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Rod Lakes Home

Lakes, R. S. and Saha, S., "Cement line motion in bone," Science, 204, 501-503 (1979). Download pdf.
Motion at the cement lines occurs in bone under prolonged torsional load. Such motion is considered responsible for the long term creep in bone. The absence of an asymptotic creep strain is consistent with an interpretation of the cement line as a viscous interface.

Lakes, R. S., Yoon, H. S. and Katz, J. L., "Slow compressional wave propagation in wet human and bovine cortical bone", Science, 220 513-515, (1983). Download pdf.
A second slow compressional ultrasonic wave is observed in wet bone. It is attributed to interaction between the fluid and solid phases.

Lakes, R. S., "Foam structures with a negative Poisson's ratio", Science, 235 1038-1040 (1987). Article in html; Download pdf.
Foams are developed in which the cross section becomes fatter when stretched. We did not call this a metamaterial though perhaps it is the first one.

Lakes, R. S., "Negative Poisson's ratio materials", Science 238 551 (1987). The negative Poisson effect is not due to Cosserat elasticity. Download pdf, gif

Lakes, R. S., "No contractile obligations", Nature, 358, 713-714, (1992). Article in pdf
Negative Poisson's ratio porous polymers are placed within the context of advances in negative Poisson's ratio materials.

Lakes, R. S., "Materials with structural hierarchy", Nature, 361, 511-515 (1993). Cover article. Article in html
Many natural and man-made materials exhibit structure on more than one length scale; in some materials, the structural elements themselves have structure. Such materials can have extreme properties. Low density cellular solids with a high ratio of strength to weight are presented.

Prall, D. and Lakes, R. S., "Properties of a chiral honeycomb with a Poisson's ratio of -1", Int. J. of Mechanical Sciences, 39, 305-314, (1997). Article in html
A two-dimensionally chiral honeycomb is developed and studied theoretically and experimentally. The honeycomb exhibits an in plane Poisson's ratio of -1 essentially independent of strain. This is the first two-dimensional metamaterial that is chiral; we did not call it by such a name. This has stimulated considerable research.

Lakes, R. S., "Lateral deformations in extreme matter", Science, 288, 1976, (2000). article link or get pdf here.
A report of negative Poisson's ratio in plasma crystals and neutron star crust is reviewed.

Lakes, R. S., "Extreme damping in compliant composites with a negative stiffness phase" Philosophical Magazine Letters, 81, 95-100 (2001). Article in pdf.
Unit cells of compliant composites in which one phase has negative stiffness are considered. Singular damping (tending to infinity) is observed.

Lakes, R. S., "Extreme damping in composite materials with a negative stiffness phase", Physical Review Letters, 86, 2897-2900, (2001). Article in pdf
Composites with a phase (constituent) of negative stiffness are analyzed. The composite stiffness can be higher than that of either constituent. Giant peaks in mechanical damping can occur.

Lakes, R. S., Lee, T., Bersie, A., and Wang, Y. C., "Extreme damping in composite materials with negative stiffness inclusions", Nature, 410, 565-567, (2001). Article in pdf
Inclusions of negative stiffness in a composite can be stabilized within a positive-stiffness matrix. Here we describe the experimental realization of this composite approach by embedding negative-stiffness inclusions of ferroelastic vanadium dioxide in a pure tin matrix. The resulting composites exhibit extreme mechanical damping and large anomalies in stiffness, as a consequence of the high local strains that result from the inclusions deforming more than the composite as a whole.

Lakes, R. S., "A broader view of membranes", Nature, 414, 503-504, 29 Nov. (2001). Article in pdf
Negative Poisson's ratio membranes are reviewed and interpreted.

Jaglinski, T., Kochmann, D., Stone, D., Lakes, R. S. "Materials with viscoelastic stiffness greater than diamond", Science 315, 620-622, Feb. 2 (2007).
We show that composite materials can exhibit a viscoelastic (Young's) modulus far higher than that of either constituent; indeed, a stiffness greater than that of diamond. These materials are almost ten times stiffer than diamond over a range of temperature. go: page.

Greaves, G. N., Greer, A. L., Lakes, R. S., and Rouxel, T., "Poisson's Ratio and Modern Materials", Nature Materials, 10, 823-837 Nov. (2011).
In comparing a material's resistance to distort under mechanical load rather than alter in volume, Poisson's ratio offers the fundamental metric by which to compare the performance of any material when strained elastically. The numerical limits are set by 1/2 and -1, between which all stable isotropic materials are found. With new experiments, computational methods and routes to materials synthesis, we assess what Poisson's ratio means in the contemporary understanding of the mechanical characteristics of modern materials. Central to these recent advances, we emphasize the significance of relationships outside the elastic limit between Poisson's ratio and densification, connectivity, ductility and the toughness of solids; and their association with the dynamic properties of the liquids from which they were condensed and into which they melt. get pdf.

Rueger, Z. and Lakes, R. S., "Strong Cosserat elasticity in a transversely isotropic polymer lattice", Physical Review Letters, 120, 065501 Feb. (2018).
Large size effects are experimentally measured in lattices of triangular unit cells: about a factor of 36 in torsion rigidity and 29 in bending rigidity. This nonclassical phenomenon is consistent with Cosserat elasticity which allows for rotation of points and distributed moments in addition to the translation of points and force stress of classical elasticity. The Cosserat characteristic length for torsion is 9.4 mm; for bending it is 8.8 mm; these values are comparable to the cell size. Nonclassical effects are much stronger than in stretch dominated lattices with uniform straight ribs. The lattice structure provides a path to attainment of arbitrarily large effect. journal reprint link; get pdf.