Question

1. Two samples of a low hardness steel were tested using a Rockwell C hardness tester and the Rockwell B scale at the same lab on the same day. The difference between the average hardness of the two samples was 0.5 Rockwell C. Do you think there is a significant difference in the hardness? Justify your answer.

2. Two manufacturers produce a steel. Manufacturer B claims their steel is better than manufacturer A because their average Rockwell B hardness is 68.4 HRBW while that of manufacturer B is 60.5 HRBW. Do you think there is a significant difference in their hardness? Justify your answer. Hint: Use the specification!!

3. Find an important engineering failure that involves some of the topics discussed in MSE 350. Describe the failure, why it occurred, the damage (human, environmental, and economic) and the changes that could have been made in the design to avoid the failure. Was the failure caused by lack of engineering knowledge at the time, engineering error, or management/government error? Discuss!!

4.

For each of the following common items, identify what they are commonly made of, the material type (composite, metal, semiconductor, polymer <thermoplastic, thermoset or elastomer>, ceramic, glass. Describe why that material type is used. Include at least two references for your answers (websites are fine, but try and find good ones). If more than one material type is used in the items, include them all! Be careful to use proper engineering vocabulary when answering this question!

Abrasives for grinding metal

Automobiles

Integrated circuits

Airplanes

Bridges

Solar panels

Latex paint

Soda bottles

Polyvinylchloride (PVC) plumbing pipes

Answer 1

1. No there is NO significant difference in their hardness. When we check the hardness of the samples we used to take three reading on the sample and take the average of it. So 0.5 HRC will not make any difference in the hardness value. Moreover, if you check the hardness in the same portion again we wont get the same hardness value. The repeatability varies. Therefore, 0.5 HRC differece will not make any difference in the hardness value.

2. Yes, there is significant diffrence in the hardness value. As we know that if hardness increases the tensile property of the material also increases. The difference in hardness here is 7.9. This difference in hardness will lead to a difference of 50-75 MPa in their tensile property. Ususally the tolerence for the hardness is plus or minus 1 only.

4.

Abrasives for grinding metal - ceramics

Automobiles - metal

Integrated circuits - semiconductor

Airplanes - composites

Bridges - metal

Solar panels - semi conductors

Latex paint - elastomers

Soda bottles - glass

Polyvinylchloride (PVC) plumbing pipes - thermoplastics