#deep-learning of #truss #metamaterials to instantly generate designs with a given anisotropic #stiffness tensor. #CC-BY
on 02022-02-092004 #pdf #paper about #antisprings for seismic isolation. Clarifies that YES, an antispring has a negative #stiffness coefficient. In this case they’re combining antisprings with regular springs to cancel out their stiffness and get near-zero restoring force for small displacements. They managed to get a resonant frequency of 0.3 Hz with #maraging steel #springs (to reduce creep), which doesn’t sound that great to me, but whatever.
on 02015-11-092007 #pdf #paper about #antisprings (negative-#stiffness springs) for seismic isolation, explaining how to improve their isolation by another order of magnitude with a counterweight rod thing that I don’t understand yet.
on 02015-11-09300nm displacements at 10Hz can be measured on their hall floor during the daytime due to human activity in the city, so they built this thing with “geometrical #antisprings”, described as “a tunable spring made by a crown of curved cantilever blades compressed each against the other” (negative #stiffness coefficient constructs?) to isolate their gravity-wave detector. They’re using electronic positive feedback to get “natural frequencies down to 0.2 Hz” and attenuate seismic noise by 80dB.
on 02015-11-0910MB catalog of Đức thắng Nguyễn’s #mechanical mechanism #video illustrations, in three PDF files, organized by topic. Including, say, a dozen or so designs for continuously variable transmissions (#cvt), a bunch of negative #stiffness mechanisms, and so on. Entirely rigid bodies as far as I can tell except for the occasional coil or leaf spring.
on 02015-08-15interesting stuff about waves propagating through strongly nonlinear #metamaterials (with negative #stiffness, actually very similar to the negative-stiffness structures being sold now to isolate turntables).
on 02015-08-14Dennis Kochmann’s #metamaterials lab at #Caltech, which participated in the work on giant-#stiffness barium-titanate/tin composite. (Did Sofia work in his lab? She was analyzing perovskite behavior under stress when I met her.) Huge list of publications on giant-stiffness materials.
on 02015-08-14Jaglinski, Kochmann, Stone, and Lakes 2007. A giant-#stiffness metamaterial of 10% barium titanate particles dispersed in a tin matrix with a Young's modulus of several TPa, greater than that of diamond at 1TPa, and more than an order of magnitude greater than that of the components (100 and 50 GPa); but only within a critical temperature range of about 58–59°. “The constraint [of the expansion of the inclusions by the matrix] stabilizes the negative bulk modulus (inverse compressibility) of the inclusions. This negative modulus arises from stored elastic energy in the inclusions, in contrast to periodic composite #metamaterials that exhibit negative refraction by inertial resonant effects.” Also note that this doesn’t help with shear (e.g. torsion) stiffness, and that their materials decayed after thermal (and load?) cycling, though they suggest that using a stronger matrix would help.
on 02015-08-14This is the actual Nicolaou and Motter 2012 paper on negative-#stiffness #metamaterials. They allude to giant-stiffness metamaterials in one of their references.
on 02015-08-14about “negative linear compressibility” (#NLC) which I think may be the same as negative #stiffness; the remarkable thing in this case is that they’re reporting it in zinc dicyanoaurate, not a metamaterial.
on 02015-08-14some PowerPoint slides showing, among other things, a sheet full of round holes (“holey sheet”) exhibiting negative #stiffness on p.63. Apparently this is from “Mullin et al, PRL 99, 2007.”
on 02015-08-14Another #abstract from Nature Materials on negative-compressibility or negative-#stiffness #metamaterials.
on 02015-08-14#Abstract of “Mechanical #metamaterials with negative compressibility transitions” (i.e. negative #stiffness, although they contrast it in figure 1). This is Nicolaou and Motter 2012.
on 02015-08-14this #paper about muscle myosin folding mentions “negative #stiffness at the point where all cross-bridges collectively flip... Similar mechanical behavior has been recently artificially engineered in #metamaterials by drawing on the #Braess paradox ... the mean-field type coupling in such materials is achieved via parallel connections with multiple shared links.” The references given are Cohen & Horowitz 1991 (the paper with the springs and strings) and Nicolaou and Motter 2012 in “Nat Mater”, which I guess is “Mechanical metamaterials with negative compressibility transitions” in Nature Materials.
on 02015-08-14a #paper on mechanical and electrical analogs of #Braess’s paradox, using zeners in the electrical case. Has a clear explanation of the mechanical version of the system; it depends only on the nonlinear stress-strain behavior of buckling string. (String! Not springs!) The fixed maximum length of the string corresponds to the fixed maximum voltage of the zener. On p.700 (the second page) there’s a diagram showing something like a negative-#stiffness region in this network! Also explains that nonlinearity is necessary to produce this effect, and gives a hydraulic analogue as well.
on 02015-08-14A #video of a mechanical demonstration of #Braess’s paradox using the #stiffness of springs.
on 02015-08-14I wonder if #Braess’s Paradox is applicable to negative-#stiffness #metamaterials? Braess’s original formulation was, "an extension of the road network may cause a redistribution of the traffic that results in longer individual running times”, but I’m pretty sure I’ve seen this in the form of a mobile that hangs higher after you cut a thread in it.
on 02015-08-14A 2011 patent application for negative-#stiffness #seismic protection. #patents
on 02015-08-12A #popsci explanation of negative-#stiffness #metamaterials or structures, with an #interview.
on 02015-08-12A #paper on negative-#stiffness #metamaterials (“structures”) through “constrained bistable structures” #3D printed in nylon with #SLS. The figures are at the end. Related to #Merkle’s buckling-spring #mechanical logic.
on 02015-08-12A company promoting negative-#stiffness #metamaterials (or “mechanisms”) for #vibration isolation, replacing air tables.
on 02015-08-12“By incorporating constituents of negative #stiffness [elasticity] in structures and composites, one can attain extremely high values of mechanical damping, stiffness considered as a viscoelastic modulus, of thermal expansion, or of other physical properties. Negative stiffness is of itself usually unstable but can be stabilized by incorporation in heterogeneous structures or composites.” #metamaterials #bibliography
on 02015-08-12