fix(elements): reject rounded loss of Hex8 bulk stiffness

2026-10-09 01:18:20 +09:00
parent 9088af7b32
commit 7fadd48e1b
3 changed files with 234 additions and 0 deletions
@@ -92,6 +92,16 @@ Result<Hex8Element> Hex8Element::Create(EntityIndex index,
    return Result<Hex8Element>::Failure(
        candidate.Failure("Hex8 Lame moduli must remain finite with "
                          "representable positive shear modulus."));
+  // Validate the rounded moduli actually used by the kernel, not merely the
+  // positive exact-real E/nu formula: cancellation near nu=-1 can erase bulk.
+  const double bulk = candidate.lambda_ + (2.0 * candidate.mu_) / 3.0;
+  const double volumetric_stress =
+      3.0 * candidate.lambda_ + 2.0 * candidate.mu_;
+  if (!std::isfinite(bulk) || bulk <= 0.0 ||
+      !std::isfinite(volumetric_stress) || volumetric_stress <= 0.0)
+    return Result<Hex8Element>::Failure(
+        candidate.Failure("Hex8 rounded Lame moduli require finite "
+                          "representable positive bulk stiffness."));
  if (density && (!std::isfinite(*density) || *density <= 0.0))
    return Result<Hex8Element>::Failure(candidate.Failure(
        "Hex8 reference density must be finite and positive."));