Showing papers on "Composite laminates published in 1974"
TL;DR: In this paper, the effect of strain biaxiality on failure of 90° layers is shown to be negligible when the laminate is subjected only to a uniaxia tension.
Abstract: Bilinear stress-strain relation of symmetric, [0/90] composite laminates is shown to be associated with gradual, not complete, degradation of 90° layers. Difference between the complete failure model and gradual failure model is discussed, complemented by pertinent experimental evidences. Experimental data on glass/epoxy and graphite/epoxy cross-ply laminates are compared with the theoretical predictions. The effect of strain biaxiality on failure of 90° layers is shown to be negligible when the laminate is subjected only to a uniaxial tension.
170 citations
TL;DR: In this paper, the authors report data indicating that Weibull theory does correctly predict strength behaviors for certain composite materials and suggest that other composite systems be tested against this theory, which has been widely used in the ceramics field.
Abstract: Ratios of flexural strengths to tensile strengths for wide varieties of brittle materials have been found to agree very well with Weibull’s statistical strength theory [ 1 4], which has been widely used in the ceramics field [5-14] . Systematic studies to determine if Weibull theory correctly predicts such strength ratios for fibrous-reinforced epoxy composites have not been reported as yet, although much data exist for making such strength comparisons. The purpose of this note is to report data indicating that Weibull theory does correctly predict strength behaviors for certain composite materials and to suggest that other composite systems be tested against this theory. Verification of this result through more detailed studies would be of importance, because less-expensive flexural specimens that are easier to
169 citations
145 citations
TL;DR: In this article, a beam bending stiffness is derived as a function of all the bending stiffness coefficients of a laminated plate, and the validity of this approach is verified by comparing theoretical results to flexure data on graphite/epoxy angle-ply and quasi-isotropic laminates.
Abstract: Equations applicable to a general class of symmetrically laminated beams are derived by considering a beam as a special case of a laminated plate. The beam bending stiffness thus becomes a function of all the bending stiffness coefficients of a laminated plate. The validity of this approach is verified by comparing theoretical results to flexure data on graphite/epoxy angle-ply and quasi-isotropic laminates. In addition, it is shown that flex strength on general composite laminates is extremely difficult to interpret, even though the stresses can be calculated from the modified beam theory. Discontinuities in the in-plane stresses at layer interfaces lead to a state of stress which is difficult to compare to standard laminate tensile coupons.
59 citations
01 Apr 1974
TL;DR: In this paper, the non-linear behavior of fiber composite laminates was examined using a Ramberg-Osgood representation of the lamina transverse and shear stress strain curves in conjunction with deformation theory.
Abstract: The non-linear behavior of fiber composite laminates which results from lamina non-linear characteristics was examined. The analysis uses a Ramberg-Osgood representation of the lamina transverse and shear stress strain curves in conjunction with deformation theory to describe the resultant laminate non-linear behavior. A laminate having an arbitrary number of oriented layers and subjected to a general state of membrane stress was treated. Parametric results and comparison with experimental data and prior theoretical results are presented.
39 citations
01 Jun 1974
TL;DR: In this article, the authors presented a study in which four biaxial test specimens suitable for composite materials are evaluated -the off-axis coupon, the bulge plate, the tubular specimen and the crossbeam.
Abstract: : A study is presented in which four biaxial test specimens suitable for composite materials are evaluated -the off-axis coupon, the bulge plate, the tubular specimen and the crossbeam. The off-axis coupon and the tubular specimen were selected as having the greatest potential for biaxial characterization of composites, and further development work is presented for these two specimens. Improved specimen design and data reduction techniques are presented for the off-axis coupon. Also, a novel technique for testing tubes without mechanical attachment is presented. End constraints are virtually eliminated from the tubular specimen by introducing tractions through the use of hydraulic pressures. Torque is applied through a non- constraining end spline coupling. Feasibility tests were conducted with both test methods, primarily on the Narmco 5505 boron-epoxy system, both in laminate and unidirectional form. The biaxial data is presented and the results are discussed. The maximum strain, Hill and Tsai-Wu failure criteria are used to predict biaxial behavior of composite materials. Hypothetical design allowable interaction diagrams are presented and compared to the biaxial data. (Author-PL)
36 citations
TL;DR: In this article, an ultrasonic resonance technique for compressional and shear wave velocity measurements in thin composite laminates is described, which utilizes a computer digitizing scheme and Fourier transform from time to frequency domain.
Abstract: An ultrasonic resonance technique for compressional and shear waves velocity measurements in thin composite laminates is described. The method utilizes a computer digitizing scheme and Fourier transform from time to frequency domain. Results showed an eight percent difference in compressional wave velocity across plies for specimens of two different fiber/resin systems. No difference was observed for specimens having different ply-orientations within a system. Shear wave velocity in one specimen was found to be 46% of the compressional wave velocity. The new technique could also be used for thickness measurements in thin-skin honeycomb structures.
29 citations
TL;DR: In this article, the effect of various parameters, including reinforcement material, fiber orientation and the structure of the reinforcement, on the various quantities which are observed in the vicinity of free edges in multidirectionally reinforced laminates is discussed.
Abstract: Experimental and theoretical studies of edge effects in rectangular composite strips under tension are discussed. The objective of the study was to investigate the effect of various parameters, including reinforcement material, fiber orientation and the structure of the reinforcement, on the various quantities which are observed in the vicinity of free edges in multidirectionally reinforced laminates. Of particular interest was the confirmation of theoretical results related to differences in response of graphite- and boron-reinforced laminates. Experiments consisted of moire measurements of surface-displacement patterns which were compared with theoretical predictions, and examination of failure levels. The experiments were carried out on AVCO 5505 boron and Whitaker 5206 MODMOR II graphite-reinforced angle-ply laminates in which both stacking sequence and fiber orientation were varied parametrically. Moire techniques were developed which allowed observation of displacements on both the wide surface and along the narrow edge of 1 in.-wide × 16-ply-thick (.085 in.-.105 in.) laminates.
24 citations
17 Apr 1974
9 citations
6 citations
TL;DR: In this paper, a finite element analysis has been used for the calculation of internal stresses and for the prediction of elastic constants and strength of the composite with a suitable model geometry and proper boundary conditions.
Abstract: In previous papers (1, 2) we have analyzed the internal stresses in spherical particle composites for the cases where the particle is softer than the matrix (1), as in rubber particle filled polymers, or for the case where the particle is harder than the matrix as in ceramic filled glasses (2). Also, the analysis has been applied to porous composites such as foams in which case spherical voids simply replace the particles (2). A finite element analysis has been used for the calculation of internal stresses and for the prediction of elastic constants and strength of the composite with a suitable model geometry and proper boundary conditions. The results have been presented as a function of the volume fraction of particles or inter-particle spacing.
01 Mar 1974
TL;DR: In this article, an orthotropic laminate composite containing a completely broken layer is considered and the strength of stress singularity at the crack tip is determined from a characteristic equation which is obtained by studying the dominant part of the singular integral equation near the end points.
Abstract: An orthotropic laminate composite containing a completely broken layer is considered. The problem is formulated in terms of integral transforms and then reduced to a singular integral equation which is solved numerically. The strength of stress singularity at the crack tip is determined from a characteristic equation which is obtained by studying the dominant part of the singular integral equation near the end points. The stress intensity factors are given for various material properties.
TL;DR: In this article, the twisting stiffness of a rectangular cross section consisting of a single row of solid circular cross-section fibers embedded in a matrix is analyzed, and the problem is formulated as a Dirichlet torsion problem of a multielement region.
Abstract: The twisting stiffness of a rectangular cross section consisting of a single row of solid circular cross-section fibers embedded in a matrix is analyzed. The problem is formulated as a Dirichlet torsion problem of a multielement region and solved by the boundary-point least-squares method. Numerical results for a single-fiber square cross section compare favorably with previous relaxation-method results. New numerical results for three and five-fiber composites suggest that the torsional rigidity of a multifiber composite can be approximated from the torsional rigidities of single and three-fiber models.
TL;DR: In this paper, the effective moduli of a composite material have been found by employing the finite-element method, and the correspondence between the actual composite and its equivalent homogeneous anisotropic material is established on the requirement of equality of the total strain energies for the two media.
Abstract: In this work the effective moduli of a composite material have been found by employing the finite-element method. The correspondence between the actual composite and its equivalent homogeneous anisotropic material is established on the requirement of equality of the total strain energies for the two media. The method is applied to the unidirectional fiber composites, the short unidirectional fiber composite, and the lamellar composite, and the results compare satisfactorily with available analytical data.
TL;DR: In this paper, a new composite material based on an aluminum alloy with dispersed particles of glass and glass-ceramic was produced, and it is possible to obtain metalceramic composite materials with a given coefficient of thermal expansion.
Abstract: 1.
New composite materials based on an aluminum alloy with dispersed particles of glass and glass-ceramic were produced.
2.
It is possible to obtain metal-ceramic composite materials with a given coefficient of thermal expansion.
19 Mar 1974
TL;DR: In this article, a three dimensional finite element modeling and analysis technique has been developed and used in the evaluation of edge stresses in angle-ply composite laminates, and excellent results have been obtained for the initial application to a four-ply + or - 45 degree laminate in tension.
Abstract: : A three dimensional finite element modeling and analysis technique has been developed and used in the evaluation of edge stresses in angle-ply composite laminates. Excellent results have been obtained for the initial application to a four-ply + or - 45 degree laminate in tension, and the method is potentially applicable to holes, notches and other boundaries of arbitrary geometry.
30 Apr 1974
TL;DR: In this paper, the elastic properties of glass-reinforced laminates and their deformation and strength properties were investigated in the presence of time and temperature effects on the deformation, strength, and elasticity of these materials.
Abstract: : ;Contents: Structural glass-reinforced laminates; The elastic properties of glass-reinforced laminates; Strength properties of glass-reinforced laminates; Effect of time on the deformation and strength of glass-reinforced laminates; The temperature effect on the deformation and strength of glass-reinforced laminates; Technology and strength of glass-reinforced laminates; Mechanical testing of glass-reinforced laminates.
TL;DR: In this article, a set of generalized graphs for all practical laminates of a given composite can now replace the current limitation of one set for each discrete laminate, by using laminate stiffnesses in conjunction with failure surface in a special strain space.
Abstract: Design of composite laminates requires the determination of changes in stiffness and strength resulting from varying the ply orientation and total laminate thickness. Graphical determination can be made simple by use of laminate stiffnesses in conjunction with failure surface in a special strain space. A set of generalized graphs for all practical laminates of a given composite can now replace the current limitation of one set for each discrete laminate.
Dissertation•
30 Oct 1974
TL;DR: In this paper, the complex modulus of boron/epoxy and graphite-epoxy laminates has been measured in forced vibration tests at frequencies rang-ing from 20 to 17, 000 Hz and temperatures varied between -50 and +300F. The data was analyzed using response surface methodo-logy.
Abstract: : The complex modulus of boron/epoxy and graphite/epoxy laminates has been measured in forced vibration tests at frequencies rang-ing from 20 to 17, 000 Hz and temperatures varied between -50 and +300F. The data was analyzed using response surface methodo-logy. Based on the response surface time- temperature shift para-meters, master curves, and probability relations have been developed.
TL;DR: In this article, the deformation response of a laminate to an applied force is calculated by means of its material constants, which are derived from a micro-macro mechanical analysis in which the characteristics of the composite are found in terms of the constituent material properties, geometry and volume percentage of fibre content.
Abstract: The basic building block of a filamentary-composite laminate is a ply or a lamina consisting of a larger number of stiff filaments (e.g. glass) embedded in a compatible material (e.g. epoxy). The laminate or multi-directional composite is considered to comprise a number of perfectly bonded laminas with different fibre orientations. The deformation response of a laminate to an applied force is calculated by means of its material constants. One of the common methods of determining these constants is by means of a micro-macro mechanical analysis in which the characteristics of the composite are found in terms of the constituent material properties, geometry, and volume percentage of fibre content. Numerous papers have been published to investigate the micro-macro mechanical approach. Some of these works are based on the mechanics of materials approach and on the variational principle of minimum potential energy, as well as on the classical theory of elasticity.