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Once a structire has developed a crack or a flaw, the stress required to fracture that structure is determined by:
- 1.Material properties: fracture toughness
- 2 structural geometry
- 3. length and location of crack
Define the endurance limit of a material.
The endurance limit is the when the number of cycles in infinite due to the applied stress being very low.
Explain how both dry friction and lubricant film friction are affected by the area of contact between the involved structures.
Dry friction is independent of area of contact. Lubricant film friction takes into account the area of fluid contact.
Briefly explain what is meant by shear thinning, in relation to lubricant film friction.
Shear thinning describe that the faster you move the less resistance you will encounter, which is related to lubricant film friction since it takes into account velocity (rate dependent).
Briefly explain the difference between creep and load-relaxation, in relation to viscoelastic behaviour.
Creep is a tissue held under constant load where the deformation is continuous increasing and the levels off. Load relaxation is where the deformation is induced at constant unchanging length and the stress on the tissue increases to the ramp loading and then gradually decreases and levels off to equilibrium.
Briefly explain how increasing the rate at which stress is applied to a viscoelastic material is likely to affect its yield stress and yield strain. Provided one potential benefit and one potential drawbacks of this with respect to tissue injury.
- The faster the loading rate the higher the elastic modulus (stiffness), the less it will deform overall (lower yield strain) and the higher the yield stress it will withstand.
- It can withstand higher loads on the joints and bones but if the load is too high then the yield strain becomes lower and
- it takes less deformation to injure.
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