Large-Scale Triaxial Tests on Dilatancy Characteristics of Lean Cemented Sand and Gravel

The dilatancy equation, which describes the plastic strain increment ratio and its dependence on the stress state, is an important component of the elastoplastic constitutive model of geotechnical materials. In order to reveal their differences of the dilatancy value determined by the total volume strain increment ratio and the real value of lean cemented sand and gravel (LCSG) materials, in this study, a series of triaxial compression tests, equiaxial loading and unloading tests, and triaxial loading and unloading tests are conducted under different cement contents and confining pressures. The results reveal that hysteretic loops appear in the stress–strain curves of equiaxial loading and unloading tests, and triaxial loading and unloading tests and that the elastic strain is an important component of the total strain. The hysteretic loop size increases with an increase in the stress level or consolidation stress, whereas the shape remains unchanged. Furthermore, with an increase in the cement content, the dilatancy value determined by the total volume strain increment ratio becomes smaller than that determined by the plastic strain increment ratio, and the influence of the elastic deformation cannot be ignored. Thus, in practical engineering scenarios, especially in the calculation of LCSG dam structures, the dilatancy equation of LCSG materials should be expressed by the plastic strain increment ratio, rather than the total volume strain increment rati.

Investigation of Lade-Kim Plastic Potential Applicability under Various Stress Paths for Rockfill Materials

The dilatancy behavior of rockfill materials shows obvious stress path dependence. Lade-Kim plastic potential equation has been proposed for a long time to model the mechanical behavior of sand and concrete materials. However, it lacks the verification of rockfill materials, especially under various stress paths. In this paper, the dilatancy performance of coarse-grained materials under various stress paths is investigated, and then the dilatancy equation description and verification method based on Lade-Kim plastic potential are given. The applicability of Lade-Kim plastic potential for different stress path tests, such as conventional triaxial tests, constant P tests, and constant stress (increment) ratio tests, are verified and evaluated. It is found that Lade-Kim plastic potential is difficult to consider the influence of stress path. Finally, the Lade-Kim plastic potential, together with nonlinear dilatancy equation, is evaluated by changing the dilatancy equation in the framework of generalized plasticity. Lade-Kim plastic potential is suitable for constant stress increment ratio loading experiments and special care should be taken when applied to other stress paths. These works are helpful to understand stress path dependence of dilatancy behavior for rockfill materials and is beneficial for the establishment of stress path constitutive model.

Low-frequency oscillations of finger skin blood flow during the initial stage of cold-induced vasodilation at different air temperatures

Background Cold-induced vasodilation (CIVD) is known to be influenced by the ambient temperature. Frequency analysis of blood flow provides information on physiological regulation of the cardiovascular system, such as myogenic, neurogenic, endothelial nitric oxide (NO) dependent, and NO-independent activities. In this study, we hypothesized that the major origin of CIVD occurs prior to the CIVD event and investigated finger skin blood flow during the initial stage of CIVD at different ambient temperatures using frequency analysis. Methods Eighteen healthy volunteers immersed their fingers in 5 °C water at air temperatures of 20 °C and 25 °C. Finger skin blood flow was measured using laser Doppler flowmetry and analyzed using Morlet mother wavelet. We defined the time when the rate of blood flow increased dramatically as the onset of CIVD, and defined three phases as the periods from the onset of cooling to minimum blood flow (vasoconstriction), from minimum blood flow to the onset of CIVD (prior to CIVD), and from the onset of CIVD to maximum blood flow (CIVD). Results The increment ratio of blood flow at CIVD was significantly higher at 20 °C air temperature. In particular, at 20 °C air temperature, arteriovenous anastomoses (AVAs) might be closed at baseline, as finger skin temperature was much lower than at 25 °C air temperature, and endothelial NO-independent activity was significantly higher and neurogenic activity significantly lower during vasoconstriction than at baseline. Additionally, the differences in both activities between vasoconstriction and prior to CIVD were significant. On the other hand, there were no significant differences in endothelial NO-dependent activity between baseline and all phases at both air temperatures. Conclusions Our results indicated that the increase of endothelial NO-independent activity and the decrease of neurogenic activity may contribute to the high increment ratio of blood flow at CIVD at 20 °C air temperature.

Transition Threshold of Granite Mechanical Characteristics at High Temperature

No unified criterion exists for the transition threshold of rock mechanical characteristics. We combine rock stress-strain curves to propose an increment ratio of axial pressure based on uniaxial compression tests on granite at high temperature. The behavior of the increment ratio of strain, elastic modulus, Poisson’s ratio, and energy with axial pressure is analyzed, and the following conclusions are drawn. (1) High temperatures aggravate rock deterioration, reduce failure strength, and enhance ductility characteristics. (2) Under loading, the compression-to-elasticity and elasticity-to-plasticity transition thresholds for rock occur, respectively, at 20%–35% and 75%–80% stress levels at temperatures of 25–800°C. (3) The source data for calculating rock deformation parameters or unloading points for unloading tests can be selected over the stress level range of 35%–75%.

Influence of load increment ratio on one-dimensional consolidation behaviour

In this study, we conducted a stage loading consolidation test with varying load increment ratio and investigated its effect. By adjusting the primary consolidation ratio of one-dimensional consolidation analysis with secondary consolidation taken into account, it is possible to reproduce the consolidation amount-time curve affected by the load increment ratio.

Wrinkling Behavior of a Woven Thermoplastic Composite Material

This article examines the prediction of wrinkling initiation in self-reinforced thermoplastic composite materials for potential application in rapid forming of this class of materials. Whilst most of recent researches concentrate on examining metallic wrinkling behavior, this article aims to introduce a wrinkling indicator for composite sheet. The material system involved in the study is a self-reinforced polypropylene woven composite with a fiber orientation of 0°/90° along the warp and weft directions. Square specimens were stretched uniaxially along diagonal direction until the onset of wrinkling. It is observed that when the wrinkling occurs, strain increment ratio exhibits an abrupt change. This fundamental observation leads to the prediction of onset of wrinkling by using abrupt changes in strain increment ratio as a metric.