Brinell Hardness Test Explained - Material Science

In this video we will be discussing hardness which is the resistance for a material to dent. I will be explaining what the equation is doing and I will be doing and experiment to show how it is found. Unfortunately I could not work a hardness testing machine into my budget…. So we will be using a ping pong ball with a diameter of 39 mm and adjust the ratios of everything to make is as if has a diameter of 10 mm. We place it on a substance which is putty and apply 3000 kgf of force which for the experiment I actually used 30 grams force. These values are the standards used for most brinell tests. We take a measurement of the diameter of indent which scaled down by dividing the indent diameter by 39 mm over 10 we get 3.3 mm diameter for the indent. To reiterate the only reason I am scalling everything and changing numbers is to match the standard brinell test you would not do this in reality assuming you have the actual equipment. Also my hardness number is going to be bogus. So the brinell hardness equation is the load… which typically is 3000 kg of force and is typically applied for 30 seconds. Divided by pi times the diameter which is the circumference of the 10 mm ball. Times ½ the diameter of the ball minus the square root of the diameter of the ball squared minus the diameter of the ident squared. What is this section doing? This looks like the pythagrean theorem to me so lets place a right triangle in the middle of the ping pong ball with one leg being the ½ indent diameter and hypotenuse or longest side being ½ the diameter of the indenting ball. Plugging these values into the Pythagorean theorem we get the other side length Now if we subtract this side length from the diameter of the ball we get the indent depth. So this portion of the equation is solving for the indent depth into the clay from the bottom of the steel indent sphere. So really the formula is the load divided by the circumference of the indent sphere times the depth of the indent Lets plug in our numbers and see what hardness we get… We get a hardness of 340.9 this of course is not the actual hardness being I scalled the numbers. Disclaimer These videos are intended for educational purposes only (students trying to pass a class) If you design or build something based off of these videos you do so at your own risk. I am not a professional engineer and this should not be considered engineering advice. Consult an engineer if you feel you may put someone at risk.