Jack R. Vinson

The Efficient Design of Adhesive Bonded Joints

Abstract A concise method of analysis is used to study the numerous parameters influencing the stress distribution within the adhesive of a single lap joint. The formulation includes transverse shear and normal strain deformations. Both isotropic or anisotropic material systems of similar or dissimilar adherends are analysed. Results indicate that the primary Youngs modulus of the adherend, the overlap length, and the adhesives material properties are the parameters most influential in optimizing the design of a single lap joint.

On the Hygrothermal Response of Laminated Composite Systems

The hygroscopic nature of polymeric systems, which find widespread application as matrices in advanced composite materials, requires that dila tations induced by the absorption of moisture be considered m the stress analysis of composite laminates. Considerable attention has recently been focused upon the reduction m both strength and constitutive properties of fiber-reinforced polymeric composites at elevated temperatures when the composite has been subjected to environments which enhance moisture diffusion. This apparent degradation in elevated temperature properties may be magnified even more by residual stresses induced by both the hygroscopic and thermoelastic characteristics of the unidirectional com posite. A unified treatment of the hygrothermal response of the laminated composite plate element is derived. The analysis develops effective mois ture inplane force resultants and bending resultants, which when coupled with mechanical and thermal loadings, yield laminae stresses resulting from the total hygrothermal and mechanical loading environment. Solutions of the classical diffusion equation are obtained yielding mois ture profiles through the laminate thickness. Typical composite laminates consisting of T300/5208 graphite-epoxy are analyzed. Results reveal both the magnitude and distribution of hygrothermally induced stresses.

On the Nonlinear Oscillations of Plates Composed of Composite Materials

In this work, the Bergers approach for large deflections and a modified Reissners variational principle are exploited to treat the nonlinear dynamic problem of plates. A system of approximate equa tions which governs the large amplitude free vibrations of orthotropic, rectangular plates is presented, including the effects of rotatory inertia and transverse shear deformation. In the example, a simplified solution is presented for the primary lateral vibration of a simply supported plate. Numerical results are based upon the elastic constants of a composite material, having boron filaments 56% by volume, imbedded in an epoxy matrix.

Modeling ballistic impact into flexible materials

The dynamic problem is approximated by a time series of static analysis problems. An algorithm is described wherein in each time step the material properties of the target and the geometry of the deflection cone are derived.An experimental program was performed involving bullets fired at Kevlar 29 fabric targets.

Optimum design of composite honeycomb sandwich panels subjected to uniaxial compression

Sandwich construction provides a very lightweight structural configuration for many load conditions. The use of composite materials with their high stiffness, high strength, and anisotropy makes sandwich construction even more competitive for many applications. It is very desirable to design these structures for minimum weight to insure their most effective use. Closed-form analytical solutions are presented herein for the analysis and design of minimum weight, composite material hex-cell and square cell honeycomb core sandwich and panels subjected to in-plane uniaxial compressive loads. These methods account for overstressing, overall buckling, core shear instability, face wrinkling, and monocell buckling. The optimum face thickness, core depth, cell wall thickness, and cell size are analytically determined. The methods insure minimum weight, as well as provide methods to compare various material systems, compare honeycomb sandwich construction with other panel architectures, and assess the weight penalties associated with using nonoptimum honeycomb sandwich constructions. A comparison of various polymer, metal, and ceramic matrix composite materials is made by way of example.

Influences of Large Amplitudes, Transverse Shear Deformation, and Rotatory Inertia on Lateral Vibrations of Transversely Isotropic Plates

In the present paper, using an improved Reissner’s variational theorem along with Berger’s hypothesis, a set of governing equations which include the effects of transverse shear deformation and rotatory inertia is derived for the large amplitude free vibrations of plates composed of a transversely isotropic material. Applying the possibility of neglecting the rotatory inertia in primarily flexural vibration (discussed in the previous work [1]2 ), the lateral free vibrations of simply supported plates are treated in detail and the solution is compared with those of previous investigators. The free vibration of beams is studied as a special case of plates, while the small amplitude vibrations are treated as a special case of large amplitude vibrations. The numerical results show that the effect of transverse shear deformation is significant when applying to the plate constructions made of pyrolytic graphite-type materials.

Nonlinear Oscillations of Laminated Specially Orthotropic Plates with Clamped and Simply Supported Edges

For large‐amplitude oscillations, the work presented previously by the authors for single‐layer plates of composite materials, simply supported on all edges, is extended to include laminated plates and six combinations of clamped and simply supported edges. Bergers hypothesis is again used to obtain a set of simplified coupled equations which governs the nonlinear motion of plates. Solutions are obtained using a Ritz‐Galerkin method in which the assumed series are products of beam characteristic functions. In addition, small‐amplitude vibrations are treated as special cases. Numerical results for fully clamped as well as various combinations of clamped and simply supported boundary conditions are presented.

Effect of moisture on the static and viscoelastic shear properties of epoxy adhesives

The effects of moisture on the structural properties of two commercially available adhesives, FM73M and FM300M, are investigated. The experimental study consists of static and viscoelastic shear measurements made from bonded joint specimens soon after they were cured and after lengthy exposure in 63% and 95% relative humidity environments. Static shear modulus and shear creep compliance data for each adhesive at each moisture level throughout a wide range of temperatures are illustrated. Also shown are the effects of temperature and moisture on the ultimate shear strength behaviour, and the temperature and moisture viscoelastic shift functions. It is concluded that the effect of moisture as an external plasticizer on the shear properties of these adhesives is equivalent to raising the environmental temperature.

Hydrothermal effects on the buckling of laminated composite plates

Abstract The combined effects of temperature and humidity (termed hygrothermal) are included in a general laminated composite plate buckling theory formulation based on the Theorem of Minimum Potential Energy which accounts for transverse shear and normal deformation and the bending-extensional coupling exhibited by non-symmetrically laminated composite plates. Parametric studies are carried out for symmetrically laminated T300/5208 graphite-epoxy plates with simply supported and clamped edges under both steady-state and transient hygrothermal conditions. Results are presented which show significant reductions in the applied surface tractions necessary to buckle composite structures due to these effects.

Fiber Orientation Effects on High Strain Rate Properties of Graphite/Epoxy Composites

Excellent mechanical properties such as high-strength, low weight, fatigue life, and impact resistance, as well as advanced manufacturing methods and flexibility of the stacking sequence make polymer matrix composites attractive candidates for use in several performance-oriented structures. However, relatively little is known of their response to impact loading, which usually occurs at strain rates higher than those used to measure the quasi-static mechanical properties of materials. In this study, the split-Hopkinson bar is used extensively to study the effect of fiber orientation on the compressive dynamic properties of a unidirectional IM7/8551-7 graphite/epoxy composite. The specimens were approximately 3/8. cubes, and were prepared using a water-cooled diamond grit blade. The off-axis angles were 0 (longitudinal direction), 15, 30, 45, 60, 75, and 90 (transverse direction) degrees. Quasi-static tests were also performed for comparison purposes. The high strain rates vary from 250-1100/s. The tests show that changing the fiber orientation changes the values of the ultimate strength and strain of the IM7/8551-7 graphite/epoxy composite. The results show that the ultimate strength in general decreases as the off-axis (test) angle is increased. However, the results show that the decrease is not uniform as in the case of the quasi-static tests. The strain increases for initial increase in the off-axis angle, but then the results don’t show any consistent trend for additional angle increments. A semi-empirical equation is obtained for this material system and can be modified to account for other polymer matrix composites.