I would like to center the text in the middle of the respective cells for the "X" columns I have defined (last six columns). I would also like to center the table itself. This is my first time using LaTeX and I am using Overleaf. Any help is much appreciated.
\documentclass{article}
% Language setting
% Replace `english' with e.g. `spanish' to change the document language
\usepackage[english]
\usepackage{biblatex}
\usepackage[nomarkers,figuresonly]{endfloat}
\usepackage{gensymb} %package for adding degree symbol
% Set page size and margins
% Replace `letterpaper' with `a4paper' for UK/EU standard size
\usepackage[letterpaper,top=2cm,bottom=2cm,left=3cm,right=3cm,marginparwidth=1.75cm]{geometry}
% Useful packages
\usepackage{textgreek}
\usepackage{amsmath}
\usepackage{graphicx}
\usepackage[colorlinks=true, allcolors=blue]{hyperref}
\usepackage{ragged2e}
\usepackage{tabularx}
\begin{document}
\begin{center}
\caption{Table 1 - Tensile Mechanical Properties}
\begin{tabularx}{1.25\textwidth}{|c|c|c|X|X|X|X|X|X|}
\hline
\multicolumn{3}{|c|}{\textbf{Measurement or Property}} &\multicolumn{6}{c|}{\textbf{Material}} \\ \hline
\textbf{Quantity} & \textbf{Symbol} & \textbf{Units} & \textbf{CI} & \textbf{1045CR} & \textbf{1045NM} & \textbf{2024 AL} & \textbf{304 SS} & \textbf{PMMA} \\ \hline
\multicolumn{9}{|c|}{\textbf{Initial Data}}\\ \hline
\textbf{Diameter}&\textbf{d0}&\textbf{mm} & \textbf{7.14} & \textbf{7.19}& \textbf{7.06}& \textbf{7.1}& \textbf{7.13}& \textbf{8.00}\\ \hline
\textbf{Cross-sect Area}&\textbf{A0}&\textbf{\[mm^2\]} & \textbf{40.04} & \textbf{40.6}& \textbf{39.1}& \textbf{39.6}& \textbf{39.9}& \textbf{50.3}\\ \hline
\multicolumn{9}{|c|}{\textbf{Strength}} \\ \hline
\textbf{Yield Load}&\textbf{\(P_{y}\)}&\textbf{kN} & \textbf{} & \textbf{19.53}& \textbf{19.84}& \textbf{13.96}& \textbf{9.11}& \textbf{}\\ \hline
\textbf{Max Load}&\textbf{\(P_{max}\)}&\textbf{kN} & \textbf{13.16} & \textbf{32.47}& \textbf{28.41}& \textbf{19.00}& \textbf{24.42}& \textbf{3.67}\\ \hline
\textbf{Shape Changes during deformation}&\textbf{-}&\textbf{-} & \textbf{None} & \textbf{Slight Necking}& \textbf{Necking}& \textbf{Very slight necking}& \textbf{Extreme Necking}& \textbf{None}\\ \hline
\textbf{Description of Fracture Surface}&\textbf{-}&\textbf{-} & \textbf{Flat, Graphite flakes} & \textbf{Cup and Cone}& \textbf{Cup and Cone}& \textbf{Shear lips and orange peel}& \textbf{Extreme Cup and Cone}& \textbf{Flat crack init. on edge}\\ \hline
\multicolumn{9}{|c|}{\textbf{Hardness}} \\ \hline
\textbf{Rockwell Hardness}&\textbf{HRB}&\textbf{-} & \textbf{100.9} & \textbf{95.5}& \textbf{89.4}& \textbf{75.4}& \textbf{71.7}& \textbf{-}\\ \hline
\multicolumn{9}{|c|}{\textbf{Ductility}} \\ \hline
\textbf{Gage Length}&\textbf{\(l_{0}\)}&\textbf{mm} & \multicolumn{6}{|c|}{\textbf{25.4}}\\ \hline
\textbf{Percent Elongation}&\textbf{\%EL}&\textbf{-} & \textbf{1.05} & \textbf{14.6}& \textbf{27.4}& \textbf{19.9}& \textbf{78.2}& \textbf{3.00}\\ \hline
\textbf{Final Diameter}&\textbf{\(d_{f}\)}&\textbf{mm} & \textbf{7.09} & \textbf{5.74}& \textbf{4.58}& \textbf{6.19}& \textbf{3.06}& \textbf{7.96}\\ \hline
\textbf{Final Area}&\textbf{\(A_{f}\)}&\textbf{\[mm^2\]} & \textbf{39.5} & \textbf{25.9}& \textbf{16.5}& \textbf{30.1}& \textbf{7.35}& \textbf{49.8}\\ \hline
\textbf{Percent Reduction of area}&\textbf{\%RA}&\textbf{-} & \textbf{1.40} & \textbf{36.3}& \textbf{57.9}& \textbf{24.0}& \textbf{81.6}& \textbf{1.00}\\ \hline
\multicolumn{9}{|c|}{\textbf{Mechanical Properties Derived from stress-strain diagram}}\\ \hline
\textbf{Young's Modulus}&\textbf{E}&\textbf{GPa} & \textbf{103} & \textbf{194}& \textbf{198}& \textbf{72}& \textbf{204}& \textbf{4.15}\\ \hline
\textbf{Yield Strength}&\textbf{\(\sigma_y\)}&\textbf{MPa} & \textbf{108} & \textbf{474}& \textbf{498}& \textbf{352}& \textbf{229}& \textbf{-}\\ \hline
\textbf{Ultimate Strength}&\textbf{\(\sigma_u\)}&\textbf{MPa} & \textbf{323} & \textbf{798}& \textbf{719}& \textbf{478}& \textbf{612}& \textbf{75}\\ \hline
%\label{}
\end{tabularx}
\end{center}
\end{document}
\end{document}
XXXXXXwith*{6}{>{\centering\arraybackslash}X}.\begin{table}\centering\caption{Tensile Mechanical Properties} \begin{tabularx}{…} … \end{tabularx}.Xcolumns are to narrow for cell contents (consequently, it overlap, prescribed table width is wider than\textwidth, consequently it spill out of right border, etc. Do you realy like to have such a table?