In this work, a finite element formulation and associated computer program is developed for the transient large deformation analysis of laminated composite plate/shell structures. In order to satisfy the plate/shell surface traction boundary conditions and to have accurate stress description while maintaining the low cost of the analysis, a newly assumed displacement field theory is formulated by adding higher-order terms to the transverse displacement component of the first-order shear deformation theory. The laminated shell theory is formulated using the Updated Lagrangian description of a general continuum-based theory with assumptions on thickness deformation. The transverse deflection is approximated through the thickness by a quartic polynomial of the thickness coordinate. As a result both the plate/shell surface tractions (including nonzero tangential tractions and nonzero normal pressure) and the interlaminar shear stress continuity conditions at interfaces are satisfied simultaneously. Furthermore, the rotational degree of freedoms become layer dependent quantities and the laminate possesses a transverse deformation capability (i.e. the normal strain is no longer zero). Analytical integration through the thickness direction is performed for both the linear analysis and the nonlinear analysis. Resultants of the stress integrations are expressed in terms of the laminate stacking sequence. Consequently, the laminate characteristics in the normal direction can be evaluated precisely and the cost of the overall analysis is reduced. The standard Newmark method and the modified Newton Raphson method are used for the solution of the nonlinear dynamic equilibrium equations. Finally, a variety of numerical examples are presented to demonstrate the validity and efficiency of the finite element program developed herein. / Ph. D.

No description available.

This study focused on the fracture and fatigue crack growth behavior in polyvinylchloride (PVC) and polyethersulfone (PES) foams. A new sandwich double cantilever beam (DCB) test specimen was implemented. Elastic foundation and finite element analysis and experimental testing confirmed that the DCB specimen is appropriate for static and cyclic crack propagation testing of soft polymer foams. A comprehensive experimental mechanical analysis was conducted on PVC foams of densities ranging from 45 to 100 kg/m3 and PES foams of densities ranging from 60 to 130 kg/m3. An in-situ scanning electron microscope study on miniature foam fracture specimens showed that crack propagation in the PVC foam was inter-cellular and in the PES foam, failure occurred predominately by extensional failure of vertical cell edges. Sandwich DCB specimens were loaded cyclically as well. For the PVC foams, the crack growth rates were substantially influenced by the density. For the PES foams, there was no clear indication about the influence of foam density on the crack growth rate. / by Elio Saenz. / Thesis (M.S.C.S.)--Florida Atlantic University, 2012. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2012. Mode of access: World Wide Web.

In an effort to obtain an improved mode III fracture toughness test suitable for a testing standard, mechanics analysis, experimental testing, and finite element analysis (FEA) have been conducted. Of particular concern are the merits of one-point and two-point edge crack torsion (ECT) test methods, the influence of specimen geometry that overhangs beyond load/support points, and the influence of crack length on the compliance and energy release rate. Shear stress distributions at the crack front are determined to examine the uniformity of mode III loading and mode II influence. The shear stress distributions in the one-point and two-point tests are virtually identical, indicating that either of the two tests could be used interchangeably. Based on the uniformity of the mode III shear stress distribution along the crack front, it was found that the ECT specimen should have minimum overhang. Longer crack lengths tend to produce nonuniform shear stress distributions. A modified two-point ECT test fixture was developed to allow testing of specimens with a range of dimensions. This development enabled experimental verification of the results from the FEA overhang series. The specimens with a minimum overhang produced consistant mode III toughness data. The most reliable way to reduce data is through the original compliance calibration method. A modified ECT specimen was developed with a staggered crack front to produce uniform mode III crack growth. Finite element analysis of the modified ECT specimen shows a uniform mode III stress distribution along the crack front with little mode II interaction. / by Grant Browning. / Thesis (M.S.C.S.)--Florida Atlantic University, 2009. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2009. Mode of access: World Wide Web.

"This study presents a general approach for an inverse problem to locate a sudden structural damage in a plate. The sudden damage is modeled as an impulse load and response data are collected at various sensor locations. In this simulation study the response data were generated by the commercial finite element code ANSYS for three square plates: one is an isotropic plate and made of aluminum and the others are two different composite plates made of graphite-epoxy. All plates are simply supported along all their edges. The responses of these plates to both narrow band and wide band loading were analyzed by a wavelet transform. The wavelet coefficient maps for each type of signal was utilized to estimate the shortest path arrival times of flexural waves resulted from the damage by locating the wavelet coefficient peak values of the response data. Using the dispersion relations of wave propagation based on the Mindlin’s plate theory, a set of nonlinear equations were derived to solve this inverse problem and the location of the applied load, which models a structural damage, was determined. The estimated locations for all different types of plates have shown an excellent agreement with the actual location of the impact loads applied. "

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1981. / Microfiche copy available in Archives and Barker. / Includes bibliographical references. / by Steven James Hollowell. / M.S.

Design of commercial aircraft structure, composed of composite material, requires the prediction of failure loads given large scale damage. In particular, a fuselage of graphite/epoxy lamination was analyzed for damage tolerance given a standard large crack that severed both skin and internal structure. Upon loading, a zone of damage is known to develop in front of a crack-tip in composite laminates; and, its material behavior within the damage zone is characterized as strain softening. This investigation sought to develop a computational model that simulates progressive damage growth and predicts failure of complex laminated shell structures subject to combined tensile and flexural load conditions. This was accomplished by assuming a macroscopic definition of orthotropic damage that is allowed to vary linearly through the shell thickness. It was further proposed that nonlocal plate strain and curvature act to force damage growth according to a set of uniaxial criteria. Damage induced strain softening is exhibited by degradation of laminate stiffness. An expression for the damage reduced laminated plate stiffness was derived which assumed the familiar laminated plate [AM] stiffness matrix format. The model was implemented in a finite element shell program for simulation of fracture and evaluation of damage tolerance. Laminates were characterized for damage resistance according to material parameters defining nonlocal strain and the damage growth criteria. These parameters were selected using an inverse method to correlate simulation with uniaxial strength and fracture test results. A novel combined tension-plus-flexure fracture test was developed to facilitate this effort. Analysis was performed on a section of pressurized composite fuselage containing a large crack. Good agreement was found between calculations and test results. / Graduation date: 1998

Polymeric composites exhibit time-dependent behavior, which raises a concern about their long term durability and leads to a viscoelastic study of these materials. Linear viscoelastic analysis has been found to be inadequate because many polymers exhibit nonlinear viscoelastic behavior. Classical laminate theory is commonly used in the study of laminated composites, but due to the plane stress/strain assumption its application has been limited to solving two dimensional, simple plate problems. A three dimensional analysis is necessary for the study of interlaminar stress and for problems involving complex geometry where certain local effects are important. The objective of this research is to develop a fully three-dimensional, nonlinear viscoelastic analysis that can be used to model the time-dependent behavior of laminated composites. To achieve this goal, a three-dimensional finite element computer program has been developed. In this program, 20-node isoparametric solid elements are used to model the individual plies. The three-dimensional constitutive equations developed for numerical calculations are based on the Lou-Schapery one-dimensional nonlinear viscoelasticity model for the uniaxial stress case. The transient creep compliance in the viscoelastic model is represented as an exponential series plus a steady-flow term, which allows for a simplification of the numerical procedure for handling hereditary effects. A cumulative damage law for three dimensional analysis was developed based on the Brinson-Dillard two-dimensional model to predict failure initiation. Calculations were performed using this program in order to evaluate its performance in applications involving complex structural response. IM7/5260-H Graphite/Bismaleimide and T300/5208 Graphite/Epoxy were the materials selected for modeling the time-dependent behavior. The cases studied include: 1) Tensile loading of unnotched laminates; 2) bending of a thick laminated plate; and 3) tensile loading of notched laminates. The analysis emphasized the study of the traction-free edge-effect of laminated composites, stress distribution around a circular hole, and stress redistribution and transformation in the layers. The results indicate that the stress redistributions over time are complicated and could have a significant effect on the long-term durability of the structure. / Graduation date: 1994

The main source of the time-dependent behavior of fiber-reinforced composites is their polymeric matrix, which causes concerns about their long term durability. Although for composites where organic fibers such as Graphite are used, the fibers are also a contributing factor. A composite material may exhibit an appreciable amount of creep, depending on the state of stress and temperature. Viscoelastic flow in the matrix and internal flaw formation and growth are the main sources of this creep. Thus a study was made on the viscoelastic behavior of GI/BMI fiber reinforced composite. An experimental method for testing a large number of composite materials in compression was developed. The samples were tested according to the test matrix consisting of combinations of static and cyclic loads and temperatures. The fixtures were calibrated to check the validity of measurements and reproducibility of results. Stress gradients were caused by frictional effects between the fixture and samples. The modulus change of samples over a period of time were studied. Bending parameters in samples were measured and analyzed for different stresses, clamping forces, temperatures and time. Mechanical models were used to explain the basic principles behind creep of a viscoelastic material followed by a theoretical explanation and study of creep. The linear and non-linear viscoelastic constants were studied and a methodology to analyze these results was presented. The linear and non-linear constants were used in a prediction model and predictions of a composite creep strain with time were made. Creep data obtained tor [45/0/-45/90]������ for a period of three months were compared to the prediction model. / Graduation date: 1994

Thesis (Ph. D.)--University of Alabama at Birmingham, 2008. / Title from PDF title page (viewed Jan. 28, 2010). Additional advisors: Michael Anderson, Fouad Fouad, Wilbur Hitchcock, Virginia Sisiopiku. Includes bibliographical references (p. 203-208).