Mechanical Properties of Materials Flashcards
What are 4 concepts in regards to mechanical properties of bone
- Bone has good fracture toughness = strong = risk of fracture
- 1 downward force on the compressive surface = shorter (drawn together)
- 2 upward forces on the tensile surface= longer
- Neutral axis/plane: the place where the forces are neither compressive or tensile
Why are having hallow bones important?
- Has a resistance for bending
- Larger diameter= stronger = more resistant
Why is an oval cross section for bone is better than round-cross section?
Pixel of bones are further away = increased distance = increased pixel of bones with resistance
What is stress?
Force/area
What is strain?
change in length/original length
What is permanent set/offset?
Damage of material- Doesn’t go back to original
What is elasticity?
- The ability of a solid to recover its shape when the deforming forces are removed
- Regardless of stiffness
- Deformation depends on Hooke’s law
- Deformation is proportional to the applied stress up to a certain point= elastic limit/yield point
- Beyond this point, will cause permanent deformation
What is compliance?
Ability to deform under force
Tendons have a _____ structure.
helical
2 components of tendons
- • Tropo-collagen strands to become larger and larger structures
- Start with collagen Microfibrils fibrils fibres fascicle tendon
- When a crimp is straightened, tendons behave elastically until failure
What is viscoelasticity?
- • Relationship between stress and strain dependent on time
- Constant stress = strain with time (creep)
- Constant strain = stress with time (relaxation)
When loaded slowly, reacts in a ____ fashion
Ductile
When loaded quickly, react in a ____ fashion
Brittle
The effective stiffness depends on _______ of the load. Why?
rate of application
- Higher the loading rate = the stiffer, stronger and more energy stored
- More cracks or pieces created o Area under the curve = energy stored
If cyclic loading is applied, _______ occurs dissipation of mechanical energy
hysteresis (a phase lag)
- Tendon gets stretched and recoiled
- 95% of energy can be reused
- 5% is lost as internal friction (heat)
Rebound of an object following impact is less than ____%
100%
- Heel fat pads held together by collagen
- Rebound is 70%, allowing them to recover/reform between foot-strike
- Provides cushioning during repeated loading and unloading
What is an isotrophic material?
A homogenous material that looks the same in every direction and exhibits material properties that are not orientation-dependent
What is an anisotrophic material?
- Behaviour changes based on microstructure
- Orientation-dependent
- Eg. bone is better at resisting longitudinal load than other directional load
Ligaments have a fairly _____ structure.
Uniform
4 components of ligaments
- Similar length pieces of collagen
- Short
- Bone to bone (over joints)
- Contains elastin o modulus
- extensibility o strength
Ligaments VS tendons during failure
-
Ligaments break in parts = graded failure
- If loading stops, might recover
- Tendons break all together = abrupt failure
Ligaments have a ___ failure.
Graded failure - break in parts If loading stops, might recover
Tendons have a ____ failure
Abrupt failure- break all together
_____ held in a pressurized fluid-gel matrix in cartilage
Collagen fibrils
Collagen is resistant to ______ forces.
Compressive
Cartilage has ______ to decrease wear and tear.
Synovial fluid. With synovial fluid = low coefficient of friction= smooth movements = little wear and tear (except osteoarthritis)
Most cells have a _____ no. of times that they can repair and regenerate. ______ occurs when the tissue has been worn out
finite Cell death
What is mechanotransduction?
• Physical adaptation • Pathological fracture healing • Therapeutic distraction osteogenesis Includes 4 stages: 1. Mechanocoupling o transduction of physical forces to a mechanical signal, which is sent to the sensor cells 2. Biochemical coupling o mechanical signal is converted into a biochemical signal 3. Transmission of signal from sensor cell to effector ell 4. Effector cell response • Mechnical stimulation of specific pathways and genes can enhance proliferation and differentiation of osteoblasts
