Optimum adhesive thickness in structural adhesives joints using statistical techniques base on Weibull distribution

The geometrical factors defining an adhesive joint are of great importance as its design greatly conditions the performance of the bonding. One of the most relevant geometrical factors is the thickness of the adhesive as it decisively influences the mechanical properties of the bonding and has a clear economic impact on the manufacturing processes or long runs. The traditional mechanical joints (riveting, welding, etc.) are characterised by a predictable performance, and are very reliable in service conditions. Thus, structural adhesive joints will only be selected in industrial applications demanding mechanical requirements and adverse environmental conditions if the suitable reliability (the same or higher than the mechanical joints) is guaranteed. For this purpose, the objective of this paper is to analyse the influence of the adhesive thickness on the mechanical behaviour of the joint and, by means of a statistical analysis based on Weibull distribution, propose the optimum thickness for the adhesive combining the best mechanical performance and high reliability. This procedure, which is applicable without a great deal of difficulty to other joints and adhesives, provides a general use for a more reliable use of adhesive bondings and, therefore, for a better and wider use in the industrial manufacturing processes

Multi-criteria selection of structural adhesives to bond ABS parts obtained by rapid prototyping

One of the most used methods in rapidprototyping is Fused Deposition Modeling (FDM), which provides components with a reasonable strength in plastic materials such as ABS and has a low environmental impact. However, the FDM process exhibits low levels of surface finishing, difficulty in getting complex and/or small geometries and low consistency in “slim” elements of the parts. Furthermore, “cantilever” elements need large material structures to be supported. The solution of these deficiencies requires a comprehensive review of the three-dimensional part design to enhance advantages and performances of FDM and reduce their constraints. As a key feature of this redesign a novel method of construction by assembling parts with structuraladhesive joints is proposed. These adhesive joints should be designed specifically to fit the plastic substrate and the FDM manufacturing technology. To achieve this, the most suitable structuraladhesiveselection is firstly required. Therefore, the present work analyzes five different families of adhesives (cyanoacrylate, polyurethane, epoxy, acrylic and silicone), and, by means of the application of technical multi-criteria decision analysis based on the analytic hierarchy process (AHP), to select the structuraladhesive that better conjugates mechanical benefits and adaptation to the FDM manufacturing proces

Influencia de la modificación de la estructura cristalina superficial de un aluminio en el valor de su energía superficial, al ser atacado con diferentes tratamientos mecano-químicos

En el trabajo se analizaron las modificaciones que diferentes ataques superficiales empleados para modificar la topografía superficial inducían en la estructura cristalina del sustrato y sus consecuencias en las características termodinámicas de la superficie con vistas a la adhesión. Se consideraron cuatro tipos diferentes de ataques superficiales y se analizaron los efectos que habían producido sobre la energía superficial del sustrato de aluminio. Se comprobó mediante XRD la modificación inducida por los distintos tratamientos en la estructura cristalina del aluminio utilizado como sustrato

Characterization of the chemical structure of vinyl ester resin in a climate chamber under different conditions of degradation

Due to the good strength and similar toughness of epoxy resins, vinyl ester resins are widely used as thermoset adhesives in structural adhesive joints and as composites for different industrial applications. However, vinyl ester adhesives are difficult to cure completely under environmental conditions, even after long periods of time because of gel formation slows the necessary diffusion of the catalyst across the polymer network. Several studies have used weathering chambers to investigate the degradation mechanisms of vinyl ester adhesives. However, a review of the scientific literature revealed both a wide variety of aging processes and several ambiguities between the recorded experimental results. In this work, post-cured vinyl ester resins at different aging cycles were aged under high temperature and relative humidity, and the changes in their structure, mechanical and adhesion properties were studied. Chemical and structural changes were observed in the vinyl ester resins after aging in a climatic chamber

Degradation in seawater of structural adhesives for hybrid fibre-metal laminated materials

The adhesives used for applications in marine environments are subject to particular chemical conditions, which are mainly characterised by an elevated chlorine ion content and intermittent wetting/drying cycles, among others.These conditions can limit the use of adhesives due to the degradation processes that they experience. In this work, the chemical degradation of two different polymers, polyurethane and vinylester, was studied in natural seawater under immersion for different periods of time.The diffusion coefficients and concentration profiles of water throughout the thickness of the adhesiveswere obtained.Microstructural changes in the polymer due to the action of water were observed by SEM, and the chemical degradation of the polymer was monitored with the Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The degradation of the mechanical properties of the adhesive was determined by creep tests withMixed Cantilever Beam (MCB) specimens at different temperatures. After 180 days of immersion of the specimens, it was concluded that the J-integral value (depending on the strain) implies a loss of stiffness of 51% and a decrease in the failure load of 59% for the adhesive tested

Influencia de las características superficiales de un sustrato en la resistencia de una unión adhesiva

Uno de los objetivos que se plantean cuando se realiza una unión adhesiva es que su resistencia sea lo más elevada posible para los esfuerzos a los que va a estar solicitada. Además de las propias características del adhesivo empleado, está la resistencia que se genera en la interfase. En trabajos anteriores se ha caracterizado la topografía de la superficie del sustrato. En este trabajo se han realizado ensayos de resistencia de la unión adhesiva sometida a ensayos de tracción pura, buscando la relación con las características de las superficies tratadas con diferentes tratamientos mecánicos y químicos. Se ha comprobado que el valor de la rugosidad influye en la resistencia, pero condicionado por el tratamiento aplicado

Efecto de la inoculación Rhizophagus irregularis y de la fertilización fosfatada sobre la comunidad local de hongos formadores de micorrizas arbusculares

Arbuscular Mycorrhizal Fungi (AMF) are important microorganisms in agricultural soils because of their positive effect on plant acquisition of phosphorus (P); of one of the fundamental nutrients for plants. Available P in the soils of the Colombian Orinoquía are low, so phosphate fertilization is necessary in crops such as cassava. The objective of this work was to study the effect of phosphate fertilization and inoculation with Rhizophagus irregularis (the model AMF species), on the resident AMF communities. The AMF diversity was described by morphological and molecular techniques from the spores present in the rhizosphere of cassava plants maintained under traditional agronomic conditions. The richness and diversity of the AMF communities were affected by the experim’ental treatments AMF inoculation and P fertilization. Changes in abundance were detected in the genera Glomus and Acaulospora. This was significantly influenced by inoculation and phosphate fertilization. The findings of this study suggest that the use of phosphate fertilizer and the application of R. irregularis in agricultural processes affect the biodiversity of native AMF communities in soils of the Colombian Orinoquía. Further research is required to understand the relationship between AMF community composition and host plant response.Los Hongos Formadores de Micorrizas Arbusculares (HFMA) son microorganismos cruciales en los suelos agrícolas por el efecto positivo que tienen sobre la movilización de uno de los nutrientes fundamentales para las plantas como es el fósforo (P). Los contenidos disponibles de P en los suelos de la Orinoquía Colombiana son bajos, por lo que la fertilización con fosfato es indispensable en cultivos comerciales como la yuca. El objetivo de este trabajo fue estudiar el efecto de la fertilización fosfatada y de la inoculación con Rhizophagus irregularis (hongo modelo de los HFMA), sobre las comunidades residentes de este grupo de hongos. La diversidad de los HFMA fue descrita a partir de las esporas presentes en la rizósfera de plantas de yuca mantenidas bajo condiciones agronómicas tradicionales. La riqueza y diversidad de las comunidades de HFMA se afectaron por la interacción de los factores analizados. En términos de estructura de la comunidad de HFMA en la rizósfera de las plantas de yuca, se detectaron cambios en la abundancia de los géneros Glomus y Acaulospora; asociados respectivamente a la inoculación y a la fertilización fosfatada. Los hallazgos de este estudio sugieren que prácticas agrícolas como la aplicación de fertilizante fosfatado y la inoculación con R. irregularis, son procesos que pueden afectar el ensamblaje de la comunidad de estos hongos, así también la diversidad de las comunidades de HFMA nativas en suelos de la Orinoquía Colombiana. Se requieren investigaciones adicionales para entender la relación entre la composición de las comunidades de HFMA y la respuesta de la planta hospedera

Effect of adding different amounts of graphite nanoplatelets on structural, thermal, mechanical and viscoelastic properties of vinylester based composites cured at 25°C

Different amounts (0.1–5wt%) of graphite nanoplatelets (GNs) were added to vinylester (VE) for improving the properties of the composites cured at 25°C. The addition of 0.1wt% GN only increased the Tg and the thermal stability of the composite cured at 25°C. Furthermore, the addition of GN increased both the tensile strength and elongation‐at‐break of the composites cured at 25°C, but the effect of adding GN was less important when cured at 100°C. The improved properties of the composites were ascribed to the interactions between the oxygen species on the GN edges and the C==O and OH groups in the VE monomer, and to the higher fraction of the partially crosslinked polymer within the matrix

Association of APOA5 and APOC3 genetic polymorphisms with severity of hypertriglyceridemia in patients with cutaneous T-Cell lymphoma treated with bexarotene

Importance: hypertriglyceridemia is the most frequent and limiting adverse effect of bexarotene therapy in cutaneous T-cell lymphoma (CTCL). Despite standard prophylactic measures, there is a wide variability in the severity of this complication, which could be associated with both genetic and environmental factors. Objectives: to analyze the association between genetic polymorphisms of apolipoprotein genes APOA5, APOC3, and APOE and the severity of hypertriglyceridemia during bexarotene therapy and to optimize patient selection for bexarotene therapy based on adverse effect profile. Design, Setting, and Participants: this case series study was conducted in 12 university referral hospitals in Spain from September 17, 2014, to February 6, 2015. One hundred twenty-five patients with a confirmed diagnosis of CTCL who had received bexarotene therapy for at least 3 months were enrolled. Nine patients were excluded owing to missing analytic triglyceride level data, leaving a study group of 116 patients. Data on demographic and cardiovascular risk factor were collected, and a complete blood analysis, including lipid profile and genetic analysis from a saliva sample, was performed. Main Outcomes and Measures: primary outcomes were the maximal triglyceride levels reported in association with the minor alleles of the polymorphisms studied. Results: among 116 patients, the mean (SD) age was 61.2 (14.7) years, 69 (59.5%) were men, and 85 (73.2%) had mycosis fungoides, the most prevalent form of CTCL. During bexarotene therapy, 96 patients (82.7%) experienced hypertriglyceridemia, which was severe or extreme in 8 of these patients (8.3%). Patients who carried minor alleles of the polymorphisms did not show significant differences in baseline triglyceride concentrations. After bexarotene treatment, carriers of at least 1 of the 2 minor alleles of APOA5 c.-1131T>C and APOC3 c.*40C>G showed lower levels of triglycerides than noncarriers (mean [SD], 241.59 [169.91] vs 330.97 [169.03] mg/dL, respectively; P = .02). Conclusions and Relevance: these results indicate that the screening of APOA5 and APOC3 genotypes may be useful to estimate changes in triglyceride concentrations during bexarotene treatment in patients with CTCL and also to identify the best candidates for bexarotene therapy based on the expected adverse effect profile

Caregiver-reported delay in presentation to pediatric emergency departments for fear of contracting COVID-19: a multi-national cross-sectional study

Objective: To determine if caregivers of children presenting to pediatric emergency departments (EDs) during the COVID-19 pandemic are delaying presenting to care for fear of contracting COVID-19. Methods: This was a pre-planned secondary analysis of a cross-sectional survey study of caregivers accompanying their children aged 0-19 years to 16 pediatric EDs in 5 countries from May to June 2020. An anonymous online survey, completed by caregivers via RedCAP, included caregiver and child demographics, presenting complaints, if they delayed presentation and whether symptoms worsened during this interval, as well as caregiver concern about the child or caregiver having COVID-19 at the time of ED visit. Results: Of 1543 caregivers completing the survey, 287 (18.6%) reported a delay in seeking ED care due to concerns of contracting COVID-19 in the hospital. Of those, 124 (43.2%) stated their child's symptoms worsened during the waiting interval. Caregiver relationship to child [mother] (OR 1.85, 95% CI 1.27-2.76), presence of chronic illness in child (OR 1.78. 95% CI 1.14-2.79), younger age of caregiver (OR 0.965, 95% CI 0.943-0.986), and caregiver concerns about lost work during the pandemic (OR 1.08, 95% CI 1.04-1.12) were independently associated with a COVID-19-related delayed presentation in multivariable regression analysis. Conclusions: Almost one in five caregivers reported delaying ED presentation for their ill or injured child specifically due to fear of contracting COVID-19 while in hospital, with mothers, younger caregivers, caregivers of children with chronic illness, and those concerned about lost work more likely to report delaying ED presentation. Keywords: COVID-19; Caregivers; Children; Emergency department; Presentation dela