About the Causes of the Bearing Capacity Loss of a Composite Beam under Three-Point Bending

Abstract

This article considers the results of an experimental and numerical study of the threepoint bending problems of a composite specimen (beam). The numerical analysis of the beam behavior, in a physically and geometrically nonlinear statement of the problem, assumed that the beam is made by layering a unidirectional carbon fiber along the specimen axis. The Tsai-Wu criterion was used to determine the ultimate load at which the composite phases of the specimen lose their strength. The comparative analysis of the specimen behavior at different values of the beam thickness and the diameter of the loading roller was carried out. The results obtained show that the failure of the short specimens occurs as the material loses its strength under the loading roller (in the middle), and the long specimens become delaminated along the adhesive layer. This effect is explained by the loss of stability of the adhesive layer in a non-classical transverse shear mode. Our study demonstrates that the roller diameter has practically no effect on the value of the ultimate load, while the load at which the layer buckles on the front surface of the specimen is very sensitive to changes in its value. A good correlation of the numerical results with the experimental data was revealed.

Study of the laminas’ stress-strain state for cross-ply composites with the [± 45°]2s lay-up: tensile tests

“…ˆĜG  = dependence stated in [18,19] and based on formulas (1), ( 3), relations ( 6) and ( 11) has a sufficient degree of accuracy in the central zone of the specimen with [± 45°]2 lay-up at 2 s  .…”

“…we construct a shear strain curve ( ) It should be noted that in tensile tests of specimens with [0°]s and [90°]s lay-ups ( s is the number of lamina in the specimen) with fibers located along and across to the direction of the acting load the mechanical characteristics of a single monolayer of fiber reinforced composite in its orthotropy axis 12 , xx have been determined earlier. The corresponding stress-strain curve for a unidirectional CFRP can be considered linear up to the failure of the specimens [15,16]. This fact makes it possible to determine elastic moduli EE  =…”

Experimental research of sandwich specimens’ failure mechanisms with facing layers from unidirectional fiber reinforced plastic with [0°] lay-up under axial compression

“…As is known [13,14], when compressing specimens from unidirectional FRP along the fibers, the values of the transverse shear modulus can be taken as the ultimate compressive stresses. In a series of works [15,16], it was shown that the theoretical identification of the shear buckling form of composite specimens under threepoint bending conditions is possible using equations based on the simple kinematic model of S. P. Timoshenko.…”