SBIR-STTR Award

The principal objective of the proposed Phase I SBIR project is the development of a reliable predictive capability for the evaluation of flaw tolerance in metallic and composite airframe components, given part specifications, material properties, initial flaws, such as voids, inclusions, heterogeneous grain structure and design load spectra. The proposed concept is based on the idea that the safe life methodology and the flaw tolerance approaches fit within the same paradigm if we associate failure initiation and crack propagation events with deformation states of representative volume elements. The paradigm applies to metals and composites. The critical values of the deformation states depend on the material systems under consideration. The methodology of verification and validation will be applied, utilizing existing experimental data and the concept of hierarchic multi-scale models already supported by ESRDs proprietary software StressCheck. Because statistical variations in the manufacture and therefore the mechanical response of structural components are unavoidable, prediction of structural and strength responses must be understood in a statistical sense.

Benefit:
The results of the proposed work will support condition based & reliability centered maintenance decisions for high value military and civilian assets through the application of mathematical models based on verified and validated numerical simulation technology. One of the important commercial applications is the support of probabilistic structural reliability analysis.

Keywords:
airframe, airframe, flaw tolerance, Reliability, Certification

The development of a procedural and computational framework for improved prediction of damage accumulation caused by cyclic loading in metallic airframe components is proposed. This framework will be based on the idea that models formulated for the prediction of crack nucleation, i.e., for the purpose of supporting flaw tolerance analysis, and models formulated for the prediction of crack growth, i.e., for the purpose of supporting damage tolerance analysis, are similar in the following sense: In both cases the physical events of interest; crack nucleation and crack growth, are highly nonlinear processes that occur on length scales less than about 0.5 mm for metals used in airframes and are controlled by stress and strain fields computable from mathematical models based on small strain and small deformation theory. Therefore the driving force for damage accumulation can be correlated with functionals that depend on models based on small strain theory. The problem is to identify the functionals that reliably correlate predicted and observed damage accumulation events. The proposed procedural and computational framework will be designed to support this effort.

Benefit:
The main benefit derived from successful completion of the proposed Phase II effort is improved reliability and scope of damage accumulation models used to meet the requirements of service life assessment programs (SLAP), service life extension programs (SLEP), condition-based maintenance programs (CBM) and reliability-centered maintenance programs (RCM).

Keywords:
error control, Safe Life, model calibration, numerical simulation, Validation, verification, Damage Tolerance, Reliability Centered Maintenance