To investigate the possible failure modes of the thermal barrier coating (TBC) used to protect the scramjet combustion chamber, the local heating via laser beam irradiation was utilized to simulate the service conditi...To investigate the possible failure modes of the thermal barrier coating (TBC) used to protect the scramjet combustion chamber, the local heating via laser beam irradiation was utilized to simulate the service condition of high thermal flux and high temperature gradient. Firstly, the experimental method and process were described and the typical fracture morphology of the TBC under test were provided. Then, the theoretical and finite element modeling were carried out to study the temperature, deformation and stresses of the specimen when the top ceramic coat was subjected to local heating, and to demonstrate the mechanism on the failure of the TBC. It is revealed that the interface delamination shall appear and ultimately lead to the failure of the TBC under such thermal loading of local quick heating. According to the outcome of this study, the driving force of the interface delamination is influenced greatly by the key structural parameters and performance matching. Moreover, by utilizing the rules of the effects of these parameters on the fracture driving force, there is some possibility for the designer to optimize the performances of the TBC.展开更多
T shaped skin-stiffener joint are one of the most commonly used structures in aerospace components.It has been proven in various studies that these joints are susceptible to failure when loaded in pull out conditions ...T shaped skin-stiffener joint are one of the most commonly used structures in aerospace components.It has been proven in various studies that these joints are susceptible to failure when loaded in pull out conditions however,in specific applications these joints undergo pull loading.De-lamination/de-bond nucleation and its growth is one of the most common failure mechanisms in a fiber reinforced composite structure.Crack growth takes place due to the induced interlaminar normal and shear stresses between different structural constituents when a load is applied.In this study,Finite Element Analysis has been performed using cohesive contact interactions on a composite T-joint to simulate the pull out test conditions.A simplified shell based model coupled with CZM is proposed,which can evaluate the failure initiation and progression accurately with lesser computational efforts.The final failure occurred at a displacement of 4.71 mm at the computed failure load of 472.57 kgf for basic configuration.Computed Failure load for the padded configuration is 672.8 kgf and corresponding displacement is 4.6 mm.The results obtained by the proposed numerical model are validated by experimental results and it is observed that predicted failure displacements and failure load calculated were correlating reasonably well with the experiment.展开更多
This research work investigated the modeling of Von Mises stress in LNG Spherical Carbon Steel Storage tank using assumed displacement Finite Element analysis based on shallow shell triangular elements. Using equation...This research work investigated the modeling of Von Mises stress in LNG Spherical Carbon Steel Storage tank using assumed displacement Finite Element analysis based on shallow shell triangular elements. Using equations of elasticity, constant thickness carbon steel spherical storage tanks were subjected to different loading conditions. This paper stresses the need for proper definition of shallow element using sector angles to obtain the shallowness. The shallow spherical triangular element has five degrees of freedom at each of its corner node, which are the essential external degrees of freedom. The assumed displacement fields of these shallow triangular elements satisfied the exact requirement of rigid body modes of motion. The FORTRAN 90 programming language was used for the programme coding to solve finite element equations resulting from the model while Von Mises stresses distribution within the spherical storage tank shell subjected to different internal pressures were determined. The results showed that the use of non-shallow elements due to improper sector angles resulted in unreliable results while real shallow elements produced results that tallied with ASME Section VIII Div 1, Part UG values.展开更多
Potential damage in composite structures caused by hail ice impact is an essential safety threat to the aircraft in flight.In this study,a nonlinear finite element(FE)model is developed to investigate the dynamic resp...Potential damage in composite structures caused by hail ice impact is an essential safety threat to the aircraft in flight.In this study,a nonlinear finite element(FE)model is developed to investigate the dynamic response and damage behavior of hybrid corrugated sandwich structures subjected to high velocity hail ice impact.The impact and breaking behavior of hail are described using the FE-smoothed particle hydrodynamics(FE-SPH)method.A rate-dependent progressive damage model is employed to capture the intra-laminar damage response;cohesive element and surface-based cohesive contact are implemented to predict the inter-laminar delamination and sheet/core debonding phenomena respectively.The transient processes of sandwich structure under different hail ice impact conditions are analyzed.Comparative analysis is conducted to address the influences of core shape and impact position on the impact performance of sandwich structures and the corresponding energy absorption characteristics are also revealed.展开更多
提出了一种Φ177.80 mm×8.05 mm K55热采井特殊螺纹设计,依照ISO/PAS 12835标准对该特殊螺纹进行材料性能评估以及材料模型和结构模型下的有限元分析。其中分析材料性能得到的不同温度下的应力-应变曲线特征点可作为数据输入到有...提出了一种Φ177.80 mm×8.05 mm K55热采井特殊螺纹设计,依照ISO/PAS 12835标准对该特殊螺纹进行材料性能评估以及材料模型和结构模型下的有限元分析。其中分析材料性能得到的不同温度下的应力-应变曲线特征点可作为数据输入到有限元软件中。采用有限元方法评估了接头在最佳上扣及温度循环条件下,不同结构公差的最差工况,材料性能变化对密封能力的影响,以及最后一次上扣扭矩要求。最后分析了特殊螺纹在温度载荷循环作用下结构的完整性。极限加载应力分析显示在整个温度加载循环条件下特殊螺纹未出现滑脱、颈缩、屈曲等现象。展开更多
This paper presents finite element modeling （FEM） to simulate the present-day stress field and crustal deformation using NE-SW structural section in the central Seismic Gap region of the Garhwal Himalaya. Our study ...This paper presents finite element modeling （FEM） to simulate the present-day stress field and crustal deformation using NE-SW structural section in the central Seismic Gap region of the Garhwal Himalaya. Our study deals with the effect of geometrical characteristics and rock layer parameters on the upper crust. Modeling results show that two types of tectonic regimes developed in the central Seismic Gap region： the geotectonics of the northern part has been controlled by regional compression, whereas southern part is characterized by regional extension. Correspondingly, thrust faults are induced in the northern part and normal faults are extensively developed in the southern front. Those evidences noticeably indicate that the compressive tectonic environment of the Himalaya becomes change into the extensional tectonic regime in its front. The computed shear stress accumulation along the northern fiat of Main Himalayan Thrust （MHT） implies that considerable amount of interseismic stress is building up along the MHT system in the Himalaya, which ultimately release through the possible future great Himalayan earthquake （M 〉 8）. The comparison between our modeled stress field, faulting pattern and horizontal shortening rate with the distribution of the microseismic events, focal mechanism solutions, active faulting and GPS data in the central Seismic Gap region shows good agreement.展开更多
Fischer–Tropsch Synthesis(FTS) constitutes catalytic technology that converts synthesis gas to synthetic liquid fuels and chemicals.While synthesis gas can be obtained from any carbonaceous feedstock,current industri...Fischer–Tropsch Synthesis(FTS) constitutes catalytic technology that converts synthesis gas to synthetic liquid fuels and chemicals.While synthesis gas can be obtained from any carbonaceous feedstock,current industrial FTS operations are almost exclusively based on natural gas.Due to the energy structure of China where cheap coal is abundant,coal to liquids(CTL) technology involving coal gasification,FTS and syncrude upgrading is increasingly being considered as a viable option to convert coal to clean transportation fuels.In this brief paper,we review some pertinent issues about Fe-and Co-based FTS catalysts.Fe is better suited to convert synthesis gas derived from coal gasification into fuels.The authors limit themselves to noting some important trends in the research on Fe-based catalysts.They focus on the preparation of phase-pure carbides and innovative cheap synthesis methods for obtaining active and stable catalysts.These approaches should be augmented by(1) computational investigations that are increasingly able to predict not only mechanism,reaction rates and selectivity but also optimum catalyst composition,as well as(2) characterization of the catalytic materials under conditions close to the operation in real reactors.展开更多
Resistance spot welding (RSW) is the most common welding method in automotive engineering due to its low cost and high ability of automation. However, physical weldability testing is costly, time consuming and depende...Resistance spot welding (RSW) is the most common welding method in automotive engineering due to its low cost and high ability of automation. However, physical weldability testing is costly, time consuming and dependent of supplies of material and equipment. Finite Element (FE) simulations have been utilized to understand, verify and optimize manufacturing processes more efficiently. The present work aims to verify the capability of FE models for the RSW process by comparing simulation results to physical experiments for materials used in automotive production, with yield strengths from approximately 280 MPa to more than 1500 MPa. Previous research has mainly focused on lower strength materials. The physical weld results were assessed using destructive testing and an analysis of expulsion limits was also carried out. Extensive new determination of material data was carried out. The material data analysis was based on physical testing of material specimens, material simulation and comparison to data from literature. The study showed good agreement between simulations and physical testing. The mean absolute error of weld nugget size was 0.68 mm and the mean absolute error of expulsion limit was 1.10 kA.展开更多
基金supported by the National Natural Science Foundation of China (Grant No. 11002145)
文摘To investigate the possible failure modes of the thermal barrier coating (TBC) used to protect the scramjet combustion chamber, the local heating via laser beam irradiation was utilized to simulate the service condition of high thermal flux and high temperature gradient. Firstly, the experimental method and process were described and the typical fracture morphology of the TBC under test were provided. Then, the theoretical and finite element modeling were carried out to study the temperature, deformation and stresses of the specimen when the top ceramic coat was subjected to local heating, and to demonstrate the mechanism on the failure of the TBC. It is revealed that the interface delamination shall appear and ultimately lead to the failure of the TBC under such thermal loading of local quick heating. According to the outcome of this study, the driving force of the interface delamination is influenced greatly by the key structural parameters and performance matching. Moreover, by utilizing the rules of the effects of these parameters on the fracture driving force, there is some possibility for the designer to optimize the performances of the TBC.
文摘T shaped skin-stiffener joint are one of the most commonly used structures in aerospace components.It has been proven in various studies that these joints are susceptible to failure when loaded in pull out conditions however,in specific applications these joints undergo pull loading.De-lamination/de-bond nucleation and its growth is one of the most common failure mechanisms in a fiber reinforced composite structure.Crack growth takes place due to the induced interlaminar normal and shear stresses between different structural constituents when a load is applied.In this study,Finite Element Analysis has been performed using cohesive contact interactions on a composite T-joint to simulate the pull out test conditions.A simplified shell based model coupled with CZM is proposed,which can evaluate the failure initiation and progression accurately with lesser computational efforts.The final failure occurred at a displacement of 4.71 mm at the computed failure load of 472.57 kgf for basic configuration.Computed Failure load for the padded configuration is 672.8 kgf and corresponding displacement is 4.6 mm.The results obtained by the proposed numerical model are validated by experimental results and it is observed that predicted failure displacements and failure load calculated were correlating reasonably well with the experiment.
文摘This research work investigated the modeling of Von Mises stress in LNG Spherical Carbon Steel Storage tank using assumed displacement Finite Element analysis based on shallow shell triangular elements. Using equations of elasticity, constant thickness carbon steel spherical storage tanks were subjected to different loading conditions. This paper stresses the need for proper definition of shallow element using sector angles to obtain the shallowness. The shallow spherical triangular element has five degrees of freedom at each of its corner node, which are the essential external degrees of freedom. The assumed displacement fields of these shallow triangular elements satisfied the exact requirement of rigid body modes of motion. The FORTRAN 90 programming language was used for the programme coding to solve finite element equations resulting from the model while Von Mises stresses distribution within the spherical storage tank shell subjected to different internal pressures were determined. The results showed that the use of non-shallow elements due to improper sector angles resulted in unreliable results while real shallow elements produced results that tallied with ASME Section VIII Div 1, Part UG values.
基金supported by the Natural Science Foundation of Jiangsu Province(Grant No.BK20180855)Research Fund of State Key Laboratory of Mechanics and Control of Mechanical Structures(Grant No.MCMS-E-0219Y01)Research and Practice Innovation Program of postgraduates in Jiangsu Province(Grant No.KYCX20-3076)。
文摘Potential damage in composite structures caused by hail ice impact is an essential safety threat to the aircraft in flight.In this study,a nonlinear finite element(FE)model is developed to investigate the dynamic response and damage behavior of hybrid corrugated sandwich structures subjected to high velocity hail ice impact.The impact and breaking behavior of hail are described using the FE-smoothed particle hydrodynamics(FE-SPH)method.A rate-dependent progressive damage model is employed to capture the intra-laminar damage response;cohesive element and surface-based cohesive contact are implemented to predict the inter-laminar delamination and sheet/core debonding phenomena respectively.The transient processes of sandwich structure under different hail ice impact conditions are analyzed.Comparative analysis is conducted to address the influences of core shape and impact position on the impact performance of sandwich structures and the corresponding energy absorption characteristics are also revealed.
文摘提出了一种Φ177.80 mm×8.05 mm K55热采井特殊螺纹设计,依照ISO/PAS 12835标准对该特殊螺纹进行材料性能评估以及材料模型和结构模型下的有限元分析。其中分析材料性能得到的不同温度下的应力-应变曲线特征点可作为数据输入到有限元软件中。采用有限元方法评估了接头在最佳上扣及温度循环条件下,不同结构公差的最差工况,材料性能变化对密封能力的影响,以及最后一次上扣扭矩要求。最后分析了特殊螺纹在温度载荷循环作用下结构的完整性。极限加载应力分析显示在整个温度加载循环条件下特殊螺纹未出现滑脱、颈缩、屈曲等现象。
文摘This paper presents finite element modeling （FEM） to simulate the present-day stress field and crustal deformation using NE-SW structural section in the central Seismic Gap region of the Garhwal Himalaya. Our study deals with the effect of geometrical characteristics and rock layer parameters on the upper crust. Modeling results show that two types of tectonic regimes developed in the central Seismic Gap region： the geotectonics of the northern part has been controlled by regional compression, whereas southern part is characterized by regional extension. Correspondingly, thrust faults are induced in the northern part and normal faults are extensively developed in the southern front. Those evidences noticeably indicate that the compressive tectonic environment of the Himalaya becomes change into the extensional tectonic regime in its front. The computed shear stress accumulation along the northern fiat of Main Himalayan Thrust （MHT） implies that considerable amount of interseismic stress is building up along the MHT system in the Himalaya, which ultimately release through the possible future great Himalayan earthquake （M 〉 8）. The comparison between our modeled stress field, faulting pattern and horizontal shortening rate with the distribution of the microseismic events, focal mechanism solutions, active faulting and GPS data in the central Seismic Gap region shows good agreement.
文摘Fischer–Tropsch Synthesis(FTS) constitutes catalytic technology that converts synthesis gas to synthetic liquid fuels and chemicals.While synthesis gas can be obtained from any carbonaceous feedstock,current industrial FTS operations are almost exclusively based on natural gas.Due to the energy structure of China where cheap coal is abundant,coal to liquids(CTL) technology involving coal gasification,FTS and syncrude upgrading is increasingly being considered as a viable option to convert coal to clean transportation fuels.In this brief paper,we review some pertinent issues about Fe-and Co-based FTS catalysts.Fe is better suited to convert synthesis gas derived from coal gasification into fuels.The authors limit themselves to noting some important trends in the research on Fe-based catalysts.They focus on the preparation of phase-pure carbides and innovative cheap synthesis methods for obtaining active and stable catalysts.These approaches should be augmented by(1) computational investigations that are increasingly able to predict not only mechanism,reaction rates and selectivity but also optimum catalyst composition,as well as(2) characterization of the catalytic materials under conditions close to the operation in real reactors.
文摘Resistance spot welding (RSW) is the most common welding method in automotive engineering due to its low cost and high ability of automation. However, physical weldability testing is costly, time consuming and dependent of supplies of material and equipment. Finite Element (FE) simulations have been utilized to understand, verify and optimize manufacturing processes more efficiently. The present work aims to verify the capability of FE models for the RSW process by comparing simulation results to physical experiments for materials used in automotive production, with yield strengths from approximately 280 MPa to more than 1500 MPa. Previous research has mainly focused on lower strength materials. The physical weld results were assessed using destructive testing and an analysis of expulsion limits was also carried out. Extensive new determination of material data was carried out. The material data analysis was based on physical testing of material specimens, material simulation and comparison to data from literature. The study showed good agreement between simulations and physical testing. The mean absolute error of weld nugget size was 0.68 mm and the mean absolute error of expulsion limit was 1.10 kA.
