wiki:sns:sns2014:interpreting_results []

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====== Interpreting Results ======

Given geometry, material, restraints, and loads, Scan&Solve™ computes several types of quantities that are useful in understanding predicted structural properties of the model:

  * **Displacements**. The primary computed property is displacement -- a vector (x-, y-, z-) quantity measuring where each point of the body moves after the loads are applied. The total displacement is a (scalar) magnitude of the displacement vector. Displacement is measured in units of length. Displacements are important for a number of reasons:
    * Recall that [[wiki:sns:sns2014:linear_static_analysis|linear static analysis]] is really a "small displacement theory" that assumes that the solid shape does not change very much. Thus, the computed displacements can be interpreted as a first approximation of the actual deformation indicating tendency and magnitude of deformation. They can be magnified and visualized in the deflected view. But if the computed displacements are large, the actual deformation may be very different.
    * Generally speaking, predicted values of displacement are always more accurate than predicted values of strains and stresses, because displacement is the primary quantity directly computed by solving a system of linear equations. In contrast to stresses, displacements have finite magnitude and do not have singularities at any points.
    * Large displacements are not necessarily bad; they simply indicate flexibility of the system to move or deform.
    * Because displacement is the primary computed quantity, it's accuracy is necessary for accurate prediction of all other properties. In particular, all computation of stresses, strains, and failure criteria require accurate displacements.
    * For the same reason, displacements provide the best measure for comparing consistency, accuracy, and convergence of computations -- in the same system or between different systems.

  * **Strains**. Informally, strains measure (directional) rate of deformation within the body. It is dimensionless because it measures change of length per unit length. Just like stress, one-dimesional strain can be measured in any direction, and there is one-to-one correspondence between components of stress and strain (normal, shear, principal, etc.).
      * At every point in the body, it is possible to orient the coordinate system in such a way that only normal strains acting in the three orthogonal coordinate axis directions remain. These three components of strain are called principal strains. The value and the direction of the principal strains changes at every point.
      * Generally, strains are proportional to stresses (i.e. large strains imply large stresses), and in linear elasticity stresses and strains are directly related by proportionality constants according to Hooke's law. Strains may be also used directly to predict material failures.

  * **Stresses**. Stress describes all forces acting at a point in a body. Different forces act in different directions. For any selected direction, stress in that direction is measured in units of Force/Area as a force acting across an imaginary plane perpendicular to the selected direction.
      * At every point in the body, it is possible to orient the coordinate system in such a way that only normal stresses acting in the three orthogonal coordinate axis directions remain. These three components of stress are called principal stresses. The value and the direction of the principal stresses changes at every point.
      * Principal stresses are the main tools in predicting failure of materials based on properties of materials and postulated theory. Von Mises criterion is popular for ductile materials, while Rankine and Mohr criteria are widely used for brittle materials.
      * Stresses tend to vary much faster than displacements and may even grow unbounded in the vicinty of stress concentrations -- in agreement with the theory of linear elasticity.

  * **Danger Level.** For a specific failure criterion, a danger level is a scalar value that ranges between 0 and 1. It is computed at every point as a ratio of the computed value of the selected failure criterion to the threshold value known to cause failure of the particular material.
      * A value greater than 1, indicates that the computed value exceeds the known threshold.
      * The values of danger level greater than 1 are not displayed, but the maximum value and location is included in the report and may be determined in the View tab.

Each of the above quantities may be visualized and queried for min/max/point values using the controls on the **[View]** tab.