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in mechanical properties of various
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solid materials two of the most
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important Concepts is that of stress and
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strain it is crucial in understanding
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how an object behave or react when you
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apply a force on it stress and strain
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help in identifying the strength
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deformation and various other mechanical
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properties of the object if you're a
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structural engineer or are looking to
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deal with different objects you got to
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know how much load or stress an object
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can withstand before it breaks distort
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or stretches so in our today's episode
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of explainer videos we're going to delve
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into the concept of stress strain how
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they're related to each other and also
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at the end we'll discuss stress strain
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graph and hooks law make sure to watch
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till the end I'm adding a spice of some
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interesting real life examples that will
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blow your mind so let's get started so
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what's the stress in physics or material
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engineering the word stress has a
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different meaning than that of the
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medical field stress is basically Force
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per unit area within materials that
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arises from externally applied forces or
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I can say it can also be due to uneven
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heating or permanent deformation well in
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other words stress is an indication that
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describes and predicts Elastic Plastic
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and fluid Behavior or any object so what
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did you be doing to determine stress
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well pretty simple you just take the sum
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of all forces acting on an object and
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divide that to the area of the object
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where force is acting and this will give
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you a measure of stress so applied
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stress or Sigma is equals to summation
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of forces divided by unit area stress
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has a unit of Newton per meter Square
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there are two basic types of stresses
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tension and compression stresses I've
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got another amazing explainer video for
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that so make sure to watch that as well
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you know why some materials are called
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brittle or some as ductal like a glass
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is brittle while a steel bar is ductal
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well that's because glass take less
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stress before failure while steel takes
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more stress before failure similarly you
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can stretch a rubber band far apart but
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you can't do that with a Wither paper
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yes it will be torn so you see different
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materials behave differently and to
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understand their behavior you got to
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understand the concept of strain so what
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is the strain well a strain is known as
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deformation in an object due to applied
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external force in a particular
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direction for example if you push down
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this spring it will have a reduced
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length so the difference of this length
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in comparison to the original length
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will be called strain in the spring
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similarly if you pull a rubber band it
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will have increased length so this
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increased length divided by the original
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length will be the strain in the rubber
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so basically we can say that strain
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explains the change in the shape of the
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object or deformation due to the loader
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Force being applied onto
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it mathematically we can Express strain
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as Epsilon equal Delta L / L now it's a
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unitless property meaning it does not
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have any unit it is a dimensionless
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quantity it is because it just compares
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the two same characteristic of an
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object there are different types of
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strain like tensil strain compressive
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strain Shear strain Etc we'll discuss
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this in our future videos so make sure
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to subscribe let's now move on to the
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next part of this video that is about
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stress strain curve when we study solids
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and their mechanical properties
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information regarding their elastic
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properties is most important we can
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learn about the elastic properties of
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materials by studying the stress strain
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relationships under different loads in
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these materials the material stress
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strain curve gives it stress strain
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relationship in a stress strain curve
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the stress and its corresponding strain
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values are plotted here's an example of
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a typical stress strain curve let's now
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discuss about the different regions of
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the stress strain curve I proportional
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limit it is the region in the stress
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strain curve that obeys Hook's law in
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this limit the stress strain ratio gives
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us a proportionality constant known as
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Young's modulus the point OA in the
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graph represents the proportional limit
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to elastic limit it is the point in the
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graph up to which the material returns
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to its original position when the load
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acting on it is completely removed
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Beyond this limit the material doesn't
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return to its original position and a
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plastic deformation starts to appear in
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it three yield point the yield point is
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defined as the point at which the
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material starts to deform plastically
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after the yield point is passed
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permanent plastic deformation occurs
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there are two yield points I upper yield
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Point new lower yield Point m v ultimate
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stress point it is a point that
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represents the maximum stress that a
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material can endure before failure
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Beyond this point failure occurs V
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fracture or breaking point it is the
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point in the stress strain curve at
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which the failure of the material takes
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place so now that you know what is
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stress and what is strain let's now see
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what is the difference between stress
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and strain well in physics stress refers
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to the force that is acting per unit
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area of the object whereas strain
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depicts the ratio of the change in an
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object's Dimension to its original
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dimension in physical parlance stress is
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equivalent to pressure and its unit is
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Pascal P or pounds on the other hand
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strain signifies the ratio of change in
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dimension to that of the original
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Dimension therefore has no units of
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measurement strain however can be
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measured by strain gauges so that's all
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about our today's episode I hope you've
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liked the video make sure to give it a
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big thumbs up I will catch you in our
