Publications

Recent technical papers written by MSC staff are available for download here. Full papers can be downloaded in Adobe PDF format. To view or print PDF files, you will need Acrobat Reader, which is available free here.

- The Effects of Marcel Defects on Composite Structural Properties
- Progressive Failure Analysis of Plain Weaves Using Damage Mechanics Based Constitutive Laws
- Material Modeling For Cross-Ply Ceramic Matrix Laminates With Progressive Damages And Environmental Degradation
- Progressive Failure Analysis Of Thin Walled Composite Tubes Under Low Energy Impact
- A General Sublaminate Analysis Method For Determining Strain Energy Release Rates In Composites
- An Efficient Stress Function Approximation For The Free-Edge Stresses In Laminates

Anthony Caiazzo, Michael Orlet, Hank McShane, Larry Strait and Chris Rachau

ABSTRACT
This paper describes a method for predicting key structural properties of carbon fiber reinforced composite materials containing ply waviness several times the nominal ply thickness. These so-called marcelled regions have been observed in a number of highly loaded thick structural components. The origins of these defects are not fully understood, although several contributing factors have been identified. The goal of this work is to develop an analysis based disposition criterion for components where fabrication process changes can not be readily implemented to eliminate marcel defects. Work to date has focused on developing a micro-mechanics based procedure for modeling the strength and stiffness properties of a marcelled region given basic properties of the material and simple geometric parameters of the marcel that can be measured non-destructively. The result is a general constitutive model that can be used in global structural analysis packages to assess the effects marcel defects have on component per-formance. Analyses of test coupons containing marcelled regions have been carried out to illus-trate the method and establish the validity of the modeling approach. Results indicate that the degree to which marcel defects affect structural properties depends not only on the maximum fiber misalignment angle, but also on the location and size of the marcelled region and nominal applied strain field.

To Appear in: Composite Structures: Theory and Practice STP 1383

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M. Kollegal, S. N. Chatterjee and G. Flanagan

ABSTRACT
The behavior of plain woven fabric composites is studied using three-dimensional finite elements which allows detailed modeling of the geometric complexities and spatial material variations within the fabric. Damages in the composite constituents viz. yarn and pure matrix are modeled on a continuum basis and related to their material constitutive behavior. The 3D constitutive laws describing pure matrix and yarn behavior are developed using a damage mechanics based approach with the dissipated energy density as the damage parameter. The strain energy dissipation (SED) concept is employed to describe the damage state and current stiffnesses of the weave constituents. A progressive failure analysis of plain woven fabrics subjected to tension and in-plane shear is carried out considering both geometric and material nonlinearities. The initiation and progression of damage within the fabric is investigated and the significant damage mechanisms outlined.

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Under review for publication

Chian-Fong Yen and Mark L. Jones

ABSTRACT
A physically-based damage model has been developed to predict the nonlinear behavior of cross-ply ceramic matrix laminates due to progressive failures. It has been shown to model the nonlinear stress-strain response of chemical vapor infiltrated (CVI) SiC/SiC composites under tension loading accurately. This model utilizes a consistent set of measurable material parameters as inputs and shows good agreement with measured tensile stress-strain curves for a variety of ply thickness ratios. The material model is also utilized to characterize the environmentally induced property degradation in CMC’s.

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Presented at the 1997 ASME International Mechanical Engineering Congres and Exposition, November 16-21, 1997, Dallas, Texas.

Chian-Fong Yen, Project Engineer, and Thomas Cassin, President

Materials Sciences Corporation

Joel Patterson, Aerospace Engineer, and Matt Triplett, Mechanical Engineer

Structures Directorate, RD&E Center
U.S. Army Missile Command
Redstone Arsenal, AL 35898-5247

ABSTRACT
Composite failure criteria have been developed for dynamic analysis of composite structures. The proposed progressive failure criteria have been integrated into an explicit dynamic analysis code for failure prediction of thin composite tubes subjected to drop weight impact tests. The results provide good correlation with experimental data for impact force histories and some critical damage modes.

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Gerry Flanagan

ABSTRACT
A method is presented for computing strain-energy-release-rates (SERR) for delamination growth in a wide variety of composite structures. The method is based on a sublaminate analysis which treats portions of a laminate as higher-order plates. The plates may be stacked such that the displacements and tractions are identical at the shared interfaces. By assuming a constant cross-section in one-dimension, the resulting systems of governing differential equations can be solved in closed form. A means of coupling plates end-to-end is also presented, allowing complex structures to be modeled in a manner similar to finite element analysis. The software (SUBLAM) that implements the analysis can be used to determine either interlaminar stresses, or SERR. The individual modes of the SERR (GI, GII, and GIII) can be computed. The present paper includes a series of examples which demonstrate the flexibility and accuracy of the SERR calculations.

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Gerry Flanagan

ABSTRACT
A solution method is derived for determining the free-edge stresses in composite laminates. The method is based on expanding stress functions in terms of a harmonic series in the thickness direction. Using the principle of minimum complementary energy, a system of ordinary differential equations is derived for the distribution in the width direction. Cross-ply and angle-ply laminates are examined to establish the validity of the solution. Eight and sixteen ply quasi-isotropic laminates are also examined to demonstrate a convergence criterion based on average stress. The method proves to be a relatively simple and efficient approach for this problem.

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