Defects in Ceramic Processing Questions and Answers

Answer: A

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives the logic. Fracture mechanics relates strength to flaw size, so surviving a known stress proves that no flaw above the corresponding size is present. That is a guarantee no amount of sampling can give, and it is why the deliberate destruction of the weakest pieces is accepted for components whose failure would be serious.

Answer: B

Survivors are known to be free of flaws above a certain size, and the failures are removed. The cost is the loss of the pieces that break and the possibility of damaging those that survive. Proof testing is reserved for components where failure is unacceptable.

Answer: C

Three per cent of 2,000 is 60, leaving 1,940 survivors. Whether that loss is acceptable depends entirely on the consequences of a failure in service. For a critical component a three per cent loss may be cheap insurance.

Answer: D

Slow crack growth under the applied load can extend a subcritical flaw, so a survivor may be nearer to failure than before. The test load and its duration are chosen with that in mind. Too severe a proof test does more harm than good.

Answer: A

A defect that appears in the kiln may have been created in the press or the dryer, so the first task is to establish where it could and could not have arisen. Changing variables before that is done usually confuses matters further.

Answer: B

Both are true and the reason gives the trap: the kiln reveals faults built into the green ware, so altering the schedule addresses the symptom while the real cause continues unchanged. Two changes at once also make the result impossible to read.

Answer: C

Laminations, drying cracks and density gradients are all created early and only appear during firing. Assuming otherwise sends the investigation to the wrong end of the process. Where a fault shows and where it starts are different questions.

Answer: D

Charting a variable such as green density or slop specific gravity shows a trend developing while the product is still acceptable. Waiting for rejects to appear means the process has already been out of control for some time.

Answer: A

Both are true and the reason gives the advantage: reject counts are a lagging measure that tells you about material already made, whereas a control chart gives warning while the output is still good. Control charts are a preventive tool rather than a record of failure.

Answer: B

Two per cent of 10,000 is 200 rejects, leaving 9,800 good tiles. Reject rate is followed closely because it carries the cost of everything spent on the piece up to the point where it failed. A tile rejected after glazing has cost far more than one rejected green.