NASA 4750 Manual

A SERVICE OF

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SUMMARY OF AVAILABLE CODES

8-3

Stiffness

Model:

Finite element analysis is used to determine a general displacement field. Periodic or

cyclic-symmetry boundary conditions are applied to the edges of the unit cell. The

finite element code is integral to the program. The user can select the degree of

mesh refinement (number of elements on an edge). Heterogeneous elements are

used, in which the material (yarn or matrix) may be different at each integration

point. The user may select a 3D solution or a plate solution. In the plate solution, A,

B, and D matrices are computed using traction free surfaces to represent the plane-

stress condition. Average stiffness is computed using both volume averaged

stresses and the summation of edge forces.

Strength

Model:

No strength prediction is given, but stress and strain distributions from the linear

analysis are available. Stresses are computed for unit applied strains (6

components).

Data

Required:

Yarn and matrix linear elastic stiffness. Different yarns may have different

properties. Points describing yarn paths and cross-sections must be generated

external to the program.

Output:

6x6 average stiffness matrix, A, B, and D matrices (plate option), thermal

expansion coefficients, and yarn volume fractions. Point stresses available for unit

strains. Finite-element nodal coordinates and connectivity arrays are also given.

Experimental

Validation

:

None offered.

Comments:

- Since the problem is solved by finite elements, no assumptions are made

regarding the internal displacement field. Point stresses are available. Unlike

isostrain models, the strains corresponding to these stresses may vary within a

constituent.