  An adjoint-based procedure to determine weaknesses, or, more generally, the
material properties of structures is developed and tested. Given a series of
load cases and corresponding displacement/strain measurements, the material
properties are obtained by minimizing the weighted differences between the
measured and computed values. In a subsequent step, techniques to minimize the
number of load cases and sensors are proposed and tested.
  Several examples show the viability, accuracy and efficiency of the proposed
methodology and its potential use for high fidelity digital twins.
