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Structures
Final Short Answer Questions
55
Aerospace Engineering
Undergraduate 4
12/08/2010

Additional Aerospace Engineering Flashcards

 


 

Cards

Term

 We derived that the stress tensor is symmetric. Is this due to force or moment equilibrium of the material element?

Definition

Due to the moment equilibrium

 

Term
What is the difference between a body force and a boundary force?
Definition
Body forces act across the whole object, not just across the boundary layer
Term
Give an example of a body force.
Definition
Gravity
Term
What does moment equilibrium of the stresses on an infinitesimal material element tell us about the stress tensor?
Definition
That it is symmetricU�kB
Term
There are never shear stresses on the principal planes.
Definition
True
Term
What is the name of the stress state for which the stress field does not change with rotation?
Definition
Hydrostatic Stress
Term
What are the principal stresses?
Definition

 

 

Stresses where the shear stress is zero and normal to principle planes

 

 

Term
What are the assumptions for plane stress?
Definition
τxy, τyz, and σz are all zero
Term

§  Give one example of a structure for which plane stress is a good assumption. Why?

Definition
Sheet metal
Term
The equations of equilibrium apply to a material that is elastic or inelastic.
Definition
True
Term
The condition l2+m2+n2 = 1 always holds.
Definition
False
Term

§  Label the stresses on an infinitesimal material element.

Definition
Term
What is the definition of τxy?
Definition

o   The Shear stress on the x plane in the y direction

Term
The maximum normal stress vector is always oriented 90° from the minimum normal stress vector.
Definition
True
Term
The maximum shear stress is always one-half the difference between the maximum and minimum principal stresses. 
Definition
True
Term

§  What are rigid body motions?

Definition
Movement of the body with no deformation
Term
Any rigid body motion can be written in terms of a ____ and a ____
Definition
Translation & a Rotation
Term
Do we use engineering strain or tensor strain in this course?
Definition
Engineering Strain
Term
What are the principal strains?
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

Term
What are the assumptions for plane strain?
Definition

o   Principle strain in the longest direction can be assumed to be zero

Term

 

§  Why do strain fields have to satisfy the compatibility equations?

 

Definition
Because the displacement fields have to be continuous
Term
A structure in a state of plane stress is also in a state of plane strain. 
Definition
False
Term
Draw the definition of engineering strain and tensor strain
Definition
[image]
Term
Sketch a stress vs. strain curve for one loading-unloading cycle for a material that is (a) elastic and (b) inelastic.
Definition
Term
What is the difference between an isotropic and orthotropic material?
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

 

Term
A viscoelastic material is one for which creep deformations are significant.
Definition
True
Term

§  A material constitutive law relates which 2 parameters?

Definition

o   Stress and Strain

Term
Stress is a single-valued function for an elastic material. 
Definition
True 
Term
Stress is a single-valued function for an inelastic material.
Definition
False
Term
An orthotropic material has how many Poisson’s ratios? 
Definition

o   Up to 6

Term
An orthotropic material has how many elastic modulii?
Definition

o   Up to 3

Term

§  Describe a creep test. 

Definition

o   Weight loaded (stress held constant) strain measured

Term

§  Describe a stress relaxation test.

Definition
specimen is deformed a given amount (Strain held constant) and decrease in stress is recorded over period of time 
Term

§  Draw the spring-damper equivalent for the Maxwell model of a viscoelastic material.

Definition
Term

 

§  Draw the spring-damper equivalent for the Voigt model of a viscoelastic material.

 

Definition
[image]
Term
What is the physical meaning of the principal axes of a beam section? Do they depend on the applied loading?
Definition
Axes about which bending moments are uncoupled.  Not dependent on loading
Term
What is the physical meaning of the neutral axis of beam section? Does it depend on the applied loading?
Definition
Axis about which the stress σz equals zero when a bending moment is applied.  It is dependent on applied loading
Term

§  For a beam in bending, the Neutral Axis always passes through the centroid of the

§  beam section.

Definition
True
Term

§  For a beam in bending, the Principal Axes always pass through the centroid of the

beam section.

Definition
False
Term
All moments of inertia of a cross-section must be greater than zero.
Definition
False
Term
For a symmetric section, the principal axes are the axes of symmetry
Definition

True

Term

§  What is the “rule of thumb” criteria for a section to be considered thin-walled? 

Definition

o   Thickness is 1/10th the length

Term

 

§  What is the physical meaning of a shear center?

 

Definition

 

Point about which moment due to shear flow is zero

 

Term

§  For what types of thin-walled sections are the shear-center and centroid located at the same point?

Definition

o   Sections with two axis of symmetry

Term

§  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 ).

Definition
(a) stringers
Term

§  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 ).

Definition
(a) stringers
Term

 

§  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 ).

 

Definition

 

§  (c) both

 

Term

§  For a typical aircraft wing section torsion is resisted by the (a) stringers, (b) skin or (c) both.

(Choose a b or c ).

Definition
(c) both.
Term

§  We neglected the hoop stress in our calculation of thin-walled beams. For what aircraft

structure would this stress component be important?

Definition
Fuselage
Term
We assume that open sections support shear loads.
Definition
True
Term

§  For a thin-walled closed section, the shear flow due to a torque is constant

Definition

True

Term

 

§  For a thin-walled closed section, the shear stress due to a torque is constant

throughout the section.

 

Definition
False
Term

 

§  For multi-cell sections, what condition do we impose at junctions to determine the amount of torque supported by each cell?

 

Definition

 

o   Shear Flow in = Shear Flow out

 

Term
We assume that open sections support torques.
Definition
False
Term
Draw the spring-damper equivalent for the Voigt model of a viscoelastic material.
Definition
[image]
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