Tests with middle-crack tension （M（T）） specimens made of Al 2324-T39 and Al 7050-T7451 are conducted to investigate the influence of low load truncation level on fatigue crack growth. The six different truncated s...Tests with middle-crack tension （M（T）） specimens made of Al 2324-T39 and Al 7050-T7451 are conducted to investigate the influence of low load truncation level on fatigue crack growth. The six different truncated spectra are obtained by removing the small cycles of which amplitudes are less than the specified percentages of the maximum amplitude in the basic flight-by-flight loading spectrum and the remainder of the spectrum is untouched. The tests indicate that the mean level of fatigue crack growth life （FCGL） increases as the load truncation level is enhanced. Considering both the time saving and the influence on FCGL, there is an applicable choice （i.e. spectrum S2 or spectrum S3 in this investigation） for full scale fatigue test. The scatter of FCGL becomes much larger than that under the basic spectrum when the load truncation level is increased to a specified high level, mainly due to the occurrence of crack slanting and branching under the high level truncated loading spectra.展开更多
he stress-strength interferenee model can be used for the structure with-out fatigue cracks. It is not available for the structure that is often damaged slightlysuch as propellers. A two-dimensional interferenee relia...he stress-strength interferenee model can be used for the structure with-out fatigue cracks. It is not available for the structure that is often damaged slightlysuch as propellers. A two-dimensional interferenee reliability model using thetwo-dimensional fatigue load distribution and the distribution of fatigue crack growththreshold for the reliability of the structure with fatigue crack is established. The relia-bility of the propeller of Y7-200B with different crack sizes is listed. A damage toler-ance analysis using an interference integration formula with the two-dimensional loaddistribution is carried out for the propeller and the fatigue crack inspection period withgiven reliability is presented.展开更多
An average failure index method based on accurate FEA was proposed for the tensile strength prediction of composite out-of-plane adhesive-bonded π joints. Based on the simple and independent maximum stress failure cr...An average failure index method based on accurate FEA was proposed for the tensile strength prediction of composite out-of-plane adhesive-bonded π joints. Based on the simple and independent maximum stress failure criterion, the failure index was introduced to characterize the degree of stress components close to their corresponding material strength. With a brief load transfer analysis, the weak fillers were prominent and further detailed discussion was performed. The maximum value among the average failure indices which were related with different stress components was filtrated to represent the failure strength of the critical surface, which is either the two curved upside surfaces or the bottom plane of the fillers for composite π joints. The tensile strength of three kinds of π joints with different material systems, configurations and lay-ups was predicted by the proposed method and corresponding experiments were conducted. Good agreements between the numerical and experimental results give evidence of the effectiveness of the proposed method. In contrast to the existed time-consuming strength prediction methods, the proposed method provides a capability of quickly assessing the failure of complex out-of-plane joints and is easy and convenient to be widely utilized in engineering.展开更多
基金National Natural Science Foundation of China (10802003)
文摘Tests with middle-crack tension （M（T）） specimens made of Al 2324-T39 and Al 7050-T7451 are conducted to investigate the influence of low load truncation level on fatigue crack growth. The six different truncated spectra are obtained by removing the small cycles of which amplitudes are less than the specified percentages of the maximum amplitude in the basic flight-by-flight loading spectrum and the remainder of the spectrum is untouched. The tests indicate that the mean level of fatigue crack growth life （FCGL） increases as the load truncation level is enhanced. Considering both the time saving and the influence on FCGL, there is an applicable choice （i.e. spectrum S2 or spectrum S3 in this investigation） for full scale fatigue test. The scatter of FCGL becomes much larger than that under the basic spectrum when the load truncation level is increased to a specified high level, mainly due to the occurrence of crack slanting and branching under the high level truncated loading spectra.
文摘he stress-strength interferenee model can be used for the structure with-out fatigue cracks. It is not available for the structure that is often damaged slightlysuch as propellers. A two-dimensional interferenee reliability model using thetwo-dimensional fatigue load distribution and the distribution of fatigue crack growththreshold for the reliability of the structure with fatigue crack is established. The relia-bility of the propeller of Y7-200B with different crack sizes is listed. A damage toler-ance analysis using an interference integration formula with the two-dimensional loaddistribution is carried out for the propeller and the fatigue crack inspection period withgiven reliability is presented.
基金Funded by the National Natural Science Foundation of China(Nos.11372020 and 10902004)
文摘An average failure index method based on accurate FEA was proposed for the tensile strength prediction of composite out-of-plane adhesive-bonded π joints. Based on the simple and independent maximum stress failure criterion, the failure index was introduced to characterize the degree of stress components close to their corresponding material strength. With a brief load transfer analysis, the weak fillers were prominent and further detailed discussion was performed. The maximum value among the average failure indices which were related with different stress components was filtrated to represent the failure strength of the critical surface, which is either the two curved upside surfaces or the bottom plane of the fillers for composite π joints. The tensile strength of three kinds of π joints with different material systems, configurations and lay-ups was predicted by the proposed method and corresponding experiments were conducted. Good agreements between the numerical and experimental results give evidence of the effectiveness of the proposed method. In contrast to the existed time-consuming strength prediction methods, the proposed method provides a capability of quickly assessing the failure of complex out-of-plane joints and is easy and convenient to be widely utilized in engineering.
