|
|
||
|
|
|
|
A comparison between the initial shell instability patterns and the final buckling shapes of a shell having a length L = 4D and subjected to a 2 kJ impact applied with different initial velocities is presented in (Fig. 1) for two materials with different strain hardening moduli. It is evident that the 30 m/s impact initiates ”progressive” buckling while a 75 m/s impact causes wrinkles along the entire shell length (Fig. 1(f,g)). However, ”progressive” buckling occurs for a 75 m/s impact, too when decreasing the material hardening modulus (Fig. 1(d,e)).
From:
D. Karagiozova (Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev St., Block 4, Sofia 1113, Bulgaria),
“’Dynamic plastic’ and ‘dynamic progressive’ buckling of elastic-plastic circular shells – revisited”, Latin America Journal of Solids and Structures, Vol. 1, No. 4, 2004, pp. 423-441
ABSTRACT: Two typical buckling patterns of circular cylindrical shells, which can occur due to axial impact loadings, are discussed. The phenomena of ”dynamic plastic” buckling (when the entire length of a cylindrical shell wrinkles before the development of large radial displacements) and ”dynamic progressive” buckling (when the folds in a cylindrical shell form sequentially) are analyzed from the viewpoint of stress wave propagation resulting from an axial impact. It is shown that the particular impact velocity, which instantaneously causes stresses that exceed the elastic limit of the material at the proximal end of a shell, and therefore can cause the initial instability pattern within a sustained axial plastic flow, depends on the material properties. The present analysis reveals that ”dynamic plastic” buckling can develop for relatively low impact velocity, too provided that a shell has certain inertia characteristics. The latter conclusion is in contrast with the established perception that the high impact velocity is a necessary condition for the initial shell instability within a sustained axial plastic flow. A phenomenological approach is used to predict the buckling mode of a circular shell under axial impact with a given initial velocity.
Page 160 / 444