As you are using LyX this mean that by default you are using babel package too (for things like that always is a must a MWE). So you need some like this in the preample:
\addto\captionsenglish{%
\renewcommand{\partname}%
{Fake Chapter}%
}
However, Lyx will put the babel package after the \makeatletter --\makeatother chunk in your code (see the complete source in the View menu), and therefore cannot work.
Hence, you need put also \usepackage{babel} before in the preamble, to obtain a file that work as this MWE:
\documentclass[english]{article}
\usepackage{babel}
\addto\captionsenglish{%
\renewcommand{\partname}%
{Fake Chapter}%
}
\begin{document}
\part{Some part or chapter}
The \textbackslash{}thepart{} is \thepart{} and the \textbackslash{}partname{} is \partname{}
That is all.
\end{document}
Or deactivate babel through Lyx menus and put only \renewcommand{\partname}{Fake Chapter} in the preamble.
reportorbook. – Werner Aug 30 '12 at 14:45\renewcommand{\partname}{Chapter}. Or better take Werner's advice. – lockstep Aug 30 '12 at 15:32\renewcommand{\partname}{Chapter}
\renewcommand\thepart{\arabic{part}} % arabic numbers for part \makeatletter @addtoreset{section}{part} % reset section number when a new part starts \makeatother \renewcommand\thesection{\thepart.\arabic{section}} % section 1.1 \renewcommand*\thesubsection{\thesection.\arabic{subsection}} % subsection 1.1.1
– Laure Aug 30 '12 at 17:27