated by CO2 laser i...One of the main factors of laser induced damage is the modulation to incident laser which is caused by the defect in the subsurface of the fused silica. In this work, the repaired damage site irradiated by CO2 laser is simplified to a Gaussian rotation according to the corresponding experimental results. Then, the three-dimensional finite-difference time-domain method is employed to simulate the electric field intensity distribution in the vicinity of this kind of defect in fused silica front subsurface. The simulated results show that the modulation is notable, the Emax is about 2.6 times the irradiated electric field intensity in the fused silica with the damage site （the width is 1.5 μm and depth is 2.3 μm） though the damage site is repaired by CO2 laser. The phenomenon and the theoretical result of the annular laser enhancement existed on the rear surface are first verified effectively, which agrees well with the corresponding experimental results. The relations between the maximal electric field intensity in fused silica with defect depth and width are given respectively. Meanwhile, the corresponding physical mechanism is analysed theoretically in detail.展开更多
CO2 laser rapid ablation mitigation(RAM)of fused silica has been used in high-power laser systems owing to its advantages of high efficiency,and ease of implementing batch and automated repairing.In order to study the...CO2 laser rapid ablation mitigation(RAM)of fused silica has been used in high-power laser systems owing to its advantages of high efficiency,and ease of implementing batch and automated repairing.In order to study the effect of repaired morphology of RAM on laser modulation and to improve laser damage threshold of optics,an finite element method(FEM)mathematical model of 351 nm laser irradiating fused silica optics is developed based on Maxwell electromagnetic field equations,to explore the 3D near-field light intensity distribution inside optics with repaired site on its surface.The influences of the cone angle and the size of the repaired site on incident laser modulation are studied as well.The results have shown that for the repaired site with a cone angle of 73.3°,the light intensity distribution has obvious three-dimensional characteristics.The relative light intensity on z-section has a circularly distribution,and the radius of the annular intensification zone increases with the decrease of z.While the distribution of maximum relative light intensity on y-section is parabolical with the increase of y.As the cone angle of the repaired site decreases,the effect of the repaired surface on light modulation becomes stronger,leading to a weak resistance to laser damage.Moreover,the large size repaired site would also reduce the laser damage threshold.Therefore,a repaired site with a larger cone angle and smaller size is preferred in practical CO2 laser repairing of surface damage.This work will provide theoretical guidance for the design of repaired surface topography,as well as the improvement of RAM process.展开更多
KH2PO4 （KDP） crystal with excellent optical properties is a very important element of inertial confinement fusion （ICF） device. However, KDP crystal surface micro-defects severely reduce the crystal laser damage t...KH2PO4 （KDP） crystal with excellent optical properties is a very important element of inertial confinement fusion （ICF） device. However, KDP crystal surface micro-defects severely reduce the crystal laser damage threshold, affecting the crystal service life. In this paper, Gaussian repaired pit is used to replace the crystal surface micro-defects, in order to improve the laser damage resistance of the KDP crystal with surface micro-defects. At first, the physical model of Gaussian repaired pit is built by Fourier model method, and the accuracy of the method is analyzed. It is found that the calculation error can be reduced by increasing the product of the width-period ratio and the truncation constant of the repaired pit. The calculation results about the physical model of Gaussian repaired pit show that the light intensity distribution within the crystal is symmetrical, and there are evidently enhanced light intensity regions in the crystal. Meanwhile, the maximum relative intensity inside the KDP crystal decreases gradually with the increase of the width of the Gaussian repaired pit. Secondly, the Gaussian repaired pits with different widths and the same depth of 20 μm are processed by micro-milling. Their surfaces are very smooth and present the ductile cutting state under the microscope. Finally, the laser damage threshold of the Gaussian repaired pits on the surface of the KDP crystal sample is measured by a 3 ω, 6-ns laser. The results showthat the maximum threshold of the Gaussian repaired pits is 3.12 J/cm2, which is 60% higher than the threshold of initial damage point, and the laser damage threshold increases with the increase of the width of the Gaussian repaired pit.展开更多
Appropriate heart rate in a failing pulmonary ventricle remains unknown, particularly in congenital heart diseasewith unique hemodynamics. A 71-year-old male with repaired tetralogy of Fallot and a pacemaker for a sin...Appropriate heart rate in a failing pulmonary ventricle remains unknown, particularly in congenital heart diseasewith unique hemodynamics. A 71-year-old male with repaired tetralogy of Fallot and a pacemaker for a sinusnode dysfunction suffered from heart failure symptoms with preserved left ventricular function. Simply changingthe pacemaker’s lower rate from 60 to 75 bpm, New York Heart Association classification improved from III to II,and hemodynamic parameters drastically improved. We regarded this case as informative. Appropriate heart ratecould be higher in congenital patients with failing right and non-failing left ventricles than in adults with malfunctioningLV.展开更多
In this work,the microstructure and tensile properties of DD32 single-crystal(SC)superalloy repaired by laser metal forming(LMF)using pulsed laser have been studied in detail.The microstructures of the deposited sampl...In this work,the microstructure and tensile properties of DD32 single-crystal(SC)superalloy repaired by laser metal forming(LMF)using pulsed laser have been studied in detail.The microstructures of the deposited samples and the tensile-ruptured samples were characterized by optical microscopy(OM),transmission electron microscope(TEM)and scanning electron microscope(SEM).Due to high cooling rate,the primary dendrite spacing in the deposited area(17.2μm)was apparently smaller than that in the substrate area(307μm),and the carbides in the deposited samples were also smaller compared with that in the substrate area.The formation of(γ+γ’)eutectic in the initial layer of repaired SC was inhibited because of the high cooling rate.As the deposition proceeded,the cooling rate decreased,and the(γ+γ’)eutectic increased gradually.The(γ+γ’)eutectic at heat-affected zone(HAZ)in the molten pool dissolved partly because of the high temperature at HAZ,but there were still residual eutectics.Tensile test results showed that tensile behavior of repaired SC at different temperatures was closely related to the MC carbides,solidification porosity,γ’phase,and(γ+γ’)eutectic.At moderate temperature,the samples tested fractured preferentially at the substrate area due to the fragmentation of the coarse MC carbide in the substrate area.At elevated temperature,the(γ+γ’)eutectic and solidification porosity in the deposited area became the source of cracks,which deteriorated the high-temperature properties and made the samples rupture at the deposited area preferentially.展开更多
Laser additive manufacturing technology with powder feeding was employed to repair wrought Ti17titanium alloy with small surface defects.The microstructure,micro-hardness and room temperature tensile properties of las...Laser additive manufacturing technology with powder feeding was employed to repair wrought Ti17titanium alloy with small surface defects.The microstructure,micro-hardness and room temperature tensile properties of laser additive repaired(LARed)specimen were investigated.The results show that,cellular substructures are observed in the laser deposited zone(LDZ),rather than the typicalαlaths morphology due to lack of enough subsequent thermal cycles.The cellular substructures lead to lower micro-hardness in the LDZ compared with the wrought substrate zone which consists of duplex microstructure.The tensile test results indicate that the tensile deformation process of the LARed specimen exhibits a characteristic of dramatic plastic strain heterogeneity and fracture in the laser repaired zone with a mixed dimple and cleavage mode.The tensile strength of the LARed specimen is slightly higher than that of the wrought specimen and the elongation of11.7%is lower.展开更多
This paper seeks to outline a novel three-layer model and a new birth-dteath element solution technique to evaluate static strength of notched metallic panel repaired with bonded com- posite patch and to optimize mate...This paper seeks to outline a novel three-layer model and a new birth-dteath element solution technique to evaluate static strength of notched metallic panel repaired with bonded com- posite patch and to optimize material parameters. The higher order 3D, 8-node isotropic solid ele- ment and 8-node anisotropic layered solid element with three degrees of freedom per node are respectively implemented to model substrate panel, adhesive layer and composite patch to establish three-layer model of repaired panel. The new solving technique based on birth-death element is developed to allow solution of the stress pattern of repaired panel for identifying failure mode. The new model and its solution are used to model failure mode and residual strength of repaired panel, and the obtained results have a good agreement with the experimental findings. Finally, the influences of material parameter of adhesive layer and composite patch on the residual strength of repaired panel are investigated for optimizing material properties to meet operational and envi- ronmental constraints.展开更多
Medical-grade synthetic poly（lactic-co-glycolic acid） polymer can be used as a biomaterial for nerve repair because of its good biocompatibility, biodegradability and adjustable degradation rate. The stress relaxati...Medical-grade synthetic poly（lactic-co-glycolic acid） polymer can be used as a biomaterial for nerve repair because of its good biocompatibility, biodegradability and adjustable degradation rate. The stress relaxation and creep properties of peripheral nerve can be greatly improved by repair with poly（lactic-co-glycolic acid） tubes. ＂Fen sciatic nerve specimens were harvested from fresh corpses within 24 hours of death, and were prepared into sciatic nerve injury models by creating a 10 mm defect in each specimen. Defects were repaired by anastomosis with nerve autografts and poly（lactic-co-glycolic acid） tubes. Stress relaxation and creep testing showed that at 7 200 seconds the sciatic nerve anastomosed by poly（lactic-co-glycolic acid） tubes exhibited a greater decrease in stress and increase in strain than those anastomosed by nerve autografts. These findings suggest that poly（lactic-co-glycolic acid） exhibits good viscoelasticity to meet the biomechanical require- ments for a biomaterial used to repair sciatic nerve injury.展开更多
Directed energy deposition has been used to repair superalloy components in aero engines and gas turbines.However,the microstructure and properties are generally inhomogeneous in components because of the different pr...Directed energy deposition has been used to repair superalloy components in aero engines and gas turbines.However,the microstructure and properties are generally inhomogeneous in components because of the different processing histories.Here,the microstructures and wear behavior of different zones(substrate,HAZ,and deposit)are investigated for the IC10 directionally solidified superalloy repaired by the directed energy deposition process.It is found that the microstructure of the deposited layers is strongly textured with a<001>-fiber texture in the building direction,and the texture intensity is continuously increased along the building direction.Two kinds ofγ’phase(primary and secondaryγ’phase)can be found in the heat-affected zone(HAZ),and the average size of primaryγ’phase is smaller than that in the substrate due to liquation.In the deposit layers,the size ofγ’phase is much smaller than those in the substrate and the primaryγ’phase of HAZ;both size and the fraction of theγ’phase decreases with the increase of building height.The wear rate of the substrate is the smallest,indicating the best wear resistance;while the wear rate of HAZ is the largest,indicating the worst wear resistance in the repaired sample.The wear rates in the deposit layers increase from the bottom to the top zones,showing a decreasing wear resistance.Abrasive wear is found to be the dominant wear mechanism of the repaired alloy,and the resistance to which is closely related to the fraction ofγ’phase in the microstructure.The understanding of the influence of microstructure on wear resistance allows for a more informed application of inhomogeneous superalloy components repaired by directed energy deposition in industry.展开更多
The bonded repair techniques seem to be the most frequent procedures in the aviation maintenance.The achieved composite repaired perforated thin-walled plate is a complex geometry with high numerical analysis cost.The...The bonded repair techniques seem to be the most frequent procedures in the aviation maintenance.The achieved composite repaired perforated thin-walled plate is a complex geometry with high numerical analysis cost.The NURBS-based Isogeometric Analysis(IGA)proposes a sensible and affordable tool to carry out such geometry analysis.In this context,a well-known technique is to divide the original geometry assembly into number of simple neighbors connected geometries.In the present study the free vibration analysis of the perforated plates repaired on one side with an external bonded composite laminated patch is investigated.A multi-patch geometry modeling approach is implemented in line with the first order shear deformation theory of plates.In order to hold the geometry integrity and uniformity,all the degrees of freedom between adjacent geometry patches are completely tied through implementing a Nitsche method.To show the effectiveness and accuracy of the developed formulation,some representative results are extracted and compared with those from literature.The effects of geometrical as well as material parameters including boundary condition,cutout shape,and repair layup on the dynamic response of the repaired perforated plates are then investigated.展开更多
Reinforcement corrosion has a serious impact on the durability and safety of reinforced concrete structures.Six reinforced concrete(RC)beam specimens are constructed.After beam specimens are subjected to accelerated c...Reinforcement corrosion has a serious impact on the durability and safety of reinforced concrete structures.Six reinforced concrete(RC)beam specimens are constructed.After beam specimens are subjected to accelerated corrosion with the constant current,beam specimens are repaired with epoxy mortar and the flexural test of beams is investigated.Then the behaviors of repaired corroded reinforced concrete beams are evaluated.The experimental results show that cracking and ultimate loads of corroded RC beams are enhanced after being repaired.And the strain distributions measured across sections of beam specimens still obey the assumption of plane section.After being repaired,the number of cracks decreases and the crack spacing increases.展开更多
Fatigue crack growth test of cracked metallic plate repaired with adhesive bonding composite patch was conducted to study the fracture behavior of crack patching. The failure mode was that crack grows along with adhes...Fatigue crack growth test of cracked metallic plate repaired with adhesive bonding composite patch was conducted to study the fracture behavior of crack patching. The failure mode was that crack grows along with adhesive debonding. The crack length and debonding area were measured at different numbers of cycles. The nonlinear three- dimensional(3D)finite element(FE)model considering adhesive debonding and crack growth simultaneously was developed. The experimental and analytical results were in good agreement with each other.展开更多
Numerical and experimental study was conducted to investigate the failure mode and strength performance of stiffened composite panel repaired by bolted joints under compressive load, and the results were then compared...Numerical and experimental study was conducted to investigate the failure mode and strength performance of stiffened composite panel repaired by bolted joints under compressive load, and the results were then compared with those from virgin stiffened composite panel without any damage. A finite element analysis model was established for repaired and virgin stiffened composite panels under compressive load, the 3D Hashin criteria was applied to identify the composite structure failure, and the secondary stress criteria was adopted to identify the adhesive failure between the base laminate and the stiffener. The failure modes of repaired stiffened composite panels were stiffened composite panels breaking off along the bolt joints. The experimental results were consistent with the finite element analysis results, indicating the reliability of the finite element analysis model.展开更多
This paper investigates the strength and deformation characteristics of reinforced normal and high-strength concrete rectangular beams which failed in shear and repaired by external bonding of carbon fiber and steel p...This paper investigates the strength and deformation characteristics of reinforced normal and high-strength concrete rectangular beams which failed in shear and repaired by external bonding of carbon fiber and steel plate. Five simply supported reinforced concrete beams with shear reinforcement are tested, three of which are made with NSC （normal-strength concrete） and the other two with HSC （high-strength concrete）. The span of the simply supported beams is 0.9 m with 100 mm wide by 200 mm deep cross section. All five beams are tested under four-point bending. Careful repair process is adopted and proved successful. The aim is to restore or increase shear strength of these beams and to monitor their post-repair load-deflection behavior. The effect of concrete compressive strength on the behavior and strength of beams before and after repair is also investigated. Shear cracks patterns and their evolution are observed and discussed.展开更多
基金support of the Mount Taishan Industrial Leading Talent Project.
文摘Repairing the Ni-based superalloy component remains challenging due to the limited understanding of the role of the defect’s morphology on microstructure and related deformation responses.To address this issue,GH4099 Ni-based superalloy plate with U-shaped and V-shaped grooves was prepared and repaired by laser-directed energy deposition method using GH4099 powders.Both grooves exhibit three similar regions at the repaired interphase,which are the base metal region with equiaxed grains,repaired region with columnar or elongated equiaxed grains,and a transition region in between.High-temperature gradient in the repaired region induced a high density of substructures,and the repaired region in U-shaped grooves has an even higher temperature gradient due to fewer passes of the melted metal,which induces more metallic carbides in the subgrain boundaries and improves the tensile strength of the repaired samples.However,due to the steep side walls,local vortex might form at the bottom corner of the U-shaped groove,leaving macroscale holes and micro-cracks there.Such defects will decrease the alloy’s ductility.The relationship among groove morphology-macro-and microstructure-mechanical properties is then established,which suggesting the preferred V-shaped groove considering the flatter sidewall and more passes induced near equilibrium microstructure.
基金supported by the National Natural Science Foundation of China(Nos.51874201 and 52074184)the Fundamental Research Funds for the Universities of Liaoning Province,China(No.LJ222410143035)。
文摘Radial-Additive Friction Stir Repairing(R-AFSR),which has been developed in recent years for the exceeded tolerance hole,is an innovative technology to realize the one-step repairing.Enhancing the repair strength of exceeded tolerance hole is necessary and meaningful from the perspective of suiting more and more wide-scrapped equipment in the industrial field.UltrasonicAssisted R-AFSR(UA-RAFSR)is proposed as a strategy to achieve the 2024 aluminum(Al)alloy repaired hole with high strength.Analyses of microstructure formation indicate that the addition of ultrasonic eliminated the kissing bond and“S”line,refined the grain size,enlarged the interfacial bonding area and enhanced the atomic diffusion.Thus,the mechanical properties of 2024 Al alloy repaired hole were heightened by ultrasonic,and the maximum compressive shear and tensile strengths respectively reached 214.5 MPa and 297.3 MPa,which were 98.6% and 94.0% of those of the standard mechanical hole.The research results confirm that the UA-RAFSR is a powerful technology for the nearly-equal-strength repair of exceeded tolerance hole.
基金support from the National Natural Science Foundation of China(Nos.52275374 and 52205414)the Xiaomi Foundation through the Xi-aomi Young Scholar Program,the Key Research and Develop-ment Projects of Shaanxi Province(No.2023-YBGY-361)as well as the Young Elite Scientists Sponsorship Program by CAST(No.2021QNRC001).
文摘High-quality repair of damaged Inconel 718(IN718)superalloy components can achieve great economic benefits.However,the directly double aging(DA)treatment by industrial standards,yields an inferior ductility on the repaired component than that of the wrought base metal.In this work,wrought IN718 components were repaired by laser-directed energy deposition(LDED),a novel tailored heat treatment(THT)schedule consisting of a short-term low-temperature homogenization,and subsequent DA was sub-sequently conducted to strengthen the repaired IN718 alloys.The microstructure evolution and mechan-ical properties of the DA and THT-treated repaired alloys were comparatively investigated.The results indicated that the THT effectively dissolved most of the hard brittle Laves precipitates in the deposition region with only slight coarsening of the grains in the substrate.As compared to the DA sample,the elon-gation of the THT sample increased remarkably by 88%with only a slight reduction of 19.2 MPa in yield stress.Moreover,the strain distribution of the THT sample was overall more even but then destabilized in a narrow abnormal coarsened grain region caused by the static recrystallization.In general,this study breaks through the limitation of the low ductility of the DA-treated repaired IN718 alloys and provides a promising way to further improve the mechanical properties.
文摘Repairs of corroded high-pressure pipelines are essential for fluids transportation under high pressure.One of the methods used in their repairs is the use of layered composites.The composite used must have the necessary strength.Therefore,the experiments and analytical solutions presented in this paper are performed according to the relevant standards and codes,including ASME PCC-2,ASME B31.8S,ASME B31.4,ISO 24817 and ASME B31.G.In addition,the experimental tests are replicated numerically using the finite element method.Setting the strain gauges at different distances from the defect location,can reduce the nonlinear effects,deformation,and fluctuations due to the high pressure.The direct relationship between the depth of an axial defect and the stress concentration is observed at the inner side edges of the defect.Composite reparation reduces the non-linearities related to the sharp variation of the geometry and a more reliable numerical simulation could be performed.
基金the financial support by the Council of Scientific&Industrial Research(CSIR)-Research Scheme,India(22/0809/2019-EMR-II)。
文摘Damage caused due to low-velocity impacts in composites leads to substantial deterioration in their residual strength and eventually provokes structural failure.This work presents an experimental investigation on the effects of different patch and parent laminate stacking sequences on the enhancement of impact strength of Carbon Fiber Reinforced Polymers(CFRP)composites by utilising the adhesively bonded external patch repair technique.Damage evolution study is also performed with the aid of Acoustic Emission(AE).Two different quasi-isotropic configurations were selected for the parent laminate,viz.,[45°/45°/0°/0°]s and[45°/0°/45°/0°]s.Quasi Static Indentation(QSI)test was performed on both the pristine laminates,and damage areas were detected by using the C-scan inspection technique.Damaged laminates were repaired by using a single-sided patch of two different configurations,viz.,[45°/45°/45°/45°]and[45°/0°/0°/45°],and employing a circular plug to fill the damaged hole.Four different combinations of repaired laminates with two configurations of each parent and patch laminate were produced,which were further subjected to the QSI test.The results reveal the effectiveness of the repair method,as all the repaired laminates show higher impact resistance compared to the respective pristine laminates.Patches of[45°/0°/0°/45°]configuration when repaired by taking[45°/45°/0°/0°]s and[45°/0°/45°/0°]s as parents exhibited 68%and 73%higher peak loads,respectively,than the respective pristine laminates.Furthermore,parent and patch of configuration[45°/0°/45°/0°]s and[45°/0°/0°/45°],respectively,attain the highest peak load,whereas[45°/45°/0°/0°]s and[45°/45°/45°/45°]combinations possess the most gradual decrease in the load.
基金Project supported by the National High Technology Research and Development Program of China (Grant No.2008AA8040508)the Youth Foundation of University of Science and Technology of China (Grant Nos.L08010401JX0834 and L08010401JX0806)the Fundamental Research Funds for the Central Universities of China
文摘One of the main factors of laser induced damage is the modulation to incident laser which is caused by the defect in the subsurface of the fused silica. In this work, the repaired damage site irradiated by CO2 laser is simplified to a Gaussian rotation according to the corresponding experimental results. Then, the three-dimensional finite-difference time-domain method is employed to simulate the electric field intensity distribution in the vicinity of this kind of defect in fused silica front subsurface. The simulated results show that the modulation is notable, the Emax is about 2.6 times the irradiated electric field intensity in the fused silica with the damage site （the width is 1.5 μm and depth is 2.3 μm） though the damage site is repaired by CO2 laser. The phenomenon and the theoretical result of the annular laser enhancement existed on the rear surface are first verified effectively, which agrees well with the corresponding experimental results. The relations between the maximal electric field intensity in fused silica with defect depth and width are given respectively. Meanwhile, the corresponding physical mechanism is analysed theoretically in detail.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51775147 and 51705105)the Science Challenge Project of China(Grant No.TZ2016006-0503-01)+2 种基金the Young Elite Scientists Sponsorship Program by CAST(Grant No.2018QNRC001)the China Postdoctoral Science Foundation funded project(Grant Nos.2018T110288 and 2017M621260)the Self-Planned Task of State Key Laboratory of Robotics and System(HIT)(Grant Nos.SKLRS201718A and SKLRS201803B).
文摘CO2 laser rapid ablation mitigation(RAM)of fused silica has been used in high-power laser systems owing to its advantages of high efficiency,and ease of implementing batch and automated repairing.In order to study the effect of repaired morphology of RAM on laser modulation and to improve laser damage threshold of optics,an finite element method(FEM)mathematical model of 351 nm laser irradiating fused silica optics is developed based on Maxwell electromagnetic field equations,to explore the 3D near-field light intensity distribution inside optics with repaired site on its surface.The influences of the cone angle and the size of the repaired site on incident laser modulation are studied as well.The results have shown that for the repaired site with a cone angle of 73.3°,the light intensity distribution has obvious three-dimensional characteristics.The relative light intensity on z-section has a circularly distribution,and the radius of the annular intensification zone increases with the decrease of z.While the distribution of maximum relative light intensity on y-section is parabolical with the increase of y.As the cone angle of the repaired site decreases,the effect of the repaired surface on light modulation becomes stronger,leading to a weak resistance to laser damage.Moreover,the large size repaired site would also reduce the laser damage threshold.Therefore,a repaired site with a larger cone angle and smaller size is preferred in practical CO2 laser repairing of surface damage.This work will provide theoretical guidance for the design of repaired surface topography,as well as the improvement of RAM process.
基金Project support by the National Natural Science Foundation of China(Grant No.51275113)the National Science and Technology Major Project of China(Grant No.2013ZX04006011-215)
文摘KH2PO4 （KDP） crystal with excellent optical properties is a very important element of inertial confinement fusion （ICF） device. However, KDP crystal surface micro-defects severely reduce the crystal laser damage threshold, affecting the crystal service life. In this paper, Gaussian repaired pit is used to replace the crystal surface micro-defects, in order to improve the laser damage resistance of the KDP crystal with surface micro-defects. At first, the physical model of Gaussian repaired pit is built by Fourier model method, and the accuracy of the method is analyzed. It is found that the calculation error can be reduced by increasing the product of the width-period ratio and the truncation constant of the repaired pit. The calculation results about the physical model of Gaussian repaired pit show that the light intensity distribution within the crystal is symmetrical, and there are evidently enhanced light intensity regions in the crystal. Meanwhile, the maximum relative intensity inside the KDP crystal decreases gradually with the increase of the width of the Gaussian repaired pit. Secondly, the Gaussian repaired pits with different widths and the same depth of 20 μm are processed by micro-milling. Their surfaces are very smooth and present the ductile cutting state under the microscope. Finally, the laser damage threshold of the Gaussian repaired pits on the surface of the KDP crystal sample is measured by a 3 ω, 6-ns laser. The results showthat the maximum threshold of the Gaussian repaired pits is 3.12 J/cm2, which is 60% higher than the threshold of initial damage point, and the laser damage threshold increases with the increase of the width of the Gaussian repaired pit.
文摘Appropriate heart rate in a failing pulmonary ventricle remains unknown, particularly in congenital heart diseasewith unique hemodynamics. A 71-year-old male with repaired tetralogy of Fallot and a pacemaker for a sinusnode dysfunction suffered from heart failure symptoms with preserved left ventricular function. Simply changingthe pacemaker’s lower rate from 60 to 75 bpm, New York Heart Association classification improved from III to II,and hemodynamic parameters drastically improved. We regarded this case as informative. Appropriate heart ratecould be higher in congenital patients with failing right and non-failing left ventricles than in adults with malfunctioningLV.
基金the National Key R&D Program of China(No.2018YFB1106600),the National Key R&D Program of China(Nos.2017YFA0700703 and 2018YFB1106000)the National Natural Science Foundation of China(NSFC)(Nos.51771190,51671189,U1508213)+1 种基金the National High Technology Research and Development Program(“863”)(No.2014AA041701)the Fund of the State Key Laboratory of Solidification Processing in NWPU(No.SKLSP201834)。
文摘In this work,the microstructure and tensile properties of DD32 single-crystal(SC)superalloy repaired by laser metal forming(LMF)using pulsed laser have been studied in detail.The microstructures of the deposited samples and the tensile-ruptured samples were characterized by optical microscopy(OM),transmission electron microscope(TEM)and scanning electron microscope(SEM).Due to high cooling rate,the primary dendrite spacing in the deposited area(17.2μm)was apparently smaller than that in the substrate area(307μm),and the carbides in the deposited samples were also smaller compared with that in the substrate area.The formation of(γ+γ’)eutectic in the initial layer of repaired SC was inhibited because of the high cooling rate.As the deposition proceeded,the cooling rate decreased,and the(γ+γ’)eutectic increased gradually.The(γ+γ’)eutectic at heat-affected zone(HAZ)in the molten pool dissolved partly because of the high temperature at HAZ,but there were still residual eutectics.Tensile test results showed that tensile behavior of repaired SC at different temperatures was closely related to the MC carbides,solidification porosity,γ’phase,and(γ+γ’)eutectic.At moderate temperature,the samples tested fractured preferentially at the substrate area due to the fragmentation of the coarse MC carbide in the substrate area.At elevated temperature,the(γ+γ’)eutectic and solidification porosity in the deposited area became the source of cracks,which deteriorated the high-temperature properties and made the samples rupture at the deposited area preferentially.
基金Project(2016YFB11000100)supported by the National Key Technologies R&D Program,ChinaProject(KP201611)supported by Research Fund of the State Key Laboratory of Solidification Processing(NWPU),ChinaProject(51475380)supported by the National Natural Science Foundation of China
文摘Laser additive manufacturing technology with powder feeding was employed to repair wrought Ti17titanium alloy with small surface defects.The microstructure,micro-hardness and room temperature tensile properties of laser additive repaired(LARed)specimen were investigated.The results show that,cellular substructures are observed in the laser deposited zone(LDZ),rather than the typicalαlaths morphology due to lack of enough subsequent thermal cycles.The cellular substructures lead to lower micro-hardness in the LDZ compared with the wrought substrate zone which consists of duplex microstructure.The tensile test results indicate that the tensile deformation process of the LARed specimen exhibits a characteristic of dramatic plastic strain heterogeneity and fracture in the laser repaired zone with a mixed dimple and cleavage mode.The tensile strength of the LARed specimen is slightly higher than that of the wrought specimen and the elongation of11.7%is lower.
基金supported by the National Natural Science Foundation (No. 51075019)Aeronautical Science Foundation of China (No. 20095251024)
文摘This paper seeks to outline a novel three-layer model and a new birth-dteath element solution technique to evaluate static strength of notched metallic panel repaired with bonded com- posite patch and to optimize material parameters. The higher order 3D, 8-node isotropic solid ele- ment and 8-node anisotropic layered solid element with three degrees of freedom per node are respectively implemented to model substrate panel, adhesive layer and composite patch to establish three-layer model of repaired panel. The new solving technique based on birth-death element is developed to allow solution of the stress pattern of repaired panel for identifying failure mode. The new model and its solution are used to model failure mode and residual strength of repaired panel, and the obtained results have a good agreement with the experimental findings. Finally, the influences of material parameter of adhesive layer and composite patch on the residual strength of repaired panel are investigated for optimizing material properties to meet operational and envi- ronmental constraints.
文摘Medical-grade synthetic poly（lactic-co-glycolic acid） polymer can be used as a biomaterial for nerve repair because of its good biocompatibility, biodegradability and adjustable degradation rate. The stress relaxation and creep properties of peripheral nerve can be greatly improved by repair with poly（lactic-co-glycolic acid） tubes. ＂Fen sciatic nerve specimens were harvested from fresh corpses within 24 hours of death, and were prepared into sciatic nerve injury models by creating a 10 mm defect in each specimen. Defects were repaired by anastomosis with nerve autografts and poly（lactic-co-glycolic acid） tubes. Stress relaxation and creep testing showed that at 7 200 seconds the sciatic nerve anastomosed by poly（lactic-co-glycolic acid） tubes exhibited a greater decrease in stress and increase in strain than those anastomosed by nerve autografts. These findings suggest that poly（lactic-co-glycolic acid） exhibits good viscoelasticity to meet the biomechanical require- ments for a biomaterial used to repair sciatic nerve injury.
基金financial support to this work from the Tribology Science Fund of the State Key Laboratory of Tribology(SKLT2020C09)National Natural Science Foundation of China(No.51675303)National Key Research and Development Program of China(2017YFB1103300)。
文摘Directed energy deposition has been used to repair superalloy components in aero engines and gas turbines.However,the microstructure and properties are generally inhomogeneous in components because of the different processing histories.Here,the microstructures and wear behavior of different zones(substrate,HAZ,and deposit)are investigated for the IC10 directionally solidified superalloy repaired by the directed energy deposition process.It is found that the microstructure of the deposited layers is strongly textured with a<001>-fiber texture in the building direction,and the texture intensity is continuously increased along the building direction.Two kinds ofγ’phase(primary and secondaryγ’phase)can be found in the heat-affected zone(HAZ),and the average size of primaryγ’phase is smaller than that in the substrate due to liquation.In the deposit layers,the size ofγ’phase is much smaller than those in the substrate and the primaryγ’phase of HAZ;both size and the fraction of theγ’phase decreases with the increase of building height.The wear rate of the substrate is the smallest,indicating the best wear resistance;while the wear rate of HAZ is the largest,indicating the worst wear resistance in the repaired sample.The wear rates in the deposit layers increase from the bottom to the top zones,showing a decreasing wear resistance.Abrasive wear is found to be the dominant wear mechanism of the repaired alloy,and the resistance to which is closely related to the fraction ofγ’phase in the microstructure.The understanding of the influence of microstructure on wear resistance allows for a more informed application of inhomogeneous superalloy components repaired by directed energy deposition in industry.
文摘The bonded repair techniques seem to be the most frequent procedures in the aviation maintenance.The achieved composite repaired perforated thin-walled plate is a complex geometry with high numerical analysis cost.The NURBS-based Isogeometric Analysis(IGA)proposes a sensible and affordable tool to carry out such geometry analysis.In this context,a well-known technique is to divide the original geometry assembly into number of simple neighbors connected geometries.In the present study the free vibration analysis of the perforated plates repaired on one side with an external bonded composite laminated patch is investigated.A multi-patch geometry modeling approach is implemented in line with the first order shear deformation theory of plates.In order to hold the geometry integrity and uniformity,all the degrees of freedom between adjacent geometry patches are completely tied through implementing a Nitsche method.To show the effectiveness and accuracy of the developed formulation,some representative results are extracted and compared with those from literature.The effects of geometrical as well as material parameters including boundary condition,cutout shape,and repair layup on the dynamic response of the repaired perforated plates are then investigated.
基金supported by the Program for the Transport Science & Technology Project of Jiangsu Province
文摘Reinforcement corrosion has a serious impact on the durability and safety of reinforced concrete structures.Six reinforced concrete(RC)beam specimens are constructed.After beam specimens are subjected to accelerated corrosion with the constant current,beam specimens are repaired with epoxy mortar and the flexural test of beams is investigated.Then the behaviors of repaired corroded reinforced concrete beams are evaluated.The experimental results show that cracking and ultimate loads of corroded RC beams are enhanced after being repaired.And the strain distributions measured across sections of beam specimens still obey the assumption of plane section.After being repaired,the number of cracks decreases and the crack spacing increases.
文摘Fatigue crack growth test of cracked metallic plate repaired with adhesive bonding composite patch was conducted to study the fracture behavior of crack patching. The failure mode was that crack grows along with adhesive debonding. The crack length and debonding area were measured at different numbers of cycles. The nonlinear three- dimensional(3D)finite element(FE)model considering adhesive debonding and crack growth simultaneously was developed. The experimental and analytical results were in good agreement with each other.
文摘Numerical and experimental study was conducted to investigate the failure mode and strength performance of stiffened composite panel repaired by bolted joints under compressive load, and the results were then compared with those from virgin stiffened composite panel without any damage. A finite element analysis model was established for repaired and virgin stiffened composite panels under compressive load, the 3D Hashin criteria was applied to identify the composite structure failure, and the secondary stress criteria was adopted to identify the adhesive failure between the base laminate and the stiffener. The failure modes of repaired stiffened composite panels were stiffened composite panels breaking off along the bolt joints. The experimental results were consistent with the finite element analysis results, indicating the reliability of the finite element analysis model.
文摘This paper investigates the strength and deformation characteristics of reinforced normal and high-strength concrete rectangular beams which failed in shear and repaired by external bonding of carbon fiber and steel plate. Five simply supported reinforced concrete beams with shear reinforcement are tested, three of which are made with NSC （normal-strength concrete） and the other two with HSC （high-strength concrete）. The span of the simply supported beams is 0.9 m with 100 mm wide by 200 mm deep cross section. All five beams are tested under four-point bending. Careful repair process is adopted and proved successful. The aim is to restore or increase shear strength of these beams and to monitor their post-repair load-deflection behavior. The effect of concrete compressive strength on the behavior and strength of beams before and after repair is also investigated. Shear cracks patterns and their evolution are observed and discussed.
