Biomechanics



- See:
      - Characteristics of Metals and Implants:
      - Elastic Strain
      - Metal Fatigue
      - Plates
      - Polyethylene
      - Screws
      - Strain
      - Stress
      - Ultimate Tensile Strength:
      - Visoelastic Materials
      - Yield Strength:
      - Young Modulus

- Biomechanical Definitions:
    - isotropic materials: possess the same properties in all directions;
    - anisotropic materials: have mechanical properties that vary w/ orientation of the loading;
    - brittle materials:
         - have little ability to exhibit plastic deformation, and therefore, exhibits a linear stress
         - strain curve up to the point of failure;
    - ductile materials:
         - undergo a large amount of plastic deformation prior to failure;
         - measure of a metal's ability to withstand considerable plastic deformation w/o breaking;
    - rigidity:
         - bending rigidity for a rectangular plate: base * ht(exp 3) / 12
         - torsional rigidity for a cylindrical rod: c * pi * r (exp 4) / l
    - endurance limit (fatigue limit)
         - the maximum stress under which a material will not fail when subjected to indefinite cyclic loading;
    - fatigue strength:
         - refers to the maximum cyclic load (10 million cycles) that a standard sized metal can absorb before fracturing;
    - toughness:
         - ability of a metal to absorb energy by bending without breakage (the strain energy in the metal at the point of ultimate stress;
         - it is the area under the stress strain curve;
               - energy a structure absorbs as it deformed by applied force is equal to the work done by that force;
    - creep:
         - describes the amount of deformation that a material undergoes with time as it is subjected a constant load;
         - when subjected to a constant load the deformation will reach a state of equilibrium;
    - moment of inertia:
         - refers to resistance to rotation


- Stress Strain Curve:
    - derived by axially loading a body and plotting stress vs strain;
    - proportional limit (yield point) is transition from elastic to plastic range; usually 0.2% strain in most metals;
    - ultimate tensile strength;
    - break point:
         - if strain increases, a point will come when the material fails;
    - plastic strain:
         - if greater stress is applied to the material, its power to recover may be exceeded, and it remains permanently deformed;
    - plastic deformation
         - change in length after removing load (before breaking point) in plastic range;

      |  1 Al2O3(ceramic)
      |     2 Co-Cr-Mo (Alloy)
      |        3 Stainless steel
  S |           4 Titanium
  t   |              5 Cortical Bone
  r   |                 6 Matrix polymers
  e  |                    7 PMMA
  s  |                      8 Polyethylene
  s  |                         9 Cancellous bone
      |                            10 Tendon/ligament
      |                                11 Cartilage
      |
      |__________________________________________
                                           Strain



- Links:

    Muller Institute for Biomechanics

    Berkely Orthopaedic Biomechanics

    Biomechanics Magazine

    Department of Orthopaedic Research and Biomechanics - University of Ulm

    Biomechanics World Wide



Original Text by Clifford R. Wheeless, III, MD.

Last updated by Data Trace Staff on Friday, September 9, 2011 12:33 pm