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In this paper, we compare the failure behaviors of CFRP single and double (S–D) lap joints and analyze the effects of hygrothermal aging on these joints through a comprehensive experiment and simulation. Firstly, we analyze and compare the degradation pattern of the residual strength of S–D​ lap joints under three hygrothermal environments, and reveal the aging mechanism in conjunction with the macro/fine-view failure surfaces of the joints. Secondly, we elucidate the probability distribution of joint aging failure using the two-parameter Weibull distribution. Finally, we develop a finite element model to simulate the failure process of the cohesive behavior, and compare not only the bending moment and contact stress distribution of the two joints, but also analyze the damage condition of the CFRP matrix/fiber. We define environmental degradation factors to express the failure behavior of lap joints after aging. Through the above analysis methods, we find that hygrothermal aging can seriously damage the CFRP and adhesive properties. The mechanical performance of DLJs is significantly superior to that of SLJs, and they also exhibit better reliability. Therefore, DLJs can be substituted for SLJs in some application scenarios. Additionally, our paper provides new insights into the selection of an appropriate lap bonding method. • This paper evaluates the aging durability of single and double lap joints from multiple perspectives. • The failure behavior of single and double lap joints is comprehensively compared by numerical simulations. • This paper provides some new insights into the selection of an appropriate lap bonding method. [ABSTRACT FROM AUTHOR]

Tanks and silos are often designed as ring-stiffened cylindrical shells. Nowadays, the load-increasing effect of closely spaced ring stiffeners under axial compression has received limited attention in research and practice. Considering the structural safety, the ring-stiffened shell needs to be estimated on the conservative side in practice. This is not desirable in terms of modern lightweight steel structures. However, material efficiency is achieved by combining thin plates with ring-stiffeners. In this paper, small specimen experimental series are carried out to calibrate numerical models, which are subsequently used in parameter studies, because the large-scale experiments are cost-intensive and therefore difficult to carry out in the laboratory. The small cylindrical shells are manufactured by welding of two half-cylindrical shells and the ring stiffeners are spot-welded to the cylindrical shell. Geometric dimension of shell specimens is measured by 3D scanning technology. The measured geometric imperfection information is directly imported into the numerical model based on a mapping relationship and the buckling tests are recalculated by means of geometrically and materially nonlinear analysis with imperfection. The results indicate that the buckling resistance calculated by the Finite Element analysis is very close to that of the test results. The initial geometric imperfection is discussed with reference to the Eurocodes design standard. Furthermore, influence of the ring-stiffener parameter, including imperfection amplitude, radius over thickness ratio, geometry of ring stiffener etc., on the buckling load and knockdown factor is discussed based on a large number of parameter study. • Experimental and numerical study of ring-stiffened cylindrical shells presented. • Geometric imperfections of stiffened cylinder were measured and mapped into FE model. • Ring-stiffener can effectively increase the buckling load of cylindrical shells. • High ring parameter for the heavy stiffened cylinder have positive influence. [ABSTRACT FROM AUTHOR]