Meaning
Non-proportional volume changes occurring in solid materials under high stress or temperature gradients deviate from linear elastic deformation models. Structural simulation models incorporate non-linear volumetric strain to predict composite panel swelling and core crushing in aerospace sandwich structures. This mechanical metric governs bulk modulus calculations and volumetric expansion limits under combined thermal and mechanical loads.
The relationship stops applying within low-stress elastic regimes where volumetric expansion remains directly proportional to applied hydrostatic pressure.
Constitutive Behavior
Material testing subjects composite coupons to combined hydrostatic pressure and thermal cycling. Stress-strain curves show non-linear slope changes as resin matrices experience plastic deformation or internal micro-cracking. High-resolution dilatometry tracks volumetric expansion across varying temperature ranges.
Structural Impact
Unbalanced volumetric strain across thick composite laminates induces severe internal shear stress, causing internal delamination. Structural cores in sandwich panels crush non-uniformly under high pressure, altering local stiffness properties. Finite element solvers update element volumes iteratively to maintain force equilibrium in complex structural calculations.
Manufacturing process controls monitor autoclave pressure ramps to prevent uncontrolled volumetric changes during curing cycles. Material certification reports document strain limits to establish safe operating envelopes for structural components.
Testing Validation
Mechanical testing frames measure triaxial displacements to validate constitutive material models under multi-axial loading. Divergence between predicted volumetric expansion and physical measurements triggers material model recalibration. Compliance documentation records maximum volumetric strain values to verify panel structural capability prior to airframe integration.
