KIN3309 BIOMECHANICS Lecture 2 Foundations of Human Movement Skeletal System Beom Chan Lee PhD Department of Health Human Performance University of Houston Hierarchy of Stuff 2 Steel Bone more complex Structural system Structure Material Based on the instructor resources from LWW 2014 Types of Solid Materials 3 Tensile materials Resist being pulled on Resist tensile stress Examples Silk Collagen found in tendons skin bone muscle and more Based on the instructor resources from LWW 2014 Types of Solid Materials 4 Pliant materials Must deform to function properly Examples Rubbers Elastin Pliant found in skin and arterial wall composites Composite mix of materials Examples Mucus Synovial fluid joint lubricant Cartilage in ears nose intervertebral disks Based on the instructor resources from LWW 2014 Types of Solid Materials 5 Rigid materials Resist stress without much deformation Rigid biological materials are nearly all composites Examples Bone Keratin hair fingernails horn feathers Wood biological ceramics dentine and enamel in teeth mollusk shells eggshells Based on the instructor resources from LWW 2014 Stress and Strain 6 A A F F Stress force applied per unit area Area is usually a cross sectional area F A measured in N m2 Pascal or lb in2 psi In other words pressure Based on the instructor resources from LWW 2014 Stress and Strain 7 tensile compressive A A F F Stress Tensile stress tension pulling Compressive stress compression pushing Based on the instructor resources from LWW 2014 Stress and Strain 8 L L L L A tension A F F compression Strain deformation caused by applied stress L L L original length L change in length Dimensionless often put in terms of change in length Based on the instructor resources from LWW 2014 Stress and Strain 9 Materials testing Tension Compression Based on the instructor resources from LWW 2014 Stress and Strain 10 The stress strain curve The slope of the curve is a measure of stiffness k or E stress strain known as the elastic modulus aka Young s modulus Material Young s modulus Sea anenome mesoglea 0 01 Aorta pig 0 5 Cartilage 20 Tendon 1 500 Wood dry with grain 10 000 Tooth dentine 15 000 Bone 18 000 Tooth enamel 60 000 Steel 200 000 Based on the instructor resources from LWW 2014 Stress Strain Curve 11 Yield point Up to yield point structure is in its elastic region Past the yield point is the structure s plastic region Failure If the applied force continues past the plastic region the tissue will eventually fail Based on the instructor resources from LWW 2014 Stress Strain Curve 12 Elastic material Linear relationship between the stress and strain Viscoelastic material Non linear relationship between the stress and strain Based on the instructor resources from LWW 2014 Stress Strain Curve 13 Based on the instructor resources from LWW 2014 Stress Strain Curve 14 In the elastic region an item will return to its original shape In the plastic region an item changes shape permanently Based on the instructor resources from LWW 2014 Stress Strain Curve 15 strength Point of failure The point where the item breaks Strength the load at failure Stress and Strain 16 Residual strain The difference between the original length of the material and the resting length resulting from stress into the plastic region Based on the instructor resources from LWW 2014 Stress and Strain 17 Safety factor strength typical load e g failure stress typical stress Engineers usually use values 5 to 10 Human tibia bone failure during jogging Based on the instructor resources from LWW 2014 Stress and Strain 18 Energy The energy stored put in when a stress is applied is proportional to the area under the curve Based on the instructor resources from LWW 2014 Stress and Strain 19 Energy can be recovered when the stress is relieved Based on the instructor resources from LWW 2014 Stress and Strain 20 A perfect elastic material would recover all of the energy put in A viscoelastic material only recovers a portion of the energy put in Based on the instructor resources from LWW 2014 Stress and Strain 21 Isotropic materials behave the same way regardless of the direction of the applied force Anisotropic materials behave differently when loaded from dierent directionsples wood meat bone Based on the instructor resources from LWW 2014 Stress and Strain 22 Isotropic materials behave the same way regardless of the direction of the applied force Examples glass metals Anisotropic materials behave differently when loaded from different directions Examples wood meat bone Based on the instructor resources from LWW 2014 Stress and Strain 23 A F How can we reduce stress Increase area Decrease load A A F F Based on the instructor resources from LWW 2014 Quiz 24 Stress is a The ration of the change in length to the resting length b The amount of force at a particular strain c The stored mechanical energy d The force per unit area Based on the instructor resources from LWW 2014 Quiz 25 Which is not a part of the stress strain curve a Elastic region b Nylon region c Yield point d Plastic region Based on the instructor resources from LWW 2014 Musculoskeletal System 26 The system of muscles and tendons and ligaments and bones and joints and associated tissues that move the body and maintain its form Anatomy Bones Ligaments Tendons Muscles Based on the instructor resources from LWW 2014 Functions of the Skeleton 27 Leverage Support Protection Storage Blood cell formation Critically important for movement Based on the instructor resources from LWW 2014 Architecture of Bone 28 Bone Matrix of inorganic salts and collagen Bone cells Osteocytes Transport metabolites sense mechanical stress communication Osteoblasts Cells that create bone deposition Osteoclasts Cells that resorb bone resorption Osseous Bone tissue Cortical Compact very dense outer layer Cancellous Spongy very porous inner layer Based on the instructor resources from LWW 2014 Types of Bone Tissue 29 Types of bone tissue Cortical bone Compact bone Dense Outer layer of bones Made of many layers Stiff strong Cancellous bone Sponge bone Porous Inner region of bones Trabeculae tiny beams Adapt to direction of loading Add strength without adding much weight High energy absorption Not as strong as cortical bone Based on the instructor resources from LWW 2014 Types of Bones 30 Long Ulna clavicle femur Short Tarsals Flat Ribs scapula sternum Irregular Skull carpals vertebrae Sesamoid Patella Based on the instructor resources from LWW 2014 Bone Tissue