Broken text on bottom of pgfplots

Question

I am using code below to create a graph. On the bottom there are two braces denoted $t_1$ and $t_2$. However numbers 1 and 2 are broken (lower part is not displayed). What is wrong with my code? I also tried to solve this problem using \pgfplotsextra to no awail.

Also, related to the code below, I would like to put into .style that all graphs have limit enlarged by fixed distance, i.e. 1 cm. If I understand the question Enlarge limits by absolute value when using symbolic coordinates right, this is not possible at all?

\documentclass[12pt,a7paper,landscape]{scrartcl}
\usepackage{pgfplots}

\pgfplotsset{standard/.style={axis x line=middle,axis y line=middle,every axis x label/.style={at={(current axis.right of origin)},anchor=north},every axis y label/.style={at={(current axis.above origin)},anchor=east}}}

\begin{document}
\begin{tikzpicture}
\begin{axis}[standard,width=8cm,height=5cm,enlarge x limits=0.11,enlarge y limits=0.19,xlabel=$t$,ylabel=$v$,xtick={20,60},xticklabels={,},ytick={25},yticklabels={$v'$}]

\addplot[thick,color=black] coordinates { (0,0) (20,25) (60,25) };
\addplot[dashed,very thin,color=black] coordinates { (20,0) (20,25) (0,25) };
\addplot[dashed,very thin,color=black] coordinates { (60,0) (60,25) };

\node at (axis cs:13.3,8.3) {$s_1$};
\node at (axis cs:40,12.5) {$s_2$};

\draw [decorate,decoration={brace,mirror,raise=2pt}] (axis cs:0,0) -- (axis cs:20,0) node [midway,below=1pt] {$t_1$};
\draw [decorate,decoration={brace,mirror,raise=2pt}] (axis cs:20,0) -- (axis cs:60,0) node [midway,below=1pt] {$t_2$};

\end{axis} 
\end{tikzpicture}
\end{document}

Answer 1

The text gets clipped at the edge of the axis area. To prevent this, you can either provide the key clip=false to the axis options, or put the \draw commands in the after end axis/.code={...} to draw the annotations outside the clipping scope:

\documentclass[12pt,a7paper,landscape]{scrartcl}
\usepackage{pgfplots}

\pgfplotsset{standard/.style={axis x line=middle,axis y line=middle,every axis x label/.style={at={(current axis.right of origin)},anchor=north},every axis y label/.style={at={(current axis.above origin)},anchor=east}}}

\begin{document}
\begin{tikzpicture}
\begin{axis}[
    standard,
    width=8cm,height=5cm,
    enlarge x limits=0.11,enlarge y limits=0.19,
    xlabel=$t$,ylabel=$v$,
    xtick={20,60},xticklabels={,},
    ytick={25},yticklabels={$v'$},
    after end axis/.code={
        \draw [decorate,decoration={brace,mirror,raise=2pt}] (axis cs:0,0) -- (axis cs:20,0) node [midway,below=1pt] {$t_1$};
        \draw [decorate,decoration={brace,mirror,raise=2pt}] (axis cs:20,0) -- (axis cs:60,0) node [midway,below=1pt] {$t_2$};
    }
]

\addplot[thick,color=black] coordinates { (0,0) (20,25) (60,25) };
\addplot[dashed,very thin,color=black] coordinates { (20,0) (20,25) (0,25) };
\addplot[dashed,very thin,color=black] coordinates { (60,0) (60,25) };

\node at (axis cs:13.3,8.3) {$s_1$};
\node at (axis cs:40,12.5) {$s_2$};

\end{axis} 
\end{tikzpicture}
\end{document}