All Terms A–Z

All key terms around FEM simulation and the Dr.Q platform, explained clearly and practically.

C

CAD: Computer-Aided Design. Software for creating 3D models (SolidWorks, Fusion 360, Inventor, etc.).

Convergence: The property of a numerical solution approaching the exact solution as the mesh is refined. A converged result doesn't change significantly when you add more elements.

D

Degree of Freedom (DOF): A possible direction of movement for a node: three translations (X, Y, Z) and three rotations = max. 6 DOF per node. Boundary conditions remove DOFs.

Density (ρ): Mass per unit volume. Required for self-weight (gravity) loads and dynamic analyses.

E

Element: The basic building block of the FEM mesh. Common types: tetrahedra (Tet4, Tet10), hexahedra (Hex8, Hex20), triangles, quads.

Strain: Relative change in length of a material under load. Dimensionless (often expressed in % or mm/mm).

Young's modulus (E): The stiffness of a material; the ratio of stress to strain in the elastic range. Unit: MPa or GPa.

F

FEM: Finite Element Method. A numerical method for calculating stresses, deformations, temperatures, etc. in structures by dividing them into small elements.

Fixed support: A boundary condition that locks all degrees of freedom at a surface (zero displacement and rotation in all directions).

J

Jacobian: A mesh quality measure. Negative Jacobian values indicate inverted (invalid) elements that cause solver errors.

L

Load case: A specific combination of boundary conditions and loads describing one loading scenario.

M

Mesh (FE mesh): The subdivision of the geometry into finite elements (triangles, tetrahedra, hexahedra, etc.).

N

Node: A point in the FE mesh at which displacements and forces are calculated. Elements are connected at their nodes.

P

Poisson's ratio (ν): Ratio of lateral strain to axial strain under uniaxial loading. Typical value: 0.3 for steel. Must be between 0 and 0.5.

Principal stress: Normal stress along a principal axis (a direction with no shear stress). The three principal stresses σ₁ ≥ σ₂ ≥ σ₃ describe the full stress state.

R

Boundary condition: A specification of how the model is supported or loaded at specific locations: supports and symmetry planes as well as forces and pressures. In Dr.Q, the region of action can also be defined via a separate surface CAD file (STEP boundary condition).

Reaction force: The force that a boundary condition exerts on the model in response to the applied loads. Sum of reaction forces = sum of applied loads (Newton's third law).

S

Singularity: A location where the mathematical stress tends to infinity, caused by sharp re-entrant corners, point loads, or point supports. A numerical artefact, not a real physical stress.

Skewness: A mesh quality metric measuring how distorted an element is from its ideal shape. Values close to 0 are good; values close to 1 indicate highly distorted elements.

Solver: The algorithm that solves the FEM equation system. Dr.Q currently enables linear static simulations; extensions such as contact analysis and nonlinear material models are on the way.

Stress: Force per unit area in the material. Unit: MPa (N/mm²).

V

Von Mises stress: A scalar equivalent stress for ductile materials. Combines the multi-axial stress state into a single value for yield assessment. Yield occurs when σ_VM ≥ R_p0.2.

Y

Yield strength (R_p0.2): The stress at which a material begins to deform plastically (permanently). FEM results are typically compared against this value to assess safety.