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Experimental determination of mechanical properties of unidirectionally reinforced composite materials (UCM) involves well-known difficulties due to the fact that materials in the form of tapes and braids have small transverse dimensions. Moreover, the behavior of UCM as structural members differs from that in independent tests.In this paper, we consider an approach that allows one to obtain information on the mechanical properties of a composite from experimental tests of structures made of this composite material (CM) [1][2][3]. The plane stress state of CM entering into a multilayer structure is studied. Examples of such structures are thin shells formed by winding or application of CM. However, certain difficulties arise here. They are due to "the fact that, when the elastic moduli are greatly different, the desired small quantities (for example, u12, E2, and G) change significantly with small variations of initial experimental data [3]. Problems of processing experimental data for nonlinear elasticity are studied, the calculation results of test problems are analyzed, and conditions imposed on an experiment are formulated.1. We formulate the necessary relations obtained in [2]. We investigate objects such as thin multilayer plates and shells formed by application or winding of reinforced orthotropic layers. We relate the Cartesian coordinate system x 1, x 2 to a reinforced layer by directing the x I axis along the axis of orthotropy having maximum stiffness and the x 2 axis perpendicular to the x 1 axis in the plane of the layer (Fig. 1).The relationship between stresses g~ and strains ~ in an arbitrary coordinate system ~71, :~2 obtained from the system xlx 2 by rotation about the x 3 axis in the plane of the tape for small strains is expressed in tensor form as we study materials whose longitudinal, transverse, and shearing stiffnesses differ greatly. An asymptotic analysis of constitutive relations (1.1) for materials of this class was performed byKazan' State Architect-Building Academy, Kazan' 420043.

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