Deformation Mechanics of Fiber-Reinforced Plastic Specimens in Tensile and Compression Tests 1. Theoretical and Experimental Methods for Determining the Mechanical Characteristics and the Parameters of Stress-Strain State

• Published in: Mechanics of composite materials 2022-07, Vol.58 (3), p.409-426
• Main Authors: Paimushin, V. N., Gazizullin, R. K., Kholmogorov, S. A., Shishov, M. A.
• Format: Article
• Language: English
• Subjects: Axial stress; Ceramics; Characterization and Evaluation of Materials; Chemistry and Materials Science; Classical Mechanics; Composite materials; Composites; Compression tests; Compressive properties; Experimental methods; Experiments; Fiber reinforced plastics; Finite element method; Glass; Lay-up; Materials Science; Mechanical properties; Natural Materials; Orthotropy; Parameters; Research methodology; Solid Mechanics; Strain measurement; Stress-strain relationships; Structural members
• ISSN: 0191-5665; 1573-8922
• DOI: 10.1007/s11029-022-10038-x

The theoretical and experimental methods for determining the mechanical characteristics of fiber-reinforced plastics (FRPs) based on tensile and compression tests of flat specimens with [0] s , [±90] s , and [±45] 2s lay-ups are analyzed. For FRPs with [±45] 2s lay-ups, relations are derived for determining the components of lamina strains and stresses in the orthotropy axes of FRP monolayer in terms of axial strains and Poisson ratios of specimens measured in experiments. They are based on an analysis of geometric strain patterns and physical relations on the assumption that, in a cross-ply FRP, two adjacent layers with [±φ] structures can be considered as one symmetrically reinforced layer with orthotropic properties. Numerical experiments for determining the parameters of the stress-strain state of specimens consisting of two laminas of a unidirectional fiber-reinforced plastics with a [±45] 2s lay-up were performed in the linear formulation of 2- and 3-D problems in the ANSYS finite-element system. The cases of tension of elongated and compression of short specimens was considered, and an analysis of the stress components forming along the fibers located in the central part and in the vicinity of specimens corner points was performed. Tensile experiments were performed on flat fiber composite specimens with a [±45] 2s lay-up to determine the strain state using a contactless strain measurement system. The results obtained made it possible to indicate the zones in which, during loading, the realization and a continuous change of the internal nonclassical buckling modes of the structural elements of FRP are possible, which is apparently one of the reasons for the physically nonlinear behavior of specimens with the [±45] 2s structure in tension and compression. The results obtained allowed us to point out the areas where strains localize during loading and the failure of test specimens begins. It is shown that, in tension (compression) of the specimens with a [±45] 2s lay-up, the fibers in the composite are under not only tangential, but also axial tensile (compressive) stresses. It is found that, in the orthotropy axes of each lamina, the axial tensile stresses significantly exceed in magnitude the transverse ones, which can be neglected.