The three-dimensional finite element method is used to solve the problem of the quarter-elliptical comer crack of the bolt-hole in mechanical joints being subjected to remote tension. The square-root stress singularit...The three-dimensional finite element method is used to solve the problem of the quarter-elliptical comer crack of the bolt-hole in mechanical joints being subjected to remote tension. The square-root stress singularity around the corner crack front is simulated using the collapsed 20-node quarter point singular elements. The contact interaction between the bolt and the hole boundary is considered in the finite element analysis. The stress intensity factors （SIFs） along the crack front are evaluated by using the displacement correlation technique. The effects of the amount of clearance between the hole and the bolt on the SIFs are investigated. The numerical results indicate that the SIF for mode I decrease with the decreases in clearance, and in the cases of clearance being present, the corner crack is in a mix-mode, even if mode I loading is dominant.展开更多
With the considerable applications of ceramic matrix composites(CMC) in aircraft engineering, the design of CMC bolted joint gains paramount attention because of its capacity to to improve load-bearing efficiency of a...With the considerable applications of ceramic matrix composites(CMC) in aircraft engineering, the design of CMC bolted joint gains paramount attention because of its capacity to to improve load-bearing efficiency of aircraft key structure. In this work, a 3 D finite element model was established to predict tensile performance and failure modes of single-lap, single-bolt 2 D C/SiC composite, and superalloy joint, which considers the progressive damage behavior of 2 D woven C/SiC composites. On the basis of the developed progressive damage model, a parametric study was carried out to illustrate the effects of bolt preload and bolt-hole clearance on mechanical behaviors of the hybrid bolted joint. It was found that the increase in the value of bolt preload made the failure load grow first and then drop, and the optimum value of bolt preload 5.00 kN generated 56.47% rise in the initial failure load and 22.83% rise in the final failure load for the bolted joint in comparison with zero preload case. As the clearance increased from 0 to 2.00%, the initial and final failure loads respectively declined by 45.88% and 24.02% for 2.00% bolt-hole clearance relative to the neat-fit case. The loss in failure loads can be reduced to compressive stress concentration around the fastening hole-edge area, leading to the appearance of earlier damages by the introduction of increasing bolt hole clearance.展开更多
Ceramic matrix composite(CMC) and superalloy bolted joints have exhibited great potential for high temperature hot structure application in hypersonic aircraft. In service conditions, the thermal expansion mismatch be...Ceramic matrix composite(CMC) and superalloy bolted joints have exhibited great potential for high temperature hot structure application in hypersonic aircraft. In service conditions, the thermal expansion mismatch between CMC and superalloy plates will cause complex thermal stress and strain distributions at hole-edge areas and assembly parameters changes of the joints under elevated temperatures. These effects might lead to early damage of joint structure, which will endanger the structural integrity and load carrying capacity of aircraft components. In the present study, transient heat transfer and thermo-structural analysis of C/SiC composite and superalloy bolted joint were carried out by using a commercial FEA software ABAQUS. The stress distributions at hole-edge areas, pre-load loosening, and variation of bolt-hole clearance of CMC bolted joints under transient temperature rises were discussed for better understanding of high temperature structural behaviors. Results showed that pre-load declined with the increase of imposed hot side temperature, due to the thermal expansion mismatch between CMC and superalloy. The bolt-hole clearance for the composite plate decreased, whereas the clearance for the superalloy plate increased with the rise of temperature.展开更多
Previously we have shown that a four-dimensional Kerr-Bolt black hole in non-extremal and also in extremal cases could be described by a holographic two-dimensional （2D） conformal field theory （CFT） [Ghezelbash A ...Previously we have shown that a four-dimensional Kerr-Bolt black hole in non-extremal and also in extremal cases could be described by a holographic two-dimensional （2D） conformal field theory （CFT） [Ghezelbash A M, Kamali V and Setare M R 2010 Phys. Rev. D 82 124051; Setare M R and Kamali V 2010 JHEP 10 074]. Motivated by recent work [Chen C M, Huang Y M, Sun J R, Wu M F and Zou S J 2010 Phys. Rev. D 82 066004], we show that there is another holographic description for these black holes. The first description is called the J-picture, whose construction is based on the black hole angular momentum. The new description is called the Q-picture, whose constructions originate from the nut charge of the black hole. Similar to the previous cases [Ghezelbash A M, Kamali V and Setare M R 2010 Phys. Rev. D 82 124051; Setare M R and Kamali V 2010 JHEP 10 0741, we show that this new picture for a low frequency limit of the wave equation of a massless charged scalar field in the background of a Kerr-Bolt black hole can be written as the Casimir of SL（2, R） symmetry. Our result shows that the entropy of the black hole is reproduced by the Cardy formula. In addition, the absorption cross section is consistent with the finite temperature absorption cross section for a two-dimensional CFT.展开更多
基金National Natural Science Foundation of China (10272036)
文摘The three-dimensional finite element method is used to solve the problem of the quarter-elliptical comer crack of the bolt-hole in mechanical joints being subjected to remote tension. The square-root stress singularity around the corner crack front is simulated using the collapsed 20-node quarter point singular elements. The contact interaction between the bolt and the hole boundary is considered in the finite element analysis. The stress intensity factors （SIFs） along the crack front are evaluated by using the displacement correlation technique. The effects of the amount of clearance between the hole and the bolt on the SIFs are investigated. The numerical results indicate that the SIF for mode I decrease with the decreases in clearance, and in the cases of clearance being present, the corner crack is in a mix-mode, even if mode I loading is dominant.
基金Sponsored by the Pre-Research Foundation of Shenyang Aircraft Design and Research Institute,the Aviation Industry Corporation of China(Grant No.JH20128255)the National Defence Basic Research Program(Grant No.JZ20180032)the Pre-Research Foundation of Equipment Development Department of People’s Republic of China Central Military Commission(Grant No.ZJJSN20200001)。
文摘With the considerable applications of ceramic matrix composites(CMC) in aircraft engineering, the design of CMC bolted joint gains paramount attention because of its capacity to to improve load-bearing efficiency of aircraft key structure. In this work, a 3 D finite element model was established to predict tensile performance and failure modes of single-lap, single-bolt 2 D C/SiC composite, and superalloy joint, which considers the progressive damage behavior of 2 D woven C/SiC composites. On the basis of the developed progressive damage model, a parametric study was carried out to illustrate the effects of bolt preload and bolt-hole clearance on mechanical behaviors of the hybrid bolted joint. It was found that the increase in the value of bolt preload made the failure load grow first and then drop, and the optimum value of bolt preload 5.00 kN generated 56.47% rise in the initial failure load and 22.83% rise in the final failure load for the bolted joint in comparison with zero preload case. As the clearance increased from 0 to 2.00%, the initial and final failure loads respectively declined by 45.88% and 24.02% for 2.00% bolt-hole clearance relative to the neat-fit case. The loss in failure loads can be reduced to compressive stress concentration around the fastening hole-edge area, leading to the appearance of earlier damages by the introduction of increasing bolt hole clearance.
基金Sponsored by the Pre-research Foundation of Shenyang Aircraft Design and Research Institute,Aviation Industry Corporation of China(Grant No.JH20128255)。
文摘Ceramic matrix composite(CMC) and superalloy bolted joints have exhibited great potential for high temperature hot structure application in hypersonic aircraft. In service conditions, the thermal expansion mismatch between CMC and superalloy plates will cause complex thermal stress and strain distributions at hole-edge areas and assembly parameters changes of the joints under elevated temperatures. These effects might lead to early damage of joint structure, which will endanger the structural integrity and load carrying capacity of aircraft components. In the present study, transient heat transfer and thermo-structural analysis of C/SiC composite and superalloy bolted joint were carried out by using a commercial FEA software ABAQUS. The stress distributions at hole-edge areas, pre-load loosening, and variation of bolt-hole clearance of CMC bolted joints under transient temperature rises were discussed for better understanding of high temperature structural behaviors. Results showed that pre-load declined with the increase of imposed hot side temperature, due to the thermal expansion mismatch between CMC and superalloy. The bolt-hole clearance for the composite plate decreased, whereas the clearance for the superalloy plate increased with the rise of temperature.
文摘Previously we have shown that a four-dimensional Kerr-Bolt black hole in non-extremal and also in extremal cases could be described by a holographic two-dimensional （2D） conformal field theory （CFT） [Ghezelbash A M, Kamali V and Setare M R 2010 Phys. Rev. D 82 124051; Setare M R and Kamali V 2010 JHEP 10 074]. Motivated by recent work [Chen C M, Huang Y M, Sun J R, Wu M F and Zou S J 2010 Phys. Rev. D 82 066004], we show that there is another holographic description for these black holes. The first description is called the J-picture, whose construction is based on the black hole angular momentum. The new description is called the Q-picture, whose constructions originate from the nut charge of the black hole. Similar to the previous cases [Ghezelbash A M, Kamali V and Setare M R 2010 Phys. Rev. D 82 124051; Setare M R and Kamali V 2010 JHEP 10 0741, we show that this new picture for a low frequency limit of the wave equation of a massless charged scalar field in the background of a Kerr-Bolt black hole can be written as the Casimir of SL（2, R） symmetry. Our result shows that the entropy of the black hole is reproduced by the Cardy formula. In addition, the absorption cross section is consistent with the finite temperature absorption cross section for a two-dimensional CFT.
