Micro-tensile Testing

Fibers have found their way into many applications such as scaffolds for tissue engineering, drug delivery, filtration devices, body armors etc. It is because of the superior properties of fibrous materials such as higher toughness, durability, and pliability [1]. The unique properties of the fibers stem from their high aspect ratio and thus there are efforts to make fibers as small as 1 µm in diameter. The size and strength of these fibers are dependent on the processing techniques that span across phase separation, template synthesis, magneto-spinning, fluidic spinning, electrospinning etc. The fiber properties are also depended on their composition that varies from polymers such as Kevlar, Nylon to organic-inorganic materials such as cellulose, collagen, alginate, and DNA.

Uniaxial vs Unpinning Test

The mechanical testing of these fibers is crucial to understand the efficiency of the manufacturing process as well as to provide customized fiber solutions to their respective applications [2]. For example, drug release and drug loading in fibers are affected by their mechanical properties [3], there is a need to mimic key mechanobiological and biochemical features of the native extracellular matrix during tissue engineering and many others. Tensile tests are widely favored experiments to measure the stiffness, yield strength and fracture strength of the fibers. However, the small dimensions reaching 1 µm in diameter presents a significant challenge to their testing.

The only possible way to perform these tensile tests is by measuring forces in µN range with a resolution of nN. The FemtoTools Micromechanical Testing and Assembly System tensile test module is the best and the only solution available commercially to perform these tests with force resolution of 0.5 nN and spatial resolution of 0.05 nm with a total travel range of 29 mm.

Tensile Test of a Fiber

We have performed tensile tests on organic and inorganic fibers with smallest fibers close to 1 µm in diameter and an average fiber diameter of 3 µm. The given figure shows the tensile test data of one fiber along with SEM images of two fibers that we tested showing the fractured end. The stiffness and yield strength of the fibers were measured along with the fracture point. The SEM images of the fibers were obtained to measure the decrease in the fiber diameter due to necking. These measurements provide very important information regarding the fiber failure mechanisms as well as the presence of elastic and plastic regimes.

The FemtoTools tensile tester is a complete scientific package which along with tensile tests can also perform nanoindentation from very soft gels to metals to measure their elastic modulus and hardness, surface topography measurements in both longitudinal and lateral direction in addition to many other unique experiments. It can also be used for the failure analysis of microstructures such as encapsulated beads, failure force of MEMS structure such as accelerometers, gyroscopes, shear strength in the lateral direction of solder bonds in circuits etc.

References and Notes

  1. G. M. Gonzalez, L. A. MacQueen, J. U. Lind, S. A. Fitzgibbons, C. O. Chantre, I. Huggler, H. M. Golecki, J. A. Goss, K. K. Parker, Macromol. Mater. Eng. 2017, 302, 1600365.
  2. Stephen R. Baker, Soham Banerjee, Keith Bonin, Martin Guthold, Materials Science and Engineering C 59 (2016) 203–212.
  3. Shih-Feng Chou, Kim A. Woodrow, Journal of the Mechanical Behavior of Biomedical Materials 65 (2017) 724–733.