documentclass[12pt,article]{elsarticle}
usepackage{pgfplots}
pgfplotsset{compat=1.11}

begin{document}
begin{figure}[!h]
    begin{minipage}{0.5textwidth}
        centering
        begin{tikzpicture}[font=sffamily]
        path (0,0) coordinate (A) (60:3) coordinate (B) (3,0) coordinate (C);
        draw[thick,path picture={
            foreach X in {A,B,C}
            {draw[line width=0.4pt] (X);}}]
        (A) node[left]{$A$} to[bend right=12]
        (B) node[above right]{$B$} to[bend right=15]
        (C) node[right]{$C$} to[bend right=20] cycle;
        %   node at (barycentric cs:A=1,B=1,C=1) {$<180^circ$};
        end{tikzpicture}
        caption{Triangle in a CAT(0) space}
        label{fig:tri1}
    end{minipage}hspace{0.05cm}%hfill
    hspace{-0.12cm}
    begin{minipage}{0.5textwidth}
    centering
    begin{tikzpicture}[font=sffamily]
    path (0,0) coordinate (A) (60:3) coordinate (B) (3,0) coordinate (C);
    draw [thick,path picture={
        foreach X in {A,B,C}
        {draw[line width=0.4pt] (X);}}] (A) node[left]{$A$} (B) node[above right]{$B$}    (C) node[right]{$C$} (0,0) --  (60:3) -- (3,0) -- cycle;
    end{tikzpicture}
    caption{Triangle in an Euclidean space}
    label{fig:tri2}
    end{minipage}%hspace{0.05cm}%hfill
end{figure}
end{document}