Experimental investigation of the initial stressed and deformed state of three-layer cylindrical shells

In modern technology more and more use is made of three-layer cylindrical shells with load-carrying layers made of high-strength composite materials and with fillers consisting of polymeric foam materials. The initial stressed state in such shells is due to residual technological stresses which can be determined from theory [1-4] or experimentally [1, 4-6]. For the assessment ef the initial stressed state of the filler and of the construction as a whole, experimental data are required on the residual stresses. The complicated theoretical account of all aspects of the interaction between the materials jeined to form the three-layer structures requires an experimental analysis of the changes in the stressed and deformed state during the manufacture of the construction. In the present work, the initial stressed and deformed state of three-layer cylindrical shelis was investigated by studying the kinetics of the technological stresses and deformations on the basis of a division of the components with respect to filler and load-carrying layers. In order to assess the initial stresses and deformations in the elements of the construction, let us discuss the sequence of the manufacturing process of the three-layer shell. In the first stage the inner load-carrying layers are formed and subjected to thermal hardening, which is in essence analogous to the formation of a wound cylindrical article. In this respect the experimental assessr~,,~ of the initial stressed state of the load-carrying layers consists in the determination of the residual stresses by a nondestructive method [1, 7, 8]. Two types of interaction between the load-carrying layers and the mandrel can take place: the contact pressure becomes equal to zero or remains different from zero. The calculations made in [1-3] and the investigations of the kinetics [7-9] of the technolegical stresses and deformations in sufficiently thick-walled articles show that usually the first variant takes place. In the following stage the filler is joined to the inner load-carrying layers and the outer load-carrying layers are wound onto the two-layer structure. The three-layer shell prepared in this way is subjected to thermal treatment. The stress redistributions occurring in this process in the winding elements [8, 9] and the thermal deformation effects in the filler result in a change of the stressed and deformed state of the shell.