Abstract
Structural components made of fibre-reinforced materials are frequently used in engineering applications. Fibre-reinforced composites are multiphase materials, and complex mechanical phenomena take place at limit conditions but also during normal service situations, especially under fatigue loading, causing a progressive deterioration and damage. Under repeated loading, the degradation mainly occurs in the matrix material and at the fibre-matrix interface, and such a degradation has to be quantified for design structural assessment purposes. To this end, damage mechanics and fracture mechanics theories can be suitably applied to examine such a problem. Damage concepts can be applied to the matrix mechanical characteristics and, by adopting a 3-D mixed mode fracture description of the fibre-matrix detachment, fatigue fracture mechanics concepts can be used to determine the progressive fibre debonding responsible for the loss of load bearing capacity of the reinforcing phase. In the present paper, a micromechanical model is used to evaluate the unixial or multiaxial fatigue behaviour of structures with equi-oriented or randomly distributed fibres. The spatial fibre arrangement is taken into account through a statistical description of their orientation angles for which a Gaussian-like distribution is assumed, whereas the mechanical effect of the fibres on the composite is accounted for by a homogenization approach aimed at obtaining the macroscopic elastic constants of the material. The composite material behaves as an isotropic one for randomly distributed fibres, while it is transversally isotropic for unidirectional fibres. The fibre arrangement in the structural component influences the fatigue life with respect to the biaxiality ratio for multiaxial constant amplitude fatigue loading. One representative parametric example is discussed.
Highlights
Composite materials are obtained mixing two or more constituents combined at a macroscopic level: typically a matrix material and a dispersed reinforcing phase are used to get very high-quality mechanical properties of the resulting material
The spatial fibre arrangement is taken into account through a statistical description of their orientation angles for which a Gaussian-like distribution is assumed, whereas the mechanical effect of the fibres on the composite is accounted for by a homogenization approach aimed at obtaining the macroscopic elastic constants of the material
Damages in the matrix and in the fibres are quantified by a damage mechanics approach, whereas the loss of fibre-matrix bonding is examined through fracture and fatigue mechanics
Summary
Composite materials are obtained mixing two or more constituents combined at a macroscopic level: typically a matrix material (made with polymers, metals or ceramics) and a dispersed reinforcing phase (fibres, particles or flakes) are used to get very high-quality mechanical properties (such as improved tensile strength, fracture resistance, durability, corrosion resistance, enhanced wear and fatigue strength) of the resulting material. The present research aims at developing a micromechanical approach for the assessment of the fatigue behaviour of short-fibre-reinforced composites under cyclic loading causing a multiaxial stress state. The assessment of the degrading effects in such non-homogeneous materials under fatigue loading is complex, and requires a reliable mechanics-based model for their quantitative evaluation. Damages in the matrix and in the fibres are quantified by a damage mechanics approach, whereas the loss of fibre-matrix bonding is examined through fracture and fatigue mechanics. All these degrading phenomena are taken into account and quantified by analysis at micro-scale level. The behaviour of a fibre-reinforced material under multiaxial fatigue conditions is examined and compared with experimental data
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