[아바쿠스] 접촉조건에서 SDI 에러가 발생하는 경우

접촉해석을 하다가 계속SDI 에러가 발생하여 에러 원인을 찾아본 결과 매뉴얼에 설명나온대로 하였더니 잘 해결 되었다.

CONTACT FORCE ERROR TORERANCE FOR CONVERT SDI=YES

이경우 아래와 같이 *.inp 파일에 SDI옵션을 추가해주거나 CAE의 Step을 수정해주면 된다.

Inp 파일 사용법 : *STEP, CONVERT SDI=NO

Abaqus/CAE 사용법 : Step Edit에 들어가서 Other탭의

                                      Convert severe discontinuity iterations: Off 로 설정한다.

이하는 매뉴얼 전문이다.

Severe discontinuities in Abaqus/Standard

Abaqus/Standard distinguishes between regular, equilibrium iterations (in which the solution varies smoothly) and severe discontinuity iterations (SDIs) in which abrupt changes in stiffness occur. The most common of such severe discontinuities involve open-close changes in contact and stick-slip changes in friction. By default, Abaqus/Standard will continue to iterate until the severe discontinuities are sufficiently small (or no severe discontinuities occur) and the equilibrium (flux) tolerances are satisfied. Alternatively, you can choose a different approach in which Abaqus/Standard will continue to iterate until no severe discontinuities occur.

For contact openings with the default approach, a force discontinuity is generated when the contact force is set to zero, and this force discontinuity leads to force residuals that are checked against the time average force in the usual way, as described in “Convergence criteria for nonlinear problems,” Section 7.2.3. Similarly, in stick-to-slip transitions the frictional force is set to a lower value, which also leads to force residuals.

For contact closures a severe discontinuity is considered sufficiently small if the penetration error is smaller than the contact compatibility tolerance times the incremental displacement. The penetration error is defined as the difference between the actual penetration and the penetration following from the contact pressure and pressure-overclosure relation. In cases where the displacement increment is essentially zero, a “zero penetration” check is used, similar to the check used for zero displacement increments (see “Convergence criteria for nonlinear problems,” Section 7.2.3). The same checks are used for slip-to-stick transitions in Lagrange friction.

To make sure that sufficient accuracy is obtained for contact between hard bodies, it is also required that the estimated contact force error is smaller than the time average force. The estimated contact force error is obtained by multiplying the penetration by an effective stiffness. For hard contact this effective stiffness is equal to the stiffness of the underlying element, whereas for softened/penalty contact the effective stiffness is obtained by adding the compliance of the contact constraint and the underlying element.

Forcing the iteration process to continue until no severe discontinuities occur is the more traditional, conservative method. However, this method can sometimes lead to convergence problems, particularly in large problems with many contact points or situations where contact conditions are only weakly determined. In such cases excessive iteration may occur and convergence may not be obtained