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We derived that the stress tensor is symmetric. Is this due to force or moment equilibrium of the material element? |
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Definition
Due to the moment equilibrium
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| What is the difference between a body force and a boundary force? |
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Definition
| Body forces act across the whole object, not just across the boundary layer |
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| Give an example of a body force. |
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Definition
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| What does moment equilibrium of the stresses on an infinitesimal material element tell us about the stress tensor? |
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Definition
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| There are never shear stresses on the principal planes. |
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Definition
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| What is the name of the stress state for which the stress field does not change with rotation? |
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Definition
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| What are the principal stresses? |
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Definition
Stresses where the shear stress is zero and normal to principle planes
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| What are the assumptions for plane stress? |
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Definition
| τxy, τyz, and σz are all zero |
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§ Give one example of a structure for which plane stress is a good assumption. Why?
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Definition
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| The equations of equilibrium apply to a material that is elastic or inelastic. |
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Definition
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| The condition l2+m2+n2 = 1 always holds. |
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Definition
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§ Label the stresses on an infinitesimal material element.
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Definition
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| What is the definition of τxy? |
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Definition
o The Shear stress on the x plane in the y direction
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| The maximum normal stress vector is always oriented 90° from the minimum normal stress vector. |
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Definition
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| The maximum shear stress is always one-half the difference between the maximum and minimum principal stresses. |
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Definition
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§ What are rigid body motions?
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Definition
| Movement of the body with no deformation |
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| Any rigid body motion can be written in terms of a ____ and a ____ |
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Definition
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| Do we use engineering strain or tensor strain in this course? |
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Definition
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| What are the principal strains? |
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Definition
o There are two mutually perpendicular planes on which the shear strain γ is zero and normal to which the direct strain is at a maximum or minimum
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| What are the assumptions for plane strain? |
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Definition
o Principle strain in the longest direction can be assumed to be zero
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§ Why do strain fields have to satisfy the compatibility equations?
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Definition
| Because the displacement fields have to be continuous |
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| A structure in a state of plane stress is also in a state of plane strain. |
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Definition
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| Draw the definition of engineering strain and tensor strain |
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Definition
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| Sketch a stress vs. strain curve for one loading-unloading cycle for a material that is (a) elastic and (b) inelastic. |
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Definition
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| What is the difference between an isotropic and orthotropic material? |
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Definition
o Orthotropic materials’ elastic properties change depending on the direction of loading
o Isotropic materials’ elastic properties are the same no matter the direction of the loading
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| A viscoelastic material is one for which creep deformations are significant. |
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Definition
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§ A material constitutive law relates which 2 parameters?
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Definition
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| Stress is a single-valued function for an elastic material. |
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Definition
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| Stress is a single-valued function for an inelastic material. |
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Definition
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| An orthotropic material has how many Poisson’s ratios? |
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Definition
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| An orthotropic material has how many elastic modulii? |
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Definition
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Definition
o Weight loaded (stress held constant) strain measured
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§ Describe a stress relaxation test.
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Definition
| specimen is deformed a given amount (Strain held constant) and decrease in stress is recorded over period of time |
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§ Draw the spring-damper equivalent for the Maxwell model of a viscoelastic material.
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Definition
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§ Draw the spring-damper equivalent for the Voigt model of a viscoelastic material.
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Definition
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| What is the physical meaning of the principal axes of a beam section? Do they depend on the applied loading? |
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Definition
| Axes about which bending moments are uncoupled. Not dependent on loading |
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| What is the physical meaning of the neutral axis of beam section? Does it depend on the applied loading? |
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Definition
| Axis about which the stress σz equals zero when a bending moment is applied. It is dependent on applied loading |
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§ For a beam in bending, the Neutral Axis always passes through the centroid of the
§ beam section.
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Definition
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§ For a beam in bending, the Principal Axes always pass through the centroid of the
beam section.
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Definition
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| All moments of inertia of a cross-section must be greater than zero. |
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Definition
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| For a symmetric section, the principal axes are the axes of symmetry |
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Definition
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§ What is the “rule of thumb” criteria for a section to be considered thin-walled?
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Definition
o Thickness is 1/10th the length
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§ What is the physical meaning of a shear center?
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Definition
Point about which moment due to shear flow is zero
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§ For what types of thin-walled sections are the shear-center and centroid located at the same point?
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Definition
o Sections with two axis of symmetry
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§ For a typical aircraft wing section the axial load is resisted by the (a) stringers, (b) skin or (c)
both. (Choose a b or c ).
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Definition
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§ For a typical aircraft wing section the axial load is resisted by the (a) stringers, (b) skin or (c) both. (Choose a b or c ).
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Definition
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§ For a typical aircraft wing section the shear load is resisted by the (a) stringers, (b) skin or (c)
both. (Choose a b or c ).
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Definition
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§ For a typical aircraft wing section torsion is resisted by the (a) stringers, (b) skin or (c) both.
(Choose a b or c ).
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Definition
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§ We neglected the hoop stress in our calculation of thin-walled beams. For what aircraft
structure would this stress component be important? |
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Definition
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| We assume that open sections support shear loads. |
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Definition
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§ For a thin-walled closed section, the shear flow due to a torque is constant
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Definition
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§ For a thin-walled closed section, the shear stress due to a torque is constant
throughout the section.
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Definition
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§ For multi-cell sections, what condition do we impose at junctions to determine the amount of torque supported by each cell?
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Definition
o Shear Flow in = Shear Flow out
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| We assume that open sections support torques. |
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Definition
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| Draw the spring-damper equivalent for the Voigt model of a viscoelastic material. |
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Definition
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