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31/08/16
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Lecture 2
Building stones of the human body: bone, car?lage, tendons and
ligaments
Bone (Ref. N&F: first part of chapter 2, E&S chapter 9)
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Bone material
!
Duc?le – large plas?c deforma?on BriNle –
no plas?c deforma?on
A long skeletal bone
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!
Blood vessel
Small channels
Hollow space
Bone cells
Periost
!
Cor?cal bone (compact bone)
Diameter of an osteon: around 0.2 mm
!
Cancellous bone (spongy bone)
!
Femoral head
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Cor?cal vs cancellous bone
Stored
ene
rgy
Stored energy
Anisotropic material behaviour
!
femoral shaT (lårbenshals)
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Different loading cases
• Compression • Tension • Bending • Shear • Torsion … or in combina?ons!
How much can bone take? • σu≈ 200 MPa in compression • σu≈ 130 Mpa in tension • σu≈ 65 MPa in shear (adult cor?cal bone)
Failure modes
!
Tension: debonding
!
Tensile fracture through the calcaneus caused by strong contradic?on of the Achilles tendon.
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Failure modes (cont.)
!
Compression: cracking
!
Compression fractures of the femoral necks (electric shock theraphy)
Car?lage (in brief)
Car?lage cell -‐ chondrocyte
Elas?c threads -‐collagen
Surrounding substance – chondroi?n
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Ar?cular car?lage
!
Articular cartilage
Func?on: • spread out the loads • allow rela?ve mo?on with minimum fric?on and wear socket
Synovia (ledvätska) Capsule
(ledkapsel) ball
!
Tendons (senor) • Cells: tendocytes • Extracellular matrix (ECM):
collagen, elas?n
Tendons and ligaments (Ref. N&F: chapter 4, E&S chapter 9)
Ligaments • Collagen, elas?n,,
proteoglycans
Anterior cruciate ligament
(främre korsbandet)
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• Protein • Trippel helix of polypep?de
chains • Can be found in bone,
tendons, intervertebral discs, ligaments and skin
Collagen
• Protein. • Can be founded in skin,
walls of blood vessels, ligaments.
• A liNle bit viscoelas?c
Elas?n
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Tendon
!Tendon sheath (senskida)
Ligaments
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Fiber structures
Unloaded ligament
Loaded ligament
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Tension tests of two different ligaments
Much collagen
Much elastin
From: Illustra?ve examples Biomechanics, LTH, 2015
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5. Consider the question of the strength of human tissues and their margin of safety when we exercise. Take the example of the tension in the Achilles tendon in our foot when we walk and when we jump. The bone structure of the foot is shown the figure. To calculate the tension in the Achilles tendon we may consider the equilibrium of forces that act on the foot. The joint between the tibia and the talus bones may be considered as a pivot.
6. The head in the picture below is considered as a rigid body for the present purpose. It rocks on the occipital condyles C where an axial force FA, a shear force, V, and a neck torque To, resist motion. An uppercut (treated as an instantaneous load B at an angle of 63o to the horizontal) is applied to the chin, and the initial linear acceleration, a, of the mass centre, G, is photographically determined to be 140g. For a head mass of 3.5 kg, a moment of inertia about an axis perpendicular to the sagittal plane of 0.0356 kg m2, and the dimensions shown, what are the reactions at the occipital condyles if torque T0, which requires muscle activation, is temporarily neglected?