This article describes experimental investigations of size effects in torsion and bending of lathe cut closed-cell polymethacrylimide and open cell copper foams. Slender specimens were found to have a slightly smaller effective stiffness than thick ones. This behaviour is consistent with a model of surface damage to the outermost cells of the foam. The surface damage layer was inferred to be from 0.13 to 0.37 cell diameters for the polymethacrylimide, depending on the grade of foam, and from 0.3 to 0.4 cells in the copper foam. Effects of Cosserat (micropolar) elasticity, which would give rise to an effective stiffening of slender specimens, were not observed.
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References
1.
LakesR.S., “Experimental micro mechanics methods for conventional and negative Poisson's ratio cellular solids as Cosserat continua”, J. of Engineering Materials and Technology, Vol. 113, 1991, 148
2.
SokolnikoffI.S., Mathematical Theory of Elasticity, Krieger, 1983
3.
FungY.C., Foundations of Solid Mechanics, Prentice Hall, 1968
4.
CosseratE. and CosseratF., Theorie des Corps Deformables, Hermann et Fils, Paris, 1909
5.
EringenA.C., Theory of micropolar elasticity.In Fracture, Vol. 1, 621, (edited by LiebowitzH.), Academic Press, 1968
6.
CowinS.C., “An incorrect inequality in micropolar elasticity theory”, J. Appl. Math. Phys. (ZAMP), Vol. 21, 1970, 494
7.
MindlinR.D., “Stress functions for a Cosserat continuum”, Int. J. Solids and Structures, Vol. 1, 1965, 265
8.
GauthierR.D. and JahsmanW.E., “A quest for micropolar elastic constants”, J. Applied Mechanics, Vol. 42, 1975, 369
9.
KrishnaReddy G.V. and VenkatasubramanianN.K., “On the flexural rigidity of a micropolar elastic circular cylinder”, J. Applied Mechanics, Vol. 45, 1978, 429
10.
YangJ.F.C. and LakesR.S., “Transient study of couple stress effects in human compact bone”, J. Biomechanical Engineering, Vol. 103, 1981, 275
11.
LakesR.S., “Experimental microelasticity of two porous solids”, International Journal of Solids and Structures, Vol. 22, 1986, 55
12.
ChenC.P. and LakesR.S., “Dynamic wave dispersion and loss properties of conventional and negative Poisson's ratio polymeric cellular materials”, Cellular Polymers, 9, 1989, 343
13.
LakesR.S., “How to experimentally distinguish Cosserat and non-local materials”, Boeing technical report, 1993
14.
BreznyR and GreenD.J., “Characterisation of edge effects in cellular materials”, J. Materials Science, Vol. 25, 1990, 4571
15.
ShipkowitzA.T., ChenC.P. and LakesR.S., “Characterisation of high-loss viscoelastic elastomers”, J. Materials Sci., 23, 1988, 3660
16.
ChenC.P. and LakesR.S., “Apparatus for determining the viscoelastic properties of materials over ten decades of frequency and time”, J. Rheology, 33, 8, 1989, 1231
17.
GibsonL.J. and AshbyM. F., Cellular Solids: Structure and Properties, Pergamon Press, Elmsford, NY, 1988
18.
Van VlackL.H., Materials for Engineering, Addison-Wesley, Reading, Mass, 1982
