The Technology

Multicontinuum Technology (MCT) incorporates the classical micromechanics-based strain decomposition technique of Hill in a numerical algorithm that extracts the stress and strain fields for constituents (fiber and matrix) of a composite. By treating the constituents as separate but linked continua, the responses of these most basic components can be determined at every point in the structure. This allows accurate representation of several material phenomena:

• Failure occurs in constituents. Failure modes for the fiber and matrix are vastly different; and caused by different loading scenarios. The Helius:MCT™ failure criteria has been developed by broadening conventional engineering failure criteria in conjunction with meticulous comparison to a wide array of experimental test data.
• Progressive matrix damage. Matrix failure often begins with a single crack and evolves by the formation of additional cracks. Helius:MCT™ does not model cracks explicitly; it uses a continuum mechanics based multi-linear post failure degradation scheme in the matrix constituent allowing the level of degradation to be correlated to the evolution of cracks.
• Catastrophic fiber failure. Fiber failure is an abrupt event where fibers are often destroyed in a rapid manner. In the Helius:MCT™ fiber stiffness is immediately reduced to a faction of the virgin stiffness.
• Constituent nonlinearity. Composite ductile material behavior occurs due to elongation of polymer chains or development of micro-voids, often only in a single constituent. Suitable constitutive relationships to capture nonlinear behavior are implemented in only this constituent. For instance, nonlinear longitudinal shear behavior is modeled by altering the stiffness of only the matrix constituent.
• Pressure-induced strength enhancement is captured. Experimental data shows polymer matrix composites exhibit significant strengthening under high pressures. Similar behavior also exists in polymers. In Helius:MCT™, a model that accurately strengthens polymers under pressure is applied to the matrix constituent.
• Interactions between constituents. Fiber and matrix material properties are vastly different by design. In the presence of temperature change or multiaxial loading, large internal stresses may develop in constituents. For example, carbon fibers often have a negative coefficient of thermal expansion (CTE) while epoxy resins have a positive CTE. When a carbon/epoxy composite is cooled, opposing CTE’s cause large internal stresses to develop within constituents even though composite stress are zero.

Helius:MCT™ has been implemented such that robust convergence is achieved upon material degradation. Run time crashes due to numerical instabilities are virtually eliminated. This enables determination of catastrophic failure of a structure from specific metrics, removing much guess work.

Helius:MCT™ has been rigorously compared to experimental test data. Superior results have been validated through two World Wide Failure Exercises (WWFE I and WWFE II), a large space structures analytical and experimental program, an unlined composite pressure vessel program, numerous technical publications, and through years of use inside the US DOD.