package inputenc error : the keyboard character used is undefined

Question

I have a simple text line that I get the above error in it , I don't see anything strange in the line , shall you please help me about it ? I am sure it's not about reading the help again ! thank you so much

\documentclass[11pt,a4paper,twoside,openright]{report}

\usepackage{setspace}
\usepackage{graphicx}
\usepackage{tabularx}
\usepackage{tabu}
\usepackage{subfigure}
\usepackage{afterpage}
\usepackage{amsmath,amssymb}            
\usepackage{rotating}  
\usepackage{fancyhdr}  
\usepackage[scriptsize]{caption} 
\hyphenation{a-gen-tiz-za-zio-ne}
\usepackage{float}
\usepackage[parfill]{parskip}
\usepackage{multicol}
\usepackage{siunitx}
\usepackage{amsmath}

\graphicspath{ {images/} }

\usepackage[a4paper,lmargin=2cm,rmargin=2cm]{geometry}

\newcommand*{\diff}{\mathop{}\!\mathrm{d}}

\newcommand*{\var}[1]{\texttt{#1}}

\usepackage[USenglish]{babel}
\usepackage[latin1]{inputenc}
\renewcommand{\captionfont}{\normalfont \sffamily \itshape \small}

\pagestyle{empty}



\begin{document}



   F.W.Zok \cite{R34} has analyzed metalic sandwich panels with textile cores  subject to combined bending and shear and then designed for minimum weight. Basic results for the weight benefits relative to solid plates are presented, with emphasis on restricted optimizations that assure robustness (non-catastrophic failure) and acceptable thinness. Select numerical simulations are used to check the analytical results and to explore the role of strain hardening beyond failure initiation. Comparisons are made with competing concepts, especially honeycomb and truss core systems. It is demonstrated that all three systems have essentially equivalent performance. The influence on the design of a concentrated compressive stress that might crush the core has been explored and found to produce relatively small effect over the stress range of practical interest. “Angle ply” cores with members in the $\pm \ang{45}$ orientation are found to be near optimal for all combinations of bending, shear and compression.

\end{document}

and also the reference R34 in the code is :

@Article{R34,
  Title                    = {Design of metallic textile core sandwich panels },
  Author                   = {F.W. Zok and H.J. Rathbun and Z. Wei and A.G. Evans},
  Journal                  = {International Journal of Solids and Structures },
  Year                     = {2003},
  Number                   = {21},
  Pages                    = {5707 - 5722},
  Volume                   = {40},

  Doi                      = {http://dx.doi.org/10.1016/S0020-7683(03)00375-5},
  ISSN                     = {0020-7683},
  Keywords                 = {Sandwich panels},
  Url                      = {http://www.sciencedirect.com/science/article/pii/S0020768303003755}
}

Answer 1

try this:

\documentclass[11pt,a4paper,twoside,openright]{report}

\usepackage{setspace}
\usepackage{graphicx}
\usepackage{tabularx}
\usepackage{tabu}
\usepackage{afterpage}
\usepackage{amsmath,amssymb}            
\usepackage{rotating}  
\usepackage{fancyhdr}  
\usepackage[scriptsize]{caption} 
\hyphenation{a-gen-tiz-za-zio-ne}
\usepackage{float}
\usepackage[parfill]{parskip}
\usepackage{multicol}
\usepackage{siunitx}
\usepackage{amsmath}

\graphicspath{ {images/} }

\usepackage[a4paper,lmargin=2cm,rmargin=2cm]{geometry}

\newcommand*{\diff}{\mathop{}\!\mathrm{d}}

\newcommand*{\var}[1]{\texttt{#1}}

\usepackage[USenglish]{babel}
\usepackage[latin1]{inputenc}
\renewcommand{\captionfont}{\normalfont \sffamily \itshape \small}

\pagestyle{empty}



\begin{document}



F.W.Zok \cite{R34} has analyzed metalic sandwich panels with textile cores  subject to combined bending and shear and then designed for minimum weight. Basic results for the weight benefits relative to solid plates are presented, with emphasis on restricted optimizations that assure robustness (non-catastrophic failure) and acceptable thinness. Select numerical simulations are used to check the analytical results and to explore the role of strain hardening beyond failure initiation. Comparisons are made with competing concepts, especially honeycomb and truss core systems. It is demonstrated that all three systems have essentially equivalent performance. The influence on the design of a concentrated compressive stress that might crush the core has been explored and found to produce relatively small effect over the stress range of practical interest. ``Angle ply'' cores with members in the $\pm \ang{45}$ orientation are found to be near optimal for all combinations of bending, shear and compression.

\end{document}

it was the quote characters that Angle ply had. this is a pretty common encoding mistake with copy-paste. in the future, please post a minimal working example - had you tried to put one together, you probably would have found the problem in the process : ).

also, my obsessive-compulsive tendencies beg that you remove your preamble line of \usepackage{amsmath} since you already have \usepackage{amsmath,amssymb} above it.