6 TH INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALS NON-AUTOCLAVE PROCESSING OF SANDWICH STRUCTURES: THE ROLE OF PREPREG THROUGH THICKNESS AIR PERMEABILITY

Abstract No

Vacuum-bag processing of sandwich structures: role of honeycomb pressure level on skin-core adhesion and skin quality

Non-autoclave processing of honeycomb sandwich structures generally leads to poor compaction and high porosity of the skins, along with a decreased skin-core adhesion. The pressure level inside the honeycomb cells plays an important role and is controlled by the permeability to air of the skins. In this work, an initial range of skin permeability to air was explored by perforating the prepregs and adhesive layer selectively. The role of the resulting pressure inside the honeycomb on skin?core adhesion and skin quality was evaluated. Prepreg air permeability was found to control skin-core adhesion through the pressure in the honeycomb and potential outgassing of the adhesive layer. An optimal range of initial pressure inside the honeycomb was found to be 40?70 kPa. A universal process window was proposed to determine the time frame of vacuum application leading to an optimal initial honeycomb pressure level

Non-autoclave processing of sandwich structures: the role of prepreg through thickness air permeability

Non-autoclave processing of honeycomb sandwich structures generally leads to poor compaction and high porosity of the skins along with a decreased skin-core adhesion. Air permeability of the skins, a critical parameter of low pressure processing, is often increased by perforating the prepregs in a patterned way, before curing of the second skin. This procedure, frequently designated as "spiking", provides an air path for the honeycomb cells voiding. Prepreg through thickness air permeability was characterised at room temperature and its evolution monitored during cure. Several spiking configurations were tested and their role on skin-core adhesion and skin quality was evaluated. Prepreg air permeability controls skin-core bonding through the pressure drop in the honeycomb cells and potential outgassing of the adhesive layer. An optimal range of skin permeability was found to be between 5×10-14 cm2 and 3×10-12 cm2, which corresponds to a range of 200-600 mbar of air pressure in the honeycomb

Non-autoclave processing of honeycomb sandwich structures: Skin through thickness air permeability during cure

In non-autoclave processing of sandwich structures, the pressure level inside the honeycomb becomes a critical process parameter, which depends on the permeability to air of the upper skin. In this work, prepreg and adhesive permeabilities were determined separately and in combination through a falling pressure method. We showed that a range of initial skin through thickness air permeability could be achieved by perforating the prepreg plies, the adhesive layer or a combination of both. A corresponding range of achievable pressure was measured inside the honeycomb. The change in the through thickness permeability with time during the cure cycle was determined for each of the studied cases. The adhesive layer was identified as the element that most reduces the initial through thickness air permeability in skin manufacturing

Management of respiratory distress following prehospital implementation of noninvasive ventilation in a physician-staffed emergency medical service: a single-center retrospective study.

Noninvasive ventilation (NIV) is recognized as first line ventilatory support for the management of acute pulmonary edema (APE) and chronic obstructive pulmonary disease (COPD) exacerbations. We aimed to study the prehospital management of patients in acute respiratory distress with an indication for NIV and whether they received it or not. This retrospective study included patients ≥18 years old who were cared for acute respiratory distress in a prehospital setting. Indications for NIV were oxygen saturation (SpO <sub>2</sub> ) <90% and/or respiratory rate (RR) >25/min with a presumptive diagnosis of APE or COPD exacerbation. Study population characteristics, initial and at hospital vital signs, presumptive and definitive diagnosis were analyzed. For patients who received NIV, dyspnea level was evaluated with a dyspnea verbal ordinal scale (D-VOS, 0-10) and arterial blood gas (ABG) values were obtained at hospital arrival. Among the 187 consecutive patients included in the study, most (n = 105, 56%) had experienced APE or COPD exacerbation, and 56 (30%) received NIV. In comparison with patients without NIV, those treated with NIV had a higher initial RR (35 ± 8/min vs 29 ± 10/min, p < 0.0001) and a lower SpO <sub>2</sub> (79 ± 10 vs 88 ± 11, p < 0.0001). The level of dyspnea was significantly reduced for patients treated with NIV (on-scene D-VOS 8.4 ± 1.7 vs 4.4 ± 1.8 at admission, p < 0.0001). Among the 131 patients not treated with NIV, 41 (31%) had an indication. In the latter group, initial SpO <sub>2</sub> was 80 ± 10% in the NIV group versus 86 ± 11% in the non-NIV group (p = 0.0006). NIV was interrupted in 9 (16%) patients due to either discomfort (n = 5), technical problem (n = 2), persistent desaturation (n = 1), or vomiting (n = 1). The results of this study contribute to a better understanding of the prehospital management of patients who present with acute respiratory distress and an indication for NIV. NIV was started on clinically more severe patients, even if predefined criteria to start NIV were present. NIV allows to improve vital signs and D-VOS in those patients. A prospective study could further elucidate why patients with a suspected diagnosis of APE and COPD are not treated with NIV, as well as the clinical impact of the different strategies. The study was approved by our institutional ethical committee ( CER-VD 2020-01363 )

Lessons from COVID-19 syndromic surveillance through emergency department activity: a prospective time series study from western Switzerland.

We aimed to assess if emergency department (ED) syndromic surveillance during the first and second waves of the COVID-19 outbreak could have improved our surveillance system. We did an observational study using aggregated data from the ED of a university hospital and public health authorities in western Switzerland. All patients admitted to the ED were included. The main outcome was intensive care unit (ICU) occupancy. We used time series methods for ED syndromic surveillance (influenza-like syndrome, droplet isolation) and usual indicators from public health authorities (new cases, proportion of positive tests in the population). Based on 37 319 ED visits during the COVID-19 outbreak, 1421 ED visits (3.8%) were positive for SARS-CoV-2. Patients with influenza-like syndrome or droplet isolation in the ED showed a similar correlation to ICU occupancy as confirmed cases in the general population, with a time lag of approximately 13 days (0.73, 95% CI 0.64 to 0.80; 0.79, 95% CI 0.71 to 0.86; and 0.76, 95% CI 0.67 to 0.83, respectively). The proportion of positive tests in the population showed the best correlation with ICU occupancy (0.95, 95% CI 0.85 to 0.96). ED syndromic surveillance is an effective tool to detect and monitor a COVID-19 outbreak and to predict hospital resource needs. It would have allowed to anticipate ICU occupancy by 13 days, including significant aberration detection at the beginning of the second wave