No abstract

The tensile behavior of single-walled nanotubes (SWNTs) having two defects (vacancy or Stone-Wales) positioned next to each other was simulated in this study to investigate the influence of the spatial arrangement of defects on the mechanical properties. The simulations were performed using classical molecular dynamics (MD) at the atomic scale. Two neighboring vacancy defects reduced the failure strength as much as 46% and the failure strain as much as 80% in comparison with those of pristine SWNTs, while two neighboring Stone-Wales defects reduced them as much as 34% and 70% respectively. SWNTs having two defects in the loading (axial) direction showed higher failure strength than SWNTs with defects perpendicular to the loading direction. For both types of defect, the closer the defects, the weaker the SWNTs. As result, the defect arrangement in the SWNT structure must be one of the key factors in determining its mechanical properties, as well as the population of defects.

Quasi-static and compressive fatigue tests on the closed cell Al-Si-Ca alloy foam specimens with three different aspect ratios were performed. It turned out that the onset of cyclic shortening of foam with a lower aspect ratio took place earlier and the fatigue strength was lower compared with the specimen with a higher aspect ratio, although all the dimensions of specimen satisfied the seven times the cell size criterion, while the quasi-static stress-strain curves were almost same having same Young's modulus, yield stress and plateau stress. Therefore, the seven times the cell size criterion for the quasi-static compression behavior was not applicable to the fatigue analysis of Al-Si-Ca alloy foam.KEY WORDS aluminum foam, aspect ratio, fatigue behavior, compressive strength

No abstract

The permanent residual strain in aluminum (Al) alloy foams induced by compressive fatigue gradually increases with the increasing number of loading cycles. Consequently, the progressive shortening of Al-alloy foam degrades the dynamic material performance by the failure and ratcheting of multi-cells in the foam. In this paper, the dynamic properties of Al-alloy foams damaged by compressive fatigue were studied. The beam specimens with various residual strains were made by cyclic compression-compression stress. The dynamic bending modulus and loss factor were evaluated by using a beam transfer function method. As a result, the dynamic bending stiffness of Al-alloy foam turned out to be decreased due to damage while the loss factor was improved because of the increasing energy dissipation of such factors as cracked cell walls formed during the shortening process of the foam. The loss factor shows a manifest dependence on the fatigue residual strain.

No abstract

No abstract

No abstract