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EM 388F Term Paper: Interface Fracture – Analysis and Numerical Assessment of SAM-SAM Fracture with ABAQUS

Masayuki Wakamatsu's picture


Self Assemble Monolayers, SAMs, can be widely used for micro to macro scale purposes such as stiction or anti-stiction coating within IC chips, as an adhesive for bonding inorganic material to organic materials, and as an anti-corrosion coating for automotive parts. However, SAMs as "a ultra thin layer adhesive" still requires extensive theoretical and experimental works. In this study, Si(111) substrate with 15.0mm, 5.00 mm, and 0.320 mm in length, width, and thickness respectively, are used to model a Si-SAM-SAM-Si sandwich specimen. Initial crack or non-bonded length is defined as 4.0 mm. This sandwich specimen will be subjected to displacement input at the end of the cantilever beam. Since SAM-SAM adhesion is considered as ultra thin adhesive, when the specimens are subjected to Mode I type loadings, a traction separation interface fracture is expected to occur. Although mode mixty may play a minor rule to fracture propagation, it is assumed to be negligible for calculation purposes. To simulate the SAMs’ behaviors, a fracture model was prepared with ABAQUS/Standard Vr.6.7 software with infinitesimal thin cohesive elements. Since SAMs can be tailored to favorable characteristics in thickness and adhesion strength, different maximum separation stresses and separation lengths are considered but with the identical energy release rate of 0.1 J/m^2. The goal of this study is to (i) understand the behavior of cohesive elements in mode I fracture, (ii) estimate required displacement to initiate fracture and compare with simple DCB Mode I fracture requirement, and (iii) if possible, the ABAQUS results will be compared with semi-numerical mathematical model with DCB on non-elastic foundations.








L. Daridon. B. Cochlin. M. Ferry. Dalamination and Fiber Bridging Modelling in Composite Samples. Journal of Composite Materials. Vol. 31. 874-888. (1997)

A. Suo. G. Bao. B. Fan. Delamination R-Curve Phenomena Due to Damage. J. Mech. Phys. Solids. Vol. 40. No.1. pp. 1-16. (1992)

M. Wang. Nanoindentation of Thin Organic Films and Self-Assembled Monolayers. Dissertation. The University of Texas at Austin (2004)

PDF icon finalpresentationMW.pdf1.44 MB
PDF icon 080509_term_paperMW.pdf785.11 KB


Masayuki Wakamatsu's picture


 Please find the attached presentation file. 





Rui Huang's picture

It is interesting to see how the shape of traction-separation curve affects the load-displacement response as well as the crack growth behavior.  


From my experience, the shape of traction-separation curve has little effect on the load-displacement curve for linear materials. The initial stiffness of the cohesive elements should affect the slope of the first part of load-displacement curve, and the "sharpness" of the peak load value depends on the strength (maximal traction) of the elements. As the crack propagates all curves should practically coincide, as we see in Case 3. But results for Case 1 look quite strange.

Masayuki Wakamatsu's picture

imechanicians & Dr. Huang,


 Please find the attached EM 388F term paper.

 If anyone is struggling to have cohesive element to work, please feel free to contact me.

 I couldn't have made numerical analysis without generous support from fellow phd. student.






 You have done an excellent work!

 Here what I want to say is that I am also working on using cohesive elements to simulate the delamination process in pizeoelectric thin films. Layers in this kind of thin films are in micrometer or even nanometer scale. What's more, my simulation is also based on a sandwiched-cantilever experiment.

In my simulation, some different kinds of cohesive zone models are used and their traction-separation laws are  programmed in the user subroutine in ABAQUS. By reading your paper attached in your blog, I know that the bilinear cohesive zone model was used in your simulation. So, did you applly other kinds of cohesive zone models in your simulation? Did you code their constitutive relations in the user subroutine?

Therefore, I am very interested in communicating with you about the cohesive zone models. Do you have spare time to have this kind of communication with me?

PS: My e-mail:




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