A method to determine Young＇s modulus of soft gels for cell adhesion

A convenient technique is reported in this note for measuring elastic modulus of extremely soft material for cellular adhesion. Specimens of bending cylinder under gravity are used to avoid contact problem between testing device and sample, and a beam model is presented for evaluating the curvatures of gel beams with large elastic deformation. A self-adaptive algorithm is also proposed to search for the best estimation of gels＇ elastic moduli by comparing the experimental bending curvatures with those computed from the beam model with preestimated moduli. Application to the measurement of the property of polyacrylamide gels indi- cates that the material compliance varies with the concentrations of bis-acrylamide, and the gels become softer after being immersed in a culture medium for a period of time, no matter to what extent they are polymerized.     

Young’s Modulus Measurement Using a Simplified Transparent Indenter Measurement Technique

In material nano- and micro-indentation research, it is well accepted to use the initial unloading stiffness of the load-depth curve to determine the material’s Young’s modulus. This approach requires the use of high-precision displacement sensors in order to calibrate the loading apparatus system compliance and thus obtain the load-depth curve accurately. In this research, using a transparent spherical indenter coupled with a multi-partial unloading technique, we present a simpler approach to measure the material’s Young’s modulus. Experimental results of several metallic alloys and related discussions are presented.     

A molecular mechanics approach for analyzing tensile nonlinear deformation behavior of single-walled carbon nanotubes

In this paper, by capturing the atomic information and reflecting the behaviour governed by the nonlinear potential function, an analytical molecular mechanics approach is proposed. A constitutive relation for single-walled carbon nanotubes (SWCNT’s) is established to describe the nonlinear stress-strain curve of SWCNT’s and to predict both the elastic properties and breaking strain of SWCNT’s during tensile deformation. An analysis based on the virtual internal bond (VIB) model proposed by P. Zhang et al. is also presented for comparison. The results indicate that the proposed molecular mechanics approach is indeed an acceptable analytical method for analyzing the mechanical behavior of SWCNT’s. The project supported by the National Natural Science Foundation of China (10121202, 90305015 and 10328203), the Key Grant Project of Chinese Ministry of Education (0306) and the Research Grants Council of the Hong Kong Special Administrative Region, China (HKU 7195/04E).     

Insensitivity to small defects of the rupture of materials governed by the Dugdale model

The goal of this work is to prove that within the framework of fracture mechanics with Dugdale’s model of cohesive forces, small defects (compared to the material characteristic length) have no influence on the limit load that a structure can sustain. For that, we treat two cases: first, we solve the case of a precracked plate in closed form, and then we compute the response of a plate with a circular hole using the finite element method.