Pat Allens first job at ABC Corporation was to analyze stres

Pat Allen\'s first job at ABC Corporation was to analyze stress on bolts used in a new lawn mower being developed for the consumer market and recommend a vendor to supply 100,000 bolts per year. Based on conservative estimates of expected service loads, Pat recommended using ¼-20 by 1 inch long SAE Grade 8 steel hex-head bolts because consumer injury could result from bolt failure.

Pat telephoned five different vendors and all five quoted about the same price for 100,000 bolts. On the very afternoon that Pat was ready to place the purchase order, Pat\'s boss said to use a different vendor, DEF Corporation, who would give ABC a much better price. Pat\'s boss then placed the order for the 100,000 bolts with DEF, whose president just happened to be an old college friend of Pat\'s boss.

When the bolts arrived, Pat was concerned that these cheaper bolts might not be strong enough. A drawing of a sample bolt head is shown in Figure 1.

1) When you first read the narrative above, did you visualize Pat as a woman or a man? When you first read the narrative above, did you visualize Pat\'s boss as a woman or a man?

2) What is a good price for one ¼-20 by 1 inch long SAE Grade 8 steel hex-head bolt in a hardware store? What is a good unit price if purchasing 100,000 of them? Remember to cite sources for your prices.

3) Why was Pat concerned that the bolts might not be strong enough?

4) What torque will cause an SAE Grade 8 bolt to fail in tension?

5) How many bolts failed below SAE Grade 8 minimum tensile strength?

6) Statistically, how many of these 100,000 bolts would fail below SAE Grade 8 minimum tensile strength?

7) Discuss at least two reasons why Pat might want to write a formal memo about using or not using these 100,000 bolts. If you were Pat, would you use these bolts?

8) Discuss at least two reasons why Pat\'s boss may have rightly or wrongly purchased these 100,000 bolts from DEF Corporation. If you were Pat\'s boss, would you use these bolts?

Figure 1 Sample Bolt Head Because ABC did not have a tensile testing machine to check bolt strength, Pat devised a simple screening method. Pat selected 20 bolts at random from the 100,000 and twisted the heads off these samples with a dial indicator torque wrench using the set-up shown in Figure 2. Pat recorded the failure torques in Table 1 bolt head leave small gap L washer between washer and vise nut leave small gap Vise nut between two nuts Vise Jaw Jaw flats of nuts must be flush must lubricate against vise jaws threads before test BOTTOM VIEW SIDE VIEW Figure 2 Bolt Screening Test Set-up Table 1 Failure Torques for Twenty %-20 Bolts Measured in Ft.Lbf (data collected by ME 415 class during Spring 1999)

Solution

answer

1. when i first read the narrative,i visualised Pat and Pat\'s boss bothas a man.

2. Price of a 1/4-20 X 1 grade 8 SAE hex head screw is approx USD 0.18. For 100,000 pieces it would cost 15000 USD.

3. Pat might have got the bolts for a less price as compared to its standard value.

4. Standard tensile strength of a Grade8 SAE 1/4-20X1 bolt is 150,000 psi. so Correspondiing to that value the safe torque is calculated to be 22.