Hydrostatic stress

About: Hydrostatic stress is a research topic. Over the lifetime, 1568 publications have been published within this topic receiving 37773 citations.

Is Terzaghi’s effective stress a stress variable under seepage conditions?

Abstract: From the continuum mechanics perspective, an attempt was made to clarify the role of Terzaghi’s effective stress in the theoretical analysis of saturated soil subjected to seepage. The necessity of performing a coupled hydromechanical analysis to solve the seepage-deformation interaction problem was illustrated by examining the equations of static equilibrium among the effective stress, seepage force, pore-water pressure and total stress. The conceptual definition of stress variable that satisfies the principles of continuum mechanics is applied in the coupled hydromechanical analysis. It is shown that Terzaghi’s effective stress is in fact not a stress variable under seepage conditions, and the seepage force acting on the soil skeleton cannot be viewed as a body force. This offers a clue to the underlying cause of a paradox between the real Pascal’s hydrostatic state and the hydrostatic state predicted by a class of continuum hydromechanical theories.

Layout optimization of CMOS Interconnects for Heating, Cooling and Improved Stress Distribution

Abstract: The reliability of CMOS circuits is influenced by local inhomogeneities in current density, temperature and mechanical stress. Mechanical stress caused by processing and post-processing sources like material mismatch, temperature steps and extrinsic sources like bonding, 3D integration and extended operating conditions becomes more and more relevant the for reliability. It can affect the life time performance of interconnects as well as the function of active devices like stress sensitive transistors.First simulations which support the development work for optimized interconnect layouts as features to improve the reliability of a circuit were prepared. The evaluations started with the heater development of self-heating test structures for higher metal layers for accelerated reliability tests. It continued with the development of a high robust metal stack. The simulations and the tests at heaters and high robust metallization test structures demonstrated the advantages of such a layout improvement.The simulations of the distribution of the temperature and the mechanical stress illustrates the important parameters and their interactions.The paper presents new ANSYS® -simulations on some exemplary heater layout variants in the highly robust metallization design. The scientific questions were the suitability and the benefits of such a heater layout for heating, cooling and stress distribution in CMOS circuits. Different heater-test line models have been analysed by ANSYS® -simulations. The variants of the models were forced or no forced current in heater and/or test line and the kind of metal layer of heater connection. The current density, temperature, their gradients, the hydrostatic stress, the Von Mises stress and the mass flux divergences have been analysed.Such simulations can be utilized to improve parts of circuits like chip corners, sensitive transistors, circuits on GaN-substrate, with TSVs or applications with 3D integration. The local temperature and stress management can be improved by the special metallization layout and the improvement can be supported by simulation data.

Some Remarks on Hydrostatic Pressure and Maxwell Model

Abstract: The difference between hydrostatic pressure and isotropic component of stress tensor was early mentioned by Reiner in his theory of dilatancy. In the recent development of the theory of viscoelasticity, however, it seems that this distinction becomes fade and is slightened. In this paper, this distinction is rigorously discussed in relation to Maxwell model. It has been shown that as far as we stay at the assumption that actual stress is equivalent to elastic stress and also to viscous stress and the condition that viscous stress vanishes when viscous strain rate becomes zero, derived Maxwell's formulas can not contain hydrostatic pressure.

An Anisotropic Creep Damage Model for Multiaxial Cyclic Loadings Histories

Abstract: The purpose of this study is the development of an anisotropic creep damage theory within the continuum damage mechanics, applicable to creep-dominated cyclic loading histories. A damage distribution is expressd in rate form as a symmetric tensor of rank necessary to match physically measured damage. A theoretical model which expresses general anisotropic creep damage phenomena with power law cavity growth is proposed. The coupling of damage with a bounding surface cyclic viscoplasticity theory is also accomplished. Comparison with experimental results are made for weakly anisotropically damaging materials, type 304 stainless steel at 593°C. Good correlation of rupture time, secondary creep, and tertiary creep has been obtained for proportional and nonproportional, isothermal, constant isochronous nominal stress loading histories. A modification of the isochronous stress (the set of stress state which have a same rupture time) for compressive hydrostatic stress state has been offered.