A set of monotonic tensile tests was performed on 3-D printed plastics following ASTM standards. The experiment tested a total of 13 “dog bone” test specimens where the material, infill percentage, infill geometry, load orientation, and strain rate were varied. Strength-to-weight ratios of the various infill geometries were compared. It was found through tensile testing that the specific ultimate tensile strength (MPa/g) decreases as the infill percentage decreases and that hexagonal pattern infill geometry was stronger and stiffer than rectilinear infill. However, in finite element analysis, rectilinear infill showed less deformation than hexagonal infill when the same load was applied. Some design guidelines and future work are presented.
In the last months of 2014, many Americans were reminded of the sad truth that policing can be brutal and that black bodies and black lives are often the targets of that brutality. In Staten Island and in Ferguson (and elsewhere), images of young black men killed by the police generated a thrum of anger. While there were people in the streets protesting the killing of Eric Garner and Michael Brown, these early protests were local, and the protestors were mostly committed activists or members of the impacted (largely black) community. The protests did not jump these limits to become national until the sympathetic bystanders saw that the officers in Missouri and New York were not indicted. Brutality was tragic, the failure to “do justice” was an outrage. This article places this observation in historical context by looking back at similar dynamics across the last two centuries. What emerges is a genealogy that links the swelling protests in 2014 to moments of broader outrage throughout the historical struggle for racial justice. Again and again, where allies stood on the sidelines silently condemning violence, it was the spectacle of the legal system – their legal system – acting unjustly that sparked action.
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