טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentBreitman Peter
SubjectDevelopment of clean dry biomimetic Adhesive
DepartmentDepartment of Mechanical Engineering
Supervisor Dr. Yuri Kligerman
Full Thesis textFull thesis text - English Version


Abstract

A gripping device, inspired by natural, adhesion based climbing and locomotion mechanisms found in reptiles and insects, is proposed. The device is based on an elastic, thin, spatula like, soft polymer growth, that is working against a rigid surface, undergoing large deformations, normal and tangential loading and lateral movements. A numerical model is created to evaluate the adhesive behavior of the proposed device, and specifically the ability of such a device to hold tangential loads without slipping.

            A bi-linear constitutive law is used to describe the adhesive behavior of the spatula and counter surface interactions in the normal direction (pull off force, etc.). Tresca law of friction is used to describe the interactions in the tangential direction: friction forces and relative motion.

As input, a range of normal forces that press the counter surface against the spatula wall was tested, as well as several different values of maximal tangential stress in the contact.

For each input, the maximal lateral load bearing capacity is evaluated, using dimensional results (force) and a dimensionless parameter that signifies the relative area of the spatula that is in contact during sliding inception.

            Comparison to experimental work is performed to assess the qualitative agreement of the results obtained by the model. The parameter that sets the maximal shear stress at the interface is identified using experimental data.

It was found that the adhesive interaction parameters, that are related to its normal strength, are of little importance for the given type of loading, while the material parameter that sets the maximal shear stress plays a bigger role in determining the load capability of the adhesive gripping device.

Good agreement with the experiment was obtained in the higher area of the normal force range, enabling the identification of adhesive parameters using the experiment.

            In an attempt to study the lower range of the normal forces tested, additional study of the experimental results was performed. Fitting a power law curve to the experimental results showed correlation between the multiplier coefficient of the power law and the length of the spatula wall.

            Overall, the model shown in this work provides an adequate tool of analysis for the proposed system, predicting its behavior. The ability to hold tangential load is of particular interest.

            Further research can be concentrated to assess the effect of different geometrical values by performing a parametric analysis on different sizes of the model. Also, different modes of loading can be tested, as well as the behavior of a spatula array and its effect on the gripping capability.