One question sir - as I understand, theory of 'contact stresses' come in to picture when the load case qualifies 2 important conditions: 1. applied force shall be significantly high 2. area between bodies shall be very very small The questions is - is there any specific ratio of force to contact area where we can say that any case having this ratio or above is a case of 'contact stresses'.
Since all contact begins as a point contact, even moderate applied forces can generate somewhat large local stress fields. So, I don't think there is a lot of concern about the applied force. If there is a normal force, there will be contact forces...but they could be small compared with external shear forces that might be applied. As to the contact patch area, when the materials go non-linear, you will not have simple analytical solutions. Honestly, in my experience, I use the simple 10% rule all the time...that is: if the contact patch diameter is less than 10% of the diameter of the smaller sample, our simple solutions will likely work. However, you can always use an FEA analysis, conducted by someone who knows what they are doing, to explore non-linear material response. But your questions are quite good and deserve more than this quick answer.
![Megan Thee Stallion - Bigger In Texas [Official Video]](http://i.ytimg.com/vi/QxTkZTLWdo4/mqdefault.jpg)
perfect explanation about - why failure initiates below the surface in case of contact stresses - superb...
Thank you for your kind words! I do appreciate it. Use my videos in any way you see fit.
One question sir - as I understand, theory of 'contact stresses' come in to picture when the load case qualifies 2 important conditions:
1. applied force shall be significantly high
2. area between bodies shall be very very small
The questions is - is there any specific ratio of force to contact area where we can say that any case having this ratio or above is a case of 'contact stresses'.
Since all contact begins as a point contact, even moderate applied forces can generate somewhat large local stress fields. So, I don't think there is a lot of concern about the applied force. If there is a normal force, there will be contact forces...but they could be small compared with external shear forces that might be applied. As to the contact patch area, when the materials go non-linear, you will not have simple analytical solutions. Honestly, in my experience, I use the simple 10% rule all the time...that is: if the contact patch diameter is less than 10% of the diameter of the smaller sample, our simple solutions will likely work. However, you can always use an FEA analysis, conducted by someone who knows what they are doing, to explore non-linear material response. But your questions are quite good and deserve more than this quick answer.
Sir, what is the physical meaning if the contact pressure ges negative ?
It is a compressive normal stress, so the sign is negative.
Thanks so much for your explanation, Can I get this PowerPoint that you are using in the explanation?
Very informative video. Thank you very much for the explanation.
Can we also get the reference book name?
This is from Shigley's Mechanical Design Book, likely 8th or 9th Edition. Wish he worked through a problem or two.
Great