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Related Concept Videos

Strain and Elastic Modulus01:15

Strain and Elastic Modulus

The quantity that describes the deformation of a body under stress is known as strain. Strain is given as a fractional change in either length, volume, or geometry under tensile, volume (also known as bulk), or shear stress, respectively, and is a dimensionless quantity. The strain experienced by a body under tensile or compressive stress is called tensile or compressive strain, respectively. In contrast, the strain experienced under bulk stress and shear stress is known as volume and shear...
Relation between Poisson's ratio, Modulus of Elasticity and Modulus of Rigidity01:15

Relation between Poisson's ratio, Modulus of Elasticity and Modulus of Rigidity

Deformation occurs in axial and transverse directions when an axial load is applied to a slender bar. This deformation impacts the cubic element within the bar, transforming it into either a rectangular parallelepiped or a rhombus, contingent on its orientation. This transformation process induces shearing strain. Axial loading elicits both shearing and normal strains. Applying an axial load instigates equal normal and shearing stresses on elements oriented at a 45° angle to the load axis.
Members Made of Elastoplastic Material01:19

Members Made of Elastoplastic Material

The behavior of elastoplastic materials under bending stresses, particularly in structural members with rectangular cross-sections, is crucial for predicting material responses and understanding failure modes. Initially, when a bending moment is applied, the stress distribution across the section follows Hooke's Law and is linear and elastic. This distribution means the stress increases from the neutral axis to the maximum at the outer fibers, up to the elastic limit.
As the bending moment...
Elastic Strain Energy for Normal Stresses01:22

Elastic Strain Energy for Normal Stresses

Strain energy quantifies the energy stored within a material due to deformation under loading conditions, a fundamental concept in materials science and engineering. The strain energy can be modeled when a material is subjected to axial loading with uniformly distributed stress. In this scenario, the stress experienced by the material is the internal force divided by the cross-sectional area, and the strain induced is directly proportional to this stress through the modulus of elasticity.
If...
Elastic Strain Energy for Shearing Stresses01:20

Elastic Strain Energy for Shearing Stresses

As discussed in previous lessons, strain energy in a material is the energy stored when it is elastically deformed, a concept crucial in materials science and mechanical engineering. This energy results from the internal work done against the cohesive forces within the material. When a material undergoes shearing stress and corresponding shearing strain, the strain energy density, which is the energy stored per unit volume, is calculated. Within the elastic limit, where the stress is...
Dynamic Modulus of Elasticity of Concrete01:16

Dynamic Modulus of Elasticity of Concrete

The dynamic modulus of elasticity assesses how a concrete structure deforms under impact or dynamic loads. It is typically higher than the static modulus of elasticity, measured under slow, steady loading conditions.
The sonic test is a common method to determine the dynamic modulus. In this test, a concrete beam, sized either 6 x 6 x 30 inches or 4 x 4 x 20 inches, is clamped at its center. Vibrations are initiated at one end of the beam by an electromagnetic exciter unit powered by a...

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Simulation of the Planetary Interior Differentiation Processes in the Laboratory
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Seismically determined elastic parameters for Earth's outer core.

Jessica C E Irving1, Sanne Cottaar2, Vedran Lekić3

  • 1Department of Geosciences, Princeton University, Princeton, NJ 08540, USA.

Science Advances
|July 3, 2018
PubMed
Summary

Earth's outer core properties were inferred from seismic data, creating a new model (EPOC) that resolves discrepancies between seismic wave types. This model suggests a lighter, more compressible core alloy than previously thought.

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Area of Science:

  • Geophysics
  • Seismology
  • Earth Science

Background:

  • Earth's magnetic field originates from turbulent convection in the liquid iron outer core.
  • Seismic properties of the outer core are crucial for understanding its composition and convection, but discrepancies exist between seismic models.
  • Experimental determination of iron alloy properties at extreme conditions is challenging, hindering compositional inferences.

Purpose of the Study:

  • To infer equation-of-state (EoS) parameters of Earth's outer core directly from seismic normal mode observations.
  • To develop a new seismic model, Elastic Parameters of the Outer Core (EPOC), that is physically realistic and resolves existing discrepancies.
  • To refine understanding of the outer core's composition based on its seismic properties.

Main Methods:

  • Directly inferred EoS parameters from normal mode center frequency observations.
  • Developed the EPOC seismic model with three parameters, ensuring physically realistic behavior with increasing pressure.
  • Compared EPOC model predictions with existing seismic models (PREM) and body wave data.

Main Results:

  • The EPOC model better predicts normal mode frequencies than the Preliminary Reference Earth Model (PREM).
  • EPOC shows improved consistency with body wave-derived seismic models, resolving a long-standing discrepancy.
  • EPOC predicts a lower velocity at the top of the outer core, a steeper velocity gradient with depth, and higher density compared to PREM.
  • These findings imply the outer core alloy is lighter and more compressible than previously inferred for PREM.

Conclusions:

  • The EPOC model provides a more accurate and consistent description of Earth's outer core seismic properties.
  • The inferred composition suggests a lighter, more compressible alloy in the outer core.
  • EPOC's velocity gradient better explains seismic wave travel times, challenging previous models of the uppermost outer core.