Mathematical Institute, University of Oxford, Woodstock Rd, Oxford, OX2 6GG, UK.
Université de Lyon, Ecole Normale Supérieure de Lyon, Université Claude Bernard, CNRS, Laboratoire de Physique, F-69342 Lyon, France.
Soft Matter. 2020 May 21;16(19):4574-4583. doi: 10.1039/c9sm02511a.
From human tissue to fruits, many soft materials are coated by a thin layer of a stiffer material. While the primary role of such a coating is often to protect the softer material, the thin, stiff coating also has an important effect on the mechanical behaviour of the composite material, making it appear significantly stiffer than the underlying material. We study this cloaking effect of a coating for the particular case of indentation tests, which measure the 'firmness' of the composite solid: we use a combination of theory and experiment to characterize the firmness quantitatively. We find that the indenter size plays a key role in determining the effectiveness of cloaking: small indenters feel a mixture of the material properties of the coating and of the substrate, while large indenters sense largely the unadulterated substrate.
从人体组织到水果，许多软材料都覆盖着一层较硬的材料。虽然这种涂层的主要作用通常是保护较软的材料，但这种薄而硬的涂层对复合材料的力学性能也有重要影响，使其表现出比其基础材料明显更硬的性能。我们研究了涂层的这种伪装效应，针对的是特定的压痕测试案例，该测试测量复合材料的“硬度”：我们使用理论和实验相结合的方法对其进行定量分析。我们发现压头尺寸在确定伪装的有效性方面起着关键作用：小压头感受到的是涂层和衬底材料性能的混合物，而大压头则主要感受到的是未受干扰的衬底。
