Antarvedi Goda Bharath, Ma Zhenwei, Fregonese Stefano, Bacca Mattia
Mechanical Engineering Department, University of British Columbia, Vancouver, BC V6T1Z4, Canada.
Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, BC V6T 2B5, Canada.
Soft Matter. 2024 Jul 31;20(30):6016-6022. doi: 10.1039/d4sm00279b.
Cutting mechanics of soft solids is gaining rapid attention thanks to its promising benefits in material characterization and other applications. However, a full understanding of the physical phenomena is still missing, and several questions remain outstanding. : How can we directly and reliably measure toughness from cutting experiments? What is the role of blade sharpness? In this paper, we explore the simple problem of wire cutting, where blade sharpness is only defined by the wire radius. Through finite element analysis, we obtain a simple scaling relation between the wire radius and the steady-state cutting force per unit sample thickness. The cutting force is independent of the wire radius if the latter is below a transition length, while larger radii produce a linear force-radius correlation. The minimum cutting force, for small radii, is given by cleavage toughness, , the surface energy required to break covalent bonds in the crack plane. The force-radius slope is instead given by the wear shear strength in the material. cutting experiments on polyacrylamide gels, we find that the magnitude of shear strength is close to the work of fracture of the material, , the critical strain energy density required to break a pristine sample in uniaxial tension. The work of fracture characterizes the toughening contribution from the fracture process zone (FPZ), which adds to cleavage toughness. Our study provides two important messages, that answer the above questions: toughness can be estimated from wire-cutting experiments from the intercept of the force-radius linear correlation, as previously explored. However, as we discovered, this only estimates cleavage toughness. Additionally, the force-radius slope is correlated with the work of fracture, giving an estimation of the dissipative contributions from the FPZ.
由于软固体切割力学在材料表征及其他应用中具有潜在优势，正迅速受到关注。然而，对其物理现象仍缺乏全面理解，仍存在一些突出问题：我们如何通过切割实验直接且可靠地测量韧性？刀刃锋利度起什么作用？在本文中，我们探讨线切割这一简单问题，其中刀刃锋利度仅由线半径定义。通过有限元分析，我们得出线半径与单位样品厚度稳态切割力之间的简单比例关系。如果线半径低于一个转变长度，切割力与线半径无关，而较大半径则产生线性的力 - 半径相关性。对于小半径，最小切割力由解理韧性给出，即裂纹平面中断裂共价键所需的表面能。相反，力 - 半径斜率由材料中的磨损剪切强度给出。通过对聚丙烯酰胺凝胶进行切割实验，我们发现剪切强度的大小接近材料的断裂功，即在单轴拉伸下破坏原始样品所需的临界应变能密度。断裂功表征了断裂过程区（FPZ）的增韧贡献，它与解理韧性相加。我们的研究提供了两条重要信息，回答了上述问题：如之前所探讨的，韧性可通过线切割实验中力 - 半径线性相关性的截距来估计。然而，正如我们所发现的，这仅估计了解理韧性。此外，力 - 半径斜率与断裂功相关，给出了FPZ耗散贡献的估计值。
