Computational Process Simulation and Energy Parameter Analysis From Mechanical Deformation of Aerospace Alunimum Alloys

Many systems that work on the processing of energy can be modeled in terms of that energy. The energy that is given to the system may be stored or dissipated in the form of heat. It was proposed to extend this concept to attainment of critical level of stored energy and/or dissipated energy for occurrence of buckling of a metal column under compressive loading. The fact that Energy Factor Parameter (E.F.P.) computed from the experimental true stress-true strain values, suddenly decreased and approached value close to zero indicated either buckling and/or softening, but deviated with the E.F.P. computed from the theoretical true stress and true strain values. The 7050-T7451 (Al-Zn-Mg-Cu-Zr) and Al-Li-Cu aluminum alloys in longitudinal and transverse grain orientations were compression tested for mechanical properties of yield strength, buckling strength, strength coefficient, strain hardening exponent. Correlation between ratio of buckling strength and yield strength with aging time for preaged ASTM compression specimens was established. The compression deformation of aluminum alloy 7050 was modeled using finite element analysis, with the experimental testing parameters and the database in the software package.

Investigation of Fracture in Transparent Glass Fiber Reinforced Polymer Composites Using Photoelasticity

Composite materials are widely used in mechanical structures where a high ratio of strength or stiffness to weight is desired. Not only are composite materials widely used in building recreational equipment such as skis, snowboards or even sports cars, but also multiple types of military aircraft are built from composite materials. Airplane bodies are in principle cyclically loaded pressure vessels and are susceptible to the formation of fatigue cracks, and it is necessary to possess knowledge of how the material behaves with a crack present. In fact, all engineering structures have to be designed with the presence of crack like defects in mind. For traditional engineering materials such as steel and aluminum there exists a large body of knowledge regarding material behavior in the presence of a crack. Furthermore, their isotropic nature eases the process of mechanical analysis. Photoelasticity, an optical method, has been widely used to study fracture in isotropic transparent materials (Irwin, 1962, 1980; Dally, 1979; Daniel, 1984; Kobayashi, et al, 1973; Chona, 1987).

Computational Methods for the Design of Deformation Processes of Porous Materials

An updated Lagrangian framework of the continuum sensitivity method (CSM) is presented to address important computational design problems in the deformation processing of porous materials. Weak sensitivity equations are developed that are consistent with the kinematic, constitutive, contact and thermal analyses used in the solution of the direct thermomechanical problem. The CSM is here used to analyze die and preform computational design problems in industrial metal forming processes wherein temperature and the accumulated damage play an important role in influencing the deformation mechanism, material state and shape of the deformed workpiece.

Study of Microstructural Effect in Particulate Composites

The effects of random and non-uniform particle distribution on the damage initiation and growth leading to a crack were investigated for particulate composites using a multi-scale technique. Damage was described at the constituent material level (i.e. micro-level) and the results compared well qualitatively and quantitatively with experimental observation. Non-uniform, random particle distribution yielded sporadic crack initiation and growth within a uniform tensile specimen. No local crack propagated beyond a certain size. Breakage of the specimens was not caused by the continuous growth of a single critical crack. Instead, coalescence of neighboring sporadic short cracks resulted in breakage of the specimens. Computer simulation indicated that random particle distribution affected the strength of the composite significantly, but as expected, not its effective stiffness.

A General Numerical Procedure for Extracting Mixed-Mode Stress Intensity Factors Along the Fronts of Three-Dimensional Nonplanar Cracks

A numerical procedure is described for extracting mixed-mode stress intensity factors along the fronts of three-dimensional, nonplanar cracks embedded in solids. The mixed-mode stress intensity factors at points along the crack front are obtained by evaluating interaction energy integrals for three-dimensional, non-planar cracks. To assess the validity of the numerical procedure, two numerical examples are considered. First, we consider the problem of a non-planar, lens-shaped crack in an infinite solid subjected to hydrostatic tension. The numerical results are shown to be in excellent agreement with available analytical results. We then consider the case of a non-planar, warped elliptical crack surface, where to our knowledge no analytical solution exists, and the results are discussed.

Modeling and Analysis of 1-3 Piezoelectric Composites

Theoretical results of the material properties of piezoelectric composites are generally limited to the transversely isotropic composites and are usually given in the form of upper and lower bounds. In most of these analyses all the material constants cannot be determined. However, the method of effective field has been used on a transversely isotropic piezoelectric composite to theoretically calculate all the ten material properties. In this work an alternative method to determine all the elastic, dielectric and piezoelectric coupling constants of 1-3 piezoelectric composite with periodic arrangement of fibers are investigated by using finite element analysis on a unit cell model. FEA of unit cell models for hexagonal, square with diagonal and square with edge orientation topologies are performed. Different mechanical and electrical loading patterns and their corresponding boundary conditions are formulated and simulated to get data necessary for deriving the various anisotropic material constants. FEA results are compared with those of the theoretical work. Effect of different parameters e.g. volume fraction, topology and electrical boundary conditions on the different material constants are discussed.

Comparison of Different Shell Theories for Large-Amplitude Vibrations of Circular Cylindrical Shells

Large-amplitude (geometrically nonlinear) vibrations of circular cylindrical shells subjected to radial harmonic excitation in the spectral neighbourhood of the lowest resonances are investigated. The Lagrange equations of motion are obtained by an energy approach, retaining damping through Rayleigh’s dissipation function. Four different nonlinear shell theories, namely Donnell’s, Sanders-Koiter, Flu¨gge-Lur’e-Byrne and Novozhilov’s theories, are used to calculate the elastic strain energy. The formulation is also valid for orthotropic and symmetric cross-ply laminated composite shells. The large-amplitude response of perfect and imperfect, simply supported circular cylindrical shells to harmonic excitation in the spectral neighbourhood of the lowest natural frequency is computed for all these shell theories. Numerical responses obtained by using these four nonlinear shell theories are also compared to results obtained by Galerkin approach, used to discretise Donnell’s nonlinear shallow-shell equation of motion. A validation of calculations by comparison to experimental results is also performed. Boundary conditions for simply supported shells are exactly satisfied. Different expansions involving from 14 to 48 generalized coordinates, associated to natural modes of simply supported shells, are used. The nonlinear equations of motion are studied by using a code based on arclength continuation method that allows bifurcation analysis.

Computational Nanomechanics

A computational technique for nanomechanics was presented for static equilibrium problems. The approach was based on atomic force equilibrium that was computed from energy potential function. This atomic model was coupled with the conventional finite element analysis model. Furthermore, a multi-scale approach relating the nano-scale behavior to the macro-scale mechanical properties was provided with an example of composite materials. Various examples were provided to demonstrate the presently developed technique.

Fatigue Analysis of a Welded Lap Joint Under Bending Load

Welded lap joints subject to cyclic loading are used in industrial vehicles and equipment. Cyclic bending loads can result in fatigue failure of these joints. It is desirable to predict the expected life of the joint as a function of a load-stress parameter. To predict the life of a typical welded structure, additional types of weld joints and loads must also be considered. The lap joint work covered here provides a building block for the structure life prediction. For the work reported here, lap joints were formed by an industrial manufacturing wire feed weld process by certified welders. Strain gages were applied to one of the joint members. A fixture was designed and built to apply a pure bending load to the welded members at the joints, and this was installed in a fatigue test machine. A number of fully reversed tests were run to failure at various loads and some were run to effective infinite life. A resulting set of stress life curves was generated based on mean life and mean life less one and two standard deviations as a function of the “hot spot” stress. This hot spot is the region near the weld toe where the stress distribution starts to deviate from linearity due to the geometric stress riser of the weld fillet and joint geometry. Measurements show that this stress can be approximated by the calculated beam bending stress for the specimens and loads used in the tests. The results of this work provide guidelines for design of welded lap joints for a desired cycle life and for predicting the expected cycle life of an existing joint including uncertainties in life due to weld and test variables. The stress needed to predict the life of a joint is obtained by strain measurements on the actual structure. For design, the stress may be approximated by calculated stresses.

Buckling and Postbuckling of Electroconducting Elastic Plates in a Magnetic Field

The basic equations of a fully nonlinear theory of electromagnetically conducting flat plates carrying an electric current and exposed to a magnetic field of arbitrary orientation are summarized. The relevant equations have been obtained by considering that both the elastic and electromagnetic media are homogeneous and isotropic. The geometrical nonlinearities are considered in the von-Ka´rma´n sense, and the soft ferromagnetic material of the plate is assumed to feature negligible hysteretic losses. Based on the electromagnetic and elastokinetic field equations, by using the standard averaging methods, the 3-D coupled problem is reduced to an equivalent 2-D one, appropriate to the theory of plates. Having in view that the elastic structures carrying an electric current are prone to buckling, by using the presently developed theory, the associated problems of buckling and post-buckling are investigated. In this context, the problem of the electrical current inducing the buckling instability of the plate, and its influence on the postbuckling behavior are analyzed. In the same context, the problem of the natural-frequencies electrical current interaction of flat plates, as influenced by a magnetic field is also addressed.