Bearing strength prediction for reinforced composite laminates for cryogenic and aerospace applications

Abstract

The procedures of bearing strength prediction for composite laminates reinforced with high-strength unidirectional fibers at room and cryogenic temperatures are discussed. The best agreement between the calculated and experimental data is observed when the temperature dependence of effective mechanical parameters of plies is allowed for within the framework of the elastic theory of laminated heterogeneous bodies.Introduction. The current tendencies in machine, aircraft, and rocket industries are towards reducing the materials consumption of manufacture while raising the service life and reliability of products. These mutually exclusive requirements can be met by means of novel composite materials. The use of composites in rocket and aircraft structures is among the greatest recent advances in aeronautics and space exploration [1][2][3].Composites, specifically carbon-, glass-, and boron-reinforced laminates, offer a high specific strength and rigidity, a required heat resistance, thermal stability and erosion resistance under various thermomechanical loading conditions. An outstanding example of composites for cryogenic service is a superconducting cable made up of dozens of thousands of fibers embedded in a copper matrix.Properties of composite materials depend on the properties of their components, the component ratios, the interactions at matrix-fiber interfaces, and the manufacturing processes. Many of mechanical parameters of composites can be calculated from the known properties of their components, based on the component ratios, the type of matrix-fiber interactions, and fabrication techniques. However, since some of the parameters, such as strength, are highly sensitive to numerous factors that cannot be fully allowed for, the application of exact mathematical solutions are not always feasible.The deformation and fracture behavior of fiber-reinforced laminates has been addressed in the publications [4][5][6][7][8][9]. Apparently, the section dealing with the determination of effective characteristics of composites should be considered the best elaborated section of the mechanics of heterogeneous media. When expressing mechanical parameters of a composite in terms of characteristics of its individual components, great possibilities are opened up for designing materials with preset properties. The major benefit offered by fiber-filled composites is that a material can be endowed with an optimal anisotropy for each particular application. No optimal combination of thermomechanical and functional characteristics of a composite can be achieved unless reliable and comprehensive experimental evidence of their mechanical behavior in a wide range of temperatures, down to ultra low temperatures, is available.Thermomechanical behavior of unidirectional fiber-reinforced polymer composites has been the objective of much research [10][11][12][13][14][15][16]. It has been found that deformation of these materials with symmetric fiber stacking configurations can be adequately described in the context of the theory of ort...

Prediction of the biaxial failure strength of composite laminates with unit cell analytic model

“…This increase in application means that strength is a more and more important mechanical property that has to be taken into account in composite design. A great number of strength theories have been proposed in the literature and used to predict the fi nal failure behavior of fiber reinforced composites [1] . Most of these theories are based on phenomenological and macromechanic considerations [2][3][4] .…”

Determination of the load-carrying ability of reinforced plastic laminates with allowance for the degradation of mechanical parameters of individual layers

“…After the calculation of all effective characteristics of a stack of layers using the formulas presented in [13,19], local stresses in the layers can be determined. We don't give here the corresponding expressions in view of their awkwardness.…”

“…where m = cos( ), θ n = sin( ), θ θ is the angle of rotation of coordinate system about the axis 3, and ′ σ ij is stress tensor components with respect to "rotated" coordinate system [13,19]. The degradation of the mechanical properties of layer depends both on the relation between stresses and on the direction of their action.…”

“…To determine the effective thermomechanical characteristics of the composite under investigation, which is composed of layers with one elastic symmetry plane, which is parallel to the layers, let us make use of the relations presented in [13,18].…”

“…On the basis of the calculated averaged strains, let us determine from the formulas presented in [13,18] the stress distribution in layers with respect to the coordinate system that coincides with the axes of composite orthotropy. To estimate the load-carrying ability of a layer, we shall use transformation formulas (5).…”