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In this paper, a semi-analytical approach is proposed to investigate the dynamic buckling behavior of functionally graded carbon nanotubes reinforced composite (FG-CNTRC) cylindrical shell under dynamic displacement load. Five types of carbon nanotubes (CNTs) distribution are considered, in which the uncertainty of CNTs distribution is also taken into account. Combining with the first-order shear deformation theory and von-Karman strains, the nonlinear governing equations for dynamic buckling analysis of FG-CNTRC cylindrical shell considering the thermal effects are derived. Then, Galerkin method and the fourth-order Runge-Kutta method are employed to solve the governing equations. And the dynamic critical buckling condition of FG-CNTRC cylindrical shell is determined by the Budiansky-Roth criterion. Compared with the published literatures, the feasibility and accuracy of proposed analysis approach are validated. Finally, the parametric studies are systematically carried out to analyze the effects of CNTs distribution type, CNTs volume fractions, the uncertainty of CNTs distribution, the loading rate and form of dynamic displacement load, structural characteristics and temperature on the dynamic buckling behavior of FG-CNTRC cylindrical shell.

Interest in damage detection and damage pattern recognition of engineering structures by non-destructive techniques has been increasingly growing. As a non-destructive technique, acoustic emission (AE) has developed rapidly to detect dynamic defects and their evolution behaviors of composite structures, based on the transient elastic waves produced by rapid energy release due to the geometry change of structures. In this paper, AE technology is utilized to monitor the real-time condition of the composite scarf joint (SJ) under tensile loading. First, after AE signal acquisition, dimensionality reduction of eight AE features is realized by employing principal component analysis such that the Curse of Dimensionality can be avoided. Second, feature selection is continued by introducing two evaluation indexes, i.e., correlation coefficient and Laplacian score. Third, after the optimal cluster number is determined, damage pattern recognition is accomplished by introducing k-means++ algorithm which explores the distribution of each pattern in the space constructed by four informative AE features. Based on the clustering results, damage initiation and evolution in SJ specimens under tensile loading are subsequently explored. The shear failure of the adhesive layer which is a characteristic damage pattern for SJ specimens shows a relatively-high activity after the early stage. Matrix cracking and fiber/matrix interface debonding are two fundamental damage patterns which keep active in the whole process.

Thin-walled cylindrical shell structure not only shows the highly efficient load carrying capacity but also is vulnerable to buckling instability failure. In practical application, these structures are more easily subjected to locally distributed axial compression load, which is a more common non-uniform loading case. However, until now, the buckling behaviors of thin-walled cylindrical shells under this kind of loading case are still unclear, and there are also few relevant buckling experiments. In order to fill this research gap as well as reveal the relevant failure mechanism of thin-walled cylindrical shell structures, in this paper buckling tests of thin-walled metallic cylindrical shell structures under non-uniform axial compression loads are successfully performed. In this regard, the design and characteristics of two cylindrical shell test specimens subjected to different pattern of non-uniform compression loads are mainly introduced. Meanwhile, as the important parts for conducting this buckling experiment, the axial compression buckling test rig as well as the real-time acquisition measurement system is also presented in details. Results indicate that locally distributed axial compression loads play a pivotal role in the buckling behaviors of thin-walled cylindrical shell, not matter from the point of view of load carrying capacity, shell deformation process or failure mode. The experiments carried out in this work can be served as a benchmark for related numerical simulation afterwards. Furthermore, the obtained test results can also provide some guides for the design and application of thin-walled cylindrical shell in actual engineering.

Thin-walled cylindrical shells subjected to axial load are prone to buckling and very sensitive to the geometric imperfections. In order to determine a rational design load for axially loaded cylindrical shells, different analytical and numerical design methods have been developed. As an extension of single perturbation load approach (SPLA), multiple perturbation load approach (MPLA) is a promising method but has not been thoroughly studied. In this paper, the buckling tests of three steel cylindrical shell specimens are conducted. Combined with experimental and numerical results, the advantages and limitations of several commonly used design methods are discussed in detail, including NASA SP-8007, the measured imperfection approach, SPLA and MPLA. The results validate that SPLA is indeed risky to be adopted as a design method for isotropic metallic cylindrical shells. Meanwhile, it indicates that MPLA can not only improve the knock-down factor but also give a more safe design load than SPLA. The comprehensive numerical investigations are performed to study the effects of each perturbation load parameter on MPLA, including the number of perturbation loads, their relative position and magnitude. It is found that the symmetry of perturbation loads plays an important role in the global buckling load of cylindrical shell. Moreover, some guidance for the future application of MPLA is provided and the four perturbation load approach (4PLA) is proposed as an improved method for the preliminary design of isotropic metallic cylindrical shells.

The effects of current on restoring velocity and deformation time of NiTiCu shape memory alloy wire were investigated by loading different electrical current. The results show that the deformation time decreases rapidly with increasing driving current, but the deformation time decreases slowly when the current increases to a certain value. The deformation angle and time shows nonlinear increasing when the driving current is constant. The rate of deformation increases firstly and then reduces with the time passing. The relationship between driving current and the deformation time of NiTiCu shape memory alloy wire can be expressed by the empirical formula I=1.41(1-e -0.0199t ) -1/2 +1, and the calculation curves agrees well with the test data.