Edward Zywicz

Elastic Yield Zone Around an Interfacial Crack Tip

A closed-form approximate solution for a small-scale yielding (SSY) plastic zone around a planar interfacial crack tip, occurring between two dissimilar ideally-bonded elastic half spaces, is obtained by equating the elastically-calculated Mises equivalent stress with the material yield strenght σ ys

A three-dimensional constitutive theory for fiber-composite laminated media

The lamina level constitutive relationship is a specific subset of general, transversely isotropic media behavior. This special class of lamina behavior permits the development of an exact lamination procedure for systems assembled from a single laminate type. The three-dimensional constitutive form for the laminate is determined in terms of the subscale lamina properties and the orientations of each lamina. The extension of this specific constitutive relationship to general transversely isotropic lamina involves separation f the five lamina-scale properties into fiber-dominated versus matrix-dominated classifications and the development of a generalized averaging procedure for the matrix-dominated properties. The resulting three-dimensional constitutive/lamination theory is evaluated through comparisons between exact solutions, using data bases appropriate for graphite and glass epoxy systems in quasi-isotropic layups. The theory is fairly simple and extremely versatile in its application.

A New Stabilized Nodal Integration Approach

A new stabilized nodal integration scheme is proposed and implemented. In this work, focus is on the natural neighbor meshless interpolation schemes. The approach is a modification of the stabilized conforming nodal integration (SCNI) scheme and is shown to perform well in several benchmark problems.

On the flexural and extensional behavior of a large-tow triaxial braided composite☆

The lamina level extensional and flexural properties of a large-tow, triaxially braided, carbon-fiber/polymeric-matrix composite are examined. The braids architecture is idealized with a single representative volume element. The homogenized lamina level properties are determined analytically by using concepts similar to beam theory as well as with three-dimensional finite-element techniques. The homogenized extensional and bending lamina properties are found to be distinct properties, not simply related to each other as in monolithic materials or in composites with very fine and highly periodic microstructures. Specifically, the ratio of the effective flexural to effective extensional Youngs moduli is 0.52 and 0.92 in the longitudinal and transverse directions, respectively. The homogenized laminate properties of a two-ply composite were measured and compared to the numerical predictions. The ratio of the effective laminate flexural to extensional moduli predicted compares favorably with the experimental findings. Thus, in laminates with relatively few laminae, the actual flexural rigidity is lower than that based solely upon the extensional moduli.

On the equivalence of stress- and strain-based failure criteria in Elastic Media *

Abstract Conditions for which strain-based and stress-based failure criteria are mathematically equivalent in elastic media are explored by expressing the criteria in the spectral eigenspace of the elasticity tensor. For scalar-valued quadratic criteria that are homogeneous functions of degree one, stress-based and strain-based criteria are most likely to be mathematically equivalent when the criterias operators are linear combinations of the elasticitys spectral eigenbasis tensors. For the commonly employed fiber-direction strain-based and fiber-direction stress-based “composite” failure criteria, the equivalence conditions are explicitly examined for orthotropic and transversely isotropic material symmetry. The difference between the two criteria decreases as the degree of extensional anisotropy increases but, in general, is unbounded for arbitrary deformation states. Over a moderate, but restricted, range of loading conditions, the difference between the criteria is small for high-modulus fiber-reinforced uni-directional lamina, often less than the uncertainties in either the elastic coefficients or failure values, and the two criteria appear interchangeable.

Accomplishments and Challenges in Code Development for Parallel and Multimechanics Simulations

The Methods Development Group at Lawrence Livermore National Laboratory has historically developed and supported software for engineering simulations, with a focus on nonlinear structural mechanics and heat transfer. The quality, quantity and complexity of engineering analyses have continued to increase over time as advances in chip speed and multiprocessing computers have empowered this simulation software. As such, the evolution of simulation software has seen a greater focus on multimechanics and the incorporation of more sophisticated algorithms to improve accuracy, robustness and usability. This paper will give an overview of the latest code technologies developed by the Methods Development group in the areas of large deformation transient analysis and implicit coupled codes. Applications were run on the state of the art hardware available at the national laboratories.

On the Elastic-Plastic Response of a Large-Tow Triaxially Braided Composite

The elastic-plastic response of a large-tow 0 / triaxially braided composite is numerically simulated to determine the elastic coefficients and post-yield behavior. The ratios of extensional to flexural effective Young’s moduli vary from 0.30 to 0.52 in the longitudinal direction and from 0.90 to 0.95 in the transverse direction. Measurements on a 2-ply 0 / 30 braid support these numerical trends. The onset of macro yield in uniaxial extension coincides with the experimental values in the longitudinal direction while it is nearly twice the experimental values in the transverse direction. In simple shear, matrix plasticity around the undulations facilitates local rotation of the braiders at the onset of macro yield. Under uniaxial flexure, modest stiffening occurs prior to strain softening in both the principal directions.