Hi there! I just wanted to say this video is fantastic! One thing I found difficult about school vs working as an engineer is attaching real world concepts and examples to the theory. So just by showing the scratch tests and reiterating the main points of the lecture, you're really helped me solidify my understanding of the hardness material property. Thank you!!!
Thanks so much. Hardness has been defined as resistance to plastic deformation. That's somehow similar to stiffness which is resistance to elastic deformation. My question is: is hardness analogous to stiffness, is it a rough equivalence of stiffness in the plastic region? I'm asking this in the hope that there's a way for me to make sense of hardness using the stress strain curve even though tensile test doesn't measure hardness. I keep wondering about that given that stiffness and hardness have the same unit and similar definitions. Would love to get your thoughts. Thanks
You make some equivalence between hardness (MPa) and the yield strength of the material which is the stress at which plastic deformation begins in tensile test. There is direct proportionality with the constant being somewhere between 2.8 to 3. Stiffness is the elastic modulus and hence not connected to hardness in the traditional sense.
Hello sir can you Make an video on How to specify Hardness for particular parts In machine tool Design most of time hard ness is used as wear resistant tool . I didn't get how we Decide hardness value for materials. If design spindles,Work head bodies,or casting material
Thanks for asking. You are right, hardness is taken as a parameter for wear resistance. In fact, the Archard's law states that wear volume of a material against another harder material is inversely proportional to the hardness of the material. The hardness value for mechanical design is basically decided through the design and performance experience. The values have been incorporated into the specifications for those applications. For example hardness of a surface hardened gear is kept in the range of 50-60 HRc (Rockwell hardness, scale C). Core of the gear is kept little softer for good amount of toughness. Core hardness can be in the range of 40 HRc.👍
Hardness test is very useful for industry. I remember when I started my first job in a steel plant, hardness test was being used for confirming that the steel was made right. Similarly, now in research we regularly use for metals and polymer (including polymer composites) to understand the changes in the material after a processing is done. For example, how much curing should be done on a thermoset polymer (epoxy etc.) can be decided after doing hardness test. These are just some examples.👍
