These old paper retrieval problems are interesting. This article is quite old, almost 40 years, and it can be that this text is never digitalised. The journal ceased publishing in 1988, so I guess no-one is taking care of its contents and future fate... You may have to visit a good university library to search for old journal issues in an archive.
If the library does not carry the journal, they can help you order a copy from another library. Here is the journal reference: Journal de Mecanique Theorique et Appliquee (ISSN 0750-7240), vol. 2, no. 3, 1983, p. 375-392.
Other ways:
It is well cited, so well that you can probably reconstruct essential parts of it. The abstract is on Researchgate, see below. There are 3 Researchgate members that have recommended this short abstract. Try contact any of them or, alternatively, an author with a very recent citation of the paper, they might be able to help you (check on Google Scholar). Perhaps.