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

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](https://chemistry.stackexchange.com/questions/164328/how-can-warm-steel-and-wood-merge-together), 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](https://www.seriouseats.com/japanese-knife-village).


**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?


[![3 Sakai Uchi Hamono knives](https://i.stack.imgur.com/FvZ5G.png)](https://i.stack.imgur.com/FvZ5G.png)




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.


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