In fatigue damage tolerance verification tests of aircraft structures,the simulation and loading of flight-byflight spectra require considerable time and resources.To improve the efficiency of load spectrum design and...In fatigue damage tolerance verification tests of aircraft structures,the simulation and loading of flight-byflight spectra require considerable time and resources.To improve the efficiency of load spectrum design and testing,an equivalent constant-amplitude spectrum design method for flight-by-flight spectra is proposed based on the equivalence of crack growth behavior.By combining the Paris crack growth model with the Walker stress ratio correction,the equivalent stress amplitude is directly calculated using structural parameters and load spectrum characteristics,enabling a rapid transformation from variable-amplitude spectra to constant-amplitude spectra.The original spectrum is discretized based on the load-exceedance curve,and the equivalence relationship between multilevel block spectra and constant-amplitude spectra is established.Taking a typical lower wing skin structure of a transport aircraft as an example,two equivalent spectra are designed and validated through fatigue crack growth tests on 2024-T351 center-hole plate specimens.The experimental results show that the fatigue life deviation between the equivalent spectra and the original flight-by-flight spectrum is within 10%,demonstrating the effectiveness of the proposed method.Moreover,the equivalent spectrum constructed under the condition of invariant mean flight stress exhibits higher equivalence accuracy.The influence of spectral shape on the equivalent stress amplitude is further analyzed,revealing that the equivalent stress amplitude increases with the spectrum shape coefficient.The proposed method provides a useful reference for load spectrum design in aircraft structural damage tolerance verification tests.展开更多
To simulate the fatigue characteristics of the pile-board structure under long-term dynamic load, using the in-situ dynamic testing system DTS-1, the forced vibration loading was repeated one million times at differen...To simulate the fatigue characteristics of the pile-board structure under long-term dynamic load, using the in-situ dynamic testing system DTS-1, the forced vibration loading was repeated one million times at different cross-sections of the pile-board structure for high-speed railway. The dynamic deformation, permanent deformation and dynamic stress of main reinforcements were measured. The test results show that the dynamic responses of the pile-board structure almost did not vary with the forced vibration times under the simulated trainload. After one million times of forced vibration, the permanent deformations of the midspan section of intermediate span and midspan section of side span were 0.7 mm and 0. 6 mm, respectively, and there was no accumulative plastic deformation at the bearing section of intermediate span.展开更多
This paper introduces the process and result of fatigue test of steel (Z direction steel) welded T tubular joints used in offshore engineering. Detailed measurement of stress concentration factor, stress distribution,...This paper introduces the process and result of fatigue test of steel (Z direction steel) welded T tubular joints used in offshore engineering. Detailed measurement of stress concentration factor, stress distribution, fatigue life and crack development has been performed. Through analysis, an empirical formula of stress concentration factor for T tubular joints, fatigue S-N curve and crack propagation rule are obtained.展开更多
In order to study the fatigue behavior of the damaged reinforced concrete （RC） beams strengthened by carbon fiber reinforced polymer （CFRP） laminate, three T-shaped beams strengthened by CFRP and one contrasting b...In order to study the fatigue behavior of the damaged reinforced concrete （RC） beams strengthened by carbon fiber reinforced polymer （CFRP） laminate, three T-shaped beams strengthened by CFRP and one contrasting beam are tested under fatigue loading, with the parameters of different modes of strengthening and different fatigue load levels considered. The main results obtained from the tests are： the width of the crack decreases 50. 2% to 66%, and the development of the crack is limited; the stress of steel decreases 24. 1% to 28. 2%, and the stiffness increases 14.9% to 16. 1% after being strengthened. Based on the technical specification for strengthening concrete structures with CFRP and the conclusions from the tests, a calculating scheme of the flexure stiffness is given, which can be used for reference in engineering design. Finally, some suggestions are given for design in fatigue strengthening.展开更多
Full scale aircraft static test is a very important process of aircraft design, it is costly and time consuming. The testing accuracy and validity mainly depend on the rationality of the test scheme design. When the a...Full scale aircraft static test is a very important process of aircraft design, it is costly and time consuming. The testing accuracy and validity mainly depend on the rationality of the test scheme design. When the aircraft is being tested, the specimen＇s safety mainly depends on monitoring and understanding the testing data by way of evaluating the coherence with the digital simulation data synchyononsly. The test digital simulation can aid realizing above requirements and improving the test efficiency significantly during test scheme design stage or testing stage respectively. The key technologies and the solving methods of test digital simulation are presented and the application example is given.展开更多
Fatigue damage of materials includes static damage and cyclic damage.Static damage is a ratio of the plastic energy in first static loading to the statictoughness, while cyclic damage is the ratio of the cyclic plasti...Fatigue damage of materials includes static damage and cyclic damage.Static damage is a ratio of the plastic energy in first static loading to the statictoughness, while cyclic damage is the ratio of the cyclic plastic hysteresis energy to thefatigue toughness. In the calculation, cyclic hardening (or softening) of a material istaken into account, which results in the increase (or decrease) of the yield stress. Forsimplification, it is assumed that stress and strain in cyclic loading vary in accordancewith the hysteresis loop. Fatigue toughness of a material can be detennined bysymmetric cyclic stress controlled fatigue test. A method, rational and convenient forengineering, is proposed to estimate the fatigue life under random loading based onplastic hysteresis energy theorem. Preliminary verification by test is satisfactory.展开更多
The Monte- Carlo method is used to simulate the surface fatigue crack growth rate for offshore structural steel E36-Z35, and to determine the distributions and relevance of the parameters in the Paris equation. By thi...The Monte- Carlo method is used to simulate the surface fatigue crack growth rate for offshore structural steel E36-Z35, and to determine the distributions and relevance of the parameters in the Paris equation. By this method, the time and cost of fatigue crack propagation testing can be reduced. The application of the method is demonstrated by use of four sets of fatigue crack propagation data for offshore structural steel E36-Z35. A comparison of the test data with the theoretical prediction for surface crack growth rate shows the application of the simulation method to the fatigue crack propagation tests is successful.展开更多
Offshore platforms are always subjected to wave action which is random variable amplitude cyclic loading. In order to simulate the stressing condition at the 'hot spot' of the tubular joints and the marine env...Offshore platforms are always subjected to wave action which is random variable amplitude cyclic loading. In order to simulate the stressing condition at the 'hot spot' of the tubular joints and the marine environment, random variable amplitude fatigue tests have been carried out on welded plate joints in sea water. The tests have been conducted under the conditions of loading frequency of 0.2 Hz/, stress ratio of -1, seawater temperature of about 20°C and cathodic protection with the potential about -850 mV, SCE. The test results have been compared with the seawater corrosion fatigue life under constant amplitude loading. Miner's linear cumulative damage summation rule has been used to predict the corrosion fatigue life under variable amplitude loading. The predicted life is in good agreement with the test data.展开更多
This paper first describes the importance of using location specific S-N curves for fatigue damage assessment of existing steel structures. It discusses the existing concepts and methods for developing S-N curves usin...This paper first describes the importance of using location specific S-N curves for fatigue damage assessment of existing steel structures. It discusses the existing concepts and methods for developing S-N curves using empirical formulae and monotonic strength parameters, such as the ultimate tensile strength and hardness. It also discusses relationships among these monotonic parameters. Then it presents formulae for developing hardness-based full range S-N curves for medium strength steels. The formulae are verified using experimental data obtained from both monotonic and cyclic testing. Finally, it describes the advantages of these hardness-based formulae for developing location specific S-N curves as hardness testing is a non-destructive test which can be carried out on specific locations in structures.展开更多
High-temperature structural ceramics have increasingly attracted scientists’ attention in the area of modern science and technology due to their excellent properties of corrosion-resistance, wear-resistance and high-...High-temperature structural ceramics have increasingly attracted scientists’ attention in the area of modern science and technology due to their excellent properties of corrosion-resistance, wear-resistance and high-temperature resistance. But their low reliability limits their application in practice. In this note, AE signals of high-temperature structural ceramics under static fatigue were picked up by AE transducer and the relation between AE signals and crack growth in structural ceramics was studied. The results show that the AE rate of structural ceramics展开更多
基金supported by the National Natural Science Foundation of China(No.52075244).
文摘In fatigue damage tolerance verification tests of aircraft structures,the simulation and loading of flight-byflight spectra require considerable time and resources.To improve the efficiency of load spectrum design and testing,an equivalent constant-amplitude spectrum design method for flight-by-flight spectra is proposed based on the equivalence of crack growth behavior.By combining the Paris crack growth model with the Walker stress ratio correction,the equivalent stress amplitude is directly calculated using structural parameters and load spectrum characteristics,enabling a rapid transformation from variable-amplitude spectra to constant-amplitude spectra.The original spectrum is discretized based on the load-exceedance curve,and the equivalence relationship between multilevel block spectra and constant-amplitude spectra is established.Taking a typical lower wing skin structure of a transport aircraft as an example,two equivalent spectra are designed and validated through fatigue crack growth tests on 2024-T351 center-hole plate specimens.The experimental results show that the fatigue life deviation between the equivalent spectra and the original flight-by-flight spectrum is within 10%,demonstrating the effectiveness of the proposed method.Moreover,the equivalent spectrum constructed under the condition of invariant mean flight stress exhibits higher equivalence accuracy.The influence of spectral shape on the equivalent stress amplitude is further analyzed,revealing that the equivalent stress amplitude increases with the spectrum shape coefficient.The proposed method provides a useful reference for load spectrum design in aircraft structural damage tolerance verification tests.
基金Key Subject for Science Research and De-velopment Plan of Railway Ministry (No.2006G004-B)
文摘To simulate the fatigue characteristics of the pile-board structure under long-term dynamic load, using the in-situ dynamic testing system DTS-1, the forced vibration loading was repeated one million times at different cross-sections of the pile-board structure for high-speed railway. The dynamic deformation, permanent deformation and dynamic stress of main reinforcements were measured. The test results show that the dynamic responses of the pile-board structure almost did not vary with the forced vibration times under the simulated trainload. After one million times of forced vibration, the permanent deformations of the midspan section of intermediate span and midspan section of side span were 0.7 mm and 0. 6 mm, respectively, and there was no accumulative plastic deformation at the bearing section of intermediate span.
文摘This paper introduces the process and result of fatigue test of steel (Z direction steel) welded T tubular joints used in offshore engineering. Detailed measurement of stress concentration factor, stress distribution, fatigue life and crack development has been performed. Through analysis, an empirical formula of stress concentration factor for T tubular joints, fatigue S-N curve and crack propagation rule are obtained.
基金The Natural Science Foundation of Jiangsu Province(NoBK2004064)the Postdoctoral Foundation of Jiangsu Province(No0701008B)
文摘In order to study the fatigue behavior of the damaged reinforced concrete （RC） beams strengthened by carbon fiber reinforced polymer （CFRP） laminate, three T-shaped beams strengthened by CFRP and one contrasting beam are tested under fatigue loading, with the parameters of different modes of strengthening and different fatigue load levels considered. The main results obtained from the tests are： the width of the crack decreases 50. 2% to 66%, and the development of the crack is limited; the stress of steel decreases 24. 1% to 28. 2%, and the stiffness increases 14.9% to 16. 1% after being strengthened. Based on the technical specification for strengthening concrete structures with CFRP and the conclusions from the tests, a calculating scheme of the flexure stiffness is given, which can be used for reference in engineering design. Finally, some suggestions are given for design in fatigue strengthening.
文摘Full scale aircraft static test is a very important process of aircraft design, it is costly and time consuming. The testing accuracy and validity mainly depend on the rationality of the test scheme design. When the aircraft is being tested, the specimen＇s safety mainly depends on monitoring and understanding the testing data by way of evaluating the coherence with the digital simulation data synchyononsly. The test digital simulation can aid realizing above requirements and improving the test efficiency significantly during test scheme design stage or testing stage respectively. The key technologies and the solving methods of test digital simulation are presented and the application example is given.
文摘Fatigue damage of materials includes static damage and cyclic damage.Static damage is a ratio of the plastic energy in first static loading to the statictoughness, while cyclic damage is the ratio of the cyclic plastic hysteresis energy to thefatigue toughness. In the calculation, cyclic hardening (or softening) of a material istaken into account, which results in the increase (or decrease) of the yield stress. Forsimplification, it is assumed that stress and strain in cyclic loading vary in accordancewith the hysteresis loop. Fatigue toughness of a material can be detennined bysymmetric cyclic stress controlled fatigue test. A method, rational and convenient forengineering, is proposed to estimate the fatigue life under random loading based onplastic hysteresis energy theorem. Preliminary verification by test is satisfactory.
文摘The Monte- Carlo method is used to simulate the surface fatigue crack growth rate for offshore structural steel E36-Z35, and to determine the distributions and relevance of the parameters in the Paris equation. By this method, the time and cost of fatigue crack propagation testing can be reduced. The application of the method is demonstrated by use of four sets of fatigue crack propagation data for offshore structural steel E36-Z35. A comparison of the test data with the theoretical prediction for surface crack growth rate shows the application of the simulation method to the fatigue crack propagation tests is successful.
文摘Offshore platforms are always subjected to wave action which is random variable amplitude cyclic loading. In order to simulate the stressing condition at the 'hot spot' of the tubular joints and the marine environment, random variable amplitude fatigue tests have been carried out on welded plate joints in sea water. The tests have been conducted under the conditions of loading frequency of 0.2 Hz/, stress ratio of -1, seawater temperature of about 20°C and cathodic protection with the potential about -850 mV, SCE. The test results have been compared with the seawater corrosion fatigue life under constant amplitude loading. Miner's linear cumulative damage summation rule has been used to predict the corrosion fatigue life under variable amplitude loading. The predicted life is in good agreement with the test data.
文摘This paper first describes the importance of using location specific S-N curves for fatigue damage assessment of existing steel structures. It discusses the existing concepts and methods for developing S-N curves using empirical formulae and monotonic strength parameters, such as the ultimate tensile strength and hardness. It also discusses relationships among these monotonic parameters. Then it presents formulae for developing hardness-based full range S-N curves for medium strength steels. The formulae are verified using experimental data obtained from both monotonic and cyclic testing. Finally, it describes the advantages of these hardness-based formulae for developing location specific S-N curves as hardness testing is a non-destructive test which can be carried out on specific locations in structures.
文摘High-temperature structural ceramics have increasingly attracted scientists’ attention in the area of modern science and technology due to their excellent properties of corrosion-resistance, wear-resistance and high-temperature resistance. But their low reliability limits their application in practice. In this note, AE signals of high-temperature structural ceramics under static fatigue were picked up by AE transducer and the relation between AE signals and crack growth in structural ceramics was studied. The results show that the AE rate of structural ceramics
