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  • Hi,guys,

  • In this episode, let's talk about the relationship between the force and objects ,

  • first this blue is an object,

  • it has contains both are convex and concave,

  • and also relatively wider and narrower parts,

  • when after the concept of the objects enters, we will to produce the proportional scale,

  • the unit is what that not the focus,

  • this an object is subjected to variety of different roles by the forces and moment couple now,

  • so it produced a certain the deformation,

  • and the dashed line is the object line after it's deformed,

  • maybe it still will start to moves or rotations after thrust surface,

  • the force will causes objects the moves dip direction,

  • the moment couple will causes objects to have rotates dip direction,

  • the soil mechanics did not use to the moment couple,

  • so it will not appear again after this episode appears.

  • that, we consider of the objects are also not rotation occurs ,

  • because the soil will not rotation,

  • ok, next let's take a look at the force.

  • first, we can see it withstand the concentrated force of F1

  • and the force of F2

  • there are also f1 and f2

  • the uniform force and distributed force,

  • that, let's explain the nouns now,

  • focusing on role by the object on 1 point is called the concentrated force,

  • the concentrated force can act on or outside the objects,

  • can be understood as the force at a distance, (but actually is vector movement), that's no problem,

  • the force of unit we use is Newton N,

  • the concentrated force actually is abstract concept,

  • assume the force acts on a certain particle,

  • this particle doesn't exist in the real world,

  • the force of real world must be demonstrated in the distributed force manner,

  • even if you poke the potato with one needle,

  • the tip also has certain area,

  • next, let's look at the distributed force,

  • the distributed force can be called uniformity force in certain case,

  • that is, it the same with role of "density"form on a certain acreage,

  • that used here was is similar to the concept of density,

  • the distributed force unit actually is how many Newtons is acts on per square meter,

  • actually also is mean the how many Newtons is acts on each unit area,

  • in fact, the distribution force can be equivalent to the concentrated force,

  • the equivalent manner is as follows:

  • first to consider this the uniform force ,

  • the density of the uniform force is f2

  • the interaction length is l2,

  • what is the equivalent concentrated force of such a force?

  • write the concentrated force as the red arrow,

  • it's value = f2 * l2

  • then multiply the unit area is 1

  • this 1 can be as length of paper surface prominence,

  • we use angle of the three dimension to see is so

  • so it acts on an area,

  • the magnitude by the concentrated force is the volume of the rectangular parallelopiped,

  • i.e f2*l2*1

  • where is such a the concentrated force acting?

  • acting on above the centroid of the rectangle,

  • the centroid is in the middle...so we draw the concentrated force right here,

  • point of application in about 1/2l2 the place,

  • another one distributed force is the triangle,

  • in fact, the distributed force can have any shape,

  • the triangle...that accordance with the rectangle,

  • the magnitude is the bottom multiplied by the height divided by two

  • point of application in 1/3l1 the place,

  • when in the exam, we used to take the uniform force

  • to calculates after change to the concentrated force,

  • because for the objects ,them are equivalent ,

  • the so-called the equivalent is the same with the effect of generated,

  • that let's consider a question now.

  • what happens after an object is cuts ?

  • we know the object is for the maintain its shape before the thrust surface,

  • when subjected to external forces, internal forces are also will generated within the object,

  • so soil mechanics is defined...

  • the force that can be observed before cutting is the external force

  • the force that emerges after being cut is called the internal force.

  • the internal force is actually very complicated,

  • and with the angle or way you cut,

  • the internal forces generated both are also different,

  • the internal forces must have appeard with form of distributed forces,

  • it main can be divided into two types,

  • one is the normal stress and one is the tangential stress,

  • the so-called the normal stress is the direction of stress vertical to the section,

  • the so-called the tangential stress is the direction of stress parallel to the section,

  • such as red arrows

  • the external force and internal force are gives to objects...

  • effects produced are not the same,

  • what's the effects produced of the external force?

  • has movement, rotation, reaction force, work and so on ...

  • for the internal force, it will make the...

  • the stress in the object changes,

  • deformation, transformation energy...and so on.

  • for in soil mechanics...

  • when the external force continue to increase in the case, the internal force will rise accordingly,

  • the normal stress in the soils will causes soil consolidation,

  • that is the density increases (strength rises),

  • the increase of the tangential stress will make the the general shear failure of soils,

  • the main form of soil damage is the general shear failure,

  • finally, let's supplement the concept of "the rigid body",

  • the rigid body is considered as the ideal objects for the internal effects are not exist.

  • can imagine the rigid body don't exist in the real world,

  • within the subjects of engineering mechanics is

  • the objects are all assumed be the rigid bodies,,

  • that is, only the effects of external and external effects are considered,

  • the material mechanics will considered of internal force the part,

  • then the soil mechanics is builted on top of these two subjects,

  • so the scope of consideration is will again broader,

  • ok, the above is all the content today. Bye ~

Hi,guys,

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B1 US concentrated internal distributed soil external stress

Soil mechanics

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    WC posted on 2020/07/07
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