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KIN 3309: CHAPTER 2
Stress |
Force applied to given area (causes strain)
Force applied to deform a structure
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Stress Equation
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Pascal |
N/m²
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Strain |
internal change in tissue resulting in deformation
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Strain equation
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Elastic Modulus
(Stiffness)
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Safety factor
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The working load of a component is 20-25% of the breaking strength.
SF= 5-10 times the stress that would normally be placed on the structure
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Stored Mechanical Energy
(equation)
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ME = ½σε
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Elastic Material
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A material that exhibits only elastic properties on a stress-strain curve
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Elastic region of stress-strain relationship
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strain is proportional to applied stress (linear relationship)
when stress is removed, material returns to resting length
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In elastic material the mechanical energy stored is?
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fully recovered
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Viscoelastic
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a material whose deformation is affected by both the rate of loading and the length of time that it is subjected to a constant load
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Hysteresis
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the loss of energy through the process of loading and then unloading
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lacunae
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spaces within bone matrix; appear as dark spots between lamellae
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Lamellae
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Layers of bone matrix in compact bone tissue
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osteocytes
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- osteoblast has become surrounded
in matrix
- maintains bone matrix
- resides in lacunae
- helps in Ca2+ homeostasis
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Osteoblast |
Produce organic fibers on which the calcium salts are deposited
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Osteoclasts
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break down bone and convert calcium salts into a soluble form that passes easily into the blood
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Cortical Bone =
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Compact bone
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Cortical bone makes up about what percentage of the skeleton?
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80%
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Cortical Bone Characteristics
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Dense
Porosity of less than 15%
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Does cortical bone have passageways for BV and nerves?
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Yes
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Porosity |
Ratio of pore space to the total volume
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When porosity increases bone mechanical strength _______?
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Deteriorates
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Tensile materials
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Resist being pulled on
ex: silk, collagen
⇒tendons, skin, bone, muscle
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Pliant materials
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Must deform to function properly
ex: rubber, elastin
→skin, arterial wall
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Composite
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= mix of materials
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Osteon/Haversion system function
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provide strength and stiffness to the skeletal system
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Osteons are oriented in what direction to the stresses placed on the bone?
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parallel
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Cortical bone can withstand high levels of stress in what direction?
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longitudinal
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Trabeculae
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irregular latticework of thin plates of spongy bone tissue
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The roles of Short bones
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Shock absorption and transmission of forces
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Role of sesamoid bone
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alter the angle of insertion and to diminish friction created by the muscle
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Role of flat bones
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protect internal structures and offer broad surfaces for muscular attachment
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Roles of irregular bones
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supporting weight, dissipating loads, protecting the spinal cord, contributing to movement, and providing sites for muscular attachment
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Ossification
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The formation and development of bone connective tissue by the activity of the osteoblasts and osteoclasts
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