Two-parameter analysis of fatigue crack growth behavior in structural acrylic adhesive joints

Conducting displacement-controlled fatigue double cantilever beam tests of a structural acrylic adhesive, two different slopes were observed in the fatigue crack growth (FCG) relationship of the FCG rate versus the strain energy release rate (SERR) parameters depending on the loading conditions. Because fatigue is a two-parameter problem where stress waveforms contain cyclic and monotonic terms, the contribution of each term toward FCG needs to be clarified. Therefore, each slope was explained using SERR with load range and mean load. In addition, cases were observed where the slope changed with an increasing number of cycles. Accordingly, the FCG rate changes. Understanding the phenomenon is important to estimate the crack position from an engineering point of view. Therefore, FCG was categorized into three types using amplitude and mean displacement. After a sufficient number of fatigue cycles, amplitude played a more dominant role than R-ratio or mean displacement to determine crack location.