*Sponsored by:* MSD Computer Simulation Committee

*Program Organizers:* S.P. Chen, Los Alamos National Lab., Los Alamos, NM
87545; M.P. Anderson, Exxon Research Center, Clinton Township, Route 22 East,
Annandale, NJ 08801

Wednesday, PM Room: Marquis 1&2

February 7, 1996 Location: Anaheim Marriott Hotel

*Session Chairman:* S. P. Chen, Los Alamos National Laboratory, Los
Alamos, NM 87545; M. P. Anderson, Exxon Research Center, Clinton Township,
Route 22 East, Annandale, NJ 08801

**2:00 pm**

**ON THE CRITICAL CONDITIONS OF KINK BAND FORMATION UNDER COMPRESSIVE LOADING
IN FIBER COMPOSITES: **Ming Dao, Robert J. Asaro, Department of Applied
Mechanics and Engineering Sciences, University of California, San Diego, La
Jolla, CA 92093-0411

Compressive loading along fiber direction in fiber composites usually results in kink band formation, which dramatically reduce the compressive strength of the fiber composites. A rate independent elasto-plastic, finite strain model is applied to study the critical conditions of kink band formation of fiber composites under compressive loading. Orientation dependent mechanical behavior of fiber composites is modeled using a simple slip model. Unlike many previous models that give separate analysis for the maximum load and the kink band angle, our model gives a unified explanation for both the critical load and the kink band angle. Elastic anisotropy id found to play a very important role in terms of the kink band angle. The predicted values of the critical load and the kink band angle are in very good agreement with available experimental data.

**2:30 pm**

**TEMPERATURE-DEPENDENT ELASTIC MODULI OF TWO PHASE COMPOSITE, CALCULATED
USING SIMPLE UNIT CELL MODELS:** K. S. Ravichandran, Department of
Metallurgical Engineering, 412 WBB, The University of Utah, Salt Lake City, UT
84112

Temperature dependence of elastic moduli are of interest to evaluate structural performance and residual stresses of composites used in structural and electronic applications. In the present research, prediction of elastic moduli of composites as a function of temperature will be made using simple, microstructure-based unit cell models. The models are based on the concept of dividing the unit cell into isostress and isostrain elements and determining the overall composite behavior by using appropriate volume fractions for these elements at different stages of division. Composites having discrete second phases in continuous matrix materials is considered for this purpose. Comparisons of predicted trends with experimental data on several composites is made. The accuracy of the present method is evaluated in the light of other models.

**3:00 pm**

**LOAD TRANSFER DURING LOADING IN PARTICLE-REINFORCED METAL MATRIX COMPOSITES:
**N. Shi, M. A. Bourke, J. A. Goldstone, Los Alamos National Lab., Los
Alamos, NM 87545, J. E. Allison, Ford Motor Company, Dearborn, MI 48121

Internal stresses in the matrix and reinforcement of a 2219Al/TiC/15p-T6 metal matrix composite were measured in situ via neutron diffraction during loading. The evolution of stresses in individual phases (phase stresses) with the applied load was also modeled using a finite element method model. The numerical predictions are in good agreement with the neutron diffraction stress measurements. Both modeling and measurements indicate that while internal normal stress parallel to the loading direction continues to transfer from the matrix to the reinforcement as applied load increases, the internal particle normal stress perpendicular to loading decreases at small loads, and reaches a minimum at a load well below the composite macroscopic yield. As the load further increases, the perpendicular particle normal stress relaxes until marcroscopic yield is reached. This kind of behavior can be numerically reproduced only when the effects of thermal residual stresses are included. It was demonstrated that thermal residual stresses result in alteration of matrix plastic flow initiation site, which is critical in affecting load transfer before macroscopic yield.

**3:30 pm**

**MODELING THE CONSOLIDATION BEHAVIOR OF METAL MATRIX COATED FIBERS:
**Joseph M. Kunze, Haydn N. G. Wadley, Department of Materials Science and
Engineering, School of Engineering and Applied Science University of Virginia,
Charlottesville, VA 22903

An experimental study has been conducted on the consolidation of randomly packed arrays of silicon carbide fibers coated via physical vapor deposition (PVD) with a Ti-6Al-4V matrix. The densification behavior of the metal matrix coated fibers was recorded in situ using an eddy current sensor. A model has subsquently been developed describing the densification of continuously reinforced metal matrix composites from fibers coated with the matrix material. The densification mechanisms considered include plasticity, power law creep and diffusion accommodated grain sliding. The model utilizes previous work on the blunting of contacts (stage I) and the closure of isolated voids (stage II) in determining the overall densification behavior. The results showed diffusion accomodates grain sliding to be the dominant densification mechanism. Model-based simulations using the process schedules of the HIP consolidation experiments were found to agree well with experimental results.

**4:00 pm**

**THE ROLE OF INTERFACES AND MATRIX VOID NUCLEATION MECHANISM ON THE DUCTILE
FRACTURE PROCESS OF DISCONTINUOUS REINFORCED COMPOSITES**: S. B. Biner, Ames
Laboratory, Iowa State University, Ames, IA 50011

The role of fiber morphology, interface failure and void nucleation mechanisms within the matrix on the deformation and fracture behavior of discontinuous reinforced composites was numerically investigated. The matrix was modeled using a constitutive relationship that accounts for strength degradation resulting from nucleation and growth of voids. For the matrix, two materials exhibiting identical strength and ductility but having different void-nucleation mechanisms (stress-controlled and strain controlled) were considered and reinforcements were assumed to be elastic. The results indicate that in the absence of interface failure, the void nucleation in the matrix is the key controlling parameter of the composite strength and ductility, hence, of the fracture toughness. The weak interfacial behavior between the fibers and the matrix can significantly increase the ductility without sacrificing strength for certain reinforcement morphology and certain matrix void-nucleation mechanisms. This work was supported by USDOE, Office of Basic Energy Sciences, Div. of Materials Science under contract no. W-7405-ENG-82.

**4:30 pm**

**THE MECHANICAL PROPERTIES OF INTERMETALLIC/METALLIC MICROLAMINATE
COMPOSITES:** J. Heathcote, G. R. Odette, G. E. Lucas, Materials Department,
University of California, Santa Barbara, CA 93106

A self-consistent procedure is used to determine the stress-displacement
function, sigma(u), of constrained metal layers in an intermetallic/metallic
microlaminate composite. A fitting procedure is used with a large scale
bridging model to determine the sigma(u) function that corresponds to measured
resistance curve (R-curve) data. In this evaluation u*, the peak stress,
sigma(p), and failure extension, u*, of the metal layers are fixed to allowable
ranges by independent measurements. Microhardness tests are used to estimate
sigma(p), and a fracture reconstruction procedure is used to determine u*.
Finally, as a test of self-consistency, the sigma(u) functions are used to
determine R-curves for tensile test samples for a bridging-crack stability
analysis of fracture strength controlled by pre-exisiting defects. Strength
predictions from this analysis are compared to measured data. The evaluation of
sigma(u), a fundamental composite property, and of how it controls mechanical
behavior gives insight into how to develop these composites to optimize this
behavior.

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