螺栓強度8.8但是直徑不同，比如M10和M20，抗拉強度分別多少？
The bolt strength is 8.8, but the diameter is different, such as M10 and M20. What are the tensile strengths respectively?
，需要糾正一點，抗拉強度是在拉伸過程中，材料經過屈服階段后進入強化階段后隨著橫向截面尺寸明顯縮小在拉斷時所承受的大力（Fb），除以試樣原橫截面積（So）所得的應力（σ），稱為抗拉強度或者強度極限（σb），單位為N/mm2（MPa）。抗拉強度是單位面積內能夠承受的拉力。
First of all, it needs to be corrected. The tensile strength is the stress obtained by dividing the strength (FB) borne by the material at the time of tensile fracture by the original cross-sectional area (so) of the sample after the material enters the strengthening stage after the yield stage（ σ）， It is called tensile strength or strength limit（ σ b) , in N / mm2 (MPA). Tensile strength is the tensile force that can be borne per unit area.
因此，螺栓強度為8.8，無論螺栓直徑如何變化，其抗拉強度是不變的，題主問的應該是小拉力載荷。
Therefore, the bolt strength is 8.8. No matter how the bolt diameter changes, its tensile strength remains unchanged. The main problem should be small tensile load.
螺栓分類
Bolt classification
螺栓按照性能等級分為：4.8、4.8、5.6、5.8、6.8、8.8、9.8、10.9、12.9共九個等級，其中8.8級以上(含8.8級)螺栓材質為低碳合金鋼或中碳鋼并經熱處理(淬火+回火)，通稱高強度螺栓，8.8級以下(不含8.8級)通稱普通螺栓。
Bolts are divided into 9 grades according to performance grades: 4.8, 4.8, 5.6, 5.8, 6.8, 8.8, 9.8, 10.9 and 12.9. Bolts above grade 8.8 (including grade 8.8) are made of low-carbon alloy steel or medium carbon steel and heat treated (quenched + tempered), which are generally referred to as high-strength bolts, and bolts below grade 8.8 (excluding grade 8.8) are generally referred to as ordinary bolts.
按照制作精度可分為：A、B、C三個等級，A、B級為精制螺栓，C級為粗制螺栓。對于鋼結構用連接螺栓，除特別注明外，一般為普通粗制C級螺栓。不同的級次通常對應加工方式如下：①A、B級螺栓的栓桿由車床加工而成，表面光滑，尺寸精 確，其材料性能等級為8.8級，制作安裝復雜，較高，很少采用;②C級螺栓用未加工的圓鋼制成，尺寸不夠精
According to the manufacturing accuracy, it can be divided into three grades: A, B and C. grade A and B are refined bolts and grade C are rough bolts. For connecting bolts for steel structure, unless otherwise specified, they are generally ordinary rough grade C bolts. The corresponding processing methods of different grades are as follows: ① the bolt rods of Grade A and B bolts are machined by lathe, with smooth surface and accurate size, and their material performance grade is grade 8.8 , the fabrication and installation are complex, the price is high, and it is rarely used; ② grade C bolts are made of unprocessed round steel, and the size is not precise enough
確，其材料性能等級為4.6級或4.8級。
Indeed, the material performance grade is 4.6 or 4.8.
螺栓性能等級的標記制度
Marking system of bolt performance grade
螺栓、螺釘和螺柱性能等級的代號，由點隔開的兩部分數(shù)字組成：
The code of performance grade of bolts, screws and studs consists of two parts separated by points:
點左邊的一或二位數(shù)字表示公稱抗拉強度的1/100，以MPa計；
One or two digits on the left of the point represent 1 / 100 of the nominal tensile strength, in MPa;
點右邊的數(shù)字表示公稱屈服強度或規(guī)定非比例延伸0.2%的公稱應力與公稱抗拉輕度比值的10倍
The number to the right of the point represents 10 times the nominal yield strength or the ratio of the nominal stress with a specified non proportional extension of 0.2% to the nominal tensile strength
題主描述的螺栓8.8，表示公稱抗拉強度σb=800MPa（d＞16mm時，σb=830MPa），公稱屈服強度σs=640。
The bolt 8.8 described in the main question represents the nominal tensile strength σ B = 800MPa (when D ＞ 16mm, σ B = 830mpa), nominal yield strength σ s=640。
螺栓性能等級8.8的小拉力載荷
Small tensile load of bolt performance grade 8.8
計算其小拉力載荷可以通過計算公式和查表得出。
The small tensile load can be calculated through the calculation formula and look-up table.
1.計算公式：F=σs*A，其中F為拉力（許用載荷），σs為材料抗拉強度，A為有效面積。
1. Calculation formula: F= σ S * a, where f is tensile force (allowable load), σ S is the tensile strength of the material and a is the effective area.
M10的有效橫截面積為58mm^2。8.8級M20小抗拉強度σb=800MPa（d＜16mm），F(xiàn)=800*58=46400N=46.4KN
The effective cross-sectional area of M10 is 58mm ^ 2. Grade 8.8 M20 small tensile strength σ b=800MPa（d＜16mm），F(xiàn)=800*58=46400N=46.4KN
M20的有效橫截面積為245mm^2。8.8級M20小抗拉強度σb=830MPa（d＞16mm），F(xiàn)=830*245=203350N=203.35KN
The effective cross-sectional area of M20 is 245mm ^ 2. Grade 8.8 M20 small tensile strength σ b=830MPa（d＞16mm），F(xiàn)=830*245=203350N=203.35KN
2.通過查表法，也可得到同樣數(shù)值，更加方便快捷。
2. The same value can be obtained by looking up the table, which is more convenient and fast.
