The Effects Of Dimension And Loading Time On Surface Creasing Instability Of Homogeneous Soft Solid

Soft, elastic materials under compression or swell may undergo a wide variety of elastic instabilities that include global buckling modes, wrinkling and creasing of surfaces, and snapping transitions. Traditionally, these deformations have usually been avoided as they often represent a means of mechanical failure. However, a new trend has emerged in recent years in which buckling mechanics can be harnessed to endow materials with beneficial functions. For many such applications, it is desirable that such deformations happen reversibly and in response to well-defined signals or changes in their environment. For example, when a soft elastic material is compressed, its initially flat surface will suddenly form creases. While creases are commonly observed, and have been exploited to control chemical patterning, enzymatic activity, and adhesion of surfaces.Here we focus on the creasing instability of surface. The creasing instability of soft material under compression is studied by a combination of experiment and numerical simulation. Experimentally, we design an apparatus to measure the nucleation and growth of creasing under plane strain loading conditions. The thin sample can measure the critical strain accurately in comparison with the nonlinear theory. The creasing patterns transit with the thickness of the specimen. Measurement of depth and spacing between creasing and the length quantitatively reveals the influence of dimension. The time-dependent creasing pattern is also found even with the thin specimen.Numerically, we simulate the instability of creases in highly deformable soft materials using a robust method of point perturbation of free surfaces. This method enables us to identify the crease instability in soft materials such as elastomers, and to ascertain the critical conditions for the onset of this mode of instability. Furthermore,we show a wide range of perturbation on surface instability. A scaling law between the depth and spacing is established by the numerical simulations,which agrees well with the statistics data of experiments. This approach provides a practical route for experimentalists in their investigations on surface instabilities, particularly crease instability.