Effect Of Loading Strain Rates On Unloading Behavior Of Shot Peened Materials

Shot peening is a process widely used in industry to improve the fatigue life of materials through induced compressive residual stresses that retard crack initiation and growth. In the peening process, there are two stages: 1) loading: shot penetrating into target; and 2) unloading: shot rebounding from the target. The strain rates in the loading process are known to be in 105-106 1/s range, having heavy impact on the materials’ properties. However, the effect of the loading strain rates on the rebounding stage is not well studied. This paper aims to determine the effects of the loading strain rates on the unloading behavior of a material using FEM method. First, to better understand the material behavior, this study evaluates the loading-unloading responses of one element at high strain rates in different scenarios. Then, it obtains the strain rates during the loading and unloading for the different elements of a material being impinged by one shot. The results show that the unloading behavior of a material depends only on the loading equivalent plastic strain and the strain rate of the unloading step

Cohesive zone modeling of ductile tearing process in brazed joints

The final publication is available at Elsevier via http://dx.doi.org/10.1016/j.engfracmech.2012.11.018 © 2013. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/Ductile tearing process in low carbon steel brazed joints with copper filler metal is studied using the Cohesive Zone Model. The Cohesive Zone Model is characterized by two parameters related to the cohesive strength and cohesive energy. A new method is developed to estimate the Cohesive Zone Model parameters through direct experimental measurements and numerical modeling. The cohesive energy of the brazed joints is obtained from the fracture test results performed on the single-edge notched bend specimens. Based on the obtained cohesive energy parameter, the fracture test is simulated using a cohesive zone finite element model. A unique value for the joint cohesive strength is determined by best fitting the finite element results to the experimental load-crack mouth opening displacement curves. The merit of the characterized Cohesive Zone Model is explored by finite element modeling of the tensile test performed on the single-edge notched tension specimens. The load-crack mouth opening displacement curve obtained from the finite element modeling conforms to the corresponding tensile test results. Furthermore, the effect of the crack tip stress constraint on the plastic zone shape and size is successfully captured by the model. The good agreement between the finite element simulation results and the experimental data demonstrates the applicability of the Cohesive Zone Model for fracture analysis of the brazed joints.Natural Sciences and Engineering Research Council of Canada, NSER

Cohesive zone modeling of fatigue crack growth in brazed joints

The final publication is available at Elsevier via http://dx.doi.org/10.1016/j.engfracmech.2014.03.014 © 2014. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/Fatigue crack growth in low carbon steel brazed joints with copper filler metal is modeled by an irreversible Cohesive Zone Model. Strain-controlled fatigue tests are performed on the brazed specimens, and the corresponding fatigue crack initiation and propagation lives are recorded. A cyclic damage evolution law is coupled to a bilinear Cohesive Zone Model to irreversibly account for the joint stiffness degradation over the number of cycles. The damage law parameters are calibrated based on Irwin's analytical solution and the experimental fatigue crack growth data. Using the characterized irreversible Cohesive Zone Model, the fatigue crack growth is simulated and the corresponding fatigue crack growth rates are obtained. The agreement between the numerical results and the experimental data shows the applicability of the Cohesive Zone Model to fatigue crack growth analysis and life estimation of brazed joints.Natural Sciences and Engineering Research Council of Canada, NSERC Strategic Grant Progra

The antioxidant and Flavonoids contents of Althaea officinalis L. flowers based on their color

Objective: There has been a growing interest in finding plants with biological active ingredients for medicinal application. Materials and Methods: Three colors of petals of Althaea officinalis (A. officinalis) flowers, i.e., pink, reddish pink, and white were examined for total antioxidant activity and flavonoids content. Results: The reddish pink flowers of A. officinalis have more antioxidant activity and the power of antioxidant activity was reddish pink > pink > white. Conclusion: Findings suggest that the dark color can serve as an indicator of antioxidant content of the plant. Flavonoid content was highest in white flower thus this result indicated that flowers with light color can be considered for medicinal uses

Polyester Sulphonic Acid Interstitial Nanocomposite Platform for Peroxide Biosensor

A novel enzyme immobilization platform was prepared on a platinum disk working electrode by polymerizing aniline inside the interstitial pores of polyester sulphonic acid sodium salt (PESA). Scanning electron microscopy study showed the formation of homogeneous sulphonated polyaniline (PANI) nanotubes (∼90 nm) and thermogravimetric analysis (TGA) confirmed that the nanotubes were stable up to 230 °C. The PANI:PESA nanocomposite showed a quasi-reversible redox behaviour in phosphate buffer saline. Horseradish peroxidase (HRP) was immobilized on to this modified electrode for hydrogen peroxide detection. The biosensor gave a sensitivity of 1.33 μA (μM)-1 and a detection limit of 0.185 μM for H2O2. Stability experiments showed that the biosensor retained more than 64% of its initial sensitivity over four days of storage at 4 °C

Prediabetes management in the Middle East, Africa and Russia: Current status and call for action:

Most data on the burden of diabetes and prediabetes are from countries where local infrastructure can support reliable estimates of the burden of non-communicable diseases. Countries in the Middle ..

Vision, challenges and opportunities for a Plant Cell Atlas

With growing populations and pressing environmental problems, future economies will be increasingly plant-based. Now is the time to reimagine plant science as a critical component of fundamental science, agriculture, environmental stewardship, energy, technology and healthcare. This effort requires a conceptual and technological framework to identify and map all cell types, and to comprehensively annotate the localization and organization of molecules at cellular and tissue levels. This framework, called the Plant Cell Atlas (PCA), will be critical for understanding and engineering plant development, physiology and environmental responses. A workshop was convened to discuss the purpose and utility of such an initiative, resulting in a roadmap that acknowledges the current knowledge gaps and technical challenges, and underscores how the PCA initiative can help to overcome them.</jats:p

On the Surface Residual Stress Measurement in Magnesium Alloys Using X-Ray Diffraction

X-ray penetration in magnesium alloys is significant due to the low X-ray mass attenuation coefficient. To measure the surface residual stresses in magnesium alloys, a correction needs to be made to account for penetration depth. The residual stresses in as-received and shot peened AZ31B-H24 rolled sheet samples were measured using two-dimensional X-ray diffraction (2D-XRD) method. The electro-polishing layer removal method was used to find the residual stress pattern at the surface and through the depth. The results show that the corrected residual stresses in a few tens of micrometers layer from the surface differ from the raw stresses. To better estimate the residual stress distribution in the surface, the grazing-incidence X-ray diffraction (GIXD) technique was applied. Additionally, micrographs of the lateral cross-section of the peened specimens confirmed the presence of microcracks in this region, causing the residual stresses to vanish. Due to the low X-ray absorption coefficient of Mg alloys, this study shows how a small uncertainty in a single raw measurement leads to high uncertainty in the corrected residual stresses. The results were corroborated with the hole drilling method of residual stress measurements. The corrected X-ray diffraction (XRD) results are in close agreement with the hole drilling and GIXD results