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

Thermal effects in high density polyethylene and low density polyethylene at high hydrostatic pressures

The temperature changes as a result of rapid hydrostatic pressure applications are reported for high density polyethylene (HDPE) and low density polyethylene (LDPE) in the reference temperature range from 298 to 423 K and in the pressure range from 13.8 to 200 MN m −2 . The adiabatic temperature changes were found to be a function of pressure and temperature. A curve fitting analysis showed that the empirical curve (∂/∂ P ) = ab (Δ P ) b−1 described the experimental thermoelastic coefficients obtained from the experiments. The data were analyzed by determining the predicted thermoelastic coefficients derived from the Thomson equation (∂/∂ P ) θ = α T 0 /ϱ C p . The experimental and predicted Grüneisen parameter γ T were also determined.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44687/1/10853_2005_Article_BF01132919.pd

Recent Developments in the Properties and Composition of Electrorheological Fluids

Recent studies suggest that an alternate if not primary way that ER fluids flow is not by chain breakage as has been assumed but by the development of slip planes parallel to the chain directions. This might help to better understand mechanisms associated with the strengths of ER fluids. This lateral slip would be essentially independent of particle interactions in the field direction. Attempts to interfere with this slip by the addition of small amounts of foreign particles have resulted in some modest but significant strength increases. An additional area of significant advancement is by making the matrix liquids ER active. Various base ER fluid compositions are shown to have dramatically enhanced shear stresses when dispersed into poly(hexyl isocyanate) solutions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68990/2/10.1106_Q2XF-N5WD-ILDY-RPYO.pd

Complex Properties and Composition of Electrorheological Fluids

Various base ER fluid compositions are shown to have dramatically enhanced shear stresses when dispersed into poly(hexyl isocyanate)/xylene solutions as compared to being dispersed into polystyrene/xylene solutions. The concentration of the PHIC solutions was 4.5% which is well below that for liquid crystallinity. Further, the additon of small amounts (1-3%) of other particles to the suspensions show significant enhancement of the shear stresses for softer particles.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68662/2/10.1177_1045389X9800900805.pd