[Tex/LaTex] Add 9 figures together (with one caption ) 3 in the same row and so on

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I have an urgent question, I am new to Latex and I have to submit my thesis by tomorrow, I have been trying to add 9 figures together however, only 2 appears and the least not like they are on the border of the file , so even I want them top to each other, I had read some related answers.. nothing working 

\begin{figure}[H]
    \centering
\begin{subfigure}[b]{0.8\textwidth}
  \centering
\includegraphics[width=1\linewidth]{pics/"figure14_1"}
\caption{3-point bending}
\label{fig:figure14_1}
\end{subfigure}%
\begin{subfigure}[b]{0.5\textwidth}
  \centering    
  \includegraphics[width=0.5\linewidth]{pics/"figure14_2"}
\caption{Elastic stress distribution}
\label{fig:figure14_2}
\end{subfigure}%
\begin{subfigure}[b]{0.5\textwidth}
  \centering
\includegraphics[width=0.5\linewidth]{pics/"figure14_3"}
\caption{Plastic stress distribution}
\label{fig:figure14_3}
\end{subfigure}%
\begin{subfigure}[b]{0.3\textwidth}
  \centering
\includegraphics[width=0.3\textwidth]{pics/"figure14_4"}
\caption{Elastic shear stress distribution}
\label{fig:figure14_4}
\end{subfigure}%
\begin{subfigure}[b]{0.5\textwidth}
  \centering
\includegraphics[width=0.5\textwidth]{pics/"figure14_5"}
\caption{Plastic shear stress distribution}
\label{fig:figure14_5}
\end{subfigure}%
\begin{subfigure}[b]{0.3\textwidth}
  \centering
\includegraphics[width=0.3\textwidth]{pics/"figure14_6"}
\caption{Shaft under torsion}
\label{fig:figure14_6}
\end{subfigure}%
\begin{subfigure}[b]{0.3\textwidth}
  \centering
\includegraphics[width=0.3\textwidth]{pics/"figure14_7"}
\caption{Elastic shear stress distribution}
\label{fig:figure14_7}
\end{subfigure}%
\begin{subfigure}[b]{0.3\textwidth}
  \centering
\includegraphics[width=0.3\textwidth]{pics/"figure14_8"}
\caption{Plastic shear stress distribution}
\label{fig:figure14_8}
\end{subfigure}%
\begin{subfigure}[b]{0.3\textwidth}
  \centering
\includegraphics[width=0.3\textwidth]{pics/"figure14_9"}
\caption{Linearly distributed load}
\label{fig:figure14_9}
\end{subfigure}%
    \caption{3-point bending, elastic and plastic stress distribution, shaft under torsion load and linearly distributed load.}
\label{figure14_99}
\end{figure}

Best Answer

probably you like to have the following arrangement of images:

enter image description here

I only cleaned up your code, removed all \centering instructions (they're not needed), corrected the widths of the subfigure environments, and inserted empty lines between each row of images:

\documentclass[a4paper]{article}
\usepackage[demo]{graphicx}
\usepackage{subcaption}

\begin{document}
\begin{figure}[htbp]
\begin{subfigure}[t]{0.3\textwidth}
    \includegraphics[width=\linewidth]{pics/"figure14_1"}
\caption{3-point bending}
\label{fig:figure14_1}
\end{subfigure}\hfill
\begin{subfigure}[t]{0.3\textwidth}
  \includegraphics[width=\linewidth]{pics/"figure14_2"}
\caption{Elastic stress distribution}
\label{fig:figure14_2}
\end{subfigure}\hfill
\begin{subfigure}[t]{0.3\textwidth}
    \includegraphics[width=\linewidth]{pics/"figure14_3"}
\caption{Plastic stress distribution}
\label{fig:figure14_3}
\end{subfigure}

\begin{subfigure}[t]{0.3\textwidth}
    \includegraphics[width=\linewidth]{pics/"figure14_4"}
\caption{Elastic shear stress distribution}
\label{fig:figure14_4}
\end{subfigure}\hfill
\begin{subfigure}[t]{0.3\textwidth}
    \includegraphics[width=\linewidth]{pics/"figure14_5"}
\caption{Plastic shear stress distribution}
\label{fig:figure14_5}
\end{subfigure}\hfill
\begin{subfigure}[t]{0.3\textwidth}
    \includegraphics[width=\textwidth]{pics/"figure14_6"}
\caption{Shaft under torsion}
\label{fig:figure14_6}
\end{subfigure}

\begin{subfigure}[t]{0.3\textwidth}
    \includegraphics[width=\linewidth]{pics/"figure14_7"}
\caption{Elastic shear stress distribution}
\label{fig:figure14_7}
\end{subfigure}\hfill
\begin{subfigure}[t]{0.3\textwidth}
    \includegraphics[width=\linewidth]{pics/"figure14_8"}
\caption{Plastic shear stress distribution}
\label{fig:figure14_8}
\end{subfigure}\hfill
\begin{subfigure}[t]{0.3\textwidth}
    \includegraphics[width=\linewidth]{pics/"figure14_9"}
\caption{Linearly distributed load}
\label{fig:figure14_9}
\end{subfigure}

\caption{3-point bending, elastic and plastic stress distribution, 
    shaft under torsion load and linearly distributed load.}
\label{figure14_99}
\end{figure}
\end{document}
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