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


Term
What does moment equilibrium of the stresses on an infinitesimal material element tell us about the stress tensor? 

Definition


Term
There are never shear stresses on the principal planes. 

Definition


Term
What is the name of the stress state for which the stress field does not change with rotation? 

Definition


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
τ_{xy}, τ_{yz}, and σ_{z} are all zero 


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


Definition


Term
The equations of equilibrium apply to a material that is elastic or inelastic. 

Definition


Term
The condition l^{2}+m^{2}+n^{2 }= 1 always holds. 

Definition


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


Term
The maximum shear stress is always onehalf the difference between the maximum and minimum principal stresses. 

Definition


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


Term
Do we use engineering strain or tensor strain in this course? 

Definition


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


Term
Draw the definition of engineering strain and tensor strain 

Definition


Term
Sketch a stress vs. strain curve for one loadingunloading 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


Term
§ A material constitutive law relates which 2 parameters?


Definition


Term
Stress is a singlevalued function for an elastic material. 

Definition


Term
Stress is a singlevalued function for an inelastic material. 

Definition


Term
An orthotropic material has how many Poisson’s ratios? 

Definition


Term
An orthotropic material has how many elastic modulii? 

Definition


Term

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 springdamper equivalent for the Maxwell model of a viscoelastic material.


Definition


Term
§ Draw the springdamper equivalent for the Voigt model of a viscoelastic material.


Definition


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 σ_{z} 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


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


Definition


Term
All moments of inertia of a crosssection must be greater than zero. 

Definition


Term
For a symmetric section, the principal axes are the axes of symmetry 

Definition


Term
§ What is the “rule of thumb” criteria for a section to be considered thinwalled?


Definition
o Thickness is 1/10^{th} 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 thinwalled sections are the shearcenter 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


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


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


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


Term
§ We neglected the hoop stress in our calculation of thinwalled beams. For what aircraft
structure would this stress component be important? 

Definition


Term
We assume that open sections support shear loads. 

Definition


Term
§ For a thinwalled closed section, the shear flow due to a torque is constant


Definition


Term
§ For a thinwalled closed section, the shear stress due to a torque is constant
throughout the section.


Definition


Term
§ For multicell 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


Term
Draw the springdamper equivalent for the Voigt model of a viscoelastic material. 

Definition

