\documentclass[tikz]{standalone}

\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[french]{babel}
\usepackage{pgfplots}
\usepackage{amssymb} 

\pgfplotsset{compat=1.14}

\begin{document}

\begin{tikzpicture}
    \begin{axis}[xmin=0.75, xmax=1.25, ymin=0, xtick={0.6,0.8,...,1.4}, ytick={0,1,2,3}, ymajorgrids, width=14cm, height=5cm, yticklabels={0}, xlabel={$x=\frac \omega{\omega_0}$}, ylabel={$U_m(x)$}]
        \addplot expression [domain=0.75:1.25, smooth, mark=none, samples=100] {abs(6*(1-x^2))/(sqrt((1-x^2)^2+(0.1/10*x*1170)^2))};
    \end{axis}
\end{tikzpicture}

\end{document}
