I Meet Three Questions in the Making Projects for Electrical Fuses

I am an electronic engineer and am making a study related to electrical fuses. Before making, I meet three questions for electrical fuses.

Here is the detailed question:

I am building a test bed, only open on hand, there is no fuse. Some people say that there is no need to open the fuse; so we searched some materials from the Internet, but found that it is very different from what they say. Today, I come to this forum to turn to you to discuss three questions I meet in the making projects for electrical fuses.

Problem 1. That empty open with thermal hysteresis, high current through the moment, open will not immediately trip, and the fuse can be done immediately fuse. This time if there is no fuse in the circuit, it will make part of the circuit is burned open after the open will be disconnected.

I would like to ask, is that true?

Question 2. Under what circumstances and the fuse can be used interchangeably, which cases can not be replaced?

In addition,

Question 3: Is there a way to test how short the short circuit is in the end? Because the ordinary ammeter in the short-circuit state directly hung up the bar.

Through this forum, I need your help to solve the questions for me. I have puzzled about these questions, so I come to this forum.

Ps: Excuse me if I was wrong in words or expressions as I am a green hand in the making projects for electrical fuses. I need continual learnings.

What is your idea ? Do you agree with my ideas ? Any of your ideas would be highly appreciated.

May someone would like to help ?

thanks in advance.