Fundamental Principles: Part I Flashcards
Who said “Selection of the correct material for a given design depends partially on understanding the elementary principles of mechanics and materials, concepts of forces, deformation and failure of structures under load, improvement in mechanical properties by heat treatment or other means, and design of structures”
Thomas Lunsford
Vertical pylons experience a force ______ _________
Directly downward
_______ _________ experience a torque at the foot plate near the proximal end of the ankle joint
Foot orthoses
Equation for torque
T= F x L
Equation for stress
Stress = F (force) / Ao (initial cross-sectional area)
Equation for strain
Strain - Delta L (change in length) / Lo (initial length)
The “o” in Ao and Lo stand for?
Initial
_______ and _______ represent normalized quantities of force and deformation
Stress and strain
What are the four primary types of stress?
Compression, tension, shear, and bending
Type of stress that pushes together
Compression
Type of stress that pulls apart
Tension
Type of stress that makes a scissoring action
Shear
Type of stress that makes a flexing action
Bending
If area of ________ surface increases, shear stress decreases
Bonded
In bending, ________ on top and ________ on bottoms
Compression, tension
What are the two forms of shear stress?
Deformation by shear force and by torsion.
Why is it important for O/P practice to have a basic understanding of material science?
Practitioners use their materials knowledge to design solutions and fabrication procedures to create devices that support a patients goals
The loading scenario from force and torque is
Stress
The materials behavior resulting from stress
Strain
a ______ ________ relationship usually occurs between stress and strain
Positive linear
How low stress, stress and strain are _________ proportional
Directly
Materials stiffness or resistance to plastic deformation
Modulus of elasticity
Hookes law equation
Stress = strain x constant (young’s modulus)
A material that requires relatively large amounts of stress to produce small amounts of strain
High stiffness
A material that requires relatively small amounts of stress to produce large amounts of strain
Low stiffness
True or False: the modulus of elasticity is NOT effected by temperature
False
As temp increases, stiffness ______
Decreases
Elastic elongation and strain are produced _________ to applied tensile force
Parallel
Deformation nor recovered from release of stress (this is permanent)
Plastic deformation
Beyond the ________ range, plastic deformation will take place
Elastic
On a stress strain graph, what is the proportional limit?
It marks the limit where a material cannot return to its original shape
Most common tensile strength test
Uniaxial tensile testing
Test used to calculate stress and strain
Uniaxial tensile testing
Max that a material can handle before failure
Tensile stress
The ability of a material to resist forces
Strength
Defined as force per unit of the cross-sectional area of material
Stress
The geometric lines that compose a prismatic beam in flexural stress
Fiber
The point at which the material begins to maintain a deformation change
Yield stress
Stress at which a material ruptures
Ultimate stress
If a material lengthens or shortens in response to stress, it is said to experience
Strain
The region where the slope is a straight line is called the
Elastic region
Defined as the point of application of the result of a uniformly distributed force acting on the area
Centroid of an area
