This video explains what is proof load or proof stress. And why proof load or proof strength is used in the fastener application. This video also explains, what is offset yield strength and why offset yield strength is used instead of yield strength for some ductile materials like aluminum cooper and alloy steels.
This video has answers to questions like what is yield strength and Proportional limit. And stress and strain curve is also explained with the help of a tensile test.
But first, if you want to know the basics of stress and strain curves. Click on the following link to watch a video on stress and strain curve.
• stress strain curve ex...
If you see the stress and strain curve of mild steel. This curve is linear up to point A. And, the stress is directly proportional to the strain up to point A. The stress corresponding to point A is known as the proportional limit. At this point A, if we remove this applied load, the object will restore its original shape without any permanent deformation.
Point B, on this curve, where the material starts to yield, is known as the yield point. And stress corresponding to this point is known as yield strength. At this point B, if we remove the tensile load. There will be a permanent deformation and the object will lose its original shape. It was the case of mild steel, which exhibits a well-defined yield point.
Unfortunately, not all materials exhibit a well-defined yield point just like mild steel does. For example aluminum, copper and alloy steels. The stress and strain curve of such material will look like this. As you can see here, this graph doesn't have a clear yield point. In such cases, where the stress and strain curve doesn't have a clear yield point. The yield strength can be determined by an offset method.
In this method. The distance O-A, which is 0.2% of the original gauge length, is marked on the X-axis. Then, a line A-Y is constructed from point A, which is parallel to the straight line of stress and strain curve. The stress value corresponding to point Y is called the offset yield strength or offset yield stress. Sometimes it is also called 0.2% offset yield strength.
Now I will answer what is proof stress. And why it is important in the design of fasteners.
In the case of fasteners, instead of yield strength, the term proof load or proof stress is frequently used.
Because, if we load the bolt up to yield strength. Bolt will have permanent deformation and it cannot be used again. Proof load is defined as the maximum tensile force that can be applied to a bolt, that will not result in plastic deformation. In other words, the material must remain in its elastic region when loaded up to its proof load. Proof load is typically between 85-95% of the yield strength.
Thus, the use of bolts according to proof load can help prevent plastic deformation. And it can be assured that it has maintained its original size and shape, and maybe safely reused.
Proof strength or proof stress is determined by offset method as explained earlier however, the offset may vary from 0.1% to 0.5 % of the original gauge length. The value of the offset percentage of strain is arbitrarily and defined by the material testing standard being used like ASTM or ISO. The most common offset is 0.2%, but this can vary depending on the material.
Following questions related to strength of materials and material science are answered in this video
what is proof load
tensile test explained
what is yield point
offset yield strength
yield strength
offset yield point
proof load
proof load means
0.2 offset yield
0.1 offset yield
offset yield and proof load
bolt proof load
yield strength
0.2 proof stress
#0.2 offset yield
#proof stress
#0.2 yield strength
#proof load
#proof load meaning
#proof strength
#offset yield strength
proof strength
what is the proportional limit 0:28 to 0:54
what is the yield strength 0:54 to 1:16
why offset yield is used 1:16 to 2:12
what is offset yield strength 1:16 to 2:12
what is the 0.2 offset yield 1:16 to 2:12
What is the proof load or proof strength 2:13 to 3:40
why proof strength is used in fastener design.
proof load definition 2:35 to 2:43
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