Question

1. technician a says a metric bolt with the marking of 8.9 has more yield strength than a 10.9 bolt. technician b says only grade 8 nuts should be used on 10.9 rated bolt. who is correct? a. technician a b. technician b c. both a and b d. neither a nor b

Explanation:

• For Technician A: The first number in the bolt marking (e.g., 8 in 8.9 and 10 in 10.9) represents \(1/100\) of the ultimate tensile strength in MPa. The second number (e.g., 9 in both cases) represents the ratio of yield strength to ultimate tensile strength (\(\frac{\text{yield strength}}{\text{ultimate tensile strength}}\)). The yield strength \(S_y\) of a bolt is calculated as \(S_y=\text{first number}\times100\times\text{second number}\times0.01\). For an 8.9 bolt, \(S_y = 8\times100\times9\times0.01=720\) MPa. For a 10.9 bolt, \(S_y=10\times 100\times9\times0.01 = 900\) MPa. So, Technician A is wrong.
• For Technician B: Grade 10 nuts should be used with 10.9 - rated bolts. Grade 8 nuts are typically used with lower - grade bolts (e.g., 8.8 bolts). So, Technician B is wrong.

Answer:

d. Neither A nor B