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MCE Jon Armour - Coggle Diagram

- - - - Acute: first few weeks
      - Chronic: Develops over time
  - - - Stem is metal but coated iwth HA for better biointegration
      - Ball is made of metal or ceramic, acetabular cup is often UHMWPE but can be ceramic or metal
      - metal/metal joints are worst, metal/ceramic/UHMWPE are best for wear debris and longevity
    - - Three types of graft
        
        Autograft: bone from elsewhere in body
        
        Allografts: Bone from someone else
        
        Synthetic graft: less issue with infection
      - Too high elastic modulus
        
        Implant takes too much of the stress, resulting of resorption of surrounding bone
      - Hydroxyapatite
        
        Correct chemical composition
        
        Lacks strength and toughness
      - Generally restricted to non load-bearing applications, AM is good
    - - Most common is glass based ceramic, 70%lithium disilicate crystals (acicular) embedded in matrix
      - Dental porcelain: glassy alumino-silicate matrix, with embedded crystalline phases e.g. quartz(strength) and pigment phases
        
        :check: Chemically stable, no deterioration, similar thermal conductivity and expansion to enamel
        :red_cross: low tensile strength and fracture toughness, sensitive to surface cracks
      - Zirconia: strongest, toughest but suffers from hydrothermal aging (attacked by moisture)
        
        Phase change (tetragonal :arrow_right: monoclinic) causes volume expansion, causes cracking on expansion \(\therefore\) yttrium used to stabilise the tetragonal phase
        
        Yttria unevenly distributed, less at grain boundaries, grain boundaries attacked by water, causes tranformation to monoclinic and volume change = cracks
        
        Engineering a nanostructure can protect against
- - - - Surface heat treatment: glass sheets heated to plastic state hten quenched. Creates compressive stress, cracks need to overcome this before growth
      - Ion Exchange: replacing some of the sodium ions with larger potassium ions, placing surface into compression
- - - - Soft: multiple layers of high strength woven fibres, bullet is caught by fibre web which absorbs and disperses energy
      - Hard: soft shell with inserts of ballistic steel or ceramic (heavy), sucked for women
    - - On impact, bullet tip is eroded causing hertzian cracks to initiate and conoidal fracture of ceramic
      - Bullet core penetrates ceramic as it erodes, backing material bulges under pressure, core comes to rest in backing material
    - - Al203
        
        Cheapest but high density and only okay mech properties
        
        Oxide means easy sintering but is usually hot pressed or HIP to increase density
        
        Often used as mosaic
      - SiC
        
        Lower density than Al2O3
        
        Hardness, strength and elastic modulus is better
        
        More expensive :moneybag:
      - B4C
        
        Lowest density and highest hardness
        
        Suffers from shatter gap - crystal structure collapses along specific orientations from shock induced amorphisation of the crystal structure
        
        Used in helicopter seats