I'm still studying the japanese knifes and must now prevent the different defects that could appear in this tool. I concider a high-carbon steel blade with a wooden handle, with the size of a Sakai Uchi Hamono knife (from 165 mm to 240 mm).

I must then find a non-destructive method to detect those defects before it's too late. Here is the list of methods I am allowed to use:

  • Penetrant Testing
  • Magnetoscopy
  • Eddy current
  • Radiography
  • Ultrasound
  • Infrared thermography
  • Shearography

My main problem is that those japanese knives are famous to be extremely well manufactured, and they have a life-time guarentee, meaning that they basically can't break... Nevertherless, let's consider 3 possibilities:

  1. The wooden handle gets a defect: highly unprobable in my opinion since you only use it with your hand, without any particular stress on the wood;
  2. There is a problem between the blade and the wood: as you can see it in my previous question here, the two components are not simply sticked together. Knowing the shape of the knife and the strength of the steel, I can't possibly imagine how I can seperate the two objetcs without applying a disproportionate force;
  3. The steel gets a defect. A "defect" would for instance mean that it doesn't cut properly anymore (maybe because of water when you need to wash it ?). You can see how this kind of blade is forged here. What kind of problem could I have, on the molecular scale for instance (fatigue failure ?) that would create such a defect ? What kind of method in the list above can I use to find it ?

Of course, if you find a potential problem linked to the handle, I'd be glad to hear about it.

Thank you in advance for your answers !

PS: If your believe this is the wrong place to ask this question, could you please tell me where I should post it ?

3 Sakai Uchi Hamono knives

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    $\begingroup$ I am afraid this is very specialized knowledge area most chemists would have trable to give useful answers. It seems to me as a question for metallurgy or material science. Not sure if there is such site on SE network. $\endgroup$
    – Poutnik
    Apr 12 at 14:37
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    $\begingroup$ @blacksmith37 Could you provide an advice and/or reference guidance to the OP? I believe you know about the topic much more than me. $\endgroup$
    – Poutnik
    Apr 12 at 14:43
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    $\begingroup$ Steel is generally full of 'defects' from a material science point of view. Whether those impact their functionality under normal conditions is a different question. And a lifetime warranty just means they might last longer than some other products. $\endgroup$
    – Jon Custer
    Apr 12 at 15:07

1 Answer 1


Wet mag would be best to examine for mechanical defects. Similar to dye pene but with fluorescent indicator and a magnetic field.. Usually done under UV light. Zyglo is one brand I recall. That will not find metallurgical flaws such as low hardness. And will not find non-metallic inclusions that may promote fatigue. These other flaws cold likely be found with eddy current (EMT) but it would likely be less costly to buy a hundred knives and throw any that fail away than to develop standards and do the testing. I suggest that you trust the vender and if there is a problem , buy another knife rather than test. PS; Same answer for traditional 13% chrome cutlery steels.

  • $\begingroup$ Thank you a lot ! Do yout agree that the potential problems will more likely appear in the blade than with the handle, thus ? $\endgroup$ Apr 12 at 16:06
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    $\begingroup$ The tang portion of the blade will not not as much stress except at the transition to the main blade so relatively low risk. $\endgroup$ Apr 12 at 16:10

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