KIN 300 Scott Fall 2016 Ch 9 lecture notes
KIN 300 Scott Fall 2016 Ch 9 lecture notes KIN 300
Long Beach State
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This 3 page Class Notes was uploaded by Natalie Wong on Sunday September 11, 2016. The Class Notes belongs to KIN 300 at California State University Long Beach taught by Kristen Scott in Fall 2016. Since its upload, it has received 4 views. For similar materials see Biomechanics in Kinesiology at California State University Long Beach.
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Date Created: 09/11/16
KIN 300: Fall 2016 – Week 3 Natalie Wong Ch. 9: “Mechanics of Biological Materials” ***Notes derived from Prof. Scott’s PPT lecture I. Stress = forces applied to an object and material that is loaded that, combined, cause deformation of the object a. Internal forces resist external forces b. Mechanical Stress = distribution of force that varies based on internal surface; force per unit of area over which the force acts i. σ (sigma) = F/A = internal force/area of internal surface ii. measured in Pascals (Pa) = N/m 2 iii. Force is proportional to stress if force increases, stress increases iv. Area is inversely proportional to stress if area increases, stress decreases c. 3 types of stress: i. Tension/Tensile Stress = axial, or longitudinal, stress that occurs due to a force or load that tends pull apart/elongate/stretch an object from the material in which it is in contact with. Ex: hanging on a bar ii. Compression Stress = axial, or longitudinal, stress that occurs when a load causes a press or squeeze on the object, causing a shortening form of deformation Ex: push up iii. Shear Stress = transverse/horizontal stress that has forces parallel to the object whose molecules, when force is applied, slide, glide, or rub past each other. Can cause blisters on skin and possibly joint dislocations or shear fractures of bones Ex: Scissors II. Mechanical Loads = combination of stresses placed on an object a. Type of load defined by: i. Number of external forces ii. Direction of external forces iii. Location of external forces iv. Shape of the object itself b. Bending = asymmetric loading that produces tension on one side of the longitudinal axis and compression on the other side c. Torsion = load that produces a twisting of a body around its longitudinal axis d. Combined loads = one or more loads that act on harder connective tissue (i.e. bone and cartilage) i. softer mechanical connective tissue (i.e. muscles, ligaments, and tendons) = softer load/1 type of load III. Strain = total deformation of an object a. Linear Strain=amount of deformation that occurs on one plane (goes one direction) divided by the original length i. ε = (lf– lo)/o KIN 300: Fall 2016 – Week 3 Natalie Wong b. Shear Strain = amount of deformation divided by the original angular orientation of the structure i. Expressed as λ (lambda) and in radians c. Poisson’s Ratio = ratio of strain in the axial direction to the strain in the transverse direction i. Exists for every material; set values of how much objects’ strain changes ii. Values from .1.5 (most materials between .25.35) d. Stress/Strain Relationship – stress applied is directly related to strain resulted IV. Elastic Behavior vs Plastic Behavior a. Elastic Behavior = strain (x), stress (y); Stretches under tensile load, but returns to original shape when load is removed i. Linearly elastic = strain increases proportionally to stress ii. Elasticity = E = ∆σ/∆ε = ration of stress to strain iii. The less stress, the more pliant; the more stress, the more stiff and object will be iv. The less strain, the more stiff; the more strain, the less pliant b. Plastic Behavior = deformation (x), load (y) i. The smaller the load the > elasticity ii. Yield point = elastic limit; point at which deformation becomes permanent iii. Ultimate failure point = when object breaks V. Mechanical Strength = ability to withstand force; strain (x), stress (y) a. Yield strength = stress/strength applied at elastic limit b. Ultimate strength = max amount of force that can be withheld in permanent deformation without breaking c. Failure strength = break or rupture occurs VI. Failure Strain = strain exhibited by material when it breaks; strain (x), stress (y) a. Stiff and ductile = (curve) less easily deformed b. Brittle = (linear) either withstand stress or break c. Pliant and ductile = (curve) easily deformed VII. Toughness = ability of material to absorb energy a. More tough more energy to cause a break because there is greater resistance to deformation VIII. Musculoskeletal System a. Connective Tissue i. Anisotropic = different mechanical properties depending on direction of load Collagen = fibrous protein that is very stiff with high tensile strength - Unable to withstand compression collapses or buckles like rope Elastin = fibrous protein that is pliable and extensible b. Bone i. Carry almost all compressive loads (strongest) and can resist large shear (weakest) and tensile loads 3035% collagen = rigid, stiff – contributes to tensile strength when intertwined with calcium salts 12% ground substance = gellike matrix KIN 300: Fall 2016 – Week 3 Natalie Wong 45% minerals – contribute to compressive strength 20% water Types: - Cortical/Compact = typically on surface of bones - Cancellous/Spongy/Trabecular = typically deep near the ends of long bones Bone Strength - Values change from location to location on bone, from bone to bone, and with the age of bone - Bone = stronger and stiffer IF load is applied quickly but weakly c. Cartilage – can withstand compressive, tensile, and shear loads i. Hyaline/Articular – located at ends of long bones at joints (composed of collagen and water) ii. Fibrous (fibrocartilage) – within/at edges of some joint cavities and at insertions of tendons/ligaments to bone iii. Elastic – external ear and other nonmusculoskeletal locations d. Tendons and Ligaments i. Components 70% water 25% collagen 5% ground substance/elastin ii. Collagen parallel or mostly parallel along functional axis stiff/high tensile strength but little resistance to compression or shear loads Stressstrain curve = tendon/ligament is pulled with light force = initial deformation (stretch) collagen extends beyond certain load, tendon becomes stiff and resists stress iii. Ligaments vs tendons Ligaments have more elastin less stiff and slightly weaker Ligaments have less wellaligned fibers > ability to carry nonaxial loads e. Muscle i. Capable of actively contracting to produce tension ii. Stiffness is dependent on the number of active contractile elments iii. Some resistance to passive, slow stretching iv. Stiffness increases when contractile elements no longer overlap
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