Fracture toughness is a key property in most engineering applications. Fracture experiments at small scale using micro-cantilever bending tests are crucial to determine fracture toughness in low volumes of materials. Furthermore, these tests provide crucial infromation to quantify the contribution of specific microstructural features to the overall crack resistance of a material. Moreover, in-situ SEM micro-cantilever bending tests provide new insights into the micromechanisms of fracture by combining the stress-strain data with direct crack path observation. The typical micro-cantilever bending test uses compression loading of a free-standing notched cantilever beams, prepared with lithography or Focused Ion Beam (FIB). For brittle fracture, the fracture toughness KIC is determined from the stress intensity factor K at the maximal load. A key requirement of the measurement system is true displacement control to avoid catastrophic failure of specimens once the crack becomes unstable, which is typical with force-controlled systems. However, for elastic-plastic fractures, ,another approach is needed. Typically, elastic-plastic fracture mechanics uses J-Integral to analyze the crack growth resistance curve (J-R curve) and elastic-plastic fracture toughness (JIC). Generally, higher KIC, JIC or steeper J-R curve indicate that a material is more resistant to fracture.Micro-cantilever bending testing using continuous stiffness measurement (CSM) enables to both monitor the evolution of crack length and compute continuous J-integral from periodic unloading segments.
By combining true displacement control, high load and displacement resolutions, a wide harmonic frequency range and fast data acquisition rate, FT-NMT04 enables the precise control of the fracture process and the quantification of the effect of individual microstructural features on the fracture toughness of materials.