Accelerated Aging Tests And Life Evaluation Technology Of Cementing Structures

With low density and superior fatigue properties, cementing structures have been widely used in the fields of aeronautics and astronautics. Owing to the effect of heat, humidity, oxygen and corrosive media, cementing structures tend to age during service or storage. As a result, the strength of the structures will decline and failure may occur. The study on the failure mechanism and life prediction of cementing structures is significant to the use and storage of cementing structures.In this paper, the cementing structures widely used in the fields of aeronautics and astronautics were studied. The cementing structures were formed by cementing two 2A12 alloy sheets with SY-24C adhesive as well as SY-D9 adhesive.In order to reduce the aging time of the cementing structures, higher stress was applied in the aging tests. In this paper, a constant stress was applied. Because cementing structures are sensitive to temperature and humidity, they were chosen as accelerated aging factors, and the aging tests were carried out under four different conditions. The relationship between the tensile shear strength and the aging time was tested. The results show that with the increase of aging time, the tensile shear strength declined quickly at the early stage, but after a time it declined slowly. The change of the tensile shear strength complied with the rule of an exponential function.According to the relationship between the tensile shear strength and the aging time under the four different conditions, it can be found that at the early stage of the aging tests, the effect of temperature on the tensile shear strength is more important; however, with the increase of aging time, the effect of humidity on tensile shear strength becomes more and more important.After aging testing, the fracture surfaces of the tensile shear samples are examined by SEM. The results show that with the increase of aging time, the damage mode of the cementing structures transforms from cohesion damage mode to the integrated mode of cohesion damage and interface damage, and the area suffering from interface damage increases gradually, which is mainly because the cementing agents on the surface of aluminum alloy were replaced by moisture. According to the tearing ridges on the fracture surfaces, it can be concluded that the fracture of the cementing structures is ductile fracture.In addition, based on the generalized Allen mode, a life prediction mode on temperature and humidity was deduced. A life prediction function for cementing structures with the share strength decline of 8% and 10% as termination indexes was obtained, and the storage life under different temperature and humidity were worked out.