Unrestrained Test Research Articles

Anisotropy and directional shrinkage of geosynthetic clay liners

ABSTRACT: Results are reported from laboratory experiments to examine the potential shrinkage of two different geosynthetic clay liners (GCLs) when subject to repeated wetting and drying cycles. One GCL had a scrim-reinforced nonwoven carrier geotextile (denoted as GCL2) and the other had a nonwoven carrier geotextile (GCL4). Tests were conducted with both restrained and unrestrained GCL specimens of the same size as well as restrained specimens with different specimen sizes and length-to-width aspect ratios. For unrestrained specimens, there was no apparent difference between shrinkage in the transverse and longitudinal directions for GCL2, whereas GCL4 tended to shrink more in the longitudinal direction. There was only a small difference between restrained and unrestrained tests, with the restrained specimens giving a maximum strain about 1.1 times higher than the unrestrained for GCL4. There was no clear effect of the specimen size on the measured shrinkage. For restrained specimens, shrinkage increased with increasing aspect ratio up to an aspect ratio of approximately 5. The dry mass per unit area of the product was found not to affect shrinkage when the mass per unit area was evenly distributed. However, specimens with an uneven bentonite distribution (typically those with a low mass per unit area) can have areas of little to no bentonite content, and these specimens experienced much higher shrinkage than other specimens. A high degree of variability between specimens for apparently similar test conditions was observed. Even more noteworthy is the fact that the maximum shrinkage observed in these tests (14.4%) was well below the maximum of 23% observed by previous investigators using the same methodology and nominally the same product. This shows the difference that can occur between different rolls of nominally the same product.

Haptic discrimination of size and texture in squirrel monkeys ( Saimiri sciureus )

The present study analyzed haptic abilities of four squirrel monkeys. Using a two-alternative forced-choice procedure, stimuli were presented in a visually opaque box, allowing unrestrained test subjects to grab through a small opening and touch the discriminanda. Difference thresholds were determined by a modified method of limits. In the first experiment we determined size difference thresholds for the discrimination of circular cylinders using standard stimuli differing in diameter from 10 mm to 35 mm. In the second experiment a texture difference threshold was obtained for the discrimination of grooved surfaces (groove width 2-7 mm).The squirrel monkeys achieved a mean size difference threshold of 8% stimulus difference. The linear increase of absolute thresholds as a function of the starting stimulus size showed that haptic size discriminations in squirrel monkeys correspond to Weber's law. Three of the animals achieved a texture difference of 10% stimulus difference, while one monkey showed a distinctively lower haptic acuity. An analysis of the exploratory behavior points to a subject-related difference in the significance of cutaneous and kinesthetic information during size discriminations. Whereas differences in the animals' exploratory behavior did not correlate with the size difference threshold a subject achieved, different thresholds for texture discrimination can be explained by the different exploratory procedures the monkeys used to touch grooved surfaces. The low difference thresholds determined for the squirrel monkeys in the present study point to the significance of unrestrained test conditions for the assessment of the haptic capacity of a species.

Loading rig in which axially compressed thin cylindrical shells buckle near theoretical values

Fifteen near-perfect electroformed nickel cylindrical shells of highR/t ratios have been buckled by axial compression using a special loading-rig system. Buckling-stress values averaged 85 percent, and ranged from 80 to 96 percent, of the classical theoretical bucklingstress value. The loading rig described in this report makes use of a simple procedure for accurately aligning the thin shell with the load axis and, also, for maintaining the circularity of the shell at its end by accommodating for slightly different diameters, with the use of tapered circular end caps which provide exact fits in each case. The rig also provides a setup in which shells may be free to twist, tip and translate, or be restrained from these motions. Comparison between restrained and unrestrained tests reveoled no noticeable change in the buckling load. However, with the restraining mechanism, slightly higher postbuckling loads, repeated buckling loads and an increased number of circumferential waves resulted.