Crack Detection and Crack Length Measurement with the DC Potential Drop Method–Possibilities, Challenges and New Developments

The direct current potential drop method (DCPDM) is widely used to determine the crack length in fatigue experiments. In practice, some special features of this method must be considered. Aside from general information on the experimental setup and calibration, some special features of the method, such as the influence of the ambient atmosphere and the application of the method to ferromagnetic materials, are presented and discussed. In addition, with the multiple potential drop measurement, a method is presented which improves the resolution of the DCPDM for detection of cracks and allows to determine crack initiation sites. The capabilities provided by this method are demonstrated on the basis of measurements undertaken on notched round bars and single edged notched specimens.

The Analysis of Resistance to Brittle Cracking of Tungsten Doped TiB2 Coatings Obtained by Magnetron Sputtering

In this work, the authors present the possibility of characterization of the fracture toughness in mode I (KIC) for TiB2 and TiB2 coatings doped with different concentration of W (3%, 6% and 10%). The Young’s modulus, hardness and fracture toughness of this coatings are extracted from nanoindentation experiments. The fracture toughness was evaluated using calculation of crack length measurement. An important observation is that increasing tungsten concentration in the range 0–10% changes the microstructure of the investigated coatings: from columnar structure for TiB2 coating to nano-composite structure for Ti-B-W (10%) coating. It can be concluded that doping with concentration 10 at.% W causes an increase of the fracture toughness for the tested coatings.

The Potential of AE Sensing in the Indentation Fracture Toughness Measurement

In this study, an attempt is made to characterize the brittleness of the material by crack formation with the Vickers indenter. To assess the critical load, the sensor of AE signal was used. After preliminary tests on a silica glass, the methodology was applied to HVOF sprayed CrC-NiCr coating in as-sprayed and annealed state. The critical value of indentation force obtained from AE sensing was correlated with the standard method of crack length measurement with good agreement

A Simple and Sensitive Method of Monitoring Crack and Load in Three-Point Bending Fracture Mechanics Specimens Using Strain Gages

In fatigue crack growth experiment and fracture toughness test, the crack length measurement is very important. Here, this paper proposes a new method for measuring crack length, namely in the case of a known load, according to the strain on the front end face of the three point bending specimen would be to get crack length.

Automatic Crack Length Measurement of Concrete Structure Based on Image Processing

The safety of concrete structure can be evaluated by manual survey through the visible crack shown on structural surface, but the manual survey is costly and time-consuming. To improve this, a novel image-based crack length measurement is proposed. The method starts with getting time varying crack images by proposed inspection system. Then retrieve crack skeleton from crack images by pre-processing, and construct crack skeleton of tree structure. After getting crack trunk by pruning small edges from crack skeleton, the length of crack is figure out. This method can measure crack length automatically, which will make contribution to enhance the stability, durability and safety of concrete structure. The validity and accuracy of the proposed method was tested by an experiment using images of a real concrete surface.

Study of Crack Length Measurement and Crack Tip Plastic Zone Determination by Infrared Thermography

This paper reports a new way to conduct fracture mechanics experiments of welded thin-walled structure for aircraft fuselage applications made of the Al 6156 ally using lock-in infrared thermography. The heat wave, generated by both the themo-mechanical coupling and intrinsic energy dissipation was detected by an infrared camera. The crack growth rate measured by the lock-in infrared thermography is found to be consistent with that measured by conventional method. It is observed that the crack can either grow underneath the stiffener or grow into the stiffener web with the crack length measured at the same time. In addition, the crack tip plastic zone was observed before the specimen was about to be destroyed.