Our bibliography of helmet documents has abstracts of over 500 helmet studies, papers, articles, etc. Most of it was done before 1996, in the era before Web searches. We have references for other bibliographies with more recent publications as well.
Our newsletters again have material scattered over the years.
Our Research page has links to statistics and such, mostly related to helmet performance rather than physical construction.
Here are two articles about motorcycle helmet construction available for about $30 each from ScienceDirect. The first covers materials and design issues and the second covers manufacturing issues. There is a third article in the series on design considerations. We do not know if they are authoritative, and do not know anything about the authors. But these are the only journal articles we have seen on helmet construction techniques. There are many others related to helmet features or performance, so you might want to look at this ScienceDirect search for them. The articles are not available from us.