Which component (fiber or matrix) breaks when stretching a fiber-reinforced composite material primarily depends on two physical properties of the fiber and matrix: strength and E-modulus. There is also the adhesion strength of the fiber to the matrix, but for simplicity we will consider it equal to the strength of the matrix. Both the strength and the modulus of elasticity of the fibers are reflected in your illustration (the modulus of elasticity corresponds to the angle of inclination of a straight line; the closer the graph is to the vertical, the higher the modulus of elasticity). Both of these properties always work together and only their combination determines the component of the composite material that will be destroyed first. For example, if the matrix consists of aluminum (low modulus at low strength), and the fibers are made of carbon (very high modulus of elasticity at very high strength), then in such a composite material the fibers will always break first. If we replace carbon fiber with glass fiber in a composite material with an aluminum matrix (a very low modulus of elasticity with a rather high strength), then now the matrix will break first.

Dear sir

Boran , Carbon HM, Carbon HS, SiC are more britle among the fibers shown in the graph, they fail first

Generally fibers break after the matrix failure, to decide , which will fail first, it dependes on properties fiber and resin.