College of Materials and Environmental Engineering, Hangzhou Dianzi University, Hangzhou 310018, People's Republic of China.
CAS Key Laboratory of Mechanical Behavior and Design of Materials, Department of Modern Mechanics, University of Science and Technology of China, Hefei, Anhui 230026, People's Republic of China.
Phys Rev E. 2019 Nov;100(5-1):052804. doi: 10.1103/PhysRevE.100.052804.
Controlled cracks are useful in a wide range of applications, including stretchable electronics, microfluidics, sensors, templates, biomimics, and surface engineering. Here we report on the spontaneous formation of hierarchical crack patterns in metal (nickel) films sputter deposited on soft elastic polydimethylsiloxane (PDMS) substrates. The experiment shows that the nickel film generates a high tensile stress during deposition, which is relieved by the formation of disordered crack networks (called primary cracks). Due to the strong interfacial adhesion and soft substrate, the cracks can penetrate into the PDMS substrate deeply. The width and depth of the primary cracks both increase with increasing film thickness, whereas the crack spacing is insensitive to the film thickness. The film pieces dividing by the primary cracks can fracture further when they are triggered by an external disturbance due to the residual tensile stress, resulting in the formation of fine crack networks (called secondary cracks). The width and spacing of the secondary cracks show different behaviors in comparison to the primary cracks. The morphological characteristics, growth behaviors, and formation mechanisms of the primary and secondary cracking modes have been discussed in detail. The report in this work could provide better understanding of two distinct cracking modes with different sizes and morphologies.
可控裂缝在广泛的应用中非常有用，包括可拉伸电子产品、微流控、传感器、模板、仿生学和表面工程。在这里，我们报告了在软弹性聚二甲基硅氧烷 (PDMS) 基底上溅射沉积的金属（镍）薄膜中自发形成分级裂缝模式。实验表明，镍膜在沉积过程中产生高拉伸应力，通过形成无序的裂缝网络（称为初级裂缝）来缓解。由于强界面附着力和软基底，裂缝可以深入渗透到 PDMS 基底中。初级裂缝的宽度和深度都随薄膜厚度的增加而增加，而裂缝间距对薄膜厚度不敏感。由于残余拉伸应力，当薄膜片受到外部干扰而被触发时，会进一步断裂，形成细裂缝网络（称为次级裂缝）。与初级裂缝相比，次级裂缝的宽度和间距表现出不同的行为。本文详细讨论了初级和次级裂缝模式的形态特征、生长行为和形成机制。本工作报告可以更好地理解具有不同尺寸和形态的两种不同的裂缝模式。
