Engineering topics

Jagota, Anand

Publications and source records attributed to Jagota, Anand.

12 records

DOE OSTI2020

Modeling of surface mechanical behaviors of soft elastic solids: theory and examples

Surfaces of soft solids can have significant surface stress, extensional modulus and bending stiffness. Previous theoretical studies have usually examined cases in which both the surface stress and bending stiffness are constant, assuming small deformation. In this work we consider a general formulation in which the surface can support large deformation and carry both surface stresses and surface bending moments. We show that the large deformation theory can be reduced to the classical linear theory (Shuttleworth equation). We obtain exact solutions for problems of an inflated cylindrical shell and bending of a plate with a finite thickness. Our analysis illustrates the different manners in which surface stiffening and surface bending stabilize these structures. We discuss how the complex surface constitutive behaviors affect the stress field of the bulk. Our calculation provides insights into effects of strain-dependent surface stress and surface bending in the large deformation regime, and can be used as a model to implement surface finite elements to study large deformation of complex structures.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Surface Mechanical Properties of Bio-Inspired Architectures (Final Report)

The majority of the work in this field, including most of our own early work, has been focused on one-sided materials. More recently, we have focused on two-sided systems, mimicking attachment systems in organisms that use shape complementarity to endow interfaces with highly enhanced and selective adhesion and friction. We discovered the spontaneous appearance of meso-scale dislocations at interfaces between shape-complementary patterned surfaces and studied how their geometry and materials properties govern macroscopic adhesion and friction. Our second major thrust was to study the influence of surface properties, specifically the surface stress, in mechanical phenomenon involving soft materials. We showed that solid surface stress often plays a very significant and pervasive role and this requires a re-thinking of several canonical surface mechanical phenomena such as adhesive contact, wetting, fracture and surface-stress-driven shape change.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Intrinsically reversible superglues via shape adaptation inspired by snail epiphragm

Significance Achieving both superstrong adhesion and reversibility is challenging, particularly for hydrogels. Here, we report a hydrogel-based, reversible, superglue-like adhesive by combining the benefits of both liquid and dry adhesives in a single material while overcoming their respective limitations. When hydrated, the softened gel conformally adapts to the target surface by low-energy deformation, which is then locked upon drying as the elastic modulus is raised from hundreds of kilopascals to a few gigapascals, analogous to the action of the epiphragm of snails. We show that reversible superstrong adhesion could be achieved from a nonstructured material when the criterion of shape adaption is met, with minimal residual strain energy stored in the system.

36 MATERIALS SCIENCE↗

DOE OSTI2019

A surface with stress, extensional elasticity, and bending stiffness

We demonstrate that the surface of a commonly used polydimethylsiloxane formulation (PDMS, Sylgard 184) treated by ultraviolet ozonolysis (UVO) has significant surface stress, considerable extensional elasticity (the “Shuttleworth Effect”), and surface bending elasticity.

Lapinski, Nicole↗

DOE OSTI2019

Effects of strain-dependent surface stress on the adhesive contact of a rigid sphere to a compliant substrate

Recent experiments have reported that the surface stress of soft elastic solids can increase rapidly with surface strain. For example, when a small hard sphere in adhesive contact with a soft silicone gel is slowly retracted from its rest position, it was found that the retraction force versus displacement relation cannot be explained either by the Johnson–Kendall–Roberts (JKR) theory or a recent indentation theory based on an isotropic surface stress that is independent of surface strain. In this paper, we address this problem using a finite element method to simulate the retraction process. Our numerical model does not have the restrictions of the aforementioned theories; that is, it can handle large nonlinear elastic deformation as well as a surface-strain-dependent surface stress. Our simulation is in good agreement with experimental force versus displacement data with no fitting parameters. Therefore, our results lend further support to the claim that significant strain-dependent surface stresses can occur in simple soft elastic gels. However, significant challenges remain in the reconciliation of theory and experiments, particularly regarding the geometry of the contact and substrate deformation.

36 MATERIALS SCIENCE↗

DOE OSTI2018