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.

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