Mechanical engineering PhD here, 1998. Grad school lasted about six years, during which time I got my MS and PhD. I had six semesters of classes, going full load most of those terms. At the highest levels (700-level courses) the subject matter was so specific that the number of students was pretty small, like 10-15, and there were no undergrad students present. At the lower end (400-level, and one 300-level), there were plenty of undergrad seniors in attendance, so that the number of students was maybe 50 or more, in a substantially-sized lecture hall.
Even while I was taking classes, I was working on my research project, holding a weekly one-on-one meeting with my faculty advisor, and having monthly meetings with my (corporate) research sponsors. Basically during “work hours,” I went to classes and then worked in the lab; at night and on weekends, I did class-related homework. Once I finished classes, my research took on the appearance of a full-time job, working 40-50 hours a week, with nights and weekends generally free. That is, until the final 9 months or so, when I started working more like 80 hours a week to get data, crunch it, and then churn out a dissertation.
Apart from the classwork and research, there were two hurdles unique to the PhD program.
The first hurdle was the PhD qualifying exam, which took place after my first two years (I had just completed my MS at that point, so this was more like the start of my doctorate program). This was basically the equivalent of four rather challenging undergraduate class final exams; we took it as two 2-hour exams on a Tuesday evening, with the remaining two a couple of days later. For us, the subjects were heat transfer, fluid mechanics, thermodynamics, and “general engineering.” In some cases the problems didn’t have obvious or specific solutions, or would have taken too long to solve, or required some assumptions to be made. In such cases, you were expected to explain your reasoning in writing. They were only partially testing your knowledge of the subject matter; the other part of the test was to evaluate your judgment, your ability to work toward a solution without having all of the facts firmly in place, or your knowledge/awareness of how unspoken factors might affect the answer to any given question. I studied for about five weeks for the qualifier, three weeks of which was during winter break. I actually enjoyed studying for it. I reviewed my undergraduate class files for the subjects, and solved all of my old homework problems again (since I had the answers in front of me). It went fast, since I wasn’t having to write legibly or show my work for a grade; I was solving them to check my own understanding. I also was able to review topics I didn’t understand very well the first time through; whether it was maturity or just a second pass (or both), I understood things much better when I was done. The grade was a simple pass/fail, you never learned your actual score. The scuttlebutt was that the scores of examinees fell into three categories:
-people who performed so badly the profs had no real choice but to fail them;
-people who performed so awesomely the profs had no real choice but to pass them;
-people who performed somewhere in the middle, allowing/requiring some discussion among the faculty as to whether they wanted these people to be in the program. In some cases examinees in this category were passed, but were required to take remedial coursework.
The second hurdle was the preliminary exam, which I took care of after completing my coursework. This was a document of just under fifty pages (and a live presentation) delivered to the faculty team who who later formed my defense committee. It explained what my research was, reviewed relevant literature/publications (this was the bulk of it), and showed why my work was unique/novel/important, and what gap(s) it would fill in the field of knowledge.
The deal with both of these was that you could fail one of them and retake it once, but you couldn’t fail both of them. I knew a couple of people who choked on the qual the first time through, and they were nervous because they knew they would only get one shot at passing their prelim exam later on. I also knew of one fellow who failed the qual twice and was ejected from the program.