springs to determine the mass required for each spring to give the same stable time increment. If this mass is too large compared to the mass of the model, Abaqus/Explicit will issue an error message that the spring is too stiff compared to the model definition.

Relative displacement definition

The relative displacement definition depends on the element type. SPRING1 elements

The relative displacement across a SPRING1 element is the ith component of displacement of the spring's node:

where i is defined as described below and can be in a local direction (see ”).

SPRING2 elements

The relative displacement across a SPRING2 element is the difference between the ith component of displacement of the spring's first node and the jth component of displacement of the spring's second node:

where i and j are defined as described below and can be in local directions (see ”).

It is important to understand how the SPRING2 element will behave according to the above relative displacement equation since the element can produce counterintuitive results. For example, a SPRING2 element set up in the following way will be a “compressive” spring:

If the nodes displace so that and , the spring appears to be in

compression, while the force in the SPRING2 element is positive. To obtain a “tensile” spring, the SPRING2 element should be set up in the following way:

SPRINGA elements

For geometrically linear analysis the relative displacement is measured along the direction of the SPRINGA element in the reference configuration:

where is the reference position of the first node of the spring and is the reference position of its second node.