Comparative study on free vibration analysis of rotating bi-directional functionally graded beams using multiple beam theories with uncertainty considerations.

The present study investigates the free vibration behavior of rotating beams made of functionally graded materials (FGMs) with a tapered geometry. The material properties of the beams are characterized by an exponential distribution model. The stiffness and mass matrices of the beams are derived using the principle of virtual energy. These matrices are then evaluated using three different beam theories: Bernoulli-Euler (BE) or Classical Beam Theory (CBT), Timoshenko (T) or First-order Shear Deformation Theory (FSDT), and Reddy (R) or Third-order Shear Deformation Theory (TSDT). Additionally, the study incorporates uncertainties in the model parameters, including rotational velocity, beam material properties, and material distribution. The mean-centered second-order perturbation method is employed to account for the randomness of these properties. To ensure the robustness and accuracy of the probabilistic framework, numerical examples are presented, and the results are compared with those obtained through the Monte Carlo simulation technique. The investigation explores the impact of critical parameters, including material distribution, taper ratios, aspect ratio, hub radius, and rotational speed, on the natural frequencies of the beams is explored within the scope of this investigation. The outcomes are compared not only with previously published research findings but also with the results of 3-Dimensional Finite Element (3D-FE) simulations conducted using ANSYS to validate the model's effectiveness. The comparisons demonstrate a strong agreement across all evaluations. Specifically, it is observed that for thick beams, the results obtained from FSDT and TSDT exhibit a greater agreement with the 3D-FE simulations compared to CBT. It is shown that the coefficient of variation (C.O.V.) of first mode eigenvalue of TSDT, FSDT and CBT are approximately identical for random rotational velocity and discernible deviations are noted in CBT compared to FSDT and TSDT in the case of random material properties. The findings suggest that TSDT outperforms FSDT by eliminating the need for a shear correction coefficient, thereby establishing its superiority in accurately predicting the natural frequencies of rotating, tapered beams composed of FGMs.

Patient radiation exposure for endovascular deep venous interventions.

OBJECTIVE: The study aimed to assess the cumulative radiation exposure from preoperative, periprocedural, and follow-up imaging to patients who underwent common endovascular deep venous interventions for acute and chronic central venous outflow obstructive diseases; namely, deep vein thrombosis (DVT) thrombolysis, unilateral chronic iliofemoral venous stenting, and inferior vena cava (IVC) reconstruction in a single center. METHODS: Patients who had DVT thrombolysis of upper extremity (UE) DVT and lower extremity (LE) DVT, unilateral chronic iliofemoral venous stenting, and endovascular IVC reconstruction between May 1, 2012, and July 31, 2017, in a single unit were retrospectively reviewed. Demographic data, anatomic DVT, imaging, technical details of the index procedure, follow-up, and radiation exposure measured in dose-length product, dose-area product (DAP), and fluoroscopy time (FT) from related computed tomography scans and interventions were analyzed. Mann-Whitney U tests were performed to assess for significance of differences between subgroups. A P value of less than .05 was considered significant. RESULTS: In total, 20 UE DVT thrombolysis, 91 LE DVT thrombolysis, 56 unilateral chronic iliofemoral venous stenting, and 39 endovascular IVC reconstruction patients were included in the study, with the following median ages: 39 years (range, 20-67 years), 44 years (range, 15-78 years), 45 years (range, 20-80 years), and 35 years (range, 18 -73 years), respectively. The median cumulative DAP for the index DVT thrombolysis was 9.2 Gycm2 (range, 0.2-176.0 Gycm2) for LE DVT and 2.0 Gycm2 (range, 0.1-11.7 Gycm2) for UE DVT (P < .0001). The median cumulative FT for the index thrombolysis was 981 seconds (range, 20-4890 seconds) and 837 seconds (range, 19-2895 seconds) for LE DVT and UE DVT, respectively (P = .18). For unilateral chronic iliofemoral venous stenting, the median cumulative DAP and FT were 32.4 Gycm2 (range, 0.1-289.6 Gycm2) and 660 seconds (range, 246-4200 seconds), respectively. Meanwhile, the median cumulative DAP and FT for the endovascular IVC reconstruction were 60.8 Gycm2 (range, 2.5-269.1 Gycm2) and 2846 seconds (range, 836-11682 seconds), respectively. The median DAP for secondary procedures during follow-up was 6.6 Gycm2 (range, 0.8 186.5 Gycm2), 1.9 Gycm2 (range, 0.2-111.7 Gycm2), and 24.3 Gycm2 (range, 0.2-157.5 Gycm2) for LE DVT thrombolysis, unilateral chronic iliofemoral venous stenting, and endovascular IVC reconstruction, respectively. CONCLUSIONS: Patient radiation exposure for endovascular deep venous interventions for central venous outflow obstruction measured in DAP and FT seemed to be less than and at most similar to anatomically comparable arterial interventions in the literature. However, these patients were usually much younger than those with arterial diseases and may need secondary interventions involving further radiation exposure in their lifetime.

Radiation-Induced DNA Damage in Operators Performing Endovascular Aortic Repair.

BACKGROUND: Radiation exposure during fluoroscopically guided interventions such as endovascular aortic repair (EVAR) is a growing concern for operators. This study aimed to measure DNA damage/repair markers in operators perfoming EVAR. METHODS: Expression of the DNA damage/repair marker, γ-H2AX and DNA damage response marker, phosphorylated ataxia telangiectasia mutated (pATM), were quantified in circulating lymphocytes in operators during the peri-operative period of endovascular (infrarenal, branched, and fenestrated) and open aortic repair using flow cytometry. These markers were separately measured in the same operators but this time wearing leg lead shielding in addition to upper body protection and compared with those operating with unprotected legs. Susceptibility to radiation damage was determined by irradiating operators' blood in vitro. RESULTS: γ-H2AX and pATM levels increased significantly in operators immediately after branched endovascular aortic repair/fenestrated endovascular aortic repair (P<0.0003 for both). Only pATM levels increased after infrarenal endovascular aortic repair (P<0.04). Expression of both markers fell to baseline in operators after 24 hours (P<0.003 for both). There was no change in γ-H2AX or pATM expression after open repair. Leg protection abrogated γ-H2AX and pATM response after branched endovascular aortic repair/fenestrated endovascular aortic repair. The expression of γ-H2AX varied significantly when operators' blood was exposed to the same radiation dose in vitro (P<0.0001). CONCLUSIONS: This is the first study to detect an acute DNA damage response in operators performing fluoroscopically guided aortic procedures and highlights the protective effect of leg shielding. Defining the relationship between this response and cancer risk may better inform safe levels of chronic low-dose radiation exposure.

Ultrasonic-assisted manufacturing processes: variational model and numerical simulations.

We present a computational study of ultrasonic assisted manufacturing processes including sheet metal forming, upsetting, and wire drawing. A fully variational porous plasticity model is modified to include ultrasonic softening effects and then utilized to account for instantaneous softening when ultrasonic energy is applied during deformation. Material model parameters are identified via inverse modeling, i.e. by using experimental data. The versatility and predictive ability of the model are demonstrated and the effect of ultrasonic intensity on the manufacturing process at hand is investigated and compared qualitatively with experimental results reported in the literature.

A variational constitutive model for soft biological tissues.

In this paper, a fully variational constitutive model of soft biological tissues is formulated in the finite strain regime. The model includes Ogden-type hyperelasticity, finite viscosity, deviatoric and volumetric plasticity, rate and microinertia effects. Variational updates are obtained via time discretization and pre-minimization of a suitable objective function with respect to internal variables. Genetic algorithms are used for model parameter identification due to their suitability for non-convex, high dimensional optimization problems. The material behavior predicted by the model is compared to available tests on swine and human brain tissue. The ability of the model to predict a wide range of experimentally observed behavior, including hysteresis, cyclic softening, rate effects, and plastic deformation is demonstrated.