Learn about the extraneous stiffness parameters required for certain element types.
Certain types of Abaqus elements (e.g., shell elements and reduced integration elements) require extraneous stiffness parameters in order to stabilize their response to deformation modes whose stiffness is not provided by material constitutive relations. Depending on the specific type of element, these extraneous stiffness parameters may include one or more of the following: transverse shear stiffnesses, hourglass control stiffnesses, thickness modulus, and thickness Poisson ratio. Provided that the finite element model uses only standard Abaqus material types, Abaqus/Standard will automatically compute all of the required extraneous stiffness parameters at runtime. However, when the finite element model contains user-defined material types, Abaqus/Standard cannot automatically compute all of the extraneous stiffness parameters that are required. In that case, the Abaqus input file must explicitly define any required extraneous stiffness parameters. These extraneous stiffness parameters are defined as options or data in the various section keyword statements (e.g., *SOLID SECTION, *SHELL SECTION, etc.).
Helius PFA includes a convenient, auxiliary program (xStiff) that automatically calculates and inserts the required extraneous stiffness parameters into the Abaqus input file. The use of xStiff is highly recommended as it greatly accelerates the model building process, while at the same time minimizing the chance for errors to be introduced into the input file. For more information on using xStiff to automatically calculate and insert the required extraneous stiffness parameters into the Abaqus input file, please refer to the Use xStiff to Insert Extraneous Stiffness Parameters section.