6834 Lecture Notes - Lecture 9: Pivot Turn, Bone, Transverse Plane
21 Jun 2018
School
Department
Course
Professor
Mechanics of biological materials
- Axial stresses
oTension: stresses that pulls the object apart
oCompression: stress that pushes the object together
oShear: stress that acts in the transverse plane pushes the object together
- Mechanical load
oBending – creates both bending and compressive forces, deforms by curving
Smaller distance = more force for more torque
Larger distance = less force needed
oTorsion – twisting. Torsion is loading in bones is common in many situations ie stop
pivot turn actions
oCombined – head of femur
- Bone
oStructure
Composite material
1) cortical (compact bone)
2) trabecular (cancellous bone)
Biomechanical properties of the bones are similar
Only differ in porosity ad density
Cortical bone is more dense
Trabeculae bone is more porous
oAs a material
Bones mechanical properties related to their function
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oBone is anisotropic; it exhibits different strength and stiffness in response to forces
applied from different directions
oCompression strength approx. 200MPa
oTensile strength approx. 125 MPa
oShear strength approx. 75 MPa (Steel approx. 500 MPa)
oBone is strongest in resisting compressive stress and weakest in resisting shear
stress
- Bone and rate of loading
oStrain rate
Modulus of elasticity or stiffness and strength of bone increase with loading
rate
Body able to withstand great stresses during traumatic activities
Bone is viscoelastic
Touch and has some bending capacity because of collagen
o
- Bone as a material – effects of age and activity
oAfter 35yo lose stiffness in bone 2.3% every decade
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Axial stresses: tension: stresses that pulls the object apart, compression: stress that pushes the object together, shear: stress that acts in the transverse plane pushes the object together. Mechanical load: bending creates both bending and compressive forces, deforms by curving. Smaller distance = more force for more torque. Larger distance = less force needed: torsion twisting. Torsion is loading in bones is common in many situations ie stop pivot turn actions: combined head of femur. Composite material: cortical (compact bone, trabecular (cancellous bone) Trabeculae bone is more porous: as a material. Bones mechanical properties related to their function: bone is anisotropic; it exhibits different strength and stiffness in response to forces applied from different directions, compression strength approx. 500 mpa: bone is strongest in resisting compressive stress and weakest in resisting shear stress. Bone and rate of loading: strain rate. Modulus of elasticity or stiffness and strength of bone increase with loading rate.
