Background/Objectives: For transcatheter aortic valve implantation (TAVI) therapy, a catheter-guided crimped valve is deployed into the aortic root. Valve types such as Edwards balloon-expandable valves and Medtronic self-expandable valves come in different sizes and are chosen based on patient-specific aortic anatomy, including aortic root diameter measurement. Complications may arise due to variations in anatomical characteristics and the implantation procedure, making pre-implantation assessment important for predicting complications. Methods: Computational modeling, particularly finite element analysis (FEA), has become popular for assessing wall stresses and deformations in TAVI. In this study, a finite element model including the aorta, native leaflets, and TAVI device was used to simulate procedures and assess patient-specific wall stresses and deformations. Results: Using the Medtronic Evolut R valve, we simulated TAVI for 14 patients to analyze the effects of geometrical variations on structural stresses. Virtual TAVIs with different valve sizes were also simulated to study the influence of TAV size on stresses. Our results show that variations in aortic wall geometries and TAV sizes significantly influence wall stresses and deformations. Conclusions: Our study is one of the first comprehensive FEA investigations of aortic geometrical variations and valve sizes on post-TAVI stresses, demonstrating the non-linear relationship between aortic dimensions, TAV sizes, and wall stresses.

For a cracked structure that exhibits isotropic elastic material properties, fracture mechanics analysis has been straightforward for a long time with wellknown parameters. In a problem with piezoelectric material behavior, fracture parameters to be used should be chosen accordingly considering the differences that arise with the introduction of the applied electric field. Studies regarding the investigation of piezoelectric materials have sought the determination of the energy release rate, J-integral and energy density factor. Application of an electric field can result in negative energy release rates which is an unrealistic physical situation. Besides, there is a common thought that negative energy release rates conflict with the positive definiteness of the energy density factor. The actual physical state corresponding to the negative energy release rate could be referred to as “closed crack”. Inclusion of poling effect and assuming specific boundary conditions for a problem have impacts on piezoelectricity formulations. Sign changes associated with the energy release rate or J-integral results are demonstrated with a numerical example from the literature. The concepts of energy release rate and energy density factor should be well understood to choose the suitable parameter for a fracture analysis. That will lead to one of the remarks in this study, which can be defined as the anisotropic-like behavior of electroelastic solids with induced poling. The objective is to contribute to overall understanding for the analysis of cracked parts with piezoelectric behavior. Proposed recommendations will be given in the final part.

Analysis of 3-D fatigue crack growth problems with mixed-mode loading has always been an interesting area in the field of fracture mechanics. Fracture failure under the influence of fatigue loading has been a common experience for various industries’ products, such as aerospace and automotive components. Any possible failure in these structures can result in high damage to these components or a serious risk for people’s health. The analysis of such failures may involve great challenges and complexities for obtaining the accurate solution. The complexities of the problem may not only be related to the loading type, but also to the specific geometry itself. Such problems are hard and costly to analyze with experimental methods. Therefore, it is important to establish the theoretical aspects of the process initially, and then having a computational procedure to solve the problem at hand. The crack growth law used in this procedure is NASGRO-type, and determination of the propagation angle is based on the maximum hoop stress criterion. Hypermesh and ANSYS APDL software are benefited during preprocessing of the propagation steps and application of submodeling procedure. Solution of the problem is performed with FRAC3D program, its enriched element methodology and newly implemented tools for crack growth. A specific example that includes cracking within an aircraft engine compressor blade is shown for demonstration purpose.