Elastic-Viscoplastic Constitutive Model of Soil under Cyclic Loading

The creep problems are often involved in soil under cyclic loading, and its behaviors of soil under cyclic loading sparks many arguments in current research field. To propose one new model to demonstrate these creep behaviors of soil under cyclic loading, the cyclic loading was simplified equivalently, and the elastic-viscoplastic model (EVPM) for soil under cyclic loading was established based on the Bingham model. The yield criterion for soil under cyclic loading with constant amplitude was proposed following the simplified load. A constitutive equation based on the EVPM was constructed by using the flow criterion related to the yield criterion. Meanwhile, the parameters of EVPM were identified and discussed. In addition, the case analysis of the EVPM was also performed. The results indicate that the stable and destructive creep behaviors of soil under cyclic loading could be well described by the recommended EVPM, and the obtained parameters in the model exhibited a clear regularity with the increase of dynamic stress amplitude. Besides, the established model could be selected to predict the stable and destructive creep behavior of soil under cyclic loading.

Visco-Elastoplastic Constitutive Fatigue Model for Rocks

The study on the constitutive fatigue model for rocks under cyclic loading has an important significance in rock engineering. In order to study the fatigue properties of rocks under cyclic loading, according to the theory of rheological mechanics and the existing three basic one-dimensional fatigue elements, i.e., elastic, viscous, and plastic fatigue elements, the three-dimensional elastic, viscous, and plastic fatigue elements were constructed. Meanwhile, a fatigue yield criterion for rocks under cyclic loading was proposed, and a three-dimensional nonlinear visco-elastoplastic fatigue constitutive model (NVPFM) for rocks was established by using the flow criterion related to the proposed fatigue yield criterion. Compared with the test results of rocks under cyclic loading, the three-dimensional NVPFM could be used to describe the transient, steady-state, and tertiary creep phases of rocks under cyclic loading.

Improving the Micropump Velocity for Orthogonal Electrode Pattern

The current research work in this paper involves optimizing an orthogonal electrode multifunctional system to transport biofluid. Orthogonal electrode patterned microfluidic device is known to produce high microflow velocity when excited by AC signals. This paper specifically investigates the fluid flow criterion by determining the direction and velocity in the selected electrode pattern actuated with AC signals. During the initial process, experiments were conducted at 100μm spacing between the orthogonal electrodes. The exact setup was placed on a hydrophobic surface to observe the change in the velocity. This process was then repeated with 150μm spacing. Fluid with conductivity 2.36 mS/cm was tested at voltage levels ranging between 5V to 10V at 50 KHz to 1MHZ frequency levels with an increment of 100 KHz. The goal of this research work is to increase microflow velocities by varying the electrode separation distance, flow surface, voltage and frequency. Trivial investigation also done on the possibility of micromixing using this pattern.

Evaluation of Strength Design Criteria and Plastic Flow Criteria for Pressure Vessels

The present paper evaluates the traditional strength design criteria and recently developed plastic flow criteria used in the structural design and integrity assessment for pressure vessels. This includes (1) a brief review of the traditional strength criteria used in ASME Boiler and Pressure Vessel (B&PV) Code, (2) a discussion of the shortcoming of existing strength criteria when used to predict the burst pressure of pressure vessels, (3) an analysis of challenges, technical gaps and basic needs to improve the traditional strength design criteria, (4) a comparison of strength theory and flow theory for ductile pressure vessels, (5) an evaluation of available flow criteria and their shortcoming in prediction of failure pressure of pressure vessels, (6) an introduction of newly developed multi-axial flow criterion and its application to pressure vessels, and (7) a demonstration of experimental validations of the new flow criterion when used to predict the burst pressure of pressure vessels. On this basis, several recommendations are made for further study to improve the existing strength design and integrity assessment methods of pressure vessels.

Better Estimate Analysis for Use in Emergency Operating Procedure During a Loss of Coolant Accident

Emergency Operating Procedures (EOPs) [1] provide prioritized response strategies that guide the operator in management of emergency transients. A desirable attribute of EOPs is optimal recovery from the transient. To achieve this, it is necessary to develop more realistic criteria rather than criteria based on traditional licensing analysis methods. One such application is evaluating measured core makeup flow during the recirculation phase of a Loss of Coolant Accident (LOCA) with adverse containment environment. During the recirculation phase of a LOCA, the adequacy of the internal recirculated water flow (from the containment sump) is confirmed by individual loop measured injection flows satisfying EOP criteria. Of particular concern is the flow split in the loop emergency cooling injection lines and the potentially large instrument uncertainty associated with measuring low flow rates. In the event one of the injection lines spills to containment (and possibly without a line spilling), traditional analysis methods based criteria would suggest adequate makeup flow may not be confirmed, and consequently the EOPs would prescribe external recirculation, which is not the preferred mode. In the present paper the EOP criteria for post LOCA core cooling flow is developed — using better estimate methods. Several (significantly) less restrictive analysis assumptions were identified and a new/materially different approach from that used in the past was taken. As result a more robust flow criterion was obtained — simpler and permitting about 0.019 m3/s [300 gpm] less flow.