Modal Assurance Criterion

TLDR

The Modal Assurance Criterion is a statistical indicator bounded between 0 and 1, most sensitive to large differences in mode shapes, often used to pair analytical and experimental mode shapes, but it only indicates consistency, not validity or orthogonality. This article reviews the use of the original Modal Assurance Criterion (MAC). The MAC considers only modal shapes, so a separate frequency comparison must be used with MAC values to identify correlated mode pairs. The MAC provides a good, easy‑to‑apply statistic indicating consistency between mode shapes without requiring system matrix estimates.

Abstract

This article reviews the using of the original Modal Assurance Criterion (MAC). The Modal Assurance Criterion is a statistical indicator that is most sensitive to large differences and relatively insensitive to small differences in the mode shapes. This yields a good statistic indicator and a degree of consistency between mode shapes. The MAC considers only modal shapes which mean that a separate frequency comparison must be used in conjunction with the MAC values to determine the correlated mode pairs. The MAC is often to used to pair modes shapes derived from analytical models with those obtained experimentally. It is easy to apply and does not require an estimate of the system matrices. It is bounded between 0 and 1, with 1 indicating fully consistent mode shapes. It can only indicate consistency and does not indicate validity or orthogonality. A value near 0 indicates that the modes are not consistent.