Basic Mechanical Concepts Flashcards
What are the 2 factors that influence mechanical competence of bones and implants for fracture fixation?
- Material properties
2. Structural properties
What thus material properties characterize?
Characterize the DEFORMATION and FAILURE of material under loading, without considering the geometry of its structure.
How to determine material stiffness?
The material is compressed, and the change in height is measured.
What is strain (or resulting compression)?
Amount of compression divided by the original height
Loading is expressed in terms of stress or strain?
Stress
How to calculate stress?
Divide the load by the area the load is acting upon.
What is Elastic (E-modulus) or Young’s modulus?
It is the expression of stress.
How to calculate E-modulus?
E = stress / strain
E- modulus describes?
Deformation in response to loading within the linear or elastic “working region” of a material.
How to determine strength of a material?
The material must be loaded beyond its elastic region to induce failure.
What is yield strength?
Load at which permanent plastic deformation begins to occur.
What is ultimate strength?
The load at which the material is fractured.
Example of a yield strength?
Contouring a metal plate.
What is ductile?
Represents a large deformation of a material before failure.
Example of a ductile material?
Stainless steel
What is brittle?
It represents very little deformation property before failure.
Example of a brittle material?
Methyl-meth-acrylate
What is fatigue failure?
Repetitive loading below the ultimate strength limit.
What thus repetitive loading below ultimate strength results to?
Micro cracks
What is fatigue limit?
Describes maximal load that will not induce micro-cracks and not lead to fatigue failure, regardless of the loading cycles.
What is a mechanical property where stiffness depends on the loading direction?
Anisotropy
What is a mechanical property where stiffness depends on the loading rate?
Viscoelasticity
What is a mechanical property where stiffness have the same properties regardless of the direction of loading?
Isotropic
What 2 materials are considered isotropic?
Titanium and Stainless steel
A sample of a viscoelastic tissue?
Articular cartilage
What do you call a gradual increase in deformation under constant loading of viscoelastic tissue?
Creep
In fracture surgery, what are the 2 objects with corresponding structural properties being considered?
- Fixation device
2. Bone
True or false, cortical bone is weaker than trabecular bone?
False: trabecular bone is far weaker than cortical bone
Structural stiffness and strength of trabecular bone are defined by this property or characteristic, what is it?
Porosity
What is the range in percentage of porosity of a trabecular bone?
30% - 90% depending on the individual and anatomic location
Method of measuring density of a trabecular bone?
Radiographic densitometry
