Mechanical behavior of nanostructured metallic films under compressive and shear loads

nanostructured thin film;helical spring;mechanics

Groysman, David ; Chasiotis ; Ioannis

关键词: nanostructured thin film;    helical spring;    mechanics;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/27733/Groysman_David.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Experimental techniques have been developed to measure the compressive and shear stiffnesses and bonding strengths of nanostructured thin films consisting of arrays of Cu and Ag helical springs. Rectangular areas of films were loaded in uniform compression and shear and the film properties were obtained through the load versus displacement response. The compressive stiffness of the nanostructured Cu films was measured to be 258 ± 12 MPa while the shear stiffness was 15 ± 3 MPa for Ag films on Si substrates and 19 ± 2 MPa and 21 ± 4.5 MPa for Cu films on Si and W, respectively. The experimental results were compared to theoretical predictions by modeling the nanostructured film elements as perfectly helical springs. The measurements were found to be typically within 20% of the theoretically-predicted values, and spring equations consistently predicted the change in stiffness between films of different materials. Bonding strength measurements showed an interfacial strength dependence on the bonded area, which is consistent with literature reports of other interfacially-bonded systems. The design of nanostructured thin films was conceptually optimized by considering both qualitative observations and by applying constitutive spring equations. The thickness of the cap layer and the morphology of the nanostructured layer were found to significantly affect the mode of debonding of the films. Optimum geometric and material parameters were also determined to maximize the amount of energy stored in the films in the elastic regime. A spring index, which is the ratio of the mean coil diameter to the wire diameter, of 2.5-3 was found to maximize the amount of elastic spring energy stored in a nanostructured film under uniform compressive loading and an index of 2.3-2.5 maximizes the stored energy under combined compressive and shear (mixed) loading.