Advisor suggesting a change in the PhD research direction resulting in less theoretically intensive thesis. I am worrying about the implications I joined for my PhD in mechanical engineering in a Canadian university almost 3 years back. I had completed the necessary coursework and preliminary exam last July. My advisor had approved my research proposal to develop a numerical procedure to predict the damage behavior of composities during a complex loading condition. It is a really challenging topic and I wanted to give my best in solving the problem. My committee members were also satisfied with my research proposal and projected timelines.

Howevever, till now, I have not been able to get any substantial progress on the research topic. I am facing a lot of theoretical issues and my research topic is very loosely related to the expertise of my advisor. As a result his technical suggestions are not quite relevant and helpful. There's no one in the department who can help me in this regard.

Last week, my advisor suggested to change my research topic to a different one within the realm of the grants objectives. The modified researh area won't require the development any numerical procedure. Instead I will be using a commercial software with inbuilt procedures to get the results. I won't be able to publish in a reputed numerical or theoretical journals and  will have to settle for decent application oriented journals. I don't want my PhD to just be one where I pressed some buttons to get the answer. I wanted it to be rigorous. 

I am not sure what would be the implications if I accept to my advisors suggestion. On one hand the modified direction would guarantee atleast 3 decent publications. On the other hand, I don't know if I will be able to solve the theoretical problem soon enough to generate results. But if solved, will lead to a theoretically intensive paper and a lot of learning opportunity as a researcher.

What should I do? I will be funded for 5 years. And I would like to stay in academia in the future.
I'd suggest, pretty strongly, that you go with your advisor's guidance and turn the original project into a longer term goal. Your research career needn't end with the doctorate and it would be good to finish with some work done on a difficult future project. 

But the short term goal should be to get out the door with good letters of recommendation and enough of a push to get you into academia. What you can do after that is up to you and the possibilities you can bring to bear on your research. 

For what it's worth. I have a friend who is a reputed computer scientist. Top education, works in top level industrial gigs. But he also writes poetry. In fact, for more than ten years he has written a poem every day, without fail. The deadline for the poem is strict. But he described his methodology to me as something like, starting out with high standards and expectations for the day and continually lowering them until he has something acceptable. He gets the job done, and saves the rest for another day.