Important Definitions – Principal Stresses and Planes – Strength of Materials
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Hello friends here in this video we will see some important definitions which are necessary to understand the chapter of principal stresses and links let us get started the first definition is of resultant stress now for resultant stress first I will draw the diagram assuming that there is a plane here I will say that this X X indicates a plane now on this plane there is a vertical stress which I will call it as the normal stress Sigma n then let there be a tangential stress Sigma T which is acting along the plane so one stress is perpendicular to the plane other is acting parallel to the plane now if I join them here this hypotenuse of this right angle triangle this is nothing but the resultant stress so I will see that resultant stress is it is the resultant of normal stress and Sigma T that is tangential stress then it is denoted by Sigma suffix R and since it is stress the unit will be Newton per mm square Newton per meter square or Newton per centimeter square so it’s unit will be Newton per mm square or Newton per centimeter square or Newton per meter square now here I have written the first definition that is the resultant stress after that angle of obligate e now angle of obliquity it is the Angle made by resultant stress with normal stress so the angle made by the resultant stress with the normal stress is called as angle of obliquity then it is denoted by Phi the letter Phi and here I can mark this on the diagram that this angle is Phi angle made by resultant stress with the normal stress then here I can write down tan Phi is equal to Sigma T that is opposite side upon adjacent side Sigma N or I can say that Phi is equal to tan inverse of Sigma T upon Sigma n that is tangential stress upon normal stress so this is the formula to calculate the angle of obliquity we have seen two definitions result in stress and angle of obliquity now the third definition that is principal plane now principle plane is a plane which carries only normal stress and no tangential stress is called a principle plane so here is the definition of principle plane that a plane which carries only normal stress that is only the value of Sigma N and no tangential stress that is no Sigma T if a plane contains only Sigma n that is normal stress that would be called as a principal plane next principle stress now I can say that the value or magnitude of stress acting on a principal plane is called as a principal stress so first principal plane a plane which carries only normal stress and no tangential stress that is the principal plane next the value of stress that is the normal stress value which is there on the principal plane is called as principal stress next the major principle stress now major principle stress is the maximum value of stress that is normal stress acting on principle plane is called as major principle stress so the maximum value of stress on the principal plane that would be called as major principle stress next minor principle stress the minimum value of stress acting on a principal plane is called as minor principle stress so the least value of stress which would be acting on the principal plane called as minor principle stress so now after minor principle stress the next definition is major principle plane now a plane which carries maximum normal stress is called as major principle plane so the plane which carries the maximum value of normal stress that would be called as major principle plane then we have minor principle plane so you’re a plane which carries minimum normal stress is called as minor principle plane so here that plane which carries minimum normal stress would be called as minor principle plane the plane which carries maximum normal stress is called as major principle plane so here we have seen in this video various definitions or I can say some important definitions to be used in principle stresses and planes because when we understand these definitions then only we can understand what we have to find in the problem or what are the unknown values to be calculated and for that you should know these terms so first we have seen resultant stress which was the resultant of normal and tangential stress then we have seen angle of obliquity which is the Angle made by resultant stress with the normal stress next we have seen principal plane a plane which carries only normal stress and no tangential stress that is called as principal plane next we have seen principal stresses the value of or magnitude of stresses acting on the principal plane is called as principal stresses then major principal stresses the maximum value of normal stress acting on the principal plane is called as major principle stress then the minimum value of normal stress acting on the principal plane is called as minor principle stress next major principle plane a plane which carries maximum normal stress called as major principle plane the plane which carries minimum normal stress is called as minor principle plane and with this we complete the definition part

27 thoughts on “Important Definitions – Principal Stresses and Planes – Strength of Materials

  1. thanks sir only with the help of your videoes i attend all the question in engineering subject SOM….. thanks again….

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  3. Sir you are just telling definitions. We can also find them in some material. Please teach us practically. Thank you

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