Slab

About: Slab is a research topic. Over the lifetime, 31617 publications have been published within this topic receiving 318693 citations.

The Fate of Descending Slabs

Abstract: Oceanic lithosphere, the stiff plate formed by the cooling of chemically diffcrentiated material that rises and mclts under mid-ocean ridges and spreads laterally in the process called sea-floor spreading, has an ephemeral residence at the surface of the Earth. Typically, within 100-200 Ma, densi­ fication of the old oceanic lithosphere leads to a dynamic instability causing it to sink into the interior, descending as a layered slab with highly anom­ alous thermal and chemical characteristics relative to the surrounding ambient mantle. The slab heats as it sinks, but the warming is sluggish, slow to overcome the effect of more than 100 Ma of cooling at the surface, and the negative buoyancy of the slab continues to drive its descent. Increasing pressure and temperature with depth drive various chemical reactions in the slab, including expulsion of water and other volatiles accumulated at the surface, and destabilization of associated hydrous phases. Suites of mineralogical phase transformations occur within the slab's crustal and depleted-mantle components. Because the slab has been processed through the melting zone at the ridge, partially hydrated, and cooled significantly, the phase equilibria within the slab differ from those of the surrounding mantle. Near 400 km depth an exothermic phase transformation occurs, with (Mg,Fe)2Si04 olivine in the slab converting to the high-pressure modified ({J) spinel structure. The spinel transition helps to drive the slab onward, although a central core of metastable olivine may persist to greater depths, with eventual transformational faulting

Modeling the thin-slab continuous-casting mold

Abstract: A three-dimensional mathematical model has been developed to compute the thermomechanical state in the mold of thin-slab continuous casters. The thin-slab mold differs from those used in conventional slab casters in that the upper portion of the broad side walls defines a funnel-shaped chamber which allows the nozzle to be submerged into the liquid metal. The chamber converges with distance down the mold, reducing to the rectangular cross section of the finished casting near the mold exit. The new mold, along with casting speeds up to 6 m/min, allows slabs to be cast 50–60 mm thick, compared with 150 to 350 mm in conventional continuous slab casting. However, the mold shape and high casting speed lead to higher mold temperatures and shorter mold life than are found in conventional slab casters. In this article, we develop mathematical models of the process to determine the role of various process parameters in determining the mold life. Finite-element analysis is used to determine the temperatures in the mold and cast slab, and these data are then used in an elastic-viscoplastic analysis to investigate the deformation of the mold wall in service. Cyclic inelastic strains up to 1.75 Pct are found in a region below the meniscus along the funnel edge. These large strains result from the combination of locally high temperatures coupled with geometric restraint of the mold. The deformation leads to short mold life because of thermal fatigue cracking of the mold. The computed locations and time to failure of the mold in fatigue agree very well with observations of the appearance of mold surface cracks in an operating caster. The models are also used to develop an improved mold design.

Vehicle Induced Dynamic Behavior of Short-Span Slab Bridges Considering Effect of Approach Slab Condition

Abstract: In this paper the vehicle induced dynamic bridge responses are calculated by modeling the bridge and vehicle as one coupled system. The dynamic behavior of short slab bridges with different span lengths induced by the AASHTO HS20 truck is investigated. A parametric study is conducted to analyze the effects of different truck speeds and different road surface conditions. Critical truck speeds that result in peaks of dynamic response are found to follow the rule that describes the resonant vibration of bridges due to train loading. The approach slab condition that consists of faulting at the ends and deformation along the span is considered in the analysis. Although the effect of the along-span deformation on the dynamic response of bridges is trivial, the faulting condition of the approach slab is found to cause significantly large dynamic responses in short-span slab bridges. Impact factors obtained from numerical analyses are compared with those values specified in the AASHTO codes.

Recent developments in slab: a software-based system for interactive spatial sound synthesis

Abstract: This paper provides an update on the features of SLAB, a software-based real-time virtual acoustic environment (VAE) rendering system designed for use in the personal computer environment. SLAB is being developed as a tool for the study of spatial hearing. The SLAB software is being released to the research community under a free-public license for non-commercial use. It is our hope that researchers will find it useful in conducting research in advanced auditory displays and will also add their own extensions to the software to provide additional functionality. Further information about the software can be found at: http://human-factors.arc.nasa.gov/SLAB.