Effect of Loading History on Stress Corrosion Cracking of 7075-T651 Aluminum Alloy in Saline Aqueous Environment

An experimental study of stress corrosion cracking (SCC) was conducted on 7075-T651 aluminum alloy in a chromate-inhibited, acidic 3.5 pct sodium chloride aqueous solution using compact tension specimens with a thickness of 3.8 mm under permanent immersion conditions. The effects of loading magnitude, overload, underload, and two-step high-low sequence loading on incubation time and crack growth behavior were investigated. The results show that the SCC process consists of three stages: incubation, transient crack growth, and stable crack growth. The incubation time is highly dependent on the load level. Tensile overload or compressive underload applied prior to SCC significantly altered the initiation time of corrosion cracking. Transition from a high to a low loading magnitude resulted in a second incubation but much shorter or disappearing transient stage. The stable crack growth rate is independent of stress intensity factor in the range of 10 to 22 MPa ?{textm} . sqrt {text{m}} .     

Strain mapping of a triple junction in nanocrystalline Pd

Aberration-corrected transmission electron microscopy was used to provide structural information on a triple junction in nanocrystalline Pd. This triple junction consists of two intersecting Σ3 twin boundaries with a Σ9 grain boundary and is connected to a quadruple point via the Σ9 grain boundary. A comprehensive strain analysis of this triple junction using geometric phase analysis is presented and compared with a molecular dynamics simulation. The main results are: (i) the strain field of the core of the triple junction shows dislocation character and extends over a distance of about 0.5 nm; (ii) the intersecting boundaries result in a net translation of , which corresponds to a Burgers vector of an dislocation in the fcc lattice; (iii) a disclination emerging from the triple junction along the Σ9 grain boundary is balanced by a disclination of opposite sign emerging from the quadruple point. Based on the observation that the core of the triple junction can be described by the strain field of a dislocation, its energy was estimated using to be about 1.7 × 10⁻⁹ J m⁻¹. The presence of a disclination dipole is thought to be essential for stabilization of the structure observed.     

Protein Expression of Angiotensin-Converting Enzyme 2 (ACE2) is Upregulated in Brains with Alzheimer’s Disease

Alzheimer’s disease is a chronic neurodegenerative disorder and represents the main cause of dementia globally. Currently, the world is suffering from the coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a virus that uses angiotensin-converting enzyme 2 (ACE2) as a receptor to enter the host cells. In COVID-19, neurological manifestations have been reported to occur. The present study demonstrates that the protein expression level of ACE2 is upregulated in the brain of patients with Alzheimer’s disease. The increased ACE2 expression is not age-dependent, suggesting the direct relationship between Alzheimer’s disease and ACE2 expression. Oxidative stress has been implicated in the pathogenesis of Alzheimer’s disease, and brains with the disease examined in this study also exhibited higher carbonylated proteins, as well as an increased thiol oxidation state of peroxiredoxin 6 (Prx6). A moderate positive correlation was found between the increased ACE2 protein expression and oxidative stress in brains with Alzheimer’s disease. In summary, the present study reveals the relationships between Alzheimer’s disease and ACE2, the receptor for SARS-CoV-2. These results suggest the importance of carefully monitoring patients with both Alzheimer’s disease and COVID-19 in order to identify higher viral loads in the brain and long-term adverse neurological consequences.     

Single-crystal growth of the complex metallic alloy phase β-Al–Mg

The development of a single-crystal growth route for the complex metallic alloy phase β-Al₃Mg₂ is presented. After initial probing of the phase diagram in the vicinity of the existence range of the β-phase, we performed single-crystal growth experiments employing various techniques. The Czochralski and self-flux growth turned out to be the most suitable for this phase, and with both we reproducibly achieved single crystals of several cubic centimeters in volume. While the Czochralski technique allows for the production of deliberately oriented single crystals, the self-flux technique is capable of producing very large but unoriented single grains.     

Prioritizing test cases with string distances

Test case prioritisation aims at finding an ordering which enhances a certain property of an ordered test suite. Traditional techniques rely on the availability of code or a specification of the program under test. We propose to use string distances on the text of test cases for their comparison and elaborate a prioritisation algorithm. Such a prioritisation does not require code or a specification and can be useful for initial testing and in cases when code is difficult to instrument. In this paper, we also report on experiments performed on the “Siemens Test Suite”, where the proposed prioritisation technique was compared with random permutations and four classical string distance metrics were evaluated. The obtained results, confirmed by a statistical analysis, indicate that prioritisation based on string distances is more efficient in finding defects than random ordering of the test suite: the test suites prioritized using string distances are more efficient in detecting the strongest mutants, and, on average, have a better APFD than randomly ordered test suites. The results suggest that string distances can be used for prioritisation purposes, and Manhattan distance could be the best choice.     

Hydrogen embrittlement associated with strain localization in a precipitation-hardened Fe–Mn–Al–C light weight austenitic steel

Hydrogen embrittlement of a precipitation-hardened Fe–26Mn–11Al-1.2C (wt.%) austenitic steel was examined by tensile testing under hydrogen charging and thermal desorption analysis. While the high strength of the alloy (>1 GPa) was not affected, hydrogen charging reduced the engineering tensile elongation from 44 to only 5%. Hydrogen-assisted cracking mechanisms were studied via the joint use of electron backscatter diffraction analysis and orientation-optimized electron channeling contrast imaging. The observed embrittlement was mainly due to two mechanisms, namely, grain boundary triple junction cracking and slip-localization-induced intergranular cracking along micro-voids formed on grain boundaries. Grain boundary triple junction cracking occurs preferentially, while the microscopically ductile slip-localization-induced intergranular cracking assists crack growth during plastic deformation resulting in macroscopic brittle fracture appearance.     

Contact Behavior of Microcrystalline Cellulose Pellets Depending on their Water Content

Microcrystalline cellulose pellets for oral drug delivery are often produced by a combined wet extrusion-spheronization process. During the entire process, the cylindrical as well as the spherical pellets are exposed to various stresses resulting in a change of their shape and size due to plastic deformation and breakage. In this work, the effect of moisture content of pellets on their mechanical behavior is studied. In static compression tests, the strong influence of water content on deformation behavior of pellets is confirmed. Moreover, impact tests are performed using a setup consisting of three high-speed cameras to record pellet-wall collisions. Material properties, such as stiffness, restitution coefficient, breakage force, and displacement, were analyzed depending on the water content.     

Thermal Properties of Copy Paper Sheets

The thermal conductivity and specific heat of paper are important in determining its response to heat pulses encountered in applications such as copying or digital printing. This work reports measurements of the thermal conductivity, contact resistance, and specific heat for a number of commercial copy paper sheets. The experimental setup was designed to measure transient and steady-state temperature distribution in stacks of paper sheets from which the thermal properties were determined. Steady-state measurements of the temperature difference were used to determine the thermal contact resistance and the thermal conductivity of the sheets. The specific heat was determined from the transient temperatures recorded during heat-up and cool-down periods. The thermal conductivity depends upon the sheet density, filler content, and nature of the fibers. It also showed a small increase with temperature of approximately 10^?4 W/(mK)/K. Models of thermal conductivity based on the resistance of the fibers and the fillers were developed. The thermal contact resistance increased with the surface roughness as measured by the Gurley permeability (referring to surface roughness). The specific heat of paper was dependent on its ash content.