Showing papers on "Composite laminates published in 1972"

Elastic Behavior of Multilayered Bidirectional Composites

Abstract: SEVERAL recent papers1–5 have addressed the problem of defining the exact (elastic) response of composite laminates under static bending. However, all of these studies have treated laminates consisting of only a few layers, while in practical applications, composite structures may consist of many layers, in some cases, 100 or more. It is therefore appropriate that we consider the response of multi-ply laminates with a view toward examining the generality of previous conclusions regarding the range of validity of the approximate theory normally used in the analysis of these bodies, namely, classical laminated plate theory (CPT).6 Open image in new window Fig. 1 Normal stress distribution.

Theory of fiber reinforced materials

Abstract: A unified and rational treatment of the theory of fiber reinforced composite materials is presented. Fundamental geometric and elasticity considerations are throughly covered, and detailed derivations of the effective elastic moduli for these materials are presented. Biaxially reinforced materials which take the form of laminates are then discussed. Based on the fundamentals presented in the first portion of this volume, the theory of fiber-reinforced composite materials is extended to include viscoelastic and thermoelastic properties. Thermal and electrical conduction, electrostatics and magnetostatics behavior of these materials are discussed. Finally, a brief statement of the very difficult subject of physical strength is included.

Experimental investigation of fracture in an advanced fiber composite.

Abstract: Pilot tests were run to determine the applicability of the concepts of linear elastic fracture mechanics (LEFM) to the description of the mechanical behavior of initially cracked specimens of advanced fiber composite laminates. It was found that the failure mechanisms in such specimens were largely crack-dominated and that LEFM procedures were applicable even when the apparent failure mechanism was not explicitly dominated by a starter crack.

Elastic and Plastic Interlaminar Shear Deformation in Laminated Composites under Generalized Plane Stress.

Abstract: : Elastic and plastic interlaminar shear deformation in a laminated fibrous composite was studied by means of a finite-element method. A composite element, constructed of orthotropic membranes separated by shear- resisting media, is developed and utilized. The effect of interlaminar shear deformation at the free edges of solid laminates and laminates containing a cutout is presented. (Author-PL)

31—the handle and bending behaviour of fabric laminates

Abstract: Certain aspects of the handle of fabric laminates are related to properties of the component fabrics. Particular attention is paid to a theoretical prediction of the bending stiffness of a laminate from the bending and tensile properties of its components. This theoretical stiffness is a minimum value; if, in practice, the observed stiffness is much greater than this, it may generally be assumed that excess of adhesive or of melted foam is the cause. The paper also reports work on other features of the bending behaviour, such as the degree of recovery from bending, and on the shearing behaviour. The work is concluded by a brief study of some faulty laminates.

Some strength properties of graphite-zirconium carbide composite materials

Abstract: 1. Some factors influencing the strength of composite materials were examined. 2. A study was made of the strength properties of graphite-zirconium carbide and graphite-zirconium carbide-zirconium composite materials having varying structures and compositions. It was found that, at 2500‡C, the tensile strength of TsG-25 type composite material is 30% higher than that of dense VPP constructional graphite. 3. It was established that, by varying the degree of impregnation of the zirconium phase with carbon, it is possible substantially to change the physicomechanical properties of the resultant composite material. At 20–2000‡C, the tensile and bend strengths of materials containing residual zirconium are 1.5–3 times those of materials containing the carbide phase alone.

A Crack Stopper Concept for Filamentary Composite Laminates

Abstract: Damage tolerance is a structural design consideration which has been used to achieve structural reliability and safety. One method of achieving damage tolerance is the use of multiple-load-path construction. The underlying purpose of such construction is, of course, to provide some load-carrying capability within a structural component which has suffered some damage. The multiple-load-path concept has been used for a number of years as a method of increasing the probable damage tolerance capability of metallic structure. In particular, usage of crack-stopper straps has been used as an effective means of stopping running cracks in panelized wing and fuselage structure. These straps are usually fastened to the parent structure by a combination of adhesive bonding and mechanical fasteners. In this paper, the results of a test program to discover effective means of introducing such straps into advanced composite structure are described. The program consisted of the fabrication and test of fourteen honeycomb sandwich panels. The description of these panels and the accompanying test results is given in the following sections.

Thermal expansion of two-phase texturized composite materials.

Abstract: Theoretical and experimental studies were made of the effects of temperature and composition on the thermal expansion of deformed (texturized) Mo-Cu two-phase composite materials, whose component phases differ markedly in their properties. The anisotropy of thermal expansion of such composite materials was investigated, and it was established that their volume expansion shows very little variation with deformation. It is demonstrated that two-phase composite materials can be formulated exhibiting thermal expansion characteristics controlled by their composition and the type and degree of plastic deformation.

On fracture phenomena in advanced fiber composite materials.

Abstract: The extension of linear elastic fracture mechanics (LEFM) from metallic alloys to advanced fiber composite laminates is considered. LEFM is shown to be valid for both isotropic and anisotropic homogeneous continua; the applicability of LEFM to advanced fiber composites is thus dependent on the validity of a homogeneous model of such materials. An experimental program to determine the validity of such a model for graphite/epoxy laminates is reviewed. Such laminates are found to have an apparent fracture toughness, from which it is inferred that a homogeneous material model is valid for the particular specimen geometry and composite laminates considered. Strain energy release rates are calculated from the experimentally determined fracture toughness of the various laminates. These strain energy release rates are found to lie in one of two groups, depending upon whether crack extension required fiber failure or matrix failure. The latter case is further investigated. It is concluded that matrix failure is governed by the tensile stress normal to the crack path.