Errors and uncertainties in the application of FEA for Composite Materials can come from the following many sources,

1) Errors that come from the inherent assumptions in the FEA theory and

2) Errors and uncertainties that get built into the system when the physics we are seeking to model gets transferred to FEA models.

A common list of these kind of errors are as mentioned below;

> Errors and uncertainties from the solver.

> Level of mesh refinement and the choice of element type.

> Averaging and calculation of stresses and strains from the primary solution variables.

> Approximations in the material properties of the model.

> Approx. and uncertainties in the loading and boundary conditions of the model.

The long list of error sources and uncertainties in the procedure makes it desirable that a framework of rules and criteria are developed for the application of finite element method.

Verification procedure includes checking the design, the software code and also investigate if the computational model accurately represents the physical system. Validation is more of a dynamic procedure and determines if the computational simulation agrees with the physical phenomenon, it examines the difference between the numerical simulation and the experimental results. Verification provides information whether the computational model is solved correctly and accurately, while validation provides evidence regarding the extent to which the mathematical model accurately correlates to experimental tests.

The blue, red and green colored areas in Figure highlight the iterative validation and verification activities in the process. The green highlighted region falls in the domain of the laboratory performing the experiments.

Comparing the issue of code verification and calculation verification of FEA for Composite Materials, the main point of difference is that calculation verification involves quantifying the discretization error in the simulation. Code verification is rather upstream in the process and is done by comparing numerical results with analytical solutions.

The validation procedure has to be developed by the analyst. The following validation guidelines were developed at Sandia National Labs [Oberkampf et al.] by experimentalists, these are applicable to all problems from computational mechanics.

#1: The validation experiment should be designed by the FEA group & experiment engineers. The experiments should be designed so that validation falls inside the application domain.

#2: The designed experiment should involve the full physics of the system, including the loading and boundary conditions.

#3: The solutions of the experiments and from the computational model should be totally independent of each other.

#4: The experiments and the validation process should start from the system level solution to the component level.

#5: Care should be taken that operator bias or process bias does not contaminate the solution or the validation process.