Applications in engineering science最新文献

Ventricular Assist Devices (VADs) have revolutionized treatment of adult heart failure with tens of thousands of devices implanted either as a “bridge” to transplant or as a permanent “destination” therapy. There is also a need for VADs for pediatric patients with congenital and/or acquired cardiac disease; yet, the small market potential of pediatrics versus adults has limited commercial interest. Under the support of two completed contract awards from the National Heart, Lung, and Blood Institute and one current award from the Department of Defense Peer Reviewed Medical Research Program, we have designed and validated an implantable, mixed-flow, fully magnetically levitated (maglev), rotodynamic blood pump, the PediaFlow™ pediatric VAD. The clinical design goal for the PediaFlow™ pediatric VAD is to support the failed circulation of infants/neonates and consequently most vulnerable patients for durations consistent with bridge-to-transplant wait list times. Our current fifth generation prototype is the size of an AA cell battery and can achieve flow rates consistent with pediatric circulatory support requirements with minimal cellular damage. We are also currently developing a “smart” closed-loop pump controller which is a quantum improvement over current clinical-use controllers that operate in fixed-output, open-loop mode.

Despite the tremendous impact that a good constitutive relation for the response of arterial tissues can have with regard to advances in cardiovascular science and medicine, and notwithstanding the intense effort to put a felicitous constitutive relation into place, no reliable constitutive relation is available in the literature. In this review article, we provide a brief survey and assessment of the evolution of constitutive relations that have been developed to describe the response of arterial tissues, their inadequacies, and the various quintessential aspects of the response that need to be taken into consideration. We then fashion a nonlinear constitutive relation to describe an inhomogeneous anisotropic compressible viscoelastic solid, which while being grossly inadequate to describe the tissue in its entirety, makes it evident that what one ought to strive for is not in capturing the complexity of tissues, but rather the development of a simple global measure that can be a reliable predictor of the onset of tissue disease, and tissue damage and failure.

A finite element modelling of dilute elastomer composites based on a Neo-Hookean elastic matrix and rigid spherical particles embedded within the matrix was performed. In particular, the deformation field in vicinity of a sphere was simulated and numerical homogenization has been used to obtain the effective modulus of the composite ${\mu }_{\text{eff}}$ for different applied extension and compression ratios. At small deformations the well-known Smallwood result for the composite is reproduced: ${\mu }_{\text{eff}}=(1+\left[\mu \right]\phi ){\mu }_0$ with the intrinsic modulus $\left[\mu \right]=2.500$. Here $\phi$ is the volume fraction of particles and ${\mu }_0$ is the modulus of the matrix solid. However at larger deformations higher values of the intrinsic modulus $\left[\mu \right]$ are obtained, which increase quadratically with the applied true strain. The homogenization procedure allowed to extract the intrinsic strain coefficients which are mirrored around the undeformed state for principle extension and compression axes. Utilizing the simulation results, stress and strain modifications of the Neo-Hookean strain energy function for dilute composites are proposed.

The current work explores the influence of process parameters such as mesh size and volume fraction of abrasives with number of passes, on the interior surface quality of a pre machined component by extrusion honing process. The finishing process is highly flexible and unconventional while modifying the surfaces in case of miniature components involving complex profiles. The method is extensively used to deburr, polish, edge contour and removing recast layers by producing compressive stresses. By, the pressurized flow of semi viscous abrasive laden across the surface to be processed. The experimental study has been carried out on Inconel-625 alloy by one way EH process, with the carrier medium silicone polymer blended with SiC as abrasives. Experiments are planned by constructing L27 orthogonal array for the factors such as mesh number 36, 46, 54 and volume fraction 40, 50, 60 % of abrasives followed by number of passes 5, 10 and 15. Also, the study focuses in developing a regression model, training neural network and comparison of experimental R_a with both regression and ANN model. The prediction of R_a is accomplished by developing a linear regression model and a feed forward back propagation neural network model. Both the developed models are able to predict the output response with an error of 5 to 12%.

The fatigue strength of structures subjected to cyclic loading depends strongly on the stress ratio. Particularly, in case of welded steel structures this fact is not considered in the corresponding standards nor in the guidelines. Experimentally, two approaches are used to study the effect of stress ratio on the fatigue life. On the one hand, based on the $S$-$N$  curves obtained from tests performed at different stress ratios, the fatigue life under a particular stress range is estimated. On the other hand, the stress amplitude corresponding to a constant fatigue life is estimated by applying the failure criteria for fluctuating stress like the Goodman–Haigh relationship. This paper presents a general probabilistic model, which estimates the $S$-$N$  and Goodman–Haigh curves for any stress ratio. Afterwards, this model is applied on data obtained from full and partial cyclic compression loading tests performed on welded specimens made of steel St 52-3. The tested details correspond to the permissible notch condition limit occurred in highly stressed structures used to build ships.

A time domain finite element (FE) framework was used to investigate the coupled electromagnetic (EM) and mechanical behavior of buried target systems. The coupling of the EM and mechanical fields is through using the Lorentz Force as the body force in the mechanical Cauchy equation of motion. The coupling is sequential where the EM fields and Lorentz force are first solved for, then they are used as inputs for the Cauchy equations of motion. Predictions were obtained for different loading conditions and the Method of Morris sensitivity analysis was used to understand how different mechanical and EM variables affect the buried target system. These predictions indicate that target permeability and depth had the most significant and dominant effects on the behavior of the buried target system.

For over a decade, the team from the Aortic Institute at Yale University has worked closely with the bioengineering team of Dr. Wei Sun at Georgia Tech University. This paper presents the products of that collaboration.

We provide clinical context by describing thoracic aortic dissection and its genesis as a prelude to the bioengineering findings. We discuss the genesis of aortic dissection, from the fundamental underlying genetic abnormality, through the degenerative aortic process, to the acute inciting factors and the dissection event itself. The inciting factor is usually an extreme hypertensive episode, occasioned by exertion or emotion.

The bioengineering findings include the following: The aortic wall is stronger in the circumferential direction than in the longitudinal. Bicuspid aortic valve and bovine aortic arch morphology do not compromise aortic strength. Biaxial testing reveals a non-liner stress-strain response of aortic tissues. Dissected tissues become stronger over time, reflecting fibrotic connective tissue ingrowth in response to the dramatic tissue injury from the dissection event. Human aortic tissues stiffen at advanced age, in contradistinction to those of aged animals (porcine).

Combining clinical and bioengineering perspectives yields a more complete and correlative understanding of the genesis of thoracic aortic dissection.

Abdominal aortic aneurysms (AAA) have been rigorously investigated to understand when their risk of rupture - which is the 13^th leading cause of death in the US – exceeds the risks associated with repair. Clinical intervention occurs when an aneurysm diameter exceeds 5.5 cm, but this “one-size fits all” criterion is insufficient, as it has been reported thatup to a quarter of AAA smaller than 5.5 cm do rupture. Therefore, there is a need for a more reliable, patient-specific, clinical tool to aide in the management of AAA. Biomechanical assessment of AAA is thought to provide critical physical insights to rupture risk, but clinical translataion of biomechanics-based tools has been limited due to the expertise, time, and computational requirements. It was estimated that through 2015, only 348 individual AAA cases have had biomechanical stress analysis performed, suggesting a deficient sample size to make such analysis relevant in the clinic. Artificial intelligence (AI) algorithms offer the potential to increase the throughput of AAA biomechanical analyses by reducing the overall time required to assess the wall stresses in these complex structures using traditional methods. This can be achieved by automatically segmenting regions of interest from medical images and using machine learning models to predict wall stresses of AAA. In this study, we present an automated AI-based methodology to predict the biomechanical wall stresses for individual AAA. The predictions using this approach were completed in a significantly less amount of time compared to a more traditional approach (∼4 hours vs 20 seconds).

A new class of coupled poroelastic problems describing fluid-driven cracks (called fractures) subjected to non-penetration conditions between opposite crack faces (fracture walls) is considered in the incremental form. The nonlinear crack problem for a plane isotropic setting in a two-phase medium is expressed in polar coordinates as a variational inequality with respect to the solid phase displacement and the pore pressure. Applying nonlinear methods, the asymptotic theory and Fourier analysis, a semi-analytic solution given as the power series in the sector of angle $2\pi$ is proven using rigorous expansions with respect to the distance to the crack-tip. Here no logarithmic terms occur in the asymptotic expansion. Consequently, a square-root singularity for the poroelastic medium with a non-penetrating crack is derived, and the integral formulas for calculating the corresponding stress intensity factors are obtained.