What kind of defects can I find in a knife made of high-carbon steel with a wooden handle?

Question

I'm still studying the Japanese knives and must now prevent the different defects that could appear in this tool. I consider 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 guarantee, meaning that they basically can't break... Nevertheless, let's consider 3 possibilities:

1. The wooden handle gets a defect: highly improbable 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 stuck together. Knowing the shape of the knife and the strength of the steel, I can't possibly imagine how I can separate the two objects 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.

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

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.