Elastic instabilities in soft layered composites with alternating interlayer spacing

Elastic instabilities, once regarded purely as a failure mode, are now routinely harnessed to program the response of soft architected materials. Here we show that the onset of buckling in a layered composite can be tuned without changing how much stiff material it contains, simply by rearranging the layers. We consider laminates in which stiff layers, embedded in a soft matrix, are separated by two alternating gaps. We analyse their stability with an analytical model, a complementary sandwich-beam approximation for closely spaced layers, and Bloch-Floquet finite element simulations. At a fixed volume fraction, the evenly spaced (periodic) arrangement is the most stable, whereas the critical strain is lowest when the smallest gap becomes comparable to the layer thickness. By comparing the two extreme arrangements, we find that the periodic composite switches from short-wavelength wrinkling to long-wavelength macroscopic buckling at a lower volume fraction than the least stable arrangement, leaving a window in which the two arrangements fail in qualitatively different ways. Deviating from perfect periodicity thus offers some degree of tunability, but in practical applications one must not uncritically rely on predictions from periodic composites if periodicity during manufacturing cannot be guaranteed. • Alternating interlayer spacing tunes buckling in layered composites at fixed volume fraction. • Periodic layered composites provide the highest critical strain. • The lowest critical strain occurs in layered composites when the smallest gap matches the layer thickness. • Alternating spacing in layered composites shifts the transition between wrinkling and long-wave buckling.