Bulk metallic glass cantilever beams: Outstanding at large-deflection deformation and their application in complaint mechanisms

Excellent combination of mechanical properties of bulk metallic glasses (BMGs) are a class of relatively young and promising candidate materials for compliant mechanisms (CMs), which are usually associated with the nonlinear large-deflection deformation. In this study, an effective design strategy was proposed to enhance the flexibility of BMG cantilever beam quantitatively, which by means of increasing the ratio of loading distance to beam thickness. Moreover, the accuracy of modulus of elasticity in bending, Eb, which measured by cantilever bending test was affected seriously by the support compliance of the fixed end, and the accurate Eb value of BMG beam can be attained after eliminating this influencing factor. The critical boundary condition of cantilever beams within the scope of small-deflection deformation was identified, which situates at non-dimensional deflection parameter, δy/L, is 0.2. Correspondingly, the critical loading distance-to-thickness ratios, (L/t)c, of cantilever beams within small-deflection deformation were derived for BMGs and conventional crystalline metals, which provide a criterion to predict the potential to achieving large-deflection deformation. It is noticed that by plotting the flexural stress-δy/L relations for BMG and several conventional crystalline metals used in CMs, the unique advantages of BMG cantilever beam in the aspect of achieving large-deflection deformation and enduring higher flexural stress can be reflected more intuitively. These advantages of BMG cantilever beam are well suitable for CMs which designed to have a small footprint and requirement of large-deflection motions, such as in the fields of microelectromechanical systems (MEMS) and biomedicines.