This research is developing an integrated system of experimentally validated computational models, for simulating the deformation, creep and fatigue failure behavior of polycrystalline metals and alloys. The system consists of computational models and software for: (a) 3D microstructure reconstruction and characterization of morphological and crystallographic information, (b) image-based microstructural computational models incorporating crystal plasticity and fracture laws, and (c) a multi-time scaling time integration algorithms for cyclic deformation, to investigate the effect of material microstructure on deformation behavior and fatigue life. The computational system is expected to assist engineers, especially in the aircraft engine industry, in their product design for enhanced performance and reliability.

Conventional commercial Finite Element Method (FEM) codes have a number of shortcomings when modeling real materials due to lack of certain key aspects, such as efficiency, accuracy in the presence high gradients and discontinuities, numerical stability, etc. Important advances are needed in computational tools and methodologies to overcome these shortcomings. Somnath Ghosh’s research group has considerable research experience in the development of advanced micromechanical computational models for material characterization and modeling that can effectively address some of these problems for polycrystalline and poly-phase materials. An important component of the development of any computational model is its validation with experiments. Collaborations with other members of CAMM and AFRL/MLLLM are providing this indispensable component to add robustness to the models.

Computational models are being developed in the proposed program to incorporate accurate microstructural morphology and crystallographic information for analyzing structure-sensitive deformation and fatigue behavior. Primary focus is on aerospace metals and alloys, e.g. IN-100, Ti-6242 and Ti-6Al-4V, with a motivation to improve performance and reliability of aerospace engine materials. A comprehensive approach is being pursued, coupling the following elements:
(i) Reconstruction of 2D and 3D microstructural models with real morphological features and crystallographic orientations from quantitative metallography combining focused ion beam (FIB) and electron back-scatter detector (EBSD) in orientation imaging microscopy, microstructural characterization, and statistical methods.
(ii) Development of experimentally validated finite deformation rate-dependent crystal plasticity models with size effects, for analyzing deformation and creep in polycrystalline aggregates.
(iii) Development of an experimentally validated cohesive zone model for inter and intra-granular fracture initiation and growth for fatigue crack modeling.
(iv) Development of a stable, accurate and efficient image-based micromechanical finite element model, for crystal plasticity and damage, incorporating real morphological and crystallographic features. A novelty of this model is in the powerful adaptive techniques for automatically changing the element resolution and topology with evolving strain localization and damage.
(v) Development of multi-scaling algorithms in the time domain for compression and localization in cyclic deformation analysis.
In summary, the proposed research is developing experimentally validated innovative high fidelity computational tools to provide improved predictive capabilities for fatigue failure analysis in materials with aerospace applications. The program is expected to advance the state of the art in analysis methodology for high confidence in component performance and life calculations.