Reading technical research papers is a matter of experience and skills in order to learn the specific vocabulary of a field. First of all, DON'T PANIC! If you approach it step by step, even an impossible-looking paper can be understood.
1. Skimming. Skim the paper quickly, carefully review for headings, figures and the purpose of the reading. This takes just a few minutes. You're not trying to understand it yet, but just to get an overview.
2. Vocabulary. Go through the paper word by word and line by line, underlining or highlighting every word and phrase you don't understand. Don't worry if there are a lot of underlining; When you start, you are not trying to make sense of the article. Now you have several things you might do with these vocabulary and questions, depending on every question you can:
a. Look for simple words and phrases. Often the question is simply vocabulary—what is an allen wrench, bult, or the semilunar valve. A tecnhical English dictionary is a good place to look for definitions. Your ordinary shelf dictionary is not a good source, because the definitions may not be precise enough or may not reflect the way in which engineers use a word (for example "stress" has a common definition, but the technical definition is totally diferent.)
b. Get an understanding from the context in which it is used. Often words that are used to describe the procedures used in Engineering can be understood from the context, and may be very specific to the paper you are reading. For example, technical procedures to extract “light Oil” or “extra heavy Oil” at well site are totally different. Of course, you should be careful when deciding that you understand a word from its context, because it might not mean what you think.
3. Comprehension, section by section. Try to deal with all the words and phrases, probably there will be a few technical terms that you won’t understand. Now go back and read the whole paper, section by section, for comprehension.
4. Reflection and criticism. After you understand the article and can summarize it, then you can return to questions and draw your own conclusions. It is very useful to keep track of your questions as you go along, returning to see whether they have been answered. Often, the simple questions may contain the seeds of very deep thoughts about the work.