Tribological Characteristics of Thermomechanically Processed 7075 Al Alloy Through Nano-scratch Characterization

Age-hardenable Al–Zn–Mg–Cu (AA 7075) alloys can be fortified by precipitation solidifying because of precipitation of the MgZn2 intermetallic stages. Furthermore, grain refinement and high dislocation density can also be opted for strengthening purposes. A low-temperature deformation enhances the dislocation density and also facilitates the grains recovery to strengthen the component. The present study combines artificial aging (at 120 °C) and sub-zero (∼−20 ˚C) temperature rolling to achieve strengthening. Various sequences and combinations of these mechanical and thermal treatments are performed and the effects of these treatments on the tribological characteristics of the alloy are studied by nano-scratch measurements. The tribological characteristics are indicated by coefficient of friction ( μ), plastic energy ( PE), recovery index ( η), recovery resistance parameter ( Rs), etc. of each sample. The widths of the scratch are further utilized to calculate the scratch hardness values ( Hs), wear resistance coefficients ( Rw) and the coefficient of wear ( K) with the help of Archard's equation.

Whose Past Counts? Collective Remembrances

Disasters and subsequent recovery efforts are guided by a number of community considerations. Least understood of these are the communities’ collective memories of past disasters and their efforts to recover. This chapter argues that disasters shape the collective memory of communities and these collective memories persist over generations, thus becoming part of a community’s gestalt. The chapter develops the concept of collective memory as it applies to disasters as a framework for examining two very different cases—the earthquake of 1775 in Lisbon and the destruction of the Second Jewish Temple in Jerusalem in 70 ce. Although these were disasters of very different forms, they were of such importance that they continue to be part of the collective consciousness of residents in both cities. The cases also illuminate four important issues that are critical to understanding disaster recovery: resistance/resilience; religion/naturalism; memorials/remembrances; and authoritarian/collective responses.

EVA Lightweight Concrete Reinforced with Piassava Fiber

The residue of Ethylene-Vinyl Acetate (EVA) generated in the footwear industry is an economic and environmental problem as it requires large area for storage in landfills and is not biodegradable or capable of transformation into other polymers. Its use as a lightweight aggregate in mortar and concrete results in a material with lower density but with reduced strength. In this paper, piassava fibers (Attalea funifera Martius) were used as reinforcement of lightweight concrete containing 4% and 6% of EVA, with the goal of improving the flexural strength of the material. The determination of density, compressive strength and flexural strength were performed at 28 days of age. The experimental results demonstrate that the addition of EVA decreases the density and flexural strength of the concrete in proportion to the amount of addition, but a recovery resistance is obtained when the piassava fibers are added in amounts of 1 to 2% by volume.

Study on Mechanical Properties of Cement Clinker and Limestone by Hertzian Indentation Method

The recovery resistance, energy dissipation, and other mechanical properties of cement materials are evaluated based on the Hertzian indentation method in this work. It is significant and efficient for engineering application. In results, the calculated energy dissipation of clinker is higher than that of limestone, which can partially be used to explain why the grinding of clinker consumes a lot of energy in cement industry. The recovery resistance for limestone under the peak load of 100N is almost higher than of clinker. However, in contrast to that of 200N, the recovery resistance for limestone is almost identical to that of clinker. It is indicated that the clinker exhibits better plasticity. and greater energy absorption capacity.

Evaluating Mechanical Properties of Cement Materials by Depth-Sensing Indentation Method

The energy consumption of crushing is directly affected by the mechanical properties of cement materials. The elastic modulus, energy dissipation, recovery resistance and other mechanical properties of cement materials are evaluated based on the depth-sensing indentation method in this work. It is significant and efficient for engineering application. In results, the calculated elastic modulus is close to that measured by dynamic method, being used to verify the correctness of the calculated data. And the calculated energy dissipation of clinker is higher than that of limestone and granite, which can partially be used to explain why the grinding of clinker consumes a lot of energy in cement industry. The recovery resistance of clinker is almost identical to that of granite, more than that of limestone. It is found that the clinker, in contrast to granite and limestone, exhibits better plasticity and greater energy absorption capacity.

Estimating Energy Dissipation of Ceramics via H-E Ratio

Mechanical properties of ceramics are important for its engineering application. It would be significant and efficient if some properties could be estimated without tests. Energy dissipation capacity of ceramics is estimated in this work via two common parameters, hardness and elastic modulus, which could be obtained from basic data of commercial ceramics or simple tests. The ratio of hardness to reduced modulus H/Er is found to be related to recovery resistance and energy dissipation capacity of the materials, and the related equations were induced. The reduced modulus can be expressed by conventional elastic modulus E. Thus, the capacity of energy dissipation and elastic recovery can be estimated simply from the H/E ratio. The calculated results indicate that the value of H/E ratio is in reverse proportion to the energy dissipation. Several ceramics with different H/E ratio are analyzed and their energy dissipation capacities are estimated.