Mode I crack tip fields: strain gradient plasticity theory versus J2 flow theory

The mode I crack tip asymptotic response of a solid characterised by strain gradient plasticity is investigated. It is found that elastic strains dominate plastic strains near the crack tip, and thus the Cauchy stress and the strain state are given asymptotically by the elastic K-field. This crack tip elastic zone is embedded within an annular elasto-plastic zone. This feature is predicted by both a crack tip asymptotic analysis and a finite element computation. When small scale yielding applies, three distinct regimes exist: an outer elastic K field, an intermediate elasto-plastic field, and an inner elastic K field. The inner elastic core significantly influences the crack opening profile. Crack tip plasticity is suppressed when the material length scale ℓ of the gradient theory is on the order of the plastic zone size estimation, as dictated by the remote stress intensity factor. A generalized J-integral for strain gradient plasticity is stated and used to characterise the asymptotic response ahead of a short crack. Finite element analysis of a cracked three point bend specimen reveals that the crack tip elastic zone persists in the presence of bulk plasticity and an outer J-field

Pre-notched dog bone small punch specimens for the estimation of fracture properties

In recent years, the pre-notched or pre-cracked small punch test (P-SPT) has been successfully used to estimate the fracture properties of metallic materials for cases in which there is not sufficient material to identify these properties from standard tests, such as CT or SENB specimens. The P-SPT basically consists of deforming a pre-notched miniature specimen, whose edges are firmly gripped by a die, using a high strength punch. The novelty of this paper lies in the estimation of fracture properties using dog-bone-shaped specimens with different confinement levels. With these specimens, three confinement variations have been studied. The results obtained enable the establishment of a variation of fracture properties depending on the level of confinement of each miniature specimen and selection of the most appropriate confinement for this goal

COVID-19 and its effects on the driving style of spanish drivers

Spain is one of the countries most affected by COVID-19. Until May 5, 2021 there have been 3.54 million people infected and 78,399 deaths according to the Johns Hopkins Institute. This has meant that Spain is one of the countries in the world where the most restrictive measures have been adopted and which have had a strong impact on the economic, social, and mental health of citizens. One of the consequences of this pandemic is a severe increase in the strain on the healthcare system. Many of those infected had to be admitted to hospitals and even to Intensive Care Units (ICU). In this scenario, it is essential to reduce traffic accidents in order to avoid overcrowded hospitals. However, the Spanish General Directorate of Traffic highlights in several traffic reports that despite the decrease in the volume and distance of trips, the number of traffic accidents has not altered significantly and even during some periods has been higher than before the pandemic. The aim of this work is to establish if there has been a change in the driving style of drivers during the pandemic and to identify the group of people adopting a more inefficient and unsafe driving style. To this end, a study was carried out with 30 volunteers and their current driving style was compared with their driving style before the pandemic. The results show that drivers have adopted a more aggressive driving style than before the pandemic, especially women and those who have suffered anxiety due to COVID-19.5311-8814-F0ED | Sara Maria da Cruz Maia de Oliveira PaivaN/

Computational assessment of biomass dust explosions in the 20L sphere

Determination of the explosion severity parameters of biomass is crucial for the safety management and dust explosion risk assessment of biomass-processing industries. These are commonly determined following experimental tests in the 20L sphere according to the international standards. Recently, CFD simulations have emerged as a reliable alternative to predict the explosion behavior with good accuracy and reduced labor and capital. In this work, numerical simulations of biomass dust explosions are conducted with the open-source CFD code OpenFOAM. The multi-phase (gas-solid) flow is treated in an Eulerian-Lagrangian framework, using a two-way coupling regime and considering the reactions of biomass conversion (moisture evaporation, devolatilization, and char oxidation), the combustion of volatile gases, and convective and radiative heat transfer. The model is validated with pressure-time and concentration-dependent experimental measurements of two biomass samples. Results suggest that the characteristics of the cold-flow (ı.e., turbulence levels, actual dust concentration, spatial distribution of the dust cloud, and turbophoresis effect) govern the course of the explosion process, and depend strongly on particle size, dust concentration, and ignition delay time effects. These findings may be relevant in the design of better dust explosion testing devices and to the reexamination of the guidelines for the operation of the experiment. Finally, a thorough discussion on the explosion pressures, degree of biomass conversion, flame temperature, flame propagation patterns, and the dust agglomeration effect is presented

Pre-notched dog bone small punch specimens for the estimation of fracture properties

In recent years, the pre-notched or pre-cracked small punch test (P-SPT) has been successfully used to estimate the fracture properties of metallic materials for cases in which there is not sufficient material to identify these properties from standard tests, such as CT or SENB specimens. The P-SPT basically consists of deforming a pre-notched miniature specimen, whose edges are firmly gripped by a die, using a high strength punch. The novelty of this paper lies in the estimation of fracture properties using dog-bone-shaped specimens with different confinement levels. With these specimens, three confinement variations have been studied. The results obtained enable the establishment of a variation of fracture properties depending on the level of confinement of each miniature specimen and selection of the most appropriate confinement for this goal

Peptide Ligands Incorporated into the Threefold Spike Capsid Domain to Re-Direct Gene Transduction of AAV8 and AAV9 In Vivo

Efficiency and specificity of viral vectors are vital issues in gene therapy. Insertion of peptide ligands into the adeno-associated viral (AAV) capsid at receptor binding sites can re-target AAV2-derived vectors to alternative cell types. Also, the use of serotypes AAV8 and -9 is more efficient than AAV2 for gene transfer to certain tissues in vivo. Consequently, re-targeting of these serotypes by ligand insertion could be a promising approach but has not been explored so far. Here, we generated AAV8 and -9 vectors displaying peptides in the threefold spike capsid domain. These peptides had been selected from peptide libraries displayed on capsids of AAV serotype 2 to optimize systemic gene delivery to murine lung tissue and to breast cancer tissue in PymT transgenic mice (PymT). Such peptide insertions at position 590 of the AAV8 capsid and position 589 of the AAV9 capsid changed the transduction properties of both serotypes. However, both peptides inserted in AAV8 did not result in the same changes of tissue tropism as they did in AAV2. While the AAV2 peptides selected on murine lung tissue did not alter tropism of serotypes 8 and -9, insertion of the AAV2-derived peptide selected on breast cancer tissue augmented tumor gene delivery in both serotypes. Further, this peptide mediated a strong but unspecific in vivo gene transfer for AAV8 and abrogated transduction of various control tissues for AAV9. Our findings indicate that peptide insertion into defined sites of AAV8 and -9 capsids can change and improve their efficiency and specificity compared to their wild type variants and to AAV2, making these insertion sites attractive for the generation of novel targeted vectors in these serotypes

Experimental and Computational Studies of the Kinetics of the Reaction of Atomic Hydrogen with Methanethiol

Article on experimental and computational studies of the kinetics of the reaction of atomic hydrogen with methanethiol

Optimal application of fluid viscous dampers in tall buildings incorporating integrated damping systems

This paper examines the detailed performance of an Integrated-Damping-System (IDS) approach which was recently introduced to provide large damping levels by enabling two parts of a building to move independently through a parallel arrangement of springs and fluid viscous dampers. Extensive assessments into the characteristics and distribution of constituent dampers are illustrated through the dynamic response of a typical 300m central-core building. Besides examining the system performance under typical wind conditions and selected seismic excitations, five damper placement methods are assessed for various linear and nonlinear damper exponents. It is shown that intermediate exponents provide the best overall response. However, when the design targets a particular damping, deformation or acceleration related performance parameter, specific combinations of damper exponent and distribution can result in an optimal application. Most importantly, due to the underlying IDS nature, which acts as an inherent large-mass damper, the findings show that the overall performance is not highly sensitive to the damper placement and does not necessitate the use of an advanced distribution. Whilst specific placements can be adopted to refine targeted performance aspects where necessary, simple and practical uniform or stiffness proportional arrangements can be consistently employed with the IDS to provide a highly effective solution