Study your flashcards anywhere!

Download the official Cram app for free >

  • Shuffle
    Toggle On
    Toggle Off
  • Alphabetize
    Toggle On
    Toggle Off
  • Front First
    Toggle On
    Toggle Off
  • Both Sides
    Toggle On
    Toggle Off
  • Read
    Toggle On
    Toggle Off
Reading...
Front

How to study your flashcards.

Right/Left arrow keys: Navigate between flashcards.right arrow keyleft arrow key

Up/Down arrow keys: Flip the card between the front and back.down keyup key

H key: Show hint (3rd side).h key

A key: Read text to speech.a key

image

Play button

image

Play button

image

Progress

1/24

Click to flip

24 Cards in this Set

  • Front
  • Back
MECHANICAL STRESS
- internal force/ cross sectional area
- stress is an internal force holding the object in place
TENSION
- pull force
- the state of an object that results from forces pulling on it
- example of a tensile stress
TENSILE STRESS
- the axial or normal stress that occurs at the analysis plane as a result of a force or load that tends to pull apart the molecules that bond the object together at the plane.
- When the bone's axis is transverse and the pone is being pulled apart the stress acts away from the analysis plane making it tensile stress.
- very large tensile loads may sprain or rupture ligaments and tendons, or tear muscles and cartilage, or break bones.
COMPRESSION
- the push force
- an axial stress that results when a load pushes molecules more tightly together.
- deforms by shortening in the direction of the external forces
SHEAR STRESS
- a transverse stress that acts parallel to the analysis plane as a result of forces acting parallel to the plane
= to the force at the analysis plane divided by the cross sectional area of the object
- represented by symbol tau
- scissors
- In body cause blisters or joint dislocations
- changes the orientation of the sides of the object
BENDING LOAD
- produces more than one stress at the analysis plane.
- When a pencil is bent by pushing away with your thumbs and pulling it towards you with your fingers it will break. The top will break first because the pencil can withstand compression more than it can withstand the tensile force. This is because the fingers applying the tensile force are further from the axis and create more torque.
- An object with greater depth (more cross sectional area farther from its neutral axis) is able to withstand greater bendinglads because it has a larger moment arm.
- torque is produced by one force and has to be counteracted by another force. T = F x r
- curving occurs
- toes of the foot will break before the ankle does. This is because the depth of the ankle is greater than the toes which creates a greater moment arm. The torque is able to overcome the pressure better.
CURVING
- An object subjected to a bending load will deform by curving. The tension side of the object will elongate, whereas the compression side will compact and shorten, causing the object to bend.
STRAIN
- quantification of the deformation of material
- result of an external force causing a deformation which overcomes the stress force.
- On x-axis of stress strain curve because it is the dependent variable
LINEAR STRAIN
- results in change of objects length
= change in length/ original length
SHEAR STRAIN
- occurs with a change in orientation of adjacent molecules as a result of these molecules slipping past each other
- Poisson's Ratio
POISSON'S RATIO
- a specific ratio of strain in the axial direction to strain in the transverse direction exists for each different type of material.
- When a rubber band is stretched its length is longer but there is also an effect on its width. It becomes narrower because the molecules are slipping past
- Intervertebral discs are loaded with compression which pushes the discs down and they bulge out. Under extreme pressure they will burst.
ELASTIC MODULUS
- Young Modulus
= change in stress/change in strain
- The stiffer the object the larger the elastic modulus
YIELD POINT
- elastic limit
- coincides with the proportional limit which is the end of the linear elastic range of the curve
- Below the point the material is elastic, but above the point it is plastic
STIFF OBJECT
- plastic
- The steeper the slope in the stress-strain curve the greater the stiffness
- when an object is elongated the tensile stress increases
PLIANT OBJECT
- elastic
- The less steep the slope in the stress-strain curve the greater the elasticity.
YIELD STRENGTH IN ELASTIC MATERIALS
- stress at the elastic limit of a materials stress strain curve
- the object fights to maintain its own shape so when the strain begins to be stronger than the stress is overcome and deformation occurs
- Past this point the material fails to regain its strength
ULTIMATE STRENGTH IN ELASTIC MATERIALS
- maximum stress a material can withstand
- measure of material's strength. Past this point and the stress decreases
FAILURE STRAIN IN ELASTIC MATERIALS
- strain exhibited by a material when breakage occurs
- materials with large failure strains are ductile materials (can be changed into new forms)
BRITTLE
- material with a moderate stress-strain curve
TOUGHNESS
- ability of a material to absorb energy before failing
- tissues are soft and ductile
- bones are stiff and ductile
BONES
- the quicker load is applied the stronger the bone
- strongest in compression and weakest in shear
TENDONS
- stronger when force is aligned axially (parallel to fibers)
- fibers run parallel
- they are less elastic (more plastic) than ligaments which makes them hard to break.
- A serious injury when tendons break
LIGAMENTS
- Fibers criss cross and mesh together
- More pliable (elastic) than tendon.
- Easy to damage but damage isn't very serious
MUSCLE
- stiffness varies as a function of the number of active contractile elements.
- produces tension within itself and the structures to which it attaches
- failure strain is much larger due to the ability of the contractile filaments to slide past each other as the muscle increases in length.