The relationship between allowable stress and thickness of steel plate
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4 steel plate parts in GB150.2 materials: The data in Table 2 shows that at the same temperature, as the thickness increases, the allowable stress of the material becomes smaller. Why is this? Under common sense, the greater the thickness, the greater the maximum force it can bear, shouldn't it?
You have confused force with stress. That is allowable stress, not force. my country’s GDP ranks second, and per capita GDP is miserable. A truth. The performance of the back plate will decrease due to low allowable stress.
What you mean is that as the thickness of the material increases, the force it bears becomes larger, but when averaged over the increased thickness, that is, the allowable stress becomes smaller, right?
It is recommended to refer to GB150.1 Chapter 4.4.1 and do the math yourself when you have time.
Stress and allowable stress are two different things. Stress means that you can eat up to 10 steamed buns in one meal. Allowable stress means that your mother only allows you to eat 8 steamed buns in one meal. After all, if you eat too many steamed buns, you will easily die.； The thicker the steel plate, the worse the core quality, and the smaller the stress it can withstand. Just like the older you are, the worse your health is. You used to be able to eat up to 10 steamed buns in a meal, but now you can only eat up to 5 in a meal. Your mother has to let you eat up to 4 buns. A truth.
Ideally, the greater the thickness, the greater the allowable stress. But in fact, the thicker the plate, the worse the internal quality. The technical term is called "hardenability", so the thicker the steel plate, the lower the allowable stress.
Steel plate rolling ratio or forging ratio - the effect of steel plate rolling (forging, rolling) processing deformation on core properties
You are confusing force with stress. What is usually called force is the load exerted on the material by the medium or the outside world. It causes the material to interact internally to balance the load. This effect is stress. When the stress reaches a certain level, it will destroy the material. Therefore, we artificially set a maximum stress value to prevent material damage, which is called the allowable stress. Theoretically, the allowable stress should be the same for the same material. However, in actual production, as the thickness of the material increases, internal defects become more and more difficult to control, resulting in a decline in material performance and a decrease in the allowable stress.
my country's steel products are consistent with the European system, and the chemical composition of the steel does not change with the thickness of the plate. Due to the disadvantages of thick plates in terms of reduction and cooling rate, the greater the thickness, the lower the strength. This is the reason for the low allowable stress of thick plates. The carbon content of the same grade of steel in ASTM gradually increases as the plate thickness increases, which ensures that the strength of materials with different plate thicknesses is consistent.