Fully Dynamic Numerical Simulation of the Hammer Peening Fatigue Life Improvement Technique

AbstractThis paper presents the results of the development process for a Finite Element Analysis of the Hammer Peening Fatigue Life Improvement Technique. The Fatigue Life of welded structures is still in need for improvement. The sheer number of Fatigue Live Improvement Techniques parameters leads to the need of simulating and predicting their results. For this study, two different materials were used, an Austenitic Stainless Steel and a Duplex Stainless Steel. Non-load carrying cruciform weld joints were produced and fatigue tested, with and without the Hammer Peening treatment. Finally a FEA code (ABAQUS®) was used to simulate the Hammer Peening technique. A fully dynamic model was used, combined with the Chaboche Kinematic-hardening material model and different Hammering parameter experimentally determined. Alongside the residual stresses introduced by the Hammer Peening Technique, the predicted Fatigue Life using the FEA model were compared with the experimental results, showing a very good agreement between them. Also the effect of several parameters, like the hammering impact load, the hammer positioning or the number of hammering passages, were analysed as a way to validate the FEA model. The most important result was of course the Fatigue Strength Gain factor, for the Hammer Peening Technique, that in both cases was found to be superior to 1.3

Cardiovascular Clinical Trials in a Pandemic: Immediate Implications of Coronavirus Disease 2019

The coronavirus disease 2019 (COVID-19) pandemic started in Wuhan, Hubei Province, China, in December 2019, and by 24 April 2020, it had affected >2.73 million people in 185 countries and caused >192,000 deaths. Despite diverse societal measures to reduce transmission of the severe acute respiratory syndrome coronavirus 2, such as implementing social distancing, quarantine, curfews and total lockdowns, its control remains challenging. Healthcare practitioners are at the frontline of defence against the virus, with increasing institutional and governmental supports. Nevertheless, new or ongoing clinical trials, not related to the disease itself, remain important for the development of new therapies, and require interactions among patients, clinicians and research personnel, which is challenging, given isolation measures. In this article, the authors summarise the acute effects and consequences of the COVID-19 pandemic on current cardiovascular trials

Cardiovascular Clinical Trials in a Pandemic: Immediate Implications of Coronavirus Disease 2019

The coronavirus disease 2019 (COVID-19) pandemic started in Wuhan, Hubei Province, China, in December 2019, and by 24 April 2020, it had affected >2.73 million people in 185 countries and caused >192,000 deaths. Despite diverse societal measures to reduce transmission of the severe acute respiratory syndrome coronavirus 2, such as implementing social distancing, quarantine, curfews and total lockdowns, its control remains challenging. Healthcare practitioners are at the frontline of defence against the virus, with increasing institutional and governmental supports. Nevertheless, new or ongoing clinical trials, not related to the disease itself, remain important for the development of new therapies, and require interactions among patients, clinicians and research personnel, which is challenging, given isolation measures. In this article, the authors summarise the acute effects and consequences of the COVID-19 pandemic on current cardiovascular trials

Elevated levels of tumor necrosis factor-alpha and TNFR1 in recurrent herniated lumbar discs correlate with chronicity of postoperative sciatic pain

BACKGROUND CONTEXT: Sciatica is a condition characterized by radicular pain that can be secondary to a lumbar disc herniation (LDH). More than 10% of patients report persistent pain after surgery. The underlying mechanisms of postoperative sciatica remain unclear. There is evidence demonstrating that inflammation plays a role in the pathophysiology of sciatica. PURPOSE: The study aimed to assess if the expression of tumor necrosis factor (TNF)-alpha and its receptors (TNFR) was correlated with the severity of pre- and postoperative leg pain in LDH patients who underwent single or multiple decompressive discectomies. SETTING: This is an experimental prospective human study of intraoperative intervertebral disc (IVD) samples, as well as a clinical scores evaluation. METHODS: We analyzed the mRNA and protein levels of TNF-alpha, TNFR1, and TNFR2 in IVD biopsies, and correlated them with visual analogue scale (VAS) scores 1 day before surgery to 6 weeks and 6 months postoperatively. RESULTS: We evaluated the correlation between the inflammation in IVD with pre- and postoperative pain scores after discectomy in LDH patients operated for the first time (fLDH, N=12) and for recurrent cases (rLDH, N=8). This analysis showed that TNF-alpha and TNFR1 mRNA levels were significantly greater in rLDH patients; there was a twofold increase for TNF-alpha and a 50% increase for TNFR1. Similarly, protein levels in IVD samples positively correlated with postoperative VAS scores, whereas TNFR2 protein levels negatively correlated with postoperative VAS scores. CONCLUSIONS: These findings indicate that rLDH patients present higher postoperative VAS scores compared with fLDH patients, and also that these scores are correlated with increased inflammation and may contribute to pain chronicity. (C) 2015 Elsevier Inc. All rights reserved

The cerebrovascular response to lower-body negative pressure vs. head-up tilt

Lower-body negative pressure (LBNP) has been proposed as a MRI-compatible surrogate for orthostatic stress. Although the effects of LBNP on cerebral hemodynamic behavior have been considered to reflect those of orthostatic stress, a direct comparison with actual orthostasis is lacking. We assessed the effects of LBNP (-50 mmHg) vs. head-up tilt (HUT; at 70°) in 10 healthy subjects (5 female) on transcranial Doppler-determined cerebral blood flow velocity (CBFv) in the middle cerebral artery and cerebral perfusion pressure (CPP) as estimated from the blood pressure signal (finger plethysmography). CPP was maintained during LBNP but decreased after 2 min in response to HUT, leading to an ~15% difference in CPP between LBNP and HUT (P ≤ 0.020). Mean CBFv initially decreased similarly in response to LBNP and for HUT, but, from minute 3 on, the decline became ~50% smaller (P ≤ 0.029) during LBNP. The reduction in end-tidal Pco2 partial pressure (PetCO2 ) was comparable but with an earlier return toward baseline values in response to LBNP but not during HUT (P = 0.008). We consider the larger decrease in CBFv during HUT vs. LBNP attributable to the pronounced reduction in PetCO2 and to gravitational influences on CPP, and this should be taken into account when applying LBNP as an MRI-compatible orthostatic stress modality.NEW & NOTEWORTHY Lower-body negative pressure (LBNP) has the potential to serve as a MRI-compatible surrogate of orthostatic stress but a comparison with actual orthostasis was lacking. This study showed that the pronounced reduction in end-tidal Pco2 together with gravitational effects on the brain circulation lead to a larger decline in cerebral blood flow velocity in response to head-up tilt than during lower-body negative pressure. This should be taken into account when employing lower-body negative pressure as MRI-compatible alternative to orthostatic stres

Assessment of middle cerebral artery diameter during hypocapnia and hypercapnia in humans using ultra-high-field MRI

In the evaluation of cerebrovascular CO2 reactivity measurements, it is often assumed that the diameter of the large intracranial arteries insonated by transcranial Doppler remains unaffected by changes in arterial CO2 partial pressure. However, the strong cerebral vasodilatory capacity of CO2 challenges this assumption, suggesting that there should be some changes in diameter, even if very small. Data from previous studies on effects of CO2 on cerebral artery diameter [middle cerebral artery (MCA)] have been inconsistent. In this study, we examined 10 healthy subjects (5 women, 5 men, age 21-30 yr). High-resolution (0.2 mm in-plane) MRI scans at 7 Tesla were used for direct observation of the MCA diameter during hypocapnia, -1 kPa (-7.5 mmHg), normocapnia, 0 kPa (0 mmHg), and two levels of hypercapnia, +1 and +2 kPa (7.5 and 15 mmHg), with respect to baseline. The vessel lumen was manually delineated by two independent observers. The results showed that the MCA diameter increased by 6.8 ± 2.9% in response to 2 kPa end-tidal P(CO2) (PET(CO2)) above baseline. However, no significant changes in diameter were observed at the -1 kPa (-1.2 ± 2.4%), and +1 kPa (+1.4 ± 3.2%) levels relative to normocapnia. The nonlinear response of the MCA diameter to CO2 was fitted as a continuous calibration curve. Cerebral blood flow changes measured by transcranial Doppler could be corrected by this calibration curve using concomitant PET(CO2) measurements. In conclusion, the MCA diameter remains constant during small deviations of the PET(CO2) from normocapnia, but increases at higher PET(CO2) value