There are lots of reasons to do PhDs, the bread-and-butter of the research world. But, leaving aside motivation for a moment, what is a PhD? Well, the most traditional, simplest and yet most challenging definition is “a substantial contribution to knowledge.”

Lets break that down, word by word.

“Knowledge” in the useful arts like materials science and engineering means our understanding of the world. So in mechanical metallurgy, this means our understanding of the mechanisms by which materials deform or fail; the effect of alloying elements on microstructure and strengthening or on defects such as dislocations and so on. But the focus is on understanding, which isn’t the same as measurement – a bunch of testing quantifying the life of a material doesn’t count (ha ha). But, generally we would aim for this to be quantitative, as in any physical science.

“Contribution” is the idea of originality, so this should be the PhD candidate’s original research work. Often, this will be a funded project conceived by the supervisor(s), possibly in collaboration, but the candidate (with their colleagues and advisors) will have elaborated this concept over the course of the PhD. Often, the project will have changed direction as we work our way into the project and find out where the most fruitful avenues are. So, what is the bottom line on originality? Well, for most of the results presented, the candidate will have collected, analysed and interpreted the data, and will have written the first draft of the results and discussion.

What about novelty? Well, the is also contained within the term “contribution,” which implies that this particular knowledge did not exist before. Clearly, in mature fields like metallurgy then this might be quite incremental, but it should still be novel in the sense that these are new results, not previously available in the literature. They should also be sufficiently novel and original that they are suitable for publication – they are of interest to other scientists working in the field.  Often a PhD specification in university regulations will specify that the contribution to knowledge be “suitable for publication in whole or in part”, of which more later in this post.

“Substantial” is perhaps the vaguest term in this entire collection of vague terms. But, given that a UK PhD is nominally a 3-year research training, I would take this to mean enough work to be turned into several full-length articles in leading journals. But where this term really bites is that a PhD is “A substantial contribution,” that is one integrated piece of work. So whilst in later life you might work on lots of different projects, a PhD is different in that its a chance to really push forward one area in an integrated fashion.  So in the UK we (mostly) still believe that PhDs should be presented in one integrated thesis that stands or falls on its merits, rather than the Scandinavian approach of obtaining a PhD by publication.

OK, so that’s the definition. Another way to look at this is now to look at what a PhD programme likely consists of, in the ideal case.

During the first year one gets to grips with the techniques and the literature in the specific subfield of study, say nickel-base superalloys, with the aim of persuading the progress examiners that one is capable of doing a PhD in this area after nine months. So most of the techniques used should be demonstrated and a review of the literature presented, together with a plan for the actual research work. So as to get some experience of writing, a report will be written and ideally, the new student would contribute to a journal article being written by another group member so as to see how the writing process works.

In the second year the main technique developments will happen, adding capability to the research group and the student will become a stalwart member of the research group. Towards the end of the second year the first journal article will be written, probably based on data stretching back to the first year. This might not be the most amazing article in the world, but it will be a chapter of the thesis and will mean that the student is now an author capable of writing on their own.  It could either be a full-length article or a letter paper, depending on how the work sits.

Then in the third year the two main articles will be written, aimed at the best journals, which form the main core of the PhD thesis. The thesis is then composed of three results chapters (journal articles), a literature review, an introduction to motivate the work and a final chapter of conclusions and suggestions for further work.  Hopefully, this will be completed within the three year timescale.

Therefore the PhD student applying for jobs will, three months prior to submission, probably have 1 co-authored article published, 1 first-author article published, 1 submitted and a final one in preparation.  Probably in final year there will be a conference presentation as well, which might have an accompanying conference paper.

So for me, that is success. 3-4 journal papers, 2 are which are proper full-length first author journal articles published in good journals; a thesis submitted on time or nearly on time; and a PhD student who goes onto a good job, be it a postdoc, in industry or in professional servies.