Effect of Curvature on the Impact Damage Characteristics and Residual Strength of Composite Plates
The results of a study of the response and failure characteristics of thin, cylindrically cusrved, composite plates subjected to low-speed impact damage are presented. The results indicate that the plate radius and the plate thickness are important structural parameters that influence the nonlinear response of a plate for a given amount of impact energy. Analytical and experimental contact-force results are compared for several plates and the results correlate well. The impact-energy levels required to cause damage initiation and barely visible impact damage are a function of the plate radius for a given plate thickness. The impact-energy levels required to initiate impact damage for plates with a certain range of radii are greater than plates with other radii. The contact-force results corresponding to these impact-energy levels follow a similar trend. Residual strength results for plates with barely visible impact damage suggest that the compression-after-impact residual strength is also a function of plate radiu. The residual strength of impact-damaged flat plates appears to be lower than the residual strength of the corresponding cylindrically curved plates.
Nonlinear impact response of thin imperfect laminated plates using a reduction method
Abstract The nonlinear transient response of thin imperfect laminated plates subjected to impact loads is studied using a 48 DOF finite element based on the classical laminated plate theory. Comparison between the first-order shear deformation theory and the classical laminated plate theory is also made to study the effect of shear deformation. The modified Hertzian law by Tan and Sun is incorporated to evaluate the impact loads due to a projectile. The transient response of an example problem is obtained using both full and reduced equations of motion. A reduction method using Ritz vectors as the basis vectors is employed to reduce the size of the nonlinear problem and thus save computational effort. The resulting reduced (but still coupled) set of equations is integrated in a step-by-step fashion using the Newmark constant-average acceleration time integration scheme along with an iterative scheme for dynamic equilibrium. It is observed that geometric imperfections cause significant changes in the impact response of thin laminated plates. The reduction method used in this study was not found to be very efficient for obtaining the nonlinear impact responses. Further research is needed to develop reduction methods that are more suitable for studying nonlinear impact responses.
Instability analysis of space trusses
Abstract Reduction methods and computational procedures are presented for the instability analysis of space trusses with both geometric and material nonlinearities subjected to combined loads. A mixed formulation is used with the fundamental unknowns consisting of both the member forces and the joint displacements. The governing equations of the truss consist of the two sets of member constitutive relations and joint equilibrium equations. The vector of fundamental unknowns is expressed as a linear combination of a small number of path derivatives (derivatives of nodal displacements and member forces with respect to path parameters), and a Bubnov-Galerkin technique is used to approximate the governing equations by a small system of algebraic equations. The reduced equations are then used to determine the stability boundary and trace the nonlinear equilibrium paths. The potential of the proposed approach is discussed and its effectiveness is demonstrated by means of numerical examples of space trusses with combined geometric and material nonlinearities. The constitutive relations in these examples are assumed, for convenience, to be represented by Rambergsgood polynomials.