Implausible Results
Stresses too high, too low, or physically nonsensical, here are the most common causes.
If you only have 2 minutes
Implausible results almost always come down to inconsistent units, incorrect boundary conditions, or a singularity mistaken for a real stress concentration. Work through the causes below, then read the Plausibility Check for the full sanity-check routine.
Most common causes
- Inconsistent units → displacements or stresses off by a large factor (a classic: Young's modulus entered as 210 GPa instead of 210,000 MPa). Dr.Q works in N and mm, stress in MPa; see Define Materials.
- Wrong boundary conditions → over-constrained gives unrealistically low (stiff) stress; under-constrained gives runaway stress or rigid-body motion. See Ineffective Boundary Conditions and Supports & Constraints.
- A singularity read as real stress → unbounded peak stress at sharp corners, point loads, or point supports. Evaluate away from the point. See Singularity Warning.
- Broken symmetry → a symmetric model under symmetric loading must give symmetric results; if it doesn't, a load or support is asymmetric. See Symmetry.
When a result quantity isn't available
Some quantities exist only for certain setups. If Dr.Q reports that a quantity can't be produced:
- Reaction force is available only on force-type supports/loads (Error 153).
- Stiffness is available only for certain boundary-condition types (Error 154).
- Plastic strain requires a plasticity material; an elastic run has none (Error 178).
- Inner-variable quantities require a solution that stored them (Error 177).
- Stress, strain, and displacement are always available; natural frequencies and mode shapes come from a modal run and buckling load factors and modes from a buckling run. There is no temperature-field output.