Use of an Impact Test in the cross section design of a component

[SurajS]

If I have impact test data showing energy absorbed by notched specimen, how do I utilize this data while designing. In my case, i am trying to design the valve which closes by striking on valve seat, how do i use the impact test results for this design?

 

[jrmichler]

Assuming that you have a part that is subject to impact and that breaks under use, then one (not the only) option is to redesign the part using a material with increased impact strength. Some typical parts where this is a concern are the hammer mechanism in an impact wrench, cold chisels, and firing pins.

Companies that build high performance machines will sometimes have material specifications that include notched impact strength. The rest of us try to avoid impact where possible, and will focus our design efforts on reducing or eliminating impact. I have over 20 years experience at designing high performance machines, and have learned that using material with high impact strength is a last resort. When parts are impacting, the machine is noisy and vibrates a lot.

 

[SurajS]

Assuming that you have a part that is subject to impact and that breaks under use, then one (not the only) option is to redesign the part using a material with increased impact strength. Some typical parts where this is a concern are the hammer mechanism in an impact wrench, cold chisels, and firing pins.

Companies that build high performance machines will sometimes have material specifications that include notched impact strength. The rest of us try to avoid impact where possible, and will focus our design efforts on reducing or eliminating impact. I have over 20 years experience at designing high performance machines, and have learned that using material with high impact strength is a last resort. When parts are impacting, the machine is noisy and vibrates a lot.

I understand your concern, but in my case it is about emergency stop valve. So action of valve is very fast (20-30 millisec). Let me rephrase the question as:
Charpy impact test data (notch (2mm * 45 degree) specimen with 10*10*55 mm size) shows energy absorbed= 45 Joules , and energy available in spring (spring closes the valve) is 30 J, How can I correlate these two energies?

 

[jrmichler]

Charpy impact test data (notch (2mm * 45 degree) specimen with 10*10*55 mm size) shows energy absorbed= 45 Joules , and energy available in spring (spring closes the valve) is 30 J, How can I correlate these two energies?

You don't. The parts are completely different, so the respective energy values cannot be directly compared.

I have designed parts comparable to what you describe. While there are published procedures for estimating impact stresses, the best approach is to build a prototype and test it. If an emergency stop valve has a design life of, say, 10 stops, then test it for 1000 cycles. If anything wears out or breaks, redesign and restart the test from scratch.

Make the first prototype from materials that seem reasonable. The testing will tell you if you need a better design or better materials. Keep in mind that fracture is only one of several different possible failure modes. Possible failure modes include creep, yielding, corrosion, stress corrosion cracking, spalling, wear, galling, and others. You can study the problem forever (paralysis by analysis) and still miss a failure mode, or you can build a prototype, test it, and find out. This is a case where test it and find out is faster, cheaper, and better than paralysis by analysis.

 

[SurajS]

Thank you for information!