ACOUSTIC BAND GAP FORMATION IN METAMATERIALS

This is an electronic version of an article published in the International Journal of Modern Physics B [© World Scientific Publishing Company].We present several new classes of metamaterials and/or locally resonant sonic crystal that are comprised of complex resonators. The proposed systems consist of multiple resonating inclusion that correspond to different excitation frequencies. This causes the formation of multiple overlapped resonance band gaps.We demonstrate theoretically and experimentally that the individual band gaps achieved, span a far greater range ( 2kHz) than previously reported cases. The position and width of the band gap is independent of the crystal’s lattice constant and forms in the low frequency regime significantly below the conventional Bragg band gap. The broad envelope of individual resonance band gaps is attractive for sound proofing applications and furthermore the devices can be tailored to attenuate lower or higher frequency ranges, i.e. from seismic to ultrasonic

Basic longitudinal texture and fracturing process in thermoset polymers

The “basic longitudinal texture”, which is present everywhere on the fracture surfaces of glassy thermosets and is the finest texture observed on such surfaces, consists of low ridges and shallow grooves that are aligned parallel with the direction of crack propagation. The periodicity of the basic longitudinal texture, i.e., the average lateral separation between the ridges (or grooves), has been found to be characteristic of materials. This and other properties were measured for a series of rigid epoxy specimens made from diglycidyl ether of bisphenol-A and methylhexahydrophthalic anhydride. For the series of epoxies studied, the glass transition temperatures varied from 76 to 143 °C, the room temperature Young's modulus varied from 2.29 to 2.97 G Pa, the room temperature yield stress in compression varied from 99 to 128 M Pa, the room temperature Knoop hardness numbers varied from 133.5 to 163.5, the rubbery modulus at 200'C varied from 12.8 to 21.6 MPa, and the periodicity of the basic longitudinal texture varied from 205 to 368 nm. Only properties of the liquid state, namely glass transition temperature and the rubbery modulus, correlated well with periodicity of the basic longitudinal texture. This suggests that the basic longitudinal texture is the remnant left on the fracture surfaces of a liquid state that must have developed during fracture. This suggests in turn that liquefaction is an intrinsic part of the brittle fracture of polymer network glasses.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44718/1/10853_2005_Article_BF01197652.pd

Plasticity of brittle epoxy resins during debonding failures

A remarkably high degree of plasticity in brittle epoxies during debonding failures is reported. The plasticity is exhibited by the presence of ridges on the debonded surfaces having a width and height above the general level of these surfaces of the order of 100 nm. The surfaces of the more rigid substrates from which the debonding has occurred, by contrast, are smooth after debonding. The ridges have been found in several forms: in more or less straight rows parallel to the debonding fracture direction; as irregularly-shapes rings or craters, probably formed from secondary crack growth; as paraboloids, which also seem to be related to secondary crack growth; and as serpentine rows more or less perpendicular to the debonding fracture direction. This behaviour has been exhibited by various epoxy formulations. The 100 nm widths and heights for the ridges suggest that during debonding, plastic deformation has occurred rather uniformly in the epoxy to a depth below the interface of this order. This behaviour is in contrast to the simple notion of brittle fracture, in which atoms or molecules separate across planes in an elastically strained body. It differs also from the bulk fracturing process with these resins, in which a smaller amplitude, more random ridge and groove texture, referred to as the “basic longitudinal” or “fingering” texture, is seen.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44693/1/10853_2005_Article_BF01168982.pd